diffusion


diffusion
/di fyooh"zheuhn/, n.
1. act of diffusing; state of being diffused.
2. prolixity of speech or writing; discursiveness.
3. Physics.
a. Also called migration. an intermingling of molecules, ions, etc., resulting from random thermal agitation, as in the dispersion of a vapor in air.
b. a reflection or refraction of light or other electromagnetic radiation from an irregular surface or an erratic dispersion through a surface; scattering.
4. Motion Pictures. a soft-focus effect resulting from placing a gelatin or silk plate in front of a studio light or a camera lens, or through the use of diffusion filters.
5. Meteorol. the spreading of atmospheric constituents or properties by turbulent motion as well as molecular motion of the air.
6. Anthropol., Sociol. the transmission of elements or features of one culture to another.
[1325-75; ME < L diffusion- (s. of diffusio) a spreading out, equiv. to diffus(us) (see DIFFUSE) + -ion- -ION]

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Process by which there is a net flow of matter from a region of high concentration to one of low concentration.

It occurs fastest in liquids and slowest in solids. Diffusion can be observed by adding a few drops of food colouring to a glass of water. The scent from an open bottle of perfume quickly permeates a room because of random motion of the vapour molecules. A spoonful of salt placed in a bowl of water will eventually spread throughout the water.

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 process resulting from random motion of molecules by which there is a net flow of matter from a region of high concentration to a region of low concentration. A familiar example is the perfume of a flower that quickly permeates the still air of a room.

      Heat conduction in fluids involves thermal energy transported, or diffused, from higher to lower temperature. Operation of a nuclear reactor involves the diffusion of neutrons through a medium that causes frequent scattering but only rare absorption of neutrons.

      The rate of flow of the diffusing substance is found to be proportional to the concentration gradient. If j is the amount of substance passing through a reference surface of unit area per unit time, if the coordinate x is perpendicular to this reference area, if c is the concentration of the substance, and if the constant of proportionality is D, then j = -D1PT(dc/dx); dc/dx is the rate of change of concentration in the direction x, and the minus sign indicates the flow is from higher to lower concentration. D is called the diffusivity and governs the rate of diffusion.

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Universalium. 2010.

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Look at other dictionaries:

  • diffusion — [ difyzjɔ̃ ] n. f. • 1587; lat. diffusio, de diffundere 1 ♦ Action de se répandre, de se diffuser. La diffusion de la lumière, de la chaleur, du son dans un milieu. Phys. Phénomène par lequel les diverses parties d un fluide deviennent homogènes… …   Encyclopédie Universelle

  • Diffusion — Dif*fu sion, n. [L. diffusio: cf. F. diffusion.] 1. The act of diffusing, or the state of being diffused; a spreading; extension; dissemination; circulation; dispersion. [1913 Webster] A diffusion of knowledge which has undermined superstition.… …   The Collaborative International Dictionary of English

  • Diffusion [1] — Diffusion. In Gasen und Lösungen gleichen sich lokale Unterschiede der Konzentration allmählich durch Wanderung der Materie aus. Diesen Vorgang bezeichnet man im ersten Falle als Gas (Atmolyse nach Graham), im zweiten als Hydrodiffusion. Unter… …   Lexikon der gesamten Technik

  • diffusion — DIFFUSION. s. f. Terme de Physique. Il se dit Des fluides en parlant De l action de se répandre, ou de l état de ce qui est répandu. Diffusion de lumière, de la lumière. Il se dit figurément Da discours, du style, lorsqu il est trop abondant en… …   Dictionnaire de l'Académie Française 1798

  • diffusion — diffusion, diffusionism Diffusion refers to the spread of cultural attributes from one culture to another through contact between different cultural groups. Diffusion theory developed in the eighteenth and nineteenth centuries, in opposition to… …   Dictionary of sociology

  • Diffusion — Diffusion, 1) Weitläufigkeit; 2) Diffusion der Gase, die Eigenschaft der elastischen Flüssigkeiten, sich, den Gesetzen der Schwere entgegen, sowohl in anderen Gasen, als auch in Flüssigkeiten u. festen Körpern zu vertheilen, s.u. Gas …   Pierer's Universal-Lexikon

  • Diffusion — (lat., »Ergießung, Ausbreitung«), der Vorgang der allmählichen Mischung zweier miteinander in Berührung befindlicher Körper, insbes. von Flüssigkeiten oder Gasen. Gießt man Weingeist vorsichtig auf in einem Gefäß befindliches Wasser, so haben… …   Meyers Großes Konversations-Lexikon

  • diffusion — UK US /dɪˈfjuːʒən/ noun [U] ► MARKETING, COMMUNICATIONS the process by which information, ideas, changes in behaviour, etc. spread through a group of people: »The research looks at factors influencing the diffusion of innovative products in… …   Financial and business terms

  • Diffusion — Diffusion. См. Диффузия. (Источник: «Металлы и сплавы. Справочник.» Под редакцией Ю.П. Солнцева; НПО Профессионал , НПО Мир и семья ; Санкт Петербург, 2003 г.) …   Словарь металлургических терминов

  • Diffusion [2] — Diffusion des Lichts, s. Reflexion …   Lexikon der gesamten Technik

  • Diffusion [3] — Diffusion im Bergbau, s. Wetterwirtschaft …   Lexikon der gesamten Technik


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