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Grain Boundary A grain boundary is the interface between two grains, or crystallites, in a polycrystalline material. Grain boundaries are 2D defects in the crystal structure, and tend to decrease the electrical and thermal conductivity of the material. Most grain boundaries are preferred sites for the onset of corrosion and for the precipitation of new phases from the solid. They are also important to many of the mechanisms of creep. On the other hand, grain boundaries disrupt the motion of dislocations through a material, so reducing crystallite size is a common way to improve mechanical strength, as described by the Hall–Petch Hall–Petch relationship [...More...]  "Grain Boundary" on: Wikipedia Yahoo 

Micrograph A micrograph or photomicrograph is a photograph or digital image taken through a microscope or similar device to show a magnified image of an item. This is opposed to a macrographic image, which is at a scale that is visible to the naked eye. Micrography Micrography is the practice or art of using microscopes to make photographs. A micrograph contains extensive details that form the features of a microstructure [...More...]  "Micrograph" on: Wikipedia Yahoo 

Degrees Of Freedom (physics And Chemistry) In physics, a degree of freedom is an independent physical parameter in the formal description of the state of a physical system. The set of all dimensions of a system is known as a phase space, and degrees of freedom are sometimes referred to as its dimensions.Contents1 Definition 2 Gas molecules 3 Independent degrees of freedom 4 Quadratic degrees of freedom4.1 Quadratic and independent degree of freedom 4.2 Equipartition theorem5 Generalizations 6 ReferencesDefinition[edit] A degree of freedom of a physical system is an independent parameter that is necessary to characterize the state of a physical system. In general, a degree of freedom may be any useful property that is not dependent on other variables. The location of a particle in threedimensional space requires three position coordinates. Similarly, the direction and speed at which a particle moves can be described in terms of three velocity components, each in reference to the three dimensions of space [...More...]  "Degrees Of Freedom (physics And Chemistry)" on: Wikipedia Yahoo 

Martensite Martensite, named after the German metallurgist Adolf Martens (1850–1914), most commonly refers to a very hard form of steel crystalline structure, but it can also refer to any crystal structure that is formed by diffusionless transformation.[1] It includes a class of hard minerals occurring as lath or plateshaped crystal grains.Contents1 Properties 2 See also 3 References 4 External linksProperties[edit] Martensite Martensite is formed in carbon steels by the rapid cooling (quenching) of the austenite form of iron at such a high rate that carbon atoms do not have time to diffuse out of the crystal structure in large enough quantities to form cementite (Fe3C). Austenite Austenite is γFe, (gammaphase iron), a solid solution of iron and alloying elements [...More...]  "Martensite" on: Wikipedia Yahoo 

Diffusion Diffusion Diffusion is the net movement of molecules or atoms from a region of high concentration (or high chemical potential) to a region of low concentration (or low chemical potential) as a result of random motion of the molecules or atoms. Diffusion Diffusion is driven by a gradient in chemical potential of the diffusing species. A gradient is the change in the value of a quantity e.g. concentration, pressure, or temperature with the change in another variable, usually distance [...More...]  "Diffusion" on: Wikipedia Yahoo 

Rate (mathematics) In mathematics, a rate is the ratio between two related quantities.[1] If the denominator of the ratio is expressed as a single unit of one of these quantities, and if it is assumed that this quantity can be changed systematically (i.e., is an independent variable), then the numerator of the ratio expresses the corresponding rate of change in the other (dependent) variable. The most common type of rate is "per unit of time", such as speed, heart rate and flux. Ratios that have a nontime denominator include exchange rates, literacy rates and electric field (in volts/meter). In describing the units of a rate, the word "per" is used to separate the units of the two measurements used to calculate the rate (for example a heart rate is expressed "beats per minute") [...More...]  "Rate (mathematics)" on: Wikipedia Yahoo 

Arrhenius Equation The Arrhenius equation Arrhenius equation is a formula for the temperature dependence of reaction rates. The equation was proposed by Svante Arrhenius Svante Arrhenius in 1889, based on the work of Dutch chemist Jacobus Henricus van 't Hoff Jacobus Henricus van 't Hoff who had noted in 1884 that Van 't Hoff's equation for the temperature dependence of equilibrium constants suggests such a formula for the rates of both forward and reverse reactions. This equation has a vast and important application in determining rate of chemical reactions and for calculation of energy of activation. Arrhenius provided a physical justification and interpretation for the formula.[1][2][3] Currently, it is best seen as an empirical relationship.[4]:188 It can be used to model the temperature variation of diffusion coefficients, population of crystal vacancies, creep rates, and many other thermallyinduced processes/reactions [...More...]  "Arrhenius Equation" on: Wikipedia Yahoo 

Misorientation Misorientation Misorientation is the difference in crystallographic orientation between two crystallites in a polycrystalline material. In crystalline materials, the orientation of a crystallite is defined by a transformation from a sample reference frame (i.e. defined by the direction of a rolling or extrusion process and two orthogonal directions) to the local reference frame of the crystalline lattice, as defined by the basis of the unit cell. In the same way, misorientation is the transformation necessary to move from one local crystal frame to some other crystal frame. That is, it is the distance in orientation space between two distinct orientations [...More...]  "Misorientation" on: Wikipedia Yahoo 

Bibcode The bibcode (also known as the refcode) is a compact identifier used by several astronomical data systems to uniquely specify literature references.Contents1 Adoption 2 Format 3 Examples 4 See also 5 ReferencesAdoption[edit] The Bibliographic Reference Code (refcode) was originally developed to be used in SIMBAD SIMBAD and the NASA/IPAC Extragalactic Database NASA/IPAC Extragalactic Database (NED), but it became a de facto standard and is now used more widely, for example, by the NASA Astrophysics Data System Astrophysics Data System who coined and prefer the term "bibcode".[1][2] Format[edit] The code has a fixed length of 19 characters and has the form YYYYJJJJJVVVVMPPPPA where YYYY is the fourdigit year of the reference and JJJJJ is a code indicating where the reference was published [...More...]  "Bibcode" on: Wikipedia Yahoo 

Digital Object Identifier In computing, a Digital Object Identifier or DOI is a persistent identifier or handle used to uniquely identify objects, standardized by the International Organization for Standardization International Organization for Standardization (ISO).[1] An implementation of the Handle System,[2][3] DOIs are in wide use mainly to identify academic, professional, and government information, such as journal articles, research reports and data sets, and official publications though they also have been used to identify other types of information resources, such as commercial videos. A DOI aims to be "resolvable", usually to some form of access to the information object to which the DOI refers. This is achieved by binding the DOI to metadata about the object, such as a URL, indicating where the object can be found. Thus, by being actionable and interoperable, a DOI differs from identifiers such as ISBNs and ISRCs which aim only to uniquely identify their referents [...More...]  "Digital Object Identifier" on: Wikipedia Yahoo 

Poisson's Ratio Poisson's ratio, denoted by the Greek letter 'nu', ν displaystyle nu , and named after Siméon Poisson, is the negative of the ratio of (signed) transverse strain to (signed) axial strain [...More...]  "Poisson's Ratio" on: Wikipedia Yahoo 

Shear Modulus In materials science, shear modulus or modulus of rigidity, denoted by G, or sometimes S or μ, is defined as the ratio of shear stress to the shear strain:[1] G = d e f τ x y γ x y = F / A Δ x / l = F l A Δ x displaystyle G stackrel mathrm def = frac tau _ xy gamma _ xy = frac F/A Delta x/l = frac Fl ADelta x where τ x y = F / A< [...More...]  "Shear Modulus" on: Wikipedia Yahoo 

Crystallography Crystallography Crystallography is the experimental science of determining the arrangement of atoms in crystalline solids (see crystal structure). The word "crystallography" derives from the Greek words crystallon "cold drop, frozen drop", with its meaning extending to all solids with some degree of transparency, and graphein "to write". In July 2012, the United Nations United Nations recognised the importance of the science of crystallography by proclaiming that 2014 would be the International Year of Crystallography.[1] Xray crystallography Xray crystallography is used to determine the structure of large biomolecules such as proteins. Before the development of Xray Xray diffraction crystallography (see below), the study of crystals was based on physical measurements of their geometry [...More...]  "Crystallography" on: Wikipedia Yahoo 

Rotation Matrix In linear algebra, a rotation matrix is a matrix that is used to perform a rotation in Euclidean space. For example, using the convention below, the matrix R = [ cos θ − sin θ sin θ cos θ ] displaystyle R= begin bmatrix cos theta &sin theta \sin theta &cos theta \end bmatrix rotates points in the xyplane counterclockwise through an angle θ about the origin of the Cartesian coordinate system. To perform the rotation using a rotation matrix R, the position of each point must be represented by a column vector v, containing the coordinates of the point [...More...]  "Rotation Matrix" on: Wikipedia Yahoo 

Multiplicative Inverse In mathematics, a multiplicative inverse or reciprocal for a number x, denoted by 1/x or x−1, is a number which when multiplied by x yields the multiplicative identity, 1. The multiplicative inverse of a fraction a/b is b/a. For the multiplicative inverse of a real number, divide 1 by the number [...More...]  "Multiplicative Inverse" on: Wikipedia Yahoo 

Annealing (metallurgy) Annealing, in metallurgy and materials science, is a heat treatment that alters the physical and sometimes chemical properties of a material to increase its ductility and reduce its hardness, making it more workable. It involves heating a material above its recrystallization temperature, maintaining a suitable temperature for a suitable amount of time, and then cooling. In annealing, atoms migrate in the crystal lattice and the number of dislocations decreases, leading to a change in ductility and hardness. As the material cools it recrystallizes. For many alloys, including carbon steel, the crystal grain size and phase composition, which ultimately determine the material properties, are dependent on the heating, and cooling rate. Hot working or cold working after the annealing process alter the metal structure, so further heat treatments may be used to achieve the properties required [...More...]  "Annealing (metallurgy)" on: Wikipedia Yahoo 