diff --git a/_index.db b/_index.db index 6fd44e1e4..28866ce93 100644 Binary files a/_index.db and b/_index.db differ diff --git a/data/en.wikipedia.org/wiki/Formal_science-0.md b/data/en.wikipedia.org/wiki/Formal_science-0.md index dbfce111a..d4a6a4cd6 100644 --- a/data/en.wikipedia.org/wiki/Formal_science-0.md +++ b/data/en.wikipedia.org/wiki/Formal_science-0.md @@ -4,7 +4,7 @@ chunk: 1/1 source: "https://en.wikipedia.org/wiki/Formal_science" category: "reference" tags: "science, encyclopedia" -date_saved: "2026-05-05T03:23:40.581119+00:00" +date_saved: "2026-05-05T03:55:46.288719+00:00" instance: "kb-cron" --- diff --git a/data/en.wikipedia.org/wiki/Nadal_formula-0.md b/data/en.wikipedia.org/wiki/Nadal_formula-0.md new file mode 100644 index 000000000..975a46129 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Nadal_formula-0.md @@ -0,0 +1,134 @@ +--- +title: "Nadal formula" +chunk: 1/1 +source: "https://en.wikipedia.org/wiki/Nadal_formula" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T03:55:34.995432+00:00" +instance: "kb-cron" +--- + +The Nadal formula, also called Nadal's formula, is an equation in railway design that relates the downward force exerted by a train's wheels upon the rail, with the lateral force of the wheel's flange against the face of the rail. This relationship is significant in railway design, as a wheel-climb derailment may occur if the lateral and vertical forces are not properly considered. +The Nadal formula is represented by: + + + + + + ( + + + L + V + + + ) + + + = + + + ( + + + + tan + ⁡ + ( + δ + ) + − + μ + + + 1 + + + μ + ∗ + tan + ⁡ + ( + δ + ) + + + + ) + + + + {\displaystyle \left({\frac {L}{V}}\right){=}\left({\frac {\tan(\delta )-\mu }{1+\mu *\tan(\delta )}}\right)} + + +In this equation, L and V refer to the lateral and vertical forces acting upon the rail and wheel, δ is the angle made when the wheel flange is in contact with the rail face, and μ is the coefficient of friction between the wheel and the rail. +Typically, the axle load for a railway vehicle should be such that the lateral forces of the wheel against the rail should not exceed 50% of the vertical down-force of the vehicle on the rail. Put another way, there should be twice as much downward force holding the wheel to the rail, as there is lateral force which will tend to cause the wheel to climb in turns. This ratio is accomplished by matching the wheelset with the appropriate rail profile to achieve the L/V ratio desired. If the L/V ratio gets too high, the wheel flange will be pressing against the rail face, and during a turn this will cause the wheel to climb the face of the rail, potentially derailing the railcar. + + +== Wagner Formula == +The Nadal formula assumes the wheel remains perpendicular to the rail—it does not take into account hunting oscillation of the wheelset, or the movement of the wheel flange contact point against the rail. +A variation of the Nadal formula, which does take these factors into consideration, is the Wagner formula. As the wheelset yaws relative to the rail, the vertical force V is no longer completely vertical, but is now acting at an angle to the vertical, β. When this angle is factored into the Nadal formula, the result is the Wagner formula: + + + + + + ( + + + L + V + + + ) + + + = + + + ( + + + + tan + ⁡ + ( + δ + ) + − + μ + ∗ + cos + ⁡ + β + + + ( + 1 + + + μ + ∗ + tan + ⁡ + ( + δ + ) + ) + ∗ + cos + ⁡ + β + ) + + + + ) + + + + {\displaystyle \left({\frac {L}{V}}\right){=}\left({\frac {\tan(\delta )-\mu *\cos \beta }{(1+\mu *\tan(\delta ))*\cos \beta )}}\right)} + + +When the vertical force is truly vertical (that is, β=0 and therefore cos(β)=1), the Wagner formula equals the Nadal formula. + + +== References == \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Nanoelectromechanical_systems-0.md b/data/en.wikipedia.org/wiki/Nanoelectromechanical_systems-0.md new file mode 100644 index 000000000..31734df7c --- /dev/null +++ b/data/en.wikipedia.org/wiki/Nanoelectromechanical_systems-0.md @@ -0,0 +1,40 @@ +--- +title: "Nanoelectromechanical systems" +chunk: 1/4 +source: "https://en.wikipedia.org/wiki/Nanoelectromechanical_systems" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T03:55:36.112304+00:00" +instance: "kb-cron" +--- + +Nanoelectromechanical systems (NEMS) are a class of devices integrating electrical and mechanical functionality on the nanoscale. NEMS form the next logical miniaturization step from so-called microelectromechanical systems, or MEMS devices. NEMS typically integrate transistor-like nanoelectronics with mechanical actuators, pumps, or motors, and may thereby form physical, biological, and chemical sensors. The name derives from typical device dimensions in the nanometer range, leading to low mass, high mechanical resonance frequencies, potentially large quantum mechanical effects such as zero point motion, and a high surface-to-volume ratio useful for surface-based sensing mechanisms. Applications include accelerometers and sensors to detect chemical substances in the air. + +== History == + +=== Background === + +As noted by Richard Feynman in his famous talk in 1959, "There's Plenty of Room at the Bottom," there are many potential applications of machines at smaller and smaller sizes; by building and controlling devices at smaller scales, all technology benefits. The expected benefits include greater efficiencies and reduced size, decreased power consumption and lower costs of production in electromechanical systems. +The first silicon dioxide field effect transistors were built by Frosch and Derick in 1957 at Bell Labs. In 1960, Atalla and Kahng at Bell Labs fabricated a MOSFET with a gate oxide thickness of 100 nm. In 1962, Atalla and Kahng fabricated a nanolayer-base metal–semiconductor junction (M–S junction) transistor that used gold (Au) thin films with a thickness of 10 nm. In 1987, Bijan Davari led an IBM research team that demonstrated the first MOSFET with a 10 nm oxide thickness. Multi-gate MOSFETs enabled scaling below 20 nm channel length, starting with the FinFET. The FinFET originates from the research of Digh Hisamoto at Hitachi Central Research Laboratory in 1989. At UC Berkeley, a group led by Hisamoto and TSMC's Chenming Hu fabricated FinFET devices down to 17 nm channel length in 1998. + +=== NEMS === +In 2000, the first very-large-scale integration (VLSI) NEMS device was demonstrated by researchers at IBM. Its premise was an array of AFM tips which can heat/sense a deformable substrate in order to function as a memory device (Millipede memory). Further devices have been described by Stefan de Haan. In 2007, the International Technical Roadmap for Semiconductors (ITRS) contains NEMS memory as a new entry for the Emerging Research Devices section. + +== Atomic force microscopy == +A key application of NEMS is atomic force microscope tips. The increased sensitivity achieved by NEMS leads to smaller and more efficient sensors to detect stresses, vibrations, forces at the atomic level, and chemical signals. AFM tips and other detection at the nanoscale rely heavily on NEMS. + +== Approaches to miniaturization == +Two complementary approaches to fabrication of NEMS can be found, the top-down approach and the bottom-up approach. +The top-down approach uses the traditional microfabrication methods, i.e. optical, electron-beam lithography and thermal treatments, to manufacture devices. While being limited by the resolution of these methods, it allows a large degree of control over the resulting structures. In this manner devices such as nanowires, nanorods, and patterned nanostructures are fabricated from metallic thin films or etched semiconductor layers. For top-down approaches, increasing surface area to volume ratio enhances the reactivity of nanomaterials. +Bottom-up approaches, in contrast, use the chemical properties of single molecules to cause single-molecule components to self-organize or self-assemble into some useful conformation, or rely on positional assembly. These approaches utilize the concepts of molecular self-assembly and/or molecular recognition. This allows fabrication of much smaller structures, albeit often at the cost of limited control of the fabrication process. Furthermore, while there are residue materials removed from the original structure for the top-down approach, minimal material is removed or wasted for the bottom-up approach. +A combination of these approaches may also be used, in which nanoscale molecules are integrated into a top-down framework. One such example is the carbon nanotube nanomotor. + +== Materials == + +=== Carbon allotropes === +Many of the commonly used materials for NEMS technology have been carbon based, specifically diamond, carbon nanotubes and graphene. This is mainly because of the useful properties of carbon based materials which directly meet the needs of NEMS. The mechanical properties of carbon (such as large Young's modulus) are fundamental to the stability of NEMS while the metallic and semiconductor conductivities of carbon based materials allow them to function as transistors. +Both graphene and diamond exhibit high Young's modulus, low density, low friction, exceedingly low mechanical dissipation, and large surface area. The low friction of CNTs, allow practically frictionless bearings and has thus been a huge motivation towards practical applications of CNTs as constitutive elements in NEMS, such as nanomotors, switches, and high-frequency oscillators. Carbon nanotubes and graphene's physical strength allows carbon based materials to meet higher stress demands, when common materials would normally fail and thus further support their use as a major materials in NEMS technological development. +Along with the mechanical benefits of carbon based materials, the electrical properties of carbon nanotubes and graphene allow it to be used in many electrical components of NEMS. Nanotransistors have been developed for both carbon nanotubes as well as graphene. Transistors are one of the basic building blocks for all electronic devices, so by effectively developing usable transistors, carbon nanotubes and graphene are both very crucial to NEMS. +Nanomechanical resonators are frequently made of graphene. As NEMS resonators are scaled down in size, there is a general trend for a decrease in quality factor in inverse proportion to surface area to volume ratio. However, despite this challenge, it has been experimentally proven to reach a quality factor as high as 2400. The quality factor describes the purity of tone of the resonator's vibrations. Furthermore, it has been theoretically predicted that clamping graphene membranes on all sides yields increased quality numbers. Graphene NEMS can also function as mass, force, and position sensors. + +==== Metallic carbon nanotubes ==== \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Nanoelectromechanical_systems-1.md b/data/en.wikipedia.org/wiki/Nanoelectromechanical_systems-1.md new file mode 100644 index 000000000..219b058ff --- /dev/null +++ b/data/en.wikipedia.org/wiki/Nanoelectromechanical_systems-1.md @@ -0,0 +1,27 @@ +--- +title: "Nanoelectromechanical systems" +chunk: 2/4 +source: "https://en.wikipedia.org/wiki/Nanoelectromechanical_systems" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T03:55:36.112304+00:00" +instance: "kb-cron" +--- + +Carbon nanotubes (CNTs) are allotropes of carbon with a cylindrical nanostructure. They can be considered a rolled up graphene. When rolled at specific and discrete ("chiral") angles, and the combination of the rolling angle and radius decides whether the nanotube has a bandgap (semiconducting) or no bandgap (metallic). +Metallic carbon nanotubes have also been proposed for nanoelectronic interconnects since they can carry high current densities. This is a useful property as wires to transfer current are another basic building block of any electrical system. Carbon nanotubes have specifically found so much use in NEMS that methods have already been discovered to connect suspended carbon nanotubes to other nanostructures. This allows carbon nanotubes to form complicated nanoelectric systems. Because carbon based products can be properly controlled and act as interconnects as well as transistors, they serve as a fundamental material in the electrical components of NEMS. + +==== CNT-based NEMS switches ==== +A major disadvantage of MEMS switches over NEMS switches are limited microsecond range switching speeds of MEMS, which impedes performance for high speed applications. Limitations on switching speed and actuation voltage can be overcome by scaling down devices from micro to nanometer scale. A comparison of performance parameters between carbon nanotube (CNT)-based NEMS switches with its counterpart CMOS revealed that CNT-based NEMS switches retained performance at lower levels of energy consumption and had a subthreshold leakage current several orders of magnitude smaller than that of CMOS switches. CNT-based NEMS with doubly clamped structures are being further studied as potential solutions for floating gate nonvolatile memory applications. + +==== Difficulties ==== +Despite all of the useful properties of carbon nanotubes and graphene for NEMS technology, both of these products face several hindrances to their implementation. One of the main problems is carbon's response to real life environments. Carbon nanotubes exhibit a large change in electronic properties when exposed to oxygen. Similarly, other changes to the electronic and mechanical attributes of carbon based materials must fully be explored before their implementation, especially because of their high surface area which can easily react with surrounding environments. Carbon nanotubes were also found to have varying conductivities, being either metallic or semiconducting depending on their helicity when processed. Because of this, special treatment must be given to the nanotubes during processing to assure that all of the nanotubes have appropriate conductivities. Graphene also has complicated electric conductivity properties compared to traditional semiconductors because it lacks an energy band gap and essentially changes all the rules for how electrons move through a graphene based device. This means that traditional constructions of electronic devices will likely not work and completely new architectures must be designed for these new electronic devices. + +==== Nanoelectromechanical accelerometer ==== +Graphene's mechanical and electronic properties have made it favorable for integration into NEMS accelerometers, such as small sensors and actuators for heart monitoring systems and mobile motion capture. The atomic scale thickness of graphene provides a pathway for accelerometers to be scaled down from micro to nanoscale while retaining the system's required sensitivity levels. +By suspending a silicon proof mass on a double-layer graphene ribbon, a nanoscale spring-mass and piezoresistive transducer can be made with the capability of currently produced transducers in accelerometers. The spring mass provides greater accuracy, and the piezoresistive properties of graphene converts the strain from acceleration to electrical signals for the accelerometer. The suspended graphene ribbon simultaneously forms the spring and piezoresistive transducer, making efficient use of space in while improving performance of NEMS accelerometers. + +=== Polydimethylsiloxane (PDMS) === +Failures arising from high adhesion and friction are of concern for many NEMS. NEMS frequently utilize silicon due to well-characterized micromachining techniques; however, its intrinsic stiffness often hinders the capability of devices with moving parts. +A study conducted by Ohio State researchers compared the adhesion and friction parameters of a single crystal silicon with native oxide layer against PDMS coating. PDMS is a silicone elastomer that is highly mechanically tunable, chemically inert, thermally stable, permeable to gases, transparent, non-fluorescent, biocompatible, and nontoxic. Inherent to polymers, the Young's Modulus of PDMS can vary over two orders of magnitude by manipulating the extent of crosslinking of polymer chains, making it a viable material in NEMS and biological applications. PDMS can form a tight seal with silicon and thus be easily integrated into NEMS technology, optimizing both mechanical and electrical properties. Polymers like PDMS are beginning to gain attention in NEMS due to their comparatively inexpensive, simplified, and time-efficient prototyping and manufacturing. +Rest time has been characterized to directly correlate with adhesive force, and increased relative humidity lead to an increase of adhesive forces for hydrophilic polymers. Contact angle measurements and Laplace force calculations support the characterization of PDMS's hydrophobic nature, which expectedly corresponds with its experimentally verified independence to relative humidity. PDMS' adhesive forces are also independent of rest time, capable of versatilely performing under varying relative humidity conditions, and possesses a lower coefficient of friction than that of Silicon. PDMS coatings facilitate mitigation of high-velocity problems, such as preventing sliding. Thus, friction at contact surfaces remains low even at considerably high velocities. In fact, on the microscale, friction reduces with increasing velocity. The hydrophobicity and low friction coefficient of PDMS have given rise to its potential in being further incorporated within NEMS experiments that are conducted at varying relative humidities and high relative sliding velocities. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Nanoelectromechanical_systems-2.md b/data/en.wikipedia.org/wiki/Nanoelectromechanical_systems-2.md new file mode 100644 index 000000000..c6b65cf28 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Nanoelectromechanical_systems-2.md @@ -0,0 +1,35 @@ +--- +title: "Nanoelectromechanical systems" +chunk: 3/4 +source: "https://en.wikipedia.org/wiki/Nanoelectromechanical_systems" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T03:55:36.112304+00:00" +instance: "kb-cron" +--- + +==== PDMS-coated piezoresistive nanoelectromechanical systems diaphragm ==== +PDMS is frequently used within NEMS technology. For instance, PDMS coating on a diaphragm can be used for chloroform vapor detection. +Researchers from the National University of Singapore invented a polydimethylsiloxane (PDMS)-coated nanoelectromechanical system diaphragm embedded with silicon nanowires (SiNWs) to detect chloroform vapor at room temperature. In the presence of chloroform vapor, the PDMS film on the micro-diaphragm absorbs vapor molecules and consequently enlarges, leading to deformation of the micro-diaphragm. The SiNWs implanted within the micro-diaphragm are linked in a Wheatstone bridge, which translates the deformation into a quantitative output voltage. In addition, the micro-diaphragm sensor also demonstrates low-cost processing at low power consumption. It possesses great potential for scalability, ultra-compact footprint, and CMOS-IC process compatibility. By switching the vapor-absorption polymer layer, similar methods can be applied that should theoretically be able to detect other organic vapors. +In addition to its inherent properties discussed in the Materials section, PDMS can be used to absorb chloroform, whose effects are commonly associated with swelling and deformation of the micro-diaphragm; various organic vapors were also gauged in this study. With good aging stability and appropriate packaging, the degradation rate of PDMS in response to heat, light, and radiation can be slowed. + +=== Biohybrid NEMS === + +The emerging field of bio-hybrid systems combines biological and synthetic structural elements for biomedical or robotic applications. The constituting elements of bio-nanoelectromechanical systems (BioNEMS) are of nanoscale size, for example DNA, proteins or nanostructured mechanical parts. Examples include the facile top-down nanostructuring of thiol-ene polymers to create cross-linked and mechanically robust nanostructures that are subsequently functionalized with proteins. + +== Simulations == +Computer simulations have long been important counterparts to experimental studies of NEMS devices. Through continuum mechanics and molecular dynamics (MD), important behaviors of NEMS devices can be predicted via computational modeling before engaging in experiments. Additionally, combining continuum and MD techniques enables engineers to efficiently analyze the stability of NEMS devices without resorting to ultra-fine meshes and time-intensive simulations. Simulations have other advantages as well: they do not require the time and expertise associated with fabricating NEMS devices; they can effectively predict the interrelated roles of various electromechanical effects; and parametric studies can be conducted fairly readily as compared with experimental approaches. For example, computational studies have predicted the charge distributions and "pull-in" electromechanical responses of NEMS devices. Using simulations to predict mechanical and electrical behavior of these devices can help optimize NEMS device design parameters. + +== Reliability and Life Cycle of NEMS == + +=== Reliability and Challenges === +Reliability provides a quantitative measure of the component's integrity and performance without failure for a specified product lifetime. Failure of NEMS devices can be attributed to a variety of sources, such as mechanical, electrical, chemical, and thermal factors. Identifying failure mechanisms, improving yield, scarcity of information, and reproducibility issues have been identified as major challenges to achieving higher levels of reliability for NEMS devices. Such challenges arise during both manufacturing stages (i.e. wafer processing, packaging, final assembly) and post-manufacturing stages (i.e. transportation, logistics, usage). + +==== Packaging ==== +Packaging challenges often account for 75–95% of the overall costs of MEMS and NEMS. Factors of wafer dicing, device thickness, sequence of final release, thermal expansion, mechanical stress isolation, power and heat dissipation, creep minimization, media isolation, and protective coatings are considered by packaging design to align with the design of the MEMS or NEMS component. Delamination analysis, motion analysis, and life-time testing have been used to assess wafer-level encapsulation techniques, such as cap to wafer, wafer to wafer, and thin film encapsulation. Wafer-level encapsulation techniques can lead to improved reliability and increased yield for both micro and nanodevices. + +==== Manufacturing ==== +Assessing the reliability of NEMS in early stages of the manufacturing process is essential for yield improvement. Forms of surface forces, such as adhesion and electrostatic forces, are largely dependent on surface topography and contact geometry. Selective manufacturing of nano-textured surfaces reduces contact area, improving both adhesion and friction performance for NEMS. Furthermore, the implementation of nanopost to engineered surfaces increase hydrophobicity, leading to a reduction in both adhesion and friction. +Adhesion and friction can also be manipulated by nanopatterning to adjust surface roughness for the appropriate applications of the NEMS device. Researchers from Ohio State University used atomic/friction force microscopy (AFM/FFM) to examine the effects of nanopatterning on hydrophobicity, adhesion, and friction for hydrophilic polymers with two types of patterned asperities (low aspect ratio and high aspect ratio). Roughness on hydrophilic surfaces versus hydrophobic surfaces are found to have inversely correlated and directly correlated relationships respectively. +Due to its large surface area to volume ratio and sensitivity, adhesion and friction can impede performance and reliability of NEMS devices. These tribological issues arise from natural down-scaling of these tools; however, the system can be optimized through the manipulation of the structural material, surface films, and lubricant. In comparison to undoped Si or polysilicon films, SiC films possess the lowest frictional output, resulting in increased scratch resistance and enhanced functionality at high temperatures. Hard diamond-like carbon (DLC) coatings exhibit low friction, high hardness and wear resistance, in addition to chemical and electrical resistances. Roughness, a factor that reduces wetting and increases hydrophobicity, can be optimized by increasing the contact angle to reduce wetting and allow for low adhesion and interaction of the device to its environment. +Material properties are size-dependent. Therefore, analyzing the unique characteristics on NEMS and nano-scale material becomes increasingly important to retaining reliability and long-term stability of NEMS devices. Some mechanical properties, such as hardness, elastic modulus, and bend tests, for nano-materials are determined by using a nano indenter on a material that has undergone fabrication processes. These measurements, however, do not consider how the device will operate in industry under prolonged or cyclic stresses and strains. The theta structure is a NEMS model that exhibits unique mechanical properties. Composed of Si, the structure has high strength and is able to concentrate stresses at the nanoscale to measure certain mechanical properties of materials. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Nanoelectromechanical_systems-3.md b/data/en.wikipedia.org/wiki/Nanoelectromechanical_systems-3.md new file mode 100644 index 000000000..9b5cd58ba --- /dev/null +++ b/data/en.wikipedia.org/wiki/Nanoelectromechanical_systems-3.md @@ -0,0 +1,29 @@ +--- +title: "Nanoelectromechanical systems" +chunk: 4/4 +source: "https://en.wikipedia.org/wiki/Nanoelectromechanical_systems" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T03:55:36.112304+00:00" +instance: "kb-cron" +--- + +==== Residual stresses ==== +To increase reliability of structural integrity, characterization of both material structure and intrinsic stresses at appropriate length scales becomes increasingly pertinent. Effects of residual stresses include but are not limited to fracture, deformation, delamination, and nanosized structural changes, which can result in failure of operation and physical deterioration of the device. +Residual stresses can influence electrical and optical properties. For instance, in various photovoltaic and light emitting diodes (LED) applications, the band gap energy of semiconductors can be tuned accordingly by the effects of residual stress. +Atomic force microscopy (AFM) and Raman spectroscopy can be used to characterize the distribution of residual stresses on thin films in terms of force volume imaging, topography, and force curves. Furthermore, residual stress can be used to measure nanostructures' melting temperature by using differential scanning calorimetry (DSC) and temperature dependent X-ray Diffraction (XRD). + +== Future == +Key hurdles currently preventing the commercial application of many NEMS devices include low-yields and high device quality variability. Before NEMS devices can actually be implemented, reasonable integrations of carbon based products must be created. A recent step in that direction has been demonstrated for diamond, achieving a processing level comparable to that of silicon. The focus is currently shifting from experimental work towards practical applications and device structures that will implement and profit from such novel devices. The next challenge to overcome involves understanding all of the properties of these carbon-based tools, and using the properties to make efficient and durable NEMS with low failure rates. +Carbon-based materials have served as prime materials for NEMS use, because of their exceptional mechanical and electrical properties. +Recently, nanowires of chalcogenide glasses have shown to be a key platform to design tunable NEMS owing to the availability of active modulation of Young's modulus. +The global market of NEMS is projected to reach $108.88 million by 2022. + +== Applications == +Nanoelectromechanical relay +Nanoelectromechanical systems mass spectrometer + +=== Nanoelectromechanical-based cantilevers === +Researchers from the California Institute of Technology developed a NEM-based cantilever with mechanical resonances up to very high frequencies (VHF). It is incorporation of electronic displacement transducers based on piezoresistive thin metal film facilitates unambiguous and efficient nanodevice readout. The functionalization of the device's surface using a thin polymer coating with high partition coefficient for the targeted species enables NEMS-based cantilevers to provide chemisorption measurements at room temperature with mass resolution at less than one attogram. Further capabilities of NEMS-based cantilevers have been exploited for the applications of sensors, scanning probes, and devices operating at very high frequency (100 MHz). + +== References == \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Performance_science-0.md b/data/en.wikipedia.org/wiki/Performance_science-0.md new file mode 100644 index 000000000..a65d1f952 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Performance_science-0.md @@ -0,0 +1,38 @@ +--- +title: "Performance science" +chunk: 1/1 +source: "https://en.wikipedia.org/wiki/Performance_science" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T03:55:37.310089+00:00" +instance: "kb-cron" +--- + +Performance science is the multidisciplinary study of human performance. It draws together methodologies across numerous scientific disciplines, including those of biomechanics, economics, physiology, psychology, and sociology, to understand the fundamental skills, mechanisms, and outcomes of performance activities and experiences. It carries implications for various domains of skilled human activity, often performed under extreme stress and/or under the scrutiny of audiences or evaluators. These include performances across the arts, sport, education, and business, particularly those occupations involving the delivery of highly trained skills such as in surgery and management. + + +== Centers of research and teaching == + +USC Performance Science Institute, University of Southern California +711th Human Performance Wing, Wright-Patterson Air Force Base +Centre for Human Performance Sciences, Stellenbosch University +Centre for Performance Science, a partnership of the Royal College of Music and Imperial College London +Human Performance Science Research Group, University of Edinburgh +Performance and Science Working Group, Theatre and Performance Research Association +Performance Science Unit, Sports Institute for Northern Ireland + + +== See also == +Environmental psychology +Industrial and organizational psychology +Military psychology +Music psychology +Sport psychology + + +== References == + + +== External links == +International Symposium on Performance Science +Frontiers in Psychology: Performance Science (journal) \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Regulatory_science-0.md b/data/en.wikipedia.org/wiki/Regulatory_science-0.md new file mode 100644 index 000000000..174c996c6 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Regulatory_science-0.md @@ -0,0 +1,37 @@ +--- +title: "Regulatory science" +chunk: 1/2 +source: "https://en.wikipedia.org/wiki/Regulatory_science" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T03:55:38.508835+00:00" +instance: "kb-cron" +--- + +Regulatory science is the scientific and technical foundations upon which regulations are based in various industries – particularly those involving health or safety. Regulatory bodies employing such principles in the United States include, for example, the FDA for food and medical products, the EPA for the environment, and the OSHA for work safety. +"Regulatory science" is contrasted with regulatory affairs and regulatory law, which refer to the administrative or legal aspects of regulation, in that the former is focused on the regulations' scientific underpinnings and concerns – rather than the regulations' promulgation, implementation, compliance, or enforcement. + +== History == +Probably the first investigator who recognized the nature of regulatory science was Alvin Weinberg, who described the scientific process used to evaluate effects of ionizing radiation as trans science. The origin of the term regulatory science is unknown. It was probably coined sometimes in the late 1970s in an undated memorandum prepared by A. Alan Moghissi, who was describing scientific issues that the newly formed US Environmental Protection Agency (EPA) was facing . During that period the EPA was forced to meet legally mandated deadlines to make decisions that would require reliance upon science that was not meeting conventional scientific requirements. At that time the prevailing view was that there was no need to establish a new scientific discipline because "science is science" regardless of its application. In the spring of 1985, Moghissi established the Institute for Regulatory Science in the commonwealth of Virginia as a nonprofit organization with the objective to perform scientific studies "at the interface between science and the regulatory system". Moghissi et al. have provided an extensive description of history of regulatory science including various perception of regulatory science leading to the acceptance of regulatory science by the FDA. + +== Definition == +Two federal regulatory agencies have provided definitions for regulatory science. According to Food and Drug Administration: “Regulatory Science is the science of developing new tools, standards, and approaches to assess the safety, efficacy, quality, and performance of all FDA-regulated products”. According to Environmental Protection Agency (EPA): “Regulatory science means scientific information including assessments, models, criteria documents, and regulatory impact analyses that provide the basis for significant regulatory decisions”. +Moghissi et al. have described the history of regulatory science and define it as: +“Regulatory science consists of an applied version of various scientific disciplines used in the regulatory process”. Based on their definition the generalized FDA definition is: Regulatory science is the science of developing new tools, standards, and approaches derived from various scientific disciplines to assess the safety, efficacy, quality, and performance of all FDA-regulated products. Similarly, the generalized EPA definition is: +Regulatory science means scientific information including assessments, models, criteria documents, and regulatory impact analyses derived from various scientific disciplines that provide the basis for EPA final significant regulatory decisions. +There have been several attempts to define regulatory science. In many cases there are claims that there is a difference between regulatory science and “normal science”, “academic science”, “research science”. or compliance with regulations. The primary problem is the lack of appreciation that many branches of science are evolving and much of the evolving science includes inherent uncertainties. + +== Application of regulatory science == +Regulatory science is included in every regulation that includes science. The regulatory science community consists of three groups of regulatory scientists: + +Those who are involved in development of regulations. Typically this group is employed by regulatory agencies +Those who must comply with regulations. Typically this group consists of employees or contractors of regulated community. +Those segments of the scientific community who perform research and development in areas relevant to the relevant regulated community. +The third group is of particular significance as they consist of organizations and individuals who support the first two groups. Included in this group are members of numerous advisory panels, organizations that provide peer reviews, and members of peer review panels. An example of this group is the National Academies consisting of the National Academy of Science, National Academy of Engineering, Institute of Medicine, and National Research Council. +The application of regulatory science occurs in three phases. During the first phase the regulators must meet a legislative or court- mandated deadline and promulgate regulations using their best judgment. The second phase provides opportunity to develop regulatory science tools. These include human health and ecological risk assessment procedures and post marketing evaluation method d processes for drugs ad medical devices. The third Standard Operating phase, used tools developed during the second phase to improve the initial decision. (Moghissi et al.) + +== Regulatory engineering == +Engineering is the development of new products and processes, hence regulatory engineering encompasses principally the development of products and processes to facilitate or better examine regulations or their scientific foundations. Another related segment of regulatory science deal with the application of engineering design or analysis to operations such as the safety of nuclear and other power plants, chemical production facilities, mining operations, and air transportation. +Sometimes the term "regulatory engineer(ing)" is misused to refer to essentially administrative or regulatory roles dealing with organizing or coordinating regulatory matters for an organization; however, "engineering" refers only to functional design of products and processes, and in many jurisdictions this definition is legally enforced (see Regulation and licensure in engineering). + +== Areas of focus == \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Regulatory_science-1.md b/data/en.wikipedia.org/wiki/Regulatory_science-1.md new file mode 100644 index 000000000..30009f6a7 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Regulatory_science-1.md @@ -0,0 +1,35 @@ +--- +title: "Regulatory science" +chunk: 2/2 +source: "https://en.wikipedia.org/wiki/Regulatory_science" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T03:55:38.508835+00:00" +instance: "kb-cron" +--- + +=== Regulatory pharmaceutical medicine === +Consistent with its mission, the Food and Drug Administration (FDA) suggests, “Regulatory science is the science of developing new tools, standards and approaches to assess the safety, efficacy, quality and performance of FDA-regulated products.” +Based on several decades of experience regulatory science is logically defined as a distinct scientific discipline constituting the scientific foundation of regulatory, legislative, and judicial decisions. Much like many scientific disciplines that have evolved within the last several decades, regulatory science is both interdisciplinary and multidisciplinary and relies upon a large number of basic and applied scientific disciplines. +Regulatory science is an emerging area of interest within pharmaceutical medicine as the shaping and implementation of legislation and guidelines. One definition of “regulatory science” is the science of developing new tools, standards and approaches to evaluate the efficacy, safety, quality and performance of medical products in order to assess benefit-risk and facilitate a sound and transparent regulatory decision-making. It has been recognized as having a significant impact on the industry’s ability to bring new medicines and medical devices to patients in need. Regulatory science challenges current concepts of benefit/risk assessment, submission and approval strategies, patient’s involvement and ethical aspects. It creates the platform for launching new ideas – not only by the pharmaceutical industry and regulatory authorities, but also by, for example, academia, who wants to contribute to better use of their research activities within medical aspects. Regulatory science has the potential as an enabler for directing companies towards more efficient global development of medical products as well as more robust quality decision-making processes. + +=== Human health === +By far the predominant foci of regulatory science pertain to human health and well-being. This realm covers a broad range of scientific areas – including pollution and toxicology, work safety, food, drugs, and numerous others. + +=== Ecology === +Regulatory ecology covers the protection of various species, protection of wetlands, and numerous other regulated areas, including ecotoxicology. +For example, the US Clean Water Act is based upon an interest in protecting water quality for its own sake, in contrast with the Clean Air Act which is premised upon protecting air quality only for the sake of human health; however, these are ideological policy premises rather than scientific matters themselves. +The US Department of Agriculture regulates animal care, and the FDA regulates humaneness for animal studies. +The US Department of Interior, Fish and Wildlife Service (USFWS), and National Oceanographic and Atmospheric Administration, National Marine Fisheries Service, implement the development and enforcement of policies required by the Federal Endangered Species Act (FESA), Migratory Bird Treaty Act, and other biological resources laws. The FESA requires that the decisions to list a species as endangered or threatened are based on the best available scientific data. To that end, the USFWS and other government agencies fund research to determine the conservation status of proposed species. Regulatory scientists within the Services review, evaluate, and incorporate data from these studies of proposed species in their published regulations. Survey protocols for listed species are also developed from scientific studies of their target species. The purpose of the protocols is to reliably and accurately determine the residency of the target species in a given study area. + +== Regulatory economics == + +There are numerous economic decisions in the regulatory process, including the economics part of cost-benefit analysis. + +== Science in legislation and in courts == +Although often less than fully recognized, the scientific foundation of legislative decisions is included in regulatory science and should be based on reliable science. Similarly, courts have recognized the need to rely upon information that meets scientific requirements. + +== References == + +== Further reading == +Honda, Hiroshi (2016). "Overview of Issues and Discussions in Regulatory Science and Engineering over the Past Four Years in Global Arena" (PDF). American Journal of Environmental Engineering and Science. 3 (1): 1–20. ISSN 2381-1153. \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Sexual_dimorphism_measures-0.md b/data/en.wikipedia.org/wiki/Sexual_dimorphism_measures-0.md new file mode 100644 index 000000000..dac516f7c --- /dev/null +++ b/data/en.wikipedia.org/wiki/Sexual_dimorphism_measures-0.md @@ -0,0 +1,579 @@ +--- +title: "Sexual dimorphism measures" +chunk: 1/3 +source: "https://en.wikipedia.org/wiki/Sexual_dimorphism_measures" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T03:55:39.844988+00:00" +instance: "kb-cron" +--- + +Although the subject of sexual dimorphism is not in itself controversial, the measures by which it is assessed differ widely. Most of the measures are used on the assumption that a random variable is considered so that probability distributions should be taken into account. In this review, a series of sexual dimorphism measures are discussed concerning both their definition and the probability law on which they are based. Most of them are sample functions, or statistics, which account for only partial characteristics, for example the mean or expected value, of the distribution involved. Further, the most widely used measure fails to incorporate an inferential support. + +== Introduction == + +It is widely known that sexual dimorphism is an important component of the morphological variation in biological populations (see, e.g., Klein and Cruz-Uribe, 1984; Oxnard, 1987; Kelley, 1993). In higher Primates, sexual dimorphism is also related to some aspects of the social organization and behavior (Alexander et al., 1979; Clutton-Brock, 1985). Thus, it has been observed that the most dimorphic species tend to polygyny and a social organization based on male dominance, whereas in the less dimorphic species, monogamy and family groups are more common. Fleagle et al. (1980) and Kay (1982), on the other hand, have suggested that the behavior of extinct species can be inferred on the basis of sexual dimorphism and, e.g. Plavcan and van Schaick (1992) think that sex differences in size among primate species reflect processes of an ecological and social nature. Some references on sexual dimorphism regarding human populations can be seen in Lovejoy (1981), Borgognini Tarli and Repetto (1986) and Kappelman (1996). +These biological facts do not appear to be controversial. However, they are based on a series of different sexual dimorphism measures, or indices. Sexual dimorphism, in most works, is measured on the assumption that a random variable is being taken into account. This means that there is a law which accounts for the behavior of the whole set of values that compose the domain of the random variable, a law which is called distribution function. Because both studies of sexual dimorphism aim at establishing differences, in some random variable, between sexes and the behavior of the random variable is accounted for by its distribution function, it follows that a sexual dimorphism study should be equivalent to a study whose main purpose is to determine to what extent the two distribution functions - one per sex - overlap (see shaded area in Fig. 1, where two normal distributions are represented). + +== Measures based on sample means == +In Borgognini Tarli and Repetto (1986) an account of indices based on sample means can be seen. Perhaps, the most widely used is the quotient, + + + + + + + + + + + X + ¯ + + + + + m + + + + + + + X + ¯ + + + + + f + + + + + , + + + {\displaystyle {\frac {{\bar {X}}_{m}}{{\bar {X}}_{f}}},} + + +where + + + + + + + + X + ¯ + + + + + m + + + + + {\displaystyle {\bar {X}}_{m}} + + is the sample mean of one sex (e.g., male) and + + + + + + + + X + ¯ + + + + + f + + + + + {\displaystyle {\bar {X}}_{f}} + + the corresponding mean of the other. Nonetheless, for instance, + + + + + log + ⁡ + + + + + + + X + ¯ + + + + + m + + + + + + + X + ¯ + + + + + f + + + + + , + + + {\displaystyle \operatorname {log} {\frac {{\bar {X}}_{m}}{{\bar {X}}_{f}}},} + + + + + + 100 + + + + + + + + X + ¯ + + + + + m + + + − + + + + + X + ¯ + + + + + f + + + + + + + + X + ¯ + + + + + f + + + + + , + + + {\displaystyle 100{\frac {{\bar {X}}_{m}-{\bar {X}}_{f}}{{\bar {X}}_{f}}},} + + + + + + 100 + + + + + + + + X + ¯ + + + + + m + + + − + + + + + X + ¯ + + + + + f + + + + + + + + + X + ¯ + + + + + f + + + + + + + + + X + ¯ + + + + + f + + + + + + , + + + {\displaystyle 100{\frac {{\bar {X}}_{m}-{\bar {X}}_{f}}{{\bar {X}}_{f}+{\bar {X}}_{f}}},} + + +have also been proposed. +Going over the works where these indices are used, the reader misses any reference to their parametric counterpart (see reference above). In other words, if we suppose that the quotient of two sample means is considered, no work can be found where, in order to make inferences, the way in which the quotient is used as a point estimate of + + + + + + + + μ + + m + + + + μ + + f + + + + + , + + + {\displaystyle {\frac {\mu _{m}}{\mu _{f}}},} + + +is discussed. +By assuming that differences between populations are the objective to analyze, when quotients of sample means are used it is important to point out that the only feature of these populations that seems to be interesting is the mean parameter. However, a population has also variance, as well as a shape which is defined by its distribution function (notice that, in general, this function depends on parameters such as means or variances). + +== Measures based on something more than sample means == +Marini et al. (1999) have illustrated that it is a good idea to consider something other than sample means when sexual dimorphism is analyzed. Possibly, the main reason is that the intrasexual variability influences both the manifestation of dimorphism and its interpretation. + +=== Normal populations === + +==== Sample functions ==== +It is likely that, within this type of indices, the one used the most is the well-known statistic with Student's t distribution see, for instance, Green, 1989. Marini et al. (1999) have observed that variability among females seems to be lower than among males, so that it appears advisable to use the form of the Student's t statistic with degrees of freedom given by the Welch-Satterthwaite approximation, + + + + + T + = + + + + + + + + X + ¯ + + + + + 1 + + + − + + + + + X + ¯ + + + + + 2 + + + − + ( + + μ + + 1 + + + − + + μ + + 2 + + + ) + + + + + + S + + 1 + + + 2 + + + + n + + 1 + + + + + + + + + + S + + 2 + + + 2 + + + + n + + 2 + + + + + + + + : + + t + + ν + + + , + + + {\displaystyle T={\frac {{\bar {X}}_{1}-{\bar {X}}_{2}-(\mu _{1}-\mu _{2})}{\sqrt {{\frac {S_{1}^{2}}{n_{1}}}+{\frac {S_{2}^{2}}{n_{2}}}}}}:t_{\nu },} + + + + + + ν + = + + + + ( + + + + S + + 1 + + + 2 + + + + n + + 1 + + + + + + + + + + S + + 2 + + + 2 + + + + n + + 2 + + + + + + ) + + 2 + + + + + + + + S + + 1 + + + 2 + + + + + n + + 1 + + + ( + + n + + 1 + + + − + 1 + ) + + + + + + + + + S + + 2 + + + 2 + + + + + n + + 2 + + + ( + + n + + 2 + + + − + 1 + ) + + + + + + + , + + + {\displaystyle \nu ={\frac {({\frac {S_{1}^{2}}{n_{1}}}+{\frac {S_{2}^{2}}{n_{2}}})^{2}}{{\frac {S_{1}^{2}}{n_{1}(n_{1}-1)}}+{\frac {S_{2}^{2}}{n_{2}(n_{2}-1)}}}},} + + +where + + + + + S + + i + + + 2 + + + , + + n + + i + + + , + i + = + 1 + , + 2 + + + {\displaystyle S_{i}^{2},n_{i},i=1,2} + + are sample variances and sample sizes, respectively. +It is important to point out the following: \ No newline at end of file diff --git a/data/en.wikipedia.org/wiki/Sexual_dimorphism_measures-1.md b/data/en.wikipedia.org/wiki/Sexual_dimorphism_measures-1.md new file mode 100644 index 000000000..d18953389 --- /dev/null +++ b/data/en.wikipedia.org/wiki/Sexual_dimorphism_measures-1.md @@ -0,0 +1,513 @@ +--- +title: "Sexual dimorphism measures" +chunk: 2/3 +source: "https://en.wikipedia.org/wiki/Sexual_dimorphism_measures" +category: "reference" +tags: "science, encyclopedia" +date_saved: "2026-05-05T03:55:39.844988+00:00" +instance: "kb-cron" +--- + +when this statistic is taken into account in sexual dimorphism studies, two normal populations are involved. From these populations two random samples are extracted, each one corresponding to a sex, and such samples are independent. +when inferences are considered, what we are testing by using this statistic is that the difference between two mathematical expectations is a hypothesized value, say + + + + + μ + + 0 + + + = + + μ + + 1 + + + − + + μ + + 2 + + + . + + + {\displaystyle \mu _{0}=\mu _{1}-\mu _{2}.} + + +However, in sexual dimorphism analyses, it does not appear reasonably (see Ipiña and Durand, 2000) to assume that two independent random samples have been selected. Rather on the contrary, when we sample we select some random observations - making up one sample - that sometimes correspond to one sex and sometimes to the other. + +==== Taking parameters into account ==== +Chakraborty and Majumder (1982) have proposed an index of sexual dimorphism that is the overlapping area - to be precise, its complement - of two normal density functions (see Fig. 1). Therefore, it is a function of four parameters + + + + + μ + + i + + + , + + σ + + i + + + 2 + + + , + i + = + 1 + , + 2 + + + {\displaystyle \mu _{i},\sigma _{i}^{2},i=1,2} + + (expected values and variances, respectively), and takes the shape of the two normals into account. Inman and Bradley (1989) have discussed this overlapping area as a measure to assess the distance between two normal densities. +Regarding inferences, Chakraborty and Majumder proposed a sample function constructed by considering the Laplace-DeMoivre's theorem (an application to binomial laws of the central limit theorem). According to these authors, the variance of such a statistic is, + + + + + var + ⁡ + ( + + + + D + ^ + + + + ) + = + + + + + + + + p + ^ + + + + + m + + + ( + 1 + − + + + + + p + ^ + + + + + m + + + ) + + + n + + m + + + + + + + + + + + + + + p + ^ + + + + + f + + + ( + 1 + − + + + + + p + ^ + + + + + f + + + ) + + + n + + f + + + + + , + + + {\displaystyle \operatorname {var} ({\widehat {D}})={\frac {{\widehat {p}}_{m}(1-{\widehat {p}}_{m})}{n_{m}}}+{\frac {{\widehat {p}}_{f}(1-{\widehat {p}}_{f})}{n_{f}}},} + + +where + + + + + + + D + ^ + + + + + + {\displaystyle {\widehat {D}}} + + is the statistic, and + + + + + + + + p + ^ + + + + + i + + + , + + n + + i + + + , + i + = + m + , + f + + + {\displaystyle {\widehat {p}}_{i},n_{i},i=m,f} + + (male, female) stand for the estimate of the probability of observing the measurement of an individual of the + + + + i + + + {\displaystyle i} + + sex in some interval of the real line, and the sample size of the i sex, respectively. Notice that this implies that two independent random variables with binomial distributions have to be regarded. One of such variables is number of individuals of the f sex in a sample of size + + + + + n + + f + + + + + {\displaystyle n_{f}} + + composed of individuals of the f sex, which seems nonsensical. + +=== Mixture models === +Authors such as Josephson et al. (1996) believe that the two sexes to be analyzed form a single population with a probabilistic behavior denominated a mixture of two normal populations. Thus, if + + + + X + + + {\displaystyle X} + + is a random variable which is normally distributed among the females of a population and likewise this variable is normally distributed among the males of the population, then, + + + + + f + ( + x + ) + = + + ∑ + + i + = + 1 + + + n + + + + π + + i + + + + f + + i + + + ( + x + ) + , + − + ∞ + < + x + < + ∞ + , + + + {\displaystyle f(x)=\sum _{i=1}^{n}\pi _{i}f_{i}(x),-\infty