diff --git a/_index.db b/_index.db index ba3347281..d8b6cebde 100644 Binary files a/_index.db and b/_index.db differ diff --git a/data/en.wikipedia.org/wiki/Decompression_theory-0.md b/data/en.wikipedia.org/wiki/Decompression_theory-0.md new file mode 100644 index 000000000..262412225 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Decompression_theory-0.md @@ -0,0 +1,25 @@ +--- +title: "Decompression theory" +chunk: 1/17 +source: "https://en.wikipedia.org/wiki/Decompression_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:49.112339+00:00" +instance: "kb-cron" +--- + +Decompression theory is the study and modelling of the transfer of the inert gas component of breathing gases from the gas in the lungs to the tissues and back during exposure to variations in ambient pressure. In the case of underwater diving and compressed air work, this mostly involves ambient pressures greater than the local surface pressure, but astronauts, high altitude mountaineers, and travellers in aircraft which are not pressurised to sea level pressure, are generally exposed to ambient pressures less than standard sea level atmospheric pressure. In all cases, the symptoms caused by decompression occur during or within a relatively short period of hours, or occasionally days, after a significant pressure reduction. +The term "decompression" derives from the reduction in ambient pressure experienced by the organism and refers to both the reduction in pressure and the process of allowing dissolved inert gases to be eliminated from the tissues during and after this reduction in pressure. The uptake of gas by the tissues is in the dissolved state, and elimination also requires the gas to be dissolved, however a sufficient reduction in ambient pressure may cause bubble formation in the tissues, which can lead to tissue damage and the symptoms known as decompression sickness, and also delays the elimination of the gas. +Decompression modeling attempts to explain and predict the mechanism of gas elimination and bubble formation within the organism during and after changes in ambient pressure, and provides mathematical models which attempt to predict acceptably low risk and reasonably practicable procedures for decompression in the field. Both deterministic and probabilistic models have been used, and are still in use. +Efficient decompression requires the diver to ascend fast enough to establish as high a decompression gradient, in as many tissues, as safely possible, without provoking the development of symptomatic bubbles. This is facilitated by the highest acceptably safe oxygen partial pressure in the breathing gas, and avoiding gas changes that could cause counterdiffusion bubble formation or growth. The development of schedules that are both safe and efficient has been complicated by the large number of variables and uncertainties, including personal variation in response under varying environmental conditions and workload. + +== Physiology of decompression == + +The evidence that decompression sickness is caused by bubble formation and growth within the body tissues resulting from supersaturated dissolved gas is strong, but research results also suggest that the quantity of those bubbles alone is not enough to predict whether someone will experience symptoms of DCS. +Gas is breathed at ambient pressure, and some of this gas dissolves into the blood and other fluids. Inert gas continues to be taken up until the gas dissolved in the tissues is in a state of equilibrium with the gas in the lungs (see saturation diving), or the ambient pressure is reduced until the inert gases dissolved in the tissues are at a higher concentration than the equilibrium state, and start diffusing out again. +The absorption of gases in liquids depends on the solubility of the specific gas in the specific liquid, the concentration of gas, customarily measured by partial pressure, and temperature. In the study of decompression theory the behaviour of gases dissolved in the tissues is investigated and modeled for variations of pressure over time. +Once dissolved, distribution of the dissolved gas may be by diffusion, where there is no bulk flow of the solvent, or by perfusion where the solvent (blood) is circulated around the diver's body, where gas can diffuse to local regions of lower concentration. Given sufficient time at a specific partial pressure in the breathing gas, the concentration in the tissues will stabilise, or saturate, at a rate depending on the solubility, diffusion rate and perfusion. +If the concentration of the inert gas in the breathing gas is reduced below that of any of the tissues, there will be a tendency for gas to return from the tissues to the breathing gas. This is known as outgassing, and occurs during decompression, when the reduction in ambient pressure or a change of breathing gas reduces the partial pressure of the inert gas in the lungs. +The combined concentrations of gases in any given tissue will depend on the history of pressure and gas composition. Under equilibrium conditions, the total concentration of dissolved gases will be less than the ambient pressure, as oxygen is metabolised in the tissues, and the carbon dioxide produced is much more soluble. However, during a reduction in ambient pressure, the rate of pressure reduction may exceed the rate at which gas can be eliminated by diffusion and perfusion, and if the concentration gets too high, it may reach a stage where bubble formation can occur in the supersaturated tissues. When the pressure of gases in a bubble exceeds the combined external pressures of ambient pressure and the surface tension from the bubble - liquid interface, the bubble will grow, and this growth can cause damage to tissues. Symptoms caused by this damage are known as decompression sickness. +The actual rates of diffusion and perfusion and the solubility of gases in specific tissues are not generally known, and they vary considerably. However, mathematical models have been proposed which approximate the real situation to a greater or lesser extent, and these models are used to predict whether symptomatic bubble formation is likely to occur for a given pressure exposure profile. +Decompression involves a complex interaction of gas solubility, partial pressures and concentration gradients, diffusion, bulk transport and bubble mechanics in living tissues. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Decompression_theory-1.md b/data/en.wikipedia.org/wiki/Decompression_theory-1.md new file mode 100644 index 000000000..53ccc8352 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Decompression_theory-1.md @@ -0,0 +1,16 @@ +--- +title: "Decompression theory" +chunk: 2/17 +source: "https://en.wikipedia.org/wiki/Decompression_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:49.112339+00:00" +instance: "kb-cron" +--- + +=== Dissolved phase gas dynamics === +Solubility of gases in liquids is influenced by the nature of the solvent liquid and the solute, the temperature, pressure, and the presence of other solutes in the solvent. Diffusion is faster in smaller, lighter molecules of which helium is the extreme example. Diffusivity of helium is 2.65 times faster than nitrogen. The concentration gradient, can be used as a model for the driving mechanism of diffusion. In this context, inert gas refers to a gas which is not metabolically active. Atmospheric nitrogen (N2) is the most common example, and helium (He) is the other inert gas commonly used in breathing mixtures for divers. Atmospheric nitrogen has a partial pressure of approximately 0.78 bar at sea level. Air in the alveoli of the lungs is diluted by saturated water vapour (H2O) and carbon dioxide (CO2), a metabolic product given off by the blood, and contains less oxygen (O2) than atmospheric air as some of it is taken up by the blood for metabolic use. The resulting partial pressure of nitrogen is about 0,758 bar. +At atmospheric pressure the body tissues are therefore normally saturated with nitrogen at 0.758 bar (569 mmHg). At increased ambient pressures due to depth or habitat pressurisation, a diver's lungs are filled with breathing gas at the increased pressure, and the partial pressures of the constituent gases will be increased proportionately. The inert gases from the breathing gas in the lungs diffuse into blood in the alveolar capillaries and are distributed around the body by the systemic circulation in the process known as perfusion. Dissolved materials are transported in the blood much faster than they would be distributed by diffusion alone. From the systemic capillaries the dissolved gases diffuse through the cell membranes and into the tissues, where it may eventually reach equilibrium. The greater the blood supply to a tissue, the faster it will reach equilibrium with gas at the new partial pressure. This equilibrium is called saturation. Ingassing appears to follow a simple inverse exponential equation. The time it takes for a tissue to take up or release 50% of the difference in dissolved gas capacity at a changed partial pressure is called the half-time for that tissue and gas. +Gas remains dissolved in the tissues until the partial pressure of that gas in the lungs is reduced sufficiently to cause a concentration gradient with the blood at a lower concentration than the relevant tissues. As the concentration in the blood drops below the concentration in the adjacent tissue, the gas will diffuse out of the tissue into the blood, and will then be transported back to the lungs where it will diffuse into the lung gas and then be eliminated by exhalation. If the ambient pressure reduction is limited, this desaturation will take place in the dissolved phase, but if the ambient pressure is lowered sufficiently, bubbles may form and grow, both in blood and other supersaturated tissues. When the partial pressure of all gas dissolved in a tissue exceeds the total ambient pressure on the tissue it is supersaturated, and there is a possibility of bubble formation. +The sum of partial pressures of the gas that the diver breathes must necessarily balance with the sum of partial pressures in the lung gas. In the alveoli the gas has been humidified and has gained carbon dioxide from the venous blood. Oxygen has also diffused into the arterial blood, reducing the partial pressure of oxygen in the alveoli. As the total pressure in the alveoli must balance with the ambient pressure, this dilution results in an effective partial pressure of nitrogen of about 758 mb (569 mmHg) in air at normal atmospheric pressure. At a steady state, when the tissues have been saturated by the inert gases of the breathing mixture, metabolic processes reduce the partial pressure of the less soluble oxygen and replace it with carbon dioxide, which is considerably more soluble in water. In the cells of a typical tissue, the partial pressure of oxygen will drop, while the partial pressure of carbon dioxide will rise. The sum of these partial pressures (water, oxygen, carbon dioxide and nitrogen) is less than the total pressure of the respiratory gas. This is a significant saturation deficit, and it provides a buffer against supersaturation and a driving force for dissolving bubbles. Experiments suggest that the degree of unsaturation increases linearly with pressure for a breathing mixture of fixed composition, and decreases linearly with fraction of inert gas in the breathing mixture. As a consequence, the conditions for maximising the degree of unsaturation are a breathing gas with the lowest possible fraction of inert gas – i.e. pure oxygen, at the maximum permissible partial pressure. This saturation deficit is also referred to as inherent unsaturation, the "Oxygen window". or partial pressure vacancy. +The location of micronuclei or where bubbles initially form is not known. The incorporation of bubble formation and growth mechanisms in decompression models may make the models more biophysical and allow better extrapolation. Flow conditions and perfusion rates are dominant parameters in competition between tissue and circulation bubbles, and between multiple bubbles, for dissolved gas for bubble growth. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Decompression_theory-10.md b/data/en.wikipedia.org/wiki/Decompression_theory-10.md new file mode 100644 index 000000000..e1318161d --- /dev/null +++ b/data/en.wikipedia.org/wiki/Decompression_theory-10.md @@ -0,0 +1,18 @@ +--- +title: "Decompression theory" +chunk: 11/17 +source: "https://en.wikipedia.org/wiki/Decompression_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:49.112339+00:00" +instance: "kb-cron" +--- + +==== Perfusion limited tissues and parallel tissue models ==== +The assumption that perfusion is the limiting mechanism leads to a model comprising a group of tissues with varied rates of perfusion, but supplied by blood of approximately equivalent gas concentration. It is also assumed that there is no gas transfer between tissue compartments by diffusion. This results in a parallel set of independent tissues, each with its own rate of ingassing and outgassing dependent on the rate of blood flowing through the tissue. Gas uptake for each tissue is generally modelled as an exponential function, with a fixed compartment half-time, and gas elimination may also be modelled by an exponential function, with the same or a longer half time, or as a more complex function, as in the exponential-linear elimination model. +The critical ratio hypothesis predicts that the development of bubbles will occur in a tissue when the ratio of dissolved gas partial pressure to ambient pressure exceeds a particular ratio for a given tissue. The ratio may be the same for all tissue compartments or it may vary, and each compartment is allocated a specific critical supersaturation ratio, based on experimental observations. +John Scott Haldane introduced the concept of half times to model the uptake and release of nitrogen into the blood. He suggested 5 tissue compartments with half times of 5, 10, 20, 40 and 75 minutes. In this early hypothesis it was predicted that if the ascent rate does not allow the inert gas partial pressure in each of the hypothetical tissues to exceed the environmental pressure by more than 2:1 bubbles will not form. Basically this meant that one could ascend from 30 m (4 bar) to 10 m (2 bar), or from 10 m (2 bar) to the surface (1 bar) when saturated, without a decompression problem. To ensure this a number of decompression stops were incorporated into the ascent schedules. The ascent rate and the fastest tissue in the model determine the time and depth of the first stop. Thereafter the slower tissues determine when it is safe to ascend further. This 2:1 ratio was found to be too conservative for fast tissues (short dives) and not conservative enough for slow tissues (long dives). The ratio also seemed to vary with depth. Haldane's approach to decompression modeling was used from 1908 to the 1960s with minor modifications, primarily changes to the number of compartments and half times used. The 1937 US Navy tables were based on research by O. D. Yarbrough and used 3 compartments: the 5- and 10-minute compartments were dropped. In the 1950s the tables were revised and the 5- and 10-minute compartments restored, and a 120-minute compartment added. +In the 1960s Robert D. Workman of the U.S. Navy Experimental Diving Unit (NEDU) reviewed the basis of the model and subsequent research performed by the US Navy. Tables based on Haldane's work and subsequent refinements were still found to be inadequate for longer and deeper dives. Workman proposed that the tolerable change in pressure was better described as a critical pressure difference, and revised Haldane's model to allow each tissue compartment to tolerate a different amount of supersaturation which varies with depth. He introduced the term "M-value" to indicate the maximum amount of supersaturation each compartment could tolerate at a given depth and added three additional compartments with 160, 200 and 240-minute half times. Workman presented his findings as an equation which could be used to calculate the results for any depth and stated that a linear projection of M-values would be useful for computer programming. +A large part of Albert A. Bühlmann's research was to determine the longest half time compartments for Nitrogen and Helium, and he increased the number of compartments to 16. He investigated the implications of decompression after diving at altitude and published decompression tables that could be used at a range of altitudes. Bühlmann used a method for decompression calculation similar to that proposed by Workman, which included M-values expressing a linear relationship between maximum inert gas pressure in the tissue compartments and ambient pressure, but based on absolute pressure, which made them more easily adapted for altitude diving. Bühlmann's algorithm was used to generate the standard decompression tables for a number of sports diving associations, and is used in several personal decompression computers, sometimes in a modified form. +B.A. Hills and D.H. LeMessurier studied the empirical decompression practices of Okinawan pearl divers in the Torres Strait and observed that they made deeper stops but reduced the total decompression time compared with the generally used tables of the time. Their analysis strongly suggested that bubble presence limits gas elimination rates, and emphasized the importance of inherent unsaturation of tissues due to metabolic processing of oxygen. This became known as the thermodynamic model. More recently, recreational technical divers developed decompression procedures using deeper stops than required by the decompression tables in use. These led to the RGBM and VPM bubble models. A deep stop was originally an extra stop introduced by divers during ascent, at a greater depth than the deepest stop required by their computer algorithm. There are also computer algorithms that are claimed to use deep stops, but these algorithms and the practice of deep stops have not been adequately validated. +A "Pyle stop" is a deep stop named after Richard Pyle, an early advocate of deep stops, at the depths halfway between the bottom and the first conventional decompression stop, and halfway between the previous Pyle stop and the deepest conventional stop, provided the conventional stop is more than 9 m shallower. A Pyle stop is about 2 minutes long. The additional ascent time required for Pyle stops is included in the dive profile before finalising the decompression schedule. Pyle found that on dives where he stopped periodically to vent the swim-bladders of his fish specimens, he felt better after the dive, and based the deep stop procedure on the depths and duration of these pauses. The hypothesis is that these stops provide an opportunity to eliminate gas while still dissolved, or at least while the bubbles are still small enough to be easily eliminated, and the result is that there will be considerably fewer or smaller venous bubbles to eliminate at the shallower stops as predicted by the thermodynamic model of Hills. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Decompression_theory-11.md b/data/en.wikipedia.org/wiki/Decompression_theory-11.md new file mode 100644 index 000000000..1ec1b63a8 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Decompression_theory-11.md @@ -0,0 +1,36 @@ +--- +title: "Decompression theory" +chunk: 12/17 +source: "https://en.wikipedia.org/wiki/Decompression_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:49.112339+00:00" +instance: "kb-cron" +--- + +For example, a diver ascends from a maximum depth of 60 metres (200 ft), where the ambient pressure is 7 bars (100 psi), to a decompression stop at 20 metres (66 ft), where the pressure is 3 bars (40 psi). The first Pyle stop would take place at the halfway pressure, which is 5 bars (70 psi) corresponding to a depth of 40 metres (130 ft). The second Pyle stop would be at 30 metres (98 ft). A third would be at 25 metres (82 ft) which is less than 9 metres (30 ft) below the first required stop, and therefore is omitted. +The value and safety of deep stops additional to the decompression schedule derived from a decompression algorithm is unclear. Decompression experts have pointed out that deep stops are likely to be made at depths where ingassing continues for some slow tissues, and that the addition of deep stops of any kind should be included in the hyperbaric exposure for which the decompression schedule is computed, and not added afterwards, so that such ingassing of slower tissues can be taken into account. Deep stops performed during a dive where the decompression is calculated in real-time are simply part of a multi-level dive to the computer, and add no risk beyond that which is inherent in the algorithm. +There is a limit to how deep a "deep stop" can be. Some off-gassing must take place, and continued on-gassing should be minimised for acceptably effective decompression. The "deepest possible decompression stop" for a given profile can be defined as the depth where the gas loading for the leading compartment crosses the ambient pressure line. This is not a useful stop depth - some excess in tissue gas concentration is necessary to drive the outgassing diffusion, however this depth is a useful indicator of the beginning of the decompression zone, in which ascent rate is part of the planned decompression. +A study by DAN in 2004 found that the incidence of high-grade bubbles could be reduced to zero providing the nitrogen concentration of the most saturated tissue was kept below 80 percent of the allowed M value and that an added deep stop was a simple and practical way of doing this, while retaining the original ascent rate. + +==== Diffusion limited tissues and the "Tissue slab", and series models ==== + +The assumption that diffusion is the limiting mechanism of dissolved gas transport in the tissues results in a rather different tissue compartment model. In this case a series of compartments has been postulated, with perfusion transport into one compartment, and diffusion between the compartments, which for simplicity are arranged in series, so that for the generalised compartment, diffusion is to and from only the two adjacent compartments on opposite sides, and the limit cases are the first compartment where the gas is supplied and removed via perfusion, and the end of the line, where there is only one neighbouring compartment. The simplest series model is a single compartment, and this can be further reduced to a one-dimensional "tissue slab" model. + +==== Bubble models ==== +Bubble decompression models are a rule based approach to calculating decompression based on the idea that microscopic bubble nuclei always exist in water and tissues that contain water and that by predicting and controlling the bubble growth, one can avoid decompression sickness. Most of the bubble models assume that bubbles will form during decompression, and that mixed phase gas elimination occurs, which is slower than dissolved phase elimination. Bubble models tend to have deeper first stops to get rid of more dissolved gas at a lower supersaturation to reduce the total bubble phase volume, and potentially reduce the time required at shallower depths to eliminate bubbles. +Decompression models that assume mixed phase gas elimination include: + +The arterial bubble decompression model of the French Tables du Ministère du Travail 1992 +The U.S. Navy Exponential-Linear (Thalmann) algorithm used for the 2008 US Navy air decompression tables (among others) +Hennessy's combined perfusion/diffusion model of the BSAC'88 tables +The Varying Permeability Model (VPM) developed by D.E. Yount and Hoffman (1986) at the University of Hawaii +The Reduced Gradient Bubble Model (RGBM) developed by Bruce Wienke in 1990 at Los Alamos National Laboratory +Michael Gernhardt proposed the Tissue Bubble Dynamics Model (1991) +Wayne Gerth and Richard Vann (1997) published the Probabilistic Gas and Bubble Dynamics Model. +Lewis and Crow introduced their Gas Formation Model (GFM) in 2008. +The Copernicus model of Gutvik and Brubakk (2009) +The most widely implemented model in dive computers is a simplified modification of the RGBM. +The models of Yount and Hoffman, and Wienke, assume that bubble formation is due to supersaturation, while Gernhardt, Gerth and Vann, and Gutvik and Brubakk assume pre-existing microscopic bubble nuclei, which grow when concentration of gases in the tissues is high enough. These models are more mathematically complex, and as of 2009 were unsuitable for real-time computation by dive computer. + +==== Goldman Interconnected Compartment Model ==== \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Decompression_theory-12.md b/data/en.wikipedia.org/wiki/Decompression_theory-12.md new file mode 100644 index 000000000..93e62826b --- /dev/null +++ b/data/en.wikipedia.org/wiki/Decompression_theory-12.md @@ -0,0 +1,12 @@ +--- +title: "Decompression theory" +chunk: 13/17 +source: "https://en.wikipedia.org/wiki/Decompression_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:49.112339+00:00" +instance: "kb-cron" +--- + +In contrast to the independent parallel compartments of the Haldanean models, in which all compartments are considered risk bearing, the Goldman model posits a relatively well perfused "active" or "risk-bearing" compartment in series with adjacent relatively poorly perfused "reservoir" or "buffer" compartments, which are not considered potential sites for bubble formation, but affect the probability of bubble formation in the active compartment by diffusive inert gas exchange with the active compartment. During compression, gas diffuses into the active compartment and through it into the buffer compartments, increasing the total amount of dissolved gas passing through the active compartment. During decompression, this buffered gas must pass through the active compartment again before it can be eliminated. If the gas loading of the buffer compartments is small, the added gas diffusion through the active compartment is slow. The interconnected models predict a reduction in gas washout rate with time during decompression compared with the rate predicted for the independent parallel compartment model used for comparison. +The Goldman model differs from the Kidd-Stubbs series decompression model in that the Goldman model assumes linear kinetics, where the K-S model includes a quadratic component, and the Goldman model considers only the central well-perfused compartment to contribute explicitly to risk, while the K-S model assumes all compartments to carry potential risk. The DCIEM 1983 model associates risk with the two outermost compartments of a four compartment series. The mathematical model based on this concept is claimed by Goldman to fit not only the Navy square profile data used for calibration, but also predicts risk relatively accurately for saturation profiles. A bubble version of the ICM model was not significantly different in predictions, and was discarded as more complex with no significant advantages. The ICM also predicted decompression sickness incidence more accurately at the low-risk recreational diving exposures recorded in DAN's Project Dive Exploration data set. The alternative models used in this study were the LE1 (Linear-Exponential) and straight Haldanean models. The Goldman model predicts a significant risk reduction following a safety stop on a low-risk dive and significant risk reduction by using nitrox (more so than the PADI tables suggest). \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Decompression_theory-13.md b/data/en.wikipedia.org/wiki/Decompression_theory-13.md new file mode 100644 index 000000000..58edd4ab6 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Decompression_theory-13.md @@ -0,0 +1,20 @@ +--- +title: "Decompression theory" +chunk: 14/17 +source: "https://en.wikipedia.org/wiki/Decompression_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:49.112339+00:00" +instance: "kb-cron" +--- + +=== Probabilistic models === +Probabilistic decompression models, also referred to as evidence-based decompression models, are designed to calculate the risk (or probability) of decompression sickness (DCS) occurring on a given decompression profile, based on actual outcomes of a statistically robust set of data. Statistical analysis is well suited to compressed air work in tunneling operations due to the large number of subjects undergoing similar exposures at the same ambient pressure and temperature, with similar workloads and exposure times, with the same decompression schedule. Large numbers of decompressions under similar circumstances have shown that it is not reasonably practicable to eliminate all risk of DCS, so it is necessary to set an acceptable risk, based on the other factors relevant to the application. For example, easy access to effective treatment in the form of hyperbaric oxygen treatment on site, or greater advantage to getting the diver out of the water sooner, may make a higher incidence acceptable, while interfering with work schedule, adverse effects on worker morale or a high expectation of litigation would shift acceptable incidence rate downward. Efficiency is also a factor, as decompression of employees occurs during working hours. +These methods can vary the decompression stop depths and times to arrive at a decompression schedule that assumes a specified probability of DCS occurring, while minimizing the total decompression time. This process can also work in reverse allowing one to calculate the probability of DCS for any decompression schedule, given sufficient reliable data. +In 1936 an incidence rate of 2% was considered acceptable for compressed air workers in the UK. The US Navy in 2000 accepted a 2% incidence of mild symptoms, but only 0.1% serious symptoms. Commercial diving in the North Sea in the 1990s accepted 0.5% mild symptoms, but almost no serious symptoms, and commercial diving in the Gulf of Mexico also during the 1990s, accepted 0.1% mild cases and 0.025% serious cases. Health and Safety authorities tend to specify the acceptable risk as as low as reasonably practicable taking into account all relevant factors, including economic factors. To analyse probability of mild and severe symptoms it is first necessary to define these classes of manifestation, as applicable to the analysis. +The necessary tools for probability estimation for decompression sickness are a biophysical model which describes the inert gas exchange and bubble formation during decompression, exposure data in the form of pressure/time profiles for the breathing gas mixtures, and the DCS outcomes for these exposures, statistical methods, such as survival analysis or Bayesian analysis to find a best fit between model and experimental data, after which the models can be quantitatively compared and the best fitting model used to predict DCS probability for the model. This process is complicated by the influence of environmental conditions on DCS probability. Factors that affect perfusion of the tissues during ingassing and outgassing, which affect rates of inert gas uptake and elimination respectively, include immersion, temperature and exercise. Exercise is also known to promote bubble formation during decompression. +The distribution of decompression stops is also known to affect DCS risk. A USN experiment using symptomatic decompression sickness as the endpoint, compared two models for dive working exposures on air using the same bottom time, water temperature and workload, with the same total decompression time, for two different depth distributions of decompression stops, also on air, and found the shallower stops to carry a statistically very significantly lower risk. The model did not attempt to optimise depth distribution of decompression time, or the use of gas switching, it just compared the effectiveness of two specific models, but for those models the results were convincing. +Another set of experiments was conducted for a series of increasing bottom time exposures at a constant depth, with varying ambient temperature. Four temperature conditions were compared: warm during the bottom sector and decompression, cold during bottom sector and decompression, warm at the bottom and cold during decompression, and cold at the bottom and warm during decompression. The effects were very clear that DCS incidence was much lower for divers that were colder during the ingassing phase and warmer during decompression than the reverse, which has been interpreted as indicating the effects of temperature on perfusion on gas uptake and elimination. +A retrospective statistical analysis of a large data set of case reports of air and nitrox dives published in 2017 indicated that for an acceptable risk of 2% for mild symptoms, and 0.1% for severe symptoms, using a linear-exponential degassing model, the severe symptom risk was the limiting factor. One of the factors complicating this analysis was the variability in methods for distinguishing between mild and severe cases. + +=== Saturation decompression === \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Decompression_theory-14.md b/data/en.wikipedia.org/wiki/Decompression_theory-14.md new file mode 100644 index 000000000..9954cae87 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Decompression_theory-14.md @@ -0,0 +1,24 @@ +--- +title: "Decompression theory" +chunk: 15/17 +source: "https://en.wikipedia.org/wiki/Decompression_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:49.112339+00:00" +instance: "kb-cron" +--- + +Saturation decompression is a physiological process of transition from a steady state of full saturation with inert gas at raised pressure to standard conditions at normal surface atmospheric pressure. It is a long process during which inert gases are eliminated at a very low rate limited by the slowest affected tissues, and a deviation can cause the formation of gas bubbles which can produce decompression sickness. Most operational procedures rely on experimentally derived parameters describing a continuous slow decompression rate, which may depend on depth and gas mixture. +In saturation diving all tissues are considered saturated and decompression which is safe for the slowest tissues will theoretically be safe for all faster tissues in a parallel model. Direct ascent from air saturation at approximately 7 msw produces venous gas bubbles but not symptomatic DCS. Deeper saturation exposures require decompression to saturation schedules. +The safe rate of decompression from a saturation dive is controlled by the partial pressure of oxygen in the inspired breathing gas. The inherent unsaturation due to the oxygen window allows a relatively fast initial phase of saturation decompression in proportion to the oxygen partial pressure and then controls the rate of further decompression limited by the half-time of inert gas elimination from the slowest compartment. However, some saturation decompression schedules specifically do not allow an decompression to start with an upward excursion. Neither the excursions nor the decompression procedures currently in use (2016) have been found to cause decompression problems in isolation, but there appears to be significantly higher risk when excursions are followed by decompression before non-symptomatic bubbles resulting from excursions have totally resolved. Starting decompression while bubbles are present appears to be the significant factor in many cases of otherwise unexpected decompression sickness during routine saturation decompression. +Application of a bubble model in 1985 allowed successful modelling of conventional decompressions, altitude decompression, no-stop thresholds, and saturation dives using one setting of four global nucleation parameters. +Research continues on saturation decompression modelling and schedule testing. In 2015 a concept named Extended Oxygen Window was used in preliminary tests for a modified saturation decompression model. This model allows a faster rate of decompression at the start of the ascent to utilise the inherent unsaturation due to metabolic use of oxygen, followed by a constant rate limited by oxygen partial pressure of the breathing gas. The period of constant decompression rate is also limited by the allowable maximum oxygen fraction, and when this limit is reached, decompression rate slows down again as the partial pressure of oxygen is reduced. The procedure remains experimental as of May 2016. The goal is an acceptably safe reduction of overall decompression time for a given saturation depth and gas mixture. + +=== Validation of models === +It is important that any theory be validated by carefully controlled testing procedures. As testing procedures and equipment become more sophisticated, researchers learn more about the effects of decompression on the body. Initial research focused on producing dives that were free of recognizable symptoms of decompression sickness (DCS). With the later use of Doppler ultrasound testing, it was realized that bubbles were forming within the body even on dives where no DCI signs or symptoms were encountered. This phenomenon has become known as "silent bubbles". +The presence of venous gas emboli is considered a low specificity predictor of decompression sickness, but their absence is recognised to be a sensitive indicator of low risk decompression, therefore the quantitative detection of VGE is thought to be useful as an indicator of decompression stress when comparing decompression strategies, or assessing the efficiency of procedures. +The US Navy 1956 tables were based on limits determined by external DCS signs and symptoms. Later researchers were able to improve on this work by adjusting the limitations based on Doppler testing. However the US Navy CCR tables based on the Thalmann algorithm also used only recognisable DCS symptoms as the test criteria. Since the testing procedures are lengthy and costly, and there are ethical limitations on experimental work on human subjects with injury as an endpoint, it is common practice for researchers to make initial validations of new models based on experimental results from earlier trials. This has some implications when comparing models. + +==== Efficiency of stop depth distribution ==== +Deep, short duration dives require a long decompression in comparison to the time at depth, which is inherently inefficient in comparison with saturation diving. Various modifications to decompression algorithms with reasonably validated performance in shallower diving have been used in the effort to develop shorter or safer decompression, but these are generally not supported by controlled experiment and to some extent rely on anecdotal evidence. A widespread belief developed that algorithms based on bubble models and which distribute decompression stops over a greater range of depths are more efficient than the traditional dissolved gas content models by minimising early bubble formation, based on theoretical considerations, largely in the absence of evidence of effectiveness, though there were low incidences of symptomatic decompression sickness. Some evidence relevant to some of these modifications exists and has been analysed, and generally supports the opposite view, that deep stops may lead to greater rates of bubble formation and growth compared to the established systems using shallower stops distributed over the same total decompression time for a given deep profile. +The integral of supersaturation over time may be an indicator of decompression stress, either for a given tissue group or for all the tissue groups. Comparison of this indicator calculated for the combined Bühlmann tissue groups for a range of equal duration decompression schedules for the same depth, bottom time, and gas mixtures, has suggested greater overall decompression stress for dives using deep stops, at least partly due to continued ingassing of slower tissues during the deep stops. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Decompression_theory-15.md b/data/en.wikipedia.org/wiki/Decompression_theory-15.md new file mode 100644 index 000000000..2277f77b6 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Decompression_theory-15.md @@ -0,0 +1,39 @@ +--- +title: "Decompression theory" +chunk: 16/17 +source: "https://en.wikipedia.org/wiki/Decompression_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:49.112339+00:00" +instance: "kb-cron" +--- + +==== Effects of inert gas component changes ==== +Gas switching during decompression on open circuit is done primarily to increase the partial pressure of oxygen to increase the oxygen window effect, while keeping below acute toxicity levels. It is well established both in theory and practice, that a higher oxygen partial pressure facilitates a more rapid and effective elimination of inert gas, both in the dissolved state and as bubbles. +In closed circuit rebreather diving the oxygen partial pressure throughout the dive is maintained at a relatively high but tolerable level to reduce the ongassing as well as to accelerate offgassing of the diluent gas. Changes from helium-based diluents to nitrogen during ascent are desirable for reducing the use of expensive helium, but have other implications. It is unlikely that changes to nitrogen based decompression gas will accelerate decompression in typical technical bounce dive profiles, but there is some evidence that decompressing on helium-oxygen mixtures is more likely to result in neurological DCS, while nitrogen based decompression is more likely to produce other symptoms if DCS occurs. However, switching from helium rich to nitrogen rich decompression gas is implicated in inner ear DCS, connected with counter-diffusion effects. This risk can be reduced by sufficient initial decompression, using high oxygen partial pressure and making the helium to nitrogen switch relatively shallow. + +==== Altitude exposure, altitude diving and flying after diving ==== + +The USAF conducted experiments on human subjects in 1982 to validate schedules for air diving no-decompression limits before immediate excursions to altitude and for altitude diving allowing immediate flying after the dive to an altitude of 8,500 feet (2,600 m). Another test series in 2004 was made to validate predictions of a bubble-model for altitude decompression using previously untested exposure profiles. Parameters included exertion, altitudes from 18,000 to 35,000 feet (5,500 to 10,700 m), prebreathe time and exposure time, but these exposures did not include recent dives. +Experiments with an endpoint of DCS symptoms using profiles near the no-decompression exposure limits for recreational diving were carried out to determine how DCS occurrence during or after flight relates to the length of pre-flight surface interval (PFSI). The dives and PFSI were followed by a four-hour exposure at 75 kPa, equivalent to the maximum permitted commercial aircraft cabin altitude of 8,000 feet (2,400 m). DCS incidence decreased as surface interval increased, with no incidence for a 17 hour surface interval. Repetitive dives profiles usually needed longer surface intervals than single dives to minimise incidence. These tests have helped inform recommendations on time to fly. +In-flight transthoracic echocardiography has shown that there is a low but non-zero probability of decompression sickness in commercial pressurised aircraft after a 24 hour pre-flight surface interval following a week of multiple repetitive recreational dives, indicated by detection of venous gas bubbles in a significant number of the divers tested. + +== Current research == +Research on decompression continues. Data is not generally available on the specifics, however Divers Alert Network (DAN) has an ongoing citizen science based programme run by DAN (Europe) which gathers data from volunteer recreational divers for analysis by DAN research staff and other researchers. This research is funded by subscription fees of DAN Europe members. The Diving Safety Laboratory is a database to which members can upload dive profiles from a wide range of dive computers converted to a standard format and other data about the dive. Data on hundreds of thousands of real dives is analysed to investigate aspects of diving safety. The large amounts of data gathered is used for probabilistic analysis of decompression risk. The data donors can get immediate feedback in the form of a simple risk analysis of their dive profiles rated as one of three nominal levels of risk (high, medium and low) based on comparison with Bühlmann ZH16c M-values computed for the same profile. +Listed projects (not all directly related to decompression) include: + +Gathering data on vascular gas bubbles and analysis of the data +Identification of optimised ascent profile +Investigating the causes of unexplained diving incidents +Stress in recreational diving +Correlation between patent foramen ovale (PFO) and risk of decompression illness +Diving with asthma and diabetes and managing the associated risk +Physiology and pathophysiology of breath-hold +Hypothermia and diving +Headache and diving +Blood changes associated with diving +Decompression risk of air travel after diving +Physiological effects of rebreather diving +Effects of decompression stress on endothelial stem cells and blood cells +Early decompression stress biomarkers +The effects of normobaric oxygen on blood and in DCI first aid \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Decompression_theory-16.md b/data/en.wikipedia.org/wiki/Decompression_theory-16.md new file mode 100644 index 000000000..c8dd2d294 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Decompression_theory-16.md @@ -0,0 +1,64 @@ +--- +title: "Decompression theory" +chunk: 17/17 +source: "https://en.wikipedia.org/wiki/Decompression_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:49.112339+00:00" +instance: "kb-cron" +--- + +=== Practical effectiveness of models === +Bubble models for decompression were popular among technical divers in the early 2000s, although there was little data to support the effectiveness of the models in practice. Since then, several comparative studies have indicated relatively larger numbers of venous gas emboli after decompression based on bubble models, and one study reported a higher rate of decompression sickness. The deeper decompression stops earlier in the ascent appear to be less effective at controlling bubble formation than the hypotheses suggested. This failure may be due to continued ingassing of slower tissues during the extended time at greater depth, resulting in these tissues being more supersaturated at shallower depths. The optimal decompression strategy for deep bounce dives remains unknown (2016). +The practical efficacy of gas switches from helium-based diluent to nitrox for accelerating decompression has not been demonstrated convincingly. These switches increase risk of inner ear decompression sickness due to counterdiffusion effects. +Besides the basic dive profile and gas mixes, and the residual gas load from previous dives, three groups of factors are considered likely to have significant influence on decompression stress, the evolution of bubbles in the diver, and development of symptoms. These are exercise, before, during and after the dive, Thermal status, during and after the dive, including the effects on perfusion distribution and changes during the dive, and the set of factors grouped under the label "predisposition", such as the state of hydration, physical fitness, age, biological health, and other characteristics which could affect the uptake and release of gases in the diver. Currently these factors cannot be used to make reproducible predictions about decompression risk, and some cannot be numerically evaluated in real time. + +== Teaching of decompression theory == + +Decompression is an area where you discover that, the more you learn, the more you know that you really don't know what is going on. For behind the "black-and-white" exactness of table entries, the second-by-second countdowns of dive computers, and beneath the mathematical purity of decompression models, lurks a dark and mysterious physiological jungle that has barely been explored. +— Karl E. Huggins, 1992 + +Exposure to the various theories, models, tables and algorithms is needed to allow the diver to make educated and knowledgeable decisions regarding their personal decompression needs. Basic decompression theory and use of decompression tables is part of the theory component of training for commercial divers, and dive planning based on decompression tables, and the practice and field management of decompression is a significant part of the work of the diving supervisor. Recreational divers are trained in the theory and practice of decompression to the extent that the certifying agency specifies in the training standard for each certification. This may vary from a rudimentary overview sufficient to allow the diver to avoid decompression obligation for entry level divers, to competence in the use of several decompression algorithms by way of personal dive computers, decompression software, and tables for advanced technical divers. The detailed understanding of decompression theory is not generally required of either commercial or recreational divers. + +== See also == +Decompression (diving) – Pressure reduction and its effects during ascent from depth +Decompression practice – Techniques and procedures for safe decompression of divers +Decompression sickness – Disorder caused by dissolved gases forming bubbles in tissues +Dive computer – Instrument to calculate decompression status in real time +Equivalent air depth – Method of comparing decompression requirements for air and a given nitrox mix +Equivalent narcotic depth – Method for comparing the narcotic effects of a mixed diving gas with air +History of decompression research and development +Hyperbaric treatment schedules – Planned hyperbaric exposure using a specified breathing gas as medical treatment +Oxygen window – Difference between the partial pressures of oxygen in arterial blood and body tissues +Physiology of decompression – Physiological basis for decompression theory and practice +Decompression models: +Bühlmann decompression algorithm – Mathematical model of tissue inert gas uptake and release with pressure change +Haldane's decompression model – Decompression model developed by John Scott Haldane +Reduced gradient bubble model – Decompression algorithm +Thalmann algorithm – Mathematical model for diver decompression +Thermodynamic model of decompression – Early diving decompression model +Varying Permeability Model – Decompression model and algorithm based on bubble physics + +== Notes == +1. ^a autochthonous: formed or originating in the place where found + +== References == + +=== Sources === +Hamilton, Robert W.; Thalmann, Edward D. (2003). "10.2: Decompression Practice". In Brubakk, Alf O.; Neuman, Tom S. (eds.). Bennett and Elliott's physiology and medicine of diving (5th Revised ed.). United States: Saunders. pp. 455–500. ISBN 978-0-7020-2571-6. OCLC 51607923. +Huggins, Karl E. (1992). Dynamics of decompression workshop. Course Taught at the University of Michigan (Report). +Thalmann, E.D. (1984). Phase II testing of decompression algorithms for use in the U.S. Navy underwater decompression computer. Navy Exp. Diving Unit Res. Report (Report). Vol. 1–84. +Thalmann, E.D. (1985). Development of a Decompression Algorithm for Constant Oxygen Partial Pressure in Helium Diving. Navy Experimental Diving Unit Research Report (Report). Vol. 1–85. +US Navy (2008). US Navy Diving Manual, 6th revision. United States: US Naval Sea Systems Command. Retrieved 15 June 2008. +Wienke, Bruce R.; O'Leary, Timothy R. (13 February 2002). "Reduced gradient bubble model: Diving algorithm, basis and comparisons" (PDF). Tampa, Florida: NAUI Technical Diving Operations. Retrieved 25 January 2012. +Yount, D.E. (1991). Hans-Jurgen, K.; Harper Jr, D.E. (eds.). "Gelatin, bubbles, and the bends". International Pacifica Scientific Diving..., (Proceedings of the American Academy of Underwater Sciences Eleventh Annual Scientific Diving Symposium Held 25–30 September 1991. University of Hawaii, Honolulu, Hawaii). + +== Further reading == +Ball, R; Himm, J; Homer, LD; Thalmann, ED (1995). "Does the time course of bubble evolution explain decompression sickness risk?". Undersea and Hyperbaric Medicine. 22 (3): 263–280. ISSN 1066-2936. PMID 7580767. +Gerth, Wayne A; Doolette, David J. (2007). "VVal-18 and VVal-18M Thalmann Algorithm – Air Decompression Tables and Procedures". Navy Experimental Diving Unit, TA 01-07, NEDU TR 07-09. +Gribble, M. de G. (1960); A comparison of the High-Altitude and High-Pressure syndromes of decompression sickness, Br. J. Ind. Med., 1960, 17, 181. +Hills. B. (1966); A thermodynamic and kinetic approach to decompression sickness. Thesis +Lippmann, John; Mitchell, Simon (2005). Deeper into Diving (2nd ed.). Melbourne, Australia: J L Publications. ISBN 0-9752290-1-X. +Parker, E. C.; S.S. Survanshi; P.K. Weathersby & E.D. Thalmann (1992). "Statistically Based Decompression Tables VIII: Linear Exponential Kinetics". Naval Medical Research Institute Report. 92–73. +Salama, Asser (2018). Deep into Deco. Florida: Best Pub. ISBN 978-1-947239-09-8. +Powell, Mark (2008). Deco for Divers. Southend-on-Sea: Aquapress. ISBN 978-1-905492-07-7. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Decompression_theory-2.md b/data/en.wikipedia.org/wiki/Decompression_theory-2.md new file mode 100644 index 000000000..7bbb3ce82 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Decompression_theory-2.md @@ -0,0 +1,17 @@ +--- +title: "Decompression theory" +chunk: 3/17 +source: "https://en.wikipedia.org/wiki/Decompression_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:49.112339+00:00" +instance: "kb-cron" +--- + +=== Bubble mechanics === +Equilibrium of forces on the surface is required for a bubble to exist. The sum of the Ambient pressure and pressure due to tissue distortion, exerted on the outside of the surface, with surface tension of the liquid at the interface between the bubble and the surroundings must be balanced by the pressure on the inside of the bubble. This is the sum of the partial pressures of the gases inside due to the net diffusion of gas to and from the bubble. The force balance on the bubble may be modified by a layer of surface active molecules which can stabilise a microbubble at a size where surface tension on a clean bubble would cause it to collapse rapidly, and this surface layer may vary in permeability, so that if the bubble is sufficiently compressed it may become impermeable to diffusion. If the solvent outside the bubble is saturated or unsaturated, the partial pressure will be less than in the bubble, and the surface tension will be increasing the internal pressure in direct proportion to surface curvature, providing a pressure gradient to increase diffusion out of the bubble, effectively "squeezing the gas out of the bubble", and the smaller the bubble the faster it will get squeezed out. A gas bubble can only grow at constant pressure if the surrounding solvent is sufficiently supersaturated to overcome the surface tension or if the surface layer provides sufficient reaction to overcome surface tension. Clean bubbles that are sufficiently small will collapse due to surface tension if the supersaturation is low. Bubbles with semipermeable surfaces will either stabilise at a specific radius depending on the pressure, the composition of the surface layer, and the supersaturation, or continue to grow indefinitely, if larger than the critical radius. Bubble formation can occur in the blood or other tissues. +A solvent can carry a supersaturated load of gas in solution. Whether it will come out of solution in the bulk of the solvent to form bubbles will depend on a number of factors. Something which reduces surface tension, or adsorbs gas molecules, or locally reduces solubility of the gas, or causes a local reduction in static pressure in a fluid may result in a bubble nucleation or growth. This may include velocity changes and turbulence in fluids and local tensile loads in solids and semi-solids. Lipids and other hydrophobic surfaces may reduce surface tension (blood vessel walls may have this effect). Dehydration may reduce gas solubility in a tissue due to higher concentration of other solutes, and less solvent to hold the gas. Another theory presumes that microscopic bubble nuclei always exist in aqueous media, including living tissues. These bubble nuclei are spherical gas phases that are small enough to remain in suspension yet strong enough to resist collapse, their stability being provided by an elastic surface layer consisting of surface-active molecules which resists the effect of surface tension. +Once a micro-bubble forms it may continue to grow if the tissues are sufficiently supersaturated. As the bubble grows it may distort the surrounding tissue and cause damage to cells and pressure on nerves resulting in pain, or may block a blood vessel, cutting off blood flow and causing hypoxia in the tissues normally perfused by the vessel. +If a bubble or an object exists which collects gas molecules this collection of gas molecules may reach a size where the internal pressure exceeds the combined surface tension and external pressure and the bubble will grow. If the solvent is sufficiently supersaturated, the diffusion of gas into the bubble will exceed the rate at which it diffuses back into solution, and if this excess pressure is greater than the pressure due to surface tension the bubble will continue to grow. When a bubble grows, the surface tension decreases, and the interior pressure drops, allowing gas to diffuse in faster, and diffuse out slower, so the bubble grows or shrinks in a positive feedback situation. The growth rate is reduced as the bubble grows because the surface area increases as the square of the radius, while the volume increases as the cube of the radius. If the external pressure is reduced due to reduced hydrostatic pressure during ascent, the bubble will also grow, and conversely, an increased external pressure will cause the bubble to shrink, but may not cause it to be eliminated entirely if a compression-resistant surface layer exists. +Decompression bubbles appear to form mostly in the systemic capillaries where the gas concentration is highest, often those feeding the veins draining the active limbs. They do not generally form in the arteries provided that ambient pressure reduction is not too rapid, as arterial blood has recently had the opportunity to release excess gas into the lungs. The bubbles carried back to the heart in the veins may be transferred to the systemic circulation via a patent foramen ovale in divers with this septal defect, after which there is a risk of occlusion of capillaries in whichever part of the body they end up in. +Bubbles which are carried back to the heart in the veins will pass into the right side of the heart, and from there they will normally enter the pulmonary circulation and pass through or be trapped in the capillaries of the lungs, which are around the alveoli and very near to the respiratory gas, where the gas will diffuse from the bubbles though the capillary and alveolar walls into the gas in the lung. If the number of lung capillaries blocked by these bubbles is relatively small, the diver will not display symptoms, and no tissue will be damaged (lung tissues are adequately oxygenated by diffusion). The bubbles which are small enough to pass through the lung capillaries may be small enough to be dissolved due to a combination of surface tension and diffusion to a lowered concentration in the surrounding blood, though the Varying Permeability Model nucleation theory implies that most bubbles passing through the pulmonary circulation will lose enough gas to pass through the capillaries and return to the systemic circulation as recycled but stable nuclei. Bubbles which form within the tissues must be eliminated in situ by diffusion, which implies a suitable concentration gradient. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Decompression_theory-3.md b/data/en.wikipedia.org/wiki/Decompression_theory-3.md new file mode 100644 index 000000000..6f782365b --- /dev/null +++ b/data/en.wikipedia.org/wiki/Decompression_theory-3.md @@ -0,0 +1,21 @@ +--- +title: "Decompression theory" +chunk: 4/17 +source: "https://en.wikipedia.org/wiki/Decompression_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:49.112339+00:00" +instance: "kb-cron" +--- + +=== Isobaric counterdiffusion (ICD) === + +Isobaric counterdiffusion is the diffusion of gases in opposite directions caused by a change in the composition of the external ambient gas or breathing gas without change in the ambient pressure. During decompression after a dive this can occur when a change is made to the breathing gas, or when the diver moves into a gas filled environment which differs from the breathing gas. While not strictly speaking a phenomenon of decompression, it is a complication that can occur during decompression, and that can result in the formation or growth of bubbles without changes in the environmental pressure. Two forms of this phenomenon have been described by Lambertsen: +Superficial ICD (also known as Steady State Isobaric Counterdiffusion) occurs when the inert gas breathed by the diver diffuses more slowly into the body than the inert gas surrounding the body. An example of this would be breathing air in an heliox environment. The helium in the heliox diffuses into the skin quickly, while the nitrogen diffuses more slowly from the capillaries to the skin and out of the body. The resulting effect generates supersaturation in certain sites of the superficial tissues and the formation of inert gas bubbles. +Deep Tissue ICD (also known as Transient Isobaric Counterdiffusion) occurs when different inert gases are breathed by the diver in sequence. The rapidly diffusing gas is transported into the tissue faster than the slower diffusing gas is transported out of the tissue. This can occur as divers switch from a nitrogen mixture to a helium mixture or when saturation divers breathing hydreliox switch to a heliox mixture. +Doolette and Mitchell's study of Inner Ear Decompression Sickness (IEDCS) shows that the inner ear may not be well-modelled by common (e.g. Bühlmann) algorithms. Doolette and Mitchell propose that a switch from a helium-rich mix to a nitrogen-rich mix, as is common in technical diving when switching from trimix to nitrox on ascent, may cause a transient supersaturation of inert gas within the inner ear and result in IEDCS. They suggest that breathing-gas switches from helium-rich to nitrogen-rich mixtures should be carefully scheduled either deep (with due consideration to nitrogen narcosis) or shallow to avoid the period of maximum supersaturation resulting from the decompression. Switches should also be made during breathing of the largest inspired oxygen partial pressure that can be safely tolerated with due consideration to oxygen toxicity. + +=== Causative role of oxygen === +Although it is commonly held that DCS is caused by inert gas supersaturation, Hempleman has stated: ...This did not lead to a sufficient cut-back in the permitted decompression ratio and an allowance in the calculations is now made for high oxygen partial pressures. Whenever the partial pressure of oxygen in air (or mixture) exceeds 0.6 bar then it is considered that significant amounts of dissolved oxygen are present in the tissues and that there is an increased decompression risk. This is estimated by adding 25% to the dive depth, and proceeding with the calculations as just outlined using assumption (1). An oxygen first stop depth is thus obtained, and 5 min is spent at this depth to allow for metabolic use of the excess dissolved oxygen gas. Following this 'oxygen stop' the calculations proceed as outlined above. + +== Decompression sickness == \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Decompression_theory-4.md b/data/en.wikipedia.org/wiki/Decompression_theory-4.md new file mode 100644 index 000000000..e315ba79f --- /dev/null +++ b/data/en.wikipedia.org/wiki/Decompression_theory-4.md @@ -0,0 +1,20 @@ +--- +title: "Decompression theory" +chunk: 5/17 +source: "https://en.wikipedia.org/wiki/Decompression_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:49.112339+00:00" +instance: "kb-cron" +--- + +Vascular bubbles formed in the systemic capillaries may be trapped in the lung capillaries, temporarily blocking them. If this is severe, the symptom called "chokes" may occur. If the diver has a patent foramen ovale (or a shunt in the pulmonary circulation), bubbles may pass through it and bypass the pulmonary circulation to enter the arterial blood. If these bubbles are not absorbed in the arterial plasma and lodge in systemic capillaries they will block the flow of oxygenated blood to the tissues supplied by those capillaries, and those tissues will be starved of oxygen. Moon and Kisslo (1988) concluded that "the evidence suggests that the risk of serious neurological DCI or early onset DCI is increased in divers with a resting right-to-left shunt through a PFO. There is, at present, no evidence that PFO is related to mild or late onset bends." +Bubbles form within other tissues as well as the blood vessels. Inert gas can diffuse into bubble nuclei between tissues. In this case, the bubbles can distort and permanently damage the tissue. As they grow, the bubbles may also compress nerves as they grow causing pain. +Extravascular or autochthonous[a] bubbles usually form in slow tissues such as joints, tendons and muscle sheaths. Direct expansion causes tissue damage, with the release of histamines and their associated affects. Biochemical damage may be as important as, or more important than mechanical effects. +The exchange of dissolved gases between the blood and tissues is controlled by perfusion and to a lesser extent by diffusion, particularly in heterogeneous tissues. +The distribution of blood flow to the tissues is variable and subject to a variety of influences. When the flow is locally high, that area is dominated by perfusion, and by diffusion when the flow is low. The distribution of flow is controlled by the mean arterial pressure and the local vascular resistance, and the arterial pressure depends on cardiac output and the total vascular resistance. Basic vascular resistance is controlled by the sympathetic nervous system, and metabolites, temperature, and local and systemic hormones have secondary and often localised effects, which can vary considerably with circumstances. Peripheral vasoconstriction in cold water decreases overall heat loss without increasing oxygen consumption until shivering begins, at which point oxygen consumption will rise, though the vasoconstriction can persist. +The composition of the breathing gas during pressure exposure and decompression is significant in inert gas uptake and elimination for a given pressure exposure profile. Breathing gas mixtures for diving will typically have a different gas fraction of nitrogen to that of air. The partial pressure of each component gas will differ from that of nitrogen in air at any given depth, and uptake and elimination of each inert gas component is proportional to the actual partial pressure over time. The two foremost reasons for use of mixed breathing gases are the reduction of nitrogen partial pressure by dilution with oxygen, to make Nitrox mixtures, primarily to reduce the rate of nitrogen uptake during pressure exposure, and the substitution of helium (and occasionally other gases) for the nitrogen to reduce the narcotic effects under high partial pressure exposure. Depending on the proportions of helium and nitrogen, these gases are called Heliox, if there is no nitrogen, or Trimix, if there is nitrogen and helium along with the essential oxygen. The inert gases used as substitutes for nitrogen have different solubility and diffusion characteristics in living tissues to the nitrogen they replace. For example, the most common inert gas diluent substitute for nitrogen is helium, which is significantly less soluble in living tissue, but also diffuses faster due to the relatively small size and mass of the He atom in comparison with the N2 molecule. +Blood flow to skin and fat are affected by skin and core temperature, and resting muscle perfusion is controlled by the temperature of the muscle itself. During exercise increased flow to the working muscles is often balanced by reduced flow to other tissues, such as kidneys spleen and liver. Blood flow to the muscles is also lower in cold water, but exercise keeps the muscle warm and flow elevated even when the skin is chilled. Blood flow to fat normally increases during exercise, but this is inhibited by immersion in cold water. Adaptation to cold reduces the extreme vasoconstriction which usually occurs with cold water immersion. Variations in perfusion distribution do not necessarily affect respiratory inert gas exchange, though some gas may be locally trapped by changes in perfusion. Rest in a cold environment will reduce inert gas exchange from skin, fat and muscle, whereas exercise will increase gas exchange. Exercise during decompression can reduce decompression time and risk, providing bubbles are not present, but can increase risk if bubbles are present. Inert gas exchange is least favourable for the diver who is warm and exercises at depth during the ingassing phase, and rests and is cold during decompression. +Other factors which can affect decompression risk include oxygen concentration, carbon dioxide levels, body position, vasodilators and constrictors, positive or negative pressure breathing. and dehydration (blood volume). Individual susceptibility to decompression sickness has components which can be attributed to a specific cause, and components which appear to be random. The random component makes successive decompressions a poor test of susceptibility. Obesity and high serum lipid levels have been implicated by some studies as risk factors, and risk seems to increase with age. Another study has also shown that older subjects tended to bubble more than younger subjects for reasons not yet known, but no trends between weight, body fat, or gender and bubbles were identified, and the question of why some people are more likely to form bubbles than others remains unclear. + +== Decompression model concepts == \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Decompression_theory-5.md b/data/en.wikipedia.org/wiki/Decompression_theory-5.md new file mode 100644 index 000000000..079412a01 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Decompression_theory-5.md @@ -0,0 +1,23 @@ +--- +title: "Decompression theory" +chunk: 6/17 +source: "https://en.wikipedia.org/wiki/Decompression_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:49.112339+00:00" +instance: "kb-cron" +--- + +Two rather different concepts have been used for decompression modelling. The first assumes that dissolved gas is eliminated while in the dissolved phase, and that bubbles are not formed during asymptomatic decompression. The second, which is supported by experimental observation, assumes that bubbles are formed during most asymptomatic decompressions, and that gas elimination must consider both dissolved and bubble phases. +Early decompression models tended to use the dissolved phase models, and adjusted them by more or less arbitrary factors to reduce the risk of symptomatic bubble formation. Dissolved phase models are of two main groups. Parallel compartment models, where several compartments with varying rates of gas absorption (half time), are considered to exist independently of each other, and the limiting condition is controlled by the compartment which shows the worst case for a specific exposure profile. These compartments represent conceptual tissues and are not intended to represent specific organic tissues, merely to represent the range of possibilities for the organic tissues. The second group uses serial compartments, where gas is assumed to diffuse through one compartment before it reaches the next. A recent variation on the serial compartment model is the Goldman interconnected compartment model (ICM). +More recent models attempt to model bubble dynamics, also by simplified models, to facilitate the computation of tables, and later to allow real time predictions during a dive. The models used to approximate bubble dynamics are varied, and range from those which are not much more complex that the dissolved phase models, to those which require considerably greater computational power. +None of the decompression models can be shown to be an accurate representation of the physiological processes, although interpretations of the mathematical models have been proposed which correspond with various hypotheses. They are all approximations which predict reality to a greater or lesser extent, and are acceptably reliable only within the bounds of calibration against collected experimental data. + +=== Range of application === +The ideal decompression profile creates the greatest possible gradient for inert gas elimination from a tissue without causing bubbles to form, and the dissolved phase decompression models are based on the assumption that bubble formation can be avoided. However, it is not certain whether this is practically possible: some of the decompression models assume that stable bubble micronuclei always exist. The bubble models make the assumption that there will be bubbles, but there is a tolerable total gas phase volume or a tolerable gas bubble size, and limit the maximum gradient to take these tolerances into account. +Decompression models should ideally accurately predict risk over the full range of exposure from short dives within the no-stop limits, decompression bounce dives over the full range of practical applicability, including extreme exposure dives and repetitive dives, alternative breathing gases, including gas switches and constant PO2, variations in dive profile, and saturation dives. This is not generally the case, and most models are limited to a part of the possible range of depths and times. They are also limited to a specified range of breathing gases, and sometimes restricted to air. +A fundamental problem in the design of decompression tables is that the simplified rules that govern a single dive and ascent do not apply when some tissue bubbles already exist, as these will delay inert gas elimination and equivalent decompression may result in decompression sickness. Repetitive diving, multiple ascents within a single dive, and surface decompression procedures are significant risk factors for DCS. These have been attributed to the development of a relatively high gas phase volume which may be partly carried over to subsequent dives or the final ascent of a sawtooth profile. +The function of decompression models has changed with the availability of Doppler ultrasonic bubble detectors, and is no longer merely to limit symptomatic occurrence of decompression sickness, but also to limit asymptomatic post-dive venous gas bubbles. A number of empirical modifications to dissolved phase models have been made since the identification of venous bubbles by Doppler measurement in asymptomatic divers soon after surfacing. + +=== Efficiency and safety === +Two criteria that have been used in comparing decompression schedules are efficiency and safety, where decompression efficiency is defined as the ability of a schedule to provide acceptable safety from decompression sickness in the shortest time spent decompressing, and decompression safety, or converely, risk, is measured by the probability of decompression sickness incurred by following a given schedule for a given dive profile. Since it is impracticable to eliminate all risk using current knowledge of the effects of several variables, risk is estimated by statistical analysis of the recorded outcomes of exposure and decompression profiles, and an acceptable risk is stipulated, which may vary depending on the circumstances of the application. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Decompression_theory-6.md b/data/en.wikipedia.org/wiki/Decompression_theory-6.md new file mode 100644 index 000000000..2923e68c7 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Decompression_theory-6.md @@ -0,0 +1,23 @@ +--- +title: "Decompression theory" +chunk: 7/17 +source: "https://en.wikipedia.org/wiki/Decompression_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:49.112339+00:00" +instance: "kb-cron" +--- + +=== Tissue compartments === +One attempt at a solution was the development of multi-tissue models, which assumed that different parts of the body absorbed and eliminated gas at different rates. These are hypothetical tissues which are designated as fast and slow to describe the rate of saturation. Each tissue, or compartment, has a different half-life. Real tissues will also take more or less time to saturate, but the models do not need to use actual tissue values to produce a useful result. Models with from one to 16 tissue compartments have been used to generate decompression tables, and dive computers have used up to 20 compartments. +For example: Tissues with a high lipid content can take up a larger amount of nitrogen, but often have a poor blood supply. These will take longer to reach equilibrium, and are described as slow, compared to tissues with a good blood supply and less capacity for dissolved gas, which are described as fast. +Fast tissues absorb gas relatively quickly, but will generally release it quickly during ascent. A fast tissue may become saturated in the course of a normal recreational dive, while a slow tissue may have absorbed only a small part of its potential gas capacity. By calculating the levels in each compartment separately, researchers are able to construct more effective algorithms. In addition, each compartment may be able to tolerate more or less supersaturation than others. The final form is a complicated model, but one that allows for the construction of algorithms and tables suited to a wide variety of diving. A typical dive computer has an 8–12 tissue model, with half times varying from 5 minutes to 400 minutes. The Bühlmann tables use an algorithm with 16 tissues, with half times varying from 4 minutes to 640 minutes. +Tissues may be assumed to be in series, where dissolved gas must diffuse through one tissue to reach the next, which has different solubility properties, in parallel, where diffusion into and out of each tissue is considered to be independent of the others, and as combinations of series and parallel tissues, which becomes computationally complex. + +=== Ingassing model === +The half time of a tissue is the time it takes for the tissue to take up or release 50% of the difference in dissolved gas capacity at a changed partial pressure. For each consecutive half time the tissue will take up or release half again of the cumulative difference in the sequence ½, ¾, 7/8, 15/16, 31/32, 63/64 etc. Tissue compartment half times range from 1 minute to at least 720 minutes. A specific tissue compartment will have different half times for gases with different solubilities and diffusion rates. Ingassing is generally modeled as following a simple inverse exponential equation where saturation is assumed after approximately four (93.75%) to six (98.44%) half-times depending on the decompression model. There is normally no phase change during ingassing after the gases are dissolved in the blood of the pulmonary circulation in the lungs. They remain in solution in whichever tissues they reach by perfusion and diffusion, so the model is fairly robust. The exception is for isobaric counterdiffusion which can induce bubble growth and possibly bubble formation when a gas of different solubility is introduced to the breathing mixture. +This model may not adequately describe the dynamics of outgassing if gas phase bubbles are present. + +=== Outgassing models === +For optimised decompression the driving force for tissue desaturation should be kept at a maximum, provided that this does not cause symptomatic tissue injury due to bubble formation and growth (symptomatic decompression sickness), or produce a condition where diffusion is retarded for any reason. +There are two fundamentally different ways this has been approached. The first is based on an assumption that there is a level of supersaturation which does not produce symptomatic bubble formation and is based on empirical observations of the maximum decompression rate which does not result in an unacceptable rate of symptoms. This approach seeks to maximise the concentration gradient providing there are no symptoms, and commonly uses a slightly modified exponential half-time model. The second assumes that bubbles will form at any level of supersaturation where the total gas tension in the tissue is greater than the ambient pressure and that gas in bubbles is eliminated more slowly than dissolved gas. These philosophies result in differing characteristics of the decompression profiles derived for the two models: The critical supersaturation approach gives relatively rapid initial ascents, which maximize the concentration gradient, and long shallow stops, while the bubble models require slower ascents, with deeper first stops, but may have shorter shallow stops. This approach uses a variety of models. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Decompression_theory-7.md b/data/en.wikipedia.org/wiki/Decompression_theory-7.md new file mode 100644 index 000000000..dd500af96 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Decompression_theory-7.md @@ -0,0 +1,35 @@ +--- +title: "Decompression theory" +chunk: 8/17 +source: "https://en.wikipedia.org/wiki/Decompression_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:49.112339+00:00" +instance: "kb-cron" +--- + +==== The critical supersaturation approach ==== +J.S. Haldane originally used a critical pressure ratio of 2 to 1 for decompression on the principle that the saturation of the body should at no time be allowed to exceed about double the air pressure. This principle was applied as a pressure ratio of total ambient pressure and did not take into account the partial pressures of the component gases of the breathing air. His experimental work on goats and observations of human divers appeared to support this assumption. However, in time, this was found to be inconsistent with incidence of decompression sickness and changes were made to the initial assumptions. This was later changed to a 1.58:1 ratio of nitrogen partial pressures. +Further research by people such as Robert Workman suggested that the criterion was not the ratio of pressures, but the actual pressure differentials. Applied to Haldane's work, this would suggest that the limit is not determined by the 1.58:1 ratio but rather by the critical pressure difference of 0.58 atmospheres between tissue pressure and ambient pressure. Most Haldanean tables since the mid 20th century, including the Bühlmann tables, are based on the critical difference assumption. +The M-value is the maximum value of absolute inert gas pressure that a tissue compartment can take at a given ambient pressure without presenting symptoms of decompression sickness. M-values are limits for the tolerated gradient between inert gas pressure and ambient pressure in each compartment. Alternative terminology for M-values include "supersaturation limits", "limits for tolerated overpressure", and "critical tensions". +Gradient factors are a way of modifying the M-value to a more conservative value for use in a decompression algorithm. The gradient factor is a percentage of the M-value chosen by the algorithm designer, and varies linearly between the maximum depth of the specific dive and the surface. They are expressed as a two number designation, where the first number is the percentage of the deep M-value, and the second is a percentage of the shallow M-value. The gradient factors are applied to all tissue compartments equally and produce an M-value which is linearly variable in proportion to ambient pressure. + +For example: A 30/85 gradient factor would limit the allowed supersaturation at depth to 30% of the designer's maximum, and to 85% at the surface. +In effect the user is selecting a lower maximum supersaturation than the designer considered appropriate. Use of gradient factors will increase decompression time, particularly in the depth zone where the M-value is reduced the most. Gradient factors may be used to force deeper stops in a model which would otherwise tend to produce relatively shallow stops, by using a gradient factor with a small first number. Several models of dive computer allow user input of gradient factors as a way of inducing a more conservative, and therefore presumed lower risk, decompression profile. Forcing a low gradient factor at the deep M-value can have the effect of increasing ingassing during the ascent, generally of the slower tissues, which must then release a larger gas load at shallower depths. This has been shown to be an inefficient decompression strategy. +The Variable Gradient Model adjusts the gradient factors to fit the depth profile on the assumption that a straight line adjustment using the same factor on the deep M-value regardless of the actual depth is less appropriate than using an M-value linked to the actual depth. (the shallow M-value is linked to actual depth of zero in both cases) + +==== The no-supersaturation approach ==== +According to the thermodynamic model of Hugh LeMessurier and Brian Andrew Hills, this condition of optimum driving force for outgassing is satisfied when the ambient pressure is just sufficient to prevent phase separation (bubble formation). +The fundamental difference of this approach is equating absolute ambient pressure with the total of the partial gas tensions in the tissue for each gas after decompression as the limiting point beyond which bubble formation is expected. +The model assumes that the natural unsaturation in the tissues due to metabolic reduction in oxygen partial pressure provides the buffer against bubble formation, and that the tissue may be safely decompressed provided that the reduction in ambient pressure does not exceed this unsaturation value. Clearly any method which increases the unsaturation would allow faster decompression, as the concentration gradient would be greater without risk of bubble formation. +The natural unsaturation increases with depth, so a larger ambient pressure differential is possible at greater depth, and reduces as the diver surfaces. This model leads to slower ascent rates and deeper first stops, but shorter shallow stops, as there is less bubble phase gas to be eliminated. + +==== The critical volume approach ==== +The critical-volume criterion assumes that whenever the total volume of gas phase accumulated in the tissues exceeds a critical value, signs or symptoms of DCS will appear. This assumption is supported by doppler bubble detection surveys. The consequences of this approach depend strongly on the bubble formation and growth model used, primarily whether bubble formation is practicably avoidable during decompression. +This approach is used in decompression models which assume that during practical decompression profiles, there will be growth of stable microscopic bubble nuclei which always exist in aqueous media, including living tissues. +Efficient decompression will minimize the total ascent time while limiting the total accumulation of bubbles to an acceptable non-symptomatic critical value. The physics and physiology of bubble growth and elimination indicate that it is more efficient to eliminate bubbles while they are very small. Models which include bubble phase have produced decompression profiles with slower ascents and deeper initial decompression stops as a way of curtailing bubble growth and facilitating early elimination, in comparison with the models which consider only dissolved phase gas. + +=== Bounce dives === +A bounce dive is any dive where the exposure to pressure is not long enough for all the tissues to reach equilibrium with the inert gases in the breathing gas. + +=== Saturation dives === \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Decompression_theory-8.md b/data/en.wikipedia.org/wiki/Decompression_theory-8.md new file mode 100644 index 000000000..669fb843d --- /dev/null +++ b/data/en.wikipedia.org/wiki/Decompression_theory-8.md @@ -0,0 +1,29 @@ +--- +title: "Decompression theory" +chunk: 9/17 +source: "https://en.wikipedia.org/wiki/Decompression_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:49.112339+00:00" +instance: "kb-cron" +--- + +A saturation exposure is where the time exposed to pressure is sufficient for all tissues to reach equilibrium with the inert gases in the breathing mixture. For practical purposes this is usually taken as 6 times the half time of the slowest tissue in the model. + +=== No-stop limits === +A no-stop limit, also called no decompression limit (NDL) is the theoretical maximum dissolved gas content of each tissue compartment of the whole body, which can be decompressed directly to surface pressure at the chosen ascent rate used by the model, without a need to stop to outgas at any depth, which has an acceptable risk of developing symptomatic decompression sickness. No decompression limit is a misnomer as the ascent at the specified ascent rate is decompression, but the term has historical inertia and continues to be used. + +=== Decompression ceiling, floor and window === +Once the gas loading of one or more tissue compartments exceeds the maximum level accepted for the no-stop limit, there is a minimum depth to which the diver can ascend at the appropriate ascent rate, at an acceptable risk for decompression sickness. This depth is known as the decompression ceiling. It may be considered a soft overhead, in that it is physically trivial to ascend above it, but that increases the risk of developing symptomatic decompression sickness according to the decompression model to a theoretically unacceptable level. The tissue that reaches its decompression ceiling first is called the limiting tissue. +The depth (or pressure) at which the controlling tissue starts to offgas for a given breathing gas is known as the decompression floor. Above this floor and below the decompression ceiling is the depth range known as the decompression window, the depth range in which safe decompression can occur according to the decompression model. Decompression stress is lower towards the floor, and decompression efficiency is greater nearer the ceiling. The floor depth depends on the concentration gradient of the inert gas, and thereby partial pressure of the inert part of the breathing gas. +Offgassing near the floor is relatively slow, and some slower tissues may still be ingassing. If the diver stays in this depth zone the decompression obligation may increase, and off-gassing will eventually stop as the floor rises. At the same time, as offgassing of the limiting tissue progresses, the ceiling will also rise, allowing the diver to ascend to follow it. However if ingassing of other tissues is sufficient, one of them may take over as the limiting tissue and bring the ceiling deeper. Off-gassing near he floor also minimises bubble growth, and near the ceiling maximises off-gassing of dissolved gas. + +=== Decompression obligation === +A decompression obligation is the presence in the tissues of sufficient dissolved gas that the risk of symptomatic decompression sickness is unacceptable if a direct ascent to surface pressure is made at the prescribed ascent rate for the decompression model in use. A diver with a decompression ceiling can be said to have a decompression obligation, meaning that time must be spent outgassing during the ascent additional to the time spent ascending at the appropriate ascent rate. This time is nominally and most efficiently spent at decompression stops, though outgassing will occur at any depth where the arterial blood and lung gas have a lower partial pressure of the inert gas than the limiting tissue. When a decompression obligation exists, there will be a theoretical safe minimum depth known as the decompression ceiling. Obligatory decompression stops will be indicated at a depth at or below the current ceiling. + +=== Time to surface === +Time to surface (TTS) is the estimated total time required for a diver to surface from a given point on a dive profile, using a given set of decompression gases, ascending at the nominal ascent rate, and doing all the stops at the specifies depths. This value may be an estimate calculated from a dive plan, and followed by the diver as the ascent schedule, or shown on the screen of a dive computer as updated in real time. It may be based on the current gas selected, or the optimum gas selection from all gases set as active gases on the computer. + +=== Staged decompression === +Staged decompression is done with stops as specified depths based on an easily followed series. For most tables this has historically been a convenient 3 metres (10 ft) interval, but any arbitrary spacing may be used provided the computation of decompression stops uses it. The diver must stay at the prescribed stop depth until the ceiling decreases to the next shallower stop depth, at which point the diver ascends to that depth for the next stop. +The calculation of stop time can also be done to follow the decompression ceiling, which will give a maximised pressure gradient for inert gas washout, and reduces the overall decompression duration by about 4 to 12% This strategy can be approximately followed when using a dive computer with the option enabled. The effect on decompression risk with this strategy is unknown, as no testing has been done as of 2022. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Decompression_theory-9.md b/data/en.wikipedia.org/wiki/Decompression_theory-9.md new file mode 100644 index 000000000..0995e2ffb --- /dev/null +++ b/data/en.wikipedia.org/wiki/Decompression_theory-9.md @@ -0,0 +1,20 @@ +--- +title: "Decompression theory" +chunk: 10/17 +source: "https://en.wikipedia.org/wiki/Decompression_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:49.112339+00:00" +instance: "kb-cron" +--- + +=== Residual inert gas === +Gas bubble formation has been experimentally shown to significantly inhibit inert gas elimination. +A considerable amount of inert gas will remain in the tissues after a diver has surfaced, even if no symptoms of decompression sickness occur. This residual gas may be dissolved or in sub-clinical bubble form, and will continue to outgas while the diver remains at the surface. If a repetitive dive is made, the tissues are preloaded with this residual gas which will make them saturate faster. +In repetitive diving, the slower tissues can accumulate gas day after day, if there is insufficient time for the gas to be eliminated between dives. This can be a problem for multi-day multi-dive situations. Multiple decompressions per day over multiple days can increase the risk of decompression sickness because of the build up of asymptomatic bubbles, which reduce the rate of off-gassing and are not accounted for in most decompression algorithms. Consequently, some diver training organisations make extra recommendations such as taking "the seventh day off". + +== Decompression models in practice == + +=== Deterministic models === +Deterministic decompression models are a rule based approach to calculating decompression. These models work from the idea that "excessive" supersaturation in various tissues is "unsafe" (resulting in decompression sickness). The models usually contain multiple depth and tissue dependent rules based on mathematical models of idealised tissue compartments. There is no objective mathematical way of evaluating the rules or overall risk other than comparison with empirical test results. The models are compared with experimental results and reports from the field, and rules are revised by qualitative judgment and curve fitting so that the revised model more closely predicts observed reality, and then further observations are made to assess the reliability of the model in extrapolations into previously untested ranges. The usefulness of the model is judged on its accuracy and reliability in predicting the onset of symptomatic decompression sickness and asymptomatic venous bubbles during ascent. +It may be reasonably assumed that in reality, both perfusion transport by blood circulation, and diffusion transport in tissues where there is little or no blood flow occur. The problem with attempts to simultaneously model perfusion and diffusion is that there are large numbers of variables due to interactions between all of the tissue compartments and the problem becomes intractable. A way of simplifying the modelling of gas transfer into and out of tissues is to make assumptions about the limiting mechanism of dissolved gas transport to the tissues which control decompression. Assuming that either perfusion or diffusion has a dominant influence, and the other can be disregarded, can greatly reduce the number of variables. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Disease_theory_of_alcoholism-0.md b/data/en.wikipedia.org/wiki/Disease_theory_of_alcoholism-0.md index aa455c8ff..7afc6a099 100644 --- a/data/en.wikipedia.org/wiki/Disease_theory_of_alcoholism-0.md +++ b/data/en.wikipedia.org/wiki/Disease_theory_of_alcoholism-0.md @@ -4,7 +4,7 @@ chunk: 1/4 source: "https://en.wikipedia.org/wiki/Disease_theory_of_alcoholism" category: "reference" tags: "science, encyclopedia" -date_saved: "2026-05-05T07:28:00.228979+00:00" +date_saved: "2026-05-05T10:06:50.381723+00:00" instance: "kb-cron" --- diff --git a/data/en.wikipedia.org/wiki/Disease_theory_of_alcoholism-1.md b/data/en.wikipedia.org/wiki/Disease_theory_of_alcoholism-1.md index 83f5ec52e..e80498b64 100644 --- a/data/en.wikipedia.org/wiki/Disease_theory_of_alcoholism-1.md +++ b/data/en.wikipedia.org/wiki/Disease_theory_of_alcoholism-1.md @@ -4,7 +4,7 @@ chunk: 2/4 source: "https://en.wikipedia.org/wiki/Disease_theory_of_alcoholism" category: "reference" tags: "science, encyclopedia" -date_saved: "2026-05-05T07:28:00.228979+00:00" +date_saved: "2026-05-05T10:06:50.381723+00:00" instance: "kb-cron" --- diff --git a/data/en.wikipedia.org/wiki/Disease_theory_of_alcoholism-2.md b/data/en.wikipedia.org/wiki/Disease_theory_of_alcoholism-2.md index 394c5c529..94df2a8b4 100644 --- a/data/en.wikipedia.org/wiki/Disease_theory_of_alcoholism-2.md +++ b/data/en.wikipedia.org/wiki/Disease_theory_of_alcoholism-2.md @@ -4,7 +4,7 @@ chunk: 3/4 source: "https://en.wikipedia.org/wiki/Disease_theory_of_alcoholism" category: "reference" tags: "science, encyclopedia" -date_saved: "2026-05-05T07:28:00.228979+00:00" +date_saved: "2026-05-05T10:06:50.381723+00:00" instance: "kb-cron" --- diff --git a/data/en.wikipedia.org/wiki/Disease_theory_of_alcoholism-3.md b/data/en.wikipedia.org/wiki/Disease_theory_of_alcoholism-3.md index a8e951bce..6e4833ff4 100644 --- a/data/en.wikipedia.org/wiki/Disease_theory_of_alcoholism-3.md +++ b/data/en.wikipedia.org/wiki/Disease_theory_of_alcoholism-3.md @@ -4,7 +4,7 @@ chunk: 4/4 source: "https://en.wikipedia.org/wiki/Disease_theory_of_alcoholism" category: "reference" tags: "science, encyclopedia" -date_saved: "2026-05-05T07:28:00.228979+00:00" +date_saved: "2026-05-05T10:06:50.381723+00:00" instance: "kb-cron" --- diff --git a/data/en.wikipedia.org/wiki/Effective_theory-0.md b/data/en.wikipedia.org/wiki/Effective_theory-0.md new file mode 100644 index 000000000..047ced511 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Effective_theory-0.md @@ -0,0 +1,63 @@ +--- +title: "Effective theory" +chunk: 1/1 +source: "https://en.wikipedia.org/wiki/Effective_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:51.573632+00:00" +instance: "kb-cron" +--- + +In science, an effective theory is a deliberately limited scientific theory applicable under specific circumstances. In practice, all theories are effective theories, with the name "effective theory" being used to signal that the limitations are built in by design. + + +== Examples == +An early example is Galileo Galilei's theory of falling bodies. Using observed values, Galileo deduced that the height of a falling body can be accounted for by constant acceleration, written here in modern notation: + + + + + + + + + d + + 2 + + + z + + + d + + t + + 2 + + + + + + = + − + g + , + + + {\displaystyle {\frac {d^{2}z}{dt^{2}}}=-g,} + +where t is the time, z is the vertical position of an object and g is gravitational acceleration near the surface of Earth. +Within the scope of objects falling on Earth, this theory works well. However, as Isaac Newton discovered in his Newton's law of universal gravitation, a more elaborate but still effective theory, has more scope at the expense of additional complications. The next layer was Albert Einstein's general relativity, with more scope but even more complications. + + +== Effective field theory == + +Effective field theory is a method used to describe physical theories when there is a hierarchy of scales. Effective field theories in physics can include quantum field theories in which the fields are treated as fundamental, and effective theories describing phenomena in solid-state physics. For instance, the BCS theory of superconduction treats vibrations of the solid-state lattice as a "field" (i.e. without claiming that there is really a field), with its own field quanta, known as phonons. Such "effective particles" derived from effective fields are also known as quasiparticles. The standard Big Bang cosmological theory, Lambda-CDM is an effective theory for some as yet undiscovered underlying physical theory. +In a certain sense, quantum field theory, and any other currently known physical theory, could be described as "effective", as in being the "low energy limit" of an as-yet unknown theory of everything. + + +== See also == + + +== References == \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Expectancy-value_theory-0.md b/data/en.wikipedia.org/wiki/Expectancy-value_theory-0.md new file mode 100644 index 000000000..f69c5e221 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Expectancy-value_theory-0.md @@ -0,0 +1,44 @@ +--- +title: "Expectancy-value theory" +chunk: 1/2 +source: "https://en.wikipedia.org/wiki/Expectancy-value_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:55.181654+00:00" +instance: "kb-cron" +--- + +Expectancy–value theory has been developed in many different fields including education, health, communications, marketing and economics. Although the model differs in its meaning and implications for each field, the general idea is that there are expectations as well as values or beliefs that affect subsequent behavior. + +== Education model == + +=== History and model overview === +John William Atkinson developed the expectancy–value theory in the 1950s and 1960s in an effort to understand the achievement motivation of individuals. In the 1980s, Jacquelynne Eccles expanded this research into the field of education. According to expectancy–value theory, students' achievement and achievement related choices are most proximally determined by two factors: expectancies for success, and subjective task values. Expectancies refer to how confident an individual is in his or her ability to succeed in a task whereas task values refer to how important, useful, or enjoyable the individual perceives the task. Theoretical and empirical work suggests that expectancies and values interact to predict important outcomes such as engagement, continuing interest, and academic achievement. Other factors, including demographic characteristics, stereotypes, prior experiences, and perceptions of others' beliefs and behaviors affect achievement related outcomes indirectly through these expectancies and values. This model has most widely been applied and used in research in the field of education. + +=== Expectancies === +Expectancies are specific beliefs individuals have regarding their success on certain tasks they will carry out in the short-term future or long-term future. An individual's expectancies are related to their behaviors as well as the choices they make. Expectancies are related to ability-beliefs such as self-concept and self-efficacy. Self-concept is a domain specific concept that involves one's beliefs about their own abilities based on their past experiences in the specific domain. Self-efficacy is the belief that an individual has the ability to successfully engage in a future specific task or series of related tasks + +=== Subjective task values === +According to Eccles and colleagues subjective task value can be thought of as the motivation that allows an individual to answer the question "Do I Want to do This Activity and Why?" Subjective task values can be broken into four subcategories: Attainment Value (Importance for identity or self), Intrinsic Value (Enjoyment or Interest), Utility Value (Usefulness or Relevance), and Cost (loss of time, overly-high effort demands, loss of valued alternatives, or negative psychological experiences such as stress). Traditionally, attainment value and intrinsic value are more highly correlated. What's more, these two constructs tend to be related to intrinsic motivation, interest, and task persistence. Alternatively, utility value has both intrinsic and extrinsic components. and has been related to both intrinsic and extrinsic outcomes such as course performance and interest. Other research shows that utility value has time-dependent characteristics as well. Cost has been relatively neglected in the empirical research; however, the construct has received some attention more recently. Feather combined subjective task values with more universal human values and suggested that the former are just one type of general human motives that help to direct behavior. + +=== Applications === + +==== Developmental trajectories ==== +Researchers have found that expectancies and values can be distinguished as separate types of motivation as early as 6 years old. Similarly, types of value (e.g., attainment vs. utility) can be distinguished within an academic domain as early as fifth grade. Generally speaking, Eccles and colleagues implicate a wide array of different factors that determine an individual's expectancies and values, including: + +the cultural milieu +socializer's beliefs and behaviors +differential aptitudes of the individual +previous achievement-related experiences +individual perceptions of social beliefs +individual's interpretations of experiences +affective memories +general goals +self-concepts +Experts agree that student motivation tends to decline throughout their time in school. Longitudinal research has confirmed this general trend of motivational decline and also demonstrated that motivation is domain specific. Researchers have also demonstrated that there are gender differences in motivation. Motivation decline is particularly steep for Math achievement, but less so for reading or sports domains among both boys and girls. Researchers offer two general explanations for these declines in motivation. The first is that students' conceptualizations of different domains become more complex and nuanced—they differentiate between subdomains, which results in an appearance of mean-level decrease. In fact, children as young as 11 years old have demonstrated that they can differentiate between academic domains. The second is that the focus of their environment changes as they age. As students reach higher grades, the focus shifts from learning to achievement. In fact, a large body of research exists showing that shifts from learning to performance as an educational focus can be detrimental to student motivation. + +==== Interventions ==== +Expectancy–value theory constructs can and have been applied to intervention programs that strive to change motivational beliefs. These interventions are able to increase expectancy and value or decrease cost. Such interventions not only target motivation, but also ultimately increase general student achievement and help to close traditionally problematic achievement gaps. For example, value- focused interventions have been developed to help teachers design their curriculum in ways that allow students to see the connections between the material they learn in the classroom and their own lives. This intervention is able to boost student's performance and interest, particularly for students who have low initial expectancy. According to the expectancy–value theory, this intervention is effective because it increases students interest in the material. + +== Psychology, health, communications, marketing, and economics model == +Expectancy–value theory was originally created in order to explain and predict individual's attitudes toward objects and actions. Originally the work of psychologist Martin Fishbein, the theory states that attitudes are developed and modified based on assessments about beliefs and values. Primarily, the theory attempts to determine the mental calculations that take place in attitude development. Expectancy–value theory has been used to develop other theories and is still utilized today in numerous fields of study. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Expectancy-value_theory-1.md b/data/en.wikipedia.org/wiki/Expectancy-value_theory-1.md new file mode 100644 index 000000000..c57adbd13 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Expectancy-value_theory-1.md @@ -0,0 +1,129 @@ +--- +title: "Expectancy-value theory" +chunk: 2/2 +source: "https://en.wikipedia.org/wiki/Expectancy-value_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:55.181654+00:00" +instance: "kb-cron" +--- + +=== History === +Dr. Martin Fishbein is credited with developing the expectancy–value theory (EVT) in the early to mid-1970s. It is sometimes referred to as Fishbein's expectancy–value theory or simply expectancy–value model. The primary work typically cited by scholars referring to EVT is Martin Fishbein and Icek Ajzen's 1975 book called Belief, Attitude, Intention, and Behavior: An Introduction to Theory and Research. The seed work of EVT can be seen in Fishbein's doctoral dissertation, A Theoretical and Empirical Investigation of the Interrelation between Belief about an Object and the Attitude toward that Object (1961, UCLA) and two subsequent articles in 1962 and 1963 in the journal Human Relations. Fishbein's work drew on the writings of researchers such as Ward Edwards, Milton J. Rosenberg, Edward Tolman, and John B. Watson. + +=== Concepts === +EVT has three basic components. First, individuals respond to novel information about an item or action by developing a belief about the item or action. If a belief already exists, it can and most likely will be modified by new information. Second, individuals assign a value to each attribute that a belief is based on. Third, an expectation is created or modified based on the result of a calculation based on beliefs and values. For example, a student finds out that a professor has a reputation for being humorous. The student assigns a positive value to humor in the classroom, so the student has the expectation that their experience with the professor will be positive. When the student attends class and finds the professor humorous, the student calculates that it is a good class. EVT also states that the result of the calculation, often called the "attitude", stems from complex equations that contain many belief/values pairs. Fishbein and Ajzen (1975) represented the theory with the following equation where attitudes (a) are a factorial function of beliefs (b) and values (v). +Theory of reasoned action: +Formula +In its simplest form, the TRA can be expressed as the following equation: + + + + + B + I + + = + + ( + A + B + ) + + W + + 1 + + + + + ( + S + N + ) + + W + + 2 + + + + + {\displaystyle BI{=}(AB)W_{1}+(SN)W_{2}} + + +where: + + + + + B + I + + + {\displaystyle BI} + + = behavioral intention + + + + + A + B + + + {\displaystyle AB} + + = one's attitude toward performing the behavior + + + + + W + + + {\displaystyle W} + + = empirically derived weights + + + + + S + N + + + {\displaystyle SN} + + = one's subjective norm related to performing the behavior +(Source: Hale, 2002) + +=== Current usage === +In the late 1970s and early 1980s, Fishbein and Ajzen expanded expectancy–value theory into the theory of reasoned action (TRA). Later Ajzen posited the theory of planned behavior (TPB) in his book Attitudes, Personality, and Behavior (1988). Both TRA and TPB address predictive and explanatory weaknesses with EVT and are still prominent theories in areas such as health communication research, marketing, and economics. Although not used as much since the early 1980s, EVT is still utilized in research within fields as diverse as audience research (Palmgreen & Rayburn, 1985) advertising (Shoham, Rose, & Kahle 1998; Smith & Vogt, 1995), child development (Watkinson, Dwyer, & Nielsen, 2005), education (Eklof, 2006; Ping, McBride, & Breune, 2006), health communication (Purvis Cooper, Burgoon, & Roter, 2001; Ludman & Curry, 1999), and organization communication (Westaby, 2002). + +== See also == +Theory of planned behavior + +== References == + +=== Education model === + +=== Health, communications, marketing, and economics model === +Ajzen, I. (1988). Attitudes, personality, and behavior (U.S. ed.). Chicago, IL: Dorsey Press. +Bandura, A. (1993). Perceived self-efficacy in cognitive development and functioning. Educational psychologist, 28(2), 117-148. +Bandura, A. (2012). On the functional properties of perceived self-efficacy revisited. Journal of Management, 38, 9–44. https://doi.org/10.1177/0149206311410606. +Eklof, H. (2006). Development and validation of scores from an instrument measuring student test-taking motivation. Educational & Psychological Measurement, 66, 643-656. +Fishbein, M. (1961). A theoretical and empirical investigation of the interrelation between belief about and object and the attitude toward that object (pp. 162): University of California, Los Angeles. Unpublished dissertation. +Fishbein, M. (1963). An investigation of relationships between beliefs about an object and the attitude toward that object. Human Relations, 16, 233-240. +Fishbein, M., & Ajzen, I. (1975). Belief, attitude, intention, and behavior : an introduction to theory and research. Reading, Mass.: Addison-Wesley Pub. +Fishbein, M., & Raven, B. (1962). The AB scales: An operational definition of belief and attitude. Human Relations, 15, 35-44. +Ludman, E. J., & Curry, S. J. (1999). Implementation of outreach telephone counseling to promote mammography participation. Health Education & Behavior, 26, 689. +Palmgreen, P., & Rayburn, J. (1985). An Expectancy–value Approach to Media Gratifications, in: "Rosengren, Karl Erik / Wenner, Lawrence A. / Palmgreen, Philip: Media Gratifications Research" (Beverly Hills, 1985, pp. 61–72). +Ping, X., McBride, R. E., & Bruene, A. (2006). Fourth-grade students' motivational changes in an elementary physical education running program. Research Quarterly for Exercise & Sport, 77, 195-207. +Purvis Cooper, C., Burgoon, M., & Roter, D. L. (2001). An expectancy–value analysis of viewer interest in television prevention news stories. Health Communication, 13, 227-240. +Shoham, A., Rose, G. M., & Kahle, L. R. (1998). Marketing of risky sports: From intention to action. Journal of the Academy of Marketing Science, 26, 307-321. +Smith, R. E., & Vogt, C. A. (1995). The effects of integrating advertising and negative word-of-mouth communications on message processing and response. Journal of Consumer Psychology, 4, 133. +Watkinson, E. J., Dwyer, S., & Nielsen, A. B. (2005). Children theorize about reasons for recess engagement: Does expectancy–value theory apply? Adapted Physical Activity Quarterly, 22, 179. + +== External links == +Icek Ajzen's webpage +Teachers Toolbox \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Expectancy_theory-0.md b/data/en.wikipedia.org/wiki/Expectancy_theory-0.md new file mode 100644 index 000000000..e3069739c --- /dev/null +++ b/data/en.wikipedia.org/wiki/Expectancy_theory-0.md @@ -0,0 +1,56 @@ +--- +title: "Expectancy theory" +chunk: 1/3 +source: "https://en.wikipedia.org/wiki/Expectancy_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:52.715379+00:00" +instance: "kb-cron" +--- + +Expectancy theory (or expectancy theory of motivation) proposes that an individual will behave or act in a certain way because they are motivated to select a specific behavior over others due to what they expect the result of that selected behavior will be. In essence, the motivation of the behavior selection is determined by the desirability of the outcome. However, at the core of the theory is the cognitive process of how an individual processes the different motivational elements. This is done before making the ultimate choice. The outcome is not the sole determining factor in making the decision of how to behave. +Expectancy theory is a motivation theory concerned with mental processes regarding choice, or choosing. First proposed by Victor Vroom of the Yale School of Management in 1964, it aims to explain the processes that an individual undergoes to make choices. In relation to the study of organizational behavior, the theory stresses "the need for organizations to relate rewards directly to performance and to ensure that the rewards provided are deserved and wanted by the recipients". +Vroom defines motivation as a process governing choices among alternative forms of voluntary activities, a process controlled by the individual. The individual makes choices based on estimates of how well the expected results of a given behavior are going to match up with or eventually lead to the desired results. Motivation is a product of the individual's expectancy that a certain effort will lead to the intended performance, the instrumentality of this performance to achieving a certain result, and the desirability of this result for the individual, known as valence. + +== Author == + +In 1964, Victor H. Vroom developed the expectancy theory through his study of the motivations behind decision-making. This theory is relevant to the study of management. + +== Key elements == +The expectancy theory of motivation explains the behavioral process of why individuals choose one behavioral option over the other. This theory explains that individuals can be motivated towards goals if they believe that there is a positive correlation between efforts and performance, the outcome of a favorable performance will result in a desirable reward, a reward from a performance will satisfy an important need, and/or the outcome satisfies their need enough to make the effort worthwhile. +Vroom introduced three variables within the expectancy theory which are valence (V), expectancy (E) and instrumentality (I). The three elements are important behind choosing one element over another because they are clearly defined: effort-performance expectancy (E>P expectancy), performance-outcome expectancy (P>O expectancy). +Expectancy theory has three components: + +Expectancy: effort → performance (E→P) +Instrumentality: performance → outcome (P→O) +Valence: V(R) outcome → reward + +=== Expectancy: effort → performance (E→P) === +Expectancy is the belief that one's effort (E) will result in attainment of desired performance (P) goals, usually based on an individual's past experience, self-confidence (self efficacy), and the perceived difficulty of the performance standard or goal. + +Self efficacy – the person's belief about their ability to successfully perform a particular behavior. The individual will assess whether they have the required skills or knowledge desired to achieve their goals. +Goal difficulty – when goals are set too high or performance expectations that are made too difficult. This will most likely lead to low expectancy. This occurs when the individual believes that their desired results are unattainable. +Perceived control – Individuals must believe that they have some degree of control over the expected outcome. When individuals perceive that the outcome is beyond their ability to influence, expectancy, and thus motivation, is low. + +=== Instrumentality: performance → outcome (P→O) === +Instrumentality is the belief that a person will receive a reward if the performance expectation is met. This reward may present itself in the form of a pay increase, promotion, recognition or sense of accomplishment. Instrumentality is low when the reward is the same for all performances given. +Another way that instrumental outcomes work is commissions. With commissions performance is directly correlated with outcome (how much money is made). If performance is high and many goods are sold, the more money the person will make. +Factors associated with the individual's instrumentality for outcomes are trust, control and policies: + +Trusting the people who will decide who gets what outcome, based on the performance, +Control of how the decision is made, of who gets what outcome, and +Policies understanding of the correlation between performance and outcomes + +=== Valence: Reward(R) === +Valence is the value an individual places on the rewards of an outcome, which is based on their needs, goals, values and sources of motivation. Influential factors include one's values, needs, goals, preferences and sources that strengthen their motivation for a particular outcome. +Valence is characterized by the extent to which a person values a given outcome or reward. This is not an actual level of satisfaction rather the expected satisfaction of a particular outcome. +The valence refers to the value the individual personally places on the rewards. -1 →0→ +1 +-1= avoiding the outcome 0 = indifferent to the outcome +1 = welcomes the outcome +In order for the valence to be positive, the person must prefer attaining the outcome to not attaining it. +Valence is one behavioral alternative, where the decision is measured on the value of the reward. The model below shows the direction of motivation, when behavior is energized: +Motivational Force (MF) = Expectancy x Instrumentality x Valence +When deciding among behavioral options, individuals select the option with the greatest amount of motivational force (MF). +Expectancy and instrumentality are attitudes (cognitions), whereas valence is rooted in an individual's value system. +Examples of valued outcomes in the workplace include, pay increases and bonuses, promotions, time off, new assignments, recognition, etc. If management can effectively determine what their employee values, this will allow the manager to motivate employees in order to get the highest result and effectiveness out of the workplace. + +== Later research == \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Expectancy_theory-1.md b/data/en.wikipedia.org/wiki/Expectancy_theory-1.md new file mode 100644 index 000000000..076a2df61 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Expectancy_theory-1.md @@ -0,0 +1,36 @@ +--- +title: "Expectancy theory" +chunk: 2/3 +source: "https://en.wikipedia.org/wiki/Expectancy_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:52.715379+00:00" +instance: "kb-cron" +--- + +=== Management === +Victor Vroom's expectancy theory is one such management theory focused on motivation. According to Holdford and Lovelace-Elmore, Vroom asserts, "intensity of work effort depends on the perception that an individual's effort will result in a desired outcome". +In order to enhance the performance-outcome tie, managers should use systems that tie rewards very closely to performance. Managers also need to ensure that the rewards provided are deserved and wanted by the recipients. In order to improve the effort-performance tie, managers should engage in training to improve their capabilities and improve their belief that added effort will in fact lead to better performance. + +Emphasizes self-interest in the alignment of rewards with employee's wants. +Emphasizes the connections among expected behaviors, rewards and organizational goals +Expectancy Theory, though well known in work motivation literature, is not as familiar to scholars or practitioners outside that field. + +=== Computer users === +Lori Baker-Eveleth and Robert Stone, University of Idaho in 2008 conducted an empirical study on 154 faculty members' reactions to the use of new software. It was found that ease of system use affects both self-efficacy (self-confidence) and anticipated usefulness. These in turn influenced the decision, or anticipated decision, to use the software. +Self-efficacy and outcome expectancy impact a person's affect and behavior separately: + +Self-efficacy is the belief that a person possesses the skills and abilities to successfully accomplish something. +Outcome expectancy is the belief that when a person accomplishes the task, a desired outcome is attained. +Self-efficacy has a direct impact on outcome expectancy and has a larger effect than outcome expectancy. Employees will accept technology if they believe the technology is a benefit to them. If an employee is mandated to use the technology, the employees will use it but may feel it is not useful. On the other hand, when an employee is not mandated, the employee may be influenced by these other factors (self-confidence and confidence in outcome) that it should be used. +The self-efficacy theory can be applied to predicting and perceiving an employee's belief for computer use. This theory associates an individual's cognitive state with effective behavioral outcomes. +Other constructs of the self-efficacy theory that impact attitudes and intentions to perform are: + +past experience or mastery with the task; +vicarious experience performing the task; +emotional or physiological arousal regarding the task; +social persuasion to perform the task + +=== Models of teacher expectancy effects === +Jere Brophy and Thomas Good provided a comprehensive model of how teacher expectations could influence children's achievement. Their model posits that teachers' expectations indirectly affect children's achievement: "teacher expectations could also affect student outcomes indirectly by leading to differential teacher treatment of students that would condition student attitudes, expectations, and behavior". The model includes the following sequence. Teachers form differential expectations for students early in the school year. Based on these expectations, they behave differently toward different students, and as a result of these behaviors the students begin to understand what the teacher expects from them. If students accept the teachers' expectations and behavior toward them then they will be more likely to act in ways that confirm the teacher's initial expectations. This process will ultimately affect student achievement so that teachers' initial expectancies are confirmed. +In discussing work related to this model, Brophy made several important observations about teacher expectation effects. First and foremost, he argued that most of the beliefs teachers hold about student are accurate, and so their expectations usually reflect students' actual performance levels. As a result, Brophy contended that self-fulfilling prophecy effects have relatively weak effects on student achievement, changing achievement 5% to 10%, although he did note that such effects usually are negative expectation effects rather than positive effects. Second, he pointed out that various situational and individual difference factors influence the extent to which teacher expectations will act as self-fulfilling prophecies. For instance, Brophy stated that expectancy effects may be larger in the early elementary grades, because teachers have more one-on-one interactions with students then, as they attempt to socialize children into the student role. In the upper elementary grades more whole-class teaching methods are used, which may minimize expectation effects. Some evidence supports this claim; expectancy effects in Rosenthal and Jacobson's study were strongest during the earlier grades. Raudenbush's meta-analysis of findings from different teacher expectancy studies in which expectancies were induced by giving teachers artificial information about children's intelligence showed that expectancy effects were stronger in grades 1 and 2 than in grades 3 through Grade 6, especially when the information was given to teachers during the first few weeks of school. These findings are particularly relevant because they show a form of the expectancy theory: how teachers have certain expectations of students, and how they treat the students differently because of those expectations. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Expectancy_theory-2.md b/data/en.wikipedia.org/wiki/Expectancy_theory-2.md new file mode 100644 index 000000000..7422a8497 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Expectancy_theory-2.md @@ -0,0 +1,33 @@ +--- +title: "Expectancy theory" +chunk: 3/3 +source: "https://en.wikipedia.org/wiki/Expectancy_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:52.715379+00:00" +instance: "kb-cron" +--- + +== Criticisms == +Critics of the expectancy model include Graen, Lawler and Porter. Their criticisms of the theory were based upon the expectancy model being too simplistic in nature; these critics started making adjustments to Vroom's model. +Edward Lawler claims that the simplicity of expectancy theory is deceptive because it assumes that if an employer makes a reward (such as a financial bonus or promotion) enticing enough, employees will increase their productivity to obtain the reward. However, this only works if the employees believe the reward is beneficial to their immediate needs. For example, a $2 increase in salary may not be desirable to an employee if the increase pushes him into a tax bracket in which he believes his net pay is actually reduced (a belief that is typically fallacious, especially in the United States). Similarly, a promotion that provides higher status but requires longer hours may be a deterrent to an employee who values evening and weekend time with their children. +As an additional example, if a person in the armed forces or security agencies is promoted, there is the possibility that he or she will be transferred to other locations. In such cases, if the new posting is far from their permanent residence where their family resides, they will not be motivated by such promotions and the results will backfire. As such, the reward is valued negatively to the person receiving it. +Lawler's new proposal for expectancy theory does not contradict Vroom's theory. Lawler argues that since there have been a variety of developments of expectancy theory since its creation in 1964 that the expectancy model needs to be updated. Lawler's new model is based on four claims. First, whenever there are a number of outcomes, individuals will usually have a preference among those outcomes. Second, there is a belief on the part of that individual that their action(s) will achieve the outcome they desire. Third, any desired outcome was generated by the individual's behavior. Fourth and finally, the actions generated by the individual were generated by the preferred outcome and expectation of the individual. +Instead of simply looking at expectancy and instrumentality, W.F. Maloney and J.M. McFillen found that expectancy theory could explain the motivation of those individuals who were employed by the construction industry. For instance, they used worker expectancy and worker instrumentality. Worker expectancy is when supervisors create an equal match between the worker and their job. Worker instrumentality is when an employee knows that any increase in their performance leads to achieving their goal. +In the chapter entitled "On the Origins of Expectancy Theory" published in Great Minds in Management by Ken G. Smith and Michael A. Hitt, Vroom himself agreed with some of these criticisms and stated that he felt that the theory should be expanded to include research conducted since the original publication of his book. + +== Related theories == +Motivation Theory is a theory that attempts to explain how and why individuals are able to achieve their goals. +Expectancy Violations Theory (EVT) is a theory that predicts communication outcomes of non-verbal communication. +Self-Actualization Theory +Maslow's hierarchy of needs +Two-factor theory +Theory X and theory Y + +== References == + +== Further reading == +Bandura, Albert (1977). "Self-efficacy: Toward a unifying theory of behavioral change". Psychological Review. 84 (2): 191–215. CiteSeerX 10.1.1.315.4567. doi:10.1037/0033-295X.84.2.191. PMID 847061. +Bandura, A. (1982). Self-Efficacy mechanism in human agency. American Psychologist, 37, 122–147. +Droar, D. (2006). Expectancy theory of motivation. Retrieved October 2, 2010, from https://web.archive.org/web/20101025133032/http://arrod.co.uk/archive/concept_vroom.php +Stone, R. W. & Henry, J. W. (1998). Computer self-efficacy and outcome expectations and their impacts on behavioral intentions to use computers in non-volitional settings. Journal of Business and Management, (1), 45–58. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Expectancy_violations_theory-0.md b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-0.md new file mode 100644 index 000000000..887c55ac0 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-0.md @@ -0,0 +1,24 @@ +--- +title: "Expectancy violations theory" +chunk: 1/17 +source: "https://en.wikipedia.org/wiki/Expectancy_violations_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:53.972000+00:00" +instance: "kb-cron" +--- + +Expectancy violations theory (EVT) is a theory of communication that analyzes how individuals respond to unanticipated violations of social norms and expectations. The theory was proposed by Judee K. Burgoon in the late 1970s and continued through the 1980s and 1990s as "nonverbal expectancy violations theory", based on Burgoon's research studying proxemics. Burgoon's work initially analyzed individuals' allowances and expectations of personal distance and how responses to personal distance violations were influenced by the level of liking and relationship to the violators. The theory was later changed to its current name when other researchers began to focus on violations of social behavior expectations beyond nonverbal communication. +This theory sees communication as an exchange of behaviors, where one individual's behavior can be used to violate the expectations of another. Participants in communication will perceive the exchange either positively or negatively, depending upon an existing personal relationship or how favorably the violation is perceived. Violations of expectancies cause arousal and compel the recipient to initiate a series of cognitive appraisals of the violation. The theory predicts that expectancies influence the outcome of the communication interaction as either positive or negative and predicts that positive violations increase the attraction of the violator and negative violations decrease the attraction of the violator. +Beyond proxemics and examining how people interpret violations in many given communicative contexts, EVT also makes specific predictions about individuals' reaction to given expectation violations: individuals reciprocate or match someone's unexpected behavior, and they also compensate or counteract by doing the opposite of the communicator's behavior. + +== Components == +The EVT examines three main components in interpersonal communication situations: Expectancies, communicator reward valence, and violation valence. + +=== Expectancy === +Expectancy refers to what an individual anticipates will happen in a given situation. Expectancies are primarily based upon social norms and specific characteristics and idiosyncrasies of the communicators. +Burgoon (1978) notes that people do not view others' behaviors as random. Rather, they have various expectations of how others should think and behave. EVT proposes that observation and interaction with others leads to expectancies. The two types of expectancies noted are predictive and prescriptive. Predictive expectations are "behaviors we expect to see because they are the most typical," (Houser, 2005) and vary across cultures. They let people know what to expect based upon what typically occurs within the context of a particular environment and relationship. For example, a husband and wife may have an evening routine in which the husband always washes the dishes. If he were to ignore the dirty dishes one night, this might be seen as a predictive discrepancy. Prescriptive expectations, on the other hand, are based upon "beliefs about what behaviors should be performed" and "what is needed and desired" (Houser, 2005). If a person walks into a police department to report a crime, the person will have an expectation that the police will file a report and follow up with an investigation. +Judee Burgoon and Jerold Hale categorize existing expectations into two types based on the process of interaction: pre-interactional and interactional expectations. Pre-interactional expectations are the package of knowledge and skills a person already has before entering a conversation. For example, aggressive attitudes may not be expected if previous experience has not included dealing with similar attitudes. Interactional expectations form the abilities equipped to conduct an ongoing conversation. Proper reactions and nodding to show listening behaviors are expected in a conversation. +When the theory was first proposed, EVT identified three factors which influence a person's expectations: Interactant variables, environmental variables, and variables related to the nature of the interaction. Interactant variables are the traits of those persons involved in the communication, such as sex, attractiveness, race, culture, status, and age. Environmental variables include the amount of space available and the nature of the territory surrounding the interaction. Interaction variables include social norms, purpose of the interaction, and formality of the situation. +These factors later evolved into communicator characteristics, relational characteristics, and context. Communicator characteristics include personal features such as an individual's appearance, personality and communication style. It also includes factors such as age, sex, and ethnic background. Relational characteristics refer to factors such as similarity, familiarity, status and liking. The type of relationship one individual shares within another (e.g. romantic, business or platonic), the previous experiences shared between the individuals, and how close they are with one another are also relational characteristics that influence expectations. Context encompasses both environment and interaction characteristics. Communicator characteristics lead to distinctions between males and females in assessing the extent to which their nonverbal expressions of power and dominance effect immediacy behaviors. Immediacy cues such as conversational distance, lean, body orientation, gaze, and touch may differ between the genders as they create psychological closeness or distance between the interactants. +Behavioural expectations may also shift depending on the environment one is experiencing. For example, a visit to a church will produce different expectations than a social function. The expected violations will therefore be altered. Similarly, expectations differ based on culture. In Europe, one may expect to be greeted with three kisses on alternating cheeks, but this is not the case in the United States. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Expectancy_violations_theory-1.md b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-1.md new file mode 100644 index 000000000..f7748d3be --- /dev/null +++ b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-1.md @@ -0,0 +1,27 @@ +--- +title: "Expectancy violations theory" +chunk: 2/17 +source: "https://en.wikipedia.org/wiki/Expectancy_violations_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:53.972000+00:00" +instance: "kb-cron" +--- + +=== Communicator reward valence === +The communicator reward valence is an evaluation one makes about the person who committed a violation of expectancy. Em Griffin summarizes the concept behind communicator reward valence as "the sum of positive and negative attributes brought to the encounter plus the potential to reward or punish in the future". The social exchange theory explains that individuals seek to reward some and seek to avoid punishing others. When one individual interacts with another, Burgoon believes he or she will assess the "positive and negative attributes that person brings to the encounter". If the person has the ability to reward or punish the receiver in the future, then the person has a positive reward valence. Rewards simply refer to the person's ability to provide a want or need. It can be represented by several features, such as communicators with high social class, reputation, knowledge, positive emotional support, physical attractiveness, and so on. The term 'communicator reward valence' is used to describe the results of this assessment. For example, people will feel encouraged during conversation when the listener is nodding, making eye contact, and responding actively. Conversely, if the listener is avoiding eye contact, yawning, and texting, it is implied they have no interest in the interaction and the speaker may feel violated. The deviation of expectations does not always yield negative results, which depends on the degree of reward held by the reward communicator. An action might be viewed as positive by a high-reward communicator, as the same action might be seen as negative by a lower-reward communicator. +When examining the context, relationship, and communicator's characteristics in a given encounter, individuals will arrive at an expectation for how that person should behave. Changing even one of these expectancy variables may lead to a different expectation. For example, in different cultures, directly looking into a speaker's eyes, especially in a personal conversation, can represent distinct meanings. + +=== Violation valence === +Behavior violations arouse and distract, calling attention to the qualities of the violator and the relationship between the interactants. A key component of EVT is the notion of violation valence, or the association the receiver places on the behavior violation. A violatee's response to an expectancy violation can be positive or negative, and is dependent on two conditions: positive or negative interpretation of the behavior and the nature (rewardingness) of the violator. The nature of the violator is evaluated through many categories – attractiveness, prestige, ability to provide resources, or associated relationship. For instance, a violation of one's personal distance might have more positive valence if committed by a wealthy, powerful, physically appealing member of the opposite sex than a filthy, poor, homeless person with foul breath. The evaluation of the violation is based upon the relationship between the particular behavior and the valence of the actor. A person's preinteractional expectancies, especially personal attributes, may cause a perceiver to evaluate the communication behavior +of a target differently in terms of assigning positive and negative valenced expectancies. +Another perspective of violation valence is that the perceived positive or negative value assigned to a breach of expectations is inconsequential of who the violator is. This perspective places much greater weight on the act of the breach itself than the violator. + +=== Arousal === +Expectancy violations refer to actions which are noticeably discrepant from an expectancy and are classified as outside the range of expectancy. The term 'arousal value' is used to describe the consequences of deviations from expectations. When individuals' expectations are violated, their interests or attentions are aroused. +When arousal occurs, one's interest or attention to the deviation increases, resulting in less attention paid to the message and more attention to the source of the arousal. There are two kinds of arousals. Cognitive arousal is an idea that people will be mentally aware of the violation. Physical occurs when people have body actions and behaviors in response to the deviations from their expectations. For example, when one experiences physical arousal, he or she chooses to move out of the physical space, keep the distance with other conversationalists, or stretch his or her body. Beth Le Poire and Judee Burgoon research to examine physical arousal in conversation. The result shows that after participants report their cognitive arousal, physically speaking, their heart rate decreases and pulse volume increase. + +=== Threat threshold === +The occurrence of arousal is aligned with threats. Burgoon introduced the term "threat threshold" to explain that people have different levels of tolerance about distant violations. The threat threshold is high when people feel good even if they keep a very close distance with the violator, whereas people with low threat threshold will be sensitive and uncomfortable about the closeness of distance with the violator. + +== Theoretical assumptions and viewpoints == \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Expectancy_violations_theory-10.md b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-10.md new file mode 100644 index 000000000..70a31346f --- /dev/null +++ b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-10.md @@ -0,0 +1,26 @@ +--- +title: "Expectancy violations theory" +chunk: 11/17 +source: "https://en.wikipedia.org/wiki/Expectancy_violations_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:53.972000+00:00" +instance: "kb-cron" +--- + +=== In educational contexts === +EVT posits that deviations from expected behavior can influence social judgments. In the context of teacher dress, formal attire aligns with expectations of a teacher's role, and such congruence typically results in favorable credibility assessments. The impact of clothing on expectations, where attire considered appropriate to the teaching context bolstered perceptions of a teacher's potential for student academic success. +A mixed method study conducted in 2023 followed first generation college students and their social expectations for their transition to college. Overall students reported negative violations when it came to partying, making new friends, and strengthening new bonds. They also experienced positive violations when it came to stress and workload. Students who reported more negative violations also reported an overall more difficult transition period. Students who reported more positive violations reported an easier transition period. + +=== Implications for teacher dress code === +The implications of these studies are twofold: they reaffirm the importance of attire as a component of nonverbal communication within educational settings, and they highlight the potential for teacher attire to align with institutional norms and expectations to enhance educational outcomes. While the preference for formality in attire may vary by educational context, the consensus points to the benefit of teachers adopting attire that reflects the scholastic values and expectations of their specific academic environments. + +==== Instructor credibility in college classroom ==== +According to Sidelinger and Bolen, students might be dissatisfied with instructors who talk a lot during class. After researching compulsive communication and communication satisfaction, they concluded that if an instructor is evaluated as credible by the students, his credibility decreases students' dissatisfaction despite his talkativeness. Particularly, instructor's goodwill, such as politeness and care for students, is the most effective characteristic to alleviate students' negative feelings towards them (the talkative instructor). +Expanding on this, EVT suggests that communication behaviors deviating from expectations can be perceived as either positive or negative violations. When an instructor's behavior, like excessive talking, contrasts with student expectations of a participatory, student-centered environment, it constitutes an expectancy violation. However, the impact of such a violation hinges on the perceived credibility of the instructor. Instructor credibility, shaped by expertise, trustworthiness, and goodwill, can act as a buffer against the negative effects of such expectancy violations. Goodwill, in particular, plays a crucial role. When students perceive an instructor as genuinely concerned about their learning and well-being, they are more likely to overlook behaviors otherwise considered negative. This is because EVT emphasizes the relationship's nature over the behavior itself in determining the outcome of expectancy violations. Furthermore, cultural differences among students, the discipline, course level, and class dynamics can influence the context and perception of expectancy violations. Future research could explore how different expectancy violations (like talkativeness, humor, strictness) interact with dimensions of instructor credibility and how cultural factors among students shape their expectations and perceptions of instructor behavior. This would provide a deeper understanding of how instructor behaviors affect student satisfaction and learning outcomes in diverse educational environments. + +==== Course ratings ==== +Most American colleges and universities employ course rating surveys as a method to gauge teacher effectiveness and the degree to which students are satisfied with the pedagogy of their professors. Expectancy violation and violation valence play a part in course ratings because a wide range of expectancies exist for students while taking a course. Common expectancies for students include stimulation and interest, instructor behavior, relevance of the course, and the student's expected and actual success in the course. A higher education study on EVT and course ratings analyzed 228 students in seven introductory sociology classes at a university of 25,000 students. Since the courses were required for most students, were open to all students, used the same textbook, and met for the same length of time during the semester, expectancy violations in the classroom could be reported more accurately. Some factors used to report the data included instructor personality, interestingness and informativeness of textbook materials, difficulty of lectures, lecturer speaking ability, and the ability to answer questions. At the end of the study, the only factor that affected course ratings was relevance. Expectancies had virtually no effect otherwise on course evaluations. This reason could be attributed to the fact that students who found a course highly relevant were already interested in the subject area and were more motivated to do well. Additionally, professors who respond to student emails quicker than the students expect, tend to receive a better course evaluation rating than if they reply slower than expected. + +==== Nontraditional college students ==== +EVT has been used to study the experiences of non-traditional college and university students who begin an undergraduate education over the age of 25. The study focused on the students' expectations of their professors and how they should behave in the classroom. Since nontraditional students often feel that they are different from their academic peers, and since the traditional university setting focuses on the 18–23-year-old demographic, studying nontraditional student classroom experiences can help higher education institutions instruct teachers on how to behave in the classroom. Traditional and non-traditional students have been shown to expect teachers to make use of examples, provide feedback, and adequately prepare them for exams. Both traditional and non-traditional students have been found to have their expectations for instructor clarity negatively violated. Surprisingly, non-traditional students differed from traditional students by responding negatively to affinity-seeking behaviors and believed that instructors should be less concerned with making class more fun and enjoyable. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Expectancy_violations_theory-11.md b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-11.md new file mode 100644 index 000000000..a24afdd1b --- /dev/null +++ b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-11.md @@ -0,0 +1,21 @@ +--- +title: "Expectancy violations theory" +chunk: 12/17 +source: "https://en.wikipedia.org/wiki/Expectancy_violations_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:53.972000+00:00" +instance: "kb-cron" +--- + +==== Student disclosures in college classroom ==== +In 2013, Frisby and Sidelinger conducted a research about student disclosures in college classroom to examine what kinds of student disclosures would violate peers' expectations and their perceptions about the disclosers. According to the study, those who make inappropriate disclosures violate others' expectations most in a classroom environment. Inappropriate disclosures are described as high frequent, negative, offensive and irrelevant topics. Disclosers of inappropriate information are more likely to be described as incompetent students, and they are less likeable than students who disclose appropriate information that are related to course materials. + +==== Students' expectations towards instructors in online classes ==== +Taking EVT as a lens, Renee Bourdeaux and Lindsie Schoenack investigate students' reasons for taking online classes, their expectations towards instructors, and the derivation of expectations of instructors' behaviors. Research shows that students expect clarity, respect, and well-designed course accommodating to the online environment. Participants consider effective communication and improving learning as behaviors bringing positive results. However, unprofessional behaviors, such as lack of use of teaching tools decreasing the productivity of classes, lead to negative results. + +=== Business communication crisis === +EVT can also apply to everyday business interaction between long-term partners, new partners, and even the consumers. Each time a business interacts with another, both sides expect a positive gain in some capacity; however, losses are inevitable. Sora Kim asserts that "expectancy violations caused by a crisis tend to increase uncertainty about an organization's performance in the crisis-related area". The author states that stakeholders, in the case of the BP Oil spill, held high levels of uncertainty towards the organization due to the high level of expectancy violations committed by BP. Sabrina Helm and Julia Tolsdorf found that firms with greater reputation and customer loyalty are set to high expectations by the public, and tend to suffer more loss in profits in the event of a crisis, while firms with low reputations suffer minor losses. This shows that the public places its trust and loyalty in corporations due to their reputation, thus resulting in favorable outcomes for corporations. This reputation is also an Achilles heel for the corporation in times of crisis because when an expectation violation is committed by the corporations it produces negative outcomes for the corporation and the public's trust in them. Sora Kim also exposes similar findings in her study, specifically on how expectations violations produces uncertainties in stakeholders and the public during times of crisis. Corporate social responsibility (CSR) is an expectation the public has set for major corporations and businesses, Nick Lin-Hi and Igor Blumberg also found that not practicing CSR negatively affect corporate reputation. +YJ Sohn and Ruthann Lariscy use EVT to investigate the role corporate reputation plays in crisis situations and how the crisis affects the reputation valence, especially in a CSR (corporate social responsibility) crisis context. The previous high reputation leads to higher expectations for the corporation, which results in more detailed investigations of the expectation violation behaviors. +In a study done surrounding the COVID-19 pandemic, Cheng, Wang, and Pan studied that employees whose expectations about their work and the company were violated with a negative valence. They found that these negative violations created uncertainty, CSR cynicism, and distrust in their employing company, which ultimately led to an increase in company turnover rate. +In a study done in 2022, research was done concerning biases Black employees experience in the workplace. Self promotion by Black employees was considered to be related to poorer job performance and lower job fit ratings as compared to their white, Hispanic, and Asian counterparts. This can be attributed to EVT because self promotion by Black employees violates other races' expectations of themselves. Because the expectation is negatively violated, the Black employee promoting themselves now carry a negative association. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Expectancy_violations_theory-12.md b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-12.md new file mode 100644 index 000000000..1d5e6221e --- /dev/null +++ b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-12.md @@ -0,0 +1,20 @@ +--- +title: "Expectancy violations theory" +chunk: 13/17 +source: "https://en.wikipedia.org/wiki/Expectancy_violations_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:53.972000+00:00" +instance: "kb-cron" +--- + +==== Business/Workplace Behaviors ==== +In another study conducted in 2025, researchers examined the aftermath of an ethical violation and how family firms suffer more than non-family firms, as well as the reasons behind this. The presence of family firm information leads individuals to perceive the firm as more trustworthy. Although family firms may be seen as more trustworthy, the opposite effect can also be greater. effects as well. An identity threat could lead to a loss of benevolence beliefs and an avoidant reaction. Similarly, a decrease in perceived integrity and benevolence was significantly greater for family firms than for non-family firms. A 2024 study investigated the effects of greenwashing effects on corporate reputation and brand hate through environmental performance and green perceived risk. The findings show that consumer perceptions of greenwashing can damage a brand's image. Additionally, the study found that greenwashing negatively affects on corporate reputation through perceived environmental performance and green perceived risk. Reducing greenwashing practices can improve consumers' perceptions of corporate environmental performance. In 2024, another study explored whether religion mattered to angel investors specifically, the influence of religion on entrepreneurial investor decision-making. The results showed that religion contributes to social trust across multiple levels of analysis. Among faith-driven investors, religious claims result in positive perceptions of the entrepreneur's authenticity. The researchers also suggested that religion has a persistent but nuanced influence on angel investment decision-making. Danyang Zhu and Xu-Hong Li conducted research in 2024 on female leadership and corporate acquisitions in Chinese State-Owned Enterprises. What they found was that female chairs are more likely than their male peers to engage in acquisition activities in Chinese state-owned enterprises. Particularly in firms with lower female representation in executive positions. Additionally, companies with female chairs conducted 22% more acquisitions than those with male chairs. However, when female-led strategies begin to fail, these firms tend to become more conservative. As female leaders may face greater gender-based bias and criticism if risky strategies are unsuccessful. There is a lot of work done surrounding the executive positions in the workplace. One study that was done in 2024 looks at leader exemplification and ethical conduct. It reflects a leaders authenticity, skills, and the extent that their employees feel that they can trust them. These attributes are all perceptual which means it is unique to everyone, and therefore is room for expectancy violation. Another study from 2025, connects EVT to supervisors (particularly in the health science world) and the importance of fulfilling promises. Park, Wolfart, King, Sicam, and Viswesvaran describe that when "perceived organizational support" is greater, a "psychological contract breach" is more impactful to the group. + +There is a lot of work done surrounding the executive positions in the workplace. One study that was done in 2024 looks at leader exemplification and ethical conduct. It reflects a leader's authenticity, skills, and the extent that their employees feel that they can trust them. These attributes are all perceptual which means it is unique to everyone, and therefore is room for expectancy violation. Another study from 2025, connects EVT to supervisors (particularly in the health science world) and the importance of fulfilling promises. Park, Wolfart, King, Sicam, and Viswesvaran describe that when "perceived organizational support" is greater, a "psychological contract breach" is more impactful to the group. In one more important study, Perry, Hunter, Corrington, and Hebl explore gender role violations from hiring managers in 2024. Hiring managers that have more extreme characteristics have a possibility of having more "violations" of their stereotypical gender role. + +=== Profanity use === +Swearing is one example of observable instance of verbal expectancy violations. Examples of swearing expectancy violations include U.S. Vice President Dick Cheney telling Patrick Leahy, Senator of Vermont, to "go fuck yourself", actor Christian Bale lashing out toward a crew member who walked in front of the camera while he was filming, and U.S. Vice President Joe Biden's remarks during a live broadcast of his speech congratulating U.S. President Barack Obama on passage of the health care reform bill, commenting that it was a "big fucking deal". Expletives also vary among different cultures, so valence of expectancy violations involving swearing may differ when used in different contexts. + +==== In workplaces ==== +Swearing is common among many workplaces. Swearing has been identified functionally as one of several ways to express emotion in response to workplace stress, to convey verbal aggression, or to engage in deviant workplace behavior (Johnson, 2012). In formal work settings, people have much stronger feelings that their expectations are violated by swearing than in casual occasions. Expletives are more prevalent in unstructured conversations than in more structured, task-oriented ones (Johnson, 2012). The use of profanity has been shown to influence the perceptions of speakers. It may also have emotional impact on the user and the audience. Research has shown that profanity users appear less trustworthy, less sociable, and less educated. The more swearing messages one expresses that violate respondent's expectations in workplaces, the more negative evaluations the respondent will generate about the speaker's incompetency. These traits are likely to appear as fixed among profanity users. Moreover, the content of the swearing messages also poses great impact on the extent of expectancy violations in formal work settings. The verbal messages include words related to sex, excretion and profaneness. Research found that respondents experience highest level of surprise about the swearing with sexual expressions. Thus their expectations are more likely to be violated by sexual swearing than excretory and profane words. A more productive approach than focusing on whether a specific word is offensive may be to make sure that those engaging in workplace swearing are aware of how they and their messages might be perceived in multiple ways (Johnson, 2012). \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Expectancy_violations_theory-13.md b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-13.md new file mode 100644 index 000000000..1b3763ad4 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-13.md @@ -0,0 +1,27 @@ +--- +title: "Expectancy violations theory" +chunk: 14/17 +source: "https://en.wikipedia.org/wiki/Expectancy_violations_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:53.972000+00:00" +instance: "kb-cron" +--- + +=== Evaluation of media figures === +Expectancy violations are tightly related to the changes of people's evaluation on their relationships with media figures. In 2010, Cohen made comparisons between relationships with friends and media figures in order to find similarities and differences of people's reactions when their expectations are violated in these two relationships. Violations were generally divided in three categories: social violations such as making offensive comments, trust violations such as making up stories about their life experience, and moral violations such as cheating in a marital relationship or drunk driving. +Research indicated that in both friendships and relationships with media figures, social and trust violations are more offensive than moral violations. Specifically, people are more intolerable about moral violations from media figures than from their friends. According to the study, the reason for the intolerance is because relationships with media figures are relatively weak that people invest less on the relationships with media figures than on friendships. The type of media figures is also an important factor to determine the changes of closeness with media figures. People have different expectations to various types of media figures. Research discussed that moral violations negatively influence relationships with athletes, damaging their positive and energetic appearance expected by the public. Social violations reduce closeness with TV hosts, whom people expect as amiable public figures. +James Bonus, Nicholas Matthews, and Tim Wulf investigate adults' expectations towards movie characters before and after movie releasing. The result shows that when the villain behaves more morally than expected, there is a warming in the parasocial relationship between participants and villains. However, when conforming to moral expectations, there is no weakening in the parasocial relationship between heroes and participants. + +=== Health and self-improvement === +Expectancy violation theory has even been applied to encouraging healthy habits and changing bad ones. In a study by Karolien van den Akker, Myrr van den Broek, Remco C. Havermans, and Anita Jansen, expectancy violation theory was tested to see if it was successful in changing ingrained cravings for chocolate. Although researchers did not find that expectancy violation mediated responses to chocolate cravings, they believe more research is needed to determine whether this theory is profitable for this kind of application to human behavior. + +=== Psychology, Behavior and Neuroscience === +Behavioral and Neural Responses to Social Exclusion in Women: The Role of Facial Attractiveness and Friendliness. This study was conducted, and it was found that being socially excluded by one's own sex is more distressing than being excluded by the opposite sex. Young women are more frequently the targets of indirect aggression than older women due to intrasexual competition, and older adults tend to be less sensitive to social exclusion than younger adults. They also found that women are more likely to select attractive women to compete against when all the potential competitors were presented as friendly and when the unattractive competitors were presented as unfriendly. +One study examined why expectation do or do not change after expectation violations. First, there are seven models for disconfirming expectations. Expectations are important for nearly any kind of psychological domain; for example, perception, motor control, decision-making, learning, motivation, and social interaction. Minimizing disconfirmation and the search for confirmation stabilizes expectations. +When dealing with relational inconsistencies, there are two ways to resolve them. In a 2025 study, researchers identified two pathways to resolve relational inconsistencies. Clinical research has shown that maladaptive expectations contribute to disorders such as depression and anxiety, where individuals often maintain dysfunctional expectations even in the face of disconfirming evidence. Additionally, extreme violations often result in resistance to change. Therapies designed to modify dysfunctional expectations, such as exposure therapy for anxiety disorders, benefit from structured interventions that introduce moderate rather than extreme violations. +The effects of parental phubbing on social withdrawal in preschool children, and the serial mediating roles of parent-child conflict and negative emotions, were examined in 2025. The study explained that Expectation Violation Theory (EVT) can be used to identify how parental phubbing reduces the quality of parent-child communication. According to EVT, when individuals' expectations are not met, negative emotions are likely to arise. Additionally, EVT suggests that parental phubbing undermines children's basic psychological needs, leading to negative emotions. +In a study done by Michael, Langeloh, Tünte, Köster, and Hoehl in 2025, they look at nine-month old infants. They look at their ability to recognize an expectancy violation. Surprisingly, none-month olds were able to recognize circumstances that defer from "regularities", which is directly linked to expectancy violations theory. They figured this out through the observation of the infants pupil dilation. Xue-Rui, Bundil, Schulreich, and Shu-Chen found in 2023 that adaptive behavior is heavily reliant on the ability to adopt new information. The asymmetry of valence dependence is directly associated with expectancy violations. + +=== Career development and job searching === +Stephanie Smith examines how recent college graduates react to expectation violations in job searching and career development through communication. Smith finds that recent college graduates employ a package of both traditional and online social networking job searching strategies. As graduates expect job searching would be difficult, they are still surprised by the required intensity and effort. Through the lens of EVT, candidates with the most realistic goals and expectations received better results during the recruitment season. EVT also helps to understand candidates' interactions with contacts with potential rewards during the networking conversation. Also, a thank-you letter is regarded as a positive deviation from expectations because it reduces uncertainty. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Expectancy_violations_theory-14.md b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-14.md new file mode 100644 index 000000000..fcb49887d --- /dev/null +++ b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-14.md @@ -0,0 +1,34 @@ +--- +title: "Expectancy violations theory" +chunk: 15/17 +source: "https://en.wikipedia.org/wiki/Expectancy_violations_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:53.972000+00:00" +instance: "kb-cron" +--- + +=== Expectations of adults with autism === +Expectancy violations theory has been applied in studies to determine whether people judge adults with autism as violating their expectations since people with autism can exhibit little-to-no eye contact, or facial expression, not recognize certain nonverbal cues, or utilize tones that non-autistic people may perceive as abnormal. In one manuscript replying to another study, Bishop describes communication deficits in autistic individuals as potentially violating one's expectations for social communication, thus being a form of expectation violation since people with autism can struggle with social communication. One study by Lim, Young, and Brewer hypothesized that people can incorrectly perceive autistic adults as having no credibility or being deceptive. They believed that due to expectancy violations theory, people will judge those who violate their expectations unfavorably in a negative light. They recorded videos of autistic and non autistic adults attempting to persuade the interviewer that they did not steal an envelope of money and the participants of the study were to judge whether they believed the individuals in the interview were lying or telling the truth. The results showed that the autistic people were perceived as deceptive and less credible than non autistic people in the videos. These findings supported the hypothesis that autistic adults can violate expectations through certain behaviors or through other's knowledge of their diagnosis. A similar study by the same researchers, also conducted through interviews, showed that the behaviors of autistic adults can affect their perceived credibility. Another study by Logos, Brewer, and Young sought to determine the effect of EVT in a court setting. Their goal was to determine whether EVT could be applied to autistic adults in a forensic setting, using autistic and non-autistic "defendants", hypothesizing that the results would show that autistic adults would be judged guilty due to violations. Results showed that their hypothesis was correct, despite evidence indicating innocence. + +=== Intergroup solidarity and political betrayal === +Recent research applies Expectancy Violations Theory to political behavior, distinguishing between violations of "stigma-based solidarity" and "relational care." Stigma-based solidarity creates a predictive expectation that marginalized groups will support one another due to shared experiences of discrimination; when a marginalized sub-group votes against these interests (e.g., Latino men supporting a candidate perceived as harmful to minorities), other marginalized groups (e.g., Black women) experience this as a severe "stigma-based solidarity betrayal." However, expectations can also stem from relational interdependence, leading to different patterns of betrayal for groups with dual identities or dominant-group connections. For instance, White women reported feeling significantly more betrayed by White men's voting behavior than by that of marginalized outgroups, despite the latter's violation of coalitional solidarity. This suggests that violations of "relational care" (expectations that close others, such as family members or partners, will protect one's rights) can supersede expectations of stigma-based solidarity, demonstrating that the psychological source of the expectancy (shared stigma versus relational ties) fundamentally shapes the experience of political betrayal. + +== Metatheoretical assumptions == + +=== Ontological assumptions === +EVT assumes that humans have a certain degree of free will. This theory assumes that humans can assess and interpret the relationship and liking between themselves and their conversational partner, and then make a decision whether or not to violate the expectations of the other person. The theory holds that this decision depends on what outcome they would like to achieve. This assumption is based on the interaction position. The interaction position is based on a person's initial stance toward an interaction as determined by a blend of personal Requirements, Expectations, and Desires (RED). These RED factors meld into a person's interaction position of what is needed, anticipated, and preferred. + +=== Epistemological assumptions === +EVT assumes that there are norms for all communication activities and if these norms are violated, there will be specific, predictable outcomes. EVT does not fully account for the overwhelming prevalence of reciprocity that has been found in interpersonal interactions. Secondly, it is silent on whether communicator valence supersedes behavior valence or vice versa when the two are incongruent, such as when a disliked partner engages in a positive violation. + +=== Axiological assumptions === +This theory seeks to be value-neutral as supporting studies have been conducted empirically and sought to objectively describe how humans react when their expectations are violated. + +== Persuasion and Negotiation == +A study done by Letwin, C., Ciuchta, M. P., Johnson, M., Stevenson, R., & Ford, C. in 2024, addresses the relationship between surface cues (attractiveness and enthusiasm) and success found in crowdfunding. They also find a relationship associated with gender involved as well. Their study delves into expectancy violation theory (EVT) and elaboration likelihood model (ELM) in order to investigate this. +The authors claim that the cues either help or hurt the speaker, depending on the degree to which the speaker aligns with gender-based expectations or not. They found that gender non-congruent behavior in speakers resulted in deeper analysis by their audience for both the speaker and the pitch. Those who followed expectations, were not as deeply analyzed and were generally more accepted. Their final findings were enthusiastic males and attractive females had more success in crowdfunding pitches. +In another study done by Moty, N., Putteeraj, M., Somanah, J., & Adnarain-Appadoo, K., also in 2024, they looked at gender stereotypes again. This time they relate it to personality traits, specifically what these two have to do with negotiation skills. They use expectancy violation theory to check in with the reactions people have to this relationship. +They focused on the reaction people would have in a violation to gender-based norms. Their findings were that gender had almost nothing to do with negotiation success. Their biggest discovery was that individuals that had a high level of neuroticism indicated poor negotiation skills. They also found that meetings that were dominated by one gender, had an effect on negotiation behavior. Altogether, their studies found that gender has no real indication of a negotiator's success, but it is rather their personality traits that matter the most. + +== Critique == \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Expectancy_violations_theory-15.md b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-15.md new file mode 100644 index 000000000..2e9548bb0 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-15.md @@ -0,0 +1,34 @@ +--- +title: "Expectancy violations theory" +chunk: 16/17 +source: "https://en.wikipedia.org/wiki/Expectancy_violations_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:53.972000+00:00" +instance: "kb-cron" +--- + +=== Predictability and testability === +EVT has undergone scrutiny for its attempt to provide a covering law for certain aspects of interpersonal communication. Some critics of EVT believe most interactions between individuals are extremely complex and there are many contingencies to consider within the theory. This makes the prediction of behavioral outcomes of a particular situation virtually impossible to consistently predict. +Another critique of the theory is the assumption that expectancy violations are mostly highly consequential acts, negative in nature, and cause uncertainty to increase between communicators. In actuality, research shows expectancy violations vary in frequency, seriousness, and valence. While it is true that many expectancy violations carry a negative valence, numerous are positive and actually reduce uncertainty because they provide additional information within the parameters of the particular relationship, context, and communicators. + +==== A First Look at Communication ==== +Emory Griffin, the author of A First Look at Communication Theory, analyzed unpredictability in EVT. His test consisted in analyzing his interaction with four students who made various requests from him. The students were given the pseudonyms Andre, Belinda, Charlie and Dawn. They start with the letters A, B, C and D to represent the increasing distance between them and Griffin when making their requests. + +Andre needed the author's endorsement for a graduate scholarship, and spoke to him from an intimate eyeball-to-eyeball distance. According to Burgoon's early model, Andre made a mistake when he crossed Griffin's threat threshold; the physical and psychological discomfort the lecturer might feel could have hurt his cause. However, later that day Griffin wrote the letter of recommendation. +Belinda needed help with a term paper for a class with another professor, and asked for it from a 2-foot distance. Just as Burgoon predicted, the narrow gap between Belinda and Griffin determined him to focus his attention on their rocky relationship, and her request was declined. +Charlie invited his lecturer to play water polo with other students, and he made the invitation from the right distance of 7 feet, just outside the range of interaction Griffin anticipated. However, his invitation was declined. +Dawn launched an invitation to Griffin to eat lunch together the next day, and she did this from across the room. According to the nonverbal expectancy violations model, launching an invitation from across the room would guarantee a poor response, but this time, the invitation was successful. +Griffin's attempt to apply Burgoon's original model to conversational distance between him and his students did not meet with much success. The theoretical scoreboard read: + +Nonverbal expectancy violations model: 1 +Unpredicted random behavior: 3 +However, when Griffin applied the revised EVT standards on his responses to "the proxemic violations of Andre, Belinda, Charlie, and Dawn," the scorecard "shows four hits and no misses." + +== Related theories == +Because EVT is sociopsychological in nature and focuses on social codes in both intrapersonal and interpersonal communication, it is closely related to communication theories such as cognitive dissonance and uncertainty reduction theory. Recently, this theory has undergone some reconstitution by Burgoon and her colleagues and has resulted in a newly proposed theory known as interaction adaptation theory, which is a more comprehensive explanation of adaptation in interpersonal interaction. +As mentioned above, EVT has strong roots in uncertainty reduction theory. The relationship between violation behavior and the level of uncertainty is under study. Research indicates that violations differ in their impact on uncertainty. To be more specific, incongruent negative violations heightened uncertainty, whereas congruent violations (both positive and negative) caused declines in uncertainty. The theory also borrows from social exchange theory in that people seek reward out of interaction with others. +Two other theories share similar outlooks to EVT – discrepancy-arousal theory (DAT) and Patterson's social facilitation model (SFM). Like EVT, DAT explains that a receiver becomes aroused when a communicative behavior does not match the receiver's expectations. In DAT, these differences are called discrepancies instead of expectancy violations. Cognitive dissonance and EVT both try to explain why and how people react to unexpected information and adjust themselves during communication process. +The social facilitation model has a similar outlook and labels these differences as unstable changes. A key difference between the theories lies in the receiver's arousal level. Both DAT and SFM maintain that the receiver experiences a physiological response whereas EVT focuses on the attention shift of the receiver. EVT posits that expectancy violations occur frequently and are not always as serious as perceived through the lenses of other theories. +Anxiety/uncertainty management theory is the uncertainty and anxiety people have towards each other, relating to EVT this anxiety and uncertainty can differ between cultures. Causing a violation for example violating someones personal distance or communicating ineffectively can cause uncertainty and anxiety. +The popularity of computer-mediated communication (CMC) as means of conducting task-oriented and socially oriented interactions is a part of the social information processing (SIP) theory. Coined by Joseph Walther, the theory explores CMC's ability to fulfill many of the same functions as the more traditional forms of interaction, especially face-to-face (FtF) interaction. SIP can be used in conjunction with EVT to examine interpersonal and hyperpersonal relationships established through CMC. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Expectancy_violations_theory-16.md b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-16.md new file mode 100644 index 000000000..8c79145b1 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-16.md @@ -0,0 +1,22 @@ +--- +title: "Expectancy violations theory" +chunk: 17/17 +source: "https://en.wikipedia.org/wiki/Expectancy_violations_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:53.972000+00:00" +instance: "kb-cron" +--- + +== Further use and development of the theory == +The concept of social norms marketing follows expectancy violation in that it is based upon the notion that messages containing facts that vary from perception of the norm will create a positive expectancy violation. Advertising, strategic communications, and public relations base social norms campaigns on this position. +Interaction adaptation theory further explores expectancy violations. Developed by Burgoon to take a more comprehensive look at social interaction, IAT posits that people enter into interactions with requirements, expectations, and desires. These factors influence both the initial behavior as well as the response behavior. When faced with behavior that meets an individual's needs, expectations, or desires, the response behavior will be positive. When faced with behavior that does not meet an individual's needs, expectations, or desires, he or she can respond either positively or negatively depending on the degree of violation and positive or negative valence of the relationship. +Expectancies exert significant influence on people's interaction patterns, on their impressions of one another, and on the outcomes of their interactions. People who can assume that they are well regarded by their audience are safer engaging in violations and more likely to profit from doing so than are those who are poorly regarded. When the violation act is one that is likely to be ambiguous in its meaning or to carry multiple interpretations that are not uniformly positive or negative, then the reward valence of the communicator can be especially significant in moderating interpretations, evaluations, and subsequent outcomes. +EVT also applies to international experience in the workplace. "A foreign newcomer who has the necessary education, work experience, and international experience will be perceived as having the ability to make valuable contribution to the group's task. Consequently, education, work experience and international experience will influence a foreign newcomer's initial task-based group acceptance" (Joardar, 2011). It can be argued that a person with significant international experience will be perceived as having had the opportunity to learn how to build valuable relationships in a cross-cultural setting. Hence, international experience will have effects on initial relationship-based group acceptance as well. Meaning, this will make for a more positive expectancy violation, in the workplace especially. EVT is also used as a framework to analyze the negative impact of mind reading expectations on romantic relationships. In 2015, Wright and Roloff explain the idea of mind reading expectations (MRE) that romantic partners should clearly know about each other's feelings even though they are not being informed. When relational partners have done something wrong without self-consciousness, people's expectations are violated. Particularly those who hold high value of MRE are more likely to become distressful once their relational partners are unaware of their violations to expectations. The study asserts that such kinds of violations related to MRE result in responses such as combative attitude and silent treatment, which is harmful to long-term romantic relationships. + +== See also == +Language expectancy theory +Social exchange theory +Transactional analysis + +== References == \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Expectancy_violations_theory-2.md b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-2.md new file mode 100644 index 000000000..a16f776f5 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-2.md @@ -0,0 +1,34 @@ +--- +title: "Expectancy violations theory" +chunk: 3/17 +source: "https://en.wikipedia.org/wiki/Expectancy_violations_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:53.972000+00:00" +instance: "kb-cron" +--- + +=== Propositions === +After assessing expectancy, violation valence, and communicator reward valence of a given situation, it becomes possible to make rather specific predictions about whether the individual who perceived the violation will reciprocate or compensate the behavior in question. Guerrero and Burgoon noticed that predictable patterns develop when considering reward valence and violation valence together. Specifically, if the violation valence is perceived as positive and the communicator reward valence is also perceived as positive, the theory predicts individuals will reciprocate the positive behavior. Similarly, if one perceives the violation valence as negative and the communicator reward valence as negative, the theory again predicts that one will reciprocate the negative behavior. Thus, if a disliked coworker is grouchy and unpleasant, people will likely reciprocate and be unpleasant in return. +Conversely, if one perceives a negative violation valence but views the communicator reward valence as positive, it is likely that the person will compensate for his or her partner's negative behavior. For example, imagine a supervisor appears sullen and throws a stack of papers in front of an employee. Rather than grunt back, EVT predicts that the employee will compensate for the boss's negativity, perhaps by asking if everything is okay. More difficult to predict, however, is the situation in which a person who is viewed unfavorably violates another with positive behavior. In this situation, the receiver may reciprocate, giving the person the "benefit of the doubt". +The assumptions discussed thus far can be summarized into six major propositions posited by EVT: + +People develop expectations about verbal and nonverbal communication behavior from other people. +Violations of these expectations cause arousal and distraction, further leading the receiver to shift his or her attention to the other, the relationship, and the meaning of the violation. +Communicator reward valence determines the interpretation of ambiguous communication. +Communicator reward valence determines how the behavior is evaluated. +Violation valences are determined by three factors: +The evaluation of the behavior +Whether or not the behavior is more or less favorable than the expectation. A positive violation occurs when the behavior is more favorable than the expectation. A negative violation occurs when the behavior is less favorable. +The magnitude of the violation. +Positive violations produce more favorable outcomes than behavior that matches expectations, and negative violations produce more unfavorable outcomes than behavior that matches expectations. + +=== Needs for personal space and affiliation === +EVT builds upon a number of communication axioms. EVT assumes that humans have two competing needs: A need for personal space and a need for affiliation. Specifically, humans all need a certain amount of personal space, also referred to as distance or privacy. People also desire a certain amount of closeness with others, or affiliation. EVT seeks to explain 'personal space', and the meanings that are formed when expectations of appropriate personal space are infringed or violated. +Another feature of personal space is territoriality. Territoriality refers to behavior which "is characterized by identification with a geographic area in a way that indicates ownership" (Hall, 1966). In humans, territoriality refers to an individual's sense of ownership over physical items, space, objects or ideas, and defensive behavior in response to territorial invasions. Territoriality involves three territory types: Primary territories, secondary territories and public territories. Primary territories are considered exclusive to an individual. Secondary territories are objects, spaces or places which "can be claimed temporarily" (Hall, 1966), but are neither central to the individual's life nor are exclusively owned. Public territories are "available to almost anyone for temporary ownership". Territoriality is frequently accompanied by prevention and reaction. When an individual perceives one of their needs has been compromised, EVT predicts that they will react. For instance, when an offensive violation occurs, the individual tends to react as though protecting their territory. + +=== Proxemics === +EVT offers an opportunity to study how individuals communicate through personal space. This part of the theory explains the notion of "personal space" and an individual's reactions to others who appear to "violate" their sense of personal space. What people define as personal space, however, varies from culture to culture and from person to person. The "success" or "failure" of violations are linked to perceived attraction, credibility, influence and involvement. The context and purpose of interaction are relevant, as are the communicator characteristics of gender, relationships, status, social class, ethnicity and culture. When it comes to different interactions between people, what each person expects out of the interaction will influence their individual willingness to risk violation. If a person feels comfortable in a situation, they are more likely to risk violation, and in turn will be rewarded for it. +Introduced by Edward Hall in 1966, proxemics deals with the amount of distance between people as they interact with one another. Spatial distance during an interaction can be an indication of what type of relationship exists between the people involved. + +There are 4 different personal zones defined by Hall. These zones include: \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Expectancy_violations_theory-3.md b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-3.md new file mode 100644 index 000000000..90f42a629 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-3.md @@ -0,0 +1,33 @@ +--- +title: "Expectancy violations theory" +chunk: 4/17 +source: "https://en.wikipedia.org/wiki/Expectancy_violations_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:53.972000+00:00" +instance: "kb-cron" +--- + +Intimate distance: (0–18 inches) – This distance is for close, intimate encounters. Normally core family, close friends, lovers, or pets. People will normally share a unique level of comfort with one another. +Personal distance: (18 inches – 4 feet) – Reserved for conversations with friends, extended family, associates, and group discussions. The personal distance will give each person more space compared with the intimate distance, but is still close enough to involve touching one another. +Social distance: (4–10 feet) – This distance is reserved for newly formed groups, and new acquaintances and colleagues one may have just met. People generally do not engage physically with one another within this section. +Public distance: (10 feet to infinity) – Reserved for a public setting with large audiences, strangers, speeches, and theaters. +Many different cultures are influenced by proxemics in different ways and respond differently to the same situation. In some cultures, those who have not formed close relationships may greet each other with kisses on the cheek, engaging one another well within the intimate range of proxemics. In other cultures, a custom greeting is a handshake which maintains a physical separation but is well within personal distance. Across the proxemic zones, actions can be interpreted differently among different cultures. For example, Japanese people do not address others by their first names unless they have been given permission. Calling someone by their first name in Japan without permission is considered an insult. In the Japanese culture, they address people using their last name and 'san', which is equivalent to 'Mr.', 'Mrs.' and 'Ms.' in the English language. The way Japanese people address each other is an example of a verbal proxemic zone. A Japanese person allowing another to call them by their first name is an example of intimate distance, because this is a privilege extended only someone very close to them. + +== Applications == + +=== Interpersonal communication === +It is important to note that EVT can apply to both non-relational interaction and close relationships. In 1998, more than twenty years after the theory was first published, several studies were conducted to catalog the types of expectancy violations commonly found in close relationships. +Participants in friendships and romantic relationships were asked to think about the last time their friend or partner did or said something unexpected. It was emphasized that the unexpected event could be either positive or negative. Participants reported events that had occurred, on average, five days earlier, suggesting that unexpected behaviors happen often in relationships. Some of the behaviors reported were relatively mundane, and others were quite serious. The outcome of the list was a list of nine general categories of expectation violations that commonly occur in relationships. + +Support or confirmation is an act that provides social support in a particular time of need, such as sitting with a friend who is sick. +Criticism or accusation is critical of the receiver and accuse the individual of an offense. These are violations because they are accusations not expected. An example is a ball player telling a teammate he should have caught the ball rather than supportively giving him or her a slap on the back and offering words of encouragement. +Relationship intensification or escalation intensifies the commitment of the communicator. For instance, saying "I love you" signifies a deepening of a romantic relationship. +Relationship de-escalation signifies a decrease in commitment of the communicator. An example might be spending more time apart. +Relational transgressions are violations of the perceived rules of the relationship. Examples include having an affair, deception, or being disloyal. +Acts of devotion are unexpected overtures that imply specialness in the relationship. Buying flowers for no particular occasion falls into this category. +Acts of disregard show that the partner is unimportant. This could be as simple as excluding a partner or a friend from a collective activity. +Gestures of inclusion are actions that show an unexpected interest in having the other included in special activities or life. Examples include invitations to spend a special holiday with someone, disclosure of personal information, or inviting the partner to meet one's family. +Uncharacteristic relational behavior is unexpected action that is not consistent with the partner's perception of the relationship. A common example is one member of an opposite-sex friendship demanding a romantic relationship of the other. +In later review of the studies, the support or confirmation category was inserted into acts of devotion and included another category, uncharacteristic social behavior. These are acts that are not relational but are unexpected, such as a quiet person raising his or her voice. +In terms of the response to expectancy violations, the sensitivity of expectancy violations varies from genders. Research found that women are less tolerant than men when their expectation are violated by negative behaviors, regardless of the types of violations such as dishonesty and immorality. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Expectancy_violations_theory-4.md b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-4.md new file mode 100644 index 000000000..024ddfe1c --- /dev/null +++ b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-4.md @@ -0,0 +1,23 @@ +--- +title: "Expectancy violations theory" +chunk: 5/17 +source: "https://en.wikipedia.org/wiki/Expectancy_violations_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:53.972000+00:00" +instance: "kb-cron" +--- + +==== Friendship ==== +Expectations with friends formulate over time and are usually brought together by a series of observations of behavior and predictions on how that friend will act in the future. When these expectations are violated, it often can be damaging and dangerous for a close friendship. It can cause an end to the friendship and create a strong negative experience in that person's life. Over time, people might expect friends to act consistently around them until a violation to this expectation takes place. For example, when they begin "breaking promises or even acting in an inauthentic manner to impress others, can have aversive consequences for close relationships" (Cohen 2010). People expect their friends to act in a social manner and adhere to all of our personal rules they set in their minds, such as being nice, kind, considerate, and refraining from any comment that puts another down. This is a part of the personal rules with a personal friendship, though in a different setting with that individual around different people, the rules may be broken. While this might be an offense in one's eyes, it may not be offensive in the others. Each negative experience can deteriorate the relationship and allow more experiences where expectations are continually violated until the relationship is dissolved. Cohen said "the more that a friendship is voluntary, easily replaceable, and disconnected from external pressures to continue, the more vulnerable it is to expectancy violation damage" (Cohen, 2010). Someone will always look for the better option if a negative experience has taken place. The more invested someone is in a friendship, the stronger the effect will have on the individual when expectations are violated. +Gender also plays a role in expectancy violation. Friendships with members of the same sex usually operate differently than those between different sexes. Women are generally less tolerant with men when violations have taken place. Relationships, whether it be with the same sex or not, tend to fail over time when one or both parties do not adhere the norms that the other is accustomed to and engage in behaviours such as hostile attitudes, sharp comments, distancing from the other, etc. Both parties are also capable of violating each other's expectations at the same time. It is not just one person in the relationship that perceives behavior as unusual. One can respond to a violation with another social violation, leaving the friendship in confusion of the direction it is going. +One study done in 2025 says that people are quick to put blame on the physical world if people are unalike from themselves. This comes from the fact that if someone has not had the same experiences as you, they will not expect the same things as you. + +==== Family relationships: phubbing ==== +Expectations in family relationships are prone to being violated via phubbing. Phubbing is a term coined to describe when an individual goes on their phone and mentally removes themselves from the conversation and physical reality, thus snubbing their interaction partners. This violates expectations in family relationships when a younger individual is around an older adult. Travis Kadylak found that "older adults feel ignored and disrespected" in situations where a younger family member is phubbing. In this case, the younger individually and unconsciously violated the older adult's expectations that stems from the adult's perception of social etiquette. Kadylak calls for further research on how phubbing expectancy violations affect the well-being of older adults. +When it comes to smartphone use in conversations overall, researchers found that proactive and reactive smartphone use, often use that interrupts the conversation, leaves to lower perceived attentiveness and politeness from the conversational partner due to their expectations of a direct conversation being violated. Whereas integrative smartphone use, when the smartphone becomes a part of the conversation, leaves no significant impact on the perception of the conversation. +In 2025, a study examining phubbing behaviors during casual and serious conversations was conducted. Seeing phubbing behavior did not relate to the perception of poor conversation quality. However, when observing phubbing behavior, female participants perceived lower conversation quality between the conversation partners compared to male participants. It is more common to observe two men spending time together and using their phones to decrease immediacy, rather than a woman. Perceived poor conversation quality was also associated with lower perceived connectedness between the conversation partners, as well as with lower perceptions of appropriateness toward the interlocutor who was phubbing. +Additionally, another research project titled "I Have to Become a Phubber": A Case Study of a Female College Counselor's Phubbing at Home was conducted. The study found that during face-to-face conversations, constantly checking smartphones without responding in time leads to inconsistent expectations. Phubbing also tends to create more conflicts between the phubber and the person being phubbed. When another person's behavior is inconsistent with an individual's expectations, this expectancy violation triggers awareness and prompts a series of cognitive evaluations of the violation. If the violation conflicts with the individual's psychological valence, the expectancy violation can damage the interpersonal interaction. +A study examining expectancy violations in text-based communication found that expectations vary considerably in extended families. Expectations are flexible in extended families, and transmitting messages at inappropriate times may breach these expectations. In addition, anticipating empathy and support when interacting with close friends leads to timely and empathetic responses that confirm favorable expectations. + +==== Romantic relationships ==== \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Expectancy_violations_theory-5.md b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-5.md new file mode 100644 index 000000000..968665788 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-5.md @@ -0,0 +1,15 @@ +--- +title: "Expectancy violations theory" +chunk: 6/17 +source: "https://en.wikipedia.org/wiki/Expectancy_violations_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:53.972000+00:00" +instance: "kb-cron" +--- + +Expectancy violations happen frequently in romantic relationships. In relationships there is an unspoken expectation when interacting and that is the significant other will give their full undivided attention when in the presence of their significant other. As the new generation evolves, the face to face contact has changed. With the access use of phones and social media the attention of individuals has shifted to their devices and continues to become worse. Since there is access to many mobile devices, there has been an increase of lack of communication face to face. This has made it difficult for some relationships to grow and has created conflict because the expectation of attention has been shifted. "Individuals expect conversational partners to be moderately involved in an interaction (Burgoon, Newton, Walther, & Baesler, 1989). Within existing relationships, partners rely on one another to show interest and immediacy in interactions (White, 2008). However, the presence of cell phones and the expectation to be constantly available (Ling, 2012) impacts partners' abilities to give full attention to one another" (Miller-Ott, A., & Kelly, L. 2015). +Regardless of where the romantic relationship takes place, people are likely to have negative valence about cell phone usage, including texting, viewing news and playing games, if their expectations of attention and intimacy are violated. In addition, excessive cell phone usage during a date has a great impact on romantic partner's negative valence towards the usage. However, Miller-Ott and Kelly found that a small amount of cell phone usage during a date is acceptable, such as responding to a text message and quickly bringing attention back to the date partner. The same behavior in different occasions and contexts is viewed differently in terms of the degree of valence. Research found that same behavior is viewed as more negative in a restaurant than at home. Since people are more likely to have higher expectations for undivided attention during formal contexts, using a cell phone in formal dates will more negatively violate partner's expectations. Divided attention is acceptable in casual contexts – therefore, the degree of expectancy violations is low under a hanging out context. +After expectation are violated in the romantic relationships, one may assume that an apology may fix expectations that were violated; however, Benjamin W Chiles and Michael E. Roloff found that "apology is positively evaluated by apologizers, this relationship is moderated by their expectations of acceptance prior to the actual response to the apology". Laura K. Guerrero and Guy F. Bachman found that high quality relationships tend to forgive more than relationships with less investments, yet they tend to inflict hurt intentionally. +In a study done in 2022, Lilly and Buehler conducted a survey measuring young adults' reaction to sexually explicit introductions on an online dating tool versus a traditional introduction. They found that young adults were much more likely to negatively react to a sexually explicit introduction as opposed to a traditionally one. The study discusses how EVT is the main cause of this negative reaction. Because the receiver is expecting a traditional introduction as opposed to a sexually explicit one, the receiver's expectations are violated and they experience a negative reaction. Lilly and Buehler recommend while using an online dating tool to wait to send a sexually explicit message until it follows potential expectations if at all. Following expectations can be critical for online dating even in a more minute sense. DelGreco and Denes found when it comes to a woman receiving a compliment from a man using an online dating tool, her response can leave a lasting impact if it violates expectations. The study found that men expect women to be thankful for the compliment. If the woman negatively violates expectations with agreement or self praise, there tends to be the biggest negative impact left on the man. If the woman positively violates expectations with denial or disagreement, there is still a significant negative impact left on the man. Ultimately, EVT and gender roles/expectations can be very applicable to one another. +Barak and Loewenstein discovered that inconsistencies in relationships are not always resolved by adjusting the relationships. Instead, people often reinterpret the inconsistencies to avoid modifying their relationships, and this is more common when the inconsistencies are large. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Expectancy_violations_theory-6.md b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-6.md new file mode 100644 index 000000000..d56bb9db2 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-6.md @@ -0,0 +1,28 @@ +--- +title: "Expectancy violations theory" +chunk: 7/17 +source: "https://en.wikipedia.org/wiki/Expectancy_violations_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:53.972000+00:00" +instance: "kb-cron" +--- + +==== Stereotypes, Gender and Sexuality ==== +A study on personality traits and gender-based stereotypes in perceived negotiation skills was conducted in 2024. The study found that women tend to perform better in same-sex negotiations than in opposite-sex negotiations, while no significant differences were observed for men-pointing to the detrimental effect of gender in negotiation. Negotiation outcomes were mostly one-sided in favor of high-powered negotiators when stereotypical masculine traits were displayed, whereas stereotypically feminine traits tended to produce win-win outcomes. When negotiators' behaviors counter gender-specific beliefs, negative expectancy violations occur, generating backlash and negatively affecting negotiators' outcomes. +When facing an unexpected negotiation partner, the impact of a hiring manager's gender-role violation on job candidates become evident. Job candidate believed that hiring managers were more extreme in characteristics that violated gender-role expectations: agentic female hiring managers were seen as more agentic than their male peers, while communal male hiring managers were perceived as more communal than their female counterparts. Job candidates were also less comfortable with an agentic female hiring manager than with an agentic male hiring manager. Further negotiating with an agentic female hiring manager would result in the least favorable outcomes, whereas those negotiating with a communal hiring manager would result in the most favorable outcomes. +Researchers Gheorghe, Andreea, Curșeu, and Petru Lucian studied Leading Through Affiliation: The Effect of Humor Type and Gender on the Likelihood of Being Perceived as a Leader. They found that people using affiliative humor had a higher perceived chance of emerging as leaders compared to those using aggressive humor, and gender itself did not have a significant effect on leadership emergence. The affiliative-aggressive humor discrepancy in leadership emergence was greater for men than for women. Moreover, men tend to receive more credit for affiliative humor, while women are penalized less for using aggressive humor in groups. + +===== Cell phone usage ===== +Cell phone usage behaviors that do not contradict intimate moment are viewed as positive violations, including sharing interesting messages and playing online games together. People have less negative valence on cell phone usage if they gain more reward from the behaviors. +Research also found the most common response to the violated cell phone usage is to do nothing. However, people have different reactions to the violations under different stages of romantic relationships. In the early stage of dating, people are more likely to respond by indirect messages and silence. While there are direct verbal responses when expectations are violated in established relationships. + +===== Sexual resistance ===== +Sexual resistance is viewed as a typical expectancy violation in romantic relationships. In 2003, Bevan used EVT to evaluate the impact of sexual resistance on close relationships. The research focused on two considerations: relational contexts and directness of the messages. +The research concluded that people who are resisted in a romantic relationship perceived the violation of sexual resistance as more negative and unexpected than those resisted in a regular cross-sex friendship. The reason might because romantic partners believe that they have clearer and deeper understanding of each other's expectations and degree of acceptance and tolerance. When it comes to message directness of sexual resistance, although the study did not find any significant difference of levels of violation valence and expectedness between direct and indirect messages, direct sexual resistance messages in close relationships proved to be more relationally important than indirect messages. Therefore, direct sexual resistance messages will be a harmful factor that affects the continuity of a romantic relationship. + +===== Hurtful events ===== +The degree of expectancy violations in romantic relationships quality affect how partners react to hurtful events caused by their partner. Partners who view their significant others as positively rewarding are more keen to use constructive communication after experiencing a negative hurtful event. EVT analysis approach also show that if the negative valence happens when partners find the other to be unrewarding, it results in destructive communication, leading to breakups. + +===== Online dating ===== +Maria DelGreco and Amanda Denes investigate men and women's expectations and interpretations of communicative cues in the initiation stage of heterosexual online dating. When women expect men's responses to compliment, women face negative deviation when men express narcissism and agreement. Moreover, women with positive deviations of expectations are assessed more negatively than those who align with expectations. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Expectancy_violations_theory-7.md b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-7.md new file mode 100644 index 000000000..9dc155926 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-7.md @@ -0,0 +1,21 @@ +--- +title: "Expectancy violations theory" +chunk: 8/17 +source: "https://en.wikipedia.org/wiki/Expectancy_violations_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:53.972000+00:00" +instance: "kb-cron" +--- + +=== Human-Technology Interaction with AI and Chatbots === +Researchers found that the communication style of chatbots can influence consumers' satisfaction, trust, and engagement in the context of service failure. This is demonstrated through interactions with social-oriented communication-style chatbots, which elevate the level of consumers' interaction satisfaction and behavioral intention. This study examined how the communication style of chatbots influences consumers' satisfaction, trust, and engagement in the context of service failure. Additionally, when consumers' expectations are violated to a higher level, chatbots using a socially oriented (vs. task-oriented) communication style are more likely to incite higher interaction satisfaction, trust, and patronage intention. +Another study about chatbot interactions examined the opposing effects of response time in human-chatbot interaction. It was found that experienced users may find a delayed response time irritating because they are aware that a chatbot can answer instantly. The results also reveal that social presence, or the feeling of being there, mediates the effect of chatbot response time on usage intentions (the willingness of a person to use a particular product, service, or system). It was also found that when perceived social presence is low, skilled users have a higher usage intention than novice users. This means that users will use it more often because of the direct answers rather than high social presence. +Researchers Deng Zhaohua, Song Dan, and Evans Richard conducted a study exploring the effects of estimated accuracy and the actual performance of AI systems on human-AI collaboration. They found that humans over trust low-performing AI systems and distrust high-performing ones. As a result, the misplaced trust reduces human-AI collaboration performance by weakening the complementarity between humans and AI. Although humans are more likely to follow the suggestions of AI systems and contribute less human knowledge when they know they are cooperating with an AI system that has high estimated accuracy. +There are two specific studies that focus on the effects that smartphones have on our face-to-face conversations. One study done by Stevic, Liftinger, and Matthes in 2025. This study had a heavy focus on the relationship between men and women in relationships. They found that the presence of smartphones in the midst of a conversation with significant others, had poor effects on the connection of the couple, the quality of the conversation, and appropriateness. Selak, Merkaš, and Ivanković, studied parents and their children in a similar way. Their 2025 study consisted of four waves. They found that parents using smartphones while interacting with their children causes problems with the children's emotions and behavior. It also had a large effect on their "subjective well-being". +Herwandito, Pawito, Utari, and Hastjarjo completed a study in 2024 that consisted of measuring one's behavior in text-based communication. It concentrates heavily on expectancy violations in relationships, specifically online violations. They argue that technological advances have changed human responses to expectancy violation. However, there is also a study that comes from Vidanalage, Lee, Hermans, Engelhard, Scheveneels, and Meyerbröker in 2025 that address the productive uses of virtual reality. They wanted to see the effects of virtual reality on adolescents and their social anxiety. They did not have a sure conclusion about the use of VR for adolescents, but it did show to help reduce social anxiety in adults. Reducing social anxiety is linked to uncertainty reduction and expectancy violation theory. + +==== Culture Misunderstandings, Online Interaction/Communication ==== +In an online interaction study on the effects of observer expectations on judgements of anti-Asian hate tweets and online activism responses, researchers found the following results. Results showed the Republicans held stronger anti-Asian attitudes than Democrats and were more likely to blame China for the pandemic. Furthermore, political conservatives found online hate content less offensive and disturbing than political liberals did. The more non-prototypical, or unexpected, a source appeared to the observer, the greater their subsequent judgments of speech act offensiveness and intention to engage in online activism. +A study on expectancy violation and discontinuance behavior in live streaming commerce explored human interaction with virtual streamers. Users' gamification interaction expectation violations could positively affect their psychological experience in negative behavioral outcomes. In addition, anthropomorphism increases customers' expectations about a chatbot's performance capabilities, resulting in expectancy violations. Consumers tend to interact with virtual streamers, particularly because of their anthropomorphic qualities. However, when consumers' beliefs fail to align with their expectations-i.e., when a negative expectancy violation occurs-their affective states are negatively impacted. +In 2023, a study titled Examining Direct Sales as a Violation of Friendship Expectations on WeChat was conducted. WeChat users perceive their friends' selling behaviors as a violation of their friendships. However, participants generally considered the violation to be moderately unexpected. Additionally, the type of relationship was found to affect the expectedness, but not the importance or valence, of the violation. Perceived expectancy can be influenced by three factors: communicator characteristics, relationship characteristics, and contextual characteristics. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Expectancy_violations_theory-8.md b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-8.md new file mode 100644 index 000000000..bd5def082 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-8.md @@ -0,0 +1,22 @@ +--- +title: "Expectancy violations theory" +chunk: 9/17 +source: "https://en.wikipedia.org/wiki/Expectancy_violations_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:53.972000+00:00" +instance: "kb-cron" +--- + +=== Computer-mediated communication and social media === +As has previously been addressed, EVT has evolved tremendously over the years, expanding beyond its original induction when it focused on FtF communication and proxemics. The advancement of information and communications technology has provided tools for expressing oneself and conveying messages beyond just typing in text. As already discussed, arousal can divert one's attention or interest from a message to the source of the arousal. Virtual realities created online through computer-mediated communication (CMC), especially those which evoke strong visual presence through media, can increase arousal levels, such as those with high violent or sexual content. Just as people may use television viewing to increase or decrease arousal levels, people may use media in online communication to increase or decrease arousal levels. People may interact with others online by assuming the identities of avatars which may take on completely different, alternate personalities. The differences in perceived intimateness, co-presence, and emotionally-based trust can very significantly between avatar communication and other communication modalities such as text chat, audio, and audio-visual. The media options available to users when communicating with others online present a host of potential expectancy violations unique to CMC. +The introduction of social media networks such as Facebook and Twitter, as well as dating social networks such as Match.com and eHarmony, has greatly contributed to the increased use of computer-mediated communication which now offers a context for studying communication devoid of nonverbal information. Though these media are relatively new, they have been in existence long enough for users to have developed norms and expectations about appropriate behaviors in the online world. However, there has been a lag by researchers to study and understand these new established norms, which makes CMC rich with heuristic possibilities from a communications theory perspective. +Ramirez and Wang studied the occurrence and timing of modality switching, or shifts from online communication to FtF interaction, from the perspective of EVT. Their research documented inconsistent findings which revealed in some instances relationships were enhanced and in others they were dampened, indicating the expectations, evaluations, and outcomes associated with initial modality switches varied amongst individuals. Additionally, studies have found that when individuals who meet online meet face-to-face for the first time, the length of time spent communicating online can determine whether individuals will rate physical characteristics of each other positively or negatively. Unlike FtF communication, CMC allows people to pretend to be connected with a person who violates their expectancy by ignoring violations or filtering news feed. Meanwhile, people can also cut the connection completely with someone who is not important by deleting friendship status when a serious violation occurs. A confrontation is much more likely for close friends than for acquaintances, and compensation is much more likely for acquaintances, a finding which contrasts typical EVT predictions. Furthermore, EVT on the Internet environment is strongly related to online privacy issues. +In a study done in 2018, Tang found that expectation violations of both the amount of likes a post gets, and the expectation violating of who likes the post, can negatively affect the original poster's mental health and perceived friend support. +Online Activism Judgments +In a study measuring the effects of third party expectations and judgements when viewing anti-Asian hate tweets, Tong and DeAndrea found how powerful expectancies can be. In the experiment, Tong and DeAndrea took 196 white active X users and measured their political ideologies on a scale from 1 (a strong republican) to 7 (a strong democrat). Then the researchers showed each participant an extremely offensive fake anti-Asian post on the platform from either a white or black poster indicated by the profile picture. Then they asked the participants a serious of questions. Tong and DeAndrea found that white republicans viewed a black poster spreading anti-Asian hate as more ethnically prototypical compared to a white poster. On the contrary, white democrats viewed a white posters spreading anti-Asian hate as more ethnically prototypical compared to a black poster. Additionally, the stronger the republican, the stronger they viewed the black poster as ethnically prototypical. The stronger the democrat, the stronger they viewed the white person as ethnically prototypical. Moderates consistently fell in the middle. + +==== Facebook ==== + +In social media, such as Facebook, people are connected online with friends and sometimes strangers. Norm violations on Facebook may include too many status updates, overly emotional status updates or Wall posts, heated interactions, name calling through Facebook's public features, and tags on posts or pictures that might reflect negatively on an individual. Research indicates that the perception of this act as a negative expectancy violation is influenced by factors such as the duration of the Facebook friendship and the nature of the personal ties between the individuals involved. Longer-standing Facebook friendships, as well as stronger personal connections, tend to result in the unfriending action being viewed as a more significant breach of social norms and expectations. This severity, in turn, plays a role in whether the individual who initiates the unfriending communicates their decision to the other party. The research highlights the intricate dynamics of online social interactions and the weighted considerations behind the decision to unfriend, reflecting the nuanced nature of digital relationships and the expectations that govern them. +In a study conducted by Fife, Nelson, and Bayles of focus groups from a Southeastern liberal arts university, five themes were ascertained regarding Facebook use and expectancy violations: \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Expectancy_violations_theory-9.md b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-9.md new file mode 100644 index 000000000..7f7d38cfa --- /dev/null +++ b/data/en.wikipedia.org/wiki/Expectancy_violations_theory-9.md @@ -0,0 +1,44 @@ +--- +title: "Expectancy violations theory" +chunk: 10/17 +source: "https://en.wikipedia.org/wiki/Expectancy_violations_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:53.972000+00:00" +instance: "kb-cron" +--- + +""Don't stalk' – and when you do, don't talk about it" +Though an understanding exists among Facebook participants that users will use the site to keep track of the behavior of others in a number of ways, excessive monitoring is likely to be perceived as an expectancy violation. +"Don't embarrass me with bad pictures" +Users may have the ability to control which pictures they post on their own Facebook page, but they do not have the ability to control what others post. Posting and "tagging" unflattering pictures of others may create expectancy violations. +"Don't mess up my profile" +Several participants expressed annoyance of others who alter their profiles knowing that their alterations could be perceived negatively, though they did not mention changing their passwords or protecting themselves in other ways. +"Choose an appropriate forum for messages" +Messages can be sent between Facebook participants through 'Facebook messages', which are not public, or 'wall postings', which can be viewed by anyone specified in the user's privacy controls. Posting messages which may be perceived as private, embarrassing, or inappropriate to a wall posting can create expectancy violations. +"Don't compete over number of friends" +Facebook users maintain a running total of 'friends' on their profile which is viewable to others. Engaging in comparisons with others over this statistic can create expectancy violations. +In 2010, Stutzman and Kramer-Duffield examined college undergraduates' motivations to have friends-only profiles on Facebook. Having a friends-only profile is a practical method to enhance privacy management on Facebook. The two authors made distinctions between intended audience, to whom one hopes to disclose the Facebook profile, and expected audience, a group of people by whom one thinks the Facebook profile has been viewed. The study indicated that "expectancy violations were identified as instances where an expected audience was not jointly identified as an intended audience". Facebook networks were categorized into different levels: strong ties of family and intimate friends, weak ties comprising "casual friends and campus acquaintances", and outsiders such as "faculty or administrators". According to the study, expectancy violations by weak ties showed greater relevance to the establishment of a friends-only profile among college undergraduates, compared to other Facebook network ties. + +==== Electronic mail ==== +Email has become one of the most widely used methods of communication within organizations and workplaces. When discussing expectancy violations +with electronic e-mail, just as with other modes of communication, a distinction +must be made between inadvertent violations of norms and purposeful violations, +referred to as 'flaming'. Flaming +is defined as hostile and aggressive interactions via text-based CMC. +One form of expectancy violation in email is the length of time between the sending of the initial email and the receiver's reply. Communicator reward valence plays a large part in how expectancy violations are handled in email communications. In computer-mediated communication, people have expectations to others' online behaviors based on individual identity. In online contexts, violations are not simply assessed as positive or negative. Some violations are ambiguous such as e-mail response latency. In 2017, Nicholls and Rice stated that "when deviation is ambiguous, the communicator's reward value will mediate the perceptions of the deviation." +Chronemic studies on email have shown that in organizations, responder status played a large part in how individuals reacted to various lapses in response to the previously sent email. Long pauses between responses for high-status responders produced positive expectancy violation valence and long pauses from low-status responders produced a negative expectancy violation valence. However, in the case of job interviews, long pauses between email for high-status candidates reflected negatively on their reviews. Expectations for email recipients to respond within a normative time limit illustrate the medium's capacity for expectancy violations to occur. + +=== Academic environment === +Permzadian and Shen assessed in 2024 that predictive validity of expectancy violation is not an accurate representation of a child's academic performance. It does, however, have a strong relationship with course grades and cognitive ability. + +==== Teacher anger ==== + +McPherson, Kearney, and Plax examined teacher anger in college classrooms through the lens of norm violations. Naturally, teachers will become frustrated and angry with students in classrooms from time to time. How teachers express themselves and convey those +emotions will determine how students respond and interpret those emotional demonstrations. +The students judged the appropriateness of teachers' anger in classrooms in the modal expressions of distributive aggression, passive aggression, integrative assertion, and nonassertive denial. Students rated the aggressive expressions as +highly intense, destructive, and inappropriate (or non-normative), including such behaviors as sarcasm or putdowns (most +frequently cited), verbal abuse, rude and condescending behaviors toward students, and acts intended to demoralize students. The students described assertive displays as appropriate and less intense. Although anger is often considered to be a negative emotion, teacher anger is not necessarily a violation of classroom norms. Based on the study, intense and aggressive displays of teacher anger are considered socially inappropriate by students. These perceived norm violations result in negative evaluations of the teacher and the course. Because only integrative-assertive expressions of teacher anger were positively related to students' perceptions of appropriateness, the study concluded that teachers should avoid intense, aggressive anger displays and should rather assertively and directly discuss the problem with students. + +==== Teacher dress ==== +Clothing is considered a form of nonverbal communication. Dress communicates status, hierarchy, credibility, and attractiveness. Specific social codes dictate what forms of dress are appropriate in various cross-cultural contexts. When individuals wear clothing that is deemed inappropriate for a given situation, or when an individual's clothing does not seem to match their perceived status or attractiveness, this can constitute an expectancy violation. Studies on clothing and teacher perceptions have shown that when teachers wear formal attire, students rate their credibility higher. However, for high-reward teachers, clothing formality did not raise perceptions of attractiveness. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Language_expectancy_theory-0.md b/data/en.wikipedia.org/wiki/Language_expectancy_theory-0.md new file mode 100644 index 000000000..f0154bcde --- /dev/null +++ b/data/en.wikipedia.org/wiki/Language_expectancy_theory-0.md @@ -0,0 +1,39 @@ +--- +title: "Language expectancy theory" +chunk: 1/2 +source: "https://en.wikipedia.org/wiki/Language_expectancy_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:56.372148+00:00" +instance: "kb-cron" +--- + +Language expectancy theory (LET) is a theory of persuasion. The theory assumes language is a rules-based system, in which people develop expected norms as to appropriate language usage in given situations. Furthermore, unexpected linguistic usage can affect the receiver's behavior resulting from attitudes towards a persuasive message. + +== Background == +Created by Michael Burgoon, a retired professor of medicine from the University of Arizona, and Gerald R. Miller, the inspiration for LET was sparked by Brooks' work on expectations of language in 1970. Burgoon, Jones and Stewart furthered the discussion with the idea of linguistic strategies and message intensity in an essay published in 1975. The essay linked linguistic strategies, or how a message is framed, to effective persuasive outcomes. The original work for the language expectation theory was published in 1978. Titled "An empirical test of a model of resistance to persuasion", it outlined the theory through 17s. + +== Expectations == +The theory views language expectancies as enduring patterns of anticipated communication behavior which are grounded in a society's psychological and cultural norms. Such societal forces influence language and enable the identification of non-normative use; violations of linguistic, syntactic and semantic expectations will either facilitate or inhibit an audience's receptivity to persuasion. Burgoon claims applications for his theory in management, media, politics and medicine, and declares that his empirical research has shown a greater effect than expectancy violations theory, the domain of which does not extend to the spoken word. +LET argues that typical language behaviors fall within a normative "bandwidth" of expectations determined by a source's perceived credibility, the individual listener's normative expectations and a group's normative social climate, and generally supports a gender-stereotypical reaction to the use of profanity, for example. +Communication expectancies are said to derive from three factors: + +The communicator – individual features, such as ethos or source credibility, personality, appearance, social status and gender. +The relationship between a receiver and a communicator, including factors such as attraction, similarity and status equality. +Context; i.e., privacy and formality constraints on interaction. + +== Violations == +Violating social norms can have a positive or negative effect on persuasion. Usually people use language to conform to social norms; but a person's intentional or accidental deviation from expected behavior can have either a positive or negative reaction. Language Expectancy Theory assumes that language is a rule-governed system and people develop expectations concerning the language or message strategies employed by others in persuasive attempts (Burgoon, 1995). Expectations are a function of cultural and sociological norms and preferences arising from cultural values and societal standards or ideals for competent communication. +When observed, behavior is preferred over what was expected or when a listener's initial negative evaluation causes a speaker to conform more closely to the expected behavior. The deviation can be seen as positive, but when language choice or behavior is perceived as unacceptable or inappropriate behavior, the violation is negatively received and can inhibit the receptivity to a persuasive appeal. +Positive violations occur (b) when negatively evaluated sources conform more closely than expected to cultural values or situational norms. This can result in overly positive evaluation of the source and change promoted by the actor (Burgoon, 1995). +Negative violations, resulting from language choices that lie outside socially acceptable behavior in a negative direction, produce no attitude or behavior change in receivers. + +== Summary of propositions == +Language expectancy theory is based on 17 propositions. Those propositions can be summarized as listed below: + +1, 2 and 3: People create expectations for language. Those expectations determine whether messages will be accepted or rejected by an individual. Breaking expectations positively results in a behavior change in favor of the persuasive message while a breaking expectations negatively results in no change or an opposite behavior change. +4, 5 and 6: Individuals with perceived credibility (those who hold power in a society) have the freedom in persuasion to select varied language strategies (wide bandwidth). Those with low credibility and those unsure of their perceived credibility are restricted to low aggression or compliance-gaining messages to be persuasive. +7, 8 and 9: Irrelevant fear and anxiety tactics are better received using low-intensity and verbally unaggressive compliance-gaining. Intense and aggressive language use result in lower levels of persuasion. +10, 11 and 12: For the persuader, an individual who is experiencing cognitive stress will use lower intensity messages. If a communicator violates his/her norms of communication, they will experience cognitive stress. +13 and 14: Pretreatments forewarn receivers of the persuasive attacks (supportive, refutational or a combination). When Persuasive messages do not violate expectations created by the pretreatments, resistance to persuasion is conferred. When pretreatment expectations of persuasive messages are violated, receivers are less resistant to persuasion. +15, 16 and 17: Low intensity attack strategies are more effective than high intensity attack strategies when overcoming resistance to persuasion created in pretreatment. The first message in a string of arguments methodically affects the acceptance of the second message. When expectations are positively violated in the first message, the second will be persuasive. When expectations are negatively violated in the first message, the second will not be persuasive. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Language_expectancy_theory-1.md b/data/en.wikipedia.org/wiki/Language_expectancy_theory-1.md new file mode 100644 index 000000000..b6c8559ba --- /dev/null +++ b/data/en.wikipedia.org/wiki/Language_expectancy_theory-1.md @@ -0,0 +1,42 @@ +--- +title: "Language expectancy theory" +chunk: 2/2 +source: "https://en.wikipedia.org/wiki/Language_expectancy_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:56.372148+00:00" +instance: "kb-cron" +--- + +== The role of intensity == +These propositions give rise to the impact of language intensity—defined by John Waite Bowers as a quality of language that "indicates the degree to which the speaker's attitude toward a concept deviates from neutrality"—on persuasive messages. Theorists have concentrated on two key areas: (1) intensity of language when it comes to gender roles and (2) credibility. +The perceived credibility of a source can greatly affect a message's persuasiveness. Researchers found that credible sources can enhance their appeal by using intense language; however, less credible speakers are more persuasive with low-intensity appeals. Similarly, females are less persuasive than males when they use intense language because it violates the expected behavior, but are more persuasive when they use low-intensity language. Males, however, are seen as weak when they argue in a less intense manner. Theorists argue further that females and speakers perceived as having low credibility have less freedom in selecting message strategies and that the use of aggressive language negatively violates expectations. + +== Example == +To better explain the theory we look at the expectations and societal norms for a man and a woman on their first date. If the man pushed for further physical intimacy after dinner, the societal expectation of a first date would be violated. The example below with Margret and Steve depicts such a scene. +Margret: "I had a really good time tonight, Steve. We should do it again." +Steve: "Let's cut the crap. Do you want to have sex?" +Margret: "Uhhh..." +Margret's language expectations of a first date were violated. Steve chooses an aggressive linguistic strategy. If Margret views Steve as a credible and appealing source, she may receive the message positively and, thus, the message would be persuasive. If Margret perceives Steve as an ambiguous or low-credible source, Steve will not be persuasive. In such a case, Steve should have used a low-aggressive message in his attempt to win Margret to his idea of having sex. + +== Criticism == +Determining whether a positive or negative violation has occurred can be difficult. When there is no attitude or behavior change it may be concluded that a negative violation has occurred (possibly related to a boomerang effect). Conversely, when an attitude or behavior change does occur it may be too easy to conclude a positive violation of expectations has occurred. +The theory has also been critiqued for being too "grand" in its predictive and explanatory goals. Burgoon counters that practical applications of his research conclusions are compelling enough to negate this criticism. + +== See also == +Physician–patient interaction +Social influence + +== Notes == + +== References == +Bowers, J.W. (1963). Language intensity, social introversion, and attitude change. Speech Monographs, 30, 345–352. +Bowers, J.W. (1964). Some correlates of language intensity. Quarterly Journal of Speech, 50, 415–420. +Burgoon, J.K. (1993). Interpersonal expectations, expectancy violations, and emotional communication. Journal of Language and Social Psychology, 12, 13–21. +Burgoon, M. (1994). Advances in Research in Social Influence: Essays in Honor of Gerald R. Miller. Charles R. Berger and Michael Burgoon (Editors), East Lansing, MI: Michigan State University Press, 1993. +Burgoon, M., Dillard, J.P., & Doran, N. (1984). Friendly or unfriendly persuasion: The effects of violations of expectations by males and females. Human Communication Research, 10, 283–294. +Burgoon, M. Jones, S.B., Stewart, D. (1975). Toward a message-centered theory or persuasion: Three empirical investigations of language intensity. Human Communication Research, 1, 240–256. +Burgoon, M. and Miller, G.R. (1977) Predictors of resistance to persuasion: propensity of persuasive attack, pretreatment language intensity, and expected delay of attack. The Journal of Psychology, 95, 105–110. +Burgoon, M., & Miller, G.R. (1985). An expectancy interpretation of language and persuasion. In H. Giles & R. Clair (Eds.) The social and psychological contexts of language (pp. 199–229). London: Lawrence Erlbaum Associates. +Burgoon, M., Hunsacker, F., & Dawson, E. (1994). Approaches to gaining compliance. Human Communication, (pp. 203–217). Thousand Oaks, CA: Sage. +Dillard, J. P., & Pfau, M. W. (2002). The Persuasion Handbook: Developments in Theory and Practice (1st ed.). Thousand Oaks, CA: SAGE \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Membrane_theory_of_shells-0.md b/data/en.wikipedia.org/wiki/Membrane_theory_of_shells-0.md new file mode 100644 index 000000000..0083e7caa --- /dev/null +++ b/data/en.wikipedia.org/wiki/Membrane_theory_of_shells-0.md @@ -0,0 +1,25 @@ +--- +title: "Membrane theory of shells" +chunk: 1/1 +source: "https://en.wikipedia.org/wiki/Membrane_theory_of_shells" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:58.715178+00:00" +instance: "kb-cron" +--- + +The membrane theory of shells, or membrane theory for short, describes the mechanical properties of shells when twisting or under bending and assumes that bending moments are small enough to be negligible. +The spectacular simplification of membrane theory makes possible the examination of a wide variety of shapes and supports, in particular, tanks and shell roofs. There are heavy penalties paid for this simplification, and such inadequacies are apparent through critical inspection, remaining within the theory, of solutions. However, this theory is more than a first approximation. If a shell is shaped and supported so as to carry the load within a membrane stress system it may be a desirable solution to the design problem, i.e., thin, light and stiff. + + +== See also == +Theory of plates and shells +Stress resultants in plates and shells + + +== References == + + +== Literature == +Ventsel, Eduard; Krauthammer, Theodor (24 August 2001). "Chapter 13. The Membrane Theory Of Shells". Thin Plates and Shells - Theory: Analysis, and Applications. CRC Press. pp. 349–372. doi:10.1201/9780203908723.ch13 (inactive 12 July 2025). ISBN 978-0-8247-0575-6. Retrieved 5 October 2014.{{cite book}}: CS1 maint: DOI inactive as of July 2025 (link) +Practical industry example for plates and shell analysis - animated video \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Mosquito-malaria_theory-0.md b/data/en.wikipedia.org/wiki/Mosquito-malaria_theory-0.md new file mode 100644 index 000000000..f5b76fe3c --- /dev/null +++ b/data/en.wikipedia.org/wiki/Mosquito-malaria_theory-0.md @@ -0,0 +1,30 @@ +--- +title: "Mosquito-malaria theory" +chunk: 1/3 +source: "https://en.wikipedia.org/wiki/Mosquito-malaria_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:59.882762+00:00" +instance: "kb-cron" +--- + +Mosquito-malaria theory (or sometimes mosquito theory) was a scientific theory developed in the latter half of the 19th century that solved the question of how malaria was transmitted. The theory proposed that malaria was transmitted by mosquitoes, in opposition to the centuries-old medical dogma that malaria was due to bad air, or miasma. The first scientific idea was postulated in 1851 by Charles E. Johnson, who argued that miasma had no direct relationship with malaria. Although Johnson's hypothesis was forgotten, the arrival and validation of the germ theory of diseases in the late 19th century began to shed new lights. When Charles Louis Alphonse Laveran discovered that malaria was caused by a protozoan parasite in 1880, the miasma theory began to subside. +An important discovery was made by Patrick Manson in 1877 that mosquitos could transmit human filarial parasite. Inferring from such novel discovery, Albert Freeman Africanus King proposed the hypothesis that mosquitoes were the source of malaria. In the early 1890s Manson himself began to formulate the complete hypothesis, which he eventually called the mosquito-malaria theory. According to Manson, malaria was transmitted from human to human by a mosquito. The theory was scientifically proved by Manson's confidant Ronald Ross of the Indian Medical Service in the late 1890s. Ross discovered that malaria was transmitted by the biting of specific species of mosquito. For this Ross won the Nobel Prize for Physiology or Medicine in 1902. Further experimental proof was provided by Manson who induced malaria in healthy human subjects from malaria-carrying mosquitoes. Thus the theory became the foundation of malariology and the strategy of control of malaria. + +== Early concepts == +Malaria was prevalent in the Roman Empire, and the Roman scholars associated the disease with the marshy or swampy lands where the disease was particularly rampant. It was from those Romans the name "malaria" originated. They called it malaria (literally meaning "bad air") as they believed that the disease was a kind of miasma that was spread in the air, as originally conceived by ancient Greeks. Since then, it was a medical consensus for centuries that malaria was spread due to miasma, the bad air. However, in medieval West Africa, specifically at Djenné, the people were able to relate mosquitos with malaria. +The first record of argument against the miasmatic nature of malaria was from Irish-American surgeon John Crawford, who wrote an article "Mosquital Origin of Malarial Disease" in Baltimore Observer in 1807, but it provoked no consequences. It was instead ridiculed as impossible, and his work has since been lost. An American physician, Charles Earl Johnson, provided a systematic and elaborate arguments against miasmatic origin of malaria in 1851 before the Medical Society of North Carolina. Some of his important points were: + +The delta of the Mississippi was a recorded healthy place although it has a nearby river, ponds, marshes and much stagnant water. +Labourers of North Carolina were the healthiest people of working classes in spite of their constant exposure to swamps, and drinking swamp water. +South American countries such as British Guiana and Brazil which were literally flooded with tropical swamps were free from malaria epidemics. +Java Island in Southeast Asia, a region known for epidemics, had luxuriant vegetation and agricultural fields, supplemented with hot and wet tropical climate, ideal for miasmatic disease, was but the healthiest part of Asia. +A highly polluted River Thames, which should cause miasmatic diseases, was but a good source of drinking water. +On the other hand, the driest regions such as Guinea in Africa, Spain, Malta, Gibraltar, and several states of America, were frequented with malarial fevers. + +== Scientific grounds == + +=== Disproof of miasma theory of malaria === +The notion that malaria was due to miasma was negated by the discovery of malarial parasite. A German physician Johann Heinrich Meckel was the first to observe in 1847 the protozoan parasites which he recognised only as black pigment granules from the blood and spleen of a patient who died of malaria. But he did not understand the parasitic nature and significance of those granules in connection with malaria. In 1849 a German pathologist Rudolf Virchow realised that it could be those granules that were responsible for the disease. In 1879 an Italian biologist Ettore Afanasiev further argued that the granules were definitely the causative agents. + +A major discovery was made by a French Army physician Charles Louis Alphonse Laveran working in Algeria, North Africa. At the hospital in Bône (now Annaba), he noticed spherical bodies from a patient's blood film, free or adherent to red blood cells. On 6 November 1880 he observed from one patient's blood the actual living parasite, describing it as "a pigmented spherical body, filiform elements which move with great vivacity, displacing the neighboring red blood cells." He also observed the process of maturation of the parasite (which is now called exflagellation of microgametocytes). He meticulously examined 200 patients, and noted the cellular bodies in all 148 cases of malaria but never in those without malaria. He also found that after treatment with quinine, the parasites disappeared from blood. These findings clearly indicated that the parasite was the cause of malaria, and establishing the germ theory (nature) of malaria. He named the parasite Oscillaria malariae (later renamed Plasmodium malariae) and reported his discovery to the French Academy of Medicine in Paris on 23 November and 28 December. For his discovery he was awarded the Nobel Prize for Physiology or Medicine in 1907. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Mosquito-malaria_theory-1.md b/data/en.wikipedia.org/wiki/Mosquito-malaria_theory-1.md new file mode 100644 index 000000000..e5b90b303 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Mosquito-malaria_theory-1.md @@ -0,0 +1,30 @@ +--- +title: "Mosquito-malaria theory" +chunk: 2/3 +source: "https://en.wikipedia.org/wiki/Mosquito-malaria_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:59.882762+00:00" +instance: "kb-cron" +--- + +=== Discovery of mosquito as disease vector === +In the early 1880s, Laveran's germ theory of malaria was generally accepted by the science community. However pivotal problems still remained, such as what transmit the malarial parasites and how. The scientific clue emerged when a British medical officer Patrick Manson discovered for the first time that parasites were transmitted by mosquitoes. In 1877 while working in Amoy, a coastal town in China, he found that the mosquito Culex fatigans (now Culex quinquefasciatus) was the vector of the filarial roundworm that he called Filaria sanguinis hominis (but now Wuchereria bancrofti). His findings were published in the China Customs Medical Report in 1878, and relayed by Spencer Cobbold to the Linnean Society in London. This was the first direct evidence that mosquitoes could transmit microscopic parasites in humans, further suggesting that the same could be true in case of malaria. + +== King's theory == +Based on the report of Manson's discovery, an American physician Albert Freeman Africanus King developed a proposition that malaria is transmitted by mosquitoes. He revealed his idea in 1881 to his colleagues C.V. Riley and L.O. Howard, who did not share the same opinion. Unfettered he developed the theory with proper justifications and presented it before the Philosophical Society of Washington on 10 February 1882, under the title "The Prevention of Malarial Disease Illustrating inter alia the Conservative Function of Ague". He went so far as to suggest the complete covering of Washington, DC along the Washington Monument with giant net to protect the city from malaria. His idea was ridiculed as inconceivable as scientists still believed malarial parasite was spread through inhalation or ingestion from air (still not far from the miasma theory). He did not give up, and instead formed a more elaborate argument which he published as a 15-page article in the September 1883 issue of The Popular Science Monthly, making an introduction as: + +I now propose to present a series of facts... with regard to the so-called “malarial poison,” and to show how they may be explicable by the supposition that the mosquito is the real source of the disease, rather than the inhalation or cutaneous of a marsh-vapor. +King carefully selected his view in 19 points. To paraphrase his lengthy arguments: occurrence of malaria always coincided with conditions that are also ideal for mosquitos, such as in the time of day, geographical area, temperature, and climate. But the flaw in his proposition was that he believed malaria was transmitted by mosquito through its eggs. + +== Manson's theory == +In 1889 Patrick Manson returned to England and worked at the Seamen's Hospital Society and also as lecturer on tropical diseases in St George's Hospital at London in 1882. His attention was soon drawn towards malaria and began to realise the implications of his own discovery of filarial transmission on malaria. He strongly supported Laveran's germ theory of malaria, which was not yet completely embraced by the entire medical community of the time. He proposed that: + +malaria is caused by protozoan parasite, +the protozoan is transmitted by mosquito, and (falsely) +humans are infected from contaminated water in which infected mosquito had died. +Manson was unfortunate that he could not investigate his theory as he was not in malaria endemic country such as India, where it could be experimentally proven. But fortunately he met a British army surgeon Ronald Ross, who was on vacation while serving in the Indian Medical Service in India. In November 1894, he revealed to Ross with his hands on Ross' shoulders, saying, "Do you know, I have formed the theory that mosquitoes carry malaria just as they carry filaria." + +Manson formally published his theory in the 8 December 1894 issue of the British Medical Journal. Under the title "On the Nature and Significance of Cresenteric and Flagellated bodies in Malarial Blood", he stated: [The] mosquito, having been shown to be the agent by which the filaria is removed from the human blood vessels, this or similar suctorial agent must be the agent which removes from the human blood vessels those forms of the malaria organism which are destined to continue the existence of this organism outside the body. It must, therefore, be in this or in a similar suctorial insect or insects that the first stages of the extracorporeal life of the malaria organism are passed... [The] hypothesis I have ventured to formulate seems so well grounded that I for one, did circumstances permit, would approach its experimental demonstration with confidence. The necessary experiments cannot for obvious reasons be carried out in England, but I would commend my hypothesis to the attention of medical men in India and elsewhere, where malarial patients and suctorial insects abound. + +== Proof == \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Mosquito-malaria_theory-2.md b/data/en.wikipedia.org/wiki/Mosquito-malaria_theory-2.md new file mode 100644 index 000000000..d14c8dff5 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Mosquito-malaria_theory-2.md @@ -0,0 +1,40 @@ +--- +title: "Mosquito-malaria theory" +chunk: 3/3 +source: "https://en.wikipedia.org/wiki/Mosquito-malaria_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:59.882762+00:00" +instance: "kb-cron" +--- + +In 1894 Patrick Manson devised an ingenious procedure for detecting malarial parasites at different developmental stages from blood samples. This would later prove to be the tool for experimental proof of his theory. Manson demonstrated to and taught Ronald Ross the technique from which Ross became convinced of Laveran's germ theory. Trained and mentored by Manson, Ross returned to India in March 1895 to start his investigation. But to the dismay of Ross it was not an easy task. His first detection of malarial parasite from patients came only after two months of hard work. The disappointed Ross had to be encouraged by Manson calling the study as the "Holy Grail" of malaria research, and that Ross was the "Sir Galahad". +After one and half years he made no significant progress. On 20 August 1897 he made a momentous discovery that some mosquitoes had malarial parasites in them. He had fed the blood of a malarial patient (Husein Khan) to different groups of mosquitoes four days before, and found that only one type (which he called "brown type" or more commonly "dappled-winged mosquitoes", not knowing the species, which in fact was Anopheles) acquired the malarial parasites in its stomach. This was the first evidence for Manson's theory that mosquito did carry the malarial parasite, and Ross would later famously call 20 August as "Malaria Day" (now adopted as World Mosquito Day). +The second experimental evidence came in the mid-1898 when Ross demonstrated the transmission of bird malaria Proteosoma relictum (now Plasmodium relictum) between larks and mosquitoes, which he called "grey mosquitos" (which were Culex fatigans, but now renamed Culex quinquefasciatus). He showed that the mosquitoes ingested the parasites from infected birds and could infect healthy birds. He further discovered that the parasites developed in the stomach wall and were later stored in salivary glands of the mosquito. This was a conclusive evidence that malarial parasites were indeed transmitted by mosquitoes. In his report Ross concluded that: + +These observations prove the mosquito theory of malaria as expounded by Dr Patrick Manson. +On 9 July 1898 Ross wrote Manson: + +Q.E.D. and [I] congratulate you on the mosquito theory indeed. +Ross' scientific evidences were soon fortified by Italian biologists including Giovanni Battista Grassi, Amico Bignami, and Giuseppe Bastianelli, who discovered that human malarial parasite was transmitted by the actual biting (disproving one of Manson's hypotheses) of female mosquito. In 1899 they reported the infection of Plasmodium falciparum with the mosquito Anopheles claviger However the practical importance of validating the theory, i.e. control of mosquito vector should be an effective management strategy for malaria, was not realised by the medical community and the public. Hence in 1900 Patrick Manson clinically demonstrated that the bite of infected anopheline mosquitoes invariably resulted in malaria. He acquired carefully reared infected mosquitoes from Bignami and Bastianelli in Rome. His volunteer at the London School of Tropical Medicine, P. Thurburn Manson gave a detailed account of his malarial fevers and treatment after bitten by the mosquitoes. As he summarised, Manson's clinical trial showed that the practical solution to malaria infection was in: + +avoiding the neighborhood of native houses where mosquitoes are abundant, +destroying the habitats of mosquitoes, and +protection from mosquito bite. + +== References == + +== Further reading == +Packard, Randall M. (2010). The Making of a Tropical Disease: A Short History of Malaria. Maryland, US: The Johns Hopkins University Press. ISBN 978-1-42-140175-1. +Cook, G.C. (2007). Tropical Medicine: an Illustrated History of The Pioneers. Oxford, UK: Elsevier. ISBN 978-0-08-055939-1. +Sherman, Irwin (2008). Reflections on a Century of Malaria Biochemistry. London: Academic Press. ISBN 978-0-0809-2183-9. +Nye, Edwin R.; Gibson, Mary E. (1997). Ronald Ross : Malariologist and Polymath : a Biography. New York: St. Martin's Press, Inc. ISBN 0-312-16296-0. +Ross, Ronald (1923). Memoirs, with a Full Account of the Great Malaria Problem and Its Solution. London: John Murray. +Haynes, Douglas M. (2001). Imperial Medicine: Patrick Manson and the Conquest of Tropical Disease. Philadelphia: University of Pennsylvania Press. ISBN 978-0-81-223598-2. +Lehrer, Steven (2006). Explorers of the Body : Dramatic Breakthroughs in Medicine from Ancient Times to Modern Science (2nd ed.). New York: iUniverse. p. 248. ISBN 978-0-595-40731-6. + +== External links == +Malaria: Past and Present +The History of Malaria, an Ancient Disease +History of Malaria: Scientific Discoveries +The History of Malaria on Stamps \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Nonequilibrium_theory-0.md b/data/en.wikipedia.org/wiki/Nonequilibrium_theory-0.md new file mode 100644 index 000000000..8f3ba970b --- /dev/null +++ b/data/en.wikipedia.org/wiki/Nonequilibrium_theory-0.md @@ -0,0 +1,67 @@ +--- +title: "Nonequilibrium theory" +chunk: 1/1 +source: "https://en.wikipedia.org/wiki/Nonequilibrium_theory" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:07:01.047591+00:00" +instance: "kb-cron" +--- + +Nonequilibrium theory refers to the idea that ecosystems are not in a stable state, but instead are fluctuating from disturbances and pressures. Disturbances like disease, predators, climate change, fires, and others lead to shifts in ecosystem characteristics and prevent the return to equilibrium. Once shifted to an altered state, it can be difficult to return to an original state. +This theory challenges traditional ideas of stability. Ecosystems are dynamic, ever changing structures that can be influenced by numerous characteristics.This perspective has important implications for conservation, prompting a shift toward strategies that embrace change, resilience, and adaptability rather than trying to preserve a single state. + + +== Disturbance driven dynamics == +Ecosystems are frequently influenced by a large variety of different disturbances. These disturbances can be periodic, unpredictable, with very different intensities. Disturbances may arise from natural events or human activities, each having the potential to drastically alter ecosystem structure and function. + + +=== Natural disturbance === +Wildfire +Hurricanes +Tornadoes +Floods and droughts +Extreme temperature fluctuations + + +=== Human disturbance === +Land use change (urbanization, crop land, deforestation) +Pollution +Invasive species introduction +Overexploitation of resources + + +== Multiple stable states == +Depending on external pressures, ecosystems can exist under alternate stable states. Even under equal environment conditions multiple states can exist (hysteresis). For example, overfishing in coral reef ecosystems can reduce herbivorous fish populations, allowing algae to overgrow and dominate the system. Even if fishing pressure is later reduced, the system may remain in this algae-dominated state unless active restoration occurs. Another possibility is a system depending on certain conditions meaning that even under identical conditions it may never revert to its previous condition. For example in rangelands, vegetation can shift from perennial grasses to shrub-dominated systems under persistent disturbance. These altered states may not recover even when conditions are reversed, showing different thresholds and hysteresis in terrestrial systems. + + +== Historical perspectives == +Historically, most ecological models were based on equilibrium theory, which thought ecosystems would self regulate, and eventually would return to a balanced state following disturbance. In the 1970's and 1980's evidence of ecosystems under disturbance, competition, and inconsistencies in natural resource management outcomes would often prevent this. This shift was further supported by rangeland studies, which challenged classical succession-based ideas and promoted the use of state-and-transition models to describe the nonlinear, dynamic change of nature. Persistent disturbances, species competition, and inconsistencies in natural resource management outcomes often prevented the re-establishment of a single equilibrium point. Not being able to reach a single stable equilibrium lead to new ideas about a non-equilibrium theory. + + +== Resilience theory == +The concept of resilience acknowledges ecosystems can show wide fluctuations under disturbance but still be resilient. Instead of stability ecosystems are able to resist and transform under certain conditions. + +Engineering resilience: The ability of an ecosystem to return to a single stable state after a disturbance. +Ecological resilience: The ability of an ecosystem to handle disturbances while maintaining the essential functions and structures +Adaptive resilience: The ability of an ecosystem to evolve and adapt to new conditions or disturbances rather to returning to a previous state. +These different modes of resilience can be found in certain ecosystems, capable of with standing certain disturbances. + + +== Conservation use == +Conservation strategies can benefit from nonequilibrium. Instead of managing for the idea of stability, managers can plan for resilience to better withstand disturbances. Preventing tipping points can be a useful target strategy. Being open to an idea of ecosystem change over time allows for thought of protecting species and habitats over a continuous period. What this means is the use of adaptive management, will allow for strategies that are flexible and responsive when needed. + + +=== Adaptive management === +This style of management is all about dynamic methods that embraces uncertainty and change. Instead of fixed solutions, it promotes using management actions as a tool to observe what is working vs what isn't working. Through long-term monitoring, continuous adjustment, and feedback, managers are able to improve ecological outcomes over time while avoiding these tipping point and critical states. + + +== See also == +Adaptive management +Ecological resilience +Disturbance (ecology) +Ecological succession +Rangeland management + + +== References == \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Scientific_socialism-0.md b/data/en.wikipedia.org/wiki/Scientific_socialism-0.md new file mode 100644 index 000000000..86cf18354 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Scientific_socialism-0.md @@ -0,0 +1,50 @@ +--- +title: "Scientific socialism" +chunk: 1/1 +source: "https://en.wikipedia.org/wiki/Scientific_socialism" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:07:02.303293+00:00" +instance: "kb-cron" +--- + +Scientific socialism in Marxism is the application of historical materialism to the development of socialism, as not just a practical and achievable outcome of historical processes, but the only possible outcome. It contrasts with utopian socialism by basing itself upon material conditions instead of concoctions and ideas, where "the final causes of all social changes and political revolutions are to be sought, not in men's brains, not in men's better insights into eternal truth and justice, but in changes in the modes of production and exchange. They are to be sought, not in the philosophy, but in the economics of each particular epoch." + +Fredrich Engels, who developed it alongside Karl Marx, described: To accomplish this act of universal emancipation [proletarian revolution and communism] is the historical mission of the modern proletariat. To thoroughly comprehend the historical conditions and thus the very nature of this act, to impart to the now oppressed proletarian class a full knowledge of the conditions and of the meaning of the momentous act it is called upon to accomplish, this is the task of the theoretical expression of the proletarian movement, scientific Socialism. The term's modern meaning is based almost totally on Engels's book Socialism: Utopian and Scientific. + + +== Origins == + +The term was originally coined in 1840 by Pierre-Joseph Proudhon in his book What is Property? to mean a society ruled by a scientific government, i.e., one whose sovereignty rests upon reason, rather than sheer will: Thus, in a given society, the authority of man over man is inversely proportional to the stage of intellectual development which that society has reached; and the probable duration of that authority can be calculated from the more or less general desire for a true government,—that is, for a scientific government. And just as the right of force and the right of artifice retreat before the steady advance of justice, and must finally be extinguished in equality, so the sovereignty of the will yields to the sovereignty of the reason, and must at last be lost in scientific socialism. +In the 1844 book The Holy Family, Karl Marx and Friedrich Engels described the writings of the socialist, communist writers Théodore Dézamy and Jules Gay as truly "scientific". But the term "scientific socialism" took on its modern meaning by 1880 with the publishing of Socialism, Utopian and Scientific, where Engels used the term "scientific socialism" to describe Marx's social-political-economic theory of historical materialism. +Although the term socialism has come to mean specifically a combination of political and economic science, it is also applicable to a broader area of science encompassing what is now considered sociology and the humanities. The distinction between Utopian and scientific socialism originated with Marx, who criticized the Utopian characteristics of French socialism and English and Scottish political economy. Engels later argued that Utopian socialists failed to recognize why it was that socialism arose in the historical context that it did, that it arose as a response to new social contradictions of a new mode of production, i.e. capitalism. In recognizing the nature of socialism as the resolution of this contradiction and applying a thorough scientific understanding of capitalism, Engels asserted that socialism had broken free from a primitive state and become a science. + + +== Methodology == +Scientific socialism is a method for understanding and predicting social, economic and material phenomena by examining their historical trends through the use of the scientific method in order to derive probable outcomes and probable future developments. It is in contrast to what later socialists referred to as utopian socialism—a method based on establishing seemingly rational propositions for organizing society and convincing others of their rationality and/or desirability. It also contrasts with classical liberal notions of natural law, which are grounded in metaphysical notions of morality rather than a dynamic materialist or physicalist conception of the world. +Scientific socialists view social and political developments as being largely determined by economic conditions, in contrast to the ideas of Utopian socialists and classical liberals, and thus believe that social relations and notions of morality are context-based relative to their specific stage of economic development. They believe that as economic systems, socialism and capitalism are not social constructs that can be established at any time based on the subjective will and desires of the population, but instead are the products of social evolution. An example of this was the advent of agriculture which enabled human communities to produce a surplus—this change in material and economic development led to a change in the social relations and rendered the old form of social organization based on subsistence-living obsolete and a hindrance to further material progress. The changing economic conditions necessitated a change in social organization. +In his collection of texts, In Defence of Marxism, Leon Trotsky defended the dialectical method of scientific socialism during the factional schisms within the American Trotskyist movement during 1939–40. Trotsky viewed dialectics as an essential method of analysis to discern the class nature of the Soviet Union. Specifically, he described scientific socialism as the "conscious expression of the unconscious historical process; namely, the instinctive and elemental drive of the proletariat to reconstruct society on communist beginnings". + + +== See also == +Anti-Dühring +Critique of Dialectical Reason – 1960 book by Jean-Paul Sartre +El Defensor del Obrero – Uruguayan newspaper +Evolutionary economics – Subject inspired by evolutionary biology +GOELRO, an early Soviet national plan for economic recovery which emphasised the importance of electrification +Historical materialism – Marxist historiography +Project Cybersyn, a decentralized form of cybernetic planning in Chile that was operational from 1971 until 1973. +OGAS, a proposed national computer network for economic planning in the Soviet Union. +Social science, one of the branches of science, devoted to the study of societies and the relationships among individuals within those societies. +Socialism with Chinese characteristics, the official ideology of the Chinese Communist Party +Scientific Outlook on Development, a socio-economic concept of the Chinese Communist Party +Scientific communism, the Soviet Union curriculum requirements for understanding Soviet orthodoxy on the subject. +Science and technology in the Soviet Union +Siad Barre, who called his mixture of Marxism-Leninism and Islam "scientific socialism". +Socialism: Utopian and Scientific +Socialist mode of production +The Open Society and Its Enemies – 1945 book by Karl Popper +"Why Socialism?" - an article written by Albert Einstein which presented a critique of modern capitalism and advocated for a planned economy. + + +== References == \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Scientific_theory-0.md b/data/en.wikipedia.org/wiki/Scientific_theory-0.md index 3eaa4f49a..3d31e652b 100644 --- a/data/en.wikipedia.org/wiki/Scientific_theory-0.md +++ b/data/en.wikipedia.org/wiki/Scientific_theory-0.md @@ -4,7 +4,7 @@ chunk: 1/7 source: "https://en.wikipedia.org/wiki/Scientific_theory" category: "reference" tags: "science, encyclopedia" -date_saved: "2026-05-05T06:29:04.644741+00:00" +date_saved: "2026-05-05T10:06:47.725273+00:00" instance: "kb-cron" --- diff --git a/data/en.wikipedia.org/wiki/Scientific_theory-1.md b/data/en.wikipedia.org/wiki/Scientific_theory-1.md index 9324e99df..5286eff9d 100644 --- a/data/en.wikipedia.org/wiki/Scientific_theory-1.md +++ b/data/en.wikipedia.org/wiki/Scientific_theory-1.md @@ -4,7 +4,7 @@ chunk: 2/7 source: "https://en.wikipedia.org/wiki/Scientific_theory" category: "reference" tags: "science, encyclopedia" -date_saved: "2026-05-05T06:29:04.644741+00:00" +date_saved: "2026-05-05T10:06:47.725273+00:00" instance: "kb-cron" --- diff --git a/data/en.wikipedia.org/wiki/Scientific_theory-2.md b/data/en.wikipedia.org/wiki/Scientific_theory-2.md index b84c1d6b2..eba3bf2b0 100644 --- a/data/en.wikipedia.org/wiki/Scientific_theory-2.md +++ b/data/en.wikipedia.org/wiki/Scientific_theory-2.md @@ -4,7 +4,7 @@ chunk: 3/7 source: "https://en.wikipedia.org/wiki/Scientific_theory" category: "reference" tags: "science, encyclopedia" -date_saved: "2026-05-05T06:29:04.644741+00:00" +date_saved: "2026-05-05T10:06:47.725273+00:00" instance: "kb-cron" --- diff --git a/data/en.wikipedia.org/wiki/Scientific_theory-3.md b/data/en.wikipedia.org/wiki/Scientific_theory-3.md index 549e129e7..9b31f8e5c 100644 --- a/data/en.wikipedia.org/wiki/Scientific_theory-3.md +++ b/data/en.wikipedia.org/wiki/Scientific_theory-3.md @@ -4,7 +4,7 @@ chunk: 4/7 source: "https://en.wikipedia.org/wiki/Scientific_theory" category: "reference" tags: "science, encyclopedia" -date_saved: "2026-05-05T06:29:04.644741+00:00" +date_saved: "2026-05-05T10:06:47.725273+00:00" instance: "kb-cron" --- diff --git a/data/en.wikipedia.org/wiki/Scientific_theory-4.md b/data/en.wikipedia.org/wiki/Scientific_theory-4.md index b8cd41ad6..25fb02bc7 100644 --- a/data/en.wikipedia.org/wiki/Scientific_theory-4.md +++ b/data/en.wikipedia.org/wiki/Scientific_theory-4.md @@ -4,7 +4,7 @@ chunk: 5/7 source: "https://en.wikipedia.org/wiki/Scientific_theory" category: "reference" tags: "science, encyclopedia" -date_saved: "2026-05-05T06:29:04.644741+00:00" +date_saved: "2026-05-05T10:06:47.725273+00:00" instance: "kb-cron" --- diff --git a/data/en.wikipedia.org/wiki/Scientific_theory-5.md b/data/en.wikipedia.org/wiki/Scientific_theory-5.md index 90741a8a2..dc99c2160 100644 --- a/data/en.wikipedia.org/wiki/Scientific_theory-5.md +++ b/data/en.wikipedia.org/wiki/Scientific_theory-5.md @@ -4,7 +4,7 @@ chunk: 6/7 source: "https://en.wikipedia.org/wiki/Scientific_theory" category: "reference" tags: "science, encyclopedia" -date_saved: "2026-05-05T06:29:04.644741+00:00" +date_saved: "2026-05-05T10:06:47.725273+00:00" instance: "kb-cron" --- diff --git a/data/en.wikipedia.org/wiki/Scientific_theory-6.md b/data/en.wikipedia.org/wiki/Scientific_theory-6.md index e64136e62..947c7c51f 100644 --- a/data/en.wikipedia.org/wiki/Scientific_theory-6.md +++ b/data/en.wikipedia.org/wiki/Scientific_theory-6.md @@ -4,7 +4,7 @@ chunk: 7/7 source: "https://en.wikipedia.org/wiki/Scientific_theory" category: "reference" tags: "science, encyclopedia" -date_saved: "2026-05-05T06:29:04.644741+00:00" +date_saved: "2026-05-05T10:06:47.725273+00:00" instance: "kb-cron" --- diff --git a/data/en.wikipedia.org/wiki/The_Limits_of_Individual_Plasticity-0.md b/data/en.wikipedia.org/wiki/The_Limits_of_Individual_Plasticity-0.md new file mode 100644 index 000000000..3eb7e6b87 --- /dev/null +++ b/data/en.wikipedia.org/wiki/The_Limits_of_Individual_Plasticity-0.md @@ -0,0 +1,20 @@ +--- +title: "The Limits of Individual Plasticity" +chunk: 1/1 +source: "https://en.wikipedia.org/wiki/The_Limits_of_Individual_Plasticity" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:57.512199+00:00" +instance: "kb-cron" +--- + +"The Limits of Individual Plasticity" is a short essay written by the science fiction author H. G. Wells (21 September 1866 – 13 August 1946) in 1895. In it, Wells speculates his theories on the plasticity of animals, explaining that the default biological form of an animal may be altered in a way that it would continue to survive even if it, in any way, no longer resembles its inherent form. This could, according to Wells, theoretically be achieved through surgical or chemical modification. Wells was fully aware that surgical modification is only a physical change, and would not alter an animal's genetic blueprint. He made note that should an animal be surgically modified, its offspring would most likely retain its parent creature's original physical form. + + +== Incorporation in novels == +Wells presented many of his ideas from "The Limits of Individual Plasticity" in his 1896 science fiction novel, The Island of Doctor Moreau. +In the novel, a shipwrecked Englishman named Edward Prendick is rescued from the sea and brought to a secluded island by a man named +Montgomery, who reveals the island is owned and operated by an eminent British physiologist named Dr. Moreau. Moreau was shunned from the scientific community when his horrific vivisection experiments were brought to the public spotlight. Moreau continued his experiments on vivisection on his private island, where animals are altered with great detail to resemble human beings. They are a defective experiment, as they will revert to their bestial forms after a period of time. + + +== References == \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Time-resolved_mass_spectrometry-0.md b/data/en.wikipedia.org/wiki/Time-resolved_mass_spectrometry-0.md new file mode 100644 index 000000000..464ebeaaf --- /dev/null +++ b/data/en.wikipedia.org/wiki/Time-resolved_mass_spectrometry-0.md @@ -0,0 +1,23 @@ +--- +title: "Time-resolved mass spectrometry" +chunk: 1/1 +source: "https://en.wikipedia.org/wiki/Time-resolved_mass_spectrometry" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:34.290244+00:00" +instance: "kb-cron" +--- + +Time-resolved mass spectrometry (TRMS) is a strategy in analytical chemistry that uses mass spectrometry platform to collect data with temporal resolution. Implementation of TRMS builds on the ability of mass spectrometers to process ions within sub-second duty cycles. It often requires the use of customized experimental setups. However, they can normally incorporate commercial mass spectrometers. As a concept in analytical chemistry, TRMS encompasses instrumental developments (e.g. interfaces, ion sources, mass analyzers), methodological developments, and applications. + + +== Applications == +An early application of TRMS was in the observation of flash photolysis process. It took advantage of a time-of-flight mass analyzer. +TRMS currently finds applications in the monitoring of organic reactions, formation of reactive intermediates, enzyme-catalyzed reactions, convection, protein folding, extraction, and other chemical and physical processes. + + +== Temporal resolution == +TRMS is typically implemented to monitor processes that occur on second to millisecond time scale. However, there exist reports from studies in which sub-millisecond resolutions were achieved. + + +== References == \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Total_internal_reflection_fluorescence_microscope-0.md b/data/en.wikipedia.org/wiki/Total_internal_reflection_fluorescence_microscope-0.md new file mode 100644 index 000000000..31be549c9 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Total_internal_reflection_fluorescence_microscope-0.md @@ -0,0 +1,36 @@ +--- +title: "Total internal reflection fluorescence microscope" +chunk: 1/4 +source: "https://en.wikipedia.org/wiki/Total_internal_reflection_fluorescence_microscope" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:35.424390+00:00" +instance: "kb-cron" +--- + +A total internal reflection fluorescence microscope (TIRFM) is a type of microscope with which a thin region of a specimen, usually less than 200 nanometers can be observed. +TIRFM is an imaging modality which uses the excitation of fluorescent cells in a thin optical specimen section that is supported on a glass slide. The technique is based on the principle that when excitation light is totally internally reflected in a transparent solid coverglass at its interface with a liquid medium, an electromagnetic field, also known as an evanescent wave, is generated at the solid-liquid interface with the same frequency as the excitation light. The intensity of the evanescent wave exponentially decays with distance from the surface of the solid so that only fluorescent molecules within a few hundred nanometers of the solid are efficiently excited. Two-dimensional images of the fluorescence can then be obtained, although there are also mechanisms in which three-dimensional information on the location of vesicles or structures in cells can be obtained. + +== History == +Widefield fluorescence was introduced in 1910 which was an optical technique that illuminates the entire sample. Confocal microscopy was then introduced in 1960 which decreased the background and exposure time of the sample by directing light to a pinpoint and illuminating cones of light into the sample. In the 1980s, the introduction of TIRFM further decreased background and exposure time by only illuminating the thin section of the sample being examined. + +== Background == +There are two common methods for producing the evanescent wave for TIRFM. The first is the prism method which uses a prism to direct the laser toward the interface between the coverglass and the media/cells at an incident angle sufficient to cause total internal reflection. This configuration has been applied to cellular microscopy for over 30 years but has never become a mainstream tool due to several limitations. Although there are many variations of the prism configuration, most restrict access to the specimen which makes it difficult to perform manipulations, inject media into the specimen space, or carry out physiological measurements. Another disadvantage is that in most configurations based on the inverted microscope designs, the illumination is introduced on the specimen side opposite of the objective optics which requires imaging of the evanescent field region through the bulk of the specimen. There is great complexity and precision required in imaging this system which meant that the prism method was not used by many biologists but rather limited to use by physicists. +The other method is known as the objective lens method which has increased the use of TIRFM in cellular microscopy and increased furthermore since a commercial solution became available. In this mechanism, one can easily switch between standard widefield fluorescence and TIRF by changing the off-axis position of the beam focus at the objective's back focal plane. There are several developed ways to change the positions of the beam such as using an actuator that can change the position in relation to the fluorescence illuminator that is attached to the microscope. + +== Application == +In cell and molecular biology, a large number of molecular events in cellular surfaces such as cell adhesion, binding of cells by hormones, secretion of neurotransmitters, and membrane dynamics have been studied with conventional fluorescence microscopes. However, fluorophores that are bound to the specimen surface and those in the surrounding medium exist in an equilibrium state. When these molecules are excited and detected with a conventional fluorescence microscope, the resulting fluorescence from those fluorophores bound to the surface is often overwhelmed by the background fluorescence due to the much larger population of non-bound molecules. TIRFM allows for selective excitation of the surface-bound fluorophores, while non-bound molecules are not excited and do not fluoresce. Due to the fact of sub-micron surface selectivity, TIRFM has become a method of choice for single molecule detection. +There are many applications of TIRFM in cellular microscopy. Some of these applications include: + +Measuring the kinetics of receptor endocytosis in response to ligand binding and receptor movement +Observing exocytic events through the loading of vesicles undergoing exocytosis with fluorescent dyes +Qualitatively and quantitatively describing the roles different proteins play in endocytosis/exocytosis +Observing the size, movement, and distance apart of the regions of contact between a cell and a solid substrate +With the ability to resolve individual vesicles optically and follow the dynamics of their interactions directly, TIRFM provides the capability to study the vast number of proteins involved in neurobiological processes in a manner that was not possible before. + +=== Benefits === +TIRFM provides several benefits over standard widefield and confocal fluorescence microscopy such as: + +The background is substantially decreased so structures can be seen clearly +There is virtually no out-of-focus fluorescence collected which decrease blurring effects +Cells are exposed to a significantly smaller amount of light which limits phototoxicity to cells \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Total_internal_reflection_fluorescence_microscope-1.md b/data/en.wikipedia.org/wiki/Total_internal_reflection_fluorescence_microscope-1.md new file mode 100644 index 000000000..64af318d2 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Total_internal_reflection_fluorescence_microscope-1.md @@ -0,0 +1,307 @@ +--- +title: "Total internal reflection fluorescence microscope" +chunk: 2/4 +source: "https://en.wikipedia.org/wiki/Total_internal_reflection_fluorescence_microscope" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:35.424390+00:00" +instance: "kb-cron" +--- + +== Overview == +The idea of using total internal reflection to illuminate cells contacting the surface of glass was first described by E.J. Ambrose in 1956. This idea was then extended by Daniel Axelrod at the University of Michigan, Ann Arbor in the early 1980s as TIRFM. A TIRFM uses an evanescent wave to selectively illuminate and excite fluorophores in a restricted region of the specimen immediately adjacent to the glass-water interface. The evanescent electromagnetic field decays exponentially from the interface, and thus penetrates to a depth of only approximately 100 nm into the sample medium. Thus the TIRFM enables a selective visualization of surface regions such as the basal plasma membrane (which are about 7.5 nm thick) of cells. Note, however, that the region visualized is at least a few hundred nanometers wide, so the cytoplasmic zone immediately beneath the plasma membrane is necessarily visualized in addition to the plasma membrane during TIRF microscopy. The selective visualization of the plasma membrane renders the features and events on the plasma membrane in living cells with high axial resolution. +TIRF can also be used to observe the fluorescence of a single molecule, making it an important tool of biophysics and quantitative biology. TIRF microscopy has also been applied in the single molecule detection of DNA biomarkers and SNP discrimination. +Cis-geometry (through-objective TIRFM) and trans-geometry (prism- and lightguide based TIRFM) have been shown to provide different quality of the effect of total internal reflection. In the case of trans-geometry, the excitation lightpath and the emission channel are separated, while in the case of objective-type TIRFM they share the objective and other optical elements of the microscope. Prism-based geometry was shown to generate clean evanescent wave, which exponential decay is close to theoretically predicted function. In the case of objective-based TIRFM, however, the evanescent wave is contaminated with intense stray light. The intensity of stray light was shown to amount 10–15% of the evanescent wave, which makes it difficult to interpret data obtained by objective-type TIRFM + +== Mechanism == + +The basic components of TIRFM devices are in the figure to the right. + +=== Objective-based vs prism-based === +Key differences between objective-based (cis) and prism-based (trans) TIRFM are that prism based TIRFM requires usage of a prism/solution interface to generate the evanescent field, while objective-based TIRFM does not require a prism and utilizes a cover slip/solution interface to generate the evanescent field. Typically objective-based TIRFM are more popularly used, however have lowered imaging quality due to stray light noise within the evanescent wave. + +==== Prism-based ==== +Less extraneous scattering +Much cheaper (hundreds instead of thousands of dollars) +Best for low-mid range magnification and water immersion objectives +Easiest with free collimated laser sources +Larger range of incidence angles +Desirable to achieve smallest evanescent field depth + +==== Objective-based ==== +High magnification and aperture +Stable, easy to set up and align +Works with free collimated laser, optical fiber, or conventional arc sources + +== Methodology == + +=== Fundamental physics === +TIRFM is predicated on the optical phenomena of total internal reflection, in which waves arriving at a medium interface do not transmit into medium 2 but are completely reflected back into medium 1. Total internal reflection requires medium 2 to have a lower refractive index than medium 1, and for the waves must be incident at sufficiently oblique angles on the interface. An observed phenomena accompanying total internal reflection is the evanescent wave, which spatially extends away perpendicularly from the interface into medium 2, and decays exponentially, as a factor of wavelength, refractive index, and incident angle. It is the evanescent wave which is used to achieve increased excitation of the fluorophores close to the surface of the sample, and diminished excitation of superfluous fluorophores within solution. +For practical purposes, in objective based TIRF, medium 1 is typically a high refractive index glass coverslip, and medium 2 is the sample in solution with a lower refractive index. There may be immersion oil between the lens and the glass coverslip to prevent significant refraction through air. + +=== Evanescent wave === +The critical angle for excitatory light incidence can be derived from Snell's law: + + + + + + θ + + c + + + = + + sin + + − + 1 + + + ⁡ + + ( + + + + n + + 1 + + + + n + + 2 + + + + + ) + + + + {\displaystyle \theta _{c}=\sin ^{-1}\left({\frac {n_{1}}{n_{2}}}\right)} + + +For + + + + + n + + 1 + + + + + {\displaystyle n_{1}} + + the refractive index of sample, + + + + + n + + 2 + + + + + {\displaystyle n_{2}} + + the refractive index of the cover slip. +Thus, as the angle of incidence reaches + + + + + θ + + c + + + + + {\displaystyle \theta _{c}} + +, we begin observing effects of total internal reflection and evanescent wave, and as it surpasses + + + + + θ + + c + + + + + {\displaystyle \theta _{c}} + + these effects are more prevalent. +The intensity of the evanescent wave is given by: + + + + + I + ( + Z + ) + = + + I + + 0 + + + + e + + − + z + + / + + d + + + + + {\displaystyle I(Z)=I_{0}e^{-z/d}} + + +With penetration depth + + + + d + + + {\displaystyle d} + + given by: + + + + + d + = + + + + λ + + 0 + + + + 4 + π + + + + + + ( + + + n + + 2 + + + 2 + + + + sin + + 2 + + + ⁡ + θ + − + + n + + 1 + + + 2 + + + + ) + + + − + 1 + + / + + 2 + + + + + {\displaystyle d={\frac {\lambda _{0}}{4\pi }}\left(n_{2}^{2}\sin ^{2}\theta -n_{1}^{2}\right)^{-1/2}} + + +Typically, + + + + d + + + {\displaystyle d} + + ≤~100 nanometers, which is typically much smaller than the wavelength of light, and much thinner than a slice from confocal microscopes. +For TIRFM imaging the wavelength of the excitation beam + + + + + λ + + 0 + + + + + {\displaystyle \lambda _{0}} + + within the sample can be selected for by filtering. Additionally, the range of incident angles + + + + θ + + + {\displaystyle \theta } + + is determined by the numerical aperture (NA) of the objective, and requires that NA > + + + + n + + + {\displaystyle n} + +. This parameter can be adjusted by changing the angle the excitation beam enters the objective lens. Finally, the reflective indices ( + + + + n + + + {\displaystyle n} + +) of the solution and cover slip can be experimentally found or reported by manufacturers. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Total_internal_reflection_fluorescence_microscope-2.md b/data/en.wikipedia.org/wiki/Total_internal_reflection_fluorescence_microscope-2.md new file mode 100644 index 000000000..c756c7acc --- /dev/null +++ b/data/en.wikipedia.org/wiki/Total_internal_reflection_fluorescence_microscope-2.md @@ -0,0 +1,71 @@ +--- +title: "Total internal reflection fluorescence microscope" +chunk: 3/4 +source: "https://en.wikipedia.org/wiki/Total_internal_reflection_fluorescence_microscope" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:35.424390+00:00" +instance: "kb-cron" +--- + +=== Excitation beam === +For complex fluoroscope microscopy techniques, lasers are the preferred light source as they are highly uniform, intense, and near-monochromatic. However, it is noted that ARC LAMP light sources and other types of sources may also work. Typically the wavelength of excitation beam is designated by the requirements of the fluorophores within the sample, with most common excitation wavelengths being in the 400–700 nm range for biological samples. +In practice, a lightbox will generate a high intensity multichromatic laser, which will then be filtered to allow the desired wavelengths through to excite the sample. For objective-based TIRFM, the excitation beam and fluoresced emission beam will be captured via the same objective lens. Thus, to split the beams, a dichromatic mirror is used to reflect the incoming excitation beam towards the objective lens, and allow the emission beam to pass through into the detector. Additional filtering may be required to further separate emission and excitation wavelengths. + +=== Emission beam === +When excited with specific wavelengths of light, fluorophore dyes will reemit light at longer wavelengths (which contain less energy). In the context of TIRFM, only fluorophores close to the interface will be readily excited by the evanescent field, while those past ~100 nm will be highly attenuated. Light emitted by the fluorophores will be undirected, and thus will pass through the objective lens at varying locations with varying intensities. This signal will then pass through the dichromatic mirror and onward to the detector. + +=== Cover slip and immersion oil === +Glass cover slips typically have a reflective index around + + + + n + = + 1.52 + + + {\displaystyle n=1.52} + +, while the immersion oil refractive index is a comparable + + + + n + = + 1.51 + + + {\displaystyle n=1.51} + +. The medium of air, which has a refractive index of + + + + n + = + 1.00 + + + {\displaystyle n=1.00} + +, would cause refraction of the excitation beam between the objective and the coverslip, thus the oil is used to buffer the region and prevent superfluous interface interactions before the beam reaches the interface between coverslip and sample. + +=== Objective lens === +The objective lens numerical aperture (NA) specifies the range of angles over which the system can accept or emit light. +To achieve the greatest incident angles, it is desirable to pass light at an off-axis angle through the peripheries of the lens. + +==== Back focal plane (BPF) ==== +The back focal plane (also called "aperture plane") is the plane through which the excitatory beam is focused before passing through the objective. Adjusting the distance between the objective and BPF can yield different imaging magnification, as the incident angle will become less or more steep. The beam must be passed through the BPF off-axis in order to pass through the objective at its ends, allowing for the angle to be sufficiently greater than the critical angle. The beam must also be focused at the BPF because this ensures that the light passing through the objective is collimated, interacting with the cover slip at the same angle and thus all totally internally reflecting. + +=== Sample === +The sample should be adsorbed to the surface of the glass cover slide and stained with appropriate fluorophores to resolve the features desired within the sample. This is in protocol with any other fluorescent microscopy technique. + +=== Dichroic (dichromatic) filter === +The dichroic filter is an edge filter used at an oblique angle of incidence (typically 45°) to efficiently reflect light in the excitation band and to transmit light in the emission band. The 45° angle of the filter separates the path of the excitation and emission beam. The filter is composed of a complex system of multiple layers of metals, metal salts and dielectrics which have been vacuum-deposited onto thin glass. This coating is designed to have high reflectivity for shorter wavelengths and high transmission for longer wavelengths. While the filter transmits the selected excitation light (shorter wavelength) through the objective and onto the plane of the specimen, it also passes emission fluorescence light (longer wavelength) to the barrier filter and reflecting any scattered excitation light back in the direction of the laser source. This maximizes the amount of exciting radiation passing through the filter and emitted fluorescence beam that is detected by the detector. + +=== Barrier filter === +The barrier filter mainly blocks off undesired wavelengths, especially shorter excitation light wavelengths. It is typically a bandpass filter that passes only the wavelengths emitted by the fluorophore and blocks all undesired light outside this band. More modern microscopes enable the barrier filter to be changed according to the wavelength of the fluorophore's specific emission. + +== Image detection and resolution == +The image is detected by a charged-coupled device (CCD) digital camera. CCD cameras have photon detectors, which are thin silicon wafers, assembled into 2D arrays of light-sensitive regions. The detector arrays capture and store image information in the form of localized electrical charge that varies with incident light intensity. As shown in the schematic the photons are transformed into electrons by the detectors and the electrons are converted to readable electrical signal in the circuit board. The electrical signal is then convoluted with a point spread function (PSF) to sample the original signal. As such, image resolution is highly dependent on the number of detectors and the point spread function will determine the image resolution. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Total_internal_reflection_fluorescence_microscope-3.md b/data/en.wikipedia.org/wiki/Total_internal_reflection_fluorescence_microscope-3.md new file mode 100644 index 000000000..0ca598e01 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Total_internal_reflection_fluorescence_microscope-3.md @@ -0,0 +1,34 @@ +--- +title: "Total internal reflection fluorescence microscope" +chunk: 4/4 +source: "https://en.wikipedia.org/wiki/Total_internal_reflection_fluorescence_microscope" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:35.424390+00:00" +instance: "kb-cron" +--- + +=== Image artifact and noise === +Most fluorescence imaging techniques exhibit background noise due to illuminating and reconstructing large slices (in the z-direction) of the samples. Since TIRFM uses an evanescent wave to fluoresce a thin slice of the sample, there is inherently less background noise and artifacts. However, there are still other noises and artifacts such as poisson noise, optical aberrations, photobleaching, and other fluorescence molecules. +Poissonian noise are fundamental uncertainties with the measurement of light. This will cause uncertainties during the detection of fluorescence photons. If N photons are measured in a particular measurement, there is a 63% probability that the true average value is in the range between N +√N and N −√N. This noise may cause misrepresentation of the object at incorrect pixel locations. +Optical aberrations can arise from diffraction of fluorescence light or microscope and objective misalignment. Diffraction of light on the sample slide can spread the fluorescence signal and result in blurring in the convoluted images. Similarly, if there is a misalignment between the objective lens, filter, and detector, the excitation or emission beam may not be in focus and can cause blurring in the images. +Photobleaching can occur when the covalent or noncovalent bonds in the fluorophores are destructed by the excitation light and can no longer fluoresce. The fluorescing substances will always degrade to some extent by the energy of the exciting radiation and will cause the fluorescence to fade and result in a dark blurry image. Photobleaching is inevitable but can be minimized by avoiding unwanted light exposure and using immersion oils to minimize light scattering. +Autofluorescence can occur in certain cell structures where the natural compound in the structure would fluoresce after being excited at relatively shorter wavelengths (similar to that of the excitation wavelength). Induced fluorescence can also occur when certain non-autofluorescent compounds become fluorescent after binding to certain chemicals (such as formaldehyde). These fluorescence can result in artifacts or background noise in the image. Noise from other fluorescence compounds can be effectively eliminated by using filters to capture the desired fluorescence wavelength, or by making sure the autofluorescence compounds are not present in the sample. + +=== Current and future work === +Modern fluorescence techniques attempt to incorporate methods to eliminate some blurring and noises. Optical aberrations are generally deterministic (it is constant throughout the image process and across different samples). Deterministic blurring can be eliminated by deconvoluting the signal and subtracting the known artifact. The deconvolution technique is simply using an inverse fourier transform to obtain the original fluorescence signal and remove the artifact. +Nevertheless, deconvolution has only been shown to work if there is a strong fluorescence signal or when the noise is clearly identified. In addition, deconvolution performs poorly because it does not include statistical information and can not reduce non-deterministic noise such as poissonian noise. To obtain better image resolution and quality, researchers have used statistical techniques to model the probability where photons may be distributed on the detector. This technique, called the maximum likelihood method, is being further improved by algorithms to improve its performance speed. + +== References == + +Axelrod, Daniel (1 November 2001). "Total Internal Reflection Fluorescence Microscopy in Cell Biology" (PDF). Traffic. 2 (11): 764–774. doi:10.1034/j.1600-0854.2001.21104.x. hdl:2027.42/72779. PMID 11733042. S2CID 15202097. + +== External links == +Interactive Fluorescence Dye and Filter Database Carl Zeiss Interactive Fluorescence Dye and Filter Database. +TIRF Microscopy: Introduction and Applications TIRF Tutorial from Microscopy U +TIRF Microscopy: Overview TIRF Tutorial from Olympus Microscopy Resource Center +Olympus TIRFM Microscopes commercial TIRF microscope systems +Carl Zeiss Laser TIRF 3 commercial TIRF microscope systems +Lightguide- and prism-based TIRF microscopy TIRF-Labs.com :Commercial TIRF Microscopy and Spectroscopy. Selecting TIRFM geometry for your application +TIRF FLIM microscopy Lambert Instruments TIRF - FLIM microscopy +Schwartz Research Group, CU-Boulder Single Molecule Imaging Research Group \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Transmission_Kikuchi_diffraction-0.md b/data/en.wikipedia.org/wiki/Transmission_Kikuchi_diffraction-0.md new file mode 100644 index 000000000..4fe851da3 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Transmission_Kikuchi_diffraction-0.md @@ -0,0 +1,33 @@ +--- +title: "Transmission Kikuchi diffraction" +chunk: 1/1 +source: "https://en.wikipedia.org/wiki/Transmission_Kikuchi_diffraction" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:39.042429+00:00" +instance: "kb-cron" +--- + +Transmission Kikuchi diffraction (TKD), also sometimes called transmission electron backscatter diffraction (t-EBSD), is a method for orientation mapping at the nanoscale. It’s used for analysing the microstructures of thin transmission electron microscopy (TEM) specimens in the scanning electron microscope (SEM). This technique has been widely utilised in the characterization of nano-crystalline materials, including oxides, superconductors, and metallic alloys. +TKD offers improved spatial resolution, enabling effective characterization of nanocrystalline materials and heavily deformed samples where high dislocation densities can prevent successful characterization using conventional Electron backscatter diffraction. Many studies have reported sub-10 nm resolution using TKD. +The main difference between diffraction spots and Kikuchi bands is that in TEM, discrete diffraction spots arise from coherent scattering of the incident beam, while the formation of Kikuchi bands is described as a two-step process consisting of incoherent scattering of the primary beam followed by coherent scattering of these forward biased electrons. TKD has also been applied to analyse fine-grained ultramylonite peridotite samples in a scanning electron microscope. The preparation of TKD samples can be done with standard methods used for transmission electron microscopy (TEM). + + +== Description == +Transmission Kikuchi diffraction (TKD or t-EBSD) is an Electron backscatter diffraction (EBSD) technique that is used to analyse the crystallographic orientation and microstructure of materials at a high spatial resolution. It is a variation of convergent-beam electron diffraction, which has been introduced around the 1970s, and has since become increasingly popular in materials science research, especially for studying materials at the nanoscale. +In TKD, a thin foil sample is prepared and placed perpendicular to the electron beam of a scanning electron microscope. The electron beam is then focused on a small spot on the sample, and the crystal lattice of the sample diffracts the transmitted electrons. The diffraction pattern is then collected by a detector and analysed to determine the crystallographic orientation and microstructure of the sample. +One of the key advantages of TKD is its high spatial resolution that can reach a few nanometres. This is achieved by using a small electron beam spot size, typically less than 10 nanometres in diameter, and by collecting the transmitted electrons with a small-angle annular dark-field detector (STEM-ADF) in a scanning transmission electron microscope (STEM). Another advantage of TKD is its high sensitivity to local variations in crystallographic orientation. This is because the transmitted electrons in TKD are diffracted at very small angles, which makes the diffraction pattern highly sensitive to local variations in the crystal lattice. +TKD can also be used to study nano-sized materials, such as nanoparticles and thin films. Thin foil samples can be prepared for TKD using a Focused ion beam (FIB) or ion milling machine. However, such machines are expensive and their operation requires particular skills and training. Additionally, the diffraction patterns obtained from TKD can be more complex to interpret than those obtained from conventional EBSD techniques due to the complex geometry of the diffracted electrons. + +On-axis and off-axis TKD methods differ in the sample's orientation with respect to the electron beam. In on-axis TKD, the sample is oriented so that the incident electron beam is nearly perpendicular to the sample surface. This results in a diffraction pattern that is nearly centred around the transmitted beam direction. On-axis TKD is typically used for analysing samples with low lattice strain and high crystallographic symmetry, such as single crystals or large grains. +In off-axis TKD, the sample is tilted with respect to the incident electron beam, typically at an angle of several degrees. This results in a diffraction pattern that is shifted away from the transmitted beam direction. Off-axis TKD is typically used for analysing samples with high lattice strain and/or low crystallographic symmetry, such as nano-crystalline materials or materials with defects. Off-axis TKD is often preferred for materials science research because it provides more information about the crystallographic orientation and microstructure of the sample, especially in samples with a high density of defects or a high degree of lattice strain. However, on-axis TKD can still be useful for studying samples with high crystallographic symmetry or for verifying the crystallographic orientation of a sample before performing off-axis TKD. The on-axis technique can speed up acquisition by more than 20 times, and a low scattering angle setup also gives rise to higher quality patterns. +EBSD resolution is influenced by multiple factors including the beam size, electron accelerating voltage, the material's atomic mass and the specimen's thickness. Out of these variables, sample thickness has the greatest effect on the pattern quality and resolution of the image. An increase in the sample thickness broadens the beam, thus reducing the lateral spatial resolution. + + +== Further reading == +Sneddon, Glenn C.; Trimby, Patrick W.; Cairney, Julie M. (2016-12-01). "Transmission Kikuchi diffraction in a scanning electron microscope: A review". Materials Science and Engineering: R: Reports. 110: 1–12. doi:10.1016/j.mser.2016.10.001. ISSN 0927-796X. +Fundenberger, J. J.; Bouzy, E.; Goran, D.; Guyon, J.; Yuan, H.; Morawiec, A. (2016-02-01). "Orientation mapping by transmission-SEM with an on-axis detector". Ultramicroscopy. 161: 17–22. doi:10.1016/j.ultramic.2015.11.002. ISSN 0304-3991. +Niessen, F.; Burrows, A.; Fanta, A. Bastos da Silva (2018-03-01). "A systematic comparison of on-axis and off-axis transmission Kikuchi diffraction". Ultramicroscopy. 186: 158–170. doi:10.1016/j.ultramic.2017.12.017. ISSN 0304-3991. + + +== References == \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-0.md b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-0.md new file mode 100644 index 000000000..550eae966 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-0.md @@ -0,0 +1,22 @@ +--- +title: "Transmission electron microscopy" +chunk: 1/13 +source: "https://en.wikipedia.org/wiki/Transmission_electron_microscopy" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:36.644553+00:00" +instance: "kb-cron" +--- + +Transmission electron microscopy (TEM) is a microscopy technique in which a beam of electrons is transmitted through a specimen to form an image. The specimen is most often an ultrathin section less than 100 nm thick or a suspension on a grid. An image is formed from the interaction of the electrons with the sample as the beam is transmitted through the specimen. The image is then magnified and focused onto an imaging device, such as a fluorescent screen, a layer of photographic film, or a detector such as a scintillator attached to a charge-coupled device or a direct electron detector. +Transmission electron microscopes are capable of imaging at a significantly higher resolution than light microscopes, owing to the smaller de Broglie wavelength of electrons. This enables the instrument to capture fine detail—even as small as a single column of atoms, which is thousands of times smaller than a resolvable object seen in a light microscope. Transmission electron microscopy is a major analytical method in the physical, chemical and biological sciences. TEMs find application in cancer research, virology, and materials science as well as pollution, nanotechnology and semiconductor research, but also in other fields such as paleontology and palynology. +TEM instruments have multiple operating modes including conventional imaging, scanning TEM imaging (STEM), diffraction, spectroscopy, and combinations of these. Even within conventional imaging, there are many fundamentally different ways that contrast is produced, called "image contrast mechanisms". Contrast can arise from position-to-position differences in the thickness or density ("mass-thickness contrast"), atomic number ("Z contrast", referring to the common abbreviation Z for atomic number), crystal structure or orientation ("crystallographic contrast" or "diffraction contrast"), the slight quantum-mechanical phase shifts that individual atoms produce in electrons that pass through them ("phase contrast"), the energy lost by electrons on passing through the sample ("spectrum imaging") and more. Each mechanism tells the user a different kind of information, depending not only on the contrast mechanism but on how the microscope is used—the settings of lenses, apertures, and detectors. What this means is that a TEM is capable of returning an extraordinary variety of nanometre- and atomic-resolution information, in ideal cases revealing not only where all the atoms are but what kinds of atoms they are and how they are bonded to each other. For this reason TEM is regarded as an essential tool for nanoscience in both biological and materials fields. +The first TEM was demonstrated by Max Knoll and Ernst Ruska in 1931, with this group developing the first TEM with resolution greater than that of light in 1933 and the first commercial TEM in 1939. In 1986, Ruska was awarded the Nobel Prize in physics for the development of transmission electron microscopy. + +== History == + +=== Initial development === + +In 1873, Ernst Abbe proposed that the ability to resolve detail in an object was limited approximately by the wavelength of the light used in imaging or a few hundred nanometres for visible light microscopes. Developments in ultraviolet (UV) microscopes, led by Köhler and Rohr, increased resolving power by a factor of two. However this required expensive quartz optics, due to the absorption of UV by glass. It was believed that obtaining an image with sub-micrometre information was not possible due to this wavelength constraint. +In 1858, Plücker observed the deflection of "cathode rays" (electrons) by magnetic fields. This effect was used by Ferdinand Braun in 1897 to build simple cathode-ray oscilloscope (CRO) measuring devices. In 1891, Eduard Riecke noticed that the cathode rays could be focused by magnetic fields, allowing for simple electromagnetic lens designs. In 1926, Hans Busch published work extending this theory and showed that the lens maker's equation could, with appropriate assumptions, be applied to electrons. +In 1928, at the Technische Hochschule in Charlottenburg (now Technische Universität Berlin), Adolf Matthias, Professor of High Voltage Technology and Electrical Installations, appointed Max Knoll to lead a team of researchers to advance the CRO design. The team consisted of several PhD students including Ernst Ruska and Bodo von Borries. The research team worked on lens design and CRO column placement, to optimize parameters to construct better CROs, and make electron optical components to generate low magnification (nearly 1:1) images. In 1931, the group successfully generated magnified images of mesh grids placed over the anode aperture. The device used two magnetic lenses to achieve higher magnifications, arguably creating the first electron microscope. In that same year, Reinhold Rudenberg, the scientific director of the Siemens company, patented an electrostatic lens electron microscope. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-1.md b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-1.md new file mode 100644 index 000000000..4b3f80f6f --- /dev/null +++ b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-1.md @@ -0,0 +1,125 @@ +--- +title: "Transmission electron microscopy" +chunk: 2/13 +source: "https://en.wikipedia.org/wiki/Transmission_electron_microscopy" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:36.644553+00:00" +instance: "kb-cron" +--- + +=== Improving resolution === +At the time, electrons were understood to be charged particles of matter; the wave nature of electrons was not fully realized until the PhD thesis of Louis de Broglie in 1924. Knoll's research group was unaware of this publication until 1932, when they realized that the de Broglie wavelength of electrons was many orders of magnitude smaller than that for light, theoretically allowing for imaging at atomic scales. (Even for electrons with a kinetic energy of just 1 electronvolt the wavelength is already as short as 1.18 nm.) In April 1932, Ruska suggested the construction of a new electron microscope for direct imaging of specimens inserted into the microscope, rather than simple mesh grids or images of apertures. With this device successful diffraction and normal imaging of an aluminium sheet was achieved. However the magnification achievable was lower than with light microscopy. Magnifications higher than those available with a light microscope were achieved in September 1933 with images of cotton fibers quickly acquired before being damaged by the electron beam. +At this time, interest in the electron microscope had increased, with other groups, such as that of Paul Anderson and Kenneth Fitzsimmons of Washington State University and that of Albert Prebus and James Hillier at the University of Toronto, who constructed the first TEMs in North America in 1935 and 1938, respectively, continually advancing TEM design. +Research continued on the electron microscope at Siemens in 1936, where the aim of the research was the development and improvement of TEM imaging properties, particularly with regard to biological specimens. At this time electron microscopes were being fabricated for specific groups, such as the "EM1" device used at the UK National Physical Laboratory. In 1939, the first commercial electron microscope, pictured, was installed in the Physics department of IG Farben-Werke. Further work on the electron microscope was hampered by the destruction of a new laboratory constructed at Siemens by an air raid, as well as the death of two of the researchers, Heinz Müller and Friedrick Krause during World War II. + +=== Further research === +After World War II, Ruska resumed work at Siemens, where he continued to develop the electron microscope, producing the first microscope with 100k magnification. The fundamental structure of this microscope design, with multi-stage beam preparation optics, is still used in modern microscopes. The worldwide electron microscopy community advanced with electron microscopes being manufactured in Manchester UK, the USA (RCA), Germany (Siemens) and Japan (JEOL). The first international conference in electron microscopy was in Delft in 1949, with more than one hundred attendees. Later conferences included the "First" international conference in Paris, 1950 and then in London in 1954. +With the development of TEM, the associated technique of scanning transmission electron microscopy (STEM) was re-investigated and remained undeveloped until the 1970s, with Albert Crewe at the University of Chicago developing the field emission gun and adding a high quality objective lens to create the modern STEM. Using this design, Crewe demonstrated the ability to image atoms using annular dark-field imaging. Crewe and coworkers at the University of Chicago developed the cold field electron emission source and built a STEM able to visualize single heavy atoms on thin carbon substrates. + +== Background == + +=== Electrons === + +Theoretically, the maximum resolution, d, that one can obtain with a light microscope is limited by the wavelength of the photons (λ) and the numerical aperture NA of the system. + + + + + d + = + + + λ + + 2 + n + sin + ⁡ + α + + + + ≈ + + + λ + + 2 + + + + NA + + + + + + + + {\displaystyle d={\frac {\lambda }{2n\sin \alpha }}\approx {\frac {\lambda }{2\,{\textrm {NA}}}}} + + +where n is the index of refraction of the medium in which the lens is working and α is the maximum half-angle of the cone of light that can enter the lens (see numerical aperture). Early twentieth century scientists theorized ways of getting around the limitations of the relatively large wavelength of visible light (wavelengths of 400–700 nanometres) by using electrons. Like all matter, electrons have both wave and particle properties (matter wave), and their wave-like properties mean that a beam of electrons can be focused and diffracted much like light can. The wavelength of electrons is related to their kinetic energy via the de Broglie equation, which says that the wavelength is inversely proportional to the momentum. Taking into account relativistic effects (as in a TEM an electron's velocity is a substantial fraction of the speed of light, c) the wavelength is + + + + + + λ + + e + + + = + + + h + + 2 + + m + + 0 + + + E + + ( + + 1 + + + + + E + + 2 + + m + + 0 + + + + c + + 2 + + + + + + + ) + + + + + + + {\displaystyle \lambda _{e}={\frac {h}{\sqrt {2m_{0}E\left(1+{\frac {E}{2m_{0}c^{2}}}\right)}}}} + + +where h is the Planck constant, m0 is the rest mass of an electron and E is the kinetic energy of the accelerated electron. + +=== Electron source === \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-10.md b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-10.md new file mode 100644 index 000000000..132d5babe --- /dev/null +++ b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-10.md @@ -0,0 +1,33 @@ +--- +title: "Transmission electron microscopy" +chunk: 11/13 +source: "https://en.wikipedia.org/wiki/Transmission_electron_microscopy" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:36.644553+00:00" +instance: "kb-cron" +--- + +A TEM can be modified into a scanning transmission electron microscope (STEM) by the addition of a system that rasters a convergent beam across the sample to form the image, when combined with suitable detectors. Scanning coils are used to deflect the beam, such as by an electrostatic shift of the beam, where the beam is then collected using a current detector such as a Faraday cup, which acts as a direct electron counter. By correlating the electron count to the position of the scanning beam (known as the "probe"), the transmitted component of the beam may be measured. The non-transmitted components may be obtained either by beam tilting or by the use of annular dark field detectors. + +Fundamentally, TEM and STEM are linked via Helmholtz reciprocity. A STEM is a TEM in which the electron source and observation point have been switched relative to the direction of travel of the electron beam. See the ray diagrams in the figure on the right. The STEM instrument effectively relies on the same optical set-up as a TEM, but operates by flipping the direction of travel of the electrons (or reversing time) during operation of a TEM. Rather than using an aperture to control detected electrons, as in TEM, a STEM uses various detectors with collection angles that may be adjusted depending on which electrons the user wants to capture. + +=== Low-voltage electron microscope === + +A low-voltage electron microscope (LVEM) is operated at relatively low electron accelerating voltage between 5–25 kV. Some of these can be a combination of SEM, TEM and STEM in a single compact instrument. Low voltage increases image contrast which is especially important for biological specimens. This increase in contrast significantly reduces, or even eliminates the need to stain. Resolutions of a few nm are possible in TEM, SEM and STEM modes. The low energy of the electron beam means that permanent magnets can be used as lenses and thus a miniature column that does not require cooling can be used. + +=== Cryo-TEM === + +Cryogenic transmission electron microscopy (Cryo-TEM or Cryo-EM) uses a TEM with a specimen holder capable of maintaining the specimen at liquid nitrogen or liquid helium temperatures. This allows imaging specimens prepared in vitreous ice, the preferred preparation technique for imaging individual molecules or macromolecular assemblies, imaging of vitrified solid-electrolye interfaces, and imaging of materials that are volatile in high vacuum at room temperature, such as sulfur. For many quantum materials or devices, low temperature or ultra-low temperature is required to access phases where emergent quantum behavior occurs. + +=== Environmental/in-situ TEM === +In-situ experiments may also be conducted in TEM using differentially pumped sample chambers, or specialized holders. Types of in-situ experiments include studying nanomaterials, biological specimens, chemical reactions of molecules, liquid-phase electron microscopy, and material deformation testing. + +=== High temperature in-situ TEM === +Many phase transformations occur during heating. Additionally, coarsening and grain growth, along with other diffusion-related processes occur more rapidly at elevated temperatures, where kinetics are improved, allowing for the observation of related phenomena under transmission electron microscopy within reasonable time scales. This also allows for the observation of phenomena that occur at elevated temperatures and disappear or are not uniformly preserved in ex-situ samples. +High temperature TEM introduces various additional challenges which must be addressed in the mechanics of high temperature holders, including but not limited to drift-correction, temperature measurement, and decreased spatial resolution at the expense of more complex holders. +Sample drift in the TEM is linearly proportional to the temperature differential between the room and holder. With temperatures as high as 1500C in modern holders, samples may experience significant drift and vertical displacement (bulging), requiring continuous focus or stage adjustments, inducing resolution loss and mechanical drift. Individual labs and manufacturers have developed software coupled with advanced cooling systems to correct for thermal drift based on the predicted temperature in the sample chamber These systems often take 30 min-many hours for sample shifts to stabilize. While significant progress has been made, no universal TEM attachment has been made to account for drift at elevated temperatures. +An additional challenge of many of these specialized holders is knowing the local sample temperature. Many high temperature holders utilize a tungsten filament to locally heat the sample. Ambiguity in temperature in furnace heaters (W wire) with thermocouples arises from the thermal contact between the furnace and the TEM grid; complicated by temperature gradients along the sample caused by varying thermal conductivity with different samples and grid materials. With different holders both commercial and lab made, different methods for creating temperature calibration are available. Manufacturers like Gatan use IR pyrometry to measure temperature gradients over their entire sample. An even better method to calibrate is Raman spectroscopy which measures the local temperature of Si powder on electron transparent windows and quantitatively calibrates the IR pyrometry. These measurements have guaranteed accuracy within 5%. Research laboratories have also performed their own calibrations on commercial holders. Researchers at NIST utilized Raman spectroscopy to map the temperature profile of a sample on a TEM grid and achieve very precise measurements to enhance their research. Similarly, a research group in Germany utilized X-ray diffraction to measure slight shifts in lattice spacing caused by changes in temperature to back calculate the exact temperature in the holder. This process required careful calibration and exact TEM optics. Other examples include the use of EELS to measure local temperature using change of gas density, and resistivity changes. +Optimal resolution in a TEM is achieved when spherical aberrations are corrected with objective lens. However, due to the geometry of most TEMs, inserting large in-situ holders requires the user to compromise the objective lens and endure spherical aberrations. Therefore, there is a compromise between the width of the pole-piece gap and spatial resolution below 0.1 nm. Research groups at various institutions have tried to overcome spherical aberrations through use of monochromators to achieve 0.05 nm resolution with a 5 mm pole piece gap. + +=== In-situ mechanical TEM === \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-11.md b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-11.md new file mode 100644 index 000000000..dbf293990 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-11.md @@ -0,0 +1,27 @@ +--- +title: "Transmission electron microscopy" +chunk: 12/13 +source: "https://en.wikipedia.org/wiki/Transmission_electron_microscopy" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:36.644553+00:00" +instance: "kb-cron" +--- + +High resolution of TEM allows for monitoring the sample in question on a length scale ranging from hundreds of nanometres to several angstroms. This allows for the visualization of both elastic and plastic deformation via strain fields as well as the motion of crystallographic defects such as lattice distortions and dislocation motion. By simultaneously observing deformation phenomena and measuring mechanical response in situ, it is possible to connect nano-mechanical testing information to models that describe both the subtlety and complexity of how materials respond to stress and strain. The material properties and data accuracy obtained from such nano-mechanical tests is largely determined by the mechanical straining holder being used. Current straining holders have the ability to perform tensile tests, nano-indentation, compression tests, shear tests and bending tests on materials. + +==== Classical mechanical holders ==== +One of the pioneers of classical holders was Heinz G.F. Wilsdorf, who conducted a tensile test inside a TEM in 1958. In a typical experiment, electron transparent TEM samples are cut to shape and glued to a deformable grid. Advances in micromanipulators have also enabled the tensile testing of nanowires and thin films. The deformable grid attaches to the classical tensile holder which stretches the sample using a long rigid shaft attached to a worm gear box actuated by an electric motor located in a housing outside the TEM. Typically strain rates range from 10 nm/s to 10 μm/s. Custom-made holders expanding simple straining actuation have enabled bending tests using a bending holder and shear tests using a shear sample holder. The typical measured sample properties in these experiments are yield strength, elastic modulus, shear modulus, tensile strength, bending strength, and shear strength. In order to study the temperature-dependent mechanical properties of TEM samples, the holder can be cooled through a cold finger connected to a liquid nitrogen reservoir. For high temperature experiments, the TEM sample can also be heated through a miniaturized furnace or a laser that can typically reach 1000 °C. + +==== Nano-indentation holders ==== +Nano-Indentation holders perform a hardness test on the material in question by pressing a hard tip into a polished flat surface and measuring the applied force and the resulting displacement on the TEM sample through a change in capacitance between a reference and a movable electrostatic plate attached to the tip. The typical measured sample properties are hardness and elastic modulus. Although nano-indentation was possible since early 1980s, its investigation using a TEM was first reported in 2001 where an aluminum sample deposited on a silicon wedge was investigated. For nanoindentation experiments, TEM samples are typically shaped as wedges using a tripod polisher, H-bar window or a micro-nanopillar using focused ion beam to create enough space for a tip to be pressed at the desired electron transparent location. The indenter tips are typically flat punch-type, pyramidal, or wedge shaped elongated in the z-direction. Pyramidal tips offer high precision on the order of 10 nm but suffer from sample slip, while wedge indenters have greater contract to prevent slipping but require finite element analysis to model the transmitted stress since the high contact area with the TEM sample makes this almost a compression test. + +==== Micro electro-mechanical systems (MEMs) ==== +Micro Electro-Mechanical Systems (MEMs) based holders provide a cheap and customizable platform to conduct mechanical tests on previously difficult samples to work with such as micropillars, nanowires, and thin films. Passive MEMs are used as simple push to pull devices for in-situ mechanical tests. Typically, a nano-indentation holder is used to apply a pushing force at the indentation site. Using a geometry of arms, this pushing force translates to a pulling force on a pair of tensile pads to which the sample is attached. Thus, a compression applied on the outside of the MEMs translates to a tension in the central gap where the TEM sample is located. The resulting force-displacement curve needs to be corrected by performing the same test on an empty MEMs without the TEM sample to account for the stiffness of the empty MEMs. The dimensions and stiffness of the MEMs can be modified to perform tensile tests on different sized samples with different loads. To smoothen the actuation process, active MEMs have been developed with built-in actuators and sensors. These devices work by applying a stress using electrical power and measuring strain using capacitance variations. Electrostatically actuated MEMs have also been developed to accommodate very low applied forces in the 1–100 nN range. +Much of current research focuses on developing sample holders that can perform mechanical tests while creating an environmental stimulus such as temperature change, variable strain rates, and different gas environments. In addition, the emergence of high resolution detectors are allowing to monitor dislocation motion and interactions with other defects and pushing the limits of sub-nanometre strain measurements. In-situ mechanical TEM measurements are routinely coupled with other standard TEM measurements such as EELS and XEDS to reach a comprehensive understanding of the sample structure and properties. + +=== Aberration corrected TEM === + +Modern research TEMs may include aberration correctors, to reduce the amount of distortion in the image. Incident beam monochromators may also be used which reduce the energy spread of the incident electron beam to less than 0.15 eV. Major aberration corrected TEM manufacturers include JEOL, Hitachi High-technologies, FEI Company, and NION. + +=== Ultrafast and dynamic TEM === \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-12.md b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-12.md new file mode 100644 index 000000000..a7d0ec265 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-12.md @@ -0,0 +1,89 @@ +--- +title: "Transmission electron microscopy" +chunk: 13/13 +source: "https://en.wikipedia.org/wiki/Transmission_electron_microscopy" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:36.644553+00:00" +instance: "kb-cron" +--- + +It is possible to reach temporal resolution far beyond that of the readout rate of electron detectors with the use of pulsed electrons. Pulses can be produced by either modifying the electron source to enable laser-triggered photoemission or by installation of an ultrafast beam blanker. This approach is termed ultrafast transmission electron microscopy when stroboscopic pump-probe illumination is used: an image is formed by the accumulation of many ultrashort electron pulses (typically of hundreds of femtoseconds) with a fixed time delay between the arrival of the electron pulse and the sample excitation. On the other hand, the use of single or a short sequence of electron pulses with a sufficient number of electrons to form an image from each pulse is called dynamic transmission electron microscopy. Temporal resolution down to hundreds of femtoseconds and spatial resolution comparable to that available with a Schottky field emission source is possible in ultrafast TEM. Using the Photon-gating approach, the temporal resolution in ultrafast electron microscope reaches to 30-fs allowing the imaging of ultrafast atomic and electron dynamics of matter. However, the technique can only image reversible processes that can be reproducibly triggered millions of times. Dynamic TEM can resolve irreversible processes down to tens of nanoseconds and tens of nanometres. +The technique has been pioneered at the early 2000s in laboratories in Germany (Technische Universität Berlin) and in the USA (Caltech +and Lawrence Livermore National Laboratory + +). Ultrafast TEM and Dynamic TEM have made possible real-time investigation of numerous physical and chemical phenomena at the nanoscale. +An interesting variant of the Ultrafast Transmission Electron Microscopy technique is the Photon-Induced Near-field Electron Microscopy (PINEM). The latter is based on the inelastic coupling between electrons and photons in presence of a surface or a nanostructure. This method allows one to investigate time-varying nanoscale electromagnetic fields in an electron microscope, as well as dynamically shape the wave properties of the electron beam. + +== Limitations == +There are a number of drawbacks to the TEM technique. Many materials require extensive sample preparation to produce a sample thin enough to be electron transparent, which makes TEM analysis a relatively time-consuming process with a low throughput of samples. The structure of the sample may also be changed during the preparation process. Also the field of view is relatively small, raising the possibility that the region analyzed may not be characteristic of the whole sample. There is potential that the sample may be damaged by the electron beam, particularly in the case of biological materials. + +=== Resolution limits === + +The limit of resolution obtainable in a TEM may be described in several ways, and is typically referred to as the information limit of the microscope. One commonly used value is a cut-off value of the contrast transfer function, a function that is usually quoted in the frequency domain to define the reproduction of spatial frequencies of objects in the object plane by the microscope optics. A cut-off frequency, qmax, for the transfer function may be approximated with the following equation, where Cs is the spherical aberration coefficient and λ is the electron wavelength: + + + + + + q + + max + + + = + + + 1 + + 0.67 + ( + + C + + s + + + + λ + + 3 + + + + ) + + 1 + + / + + 4 + + + + + + . + + + {\displaystyle q_{\max }={\frac {1}{0.67(C_{\text{s}}\lambda ^{3})^{1/4}}}.} + + +For a 200 kV microscope, with partly corrected spherical aberrations ("to the third order") and a Cs value of 1 μm, a theoretical cut-off value might be 1/qmax = 42 pm. The same microscope without a corrector would have Cs = 0.5 mm and thus a 200 pm cut-off. The spherical aberrations are suppressed to the third or fifth order in the "aberration-corrected" microscopes. Their resolution is however limited by electron source geometry and brightness and chromatic aberrations in the objective lens system. +The frequency domain representation of the contrast transfer function may often have an oscillatory nature, which can be tuned by adjusting the focal value of the objective lens. This oscillatory nature implies that some spatial frequencies are faithfully imaged by the microscope, whilst others are suppressed. By combining multiple images with different spatial frequencies, the use of techniques such as focal series reconstruction can be used to improve the resolution of the TEM in a limited manner. The contrast transfer function can, to some extent, be experimentally approximated through techniques such as Fourier transforming images of amorphous material, such as amorphous carbon. +More recently, advances in aberration corrector design have been able to reduce spherical aberrations and to achieve resolution below 0.5 ångströms (50 pm) at magnifications above 50 million times. Improved resolution allows for the imaging of lighter atoms that scatter electrons less efficiently, such as lithium atoms in lithium battery materials. The ability to determine the position of atoms within materials has made the HRTEM an indispensable tool for nanotechnology research and development in many fields, including heterogeneous catalysis and the development of semiconductor devices for electronics and photonics. + +== See also == + +== References == + +== External links == + +The National Center for Electron Microscopy, Berkeley California USA +The National Center for Macromolecular Imaging, Houston Texas USA +The National Resource for Automated Molecular Microscopy, New York USA +Tutorial courses in Transmission Electron Microscopy +Cambridge University Teaching and Learning Package on TEM +Online course on Transmission Electron Microscopy and Crystalline Imperfections Eric Stach (2008). +Transmission electron microscope simulator (Teaching tool). +animations and explanations on various types of microscopes including electron microscopes (Université Paris Sud) \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-2.md b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-2.md new file mode 100644 index 000000000..acaf630c5 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-2.md @@ -0,0 +1,29 @@ +--- +title: "Transmission electron microscopy" +chunk: 3/13 +source: "https://en.wikipedia.org/wiki/Transmission_electron_microscopy" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:36.644553+00:00" +instance: "kb-cron" +--- + +From the top down, the TEM consists of an emission source or cathode, which may be a tungsten filament, a lanthanum hexaboride (LaB6) single crystal or a field emission gun. The gun is connected to a high voltage source (typically ~100–300 kV) and emits electrons either by thermionic or field electron emission into the vacuum. In the case of a thermionic source, the electron source is mounted in a Wehnelt cylinder to provide preliminary focus of the emitted electrons into a beam while also stabilizing the current using a passive feedback circuit. A field emission source uses instead electrostatic electrodes called an extractor, a suppressor, and a gun lens, with different voltages on each, to control the electric field shape and intensity near the sharp tip. The combination of the cathode and these first electrostatic lens elements is collectively called the "electron gun". After it leaves the gun, the beam is typically accelerated until it reaches its final voltage and enters the next part of the microscope: the condenser lens system. These upper lenses of the TEM then further focus the electron beam to the desired size and location on the sample. +Manipulation of the electron beam is performed using two physical effects. The interaction of electrons with a magnetic field will cause electrons to move according to the left hand rule, thus allowing electromagnets to manipulate the electron beam. Additionally, electrostatic fields can cause the electrons to be deflected through a constant angle. Coupling of two deflections in opposing directions with a small intermediate gap allows for the formation of a shift in the beam path, allowing for beam shifting. + +=== Optics === +The lenses of a TEM are what gives it its flexibility of operating modes and ability to focus beams down to the atomic scale and magnify them to get an image. A lens is usually made of a solenoid coil nearly surrounded by ferromagnetic materials designed to concentrate the coil's magnetic field into a precise, confined shape. When an electron enters and leaves this magnetic field, it spirals around the curved magnetic field lines in a way that acts very much as an ordinary glass lens does for light—it is a converging lens. But, unlike a glass lens, a magnetic lens can very easily change its focusing power by adjusting the current passing through the coils. +Equally important to the lenses are the apertures. These are circular holes in thin strips of heavy metal. Some are fixed in size and position and play important roles in limiting x-ray generation and improving the vacuum performance. Others can be freely switched among several different sizes and have their positions adjusted. Variable apertures after the sample allow the user to select the range of spatial positions or electron scattering angles to be used in the formation of an image or a diffraction pattern. +The electron-optical system also includes deflectors and stigmators, usually made of small electromagnets. The deflectors allow the position and angle of the beam at the sample position to be independently controlled and also ensure that the beams remain near the low-aberration centers of every lens in the lens stacks. The stigmators compensate for slight imperfections and aberrations that cause astigmatism—a lens having a different focal strength in different directions. +Typically a TEM consists of three stages of lensing. The stages are the condenser lenses, the objective lenses, and the projector lenses. The condenser lenses are responsible for primary beam formation, while the objective lenses focus the beam that comes through the sample itself (in STEM scanning mode, there are also objective lenses above the sample to make the incident electron beam convergent). The projector lenses are used to expand the beam onto the phosphor screen or other imaging device, such as film. The magnification of the TEM is due to the ratio of the distances between the specimen and the objective lens' image plane. TEM optical configurations differ significantly with implementation, with manufacturers using custom lens configurations, such as in spherical aberration corrected instruments, or TEMs using energy filtering to correct electron chromatic aberration. + +==== Reciprocity ==== +The optical reciprocity theorem, or principle of Helmholtz reciprocity, generally holds true for elastically scattered electrons, as is often the case under standard TEM operating conditions. The theorem states that the wave amplitude at some point B as a result of electron point source A would be the same as the amplitude at A due to an equivalent point source placed at B. Simply stated, the wave function for electrons focused through any series of optical components that includes only scalar (i.e. not magnetic) fields will be exactly equivalent if the electron source and observation point are reversed. +Reciprocity is used to understand scanning transmission electron microscopy (STEM) in the familiar context of TEM, and to obtain and interpret images using STEM. + +=== Display and detectors === + +The key factors when considering electron detection include detective quantum efficiency (DQE), point spread function (PSF), modulation transfer function (MTF), pixel size and array size, noise, data readout speed, and radiation hardness. +Imaging systems in a TEM consist of a phosphor screen, which may be made of fine (10–100 μm) particulate zinc sulfide, for direct observation by the operator, and an image recording system such as photographic film, doped YAG screen coupled CCDs, or other digital detector. Typically these devices can be removed or inserted into the beam path as required. (Photograph film is no longer used.) The first report of using a Charge-Coupled Device (CCD) detector for TEM was in 1982, but the technology didn't find widespread use until the late 1990s/early 2000s. Monolithic active-pixel sensors (MAPSs) were also used in TEM. CMOS detectors, which are faster and more resistant to radiation damage than CCDs, have been used for TEM since 2005. In the early 2010s, further development of CMOS technology allowed for the detection of single electron counts ("counting mode"). These Direct Electron Detectors are available from Gatan, FEI, Quantum Detectors and Direct Electron. + +== Components == \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-3.md b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-3.md new file mode 100644 index 000000000..739fd9386 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-3.md @@ -0,0 +1,19 @@ +--- +title: "Transmission electron microscopy" +chunk: 4/13 +source: "https://en.wikipedia.org/wiki/Transmission_electron_microscopy" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:36.644553+00:00" +instance: "kb-cron" +--- + +A TEM is composed of several components, which include a vacuum system in which the electrons travel, an electron emission source for generation of the electron stream, a series of electromagnetic lenses, as well as electrostatic plates. The latter two allow the operator to guide and manipulate the beam as required. Also required is a device to allow the insertion into, motion within, and removal of specimens from the beam path. Imaging devices are subsequently used to create an image from the electrons that exit the system. + +=== Vacuum system === +To increase the mean free path of the electron gas interaction, a standard TEM is evacuated to low pressures, typically on the order of 10−4 Pa. The need for this is twofold: first the allowance for the voltage difference between the cathode and the ground without generating an arc, and secondly to reduce the collision frequency of electrons with gas atoms to negligible levels—this effect is characterized by the mean free path. TEM components such as specimen holders and film cartridges must be routinely inserted or replaced requiring a system with the ability to re-evacuate on a regular basis. As such, TEMs are equipped with multiple pumping systems and airlocks and are not permanently vacuum sealed. +The vacuum system for evacuating a TEM to an operating pressure level consists of several stages. Initially, a low or roughing vacuum is achieved with either a rotary vane pump or diaphragm pumps setting a sufficiently low pressure to allow the operation of a turbo-molecular or diffusion pump establishing high vacuum level necessary for operations. To allow for the low vacuum pump to not require continuous operation, while continually operating the turbo-molecular pumps, the vacuum side of a low-pressure pump may be connected to chambers which accommodate the exhaust gases from the turbo-molecular pump. Sections of the TEM may be isolated by the use of pressure-limiting apertures to allow for different vacuum levels in specific areas such as a higher vacuum of 10−4 to 10−7 Pa or higher in the electron gun in high-resolution or field-emission TEMs. +High-voltage TEMs require ultra-high vacuums on the range of 10−7 to 10−9 Pa to prevent the generation of an electrical arc, particularly at the TEM cathode. As such for higher voltage TEMs a third vacuum system may operate, with the gun isolated from the main chamber either by gate valves or a differential pumping aperture – a small hole that prevents the diffusion of gas molecules into the higher vacuum gun area faster than they can be pumped out. For these very low pressures, either an ion pump or a getter material is used. +Poor vacuum in a TEM can cause several problems ranging from the deposition of gas inside the TEM onto the specimen while viewed in a process known as electron beam induced deposition to more severe cathode damages caused by electrical discharge. The use of a cold trap to adsorb sublimated gases in the vicinity of the specimen largely eliminates vacuum problems that are caused by specimen sublimation. + +=== Specimen stage === \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-4.md b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-4.md new file mode 100644 index 000000000..b1e7479b7 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-4.md @@ -0,0 +1,59 @@ +--- +title: "Transmission electron microscopy" +chunk: 5/13 +source: "https://en.wikipedia.org/wiki/Transmission_electron_microscopy" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:36.644553+00:00" +instance: "kb-cron" +--- + +TEM specimen stage designs include airlocks to allow for insertion of the specimen holder into the vacuum with minimal loss of vacuum in other areas of the microscope. The specimen holders hold a standard size of sample grid or self-supporting specimen. Standard TEM grid sizes are 3.05 mm diameter, with a thickness and mesh size ranging from a few to 100 μm. The sample is placed onto the meshed area having a diameter of approximately 2.5 mm. Usual grid materials are copper, molybdenum, gold or platinum. This grid is placed into the sample holder, which is paired with the specimen stage. A wide variety of designs of stages and holders exist, depending upon the type of experiment being performed. In addition to 3.05 mm grids, 2.3 mm grids are sometimes, if rarely, used. These grids were particularly used in the mineral sciences where a large degree of tilt can be required and where specimen material may be extremely rare. Electron transparent specimens have a thickness usually less than 100 nm, but this value depends on the accelerating voltage. +Once inserted into a TEM, the sample has to be manipulated to locate the region of interest to the beam, such as in single grain diffraction, in a specific orientation. To accommodate this, the TEM stage allows movement of the sample in the XY plane, Z height adjustment, and commonly a single tilt direction parallel to the axis of side entry holders. Sample rotation may be available on specialized diffraction holders and stages. Some modern TEMs provide the ability for two orthogonal tilt angles of movement with specialized holder designs called double-tilt sample holders. Some stage designs, such as top-entry or vertical insertion stages once common for high resolution TEM studies, may simply only have X-Y translation available. The design criteria of TEM stages are complex, owing to the simultaneous requirements of mechanical and electron-optical constraints and specialized models are available for different methods. +A TEM stage is required to have the ability to hold a specimen and be manipulated to bring the region of interest into the path of the electron beam. As the TEM can operate over a wide range of magnifications, the stage must simultaneously be highly resistant to mechanical drift, with drift requirements as low as a few nm/minute while being able to move several μm/minute, with repositioning accuracy on the order of nanometres. Earlier designs of TEM accomplished this with a complex set of mechanical downgearing devices, allowing the operator to finely control the motion of the stage by several rotating rods. Modern devices may use electrical stage designs, using screw gearing in concert with stepper motors, providing the operator with a computer-based stage input, such as a joystick or trackball. +Two main designs for stages in a TEM exist, the side-entry and top entry version. Each design must accommodate the matching holder to allow for specimen insertion without either damaging delicate TEM optics or allowing gas into TEM systems under vacuum. + +The most common is the side entry holder, where the specimen is placed near the tip of a long metal (brass or stainless steel) rod, with the specimen placed flat in a small bore. Along the rod are several polymer vacuum rings to allow for the formation of a vacuum seal of sufficient quality, when inserted into the stage. The stage is thus designed to accommodate the rod, placing the sample either in between or near the objective lens, dependent upon the objective design. When inserted into the stage, the side entry holder has its tip contained within the TEM vacuum, and the base is presented to atmosphere, the airlock formed by the vacuum rings. +Insertion procedures for side-entry TEM holders typically involve the rotation of the sample to trigger micro switches that initiate evacuation of the airlock before the sample is inserted into the TEM column. +The second design is the top-entry holder consists of a cartridge that is several cm long with a bore drilled down the cartridge axis. The specimen is loaded into the bore, possibly using a small screw ring to hold the sample in place. This cartridge is inserted into an airlock with the bore perpendicular to the TEM optic axis. When sealed, the airlock is manipulated to push the cartridge such that the cartridge falls into place, where the bore hole becomes aligned with the beam axis, such that the beam travels down the cartridge bore and into the specimen. Such designs are typically unable to be tilted without blocking the beam path or interfering with the objective lens. + +=== Electron gun === + +The electron gun is formed from several components: the filament, a biasing circuit, a Wehnelt cap, and an extraction anode. By connecting the filament to the negative component power supply, electrons can be "pumped" from the electron gun to the anode plate and the TEM column, thus completing the circuit. The gun is designed to create a beam of electrons exiting from the assembly at some given angle, known as the gun divergence semi-angle, α. By constructing the Wehnelt cylinder such that it has a higher negative charge than the filament itself, electrons that exit the filament in a diverging manner are, under proper operation, forced into a converging pattern the minimum size of which is the gun crossover diameter. +The thermionic emission current density, J, can be related to the work function of the emitting material via Richardson's law + + + + + J + = + A + + T + + 2 + + + exp + ⁡ + + ( + + + + − + Φ + + + k + T + + + + ) + + , + + + {\displaystyle J=AT^{2}\exp \left({\frac {-\Phi }{kT}}\right),} + \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-5.md b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-5.md new file mode 100644 index 000000000..08d10cc85 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-5.md @@ -0,0 +1,91 @@ +--- +title: "Transmission electron microscopy" +chunk: 6/13 +source: "https://en.wikipedia.org/wiki/Transmission_electron_microscopy" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:36.644553+00:00" +instance: "kb-cron" +--- + +where A is the Richardson's constant, Φ is the work function and T is the temperature of the material. +This equation shows that in order to achieve sufficient current density it is necessary to heat the emitter, taking care not to cause damage by application of excessive heat. For this reason materials with either a high melting point, such as tungsten, or those with a low work function (LaB6) are required for the gun filament. Furthermore, both lanthanum hexaboride and tungsten thermionic sources must be heated in order to achieve thermionic emission, this can be achieved by the use of a small resistive strip. To prevent thermal shock, there is often a delay enforced in the application of current to the tip, to prevent thermal gradients from damaging the filament, the delay is usually a few seconds for LaB6, and significantly lower for tungsten. + +=== Electron lens === + +Electron lenses are designed to act in a manner emulating that of an optical lens, by focusing parallel electrons at some constant focal distance. Electron lenses may operate electrostatically or magnetically. The majority of electron lenses for TEM use electromagnetic coils to generate a convex lens. The field produced for the lens must be radially symmetrical, as deviation from the radial symmetry of the magnetic lens causes aberrations such as astigmatism, and worsens spherical and chromatic aberration. Electron lenses are manufactured from iron, iron-cobalt or nickel cobalt alloys, such as permalloy. These are selected for their magnetic properties, such as magnetic saturation, hysteresis and permeability. +The components include the yoke, the magnetic coil, the poles, the polepiece, and the external control circuitry. The pole piece must be manufactured in a very symmetrical manner, as this provides the boundary conditions for the magnetic field that forms the lens. Imperfections in the manufacture of the pole piece can induce severe distortions in the magnetic field symmetry, which induce distortions that will ultimately limit the lenses' ability to reproduce the object plane. The exact dimensions of the gap, pole piece internal diameter and taper, as well as the overall design of the lens is often performed by finite element analysis of the magnetic field, whilst considering the thermal and electrical constraints of the design. +The coils which produce the magnetic field are located within the lens yoke. The coils can contain a variable current, but typically use high voltages, and therefore require significant insulation in order to prevent short-circuiting the lens components. Thermal distributors are placed to ensure the extraction of the heat generated by the energy lost to resistance of the coil windings. The windings may be water-cooled, using a chilled water supply in order to facilitate the removal of the high thermal duty. + +=== Apertures === +Apertures are annular metallic plates, through which electrons that are further than a fixed distance from the optic axis may be excluded. These consist of a small metallic disc that is sufficiently thick to prevent electrons from passing through the disc, whilst permitting axial electrons. This permission of central electrons in a TEM causes two effects simultaneously: firstly, apertures decrease the beam intensity as electrons are filtered from the beam, which may be desired in the case of beam sensitive samples. Secondly, this filtering removes electrons that are scattered to high angles, which may be due to unwanted processes such as spherical or chromatic aberration, or due to diffraction from interaction within the sample. +Apertures are either a fixed aperture within the column, such as at the condenser lens, or are a movable aperture, which can be inserted or withdrawn from the beam path, or moved in the plane perpendicular to the beam path. Aperture assemblies are mechanical devices which allow for the selection of different aperture sizes, which may be used by the operator to trade off intensity and the filtering effect of the aperture. Aperture assemblies are often equipped with micrometers to move the aperture, required during optical calibration. + +== Imaging methods == +Imaging methods in TEM use the information contained in the electron waves exiting from the sample to form an image. The projector lenses allow for the correct positioning of this electron wave distribution onto the viewing system. The observed intensity, I, of the image, assuming sufficiently high quality of imaging device, can be approximated as proportional to the time-averaged squared absolute value of the amplitude of the electron wavefunctions, where the wave that forms the exit beam is denoted by Ψ. + + + + + I + ( + x + ) + = + + + k + + + t + + 1 + + + − + + t + + 0 + + + + + + + ∫ + + + t + + 0 + + + + + + t + + 1 + + + + + Ψ + + Ψ + + + ∗ + + + + + d + t + + + {\displaystyle I(x)={\frac {k}{t_{1}-t_{0}}}\int _{t_{0}}^{t_{1}}\Psi \Psi ^{\mathrm {*} }\,dt} + + +Different imaging methods therefore attempt to modify the electron waves exiting the sample in a way that provides information about the sample, or the beam itself. From the previous equation, it can be deduced that the observed image depends not only on the amplitude of beam, but also on the phase of the electrons, although phase effects may often be ignored at lower magnifications. Higher resolution imaging requires thinner samples and higher energies of incident electrons, which means that the sample can no longer be considered to be absorbing electrons (i.e., via a Beer's law effect). Instead, the sample can be modeled as an object that does not change the amplitude of the incoming electron wave function, but instead modifies the phase of the incoming wave; in this model, the sample is known as a pure phase object. For sufficiently thin specimens, phase effects dominate the image, complicating analysis of the observed intensities. To improve the contrast in the image, the TEM may be operated at a slight defocus to enhance contrast, owing to convolution by the contrast transfer function of the TEM, which would normally decrease contrast if the sample was not a weak phase object. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-6.md b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-6.md new file mode 100644 index 000000000..ed341edfd --- /dev/null +++ b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-6.md @@ -0,0 +1,23 @@ +--- +title: "Transmission electron microscopy" +chunk: 7/13 +source: "https://en.wikipedia.org/wiki/Transmission_electron_microscopy" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:36.644553+00:00" +instance: "kb-cron" +--- + +The figure on the right shows the two basic operation modes of TEM – imaging and diffraction modes. In both cases the specimen is illuminated with the parallel beam, formed by electron beam shaping with the system of Condenser lenses and Condenser aperture. After interaction with the sample, on the exit surface of the specimen two types of electrons exist – unscattered (which will correspond to the bright central beam on the diffraction pattern) and scattered electrons (which change their trajectories due to interaction with the material). +In Imaging mode, the objective aperture is inserted in a back focal plane (BFP) of the objective lens (where diffraction spots are formed). If using the objective aperture to select only the central beam, the transmitted electrons are passed through the aperture while all others are blocked, and a bright field image (BF image) is obtained. If we allow the signal from a diffracted beam, a dark field image (DF image) is received. The selected signal is magnified and projected on a screen (or on a camera) with the help of Intermediate and Projector lenses. An image of the sample is thus obtained. +In Diffraction mode, a selected area aperture may be used to determine more precisely the specimen area from which the signal will be displayed. By changing the strength of current to the intermediate lens, the diffraction pattern is projected on a screen. Diffraction is a very powerful tool for doing a cell reconstruction and crystal orientation determination. + +=== Contrast formation === +The contrast between two adjacent areas in a TEM image can be defined as the difference in the electron densities in image plane. Due to the scattering of the incident beam by the sample, the amplitude and phase of the electron wave change, which results in amplitude contrast and phase contrast, correspondingly. Most images have both contrast components. +Amplitude–contrast is obtained due to removal of some electrons before the image plane. During their interaction with the specimen some of electrons will be lost due to absorption, or due to scattering at very high angles beyond the physical limitation of microscope or are blocked by the objective aperture. While the first two losses are due to the specimen and microscope construction, the objective aperture can be used by operator to enhance the contrast. + +Figure on the right shows a TEM image (a) and the corresponding diffraction pattern (b) of Pt polycrystalline film taken without an objective aperture. In order to enhance the contrast in the TEM image the number of scattered beams as visible in the diffraction pattern should be reduced. This can be done by selecting a certain area in the back focal plane such as only the central beam or a specific diffracted beam (angle), or combinations of such beams. By intentionally selecting an objective aperture which only permits the non-diffracted beam to pass beyond the back focal plane (and onto the image plane): one creates a Bright-Field (BF) image (c), whereas if the central, non-diffracted beam is blocked: one may obtain dark-field (DF) images such as those shown in (d–e). The DF images (d–e) were obtained by selecting the diffracted beams indicated in diffraction pattern with circles (b) using an aperture at the back focal plane. Grains from which electrons are scattered into these diffraction spots appear brighter. More details about diffraction contrast formation are given further. +There are two types of amplitude contrast – mass–thickness and diffraction contrast. First, let's consider mass–thickness contrast. When the beam illuminates two neighbouring areas with low mass (or thickness) and high mass (or thickness), the heavier region scatters electrons at bigger angles. These strongly scattered electrons are blocked in BF TEM mode by objective aperture. As a result, heavier regions appear darker in BF images (have low intensity). Mass–thickness contrast is most important for non–crystalline, amorphous materials. +Diffraction contrast occurs due to a specific crystallographic orientation of a grain. In such a case the crystal is oriented in a way that there is a high probability of diffraction. Diffraction contrast provides information on the orientation of the crystals in a polycrystalline sample, as well as other information such as defects. Note that in case diffraction contrast exists, the contrast cannot be interpreted as due to mass or thickness variations. + +==== Diffraction contrast ==== \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-7.md b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-7.md new file mode 100644 index 000000000..3b806e7b3 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-7.md @@ -0,0 +1,33 @@ +--- +title: "Transmission electron microscopy" +chunk: 8/13 +source: "https://en.wikipedia.org/wiki/Transmission_electron_microscopy" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:36.644553+00:00" +instance: "kb-cron" +--- + +Samples can exhibit diffraction contrast, whereby the electron beam undergoes diffraction which in the case of a crystalline sample, disperses electrons into discrete locations in the back focal plane. By the placement of apertures in the back focal plane, i.e. the objective aperture, the desired reciprocal lattice vectors can be selected (or excluded), thus only parts of the sample that are causing the electrons to scatter to the selected reflections will end up projected onto the imaging apparatus. +If the reflections that are selected do not include the unscattered beam (which will appear up at the focal point of the lens), then the image will appear dark wherever no sample scattering to the selected peak is present, as such a region without a specimen will appear dark. This is known as a dark-field image. +Modern TEMs are often equipped with specimen holders that allow the user to tilt the specimen to a range of angles in order to obtain specific diffraction conditions, and apertures placed above the specimen allow the user to select electrons that would otherwise be diffracted in a particular direction from entering the specimen. +Applications for this method include the identification of lattice defects in crystals. By carefully selecting the orientation of the sample, it is possible not just to determine the position of defects but also to determine the type of defect present. If the sample is oriented so that one particular plane is only slightly tilted away from the strongest diffracting angle (known as the Bragg Angle), any distortion of the crystal plane that locally tilts the plane to the Bragg angle will produce particularly strong contrast variations. However, defects that produce only displacement of atoms that do not tilt the crystal towards the Bragg angle (i. e. displacements parallel to the crystal plane) will produce weaker contrast. + +==== Phase contrast ==== + +Crystal structure can also be investigated by high-resolution transmission electron microscopy (HRTEM), also known as phase contrast. When using a field emission source and a specimen of uniform thickness, the images are formed due to differences in phase of electron waves, which is caused by specimen interaction. Image formation is given by the complex modulus of the incoming electron beams. As such, the image is not only dependent on the number of electrons hitting the screen, making direct interpretation of phase contrast images slightly more complex. However this effect can be used to an advantage, as it can be manipulated to provide more information about the sample, such as in complex phase retrieval techniques. + +=== Diffraction === + +As previously stated, by adjusting the magnetic lenses such that the back focal plane of the lens rather than the imaging plane is placed on the imaging apparatus a diffraction pattern can be generated. For thin crystalline samples, this produces an image that consists of a pattern of dots in the case of a single crystal, or a series of rings in the case of a polycrystalline or amorphous solid material. For the single crystal case the diffraction pattern is dependent upon the orientation of the specimen and the structure of the sample illuminated by the electron beam. This image provides the investigator with information about the space group symmetries in the crystal and the crystal's orientation to the beam path. This is typically done without using any information but the position at which the diffraction spots appear and the observed image symmetries. +Diffraction patterns can have a large dynamic range, and for crystalline samples, may have intensities greater than those recordable by CCD. As such, TEMs may still be equipped with film cartridges for the purpose of obtaining these images, as the film is a single use detector. + +Analysis of diffraction patterns beyond point-position can be complex, as the image is sensitive to a number of factors such as specimen thickness and orientation, objective lens defocus, and spherical and chromatic aberration. Although quantitative interpretation of the contrast shown in lattice images is possible, it is inherently complicated and can require extensive computer simulation and analysis, such as electron multislice analysis. +More complex behavior in the diffraction plane is also possible, with phenomena such as Kikuchi lines arising from multiple diffraction within the crystalline lattice. In convergent beam electron diffraction (CBED) where a non-parallel, i.e. converging, electron wavefront is produced by concentrating the electron beam into a fine probe at the sample surface, the interaction of the convergent beam can provide information beyond structural data such as sample thickness. + +==== Electron energy loss spectroscopy (EELS) ==== + +Using the advanced technique of electron energy loss spectroscopy (EELS), for TEMs appropriately equipped, electrons can be separated into a spectrum based upon their velocity (which is closely related to their kinetic energy, and thus energy loss from the beam energy), using magnetic sector based devices known as EEL spectrometers. These devices allow for the selection of particular energy values, which can be associated with the way the electron has interacted with the sample. For example, different elements in a sample result in different electron energies in the beam after the sample. This normally results in chromatic aberration – however this effect can, for example, be used to generate an image which provides information on elemental composition, based upon the atomic transition during electron-electron interaction. +EELS spectrometers can often be operated in both spectroscopic and imaging modes, allowing for isolation or rejection of elastically scattered beams. As for many images inelastic scattering will include information that may not be of interest to the investigator thus reducing observable signals of interest, EELS imaging can be used to enhance contrast in observed images, including both bright field and diffraction, by rejecting unwanted components. + +=== Three-dimensional imaging === \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-8.md b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-8.md new file mode 100644 index 000000000..aeb62f603 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-8.md @@ -0,0 +1,22 @@ +--- +title: "Transmission electron microscopy" +chunk: 9/13 +source: "https://en.wikipedia.org/wiki/Transmission_electron_microscopy" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:36.644553+00:00" +instance: "kb-cron" +--- + +As TEM specimen holders typically allow for the rotation of a sample by a desired angle, multiple views of the same specimen can be obtained by rotating the angle of the sample along an axis perpendicular to the beam. By taking multiple images of a single TEM sample at differing angles, typically in 1° increments, a set of images known as a "tilt series" can be collected. This methodology was proposed in the 1970s by Walter Hoppe. Under purely absorption contrast conditions, this set of images can be used to construct a three-dimensional representation of the sample. +The reconstruction is accomplished by a two-step process, first images are aligned to account for errors in the positioning of a sample; such errors can occur due to vibration or mechanical drift. Alignment methods use image registration algorithms, such as autocorrelation methods to correct these errors. Secondly, using a reconstruction algorithm, such as filtered back projection, the aligned image slices can be transformed from a set of two-dimensional images, Ij(x, y), to a single three-dimensional image, I′j(x, y, z). This three-dimensional image is of particular interest when morphological information is required, further study can be undertaken using computer algorithms, such as isosurfaces and data slicing to analyse the data. +As TEM samples cannot typically be viewed at a full 180° rotation, the observed images typically suffer from a "missing wedge" of data, which when using Fourier-based back projection methods decreases the range of resolvable frequencies in the three-dimensional reconstruction. Mechanical refinements, such as multi-axis tilting (two tilt series of the same specimen made at orthogonal directions) and conical tomography (where the specimen is first tilted to a given fixed angle and then imaged at equal angular rotational increments through one complete rotation in the plane of the specimen grid) can be used to limit the impact of the missing data on the observed specimen morphology. Using focused ion beam milling, a new technique has been proposed which uses pillar-shaped specimen and a dedicated on-axis tomography holder to perform 180° rotation of the sample inside the pole piece of the objective lens in TEM. Using such arrangements, quantitative electron tomography without the missing wedge is possible. In addition, numerical techniques exist which can improve the collected data. +All the above-mentioned methods involve recording tilt series of a given specimen field. This inevitably results in the summation of a high dose of reactive electrons through the sample and the accompanying destruction of fine detail during recording. The technique of low-dose (minimal-dose) imaging is therefore regularly applied to mitigate this effect. Low-dose imaging is performed by deflecting illumination and imaging regions simultaneously away from the optical axis to image an adjacent region to the area to be recorded (the high-dose region). This area is maintained centered during tilting and refocused before recording. During recording the deflections are removed so that the area of interest is exposed to the electron beam only for the duration required for imaging. An improvement of this technique (for objects resting on a sloping substrate film) is to have two symmetrical off-axis regions for focusing followed by setting focus to the average of the two high-dose focus values before recording the low-dose area of interest. +Non-tomographic variants on this method, referred to as single particle analysis, use images of multiple (hopefully) identical objects at different orientations to produce the image data required for three-dimensional reconstruction. If the objects do not have significant preferred orientations, this method does not suffer from the missing data wedge (or cone) which accompany tomographic methods nor does it incur excessive radiation dosage, however it assumes that the different objects imaged can be treated as if the 3D data generated from them arose from a single stable object. + +== Sample preparation == + +Sample preparation in TEM can be a complex procedure. TEM specimens should be less than 100 nanometres thick for a conventional TEM. Unlike neutron or X-ray radiation the electrons in the beam interact readily with the sample, an effect that increases roughly with atomic number squared (Z2). High quality samples will have a thickness that is comparable to the mean free path of the electrons that travel through the samples, which may be only a few tens of nanometres. Preparation of TEM specimens is specific to the material under analysis and the type of information to be obtained from the specimen. +Materials that have dimensions small enough to be electron transparent, such as powdered substances, small organisms, viruses, or nanotubes, can be quickly prepared by the deposition of a dilute sample containing the specimen onto films on support grids. Biological specimens may be embedded in resin to withstand the high vacuum in the sample chamber and to enable cutting tissue into electron transparent thin sections. The biological sample can be stained using either a negative staining material such as uranyl acetate for bacteria and viruses, or, in the case of embedded sections, the specimen may be stained with heavy metals, including osmium tetroxide. Alternately samples may be held at liquid nitrogen temperatures after embedding in vitreous ice. In material science and metallurgy the specimens can usually withstand the high vacuum, but still must be prepared as a thin foil, or etched so some portion of the specimen is thin enough for the beam to penetrate. Constraints on the thickness of the material may be limited by the scattering cross-section of the atoms from which the material is comprised. + +=== Tissue sectioning === \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-9.md b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-9.md new file mode 100644 index 000000000..f4f1b2636 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy-9.md @@ -0,0 +1,47 @@ +--- +title: "Transmission electron microscopy" +chunk: 10/13 +source: "https://en.wikipedia.org/wiki/Transmission_electron_microscopy" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:36.644553+00:00" +instance: "kb-cron" +--- + +Before sectioning, biological tissue is often embedded in an epoxy resin block and first trimmed using a razor blade into a trapezoidal block face. Thick sections are then cut from the block face. The thick sections are crudely stained with toluidine blue and examined for specimen and block orientation before thin sectioning. +Biological tissue is then thinned to less than 100 nm on an ultramicrotome. The resin block is fractured as it passes over a glass or diamond knife edge. This method is used to obtain thin, minimally deformed samples that allow for the observation of tissue ultrastructure. Inorganic samples, such as aluminium, may also be embedded in resins and ultrathin sectioned in this way, using either coated glass, sapphire or larger angle diamond knives. To prevent charge build-up at the sample surface when viewing in the TEM, tissue samples need to be coated with a thin layer of conducting material, such as carbon. + +=== Sample staining === + +TEM samples of biological tissues need high atomic number stains to enhance contrast. The stain absorbs the beam electrons or scatters part of the electron beam which otherwise is projected onto the imaging system. Compounds of heavy metals such as osmium, lead, uranium or gold (in immunogold labelling) may be used prior to TEM observation to selectively deposit electron dense atoms in or on the sample in desired cellular or protein region. This process requires an understanding of how heavy metals bind to specific biological tissues and cellular structures. +Another form of sample staining is negative stain, where a larger amount of heavy metal stain is applied to the sample. The result is a sample with a dark background and the topological surface of the sample appearing lighter. Negative stain electron microscopy can be ideal for visualizing or forming 3D topological reconstructions of large proteins or macromolecular complexes (> 150 kDa). For smaller proteins, negative stain can be used as a screening step to find ideal sample concentration for cryogenic electron microscopy. + +=== Mechanical milling === +Mechanical polishing is also used to prepare samples for imaging on the TEM. Polishing needs to be done to a high quality, to ensure constant sample thickness across the region of interest. A diamond, or cubic boron nitride polishing compound may be used in the final stages of polishing to remove any scratches that may cause contrast fluctuations due to varying sample thickness. Even after careful mechanical milling, additional fine methods such as ion etching may be required to perform final stage thinning. + +=== Chemical etching === + +Certain samples may be prepared by chemical etching, particularly metallic specimens. These samples are thinned using a chemical etchant, such as an acid, to prepare the sample for TEM observation. Devices to control the thinning process may allow the operator to control either the voltage or current passing through the specimen, and may include systems to detect when the sample has been thinned to a sufficient level of optical transparency. + +=== Ion etching === + +Ion etching is a sputtering process that can remove very fine quantities of material. This is used to perform a finishing polish of specimens polished by other means. Ion etching uses an inert gas passed through an electric field to generate a plasma stream that is directed to the sample surface. Acceleration energies for gases such as argon are typically a few kilovolts. The sample may be rotated to promote even polishing of the sample surface. The sputtering rate of such methods is on the order of tens of micrometres per hour, limiting the method to only extremely fine polishing. +Ion etching by argon gas has been recently shown to be able to file down MTJ stack structures to a specific layer which has then been atomically resolved. The TEM images taken in plan view rather than cross-section reveal that the MgO layer within MTJs contains a large number of grain boundaries that may be diminishing the properties of devices. + +=== Ion milling (FIB) === + +More recently focused ion beam (FIB) methods have been used to prepare samples. FIB is a relatively new technique to prepare thin samples for TEM examination from larger specimens. Because FIB can be used to micro-machine samples very precisely, it is possible to mill very thin membranes from a specific area of interest in a sample, such as a semiconductor or metal. Unlike inert gas ion sputtering, FIB makes use of significantly more energetic gallium ions and may alter the composition or structure of the material through gallium implantation. + +=== Nanowire assisted transfer === +For a minimal introduction of stress and bending to transmission electron microscopy (TEM) samples (lamellae, thin films, and other mechanically and beam sensitive samples), when transferring inside a focused ion beam (FIB), flexible metallic nanowires can be attached to a typically rigid micromanipulator. +The main advantages of this method include a significant reduction of sample preparation time (quick welding and cutting of nanowire at low beam current), and minimization of stress-induced bending, Pt contamination, and ion beam damage. +This technique is particularly suitable for in situ electron microscopy sample preparation. + +=== Replication === + +Samples may also be replicated using cellulose acetate film, the film subsequently coated with a heavy metal such as platinum, the original film dissolved away, and the replica imaged on the TEM. Variations of the replica technique are used for both materials and biological samples. In materials science a common use is for examining the fresh fracture surface of metal alloys. + +== Modifications == +The capabilities of the TEM can be further extended by additional stages and detectors, sometimes incorporated on the same microscope. + +=== Scanning TEM === \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Transmission_electron_microscopy_DNA_sequencing-0.md b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy_DNA_sequencing-0.md new file mode 100644 index 000000000..551191cfe --- /dev/null +++ b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy_DNA_sequencing-0.md @@ -0,0 +1,39 @@ +--- +title: "Transmission electron microscopy DNA sequencing" +chunk: 1/3 +source: "https://en.wikipedia.org/wiki/Transmission_electron_microscopy_DNA_sequencing" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:37.867972+00:00" +instance: "kb-cron" +--- + +Transmission electron microscopy DNA sequencing is a single-molecule sequencing technology that uses transmission electron microscopy techniques. The method was conceived and developed in the 1960s and 70s, but lost favor when the extent of damage to the sample was recognized. +In order for DNA to be clearly visualized under an electron microscope, it must be labeled with heavy atoms. In addition, specialized imaging techniques and aberration corrected optics are beneficial for obtaining the resolution required to image the labeled DNA molecule. In theory, transmission electron microscopy DNA sequencing could provide extremely long read lengths, but the issue of electron beam damage may still remain and the technology has not yet been commercially developed. + +== History == +Only a few years after James Watson and Francis Crick deduced the structure of DNA, and nearly two decades before Frederick Sanger published the first method for rapid DNA sequencing, Richard Feynman, an American physicist, envisioned the electron microscope as the tool that would one day allow biologists to "see the order of bases in the DNA chain". Feynman believed that if the electron microscope could be made powerful enough, then it would become possible to visualize the atomic structure of any and all chemical compounds, including DNA. +In 1970, Albert Crewe developed the high-angle annular dark-field imaging (HAADF) imaging technique in a scanning transmission electron microscope. Using this technique, he visualized individual heavy atoms on thin amorphous carbon films. In 2010 Krivanek and colleagues reported several technical improvements to the HAADF method, including a combination of aberration corrected electron optics and low accelerating voltage. The latter is crucial for imaging biological objects, as it allows to reduce damage by the beam and increase the image contrast for light atoms. As a result, single atom substitutions in a boron nitride monolayer could be imaged. +Despite the invention of a multitude of chemical and fluorescent sequencing technologies, electron microscopy is still being explored as a means of performing single-molecule DNA sequencing. For example, in 2012 a collaboration between scientists at Harvard University, the University of New Hampshire and ZS Genetics demonstrated the ability to read long sequences of DNA using the technique, however transmission electron microscopy DNA sequencing technology is still far from being commercially available. + +== Principle == +The electron microscope has the capacity to obtain a resolution of up to 100 pm, whereby microscopic biomolecules and structures such as viruses, ribosomes, proteins, lipids, small molecules and even single atoms can be observed. +Although DNA is visible when observed with the electron microscope, the resolution of the image obtained is not high enough to allow for deciphering the sequence of the individual bases, i.e., DNA sequencing. However, upon differential labeling of the DNA bases with heavy atoms or metals, it is possible to both visualize and distinguish between the individual bases. Therefore, electron microscopy in conjunction with differential heavy atom DNA labeling could be used to directly image the DNA in order to determine its sequence. + +== Workflow == + +=== Step 1 – DNA denaturation === +As in a standard polymerase chain reaction (PCR), the double stranded DNA molecules to be sequenced must be denatured before the second strand can be synthesized with labeled nucleotides. + +=== Step 2 – Heavy atom labeling === +The elements that make up biological molecules (C, H, N, O, P, S) are too light (low atomic number, Z) to be clearly visualized as individual atoms by transmission electron microscopy. To circumvent this problem, the DNA bases can be labeled with heavier atoms (higher Z). Each nucleotide is tagged with a characteristic heavy label, so that they can be distinguished in the transmission electron micrograph. + +ZS Genetics proposes using three heavy labels: bromine (Z=35), iodine (Z=53), and trichloromethane (total Z=63). These would appear as differential dark and light spots on the micrograph, and the fourth DNA base would remain unlabeled. +Halcyon Molecular, in collaboration with the Toste group, proposes that purine and pyrimidine bases can be functionalized with platinum diamine or osmium tetraoxide bipyridine, respectively. Heavy metal atoms such as osmium (Z=76), iridium (Z=77), gold (Z=79), or uranium (Z=92) can then form metal-metal bonds with these functional groups to label the individual bases. + +=== Step 3 – DNA alignment on substrate === +The DNA molecules must be stretched out on a thin, solid substrate so that order of the labeled bases will be clearly visible on the electron micrograph. Molecular combing is a technique that utilizes the force of a receding air-water interface to extend DNA molecules, leaving them irreversibly bound to a silane layer once dry. This is one means by which alignment of the DNA on a solid substrate may be achieved. + +=== Step 4 – TEM imaging === + +Transmission electron microscopy (TEM) produces high magnification, high resolution images by passing a beam of electrons through a very thin sample. Whereas atomic resolution has been demonstrated with conventional TEM, further improvement in spatial resolution requires correcting the spherical and chromatic aberrations of the microscope lenses. This has only been possible in scanning transmission electron microscopy where the image is obtained by scanning the object with a finely focused electron beam, in a way similar to a cathode ray tube. However, the achieved improvement in resolution comes together with irradiation of the studied object by much higher beam intensities, the concomitant sample damage and the associated imaging artefacts. Different imaging techniques are applied depending on whether the sample contains heavy or light atoms: \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Transmission_electron_microscopy_DNA_sequencing-1.md b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy_DNA_sequencing-1.md new file mode 100644 index 000000000..ed95cdc11 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy_DNA_sequencing-1.md @@ -0,0 +1,33 @@ +--- +title: "Transmission electron microscopy DNA sequencing" +chunk: 2/3 +source: "https://en.wikipedia.org/wiki/Transmission_electron_microscopy_DNA_sequencing" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:37.867972+00:00" +instance: "kb-cron" +--- + +Annular dark-field imaging measures the scattering of electrons as they deflect off the nuclei of the atoms in the transmission electron microscopy sample. This is best suited to samples containing heavy atoms, as they cause more scattering of electrons. The technique has been used to image atoms as light as boron, nitrogen, and carbon; however, the signal is very weak for such light atoms. If annular dark-field microscopy is put to use for transmission electron microscopy DNA sequencing, it will certainly be necessary to label the DNA bases with heavy atoms so that a strong signal can be detected. +Annular bright-field imaging detects electrons transmitted directly through the sample, and measures the wave interference produced by their interactions with the atomic nuclei. This technique can detect light atoms with greater sensitivity than annular dark-field imaging methods. In fact, oxygen, nitrogen, lithium, and hydrogen in crystalline solids have been imaged using annular bright-field electron microscopy. Thus, it is theoretically possible to obtain direct images of the atoms in the DNA chain; however, the structure of DNA is much less geometric than crystalline solids, so direct imaging without prior labeling may not be achievable. + +=== Step 5 – Data analysis === +Dark and bright spots on the electron micrograph, corresponding to the differentially labeled DNA bases, are analyzed by computer software. + +== Applications == +Transmission electron microscopy DNA sequencing is not yet commercially available, but the long read lengths that this technology may one day provide will make it useful in a variety of contexts. + +=== De novo genome assembly === +When sequencing a genome, it must be broken down into pieces that are short enough to be sequenced in a single read. These reads must then be put back together like a jigsaw puzzle by aligning the regions that overlap between reads; this process is called de novo genome assembly. The longer the read length that a sequencing platform provides, the longer the overlapping regions, and the easier it is to assemble the genome. From a computational perspective, microfluidic Sanger sequencing is still the most effective way to sequence and assemble genomes for which no reference genome sequence exists. The relatively long read lengths provide substantial overlap between individual sequencing reads, which allows for greater statistical confidence in the assembly. In addition, long Sanger reads are able to span most regions of repetitive DNA sequence which otherwise confound sequence assembly by causing false alignments. However, de novo genome assembly by Sanger sequencing is extremely expensive and time-consuming. Second generation sequencing technologies, while less expensive, are generally unfit for de novo genome assembly due to short read lengths. In general, third generation sequencing technologies, including transmission electron microscopy DNA sequencing, aim to improve read length while maintaining low sequencing cost. Thus, as third generation sequencing technologies improve, rapid and inexpensive de novo genome assembly will become a reality. + +=== Full haplotypes === +A haplotype is a series of linked alleles that are inherited together on a single chromosome. DNA sequencing can be used to genotype all of the single nucleotide polymorphisms (SNPs) that constitute a haplotype. However, short DNA sequencing reads often cannot be phased; that is, heterozygous variants cannot be confidently assigned to the correct haplotype. In fact, haplotyping with short read DNA sequencing data requires very high coverage (average >50x coverage of each DNA base) to accurately identify SNPs, as well as additional sequence data from the parents so that Mendelian transmission can be used to estimate the haplotypes. Sequencing technologies that generate long reads, including transmission electron microscopy DNA sequencing, can capture entire haploblocks in a single read. That is, haplotypes are not broken up among multiple reads, and the genetically linked alleles remain together in the sequencing data. Therefore, long reads make haplotyping easier and more accurate, which is beneficial to the field of population genetics. + +=== Copy number variants === +Genes are normally present in two copies in the diploid human genome; genes that deviate from this standard copy number are referred to as copy number variants (CNVs). Copy number variation can be benign (these are usually common variants, called copy number polymorphisms) or pathogenic. CNVs are detected by fluorescence in situ hybridization (FISH) or comparative genomic hybridization (CGH). To detect the specific breakpoints at which a deletion occurs, or to detect genomic lesions introduced by a duplication or amplification event, CGH can be performed using a tiling array (array CGH), or the variant region can be sequenced. Long sequencing reads are especially useful for analyzing duplications or amplifications, as it is possible to analyze the orientation of the amplified segments if they are captured in a single sequencing read. + +=== Cancer === +Cancer genomics, or oncogenomics, is an emerging field in which high-throughput, second generation DNA sequencing technology is being applied to sequence entire cancer genomes. Analyzing this short read sequencing data encompasses all of the problems associated with de novo genome assembly using short read data. Furthermore, cancer genomes are often aneuploid. These aberrations, which are essentially large scale copy number variants, can be analyzed by second-generation sequencing technologies using read frequency to estimate the copy number. Longer reads would, however, provide a more accurate picture of copy number, orientation of amplified regions, and SNPs present in cancer genomes. + +=== Microbiome sequencing === +The microbiome refers the total collection of microbes present in a microenvironment and their respective genomes. For example, an estimated 100 trillion microbial cells colonize the human body at any given time. The human microbiome is of particular interest, as these commensal bacteria are important for human health and immunity. Most of the Earth's bacterial genomes have not yet been sequenced; undertaking a microbiome sequencing project would require extensive de novo genome assembly, a prospect which is daunting with short read DNA sequencing technologies. Longer reads would greatly facilitate the assembly of new microbial genomes. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Transmission_electron_microscopy_DNA_sequencing-2.md b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy_DNA_sequencing-2.md new file mode 100644 index 000000000..b8235012f --- /dev/null +++ b/data/en.wikipedia.org/wiki/Transmission_electron_microscopy_DNA_sequencing-2.md @@ -0,0 +1,30 @@ +--- +title: "Transmission electron microscopy DNA sequencing" +chunk: 3/3 +source: "https://en.wikipedia.org/wiki/Transmission_electron_microscopy_DNA_sequencing" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:37.867972+00:00" +instance: "kb-cron" +--- + +== Strengths and weaknesses == +Compared to other second- and third-generation DNA sequencing technologies, transmission electron microscopy DNA sequencing has a number of potential key strengths and weaknesses, which will ultimately determine its usefulness and prominence as a future DNA sequencing technology. + +=== Strengths === +Longer read lengths: ZS Genetics has estimated potential read lengths of transmission electron microscopy DNA sequencing to be 10,000 to 20,000 base pairs with a rate of 1.7 billion base pairs per day. Such long read lengths would allow easier de novo genome assembly and direct detection of haplotypes, among other applications. +Lower cost: Transmission electron microscopy DNA sequencing is estimated to cost just US$5,000-US$10,000 per human genome, compared to the more expensive second-generation DNA sequencing alternatives. +No dephasing: Dephasing of the DNA strands due to loss in synchronicity during synthesis is a major problem of second-generation sequencing technologies. For transmission electron microscopy DNA sequencing and several other third-generation sequencing technologies, synchronization of the reads is unnecessary as only one molecule is being read at a time. +Shorter turnaround time: The capacity to read native fragments of DNA renders complex template preparation an unnecessary step in the general workflow of whole genome sequencing. Consequently, shorter turnaround times are possible. + +=== Weaknesses === +High capital cost: A transmission electron microscope with sufficient resolution required for transmission electron microscopy DNA sequencing costs approximately US$1,000,000, therefore pursuing DNA sequencing by this method requires a substantial investment. +Technically challenging: Selective heavy atom labeling and attaching and straightening the labeled DNA to a substrate are a serious technical challenge. Further, the DNA sample should be stable to the high vacuum of electron microscope and irradiation by a focused beam of high-energy electrons. +Potential PCR bias and artefacts: Although PCR is only being utilized in transmission electron microscopy DNA sequencing as a means to label the DNA strand with heavy atoms or metals, there could be the possibility of introducing bias in template representation or errors during the single amplification. + +=== Comparison to other sequencing technologies === +Many non-Sanger second- and third-generation DNA sequencing technologies have been or are currently being developed with the common aim of increasing throughput and decreasing cost such that personalized genetic medicine can be fully realized. +Both the US$10 million Archon X Prize for Genomics supported by the X Prize Foundation (Santa Monica, CA, USA) and the US$70 million in grant awards supported by the National Human Genome Research Institute of the National Institutes of Health (NIH-NHGRI) are fueling the rapid burst of research activity in the development of new DNA sequencing technologies. +Since different approaches, techniques, and strategies are what define each DNA sequencing technology, each has its own strengths and weaknesses. Comparison of important parameters between various second- and third-generation DNA sequencing technologies are presented in Table 1. + +== References == \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Two-dimensional_correlation_analysis-0.md b/data/en.wikipedia.org/wiki/Two-dimensional_correlation_analysis-0.md new file mode 100644 index 000000000..a3bb8dfe5 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Two-dimensional_correlation_analysis-0.md @@ -0,0 +1,167 @@ +--- +title: "Two-dimensional correlation analysis" +chunk: 1/2 +source: "https://en.wikipedia.org/wiki/Two-dimensional_correlation_analysis" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:40.213046+00:00" +instance: "kb-cron" +--- + +Two dimensional correlation analysis is a mathematical technique that is used to study changes in measured signals. As mostly spectroscopic signals are discussed, sometime also two dimensional correlation spectroscopy is used and refers to the same technique. +In 2D correlation analysis, a sample is subjected to an external perturbation while all other parameters of the system are kept at the same value. This perturbation can be a systematic and controlled change in temperature, pressure, pH, chemical composition of the system, or even time after a catalyst was added to a chemical mixture. As a result of the controlled change (the perturbation), the system will undergo variations which are measured by a chemical or physical detection method. The measured signals or spectra will show systematic variations that are processed with 2D correlation analysis for interpretation. +When one considers spectra that consist of few bands, it is quite obvious to determine which bands are subject to a changing intensity. Such a changing intensity can be caused for example by chemical reactions. However, the interpretation of the measured signal becomes more tricky when spectra are complex and bands are heavily overlapping. Two dimensional correlation analysis allows one to determine at which positions in such a measured signal there is a systematic change in a peak, either continuous rising or drop in intensity. 2D correlation analysis results in two complementary signals, which referred to as the 2D synchronous and 2D asynchronous spectrum. These signals allow amongst others + +to determine the events that are occurring at the same time (in phase) and those events that are occurring at different times (out of phase) +to determine the sequence of spectral changes +to identify various inter- and intramolecular interactions +band assignments of reacting groups +to detect correlations between spectra of different techniques, for example near infrared spectroscopy (NIR) and Raman spectroscopy + +== History == +2D correlation analysis originated from 2D NMR spectroscopy. Isao Noda developed perturbation based 2D spectroscopy in the 1980s. This technique required sinusoidal perturbations to the chemical system under investigation. This specific type of the applied perturbation severely limited its possible applications. Following research done by several groups of scientists, perturbation based 2D spectroscopy could be developed to a more extended and generalized broader base. Since the development of generalized 2D correlation analysis in 1993 based on Fourier transformation of the data, 2D correlation analysis gained widespread use. Alternative techniques that were simpler to calculate, for example the disrelation spectrum, were also developed simultaneously. Because of its computational efficiency and simplicity, the Hilbert transform is nowadays used for the calculation of the 2D spectra. To date, 2D correlation analysis is used for the interpretation of many types of spectroscopic data (including XRF, UV/VIS spectroscopy, fluorescence, infrared, and Raman spectra), although its application is not limited to spectroscopy. + +== Properties of 2D correlation analysis == + 2D correlation analysis is frequently used for its main advantage: increasing the spectral resolution by spreading overlapping peaks over two dimensions and as a result simplification of the interpretation of one-dimensional spectra that are otherwise visually indistinguishable from each other. Further advantages are its ease of application and the possibility to make the distinction between band shifts and band overlap. Each type of spectral event, band shifting, overlapping bands of which the intensity changes in the opposite direction, band broadening, baseline change, etc. has a particular 2D pattern. See also the figure with the original dataset on the right and the corresponding 2D spectrum in the figure below. + +== Presence of 2D spectra == +2D synchronous and asynchronous spectra are basically 3D-datasets and are generally represented by contour plots. X- and y-axes are identical to the x-axis of the original dataset, whereas the different contours represent the magnitude of correlation between the spectral intensities. The 2D synchronous spectrum is symmetric relative to the main diagonal. The main diagonal thus contains positive peaks. As the peaks at (x,y) in the 2D synchronous spectrum are a measure for the correlation between the intensity changes at x and y in the original data, these main diagonal peaks are also called autopeaks and the main diagonal signal is referred to as autocorrelation signal. The off-diagonal cross-peaks can be either positive or negative. On the other hand, the asynchronous spectrum is asymmetric and never has peaks on the main diagonal. +Generally contour plots of 2D spectra are oriented with rising axes from left to right and top to down. Other orientations are possible, but interpretation has to be adapted accordingly. + +== Calculation of 2D spectra == +Suppose the original dataset D contains the n spectra in rows. The signals of the original dataset are generally preprocessed. The original spectra are compared to a reference spectrum. By subtracting a reference spectrum, often the average spectrum of the dataset, so called dynamic spectra are calculated which form the corresponding dynamic dataset E. The presence and interpretation may be dependent on the choice of reference spectrum. The equations below are valid for equally spaced measurements of the perturbation. + +=== Calculation of the synchronous spectrum === +A 2D synchronous spectrum expresses the similarity between spectral of the data in the original dataset. In generalized 2D correlation spectroscopy this is mathematically expressed as covariance (or correlation). + + + + + ϕ + ( + + ν + + 1 + + + , + + ν + + 2 + + + ) + = + + + 1 + + n + − + 1 + + + + + y + + T + + + ( + + ν + + 1 + + + ) + . + y + ( + + ν + + 2 + + + ) + + + {\displaystyle \phi (\nu _{1},\nu _{2})={\frac {1}{n-1}}y^{T}(\nu _{1}).y(\nu _{2})} + + +where: + +Φ is the 2D synchronous spectrum +ν1 and ν2 are two spectral channels +yν is the vector composed of the signal intensities in E in column ν +n the number of signals in the original dataset + +=== Calculation of the asynchronous spectrum === +Orthogonal spectra to the dynamic dataset E are obtained with the Hilbert-transform: + + + + + ψ + ( + + ν + + 1 + + + , + + ν + + 2 + + + ) + = + + + 1 + + n + − + 1 + + + + + y + + T + + + ( + + ν + + 1 + + + ) + . + N + . + y + ( + + ν + + 2 + + + ) + + + {\displaystyle \psi (\nu _{1},\nu _{2})={\frac {1}{n-1}}y^{T}(\nu _{1}).N.y(\nu _{2})} + + +where: \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Two-dimensional_correlation_analysis-1.md b/data/en.wikipedia.org/wiki/Two-dimensional_correlation_analysis-1.md new file mode 100644 index 000000000..824a2e98e --- /dev/null +++ b/data/en.wikipedia.org/wiki/Two-dimensional_correlation_analysis-1.md @@ -0,0 +1,76 @@ +--- +title: "Two-dimensional correlation analysis" +chunk: 2/2 +source: "https://en.wikipedia.org/wiki/Two-dimensional_correlation_analysis" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:40.213046+00:00" +instance: "kb-cron" +--- + +Ψ is the 2D asynchronous spectrum +ν1 en ν2 are two spectral channels +yν is the vector composed of the signal intensities in E in column ν +n the number of signals in the original dataset +N the Noda-Hilbert transform matrix +The values of N, Nj, k are determined as follows: + +0 if j = k + + + + + + + 1 + + π + ( + k + − + j + ) + + + + + + {\displaystyle {\frac {1}{\pi (k-j)}}} + + if j ≠ k +where: + +j the row number +k the column number + +== Interpretation == +Interpretation of two-dimensional correlation spectra can be considered to consist of several stages. + +=== Detection of peaks of which the intensity changes in the original dataset === +As real measurement signals contain a certain level of noise, the derived 2D spectra are influenced and degraded with substantial higher amounts of noise. Hence, interpretation begins with studying the autocorrelation spectrum on the main diagonal of the 2D synchronous spectrum. In the 2D synchronous main diagonal signal on the right 4 peaks are visible at 10, 20, 30, and 40 (see also the 4 corresponding positive autopeaks in the 2D synchronous spectrum on the right). This indicates that in the original dataset 4 peaks of changing intensity are present. The intensity of peaks on the autocorrelation spectrum are directly proportional to the relative importance of the intensity change in the original spectra. Hence, if an intense band is present at position x, it is very likely that a true intensity change is occurring and the peak is not due to noise. +Additional techniques help to filter the peaks that can be seen in the 2D synchronous and asynchronous spectra. + +=== Determining the direction of intensity change === +It is not always possible to unequivocally determine the direction of intensity change, such as is for example the case for highly overlapping signals next to each other and of which the intensity changes in the opposite direction. This is where the off diagonal peaks in the synchronous 2D spectrum are used for: +if there is a positive cross-peak at (x, y) in the synchronous 2D spectrum, the intensity of the signals at x and y changes in the same direction +if there is a negative cross-peak at (x, y) in the synchronous 2D spectrum, the intensity of the signals at x and y changes in the opposite direction +As can be seen in the 2D synchronous spectrum on the right, the intensity changes of the peaks at 10 and 30 are related and the intensity of the peak at 10 and 30 changes in the opposite direction (negative cross-peak at (10,30)). The same is true for the peaks at 20 and 40. + +=== Determining the sequence of events === +Most importantly, with the sequential order rules, also referred to as Noda's rules, the sequence of the intensity changes can be determined. By carefully interpreting the signs of the 2D synchronous and asynchronous cross peaks with the following rules, the sequence of spectral events during the experiment can be determined: + +if the intensities of the bands at x and y in the dataset are changing in the same direction, the synchronous 2D cross peak at (x,y) is positive +if the intensities of the bands at x and y in the dataset are changing in the opposite direction, the synchronous 2D cross peak at (x,y) is negative +if the change at x mainly precedes the change in the band at y, the asynchronous 2D cross peak at (x,y) is positive +if the change at x mainly follows the change in the band at y, the asynchronous 2D cross peak at (x,y) is negative +if the synchronous 2D cross peak at (x,y) is negative, the interpretation of rule 3 and 4 for the asynchronous 2D peak at (x,y) has to be reversed +where x and y are the positions on the x-xaxis of two bands in the original data that are subject to intensity changes. +Following the rules above. It can be derived that the changes at 10 and 30 occur simultaneously and the changes in intensity at 20 and 40 occur simultaneously as well. Because of the positive asynchronous cross-peak at (10, 20), the changes at 10 and 30 (predominantly) occur before the intensity changes at 20 and 40. +In some cases the Noda rules cannot be so readily implied, predominately when spectral features are not caused by simple intensity variations. This may occur when band shifts occur, or when a very erratic intensity variation is present in a given frequency range. + +== See also == +Correlation spectroscopy +Fluorescence correlation spectroscopy +Two-dimensional infrared spectroscopy + +== References == \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Ultraviolet–visible_spectroscopy-0.md b/data/en.wikipedia.org/wiki/Ultraviolet–visible_spectroscopy-0.md new file mode 100644 index 000000000..87a5c250f --- /dev/null +++ b/data/en.wikipedia.org/wiki/Ultraviolet–visible_spectroscopy-0.md @@ -0,0 +1,28 @@ +--- +title: "Ultraviolet–visible spectroscopy" +chunk: 1/5 +source: "https://en.wikipedia.org/wiki/Ultraviolet–visible_spectroscopy" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:41.378064+00:00" +instance: "kb-cron" +--- + +Ultraviolet–visible spectrophotometry (UV–Vis or UV-VIS) refers to absorption spectroscopy or reflectance spectroscopy in part of the ultraviolet and the full, adjacent visible regions of the electromagnetic spectrum. Being relatively inexpensive and easily implemented, this methodology is widely used in diverse applied and fundamental applications. The only requirement is that the sample absorb in the UV–Vis region, i.e. be a chromophore. Absorption spectroscopy is complementary to fluorescence spectroscopy. Parameters of interest, besides the wavelength of measurement, are absorbance (A) or transmittance (%T) or reflectance (%R), and its change with time. +A UV–Vis spectrophotometer is an analytical instrument that measures the amount of ultraviolet (UV) and visible light that is absorbed by a sample. It is a widely used technique in chemistry, biochemistry, and other fields, to identify and quantify compounds in a variety of samples. +UV–Vis spectrophotometers work by passing a beam of light through the sample and measuring the amount of light that is absorbed at each wavelength. The amount of light absorbed is proportional to the concentration of the absorbing compound in the sample. + +== Optical transitions == +Most molecules and ions absorb energy in the ultraviolet or visible range, i.e., they are chromophores. The absorbed photon excites an electron in the chromophore to higher energy molecular orbitals, giving rise to an excited state. For organic chromophores, four possible types of transitions are assumed: π–π*, n–π*, σ–σ*, and n–σ*. Transition metal complexes are often colored (i.e., absorb visible light) owing to the presence of multiple electronic states associated with incompletely filled d orbitals. + +== Applications == + +UV–Vis can be used to monitor structural changes in DNA. +UV–Vis spectroscopy is routinely used in analytical chemistry for the quantitative determination of diverse analytes or sample, such as transition metal ions, highly conjugated organic compounds, and biological macromolecules. Spectroscopic analysis is commonly carried out in solutions but solids and gases may also be studied. + +Organic compounds, especially those with a high degree of conjugation, also absorb light in the UV or visible regions of the electromagnetic spectrum. The solvents for these determinations are often water for water-soluble compounds, or ethanol for organic-soluble compounds. (Organic solvents may have significant UV absorption; not all solvents are suitable for use in UV spectroscopy. Ethanol absorbs very weakly at most wavelengths.) Solvent polarity and pH can affect the absorption spectrum of an organic compound. Tyrosine, for example, increases in absorption maxima and molar extinction coefficient when pH increases from 6 to 13 or when solvent polarity decreases. +While charge transfer complexes also give rise to colors, the colors are often too intense to be used for quantitative measurement. +The Beer–Lambert law states that the absorbance of a solution is directly proportional to the concentration of the absorbing species in the solution and the path length. Thus, for a fixed path length, UV–Vis spectroscopy can be used to determine the concentration of the absorber in a solution. It is necessary to know how quickly the absorbance changes with concentration. This can be taken from references (tables of molar extinction coefficients), or more accurately, determined from a calibration curve. +A UV–Vis spectrophotometer may be used as a detector for HPLC. The presence of an analyte gives a response assumed to be proportional to the concentration. For accurate results, the instrument's response to the analyte in the unknown should be compared with the response to a standard; this is very similar to the use of calibration curves. The response (e.g., peak height) for a particular concentration is known as the response factor. +The wavelengths of absorption peaks can be correlated with the types of bonds in a given molecule and are valuable in determining the functional groups within a molecule. The Woodward–Fieser rules, for instance, are a set of empirical observations used to predict λmax, the wavelength of the most intense UV–Vis absorption, for conjugated organic compounds such as dienes and ketones. The spectrum alone is not, however, a specific test for any given sample. The nature of the solvent, the pH of the solution, temperature, high electrolyte concentrations, and the presence of interfering substances can influence the absorption spectrum. Experimental variations such as the slit width (effective bandwidth) of the spectrophotometer will also alter the spectrum. To apply UV–Vis spectroscopy to analysis, these variables must be controlled or accounted for in order to identify the substances present. +The method is most often used in a quantitative way to determine concentrations of an absorbing species in solution, using the Beer–Lambert law: \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Ultraviolet–visible_spectroscopy-1.md b/data/en.wikipedia.org/wiki/Ultraviolet–visible_spectroscopy-1.md new file mode 100644 index 000000000..d414a4f44 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Ultraviolet–visible_spectroscopy-1.md @@ -0,0 +1,117 @@ +--- +title: "Ultraviolet–visible spectroscopy" +chunk: 2/5 +source: "https://en.wikipedia.org/wiki/Ultraviolet–visible_spectroscopy" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:41.378064+00:00" +instance: "kb-cron" +--- + + + + + A + = + + log + + 10 + + + ⁡ + ( + + I + + 0 + + + + / + + I + ) + = + ε + c + L + + + {\displaystyle A=\log _{10}(I_{0}/I)=\varepsilon cL} + +, +where A is the measured absorbance (formally dimensionless but generally reported in absorbance units (AU)), + + + + + I + + 0 + + + + + {\displaystyle I_{0}} + + is the intensity of the incident light at a given wavelength, + + + + I + + + {\displaystyle I} + + is the transmitted intensity, L the path length through the sample, and c the concentration of the absorbing species. For each species and wavelength, ε is a constant known as the molar absorptivity or extinction coefficient. This constant is a fundamental molecular property in a given solvent, at a particular temperature and pressure, and has units of + + + + 1 + + / + + M + ∗ + c + m + + + {\displaystyle 1/M*cm} + +. +The absorbance and extinction ε are sometimes defined in terms of the natural logarithm instead of the base-10 logarithm. +The Beer–Lambert law is useful for characterizing many compounds but does not hold as a universal relationship for the concentration and absorption of all substances. A 2nd order polynomial relationship between absorption and concentration is sometimes encountered for very large, complex molecules such as organic dyes (xylenol orange or neutral red, for example). +UV–Vis spectroscopy is also used in the semiconductor industry to measure the thickness and optical properties of thin films on a wafer. UV–Vis spectrometers are used to measure the reflectance of light, and can be analyzed via the Forouhi–Bloomer dispersion equations to determine the index of refraction ( + + + + n + + + {\displaystyle n} + +) and the extinction coefficient ( + + + + k + + + {\displaystyle k} + +) of a given film across the measured spectral range. + +=== Practical considerations === +The Beer–Lambert law has implicit assumptions that must be met experimentally for it to apply; otherwise there is a possibility of deviations from the law. For instance, the chemical makeup and physical environment of the sample can alter its extinction coefficient. The chemical and physical conditions of a test sample therefore must match reference measurements for conclusions to be valid. Worldwide, pharmacopoeias such as the American (USP) and European (Ph. Eur.) pharmacopeias demand that spectrophotometers perform according to strict regulatory requirements encompassing factors such as stray light and wavelength accuracy. + +==== Spectral bandwidth ==== +Spectral bandwidth of a spectrophotometer is the range of wavelengths that the instrument transmits through a sample at a given time. It is determined by the light source, the monochromator, its physical slit-width and optical dispersion and the detector of the spectrophotometer. The spectral bandwidth affects the resolution and accuracy of the measurement. A narrower spectral bandwidth provides higher resolution and accuracy, but also requires more time and energy to scan the entire spectrum. A wider spectral bandwidth allows for faster and easier scanning, but may result in lower resolution and accuracy, especially for samples with overlapping absorption peaks. Therefore, choosing an appropriate spectral bandwidth is important for obtaining reliable and precise results. +It is important to have a monochromatic source of radiation for the light incident on the sample cell to enhance the linearity of the response. The closer the bandwidth is to be monochromatic (transmitting unit of wavelength) the more linear will be the response. The spectral bandwidth is measured as the number of wavelengths transmitted at half the maximum intensity of the light leaving the monochromator. +The best spectral bandwidth achievable is a specification of the UV spectrophotometer, and it characterizes how monochromatic the incident light can be. If this bandwidth is comparable to (or more than) the width of the absorption peak of the sample component, then the measured extinction coefficient will not be accurate. In reference measurements, the instrument bandwidth (bandwidth of the incident light) is kept below the width of the spectral peaks. When a test material is being measured, the bandwidth of the incident light should also be sufficiently narrow. Reducing the spectral bandwidth reduces the energy passed to the detector and will, therefore, require a longer measurement time to achieve the same signal to noise ratio. + +==== Wavelength error ==== +The extinction coefficient of an analyte in solution changes gradually with wavelength. A peak (a wavelength where the absorbance reaches a maximum) in the absorbance curve vs wavelength, i.e. the UV–VIS spectrum, is where the rate of change of absorbance with wavelength is the lowest. Therefore, quantitative measurements of a solute are usually conducted, using a wavelength around the absorbance peak, to minimize inaccuracies produced by errors in wavelength, due to the change of extinction coefficient with wavelength. + +==== Stray light ==== \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Ultraviolet–visible_spectroscopy-2.md b/data/en.wikipedia.org/wiki/Ultraviolet–visible_spectroscopy-2.md new file mode 100644 index 000000000..d822c9dcd --- /dev/null +++ b/data/en.wikipedia.org/wiki/Ultraviolet–visible_spectroscopy-2.md @@ -0,0 +1,99 @@ +--- +title: "Ultraviolet–visible spectroscopy" +chunk: 3/5 +source: "https://en.wikipedia.org/wiki/Ultraviolet–visible_spectroscopy" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:41.378064+00:00" +instance: "kb-cron" +--- + +Stray light in a UV spectrophotometer is any light that reaches its detector that is not of the wavelength selected by the monochromator. This can be caused, for instance, by scattering of light within the instrument, or by reflections from optical surfaces. +Stray light can cause significant errors in absorbance measurements, especially at high absorbances, because the stray light will be added to the signal detected by the detector, even though it is not part of the actually selected wavelength. The result is that the measured and reported absorbance will be lower than the actual absorbance of the sample. +The stray light is an important factor, as it determines the purity of the light used for the analysis. The most important factor affecting it is the stray light level of the monochromator. +Typically a detector used in a UV–VIS spectrophotometer is broadband; it responds to all the light that reaches it. If a significant amount of the light passed through the sample contains wavelengths that have much lower extinction coefficients than the nominal one, the instrument will report an incorrectly low absorbance. Any instrument will reach a point where an increase in sample concentration will not result in an increase in the reported absorbance, because the detector is simply responding to the stray light. In practice the concentration of the sample or the optical path length must be adjusted to place the unknown absorbance within a range that is valid for the instrument. Sometimes an empirical calibration function is developed, using known concentrations of the sample, to allow measurements into the region where the instrument is becoming non-linear. +As a rough guide, an instrument with a single monochromator would typically have a stray light level corresponding to about 3 Absorbance Units (AU), which would make measurements above about 2 AU problematic. A more complex instrument with a double monochromator would have a stray light level corresponding to about 6 AU, which would therefore allow measuring a much wider absorbance range. + +==== Deviations from the Beer–Lambert law ==== +At sufficiently high concentrations, the absorption bands will saturate and show absorption flattening. The absorption peak appears to flatten because close to 100% of the light is already being absorbed. The concentration at which this occurs depends on the particular compound being measured. One test that can be used to test for this effect is to vary the path length of the measurement. In the Beer–Lambert law, varying concentration and path length has an equivalent effect—diluting a solution by a factor of 10 has the same effect as shortening the path length by a factor of 10. If cells of different path lengths are available, testing if this relationship holds true is one way to judge if absorption flattening is occurring. +Solutions that are not homogeneous can show deviations from the Beer–Lambert law because of the phenomenon of absorption flattening. This can happen, for instance, where the absorbing substance is located within suspended particles. The deviations will be most noticeable under conditions of low concentration and high absorbance. The last reference describes a way to correct for this deviation. +Some solutions, like copper(II) chloride in water, change visually at a certain concentration because of changed conditions around the colored ion (the divalent copper ion). For copper(II) chloride it means a shift from blue to green, which would mean that monochromatic measurements would deviate from the Beer–Lambert law. + +==== Measurement uncertainty sources ==== +The above factors contribute to the measurement uncertainty of the results obtained with UV–Vis spectrophotometry. If UV–Vis spectrophotometry is used in quantitative chemical analysis then the results are additionally affected by uncertainty sources arising from the nature of the compounds and/or solutions that are measured. These include spectral interferences caused by absorption band overlap, fading of the color of the absorbing species (caused by decomposition or reaction) and possible composition mismatch between the sample and the calibration solution. + +== Ultraviolet–visible spectrophotometer == + +The instrument used in ultraviolet–visible spectroscopy is called a UV–Vis spectrophotometer. It measures the intensity of light after passing through a sample ( + + + + I + + + {\displaystyle I} + +), and compares it to the intensity of light before it passes through the sample ( + + + + + I + + o + + + + + {\displaystyle I_{o}} + +). The ratio + + + + I + + / + + + I + + o + + + + + {\displaystyle I/I_{o}} + + is called the transmittance, and is usually expressed as a percentage (%T). The absorbance, + + + + A + + + {\displaystyle A} + +, is based on the transmittance: + + + + + A + = + − + log + ⁡ + ( + % + T + + / + + 100 + % + ) + + + {\displaystyle A=-\log(\%T/100\%)} + \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Ultraviolet–visible_spectroscopy-3.md b/data/en.wikipedia.org/wiki/Ultraviolet–visible_spectroscopy-3.md new file mode 100644 index 000000000..ed4c1c830 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Ultraviolet–visible_spectroscopy-3.md @@ -0,0 +1,83 @@ +--- +title: "Ultraviolet–visible spectroscopy" +chunk: 4/5 +source: "https://en.wikipedia.org/wiki/Ultraviolet–visible_spectroscopy" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:41.378064+00:00" +instance: "kb-cron" +--- + +The UV–visible spectrophotometer can also be configured to measure reflectance. In this case, the spectrophotometer measures the intensity of light reflected from a sample ( + + + + I + + + {\displaystyle I} + +), and compares it to the intensity of light reflected from a reference material ( + + + + + I + + o + + + + + {\displaystyle I_{o}} + +) (such as a white tile). The ratio + + + + I + + / + + + I + + o + + + + + {\displaystyle I/I_{o}} + + is called the reflectance, and is usually expressed as a percentage (%R). +The basic parts of a spectrophotometer are a light source, a holder for the sample, a diffraction grating or a prism as a monochromator to separate the different wavelengths of light, and a detector. The radiation source is often a tungsten filament (300–2500 nm), a deuterium arc lamp, which is continuous over the ultraviolet region (190–400 nm), a xenon arc lamp, which is continuous from 160 to 2,000 nm; or more recently, light emitting diodes (LED) for the visible wavelengths. The detector is typically a photomultiplier tube, a photodiode, a photodiode array or a charge-coupled device (CCD). Single photodiode detectors and photomultiplier tubes are used with scanning monochromators, which filter the light so that only light of a single wavelength reaches the detector at one time. The scanning monochromator moves the diffraction grating to "step-through" each wavelength so that its intensity may be measured as a function of wavelength. Fixed monochromators are used with CCDs and photodiode arrays. As both of these devices consist of many detectors grouped into one or two dimensional arrays, they are able to collect light of different wavelengths on different pixels or groups of pixels simultaneously. + +A spectrophotometer can be either single beam or double beam. In a single beam instrument (such as the Spectronic 20), all of the light passes through the sample cell. + + + + + I + + o + + + + + {\displaystyle I_{o}} + + must be measured by removing the sample. This was the earliest design and is still in common use in both teaching and industrial labs. +In a double-beam instrument, the light is split into two beams before it reaches the sample. One beam is used as the reference; the other beam passes through the sample. The reference beam intensity is taken as 100% Transmission (or 0 Absorbance), and the measurement displayed is the ratio of the two beam intensities. Some double-beam instruments have two detectors (photodiodes), and the sample and reference beam are measured at the same time. In other instruments, the two beams pass through a beam chopper, which blocks one beam at a time. The detector alternates between measuring the sample beam and the reference beam in synchronism with the chopper. There may also be one or more dark intervals in the chopper cycle. In this case, the measured beam intensities may be corrected by subtracting the intensity measured in the dark interval before the ratio is taken. +In a single-beam instrument, the cuvette containing only a solvent has to be measured first. Mettler Toledo developed a single beam array spectrophotometer that allows fast and accurate measurements over the UV–Vis range. The light source consists of a Xenon flash lamp for the ultraviolet (UV) as well as for the visible (VIS) and near-infrared wavelength regions covering a spectral range from 190 up to 1100 nm. The lamp flashes are focused on a glass fiber which drives the beam of light onto a cuvette containing the sample solution. The beam passes through the sample and specific wavelengths are absorbed by the sample components. The remaining light is collected after the cuvette by a glass fiber and driven into a spectrograph. The spectrograph consists of a diffraction grating that separates the light into the different wavelengths, and a CCD sensor to record the data, respectively. The whole spectrum is thus simultaneously measured, allowing for fast recording. +Samples for UV–Vis spectrophotometry are most often liquids, although the absorbance of gases and even of solids can also be measured. Samples are typically placed in a transparent cell, known as a cuvette. Cuvettes are typically rectangular in shape, commonly with an internal width of 1 cm. (This width becomes the path length, + + + + L + + + {\displaystyle L} + +, in the Beer–Lambert law.) Test tubes can also be used as cuvettes in some instruments. The type of sample container used must allow radiation to pass over the spectral region of interest. The most widely applicable cuvettes are made of high-quality fused silica or quartz glass because these are transparent throughout the UV, visible and near infrared regions. Glass and plastic cuvettes are also common, although glass and most plastics absorb in the UV, which limits their usefulness to visible wavelengths. +Specialized instruments have also been made. These include attaching spectrophotometers to telescopes to measure the spectra of astronomical features. UV–visible microspectrophotometers consist of a UV–visible microscope integrated with a UV–visible spectrophotometer. +A complete spectrum of the absorption at all wavelengths of interest can often be produced directly by a more sophisticated spectrophotometer. In simpler instruments the absorption is determined one wavelength at a time and then compiled into a spectrum by the operator. By removing the concentration dependence, the extinction coefficient (ε) can be determined as a function of wavelength. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Ultraviolet–visible_spectroscopy-4.md b/data/en.wikipedia.org/wiki/Ultraviolet–visible_spectroscopy-4.md new file mode 100644 index 000000000..dbf3bf490 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Ultraviolet–visible_spectroscopy-4.md @@ -0,0 +1,33 @@ +--- +title: "Ultraviolet–visible spectroscopy" +chunk: 5/5 +source: "https://en.wikipedia.org/wiki/Ultraviolet–visible_spectroscopy" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:41.378064+00:00" +instance: "kb-cron" +--- + +== Microspectrophotometry == +UV–visible spectroscopy of microscopic samples is done by integrating an optical microscope with UV–visible optics, white light sources, a monochromator, and a sensitive detector such as a charge-coupled device (CCD) or photomultiplier tube (PMT). As only a single optical path is available, these are single beam instruments. Modern instruments are capable of measuring UV–visible spectra in both reflectance and transmission of micron-scale sampling areas. The advantages of using such instruments is that they are able to measure microscopic samples but are also able to measure the spectra of larger samples with high spatial resolution. As such, they are used in the forensic laboratory to analyze the dyes and pigments in individual textile fibers, microscopic paint chips and the color of glass fragments. They are also used in materials science and biological research and for determining the energy content of coal and petroleum source rock by measuring the vitrinite reflectance. Microspectrophotometers are used in the semiconductor and micro-optics industries for monitoring the thickness of thin films after they have been deposited. In the semiconductor industry, they are used because the critical dimensions of circuitry is microscopic. A typical test of a semiconductor wafer would entail the acquisition of spectra from many points on a patterned or unpatterned wafer. The thickness of the deposited films may be calculated from the interference pattern of the spectra. In addition, ultraviolet–visible spectrophotometry can be used to determine the thickness, along with the refractive index and extinction coefficient of thin films. A map of the film thickness across the entire wafer can then be generated and used for quality control purposes. + +== Additional applications == +UV–Vis can be applied to characterize the rate of a chemical reaction. Illustrative is the conversion of the yellow-orange and blue isomers of mercury dithizonate. This method of analysis relies on the fact that concentration is linearly proportional to concentration. In the same approach allows determination of equilibria between chromophores. +From the spectrum of burning gases, it is possible to determine a chemical composition of a fuel, temperature of gases, and air-fuel ratio. + +== See also == +Applied spectroscopy +Benesi–Hildebrand method +Color – Vis spectroscopy with the human eye +Charge modulation spectroscopy +DU spectrophotometer – first UV–Vis instrument +Fourier-transform spectroscopy +Infrared spectroscopy and Raman spectroscopy are other common spectroscopic techniques, usually used to obtain information about the structure of compounds or to identify compounds. Both are forms of vibrational spectroscopy. +Isosbestic point – a wavelength where absorption does not change as the reaction proceeds. Important in kinetics measurements as a control. +Near-infrared spectroscopy +Rotational spectroscopy +Slope spectroscopy +Ultraviolet–visible spectroscopy of stereoisomers +Vibrational spectroscopy + +== References == \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Weisz–Prater_criterion-0.md b/data/en.wikipedia.org/wiki/Weisz–Prater_criterion-0.md new file mode 100644 index 000000000..eac717008 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Weisz–Prater_criterion-0.md @@ -0,0 +1,299 @@ +--- +title: "Weisz–Prater criterion" +chunk: 1/1 +source: "https://en.wikipedia.org/wiki/Weisz–Prater_criterion" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:42.548723+00:00" +instance: "kb-cron" +--- + +The Weisz–Prater criterion is a method used to estimate the influence of pore diffusion on reaction rates in heterogeneous catalytic reactions. If the criterion is satisfied, pore diffusion limitations are negligible. The criterion is + + + + + + N + + W + − + P + + + = + + + + + + + R + + + + R + + p + + + 2 + + + + + + C + + s + + + + D + + e + f + f + + + + + + + ≤ + 3 + β + + + {\displaystyle N_{W-P}={\dfrac {{\mathfrak {R}}R_{p}^{2}}{C_{s}D_{eff}}}\leq 3\beta } + + +Where + + + + + + R + + + + + {\displaystyle {\mathfrak {R}}} + + is the reaction rate per volume of catalyst, + + + + + R + + p + + + + + {\displaystyle R_{p}} + + is the catalyst particle radius, + + + + + C + + s + + + + + {\displaystyle C_{s}} + + is the reactant concentration at the particle surface, and + + + + + D + + e + f + f + + + + + {\displaystyle D_{eff}} + + is the effective diffusivity. Diffusion is usually in the Knudsen regime when average pore radius is less than 100 nm. +For a given effectiveness factor, + + + + η + + + {\displaystyle \eta } + +, and reaction order, n, the quantity + + + + β + + + {\displaystyle \beta } + + is defined by the equation: + + + + + η + = + + + + 3 + + R + + p + + + 3 + + + + + + + ∫ + + 0 + + + + R + + p + + + + + [ + 1 + − + β + ( + 1 + − + r + + / + + + R + + p + + + + ) + + n + + + ] + + r + + 2 + + + + d + r + + + {\displaystyle \eta ={\dfrac {3}{R_{p}^{3}}}\int _{0}^{R_{p}}[1-\beta (1-r/R_{p})^{n}]r^{2}\ dr} + + +for small values of beta this can be approximated using the binomial theorem: + + + + + η + = + 1 + − + + + + + n + β + + 4 + + + + + + {\displaystyle \eta =1-{\dfrac {n\beta }{4}}} + + +Assuming + + + + η + = + 0.95 + + + {\displaystyle \eta =0.95} + + with a reaction order + + + + n + = + 2 + + + {\displaystyle n=2} + + gives value of + + + + β + + + {\displaystyle \beta } + + equal to 0.1. Therefore, for many conditions, if + + + + + N + + W + − + P + + + ≤ + 0.3 + + + {\displaystyle N_{W-P}\leq 0.3} + + then pore diffusion limitations can be excluded. + + +== References == \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/X-ray_crystal_truncation_rod-0.md b/data/en.wikipedia.org/wiki/X-ray_crystal_truncation_rod-0.md new file mode 100644 index 000000000..0710b535e --- /dev/null +++ b/data/en.wikipedia.org/wiki/X-ray_crystal_truncation_rod-0.md @@ -0,0 +1,331 @@ +--- +title: "X-ray crystal truncation rod" +chunk: 1/1 +source: "https://en.wikipedia.org/wiki/X-ray_crystal_truncation_rod" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:43.719814+00:00" +instance: "kb-cron" +--- + +X-ray crystal truncation rod scattering is a powerful method in surface science, based on analysis of surface X-ray diffraction (SXRD) patterns from a crystalline surface. +For an infinite crystal, the diffracted pattern is concentrated in Dirac delta function like Bragg peaks. Presence of crystalline surfaces results in additional structure along so-called truncation rods (linear regions in momentum space normal to the surface). Crystal Truncation Rod (CTR) measurements allow detailed determination of atomic structure at the surface, especially useful in cases of oxidation, epitaxial growth, and adsorption studies on crystalline surfaces. + + +== Theory == + +A particle incident on a crystalline surface with momentum + + + + + K + + 0 + + + + + {\displaystyle K_{0}} + + will undergo scattering through a momentum change of + + + + + Q + + + + {\displaystyle \mathbf {Q} } + +. If + + + + x + + + {\displaystyle x} + + and + + + + y + + + {\displaystyle y} + + represent directions in the plane of the surface and + + + + z + + + {\displaystyle z} + + is perpendicular to the surface, then the scattered intensity as a function of all possible values of + + + + + Q + + + + {\displaystyle \mathbf {Q} } + + is given by + +Where + + + + α + + + {\displaystyle \alpha } + + is the penetration coefficient, defined as the ratio of x-ray amplitudes scattered from successive planes of atoms in the crystal, and + + + + + a + + x + + + + + {\displaystyle a_{x}} + +, + + + + + a + + y + + + + + {\displaystyle a_{y}} + +, and + + + + c + + + {\displaystyle c} + + are the lattice spacings in the x, y, and z directions, respectively. +In the case of perfect absorption, + + + + α + = + 0 + + + {\displaystyle \alpha =0} + +, and the intensity becomes independent of + + + + + Q + + z + + + + + {\displaystyle Q_{z}} + +, with a maximum for any + + + + + + Q + + ∥ + + + + + + {\displaystyle \mathbf {Q_{\parallel }} } + + (the component of + + + + + Q + + + + {\displaystyle \mathbf {Q} } + + parallel to the crystal surface) that satisfies the 2D Laue condition in reciprocal space + +for integers + + + + h + + + {\displaystyle h} + + and + + + + k + + + {\displaystyle k} + +. This condition results in rods of intensity in reciprocal space, oriented perpendicular to the surface and passing through the reciprocal lattice points of the surface, as in Fig. 1. These rods are known as diffraction rods, or crystal truncation rods. + +When + + + + α + + + {\displaystyle \alpha } + + is allowed to vary from 0, the intensity along the rods varies according to Fig. 2. Note that in the limit as + + + + α + + + {\displaystyle \alpha } + + approaches unity, the x-rays are fully penetrating, and the scattered intensity approaches a periodic delta function, as in bulk diffraction. +This calculation has been done according to the kinematic (single-scattering) approximation. This has been shown to be accurate to within a factor of + + + + + 10 + + − + 7 + + + + + {\displaystyle 10^{-7}} + + of the peak intensity. Adding dynamical (multiple-scattering) considerations to the model can result in even more accurate predictions of CTR intensity. + + +== Instrumentation == +To obtain high-quality data in X-ray CTR measurements, it is desirable that the detected intensity be on the order of at least + + + + + 10 + + 9 + + + + + + + p + h + o + t + o + n + s + + + m + + m + + 2 + + + s + + + + + + + {\displaystyle 10^{9}{\tfrac {photons}{mm^{2}s}}} + +. To achieve this level of output, the X-ray source must typically be a synchrotron source. More traditional, inexpensive sources such as rotating anode sources provide 2-3 orders of magnitude less X-ray flux and are only suitable for studying high-atomic number materials, which return a higher diffracted intensity. The maximum diffracted intensity is roughly proportional to the square of the atomic number, + + + + Z + + + {\displaystyle Z} + +. Anode X-ray sources have been successfully used to study gold ( + + + + Z + = + 79 + + + {\displaystyle Z=79} + +) for example. +When doing X-ray measurements of a surface, the sample is held in Ultra-High Vacuum and the X-rays pass into and out of the UHV chamber through Beryllium windows. There are 2 approaches to chamber and diffractometer design that are in use. In the first method, the sample is fixed relative to the vacuum chamber, which is kept as small and light as possible and mounted on the diffractometer. In the second method, the sample is rotated within the chamber by bellows coupled to the outside. This approach avoids putting a large mechanical load on the diffractometer goniometer, making it easier to maintain fine angular resolution. One drawback of many configurations is that the sample must be moved in order to use other surface analysis methods such as LEED or AES, and after moving the sample back into the X-ray diffraction position, it must be realigned. In some setups, the sample chamber can be detached from the diffractometer without breaking vacuum, allowing for other users to have access. For examples of X-ray CTR diffractometer apparatus, see refs 15–17 in + + +== CTR Rodscans == +For a given incidence angle of X-rays onto a surface, only the intersections of the crystal truncation rods with the Ewald sphere can be observed. To measure the intensity along a CTR, the sample must be rotated in the X-ray beam so that the origin of the Ewald sphere is translated and the sphere intersects the rod at a different location in reciprocal space. Performing a rodscan in this way requires accurate coordinated motion of the sample and the detector along different axes. To achieve this motion, the sample and detector are mounted in an apparatus called a four-circle diffractometer. The sample is rotated in the plane bisecting the incoming and diffracted beam and the detector is moved into the position necessary to capture the diffracted CTR intensity. + + +== Surface Structures == + +Surface features in a material produce variations in the CTR intensity, which can be measured and used to evaluate what surface structures may be present. Two examples of this are shown in Fig. 3. In the case of a miscut at an angle + + + + α + + + {\displaystyle \alpha } + +, a second set of rods is produced in reciprocal space called superlattice rods, tilted from the regular lattice rods by the same angle, + + + + α + + + {\displaystyle \alpha } + +. The X-ray intensity is strongest in the region of intersection between the lattice rods (grey bars) and superlattice rods (black lines). In the case of ordered alternating steps, the CTR intensity is chopped into segments, as shown. In real materials, the occurrence of surface features will rarely be so regular, but these two examples show the way in which surface miscuts and roughness are manifested in the obtained diffraction patterns. + + +== References == \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/X-ray_fluorescence-0.md b/data/en.wikipedia.org/wiki/X-ray_fluorescence-0.md new file mode 100644 index 000000000..3adef84f9 --- /dev/null +++ b/data/en.wikipedia.org/wiki/X-ray_fluorescence-0.md @@ -0,0 +1,74 @@ +--- +title: "X-ray fluorescence" +chunk: 1/6 +source: "https://en.wikipedia.org/wiki/X-ray_fluorescence" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:44.876284+00:00" +instance: "kb-cron" +--- + +X-ray fluorescence (XRF) is the emission of characteristic "secondary" (or fluorescent) X-rays from a material that has been excited by being bombarded with high-energy X-rays or gamma rays. When a material is illuminated with high-energy X-rays, its atoms can become excited and emit their own unique, characteristic X-rays—a process similar to how a blacklight makes certain colors fluoresce. By measuring the energy and intensity of these emitted "secondary" X-rays, scientists can identify which elements are present in the sample and in what quantities. Thus, XRF is the basis of a non-destructive analytical technique widely used for elemental analysis and chemical analysis, particularly in the investigation of metals, glass, ceramics and building materials, and for research in geochemistry, forensic science, archaeology and art objects such as paintings. + +== Underlying physics == + +When materials are exposed to short-wavelength X-rays or to gamma rays, ionization of their component atoms may take place. Ionization consists of the ejection of one or more electrons from the atom, and may occur if the atom is exposed to radiation with an energy greater than its ionization energy. X-rays and gamma rays can be energetic enough to expel tightly held electrons from the inner orbitals of the atom. +The removal of an electron in this way makes the electronic structure of the atom unstable, and electrons in higher orbitals "fall" into the lower orbital to fill the hole left behind. In falling, energy is released in the form of a photon, the energy of which is equal to the energy difference of the two orbitals involved. Thus, the material emits radiation, which has energy characteristic of the atoms present. The term fluorescence is applied to phenomena in which the absorption of radiation of a specific energy results in the re-emission of radiation of a different energy (generally lower). + +=== Characteristic radiation === +Each element has electronic orbitals of characteristic energy. Following removal of an inner electron by an energetic photon provided by a primary radiation source, an electron from an outer shell drops into its place. There are a limited number of ways in which this can happen, as shown in Figure 1. The main transitions are given names: an L→K transition is traditionally called Kα, an M→K transition is called Kβ, an M→L transition is called Lα, and so on. Each of these transitions yields a fluorescent photon with a characteristic energy equal to the difference in energy of the initial and final orbital. The wavelength of this fluorescent radiation can be calculated from Planck's law: + + + + + λ + = + + + + h + c + + E + + + + + {\displaystyle \lambda ={\frac {hc}{E}}} + + +The fluorescent radiation can be analysed either by sorting the energies of the photons (energy-dispersive analysis) or by separating the wavelengths of the radiation (wavelength-dispersive analysis). Once sorted, the intensity of each characteristic radiation is directly related to the amount of each element in the material. This is the basis of a powerful technique in analytical chemistry. The typical form of the sharp fluorescent spectral lines obtained in the wavelength-dispersive method is illustrated in Figure 2 (see Moseley's law). + +=== Primary radiation sources === +In order to excite the atoms, a source of radiation is required, with sufficient energy to expel tightly held inner electrons. Conventional X-ray generators, based on electron bombardment of a heavy metal (i.e. tungsten or rhodium) target are most commonly used, because their output can readily be "tuned" for the application, and because higher power can be deployed relative to other techniques. X-ray generators in the range 20–60 kV are used, which allow excitation of a broad range of atoms. The continuous spectrum consists of "bremsstrahlung" radiation: radiation produced when high-energy electrons passing through the tube are progressively decelerated by the material of the tube anode (the "target"). A typical tube output spectrum is shown in Figure 3. +For portable XRF spectrometers, copper target is usually bombarded with high energy electrons, that are produced either by impact laser or by pyroelectric crystals. +Alternatively, gamma ray sources, based on radioactive isotopes (such as 109Cd, 57Co, 55Fe, 238Pu and 241Am) can be used without the need for an elaborate power supply, allowing for easier use in small, portable instruments. +When the energy source is a synchrotron or the X-rays are focused by an optic like a polycapillary, the X-ray beam can be very small and very intense. As a result, atomic information on the sub-micrometer scale can be obtained. + +=== Dispersion === +In energy-dispersive analysis, the fluorescent X-rays emitted by the material sample are directed into a solid-state detector which produces a "continuous" distribution of pulses, the voltages of which are proportional to the incoming photon energies. This signal is processed by a multichannel analyzer (MCA) which produces an accumulating digital spectrum that can be processed to obtain analytical data. +In wavelength-dispersive analysis, the fluorescent X-rays emitted by the sample are directed into a diffraction grating-based monochromator. The diffraction grating used is usually a single crystal. By varying the angle of incidence and take-off on the crystal, a small X-ray wavelength range can be selected. The wavelength obtained is given by Bragg's law: + + + + + n + ⋅ + λ + = + 2 + d + ⋅ + sin + ⁡ + ( + θ + ) + + + {\displaystyle n\cdot \lambda =2d\cdot \sin(\theta )} + + +where d is the spacing of atomic layers parallel to the crystal surface. + +=== Detection === \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/X-ray_fluorescence-1.md b/data/en.wikipedia.org/wiki/X-ray_fluorescence-1.md new file mode 100644 index 000000000..c91d9b7af --- /dev/null +++ b/data/en.wikipedia.org/wiki/X-ray_fluorescence-1.md @@ -0,0 +1,32 @@ +--- +title: "X-ray fluorescence" +chunk: 2/6 +source: "https://en.wikipedia.org/wiki/X-ray_fluorescence" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:44.876284+00:00" +instance: "kb-cron" +--- + +In energy-dispersive analysis, dispersion and detection are a single operation, as already mentioned above. Proportional counters or various types of solid-state detectors (PIN diode, Si(Li), Ge(Li), silicon drift detector SDD) are used. They all share the same detection principle: An incoming X-ray photon ionizes a large number of detector atoms with the amount of charge produced being proportional to the energy of the incoming photon. The charge is then collected and the process repeats itself for the next photon. Detector speed is obviously critical, as all charge carriers measured have to come from the same photon to measure the photon energy correctly (peak length discrimination is used to eliminate events that seem to have been produced by two X-ray photons arriving almost simultaneously). The spectrum is then built up by dividing the energy spectrum into discrete bins and counting the number of pulses registered within each energy bin. EDXRF detector types vary in resolution, speed and the means of cooling (a low number of free charge carriers is critical in the solid state detectors): proportional counters with resolutions of several hundred eV cover the low end of the performance spectrum, followed by PIN diode detectors, while the Si(Li), Ge(Li) and SDDs occupy the high end of the performance scale. +In wavelength-dispersive analysis, the single-wavelength radiation produced by the monochromator is passed into a chamber containing a gas that is ionized by the X-ray photons. A central electrode is charged at (typically) +1700 V with respect to the conducting chamber walls, and each photon triggers a pulse-like cascade of current across this field. The signal is amplified and transformed into an accumulating digital count. These counts are then processed to obtain analytical data. + +=== X-ray intensity === +The fluorescence process is inefficient, and the secondary radiation is much weaker than the primary beam. Furthermore, the secondary radiation from lighter elements is of relatively low energy (long wavelength) and has low penetrating power, and is severely attenuated if the beam passes through air for any distance. Because of this, for high-performance analysis, the path from tube to sample to detector is maintained under vacuum (around 10 Pa residual pressure). This means in practice that most of the working parts of the instrument have to be located in a large vacuum chamber. The problems of maintaining moving parts in vacuum, and of rapidly introducing and withdrawing the sample without losing vacuum, pose major challenges for the design of the instrument. For less demanding applications, or when the sample is damaged by a vacuum (e.g. a volatile sample), a helium-swept X-ray chamber can be substituted, with some loss of low-Z (Z = atomic number) intensities. + +== Chemical analysis == +The use of a primary X-ray beam to excite fluorescent radiation from the sample was first proposed by Glocker and Schreiber in 1928. Today, the method is used as a non-destructive analytical technique, and as a process control tool in many extractive and processing industries. In principle, the lightest element that can be analysed is beryllium (Z = 4), but due to instrumental limitations and low X-ray yields for the light elements, it is often difficult to quantify elements lighter than sodium (Z = 11), unless background corrections and very comprehensive inter-element corrections are made. + +== Energy dispersive spectrometry == + +In energy-dispersive spectrometers (EDX or EDS), the detector allows the determination of the energy of the photon when it is detected. Detectors historically have been based on silicon semiconductors, in the form of lithium-drifted silicon crystals, or high-purity silicon wafers. + +=== Si(Li) detectors === +These consist essentially of a 3–5 mm thick silicon junction type p-i-n diode (same as PIN diode) with a bias of −1000 V across it. The lithium-drifted centre part forms the non-conducting i-layer, where Li compensates the residual acceptors which would otherwise make the layer p-type. When an X-ray photon passes through, it causes a swarm of electron-hole pairs to form, and this causes a voltage pulse. To obtain sufficiently low conductivity, the detector must be maintained at low temperature, and liquid-nitrogen cooling must be used for the best resolution. With some loss of resolution, the much more convenient Peltier cooling can be employed. + +=== Wafer detectors === +More recently, high-purity silicon wafers with low conductivity have become routinely available. Cooled by the Peltier effect, this provides a cheap and convenient detector, although the liquid nitrogen cooled Si(Li) detector still has the best resolution (i.e. ability to distinguish different photon energies). + +=== Amplifiers === +The pulses generated by the detector are processed by pulse-shaping amplifiers. It takes time for the amplifier to shape the pulse for optimum resolution, and there is therefore a trade-off between resolution and count-rate: long processing time for good resolution results in "pulse pile-up" in which the pulses from successive photons overlap. Multi-photon events are, however, typically more drawn out in time (photons did not arrive exactly at the same time) than single photon events and pulse-length discrimination can thus be used to filter most of these out. Even so, a small number of pile-up peaks will remain and pile-up correction should be built into the software in applications that require trace analysis. To make the most efficient use of the detector, the tube current should be reduced to keep multi-photon events (before discrimination) at a reasonable level, e.g. 5–20%. +Therefore, managing this trade-off between speed and accuracy is a fundamental consideration in modern XRF instrument design, especially for high-throughput industrial applications. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/X-ray_fluorescence-2.md b/data/en.wikipedia.org/wiki/X-ray_fluorescence-2.md new file mode 100644 index 000000000..823fe339d --- /dev/null +++ b/data/en.wikipedia.org/wiki/X-ray_fluorescence-2.md @@ -0,0 +1,29 @@ +--- +title: "X-ray fluorescence" +chunk: 3/6 +source: "https://en.wikipedia.org/wiki/X-ray_fluorescence" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:44.876284+00:00" +instance: "kb-cron" +--- + +==== Processing ==== +Considerable computer power is dedicated to correcting for pulse-pile up and for extraction of data from poorly resolved spectra. These elaborate correction processes tend to be based on empirical relationships that may change with time, so that continuous vigilance is required in order to obtain chemical data of adequate precision. +Digital pulse processors are widely used in high performance nuclear instrumentation. They are able to effectively reduce pile-up and base line shifts, allowing for easier processing. A low pass filter is integrated, improving the signal to noise ratio. The digital pulse processor requires a significant amount of energy to run, but it provides precise results. + +==== Usage ==== +Energy-dispersive X-ray (EDX) spectrometers are different from wavelength dispersive X-ray (WDX) spectrometers in that they are smaller, simpler in design and have fewer engineered parts; however, the accuracy and resolution of EDX spectrometers are lower than for WDX. EDX spectrometers can also use miniature X-ray tubes or gamma sources, which makes them cheaper and allows miniaturization and portability. This type of instrument is commonly used for portable quality control screening applications, such as testing toys for lead (Pb) content, sorting scrap metals, and measuring the lead content of residential paint. On the other hand, the low resolution and problems with low count rate and long dead-time makes them inferior for high-precision analysis. They are, however, very effective for high-speed, multi-elemental analysis. Field portable XRF analysers currently on the market weigh less than 2 kg, and have limits of detection on the order of 2 parts per million of lead (Pb) in pure sand. Using a scanning electron microscope and using EDX, studies have been broadened to organic based samples such as biological samples and polymers. + +=== Wavelength dispersive spectrometry === +In wavelength dispersive spectrometers (WDX or WDS), the emitted photons are separated by diffraction on a single crystal before being detected. Although wavelength dispersive spectrometers are occasionally used to scan a wide range of wavelengths, producing a spectrum plot as in EDS, they are usually set up to make measurements only at the wavelength of the emission lines of the elements of interest. This is achieved in two different ways: + +"Simultaneous" spectrometers have a number of "channels" dedicated to analysis of a single element, each consisting of a fixed-geometry crystal monochromator, a detector, and processing electronics. This allows a number of elements to be measured simultaneously, and in the case of high-powered instruments, complete high-precision analyses can be obtained in under 30 s. Another advantage of this arrangement is that the fixed-geometry monochromators have no continuously moving parts, and so are very reliable. Reliability is important in production environments where instruments are expected to work without interruption for months at a time. Disadvantages of simultaneous spectrometers include relatively high cost for complex analyses, since each channel used is expensive. The number of elements that can be measured is limited to 15–20, because of space limitations on the number of monochromators that can be crowded around the fluorescing sample. The need to accommodate multiple monochromators means that a rather open arrangement around the sample is required, leading to relatively long tube-sample-crystal distances, which leads to lower detected intensities and more scattering. The instrument is inflexible, because if a new element is to be measured, a new measurement channel has to be bought and installed. +"Sequential" spectrometers have a single variable-geometry monochromator (but usually with an arrangement for selecting from a choice of crystals), a single detector assembly (but usually with more than one detector arranged in tandem), and a single electronic pack. The instrument is programmed to move through a sequence of wavelengths, in each case selecting the appropriate X-ray tube power, the appropriate crystal, and the appropriate detector arrangement. The length of the measurement program is essentially unlimited, so this arrangement is very flexible. Because there is only one monochromator, the tube-sample-crystal distances can be kept very short, resulting in minimal loss of detected intensity. The obvious disadvantage is relatively long analysis time, particularly when many elements are being analysed, not only because the elements are measured in sequence, but also because a certain amount of time is taken in readjusting the monochromator geometry between measurements. Furthermore, the frenzied activity of the monochromator during an analysis program is a challenge for mechanical reliability. However, modern sequential instruments can achieve reliability almost as good as that of simultaneous instruments, even in continuous-usage applications. + +==== Sample preparation ==== +In order to keep the geometry of the tube-sample-detector assembly constant, the sample is normally prepared as a flat disc, typically of diameter 20–50 mm. This is located at a standardized, small distance from the tube window. Because the X-ray intensity follows an inverse-square law, the tolerances for this placement and for the flatness of the surface must be very tight in order to maintain a repeatable X-ray flux. Ways of obtaining sample discs vary: metals may be machined to shape, minerals may be finely ground and pressed into a tablet, and glasses may be cast to the required shape. A further reason for obtaining a flat and representative sample surface is that the secondary X-rays from lighter elements often only emit from the top few micrometers of the sample. In order to further reduce the effect of surface irregularities, the sample is usually spun at 5–20 rpm. It is necessary to ensure that the sample is sufficiently thick to absorb the entire primary beam. For higher-Z materials, a few millimeters thickness is adequate, but for a light-element matrix such as coal, a thickness of 30–40 mm is needed. + +==== Monochromators ==== +The common feature of monochromators is the maintenance of a symmetrical geometry between the sample, the crystal and the detector. In this geometry the Bragg diffraction condition is obtained. +The X-ray emission lines are very narrow (see figure 2), so the angles must be defined with considerable precision. This is achieved in two ways: \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/X-ray_fluorescence-3.md b/data/en.wikipedia.org/wiki/X-ray_fluorescence-3.md new file mode 100644 index 000000000..a943d40c4 --- /dev/null +++ b/data/en.wikipedia.org/wiki/X-ray_fluorescence-3.md @@ -0,0 +1,172 @@ +--- +title: "X-ray fluorescence" +chunk: 4/6 +source: "https://en.wikipedia.org/wiki/X-ray_fluorescence" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:44.876284+00:00" +instance: "kb-cron" +--- + +===== Flat crystal with Söller collimators ===== +A Söller collimator is a stack of parallel metal plates, spaced a few tenths of a millimeter apart. To improve angular resolution, one must lengthen the collimator, and/or reduce the plate spacing. This arrangement has the advantage of simplicity and relatively low cost, but the collimators reduce intensity and increase scattering, and reduce the area of sample and crystal that can be "seen". The simplicity of the geometry is especially useful for variable-geometry monochromators. + +===== Curved crystal with slits ===== +The Rowland circle geometry ensures that the slits are both in focus, but in order for the Bragg condition to be met at all points, the crystal must first be bent to a radius of 2R (where R is the radius of the Rowland circle), then ground to a radius of R. This arrangement allows higher intensities (typically 8-fold) with higher resolution (typically 4-fold) and lower background. However, the mechanics of keeping Rowland circle geometry in a variable-angle monochromator is extremely difficult. In the case of fixed-angle monochromators (for use in simultaneous spectrometers), crystals bent to a logarithmic spiral shape give the best focusing performance. The manufacture of curved crystals to acceptable tolerances increases their price considerably. + +==== Crystal materials ==== +An intuitive understanding of X-ray diffraction can be obtained from the Bragg model of diffraction. In this model, a given reflection is associated with a set of evenly spaced sheets running through the crystal, usually passing through the centers of the atoms of the crystal lattice. +The orientation of a particular set of sheets is identified by its three Miller indices (h, k, l), and let their spacing be noted by d. +William Lawrence Bragg proposed a model in which the incoming X-rays are scattered specularly (mirror-like) from each plane; from that assumption, X-rays scattered from adjacent planes will combine constructively (constructive interference) when the angle θ between the plane and the X-ray results in a path-length difference that is an integer multiple n of the X-ray wavelength λ.(Fig.7) + + + + + 2 + d + sin + ⁡ + θ + = + n + λ + . + + + {\displaystyle 2d\sin \theta =n\lambda .} + + +The desirable characteristics of a diffraction crystal are: + +High diffraction intensity +High dispersion +Narrow diffracted peak width +High peak-to-background +Absence of interfering elements +Low thermal coefficient of expansion +Stability in air and on exposure to X-rays +Ready availability +Low cost +Crystals with simple structures tend to give the best diffraction performance. Crystals containing heavy atoms can diffract well, but also fluoresce more in the higher energy region, causing interference. Crystals that are water-soluble, volatile or organic tend to give poor stability. +Commonly used crystal materials include LiF (lithium fluoride), ADP (ammonium dihydrogen phosphate), Ge (germanium), Si (silicon), graphite, InSb (indium antimonide), PE (tetrakis-(hydroxymethyl)-methane, also known as pentaerythritol), KAP (potassium hydrogen phthalate), RbAP (rubidium hydrogen phthalate) and TlAP (thallium(I) hydrogen phthalate). In addition, there is an increasing use of "layered synthetic microstructures" (LSMs), which are "sandwich" structured materials comprising successive thick layers of low atomic number matrix, and monatomic layers of a heavy element. These can in principle be custom-manufactured to diffract any desired long wavelength, and are used extensively for elements in the range Li to Mg. +In scientific methods that use X-ray/neutron or electron diffraction the before mentioned planes of a diffraction can be doubled to display higher order reflections. The given planes, resulting from Miller indices, can be calculated for a single crystal. The resulting values for h, k and l are then called Laue indices. +So a single crystal can be variable in the way, that many reflection configurations of that crystal can be used to reflect different energy ranges. +The germanium (Ge111) crystal, for example, can also be used as a Ge333, Ge444 and more. +For that reason, the corresponding indices used for a particular experimental setup always get noted behind the crystal material (e.g. Ge111, Ge444). +The Ge222 configuration is forbidden due to diffraction rules stating that all allowed reflections must be with all odd or all even Miller indices that, combined, result in + + + + 4 + n + + + {\displaystyle 4n} + +, +where + + + + n + + + {\displaystyle n} + + is the order of reflection. + +==== Elemental analysis lines ==== +The spectral lines used for elemental analysis of chemicals are selected on the basis of intensity, accessibility by the instrument, and lack of line overlaps. The energies of the spectral lines are given by the Moseley law. Typical lines used, and their wavelengths and energies, are as follows: + +Other lines are often used, depending on the type of sample and equipment available. + +==== Structural analysis lines ==== + +X-ray diffraction (XRD) is still the most used method for structural analysis of crystallographic compounds. Yet, with increasing detail on the relation of + + + + K + β + + + {\displaystyle K\beta } + +-line spectra and the surrounding chemical environment of the ionized metal atom, measurements of the so-called valence-to-core (VtC) energy region become increasingly viable. +Scientists noted that after ionization of 3d-transition metal atom, the + + + + K + β + + + {\displaystyle K\beta } + +-line intensities and energies shift with oxidation state of the metal and with the species of ligand(s). Spin states in a compound tend to affect this kind of measurement. +This means, that by intense study of these spectral lines, one can obtain several crucial pieces of information from a sample. Especially, if there are references that have been studied in detail and can be used to make out differences. The information collected from this kind of measurement include: + +Oxidation state of the central metal atom in a compound (shifts of + + + + K + + β + + 1 + , + 3 + + + + + {\displaystyle K\beta _{1,3}} + +-mainline in low-spin complexes) +Spin states of transition metal complexes (general shape of + + + + K + + β + + 1 + , + 3 + + + + + {\displaystyle K\beta _{1,3}} + +- and + + + + K + + β + ′ + + + + {\displaystyle K\beta '} + +-mainlines) +Identity and orientation of ligands bonded to the central metal atom (from the + + + + K + + β + ″ + + + + {\displaystyle K\beta ''} + + satellite) +These measurements are mostly done at synchrotron facilities, although a number of so-called "in-lab"-spectrometers have been developed and used for pre-beamtime (time at a synchrotron) measurements. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/X-ray_fluorescence-4.md b/data/en.wikipedia.org/wiki/X-ray_fluorescence-4.md new file mode 100644 index 000000000..ff9b04830 --- /dev/null +++ b/data/en.wikipedia.org/wiki/X-ray_fluorescence-4.md @@ -0,0 +1,25 @@ +--- +title: "X-ray fluorescence" +chunk: 5/6 +source: "https://en.wikipedia.org/wiki/X-ray_fluorescence" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:44.876284+00:00" +instance: "kb-cron" +--- + +==== Detectors ==== +Detectors used for wavelength dispersive spectrometry need to have high pulse processing speeds in order to cope with the very high photon count rates that can be obtained. In addition, they need sufficient energy resolution to allow filtering-out of background noise and spurious photons from the primary beam or from crystal fluorescence. There are four common types of detector: + +gas flow proportional counters +sealed gas detectors +scintillation counters +semiconductor detectors + +Gas flow proportional counters are used mainly for detection of longer wavelengths. Gas flows through it continuously. Where there are multiple detectors, the gas is passed through them in series, then led to waste. The gas is usually 90% argon, 10% methane ("P10"), although the argon may be replaced with neon or helium where very long wavelengths (over 5 nm) are to be detected. The argon is ionized by incoming X-ray photons, and the electric field multiplies this charge into a measurable pulse. The methane suppresses the formation of fluorescent photons caused by recombination of the argon ions with stray electrons. The anode wire is typically tungsten or nichrome of 20–60 μm diameter. Since the pulse strength obtained is essentially proportional to the ratio of the detector chamber diameter to the wire diameter, a fine wire is needed, but it must also be strong enough to be maintained under tension so that it remains precisely straight and concentric with the detector. The window needs to be conductive, thin enough to transmit the X-rays effectively, but thick and strong enough to minimize diffusion of the detector gas into the high vacuum of the monochromator chamber. Materials often used are beryllium metal, aluminised PET film and aluminised polypropylene. Ultra-thin windows (down to 1 μm) for use with low-penetration long wavelengths are very expensive. The pulses are sorted electronically by "pulse height selection" in order to isolate those pulses deriving from the secondary X-ray photons being counted. +Sealed gas detectors are similar to the gas flow proportional counter, except that the gas does not flow through it. The gas is usually krypton or xenon at a few atmospheres pressure. They are applied usually to wavelengths in the 0.15–0.6 nm range. They are applicable in principle to longer wavelengths, but are limited by the problem of manufacturing a thin window capable of withstanding the high pressure difference. +Scintillation counters consist of a scintillating crystal (typically of sodium iodide doped with thallium) attached to a photomultiplier. The crystal produces a group of scintillations for each photon absorbed, the number being proportional to the photon energy. This translates into a pulse from the photomultiplier of voltage proportional to the photon energy. The crystal must be protected with a relatively thick aluminium/beryllium foil window, which limits the use of the detector to wavelengths below 0.25 nm. Scintillation counters are often connected in series with a gas flow proportional counter: the latter is provided with an outlet window opposite the inlet, to which the scintillation counter is attached. This arrangement is particularly used in sequential spectrometers. +Semiconductor detectors can be used in theory, and their applications are increasing as their technology improves, but historically their use for WDX has been restricted by their slow response (see EDX). + +==== Extracting analytical results ==== +At first sight, the translation of X-ray photon count-rates into elemental concentrations would appear to be straightforward: WDX separates the X-ray lines efficiently, and the rate of generation of secondary photons is proportional to the element concentration. However, the number of photons leaving the sample is also affected by the physical properties of the sample: so-called "matrix effects". These fall broadly into three categories: \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/X-ray_fluorescence-5.md b/data/en.wikipedia.org/wiki/X-ray_fluorescence-5.md new file mode 100644 index 000000000..6d08d6448 --- /dev/null +++ b/data/en.wikipedia.org/wiki/X-ray_fluorescence-5.md @@ -0,0 +1,53 @@ +--- +title: "X-ray fluorescence" +chunk: 6/6 +source: "https://en.wikipedia.org/wiki/X-ray_fluorescence" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:44.876284+00:00" +instance: "kb-cron" +--- + +X-ray absorption +X-ray enhancement +sample macroscopic effects +All elements absorb X-rays to some extent. Each element has a characteristic absorption spectrum which consists of a "saw-tooth" succession of fringes, each step-change of which has wavelength close to an emission line of the element. Absorption attenuates the secondary X-rays leaving the sample. For example, the mass absorption coefficient of silicon at the wavelength of the aluminium Kα line is 50 m2/kg, whereas that of iron is 377 m2/kg. This means that fluorescent X-rays generated by a given concentration of aluminium in a matrix of iron are absorbed about seven times more (that is 377/50) compared with the fluorescent X-rays generated by the same concentration of aluminium, but in a silicon matrix. That would lead to about one seventh of the count rate, once the X-rays are detected. Mass absorption coefficients are well known and can be calculated. However, to calculate the absorption for a multi-element sample, the composition must be known. For analysis of an unknown sample, an iterative procedure is therefore used. To derive the mass absorption accurately, data for the concentration of elements not measured by XRF may be needed, and various strategies are employed to estimate these. As an example, in cement analysis, the concentration of oxygen (which is not measured) is calculated by assuming that all other elements are present as standard oxides. +Enhancement occurs where the secondary X-rays emitted by a heavier element are sufficiently energetic to stimulate additional secondary emission from a lighter element. This phenomenon can also be modelled, and corrections can be made provided that the full matrix composition can be deduced. +Sample macroscopic effects consist of effects of inhomogeneities of the sample, and unrepresentative conditions at its surface. Samples are ideally homogeneous and isotropic, but they often deviate from this ideal. Mixtures of multiple crystalline components in mineral powders can result in absorption effects that deviate from those calculable from theory. When a powder is pressed into a tablet, the finer minerals concentrate at the surface. Spherical grains tend to migrate to the surface more than do angular grains. In machined metals, the softer components of an alloy tend to smear across the surface. Considerable care and ingenuity are required to minimize these effects. Because they are artifacts of the method of sample preparation, these effects can not be compensated by theoretical corrections, and must be "calibrated in". This means that the calibration materials and the unknowns must be compositionally and mechanically similar, and a given calibration is applicable only to a limited range of materials. Glasses most closely approach the ideal of homogeneity and isotropy, and for accurate work, minerals are usually prepared by dissolving them in a borate glass, and casting them into a flat disc or "bead". Prepared in this form, a virtually universal calibration is applicable. +Further corrections that are often employed include background correction and line overlap correction. The background signal in an XRF spectrum derives primarily from scattering of primary beam photons by the sample surface. Scattering varies with the sample mass absorption, being greatest when mean atomic number is low. When measuring trace amounts of an element, or when measuring on a variable light matrix, background correction becomes necessary. This is really only feasible on a sequential spectrometer. Line overlap is a common problem, bearing in mind that the spectrum of a complex mineral can contain several hundred measurable lines. Sometimes it can be overcome by measuring a less-intense, but overlap-free line, but in certain instances a correction is inevitable. For instance, the Kα is the only usable line for measuring sodium, and it overlaps the zinc Lβ (L2-M4) line. Thus zinc, if present, must be analyzed in order to properly correct the sodium value. + +== Other spectroscopic methods using the same principle == +It is also possible to create a characteristic secondary X-ray emission using other incident radiation to excite the sample: + +electron beam: electron microprobe; +ion beam: particle induced X-ray emission (PIXE). +When radiated by an X-ray beam, the sample also emits other radiations that can be used for analysis: + +electrons ejected by the photoelectric effect: X-ray photoelectron spectroscopy (XPS), also called electron spectroscopy for chemical analysis (ESCA) +The de-excitation also ejects Auger electrons, but Auger electron spectroscopy (AES) normally uses an electron beam as the probe. +Confocal microscopy X-ray fluorescence imaging is a newer technique that allows control over depth, in addition to horizontal and vertical aiming, for example, when analysing buried layers in a painting. + +== Instrument qualification == + +A 2022 review addresses the application of portable instrumentation from quality assurance/quality control perspectives. It provides a guide to the development of a set of Standard Operating Procedures if regulatory compliance guidelines are not available. + +== See also == +Emission spectroscopy – Frequencies of light emitted by atoms or chemical compoundsPages displaying short descriptions of redirect targets +List of materials analysis methods +Micro-X-ray fluorescence +Mössbauer effect – Resonant and recoil-free emission and absorption of gamma radiation by atomic nuclei, resonant fluorescence of gamma rays +X-ray fluorescence holography + +== Notes == + +== References == +Beckhoff, B., Kanngießer, B., Langhoff, N., Wedell, R., Wolff, H., Handbook of Practical X-Ray Fluorescence Analysis, Springer, 2006, ISBN 3-540-28603-9 +Bertin, E. P., Principles and Practice of X-ray Spectrometric Analysis, Kluwer Academic / Plenum Publishers, ISBN 0-306-30809-6 +Buhrke, V. E., Jenkins, R., Smith, D. K., A Practical Guide for the Preparation of Specimens for XRF and XRD Analysis, Wiley, 1998, ISBN 0-471-19458-1 +Jenkins, R., X-ray Fluorescence Spectrometry, Wiley, ISBN 0-471-29942-1 +Jenkins, R., De Vries, J. L., Practical X-ray Spectrometry, Springer-Verlag, 1973, ISBN 0-387-91029-8 +Jenkins, R., R.W. Gould, R. W., Gedcke, D., Quantitative X-ray Spectrometry, Marcel Dekker, ISBN 0-8247-9554-7 +Penner-Hahn, James E. (2013). "Chapter 2. Technologies for Detecting Metals in Single Cells. Section 4, Intrinsic X-Ray Fluorescence". In Banci, Lucia (ed.). Metallomics and the Cell. Metal Ions in Life Sciences. Vol. 12. Springer. pp. 15–40. doi:10.1007/978-94-007-5561-1_2. ISBN 978-94-007-5560-4. PMID 23595669.electronic-book ISBN 978-94-007-5561-1 ISSN 1559-0836electronic-ISSN 1868-0402 +Van Grieken, R. E., Markowicz, A. A., Handbook of X-Ray Spectrometry 2nd ed.; Marcel Dekker Inc.: New York, 2002; Vol. 29; ISBN 0-8247-0600-5 + +== External links == \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/X-ray_telescope-0.md b/data/en.wikipedia.org/wiki/X-ray_telescope-0.md new file mode 100644 index 000000000..29b7e46cc --- /dev/null +++ b/data/en.wikipedia.org/wiki/X-ray_telescope-0.md @@ -0,0 +1,37 @@ +--- +title: "X-ray telescope" +chunk: 1/3 +source: "https://en.wikipedia.org/wiki/X-ray_telescope" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:46.164760+00:00" +instance: "kb-cron" +--- + +An X-ray telescope (XRT) is a telescope that is designed to observe remote objects in the X-ray spectrum. X-rays are absorbed by the Earth's atmosphere, so instruments to detect X-rays must be taken to high altitude by balloons, sounding rockets, and satellites. +The basic elements of the telescope are the optics (focusing or collimating), that collects the radiation entering the telescope, and the detector, on which the radiation is collected and measured. A variety of different designs and technologies have been used for these elements. +Many X-ray telescopes on satellites are compounded of multiple small detector-telescope systems whose capabilities add up or complement each other, and additional fixed or removable elements (filters, spectrometers) that add functionalities to the instrument. + +== History of X-ray telescopes == + +X-ray telescopes were first used for astronomy to observe the Sun, which was the only source in the sky bright enough in X-rays for those early telescopes to detect. Because the Sun is so bright in X-rays, early X-ray telescopes could use a small focusing element and the X-rays would be detected with photographic film. The first X-ray picture of the Sun from a rocket-borne telescope was taken by John V. Lindsay of the NASA Goddard Space Flight Center and collaborators in 1963. The first orbiting X-ray telescope flew on Skylab in the early 1970s and recorded more than 35,000 full-disk images of the Sun over a 9-month period. +First specialised X-ray satellite, Uhuru, was launched by NASA in 1970. It detected 339 X-ray sources in its 2.5-year lifetime. +The Einstein Observatory, launched in 1978, was the first imaging X-ray observatory. It obtained high-resolution X-ray images in the energy range from 0.1 to 4 keV of stars of all types, supernova remnants, galaxies, and clusters of galaxies. Another large project was ROSAT (active from 1990 to 1999), which was a heavy X-ray space observatory with focusing X-ray optics, and European EXOSAT. +The Chandra X-ray Observatory was launched by NASA in 1999 and has operated for more than 25 years in a high elliptical orbit, returning thousands 0.5 arc-second images and high-resolution spectra of all kinds of astronomical objects in the energy range from 0.5 to 8.0 keV. Chandra's resolution is about 50 times superior to that of ROSAT. + +== Active X-ray observatory satellites == +Satellites in use today include ESA's XMM-Newton observatory (low to mid energy X-rays 0.1-15 keV), NASA's Swift observatory, Chandra observatory and IXPE telescope. JAXA has launched the XRISM telescope, while ISRO has launched Aditya-L1 and XPoSat. +The GOES 14 spacecraft carries on board a Solar X-ray Imager to monitor the Sun's X-rays for the early detection of solar flares, coronal mass ejections, and other phenomena that impact the geospace environment. It was launched into orbit on June 27, 2009, at 22:51 GMT from Space Launch Complex 37B at the Cape Canaveral Air Force Station. +The Chinese Hard X-ray Modulation Telescope was launched on June 15, 2017 to observe black holes, neutron stars, active galactic nuclei and other phenomena based on their X-ray and gamma-ray emissions. +The Lobster-Eye X-ray Satellite was launched on 25 July 2020 by CNSA making it is the first in-orbit telescope to utilize the lobster-eye imaging technology of ultra-large field of view imaging to search for dark matter signals in the x-ray energy range. Lobster Eye Imager for Astronomy was launched on 27 July 2022 as a technology demonstrator for Einstein Probe, launched on January 9, 2024, dedicated to time-domain high-energy astrophysics. The Space Variable Objects Monitor observatory launched on 22 June 2024 is directed towards studying the explosions of massive stars and analysis of gamma-ray bursts. +A soft X-ray solar imaging telescope is on board the GOES-13 weather satellite launched using a Delta IV from Cape Canaveral LC37B on May 24, 2006. However, there have been no GOES 13 SXI images since December 2006. +The Russian-German Spektr-RG carries the eROSITA telescope array as well as the ART-XC telescope. It was launched by Roscosmos on 13 July 2019 from Baikonur and began collecting data in October 2019. + +== Optics == + +The most common methods used in X-ray optics are grazing incidence mirrors and collimated apertures. Only three geometries that use grazing incidence reflection of X-rays to produce X-ray images are known: Wolter system, Kirkpatrick-Baez system, and lobster-eye optics. + +=== Focusing mirrors === + +A simple parabolic mirror was originally proposed in 1960 by Riccardo Giacconi and Bruno Rossi, the founders of extrasolar X-ray astronomy. This type of mirror is often used as the primary reflector in an optical telescope. However, images of off-axis objects would be severely blurred. The German physicist Hans Wolter showed in 1952 that the reflection off a combination of two elements, a paraboloid followed by a hyperboloid, would work far better for X-ray astronomy applications. Wolter described three different imaging configurations, the Types I, II, and III. The design most commonly used by X-ray astronomers is the Type I since it has the simplest mechanical configuration. In addition, the Type I design offers the possibility of nesting several telescopes inside one another, thereby increasing the useful reflecting area. The Wolter Type II is useful only as a narrow-field imager or as the optic for a dispersive spectrometer. The Wolter Type III has never been employed for X-ray astronomy. +With respect to collimated optics, focusing optics allow: \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/X-ray_telescope-1.md b/data/en.wikipedia.org/wiki/X-ray_telescope-1.md new file mode 100644 index 000000000..8400f57b3 --- /dev/null +++ b/data/en.wikipedia.org/wiki/X-ray_telescope-1.md @@ -0,0 +1,38 @@ +--- +title: "X-ray telescope" +chunk: 2/3 +source: "https://en.wikipedia.org/wiki/X-ray_telescope" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:46.164760+00:00" +instance: "kb-cron" +--- + +a high resolution imaging +a high telescope sensitivity: since radiation is focused on a small area, Signal-to-noise ratio is much higher for this kind of instruments. +The mirrors can be made of ceramic or metal foil coated with a thin layer of a reflective material (typically gold or iridium). Mirrors based on this construction work on the basis of total reflection of light at grazing incidence. +This technology is limited in energy range due to the fact that the critical angle for total reflection is inversely proportional to the X-ray photon energy, meaning that higher energy photons require smaller incidence angles and therefore longer telescope designs. The limit in the early 2000s with Chandra and XMM-Newton X-ray observatories was about 15 kilo-electronvolt (keV) light. Using new multi-layered coated mirrors, the X-ray mirror for the NuSTAR telescope pushed this up to 79 keV light. To reflect at this level, glass layers were multi-coated with tungsten (W)/silicon (Si) or platinum (Pt)/silicon carbide(SiC). + +=== Collimating optics === + +While earlier X-ray telescopes were using simple collimating techniques (e.g. rotating collimators, wire collimators), the technology most used in the present day employs coded aperture masks. This technique uses a flat aperture patterned grille in front of the detector. Compared to grazing incidence (focusing) telescopes, this design offers a larger field of view and can be employed at higher energies, making it more useful for imaging 'hard' (high energy) X-rays and gamma rays, where the photon energy exceeds 10-20 keV. On the other hand, coded aperture telescopes are less sensitive than grazing incidence techniques, meaning that the latter may be preferred for imaging lower enregy X-rays. +Example X-ray telescopes that use coded apertures include the Ultra-Fast Flash Observatory Pathfinder (launched 2016), the Cadmium Zinc Telluride Imager (CZTI) aboard Astrosat (launched 2015), and the ECLAIRs camera aboard Space Variable Objects Monitor (launced 2024). + +== Detection and imaging of X-rays == + +X-rays has a huge span in wavelength (~8 nm - 8 pm), frequency (~50 PHz - 50 EHz) and energy (~0.12 - 120 keV). In terms of temperature, 1 eV = 11,604 K. Thus X-rays (0.12 to 120 keV) correspond to 1.39 million to 1.39 billion K. From 10 to 0.1 nanometers (nm) (about 0.12 to 12 keV) they are classified as soft X-rays, and from 0.1 nm to 0.01 nm (about 12 to 120 keV) as hard X-rays. +Closer to the visible range of the electromagnetic spectrum is the ultraviolet. The draft ISO standard on determining solar irradiances (ISO-DIS-21348) describes the ultraviolet as ranging from ~10 nm to ~400 nm. That portion closest to X-rays is often referred to as the "extreme ultraviolet" (EUV or XUV). When an EUV photon is absorbed, photoelectrons and secondary electrons are generated by ionization, much like what happens when X-rays or electron beams are absorbed by matter. +The distinction between X-rays and gamma rays has changed in recent decades. Originally, the electromagnetic radiation emitted by X-ray tubes had a longer wavelength than the radiation emitted by radioactive nuclei (gamma rays). So older literature distinguished between X- and gamma radiation on the basis of wavelength, with radiation shorter than some arbitrary wavelength, such as 10−11 m, defined as gamma rays. However, as shorter wavelength continuous spectrum "X-ray" sources such as linear accelerators and longer wavelength "gamma ray" emitters were discovered, the wavelength bands largely overlapped. The two types of radiation are now usually distinguished by their origin: X-rays are emitted by electrons outside the nucleus, while gamma rays are emitted by the nucleus. +Although the more energetic X-rays, photons with an energy greater than 30 keV (4,800 aJ), can penetrate the Earth's atmosphere at least for distances of a few meters, the Earth's atmosphere is thick enough that virtually none are able to penetrate from outer space all the way to the Earth's surface. X-rays in the 0.5 to 5 keV (80 to 800 aJ) range, where most celestial sources give off the bulk of their energy, can be stopped by a few sheets of paper; 90% of the photons in a beam of 3 keV (480 aJ) X-rays are absorbed by traveling through just 10 cm of air. + +=== Proportional counters === + +A proportional counter is a type of gaseous ionization detector that counts particles of ionizing radiation and measures their energy. It works on the same principle as the Geiger-Müller counter, but uses a lower operating voltage. All X-ray proportional counters consist of a windowed gas cell. Often this cell is subdivided into a number of low- and high-electric field regions by some arrangement of electrodes. +Proportional counters were used on EXOSAT, on the US portion of the Apollo–Soyuz mission (July 1975), and on French TOURNESOL instrument. + +=== X-ray monitor === +Monitoring generally means to be aware of the state of a system. A device that displays or sends a signal for displaying X-ray output from an X-ray generating source so as to be aware of the state of the source is referred to as an X-ray monitor in space applications. +On Apollo 15 in orbit above the Moon, for example, an X-ray monitor was used to follow the possible variation in solar X-ray intensity and spectral shape while mapping the lunar surface with respect to its chemical composition due to the production of secondary X-rays. +The X-ray monitor of Solwind, designated NRL-608 or XMON, was a collaboration between the Naval Research Laboratory and Los Alamos National Laboratory. The monitor consisted of 2 collimated argon proportional counters. + +=== Scintillation detector === \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/X-ray_telescope-2.md b/data/en.wikipedia.org/wiki/X-ray_telescope-2.md new file mode 100644 index 000000000..bcb03a8c7 --- /dev/null +++ b/data/en.wikipedia.org/wiki/X-ray_telescope-2.md @@ -0,0 +1,40 @@ +--- +title: "X-ray telescope" +chunk: 3/3 +source: "https://en.wikipedia.org/wiki/X-ray_telescope" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T10:06:46.164760+00:00" +instance: "kb-cron" +--- + +A scintillator is a material which exhibits the property of luminescence when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, such as an X-ray photon, absorb its energy and scintillate, i.e. reemit the absorbed energy in the form of a small flash of light, typically in the visible range. +The scintillation X-ray detector were used on Vela 5A and its twin Vela 5B; the X-ray telescope onboard OSO 4 consisted of a single thin NaI(Tl) scintillation crystal plus phototube assembly enclosed in a CsI(Tl) anti-coincidence shield. OSO 5 carried a CsI crystal scintillator. The central crystal was 0.635 cm thick, had a sensitive area of 70 cm2, and was viewed from behind by a pair of photomultiplier tubes. +The PHEBUS had two independent detectors, each detector consisted of a bismuth germinate (BGO) crystal 78 mm in diameter by 120 mm thick. The KONUS-B instrument consisted of seven detectors distributed around the spacecraft that responded to photons of 10 keV to 8 MeV energy. They consisted of NaI(Tl) scintillator crystals 200 mm in diameter by 50 mm thick behind a Be entrance window. Kvant-1 carried the HEXE, or High Energy X-ray Experiment, which employed a phoswich of sodium iodide and caesium iodide. + +=== Modulation collimator === +In electronics, modulation is the process of varying one waveform in relation to another waveform. With a 'modulation collimator' the amplitude (intensity) of the incoming X-rays is reduced by the presence of two or more 'diffraction gratings' of parallel wires that block or greatly reduce that portion of the signal incident upon the wires. +An X-ray collimator is a device that filters a stream of X-rays so that only those traveling parallel to a specified direction are allowed through. +Minoru Oda, President of Tokyo University of Information Sciences, invented the modulation collimator, first used to identify the counterpart of Sco X-1 in 1966, which led to the most accurate positions for X-ray sources available, prior to the launch of X-ray imaging telescopes. +SAS 3 carried modulation collimators (2-11 keV) and Slat and Tube collimators (1 up to 60keV). +On board the Granat Observatory were four WATCH instruments that could localize bright sources in the 6 to 180 keV range to within 0.5° using a Rotation Modulation Collimator. Taken together, the instruments' three fields of view covered approximately 75% of the sky. +The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), Explorer 81, images solar flares from soft X-rays to gamma rays (~3 keV to ~20 MeV). Its imaging capability is based on a Fourier-transform technique using a set of 9 Rotational Modulation Collimators. + +=== X-ray spectrometer === +OSO 8 had on board a Graphite Crystal X-ray Spectrometer, with energy range of 2-8 keV, FOV 3°. +The Granat ART-S X-ray spectrometer covered the energy range 3 to 100 keV, FOV 2° × 2°. The instrument consisted of four detectors based on spectroscopic MWPCs, making an effective area of 2,400 cm2 at 10 keV and 800 cm2 at 100 keV. The time resolution was 200 microseconds. +The X-ray spectrometer aboard ISEE-3 was designed to study both solar flares and cosmic gamma-ray bursts over the energy range 5-228 keV. The experiment consisted of 2 cylindrical X-ray detectors: a Xenon filled proportional counter covering 5-14 keV, and a NaI(Tl) scintillator covering 12-1250 keV. + +=== CCDs === +Most existing X-ray telescopes use CCD detectors, similar to those in visible-light cameras. In visible-light, a single photon can produce a single electron of charge in a pixel, and an image is built up by accumulating many such charges from many photons during the exposure time. When an X-ray photon hits a CCD, it produces enough charge (hundreds to thousands of electrons, proportional to its energy) that the individual X-rays have their energies measured on read-out. + +=== Microcalorimeters === +Microcalorimeters can only detect X-rays one photon at a time (but can measure the energy of each). + +=== Transition edge sensors === +Transition-edge sensors are the next step in microcalorimetry. In essence they are super-conducting metals kept as close as possible to their transition temperature. This is the temperature at which these metals become super-conductors and their resistance drops to zero. These transition temperatures are usually just a few degrees above absolute zero (usually less than 10 K). + +== See also == +List of telescope types + +== References == \ No newline at end of file