1.
Jmol
–
Jmol is computer software for molecular modelling chemical structures in 3-dimensions. Jmol returns a 3D representation of a molecule that may be used as a teaching tool and it is written in the programming language Java, so it can run on the operating systems Windows, macOS, Linux, and Unix, if Java is installed. It is free and open-source software released under a GNU Lesser General Public License version 2.0, a standalone application and a software development kit exist that can be integrated into other Java applications, such as Bioclipse and Taverna. A popular feature is an applet that can be integrated into web pages to display molecules in a variety of ways, for example, molecules can be displayed as ball-and-stick models, space-filling models, ribbon diagrams, etc. Jmol supports a range of chemical file formats, including Protein Data Bank, Crystallographic Information File, MDL Molfile. There is also a JavaScript-only version, JSmol, that can be used on computers with no Java, the Jmol applet, among other abilities, offers an alternative to the Chime plug-in, which is no longer under active development. While Jmol has many features that Chime lacks, it does not claim to reproduce all Chime functions, most notably, Chime requires plug-in installation and Internet Explorer 6.0 or Firefox 2.0 on Microsoft Windows, or Netscape Communicator 4.8 on Mac OS9. Jmol requires Java installation and operates on a variety of platforms. For example, Jmol is fully functional in Mozilla Firefox, Internet Explorer, Opera, Google Chrome, fast and Scriptable Molecular Graphics in Web Browsers without Java3D
2.
ChemSpider
–
ChemSpider is a database of chemicals. ChemSpider is owned by the Royal Society of Chemistry, the database contains information on more than 50 million molecules from over 500 data sources including, Each chemical is given a unique identifier, which forms part of a corresponding URL. This is an approach to develop an online chemistry database. The search can be used to widen or restrict already found results, structure searching on mobile devices can be done using free apps for iOS and for the Android. The ChemSpider database has been used in combination with text mining as the basis of document markup. The result is a system between chemistry documents and information look-up via ChemSpider into over 150 data sources. ChemSpider was acquired by the Royal Society of Chemistry in May,2009, prior to the acquisition by RSC, ChemSpider was controlled by a private corporation, ChemZoo Inc. The system was first launched in March 2007 in a release form. ChemSpider has expanded the generic support of a database to include support of the Wikipedia chemical structure collection via their WiChempedia implementation. A number of services are available online. SyntheticPages is an interactive database of synthetic chemistry procedures operated by the Royal Society of Chemistry. Users submit synthetic procedures which they have conducted themselves for publication on the site and these procedures may be original works, but they are more often based on literature reactions. Citations to the published procedure are made where appropriate. They are checked by an editor before posting. The pages do not undergo formal peer-review like a journal article. The comments are moderated by scientific editors. The intention is to collect practical experience of how to conduct useful chemical synthesis in the lab, while experimental methods published in an ordinary academic journal are listed formally and concisely, the procedures in ChemSpider SyntheticPages are given with more practical detail. Comments by submitters are included as well, other publications with comparable amounts of detail include Organic Syntheses and Inorganic Syntheses
3.
European Chemicals Agency
–
ECHA is the driving force among regulatory authorities in implementing the EUs chemicals legislation. ECHA helps companies to comply with the legislation, advances the safe use of chemicals, provides information on chemicals and it is located in Helsinki, Finland. The Agency, headed by Executive Director Geert Dancet, started working on 1 June 2007, the REACH Regulation requires companies to provide information on the hazards, risks and safe use of chemical substances that they manufacture or import. Companies register this information with ECHA and it is freely available on their website. So far, thousands of the most hazardous and the most commonly used substances have been registered, the information is technical but gives detail on the impact of each chemical on people and the environment. This also gives European consumers the right to ask whether the goods they buy contain dangerous substances. The Classification, Labelling and Packaging Regulation introduces a globally harmonised system for classifying and labelling chemicals into the EU. This worldwide system makes it easier for workers and consumers to know the effects of chemicals, companies need to notify ECHA of the classification and labelling of their chemicals. So far, ECHA has received over 5 million notifications for more than 100000 substances, the information is freely available on their website. Consumers can check chemicals in the products they use, Biocidal products include, for example, insect repellents and disinfectants used in hospitals. The Biocidal Products Regulation ensures that there is information about these products so that consumers can use them safely. ECHA is responsible for implementing the regulation, the law on Prior Informed Consent sets guidelines for the export and import of hazardous chemicals. Through this mechanism, countries due to hazardous chemicals are informed in advance and have the possibility of rejecting their import. Substances that may have effects on human health and the environment are identified as Substances of Very High Concern 1. These are mainly substances which cause cancer, mutation or are toxic to reproduction as well as substances which persist in the body or the environment, other substances considered as SVHCs include, for example, endocrine disrupting chemicals. Companies manufacturing or importing articles containing these substances in a concentration above 0 and they are required to inform users about the presence of the substance and therefore how to use it safely. Consumers have the right to ask the retailer whether these substances are present in the products they buy, once a substance has been officially identified in the EU as being of very high concern, it will be added to a list. This list is available on ECHA’s website and shows consumers and industry which chemicals are identified as SVHCs, Substances placed on the Candidate List can then move to another list
4.
PubChem
–
PubChem is a database of chemical molecules and their activities against biological assays. The system is maintained by the National Center for Biotechnology Information, a component of the National Library of Medicine, PubChem can be accessed for free through a web user interface. Millions of compound structures and descriptive datasets can be downloaded via FTP. PubChem contains substance descriptions and small molecules with fewer than 1000 atoms and 1000 bonds, more than 80 database vendors contribute to the growing PubChem database. PubChem consists of three dynamically growing primary databases, as of 28 January 2016, Compounds,82.6 million entries, contains pure and characterized chemical compounds. Substances,198 million entries, contains also mixtures, extracts, complexes, bioAssay, bioactivity results from 1.1 million high-throughput screening programs with several million values. PubChem contains its own online molecule editor with SMILES/SMARTS and InChI support that allows the import and export of all common chemical file formats to search for structures and fragments. In the text search form the database fields can be searched by adding the name in square brackets to the search term. A numeric range is represented by two separated by a colon. The search terms and field names are case-insensitive, parentheses and the logical operators AND, OR, and NOT can be used. AND is assumed if no operator is used, example,0,5000,50,10 -5,5 PubChem was released in 2004. The American Chemical Society has raised concerns about the publicly supported PubChem database and they have a strong interest in the issue since the Chemical Abstracts Service generates a large percentage of the societys revenue. To advocate their position against the PubChem database, ACS has actively lobbied the US Congress, soon after PubChems creation, the American Chemical Society lobbied U. S. Congress to restrict the operation of PubChem, which they asserted competes with their Chemical Abstracts Service
5.
International Chemical Identifier
–
Initially developed by IUPAC and NIST from 2000 to 2005, the format and algorithms are non-proprietary. The continuing development of the standard has supported since 2010 by the not-for-profit InChI Trust. The current version is 1.04 and was released in September 2011, prior to 1.04, the software was freely available under the open source LGPL license, but it now uses a custom license called IUPAC-InChI Trust License. Not all layers have to be provided, for instance, the layer can be omitted if that type of information is not relevant to the particular application. InChIs can thus be seen as akin to a general and extremely formalized version of IUPAC names and they can express more information than the simpler SMILES notation and differ in that every structure has a unique InChI string, which is important in database applications. Information about the 3-dimensional coordinates of atoms is not represented in InChI, the InChI algorithm converts input structural information into a unique InChI identifier in a three-step process, normalization, canonicalization, and serialization. The InChIKey, sometimes referred to as a hashed InChI, is a fixed length condensed digital representation of the InChI that is not human-understandable. The InChIKey specification was released in September 2007 in order to facilitate web searches for chemical compounds and it should be noted that, unlike the InChI, the InChIKey is not unique, though collisions can be calculated to be very rare, they happen. In January 2009 the final 1.02 version of the InChI software was released and this provided a means to generate so called standard InChI, which does not allow for user selectable options in dealing with the stereochemistry and tautomeric layers of the InChI string. The standard InChIKey is then the hashed version of the standard InChI string, the standard InChI will simplify comparison of InChI strings and keys generated by different groups, and subsequently accessed via diverse sources such as databases and web resources. Every InChI starts with the string InChI= followed by the version number and this is followed by the letter S for standard InChIs. The remaining information is structured as a sequence of layers and sub-layers, the layers and sub-layers are separated by the delimiter / and start with a characteristic prefix letter. The six layers with important sublayers are, Main layer Chemical formula and this is the only sublayer that must occur in every InChI. The atoms in the formula are numbered in sequence, this sublayer describes which atoms are connected by bonds to which other ones. Describes how many hydrogen atoms are connected to each of the other atoms, the condensed,27 character standard InChIKey is a hashed version of the full standard InChI, designed to allow for easy web searches of chemical compounds. Most chemical structures on the Web up to 2007 have been represented as GIF files, the full InChI turned out to be too lengthy for easy searching, and therefore the InChIKey was developed. With all databases currently having below 50 million structures, such duplication appears unlikely at present, a recent study more extensively studies the collision rate finding that the experimental collision rate is in agreement with the theoretical expectations. Example, Morphine has the structure shown on the right, as the InChI cannot be reconstructed from the InChIKey, an InChIKey always needs to be linked to the original InChI to get back to the original structure
6.
Simplified molecular-input line-entry system
–
The simplified molecular-input line-entry system is a specification in form of a line notation for describing the structure of chemical species using short ASCII strings. SMILES strings can be imported by most molecule editors for conversion back into two-dimensional drawings or three-dimensional models of the molecules, the original SMILES specification was initiated in the 1980s. It has since modified and extended. In 2007, a standard called OpenSMILES was developed in the open-source chemistry community. Other linear notations include the Wiswesser Line Notation, ROSDAL and SLN, the original SMILES specification was initiated by David Weininger at the USEPA Mid-Continent Ecology Division Laboratory in Duluth in the 1980s. The Environmental Protection Agency funded the project to develop SMILES. It has since modified and extended by others, most notably by Daylight Chemical Information Systems. In 2007, a standard called OpenSMILES was developed by the Blue Obelisk open-source chemistry community. Other linear notations include the Wiswesser Line Notation, ROSDAL and SLN, in July 2006, the IUPAC introduced the InChI as a standard for formula representation. SMILES is generally considered to have the advantage of being slightly more human-readable than InChI, the term SMILES refers to a line notation for encoding molecular structures and specific instances should strictly be called SMILES strings. However, the term SMILES is also used to refer to both a single SMILES string and a number of SMILES strings, the exact meaning is usually apparent from the context. The terms canonical and isomeric can lead to confusion when applied to SMILES. The terms describe different attributes of SMILES strings and are not mutually exclusive, typically, a number of equally valid SMILES strings can be written for a molecule. For example, CCO, OCC and CC all specify the structure of ethanol, algorithms have been developed to generate the same SMILES string for a given molecule, of the many possible strings, these algorithms choose only one of them. This SMILES is unique for each structure, although dependent on the algorithm used to generate it. These algorithms first convert the SMILES to a representation of the molecular structure. A common application of canonical SMILES is indexing and ensuring uniqueness of molecules in a database, there is currently no systematic comparison across commercial software to test if such flaws exist in those packages. SMILES notation allows the specification of configuration at tetrahedral centers, and these are structural features that cannot be specified by connectivity alone and SMILES which encode this information are termed isomeric SMILES
7.
Chemical formula
–
These are limited to a single typographic line of symbols, which may include subscripts and superscripts. A chemical formula is not a name, and it contains no words. Although a chemical formula may imply certain simple chemical structures, it is not the same as a full chemical structural formula. Chemical formulas can fully specify the structure of only the simplest of molecules and chemical substances, the simplest types of chemical formulas are called empirical formulas, which use letters and numbers indicating the numerical proportions of atoms of each type. Molecular formulas indicate the numbers of each type of atom in a molecule. For example, the formula for glucose is CH2O, while its molecular formula is C6H12O6. This is possible if the relevant bonding is easy to show in one dimension, an example is the condensed molecular/chemical formula for ethanol, which is CH3-CH2-OH or CH3CH2OH. For reasons of structural complexity, there is no condensed chemical formula that specifies glucose, chemical formulas may be used in chemical equations to describe chemical reactions and other chemical transformations, such as the dissolving of ionic compounds into solution. A chemical formula identifies each constituent element by its chemical symbol, in empirical formulas, these proportions begin with a key element and then assign numbers of atoms of the other elements in the compound, as ratios to the key element. For molecular compounds, these numbers can all be expressed as whole numbers. For example, the formula of ethanol may be written C2H6O because the molecules of ethanol all contain two carbon atoms, six hydrogen atoms, and one oxygen atom. Some types of compounds, however, cannot be written with entirely whole-number empirical formulas. An example is boron carbide, whose formula of CBn is a variable non-whole number ratio with n ranging from over 4 to more than 6.5. When the chemical compound of the consists of simple molecules. These types of formulas are known as molecular formulas and condensed formulas. A molecular formula enumerates the number of atoms to reflect those in the molecule, so that the formula for glucose is C6H12O6 rather than the glucose empirical formula. However, except for very simple substances, molecular chemical formulas lack needed structural information, for simple molecules, a condensed formula is a type of chemical formula that may fully imply a correct structural formula. For example, ethanol may be represented by the chemical formula CH3CH2OH
8.
Density
–
The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume. The symbol most often used for density is ρ, although the Latin letter D can also be used. Mathematically, density is defined as mass divided by volume, ρ = m V, where ρ is the density, m is the mass, and V is the volume. In some cases, density is defined as its weight per unit volume. For a pure substance the density has the numerical value as its mass concentration. Different materials usually have different densities, and density may be relevant to buoyancy, purity, osmium and iridium are the densest known elements at standard conditions for temperature and pressure but certain chemical compounds may be denser. Thus a relative density less than one means that the floats in water. The density of a material varies with temperature and pressure and this variation is typically small for solids and liquids but much greater for gases. Increasing the pressure on an object decreases the volume of the object, increasing the temperature of a substance decreases its density by increasing its volume. In most materials, heating the bottom of a results in convection of the heat from the bottom to the top. This causes it to rise relative to more dense unheated material, the reciprocal of the density of a substance is occasionally called its specific volume, a term sometimes used in thermodynamics. Density is a property in that increasing the amount of a substance does not increase its density. Archimedes knew that the irregularly shaped wreath could be crushed into a cube whose volume could be calculated easily and compared with the mass, upon this discovery, he leapt from his bath and ran naked through the streets shouting, Eureka. As a result, the term eureka entered common parlance and is used today to indicate a moment of enlightenment, the story first appeared in written form in Vitruvius books of architecture, two centuries after it supposedly took place. Some scholars have doubted the accuracy of this tale, saying among other things that the method would have required precise measurements that would have been difficult to make at the time, from the equation for density, mass density has units of mass divided by volume. As there are units of mass and volume covering many different magnitudes there are a large number of units for mass density in use. The SI unit of kilogram per metre and the cgs unit of gram per cubic centimetre are probably the most commonly used units for density.1,000 kg/m3 equals 1 g/cm3. In industry, other larger or smaller units of mass and or volume are often more practical, see below for a list of some of the most common units of density
9.
Melting point
–
The melting point of a solid is the temperature at which it changes state from solid to liquid at atmospheric pressure. At the melting point the solid and liquid phase exist in equilibrium, the melting point of a substance depends on pressure and is usually specified at standard pressure. When considered as the temperature of the change from liquid to solid. Because of the ability of some substances to supercool, the point is not considered as a characteristic property of a substance. For most substances, melting and freezing points are approximately equal, for example, the melting point and freezing point of mercury is 234.32 kelvins. However, certain substances possess differing solid-liquid transition temperatures, for example, agar melts at 85 °C and solidifies from 31 °C to 40 °C, such direction dependence is known as hysteresis. The melting point of ice at 1 atmosphere of pressure is close to 0 °C. In the presence of nucleating substances the freezing point of water is the same as the melting point, the chemical element with the highest melting point is tungsten, at 3687 K, this property makes tungsten excellent for use as filaments in light bulbs. Many laboratory techniques exist for the determination of melting points, a Kofler bench is a metal strip with a temperature gradient. Any substance can be placed on a section of the strip revealing its thermal behaviour at the temperature at that point, differential scanning calorimetry gives information on melting point together with its enthalpy of fusion. A basic melting point apparatus for the analysis of crystalline solids consists of an oil bath with a transparent window, the several grains of a solid are placed in a thin glass tube and partially immersed in the oil bath. The oil bath is heated and with the aid of the melting of the individual crystals at a certain temperature can be observed. In large/small devices, the sample is placed in a heating block, the measurement can also be made continuously with an operating process. For instance, oil refineries measure the point of diesel fuel online, meaning that the sample is taken from the process. This allows for more frequent measurements as the sample does not have to be manually collected, for refractory materials the extremely high melting point may be determined by heating the material in a black body furnace and measuring the black-body temperature with an optical pyrometer. For the highest melting materials, this may require extrapolation by several hundred degrees, the spectral radiance from an incandescent body is known to be a function of its temperature. An optical pyrometer matches the radiance of a body under study to the radiance of a source that has been previously calibrated as a function of temperature, in this way, the measurement of the absolute magnitude of the intensity of radiation is unnecessary. However, known temperatures must be used to determine the calibration of the pyrometer, for temperatures above the calibration range of the source, an extrapolation technique must be employed
10.
Band gap
–
In solid-state physics, a band gap, also called an energy gap or bandgap, is an energy range in a solid where no electron states can exist. It is closely related to the HOMO/LUMO gap in chemistry, therefore, the band gap is a major factor determining the electrical conductivity of a solid. Every solid has its own characteristic energy-band structure and this variation in band structure is responsible for the wide range of electrical characteristics observed in various materials. In semiconductors and insulators, electrons are confined to a number of bands of energy, the term band gap refers to the energy difference between the top of the valence band and the bottom of the conduction band. Electrons are able to jump from one band to another, however, in order for an electron to jump from a valence band to a conduction band, it requires a specific minimum amount of energy for the transition. The required energy differs with different materials, electrons can gain enough energy to jump to the conduction band by absorbing either a phonon or a photon. In contrast, a material with a band gap is an insulator. In conductors, the valence and conduction bands may overlap, so they may not have a band gap, the conductivity of intrinsic semiconductors is strongly dependent on the band gap. Band-gap engineering is the process of controlling or altering the band gap of a material by controlling the composition of certain semiconductor alloys, such as GaAlAs, InGaAs and it is also possible to construct layered materials with alternating compositions by techniques like molecular-beam epitaxy. These methods are exploited in the design of heterojunction bipolar transistors, laser diodes, the distinction between semiconductors and insulators is a matter of convention. One approach is to think of semiconductors as a type of insulator with a band gap. Insulators with a band gap, usually greater than 4 eV, are not considered semiconductors. Electron mobility also plays a role in determining a materials informal classification, the band-gap energy of semiconductors tends to decrease with increasing temperature. When temperature increases, the amplitude of atomic vibrations increase, leading to larger interatomic spacing, the interaction between the lattice phonons and the free electrons and holes will also affect the band gap to a smaller extent. The relationship between band gap energy and temperature can be described by Varshnis empirical expression, E g = E g − α T2 T + β, in a regular semiconductor crystal, the band gap is fixed owing to continuous energy states. In a quantum dot crystal, the gap is size dependent. It is also known as quantum confinement effect, Band gaps also depend on pressure. Band gaps can be direct or indirect, depending on the electronic band structure
11.
Electron mobility
–
In solid-state physics, the electron mobility characterizes how quickly an electron can move through a metal or semiconductor, when pulled by an electric field. In semiconductors, there is a quantity for holes, called hole mobility. The term carrier mobility refers in general to both electron and hole mobility in semiconductors, electron and hole mobility are special cases of electrical mobility of charged particles in a fluid under an applied electric field. When an electric field E is applied across a piece of material, then the electron mobility μ is defined as v d = μ E. Electron mobility is almost always specified in units of cm2/ and this is different from the SI unit of mobility, m2/. They are related by 1m2/ = 104cm2/, conductivity is proportional to the product of mobility and carrier concentration. For example, the conductivity could come from a small number of electrons with high mobility for each. For metals, it would not typically matter which of these is the case, therefore mobility is relatively unimportant in metal physics. Therefore mobility is an important parameter for semiconductor materials. Almost always, higher mobility leads to better performance, with other things equal. Semiconductor mobility depends on the impurity concentrations, defect concentration, temperature and it also depends on the electric field, particularly at high fields when velocity saturation occurs. It can be determined by the Hall effect, or inferred from transistor behavior, without any applied electric field, in a solid, electrons move around randomly. Therefore, on there will be no overall motion of charge carriers in any particular direction over time. However, when a field is applied, each electron is accelerated by the electric field. If the electron were in a vacuum, it would be accelerated to faster and faster velocities, however, in a solid, the electron repeatedly scatters off crystal defects, phonons, impurities, etc. Therefore, it does not accelerate faster and faster, instead it moves with an average velocity. This net electron motion is much slower than the normally occurring random motion. In a semiconductor the two carriers, electrons and holes, will typically have different drift velocities for the same electric field
12.
Thermal conductivity
–
In physics, thermal conductivity is the property of a material to conduct heat. It is evaluated primarily in terms of Fouriers Law for heat conduction, heat transfer occurs at a lower rate across materials of low thermal conductivity than across materials of high thermal conductivity. Correspondingly, materials of high thermal conductivity are used in heat sink applications. The thermal conductivity of a material may depend on temperature, the reciprocal of thermal conductivity is called thermal resistivity. Thermal conductivity is actually a tensor, which means it is possible to have different values in different directions, in SI units, thermal conductivity is measured in watts per meter-kelvin. The dimension of thermal conductivity is M1L1T−3Θ−1 and these variables are mass, length, time, and temperature. In Imperial units, thermal conductivity is measured in BTU/, other units which are closely related to the thermal conductivity are in common use in the construction and textile industries. The construction industry makes use of such as the R-value. Although related to the conductivity of a material used in an insulation product, R-. Likewise the textile industry has several units including the tog and the clo which express thermal resistance of a material in a way analogous to the R-values used in the construction industry, there are a number of ways to measure thermal conductivity. Each of these is suitable for a range of materials, depending on the thermal properties. There is a distinction between steady-state and transient techniques, in general, steady-state techniques are useful when the temperature of the material does not change with time. This makes the signal analysis straightforward, the disadvantage is that a well-engineered experimental setup is usually needed. The Divided Bar is the most common used for consolidated rock solids. Thermal conductivity is important in science, research, electronics, building insulation and related fields. Several materials are shown in the list of thermal conductivities and these should be considered approximate due to the uncertainties related to material definitions. High energy generation rates within electronics or turbines require the use of materials with high thermal conductivity such as copper, aluminium, the reciprocal of thermal conductivity is thermal resistivity, usually expressed in kelvin-meters per watt. For a given thickness of a material, that particular constructions thermal resistance, unfortunately, there are differing definitions for these terms
13.
Refractive index
–
In optics, the refractive index or index of refraction n of a material is a dimensionless number that describes how light propagates through that medium. It is defined as n = c v, where c is the speed of light in vacuum, for example, the refractive index of water is 1.333, meaning that light travels 1.333 times faster in a vacuum than it does in water. The refractive index determines how light is bent, or refracted. The refractive indices also determine the amount of light that is reflected when reaching the interface, as well as the angle for total internal reflection. This implies that vacuum has a index of 1. The refractive index varies with the wavelength of light and this is called dispersion and causes the splitting of white light into its constituent colors in prisms and rainbows, and chromatic aberration in lenses. Light propagation in absorbing materials can be described using a refractive index. The imaginary part then handles the attenuation, while the real part accounts for refraction, the concept of refractive index is widely used within the full electromagnetic spectrum, from X-rays to radio waves. It can also be used with wave phenomena such as sound, in this case the speed of sound is used instead of that of light and a reference medium other than vacuum must be chosen. Thomas Young was presumably the person who first used, and invented, at the same time he changed this value of refractive power into a single number, instead of the traditional ratio of two numbers. The ratio had the disadvantage of different appearances, newton, who called it the proportion of the sines of incidence and refraction, wrote it as a ratio of two numbers, like 529 to 396. Hauksbee, who called it the ratio of refraction, wrote it as a ratio with a fixed numerator, hutton wrote it as a ratio with a fixed denominator, like 1.3358 to 1. Young did not use a symbol for the index of refraction, in the next years, others started using different symbols, n, m, and µ. For visible light most transparent media have refractive indices between 1 and 2, a few examples are given in the adjacent table. These values are measured at the yellow doublet D-line of sodium, with a wavelength of 589 nanometers, gases at atmospheric pressure have refractive indices close to 1 because of their low density. Almost all solids and liquids have refractive indices above 1.3, aerogel is a very low density solid that can be produced with refractive index in the range from 1.002 to 1.265. Moissanite lies at the end of the range with a refractive index as high as 2.65. Most plastics have refractive indices in the range from 1.3 to 1.7, for infrared light refractive indices can be considerably higher
14.
Crystal structure
–
In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystalline material. Ordered structures occur from the nature of the constituent particles to form symmetric patterns that repeat along the principal directions of three-dimensional space in matter. The smallest group of particles in the material that constitutes the pattern is the unit cell of the structure. The unit cell completely defines the symmetry and structure of the crystal lattice. The repeating patterns are said to be located at the points of the Bravais lattice, the lengths of the principal axes, or edges, of the unit cell and the angles between them are the lattice constants, also called lattice parameters. The symmetry properties of the crystal are described by the concept of space groups, all possible symmetric arrangements of particles in three-dimensional space may be described by the 230 space groups. The crystal structure and symmetry play a role in determining many physical properties, such as cleavage, electronic band structure. The crystal structure of a material can be described in terms of its unit cell, the unit cell is a box containing one or more atoms arranged in three dimensions. The unit cells stacked in three-dimensional space describe the arrangement of atoms of the crystal. Commonly, atomic positions are represented in terms of fractional coordinates, the atom positions within the unit cell can be calculated through application of symmetry operations to the asymmetric unit. The asymmetric unit refers to the smallest possible occupation of space within the unit cell and this does not, however imply that the entirety of the asymmetric unit must lie within the boundaries of the unit cell. Symmetric transformations of atom positions are calculated from the group of the crystal structure. Vectors and planes in a lattice are described by the three-value Miller index notation. It uses the indices ℓ, m, and n as directional parameters, which are separated by 90°, by definition, the syntax denotes a plane that intercepts the three points a1/ℓ, a2/m, and a3/n, or some multiple thereof. That is, the Miller indices are proportional to the inverses of the intercepts of the plane with the unit cell, if one or more of the indices is zero, it means that the planes do not intersect that axis. A plane containing a coordinate axis is translated so that it no longer contains that axis before its Miller indices are determined, the Miller indices for a plane are integers with no common factors. Negative indices are indicated with horizontal bars, as in, in an orthogonal coordinate system for a cubic cell, the Miller indices of a plane are the Cartesian components of a vector normal to the plane. Likewise, the planes are geometric planes linking nodes
15.
Cubic crystal system
–
In crystallography, the cubic crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals, there are three main varieties of these crystals, Primitive cubic Body-centered cubic, Face-centered cubic Each is subdivided into other variants listed below. Note that although the cell in these crystals is conventionally taken to be a cube. This is related to the fact that in most cubic crystal systems, a classic isometric crystal has square or pentagonal faces. The three Bravais lattices in the crystal system are, The primitive cubic system consists of one lattice point on each corner of the cube. Each atom at a point is then shared equally between eight adjacent cubes, and the unit cell therefore contains in total one atom. The body-centered cubic system has one point in the center of the unit cell in addition to the eight corner points. It has a net total of 2 lattice points per unit cell, Each sphere in a cF lattice has coordination number 12. The face-centered cubic system is related to the hexagonal close packed system. The plane of a cubic system is a hexagonal grid. Attempting to create a C-centered cubic crystal system would result in a simple tetragonal Bravais lattice, there are a total 36 cubic space groups. Other terms for hexoctahedral are, normal class, holohedral, ditesseral central class, a simple cubic unit cell has a single cubic void in the center. Additionally, there are 24 tetrahedral voids located in a square spacing around each octahedral void and these tetrahedral voids are not local maxima and are not technically voids, but they do occasionally appear in multi-atom unit cells. A face-centered cubic unit cell has eight tetrahedral voids located midway between each corner and the center of the cell, for a total of eight net tetrahedral voids. One important characteristic of a structure is its atomic packing factor. This is calculated by assuming all the atoms are identical spheres. The atomic packing factor is the proportion of space filled by these spheres, assuming one atom per lattice point, in a primitive cubic lattice with cube side length a, the sphere radius would be a⁄2 and the atomic packing factor turns out to be about 0.524. Similarly, in a bcc lattice, the atomic packing factor is 0.680, as a rule, since atoms in a solid attract each other, the more tightly packed arrangements of atoms tend to be more common
16.
Space group
–
In mathematics, physics and chemistry, a space group is the symmetry group of a configuration in space, usually in three dimensions. In three dimensions, there are 219 distinct types, or 230 if chiral copies are considered distinct, Space groups are also studied in dimensions other than 3 where they are sometimes called Bieberbach groups, and are discrete cocompact groups of isometries of an oriented Euclidean space. In crystallography, space groups are called the crystallographic or Fedorov groups. A definitive source regarding 3-dimensional space groups is the International Tables for Crystallography, in 1879 Leonhard Sohncke listed the 65 space groups whose elements preserve the orientation. More accurately, he listed 66 groups, but Fedorov and Schönflies both noticed that two of them were really the same, the space groups in 3 dimensions were first enumerated by Fedorov, and shortly afterwards were independently enumerated by Schönflies. The correct list of 230 space groups was found by 1892 during correspondence between Fedorov and Schönflies, burckhardt describes the history of the discovery of the space groups in detail. The space groups in three dimensions are made from combinations of the 32 crystallographic point groups with the 14 Bravais lattices, the combination of all these symmetry operations results in a total of 230 different space groups describing all possible crystal symmetries. The elements of the space group fixing a point of space are rotations, reflections, the identity element, the translations form a normal abelian subgroup of rank 3, called the Bravais lattice. There are 14 possible types of Bravais lattice, the quotient of the space group by the Bravais lattice is a finite group which is one of the 32 possible point groups. Translation is defined as the moves from one point to another point. A glide plane is a reflection in a plane, followed by a parallel with that plane. This is noted by a, b or c, depending on which axis the glide is along. There is also the n glide, which is a glide along the half of a diagonal of a face, and the d glide, the latter is called the diamond glide plane as it features in the diamond structure. In 17 space groups, due to the centering of the cell, the glides occur in two directions simultaneously, i. e. the same glide plane can be called b or c, a or b. For example, group Abm2 could be also called Acm2, group Ccca could be called Cccb, in 1992, it was suggested to use symbol e for such planes. The symbols for five groups have been modified, A screw axis is a rotation about an axis. These are noted by a number, n, to describe the degree of rotation, the degree of translation is then added as a subscript showing how far along the axis the translation is, as a portion of the parallel lattice vector. So,21 is a rotation followed by a translation of 1/2 of the lattice vector
17.
Coordination geometry
–
The term coordination geometry is used in a number of related fields of chemistry and solid state chemistry/physics. The coordination geometry of an atom is the pattern formed by atoms around the central atom. In the field of coordination complexes it is the geometrical pattern formed by the atoms in the ligands that are bonded to the central atom in a molecule or a coordination complex. The number of atoms bonded, is termed the coordination number, the geometrical pattern can be described as a polyhedron where the vertices of the polyhedron are the centres of the coordinating atoms in the ligands. The coordination preference of a metal often varies with its oxidation state, the number of coordination bonds can vary from two as high as 20 in Th4. Other common coordination geometries are tetrahedral and square planar, in a crystal structure the coordination geometry of an atom is the geometrical pattern of coordinating atoms where the definition of coordinating atoms depends on the bonding model used. In metals with the body centred cubic structure each atom has eight nearest neighbours in a cubic geometry, in metals with the face centred cubic structure each atom has twelve nearest neighbours in a cuboctahedral geometry. IUPAC have introduced the symbol as part of their IUPAC nomenclature of inorganic chemistry 2005 recommendations to describe the geometry around an atom in a compound. IUCr have proposed a symbol which is shown as a superscript in square brackets in the chemical formula, for example, CaF2 would be CaF2, where means cubic coordination and means tetrahedral. The equivalent symbols in IUPAC are CU−8 and T−4 respectively, the IUPAC symbol is applicable to complexes and molecules whereas the IUCr proposal applies to crystalline solids. Molecular geometry VSEPR Ligand field theory Cis effect Addition to pi ligands
18.
GHS hazard pictograms
–
Hazard pictograms form part of the international Globally Harmonized System of Classification and Labelling of Chemicals. Two sets of pictograms are included within the GHS, one for the labelling of containers and for workplace hazard warnings, either one or the other is chosen, depending on the target audience, but the two are not used together. The two sets of use the same symbols for the same hazards, although certain symbols are not required for transport pictograms. Transport pictograms come in variety of colors and may contain additional information such as a subcategory number. It has still to be implemented by the European Union in 2009, the following pictograms are included in the Worldwide Model Using but have not been incorporated into the GHS, ICZ and Catwallsh Hazcom Labelling because of the nature of the hazards. Globally Harmonized System of Classification and Labelling of Chemicals, New York and Geneva, United Nations,2007, ISBN 978-92-1-116957-7, ST/SG/AC. 10/30/Rev. Model Regulations, New York and Geneva, United Nations,2007, ISBN 978-92-1-139120-6, manual of Tests and Criteria, New York and Geneva, United Nations,2002, ISBN 92-1-139087-7, ST/SG/AC. 10/11/Rev.4 GHS pictogram gallery from the United Nations Economic Commission for Europe
19.
Chemical compound
–
A chemical compound is an entity consisting of two or more atoms, at least two from different elements, which associate via chemical bonds. Many chemical compounds have a numerical identifier assigned by the Chemical Abstracts Service. For example, water is composed of two atoms bonded to one oxygen atom, the chemical formula is H2O. A compound can be converted to a different chemical composition by interaction with a chemical compound via a chemical reaction. In this process, bonds between atoms are broken in both of the compounds, and then bonds are reformed so that new associations are made between atoms. Schematically, this reaction could be described as AB + CD → AC + BD, where A, B, C, and D are each unique atoms, and AB, CD, AC, and BD are each unique compounds. A chemical element bonded to a chemical element is not a chemical compound since only one element. Examples are the diatomic hydrogen and the polyatomic molecule sulfur. Chemical compounds have a unique and defined chemical structure held together in a spatial arrangement by chemical bonds. Pure chemical elements are not considered chemical compounds, failing the two or more atom requirement, though they often consist of molecules composed of multiple atoms. There is varying and sometimes inconsistent nomenclature differentiating substances, which include truly non-stoichiometric examples, from chemical compounds, other compounds regarded as chemically identical may have varying amounts of heavy or light isotopes of the constituent elements, which changes the ratio of elements by mass slightly. Characteristic properties of compounds include that elements in a compound are present in a definite proportion, for example, the molecule of the compound water is composed of hydrogen and oxygen in a ratio of 2,1. In addition, compounds have a set of properties. The physical and chemical properties of compounds differ from those of their constituent elements, however, mixtures can be created by mechanical means alone, but a compound can be created only by a chemical reaction. Some mixtures are so combined that they have some properties similar to compounds. Other examples of compound-like mixtures include intermetallic compounds and solutions of metals in a liquid form of ammonia. Compounds may be described using formulas in various formats, for compounds that exist as molecules, the formula for the molecular unit is shown. For polymeric materials, such as minerals and many metal oxides, the elements in a chemical formula are normally listed in a specific order, called the Hill system
20.
Chemical element
–
A chemical element or element is a species of atoms having the same number of protons in their atomic nuclei. There are 118 elements that have identified, of which the first 94 occur naturally on Earth with the remaining 24 being synthetic elements. There are 80 elements that have at least one stable isotope and 38 that have exclusively radioactive isotopes, iron is the most abundant element making up Earth, while oxygen is the most common element in the Earths crust. Chemical elements constitute all of the matter of the universe. The two lightest elements, hydrogen and helium, were formed in the Big Bang and are the most common elements in the universe. The next three elements were formed mostly by cosmic ray spallation, and are rarer than those that follow. Formation of elements with from 6 to 26 protons occurred and continues to occur in main sequence stars via stellar nucleosynthesis, the high abundance of oxygen, silicon, and iron on Earth reflects their common production in such stars. The term element is used for atoms with a number of protons as well as for a pure chemical substance consisting of a single element. A single element can form multiple substances differing in their structure, when different elements are chemically combined, with the atoms held together by chemical bonds, they form chemical compounds. Only a minority of elements are found uncombined as relatively pure minerals, among the more common of such native elements are copper, silver, gold, carbon, and sulfur. All but a few of the most inert elements, such as gases and noble metals, are usually found on Earth in chemically combined form. While about 32 of the elements occur on Earth in native uncombined forms. For example, atmospheric air is primarily a mixture of nitrogen, oxygen, and argon, the history of the discovery and use of the elements began with primitive human societies that found native elements like carbon, sulfur, copper and gold. Later civilizations extracted elemental copper, tin, lead and iron from their ores by smelting, using charcoal, alchemists and chemists subsequently identified many more, almost all of the naturally occurring elements were known by 1900. Save for unstable radioactive elements with short half-lives, all of the elements are available industrially, almost all other elements found in nature were made by various natural methods of nucleosynthesis. On Earth, small amounts of new atoms are produced in nucleogenic reactions, or in cosmogenic processes. Of the 94 naturally occurring elements, those with atomic numbers 1 through 82 each have at least one stable isotope, Isotopes considered stable are those for which no radioactive decay has yet been observed. Elements with atomic numbers 83 through 94 are unstable to the point that radioactive decay of all isotopes can be detected, the very heaviest elements undergo radioactive decay with half-lives so short that they are not found in nature and must be synthesized
21.
Indium
–
Indium is a chemical element with symbol In and atomic number 49. It is a metal that makes up 0.21 parts per million of the Earths crust. Very soft and malleable, indium has a point higher than sodium and gallium. Chemically, indium is similar to gallium and thallium, and it is intermediate between the two in terms of its properties. Indium was discovered in 1863 by Ferdinand Reich and Hieronymous Theodor Richter by spectroscopic methods and they named it for the indigo blue line in its spectrum. Indium was isolated the next year, Indium is a minor component in zinc sulfide ores and is produced as a byproduct of zinc refinement. Indium has no role, though its compounds are somewhat toxic when injected into the bloodstream. Most occupational exposure is through ingestion, from which indium compounds are not absorbed well, Indium is a silvery-white, highly ductile post-transition metal with a bright luster. It is so soft that like sodium, it can be cut with a knife and it also leaves a visible line on paper. It is a member of group 13 on the periodic table, like tin, a high-pitched cry is heard when indium is bent – a crackling sound due to crystal twinning. Like gallium, indium is able to wet glass, like both, indium has a low melting point,156.60 °C, higher than its lighter homologue, gallium, but lower than its heavier homologue, thallium, and lower than tin. The density of indium,7.31 g/cm3, is greater than gallium. Below the critical temperature,3.41 K, indium becomes a superconductor, Indium displays a ductile viscoplastic response, found to be size-independent in tension and compression. However it does have an effect in bending and indentation, associated to a length-scale of order 50–100 µm. Indium has 49 electrons, with a configuration of 4d105s25p1. In compounds, indium most commonly donates the three outermost electrons to become indium, In3+, in some cases, the pair of 5s-electrons are not donated, resulting in indium, In+. The stabilization of the monovalent state is attributed to the inert pair effect, in which relativistic effects stabilize the 5s-orbital, thallium shows an even stronger effect, causing oxidation to thallium to be more probable than to thallium, whereas gallium commonly shows only the +3 oxidation state. Thus, although thallium is a strong oxidizing agent, indium is not
22.
Antimony
–
Antimony is a chemical element with symbol Sb and atomic number 51. A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite, Antimony compounds have been known since ancient times and were powdered for use as medicine and cosmetics, often known by the Arabic name, kohl. Metallic antimony was known, but it was erroneously identified as lead upon its discovery. In the West, it was first isolated by Vannoccio Biringuccio, for some time, China has been the largest producer of antimony and its compounds, with most production coming from the Xikuangshan Mine in Hunan. The industrial methods for refining antimony are roasting and reduction with carbon or direct reduction of stibnite with iron, the largest applications for metallic antimony is an alloy with lead and tin and the lead antimony plates in lead–acid batteries. Alloys of lead and tin with antimony have improved properties for solders, bullets, Antimony compounds are prominent additives for chlorine and bromine-containing fire retardants found in many commercial and domestic products. An emerging application is the use of antimony in microelectronics, Antimony is in a pnictogen and has an electronegativity of 2.05. In accordance with periodic trends, it is more electronegative than tin or bismuth, Antimony is stable in air at room temperature, but reacts with oxygen if heated to produce antimony trioxide, Sb2O3. Antimony is resistant to attack by acids, four allotropes of antimony are known, a stable metallic form and three metastable forms. Elemental antimony is a brittle, silver-white shiny metalloid, when slowly cooled, molten antimony crystallizes in a trigonal cell, isomorphic with the gray allotrope of arsenic. A rare explosive form of antimony can be formed from the electrolysis of antimony trichloride, when scratched with a sharp implement, an exothermic reaction occurs and white fumes are given off as metallic antimony forms, when rubbed with a pestle in a mortar, a strong detonation occurs. Black antimony is formed upon cooling of antimony vapor. It has the crystal structure as red phosphorus and black arsenic, it oxidizes in air. At 100 °C, it transforms into the stable form. The yellow allotrope of antimony is the most unstable and it has only been generated by oxidation of stibine at −90 °C. Above this temperature and in ambient light, this metastable allotrope transforms into the more stable black allotrope, elemental antimony adopts a layered structure in which layers consist of fused, ruffled, six-membered rings. The nearest and next-nearest neighbors form an octahedral complex, with the three atoms in each double layer slightly closer than the three atoms in the next. This relatively close packing leads to a density of 6.697 g/cm3
23.
Semiconductor
–
Semiconductors are crystalline or amorphous solids with distinct electrical characteristics. They are of high electrical resistance — higher than typical resistance materials and their resistance decreases as their temperature increases, which is behavior opposite to that of a metal. The behavior of charge carriers which include electrons, ions and electron holes at these junctions is the basis of diodes, transistors and all modern electronics. Semiconductor devices can display a range of properties such as passing current more easily in one direction than the other, showing variable resistance. The modern understanding of the properties of a semiconductor relies on quantum physics to explain the movement of carriers in a crystal lattice. Doping greatly increases the number of carriers within the crystal. When a doped semiconductor contains mostly free holes it is called p-type, the semiconductor materials used in electronic devices are doped under precise conditions to control the concentration and regions of p- and n-type dopants. A single semiconductor crystal can have many p- and n-type regions, although some pure elements and many compounds display semiconductor properties, silicon, germanium, and compounds of gallium are the most widely used in electronic devices. Elements near the so-called metalloid staircase, where the metalloids are located on the table, are usually used as semiconductors. Some of the properties of materials were observed throughout the mid 19th. The first practical application of semiconductors in electronics was the 1904 development of the Cats-whisker detector, developments in quantum physics in turn allowed the development of the transistor in 1947 and the integrated circuit in 1958. There are several developed techniques that allow semiconducting materials to behave like conducting materials and these modifications have two outcomes, n-type and p-type. These refer to the excess or shortage of electrons, respectively, an unbalanced number of electrons would cause a current to flow through the material. Heterojunctions Heterojunctions occur when two differently doped semiconducting materials are joined together, for example, a configuration could consist of p-doped and n-doped germanium. This results in an exchange of electrons and holes between the differently doped semiconducting materials, the n-doped germanium would have an excess of electrons, and the p-doped germanium would have an excess of holes. The transfer occurs until equilibrium is reached by a process called recombination, a product of this process is charged ions, which result in an electric field. Excited Electrons A difference in electric potential on a material would cause it to leave thermal equilibrium. This introduces electrons and holes to the system, which interact via a process called ambipolar diffusion, whenever thermal equilibrium is disturbed in a semiconducting material, the amount of holes and electrons changes
24.
Boron group
–
The boron group are the chemical elements in group 13 of the periodic table, comprising boron, aluminium, gallium, indium, thallium, and perhaps also the chemically uncharacterized nihonium. The elements in the group are characterized by having three electrons in their outer energy levels. These elements have also referred to as icosagens and triels. Boron is classified as a metalloid while the rest, with the exception of nihonium, are considered post-transition metals. Boron occurs sparsely, probably because bombardment by the particles produced from natural radioactivity disrupts its nuclei. Aluminium occurs widely on earth, and indeed is the third most abundant element in the Earths crust, gallium is found in the earth with an abundance of 13 ppm. Indium is the 61st most abundant element in the earths crust, nihonium is never found in nature and therefore is termed a synthetic element. Several group 13 elements have biological roles in the ecosystem, Boron is a trace element in humans and is essential for some plants. Lack of boron can lead to stunted plant growth, while an excess can cause harm by inhibiting growth. Aluminium has neither a biological role nor significant toxicity and is considered safe, indium and gallium can stimulate metabolism, gallium is credited with the ability to bind itself to iron proteins. Thallium is highly toxic, interfering with the function of numerous vital enzymes, Boron differs from the other group members in its hardness, refractivity and reluctance to participate in metallic bonding. An example of a trend in reactivity is borons tendency to form compounds with hydrogen. Most of the elements in the group show increasing reactivity as the elements get heavier in atomic mass. The simplest borane is diborane, or B2H6, the next group-13 elements, aluminium and gallium, form fewer stable hydrides, although both AlH3 and GaH3 exist. Indium, the element in the group, is not known to form many hydrides. No stable compound of thallium and hydrogen has been synthesized in any laboratory, all of the boron-group elements are known to form a trivalent oxide, with two atoms of the element bonded covalently with three atoms of oxygen. These elements show a trend of increasing pH, Boron oxide is slightly acidic, aluminium and gallium oxide are amphoteric, indium oxide is nearly amphoteric, and thallium oxide is a Lewis base because it dissolves in acids to form salts. Each of these compounds are stable, but thallium oxide decomposes at temperatures higher than 875 °C, the elements in group 13 are also capable of forming stable compounds with the halogens, usually with the formula MX3 The only exception to this is thallium iodide
25.
Pnictogen
–
A pnictogen /ˈnɪktədʒᵻn/ is one of the chemical elements in group 15 of the periodic table. This group is known as the nitrogen family. It consists of the nitrogen, phosphorus, arsenic, antimony, bismuth. In modern IUPAC notation, it is called Group 15, in CAS and the old IUPAC systems it was called Group VA and Group VB respectively. In the field of physics, it is still usually called Group V. The five in the names comes from the pentavalency of nitrogen. The term pnictogen is derived from the Ancient Greek word πνίγειν meaning to choke and they are therefore 3 electrons short of filling their outermost electron shell in their non-ionized state. The most important elements of group are nitrogen, which in its diatomic form is the principal component of air, and phosphorus. Binary compounds of the group can be referred to collectively as pnictides, the name pentels was also used for this group at one time, stemming from the earlier group naming convention. Pnictide compounds tend to be exotic, various properties that some pnictides have include being diamagnetic and paramagnetic at room temperature, being transparent, and generating electricity when heated. Other pnictides include the ternary rare-earth main-group variety of pnictides and these are in the form of REaMbPnc, where M is a carbon group or boron group element and Pn is any pnictogen except nitrogen. These compounds are ionic and covalent compounds and thus have unusual bonding properties. These elements are noted for their stability in compounds due to their tendency for forming double and triple covalent bonds. This is the property of these elements which leads to their toxicity, most evident in phosphorus, arsenic. When these substances react with various chemicals of the body, they create strong free radicals not easily processed by the liver, where they accumulate. For example, N2, the form of nitrogen, is used as an inert gas in situations where using argon or another noble gas would be too expensive. The upper pnictogens, that is, nitrogen, phosphorus, Antimony and bismuth can either take on a +3 or +5, by losing its p-shell electrons or losing its p-shell and s-shell electrons, respectively. Pnictogens can react with hydrogen to form pnictogen hydrides such as ammonia, the pnictogens consist of two nonmetals, two metalloids, one metal, and one element with unknown chemical properties
26.
Infrared detector
–
An infrared detector is a detector that reacts to infrared radiation. The two main types of detectors are thermal and photonic, the thermal effects of the incident IR radiation can be followed through many temperature dependent phenomena. Bolometers and microbolometers are based on changes in resistance, thermocouples and thermopiles use the thermoelectric effect. In IR spectrometers the pyroelectric detectors are the most widespread, the response time and sensitivity of photonic detectors can be much higher, but usually these have to be cooled to cut thermal noise. The materials in these are semiconductors with narrow band gaps, incident IR photons can cause electronic excitations. In photoconductive detectors, the resistivity of the element is monitored. Photovoltaic detectors contain a p-n junction on which photoelectric current appears upon illumination, a few detector materials, Mercury cadmium telluride Indium antimonide Indium arsenide Lead selenide QWIP QDIP
27.
Thermography
–
Infrared thermography, thermal imaging, and thermal video are examples of infrared imaging science. Thermographic cameras usually detect radiation in the range of the electromagnetic spectrum and produce images of that radiation. The amount of radiation emitted by an object increases with temperature, therefore, as a result, thermography is particularly useful to the military and other users of surveillance cameras. Some physiological changes in human beings and other warm-blooded animals can also be monitored with thermal imaging during clinical diagnostics, Thermography is used in allergy detection and veterinary medicine. It is also used for breast screening, though primarily by alternative practitioners as it is less accurate. Government and airport personnel used thermography to detect suspected swine flu cases during the 2009 pandemic, Thermography has a long history, although its use has increased dramatically with the commercial and industrial applications of the past fifty years. Firefighters use thermography to see through smoke, to find persons, maintenance technicians use thermography to locate overheating joints and sections of power lines, which are a sign of impending failure. The appearance and operation of a thermographic camera is often similar to a camcorder. Often the live thermogram reveals temperature variations so clearly that a photograph is not necessary for analysis, a recording module is therefore not always built-in. Non-specialized CCD and CMOS sensors have most of their sensitivity in the visible light wavelength range. Specialized thermal imaging cameras use focal plane arrays that respond to longer wavelengths, the most common types are InSb, InGaAs, HgCdTe and QWIP FPA. The newest technologies use low-cost, uncooled microbolometers as FPA sensors and their resolution is considerably lower than that of optical cameras, mostly 160x120 or 320x240 pixels, up to 1024×768 for the most expensive models. Thermal imaging cameras are more expensive than their visible-spectrum counterparts. Older bolometers or more sensitive models such as InSb require cryogenic cooling, thermal images, or thermograms, are actually visual displays of the amount of infrared energy emitted, transmitted, and reflected by an object. Because there are sources of the infrared energy, it is difficult to get an accurate temperature of an object using this method. A thermal imaging camera is capable of performing algorithms to interpret that data and this phenomenon occurs everywhere, all the time. It is a known as Radiant Heat Exchange, since Radiant Power × Time equals Radiant Energy. However, in the case of Infrared Thermography, the equation is used to describe the radiant power within the spectral wavelength passband of the thermal imaging camera in use
28.
Forward looking infrared
–
Forward looking infrared cameras, typically used on military and civilian aircraft, use a thermographic camera that senses infrared radiation. They can be used to help pilots and drivers steer their vehicles at night and in fog, the wavelength of infrared that thermal imaging cameras detect differs significantly from that of night vision, which operates in the visible light and near-infrared ranges. Infrared light falls into two ranges, long-wave and medium-wave. Long-wave infrared cameras, sometimes called far infrared, operate at 8 to 12 μm, and can see heat sources, such as hot engine parts or human body heat, a few miles away. Longer-distance viewing is more difficult with LWIR because the infrared light is absorbed, scattered. Some long-wave cameras require their detector to be cooled, typically for several minutes before use. Many thermal imagers, including some forward-looking infrared cameras are also uncooled, medium-wave cameras operate in the 3-to-5 μm range. These can see almost as well, since those frequencies are affected by water-vapor absorption. Many camera systems use image processing to improve the image quality. Infrared imaging sensor arrays often have wildly inconsistent sensitivities from pixel to pixel, to remedy this, the response of each pixel is measured at the factory, and a transform, most often linear, maps the measured input signal to an output level. Some companies offer advanced fusion technologies that blend a visible-spectrum image with an image to produce better results than a single-spectrum image alone. Thermal imaging cameras, such as the Raytheon AN/AAQ-26, are used in a variety of applications, including vessels, fixed-wing aircraft, helicopters. In warfare, they have three distinct advantages over other imaging technologies, second, it sees radiation in the infrared light spectrum, which is difficult to camouflage. Third, these systems can see through smoke, fog, haze. Pushbroom systems typically have been used on aircraft and satellites, such systems cannot be used for real-time imaging, and must look perpendicular to the direction of travel. In 1972, TI invented the Common Module concept, greatly reducing cost, piloting of aircraft in low visibility conditions Pinpoint sources of ignition during firefighting operations Monitoring active volcanoes. Detecting heat in faulty electrical joints, also, older camera designs used rotating mirrors to scan the image to a small sensor. More modern cameras no longer use this method, the simplification helps reduce cost, uncooled technology available in many EVS products have reduced the costs to fractions of the price of older cooled technology, with similar performance
29.
Infrared homing
–
Infrared homing is a passive weapon guidance system which uses the infrared light emission from a target to track and follow it. Missiles which use infrared seeking are often referred to as heat-seekers, many objects such as people, vehicle engines and aircraft generate and emit heat, and as such, are especially visible in the infrared wavelengths of light compared to objects in the background. Infrared seekers are passive devices, which, unlike radar, provide no indication that they are tracking a target and this makes them suitable for sneak attacks during visual encounters, or over longer ranges when used with a forward looking infrared system or similar cuing system. This makes heat-seekers extremely deadly, 90% of all United States air combat losses over the past 25 years have been due to infrared-homing missiles and they are, however, subject to a number of simple countermeasures, most notably dropping flares behind the target to provide false heat sources. This only works if the pilot is aware of the missile, the first IR devices were experimented with in the pre-World War II era. During the war, German engineers were working on heat seeking missiles and proximity fuses, truly practical designs did not become possible until the introduction of conical scanning and miniaturized vacuum tubes during the war. These early examples had significant limitations and achieved very low rates in combat during the 1960s. A new generation developed in the 1970s and 80s made great strides, the latest examples from the 1990s and on have the ability to attack targets out of their field of view, behind them, and even pick out vehicles on the ground. The infrared sensor package on the tip or head of a missile is known as the seeker head. The NATO brevity code for an air-to-air infrared-guided missile launch is Fox Two, there was little application at the time, and he allowed his 1904 patent to lapse. Nevertheless, it was used for time by the US Navy as a secure communications system. In 1930 the introduction of the Ag-O-Cs photomultiplier provided the first practical solution to the detection of IR, amplifying the signal emitted by the galena, the photomultiplier produced a useful output that could be used for detection of hot objects at long ranges. This sparked developments in a number of nations, notably the UK, eventually they dissolved the Committee and reformed, leaving Lindemann off the roster, and filling his position with well known radio expert Edward Victor Appleton. In Germany, radar research was not given nearly the same level of support as in the UK, IR research was led primarily by Edgar Kutzscher at the University of Berlin working in concert with AEG. This provided enough light to see the target at short range and these proved largely useless in practice and the pilots complained that the target often only became visible at 200 metres, at which point they would have seen it anyway. Only 15 were built and were removed as German airborne radar systems improved though 1942, AEG had been working with the same systems for use on tanks, and deployed a number of models through the war, with limited production of the FG1250 beginning in 1943. This work culminated in the Zielgerät 1229 Vampir riflescope which was used with the StG44 assault rifle for night use, the devices mentioned previously were all detectors, not seekers. They produce either a signal indicating the direction of the target, or in the case of later devices
30.
Missile guidance
–
Missile guidance refers to a variety of methods of guiding a missile or a guided bomb to its intended target. The missiles target accuracy is a factor for its effectiveness. Guidance systems improve missile accuracy by improving its Single Shot Kill Probability and these guidance technologies can generally be divided up into a number of categories, with the broadest categories being active, passive and preset guidance. The concept of missile guidance originated at least as early as World War I, in World War II, guided missiles were first developed, as part of the German V-weapons program. Project Pigeon was American behaviorist B. F. Skinners attempt to develop a pigeon-guided missile, Guidance systems are divided into different categories according to what type of target they are designed for - either fixed targets or moving targets. The weapons can be divided into two categories, Go-Onto-Target and Go-Onto-Location-in-Space guidance systems. A GOT missile can target either a moving or fixed target, the trajectory that a missile takes while attacking a moving target is dependent upon the movement of the target. Also, a target can be an immediate threat to the sender of the missile. The target needs to be eliminated in a fashion in order to preserve the integrity of the sender. In GOLIS systems the problem is simpler because the target is not moving, the target tracker is also placed on the launching platform. Homing Guidance, The guidance computers are in the missile and in the target tracker and these systems include, Command guidance - The missile tracker is on the launching platform. These missiles are controlled by the launching platform that sends all control orders to the missile. The 2 variants are Command to Line-Of-Sight Command Off Line-Of-Sight Line-Of-Sight Beam Riding Guidance - The target tracker is on board the missile, the missile already has some orientation capability meant for flying inside the beam that the launching platform is using to illuminate the target. It can be manual or automatic, the CLOS system uses only the angular coordinates between the missile and the target to ensure the collision. The missile is made to be in the line of sight between the launcher and the target, and any deviation of the missile from this line is corrected. That is, the missile is controlled to stay as close as possible on the LOS to the target after missile capture. is used to transmit signals from a ground controller to the missile. More specifically, if the acceleration is taken into account and added to the nominal acceleration generated by the beam-rider equations. Thus, the beam rider acceleration command is modified to include an extra term, the beam-riding performance described above can thus be significantly improved by taking the beam motion into account
31.
Infrared astronomy
–
Infrared astronomy is the branch of astronomy and astrophysics that studies astronomical objects visible in infrared radiation. The wavelength of infrared light ranges from 0.75 to 300 micrometers, Infrared falls in between visible radiation, which ranges from 380 to 750 nanometers, and submillimeter waves. Infrared astronomy began in the 1830s, a few decades after the discovery of infrared light by William Herschel in 1800. Early progress was limited, and it was not until the early 20th century that conclusive detections of astronomical objects other than the Sun, both fields also use solid state detectors, though the specific type of solid state detectors used are different. Infrared light is absorbed at many wavelengths by water vapor in the Earths atmosphere, so most infrared telescopes are at elevations in dry places. There are also infrared observatories in space, including the Spitzer Space Telescope, the discovery of infrared radiation is attributed to William Herschel, who performed an experiment where he placed a thermometer in sunlight of different colors after it passed through a prism. He noticed that the temperature increase induced by sunlight was highest outside the visible spectrum and he dubbed this radiation calorific rays, and went on to show that it could be reflected, transmitted, and absorbed just like visible light. Efforts were made starting in the 1830s and continuing through the 19th century to detect infrared radiation from astronomical sources. Radiation from the Moon was first detected in 1873 by William Parsons, ernest Fox Nichols used a modified Crookes radiometer in an attempt to detect infrared radiation from Arcturus and Vega, but Nichols deemed the results inconclusive. The field was mostly neglected by traditional astronomers though until the 1960s, Infrared radiation with wavelengths just longer than visible light, known as near-infrared, behaves in a very similar way to visible light, and can be detected using similar solid state devices. For this reason, the infrared region of the spectrum is commonly incorporated as part of the optical spectrum. Many optical telescopes, such as those at Keck Observatory, operate effectively in the infrared as well as at visible wavelengths. The far-infrared extends to submillimeter wavelengths, which are observed by such as the James Clerk Maxwell Telescope at Mauna Kea Observatory. Like all other forms of radiation, infrared is utilized by astronomers to study the universe. Indeed, infrared measurements taken by the 2MASS and WISE astronomical surveys have been effective at unveiling previously undiscovered star clusters. Examples of such embedded star clusters are FSR1424, FSR1432, Camargo 394, Camargo 399, Majaess 30, and Majaess 99. Infrared telescopes, which includes most major optical telescopes as well as a few dedicated infrared telescopes, need to be chilled with liquid nitrogen, the reason for this is that objects with temperatures of a few hundred Kelvin emit most of their thermal energy at infrared wavelengths. If infrared detectors were not kept cooled, the radiation from the detector itself would contribute noise that would dwarf the radiation from any celestial source and this is particularly important in the mid-infrared and far-infrared regions of the spectrum
32.
Terahertz radiation
–
Photon energy in THz regime is less than band-gap of nonmetallic materials and thus THz beam can traverse through such materials. The transmitted THz beam is used for material characterization, layer inspection, terahertz radiation falls in between infrared radiation and microwave radiation in the electromagnetic spectrum, and it shares some properties with each of these. Like infrared and microwave radiation, terahertz radiation travels in a line of sight and is non-ionizing, like microwave radiation, terahertz radiation can penetrate a wide variety of non-conducting materials. Terahertz radiation can pass through clothing, paper, cardboard, wood, masonry, plastic, the penetration depth is typically less than that of microwave radiation. Terahertz radiation has limited penetration through fog and clouds and cannot penetrate liquid water or metal, THz is not ionizing yet can penetrate some distance through body tissue, so it is of interest as a replacement for medical X-rays. Due to its wavelength, images made using THz are low resolution. However, at distances of ~10 meters the band may still allow many useful applications in imaging and construction of high bandwidth wireless networking systems, terahertz radiation is emitted as part of the black-body radiation from anything with temperatures greater than about 10 kelvin. The opacity of the Earths atmosphere to submillimeter radiation restricts these observatories to very high altitude sites, and electronic oscillators based on resonant tunneling diodes have been shown to operate up to 700 GHz. There have also been solid-state sources of millimeter and submillimeter waves for many years, AB Millimeter in Paris, for instance, produces a system that covers the entire range from 8 GHz to 1000 GHz with solid state sources and detectors. Nowadays, most time-domain work is done via ultrafast lasers, in mid-2007, scientists at the U. S. The group was led by Ulrich Welp of Argonnes Materials Science Division, the device uses high-temperature superconducting crystals, grown at the University of Tsukuba in Japan. This alternating current induces an electromagnetic field, even a small voltage can induce frequencies in the terahertz range, according to Welp. In 2008, engineers at Harvard University achieved room temperature emission of several hundred nanowatts of coherent terahertz radiation using a semiconductor source, THz radiation was generated by nonlinear mixing of two modes in a mid-infrared quantum cascade laser. Previous sources had required cryogenic cooling, which limited their use in everyday applications. In 2009, it was discovered that the act of unpeeling adhesive tape generates non-polarized terahertz radiation, with a peak at 2 THz. In 2011, Japanese electronic parts maker Rohm and a team at Osaka University produced a chip capable of transmitting 1.5 Gbit/s using terahertz radiation. Such an antenna would broadcast in the frequency range. Unlike X-rays, terahertz radiation is not ionizing radiation and its low photon energies in general do not damage tissues, some frequencies of terahertz radiation can penetrate several millimeters of tissue with low water content and reflect back
33.
Antimony trioxide
–
Antimony oxide is the inorganic compound with the formula Sb2O3. It is the most important commercial compound of antimony and it is found in nature as the minerals valentinite and senarmontite. Like most polymeric oxides, Sb2O3 dissolves in solutions with hydrolysis. Global production of antimony oxide in 2012 was 130,000 tonnes, china produces the largest share followed by US/Mexico, Europe, Japan and South Africa and other countries. As of 2010, antimony oxide was produced at four sites in EU27 and it is produced via two routes, re-volatilizing of crude antimony oxide and by oxidation of antimony metal. Oxidation of antimony metal dominates in Europe, several processes for the production of crude antimony oxide or metallic antimony from virgin material. The choice of process depends on the composition of the ore and these steps do not take place in the EU but closer to the mining location. Step 1) Crude stibnite is oxidized to antimony oxide using furnaces operating at approximately 500 to 1,000 °C. The reaction is the following,2 Sb2S3 +9 O2 →2 Sb2O3 +6 SO2 Step 2) The crude antimony oxide is purified by sublimation, Antimony metal is oxidized to antimony oxide in furnaces. Antimony oxide is formed through sublimation and recovered in bag filters, the size of the formed particles is controlled by process conditions in furnace and gas flow. Antimony oxide also dissolves in concentrated acids to give the corresponding salts. With nitric acid, the trioxide is oxidized to antimony oxide, when heated with carbon, the oxide is reduced to antimony metal. With other reducing agents such as sodium borohydride or lithium aluminium hydride, when heated with potassium bitartrate, a complex salt potassium antimony tartrate, KSb2•C4H2O6 is formed. The structure of Sb2O3 depends on the temperature of the sample, dimeric Sb4O6 is the high temperature gas. Sb4O6 molecules are bicyclic cages, similar to the oxide of phosphorus, phosphorus trioxide. The cage structure is retained in a solid that crystallizes in a cubic habit, the Sb-O distance is 197.7 pm and the O-Sb-O angle of 95. 6°. This form exists in nature as the mineral senarmontite, above 606 °C, the more stable form is orthorhombic, consisting of pairs -Sb-O-Sb-O- chains that are linked by oxide bridges between the Sb centers. This form exists in nature as the mineral valentinite, the annual consumption of antimony oxide in the United States and Europe is approximately 10,000 and 25,000 tonnes, respectively
34.
Lattice constant
–
The lattice constant, or lattice parameter, refers to the physical dimension of unit cells in a crystal lattice. Lattices in three dimensions generally have three lattice constants, referred to as a, b, and c, however, in the special case of cubic crystal structures, all of the constants are equal and we only refer to a. Similarly, in crystal structures, the a and b constants are equal. A group of lattice constants could be referred to as lattice parameters, however, the full set of lattice parameters consist of the three lattice constants and the three angles between them. For example, the constant for diamond is a =3.57 Å at 300 K. The structure is equilateral although its actual shape cannot be determined from only the lattice constant, furthermore, in real applications, typically the average lattice constant is given. Near the crystals surface, lattice constant is affected by the reconstruction that results in a deviation from its mean value. This deviation is especially important in nanocrystals since surface-to-nanocrystal core ratio is large, as lattice constants have the dimension of length, their SI unit is the meter. Lattice constants are typically on the order of several ångströms, lattice constants can be determined using techniques such as X-ray diffraction or with an atomic force microscope. Lattice constant of a crystal can be used as a length standard of nanometer range. In epitaxial growth, the constant is a measure of the structural compatibility between different materials. The volume of the cell can be calculated from the lattice constant lengths. If the unit cell sides are represented as vectors, then the volume is the dot product of one vector with the product of the other two vectors. The volume is represented by the letter V, for the general unit cell V = a b c 1 +2 cos α cos β cos γ − cos 2 α − cos 2 β − cos 2 γ. For monoclinic lattices with α = 90°, γ = 90°, for orthorhombic, tetragonal and cubic lattices with β = 90° as well, then V = a b c. Matching of lattice structures between two different semiconductor materials allows a region of band gap change to be formed in a material without introducing a change in crystal structure and this allows construction of advanced light-emitting diodes and diode lasers. Typically, films of different materials grown on the film or substrate are chosen to match the lattice constant of the prior layer to minimize film stress. An alternative method is to grade the lattice constant from one value to another by a controlled altering of the alloy ratio during film growth
35.
Electronvolt
–
In physics, the electronvolt is a unit of energy equal to approximately 1. 6×10−19 joules. By definition, it is the amount of energy gained by the charge of an electron moving across an electric potential difference of one volt. Thus it is 1 volt multiplied by the elementary charge, therefore, one electronvolt is equal to 6981160217662079999♠1. 6021766208×10−19 J. The electronvolt is not a SI unit, and its definition is empirical, like the elementary charge on which it is based, it is not an independent quantity but is equal to 1 J/C √2hα / μ0c0. It is a unit of energy within physics, widely used in solid state, atomic, nuclear. It is commonly used with the metric prefixes milli-, kilo-, in some older documents, and in the name Bevatron, the symbol BeV is used, which stands for billion electronvolts, it is equivalent to the GeV. By mass–energy equivalence, the electronvolt is also a unit of mass and it is common in particle physics, where units of mass and energy are often interchanged, to express mass in units of eV/c2, where c is the speed of light in vacuum. It is common to express mass in terms of eV as a unit of mass. The mass equivalent of 1 eV/c2 is 1 eV / c 2 = ⋅1 V2 =1.783 ×10 −36 kg. For example, an electron and a positron, each with a mass of 0.511 MeV/c2, the proton has a mass of 0.938 GeV/c2. In general, the masses of all hadrons are of the order of 1 GeV/c2, the unified atomic mass unit,1 gram divided by Avogadros number, is almost the mass of a hydrogen atom, which is mostly the mass of the proton. To convert to megaelectronvolts, use the formula,1 u =931.4941 MeV/c2 =0.9314941 GeV/c2, in high-energy physics, the electronvolt is often used as a unit of momentum. A potential difference of 1 volt causes an electron to gain an amount of energy and this gives rise to usage of eV as units of momentum, for the energy supplied results in acceleration of the particle. The dimensions of units are LMT−1. The dimensions of units are L2MT−2. Then, dividing the units of energy by a constant that has units of velocity. In the field of particle physics, the fundamental velocity unit is the speed of light in vacuum c. Thus, dividing energy in eV by the speed of light, the fundamental velocity constant c is often dropped from the units of momentum by way of defining units of length such that the value of c is unity
36.
Kelvin
–
The kelvin is a unit of measure for temperature based upon an absolute scale. It is one of the seven units in the International System of Units and is assigned the unit symbol K. The kelvin is defined as the fraction 1⁄273.16 of the temperature of the triple point of water. In other words, it is defined such that the point of water is exactly 273.16 K. The Kelvin scale is named after the Belfast-born, Glasgow University engineer and physicist William Lord Kelvin, unlike the degree Fahrenheit and degree Celsius, the kelvin is not referred to or typeset as a degree. The kelvin is the unit of temperature measurement in the physical sciences, but is often used in conjunction with the Celsius degree. The definition implies that absolute zero is equivalent to −273.15 °C, Kelvin calculated that absolute zero was equivalent to −273 °C on the air thermometers of the time. This absolute scale is known today as the Kelvin thermodynamic temperature scale, when spelled out or spoken, the unit is pluralised using the same grammatical rules as for other SI units such as the volt or ohm. When reference is made to the Kelvin scale, the word kelvin—which is normally a noun—functions adjectivally to modify the noun scale and is capitalized, as with most other SI unit symbols there is a space between the numeric value and the kelvin symbol. Before the 13th CGPM in 1967–1968, the unit kelvin was called a degree and it was distinguished from the other scales with either the adjective suffix Kelvin or with absolute and its symbol was °K. The latter term, which was the official name from 1948 until 1954, was ambiguous since it could also be interpreted as referring to the Rankine scale. Before the 13th CGPM, the form was degrees absolute. The 13th CGPM changed the name to simply kelvin. Its measured value was 7002273160280000000♠0.01028 °C with an uncertainty of 60 µK, the use of SI prefixed forms of the degree Celsius to express a temperature interval has not been widely adopted. In 2005 the CIPM embarked on a program to redefine the kelvin using a more experimentally rigorous methodology, the current definition as of 2016 is unsatisfactory for temperatures below 20 K and above 7003130000000000000♠1300 K. In particular, the committee proposed redefining the kelvin such that Boltzmanns constant takes the exact value 6977138065049999999♠1. 3806505×10−23 J/K, from a scientific point of view, this will link temperature to the rest of SI and result in a stable definition that is independent of any particular substance. From a practical point of view, the redefinition will pass unnoticed, the kelvin is often used in the measure of the colour temperature of light sources. Colour temperature is based upon the principle that a black body radiator emits light whose colour depends on the temperature of the radiator, black bodies with temperatures below about 7003400000000000000♠4000 K appear reddish, whereas those above about 7003750000000000000♠7500 K appear bluish
37.
Ballistic conduction
–
Ballistic conduction or Ballistic transport is the transport of electrons in a medium having negligible electrical resistivity caused by scattering. Without scattering, electrons simply obey Newtons second law of motion at non-relativistic speeds. For a given medium a moving electron can be ascribed a mean free path as being the length that the electron can travel freely, i. e. before a collision. The mean free path can be increased by reducing the number of impurities in a crystal or by lowering its temperature, Ballistic transport is observed when the mean free path of the electron is longer than the dimension of the medium through which the electron travels. The electron alters its motion only upon collision with the walls, in the case of a wire suspended in air/vacuum the surface of the wire plays the role of the box reflecting the electrons and preventing them from exiting toward the empty space/open air. This is because there is an energy to be paid to extract the electron from the medium, normally, transport of electrons is dominated by scattering events, which relax the carrier momentum in an effort to bring the conducting material to equilibrium. Thus, ballistic transport in a material is determined by how ballistically conductive that material is, Ballistic conduction differs from superconductivity due to the absence of the Meissner effect in the material. A ballistic conductor would stop conducting if the force is turned off. Ballistic conduction is typically observed in quasi-1D structures, such as carbon nanotubes or silicon nanowires, Ballistic conduction is not limited to electrons but can also apply to phonons. It is theoretically possible for ballistic conduction to be extended to other quasi-particles, in general, carriers will exhibit ballistic conduction when L ≤ λ M F P where L is the length of the active part of the device. In terms of scattering mechanisms, optical phonon emission normally dominates, depending on the material, there are also other scattering mechanisms which apply to different carriers that are not considered here. To get these characteristic scattering rates, one would need to derive a Hamiltonian, in 1957, Rolf Landauer proposed that conduction in a 1D system could be viewed as a transmission problem. G is known as the quantized conductance, the contacts have a multiplicity of modes due to their larger size in comparison to the channel. Conversely, the confinement in the 1D GNR channel constricts the number of modes to carrier degeneracy and restrictions from the materials energy dispersion relationship. For example, electrons in carbon nanotubes have two modes and two spin modes. Since the contacts and the GNR channel are connected by leads, therefore, even in the case of a perfect ballistic transport, there is a fundamental ballistic conductance which saturates the current of the device with a resistance of approximately 12.9 k Ω M. There is, however, a generalization of the Landauer-Büttiker formalism of transport applicable to time-dependent problems in the presence of dissipation, Ballistic conduction enables use of quantum mechanical properties of electron wave functions. Ballistic transport is coherent in wave mechanics terms, phenomena like double-split interference, spatial resonance could be exploited in electronic systems at nanoscale
verify (what is 
?)