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1

Cytoplasmic hydrogen ion diffusion coefficient.  

PubMed Central

The apparent cytoplasmic proton diffusion coefficient was measured using pH electrodes and samples of cytoplasm extracted from the giant neuron of a marine invertebrate. By suddenly changing the pH at one surface of the sample and recording the relaxation of pH within the sample, an apparent diffusion coefficient of 1.4 +/- 0.5 x 10(-6) cm2/s (N = 7) was measured in the acidic or neutral range of pH (6.0-7.2). This value is approximately 5x lower than the diffusion coefficient of the mobile pH buffers (approximately 8 x 10(-6) cm2/s) and approximately 68x lower than the diffusion coefficient of the hydronium ion (93 x 10(-6) cm2/s). A mobile pH buffer (approximately 15% of the buffering power) and an immobile buffer (approximately 85% of the buffering power) could quantitatively account for the results at acidic or neutral pH. At alkaline pH (8.2-8.6), the apparent proton diffusion coefficient increased to 4.1 +/- 0.8 x 10(-6) cm2/s (N = 7). This larger diffusion coefficient at alkaline pH could be explained quantitatively by the enhanced buffering power of the mobile amino acids. Under the conditions of these experiments, it is unlikely that hydroxide movement influences the apparent hydrogen ion diffusion coefficient.

al-Baldawi, N F; Abercrombie, R F

1992-01-01

2

Altitude Dependent Auroral Ion Diffusion Coefficients  

NASA Astrophysics Data System (ADS)

Simultaneous upgoing auroral H+ and O+ ion beams generate ion acoustic waves which have both parallel and oblique wave vectors with respect to the ambient magnetic field. A parallel mode is investigated with phase velocity UO + CO in the direction of beam propagation, where UO is the oxygen beam velocity and CO is the oxygen ion sound speed. Due to the mass difference, this mode preferentially resonates with the oxygen beam through the n = 1 cyclotron resonance, causing O+ ions to diffuse in a direction that is primarily perpendicular to the background magnetic field. The Landau resonance (n = 0) is very narrow in parallel velocity and does not interact with either ion beam. In one case study the parallel acoustic mode begins to resonate with O+ ions within the auroral acceleration region and this resonant region in velocity space sweeps through the entire O+ beam as it moves into weaker magnetic field regions. The O+ quasilinear diffusion coefficients are examined during this process. Perpendicular diffusion becomes significant when the parallel resonant velocity is close to the parallel group velocity of the waves. This selects regions of velocity space where perpendicular diffusion is maximum which occurs at the leading edge of the resonant region as it sweeps through the O+ beam. In k - space these resonant velocities correspond to the regions of peak growth rate. The relevance of this work to the selective energization of heavy auroral ion beams will be discussed.

Ludlow, G. R.

2011-12-01

3

Estimation of tracer diffusion coefficients of ions in aqueous solution  

SciTech Connect

Equations are given for estimating tracer diffusion coefficients D/sub i//sup 0/ of ions at infinite dilution in terms of limiting ionic conductances ..lambda../sub i//sup 0/. Also given are generalized Nernst-Hartley equations for binary and multicomponent diffusion coefficients D/sup 0/ and D/sub ij//sup 0/, respectively, at infinite dilution. Data, estimates, and correlations for ..lambda../sub i//sup 0/ at 25/sup 0/C and other temperatures are discussed. Estimated values of ..lambda../sub i//sup 0/ are tabulated from 0-300/sup 0/C for ions of waste isolation interest and for ions of economic interest in geothermal brines. Estimates of their tracer diffusion coefficients at infinite dilution are tabulated. A rule of thumb, good to a factor of 2, is presented. Very limited data (available only at 25/sup 0/C) indicate that D/sub i//D/sub i//sup 0/ generally declines as the concentration of salt or supporting electrolyte increases. 6 figures, 2 tables.

Miller, D.G.

1982-09-07

4

Role of surface energy coefficients and nuclear surface diffuseness in the fusion of heavy-ions  

SciTech Connect

We discuss the effect of surface energy coefficients as well as nuclear surface diffuseness in the proximity potential and ultimately in the fusion of heavy-ions. Here we employ different versions of surface energy coefficients. Our analysis reveals that these technical parameters can influence the fusion barriers by a significant amount. A best set of these parameters is also given that explains the experimental data nicely.

Dutt, Ishwar; Puri, Rajeev K. [Department of Physics, Panjab University, Chandigarh 160 014 (India)

2010-04-15

5

Longitudinal and Transverse Diffusion Coefficients of Mass-Identified n(+) And N2(+) Ions in Nitrogen.  

National Technical Information Service (NTIS)

Longitudinal and transverse diffusion coefficients for mass-identified N(+) and N2(+) ions in nitrogen in an applied electric field have been measured at room temperature on the E/N range. For E/N below about 30 x 10 to the minus 17th power V cm2 the long...

J. T. Moseley R. M. Snuggs D. W. Martin E. W. McDaniel

1968-01-01

6

Diffusion coefficients of energetic water group ions near Comet Giacobini-Zinner  

NASA Astrophysics Data System (ADS)

Data from the ultralow-energy charge analyzer and energetic particle anisotropy spectrometer sensors, acquired when the ICE spacecraft flew past Comet Giacobini-Zinner on September 11, 1985, are combined, and a single, self-consistent analysis technique is applied to derive a single-particle spectrum from about 200 to 1600 km/s. This information, together with the deduced bulk flow speed of the ions, is used to calculate a parallel diffusion coefficient in the transition region downstream of the bow wave (2.3 +/- 0.5) x 10 exp 17 sq cm/s; the corresponding scattering mean free path is (6 +/- 1) x 10 exp 4 km. The parallel diffusion coefficient is found to depend on the collision frequency of water group ions with Alfven waves, which are assumed to be propagating parallel (antiparallel) to the magnetic field.

Tan, L. C.; Mason, G. M.; Richardson, I. G.; Ipavich, F. M.

1993-03-01

7

Diffusion Coefficients of Fe(3+) Ions in Chloride Melts (Koeffitsienty Diffuzii iona Trekhvalentnogo zheleza V Rasplavakh Khloristykh Solei).  

National Technical Information Service (NTIS)

The diffusion of ferric ions in molten KCl and NaCl were measured in the temperature range 1123 to 1213K using Levich's experimental technique of a rotating disk. The experimentally determined diffusion coefficients agree well with those calculated by the...

A. B. Bezuklandnikov V. A. Bezvoritnic

1974-01-01

8

Mobilities, Diffusion Coefficients, and Reactions of Mass-Identified Hydrogen Ions in H2 and Deuterium Ions in D2 Gas.  

National Technical Information Service (NTIS)

The authors have measured in a drift tube mass spectrometer the mobilities and longitudinal diffusion coefficients of H(+), H3(+), and H(-) ions in H2 gas and D(+), D3(+), and D(-) ions in D2 gas. These measurements were made at 300K and over a substantia...

E. Graham D. R. James W. C. Keever I. R. Gatland E. W. McDaniel

1973-01-01

9

Diffusion coefficient measurement of lithium ion in sintered Li 1.33Ti 1.67O 4 by means of neutron radiography  

Microsoft Academic Search

Neutron radiography (NR) using cold neutron beam was applied to the tracer diffusion coefficient measurement of lithium ion in Li1.33Ti1.67O4. The diffusion couples with different lithium isotope concentrations were annealed at 860 to 900°C and the isotope profiles of lithium ion in the sample were measured by NR. The diffusion profiles obtained for the samples annealed at higher temperatures show

Shigeomi Takai; Masahiro Kamata; Shigenori Fujine; Kenji Yoneda; Keiji Kanda; Takao Esaka

1999-01-01

10

Portable vapor diffusion coefficient meter  

DOEpatents

An apparatus for measuring the effective vapor diffusion coefficient of a test vapor diffusing through a sample of porous media contained within a test chamber. A chemical sensor measures the time-varying concentration of vapor that has diffused a known distance through the porous media. A data processor contained within the apparatus compares the measured sensor data with analytical predictions of the response curve based on the transient diffusion equation using Fick's Law, iterating on the choice of an effective vapor diffusion coefficient until the difference between the predicted and measured curves is minimized. Optionally, a purge fluid can forced through the porous media, permitting the apparatus to also measure a gas-phase permeability. The apparatus can be made lightweight, self-powered, and portable for use in the field.

Ho, Clifford K. (Albuquerque, NM)

2007-06-12

11

Diffusion coefficients of indium and tin in In—Sn alloys determined by Auger electron spectroscopy using xenon ion bombardment  

Microsoft Academic Search

The diffusion coefficient of an element in a solid material has long been determined by means of a tracer method. Recently, Auger electron spectroscopy (AES) has also been applied to the same end through the measurement of the surface segregation kinetics [1 5]. One of the advantages of the AES method over the tracer method is its extremely short experimental

Masaharu Komiyama; Hiroyuki Tsukamoto; Tsuyoshi Matsuda; Yoshisada Ogino

1986-01-01

12

Experimental techniques for the measurement of diffusion coefficients  

SciTech Connect

This paper describes techniques for the measurement of diffusion coefficients in solids. The focus is on depth profiling by various ion beam techniques, especially secondary ion mass spectrometry, Rutherford backscattering, and nuclear reaction analysis. 35 refs., 10 figs.

Rothman, S.J.

1989-03-01

13

Diffusion coefficients and conductivities of alkylimidazolium tetrafluoroborates and hexafluorophosphates  

Microsoft Academic Search

In this study, diffusion coefficients of alkylimidazolium tetrafluoroborates and hexafluorophosphates ionic liquids in water at room temperature were measured by the Taylor dispersion experiment. The Wilke–Chang equation underestimated the diffusion coefficient, but a modified Wilke–Chang equation correlated diffusion coefficients well with molar volumes. The conductivities of these ion liquids were also measured. Infinite dilute conductances were calculated. The Nernst–Haskell equation

Wen Cheng Su; Cheng Huang Chou; David Shan Hill Wong; Meng Hui Li

2007-01-01

14

Diffusion coefficients for stellar plasmas  

NASA Astrophysics Data System (ADS)

The diffusion coefficients of relatively dense plasmas that are typical of white dwarf envelopes are presently computed by means of an approximate method, based on the numerical evaluation of collision integrals for a screened Coulomb potential, which becomes rigorously valid in the limit of a dilute plasma. The plasmas encountered in white dwarf envelopes are noted to be neither weakly nor strongly coupled; a comparison with the results of rigorous Monte Carlo calculations applicable at very high densities indicates, however, that the region of intermediate coupling is probably reasonably bridged. Results are presented in the form of high accuracy analytic fits for the collision integrals.

Paquette, C.; Pelletier, C.; Fontaine, G.; Michaud, G.

1986-05-01

15

Turbulent diffusion coefficients of toroidal plasmas  

Microsoft Academic Search

The difussion coefficient of a plasma with density gradient-produced fluctuations was calculated. Two different methods of deriving the diffusion coefficients were used. Then, the condition that two methods yield the same result is used to determine the phase angle a between the density and the potential fluctuations. The result shows the pseudo-classical diffusion coefficients. Agreement with experimentally determined plasma confinement

S. Yoshikawa

1973-01-01

16

Eddy diffusion coefficients in the lower thermosphere  

NASA Astrophysics Data System (ADS)

The seasonal variation of the eddy diffusion coefficient is deduced for a height of 94 km at 23 deg S based on two independent methods of analysis. One is related to indirect measurements of atomic oxygen and the other to measurements of the density of upper atmospheric sodium. The results are mutually consistent giving a maximum eddy diffusion coefficient during summer.

Kirchhoff, V. W. J. H.; Clemesha, B. R.

1982-08-01

17

Radon diffusion coefficients for residential concretes  

SciTech Connect

Radon gas diffusion through concrete can be a significant mechanism for radon entry into dwellings. Measurements of radon diffusion coefficients in the pores of residential concretes ranged from 2.1 x 10{sup {minus}8} m{sup 2} s{sup {minus}1} to 5.2 x 10{sup {minus}7} m{sup 2} s{sup {minus}1}. The pore diffusion coefficients generally increased with the water-cement ratio of the concrete and decreased with its density. A least-squares regression of the diffusion coefficients on concrete density gave an r value of -0.73. 16 refs., 2 figs., 3 tabs.

Rogers, V.C.; Nielson, K.K.; Holt, R.B. [Rogers and Associates Engineering Corp., Salt Lake City, UT (United States); Snoddy, R. [Acurex Environmental Corp., Research Triangle Park, NC (United States)

1994-09-01

18

Influence of concentrations of copper, levelling agents and temperature on the diffusion coefficient of cupric ions in industrial electro-refining electrolytes  

Microsoft Academic Search

Few data are available for diffusion coefficients measured in industrial copper electrolytes. In the present work the influence\\u000a of copper concentration (19.9–58.1 g dm?3), temperature (20–60?C) and concentrations levelling agents i.e. animal glue (0–5 mg dm?3) and thiourea (0–5 mg dm?3) on diffusion coefficients of copper was studied in industrial copper refinery electrolytes. Chronoamperometry at ultramicroelectrodes\\u000a was used as an electrochemical technique. Apparent bulk diffusion coefficients

O. Gladysz; P. Los; E. Krzyzak

2007-01-01

19

Eddy diffusion coefficients in the lower thermosphere  

NASA Astrophysics Data System (ADS)

The seasonal variation of the eddy diffusion coefficient is deduced for a height of 94 km at 23 deg S on the basis of two independent methods of analysis. One of these methods, already used in the past, is related to indirect measurements of atomic oxygen, and the other one is a new method related to measurements of the density of upper atmospheric sodium. The results are mutually consistent, giving a maximum eddy diffusion coefficient during summer.

Kirchhoff, V. W. J. H.; Clemesha, B. R.

1983-07-01

20

Diffusion coefficient of modern humans outcompeting Neanderthals.  

PubMed

A nonlinear mathematical model is used to describe Neanderthals extinction about 35,000 years before present. Using archaeological data, radiocarbon re-calibrate speed among others, we show that the diffusion coefficient describing Modern Humans spread corresponds to 1596 km(2)/yr. The model is well established since all archaeological parameters, including Neanderthal-Modern interaction coefficient, become estimated. PMID:21540038

Flores, J C

2011-04-17

21

Diffusion Coefficients in Gravel Under Unsaturated Conditions  

Microsoft Academic Search

Diffusion coefficients were experimentally determined in unsaturated gravel to evaluate the effectiveness of gravel as a diffusion barrier to ionic transport in the vadose zone. Water contents were fixed by use of an ultracentrifuge with an ultralow constant rate flow pump supplying solution to the sample via a rotating seal. Once the gravel was at hydraulic steady state, the electrical

James L. Conca; Judith Wright

1990-01-01

22

Molecular Diffusion Coefficients: Experimental Determination and Demonstration.  

ERIC Educational Resources Information Center

|Presented are laboratory methods which allow the demonstration and determination of the diffusion coefficients of compounds ranging in size from water to small proteins. Included are the procedures involving the use of a spectrometer, UV cell, triterated agar, and oxygen diffusion. Results including quantification are described. (CW)|

Fate, Gwendolyn; Lynn, David G.

1990-01-01

23

Diffusion and transport coefficients in synthetic opals  

SciTech Connect

Opals are structures composed of close-packed spheres in the size range of nano to micrometers. They are sintered to create small necks at the points of contact. We have solved the diffusion problem in such structures. The relation between the diffusion coefficient and the thermal and electrical conductivity is used to estimate the transport coefficients of opal structures as a function of the neck size and the mean free path of the carriers. The theory presented is also applicable to the diffusion problem in other periodic structures. (c) 2000 The American Physical Society.

Sofo, J. O. [Centro Atomico Bariloche and Instituto Balseiro, Comision Nacional de Energia Atomica, (8400) Bariloche RN, (Argentina); Mahan, G. D. [Solid State Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831-6030 (United States); Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee 37996-1200 (United States)

2000-07-15

24

Micro-Fluidic Diffusion Coefficient Measurement  

SciTech Connect

A new method for diffusion coefficient measurement applicable to micro-fluidics is pre- sented. The method Iltilizes an analytical model describing laminar dispersion in rect- anglllar ~llicro_channe]s. The Illethod ~vas verified throllgh measllremen~ of fllloresceill diffusivity in water and aqueolls polymer solutions of differing concentration. The diffll- sivity of flllorescein was measlmed as 0.64 x 10-gm2/s in water, 0.49 x 10-gm2/s in the 4 gm/dl dextran solution and 0.38 x 10-9n12/s in the 8 gnl/dl dextran solution.

Forster, F.K.; Galambos, P.

1998-10-06

25

Water permeability of plant cuticles: permeance, diffusion and partition coefficients  

Microsoft Academic Search

Using isolated cuticular membranes from ten woody and herbaceous plant species, permeance and diffusion coefficients for water were measured, and partition coefficients were calculated. The cuticular membranes of fruit had much higher permeance and diffusion coefficients than leaf cuticular membranes from either trees or herbs. Both diffusion and partition coefficients increased with increasing membrane thickness. Thin cuticles, therefore, tend to

Matthias Becker; Gerhard Kerstiens; Jörg Schönherr

1986-01-01

26

A computer simulation of charged particles in solution. II. Polyion diffusion coefficient  

Microsoft Academic Search

A computer simulation study was conducted on the effects of the polyion–small ion electrostatic interaction upon the translational diffusion of polyions in polyelectrolyte solutions at thermodynamic equilibrium. This interaction increased the polyion diffusion coefficient and the increase was strongly dependent upon the polyion charge and size, and the small ion charge and mobility, while only slightly affected by changes in

Donald L. Ermak

1975-01-01

27

A Test for Diffusion Coefficient Measurement using Containerless Processing  

Microsoft Academic Search

Our purpose is the diffusion coefficient measurement using containerless processing to clarify the mass transfer mechanism in high temperature melts. Therefore, diffusion experiments as couples of molten Si-Ge and Al-Ag alloys have been performed using electromagnetic levitator combined with superconducting magnet. In this result, possibility of diffusion coefficient measurement in levitated melts applied static magnet field can be suggested, because

Kensuke Higuchi; Yuko Inatomi

28

An Ion Diffusion Model in Semi-Permeable Clay Materials  

SciTech Connect

Ion diffusion in semi-impermeable clay materials dynamically interacts with electrostatic fields (or diffuse double layers) associated with clay particles. Current theory of ion transport in porous media containing fixed charges on solid materials, however, cannot explicitly account for the dynamic interactions. Here we proposed a model by coupling electrodynamics and nonequilibrium thermodynamics to describe ion diffusion in the clay materials. The developed model was validated by comparing the calculated and measured apparent ion diffusion coefficients in clay materials as a function of ionic strength, which affects the overlap extent of the electrostatic double layers associated with adjacent clay particles. The model shows that ion diffusion in clay materials is a complex function of factors including surface charge density, tortuosity, porosity, chemico-osmotic coefficient, and ion self-diffusivity. At transitional states, ion diffusive fluxes are dynamically related to the electrostatic fields, which shrink or expand as ion diffusion. At steady states, the electrostatic fields are time-invariant and ion diffusive fluxes conform to flux and concentration gradient relationships; and apparent diffusivity can be expressed by the ion diffusivity in bulk electrolytes corrected by a tortuosity factor and concentration gradient variations at the interfaces between clay materials and bulk solutions.

Liu, Chongxuan

2007-08-01

29

Measurement of diffusion coefficients of francium and rubidium in yttrium based on laser spectroscopy  

Microsoft Academic Search

We report the measurement of the diffusion coefficients of francium and rubidium ions implanted in a yttrium foil. We developed a methodology, based on laser spectroscopy, which can be applied to radioactive and stable species, and allows us to directly take record of the diffusion time. Francium isotopes are produced via fusion-evaporation nuclear reaction of a O18 beam on a

C. de Mauro; R. Calabrese; L. Corradi; A. Dainelli; A. Khanbekyan; E. Mariotti; P. Minguzzi; L. Moi; S. Sanguinetti; G. Stancari; L. Tomassetti; S. Veronesi

2008-01-01

30

Flux-limited diffusion coefficient applied to reactor analysis  

NASA Astrophysics Data System (ADS)

A new definition of the diffusion coefficient for use in reactor physics calculations is evaluated in this thesis. It is based on naturally flux-limited diffusion theory (FDT), sometimes referred to as Levermore-Pomraning diffusion theory. Another diffusion coefficient more loosely based on FDT is also evaluated in this thesis. Flux-limited diffusion theory adheres to the physical principle of flux-limiting, which is that the magnitude of neutron current is not allowed to exceed the scalar flux. Because the diffusion coefficients currently used in the nuclear industry are not flux-limited they may violate this principle in regions of large spatial gradients, and because they encompass other assumptions, they are only accurate when used in the types of calculations for which they were intended. The evaluations were performed using fine-mesh diffusion theory. They are in one spatial dimension and in 47, 4, and 2 energy groups, and were compared against a transport theory benchmark using equivalent energy structures and spatial discretizations. The results show that the flux-limited diffusion coefficient (FD) outperforms the standard diffusion coefficient in calculations of single assemblies with vacuum boundaries, according to flux- and eigenvalue-errors. In single assemblies with reflective boundary calculations, the FD yielded smaller improvements, and tended to improve only the fast-group results. The results also computationally confirm that the FD adheres to flux-limiting, while the standard diffusion coefficient does not.

Keller, Steven Ede

31

Measurement of the diffusion coefficient for chrysotile and crocidolite fibers  

NASA Astrophysics Data System (ADS)

Diffusion coefficients for chrysolite and crocidolite fibers were measured with a Sinclair collimated hole diffusion battery and a condensation nuclei counter. The diffusion coefficient for the chrysotile fibers was found to be ~ 4-5 × 10 -7cm 2s -1 and was independent of the frequency of the generator. The crocidolite fibers were 6 × 10 -7cm 2s -1 and show somewhat more scatter. Comparison of the measured diffusion coefficients with calculated values from scanning electron micrographs indicated good agreement for the crocidolite fibers; but that experimental values were twice that of the calculated values for chrysotile.

Gentry, J. W.; Spurny, K. R.; Schormann, J.; Opiela, H.; Weiss, G.

32

The solubility and diffusion coefficient of helium in uranium dioxide  

NASA Astrophysics Data System (ADS)

The solubility and diffusion coefficient of helium in the single-crystal UO2 samples were determined by a Knudsen-effusion mass-spectrometric method. The measured helium solubilities were found to lie within the scatter of the available data, but to be much lower than those for the polycrystalline samples. The diffusion analysis was conducted based on a hypothetical equivalent sphere model and the simple Fick's law. The helium diffusion coefficient was determined by using the pre-exponential factor and activation energy as the fitting parameters for the measured and calculated fractional releases of helium. The optimized diffusion coefficients were in good agreement with those obtained by a nuclear reaction method reported in the past. It was also found that the pre-exponential factors of the determined diffusion coefficients were much lower than those analyzed in terms of a simple interstitial diffusion mechanism.

Nakajima, Kunihisa; Serizawa, Hiroyuki; Shirasu, Noriko; Haga, Yoshinori; Arai, Yasuo

2011-12-01

33

A Diffusional Model with a Moisture-Dependent Diffusion Coefficient  

Microsoft Academic Search

Many investigators point out that a more realistic diffusion model is obtained when the effective diffusivity is considered with both temperature and moisture content dependent. Two mathematical models to predict the drying curves of pineapple at different temperatures have been compared. The simulation provided by model I, where the effective diffusion coefficient was considered as a function of the temperature,

S. Simal; M. C. Garau; A. Femenia; C. Rosselló

2006-01-01

34

Effect of the formation of EDTA complexes on the diffusion of metal ions in water  

NASA Astrophysics Data System (ADS)

The diffusion coefficients of aquo metal ions (Mz+) and their EDTA complexes (M EDTA(z-4)+) were compared to understand the effect of EDTA complexation on the diffusion of metal ions by the diffusion cell method for Co2+, Ga3+, Rb+, Sr2+, Ag+, Cd2+, Cs+, Th4+, UO22+, and trivalent lanthanides. Most studies about ionic diffusion in water have dealt with free ion (hydrated ion). In many cases, however, polyvalent ions are dissolved as complexed species in natural waters. Hence, we need to study the diffusion behavior of complexes in order to understand the diffusion phenomenon in natural aquifer and to measure speciation by diffusive gradient in thin films (DGT), which requires the diffusion coefficients of the species examined. For many ions, the diffusion coefficients of M EDTA(z-4)+ are smaller than those of hydrated ions, but the diffusion coefficients of M EDTA(z-4)+ are larger than those of hydrated ions for ions with high ionic potentials (Ga3+ and Th4+). As a result, the diffusion coefficients of EDTA complexes are similar among various metal ions. In other words, the diffusion of each ion loses its characteristics by the complexation with EDTA. Although the difference is subtle, it was also found that the diffusion coefficients of EDTA complexes increase as the ionic potential increases, which can be explained by the size of the EDTA complex of each metal ion.

Furukawa, Kenji; Takahashi, Yoshio; Sato, Haruo

2007-09-01

35

Simplified equation to extract diffusion coefficients from confocal FRAP data.  

PubMed

Quantitative measurements of diffusion can provide important information about how proteins and lipids interact with their environment within the cell and the effective size of the diffusing species. Confocal fluorescence recovery after photobleaching (FRAP) is one of the most widely accessible approaches to measure protein and lipid diffusion in living cells. However, straightforward approaches to quantify confocal FRAP measurements in terms of absolute diffusion coefficients are currently lacking. Here, we report a simplified equation that can be used to extract diffusion coefficients from confocal FRAP data using the half time of recovery and effective bleach radius for a circular bleach region, and validate this equation for a series of fluorescently labeled soluble and membrane-bound proteins and lipids. We show that using this approach, diffusion coefficients ranging over three orders of magnitude can be obtained from confocal FRAP measurements performed under standard imaging conditions, highlighting its broad applicability. PMID:22984916

Kang, Minchul; Day, Charles A; Kenworthy, Anne K; DiBenedetto, Emmanuele

2012-10-10

36

Analysis of pattern formation in reaction diffusion models with spatially inhomogenous diffusion coefficients  

Microsoft Academic Search

We consider a reaction diffusion system in one spatial dimension in which the diffusion coefficients are spatially varying. We present a non-standard linear analysis for a certain class of spatially varying diffusion coefficients and show that it accurately predicts the behaviour of the full nonlinear system near bifurcation. We show that the steady state solutions exhibit qualitatively different behaviour to

D. L. BENSON; P. K. MAINI; A. SHERRATT

1993-01-01

37

Diffusion coefficient and shear viscosity of rigid water models  

Microsoft Academic Search

We report the diffusion coefficient and viscosity of popular rigid water models: two non-polarizable ones (SPC\\/E with three sites, and TIP4P\\/2005 with four sites) and a polarizable one (Dang–Chang, four sites). We exploit the dependence of the diffusion coefficient on the system size (Yeh and Hummer 2004 J. Phys. Chem. B 108 15873) to obtain the size-independent value. This also

Sami Tazi; Alexandru Bo?an; Mathieu Salanne; Virginie Marry; Pierre Turq; Benjamin Rotenberg

2012-01-01

38

Eddy diffusion coefficients in the lower thermospheres, revised  

NASA Astrophysics Data System (ADS)

The seasonal variation of the eddy diffusion coefficient is deduced for a height of 94 km at 23 S based on two independent methods of analysis. One of these methods is related to indirect measurements of atomic oxygen and the other one is a new method related to measurements of the density of upper atmospheric sodium. The results are mutually consistent giving a maximum eddy diffusion coefficient during summer.

Kirchhoff, V. W. J. H.; Clemesha, B. R.

1982-08-01

39

Diffusion Coefficient of Tin(II) Methanesulfonate in Ionic Liquid and Methane Sulfonic Acid (MSA) Solvent  

NASA Astrophysics Data System (ADS)

Voltammetry and chronoamperometry for the electrodeposition of tin from Tin(II) methane sulfonate mixed with ionic liquid and methane sulfonate acid at room temperature was studied. Cyclic voltammetry shows redox waves of Tin(II), which proves that the electrodeposition of tin from Tin(II) methane sulfonate is a diffusion-controlled process. The diffusion coefficient of Tin(II) ions in the solvent mixture showed good agreement from both voltammetry and chronoamperometry results. The diffusion coefficient of Tin(II) in the mixture was much smaller than in aqueous solution, and it depends on the anion of the ionic liquid.

Yang, Kok Kee; Mahmoudian, M. R.; Ebadi, Mehdi; Koay, Hun Lee; Basirun, Wan Jeffrey

2011-12-01

40

HOW DUAL-SCALE DIFFUSIVE PROPERTY HETEROGENEITY AFFECTS EFFECTIVE MATRIX DIFFUSION COEFFICIENT IN FRACTURED ROCK  

SciTech Connect

Matrix diffusion can significantly retard solute transport in fractured formations. Understanding matrix diffusion is crucial for predicting the arrival time, peak concentration, and tail of a contaminant breakthrough curve. Previous studies show that the effective matrix diffusion coefficient may be scale dependent. This study examines how heterogeneities of diffusion properties affect the effective matrix diffusion coefficient. Two types of heterogeneity in a channelized flow system are considered in the study: (1) interchannel heterogeneity, and (2) intrachannel heterogeneity. The objectives of this study are (1) to examine if it is appropriate to use a single, effective matrix diffusion coefficient in a standard solution model to predict breakthrough curves (BTC) in a fractured formation, (2) if so, how this effective value is related to the degree of the matrix diffusion coefficient variability; and (3) to examine if the observed scale dependence of the effective matrix-diffusion coefficient is caused by heterogeneity in diffusion properties. The results show that the use of a single effective matrix diffusion coefficient is appropriate only if the inter- and intrachannel variability of diffusion properties is small. The scale dependence of the effective matrix diffusion coefficient is not caused by either type of the studied heterogeneity.

Y. Zhang; H. Liu; Q. Zhou; S. Finsterle

2005-09-07

41

Normative apparent diffusion coefficient values in the developing fetal brain  

Microsoft Academic Search

BACKGROUND AND PURPOSE: Previous studies of diffusion-weighted imaging (DWI) in fetuses are limited. Because of the need for normative data for comparison with young fetuses and preterm neonates with suspected brain abnormalities, we studied apparent diffusion coefficient (ADC) values in a population of singleton, nonsedated, healthy fetuses. MATERIALS AND METHODS: DWI was performed in 28 singleton nonsedated fetuses with normal

M. M. Schneider; J. I. Berman; F. M. Baumer; H. C. Glass; S. Jeng; R. J. Jeremy; M. Esch; V. Biran; A. J. Barkovich; C. Studholme; D. Xu; O. A. Glenn

2009-01-01

42

Anomalous behavior of the diffusion coefficient in thin active films  

NASA Astrophysics Data System (ADS)

Inspired by recent experiments in cell biology, we elucidate the visco-elastic properties of an active gel by studying the dynamics of a small tracer particle inside it. In a stochastic hydrodynamic approach for an active gel of finite thickness L, we calculate the mean square displacement of a particle. These particle displacements are governed by fluctuations in the velocity field. We characterize the short-time behavior when the gel is a solid as well as the limit of long times when the gel becomes a fluid and the particle shows simple diffusion. Active stresses together with local polar order give rise to velocity fluctuations that lead to characteristic behaviors of the diffusion coefficient that differ fundamentally from those found in a passive system: the diffusion coefficient can depend on system size and diverges as L approaches an instability threshold. Furthermore, the diffusion coefficient becomes independent of the particle size in this case.

Basu, Abhik; Joanny, Jean-Francois; Jülicher, Frank; Prost, Jacques

2012-11-01

43

Diffusion coefficient and shear viscosity of rigid water models.  

PubMed

We report the diffusion coefficient and viscosity of popular rigid water models: two non-polarizable ones (SPC/E with three sites, and TIP4P/2005 with four sites) and a polarizable one (Dang-Chang, four sites). We exploit the dependence of the diffusion coefficient on the system size (Yeh and Hummer 2004 J. Phys. Chem. B 108 15873) to obtain the size-independent value. This also provides an estimate of the viscosity of all water models, which we compare to the Green-Kubo result. In all cases, a good agreement is found. The TIP4P/2005 model is in better agreement with the experimental data for both diffusion and viscosity. The SPC/E and Dang-Chang models overestimate the diffusion coefficient and underestimate the viscosity. PMID:22739097

Tazi, Sami; Bo?an, Alexandru; Salanne, Mathieu; Marry, Virginie; Turq, Pierre; Rotenberg, Benjamin

2012-06-27

44

Hydration structure and diffusion of ions in supercooled water: Ion size effects  

NASA Astrophysics Data System (ADS)

We have performed a series of molecular dynamics simulations of alkali metal (Li+, Na+, K+, Rb+, and Cs+) and halide (F-, Cl-, Br-, and I-) ions in water at infinite dilution at T=258 K to investigate the effects of ion size on the hydration structure and diffusion of ions in supercooled water. Simulations are also performed at T=298 K in order to compare the results of the hydration structure and diffusion in supercooled water with those in ambient water. With increase of ion size, like in ambient water, in supercooled water also the diffusion coefficients of alkali metal and halide ions are found to fall in different curves with distinct maxima. However, the relative increases of the diffusion coefficients of larger ions compared to those of Li+ and F- are found to be significantly higher in the supercooled water.

Chowdhuri, Snehasis; Chandra, Amalendu

2003-06-01

45

Diffusion coefficients of alkaline cations in Bure mudrock  

NASA Astrophysics Data System (ADS)

In this work, the diffusivities of alkaline cations (Li+, Na+, K+, Rb+ and Cs+) were measured in a mudrock sample from Bure (ANDRA site, Meuse/Haute-Marne, France). The material is a natural rock, mainly composed of interstratified illite/smectite, quartz and calcite. It was saturated with a Na-Cl-dominated synthetic solution with an ionic strength of 57 mM and a pH ˜8.0. The effective diffusion coefficients (De) for the cations were determined from their steady-state flux through mudrock slices at 23 °C (through-diffusion technique). HTO diffusion coefficients were systematically measured as well. Measured De for the cations were found to be higher than values predicted from water diffusion alone. Moreover, this observation appeared to depend on the considered species: the ratio between measured and calculated effective diffusion coefficients ranged between two for lithium and nearly one order of magnitude for rubidium and cesium. An interpretation with different models dealing with sorption diffusion processes is proposed and discussed.

Melkior, T.; Yahiaoui, S.; Thoby, D.; Motellier, S.; Barthès, V.

46

Photon diffusion coefficient in scattering and absorbing media.  

PubMed

We present a unified derivation of the photon diffusion coefficient for both steady-state and time-dependent transport in disordered absorbing media. The derivation is based on a modal analysis of the time-dependent radiative transfer equation. This approach confirms that the dynamic diffusion coefficient is given by the random-walk result D = cl(*)/3, where l(*) is the transport mean free path and c is the energy velocity, independent of the level of absorption. It also shows that the diffusion coefficient for steady-state transport, often used in biomedical optics, depends on absorption, in agreement with recent theoretical and experimental works. These two results resolve a recurrent controversy in light propagation and imaging in scattering media. PMID:16642188

Pierrat, Romain; Greffet, Jean-Jacques; Carminati, Rémi

2006-05-01

47

Distinct diffusion coefficients in binary nonelectrolyte mixtures. Frames of reference  

SciTech Connect

Generalized transport coefficients are indispensable for the study of interactions between species of the same kind in binary solutions. Distinct diffusion coefficients are best suited for this purpose because of their finite limiting values and inherent symmetry. Equations are derived for the calculation of these coefficients from experimental data for the mass-, volume-, number-, and solvent-fixed frames of reference. Distinct diffusion coefficients in the 4 reference frames computed for 14 binary nonelectrolyte solutions show that the number-fixed frame is probably best suited for the comparison of the macroscopic properties of these solutions. A point of contention has been the frame of reference of the Friedman-Mills equation; surprisingly, the mass-fixed frame describes its D[sub ij][sup d] values closely. 19 refs., 12 figs., 4 tabs.

Mills, R.; Malhotra, R.; Woolf, L.A. (Australian National Univ., Canberra (Australia)); Miller, D.G. (Lawrence Livermore National Lab., CA (United States))

1994-05-26

48

THE DETERMINATION OF DIFFUSION COEFFICIENT OF INVERT MATERIALS  

SciTech Connect

The Engineered Barrier System (EBS) Testing Department is performing tests in the Department of Energy's Atlas Facility to evaluate the performance of various means for increasing the time for breakthrough of radionuclides from the waste package to the base of the invert. This includes testing various barriers in the invert as a means of increasing breakthrough time through the process of diffusion. A diffusion barrier may serve as an invert material for the emplacement drifts. The invert material may consist of crushed tuff from the repository excavation at Yucca Mountain or silica sand. The objective of this report is to determine the diffusion coefficient of the crushed tuff and silica sand invert materials specified by the EBS Testing Department. The laboratory derived information from the testing was used in the Nernst-Einstein equation (Jurinak et al. 1987, p. 626) to determine the diffusion coefficient of the invert material. This report transmits the results and describes the methodology and interpretation. The scope of this report is to determine the diffusion coefficients of the invert materials mentioned above using the centrifuge at UFA Ventures. Standard laboratory procedures, described in Section 2 of this report, were used. The diffusion coefficients are to be determined over a range of moisture contents. The report contains the diffusion coefficients calculated by the Nernst-Einstein equation (Jurinak et al. 1987, p. 626) that become a part of the Technical Database. Raw data is also included in the report, however this data does not become part of the Technical Database as per Section 3.23 of AP-SIII.3Q ''Submittal and Incorporation of Data to the Technical Data Management System''. A sieve analysis of the samples was not conducted as part of this report, but sieve analysis may be accomplished as part of other reports. Two samples of crushed tuff and two samples of silica sand were tested.

P. Heller and J. Wright

2000-01-11

49

POTENTIAL SCALE DEPENDENCE OF EFFECTIVE MATRIX DIFFUSION COEFFICIENT  

SciTech Connect

It is well known that matrix diffusion (mass transfer between fractures and the rock matrix through molecular diffusion) can significantly retard solute transport processes in fractured rock, and therefore is important for analyzing a variety of problems, including geological disposal of nuclear waste. Matrix-diffusion-coefficient values measured from small rock samples in the laboratory are generally used for modeling field-scale solute transport in fractured rock. However, by compiling results from a number of field tracer tests corresponding to different geological settings, this study demonstrates that the effective matrix diffusion coefficient at field scale is generally larger than that at lab scale and tends to increase with testing scale. Preliminary interpretations of this observation are also investigated. We found that this interesting scale dependence may be related to the complexity of flow-path geometry in fractured rock.

H. Liu; Q. Zhou; Y. Zhang

2006-03-13

50

Investigation of Apparent Diffusion Coefficient and Diffusion Tensor Anisotropy in Acute and Chronic Multiple Sclerosis Lesions  

Microsoft Academic Search

BACKGROUND AND PURPOSE: The various stages of multiple sclerosis (MS) are charac- terized by de- and remyelination as well as by inflammation. Diffusion MR imaging is sensitive to tissue water motion, which might correspond to these pathologic processes. Our purpose was to demonstrate differences in apparent diffusion coefficient (ADC) and diffusion tensor anisotropy in acute and chronic MS plaques and

Andrew L. Tievsky; Thomas Ptak; Jeffrey Farkas

51

Calculation of diffusion coefficients in air-metal thermal plasmas  

Microsoft Academic Search

This paper presents the combined diffusion coefficients of metal vapours (silver, copper and iron) in air thermal plasmas for temperatures ranging from 300 to 30 000 K. The theory used to calculate these coefficients is remembered and validated by comparison with the literature values in several cases such as Ar-He, Ar-Cu and N2-O2 mixtures. The results are discussed showing the

Y. Cressault; A. Gleizes

2010-01-01

52

Diffusion coefficients of model contaminants in dense CO 2  

Microsoft Academic Search

Dense CO2 extraction is an emerging technology in cleaning and remediation. The successful design and implementation of processes based on this technology require the accurate determination of solute diffusivities in the systems. In this work, a Taylor dispersion apparatus was constructed for measuring binary diffusion coefficients of benzoic acid, biphenyl, and p-dichlorobenzene in dense CO2 at temperatures of 293.15, 298.15,

Hong Fu; L. A. F Coelho; Michael A Matthews

2000-01-01

53

Scale dependency of the effective matrix diffusion coefficient  

SciTech Connect

It has been recognized that matrix diffusion is an important process for retarding solute transport in fractured rock. Based on analyses of tracer transport data from a number of field tests, we demonstrate for the first time that the effective matrix-diffusion coefficient may be scale dependent and generally increases with test scale. A preliminary theoretical explanation of this scale dependency is also presented, based on the hypothesis that solute travel paths within a fracture network are fractals.

Liu, H.H.; Bodvarsson, G.S.; Zhang, G.

2003-05-30

54

Photoelectric and diffusion component measurements of germanium interference absorption coefficient  

NASA Astrophysics Data System (ADS)

The photoelectric ?ph and diffusion ?ds components of the interference absorption coefficient ?i of germanium is measured using the synchrotron radiation of the Yerevan Electron Accelerator. There is a good agreement between the experimental and calculated values of ?ds, ? ph and?i for perfect Ge samples. Copper-decorated galium admixtures up to ~1018 at./cm3 change the absolute values of ?ph in the range of 9-11%, but do not influence the diffusion component of ?i.

Karabekov, I. P.; Egikian, D. L.; Mikaelian, R. A.; Bagdasarian, V. G.

1987-11-01

55

Acinar determinants of the apparent diffusion coefficient for helium-3.  

PubMed

The apparent diffusion coefficient (ADC) obtained by helium-3 magnetic resonance imaging over several seconds is thought to reflect diffusion impairment due to both intra- and interacinar structure. In this study, numerical simulations of intra-acinar gas mixing and effective diffusion were performed in a multiple-branch-point model of the human acinus. Using a previously described method, we computed the instantaneous effective diffusion resulting from the diffusive impairment imposed by intra-acinar branching for varying times up to 5 s. We also tested the influence on effective diffusion of intra-acinar collateral channels in the fully alveolated intra-acinar airways to mimic the effect of emphysema. Randomly connecting two or four pairs of airways per generation (in generations 19-25) led to a 40 and 142% increase, respectively, in effective diffusion coefficient cumulated over the time interval of 0.2-5 s. Finally, we also used a system of two coupled multiple branch-point models to simulate diffusive attenuation over a 50-s interval in cases of purely acinar tagging (i.e., the initial gas concentration = 1 in one acinus and 0 in the other) and of partial tagging astride on two acini. It is shown that, in the latter case, the decay rate cannot be approximated by a mono-exponential with a several-fold faster decay for times below 10 s due to intra-acinar diffusion. We conclude that both the characteristic biphasic time dependence of simulated effective diffusion and its sensitivity to intra-acinar structural change mimic experimental ADC behavior. Additional simulations of combined inter- and intra-acinar diffusion strongly suggest that neglecting intra-acinar branching would in fact lead to considerable error of simulated ADC. PMID:20167670

Verbanck, Sylvia; Paiva, Manuel

2010-02-18

56

Effect of geometry on the effective moisture transfer diffusion coefficient  

Microsoft Academic Search

The effective moisture transfer diffusion coefficient (Deff) of ready-to-eat breakfast cereals (RTE) is determined either from an individual particle or a bulk of material in the literature. The Deff is assumed to be the same in both cases which can be dependent on the material thickness. In this study, the effect of bed depth of a bulk of two types

M. Ahmet Tütüncü; T. P. Labuza

1996-01-01

57

A model for the diffuse attenuation coefficient of downwelling irradiance  

Microsoft Academic Search

The diffuse attenuation coefficient for downwelling irradiance (Kd) is an important parameter for ocean studies. For the vast ocean the only feasible means to get fine-scale measurements of Kd is by ocean color remote sensing. At present, values of Kd from remote sensing are estimated using empirical algorithms. Such an approach is insufficient to provide an understanding regarding the variation

Zhong-Ping Lee; Ke-Ping Du; Robert Arnone

2005-01-01

58

Capillary transfer coefficient of polynomial type in the diffusion equation  

NASA Astrophysics Data System (ADS)

Problem of the capillary transfer of the liquids in porous media is very actual because most of the standard building materials are characterized by a porous structure. In the present paper, we describe the process of absorbtion by a diffusion equation and investigate an inverse problem for this equation to express capillary transfer coefficient in a form of a polynomial.

Škripková, L.

2013-10-01

59

Comparison of field-measured radon diffusion coefficients with laboratory-measured coefficients  

SciTech Connect

Experiments were conducted to compare radon diffusion coefficients determined for 0.1-m depths of soils by a steady-state method in the laboratory and diffusion coefficients evaluated from radon fluxes through several-fold greater depths of the same soils covering uranium-mill tailings. The coefficients referred to diffusion in the total pore volume of the soils and are equivalent to values for the quantity, D/P, in the Generic Environmental Impact Statement on Uranium Milling prepared by the US Nuclear Regulatory Commission. Two soils were tested: a well-graded sand and an inorganic clay of low plasticity. For the flux evaluations, radon was collected by adsorption on charcoal following passive diffusion from the soil surface and also from air recirculating through an aluminum tent over the soil surface. An analysis of variance in the flux evaluations showed no significant difference between these two collection methods. Radon diffusion coefficients evaluated from field data were statistically indistinguishable, at the 95% confidence level, from those measured in the laboratory; however, the low precision of the field data prevented a sensitive validation of the laboratory measurements. From the field data, the coefficients were calculated to be 0.03 +- 0.03 cm/sup 2//s for the sand cover and 0.0036 +- 0.0004 cm/sup 2//s for the clay cover. The low precision in the coefficients evaluated from field data was attributed to high variation in radon flux with time and surface location at the field site.

Lepel, E.A.; Silker, W.B.; Thomas, V.W.; Kalkwarf, D.R.

1983-04-01

60

Measurement of the local particle diffusion coefficient in a magnetized plasma  

SciTech Connect

Local impurity particle diffusion coefficients have been measured in a low temperature plasma by the injection of test particles at the center of the plasma. The injection is accomplished by a high voltage discharge between two small graphite electrodes on a probe. The probe can be located anywhere in the plasma. The diffusion is observed spectroscopically. An analysis of the spatial and temporal evolution of the CII radiation from the carbon discharge can determine the parallel and perpendicular diffusion of the impurity ions. Results with the diagnostic have been obtained in the Proto S-1/C spheromak. The measured value of the diffusion coefficient in the afterglow plasma is in good agreement with classical predictions.

Meyerhofer, D.D.; Levinton, F.M.

1987-02-01

61

Diffusion coefficients of two metastable states of the nitrogen molecule  

NASA Astrophysics Data System (ADS)

Previous experiments of Ernest et al. (1986) showed the existence of a metastable state of the nitrogen molecule with a coefficient for diffusion through ground-state nitrogen of about one quarter of that of the well-known A 3? u+ state. Both states were populated by pre-breakdown discharges through pure nitrogen. This paper presents further results on the diffusion of metastable excited molecules through nitrogen. The effects of varying background gas number density N and the reduced electric field E/N were explored, and data were taken in two ionization chambers with two different cathode materials. Consistent results are obtained with the different chambers and cathodes. The characteristic times for the decay of metastable population density are independent of E/N but scale with 1/ N, consistent with the existence of two slowly diffusing metastable states of nitrogen. The values at 295 ± 4 K of the product DmN, where Dm is the metastable diffusion coefficient, are 551 ± 25 am -1s -1 ((5.51 ± 0.25) × 10 16cm -1s -1) for the first slowly diffusing state and 158 ± 17 am -1s -1 for the second. Both states show very small quenching in collisions with ground-state nitrogen molecules. The first state is identified as the A 3?u+ state. Far from having a small effect, the action of molecules in the second slowly diffusing state can dominate the ionization growth near breakdown.

Haydon, S. C.; Fewell, M. P.; Ernest, A. D.; Baldwin, M. J.

1996-05-01

62

The Evaluation of Grain Boundary Difussion Coefficient of Iron Ions in Wustite  

Microsoft Academic Search

In this study, the effect of grain boundarry diffusion on the iron nuclei formation during wüstite reduction process was investigated.\\u000a Combined with the measurement of width of the iron nucleation dominant zone from grain boundaries with time and a grain boundary\\u000a diffusion model, the grain boundary diffusion coefficient of Fe2+ ion in wüstite at 1073K has been evaluated.

Yasushi Sasaki; Manabu Iguch; Mitsutaka Hino

63

The diffusion of ions in polyethylene  

Microsoft Academic Search

It was demonstrated that inorganic ions dissolved in water which is in contact with polyethylene will diffuse into the polyethylene. Not all ions were found to diffuse at the same rate. It was also found that polyethylene in contact with salt solutions will absorb water, with more water being absorbed as the salt concentration is increased. The diffusion was found

T. Bao; J. Tanaka

1991-01-01

64

The effects of unequal diffusion coefficients on periodic travelling waves in oscillatory reaction diffusion systems  

NASA Astrophysics Data System (ADS)

Many oscillatory biological systems show periodic travelling waves. These are often modelled using coupled reaction diffusion equations. However, the effects of different movement rates (diffusion coefficients) of the interacting components on the predictions of these equations are largely unknown. Here we investigate the ways in which varying the diffusion coefficients in such equations alters the wave speed, time period, wavelength, amplitude and stability of periodic wave solutions. We focus on two sets of kinetics that are commonly used in ecological applications: lambda omega equations, which are the normal form of an oscillatory coupled reaction diffusion system close to a supercritical Hopf bifurcation, and a standard predator prey model. Our results show that changing the ratio of the diffusion coefficients can significantly alter the shape of the one-parameter family of periodic travelling wave solutions. The position of the boundary between stable and unstable waves also depends on the ratio of the diffusion coefficients: in all cases, stability changes through an Eckhaus (‘sideband’) instability. These effects are always symmetrical in the two diffusion coefficients for the lambda omega equations, but are asymmetric in the predator prey equations, especially when the limit cycle of the kinetics is of large amplitude. In particular, there are two separate regions of stable waves in the travelling wave family for some parameter values in the predator prey scenario. Our results also show the existence of a one-parameter family of travelling waves, but not necessarily a Hopf bifurcation, for all values of the diffusion coefficients. Simulations of the full partial differential equations reveals that varying the ratio of the diffusion coefficients can significantly change the properties of periodic travelling waves that arise from particular wave generation mechanisms, and our analysis of the travelling wave families assists in the understanding of these effects.

Smith, Matthew J.; Sherratt, Jonathan A.

2007-12-01

65

Diffusion Coefficient of Tritium Through Molten Salt Flibe and Rate of Tritium Leak from Fusion Reactor System  

Microsoft Academic Search

Diffusion coefficients of hydrogen isotopes in Flibe were correlated with making reference to previous relating data of F⁻ ion self-diffusivity and Flibe viscosity and so on. Rates of tritium permeation through structural materials in a fusion reactor system with Flibe blanket were estimated comparatively under conditions with or without a Flibe permeation barrier. A way to lower the tritium leak

Satoshi Fukada; Robert A. Anderl; Akio Sagara; Masabumi Nishikawa

2005-01-01

66

The Perpendicular Diffusion Coefficient for Charged Particles of Arbitrary Energy  

NASA Astrophysics Data System (ADS)

The problem of perpendicular diffusion by a particle in a turbulent plasma is a problem of enduring interest, and one that has yet to be fully solved. Analytic models do not agree with either observations or numerical simulations. Recently, a nonlinear theory was developed by Matthaeus et al. [2003] which, for the first time, appears to be consistent with numerical simulations in both the high- and low-energy particle regimes. Their approach is to assume that perpendicular transport is governed by the velocity of gyrocenters that follow magnetic field lines. Qin et al. [2002a,b] showed using numerical simulations that perpendicular diffusion could occur only in the presence of a transverse complex magnetic field. Flux surfaces with high transverse complexity are characterized by the rapid separation of nearby magnetic field lines and are therefore important to perpendicular diffusion. In particular, it appears that the combination of slab and 2D turbulence (a ``two-component'' model) is necessary to produce transverse complexity, and that slab turbulence alone, for example, is insufficient. The nonlinear theory is expressed through the solution of an integral equation. While the numerical solution of the integral equation in the appropriate parameter regime shows excellent agreement with numerical simulations for both high- and low-energy particles, the physical content is difficult to evaluate, nor is it evident how ? xx scales with parameters such as the energy density in magnetic fluctuations, mean field strength, particle gyroradius, MHD turbulence correlation length scales, parallel diffusion coefficient, etc. Furthermore, the integral equation formulation is not readily amenable to inclusion in models and numerical codes that require the perpendicular diffusion coefficient explicitly, such as heliospheric cosmic ray modulation models. We therefore introduce an explicit model for turbulence in the solar wind and solve the integral equation approximately for ? xx. We show that our approximate solution agrees very well with the numerical solution of the fully nonlinear integral equation. The approximate solution reveals the dependence of ? xx on the characteristics of the turbulent magnetofluid and particle energy (through the particle gyroradius). We conclude by using the perpendicular diffusion coefficient to evaluate 1) the particle acceleration timescale for diffusive shock acceleration at perpendicular shocks, and 2) the diffusion coefficient for cosmic ray modulation throughout the heliosphere.

Zank, G. P.; Li, G.; Florinski, V.; Webb, G. M.; Le Roux, J. A.; Matthaeus, W. H.

2003-12-01

67

Precise Measurement of Diffusion Coefficients using Scanning Fluorescence Correlation Spectroscopy  

Microsoft Academic Search

We have implemented scanning fluorescence correlation spectroscopy (sFCS) for precise determination of diffusion coefficients of fluorescent molecules in solution. The measurement volume where the molecules are excited, and from which the fluorescence is detected, was scanned in a circle with radius comparable to its size at frequencies 0.5–2kHz. The scan radius R, determined with high accuracy by careful calibration, provides

Zden?k Petrášek; Petra Schwille

2008-01-01

68

The coefficient of self-diffusion of liquid neon  

Microsoft Academic Search

The coefficient of self-diffusion of liquid neon is measured by means of the capillary method within the temperature range of 25–43 K and in the pressure range of 10–100 atm. A natural neon-isotope mixture with 9.1%22Ne and a mixture enriched to 99%22Ne were available for the measurements. The measured runs show in the representation log D=f(1\\/T) and logD=f(p), respectively, straight

L. Beilogua; C. Gladun; B. Kubsch

1971-01-01

69

The effect of recombination and attachment on meteor radar diffusion coefficient profiles  

NASA Astrophysics Data System (ADS)

Estimates of the ambipolar diffusion coefficient producedusing meteor radar echo decay times display an increasing trend below 80-85 km, which is inconsistent with a diffusion-only theory of the evolution of meteor trails. Data from the 33 MHz meteor radar at King Sejong Station, Antarctica, have been compared with observations from the Aura Earth Observing System Microwave Limb Sounder satellite instrument. It has been found that the height at which the diffusion coefficient gradient reverses follows the height of a constant neutral atmospheric density surface. Numerical simulations of meteor trail diffusion including dissociative recombination with atmospheric ions and three-body attachment of free electrons to neutral molecules indicate that three-body attachment is responsible for the distortion of meteor radar diffusion coefficient profiles at heights below 90 km, including the gradient reversal below 80-85 km. Further investigation has revealed that meteor trails with low initial electron line density produce decay times more consistent with a diffusion-only model of meteor trail evolution.

Lee, C. S.; Younger, J. P.; Reid, I. M.; Kim, Y. H.; Kim, J.-H.

2013-04-01

70

Fluctuations Effects on Block Copolymer Dynamics: Self-Diffusion Coefficient.  

NASA Astrophysics Data System (ADS)

The Polymer Mode Coupling (PMC) theory for the dynamics of entangled polymeric fluids has been extended to treat block copolymer fluids(H.Tang and K.S.Schweizer J.C.P. 103), 6296 (1995).. The PRISM theory for block copolymers (E.F.David and K.S.Schweizer, J.C.P. 100), 7767, 7784 (1994). provides the static input to PMC, as it accurately describes the structure of the block copolymer fluid with the fluctuation concentration stabilization effects across the order-disorder phase transition. While no signature of the order-disorder phase transition appear in the resulting diffusion coefficients, we observe a change in the apparent scaling exponents with the molecular weight and polymer volume fraction. Near the ODT strongly temperature-dependent suppression of the self-diffusion is predicted followed by a saturation of the frictional enhancement at low temperature. These effects are in agreement with experimental findings on lamellae forming entangled polyolefin diblock melts(T.P.Lodge and M.C.Dalvi, Phys. Rev. Lett. 75), 657 (1995).. New predictions for the diffusion coefficient as a function of copolymer composition, bare friction coefficient asymmetry, and polymer volume fraction in good and theta solvents are presented.

Tang, Hai; Guenza, Marina; Schweizer, Kenneth S.

1997-03-01

71

An axisymmetric diffusion experiment for the determination of diffusion and sorption coefficients of rock samples.  

PubMed

Diffusion anisotropy is a critical property in predicting migration of substances in sedimentary formations with very low permeability. The diffusion anisotropy of sedimentary rocks has been evaluated mainly from laboratory diffusion experiments, in which the directional diffusivities are separately estimated by through-diffusion experiments using different rock samples, or concurrently by in-diffusion experiments in which only the tracer profile in a rock block is measured. To estimate the diffusion anisotropy from a single rock sample, this study proposes an axisymmetric diffusion test, in which tracer diffuses between a cylindrical rock sample and a surrounding solution reservoir. The tracer diffusion between the sample and reservoir can be monitored from the reservoir tracer concentrations, and the tracer profile could also be obtained after dismantling the sample. Semi-analytical solutions are derived for tracer concentrations in both the reservoir and sample, accounting for an anisotropic diffusion tensor of rank two as well as the dilution effects from sampling and replacement of reservoir solution. The transient and steady-state analyses were examined experimentally and numerically for different experimental configurations, but without the need for tracer profiling. These experimental configurations are tested for in- and out-diffusion experiments using Koetoi and Wakkanai mudstones and Shirahama sandstone, and are scrutinized by a numerical approach to identify favorable conditions for parameter estimation. The analysis reveals the difficulty in estimating diffusion anisotropy; test configurations are proposed for enhanced identifiability of diffusion anisotropy. Moreover, it is demonstrated that the axisymmetric diffusion test is efficient in obtaining the sorption parameter from both steady-state and transient data, and in determining the effective diffusion coefficient if isotropic diffusion is assumed. Moreover, measuring reservoir concentrations in an axisymmetric diffusion experiment coupled with tracer profiling may be a promising approach to estimate of diffusion anisotropy of sedimentary rocks. PMID:21288593

Takeda, M; Hiratsuka, T; Ito, K; Finsterle, S

2011-01-09

72

An asixymmetric diffusion experiment for the determination of diffusion and sorption coefficients of rock samples  

SciTech Connect

Diffusion anisotropy is a critical property in predicting migration of substances in sedimentary formations with very low permeability. The diffusion anisotropy of sedimentary rocks has been evaluated mainly from laboratory diffusion experiments, in which the directional diffusivities are separately estimated by through-diffusion experiments using different rock samples, or concurrently by in-diffusion experiments in which only the tracer profile in a rock block is measured. To estimate the diffusion anisotropy from a single rock sample, this study proposes an axisymmetric diffusion test, in which tracer diffuses between a cylindrical rock sample and a surrounding solution reservoir. The tracer diffusion between the sample and reservoir can be monitored from the reservoir tracer concentrations, and the tracer profile could also be obtained after dismantling the sample. Semi-analytical solutions are derived for tracer concentrations in both the reservoir and sample, accounting for an anisotropic diffusion tensor of rank two as well as the dilution effects from sampling and replacement of reservoir solution. The transient and steady-state analyses were examined experimentally and numerically for different experimental configurations, but without the need for tracer profiling. These experimental configurations are tested for in- and out-diffusion experiments using Koetoi and Wakkanai mudstones and Shirahama sandstone, and are scrutinized by a numerical approach to identify favorable conditions for parameter estimation. The analysis reveals the difficulty in estimating diffusion anisotropy; test configurations are proposed for enhanced identifiability of diffusion anisotropy. Moreover, it is demonstrated that the axisymmetric diffusion test is efficient in obtaining the sorption parameter from both steady-state and transient data, and in determining the effective diffusion coefficient if isotropic diffusion is assumed. Moreover, measuring reservoir concentrations in an axisymmetric diffusion experiment coupled with tracer profiling may be a promising approach to estimate of diffusion anisotropy of sedimentary rocks.

Takeda, M.; Hiratsuka, T.; Ito, K.; Finsterle, S.

2011-02-01

73

Dependence of the water vapor diffusion coefficient of aspen ( Populus spec. ) on moisture content  

Microsoft Academic Search

The dependence of the diffusion coefficient of water in aspen (Populus sp.) on moisture content over the range of 0 to 18 percent moisture content at 43 °C was determined. The method requires a series of adsorption experiments and application of a numerical method for solving the diffusion equation with a moisture-content-dependent diffusion coefficient. The diffusion coefficient was found to

W. T. Simpson; J. Y. Liu

1991-01-01

74

Viscosity of aqueous NH/sub 4/Cl and tracer diffusion coefficients of ions, water and non-electrolytes in aqueous NH/sub 4/Cl, KI, and MgCl/sub 2/ at 25/sup 0/C  

SciTech Connect

Viscosities for aqueous NH/sub 4/Cl and tracer diffusion coefficients for /sup 22/Na/sup +/, /sup 36/Cl/sup -/, HTO, and CH/sub 3/OH, acetone and dimethylformamide (all /sup 14/C-labelled) in NH/sub 4/Cl supporting electrolyte are reported for 25/sup 0/, together with tracer diffusion coefficients for /sup 22/Na/sup +/, /sup 36/Cl/sup -/, and /sup 14/CH/sub 3/OH in 1M KI, and for /sup 14/CH/sub 3/OH in 1M MgCl/sub 2/. The diffusion coefficient of HTO in NH/sub 4/Cl solutions is slightly larger, for most of the concentration range investigated (0.05 to 4.5M), than the value for pure water and is almost unaffected by the supporting electrolyte up to about 4M. Similar behavior is shown by CH/sub 3/OH, acetone and dimethylformamide in NH/sub 4/Cl solutions. Onsager limiting law behavior is approached by Cl/sup -/ at NH/sub 4/Cl concentrations in the 0.05-0.1M region but at much lower concentrations by Na/sup +/.

Easteal, A.J.; Woolf, L.A.

1988-05-01

75

Molecular dynamics simulation of imidazolium-based ionic liquids. I. Dynamics and diffusion coefficient  

NASA Astrophysics Data System (ADS)

Molecular dynamics simulations are used to study the dynamics and transport properties of 12 room-temperature ionic liquids of the 1-alkyl-3-methylimidazolium [amim]+ (alkyl=methyl, ethyl, propyl, and butyl) family with PF6-, NO3-, and Cl- counterions. The explicit atom transferable force field of Canongia Lopes et al. [J. Phys. Chem. B 108, 2038 (2004)] is used in the simulations. In this first part, the dynamics of the ionic liquids are characterized by studying the mean-square displacement (MSD) and the velocity autocorrelation function (VACF) for the centers of mass of the ions at 400 K. Trajectory averaging was employed to evaluate the diffusion coefficients at two temperatures from the linear slope of MSD(t) functions in the range of 150-300 ps and from the integration of the VACF(t) functions at 400 K. Detailed comparisons are made between the diffusion results from the MSD and VACF methods. The diffusion coefficients from the integration of the VACFs are closer to experimental values than the diffusion coefficients calculated from the slope of MSDs. Both methods can show good agreement with experiment in predicting relative trends in the diffusion coefficients and determining the role of the cation and anion structures on the dynamical behavior of this family of ionic liquids. The MSD and self-diffusion of relatively heavier imidazolium cations are larger than those of the lighter anions from the Einstein results, except for the case of [bmim][Cl]. The cationic transference number generally decreases with temperature, in good agreement with experiments. For the same anion, the cationic transference numbers decrease with increasing length of the alkyl chain, and for the same cation, the trends in the cationic transference numbers are [NO3]-<[Cl]-<[PF6]-. The trends in the diffusion coefficient in the series of cations with identical anions are [emim]+>[pmim]+>[bmim]+ and those for anions with identical cations are [NO3]->[PF6]->[Cl]-. The [dmim]+ has a relatively low diffusion coefficient due to its symmetric structure and good packing in the liquid phase. The major factor for determining the magnitude of the self-diffusion is the geometric shape of the anion of the ionic liquid. Other important factors are the ion size and the charge delocalization in the anion.

Kowsari, M. H.; Alavi, Saman; Ashrafizaadeh, Mahmud; Najafi, Bijan

2008-12-01

76

Diffusion coefficients of Cu(II) complexes with ligands used in alkaline electroless copper plating solutions  

Microsoft Academic Search

The diffusion coefficient values of the Cu(II) complex compounds with EDTA, DTPA, NTA, Quadrol, glycerol, saccharose, (+)- and (±)-tartaric acid, OH- ions obtained by polarographic measurements in alkaline solutions lie in the range (1.2–5.7) × 10-6 cm2 s-1 (at 20 °C and J = 3) depending on the size of complex species, and are less than those of free (hydrated)

E. Norkus

2000-01-01

77

Velocity slip and temperature jump coefficients for gaseous mixtures. III. Diffusion slip coefficient  

Microsoft Academic Search

The diffusion slip coefficient is calculated for binary gaseous mixtures on the basis of the McCormack kinetic model of the Boltzmann equation, which is solved by the discrete velocity method. The calculations are carried out for the three mixtures of noble gases: neon-argon, helium-argon, and helium-xenon. Two models of the intermolecular interaction potential were considered. It was shown that this

Felix Sharipov; Denize Kalempa

2004-01-01

78

CALCULATION OF THE DIFFUSION COEFFICIENT OF DILUTE GASES AND OF THE SELF DIFFUSION COEFFICIENT OF DENSE GASES  

Microsoft Academic Search

A corresponding-states correlation of low-density binary- and self-diffusion coefficients is presented. The equations are simple to use, are sdciently accurate for most calculations, and correlate those data used in their derivation somewhat better than calculations based on the Lennard-Jones potential if potential parameters have to be estimated from the critical properties. The Enskog kinetic theory of dense gases is used

John C. Slattery; R. Byron Bird

1958-01-01

79

Drag and diffusion coefficients of B mesons in hot hadronic matter  

NASA Astrophysics Data System (ADS)

The drag and diffusion coefficients of a hot hadronic medium consisting of pions, kaons and eta using open beauty mesons as a probe have been evaluated. The interaction of the probe with the hadronic matter has been treated in the framework of chiral perturbation theory. It is observed that the magnitude of both the transport coefficients is significant, indicating a substantial amount of interaction of the heavy mesons with the thermal bath. The results may have significant impact on the experimental observables like the suppression of single-electron spectra originating from the decays of heavy mesons produced in nuclear collisions at Relativistic Heavy Ion Collider and LHC energies.

Das, Santosh K.; Ghosh, Sabyasachi; Sarkar, Sourav; Alam, Jan-e.

2012-04-01

80

Comparison of radon diffusion coefficients measured by transient-diffusion and steady-state laboratory methods  

SciTech Connect

A method was developed and used to determine radon diffusion coefficients in compacted soils by transient-diffusion measurements. A relative standard deviation of 12% was observed in repeated measurements with a dry soil by the transient-diffusion method, and a 40% uncertainty was determined for moistures exceeding 50% of saturation. Excellent agreement was also obtained between values of the diffusion coefficient for radon in air, as measured by the transient-diffusion method, and those in the published literature. Good agreement was also obtained with diffusion coefficients measured by a steady-state method on the same soils. The agreement was best at low moistures, averaging less than ten percent difference, but differences of up to a factor of two were observed at high moistures. The comparison of the transient-diffusion and steady-state methods at low moistures provides an excellent verification of the theoretical validity and technical accuracy of these approaches, which are based on completely independent experimental conditions, measurement methods and mathematical interpretations.

Kalwarf, D.R.; Nielson, K.K.; Rich, D.C.; Rogers, V.C.

1982-11-01

81

Deuterium profilemetry and diffusion coefficient in electrocharged stainless steel  

SciTech Connect

The method of nuclear microanalysis using the reaction D(d,p)T is used to measure concentration-depth profiles of deuterium in austenitic Type 310 stainless steel electrocharged in 1 N D/sub 2/SO/sub 4/ with arsenic poison at room temperature. The influence of aging after charging is examined. A near-surface density of 0.6 deuterium atoms per metal atom (i.e., 38 at. %) is found for the initially charged condition. Associated with this high gas concentration is considerable microstructural damage. An analysis of the deuterium depth profiles yields a room-temperature diffusion coefficient for deuterium of 1.4 x 10/sup -16/ m/sup 2/s/sup -1/ at high concentrations which is consistent with extrapolation of higher-temperature data available from other techniques for annealed material. At lower deuterium concentrations, < 10/sup -2/, in the aged material the extracted diffusion coefficient is a factor of three higher, implying a dependence on concentration. At concentrations < 10/sup -3/, diffusion may be hindered by dislocation trapping.

Lewis, M.B.; Farrell, K.

1980-01-01

82

Radon diffusion coefficients in soils of varying moisture content  

NASA Astrophysics Data System (ADS)

Radon is a naturally occurring radioactive gas that is generated in the Earth's crust and is free to migrate through soil and be released to the atmosphere. Due to its unique properties, soil gas radon has been established as a powerful tracer used for a variety of purposes, such as exploring uranium ores, locating geothermal resources and hydrocarbon deposits, mapping geological faults, predicting seismic activity or volcanic eruptions and testing atmospheric transport models. Much attention has also been given to the radiological health hazard posed by increased radon concentrations in the living and working environment. In order to exploit radon profiles for geophysical purposes and also to predict its entry indoors, it is necessary to study its transport through soils. Among other factors, the importance of soil moisture in such studies has been largely highlighted and it is widely accepted that any measurement of radon transport parameters should be accompanied by a measurement of the soil moisture content. In principle, validation of transport models in the field is encountered by a large number of uncontrollable and varying parameters; laboratory methods are therefore preferred, allowing for experiments to be conducted under well-specified and uniform conditions. In this work, a laboratory technique has been applied for studying the effect of soil moisture content on radon diffusion. A vertical diffusion chamber was employed, in which radon was produced from a 226Ra source, was allowed to diffuse through a soil column and was finally monitored using a silicon surface barrier detector. By solving the steady-state radon diffusion equation, diffusion coefficients (D) were determined for soil samples of varying moisture content (m), from null (m=0) to saturation (m=1). For dry soil, a D value of 4.1×10-7 m2s-1 was determined, which increased moderately by a factor of ~3 for soil with low moisture content, i.e. up to m ~0.2. At higher water fractions, a decrease in D was initiated and became particularly pronounced approaching complete saturation; at m =0.9, D was as low as 2×10-9 m2s-1. A series of field experiments has also been conducted using alpha-track CR-39 detectors to follow the moisture-dependence of radon diffusion through soil under natural conditions. Diffusion coefficients were determined as a function of surface soil moisture assuming a one-dimensional diffusive radon transport model. Comparison between results obtained by the two methods showed that laboratory studies may provide a good indication of radon diffusion coefficients to be expected in the field. However, values determined in the field were systematically lower than those assessed in the laboratory. This finding could be attributed to soil-dependent parameters, such as differences in pore space geometry between the soil used in laboratory experiments and the undisturbed soil. In the latter case, the higher degree of compaction imposes a more tortuous pathway to soil gas, while at the same time the diffusive gas flux is hindered by local-scale zones of higher bulk density or water content.

Papachristodoulou, C.; Ioannides, K.; Pavlides, S.

2009-04-01

83

Coefficient inverse problem for a fractional diffusion equation  

NASA Astrophysics Data System (ADS)

In this paper, we consider an initial/boundary value problem for a fractional diffusion equation in a bounded domain ?: \\partial _t^{\\alpha }u = \\Delta u + p(x)u where \\partial _t^{\\alpha } is the Caputo derivative and 0 < ? < 2, ? ? 1. We discuss an inverse problem of determining spatial coefficient p(x), x ? ? and/or order ? of the fractional derivative by data u|? × (0, T), where ??? is a sub-domain. Our main result is the uniqueness under conditions where the initial value is positive and ? is a neighbourhood of ??. The proof is done by transforming the solution u to the solution of the wave equation.

Miller, Luc; Yamamoto, Masahiro

2013-07-01

84

Self-diffusion of sodium ions in compacted sodium montmorillonite  

SciTech Connect

Diffusion of sodium ions through compacted sodium montmorillonite in a water-saturated state was studied to obtain fundamental information for performance assessments of geological disposal of high-level radioactive waste. Basal spacings obtained from X-ray diffraction measurements indicated a decrease in the interlamellar spacing with increasing dry density of the montmorillonite; the three-water-layer hydrate was observed at low dry density, and the two-water-layer hydrate was observed at high dry density, whereas both were observed at dry densities between 1.4 and 1.5 Mg/m{sup 3}. Activation energies from 14.1 to 24.7 kJ/mol were obtained from the temperature dependence of the self-diffusion coefficients of sodium ions. Activation energies lower than that for the diffusion of sodium ions in free water were found for montmorillonite specimens with dry densities of {le} 1.2 Mg/m{sup 3}, while higher activation energies were observed at dry densities {ge} 1.4 Mg/m{sup 3}. The pore water diffusion model, the general model used for migration of nuclides, is based on geometric parameters; however, findings cannot be explained by only the changes in the geometric parameters. Possible explanations for the dry density dependence of the activation energy are changes in the temperature dependence of the distribution coefficients of sodium ions on the montmorillonite, changes in the diffusion process with an increase in dry density, or both.

Kozaki, Tamotsu; Fujishima, Atsushi; Sato, Seichi; Ohashi, Hiroshi [Hokkaido Univ., Sapporo (Japan)

1998-01-01

85

Molecular Dynamics Simulation of Diffusion Coefficients of Oxygen, Nitrogen and Sodium Chloride in Supercritical Water  

NASA Astrophysics Data System (ADS)

Molecular dynamics simulation has been performed to determine the infinite-dilution diffusion coefficients of oxygen and nitrogen, and the diffusion coefficients of NaCl in supercritical water from 703.2-763.2 K and 30-45 MPa. The results obtained show that the diffusion coefficients in supercritical water increase with temperature, while decreasing with pressure. Nevertheless, the diffusion coefficients in supercritical water are much larger than those in normal water.

Xiao, Ji; Lu, Jiu-Fang; Chen, Jian; Li, Yi-Gui

2001-07-01

86

A study of Li-ion diffusion kinetics in the fullerene-coated Si anodes of lithium ion batteries  

Microsoft Academic Search

The diffusion coefficient of lithium ions in fullerene-coated silicon thin film electrodes, prepared by the plasma-assisted deposition technique, was estimated by a specific electrochemical measurement known as cyclic voltammetry (CV) and then compared with that of a bare silicon film used as the anode in lithium ion batteries. Based on our experimental range, the diffusion coefficient of the fullerene-coated Si

Arenst Andreas Arie; Joong Kee Lee

2010-01-01

87

ESTIMATION OF THE MOISTURE DIFFUSION COEFFICIENT OF POTATO DURING HOT-AIR DRYING  

Microsoft Academic Search

The purpose of this work, is to evaluate the moisture diffusion coefficient of potato during convective drying. Two models of diffusion have been performed to evaluate that coefficient. The first one based on Fick's law, when a model fitting procedure was applied to experimental drying data. The diffusion coefficient was found to vary with air temperature and also increase with

L. Hassini; S. Azzouz; A. Belghith

2004-01-01

88

Determination of lithium ion diffusion in lithium–manganese-oxide-spinel thin films by secondary-ion mass spectrometry  

Microsoft Academic Search

Lithium ion chemical diffusion coefficients in 6LiMn2O4 thin sputtered films (?2?m) were determined by the depth profiles of 7Li concentration after adopting the potential step in 7LiClO4\\/propylene carbonate solution by using secondary-ion mass spectrometry (SIMS). Lithium chemical diffusion coefficient via bulk (Dbulk) and grain boundary diffusion coefficient normalized with width (dDgb) were determined as 1.23×10?15m2s?1 and 6.55×10?20m3s?1, respectively.

Toyoki Okumura; Tomokazu Fukutsuka; Yoshiharu Uchimoto; Natsuko Sakai; Katsuhiko Yamaji; Harumi Yokokawa

2009-01-01

89

Proton transfer and the diffusion of H+ and OH- ions along water wires  

NASA Astrophysics Data System (ADS)

Hydrogen and hydroxide ion transport in narrow carbon nanotubes (CNTs) of diameter 8.1 Å and lengths up to 582 Å are investigated by molecular dynamics simulations using a dissociating water model. The diffusion coefficients of the free ions in an open chain are significantly larger than in periodically replicated wires that necessarily contain D or L end defects, and both are higher than they are in bulk water. The free hydroxide ion diffuses faster than the free hydronium ion in short CNTs, unlike diffusion in liquid water, and both coefficients increase and converge to nearly the same value with increasing tube length. The diffusion coefficients of the two ions increase further when the tubes are immersed in a water reservoir and they move easily out of the tube, suggesting an additional pathway for proton transport via OH- ions in biological channels.

Lee, Song Hi; Rasaiah, Jayendran C.

2013-09-01

90

Lead diffusion in apatite and zircon using ion implantation and Rutherford Backscattering techniques  

Microsoft Academic Search

Ion implantation was used to introduce Pb into the minerals zircon and apatite. Diffusion profiles were obtained using Rutherford Backscattering, and the results were fitted with a model to determine the diffusion coefficients. This approach is both simple and useful in studying diffusion over a temperature range of geologic interest without inordinate annealing times. Results for apatite over the temperature

D. J. Cherniak; W. A. Lanford; F. J. Ryerson

1991-01-01

91

Ca-Mg diffusion in diopside: tracer and chemical inter-diffusion coefficients  

NASA Astrophysics Data System (ADS)

We have experimentally determined the tracer diffusion coefficients (D*) of 44Ca and 26Mg in a natural diopside (~Di96) as function of crystallographic direction and temperature in the range of 950-1,150 °C at 1 bar and f(O2) corresponding to those of the WI buffer. The experimental data parallel to the a*, b, and c crystallographic directions show significant diffusion anisotropy in the a-c and b-c planes, with the fastest diffusion being parallel to the c axis. With the exception of logD*(26Mg) parallel to the a* axis, the experimental data conform to the empirical diffusion “compensation relation”, converging to logD ~ -19.3 m2/s and T ~ 1,155 °C. Our data do not show any change of diffusion mechanism within the temperature range of the experiments. Assuming that D* varies roughly linearly as a function of angle with respect to the c axis in the a-c plane, at least within a limited domain of ~20° from the c-axis, our data do not suggest any significant difference between D*(//c) and D*(?(001)), the latter being the diffusion data required to model compositional zoning in the (001) augite exsolution lamellae in natural clinopyroxenes. Since the thermodynamic mixing property of Ca and Mg is highly nonideal, calculation of chemical diffusion coefficient of Ca and Mg must take into account the effect of thermodynamic factor (TF) on diffusion coefficient. We calculate the dependence of the TF and the chemical interdiffusion coefficient, D(Ca-Mg), on composition in the diopside-clinoenstatite mixture, using the available data on mixing property in this binary system. Our D*(Ca) values parallel to the c axis are about 1-1.5 log units larger than those Dimanov et al. (1996). Incorporating the effect of TF, the D(Ca-Mg) values calculated from our data at 1,100-1,200 °C is ~0.6-0.7 log unit greater than the experimental quasibinary D((Ca-Mg + Fe)) data of Fujino et al. (1990) at 1 bar, and ~0.6 log unit smaller than that of Brady and McCallister (1983) at 25 kb, 1,150 °C, if our data are normalized to 25 kb using activation volume (~4 and ~6 cm3/mol for Mg and Ca diffusion, respectively) calculated from theoretical considerations.

Zhang, Xiaoyu; Ganguly, Jibamitra; Ito, Motoo

2009-08-01

92

Anomalous ion diffusion within skeletal muscle transverse tubule networks  

PubMed Central

Background Skeletal muscle fibres contain transverse tubular (t-tubule) networks that allow electrical signals to rapidly propagate into the fibre. These electrical signals are generated by the transport of ions across the t-tubule membranes and this can result in significant changes in ion concentrations within the t-tubules during muscle excitation. During periods of repeated high-frequency activation of skeletal muscle the t-tubule K+ concentration is believed to increase significantly and diffusive K+ transport from the t-tubules into the interstitial space provides a mechanism for alleviating muscle membrane depolarization. However, the tortuous nature of the highly branched space-filling t-tubule network impedes the diffusion of material through the network. The effective diffusion coefficient for ions in the t-tubules has been measured to be approximately five times lower than in free solution, which is significantly different from existing theoretical values of the effective diffusion coefficient that range from 2–3 times lower than in free solution. To resolve this discrepancy, in this paper we study the process of diffusion within electron microscope scanned sections of the skeletal muscle t-tubule network using mathematical modelling and computer simulation techniques. Our model includes t-tubule geometry, tautness, hydrodynamic and non-planar network factors. Results Using our model we found that the t-tubule network geometry reduced the K+ diffusion coefficient to 19–27% of its value in free solution, which is consistent with the experimentally observed value of 21% and is significantly smaller than existing theoretical values that range from 32–50%. We also found that diffusion in the t-tubules is anomalous for skeletal muscle fibres with a diameter of less than approximately 10–20 ?m as a result of obstructed diffusion. We also observed that the [K+] within the interior of the t-tubule network during high-frequency activation is greater for fibres with a larger diameter. Smaller skeletal muscle fibres are therefore more resistant to membrane depolarization. Because the t-tubule network is anisotropic and inhomogeneous, we also found that the [K+] distribution generated within the network was irregular for fibres of small diameter. Conclusion Our model explains the measured effective diffusion coefficient for ions in skeletal muscle t-tubules.

Shorten, Paul R; Soboleva, Tanya K

2007-01-01

93

Evaluation of ligand-selector interaction from effective diffusion coefficient.  

PubMed

We present an analytical technique for determination of ligand-selector equilibrium binding constants. The method is based on the measurements of effective molecular diffusion coefficient of the ligand during Poiseuille flow through a long (approximately 25 m), thin (0.254 mm +/- 0.05 mm ID) capillary with and without the selector. The data are analyzed using the Taylor dispersion theory. Bovine Serum Albumin (BSA) and cyclodextrin (CD) were taken as model selectors. We have tested our method on the following selector-ligand complexes: BSA with warfarin, propranolol, noscapine, salicylic acid, and riboflavin, and cyclodextrin with 4-nitrophenol. The results are in good agreement with data from the literature and with our own results obtained within classical chromatography. This method works equally well for uncharged and charged compounds. PMID:20536185

Bielejewska, Anna; Bylina, Andrzej; Duszczyk, Kazimiera; Fia?kowski, Marcin; Ho?yst, Robert

2010-07-01

94

CRRES electric field power spectra and radial diffusion coefficients  

NASA Astrophysics Data System (ADS)

Combined Release and Radiation Effects Satellite (CRRES) Electric Field Instrument (EFI) data are used to determine the electric field power spectral density as a function of L and Kp over the frequency range 0.2 to 15.9 mHz. The power at each frequency is fit to the function P(L, Kp) = a Lb exp(cKp). Assuming a purely electrostatic field and making several other assumptions regarding the azimuthal dependence of the field fluctuations, a Kp-dependent radial diffusion coefficient DLLE is computed from the power spectra. The model average DLLE for high activity (Kp = 6) are between 1 to 2 orders of magnitude larger than that for low activity (Kp = 1), dependent upon L and first invariant.

Brautigam, D. H.; Ginet, G. P.; Albert, J. M.; Wygant, J. R.; Rowland, D. E.; Ling, A.; Bass, J.

2005-02-01

95

Binary diffusion coefficients of low-density mixtures of alkanes  

NASA Astrophysics Data System (ADS)

The aim of this study is to present a reliable procedure for the calculation of the temperature dependencies of binary diffusion coefficients DAB of low-density mixtures of small alkanes CmH2m+2 (m<6) by means of the (nAB-6) Lennard Jones temperature dependent potential (LJTDP) in the temperature range 200 - 1200 K and pressures p <=0.10MPa. The parameters of the potential of interaction of unlike particles - potential well depth epsilonAB(T) and equilibrium distance RmAB(T) are obtained from corresponding pure alkanes potential parameters using the Hohm-Zarkova-Damyanova (HZD) mixing rule. A good agreement between the calculated and experimental values is obtained for those systems for which direct measurements and recalculations from mixture viscosity data are available.

Zarkova, L.; Hohm, U.; Damyanova, M.

2008-05-01

96

Diffusion Coefficient of Tritium Through Molten Salt Flibe and Rate of Tritium Leak from Fusion Reactor System  

SciTech Connect

Diffusion coefficients of hydrogen isotopes in Flibe were correlated with making reference to previous relating data of F{sup -} ion self-diffusivity and Flibe viscosity and so on. Rates of tritium permeation through structural materials in a fusion reactor system with Flibe blanket were estimated comparatively under conditions with or without a Flibe permeation barrier. A way to lower the tritium leak rate below a level regulated by law was proposed, and its effectiveness was discussed.

Fukada, Satoshi [Kyushu University (Japan); Anderl, Robert A. [Idaho National Engineering and Environmental Laboratory (United States); Sagara, Akio [National Institute for Fusion Science (Japan); Nishikawa, Masabumi [Kyushu University (Japan)

2005-07-15

97

Measurements of reflection coefficient of ion waves in an ion beam-plasma system  

NASA Astrophysics Data System (ADS)

The reflection coefficient of ion waves in an ion beam-plasma system is studied using a bipolar electrode as a reflector. It is found that the reflection coefficient of the beam mode is independent of the pulse widths of incident waves, while that of ion-acoustic waves is a decreasing function of frequency.

Noda, Shunichi; Nakamura, Yoshiharu; Kawai, Yoshinobu; Akazaki, Masanori

1988-12-01

98

Diffusion coefficients of cerium and gadolinium in molten LiCl-KCl  

SciTech Connect

The most important step in the pyrometallurgical reprocessing is the electrorefining in molten chlorides. In this step, spent metal fuel is anodically dissolved into LiCl-KCl eutectic melt, and the actinides are selectively recovered at the cathodes due to the differences among the redox potentials of the elements, while fission products remain in the anode and in the electrolyte salt. The diffusion coefficients of Ce(III) and Gd(III) in LiCl-KCl eutectic melt were determined in the temperature range between 673 and 823 K by chronopotentiometry. A new method was devised to minimize the error in defining the surface area of the working electrode. The immersed depth of the working electrode was changed by stages, and the relation between the change in the square root of the transition time and that in the surface area of the working electrode was substituted into the Sand equation instead of their absolute values. The activation energies for diffusion and the diffusion coefficients of lanthanide ions in LiCl-KCl are discussed in connection with their ionic radii and the stability of their complex ions.

Iizuka, Masatoshi [Central Research Inst. of Electric Power Industry, Tokyo (Japan)

1998-01-01

99

Numerical study of one-dimensional replicating patterns in reaction- diffusion systems with non-linear diffusion coefficients.  

National Technical Information Service (NTIS)

A numerical study of the dynamics of pattern evolution in reaction- diffusion systems is performed, although limited to one spatial dimension. The diffusion coefficients are nonlinear, based on powers of the scalar variables. The system keeps the dynamics...

J. Ferreri A. Carmen

1998-01-01

100

Translational diffusion coefficient of cycloamylose in aqueous sodium hydroxide.  

PubMed

Seven cyclic (1 --> 4)-alpha-D-glucan (cycloamylose) samples ranging in weight-average molecular weight from 5 x 10(3) to 1.8 x 10(4) and gamma-cyclodextrin have been studied by sedimentation equilibrium in dimethylsulfoxide (at 25 degrees C) and by dynamic light scattering in 0.5 N aqueous sodium hydroxide (at 25 degrees C), a good solvent for linear amylose. The measured translational diffusion coefficients D in the aqueous NaOH agree fairly closely with previous Monte Carlo results for cyclic (1 --> 4)-alpha-D-glucan chains with excluded volume, when correction is made for the effects of bead diameter and fluctuating hydrodynamic interaction (HI) on the Kirkwood theory on which the computation of D was based. These D data are also explained almost quantitatively by Yamakawa and Fujii's expression for the associated KP ring (based on the Kratky-Porod wormlike chain) with the molecular parameters for linear amylose if the fluctuating HI and excluded-volume effects are taken into account. It is concluded that the translational diffusion behavior of cycloamylose in the aqueous NaOH is consistent with the conformational characteristics derived from the conformational energy of maltose and dilute-solution data for linear amylose. PMID:12879496

Nakata, Yasushi; Amitani, Keiji; Norisuye, Takashi; Kitamura, Shinichi

2003-08-01

101

Defect diffusion in ion implanted glasses  

Microsoft Academic Search

Ion implantation in glasses produces structure modifications at depths greater than those of the implanted ion range. Such a result is evidenced by means of leaching experiments, alkali element depletion, distribution of gaseous implanted species, etching rate as function of depth. A systematic study with the aim to evidence a threshold in the nuclear deposited energy for defect diffusion is

G. W. Arnold; G. Battaglin; A. Boscolo-Boscoletto; F. Caccavale; G. de Marchi; P. Mazzoldi; A. Miotello

1992-01-01

102

Defect diffusion in ion implanted glasses  

Microsoft Academic Search

Ion implantation in glasses produces structure modifications at depths greater than those of the implanted ion range. Such a result is evidenced by means of leaching experiments, alkali element depletion, distribution of gaseous implanted species, etching rate as function of depth. A systematic study with the aim to evidence a threshold in the nuclear deposited energy for defect diffusion is

G. W. Arnold; G. Battaglin; A. Boscolo-Boscoletto; F. Caccavale; G. De Marchi; P. Mazzoldi; A. Miotello

1991-01-01

103

Diffusion of ion-exchanging electrolytes in montmorillonite gels  

SciTech Connect

The primary contributions of this work are: (1) Development of a unique radially perfused diffusion cell suitable for measuring transient diffusion rates in compacted, highly adsorbing and swelling porous media such as montmorillonite clay gels; (2) examination of the effective diffusion coefficient (D{sub 6}) of electrolytes in montmorillonite clay gels; and (3) Measurement of the transient diffusion rates of cesium, chloride and tritium in 15 w/o montmorillonite clay gels at pH 9 and sodium chloride backgrounds of 10{sup {minus}1} to 10{sup {minus}3} kmol/m{sup 3}. Results are interpreted by using the dilute limit of the multicomponent transport equations derived for species migration in a single clay pore after macroscopic averaging. The tortuosity of the clay gel is found by tritium diffusion. Transient chloride diffusion rates are found to be at molecular rates. Negative adsorption of anions from the clay gel, required for an a priori prediction of chloride profiles, are calculated from site-binding theory. Surface diffusion is the primary mode of cesium transport in montmorillonite clay gels. Migration of cesium is primarily along the inner Helmholtz plane of clay particles. The primary implication for the montmorillonite clay-based packing as a nuclear waste migration barrier is that surface diffusion must be included to describe properly diffusion rates of either anions or cations. Currently surface diffusion is neglected and cesium penetration into the packing is drastically underestimated. Penetration depths of anions is grossly overestimated. In either case, the appropriate diffusion coefficient of ions in compacted packing will be in considerable error relative to current design recommendations.

Jahnke, F.M.

1987-01-01

104

Analysis of fluorophore diffusion by continuous distributions of diffusion coefficients: application to photobleaching measurements of multicomponent and anomalous diffusion.  

PubMed Central

Fluorescence recovery after photobleaching (FRAP) is widely used to measure fluorophore diffusion in artificial solutions and cellular compartments. Two new strategies to analyze FRAP data were investigated theoretically and applied to complex systems with anomalous diffusion or multiple diffusing species: 1) continuous distributions of diffusion coefficients, alpha(D), and 2) time-dependent diffusion coefficients, D(t). A regression procedure utilizing the maximum entropy method was developed to resolve alpha(D) from fluorescence recovery curves, F(t). The recovery of multi-component alpha(D) from simulated F(t) with random noise was demonstrated and limitations of the method were defined. Single narrow Gaussian alpha(D) were recovered for FRAP measurements of thin films of fluorescein and size-fractionated FITC-dextrans and Ficolls, and multi-component alpha(D) were recovered for defined fluorophore mixtures. Single Gaussian alpha(D) were also recovered for solute diffusion in viscous media containing high dextran concentrations. To identify anomalous diffusion from FRAP data, a theory was developed to compute F(t) and alpha(D) for anomalous diffusion models defined by arbitrary nonlinear mean-squared displacement versus time relations. Several characteristic alpha(D) profiles for anomalous diffusion were found, including broad alpha(D) for subdiffusion, and alpha(D) with negative amplitudes for superdiffusion. A method to deduce apparent D(t) from F(t) was also developed and shown to provide useful complementary information to alpha(D). alpha(D) and D(t) were determined from photobleaching measurements of systems with apparent anomalous subdiffusion (nonuniform solution layer) and superdiffusion (moving fluid layer). The results establish a practical strategy to characterize complex diffusive phenomena from photobleaching recovery measurements.

Periasamy, N; Verkman, A S

1998-01-01

105

Determination of the diffusion coefficient of tissue, cuticle, cutin and wax of apple  

Microsoft Academic Search

The cuticle of apple basically consists of a cutin and wax layer in parallel each with different diffusion properties. Diffusion coefficients were determined for the apple cultivars ‘Jonagold’, ‘Jonagored’ and ‘Elstar’ to accurately describe moisture transport through the cuticular membrane. Separate diffusion coefficients were estimated for tissue, cutin and wax of each cultivar by fitting model predictions, obtained with the

Els A Veraverbeke; Pieter Verboven; Nico Scheerlinck; My Lan Hoang

2003-01-01

106

A new way for determining the chloride diffusion coefficient in concrete from steady state migration test  

Microsoft Academic Search

This paper presents a new method for measuring the chloride diffusion coefficient in concrete from steady state migration tests. First, we review concepts of the steady-state diffusion and migration tests. We emphasize that these tests have limitations if we use them in the classical way. Then, we show how it is possible to determine the chloride diffusion coefficient from a

O. Truc; J. P. Ollivier; M. Carcassès

2000-01-01

107

Diffusion coefficients of methanol and water and the mutual diffusion coefficient in methanol-water solutions at 278 and 298 K  

SciTech Connect

Diffusion coefficients have been measured for methanol and water in their mixtures over the full composition range at 278.15 and 298.15 K. By defining a reduced coefficient D/sup +/+/ for each component an extensive correlation in diffusional behavior has been identified for the two species. The correlation increases with decreasing temperature. Examination of literature data for acetonitrile-water and acetone-water at 298.15 K shows that similar correlations are not present in those systems. Data are also reported for the mutual diffusion coefficients for the methanol-water system at both temperatures and these are used to obtain velocity correlation coefficients. The Albright equation relating the shear viscosity of a mixture to the diffusion coefficients of its components is examined by using the diffusion data and an interaction parameter introduced. 21 references, 5 figures, 5 tables.

Derlacki, Z.J.; Easteal, A.J.; Edge, A.V.J.; Woolf, L.A.; Roksandic, Z.

1985-11-21

108

Molecular dynamics simulations on oxygen ion diffusion in strained YSZ\\/CeO 2 superlattice  

Microsoft Academic Search

Our earlier molecular dynamics results show that the construction of a strained yttria-stabilized zirconia (YSZ)\\/CeO2 superlattice considerably enhances oxygen ion diffusion. In the present study, effect of several parameters (e.g., Y2O3 concentrations, stacking periodicity, and temperature) on oxygen ion diffusion in strained YSZ\\/CeO2 superlattice were optimized to rationalize the understanding of the process mechanism. We found that self-diffusion coefficient of

Ken Suzuki; Akira Endou; Ryuji Miura; Yasunori Oumi; Hiromitsu Takaba; Momoji Kubo; Abhijit Chatterjee; Adil Fahmi; Akira Miyamoto

1998-01-01

109

Diffusion studies with radioactive ions  

NASA Astrophysics Data System (ADS)

An overview of the modified radiotracer based diffusion studies carried out at IGISOL is provided. The experimental procedures are briefly described followed by examples involving IGISOL as the key facility. In this respect the studies related to silicon-germanium (Si1 - xGex) alloys and on the related diffusion systematics are summarized. Another group of examples is related to mobility determination of lead isotopes in glass for verifying retrospective radon measurements. Finally an outlook to future possibilities related to employing radiotracers in solid state research is provided.

Räisänen, J.; Whitlow, H. J.

2012-03-01

110

Efficient Method for Calculating Axial Diffusion Coefficients in Two-Dimensional Low Density Channel  

Microsoft Academic Search

An efficient calculation method of an axial diffusion coefficient which is applicable to multi-region and two-dimensional geometries has been developed. This diffusion coefficient which requires biquadratic numerical integration is quickly calculated by using a Good Lattice Point Method. Total computational time is about one-thirty hundredth that of Romberg's Method. The geometry dependency of axial diffusion coefficient is investigated. As a

Kaoru KOBAYASHI

1991-01-01

111

Oxygen diffusion in ion-implanted layer of Nb-doped SrTiO3  

Microsoft Academic Search

Oxygen diffusion phenomena were investigated on Nb-doped SrTiO3 crystals after Ar or F ion implantation. SIMS measurements indicated that oxygen diffusion profiles consisted of high and low diffusivity regions; the profiles were analyzed by a two-layer model and diffusion coefficients were evaluated. According to TEM observation, there existed three layers in the implanted region whose boundaries were in good agreement

I. Sakaguchi; H. Haneda; S. Hishita; A. Watanabe; J. Tanaka

1994-01-01

112

Parameter estimation method for flash thermal diffusivity with two different heat transfer coefficients.  

National Technical Information Service (NTIS)

Determining thermal diffusivity using flash diffusivity tests at high temperatures is investigated using parameter estimation. One aspect is development of a method for determining two different heat transfer coefficients, one at the heated face and one a...

J. V. Beck R. Dinwiddie

1995-01-01

113

Estimation of diffusion coefficients for electrolytes in hot water. Final report. [PWR  

SciTech Connect

Diffusion coefficients are calculated for electrolytes dissolved in water at temperatures 25 to 300/sup 0/C and saturation pressures. Plots and tables are given of estimated diffusion coefficients for NaCl at concentrations from infinite dilution to 4 molal, limiting diffusion coefficients for divalent metal chlorides and for sodium phosphates of several compositions, and tracer diffusion coefficients for hydrochloric acid in sodium chloride solutions up to 4 molal. These data are useful for analysis of mass transport processes, such as concentration, corrosion, deposition, dissolution, dilution and neutralization, that can occur in nuclear steam generators and other power station apparatus.

Lindsay, W.T. Jr.

1981-08-01

114

Defect diffusion in ion implanted glasses  

SciTech Connect

Ion implantation in glasses produces structure modifications at depths greater than those of the implanted ion range. Such a result is evidenced by means of leaching experiments, alkali element depletion, distribution of gaseous implanted species, etching rate as function of depth. A systematic study with the aim to evidence a threshold in the nuclear deposited energy for defect diffusion is presented. Fourier transform infrared spectroscopy measurements confirm the glass modifications at extended depths. 20 refs., 5 figs.

Arnold, G.W. (Sandia National Labs., Albuquerque, NM (United States)); Battaglin, G. (Venice Univ. (Italy). Dipt. di Chimica Fisica); Boscolo-Boscoletto, A. (Centro Ricerche Montedipe, Venice (Italy)); Caccavale, F.; De Marchi, G.; Mazzoldi, P. (Pauda Univ. (Italy). Dipt. di Fisica); Miotello, A. (Trento Univ. (Italy). Dipt. di Fisica)

1991-01-01

115

Brain Tumors: Apparent Diffusion Coefficient at Magnetic Resonance Imaging  

Microsoft Academic Search

\\u000a Diffusion-weighted magnetic resonance imaging (MRI) provides information on water mobility or diffusion within tissues by\\u000a allowing visualization of the Brownian motion in those tissues. Also called diffusion-weighted imaging (DWI), this technique\\u000a involves the use of phase-defocusing and phase-refocusing gradients to evaluate the rates of microscopic water diffusion within\\u000a tissues, which allows visualization and characterization of biological tissues at a microscopic

Fumiyuki Yamasaki; Kazuhiko Sugiyama; Kaoru Kurisu

116

Apparent diffusion coefficient mapping of experimental focal cerebral ischemia using diffusion-weighted echo-planar imaging  

Microsoft Academic Search

Diffusion-weighted, echo-planar imaging (EPI) was used to map regional changes in the apparent diffusion coefficient (ADC) during experimental focal ischemia in the rat brain following permanent middle cerebral arterial occlusion (MCAO). Sixteen 64 x 64 diffusion-weighted EPIs were acquired in 32 s with successively increasing amplitudes of the diffusion-sensitive gradient pulses. A linear least-squares regression algorithm was used to fit

Bernard J. Dardzinski; Christopher H. Sotak; Marc Fisher; Yasuhiro Hasegawa; Lirnin Li; Kazuo Minematsu

1993-01-01

117

Radon diffusion coefficients of vapour barrier membranes used in Canadian building construction.  

PubMed

Vapour barrier membranes are often used as soil gas retarder in building construction. While vapour permeance characteristics of these membranes are well known and specified in Canadian standards, their radon diffusion coefficients are yet not available. This study provides test results of radon diffusion coefficients for 10 vapour barrier membranes commonly used in Canadian building construction. PMID:19214548

Chen, Jing; Ly, Jim; Schroth, Eveline; Hnatiuk, Stan; Frenette, Etienne; Blain, Marie-France

2009-02-12

118

Mutual Diffusion Coefficient and Dynamic Viscosity Near the Critical Consolute Point Probed by Dynamic Light Scattering  

Microsoft Academic Search

The possibility of applying dynamic light scattering to simultaneous determination of the mutual diffusion coefficient and the viscosity of binary liquid systems was studied near the critical consolute point. When seed particles are added to the system, the particle diffusion coefficient is measured, and the viscosity is obtained using the Stokes–Einstein relation. Since the amplitude of light scattered from concentration

S. Will; A. Leipertz

1999-01-01

119

Simulating the Gas Diffusion Coefficient in Macropore Network Images: Influences of Soil Pore Morphology  

Technology Transfer Automated Retrieval System (TEKTRAN)

Knowledge of the diffusion coefficient is necessary for modeling gas transport in soils and other porous media. This study was conducted to determine the relationship between the diffusion coefficient and pore structure parameters, such as the fractal dimension of pores (Dmp), the shortest path leng...

120

Diffusion Coefficients of Three Organic Solutes in Aqueous Sodium Dodecyl Sulfate Solutions  

Microsoft Academic Search

Tracer diffusion coefficients of phenol, toluene, and benzoic acid in aqueous solutions of sodium dodecyl sulfate (SDS) were measured by the Taylor dispersion technique. In addition, the viscosities and densities of the SDS solutions were measured. For phenol and toluene, the effect of micelle formation on the diffusion coefficient is pronounced. When the SDS concentration is below the critical micelle

Xiao-ning Yang; Michael A. Matthews

2000-01-01

121

Diffusion coefficients for some organic and organometallic compounds using quartz crystal microbalance  

Microsoft Academic Search

The diffusion coefficient data for organometallic substances are scarce in the literature. A recently developed quartz crystal microbalance (QCM) system has been used to measure the binary diffusion coefficients. The system consists of a QCM with a driving oscillator circuit, a closed Stefan tube, a temperature controlled unit, a data logger, and a frequency counter. The QCM crystal is placed

M. Aslam Siddiqi; Rehan A. Siddiqui; Burak Atakan

122

Estimation of Diffusion Coefficients for Electrolytes in Hot Water. Final Report.  

National Technical Information Service (NTIS)

Diffusion coefficients are calculated for electrolytes dissolved in water at temperatures 25 to 300 exp 0 C and saturation pressures. Plots and tables are given of estimated diffusion coefficients for NaCl at concentrations from infinite dilution to 4 mol...

W. T. Lindsay

1981-01-01

123

Self-diffusion of lithium ions in a lithium niobate single crystal  

Microsoft Academic Search

Using stable Li 6 and Li 7 isotopes, the authors measured the coefficients of diffusion of lithium ions in an LiNb0â single crystal in the direction of growth of the crystal. Comparison of the experimentally measured electrical conductivity at a partial oxygen pressure of 10⁵ Pa with the value calculated from the values of the coefficient of diffusion using the

V. B. Ptashnik; T. Y. Dunaeva; I. V. Myasnikov

1986-01-01

124

Diffusion coefficient of an inclusion in a liquid membrane supported by a solvent of arbitrary thickness  

NASA Astrophysics Data System (ADS)

The diffusion coefficient of an inclusion in a liquid membrane is investigated by taking into account the interaction between membranes and bulk solvents of arbitrary thickness. As illustrative examples, the diffusion coefficients of two types of inclusions, a circular domain composed of fluid with the same viscosity as the host membrane and that of a polymer chain embedded in the membrane, are studied. The diffusion coefficients are expressed in terms of the hydrodynamic screening lengths, which vary according to the solvent thickness. When the membrane fluid is dragged by the solvent of finite thickness, via stick boundary conditions, multiple hydrodynamic screening lengths together with the weight factors to the diffusion coefficients are obtained from the characteristic equation. The conditions for which the diffusion coefficients can be approximated by the expression including only a single hydrodynamic screening length are also shown.

Seki, Kazuhiko; Ramachandran, Sanoop; Komura, Shigeyuki

2011-08-01

125

Diffusion coefficient of an inclusion in a liquid membrane supported by a solvent of arbitrary thickness.  

PubMed

The diffusion coefficient of an inclusion in a liquid membrane is investigated by taking into account the interaction between membranes and bulk solvents of arbitrary thickness. As illustrative examples, the diffusion coefficients of two types of inclusions, a circular domain composed of fluid with the same viscosity as the host membrane and that of a polymer chain embedded in the membrane, are studied. The diffusion coefficients are expressed in terms of the hydrodynamic screening lengths, which vary according to the solvent thickness. When the membrane fluid is dragged by the solvent of finite thickness, via stick boundary conditions, multiple hydrodynamic screening lengths together with the weight factors to the diffusion coefficients are obtained from the characteristic equation. The conditions for which the diffusion coefficients can be approximated by the expression including only a single hydrodynamic screening length are also shown. PMID:21929018

Seki, Kazuhiko; Ramachandran, Sanoop; Komura, Shigeyuki

2011-08-04

126

PITCH-ANGLE DIFFUSION COEFFICIENTS OF CHARGED PARTICLES FROM COMPUTER SIMULATIONS  

SciTech Connect

Pitch-angle diffusion is a key process in the theory of charged particle scattering by turbulent magnetic plasmas. This process is usually assumed to be diffusive and can, therefore, be described by a pitch-angle diffusion or Fokker-Planck coefficient. This parameter controls the parallel spatial diffusion coefficient as well as the parallel mean free path of charged particles. In the present paper, we determine pitch-angle diffusion coefficients from numerical computer simulations. These results are then compared with results from analytical theories. Especially, we compare the simulations with quasilinear, second-order, and weakly nonlinear diffusion coefficients. Such a comparison allows the test of previous theories and will lead to an improved understanding of the mechanism of particle scattering.

Qin, G. [State Key Laboratory of Space Weather, Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing 100190 (China); Shalchi, A. [Permanent Address: Institut fuer Theoretische Physik, Lehrstuhl IV: Weltraum- und Astrophysik, Ruhr-Universitaet Bochum, D-44780 Bochum, Germany. (Germany)

2009-12-10

127

Single-Image Diffusion Coefficient Measurements of Proteins in Free Solution  

PubMed Central

Diffusion coefficient measurements are important for many biological and material investigations, such as studies of particle dynamics and kinetics, and size determinations. Among current measurement methods, single particle tracking (SPT) offers the unique ability to simultaneously obtain location and diffusion information about a molecule while using only femtomoles of sample. However, the temporal resolution of SPT is limited to seconds for single-color-labeled samples. By directly imaging three-dimensional diffusing fluorescent proteins and studying the widths of their intensity profiles, we were able to determine the proteins' diffusion coefficients using single protein images of submillisecond exposure times. This simple method improves the temporal resolution of diffusion coefficient measurements to submilliseconds, and can be readily applied to a range of particle sizes in SPT investigations and applications in which diffusion coefficient measurements are needed, such as reaction kinetics and particle size determinations.

Zareh, Shannon Kian; DeSantis, Michael C.; Kessler, Jonathan M.; Li, Je-Luen; Wang, Y.M.

2012-01-01

128

Single-image diffusion coefficient measurements of proteins in free solution.  

PubMed

Diffusion coefficient measurements are important for many biological and material investigations, such as studies of particle dynamics and kinetics, and size determinations. Among current measurement methods, single particle tracking (SPT) offers the unique ability to simultaneously obtain location and diffusion information about a molecule while using only femtomoles of sample. However, the temporal resolution of SPT is limited to seconds for single-color-labeled samples. By directly imaging three-dimensional diffusing fluorescent proteins and studying the widths of their intensity profiles, we were able to determine the proteins' diffusion coefficients using single protein images of submillisecond exposure times. This simple method improves the temporal resolution of diffusion coefficient measurements to submilliseconds, and can be readily applied to a range of particle sizes in SPT investigations and applications in which diffusion coefficient measurements are needed, such as reaction kinetics and particle size determinations. PMID:22500769

Zareh, Shannon Kian; DeSantis, Michael C; Kessler, Jonathan M; Li, Je-Luen; Wang, Y M

2012-04-03

129

Analysis of diffusion coefficient distributions in humic and fulvic acids by means of diffusion ordered NMR spectroscopy.  

PubMed

The use of the computer program CONTIN to analyze pulsed-field gradient NMR (PFG-NMR) data for several standard humic and fulvic acids is described. An advantage of PFG-NMR analysis is that integration of different spectral regions provides a picture of how the diffusion coefficients vary with functional group composition for a given sample. Using prior knowledge of the sample and the principle of parsimony, CONTIN approximates a solution to the inverse Laplace transform applied to the decay of peak intensity with gradient area in the PFG-NMR experiment. Thus, a continuous distribution of diffusion coefficients is resolved for the polydisperse humic and fulvic acids. The results of the CONTIN analyses are in the form of a distribution function and a two-dimensional DOSY plot. The 2D DOSY spectrum displays chemical shifts along one axis and diffusion coefficients along the other, while a number-average diffusion coefficient, D(N), a weight-average diffusion coefficient, D(W), and a most probable diffusion coefficient, D(P), are realized from the diffusion coefficient distribution. For all spectral regions of each humic sample, D(W) was greater than D(N), which in turn was greater than or equal to the D(P), suggesting that the diffusion coefficient distribution is weighted toward smaller, more rapidly diffusing molecules. Polydispersities, estimated from the ratio D(W)/D(N), were less than the reported M(W)/M(N) values for similar humic substances. Thus, the D(W)/D(N) ratio obtained by CONTIN analysis of PFG-NMR data can be at least a qualitative, and at best a semiquantitative, indication of the polydispersity of the humic sample, but should not be used as a quantitative measure of polydispersity. PMID:21662729

Morris, K F; Cutak, B J; Dixon, A M; Larive, C K

1999-12-01

130

Correlation of transverse and rotational diffusion coefficient: a probe of chemical composition in hydrocarbon oils.  

PubMed

Measurements of relaxation time and diffusion coefficient by nuclear magnetic resonance are well-established techniques to study molecular motions in fluids. Diffusion measurements sense the translational diffusion coefficients of the molecules, whereas relaxation times measured at low magnetic fields probe predominantly the rotational diffusion of the molecules. Many complex fluids are composed of a mixture of molecules with a wide distribution of sizes and chemical properties. This results in correspondingly wide distributions of measured diffusion coefficients and relaxation times. To first order, these distributions are determined by the distribution of molecular sizes. Here we show that additional information can be obtained on the chemical composition by measuring two-dimensional diffusion-relaxation distribution functions, a quantity that depends also on the shape and chemical interactions of molecules. We illustrate this with experimental results of diffusion-relaxation distribution functions on a series of hydrocarbon mixtures. For oils without significant amounts of asphaltenes, the diffusion-relaxation distribution functions follow a power-law behavior with an exponent that depends on the relative abundance of saturates and aromatics. Oils with asphaltene deviate from this trend, as asphaltene molecules act as relaxation contrast agent for other molecules without affecting their diffusion coefficient significantly. In waxy oils below the wax appearance temperature a gel forms. This is reflected in the measured diffusion-relaxation distribution functions, where the restrictions due to the gel network reduce the diffusion coefficients without affecting the relaxation rates significantly. PMID:18335907

Mutina, Albina R; Hürlimann, Martin D

2008-03-12

131

The infinite dilution diffusion coefficient for A1(OH) 4- at 25°C  

NASA Astrophysics Data System (ADS)

The infinite dilution diffusion coefficient for Al(OH) 4- necessary to calculate fluxes of dissolved Al between sediments and overlying waters, was determined at 25°C. Measurements were made using the diaphragm-cell method by diffusing Al(OH) 4- spiked KBr solutions against KCL over a range of ionic strengths. The mean of 9 separate measurements gives 1.04 ± .02 × 10 -5cm 2/s as the infinite dilution diffusion coefficient for Al(OH) 4- at 25°C.

Mackin, James E.; Aller, Robert C.

1983-05-01

132

Ion diffusion at interfaces in hot plasmas  

SciTech Connect

There are many laboratory applications in which it is important to know how fast two hot, ionized materials mix across an initially sharp interface. The speed of this process is regulated by the interdiffusion coefficient for the species involved. In a previous work, a theoretical method for calculating the interdiffusion coefficient in a Binary Ionic Mixture (classical ions in a uniform, neutralizing background) was described and found to give excellent agreement with Molecular Dynamics estimates. The purpose of this report is to show how these results may be applied to a model of the plasma interface, including electric field effects, to give a good description of the mixing across it.

Boercker, D.B.; Warren, K.; Haggin, G.

1986-04-01

133

NMR measurements of solvent self-diffusion coefficients in polymer solutions  

NASA Astrophysics Data System (ADS)

The transport of solvents and other small molecules in polymer solutions is important in many areas such as reaction rates, drying of coatings, plasticizer loss, curing of resins, elimination of residual monomer, and controlled drug release. Some of the work done in our laboratory on the diffusion of small molecules in polymer solutions and dispersions is reviewed. The diffusion data was used to test the Vrentas and Duda's free-volume theory for self-diffusion coefficients; test the independence of the normalized solvent self-diffusion for several polymer-solvent systems; and predict the solvent loss curves for drying of coatings based on solvent self-diffusion coefficients.

Blum, Frank D.; Pickup, Stephen; Waggoner, R. Allen

1989-11-01

134

Lanthanide transport in stabilized zirconias: Interrelation between ionic radius and diffusion coefficient  

Microsoft Academic Search

The diffusion of all stable lanthanides was measured both in calcia stabilized zirconia (CSZ) and in yttria stabilized zirconia (YSZ) in the temperature range between 1286 and 1600 °C. The lanthanide diffusion coefficients obtained increase with increasing ionic radius. The experimental activation enthalpy of diffusion is near 6 eV for CSZ and between 4 and 5 eV for YSZ and

Martin Kilo; Marcela A. Taylor; Christos Argirusis; Günter Borchardt; Sylvain Weber; Hubert Scherrer; Robert A. Jackson

2004-01-01

135

Tracer-diffusion of cobalt ions in sodium and potassium nitrates in agar gel  

Microsoft Academic Search

Tracer-diffusion of Co2+ ions is studied in agar gel in the presence of sodium and potassium nitrates at 25°C. The diffusion coefficient values at various electrolyte concentrations are compared with the corresponding theoretical values computed on the basis of Onsager's theory. The deviations from the theory are attributed to the various co-occurring effects in the diffusion medium. The activation energy

Mahendrakumar K. Patil

1986-01-01

136

Non-metal diffusion coefficients for the Ta-C and Ta-N systems  

SciTech Connect

The diffusivity of carbon in tantalum and tantalum carbides was investigated in the temperature range 1,700--2,200 C, and that of nitrogen in tantalum and tantalum nitrides between 1,700--1,950 C. The concentration-independent diffusion coefficients were obtained in all phases by investigating the enhanced layer growth in wedge-shaped specimens. In the nonmetal-rich phases having a broad homogeneity range, i.e., in {delta}-TaC{sub 1{minus}x}, {beta}-Ta{sub 2}C{sub 1{minus}x} and {beta}-Ta{sub 2}N{sub 1{minus}x}, also the concentration-dependent diffusion coefficients were calculated and compared with the concentration-independent diffusion coefficients. The calculation of the concentration-dependent diffusion coefficients was performed by fitting a modified error function on the measured concentration profiles assuming the nonmetal diffusivity being an exponential function of the nonmetal concentration. Strong dependence of the diffusion coefficient on the nonmetal concentration was found for the {delta}-TaC{sub 1{minus}x} phase, whereas the nonmetal diffusion coefficients were nearly concentration-independent for {beta}-Ta{sub 2}C{sub 1{minus}x} and {beta}-Ta{sub 2}N{sub 1{minus}x}.

Rafaja, D.; Lengauer, W.; Wisenberger, H. [Vienna Univ. of Technology (Austria). Inst. for Chemical Technology of Inorganic Materials

1998-06-12

137

Glucocorticoid treatment of brain tumor patients: changes of apparent diffusion coefficient values measured by MR diffusion imaging  

Microsoft Academic Search

Glucocorticoids (GCC) generally are administered to patients with brain tumors to relieve neurological symptoms by decreasing the water content in a peritumoral zone of edema. We hypothesized that diffusion imaging and apparent diffusion coefficient (ADC) values could detect subtle changes of water content in brain tumors and in peritumoral edema after GCC therapy. The study consisted of 13 patients with

Sosuke Minamikawa; Kinuko Kono; Keiko Nakayama; Hiroyuki Yokote; Takahiko Tashiro; Akimasa Nishio; Mitsuhiro Hara; Yuichi Inoue

2004-01-01

138

The finger regime of thermosolutal convection with the equal diffusivity coefficients and mixed boundary conditions  

Microsoft Academic Search

As emphasized by Welander [Tellus 41A, 66, (1989)] in application to the diffusive regime of thermosolutal convection, double-diffusive effects can eventually manifest themselves even as the diffusivity coefficients are equal, when the components are governed by the ''mixed'' boundary conditions. In the present work, the equal-diffusivity analogue of another regime of thermosolutal convection, the finger regime, was considered. The stabilizing

Naftali Tsitverblit

1996-01-01

139

Scale dependence of the effective matrix diffusion coefficient:Evidence and preliminary interpretation  

SciTech Connect

The exchange of solute mass (through molecular diffusion) between fluid in fractures and fluid in the rock matrix is called matrix diffusion. Owing to the orders-of-magnitude slower flow velocity in the matrix compared to fractures, matrix diffusion can significantly retard solute transport in fractured rock, and therefore is an important process for a variety of problems, including remediation of subsurface contamination and geological disposal of nuclear waste. The effective matrix diffusion coefficient (molecular diffusion coefficient in free water multiplied by matrix tortuosity) is an important parameter for describing matrix diffusion, and in many cases largely determines overall solute transport behavior. While matrix diffusion coefficient values measured from small rock samples in the laboratory are generally used for modeling field-scale solute transport in fractured rock (Boving and Grathwohl, 2001), several research groups recently have independently found that effective matrix diffusion coefficients much larger than laboratory measurements are needed to match field-scale tracer-test data (Neretnieks, 2002; Becker and Shapiro, 2000; Shapiro, 2001; Liu et al., 2003, 2004a). In addition to the observed enhancement, Liu et al. (2004b), based on a relatively small number of field-test results, reported that the effective matrix diffusion coefficient might be scale dependent, and, like permeability and dispersivity, it seems to increases with test scale. This scale-dependence has important implications for large-scale solute transport in fractured rock. Although a number of mechanisms have been proposed to explain the enhancement of the effective matrix diffusion coefficient, the potential scale dependence and its mechanisms are not fully investigated at this stage. The major objective of this study is to again demonstrate (based on more data published in the literature than those used in Liu et al. [2004b]) the potential scale dependence of the effective matrix-diffusion coefficient, and to develop a preliminary explanation for this scale-dependent behavior.

Liu, Hui-Hai; Zhang, Yingqi; Molz, Fred J.

2006-04-30

140

Scale Dependence of Effective Matrix Diffusion Coefficient Evidence and Preliminary Interpertation  

SciTech Connect

The exchange of solute mass (through molecular diffusion) between fluid in fractures and fluid in the rock matrix is called matrix diffusion. Owing to the orders-of-magnitude slower flow velocity in the matrix compared to fractures, matrix diffusion can significantly retard solute transport in fractured rock, and therefore is an important process for a variety of problems, including remediation of subsurface contamination and geological disposal of nuclear waste. The effective matrix diffusion coefficient (molecular diffusion coefficient in free water multiplied by matrix tortuosity) is an important parameter for describing matrix diffusion, and in many cases largely determines overall solute transport behavior. While matrix diffusion coefficient values measured from small rock samples in the laboratory are generally used for modeling field-scale solute transport in fractured rock (Boving and Grathwohl, 2001), several research groups recently have independently found that effective matrix diffusion coefficients much larger than laboratory measurements are needed to match field-scale tracer-test data (Neretnieks, 2002; Becker and Shapiro, 2000; Shapiro, 2001; Liu et al., 2003,2004a). In addition to the observed enhancement, Liu et al. (2004b), based on a relatively small number of field-test results, reported that the effective matrix diffusion coefficient might be scale dependent, and, like permeability and dispersivity, it seems to increases with test scale. This scale-dependence has important implications for large-scale solute transport in fractured rock. Although a number of mechanisms have been proposed to explain the enhancement of the effective matrix diffusion coefficient, the potential scale dependence and its mechanisms are not fully investigated at this stage. The major objective of this study is to again demonstrate (based on more data published in the literature than those used in Liu et al. [2004b]) the potential scale dependence of the effective matrix-diffusion coefficient, and to -develop a preliminary explanation for this scale-dependent behavior.

H.H. Liu; Y. Zhang

2006-06-20

141

Diffusion coefficients of methanol and water and the mutual diffusion coefficient in methanol-water solutions at 278 and 298 K  

Microsoft Academic Search

Diffusion coefficients have been measured for methanol and water in their mixtures over the full composition range at 278.15 and 298.15 K. By defining a reduced coefficient D\\/sup +\\/+\\/ for each component an extensive correlation in diffusional behavior has been identified for the two species. The correlation increases with decreasing temperature. Examination of literature data for acetonitrile-water and acetone-water at

Z. J. Derlacki; A. J. Easteal; A. V. J. Edge; L. A. Woolf; Z. Roksandic

1985-01-01

142

Experimental study of oxygen diffusion coefficients in clean water containing salt, glucose or surfactant: Consequences on the liquid-side mass transfer coefficients  

Microsoft Academic Search

This present paper proposes new investigations aiming at: (i) studying the effect on oxygen diffusion coefficients of the presence in clean water of some compounds usually encountered in biological media and (ii) quantifying their consequences on liquid-side mass transfer coefficients. The oxygen diffusion coefficients D were firstly measured in various synthetic liquid phases containing either salt (NaCl), sugar (glucose) or

Marupatch Jamnongwong; Karine Loubiere; Nicolas Dietrich; Gilles Hébrard

2010-01-01

143

Determination of the diffusion coefficient between corn syrup and distilled water using a digital camera  

NASA Astrophysics Data System (ADS)

A simple technique for determining the diffusion coefficient between two miscible liquids is presented based on observing concentration-dependent ultraviolet-excited fluorescence using a digital camera. The ultraviolet-excited visible fluorescence of corn syrup is proportional to the concentration of the syrup. The variation of fluorescence with distance from the transition zone between the fluids is fit by the Fick's law solution to the diffusion equation. By monitoring the concentration at successive times, the diffusion coefficient can be determined in otherwise transparent materials. The technique is quantitative and makes measurement of diffusion accessible in the advanced undergraduate physics laboratory.

Ray, E.; Bunton, P.; Pojman, J. A.

2007-10-01

144

Determination of pollutant diffusion coefficients in naturally formed biofilms using a single tube extractive membrane bioreactor  

SciTech Connect

A novel technique has been used to determine the effective diffusion coefficients for 1,1,2-trichloroethane (TCE), a nonreacting tracer, in biofilms growing on the external surface of a silicone rubber membrane tube during degradation of 1,2-dichloroethane (DCE) by Xanthobacter autotrophicus GJ10 and monochlorobenzene (MCB) by Pseudomonas JS150. Experiments were carried out in a single tube extractive membrane bioreactor (STEMB), whose configuration makes it possible to measure the transmembrane flux of substrates. A video imaging technique (VIT) was employed for in situ biofilm thickness measurement and recording. Diffusion coefficients of TCE in the biofilms and TCE mass transfer coefficients in the liquid films adjacent to the biofilms were determined simultaneously using a resistances-in-series diffusion model. It was found that the flux and overall mass transfer coefficient of TCE decrease with increasing biofilm thickness, showing the importance of biofilm diffusion on the mass transfer process. Similar fluxes were observed for the nonreacting tracer (TCE) and the reactive substrates (MCB or DCE), suggesting that membrane-attached biofilm systems can be rate controlled primarily by substrate diffusion. The TCE diffusion coefficient in the JS150 biofilm appeared to be dependent on biofilm thickness, decreasing markedly for biofilm thicknesses of >1 mm. The values of the TCE diffusion coefficients in the JS150 biofilms <1-mm thick are approximately twice those in water and fall to around 30% of the water value for biofilms >1-mm thick.

Zhang, S.F.; Splendiani, A.; Freitas dos Santos, L.M.; Livingston, A.G. [Imperial College of Science, Technology and Medicine, London (United Kingdom). Dept. of Chemical Engineering and Chemical Technology

1998-07-05

145

From free to effective diffusion coefficients in fluorescence correlation spectroscopy experiments.  

PubMed

Diffusion is one of the main transport processes that occur inside cells determining the spatial and time distribution of relevant action molecules. In most cases these molecules not only diffuse but also interact with others as they get transported. When these interactions occur faster than diffusion the resulting transport can be characterized by "effective diffusion coefficients" that depend on both the reaction rates and the "free" diffusion coefficients. Fluorescence correlation spectroscopy (FCS) gives information on effective rather than free diffusion coefficients under this condition. In the present paper we investigate what coefficients can be drawn from FCS experiments for a wide range of values of the ratio of reaction to diffusion time scales, using different fitting functions. We find that the effective coefficients can be inferred with relatively small errors even when the condition of fast reactions does not exactly hold. Since the diffusion time scale depends on the size of the observation volume and the reaction time scale depends on concentrations, we also discuss how by changing either one or the other property one can switch between the two limits and extract more information on the system under study. PMID:23496547

Ipiña, Emiliano Pérez; Dawson, Silvina Ponce

2013-02-13

146

From free to effective diffusion coefficients in fluorescence correlation spectroscopy experiments  

NASA Astrophysics Data System (ADS)

Diffusion is one of the main transport processes that occur inside cells determining the spatial and time distribution of relevant action molecules. In most cases these molecules not only diffuse but also interact with others as they get transported. When these interactions occur faster than diffusion the resulting transport can be characterized by “effective diffusion coefficients” that depend on both the reaction rates and the “free” diffusion coefficients. Fluorescence correlation spectroscopy (FCS) gives information on effective rather than free diffusion coefficients under this condition. In the present paper we investigate what coefficients can be drawn from FCS experiments for a wide range of values of the ratio of reaction to diffusion time scales, using different fitting functions. We find that the effective coefficients can be inferred with relatively small errors even when the condition of fast reactions does not exactly hold. Since the diffusion time scale depends on the size of the observation volume and the reaction time scale depends on concentrations, we also discuss how by changing either one or the other property one can switch between the two limits and extract more information on the system under study.

Ipiña, Emiliano Pérez; Dawson, Silvina Ponce

2013-02-01

147

Self-diffusion of lithium ions in a lithium niobate single crystal  

SciTech Connect

Using stable Li 6 and Li 7 isotopes, the authors measured the coefficients of diffusion of lithium ions in an LiNb0/sub 3/ single crystal in the direction of growth of the crystal. Comparison of the experimentally measured electrical conductivity at a partial oxygen pressure of 10/sup 5/ Pa with the value calculated from the values of the coefficient of diffusion using the Nernst-Einstein equation shows conclusively that the ionic conductivity in LiNb0/sub 3/ is determined solely by lithium ions.

Ptashnik, V.B.; Dunaeva, T.Y.; Myasnikov, I.V.

1986-05-01

148

The Perpendicular Diffusion Coefficient for Charged Particles of Arbitrary Energy  

Microsoft Academic Search

The problem of perpendicular diffusion by a particle in a turbulent plasma is a problem of enduring interest, and one that has yet to be fully solved. Analytic models do not agree with either observations or numerical simulations. Recently, a nonlinear theory was developed by Matthaeus et al. [2003] which, for the first time, appears to be consistent with numerical

G. P. Zank; G. Li; V. Florinski; G. M. Webb; J. A. Le Roux; W. H. Matthaeus

2003-01-01

149

Charge transport in DNA: dependence of diffusion coefficient on temperature and electron-phonon coupling constant.  

PubMed

The diffusion coefficient is calculated for a charge propagating along a double-stranded DNA, while it interacts with the nonlinear fluctuational openings of base pairs. The latter structural dynamics of DNA is described by the Peyrard-Bishop-Dauxois model [T. Dauxois, M. Peyrard, and A. R. Bishop, Phys Rev. E 47 R44 (1993)], which represents essential anharmonicities of base-pair stretchings. The dependence of the diffusion coefficient on the temperature and the electron-phonon coupling constant is presented. The diffusion coefficient decreases when either the temperature or the electron-phonon coupling increases. Analytical expressions are provided that describe the temperature dependence of the diffusion coefficient. The variation of the parameters of these expressions with the electron-phonon coupling constant is also discussed. These results quantitatively demonstrate how DNA structural nonlinear dynamics affects macroscopic charge transport properties. PMID:22181442

Kalosakas, G

2011-11-10

150

Measurement of molecular diffusion coefficients in supercritical carbon dioxide using a coated capillary column  

SciTech Connect

Molecular diffusion coefficients of ethyl acetate, toluene, phenol, and caffeine in supercritical carbon dioxide were measured by a chromatographic peak broadening technique in a coated capillary column at temperatures of 308, 318, and 328 K and pressures up to 145 bar. A linear adsorption in the polymer layer coated on the inner wall of the capillary column was observed. The experimentally determined diffusion coefficients showed substantial agreement with those reported in the literature. The diffusion coefficients were in the order of 10[sup [minus]4] cm[sup 2]/s and decreased with increasing carbon dioxide density. Based on the molecular diffusion coefficient data reported here and those published elsewhere, an empirically modified Wilke-Chang equation was proposed which was found to be more quantitative than some existing equations such as the Stokes-Einstein and Wilke-Chang equations.

Lai, C.C.; Tan, C.S. (National Tsing Hua Univ., Hsinchu (Taiwan, Province of China). Dept. of Chemical Engineering)

1995-02-01

151

Regularity of the diffusion coefficient matrix for the lattice gas with energy  

Microsoft Academic Search

In this paper we obtain the smoothness of the diffusion coefficient matrix for the lattice gas with energy. Furthermore we also obtain the smoothness of the central limit theorem variances for certain functions.

Yukio Nagahata

2005-01-01

152

The size of the unstirred layer as a function of the solute diffusion coefficient.  

PubMed Central

By monitoring the concentration distribution of several solutes that are diffusing at the same time under given mixing conditions, it was established that the unstirred layer (USL) has no clearly defined boundary. For the cases of solute permeation and water movement across planar bilayer lipid membranes, respectively, experiments carried out with double-barreled microelectrodes have shown that the thickness of the USL depends on which species is diffusing. Small molecules with a larger diffusion coefficient encounter an apparently thicker USL than larger molecules with a smaller diffusion coefficient. The ratio of the USL thicknesses of two different substances is equal to the third root of the ratio of the respective diffusion coefficients. This experimental finding is in good agreement with theoretical predictions from the theory of physicochemical hydrodynamics.

Pohl, P; Saparov, S M; Antonenko, Y N

1998-01-01

153

First-principles study of temperature-dependent diffusion coefficients for helium in ?-Ti  

NASA Astrophysics Data System (ADS)

The temperature-dependent diffusion coefficients of interstitial helium atom in ?-Ti are predicted using the transition state theory. The microscopic parameters in the pre-factor and activation energy of the impurity diffusion coefficients are obtained from first-principles total energy and phonon calculations including the full coupling between the vibrational modes of the diffusing atom and the host lattice. The climbing image nudged elastic band method is used to search for the minimum energy pathways and associated saddle point structures. It is demonstrated that the diffusion coefficients within the xy plane (Dxy) is always higher than that along the z axis (Dz), showing remarkable anisotropy. Also, it is found that the formation of helium dimer centered at the octahedral site reduces the total energy and confines the diffusion of helium atoms.

Lu, Yong; Zheng, Fawei; Zhang, Ping

2013-10-01

154

Diffusion, Deexcitation, and Three-Body Collision Coefficients for Excited Neon Atoms  

Microsoft Academic Search

Diffusion coefficients, de-excitation cross sections, and three-body collision coefficients for neon atoms of the 1s22s22p53s configuration are obtained from optical absorption measurements of relative decay rates and relative densities of excited atoms following a pulsed discharge. Atoms in the lower metastable (3P2) and the lower radiating (3P1) states are destroyed by diffusion to the wall, three-body collisions involving two ground

A. V. Phelps

1959-01-01

155

Turbulent energy dissipation rates and eddy diffusion coefficients derived from foil cloud measurements  

Microsoft Academic Search

Turbulent energy dissipation rates and eddy diffusion coefficients in the 66-90 km altitude range using the foil cloud technique are presented. Turbulent energy dissipation rates vary between 3.2E-5 and 8.6E-2 W\\/kg, and between 0.1 and 170 sq m\\/s for eddy diffusion coefficients. These derived quantities are in good agreement with the values discussed in the literature. The average value of

Yong-Fu Wu; Hans-Ulrich Widdel

1989-01-01

156

Infinite dilution diffusion coefficients of several aromatic hydrocarbons in octane and 2,2,4-trimethylpentane  

SciTech Connect

Diffusion coefficient measurements are required in a number of engineering applications and also in testing transport property theories. The diffusion coefficients of benzene, toluene, p-xylene, o-xylene, ethylbenzene, and mesitylene at infinite dilution in octane and in 2,2,4-trimethylpentane in the temperature range 303.2--333.2 K were determined by the Taylor dispersion technique. A correlation based on a free-volume-type expression represented the results to within experimental uncertainty.

Fan, Y.; Qian, R.; Shi, M.; Shi, J. [Nanjing Institute of Chemical Technology (China). Dept. of Chemical Engineering

1995-09-01

157

Note on coefficient matrices from stochastic Galerkin methods for random diffusion equations  

SciTech Connect

In a recent work by Xiu and Shen [D. Xiu, J. Shen, Efficient stochastic Galerkin methods for random diffusion equations, J. Comput. Phys. 228 (2009) 266-281], the Galerkin methods are used to solve stochastic diffusion equations in random media, where some properties for the coefficient matrix of the resulting system are provided. They also posed an open question on the properties of the coefficient matrix. In this work, we will provide some results related to the open question.

Zhou Tao, E-mail: tzhou@lsec.cc.ac.c [Institute of Computational Mathematics, The Chinese Academy of Sciences, Beijing 100190 (China); Tang Tao, E-mail: ttang@hkbu.edu.h [Department of Mathematics, Hong Kong Baptist University, Kowloon Tong (Hong Kong)

2010-11-01

158

Parvalbumin concentration and diffusion coefficient in frog myoplasm  

Microsoft Academic Search

The concentrations and diffusivity of two isoforms of parvalbumin, IVa and IVb, were measured using quantitative SDS PAGE in single fibers from semitendinosus muscles of the frog Rana temporaria. The concentrations of IVa and IVb were 2.9 ± 0.3 (SEM) and 4.5 ± 0.5 gl-1 total fiber volume, respectively. The total concentration of parvalbumin (7.4 ± 0.8 gl-1 total fiber)

David W. Maughan; Robert E. Godt

1999-01-01

159

Intrinsic diffusion coefficients and the vacancy flow factor in Dilute Cu-Zn Alloys  

NASA Astrophysics Data System (ADS)

Interdiffusion coefficients in copper-rich copper-zinc solid solutions containing up to 8 at. pct of Zn at 1168 K have been determined by Matano's analysis using semi-infinite diffusion couples consisting of pure copper and Cu-Zn alloys with Kirkendall markers. From the marker shift and Darken's relation, intrinsic diffusion coefficients, DZn and DCu, in the alloys containing 3.2 and 4.7 at. pct of Zn have been determined. Further, using thin plate couples, DZn and DCu in Cu alloys containing 0.9, 2.3, 3.5, and 4.6 at. pct of Zn at 1168 K have been determined by Heumann's method. The ratio of the intrinsic diffusion coefficients, DZn/DCu, has been found to be about two for all the compositions examined. Using the values of the intrinsic diffusion coefficient of copper at infinite dilution of zinc obtained by extrapolating the concentration dependence of DCu, and the self- and impurity diffusion coefficients in pure copper, the vacancy flow factor has been estimated to be - 0.22-0.15 +0.06 at 1168 K. By combining this value of the vacancy flow factor with the solute enhancement factor of solvent diffusion determined by Peterson and Rothman, the correlation factor for impurity diffusion of Zn in Cu at 1168 K has been evaluated to be 0.5, which is in good agreement with the value of 0.47 determined by Peterson and Rothman based on the isotope effect measurement.

Hoshino, Kazutomo; Iijima, Yoshiaki; Hirano, Ken-Ichi

1982-07-01

160

An atmospheric electrical method to determine the eddy diffusion coefficient  

Microsoft Academic Search

The ion-aerosol balance equations are solved to get the profiles of atmospheric electric parameters over the ground surface in an aerosol-rich environment under the conditions of surface radioactivity. Combining the earlier results for low aerosol concentrations and the present results for high aerosol concentrations, a relation is obtained between the average value of atmospheric electric space charge in the lowest

M. N. Kulkarni; A. K. Kamra

2010-01-01

161

NITRIC ACID-AIR DIFFUSION COEFFICIENT: EXPERIMENTAL DETERMINATION  

EPA Science Inventory

Trace gaseous HNO3 in air is removed in a laminar flow nylon tube. The HNO3 deposition pattern was obtained by sectioning the tube, extracting with an aqueous solution, and measuring the concentration by ion chromatography. Mass transport analysis of the deposition pattern demons...

162

Strong solutions of SDES with singular drift and Sobolev diffusion coefficients  

Microsoft Academic Search

In this paper we prove the existence of a unique strong solution up to the explosion time for an SDE with a uniformly non-degenerate Sobolev diffusion coefficient (non-Lipschtiz) and locally integrable drift coefficient. Moreover, two non-explosion conditions are given.

Xicheng Zhang

2005-01-01

163

The Effective Diffusion\\/Dispersion Coefficient in Vapor Extraction of Heavy Oil  

Microsoft Academic Search

In this study, a new correlation for determination of effective diffusion\\/dispersion coefficients in the vapor extraction of heavy oil\\/bitumen (VAPEX) is introduced. This model takes into account the solvent concentration as well as the drainage height and permeability dependency of these coefficients. The concentration dependency in this model stems from the mixture viscosity changes, while the height dependency appears directly

A. Yazdani; B. Maini

2009-01-01

164

Foreign-ion and self-ion diffusion in a crosslinked salt-in-polyether electrolyte.  

PubMed

We present an extensive study of ionic transport in PolyG(30)LiPF(6), which is a crosslinked poly(ethylene oxide)-poly(propylene oxide(PEO-PPO) random copolymer complexed with LiPF(6) to an oxygen-to-cation ratio of 30 : 1. Self-diffusion coefficients of the constituent ions were measured by pulsed field gradient nuclear magnetic resonance (PFG-NMR) as a function of temperature using the signals of (7)Li and (19)F. These data were compared with the charge diffusivity as derived with the Nernst-Einstein equation from the ion conductivity obtained by impedance spectroscopy. In addition, the diffusion behaviour of a foreign cation (sodium) and that of a foreign anion (iodine) in PolyG(30)LiPF(6) were investigated by means of the radiotracers (22)Na and (125)I. All different types of diffusivities were evaluated in a comprehensive ion transport model which allows for the occurrence of charged single ions and neutral ion pairs. Simultaneous fitting of all data within this model yields best values of the model parameters which include Vogel-Tammann-Fulcher parameters and enthalpies/entropies of pair formation. Two distinct variants of the same general model reproduce the experimental data equally well, i.e., with closely similar results for the pair contribution to the migration of each ionic species. In the first variant, this pair contribution is due to a small fraction of ion pairs with a high mobility. By contrast, the second variant results in a very large fraction of pairs characterized by a relatively low mobility. The assumptions and implications connected with both model variants are discussed in detail. PMID:20480092

Fögeling, J; Kunze, M; Schönhoff, M; Stolwijk, N A

2010-05-18

165

Relationship between choline and apparent diffusion coefficient in patients with gliomas  

Microsoft Academic Search

Purpose: To examine the relationship between apparent diffusion coefficients (ADC) from diffusion weighted imag- ing (DWI) and choline levels from proton magnetic reso- nance spectroscopic imaging (MRSI) in newly diagnosed Grade II and IV gliomas within distinct anatomic regions. Materials and Methods: A total of 37 patients with Grade II and 28 patients with Grade IV glioma were scanned on

Inas S. Khayal; Forrest W. Crawford; Suja Saraswathy; Kathleen R. Lamborn; Susan M. Chang; Soonmee Cha; Tracy R. McKnight; Sarah J. Nelson

2008-01-01

166

First principles calculations of alloying element diffusion coefficients in Ni using the five-frequency model  

NASA Astrophysics Data System (ADS)

The diffusion coefficients of several alloying elements (Al, Mo, Co, Ta, Ru, W, Cr, Re) in Ni are directly calculated using the five-frequency model and the first principles density functional theory. The correlation factors provided by the five-frequency model are explicitly calculated. The calculated diffusion coefficients show their excellent agreement with the available experimental data. Both the diffusion pre-factor (D0) and the activation energy (Q) of impurity diffusion are obtained. The diffusion coefficients above 700 K are sorted in the following order: DAl > DCr > DCo > DTa > DMo > DRu > DW > DRe. It is found that there is a positive correlation between the atomic radius of the solute and the jump energy of Ni that results in the rotation of the solute-vacancy pair (E1). The value of E2-E1 (E2 is the solute diffusion energy) and the correlation factor each also show a positive correlation. The larger atoms in the same series have lower diffusion activation energies and faster diffusion coefficients.

Wu, Qiong; Li, Shu-Suo; Ma, Yue; Gong, Sheng-Kai

2012-10-01

167

Solute diffusion coefficient in the internal medium of a new gel based controlled release fertilizer  

Microsoft Academic Search

The diffusion of solutes in a new controlled release device was investigated and in situ measurements of constant and variable diffusion coefficients were obtained. The new controlled release device consists of a dry mixture of fertilizer and gel forming thickener contained in a nonpermeable coating having at least one opening. Water penetrates into the device through the opening, forms a

Uri Shavit; Avi Shaviv; Dan Zaslavsky

1995-01-01

168

Ionic conduction mechanisms of lithium gel polymer electrolytes investigated by the conductivity and diffusion coefficient  

Microsoft Academic Search

Conduction properties of the polymer gel electrolytes of lithium were investigated based on the electrical conductivity and diffusion coefficient using the pulsed gradient spin echo NMR technique. The gel electrolytes prepared by the phase inversion method showed characteristic features in diffusive behavior depending on the kind of immiscible solvent used during the preparation process of the porous polymer membranes. The

Yuria Saito; A. Manuel Stephan; Hiroshi Kataoka

2003-01-01

169

Inverse Problem for a Class of Two-Dimensional Diffusion Equations with Piecewise Constant Coefficients  

Microsoft Academic Search

In this paper, we consider an inverse problem for a class of two-dimensional diffusion equations with piecewise constant coefficients. This problem is studied using an explicit formula for the relevant spectral measures and an asymptotic expansion of the solution of the diffusion equations. A numerical method that reduces the inverse problem to a sequence of nonlinear least-square problems is proposed

M. Mochi; G. Pacelli; M. C. Recchioni; F. Zirilli

1999-01-01

170

Renormalization Group Analysis of Nonlinear Diffusion Equations with Time Dependent Coefficients and Marginal Perturbations  

NASA Astrophysics Data System (ADS)

In this paper we use a Renormalization Group (RG) method to study the long-time asymptotics of nonlinear diffusion equations with time-dependent diffusion coefficients and nonlinearities which are marginal (or critical) with respect to the RG operator. These equations describe the time evolution of the average concentration of a passive scalar being advected by a random velocity field. We prove that, besides the expected diffusive behavior, there is an extra logarithmic correction which is the imprint of the critical nonlinearity.

Braga, Gastão A.; Moreira, Jussara M.

2012-08-01

171

An atmospheric electrical method to determine the eddy diffusion coefficient  

Microsoft Academic Search

The ion-aerosol balance equations are solved to get the profiles of atmospheric electric parameters over the ground surface\\u000a in an aerosol-rich environment under the conditions of surface radioactivity. Combining the earlier results for low aerosol\\u000a concentrations and the present results for high aerosol concentrations, a relation is obtained between the average value of\\u000a atmospheric electric space charge in the lowest

M. N. Kulkarni; A. K. Kamra

2010-01-01

172

Fick diffusion coefficients of liquid mixtures directly obtained from equilibrium molecular dynamics.  

PubMed

A methodology for computing Fick diffusivities directly from equilibrium molecular dynamics (MD) simulations is presented and validated for acetone-methanol and acetone-tetrachloromethane liquid mixtures. Fick diffusivities are obtained from Maxwell-Stefan (MS) diffusivities and the so-called thermodynamic factor. MS diffusivities describe the friction between different components, while the thermodynamic factor is the concentration derivative of the activity describing the deviation from ideal mixing behavior. It is important to note that all mutual diffusion experiments measure Fick diffusion coefficients, while molecular simulation provides MS diffusivities. The required thermodynamic factor to convert MS into Fick diffusivities and vice versa, however, is usually difficult to extract from both simulations and experiments leaving a gap between theory and application. Here, we employ our novel method to compute the thermodynamic factor from small-scale density fluctuations in equilibrium MD simulations [Chem. Phys. Lett.2011, 504, 199-201]. Previously, this method was developed and validated for molecules with single interaction sites only. In this work, we applied this method to acetone-methanol and acetone-tetrachloromethane liquid mixtures and show that the method also works well in these more complex systems. This provides the missing step to extract Fick diffusion coefficients directly from equilibrium MD simulations. The computed Fick diffusivities of acetone-methanol and acetone-tetrachloromethane mixtures are in excellent agreement with experimental values. The suggested framework thus provides an efficient route to model diffusion in liquids on the basis of a consistent molecular picture. PMID:21954841

Liu, Xin; Schnell, Sondre K; Simon, Jean-Marc; Bedeaux, Dick; Kjelstrup, Signe; Bardow, André; Vlugt, Thijs J H

2011-10-18

173

Transport coefficients of ions in electrolyte solutions by Brownian dynamics  

SciTech Connect

Transport coefficients of model electrolyte solutions are calculated using Brownian dynamics (BD) simulation methodology. The authors have implemented both equilibrium Brownian dynamics (EBD) and nonequilibrium Brownian dynamics (NEBD) to determine the self and distinct diffusion coefficients as well as the ionic conductivities for models of aqueous 1M NaCl, 0.5M K[sub 2]SO[sub 4], and 0.5M CuSO[sub 4] solutions. The results from these computer experiments are compared with those obtained from an integral equation approximation applied to the same models. They find that the simulation results are in good agreement with the integral equation theory for the model 1M NaCl solution, whereas the agreement is not as good for the 0.5M K[sub 2]SO[sub 4] model and there are large discrepancies between the integral equation theory and the BD results for the model for 0.5M CuSO[sub 4]. In addition, the novel NEBD technique that was developed was used to explore the nonequilibrium structural properties of these model solutions. The authors find that the two particle distribution function showed a significant angular dependence in the presence of an electric field.

Wood, M.D.

1992-01-01

174

Development of phase-shifting interferometry for measurement of isothermal diffusion coefficients in binary solutions  

NASA Astrophysics Data System (ADS)

In this study, a phase-shifting interferometer to conduct real-time high-resolution measurements of concentration profiles in binary diffusion fields was developed. The phase-shifting interferometer comprises a Mach-Zehnder interferometer, a rotating polarizer, a CCD camera, and an image-processing unit. A phase-shifting technique was used to determine the phase difference between a test beam and a reference beam by using three images taken at intervals of 1/30 s. The phase difference is obtained for a spatial resolution of 640×240. This data is further processed in real-time to visualize the concentration profile inside a diffusion cell. The diffusion coefficient is determined by performing an inverse analysis of the experimental concentration profile. The objective function makes use of a numerical calculation, based on Fick's law, for which the initial experimental concentration profile is taken as initial condition. The diffusion field was formed inside a thermally controlled diffusion cell with optical paths as large as 20 mm. This large optical path allows measurements of diffusion fields with concentration differences as narrow as 1 mg/ml. In order to validate the measurement method, the concentration dependence of the isothermal diffusion coefficient of NaCl and Sucrose was determined in the dilute region at 25 °C, such values being extensively reported in the literature. It was found that our optical system is much faster and accurate than similar optical systems to determine the diffusion coefficients in binary systems.

Torres, Juan F.; Komiya, Atsuki; Shoji, Eita; Okajima, Junnosuke; Maruyama, Shigenao

2012-09-01

175

Molecular Dynamics Study of Superlattice Superionic Conductor: Enhancement of Oxygen Ion Diffusion in YSZ  

Microsoft Academic Search

A constant-volume molecular dynamics calculation has been performed for a cubic yttria-stabilized zirconia (Y2O3)c(ZrO2)1-c, where Y layers and Zr layers are alternately accumulated to form a superlattice. A considerable enhancement of the diffusion of oxygen ions was observed at the composition c=0.33, at which the diffusion coefficient in the superlattice is about three times larger than the case of a

Hideo Okazaki; Hisashi Suzuki; Katsuyoshi Ihata

1994-01-01

176

IR-ATR spectroscopic determination of the diffusion coefficients of carbohydrates in polymer matrices  

NASA Astrophysics Data System (ADS)

During the past few years, the importance of membranes in chemical and biotechnological applications, such as separation processes and biosensor construction, has dramatically increased. As a consequence, membrane properties have to be characterized very thoroughly with special respect to diffusivity and selectivity. Whereas most techniques for the determination of diffusion coefficients require sophisticated and often indirect methods for the detection of the analyte diffusing through the membrane, which generally do not allow monitoring of the diffusion process continuously, we present in this work an experimentally simple and straightforward method employing FTIR-ATR spectroscopy. The diffusion of glucose into a PVA membrane is chosen as a model example for the determination of carbohydrates in polymer matrices due to its special relevance in biosensor construction. The method is based on monitoring the time-dependent change in absorption due to the diffusion of the glucose into the polymer membrane. After reaching a steady-state, the normalized absorbance plot (A/A(infinity) ) versus time can be used for numerical evaluation. The diffusion coefficient is determined by comparing the experimental with simulated data using the membrane thickness (iota) and the diffusion coefficient D as simulation parameters. For this reason, the performance of a recursive and two non-recursive models for the description of the diffusion process is examined. Modifications in the second non-recursive algorithm finally resulted in very good agreement with the experimental data. This work marks the first application of IR-ATR spectroscopy for the determination of diffusion coefficients even as large as of the order of 10-6 cm2/sec.

Rosenberg, E.; Kellner, Robert A.

1992-03-01

177

Determination of the Diffusion Coefficients of Hydrogen and CO in Ni by Means of a Mass Spectrometer (Viznachennaya Koefitsientiv Difuzii Vodnyu na CO v Nikeli z Dopomogoyu Masspektrometra).  

National Technical Information Service (NTIS)

The methods of constant and variable diffusion rates are used in determing the diffusion coefficients of gases into metals. The constant diffusion rate method used for measuring permeability, 'P', which is connected with the diffusion coefficient, by the ...

L. M. Ryabchykov

1970-01-01

178

Estimation of radon diffusion coefficients in soil using an updated experimental system  

NASA Astrophysics Data System (ADS)

Radon diffusion through soil is strongly affected by the degree of water saturation of the soil pores. Methods have been developed by many researchers to measure radon diffusion coefficient. We developed an updated experimental system to estimate radon diffusion coefficients for typical types of soil in Japan and applied it to a typical loam with different water saturation levels (0-0.82). The system consists of a passive-type scintillation cell, soil column, accumulation tank, and radon source. The radon concentration in the accumulation tank is kept stable, and radon diffused through the soil column is continuously measured with the passive-type scintillation cell. We found the radon diffusion coefficients vary from 9.60 × 10-6 m2 s-1 to 1.27 × 10-7 m2 s-1 for the loam samples. Generally, the diffusion coefficients are almost constant for a water saturation range of 0-0.4 and decrease with increasing water saturation from 0.4 to 0.82.

Prasad, Ganesh; Ishikawa, Tetsuo; Hosoda, Masahiro; Sorimachi, Atsuyuki; Janik, Miroslaw; Sahoo, Sarata Kumar; Tokonami, Shinji; Uchida, Shigeo

2012-09-01

179

Diffusion and Coulomb Separation of Ions in Dense Matter  

NASA Astrophysics Data System (ADS)

We analyze diffusion equations in strongly coupled Coulomb mixtures of ions in dense stellar matter. Strong coupling of ions in the presence of gravitational forces and electric fields (induced by plasma polarization in the presence of gravity) produces a specific diffusion current which can separate ions with the same A/Z (mass to charge number) ratios but different Z. This Coulomb separation of ions can be important for the evolution of white dwarfs and neutron stars.

Beznogov, M. V.; Yakovlev, D. G.

2013-10-01

180

Measurement and correlation of ion activity coefficients in aqueous solutions of mixed electrolyte with a common ion  

Microsoft Academic Search

Ion selective electrodes have been used to measure the activity coefficients at 298.2 K of individual ions in aqueous solutions of mixtures of NaCl and KCl up to 4 molal total chloride ion concentration, and of NaCl and NaBr up to 4 molal total sodium ion concentration. The experimental results show that the activity coefficient of an ion in the

M. K. Khoshkbarchi; J. H. Vera

1996-01-01

181

Li+ ions diffusion into sol-gel V2O5 thin films: electrochromic properties  

Microsoft Academic Search

V{2}O{5} thin films were prepared by the sol-gel spin coating process. The Li+ ions insertion effect on optical and electrochromic properties of those films was studied. The diffusion coefficient was calculated using both cyclic voltammograms and chronoamperometric curves. The amount x of Li+ ions in LixV{2}O{5} was also calculated. Finally, the electrochromic performance evolution characteristics such as the reversibility, coloration

M. Benmoussa; A. Outzourhit; A. Bennouna; A. Ihlal

2009-01-01

182

Effective molecular diffusion coefficient in a two-phase gel medium  

NASA Astrophysics Data System (ADS)

We derive a mean-field expression for the effective diffusion coefficient of a probe molecule in a two-phase medium consisting of a hydrogel with large gel-free solvent inclusions, in terms of the homogeneous diffusion coefficients in the gel and in the solvent. Upon comparing with exact numerical lattice calculations, we find that our expression provides a remarkably accurate prediction for the effective diffusion coefficient, over a wide range of gel concentration and relative volume fraction of the two phases. Moreover, we extend our model to handle spatial variations of viscosity, thereby allowing us to treat cases where the solvent viscosity itself is inhomogeneous. This work provides robust grounds for the modeling and design of multiphase systems for specific applications, e.g., hydrogels as novel food agents or efficient drug-delivery platforms.

Hickey, Owen A.; Mercier, Jean-François; Gauthier, Michel G.; Tessier, Frédéric; Bekhechi, Smaine; Slater, Gary W.

2006-05-01

183

Asymptotic diffusion coefficients and anomalous diffusion in a meandering jet flow under environmental fluctuations.  

PubMed

The nontrivial dependence of the asymptotic diffusion on noise intensity has been studied for a Hamiltonian flow mimicking the Gulf Jet Stream. Three different diffusion regimes have been observed depending on the noise intensity. For intermediate noise the asymptotic diffusion decreases with noise intensity at a rate which is linearly dependent to the flow's meander amplitude. Increasing the noise the fluid transport passes through a superdiffusive regime and finally becomes diffusive again at large noise intensities. The presence of inner circulation regimes in the flow has been found to be determinant to explain the observed behavior. PMID:22400707

von Kameke, A; Huhn, F; Pérez-Muñuzuri, V

2012-01-27

184

Comparison between different spectral models of the diffuse attenuation and absorption coefficients of seawater  

NASA Astrophysics Data System (ADS)

The goal of this work is to verify different spectral models of the diffuse attenuation and absorption coefficients of sea water and to work out a recommendation for their use. It is shown that the spectral models of the diffuse attenuation coefficient Kd((lambda) ) developed by Austin, Petzold, 1984 and by Volynsky, Sud'bin, 1992 correspond with each other, as well the models of Ivanov, Shemshura, 1973 and of Kopelevich, Shemshura, 1988 for calculation of the spectral absorption coefficient a((lambda) ) on the values of Kd((lambda) ). Theoretical foundation of the relation between a((lambda) ) and Kd((lambda) ) is given. The up-to-date physical model of the sea water light absorption is considered and checked by means of comparison with measured values of the attenuation coefficient at the ultraviolet and visible spectral ranges.

Kopelevich, Oleg V.; Filippov, Yury V.

1994-10-01

185

Off-center effect on the diffusion coefficient of Cu(sup +) and Li(sup +) in the KCl lattice.  

National Technical Information Service (NTIS)

It is well known that the diffusion coefficients of the Cu(sup +) cation in the NaCl and KCl lattices exceeds by three or four orders of magnitude the corresponding self-diffusion coefficients in the intrinsic temperature regions. This fast diffusion of t...

F. Despa

1994-01-01

186

Field-Scale Effective Matrix Diffusion Coefficient for FracturedRock: Results From Literature Survey  

SciTech Connect

Matrix diffusion is an important mechanism for solutetransport in fractured rock. We recently conducted a literature survey onthe effective matrix diffusion coefficient, Dem, a key parameter fordescribing matrix diffusion processes at the field scale. Forty fieldtracer tests at 15 fractured geologic sites were surveyed and selectedfor study, based on data availability and quality. Field-scale Dem valueswere calculated, either directly using data reported in the literature orby reanalyzing the corresponding field tracer tests. Surveyed dataindicate that the effective-matrix-diffusion-coefficient factor FD(defined as the ratio of Dem to the lab-scale matrix diffusioncoefficient [Dem]of the same tracer) is generally larger than one,indicating that the effective matrix diffusion coefficient in the fieldis comparatively larger than the matrix diffusion coefficient at therock-core scale. This larger value could be attributed to the manymass-transfer processes at different scales in naturally heterogeneous,fractured rock systems. Furthermore, we observed a moderate trend towardsystematic increase in the emDFmDDF value with observation scale,indicating that the effective matrix diffusion coefficient is likely tobe statistically scale dependent. The FD value ranges from 1 to 10,000for observation scales from 5 to 2,000 m. At a given scale, the FD valuevaries by two orders of magnitude, reflecting the influence of differingdegrees of fractured rock heterogeneity at different sites. In addition,the surveyed data indicate that field-scale longitudinal dispersivitygenerally increases with observation scale, which is consistent withprevious studies. The scale-dependent field-scale matrix diffusioncoefficient (and dispersivity) may have significant implications forassessing long-term, large-scale radionuclide and contaminant transportevents in fractured rock, both for nuclear waste disposal and contaminantremediation.

Zhou, Quanlin; Liu, Hui Hai; Molz, Fred J.; Zhang, Yingqi; Bodvarsson, Gudmundur S.

2005-03-28

187

Lead diffusion in apatite and zircon using ion implantation and Rutherford Backscattering techniques  

SciTech Connect

Ion implantation was used to introduce Pb into the minerals zircon and apatite. Diffusion profiles were obtained using Rutherford Backscattering, and the results were fitted with a model to determine the diffusion coefficients. This approach is both simple and useful in studying diffusion over a temperature range of geologic interest without inordinate annealing times. Results for apatite over the temperature range 600-900C are in good agreement with earlier results obtained for higher temperatures (Watson et al., 1985) and are described. This suggests that radiation damage induced by ion implantation has little effect on Pb diffusion in this case due to rapid annealing of induced damage at low temperatures. The activation energy stated above is somewhat smaller than that previously determined (70 kcal mol{sup {minus}1}), reflecting the larger range in 1/T sampled by the present results. Closure temperatures calculated with these diffusion parameters are in good agreement with those inferred from geochronologic data. Diffusion coefficients for Pb in zircon determined in this study are greater than those obtained from a single experimental measurement and estimates of Pb diffusion based on geochronologic data and U/Pb zoning in natural zircons. The differing results for zircon and apatite obtained in this study appear to be related to each mineral's ability to anneal the radiation damage induced by ion implantation.

Cherniak, D.J.; Lanford, W.A. (State Univ. of New York, Albany (United States)); Ryerson, F.J. (Lawrence Livermore National Lab., CA (United States))

1991-06-01

188

Flow injection analysis simulations and diffusion coefficient determination by stochastic and deterministic optimization methods.  

PubMed

Stochastic and deterministic simulations of dispersion in cylindrical channels on the Poiseuille flow have been presented. The random walk (stochastic) and the uniform dispersion (deterministic) models have been used for computations of flow injection analysis responses. These methods coupled with the genetic algorithm and the Levenberg-Marquardt optimization methods, respectively, have been applied for determination of diffusion coefficients. The diffusion coefficients of fluorescein sodium, potassium hexacyanoferrate and potassium dichromate have been determined by means of the presented methods and FIA responses that are available in literature. The best-fit results agree with each other and with experimental data thus validating both presented approaches. PMID:23845484

Kucza, Witold

2013-06-19

189

A method for calculating the self-diffusion coefficients of molecules in multicomponent mixtures of liquids  

NASA Astrophysics Data System (ADS)

A method for calculating the self-diffusion coefficients of molecules in multicomponent liquid mixtures with arbitrary compositions was suggested. The method was based on the Stokes-Einstein equation and the assumption of the volume-additive character of the numerical multiplier in this equation. The self-diffusion coefficients of molecules of separate components in the individual state at infinite dilution in each of mixture components and dynamic viscosities of separate individual components and a mixture of a given composition are necessary and were used for calculations.

Arkhipov, V. P.

2011-03-01

190

Transport coefficients of the Lennard-Jones model fluid. II Self-diffusion.  

PubMed

In an extensive computer simulation study, the transport coefficients of the Lennard-Jones model fluid were determined with high accuracy from equilibrium molecular-dynamics simulations. In the frame of time-correlation function theory, the generalized Einstein relations were employed to evaluate the transport coefficients. This second of a series of four papers presents the results for the self-diffusion coefficient, and discusses and interprets the behavior of this transport coefficient in the fluid region of the phase diagram. The uncertainty of the self-diffusion data is estimated to be 1% in the gas region and 0.5% at high-density liquid states. With the very accurate data, even fine details in the shape of the self-diffusion isotherms are resolved, and the previously little-investigated behavior of the self-diffusion coefficient at low-density gaseous states is analyzed in detail. Finally, aspects of the mass transport mechanisms on the molecular scale are explored by an analysis of the velocity autocorrelation functions. PMID:15538874

Meier, Karsten; Laesecke, Arno; Kabelac, Stephan

2004-11-15

191

Prediction of Diffusion Coefficients in Porous Media using Tortuosity Factors Based on Interfacial Areas  

SciTech Connect

Determination of aqueous phase diffusion coefficients of solutes through porous media is essential for understanding and modeling contaminant transport. Prediction of diffusion coefficients in both saturated and unsaturated zones requires knowledge of tortuosity and constrictivity factors. No methods are available for the direct measurement of these factors, which are empirical in their definition. In this paper, a new definition for the tortuosity factor is proposed, as the real to ideal interfacial area ratio. We define the tortuosity factor for saturated porous media (ts) as the ratio S/So (specific surface of real porous medium to that of an idealized capillary bundle). For unsaturated media, tortuosity factor (ta) is defined as aaw/aaw,o (ratio of the specific air-water interfacial area of real and the corresponding idealized porous medium). This tortuosity factor is suitably measured using sorptive tracers (e.g., nitrogen adsorption method) for saturated media and interfacial tracers for unsaturated media. A model based on this new definition of tortuosity factors, termed the Interfacial Area Ratio (IAR) model, is presented for the prediction of diffusion coefficients as a function of the degree of water saturation. Diffusion coefficients and diffusive resistances measured in a number of saturated and unsaturated granular porous media, for solutes in dilute aqueous solutions, agree well with the predictions of the IAR model. A comparison of permeability of saturated sands estimated based on ts and the same based on the Kozeny-Carman equation confirm the usefulness of the ts parameter as a measure of tortuosity.

Saripalli, Kanaka P.; Serne, R. Jeffrey; Meyer, Philip D.; McGrail, B. Peter

2002-08-01

192

Angstrom methods applied to simultaneous measurements of thermal diffusivity and heat transfer coefficients: Part 1, Theory  

SciTech Connect

The authors present a method for simultaneous measurement of thermal diffusivity and local heat transfer coefficient based on a theory originally stated by Angstrom. They apply a sinusoidally varying thermal flux incident on one face of a one-dimensional specimen and convectively cool its opposite face. This results in a sinusoidally varying temperature on the cooled face with a measurable phase lag between the incident and transmitted waves that depends upon the material properties and the heat transfer coefficient.

Kosky, P.G.; Maylotte, D.H.; Gallo, J.P.

1999-11-01

193

Diffusion and virial coefficient in a mercury-argon gas mixture  

NASA Astrophysics Data System (ADS)

Theoretical and experimental data on molecular beams and the mutual diffusion coefficient (MDC) and second virial coefficient (SVC) for an Hg-Ar gas mixture as a representative of the mercuryinert gas family are matched on basis of the Morse potential and the relations of the molecular kinetic theory of rarefied gases. Tables of the MDC and SVC values in the temperature range of 200-2000 K are calculated, and estimates of their accuracy are presented.

Popov, V. N.; Fokin, L. R.

2013-04-01

194

FIELD-SCALE EFFECTIVE MATRIX DIFFUSION COEFFICIENT FOR FRACTURED ROCK:RESULTS FROM LITERATURE SURVEY  

SciTech Connect

Matrix diffusion is an important mechanism for solute transport in fractured rock. We recently conducted a literature survey on the effective matrix diffusion coefficient, D{sub m}{sup e}, a key parameter for describing matrix diffusion processes at the field scale. Forty field tracer tests at 15 fractured geologic sites were surveyed and selected for the study, based on data availability and quality. Field-scale D{sub m}{sup e} values were calculated, either directly using data reported in the literature or by reanalyzing the corresponding field tracer tests. Surveyed data indicate that the effective-matrix-diffusion-coefficient factor F{sub D} (defined as the ratio of D{sub m}{sup e} to the lab-scale matrix diffusion coefficient [D{sub m}] of the same tracer) is generally larger than one, indicating that the effective matrix diffusion coefficient in the field is comparatively larger than the matrix diffusion coefficient at the rock-core scale. This larger value can be attributed to the many mass-transfer processes at different scales in naturally heterogeneous, fractured rock systems. Furthermore, we observed a moderate trend toward systematic increase in the F{sub D} value with observation scale, indicating that the effective matrix diffusion coefficient is likely to be statistically scale dependent. The F{sub D} value ranges from 1 to 10,000 for observation scales from 5 to 2,000 m. At a given scale, the F{sub D} value varies by two orders of magnitude, reflecting the influence of differing degrees of fractured rock heterogeneity at different sites. In addition, the surveyed data indicate that field-scale longitudinal dispersivity generally increases with observation scale, which is consistent with previous studies. The scale-dependent field-scale matrix diffusion coefficient (and dispersivity) may have significant implications for assessing long-term, large-scale radionuclide and contaminant transport events in fractured rock, both for nuclear waste disposal and contaminant remediation.

Q. Zhou; Hui-Hai Liu; F.J. Molz; Y. Zhang; G.S. Bodvarsson

2005-04-08

195

Methods to determine slow diffusion coefficients of biomolecules. Applications to Engrailed 2, a partially disordered protein  

Microsoft Academic Search

We present new NMR methods to measure slow translational diffusion coefficients of biomolecules. Like the heteronuclear stimulated\\u000a echo experiment (XSTE), these new methods rely on the storage of information about spatial localization during the diffusion\\u000a delay as longitudinal polarization of nuclei with long T1 such as nitrogen-15. The new BEST-XSTE sequence combines features of Band-selective Excitation Short-Transient (BEST) and\\u000a XSTE

Rafal Augustyniak; Fabien Ferrage; Raphaël Paquin; Olivier Lequin; Geoffrey Bodenhausen

196

Pc 5 Spectral Density at ULTIMA stataions and its Radial Diffusion Coefficients for REE  

NASA Astrophysics Data System (ADS)

Pc 5 magnetic pulsations with frequencies between 1.67 and 6.67 mHz, are believed to contribute to the Relativistic Electron Enhancement (REE) in the outer radiation belt during magnetic storms. Ground-based observations suggested that high-speed solar wind and large-amplitude Pc 5 waves with a long duration during the storm recovery phase are closely associated with the production of relativistic electrons [Baker et al., 1998; Rostoker et al., 1998; Mathie and Mann, 2000; O’Brien et al., 2001, 2003]. On the other hand, many relativistic electron acceleration mechanisms have been proposed theoretically. They are separated roughly into two themes: in situ acceleration at L lower than 6.6 by wave particle interactions (as internal source acceleration mechanisms) [Liu et al., 1999; Summers et al., 1999; Summers and Ma, 2000] and acceleration by radial diffusion to transport and accelerate a source population of electrons from the outer to the inner magnetosphere (as external source acceleration mechanisms) [Elkington et al., 1999, 2003; Hudson et al., 2000; Kim et al., 2001]. One possible external source acceleration mechanism is the resonant interaction with ULF toroidal and poloidal waves. In order to verify which of the two mechanisms is more effective for the REE, we have to examine the time variation of electron phase space density. Electron phase space density is not directly measured, but we can estimate radial diffusion coefficients using observational electric and magnetic data. The goal of this paper is to get more reliable radial diffusion coefficient from ground-based observational magnetic field and to show reasonability of it for radial diffusion model. We use the global magnetometer data obtained from ULTIMA (Ultra Large Terrestrial International Magnetic Array, see http://www.serc.kyushu-u.ac.jp/ultima/ultima.html) stations, to precisely define the radial diffusion timescales. The ULTIMA includes McMAC, CARISAM, 210MM and MAGDAS/CPMN magnetometer arrays. The radial diffusion coefficient can be given from the magnetic field power spectral density as a function of L, frequency (f) and m-number (m) in the Pc 5 frequency range during the REE related magnetic storms [see Brautigam et al., 2005]. We can fit Pc 5 power spectral density (L, f, m) using the ULTIMA data. The m-number of global Pc 5 pulsation on the ground is found to be almost less than 5. This is consistent with m-number required in the radial diffusion theory by Elkington et al. [1999, 2003]. We will compare the observationally estimated diffusion coefficient with theoretical diffusion coefficient [e.g. Elkington et al., 2006], and discuss adequacy of our diffusion coefficient.

Fujimoto, A.; Tokunaga, T.; Abe, S.; Uozumi, T.; Yoshikawa, A.; Mann, I. R.; Chi, P. J.; Engebretson, M. J.; Yumoto, K.

2009-12-01

197

An experimental study on the properties of resistance to diffusion of chloride ions of fly ash and blast furnace slag concrete  

Microsoft Academic Search

This paper uses the Nernst–Einstein equation to calculate the diffusion coefficient of chloride ions of high-performance concrete (HPC), analyzing and discussing the property of resistance to chloride ion of HPC with fly ash or blast furnace slag. The experimental results show that the diffusion coefficient of chloride ion increases with the rise of the water–binder ratio and decreases with the

Faguang Leng; Naiqian Feng; Xinying Lu

2000-01-01

198

Reorientational angle distribution and diffusion coefficient for nodal and cylindrical surfaces  

NASA Astrophysics Data System (ADS)

We present a catalogue of diffusion coefficients and reorientational angle distribution (RAD) for various periodic surfaces, such as I-WP, F-RD, S, and S1 nodal surfaces; cylindrical structures like simple, undulated, and spiral cylinders, and a three-dimensional interconnected-rod structures. The results are obtained on the basis of a simulation algorithm for a diffusion on a surface given by the general equation ?(r)=0 [Ho?yst et al., Phys Rev. E 60, 302 (1999)]. I-WP, S, and S1 surfaces have a spherelike RAD, while F-RD has a cubelike RAD. The average of the second Legendre polynomial with RAD function for all nodal surfaces, except the F-RD nodal surface, decays exponentially with time for short times. The decay time is related to the Euler characteristic and the area per unit cell of a surface. This analytical formula, first proposed by B. Halle, S. Ljunggren, and S. Lidin in J. Chem. Phys. 97, 1401 (1992), is checked here on nodal surfaces, and its range of validity is determined. RAD function approaches its stationary limit exponentially with time. We determine the time to reach stationary state for all surfaces. In the case of the value of the effective diffusion coefficient the mean curvature and a connectivity between parts of surfaces have the main influence on it. The surfaces with low mean curvature at every point of the surface are characterized by high-diffusion coefficient. However if a surface has globally low mean curvature with large regions of nonzero mean curvature (negative and positive) the effective diffusion coefficient is low, as for example, in the case of undulated cylinders. Increasing the connectivity, at fixed curvatures, increases the diffusion coefficient.

Plewczy?ski, D.; Ho?yst, R.

2000-12-01

199

Solvable Examples of Drift and Diffusion of Ions in Non-uniform Electric Fields  

SciTech Connect

The drift and diffusion of a cloud of ions in a fluid are distorted by an inhomogeneous electric field. If the electric field carries the center of the distribution in a straight line and the field configuration is suitably symmetric, the distortion can be calculated analytically. We examine the specific examples of fields with cylindrical and spherical symmetry in detail assuming the ion distributions to be of a generally Gaussian form. The effects of differing diffusion coefficients in the transverse and longitudinal directions are included.

Cahn, Robert; Cahn, Robert N.; Jackson, John David

2008-05-30

200

Combined effect of periodic gates and external fields on the diffusion coefficient of a single particle.  

PubMed

A general analytical expression to describe the diffusion of a single particle in a one-dimensional lattice with periodically distributed gates of lifetime (tau) and while under the influence of a constant external field is calculated. A formulation based on a microscopic model and a diffusion relaxation condition is used to derive an equation for the diffusion coefficient as a function of the concentration of gates (c), the lifetime (tau) of such gates, and the strength of the external field (p). The theory is compared against Monte Carlo simulations, and limiting cases are used to reproduce previously published results on a variety of phenomena. PMID:12636490

Oum, Lida; Parrondo, Juan M R; Martinez, Hernan L

2003-01-31

201

Comparison between Gleason score and apparent diffusion coefficient obtained from diffusion-weighted imaging of prostate cancer patients.  

PubMed

Objectives: To correlate the apparent diffusion coefficient (ADC) of prostate cancer patients with pathological Gleason scores (GS). Methods: 40 patients with GS 2 + 3, 3 + 3, 3 + 4, or 4 + 4 were selected. The magnetic resonance imaging (MRI) study was performed adding axial diffusion-weighted imaging (DWI) sequences to the standard MRI protocol. ADC values obtained were correlated with the GS data. Results: Statistically significant differences of ADC (p < .05) were found among GS groups with a trend of decreasing ADC values with increasing GS. Conclusions: The ADC values may help clinicians to delineate prostate carcinoma, recognizing its high- or low-grade compartments. PMID:24138289

Caivano, Rocchina; Rabasco, Paola; Lotumolo, Antonella; Cirillo, Patrizia; D'Antuono, Felice; Zandolino, Alexis; Villonio, Antonio; Macarini, Luca; Salvatore, Marco; Cammarota, Aldo

2013-10-18

202

Electro-diffusion in a plasma with two ion species  

SciTech Connect

Electric field is a thermodynamic force that can drive collisional inter-ion-species transport in a multicomponent plasma. In an inertial confinement fusion capsule, such transport causes fuel ion separation even with a target initially prepared to have equal number densities for the two fuel ion species. Unlike the baro-diffusion driven by ion pressure gradient and the thermo-diffusion driven by ion and electron temperature gradients, electro-diffusion has a critical dependence on the charge-to-mass ratio of the ion species. Specifically, it is shown here that electro-diffusion vanishes if the ion species have the same charge-to-mass ratio. An explicit expression for the electro-diffusion ratio is obtained and used to investigate the relative importance of electro- and baro-diffusion mechanisms. In particular, it is found that electro-diffusion reinforces baro-diffusion in the deuterium and tritium mix, but tends to cancel it in the deuterium and helium-3 mix.

Kagan, Grigory; Tang Xianzhu [Theoretical Division Los Alamos National Laboratory Los Alamos, New Mexico 87545 (United States)

2012-08-15

203

Diffusion Coefficients from Molecular Dynamics Simulations in Binary and Ternary Mixtures  

NASA Astrophysics Data System (ADS)

Multicomponent diffusion in liquids is ubiquitous in (bio)chemical processes. It has gained considerable and increasing interest as it is often the rate limiting step in a process. In this paper, we review methods for calculating diffusion coefficients from molecular simulation and predictive engineering models. The main achievements of our research during the past years can be summarized as follows: (1) we introduced a consistent method for computing Fick diffusion coefficients using equilibrium molecular dynamics simulations; (2) we developed a multicomponent Darken equation for the description of the concentration dependence of Maxwell-Stefan diffusivities. In the case of infinite dilution, the multicomponent Darken equation provides an expression for [InlineEquation not available: see fulltext.] which can be used to parametrize the generalized Vignes equation; and (3) a predictive model for self-diffusivities was proposed for the parametrization of the multicomponent Darken equation. This equation accurately describes the concentration dependence of self-diffusivities in weakly associating systems. With these methods, a sound framework for the prediction of mutual diffusion in liquids is achieved.

Liu, Xin; Schnell, Sondre K.; Simon, Jean-Marc; Krüger, Peter; Bedeaux, Dick; Kjelstrup, Signe; Bardow, André; Vlugt, Thijs J. H.

2013-07-01

204

Pattern formation in reaction-diffusion models with spatially inhomogeneous diffusion coefficients  

Microsoft Academic Search

Reaction-diffusion models for biological pattern formation have been studied extensively in a variety of embryonic and ecological contexts. However, despite experimental evidence pointing to the existence of spatial inhomogeneities in various biological systems, most models have only been considered in a spatially homogeneous environment. The authors consider a two-chemical reaction-diffusion mechanism in one space dimension in which one of the

PHILIP K. MAINI; DEBBIE L. BENSON; JONATHAN A. SHERRATT

1992-01-01

205

Determination of Effective Diffusivity Coefficient and Activation Energy Of shelled pistachio by using fluidized bed dryer  

Microsoft Academic Search

Knowledge of desorption kinetics is essential to predict the behavior of the material during drying process and to design dryer equipment .The main objective of this study is to obtain the effective diffusivity coefficient and activation energy of shelled pistachio. Another goal is to find drying kinetics of shelled pistachio in fluidized bed dryer and so thin-layer characteristics of shelled

V. Mohammadpour; M. T. Hamed Mosavian; A. Etemadi

206

On dendritic solidification of multicomponent alloys with unequal liquid diffusion coefficients  

Microsoft Academic Search

A model has been developed previously by Rappaz and Thévoz (Acta metall., 1987, 35, 1478; 1987, 35, 2929) for the solidification of binary alloys having an equiaxed dendritic morphology. The extension of this model to multicomponent alloys is straightforward if the diffusion coefficients in the liquid of the various solute elements are equal. When they are different however, it becomes

M. Rappaz; W. J. Boettinger

1999-01-01

207

ACE Guided-Transformation Method for Estimation of the Coefficient of Soil-Water Diffusivity  

Microsoft Academic Search

Data-analytic tools for choosing transformations to increase linear association are applied to a basic problem of soil physics, the determination of the coefficient of soil-water diffusivity D(?). Data on Manawatu sandy loam illustrate the decisions the analyst must face and the quality of the estimates that the analyst can expect.

Richard D. De Veaux; J. Michael Steele

1989-01-01

208

Backscattering coefficient and drift-diffusion mobility extraction in short channel MOS devices  

Microsoft Academic Search

A new method for the extraction of the backscattering coefficient in nanoMOS devices has been demonstrated. The method, which relies on mobility measurements in linear operation, proves very simple and reliable for the determination of the ballistic rate of transport. Moreover, it allows to obtain the drift-diffusion mobility corrected from ballistic effects and therefore to make a diagnostic of the

I. Pappas; G. Ghibaudo; C. A. Dimitriadis; C. Fenouilletberanger

2009-01-01

209

Unified Derivation of the Various Definitions of Lattice Cell Diffusion Coefficient.  

National Technical Information Service (NTIS)

The various definitions of lattice cell diffusion coefficients are discussed within the context of a one-dimensional slab lattice in one energy group. It is shown how each definition, although originally derived in its own particular way, can be derived f...

R. P. Hughes

1976-01-01

210

Studies on molten glass sealing in diffusion coefficient measurements using shear cell technique  

Microsoft Academic Search

To develop a shear cell technique for measuring the diffusion coefficient of molten materials with high vapor pressure, molten silica glass was used to seal the vapor leak from the clearance between the cell and the rotating rod. An apparatus was designed to investigate the sealing ability of several molten silica glasses. Using Corning 0211, 7059, and 7740 silica glasses,

Jianding Yu; Makoto Natsuisaka; Hirokazu Kato; Satoshi Matsumoto; Kyoichi Kinoshita; Toshio Itami; Shinichi Yoda

2000-01-01

211

The diffusion coefficient of Bi in dilute liquid alloys of Bi in Sn  

Microsoft Academic Search

In analyzing solidification experiments on Sn-Bi alloys it became necessary to know the diffusion coefficient of Bi in liquid Sn-Bi alloys at the liquidus temperature. A literature search revealed two studies 1'~on dilute liquid alloys of Bi in Sn. The work of Niwa et al \\

J. D. Verhoeven; E. D. Gibson; M. B. Beardsley

1975-01-01

212

On Determining Magnetospheric Diffusion Coefficients from the Observed Effects of Jupiter’s Satellite Io  

Microsoft Academic Search

Several previously proposed techniques for determining the radial diffusion coefficient from the observed effects of the inner Jovian satellites on the energetic particle fluxes are discussed, and important shortcomings are pointed out. A new method is proposed which avoids the most important shortcoming by dealing with data from regions somewhat removed from the actual sweeping region. The new technique is

M. F. Thomsen; C. K. Goertz; J. A. Van Allen

1977-01-01

213

Extending the Diffuse Layer Model of Surface Acidity Behavior: III. Estimating Bound Site Activity Coefficients  

EPA Science Inventory

Although detailed thermodynamic analyses of the 2-pK diffuse layer surface complexation model generally specify bound site activity coefficients for the purpose of accounting for those non-ideal excess free energies contributing to bound site electrochemical potentials, in applic...

214

Measurement of the diffusion coefficients of metal vapors in graphite furnaces  

Microsoft Academic Search

Atomic dissipation in a graphite furnace, heated at a rate of approximately 10 Kms?1, has been investigated. At such heating rates, atomic dissipation is separated by time from the atomization process, and the decay portion of the absorbance signal reflects the removal function. The diffusion coefficients of Ag, Au, Bi, Cd, Ga, In, Mn, Pb, Sb, Sn, Tl and Zn

Yuri M Sadagoff

2000-01-01

215

Calculation of effective diffusion coefficient in even approximations of the surface pseudo source method  

SciTech Connect

The preference of even approximations of the surface pseudo source method for calculation of the diffusion coefficient is substantiated. The homogenization limit for the G{sub 0} approximation in the case of the cell size tending to zero is analytically proved.

Kovalishin, A. A., E-mail: kaa@adis.vver.kiae.ru; Laletin, N. I. [Russian Research Centre Kurchatov Institute (Russian Federation)

2011-12-15

216

Evaluation of water and sucrose diffusion coefficients in potato tissue during osmotic concentration  

Microsoft Academic Search

The water and sucrose effective diffusion coefficients behavior were studied in potato tubers immersed in aqueous sucrose solution, 50% (w\\/w), at 27 °C. Water and sucrose concentration profiles were measured as function of the position for 3, 6 and 12 h of immersion. These were adjusted to a mathematical model for three components that take into account the bulk flow

Maria Aparecida Mauro; Florencia Cecilia Menegalli

2003-01-01

217

Dynamic light scattering system with a novel scattering cell for the measurement of particle diffusion coefficients  

Microsoft Academic Search

We present a novel optical scattering cell for the determination of the particle diffusion coefficient by dynamic light scattering, which can be utilized for particle size analysis and viscosity measurements. A major advantage of the light scattering setup introduced is the possibility of performing measurements without having to know the refractive index of the liquid used. Test results are given

Stefan Will; Alfred Leipertz

1996-01-01

218

Diffusion coefficient of krypton atoms in helium gas at low and moderate temperatures  

NASA Astrophysics Data System (ADS)

In the present work, using the Chapman-Enskog method for dilute gases, the diffusion coefficients of ground krypton atoms in a very weakly ionized helium buffer gas are revisited. The calculations are carried out quantum mechanically in the range of low and moderate temperatures. The 1 ?+ potential-energy curve via which Kr approaches He is constructed from the most recent ab initio energy points. The reliable data points used in the construction are smoothly connected to adequate long- and short-range forms. The calculations of the classical second virial coefficients and the Boyle temperature of the helium-krypton mixture are also discussed. These coefficients and their variations in terms of temperature are analysed by adopting the constructed HeKr potential and the Lennard-Jones form that fits it. The diffusion and elastic cross sections are also explored and the resonance features they exhibit are closely examined. The variation law of the diffusion coefficients with temperature is determined for typical values of density and pressure. The coefficients show excellent agreement with the available experimental data; the discrepancies do not exceed 5%.

Bouazza, M. T.; Bouledroua, M.

219

On the anomalous fast ion energy diffusion in toroidal plasmas due to cavity modes  

NASA Astrophysics Data System (ADS)

An enormous wave-particle diffusion coefficient along paths suitable for alpha channeling had been deduced in mode-converted ion Bernstein wave experiments on the Tokamak Fusion Test Reactor (TFTR). The only plausible explanation advanced for such a large diffusion coefficient was the excitation of internal cavity modes which induce particle diffusion along identical diffusion paths, but at much higher rates. Although such a mode was conjectured, it was never observed. However, recent detailed observations of high frequency compressional Alfvén eigenmodes (CAEs) on the National Spherical Torus Experiment (NSTX) indirectly support the existence of the related conjectured modes on TFTR. The eigenmodes responsible for the high frequency magnetic activity can be identified as CAEs through the polarization of the observed magnetic field oscillations in NSTX and through a comparison with the theoretically derived frequency dispersion relation. Here, we show how these recent observations of high frequency CAEs lend support to this explanation of the long-standing puzzle of anomalous fast ion energy diffusion on TFTR. The support of the conjecture that these internal modes could have caused the remarkable ion energy diffusion on TFTR carries significant and favorable implications for the possibilities in achieving the alpha channeling effect with small injected power in a tokamak reactor.

Gorelenkov, N. N.; Fisch, N. J.; Fredrickson, E.

2010-05-01

220

Comparison of diffusion coefficients of electroactive species in aqueous fluid electrolytes and polyacrylate gels: Step generation-collection diffusion measurements and operation of electrochemical devices  

SciTech Connect

The authors report electrochemical measurement of diffusion coefficients and operation of electrochemical devices in aqueous polyacrylate gels formed by neutralization of poly(acrylic acid), MW = 4 [times] 10[sup 6]. Upon neutralization, dilute aqueous solutions become gels with viscosities as high as 5 [times] 10[sup 4] cP at low shear rates. Diffusivity was measured using potential step generation-collection on arrays of closely spaced microelectrodes. The diffusion coefficient, D, of 1,1[prime]-bis(hydroxymethyl)ferrocenium was found to be (5.8 [+-] 0.4) [times] 10[sup [minus]6] cm[sup 2]/s in the gel electrolyte (aqueous 0.5% poly(acrylic acid) at pH 7) and (8.8 [+-] 0.8) [times] 10[sup [minus]6] cm[sup 2]/s in the aqueous fluid electrolyte 0.1 M NaCH[sub 3]CO[sub 2] (pH 7). The small decrease observed in D for the gel vs the fluid with such a large increase in viscosity is contrary to the Stokes-Einstein mode for diffusion in viscous solutions but is in accord with the structure of polyacrylate gels which consists of two phases. The continuous, aqueous phase allows for high diffusivity. Electrochemical transistors based on ruthenium oxide exhibit similar operating characteristics in both polyacrylate gel and aqueous fluid electrolytes. Response times of electrochromic polymer films made from N,N[prime]-bis[p-(trimethoxysilyl)benzyl]-4,4[prime]-bipyridinium are slower in gel by about a factor of 10 compared to aqueous fluid electrolytes. The slow electrochromic switching is likely due to sluggish ion motion, owing to the effects of charge compensation by the polyacrylate. 30 refs., 11 figs., 2 tabs.

Tatistcheff, H.B.; Fritsch-Faules, I.; Wrighton, M.S. (Massachusetts Inst. of Technology, Cambridge (United States))

1993-03-18

221

Simultaneous Measurement of Tracer and Interdiffusion Coefficients: An Isotopic Phenomenological Diffusion Formalism for the Binary Alloy  

SciTech Connect

In this paper, a new development of the classic Onsager phenomenological formalism is derived using relations based on linear response theory. The development concerns the correct description of the fluxes of the atomic isotopes. The resulting expressions in the laboratory frame are surprisingly simple and consist of terms coming from the standard interdiffusion expressions and from Fick s first law where the tracer diffusion coefficient is involved thus providing a better understanding of the relationship between the two approaches - Fick s first law and the Onsager phenomenological formalism. From an experimental application perspective, the new development is applied to the binary alloy case. The formalism provides the means to obtain the interdiffusion coefficient and tracer diffusion coefficients simultaneously from analysis of the interdiffusion concentration profiles in a single experiment.

Belova, Irina [University of Newcastle, NSW, Australia; Kulkarni, Nagraj S [ORNL; Sohn, Yong Ho [University of Central Florida; Murch, Prof. Graeme [University of Newcastle, NSW, Australia

2013-01-01

222

Calculation of the mutual diffusion coefficient by equilibrium and nonequilibrium molecular dynamics  

SciTech Connect

A nonequilibrium molecular dynamics method for the calculation of the mutual diffusion coefficient for a mixture of hard spheres is described. The method is applied to a 50-50 mixture of equidiameter particles having a mass ratio of 0.1 for the two species, at a volume of three times close-packing. By extrapolating the results to the limit of vanishing concentration gradient and infinite system size, we obtain a value in statistical agreement with the result obtained using a Green-Kubo molecular dynamics procedure which is also described. The nonequilibrium calculation yields a mutual diffusion coefficient which decreases slightly with increasing concentration gradient. The Green-Kubo time correlation function for mutual diffusion displays a slow decay with time, qualitatively similar to the long-time tail which has been predicted by the hydrodynamic theory of Pomeau.

Erpenbeck, J.J.; Kincaid, J.M.

1985-01-01

223

Atomistic Simulations of Ion Diffusion in Clay Barriers: Diffusive Path Energy Barriers  

NASA Astrophysics Data System (ADS)

Ion diffusion in clay-rich media is an important transport process relevant to models of contaminant fate and transport in groundwater and risk assessments for the geologic disposal of high-level radioactive waste (HLW). Smectite clay minerals are used as a buffer material in the geologic disposal of HLW due to their low permeability. Ion diffusion experiments with water-saturated, compacted clays have revealed a non-linear trend in which the diffusive energy barrier in clay media at dry densities near 1.0 Mg m-3 exhibited a smaller energy barrier to diffusion than in liquid water (Kozaki, et al. 2005). Although it is likely that the decreased energy barrier is related to preferential diffusion along smectite basal surfaces, experimental methods cannot unambiguously isolate this diffusion pathway. Atomistic simulations were designed to isolate this diffusive pathway and to test if the decreased energy barrier is related to preferential diffusion along the smectite basal surface. In addition, the simulations provide an atomic-scale perspective of this diffusion pathway as a function of temperature. In the present study, we report the energy barrier to diffusion for sodium ions (Na+) at the smectite basal surface. The energy barrier to diffusion at the Na-montmorillonite basal surface was determined by investigating the temperature dependence of ion diffusion through a series of long (9.0 ns) molecular dynamics (MD) simulations in the canonical ensemble (NVT). We show that the energy barrier to diffusion at the clay basal surface is less than the energy barrier to diffusion in free water and demonstrate that this methodology can provide results that are consistent with laboratory diffusion experiments and nanoscale insights into the interpretation of macroscale experimental investigations of ion diffusion in smectite-rich media. Kozaki, T., A. Fujishima, et al. (2005). Engineering Geology, 81(3): 246-254.

Newton, A. G.; Kozaki, T.

2010-12-01

224

Importance of diffuse metal ion binding to RNA.  

PubMed

RNAs are highly charged polyanionic molecules. RNA structure and function are strongly correlated with the ionic condition of the solution. The primary focus of this article is on the role of diffusive ions in RNA folding. Due to the long-range nature of electrostatic interactions, the diffuse ions can contribute significantly to RNA structural stability and folding kinetics. We present an overview of the experimental findings as well as the theoretical developments on the diffuse ion effects in RNA folding. This review places heavy emphasis on the effect of magnesium ions. Magnesium ions play a highly efficient role in stabilizing RNA tertiary structures and promoting tertiary structural folding. The highly efficient role goes beyond the mean-field effect such as the ionic strength. In addition to the effects of specific ion binding and ion dehydration, ion-ion correlation for the diffuse ions can contribute to the efficient role of the multivalent ions such as the magnesium ions in RNA folding. PMID:22010269

Tan, Zhi-Jie; Chen, Shi-Jie

2011-01-01

225

Estimation of the radial diffusion coefficient using REE-associated ground Pc 5 pulsations  

NASA Astrophysics Data System (ADS)

Pc 5 pulsations with frequencies between 1.67 and 6.67 mHz are believed to contribute to the REE in the outer radiation belt during magnetic storms, by means of the observations [Baker et al., 1998; Rostoker et al., 1998; Mathie and Mann, 2000; O'Brien et al., 2001, 2003] and several theoretical studies. The latter studies are roughly categorized into two themes: in-situ acceleration at L lower than 6.6 by wave-particle interactions [Liu et al., 199 9; Summers et al., 1999; Summers and Ma, 2000] and acceleration by radial diffusion from the outer to the inner magnetosphere [Elkington et al., 1999, 2003; Hudson et al., 2000; Kim et al., 2001]. One possible acceleration mechanism is the resonant interaction with Pc 5 toroidal and poloidal pulsations, referred as the radial diffusion mechanism. One of unsolved problems is where and which Pc 5 pulsation mode (toroidal and/or poloidal) play effective role in the radial diffusion process. In order to verify Pc 5 pulsation as the major roles for REEs, we have to examine the time variation of electron phase space density (cf. Green et al., 2004). Electron phase space density is not directly measured, but we can estimate radial diffusion coefficients which determine the electron transportation efficiency, using ground-based magnetic field data. We estimated the radial diffusion coefficient of ground Pc 5 pulsations associated with the Relativistic Electron Enhancement (REE) in the geosynchronous orbit. In order to estimate the radial diffusion coefficient D_LL, we need the value of in-situ Pc 5 electric field power spectral density. In this paper, however, we estimated the equatorial electric field mapped from Pc 5 pulsations power spectral density on the ground. Reciprocal of radial diffusion coefficient describes the timescale T_LL for an electron to diffuse 1 Re. Applying a superposed epoch analysis about timescales T_LL of the radial diffusion for 12 REE events in 2008, we found that when the relativistic electron enhancements occur, T_LL at higher latitude (L larger than 5) is predominantly diffusional, whereas T_LL at lower latitude (L less than 4) is mainly convectional. We concluded that higher-latitude Pc 5 pulsations play more effective roles than lower latitude Pc 5 pulsations in the radial diffusion process.

Fujimoto, A.; Yumoto, K.

2010-12-01

226

Solar wind bulk velocity fluctuations acting as velocity space diffusion on comoving ions  

NASA Astrophysics Data System (ADS)

From most in-situ plasma observations made in the outer heliosphere it became evident that above the injection border of pick-up ions (?1 keV), an extended suprathermal ion tail is found which in most cases can be fitted by a power law with velocity power indices of (-6) ? ?v ? (-4). As has been shown by theory such energetic ion tails cannot be explained by Fermi-2 type velocity diffusion, since in the outer heliosphere both Alfvenic and magnetoacoustic turbulences become too weak. Here we come to a new solution of this unsolved problem by studying the action of solar wind bulk velocity fluctuations on ions co-moving with the wind. As we show the passage of such fluctuations results in energization of each individual ion and systematic evolution of the ion distribution function towards suprathermal tails. From the basic knowledge that we can obtain on this process we can calculate the velocity divergence of the ion phasespace flow and thus can derive a velocity diffusion operator. As we can show here this operator leads to a velocity diffusion coefficient proportional to the square of the ion velocity and, when employed in the phasespace transport equation, together with terms for convective changes, cooling processes and pick-up ion injection, interestingly enough, permits to find solutions for suprathermal power law tails with power indices of ?v ? -5 as very often observed.

Fahr, H.-J.; Chashei, I. V.; Siewert, M.

2012-01-01

227

Diffusion coefficients from resonant interactions with electrostatic electron cyclotron harmonic waves  

SciTech Connect

Pitch-angle diffusion coefficients have been calculated for resonant interaction with electrostatic electron cyclotron harmonic (ECH) waves using quasilinear diffusion theory. Unlike previous calculations, the parallel group velocity has been included in this study. Further, ECH wave intensity is expressed as a function of wave frequency and wave normal angle with respect to ambient magnetic field. It is found that observed wave electric field amplitudes in Earth's magnetosphere are sufficient to set electrons on strong diffusion in the energy ranges of a few hundred eV. However, the required amplitudes are larger than the observed values for keV electrons and higher by about a factor of 3 compared to past calculations. Required electric field amplitudes are smaller at larger radial distances. It is concluded that ECH waves are responsible for diffuse auroral precipitation of electrons with energies less than about 500 eV.

Tripathi, A. K.; Singhal, R. P. [Department of Applied Physics, Institute of Technology, Banaras Hindu University, Varanasi U.P. 221005 (India)

2009-11-15

228

The 2D-J-DOSY Experiment: Resolving Diffusion Coefficients in Mixtures  

NASA Astrophysics Data System (ADS)

Many diffusion-ordered spectroscopy (DOSY) NMR techniques have recently been developed to aid in the deconvolution of complex mixtures. Spectroscopic separation based on chemical and physical properties facilitates the identification of mixture components while eliminating time-consuming separation steps and preserving the chemical environment. One way to improve resolution in such experiments is to spread the spectroscopic information into two dimensions. The 2D-J-DOSY experiment has been designed to resolve mixture components in terms of a chemical shift and proton coupling constant as well as distinguishing them on the basis of translational diffusion. Acquiring a series of spectra as a function of gradient amplitude permits the determination of diffusion coefficients for components that cannot be resolved in the one-dimensional (1D) 1H NMR spectrum. Comparison of the resulting values with those obtained through the traditional 1D diffusion experiment for a mixture of sugars validates The 2D-J-DOSY technique.

Lucas, Laura H.; Otto, William H.; Larive, Cynthia K.

2002-05-01

229

Bounce-averaged diffusion coefficients in non-dipole field for field-aligned chorus waves  

NASA Astrophysics Data System (ADS)

Scattering rates calculated in a dipole field are used in radiation belt codes. We present the results of calculations of the bounce-averaged quasi-linear diffusion coefficients in momentum Dpp, pitch-angle D?? and mixed pitch angle-momentum D?p for field lines (at different distances and MLT) in two non-dipole fields: the Dungey field and the Tsyganenko 89 (T89c) magnetic field. In the T89c field the coefficients were computed for quiet conditions (Kp=2) and storm-time conditions (Kp=6). To calculate diffusion coefficients, we assume that electrons are scattered by the field aligned chorus waves (of Gaussian spectrum) outside the plasmasphere. These waves are observed for MLT between approximately 0 and 12. We also take into consideration the maximum latitude where waves are assumed to be present. We compare calculations of bounce-averaged diffusion coefficients in non-dipole fields with those in the dipole field and discuss the differences. We demonstrate that the effect of bounce averaging in a non-dipole field is negligible at L-shells less than 4, at higher L-shells changes in the field may dramatically alter the scattering rates.

Orlova, K.; Shprits, Y.

2009-12-01

230

Measuring precise diffusion coefficients with two-focus fluorescence correlation spectroscopy  

NASA Astrophysics Data System (ADS)

We present a new method for precisely measuring diffusion coefficients of fluorescent molecules at nanomolar concentrations. The method is based on a modified Fluorescence Correlation Spectroscopy (FCS)-setup which is robust against many artifacts that are inherent to standard FCS 1, 2. The core idea of the new method is the introduction of an external ruler by generating two laterally shifted and overlapping laser foci at a fixed and known distance. Data fitting is facilitated by ab initio calculations of resulting correlation curves and subsequent affine transformation of these curves to match the measured auto- and cross-correlation functions. The affine transformation coefficient along the time axis then directly yields the correct diffusion coefficient. This method is not relying on the rather inexact assumption of a 3D Gaussian shaped detection volume. We measured the diffusion coefficient of the red fluorescent dye Atto-655 (Atto-Tec GmbH) in water and compared the obtained value with results from Gradient Pulsed Field NMR (GPF-NMR).

Dertinger, Thomas; Gregor, Ingo; von der Hocht, Iris; Erdmann, Rainer; Krämer, Benedikt; Koberling, Felix; Hartmann, Rudolf; Enderlein, Jörg

2006-03-01

231

Potential Scale Dependence of Effective Matrix Diffusion Coefficient:Evidence and Preliminary Interpretation  

NASA Astrophysics Data System (ADS)

Owing to the orders-of-magnitude slower flow velocity in the matrix and significantly larger matrix porosity (compared to fractures), matrix diffusion can significantly retard and dilute solute transport process in fractured rock.Therefore, this phenomenon is important for analyzing a variety of problems, including geological disposal of nuclear waste. Matrix diffusion coefficient values measured from small rock samples in the laboratory are generally used for modeling field-scale solute transport in fractured rock. However, by compiling results from a number of field tracer tests corresponding to different geological settings, this study demonstrates that the effective matrix diffusion coefficient at field scale is generally larger than that at lab scale and tends to increase with testing scale. Preliminary interpretations of this observation are investigated by performing numerical experiments for solute transport in flow paths having geometries consistent with percolation theories and characterized by local flow loops formed mainly by sub-fractures. The flow-path geometries under consideration could result in scale-dependent behavior of the effective matrix diffusion coefficient, with large values being observed at intermediate to large travel distances. Ignoring such values would to systematically under-estimating travel times in fractured rock environments.

Liu, H.; Zhang, Y.; Zhou, Q.; Molz, F.

2005-12-01

232

An interpretation of potential scale dependence of the effectivematrix diffusion coefficient  

SciTech Connect

Matrix diffusion is an important process for solutetransport in fractured rock, and the matrix diffusion coefficient is akey parameter for describing this process. Previous studies indicatedthat the effective matrix diffusion coefficient values, obtained from alarge number of field tracer tests, are enhanced in comparison with localvalues and may increase with test scale. In this study, we have performednumerical experiments to investigate potential mechanisms behind possiblescale-dependent behavior. The focus of the experiments is on solutetransport in flow paths having geometries consistent with percolationtheories and characterized by local flow loops formed mainly bysmall-scale fractures. The water velocity distribution through a flowpath was determined using discrete fracture network flow simulations, andsolute transport was calculated using a previously derivedimpulse-response function and a particle-tracking scheme. Values foreffective (or up-scaled) transport parameters were obtained by matchingbreakthrough curves from numerical experiments with an analyticalsolution for solute transport along a single fracture. Results indicatethat a combination of local flow loops and the associated matrixdiffusion process, together with scaling properties in flow pathgeometry, seems to be the dominant mechanism causing the observed scaledependence of theeffective matrix diffusion coefficient (at a range ofscales).

Liu, H.H.; Zhang, Y.Q.; Zhou, Q.; Molz, F.J.

2005-11-30

233

Determination of the diffusion coefficient of hydrogen in gamma titanium aluminides during electrolytic charging  

SciTech Connect

The diffusion coefficient of hydrogen in some gamma based titanium aluminide alloys was determined at room temperature using an electrochemical techniques. A cast Ti-48Al-2Cr alloy as well as Ti-46.5Al-4(Cr,Nb,Ta,B) sheet material with primary annealed and designed fully lamellar microstructures were subjected to cathodic hydrogen charging at room temperature in the galvanostatic mode. The potential variation with time was monitored form which data the values of the diffusion coefficient of hydrogen, D were calculated form well known error function/infinite series solutions to Fick's second law. Very good correlation was obtained with respect to theoretical calculations. The diffusion coefficients appear to be in close agreement with those for the cast alloy calculated from microhardness measurements. The value of D can be overestimated for thick specimens. Results show that neither the microstructure in terms of grain/lamellar colony size, nor the charging current density, appear to have a significant effect on the value of D. Lattice diffusion appears to be rate controlling.

Sundaram, P.A.; Wessel, E.; Clemens, H.; Kestler, H.; Ennis, P.J.; Quadakkers, W.J.; Singheiser, L.

2000-03-14

234

A new model of thermal diffusion coefficients in binary hydrocarbon mixtures  

SciTech Connect

Thermal diffusion is important for the study of composition variations in hydrocarbon reservoirs, and it can either enhance or weaken the separation in mixtures. The authors present a new model for the prediction of thermal diffusion coefficients in binary mixtures of reservoir fluids using the thermodynamics of irreversible processes. the model needs equilibrium properties of mixtures and energy of viscous flow. Equilibrium properties are obtained from the volume translated Peng-Robinson equation of state, and the energy of viscous flow is estimated from viscosity. The model has been applied to predict thermal diffusion coefficients of several mixtures consisting of nonhydrocarbon and hydrocarbon fluids. Comparisons of theoretical results with experimental data show a good performance of the model except in the near-critical region where all existing models are deficient. In particular, the predicted sign of thermal diffusion coefficients is consistent with experimental observations in systems investigated here, namely, C{sub 1}/C{sub 3}, C{sub 1}/C{sub 4}, C{sub 7}/C{sub 12}, C{sub 7}/C{sub 16}, Ar/CO{sub 2}, N{sub 2}/CO{sub 2}, H{sub 2}/N{sub 2}, H{sub 2}/CO{sub 2}, and C{sub 1}/CO{sub 2}, except in C{sub 1}/N{sub 2}, in which the values of thermal diffusion coefficients are extremely low. The authors have also modified some of the earlier models, such as the Kempers, Haase, and Rutherford models, which are based on phenomenological and kinetic approaches. In general, the model has been found to be most reliable and represents a significant improvement over the earlier models.

Shukla, K.; Firoozabadi, A. [Reservoir Engineering Research Inst., Palo Alto, CA (United States)

1998-08-01

235

Diffuse minor ions upstream of simulated quasi-parallel shocks  

Microsoft Academic Search

We have performed a number of one-dimensional hybrid (particle ions, massless fluid electrons) simulations of quasi-parallel collisionless shocks in order to elucidate the origin of diffuse upstream minor ions. Minor ions are treated self-consistently by the hybrid code; however, a number of runs have also been performed wherein the minor ions are treated as test particles. We have investigated the

K. J. Trattner; M. Scholer

1994-01-01

236

Calculation of radon diffusion coefficient and diffusion length for different building construction materials  

Microsoft Academic Search

The diffusion of radon in dwellings is a process determined by the radon concentration gradient across the building material\\u000a structure between the radon source and the surrounding air, and can be a significant contributor to indoor radon inflow. Radon\\u000a can originate from the deeply buried deposit beneath homes and can migrate to the surface of earth. Radon emanates to the

A. K. Narula; S. K. Goyal; Savita Saini; R. P. Chauhan; S. K. Chakarvarti

2009-01-01

237

Water and solute diffusion coefficients of carrot as a function of temperature and concentration during osmotic dehydration  

Microsoft Academic Search

Mass transfer was quantitatively investigated during osmotic dehydration of fresh carrot over a range of concentration (40–70 °B) and temperature (30–50 °C) of osmotic solution. Effective diffusion coefficients of water as well as sucrose were estimated using the solution of Fick's unsteady state law. Multilinear analysis of the estimated effective diffusion coefficients of water and solute revealed that these values

N. K. Rastogi; K. S. M. S. Raghavarao

1997-01-01

238

Nuclear magnetic resonance measurement of skeletal muscle: anisotrophy of the diffusion coefficient of the intracellular water.  

PubMed Central

The anisotropy of the spin-diffusion coefficient Ds of water protons in skeletal muscle has been studied by pulsed NMR methods. The mid-portion of the tibialis anterior muscle of mature male rats was placed in a special sample holder by means of which the muscle fiber orientation theta relative to the diffusion direction could be varied over the range 0 degrees less than or equal to theta less than or equal to 90 degrees. The value of Ds(theta) was determined for theta = 0 degrees, 45 degrees, and 90 degrees. The measured anisotropy Ds(0)/Ds(90) was 1.39, and the value of Ds(0) was 1.39 X 10(-5) cm2/s. These results are interpreted within the framework of a model calculation in which the diffusion equation is solved for a regular hexagonal network similar to the actin-myosin filament network. The large anisotropy, and the large reduction in the value of Ds measured parallel to the filament axes lead to two major conclusions: (a) interpretations in which the reduction in Ds is ascribed to the effect of geometrical obstructions on the diffusion of "free" water are ruled out; and, (b) there is a large fraction of the cellular water associated with the proteins in such a way that its diffusion coefficient is substantially reduced.

Cleveland, G G; Chang, D C; Hazlewood, C F; Rorschach, H E

1976-01-01

239

Effective medium theory for reaction rates and diffusion coefficients of heterogeneous systems.  

PubMed

A simple effective medium theory is derived for spatially heterogeneous nonlinear reaction-diffusion media. Its validity is tested through comparisons with simulations of front and pulse propagation in systems with spatially varying diffusion coefficients and reaction rates. The theory is able to predict wave speeds if the characteristic front width is much larger than the length scale of the heterogeneities. This condition is violated in media with isolated or weakly connected sites. However, the theory nevertheless provides good results in cases where it correctly predicts the percolation threshold of the medium. PMID:19658977

Alonso, Sergio; Kapral, Raymond; Bär, Markus

2009-06-12

240

Effective Medium Theory for Reaction Rates and Diffusion Coefficients of Heterogeneous Systems  

NASA Astrophysics Data System (ADS)

A simple effective medium theory is derived for spatially heterogeneous nonlinear reaction-diffusion media. Its validity is tested through comparisons with simulations of front and pulse propagation in systems with spatially varying diffusion coefficients and reaction rates. The theory is able to predict wave speeds if the characteristic front width is much larger than the length scale of the heterogeneities. This condition is violated in media with isolated or weakly connected sites. However, the theory nevertheless provides good results in cases where it correctly predicts the percolation threshold of the medium.

Alonso, Sergio; Kapral, Raymond; Bär, Markus

2009-06-01

241

Ion implantation and diffusion of Al in a SiO2/Si system  

NASA Astrophysics Data System (ADS)

The diffusion and segregation of ion implanted Al in SiO2 and Si layers were studied for several experimental conditions. Al ions were implanted into SiO2, Si and through a SiO2 layer into Si substrates at several energies (80, 300, 650 and 6000 keV) and doses (3.4 × 1014 - 1 × 1015 cm-2). The Al diffusion coefficient in SiO2 was measured at 1200°C for times up to 5 days, and it results five orders of magnitude lower than in Si. The experiments show that the Al atoms implanted into Si do not out-diffuse during thermal treatments from the SiO2 capping layer, but segregate at the SiO2/Si interface. The high segregation coefficient gives rise to a trapping of Al into the oxide layer comparable to the out-diffusion of Al from uncapped Si substrates. The determined parameters for Al diffusion and segregation in the SiO2/Si system were introduced in a simulation code to calculate the Al diffusion profiles which result in agreement with the experimental data.

Galvagno, G.; La Ferla, A.; Rimini, E.; Raineri, V.; Franco, G.; Camalleri, M.; Gasparotto, A.; Carnera, A.; Rinaudo, S.

1996-08-01

242

Defect diffusion in ion implanted glasses.  

National Technical Information Service (NTIS)

Ion implantation in glasses produces structure modifications at depths greater than those of the implanted ion range. Such a result is evidenced by means of leaching experiments, alkali element depletion, distribution of gaseous implanted species, etching...

G. W. Arnold G. Battaglin A. Boscolo-Boscoletto F. Caccavale G. De Marchi

1991-01-01

243

Quantitative photoacoustic microscopy of optical absorption coefficients from acoustic spectra in the optical diffusive regime  

NASA Astrophysics Data System (ADS)

Photoacoustic (PA) microscopy (PAM) can image optical absorption contrast with ultrasonic spatial resolution in the optical diffusive regime. Conventionally, accurate quantification in PAM requires knowledge of the optical fluence attenuation, acoustic pressure attenuation, and detection bandwidth. We circumvent this requirement by quantifying the optical absorption coefficients from the acoustic spectra of PA signals acquired at multiple optical wavelengths. With the acoustic spectral method, the absorption coefficients of an oxygenated bovine blood phantom at 560, 565, 570, and 575 nm were quantified with errors of <3%. We also quantified the total hemoglobin concentration and hemoglobin oxygen saturation in a live mouse. Compared with the conventional amplitude method, the acoustic spectral method provides greater quantification accuracy in the optical diffusive regime. The limitations of the acoustic spectral method was also discussed.

Guo, Zijian; Favazza, Christopher; Garcia-Uribe, Alejandro; Wang, Lihong V.

2012-06-01

244

A comprehensive study of diffusion, thermodiffusion, and Soret coefficients of water-isopropanol mixtures  

NASA Astrophysics Data System (ADS)

We report on the measurement of diffusion (D), thermodiffusion (DT), and Soret (ST) coefficients in water-isopropanol mixtures by three different instrumental techniques: thermogravitational column in combination with sliding symmetric tubes, optical beam deflection, and optical digital interferometry. All the coefficients have been measured over the full concentration range. Results from different instruments are in excellent agreement over a broad overlapping composition (water mass fraction) range 0.2 < c < 0.7, providing new reliable benchmark data. Comparison with microgravity measurements (SODI/IVIDIL (Selected Optical Diagnostic Instrument/Influence of VIbration on DIffusion in Liquids)) onboard the International Space Station and with literature data (where available) generally gives a good agreement. Contrary to theoretical predictions and previous experimental expectations we have not observed a second sign change of ST at low water concentrations.

Mialdun, A.; Yasnou, V.; Shevtsova, V.; Königer, A.; Köhler, W.; Alonso de Mezquia, D.; Bou-Ali, M. M.

2012-06-01

245

Quantitative photoacoustic microscopy of optical absorption coefficients from acoustic spectra in the optical diffusive regime.  

PubMed

Photoacoustic (PA) microscopy (PAM) can image optical absorption contrast with ultrasonic spatial resolution in the optical diffusive regime. Conventionally, accurate quantification in PAM requires knowledge of the optical fluence attenuation, acoustic pressure attenuation, and detection bandwidth. We circumvent this requirement by quantifying the optical absorption coefficients from the acoustic spectra of PA signals acquired at multiple optical wavelengths. With the acoustic spectral method, the absorption coefficients of an oxygenated bovine blood phantom at 560, 565, 570, and 575 nm were quantified with errors of <3%. We also quantified the total hemoglobin concentration and hemoglobin oxygen saturation in a live mouse. Compared with the conventional amplitude method, the acoustic spectral method provides greater quantification accuracy in the optical diffusive regime. The limitations of the acoustic spectral method was also discussed. PMID:22734767

Guo, Zijian; Favazza, Christopher; Garcia-Uribe, Alejandro; Wang, Lihong V

2012-06-01

246

Thermal diffusivity coefficient of glycerin determined on an acoustically levitated drop.  

PubMed

We present a technique that can be used to determine the thermal diffusivity coefficient of undercooled liquids that exist at temperatures below their freezing points. The technique involves levitation of a small amount of liquid in the shape of a flattened drop using an acoustic levitator and heating it with a CO2 laser. The heated drop is then allowed to cool naturally by heat loss from the surface. Due to acoustic streaming, heat loss is highly non-uniform and appears to mainly occur at the drop circumference (equatorial region). This fact allows us to relate the heat loss rate with a heat transfer model to determine the thermal diffusion coefficient. We demonstrate the feasibility of the technique using glycerin drops as a model liquid. PMID:12446319

Ohsaka, K; Rednikov, A; Sadhal, S S

2002-10-01

247

A Monte Carlo model for determination of binary diffusion coefficients in gases  

SciTech Connect

A Monte Carlo method has been developed for the calculation of binary diffusion coefficients in gas mixtures. The method is based on the stochastic solution of the linear Boltzmann equation obtained for the transport of one component in a thermal bath of the second one. Anisotropic scattering is included by calculating the classical deflection angle in binary collisions under isotropic potential. Model results are compared to accurate solutions of the Chapman-Enskog equation in the first and higher orders. We have selected two different cases, H{sub 2} in H{sub 2} and O in O{sub 2}, assuming rigid spheres or using a model phenomenological potential. Diffusion coefficients, calculated in the proposed approach, are found in close agreement with Chapman-Enskog results in all the cases considered, the deviations being reduced using higher order approximations.

Panarese, A. [Department Physics, University of Bari, Bari (Italy); Bruno, D.; Colonna, G. [CNR IMIP Bari (Italy); Diomede, P. [Department Chemistry, University of Bari, Bari (Italy); Laricchiuta, A. [CNR IMIP Bari (Italy); Longo, S., E-mail: savino.longo@ba.imip.cnr.i [Department Chemistry, University of Bari, Bari (Italy); CNR IMIP Bari (Italy); Capitelli, M. [Department Chemistry, University of Bari, Bari (Italy); CNR IMIP Bari (Italy)

2011-06-20

248

Determination of the diffusion coefficient and solubility of radon in plastics.  

PubMed

This paper describes a method for determination of the diffusion coefficient and the solubility of radon in plastics. The method is based on the absorption and desorption of radon in plastics. Firstly, plastic specimens are exposed for controlled time to referent (222)Rn concentrations. After exposure, the activity of the specimens is followed by HPGe gamma spectrometry. Using the mathematical algorithm described in this report and the decrease of activity as a function of time, the diffusion coefficient can be determined. In addition, if the referent (222)Rn concentration during the exposure is known, the solubility of radon can be determined. The algorithm has been experimentally applied for different plastics. The results show that this approach allows the specified quantities to be determined with a rather high accuracy-depending on the quality of the counting equipment, it can be better than 10 %. PMID:21467078

Pressyanov, D; Georgiev, S; Dimitrova, I; Mitev, K; Boshkova, T

2011-04-05

249

Determination of the helium thermal diffusion coefficient in britholite using a NRA method: new results  

NASA Astrophysics Data System (ADS)

Dimensioning of actinides waste packages for long duration storage has to take into account helium production from natural decay and release rates from the material. For the latter, we propose here an improved method for the determination of the helium diffusion coefficient in britholite, to be used for minor actinides storage. This work is based on results we previously published using the classical three steps method: 3He implantation on a Van de Graaff facility, 3He profile determination analysing the protons resulting from the 3He(d,p)4He reaction in a nuclear microprobe, evolution of the helium profile during annealings. Taking explicitly into account the incident deuterons energy stragglings allows us to show that the implanted helium profiles are bimodal, each component leading to a different helium diffusion coefficient.

Gosset, Dominique; Trocellier, Patrick

2005-02-01

250

Quantitative photoacoustic microscopy of optical absorption coefficients from acoustic spectra in the optical diffusive regime  

PubMed Central

Abstract. Photoacoustic (PA) microscopy (PAM) can image optical absorption contrast with ultrasonic spatial resolution in the optical diffusive regime. Conventionally, accurate quantification in PAM requires knowledge of the optical fluence attenuation, acoustic pressure attenuation, and detection bandwidth. We circumvent this requirement by quantifying the optical absorption coefficients from the acoustic spectra of PA signals acquired at multiple optical wavelengths. With the acoustic spectral method, the absorption coefficients of an oxygenated bovine blood phantom at 560, 565, 570, and 575 nm were quantified with errors of <3%. We also quantified the total hemoglobin concentration and hemoglobin oxygen saturation in a live mouse. Compared with the conventional amplitude method, the acoustic spectral method provides greater quantification accuracy in the optical diffusive regime. The limitations of the acoustic spectral method was also discussed.

Guo, Zijian; Favazza, Christopher; Garcia-Uribe, Alejandro; Wang, Lihong V.

2012-01-01

251

Bounce-averaged diffusion coefficients in the Tsyganenko field model for oblique chorus waves  

NASA Astrophysics Data System (ADS)

The assessment of the importance of various acceleration and loss mechanisms of relativistic electrons is crucially important for predicting and understanding the dynamics of the radiation belts. It is commonly accepted that resonant wave-particle interactions play a major role in these processes. Bounce-averaged momentum, pitch-angle, and mixed diffusion coefficients, calculated using various models of spectral properties of waves and spatial distributions of plasma waves, are used in modern radiation belt codes as inputs. The diffusion coefficients for radiation belt models are usually computed using the quasi-linear theory and are bounce-averaged in the dipole magnetic field. During magnetic storms, however, the configuration and the value of the magnetic field are significantly changed, which may potentially influence the scattering rates. The purpose of this work is to estimate the role of a realistic magnetic field model on the bounce-averaged diffusion coefficients. We present the results of computations of bounce-averaged quasi-linear momentum Dpp, pitch-angle D?? and mixed pitch angle-momentum D?p diffusion coefficients in the Tsyganenko magnetic field model. We assume that electrons are scattered by oblique whistler mode chorus waves of Gaussian spread of wave power spectral density and wave normal angle outside the plasmasphere. The scattering rates are computed using the full electromagnetic dispersion relation and up to ±5-order resonance condition including Landau resonance. The diffusion coefficients are calculated for quiet conditions (Kp=2) and storm-time conditions (Kp=6) for the day and night sides. We compare scattering rates bounce-averaged in the Tsyganenko field model with those in the dipole field and discuss the differences. The results are followed by a physical explanation of how the magnetic field model can change the bounce-averaged scattering rates. The calculations show that, during active conditions, the pitch-angle scattering by chorus waves in the realistic magnetic field can diffuse relativistic electrons to the loss cone not only on the day side, as was previously shown, but also on the night side. This explains the often observed microburst precipitation on the night side. Our study shows that while there are still a number of unknown parameters that determine scattering rates, inclusion of bounce-averaging in the realistic field will be crucially important for future radiation belt modeling.

Orlova, Ksenia; Shprits, Yuri

2010-05-01

252

Ion beam analysis of diffusion in heterogeneous materials  

NASA Astrophysics Data System (ADS)

Ion-beam analysis has been applied to a variety of problems involving diffusion in heterogeneous materials. An energy loss technique has been used to study both the diffusion of water and the surface segregation of fluoropolymers in polymeric matrices. A scanning micro-beam technique has been developed to allow water concentrations in hydrophilic polymers and cements to be measured together with associated solute elements. It has also been applied to the diffusion of shampoo into hair.

Clough, A. S.; Jenneson, P. M.

1998-04-01

253

Simulating the time-dependent diffusion coefficient in mixed-pore-size materials  

Microsoft Academic Search

Porous media with a wide distribution of pore sizes are quite common. We show that variable-step-size random walk simulations can be used to model the time-dependent diffusion coefficient D(t) in such porous media. The issue to be overcome is that, in variable-step-size walks, each walker carries its own ``clock,'' and its position is known only at a random set of

Zhigang Zhang; David L. Johnson; Lawrence M. Schwartz

2011-01-01

254

THE PARALLEL DIFFUSION COEFFICIENT AND ADIABATIC FOCUSING OF COSMIC-RAY PARTICLES  

SciTech Connect

In this paper, the problem of focused particle transport is revisited. A description in terms of a system of stochastic differential equations, completely equivalent to the Fokker-Planck equation, is suggested. The coefficient for spatial diffusion parallel to the mean magnetic field is calculated. The case of isotropic pitch angle scattering and weak focusing is analyzed in detail. The disagreement between a recent analysis by Shalchi and other treatments of the same problem is discussed.

Litvinenko, Yuri E. [Department of Mathematics, University of Waikato, P.B. 3105, Hamilton (New Zealand)

2012-01-20

255

Mass and temperature-dependent diffusion coefficients for lightnoble gases for the TOUGH2-EOSN Model  

Microsoft Academic Search

This report describes modifications made to the EOSN module(Shan and Pruess, 2003) of the nonisothermal multiphase flow simulatorTOUGH2 (Pruess, et al., 1999). The EOSN fluid property module simulatestransport of water, brine, air, and noble gases or CO2 in the subsurface.In the standard version of the EOSN module, diffusion coefficients can bespecified by the user, but there is no allowance for

J. L. Andrews; S. Finsterle; M. O. Saar

2007-01-01

256

Chemical diffusion coefficient of Ag 1.92Te obtained from galvanostatic polarization measurements  

Microsoft Academic Search

Galvanostatic polarization experiments are performed on the asymmetric electrochemical cell Ag|AgI|Ag1.92Te|Pt in order to determine the chemical diffusion coefficient of AgyTe (1.912 < y < 1.920) at 160°C as a function of composition, the latter being varied by coulometric titration. As the specimen shows comparable ionic and electronic conductivities (the electronic transport number is around 0.8–0.9), new evaluation formulas are

W. Preis; W. Sitte

1997-01-01

257

Diffusion coefficients of some solutes in fcc and liquid Al: critical evaluation and correlation  

Microsoft Academic Search

The diffusion coefficients of several transition elements (Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) and a few non-transition elements (Mg, Si, Ga, and Ge) in fcc and liquid Al are critically reviewed and assessed by means of the least-squares method and semi-empirical correlations. Inconsistent experimental data are identified and ruled out. In the case of the elements,

Yong Du; Y. A Chang; Baiyun Huang; Weiping Gong; Zhanpeng Jin; Honghui Xu; Zhaohui Yuan; Yong Liu; Yuehui He; F.-Y Xie

2003-01-01

258

Synoptic water clarity assessment in the Florida Keys using diffuse attenuation coefficient estimated from Landsat imagery  

Microsoft Academic Search

The diffuse attenuation coefficient, K (m–1), is a measure of the effective attenuation of light in the water column. It characterizes water clarity and is used as a\\u000a proxy for water quality. Mapping of shallow water benthic habitats using optical means, including daytime visible satellite\\u000a imagery, requires knowledge of K to correct for water column effects such as light absorption

D. Palandro; C. Hu; S. Andréfouët; F. E. Muller-Karger

259

Kubo number and magnetic field line diffusion coefficient for anisotropic magnetic turbulence  

Microsoft Academic Search

The magnetic field line diffusion coefficients Dx and Dy are obtained by numerical simulations in the case that all the magnetic turbulence correlation lengths lx, ly, and lz are different. We find that the variety of numerical results can be organized in terms of the Kubo number, the definition of which is extended from R=(deltaB\\/B0)(l||\\/l?) to R=(deltaB\\/B0)(lz\\/lx), for lx>=ly. Here,

P. Pommois; P. Veltri; G. Zimbardo

2001-01-01

260

Apparent diffusion coefficient and MR relaxation during osmotic manipulation in isolated turtle cerebellum  

Microsoft Academic Search

ABSTRACT The apparent diffusion coefficient (ADC) and relaxation times of water were measured,by magnetic resonance imaging (MRI) in the isolated turtle cerebellum during osmotic cell volume manipulation. The aim was to study effects of cell volume changes, a factor in ischaemia and spreading depression, in isolation from considerations of blood flow and metabolism. Cerebella were superfused at 12-14°C with solutions

Jacqueline M. O'Shea; Stephen R. Williams; Nick van Bruggen; Anthony R. Gardner-Medwin

2000-01-01

261

Diffuse reflectance spectroscopy as a tool to measure the absorption coefficient in skin: system calibration.  

PubMed

An individualised laser skin treatment may enhance the treatment and reduces risks and side-effects. The optical properties (absorption and scattering coefficients) are important parameters in the propagation of laser light in skin tissue. The differences in the melanin content of different skin phototypes influence the absorption of the light. The absorption coefficient at the treatment wavelength for an individual can be determined by diffuse reflectance spectroscopy, using a probe containing seven fibres. Six of the fibres deliver the light to the measurement site and the central fibre collects the diffused reflected light. This is an in vivo technique, offering benefits for near-real-time results. Such a probe, with an effective wavelength band from 450 to 800 nm, was used to calibrate skin-simulating phantoms consisting of intralipid and ink. The calibration constants were used to calculate the absorption coefficients from the diffuse reflectance measurements of three volunteers (skin phototypes, II, IV and V) for sun-exposed and non-exposed areas on the arm. PMID:22410734

Karsten, A E; Singh, A; Karsten, P A; Braun, M W H

2012-03-13

262

Effective molecular diffusion coefficient in a two-phase gel medium  

NASA Astrophysics Data System (ADS)

Our group has previously derived a mean-field expression for the effective diffusion coefficient of a probe molecule in a two-phase medium consisting of a hydrogel with large gel-free solvent inclusions. The diffusion coefficient is expressed in terms of the homogeneous diffusion coefficient in the gel and in the solvent, the gel concentration, the relative volume of the inclusions and the viscosities of the two phases. The expression was compared with exact numerical lattice calculations and was found to provide remarkably accurate predictions. The work presented here is an extension of the previously described study. The goal is to investigate more characteristics of a two-phase medium using further exact numerical calculations and then bring everything into one final expression. Some of the parameters we now include are the possible presence of gel fibers inside the inclusions, the local affinity effects (attractive obstacles) and the interfacial effects between the two phases. This work provides robust grounds for the modeling and design of multiphase systems for specific applications, e.g., phase-separated hydrogels as novel food agents or efficient drug-delivery platforms.

Kingsburry, Christine; Slater, Gary W.

2007-03-01

263

Molecular dynamics simulation of enhanced oxygen ion diffusion in strained yttria-stabilized zirconia  

Microsoft Academic Search

The application of strain to yttria-stabilized zirconia (YSZ), which can be realized by sandwiching a thin YSZ film epitaxially between layers of a material with larger lattice constants, is proposed as a means to enhance oxygen ion mobility. The possible mechanism of such an enhancement was investigated by molecular dynamics using a CeO2-YSZ superlattice. The calculated diffusion coefficient of oxygen

Ken Suzuki; Momoji Kubo; Yasunori Oumi; Ryuji Miura; Hiromitsu Takaba; Adil Fahmi; Abhijit Chatterjee; Kazuo Teraishi; Akira Miyamoto

1998-01-01

264

a New Method for Measuring Diffusion Coefficient of Gases in Liquids by Plif  

NASA Astrophysics Data System (ADS)

Gas-liquid mass transfer is a major issue in engineering processes such as wastewater treatment or biogas production since this phenomenon is directly linked to their design and efficiency. In recent years, much research has been done in this area but some gaps still remain in our knowledge of gas-liquid transfer, in particular concerning molecular diffusivity. The determination of molecular diffusivity is commonly based on empirical correlations, such as the widely used Wilke and Chang13 expression, valid under specific conditions and with relatively high uncertainties. In the present work, an innovative and promising technique is proposed to determine diffusion coefficients of gases in liquids. This technique is based on visualizing and quantifying oxygen diffusion across a flat gas-liquid interface, in a Newtonian medium, using planar laser induced fluorescence (PLIF) with inhibition. Particle image velocimetry (PIV) experiments were conducted to confirm the hydrodynamic flow field in the liquid phase. Results included the visualization of oxygen diffusion over time, and the quantification of this visualization. The oxygen diffusivity thus determined is in agreement with values found in the literature.

Jimenez, Mélanie; Dietrich, Nicolas; Hebrard, Gilles

265

A novel method to measure diffusion coefficients in porous metal-organic frameworks.  

PubMed

We present a novel method to determine diffusion constants of small molecules within highly porous metal-organic frameworks (MOFs). The method is based on the recently proposed liquid-phase epitaxy (LPE) process to grow MOF thin films (SURMOFs) on appropriately functionalized substrates, in particular on organic surfaces exposed by thiolate-based self-assembled monolayers (SAMs). By applying the LPE-method to SAM-coated quartz crystals, the time-dependence of the mass-uptake of the MOF when exposing it to a gas is measured by a quartz-crystal microbalance (QCM). The homogenous nature of the SURMOFs together with their well-defined thickness allow to analyze the QCM-data using Fickian diffusion to yield the diffusion constant. We demonstrate the potential of this method for the case of pyridine diffusion within HKUST-1 (Cu(3)(BTC)(2)) MOF, for which the diffusion coefficient at room temperature is found to amount to 1.5 x 10(-19) m(2) s(-1). Assuming a Fickian diffusion and a hopping mechanism, we yield a binding energy of 0.78 eV of the pyridine to the Cu(2+) sites within the HKUST-1 MOF, a value in good agreement with the results of precise ab initio quantum chemistry calculations. PMID:20532258

Zybaylo, Olexandra; Shekhah, Osama; Wang, Hui; Tafipolsky, Maxim; Schmid, Rochus; Johannsmann, Diethelm; Wöll, Christof

2010-06-07

266

Raman spectroscopy as a tool for measuring mutual-diffusion coefficients in hydrogels.  

PubMed

Raman spectroscopy has been exploited to characterize the diffusion properties of solutes in hydrogels. Raman active vibrations were used as intrinsic probes of the solute concentration along gel cylinders. The resulting one-dimensional solute distribution, characterized as a function of both time and space, could be analyzed with a model based on Fick's diffusion law, and the mutual-diffusion coefficient (Dm) was then determined. To illustrate the potential of this approach, we measured the Dm of two polyethylene glycols (PEG) in Ca-alginate gels. In this case, the intensity of the CH stretching band was used to obtain the concentration profiles of PEGs, whereas the OH stretching band of water was used as an internal intensity standard. In addition to providing a straightforward approach to measuring diffusion coefficients, the Raman profile analysis provides information relative to the accessibility of gels to large molecules. As an example, it was found that the PEG penetration in Ca-alginate gels was restricted, a phenomenon that was dependent on PEG size. The Raman technique presented here effectively characterizes transport properties of solutes in gels, and such characterization is required for developing several technical applications of gels, such as their use as materials for controlled release of drugs. PMID:14658654

Kwak, Sungjong; Lafleur, Michel

2003-07-01

267

Diffusion of heavy ions in the solar corona  

Microsoft Academic Search

The steady-state diffusive motion of ionized atoms (more massive than hydrogen) in the solar corona has been investigated theoretically, with special emphasis on relating the flow velocity and density of these ions to the flow properties of the ionized hydrogen background. The basic approach taken in this study was to regard the ions as 'test particles' interacting with the background

Y. Alloucherie

1970-01-01

268

Diffusivity measurement of heavy ions in Wyoming montmorillonite gels by X-ray computed tomography.  

PubMed

Medical X-ray computed tomography (CT) was applied to the measurement of the diffusion coefficients of heavy ions in an artificial barrier material for the disposal of nuclear wastes. Cs(+), Sr(2+), I(-), and Br(-) are the heavy ions measured and the barrier used is the water-rich gel of Wyoming montmorillonite (86.5-100 wt.% H(2)O). X-ray CT yields an inevitable artifact (beam-hardening) in the obtained images. Before the diffusion experiments, the polychromatic primary X-ray spectrum of the CT scanner was measured by a CdZnTe detector, and the effects of the artifact were examined for an aqueous CsCl solution sample. The results show that the beam-hardening artifact derived from the polychromatic photon energy distribution can be suppressed by applying a special image reconstruction method assuming the chemical composition of samples. The transient one-dimensional diffusion of heavy ions in a plastic container filled with the gel was imaged nondestructively by the X-ray CT scanner with an in-plane resolution of 0.31 mm and slice thickness of 2 mm. The results show that diffusivities decrease with increasing clay weight fraction. The degree of the diffusivity decrease was high for cations (Cs(+) and Sr(2+)) and low for anions (I(-) and Br(-)). The quantitative decomposition of the contribution of the geometrical tortuosity and of the sorption to the diffusivity was performed by subtracting the diffusivity of nonsorbing I(-) from the measured diffusivities. The results show that the contribution of the sorption is large for Cs(+), Sr(2+) and small for Br(-). Because X-ray CT allows nondestructive and quick measurements of diffusivities, the technique would be useful particularly for measuring the diffusive migration of harmful radioactive elements. PMID:12598101

Nakashima, Yoshito

2003-03-01

269

Diffusion barrier layer fabrication by plasma immersion ion implantation  

NASA Astrophysics Data System (ADS)

Plasma immersion Ion Implantation technique has been used to modify the diffusion barrier properties of titanium (Ti) metal layer against copper diffusion. Ti coated silicon wafer were implanted with doses viz. 1015ions/cm2 and 1017ions/cm2 corresponding to low and high dose regime. High dose of implantation of nitrogen ions in the film render it to become Ti(N). Cu/Ti(N)/Si structures were formed by depositing copper over the implanted samples. Diffusion barrier properties of Ti(N) was evaluated after annealing the samples up to 700ºC for 30 minutes. Sheet resistance, X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) measurements were carried out to investigate the effect of annealing. Low dose implanted Ti layer does not show any change in its diffusion barrier properties and fails at about 400ºC. The failure of diffusion barrier properties of low dose implanted samples is attributed to the chemical reaction between titanium and copper films. The high dose implanted layer stops the diffusion of Cu metal through it even at high annealing temperature. The enhancement in its diffusion barrier properties is supposed to be due to nitridation of titanium film which increases the activation energy involved for its chemical reaction with copper metal film.

Kumar, Mukesh; Rajkumar, %; Kumar, Dinesh; George, P. J.; Paul, A. K.

2003-04-01

270

Self-consistent pitch angle diffusion of newborn ions  

NASA Astrophysics Data System (ADS)

A self-consistent analysis of pitch angle diffusion of newborn ions by low-frequency hydromagnetic waves predominantly propagating in one direction has been carried out. It is found that in the wave frame defined in velocity space the time evolution of an ion distribution can be described as undergoing purely pitch angle diffusion. The role of the resonant versus nonresonant diffusion is discussed in detail, and it is shown that a time-asymptotic distribution of a particular form develops. It is analytically and numerically shown that the self-consistent diffusion process leads to a time-asymptotic partial shell distributions. The relevance of this finding to observations that the ion distributions in the far upstream of cometary bow shocks have a partial shell structure rather than a complete shell is pointed out.

Yoon, P. H.; Ziebell, L. F.; Wu, C. S.

1991-04-01

271

Mechanisms of Stochastic Diffusion of Energetic Ions in Spherical Tori  

SciTech Connect

Stochastic diffusion of the energetic ions in spherical tori is considered. The following issues are addressed: (I) Goldston-White-Boozer diffusion in a rippled field; (ii) cyclotron-resonance-induced diffusion caused by the ripple; (iii) effects of non-conservation of the magnetic moment in an axisymmetric field. It is found that the stochastic diffusion in spherical tori with a weak magnetic field has a number of peculiarities in comparison with conventional tokamaks; in particular, it is characterized by an increased role of mechanisms associated with non-conservation of the particle magnetic moment. It is concluded that in current experiments on National Spherical Torus eXperiment (NSTX) the stochastic diffusion does not have a considerable influence on the confinement of energetic ions.

Ya.I. Kolesnichenko; R.B. White; Yu.V. Yakovenko

2001-01-18

272

Water diffusion coefficients of horizontal soil columns from natural saline-alkaline wetlands in a semiarid area  

NASA Astrophysics Data System (ADS)

Water diffusion coefficients of soils directly control the solute (such as nitrogen and phosphorous) movement in wetlands, which greatly influences the water quality of rivers. The processes of water diffusion in natural saline-alkaline wetland soils were simulated by using horizontal soil columns from the Erbaifangzi (EBFZ) wetland in the Xianghai National Natural Reserve of China in 2001. The results showed that the water diffusion coefficient was the lowest in the topsoil. It followed the order 0-10 cm < 10-20 cm < 20-60 cm. The water diffusion coefficients decreased exponentially with an increase in the distance but increased exponentially with increases in the volumetric soil water contents. The changing curve of the topsoil was steeper, and the water diffusion coefficients were closely linked with the soil properties such as the SOM and clay contents.

Bai, Junhong; Deng, Wei; Cui, Baoshan; Ouyang, Hua

2007-06-01

273

Ion diffusion modified by tortuosity and volume fraction in the extracellular microenvironment of the rat cerebellum.  

PubMed Central

1. The validity of the macroscopic laws of ion diffusion was critically examined within the microenvironment of the extracellular space in the rat cerebellum using ion-selective micropipettes and ionophoretic point sources. 2. The concepts of volume averaging, volume fraction (alpha) and tortuosity (lambda) were defined and shown to be theoretically appropriate for quantifying diffusion in a complex medium such as the brain. 3. Diffusion studies were made with the cations tetramethylammonium and tetraethylammonium and the anions alpha-naphthalene sulphonate and hexafluoro-arsenate, all of which remained essentially extracellular during the measurements. Diffusion parameters were measured for a period of 50s and over distances of the order of 0.1 mm. 4. Measurements of the diffusion coefficients of the ions in agar gel gave values that were very close to those derivable from the literature, thus confirming the validity of the method. 5. Measurements in the cerebellum did not reveal any systematic influences of ionophoretic current strength, electrode separation, anisotropy, inhomogeneity, charge discrimination or uptake, within the limits tested. 6. The pooled data from measurements with all the ions gave alpha = 0.21 +/- 0.02 (mean +/- S.E. of mean) and lambda = 1.55 +/- 0.05 (mean +/- S.E. of mean). 7. These results show that the extracellular space occupies about 20% of the rat cerebellum and that the diffusion coefficient for small monovalent extracellular ions is reduced by a factor of 2.4 (i.e. lambda 2) without regard to charge sign. The over-all effect of this is to increase the apparent strength of any ionic source in the cerebellum by a factor of lambda 2/alpha, about 12-fold in the present case, and to modify the time course of diffusion. 8. These conclusions confirm that the laws of macroscopic diffusion are closely obeyed in the cerebellum for small ions in the extracellular space, provided that volume fraction and tortuosity are explicitly taken into account. It is likely that these conclusions are generally applicable to other brain regions and other diffusing substances.

Nicholson, C; Phillips, J M

1981-01-01

274

Correlation of Apparent Diffusion Coefficient and Fractional Anisotropy Values in the Developing Infant Brain  

PubMed Central

OBJECTIVE The purpose of our study was to correlate decrease in apparent diffusion coefficient (ADC) and increase in fractional anisotropy (FA) in various white matter (WM) regions using diffusion tenor imaging (DTI) within the first year of life. MATERIALS AND METHODS We performed DTI on 53 infants and measured FA and ADC within 10 WM regions important in brain development. For each region, we calculated the slope of ADC as a function of FA, the correlation coefficient (r) and correlation of determination (r2). We performed a group analysis of r values and r2 values for six WM regions primarily composed of crossing fibers and four regions primarily having parallel fibers. Upon finding that a strong correlation of FA with age existed, we adjusted for age and calculated partial correlation coefficients. RESULTS Slopes of FA versus ADC ranged from ?1.00711 to ?1.67592 (p < 0.05); r values ranged from ?0.81 to ?0.50 and r2 values from 0.25 to 0.66. The four greatest r2 values were within WM regions having large numbers of crossing fibers and the three lowest r2 values were in regions having predominantly parallel fibers. After adjusting for age, slopes ranged from ?1.08095 to 0.09612 (p < 0.05 in five cases); partial correlation coefficients ranged from ?0.49 to 0.03 and r2 values from 0.31 to 0.79. The highest partial correlation coefficients were then relatively equally distributed between the two types of WM regions. CONCLUSION In various regions, FA and ADC evolved with differing degrees of correlation. We found a strong influence of age on the relationship between FA and ADC.

Provenzale, James M.; Isaacson, Jared; Chen, Steven; Stinnett, Sandra; Liu, Chunlei

2013-01-01

275

Different K+-Na+ inter-diffusion kinetics between the air side and tin side of an ion-exchanged float aluminosilicate glass  

NASA Astrophysics Data System (ADS)

The difference between the inter-diffusion kinetics of K+-Na+ in the air and tin sides of an ion-exchanged float aluminosilicate glass was investigated as a function of the exchange temperature and time. The potassium concentration profiles of the ion-exchanged glass surface were experimentally measured by electron microprobe analysis, and the diffusion coefficient was calculated by the Boltzmann-Montano approach. On the tin side of the ion-exchanged glass, the diffusion of K+-Na+ ions is hindered by tin. The diffusion coefficient is also more sensitive to temperature and time on the tin than on the air sides. The results would be useful in guiding the strengthening process of float glass by one step ion-exchange or two step ion-exchange to obtain engineered stress profile (ESP) glasses.

Jiang, Liangbao; Guo, Xintao; Li, Xiaoyu; Li, Lei; Zhang, Guanli; Yan, Yue

2013-01-01

276

Mass- and temperature-dependent diffusion coefficients for lightnoble gases for the TOUGH2-EOSN Model  

SciTech Connect

This report describes modifications made to the EOSN module(Shan and Pruess, 2003) of the nonisothermal multiphase flow simulatorTOUGH2 (Pruess, et al., 1999). The EOSN fluid property module simulatestransport of water, brine, air, and noble gases or CO2 in the subsurface.In the standard version of the EOSN module, diffusion coefficients can bespecified by the user, but there is no allowance for liquid-phasediffusion coefficients to change with temperature. Furthermore, usersmust specify radiogenic sources of heat and helium for each element indata block GENER, which can be a time-consuming task for models withlarge numbers of elements. Our modifications seek to increase thefunctionality and efficiency of using TOUGH2-EOSN by allowing for mass-and temperature-dependent liquid-phase diffusion coefficients for heliumand neon and specification of radiogenic heat and helium production as aproperty of a material. The modified version is based on TOUGH2-EOSN andthus requires familiarity with the capabilities and input formats of theTOUGH2 code (Pruess, et al., 1999) and the EOSN module (Shan and Pruess,2003). This report only details our modifications and how to properlyutilize them.

Andrews, J.L.; Finsterle, S.; Saar, M.O.

2007-04-13

277

Bounce-averaged diffusion coefficients in the Tsyganenko field model for oblique chorus waves  

NASA Astrophysics Data System (ADS)

We present the results of computations of bounce-averaged quasi-linear momentum Dpp, pitch-angle D?? and mixed D?p diffusion coefficients in the Tsyganenko magnetic field model. We assume that electrons are scattered by oblique whistler mode chorus waves of Gaussian spread of wave power spectral density and wave normal angle outside the plasmasphere. The scat-tering rates are computed using the full electromagnetic dispersion relation and up to 5-order resonance condition including Landau resonance. The diffusion coefficients are calculated for quiet conditions and storm-time conditions for the day and night sides. We compare scattering rates bounce-averaged in the Tsyganenko field model with those in the dipole field and discuss the differences. The results are followed by a physical explanation of how the magnetic field model can change the bounce-averaged scattering rates. The calculations show that, during active conditions, the pitch-angle scattering by chorus waves in the realistic magnetic field can diffuse relativistic electrons to the loss cone not only on the day side, but also on the night side. Our study shows that while there are still a number of unknown parameters that determine scattering rates, inclusion of bounce-averaging in the realistic field will be crucially important for future radiation belt modeling.

Orlova, Ksenia; Shprits, Yuri

278

Methods to determine slow diffusion coefficients of biomolecules: applications to Engrailed 2, a partially disordered protein.  

PubMed

We present new NMR methods to measure slow translational diffusion coefficients of biomolecules. Like the heteronuclear stimulated echo experiment (XSTE), these new methods rely on the storage of information about spatial localization during the diffusion delay as longitudinal polarization of nuclei with long T(1) such as nitrogen-15. The new BEST-XSTE sequence combines features of Band-selective Excitation Short-Transient (BEST) and XSTE methods. By avoiding the saturation of all protons except those of amide groups, one can increase the sensitivity by 45% in small proteins. The new experiment which combines band-Selective Optimized Flip-Angle Short-Transient with XSTE (SOFAST-XSTE) offers an alternative when very short recovery delays are desired. A modification of the HSQC-edited version of the XSTE experiment offers enhanced sensitivity and access to higher resolution in the indirect dimension. These new methods have been applied to detect changes in diffusion coefficients due to dimerization or proteolysis of Engrailed 2, a partially disordered protein. PMID:21603954

Augustyniak, Rafal; Ferrage, Fabien; Paquin, Raphaël; Lequin, Olivier; Bodenhausen, Geoffrey

2011-05-21

279

Comparison of Diffusion Coefficients of Aryl Carbonyls and Aryl Alcohols in Hydroxylic Solvents. Evidence that the Diffusion of Ketyl Radicals in Hydrogen-Bonding Solvents is Not Anomalous?  

SciTech Connect

The diffusion coefficients of a benzyl-, sec-phenethyl-, and diphenylmethyl alcohol and the corresponding aryl carbonyls (benzaldehyde, acetophenone and benzophenone) were measured by Taylor's dispersion method in both ethyl and isopropyl alcohol. The experimental values are compared to published transient grating measurements of the corresponding aryl ketyl radicals (benzyl-, sec-phenethyl-, and diphenylmethyl-ketyl radical). In general, the diffusion coefficient of the aryl alcohols and the corresponding aryl ketyl radicals are equivalent within experimental error. This work shows that the diffusion of ketyl radicals is not anomalously slow and that aryl alcohols are significantly better models than the corresponding aryl ketones for analyzing the diffusion of aryl ketyl radicals in both ethyl and isopropyl alcohol. Empirical estimates of the diffusion coefficients of aryl alcohols using the Spernol-Wirtz and Wilke-Chang modifications to the Stokes-Einstein diffusion equation do not adequately account for the interactions between the aryl ketyl radicals or aryl alcohols with the hydroxylic solvents ethyl and isopropyl alcohol. The excellent agreement between the experimental diffusion coefficients of the aryl alcohols and the corresponding ketyl radicals show that the transient grating method can provide accurate estimates for the diffusion coefficients of transient species. This is especially important when a stable model is not available, for example the pyranyl radical.

Autrey, S Thomas (BATTELLE (PACIFIC NW LAB)); Camaioni, Donald M. (BATTELLE (PACIFIC NW LAB)); Kandanarachchi, Pramod H. (ASSOC WESTERN UNIVERSITY); Franz, James A. (BATTELLE (PACIFIC NW LAB))

2000-12-01

280

Influence of the scattering and absorption coefficients on homogeneous room simulations that use a diffusion equation model.  

PubMed

The diffusion equation model was used for room acoustic simulations to predict the sound pressure level and the reverberation time. The technical literature states that the diffusion equation method accurately models the late portion of the room impulse response if the energy is sufficiently scattered. This work provides conclusions on the validity of the diffusion equation model for rooms with homogeneous dimensions in relation to the scattering coefficients of the boundaries. A systematic evaluation was conducted out to determine the ranges of the absorption and scattering coefficient values that result in low noticeable differences between the predictions from a geometrical acoustic model and those from the diffusion equation model. PMID:23463993

Navarro, Juan M; Escolano, José; Cobos, Maximo; López, José J

2013-03-01

281

Effect of silica sand on activation energy for diffusion of sodium ions in montmorillonite and silica sand mixture.  

PubMed

The effect of silica sand on the diffusion of sodium ions in mixtures of montmorillonite and silica sand was studied by measuring the apparent diffusion coefficients, activation energies for diffusion, and the basal spacing of the mixed samples. These diffusion experiments suggest that the apparent diffusion coefficients of sodium ions in the mixed samples were almost the same as those of pure montmorillonite samples having the same partial dry densities of montmorillonite. The activation energy dependence for diffusion of sodium ions on the partial dry density was different between the mixed samples and the pure montmorillonite samples. The activation energy increased by adding silica sand at the partial dry density of 1.0 Mg m(-3), and decreased by adding silica sand at the partial dry densities higher than 1.2 Mg m(-3). A change in the XRD profile was observed after adding silica sand at the partial dry density of 1.6 Mg m(-3). Here, a three-water-layer hydrate state of montmorillonite was found in the mixed sample whereas only a two-water-layer hydrate state was observed in the pure montmorillonite sample. These experimental results suggest that silica sand changed the montmorillonite microstructure in the mixed samples, which then altered the sodium-ion diffusion process. PMID:12598096

Liu, Jinhong; Yamada, Hiromichi; Kozaki, Tamotsu; Sato, Seichi; Ohashi, Hiroshi

2003-03-01

282

Graded functional diffusion map-defined characteristics of apparent diffusion coefficients predict overall survival in recurrent glioblastoma treated with bevacizumab  

PubMed Central

Diffusion imaging has shown promise as a predictive and prognostic biomarker in glioma. We assessed the ability of graded functional diffusion maps (fDMs) and apparent diffusion coefficient (ADC) characteristics to predict overall survival (OS) in recurrent glioblastoma multiforme (GBM) patients treated with bevacizumab. Seventy-seven patients with recurrent GBMs were retrospectively examined. MRI scans were obtained before and approximately 6 weeks after treatment with bevacizumab. Graded fDMs were created by registering datasets to each patient's pretreatment scan and then performing voxel-wise subtraction between post- and pretreatment ADC maps. Voxels were categorized according to the degree of change in ADC within pretreatment fluid-attenuated inversion recovery (FLAIR) and contrast-enhancing regions of interest (ROIs). We found that the volume of tissue showing decreased ADC within both FLAIR and contrast-enhancing regions stratified OS (log-rank, P < .05). fDMs applied to contrast-enhancing ROIs more accurately predicted OS compared with fDMs applied to FLAIR ROIs. Graded fDMs (showing voxels with decreased ADC between 0.25 and 0.4 µm2/ms) were more predictive of OS than traditional (single threshold) fDMs, and the predictive ability of graded fDMs could be enhanced even further by adding the ADC characteristics from the fDM-classified voxels to the analysis (log-rank, P < .001). These results demonstrate that spatially resolved diffusion-based tumor metrics are a powerful imaging biomarker of survival in patients with recurrent GBM treated with bevacizumab.

Ellingson, Benjamin M.; Cloughesy, Timothy F.; Lai, Albert; Mischel, Paul S.; Nghiemphu, Phioanh L.; Lalezari, Shadi; Schmainda, Kathleen M.; Pope, Whitney B.

2011-01-01

283

Bounce-averaged diffusion coefficients in a realistic field model for oblique chorus waves  

NASA Astrophysics Data System (ADS)

We present the results of computations of bounce-averaged quasi-linear momentum ba , pitch-angle ba, and mixed ba diffusion coefficients in a realistic magnetic field model. We assume that electrons are scattered by oblique whistler mode chorus waves with Gaussian distribution of wave power spectral density and wave normal angle outside the plasmasphere. The scattering rates are computed using the full electromagnetic dispersion relation and up to ±5-order harmonic resonances including Landau resonance. The diffusion coefficients are calculated for geomagnetically quiet and disturbed conditions at different MLT locations and distances. We compare bounce-averaged scattering rates in different Tsyganenko models with those in the dipole field and discuss the differences. We focus on electron energies from 10 keV to 10 MeV. Latitudinal distribution of plasma density is also taken into account. The results are followed by a physical explanation of how the magnetic field model can change the bounce-averaged scattering rates. Our study shows that inclusion of bounce-averaging in the realistic ambient magnetic field is crucially important for future modeling of radiation belt dynamics and resonant wave-particle interactions on other planets. When calculating bounce period and bounce-averaged momentum diffusion coefficients we have singularities in mirror points. Most of the codes use approximate methods to avoid singularities. We show the exact method of performing bounce averaging. The inaccuracies of the approximate approach can introduce errors up to an order in magnitude. We also give the new more accurate approximations for particle bounce time in the dipole magnetic field.

Orlova, K.; Shprits, Y.; Ni, B.

2010-12-01

284

Calculating diffusion and permeability coefficients with the oscillating forward-reverse method  

NASA Astrophysics Data System (ADS)

The forward-reverse or FR method is an efficient bidirectional work method for determining the potential of mean force w(z) and also supposedly gives in principle the position-dependent diffusion coefficient D(z). Results from a variation called the OFR (oscillating FR) method suggest inconsistencies in the D(z) values when calculated as prescribed by the FR method. A new steering protocol has thus been developed and applied to the OFR method for the accurate determination of D(z) and also provides greater convergence for w(z) in molecular dynamics simulations. The bulk diffusion coefficient for water was found to be (6.03±0.16)×10-5 cm2/s at 350 K with system size dependence within the statistical error bars. Using this steering protocol, D(z) and w(z) for water permeating a dipalmitoylphosphatidylcholine (DPPC) bilayer were determined. The potential of mean force is shown to have a barrier of peak height, wmax/(kBT)=8.4, with a width of about 10 Å on either side from the membrane center. The diffusion constant is shown to be highest in the core region of the membrane [peak value ˜(8.0±0.8)×10-5 cm2/s], lowest in the head-group region [minimum value ˜(2.0±0.3)×10-5 cm2/s], and to tend toward the bulk value as the water molecule leaves the membrane. The permeability coefficient P for H2O in DPPC was determined using the simulated D(z) and w(z) to give values of (0.129±0.075) cm/s at 323 K and (0.141±0.043) cm/s at 350 K. The results show more spatial detail than results presented in previous work while reducing the computational and user effort.

Holland, Bryan W.; Gray, Chris G.; Tomberli, Bruno

2012-09-01

285

Collective diffusion coefficient of proteins with hydrodynamic, electrostatic, and adhesive interactions.  

PubMed

A theory is presented for lambdaC, the coefficient of the first-order correction in the density of the collective diffusion coefficient, for protein spheres interacting by electrostatic and adhesive forces. An extensive numerical analysis of the Stokesian hydrodynamics of two moving spheres is given so as to gauge the precise impact of lubrication forces. An effective stickiness is introduced and a simple formula for lambdaC in terms of this variable is put forward. A precise though more elaborate approximation for lambdaC is also developed. These and numerically exact expressions for lambdaC are compared with experimental data on lysozyme at pH 4.5 and a range of ionic strengths between 0.05M and 2M. PMID:17887883

Prinsen, Peter; Odijk, Theo

2007-09-21

286

Diffusion Coefficients in Liquid and Grain Boundary Predicted by Ab Initio Molecular Dynamics  

SciTech Connect

Molecular dynamics (MD) is a powerful tool to probe the thermodynamic and kinetic properties of solid, glass and liquid phases. In classical molecular dynamics (CMD), empirical models are used to describe the force by considering bond, bend and dihedral angle contributions with parameters fitted to experimental data or first-principles calculations of small clusters. In the ab initio molecular dynamics (AIMD), the forces are calculated on the fly using the first-principles density functional theory as discussed above. In the present work, we use AIMD simulations to follow the random walk of atoms in the liquid state. Based on the mean square displacements (MSD), the diffusion coefficients are calculated from the Einstein equation. Furthermore, we extend this approach to understand the diffusion in grain boundaries.

Jablonski, P.D.; Liu, Z.; Fang, H.; Wang, B.

2011-04-01

287

Results of a monte carlo investigation of the diffuse attenuation coefficient.  

PubMed

There has been a large effort to relate the apparent optical properties of ocean water to the inherent optical properties, which are the absorption coefficient a, the scattering coefficient b, and the scattering phase function rho(theta). The diffuse attenuation coefficient kdiff' has most often been considered an apparent optical property. However, kdiff' can be considered a quasi-inherent property kdiff' when defined as a steady-state light distribution attenuation coefficient. The Honey-Wilson research empirically relates kdiff' to a and b. The Honey-Wilson relation most likely applies to a limited range of water types because it does not include dependence on rho(theta). A series of Monte Carlo simulations were initiated to calculate kdiff' in an unstratified water column. The calculations, which reflected open ocean water types, used ranges of the single-scattering albedo omega(0) and the mean forward-scattering angle theta(m) for two analytic phase functions with different shapes. It was found that kdiff' is nearly independent of the shape of rho(theta) and can be easily parameterized in terms of a, b, and theta(m) for 0.11

Concannon, B M; Davis, J P

1999-08-20

288

Apparent Diffusion Coefficient, Fractional Anisotropy and T2 Relaxation Time Measurement  

Microsoft Academic Search

Background:  Quantification of apparent diffusion coefficient (ADC), fractional anisotropy (FA), and T2 relaxation time are increasingly\\u000a important for neuroradiologic applications. A transfer of the values established for 1.5-T to 3-T MRI must be supported by\\u000a a dedicated comparison with special emphasis on possible differences in the spatial distribution.\\u000a \\u000a \\u000a \\u000a Material and Methods:  In the present study, brain scans were carried out in 16

Xiao-Qi Ding; Jürgen Finsterbusch; Oliver Wittkugel; Christian Saager; Einar Goebell; Thies Fitting; Ulrich Grzyska; Hermann Zeumer; Jens Fiehler

2007-01-01

289

Measuring diffusion coefficients and distribution functions using a longitudinal beam echo  

SciTech Connect

Longitudinal echo signals can be produced in the CERN-SPS by exciting a coasting proton beam at 120 GeV/c with two short RF pulses at different harmonics of the revolution frequency, separated by a suitable time-delay. We show here how one can measure energy distributions and longitudinal diffusion coefficients by using longitudinal beam echoes. The energy spread measured in this manner is in an excellent agreement with the data obtained from the Schottky signal. {copyright} {ital 1997 American Institute of Physics.}

Bruening, O.; Linnecar, T.; Ruggiero, F.; Scandale, W.; Shaposhnikova, E. [CERN, Geneva 23 (Switzerland)

1997-02-01

290

Apparent diffusion coefficient measurement in a moving phantom simulating linear respiratory motion  

Microsoft Academic Search

Purpose  The aim of this study was to examine the effect of simulated linear respiratory motion on apparent diffusion coefficient (ADC)\\u000a measurements.\\u000a \\u000a \\u000a \\u000a \\u000a Materials and methods  Six rectangular test tubes (14 × 92 mm) filled with either water, tomato ketchup, or mayonnaise were positioned in a box containing\\u000a agarose gel. This box was connected to a double-acting pneumatic cylinder, capable of inducing periodic

Thomas C. Kwee; Taro Takahara; Isao Muro; Marc Van Cauteren; Yutaka Imai; Rutger A. J. Nievelstein; Willem P. T. M. Mali; Peter R. Luijten

2010-01-01

291

Temperature dependence of the mutual diffusion coefficients in aqueous solutions of alkali metal chlorides  

Microsoft Academic Search

Measurements of mutual diffusion coefficients at infinite dilution in aqueous solutions of alkali-metal chlorides have been made with the Taylor dispersion technique. Data were obtained for the series LiCl\\/H2O, NaCl\\/H2O, KCl\\/H2O, RbCl\\/H2O, and CsCl\\/H2O, at five temperatures between 298.15 and 318.15 K. A linear dependence with temperature was found. This technique is very convenient in comparison with other more time-consuming

R. Castillo; C. Garza

1993-01-01

292

Temperature dependence of the mutual diffusion coefficients in aqueous solutions of alkali metal chlorides  

NASA Astrophysics Data System (ADS)

Measurements of mutual diffusion coefficients at infinite dilution in aqueous solutions of alkali-metal chlorides have been made with the Taylor dispersion technique. Data were obtained for the series LiCl/H2O, NaCl/H2O, KCl/H2O, RbCl/H2O, and CsCl/H2O, at five temperatures between 298.15 and 318.15 K. A linear dependence with temperature was found. This technique is very convenient in comparison with other more time-consuming techniques.

Castillo, R.; Garza, C.

1993-11-01

293

Quantification of optical absorption coefficient from acoustic spectra in the optical diffusive regime using photoacoustic microscopy  

NASA Astrophysics Data System (ADS)

Photoacoustic (PA) tomography (PAT) can image optical absorption contrast with ultrasonic spatial resolution in the optical diffusive regime. Multi-wavelength PAT can noninvasively monitor hemoglobin oxygen saturation (sO2) with high sensitivity and fine spatial resolution. However, accurate quantification in PAT requires knowledge of the optical fluence distribution, acoustic wave attenuation, and detection system bandwidth. We propose a method to circumvent this requirement using acoustic spectra of PA signals acquired at two optical wavelengths. With the acoustic spectral method, the absorption coefficients of an oxygenated bovine blood phantom at 560 and 575 nm were quantified with errors of ><5%.

Guo, Zijian; Favazza, Christopher; Wang, Lihong V.

2012-02-01

294

Modeling of ion implantation and diffusion in Si  

SciTech Connect

Classical molecular dynamics simulations are used to study damage produced during implantation of semiconductors with different ion masses and energies between 1-25 keV. The time scale for these simulations is only on the order of ns, and therefore problems like transient enhanced diffusion of dopants or formation of extended defects can not be studied with these models. Monte Carlo simulations, including as input the results obtained from molecular dynamics calculations, are used to extend the simulation time, and in particular, to study processes like ion implantation and defects diffusion in semiconductors. As an example, we show results for diffusion of the damage produced by implantation of Si with 5 keV Xe ions at low doses. Results of the simulations are compared with experiments in order to validate the model.

Caturla, M-J; Diaz de la Rubia, T.; Bedrossian, P.J.

1996-09-01

295

Electrowinning of Copper from Copper (I) Electrolytes. 3: Diffusion Coefficients and Rates of Electron Transfer in Copper (I) Electrolytes.  

National Technical Information Service (NTIS)

The object of this work was to measure diffusion coefficients and Tafel parameters in practical systems closely related to those employed in the CLEAR, Dextec or Parker processes and to compare values with the conventional copper (II) electrolytes. In thi...

D. M. Muir

1982-01-01

296

Diffusion Coefficients of Tris( ? -diketonato)ruthenium Complexes of Different Charge Numbers in Acetonitrile Solutions, Measured by Chronoamperometry  

Microsoft Academic Search

The diffusion coefficients of several tris(?-diketonato) ruthenium complexes in acetonitrile solutions containing a supporting electrolyte were determined by chronoamperometry.\\u000a The diffusion coefficients of the charged complexes, which were produced by electrochemical oxidation or reduction, were also\\u000a determined by double potential step chronoamperometry. Two kinds of radii of the complexes were evaluated. One was the Van\\u000a der Waals radius and the

Haruko Ikeuchi; Kaoru Naganuma; Marie Ichikawa; Hiromichi Ozawa; Tomoya Ino; Makoto Sato; Hiroko Yonezawa; Sonomi Mukaida; Akihiro Yamamoto; Takeshi Hashimoto

2007-01-01

297

Self-diffusion coefficient of water in Nafion-117 membrane with different monovalent counterions: a radiotracer study  

Microsoft Academic Search

The self-diffusion coefficient of water in Nafion-117 membrane in different cationic forms was measured by the transient radiotracer method, which is based on an analytical solution of Fick's second law. The self-diffusion coefficient of water in the membrane was obtained from the analysis of time-dependent isotopic-exchange rates of tritium tagged water between sample of Nafion-117 membrane and equilibrating water. This

G. Suresh; Y. M. Scindia; A. K. Pandey; A. Goswami

2005-01-01

298

A comparison of diffusion coefficients for ternary mixed micelle solutions measured by macroscopic gradient and dynamic light scattering techniques.  

PubMed

Taylor dispersion is used to measure ternary mutual diffusion coefficients (D(ik)) for aqueous solutions of decylsulfobetaine (SB10) (1) + dodecylsulfobetaine (SB12) (2), SB10 (1) + SB14 (2), and SB12 (1) + SB14 (2) mixed zwitterionic micelles. Cross-coefficient D(21) for the coupled flow of surfactant 1 produced by a concentration gradient in surfactant 2 is relatively small for these solutions, but D(12) reaches values as large as the main D(ii) coefficients. The results are interpreted by using the equation D(ik) = partial differential(C(i)D(i))/ partial differentialC(k) to relate the ternary mutual diffusion coefficients to the concentration-weighted average diffusion coefficients D(i) of the micellar and free-monomer forms of the surfactants. The macroscopic-gradient Taylor measurements are compared with diffusion coefficients measured by dynamic light scattering (DLS), which monitors microscopic concentration fluctuations. At most compositions, the intensity autocorrelation function G(tau) is a single exponential decay in D((2)), the smaller eigenvalue of the mutual diffusion coefficient matrix. A contribution from D((1)) is identified at high solute fractions of surfactant 1. The DLS results are consistent with contributions to G(tau) from uncoupled fluctuations in the concentrations of eigencomponents defined as the linear combinations of surfactants 1 and 2 that diagonalize the D(ik) matrix. A procedure for the rapid and convenient DLS measurement of ternary mutual diffusion coefficients, including the cross-coefficients for coupled diffusion, is suggested, using the Onsager reciprocal relation together with the eigenvalues and pre-exponential factors from G(tau). PMID:18688372

Das, Bijan; Maitra, Basanti; Mercer, Sean M; Everist, Michelle; Leaist, Derek G

2008-04-03

299

Effective Diffusion Coefficient and Controlling Process of P Diffusion in Si Based on the Pair Diffusion Models of Vacancy and Interstitial Mechanisms  

NASA Astrophysics Data System (ADS)

Based on the pair diffusion models of vacancy and interstitial (V and I) mechanisms, the V and I components of effective P diffusion coefficient, DP^+,Veff and DP^+,Ieff, and the controlling process of P diffusion in Si are obtained. Assuming that the I mechanism is dominant, not only the I- concentration, CI^-, but also its gradient, d CI^-/d ? , is effective on DP^+,Ieff at high CP^+. DP^+,Ieff is large at d CI^-/d ? <0 and small at d CI^-/d ? >0. P+ and I- are generated by the dissociation of P-I pair. When excess I- thus generated is removed, d CI^-/d ? <0 is obtained. d CI^-/d ? <0 is also obtained by the decrease in quasi self-interstitial formation energy. Several diffusion models simulate the P diffusion profile well under an inert atmosphere. Applying the controlling process to them, the reason why they simulate the P profile well is investigated. Because all of them simulate the P profile well, it is difficult to conclude which model is correct. It is suggested that it is possible to conclude which model is correct from the P profile under oxidation at CP^+s >1× 1020 cm-3 (s: surface).

Yoshida, Masayuki; Morooka, Masami; Takahashi, Manabu; Tomokage, Hajime

2000-05-01

300

Methodology for using prompt gamma activation analysis to measure the binary diffusion coefficient of a gas in a porous medium  

NASA Astrophysics Data System (ADS)

Diffusion plays a critical role in determining the rate at which gases migrate through porous systems. Accurate estimates of diffusion coefficients are essential if gas transport is to be accurately modeled and better techniques are needed that can be used to measure these coefficients non-invasively. Here we present a novel method for using prompt gamma activation analysis to determine the binary diffusion coefficients of a gas in a porous system. Argon diffusion experiments were conducted in a 1 m long, 10 cm diameter, horizontal column packed with a SiO2 sand. The temporal variation of argon concentration within the system was measured using prompt gamma activation analysis. The binary diffusion coefficient was obtained by comparing the experimental data with the predictions from a numerical model in which the diffusion coefficient was varied until the sum of square errors between experiment and model data was minimized. Predictions of argon concentration using the optimal diffusivity fit experimental measurements with an R2 of 0.983.

Rios Perez, Carlos A.; Biegalski, Steve R.; Deinert, Mark R.

2012-12-01

301

Quantification of diffusion-weighted images (DWI) and apparent diffusion coefficient maps (ADC) in the detection of acute stroke  

NASA Astrophysics Data System (ADS)

Magnetic resonance (MR) imaging is an imaging modality that is used in the management and diagnosis of acute stroke. Common MR imaging techniques such as diffusion weighted imaging (DWI) and apparent diffusion coefficient maps (ADC) are used routinely in the diagnosis of acute infarcts. However, advances in radiology information systems and imaging protocols have led to an overload of image information that can be difficult to manage and time consuming. Automated techniques to assist in the identification of acute ischemic stroke can prove beneficial to 1) the physician by providing a mechanism for early detection and 2) the patient by providing effective stroke therapy at an early stage. We have processed DW images and ADC maps using a novel automated Relative Difference Map (RDM) method that was tailored to the identification and delineation of the stroke region. Results indicate that the technique can delineate regions of acute infarctions on DW images and ADC maps. A formal evaluation of the RDM algorithm was performed by comparing accuracy measurements between 1) expert generated ground truths with the RDM delineated DWI infarcts and 2) RDM delineated DWI infarcts with RDM delineated ADC infarcts. The accuracy measurements indicate that the RDM delineated DWI infarcts are comparable to the expert generated ground truths. The true positive volume fraction value (TPVF), between RDM delineated DWI and ADC infarcts, is nonzero for all cases with an acute infarct while the value for non-acute cases remains zero.

Tulipano, P. Karina; Millar, William S.; Imielinska, Celina; Liu, Xin; Rosiene, Joel; D'Ambrosio, Anthony L.

2006-03-01

302

Selecting the best index for following the temporal evolution of apparent diffusion coefficient and diffusion anisotropy after hypoxic-ischemic white matter injury in neonates  

Microsoft Academic Search

BACKGROUND AND PURPOSE: Diffusion-weighted (DW) MR imaging is a useful technique for detecting ischemia. In adults and neonates, however, temporal changes on DW images after ischemia complicate interpretation. Our purpose was to investigate the temporal evolution of the apparent diffusion coefficient (ADC), diffusion-tensor (DT) imaging components, and anisotropy in neonatal brain after hypoxic-ischemic white matter injury and to determine which

Carola van Pul; Jan Buijs; Maurice J. A. Janssen; FG Roos; Marinus T. Vlaardingerbroek; Pieter F. F. Wijn

2005-01-01

303

Kubo number and magnetic field line diffusion coefficient for anisotropic magnetic turbulence.  

PubMed

The magnetic field line diffusion coefficients Dx and D(y) are obtained by numerical simulations in the case that all the magnetic turbulence correlation lengths l(x), l(y), and l(z) are different. We find that the variety of numerical results can be organized in terms of the Kubo number, the definition of which is extended from R=(deltaB/B(0))(l(parallel)/l(perpendicular)) to R=(deltaB/B(0))(l(z)/l(x)), for l(x) > or = l(y). Here, l(parallel) (l(perpendicular)) is the correlation length along (perpendicular to) the average field B(0)=B(0)ê(z). We have anomalous, non-Gaussian transport for R less, similar 0.1, in which case the mean square deviation scales nonlinearly with time. For R greater, similar 1 we have several Gaussian regimes: an almost quasilinear regime for 0.1 less, similar R less, similar 1, an intermediate, transition regime for 1 less, similar R less, similar 10, and a percolative regime for R greater, similar 10. An analytical form of the diffusion coefficient is proposed, D(i)=D(deltaBl(z)/B(0)l(x))(mu)(l(i)/l(x))(nu)l(2)(x)/l(z), which well describes the numerical simulation results in the quasilinear, intermediate, and percolative regimes. PMID:11415233

Pommois, P; Veltri, P; Zimbardo, G

2001-05-22

304

A method for measuring internal diffusion and equilibrium partition coefficients of volatile organic compounds for building materials  

Microsoft Academic Search

An experimental method for the determination of the internal diffusion coefficient (D) and partition coefficient (ke) of volatile organic compounds (VOCs) is developed for dry building materials (such as carpet, vinyl flooring, plywood, etc.). The method is used to determine D and ke for four VOCs (toluene, nonane, decane, and undecane ) through the backing material of a carpet specimen,

A. Bodalal; J. S. Zhang; E. G. Plett

2000-01-01

305

LABORATORY MEASUREMENTS OF THE RADON GAS DIFFUSION COEFFICIENT FOR A FRACTURED CONCRETE SAMPLE AND RADON GAS BARRIER SYSTEMS  

Microsoft Academic Search

Radon diffusion through cracked concrete is a major radon entry route in residential construction. This paper presents the preliminary experimental results of the influence of cracks on the radon gas diffusion coefficient through concrete. Concrete samples of 10.16 cm (4\\

Wessam Z. Daoud; Kevin J. Renken

306

The significance of isotope specific diffusion coefficients for reaction-transport models of sulfate reduction in marine sediments  

Microsoft Academic Search

Modeling isotopic signatures in systems affected by diffusion, advection, and a reaction which modifies the isotopic abundance of a given species, is a discipline in its infancy. Traditionally, much emphasis has been placed on kinetic isotope effects during biochemical reactions, while isotope effects caused by isotope specific diffusion coefficients have been neglected. A recent study by Donahue et al. (2008)

Ulrich G. Wortmann; Boris M. Chernyavsky

2011-01-01

307

In-situ estimate of submesoscale horizontal eddy diffusion coefficients across a front  

NASA Astrophysics Data System (ADS)

Fronts, jets and eddies are ubiquitous features of the world oceans, and play a key role in regulating energy budget, heat transfer, horizontal and vertical transport, and biogeochemical processes. Although recent advances in computational power have favored the analysis of mesoscale and submesoscale dynamics from high-resolution numerical simulations, studies from in-situ observations are still relatively scarce. The small dimensions and short duration of such structures still pose major challenges for fine-scale dedicated field experiments. As a consequence, in-situ quantitative estimates of key physical parameters for high-resolution numerical models, such as horizontal eddy diffusion coefficients, are still lacking. The Latex10 campaign (September 1-24, 2010), within the LAgrangian Transport EXperiment (LATEX), adopted an adaptive sampling strategy that included satellite data, ship-based current measurements, and iterative Lagrangian drifter releases to successfully map coherent transport structures in the western Gulf of Lion. Comparisons with AVHRR imagery evidenced that the detected structures were associated with an intense frontal feature, originated by the convergence and subsequent stirring of colder coastal waters with warmer open-sea waters. We present a method for computing horizontal eddy diffusion coefficients by combining the stirring rates estimated from the Lagrangian drifter trajectories with the shapes of the surface temperature and salinity gradient (assumed to be at the equilibrium) from the ship thermosalinograph. The average value we obtained from various sections across the front is 2.5 m2s-1, with horizontal scales (width of the front) ranging between 0.5 and 2.5 km. This is in line with the values commonly used for high-resolution numerical simulations. Further field experiment will be required to extend the results to different ocean regions and regimes, and to thoroughly test the robustness of the equilibrium hypothesis. Remote sensed measurements of sea surface temperature and elevation could also be used to compute fine-scale horizontal eddy diffusion coefficients over larger areas and for different ocean regions. However, the coarse resolution of current sea surface topography observations, and their unreliability over coastal regions, represent important limitations for this type of application. The velocity fields provided by the SWOT mission will allow to retrieve accurate high-resolution stirring rates across the ocean. Combining these rates with remote-sensed SST gradients will make possible to extend our analysis and investigate patterns and variability of submesoscale horizontal eddy diffusion at the global scale.

Nencioli, Francesco; d'Ovidio, Francesco; Doglioli, Andrea; Petrenko, Anne

2013-04-01

308

Alumina Solubility and Diffusion Coefficient of the Dissolved Alumina Species in Low-Temperature Fluoride Electrolytes  

NASA Astrophysics Data System (ADS)

The solubility of alumina was measured by rotating an alumina cylinder (~500 rpm) in a high-purity melt for ~3 to 6 hours, crushing and sampling the frozen melt, and determining the oxygen content in a Leco analyzer. The alumina solubilities determined were as follows: (1) 3.2 ± 0.3 wt pct in NaF-AlF3 eutectic at 1023 K (750 °C); (2) 3.0 ± 0.3 wt pct in NaF-AlF3-CaF2 (5 wt pct) at 1023 K (750 °C); and (3) 5.2 ± 0.5 wt pct in a KF-AlF3 eutectic at 1003 K (730 °C). The alumina solubility in the KF-AlF3 eutectic was 2 wt pct more than in the sodium analogue, offering the possibility of operating a low-temperature aluminum smelting cell without the need for an alumina slurry. The diffusion coefficient of the dissolved alumina species was determined in the NaF-AlF3 eutectic at 1023 K (750 °C) using the rotating disc method and applying the Levich equation. Through a limited range of rotation rates, the system seemed to be mass-transfer controlled, and the diffusion coefficient was estimated to be in the range 1.8 to 2.2 × 10-6 cm2 s-1. This value is about five times lower than the values encountered at traditional aluminum smelting temperatures (~1233 K (960 °C)) and would result in relatively low mass transfer coefficients.

Frazer, E. J.; Thonstad, J.

2010-06-01

309

On the density dependence of the self-diffusion coefficient of interacting Brownian particles  

NASA Astrophysics Data System (ADS)

A brief summary is given of our theoretical approach to the statistical description of interacting Brownian particles. For the discussion of particle transport processes on the Smoluchowski level a hierarchy of coupled diffusion-like equations in configuration space for the reduced particle density functions and the corresponding particle flows is derived. Non-equilibrium processes are taken into account by means of linear perturbation theory. Applying the direct correlation force formalism, the hierarchy is cut off by replacing the three-particle density function nabc(r1, r2, r3, t). Here closure relations between the direct correlation force and nab(r1, r2, t) have to be added. Specializing the brownons to hard spheres and neglecting the hydrodynamic interaction, the two-particle density function is evaluated from the well-known equilibrium PY approximation and (as a first step) from the low-density limit of the non-equilibrium closure. Using a linear response theory of particle transport, the self-diffusion coefficient in a one-component hard sphere system of Brownian particles is calculated through a formal non-equilibrium picture based on tracer diffusion.

Sonnenburg, Jörn; Kremp, Dietrich; Sändig, Rainer

310

Effective scattering coefficient of the cerebral spinal fluid in adult head models for diffuse optical imaging  

NASA Astrophysics Data System (ADS)

An efficient computation of the time-dependent forward solution for photon transport in a head model is a key capability for performing accurate inversion for functional diffuse optical imaging of the brain. The diffusion approximation to photon transport is much faster to simulate than the physically correct radiative transport equation (RTE); however, it is commonly assumed that scattering lengths must be much smaller than all system dimensions and all absorption lengths for the approximation to be accurate. Neither of these conditions is satisfied in the cerebrospinal fluid (CSF). Since line-of-sight distances in the CSF are small, of the order of a few millimeters, we explore the idea that the CSF scattering coefficient may be modeled by any value from zero up to the order of the typical inverse line-of-sight distance, or approximately 0.3 mm-1, without significantly altering the calculated detector signals or the partial path lengths relevant for functional measurements. We demonstrate this in detail by using a Monte Carlo simulation of the RTE in a three-dimensional head model based on clinical magnetic resonance imaging data, with realistic optode geometries. Our findings lead us to expect that the diffusion approximation will be valid even in the presence of the CSF, with consequences for faster solution of the inverse problem.

Custo, Anna; Wells, William M., III; Barnett, Alex H.; Hillman, Elizabeth M. C.; Boas, David A.

2006-07-01

311

Effective scattering coefficient of the cerebral spinal fluid in adult head models for diffuse optical imaging.  

PubMed

An efficient computation of the time-dependent forward solution for photon transport in a head model is a key capability for performing accurate inversion for functional diffuse optical imaging of the brain. The diffusion approximation to photon transport is much faster to simulate than the physically correct radiative transport equation (RTE); however, it is commonly assumed that scattering lengths must be much smaller than all system dimensions and all absorption lengths for the approximation to be accurate. Neither of these conditions is satisfied in the cerebrospinal fluid (CSF). Since line-of-sight distances in the CSF are small, of the order of a few millimeters, we explore the idea that the CSF scattering coefficient may be modeled by any value from zero up to the order of the typical inverse line-of-sight distance, or approximately 0.3 mm(-1), without significantly altering the calculated detector signals or the partial path lengths relevant for functional measurements. We demonstrate this in detail by using a Monte Carlo simulation of the RTE in a three-dimensional head model based on clinical magnetic resonance imaging data, with realistic optode geometries. Our findings lead us to expect that the diffusion approximation will be valid even in the presence of the CSF, with consequences for faster solution of the inverse problem. PMID:16799690

Custo, Anna; Wells, William M; Barnett, Alex H; Hillman, Elizabeth M C; Boas, David A

2006-07-01

312

Optimized numerical pharmacokinetics model for optical molecular probes based on diffusion coefficients in matrigel measured using fluorescence imaging.  

PubMed

An original algorithm for measuring diffusion coefficients of optical molecular probes in matrigel from fluorescence data is introduced. The algorithm was developed in Fortran and linked to Graphic User Interface in LabVIEW software that also performs image acquisition and processing. The software models pharmacokinetics of optical molecular probes providing the best fit of experimental data. The paper offers an original way for estimating the diffusion path length through extracellular matrix (ECM) from the rate constants given by the model and from measured diffusion coefficients. PMID:19963869

Ciocan, Eugenia; Ciocan, Razvan

2009-01-01

313

Isotope effects in water. Tracer diffusion coefficients for H/sub 2/ /sup 18/O in ordinary water  

SciTech Connect

A method is described for measuring the tracer diffusion coefficient of H/sub 2/ /sup 18/O in ordinary water. The method combines the conventional diaphragm cell technique with isotope ratio mass-spectrometric determination of tracer concentrations and gives diffusion coefficients of very high precision. The accuracy of the method is limited only by the accuracy of calibration of diaphragm cells and is such that the isotope effect for water diffusion has been measured precisely. Results are presented for temperatures from 278 to 323 K at 0.1 MPa, and for pressures up to 262.5 MPa at 323 K.

Easteal, A.J.; Edge, A.V.J.; Woolf, L.A.

1984-11-22

314

Diffusion coefficients of small gas molecules in amorphous cis-1,4-polybutadiene estimated by molecular dynamics simulations  

NASA Astrophysics Data System (ADS)

Molecular dynamics (MD) simulations were employed to estimate the diffusion coefficients of small gas molecules (Ar, O2, N2, CO2, and CH4) in amorphous cis-1,4-polybutadiene in the temperature range of 250-400 K. The VT diagram and solubility parameter of the amorphous polymer have been successfully reproduced using a full atomistic potential. Diffusion coefficients were calculated from long NPT MD runs (up to 3 ns) at temperature ranging from 250 up to 400 K. Calculated diffusion coefficients compare well with experimental data as well as previous published work, though a systematic overestimation is found due to the finite-size effect of the model. The influence of various physical and computational parameters on the results is discussed. The diffusion mechanism is examined at the different temperatures of study.

Meunier, M.

2005-10-01

315

Self-consistent pitch angle diffusion of newborn ions  

SciTech Connect

It is well known from the study of ion pickup process by the solar wind that hydromagnetic turbulence can cause the newborn ions to undergo rapid pitch angle diffusion or scattering, thus forming a partial or complete velocity shell distribution. In most of the recent discussions based on quasi-linear theory it is assumed that the spectral wave energy density associated with the hydromagnetic turbulence is constant in time, implying a saturated turbulence level. In contrast, in this work the effect of self-consistently generated waves on the ion dynamics is discussed on the basis of a simple theoretical model, and it is shown both analytically and numerically that the self-consistent diffusion process leads to a time-asymptotic partial shell distribution which extends approximately from the initial pitch angle cos{sup {minus}1}{mu}{sub 0} to {approximately}{pi}/2 in pitch angle space. Particularly, the role of resonant versus nonresonant diffusion processes is discussed in detail. In addition, the effect of continuous ion source term is also incorporated in the numerical analysis since in cometary environment the ions are continuously created.

Yoon, P.H.; Ziebell, L.F.; Wu, C.S. (Univ. of Maryland, College Park (USA))

1991-04-01

316

Calculation of multicomponent ionic diffusion from zero to high concentration: II. Inclusion of associated ion species  

NASA Astrophysics Data System (ADS)

This paper presents a theoretical model of multicomponent ionic diffusion which is valid to high concentration for systems which show ion association. The development is completely general for species which do not react with the solvent. It is demonstrated that the Onsager phenomenological coefficients for associated ion species can be unambiguously determined only in solutions where the concentration of these species can be independently measured. In all other instances, only combinations of the Onsager coefficients for the bare ions and the ion pairs can be experimentally determined. The results of our formulations are contrasted with those of more simplified models for systems containing Na 2 SO 4 and MgSO 4 , as well as for multicomponent natural seawater. The differences between our model and simplified models are significant, especially at high concentration. Inconsistencies which may develop with the use of the simplified approaches are demonstrated. Our approach requires considerable data which are not available at temperatures other than 25°C. Therefore, other approaches which are based only on data at infinite dilution are of great interest. We show here that, if chemical potential derivatives are included in the infinite dilution model of Nernst and Hartley which uses only infinite dilution mobilities, the model can be extended to slightly concentrated solutions. This extended Nernst-Hartley model gives good agreement with all of the existing experimental mutual diffusion coefficient data at concentrations below about 0.2 M in the six component system Na-K-Ca-Mg-Cl-SO 4 -H 2 O. This may be the most reliable way to extend infinite dilution data into more concentrated regions. In the systems we have studied, the inclusion of ion-association species for weakly interacting species does not appear to provide significant improvement over our generalized Nernst-Hartley model.

Felmy, Andrew R.; Weare, John H.

1991-01-01

317

Electrostatic Ion Cyclotron Waves and Ion Energy Diffusion in a Mirror Machine.  

National Technical Information Service (NTIS)

Measurements of ion cyclotron fluctuations and ion energy diffusion in the neutral beam injected 2XIIB mirror machine are presented. A narrow band single mode spectrum is always observed. When the plasma is de-stabilized by turning off axially injected st...

W. C. Turner

1977-01-01

318

Relationships between brain water content and diffusion tensor imaging parameters (apparent diffusion coefficient and fractional anisotropy) in multiple sclerosis.  

PubMed

Fifteen multiple sclerosis patients were examined by diffusion tensor imaging (DTI) to determine fractional anisotropy (FA) and apparent diffusion coefficient (ADC) in a superventricular volume of interest of 8 x 8 x 2 cm(3) containing gray matter (GM) and white matter (WM) tissue. Point resolved spectroscopy 2D-chemical shift imaging of the same volume was performed without water suppression. The water contents and DTI parameters in 64 voxels of 2 cm(3) were compared. The water content was increased in patients compared with controls (GM: 244+/-21 vs. 194+/-10 a.u.; WM: 245+/-32 vs. 190+/-11 a.u.), FA decreased (GM: 0.226+/-0.038 vs. 0.270+/-0.020; WM: 0.337+/-0.044 vs. 0.402+/-0.011) and ADC increased [GM: 1134+/-203 vs. 899+/-28 (x10(-6) mm(2)/s); WM: 901+/-138 vs. 751+/-17 (x10(-6) mm(2)/s)]. Correlations of water content with FA and ADC in WM were strong (r=-0.68, P<0.02; r=0.75; P<0.01, respectively); those in GM were weaker (r=-0.50, P<0.05; r=0.45, P<0.1, respectively). Likewise, FA and ADC were more strongly correlated in WM (r=-0.88; P<0.00001) than in GM (r=-0.69, P<0.01). The demonstrated relationship between DTI parameters and water content in multiple sclerosis patients suggests a potential for therapy monitoring in normal-appearing brain tissue. PMID:16331463

Sijens, Paul E; Irwan, Roy; Potze, Jan Hendrik; Mostert, Jop P; De Keyser, Jacques; Oudkerk, Matthijs

2005-12-06

319

Hemodialysis increases apparent diffusion coefficient of brain water in nephrectomized rats measured by isotropic diffusion-weighted magnetic resonance imaging.  

PubMed Central

The nature of brain edema in dialysis disequilibrium syndrome (DDS) was investigated by diffusion-weighted magnetic resonance imaging (DWI). DWI was performed on normal or bilaterally nephrectomized rats before, and immediately after, hemodialysis. Hemodialysis was performed with a custom-made dialyzer (surface area 150 cm2) against a bicarbonate-buffered bath for 90 min with or without 70 mM urea. Hemodialysis with non-urea bath decreased plasma urea by 21 mM, and plasma osmolality by 22 mosmol/kg H2O, and increased brain water content by 8.0% (all < 0.05), while hemodialysis with urea bath did not affect plasma urea, osmolality, or brain water content. Three sets of axial DWI images of the brain were obtained at different gradient weighing factors with an in-plane resolution of 0.39 mm2. The apparent diffusion coefficient (Dapp) of the brain water was not affected by bilateral nephrectomy, or by hemodialysis in normal rats. In nephrectomized rats, brain Dapp was significantly increased after dialysis with non-urea bath (1.15 +/- 0.08 vs 0.89 +/- 0.07 x 10(-9)m2/sec, P < 0.01). No significant changes of brain water Dapp could be observed after dialysis with urea bath. The increased Dapp associated with DDS indicates that brain extracellular water increases and/or intracellular water decreases after hemodialysis. Our results strongly suggest that the brain edema induced by hemodialysis in uremic rats is due to interstitial edema rather than cytotoxic edema. Furthermore, our results support a primary role for the "reverse urea effect" in the pathogenesis of brain edema in DDS.DWI may be a useful diagnostic tool for DDS in patients with end-stage renal disease.

Galons, J P; Trouard, T; Gmitro, A F; Lien, Y H

1996-01-01

320

Hemodialysis increases apparent diffusion coefficient of brain water in nephrectomized rats measured by isotropic diffusion-weighted magnetic resonance imaging.  

PubMed

The nature of brain edema in dialysis disequilibrium syndrome (DDS) was investigated by diffusion-weighted magnetic resonance imaging (DWI). DWI was performed on normal or bilaterally nephrectomized rats before, and immediately after, hemodialysis. Hemodialysis was performed with a custom-made dialyzer (surface area 150 cm2) against a bicarbonate-buffered bath for 90 min with or without 70 mM urea. Hemodialysis with non-urea bath decreased plasma urea by 21 mM, and plasma osmolality by 22 mosmol/kg H2O, and increased brain water content by 8.0% (all < 0.05), while hemodialysis with urea bath did not affect plasma urea, osmolality, or brain water content. Three sets of axial DWI images of the brain were obtained at different gradient weighing factors with an in-plane resolution of 0.39 mm2. The apparent diffusion coefficient (Dapp) of the brain water was not affected by bilateral nephrectomy, or by hemodialysis in normal rats. In nephrectomized rats, brain Dapp was significantly increased after dialysis with non-urea bath (1.15 +/- 0.08 vs 0.89 +/- 0.07 x 10(-9)m2/sec, P < 0.01). No significant changes of brain water Dapp could be observed after dialysis with urea bath. The increased Dapp associated with DDS indicates that brain extracellular water increases and/or intracellular water decreases after hemodialysis. Our results strongly suggest that the brain edema induced by hemodialysis in uremic rats is due to interstitial edema rather than cytotoxic edema. Furthermore, our results support a primary role for the "reverse urea effect" in the pathogenesis of brain edema in DDS.DWI may be a useful diagnostic tool for DDS in patients with end-stage renal disease. PMID:8698867

Galons, J P; Trouard, T; Gmitro, A F; Lien, Y H

1996-08-01

321

A comparative study on temperature dependent diffusion coefficient of liquid Fe  

NASA Astrophysics Data System (ADS)

The self-diffusion coefficients, D, of liquid Fe at different temperatures have been investigated using hard sphere (HS) theory and universal scaling laws (USLs). Inter-ionic interaction is derived from both pseudopotential proposed by Brettonet-Silbert (BS) and many body potential obtained from embedded atom method (EAM). Temperature dependent effective HS diameter, ?(T), and excess entropy, Sex, are the premier ingredients of the study. The former ingredient is calculated using both variational modified hypernetted chain, VMHNC, integral equation theory and Linearized Weeks-Chandler-Andersen, LWCA, thermodynamic perturbation theory together with an empirical relation of Protopapas et al. (1973) [2] whereas the later one is calculated using VMHNC theory alone, with BS and EAM potentials. We observe that D increases with increasing temperatures. The obtained results are compared with those predicted by Protopapas et al. The comparison suggests that USL of Dzugutov and HS theory with BS potential are better choices to predict D(T) of liquid Fe.

Gosh, R. C.; Syed, Ishtiaque M.; Amin, Zahurul; Bhuiyan, G. M.

2013-10-01

322

Curing and diffusion coefficient study in past?rma, a Turkish traditional meat product.  

PubMed

Changes in water activity (aw), moisture and salt contents and salt effective diffusion coefficients (Deff) of past?rma samples during the curing process were determined. At the end of the curing stage, aw values decreased to 0.942. The average initial moisture content of the samples decreased from 74.56% to 66.64%, depending on the curing time and the average salt content increased to 15.65g NaCl/100g dry matter at the end of the 48-hour curing process. Past?rma samples were assumed the geometry of endless slices, and the analytical solution of Fick's second equation was used for determination of salt Deff values. Salt Deff values were found to vary between 1.49×10(-9)-4.08×10(-9)m(2)/s. PMID:23927919

Akköse, Ahmet; Akta?, Nesimi

2013-07-24

323

The effective diffusion coefficient of a small molecule in a two-phase gel medium  

NASA Astrophysics Data System (ADS)

Using simple theoretical arguments and exact numerical lattice calculations, Hickey et al. [J. Chem. Phys. 124, 204903 (2006)] derived and tested an expression for the effective diffusion coefficient of a probe molecule in a two-phase medium consisting of a hydrogel with large gel-free inclusions. Although providing accurate predictions, this expression neglects important characteristics that such two-phase systems can present. In this article, we extend the previously derived expression in order to include local interactions between the gel and the analyte, interfacial effects between the main phase and the inclusions, and finally a possible incomplete separation between the two phases. We test our new, generalized expressions using exact numerical calculations. These generalized equations should be a useful tool for the development of novel multiphase systems for specific applications, such as drug-delivery platforms.

Kingsburry, Christine; Slater, Gary W.

2009-12-01

324

Survival analysis for apparent diffusion coefficient measures in children with embryonal brain tumours.  

PubMed

Embryonal brain tumors constitute a large and important subgroup of pediatric brain tumors. Apparent diffusion coefficient (ADC) measures have been previously used in the analysis of these tumors. We investigated a newly described ADC-derived parameter, the apparent transient coefficient in tumor (ATCT), a measure of the gradient change of ADC from the peri-tumoral edema into the tumor core, to study whether ATCT correlates with survival outcome. Sixty-one patients with histologically proven embryonal brain tumors and who had diffusion-weighted imaging (DWI) as part of their clinical imaging were enrolled in a retrospective study correlating ADC measures with survival. Kaplan-Meier survival curves were constructed for extent of surgical resection, age <3 years at diagnosis, tumor type, and metastasis at presentation. A multivariate survival analysis was performed that took into consideration ATCT and variables found to be significant in the Kaplan-Meier analysis as covariates. Results from the multivariate analysis showed that ATCT was the only significant covariate (P < .001). Survival analysis using Kaplan-Meier curves, dividing the patients into 4 groups of increasing values of ATCT, showed that more negative values of ATCT were significantly associated with a poorer prognosis (P < .001). A statistically significant difference was observed for survival data with respect to the change in ADC from edema into the tumor volume. Results show that more negative ATCT values are significantly associated with a poorer survival among children with embryonal brain tumors, irrespective of tumor type, extent of resection, age <3 years at diagnosis, and metastasis at presentation. PMID:22954494

Grech-Sollars, Matthew; Saunders, Dawn E; Phipps, Kim P; Clayden, Jonathan D; Clark, Chris A

2012-09-06

325

Kubo number and magnetic field line diffusion coefficient for anisotropic magnetic turbulence  

SciTech Connect

The magnetic field line diffusion coefficients D{sub x} and D{sub y} are obtained by numerical simulations in the case that all the magnetic turbulence correlation lengths l{sub x}, l{sub y}, and l{sub z} are different. We find that the variety of numerical results can be organized in terms of the Kubo number, the definition of which is extended from R=({delta}B/B{sub 0})(l{sub {parallel}}/l{sub {perpendicular}}) to R=({delta}B/B{sub 0})(l{sub z}/l{sub x}), for l{sub x}{ge}l{sub y}. Here, l{sub {parallel}} (l{sub {perpendicular}}) is the correlation length along (perpendicular to) the average field B{sub 0}=B{sub 0}{cflx e}{sub z}. We have anomalous, non-Gaussian transport for R{approx_lt}0.1, in which case the mean square deviation scales nonlinearly with time. For R{approx_gt}1 we have several Gaussian regimes: an almost quasilinear regime for 0.1{approx_lt}R{approx_lt}1, an intermediate, transition regime for 1{approx_lt}R{approx_lt}10, and a percolative regime for R{approx_gt}10. An analytical form of the diffusion coefficient is proposed, D{sub i}=D({delta}Bl{sub z}/B{sub 0}l{sub x}){sup {mu}}(l{sub i}/l{sub x}){sup {nu}}l{sub x}{sup 2}/l{sub z}, which well describes the numerical simulation results in the quasilinear, intermediate, and percolative regimes.

Pommois, P.; Veltri, P.; Zimbardo, G.

2001-06-01

326

Research on the effective gas diffusion coefficient in dry porous media embedded with a fractal-like tree network  

NASA Astrophysics Data System (ADS)

A theoretical model for the relative gas diffusion coefficient in dry porous media embedded with a Y-shaped fractal-like tree network is presented under the combination of bulk diffusion and Knudsen diffusion. The proposed model is expressed as a function of the length ratio, the diameter ratio, the branching level, the branching angle and the relative areal porosity. The effect of the structural parameters of the medium and the tortuosity on gas diffusion is analyzed in detail. Model predictions are compared with available experimental data, and a fair agreement between them is found.

Zheng, Qian; Xu, Jian; Yang, Bin; Yu, Boming

2013-03-01

327

The significance of isotope specific diffusion coefficients for reaction-transport models of sulfate reduction in marine sediments  

NASA Astrophysics Data System (ADS)

Modeling isotopic signatures in systems affected by diffusion, advection, and a reaction which modifies the isotopic abundance of a given species, is a discipline in its infancy. Traditionally, much emphasis has been placed on kinetic isotope effects during biochemical reactions, while isotope effects caused by isotope specific diffusion coefficients have been neglected. A recent study by Donahue et al. (2008) suggested that transport related isotope effects may be of similar magnitude as microbially mediated isotope effects. Although it was later shown that the assumed differences in the isotope specific diffusion coefficients were probably overstated by one or two orders of magnitude ( Bourg, 2008), this study raises several important issues: (1) Is it possible to directly calculate isotopic enrichment factors from measured concentration data without modeling the respective system? (2) Do changes in porosity and advection velocity modulate the influence of isotope specific diffusion coefficients on the fractionation factor ?? (3) If one has no a priori knowledge whether diffusion coefficients are isotope specific or not, what is the nature and magnitude of the error introduced by either assumption? Here we argue (A) That the direct substitution of measured data into a differential equation is problematic and cannot be used as a replacement for a reaction-transport model; (B) That the transport related fractionation scales linearly with the difference between the respective diffusion coefficients of a given isotope system, but depends in a complex non-linear way on the interplay between advection velocity, and downcore changes of temperature and porosity. Last but not least, we argue that the influence of isotope specific diffusion coefficients on microbially mediated sulfate reduction in typical marine sediments is considerably smaller than the error associated with the determination of the fractionation factor.

Wortmann, Ulrich G.; Chernyavsky, Boris M.

2011-06-01

328

Radon (222Rn) in ground water of fractured rocks: A diffusion/ion exchange model  

USGS Publications Warehouse

Ground waters from fractured igneous and high-grade sialic metamorphic rocks frequently have elevated activity of dissolved radon (222Rn). A chemically based model is proposed whereby radium (226Ra) from the decay of uranium (238U) diffuses through the primary porosity of the rock to the water-transmitting fracture where it is sorbed on weathering products. Sorption of 226Ra on the fracture surface maintains an activity gradient in the rock matrix, ensuring a continuous supply of 226Ra to fracture surfaces. As a result of the relatively long half-life of 226Ra (1601 years), significant activity can accumulate on fracture surfaces. The proximity of this sorbed 226Ra to the active ground water flow system allows its decay progeny 222Rn to enter directly into the water. Laboratory analyses of primary porosity and diffusion coefficients of the rock matrix, radon emanation, and ion exchange at fracture surfaces are consistent with the requirements of a diffusion/ion- exchange model. A dipole-brine injection/withdrawal experiment conducted between bedrock boreholes in the high-grade metamorphic and granite rocks at the Hubbard Brook Experimental Forest, Grafton County, New Hampshire, United States (42??56???N, 71??43???W) shows a large activity of 226Ra exchanged from fracture surfaces by a magnesium brine. The 226Ra activity removed by the exchange process is 34 times greater than that of 238U activity. These observations are consistent with the diffusion/ion-exchange model. Elutriate isotopic ratios of 223Ra/226Ra and 238U/226Ra are also consistent with the proposed chemically based diffusion/ion-exchange model.

Wood, W. W.; Kraemer, T. F.; Shapiro, A.

2004-01-01

329

Effects of particle drift on the transport of cosmic rays. IV. more realistic diffusion coefficients  

SciTech Connect

New results from numerical simulations of cosmic-ray modulation by the solar wind are presented. It is argued that the scattering mean free path should be larger than the particle gyroradius in the average magnetic field. Since this constraint was violated in our previous paper, we discuss here simulations which incorporate the larger diffusion, as anticipated, and the difference between drift and no-drift solutions is not so great as before. Nonetheless, we still find profound effects of the drifts. The drifts still determine the origin of the bulk of the cosmic rays seen at any given time in the inner solar system. Thus, during the 1975 solar minimum, positively charged cosmic rays seen in the inner solar system came primarily from the outer boundary near the heliosphereic poles, and negative particles came from the equatorial regions of the boundary. The situation reverses during alternate solar cycles and with the sign of the particle charge. The calculated energy spectra agree reasonably well with observations and are insensitive to the magnitude of the diffusion coefficient.

Jokipii, J.R.; Davila, J.M.

1981-09-15

330

On the parametrization of the energetic-particle pitch-angle diffusion coefficient  

NASA Astrophysics Data System (ADS)

Context: Solar energetic particle (SEP) events are one of the key ingredients of the near-Earth radiation environment. Pitch-angle scattering by fluctuations imposed on the large-scale magnetic field is assumed to be the basic physical process behind diffusive propagation of SEPs in the heliosphere. Various pitch-angle diffusion models have been suggested to parametrize the wave-particle interactions, based on the original results of the classical quasi-linear theory of particle scattering and improved new approaches. Aims: We investigate under which circumstances the different functional forms of the pitch-angle diffusion coefficient can lead to equivalent results. In particular, we use two forms that are commonly used in two types of numerical methods to solve the particle transport equation, i.e., finite difference methods and Monte Carlo simulations. Methods: We estimate the corresponding values of the parameters of the two scattering models by performing a least-square fitting of the functional form of one of the scattering-frequency models to the other. We also perform Monte Carlo simulations of near-relativistic solar electrons to investigate the similarity of the models in terms of observables at 1 AU. Results: Our study shows that the two forms of pitch-angle scattering frequency lead to nearly equivalent results for electron transport from the Sun to 1 AU. We give the equivalent scattering parameters of the two models as curves that can be easily used when comparing the results of the two models. Conclusions: By providing the equivalent parametrizations of two commonly used scattering models, we provide key information on how to relate the results from the two parametrizations to each other and to the theory of particle transport.

Agueda, Neus; Vainio, Rami

2013-03-01

331

Small effect of water on upper-mantle rheology based on silicon self-diffusion coefficients.  

PubMed

Water has been thought to affect the dynamical processes in the Earth's interior to a great extent. In particular, experimental deformation results suggest that even only a few tens of parts per million of water by weight enhances the creep rates in olivine by orders of magnitude. However, those deformation studies have limitations, such as considering only a limited range of water concentrations and very high stresses, which might affect the results. Rock deformation can also be understood as an effect of silicon self-diffusion, because the creep rates of minerals at temperatures as high as those in the Earth's interior are limited by self-diffusion of the slowest species. Here we experimentally determine the silicon self-diffusion coefficient DSi in forsterite at 8?GPa and 1,600?K to 1,800?K as a function of water content CH2O from less than 1 to about 800 parts per million of water by weight, yielding the relationship, DSi???(CH2O)(1/3). This exponent is strikingly lower than that obtained by deformation experiments (1.2; ref. 7). The high nominal creep rates in the deformation studies under wet conditions may be caused by excess grain boundary water. We conclude that the effect of water on upper-mantle rheology is very small. Hence, the smooth motion of the Earth's tectonic plates cannot be caused by mineral hydration in the asthenosphere. Also, water cannot cause the viscosity minimum zone in the upper mantle. And finally, the dominant mechanism responsible for hotspot immobility cannot be water content differences between their source and surrounding regions. PMID:23765497

Fei, Hongzhan; Wiedenbeck, Michael; Yamazaki, Daisuke; Katsura, Tomoo

2013-06-13

332

Quantitative diffusion tensor MR imaging of the brain: field strength related variance of apparent diffusion coefficient (ADC) and fractional anisotropy (FA) scalars  

Microsoft Academic Search

The objectives were to study the “impact” of the magnetic field strength on diffusion tensor imaging (DTI) metrics and also to determine whether magnetic-field-related differences in T2-relaxation times of brain tissue influence DTI measurements. DTI was performed on 12 healthy volunteers at 1.5 and 3.0 Tesla (within 2 h) using identical DTI scan parameters. Apparent diffusion coefficient (ADC) and fractional

Thierry A. G. M. Huisman; Thomas Loenneker; Gerd Barta; Matthias E. Bellemann; Juergen Hennig; Joachim E. Fischer; Kamil A. Il’yasov

2006-01-01

333

Diffusion-weighted imaging of the abdomen at 3.0 Tesla: image quality and apparent diffusion coefficient reproducibility compared with 1.5 Tesla  

Microsoft Academic Search

PURPOSE: To compare single-shot echo-planar imaging (SS EPI) diffusion-weighted MRI (DWI) of abdominal organs between 1.5 Tesla (T) and 3.0T in healthy volunteers in terms of image quality, apparent diffusion coefficient (ADC) values, and ADC reproducibility. MATERIALS AND METHODS: Eight healthy volunteers were prospectively imaged in this HIPAA-compliant IRB-approved study. Each subject underwent two consecutive scans at both 1.5 and

A. B. Rosenkrantz; M. T. H. Oei; J. S. Babb; B. E. Niver; B. Taouli

2011-01-01

334

Diffusion of a Highly-Charged Supramolecular Assembly: Direct Observation of Ion-Association in Water  

SciTech Connect

Understanding the solution behavior of supramolecular assemblies is essential for a full understanding of the formation and chemistry of synthetic host-guest systems. While the interaction between host and guest molecules is generally the focus of mechanistic studies of host-guest complexes, the interaction of the host-guest complex with other species in solution remains largely unknown, although in principle accessible by diffusion studies. Several NMR techniques are available to monitor diffusion and have recently been reviewed. Pulsed gradient spin-echo (PGSE) NMR methods have attracted increasing interest, since they allow diffusion coefficients to be measured with high accuracy; they have been successfully used with observation of {sup 7}Li and {sup 31}P nuclei as well as with {sup 1}H NMR. We report here the direct measurement of diffusion coefficients to observe ion-association interactions by counter cations with a highly-charged supramolecular assembly. Raymond and coworkers have described the design and chemistry of a class of metal-ligand supramolecular assemblies over the past decade. The [Ga{sub 4}L{sub 6}]{sup 12-} (L = 1,5-bis(2,3-dihydroxybenzamido)naphthalene) (1) (Figure 1) assembly has garnered the most attention, with the exploration of the dynamics and mechanism of guest exchange as well as the ability of 1 to achieve either stoichiometric or catalytic reactions inside its interior cavity. Recent studies have revealed the importance of counter cations in solution on the chemistry of 1. During the mechanistic study of the C-H bond activation of aldehydes by [Cp*Ir(PMe{sub 3})(olefin){sup +} {contained_in} 1]{sup 11-} a stepwise guest dissociation mechanism with an ion-paired intermediate was proposed. Similarly, in the mechanism for the hydrolysis of iminium cations generated from the 3-aza Cope rearrangement of enammonium cations in 1, the presence of an exterior ion association was part of the kinetic model. To further substantiate the indirect kinetic evidence for such ion-paired species, we sought to explore the solution behavior of 1 by studying the diffusion of 1 with varying alkali and tetraalkyl ammonium cations. For large molecules in solution, such as synthetic supramolecular assemblies, the diffusion behavior of host and guest molecules can provide valuable information on host-guest interaction. One characteristic feature of a stable host-guest complex is that the host and guest molecules diffuse at the same rate in solution; this has been observed in a number of supramolecular systems. In order to confirm that this system was suitable for study by diffusion NMR spectroscopy, a PGSE-DOSY spectrum was acquired of [NEt{sub 4} {contained_in} 1]{sup 11-} (Figure 2), which shows that the host and guest molecules diffuse at the same rate. Quantitative analysis of the data, from monitoring the integral of host and guest resonances as a function of applied gradient strength, gave identical diffusion coefficients, confirming that the host and guest molecules diffuse together.

University of California, Berkeley; Lawrence Berkeley National Laboratory; Raymond, Kenneth; Pluth, Michael D.; Tiedemann, Bryan E.F.; van Halbeek, Herman; Nunlist, Rudi; Raymond, Kenneth N.

2007-10-22

335

Diffuse Ion Scattering in front of the Earth's Quasi-Parallel Bow Shock: What Can We Learn from Cluster Simultaneous Multipoint Observations?  

NASA Astrophysics Data System (ADS)

We analyze simultaneous multipoint observations of several diffuse ion events observed upstream of Earth’s quasi-parallel bow shock. Each upstream ion event is treated individually in order to determine the similarities and differences of the physical process of energetic ion scattering as a function of interplanetary magnetic field and plasma conditions. The data were provided by the CIS and the FGM instruments onboard Cluster SC1 and SC3 at times of large (i.e., 1-1.5 Re) interspacecraft separation distance. The diffuse ion partial density gradients were determined at different distances from the quasi-parallel bow shock along the magnetic field lines and the e-folding distances (and the diffusion coefficients) were calculated. Our results show that during times of quiet interplanetary magnetic field (IMF) conditions (i.e., when the IMF presents a substantial directional stability) the field aligned beam (FAB) intensity is high which has an impact on the diffuse ion scattering process. We demonstrate that high intensity FAB generated waves are convected deep in the foreshock region and scatter especially the lower energy (i.e., 10-18 keV) diffuse ions efficiently which results in unusually low e-folding distance (and diffusion coefficient). These new results reveal the complexity of the energetic ion scattering process in the foreschock region and help to understand the process of ion acceleration at Earth’s bow shock.

Kis, A.; Scholer, M.; Klecker, B.; Lucek, E. A.; Reme, H.; Lemperger, I.; Wesztergom, V.

2010-12-01

336

Inter-diffusion coefficients parallel to the C-Axis in iron-rich clinopyroxenes calculated from microstructures  

NASA Astrophysics Data System (ADS)

Subsolidus marginal zoning in calcium-poor clinopyroxenes and intermediate zoning in discontinuously zoned subcalcic- to calcium-rich clinopyroxenes from ironrich igneous rocks is used to calculate the interdiffusion coefficient, DCa-(Fe,Mg), parallel to the crystallographic caxis. Wagner's mathematical models describing the displacement of interfaces in solids as the result of isothermal diffusion are adopted. The steady-state heat flow equation is used to approximate the diffusion times. The calculated interdiffusion coefficients are of a reasonable order of magnitude, viz. 6.0×10-20-2.0×10-17cm2· sec-1 at about 900° C.

Rietmeijer, Frans J. M.

1983-08-01

337

Determination of the diffusion coefficient of CO2, O2, and water vapor for poly-3-hydroxy octanoate membranes  

NASA Astrophysics Data System (ADS)

The constant use of norecyclable material throughout the last century has become a huge pollution problem. Consequently, the development of biocompatible and biodegradable material plays an important role nowadays in this context. In order to contribute to this aim, this article is concerned with the use of photoacoustic methodologies to investigate the diffusion coefficient of CO2 and water vapors for poly-3-hydroxy octanoate which is a biodegradable and biocompatible material. In addition, a second methodology based on the paramagnetic properties of O2 molecules was also applied to investigate the diffusion coefficient of O2.

da Silva, M. G.; Gonçalves, S. S.; Sthel, M. S.; Schramm, D. U.; Sanchez, R. R.; Rieumont, J. B.; Vargas, H.

2003-01-01

338

Values for Selected Collisional Dissociation Rate Coefficients of Positive Clustered Ions.  

National Technical Information Service (NTIS)

Values of the rate coefficient, kr, for 15 gas-phase, two-body, collisional-dissociation reactions involving positive cluster ion of aeronomic interest have been tabulated. These values have been cast into the form kr = A (T/300) to the Bth power exp (C/T...

J. M. Heimerl

1976-01-01

339

Variable-coefficient KP equation and solitonic solution for two-temperature ions in dusty plasma  

Microsoft Academic Search

In this Letter, the cylindrical KP equation, which is a variable-coefficient equation, is obtained by using the reductive perturbation method for unmagnified, collisionless and two-temperature ions in dusty plasma. With the help of generalized projected Riccati equation expansion method, the cylindrical KP equation is solved and many solitonic solutions are obtained. Some important parameters for the existence of the compressive

Yue-Yue Wang; Jie-Fang Zhang

2006-01-01

340

Transport of magnetic flux and the vertical structure of accretion discs - II. Vertical profile of the diffusion coefficients  

NASA Astrophysics Data System (ADS)

We investigate the radial transport of magnetic flux in a thin accretion disc, the turbulence being modelled by effective diffusion coefficients (viscosity and resistivity). Both turbulent diffusion and advection by the accretion flow contribute to flux transport, and they are likely to act in opposition. We study the consequences of the vertical variation of the diffusion coefficients, due to a varying strength of the turbulence. For this purpose, we consider three different vertical profiles of these coefficients. The first one is aimed at mimicking the turbulent stress profile observed in numerical simulations of magnetohydrodynamic turbulence in stratified discs. This enables us to confirm the robustness of the main result of Paper I obtained for uniform diffusion coefficients that, for weak magnetic fields, the contribution of the accretion flow to the transport velocity of magnetic flux is much larger than the transport velocity of mass. We then consider the presence of a dead zone around the equatorial plane where the physical resistivity is high while the turbulent viscosity is low. We find that it amplifies the previous effect: weak magnetic fields can be advected orders of magnitude faster than mass, for dead zones with a large vertical extension. The ratio of advection to diffusion, determining the maximum inclination of the field at the surface of the disc, is however not much affected. Finally, we study the effect of a non-turbulent layer at the surface of the disc, which has been suggested as a way to reduce the diffusion of the magnetic flux. We find that the reduction of the diffusion requires the conducting layer to extend below the height at which the magnetic pressure equals the thermal pressure. As a consequence, if the absence of turbulence is caused by the large-scale magnetic field, the highly conducting layer is inefficient at reducing the diffusion.

Guilet, Jérôme; Ogilvie, Gordon I.

2013-04-01

341

Experimental determination of Ni diffusion coefficients in olivine and their dependence on temperature, composition, oxygen fugacity, and crystallographic orientation  

Microsoft Academic Search

Diffusion couple experiments were carried out with San Carlos olivine (Fo90) and NiFe alloys (Ni100, Ni97Fe3, Ni90Fe10) or other olivine compositions (Fo100, Fo25) in order to determine the dependence on temperature, oxygen fugacity, composition and crystallographic orientation of Ni diffusion coefficient (DNi) in olivine. Experiments at 1 atmosphere total pressure cover a temperature range of 900–1445°C with run durations from

Christof Petry; Sumit Chakraborty; Herbert Palme

2004-01-01

342

Water diffusion coefficients of horizontal soil columns from natural saline-alkaline wetlands in a semiarid area  

Microsoft Academic Search

Water diffusion coefficients of soils directly control the solute (such as nitrogen and phosphorous) movement in wetlands,\\u000a which greatly influences the water quality of rivers. The processes of water diffusion in natural saline-alkaline wetland\\u000a soils were simulated by using horizontal soil columns from the Erbaifangzi (EBFZ) wetland in the Xianghai National Natural\\u000a Reserve of China in 2001. The results showed

Junhong Bai; Wei Deng; Baoshan Cui; Hua Ouyang

2007-01-01

343

Diffusion of Mn in GaAs studied by quantitative time-of-flight secondary ion mass spectrometry  

SciTech Connect

Diffusion coefficients and the activation energy for Mn diffusion in ion-implanted and layered epitaxial structures of Ga{sub 1-x}Mn{sub x}As/GaAs are reported from quantitative time-of-flight secondary ion mass spectrometry. Samples are annealed between the growth temperature (as low as 200 deg. C) and approximately 400 deg. C. This temperature range is reported to improve the Curie temperature, which is important for the spintronic applications of these materials. Quantitative diffusion information is obtained by calibrating the Mn concentration to ion-implanted standards and the depth scale to profilometry measurements. Depth profiles obtained for ion-implanted Mn in GaAs at a dose of 1.35x10{sup 15} atoms/cm{sup 2} show increased Mn concentration within the top 5 nm of the sample but otherwise reveal no significant differences in the implantation shape after annealing up to 350 deg. C. For a higher implantation dose of 8.10x10{sup 15} Mn atoms/cm{sup 2}, diffusion is initiated after annealing at 300 deg. C with more significant diffusion at higher temperatures. The analysis of annealed epitaxial films of even higher concentration (Ga{sub 0.89}Mn{sub 0.11}As) exhibits diffusion at all temperatures measured (200-400 deg. C) and an activation energy of 0.67+-0.09 eV is calculated by fitting the profiles to an error function.

Goacher, Robyn E.; Gardella, Joseph A. Jr. [Department of Chemistry, State University of New York at Buffalo, Buffalo, New York 14260 (United States); Hegde, Shridhar; Luo Hong [Department of Physics, State University of New York at Buffalo, Buffalo, New York 14260 (United States)

2009-08-15

344

Gas Diffusion Coefficient in Variably Saturated Peat Soil: Development and Tests of Predictive Models  

NASA Astrophysics Data System (ADS)

The soil-gas diffusion coefficient (Dp) and its dependency on air-filled porosity (?) govern gas diffusion and reaction processes in soil. Accurate Dp(?) prediction models for variably saturated peat soils are needed to evaluate vadose zone transport and fate of greenhouse gases such as methane in peaty wetlands. In this study, we measured Dp on undisturbed peat soil samples at different soil-water matric potentials, and developed new, linear and nonlinear expressions for describing and predicting Dp(?). The new Dp(?) models together with existing Dp(?) models were tested against both measured data and independent data sets from literature. Twelve undisturbed 100cm3 peat soil cores were taken between the soil surface and down to 30-cm depth at Bibai wetland, Hokkaido, Japan. The soil cores were initially saturated with water, and drained at given matric potentials, pF=1.0, 1.5, 1.8, 2.0, 3.0, and 4.1 (where pF equals to log | ? | , ?: the soil-water matric potential in cm H2O), using the hanging water and pressure plate methods. At each matric potential, simultaneous measurements of volume shrinkage, soil-water retention, and Dp were conducted. Literature datasets of Dp(?) for peat soil cores taken from different areas within the same wetland, specifically 12 samples from Iiyama and Hasegawa (2005) and 12 samples from Iiduka et al. (2008), were also used. A total of 191 measurements of Dp(?) at pF ? 2.0 were applied for developing new Dp(?) models for pF ? 2.0 where effects of shrinkage on Dp were assumed negligible. By modifying 3 existing Dp(?) models, the Buckingham (1904) model, the Macroporosity-Dependent Model (MPD; Moldrup et al., 2000), and the Penman-Call model (Moldrup et al., 2005), we suggested 3 new Dp(?) expressions for peat soil. In the Buckingham-based Dp(?) model, a variable X(?"w relationship (where X is the pore connectivity factor) derived from measurements was introduced in the Dp(?) expression. In the Penman-Call-based Dp(?) model, new expressions for the model parameters defining the linear Dp(?) relationship, the slope of Dp(?)/D0 and the threshold air-filled porosity where gas diffusion ceases due to complete water blockage, were derived from measured data. In the MPD-based Dp(?) model, a new Dp,100(?100) relationship for peat soil (where Dp,100 and ?100 are the gas diffusion coefficient and the air-filled porosity at pF2.0) was introduced in the model. To validate the new Dp(?) models, we tested the models against independent data for peat soil samples from Freijer (1994). The new Dp(?) models, except for the Penman-Call-based model, predicted well the independent data, and the Buckingham-based Dp(?) model performed the best among the existing and newly-developed models.

Unno, M.; Kawamoto, K.; Moldrup, P.; Komatsu, T.

2008-12-01

345

Diffusion of dissolved ions from wet silica sol-gel monoliths: implications for biological encapsulation.  

PubMed

Divalent nickel (Ni(2+)), Cu(II)EDTA, methyl orange, and dichromate were used to investigate diffusion from hydrated silica sol-gel monoliths. The objective was to examine diffusion of compounds on a size regime relevant to supporting biological components encapsulated within silica gel prepared in a biologically compatible process space with no post-gelation treatments. With an initial sample set, gels prepared from tetraethoxysilane were explored in a factorial design with Ni(2+) as the tracer, varying water content during hydrolysis, acid catalyst present during hydrolysis, and the final concentration of silica. A second sample set explored diffusion of all four tracers in gels prepared with aqueous silica precursors and a variety of organically modified siloxanes. Excluding six outliers which displayed significant syneresis, the mean diffusion constant (D(gel)) across the entire process space of sample set 1 was 2.42×10(-10) m(2) s(-1); approximately 24% of the diffusion coefficient of Ni(2+) in unconfined aqueous solution. In sample set 2, the tracer size and not gel hydrophobicity was the primary determinant of changes in diffusion rates. A strong linear inverse correlation was found between tracer size and the magnitude of D(gel). Based on correlation with the tracers used in this investigation, the characteristic 1-h diffusion distance for carbonate species relevant to supporting active phototrophic organisms was approximately 1.5mm. These results support the notion that silica sol-gel formulations may be optimized for a given biological entity of interest with manageable impact to the diffusion of small ions and molecules. PMID:23104032

Dickson, David J; Lassetter, Bethany; Glassy, Benjamin; Page, Catherine J; Yokochi, Alexandre F T; Ely, Roger L

2012-09-10

346

Apparent diffusion coefficient on rat brain and nerves intoxicated with methylmercury.  

PubMed

The effects of methylmercury chloride (MMC) on the degenerative changes in rat brain and cranial nerves were studied. Twelve Wistar rats were divided into two equal groups. The rat model of methylmercury intoxication (MMC group) was made by subcutaneously administering 10 mg mercury/g body weight daily for 7 days. Control group rats were infused with the same amount of normal saline during this period. Magnetic resonance imaging (MRI) measurements were performed before and 14 days after the first MMC administration, using a 4.7-T MR system. No significant focal changes were observed on T1- and T2-weighted MR images regarding the internal structures of the brains of the MMC-intoxicated rats, atrophy of the cerebellum, and dilatation of the arachnoid space around the brain stem of MMC-treated rats, but were demonstrated without edematous change. The apparent diffusion coefficients (ADC) of the cortex, caudate-putamen, and trigeminal nerve were not significantly different between the MMC-treated and control rats. However, the ADC parallel to the optic nerves were significantly increased in the MMC group, in contrast to the unchanged ADC perpendicular to the optic nerves. An electron microscopy study revealed a marked decrease of microtubules and moderate decrease of neurofilaments in the axons of myelinated fibers of optic nerves of the MMC-treated rats. We have thus demonstrated a disturbance in the integrity of microtubules and neurofilaments as a toxic action of MMC in the rat nervous system in vivo, particularly in the optic nerves. The use of ADC values calculated by diffusion-weighted MRI is a promising approach for the evaluation of changes in brains and nerves in methylmercury intoxication research. PMID:10330308

Kinoshita, Y; Ohnishi, A; Kohshi, K; Yokota, A

1999-05-01

347

The Sinc-Legendre collocation method for a class of fractional convection-diffusion equations with variable coefficients  

NASA Astrophysics Data System (ADS)

This paper deals with the numerical solution of classes of fractional convection-diffusion equations with variable coefficients. The fractional derivatives are described based on the Caputo sense. Our approach is based on the collocation techniques. The method consists of reducing the problem to the solution of linear algebraic equations by expanding the required approximate solution as the elements of shifted Legendre polynomials in time and the Sinc functions in space with unknown coefficients. The properties of Sinc functions and shifted Legendre polynomials are then utilized to evaluate the unknown coefficients. Several examples are given and the numerical results are shown to demonstrate the efficiency of the newly proposed method.

Saadatmandi, Abbas; Dehghan, Mehdi; Azizi, Mohammad-Reza

2012-11-01

348

ELECTRON-ION RECOMBINATION RATE COEFFICIENTS FOR C II FORMING C I  

SciTech Connect

We have determined absolute dielectronic recombination rate coefficients for C II, using the CRYRING heavy-ions storage ring. The resonances due to 2s-2p (n = 0) core excitations are detected in the center-of-mass energy range of 0-15 eV. The experimental results are compared with intermediate coupling AUTOSTRUCTURE calculations. Plasma rate coefficients are obtained from the DR spectrum by convoluting it with a Maxwell-Boltzmann energy distribution for temperatures in the range of 10{sup 3}-10{sup 6} K. The derived temperature-dependent plasma recombination rate coefficients are presented graphically and parameterized by using a fit formula for convenient use in plasma modeling codes. The experimental rate coefficients are also compared with the theoretical data available in literature. In the temperature range of 10{sup 3}-2 Multiplication-Sign 10{sup 4} K, our experimental results show that previous calculations severely underestimate the plasma rate coefficients and also our AUTOSTRUCTURE calculation does not reproduce the experimental plasma rate coefficients well. Above 2 Multiplication-Sign 10{sup 4} K, the agreement between the experimental and theoretical rate coefficients is much better, and the deviations are smaller than the estimated uncertainties.

Ali, S.; Orban, I.; Mahmood, S.; Schuch, R. [Department of Physics, Stockholm University, AlbaNova S-106 91 Stockholm (Sweden); Altun, Z. [Department of Physics, Marmara University, 81040 Istanbul (Turkey); Glans, P., E-mail: schuch@fysik.su.se [Department of Physics Natural Sciences, Engineering and Mathematics, Mid Sweden University, 85170 Sundsvall (Sweden)

2012-07-10

349

The role of diffusion in ISOL targets for the production of radioactive ion beams  

NASA Astrophysics Data System (ADS)

On-line isotope separation techniques (ISOL) for production of ion beams of short-lived radionuclides require fast separation of nuclear reaction products from irradiated target materials followed by a transfer into an ion source. As a first step in this transport chain the release of nuclear reaction products from refractory metals has been studied systematically and will be reviewed. High-energy protons (500-1000 MeV) produce a large number of radionuclides in irradiated materials via the nuclear reactions spallation, fission and fragmentation. Foils and powders of Re, W, Ta, Hf, Mo, Nb, Zr, Y, Ti and C were irradiated with protons (600-1000 MeV) at the Dubna synchrocyclotron, the CERN synchrocyclotron and at the CERN PS-booster to produce different nuclear reaction products. The main topic of the paper is the determination of diffusion coefficients of the nuclear reaction products in the target matrix, data evaluation and a systematic interpretation of the data. The influence of the ionic radius of the diffusing species and the lattice type of the host material used as matrix or target on the diffusion will be evaluated from these systematics. Special attention was directed to the release of group I-, II- and III-elements. Arrhenius plots lead to activation energies of the diffusion process.Results: A strong radius determined diffusion behaviour was found: DIIIB>DIIA>DIA>DVIIIA, (DY>DSr>DRb>DKr). Rare earth elements diffuse as Me3+-species. Within the host elements of one period of the periodic table the diffusion of the trace elements changes in the following order: DIIIB>DIVB>DVB>DVIB. In a given target trace elements of group I and II of a lower period diffuse faster than the corresponding elements of the higher period of the periodic table. D2ndperiod>D5thperiod>D6thperiod, (DBe>DSr>DBa). The diffusion determined transport rate of nuclear reaction products in solid target materials is often satisfactory, and consequently several refractory metals are suited as targets for fast on-line separation of short-lived nuclear reaction products. The delay times measured in on-line mode at ISOLDE, however, are significantly shorter. An enhancement of the diffusion under radiation condition is considered, subject for further systematic studies. The results obtained in this systematic study may also be applied in the development of alternative separation technologies in medical radionuclide production.

ISOLDE Collaboration; Beyer, G. J.; Hagebø, E.; Novgorodov, A. F.; Ravn, H. L.

2003-05-01

350

Isotopic mass dependence of metal cation diffusion coefficients in liquid water  

NASA Astrophysics Data System (ADS)

Isotope distributions in natural systems can be highly sensitive to the mass ( m) dependence of solute diffusion coefficients ( D) in liquid water. Isotope geochemistry studies routinely have assumed that this mass dependence either is negligible (as predicted by hydrodynamic theories) or follows a kinetic-theory-like inverse square-root relationship ( D ? m-0.5). However, our recent experimental results and molecular dynamics (MD) simulations showed that the mass dependence of D is intermediate between hydrodynamic and kinetic theory predictions ( D ? m-? with 0 ? ? < 0.2 for Li +, Cl -, Mg 2+, and the noble gases). In this paper, we present new MD simulations and experimental results for Na +, K +, Cs +, and Ca 2+ that confirm the generality of the inverse power-law relation D ? m-?. Our new findings allow us to develop a general description of the influence of solute valence and radius on the mass dependence of D for monatomic solutes in liquid water. This mass dependence decreases with solute radius and with the magnitude of solute valence. Molecular-scale analysis of our MD simulation results reveals that these trends derive from the exponent ? being smallest for those solutes whose motions are most strongly coupled to solvent hydrodynamic modes.

Bourg, Ian C.; Richter, Frank M.; Christensen, John N.; Sposito, Garrison

2010-04-01

351

Monte Carlo study of cycloamylose: chain conformation, radius of gyration, and diffusion coefficient.  

PubMed

Cyclic (1 --> 4)-alpha-D-glucan chains with or without excluded volume have been collected from a huge number (about 10(7)) of linear amylosic chains generated by the Monte Carlo method with a conformational energy map for maltose, and their mean-square radii of gyration and translational diffusion coefficients D (based on the Kirkwood formula) have been computed as functions of x (the number of glucose residues in a range from 7 to 300) and the excluded-volume strength represented by the effective hard-core radius. Both /x and D in the unperturbed state weakly oscillate for x < 30 and the helical nature of amylose appears more pronouncedly in cyclic chains than in linear chains. As x increases, these properties approach the values expected for Gaussian rings. Though excluded-volume effects on them are always larger in cycloamylose than in the corresponding linear amylose, the ratios of and the hydrodynamic radius of the former to the respective properties of the latter in good solvents can be slightly lower than or comparable to the (asymptotic) Gaussian-chain values when x is not sufficiently large. An interpolation expression is constructed for the relation between the gyration-radius expansion factors for linear and cyclic chains from the present Monte Carlo data and the early proposed asymptotic relation with the aid of the first-order perturbation theories. PMID:11979517

Nakata, Yasushi; Norisuye, Takashi; Kitamura, Shinichi

2002-07-01

352

Diffusion Coefficients In a Water\\/Sodium Dodecyl Sulfate\\/ Penlanol Mlcroemulslon Base and Its Ammonium Hydroxide Analogue  

Microsoft Academic Search

The self-diffusion coefficients were determined in sodium dodecyl sutfale\\/pcnlanol solutions with water and an aqueous concentrated ammonium hydroxide solution using NMR.Replacing water by the ammonium hydroxide solution destabilized the liquid crystalline phase in the system and also reduced the size of the colloidal association structures in the isotropic liquid part.

Roald Skurtveit; Johan Sjöblom; Stig E. Fribcrg; Ching-Chang Yang; Ahsan U. Ahmed

1993-01-01

353

ANN-Based Models for Moisture Diffusivity Coefficient and Moisture Loss at Equilibrium in Osmotic Dehydration Process  

Microsoft Academic Search

Equations were developed using artificial neural networks to predict water diffusivity coefficient (De) and moisture loss at equilibrium point (ML?) in order to get the moisture loss (ML) at any time in osmotic dehydration of fruits. These models mathematically correlate nine processing variables (temperature and concentration of osmotic solution, water and solid composition of the fruit, porosity, surface area, characteristic

C. I. Ochoa-Martínez; H. S. Ramaswamy; A. A. Ayala-Aponte

2007-01-01

354

Correct Diffusion Coefficients of Proteins in Fluorescence Correlation Spectroscopy. Application to Tubulin Oligomers Induced by Mg 2+ and Paclitaxel  

Microsoft Academic Search

In view of recent warnings for artifacts in fluorescence correlation spectroscopy, the diffusion coefficient of a series of labeled proteins in a wide range of molecular mass (43–670 kD) was determined and shown to be correct with respect to published values and the theory. Fluorescence correlation spectroscopy was then applied to the study of fluorescently labeled tubulin and its oligomerization

Tatiana Krouglova; J. Vercammen; Yves Engelborghs

2004-01-01

355

Combination of Single-Voxel Proton MR Spectroscopy and Apparent Diffusion Coefficient Calculation in the Evaluation of Common Brain Tumors  

Microsoft Academic Search

BACKGROUND AND PURPOSE: MR spectroscopy and apparent diffusion coefficient (ADC) calculation have been used frequently for tumor grading and differentiation during the last decade. We evaluated whether the combination of these two techniques can improve the diagnostic effectiveness of MR imaging in patients with brain tumors. METHODS: Forty-nine patients with histologically proved brain tumors (eight high- and 12 low-grade astrocytomas,

Nail Bulakbasi; Murat Kocaoglu; Fatih Ors; Cem Tayfun; Taner Ucoz

356

Effect of temperature and an ion-exchange resin on cation diffusion through silicone polymer tubing.  

PubMed

Permeation of cations through silicone rubber tubing was measured, and the effect of an ion-exchange resin on the cation diffusion was determined. Silicone rubber has been used as a biomedical polymer and shows a very low solubility to ionizable species. Correlations between the calculated diffusion coefficients, with and without the resin, depended on the charge and number of waters of hydration for each cation. These increases ranged from 1.11 for potassium to 3.06 for iron, multiplied by the diffusion coefficient as a result of the resin. Solubilities of each cation in the polymer were temperature dependent. Activation energies were calculated for each cation by measuring the increased permeation with increasing temperature, with and without the resin. Decreasing magnitudes of activation energies ranged from 0.91 for sodium to 0.57 for iron when the resin was present. Correlations were established between the measured activation energies and reported free energy change for the hydration of each cation. PMID:501529

Christy, D P; Kim, S W; Petersen, R V

1979-09-01

357

Measurement of diffusion coefficient of tritium in alpha-phase of zirconium based on glow discharge implantation method  

SciTech Connect

A tritium implantation method based on a glow discharge of tritium gas was applied to the measurement of diffusion coefficient of tritium in alpha-phase of zirconium. The diffusion experiment was carried out in a temperature region from 673 K to 873K, and the diffusion coefficient of tritium was determined as follows, D / (cm{sup 2}/s) = 3.14x10{sup -3} exp (-42.7 RT / (kJ / mol)). The present data were in good agreement with our previous data, which were determined with an usual implantation method based on a nuclear reaction{sup 6}Li(n,{alpha})T. 12 refs., 2 figs., 1 tab.

Hashizume, Ken-ichi; Hatano, Yuji; Sakamoto, Kan; Sugisaki, Masayasu [Kyushu Univ., Fukuoka (Japan)

1995-10-01

358

Diffusion-weighted 19F-MRI of lung periphery: Influence of pressure and air-SF6 composition on apparent diffusion coefficients.  

PubMed

Lung functional magnetic resonance imaging (MRI) has become a reality using different inert hyperpolarized gases, such as 3He and 129Xe, which have provided an extraordinary boost in lung imaging and has also attracted interest to other chemically inert gaseous contrast agents. In this context, we have recently demonstrated the first diffusion-weighted images using thermally polarized inhaled sulfur hexafluoride (SF6) in small animals. The aim of this study was to evaluate whether or not the diffusion coefficient of this fluorinated gas is sensitive to pulmonary structure, gas concentration and air pressure in the airways. Diffusion coefficients of SF6 (both pure and in air mixtures) measured in vitro at different pressures and 20 degrees C showed an excellent agreement with theoretical values. Measurements of diffusion coefficients were also performed in vivo and post-mortem on healthy rats, achieving satisfactory signal-to-noise ratios (SNRs), and SF6 gas was found to be in an almost completely restricted diffusion regime in the lung, i.e., the transport by molecular diffusion is delayed by collisions with barriers such as the alveolar septa. This observed low diffusivity means that this gas will be less sensitive to structural changes in the lungs than other magnetic resonance sensitive gas such as 3He, particularly at human scale. However, it is still possible that SF6 plays a role since it opens a new structural window. Thus, the interest of researchers in delimiting the important limiting technical factors that makes this process very challenging is obvious. Among them, T2 relaxation is very fast, so gradient systems with very fast switching rate and probably large radiofrequency (RF) power and high field systems will be needed for hexafluoride to be used in human studies. PMID:16098469

Ruiz-Cabello, Jesús; Pérez-Sánchez, José Manuel; Pérez de Alejo, Rigoberto; Rodríguez, Ignacio; González-Mangado, Nicolás; Peces-Barba, Germán; Cortijo, Manuel

2005-08-25

359

Electron-Ion Recombination Rate Coefficients, Photoionization Cross Sections, and Ionization Fractions for Astrophysically Abundant Elements. II. Oxygen Ions  

Microsoft Academic Search

A comprehensive and self-consistent set of new atomic data for photoionization cross sections, sigma_PI, and total unified recombination rate coefficients, alpha_R(T), of oxygen ions are obtained. The calculations are carried out in the close coupling approximation employing the R-matrix method. The unified treatment of total recombination includes both the radiative and dielectronic processes. The analysis of astrophysical spectra and ionization

Sultana N. Nahar

1999-01-01

360

Measurement of ion diffusion using magnetic resonance electrical impedance tomography  

NASA Astrophysics Data System (ADS)

In magnetic resonance electrical impedance tomography (MREIT), currents are applied to an object, the resulting magnetic flux density measured using MRI and the conductivity distribution reconstructed using these MRI data. In this study, we assess the ability of MREIT to monitor changes in the conductivity distribution of an agarose gel phantom, using injected current pulses of 900 µA. The phantom initially contained a distinct region of high sodium chloride concentration which diffused into the background over time. MREIT data were collected over a 12 h span, and conductivity images were reconstructed using the iterative sensitivity matrix method with Tikhonov regularization. The results indicate that MREIT was able to monitor the changing conductivity and concentration distributions resulting from the diffusion of ions within the agarose gel phantom.

Hamamura, Mark J.; Tugan Muftuler, L.; Birgul, Ozlem; Nalcioglu, Orhan

2006-06-01

361

Bayesian estimation of export coefficients from diffuse and point sources in Swiss watersheds  

NASA Astrophysics Data System (ADS)

By combining prior knowledge with data from 11 watershed outlets in Switzerland we estimated export coefficients for soluble reactive phosphorus (SRP), nitrate, total nitrogen, chloride, potassium and alkalinity from different land use categories over a 24 year investigation period. The analysis clearly attributes the observed reduction of SRP loads in the rivers to a decrease in contributions from urban areas from about 0.5 to about 0.04 kg P inhab-1 a-1 between 1980 and 1990. This reflects measures taken to reduce phosphate discharge from urban areas into receiving water bodies and it significantly increases the relative contribution from intensively used agricultural land (about 0.03 g P m-2 a-1) to total SRP load. At the relatively coarse resolution level of this study, there was no significant trend in any of the other export coefficients. Dominant sources of nitrate, chloride and potassium are intensive agriculture with contributions of about 2.9 g N m-2 a-1, 8.7 g Cl m-2 a-1, and 1.9 g K m-2 a-1, and urban diffuse and point sources with contributions of about 2.1 kg N inhab-1 a-1, 20 kg Cl inhab-1 a-1, and 2.5 kg K inhab-1 a-1. Contributions from intensively used agricultural land are significantly higher than the background exports from extensively used land, forests and barren land which are in the order of 0.5 g N m-2 a-1, 1.1 g Cl m-2 a-1 and 0.6 g K m-2 a-1 (2.2 for barren land). Dependence of alkalinity exports on land use was much smaller with contributions between 1.6 and 3.8 mol m-2 a-1. From a methodological point of view, our results reveal that Bayesian inference is an excellent mathematical framework to overcome the identification problems resulting from a partially ill-defined regression problem if prior knowledge is available.

Zobrist, Jürg; Reichert, Peter

2006-09-01

362

Variable-coefficient KP equation and solitonic solution for two-temperature ions in dusty plasma  

NASA Astrophysics Data System (ADS)

In this Letter, the cylindrical KP equation, which is a variable-coefficient equation, is obtained by using the reductive perturbation method for unmagnified, collisionless and two-temperature ions in dusty plasma. With the help of generalized projected Riccati equation expansion method, the cylindrical KP equation is solved and many solitonic solutions are obtained. Some important parameters for the existence of the compressive and rarefactive solitons are discussed and the effects caused by transverse perturbations are also discussed.

Wang, Yue-Yue; Zhang, Jie-Fang

2006-03-01

363

Electrochemistry of oxygen in concentrated NaOH solutions: solubility, diffusion coefficients, and superoxide formation.  

PubMed

The diffusion coefficient (D(O(2))), solubility (C(O(2))), and electrochemical behavior of oxygen reduction were investigated by cyclic voltammetry and transient amperometry on a Pt ultramicroelectrode in aqueous solutions containing various concentrations of NaOH (1-12 M). The results show that both D(O(2)) and C(O(2)) decrease as the solution viscosity (eta) increases significantly with increasing concentration of NaOH. The Stokes-Einstein relationship (D(O(2)) vs 1/eta) is followed, yielding a radius for the O(2) molecule, 2.8 A, that does not change over the concentration range of NaOH studied. From results reported previously for C(O(2)) in more dilute NaOH solutions and the new results here, the number of electrons, n, involved in the first step of the oxygen reduction reaction (ORR) was found to change with the concentration of NaOH, from n = 2 at low NaOH concentrations (1-2 M) to n = 1 at high concentrations (>6 M), in line with the changing water activity. Scanning electrochemical microscopy (SECM) was employed as a sensitive tool to investigate the electrochemical behavior of the product of the ORR in 10 M NaOH solution, O(2)(*-), as a function of potential. The SECM approach curves depend on the substrate bias and state of the Pt substrate surface, and the apparent rate constant for the redox couple of O(2)/O(2)(*-) is determined to be about 2.6 x 10(-4) cm/s in this solution. PMID:19063634

Zhang, Cunzhong; Fan, Fu-Ren F; Bard, Allen J

2009-01-14

364

Calculating potentials of mean force and diffusion coefficients from nonequilibrium processes without Jarzynski's equality.  

PubMed

In general, the direct application of the Jarzynski equality (JE) to reconstruct potentials of mean force (PMFs) from a small number of nonequilibrium unidirectional steered molecular-dynamics (SMD) paths is hindered by the lack of sampling of extremely rare paths with negative dissipative work. Such trajectories that transiently violate the second law of thermodynamics are crucial for the validity of JE. As a solution to this daunting problem, we propose a simple and efficient method, referred to as the FR method, for calculating simultaneously both the PMF U(z) and the corresponding diffusion coefficient D(z) along a reaction coordinate z for a classical many-particle system by employing a small number of fast SMD pullings in both forward (F) and time reverse (R) directions, without invoking JE. By employing Crooks [Phys. Rev. E 61, 2361 (2000)] transient fluctuation theorem (that is more general than JE) and the stiff-spring approximation, we show that (i) the mean dissipative work W(d) in the F and R pullings is the same, (ii) both U(z) and W(d) can be expressed in terms of the easily calculable mean work of the F and R processes, and (iii) D(z) can be expressed in terms of the slope of W(d). To test its viability, the FR method is applied to determine U(z) and D(z) of single-file water molecules in single-walled carbon nanotubes (SWNTs). The obtained U(z) is found to be in very good agreement with the results from other PMF calculation methods, e.g., umbrella sampling. Finally, U(z) and D(z) are used as input in a stochastic model, based on the Fokker-Planck equation, for describing water transport through SWNTs on a mesoscopic time scale that in general is inaccessible to MD simulations. PMID:16483195

Kosztin, Ioan; Barz, Bogdan; Janosi, Lorant

2006-02-14

365

Measurement of Diffusion Coefficients of Air in Silicone Oil and in Hydraulic Oil  

Microsoft Academic Search

A piston-cylinder apparatus was established to measure the solubility and diffusivity of air in dimethyl silicone oils and in hydraulic oils based on the PVT state equation of air and the solution of unsteady one-dimensional diffusion equation. The measured diffusivity-temperature relation can be well fitted by the Arrhenius equation for engineering applications. The correlation between the solute diffusivity D and

Chuan DING; Yurun FAN

2011-01-01

366

Electrochemical measurements of diffusion coefficients of redox-labeled poly(ethylene glycol) dissolved in poly(ethylene glycol) melts  

SciTech Connect

Ferrocene labeled monomethoxy-poly(ethylene glycol)s (MPEG) with molecular weights of 1900 and 750 were used as redox probe solutes in poly(ethylene glycol) melt solvents of molecular weight 750, 2000, and 20000. Cyclic voltammetry and chronoamperometry at microdisk electrodes were employed to measure the diffusion coefficients of the redox probes, which were independent of the probe concentration and varied between 10{sup -7} and 10{sup -10} cm{sup 2}/s. Diffusional activation barrier results also suggest that the ferrocene label does not significantly influence the diffusivity of the probe molecule in the host solvent. Activation barrier, viscosity, and ionic conductivity results show that the LiClO{sub 4} electrolyte does not influence the diffusion barrier or viscosity as long as the ether O/Li{sup +} ratio is >=250 (ca. 0.1 M) which is still a sufficient electrolyte concentration to allow quantitative electrochemical diffusion measurements. 21 refs., 7 figs., 2 tabs.

Haas, O.; Velazquez, C.S.; Porat, Z.; Murray, R.W. [Univ. of North Carolina, Chapel Hill, NC (United States)

1995-10-12

367

Determination of diffusion coefficients of glycerol and glucose from starch based thermoplastic compounds on simulated physiological solution.  

PubMed

Blends of corn starch with poly(ethylene-vinylalcohol) copolymer (SEVA-C) have been studied and reported as biodegradable. These materials are known to be sensitive to enzymatic action, evidencing a degradation of the starch phase in alpha-amylase assays. However, from the physical-chemical point of view the degradation of the blend is mainly associated with the leaching of glycerol, since other compounds are not released and no carbohydrates were found in the degradation solution. Based on these results, the present work attempts to determinate the respective diffusion coefficients. Four different experiments were performed, using samples with different thicknesses that were immersed in a simulated physiological solution. High performance liquid chromatography (HPLC) was used to separate the sugar derivatives and glycerol from the degradation solutions. The obtained data were fitted to an empirical model to allow the estimation of the diffusion coefficient for glycerol and glucose, based on the analytical solution for Fick's law of diffusion, and a good agreement was found (R(2) equals approximately 1). The glycerol leaches quickly out during the first few days of immersion, stabilizing thereafter, presenting greater diffusion coefficients for thicker samples. As the quantity of saccharides in the solution remains almost invariable along the experiments, this work also confirms that the degradation process is difficult without the action of enzymes. PMID:15744615

Alberta Araújo, M; Ferreira, Eugénio C; Cunha, António M; Mota, Manuel

2005-03-01

368

Multiplicity of equilibrium states in laterally heated thermosolutal systems with equal diffusivity coefficients  

Microsoft Academic Search

This work uncovers the instabilities arising in laterally heated stably stratified systems when the diffusivities of the two involved components are equal. These instabilities are demonstrated to be the result of the differential diffusion caused by the unequal lateral diffusion gradients of the components. Such gradients form in the perturbed state due to the different side-wall boundary conditions. Examination of

N. Tsitverblit

1999-01-01

369

Correlation of diffusion coefficients with the electronic structure of interacting atoms  

Microsoft Academic Search

spect to the electron-phonon structure of solids, the interaction between the diffusion parameters and the electronic structure of atoms interecting during the diffusion was followed. An analysis of diagrams constructed from experimental data on the activation energy A and the preexponential factor D o of elements diffusing into the matrix shows that both quantities are very sensitive to the electronic

G. V. Samsonov; I. S. Kiva; N. G. Kaidash; E. G. Borisenko

1976-01-01

370

Salivary glands and lesions: evaluation of apparent diffusion coefficients with split-echo diffusion-weighted MR imaging--initial results.  

PubMed

The authors investigated the feasibility of performing diffusion-weighted (DW) magnetic resonance (MR) imaging with split acquisition of fast spin-echo signals (hereafter, split echo) for the assessment of salivary glands and salivary lesions. Eighteen patients without salivary disease and 10 patients with Sjögren syndrome, chronic parotitis, or focal salivary masses underwent split-echo and echo-planar DW MR imaging. DW MR images and apparent diffusion coefficient maps of the salivary gland had higher quality with split-echo rather than with echo-planar DW MR imaging. PMID:11719687

Yoshino, N; Yamada, I; Ohbayashi, N; Honda, E; Ida, M; Kurabayashi, T; Maruyama, K; Sasaki, T

2001-12-01

371

Measurement of Binary Diffusion Coefficients for Neon-Argon Gas Mixtures Using a Loschmidt Cell Combined with Holographic Interferometry  

NASA Astrophysics Data System (ADS)

The paper reports on experimental binary diffusion coefficient data of neon-argon gas mixtures. Measurements were performed in the temperature range between 293.15 K and 333.15 K and for pressures between 1 bar and 10 bar over almost the whole composition range using a Loschmidt diffusion cell combined with holographic interferometry. The thermostated Loschmidt cell is divided into two half-cells, which can be separated and connected by a sliding plate. Prior to the measurements, two different pure gases are filled into the two half-cells. After starting the diffusion process, the temporal change of the partial molar densities, or rather of the refractive index of the gases, is detected in both half-cells using two holographic interferometers. With this apparatus, the temperature, pressure, and concentration dependence of the binary diffusion coefficient can be determined. The relative uncertainty of a diffusion measurement is between 0.4 % and 1.4 % depending on the pressure. The experimental data are compared with data from the literature and with new theoretical data based on quantum-mechanical ab initio calculations combined with the kinetic theory of gases. Due to a systematic error, the concentration dependence determined in the upper half-cell shows deviations from the theoretical values and from most of the literature data. The concentration, temperature, and pressure dependence obtained from the data from the lower half-cell, however, are in very good agreement with available data. The product of the binary gas diffusion coefficient and the molar density of the gas mixture shows no significant dependence on pressure for the studied neon-argon noble gas system.

Kugler, T.; Jäger, B.; Bich, E.; Rausch, M. H.; Fröba, A. P.

2013-01-01

372

Diffusion Coefficients and Viscosities of CO2 + H2O, CO2 + CH3OH, NH3 + H2O, and NH3 + CH3OH Liquid Mixtures  

Microsoft Academic Search

To evaluate quantitatively the results of gas-liquid absorption experiments, accurate liquid-phase diffusion coefficients and viscosities are needed. In this paper experimental values of these quantities will be reported for the binary systems carbon dioxide + water, carbon dioxide + methanol, ammonia + water, and ammonia + methanol. The diffusion coefficients have been measured using the Taylor-Aris dispersion method, and the

Marco J. W. Frank; Johannes A. M. Kuipers; Swaaij van W. P. M

1996-01-01

373

Diffusion coefficients and viscosities of COâ + HâO, COâ + CHâOH, NHâ + HâO, and NHâ + CHâOH liquid mixtures  

Microsoft Academic Search

To evaluate quantitatively the results of gas-liquid absorption experiments, accurate liquid-phase diffusion coefficients and viscosities are needed. In this paper experimental values of these quantities will be reported for the binary systems carbon dioxide + water, carbon dioxide + methanol, ammonia + water, and ammonia + methanol. The diffusion coefficients have been measured using the Taylor-Aris dispersion method, and the

M. J. W. Frank; J. A. M. Kuipers; W. P. M. van Swaaij

1996-01-01

374

Pyroxene-high silica rhyolite trace element partition coefficients measured by ion microprobe  

SciTech Connect

Pyroxene-liquid trace element partition coefficients have been measured in situ by ion microprobe in high silica rhyolites. Partition coefficients are reported for La, Ce, Nd, Sm, Dy, Er, Yb, Sc, Ti, V, Cr, Sr, Y, and Zr. The in situ analyses avoid the problem of contamination of the pyroxene phase by trace element-rich accessory mineral inclusions encountered in traditional bulk phenocryst-glass partitioning studies. Pyroxenes and glasses which have been analyzed are typical of high silica rhyolites worldwide. The samples analyzed are Bishop Tuff, California (augite, hypersthene): Sierra La Primavera, Mexico (ferrohedenbergite); and two samples of the Huckleberry Ridge Tuff, Wyoming (ferroaugite). Rare earth element (REE) partition coefficient patterns are convex-upward and resemble patterns determined in less silicic bulk compositions. Partition coefficients for the REEs Sr, Zr, and Cr show correlations with the Mg{number sign} of clinopyroxene, suggesting that crystal composition influences the fine structure of partitioning patterns. The overall similarity of partitioning patterns between samples indicates that the partition coefficients determined in this study can be generally applied in the geochemical modeling of high silica rhyolites.

Sisson, T.W. (Massachusetts Inst. of Tech., Cambridge (United States))

1991-06-01

375

Analysis of monopolar ionized field as influenced by ion diffusion  

SciTech Connect

High voltage dc has many advantages over conventional ac liens for long distance power transmission. Recently, the economic feasibility of dc transmission has increased with the development of the hv terminal equipment. One of the problems associated with the HVDC transmission is the corona occurring on the transmission lines and the power loss, audible noise, radio interference, and television interference. Many attempts were made to solve the ionized field problem using the finite-element technique (FET). None of them included the ion diffusion in the solution of the describing equations. A few attempts included ion diffusion but using other numerical techniques. Ghione and Graglia adopted the finite-boxes technique for the solution of ionized field in conductor-to-plane configurations and wire-duct precipitators. Levin and Hoburg used the donor cell-finite element technique for the solution of the ionized field in wire-duct precipitators. In the present paper, a new iterative FET is proposed as a numerical tool to solve Poisson`s equation while the current continuity condition is satisfied by applying Kirchoff`s current balance-law at each node of the FE grid. In addition, the constancy of the conductor surface field at the corona onset value is implemented directly into the proposed FE formulation.

Abdel-Salam, M.; Al-Hamouz, Z. [King Fahd Univ. of Petroleum and Minerals, Dhahran (Saudi Arabia). Dept. of Electrical Engineering

1995-05-01

376

A light scattering study of non equilibrium fluctuations in liquid mixtures to measure the Soret and mass diffusion coefficient  

NASA Astrophysics Data System (ADS)

We use dynamic near field scattering to measure the dynamics of concentration non equilibrium fluctuations at the steady-state of Soret separation. The analysis reveals that above a threshold wave vector qc, the dynamics is governed by diffusion while at smaller wave vectors, gravity dominates. From the measurements, we extract both the mass diffusion and the Soret coefficients. Comparing our results with literature data, we find good agreement confirming that the proposed experimental technique can be considered a sound approach for the study of thermodiffusion processes.

Croccolo, F.; Bataller, H.; Scheffold, F.

2012-12-01

377

Relationships of radon diffusion coefficient with saturated hydraulic conductivity, fines content and moisture saturation of radon/infiltration barriers for the UMTRA Project  

SciTech Connect

The release of {sup 222}Radon to the atmosphere is controlled by the rate of its gas transport through earthen materials. Of the many soil-related parameters, radon diffusion coefficient is the key parameter that characterizes this transport. We compared the radon diffusion coefficients measured at the laboratories for the UMTRA Project with simple empirical correlations developed by others. The empirical correlations predict the radon diffusion coefficient based on the fraction of moisture saturation and porosity. One of the more recent correlations agrees reasonably well with the measurements. In addition, by using a series of correlation curves, we studied the empirical relationships of the. radon diffusion coefficient with the saturated hydraulic conductivity, the fines content, and the moisture saturation in soil. The results reveal that a reliable determination of the long-term moisture and porosity is essential in the design of an adequate radon barrier with respect to the radon diffusion coefficient.

Li, P.Y.; Chen, P.K. [Morrison-Knudsen Co., Inc., Boise, ID (United States)

1994-01-24

378

Evaluation of Fourier transform coefficients for the diagnosis of rheumatoid arthritis from diffuse optical tomography images  

NASA Astrophysics Data System (ADS)

We apply the Fourier Transform to absorption and scattering coefficient images of proximal interphalangeal (PIP) joints and evaluate the performance of these coefficients as classifiers using receiver operator characteristic (ROC) curve analysis. We find 25 features that yield a Youden index over 0.7, 3 features that yield a Youden index over 0.8, and 1 feature that yields a Youden index over 0.9 (90.0% sensitivity and 100% specificity). In general, scattering coefficient images yield better one-dimensional classifiers compared to absorption coefficient images. Using features derived from scattering coefficient images we obtain an average Youden index of 0.58 +/- 0.16, and an average Youden index of 0.45 +/- 0.15 when using features from absorption coefficient images.

Montejo, Ludguier D.; Jia, Jingfei; Kim, Hyun K.; Hielscher, Andreas H.

2013-03-01

379

Fortran computer-code package for the evaluation of gas-phase viscosities, conductivities, and diffusion coefficients. [CHEMKIN  

SciTech Connect

A Fortran computer-code package is described that is used for the evaluation of viscosities, thermal conductivities, diffusion coefficients, and thermal diffusion ratios. The package is in two parts. The first computes polynomial fits to the temperature dependent parts of the properties. The coefficients of these fits are passed to a subroutine package via a linking file. Then, any subroutine from a library of subroutines may be called to return either pure species properties or gas mixture properties. The fitting procedure significantly increases the computational efficiency of the subroutine package, yet typically it degrades accuracy by less than one percent. This package uses the chemical kinetics package CHEMKIN, and transport property subroutines are designed to be used in conjunction with the CHEMKIN subroutine library.

Kee, R.J.; Warnatz, J.; Miller, J.A.

1983-03-01

380

Measurement setup for the simultaneous determination of diffusivity and Seebeck coefficient in a multi-anvil apparatus.  

PubMed

In this paper, a high pressure setup is presented for performing simultaneous measurements of Seebeck coefficient and thermal diffusivity in multianvil apparatus for the purpose of enhancing the study of transport phenomena. Procedures for the derivation of Seebeck coefficient and thermal diffusivity/conductivity, as well as their associated sources of errors, are presented in detail, using results obtained on the filled skutterudite, Ce(0.8)Fe(3)CoSb(12,) up to 12 GPa at ambient temperature. Together with recent resistivity and sound velocity measurements in the same apparatus, these developments not only provide the necessary data for a self-consistent and complete characterization of the figure of merit of thermoelectric materials under pressure, but also serve as an important tool for furthering our knowledge of the dynamics and interplay between these transport phenomena. PMID:23020390

Jacobsen, M K; Liu, W; Li, B

2012-09-01

381

The use of Kirkendall effect for calculating intrinsic diffusion coefficients in a 316L/Ti6242 diffusion bonded couple  

SciTech Connect

Some extreme applications require the metallurgical bonding of a corrosion resistant clad alloy and a high strength steel, since it is difficult to achieve the required mechanical properties and corrosion resistance in a single material. Ti alloys are good candidates to be used as the corrosion resistant cladding material, thus several combinations of steels and Ti alloys have been analyzed. Carbon steels are not suitable for this application because the carbon reacts with Ti and gives rise to the formation of Ti-carbides at the interface which impede the diffusion of the substitutional elements. Here the diffusion processes that take place across the interface are studied in more detail.

Aleman, B.; Gutierrez, I.; Urcola, J.J.

1997-03-01

382

Effective conductivity, dielectric constant, and diffusion coefficient of digitized composite media via first-passage-time equations  

Microsoft Academic Search

We generalize the Brownian motion simulation method of Kim and Torquato [J. Appl. Phys. 68, 3892 (1990)] to compute the effective conductivity, dielectric constant and diffusion coefficient of digitized composite media. This is accomplished by first generalizing the first-passage-time equations to treat first-passage regions of arbitrary shape. We then develop the appropriate first-passage-time equations for digitized media: first-passage squares in

Salvatore Torquato; Dinko Cule

1999-01-01

383

Microscopic derivation of transport coefficients and boundary conditions in discrete drift-diffusion models of weakly coupled superlattices  

Microsoft Academic Search

A discrete drift-diffusion model is derived from a microscopic sequential tunneling model of charge transport in weakly-coupled superlattices provided temperatures are low or high enough. Realistic transport coefficients and contact current-field characteristic curves are calculated from microscopic expressions, knowing the design parameters of the superlattice. Boundary conditions clarify when possible self-sustained oscillations of the current are due to monopole or

L. L. Bonilla; G. Platero; D. Sánchez

2000-01-01

384

Effects of molecular weight and degree of unsaturation on binary diffusion coefficients for lipids in supercritical carbon dioxide  

Microsoft Academic Search

Infinite dilution binary diffusion coefficients and retention factors for the oleic acid family such as oleic acid, methyl- and ethyl esters, and mono-, di-, and triglycerides at 313.21K and 8–30MPa, and for other 13 lipids consisting of C18–C22 unsaturated fatty acid constituents at 313.21K and 11MPa were measured in carbon dioxide by a chromatographic impulse response method with a polymer

T. Funazukuri; C. Y. Kong; S. Kagei

2004-01-01

385

Reduction in Water and Metabolite Apparent Diffusion Coefficients During Energy Failure Involves Cation-Dependent Mechanisms. A Proton Nuclear Magnetic Resonance Study of Rat Cortical Brain Slices  

Microsoft Academic Search

Proton (1H) nuclear magnetic resonance (NMR) diffusion spectroscopy was used to assess apparent diffusion coefficients (ADCs) in rat brain slices. Aglycemic hypoxia caused reductions in the ADC of N-acetylaspartate (NAA) (0.15 to 0.09 × 10?3 mm2\\/s) and “slow” diffusion coefficient (D2) of tissue water (0.51 to 0.37 × 10?3 mm2\\/s), together with a 32 ± 11% increase in tissue water

Juhana M Hakumäki; Risto A. Kauppinen

2000-01-01

386

Can the Lambert-Beer law be applied to the diffuse attenuation coefficient of ocean water?  

Microsoft Academic Search

Radiative transfer theory is combined with a bio-optical model of Case 1 waters and an optical model of the atmosphere to simulate the transport of radiation in the ocean-atmosphere system. The results are treated as experimental data to study the downwelling irradiance attenuation coefficient. It is shown that the downwelling irradiance attenuation coefficient just beneath the surface and the mean

HOWARD R. GORDON

1989-01-01

387

Chemical formation of spatial patterns induced by nonlinearity in a concentration-dependent diffusion coefficient  

Microsoft Academic Search

1. Background The study of spatial pattern formation driven by the coupling of reaction with diffusion has been confined, by and large, to strong nonlinearities in the chemical kinetics terms.' The aim of this report is to demonstrate that if nonlinearity is introduced into the diffusion term, patterns evolve through coupling with even simple chemical reactions (which otherwise show no

Michael L. Kagan; Ronnie Kosloff; Ofra Citri; David Avnir

1989-01-01

388

Calculation of multicomponent ionic diffusion from zero to high concentration: II. Inclusion of associated ion species  

SciTech Connect

This paper presents a theoretical model of multicomponent ionic diffusion which is valid to high concentration for systems which show ion association. The results of the authors' formulations are contrasted with those of more simplified models for systems containing Na{sub 2}SO{sub 4} and MgSO{sub 4}, as well as for multicomponent natural seawater. The differences between their model and simplified models are significant, especially at high concentration. Inconsistencies which may develop with the use of the simplified approaches are demonstrated. The authors' approach requires considerable data which are not available at temperatures other than 25{degree}C. Therefore, other approaches which are based only on data at infinite dilution are of great interest. They show here that, if chemical potential derivatives are included in the infinite dilution model of Nernst and Hartley which uses only infinite dilution mobilities, the model can be extended to slightly concentrated solutions. This extended Nernst-Hartley model gives good agreement with all of the existing experimental mutual diffusion coefficient data at concentrations below about 0.2 M in the six component system Na-K-Ca-Mg-Cl-SO{sub 4}-H{sub 2}O. This may be the most reliable way to extend infinite dilution data into more concentrated regions. In the systems they have studied, the inclusion of ion-association species for weakly interacting species does not appear to provide significant improvement over the generalized Nernst-Hartley model.

Felmy, A.R.; Weare, J.H. (Univ. of California, San Diego, La Jolla (USA))

1991-01-01

389

Apparent diffusion coefficient decreases and magnetic resonance imaging perfusion parameters are associated in ischemic tissue of acute stroke patients.  

PubMed

Perfusion-and diffusion-weighted magnetic resonance imaging scans are thought to allow the characterization of tissue at risk of infarction. The authors tested the hypothesis that the apparent diffusion coefficient (ADC) decrease should be associated with the severity of the perfusion deficit in ischemic tissue of acute stroke patients. Perfusion-and diffusion-weighted scans were performed in 11 patients with sudden onset of neurologic deficits within the last 6 hours and T2-weighted magnetic resonance imaging scans were obtained after 6 days. Parameter images of the maximum of the contrast agent concentration, time to peak, relative cerebral blood volume, relative cerebral blood flow, and relative mean transit time were computed from the perfusion-weighted data. A threshold function was used to identify tissue volumes with stepwise ADC decreases. An onionlike distribution of successively decreasing ADC values was found, with the lowest ADC in the center of the ischemic region. Correspondingly, tissue perfusion decreased progressively from the periphery toward the ischemic core. This effect was most pronounced in the time-to-peak maps, with a linear association between ADC decrease and time-to-peak increase. Apparent diffusion coefficient values decreased from the periphery toward the ischemic core, and this distribution of ADC values was strongly associated with the severity of the perfusion deficit. PMID:11333368

Fiehler, J; Knab, R; Reichenbach, J R; Fitzek, C; Weiller, C; Röther, J

2001-05-01

390

Remarks concerning the validity of the measured diffusion coefficients in liquid metal systems on the Russian MIR space station  

NASA Astrophysics Data System (ADS)

Acta Astronautica, Vol. 48 (2001), contains in pp. 59-70 an article discussing the benefits of conducting liquid metal diffusion experiments in space using the Canadian Microgravity Vibration Isolation Mount (MIM) [B.V. Tryggvason, R.F. Redden, R.A. Herring, W.M.B. Duval, R.W. Smith, K.S. Rezkallah, S.Varma, The vibration environment on the International Space Station: its significance to fluid-based experiments, Acta Astronautica 48 (2001) 59-70]. Two main problems have been identified with this published article: (1) On the basis of experimental results, the authors claim that the diffusion coefficients of gold in lead measured on the ground are much higher than those obtained under microgravity conditions. Close examination of the problems encountered during processing of the capillary diffusion couples on the MIR space station reveals that this claim cannot be justified. (2) The authors further conclude that there is a linear relationship between diffusion coefficient (D) and temperature (T) when g-jitter is suppressed. This conclusion is questionable because the methodology used to determine the processing time and temperatures on the MIR space station does not seem to be scientific.

Shirkhanzadeh, M.

2008-02-01

391

Effect of brine injection on water dynamics in postmortem muscle: study of T2 and diffusion coefficients by MR microscopy.  

PubMed

The dynamics of water in postmortem muscle were studied by magnetic resonance microscopy (MRM). Rabbit muscles were arterially injected with 3 and 5 M NaCl brine. T2 and diffusion mapping were performed during the onset of rigor mortis. A wide spread of T2 values and widely differing postmortem evolutions were observed for injected muscles, whereas T2 was spatially homogeneous for intact muscle. Also, highly variable spatial distribution of diffusion coefficients along (Dz) and across (Dx) the muscle fibers was observed and diffusion anisotropy Dz/Dx) was less marked in injected muscles. The results indicate heterogeneity of brine distribution far from the injection site soon after injection. The postmortem evolution of the parameters is discussed in terms of structural changes induced by brine injection. MRM provides insight into how water dynamics respond to different NaCl concentrations inside muscle. PMID:7739368

Foucat, L; Benderbous, S; Bielicki, G; Zanca, M; Renou, J P

1995-01-01

392

Molecular dynamics simulations of oxygen ion diffusion in yttria-stabilized zirconia  

Microsoft Academic Search

Oxygen ion diffusion in yttria-stabilized zirconia (YSZ) is studied employing molecular dynamics simulation. Oxygen ions migrate mainly by nearest neighbour hopping amongst the tetrahedral lattice sites of zirconium ions. A linear relation between the mean square displacement and time is found, after the oxygen ions have moved over distances much larger than the characteristic distances of the underlying crystal structure.

T. Pramananda Perumal; V. Sridhar; K. P. N. Murthy; K. S. Easwarakumar; S. Ramasamy

2002-01-01

393

Interstitial diffusion in lithium-ion battery electrodes and structural phase transitions in crystalline solids from first principles  

NASA Astrophysics Data System (ADS)

We perform first-principles investigations of thermally activated phase transitions and diffusion in solids. The atomic scale energy landscapes are evaluated with first-principles total energy calculations for different structural and configurational microstates. Effective Hamiltonians constructed from the total energies are subjected to Monte Carlo simulations to study thermodynamic and kinetic properties of the solids at finite temperatures. Cubic to tetragonal martensitic phase transitions are investigated beyond the harmonic approximation. As an example, stoichiometric TiH2 is studied where a cubic phase becomes stable at high temperature while ab-initio energy calculations predict the cubic phase to be mechanically unstable with respect to tetragonal distortions at zero Kelvin. An anharmonic Hamiltonian is used to explain the stability of the cubic phase at higher temperature. The importance of anharmonic terms is emphasized and the true nature of the high temperature phase is elucidated beyond the traditional Landau-like explanation. In Li-ion battery electrodes, phase transitions due to atomic redistribution with changes in Li concentration occur with insertion (removal) of Li-ions during discharge (charge). A comprehensive study of the thermodynamics and the non-dilute Li-diffusion mechanisms in spinel-Li1+xTi2 O4 is performed. Two distinct phases are predicted at different lithium compositions. The predicted voltage curve qualitatively matches with experimental observation. The predicted fast diffusion arises from crystallographic features unique to the spinel crystal structure elucidating the crucial role of crystal structure on Li diffusion in intercalation compounds. Effects of anion and guest species on diffusion are elucidated with Li- and Cu-diffusion in spinel-LixTiS2. We predict strong composition dependence of the diffusion coefficients. A unique feature about spinel-LixTiS2 is that the intermediate site of a Li-hop is coordinated by four Li-sites. This results in di- and triple-vacancy mechanisms at non-dilute concentrations with very different migration barriers. The strong dependence of hop mechanisms on local Li-arrangement is at the origin of large concentration dependence of the diffusion coefficients. This contrasts with spinel-Li xTiO2 where the transition states are coordinated only by the end states of the hop, thereby restricting hops to a single vacancy mechanism. Cu ions are predicted to have much slower diffusion rate in TiS 2 host compared to Li ions.

Bhattacharya, Jishnu

394

Angstrom methods applied to simultaneous measurements of thermal diffusivity and heat transfer coefficients: Part 2, Experimental  

SciTech Connect

To predict operational temperatures of turbine buckets, two of the fundamental properties needed are: the effective thermal conductivity of the bucket material(s) and the heat transfer coefficient of any active cooling within internal passages. For their simultaneous measurement the authors applied a thermal wave method as outlined in Part 1 to a simulated turbine bucket. They employed a modulated electron beam as the heating source and used a previously measured alloy for the bucket wall so only the heat transfer coefficients were needed. They measured the heat transfer coefficients to {+-}10%.

Maylotte, D.H.; Kosky, P.G.; Gallo, J.P.

1999-11-01

395

Direct radiative recombination of electrons with atomic ions Cross sections and rate coefficients  

NASA Astrophysics Data System (ADS)

Scaling laws for direct radiative recombination (DRR) cross sections are found which allow the computation and characterization of rate coefficients for DRR of fast electrons with atomic ions of various ionic species. A general overview of the problem is given, and the study of DRR cross sections is extended to Fe and W. These data are used to examine scaling properties of the total cross sections considered as functions of the nuclear charge, ionic charge, incident kinetic energy, and the electron configuration of the initial ion. Using the scaling properties of this formula, the radiative recombination rate and the rate of loss of electron kinetic energy due to the recombination process are obtained. A method to calculate the radiated power rate with these procedures is described, and the validity of the power loss rate estimates for tokamak plasmas is discussed.

Kim, Y. S.; Pratt, R. H.

1983-06-01

396

Approximation of super-ions for single-file diffusion of multiple ions through narrow pores  

NASA Astrophysics Data System (ADS)

The general theory of the single-file multiparticle diffusion in the narrow pores could be greatly simplified in the case of inverted bell-like shape of the single-particle energy profile, which is often observed in biological ion channels. There is a narrow and deep groove in the energy landscape of multiple interacting ions in such profiles, which corresponds to the pre-defined optimal conduction pathway in the configurational space. If such groove exists, the motion of multiple ions can be reduced to the motion of single quasiparticle, called the superion, which moves in one-dimensional effective potential. The concept of the superions dramatically reduces the computational complexity of the problem and provides very clear physical interpretation of conduction phenomena in the narrow pores.

Kharkyanen, Valery N.; Yesylevskyy, Semen O.; Berezetskaya, Natalia M.

2010-11-01

397

Approximation of super-ions for single-file diffusion of multiple ions through narrow pores.  

PubMed

The general theory of the single-file multiparticle diffusion in the narrow pores could be greatly simplified in the case of inverted bell-like shape of the single-particle energy profile, which is often observed in biological ion channels. There is a narrow and deep groove in the energy landscape of multiple interacting ions in such profiles, which corresponds to the pre-defined optimal conduction pathway in the configurational space. If such groove exists, the motion of multiple ions can be reduced to the motion of single quasiparticle, called the superion, which moves in one-dimensional effective potential. The concept of the superions dramatically reduces the computational complexity of the problem and provides very clear physical interpretation of conduction phenomena in the narrow pores. PMID:21230433

Kharkyanen, Valery N; Yesylevskyy, Semen O; Berezetskaya, Natalia M

2010-11-03

398

Multiplicity of equilibrium states in laterally heated thermosolutal systems with equal diffusivity coefficients  

NASA Astrophysics Data System (ADS)

This work uncovers the instabilities arising in laterally heated stably stratified systems when the diffusivities of the two involved components are equal. These instabilities are demonstrated to be the result of the differential diffusion caused by the unequal lateral diffusion gradients of the components. Such gradients form in the perturbed state due to the different side-wall boundary conditions. Examination of the bifurcation phenomena in the finite enclosures with equal diffusivities exhibited most qualitative features established by Tsitverblit and Kit [Phys. Fluids A 5, 1062 (1993)] and Tsitverblit [Phys. Fluids 7, 718 (1995)] for such phenomena in the heat-salt problem. In the behavior of singularities and steady flows, a number of the regularities that are not distinct in the heat-salt case were distinguished. Additional results obtained with the solute sidewall boundary conditions being of the same (fixed-value) type as the temperature conditions were also discussed.

Tsitverblit, N.

1999-09-01

399

Apparent Diffusion Coefficient: a quantitative parameter for in vivo tumor characterization  

Microsoft Academic Search

Purpose: The purpose of the this study was to evaluate the potential of diffusion weighted imaging (DWI) to distinguish different tissue compartments in early, intermediate and advanced tumor stages. Materials and methods: Twenty-two male mice were induced with squamous cell tumor (SCCVII) and scanned with a clinical 1.5 T scanner. T1-SE, T2-FSE, diffusion weighted Line-Scan-MRI and contrast enhanced T1-SE were

Andreas M Herneth; Samira Guccione; Mark Bednarski

2003-01-01

400

Measurement of Soret and Fickian diffusion coefficients by orthogonal phase-shifting interferometry and its application to protein aqueous solutions  

NASA Astrophysics Data System (ADS)

We have developed a method to measure thermodiffusion and Fickian diffusion in transparent binary solutions. The measuring instrument consists of two orthogonally aligned phase-shifting interferometers coupled with a single rotating polarizer. This high-resolution interferometer, initially developed to measure isothermal diffusion coefficients in liquid systems [J. F. Torres, A. Komiya, E. Shoji, J. Okajima, and S. Maruyama, Opt. Lasers Eng. 50, 1287 (2012)], was modified to measure transient concentration profiles in binary solutions subject to a linear temperature gradient. A convectionless thermodiffusion field was created in a binary solution sample that is placed inside a Soret cell. This cell consists of a parallelepiped cavity with a horizontal cross-section area of 10 × 20 mm2, a variable height of 1-2 mm, and transparent lateral walls. The small height of the cell reduces the volume of the sample, shortens the measurement time, and increases the hydrodynamic stability of the system. An additional free diffusion experiment with the same optical apparatus provides the so-called contrast factors that relate the unwrapped phase and concentration gradients, i.e., the measurement technique is independent and robust. The Soret coefficient is determined from the concentration and temperature differences between the upper and lower boundaries measured by the interferometer and thermocouples, respectively. The Fickian diffusion coefficient is obtained by fitting a numerical solution to the experimental concentration profile. The method is validated through the measurement of thermodiffusion in the well-known liquid pairs of ethanol-water (ethanol 39.12 wt.%) and isobutylbenzene-dodecane (50.0 wt.%). The obtained coefficients agree with the literature values within 5.0%. Finally, the developed technique is applied to visualize biomolecular thermophoresis. Two protein aqueous solutions at 3 mg/ml were used as samples: aprotinin (6.5 kDa)-water and lysozyme (14.3 kDa)-water. It was found that the former protein molecules are thermophilic and the latter thermophobic. In contrast to previously reported methods, this technique is suitable for both short time and negative Soret coefficient measurements.

Torres, Juan F.; Komiya, Atsuki; Henry, Daniel; Maruyama, Shigenao

2013-08-01

401

Force-Clamp Experiments Reveal the Free-Energy Profile and Diffusion Coefficient of the Collapse of Protein Molecules  

NASA Astrophysics Data System (ADS)

We present force-clamp data on the collapse of ubiquitin polyproteins from a highly extended state to the folded length, in response to a quench in the force from 110 pN to 5 or 10 pN. Using a recent method for free-energy reconstruction from the observed nonequilibrium trajectories, we find that their statistics is captured by simple diffusion along the end-to-end length. The estimated diffusion coefficient of ˜100nm2s-1 is significantly slower than expected from viscous effects alone, possibly because of the internal degrees of freedom of the protein. The free-energy profiles give validity to a physical model in which the multiple protein domains collapse all at once and the role of the force is approximately captured by the Bell model.

Lannon, H.; Haghpanah, J. S.; Montclare, J. K.; Vanden-Eijnden, E.; Brujic, J.

2013-03-01

402

Field-assisted ion diffusion of transition metals for the synthesis of nanocomposite silicate glasses  

Microsoft Academic Search

Field-assisted ion diffusion of metals was realized for the controlled doping of silicate glasses. Metallic films deposited onto the substrates by the rf-sputtering technique were used as the metal ions source. In particular, cobalt was, for the first time, introduced into a soda-lime glass by field-assisted ion exchange, giving rise to diffusion profiles that were observed to depend on the

F. Gonella; P. Canton; E. Cattaruzza; A. Quaranta; C. Sada; A. Vomiero

2006-01-01

403

Precision bandgap circuit using high temperature coefficient diffusion resistor in a CMOS process  

US Patent & Trademark Office Database

Disclosed are bandgap circuits that use a resistive divider circuit to modulate the gate voltage of a reference source transistor. The reference voltage transistor is modulated at the base by a voltage that varies inversely with temperature. In this fashion, high sheet resistance poly resistors and diffusion resistors can be used that have very low process variation and minimize the use of die space.

2007-10-02

404

Oxygen Quantification Methods and Application to the Determination of Oxygen Diffusion and Solubility Coefficients in Food  

Microsoft Academic Search

Oxygen solubility and diffusivity in food are two key parameters to understand and quantify the impact of oxygen on food oxidation. A limiting step to the acquisition of these data is the availability and feasibility of methodologies to quantify oxygen content in food and especially in solid foods, even though some recent and significant progress has been made in this

C. Pénicaud; S. Peyron; N. Gontard; V. Guillard

2012-01-01

405

Oxygen quantification methods and application to the determination of oxygen diffusion and solubility coefficients in food  

Microsoft Academic Search

Oxygen solubility and diffusivity in food are two key parameters to understand and quantify the impact of oxygen on food oxidation. A limiting step to the acquisition of these data is the availability and feasibility of methodologies to quantify oxygen content in food and especially in solid foods, even though some recent and significant progress has been made in this

C. Pénicaud; S. Peyron; N. Gontard; V. Guillard

2011-01-01

406

A knowledge base for the apparent mass diffusion coefficient (DEFF) of foods  

Microsoft Academic Search

A Database of Physical Properties of Foods is to be created in the frame of the European Concerted action project (DOPPOF). Among the various properties, the diffusion properties of foods with respect to moisture, salt and other solute components are to be covered. The aim of the Database is to provide data which were carefully selected, evaluated and entered the

Danae Doulia; K. Tzia; V. Gekas

2000-01-01

407

Temperature dependence of the surface diffusion coefficient of K atoms on Pd{111} measured with PEEM  

Microsoft Academic Search

The surface diffusion of potassium on Pd{111} has been studied in real time as a function of temperature between 100 and 190 K in the limit of zero concentration (? < 0.05 ML) using photoelectron emission microscopy (PEEM). Very fast migration of K atoms was observed on flat, quasi-one-dimensional regions of the surface between the step bunches. The temperature dependence

M. Šnábl; M. Ond?ej?ek; V. Cháb; W. Stenzel; H. Conrad; A. M. Bradshaw

1996-01-01

408

A thin film dryer approach for the determination of water diffusion coefficients in viscous products  

Microsoft Academic Search

A thin film dryer (TFD) device has been used to study the drying behavior of viscous products and their water diffusivities. The thin product film was dried convectively using different air velocities, air temperatures, air humidities, initial solid concentrations, initial film thicknesses and optional addition of agar.A mathematical model was developed based on the external and internal heat and mass

Marc Räderer; Alain Besson; Karl Sommer

2002-01-01

409

MASS TRANSFER AND DIFFUSION COEFFICIENT DETERMINATION IN THE WET AND DRY SALTING OF MEAT  

Microsoft Academic Search

Dehydrated salted meat is widely used in Brazil as a very important source of animal protein. The main objective of this kind of processing is water removal. initially by osmotic pressure changes and then by drying, resulting in a product with intermediate moisture levels.In this work, mass transfer and salt diffusion in pieces of meat submitted to wet and dry

E. Sabadini; B. C. Carvalho Jr; P. J do A. Sobral; M. D. Hubinger

1998-01-01

410

Study on anisotropy of effective diffusion coefficient and activation energy for deuterated water in compacted sodium bentonite.  

PubMed

To quantify the effects of temperature on the diffusivity of deuterated water (HDO) in compacted sodium bentonite, through-diffusion experiments were conducted at elevated temperatures ranging from 298 to 333 K. Kunipia F (Na-montmorillonite content>98 wt.%; Kunimine Industries) was compacted to a dry density of 0.9 or 1.35 Mg/m(3). As montmorillonite particles were oriented perpendicular to the direction of compaction, the anisotropy of diffusivity was investigated both parallel and normal to the preferred orientation of the montmorillonite. The effective diffusion coefficient D(e) of HDO was larger when the diffusional direction was parallel as opposed to normal to the preferred orientation for both dry densities. The magnitude of D(e) and the anisotropy for HDO were in good accordance with previously reported results for tritiated water at room temperature. Activation energies of D(e) were isotropic and increased with increasing dry density over the range of 19-25 kJ/mol. This relationship was considered to be due to both pore structure development and the high activation energy of water near the montmorillonite surface. PMID:14698869

Suzuki, Satoru; Sato, Haruo; Ishidera, Takamitsu; Fujii, Naoki

2004-01-01

411

Measurement of Diffusion Coefficients of Short-Lived Species in Solution and in Amorphous Glasses. Final Report, May 1, 1967--August 31, 1978.  

National Technical Information Service (NTIS)

The diffusion coefficients of 1-propyl, 1-pentyl, 1-dodecyl, 1-octadecyl, cyclohexyl and benzyl radicals have been measured in hydrocarbon solvents at room temperature using the method of photochemical space intermittency. The results indicate that rather...

R. D. Burkhart

1978-01-01

412

Electrode polarization and interface effects in liquid crystal systems with mobile ions: development of a model of bipolar diffusion  

NASA Astrophysics Data System (ADS)

The influence of mobile ions on the results of impedance spectroscopy (dielectric spectroscopy) measurements performed on a liquid crystal cell using the new mathematical model recently described was investigated. This mathematical model reformulates the fundamental equation system of continuity for mobile charge carriers and the Poisson equation using new variables. One makes the following assumptions: ions have different mobilities and diffusion coefficients, there is no generation-recombination process, the equilibrium carrier concentrations are uniform and equal each other, the electrodes are either completely blocking or blocked with adsorption-desorption processes. The final result is the analytical expression of the equivalent admittance for the system, allowing to have a clearer picture of the mobile ions and of the processes that occur at the electrode interface influencing the dielectric behavior.

Ganea, Constantin P.

2013-04-01

413

Prediction of self-diffusion coefficient and shear viscosity of water and its binary mixtures with methanol and ethanol by molecular simulation  

Microsoft Academic Search

Density, self-diffusion coefficient, and shear viscosity of pure liquid water are predicted for temperatures between 280 and 373 K by molecular dynamics simulation and the Green-Kubo method. Four different rigid nonpolarizable water models are assessed: SPC, SPC\\/E, TIP4P, and TIP4P\\/2005. The pressure dependence of the self-diffusion coefficient and the shear viscosity for pure liquid water is also calculated and the

Gabriela Guevara-Carrion; Jadran Vrabec; Hans Hasse

2011-01-01

414

Mass-transfer through ion exchange membranes: comparison between the diffusion and the diffusion-convection Stefan-Maxwell equations  

Microsoft Academic Search

We develop the mass transfer equations for a weak-acid ion exchange membrane in the dusty gas model using the generalised diffusion Stefan-Maxwell equation and the generalized convection-diffusion Stefan-Maxwell equation. Electrical conductivity, hydraulic permeability and water transport number are computed at variable ionization rates of the membrane. The viscous flux is computed from the Carman-Kozeni equation. It is shown that electrical

P. Schaetzel; E. Favre; B. Auclair; Q. T. Nguyen

1997-01-01

415

Measuring partition and diffusion coefficients for volatile organic compounds in vinyl flooring  

Microsoft Academic Search

Interactions between volatile organic compounds (VOCs) and vinyl flooring (VF), a relatively homogenous, diffusion-controlled building material, were characterized. The sorption\\/desorption behavior of VF was investigated using single-component and binary systems of seven common VOCs ranging in molecular weight from n-butanol to n-pentadecane. The simultaneous sorption of VOCs and water vapor by VF was also investigated. Rapid determination of the material\\/air

Steven S. Cox; Dongye Zhao; John C. Little

2001-01-01

416

Effect of oxygen vacancy on Li-ion diffusion in a V2O5 cathode: a first-principles study  

NASA Astrophysics Data System (ADS)

The energy barriers of lithium-ion mobility in a V2O5 cathode are calculated using the nudged elastic band method. The low activation energy of the hopping pathway along the <0?1?0> direction (paralleling with the b-axis, the shortest lattice parameter) indicates that V2O5 has a one-dimensional diffusion pattern at the initial stage of charging and discharging. At a temperature of 300 K, the estimated diffusion coefficient is 2.520 × 10-8 cm2 s-1, which is consistent with the range of diffusivity of the previous reported fast ionic conductors. A systematic investigation of the effect of oxygen vacancy on Li-ion diffusion suggests that the bridging oxygen O(2) plays a very positive role in the Li-ion diffusion along the <0?1?0> direction and the activation energy is reduced from 0.340 to 0.215 eV, while the existence of O(1) and O(3) vacancies can hinder the lithium diffusion along this direction due to the increase in the activation energy, respectively. The oxygen vacancies make the energy barriers of the other two potential diffusion pathways reduced to some extent, which is still very large compared with the energy barrier of diffusion along the b-axis.

Ma, W. Y.; Zhou, B.; Wang, J. F.; Zhang, X. D.; Jiang, Z. Y.

2013-03-01

417

Precise determination of the Soret, thermal diffusion and mass diffusion coefficients of binary mixtures of dodecane, isobutylbenzene and 1,2,3,4-tetrahydronaphthalene by a holographic grating technique  

NASA Astrophysics Data System (ADS)

Within the framework of an international benchmark test, the Soret coefficient ST, thermal diffusion coefficient DT and mutual mass diffusion coefficient D of the three binary mixtures of dodecane, isobutylbenzene and 1,2,3,4-tetrahydronaphthalene with a concentration of 50 wt% of each component at a temperature of 25°C have been measured with a holographic grating technique. For the analysis of the experimental data a new numerical correction algorithm based on linear response theory has been employed. The corrections applied are on the order of 1% for ST and 5% for D. The coefficients ST, D and DT are determined with relative errors of a few per cent.

Wittko, Gerhard; Köhler, Werner

2003-06-01

418

Photorecombination of ? ions: search for interference effects, recombination at low energies and rate coefficient in plasmas  

Microsoft Academic Search

In the search for interference between radiative and dielectronic recombination (RR and DR), absolute recombination rate coefficients for Ar-like 0953-4075\\/31\\/21\\/017\\/img12 ions have been measured at the Heidelberg Test Storage Ring in the centre-of-mass energy range 0-80 eV. The dominant recombination channels beside RR is 0953-4075\\/31\\/21\\/017\\/img13 DR via the formation of 0953-4075\\/31\\/21\\/017\\/img14(30953-4075\\/31\\/21\\/017\\/img153d 0953-4075\\/31\\/21\\/017\\/img16) and 0953-4075\\/31\\/21\\/017\\/img14(30953-4075\\/31\\/21\\/017\\/img153d 0953-4075\\/31\\/21\\/017\\/img19) intermediate doubly excited states. The

S. Schippers; T. Bartsch; C. Brandau; G. Gwinner; J. Linkemann; A. Müller; A. A. Saghiri; A. Wolf

1998-01-01

419

Ankyrin G restricts ion channel diffusion at the axonal initial segment before the establishment of the diffusion barrier  

PubMed Central

In mammalian neurons, the precise accumulation of sodium channels at the axonal initial segment (AIS) ensures action potential initiation. This accumulation precedes the immobilization of membrane proteins and lipids by a diffusion barrier at the AIS. Using single-particle tracking, we measured the mobility of a chimeric ion channel bearing the ankyrin-binding motif of the Nav1.2 sodium channel. We found that ankyrin G (ankG) limits membrane diffusion of ion channels when coexpressed in neuroblastoma cells. Site-directed mutants with decreased affinity for ankG exhibit increased diffusion speeds. In immature hippocampal neurons, we demonstrated that ion channel immobilization by ankG is regulated by protein kinase CK2 and occurs as soon as ankG accumulates at the AIS of elongating axons. Once the diffusion barrier is formed, ankG is still required to stabilize ion channels. In conclusion, our findings indicate that specific binding to ankG constitutes the initial step for Nav channel immobilization at the AIS membrane and precedes the establishment of the diffusion barrier.

Brachet, Anna; Leterrier, Christophe; Irondelle, Marie; Fache, Marie-Pierre; Racine, Victor; Sibarita, Jean-Baptiste; Choquet, Daniel; Dargent, Benedicte

2010-01-01

420

Simulations of pitch angle scattering of relativistic electrons with MLT-dependent diffusion coefficients  

Microsoft Academic Search

We present magnetic local time (MLT)-dependent simulations of pitch angle scattering of relativistic (approximately MeV) electrons by chorus and electromagnetic ion cyclotron (EMIC) waves. Numerical simulations indicate that in the case of scattering by chorus waves, the pitch angle distribution is relatively independent of MLT. In the case of scattering by EMIC and chorus waves, the modeled pitch angle distribution

Yuri Y. Shprits; Lunjin Chen; Richard M. Thorne

2009-01-01

421

Measurement of Parallel and Perpendicular Diffusion Coefficients in a Linear Plasma Device  

Microsoft Academic Search

The plasma generator PSI-2 has been used to study the particle transport parallel and perpendicular to the magnetic field (B = 0.1 T). For this purpose first the streaming velocity of the argon background plasma was determined by injecting small amounts of krypton into the discharge and observing the propagation of the Kr+-ions along the field lines. From the transit

Gerd Fussmann; Werner Bohmeyer; Svren Klose

2000-01-01

422

Vertical diffuse attenuation coefficient (Kd) based optical classification of IRS-P3 MOS-B satellite ocean colour data  

NASA Astrophysics Data System (ADS)

The optical classification of the different water types provides vital input for studies related to primary productivity, water clarity and determination of euphotic depth. Image data of the IRSP3 MOS-B, for Path 90 of 27th February, 1998 was used for deriving vertical diffuse attenuation coefficient (Kd) and an optical classification based on K d values was performed. An atmospheric correction scheme was used for retrieving water leaving radiances in blue and green channels of 412, 443, 490 and 550 nm. The upwelling radiances from 443 nm and 550 nm spectral channels were used for computation of vertical diffuse attenuation coefficient K d at 490 nm. The waters off the Gujarat coast were classified into different water types based on Jerlov classification scheme. The oceanic water type IA ( K d range 0.035-0.040m-1), type IB (0.042-0.065 m-1), type II (0.07-0.1m-1) and type III (0.115-0.14m-1) were identified. For the coastal waters along Gujarat coast and Gulf of Kachchh, Kd( 490) values ranged between 0.15 m-1 and 0.35 m-1. The depth of 1% of surface light for water type IA, IB, II and III corresponds to 88, 68, 58 and 34 meters respectively. Classification of oceanic and coastal waters based on K d is useful in understanding the light transmission characteristics for sub-marine navigation and under-water imaging.

Sarangi, R. K.; Chauhan, Prakash; Nayak, S. R.

2002-09-01

423

Diffusion coefficients of hemoglobin by intensity fluctuation spectroscopy: effects of varying pH and ionic strength.  

PubMed Central

Measurements of the mutual diffusion coefficients (D) of the liganded human hemoglobins (Hb) oxy-HbA and oxy-HbS were performed as a function of Hb concentration (CHb), pH, and ionic strength (tau) by intensity fluctuation spectroscopy (IFS). Average diffusion coefficients, (D), and normalized variances, ((D/(D) - 1)2), were recorded. Results are reported and select features are discussed quantitatively. (a) for tau = 0.15 M, the shape of the (d) vs. CHb curve is found to vary with pH. We developed a precise description of this effect in the form of an algebraic relationship between (D), CHb, and Z, the titration charge. (b) only slight differences between the (D) values of oxy-HbS and oxy-HbA are observed, at tau = 0.15 M, for CHb Less Than or Equal To 10 g%. These differences are explained by the theory of part a. (c) No evidence of aggregation is found in solutions of oxy-HbA or oxy-HbS, at tau = 0.15 M, for CHb Less Than or Equal To 10 g%. (d) Indications of aggregation appear in oxy-HbA solutions at very low concentrations of salt. An estimate is made of the extent of aggregation, and the average radius of a cluster is determined.

LaGattuta, K J; Sharma, V S; Nicoli, D F; Kothari, B K

1981-01-01

424

Ex vivo MR determined apparent diffusion coefficients correlate with motor recovery mediated by intraspinal transplants of fibroblasts genetically modified to express BDNF  

Microsoft Academic Search

The purpose of this study was to determine whether apparent diffusion coefficients (ADCs) in ex vivo spinal cord white matter, calculated from diffusion weighted MR (DWI) images, correlate with axonal growth and behavioral recovery following subtotal hemisection and transplantation of fibroblasts genetically modified to express brain derived neurotrophic factor (BDNF). These genetically modified fibroblasts have been shown to promote axonal

Eric D Schwartz; Jed S Shumsky; Suzanne Wehrli; Alan Tessler; Marion Murray; David B Hackney

2003-01-01

425

Imaging Lead Dendrite Formation and Ion Diffusion in Aqueous Solution with Scanning Transmission Electron Microscopy  

NASA Astrophysics Data System (ADS)

Using a scanning transmission electron microscope, we image the formation of lead dendrites and the local Pb^2+ concentration in an electrochemical cell containing a saturated solution of lead(II) nitrate. We control the morphology of the lead deposits with the rate of potential change, which can result in dendrites or compact layers. The processes are reversible and can be repeated. During lead stripping and plating the local Pb^2+ concentration can be measured as an increase or decrease in signal intensity, respectively, as ions come into and out of solution. Quantitative digital image analysis reveals excellent correlation between changes in the Pb^2+ concentration, the rate of lead deposition, and the current passed by the electrochemical cell. Furthermore imaging the ionic concentration as a function of time and distance from the electrode provides a measurement of the diffusion coefficient of the Pb^2+ ion. Real-time electron microscopy of dendritic growth dynamics and the associated local ionic concentrations can provide new insight into the functional electrochemistry of batteries and related energy storage technologies.

White, Edward; Singer, Scott; Augustyn, Veronica; Hubbard, William; Mecklenburg, Matthew; Dunn, Bruce; Regan, B. C.

2013-03-01

426

Activity Coefficient Derivatives of Ternary Systems Based on Scatchard's Neutral Electrolyte Description.  

National Technical Information Service (NTIS)

Activity coefficient derivatives with respect to molality are presented for the Scatchard Neutral Electrolyte description of a ternary common-ion electrolyte system. These quantities are needed for the calculation of 'diffusion Onsager coefficients' and i...

D. G. Miller

2007-01-01

427

About the dependence of the effective diffusivity and dispersion coefficients on chemical reaction in homogeneous porous media  

NASA Astrophysics Data System (ADS)

This work is devoted to analyze the dependence of effective mass transport coefficients with the type of chemical reaction in homogeneous porous media. To this end, we use the method of volume averaging to carry out the upscaling of the corresponding microscale balance equations. As a first approach we studied cases in which there is only one chemical species undergoing a first-order reaction either in the fluid that saturates the porous matrix or at the solid-fluid interface. In both cases the upscaling process leads to effective medium equations expressed in terms of average diffusion or dispersion coefficients and an effective reaction term. Our analysis shows that these effective coefficients depend, in general, upon the nature and magnitude of the microscopic reaction rate as well as of the essential geometrical structure of the solid matrix and the flow rate. This study also shows that if the reaction rate at the microscale is arbitrarily large, the capabilities of the upscaled models are hindered, which is in agreement with the breakdown of the physical sense of the microscale formulation.

Valdes-Parada, F. J.; Aguilar-Madera, C. G.; Alvarez-Ramirez, J.

2011-12-01

428

Universal model for accurate calculation of tracer diffusion coefficients in gas, liquid and supercritical systems.  

PubMed

In this work it is presented a new model for accurate calculation of binary diffusivities (D12) of solutes infinitely diluted in gas, liquid and supercritical solvents. It is based on a Lennard-Jones (LJ) model, and contains two parameters: the molecular diameter of the solvent and a diffusion activation energy. The model is universal since it is applicable to polar, weakly polar, and non-polar solutes and/or solvents, over wide ranges of temperature and density. Its validation was accomplished with the largest database ever compiled, namely 487 systems with 8293 points totally, covering polar (180 systems/2335 points) and non-polar or weakly polar (307 systems/5958 points) mixtures, for which the average errors were 2.65% and 2.97%, respectively. With regard to the physical states of the systems, the aver