/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]
* * *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.
* * *▪ physicsprocess 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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