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Topic: Diffusion coefficient

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	Diffusion Coefficient - The relationship between the formation factor and the diffusion coefficient of porous ...
		Diffusion Coefficient - The relationship between the formation factor and the diffusion coefficient of porous materials saturated with concentrated electrolytes: Theoretical and experimental considerations - Diffusion Coefficient
		This approach, however, yields a diffusion coefficient tensor that characterizes a particular experiment and cannot, in general, be applied to different scenarios.
		In those cases where the self-diffusion coefficients of all the diffusing species are nearly identical, the diffusion potential will be nearly zero, and the apparent bulk diffusion coefficient will be nearly equal to the agglomerated diffusion coefficient.
	ciks.cbt.nist.gov /~garbocz/FFvDiff/FFvDiff/node3.html (417 words)

	Diffusion equation - Wikipedia, the free encyclopedia
		The diffusion equation is a nonlinear partial differential equation, which describes the density fluctuations in a material undergoing diffusion.
		It is also used in population genetics to describe the 'diffusion' of alleles in a finite population.
		The diffusion equation can be derived in a straightforward way from the continuity equation, which states that a change in density in any part of the system is due to inflow and outflow of material into and out of that part of the system.
	en.wikipedia.org /wiki/Diffusion_equation (193 words)

	Fick's law of diffusion - Wikipedia, the free encyclopedia
		Fick's laws of diffusion were derived by Adolf Fick in the year 1855.
		D is the diffusion coefficient or diffusivity in dimensions of [length
		Carbon dioxide in air has a diffusion coefficient of 16 mm²/s, and in water, its coefficient is 0.0016 mm²/s [1].
	en.wikipedia.org /wiki/Fick's_law_of_diffusion (593 words)

	Diffusion: Glossary (Site not responding. Last check: 2007-10-22)
		Diffusion coefficient: Diffusion coefficient is a parameter expressing the transfer rate of a substance by random molecular motion.
		Diffusing medium: A diffusing medium is a heterogeneous, multi-species system, in which the molecules or ions of all the component species are under constant, random motion.
		Partition coefficient: Partition coefficient is the ratio of the concentration of a chemical species adsorbed on a soil to the concentration of the species in the soil solution.
	soilphysics.okstate.edu /toolkit/diffusion/glossary.htm (381 words)

	Microstructural development of Human Newborn Cerebral White Matter Assessed in Vivo by Diffusion Tension MRI (Site not responding. Last check: 2007-10-22)
		Diffusion of water in the cerebral white matter depends upon the extent to which molecular displacement of water is free or restricted by such structures as fiber tracts.
		Diffusion was measured in terms of the apparent-diffusion coefficient, according to the Stejskal and Tanner equation [18].
		Apparent diffusion coefficients in the posterior limb of the internal capsule were similar in the preterm infants at term and in the fullterm infants (Figure 3B, Table 2).
	www.spl.harvard.edu:8000 /pages/papers/petra/dwi/dwi.html (4333 words)

	Molecular Diffusion: Model description
		Diffusion in a medium with a constant diffusion coefficient is often described using the equation (Carslaw and Jaeger, 1967; Crank, 1956;Kirkham and Powers, 1976)
		Diffusion coefficient may vary with the concentration of a diffusing substance and the medium in which a substance diffuses.
		Diffusion coefficient may vary with location if the diffusing medium is not homogeneous.
	soilphysics.okstate.edu /toolkit/diffusion/model.htm (528 words)

	Oxygen Diffusion/Air
		Diffusion theory for gases is based on the kinetic molecular theory of gases, initially developed by Ludwig Boltzman and James C.
		The diffusion coefficient D is a function of both temperature and pressure.
		We can also estimate the oxygen diffusion coefficient in water under conditions typical of composting systems A comparison between the diffusion coefficients in these two phases illustrates why adequate air filled porosity is essential for aerobic composting.
	www.css.cornell.edu /compost/oxygen/oxygen.diff.air.html (569 words)

	[No title]
		The bulk radon diffusion coefficient, D, is defined as the ratio of the diffusive flux density of radon activity across a geometric or superficial area of the medium, J
		In general, the diffusion coefficient in porous media is a property of the diffusing species, the pore structure, the type of fluids present in the pores, the adsorption properties of the solid matrix, the fluid saturations, and temperature.
		The radon emanation coefficient,, is one of the characteristic soil parameters that determine the rate of radon emanation into the pores of the soil matrix.
	web.ead.anl.gov /resrad/datacoll/radon.htm (2799 words)

	Diffusion — useful equations (Site not responding. Last check: 2007-10-22)
		Diffusion coefficient depends on size and shape of molecule, interaction with solvent and viscosity of solvent.
		For target diameter y, and diffusion distance x, the diffusion of a particle to a target depends strongly on dimension.
		The time for diffusion is linear in y/x for 3 dimensions; proportional to log(y/x) for 2 dimensions; and independent of y/x for 1 dimension.
	www.biologie.uni-hamburg.de /b-online/library/crofts/bioph354/diffusion1.html (272 words)

	[No title] (Site not responding. Last check: 2007-10-22)
		Variable Diffusion Coefficient: The figures in the section labeled “Diffusion Coefficient Variable with Depth” follow the same pattern in the previous graphs, with the difference that now we are using vacancy assisted diffusion.
		The diffusion coefficient can be estimated as D=D0exp(Evf/kT)exp(Evm/kT)=D0exp(E/kT) where Evf is the energy for vacancy formation, Evm is the energy for vacancy motion, and E is the overall energy.
		Thus we have the diffusion coefficient at all points in the sample, though as before for some runs I’m setting the diffusion coefficient for all species to be equal for testing.
	www.lpl.arizona.edu /~jweirich/Research/Progress_Report_7-13-08.doc (1209 words)

	Diffusion
		Diffusion is a consequence of the constant thermal motion of atoms, molecules, and particles, and results in material moving from areas of high to low concentration.
		We understand diffusion in terms of the movements of the individual particles, and can calculate the diffusion coefficient of a molecule if we know its size (or more commonly calculate the size of the molecule after experimental determination of the diffusion coefficient).
		The diffusion coefficient is inversely proportional to the radius of a particle, or the cube root of the volume.
	www.scienceisart.com /A_Diffus/DiffusMain_1.html (1703 words)

	EPA On-line Tools for Site Assessment Calculations--Diffusion Coefficient Calculator, US EPA
		Diffusion coefficients, along with other parameters, are required inputs to some environmental transport or risk assessment models.
		These estimation methods were developed by Diffusion Coefficients in Air and Water by William A. Tucker and Leslie H. Nelken, Chapter 17 in Handbook of Chemical Property Estimation Methods, Warren J. Lyman, William F. Reehl and David H. Rosenblatt, editors, American Chemical Society, 1982.
		Hayduk and Laudie Diffusion Coefficient in Water for ethyl acetate
	www.epa.gov /athens/learn2model/part-two/onsite/estdiffusion.htm (350 words)

	Diffusion
		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)

	Diffusion (Site not responding. Last check: 2007-10-22)
		In soils, the diffusion coefficient is affected by processes such as tortuosity and retardation, rendering an effective diffusion coefficient (see related discussion and references in Mitchell, 1993).
		Besides these corrections, which are affected by the specific surface of the soil, the essence of the diffusion coefficient as predicted by Einstein's equation is not affected by grain size (In soils, the range in D is two orders of magnitude; for comparison, the range in k may exceed 10 orders of magnitude).
		Chemical diffusion should be fairly independent of the variability in local porosity and grain size within typical soils.
	www.ce.gatech.edu /~carlos/scales/Diffusion.htm (265 words)

	SEDIMENTATION, CREAMING, CENTRIFUGATION AND DIFFUSION
		is the sedimentation coefficient reduced to a standard temperature, usually 20 and to a standard solvent, usually water.
		Different diffusion coefficients may be defined depending on the choice of the frame of reference used for
		is the diffusion coefficient in the absence of a chemical potential gradient.
	www.iupac.org /reports/2001/colloid_2001/manual_of_s_and_t/node40.html (272 words)

	Research and Reviews: Meat, Special Circular 172-99, Diffusion Coefficient of Salt During Meat Salting in the ...
		A recent reference attributes a unique diffusion coefficient for salt migration in ham processing that could be used to predict salt penetration during salting (Palmia, 1992).
		The effective diffusion coefficient in each salting period was evaluated according to Crank (1957) from the total amount of salt penetrating per square meter at the evaluated zone:
		As salt diffuses into the tissues, there is an interaction with meat proteins that increases their WHC (Hamm, 1960).
	ohioline.osu.edu /sc172/sc172_11.html (1224 words)

	Transition-Metal Physics
		Several attempts to calculate the intrinsic Cu diffusivity by using various assumptions for the interaction potential between Cu and B from either the data of Hall and Racette [4] or from data points obtained by the transient ion drift (TID) technique at room temperature [5][6] were reported.
		The intrinsic diffusion coefficient was defined in Ref. [1] as the diffusion coefficient of Cu in intrinsic float zone with low levels of oxygen and carbon.
		Utzig [14] estimated the elastic component of the diffusion coefficient of 3d metals in Si and obtained results surprisingly close to the experimental data for the majority of transition metals, with the exception of the ionized copper Cu, whose ionic radius was so small that Utzig's model predicted a zero diffusion barrier for it.
	www.mse.berkeley.edu /groups/weber/research/si_phys.html (1371 words)

	Oxygen Diffusion/Air
		Diffusion increases with increasing temperature (as molecules move more rapidly), and decreases with increasing pressure (which packs more molecules in a given volume, making it harder for them to move).
		diffusion coefficient under these various conditions, we need to consider the relative proportions of all the gases in the mixture.
		It is important to remember that the oxygen concentration enters the diffusion equation in two ways, both embedded in the diffusion coefficient (as described above), and as the driving force through its concentration gradient.
	compost.css.cornell.edu /oxygen/oxygen.diff.air.html (569 words)

	Diffusion — useful equations (Site not responding. Last check: 2007-10-22)
		Diffusion coefficient depends on size and shape of molecule, interaction with solvent and viscosity of solvent.
		For target diameter y, and diffusion distance x, the diffusion of a particle to a target depends strongly on dimension.
		The time for diffusion is linear in y/x for 3 dimensions; proportional to log(y/x) for 2 dimensions; and independent of y/x for 1 dimension.
	www.life.uiuc.edu /crofts/bioph354/diffusion1.html (272 words)

	[No title]
		The diffusivity can be inferred by measuring the second moment of the conditional probability distribution of the diffusing species.
		DIFFUSION AND NMR Basic Principles The dependence of diffusion coefficient on the NMR signal can be described from the experiment of a simple bipolar pulsed gradient experiment.
		This technique to measure the diffusion coefficient is the highest accurate method if the relaxation time T2 of the medium is long enough to make the signal attenuation measurable.
	www.ps.uci.edu /~markm/mri/diffusion_young.doc (2070 words)

	Ambipolar Diffusion
		The diffusion component is that which we are familiar with: a diffusion coefficient multiplied by the negative gradient of concentration.
		We thus end up with an expression in which the flux of charged species J is simply proportional to the negative gradient of the concentration: that is, we're back to a simple diffusion equation, but with a new "ambipolar" diffusion coefficient Da.
		We find that the diffusion coefficient is essentially that of the ions multiplied by the ratio of electron and ion temperatures.
	www.timedomaincvd.com /CVD_Fundamentals/plasmas/ambipolar_diffusion.html (629 words)

	Calcium Diffusion Coefficient in Rod Photoreceptor Outer Segments -- Nakatani et al. 82 (2): 728 -- Biophysical Journal
		diffusion coefficient and the activity of the exchanger.
		An important concern with using a fluorescent probe for measuring the diffusion coefficient of Ca is whether the mobility of the probe affects the Ca mobility measurements.
		Diffusion coefficient of the cyclic GMP analog, 8-(fluoresceinyl)thioguanosine 3',5'-cyclic monophosphate in the salamander rod outer segment.
	www.biophysj.org /cgi/content/full/82/2/728 (7315 words)

	Radon diffusion coefficients / NGD Radon Group
		Radon diffusion is an important release mechanisms for radon that is produced inside a building material.
		With the assumption that radon release at the top and the bottom surfaces is zero and starting from the one-dimensional radial-radon-diffusion equation, an analytical expression was derived for the ratio of the radon-release rate of the radon source enclosed in a hollow cylinder Rcs and the bare source Rs.
		The value of the bulk diffusion coefficient of radon of the building material is then deduced from intersecting the experimental result with the calculated ratio.
	ngd.kvi.nl /radon/services/radon_diffusion_coefficients.shtml (287 words)

	polymers & composites \| gas diffusion, solubility, permeability
		is the "zero concentration" mutual diffusion coefficient according to free volume theory for diffusion.
		D is the "weighted average" mutual diffusion coefficient according to free volume theory for diffusion**.
		gas diffusion diffusivity, solubility, adsorption, migration coefficient, permeability coefficient polymers, plastics, polymer, plastic, solubility of gas in polymers, Experimental Conditions Temperature: 25 degrees Celsius (298 Kelvin) Note: figures are applicable at 298 Kelvin and in the pressure range of 0.1 - ~ 3 Bar.
	www.diffusion-polymers.com /gas_diffusion.htm (127 words)

	Diffusion of Gases Through the Respiratory Membrane
		The diffusion coefficient is a measure of how easily a gas will diffuse through a liquid or tissue, taking into account the solubility of the gas in the liquid and the size of the gas molecule (molecular weight).
		If the diffusion coefficient of oxygen is assigned a value of 1, then the relative diffusion coefficient of carbon dioxide is 20 (i.e., carbon dioxide will diffuse through the respiratory membrane 20 times more rapidly than oxygen).
		However, if life is being maintained by extensive oxygen therapy, which increases the concentration of oxygen in the lung alveoli, the reduced capacity for the diffusion of carbon dioxide across the respiratory membrane can result in substantial increases of carbon dioxide in the blood.
	www.pdh-odp.co.uk /diffusion.htm (671 words)

	Diffusion (Site not responding. Last check: 2007-10-22)
		The diffusion coefficient is a property of a compound which depends on the size, shape, and degree of solvation.
		The extent of diffusion is given by the second derivative of the spatial concentration.
		The radius that we obtain is concentration dependent, because the diffusion coefficient is concentration dependent.
	faculty1.coloradocollege.edu /~hdrossman/CH345/Diff.htm (1693 words)

	Relation of Tracer Diffusion Coefficient and Solvent Self-Diffusion Coefficient (Site not responding. Last check: 2007-10-22)
		It is shown that the tracer diffusion and self-diffusion coefficients of liquids are in a simple linear relation with a constant coefficient, which depends on only the molecular size ratio and the mass ratio of the solute and the solvent molecule.
		By estimation of the size ratio with the van der Waals radii of the constituent molecules, the relation is shown to account excellently for the experimental data on diffusion of various solutes, such as a series of benzene derivatives, ketones, alcohols, and so on, in organic solvents or water.
		The relation of diffusion coefficients presented is thus shown to be an excellent means to estimate molecular sizes from the data on diffusion coefficients measurable by various methods including NMR techniques.
	pubs.acs.org /cgi-bin/abstract.cgi/jpcafh/2002/106/i48/abs/jp021659p.html (237 words)

	Molar Mass Dependence of the Apparent Diffusion Coefficient of Flexible Highly Charged Polyelectrolytes in the Dilute ... (Site not responding. Last check: 2007-10-22)
		The apparent diffusion coefficient was determined for five molar masses at a fixed ionic strength of 0.1 M at dilute polyelectrolyte concentrations.
		From the polyelectrolyte concentration dependence of the apparent diffusion coefficient, the diffusion second virial coefficient could be obtained.
		The molar mass dependence of the diffusion second virial coefficient was found to be linearly proportional to the molar mass and could be interpreted with small ion-polyion coupled mode theories.
	pubs.acs.org /cgi-bin/abstract.cgi/jpcafh/1997/101/i45/abs/jp971086u.html (235 words)

	SEVIEW REVIEW - SESOIL Chemical Parameters
		Diffusion consists of the random motion of atoms or molecules in a gas or liquid.
		Diffusion is controlled by molecular weight, in that lighter atoms or molecules are dispersed at higher rates.
		Addition of this parameter means that users no longer need to edit the water diffusion coefficient in AT123D prior to running the model.
	www.seview.com /newsletter/chemical.html (935 words)

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