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The Collaborative International Dictionary

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.

    A diffusion of knowledge which has undermined superstition.

  2. (Physiol.) The act of passing by osmosis through animal membranes, as in the distribution of poisons, gases, etc., through the body. Unlike absorption, diffusion may go on after death, that is, after the blood ceases to circulate.

    Syn: Extension; spread; propagation; circulation; expansion; dispersion.

Douglas Harper's Etymology Dictionary

late 14c., from Latin diffusionem (nominative diffusio) "a pouring forth," noun of action from past participle stem of diffundere "scatter, pour out," from dis- "apart, in every direction" (see dis-) + fundere "pour" (see found (v.2)).


n. 1 the act of diffusing or dispersing something, or the property of being diffused or dispersed; dispersion 2 (context physics English) the scattering of light by reflection from a rough surface, or by passage through a translucent medium 3 (context physics English) the intermingling of the molecules of a fluid due to random thermal agitation 4 the spread of cultural or linguistic practices, or social institutions, in one or more communities 5 (context physics weather English) exchange of airborne media between regions in space in an apparently random motion of a small scale. 6 the movement of water vapor from regions of high concentration (high water vapor pressure) toward regions of lower concentration.

  1. n. (physics) the process of diffusing; the intermingling of molecules in gases and liquids as a result of random thermal agitation

  2. the spread of social institutions (and myths and skills) from one society to another

  3. the property of being diffused or dispersed [syn: dissemination]

  4. the act of dispersing or diffusing something; "the dispersion of the troops"; "the diffusion of knowledge" [syn: dispersion, dispersal, dissemination]

Diffusion (business)

Diffusion is the process by which a new idea or new product is accepted by the market. The rate of diffusion is the speed that the new idea spreads from one consumer to the next. Adoption (the reciprocal process as viewed from a consumer perspective rather than distributor) is similar to diffusion except that it deals with the psychological processes an individual goes through, rather than an aggregate market process. In economics it is more often named " technological change".

Diffusion (disambiguation)

Diffusion is a time-dependent random process causing a spread in space.

Diffusion may also refer to:

In 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
  • Eddy diffusion
In physical sciences, more specific or modified meanings:
  • 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
  • Photon diffusion, an optical effect
    • Diffuse reflection, the reflection of light from an uneven or granular surface
  • Reverse diffusion
  • Rotational diffusion
  • Self-diffusion
  • Surface diffusion
  • Thermodiffusion
In the social sciences:
  • Diffusion of innovations within a society or a culture or between them
  • Lexical diffusion within a culture
  • Trans-cultural diffusion of culture items between cultures
In computer science:
  • Diffusion (cryptography), the spreading of influence of bits in a cipher
  • Error diffusion in image processing
  • In CMOS technology, doped semiconductor is sometimes referred to as "diffusion".
In other areas:
  • Diffusion (business), the process by which a new idea or new product is accepted by the market
  • Diffusion line, a secondary line of merchandise created by a high-end fashion designer
  • Diffusion Pharmaceuticals, a drug development company
  • Diffusion process, in probability theory the solution to a stochastic differential equation
  • Diffusion of responsibility
  • Society for the Diffusion of Useful Knowledge
  • Diffusion Science Radio Show, a science radio show and podcast on 2SER in Sydney
  • Diffusion Records, an independent record label
  • Diffusion (album), a 2008 album by 7for4
Diffusion (acoustics)

Diffusion, in acoustics and architectural engineering, is the efficacy by which sound energy is spread evenly in a given environment. A perfectly diffusive sound space is one that has certain key acoustic properties which are the same anywhere in the space. A non-diffuse sound space would have considerably different reverberation time as the listener moved around the room. Virtually all spaces are non-diffuse. Spaces which are highly non-diffuse are ones where the acoustic absorption is unevenly distributed around the space, or where two different acoustic volumes are coupled. The diffusiveness of a sound field can be measured by taking reverberation time measurements at a large number of points in the room, then taking the standard deviation on these decay times . Alternately, the spatial distribution of the sound can be examined. Small sound spaces generally have very poor diffusion characteristics at low frequencies due to room modes.


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). This is also referred to as the movement of a substance down a concentration gradient. A gradient is the change in the value of a quantity (e.g., concentration, pressure, temperature) with the change in another variable (usually distance). For example, a change in concentration over a distance is called a concentration gradient, a change in pressure over a distance is called a pressure gradient, and a change in temperature over a distance is a called a temperature gradient.

The word diffusion derives from the Latin word, diffundere, which means "to spread out" (a substance that “spreads out” is moving from an area of high concentration to an area of low concentration). A distinguishing feature of diffusion is that it results in mixing or mass transport, without requiring bulk motion (bulk flow). Thus, diffusion should not be confused with convection, or advection, which are other transport phenomena that utilize bulk motion to move particles from one place to another.

Usage examples of "diffusion".

That the Universe might endure throughout an aera at all commensurate with the grandeur of its component material portions and with the high majesty of its spiritual purposes, it was necessary that the original atomic diffusion be made to so inconceivable an extent as to be only not infinite.

Uranium appears as uranium hexafluoride, all ready for the diffusion process.

Uranium-235, U-238, uranium hexafluoride, centrifuges, gaseous diffusion, thermal diffusion .

The more nearly the composition of the external air approaches that of the expired air, the slower will be the diffusion of carbonic acid outwards and of oxygen inwards, and the more charged with carbonic acid and deficient in oxygen will the blood in the lungs become.

By the action of currents and eddies and by the rapid diffusion of gas particles, the air from the outside mixes with that in the alveoli and comes in contact with the membranous walls.

Whether time, and a greater diffusion of sporting propensities, and sporting feelings, may alter this for the better or no, I leave to sager and more politic pates than mine.

Without reservoirs of wealth there would be no great universities, schools of science, museums, galleries of art, libraries, solid institutions of charity, and perhaps not the wide diffusion of culture which is the avowed aim of modern civilization.

The diffusion would, it is probable, be slower with the terrestrial inhabitants of distinct continents than with the marine inhabitants of the continuous sea.

Tibet are said to have restored the religion in Lhasa at the end of the tenth century, but it was the patronage of the western kingdom of Gu-ge with its capital at Tsaparang that gave the most powerful impetus to what is called the Second Diffusion of the religion, which from then onward became centred in the monasteries, the larger of which, well endowed and populous, began to play the part of landowner and noble in the political and economic structure of a fragmented and decentralised country.

The gradual diffusion of dominant forms, with the slow modification of their descendants, causes the forms of life, after long intervals of time, to appear as if they had changed simultaneously throughout the world.

In such cases the geometrical ratio of increase, the result of which never fails to be surprising, simply explains the extraordinarily rapid increase and wide diffusion of naturalised productions in their new homes.

Research, for Research Defence, for World Indexing, for the translation of Scientific Papers, for the Diffusion of New Knowledge, the surplus energies of a great number of Open Conspirators can be directed to entirely creative ends and a new world system of scientific work built up, within which such dear old institutions as the Royal Society of London, the various European Academies of Science and the like, now overgrown and inadequate, can maintain their venerable pride in themselves, their mellowing prestige, and their distinguished exclusiveness, without their present privilege of inflicting cramping slights and restrictions upon the more abundant scientific activities of to-day.

Substantial, wholesome, and clean--though generated by a wet, helpless creature having no personal charms, and which, having passed the phase of life in which it enjoyed the gift of locomotion, has become a plant-like fixture to one spot--the gas mingles with other diffusions of the reef, recalling villanous salt-petre and sheepdips and brimstone and treacle to the stimulation of the mental faculties generally.

Second Diffusion, followers of the older Tantras and venerating Padmasambhava as a second Buddha eclipsing the historical Buddha, cannot be regarded as preserving an uncontaminated tradition from the earlier Diffusion.

There were, within sight, an auctioneer's and fire-agency office, a corn-factor's, a linen-draper's, a saddler's, a distiller's, a grocer's, and a shoe-shop--the lastmentioned warehouse being also appropriated to the diffusion of hats, bonnets, wearing apparel, cotton umbrellas, and useful knowledge.