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Topic: Diffusion

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  DIFFUSION - LoveToKnow Article on DIFFUSION   (Site not responding. Last check: 2007-10-22)
Diffusion may take place in solids, that is, in regions occupied by matter which continues to exhibit the properties of the solid state.
Diffusion of gases may be shown to exist by taking glass jars containing vapours of hydrochloric acid and ammonia, and placing them in communication with the heavier gas downmost.
From the considerations of the preceding section, the effects of inertia of the diffusing gases may be neglected, and at any instant of the process either of the gases is to be treated as kept in equilibrium by its partial pressure and the resistance to diffusion produced by the other gas.
47.1911encyclopedia.org /D/DI/DIFFUSION.htm   (6120 words)

 Diffusion (anthropology) - Wikipedia, the free encyclopedia
The term diffusion is used in cultural anthropology to describe the spread of cultural items — such as ideas, styles, religions, technologies, etc. — between individuals, whether within a single culture or from one culture to another.
For example, the practice of agriculture is widely believed to have diffused from somewhere in the Middle East to all of Eurasia, less than 10,000 years ago, having been adopted by many pre-existing cultures.
Those disputed are fueled in part by the overuse of cultural diffusion, starting in the late 19th century, as a blanket explanation for all similarities between widely dispersed cultures.
en.wikipedia.org /wiki/Diffusion_(anthropology)   (759 words)

 Diffusion - MSN Encarta
The rate of diffusion is also proportional to a specific property of the substance, which in the case of heat or electricity is called conductivity; in the case of matter, this property is called diffusivity or diffusion coefficient (see Conductor, Electrical; Heat; Resistance).
The amount of material that diffuses in a certain time, or the distance it traverses, is proportional to the square root of the time; thus, if it takes sugar one week to diffuse through water 1 cm from its starting point, it will take four weeks to diffuse through 2 cm.
Metallic thorium, for example, diffuses rapidly through metallic tungsten at temperatures around 2000° C (3632° F); the operation of certain vacuum tubes is based on this diffusion.
encarta.msn.com /encyclopedia_761574305/Diffusion.html   (800 words)

 AllRefer.com - diffusion (Chemistry) - Encyclopedia
The spontaneous redistribution of a substance is due to the random motion of the molecules (or atoms or ions) of the substance.
Because of the random nature of the motion of molecules, the rate of diffusion of molecules out of any region in a substance is proportional to the concentration of molecules in that region, and the rate of diffusion into the region is proportional to the concentration of molecules in the surrounding regions.
Diffusion of a solute across a membrane is called dialysis, especially when some solutes pass and others are retained.
reference.allrefer.com /encyclopedia/D/diffusio.html   (610 words)

 Diffusion (business) - Wikipedia, the free encyclopedia
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 is similar to diffusion except that it deals with the psychological processes an individual goes through, rather than an aggregate market process.
en.wikipedia.org /wiki/Early_adopter   (483 words)

 Diffusion and Osmosis
Diffusion refers to the process by which molecules intermingle as a result of their kinetic energy of random motion.
The tendency toward diffusion is very strong even at room temperature because of the high molecular velocities associated with the thermal energy of the particles.
Osmosis is a selective diffusion process driven by the internal energy of the solvent molecules.
hyperphysics.phy-astr.gsu.edu /hbase/kinetic/diffus.html   (771 words)

 Diffusion Theory & Instructional Technology
Diffusion is defined as the process by which an innovation is adopted and gains acceptance by members of a certain community.
Diffusion research, in its simplest form, investigates how theàse major factors, and a multitude of other factors, interact to facilitate or impede the adoption of a specific product or practice among members of a particular adopter group.
Diffusion is not an element overtly described in a typical ID model (Andrews and Goodson, 1991), but the adoption of an innovation does have an implied place in the ID process.
www.gsu.edu /~wwwitr/docs/diffusion   (4387 words)

D is a diffusion coefficient, which we usually assume to be a constant.
Diffusion fluxes can cause changes in the concentration distribution of the diffusing molecules, and to deal with these we need the full differential equation for diffusion, which can be written
Let's assume that the atmosphere is well-mixed by wind and turbulance at a height of 100 meters, and that diffusion is called upon to move CO from 100 meters to the ground.
www.cco.caltech.edu /~brokawc/Bi145/Diffusion.html   (1796 words)

A special form of stimulus diffusion, which usually involves behavior as well as ideas, is proselytism, or the deliberate dissemination of beliefs.
In the field of mythology, one of the strongest advocates of the Diffusionist School of interpretation was folklorist Fitzroy Somerset, Lord Raglan, who argued that the transmission of traditional narratives is overwhelmingly imitative and that invention of such narratives is minimal (Somerset 1965).
When diffused, each invention has to be, to some extent, reinvented in the minds of the receivers.
www.neara.org /topics/diffuse.htm   (3540 words)

 Auralex Acoustics - Acoustic sound diffusion products.
In fact, sound diffusion greatly widens the "sweet spot" and lends a strong, 3D sense of openness to a room, making it easier to hear "into" a mix.
Diffusion obliterates standing waves and flutter echoes without simply removing acoustic energy from the space or greatly changing the frequency content of the sound.
In conjunction with sound absorption, sound diffusion can effectively turn virtually any space into one that is appropriate and useful for the purpose of recording or monitoring sound with a high degree of accuracy.
www.auralex.com /c_sound_diffusion/c_sound_diffusion.asp   (194 words)

 Diffusion of Innovation Theory
Rogers differentiates the adoption process from the diffusion process in that the diffusion process occurs within society, as a group process; whereas, the adoption process is pertains to an individual.
Diffusion research is emerging as a single, integrated body of concepts and generalizations, even though the investigations are conducted by researchers in several scientific disciplines.
The diffusion of innovation process can be tracked on a micro level as is the case of an individual who is a targeted member of an audience, or traced at the macro level when considering economic development or technological advances.
ciadvertising.org /studies/student/98_fall/theory/hornor/paper1.html   (2713 words)

 The Piecewise Diffusion of the Silicon Dimer
Because of the strong anisotropy of the Si(001) reconstructed surface, diffusion is strongly one dimensional.
In addition to the good theoretical and experimental agreement on activation energies for diffusion, atom-tracking data also confirms that all hops during row diffusion are between adjacent sites along the row, as expected for the proposed pathway.
The elevated percentage of single hops observed for trough diffusion may be attributed to a weak interaction between the atoms when they are only one site apart that results in a slightly enhanced probability for reforming the dimer.
groups.physics.umn.edu /stmlab/dimer_diffusion/piecewise.html   (1843 words)

 Student Background Information
Diffusion is the movement of molecules from a region in which they are highly concentrated to a region in which they are less concentrated.
It depends on the motion of the molecules and continues until the system in which the molecules are found reaches a state of equilibrium, which means that the molecules are randomly distributed throughout the system.
The starch molecule is too large to pass through the pores in the cell membrane, so it cannot diffuse from one side of the membrane to the other.
biology.arizona.edu /sciconn/lessons/mccandless/reading.html   (1281 words)

Diffusion is defined as the spreading out from a concentrated source which results in an increase in the entropy (degree of disorder) of the substance.
He concluded from his investigation that the Rate of diffusion was inversely proportional to the square root of the molecular mass of the gas.
The Rate of diffusion of a gas is inversely proportional as to the square root of the density of the gas.
members.aol.com /profchm/graham.html   (1593 words)

 Scientific Method   (Site not responding. Last check: 2007-10-22)
Diffusion - the process by which molecules spread from areas of high concentratiion, to areas of low concentration.
This is also why "salting fields" was a common tactic during war, it would kill the crops in the field, thus causing food shortages.
Diffusion and Osmosis are both types of PASSIVE TRANSPORT - that is, no energy is required for the molecules to move into or out of the cell.
www.biologycorner.com /bio1/diffusion.html   (460 words)

 Diffusion   (Site not responding. Last check: 2007-10-22)
Diffusion is a vitally important phenomena in the semiconductor industry.
This is because a large number of semiconductor devices from silicon chips to solid state lasers now have features of the order of 10 nm, which corresponds to approximately 40 atoms.
In particular we are interested in characterising the diffusion in materials in which there is a miscibility gap.
mmpwww.ph.qmw.ac.uk /diffusion.html   (427 words)

 Transport Across Cell Membranes
The diffusion of water through the plasma membrane is of such importance to the cell that it is given a special name: osmosis.
Note that in all cases of facilitated diffusion through channels, the channels are selective; that is, the structure of the protein admits only certain types of molecules through.
Water passes by diffusion from a region of higher to a region of lower concentration.
users.rcn.com /jkimball.ma.ultranet/BiologyPages/D/Diffusion.html   (2786 words)

 Diffusion Pharmaceuticals, LLC
Diffusion Pharmaceuticals is a drug discovery and development company pioneering a revolutionary mechanism of action to treat life-threatening diseases.
Clinical trials are planned to begin in 2006 to support the use of TSC in ischemic indications.
Diffusion Pharmaceuticals LLC is a privately-held company located in Charlottesville, Virginia.
www.diffusionpharma.com   (202 words)

 Random Walks and Anomalous Diffusion
The diffusion constant is the rate at which the variance grows.
The actual formula for the diffusion constant is D=< L^2 >/T. The meaning of < L^2 > is the average of the square of the step size, and T stands for the average time between each step.
The exponent gamma is equal to one for the normal diffusion case.
chaos.ph.utexas.edu /research/annulus/rwalk.html   (1697 words)

Be careful not to confuse diffusion with convection currents caused by unequal heating of solutions or with the kind of mixing that can come about by stirring a solution.
Diffusion requires kinetic energy from the environment but does not require cellular energy.
In this animation, the large molecules, the solute dissolved in the water, are in greater concentration in the solution to the left of the membrane.
staff.jccc.net /pdecell/cells/diffusion.html   (525 words)

 [No title]   (Site not responding. Last check: 2007-10-22)
DIFFUSION eBooks are PDF files for readers to download, print out and make into booklets – a simple and effective mode of publishing that bypasses typical distribution problems encountered by small presses and specialist publishers.
The DIFFUSION format challenges conventions of interactivity – blending the physical and the virtual and breaking the dominance of mouse and screen as the primary forms of human computer interaction.
DIFFUSION eBooks are currently resourced by Proboscis as part of our core artistic activity.
www.diffusion.org.uk /quick_diffusion.html   (598 words)

 55mm Diffusion   (Site not responding. Last check: 2007-10-22)
Diffusion creates atmosphere by reducing contrast while creating a glow around highlights or shadows.
It simulates diffusion and fog filters as well as glows.
In addition, a pre-built texture library allows you to add realistic diffusion to scenes as if you were adding diffusion directly to your camera lens.
www.digitalfilmtools.com /55mm/Diffusion.htm   (49 words)

 Membrane Transport
Diffusion of different substances do not interfere with each other (no competition).
Diffusion of water down its concentration gradient is called osmosis.
Proteins act as carriers or pores permit flux of substances that cannot diffuse directly through the membrane.
physioweb.med.uvm.edu /bodyfluids/membrane.htm   (422 words)

 Diffusion Simulator   (Site not responding. Last check: 2007-10-22)
In its simplest form, diffusion is the transport of a material or chemical by molecular motion.
As in chemical diffusion, heat migrates from regions of high heat to regions of low heat.
For example, a well-insulated room with a not-well-insulated window can be represented as an inner rectangle of high diffusivity (the room) which is framed by a rectangular region of zero diffusivity (the walls) with a segment of this frame defined as low diffusivity (the window)., i.e.,
www.jhu.edu /~virtlab/diffus/diff_txt.htm   (959 words)

 Cell Membranes Problem Set
Simple diffusion can only move material in the direction of a concentration gradient; facilitated diffusion moves materials with and against a concentration gradient.
Simple diffusion is not saturable; facilitated diffusion rates are limited by the number of functional membrane proteins and can be saturated
Simple diffusion is found only in prokaryotes while facilitated diffusion is found only in eukaryotes.
www.biology.arizona.edu /cell_bio/problem_sets/membranes/07q.html   (85 words)

To be able to view the math in this document, use the PDF version, or please consider using another browser, such as Mozilla, Netscape 7 or above or Microsoft Internet Explorer 6 or above (MathPlayer required for IE).
This leads us to a rather obvious statement that the flux of carriers is proportional to the gradient of their density.
This is a somewhat specialized form of an equation called the ambipolar diffusion equation.
cnx.org /content/m1010/latest   (1018 words)

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