# kb

id: stark-effect-20260505-1
file: data/en.wikipedia.org/wiki/Stark_effect-1.md
category: reference
title: Stark effect
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Stark_effect
date_saved: 2026-05-05T10:56:28.115020+00:00
instance: kb-cron
parent: stark-effect-20260505-0
summary:
where q {\displaystyle q} and μ {\displaystyle {\boldsymbol {\mu }}} are, respectively, the total charge (zero moment) and the dipole moment of the charge distribution. Classical macroscopic objects are usually neutral or quasi-neutral ( q = 0 {\displaystyle q=0} ), so the first, monopole, term in the expression above is identically zero. This is also the case for a neutral atom or molecule. However, for an ion this is no longer true. Nevertheless, it is often justified to omit it in this case, too. Indeed, the Stark effect is observed in spectral lines, which are emitted when an electron "jumps" between two bound states. Since such a transition only alters the internal degrees of freedom of the radiator but not its charge, the effects of the monopole interaction on the initial and final states exactly cancel each other. === Perturbation theory === Turning now to quantum mechanics an atom or a molecule can be thought of as a collection of point charges (electrons and nuclei), so that the second definition of the dipole applies. The interaction of atom or molecule with a uniform external field is described by the operator V i n t = − F ⋅ μ .


id: stark-effect-20260505-2
file: data/en.wikipedia.org/wiki/Stark_effect-2.md
category: reference
title: Stark effect
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Stark_effect
date_saved: 2026-05-05T10:56:28.115020+00:00
instance: kb-cron
parent: stark-effect-20260505-0
summary:
E k ( 2 ) = ∑ k ′ ≠ k ⟨ ψ k 0 | V i n t | ψ k ′ 0 ⟩ ⟨ ψ k ′ 0 | V i n t | ψ k 0 ⟩ E k ( 0 ) − E k ′ ( 0 ) ≡ − 1 2 ∑ i , j = 1 3 α i j F i F j {\displaystyle E_{k}^{(2)}=\sum _{k'\neq k}{\frac {\langle \psi _{k}^{0}|V_{\mathrm {int} }|\psi _{k^{\prime }}^{0}\rangle \langle \psi _{k'}^{0}|V_{\mathrm {int} }|\psi _{k}^{0}\rangle }{E_{k}^{(0)}-E_{k'}^{(0)}}}\equiv -{\frac {1}{2}}\sum _{i,j=1}^{3}\alpha _{ij}F_{i}F_{j}} with the components of the polarizability tensor α defined by α i j = − 2 ∑ k ′ ≠ k ⟨ ψ k 0 | μ i | ψ k ′ 0 ⟩ ⟨ ψ k ′ 0 | μ j | ψ k 0 ⟩ E k ( 0 ) − E k ′ ( 0 ) . {\displaystyle \alpha _{ij}=-2\sum _{k'\neq k}{\frac {\langle \psi _{k}^{0}|\mu _{i}|\psi _{k'}^{0}\rangle \langle \psi _{k'}^{0}|\mu _{j}|\psi _{k}^{0}\rangle }{E_{k}^{(0)}-E_{k'}^{(0)}}}.} The energy E(2) gives the quadratic Stark effect. Neglecting the hyperfine structure (which is often justified — unless extremely weak electric fields are considered), the polarizability tensor of atoms is isotropic,


id: stimulated-emission-20260505-0
file: data/en.wikipedia.org/wiki/Stimulated_emission-0.md
category: reference
title: Stimulated emission
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Stimulated_emission
date_saved: 2026-05-05T10:56:29.293495+00:00
instance: kb-cron
parent: stimulated-emission-20260505-0
summary:
Stimulated emission is the process by which an incoming photon of a specific frequency can interact with an excited atomic electron (or other excited molecular state), causing it to drop to a lower energy level. The liberated energy transfers to the electromagnetic field, creating a new photon with a frequency, polarization, and direction of travel that are all identical to the photons of the incident wave. This is in contrast to spontaneous emission, which occurs at a characteristic rate for each of the atoms/oscillators in the upper energy state regardless of the external electromagnetic field. According to the American Physical Society, the first person to correctly predict the phenomenon of stimulated emission was Albert Einstein in a series of papers starting in 1916, culminating in what is now called the Einstein B Coefficient. Einstein's work became the theoretical foundation of the maser and the laser. The process is identical in form to atomic absorption in which the energy of an absorbed photon causes an identical but opposite atomic transition: from the lower level to a higher energy level. In normal media at thermal equilibrium, absorption exceeds stimulated emission because there are more electrons in the lower energy states than in


id: stimulated-emission-20260505-1
file: data/en.wikipedia.org/wiki/Stimulated_emission-1.md
category: reference
title: Stimulated emission
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Stimulated_emission
date_saved: 2026-05-05T10:56:29.293495+00:00
instance: kb-cron
parent: stimulated-emission-20260505-0
summary:
where the proportionality constant B21 is known as the Einstein B coefficient for that particular transition, and ρ(ν) is the radiation density of the incident field at frequency ν. The rate of emission is thus proportional to the number of atoms in the excited state N2, and to the density of incident photons. At the same time, there will be a process of atomic absorption which removes energy from the field while raising electrons from the lower state to the upper state. Its rate is precisely the negative of the stimulated emission rate, ∂ N 2 ∂ t = − ∂ N 1 ∂ t = B 12 ρ ( ν ) N 1 . {\displaystyle {\frac {\partial N_{2}}{\partial t}}=-{\frac {\partial N_{1}}{\partial t}}=B_{12}\,\rho (\nu )\,N_{1}.} The rate of absorption is thus proportional to the number of atoms in the lower state, N1. The B coefficients can be calculated using dipole approximation and time dependent perturbation theory in quantum mechanics as: B a b = e 2 6 ϵ 0 ℏ 2 | ⟨ a | r → | b ⟩ | 2 {\displaystyle B_{ab}={\frac {e^{2}}{6\epsilon _{0}\hbar ^{2}}}|\langle a|{\vec {r}}|b\rangle |^{2}} where B corresponds to energy distribution in terms of frequency


id: stimulated-emission-20260505-2
file: data/en.wikipedia.org/wiki/Stimulated_emission-2.md
category: reference
title: Stimulated emission
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Stimulated_emission
date_saved: 2026-05-05T10:56:29.293495+00:00
instance: kb-cron
parent: stimulated-emission-20260505-0
summary:
== Optical amplification == Stimulated emission can provide a physical mechanism for optical amplification. If an external source of energy stimulates more than 50% of the atoms in the ground state to transition into the excited state, then what is called a population inversion is created. When light of the appropriate frequency passes through the inverted medium, the photons are either absorbed by the atoms that remain in the ground state or the photons stimulate the excited atoms to emit additional photons of the same frequency, phase, and direction. Since more atoms are in the excited state than in the ground state then an amplification of the input intensity results. The population inversion, in units of atoms per cubic metre, is Δ N 21 = N 2 − g 2 g 1 N 1 {\displaystyle \Delta N_{21}=N_{2}-{g_{2} \over g_{1}}N_{1}} where g1 and g2 are the degeneracies of energy levels 1 and 2, respectively. === Small signal gain equation === The intensity (in watts per square metre) of the stimulated emission is governed by the following differential equation: d I d z = σ 21 ( ν ) ⋅ Δ N 21 ⋅ I ( z ) {\displaystyle {dI \over dz}=\sigma


id: suction-20260505-0
file: data/en.wikipedia.org/wiki/Suction-0.md
category: reference
title: Suction
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Suction
date_saved: 2026-05-05T10:56:30.451492+00:00
instance: kb-cron
parent: suction-20260505-0
summary:
Suction is the day-to-day term for the movement of gases or liquids along a pressure gradient with the implication that the movement occurs because the lower pressure pulls the gas or liquid. However, the forces acting in this case do not originate from just the lower pressure side, but instead from the side of the higher pressure, as a reaction to the pressure difference. When the pressure in one part of a physical system is reduced relative to another, the fluid or gas in the higher pressure region will exert a force relative to the region of lowered pressure, referred to as pressure-gradient force. If all gas or fluid is removed the result is a perfect vacuum in which the pressure is zero. Hence, no negative pressure forces can be generated. Accordingly, from a physics point of view, the objects are not pulled but pushed. == Examples == Pressure reduction may be static, as in a piston and cylinder arrangement, or dynamic, as in the case of a vacuum cleaner when air flow results in a reduced pressure region. When animals breathe, the diaphragm and muscles around the rib cage cause a change of volume in the lungs. With increasing


id: superconductivity-20260505-0
file: data/en.wikipedia.org/wiki/Superconductivity-0.md
category: reference
title: Superconductivity
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Superconductivity
date_saved: 2026-05-05T10:56:31.658062+00:00
instance: kb-cron
parent: superconductivity-20260505-0
summary:
Superconductivity is a set of physical properties observed in superconductors: materials where electrical resistance vanishes and magnetic fields are expelled from the material. Unlike an ordinary metallic conductor, whose resistance decreases gradually as its temperature is lowered, even down to near absolute zero, a superconductor has a characteristic critical temperature below which the resistance drops abruptly to zero. An electric current through a loop of superconducting wire can persist indefinitely with no power source. The superconductivity phenomenon was discovered in 1911 by Dutch physicist Heike Kamerlingh Onnes. Like ferromagnetism and atomic spectral lines, superconductivity is a phenomenon which can only be explained by quantum mechanics. It is characterized by the Meissner effect, the complete cancellation of the magnetic field in the interior of the superconductor during its transitions into the superconducting state. The occurrence of the Meissner effect indicates that superconductivity cannot be understood simply as the idealization of perfect conductivity in classical physics. In 1986, it was discovered that some cuprate-perovskite ceramic materials have a critical temperature above 35 K (−238 °C). It was shortly found (by Ching-Wu Chu) that replacing the lanthanum with yttrium, i.e. making YBCO, raised the critical temperature to 92 K (−181 °C), which was


id: superconductivity-20260505-1
file: data/en.wikipedia.org/wiki/Superconductivity-1.md
category: reference
title: Superconductivity
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Superconductivity
date_saved: 2026-05-05T10:56:31.658062+00:00
instance: kb-cron
parent: superconductivity-20260505-0
summary:
=== Niobium === The first practical application of superconductivity was developed in 1954 with Dudley Allen Buck's invention of the cryotron. Two superconductors with greatly different values of the critical magnetic field are combined to produce a fast, simple switch for computer elements. Soon after discovering superconductivity in 1911, Kamerlingh Onnes attempted to make an electromagnet with superconducting windings but found that relatively low magnetic fields destroyed superconductivity in the materials he investigated. Much later, in 1955, G. B. Yntema succeeded in constructing a small 0.7-tesla iron-core electromagnet with superconducting niobium wire windings. Then, in 1961, J. E. Kunzler, E. Buehler, F. S. L. Hsu, and J. H. Wernick made the startling discovery that, at 4.2 kelvin, niobium–tin, a compound consisting of three parts niobium and one part tin, was capable of supporting a current density of more than 100,000 amperes per square centimeter in a magnetic field of 8.8 tesla. The alloy was brittle and difficult to fabricate, but niobium–tin proved useful for generating magnetic fields as high as 20 tesla. In 1962, T. G. Berlincourt and R. R. Hake discovered that more ductile alloys of niobium and titanium are suitable for applications up to 10 tesla. Commercial production


id: superconductivity-20260505-2
file: data/en.wikipedia.org/wiki/Superconductivity-2.md
category: reference
title: Superconductivity
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Superconductivity
date_saved: 2026-05-05T10:56:31.658062+00:00
instance: kb-cron
parent: superconductivity-20260505-0
summary:
=== Theory of operation === A superconductor is conventional if it is driven by electron–phonon interaction and explained by the BCS theory or its extension, the Eliashberg theory. Otherwise, it is unconventional. Alternatively, a superconductor is called unconventional if the superconducting order parameter transforms according to a non-trivial irreducible representation of the system's point group or space group. === Critical temperature === A superconductor is generally considered high-temperature if it reaches a superconducting state above a temperature of 30 K (−243.15 °C); as in the initial discovery by Georg Bednorz and K. Alex Müller. It may also reference materials that transition to superconductivity when cooled using liquid nitrogen – that is, at only Tc > 77 K, although this is generally used only to emphasize that liquid nitrogen coolant is sufficient. Low temperature superconductors refer to materials with a critical temperature below 30 K, and are cooled mainly by liquid helium (Tc > 4.2 K). One exception to this rule is the iron pnictide group of superconductors that display behaviour and properties typical of high-temperature superconductors, yet some of the group have critical temperatures below 30 K. === Material === Superconductor material classes include chemical elements (e.g. mercury or lead),


id: superconductivity-20260505-3
file: data/en.wikipedia.org/wiki/Superconductivity-3.md
category: reference
title: Superconductivity
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Superconductivity
date_saved: 2026-05-05T10:56:31.658062+00:00
instance: kb-cron
parent: superconductivity-20260505-0
summary:
In superconducting materials, the characteristics of superconductivity appear when the temperature T is lowered below a critical temperature Tc. The value of this critical temperature varies from material to material. Conventional superconductors usually have critical temperatures ranging from around 20 K to less than 1 K. Solid mercury, for example, has a critical temperature of 4.2 K. As of 2015, the highest critical temperature found for a conventional superconductor is 203 K for H2S, although high pressures of approximately 90 gigapascals were required. Cuprate superconductors can have much higher critical temperatures: YBa2Cu3O7, one of the first cuprate superconductors to be discovered, has a critical temperature above 90 K, and mercury-based cuprates have been found with critical temperatures in excess of 130 K. The basic physical mechanism responsible for the high critical temperature is not yet clear. However, it is clear that a two-electron pairing is involved, although the nature of the pairing ( s {\displaystyle s} wave vs. d {\displaystyle d} wave) remains controversial. Similarly, at a fixed temperature below the critical temperature, superconducting materials cease to superconduct when an external magnetic field is applied which is greater than the critical magnetic field. This is because the Gibbs free energy


id: superconductivity-20260505-4
file: data/en.wikipedia.org/wiki/Superconductivity-4.md
category: reference
title: Superconductivity
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Superconductivity
date_saved: 2026-05-05T10:56:31.658062+00:00
instance: kb-cron
parent: superconductivity-20260505-0
summary:
When a superconductor is placed in a weak external magnetic field Ba=Ha, and cooled below its transition temperature, the magnetic field is ejected. The Meissner effect does not cause the field to be completely ejected but instead, the field penetrates the superconductor but only to a very small distance, characterized by a parameter λ, called the London penetration depth, decaying exponentially to zero within the bulk of the material. The Meissner effect is a defining characteristic of superconductivity. For most superconductors, the London penetration depth is on the order of 100 nm. The Meissner effect is sometimes confused with the kind of diamagnetism one would expect in a perfect electrical conductor: according to Lenz's law, when a changing magnetic field is applied to a conductor, it will induce an electric current in the conductor that creates an opposing magnetic field. In a perfect conductor, an arbitrarily large current can be induced, and the resulting magnetic field exactly cancels the applied field. The Meissner effect is distinct from this – it is the spontaneous expulsion that occurs during transition to superconductivity. Suppose we have a material in its normal state, containing a constant internal magnetic field. When the material is cooled


id: superconductivity-20260505-5
file: data/en.wikipedia.org/wiki/Superconductivity-5.md
category: reference
title: Superconductivity
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Superconductivity
date_saved: 2026-05-05T10:56:31.658062+00:00
instance: kb-cron
parent: superconductivity-20260505-0
summary:
Superconductors are promising candidate materials for devising fundamental circuit elements of electronic, spintronic, and quantum technologies. One such example is a superconducting diode, in which supercurrent flows along one direction only, that promise dissipationless superconducting and semiconducting-superconducting hybrid technologies. Superconducting magnets are some of the most powerful electromagnets known. They are used in MRI/NMR machines, mass spectrometers, the beam-steering magnets used in particle accelerators and plasma confining magnets in some tokamaks. They can also be used for magnetic separation, where weakly magnetic particles are extracted from a background of less or non-magnetic particles, as in the pigment industries. They can also be used in large wind turbines to overcome the restrictions imposed by high electrical currents, with an industrial grade 3.6 megawatt superconducting windmill generator having been tested successfully in Denmark. In the 1950s and 1960s, superconductors were used to build experimental digital computers using cryotron switches. More recently, superconductors have been used to make digital circuits based on rapid single flux quantum technology and RF and microwave filters for mobile phone base stations. Superconductors are used to build Josephson junctions which are the building blocks of SQUIDs (superconducting quantum interference devices), the most sensitive magnetometers known. SQUIDs are used


id: superfluidity-20260505-0
file: data/en.wikipedia.org/wiki/Superfluidity-0.md
category: reference
title: Superfluidity
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Superfluidity
date_saved: 2026-05-05T10:56:32.870694+00:00
instance: kb-cron
parent: superfluidity-20260505-0
summary:
Superfluidity is the characteristic property of a fluid with zero viscosity which therefore flows without any loss of kinetic energy. When stirred, a superfluid forms vortices that continue to rotate indefinitely. Superfluidity occurs in two isotopes of helium (helium-3 and helium-4) when they are liquefied by cooling to cryogenic temperatures. It is also a property of various other exotic states of matter theorized to exist in astrophysics, high-energy physics, and theories of quantum gravity. The semi-phenomenological theory of superfluidity was developed by Soviet theoretical physicists Lev Landau and Isaak Khalatnikov. Superfluidity often co-occurs with Bose–Einstein condensation (BEC), but neither phenomenon is directly related to the other; not all Bose–Einstein condensates can be regarded as superfluids, and not all superfluids are Bose–Einstein condensates. Even when superfluidity and condensation co-occur, their magnitudes are not linked: at low temperature, liquid helium has a large superfluid fraction but a low condensate fraction; while a weakly interacting BEC, with almost unity condensate fraction, can display a vanishing superfluid fraction. Superfluids have some potential practical uses, such as dissolving substances in a quantum solvent. == Superfluidity of liquid helium == Superfluidity was discovered in helium-4 by Pyotr Kapitsa and independently by John F. Allen and Don


id: thermo-dielectric-effect-20260505-0
file: data/en.wikipedia.org/wiki/Thermo-dielectric_effect-0.md
category: reference
title: Thermo-dielectric effect
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thermo-dielectric_effect
date_saved: 2026-05-05T10:56:34.048783+00:00
instance: kb-cron
parent: thermo-dielectric-effect-20260505-0
summary:
The thermo-dielectric effect is the production of electric currents and charge separation during phase transition. This interesting effect was discovered by Joaquim da Costa Ribeiro in 1944. The Brazilian physicist observed that solidification and melting of many dielectrics are accompanied by charge separation. A thermo-dielectric effect was demonstrated with carnauba wax, naphthalene and paraffin. Charge separation in ice was also expected. This effect was observed during water freezing period, electrical storm effects can be caused by this strange phenomenon. Effect was measured by many researches - Bernhard Gross, Armando Dias Tavares, Sergio Mascarenhas etc. César Lattes (co-discoverer of the pion) supposed that this was the only effect ever to be discovered entirely in Brazil. == Further reading == Gross, B. (1954). "Theory of Thermodielectric effect". Physical Review. 94 (6): 1545–1551. Bibcode:1954PhRv...94.1545G. doi:10.1103/PhysRev.94.1545. Saldaña, Juan José (2006). Science in Latin America: a history. University of Texas Press. ISBN 978-0-292-71271-3. == External links == Thermodielectric effect measurement


id: thermoelectric-effect-20260505-0
file: data/en.wikipedia.org/wiki/Thermoelectric_effect-0.md
category: reference
title: Thermoelectric effect
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thermoelectric_effect
date_saved: 2026-05-05T10:56:35.204054+00:00
instance: kb-cron
parent: thermoelectric-effect-20260505-0
summary:
The thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice versa via a thermocouple. A thermoelectric device creates a voltage when there is a different temperature on each side. Conversely, when a voltage is applied to it, heat is transferred from one side to the other, creating a temperature difference. This effect can be used to generate electricity, measure temperature or change the temperature of objects. Because the direction of heating and cooling is affected by the applied voltage, thermoelectric devices can be used as temperature controllers. The term "thermoelectric effect" encompasses three separately identified effects: the Seebeck effect (temperature differences cause electromotive forces), the Peltier effect (thermocouples create temperature differences), and the Thomson effect (the Seebeck coefficient varies with temperature). The Seebeck and Peltier effects are different manifestations of the same physical process; textbooks may refer to this process as the Peltier–Seebeck effect (the separation derives from the independent discoveries by Jean Charles Athanase Peltier and Thomas Johann Seebeck). The Thomson effect is an extension of the Peltier–Seebeck model and is credited to Lord Kelvin. Joule heating, the heat that is generated whenever a current is passed through a conductive material, is not generally


id: thermoelectric-effect-20260505-1
file: data/en.wikipedia.org/wiki/Thermoelectric_effect-1.md
category: reference
title: Thermoelectric effect
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thermoelectric_effect
date_saved: 2026-05-05T10:56:35.204054+00:00
instance: kb-cron
parent: thermoelectric-effect-20260505-0
summary:
=== Applications === In practice, thermoelectric effects are essentially unobservable for a localized hot or cold spot in a single homogeneous conducting material, since the overall EMFs from the increasing and decreasing temperature gradients will perfectly cancel out. Attaching an electrode to the hotspot in an attempt to measure the locally shifted voltage will only partly succeed: It means another temperature gradient will appear inside of the electrode, so the overall EMF will depend on the difference in Seebeck coefficients between the electrode and the conductor it is attached to. Thermocouples involve two wires, each of a different material, that are electrically joined in a region of unknown temperature. The loose ends are measured in an open-circuit state (without any current, J = 0 {\displaystyle \mathbf {J} =0} ). Although the materials' Seebeck coefficients S {\displaystyle S} are nonlinearly temperature dependent and different for the two materials, the open-circuit condition means that ∇ V = − S ∇ T {\displaystyle \nabla V=-S\nabla T} everywhere. Therefore (see the thermocouple article for more details) the voltage measured at the loose ends of the wires is directly dependent on the unknown temperature, and yet totally independent of other details such as the exact


id: thermoelectric-effect-20260505-2
file: data/en.wikipedia.org/wiki/Thermoelectric_effect-2.md
category: reference
title: Thermoelectric effect
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thermoelectric_effect
date_saved: 2026-05-05T10:56:35.204054+00:00
instance: kb-cron
parent: thermoelectric-effect-20260505-0
summary:
== Thomson effect == For certain materials, the Seebeck coefficient is not constant in temperature, and so a spatial gradient in temperature can result in a gradient in the Seebeck coefficient. If a current is driven through this gradient, then a continuous version of the Peltier effect will occur. This Thomson effect was predicted and later observed in 1851 by Lord Kelvin (William Thomson). It describes the heating or cooling of a current-carrying conductor with a temperature gradient. If a current density J {\displaystyle \mathbf {J} } is passed through a homogeneous conductor, the Thomson effect predicts a heat production rate per unit volume. q ˙ = − K J ⋅ ∇ T , {\displaystyle {\dot {q}}=-{\mathcal {K}}\mathbf {J} \cdot \nabla T,} where ∇ T {\displaystyle \nabla T} is the temperature gradient, and K {\displaystyle {\mathcal {K}}} is the Thomson coefficient. The Thomson effect is a manifestation of the direction of flow of electrical carriers with respect to a temperature gradient within a conductor. These absorb energy (heat) flowing in a direction opposite to a thermal gradient, increasing their potential energy, and, when flowing in the same direction as a thermal gradient, they liberate heat, decreasing their potential energy. The


id: thermoelectric-effect-20260505-3
file: data/en.wikipedia.org/wiki/Thermoelectric_effect-3.md
category: reference
title: Thermoelectric effect
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thermoelectric_effect
date_saved: 2026-05-05T10:56:35.204054+00:00
instance: kb-cron
parent: thermoelectric-effect-20260505-0
summary:
This relation expresses a subtle and fundamental connection between the Peltier and Seebeck effects. It was not satisfactorily proven until the advent of the Onsager relations, and it is worth noting that this second Thomson relation is only guaranteed for a time-reversal symmetric material; if the material is placed in a magnetic field or is itself magnetically ordered (ferromagnetic, antiferromagnetic, etc.), then the second Thomson relation does not take the simple form shown here. Now, using the second relation, the first Thomson relation becomes K = T d S d T {\displaystyle {\mathcal {K}}=T{\tfrac {dS}{dT}}} The Thomson coefficient is unique among the three main thermoelectric coefficients because it is the only one directly measurable for individual materials. The Peltier and Seebeck coefficients can only be easily determined for pairs of materials; hence, it is difficult to find values of absolute Seebeck or Peltier coefficients for an individual material. If the Thomson coefficient of a material is measured over a wide temperature range, it can be integrated using the Thomson relations to determine the absolute values for the Peltier and Seebeck coefficients. This needs to be done only for one material, since the other values can be determined by measuring pairwise


id: time-20260505-0
file: data/en.wikipedia.org/wiki/Time-0.md
category: reference
title: Time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Time
date_saved: 2026-05-05T10:56:36.398112+00:00
instance: kb-cron
parent: time-20260505-0
summary:
Time is the continuous progression of existence that occurs in an apparently irreversible succession from the past, through the present, and into the future. Time dictates all forms of action, age, and causality, being a component quantity of various measurements used to sequence events, to compare the duration of events (or the intervals between them), and to quantify rates of change of quantities in material reality or in the conscious experience. Time is often referred to as a fourth dimension, along with three spatial dimensions. Time is primarily measured in linear spans or periods, ordered from shortest to longest. Practical, human-scale measurements of time are performed using clocks and calendars, reflecting a 24-hour day collected into a 365-day year linked to the astronomical motion of the Earth. Scientific measurements of time instead vary from Planck time at the shortest to billions of years at the longest. Measurable time is believed to have effectively begun with the Big Bang 13.8 billion years ago, encompassed by the chronology of the universe. Modern physics understands time to be inextricable from space within the concept of spacetime described by general relativity. Time can therefore be dilated by velocity and matter to pass faster or


id: time-20260505-1
file: data/en.wikipedia.org/wiki/Time-1.md
category: reference
title: Time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Time
date_saved: 2026-05-05T10:56:36.398112+00:00
instance: kb-cron
parent: time-20260505-0
summary:
Artifacts from the Paleolithic suggest that the moon was being used to reckon time by at least 6,000 years ago. Lunar calendars were among the first to appear, with years of either 12 or 13 lunar months (either 354 or 384 days). Without intercalation to add days or months to some years, seasons quickly drift in a calendar based solely on twelve lunar months. Lunisolar calendars have a thirteenth month added to some years to make up for the difference between a full year (now known to be about 365.24 days) and a year of just twelve lunar months. The numbers twelve and thirteen came to feature prominently in many cultures, at least partly due to this relationship of months to years. Other early forms of calendars originated in Mesoamerica, particularly in ancient Mayan civilization, in which they developed the Maya calendar, consisting of multiple interrelated calendars. These calendars were religiously and astronomically based; the Haab' calendar has 18 months in a year and 20 days in a month, plus five epagomenal days at the end of the year. In conjunction, the Maya also used a 260-day sacred calendar called the Tzolk'in. The reforms of Julius Caesar in 45 BC


id: time-20260505-2
file: data/en.wikipedia.org/wiki/Time-2.md
category: reference
title: Time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Time
date_saved: 2026-05-05T10:56:36.398112+00:00
instance: kb-cron
parent: time-20260505-0
summary:
Incense sticks and candles were, and are, commonly used to measure time in temples and churches across the globe. Water clocks, and, later, mechanical clocks, were used to mark the events of the abbeys and monasteries of the Middle Ages. The passage of the hours at sea can also be marked by bell. The hours were marked by bells in abbeys as well as at sea. Richard of Wallingford (1292–1336), abbot of St. Alban's abbey, famously built a mechanical clock as an astronomical orrery about 1330. The hourglass uses the flow of sand to measure the flow of time. They were also used in navigation. Ferdinand Magellan used 18 glasses on each ship for his circumnavigation of the globe (1522). The English word clock probably comes from the Middle Dutch word klocke which, in turn, derives from the medieval Latin word clocca, which ultimately derives from Celtic and is cognate with French, Latin, and German words that mean bell. Great advances in accurate time-keeping were made by Galileo Galilei and especially Christiaan Huygens with the invention of pendulum-driven clocks along with the invention of the minute hand by Jost Burgi. There is also a clock that was designed to keep


id: time-20260505-3
file: data/en.wikipedia.org/wiki/Time-3.md
category: reference
title: Time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Time
date_saved: 2026-05-05T10:56:36.398112+00:00
instance: kb-cron
parent: time-20260505-0
summary:
Many ancient cultures, particularly in the East, had a cyclical view of time. In these traditions, time was often seen as a recurring pattern of ages or cycles, where events and phenomena repeated themselves in a predictable manner. One of the most famous examples of this concept is found in Hindu philosophy, where time is depicted as a wheel called the "Kalachakra" or "Wheel of Time." According to this belief, the universe undergoes endless cycles of creation, preservation, and destruction. Similarly, in other ancient cultures such as those of the Mayans, Aztecs, and Chinese, there were also beliefs in cyclical time, often associated with astronomical observations and calendars. These cultures developed complex systems to track time, seasons, and celestial movements, reflecting their understanding of cyclical patterns in nature and the universe. The cyclical view of time contrasts with the linear concept of time more common in Western thought, where time is seen as progressing in a straight line from past to future without repetition. ==== Time in Abrahamic religions ==== In general, the Islamic and Judeo-Christian world-view regards time as linear and directional, beginning with the act of creation by God. The traditional Christian view sees time ending, teleologically, with


id: time-20260505-4
file: data/en.wikipedia.org/wiki/Time-4.md
category: reference
title: Time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Time
date_saved: 2026-05-05T10:56:36.398112+00:00
instance: kb-cron
parent: time-20260505-0
summary:
Two contrasting viewpoints on time divide prominent philosophers. One view is that time is part of the fundamental structure of the universe—a dimension independent of events, in which events occur in sequence. Isaac Newton subscribed to this realist view, and hence it is sometimes referred to as Newtonian time. The opposing view is that time does not refer to any kind of "container" that events and objects "move through", nor to any entity that "flows", but that it is instead part of a fundamental intellectual structure (together with space and number) within which humans sequence and compare events. This second view, in the tradition of Gottfried Leibniz and Immanuel Kant, holds that time is neither an event nor a thing, and thus is not itself measurable nor can it be travelled. Furthermore, it may be that there is a subjective component to time, but whether or not time itself is "felt", as a sensation, or is a judgment, is a matter of debate. In philosophy, time was questioned throughout the centuries; what time is and if it is real or not. Ancient Greek philosophers asked if time was linear or cyclical and if time was endless or finite. These philosophers


id: time-20260505-5
file: data/en.wikipedia.org/wiki/Time-5.md
category: reference
title: Time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Time
date_saved: 2026-05-05T10:56:36.398112+00:00
instance: kb-cron
parent: time-20260505-0
summary:
Immanuel Kant, in the Critique of Pure Reason, described time as an a priori intuition that allows us (together with the other a priori intuition, space) to comprehend sense experience. With Kant, neither space nor time are conceived as substances, but rather both are elements of a systematic mental framework that necessarily structures the experiences of any rational agent, or observing subject. Kant thought of time as a fundamental part of an abstract conceptual framework, together with space and number, within which we sequence events, quantify their duration, and compare the motions of objects. In this view, time does not refer to any kind of entity that "flows," that objects "move through," or that is a "container" for events. Spatial measurements are used to quantify the extent of and distances between objects, and temporal measurements are used to quantify the durations of and between events. Time was designated by Kant as the purest possible schema of a pure concept or category. Henri Bergson believed that time was neither a real homogeneous medium nor a mental construct, but possesses what he referred to as Duration. Duration, in Bergson's view, was creativity and memory as an essential component of reality. According to


id: time-20260505-6
file: data/en.wikipedia.org/wiki/Time-6.md
category: reference
title: Time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Time
date_saved: 2026-05-05T10:56:36.398112+00:00
instance: kb-cron
parent: time-20260505-0
summary:
Until Einstein's reinterpretation of the physical concepts associated with time and space in 1907, time was considered to be the same everywhere in the universe, with all observers measuring the same time interval for any event. Non-relativistic classical mechanics is based on this Newtonian idea of time. Einstein, in his special theory of relativity, postulated the constancy and finiteness of the speed of light for all observers. He showed that this postulate, together with a reasonable definition for what it means for two events to be simultaneous, requires that distances appear compressed and time intervals appear lengthened for events associated with objects in motion relative to an inertial observer. The theory of special relativity finds a convenient formulation in Minkowski spacetime, a mathematical structure that combines three dimensions of space with a single dimension of time. In this formalism, distances in space can be measured by how long light takes to travel that distance, e.g., a light-year is a measure of distance, and a meter is now defined in terms of how far light travels in a certain amount of time. Two events in Minkowski spacetime are separated by an invariant interval, which can be either space-like, light-like, or time-like.


id: time-20260505-7
file: data/en.wikipedia.org/wiki/Time-7.md
category: reference
title: Time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Time
date_saved: 2026-05-05T10:56:36.398112+00:00
instance: kb-cron
parent: time-20260505-0
summary:
Time has historically been closely related with space, the two together merging into spacetime in Einstein's special relativity and general relativity. According to these theories, the concept of time depends on the spatial reference frame of the observer, and the human perception, as well as the measurement by instruments such as clocks, are different for observers in relative motion. For example, if a spaceship carrying a clock flies through space at (very nearly) the speed of light, its crew does not notice a change in the speed of time on board their vessel because everything traveling at the same speed slows down at the same rate (including the clock, the crew's thought processes, and the functions of their bodies). However, to a stationary observer watching the spaceship fly by, the spaceship appears flattened in the direction it is traveling and the clock on board the spaceship appears to move very slowly. On the other hand, the crew on board the spaceship also perceives the observer as slowed down and flattened along the spaceship's direction of travel, because both are moving at very nearly the speed of light relative to each other. Because the outside universe appears flattened to the spaceship,


id: time-20260505-8
file: data/en.wikipedia.org/wiki/Time-8.md
category: reference
title: Time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Time
date_saved: 2026-05-05T10:56:36.398112+00:00
instance: kb-cron
parent: time-20260505-0
summary:
Time quantization refers to the theory that time has a smallest possible unit. Time quantization is a hypothetical concept. In the modern established physical theories like the Standard Model of particle physics and general relativity time is not quantized. Planck time (c. 5.4 × 10−44 seconds) is the unit of time in the system of natural units known as Planck units. Current established physical theories are believed to fail at this time scale, and many physicists expect that the Planck time might be the smallest unit of time that could ever be measured, even in principle. Though tentative physical theories that attempt to describe phenomena at this scale exist; an example is loop quantum gravity. Loop quantum gravity suggests that time is quantized; if gravity is quantized, spacetime is also quantized. == Travel == Time travel is the concept of moving backwards or forwards to different points in time, in a manner analogous to moving through space, and different from the normal "flow" of time to an earthbound observer. In this view, all points in time (including future times) "persist" in some way. Time travel has been a plot device in fiction since the 19th century. Travelling backwards or forwards


id: time-20260505-9
file: data/en.wikipedia.org/wiki/Time-9.md
category: reference
title: Time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Time
date_saved: 2026-05-05T10:56:36.398112+00:00
instance: kb-cron
parent: time-20260505-0
summary:
=== Biopsychology === The brain's judgment of time is known to be a highly distributed system, including at least the cerebral cortex, cerebellum, and basal ganglia as its components. One particular component, the suprachiasmatic nuclei, is responsible for the circadian (or daily) rhythm, while other cell clusters appear capable of shorter-range (ultradian) timekeeping. Mental chronometry is the use of response time in perceptual-motor tasks to infer the content, duration, and temporal sequencing of cognitive operations. Judgments of time can be altered by temporal illusions (like the kappa effect), age, psychoactive drugs, and hypnosis. The sense of time is impaired in some people with neurological diseases such as Parkinson's disease and attention deficit disorder. Psychoactive drugs can impair the judgment of time. Stimulants can lead both humans and rats to overestimate time intervals, while depressants can have the opposite effect. The level of activity in the brain of neurotransmitters such as dopamine and norepinephrine may be the reason for this. Such chemicals will either excite or inhibit the firing of neurons in the brain, with a greater firing rate allowing the brain to register the occurrence of more events within a given interval (speed up time) and a decreased firing rate


id: time-20260505-10
file: data/en.wikipedia.org/wiki/Time-10.md
category: reference
title: Time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Time
date_saved: 2026-05-05T10:56:36.398112+00:00
instance: kb-cron
parent: time-20260505-0
summary:
In sociology and anthropology, time discipline is the general name given to social and economic rules, conventions, customs, and expectations governing the measurement of time, the social currency and awareness of time measurements, and people's expectations concerning the observance of these customs by others. Arlie Russell Hochschild and Norbert Elias have written on the use of time from a sociological perspective. The use of time is an important issue in understanding human behavior, education, and travel behavior. Time-use research is a developing field of study. The question concerns how time is allocated across a number of activities (such as time spent at home, at work, shopping, etc.). Time use changes with technology, as the television or the Internet created new opportunities to use time in different ways. However, some aspects of time use are relatively stable over long periods of time, such as the amount of time spent traveling to work, which despite major changes in transport, has been observed to be about 20–30 minutes one-way for a large number of cities over a long period. Time management is the organization of tasks or events by first estimating how much time a task requires and when it must be completed,


id: time-dilation-20260505-0
file: data/en.wikipedia.org/wiki/Time_dilation-0.md
category: reference
title: Time dilation
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Time_dilation
date_saved: 2026-05-05T10:56:37.611725+00:00
instance: kb-cron
parent: time-dilation-20260505-0
summary:
Time dilation is the difference in elapsed time as measured by two clocks, either because of a relative velocity, a consequence of special relativity, or a difference in gravitational potential between their locations due to gravitational time dilation. When unspecified, "time dilation" usually refers to the effect due to velocity. The dilation compares "wristwatch" clock readings between events measured in different inertial frames and is not observed by visual comparison of clocks across moving frames. These predictions of the theory of relativity have been repeatedly confirmed by experiment, and they are of practical concern, for instance in the operation of satellite navigation systems such as GPS and Galileo. == Invisibility == Time dilation is a relationship between clock readings. Visually observed clock readings involve delays due to the propagation speed of light from the clock to the observer. Thus there is no direct way to observe time dilation. As an example of time dilation, two experimenters measuring a passing train traveling at .86 light speed may see a 2 second difference on their clocks while on the train the engineer reports only one second elapsed when the experimenters went by. Observations of a clock on the front of the train


id: time-dilation-20260505-1
file: data/en.wikipedia.org/wiki/Time_dilation-1.md
category: reference
title: Time dilation
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Time_dilation
date_saved: 2026-05-05T10:56:37.611725+00:00
instance: kb-cron
parent: time-dilation-20260505-0
summary:
which expresses the fact that the moving observer's period of the clock Δ t ′ {\displaystyle \Delta t'} is longer than the period Δ t {\displaystyle \Delta t} in the frame of the clock itself. The Lorentz factor gamma (γ) is defined as γ = 1 1 − v 2 c 2 {\displaystyle \gamma ={\frac {1}{\sqrt {1-{\frac {v^{2}}{c^{2}}}}}}} Because all clocks that have a common period in the resting frame should have a common period when observed from the moving frame, all other clocks—mechanical, electronic, optical (such as an identical horizontal version of the clock in the example)—should exhibit the same velocity-dependent time dilation. === Reciprocity === Given a certain frame of reference, and the "stationary" observer described earlier, if a second observer accompanied the "moving" clock, each of the observers would measure the other's clock as ticking at a slower rate than their own local clock, due to them both measuring the other to be the one that is in motion relative to their own stationary frame of reference. Common sense would dictate that, if the passage of time has slowed for a moving object, said object would observe the external world's time to be correspondingly sped up. Counterintuitively,


id: time-dilation-20260505-2
file: data/en.wikipedia.org/wiki/Time_dilation-2.md
category: reference
title: Time dilation
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Time_dilation
date_saved: 2026-05-05T10:56:37.611725+00:00
instance: kb-cron
parent: time-dilation-20260505-0
summary:
In the Minkowski diagram from the first image on the right, clock C resting in inertial frame S′ meets clock A at d and clock B at f (both resting in S). All three clocks simultaneously start to tick in S. The worldline of A is the ct-axis, the worldline of B intersecting f is parallel to the ct-axis, and the worldline of C is the ct′-axis. All events simultaneous with d in S are on the x-axis, in S′ on the x′-axis. The proper time between two events is indicated by a clock present at both events. It is invariant, i.e., in all inertial frames it is agreed that this time is indicated by that clock. Interval df is, therefore, the proper time of clock C, and is shorter with respect to the coordinate times ef=dg of clocks B and A in S. Conversely, also proper time ef of B is shorter with respect to time if in S′, because event e was measured in S′ already at time i due to relativity of simultaneity, long before C started to tick. From that it can be seen, that the proper time between two events indicated by an unaccelerated clock


id: time-dilation-20260505-3
file: data/en.wikipedia.org/wiki/Time_dilation-3.md
category: reference
title: Time dilation
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Time_dilation
date_saved: 2026-05-05T10:56:37.611725+00:00
instance: kb-cron
parent: time-dilation-20260505-0
summary:
x ( τ ) = c 2 g ( cosh ⁡ g τ c − 1 ) {\displaystyle x(\tau )={\frac {c^{2}}{g}}\left(\cosh {\frac {g\tau }{c}}-1\right)} Velocity: v ( τ ) = c tanh ⁡ g τ c {\displaystyle v(\tau )=c\tanh {\frac {g\tau }{c}}} Coordinate time as function of proper time: t ( τ ) = c g sinh ⁡ g τ c {\displaystyle t(\tau )={\frac {c}{g}}\sinh {\frac {g\tau }{c}}} === Clock hypothesis === The clock hypothesis is the assumption that the rate at which a clock is affected by time dilation does not depend on its acceleration but only on its instantaneous velocity. This is equivalent to stating that a clock moving along a path P {\displaystyle P} measures the proper time, defined by: τ = ∫ P d t 2 − d x 2 / c 2 − d y 2 / c 2 − d z 2 / c 2 {\displaystyle \tau =\int _{P}{\sqrt {dt^{2}-dx^{2}/c^{2}-dy^{2}/c^{2}-dz^{2}/c^{2}}}} The clock hypothesis was implicitly (but not explicitly) included in Einstein's original 1905 formulation of special relativity. Since then, it has become a standard assumption and is usually included in the axioms of special relativity, especially in light of experimental verification up to very


id: time-dilation-20260505-4
file: data/en.wikipedia.org/wiki/Time_dilation-4.md
category: reference
title: Time dilation
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Time_dilation
date_saved: 2026-05-05T10:56:37.611725+00:00
instance: kb-cron
parent: time-dilation-20260505-0
summary:
d t E d t c = 1 + 2 U c 2 − v 2 c 2 + ( c 2 2 U + 1 ) − 1 v ∥ 2 c 2 = 1 − ( β 2 + β e 2 + β ∥ 2 β e 2 1 − β e 2 ) {\displaystyle {\frac {dt_{\text{E}}}{dt_{\text{c}}}}={\sqrt {1+{\frac {2U}{c^{2}}}-{\frac {v^{2}}{c^{2}}}+\left({\frac {c^{2}}{2U}}+1\right)^{-1}{\frac {{v_{\shortparallel }}^{2}}{c^{2}}}}}={\sqrt {1-\left(\beta ^{2}+\beta _{e}^{2}+{\frac {\beta _{\shortparallel }^{2}\beta _{e}^{2}}{1-\beta _{e}^{2}}}\right)}}} where: v ∥ {\displaystyle v_{\shortparallel }} is the radial velocity, v e = 2 G M i r i {\displaystyle v_{e}={\sqrt {\frac {2GM_{i}}{r_{i}}}}} is the escape speed, β = v / c {\displaystyle \beta =v/c} , β e = v e / c {\displaystyle \beta _{e}=v_{e}/c} and β ∥ = v ∥ / c {\displaystyle \beta _{\shortparallel }=v_{\shortparallel }/c} are velocities as a percentage of speed of light c, U = − G M i r i {\displaystyle U={\frac {-GM_{i}}{r_{i}}}} is the Newtonian potential; hence − U {\displaystyle -U} equals half the square of the escape speed. The above equation is exact under the assumptions of the Schwarzschild solution. It reduces to velocity time dilation equation in the presence of motion and absence of gravity, i.e.


id: time-dilation-20260505-5
file: data/en.wikipedia.org/wiki/Time_dilation-5.md
category: reference
title: Time dilation
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Time_dilation
date_saved: 2026-05-05T10:56:37.611725+00:00
instance: kb-cron
parent: time-dilation-20260505-0
summary:
== In fiction == Velocity and gravitational time dilation have been the subject of science fiction works in a variety of media. Some examples in film are the movies Interstellar and Planet of the Apes. In Interstellar, a key plot point involves a planet, which is close to a rotating black hole and on the surface of which one hour is equivalent to seven years on Earth due to time dilation. Physicist Kip Thorne collaborated in making the film and explained its scientific concepts in the book The Science of Interstellar. The Queen song '39 was written by astrophysicist as well as musician Brian May, and is centred around the time dilation effect on spacefarers searching for a new home for mankind, as we gradually ruin planet Earth. They return successful, only to find that all and everything they knew has long since passed away. Time dilation was used in the Doctor Who episodes "World Enough and Time" and "The Doctor Falls", which take place on a spaceship in the vicinity of a black hole. Due to the immense gravitational pull of the black hole and the ship's length (400 miles), time moves faster at one end than the other.


id: total-internal-reflection-20260505-0
file: data/en.wikipedia.org/wiki/Total_internal_reflection-0.md
category: reference
title: Total internal reflection
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Total_internal_reflection
date_saved: 2026-05-05T10:56:39.016628+00:00
instance: kb-cron
parent: total-internal-reflection-20260505-0
summary:
In physics, total internal reflection (TIR) is the phenomenon in which waves arriving at the interface (boundary) from one medium to another (e.g., from water to air) are not refracted into the second ("external") medium, but completely reflected back into the first ("internal") medium. It occurs when the second medium has a higher wave speed (i.e., lower refractive index) than the first, and the waves are incident at a sufficiently oblique angle on the interface. For example, the water-to-air surface in a typical fish tank, when viewed obliquely from below, reflects the underwater scene like a mirror with no loss of brightness (Fig. 1). A scenario opposite to TIR, referred to as total external reflection, occurs in the extreme ultraviolet and X-ray regimes. TIR occurs not only with electromagnetic waves such as light and microwaves, but also with other types of waves, including sound and water waves. If the waves are capable of forming a narrow beam (Fig. 2), the reflection tends to be described in terms of "rays" rather than waves; in a medium whose properties are independent of direction, such as air, water or glass, the "rays" are perpendicular to associated wavefronts. The total internal reflection occurs when


id: total-internal-reflection-20260505-1
file: data/en.wikipedia.org/wiki/Total_internal_reflection-1.md
category: reference
title: Total internal reflection
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Total_internal_reflection
date_saved: 2026-05-05T10:56:39.016628+00:00
instance: kb-cron
parent: total-internal-reflection-20260505-0
summary:
== Critical angle == The critical angle is the smallest angle of incidence that yields total reflection, or equivalently the largest angle for which a refracted ray exists. For light waves incident from an "internal" medium with a single refractive index n1, to an "external" medium with a single refractive index n2, the critical angle is given by θ c = arcsin ⁡ ( n 2 / n 1 ) {\displaystyle \theta _{\text{c}}=\arcsin(n_{2}/n_{1})} and is defined if n2 ≤ n1. For some other types of waves, it is more convenient to think in terms of propagation velocities rather than refractive indices. The explanation of the critical angle in terms of velocities is more general and will therefore be discussed first. When a wavefront is refracted from one medium to another, the incident (incoming) and refracted (outgoing) portions of the wavefront meet at a common line on the refracting surface (interface). Let this line, denoted by L, move at velocity u across the surface, where u is measured normal to L (Fig. 4). Let the incident and refracted wavefronts propagate with normal velocities v 1 {\displaystyle v_{1}} and v 2 {\displaystyle v_{2}} respectively, and let them make the dihedral angles θ1


id: total-internal-reflection-20260505-2
file: data/en.wikipedia.org/wiki/Total_internal_reflection-2.md
category: reference
title: Total internal reflection
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Total_internal_reflection
date_saved: 2026-05-05T10:56:39.016628+00:00
instance: kb-cron
parent: total-internal-reflection-20260505-0
summary:
When standing beside an aquarium with one's eyes below the water level, one is likely to see fish or submerged objects reflected in the water-air surface (Fig. 1). The brightness of the reflected image – just as bright as the "direct" view – can be startling. A similar effect can be observed by opening one's eyes while swimming just below the water's surface. If the water is calm, the surface outside the critical angle (measured from the vertical) appears mirror-like, reflecting objects below. The region above the water cannot be seen except overhead, where the hemispherical field of view is compressed into a conical field known as Snell's window, whose angular diameter is twice the critical angle (cf. Fig. 6). The field of view above the water is theoretically 180° across, but seems less because as we look closer to the horizon, the vertical dimension is more strongly compressed by the refraction; e.g., by Eq. (3), for air-to-water incident angles of 90°, 80°, and 70°, the corresponding angles of refraction are 48.6° (θcr in Fig. 6), 47.6°, and 44.8°, indicating that the image of a point 20° above the horizon is 3.8° from the edge of Snell's window‍ while the


id: total-internal-reflection-20260505-3
file: data/en.wikipedia.org/wiki/Total_internal_reflection-3.md
category: reference
title: Total internal reflection
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Total_internal_reflection
date_saved: 2026-05-05T10:56:39.016628+00:00
instance: kb-cron
parent: total-internal-reflection-20260505-0
summary:
But, if the reflection is total, the spatial penetration of the fields into medium 2 must be limited somehow, or else the total extent and hence the total energy of those fields would continue to increase, draining power from medium 1. Total reflection of a continuing wavetrain permits some energy to be stored in medium 2, but does not permit a continuing transfer of power from medium 1 to medium 2. Thus, using mostly qualitative reasoning, we can conclude that total internal reflection must be accompanied by a wavelike field in the "external" medium, traveling along the interface in synchronism with the incident and reflected waves, but with some sort of limited spatial penetration into the "external" medium; such a field may be called an evanescent wave. Fig. 9 shows the basic idea. The incident wave is assumed to be plane and sinusoidal. The reflected wave, for simplicity, is not shown. The evanescent wave travels to the right in lock-step with the incident and reflected waves, but its amplitude falls off with increasing distance from the interface. (Two features of the evanescent wave in Fig. 9 are to be explained later: first, that the evanescent wave crests are perpendicular to


id: total-internal-reflection-20260505-4
file: data/en.wikipedia.org/wiki/Total_internal_reflection-4.md
category: reference
title: Total internal reflection
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Total_internal_reflection
date_saved: 2026-05-05T10:56:39.016628+00:00
instance: kb-cron
parent: total-internal-reflection-20260505-0
summary:
where k 0 = ω / c {\displaystyle k_{0}=\omega /c} is the wavenumber in vacuum. From (5), the electric field in the "external" medium has the form where kt is the wave vector for the transmitted wave (we assume isotropic media, but the transmitted wave is not yet assumed to be evanescent). In Cartesian coordinates (x, y, z), let the region y < 0 have refractive index n1, and let the region y > 0 have refractive index n2. Then the xz plane is the interface, and the y axis is normal to the interface (Fig. 11). Let i and j be the unit vectors in the x and y directions respectively. Let the plane of incidence (containing the incident wave-normal and the normal to the interface) be the xy plane (the plane of the page), with the angle of incidence θi measured from j towards i. Let the angle of refraction, measured in the same sense, be θt ("t" for transmitted, reserving "r" for reflected). From (6), the transmitted wave vector kt has magnitude n2k0. Hence, from the geometry, k t = n 2 k 0 ( i sin ⁡ θ t + j cos ⁡ θ t )


id: total-internal-reflection-20260505-5
file: data/en.wikipedia.org/wiki/Total_internal_reflection-5.md
category: reference
title: Total internal reflection
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Total_internal_reflection
date_saved: 2026-05-05T10:56:39.016628+00:00
instance: kb-cron
parent: total-internal-reflection-20260505-0
summary:
== Phase shifts == Between 1817 and 1823, Augustin-Jean Fresnel discovered that total internal reflection is accompanied by a non-trivial phase shift (that is, a phase shift that is not restricted to 0° or 180°), as the Fresnel reflection coefficient acquires a non-zero imaginary part. We shall now explain this effect for electromagnetic waves in the case of linear, homogeneous, isotropic, non-magnetic media. The phase shift turns out to be an advance, which grows as the incidence angle increases beyond the critical angle, but which depends on the polarization of the incident wave. In equations (5), (7), (8), (10), and (11), we advance the phase by the angle ϕ if we replace ωt by ωt + ϕ (that is, if we replace −ωt by −ωt − ϕ), with the result that the (complex) field is multiplied by e−iϕ. So a phase advance is equivalent to multiplication by a complex constant with a negative argument. This becomes more obvious when (e.g.) the field (5) is factored as E k e i k ⋅ r e − i ω t , {\displaystyle \mathbf {E_{k}} e^{i\mathbf {k\cdot r} }e^{-i\omega t},} where the last factor contains the time dependence. To represent the polarization of


id: total-internal-reflection-20260505-6
file: data/en.wikipedia.org/wiki/Total_internal_reflection-6.md
category: reference
title: Total internal reflection
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Total_internal_reflection
date_saved: 2026-05-05T10:56:39.016628+00:00
instance: kb-cron
parent: total-internal-reflection-20260505-0
summary:
which is positive for all angles of incidence with a transmitted ray (since θt > θi), giving a phase shift δs of zero. If we do likewise with (15), the result is easily shown to be equivalent to which is negative for small angles (that is, near normal incidence), but changes sign at Brewster's angle, where θi and θt are complementary. Thus the phase shift δp is 180° for small θi but switches to 0° at Brewster's angle. Combining the complementarity with Snell's law yields θi = arctan (1/n) as Brewster's angle for dense-to-rare incidence. (Equations (19) and (20) are known as Fresnel's sine law and Fresnel's tangent law. Both reduce to 0/0 at normal incidence, but yield the correct results in the limit as θi → 0. That they have opposite signs as we approach normal incidence is an obvious disadvantage of the sign convention used in this article; the corresponding advantage is that they have the same signs at grazing incidence.) That completes the information needed to plot δs and δp for all angles of incidence. This is done in Fig. 13, with δp in red and δs in blue, for three refractive indices. On the angle-of-incidence scale


id: total-internal-reflection-20260505-7
file: data/en.wikipedia.org/wiki/Total_internal_reflection-7.md
category: reference
title: Total internal reflection
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Total_internal_reflection
date_saved: 2026-05-05T10:56:39.016628+00:00
instance: kb-cron
parent: total-internal-reflection-20260505-0
summary:
Image-erecting prisms for binoculars and spotting scopes include paired 45°-90°-45° Porro prisms (Fig. 14), the Porro–Abbe prism, the inline Koenig and Abbe–Koenig prisms, and the compact inline Schmidt–Pechan prism. (The last consists of two components, of which one is a kind of Bauernfeind prism, which requires a reflective coating on one of its two reflecting faces, due to a sub-critical angle of incidence.) These prisms have the additional function of folding the optical path from the objective lens to the prime focus, reducing the overall length for a given primary focal length. A prismatic star diagonal for an astronomical telescope may consist of a single Porro prism (configured for a single reflection, giving a mirror-reversed image) or an Amici roof prism (which gives a non-reversed image). Roof prisms use TIR at two faces meeting at a sharp 90° angle. This category includes the Koenig, Abbe–Koenig, Schmidt–Pechan, and Amici types (already mentioned), and the roof pentaprism used in SLR cameras; the last of these requires a reflective coating on one non-TIR face. A prismatic corner reflector uses three total internal reflections to reverse the direction of incoming light. The Dove prism gives an inline view with mirror-reversal. Polarizing prisms: Although the


id: total-internal-reflection-20260505-8
file: data/en.wikipedia.org/wiki/Total_internal_reflection-8.md
category: reference
title: Total internal reflection
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Total_internal_reflection
date_saved: 2026-05-05T10:56:39.016628+00:00
instance: kb-cron
parent: total-internal-reflection-20260505-0
summary:
Theodoric having fallen into obscurity, the discovery of TIR was generally attributed to Johannes Kepler, who published his findings in his Dioptrice in 1611. Although Kepler failed to find the true law of refraction, he showed by experiment that for air-to-glass incidence, the incident and refracted rays rotated in the same sense about the point of incidence, and that as the angle of incidence varied through ±90°, the angle of refraction (as we now call it) varied through ±42°. He was also aware that the incident and refracted rays were interchangeable. But these observations did not cover the case of a ray incident from glass to air at an angle beyond 42°, and Kepler promptly concluded that such a ray could only be reflected. René Descartes rediscovered the law of refraction and published it in his La Dioptrique of 1637. In the same work he mentioned the senses of rotation of the incident and refracted rays and the condition of TIR. But he neglected to discuss the limiting case, and consequently failed to give an expression for the critical angle, although he could easily have done so. === Huygens and Newton: Rival explanations === Christiaan Huygens, in his Treatise on


id: total-internal-reflection-20260505-9
file: data/en.wikipedia.org/wiki/Total_internal_reflection-9.md
category: reference
title: Total internal reflection
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Total_internal_reflection
date_saved: 2026-05-05T10:56:39.016628+00:00
instance: kb-cron
parent: total-internal-reflection-20260505-0
summary:
=== Laplace, Malus, and attenuated total reflectance (ATR) === William Hyde Wollaston, in the first of a pair of papers read to the Royal Society of London in 1802, reported his invention of a refractometer based on the critical angle of incidence from an internal medium of known "refractive power" (refractive index) to an external medium whose index was to be measured. With this device, Wollaston measured the "refractive powers" of numerous materials, some of which were too opaque to permit direct measurement of an angle of refraction. Translations of his papers were published in France in 1803, and apparently came to the attention of Pierre-Simon Laplace. According to Laplace's elaboration of Newton's theory of refraction, a corpuscle incident on a plane interface between two homogeneous isotropic media was subject to a force field that was symmetrical about the interface. If both media were transparent, total reflection would occur if the corpuscle were turned back before it exited the field in the second medium. But if the second medium were opaque, reflection would not be total unless the corpuscle were turned back before it left the first medium; this required a larger critical angle than the one given by Snell's


id: total-internal-reflection-20260505-10
file: data/en.wikipedia.org/wiki/Total_internal_reflection-10.md
category: reference
title: Total internal reflection
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Total_internal_reflection
date_saved: 2026-05-05T10:56:39.016628+00:00
instance: kb-cron
parent: total-internal-reflection-20260505-0
summary:
calculating the angle of incidence that would introduce a total phase difference of 90° between the s and p components, for various numbers of total internal reflections at that angle (generally there were two solutions), subjecting light to that number of total internal reflections at that angle of incidence, with an initial linear polarization at 45° to the plane of incidence, and checking that the final polarization was circular. This procedure was necessary because, with the technology of the time, one could not measure the s and p phase-shifts directly, and one could not measure an arbitrary degree of ellipticality of polarization, such as might be caused by the difference between the phase shifts. But one could verify that the polarization was circular, because the brightness of the light was then insensitive to the orientation of the analyzer. For glass with a refractive index of 1.51, Fresnel calculated that a 45° phase difference between the two reflection coefficients (hence a 90° difference after two reflections) required an angle of incidence of 48°37' or 54°37'. He cut a rhomb to the latter angle and found that it performed as expected. Thus the specification of the Fresnel rhomb was completed. Similarly, Fresnel


id: total-internal-reflection-20260505-11
file: data/en.wikipedia.org/wiki/Total_internal_reflection-11.md
category: reference
title: Total internal reflection
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Total_internal_reflection
date_saved: 2026-05-05T10:56:39.016628+00:00
instance: kb-cron
parent: total-internal-reflection-20260505-0
summary:
== Bibliography == S. Bochner (June 1963), "The significance of some basic mathematical conceptions for physics", Isis, 54 (2): 179–205; JSTOR 228537. M. Born and E. Wolf, 1970, Principles of Optics, 4th Ed., Oxford: Pergamon Press. C.B. Boyer, 1959, The Rainbow: From Myth to Mathematics, New York: Thomas Yoseloff. J.Z. Buchwald (December 1980), "Experimental investigations of double refraction from Huygens to Malus", Archive for History of Exact Sciences, 21 (4): 311–373. J.Z. Buchwald, 1989, The Rise of the Wave Theory of Light: Optical Theory and Experiment in the Early Nineteenth Century, University of Chicago Press, ISBN 0-226-07886-8. O. Darrigol, 2012, A History of Optics: From Greek Antiquity to the Nineteenth Century, Oxford, ISBN 978-0-19-964437-7. R. Fitzpatrick, 2013, Oscillations and Waves: An Introduction, Boca Raton, FL: CRC Press, ISBN 978-1-4665-6608-8. R. Fitzpatrick, 2013a, "Total Internal Reflection", University of Texas at Austin, accessed 14 March 2018. A. Fresnel, 1866 (ed. H. de Senarmont, E. Verdet, and L. Fresnel), Oeuvres complètes d'Augustin Fresnel, Paris: Imprimerie Impériale (3 vols., 1866–70), vol. 1 (1866). E. Hecht, 2017, Optics, 5th Ed., Pearson Education, ISBN 978-1-292-09693-3. C. Huygens, 1690, Traité de la Lumière (Leiden: Van der Aa), translated by S.P. Thompson as Treatise on Light, University of


id: trilobal-20260505-0
file: data/en.wikipedia.org/wiki/Trilobal-0.md
category: reference
title: Trilobal
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Trilobal
date_saved: 2026-05-05T10:56:40.226028+00:00
instance: kb-cron
parent: trilobal-20260505-0
summary:
In fibers, trilobal is a cross-section shape with three distinct sides. The shape is advantageous for optical reflective properties and is used in textile fibers. Silk fibers' rounded edges and triangular cross section contribute to their luster; in some cases, synthetic fibers are manufactured to mimic this trilobal shape to give them a silk-like appearance. Filaments with a round cross section have less brilliance than trilobal filaments. == Etymology == The dictionary definition of Trilobal at Wiktionary is a combination of the words "Tri" for three and "lobal" for sides. == Objective == Trilobal shape helps in altering hand and increasing the luster. Many synthetic fibres, such as polyester and nylon, are manufactured in Trilobal cross sectional shape for the purpose of enhancing the brilliance and changing the handle. Luster adds aesthetic values in fabrics, contributes to their attractiveness. Occasionally, this adds value to their quality assessment. == Use == Synthetic fibers are particularly suitable for specific effects such as crimping and texturizing due to their adaptability during production. Trilobal cross section helps alter texture and several physical attributes such as strength and static properties, in addition to providing brightness to the fibres. The trilobal cross sectional shape helps to


id: ultraviolet-catastrophe-20260505-0
file: data/en.wikipedia.org/wiki/Ultraviolet_catastrophe-0.md
category: reference
title: Ultraviolet catastrophe
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Ultraviolet_catastrophe
date_saved: 2026-05-05T10:56:41.419374+00:00
instance: kb-cron
parent: ultraviolet-catastrophe-20260505-0
summary:
The ultraviolet catastrophe, also called the Rayleigh–Jeans catastrophe, was the prediction of late 19th century and early 20th century classical physics that an ideal black body at thermal equilibrium would emit an unbounded quantity of energy as wavelength decreased into the ultraviolet range. The term "ultraviolet catastrophe" was first used in 1911 by the Austrian physicist Paul Ehrenfest, but the concept originated with the 1900 statistical derivation of the Rayleigh–Jeans law. The phrase refers to the fact that the empirically derived Rayleigh–Jeans law, which accurately predicted experimental results at large wavelengths, failed to do so for short wavelengths. (See the image for further elaboration.) As the theory diverged from empirical observations when these frequencies reached the ultraviolet region of the electromagnetic spectrum, there was a problem. This problem was later found to be due to a property of quanta as proposed by Max Planck: There could be no fraction of a discrete energy package already carrying minimal energy. Since the first use of this term, it has also been used for other predictions of a similar nature, as in quantum electrodynamics and such cases as ultraviolet divergence. == Problem == The Rayleigh-Jeans law is an approximation to the spectral radiance


id: unruh-effect-20260505-0
file: data/en.wikipedia.org/wiki/Unruh_effect-0.md
category: reference
title: Unruh effect
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Unruh_effect
date_saved: 2026-05-05T10:56:42.662629+00:00
instance: kb-cron
parent: unruh-effect-20260505-0
summary:
The Unruh effect (also known as the Fulling–Davies–Unruh effect) is a hypothetical, observer-dependent prediction of quantum field theory that an observer who is uniformly accelerating through empty space (Minkowski vacuum) will perceive a thermal bath. This means that even in the absence of any external heat sources, an accelerating observer will detect particles and experience a temperature. In contrast, an inertial observer in the same region of spacetime would observe no particles and no temperature. In other words, the background appears to be warm from an accelerating reference frame. In layman's terms, an accelerating thermometer in empty space (like one being waved around), without any other contribution to its temperature, will record a non-zero temperature, just from its acceleration. Heuristically, for a uniformly accelerating observer, the ground state of an inertial observer is seen as a mixed state in thermodynamic equilibrium with a non-zero temperature bath. The Unruh effect was first described by Stephen Fulling in 1973, Paul Davies in 1975 and W. G. Unruh in 1976. It is currently not clear whether the Unruh effect has actually been observed, since the claimed observations are disputed. There is also some doubt about whether the Unruh effect implies the existence of


id: unruh-effect-20260505-1
file: data/en.wikipedia.org/wiki/Unruh_effect-1.md
category: reference
title: Unruh effect
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Unruh_effect
date_saved: 2026-05-05T10:56:42.662629+00:00
instance: kb-cron
parent: unruh-effect-20260505-0
summary:
== Explanation == Unruh demonstrated theoretically that the notion of vacuum depends on the path of the observer through spacetime. From the viewpoint of the accelerating observer, the vacuum of the inertial observer will look like a state containing many particles in thermal equilibrium—a warm gas. The Unruh effect would only appear to an accelerating observer. And although the Unruh effect would initially be perceived as counter-intuitive, it makes sense if the word vacuum is interpreted in the following specific way. In quantum field theory, the concept of "vacuum" is not the same as "empty space": Space is filled with the quantized fields that make up the universe. Vacuum is simply the lowest possible energy state of these fields. The energy states of any quantized field are defined by the Hamiltonian, based on local conditions, including the time coordinate. According to special relativity, two observers moving relative to each other must use different time coordinates. If those observers are accelerating, there may be no shared coordinate system. Hence, the observers will see different quantum states and thus different vacua. In some cases, the vacuum of one observer is not even in the space of quantum states of the other. In


id: unruh-effect-20260505-2
file: data/en.wikipedia.org/wiki/Unruh_effect-2.md
category: reference
title: Unruh effect
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Unruh_effect
date_saved: 2026-05-05T10:56:42.662629+00:00
instance: kb-cron
parent: unruh-effect-20260505-0
summary:
A path integral with real time coordinate is dual to a thermal partition function, related by a Wick rotation. The periodicity β {\displaystyle \beta } of imaginary time corresponds to a temperature of β = 1 / T {\displaystyle \beta =1/T} in thermal quantum field theory. Note that the path integral for this Hamiltonian is closed with period 2π. This means that the H modes are thermally occupied with temperature ⁠1/2π⁠. This is not an actual temperature, because H is dimensionless. It is conjugate to the timelike polar angle σ, which is also dimensionless. To restore the length dimension, note that a mode of fixed frequency f in σ at position ρ has a frequency which is determined by the square root of the (absolute value of the) metric at ρ, the redshift factor. This can be seen by transforming the time coordinate of a Rindler observer at fixed ρ to an inertial, co-moving observer observing a proper time. From the Rindler-line-element given above, this is just ρ. The actual inverse temperature at this point is therefore β = 2 π ρ . {\displaystyle \beta =2\pi \rho .} It can be shown that the acceleration of a trajectory at constant


id: upstream-contamination-20260505-0
file: data/en.wikipedia.org/wiki/Upstream_contamination-0.md
category: reference
title: Upstream contamination
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Upstream_contamination
date_saved: 2026-05-05T10:56:43.867068+00:00
instance: kb-cron
parent: upstream-contamination-20260505-0
summary:
Upstream contamination by floating particles is a counterintuitive phenomenon in fluid dynamics. When pouring water from a higher container to a lower one, particles floating in the latter can climb upstream into the upper container. A definitive explanation is still lacking: experimental and computational evidence indicates that the contamination is chiefly driven by surface tension gradients, however the phenomenon is also affected by the dynamics of swirling flows that remain to be fully investigated. == Origins == The phenomenon was observed in 2008 by the Argentine Sebastian Bianchini during mate tea preparation, while studying physics at the University of Havana. It rapidly attracted the interest of professor Alejandro Lage-Castellanos, who performed, with Bianchini, a series of controlled experiments. Later on professor Ernesto Altshuler completed the trio in Havana, which resulted in the Diploma thesis of Bianchini and a short original paper posted in the web arXiv and mentioned as a surprising fact in some online journals. Bianchini's Diploma thesis showed that the phenomenon could be reproduced in a controlled laboratory setting using mate leaves or chalk powder as contaminants, and that temperature gradients (hot in the top, cold in the bottom) were not necessary to generate the effect. The research


id: vacuum-20260505-0
file: data/en.wikipedia.org/wiki/Vacuum-0.md
category: reference
title: Vacuum
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Vacuum
date_saved: 2026-05-05T10:56:45.128605+00:00
instance: kb-cron
parent: vacuum-20260505-0
summary:
A vacuum (pl.: vacuums or vacua) is space devoid of matter. The word is derived from the Latin adjective vacuus (neuter vacuum) meaning "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often discuss ideal test results that would occur in a perfect vacuum, which they sometimes simply call "vacuum" or free space, and use the term partial vacuum to refer to an actual imperfect vacuum as one might have in a laboratory or in space. In engineering and applied physics on the other hand, vacuum refers to any space in which the pressure is considerably lower than atmospheric pressure. The Latin term in vacuo is used to describe an object that is surrounded by a vacuum. The quality of a partial vacuum refers to how closely it approaches a perfect vacuum. Other things equal, lower gas pressure means higher-quality vacuum. For example, a typical vacuum cleaner produces enough suction to reduce air pressure by around 20%. But higher-quality vacuums are possible. Ultra-high vacuum chambers, common in chemistry, physics, and engineering, operate below one trillionth (10−12) of atmospheric pressure (100 nPa), and can reach around 100 particles/cm3. Outer


id: vacuum-20260505-1
file: data/en.wikipedia.org/wiki/Vacuum-1.md
category: reference
title: Vacuum
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Vacuum
date_saved: 2026-05-05T10:56:45.128605+00:00
instance: kb-cron
parent: vacuum-20260505-0
summary:
Medieval thought experiments into the idea of a vacuum considered whether a vacuum was present, if only for an instant, between two flat plates when they were rapidly separated. There was much discussion of whether the air moved in quickly enough as the plates were separated, or, as Walter Burley postulated, whether a 'celestial agent' prevented the vacuum arising. Jean Buridan reported in the 14th century that teams of ten horses could not pull open bellows when the port was sealed. The 17th century saw the first attempts to quantify measurements of partial vacuum. Evangelista Torricelli's mercury barometer of 1643 and Blaise Pascal's experiments both demonstrated a partial vacuum. In 1654, Otto von Guericke invented the first vacuum pump and conducted his famous Magdeburg hemispheres experiment, showing that, owing to atmospheric pressure outside the hemispheres, teams of horses could not separate two hemispheres from which the air had been partially evacuated. Robert Boyle improved Guericke's design and with the help of Robert Hooke further developed vacuum pump technology. Thereafter, research into the partial vacuum lapsed until 1850 when August Toepler invented the Toepler pump and in 1855 when Heinrich Geissler invented the mercury displacement pump, achieving a partial vacuum of


id: vacuum-20260505-2
file: data/en.wikipedia.org/wiki/Vacuum-2.md
category: reference
title: Vacuum
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Vacuum
date_saved: 2026-05-05T10:56:45.128605+00:00
instance: kb-cron
parent: vacuum-20260505-0
summary:
In quantum mechanics and quantum field theory, the vacuum is defined as the state (that is, the solution to the equations of the theory) with the lowest possible energy (the ground state of the Hilbert space). In quantum electrodynamics this vacuum is referred to as 'QED vacuum' to distinguish it from the vacuum of quantum chromodynamics, denoted as QCD vacuum. QED vacuum is a state with no matter particles (hence the name), and no photons. As described above, this state is impossible to achieve experimentally. (Even if every matter particle could somehow be removed from a volume, it would be impossible to eliminate all the blackbody photons.) Nonetheless, it provides a good model for realizable vacuum, and agrees with a number of experimental observations as described next. QED vacuum has interesting and complex properties. In QED vacuum, the electric and magnetic fields have zero average values, but their variances are not zero. As a result, QED vacuum contains vacuum fluctuations (virtual particles that hop into and out of existence), and a finite energy called vacuum energy. Vacuum fluctuations are an essential and ubiquitous part of quantum field theory. Some experimentally verified effects of vacuum fluctuations include spontaneous emission and the


id: vacuum-20260505-3
file: data/en.wikipedia.org/wiki/Vacuum-3.md
category: reference
title: Vacuum
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Vacuum
date_saved: 2026-05-05T10:56:45.128605+00:00
instance: kb-cron
parent: vacuum-20260505-0
summary:
=== Relative versus absolute measurement === Vacuum is measured in units of pressure, typically as a subtraction relative to ambient atmospheric pressure on Earth. But the amount of relative measurable vacuum varies with local conditions. On the surface of Venus, where ground-level atmospheric pressure is much higher than on Earth, much higher relative vacuum readings would be possible. On the surface of the Moon with almost no atmosphere, it would be extremely difficult to create a measurable vacuum relative to the local environment. Similarly, much higher than normal relative vacuum readings are possible deep in the Earth's ocean. A submarine maintaining an internal pressure of 1 atmosphere submerged to a depth of 10 atmospheres (98 metres; a 9.8-metre column of seawater has the equivalent weight of 1 atm) is effectively a vacuum chamber keeping out the crushing exterior water pressures, though the 1 atm inside the submarine would not normally be considered a vacuum. Therefore, to properly understand the following discussions of vacuum measurement, it is important that the reader assumes the relative measurements are being done on Earth at sea level, at exactly 1 atmosphere of ambient atmospheric pressure. === Measurements relative to 1 atm === The SI unit


id: vacuum-20260505-4
file: data/en.wikipedia.org/wiki/Vacuum-4.md
category: reference
title: Vacuum
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Vacuum
date_saved: 2026-05-05T10:56:45.128605+00:00
instance: kb-cron
parent: vacuum-20260505-0
summary:
Vacuum is useful in a variety of processes and devices. Its first widespread use was in the incandescent light bulb to protect the filament from chemical degradation. The chemical inertness produced by a vacuum is also useful for electron-beam welding, cold welding, vacuum packing and vacuum frying. Ultra-high vacuum is used in the study of atomically clean substrates, as only a very good vacuum preserves atomic-scale clean surfaces for a reasonably long time (on the order of minutes to days). High to ultra-high vacuum removes the obstruction of air, allowing particle beams to deposit or remove materials without contamination. This is the principle behind chemical vapor deposition, physical vapor deposition, and dry etching which are essential to the fabrication of semiconductors and optical coatings, and to surface science. The reduction of convection provides the thermal insulation of thermos bottles. Deep vacuum lowers the boiling point of liquids and promotes low temperature outgassing which is used in freeze drying, adhesive preparation, distillation, metallurgy, and process purging. The electrical properties of vacuum make electron microscopes and vacuum tubes possible, including cathode-ray tubes. Vacuum interrupters are used in electrical switchgear. Vacuum arc processes are industrially important for production of certain grades of steel


id: vacuum-20260505-5
file: data/en.wikipedia.org/wiki/Vacuum-5.md
category: reference
title: Vacuum
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Vacuum
date_saved: 2026-05-05T10:56:45.128605+00:00
instance: kb-cron
parent: vacuum-20260505-0
summary:
The above explanation is merely a simple introduction to vacuum pumping, and is not representative of the entire range of pumps in use. Many variations of the positive displacement pump have been developed, and many other pump designs rely on fundamentally different principles. Momentum transfer pumps, which bear some similarities to dynamic pumps used at higher pressures, can achieve much higher quality vacuums than positive displacement pumps. Entrapment pumps can capture gases in a solid or absorbed state, often with no moving parts, no seals and no vibration. None of these pumps are universal; each type has important performance limitations. They all share a difficulty in pumping low molecular weight gases, especially hydrogen, helium, and neon. The lowest pressure that can be attained in a system is also dependent on many things other than the nature of the pumps. Multiple pumps may be connected in series, called stages, to achieve higher vacuums. The choice of seals, chamber geometry, materials, and pump-down procedures will all have an impact. Collectively, these are called vacuum technique. And sometimes, the final pressure is not the only relevant characteristic. Pumping systems differ in oil contamination, vibration, preferential pumping of certain gases, pump-down speeds, intermittent duty


id: hydraulic-shock-20260505-0
file: data/en.wikipedia.org/wiki/Hydraulic_shock-0.md
category: reference
title: Hydraulic shock
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Hydraulic_shock
date_saved: 2026-05-05T10:56:46.344223+00:00
instance: kb-cron
parent: hydraulic-shock-20260505-0
summary:
Hydraulic shock (colloquial: water hammer; fluid hammer) is a pressure surge or wave caused when a fluid in motion is forced to stop or change direction suddenly: a momentum change. It is usually observed in a liquid but gases can also be affected. This phenomenon commonly occurs when a valve closes suddenly at an end of a pipeline system and a pressure wave propagates in the pipe. This pressure wave can cause major problems, from noise and vibration to pipe rupture and collapse. It is possible to reduce the effects of the water hammer pulses with accumulators, expansion tanks, surge tanks, blowoff valves, and other features. The effects can be avoided by ensuring that no valves will close too quickly with significant flow, but there are many situations that can cause the effect. Rough calculations can be made using the Zhukovsky (Joukowsky) equation, or more accurate ones using the method of characteristics. == History == In the 1st century B.C., Marcus Vitruvius Pollio described the effect of water hammer in lead pipes and stone tubes of the Roman public water supply. In 1772, Englishman John Whitehurst built a hydraulic ram for a home in Cheshire, England. In 1796, French inventor


id: hydraulic-shock-20260505-1
file: data/en.wikipedia.org/wiki/Hydraulic_shock-1.md
category: reference
title: Hydraulic shock
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Hydraulic_shock
date_saved: 2026-05-05T10:56:46.344223+00:00
instance: kb-cron
parent: hydraulic-shock-20260505-0
summary:
Water hammers have caused accidents and fatalities, but usually, damage is limited to the breakage of pipes or appendages. An engineer should always assess the risk of a pipeline burst. Pipelines transporting hazardous liquids or gases warrant special care in design, construction, and operation. Hydroelectric power plants, especially, must be carefully designed and maintained because the water hammer can cause water pipes to fail catastrophically. The following characteristics may reduce or eliminate water hammer: Reduce the pressure of the water supply to the building by fitting a regulator. Lower fluid velocities. To keep water hammer low, pipe-sizing charts for some applications recommend flow velocity at or below 1.5 m/s (4.9 ft/s). Fit slowly closing valves. Toilet fill valves are available in a quiet fill type that closes quietly. Non-slam check valves do not rely on fluid flow to close and will do so before the water flow reaches significant velocity. High pipeline pressure rating (does not reduce the effect but protects against damage). Good pipeline control (start-up and shut-down procedures). Water towers (used in many drinking water systems) or surge tanks help maintain steady flow rates and trap large pressure fluctuations. Air vessels such as expansion tanks and some types


id: hydraulic-shock-20260505-2
file: data/en.wikipedia.org/wiki/Hydraulic_shock-2.md
category: reference
title: Hydraulic shock
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Hydraulic_shock
date_saved: 2026-05-05T10:56:46.344223+00:00
instance: kb-cron
parent: hydraulic-shock-20260505-0
summary:
where P1 is the inlet pressure in psi, V is the flow velocity in ft/s, t is the valve closing time in seconds, and L is the upstream pipe length in feet. Hence, we can say that the magnitude of the water hammer largely depends upon the time of closure, the elastic components of the pipe & fluid properties. == Expression for the excess pressure due to water hammer == When a valve with a volumetric flow rate Q is closed, an excess pressure ΔP is created upstream of the valve, whose value is given by the Joukowsky equation: Δ P = Z Q . {\displaystyle \Delta P=ZQ.} In this expression: ΔP is the overpressurization in Pa; Q is the volumetric flow in m3/s; Z is the hydraulic impedance, expressed in kg/m4/s. The hydraulic impedance Z of the pipeline determines the magnitude of the water hammer pulse. It is itself defined by Z = ρ B A , {\displaystyle Z={\frac {\sqrt {\rho B}}{A}},} where ρ the density of the liquid, expressed in kg/m3; A cross sectional area of the pipe, m2; B equivalent modulus of compressibility of the liquid in the pipe, expressed in Pa. The latter follows from a


id: wigner-effect-20260505-0
file: data/en.wikipedia.org/wiki/Wigner_effect-0.md
category: reference
title: Wigner effect
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Wigner_effect
date_saved: 2026-05-05T10:56:47.516234+00:00
instance: kb-cron
parent: wigner-effect-20260505-0
summary:
The Wigner effect (named for its discoverer, Eugene Wigner), also known as the discomposition effect or Wigner's disease, is the displacement of atoms in a solid caused by neutron radiation. Any solid can display the Wigner effect. The effect is of most concern in neutron moderators, such as graphite, intended to reduce the speed of fast neutrons, thereby turning them into thermal neutrons capable of sustaining a nuclear chain reaction involving uranium-235. == Cause == To cause the Wigner effect, neutrons that collide with the atoms in a crystal structure must have enough energy to displace them from the lattice. This amount (threshold displacement energy) is approximately 25 eV. A neutron's energy can vary widely, but it is not uncommon to have energies up to and exceeding 10 MeV (10,000,000 eV) in the centre of a nuclear reactor. A neutron with a significant amount of energy will create a displacement cascade in a matrix via elastic collisions. For example, a 1 MeV neutron striking graphite will create 900 displacements. Not all displacements will create defects, because some of the struck atoms will find and fill the vacancies that were either small pre-existing voids or vacancies newly formed by the other


id: wrinklon-20260505-0
file: data/en.wikipedia.org/wiki/Wrinklon-0.md
category: reference
title: Wrinklon
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Wrinklon
date_saved: 2026-05-05T10:56:48.717684+00:00
instance: kb-cron
parent: wrinklon-20260505-0
summary:
A wrinklon is a type of quasiparticle introduced in the study of wrinkling behavior in thin sheet materials, such as graphene or fabric. It is a localized excitation corresponding to wrinkles in a constrained two dimensional system. It represents a localized region where two wrinkles in the material merge into one, serving as part of the pattern seen when the material forms wrinkles. The term "wrinklon" is derived from "wrinkle" and the suffix "-on", the latter commonly used in physics to denote quasiparticles such as the "phonon" or "polaron", as well as particles (photon, electron). The concept of wrinklons aids in understanding and describing the complex wrinkling patterns observed in a variety of materials. This understanding could prove useful in fields such as material science and nanotechnology, particularly in the study and development of two-dimensional materials such as graphene. Further studies have expanded the understanding of wrinklons, demonstrating that the behavior of these wrinkles in thin films, such as graphene, can differ depending on the substrate they are on. For instance, when graphene is on a compliant polymer substrate, the properties of the wrinklons change with the thickness of the graphene. This suggests that the characteristics of the substrate have


id: zeeman-energy-20260505-0
file: data/en.wikipedia.org/wiki/Zeeman_energy-0.md
category: reference
title: Zeeman energy
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Zeeman_energy
date_saved: 2026-05-05T10:56:49.941247+00:00
instance: kb-cron
parent: zeeman-energy-20260505-0
summary:
Zeeman energy, or the external field energy, is the potential energy of a magnetised body in an external magnetic field. It is named after the Dutch physicist Pieter Zeeman, primarily known for the Zeeman effect. In SI units, it is given by E Z e e m a n = − μ 0 ∫ V M ⋅ H E x t d V {\displaystyle E_{\rm {Zeeman}}=-\mu _{0}\int _{V}\,{\textbf {M}}\cdot {\textbf {H}}_{\rm {Ext}}\,\mathrm {d} V} where HExt is the external field, M the local magnetisation, and the integral is done over the volume of the body. This is the statistical average (over a unit volume macroscopic sample) of a corresponding microscopic Hamiltonial (energy) for each individual magnetic moment m, which is however experiencing a local induction B: H = − m ⋅ B {\displaystyle H=-{\textbf {m}}\cdot {\textbf {B}}} == References == F. Barozzi, F. Gasparini, Fondamenti di Elettrotecnica: Elettromagnetismo, UTET Torino, 1989 Hubert, A. and Schäfer, R. Magnetic domains: the analysis of magnetic microstructures, Springer-Verlag, 1998


id: thermodynamic-process-20260505-0
file: data/en.wikipedia.org/wiki/Thermodynamic_process-0.md
category: reference
title: Thermodynamic process
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thermodynamic_process
date_saved: 2026-05-05T10:56:51.523233+00:00
instance: kb-cron
parent: thermodynamic-process-20260505-0
summary:
Classical thermodynamics considers three main kinds of thermodynamic processes: (1) changes in a system, (2) cycles in a system, and (3) flow processes. (1) A Thermodynamic process is a process in which the thermodynamic state of a system is changed. A change in a system is defined by a passage from an initial to a final state of thermodynamic equilibrium. In classical thermodynamics, the actual course of the process is not the primary concern, and often is ignored. A state of thermodynamic equilibrium endures unchangingly unless it is interrupted by a thermodynamic operation that initiates a thermodynamic process. The equilibrium states are each respectively fully specified by a suitable set of thermodynamic state variables, that depend only on the current state of the system, not on the path taken by the processes that produce the state. In general, during the actual course of a thermodynamic process, the system may pass through physical states which are not describable as thermodynamic states, because they are far from internal thermodynamic equilibrium. Non-equilibrium thermodynamics, however, considers processes in which the states of the system are close to thermodynamic equilibrium, and aims to describe the continuous passage along the path, at definite rates of progress.


id: thermodynamic-process-20260505-1
file: data/en.wikipedia.org/wiki/Thermodynamic_process-1.md
category: reference
title: Thermodynamic process
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thermodynamic_process
date_saved: 2026-05-05T10:56:51.523233+00:00
instance: kb-cron
parent: thermodynamic-process-20260505-0
summary:
An isobaric process occurs at constant pressure. An example would be to have a movable piston in a cylinder, so that the pressure inside the cylinder is always at atmospheric pressure, although it is separated from the atmosphere. In other words, the system is dynamically connected, by a movable boundary, to a constant-pressure reservoir. An isochoric process is one in which the volume is held constant, with the result that the mechanical PV work done by the system will be zero. On the other hand, work can be done isochorically on the system, for example by a shaft that drives a rotary paddle located inside the system. It follows that, for the simple system of one deformation variable, any heat energy transferred to the system externally will be absorbed as internal energy. An isochoric process is also known as an isometric process or an isovolumetric process. An example would be to place a closed tin can of material into a fire. To a first approximation, the can will not expand, and the only change will be that the contents gain internal energy, evidenced by increase in temperature and pressure. Mathematically, δ Q = d U {\displaystyle \delta Q=dU} . The


id: adiabatic-accessibility-20260505-0
file: data/en.wikipedia.org/wiki/Adiabatic_accessibility-0.md
category: reference
title: Adiabatic accessibility
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Adiabatic_accessibility
date_saved: 2026-05-05T10:56:52.701422+00:00
instance: kb-cron
parent: adiabatic-accessibility-20260505-0
summary:
In thermodynamics, adiabatic accessibility determines if one equilibrium state of a system can transition to another solely through an adiabatic process, meaning no heat is exchanged with the environment. The concept was coined by Constantin Carathéodory in 1909 ("adiabatische Erreichbarkeit") and taken up 90 years later by Elliott Lieb and J. Yngvason in their axiomatic approach to the foundations of thermodynamics. It was also used by R. Giles in his 1964 monograph. Adiabatic accessibility plays a crucial role in defining fundamental concepts such as entropy and understanding the limitations on state transformations in thermodynamic systems. == Description == A system in a state Y is said to be adiabatically accessible from a state X if X can be transformed into Y without the system suffering transfer of energy as heat or transfer of matter. X may, however, be transformed to Y by doing work on X. For example, a system consisting of one kilogram of warm water is adiabatically accessible from a system consisting of one kilogram of cool water, since the cool water may be mechanically stirred to warm it. However, the cool water is not adiabatically accessible from the warm water, since no amount or type of work


id: list-of-adiabatic-concepts-20260505-0
file: data/en.wikipedia.org/wiki/List_of_adiabatic_concepts-0.md
category: reference
title: List of adiabatic concepts
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/List_of_adiabatic_concepts
date_saved: 2026-05-05T10:56:53.965483+00:00
instance: kb-cron
parent: list-of-adiabatic-concepts-20260505-0
summary:
Adiabatic (from Gr. ἀ negative + διάβασις passage; transference) refers to any process that occurs without heat transfer. This concept is used in many areas of physics and engineering. Notable examples are listed below. == Automobiles == Engine braking, a feature of some diesel engines, uses adiabatic expansion to diminish the vehicle's forward momentum. == Meteorology == Adiabatic lapse rate, the change in air temperature with changing height, resulting from pressure change. == Quantum chemistry == Adiabatic invariant Born–Oppenheimer approximation == Thermodynamics == Adiabatic process Adiabatic ionization Adiabatic index Adiabatic accessibility == Quantum mechanics == Adiabatic theorem Adiabatic quantum motor == Electronics == Adiabatic circuit Adiabatic logic == References ==


id: adiabatic-process-20260505-0
file: data/en.wikipedia.org/wiki/Adiabatic_process-0.md
category: reference
title: Adiabatic process
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Adiabatic_process
date_saved: 2026-05-05T10:56:55.166101+00:00
instance: kb-cron
parent: adiabatic-process-20260505-0
summary:
An adiabatic process (adiabatic from Ancient Greek ἀδιάβατος (adiábatos) 'impassable') is a type of thermodynamic process whereby a transfer of energy between the thermodynamic system and its environment is accompanied neither by a transfer of entropy nor of amounts of constituents. Unlike an isothermal process, an adiabatic process transfers energy to the surroundings only as work and/or mass flow. As a key concept in thermodynamics, the adiabatic process supports the theory that explains the first law of thermodynamics. The opposite term to "adiabatic" is diabatic. Some chemical and physical processes occur too rapidly for energy to enter or leave the system as heat, allowing a convenient "adiabatic approximation". For example, the adiabatic flame temperature uses this approximation to calculate the upper limit of flame temperature by assuming combustion loses no heat to its surroundings. In meteorology, adiabatic expansion and cooling of moist air, which can be triggered by winds flowing up and over a mountain for example, can cause the water vapor pressure to exceed the saturation vapor pressure. Expansion and cooling beyond the saturation vapor pressure is often idealized as a pseudo-adiabatic process whereby excess vapor instantly precipitates into water droplets. The change in temperature of air undergoing pseudo-adiabatic


id: adiabatic-process-20260505-1
file: data/en.wikipedia.org/wiki/Adiabatic_process-1.md
category: reference
title: Adiabatic process
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Adiabatic_process
date_saved: 2026-05-05T10:56:55.166101+00:00
instance: kb-cron
parent: adiabatic-process-20260505-0
summary:
If the system has such rigid walls that work cannot be transferred in or out (W = 0), and the walls are not adiabatic and energy is added in the form of heat (Q > 0), and there is no phase change, then the temperature of the system will rise. If the system has such rigid walls that pressure–volume work cannot be done, but the walls are adiabatic (Q = 0), and energy is added as isochoric (constant volume) work in the form of friction or the stirring of a viscous fluid within the system (W < 0), and there is no phase change, then the temperature of the system will rise. If the system walls are adiabatic (Q = 0) but not rigid (W ≠ 0), and, in a fictive idealized process, energy is added to the system in the form of frictionless, non-viscous pressure–volume work (W < 0), and there is no phase change, then the temperature of the system will rise. Such a process is called an isentropic process and is said to be "reversible". Ideally, if the process were reversed the energy could be recovered entirely as work done by the system. If the system contains


id: adiabatic-process-20260505-2
file: data/en.wikipedia.org/wiki/Adiabatic_process-2.md
category: reference
title: Adiabatic process
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Adiabatic_process
date_saved: 2026-05-05T10:56:55.166101+00:00
instance: kb-cron
parent: adiabatic-process-20260505-0
summary:
=== Adiabatic expansion === Adiabatic expansion occurs when the pressure on an adiabatically isolated system is decreased, allowing it to expand in size, thus causing it to do work on its surroundings. When the pressure applied on a parcel of gas is reduced, the gas in the parcel is allowed to expand; as the volume increases, the temperature falls as its internal energy decreases. Adiabatic expansion occurs in the Earth's atmosphere with orographic lifting and lee waves, and this can form pilei or lenticular clouds. Due in part to adiabatic expansion in mountainous areas, snowfall actually occurs in some parts of the Sahara desert. Adiabatic expansion does not have to involve a fluid. One technique used to reach very low temperatures (thousandths and even millionths of a degree above absolute zero) is via adiabatic demagnetisation, where the change in magnetic field on a magnetic material is used to provide adiabatic expansion. Also, the contents of an expanding universe can be described (to first order) as an adiabatically expanding fluid. (See heat death of the universe.) Rising magma also undergoes adiabatic expansion before eruption, particularly significant in the case of magmas that rise quickly from great depths such as kimberlites. In


id: adiabatic-process-20260505-3
file: data/en.wikipedia.org/wiki/Adiabatic_process-3.md
category: reference
title: Adiabatic process
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Adiabatic_process
date_saved: 2026-05-05T10:56:55.166101+00:00
instance: kb-cron
parent: adiabatic-process-20260505-0
summary:
or 25.1 bar. This pressure increase is more than a simple 10:1 compression ratio would indicate; this is because the gas is not only compressed, but the work done to compress the gas also increases its internal energy, which manifests itself by a rise in the gas temperature and an additional rise in pressure above what would result from a simplistic calculation of 10 times the original pressure. We can solve for the temperature of the compressed gas in the engine cylinder as well, using the ideal gas law, P V = n R T (n is amount of gas in moles and R the gas constant for that gas). Our initial conditions being 100 kPa of pressure, 1 L volume, and 300 K of temperature, our experimental constant (n R ) is: P V T = c o n s t a n t 2 = 10 5 P a × 10 − 3 m 3 300 K = 0.333 P a m 3 K − 1 . {\displaystyle {\begin{aligned}{\frac {P\ V}{T}}&={\mathsf {constant}}_{2}\\&={\frac {10^{5}~{\mathsf {Pa}}\times 10^{-3}~{\mathsf {m}}^{3}}{300~{\mathsf {K}}}}\\&=0.333~{\mathsf {Pa}}\ {\mathsf {m}}^{3}{\mathsf {K}}^{-1}~.\end{aligned}}} We know the compressed gas has V = 0.1 L and P = 2.51×106 Pa, so we


id: adiabatic-process-20260505-4
file: data/en.wikipedia.org/wiki/Adiabatic_process-4.md
category: reference
title: Adiabatic process
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Adiabatic_process
date_saved: 2026-05-05T10:56:55.166101+00:00
instance: kb-cron
parent: adiabatic-process-20260505-0
summary:
P = P 1 ( V 1 V ) γ . {\displaystyle P=P_{1}\ \left({\frac {V_{1}}{V}}\right)^{\gamma }~.} Substituting this into (b2) gives W = ∫ V 1 V 2 P 1 ( V 1 V ) γ d V . {\displaystyle W=\int _{V_{1}}^{V_{2}}P_{1}\ \left({\frac {V_{1}}{V}}\right)^{\gamma }\ \mathrm {d} V~.} Integrating, we obtain the expression for work, W = P 1 V 1 γ V 2 1 − γ − V 1 1 − γ 1 − γ = P 2 V 2 − P 1 V 1 1 − γ . {\displaystyle {\begin{aligned}W&=P_{1}\ V_{1}^{\gamma }\ {\frac {V_{2}^{1-\gamma }-V_{1}^{1-\gamma }}{1-\gamma }}\\[1ex]&={\frac {P_{2}\ V_{2}-P_{1}\ V_{1}}{1-\gamma }}.\end{aligned}}} Substituting γ = ⁠α + 1/α⁠ in the second term, W = − α P 1 V 1 γ ( V 2 1 − γ − V 1 1 − γ ) . {\displaystyle W=-\alpha \ P_{1}\ V_{1}^{\gamma }\ \left(V_{2}^{1-\gamma }-V_{1}^{1-\gamma }\right)~.} Rearranging, W = − α P 1 V 1 ( ( V 2 V 1 ) 1 − γ − 1 ) . {\displaystyle W=-\alpha \ P_{1}\ V_{1}\ \left(\left({\frac {V_{2}}{V_{1}}}\right)^{1-\gamma }-1\right)~.} Using the ideal gas law and assuming a constant molar quantity (as often happens in practical cases), W = − α n R T


id: adiabatic-process-20260505-5
file: data/en.wikipedia.org/wiki/Adiabatic_process-5.md
category: reference
title: Adiabatic process
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Adiabatic_process
date_saved: 2026-05-05T10:56:55.166101+00:00
instance: kb-cron
parent: adiabatic-process-20260505-0
summary:
An adiabat is a curve of constant entropy in a diagram. Some properties of adiabats on a P – V diagram are indicated. These properties may be read from the classical behaviour of ideal gases, except in the region where P V becomes small (low temperature), where quantum effects become important. Every adiabat asymptotically approaches both the V axis and the P axis (just like isotherms). Each adiabat intersects each isotherm exactly once. An adiabat looks similar to an isotherm, except that during an expansion, an adiabat loses more pressure than an isotherm, so it has a steeper inclination (more vertical). If isotherms are concave towards the north-east direction (45° from V axis), then adiabats are concave towards the east north-east (31° from V axisaxis). If adiabats and isotherms are graphed at regular intervals of entropy and temperature, respectively (like altitude on a contour map), then as the eye moves towards the axes (towards the south-west), it sees the density of isotherms stay constant, but it sees the density of adiabats grow. The exception is very near absolute zero, where the density of adiabats drops sharply and they become rare (see Nernst's theorem). == Etymology == The term adiabatic ()


id: adiabatic-process-20260505-6
file: data/en.wikipedia.org/wiki/Adiabatic_process-6.md
category: reference
title: Adiabatic process
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Adiabatic_process
date_saved: 2026-05-05T10:56:55.166101+00:00
instance: kb-cron
parent: adiabatic-process-20260505-0
summary:
== Divergent usages of the word adiabatic == This present article is written from the viewpoint of macroscopic thermodynamics, and the word adiabatic is used in this article in the traditional way of thermodynamics, introduced by Rankine. It is pointed out in the present article that, for example, if a compression of a gas is rapid, then there is little time for heat transfer to occur, even when the gas is not adiabatically isolated by a definite wall. In this sense, a rapid compression of a gas is sometimes approximately or loosely said to be adiabatic, though often far from isentropic, even when the gas is not adiabatically isolated by a definite wall. Some authors, like Pippard, recommend using "adiathermal" to refer to processes where no heat-exchange occurs (such as Joule expansion), and "adiabatic" to reversible quasi-static adiathermal processes (so that rapid compression of a gas is not "adiabatic"). And Laidler has summarized the complicated etymology of "adiabatic". Quantum mechanics and quantum statistical mechanics, however, use the word adiabatic in a very different sense, one that can at times seem almost opposite to the classical thermodynamic sense. In quantum theory, the word adiabatic can mean something perhaps near isentropic, or


id: air-separation-20260505-0
file: data/en.wikipedia.org/wiki/Air_separation-0.md
category: reference
title: Air separation
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Air_separation
date_saved: 2026-05-05T10:56:56.320357+00:00
instance: kb-cron
parent: air-separation-20260505-0
summary:
An air separation plant separates atmospheric air into its primary components, typically nitrogen and oxygen, and sometimes also argon and other rare inert gases. The most common method for air separation is fractional distillation. Cryogenic air separation units (ASUs) are built to provide nitrogen or oxygen and often co-produce argon. Other methods such as membrane, pressure swing adsorption (PSA) and vacuum pressure swing adsorption (VPSA) are commercially used to separate a single component from ordinary air. High purity oxygen, nitrogen, and argon, used for semiconductor device fabrication, require cryogenic distillation. Similarly, the only viable source of the rare gases neon, krypton, xenon is the distillation of air using at least two distillation columns. Helium is also recovered in advanced air separation processes. == Cryogenic distillation process == Pure gases can be separated from air by first cooling it until it liquefies, then selectively distilling the components at their various boiling temperatures. The process can produce high purity gases but is energy-intensive. This process was pioneered by Carl von Linde in the early 20th century and is still used today to produce high purity gases. He developed it in the year 1895; the process remained purely academic for seven years before


id: air-separation-20260505-1
file: data/en.wikipedia.org/wiki/Air_separation-1.md
category: reference
title: Air separation
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Air_separation
date_saved: 2026-05-05T10:56:56.320357+00:00
instance: kb-cron
parent: air-separation-20260505-0
summary:
Pressure swing adsorption provides separation of oxygen or nitrogen from air without liquefaction. The process operates around ambient temperature; a zeolite (molecular sponge) is exposed to high pressure air, then the air is released and an adsorbed film of the desired gas is released. The size of compressor is much reduced over a liquefaction plant, and portable oxygen concentrators are made in this manner to provide oxygen-enriched air for medical purposes. Vacuum swing adsorption is a similar process; the product gas is evolved from the zeolite at sub-atmospheric pressure. Membrane technologies can provide alternate, lower-energy approaches to air separation. For example, a number of approaches are being explored for oxygen generation. Polymeric membranes operating at ambient or warm temperatures, for example, may be able to produce oxygen-enriched air (25-50% oxygen). Ceramic membranes can provide high-purity oxygen (90% or more) but require higher temperatures (800-900 deg C) to operate. These ceramic membranes include ion transport membranes (ITM) and oxygen transport membranes (OTM). Air Products and Chemicals Inc and Praxair are developing flat ITM and tubular OTM systems. Membrane gas separation is used to provide oxygen-poor and nitrogen-rich gases instead of air to fill the fuel tanks of jet liners, thus greatly


id: cascade-refrigeration-20260505-0
file: data/en.wikipedia.org/wiki/Cascade_refrigeration-0.md
category: reference
title: Cascade refrigeration
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Cascade_refrigeration
date_saved: 2026-05-05T10:56:57.506538+00:00
instance: kb-cron
parent: cascade-refrigeration-20260505-0
summary:
A cascade refrigeration cycle is a multi-stage thermodynamic cycle. An example two-stage process is shown at right (bottom on mobile). The cascade cycle is often employed for devices such as ULT freezers. In a cascade refrigeration system, two or more vapor-compression cycles with different refrigerants are used. The evaporation-condensation temperatures of each cycle are sequentially lower with some overlap to cover the total temperature drop desired, with refrigerants selected to work efficiently in the temperature range they cover. The low temperature system removes heat from the space to be cooled using an evaporator, and transfers it to a heat exchanger that is cooled by the evaporation of the refrigerant of the high temperature system. Alternatively, a liquid-to-liquid or similar heat exchanger may be used instead. The high-temperature system transfers heat to a conventional condenser that carries the entire heat output of the system and may be passive, fan, or water-cooled. Cascade cycles may be separated by either being sealed in separated loops or in what is referred to as an "auto-cascade", where the gases are compressed as a mixture but separated as one refrigerant condenses into a liquid while the other continues as a gas through the rest of the


id: coil-globule-transition-20260505-0
file: data/en.wikipedia.org/wiki/Coil–globule_transition-0.md
category: reference
title: Coil–globule transition
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Coil–globule_transition
date_saved: 2026-05-05T10:56:58.729143+00:00
instance: kb-cron
parent: coil-globule-transition-20260505-0
summary:
In polymer physics, the coil–globule transition is the collapse of a macromolecule from an expanded coil state through an ideal coil state to a collapsed globule state, or vice versa. The coil–globule transition is of importance in biology due to the presence of coil-globule transitions in biological macromolecules such as proteins and DNA. It is also analogous with the swelling behavior of a crosslinked polymer gel and is thus of interest in biomedical engineering for controlled drug delivery. A particularly prominent example of a polymer possessing a coil-globule transition of interest in this area is that of Poly(N-isopropylacrylamide) (PNIPAAm). == Description == In its coil state, the radius of gyration of the macromolecule scales as its chain length to the three-fifths power. As it passes through the coil–globule transition, it shifts to scaling as chain length to the half power (at the transition) and finally to the one third power in the collapsed state. The direction of the transition is often specified by the constructions 'coil-to-globule' or 'globule-to-coil' transition. == Origin == This transition is associated with the transition of a polymer chain from good solvent behavior through ideal or theta solvent behavior to poor solvent behavior. The canonical coil–globule


id: dissipation-20260505-0
file: data/en.wikipedia.org/wiki/Dissipation-0.md
category: reference
title: Dissipation
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Dissipation
date_saved: 2026-05-05T10:56:59.949966+00:00
instance: kb-cron
parent: dissipation-20260505-0
summary:
In thermodynamics, dissipation is the result of an irreversible process that affects a thermodynamic system. In a dissipative process, energy (internal, bulk flow kinetic, or system potential) transforms from an initial form to a final form, where the capacity of the final form to do thermodynamic work is less than that of the initial form. For example, transfer of energy as heat is dissipative because it is a transfer of energy other than by thermodynamic work or by transfer of matter, and spreads previously concentrated energy. Following the second law of thermodynamics, in conduction and radiation from one body to another, the entropy varies with temperature (reduces the capacity of the combination of the two bodies to do work), but never decreases in an isolated system. In mechanical engineering, dissipation is the irreversible conversion of mechanical energy into thermal energy with an associated increase in entropy. Processes with defined local temperature produce entropy at a certain rate. The entropy production rate times local temperature gives the dissipated power. Important examples of irreversible processes are: heat flow through a thermal resistance, fluid flow through a flow resistance, diffusion (mixing), chemical reactions, and electric current flow through an electrical resistance (Joule heating).


id: electron-bifurcation-20260505-0
file: data/en.wikipedia.org/wiki/Electron_bifurcation-0.md
category: reference
title: Electron bifurcation
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Electron_bifurcation
date_saved: 2026-05-05T10:57:01.118901+00:00
instance: kb-cron
parent: electron-bifurcation-20260505-0
summary:
In biochemistry, electron bifurcation (EB) refers to a system that enables an unfavorable (endergonic) transformation by coupling to a favorable (exergonic) transformation. Two electrons are involved: one flows to an acceptor with a "higher reduction potential and the other with a lower reduction potential" than the donor. The process is suspected of being common in bioenergetics. Two versions of EB are recognized. One involves redox of quinones and the other involves flavins. Quinones and flavins are cofactors that are capable of undergoing 2 e− – 2 proton redox. A pervasive example of electron bifurcation is the Q cycle, which is part of the machinery that results in oxidative phosphorylation. In that case one electron from ubiquinol is directed to a Rieske cluster and the other electron is directed to a cytochrome b. == References ==


id: endergonic-reaction-20260505-0
file: data/en.wikipedia.org/wiki/Endergonic_reaction-0.md
category: reference
title: Endergonic reaction
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Endergonic_reaction
date_saved: 2026-05-05T10:57:02.332457+00:00
instance: kb-cron
parent: endergonic-reaction-20260505-0
summary:
In chemical thermodynamics, an endergonic reaction (from Greek ἔνδον (endon) 'within' and ἔργον (ergon) 'work'; also called a heat absorbing nonspontaneous reaction or an unfavorable reaction) is a chemical reaction in which the standard change in free energy is positive, and an additional driving force is needed to perform this reaction. In layman's terms, the total amount of useful energy is negative (it takes more energy to start the reaction than what is received out of it) so the total energy is a net negative result, as opposed to a net positive result in an exergonic reaction. Another way to phrase this is that useful energy must be absorbed from the surroundings into the workable system for the reaction to happen. Under constant temperature and constant pressure conditions, this means that the change in the standard Gibbs free energy would be positive, Δ G ∘ > 0 {\displaystyle \Delta G^{\circ }>0} for the reaction at standard state (i.e. at standard pressure (1 bar), and standard concentrations (1 molar) of all the reagents). In metabolism, an endergonic process is anabolic, meaning that energy is stored; in many such anabolic processes, energy is supplied by coupling the reaction to adenosine triphosphate (ATP)


id: endothermic-process-20260505-0
file: data/en.wikipedia.org/wiki/Endothermic_process-0.md
category: reference
title: Endothermic process
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Endothermic_process
date_saved: 2026-05-05T10:57:03.568543+00:00
instance: kb-cron
parent: endothermic-process-20260505-0
summary:
An endothermic process is a chemical or physical process that absorbs heat from its surroundings. In terms of thermodynamics, it is a thermodynamic process with an increase in the enthalpy H (or internal energy U) of the system. In an endothermic process, the heat that a system absorbs is thermal energy transfer into the system. Thus, an endothermic reaction generally leads to a decrease in the temperature of the surroundings. The term was coined by 19th-century French chemist Marcellin Berthelot. The term endothermic comes from the Greek ἔνδον (endon) meaning 'within' and θερμ- (therm) meaning 'hot' or 'warm'. An endothermic process may be a chemical process, such as dissolving ammonium nitrate (NH4NO3) in water (H2O), or a physical process, such as the melting of ice cubes. The opposite of an endothermic process is an exothermic process, one that releases or "gives out" energy, usually in the form of heat and sometimes as electrical energy. Thus, endo in endothermic refers to energy or heat going in, and exo in exothermic refers to energy or heat going out. In each term (endothermic and exothermic) the prefix refers to where heat (or electrical energy) goes as the process occurs. == In chemistry ==


id: exergonic-process-20260505-0
file: data/en.wikipedia.org/wiki/Exergonic_process-0.md
category: reference
title: Exergonic process
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Exergonic_process
date_saved: 2026-05-05T10:57:04.702364+00:00
instance: kb-cron
parent: exergonic-process-20260505-0
summary:
An exergonic process is one which there is a positive flow of energy from the system to the surroundings. This is in contrast with an endergonic process. Constant pressure, constant temperature reactions are exergonic if and only if the Gibbs free energy change is negative (∆G < 0). "Exergonic" (from the prefix exo-, derived for the Greek word ἔξω exō, "outside" and the suffix -ergonic, derived from the Greek word ἔργον ergon, "work") means "releasing energy in the form of work". In thermodynamics, work is defined as the energy moving from the system (the internal region) to the surroundings (the external region) during a given process. All physical and chemical systems in the universe follow the second law of thermodynamics and proceed in a downhill, i.e., exergonic, direction. Thus, left to itself, any physical or chemical system will proceed, according to the second law of thermodynamics, in a direction that tends to lower the free energy of the system, and thus to expend energy in the form of work. These reactions occur spontaneously. A chemical reaction is also exergonic when spontaneous. Thus in this type of reactions the Gibbs free energy decreases. The entropy is included in any change of


id: exergonic-reaction-20260505-0
file: data/en.wikipedia.org/wiki/Exergonic_reaction-0.md
category: reference
title: Exergonic reaction
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Exergonic_reaction
date_saved: 2026-05-05T10:57:05.879383+00:00
instance: kb-cron
parent: exergonic-reaction-20260505-0
summary:
In chemical thermodynamics, an exergonic reaction is a chemical reaction where the change in the free energy is negative (there is a net release of free energy). This indicates a spontaneous reaction if the system is closed and initial and final temperatures are the same. For processes that take place in a closed system at constant pressure and temperature, the Gibbs free energy is used, whereas the Helmholtz energy is relevant for processes that take place at constant volume and temperature. Any reaction occurring at constant temperature without input of electrical or photon energy is exergonic, according to the second law of thermodynamics. An example is cellular respiration. Symbolically, the release of free energy, ⁠ G {\displaystyle G} ⁠, in an exergonic reaction (at constant pressure and temperature) is denoted as Δ G = G p − G r < 0. {\displaystyle \Delta G=G_{\rm {p}}-G_{\rm {r}}<0.\,} Although exergonic reactions are said to occur spontaneously, this does not imply that the reaction will take place at an observable rate. For instance, the disproportionation of hydrogen peroxide releases free energy but is very slow in the absence of a suitable catalyst. It has been suggested that eager would be a more intuitive


id: exothermic-process-20260505-0
file: data/en.wikipedia.org/wiki/Exothermic_process-0.md
category: reference
title: Exothermic process
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Exothermic_process
date_saved: 2026-05-05T10:57:07.159794+00:00
instance: kb-cron
parent: exothermic-process-20260505-0
summary:
In thermodynamics, an exothermic process (from Ancient Greek έξω (éxō) 'outward' and θερμικός (thermikós) 'thermal') is a thermodynamic process or reaction that releases energy from the system to its surroundings, usually in the form of heat, but also in a form of light (e.g. a spark, flame, or flash), electricity (e.g. a battery), or sound (e.g. explosion heard when burning hydrogen). The term exothermic was coined by 19th-century French chemist Marcellin Berthelot. The opposite of an exothermic process is an endothermic process, one that absorbs energy, usually in the form of heat. The concept is frequently applied in the physical sciences to chemical reactions where chemical bond energy is converted to thermal energy (heat). == Two types of chemical reactions == Exothermic and endothermic describe two types of chemical reactions or systems found in nature, as follows: === Exothermic === An exothermic reaction occurs when heat is released to the surroundings. According to the IUPAC, an exothermic reaction is "a reaction for which the overall standard enthalpy change ΔH° is negative". Some examples of exothermic process are fuel combustion, condensation and nuclear fission, which is used in nuclear power plants to release large amounts of energy. === Endothermic === In


id: gas-slug-20260505-0
file: data/en.wikipedia.org/wiki/Gas_slug-0.md
category: reference
title: Gas slug
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Gas_slug
date_saved: 2026-05-05T10:57:08.375191+00:00
instance: kb-cron
parent: gas-slug-20260505-0
summary:
A gas slug is a conglomerate of high pressure gas bubbles that forms within certain volcanoes, the agitation of which is a driving factor in Strombolian eruptions. They start out as small bubbles of gas inside of volcanic magma. These accumulate into one large bubble, which starts to rise through the lava plume. Gas slugs also consist of many chemical properties that assist scientists in monitoring volcanic eruptions. == Chemistry == Volcanic eruptions consist of mostly water vapor gases, with sulfur dioxide and carbon dioxide playing a huge part in gas release as well. Volcanic gases also rely on the composition of magma in the chamber of the volcano and gas separation processes before the point of eruption. Taylor bubbles, named after G. I. Taylor, refer to elongated gas bubbles in a liquid flow of a system. Taylor bubbles are distinctly "bullet shaped" and are involved in fluid dynamics. Within volcanic activity, magma rises in the volcanic chamber, slowing the movement of gas particles (H2O, SO2, CO2) and allowing for them to separate. As a result, this creates Taylor bubbles, which play a big part in Strombolian eruptions. == Formation == Once the accumulated slug reaches the top of the


id: isenthalpic-process-20260505-0
file: data/en.wikipedia.org/wiki/Isenthalpic_process-0.md
category: reference
title: Isenthalpic process
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Isenthalpic_process
date_saved: 2026-05-05T10:57:09.549646+00:00
instance: kb-cron
parent: isenthalpic-process-20260505-0
summary:
An isenthalpic process or isoenthalpic process is a process that proceeds without any change in enthalpy, H; or specific enthalpy, h. If a steady-state, steady-flow process is analysed using a control volume, everything outside the control volume is considered to be the surroundings. == Definition and formula == Such a process will be isenthalpic if there is no transfer of heat to or from the surroundings, no work done on or by the surroundings, and no change in the kinetic energy of the fluid. This is a sufficient but not necessary condition for isoenthalpy. The necessary condition for a process to be isoenthalpic is that the sum of each of the terms of the energy balance other than enthalpy (work, heat, changes in kinetic energy, etc.) cancel each other, so that the enthalpy remains unchanged. For a process in which magnetic and electric effects (among others) give negligible contributions, the associated energy balance can be written as d K + d u = Q + W {\displaystyle dK+du=Q+W} d u = d ( h − P V ) = d h − d ( P V ) {\displaystyle du=d(h-PV)=dh-d(PV)} d K + d h − d ( P V )


id: isentropic-expansion-waves-20260505-0
file: data/en.wikipedia.org/wiki/Isentropic_expansion_waves-0.md
category: reference
title: Isentropic expansion waves
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Isentropic_expansion_waves
date_saved: 2026-05-05T10:57:10.815910+00:00
instance: kb-cron
parent: isentropic-expansion-waves-20260505-0
summary:
In fluid dynamics, isentropic expansion waves are created when a supersonic flow is redirected along a curved surface. These waves are studied to obtain a relation between deflection angle and Mach number. Each wave in this case is a Mach wave, so it is at an angle α = sin − 1 ⁡ 1 M , {\displaystyle \alpha =\sin ^{-1}{\tfrac {1}{M}},} where M is the Mach number immediately before the wave. Expansion waves are divergent because as the flow expands the value of Mach number increases, thereby decreasing the Mach angle. In an isentropic wave, the speed changes from v to v + dv, with deflection dθ. We have oriented the coordinate system orthogonal to the wave. We write the basic equations (continuity, momentum and the first and second laws of thermodynamics) for this infinitesimal control volume. == Relation between θ, M and v == Assumptions: Steady flow. Negligible body forces. Adiabatic flow. No work terms. Negligible gravitational effect. The continuity equation is ∂ ∂ t ∫ C V ρ d V + ∫ C S ρ v ¯ d A ¯ = 0 ( 1.1 ) {\displaystyle {\frac {\partial }{\partial t}}\int \limits _{CV}\rho dV+\int \limits _{CS}\rho {\bar {v}}\,d{\bar {A}}=0\qquad


id: isentropic-expansion-waves-20260505-1
file: data/en.wikipedia.org/wiki/Isentropic_expansion_waves-1.md
category: reference
title: Isentropic expansion waves
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Isentropic_expansion_waves
date_saved: 2026-05-05T10:57:10.815910+00:00
instance: kb-cron
parent: isentropic-expansion-waves-20260505-0
summary:
d v v = d M M − v d v 2 c p T = d M M − d v v 2 c p T 2 v = d M M − d v M 2 c 2 c p T 2 v = d M M − d v M 2 k R T c p T 2 v = d M M − d v [ M 2 ( k − 1 ) ] 2 v {\displaystyle {\begin{aligned}{\frac {dv}{v}}&={\frac {dM}{M}}-{\frac {vdv}{2c_{p}T}}\\[2pt]&={\frac {dM}{M}}-{\frac {dv{\frac {v^{2}}{c_{p}T}}}{2v}}\\[2pt]&={\frac {dM}{M}}-{\frac {dv{\frac {M^{2}c^{2}}{c_{p}T}}}{2v}}\\[2pt]&={\frac {dM}{M}}-{\frac {dv{\frac {M^{2}kRT}{c_{p}T}}}{2v}}\\[2pt]&={\frac {dM}{M}}-{\frac {dv[M^{2}(k-1)]}{2v}}\end{aligned}}} Hence, d v v = 2 2 + M 2 ( k − 1 ) d M M ( 1.7 ) {\displaystyle {\frac {dv}{v}}={\frac {2}{2+M^{2}(k-1)}}{\frac {dM}{M}}\qquad \qquad (1.7)} Combining (1.4) and (1.7) d θ 2 M 2 − 1 = − 1 2 + M 2 ( k − 1 ) d M M ( 1.8 ) {\displaystyle {\frac {d\theta }{2{\sqrt {M^{2}-1}}}}=-{\frac {1}{2+M^{2}(k-1)}}{\frac {dM}{M}}\qquad \qquad (1.8)} We generally apply the above equation to negative d θ {\displaystyle d\theta } , let d ω = d θ {\displaystyle d\omega =d\theta } . We can integrate this between the initial and final Mach numbers of given


id: isentropic-nozzle-flow-20260505-0
file: data/en.wikipedia.org/wiki/Isentropic_nozzle_flow-0.md
category: reference
title: Isentropic nozzle flow
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Isentropic_nozzle_flow
date_saved: 2026-05-05T10:57:11.982282+00:00
instance: kb-cron
parent: isentropic-nozzle-flow-20260505-0
summary:
In fluid mechanics, isentropic nozzle flow describes the movement of a fluid through a narrow opening without an increase in entropy (an isentropic process). == Overview == Whenever a gas is forced through a tube, the gaseous molecules are deflected by the tube's walls. If the speed of the gas is much less than the speed of sound, the gas density will remain constant and the velocity of the flow will increase. However, as the speed of the flow approaches the speed of sound, compressibility effects on the gas are to be considered. The density of the gas becomes position dependent. While considering flow through a tube, if the flow is very gradually compressed (i.e. area decreases) and then gradually expanded (i.e. area increases), the flow conditions are restored (i.e. return to its initial position). So, such a process is a reversible process. According to the second law of thermodynamics, whenever there is a reversible and adiabatic flow, constant value of entropy is maintained. Engineers classify this type of flow as an isentropic flow of fluids. Isentropic is the combination of the Greek word "iso" (which means - same) and entropy. When the change in flow variables is small and


id: isentropic-nozzle-flow-20260505-1
file: data/en.wikipedia.org/wiki/Isentropic_nozzle_flow-1.md
category: reference
title: Isentropic nozzle flow
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Isentropic_nozzle_flow
date_saved: 2026-05-05T10:57:11.982282+00:00
instance: kb-cron
parent: isentropic-nozzle-flow-20260505-0
summary:
== Flow analysis == The isentropic efficiency is h 1 − h 2 a h 1 − h 2 {\displaystyle {\frac {h_{1}-h_{2a}}{h_{1}-h_{2}}}} . The variation of fluid density for compressible flows requires attention to density and other fluid property relationships. The fluid equation of state, often unimportant for incompressible flows, is vital in the analysis of compressible flows. Also, temperature variations for compressible flows are usually significant and thus the energy equation is important. Curious phenomena can occur with compressible flows. For simplicity, the gas is assumed to be an ideal gas. The gas flow is isentropic. The gas flow is constant. The gas flow is along a straight line from gas inlet to exhaust gas exit. The gas flow behavior is compressible. There are numerous applications where a steady, uniform, isentropic flow is a good approximation to the flow in conduits. These include the flow through a jet engine, through the nozzle of a rocket, from a broken gas line, and past the blades of a turbine. M = Mach number V = velocity R = universal gas constant p = pressure k = specific heat ratio T = temperature * = sonic conditions ρ = density A =


id: isentropic-nozzle-flow-20260505-2
file: data/en.wikipedia.org/wiki/Isentropic_nozzle_flow-2.md
category: reference
title: Isentropic nozzle flow
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Isentropic_nozzle_flow
date_saved: 2026-05-05T10:57:11.982282+00:00
instance: kb-cron
parent: isentropic-nozzle-flow-20260505-0
summary:
T ∗ = 0.833333 ⋅ T 0 p ∗ = 0.528282 ⋅ p 0 ρ ∗ = 0.633938 ⋅ ρ 0 {\displaystyle {\begin{aligned}T^{*}&=0.833333\cdot T_{0}\\p^{*}&=0.528282\cdot p_{0}\\\rho ^{*}&=0.633938\cdot \rho _{0}\end{aligned}}} The mass flux through the nozzle is of interest and is given by: m ˙ = ρ A V = p R T ⋅ A ⋅ M k R s p e c i f i c T = p k M m R T A M {\displaystyle {\dot {m}}=\rho AV={\frac {p}{RT}}\cdot A\cdot M{\sqrt {kR_{specific}T}}=p{\sqrt {kM_{m} \over RT}}AM} With the use of Eq. (9.28), the mass flux, after applying some algebra, can be expressed as m ˙ = p 0 M A k M m R T 0 ( 1 + k − 1 2 M 2 ) k + 1 − 2 ( k − 1 ) {\displaystyle {\dot {m}}=p_{0}MA{\sqrt {\frac {kM_{m}}{RT_{0}}}}\left(1+{\frac {k-1}{2}}M^{2}\right)^{\frac {k+1}{-2(k-1)}}} If the critical area is selected where M = 1, this takes the form m ˙ = p 0 A ∗ k M m R T 0 ( 1 + k − 1 2 ) k + 1 − 2 ( k − 1 ) {\displaystyle {\dot {m}}=p_{0}A^{*}{\sqrt {\frac {kM_{m}}{RT_{0}}}}\left(1+{\frac {k-1}{2}}\right)^{\frac {k+1}{-2(k-1)}}} which, when combined with previous


id: isentropic-process-20260505-0
file: data/en.wikipedia.org/wiki/Isentropic_process-0.md
category: reference
title: Isentropic process
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Isentropic_process
date_saved: 2026-05-05T10:57:13.245109+00:00
instance: kb-cron
parent: isentropic-process-20260505-0
summary:
An isentropic process is an idealized thermodynamic process that is both adiabatic and reversible. In thermodynamics, adiabatic processes are reversible. Clausius (1875) adopted "isentropic" as meaning the same as Rankine's word: "adiabatic". The work transfers of the system are frictionless, and there is no net transfer of heat or matter. Such an idealized process is useful in engineering as a model of and basis of comparison for real processes. This process is idealized because reversible processes do not occur in reality; thinking of a process as both adiabatic and reversible would show that the initial and final entropies are the same, thus, the reason it is called isentropic (entropy does not change). Thermodynamic processes are named based on the effect they would have on the system (ex. isovolumetric/isochoric: constant volume, isenthalpic: constant enthalpy). Even though in reality it is not necessarily possible to carry out an isentropic process, some may be approximated as such. The word "isentropic" derives from the process being one in which the entropy of the system remains unchanged, in addition to a process which is both adiabatic and reversible. == Background == The second law of thermodynamics states that T surr d S ≥ δ Q


id: isentropic-process-20260505-1
file: data/en.wikipedia.org/wiki/Isentropic_process-1.md
category: reference
title: Isentropic process
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Isentropic_process
date_saved: 2026-05-05T10:57:13.245109+00:00
instance: kb-cron
parent: isentropic-process-20260505-0
summary:
Then for a process that is both reversible and adiabatic (i.e. no heat transfer occurs), δ Q rev = 0 {\displaystyle \delta Q_{\text{rev}}=0} , and so d S = δ Q rev / T = 0 {\displaystyle dS=\delta Q_{\text{rev}}/T=0} All reversible adiabatic processes are isentropic. This leads to two important observations: d U = δ W + δ Q = − p d V + 0 , {\displaystyle dU=\delta W+\delta Q=-p\,dV+0,} d H = δ W + δ Q + p d V + V d p = − p d V + 0 + p d V + V d p = V d p . {\displaystyle dH=\delta W+\delta Q+p\,dV+V\,dp=-p\,dV+0+p\,dV+V\,dp=V\,dp.} Next, a great deal can be computed for isentropic processes of an ideal gas. For any transformation of an ideal gas, it is always true that d U = n C v d T {\displaystyle dU=nC_{v}\,dT} , and d H = n C p d T . {\displaystyle dH=nC_{p}\,dT.} Using the general results derived above for d U {\displaystyle dU} and d H {\displaystyle dH} , then d U = n C v d T = − p d V , {\displaystyle dU=nC_{v}\,dT=-p\,dV,} d H = n C p


id: isobaric-process-20260505-0
file: data/en.wikipedia.org/wiki/Isobaric_process-0.md
category: reference
title: Isobaric process
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Isobaric_process
date_saved: 2026-05-05T10:57:14.483031+00:00
instance: kb-cron
parent: isobaric-process-20260505-0
summary:
In thermodynamics, an isobaric process is a type of thermodynamic process in which the pressure of the system stays constant: ΔP = 0. The heat transferred to the system does work, but also changes the internal energy (U) of the system. This article uses the physics sign convention for work, where positive work is work done by the system. Using this convention, by the first law of thermodynamics, Q = Δ U + W {\displaystyle Q=\Delta U+W\,} where W is work, U is internal energy, and Q is heat. Pressure-volume work by the closed system is defined as: W = ∫ p d V {\displaystyle W=\int \!p\,dV\,} where Δ means change over the whole process, whereas d denotes a differential. Since pressure is constant, this means that W = p Δ V {\displaystyle W=p\Delta V\,} . Applying the ideal gas law, this becomes W = n R Δ T {\displaystyle W=n\,R\,\Delta T} with R representing the gas constant, and n representing the amount of substance, which is assumed to remain constant (e.g., there is no phase transition during a chemical reaction). According to the equipartition theorem, the change in internal energy is related to the temperature of the system by


id: isobaric-process-20260505-1
file: data/en.wikipedia.org/wiki/Isobaric_process-1.md
category: reference
title: Isobaric process
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Isobaric_process
date_saved: 2026-05-05T10:57:14.483031+00:00
instance: kb-cron
parent: isobaric-process-20260505-0
summary:
In the first process example, a cylindrical chamber 1 m2 in area encloses 81.2438 mol of an ideal diatomic gas of molecular mass 29 g mol−1 at 300 K. The surrounding gas is at 1 atm and 300 K, and separated from the cylinder gas by a thin piston. For the limiting case of a massless piston, the cylinder gas is also at 1 atm pressure, with an initial volume of 2 m3. Heat is added slowly until the gas temperature is uniformly 600 K, after which the gas volume is 4 m3 and the piston is 2 m above its initial position. If the piston motion is sufficiently slow, the gas pressure at each instant will have practically the same value (psys = 1 atm) throughout. For a thermally perfect diatomic gas, the molar specific heat capacity at constant pressure (cp) is 7/2R or 29.1006 J mol−1 deg−1. The molar heat capacity at constant volume (cv) is 5/2R or 20.7862 J mol−1 deg−1. The ratio γ {\displaystyle \gamma } of the two heat capacities is 1.4. The heat Q required to bring the gas from 300 to 600 K is Q = Δ H = n c p Δ


id: isochoric-process-20260505-0
file: data/en.wikipedia.org/wiki/Isochoric_process-0.md
category: reference
title: Isochoric process
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Isochoric_process
date_saved: 2026-05-05T10:57:15.681952+00:00
instance: kb-cron
parent: isochoric-process-20260505-0
summary:
In thermodynamics, an isochoric process, also called a constant-volume process, an isovolumetric process, or an isometric process, is a thermodynamic process during which the volume of the closed system undergoing such a process remains constant. An isochoric process is exemplified by the heating or the cooling of the contents of a sealed, inelastic container: The thermodynamic process is the addition or removal of heat; the isolation of the contents of the container establishes the closed system; and the inability of the container to deform imposes the constant-volume condition. == Formalism == An isochoric thermodynamic quasi-static process is characterized by constant volume, i.e., ΔV = 0. The process does no pressure-volume work, since such work is defined by W = P Δ V , {\displaystyle W=P\Delta V,} where P is pressure. The sign convention is such that positive work is performed by the system on the environment. If the process is not quasi-static, the work can perhaps be done in a volume constant thermodynamic process. For a reversible process, the first law of thermodynamics gives the change in the system's internal energy: d U = d Q − d W {\displaystyle dU=dQ-dW} Replacing work with a change in volume gives d


id: isothermal-process-20260505-0
file: data/en.wikipedia.org/wiki/Isothermal_process-0.md
category: reference
title: Isothermal process
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Isothermal_process
date_saved: 2026-05-05T10:57:16.881965+00:00
instance: kb-cron
parent: isothermal-process-20260505-0
summary:
An isothermal process is a type of thermodynamic process in which the temperature T of a system remains constant: ΔT = 0. This typically occurs when a system is in contact with an outside thermal reservoir, and a change in the system occurs slowly enough to allow the system to be continuously adjusted to the temperature of the reservoir through heat exchange (see quasi-equilibrium). In contrast, an adiabatic process is where a system exchanges no heat with its surroundings (Q = 0). Simply, we can say that in an isothermal process T = constant {\displaystyle T={\text{constant}}} Δ T = 0 {\displaystyle \Delta T=0} d T = 0 {\displaystyle dT=0} For ideal gases only, internal energy Δ U = 0 {\displaystyle \Delta U=0} while in adiabatic processes: Q = 0. {\displaystyle Q=0.} == Etymology == The noun isotherm is derived from the Ancient Greek words ἴσος (ísos), meaning "equal", and θέρμη (thérmē), meaning "heat". == Examples == Isothermal processes can occur in any kind of system that has some means of regulating the temperature, including highly structured machines, and even living cells. Some parts of the cycles of some heat engines are carried out isothermally (for example, in the Carnot cycle).


id: isothermal-process-20260505-1
file: data/en.wikipedia.org/wiki/Isothermal_process-1.md
category: reference
title: Isothermal process
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Isothermal_process
date_saved: 2026-05-05T10:57:16.881965+00:00
instance: kb-cron
parent: isothermal-process-20260505-0
summary:
In IUPAC convention, work is defined as work on a system by its surroundings. If, for example, the system is compressed, then the work is done on the system by the surrounding so the work is positive and the internal energy of the system increases. Conversely, if the system expands (i.e., system surrounding expansion, so free expansions not the case), then the work is negative as the system does work on the surroundings. It is also worth noting that for ideal gases, if the temperature is held constant, the internal energy of the system U also is constant, and so ΔU = 0. Since the first law of thermodynamics states that ΔU = Q + W in IUPAC convention, it follows that Q = −W for the isothermal compression or expansion of ideal gases. == Example of an isothermal process == The reversible expansion of an ideal gas can be used as an example of work produced by an isothermal process. Of particular interest is the extent to which heat is converted to usable work, and the relationship between the confining force and the extent of expansion. During isothermal expansion of an ideal gas, both p and V change along


id: isothermal-process-20260505-2
file: data/en.wikipedia.org/wiki/Isothermal_process-2.md
category: reference
title: Isothermal process
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Isothermal_process
date_saved: 2026-05-05T10:57:16.881965+00:00
instance: kb-cron
parent: isothermal-process-20260505-0
summary:
Δ S = n R ln ⁡ P A P B {\displaystyle \Delta S=nR\ln {\frac {P_{\text{A}}}{P_{\text{B}}}}} . Once obtained, these formulas can be applied to an irreversible process, such as the free expansion of an ideal gas. Such an expansion is also isothermal and may have the same initial and final states as in the reversible expansion. Since entropy is a state function (that depends on an equilibrium state, not depending on a path that the system takes to reach that state), the change in entropy of the system is the same as in the reversible process and is given by the formulas above. Note that the result Q = 0 for the free expansion can not be used in the formula for the entropy change since the process is not reversible. The difference between the reversible and irreversible is found in the entropy of the surroundings. In both cases, the surroundings are at a constant temperature, T, so that ΔSsur = −⁠Q/T⁠; the minus sign is used since the heat transferred to the surroundings is equal in magnitude and opposite in sign to the heat Q transferred to the system. In the reversible case, the change in entropy of


id: mass-injection-flow-20260505-0
file: data/en.wikipedia.org/wiki/Mass_injection_flow-0.md
category: reference
title: Mass injection flow
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Mass_injection_flow
date_saved: 2026-05-05T10:57:18.086943+00:00
instance: kb-cron
parent: mass-injection-flow-20260505-0
summary:
Mass injection flow (a.k.a. Limbach Flow) refers to inviscid, adiabatic flow through a constant area duct where the effect of mass addition is considered. For this model, the duct area remains constant, the flow is assumed to be steady and one-dimensional, and mass is added within the duct. Because the flow is adiabatic, unlike in Rayleigh flow, the stagnation temperature is a constant. Compressibility effects often come into consideration, though this flow model also applies to incompressible flow. For supersonic flow (an upstream Mach number greater than 1), deceleration occurs with mass addition to the duct and the flow can become choked. Conversely, for subsonic flow (an upstream Mach number less than 1), acceleration occurs and the flow can become choked given sufficient mass addition. Therefore, mass addition will cause both supersonic and subsonic Mach numbers to approach Mach 1, resulting in choked flow. == Theory == The 1D mass injection flow model begins with a mass-velocity relation derived for mass injection into a steady, adiabatic, frictionless, constant area flow of calorically perfect gas: d m m = − d u u ( M 2 − 1 ) {\displaystyle \ {\frac {dm}{m}}=-{\frac {du}{u}}\left(M^{2}-1\right)} where m {\displaystyle m} represents a mass


id: polytropic-process-20260505-0
file: data/en.wikipedia.org/wiki/Polytropic_process-0.md
category: reference
title: Polytropic process
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Polytropic_process
date_saved: 2026-05-05T10:57:19.316858+00:00
instance: kb-cron
parent: polytropic-process-20260505-0
summary:
A polytropic process is a thermodynamic process that obeys the relation: p V n = C {\displaystyle pV^{n}=C} where p is the pressure, V is volume, n is the polytropic index, and C is a constant. The polytropic process equation describes expansion and compression processes which include heat transfer. == Particular cases == Some specific values of n correspond to particular cases: n = 0 {\displaystyle n=0} for an isobaric process, n = + ∞ {\displaystyle n=+\infty } for an isochoric process. In addition, when the ideal gas law applies: n = 1 {\displaystyle n=1} for an isothermal process, n = γ {\displaystyle n=\gamma } for an isentropic process. Where γ {\displaystyle \gamma } is the ratio of the heat capacity at constant pressure ( C P {\displaystyle C_{P}} ) to heat capacity at constant volume ( C V {\displaystyle C_{V}} ). == Equivalence between the polytropic coefficient and the ratio of energy transfers == For an ideal gas in a closed system undergoing a slow process with negligible changes in kinetic and potential energy the process is polytropic, such that p v ( 1 − γ ) K + γ = C {\displaystyle pv^{(1-\gamma )K+\gamma }=C} where C is


id: quasistatic-process-20260505-0
file: data/en.wikipedia.org/wiki/Quasistatic_process-0.md
category: reference
title: Quasistatic process
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Quasistatic_process
date_saved: 2026-05-05T10:57:20.519703+00:00
instance: kb-cron
parent: quasistatic-process-20260505-0
summary:
In thermodynamics, a quasi-static process, also known as a quasi-equilibrium process (from Latin quasi, meaning ‘as if’), is a thermodynamic process that happens slowly enough for the system to remain in internal physical (but not necessarily chemical) thermodynamic equilibrium. An example of this is quasi-static expansion of a mixture of hydrogen and oxygen gas, where the volume of the system changes so slowly that the pressure remains uniform throughout the system at each instant of time during the process. Such an idealized process is a succession of physical equilibrium states, characterized by infinite slowness. Only in a quasi-static thermodynamic process can we exactly define intensive quantities (such as pressure, temperature, specific volume, specific entropy) of the system at any instant during the whole process; otherwise, since no internal equilibrium is established, different parts of the system would have different values of these quantities, so a single value per quantity may not be sufficient to represent the whole system. In other words, when an equation for a change in a state function contains P or T, it implies a quasi-static process. == Relation to reversible process == While all reversible processes are quasi-static, most authors do not require a general quasi-static


id: reversible-process-thermodynamics-20260505-0
file: data/en.wikipedia.org/wiki/Reversible_process_(thermodynamics)-0.md
category: reference
title: Reversible process (thermodynamics)
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Reversible_process_(thermodynamics)
date_saved: 2026-05-05T10:57:21.720507+00:00
instance: kb-cron
parent: reversible-process-thermodynamics-20260505-0
summary:
In thermodynamics, a reversible process is a process, involving a system and its surroundings, whose direction can be reversed by infinitesimal changes in some properties of the surroundings, such as pressure or temperature. Throughout an entire reversible process, the system is in thermodynamic equilibrium, both physical and chemical, and nearly in pressure and temperature equilibrium with its surroundings. This prevents unbalanced forces and acceleration of moving system boundaries, which in turn avoids friction and other dissipation. To maintain equilibrium, reversible processes are extremely slow (quasistatic). The process must occur slowly enough that after some small change in a thermodynamic parameter, the physical processes in the system have enough time for the other parameters to self-adjust to match the new, changed parameter value. For example, if a container of water has sat in a room long enough to match the steady temperature of the surrounding air, for a small change in the air temperature to be reversible, the whole system of air, water, and container must wait long enough for the container and air to settle into a new, matching temperature before the next small change can occur. While processes in isolated systems are never reversible, cyclical processes can be reversible


id: supercooling-20260505-0
file: data/en.wikipedia.org/wiki/Supercooling-0.md
category: reference
title: Supercooling
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Supercooling
date_saved: 2026-05-05T10:57:22.942902+00:00
instance: kb-cron
parent: supercooling-20260505-0
summary:
Supercooling, also known as undercooling, is the process of lowering the temperature of a liquid below its freezing point without it becoming a solid. Per the established international definition, supercooling means "cooling a substance below the normal freezing point without solidification". While it can be achieved by different physical means, the postponed solidification is most often due to the absence of seed crystals or nuclei around which a crystal structure can form. The supercooling of water can be achieved without any special techniques other than chemical demineralization, down to −48.3 °C (−54.9 °F). Supercooled water can occur naturally, for example in the atmosphere, animals or plants. This phenomenon was first described in 1724 by Daniel Gabriel Fahrenheit, while developing the Fahrenheit scale. == Explanation == A liquid crossing its standard freezing point will crystallize in the presence of a seed crystal or nucleus around which a crystal structure can form creating a solid. Lacking any such nuclei, the liquid phase can be maintained all the way down to the temperature at which crystal homogeneous nucleation occurs. Homogeneous nucleation can occur above the glass transition temperature, but if homogeneous nucleation has not occurred above that temperature, an amorphous (non-crystalline) solid will


id: supercooling-20260505-1
file: data/en.wikipedia.org/wiki/Supercooling-1.md
category: reference
title: Supercooling
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Supercooling
date_saved: 2026-05-05T10:57:22.942902+00:00
instance: kb-cron
parent: supercooling-20260505-0
summary:
== In animals == In order to survive extreme low temperatures in certain environments, some animals use the phenomenon of supercooling that allow them to remain unfrozen and avoid cell damage and death. There are many techniques that aid in maintaining a liquid state, such as the production of antifreeze proteins, or AFPs, which bind to ice crystals to prevent water molecules from binding and spreading the growth of ice. The winter flounder is one such fish that utilizes these proteins to survive in its frigid environment. The liver secretes noncolligative proteins into the bloodstream. Other animals use colligative antifreezes, which increase the concentration of solutes in their bodily fluids, thus lowering their freezing point. Fish that rely on supercooling for survival must also live well below the water surface, because if they came into contact with ice nuclei they would freeze immediately. Animals that undergo supercooling to survive must also remove ice-nucleating agents from their bodies because they act as a starting point for freezing. Supercooling is also a common feature in some insect, reptile, and other ectotherm species. The potato cyst nematode larva (Globodera rostochiensis) could survive inside their cysts in a supercooled state to temperatures as low


id: supercooling-20260505-2
file: data/en.wikipedia.org/wiki/Supercooling-2.md
category: reference
title: Supercooling
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Supercooling
date_saved: 2026-05-05T10:57:22.942902+00:00
instance: kb-cron
parent: supercooling-20260505-0
summary:
== Applications == One commercial application of supercooling is in refrigeration. Freezers can cool drinks to a supercooled level so that when they are opened, they form a slush. Another example is a product that can supercool the beverage in a conventional freezer. The Coca-Cola Company briefly marketed special vending machines containing Sprite in the UK, and Coke in Singapore, which stored the bottles in a supercooled state so that their content would turn to slush upon opening. Supercooling was successfully applied to organ preservation at Massachusetts General Hospital/Harvard Medical School. Livers that were later transplanted into recipient animals were preserved by supercooling for up to 4 days, quadrupling the limits of what could be achieved by conventional liver preservation methods. The livers were supercooled to a temperature of −6 °C (21 °F) in a specialized solution that protected against freezing and injury from the cold temperature. Another potential application is drug delivery. In 2015, researchers crystallized membranes at a specific time. Liquid-encapsulated drugs could be delivered to the site and, with a slight environmental change, the liquid rapidly changes into a crystalline form that releases the drug. In 2016, a team at Iowa State University proposed a method for


id: superheating-20260505-0
file: data/en.wikipedia.org/wiki/Superheating-0.md
category: reference
title: Superheating
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Superheating
date_saved: 2026-05-05T10:57:24.142400+00:00
instance: kb-cron
parent: superheating-20260505-0
summary:
In thermodynamics, superheating (sometimes referred to as boiling retardation, or boiling delay) is the phenomenon in which a liquid is heated to a temperature higher than its boiling point, without boiling. This is a so-called metastable state or metastate, where boiling might occur at any time, induced by external or internal effects. Superheating is achieved by heating a homogeneous substance in a clean container, free of nucleation sites, while taking care not to disturb the liquid. This may occur by microwaving water in a very smooth container. Disturbing the water may cause an unsafe eruption of hot water and result in burns. == Cause == Water is said to "boil" when bubbles of water vapor grow without bound, bursting at the surface. For a vapor bubble to expand, the temperature must be high enough that the vapor pressure exceeds the ambient pressure (the atmospheric pressure, primarily). Below that temperature, a water vapor bubble will shrink and vanish. Superheating is an exception to this simple rule; a liquid is sometimes observed not to boil even though its vapor pressure does exceed the ambient pressure. The cause is an additional force, the surface tension, which suppresses the growth of bubbles. Surface tension


id: thermodynamic-cycle-20260505-0
file: data/en.wikipedia.org/wiki/Thermodynamic_cycle-0.md
category: reference
title: Thermodynamic cycle
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thermodynamic_cycle
date_saved: 2026-05-05T10:57:25.331304+00:00
instance: kb-cron
parent: thermodynamic-cycle-20260505-0
summary:
A thermodynamic cycle consists of linked sequences of thermodynamic processes that involve transfer of heat and work into and out of the system, while varying pressure, temperature, and other state variables within the system, and that eventually returns the system to its initial state. In the process of passing through a cycle, the working fluid (system) may convert heat from a warm source into useful work, and dispose of the remaining heat to a cold sink, thereby acting as a heat engine. Conversely, the cycle may be reversed and use work to move heat from a cold source and transfer it to a warm sink thereby acting as a heat pump. If at every point in the cycle the system is in thermodynamic equilibrium, the cycle is reversible. Whether carried out reversibly or irreversibly, the net entropy change of the system is zero, as entropy is a state function. During a closed cycle, the system returns to its original thermodynamic state of temperature and pressure. Process quantities (or path quantities), such as heat and work are process dependent. For a cycle for which the system returns to its initial state the first law of thermodynamics applies: Δ U = E


id: thermodynamic-cycle-20260505-1
file: data/en.wikipedia.org/wiki/Thermodynamic_cycle-1.md
category: reference
title: Thermodynamic cycle
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thermodynamic_cycle
date_saved: 2026-05-05T10:57:25.331304+00:00
instance: kb-cron
parent: thermodynamic-cycle-20260505-0
summary:
1→2: Isentropic / adiabatic expansion: Constant entropy (s), Decrease in pressure (P), Increase in volume (v), Decrease in temperature (T) 2→3: Isochoric cooling: Constant volume(v), Decrease in pressure (P), Decrease in entropy (S), Decrease in temperature (T) 3→4: Isentropic / adiabatic compression: Constant entropy (s), Increase in pressure (P), Decrease in volume (v), Increase in temperature (T) 4→1: Isochoric heating: Constant volume (v), Increase in pressure (P), Increase in entropy (S), Increase in temperature (T) === Power cycles === Thermodynamic power cycles are the basis for the operation of heat engines, which supply most of the world's electric power and run the vast majority of motor vehicles. Power cycles can be organized into two categories: real cycles and ideal cycles. Cycles encountered in real world devices (real cycles) are difficult to analyze because of the presence of complicating effects (friction), and the absence of sufficient time for the establishment of equilibrium conditions. For the purpose of analysis and design, idealized models (ideal cycles) are created; these ideal models allow engineers to study the effects of major parameters that dominate the cycle without having to spend significant time working out intricate details present in the real cycle model. Power cycles can


id: thermodynamic-cycle-20260505-2
file: data/en.wikipedia.org/wiki/Thermodynamic_cycle-2.md
category: reference
title: Thermodynamic cycle
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thermodynamic_cycle
date_saved: 2026-05-05T10:57:25.331304+00:00
instance: kb-cron
parent: thermodynamic-cycle-20260505-0
summary:
TOP (A) and BOTTOM (C) of the loop: a pair of parallel isobaric processes RIGHT (B) and LEFT (D) of the loop: a pair of parallel isochoric processes If the working substance is a perfect gas, U {\displaystyle U} is only a function of T {\displaystyle T} for a closed system since its internal pressure vanishes. Therefore, the internal energy changes of a perfect gas undergoing various processes connecting initial state a {\displaystyle a} to final state b {\displaystyle b} are always given by the formula Δ U = ∫ a b C v d T {\displaystyle \Delta U=\int _{a}^{b}C_{v}dT} Assuming that C v {\displaystyle C_{v}} is constant, Δ U = C v Δ T {\displaystyle \Delta U=C_{v}\Delta T} for any process undergone by a perfect gas. Under this set of assumptions, for processes A and C we have W = p Δ v {\displaystyle W=p\Delta v} and Q = C p Δ T {\displaystyle Q=C_{p}\Delta T} , whereas for processes B and D we have W = 0 {\displaystyle W=0} and Q = Δ U = C v Δ T {\displaystyle Q=\Delta U=C_{v}\Delta T} . The total work done per cycle is W c y c l e =


id: thermodynamic-efficiency-limit-20260505-0
file: data/en.wikipedia.org/wiki/Thermodynamic_efficiency_limit-0.md
category: reference
title: Thermodynamic efficiency limit
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thermodynamic_efficiency_limit
date_saved: 2026-05-05T10:57:26.518623+00:00
instance: kb-cron
parent: thermodynamic-efficiency-limit-20260505-0
summary:
The thermodynamic efficiency limit is the absolute maximum theoretically possible conversion efficiency of sunlight to electricity. Its value is about 86%, which is the Chambadal-Novikov efficiency, an approximation related to the Carnot limit, based on the temperature of the photons emitted by the Sun's surface. == Effect of band gap energy == Solar cells operate as quantum energy conversion devices, and are therefore subject to the thermodynamic efficiency limit. Photons with an energy below the band gap of the absorber material cannot generate an electron-hole pair, and so their energy is not converted to useful output and only generates heat if absorbed. For photons with an energy above the band gap energy, only a fraction of the energy above the band gap can be converted to useful output. When a photon of greater energy is absorbed, the excess energy above the band gap is converted to kinetic energy of the carrier recombination. The excess kinetic energy is converted to heat through phonon interactions as the kinetic energy of the carriers slows to equilibrium velocity. Hence, the solar energy cannot be converted to electricity beyond a certain limit. Solar cells with multiple band gap absorber materials improve efficiency by dividing the


id: thermodynamic-equilibrium-20260505-0
file: data/en.wikipedia.org/wiki/Thermodynamic_equilibrium-0.md
category: reference
title: Thermodynamic equilibrium
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thermodynamic_equilibrium
date_saved: 2026-05-05T10:57:27.731222+00:00
instance: kb-cron
parent: thermodynamic-equilibrium-20260505-0
summary:
Thermodynamic equilibrium is a notion of thermodynamics with axiomatic status referring to an internal state of a single thermodynamic system, or a relation between several thermodynamic systems connected by more or less permeable or impermeable walls. In thermodynamic equilibrium, there are no net macroscopic flows of mass nor of energy within a system or between systems. In a system that is in its own state of internal thermodynamic equilibrium, not only is there an absence of macroscopic change, but there is an "absence of any tendency toward change on a macroscopic scale." Systems in mutual thermodynamic equilibrium are simultaneously in mutual thermal, mechanical, chemical, and radiative equilibria. Systems can be in one kind of mutual equilibrium, while not in others. In thermodynamic equilibrium, all kinds of equilibrium hold at once and indefinitely, unless disturbed by a thermodynamic operation. In a macroscopic equilibrium, perfectly or almost perfectly balanced microscopic exchanges occur; this is the physical explanation of the notion of macroscopic equilibrium. A thermodynamic system in a state of internal thermodynamic equilibrium has a spatially uniform temperature. Its intensive properties, other than temperature, may be driven to spatial inhomogeneity by an unchanging long-range force field imposed on it by its surroundings.


id: thermodynamic-equilibrium-20260505-1
file: data/en.wikipedia.org/wiki/Thermodynamic_equilibrium-1.md
category: reference
title: Thermodynamic equilibrium
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thermodynamic_equilibrium
date_saved: 2026-05-05T10:57:27.731222+00:00
instance: kb-cron
parent: thermodynamic-equilibrium-20260505-0
summary:
== Relation of exchange equilibrium between systems == Often the surroundings of a thermodynamic system may also be regarded as another thermodynamic system. In this view, one may consider the system and its surroundings as two systems in mutual contact, with long-range forces also linking them. The enclosure of the system is the surface of contiguity or boundary between the two systems. In the thermodynamic formalism, that surface is regarded as having specific properties of permeability. For example, the surface of contiguity may be supposed to be permeable only to heat, allowing energy to transfer only as heat. Then the two systems are said to be in thermal equilibrium when the long-range forces are unchanging in time and the transfer of energy as heat between them has slowed and eventually stopped permanently; this is an example of a contact equilibrium. Other kinds of contact equilibrium are defined by other kinds of specific permeability. When two systems are in contact equilibrium with respect to a particular kind of permeability, they have common values of the intensive variable that belongs to that particular kind of permeability. Examples of such intensive variables are temperature, pressure, chemical potential. A contact equilibrium may be regarded


id: thermodynamic-equilibrium-20260505-2
file: data/en.wikipedia.org/wiki/Thermodynamic_equilibrium-2.md
category: reference
title: Thermodynamic equilibrium
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thermodynamic_equilibrium
date_saved: 2026-05-05T10:57:27.731222+00:00
instance: kb-cron
parent: thermodynamic-equilibrium-20260505-0
summary:
== Multiple contact equilibrium == The thermodynamic formalism allows that a system may have contact with several other systems at once, which may or may not also have mutual contact, the contacts having respectively different permeabilities. If these systems are all jointly isolated from the rest of the world those of them that are in contact then reach respective contact equilibria with one another. If several systems are free of adiabatic walls between each other, but are jointly isolated from the rest of the world, then they reach a state of multiple contact equilibrium, and they have a common temperature, a total internal energy, and a total entropy. Amongst intensive variables, this is a unique property of temperature. It holds even in the presence of long-range forces. (That is, there is no "force" that can maintain temperature discrepancies.) For example, in a system in thermodynamic equilibrium in a vertical gravitational field, the pressure on the top wall is less than that on the bottom wall, but the temperature is the same everywhere. A thermodynamic operation may occur as an event restricted to the walls that are within the surroundings, directly affecting neither the walls of contact of the system of


id: thermodynamic-equilibrium-20260505-3
file: data/en.wikipedia.org/wiki/Thermodynamic_equilibrium-3.md
category: reference
title: Thermodynamic equilibrium
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thermodynamic_equilibrium
date_saved: 2026-05-05T10:57:27.731222+00:00
instance: kb-cron
parent: thermodynamic-equilibrium-20260505-0
summary:
== Local and global equilibrium == It can be useful to distinguish between global and local thermodynamic equilibrium. In thermodynamics, exchanges within a system and between the system and the outside are controlled by intensive parameters. As an example, temperature controls heat exchanges. Global thermodynamic equilibrium (GTE) means that those intensive parameters are homogeneous throughout the whole system, while local thermodynamic equilibrium (LTE) means that those intensive parameters are varying in space and time, but are varying so slowly that, for any point, one can assume thermodynamic equilibrium in some neighborhood about that point. If the description of the system requires variations in the intensive parameters that are too large, the very assumptions upon which the definitions of these intensive parameters are based will break down, and the system will be in neither global nor local equilibrium. For example, it takes a certain number of collisions for a particle to equilibrate to its surroundings. If the average distance it has moved during these collisions removes it from the neighborhood it is equilibrating to, it will never equilibrate, and there will be no LTE. Temperature is, by definition, proportional to the average internal energy of an equilibrated neighborhood. Since there is


id: thermodynamic-equilibrium-20260505-4
file: data/en.wikipedia.org/wiki/Thermodynamic_equilibrium-4.md
category: reference
title: Thermodynamic equilibrium
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thermodynamic_equilibrium
date_saved: 2026-05-05T10:57:27.731222+00:00
instance: kb-cron
parent: thermodynamic-equilibrium-20260505-0
summary:
== Definitions == The most general kind of thermodynamic equilibrium of a system is through contact with the surroundings that allows simultaneous passages of all chemical substances and all kinds of energy. A system in thermodynamic equilibrium may move with uniform acceleration through space but must not change its shape or size while doing so; thus it is defined by a rigid volume in space. It may lie within external fields of force, determined by external factors of far greater extent than the system itself, so that events within the system cannot in an appreciable amount affect the external fields of force. The system can be in thermodynamic equilibrium only if the external force fields are uniform, and are determining its uniform acceleration, or if it lies in a non-uniform force field but is held stationary there by local forces, such as mechanical pressures, on its surface. Thermodynamic equilibrium is a primitive notion of the theory of thermodynamics. According to P.M. Morse: "It should be emphasized that the fact that there are thermodynamic states, ..., and the fact that there are thermodynamic variables which are uniquely specified by the equilibrium state ... are not conclusions deduced logically from some philosophical


id: thermodynamic-equilibrium-20260505-5
file: data/en.wikipedia.org/wiki/Thermodynamic_equilibrium-5.md
category: reference
title: Thermodynamic equilibrium
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thermodynamic_equilibrium
date_saved: 2026-05-05T10:57:27.731222+00:00
instance: kb-cron
parent: thermodynamic-equilibrium-20260505-0
summary:
He then writes: "When the conditions for all three types of equilibrium are satisfied, the system is said to be in a state of thermodynamic equilibrium". P.M. Morse writes that thermodynamics is concerned with "states of thermodynamic equilibrium". He also uses the phrase "thermal equilibrium" while discussing transfer of energy as heat between a body and a heat reservoir in its surroundings, though not explicitly defining a special term 'thermal equilibrium'. J.R. Waldram writes of "a definite thermodynamic state". He defines the term "thermal equilibrium" for a system "when its observables have ceased to change over time". But shortly below that definition he writes of a piece of glass that has not yet reached its "full thermodynamic equilibrium state". Considering equilibrium states, M. Bailyn writes: "Each intensive variable has its own type of equilibrium." He then defines thermal equilibrium, mechanical equilibrium, and material equilibrium. Accordingly, he writes: "If all the intensive variables become uniform, thermodynamic equilibrium is said to exist." He is not here considering the presence of an external force field. J.G. Kirkwood and I. Oppenheim define thermodynamic equilibrium as follows: "A system is in a state of thermodynamic equilibrium if, during the time period allotted for experimentation, (a)


id: thermodynamic-equilibrium-20260505-6
file: data/en.wikipedia.org/wiki/Thermodynamic_equilibrium-6.md
category: reference
title: Thermodynamic equilibrium
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thermodynamic_equilibrium
date_saved: 2026-05-05T10:57:27.731222+00:00
instance: kb-cron
parent: thermodynamic-equilibrium-20260505-0
summary:
== Characteristics of a state of internal thermodynamic equilibrium == === Homogeneity in the absence of external forces === A thermodynamic system consisting of a single phase in the absence of external forces, in its own internal thermodynamic equilibrium, is homogeneous. This means that the material in any small volume element of the system can be interchanged with the material of any other geometrically congruent volume element of the system, and the effect is to leave the system thermodynamically unchanged. In general, a strong external force field makes a system of a single phase in its own internal thermodynamic equilibrium inhomogeneous with respect to some intensive variables. For example, a relatively dense component of a mixture can be concentrated by centrifugation. === Uniform temperature === Such equilibrium inhomogeneity, induced by external forces, does not occur for the intensive variable temperature. According to E.A. Guggenheim, "The most important conception of thermodynamics is temperature." Planck introduces his treatise with a brief account of heat and temperature and thermal equilibrium, and then announces: "In the following we shall deal chiefly with homogeneous, isotropic bodies of any form, possessing throughout their substance the same temperature and density, and subject to a uniform pressure acting


id: thermodynamic-equilibrium-20260505-7
file: data/en.wikipedia.org/wiki/Thermodynamic_equilibrium-7.md
category: reference
title: Thermodynamic equilibrium
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thermodynamic_equilibrium
date_saved: 2026-05-05T10:57:27.731222+00:00
instance: kb-cron
parent: thermodynamic-equilibrium-20260505-0
summary:
=== Approach to thermodynamic equilibrium within an isolated system === When a body of material starts from a non-equilibrium state of inhomogeneity or chemical non-equilibrium, and is then isolated, it spontaneously evolves towards its own internal state of thermodynamic equilibrium. It is not necessary that all aspects of internal thermodynamic equilibrium be reached simultaneously; some can be established before others. For example, in many cases of such evolution, internal mechanical equilibrium is established much more rapidly than the other aspects of the eventual thermodynamic equilibrium. Another example is that, in many cases of such evolution, thermal equilibrium is reached much more rapidly than chemical equilibrium. === Fluctuations within an isolated system in its own internal thermodynamic equilibrium === In an isolated system, thermodynamic equilibrium by definition persists over an indefinitely long time. In classical physics it is often convenient to ignore the effects of measurement and this is assumed in the present account. To consider the notion of fluctuations in an isolated thermodynamic system, a convenient example is a system specified by its extensive state variables, internal energy, volume, and mass composition. By definition they are time-invariant. By definition, they combine with time-invariant nominal values of their conjugate intensive functions


id: thermodynamic-equilibrium-20260505-8
file: data/en.wikipedia.org/wiki/Thermodynamic_equilibrium-8.md
category: reference
title: Thermodynamic equilibrium
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thermodynamic_equilibrium
date_saved: 2026-05-05T10:57:27.731222+00:00
instance: kb-cron
parent: thermodynamic-equilibrium-20260505-0
summary:
A system's internal state of thermodynamic equilibrium should be distinguished from a "stationary state" in which thermodynamic parameters are unchanging in time but the system is not isolated, so that there are, into and out of the system, non-zero macroscopic fluxes which are constant in time. Non-equilibrium thermodynamics is a branch of thermodynamics that deals with systems that are not in thermodynamic equilibrium. Most systems found in nature are not in thermodynamic equilibrium because they are changing or can be triggered to change over time, and are continuously and discontinuously subject to flux of matter and energy to and from other systems. The thermodynamic study of non-equilibrium systems requires more general concepts than are dealt with by equilibrium thermodynamics. Many natural systems still today remain beyond the scope of currently known macroscopic thermodynamic methods. Laws governing systems which are far from equilibrium are also debatable. One of the guiding principles for these systems is the maximum entropy production principle. It states that a non-equilibrium system evolves such as to maximize its entropy production. == See also == Thermodynamic models Non-random two-liquid model (NRTL model) - Phase equilibrium calculations UNIQUAC model - Phase equilibrium calculations Time crystal Topics in control theory


id: thermodynamic-equilibrium-20260505-9
file: data/en.wikipedia.org/wiki/Thermodynamic_equilibrium-9.md
category: reference
title: Thermodynamic equilibrium
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thermodynamic_equilibrium
date_saved: 2026-05-05T10:57:27.731222+00:00
instance: kb-cron
parent: thermodynamic-equilibrium-20260505-0
summary:
== Cited bibliography == Adkins, C.J. (1968/1983). Equilibrium Thermodynamics, third edition, McGraw-Hill, London, ISBN 0-521-25445-0. Bailyn, M. (1994). A Survey of Thermodynamics, American Institute of Physics Press, New York, ISBN 0-88318-797-3. Beattie, J.A., Oppenheim, I. (1979). Principles of Thermodynamics, Elsevier Scientific Publishing, Amsterdam, ISBN 0-444-41806-7. Boltzmann, L. (1896/1964). Lectures on Gas Theory, translated by S.G. Brush, University of California Press, Berkeley. Buchdahl, H.A. (1966). The Concepts of Classical Thermodynamics, Cambridge University Press, Cambridge UK. Callen, H.B. (1960/1985). Thermodynamics and an Introduction to Thermostatistics, (1st edition 1960) 2nd edition 1985, Wiley, New York, ISBN 0-471-86256-8. Carathéodory, C. (1909). Untersuchungen über die Grundlagen der Thermodynamik, Mathematische Annalen, 67: 355–386. A translation may be found here. Also a mostly reliable translation is to be found at Kestin, J. (1976). The Second Law of Thermodynamics, Dowden, Hutchinson & Ross, Stroudsburg PA. Chapman, S., Cowling, T.G. (1939/1970). The Mathematical Theory of Non-uniform gases. An Account of the Kinetic Theory of Viscosity, Thermal Conduction and Diffusion in Gases, third edition 1970, Cambridge University Press, London. Crawford, F.H. (1963). Heat, Thermodynamics, and Statistical Physics, Rupert Hart-Davis, London, Harcourt, Brace & World, Inc. de Groot, S.R., Mazur, P. (1962). Non-equilibrium Thermodynamics, North-Holland, Amsterdam. Reprinted (1984), Dover Publications Inc.,


id: thermodynamic-system-20260505-0
file: data/en.wikipedia.org/wiki/Thermodynamic_system-0.md
category: reference
title: Thermodynamic system
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thermodynamic_system
date_saved: 2026-05-05T10:57:28.904227+00:00
instance: kb-cron
parent: thermodynamic-system-20260505-0
summary:
A thermodynamic system is a body of matter and/or radiation separate from its surroundings that can be studied using the laws of thermodynamics. Thermodynamic systems can be passive and active according to internal processes. According to internal processes, passive systems and active systems are distinguished: passive, in which there is a redistribution of available energy, active, in which one type of energy is converted into another. Depending on its interaction with the environment, a thermodynamic system may be an isolated system, a closed system, or an open system. An isolated system does not exchange matter or energy with its surroundings. A closed system may exchange heat, experience forces, and exert forces, but does not exchange matter. An open system can interact with its surroundings by exchanging both matter and energy. The physical condition of a thermodynamic system at a given time is described by its state, which can be specified by the values of a set of thermodynamic state variables. A thermodynamic system is in thermodynamic equilibrium when there are no macroscopically apparent flows of matter or energy within it or between it and other systems. == Overview == Thermodynamic equilibrium is characterized not only by the absence of any


id: thermodynamic-system-20260505-1
file: data/en.wikipedia.org/wiki/Thermodynamic_system-1.md
category: reference
title: Thermodynamic system
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thermodynamic_system
date_saved: 2026-05-05T10:57:28.904227+00:00
instance: kb-cron
parent: thermodynamic-system-20260505-0
summary:
== Systems in equilibrium == In isolated systems it is consistently observed that as time goes on internal rearrangements diminish and stable conditions are approached. Pressures and temperatures tend to equalize, and matter arranges itself into one or a few relatively homogeneous phases. A system in which all processes of change have gone practically to completion is considered in a state of thermodynamic equilibrium. The thermodynamic properties of a system in equilibrium are unchanging in time. Equilibrium system states are much easier to describe in a deterministic manner than non-equilibrium states. In some cases, when analyzing a thermodynamic process, one can assume that each intermediate state in the process is at equilibrium. Such a process is called quasistatic. For a process to be reversible, each step in the process must be reversible. For a step in a process to be reversible, the system must be in equilibrium throughout the step. That ideal cannot be accomplished in practice because no step can be taken without perturbing the system from equilibrium, but the ideal can be approached by making changes slowly. The very existence of thermodynamic equilibrium, defining states of thermodynamic systems, is the essential, characteristic, and most fundamental postulate of thermodynamics,


id: thermodynamic-system-20260505-2
file: data/en.wikipedia.org/wiki/Thermodynamic_system-2.md
category: reference
title: Thermodynamic system
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thermodynamic_system
date_saved: 2026-05-05T10:57:28.904227+00:00
instance: kb-cron
parent: thermodynamic-system-20260505-0
summary:
Adiabatic boundary – not allowing any heat exchange: A thermally isolated system Rigid boundary – not allowing exchange of work: A mechanically isolated system One example is fluid being compressed by a piston in a cylinder. Another example of a closed system is a bomb calorimeter, a type of constant-volume calorimeter used in measuring the heat of combustion of a particular reaction. Electrical energy travels across the boundary to produce a spark between the electrodes and initiates combustion. Heat transfer occurs across the boundary after combustion but no mass transfer takes place either way. The first law of thermodynamics for energy transfers for closed system may be stated: Δ U = Q − W {\displaystyle \Delta U=Q-W} where U {\displaystyle U} denotes the internal energy of the system, Q {\displaystyle Q} heat added to the system, W {\displaystyle W} the work done by the system. For infinitesimal changes the first law for closed systems may stated: d U = δ Q − δ W . {\displaystyle \mathrm {d} U=\delta Q-\delta W.} If the work is due to a volume expansion by d V {\displaystyle \mathrm {d} V} at a pressure P {\displaystyle P} then: δ W = P d V


id: thermodynamic-system-20260505-3
file: data/en.wikipedia.org/wiki/Thermodynamic_system-3.md
category: reference
title: Thermodynamic system
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thermodynamic_system
date_saved: 2026-05-05T10:57:28.904227+00:00
instance: kb-cron
parent: thermodynamic-system-20260505-0
summary:
== Selective transfer of matter == For a thermodynamic process, the precise physical properties of the walls and surroundings of the system are important, because they determine the possible processes. An open system has one or several walls that allow transfer of matter. To account for the internal energy of the open system, this requires energy transfer terms in addition to those for heat and work. It also leads to the idea of the chemical potential. A wall selectively permeable only to a pure substance can put the system in diffusive contact with a reservoir of that pure substance in the surroundings. Then a process is possible in which that pure substance is transferred between system and surroundings. Also, across that wall a contact equilibrium with respect to that substance is possible. By suitable thermodynamic operations, the pure substance reservoir can be dealt with as a closed system. Its internal energy and its entropy can be determined as functions of its temperature, pressure, and mole number. A thermodynamic operation can render impermeable to matter all system walls other than the contact equilibrium wall for that substance. This allows the definition of an intensive state variable, with respect to a reference


id: thermodynamic-system-20260505-4
file: data/en.wikipedia.org/wiki/Thermodynamic_system-4.md
category: reference
title: Thermodynamic system
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thermodynamic_system
date_saved: 2026-05-05T10:57:28.904227+00:00
instance: kb-cron
parent: thermodynamic-system-20260505-0
summary:
== Sources == Abbott, M.M.; van Hess, H. G. (1989). Thermodynamics with Chemical Applications (2nd ed.). McGraw Hill. Bailyn, M. (1994). A Survey of Thermodynamics. New York: American Institute of Physics Press. ISBN 0-88318-797-3. Callen, H. B. (1985) [1960]. Thermodynamics and an Introduction to Thermostatistics (2nd ed.). New York: Wiley. ISBN 0-471-86256-8. Carnot, Sadi (1824). Réflexions sur la puissance motrice du feu et sur les machines propres à développer cette puissance (in French). Paris: Bachelier. Haase, R. (1971). "Survey of Fundamental Laws". In Eyring, H.; Henderson, D.; Jost, W. (eds.). Thermodynamics. Physical Chemistry: An Advanced Treatise. Vol. 1. New York: Academic Press. pp. 1–97. LCCN 73-117081. Dobroborsky B.S. Machine safety and the human factor / Edited by Doctor of Technical Sciences, prof. S.A. Volkov. — St. Petersburg: SPbGASU, 2011. — pp. 33–35. — 114 p. — ISBN 978-5-9227-0276-8. (Ru) Halliday, David; Resnick, Robert; Walker, Jearl (2008). Fundamentals of Physics (8th ed.). Wiley. Moran, Michael J.; Shapiro, Howard N. (2008). Fundamentals of Engineering Thermodynamics (6th ed.). Wiley. Rex, Andrew; Finn, C. B. P. (2017). Finn's Thermal Physics (3rd ed.). Taylor & Francis. ISBN 978-1-498-71887-5. Tisza, László (1966). Generalized Thermodynamics. MIT Press. Tschoegl, N. W. (2000). Fundamentals of Equilibrium and Steady-State Thermodynamics.


id: thermogravitational-cycle-20260505-0
file: data/en.wikipedia.org/wiki/Thermogravitational_cycle-0.md
category: reference
title: Thermogravitational cycle
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thermogravitational_cycle
date_saved: 2026-05-05T10:57:30.084117+00:00
instance: kb-cron
parent: thermogravitational-cycle-20260505-0
summary:
A thermogravitational cycle is a reversible thermodynamic cycle using the gravitational works of weight and buoyancy to respectively compress and expand a working fluid. == Theoretical framework == Consider a column filled with a transporting medium and a balloon filled with a working fluid. Due to the hydrostatic pressure of the transporting medium, the pressure inside the column increases along the z axis (see figure). Initially, the balloon is inflated by the working fluid at temperature TC and pressure P0 and located on top of the column. A thermogravitational cycle is decomposed into four ideal steps: 1→2: Descent of the balloon towards the bottom of the column. The working fluid undergoes adiabatic compression with its temperature increasing and its pressure reaching value Ph at the bottom (Ph>P0). 2→3: While the ballon lays at the bottom, the working fluid receives heat from the hot source at temperature TH and undergoes isobaric expansion at pressure Ph. 3→4: The balloon rises towards the column top. The working fluid undergoes adiabatic expansion with a drop in temperature and reaches pressure P0 after expansion when the balloon is on top. 4→1: Once arrived on top, the working fluid supplies heat to the cold source at


id: transpiration-cooling-20260505-0
file: data/en.wikipedia.org/wiki/Transpiration_cooling-0.md
category: reference
title: Transpiration cooling
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Transpiration_cooling
date_saved: 2026-05-05T10:57:31.278415+00:00
instance: kb-cron
parent: transpiration-cooling-20260505-0
summary:
Transpiration cooling is a thermodynamic process where cooling is achieved by a process of moving a liquid or a gas through the wall of a structure to absorb some portion of the heat energy from the structure while simultaneously actively reducing the convective and radiative heat flux coming into the structure from the surrounding space. One approach to transpiration cooling is to move liquid through small pores in the outer wall of a body leading to evaporation of the liquid to a gas via the physical mechanism of evaporative cooling. Other approaches are possible. == Applications == Transpiration cooling is used in the aerospace industry, in jet and rocket engines. In 2018, researchers at the University of Oxford were experimentally testing transpiration cooling as a Thermal Protection System for Hypersonic Vehicles such as rockets or spaceplanes. Transpiration cooling is one of a variety of cooling techniques that may be used to reduce regenerative cooling loads in rocket engines and subsequently reduce propellant requirements. Other techniques exist, such as film cooling, ablative cooling, radiative cooling, heat sink cooling and dump cooling. Transpiration cooling is being considered for use in space vehicles reentering the Earth's atmosphere at hypersonic velocities where a transpirationally


id: charles-karsner-mills-20260505-0
file: data/en.wikipedia.org/wiki/Charles_Karsner_Mills-0.md
category: reference
title: Charles Karsner Mills
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Charles_Karsner_Mills
date_saved: 2026-05-05T10:57:32.860331+00:00
instance: kb-cron
parent: charles-karsner-mills-20260505-0
summary:
Charles Karsner Mills, M.D. (December 4, 1845 – May 28, 1931) was an American physician and a pioneer in neurology. He founded the first neurology department in a general hospital in the United States at the Philadelphia General Hospital in 1877 and served as chief of neurology at the Hospital of the University of Pennsylvania. He was a professor of neurology at the University of Pennsylvania from 1877 to 1915. He founded the Philadelphia Polyclinic and taught there as professor of diseases of the mind and nervous system from 1883 to 1898. He led major reforms to psychiatric hospitals in the Philadelphia area including the closing of the Blockley Almshouse and the construction of the Philadelphia General Hospital and Byberry Hospital for Mental Diseases. He published over 300 scientific papers on neurology topics including cerebral localization, electrotherapeutics, aphasias and the effects of tumors in the central nervous system. In 1900, he first described a case of ascending paralysis, a rare motor neuron condition that has become known as Mills' syndrome. == Early life and education == Mills was born on December 4, 1845, in Philadelphia, Pennsylvania, to James and Lavinia Ann (Fitzgerald) Mills. He attended Central High School but left


id: silas-weir-mitchell-physician-20260505-0
file: data/en.wikipedia.org/wiki/Silas_Weir_Mitchell_(physician)-0.md
category: reference
title: Silas Weir Mitchell (physician)
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Silas_Weir_Mitchell_(physician)
date_saved: 2026-05-05T10:57:34.104016+00:00
instance: kb-cron
parent: silas-weir-mitchell-physician-20260505-0
summary:
Silas Weir Mitchell (February 15, 1829 – January 4, 1914) was an American physician, scientist, novelist, and poet. He is considered the father of medical neurology, and he discovered causalgia (complex regional pain syndrome) and erythromelalgia, and pioneered the rest cure. == Early life == Silas Weir Mitchell was born on February 15, 1829, in Philadelphia, Pennsylvania, to prominent physician and writer John Kearsley Mitchell (1792–1858) and Sarah Henry Mitchell (1800–1872). His father was a doctor and pathologist interested in snake venom, and Mitchell would continue his research later on. Dr. Mitchell studied at the University of Pennsylvania and later earned the degree of MD at the city's Jefferson Medical College in 1850. == Career == During the Civil War, he was director of treatment of nervous injuries and maladies at Turner's Lane Hospital, Philadelphia, and at the close of the war became a specialist in neurology. In this field Mitchell pioneered the rest cure for diseases now termed "psychiatric", particularly neurasthenia and hysteria, subsequently taken up by the medical world. The treatment consisted primarily in isolation, confinement to bed, dieting, electrotherapy and massage; and was popularly known as 'Dr Diet and Dr Quiet'. Mitchell also urged his female patients


id: silas-weir-mitchell-physician-20260505-1
file: data/en.wikipedia.org/wiki/Silas_Weir_Mitchell_(physician)-1.md
category: reference
title: Silas Weir Mitchell (physician)
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Silas_Weir_Mitchell_(physician)
date_saved: 2026-05-05T10:57:34.104016+00:00
instance: kb-cron
parent: silas-weir-mitchell-physician-20260505-0
summary:
John Kearsley Mitchell (1859–1917), a neurologist who married Anne Keppele Williams in 1890. Langdon Elwyn Mitchell (1862–1935), a playwright who married actress Marion Lea in 1891. On June 23, 1875, Mitchell was married to Mary Cadwalader (1835–1914), who was from one of Philadelphia's most prestigious families. She was a daughter of Thomas McCall Cadwalader and Maria Charlotte Gouverneur (niece of Elizabeth Kortright, who had married U.S. President James Monroe). The marriage "propelled him to one of the city's highest social circles and he became a trustee of the University of Pennsylvania the following year." Together, they were the parents of a daughter: Marie Gouverneur Cadwalader Mitchell (1876–1898), who died unmarried. Mitchell died on January 4, 1914, in Philadelphia and is interred at The Woodlands Cemetery. His widow died a week after his funeral. === Cultural Club Founder === Mitchell and 8 other members of the University Club at Penn founded The Franklin Inn Club in 1902. === Art patron === He was a friend and patron of the artist Thomas Eakins, and owned the painting Whistling for Plover. The Philadelphia Chippendale chairs seen in several Eakins paintings – such as William Rush Carving his Allegorical Figure of Schuylkill River (1877)


id: silas-weir-mitchell-physician-20260505-2
file: data/en.wikipedia.org/wiki/Silas_Weir_Mitchell_(physician)-2.md
category: reference
title: Silas Weir Mitchell (physician)
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Silas_Weir_Mitchell_(physician)
date_saved: 2026-05-05T10:57:34.104016+00:00
instance: kb-cron
parent: silas-weir-mitchell-physician-20260505-0
summary:
== Further reading == Anna Robeson Brown Burr, Weir Mitchell: His Life and Letters (Duffield & Company 1929). Nancy Cervetti, S. Weir Mitchell, 1829–1914: Philadelphia's Literary Physician. University Park, PA: Pennsylvania State University Press, 2012. ISBN 0271054042 E. P. Oberholtzer, "Personal Memories of Weir Mitchell," in the Bookman, vol. 39 (1914). p. 132 A. Proust and G. Ballet, The Treatment of Neurasthenia. 1902. Tucker, Beverly R., S. Weir Mitchell. Gorham Press, Boston, 1914. Talcott Williams, "Dr. S. Weir Mitchell" in the Century Magazine, vol. 57 (1898). Talcott Williams, in several articles in the Book News Monthly, vol. 26 (1907). A Catalogue of the Scientific and Literary Work of S. Weir Mitchell. Philadelphia, 1894. == External links == Finding aid to the S. Weir Mitchell collection at the University of Pennsylvania Libraries Silas Weir Mitchell. Biography at WhoNamedIt Silas Weir Mitchell papers from the Historic Psychiatry Collection, Menninger Archives, Kansas Historical Society Works by Silas Weir Mitchell at Project Gutenberg Works by or about Silas Weir Mitchell at the Internet Archive Works by Silas Weir Mitchell in the Ball State University Digital Media Repository Portrait of Silas Weir Mitchell by John Singer Sargent Archived July 5, 2007, at the Wayback Machine


id: andr-strohl-20260505-0
file: data/en.wikipedia.org/wiki/André_Strohl-0.md
category: reference
title: André Strohl
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/André_Strohl
date_saved: 2026-05-05T10:57:35.333123+00:00
instance: kb-cron
parent: andr-strohl-20260505-0
summary:
André Strohl (20 March 1887 – 10 March 1977) was a French physiologist who was a native of Poitiers. He is remembered for his role in the diagnosis of Guillain–Barré syndrome (sometimes called Guillain–Barré–Strohl syndrome), a form of areflexic paralysis that exhibits normal cell count but with an abnormal increase in spinal fluid protein. The syndrome is named after two French neurologists; Georges Guillain and Jean Alexandre Barré. In 1916, during World War I, Strohl was serving in the Neurological Centre of the French Sixth Army with Guillain and Barré. The three doctors noticed that two soldiers, who were suffering from muscular weakening and pain along with paresthesias, had an unexpected amount of spinal fluid protein production. Strohl is credited with performing the electrophysiological tests on the soldiers. Eventually, the two patients were able to recover from their illness. In 1916, Guillain, Barré and Strohl reported their findings in a medical journal. In 1927, H. Draganesco and J. Claudion coined the term "Guillain–Barré syndrome", apparently overlooking Strohl's contributions. In 1924 Strohl became a professor of physiological medicine in Algiers, and two years later acquired the same position at the University of Paris. He retired from there in 1957. He was


