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Diffusion (other)
Diffusion is a time-dependent random process causing a spread in space. Diffusion may also refer to: Physical sciences * Molecular diffusion, spontaneous dispersion of mass (distinct from migration, caused by an external force) * Conduction of heat * Momentum diffusion * Diffusion equation ** Heat equation ** Schrödinger equation * Eddy diffusion More specific meanings * Anomalous diffusion, the movement of particles from a region of lower concentration to a region of higher concentration * Diffusion MRI * Diffusion (acoustics), sound waves * Atomic diffusion * Brownian motion * Collective diffusion * Facilitated diffusion * Effusion of a gas through small holes * Gaseous diffusion * Itō diffusion * Knudsen diffusion of particles from very small containers * Osmosis, the movement of molecules through a membrane * Reverse osmosis, a process to separate unwanted particles from a fluid * Photon diffusion, an optical effect ** Diffuse reflection, the reflection of light fro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diffusion
Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical potential. It is possible to diffuse "uphill" from a region of lower concentration to a region of higher concentration, like in spinodal decomposition. The concept of diffusion is widely used in many fields, including physics (particle diffusion), chemistry, biology, sociology, economics, and finance (diffusion of people, ideas, and price values). The central idea of diffusion, however, is common to all of these: a substance or collection undergoing diffusion spreads out from a point or location at which there is a higher concentration of that substance or collection. A gradient is the change in the value of a quantity, for example, concentration, pressure, or temperature with the change in another variable, usually distance. A change in c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Itō Diffusion
Itō may refer to: *Itō (surname), a Japanese surname *Itō, Shizuoka, Shizuoka Prefecture, Japan *Ito District, Wakayama Prefecture, Japan See also * Itô's lemma, used in stochastic calculus *Itoh–Tsujii inversion algorithm, in field theory *Itô calculus, an extension of calculus to stochastic processes, named after Kiyoshi Itô *Ito (other) *ITO (other) Ito may refer to: Places * Ito Island, an island of Milne Bay Province, Papua New Guinea * Ito Airport, an airport in the Democratic Republic of the Congo * Ito District, Wakayama, a district located in Wakayama Prefecture, Japan * Itō, Shizuok ..., for the three-letter acronym {{DEFAULTSORT:Ito es:Ito fr:Ito nl:Ito ja:いとう pt:Ito ru:Ито ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Trans-cultural Diffusion
In cultural anthropology and cultural geography, cultural diffusion, as conceptualized by Leo Frobenius in his 1897/98 publication ''Der westafrikanische Kulturkreis'', is the spread of cultural items—such as ideas, styles, religions, technologies, languages—between individuals, whether within a single culture or from one culture to another. It is distinct from the diffusion of innovations within a specific culture. Examples of diffusion include the spread of the war chariot and iron smelting in ancient times, and the use of automobiles and Western business suits in the 20th century. Types Five major types of cultural diffusion have been defined: * Expansion diffusion: an innovation or idea that develops in a source area and remains strong there, while also spreading outward to other areas. This can include hierarchical, stimulus, and contagious diffusion. * Relocation diffusion: an idea or innovation that migrates into new areas, leaving behind its origin or source o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lexical Diffusion
Lexical diffusion is the hypothesis that a sound change is an abrupt change that spreads gradually across the words in a language to which it is applicable. It contrasts with the Neogrammarian view that a sound change results from phonetically-conditioned articulatory drift acting uniformly on all applicable words, which implies that sound changes are regular, with exceptions attributed to analogy and dialect borrowing. Similar views were expressed by Romance dialectologists in the late 19th century but were reformulated and renamed by William Wang and coworkers studying varieties of Chinese in the 1960s and the 1970s. William Labov found evidence for both processes but argued that they operate at different levels. Neogrammarians and dialectologists A key assumption of historical linguistics is that sound change is regular. The principle was summarized by the Neogrammarians in the late 19th century in the slogan "sound laws suffer no exceptions" and forms the basis of the comp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diffusion Of Innovations
Diffusion of innovations is a theory that seeks to explain how, why, and at what rate new ideas and technology spread. Everett Rogers, a professor of communication studies, popularized the theory in his book ''Diffusion of Innovations''; the book was first published in 1962, and is now in its fifth edition (2003). Rogers argues that diffusion is the process by which an innovation is communicated over time among the participants in a social system. The origins of the diffusion of innovations theory are varied and span multiple disciplines. Rogers proposes that five main elements influence the spread of a new idea: the innovation itself, adopters, communication channels, time, and a social system. This process relies heavily on social capital. The innovation must be widely adopted in order to self-sustain. Within the rate of adoption, there is a point at which an innovation reaches critical mass. In 1989, management consultants working at the consulting firm Regis Mckenna Inc. th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thermodiffusion
Thermophoresis (also thermomigration, thermodiffusion, the Soret effect, or the Ludwig–Soret effect) is a phenomenon observed in mixtures of mobile particles where the different particle types exhibit different responses to the force of a temperature gradient. This phenomenon tends to move light molecules to hot regions and heavy molecules to cold regions. The term ''thermophoresis'' most often applies to aerosol mixtures whose mean free path \lambda is comparable to its characteristic length scale L, but may also commonly refer to the phenomenon in all phases of matter. The term ''Soret effect'' normally applies to liquid mixtures, which behave according to different, less well-understood mechanisms than gaseous mixtures. Thermophoresis may not apply to thermomigration in solids, especially multi-phase alloys. Thermophoretic force The phenomenon is observed at the scale of one millimeter or less. An example that may be observed by the naked eye with good lighting is when the ho ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Surface Diffusion
Surface diffusion is a general process involving the motion of adatoms, molecules, and atomic clusters (adparticles) at solid material surfaces.Oura, Lifshits, Saranin, Zotov, and Katayama 2003, p. 325 The process can generally be thought of in terms of particles jumping between adjacent adsorption sites on a surface, as in figure 1. Just as in bulk diffusion, this motion is typically a thermally promoted process with rates increasing with increasing temperature. Many systems display diffusion behavior that deviates from the conventional model of nearest-neighbor jumps. Tunneling diffusion is a particularly interesting example of an unconventional mechanism wherein hydrogen has been shown to diffuse on clean metal surfaces via the quantum tunneling effect. Various analytical tools may be used to elucidate surface diffusion mechanisms and rates, the most important of which are field ion microscopy and scanning tunneling microscopy.Oura, Lifshits, Saranin, Zotov, and Katayama 2003, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Self-diffusion
According to IUPAC definition, self-diffusion coefficient is the diffusion coefficient D_i^* of species i when the chemical potential gradient equals zero. It is linked to the diffusion coefficient D_i by the equation: D_i^*=D_i\frac. Here, a_i is the activity of the species i in the solution and c_i is the concentration of i. This term is commonly assumed to be equal to the tracer diffusion determined by watching the movement of an isotope in the material of interest. See also * Brownian motion * Diffusion * Molecular diffusion References Diffusion {{physics-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rotational Diffusion
Rotational diffusion is the rotational movement which acts upon any object such as particles, molecules, atoms when present in a fluid, by random changes in their orientations. Whilst the directions and intensities of these changes are statistically random, they do not arise randomly and are instead the result of interactions between particles. One example occurs in colloids, where relatively large insoluble particles are suspended in a greater amount of fluid. The changes in orientation occur from collisions between the particle and the many molecules forming the fluid surrounding the particle, which each transfer kinetic energy to the particle, and as such can be considered random due to the varied speeds and amounts of fluid molecules incident on each individual particle at any given time. The analogue to translational diffusion which determines the particle's position in space, rotational diffusion randomises the orientation of any particle it acts on. Anything in a solution ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reverse Diffusion
Reverse diffusion refers to a situation where the transport of particles (atoms or molecules) in a medium occurs towards regions of higher concentration gradients, opposite to that observed during diffusion. This phenomenon occurs during phase separation and is described by the Cahn–Hilliard equation. Reverse diffusion also refers to when water is forced from a region of lower concentration to high. It can occur in osmosis Osmosis (, ) is the spontaneous net movement or diffusion of solvent molecules through a selectively-permeable membrane from a region of high water potential (region of lower solute concentration) to a region of low water potential (region of .... Diffusion {{Physics-stub cs:Reverzní osmóza ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diffuse Reflection
Diffuse reflection is the reflection of light or other waves or particles from a surface such that a ray incident on the surface is scattered at many angles rather than at just one angle as in the case of specular reflection. An ''ideal'' diffuse reflecting surface is said to exhibit Lambertian reflection, meaning that there is equal luminance when viewed from all directions lying in the half-space adjacent to the surface. A surface built from a non-absorbing powder such as plaster, or from fibers such as paper, or from a polycrystalline material such as white marble, reflects light diffusely with great efficiency. Many common materials exhibit a mixture of specular and diffuse reflection. The visibility of objects, excluding light-emitting ones, is primarily caused by diffuse reflection of light: it is diffusely-scattered light that forms the image of the object in the observer's eye. Mechanism Diffuse reflection from solids is generally not due to surface roughness. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photon Diffusion
Photon diffusion is a situation where photons travel through a material without being absorbed, but rather undergoing repeated scattering events which change the direction of their path. The path of any given photon is then effectively a random walk. A large ensemble of such photons can be said to exhibit diffusion in the material, and can be described with a diffusion equation. Astrophysics In astrophysics, photon diffusion occurs inside a stellar atmosphere. To describe this phenomenon, one should develop the transfer equation in moments and use the Eddington approximation to radiative transfer (i.e. the diffusion approximation). In 3D the results are two equations for the photon energy flux: :\vec F = -\frac\vec \nabla U, :\vec \nabla \cdot \vec F = 0, where \sigma is the opacity. By substituting the first equation into the second, one obtains the diffusion equation for the photon energy density: :\nabla^2 U -\frac\vec \nabla U \cdot \vec \nabla \sigma=0. Medical science In med ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
