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1

Ion diffusion coefficient measurements in nanochannels at various concentrations.  

PubMed

Diffusion is one of the most fundamental properties of ionic transport in solutions. Here, we present experimental studies and theoretical analysis on the ion diffusion in nanochannels. Based on Fick's second law, we develop a current monitoring method to measure ion diffusion coefficient of high solution concentrations in nanochannels. This method is further extended to the cases at medium and low concentrations. Through monitoring ionic current during diffusion, we obtain diffusion coefficients of potassium chloride solution at different concentrations in nanochannels. These diffusion coefficients within the confined space are close to theirs bulk values. It is also found that the apparent ion diffusion equilibrium in the present experiments is very slow at low concentration, which we attribute to the slow equilibrium of the nanochannel surface charge. Finally, we get a primary acknowledge of the equilibrium rate between the nanochannel surface charge and electrolyte solution. The results in this work have improved the understanding of nanoscale diffusion and nanochannel surface charge and may be useful in nanofluidic applications such as ion-selective transport, energy conversion, and nanopore biosensors. PMID:24803967

Wang, Junrong; Zhang, Li; Xue, Jianming; Hu, Guoqing

2014-03-01

2

Applicability of Simplified Models for the Estimation of Ion Exchange Diffusion Coefficients in Zeolites  

Microsoft Academic Search

The applicability of simplified models for the determination of ion exchange diffusion coefficients in zeolites is examined. The simplified models examined are Vermeulen's, Paterson's, and Nernst–Plank's approximations for isotopic and ion exchange processes, used in ion exchange systems analysis. Parameter analysis indicates the limits for fractional attainment of equilibrium U(t), the ratio of exchangeable ions in liquid to solid phase

Vassilis J. Inglezakis; Helen P. Grigoropoulou

2001-01-01

3

Third-order transport properties of ion-swarms from mobility and diffusion coefficients  

NASA Astrophysics Data System (ADS)

A method is presented for the calculation of third order transport properties of ions drifting in gases under the action of an electrostatic field with the use of mobility and ion-diffusion coefficients. The approach is based on a three-temperature treatment of the Boltzmann equation for the ion transport and follows the development of generalized Einstein relations (GER), between diffusion coefficients and mobility. The whole procedure is tested by comparison with numerical and molecular dynamics simulation results for three available alkali ion-noble gas systems. Extension to systems involving internal degrees of freedom and inelastic collisions is shown to follow the development of molecular GER.

Koutselos, Andreas D.

2005-08-01

4

Modeling ion exchange in glass with concentration-dependent diffusion coefficients and mobilities  

Microsoft Academic Search

Multimode buried waveguides made in silicate glass by field-assisted ion exchange present very asymmetric profiles. We show how this phenomenon originates in the large dependence of the kinetics on the local ion concentrations. For this purpose, we derive an interdiffusion equation that includes the effects of concentration-dependent diffusion coefficients and mobilities. We show how to deduce this dependence from measurements

Alexandru I. Lupascu; Antoine P. Kevorkian; Thierry Boudet; Francoise Saint-Andre; Dominique Persegol; Michel Levy

1996-01-01

5

Comparison of ICRF-Induced Ion Diffusion Coefficients Calculated with the DC and AORSA Codes  

SciTech Connect

The DC (Diffusion Coefficient) code obtains RF diffusion coefficients by direct numerical integration of the Lorentz force equation for ion motion in the combined equilibrium fields and the RF full wave EM fields from the AORSA full-wave code. Suitable averaging over initial gyro- and toroidal-angle of coordinate 'kicks' after a bounce-period, gives noise-free bounce-averaged diffusion coefficients. For direct comparison with zero-banana-width coefficients from AORSA, perpendicular-drift terms in the Lorentz equation are subtracted off the integration. The DC code has been coupled to the CQL3D Fokker-Planck code. For a C-Mod minority ion ICRF heating test case, the total power absorption using the diffusion coefficients agree well, and the profiles are similarly close. This supports the DC calculation and the Kennel-Engelmann-based, no-correlations, coefficient calculation in AORSA. However, resonance correlations cause large differences in the pitch angle variations of the diffusion coefficients, and in the resulting evolution of the ion distribution functions.

Harvey, R. W.; Petrov, Yu. [CompX, P.O. Box 2672, Del Mar, CA 92014-5672 (United States); Jaeger, E. F.; Berry, L. A.; Batchelor, D. B. [Oak Ridge National Laboratory, Oak Ridge (United States); Bonoli, P. T.; Wright, J. C. [MIT Plasma Science and Fusion Center, Cambridge (United States)

2009-11-26

6

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

7

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

8

Electrochemical methods for the determination of the diffusion coefficient of ionophores and ionophore-ion complexes in plasticized PVC membranes.  

PubMed

The diffusion coefficients of active components in ion-selective membranes have a decisive influence on the life-time and detection limit of the respective ion-selective electrodes, as well as influencing the rate of polarization and relaxation processes of electrically perturbed ion sensors. Therefore, the rational design of mass transport controlled ion-selective electrodes with sub-nanomolar detection limits requires reliable data on the diffusion coefficients. We have implemented electrochemical methods for the quantitative assessment of both the diffusion coefficients of free ionophores and ion-ionophore complexes. The diffusion coefficients of the pH-sensitive chromoionophore ETH 5294 and the calcium-selective ionophore ETH 5234 were determined in plasticized PVC membranes with different PVC to plasticizer ratios. The diffusion coefficient of the free chromoionophore determined by a chronoamperometric method was validated with optical methods for a variety of membrane compositions. The calcium-selective ionophore ETH 5234 was used as a model compound to assess the diffusion coefficient of the ion-ionophore complex calculated from the time required for the complexes to cross a freshly prepared membrane during potentiometric ion-breakthrough experiments. The difference between the diffusion coefficients of the free ionophore ETH 5234 and the ion-ionophore complex was found to be significant and correlated well with the geometry of the respective species. PMID:18427685

Bodor, Sándor; Zook, Justin M; Lindner, Erno; Tóth, Klára; Gyurcsányi, Róbert E

2008-05-01

9

Measurement of Ferric Ion Diffusion Coefficient in Fricke-Infused Agarose Gel From MR Image Intensity Changes.  

National Technical Information Service (NTIS)

A mathematical modeling was adopted to calculate the ferric ion diffusion coefficient based on the radiation induced magnetic resonance (MR) image intensity change in Fricke-agarose gels. A fast magnetic resonance imaging acquisition technique was employe...

Y. Tseng W. Chu S. Huang

2001-01-01

10

The use of X-ray CT to measure diffusion coefficients of heavy ions in water-saturated porous media  

Microsoft Academic Search

X-ray computerized tomography (CT) was applied for the first time to the measurement of diffusion coefficients of heavy ions in water-saturated clay and rock. The mass absorption coefficient of X-rays is high for heavy elements. Thus the migration of heavy ions in the porous samples was measured by the spatio-temporal change in intensity of X-ray CT images. The measurements of

Yoshito Nakashima

2000-01-01

11

Mobilities and longitudinal diffusion coefficients for K+ ions in nitrogen and argon  

NASA Astrophysics Data System (ADS)

We have constructed a drift tube with a movable ion source and measured the mobilities and longitudinal diffusion coefficients for K+ ions at 303 °K in N2 and at 305 °K in Ar in the pressure range 0.3-5.0 Torr, over the E/N range 4-346 Td in N2 and 3-320 Td in Ar. The zero-field reduced mobilities for K+ ions in N2 and Ar were determined to be 2.50+/-0.03 and 2.63+/-0.03 cm2/V sec, respectively. Both values are in excellent agreement with the values reported by Elford and Milloy. When our data are compared with the values obtained by Thomson et al. in N2 and the values obtained by James et al. in Ar over the entire E/N range, we find that the mean deviations are about 1.7%, independent of gas species and E/N. Our zero-field reduced mobilities are about 1.2% lower in both cases than the values compiled by Ellis et al. It is concluded that the discrepancy is due to a systematic error and is not caused by clustering reactions. The mean values of NDL over the E/N range 4-7 Td in N2 and 5-10 Td in Ar were found to be 1.96×1018 and 2.09×1018 cm-1 sec-1, respectively. Both values are about 7% higher than the values calculated from our mobility data by the generalized Einstein relation and from the same parameters reported by Pai et al.

Takebe, M.; Satoh, Y.; Iinuma, K.; Seto, K.

1980-10-01

12

Predicting protein diffusion coefficients.  

PubMed Central

Diffusion coefficients for proteins in water are predicted. The numerical method developed is general enough to be applied to a wide range of protein surface shapes, from rodlike to globular. Results are presented for lysozyme and tobacco mosaic virus, and they are compared with actual data and with predictions made by less general methods. Images Fig. 2

Brune, D; Kim, S

1993-01-01

13

Determining the coefficients of ambipolar ion diffusion by the method of laser optogalvanic spectroscopy in a luminous gas-air flame  

SciTech Connect

The coefficients of ambipolar diffusion of lithium, sodium, nickel, indium, platinum, and lead ions were measured by laser optogalvanic spectroscopy in the upper cone of a luminous gas-air flame at atmospheric pressure in the absence of an electric field in the flame. The coefficients of diffusion and mobility of the singly charged ions of these elements were calculated from the experimental data.

Novodvorskii, O.A.; Ilyukhin, A.B.; Kuzyakov, Yu.Ya.

1988-03-01

14

Determining the coefficients of ambipolar ion diffusion by the method of laser optogalvanic spectroscopy in a luminous gas-air flame  

Microsoft Academic Search

The coefficients of ambipolar diffusion of lithium, sodium, nickel, indium, platinum, and lead ions were measured by laser optogalvanic spectroscopy in the upper cone of a luminous gas-air flame at atmospheric pressure in the absence of an electric field in the flame. The coefficients of diffusion and mobility of the singly charged ions of these elements were calculated from the

O. A. Novodvorskii; A. B. Ilyukhin; Yu. Ya. Kuzyakov

1988-01-01

15

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

16

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

National Technical Information Service (NTIS)

The authors 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 substantial ran...

E. Graham D. R. James W. C. Keever D. L. Albritton E. W. McDaniel

1973-01-01

17

Sensitivity of Rabbit Ventricular Action Potential and Ca2+ Dynamics to Small Variations in Membrane Currents and Ion Diffusion Coefficients  

PubMed Central

Little is known about how small variations in ionic currents and Ca2+ and Na+ diffusion coefficients impact action potential and Ca2+ dynamics in rabbit ventricular myocytes. We applied sensitivity analysis to quantify the sensitivity of Shannon et al. model (Biophys. J., 2004) to 5%–10% changes in currents conductance, channels distribution, and ion diffusion in rabbit ventricular cells. We found that action potential duration and Ca2+ peaks are highly sensitive to 10% increase in L-type Ca2+ current; moderately influenced by 10% increase in Na+-Ca2+ exchanger, Na+-K+ pump, rapid delayed and slow transient outward K+ currents, and Cl? background current; insensitive to 10% increases in all other ionic currents and sarcoplasmic reticulum Ca2+ fluxes. Cell electrical activity is strongly affected by 5% shift of L-type Ca2+ channels and Na+-Ca2+ exchanger in between junctional and submembrane spaces while Ca2+-activated Cl?-channel redistribution has the modest effect. Small changes in submembrane and cytosolic diffusion coefficients for Ca2+, but not in Na+ transfer, may alter notably myocyte contraction. Our studies highlight the need for more precise measurements and further extending and testing of the Shannon et al. model. Our results demonstrate usefulness of sensitivity analysis to identify specific knowledge gaps and controversies related to ventricular cell electrophysiology and Ca2+ signaling.

Lo, Yuan Hung; Peachey, Tom; Abramson, David; McCulloch, Andrew

2013-01-01

18

A least-squares error minimization approach in the determination of ferric ion diffusion coefficient of Fricke-infused dosimeter gels  

SciTech Connect

A least-squares error minimization approach was adopted to assess ferric ion diffusion coefficient of Fricke-agarose gels. Ferric ion diffusion process was modeled as a Gaussian-shaped degradation kernel operating on an initial concentration distribution. Diffusion coefficient was iteratively determined by minimizing the error function defined as the difference between the theoretically calculated and the experimentally measured dose distributions. A rapid MR image-based differential gel dosimetry technique that time resolves the evolution of the ferric ion diffusion process minimizes smearing of the dose distribution. Our results showed that for a Fricke-agarose gel contained 1 mM ammonium ferrous sulfate, 1% agarose, 1 mM sodium chloride, and 50 mM sulfuric acid, its ferric ion diffusion coefficient is (1.59{+-}0.28)x10{sup -2} cm{sup 2} h{sup -1} at room temperature. This value falls within the 1.00-2.00x10{sup -2} cm{sup 2} h{sup -1} range previously reported under varying gelling ingredients and concentrations. This method allows a quick, nondestructive evaluation of the ferric ion diffusion coefficient that can be used in conjunction with the in situ gel dosimetry experiment to provide a practical diffusion characterization of the dosimeter gel.

Tseng, Y.J.; Huang, S.-C.; Chu, W.C. [Institute of Biomedical Engineering, University Systems of Taiwan-National Yang Ming University, Pei-Tou, Taipei, Taiwan (China); Department of Molecular and Medical Pharmacology, UCLA David Geffen School of Medicine, Los Angeles, California 90095 (United States); Institutes of Biomedical Engineering and Radiological Sciences, University Systems of Taiwan-National Yang Ming University, Pei-Tou, Taipei, Taiwan (China)

2005-04-01

19

Limit Diffusion Coefficients and Hydrated Radii of Eu exp 3+ , Am exp 3+ , Cm exp 3+ , Cf exp 3+ and Es exp 3+ Ions.  

National Technical Information Service (NTIS)

Diffusion of the hydrated ions of Am exp 3+ , Cm exp 3+ , Cf exp 3+ and Es exp 3+ has been investigated in aquous LiCl.HCl solutions (pH = 2,5) at 25,00 exp 0 C. A preliminary study on Eu exp 3+ shows that the diffusion coefficients obtained in the limit ...

B. Fourest J. Duplessis F. David

1982-01-01

20

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

21

Experimental Techniques for the Measurement of Diffusion Coefficients.  

National Technical Information Service (NTIS)

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. ...

S. J. Rothman

1989-01-01

22

A possible way to measure lithium ion diffusion coefficient for Li insertion thin film with unknown Li composition: application to LialphaCoO2 and WO3  

Microsoft Academic Search

In this paper, a new experimental method of lithium ion diffusion coefficient measurement for lithium intercalation thin film material is presented. This experimental method is feasible and can be applied to thin films with unknown lithium composition such as LialphaCoO2 etc. To check its validity, we used the impedance spectroscopy method to make a verification on the WO3 thin film

Wen Shi-jie; Chen Li-quan

1996-01-01

23

Diffusion coefficients of several aqueous alkanolamine solutions  

SciTech Connect

In absorption processes of acid gases (H[sub 2]S, CO[sub 2], COS) in alkanolamine solutions, diffusion coefficients are used for the calculation of the mass transfer rate. The Taylor dispersion technique was applied for the determination of diffusion coefficients of various systems. Experiments with the system KCl in water showed that the experimental setup provides accurate data. For the alkanolamines monoethanolamine (MEA), diethanolamine (DEA), methyldiethanolamine (MDEA), and di-2-propanolamine (DIPA), correlations for the diffusion coefficient as a function of temperature at different concentrations are given. A single relation for every amine has been derived which correlates the diffusion coefficients as a function of temperature and concentration. The temperature was varied between 298 and 348 K, and the concentration between 0 and 4000-5000 mol/m[sup 3]. Furthermore, a modified Stokes-Einstein relation is presented for the prediction of the diffusion coefficients in the alkanolamines in relation to the viscosity of the solvent and the diffusion coefficient at infinite dilution. The diffusion coefficients at low concentrations are compared with some available relations for the estimation of diffusion coefficients at infinite dilution, and it appears that the agreement is fairly good.

Snijder, E.D.; Riele, M.J.M. te; Versteeg, G.F.; Swaaij, W.P.M. van (Twente Univ. of Technology, Enschede (Netherlands). Dept. of Chemical Engineering)

1993-07-01

24

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

25

Radon diffusion coefficients for residential concretes  

Microsoft Academic Search

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 10⁻⁸ m² s⁻¹ to 5.2 x 10⁻⁷ m² s⁻¹. The pore diffusion coefficients generally increased with the water-cement ratio of the concrete and decreased with its density. A least-squares regression

Vern C. Rogers; Kirk K. Nielson; Rodger B. Holt; Richard Snoddy

1994-01-01

26

Obtaining transport diffusion coefficients from self-diffusion coefficients in nanoporous adsorption systems  

NASA Astrophysics Data System (ADS)

In a continuation of the study of the adsorption and transport properties in a nanoporous adsorption system, transport diffusion coefficients are predicted from the self-diffusion coefficients using the Darken equation, modified for use in the adsorbed phase. We obtain self-diffusion coefficients using equilibrium molecular dynamics (MD) simulations. Adsorption equilibrium data are required in this modified form, which are obtained using grand canonical Monte Carlo (GCMC) simulations. We show that principal component regression provides an elegant and robust method to integrate the data available from the MD and GCMC simulations for the prediction of transport diffusivities. We investigate the effect of the adsorbed phase concentration, mole fraction and temperature on the transport diffusion coefficient thus predicted. We show that the self- and the transport diffusion coefficients decrease with increasing adsorbed phase concentration. We also show that the transport diffusion coefficients decrease with increasing methane mole fraction, in contrast to the behaviour of the self-diffusion coefficients.

Adhangale, Parag; Keffer, David J.

27

Dependence of the broad frequency dielectric spectra of colloidal polystyrene particle suspensions on the difference between the counterion and co-ion diffusion coefficients.  

PubMed

Dielectric properties of four suspensions of spherical polystyrene particles were measured at 25 degrees C over a broad frequency range extending from 100 Hz to 10 MHz, using a HP 4192 A Impedance Analyzer. The instrument was coupled to a cell with parallel platinum black electrodes and variable spacing, and the quadrupole calibration method was used. The aqueous electrolyte solutions were prepared using equal concentrations of NaCl, KCl, NaAc, or KAc, so that the calculated Debye screening length and Zeta potential remained constant, while the conductivity changed. The polystyrene particles used (Interfacial Dynamics Corp., surfactant-free white sulfate latex) have a diameter of 1 micron and a surface charge density that is independent of the pH. The dielectric spectra were described using the Nettelblad-Niklasson expression combined with a Debye type high-frequency term and analyzed using the Shilov-Dukhin theory and numerical results. The theoretical prediction that the low-frequency dispersion parameters are determined by the co-ion diffusion coefficient was experimentally confirmed. This also allowed to justify an alternative definition of the characteristic time of the low-frequency dispersion. On the contrary, the prediction that the high-frequency dispersion parameters are determined by the diffusion coefficient of counterions could not be confirmed, possibly due to experimental problems. However, the zeta-potential values deduced from high-frequency data were compatible with values deduced from electrophoretic mobility measurements. PMID:16460750

Tirado, Mónica; Grosse, Constantino

2006-06-15

28

Recombination coefficients for iron ions  

NASA Technical Reports Server (NTRS)

Radiative recombination coefficients for all Fe ions are calculated by use of the Milne relation of detailed balance. Analytic fits are made to the dielectronic recombination rates computed by Jacobs (1977) and the Burgess general formula (1965). Higher level rates are treated hydrogenically by a quantum defect method based on the energies of the levels. Recombination coefficients for Fe I to Fe 26 are listed.

Woods, D. T.; Shull, J. M.; Sarazin, C. L.

1981-01-01

29

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

30

The effective diffusion coefficient for porous rubble  

Microsoft Academic Search

Each waste package in the proposed Yucca Mountain repository is to be separated from surrounded unsaturated rock by a 2-cm air gap annulus. However, if the annulus becomes filled with rock and rubble, there can exist pathways for diffusive release of radionuclides through pore liquid, even if the repository remains unsaturated. The effective diffusion coefficient for radionuclide release through pore

M. M. Sadeghi; W. W.-L. Lee; T. H. Pigford; P. L. Chambre

1990-01-01

31

Diffuse reflection coefficient of a stratified sea.  

PubMed

A differential equation of a Riccati type for the diffuse reflection coefficient of a stratified sea is proposed. For a homogeneous sea with arbitrary inherent optical properties this equation is solved analytically. For an inhomogeneous sea it is solved approximately for any arbitrary stratification. The resulting equation expresses the diffuse reflection coefficient of the sea through vertical profiles of absorption and backscattering coefficients, bottom albedo, and sea depth. The results of calculations with this equation are compared with Monte Carlo computations. It was found that the precision of this approach is in the range of 15%. PMID:18305694

Haltrin, V I

1999-02-20

32

Diffusion coefficients of two mobile ions in three AB3In7VI12 single crystals (AB=Cu and Ag VI=Se or Te). Proposition of an equivalent electrical circuit  

NASA Astrophysics Data System (ADS)

Diffusion coefficients of two mobile ions are computed from the conductivity variation with time of three In-rich chalcopyrite single crystals of the ABn-3Inn+1VI2n system (AB=Cu and Ag and VI=Se or Te). The coefficients have similar values in the three compounds, higher than in chalcopyrite compounds (ABInSe2) due to a higher number of (2VCu+InCu) defect pairs in the lattice. In each compound, the potential across the sample or the current intensity, Vm and I, can increase or decrease within time due to a change in the interface potential by the ion arrival, where the decrease could be explained by a charge decrease. Mobile ions arrive while others, with higher charge, should leave related to the formation or disappearance of (2VCu+InCu) defect pairs. Compositional measurements confirm the motion of Cu ions and In antisites, InCu, in the Cu sublattice. Therefore, these compounds are mixed ionic and electronic conductors, MIECs, with two mobile ions, where the electronic and ionic conductions are non-blocked and blocked in the metal/semiconductor interface respectively. An equivalent electrical circuit is proposed, extensible at MIECs with j mobile ions, where the interface potential is similar to the potential drop in the charge or discharge in the capacitor. The analysis of the total flux of ions due to diffusion, jdiff, and to the action of electrical field, jdrift, permits compute the number of ions, their diffusion coefficients and the change of the potential drop within time in the interface in compounds with several mobile ions. This electrical model is checked using the experimental data in the three single crystals in a computer program. To know different mobile ions in In-rich chalcopyrites and their diffusion coefficients will permit to understand and have mechanisms of control in solar cell fabrication based in chalcopyrite thin films.

Díaz, R.

2012-06-01

33

Composition dependence of ion-transport coefficients in gas mixtures  

NASA Technical Reports Server (NTRS)

Simple momentum-transfer theory for the composition dependence of ion mobilities and diffusion coefficients in gas mixtures at arbitrary field strengths is corrected and extended, and compared with a similar theory based on momentum and energy transfer, and with results based on direct solution of the Boltzmann equation by Kihara's method. Final equations are recommended for predicting composition dependences, given only results on ion mobilities and diffusion coefficients in the pure component gases.

Whealton, J. H.; Mason, E. A.; Robson, R. E.

1974-01-01

34

Composition dependence of ion transport coefficients in gas mixtures  

NASA Technical Reports Server (NTRS)

A simple momentum-transfer theory for the composition dependence of ion mobilities and diffusion coefficients in gas mixtures at arbitrary field strengths is corrected, extended, and compared with a similar theory based on momentum and energy transfer, and with results based on direct solution of the Boltzmann equation by Kihara's method. Final equations are recommended for predicting composition dependences, given only results on ion mobilities and diffusion coefficients in the pure component gases.

Whealton, J. H.; Mason, E. A.; Robson, R. E.

1973-01-01

35

Self-diffusion coefficients of expanded rubidium  

NASA Astrophysics Data System (ADS)

The second-order and fourth-order frequency sum rules of the velocity autocorrelation function (VACF) of Rb have been evaluated for six thermodynamic states along the liquid - vapour coexistence curve by using the Ashcroft pseudopotential and corresponding pair distribution function obtained by molecular dynamics (MD) simulation. These sum rules and a model for the self-diffusion coefficient have been used to study the time evolution of the VACF and self-diffusion coefficients. The results obtained have been compared with MD simulation data. It is found that our model provides the first semiquantitative explanation for the density and temperature dependences of the VACF and self-diffusion coefficients of expanded Rb.

Sharma, Saroj K.; Tankeshwar, K.

1996-12-01

36

Radial diffusion coefficients in the outer heliosphere  

NASA Astrophysics Data System (ADS)

When cosmic ray streaming in the heliosphere is negligible, the basic onedimensional transport model gives a simple approximation for the diffusion coefficient of cosmic ray particles, ~Zrr=CVSW/gr, where C is the Compton-Gettiing factor, VSW is the solar wind velocity and gr is the radial intensity gradients. In a separate paper at this conference we made detailed measurement of radial intensity gradients in the outer heliosphere from the combined data set observed over the solar activity minima of 1977/1997(qA>0). Using these detailed gradients and onedimensional transport model we calculate the diffusion coefficients in the outerheliosphere. These diffusion coefficients are compared with those of 1987 to also search for drift effects as manifested over two successive solar minima periods

Fujii, Z.; McDonald, F. B.; Moraal, H.

2001-08-01

37

Radon diffusion coefficients for aged residential concretes  

Microsoft Academic Search

This note reports radon gas pore diffusion coefficient measurements for residential concretes from Florida, ranging in age from 12 y to 45 y. The coefficients ranged from 1.5 x 10⁻⁷ m² s⁻¹ to 5.5 x 10⁻⁷ m² s⁻¹. On the average, these values are about a factor of 1.6 higher than average values previously reported for new residential concretes in

Vern C. Rogers; Kirk K. Nielson; Rodger B. Holt

1995-01-01

38

Calculation of the Anisotropic Diffusion Coefficient  

Microsoft Academic Search

The one-group anisotropic diffusion coefficient is calculated for slab and square lattice cells with use made of Benoist's formula. In utilizing the integral transport theory, only several collisions suffered by a neutron have hitherto been considered. In this paper, we adopt the integral theory and take into consideration the effect of an infinite number of collisions suffered by a neutron,

Toshikazu TAKEDA; Tamotsu SEKIYA

1972-01-01

39

The electron diffusion coefficient in Jupiter's magnetosphere  

NASA Technical Reports Server (NTRS)

A steady-state model of Jupiter's electron radiation belt is developed. The model includes injection from the solar wind, radial diffusion, energy degradation by synchrotron radiation, and absorption at Jupiter's surface. A diffusion coefficient of the form D sub RR/R sub J squared = k times R to the m-th power is assumed, and then observed data on synchrotron radiation are used to fit the model. The free parameters determined from this fit are m = 1.95 plus or minus 0.5, k = 1.7 plus or minus 0.5 x 10 to the 9th power per sec, and the magnetic moment of injected particles equals 770 plus or minus 300 MeV/G. The value of m shows quite clearly that the diffusion is not caused by magnetic pumping by a variable solar wind or by a fluctuating convection electric field. The process might be field line exchange driven by atmospheric-ionospheric winds; our diffusion coefficient has roughly the same radial dependence but is considerably smaller in magnitude than the upper bound diffusion coefficients recently suggested for this process by Brice and McDonough (1973) and Jacques and Davis (1972).

Birmingham, T.; Northrop, T.; Baxter, R.; Hess, W.; Lojko, M.

1974-01-01

40

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

41

Trace-Element Diffusion Coefficients in Olivine  

NASA Astrophysics Data System (ADS)

We have undertaken chemical diffusion experiments at 1300°C to determine both crystal/melt partition coefficients and diffusion coefficients for a wide range of trace elements in forsteritic olivine. Experiments were conducted at 1 atm under controlled fO2 for up to 25 days using synthetic melts made to a composition in equilibrium with olivine for major elements, and doped with selected trace elements. The melt was put into a 5 mm diameter cylindrical hole in gem quality San Carlos olivine crystals drilled paralell to the a axis. Diffusion profiles were obtained both for trace elements that were added to the starting material and diffuse into the olivine, and also for several trace elements present at natural abundances in the olivine that diffuse out. The profiles were measured across sections perpendicular to crystal/melt boundary at a variety of crystallographic orientations (confirmed by EBSD) by laser-ablation ICP-MS. A thin laser slit oriented parallel to the crystal/melt interface was traversed from the melt through the crystal. Element concentrations were fitted to the diffusion equation to obtain both diffusion coefficients and concentrations at the crystal/melt interface, and hence partition coefficients. Calculated diffusivities for many trace elements (Ca, REE, Y, Sc, V, Cr, Ni, Co, Mn, Na, Li, Be, Ti) are relatively fast (D = 10-16 to 10^{-13 m2/s at 1300°C). The diffusion of Li in olivine (approx. D = 10^{-15} m2/s) is only slightly slower than REEs and similar to divalent cations, in good agreement with inferences from zoning profiles in natural olivine [1]. This rate is considerably slower than for plagioclase and clinopyroxene [2], a result which has important implications for interpreting Li isotopic data from mantle-derived rocks. The fastest diffusing trace element we observe is Be. Applying our diffusion and partition coefficients to the model of Qin et al. [3], we calculate that the REEs of olivine-hosted melt inclusions in the mantle will extensively re-equilibrate with external magma in weeks (heavy REEs) to a few years (light REEs). These timescales are significantly shorter than the times estimated for the production and extraction of magma from the mantle or magma residence in the lower crust, implying anomalous melt inclusions are probably not a direct result of melting of heterogeneities in the mantle. Instead, anomalous melt inclusions likely form by assimilation processes shortly before eruption [4] and so may be useful monitors of such processes. Refs: [1] Parkinson et al., Abstract, Goldschmidt Conference 2006; [2] Coogan et al., EPSL 240, 415-424 (2005); [3] Qin et al. Am. Min. 77, 565-576 (1992); [4] Danyushevsky et al., J. Petrol. 45, 2531-2553 (2004).

Spandler, C.; O'Neill, H. S.

2006-12-01

42

Micro-Fluidic Diffusion Coefficient Measurement  

Microsoft Academic Search

A new method for diffusion coefficient measurement applicable to micro-fluidics is pre-;\\u000asented. The method Iltilizes an analytical model describing laminar dispersion in rect-;\\u000aanglllar ~llicro_channe]s. The Illethod ~vas verified throllgh measllremen~ of fllloresceill;\\u000adiffusivity in water and aqueolls polymer solutions of differing concentration. The diffll-;\\u000asivity of flllorescein was measlmed as 0.64 x 10-gm2\\/s in water, 0.49 x 10-gm2\\/s

F. K. Forster; P. Galambos

1998-01-01

43

Ion concentration diffusion in inertially confined plasmas  

NASA Astrophysics Data System (ADS)

Optimizing fusion yield in inertial confinement fusion (ICF) experiments requires number densities of the reactants to be equal throughout the fuel assembly. This condition can be easily satisfied during target fabrication. However, dynamical process of implosion gives rise to the inter-ion-species transport, resulting in these species' concentrations being perturbed from their initial values. In particular, classical, baro-, electro- and thermo-diffusive mechanisms of such a transport should be distinguished. Baro- and electro-diffusion ratios are obtained from ion fluid equations without invoking a kinetic calculation. Interestingly, plasma baro-diffusion is found to be identical to its neutral counterpart. On the other hand, thermo-diffusion ratios appearing in front of the ion and electron temperature gradients, as well as the classical diffusion coefficient, are intrinsically non-thermodynamic quantities. Their evaluation therefore does require a kinetic approach. By employing such an approach explicit dependence of the diffusion coefficients on the species' concentrations is found numerically for selected pairs of ion species. Initial implications of these newly obtained results are discussed.

Kagan, Grigory; Tang, Xian-Zhu

2012-10-01

44

Fricke gel diffusion coefficient measurements for applications in radiotherapy level dosimetry  

NASA Astrophysics Data System (ADS)

In gel dosimetry applied to radiotherapy, the space-time corrections are necessary due to the diffusion of ions in the oxidized solution dosimetry. Consequently, methodologies are applied in order to determine diffusion coefficients corrected in space and time. Therefore, in this study the dosimetric solution Fricke Xylenol Gel (FXG) was modified and applied to two Gaussian and ISQR methodologies for comparison of the diffusion coefficients obtained. The results show that the FXG system can be modified for new applications in radiotherapy, and it may be corrected in space-time to the appropriate methodologies in the determination of diffusion coefficients.

de Oliveira, Lucas Nonato; de Almeida, Adelaide; Caldas, Linda V. E.

2014-05-01

45

Diffusion coefficient of three-dimensional Yukawa liquids  

SciTech Connect

The purpose of this work is an investigation of the diffusion coefficient of the dust component in complex plasma. The computer simulation of the Yukawa liquids was made on the basis of the Langevin equation, which takes into account the influence of buffer plasma on the dust particles dynamics. The Green–Kubo relation was used to calculate the diffusion coefficient. Calculations of the diffusion coefficient for a wide range of the system parameters were performed. Using obtained numerical data, we constructed the interpolation formula for the diffusion coefficient. We also show that the interpolation formula correctly describes experimental data obtained under microgravity conditions.

Dzhumagulova, K. N.; Ramazanov, T. S.; Masheeva, R. U. [IETP, Al Farabi Kazakh National University, 71, al Farabi ave., Almaty 050040 (Kazakhstan)] [IETP, Al Farabi Kazakh National University, 71, al Farabi ave., Almaty 050040 (Kazakhstan)

2013-11-15

46

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

Microsoft Academic Search

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,

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

1983-01-01

47

Effective concentration difference model to study the effect of various factors on the effective diffusion coefficient in the dialysis membrane  

Microsoft Academic Search

Cellulose acetate dialysis membrane (CDM) has been used in the diffusive gradients in thin films (DGT) technique, where accurate diffusion coefficients are essential for the assessment of the concentrations of labile metal in solution. Effective concentration difference model (ECDM), based on the assumption that the effective diffusion coefficient of metal ion in the dialysis membrane is determined by the effective

Hong Chen; Ting Sun; Dianpeng Sui; Jia Dong

2011-01-01

48

Surface diffusion coefficients for room acoustics: free-field measures.  

PubMed

A surface diffusion coefficient is needed in room acoustics to enable the quality of diffusing surfaces to be evaluated. It may also facilitate more accurate geometric room acoustic models. This paper concentrates on diffusion coefficients derived from free-field polar responses. An extensive set of two- and three-dimensional measurements and predictions was used to test the worth of different diffusion coefficient definitions. The merits and problems associated with these types of coefficients are discussed, and past parameters reviewed. Two new coefficients are described. The new measure based on the autocorrelation function is forwarded as the best free-field coefficient. The strengths and weaknesses of the coefficient are defined. PMID:11051498

Hargreaves, T J; Cox, T J; Lam, Y W; D'Antonio, P

2000-10-01

49

Oxygen and chloride diffusion in cement pastes as a validation of chloride diffusion coefficients obtained by steady-state migration tests  

Microsoft Academic Search

When chloride ions diffuse through concrete, it has been found that they interact with the surface charge and electrical double layer developed at the cementitious matrix\\/pore solution interface. As a consequence of this interaction, the diffusion of chloride ions is retarded in comparison with that of dissolved oxygen molecules, although the two species have very similar diffusion coefficients in infinitely

M Castellote; C Alonso; C Andrade; G. A Chadbourn; C. L Page

2001-01-01

50

An ion diffusion model in semi-permeable clay materials.  

PubMed

Clay materials typically contain negative surface charges that induce electrostatic fields (or diffuse double layers) in electrolytes. During ion diffusion in a porous medium of clay materials, ions dynamically interact with the electrostatic fields associated with individual clay grains by depressing or expanding the electrostatic double layers, which subsequently affects ionic fluxes. Current theory of ion transport in porous media, however, cannot explicitly account for the dynamic interactions. Here we proposed a model by coupling electrodynamics and nonequilibrium thermodynamics (EDNT) to describe ion diffusion in clay materials as a complex function of factors including clay surface charge density, tortuosity, porosity, chemicoosmotic coefficient, and ion self-diffusivity. The model was validated by comparing the calculated and measured apparent ion diffusion coefficients in clay materials as a function of ionic strength. At transitional states, ion diffusive fluxes are dynamically related to the electrostatic fields, which shrink or expand as ion diffusion occurs. 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 approximated by the ion diffusivity in bulk electrolytes corrected by a tortuosity factor and macroscopic concentration discontinuities at the interfaces between clay materials and bulk solutions. PMID:17822109

Liu, Chongxuan

2007-08-01

51

Modelling intracellular H(+) ion diffusion.  

PubMed

Intracellular pH, an important modulator of cell function, is regulated by plasmalemmal proteins that transport H(+), or its equivalent, into or out of the cell. The pH(i) is also stabilised by high-capacity, intrinsic buffering on cytoplasmic proteins, oligopeptides and other solutes, and by the extrinsic CO(2)/HCO(3)(-) (carbonic) buffer. As mobility of these buffers is lower than for the H(+) ion, they restrict proton diffusion. In this paper we use computational approaches, based on the finite difference and finite element methods (FDM and FEM, respectively), for analysing the spatio-temporal behaviour of [H(+)] when it is locally perturbed. We analyse experimental data obtained for various cell-types (cardiac myocytes, duodenal enterocytes, molluscan neurons) where pH(i) has been imaged confocally using intracellular pH-sensitive dyes. We design mathematical algorithms to generate solutions for two-dimensional diffusion that fit data in terms of an apparent intracellular H(+) diffusion coefficient, D(H)(app). The models are used to explore how the spatial distribution of [H(+)](i) is affected by membrane H(+)-equivalent transport and by cell geometry. We then develop a mechanistic model, describing spatio-temporal changes of [H(+)](i) in a cardiac ventricular myocyte in terms of H(+)-shuttling on mobile buffers and H(+)-anchoring on fixed buffers. We also discuss how modelling may include the effects of extrinsic carbonic-buffering. Overall, our computational approach provides a framework for future analyses of the physiological consequences of pH(i) non-uniformity. PMID:12865074

Swietach, Pawel; Zaniboni, Massimiliano; Stewart, Andrew K; Rossini, Alessandra; Spitzer, Kenneth W; Vaughan-Jones, Richard D

2003-10-01

52

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

53

Temperature dependence of the diffusion coefficient of nanoparticles  

NASA Astrophysics Data System (ADS)

The temperature dependence of the diffusion coefficient of nanoparticles in gases has been experimentally studied. It is established that this dependence significantly differs from that predicted by various correlations, in particular, by the Cunningham-Millikan-Davies correlation that is used as an instrumental basis for virtually all methods of measurement of the diffusion coefficient in aerosols.

Rudyak, V. Ya.; Dubtsov, S. N.; Baklanov, A. M.

2008-06-01

54

IDENTIFICATION OF DIFFUSION COEFFICIENTS DURING POST-DISCHARGE NITRIDING  

Microsoft Academic Search

This work presents a model for computing the diffusion coefficients during post-discharge nitriding through an inverse problem of coefficient identification in a diffusion model, which considers several layers and Stefan type conditions. An approximate solution corresponding to a quasi-stationary state is obtained for the model, using qualitative and quantitative information from experimental results. To study the inverse problem we assume

J. A. GÓMEZ

55

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

Microsoft Academic Search

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

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

1982-01-01

56

Analysis of Fluorophore Diffusion by Continuous Distributions of Diffusion Coefficients: Application to Photobleaching Measurements of Multicomponent and Anomalous Diffusion  

Microsoft Academic Search

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, ?(D), and 2) time-dependent diffusion coefficients, D(t). A regression procedure utilizing the maximum entropy

N. Periasamy; A. S. Verkman

1998-01-01

57

Comparison of Radon Diffusion Coefficients Measured by Transient-Diffusion and Steady-State Laboratory Methods.  

National Technical Information Service (NTIS)

A method was developed and used to determine radon diffusion coefficients in compacted soils by transient-diffusion measurements. A relative standard deviation of 12 percent was observed in repeated measurements with a dry soil by the transient-diffusion ...

D. R. Kalkwarf K. K. Nielson D. C. Rich V. C. Rogers

1982-01-01

58

Self-diffusion coefficient study of liquid lithium  

NASA Astrophysics Data System (ADS)

Little liquid lithium experimental self-diffusion coefficient were reported in the literature because of higher risk of radiation measurement method of diffusion coefficient. In the paper, the EAM potential is applied to calculate self-diffusion coefficient of liquid lithium with emphasis on a wide range of temperature, pressure, magnetic field, and gravity acceleration. The results show that the liquid lithium self-diffusion coefficient increases with temperature increasing and decreases with pressure increasing. Calculated self-diffusion coefficient is in good agreement with Murday's experiment results in atmosphere. We get the Arrhenius equation according to the simulation results. The increasing of pressure enlarges the liquid lithium activation energy and lowers the movement of atom in liquid lithium.

Wang, Z. H.; Ni, M. J.

2012-02-01

59

Determination of the zincate diffusion coefficient and its application to alkaline battery problems  

NASA Technical Reports Server (NTRS)

The diffusion coefficient for the zincate ion at 24 C was found to be 9.9 X 10 to the minus 7th power squared cm per sec + or - 30 percent in 45 percent potassium hydroxide and 1.4 x 10 to the minus 7 squared cm per sec + or - 25 percent in 40 percent sodium hydroxide. Comparison of these values with literature values at different potassium hydroxide concentrations show that the Stokes-Einstein equation is obeyed. The diffusion coefficient is characteristic of the zincate ion (not the cation) and independent of its concentration. Calculations with the measured value of the diffusion coefficient show that the zinc concentration in an alkaline zincate half cell becomes uniform throughout in tens of hours by diffusion alone. Diffusion equations are derived which are applicable to finite size chambers. Details and discussion of the experimental method are also given.

May, C. E.; Kautz, Harold E.

1978-01-01

60

Optical determination of ionophore diffusion coefficients in plasticized poly(vinyl chloride) sensing films  

Microsoft Academic Search

The knowledge of accurate diffusion coefficients of electrically neutral ionophores in solvent polymeric membranes is important in view of understanding and optimizing important sensor characteristics of ion-selective electrodes (ISEs) and their corresponding optical sensors. A spectroscopic imaging technique is introduced here to determine the diffusion coefficient of the chromoionophore (N,N-diethyl-5-(octadecanoylimino)-5H-benzo[a]phenoxazine-9-amine, ETH 5294) in solvent polymeric membranes with different types of

Robert Long; Eric Bakker

2004-01-01

61

Velocity-Space Diffusion Coefficients Due to Full-Wave ICRF Fields in Toroidal Geometry  

SciTech Connect

Jaeger et al. have calculated bounce-averaged QL diffusion coefficients from AORSA full-wave fields, based on non-Maxwellian distributions from CQL3D Fokker-Planck code. A zero banana-width approximation is employed. Complementing this calculation, a fully numerical calculation of ion velocity diffusion coefficients using the full-wave fields in numerical tokamak equilibria has been implemented to determine the finite orbit width effects. The un-approximated Lorentz equation of motion is integrated to obtain the change in velocity after one complete poloidal transit of the tokamak. Averaging velocity changes over initial starting gyro-phase and toroidal angle gives bounce-averaged diffusion coefficients. The coefficients from the full-wave and Lorentz orbit methods are compared for an ITER DT second harmonic tritium ICRF heating case: the diffusion coefficients are similar in magnitude but reveal substantial finite orbit effects.

Harvey, R.W. [CompX, P.O. Box 2672, Del Mar, CA 92014-5672 (United States); Jaeger, F.; Berry, L.A.; Batchelor, D.B.; D'Azevedo, E.; Carter, M.D. [ORNL, Oak Ridge, TN (United States); Ershov, N.M.; Smirnov, A.P. [Moscow State Univ. (Russian Federation); Bonoli, P.; Wright, J.C. [PSFC, MIT, Boston, MA (United States); Smithe, D.N. [ATK-Mission Research (United States)

2005-09-26

62

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 (M z+ ) 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 Co 2+, Ga 3+, Rb +, Sr 2+, Ag +, Cd 2+, Cs +, Th 4+, 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 (Ga 3+ and Th 4+). 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

63

Improved diffusion coefficients generated from Monte Carlo codes  

SciTech Connect

Monte Carlo codes are becoming more widely used for reactor analysis. Some of these applications involve the generation of diffusion theory parameters including macroscopic cross sections and diffusion coefficients. Two approximations used to generate diffusion coefficients are assessed using the Monte Carlo code MC21. The first is the method of homogenization; whether to weight either fine-group transport cross sections or fine-group diffusion coefficients when collapsing to few-group diffusion coefficients. The second is a fundamental approximation made to the energy-dependent P1 equations to derive the energy-dependent diffusion equations. Standard Monte Carlo codes usually generate a flux-weighted transport cross section with no correction to the diffusion approximation. Results indicate that this causes noticeable tilting in reconstructed pin powers in simple test lattices with L2 norm error of 3.6%. This error is reduced significantly to 0.27% when weighting fine-group diffusion coefficients by the flux and applying a correction to the diffusion approximation. Noticeable tilting in reconstructed fluxes and pin powers was reduced when applying these corrections. (authors)

Herman, B. R.; Forget, B.; Smith, K. [Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States)] [Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States); Aviles, B. N. [Knolls Atomic Power Laboratory, Bechtel Marine Propulsion Corporation, P.O. Box 1072, Schenectady, NY 12301-1072 (United States)] [Knolls Atomic Power Laboratory, Bechtel Marine Propulsion Corporation, P.O. Box 1072, Schenectady, NY 12301-1072 (United States)

2013-07-01

64

Local carbon diffusion coefficient measurement in the S-1 spheromak  

SciTech Connect

The local carbon diffusion coefficient was measured in the S - 1 spheromak by detecting the radial spread of injected carbon impurity. The radial impurity density profile is determined by the balance of ionization and diffusion. Using measured local electron temperature T/sub e/ and density n/sub e/, the ionization rate is determined from which the particle diffusion coefficient is inferred. The results found in this work are consistent with Bohm diffusion. The absolute magnitude of D/sub /perpendicular// was determined to be (4/approximately/6) /times/ D/sub Bohm/. 25 refs., 13 figs., 2 tabs.

Mayo, R.M.; Levinton, F.M.; Meyerhofer, D.D.; Chu, T.K.; Paul, S.F.; Yamada, M.

1988-10-01

65

Estimation of Effective Diffusion Coefficients in Porous Solids.  

National Technical Information Service (NTIS)

A major difficulty for reliable estimation of effective diffusion coefficients of gases in porous solids resides in the proper description of their highly complex internal structure. Within the concepts of percolation theory we make use of a network model...

S. Reyes K. F. Jensen

1984-01-01

66

Variable Eddington Factors and Flux-Limiting Diffusion Coefficients.  

National Technical Information Service (NTIS)

Variable Eddington factors and flux limiting diffusion coefficients arise in two common techniques of closing the moment equations of transport. The first two moment equations of the full transport equation are still frequently used to solve many problems...

P. P. Whalen

1982-01-01

67

The temperature variation of hydrogen diffusion coefficients in metal alloys  

NASA Technical Reports Server (NTRS)

Hydrogen diffusion coefficients were measured as a function of temperature for a few metal alloys using an electrochemical evolution technique. Results from these measurements are compared to those obtained by the time-lag method. In all cases, diffusion coefficients obtained by the electrochemical method are larger than those by the time-lag method by an order of magnitude or more. These differences are attributed mainly to hydrogen trapping.

Danford, M. D.

1990-01-01

68

Study of diffusion coefficients of glasses under zero-G  

NASA Technical Reports Server (NTRS)

Diffusion studies of the glass forming ion are examined in zero-g environments and diffusion data obtained from these experiments are unique because of earth based experimental problems. The choice of system for diffusion studies is discussed along with the lab processing. The space processing is described consisting of a heating cycle designed to maximize time exposed to the diffusion temperature without exposing the low viscosity melt to gravitational forces.

Kinser, D. L.

1975-01-01

69

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

70

Calculation of self-diffusion coefficients in iron  

NASA Astrophysics Data System (ADS)

On the basis of available P-V-T equation of state of iron, the temperature and pressure dependence of self-diffusion coefficients in iron polymorphs (?, ?, ? and ? phases) have been successfully reproduced in terms of the bulk elastic and expansivity data by means of a thermodynamical model that interconnects point defects parameters with bulk properties. The calculated diffusion parameters, such as self-diffusion coefficient, activation energy and activation volume over a broad temperature range (500-2500 K) and pressure range (0-100 GPa), compare favorably well with experimental or theoretical ones when the uncertainties are considered.

Zhang, Baohua

2014-01-01

71

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

72

Relationships between Atomic Diffusion Mechanisms and Ensemble Transport Coefficients in Crystalline Polymorphs.  

PubMed

Ionic transport in conventional ionic solids is generally considered to proceed via independent diffusion events or "hops." This assumption leads to well-known Arrhenius expressions for transport coefficients, and is equivalent to assuming diffusion is a Poisson process. Using molecular dynamics simulations of the low-temperature B1, B3, and B4 AgI polymorphs, we have compared rates of ion hopping with corresponding Poisson distributions to test the assumption of independent hopping in these common structure types. In all cases diffusion is a non-Poisson process, and hopping is strongly correlated in time. In B1 the diffusion coefficient can be approximated by an Arrhenius expression, though the physical significance of the parameters differs from that commonly assumed. In low temperature B3 and B4, diffusion is characterized by concerted motion of multiple ions in short closed loops. Diffusion coefficients cannot be expressed in a simple Arrhenius form dependent on single-ion free energies, and intrinsic diffusion must be considered a many-body process. PMID:24765989

Morgan, Benjamin J; Madden, Paul A

2014-04-11

73

Lateral diffusion in an archipelago. Distance dependence of the diffusion coefficient.  

PubMed Central

An understanding of the distance dependence of the lateral diffusion coefficient is useful in comparing the results of diffusion measurements made over different length scales, and in analyzing the kinetics of mobile redox carriers in organelles. A distance-dependent, concentration-dependent diffusion coefficient is defined, and it is evaluated by Monte Carlo calculations of a random walk by mobile point tracers in the presence of immobile obstacles on a triangular lattice, representing the diffusion of a lipid or a small protein in the presence of immobile membrane proteins. This work confirms and extends the milling crowd model of Eisinger, J., J. Flores, and W. P. Petersen (1986. Biophys J. 49:987-1001). Similar calculations for diffusion of mobile particles interacting by a hard-core repulsion yield the distance dependence of the self-diffusion coefficient. An expression for the range of short-range diffusion is obtained, and the distance scales for various diffusion measurements are summarized.

Saxton, M J

1989-01-01

74

Study of diffusion coefficients of glasses under Zero-G  

NASA Technical Reports Server (NTRS)

A diffusion experiment for glasses was formulated, such theoretical and earth bound results as were available were outlined, and the preliminary earth based experimental work in preparation for a weightless experiment was done. The fundamental premise of the work was that diffusion studies of the glass forming ion can be conducted in zero-g environments, and diffusion data obtained from these experiments are unique and valuable because of earth based experimental difficulties.

Kinser, D. L.

1977-01-01

75

Measurement of Diffusion Coefficients for the Reduction of Copper(I) and (II) in Acetonitrile.  

National Technical Information Service (NTIS)

Values of the diffusion coefficients in the reductions Cu(II) to Cu(I), Cu(II) to Cu(0), and Cu(I) to Cu(0) have been determined. Owing to the fast exchange of coordinated and uncoordinated acetonitrile molecules, the greater probability of ion-pair forma...

R. R. Bessette, J. W. Olver

1968-01-01

76

Determination of the Zincate Diffusion Coefficient and Its Application to Alkaline Battery Problems.  

National Technical Information Service (NTIS)

The diffusion coefficient for the zincate ion at 24 C was found to be 9.9 X 10 to the minus 7th power squared cm per sec + or - 30 percent in 45 percent potassium hydroxide and 1.4 x 10 to the minus 7 squared cm per sec + or - 25 percent in 40 percent sod...

C. E. May

1978-01-01

77

Determination of the zincate diffusion coefficient and its application to alkaline battery problems  

Microsoft Academic Search

The diffusion coefficient for the zincate ion at 24 C was found to be 9.9 X 10 to the minus 7th power squared cm per sec + or - 30 percent in 45 percent potassium hydroxide and 1.4 x 10 to the minus 7 squared cm per sec + or - 25 percent in 40 percent sodium hydroxide. Comparison of

C. E. May; Harold E. Kautz

1978-01-01

78

The Diffusion Coefficient of Ferricyanide in Aqueous Potassium Chloride Solutions with and without Polyethylene Oxide.  

National Technical Information Service (NTIS)

The diffusion coefficient of the ferricyanide ion was determined in the temperature range 20-35C in equimolar solutions of ferri- and ferro-cyanide (.005M) with potassium chloride (0,5; 1,0; 2,0 M) as a carrier electrolyte and with and without polyethylen...

J. J. Graaf

1975-01-01

79

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

80

Following Ion Diffusion in Solution  

NASA Astrophysics Data System (ADS)

An x-ray projection microscope equipped with a charge-coupled device camera allows direct observation of zinc (Zn2+) ions diffusing in aqueous hydrochloric acid solution during the corrosion of zinc foil and pellets. Time series of microradiographic images with a lateral resolution on the order of 10 micrometers allow observation of the time and spatial evolution of the colorless Zn2+ ions in solution without any previous treatment. The concentration distribution of the ions can be quantified from these images. This technique should find applications in the biology, chemistry, and electrochemistry of aqueous solutions, allowing direct observation of the behavior and concentration fluctuations of medium or heavy ions moving in a weakly absorbing medium.

Rondot, S.; Cazaux, J.; Aaboubi, O.; Chopart, J. P.; Olivier, A.

1994-03-01

81

Following ion diffusion in solution.  

PubMed

An x-ray projection microscope equipped with a charge-coupled device camera allows direct observation of zinc (Zn(2+)) ions diffusing in aqueous hydrochloric acid solution during the corrosion of zinc foil and pellets. Time series of microradiographic images with a lateral resolution on the order of 10 micrometers allow observation of the time and spatial evolution of the colorless Zn(2+) ions in solution without any previous treatment. The concentration distribution of the ions can be quantified from these images. This technique should find applications in the biology, chemistry, and electrochemistry of aqueous solutions, allowing direct observation of the behavior and concentration fluctuations of medium or heavy ions moving in a weakly absorbing medium. PMID:17795379

Rondot, S; Cazaux, J; Aaboubi, O; Chopart, J P; Olivier, A

1994-03-25

82

Predicting cation diffusion coefficients in clays and clay rocks  

NASA Astrophysics Data System (ADS)

Clay rocks are considered in several European countries as potential host rock formations for the underground disposal of radioactive waste. Because of their very low hydraulic conductivities, spreading of radionuclides through such formations may predominantly occur by molecular diffusion. Many experimental studies are thus being performed to investigate the diffusion of cations and other potential contaminants through various clay rocks as well as through pure swelling clays that may be used as additional buffer material. Whereas determining the diffusion properties of mobile tracers like tritiated water can be done within reasonable time, the measurements involving sorbing tracers are more complex and very time-consuming. It is thus tempting to determine diffusion coefficients of sorbing cations in an indirect way from more readily measurable quantities and based on cation diffusion coefficients measured for other materials. Various models exist that try to estimate cation diffusion coefficients from parameters like the bulk density, the porosity or the pore sizes of the rock, and the sorption distribution coefficient. In some models, an average mobility of cations that are sorbed on clay surfaces is in addition required, whereas other models rely on a constrictivity factor for transport in the interlayer space of the clays. In this contribution, we outline the differences and the commonalities of such models regarding some key parameters. We then compare model estimates with measured data from the literature, with a special emphasis on the associated uncertainties. Because some of the required parameters, notably the surface mobilities as well as the interlayer constrictivities, have typically large uncertainties, it is difficult to judge which model is best suited. However, it seems that several models can be used to set reasonable limits for cation diffusion coefficients in clay rocks that have not been investigated so far.

Gimmi, Thomas; Kosakowski, Georg; Glaus, Martin A.

2010-05-01

83

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

84

Apparatus for determining thermal-diffusion coefficients in gas mixtures  

Microsoft Academic Search

A description is given of the construction of, and the technique of measuring separation effects in a single-stage thermal-diffusion apparatus. For the separation analysis, use is made of the dependence of the viscosity of gas mixtures on composition. Results are presented of a determination of the coefficient of thermal diffusion of a He\\/N2 mixture in the pressure range 0. 0005–0.

L. S. Kotousov; A. V. Panyushkin

1965-01-01

85

Scaling Laws for Diffusion Coefficients in Mixtures of Alkanes  

NASA Astrophysics Data System (ADS)

Natural fluids, such as crude oils, are often mixtures of a broad range of different molecules, and in situ measurement of their composition is highly desirable. Furthermore, the relationship between their composition and their physical properties has always been a challenge for such mixtures. We have analyzed diffusion in alkane mixtures to find a power law for the self-diffusion coefficient in terms of molecular sizes. We demonstrate that this power law can be used to obtain the molecular size distribution of crude oils using noninvasive measurements of diffusion distributions.

Freed, Denise E.; Burcaw, Lauren; Song, Yi-Qiao

2005-02-01

86

Experimental system to evaluate the effective diffusion coefficient of radon  

NASA Astrophysics Data System (ADS)

The effective diffusion coefficient of radon is a very important factor in estimating the rate of radon exhalation from the ground surface. In this study, we developed an experimental system that overcomes technical problems in previous studies to accurately evaluate the effective diffusion coefficient. The radon source used for this system was the National Institute of Radiological Sciences radon chamber. This chamber is a calibrated international standard facility that can produce stable radon concentrations for long periods of time. Our tests showed that leakage of radon from the system was negligible. After the leakage test, we evaluated the effective diffusion coefficient in free-space and in dry porous materials at porosities of 35% and 45%. To ensure that the porous material in the column was as homogeneous as possible, we filled the column with an artificial soil with controlled grain size and grain composition. The measured values and theoretical calculations agreed well, which indicate that the proposed system can be used to accurately and quickly evaluate the effective diffusion coefficient.

Hosoda, Masahiro; Tokonami, Shinji; Sorimachi, Atsuyuki; Janik, Miroslaw; Ishikawa, Tetsuo; Yatabe, Yoshinori; Yamada, Junya; Uchida, Shigeo

2009-01-01

87

Molecular dynamics calculations of point defect diffusion coefficients in vanadium  

NASA Astrophysics Data System (ADS)

Diffusion coefficients for vacancies and self-interstitial atoms (SIA) in vanadium at several temperatures have been calculated by the molecular dynamics method using EAM potential proposed by Foiles and Adams. Apart from the migration energy the preexponential factor was an object of interest. Simulation results show that the SIA in vanadium exists in a <111>-dumbbell configuration and migrates exceptionally along <111> directions.

Minashin, A. M.; Ryabov, V. A.

1996-10-01

88

Experimental system to evaluate the effective diffusion coefficient of radon.  

PubMed

The effective diffusion coefficient of radon is a very important factor in estimating the rate of radon exhalation from the ground surface. In this study, we developed an experimental system that overcomes technical problems in previous studies to accurately evaluate the effective diffusion coefficient. The radon source used for this system was the National Institute of Radiological Sciences radon chamber. This chamber is a calibrated international standard facility that can produce stable radon concentrations for long periods of time. Our tests showed that leakage of radon from the system was negligible. After the leakage test, we evaluated the effective diffusion coefficient in free-space and in dry porous materials at porosities of 35% and 45%. To ensure that the porous material in the column was as homogeneous as possible, we filled the column with an artificial soil with controlled grain size and grain composition. The measured values and theoretical calculations agreed well, which indicate that the proposed system can be used to accurately and quickly evaluate the effective diffusion coefficient. PMID:19191431

Hosoda, Masahiro; Tokonami, Shinji; Sorimachi, Atsuyuki; Janik, Miroslaw; Ishikawa, Tetsuo; Yatabe, Yoshinori; Yamada, Junya; Uchida, Shigeo

2009-01-01

89

Highly oblique shocks: Diffusion coefficients, acceleration rate and maximum energy  

NASA Astrophysics Data System (ADS)

We examine numerically using Monte Carlo simulations the effect of the diffusion coefficients and the obliquity of the magnetic field to the shock front on the energy gain and the acceleration rate of the accelerated particles in non-relativistic highly oblique shocks. Previous analytical work is justified showing that in highly oblique shocks the smaller the perpendicular diffusion gets compared to the parallel diffusion coefficient values, the greater the energy gain of the cosmic rays to be obtained and under specific conditions the acceleration rate of the particles allows for critical energies to be reached. Based on these circumstances and other striking findings, the cosmic ray spectrum in high energies between 1015eV and about 1018eV can be explained. We estimate the upper limit of energy that cosmic rays could gain in astrophysical sources following models of such as, Supernovae which explode into the interstellar medium, Red Supergiants, and Wolf-Rayet stars.

Meli, A.; Biermann, P. L.

2005-11-01

90

Diffusion of ions in sea water and in deep-sea sediments  

Microsoft Academic Search

The tracer-diffusion coefficient of ions in water, D j 0 , and in sea water, D j * , differ by no more than zero to 8 per cent. When sea water diffuses into a dilute solution of water, in order to maintain the electro-neutrality, the average diffusion coefficients of major cations become greater but of major anions smaller than

Yuan-Hui Li; Sandra Gregory

1974-01-01

91

Diffusion coefficients of molecular iodine in aqueous solutions  

SciTech Connect

In the event of a severe accident on a light water nuclear reactor (LWR), resulting in overheating of the core, the fission products would be released into the containment building. Among the fission products, iodine represents a biological hazard for the environment by reason of the {sup 131}I radioactive isotope. As iodine is a highly reactive and volatile compound, it is involved in mass transfer from the liquid phase to the gas phase of the containment vessel. In order to determine the quantity of iodine present in the gas phase, it is necessary to know the diffusion coefficient of iodine in water at several temperatures. The diffusion coefficients of iodine in 0.075 mol/dm{sup 3} sulfuric acid have been determined between 298 K and 358 K, by measuring the limiting reduction currents at a platinum rotating disk electrode. A Stokes-Einstein relation is verified over the range of temperature studied. The experimental value obtained at 298 K is compared with some available relations for the estimation of diffusion coefficients at infinite dilution. The agreement is good.

Cantrel, L. [CEA Cadarache, Saint Paul lez Durance (France). Inst. de Protection et de Surete Nucleaire] [CEA Cadarache, Saint Paul lez Durance (France). Inst. de Protection et de Surete Nucleaire; Chaouche, R.; Chopin-Dumas, J. [Ecole Nationale Superieure de Syntheses, Marseille (France)] [Ecole Nationale Superieure de Syntheses, Marseille (France)

1997-01-01

92

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

93

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

94

Highly oblique shocks: Diffusion coefficients, acceleration rate and maximum energy  

NASA Astrophysics Data System (ADS)

We examine numerically using Monte Carlo simulations the effect of the diffusion coefficients and the obliquity of the magnetic field to the shock front, on the energy gain and the acceleration rate of the accelerated particles in non-relativistic highly oblique shocks. Previous analytical work (Jokipii 1987) is justified showing that in highly oblique shocks the smaller the perpendicular diffusion gets compared to the parallel diffusion coefficient values, the greater the energy gain of the cosmic rays to be obtained and under specific conditions the acceleration rate of the particles allows for critical energies to be reached. It is confirmed that the diffusive shock acceleration mechanism in non-relativistic highly oblique shocks is indeed efficient to accelerate particles up to energies just above the 'knee' and down close to the 'ankle'. The seed of particles which get accelerated in these shock fronts and in such energies, may come from the remnant winds of astrophysical sources with such magnetic field/plasma nearly perpendicular configurations.

Meli, A.; Biermann, P. L.

95

Diffusion coefficients of fluorescent organic molecules in inert gases  

NASA Astrophysics Data System (ADS)

We use arrested-flow pulse broadening to measure the diffusion coefficients of four archetype organic semiconductors in two carrier gases, N2 and Ar, with a precision of 5%. The measurements are realized by the injection and transport of pulses of organic molecules in an organic vapor phase deposition chamber, followed by their detection using laser induced fluorescence that dynamically measures the organic concentration in the gas phase. Measurements show that the diffusivity of tris(8-hydroxyquinoline) aluminum (Alq3) in N2 and Ar varies as the square of the temperature and inversely with pressure over a large range of gas conditions. We show that classical Chapman-Enskog theory can be used to approximate the diffusivity with an accuracy that depends on the physical dimensions of the organic molecular species, with the most accurate predictions for spherical and rigid molecules such as Alq3.

Rolin, Cedric; Forrest, Stephen R.

2013-07-01

96

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

97

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

PubMed

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 PF(6)(-), NO(3)(-), 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 [NO(3)](-) < [Cl](-) < [PF(6)](-). 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 [NO(3)](-) > [PF(6)](-) > [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. PMID:19071929

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

2008-12-14

98

Network modeling of diffusion coefficients for porous media: II. Simulations  

SciTech Connect

Gas diffusion often dominates constituent in porous media (PM) and it dependent on pore geometry, water content, and water distribution in PM. Network models of PM offer the ability to investigate the influence and interaction of pore-scale PM properties and fluid properties on macroscopic properties of the system. This study was conducted to investigate the macroscopic relative gas diffusion coefficient vs. air-filled porosity relationship or diffusion characteristic (DC) of PM using a network model. The network model was used to simulate DCs in wetting and drying PM containing air and water. A network size of nine by nine spheres was used; increasing the network size to 19 by 19 by 19 produced essentially no change in the DC. The DC was independent of Henry`s law gas-liquid partition coefficient (H) for H values of 0.1, 1.0, and 5.0. The product HR{sub W}, where R{sub W} is the ratio between the bulk gas- and liquid-phase diffusion coefficients, strongly influences the DC when H values of 1000 to 10 000 are considered; this indicates that certain organic compounds have DCs independent of air-filled porosity. Hysteresis in DCs was found in selected network cases, with the wetting DCs being greater than the drying DCs for most air-filled porosities, in accord with some experimental results reported in the literature. Spatial correlation of network pore space was shown to bring the simulated DCs into better agreement with some experimental DCs. 23 refs., 10 figs., 3 tabs.

Steele, D.D. [North Dakota State Univ., Fargo, ND (United States); Nieber, J.L. [Univ. of Minnesota, St. Paul, MN (United States)

1994-09-01

99

Effect of concentration dependence of the diffusion coefficient on homogenization kinetics in multiphase binary alloy systems  

NASA Technical Reports Server (NTRS)

Diffusion calculations were performed to establish the conditions under which concentration dependence of the diffusion coefficient was important in single, two, and three phase binary alloy systems. Finite-difference solutions were obtained for each type of system using diffusion coefficient variations typical of those observed in real alloy systems. Solutions were also obtained using average diffusion coefficients determined by taking a logarithmic average of each diffusion coefficient variation considered. The constant diffusion coefficient solutions were used as reference in assessing diffusion coefficient variation effects. Calculations were performed for planar, cylindrical, and spherical geometries in order to compare the effect of diffusion coefficient variations with the effect of interface geometries. In most of the cases considered, the diffusion coefficient of the major-alloy phase was the key parameter that controlled the kinetics of interdiffusion.

Tenney, D. R.; Unnam, J.

1978-01-01

100

Transient radon diffusion through radon-proof membranes: A new technique for more precise determination of the radon diffusion coefficient  

Microsoft Academic Search

The following paper is focused on the numerical modelling of the transient radon diffusion through radon-proof membranes during the measurement of their radon diffusion coefficient. The major aim of such numerical modelling is to increase the accuracy of radon diffusion coefficients derived from the measured data sets. The developed complex “transient” numerical model is able to calculate the radon diffusion

Martin Jiranek; Zbynek Svoboda

2009-01-01

101

Assessment of scale effects on effective diffusion coefficients  

NASA Astrophysics Data System (ADS)

Understanding contaminant movement in diffusion-dominated systems is important for the accurate prediction of long-term solute transport. At present, measurement of the effective diffusion coefficient (De) of clay-rich systems is determined using small-scale laboratory experiments. The application of these measurements to field studies assumes that De is not scale-dependent. Because of the empirical nature of equations describing the diffusion process, as well as the scale-dependent nature of other properties (e.g., hydraulic conductivity) controlling contaminant transport, this assumption warrants investigation. The objective of this study was to assess the scale dependence of De by comparing the De values obtained from three conservative tracers (?D, ?18O and chloride) at two scales of field-testing and laboratory-based double reservoir diffusion testing. Thein situ field-testing system consisted of purpose-built piezometers, pressure transducers, inflatable packers, and a circulation pump. All testing was conducted on an 80 m thick, clay-rich till sequence located in Saskatchewan, Canada. Results indicate the scale effects on conservative transport by diffusion are minimal. Using the same methodology, ongoing studies are being conducted in this system to determine effects of scaling on reactive transport.

Ingram, L.; Hendry, J.; Wassenaar, L.; Barbour, L.

2003-04-01

102

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

103

Electrochemical evidences and consequences of significant differences in ions diffusion rate in polyacrylate-based ion-selective membranes.  

PubMed

The origin and effect of surface accumulation of primary ions within the ion-selective poly(n-butyl acrylate)-based membrane, obtained by thermal polymerization, is discussed. Using a new method, based on the relation between the shape of a potentiometric plot and preconditioning time, the diffusion of copper ions in the membrane was found to be slow (the diffusion coefficient estimated to be close to 10(-11) cm(2) s(-1)), especially when compared to ion-exchanger counter ions--sodium cations diffusion (a diffusion coefficient above 10(-9) cm(2) s(-1)). The higher mobility of sodium ions than those of the copper-ionophore complex results in exposed ion-exchanger role leading to undesirably exposed sensitivity to sodium or potassium ions. PMID:21957488

Wo?nica, Emilia; Mieczkowski, Józef; Michalska, Agata

2011-11-21

104

Distributions of the diffusion coefficient for the quantum and classical diffusion in disordered media  

NASA Astrophysics Data System (ADS)

It is shown that the distribution functions of the diffusion coefficient are very similar in the standard model of quantum diffusion in a disordered metal and in a model of classical diffusion in a disordered medium: in both cases the distribution functions have lognormal tails, their part increasing with the increase of the disorder. The similarity is based on a similar behaviour of the high-gradient operators determining the high-order cumulants. The one-loop renormalization- group corrections make the anomalous dimension of the operator that governs the sth cumulant proportional to s( s-1) thus overtaking for large s the negative normal dimension. As behaviour of the ensemble-averaged diffusion coefficient is quite different in these models, it suggests that a possible universality in the distribution functions is independent of the behaviour of average quantities.

Lerner, Igor V.

1993-07-01

105

Chemical sensor as physical sensor: ISFET-based flow-velocity, flow-direction and diffusion-coefficient sensor  

Microsoft Academic Search

An ion-sensitive field-effect transistor (ISFET), which is well known as a (bio-)chemical sensor is utilised for the development of a novel flow-velocity, flow-direction and diffusion-coefficient sensor. The proposed sensor presents a sensor-actuator system and consists of an ion generator and a pH ISFET that detects the in situ electrochemically generated H+- or OH?-ions. A good linearity between the measured flow-velocity

Arshak Poghossian; Lars Berndsen; Michael J. Schöning

2003-01-01

106

Calculation of diffusion coefficients for aqueous organic species at temperatures from 0 to 350 °C  

NASA Astrophysics Data System (ADS)

Evaluation of hydrocarbon transport through the pore spaces of saturated rock in the subsurface as a function of time and distance requires accurate values of diffusion coefficients for aqueous organic species. Analysis of aqueous tracer diffusion coefficients ( D0) for normal alkanes, alcohols, amides, carboxylic acids, alkylbenzenes, and alkylnaphthalenes reported in the literature indicates that diffusional activation energies decrease with increasing temperature, reaching a constant limiting value of ~3300 cal mol -1 at temperatures a: 1?00°C. This observation is consistent with the modified Arrhenius expression reported by OELKERS and HELGESON (1988). The Kirkwood-Riseman equation is used to predict D0 values as a function of the polymer chain length of hydrocarbons. Regression of experimental D0 data with a combined expression of the Kirkwood-Riseman and modified Arrhenius equations yields parameters which permit calculation of tracer diffusion coefficients for over 50 aqueous organic species at temperatures from 0° to 350°C and Psat. ( psat refers to pressures corresponding to the liquid-vapor equilibrium curve for H 2O at temperatures greater than 100°C and 1 bar at lower temperatures.) Resulting values of D0 permit evaluation of the extent of diffusional mass transfer in both contaminated near-surface environments and in the porewater adjoining oil field reservoirs. The computed tracer diffusion coefficients, which are qualitatively similar to D0 values previously calculated for aqueous ions, increase substantially with increasing temperature. For example, the tracer diffusion coefficient of aqueous toluene increases from 0.36 to 27.1 × 10 -5 cm 2sec-1 in response to increasing temperature from 0 to 350°C.

Oelkers, Eric H.

1991-12-01

107

Analytical solution of a spatially variable coefficient advection–diffusion equation in up to three dimensions  

Microsoft Academic Search

Analytical solutions are provided for the two- and three-dimensional advection–diffusion equation with spatially variable velocity and diffusion coefficients. We assume that the velocity component is proportional to the distance and that the diffusion coefficient is proportional to the square of the corresponding velocity component. There is a simple transformation which reduces the spatially variable equation to a constant coefficient problem

C. Zoppou; J. H. Knight

1999-01-01

108

Lithium ion diffusion in Li ?-alumina single crystals measured by pulsed field gradient NMR spectroscopy  

NASA Astrophysics Data System (ADS)

The lithium ion diffusion coefficient of a 93% Li ?-alumina single crystal was measured for the first time using pulsed field gradient (PFG) NMR spectroscopy with two different crystal orientations. The diffusion coefficient was found to be 1.2 × 10-11 m2/s in the direction perpendicular to the c axis at room temperature. The Li ion diffusion coefficient along the c axis direction was found to be very small (6.4 × 10-13 m2/s at 333 K), which suggests that the macroscopic diffusion of the Li ion in the ?-alumina crystal is mainly two-dimensional. The diffusion coefficient for the same sample was also estimated using NMR line narrowing data and impedance measurements. The impedance data show reasonable agreement with PFG-NMR data, while the line narrowing measurements provided a lower value for the diffusion coefficient. Line narrowing measurements also provided a relatively low value for the activation energy and pre-exponential factor. The temperature dependent diffusion coefficient was obtained in the temperature range 297-333 K by PFG-NMR, from which the activation energy for diffusion of the Li ion was estimated. The activation energy obtained by PFG-NMR was smaller than that obtained by impedance measurements, which suggests that thermally activated defect formation energy exists for 93% Li ?-alumina single crystals. The diffusion time dependence of the diffusion coefficient was observed for the Li ion in the 93% Li ?-alumina single crystal by means of PFG-NMR experiments. Motion of Li ion in fractal dimension might be a possible explanation for the observed diffusion time dependence of the diffusion coefficient in the 93% Li ?-alumina system.

Chowdhury, Mohammed Tareque; Takekawa, Reiji; Iwai, Yoshiki; Kuwata, Naoaki; Kawamura, Junichi

2014-03-01

109

Lithium ion diffusion in Li ?-alumina single crystals measured by pulsed field gradient NMR spectroscopy.  

PubMed

The lithium ion diffusion coefficient of a 93% Li ?-alumina single crystal was measured for the first time using pulsed field gradient (PFG) NMR spectroscopy with two different crystal orientations. The diffusion coefficient was found to be 1.2 × 10(-11) m(2)/s in the direction perpendicular to the c axis at room temperature. The Li ion diffusion coefficient along the c axis direction was found to be very small (6.4 × 10(-13) m(2)/s at 333 K), which suggests that the macroscopic diffusion of the Li ion in the ?-alumina crystal is mainly two-dimensional. The diffusion coefficient for the same sample was also estimated using NMR line narrowing data and impedance measurements. The impedance data show reasonable agreement with PFG-NMR data, while the line narrowing measurements provided a lower value for the diffusion coefficient. Line narrowing measurements also provided a relatively low value for the activation energy and pre-exponential factor. The temperature dependent diffusion coefficient was obtained in the temperature range 297-333 K by PFG-NMR, from which the activation energy for diffusion of the Li ion was estimated. The activation energy obtained by PFG-NMR was smaller than that obtained by impedance measurements, which suggests that thermally activated defect formation energy exists for 93% Li ?-alumina single crystals. The diffusion time dependence of the diffusion coefficient was observed for the Li ion in the 93% Li ?-alumina single crystal by means of PFG-NMR experiments. Motion of Li ion in fractal dimension might be a possible explanation for the observed diffusion time dependence of the diffusion coefficient in the 93% Li ?-alumina system. PMID:24697461

Chowdhury, Mohammed Tareque; Takekawa, Reiji; Iwai, Yoshiki; Kuwata, Naoaki; Kawamura, Junichi

2014-03-28

110

Effective concentration difference model to study the effect of various factors on the effective diffusion coefficient in the dialysis membrane.  

PubMed

Cellulose acetate dialysis membrane (CDM) has been used in the diffusive gradients in thin films (DGT) technique, where accurate diffusion coefficients are essential for the assessment of the concentrations of labile metal in solution. Effective concentration difference model (ECDM), based on the assumption that the effective diffusion coefficient of metal ion in the dialysis membrane is determined by the effective concentration difference (?C(e)) across the dialysis membrane, is proposed and applied to study the effect of ionic strength, binding agent, ligands and Donnan potential on the effective diffusion coefficient. The effective diffusion coefficients of Cd(2+) through the dialysis membrane immersed in receptor solutions with binding agent were almost the same as those in receptor solutions without binding agent at higher ionic strengths (0.01-1 M) but much higher than those at lower ionic strengths (0.001-0.0001 M). The effective diffusion coefficients of Cd(2+) through the dialysis membrane immersed in deionized water receptor solutions with binding agent were not significantly different from those in synthetic receptor solutions (receptor solutions with various ionic strengths) with binding agent. The DGT-labile fractions were measured in synthetic solutions and natural waters, which indicated that the effective diffusion coefficients, through the dialysis membrane immersed in the deionized water solution with binding agent as receptor solution and in the spiked natural water as source solution, were more suitable for DGT application. PMID:21645656

Chen, Hong; Sun, Ting; Sui, Dianpeng; Dong, Jia

2011-07-18

111

Nanoscale mapping of ion diffusion in a lithium-ion battery cathode  

NASA Astrophysics Data System (ADS)

The movement of lithium ions into and out of electrodes is central to the operation of lithium-ion batteries. Although this process has been extensively studied at the device level, it remains insufficiently characterized at the nanoscale level of grain clusters, single grains and defects. Here, we probe the spatial variation of lithium-ion diffusion times in the battery-cathode material LiCoO2 at a resolution of ~100 nm by using an atomic force microscope to both redistribute lithium ions and measure the resulting cathode deformation. The relationship between diffusion and single grains and grain boundaries is observed, revealing that the diffusion coefficient increases for certain grain orientations and single-grain boundaries. This knowledge provides feedback to improve understanding of the nanoscale mechanisms underpinning lithium-ion battery operation.

Balke, N.; Jesse, S.; Morozovska, A. N.; Eliseev, E.; Chung, D. W.; Kim, Y.; Adamczyk, L.; García, R. E.; Dudney, N.; Kalinin, S. V.

2010-10-01

112

Doping by diffusion and implantation of V, Cr, Mn and Fe ions in uncoloured beryl crystals  

NASA Astrophysics Data System (ADS)

Colouration in a natural single crystal of uncoloured beryl was carried out using doping by diffusion and ion implantation with ion species of V, Cr, Mn or Fe. The experimental results obtained for the diffused samples using optical absorption, electron paramagnetic resonance and inductively coupled plasma-laser ablation-mass spectroscopy techniques revealed that these ions could be doped and diffused in the crystal. It was impossible to ascertain experimentally whether implanted ions were introduced into the samples because of a low dose used (2 × 10 16 ions/cm 2). It was found that two ions existent in the natural sample, that is, Mn 2+ ions in octahedral coordination and Fe 3+ ions in the structural channels characteristic of beryl, were converted into Mn 3+ and Fe 2+ ions, respectively, during the ion implantation process. In diffusion processes, Fe-diffused samples showed low activation energy and high diffusion coefficient than the other diffused samples. This is in accordance of a finding of Batra et al. that Fe 3+ ions have the spherically symmetric coordination d 5. Difference in the energy activation and diffusion coefficient was also found in samples diffused along and perpendicular to c-axis.

Mittani, J. C. R.; Watanbe, S.; Matsuoka, M.; Baptista, D. L.; Zawislak, F. C.

2004-06-01

113

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

114

Diffusion behavior of chloride ions in concrete  

SciTech Connect

In the present paper, an analysis of the diffusion behavior of chloride ions in concrete is presented. In concentrated electrolytic aqueous solutions such as seawater or that typically used in laboratory experiments, the effect of ionic interaction may significantly reduce the chemical potential and thus the driving force of the diffusing species. Because of different drift velocities of the cations and chloride ions in the solution, the lagging motion of the cations will also retard the drift velocity of the chlorides. In addition, both the electrical double layer forming on the solid surface and the chemical binding may significantly interfere with the transport of the chloride ions. As a result, the diffusion behavior of the chloride ions in concrete is a more complex and complicated transport process than what can be described by Fick`s law of diffusion.

Zhang, T.; Gjoerv, O.E. [Norwegian Univ. of Science and Technology, Trondheim (Norway). Div. of Building Materials] [Norwegian Univ. of Science and Technology, Trondheim (Norway). Div. of Building Materials

1996-06-01

115

Messages Do Diffuse Faster than Messengers: Reconciling Disparate Estimates of the Morphogen Bicoid Diffusion Coefficient  

PubMed Central

The gradient of Bicoid (Bcd) is key for the establishment of the anterior-posterior axis in Drosophila embryos. The gradient properties are compatible with the SDD model in which Bcd is synthesized at the anterior pole and then diffuses into the embryo and is degraded with a characteristic time. Within this model, the Bcd diffusion coefficient is critical to set the timescale of gradient formation. This coefficient has been measured using two optical techniques, Fluorescence Recovery After Photobleaching (FRAP) and Fluorescence Correlation Spectroscopy (FCS), obtaining estimates in which the FCS value is an order of magnitude larger than the FRAP one. This discrepancy raises the following questions: which estimate is "correct''; what is the reason for the disparity; and can the SDD model explain Bcd gradient formation within the experimentally observed times? In this paper, we use a simple biophysical model in which Bcd diffuses and interacts with binding sites to show that both the FRAP and the FCS estimates may be correct and compatible with the observed timescale of gradient formation. The discrepancy arises from the fact that FCS and FRAP report on different effective (concentration dependent) diffusion coefficients, one of which describes the spreading rate of the individual Bcd molecules (the messengers) and the other one that of their concentration (the message). The latter is the one that is more relevant for the gradient establishment and is compatible with its formation within the experimentally observed times.

Sigaut, Lorena; Pearson, John E.; Colman-Lerner, Alejandro; Ponce Dawson, Silvina

2014-01-01

116

Messages do diffuse faster than messengers: reconciling disparate estimates of the morphogen bicoid diffusion coefficient.  

PubMed

The gradient of Bicoid (Bcd) is key for the establishment of the anterior-posterior axis in Drosophila embryos. The gradient properties are compatible with the SDD model in which Bcd is synthesized at the anterior pole and then diffuses into the embryo and is degraded with a characteristic time. Within this model, the Bcd diffusion coefficient is critical to set the timescale of gradient formation. This coefficient has been measured using two optical techniques, Fluorescence Recovery After Photobleaching (FRAP) and Fluorescence Correlation Spectroscopy (FCS), obtaining estimates in which the FCS value is an order of magnitude larger than the FRAP one. This discrepancy raises the following questions: which estimate is "correct''; what is the reason for the disparity; and can the SDD model explain Bcd gradient formation within the experimentally observed times? In this paper, we use a simple biophysical model in which Bcd diffuses and interacts with binding sites to show that both the FRAP and the FCS estimates may be correct and compatible with the observed timescale of gradient formation. The discrepancy arises from the fact that FCS and FRAP report on different effective (concentration dependent) diffusion coefficients, one of which describes the spreading rate of the individual Bcd molecules (the messengers) and the other one that of their concentration (the message). The latter is the one that is more relevant for the gradient establishment and is compatible with its formation within the experimentally observed times. PMID:24901638

Sigaut, Lorena; Pearson, John E; Colman-Lerner, Alejandro; Ponce Dawson, Silvina

2014-06-01

117

Diffusion behavior of chloride ions in concrete  

Microsoft Academic Search

In the present paper, an analysis of the diffusion behavior of chloride ions in concrete is presented. In concentrated electrolytic aqueous solutions such as seawater or that typically used in laboratory experiments, the effect of ionic interaction may significantly reduce the chemical potential and thus the driving force of the diffusing species. Because of different drift velocities of the cations

Tiewei Zhang; Odd E. Gjørv

1996-01-01

118

Diffusion and Ion Mixing in Amorphous Alloys.  

National Technical Information Service (NTIS)

Tracer impurity diffusion and ion beam mixing in amorphous (a-)Ni sub 50 Zr sub 50 were measured. A correlation between the metallic radius of an impurity and its tracer diffusivity was observed; it is similar to that found in crystalline alpha -Zr and al...

H. Hahn R. S. Averback F. Ding C. Loxton J. Baker

1986-01-01

119

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

120

Computing quasi-linear diffusion coefficients using the delta-f particle-in-cell method  

SciTech Connect

Linear wave codes AORSA and TORIC couple to the bounce-averaged nonlinear Fokker-Planck code CQL3D through quasi-linear diffusion coefficients. Both linear wave codes rely on the quasi-local approximation that includes only first-order parallel and perpendicular gradient variations of cyclotron frequency and ignores field line curvature along with temperature and density gradient effects. The delta-f particle-in-cell (DFPIC) method has been successfully used for simulating ion-cyclotron fast wave behavior. This method also permits particle behavior such as multiple pass resonance, banana orbits, and superadiabaticity. We present new work on generating quasi-linear diffusion coefficients using the DFPIC method that will permit the electromagnetic particle-in-cell (EMPIC) code, VORPAL, to couple to CQL3D and to compare to AORSA and TORIC. A new multiple weight delta-f approach will be presented that converts velocity derivatives to action derivatives and yields a full tensor quasi-linear diffusion coefficient.

Austin, T. M.; Smithe, D. N.; Ranjbar, V. [Tech-X Corporation, 5621 Arapahoe Ave., Suite A, Boulder, CO 80303 (United States)

2009-11-26

121

Computing quasi-linear diffusion coefficients using the delta-f particle-in-cell method  

NASA Astrophysics Data System (ADS)

Linear wave codes AORSA and TORIC couple to the bounce-averaged nonlinear Fokker-Planck code CQL3D through quasi-linear diffusion coefficients. Both linear wave codes rely on the quasi-local approximation that includes only first-order parallel and perpendicular gradient variations of cyclotron frequency and ignores field line curvature along with temperature and density gradient effects. The delta-f particle-in-cell (DFPIC) method has been successfully used for simulating ion-cyclotron fast wave behavior. This method also permits particle behavior such as multiple pass resonance, banana orbits, and superadiabaticity. We present new work on generating quasi-linear diffusion coefficients using the DFPIC method that will permit the electromagnetic particle-in-cell (EMPIC) code, VORPAL, to couple to CQL3D and to compare to AORSA and TORIC. A new multiple weight delta-f approach will be presented that converts velocity derivatives to action derivatives and yields a full tensor quasi-linear diffusion coefficient.

Austin, T. M.; Smithe, D. N.; Ranjbar, V.

2009-11-01

122

Biologistics--Diffusion coefficients for complete proteome of Escherichia coli  

PubMed Central

Motivation: Biologistics provides data for quantitative analysis of transport (diffusion) processes and their spatio-temporal correlations in cells. Mobility of proteins is one of the few parameters necessary to describe reaction rates for gene regulation. Although understanding of diffusion-limited biochemical reactions in vivo requires mobility data for the largest possible number of proteins in their native forms, currently, there is no database that would contain the complete information about the diffusion coefficients (DCs) of proteins in a given cell type. Results: We demonstrate a method for the determination of in vivo DCs for any molecule—regardless of its molecular weight, size and structure—in any type of cell. We exemplify the method with the database of in vivo DC for all proteins (4302 records) from the proteome of K12 strain of Escherichia coli, together with examples of DC of amino acids, sugars, RNA and DNA. The database follows from the scale-dependent viscosity reference curve (sdVRC). Construction of sdVRC for prokaryotic or eukaryotic cell requires ~20 in vivo measurements using techniques such as fluorescence correlation spectroscopy (FCS), fluorescence recovery after photobleaching (FRAP), nuclear magnetic resonance (NMR) or particle tracking. The shape of the sdVRC would be different for each organism, but the mathematical form of the curve remains the same. The presented method has a high predictive power, as the measurements of DCs of several inert, properly chosen probes in a single cell type allows to determine the DCs of thousands of proteins. Additionally, obtained mobility data allow quantitative study of biochemical interactions in vivo. Contact: rholyst@ichf.edu.pl Supplementary information: Supplementary data are available at Bioinformatics Online.

Kalwarczyk, Tomasz; Tabaka, Marcin; Holyst, Robert

2012-01-01

123

A theoretical framework for quantitatively characterizing sound field diffusion based on scattering coefficient and absorption coefficient of walls.  

PubMed

This paper describes the development of a theoretical framework for quantitatively characterizing sound field diffusion based on scattering coefficient and absorption coefficient of walls. The concepts of equivalent scattering area, equivalent scatter reflection area, average scattering coefficient and average scatter reflection coefficient are introduced in order to express all walls' capability of scatter in a room. Using these concepts and the mean free path, scatter-to-absorption ratio, mean scatter time and diffusion time are defined in order to evaluate degree of diffusion of a space. Furthermore the effect of spatial scattering objects to sound field diffusion is formulated. In addition the time variation of specular and scattered components in a room impulse response is formulated. The verification of these characterization methods was performed with computer simulations based on the sound ray tracing method. The results supported that the ideas presented are basically valid. PMID:20815450

Hanyu, Toshiki

2010-09-01

124

Molar extinction coefficients of the cupric ion in silicate glasses  

Microsoft Academic Search

The absorption characteristics of Cu2+ ions in binary alkali silicate and ternary silicate glasses were investigated. The molar extinction coefficients of the Cu2+ ion were determined in a series of binary alkali silicate and a ternary soda-lime-silica glasses for the actual intensities of the observed bands at their wavelength maxima. The absorption maxima due to Cu2+ ions were found to

S. P. Singh; A. Kumar

1995-01-01

125

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

126

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

PubMed

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. PMID:9649418

Periasamy, N; Verkman, A S

1998-07-01

127

Colloid diffusion coefficients in compacted and consolidated clay barriers: Compaction density and colloid size effects  

NASA Astrophysics Data System (ADS)

An experimental methodology applying the nuclear ion beam technique Rutherford Backscattering Spectrometry (RBS) is used to measure colloid diffusion profiles within three different types of clay: consolidated Opalinus clay (Switzerland), Callovo-Oxfordian clay (France) and FEBEX bentonite (Spain) compacted at different densities. The RBS technique is widely applied in materials science and it was selected because it allows the measurement of concentration profiles at short range distances (?m). The effects of colloid size, clay type and clay density were analyzed with negatively charged Au colloids of 2, 20 and 40 nm. Apparent diffusion coefficients ( Da) for gold colloids could be measured and Da values ranged from (10 -18 to 10 -19 m 2/s). The larger diffusion coefficient was measured for 2 nm colloids in the Opalinus clay with Da(Au 2 nm) = (2.1 ± 0.5) × 10 -18 m 2/s. The accessible porosity for colloids is even lower than that measured for anions, since not only anion exclusion but also size exclusion hinders diffusion. For example, 40 nm colloids did not accede at all to bentonite compacted at higher densities.

Alonso, Ursula; Missana, Tiziana; Garcia-Gutierrez, Miguel; Patelli, Alessandro; Albarran, Nairoby; Rigato, Valentino

128

Determination of the concentration dependence of polyelectrolyte diffusion coefficients by application of the Boltzmann gradient method  

Microsoft Academic Search

The concentration dependence of a polyelectrolyte diffusion coefficient in aqueous low salt solution (KCl, 1 mM) is determined from a single dynamic gradient experiment. The Boltzmann method is applied to calculate the diffusion coefficient. A special diffusion cell is constructed that minimizes aberrations in the optical detection of the polyion concentration profile. Bovine serum albumin (BSA) is chosen as a

A. T. Wagner; H.-H. Kohler

2008-01-01

129

Anisotropic Diffusion Coefficient in a Cylindrical Cell by Integral Transport Theory  

Microsoft Academic Search

The anisotropic diffusion coefficient has been calculated in a cylindrical cell with use made of the integral transport theory. The previous method of calculating the diffusion coefficient requires much computer time to evaluate the generalized first-flight collision probabilities between two mesh points for a square cell. To circumvent this drawback, we introduce new calculation methods for determining the anisotropic diffusion

Toshikazu TAKEDA; Tamotsu SEKIYA

1973-01-01

130

Effect of detector exposure time on the apparent diffusion coefficient measured by single particle tracking  

Microsoft Academic Search

We present results from simulation of Brownian motion of nanoparticles where we also take into account the averaging imposed by the exposure period E of the detector. The diffusion coefficient is estimated from the measured displacements of the particles over a prescribed delay time deltat. Results from free diffusion simulations show a clear dependency of the estimated diffusion coefficient on

Shahram Pouya; Manoochehr Koochesfahani; Richard di Liu

2008-01-01

131

Continuum Absorption Coefficient of Atoms and Ions  

NASA Technical Reports Server (NTRS)

The rate of heat transfer to the heat shield of a Jupiter probe has been estimated to be one order of magnitude higher than any previously experienced in an outer space exploration program. More than one-third of this heat load is due to an emission of continuum radiation from atoms and ions. The existing computer code for calculating the continuum contribution to the total load utilizes a modified version of Biberman's approximate method. The continuum radiation absorption cross sections of a C - H - O - N ablation system were examined in detail. The present computer code was evaluated and updated by being compared with available exact and approximate calculations and correlations of experimental data. A detailed calculation procedure, which can be applied to other atomic species, is presented. The approximate correlations can be made to agree with the available exact and experimental data.

Armaly, B. F.

1979-01-01

132

Examination of three methods for studying ion diffusion in cement pastes, mortars and concrete  

Microsoft Academic Search

Three laboratory techniques for studying ion diffusion in hydrated cement pastes, mortars and concrete are described and compared.\\u000a In the first method, concentration profiles are produced by analysing material sampled at various distances from the surface\\u000a exposed to the selected ion, after various periods of exposure. The second technique employs a diffusion cell and calculation\\u000a of an effective diffusion coefficient

N. R. Buenfeld; J. B. Newman

1987-01-01

133

Coordinate-dependent diffusion coefficients: Decay rate in open quantum systems  

SciTech Connect

Based on a master equation for the reduced density matrix of an open quantum collective system, the influence of coordinate-dependent microscopical diffusion coefficients on the decay rate from a metastable state is treated. For various frictions and temperatures larger than a crossover temperature, the quasistationary decay rates obtained with the coordinate-dependent microscopical set of diffusion coefficients are compared with those obtained with the coordinate-independent microscopical set of diffusion coefficients and coordinate-independent and -dependent phenomenological sets of diffusion coefficients. Neglecting the coordinate dependence of diffusion coefficients, one can strongly overestimate or underestimate the decay rate at low temperature. The coordinate-dependent phenomenological diffusion coefficient in momentum are shown to be suitable for applications.

Sargsyan, V. V. [Joint Institute for Nuclear Research, 141980 Dubna (Russian Federation); Institut fuer Theoretische Physik der Justus-Liebig-Universitaet, D-35392 Giessen (Germany); Palchikov, Yu. V.; Antonenko, N. V. [Joint Institute for Nuclear Research, 141980 Dubna (Russian Federation); Kanokov, Z. [Joint Institute for Nuclear Research, 141980 Dubna (Russian Federation); National University, 700174 Tashkent (Uzbekistan); Adamian, G. G. [Joint Institute for Nuclear Research, 141980 Dubna (Russian Federation); Institute of Nuclear Physics, 702132 Tashkent (Uzbekistan)

2007-06-15

134

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.

2014-01-01

135

Evaluation of the vertical diffusion coefficients from ERA-40 with 222Rn simulations  

NASA Astrophysics Data System (ADS)

Boundary layer turbulence has a profound influence on the distribution of tracers with sources or sinks at the surface. The 40-year ERA-40 meteorological data set of the European Centre for Medium-range Weather Forecasts contains archived vertical diffusion coefficients. We evaluated the use of these archived diffusion coefficients instead of off-line diagnosed coefficients based on other meteorological parameters archived during ERA-40 by investigation of the effect on the distribution of the radioactive tracer 222Rn in the chemistry transport model TM3. In total four different sets of vertical diffusion coefficients are compared: (i) 3-hourly vertical diffusion coefficients archived during the ERA-40 project, (ii) 3-hourly off-line diagnosed coefficients from a non-local scheme based on Holtslag and Boville (1993), Vogelezang and Holtslag (1996), and Beljaars and Viterbo (1999), (iii) 6-hourly coefficients archived during the ERA-40 project, and (iv) 6-hourly off-line diagnosed coefficients based on a local scheme described in Louis (1979) and Louis et al. (1982). The diffusion scheme to diagnose the coefficients off-line in (ii) is similar to the diffusion scheme used during the ERA-40 project (i and iii). The archived diffusion coefficients from the ERA-40 project which are time-averaged cause stronger mixing than the instantaneous off-line diagnosed diffusion coefficients. This can be partially attributed to the effect of instantaneous versus time-averaged coefficients, as well as to differences in the diffusion schemes. The 3-hourly off-line diagnosis of diffusion coefficients can reproduce quite well the 3-hourly archived diffusion coefficients. Boundary layer heights are also available for the sets (ii) and (iii). Both were found to be in reasonable agreement with observations of the boundary layer height from Cabauw in the Netherlands and from the FIFE-campaign in the United States. Simulations of 222Rn with the TM3 model using these four sets of vertical diffusion coefficients are compared to surface measurements of 222Rn in Freiburg, Schauinsland, Cincinnati and Socorro in order to evaluate the effect of these different sets of diffusion coefficients on the tracer transport. It is found that the daily cycle of the 222Rn concentration is well represented using 3-hourly diffusion coefficients. Comparison with observations of 222Rn data with the station in Schauinsland which is situated on a hill shows that all considered schemes underestimate the amplitude of the daily cycle of the 222Rn concentration in the upper part of the atmospheric boundary layer. We conclude that the 3-hourly archived diffusion coefficients from ERA-40 are well suited for use in chemistry transport models.

Olivié, D. J. L.; van Velthoven, P. F. J.; Beljaars, A. C. M.

2004-08-01

136

High silicon self-diffusion coefficient in dry forsterite  

NASA Astrophysics Data System (ADS)

Plastic deformation of mantle minerals is believed to be controlled by self-diffusion of the slowest species, which is silicon in silicate minerals. Olivine is the main constituent of upper mantle. Therefore, silicon self-diffusion coefficient (DSi) in olivine provides the basic information of upper mantle rheology. Dohmen et al. [1] and Jaoul et al. [2] measured the DSi at ambient pressure under dry conditions in natural olivine and iron-free forsterite, respectively. However, their results were ~2-3 orders of magnitude lower than that estimated from deformation experiments [3]. In this study, we revisited DSi in forsterite and resolved this discrepancy [4]. Forsterite single crystals were polished in colloidal silica solution, deposited with 300-500 nm of 29Si enriched Mg2SiO4 films, covered by 100 nm of ZrO2 films, and annealed at 1600-1800 K from ambient pressure up to 13 GPa using an ambient pressure furnace and multi-anvil apparatus. The surface roughness after diffusion were reduced to <50 nm by polishing again in colloidal silica solution. Diffusion profiles were obtained by SIMS. Water contents in the samples were <1 ?g/g by FT-IR [4]. logDSi were determined to be -19.7±0.4 and -18.1±0.3 log[m2/s] under ambient pressure at 1600 and 1800 K, respectively. These values were 2.4 orders of magnitude higher than that determined by Jaoul et al. [2] in forsterite, as well as that reprted by Dohmen et al. [1] in natural olivine. Their low DSi could be obtained due to the bad contact of the coated films with the substrate. Our results well explain the high dislocation climb rates in deformation experiments [4]. We also determined a small negative pressure dependence of DSi with an activation volume of 1.7±0.4 cm3/mol, and an activation energy of ~410 kJ/mol. Calibratied to the same temperature, the nearly linear relationship of DSi against pressure in dry forsterite in this study, iron and water bearing wadsleyite and ringwoodite by Shimojuku et al. [5] demostrates that effects of iron, water, and structural difference of (Mg,Fe)2SiO4 polymorphs on silicon diffusion are small. Viscosity in upper mantle should be almost constant with depth by assuming it inversely proportional to DSi [4]. [1] Dohmen et al. (2002), GRL 29 (21), 2030. [2] Jaoul et al. (1981), Anelasticity in the Earth, Geodyn. 4, 95-100. [3] Goetze and Kohlstedt (1973), JGR 78 (26), 5961-5971. [4] Fei et al. (2012), EPSL 345-348, 95-103. [5] Shimojuku et al. (2009), EPSL 284, 103-112.

Katsura, T.; Fei, H.; Hegoda, C.; Yamazaki, D.; Wiedenbeck, M.; Yurimoto, H.; Shcheka, S.

2012-12-01

137

Quasi-linear diffusion coefficients for field-aligned electromagnetic waves with applications to the magnetosphere  

NASA Astrophysics Data System (ADS)

Much current research in magnetospheric physics is directed toward understanding the dramatic variations in relativistic (>1 MeV) electron fluxes that can take place in the Earth's outer zone during magnetic storms. The behavior of outer-zone energetic electrons is partly controlled by the competing mechanisms of acceleration and loss that result from wave-particle interactions, in particular electron gyroresonance with ELF, VLF, and electromagnetic ion cyclotron (EMIC) waves. Powerful techniques for treating gyroresonant wave-particle interactions are provided by quasi-linear diffusion theory. In this paper, we derive formulae for the quasi-linear (momentum, mixed, and pitch-angle) diffusion coefficients for cyclotron resonance with field-aligned electromagnetic waves of any mode and general spectral density. The formulae are fully exact, expressed in closed analytical form, and easily computable. Our results can therefore be readily used to determine accurate diffusion rates for many forms of wave-particle interaction in the magnetosphere and other space plasmas. We find that momentum diffusion rates for MeV electrons in gyroresonance with VLF chorus can be less than a day in the lower-density regions outside the plasmasphere. The mechanism of stochastic acceleration by VLF chorus could therefore be instrumental in generating relativistic electrons during the recovery phase of a magnetic storm. Pitch-angle diffusion rates of MeV electrons scattered by EMIC waves along the plasmapause can approach the limit of strong diffusion. EMIC wave scattering could hence contribute significantly to electron precipitation loss over the course of a storm. Codes designed to model electron dynamics in the radiation belts need to incorporate, in addition to radial (cross-L) diffusion, resonant diffusion due to electron gyroresonance with ELF, VLF, and EMIC waves. In order to determine the quasi-linear diffusion coefficients for such codes, observational data are required on the power spectral density, spatial distribution, and temporal variation of these wave modes. Currently, only limited wave data sets are available. In addition, problems of numerical instability associated with diffusion codes need to be solved. The development of fully comprehensive models of radiation belt electron dynamics remains a considerable scientific challenge.

Summers, Danny

2005-08-01

138

Spin Diffusion Coefficient of A1-PHASE of Superfluid 3He at Low Temperatures  

NASA Astrophysics Data System (ADS)

The spin diffusion coefficient tensor of the A1-phase of superfluid 3He at low temperatures and melting pressure is calculated using the Boltzmann equation approach and Pfitzner procedure. Then considering Bogoliubov-normal interaction, we show that the total spin diffusion is proportional to 1/T2, the spin diffusion coefficient of superfluid component D\\uparrowxzxz is proportional to T-2, and the spin diffusion coefficient of super-fluid component D\\uparrowxxxx (=D\\uarrowxyxy) is independent of temperature. Furthermore, it is seen that superfluid components play an important role in spin diffusion of the A1-phase.

Afzali, R.; Pashaee, F.

139

Diffusion (or conduction) along a slightly tapering tube, and its application to the determination of diffusion coefficients  

Microsoft Academic Search

The diffusion equation has been solved for the case of diffusion from a slightly tapering tube into an infinite medium of zero concentration. The theory provides a means of correcting results obtained for diffusion coefficients in the capillary tube method of Anderson and Saddington, when the tube is not of uniform bore throughout its length. This is frequently the case

A. Talbot; J. A. Kitchener

1956-01-01

140

Measurement of diffusion coefficients important in modeling the absorption rate of carbon dioxide into aqueous N-methyldiethanolamine  

SciTech Connect

Natural gas processors use amine treating processes to remove the acid gases H{sub 2}S and CO{sub 2} from gas streams. Absorption rates of gaseous CO{sub 2} into aqueous N-methyldiethanolamine (MDEA) solutions were measured in a quiescent, inverted-tube diffusiometer by monitoring the rate of pressure drop. The absorption rate was found to be insensitive to the diffusion coefficient of CO{sub 2} in solution but very sensitive to the diffusion rate of bicarbonate and protonated MDEA ions. Evidence also suggested that chemical reaction equilibrium is rapid relative to diffusion. A numerical model was developed on the basis of these observations. The model was used to regress diffusion coefficients of bicarbonate and protonated amine, which must be equivalent by electroneutrality arguments, from measured absorption rates. Complete modeling of the absorption process also required data for the diffusion coefficient of MDEA in water. These were measured using a Taylor dispersion apparatus. CO{sub 2} absorption rates and diffusion coefficients of bicarbonate and protonated MDEA were obtained at 298.2 K and 318.2 K in solutions containing 20, 35, and 50 mass % MDEA in water.

Rowley, R.L.; Adams, M.E.; Marshall, T.L.; Oscarson, J.L.; Wilding, W.V.; Anderson, D.J. [Brigham Young Univ., Provo, UT (United States). Dept. of Chemical Engineering] [Brigham Young Univ., Provo, UT (United States). Dept. of Chemical Engineering

1997-03-01

141

The Total Absorption Coefficient of the Negative Hydrogen Ion.  

National Technical Information Service (NTIS)

The free-free absorption coefficient of the negative hydrogen ion is calculated in both the length and velocity formulations using the method of polarized orbitals to describe the free electron. The bound-free cross section of Bell and Kingston(1967) is c...

K. L. Bell A. E. Kingston W. A. McIlveen

1974-01-01

142

Microstructure of montmorillonite\\/silica sand mixture and its effects on the diffusion of strontium ions  

Microsoft Academic Search

A mixture of bentonite and silica sand is expected to be an important engineered barrier in a high-level radioactive waste repository. Therefore, the diffusion behavior of radionuclides in this mixture is a key issue for the safety assessment of geological disposal.This study determined the apparent diffusion coefficients of strontium ions in montmorillonite and silica sand mixtures under different temperatures at

J. Liu; T. Kozaki; Y. Horiuchi; S. Sato

2003-01-01

143

Solute diffusion in ?-Zr: Rutherford backscattering and secondary-ion mass spectrometry study  

Microsoft Academic Search

Substitutional diffusion coefficients D of Hf, Ta and Pb have been measured ?- Zr single crystals and the diffusion profiles analysed by Rutherford backscattering (Hf, Ta and Pb) and secondary-ion mass spectrometry (Hf). Measurements were made either parallel (D?) or perpendicular (D?) to the specimen c axis. Although the main study is concerned with the influence of Fe on the

G. M. Hood; T. Laursen; J. A. Jackman; R. Belec; R. J. Schultz; J. L. Whitton

1991-01-01

144

Protein Diffusion Coefficients Determined by Macroscopic-Gradient Rayleigh Interferometry and Dynamic Light Scattering  

Microsoft Academic Search

Dynamic light scattering (DLS) is extensively used for measuring macromolecule diffusion coefficients. Contrary to classical techniques based on macroscopic concentration gradients, DLS probes microscopic fluctuations in concentration. DLS accuracy and its concordance with macroscopic-gradient techniques remains an outstanding important issue. We measured lysozyme diffusion coefficients in aqueous salt using both DLS and Rayleigh interferometry, a highly accurate macroscopic-gradient technique. The

Onofrio Annunziata; Daniela Buzatu; John G. Albright

2005-01-01

145

Fractal scaling of effective diffusion coefficient of solute in porous media.  

PubMed

Fractal approach is used to derive a power law relation between effective diffusion coefficient of solute in porous media and the geometry parameter characterizing the media. The results are consistent with the empirical equations analogous to Archie's law and are expected to be applied to prediction of effective diffusion coefficient. PMID:11590736

Liu, J G; Nie, Y F

2001-04-01

146

Effect of therapeutic ultrasound on partition and diffusion coefficients in human stratum corneum  

Microsoft Academic Search

Application of various enhancers including ultrasound and chemicals has been shown to enhance transdermal drug transport. Most of these enhancers increase transdermal transport by increasing either partition or diffusion coefficients in lipid bilayers. Although the effect of such enhancers on skin permeability has been measured in many cases, the effect of the same enhancers on solute partition and diffusion coefficients

Samir Mitragotri

2001-01-01

147

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

2009-04-01

148

Evaluation of Effective Diffusion Coefficient in Various Building Materials and Absorbents by Mercury Intrusion Porosimetry  

Microsoft Academic Search

An effective diffusion coefficient plays an important role in the numerical analysis model to predict the emission rate of VOCs from building materials. This research evaluates the effective diffusion coefficient of VOCs (toluene, formaldehyde, etc.) in building materials (gypsum boards, medium density fiberboard, etc.) and adsorbents (activated carbon, charcoal, etc.) using the mercury intrusion porosimetry (MIP) test. The MIP test

J Seo; S Kato; Y Ataka; Q Zhu

2005-01-01

149

MEASUREMENT OF EFFECTIVE AIR DIFFUSION COEFFICIENTS FOR TRICHLOROETHENE IN UNDISTURBED SOIL CORES. (R826162)  

EPA Science Inventory

Abstract In this study, we measure effective diffusion coefficients for trichloroethene in undisturbed soil samples taken from Picatinny Arsenal, New Jersey. The measured effective diffusion coefficients ranged from 0.0053 to 0.0609 cm2/s over a range of air...

150

Intrinsic diffusion coefficients and the vacancy flow factor in dilute Cu-Zn alloys  

SciTech Connect

The interdiffusion coefficient and the intrinsic diffusion coefficient of Zn and Cu in dilute alloys at 1168 K have been determined with semi-infinite couples using Darken's relation. In addition, the Kirkendall effect in thin plate couples at 1168 K has been examined using Heumann's method to determine the ratio of the intrinsic diffusion coefficients in very dilute alloys. The correlation factor for impurity diffusion of zinc in copper has been estimated by combining the vacancy flow factor with the enhancement factor. This permits an estimate of the kinetic energy factor for impurity diffusion. 26 refs.

Hoshino, K.; Iijima, Y.; Hirano, K.

1982-07-01

151

Imaging cell size and permeability in biological tissue using the diffusion-time dependence of the apparent diffusion coefficient.  

PubMed

The purpose of this study was to analyze and evaluate a model of restricted water diffusion between equidistant permeable membranes for cell-size and permeability measurements in biological tissue. Based on the known probability distribution of diffusion distances after the diffusion time ? in a system of permeable membranes characterized by three parameters (membrane permeability P, membrane distance L, and free diffusivity D0), an equivalent dimensionless model was derived with a probability distribution characterized by only a single (dimensionless) tissue parameter [Formula: see text]. Evaluating this proposed model function, the dimensionless diffusion coefficient [Formula: see text] was numerically calculated for 60 values of the dimensionless diffusion time [Formula: see text] and 35 values of [Formula: see text]. Diffusion coefficients were measured in a carrot by diffusion-weighted magnetic resonance imaging (MRI) at 18 diffusion times between 9.9 and 1022.7 ms and fitted to the simulation results [Formula: see text] to determine L, P, and D0. The measured diffusivities followed the simulated dependence of [Formula: see text]. Determined cell sizes varied from 21 to 76 ?m, permeabilities from 0.007 to 0.039 ?m(-1), and the free diffusivities from 1354 to 1713 ?m(2)?s(-1). In conclusion, the proposed dimensionless tissue model can be used to determine tissue parameters (D0, L, P) based on diffusion MRI with multiple diffusion times. Measurements in a carrot showed a good agreement of the cell diameter, L, determined by diffusion MRI and by light microscopy. PMID:24839979

Dietrich, Olaf; Hubert, Alexander; Heiland, Sabine

2014-06-21

152

Temperature effects on diffusion coefficient for 6-gingerol and 6-shogaol in subcritical water extraction  

NASA Astrophysics Data System (ADS)

6-gingerol and 6-shogaol are the main constituents as anti-inflammatory or bioactive compounds from zingiber officinale Roscoe. These bioactive compounds have been proven for inflammatory disease, antioxidatives and anticancer. The effect of temperature on diffusion coefficient for 6-gingerol and 6-shogaol were studied in subcritical water extraction. The diffusion coefficient was determined by Fick's second law. By neglecting external mass transfer and solid particle in spherical form, a linear portion of Ln (1-(Ct/Co)) versus time was plotted in determining the diffusion coefficient. 6-gingerol obtained the higher yield at 130°C with diffusion coefficient of 8.582x10?11 m2/s whilst for 6-shogaol, the higher yield and diffusion coefficient at 170°C and 19.417 × 10?11 m2/s.

Ilia Anisa, Nor; Azian, Noor; Sharizan, Mohd; Iwai, Yoshio

2014-04-01

153

Controlling chloride ions diffusion in concrete.  

PubMed

The corrosion of steel in concrete is mainly due to the chemical reaction between the chloride ions and iron ions. Indeed, this is a serious threaten for reinforced concrete structure, especially for the reinforced concrete structure in the sea. So it is urgent and important to protect concrete against chloride ions corrosion. In this work, we report multilayer concrete can cloak chloride ions. We formulated five kinds of concrete A, B, C, D and E, which are made of different proportion of cement, sand and glue, and fabricated six-layer (ABACAD) cylinder diffusion cloak and background media E. The simulation results show that the six-layer mass diffusion cloak can protect concrete against chloride ions penetration, while the experiment results show that the concentration gradients are parallel and equal outside the outer circle in the diffusion flux lines, the iso-concentration lines are parallel outside the outer circle, and the concentration gradients in the inner circle are smaller than those outside the outer circle. PMID:24285220

Zeng, Lunwu; Song, Runxia

2013-01-01

154

Controlling chloride ions diffusion in concrete  

NASA Astrophysics Data System (ADS)

The corrosion of steel in concrete is mainly due to the chemical reaction between the chloride ions and iron ions. Indeed, this is a serious threaten for reinforced concrete structure, especially for the reinforced concrete structure in the sea. So it is urgent and important to protect concrete against chloride ions corrosion. In this work, we report multilayer concrete can cloak chloride ions. We formulated five kinds of concrete A, B, C, D and E, which are made of different proportion of cement, sand and glue, and fabricated six-layer (ABACAD) cylinder diffusion cloak and background media E. The simulation results show that the six-layer mass diffusion cloak can protect concrete against chloride ions penetration, while the experiment results show that the concentration gradients are parallel and equal outside the outer circle in the diffusion flux lines, the iso-concentration lines are parallel outside the outer circle, and the concentration gradients in the inner circle are smaller than those outside the outer circle.

Zeng, Lunwu; Song, Runxia

2013-11-01

155

Diffusion in mixed solvents. III - The heat of mixing parameter and the Soret coefficient  

NASA Technical Reports Server (NTRS)

New evidence is presented that for aqueous glycerol solutions, the Soret coefficient of glycerol, sigma sub 1 = D sub 1 T/D sub 1 (where D sub 1 T and D sub 1 are the thermal and self-diffusion coefficients, respectively, of glycerol in aqueous solutions), is an integral part of the heat of mixing parameter. Expressions are presented indicating the importance of the Soret coefficients to correlations for diffusion processes in glycerol water solvents.

Carapellucci, P. A.

1976-01-01

156

Oxidation Rate and Phase Diagram of Mu-Zn Ferrite Determined from the Cation Diffusion Coefficient  

Microsoft Academic Search

Oxidation rate of Mn-Zn ferrite, which means the rate of change in oxygen content in spinel phase, was determined from the diffusion coefficient of 59Fe, by assuming that the diffusion coefficient was proportional to the cation vacancy density, i.e., the excess oxygen content. Volume oxidation rate and grain boundary oxidation rate are expressed by coefficients having the same dimension as

Seiya Ogawa

1967-01-01

157

Diffusion coefficients of vacancies and interstitials along tilt grain boundaries in molybdenum  

NASA Astrophysics Data System (ADS)

The diffusion coefficients of vacancies and interstitials along symmetrical tilt grain boundaries in molybdenum have been calculated using the molecular dynamics method. The migration energies of defects have been obtained. The activation energy and coefficients of grain boundary self-diffusion have been deter-mined. A comparison of the obtained results with the studies of other authors indicates that boundaries formed between particles in the powder in sintering experiments have a higher diffusion activity as compared to stable grain boundaries in polycrystals.

Novoselov, I. I.; Kuksin, A. Yu.; Yanilkin, A. V.

2014-05-01

158

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

159

Generating quasi-linear diffusion coefficients using the delta-f PIC method  

NASA Astrophysics Data System (ADS)

Linear wave codes, AORSA and TORIC, used by the SciDAC Center for Simulation of Wave-Plasma Interaction couple to the bounce-averaged nonlinear Fokker-Planck code CQL3D through quasi-linear diffusion coefficients. Both AORSA and TORIC rely on the quasi-local approximation that only includes first-order parallel and perpendicular gradient variations of cyclotron frequency and ignores field line curvature along with temperature and density gradient effects. Previously, the delta-f particle-in-cell (DFPIC) method has been used for simulating ion-cyclotron fast wave behavior. Particle behavior such as multiple pass resonance, banana orbits, and superadiabaticity can also be examined with this method. We present recent results on using eqdisk fusion data to generate quasi-linear diffusion coefficients that permit the VORPAL code to compare to AORSA and TORIC and to eventually couple to CQL3D. The results are generated for a single toroidal mode using DFPIC simulations in RZ geometry.

Austin, Travis; Smithe, David; Wrobel, Matthew; Ranjbar, Vahid

2009-05-01

160

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

161

First-principles study of temperature-dependent diffusion coefficients: Hydrogen, deuterium, and tritium in ?-Ti  

NASA Astrophysics Data System (ADS)

We report the prediction of temperature-dependent diffusion coefficients of interstitial hydrogen, deuterium, and tritium atoms in ?-Ti using 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 with the host lattice. The dual occupancy case of impurity atom in the hcp matrix is considered, and four diffusion paths are combined to obtain the final diffusion coefficients. The calculated diffusion parameters show good agreement with experiments. Our numerical results indicate that the diffusions of deuterium and tritium atoms are slower than that of the hydrogen atom at temperatures above 425 K and 390 K, respectively.

Lu, Yong; Zhang, Ping

2013-05-01

162

Measurement of the diffusion coefficient for salt in salt flat and mangrove soils  

Microsoft Academic Search

Excluded salt accumulated at mangrove roots must be transported away from the root zone by diffusive processes, due to the low permeability of most mangrove soils. The diffusion coefficient for salt in mangrove soils determines the rate of this diffusive transport but has not been determined experimentally before. In this work we used a 12-month long-time series of salt concentration

S. E. Hollins; P. V. Ridd; W. W. Read

2000-01-01

163

A comparison of ambipolar diffusion coefficients in meteor trains using VHF radar and UV lidar  

Microsoft Academic Search

In this paper we present the first comparative estimations of ionic diffusion rates for sporadic meteor trains near the mesopause made using VHF radar and UV Rayleigh lidar observations. In both cases we initially assumed that the meteor trains dissipate primarily through ambipolar diffusion. For the radar data, the diffusion coefficient within the meteor train was determined from the decay

Phillip B. Chilson; Peter Czechowsky; Gerhard Schmidt

1996-01-01

164

Impurity Diffusion Coefficients of Al and Zn in Mg Determined from Solid-to-Solid Diffusion Couples  

SciTech Connect

Increasing use and development of lightweight Mgalloys have led to the desire for more fundamental research in and understanding of Mg-based systems. As property enhancing components, Al and Zn are two of the most important and common alloying elements for Mg-alloys. We have investigated the concentration dependent interdiffusion of Al and Zn in Mg using diffusion couples of pure polycrystalline Mg mated to Mg solid solutions containing either <9 at.% Al or <3 at.% Zn. Concentration profiles were determined by electron micro-probe microanalysis of the diffusion zone. The interdiffusion coefficients were determined by the classical Boltzmann-Matano method within the Mg solid solution. As the concentration of Al or Zn approaches the dilute ends, we employ an analytical approach based on the Hall method to estimate the impurity diffusion coefficients. Results of Al and Zn impurity diffusion in Mg are reported and compared to published impurity diffusion coefficients typically determined by thin film techniques.

Kammerer, Catherine [University of Central Florida, Orlando; Kulkarni, Nagraj S [ORNL; Warmack, Robert J Bruce [ORNL; Perry, Kelly A [ORNL; Belova, Irina [University of Newcastle, NSW, Australia; Murch, Prof. Graeme [University of Newcastle, NSW, Australia; Sohn, Yong Ho [University of Central Florida

2013-08-01

165

Measurement of ageing effect on chloride diffusion coefficients in cementitious matrices  

NASA Astrophysics Data System (ADS)

Most of the low-level nuclear waste disposal facilities are based in engineered multi barrier systems where reinforced concrete is one of the basic materials. The calculation of the time until steel reinforcement depassivation is a need due to the demand of prediction of the service life of concrete structures in radioactive repositories. In doing that, one of the main steps is the transport of chloride ions towards the reinforcement, as one of the most aggressive agents for the rebars in concrete is chloride ions. Ageing of concrete related to chloride penetration leads to significant decrease of the "apparent diffusion" coefficient with time. If this effect is not considered, considerable bias can be introduced when predicting service life of reinforced concrete of repositories. Several effects have been addressed on their influence on the ageing of concrete, including the evolution with time of the concrete pore refinement, the binding of chlorides to the cement phases and to the changes of chloride "surface concentration". These effects have been studied in specimens made with different mixes trying to represent a wide range of mineral addition proportions. The analysis of their evolution with time has shown that the resistivity alone or the joint consideration of resistivity and binding capacity ( Cb/ Cf), are appropriate parameters to appraise the diffusivity ageing. For practical reasons, an accelerated procedure is proposed in order to calculate ageing for short periods of time.

Andrade, C.; Castellote, M.; d'Andrea, R.

2011-05-01

166

Nonlinearity Effects of Lateral Density Diffusion Coefficient on Gain-Guided VCSEL Performance  

NASA Technical Reports Server (NTRS)

Electron and hole diffusions in the plane of semiconductor quantum wells play an important part in the static and dynamic operations of semiconductor lasers. In this paper, we apply a hydrodynamic model developed from the semiconductor Bloch equations to numerically study the effects of nonlinearity in the diffusion coefficient on single mode operation and direct modulation of a gain-guided InGaAs/GaAs multiple quantum well laser, operating not too far from threshold. We found that a small diffusion coefficient is advantageous for lowering the threshold current and increasing the modulation bandwidth. Most importantly, the effects of nonlinearity in the coefficient can be approximately reproduced by replacing the coefficient with an effective constant diffusion coefficient, which corresponds roughly to the half height density of the density distribution.

Li, Jian-Zhong; Cheung, Samson H.; Ning, C. Z.; Biegel, Bryan (Technical Monitor)

2001-01-01

167

Evolution of Lesions in Susac Syndrome at Serial MR Imaging with Diffusion-Weighted Imaging and Apparent Diffusion Coefficient Values  

Microsoft Academic Search

BACKGROUND AND PURPOSE: Susac syndrome is a rare disorder consisting of encepha- lopathy, hearing loss, and retinal arteriolar occlusions. The purpose of this study was to evaluate the evolution of lesions in this disease by using serial MR imaging with diffusion- weighted imaging (DWI) and apparent diffusion coefficients (ADCs). Abnormalities in the nonlesional white matter (NLWM) were also analyzed. METHODS:

Matthew L. White; Yan Zhang; Wendy R. K. Smoker

168

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

169

Measurement of effective air diffusion coefficients for trichloroethene in undisturbed soil cores  

NASA Astrophysics Data System (ADS)

In this study, we measure effective diffusion coefficients for trichloroethene in undisturbed soil samples taken from Picatinny Arsenal, New Jersey. The measured effective diffusion coefficients ranged from 0.0053 to 0.0609 cm 2/s over a range of air-filled porosity of 0.23-0.49. The experimental data were compared to several previously published relations that predict diffusion coefficients as a function of air-filled porosity and porosity. A multiple linear regression analysis was developed to determine if a modification of the exponents in Millington's [Science 130 (1959) 100] relation would better fit the experimental data. The literature relations appeared to generally underpredict the effective diffusion coefficient for the soil cores studied in this work. Inclusion of a particle-size distribution parameter, d10, did not significantly improve the fit of the linear regression equation. The effective diffusion coefficient and porosity data were used to recalculate estimates of diffusive flux through the subsurface made in a previous study performed at the field site. It was determined that the method of calculation used in the previous study resulted in an underprediction of diffusive flux from the subsurface. We conclude that although Millington's [Science 130 (1959) 100] relation works well to predict effective diffusion coefficients in homogeneous soils with relatively uniform particle-size distributions, it may be inaccurate for many natural soils with heterogeneous structure and/or non-uniform particle-size distributions.

Bartelt-Hunt, Shannon L.; Smith, James A.

2002-06-01

170

Diffusion-weighted imaging with apparent diffusion coefficient mapping and spectroscopy in prostate cancer.  

PubMed

Prostate cancer is a major health problem, and the exploration of noninvasive imaging methods that have the potential to improve specificity while maintaining high sensitivity is still critically needed. Tissue changes induced by tumor growth can be visualized by magnetic resonance imaging (MRI) methods. Current MRI methods include conventional T2-weighted imaging, diffusion-weighted imaging (DWI) with apparent diffusion coefficient (ADC) mapping and magnetic resonance spectroscopy (MRS). Techniques such as DWI/ADC provide functional information about the behavior of water molecules in tissue; MRS can provide biochemical information about the presence or absence of certain metabolites, such as choline, creatine, and citrate. Finally, vascular parameters can be investigated using dynamic contrast-enhanced MRI. Moreover, with whole-body MRI and DWI, metastatic disease can be evaluated in 1 session and may provide a way to monitor treatment. Therefore, when combining these various methods, a multiparametric data set can be built to assist in the detection, localization, assessment of prostate cancer aggressiveness, and tumor staging. Such a comprehensive approach offers more power to evaluate prostate disease than any single measure alone. In this article, we focus on the role of DWI/ADC and MRS in the detection and characterization using both in vivo and ex vivo imaging of prostate pathology. PMID:19512848

Jacobs, Michael A; Ouwerkerk, Ronald; Petrowski, Kyle; Macura, Katarzyna J

2008-12-01

171

Cation Diffusion Coefficients and Vacancy Densities in Mn-Zn Ferrites  

Microsoft Academic Search

Cation diffusion in Mn-Zn ferrites having excess iron was investigated by means of the isotope tracer method using single and polycrystalline samples. In polycrystalline samples ``volume diffusion'' and ``grain boundary diffusion'' were observed and separated from each other. The results are: (1) The volume diffusion coefficient of 59Fe varied with the oxygen content, i.e., the density of cation vacancies in

Seiya Ogawa; Yasuaki Nakagawa

1967-01-01

172

Low coefficient of thermal expansion polyimides containing metal ion additives  

NASA Technical Reports Server (NTRS)

Polyimides have become widely used as high performance polymers as a result of their excellent thermal stability and toughness. However, lowering their coefficient of thermal expansion (CTE) would increase their usefulness for aerospace and electronic applications where dimensional stability is a requirement. The incorporation of metal ion-containing additives into polyimides, resulting in significantly lowered CTE's, has been studied. Various metal ion additives have been added to both polyamic acid resins and soluble polyimide solutions in the concentration range of 4-23 weight percent. The incorporation of these metal ions has resulted in reductions in the CTE's of the control polyimides of 12 percent to over 100 percent depending on the choice of additive and its concentration.

Stoakley, D. M.; St. Clair, A. K.

1992-01-01

173

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

174

Assessment of diffusion coefficient of glycerol into the skin ex vivo  

NASA Astrophysics Data System (ADS)

In present study we have considered diffusion of immersion agent into the skin through thermally pretreated stratum corneum solving the corresponding diffusion problem. Algorithm of refractive index of interstitial liquid and diffusion coefficient of immersion agent into biotissue estimations at a creation of lattice-like pattern of localized thermal damage islets in the stratum corneum, was develop. Theoretical model which sufficiently describes the influence of immersion agents on skin optical properties was presented. The diffusion coefficient of glycerol into pig skin ex vivo at creating a lattice of islets of damage in the stratum corneum is 0.84+/-0.08 ?m2/s.

Gavrilova, Anna A.; Pravdin, Alexander B.; Tuchin, Valery V.; Altshuler, Gregory B.; Yaroslavsky, Ilya V.

2007-05-01

175

Diffusion coefficients of water and leachables in methacrylate-based crosslinked polymers using absorption experiments.  

PubMed

The diffusion of water into dentin adhesive polymers and leaching of unpolymerized monomer from the adhesive are linked to their mechanical softening and hydrolytic degradation. Therefore, diffusion coefficient data are critical for the mechanical design of these polymeric adhesives. In this study, diffusion coefficients of water and leachables were obtained for sixteen methacrylate-based crosslinked polymers using absorption experiments. The experimental mass change data was interpreted using numerical solution of the two-dimensional diffusion equations. The calculated diffusion coefficients varied from 1.05 × 10(-8) cm(2)/sec (co-monomer TMTMA) to 3.15 × 10(-8) cm(2)/sec (co-monomer T4EGDMA). Correlation of the diffusion coefficients with crosslink density and hydrophilicity showed an inverse trend (R(2) = 0.41). The correlation of diffusion coefficient with crosslink density and hydrophilicity are closer for molecules differing by simple repeat units (R(2) = 0.95). These differences in the trends reveal mechanisms of interaction of the diffusing water with the polymer structure. PMID:22430592

Parthasarathy, Ranganathan; Misra, Anil; Park, Jonggu; Ye, Qiang; Spencer, Paulette

2012-05-01

176

On the determinatino of high-pressure mass-diffusion coefficients for binary mixtures  

NASA Technical Reports Server (NTRS)

A model for high-pressure binary diffusion coefficient calculation is proposed based on considerations originating from recasting both the low pressure kinetic theory and the Stokes-Einstein infinite dilution expressions into forms consistent with corresponding states theory.

Bellan, J.; Harstad, K.

2003-01-01

177

A study of strontium diffusion in apatite using Rutherford backscattering spectroscopy and ion implantation  

SciTech Connect

Strontium diffusion in Durango fluorapatite has been measured under anhydrous conditions using a combination of techniques. Diffusants were introduced into the apatite by two methods: (1) ion implantation of Sr, and (2) immersion in a strontium oxide reservoir. Resulting diffusion profiles were measured by Rutherford Backscattering Spectrometry (RBS) and fit to the appropriate solutions of the diffusion equation to obtain diffusion coefficients. Previous determinations of Sr diffusion in apatite obtained under hydrous conditions (Farver and Giletti, 1989) indicate that a decrease in activation energy occurs at approximately 1000[degrees]C. In contrast, diffusivities obtained in the present work may be described by a simple Arrhenius relationship for diffusion perpendicular to c over the temperature range 700-1050[degrees]C. Similar results are obtained for transport parallel to c. As in the case of Pb diffusion in apatite (Cherniak et al., 1991), the results of the present study lie on the down-temperature extrapolation of diffusion coefficients determined under dry conditions at higher temperatures (Watson et al., 1985). Radiation damage induced by ion implantation may, in some cases, enhance or otherwise affect diffusion parameters. To assess the significance of such effects in apatite, the Sr results obtained by ion implantation were compared with those from a set of experiments in which Sr was introduced by immersion of the crystals in strontium oxide powder. Excellent agreement of diffusion coefficients from the two data sets indicates that radiation damage does not adversely affect these measurements of Sr diffusion in apatite made under anhydrous conditions. The measured diffusivities suggest that strontium isotope ratios in the cores of apatite crystals entrained in felsic magmas or residual to crustal anatexis may be unaffected by the strontium isotopic compositions of their surroundings for the temperatures and durations typical of these events.

Cherniak, D.J. (Rensselaer Polytechnic Institute, Troy, NY (United States)); Ryerson, F.J. (Lawrence Livermore Lab., CA (United States))

1993-10-01

178

Nitric oxide diffusion coefficients in solutions, proteins and membranes determined by phosphorescence.  

PubMed

The reactivity of nitric oxide under a given condition is a complex function of its diffusivity and the concentration of reacting partners. Quenching by NO of luminescence from Ru and Pd chelates of mesoporphyrin IX, two molecules which exhibit phosphorescence at room temperature, was utilized to evaluate the gas concentration and apparent diffusion coefficients. The properties of Ru-mesoporphyrin, a dye not previously employed as a probe for O2 or NO, were determined and the assay was verified and used to quantify NO produced by decomposition of nitrosocysteine. The pseudo-second order quenching constants were obtained from Stern-Volmer plots measured under various conditions and used to calculate diffusion coefficients for nitric oxide in solutions, proteins and membranes. The diffusion coefficients were greater at 37 than at 25 degrees C and, at a given temperature, smaller in proteins and membranes than in water. The conclusion is that NO and O2 closely resemble each other in diffusivity but that NO is slightly less lipophilic, resulting in somewhat faster apparent diffusion in protein and slower diffusivity in lipid, relative to O2. Taking a mean diffusion coefficient for NO of 10(-7) cm2s-1, then within 10 s the mean path is 10(-3) cm, or less than the diameter of a single cell. However, at low NO and O2 concentrations, the halflife of NO will be considerably longer than 10 s, and consequently the path of NO diffusion much greater. PMID:8075157

Vanderkooi, J M; Wright, W W; Erecinska, M

1994-08-17

179

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

180

Imaging cell size and permeability in biological tissue using the diffusion-time dependence of the apparent diffusion coefficient  

NASA Astrophysics Data System (ADS)

The purpose of this study was to analyze and evaluate a model of restricted water diffusion between equidistant permeable membranes for cell-size and permeability measurements in biological tissue. Based on the known probability distribution of diffusion distances after the diffusion time ? in a system of permeable membranes characterized by three parameters (membrane permeability P, membrane distance L, and free diffusivity D0), an equivalent dimensionless model was derived with a probability distribution characterized by only a single (dimensionless) tissue parameter \\tilde{P}. Evaluating this proposed model function, the dimensionless diffusion coefficient \\tilde{D}_{eff}(\\tilde{\\tau };\\,\\tilde{P}) was numerically calculated for 60 values of the dimensionless diffusion time \\tilde{\\tau } and 35 values of \\tilde{P}. Diffusion coefficients were measured in a carrot by diffusion-weighted magnetic resonance imaging (MRI) at 18 diffusion times between 9.9 and 1022.7 ms and fitted to the simulation results \\tilde{D}_{eff}(\\tilde{\\tau };\\,\\tilde{P}) to determine L, P, and D0. The measured diffusivities followed the simulated dependence of \\tilde{D}_{eff}(\\tilde{\\tau };\\tilde{P}). Determined cell sizes varied from 21 to 76 ?m, permeabilities from 0.007 to 0.039 ?m?1, and the free diffusivities from 1354 to 1713 ?m2?s?1. In conclusion, the proposed dimensionless tissue model can be used to determine tissue parameters (D0, L, P) based on diffusion MRI with multiple diffusion times. Measurements in a carrot showed a good agreement of the cell diameter, L, determined by diffusion MRI and by light microscopy.

Dietrich, Olaf; Hubert, Alexander; Heiland, Sabine

2014-06-01

181

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

182

Chemical diffusion coefficient measurements in pure and lithium doped cobaltous oxide  

Microsoft Academic Search

The chemical diffusion coefficient in pure and lithium doped cobaltous oxide has been deduced from electrical conductivity measurements performed during the equilibration of the gas-oxide system, in the temperature range 1000-1400° and for oxygen partial pressures higher than 10 atm.The results obtained for the pure Co1-?O single crystals show a small decrease of the values of the chemical diffusion coefficient

G. Petot-ervas; O. Radji; B. Sossa; P. Ochin

1983-01-01

183

Correlations for predicting air permeabilities and 222Rn diffusion coefficients of soils  

Microsoft Academic Search

The rate of 222Rn gas transport through earthen materials controls 222Rn releases to the atmosphere and to indoor environments. The key soil-related parameters characterizing 222Rn transport in earthen materials are the 222Rn diffusion coefficient and the soil air permeability. Simple correlations have been developed for predicting the 222Rn diffusion coefficient and the air permeability of soils based on fraction of

V. C. Rogers; K. K. Nielson

1991-01-01

184

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

Microsoft Academic Search

Vapour barrier membranes are often used as soil gas retarder in building construction. While vapour permeance characteristics\\u000a of these membranes are well known and specified in Canadian standards, their radon diffusion coefficients are yet not available.\\u000a This study provides test results of radon diffusion coefficients for 10 vapour barrier membranes commonly used in Canadian\\u000a building construction.

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

2009-01-01

185

Influence of binder composition and concrete pore structure on chloride diffusion coefficient in concrete  

Microsoft Academic Search

The influence of binder composition and pore structure of concrete on chloride diffusion coefficient in concrete were investigated\\u000a by the natural immersion test, MIP test, SEM and EDS test, respectively. The experimental results showed that the effect of\\u000a binder composition on chloride diffusion coefficient was the comprehensive result of concrete pore structure and binder hydration\\u000a products, and the porosity and

Pengping Li; Dagen Su; Shengnian Wang; Zhihong Fan

2011-01-01

186

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

Microsoft Academic Search

Interdiffusion coefficients in copper-rich copper-zinc solid solutions containing up to 8 at. pct of Zn at 1168 K have been\\u000a determined by Matano's analysis using semi-infinite diffusion couples consisting of pure copper and Cu-Zn alloys with Kirkendall\\u000a 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

Kazutomo Hoshino; Yoshiaki Iijima; Ken-Ichi Hirano

1982-01-01

187

Effect of gamma irradiation on the structural properties and diffusion coefficient in Co–Zn ferrite  

Microsoft Academic Search

A series of samples of Co1?xZnxFe2O4 were prepared by the usual ceramic technique where x=0.3,0.5,0.6, and 0.8. The samples were irradiated by Co60 gamma source with a high dose equal to 106rad\\/h. The diffusion coefficient of oxygen vacancies was estimated from DC conductivity measurements. It was noticed that the diffusion coefficient increased after gamma irradiation for all Zn2+ concentrations. This

O. M. Hemeda; M. El-Saadawy

2003-01-01

188

The measurement of precise solute diffusion coefficients in molten metals and semiconductors  

NASA Astrophysics Data System (ADS)

The measurement of precise solute diffusion coefficients in molten metals and semiconductors is of fundamental importance when studying and modeling metallurgical and crystal growth processes. Unfortunately, buoyancy-driven convection influences terrestrial experimentation so precise solute diffusion data cannot be generated without the use of a microgravity environment. In order to perform diffusion experiments in space, existing experimental techniques must be modified. The long capillary and the shear cell techniques have been adopted for our planned liquid diffusion experiments in microgravity conditions. Experimental parameters, such as the sample dimensions and diffusion time have been determined and are fully discussed in this report. The cast-coating technique for long capillary diffusion couple preparation has been refined. A modified shear cell has been developed, which can be used to measure the diffusion coefficient of the liquids with high vapor pressure and also provide for safe operation in a manned space vehicle. Comparative experiments have shown that buoyancy-driven convection exists in the liquid during ground-based diffusion experiments even when used in a vertical orientation in a small temperature gradient to reduce convection. It was found that the diffusion coefficients of antimony in lead obtained terrestrially are remarkably similar to the values obtained in space. This suggests that radial temperature gradients in the diffusion samples cause buoyancy-driven convection, which enhances solute transport and increases the measured diffusion coefficient value. However, if the density of the solute is significantly less than that of the solvent, then the radial-temperature-gradient-induced flow will be minimized. The significance of this effect may be gauged from the fact that, while the solute antimony gave 1 g results close to the microgravity values, it was present only in a small section of 1% alloy at the upper end of the diffusion couple at the start of the diffusion period.

Huang, Weidong

189

Diffusion Coefficients of SO2 in Water and Partition Coefficients of SO2 in Water-Air Interface at Different Temperature and pH Values  

Microsoft Academic Search

Reversed flow gas chromatography was applied to measure the diffusion coefficient of SO2 in water, the partition coefficient of SO2 in air–water interface, and the rate constant, kR, for chemical reaction between SO2 and water at various temperature and pH values. A linear increment of the diffusion coefficients of SO2 in water with temperature is drawn while the partition coefficients

A. Koliadima; J. Kapolos; L. Farmakis

2009-01-01

190

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

191

Comparison of diffusion coefficients obtained from ternary polymer solutions using dynamic light scattering and ultra centrifugation  

Microsoft Academic Search

Dynamic light scattering has been used to measure the interpenetration diffusion coeffient of ternary polymer solutions formed with 233 000 dalton polystyrene and a trace amount of 330 000 dalton PMMA dissolved in thiophenol. These measurements have been compared with the diffusion coefficients obtained from ultracentrifuge studies of the same solutions by observing the change in shape of the sedimentation

D. N. Pinder; T. Ueleni; J. A. Lewis

1996-01-01

192

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

193

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

194

An alternative model for estimating liquid diffusion coefficients requiring no viscosity data  

NASA Technical Reports Server (NTRS)

An equation, based on the free volume of a liquid solvent, was derived via dimensional analysis, to predict binary diffusion coefficients. The equation assumed that interaction between the solute and liquid solvent molecules followed a Lennard-Jones potential. The equation was compared to other diffusivity equations and was found to give good results over the temperature range examined.

Morales, Wilfredo

1993-01-01

195

Association of Early CT Abnormalities, Infarct Size, and Apparent Diffusion Coefficient Reduction in Acute Ischemic Stroke  

Microsoft Academic Search

BACKGROUND AND PURPOSE: Diffusion-weighted (DW) imaging is more sensitive for early ischemia than CT, and apparent diffusion coefficient (ADC) mapping permits quantification of the severity of cytotoxic edema. We examined the relationship between early CT findings, ischemic lesion volume on DW images, and edema subtype. METHODS: Patients in whom early signs of ischemia were detected on baseline CT scans were

Diederik M. Somford; Michael P. Marks; Vincent N. Thijs; David C. Tong

196

A theoretical approach to the measurement of radon diffusion and adsorption coefficients in radonproof membranes  

Microsoft Academic Search

Theoretical expressions for the determination of radon diffusion and adsorption coefficients in radonproof membranes using the standard method for testing the radon insulation effectiveness of a membrane tightly placed between two compartments are derived from the steady-state solution of the differential equation for radon diffusion. These expressions are applied to an experimental set-up designed specifically to carry out such a

Pedro L. Fernández; Luis S. Quindós; Carlos Sainz; José Gómez

2004-01-01

197

Measuring Oxygen, Carbon Monoxide and Hydrogen Sulfide Diffusion Coefficient and Solubility in Nafion Membranes  

Microsoft Academic Search

A Devanathan-Stachurski type diffusion cell made from a fuel cell assembly is designed to evaluate the gas transport properties of a proton exchange membrane as a function of cell temperature and gas pressure. Data obtained on this cell using the electrochemical monitoring technique (EMT) is used to estimate solubility and diffusion coefficient of oxygen (O2), carbon monoxide (CO) and hydrogen

Vijay A. Sethuraman; Saahir Khan; Jesse S. Jur; Andrew T. Haug; John W. Weidner

2011-01-01

198

Measuring oxygen, carbon monoxide and hydrogen sulfide diffusion coefficient and solubility in Nafion membranes  

Microsoft Academic Search

A Devanathan–Stachurski type diffusion cell made from a fuel cell assembly is designed to evaluate the gas transport properties of a proton exchange membrane as a function of cell temperature and gas pressure. Data obtained on this cell using the electrochemical monitoring technique (EMT) is used to estimate solubility and diffusion coefficient of oxygen (O2), carbon monoxide (CO) and hydrogen

Vijay A. Sethuraman; Saahir Khan; Jesse S. Jur; Andrew T. Haug; John W. Weidner

2009-01-01

199

Determination of Effective Diffusion Coefficients of Nitrogen in Extruded Polystyrene Foam by Gravimetric Sorption  

Microsoft Academic Search

A macrogravimctric sorption technique has been employed to obtain time-dependent weight gain data for thin-sliced closed-cell extruded polystyrene foam samples Effective diffusion thickness and diffusion time were used to compute a scaled age parameter The weighing apparatus operated in an isolated chamber filled with pure nitrogen gas The effective diffusion coefficient of the gas in the foam structure was computed

J. R. Booth; T. J. Holstein

1993-01-01

200

A first-principles methodology for diffusion coefficients in metals and dilute alloys  

Microsoft Academic Search

This work is a study exploring the extent of suitability of static first-principles calculations for studying diffusion in metallic systems. Specifically, vacancy-mediated volume diffusion in pure elements and alloys with dilute concentration of impurities is studied. A novel procedure is discovered for predicting diffusion coefficients that overcomes the shortcomings of the well-known transition state theory, by Vineyard. The procedure that

Manjeera Mantina

2008-01-01

201

Determination of methanol diffusion and electroosmotic drag coefficients in proton-exchange-membranes for DMFC  

NASA Astrophysics Data System (ADS)

Methanol diffusion and electroosmotic drag coefficients for different polymer-electrolyte-membranes have been investigated. It is essential to understand the transport phenomena of water and methanol transport in perfluoro sulfonic acid (PSA) membranes under different methanol concentrations and current densities in order to optimize cell performance and operation. The dependence of the methanol diffusion coefficient as well as the electroosmotic drag coefficient on methanol concentration and current density were observed. The results are discussed in comparison to measured values obtained by other scientific groups.

Schaffer, Thomas; Tschinder, Thomas; Hacker, Viktor; Besenhard, Jürgen O.

202

Fast Ion Diffusion by Driven Contained Modes  

NASA Astrophysics Data System (ADS)

Extremely high fast ion loss rates have been deduced from TFTR mode conversion experiments. While the distribution of losses in pitch angle, energy, and poloidal angle is in accurate agreement with accepted ideas of particle interaction with a MCIBW (such as quasilinear theory and ray-tracing), the magnitude of the losses was under-predicted by a factor of 30-70. A theory involving the excitation of a contained mode to high amplitude has been proposed to explain this enhanced loss. More detailed comparisons of the implications of this theory with the data base of TFTR MCIBW experiments reveal no evident discrepancies. The possibility of a contained mode inducing rapid fast ion diffusion in tokamaks is of more than academic interest; among other possibilities, it might enhance the prospects for alpha particle channeling in a future fusion reactor.

Clark, Daniel; Fisch, Nathaniel

1999-11-01

203

Temperature-Dependent Diffusion Coefficients from ab initio Computations: Hydrogen in Nickel  

SciTech Connect

The temperature-dependent mass diffusion coefficient is computed using transition state theory. Ab initio supercell phonon calculations of the entire system provide the attempt frequency, the activation enthalpy, and the activation entropy as a function of temperature. Effects due to thermal lattice expansion are included and found to be significant. Numerical results for the case of hydrogen in nickel demonstrate a strong temperature dependence of the migration enthalpy and entropy. Trapping in local minima along the diffusion path has a pronounced effect especially at low temperatures. The computed diffusion coefficients with and without trapping bracket the available experimental values over the entire temperature range between 0 and 1400 K.

E Wimmer; W Wolf; J Sticht; P Saxe; C Geller; R Najafabadi; G Young

2006-03-16

204

Temperature dependence of diffusion coefficient of nitrogen gas in water: A molecular dynamics study  

NASA Astrophysics Data System (ADS)

We have carried out the molecular dynamics (MD) simulation to study the structural properties and to estimate the diffusivity of molecular nitrogen (N2) gas (solute) in extended simple point charge model (SPC/E) water (solvent) with N2 mole fraction of 0.018 at different temperatures. For the structural properties of the system, we have determined radial distribution function (RDF). The solute-solute, solute-solvent and solvent-solvent RDF have been evaluated. Self-diffusion coefficient of N2 was estimated by evaluating mean-squared displacement (MSD) and velocity autocorrelation function (VACF) separately. The diffusion coefficients obtained from the two methods agree within 3%. The results are in agreement with the experimentally determined values within 10%. The self-diffusion coefficient of water (H2O) was also estimated by evaluating MSD. Mutual diffusion coefficient of the system have also been estimated invoking Darken's relation. The temperature dependance of the diffusion coefficients were found to follow Arrhenius relation.

Sharma, Keshav; Adhikari, Narayan P.

2014-04-01

205

Deconvolution of Compartmental Water Diffusion Coefficients in Yeast-Cell Suspensions Using Combined T1 and Diffusion Measurements  

Microsoft Academic Search

An NMR method is presented for measuring compartment-specific water diffusion coefficient (D) values. It uses relaxography, employing an extracellular contrast reagent (CR) to distinguish intracellular (IC) and extracellular (EC) 1H2O signals by differences in their respective longitudinal (T1) relaxation times. A diffusion-weighted inversion-recovery spin-echo (DW-IRSE) pulse sequence was used to acquire IR data sets with systematically and independently varying inversion

Matthew D. Silva; Karl G. Helmer; Jing-Huei Lee; Sam S. Han; Charles S. Springer; Christopher H. Sotak

2002-01-01

206

Deconvolution of Compartmental Water Diffusion Coefficients in Yeast-Cell Suspensions Using Combined T 1 and Diffusion Measurements  

Microsoft Academic Search

An NMR method is presented for measuring compartment-specific water diffusion coefficient (D) values. It uses relaxography, employing an extracellular contrast reagent (CR) to distinguish intracellular (IC) and extracellular (EC) 1H2O signals by differences in their respective longitudinal (T1) relaxation times. A diffusion-weighted inversion-recovery spin-echo (DW-IRSE) pulse sequence was used to acquire IR data sets with systematically and independently varying inversion

Matthew D. Silva; Karl G. Helmer; Jing-Huei Lee; Sam S. Han; Charles S. Springer; Christopher H. Sotak

2002-01-01

207

Effect of pore wall model on prediction of diffusion coefficients for graphitic slit pores.  

PubMed

The effect of the pore wall model on the self-diffusion coefficient and transport diffusivity predicted for methane in graphitic slit pores by equilibrium molecular dynamics (EMD) and non-equilibrium MD (NEMD) is investigated. Three pore wall models are compared--a structured wall and a smooth (specular) wall, both with a thermostat applied to the fluid to maintain the desired temperature, and a structured wall combined with the diffuse thermalizing scattering algorithm of MacElroy and Boyle (Chem. Eng. J., 1999, 74, 85). Pore sizes ranging between 7 and 35 angstroms and five pressures in the range of 1-40 bar are considered. The diffuse thermalizing wall yields incorrect self-diffusion coefficients and transport diffusivities for the graphitic slit pore model and should not be used. Surprisingly, the smooth specular wall gives self-diffusion coefficients inline with those obtained using the structured wall, indicating that this computationally much faster wall can be used for studying this phenomenon provided the fluid-wall interactions are somewhat weaker than the fluid-fluid interactions. The structured wall is required, however, if the transport diffusivity is of interest. PMID:18446252

Cai, Qiong; Biggs, Mark J; Seaton, Nigel A

2008-05-14

208

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

209

Measurement of Diffusion Coefficient of Liquids by Using an Asymmetric Liquid-Core Cylindrical Lens: Observing the Diffusion Process Directly  

NASA Astrophysics Data System (ADS)

We report a method for measuring diffusion coefficient D of liquids by using an aplanatic and asymmetric cylinder lens with a liquid core, which is designed as both a diffusion pool and the main imaging element. The precision is better than 10?4 RIU in measuring refractive index. The D values of ethylene glycol (EG) in water are measured for various EG concentrations at 25°C, and Dinf = 1.043 × 10?5 cm2/s under the condition of infinite dilution is obtained. The method is characterized by observing the diffusion process directly, faster measurement and obtaining the D value under the condition of infinite dilution.

Li, Qiang; Pu, Xiao-Yun; Yang, Rui-Fen; Zhai, Ying

2014-05-01

210

Experimental method development for estimating solid-phase diffusion coefficients and material/air partition coefficients of SVOCs  

NASA Astrophysics Data System (ADS)

The solid-phase diffusion coefficient (Dm) and material/air partition coefficient (Kma) are key parameters for characterizing the sources and transport of semivolatile organic compounds (SVOCs) in the indoor environment. In this work, a new experimental method was developed to estimate parameters Dm and Kma. The SVOCs chosen for study were polychlorinated biphenyl (PCB) congeners, including PCB-52, PCB-66, PCB-101, PCB-110, and PCB-118. The test materials included polypropylene, high density polyethylene, low density polyethylene, polytetrafluoroethylene, polyether ether ketone, glass, stainless steel and concrete. Two 53-L environmental chambers were connected in series, with the relatively stable SVOCs source in the source chamber and the test materials, made as small “buttons”, in the test chamber. Prior to loading the test chamber with the test materials, the test chamber had been dosed with SVOCs for 12 days to “coat” the chamber walls. During the tests, the material buttons were removed from the test chamber at different exposure times to determine the amount of SVOC absorbed by the buttons. SVOC concentrations at the inlet and outlet of the test chamber were also monitored. The data were used to estimate the partition and diffusion coefficients by fitting a sink model to the experimental data. The parameters obtained were employed to predict the accumulation of SVOCs in the sink materials using an existing mass transfer model. The model prediction agreed reasonably well with the experimental data.

Liu, Xiaoyu; Guo, Zhishi; Roache, Nancy F.

2014-06-01

211

Sublimation kinetics and diffusion coefficients of TNT, PETN, and RDX in air by thermogravimetry.  

PubMed

The diffusion coefficients of explosives are crucial in their trace detection and lifetime estimation. We report on the experimental values of diffusion coefficients of three of the most important explosives in both military and industry: TNT, PETN, and RDX. Thermogravimetric analysis (TGA) was used to determine the sublimation rates of TNT, PETN, and RDX powders in the form of cylindrical billets. The TGA was calibrated using ferrocene as a standard material of well-characterized sublimation rates and vapor pressures to determine the vapor pressures of TNT, PETN, and RDX. The determined sublimation rates and vapor pressures were used to indirectly determine the diffusion coefficients of TNT, PETN, and RDX for the first time. A linear log-log dependence of the diffusion coefficients on temperature is observed for the three materials. The diffusion coefficients of TNT, PETN, and RDX at 273 K were determined to be 5.76×10(-6)m(2)/sec, 4.94×10(-6)m(2)/s, and 5.89×10(-6)m(2)/s, respectively. Values are in excellent agreement with the theoretical values in literature. PMID:24840410

Hikal, Walid M; Weeks, Brandon L

2014-07-01

212

Theoretical evaluation of diffusion coefficients of (Al2O3)n clusters in different bath gases  

NASA Astrophysics Data System (ADS)

The binary diffusion coefficients of two low lying isomers of (Al2O3) n , n = 1...4, clusters in different bath gases, that most frequently met in the nature and in the technical applications: H2, N2, O2, CO, H2O as well as their self-diffusion coefficients have been calculated on the basis of kinetic theory and dipole reduced formalism. The parameters of interaction potential have been determined taking into account the contributions of a dispersion, dipole-dipole and dipole-induced dipole interactions between alumina clusters and bath molecules. The dipole moments, polarizabilities and collision diameters of clusters have been obtained by using quantum chemical calculations of cluster structure. The approximations for temperature dependencies of diffusion coefficients for two low-lying isomers of each considered alumina clusters are reported. It is demonstrated that an account for the contributions of the second for each type of clusters does not affect substantially the value of net diffusion coefficient. The diffusion coefficients of the isomers of small (Al2O3) n clusters can differ notably in the case when their dipole moments are distinct and they interact with strongly dipole molecules.

Sharipov, Alexander S.; Loukhovitski, Boris I.; Tsai, Chuen-Jinn; Starik, Alexander M.

2014-04-01

213

Mutual diffusion coefficients of heptane isomers in nitrogen: A molecular dynamics study  

NASA Astrophysics Data System (ADS)

The accurate knowledge of transport properties of pure and mixture fluids is essential for the design of various chemical and mechanical systems that include fluxes of mass, momentum, and energy. In this study we determine the mutual diffusion coefficients of mixtures composed of heptane isomers and nitrogen using molecular dynamics (MD) simulations with fully atomistic intermolecular potential parameters, in conjunction with the Green-Kubo formula. The computed results were compared with the values obtained using the Chapman-Enskog (C-E) equation with Lennard-Jones (LJ) potential parameters derived from the correlations of state values: MD simulations predict a maximum difference of 6% among isomers while the C-E equation presents that of 3% in the mutual diffusion coefficients in the temperature range 500-1000 K. The comparison of two approaches implies that the corresponding state principle can be applied to the models, which are only weakly affected by the anisotropy of the interaction potentials and the large uncertainty will be included in its application for complex polyatomic molecules.The MD simulations successfully address the pure effects of molecular structure among isomers on mutual diffusion coefficients by revealing that the differences of the total mutual diffusion coefficients for the six mixtures are caused mainly by heptane isomers. The cross interaction potential parameters, collision diameter ?12, and potential energy well depth ?12 of heptane isomers and nitrogen mixtures were also computed from the mutual diffusion coefficients.

Chae, Kyungchan; Violi, Angela

2011-01-01

214

Estimation of diffusion coefficients from voltammetric signals by support vector and gaussian process regression  

PubMed Central

Background Support vector regression (SVR) and Gaussian process regression (GPR) were used for the analysis of electroanalytical experimental data to estimate diffusion coefficients. Results For simulated cyclic voltammograms based on the EC, Eqr, and EqrC mechanisms these regression algorithms in combination with nonlinear kernel/covariance functions yielded diffusion coefficients with higher accuracy as compared to the standard approach of calculating diffusion coefficients relying on the Nicholson-Shain equation. The level of accuracy achieved by SVR and GPR is virtually independent of the rate constants governing the respective reaction steps. Further, the reduction of high-dimensional voltammetric signals by manual selection of typical voltammetric peak features decreased the performance of both regression algorithms compared to a reduction by downsampling or principal component analysis. After training on simulated data sets, diffusion coefficients were estimated by the regression algorithms for experimental data comprising voltammetric signals for three organometallic complexes. Conclusions Estimated diffusion coefficients closely matched the values determined by the parameter fitting method, but reduced the required computational time considerably for one of the reaction mechanisms. The automated processing of voltammograms according to the regression algorithms yields better results than the conventional analysis of peak-related data.

2014-01-01

215

Radon diffusion coefficients in 360 waterproof materials of different chemical composition.  

PubMed

This paper summarises the results of radon diffusion coefficient measurements in 360 common waterproof materials available throughout Europe. The materials were grouped into 26 categories according to their chemical composition. It was found that the diffusion coefficients of materials used for protecting houses against radon vary within eight orders from 10(-15) to 10(-8) m(2) s(-1). The lowest values were obtained for bitumen membranes with an Al carrier film and for ethylene vinyl acetate membranes. The highest radon diffusion coefficient values were discovered for sodium bentonite membranes, rubber membranes made of ethylene propylene diene monomer and polymer cement coatings. The radon diffusion coefficients for waterproofings widely used for protecting houses, i.e. flexible polyvinyl chloride, high-, low-density polyethylene, polypropylene and bitumen membranes, vary in the range from 3 × 10(-12) to 3 × 10(-11) m(2) s(-1). Tests were performed which confirmed that the radon diffusion coefficient is also an effective tool for verifying the air-tightness of joints. PMID:21450700

Jiránek, M; Kotrbatá, M

2011-05-01

216

A first-principles methodology for diffusion coefficients in metals and dilute alloys  

NASA Astrophysics Data System (ADS)

This work is a study exploring the extent of suitability of static first-principles calculations for studying diffusion in metallic systems. Specifically, vacancy-mediated volume diffusion in pure elements and alloys with dilute concentration of impurities is studied. A novel procedure is discovered for predicting diffusion coefficients that overcomes the shortcomings of the well-known transition state theory, by Vineyard. The procedure that evolves from Eyring's reaction rate theory yields accurate diffusivity results that include anharmonic effects within the quasi-harmonic approximation. Alongside, the procedure is straightforward in its application within the conventional harmonic approximation, from the results of static first-principles calculations. To prove the extensibility of the procedure, diffusivities have been computed for a variety of systems. Over a wide temperature range, the calculated self-diffusion and impurity diffusion coefficients using local density approximation (LDA) of density functional theory (DFT) are seen to be in excellent match with experimental data. Self-diffusion coefficients have been calculated for: (i) fcc Al, Cu, Ni and Ag (ii) bcc W and Mo (v) hcp Mg, Ti and Zn. Impurity diffusion coefficients have been computed for: (i) Mg, Si, Cu, Li, Ag, Mo and 3d transition elements in fcc Al (ii) Mo, Ta in bcc W and Nb, Ta and W in bcc Mo (iii) Sn and Cd in hcp Mg and Al in hcp Ti. It is also an observation from this work, that LDA does not require surface correction for yielding energetics of vacancy-containing system in good comparison with experiments, unlike generalized gradient approximation (GGA). It is known that first-principles' energy minimization procedures based on electronic interactions are suited for metallic systems wherein the valence electrons are freely moving. In this thesis, research has been extended to study suitability of first-principles calculations within LDA/GGA including the localization parameter U, for Al system with transition metal solutes, in which charges are known to localize around the transition metal element. U parameter is determined from matching the diffusivities of 3d transition metal impurity in aluminum with reliable experimental data. The effort yielded activation energies in systematic agreement with experiments and has proved useful in obtaining insights into the complex interactions in these systems. Besides the prediction of diffusion coefficients, this research has been helpful in understanding the physics underlying diffusion. Within the scope of observations from the systems studied, certain diffusion related aspects that have been clarified are: (i) cause for non-Arrnenius' nature of diffusion plots (ii) definitions of atom migration properties (iii) magnitude and sign of diffusion parameters enthalpy and entropy of formation and migration and characteristic vibrational frequency (iv) trends in diffusivities based on activation energy and diffusion prefactor (vi) cause for anomalous diffusion behavior of 3d transition metals in Al, and their magnetic nature (vii) contributions from electronic contributions to curvature at very high temperatures of bcc refractory elements (viii) temperature dependence of impurity diffusion correlation factors. Finally, the double-well potential of diffusion by vacancy mechanism has been calculated from first-principles. This aided calculation of entropy of migration and thus free energy of migration along with characteristic vibrational frequency. Also for the first time, temperature dependence of enthalpy of migration and thus atom jump frequency has been accurately predicted. From the broad perspective of predicting diffusion coefficients from computational methodologies, it can be stated as a result of this work that: static first-principles extend an irreplaceable contribution to the future of diffusion modeling. The procedure obviated the use of (i) redundant approximations that limit its accuracy and (ii) support from other computational techniques that restrict its extensibility due to insufficient i

Mantina, Manjeera

217

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

PubMed

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) m(2) s(-1) to 1.27 × 10(-7) m(2) 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. PMID:23020372

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

2012-09-01

218

A multiscale approach to ion diffusion in clays: building a two-state diffusion-reaction scheme from microscopic dynamics.  

PubMed

The mobility of particles is generally lowered by the presence of a confining medium, both because of geometrical effects, and because of the interactions with the confining surfaces, especially when the latter are charged. The water/mineral interface plays a central role in the dynamics of ions. The ionic mobility in clays is often understood as an interplay between the diffusion of mobile ions and their possible trapping at the mineral surfaces. We describe how to build a two-state diffusion-reaction scheme from the microscopic dynamics of ions, controlled by their interaction with a mineral surface. The starting point is an atomic description of the clay interlayer using molecular simulations. These provide a complete description of the ionic dynamics on short time and length scales. Using the results of these simulations, we then build a robust mesoscopic (Fokker-Planck) description. In turn, this mesoscopic description is used to determine the mobility of the ions in the interlayer. These results can then be cast into a diffusion-reaction scheme, introducing in particular the fraction of mobile ions, or equivalently the distribution coefficient Kd. This coefficient is of great importance in characterizing electrokinetic phenomena in porous materials. PMID:17349652

Rotenberg, Benjamin; Marry, Virginie; Dufrêche, Jean-François; Giffaut, Eric; Turq, Pierre

2007-05-15

219

Combined measurement of surface, grain boundary and lattice diffusion coefficients on olivine bi-crystals  

NASA Astrophysics Data System (ADS)

Diffusion along interface and grain boundaries provides an efficient pathway and may control chemical transport in rocks as well as their mechanical strength. Besides the significant relevance of these diffusion processes for various geologic processes, experimental data are still very limited (e.g., Dohmen & Milke, 2010). Most of these data were measured using polycrystalline materials and the formalism of LeClaire (1951) to fit integrated concentration depth profiles. To correctly apply this formalism, certain boundary conditions of the diffusion problem need to be fulfilled, e.g., surface diffusion is ignored, and furthermore the lattice diffusion coefficient has to be known from other studies or is an additional fitting parameter, which produces some ambiguity in the derived grain boundary diffusion coefficients. We developed an experimental setup where we can measure the lattice and grain boundary diffusion coefficients simultaneously but independent and demonstrate the relevance of surface diffusion for typical grain boundary diffusion experiments. We performed Mg2SiO4 bicrystal diffusion experiments, where a single grain boundary is covered by a thin-film of pure Ni2SiO4 acting as diffusant source, produced by pulsed laser deposition. The investigated grain boundary is a 60° (011)/[100]. This specific grain boundary configuration was modeled using molecular dynamics for comparison with the experimental observations in the transmission electron microscope (TEM). Both, experiment and model are in good agreement regarding the misorientation, whereas there are still some disagreements regarding the strain fields along the grain boundary that are of outmost importance for the strengths of the material. The subsequent diffusion experiments were carried out in the temperature range between 800° and 1450° C. The inter diffusion profiles were measured using the TEMs energy dispersive x-ray spectrometer standardized using the Cliff-Lorimer equation and EMPA measurements. To evaluate the obtained diffusion profiles we adapted the isolated grain boundary model, first proposed by Fisher (1951) to match several observations: (i) Anisotropic diffusion in forsterite, (ii) fast diffusion along the grain boundary, (iii) fast diffusion on the surface of the sample. The latter process is needed to explain an additional flux of material from the surface into the grain boundary. Surface and grain boundary diffusion coefficients are on the order of 10000 times faster than diffusion in the lattice. Another observation was that in some regions the diffusion profiles in the lattice were greatly extended. TEM observations suggest here that surface defects (nano-cracks, ect.) have been present, which apparently enhanced the diffusion through the bulk lattice. Dohmen, R., & Milke, R. (2010). Diffusion in Polycrystalline Materials: Grain Boundaries, Mathematical Models, and Experimental Data. Reviews in Mineralogy and Geochemistry, 72(1), 921-970. Fisher, J. C. (1951). Calculations of Diffusion Penetration Curves for Surface and Grain Boundary Diffusion. Journal of Applied Physics, 22(1), 74-77. Le Claire, A. D. (1951). Grain boundary diffusion in metals. Philosophical Magazine A, 42(328), 468-474.

Marquardt, Katharina; Dohmen, Ralf; Wagner, Johannes

2014-05-01

220

Moisture loss from wood products during drying. Part 1: Moisture diffusivities and moisture transfer coefficients  

SciTech Connect

This study deals with the development of an analytical technique for determining the moisture diffusivities and moisture transfer coefficients for wood products subjected to drying. The wood products are idealized in the modeling as either infinite plates or long cylinders. The analysis of transient moisture diffusion is carried out on the basis of two important practical criteria: 0.1 < Bi < 100 and Bi> 100 where Bi = Biot number. The drying coefficients and lag factors were incorporated into the models. The developed analytical models are then verified by experimental measurements taken from the literature. Results show that the method presented here is capable of accurately determining the moisture diffusivities and moisture transfer coefficients for such objects. The models can be used for a variety of wood-drying applications.

Dincer, I. [Tubitak-Marmara Research Center, Gebze (Turkey)

1998-01-01

221

Crack diffusion coefficient - A candidate fracture toughness parameter for short fiber composites  

NASA Technical Reports Server (NTRS)

In brittle matrix composites, crack propagation occurs along random trajectories reflecting the heterogeneous nature of the strength field. Considering the crack trajectory as a diffusive process, the 'crack diffusion coefficient' is introduced. From fatigue crack propagation experiments on a set of identical SEN polyester composite specimens, the variance of the crack tip position along the loading axis is found to be a linear function of the effective 'time'. The latter is taken as the effective crack length. The coefficient of proportionality between variance of the crack trajectory and the effective crack length defines the crack diffusion coefficient D which is found in the present study to be 0.165 mm. This parameter reflects the ability of the composite to deviate the crack from the energetically most efficient path and thus links fracture toughness to the microstructure.

Mull, M. A.; Chudnovsky, A.; Moet, A.

1987-01-01

222

Diffusion coefficient of CO(2) molecules as determined by (13)C NMR in various carbonated beverages.  

PubMed

In this paper, the NMR technique was used, for the first time, to accurately determine the diffusion coefficient D of CO(2)-dissolved molecules in various carbonated beverages, including champagne and sparkling wines. This parameter plays an important role concerning the bubble growth during its rise through the liquid (see ref 3). The diffusion coefficient of CO(2)-dissolved molecules D was compared with that deduced from the well-known Stokes-Einstein equation and found to significantly deviate from the general trend expected from Stokes-Einstein theory, i.e, D(SE) proportional, variant 1/eta, where D(SE) is the Stokes-Einstein diffusion coefficient and eta the viscosity of the liquid medium. PMID:14664507

Liger-Belair, Gerard; Prost, Elise; Parmentier, Maryline; Jeandet, Philippe; Nuzillard, Jean-Marc

2003-12-17

223

Diffusion and Coulomb separation of ions in dense matter.  

PubMed

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. PMID:24182248

Beznogov, M V; Yakovlev, D G

2013-10-18

224

Approximating high angular resolution apparent diffusion coefficient profiles using spherical harmonics under BiGaussian assumption  

NASA Astrophysics Data System (ADS)

Magnetic Resonance Imaging (MRI) techniques have achieved much importance in providing visual and quantitative information of human body. Diffusion MRI is the only non-invasive tool to obtain information of the neural fiber networks of the human brain. The traditional Diffusion Tensor Imaging (DTI) is only capable of characterizing Gaussian diffusion. High Angular Resolution Diffusion Imaging (HARDI) extends its ability to model more complex diffusion processes. Spherical harmonic series truncated to a certain degree is used in recent studies to describe the measured non-Gaussian Apparent Diffusion Coefficient (ADC) profile. In this study, we use the sampling theorem on band-limited spherical harmonics to choose a suitable degree to truncate the spherical harmonic series in the sense of Signal-to-Noise Ratio (SNR), and use Monte Carlo integration to compute the spherical harmonic transform of human brain data obtained from icosahedral schema.

Cao, Ning; Liang, Xuwei; Zhuang, Qi; Zhang, Jun

2009-02-01

225

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, Yuri V.

1994-10-01

226

Influence of crystal orientation and ion bombardment on the nitrogen diffusivity in single-crystalline austenitic stainless steel  

NASA Astrophysics Data System (ADS)

The nitrogen diffusivity in single-crystalline AISI 316L austenitic stainless steel (ASS) during ion nitriding has been investigated at different crystal orientations ((001), (110), (111)) under variations of ion flux (0.3-0.7 mA cm-2), ion energy (0.5-1.2 keV), and temperature (370-430 °C). The nitrogen depth profiles obtained from nuclear reaction analysis are in excellent agreement with fits using the model of diffusion under the influence of traps, from which diffusion coefficients were extracted. At fixed ion energy and flux, the diffusivity varies by a factor up to 2.5 at different crystal orientations. At (100) orientation, it increases linearly with increasing ion flux or energy. The findings are discussed on the basis of atomistic mechanisms of interstitial diffusion, potential lattice distortions, local decomposition, and ion-induced lattice vibrational excitations.

Martinavi?ius, A.; Abrasonis, G.; Möller, W.

2011-10-01

227

Influence of crystal orientation and ion bombardment on the nitrogen diffusivity in single-crystalline austenitic stainless steel  

SciTech Connect

The nitrogen diffusivity in single-crystalline AISI 316L austenitic stainless steel (ASS) during ion nitriding has been investigated at different crystal orientations ((001), (110), (111)) under variations of ion flux (0.3-0.7 mA cm{sup -2}), ion energy (0.5-1.2 keV), and temperature (370-430 deg. C). The nitrogen depth profiles obtained from nuclear reaction analysis are in excellent agreement with fits using the model of diffusion under the influence of traps, from which diffusion coefficients were extracted. At fixed ion energy and flux, the diffusivity varies by a factor up to 2.5 at different crystal orientations. At (100) orientation, it increases linearly with increasing ion flux or energy. The findings are discussed on the basis of atomistic mechanisms of interstitial diffusion, potential lattice distortions, local decomposition, and ion-induced lattice vibrational excitations.

Martinavicius, A.; Abrasonis, G.; Moeller, W. [Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf (HZDR), P.O. Box 510119, Dresden 01314 (Germany)

2011-10-01

228

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

2013-07-25

229

LETTER TO THE EDITOR: Fractal diffusion coefficient from dynamical zeta functions  

NASA Astrophysics Data System (ADS)

Dynamical zeta functions provide a powerful method to analyse low-dimensional dynamical systems when the underlying symbolic dynamics is under control. On the other hand, even simple one-dimensional maps can show an intricate structure of the grammar rules that may lead to a non-smooth dependence of global observables on parameters changes. A paradigmatic example is the fractal diffusion coefficient arising in a simple piecewise linear one-dimensional map of the real line. Using the Baladi-Ruelle generalization of the Milnor-Thurnston kneading determinant, we provide the exact dynamical zeta function for such a map and compute the diffusion coefficient from its smallest zero.

Cristadoro, Giampaolo

2006-03-01

230

Density scaling of the diffusion coefficient at various pressures in viscous liquids.  

PubMed

Fundamental thermodynamics and an earlier elastic solid-state point defect model [P. Varotsos and K. Alexopoulos, Phys. Rev. B 15, 4111 (1977); Phys. Rev. B 18, 2683 (1978)] are employed to formulate an analytical second-order polynomial function describing the density scaling of the diffusion coefficient in viscous liquids. The function parameters are merely determined by the scaling exponent, which is directly connected with the Grüneisen constant. Density scaling diffusion coefficient isotherms obtained at different pressures collapse on a unique master curve, in agreement with recent computer simulation results of Lennard-Jones viscous liquids [D. Coslovich and C. M. Roland, J. Phys. Chem. 112, 1329 (2008)]. PMID:19391997

Papathanassiou, A N

2009-03-01

231

1st International comparison measurement on assessing the diffusion coefficient of radon.  

PubMed

Radon diffusion coefficient is a material parameter which is usually used in the radon mitigation measures design. There are different approaches used for radon diffusion coefficient measurement and assessment. The International comparison measurement which was jointly organised by National Radiation Protection Institute and Faculty of Civil Engineering CTU Prague in 2009 and 2010 has registered 11 laboratories from all over the world. Three sets of samples of polyethylene damp-proof membranes were sent to these laboratories for measurement. Till today, the organisers received only five sets of results. The results showed a great variability among laboratories involved. PMID:21471130

Rovenska, Katerina; Jiránek, Martin

2011-05-01

232

Density scaling of the diffusion coefficient at various pressures in viscous liquids  

NASA Astrophysics Data System (ADS)

Fundamental thermodynamics and an earlier elastic solid-state point defect model [P. Varotsos and K. Alexopoulos, Phys. Rev. B 15, 4111 (1977); Phys. Rev. B 18, 2683 (1978)] are employed to formulate an analytical second-order polynomial function describing the density scaling of the diffusion coefficient in viscous liquids. The function parameters are merely determined by the scaling exponent, which is directly connected with the Grüneisen constant. Density scaling diffusion coefficient isotherms obtained at different pressures collapse on a unique master curve, in agreement with recent computer simulation results of Lennard-Jones viscous liquids [D. Coslovich and C. M. Roland, J. Phys. Chem. 112, 1329 (2008)].

Papathanassiou, A. N.

2009-03-01

233

Determination of diffusion coefficients in polypyrrole thin films using a current pulse relaxation method  

NASA Technical Reports Server (NTRS)

The current pulse E sub oc relaxation method and its application to the determination of diffusion coefficients in electrochemically synthesized polypyrrole thin films is described. Diffusion coefficients for such films in Et4NBF4 and MeCN are determined for a series of submicron film thicknesses. Measurement of the double-layer capacitance, C sub dl, and the resistance, R sub u, of polypyrrole thin films as a function of potential obtained with the galvanostatic pulse method is reported. Measurements of the electrolyte concentration in reduced polypyrrole films are also presented to aid in the interpretation of the data.

Penner, Reginald M.; Vandyke, Leon S.; Martin, Charles R.

1987-01-01

234

Minority carrier diffusion lengths and absorption coefficients in silicon sheet material  

SciTech Connect

One of the indicators which determine a material's potential for use as a solar cell is the minority carrier diffusion length (L/sub D/) of the material. To determine L/sub D/ a surface photovoltage (SPV) technique is used. This method is dependent upon an accurate knowledge of the optical absorption coefficient as function of wavelength. The results for the absorption coefficients for various types of silicon sheet material are compared to those previously used in the two models. The resultant effect upon the diffusion length is also discussed in detail. 7 refs.

Dumas, K.A.; Swimm, R.T.

1980-01-01

235

Effect of particle-hole symmetry on the behavior of tracer and jump diffusion coefficients.  

PubMed

This paper analyzes the effect of particle-hole symmetry on the behavior of the tracer diffusion coefficient as well as the jump diffusion coefficient. The coefficients are obtained by performing a random walk of individual atoms in a two-dimensional square lattice at monolayer, using the n-fold way Monte Carlo simulation. Different hopping mechanisms have been introduced to study the effect of particle-hole symmetry. For hopping kinetics where the initial-state interactions are involved, the diffusion coefficient at high coverage falls several orders of magnitude due to the effect of particle-hole symmetry. For hopping kinetics where the final-state interactions are present, the effect is the opposite. For those involving both initial- and final-state interactions, like the so-called interaction kinetics, the effect of particle-hole symmetry is also discussed. This effect seems to be critical for repulsive lateral interactions, for which the behavior of the diffusion coefficients is modified by introducing the particle-hole symmetry condition. PMID:23767481

Torrez Herrera, J J; Ranzuglia, G A; Manzi, S J; Pereyra, V D

2013-05-01

236

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

237

Determining diffusion coefficients of ionic liquids by means of field cycling nuclear magnetic resonance relaxometry.  

PubMed

Field Cycling Nuclear Magnetic Resonance (FC NMR) relaxation studies are reported for three ionic liquids: 1-ethyl-3- methylimidazolium thiocyanate (EMIM-SCN, 220-258 K), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4, 243-318 K), and 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6, 258-323 K). The dispersion of (1)H spin-lattice relaxation rate R1(?) is measured in the frequency range of 10 kHz-20 MHz, and the studies are complemented by (19)F spin-lattice relaxation measurements on BMIM-PF6 in the corresponding frequency range. From the (1)H relaxation results self-diffusion coefficients for the cation in EMIM-SCN, BMIM-BF4, and BMIM-PF6 are determined. This is done by performing an analysis considering all relevant intra- and intermolecular relaxation contributions to the (1)H spin-lattice relaxation as well as by benefiting from the universal low-frequency dispersion law characteristic of Fickian diffusion which yields, at low frequencies, a linear dependence of R1 on square root of frequency. From the (19)F relaxation both anion and cation diffusion coefficients are determined for BMIM-PF6. The diffusion coefficients obtained from FC NMR relaxometry are in good agreement with results reported from pulsed- field-gradient NMR. This shows that NMR relaxometry can be considered as an alternative route of determining diffusion coefficients of both cations and anions in ionic liquids. PMID:24985656

Kruk, D; Meier, R; Rachocki, A; Korpa?a, A; Singh, R K; Rössler, E A

2014-06-28

238

Estimation of cell membrane permeability and intracellular diffusion coefficient of human gray matter.  

PubMed

The signal intensity of diffusion-weighted imaging (DWI) is sensitive to the intra- and extracellular diffusion coefficient of water and cell membrane permeability. We applied a method we proposed in previous papers to estimate noninvasively the membrane permeability and intracellular diffusion coefficient of normal human brain (gray matter) in 3 normal volunteers. We theoretically compared predicted signals and experiment results using a 1.5-tesla magnetic resonance (MR) imaging system. We acquired images using an echo planar imaging (EPI) sequence, applying motion-probing gradient (MPG) pulses in 3 directions. We periodically performed numerical simulations for various combinations of membrane permeability and intracellular diffusion coefficients using the finite-difference method. By minimizing the difference between signals obtained experimentally and those from numerical simulation, we could estimate membrane permeability (76+/-9 mm2/s mum) and intracellular diffusion coefficient (1.0+/-0.0 mm2/s) for the human brain. The estimated membrane permeability was the criterion value for diagnosing disease in gray matter. PMID:19336983

Imae, Toshikazu; Shinohara, Hiroyuki; Sekino, Masaki; Ueno, Shoogo; Ohsaki, Hiroyuki; Mima, Kazuo; Ohtomo, Kuni

2009-01-01

239

A numerical method for determination of moisture transfer coefficient according to the diffusion moisture profiles  

Microsoft Academic Search

For a set of the measured diffusion moisture profiles, a numerical method for determination of moisture transfer coefficient\\u000a D(w, t) is suggested. The transfer coefficient is found as a sum of the degree $$\\u000ap_0 w^{p(t)} \\u000a$$ and exponential $$\\u000aAe^{\\\\mu (w - v_0 )} \\u000a$$ functions of the moisture concentration w, as opposite to the previous works. The exponent

E. Pavlusová; M. Pavlus; I. Sarhadov; I. V. Amirkhanov; T. P. Puzynina; I. V. Puzynin

2008-01-01

240

Non-Fermi liquid behavior of the drag and diffusion coefficients in QED plasma  

SciTech Connect

We calculate the drag and diffusion coefficients in low temperature QED plasma and go beyond the leading order approximation. The non-Fermi-liquid behavior of these coefficients are clearly revealed. We observe that the subleading contributions due to the exchange of soft transverse photon in both cases are larger than the leading order terms coming from the longitudinal sector. The results are presented in closed form at zero and low temperature.

Sarkar, Sreemoyee; Dutt-Mazumder, Abhee K. [High Energy Nuclear and Particle Physics Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata-700 064 (India)

2011-11-01

241

In-reactor experiment and the tritium diffusion coefficient in molten lithium–tin alloy  

Microsoft Academic Search

The measurement of the tritium diffusion coefficient in molten Li20Sn80 alloy was carried out using an in-reactor tritium release experiment. The analysis of the measurements is based on a diffusion-controlled steady state model. When the hydrogen partial pressure was higher than 1100 Pa in the purge gas, and the temperature was 873 K or higher, it satisfied the requirements of

Y. Kang; Takayuki Terai

2004-01-01

242

Characterisation of the gas transport properties of porous materials by determining the radon diffusion coefficient  

Microsoft Academic Search

A method for the determination of the diffusion coefficient of materials by using the radioactive gas radon is presented.\\u000a This gas is inert and extremely low concentrations can be detected because of the radioactive decay. The method was applied\\u000a to mortars and concretes in order to optimise their composition with respect to a low radon diffusion rate. These optimised\\u000a materials

T. Klink; K. Gaber; E. Schlattner; M. J. Setzer

1999-01-01

243

Self-Diffusion Coefficient of fcc Mg: First-Principles Calculations and SemiEmpirical Predictions  

Microsoft Academic Search

First-principles calculations and semi-empirical equations are employed to determine the self-diffusion mobility of fcc Mg.\\u000a All factors entering the vacancy-mediated self-diffusion coefficient, which include the equilibrium lattice parameter, the\\u000a enthalpy of vacancy formation and atom migration, and the vibrational entropy of vacancy formation as well as the effective\\u000a frequency, are evaluated with the local density approximation (LDA) and generalized gradient

Dongdong Zhao; Yi Kong; Aijun Wang; Liangcai Zhou; Senlin Cui; Xiaoming Yuan; Lijun Zhang; Yong Du

2011-01-01

244

Measurement of the ferric diffusion coefficient in agarose and gelatine gels by utilization of the evolution of a radiation induced edge as reflected in relaxation rate images  

NASA Astrophysics Data System (ADS)

A method has been developed to determine the diffusion coefficients of ferric ions in ferrous sulphate doped gels. A radiation induced edge was created in the gel, and two spin-echo sequences were used to acquire a pair of images of the gel at different points of time. For each of these image pairs, a longitudinal relaxation rate image was derived. From profiles through these images, the standard deviations of the Gaussian functions that characterize diffusion were determined. These data provided the basis for the determination of the ferric diffusion coefficients by two different methods. Simulations indicate that the use of single spin-echo images in this procedure may in some cases lead to a significant underestimation of the diffusion coefficient. The technique was applied to different agarose and gelatine gels that were prepared, irradiated and imaged simultaneously. The results indicate that the diffusion coefficient is lower in a gelatine gel than in an agarose gel. Addition of xylenol orange to a gelatine gel lowers the diffusion coefficient from 1.45 to , at the cost of significantly lower sensitivity. The addition of benzoic acid to the latter gel did not increase the sensitivity.

Pedersen, Torje V.; Olsen, Dag R.; Skretting, Arne

1997-08-01

245

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

246

Semiconductor surface diffusion: Effects of low-energy ion bombardment  

SciTech Connect

We offer a revised mechanism to describe our previous measurements of surface diffusion under low-energy ion bombardment in the Ge/Si(111) system. We show that direct ion-induced motion of diffusing atoms (the effect commonly cited as important in ion beam assisted deposition) cannot account for these observations. Instead, we rationalize the results through processes in which ions create long-lived surface vacancies or spatially extended defects that heal continuously during bombardment. These ideas rationalize several important aspects of the experimental data that were previously unexplained, including the appearance of ion effects at very low ion fluxes, the simple Arrhenius behavior of the diffusivity, the rough magnitudes of the observed energy thresholds, and the ion-induced inhibition of diffusion at high temperatures.

Ditchfield, R.; Seebauer, E. G.

2001-03-15

247

Diffusion coefficient, correlation function, and power spectral density of velocity fluctuations in monolayer graphene  

NASA Astrophysics Data System (ADS)

In this paper, the diffusivity in suspended monolayer graphene at low and high electric fields is investigated. The knowledge of this quantity and its dependence on the electric field is of primary importance not only for the investigation of the electronic transport properties of this material but also for the development of accurate drift-diffusion models. The results have been obtained by means of an ensemble Monte Carlo simulation. For the calculation of the diffusion coefficient, two different methods are considered, one based on the second central moment and the other one based on the Fourier analysis of velocity fluctuations, which are directly related to the noise behaviour at high frequencies. The diffusion coefficient is analyzed considering both parallel and transversal directions with regard to the applied field. Taking into account the importance of degeneracy in this material, the calculations are properly performed by considering an excess electron population obeying a linearized Boltzmann transport equation, which allows studying in an adequate fashion the diffusivity phenomena. The results show the importance of degeneracy effects at very low fields in which transport is mainly dominated by acoustic phonon scattering. Values of the diffusion coefficient larger than 40 000 cm2/Vs are obtained for a carrier concentration equal to 1012 cm-2. The correlation function of instantaneous velocity fluctuation is explained in terms of the wavevector distribution, and their power spectral density is evaluated in the THz range, showing an important dependence on the applied field and being strongly related to microscopic transport processes.

Rengel, R.; Martín, M. J.

2013-10-01

248

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

249

Diffusion mechanism of chloride ions in sodium montmorillonite  

Microsoft Academic Search

For safety assessment of geological disposal of HLW, it is necessary to understand the diffusion mechanism of radionuclides in compacted bentonite. In this study, the diffusion behavior of chloride ions in compacted montmorillonite was studied from the viewpoints of the activation energy for apparent diffusion and the basal spacing of the compacted montmorillonite. A unique change in the activation energy

Tamotsu Kozaki; Koichi Inada; Seichi Sato; Hiroshi Ohashi

2001-01-01

250

Diffusion-weighted imaging in the prostate: an apparent diffusion coefficient comparison of half-Fourier acquisition single-shot turbo spin-echo and echo planar imaging  

Microsoft Academic Search

Prostate cancer detection using diffusion-weighted imaging is highly affected by the accuracy of the apparent diffusion coefficient (ADC) values in an image. Echo planar imaging (EPI) is a fast sequence commonly used for diffusion imaging but has inherent magnetic susceptibility and chemical shift artefacts associated. A diffusion sequence that is less affected by these artefacts is therefore advantageous. The half-Fourier

Ben Babourina-Brooks; Gary J. Cowin; Deming Wang

251

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

252

Measurement and modeling of CO2 diffusion coefficient in Saline Aquifer at reservoir conditions  

NASA Astrophysics Data System (ADS)

Storage of CO2 in deep saline aquifers is a promising techniques to mitigate global warming and reduce greenhouse gases (GHG). Correct measurement of diffusivity is essential for predicting rate of transfer and cumulative amount of trapped gas. Little information is available on diffusion of GHG in saline aquifers. In this study, diffusivity of CO2 into a saline aquifer taken from oil field was measured and modeled. Equilibrium concentration of CO2 at gas-liquid interface was determined using Henry's law. Experimental measurements were reported at temperature and pressure ranges of 32-50°C and 5900-6900 kPa, respectively. Results show that diffusivity of CO2 varies between 3.52-5.98×10-9 m2/s for 5900 kPa and 5.33-6.16×10-9 m2/s for 6900 kPa initial pressure. Also, it was found that both pressure and temperature have a positive impact on the measures of diffusion coefficient. Liquid swelling due to gas dissolution and variations in gas compressibility factor as a result of pressure decay was found negligible. Measured diffusivities were used model the physical model and develop concentration profile of dissolved gas in the liquid phase. Results of this study provide unique measures of CO2 diffusion coefficient in saline aquifer at high pressure and temperature conditions, which can be applied in full-field studies of carbon capture and sequestration projects.

Azin, Reza; Mahmoudy, Mohamad; Raad, Seyed Mostafa Jafari; Osfouri, Shahriar

2013-12-01

253

Self-diffusion coefficients of methane or ethane mixtures with hydrocarbons at high pressure by NMR  

SciTech Connect

Self-diffusion coefficients have been measured in homogeneous mixtures of methane + hexane, ethane + hexane, methane + octane, ethane + octan, methane + decane, ethane + decane, and methane + hexane + benzene over the whole concentration range, at 303.2 K and 333.2 K and 30 MPa, 40 MPa, and 50 MPa. The experiments were performed in a glass cell by application of the NMR-PGSE technique. The estimated accuracy of the measurements is {+-}5%. Experimental self-diffusion coefficients were compared to the Sigmund correlation, which was found not to fit the experimental data. The main motivation for this work was the need for diffusion data in reservoir studies. Gas injection in heterogeneous or fractured reservoirs and gas diffusion through cap rock are processes where diffusion may play a significant role. Although these processes occur in porous oil- and water-saturated rock, diffusion data pertaining to bulk liquids are useful because the effect of the tortuosity of the rock can be represented by formation resistivity data. Moreover, a diffusion model at the molecular level can include rock-fluid interactions.

Helbaek, M. [Nord-Troendelag Coll., Levanger (Norway). Dept. of Engineering] [Nord-Troendelag Coll., Levanger (Norway). Dept. of Engineering; Hafskjold, B.; Dysthe, D.K.; Soerland, G.H. [Norwegian Univ. of Science and Technology, Trondheim (Norway). Dept. of Physical Chemistry] [Norwegian Univ. of Science and Technology, Trondheim (Norway). Dept. of Physical Chemistry

1996-05-01

254

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

255

VARYING COEFFICIENT MODEL FOR MODELING DIFFUSION TENSORS ALONG WHITE MATTER TRACTS  

PubMed Central

Diffusion tensor imaging provides important information on tissue structure and orientation of fiber tracts in brain white matter in vivo. It results in diffusion tensors, which are 3×3 symmetric positive definite (SPD) matrices, along fiber bundles. This paper develops a functional data analysis framework to model diffusion tensors along fiber tracts as functional data in a Riemannian manifold with a set of covariates of interest, such as age and gender. We propose a statistical model with varying coefficient functions to characterize the dynamic association between functional SPD matrix-valued responses and covariates. We calculate weighted least squares estimators of the varying coefficient functions for the Log-Euclidean metric in the space of SPD matrices. We also develop a global test statistic to test specific hypotheses about these coefficient functions and construct their simultaneous confidence bands. Simulated data are further used to examine the finite sample performance of the estimated varying co-efficient functions. We apply our model to study potential gender differences and find a statistically significant aspect of the development of diffusion tensors along the right internal capsule tract in a clinical study of neurodevelopment.

Yuan, Ying; Zhu, Hongtu; Styner, Martin; Gilmore, John H.; Marron, J. S.

2012-01-01

256

Diffusion Coefficients and Heats of Mixing in Aqueous Alkanolamines. Annual Report, January-December 1992.  

National Technical Information Service (NTIS)

The objective of the work is to provide accurate data on diffusion coefficients and heats of absorption of acid gases in aqueous amine solutions to assist in the design of economical new amine treating systems and to improve the efficiency of existing pla...

R. L. Rowley J. L. Oscarson

1993-01-01

257

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

258

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

259

Experimental determination of the theophylline diffusion coefficient in swollen sodium-alginate membranes  

Microsoft Academic Search

In this paper attention is focused on the determination of the drug diffusion coefficient in a swollen polymeric membrane referring to a recent mathematical model (linear model). The main advantage deriving from its use is that, despite its analytical nature and its ability to account for the most important aspects characterising a permeation experiment, it can also be applied in

M. Grassi; I. Colombo; R. Lapasin

2001-01-01

260

A method for measuring effective radon diffusion coefficients in radon barriers by using modified Lucas cells  

Microsoft Academic Search

Radon proof barriers are used for lowering of radon transport from the soil into the house and the determination of the radon diffusion coefficient is an important parameter to be determined in order to design the minimal thickness of the radon proof insulation. A method has been developed in our laboratory by using modified Lucas cells connected to a radon

L. S. Quindos Poncela; P. L. Fernandez; J. Gomez Arozamena; C. Sainz Fernandez

2005-01-01

261

The Value of Apparent Diffusion Coefficient Maps in Early Cerebral Ischemia  

Microsoft Academic Search

BACKGROUND AND PURPOSE: Prediction of the regions of the ischemic penumbra that are likely to progress to infarction is of great clinical interest. Whether lowered apparent diffusion coefficient (ADC) values were present in the ischemic penumbra of patients presenting with acute ischemic stroke and were specific to regions of the penumbra that proceeded to infarction was investigated. METHODS: Nineteen patients

Patricia M. Desmond; Amanda C. Lovell; Andrew A. Rawlinson; Mark W. Parsons; P. Alan Barber; Qing Yang; Ting Li; David G. Darby; Richard P. Gerraty; Steven M. Davis; Brian M. Tress

2001-01-01

262

Correlation Between the Field Line and Particle Diffusion Coefficients in the Stochastic Fields of a Tokamak  

Microsoft Academic Search

We use the method of quasi-magnetic surfaces to calculate the correlation between the field line and particle diffusion coefficients. The magnetic topology of a tokamak is perturbed by a spectrum of neighboring resonant resistive modes. The Hamiltonian equations of motion for the field line are integrated numerically. Poincare plots of the quasi-magnetic surfaces are generated initially and after the field

Mark Calvin; Alkesh Punjabi

1996-01-01

263

DIFFUSION COEFFICIENTS OF CRITICAL RADIONUCLIDES FROM RADIOACTIVE WASTE IN GEOLOGICAL MEDIUM  

Microsoft Academic Search

Diffusion (Ds) and distribution coefficients (K d) are needed to assess the migration of radionuclides through the geological medium proposed to locate the low and intermediate level radioactive waste disposal (an intermediate level radioactive waste is considered that waste who have an activity less than 10 4 Ci\\/m 3 ).

C. Bucur; A. Popa; C. Arsene; M. Olteanu

2000-01-01

264

Normed Bellman Equation with Degenerate Diffusion Coefficients and Its Application to Differential Equations.  

National Technical Information Service (NTIS)

The purpose of this paper is to prove the existence and uniqueness of generalized solution of the normed bellman equation with degenerate diffusion coefficients and also to prove that this unique solution is the cost function of a stochastic control probl...

M. Fujisaki

1987-01-01

265

Single-relaxation-time lattice Boltzmann scheme for advection-diffusion problems with large diffusion-coefficient heterogeneities and high-advection transport  

NASA Astrophysics Data System (ADS)

The paper presents an approach that extends the flexibility of the standard lattice Boltzmann single relaxation time scheme in terms of spatial variation of dissipative terms (e.g., diffusion coefficient) and stability for high Péclet mass transfer problems. Spatial variability of diffusion coefficient in SRT is typically accommodated through the variation of relaxation time during the collision step. This method is effective but cannot deal with large diffusion coefficient variations, which can span over several orders of magnitude in some natural systems. The approach explores an alternative way of dealing with large diffusion coefficient variations in advection-diffusion transport systems by introducing so-called diffusion velocity. The diffusion velocity is essentially an additional convective term that replaces variations in diffusion coefficients vis-à-vis a chosen reference diffusion coefficient which defines the simulation time step. Special attention is paid to the main idea behind the diffusion velocity formulation and its implementation into the lattice Boltzmann framework. Finally, the performance, stability, and accuracy of the diffusion velocity formulation are discussed via several advection-diffusion transport benchmark examples. These examples demonstrate improved stability and flexibility of the proposed scheme with marginal consequences on the numerical performance.

Perko, Janez; Patel, Ravi A.

2014-05-01

266

Expression of optical diffusion coefficient in high-absorption turbid media  

NASA Astrophysics Data System (ADS)

The optical diffusion coefficient in a homogeneous turbid medium with high absorption was determined by steady-state measurements of the light transmission under the infinite-boundary condition. The intensity of the transmission was well described by the solution of the optical diffusion equation. Moreover, the optical diffusion coefficient D was given by a constant, , where is the reduced scattering coefficient, up to the absorption coefficient of about . These results mean that attenuation by absorption only contributes to exponential attenuation along the optical path defined by the scattering coefficient and geometry of the system even in high-absorption turbid media such as the pathological living tissues of bleeding or haematoma.

Nakai, T.; Nishimura, G.; Yamamoto, K.; Tamura, M.

1997-12-01

267

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

268

Heavy Ion Distribution Function in Magnetic Reconnection Diffusion Region  

NASA Astrophysics Data System (ADS)

While the plasma in the magnetotail predominantly consists of protons and electrons, there are times when a significant amount of O+ is present. When magnetic reconnection occurs, the behavior of the heavy ions can be significantly different than the protons, due to its larger gyroradius. In this study, we investigate the heavy ion acceleration process in the ion diffusion region by using 2.5D particle-in-cell numerical simulation and comparison with observations. From the simulation, we find that heavy ions are demagnetized and accelerated in a larger diffusion region. The ion velocity distribution function shows that, in the heavy ion diffusion region, heavy ions carry the out of plane current and counter stream in a plane. We compare this result with Cluster observations in the vicinity of reconnection regions in the magnetotail and find that the observed heavy ion distribution functions in the ion diffusion region agree very well with the simulation prediction. We find that the meandering motion of the heavy ion forms a counter-streaming distribution and the mixture of ions that enter the diffusion region at different distances from the neutral line plays a significant role in the evolution of non-maxwellian distributions going downstream from the x-type region. In the fluid description, the pressure force due to particle anisotropy becomes significant in the momentum equation and affects the flow jet acceleration process.

Liu, Y.; Kistler, L. M.; Mouikis, C.; Karimabadi, H.; Roytershteyn, V.; Wang, S.

2013-12-01

269

Ion movement through gramicidin A channels. Studies on the diffusion-controlled association step.  

PubMed Central

The permeability characteristics of gramicidin A channels are generally considered to reflect accurately the intrinsic properties of the channels themselves; i.e., the aqueous convergence regions are assumed to be negligible barriers for ion movement through the channels. The validity of this assumption has been examined by an analysis of gramicidin A single-channel current-voltage characteristics up to very high potentials (500 mV). At low permeant ion concentrations the currents approach a voltage-independent limiting value, whose magnitude is proportional to the permeant ion concentration. The magnitude of this current is decreased by experimental maneuvers that decrease the aqueous diffusion coefficient of the ions. It is concluded that the magnitude of this limiting current is determined by the diffusive ion movement through the aqueous convergence regions up to the channel entrance. It is further shown that the small-signal (ohmic) permeability properties also reflect the existence of the aqueous diffusion limitation. These results have considerable consequences for the construction of kinetic models for ion movement through gramicidin A channels. It is shown that the simple two-site-three-barrier model commonly used to interpret gramicidin A permeability data may lead to erroneous conclusions, as biionic potentials will be concentration dependent even when the channel is occupied by at most one ion. The aqueous diffusion limitation must be considered explicitly in the analysis of gramicidin A permeability characteristics. Some implications for understanding the properties of ion-conducting channels in biological membranes will be considered.

Andersen, O S

1983-01-01

270

Theoretical prediction of thermal diffusion coefficients for ternary hydrocarbon mixtures based on the irreversible thermodynamics theory  

NASA Astrophysics Data System (ADS)

An accurate thermodiffusion model is of paramount importance to the petroleum industry for the prediction of the compositional variation in hydrocarbon reservoirs. Several theoretical models have been developed. Kempers and Firoozabadi models are the latest two models, which are not only applicable for binary mixtures but also for multi-component mixtures. In this paper, we applied the Firoozabadi model to a ternary hydrocarbon mixture of n-Dodecane, n-Butane and Methane with different mass fraction. It reveals that the accuracy of the thermal diffusion coefficients for a specific mixture of interest relies on the accuracy of the thermodynamic properties from equations of state, corresponding Fick's diffusion coefficients, and the thermal diffusion modeling.

Jaber, T. J.; Yan, Y.; Pan, S.; Saghir, M. Z.

2009-10-01

271

Effect of computed horizontal diffusion coefficients on two-dimensional N2O model distributions  

NASA Technical Reports Server (NTRS)

The effects of horizontal diffusion coefficients K(yy) and K(yz), computed directly from the residual circulation, on the N2O distribution in a photochemical model were investigated, using a modified version of the two-dimensional model of Guthrie et al. (1984). The residual circulation was computed using the NMC's temperature data and the heating rates reported by Rosenfield et al. (1987). As compared with the effect of the residual circulation alone, the use of horizontal diffusion coefficients produced substantial changes in the N2O distribution and increased the N2O's lifetime values by a few percent. It is suggested that trace gases, such as CH4, CFCl3, CF2Cl2, CH3Cl, and CCl4, which impact the NO(x), HO(x), and Cl(x) radical distributions and therefore ozone, will be influenced in a similar manner by the addition of more realistic diffusion fields.

Jackman, Charles H.; Guthrie, Paul D.; Schoeberl, Mark R.; Newman, Paul A.

1988-01-01

272

Compilation and evaluation of gas-phase diffusion coefficients of inorganic reactive trace gases in the atmosphere  

NASA Astrophysics Data System (ADS)

Diffusion of gas molecules to the surface is the first step for all gas-surface reactions. Gas phase diffusion can influence and sometimes even limit the overall rates of these reactions; however, there is no database of the gas phase diffusion coefficients of atmospheric reactive trace gases. Here we compile and evaluate, for the first time, the diffusivities (pressure-independent diffusion coefficients) of atmospheric inorganic reactive trace gases reported in the literature. The measured diffusivities are then compared with estimated values using a semi-empirical method developed by Fuller et al. (1966). The diffusivities estimated using Fuller's method are typically found to be in good agreement with the measured values within ±30%, and therefore Fuller's method can be used to estimate the diffusivities of trace gases for which experimental data are not available. The two experimental methods used in the atmospheric chemistry community to measure the gas phase diffusion coefficients are also discussed.

Tang, M. J.; Cox, R. A.; Kalberer, M.

2014-06-01

273

Network modeling of diffusion coefficients for porous media: I. Theory and model development  

SciTech Connect

Gas diffusion often dominates constituent transport in porous media and is dependent on pore geometry, water content, and water distribution in a porous medium. Network models of porous media offer the ability to investigate the influence and interaction of pore-scale porous media properties and fluid properties on macroscopic properties of the medium. This study was conducted to investigate the macroscopic relative gas diffusion coefficient vs. air-filled porosity relationship (diffusion characteristic) of porous media using a network modeling approach. A cubic sphere-and-tube network model of porous media was adapted from petroleum engineering using Fick`s law and the principle of conservation of mass to simulate one-dimensional, steady-state, isothermal, isobaric, molecular diffusion of a dilute binary gas in a nonadsorbing porous medium containing a single nonwetting fluid (air) and a single wetting fluid (water). The network model simulates hysteresis in air and water distribution in porous media for boundary drying and wetting curves of the soil water characteristic and demonstrates the effect of air-filled porosity, Henry`s law liquid-gas partitioning coefficient, the ratio between gas- and liquid-phase diffusion rates, and pore geometry on the diffusion characteristic. 41 refs., 8 figs.

Steele, D.D. [North Dakota State Univ., Fargo, ND (United States); Neiber, J.L. [Univ. of Minnesota, St. Paul, MN (United States)

1994-09-01

274

Estimating diffusion coefficients in low-permeability porous media using a macropore column  

SciTech Connect

Diffusion coefficients in an aquitard material were measured by conducting miscible solute transport experiments through a specially constructed macropore column. Stainless steel HPLC columns were prepared in a manner that created an annular region of repacked aquitard material and a central core of medium-grained quartz sand. The column transport approach minimizes volatilization and sorption losses that can be problematic when measuring hydrophobic organic chemical diffusion with diffusion-cell methods or column-sectioning techniques. In the transport experiments, solutes (triated water, 1,2,4-trichlorobenzene, and tetrachloroethene) were transported through the central core by convection and hydrodynamic dispersion and through the low-permeability annulus by radial diffusion. All transport parameters were independently measured except for the effective diffusion coefficient in the aquitard material, which was obtained by model fitting. Batch-determined retardation factors agreed very closely with moment-derived retardation factors determined from the column experiments, and no evidence of pore exclusion was found. A model with retarded diffusion was found to apply, and the effective tortuosity factor of the aquitard material was estimated at an average value of 5.1.

Young, D.F.; Ball, W.P. [Johns Hopkins Univ., Baltimore, MD (United States). Dept. of Geography and Environmental Engineering] [Johns Hopkins Univ., Baltimore, MD (United States). Dept. of Geography and Environmental Engineering

1998-09-01

275

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

276

Self-diffusion coefficients and shear viscosity of model nanocolloidal dispersions by molecular dynamics simulation  

NASA Astrophysics Data System (ADS)

The self-diffusion coefficients D of both species in model nanocolloidal dispersions have been computed using molecular dynamics (MD) simulation, in which three-dimensional model spherical colloidal particles were in a molecularly discrete solvent. The effects of the relative density, size, and concentration of the two species were explored. Simulations were carried out at infinite dilution (a single colloidal particle) and at finite packing fractions (many colloidal particles) in the simulation cell using single interaction centers between the model colloidal particles and solvent molecules. The calculations used the Weeks-Chandler-Andersen (WCA) or Lennard-Jones (LJ), interaction potentials between all species. Nanocolloid particles with diameters up to ~6 times the solvent molecule were modeled. At liquidlike densities the self-diffusion coefficients of the colloidal particles, Dc, for all sizes and packing fractions, statistically exhibited no mass dependence but a significant colloid particle size dependence. This can be interpreted in a systematic manner using a Mori series expansion. The first Mori coefficient (which is inversely proportional to particle mass) dominates the value of the self-diffusion coefficient for both species, and which also leads to a formal cancellation of the mass dependence at the order of the first Mori coefficient KB1 (the self-diffusion coefficient is therefore determined by a ``static'' property to this order). The values of Dc at each packing fraction are found to be approximately inversely proportional to the colloidal particle diameter, quantitatively following the same trend as the Stokes-Einstein equation, even for the small colloidal particle sizes and finite colloidal particle concentrations studied here. Another consequence of the dominance of the first Mori coefficient is that the normalized velocity autocorrelation function of the colloidal particle at a short time can be represented well at all state points and packing fractions by the analytic form ~=cos(?0t), where ?0=KB1, which is the so-called Einstein frequency. LJ and WCA systems with otherwise the same system parameters manifest the same oscillation frequency, but the LJ oscillation amplitudes are larger and the values of Dc are smaller. The self-diffusion coefficients and shear viscosities obey a volume fraction dependence similar to that found for much larger colloidal particles.

Nuevo, María J.; Morales, Juan J.; Heyes, David M.

1998-11-01

277

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

278

Measurements of the Fe(3+) diffusion coefficient in Fricke Xylenol gel using optical density measurements.  

PubMed

In Fricke dosimetry, optical density measurements are performed some time after dosimeter irradiation. Values of the diffusion coefficient of Fe(3+) in Fricke Xylenol gel (FXG) are necessary for determining the spatial distribution of the absorbed dose from measurements of the optical density. Five sets of FXG dosimeters, kept at different constant temperatures, were exposed to collimated 6MV photons. The optical density profile, proportional to the Fe(3+) concentration, at the boundary between irradiated and non-irradiated parts of each dosimeter was measured periodically over a period of 60h. By comparing the experimental data with a function that accounts for the unobserved initial concentration profile of Fe(3+) in the FXG, we obtained diffusion coefficients 0.30±0.05, 0.40±0.05, 0.50±0.05, 0.60±0.05 and 0.80±0.05mm(2)/h for the temperatures 283.0±0.5, 286.0±0.5, 289.0±0.5, 292.0±0.5, and 296.0±0.5K, respectively. The activation energy of Fe(3+) diffusion in the gel, 0.54±0.06eV, was determined from the temperature dependence of the diffusion coefficients. PMID:24836903

de Oliveira, Lucas Nonato; Sampaio, Francisco Glaildo Almeida; Moreira, Marcos Vasques; de Almeida, Adelaide

2014-08-01

279

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

280

Measurement and correlation of diffusion coefficients for CO/sub 2/ and rich-gas applications  

SciTech Connect

A novel in-situ method for measuring molecular diffusion coefficients of CO/sub 2/ and other solvent gases in consolidated porous media at high pressure has been developed and is described. This technique is unique because visual observations and measurements of composition are not required. Experimental diffusion coefficients are reported for CO/sub 2/ in decane up to 850 psia (5.86 MPa), for CO/sub 2/ in 0.25 N NaCl brine up to 850 psia (5.86 MPa), and for ethane in decane up to 600 psia (4.14 MPa). All tests were conducted in Berea cores saturated with liquid phase at 100/sup 0/F (311 K). Cores were oriented both vertically and horizontally to assess the effects of gravity-induced convection on the observed mass transfer. The experimental diffusion coefficients obtained from this study have also been correlated, together with literature data for methane, ethane, and propane, as a function of liquid viscosity and thermophysical properties of the diffusing gases.

Renner, T.A.

1988-05-01

281

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)] [Reservoir Engineering Research Inst., Palo Alto, CA (United States)

1998-08-01

282

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

283

New Consistent Definition of the Homogenized Diffusion Coefficient of a Lattice, Limitations of the Homogenization Concept, and Discussion of Previously Defined Coefficients.  

National Technical Information Service (NTIS)

The problem concerned with the correct definition of the homogenized diffusion coefficient of a lattice, and the concurrent problem of whether or not a homogenized diffusion equation can be formally set up, is studied by a space-energy angle dependent tre...

V. C. Deniz

1978-01-01

284

Determination of time-dependent partition coefficients for several pesticides using diffusion theory.  

PubMed

Diffusion-retarded partitioning of pesticides with aggregated soils results in a time-dependent partition coefficient (Kd') which is different at equilibrium from the partition coefficient derived from conventional 24-h batch studies (Kd) measured on dispersed soil. An experiment was undertaken to determine the importance of Kd' for the prediction of pesticide concentrations in solutions bathing artificial soil aggregates and to determine whether diffusion theory could accurately predict the concentrations. Two clay soils were mixed with polyacrylamide to create artificial aggregates of 0.8, 1.4 and 1.7 cm diameter when dry. After saturation, the aggregates were immersed in solutions containing isoproturon or a mixture of isoproturon, chlorotoluron and triasulfuron. The decline with time of the pesticide concentrations in the bathing solution was monitored and the results were compared with predictions from a diffusion-based model. The effective diffusion coefficients of the compounds were obtained by either fitting the non-linear diffusion model to the data (D(ef)) or by independent calculations based on the properties of the compounds and of the aggregates (D(ec)). The diffusion model was able to predict the temporal variation in pesticide concentrations in the bathing solution reasonably well whether D(ef) or D(ec) values were used. However, equilibrium concentrations in solution were sometimes overestimated due to increased sorption with time at the particle scale. Overall, the ratio between D(ef) and D(ec) ranged from 0.23 to 0.95 which was a reasonable variation when compared to the range of aggregate sizes used in the experiments and of the Kd values of the compounds. PMID:15519397

Renaud, Fabrice G; Leeds-Harrison, Peter B; Brown, Colin D; van Beinum, Wendy

2004-12-01

285

Measurement of the absorption coefficient of sound absorbing materials under a synthesized diffuse acoustic field.  

PubMed

This letter proposes an experimental method to estimate the absorption coefficient of sound absorbing materials under a synthesized diffuse acoustic field in free-field conditions. Comparisons are made between experiments conducted with this approach, the standard reverberant room method, and numerical simulations using the transfer matrix method. With a simple experimental setup and smaller samples than those required by standards, the results obtained with the proposed approach do not exhibit non-physical trends of the reverberant room method and provide absorption coefficients in good agreement with those obtained by simulations for a laterally infinite material. PMID:24993232

Robin, Olivier; Berry, Alain; Doutres, Olivier; Atalla, Noureddine

2014-07-01

286

Thermal Expansion and Diffusion Coefficients of Carbon Nanotube-Polymer Composites  

NASA Technical Reports Server (NTRS)

Classical molecular dynamics (MD) simulations employing Brenner potential for intra-nanotube interactions and van der Waals forces for polymer-nanotube interface have been used to investigate thermal expansion and diffusion characteristics of carbon nanotube-polyethylene composites. Addition of carbon nanotubes to polymer matrix is found to significantly increase the glass transition temperature Tg, and thermal expansion and diffusion coefficients in the composite above Tg. The increase has been attributed to the temperature dependent increase of the excluded volume for the polymer chains, and the findings could have implications in the composite processing, coating and painting applications.

Wei, Chengyu; Srivastava, Deepak; Cho, Kyeongjae; Biegel, Bryan (Technical Monitor)

2001-01-01

287

The role of apparent diffusion coefficient values in differentiation between adrenal masses.  

PubMed

The aim of this study was to evaluate the utility of apparent diffusion coefficient (ADC) values in differentiation between solid adrenal masses. The ADC values of 73 adrenal lesions (54 benign, 19 malignant) in 69 patients were measured at b 100, 600 and 1000 gradients on diffusion-weighted magnetic resonance imaging (DW-MRI). No statistically significant difference was found between ADC values of benign and malignant adrenal masses, nonadenomatous benign adrenal masses and malignant adrenal masses, adrenal adenomas and nonadenomatous lesions, adenomas and metastases, adenomas and pheochromocytomas, metastases and pheochromocytomas. ADC values are not helpful in the differentiation between solid adrenal masses. PMID:24332557

Ciçekçi, Mehtap; Onur, Mehmet Ruhi; Aydin, Ayse Murat; Gül, Yeliz; Ozkan, Yusuf; Akpolat, Nusret; Kocakoç, Ercan

2014-01-01

288

A MATLAB program to calculate translational and rotational diffusion coefficients of a single particle  

NASA Astrophysics Data System (ADS)

We developed a graphical user interface, MATLAB based program to calculate the translational diffusion coefficients in three dimensions for a single diffusing particle, suspended inside a fluid. When the particles are not spherical, in addition to their translational motion also a rotational freedom is considered for them and in addition to the previous translational diffusion coefficients a planar rotational diffusion coefficient can be calculated in this program. Time averaging and ensemble averaging over the particle displacements are taken to calculate the mean square displacement variations in time and so the diffusion coefficients. To monitor the random motion of non-spherical particles a reference frame is used that the particle just have translational motion in it. We call it the body frame that is just like the particle rotates about the z-axis of the lab frame. Some statistical analysis, such as velocity autocorrelation function and histogram of displacements for the particle either in the lab or body frames, are available in the program. Program also calculates theoretical values of the diffusion coefficients for particles of some basic geometrical shapes; sphere, spheroid and cylinder, when other diffusion parameters like temperature and fluid viscosity coefficient can be adjusted. Program summaryProgram title: KOJA Catalogue identifier: AEHK_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEHK_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 48 021 No. of bytes in distributed program, including test data, etc.: 1 310 320 Distribution format: tar.gz Programming language: MatLab (MathWorks Inc.) version 7.6 or higher. Statistics Toolbox and Curve Fitting Toolbox required. Computer: Tested on windows and linux, but generally it would work on any computer running MatLab (MathWorks Inc.). There is a bug in windows 7, if the user is not the administrator sometimes the program was not able to overwrite some internal files. Operating system: Any supporting MatLab (MathWorks Inc.) v7.6 or higher. RAM: About eight times that of loaded data Classification: 12 Nature of problem: In many areas of physics, knowing diffusion coefficients is vital and gives useful information about the physical properties of diffusive particles and the environment. In many cases a diffusive particle is not a sphere and has rotation during its movements. In these cases information about a particle's trajectory both in lab and body frame would be useful. Also some statistical analysis is needed to obtain more information about a particle's motion. Solution method: This program tries to gather all required tools to analyse raw data from the Brownian motion of a diffusing particle. Ability to switch between different methods of calculation of mean square displacement to find diffusion coefficients depends on the correlations between data points. There are three methods in the program: time average, ensemble average and their combinations. A linear fit is done to measure Diffusion Coefficient (D), the weight and fraction of data points is controllable. Given physical properties of the system, the program can calculates D theoretically for some basic geometrical shapes; sphere, spheroid and cylinder. In the case of non-spherical particles if data of rotation is available, the code can calculate trajectory and diffusion also in body frame. There are more statistical tools available in the program, such as histogram and autocorrelation function to obtain more information e.g. relaxation time to ideal diffusion motion. Code uses log-log diagram of mean square displacement (MSD) to calculate the amount of deviation from normal diffusion to sub- or super-diffusion. Running time: It is dependent on the input data, but for typical data in the order of mega bytes, it would take tens of minutes.

Charsooghi, Mohammad A.; Akhlaghi, Ehsan A.; Tavaddod, Sharareh; Khalesifard, H. R.

2011-02-01

289

Determination of activation energy for Li ion diffusion in electrodes.  

PubMed

Higher power Li ion rechargeable batteries are important in many practical applications. Higher power output requires faster charge transfer reactions in the charge/discharge process. Because lower activation energy directly correlates to faster Li ion diffusion, the activation energy for ionic diffusion throughout the electrode materials is of primary importance. In this study, we demonstrate a simple, versatile electrochemical method to determine the activation energy for ionic diffusion in electrode materials via temperature dependent capacitometry. A generalized form of the temperature dependence of the discharge capacity was derived from the diffusion equation. This method yielded activation energy values for Li ion diffusion in LiCoO2 comparable to those obtained from ab initio calculations. PMID:19708215

Okubo, Masashi; Tanaka, Yoshinori; Zhou, Haoshen; Kudo, Tetsuichi; Honma, Itaru

2009-03-01

290

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

291

Diffusion coefficients and heats of mixing in aqueous alkanolamines. Annual report, January-December 1992  

SciTech Connect

The objective of the work is to provide accurate data on diffusion coefficients and heats of absorption of acid gases in aqueous amine solutions to assist in the design of economical new amine treating systems and to improve the efficiency of existing plants. Specifically covered in the report are measurements of the mutual diffusion coefficient of methyldiethanolamine(MDEA) and diethanolamine in water. Measurements have been made at 25, 50 and 75C and at 0, 20, 35 and 50 wt% amine. Heats of absorption of CO2 into aqueous mixtures of MDEA have also been measured calorimetrically. Results are reported at temperatures of 120 and 260F and pressures of 500 and 1000 psia at total MDEA concentrations of 20, 35 and 50%.

Rowley, R.L.; Oscarson, J.L.

1993-01-01

292

Molecular dynamics simulation of self-diffusion coefficients for liquid metals  

NASA Astrophysics Data System (ADS)

The temperature-dependent coefficients of self-diffusion for liquid metals are simulated by molecular dynamics methods based on the embedded-atom-method (EAM) potential function. The simulated results show that a good inverse linear relation exists between the natural logarithm of self-diffusion coefficients and temperature, though the results in the literature vary somewhat, due to the employment of different potential functions. The estimated activation energy of liquid metals obtained by fitting the Arrhenius formula is close to the experimental data. The temperature-dependent shear-viscosities obtained from the Stokes—Einstein relation in conjunction with the results of molecular dynamics simulation are generally consistent with other values in the literature.

Ju, Yuan-Yuan; Zhang, Qing-Ming; Gong, Zi-Zheng; Ji, Guang-Fu

2013-08-01

293

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

2011-05-01

294

New technique for the determination of radon diffusion coefficient in radon-proof membranes.  

PubMed

This paper describes a new device and a method to determine the radon diffusion coefficient in damp-proof membranes developed in the Czech Republic. The main advantage of the device is that it enables tests to be carried out in all the known measuring modes used throughout Europe. Two recently developed computer programs are presented for the numerical modelling of the time-dependent radon transport through damp-proof membranes. According to this method, the radon diffusion coefficient is derived from the process of fitting the numerical solution to the measured curve of radon concentration in a receiver container. Numerical simulation and measured data are also compared. Reasons for disagreements between different methods and specific configurations of the measuring device are also discussed. PMID:18397928

Jiránek, M; Fronka, A

2008-01-01

295

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

296

Determination of the diffusion coefficient of protons in Nafion thin films by ac-electrogravimetry.  

PubMed

This letter deals with an adaptation of the ac-electrogravimetry technique to extract separately the dynamic properties of H(+) and water in Nafion nanometric thin films (average thickness of 400 nm). An original theoretical approach was developed to extract the representative parameters from ac-electrogravimetry data. The concentration change of the exchanged species and the diffusion coefficient of the protons in a Nafion nanometric thin film (D = 0.5 × 10(-6) cm(2) s(-1) at 0.3 V vs SCE) were estimated for the first time according to the applied potential. The conductivity value of Nafion thin films was calculated from the Nernst-Einstein equation using diffusion coefficients and concentration values extracted from ac-electrogravimetry data. The calculated conductivity results agree well with the experimental proton conductivity values of Nafion thin films. PMID:24131383

Sel, Ozlem; To Thi Kim, L; Debiemme-Chouvy, Catherine; Gabrielli, Claude; Laberty-Robert, Christel; Perrot, Hubert

2013-11-12

297

Radial Diffusion Coefficients of Galactic and Anomalous Cosmic Rays in the Heliosphere  

NASA Astrophysics Data System (ADS)

When cosmic ray streaming in the heliosphere is negligible, the basic transport equation gives a simple approximation for the diffusion coefficient of cosmic ray particles, ?=CVSW/gr, where C is the Compton-Getting factor, VSW is the solar wind velocity and gr is the radial intensity gradients. In a separate paper at this conference, Fujii and McDonald (1999) have shown that the measured radial intensity gradients are well described with a functional form of dJ/Jdr= G0r, and have determined G0 and for selected galactic and anomalous cosmic rays. Using these values of gr, we obtained first order estimates of the particle diffusion coefficient over period from 1974 to 1997 out to heliocentric distance of 60 AU.

Fujii, Zenjiro

298

Ion Beam Analysis of Diffusion in Polymer Glasses.  

National Technical Information Service (NTIS)

Rutherford backscattering spectrometry (RBS) and forward recoil spectrometry (FRES) have been used to the fundamentals of Case II diffusion of organic molecules (solvent) into glassy polymers. These ion beam techniques were employed to measure the velocit...

E. J. Kramer

1989-01-01

299

In situ effective diffusion coefficient profiles in live biofilms using pulsed-field gradient nuclear magnetic resonance  

PubMed Central

Diffusive mass transfer in biofilms is characterized by the effective diffusion coefficient. It is well-documented that the effective diffusion coefficient can vary by location in a biofilm. The current literature is dominated by effective diffusion coefficient measurements for distinct cell clusters and stratified biofilms showing this spatial variation. Regardless of whether distinct cell clusters or surface-averaging methods are used, position-dependent measurements of the effective diffusion coefficient are currently: 1) invasive to the biofilm, 2) performed under unnatural conditions, 3) lethal to cells, and/or 4) spatially restricted to only certain regions of the biofilm. Invasive measurements can lead to inaccurate results and prohibit further (time-dependent) measurements which are important for the mathematical modeling of biofilms. In this study our goals were to: 1) measure the effective diffusion coefficient for water in live biofilms, 2) monitor how the effective diffusion coefficient changes over time under growth conditions, and 3) correlate the effective diffusion coefficient with depth in the biofilm. We measured in situ two-dimensional effective diffusion coefficient maps within Shewanella oneidensis MR-1 biofilms using pulsed-field gradient nuclear magnetic resonance methods, and used them to calculate surface-averaged relative effective diffusion coefficient (Drs) profiles. We found that 1) Drs decreased from the top of the biofilm to the bottom, 2) Drs profiles differed for biofilms of different ages, 3) Drs profiles changed over time and generally decreased with time, 4) all the biofilms showed very similar Drs profiles near the top of the biofilm, and 5) the Drs profile near the bottom of the biofilm was different for each biofilm. Practically, our results demonstrate that advanced biofilm models should use a variable effective diffusivity which changes with time and location in the biofilm.

Renslow, Ryan S.; Majors, Paul D.; McLean, Jeffrey S.; Fredrickson, Jim K.; Ahmed, Bulbul; Beyenal, Haluk

2010-01-01

300

Determination of the lithium diffusion coefficient in irradiated boron carbide pellets  

Microsoft Academic Search

During neutron irradiation, 10B atoms in B4C are destroyed, producing lithium and helium atoms according to the well-known 10B(n,?)7Li reaction. The aim of this work is to measure the lithium diffusion coefficient of high density boron carbide material. The nuclear microprobe technique is used to determine lithium concentration profiles in irradiated B4C pellets. The analysis of the measured lithium concentration

X. Deschanels; D. Simeone; J. P. Bonal

1999-01-01

301

Scaling Limits of a Tagged Particle in the Exclusion Process with Variable Diffusion Coefficient  

NASA Astrophysics Data System (ADS)

We prove a law of large numbers and a central limit theorem for a tagged particle in a symmetric simple exclusion process in ? with variable diffusion coefficient. The scaling limits are obtained from a similar result for the current through -1/2 for a zero-range process with bond disorder. For the CLT, we prove convergence to a fractional Brownian motion of Hurst exponent 1/4.

Gonçalves, Patrícia; Jara, Milton

2008-09-01

302

Apparent Diffusion Coefficient Thresholds Do Not Predict the Response to Acute Stroke Thrombolysis  

Microsoft Academic Search

Background and Purpose—Apparent diffusion coefficient (ADC) thresholds for tissue infarction have been identified in acute stroke. IV tissue plasminogen activator (tPA) is associated with tissue salvage. We hypothesized that tPA would lower the ADC threshold for infarction. Methods—ADC and mean transit time (MTT) maps were generated for 26 patients imaged within 6 hours of stroke onset (12 tPA and 14

Poh-Sien Loh; Ken S. Butcher; Mark W. Parsons; Lachlan MacGregor; Patricia M. Desmond; Brian M. Tress; Stephen M. Davis

2010-01-01

303

Effective Diffusion Coefficients of CO2 and HCFC22 in Polyurethane and Polyisocyanurate Foams  

Microsoft Academic Search

Thin-slice accelerated desorption of gases using a gravimetric methodology has been used to determine effective diffusion coefficients of both carbon dioxide and HCFC-22 in thermoset foam structures. Foam samples consisting of a polyurethane appliance foam and a polyisocyanurate boardstock foam both blown with CFC-11, and polyurethane foams blown with HCFC-22 and carbondioxide have been employed as polymer substrates for the

D. Bhattacharjee; J. R. Booth

1995-01-01

304

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

305

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

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

2004-01-01

306

An absorbance-based micro-fluidic sensor for diffusion coefficient and molar mass determinations  

Microsoft Academic Search

The H-Sensor reported herein is a micro-fluidic device compatible with flow injection analysis (FIA) and high performance liquid chromatography (HPLC). The device detects analytes at two separate off-chip absorbance flow cells, providing two simultaneous absorbance measurements. The ratio of these two absorbance signals contains analyte diffusion coefficient information. A theoretical model for the sensing mechanism is presented. The model relates

Adam D. McBrady; Rattikan Chantiwas; Ana Kristine Torgerson; Kate Grudpan; Robert E. Synovec

2006-01-01

307

Electrical conductivity and chemical diffusion coefficient of Sr-doped lanthanum chromites  

Microsoft Academic Search

The electrical conductivity and chemical diffusion coefficient of Sr-doped lanthanum chromites were measured as a function of oxygen partial pressure (Po2) and temperature, and the results were discussed in light of defect chemistry. The electrical conductivity was independent of Po2 and in proportion to the Sr-content at high Po2, while at low Po2, the conductivity decreased exponentially with decrease of

I. Yasuda; M. Hishinuma

1995-01-01

308

Sorption kinetics of polycyclic aromatic hydrocarbons removal using granular activated carbon: intraparticle diffusion coefficients.  

PubMed

Granular activated carbon (GAC) was evaluated as a suitable sorbent for polycyclic aromatic hydrocarbons (PAHs) removal from aqueous solutions. For this purpose, kinetic measurements on the extraction of a family of six PAHs were taken. A morphology study was performed by means of a scanning electron microscopy (SEM) analysis of GAC samples. Analyses of the batch rate data for each PAH were carried out using two kinetic models: the homogenous particle diffusion model (HPDM) and the shell progressive model (SPM). The process was controlled by diffusion rate the solutes (PAHs) that penetrated the reacted layer at PAH concentrations in the range of 0.2-10 mg L(-1). The effective particle diffusion coefficients (D(eff)) derived from the two models were determined from the batch rate data. The Weber and Morris intraparticle diffusion model made a double contribution to the surface and pore diffusivities in the sorption process. The D(eff) values derived from both the HPMD and SPM equations varied from 1.1 x 10(-13) to 6.0 x 10(-14) m(2) s(-1). The simplest model, the pore diffusion model, was applied first for data analysis. The model of the next level of complexity, the surface diffusion model, was applied in order to gain a deeper understanding of the diffusion process. This model is able to explain the data, and the apparent surface diffusivities are in the same order of magnitude as the values for the sorption of functionalized aromatic hydrocarbons (phenols and sulphonates) that are described in the literature. PMID:18308468

Valderrama, C; Gamisans, X; de las Heras, X; Farrán, A; Cortina, J L

2008-09-15

309

Experimental determination of the diffusion coefficient in two-dimensions in ferrous sulphate gels using the finite element method  

Microsoft Academic Search

A novel two-dimensional finite element method for modelling the diffusion which occurs in Fricke or ferrous sulphate type\\u000a radiation dosimetry gels is presented. In most of the previous work, the diffusion coefficient has been estimated using simple\\u000a one-dimensional models. This work presents a two-dimensional model which enables the diffusion coefficient to be determined\\u000a in a much wider range of experimental

C. Baldock; P. J. Harris; A. R. Piercy; B. Healy

2001-01-01

310

A new method for determining the initial mobile formaldehyde concentrations, partition coefficients, and diffusion coefficients of dry building materials.  

PubMed

The initial mobile formaldehyde concentration, C(m,0); the partition coefficient, K; and the diffusion coefficient, D, of a dry building material are key parameters to characterize formaldehyde emissions from the building material. The solvent extraction method and direct thermal desorption method can overestimate C(m,0) because of high temperature. A new method has been developed to determine C(m,0) under similar conditions to common indoor environment, together with K and D. In the proposed method, the tested materials are placed in an airtight environmental chamber for which the temperature can be controlled by a water bath, then the materials undergo a multisorption/emission process and the instantaneous formaldehyde concentration in the chamber is recorded. The K and C(m,0) are determined from the equilibrium concentrations after every sorption by means of the linear least-square regression, and D is obtained by fitting the concentration at the emission stage into a mass-transfer-based model in the literature. Four kinds of wooden medium-density boards are tested. The C(m,0) measured using this method is the mobile formaldehyde concentration in the material, which differs significantly from the total formaldehyde concentration in the material measured by using the traditional method recommended by the Chinese standard (GB/T 17657-1999) extraction method. This means that the mobile formaldehyde takes only a small portion of the total quantity in the tested material. The K, D, and C(m,0) values measured using this new method are used to predict formaldehyde concentrations for sorption processes. The results agree well with experimental data. In addition, some factors influencing the accuracy are analyzed. PMID:19645266

Wang, Xinke; Zhang, Yinping

2009-07-01

311

Partial structure factors and diffusion coefficients of liquid potassium-cesium alloys  

NASA Astrophysics Data System (ADS)

With use of the square-well potential as a perturbation on the hard-sphere potential, the partial structure factors defined by Ascroft and Langreth [Phys. Rev. 159, 500 (1967)] and also the number-number, number-concentration, and concentration-concentration structure factors of Bhatia and Thornton [Phys. Rev. 32, 3004 (1970)] are calculated for liquid potassium-cesium alloys at various concentrations at 100 °C. From the partial structure factors, the total structure factors are also calculated and compared with experimental values. The hard-sphere values are also computed for the same concentrations. The difference plots of the total structure factors of the square well and those of the hard spheres are also presented. The total structure factors obtained from these partial structure factors in the long-wavelength limit are used to calculate the isothermal compressibilities. With the partial structure factors and using Helfand's prescription extended by Davies and Polyvos, we calculate the self-diffusion coefficients. From the self-diffusion coefficients, an estimate of the mutual diffusion coefficients has been made to a good approximation.

Gopala Rao, R. V.; Das Gupta, B.

1985-11-01

312

The Diffusion Coefficient of Scandium in Dilute Aluminum-Scandium Alloys  

NASA Astrophysics Data System (ADS)

The diffusion coefficient of Sc in dilute Al-Sc alloys has been determined at 748 K, 823 K, and 898 K (475 °C, 550 °C, and 625 °C, respectively) using semi-infinite diffusion couples. Good agreement was found between the results of the present study and both the higher temperature, direct measurements and lower temperature, indirect measurements of these coefficients reported previously in the literature. The temperature-dependent diffusion coefficient equation derived from the data obtained in the present investigation was found to be D left( {{text{m}}2 /{text{s}}} right) = left( {2.34 ± 2.16} right) × 10^{ - 4} left( {{text{m}}2 /{text{s}}} right) { exp }left( {{ - left( {167 ± 6} right) left( {{text{kJ}}/{text{mol}}} right)}/RT} right). Combining these results with data from the literature and fitting all data simultaneously to an Arrhenius relationship yielded the expression D left( {{text{m}}2 /{text{s}}} right) = left( {2.65 ± 0.84} right) × 10^{ - 4} left( {{text{m}}2 /{text{s}}} right) { exp }left( {{ - left( {168 ± 2} right) left( {{text{kJ}}/{text{mol}}} right)}/RT} right). In each equation given above, R is 0.0083144 kJ/mol K, T is in Kelvin, and the uncertainties are ±1 standard error.

Kerkove, Marcel A.; Wood, Thomas D.; Sanders, Paul G.; Kampe, Stephen L.; Swenson, Douglas

2014-06-01

313

Radial diffusion coefficients and the distance to the modulation boundary for galactic and anomalous cosmic rays  

NASA Astrophysics Data System (ADS)

When cosmic ray streaming in the heliosphere is negligible, the basic transport equation gives a simple approximation for the diffusion coefficient of cosmic ray particles, Krr = CVSW/ gr, where C is the Compton-Getting factor, VSW is the solar wind velocity and gr is the radial intensity gradients. Using this equation we calculated the particle diffusion coefficients from 1974 to 1995 out to heliocentric distances of ˜70 AU, using the measured gr for galactic 180-450 MeV/n He, 130-220 MeV H and anomalous 30-57 MeV/n He and 10-20 MeV/n He. Further we made first order estimates of the distance to the modulation boundary, using these diffusion coefficients and the modulation function for galactic 180-450 MeV/n He. It was shown that the distance is from about 65 AU to 110 AU varying inversely proportional to the solar activity for the period from 1978 to 1990. After 1990 these estimation were not significant because of the very small gradients in the outer heliosphere.

Fujii, Z.; McDonald, F. B.

314

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

315

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

316

Evaluation of archived and off-line diagnosed vertical diffusion coefficients from ERA-40 with 222Rn simulations  

NASA Astrophysics Data System (ADS)

Boundary layer turbulence has a profound influence on the distribution of tracers with sources or sinks at the surface. The 40-year ERA-40 meteorological data set of the European Centre for Medium-range Weather Forecasts contains archived vertical diffusion coefficients. We evaluated the use of these archived diffusion coefficients versus off-line diagnosed coefficients based on other meteorological parameters archived during ERA-40 by examining the influence on the distribution of the radionuclide 222Rn in the chemistry transport model TM3. In total four different sets of vertical diffusion coefficients are compared: (i) 3-hourly vertical diffusion coefficients archived during the ERA-40 project, (ii) 3-hourly off-line diagnosed coefficients from a non-local scheme based on Holtslag and Boville (1993), Vogelezang and Holtslag (1996), and Beljaars and Viterbo (1999), (iii) 6-hourly coefficients archived during the ERA-40 project, and (iv) 6-hourly off-line diagnosed coefficients based on a local scheme described in Louis (1979) and Louis et al. (1982). The diffusion scheme to diagnose the coefficients off-line in (ii) is similar to the diffusion scheme used during the ERA-40 project (i and iii).

Olivié, D. J. L.; van Velthoven, P. F. J.; Beljaars, A. C. M.

2004-11-01

317

Minority carrier diffusion lengths and absorption coefficients in silicon sheet material  

NASA Technical Reports Server (NTRS)

Most of the methods which have been developed for the measurement of the minority carrier diffusion length of silicon wafers require that the material have either a Schottky or an ohmic contact. The surface photovoltage (SPV) technique is an exception. The SPV technique could, therefore, become a valuable diagnostic tool in connection with current efforts to develop low-cost processes for the production of solar cells. The technique depends on a knowledge of the optical absorption coefficient. The considered investigation is concerned with a reevaluation of the absorption coefficient as a function of silicon processing. A comparison of absorption coefficient values showed these values to be relatively consistent from sample to sample, and independent of the sample growth method.

Dumas, K. A.; Swimm, R. T.

1980-01-01

318

The diffusion coefficients of gaseous and volatile species during the irradiation of uranium dioxide  

NASA Astrophysics Data System (ADS)

Measurements of release for rare gas fission products from single and polycrystalline uranium dioxide during irradiation are described. The fuel samples were enriched to 20% in 235U to avoid uncertainties in the fission rate due to plutonium production. The surface area of the single crystals was determined optically to provide a reference of known surface-to-volume ratio for the determination of diffusion coefficients for the rare gases and their halogen precursors. The initial part of the experiment was isothermal, during which the time dependence of release was observed and the polycrystalline material developed extensively interlinked grain-boundary porosity. Subsequently the temperature dependence of the release process was studied. It is concluded that the diffusion of rare gas atoms in UO 2 during irradiation is a complex process involving more than one rate-controlling mechanism and bears a close similarity to cation self-diffusion. In both cases, the low-temperature kinetics are radically affected by irradiation damage. The present results are well represented by a composite diffusion coefficient containing three terms — one representing high-temperature intrinsic behaviour whilst the other two represent the effect of irradiation enhancement. This equation should be modified to take account of intragranular bubbles at all temperatures for stable gas release, and at high temperatures in the case of unstable species.

Turnbull, J. A.; Friskney, C. A.; Findlay, J. R.; Johnson, F. A.; Walter, A. J.

1982-06-01

319

Single master curve for self-diffusion coefficients in distinctly different glass-forming liquids  

NASA Astrophysics Data System (ADS)

An existence of a single master curve for the long-time self-diffusion coefficients DSL(T) in diversely different glass-forming liquids is predicted over wide temperature T ranges above the glass transition point Tg by analyzing various experimental and simulation data consistently from a unified point of view based on the mean-field theory recently developed. In order to scale those data appropriately, the power-law dependence of the ? - and the ? -relaxation times on DSL is used. Then, it is shown that any equilibrium data for self-diffusion of atom in different systems are all collapsed onto a singular function f(Tf(?)/T) , where Tf(?) is a fictive singular temperature of atom ? . Thus, we emphasize that any equilibrium self-diffusion data can be described by a single master curve f(x) above Tg(>Tf) , while the data out of equilibrium start to deviate from f(x) around Tg .

Tokuyama, Michio

2010-10-01

320

Relationship between the pulse rate of atmospherics and the diffusion time of ions in gelatin films  

Microsoft Academic Search

The pulse rates of natural atmospherics, recorded at the frequencies of 10 and 27 kHz respectively, were correlated with the measured diffusion times (TD) of ions in gelatin films. It was found that the difference ?S of the atmospherics pulse rates at 10 and 27 kHz correlates well with the variations of the TD-values. The correlation coefficient is 0.75 (?S\\/TD)

H. Baumer; J. Eichmeier

1980-01-01

321

Lithium chemical diffusion coefficients in poly(ethylene oxide)-molybdenum sulfide nanocomposites  

Microsoft Academic Search

The intercalation of poly(ethylene oxide) (PEO) in molybdenum sulfide (MoS2) forms the nanocomposites LixMoS2(PEO)0.5 and LixMoS2(PEO)1.0. The lithium ion diffusivity in PEO-containing phases, which depends on both PEO and lithium content, is always higher than in pure MoS2. The maximal observed diffusivity values, but also the strongest dependence on lithium concentration, are observed for LixMoS2(PEO)0.5, possibly due to their relatively

G. Gonzalez; M. A. Santa Ana; E. Benavente

1997-01-01

322

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

323

Ion beam microtexturing and enhanced surface diffusion  

NASA Technical Reports Server (NTRS)

Ion beam interactions with solid surfaces are discussed with particular emphasis on microtexturing induced by the deliberate deposition of controllable amounts of an impurity material onto a solid surface while simultaneously sputtering the surface with an ion beam. Experimental study of the optical properties of microtextured surfaces is described. Measurements of both absorptance as a function of wavelength and emissivity are presented. A computer code is described that models the sputtering and ion reflection processes involved in microtexture formation.

Robinson, R. S.

1982-01-01

324

Evaluation of apparent diffusion coefficient thresholds for diagnosis of medulloblastoma using diffusion-weighted imaging.  

PubMed

We assess a diffusion-weighted imaging (DWI) analysis technique as a potential basis for computer-aided diagnosis (CAD) of pediatric posterior fossa tumors. A retrospective medical record search identified 103 children (mean age: 87 months) with posterior fossa tumors having a total of 126 preoperative MR scans with DWI. The minimum ADC (ADCmin) and normalized ADC (nADC) values [ratio of ADCmin values in tumor compared to normal tissue] were measured by a single observer blinded to diagnosis. Receiver operating characteristic (ROC) curves were generated to determine the optimal threshold for which the nADC and ADCmin values would predict tumor histology. Inter-rater reliability for predicting tumor type was evaluated using values measured by two additional observers. At histology, ten tumor types were identified, with astrocytoma (n=50), medulloblastoma (n=33), and ependymoma (n=9) accounting for 89%. Mean ADCmin (0.54 × 10(-3) mm(2)/s) and nADC (0.70) were lowest for medulloblastoma. Mean ADCmin (1.28 × 10(-3) mm(2)/s) and nADC (1.64) were highest for astrocytoma. For the ROC analysis, the area under the curve when discriminating medulloblastoma from other tumors using nADC was 0.939 and 0.965 when using ADCmin. The optimal ADCmin threshold was 0.66 × 10(-3) mm(2)/s, which yielded an 86% positive predictive value, 97% negative predictive value, and 93% accuracy. Inter-observer variability was very low, with near perfect agreement among all observers in predicting medulloblastoma. Our data indicate that both ADCmin and nADC could serve as the basis for a CAD program to distinguish medulloblastoma from other posterior fossa tumors with a high degree of accuracy. PMID:24571835

Pierce, Theodore Thomas; Provenzale, James M

2014-02-01

325

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 700 degrees C 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 400 degrees C. 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

326

Fast-ion radial diffusivity evaluated from vertical neutral particle measurements following short pulse beam injection into a TFTR ohmic plasma  

SciTech Connect

The radial diffusivity of fast ions was evaluated from vertical neutral particle measurements in experiments where a short pulse of neutral deuterium beams was injected into a TFTR ohmic deuterium plasma. A comparison between the temporal evolution of the measured neutral particle flux and theoretical calculations showed that the spatially-averaged diffusion coefficient of fast ions is {le} 0.1 m{sup 2}/sec. This value is approximately an order of magnitude less than the diffusion coefficient for thermal ions and is consistent with results obtained previously on TFTR from other diagnostics.

Kusama, Y. (Japan Atomic Energy Research Inst., Naka, Ibaraki (Japan). Naka Fusion Research Establishment); Heidbrink, W.W. (California Univ., Irvine, CA (United States)); Barnes, C.W. (Los Alamos National Lab., NM (United States)); Beer, M.; Hammett, G.W.; McCune, D.C.; Medley, S.S.; Scott, S.D.; Zarnstorff, M.C. (Princeton Univ., NJ (United States). Plasma Physics Lab.)

1992-01-01

327

Theory and simulation of the time-dependent rate coefficients of diffusion-influenced reactions.  

PubMed Central

A general formalism is developed for calculating the time-dependent rate coefficient k(t) of an irreversible diffusion-influenced reaction. This formalism allows one to treat most factors that affect k(t), including rotational Brownian motion and conformational gating of reactant molecules and orientation constraint for product formation. At long times k(t) is shown to have the asymptotic expansion k(infinity)[1 + k(infinity) (pie Dt)-1/2 /4 pie D + ...], where D is the relative translational diffusion constant. An approximate analytical method for calculating k(t) is presented. This is based on the approximation that the probability density of the reactant pair in the reactive region keeps the equilibrium distribution but with a decreasing amplitude. The rate coefficient then is determined by the Green function in the absence of chemical reaction. Within the framework of this approximation, two general relations are obtained. The first relation allows the rate coefficient for an arbitrary amplitude of the reactivity to be found if the rate coefficient for one amplitude of the reactivity is known. The second relation allows the rate coefficient in the presence of conformational gating to be found from that in the absence of conformational gating. The ratio k(t)/k(0) is shown to be the survival probability of the reactant pair at time t starting from an initial distribution that is localized in the reactive region. This relation forms the basis of the calculation of k(t) through Brownian dynamics simulations. Two simulation procedures involving the propagation of nonreactive trajectories initiated only from the reactive region are described and illustrated on a model system. Both analytical and simulation results demonstrate the accuracy of the equilibrium-distribution approximation method.

Zhou, H X; Szabo, A

1996-01-01

328

On the thickness-dependent diffusion coefficient of perfluoropolyether lubricants on a thin diamond-like film  

NASA Astrophysics Data System (ADS)

Diffusion of perfluoropolyethers (PFPEs) lubricants on a hard disk surface is an important self healing characteristic to replenish PFPEs lubricants on their uncovered surface. In the present paper, we study the diffusion coefficients of non-functional PFPE Z and PFPE Zdol with functional end groups as a function of lubricant film thickness on a thin DLC (diamond-like) film. Diffusion coefficients of PFPE Z and PFPE Zdol molecules on a DLC film are calculated using the equation of Einstein's law of diffusion (Guo et al. J. Appl. Phys 93:8707, 2003; Guo Ph.D. thesis, 2006; Chung et al. IEEE Trans. Magn. 45:3644, 2009) considering the movement of their center of mass to reach their equilibrium positions from their original configurations. And it is averaged with the film thickness to show the thickness dependence on the diffusion of PFPEs lubricants on a DLC substrate. Firstly diffusion coefficients of sub-monolayer of partially coverage PFPE Z and PFPE Zdol on a DLC substrate are studied briefly and secondly the diffusion coefficient of monolayer PFPE Zdol on a DLC substrate is also studied elaborately. To support our results, we compare our thickness-dependent diffusion coefficients of PFPE Z and PFPE Zdol with those of published theoretical (Guo Ph.D. thesis, 2006; Chung et al. IEEE Trans. Magn. 45:3644, 2009) and experimental results (Chung et al. Tribol. Lett. 32:35, 2008; Ma et al. Tribol. Lett. 10:203, 2001). Here we study how lubricant film thickness plays an important role on its diffusion. Effects of polar end bead functionality, lubricant film thickness enhance the anisotropic behavior of diffusion coefficients of PFPE Zdol on the DLC substrate. But in the present analysis we consider hard disk carbon overcoat as a thin DLC film and we include all of their atoms within the force cut-off distance with PFPEs lubricant molecules for the interactions to study the thickness dependence on their diffusion coefficients.

Deb Nath, S. K.

2014-05-01

329

Physics-based ULF Wave Radial Diffusion Coefficients in the Van Allen Belts  

NASA Astrophysics Data System (ADS)

Power in the Pc5 ULF wave band is believed to have strong impact on the acceleration and transport of MeV energy electrons in the outer radiation belt. Typically, radial belt diffusion coefficients are defined from empirical approaches, based on observed flux variations and param-eterised by geomagnetic indices. We report the results of new ULF wave diffusion coefficients derived from statistical analyses of ULF wave power from ground-based magnetometers from the CARISMA chain, as well as from in-situ data from GOES and THEMIS. These results are compared to previous empirical results, and the dependence of the wave-driven coefficients on energy and solar wind speed presented. The ULF wave physics model illustrates the importance of global measurements for identifying dominant or active acceleration mechanisms. Future in-situ radiation belt missions such as the Canadian Space Agency Outer Radiation Belt Injec-tion, Transport, Acceleration and Loss Satellite (ORBITALS) will enable these physics-based models to be tested and the relative importance of various ULF and VLF wave acceleration and loss processes established. In combination with the approved NASA LWS RBSP mission, and the proposed Japanese ERG satellite, the ORBITALS-RBSP-ERG three petal constella-tion together with supporting ground-based and geosynchronous measurements will resolve the spatio-temporal ambiguities and global dynamics and morphology of the Earths radiation belts.

Mann, Ian; Rae, Jonathan; Murphy, Kyle; Ozeke, Louis; Milling, David; Chan, Anthony; Elkington, Scot; Angelopoulos, Vassilis

330

Lateral Diffusion Coefficients of an Eicosanyl-Based Bisglycerophosphocholine Determined by PFG-NMR and FRAP  

PubMed Central

We report the lateral diffusion properties of 2,2?-di-O-decyl-3,3?-di-O-(eicosanyl)-bis-(rac-glycero)-1,1?-diphosphocholine (C20BAS) using pulsed-field gradient NMR (PFG-NMR) and fluorescence recovery after photobleaching (FRAP). C20BAS membranes display a melting transition at Tm = 15.7 °C as determined by differential scanning calorimetry and 31P NMR chemical shift anisotropy. The lateral diffusion coefficient of C20BAS, as determined by PFG-NMR and FRAP, at 25 °C, were DPFG-NMR = 1.9 ± 0.6 × 10?8 cm2/s and DFRAP C20BAS = 1.2 ± 0.1 × 10?8 cm2/s, respectively. In comparison, the lateral diffusion coefficient of the monopolar phospholipid, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), was 1.8 ± 0.9 × 10?8 and 2.5 ± 0.9 × 10?8 cm2/s using PFG-NMR and FRAP, respectively.

Febo-Ayala, Wilma; Holland, David P.; Bradley, Scott A.; Thompson, David H.

2008-01-01

331

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

332

System size dependence of the diffusion coefficient in a simple liquid  

NASA Astrophysics Data System (ADS)

An equation to estimate the system size dependence of the self-diffusion coefficient of a tagged particle moving in a simple fluid is given using linear-response theory and linearized hydrodynamics. Estimates made by the equation are compared with the results of the molecular dynamics simulation for a hard-sphere fluid at two densities, ??3?0.88 and 0.47, where ? is the hard-sphere diameter. Good agreement between theory and simulation is obtained at the higher density. At the lower density, the agreement becomes poorer, but it is improved by taking into account the diffusion effect of the tagged particle. The equation gives the same diffusion coefficient for the infinite system as that obtained by taking into account the long-time tail contribution of the velocity autocorrelation function [B. J. Alder, D. M. Gass, and T. E. Wainwright, J. Chem. Phys. 53, 3813 (1970)]. When the tagged particle has a larger mass than the fluid particles, the equation presented here gives the better estimates. It is confirmed by the molecular dynamics calculation.

Fushiki, M.

2003-08-01

333

Optimal estimation of the diffusion coefficient from non-averaged and averaged noisy magnitude data  

NASA Astrophysics Data System (ADS)

The magnitude operation changes the signal distribution in MRI images from Gaussian to Rician. This introduces a bias that must be taken into account when estimating the apparent diffusion coefficient. Several estimators are known in the literature. In the present paper, two novel schemes are proposed. Both are based on simple least squares fitting of the measured signal, either to the median (MD) or to the maximum probability (MP) value of the Probability Density Function (PDF). Fitting to the mean (MN) or a high signal-to-noise ratio approximation to the mean (HS) is also possible. Special attention is paid to the case of averaged magnitude images. The PDF, which cannot be expressed in closed form, is analyzed numerically. A scheme for performing maximum likelihood (ML) estimation from averaged magnitude images is proposed. The performance of several estimators is evaluated by Monte Carlo (MC) simulations. We focus on typical clinical situations, where the number of acquisitions is limited. For non-averaged data the optimal choice is found to be MP or HS, whereas uncorrected schemes and the power image (PI) method should be avoided. For averaged data MD and ML perform equally well, whereas uncorrected schemes and HS are inadequate. MD provides easier implementation and higher computational efficiency than ML. Unbiased estimation of the diffusion coefficient allows high resolution diffusion tensor imaging (DTI) and may therefore help solving the problem of crossing fibers encountered in white matter tractography.

Kristoffersen, Anders

2007-08-01

334

A method for determining the diffusion coefficient in Fe(II/III) radiation dosimetry gels using finite elements  

NASA Astrophysics Data System (ADS)

Magnetic resonance imaging (MRI) may be used to image three-dimensional dose distributions of ionizing radiation in tissue equivalent gels infused with ferrous sulphate solutions, commonly known as Fricke gels. In this technique, ferrous ions are oxidized to ferric ions by free radicals produced by ionizing radiation. A limitation on this technique is the diffussion of ferric ions in the gel. A method is presented for evaluating the diffusion coefficient in Fricke gels. Finite elements are used to model variations of the concentration in space, coupled with an analytical scheme to integrate the resulting system of equations through time. This method may be used for problems with one, two or three space dimensions and with arbitrary initial and boundary conditions. Results are presented for one- and two-dimensional data.

Harris, P. J.; Piercy, A.; Baldock, C.

1996-09-01

335

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

336

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

337

Cathodic reduction of sulfur dioxide in nonaqueous electrolytes. The effect of solution composition on the diffusion coefficient of sulfur dioxide  

SciTech Connect

The authors measured the diffusion coefficients of SO/sub 2/ in electrolytes based on propylene carbonate, acetonitrile, dimethylformamide and dimethylsulfoxide in order to estimate possible diffusion limitations with respect to SO/sub 2/ and to establish the influence exerted by the solvent type on the process. The diffusion coefficients were calculated from the limiting diffusion currents of steady-state polarization curves for sulfur dioxide reduction recorded at a gold microdisk electrode which had a diameter of 2 x 10/sup -3/ cm. In lithium salt solutions the potentiodynamic curves recorded at the microelectrode do not exhibit a limiting current but are characterized by a current maximum.

Shembel, E.M.; Ksenzhek, O.S.; Lituinova, V.I.; Lobach, G.A.

1986-09-01

338

Deconvolution of Compartmental Water Diffusion Coefficients in Yeast-Cell Suspensions Using Combined T1 and Diffusion Measurements  

NASA Astrophysics Data System (ADS)

An NMR method is presented for measuring compartment-specific water diffusion coefficient ( D) values. It uses relaxography, employing an extracellular contrast reagent (CR) to distinguish intracellular (IC) and extracellular (EC) 1H 2O signals by differences in their respective longitudinal ( T1) relaxation times. A diffusion-weighted inversion-recovery spin-echo (DW-IRSE) pulse sequence was used to acquire IR data sets with systematically and independently varying inversion time (TI) and diffusion-attenuation gradient amplitude ( g) values. Implementation of the DW-IRSE technique was demonstrated and validated using yeast cells suspended in 3 mM Gd-DTPA 2- with a wet/dry mass ratio of 3.25:1.0. Two-dimensional (2D) NMR data were acquired at 2.0 T and analyzed using numerical inverse Laplace transformation (2D- and sequential 1D-ILT) and sequential exponential fitting to yield T1 and water D values. All three methods gave substantial agreement. Exponential fitting, deemed the most accurate and time efficient, yielded T1: D (relative contribution) values of 304 ms:0.023×10 -5 cm 2/s (47%) and 65 ms:1.24×10 -5 cm 2/s (53%) for the IC and EC components, respectively. The compartment-specific D values derived from direct biexponential fitting of diffusion-attenuation data were also in good agreement. Extension of the DW-IRSE method to in vivo models should provide valuable insights into compartment-specific water D changes in response to injury or disease.

Silva, Matthew D.; Helmer, Karl G.; Lee, Jing-Huei; Han, Sam S.; Springer, Charles S.; Sotak, Christopher H.

2002-05-01

339

Deconvolution of compartmental water diffusion coefficients in yeast-cell suspensions using combined T(1) and diffusion measurements.  

PubMed

An NMR method is presented for measuring compartment-specific water diffusion coefficient (D) values. It uses relaxography, employing an extracellular contrast reagent (CR) to distinguish intracellular (IC) and extracellular (EC) (1)H(2)O signals by differences in their respective longitudinal (T(1)) relaxation times. A diffusion-weighted inversion-recovery spin-echo (DW-IRSE) pulse sequence was used to acquire IR data sets with systematically and independently varying inversion time (TI) and diffusion-attenuation gradient amplitude (g) values. Implementation of the DW-IRSE technique was demonstrated and validated using yeast cells suspended in 3 mM Gd-DTPA(2-) with a wet/dry mass ratio of 3.25:1.0. Two-dimensional (2D) NMR data were acquired at 2.0 T and analyzed using numerical inverse Laplace transformation (2D- and sequential 1D-ILT) and sequential exponential fitting to yield T(1) and water D values. All three methods gave substantial agreement. Exponential fitting, deemed the most accurate and time efficient, yielded T(1):D (relative contribution) values of 304 ms:0.023x10(-5) cm(2)/s (47%) and 65 ms:1.24x10(-5) cm(2)/s (53%) for the IC and EC components, respectively. The compartment-specific D values derived from direct biexponential fitting of diffusion-attenuation data were also in good agreement. Extension of the DW-IRSE method to in vivo models should provide valuable insights into compartment-specific water D changes in response to injury or disease. (c) 2002 Elsevier Science (USA). PMID:12081442

Silva, Matthew D; Helmer, Karl G; Lee, Jing-Huei; Han, Sam S; Springer, Charles S; Sotak, Christopher H

2002-05-01

340

Determination of diffusion coefficients by supercritical fluid chromatography: Effects of mobile phase mean velocity and column orientation.  

PubMed

The supercritical fluid (SCF) chromatographic technique based on the Taylor dispersion theory has been widely applied in determination of diffusion coefficients of various organic compounds in SCFs. This study was aimed to understand impacts of mobile phase mean velocity (MPMV) and column orientation on diffusion coefficient measurements. The benzene/SCCO(2) system was investigated. Experiments were carried out at 40 and 60 degrees C and 9-15 MPa over a wide range of CO(2) densities at varying MPMV and repeated in two column orientations, vertical and horizontal. It was found that both MPMV and column orientation significantly affected measurements of diffusion coefficients in SCFs. When the column was installed vertically, apparent diffusion coefficients obtained at relatively low CO(2) density (<580 kg/m(3)) increased with increasing MPMV over the entire velocity ranges. This results in a conclusion that diffusion coefficients cannot be accurately determined under these conditions using a vertically installed column. Under all other conditions, as MPMV increased, apparent diffusion coefficients initially increased, then remained constant, and finally increased again. The initial increase of apparent diffusion coefficients was associated with significant decline of curve-fitting errors, which indicates that the buoyancy effects are non-negligible and will cause larger errors. Accordingly, a new generalized D(12)-U diagram comprised of three regions is proposed. Column orientation affected diffusion coefficient measurements mainly by enhancing or weakening the buoyancy effects. When the column was installed vertically, the buoyancy effects were enhanced, leading to lower apparent diffusion coefficients, especially when CO(2) density was relatively low. In addition, it was found that when CO(2) density was below approximately 580 kg/m(3), diffusion coefficients obtained when the column was horizontally installed were higher than those obtained when the same column was vertically installed. When CO(2) density was above that value, opposite outcomes resulted. Finally, the horizontal orientation of a diffusion column is recommended for diffusion coefficient measurements by the SCF chromatographic technique, especially when densities of SCFs are relatively low. PMID:20493492

Lin, Ronghong; Tavlarides, Lawrence L

2010-06-25

341

Interdiffusion in Ni-rich, Ni-Cr-Al alloys at 1100 and 1200 C. I - Diffusion paths and microstructures. II - Diffusion coefficients and predicted concentration profiles  

NASA Technical Reports Server (NTRS)

Interdiffusion in Ni-rich Ni-Cr-Al alloys is investigated experimentally after annealing at 1100 and 1200 C using gamma/gamma, gamma/gamma+beta, gamma/gamma+gamma prime, and gamma/gamma+alpha diffusion couples. The amount and location of Kirkendall porosity suggests that Al diffuses more rapidly than Cr which diffuses more rapidly than Ni in the gamma phase of Ni-Cr-Al alloys. The location and extent of maxima and minima in the concentration profiles of the diffusion couples indicate that both cross-term diffusion coefficients are positive. Measurements are also presented of the ternary interdiffusion coefficients of the gamma phase in the Ni-Cr-Al system. It is shown that the interdiffusion coefficients can be accurately predicted by using a ternary finite-difference interdiffusion model.

Nesbitt, J. A.; Heckel, R. W.

1987-01-01

342

Intercentre reproducibility of cardiac apparent diffusion coefficient and fractional anisotropy in healthy volunteers  

PubMed Central

Background Diffusion tensor cardiac magnetic resonance (DT-CMR) enables probing of the microarchitecture of the myocardium, but the apparent diffusion coefficient (ADC) and fractional anisotropy (FA) reported in healthy volunteers have been inconsistent. The aim of this study was to validate a stimulated-echo diffusion sequence using phantoms, and to assess the intercentre reproducibility of in-vivo diffusion measures using the sequence. Methods and results A stimulated-echo, cardiac-gated DT-CMR sequence with a reduced-field-of-view, single-shot EPI readout was used at two centres with 3 T MRI scanners. Four alkane phantoms with known diffusivities were scanned at a single centre using a stimulated echo sequence and a spin-echo Stejskal-Tanner diffusion sequence. The median (maximum, minimum) difference between the DT-CMR sequence and Stejskal-Tanner sequence was 0.01 (0.04, 0.0006) × 10-3 mm2/s (2%), and between the DT-CMR sequence and literature diffusivities was 0.02 (0.05, 0.006) × 10-3 mm2/s (4%). The same ten healthy volunteers were scanned using the DT-CMR sequence at the two centres less than seven days apart. Average ADC and FA were calculated in a single mid-ventricular, short axis slice. Intercentre differences were tested for statistical significance at the p??0.05), and only the diastolic ADC showed a statistically significant, but numerically small, difference of 0.07 × 10-3 mm2/s (p?=?0.047). The intercentre, intrasubject coefficients of variance were: systolic ADC 7%, FA 6%; diastolic ADC 7%, FA 3%. Conclusions This is the first study to demonstrate the accuracy of a stimulated-echo DT-CMR sequence in phantoms, and demonstrates the feasibility of obtaining reproducible ADC and FA in healthy volunteers at separate centres with well-matched sequences and processing.

2014-01-01

343

Mesure des coefficients de la matrice de diffusion d'une jonction mécanique  

NASA Astrophysics Data System (ADS)

La caractérisation expérimentale des jonctions mécaniques souvent complexes rencontrées dans nombre d'applications industrielles est un élément essentiel intervenant dans l'élaboration de modèles vibratoires. Les jonctions permettant de relier des structures simples de type plaque ou poutre peuvent être représentées à l'aide de matrice de diffusion. L'objet de cette communication est de présenter un dispositif expéri mental permettant la mesure des caractéristiques d'une jonction constituée d'une masse symétrique raccordant deux poutres soumises à des vibrations de flexion. La méthode de mesure et ses conditions optimales de mise en oeuvre sont présentées et permettent d'obtenir les coefficients de transmission et de réflexion. Un modèle, tenant compte de l'élasticité des liaisons poutre/masse permet de rendre compte des coefficients mesurés et d'interpréter leur variation fréquentielle à l'aide du phénomène de masse bloquante.

Moulet, M.-H.; Gautier, F.; Pascal, J.-C.

2002-12-01

344

Evaluation of the diffusion coefficient of fluorine during the electropolishing of niobium  

NASA Astrophysics Data System (ADS)

Future accelerators require unprecedented cavity performance, which is strongly influenced by interior surface nanosmoothness. Electropolishing (EP) is the technique of choice being developed for high-field superconducting radio frequency (SRF) cavities. Previous study has shown that the mechanism of Nb electropolishing proceeds by formation and dissolution of a compact salt film under fluorine diffusion-limited mass transport control. We pursue an improved understanding of the microscopic conditions required for optimum surface finishing. The viscosity of the standard electrolyte has been measured using a commercial viscometer, and the diffusion coefficient of fluorine was derived at a variety of temperatures from 0 to 50°C using a Nb rotating disk electrode. In addition, data indicate that electrode kinetics becomes competitive with the mass transfer current limitation and increases dramatically with temperature. These findings are expected to guide the optimization of EP process parameters for achieving controlled, reproducible, and uniform nanosmooth surface finishing of SRF cavities.

Tian, Hui; Reece, Charles E.

2010-08-01

345

Soliton-like solutions of certain types of nonlinear diffusion reaction equations with variable coefficient  

NASA Astrophysics Data System (ADS)

With a view to exploring new soliton-like solutions of certain types of nonlinear diffusion-reaction (DR) equations with a variable coefficient, we demonstrate the viability of a method which is the combination of both the symbolic computation technique of Gao and Tian [Y.T. Gao, B. Tian, Comput. Phys. Commun. 133 (2001) 158] and auxiliary equation method of Sirendaoreji [Sirendaoreji, Phys. Lett. A 356 (2006) 124] and used recently for the KdV equation. In particular, the DR equations with quadratic and cubic nonlinearities with a time-dependent velocity in the convective flux term are studied and the existence of soliton-like solutions is shown.

Kumar, Ranjit; Kaushal, R. S.; Prasad, Awadhesh

2008-03-01

346

Phospholipid Diffusion Coefficients of Cushioned Model Membranes determined via Z-Scan Fluorescence Correlation Spectroscopy  

PubMed Central

Model cellular membranes enable the study of biological processes in a controlled environment and reduce the traditional challenges associated with live or fixed cell studies. However, model membrane systems based on the air/water or oil/solution interface do not allow for incorporation of transmembrane proteins, or for the study of protein transport mechanisms. Conversely, a phospholipid bilayer deposited via the Langmuir-Blodgett/Langmuir Schaefer method on a hydrogel layer is potentially an effective mimic of the cross-section of a biological membrane, and facilitates both protein incorporation and transport studies. Prior to application, however, such membranes must be fully characterized, particularly with respect to the phospholipid bilayer phase transition temperature. Here we present a detailed characterization of the phase transition temperature of the inner and outer leaflets of a chitosan supported model membrane system. Specifically, the lateral diffusion coefficient of each individual leaflet has been determined as a function of temperature. Measurements were performed utilizing z-scan fluorescence correlation spectroscopy (FCS), a technique that yields calibration-free diffusion information. Analysis via the method of Wawrezinieck and coworkers, revealed that phospholipid diffusion changes from raft-like to free diffusion as the temperature is increased; an insight into the dynamic behavior of hydrogel supported membranes not previously reported.

Sterling, Sarah M.; Allgeyer, Edward S.; Fick, Jorg; Prudovsky, Igor; Mason, Michael D.; Neivandt, David J.

2013-01-01

347

Scaling invariance of the diffusion coefficient in a family of two-dimensional Hamiltonian mappings.  

PubMed

We consider a family of two-dimensional nonlinear area-preserving mappings that generalize the Chirikov standard map and model a variety of periodically forced systems. The action variable diffuses in increments whose phase is controlled by a negative power of the action and hence effectively uncorrelated for small actions, leading to a chaotic sea in phase space. For larger values of the action the phase space is mixed and contains a family of elliptic islands centered on periodic orbits and invariant Kolmogorov-Arnold-Moser (KAM) curves. The transport of particles along the phase space is considered by starting an ensemble of particles with a very low action and letting them evolve in the phase until they reach a certain height h. For chaotic orbits below the periodic islands, the survival probability for the particles to reach h is characterized by an exponential function, well modeled by the solution of the diffusion equation. On the other hand, when h reaches the position of periodic islands, the diffusion slows markedly. We show that the diffusion coefficient is scaling invariant with respect to the control parameter of the mapping when h reaches the position of the lowest KAM island. PMID:23848745

de Oliveira, Juliano A; Dettmann, Carl P; da Costa, Diogo R; Leonel, Edson D

2013-06-01

348

Determination of a Diffusion Coefficient by Capillary Electrophoresis. An Experiment for the Physical and Biophysical Chemistry Laboratories  

Microsoft Academic Search

Students measure the diffusion coefficient of dopamine (3-hydroxytyramine) by capillary electrophoresis using three evaluation methods: single-point, graphical, and stopped migration. The experiment combines instruction of modern instrumentation with the determination of a biologically significant physical constant.

Kathryn R. Williams; Bhavin Adhyaru; Igor German; Thomas Russell

2002-01-01

349

Analytical expressions for the NMR apparent diffusion coefficients in an anisotropic system and a simplified method for determining fiber orientation.  

PubMed

NMR measurements of anisotropic diffusion were studied using a three-dimensional random-walk model. It was found that the apparent diffusion coefficient can be expressed in a canonical form as the product of a diagonal matrix, an orthonormal rotation matrix, and a vector representing the encoding magnetic field gradient. The diffusion coefficient can be interpreted as the sum of the corresponding coefficients measured along the principal diffusion axes, weighted by the squares of the directional cosines of the encoding direction with respect to the principal axes. The analysis revealed that determining the orientation of anisotropy, in a cylindrically symmetric system, requires a minimum of four diffusion measurements. A special pulse sequence which minimized gradient cross-terms and possible restricted diffusion effects was used to characterize diffusion anisotropy in cut chicken gizzards. Diffusion coefficients parallel to the muscle fibers were found to be approximately two to three times larger than those in the transverse direction. Furthermore, the method was successful in detecting the angular change when the sample was rotated by 30 degrees. Results indicate that the proposed approach to measure fiber orientation is valid and may be used to improve the time efficiency of diffusion anisotropy measurements. PMID:7476078

Hsu, E W; Mori, S

1995-08-01

350

ON THE DIFFERENT ANALYTICAL RESULTS OBTAINED FOR THE PARALLEL DIFFUSION COEFFICIENT OF COSMIC PARTICLES WITH ADIABATIC FOCUSING  

SciTech Connect

A spatially varying mean magnetic field gives rise to so-called adiabatic focusing of energetic particles propagating through the universe. In the past, different analytical approaches have been proposed to calculate the particle diffusion coefficient along the mean field with focusing. In the present paper, we show how these different results are related to each other. New results for the parallel diffusion coefficient that are more general than previous results are also presented.

Shalchi, A.; Danos, R. J., E-mail: andreasm4@yahoo.com [Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2 (Canada)

2013-03-10

351

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

352

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

353

Effect of cation on diffusion coefficient of ionic liquids at onion-like carbon electrodes.  

PubMed

While most supercapacitors are limited in their performance by the stability of the electrolyte, using neat ionic liquids (ILs) as the electrolyte can expand the voltage window and temperature range of operation. In this study, ILs with bis(trifluoromethylsulfonyl)imide (Tf2N) as the anion were investigated as the electrolyte in onion-like carbon-based electrochemical capacitors. To probe the influence of cations on the electrochemical performance of supercapacitors, three different cations were used: 1-ethyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium and 1,6-bis(3-methylimidazolium-1-yl). A series of electrochemical characterization tests was performed using cyclic voltammetry (CV), galvanostatic cycling and electrochemical impedance spectroscopy (EIS). Diffusion coefficients were measured using EIS and correlated with quasielastic neutron scattering and molecular dynamics simulation. These three techniques were used in parallel to confirm a consistent trend between the three ILs. It was found that the IL with the smaller sized cation had a larger diffusion coefficient, leading to a higher capacitance at faster charge-discharge rates. Furthermore, the IL electrolyte performance was correlated with increasing temperature, which limited the voltage stability window and led to the formation of a solid electrolyte interphase on the carbon electrode surface, evident in both the CV and EIS experiments. PMID:24920163

Van Aken, Katherine L; McDonough, John K; Li, Song; Feng, Guang; Chathoth, Suresh M; Mamontov, Eugene; Fulvio, Pasquale F; Cummings, Peter T; Dai, Sheng; Gogotsi, Yury

2014-07-16

354

Effect of cation on diffusion coefficient of ionic liquids at onion-like carbon electrodes  

NASA Astrophysics Data System (ADS)

While most supercapacitors are limited in their performance by the stability of the electrolyte, using neat ionic liquids (ILs) as the electrolyte can expand the voltage window and temperature range of operation. In this study, ILs with bis(trifluoromethylsulfonyl)imide (Tf2N) as the anion were investigated as the electrolyte in onion-like carbon-based electrochemical capacitors. To probe the influence of cations on the electrochemical performance of supercapacitors, three different cations were used: 1-ethyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium and 1,6-bis(3-methylimidazolium-1-yl). A series of electrochemical characterization tests was performed using cyclic voltammetry (CV), galvanostatic cycling and electrochemical impedance spectroscopy (EIS). Diffusion coefficients were measured using EIS and correlated with quasielastic neutron scattering and molecular dynamics simulation. These three techniques were used in parallel to confirm a consistent trend between the three ILs. It was found that the IL with the smaller sized cation had a larger diffusion coefficient, leading to a higher capacitance at faster charge–discharge rates. Furthermore, the IL electrolyte performance was correlated with increasing temperature, which limited the voltage stability window and led to the formation of a solid electrolyte interphase on the carbon electrode surface, evident in both the CV and EIS experiments.

Van Aken, Katherine L.; McDonough, John K.; Li, Song; Feng, Guang; Chathoth, Suresh M.; Mamontov, Eugene; Fulvio, Pasquale F.; Cummings, Peter T.; Dai, Sheng; Gogotsi, Yury

2014-07-01

355

A comparison study of linear reconstruction techniques for diffuse optical tomographic imaging of absorption coefficient  

NASA Astrophysics Data System (ADS)

We compare, through simulations, the performance of four linear algorithms for diffuse optical tomographic reconstruction of the three-dimensional distribution of absorption coefficient within a highly scattering medium using the diffuse photon density wave approximation. The simulation geometry consisted of a coplanar array of sources and detectors at the boundary of a half-space medium. The forward solution matrix is both underdetermined, because we estimate many more absorption coefficient voxels than we have measurements, and ill-conditioned, due to the ill-posedness of the inverse problem. We compare two algebraic techniques, ART and SIRT, and two subspace techniques, the truncated SVD and CG algorithms. We compare three-dimensional reconstructions with two-dimensional reconstructions which assume all inhomogeneities are confined to a known horizontal slab, and we consider two `object-based' error metrics in addition to mean square reconstruction error. We include a comparison using simulated data generated using a different FDFD method with the same inversion algorithms to indicate how our conclusions are affected in a somewhat more realistic scenario. Our results show that the subspace techniques are superior to the algebraic techniques in localization of inhomogeneities and estimation of their amplitude, that two-dimensional reconstructions are sensitive to underestimation of the object depth, and that an error measure based on a location parameter can be a useful complement to mean squared error.

Gaudette, Richard J.; Brooks, Dana H.; Di Marzio, Charles A.; Kilmer, Misha E.; Miller, Eric L.; Gaudette, Thomas; Boas, David A.

2000-04-01

356

Radial Intensity Gradients and Diffusion Coefficients of Cosmic Rays in the Outer Heliosphere at Solar Maximum  

NASA Astrophysics Data System (ADS)

The IMP-8, Voyager and Pioneer cosmic ray observations now cover the solar maximum of cycles 21, 22, and 23 and out to a heliocentric distance of 88 AU. In an accompanying paper we showed that the radial dependences of intensities J are different in the inner and outer heliosphere with a transition over the radial distance of 10 to 15 AU, and that those intensity gradients are well described as dJ/Jdr= G0 /r where r is heliocentric radial distance and G0 is constant with a different value in the inner and outer heliosphere. Using the obtained gradients and a simple one-dimensional modulation model we determined the diffusion coefficients as a function of radial distance and rigidity in the outer heliosphere at solar maximum. It is found that the diffusion coefficient, K, depends on radial distance r as r˜1.2 and on rigidity R as ? R˜1.0 respectively in the outer heliosphere beyond 10 AU, where ? is particle velocity over light velocity. K is determined on the assumption that K is a separable function of r and R.

Fujii, Z.; McDonald, Frank B.; Caballero-Lopez, R.A.; Moraal, Harm

2003-07-01

357

Diffusion of neptunyl(V) and pertechnetate ions in marine sediments  

SciTech Connect

The diffusion of the /sup 235/NpO/sub 2//sup +/ and /sup 95m/TcO/sub 4//sup -/ ions has been measured directly in sample cylinders of two different sediments from the floor of the deep sea. In smectite-rich sediment not shielded from contact with atmospheric oxygen the following values were obtained for the effective diffusion coefficients of neptunyl and pertechnetate ions, respectively: D/sub eff/(NpO/sub 2//sup +/) = 1.5 x 10/sup -8/ cm/sup 2/s/sup -1/ and D/sub eff/(TcO/sub 4//sup -/) = 3.2 x 10/sup -6/ cm/sup 2/s/sup -1/. Under anoxic conditions in sediment with known reducing properties, the pertechnetate ion appears to undergo slow reduction and the effective diffusion coefficient of the reduced species of D/sub eff/(Tc,red) = 1.1 x 10/sup -10/ cm/sup 2/s/sup -1/ reflects a substantial decrease of the mobility of the lower-valent technetium. 5 figures.

Schreiner, F.; Fried, S.; Friedman, A.

1981-01-01

358

Determination of the diffusion coefficient of hydrogen in metals from the rate of change in the electrical resistance in desorption  

SciTech Connect

A proposed method of measuring the diffusion coefficient of hydrogen D from the rate of change in electrical resistance in degassing of hydrogenimpregnated specimens is presented. Distinguished by simplicity, the method makes it possible to determine the coefficients with any method of hydrogen impregnation in a broad temperature range.

Mikitishin, S.I.; Fedorov, V.V.; Sergienko, O.M.; Sokolovskii, O.R.; Spas, Y.M.

1985-07-01

359

Diffusion coefficients varying with a power of the concentration: Convenient solutions and a reexamination of Zn in GaAs  

Microsoft Academic Search

Diffusion, at constant surface concentration, with coefficient varying to the positive nth power is considered. It is shown that the diffusion equation for these cases has a unique solution whose leading term is concentration ~Z1\\/n, where z = 1-(x\\/x+), x being the distance from the surface and x+ the distance at which the concentration just reaches zero. Numerical solutions can

Joseph Blanc

1974-01-01

360

Short-time behavior of the diffusion coefficient as a geometrical probe of porous media  

NASA Astrophysics Data System (ADS)

We investigate the time-dependent diffusion coefficient, D(t)=/(6t), of random walkers in porous media with piecewise-smooth pore-grain interfaces. D(t) is measured in pulsed-field-gradient spin-echo (PFGSE) experiments on fluid-saturated porous media. For reflecting boundary conditions at the interface we show that for short times D(t)/D0 =1-A0(D0t)1/2+B0D0t+O[(D0t)3/2], where A0=4S/(9 ?? VP) and B0=-HS/(12VP)-tsumi(Li/VP)f(?i). Here D0 is the diffusion constant of the bulk fluid, S/VP is the surface area to pore volume ratio, H is the mean curvature of the smooth portions of the surface, Li is the length of a wedge of angle ?i, and the function f(?) is defined below. More generally, we consider partially absorbing boundary conditions, where the absorption strength is controlled by a surface-relaxivity parameter ?. Here, the density of walkers (i.e., the net magnetization) decays as M(t)=1-?St/VP+..., and D(t) is defined as s/(6t), where s is the mean-square displacement of surviving walkers. When ??0 we find that the coefficient A0 of the ?D0t term in the above equation is unchanged, while the coefficient of the linear term changes to B0+?S/(6VP). Thus, data on D(t) and M(t) at short times may be used simultaneously to determine S/VP and ?. The limiting behavior of D(t) as ?-->? is also discussed.

Mitra, Partha P.; Sen, Pabitra N.; Schwartz, Lawrence M.

1993-04-01

361

Diffusion coefficient of cyclic GMP in salamander rod outer segments estimated with two fluorescent probes.  

PubMed

Experiments have demonstrated that single photoisomerizations in amphibian and primate rods can cause the suppression of 3-5% of the dark circulating current at the response peak (Baylor, D. A., T. D. Lamb, and K. W. Yau. 1979. J. Physiol. (Lond.). 288:613-634; Baylor, D. A., B. J. Nunn, and J. L. Schnapf. 1984. J. Physiol. (Lond.). 357:575-607). These results indicate that the change in [cGMP] effected by a single isomerization must spread longitudinally over at least the corresponding fractional length of the outer segment. The effective longitudinal diffusion coefficient, Dx, of cGMP is thus an important determinant of rod sensitivity. We report here measurements of the effective longitudinal diffusion coefficients, Dx, of two fluorescently labeled molecules: 5/6-carboxyfluorescein and 8-(fluoresceinyl)thioguanosine 3',5'-cyclic monophosphate, introduced into detached outer segments via whole-cell patch electrodes. For these compounds, the average time for equilibration of the entire outer segment with the patch pipette was approximately 6 min. Fluorescence images of rods were analyzed with a one-dimensional diffusion model that included limitations on transfer between the electrode and outer segment and the effects of intracellular binding of the dyes. The analyses yielded estimates of Dx of 1.9 and 1.0 microns 2.s-1 for the two dyes. It is shown that these results place an upper limit on Dx for cGMP of 11 microns2.s-1. The actual value of Dx for cGMP in the rod will depend on the degree of intracellular binding of cGMP. Estimates of the effective buffering power for cGMP in the rod at rest range from two to six (Lamb and Pugh, 1992; Cote and Brunnock, 1993). When combined with these estimates, our results predict that for cGMP itself, Dx falls within the range of 1.4-5.5 microns 2.s-1. PMID:8241412

Olson, A; Pugh, E N

1993-09-01

362

Determinations of equilibrium segregation, effective segregation and diffusion coefficients for Nd+3 doped in molten YAG  

NASA Astrophysics Data System (ADS)

In this paper, a new mathematical model has been presented to determine the equilibrium segregation (k0) and effective segregation (keff) coefficients for neodymium (Nd) in YAG crystal grown by Czochralski (CZ) method. Determination of diffusion coefficient (DL) of Nd impurity in molten YAG is also investigated. In this model, utilizing Lambert W-function is a new idea to solve the Scheil equation for calculation of effective segregation coefficient. The Nd concentration in the crystal has been measured by optical absorption method to calculate keff. The analyses show that the keff is related to the growth parameters such as crystal growth rate (ug) and crystal rotation rate (?), ( ug/?{?}) but it is independent of the Nd concentration in the initial melt (C0). Based on obtained keff and experimental growth data, k0 and DL of Nd in molten YAG have been calculated. For all experiments, the average value of k0=0.216 and DL=1.4×10-6 (cm2/s) are obtained. Our results are corroborated by the theoretical and experimental data from the literature.

Asadian, M.; Saeedi, H.; Yadegari, M.; Shojaee, M.

2014-06-01

363

In vivo measurement of apparent diffusion coefficients of hyperpolarized (13) C-labeled metabolites.  

PubMed

The combination of hyperpolarized MRS with diffusion weighting (dw) allows for determination of the apparent diffusion coefficient (ADC), which is indicative of the intra- or extracellular localization of the metabolite. Here, a slice-selective pulsed-gradient spin echo sequence was implemented to acquire a series of dw spectra from rat muscle in vivo to determine the ADCs of multiple metabolites after a single injection of hyperpolarized [1-(13) C]pyruvate. An optimal control optimized universal-rotation pulse was used for refocusing to minimize signal loss caused by B1 imperfections. Non-dw spectra were acquired interleaved with the dw spectra and these were used to correct for signal decay during the acquisition as a result of T1 decay, pulse imperfections, flow etc. The data showed that the ADC values for [1-(13) C]lactate (0.4-0.7?µm(2) /ms) and [1-(13) C]alanine (0.4-0.9?µm(2) /ms) were about a factor of two lower than the ADC of [1-(13) C]pyruvate (1.1-1.5?µm(2) /ms). This indicates a more restricted diffusion space for the former two metabolites consistent with lactate and alanine being intracellular. The higher ADC for pyruvate (similar to the proton ADC) reflected that the injected substance was not confined inside the muscle cells but also present extracellular. Copyright © 2014 John Wiley & Sons, Ltd. PMID:24664927

Søgaard, Lise Vejby; Schilling, Franz; Janich, Martin A; Menzel, Marion I; Ardenkjaer-Larsen, Jan Henrik

2014-05-01

364

Blackness coefficients, effective diffusion parameters, and control rod worths for thermal reactors  

SciTech Connect

Simple diffusion theory cannot be used to evaluate control rod worths in thermal reactors because of the strongly absorbing character of the control material. However, good results can be obtained from a diffusion calculation by representing the absorber slab by means of a suitable pair of internal boundary conditions, ..cap alpha.. and ..beta.., which are ratios of neutron flux to neutron current. Methods for calculating ..cap alpha.. and ..beta.. in the P/sub 1/, P/sub 3/, and P/sub 5/ approximations, with and without scattering, are presented. By appropriately weighting the fine-group blackness coefficients, broad group values, <..cap alpha..> and <..beta..>, are obtained. The technique is applied to the calculation of control rod worths of Cd, Ag-In-Cd, and Hf control elements. Results are found to compare very favorably with detailed Monte Carlo calculations. For control elements whose geometry does not permit a thin slab treatment, other methods are needed for determining the effective diffusion parameters. One such method is briefly discussed and applied to the calculation of control rod worths in the Ford Nuclear Reactor at the University of Michigan. Calculated and measured worths are found to be in good agreement.

Bretscher, M.M.

1984-09-01

365

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

366

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

367

Apparent diffusion coefficient measurements to support a diagnosis of intracranial hypotension.  

PubMed

Objective: Intracranial hypotension (ICH) can be a challenging diagnosis, as cerebrospinal fluid leaks may be difficult to confirm, patients may have other causes for clinical symptoms and imaging findings can be non-specific, particularly in the setting of comorbidities. We investigate the use of brain diffusion measurements [apparent diffusion coefficient (ADC) values] in the assessment of ICH. Methods: 13 cases of ICH were identified retrospectively based on imaging findings and their clinical histories were compared with 13 control subjects. Regional ADC values and average diffusion constant (Dav) from brain slice ADC histograms were measured. Results: ADC values trended higher in all brain regions in patients with ICH than those in control subjects, with statistically significant differences in frontal white matter, mid-brain and deep grey structures. Dav determined by a single-slice ADC histogram was significantly higher in patients with ICH than in the control group (p?=?0.008). In two cases followed longitudinally, Dav correlated with the patient's symptoms and decreased towards normal value with blood patch. In one case, decreased Dav correlated with the formation of subdural collections. Conclusion: Cerebral oedema as assessed by increased ADC is strongly correlated with ICH (10 of 13 cases). Histographic analysis of ADC values may offer increased accuracy of ADC measurement. ADC value assessment in the determination of ICH may be particularly useful in complex clinical cases, where treatment is followed over time or where gadolinium is not used and meningeal enhancement cannot be assessed. Advances in knowledge: This article investigates the use of brain diffusion measurements in the assessment of ICH in the clinical setting. PMID:24896198

Cauley, K A; Fulwadhva, U; Dundmadappa, S K

2014-08-01

368

Self-Diffusion of Co2+ Ions in CoBr2, CoI2 and Electrolyte-Diffusion of ZnSO4 in Agar Gel Medium  

Microsoft Academic Search

Self-diffusion of Co2+ ions in CoBr2 and CoI2 is reported in the concentration range of 10–5 to 0.25M in 1% agar gel at 25 °C. The deviations observed between the experimental and theoretical values of diffusion coefficients are explained by considering different types of interactions occurring in the ion-gel water system. The applicability of the transition state theory to the

S. F. Patil; P. R. Patil

2000-01-01

369

Diffusion-weighted MRI with parallel imaging technique: apparent diffusion coefficient determination in normal kidneys and in nonmalignant renal diseases.  

PubMed

The purpose of the study was to assess the capability and the reliability of apparent diffusion coefficient (ADC) measurements in the evaluation of different benign renal abnormalities. Twenty-five healthy volunteers and 31 patients, divided into seven different groups (A-G) according to pathology, underwent diffusion-weighted magnetic resonance imaging (DW MRI) of the kidneys using 1.5-T system. DW images were obtained in the axial plane with a spin-echo echo planar imaging single-shot sequence with three b values (0, 300, and 600 s/mm²). Before acquisition of DW sequences, we performed in each patient a morphological study of the kidneys. ADC was 2.40±0.20×10?³ mm² s?¹ in volunteers. A significant difference was found between Groups A (cysts=3.39±0.51×10?³ mm² s?¹) and B (acute/chronic renal failure=1.38±0.40×10?³ mm² s?¹) and between Groups A and C (chronic pyelonephritis=1.53±0.21×10?³ mm² s?¹) (P<.05). An important difference was also observed among Group D (hydronephrosis=4.82±0.35×10?³ mm² s?¹) and Groups A, B, and C (P<.05), whereas no differences were found between Groups B and C (P>.05). A considerable correlation between glomerular filtration rate and ADC was found (P=.04). In conclusion, significant differences were detected among different patient groups, and this suggests that ADC measurements can be useful in differentiating normal renal parenchyma from most commonly encountered nonmalignant renal lesions. PMID:21092872

Macarini, Luca; Stoppino, Luca Pio; Milillo, Paola; Ciuffreda, Pierpaolo; Fortunato, Francesca; Vinci, Roberta

2010-01-01

370

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

371

Diffusion enhancement due to low-energy ion bombardment during sputter etching and deposition  

SciTech Connect

The effects of low-energy ion bombardment on enhancing elemental diffusion rates at both heterojunction interfaces during film deposition and over the compositionally altered layer created during sputter etching alloy targets have been considered. Depth dependent enhanced interdiffusion coefficients, expressed as D*(x)=D*(0) exp(-x/L/sub d/), where D*(0) is more than five orders of magnitude greater than thermal diffusion values, were measured in InSb/GaSb multilayer structures deposited by multitarget bias sputering. D*(0) was determined from the amplitude u of the compositional modulation in the multilayered films (layer thicknesses between 20 and 45 A) as measured by superlattice x-ray diffraction techniques. The value of D*(0) was found to increase from 3 x 10/sup -17/ to 1 x 10/sup -16/ cm/sup 2//sec as the applied substrate bias was increased from 0 to -75 V. However even at V/sub a/=0, the diffusion coefficient was enhanced owing to an induced substrate potential with respect to the positive space-charge region in the Ar discharge. The diffusion length of L/sub d/ of the ion bombardment created defects was approx.1000 A. Enhanced diffusion also has a significiant effect on the altered layer thickness x/sub e/ and the total sputtering time t/sub e/ (or ion dose) required to reach steady state during ion etching of multielement targets. The effects of using an exponentially depth dependent versus a constant value of the enhanced diffusion coefficient on calculated values of x/sub e/ and t/sub e/ in single-phase binary alloys were considered. The results show that both x/sub e/ and t/sub e/ are considerably larger using a depth dependent D*(x), when L/sub d/D*(0)/v, the usual case for most sputtering applications, the two solutions approach each other.

Eltoukhy, A.H.; Greene, J.E.

1980-08-01

372

Estimation of trioctylphosphine oxide (TOPO) diffusion coefficients by dynamic adsorption measurements in model extraction systems.  

PubMed

Equilibrium interfacial tension and surface excess isotherms for trioctylphosphine oxide (TOPO) were determined and interpreted. Despite its high hydrophobicity, TOPO adsorbs at the hydrocarbon/water interfaces and decreases effectively the interfacial tension. The interfacial activity of TOPO is affected by the type of organic diluent and the composition of the aqueous phase, i.e., the kind (HNO(3), KNO(3)) and the concentration of nonorganic electrolyte present in the system. Significant lowering of TOPO interfacial activity is observed with an increase of the aqueous phase acidity. The dynamic interfacial tension for TOPO was measured by using the drop volume technique. With the aid of the Ward and Tordai equation the values of the diffusion coefficients of TOPO were estimated. The values determined were in the right order of magnitude compared with the literature data. PMID:16290515

Prochaska, Krystyna; Walczak, Marzena; Staszak, Katarzyna

2002-04-01

373

Eddy Diffusion Coefficients of Suspended Particulate Matter: Effects of Wind Energy Transfer and Stratification  

NASA Astrophysics Data System (ADS)

Gross sedimentation rates (GSR) have been measured using sediment traps placed at nine different levels above the bed (0·3, 0·5, 0·8, 1·0, 2·0, 4·0, 6·0, 8·0 and 10·0 m). The sediment traps were deployed for 1·25 years and recovered 28 times during the study period. Low average GSR values of 5·5 g m -2 day -1 were obtained at 10·0 m, and high average GSR values of 114·8 g m -2 day -1 were obtained at 0·3 m. An expression for the eddy diffusion coefficient of suspended particulate matter ( K s), based on the measured GSR is given. The expression has been used for modelling of K s at the different trap levels above the bed. High values (?42 cm 2 s -1) of K s were obtained at the upper traps, whereas low values (?2 cm 2 s -1) were obtained near the bed. Comparison between level of turbulent energy in terms of shear stress at the boundaries of the water column, i.e. from the wind and the bed flow, showed that wind energy exceeded that of the bed flow by a factor 16. At 5·0 m K s was positively correlated ( r=0·66) to the eddy diffusion coefficient of momentum ( K m) derived from the wind energy transfer to the water, giving an average ? of 0·5 for K s =? K m. The density difference between surface and bottom waters has been designated a parameter of stratification, and is discussed in relation to variations of K s and K m .

Lund-Hansen, Lars Chresten; Pejrup, Morten; Valeur, Jens; Jensen, Anders

1994-06-01

374

Correlation of apparent diffusion coefficient with ki-67 proliferation index in grading meningioma.  

PubMed

OBJECTIVE. A noninvasive method to predict aggressiveness of high-grade meningiomas would be desirable because it would help anticipate tumor recurrence and improve tumor management and the treatment outcomes. The Ki-67 protein is a marker of tumor proliferation, and apparent diffusion coefficient (ADC) is related to tumor cellularity. Therefore, we sought to determine whether there is a statistically significant correlation between ADC and Ki-67 values in meningiomas and whether ADC values can differentiate various meningioma subtypes. MATERIALS AND METHODS. MRI examinations and histopathology of 68 surgically treated meningiomas were retrospectively reviewed. Mean ADC values were derived from diffusion imaging. Correlation coefficients were calculated for mean ADC and Ki-67 proliferation index values using linear regression. An independent unpaired Student t test was used to compare the ADC and Ki-67 proliferation index values from low-grade and more aggressive meningiomas. RESULTS. A statistically significant inverse correlation was found between ADC and Ki-67 proliferation index for low-grade and aggressive meningiomas (r(2) = -0.33, p = 0.0039). ADC values (± SD) of low-grade meningiomas (0.84 ± 0.14 × 10(-3) mm(2)/s) and aggressive (atypical or anaplastic) meningiomas (0.75 ± 0.03 × 10(-3) mm(2)/s) were significantly different (p = 0.0495). Using an ADC cutoff value of 0.70 × 10(-3) mm(2)/s, the sensitivity for diagnosing aggressive meningiomas was 29%, specificity was 94%, positive predictive value was 67%, and negative predictive value was 75%. CONCLUSION. ADC values correlate inversely with Ki-67 proliferation index and help differentiate low-grade from aggressive meningiomas. PMID:24848829

Tang, Yi; Dundamadappa, Sathish K; Thangasamy, Senthur; Flood, Thomas; Moser, Richard; Smith, Thomas; Cauley, Keith; Takhtani, Deepak

2014-06-01

375

Macro-meso two-scale model for predicting the VOC diffusion coefficients and emission characteristics of porous building materials  

NASA Astrophysics Data System (ADS)

Through the observation of the pore structure and mercury intruding porosimetry (MIP) experiments of some typical porous building materials, we found that the diffusion coefficient of the material can be expressed by that of a representative elementary volume (REV) in which the pore structure can be simplified as a connection in series of macro and meso pores. Based upon that, a macro-meso two-scale model for predicting the diffusion coefficient of porous building materials is proposed. In contrast to the traditional porous mass transfer model for determining the diffusion coefficient described in the literature [Blondeau, P., Tiffonnet, A.L., Damian, A., Amiri, O., Molina, J.L., 2003. Assessment of contaminant diffusivities in building materials from porosimetry tests. Indoor Air 13, 302-310; Seo, J., Kato, S., Ataka, Y., Zhu, Q., 2005. Evaluation of effective diffusion coefficient in various building materials and absorbents by mercury intrusion porosimetry. In Proceedings of the Indoor Air, Beijing, China, pp. 1854-1859], the proposed model relates the volatile organic compound (VOC) diffusion coefficient of building material not only to the porosity of the building material, but also to the pore size distribution and pore connection modes. To verify the model, a series of experiments of VOC emissions of three types of medium-density board were conducted. The comparison of the model and experimental results shows that the proposed model agrees much better with the experimental results than the traditional models in the literature. More validation for other building materials is needed. The proposed model is useful for predicting the VOC diffusion coefficient of porous building materials and for developing low VOC emission building materials.

Xiong, Jianyin; Zhang, Yinping; Wang, Xinke; Chang, Dongwu

376

Easy Measurement of Diffusion Coefficients of EGFP-tagged Plasma Membrane Proteins Using k-Space Image Correlation Spectroscopy.  

PubMed

Lateral diffusion and compartmentalization of plasma membrane proteins are tightly regulated in cells and thus, studying these processes will reveal new insights to plasma membrane protein function and regulation. Recently, k-Space Image Correlation Spectroscopy (kICS)(1) was developed to enable routine measurements of diffusion coefficients directly from images of fluorescently tagged plasma membrane proteins, that avoided systematic biases introduced by probe photophysics. Although the theoretical basis for the analysis is complex, the method can be implemented by nonexperts using a freely available code to measure diffusion coefficients of proteins. kICS calculates a time correlation function from a fluorescence microscopy image stack after Fourier transformation of each image to reciprocal (k-) space. Subsequently, circular averaging, natural logarithm transform and linear fits to the correlation function yields the diffusion coefficient. This paper provides a step-by-step guide to the image analysis and measurement of diffusion coefficients via kICS. First, a high frame rate image sequence of a fluorescently labeled plasma membrane protein is acquired using a fluorescence microscope. Then, a region of interest (ROI) avoiding intracellular organelles, moving vesicles or protruding membrane regions is selected. The ROI stack is imported into a freely available code and several defined parameters (see Method section) are set for kICS analysis. The program then generates a "slope of slopes" plot from the k-space time correlation functions, and the diffusion coefficient is calculated from the slope of the plot. Below is a step-by-step kICS procedure to measure the diffusion coefficient of a membrane protein using the renal water channel aquaporin-3 tagged with EGFP as a canonical example. PMID:24893770

Arnspang, Eva C; Koffman, Jennifer S; Marlar, Saw; Wiseman, Paul W; Nejsum, Lene N

2014-01-01

377

Remote sensing of the diffuse attenuation coefficient of ocean water. [coastal zone color scanner  

NASA Technical Reports Server (NTRS)

A technique was devised which uses remotely sensed spectral radiances from the sea to assess the optical diffuse attenuation coefficient, K (lambda) of near-surface ocean water. With spectral image data from a sensor such as the coastal zone color scanner (CZCS) carried on NIMBUS-7, it is possible to rapidly compute the K (lambda) fields for large ocean areas and obtain K "images" which show synoptic, spatial distribution of this attenuation coefficient. The technique utilizes a relationship that has been determined between the value of K and the ratio of the upwelling radiances leaving the sea surface at two wavelengths. The relationship was developed to provide an algorithm for inferring K from the radiance images obtained by the CZCS, thus the wavelengths were selected from those used by this sensor, viz., 443, 520, 550 and 670 nm. The majority of the radiance arriving at the spacecraft is the result of scattering in the atmospheric and is unrelated to the radiance signal generated by the water. A necessary step in the processing of the data received by the sensor is, therefore, the effective removal of these atmospheric path radiance signals before the K algorithm is applied. Examples of the efficacy of these removal techniques are given together with examples of the spatial distributions of K in several ocean areas.

Austin, R. W.

1981-01-01

378

Diffusion Coefficient of Fluorescent Phosphatidylinositol 4,5-bisphosphate in the Plasma Membrane of Cells  

PubMed Central

Phosphatidylinositol 4,5-bisphosphate (PIP2) controls a surprisingly large number of processes in cells. Thus, many investigators have suggested that there might be different pools of PIP2 on the inner leaflet of the plasma membrane. If a significant fraction of PIP2 is bound electrostatically to unstructured clusters of basic residues on membrane proteins, the PIP2 diffusion constant, D, should be reduced. We microinjected micelles of Bodipy TMR-PIP2 into cells, and we measured D on the inner leaflet of fibroblasts and epithelial cells by using fluorescence correlation spectroscopy. The average ± SD value from all cell types was D = 0.8 ± 0.2 ?m2/s (n = 218; 25°C). This is threefold lower than the D in blebs formed on Rat1 cells, D = 2.5 ± 0.8 ?m2/s (n = 26). It is also significantly lower than the D in the outer leaflet or in giant unilamellar vesicles and the diffusion coefficient for other lipids on the inner leaflet of these cell membranes. The simplest interpretation is that approximately two thirds of the PIP2 on inner leaflet of these plasma membranes is bound reversibly.

Golebiewska, Urszula; Nyako, Marian; Woturski, William; Zaitseva, Irina

2008-01-01

379

Diffusion coefficients of phenylbutazone in supercritical CO2 and in ethanol.  

PubMed

The diffusion coefficients D(12) of phenylbutazone at infinite dilution in supercritical CO(2) were measured by the chromatographic impulse response (CIR) method. The measurements were carried out over the temperature range from 308.2 to 343.2 K at pressures up to 40.0 MPa. In addition, the D(12) data of phenylbutazone at infinite dilution in ethanol were also measured by the Taylor dispersion method at 298.2-333.2K and at atmospheric pressure. The D(12) value of phenylbutazone increased from 4.45×10(-10) m(2) s(-1) at 298.2 K and 0.1 MPa in ethanol to about 1.43×10(-8) m(2) s(-1) at 343.2 K and 14.0 MPa in supercritical CO(2). It was found that all diffusion data of phenylbutazone measured in this study in supercritical CO(2) and in ethanol can be satisfactorily represented by the hydrodynamic equation over a wide range of fluid viscosity from supercritical state to liquid state with average absolute relative deviation of 5.4% for 112 data points. PMID:23369749

Kong, Chang Yi; Watanabe, Kou; Funazukuri, Toshitaka

2013-03-01

380

A uniqueness result for the identification of a time-dependent diffusion coefficient  

NASA Astrophysics Data System (ADS)

This paper deals with the problem of determining the time-dependent thermal diffusivity coefficient of a medium, when the evolution of the temperature in a part of it is known. Such situations arise in the context of food technology, when thermal processes at high pressures are used for extending the shelf life of the food, in order to preserve its nutritional and organoleptic properties (Infante et al 2009 On the Modelling and Simulation of High Pressure Processes and Inactivation of Enzymes in Food Engineering pp 2203-29 and Otero et al 2007 J. Food Eng. 78 1463-70). The phenomenon is modeled by the heat equation involving a term which depends on the source temperature and pressure increase, and appropriate initial and boundary conditions. We study the inverse problem of determining time-dependent thermal diffusivities k, when some temperature measurements at the border and inside the medium are known. We prove the uniqueness of the inverse problem solution under suitable a priori assumptions on regularity, size and growth of k.

Fraguela, A.; Infante, J. A.; Ramos, A. M.; Rey, J. M.

2013-12-01

381

Secondary Signal Change and an Apparent Diffusion Coefficient Decrease of the Substantia Nigra After Striatal Infarction  

PubMed Central

Background and Purpose Diffusion-weighted imaging can depict secondary signal change of the substantia nigra of patients with ipsilateral striatal infarction via a decrease in the apparent diffusion coefficient (ADC). Clinical predictors of this phenomenon remain unclear. Methods We assessed 98 stroke patients with acute ischemic lesions in the hemilateral basal ganglia, external capsule, or internal capsule. The ADC values of the bilateral substantia nigra obtained from a follow-up MRI, various clinical factors, and patients’ outcome were analyzed. Nineteen patients who underwent a follow-up MRI within 3 days were excluded from analysis because none of them demonstrated a significant ADC change of substantia nigra. Results Of 79 patients, 21 (26.6%) revealed a decreased ADC in the substantia nigra. Ischemic lesions in the globus pallidus (odds ratio 12.90) and the presence of emboligenic diseases (odds ratio 6.95) were independent predictors for an ADC decrease in the substantia nigra. The clinical outcome 3 months after stroke onset was not different between patients with an ADC decrease and patients without. Conclusions A reduction of ADC in the substantia nigra after acute striatal infarction was more frequently observed when the globus pallidus was affected or when the patient had emboligenic diseases, however, did not necessarily relate to the patient's clinical outcome.

Nakajima, Makoto; Inatomi, Yuichiro; Okigawa, Takashi; Yonehara, Toshiro; Hirano, Teruyuki

2014-01-01

382

Determination of chemical diffusion coefficients in metal hydride particles with a microelectrode technique  

SciTech Connect

Microelectrochemical studies for hydrogen storage materials have been carried out by using a microelectrode technique. A carbon fiber filament was contacted with single particles of LaNi{sub 4.5}Al{sub 0.5}, LmNi{sub 4.0}Cr{sub 0.4}Mn{sub 0.3}Al{sub 0.3}, ZrNi{sub 1.4}, ZrMn{sub 0.6}Co{sub 0.1}V{sub 0.2}Ni{sub 1.2}, and ZrMn{sub 0.4}Cr{sub 0.4}Ni{sub 1.2} in 1 M KOH solutions by using a micromanipulator, where Lm indicates the lanthanum-rich rare-earth metal. In this way, cyclic voltammetry and potential step experiments, together with the in situ x-ray diffraction experiments, were conducted and the apparent hydrogen diffusion coefficients in solid phases were determined. The current responses recorded as a function of time were analyzed with a spherical diffusion model and the results are reported herein.

Nishina, Tatsuo; Ura, Hironori; Uchida, Isamu [Tohoku Univ., Sendai (Japan)

1997-04-01

383

Study of cadmium-humic interactions and determination of stability constants of cadmium-humate complexes from their diffusion coefficients obtained by scanned stripping voltammetry and dynamic light scattering techniques.  

PubMed

Diffusion coefficients of Cd-humate complexes are dependent on pH and [Cd]/[Humic] Acid (HA)] ratio in a Cd-HA system. These two factors mainly control the mass transport and complexation kinetics of Cd that may influence bioavailability and toxicity of Cd species in environmental systems. Determination of diffusion coefficients of Cd-HA systems by Scanned stripping voltammetry and dynamic light scattering techniques can provide a better understanding of the systems and can be very useful for extracting other speciation parameters of the systems. This study revealed that Cd(2+) ion along with small dynamic Cd complexes was predominantly present in a Cd-HA system at pH 5 with high diffusion coefficients. HA molecules were in aggregated form at pH 5. However, HA molecules were in disaggregated form at pH 6 and concentrations of Cd(2+) ion and small Cd-dynamic complexes decreased with a decrease in diffusion coefficients of Cd complexes at this pH due to formation of Cd-humate complexes. No further decrease in the hydrodynamic radii of HA was observed with the increase of pH from 6 to 7. The Cd-humate system partially lost its lability at pH 7. Conditional stability constants were calculated for Cd-humate complexes by combining the diffusion coefficient data obtained by two techniques. The log K values calculated in this study are in good agreement with the data available from the literature. PMID:20103116

Chakraborty, Parthasarathi

2010-02-01

384

Apparent diffusion coefficient values of normal testis and variations with age  

PubMed Central

The usefulness of diffusion-weighted magnetic resonance imaging (DWI) in the evaluation of scrotal pathology has recently been reported. A standard reference of normal testicular apparent diffusion coefficient (ADC) values and their variations with age is necessary when interpreting normal testicular anatomy and pathology. We evaluated 147 normal testes using DWI, including 71 testes from 53 men aged 20–39 years (group 1), 67 testes from 42 men aged 40–69 years (group 2) and nine testes from six men older than 70 years (group 3). DWI was performed along the axial plane, using a single shot, multislice spin-echo planar diffusion pulse sequence and b-values of 0 and 900 s mm?2. The mean and standard deviation of the ADC values of normal testicular parenchyma were calculated for each age group separately. Analysis of variance (ANOVA) followed by post hoc analysis (Dunnett T3) was used for statistical purposes. The ADC values (× 10?3 mm2 s?1) of normal testicular tissue were different among age groups (group 1: 1.08 ± 0.13; group 2: 1.15 ± 0.15 and group 3: 1.31 ± 0.22). ANOVA revealed differences in mean ADC among age groups (F = 11.391, P < 0.001). Post hoc analysis showed differences between groups 1 and 2 (P = 0.008) and between groups 1 and 3 (P = 0.043), but not between groups 2 and 3 (P = 0.197). Our findings suggest that ADC values of normal testicular tissue increase with advancing age.

Tsili, Athina C; Giannakis, Dimitrios; Sylakos, Anastasios; Ntorkou, Alexandra; Astrakas, Loukas G; Sofikitis, Nikolaos; Argyropoulou, Maria I

2014-01-01

385

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

386

The Free-Free Absorption Coefficients of the Negative Helium Ion  

NASA Astrophysics Data System (ADS)

Free-free absorption coefficients of the negative helium ion are calculated by a phaseshift approximation, using continuum data that accurately account for electron-atom correlation and polarization. The approximation is considered to yield results within a few per cent of numerical values for wavelengths greater than 1 m, over the temperature range 1400-10080 K. These coefficients are expected to give the best current estimates of He - continuous absorption. Key words: atomic data - atomic processes - stars: atmospheres - infrared: general.

John, T. L.

1994-08-01

387

Meaurements of low energy hydrogen ion effective sticking coefficients on titanium in the Wisconsin Levitated Octupole  

Microsoft Academic Search

The effective sticking coefficient for low energy ( 30 eV) hydrogen ions on titanium gettered aluminium walls was measured in the Wisconsin Levitated Octupole. A value of greater than 0.75 was measured. The H2 effective sticking coefficient for the same conditions is less than 0.01. Seventy-four percent of the wall area of the Octupole is gettered. The effects of recycling

H. Garner; R. S. Post

1981-01-01

388

Measurements of low energy hydrogen ion effective sticking coefficients on titanium in the Wisconsin Levitated Octupole  

Microsoft Academic Search

The effective sticking coefficient for low energy (< 30 eV) hydrogen ions on titanium gettered aluminium walls has been measured in the Wisconsin Levitated Octupole. A value of greater than 0.75 was measured. The Hâ effective sticking coefficient for the same conditions is less than 0.01. Seventy-four percent of the wall area of the Octupole is gettered. The effects of

H. Garner; R. S. Post

1981-01-01

389

Ab initio transport coefficients of Ar+ ions in Ar for cold plasma jet modeling  

NASA Astrophysics Data System (ADS)

Collision cross sections and transport coefficients are calculated for Ar+ ions, in the ground state 2P3/2 and in the metastable state 2P1/2, colliding with their parent gas. Differential and integral collision cross sections are obtained using a numerical integration of the nuclear Schrödinger equation for several published interaction potentials. The Cohen-Schneider semi-empirical model is used for the inclusion of the spin-orbit interaction. The corresponding differential collision cross sections are then used in an optimized Monte Carlo code to calculate the ion transport coefficients for each initial ion state over a wide range of reduced electric field. Ion swarm data results are then compared with available experimental data for different proportions of ions in each state. This allows us to identify the most reliable interaction potential which reproduces ion transport coefficients falling within the experimental error bars. Such ion transport data will be used in electrohydrodynamic and chemical kinetic models of the low temperature plasma jet to quantify and to tune the active species production for a better use in biomedical applications.

Chicheportiche, A.; Lepetit, B.; Gadéa, F. X.; Benhenni, M.; Yousfi, M.; Kalus, R.

2014-06-01

390

Stability of an alloy/oxide interface with oxygen ions being the dominant diffusing species in the oxide scale  

SciTech Connect

The criterion for interfacial stability between an alloy and its oxide was formulated by Wagner for the specific case when the cations are the diffusing species in the oxide scale. However, for the oxidation of (Pb, In) and (Pb, Sn) alloys, oxygen is the predominant diffusing species in the oxide scales. The criterion formulated by Wagner is no longer applicable. In the present study, the criterion was formulated for the case when oxygen ions are the dominant diffusing species, following the approach used by Wagner. The criterion was used to determine the interfacial stability of (Pb, In)/In[sub 2]O[sub 3]. In order to determine the (Pb, In)/In[sub 2]O[sub 3] interfacial stability, it is necessary to know the interdiffusion coefficient of (Pb, In) and the intrinsic diffusion coefficient of oxygen in In[sub 2]O[sub 3]. Intrinsic diffusion coefficients for In[sub 2]O[sub 3] are not available and are estimated from the parabolic rate constants for the oxidation of (Pb, In) alloys. Calculations using the interdiffusion coefficient of (Pb, In) from the literature and the estimated intrinsic diffusivity of oxygen indicated that the (Pb, In)/In[sub 2]O[sub 3] interface should be planar.

Zhang, M.X.; Chang, Y.A. (Univ. of Wisconsin, Madison, WI (United States). Dept. of Materials Science and Engineering)

1993-03-01

391

Determination of mass diffusion coefficients of oxygenated fuel additives in air using digital real-time holographic interferometry  

NASA Astrophysics Data System (ADS)

In this work, an experimental system based on digital real-time holographic interferometry for measuring the mass diffusion coefficients of fluid is introduced. The method of processing interference fringe hologram is also introduced thoroughly. By uncertainties analysis and experimental verification, the accuracy of this system is validated. The experimental uncertainties in temperature and mass diffusion coefficient are estimated to be no greater than ± 0.16 K and ± 0.2 %, respectively. On this basis, the mass diffusion coefficients of three fuel additives, diethyl 1,6-hexanedioate (diethyl adipate, DEA), dimethyl carbonate (DMC) and diethyl carbonate (DEC) in air were measured at T = (278.15 to 338.15) K under atmospheric pressure, and polynomial was fitted by the experimental data.

He, Maogang; Guo, Ying; Zhong, Qiu; Zhang, Ying

2009-02-01

392

Diffusion of non-Gaussianity in heavy ion collisions  

NASA Astrophysics Data System (ADS)

We investigate the time evolution of higher order cumulants of bulk fluctuations of conserved charges in the hadronic stage in relativistic heavy ion collisions. The dynamical evolution of non-Gaussian fluctuations is modeled by the diffusion master equation. Using this model we predict that the fourth-order cumulant of net-electric charge is suppressed compared with the recently observed second-order one at ALICE for a reasonable parameter range. Significance of the measurements of various cumulants as functions of rapidity window to probe dynamical history of the hot medium created by heavy ion collisions is emphasized.

Kitazawa, Masakiyo; Asakawa, Masayuki; Ono, Hirosato

2014-05-01

393

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

394

The role of Anderson-Gruneisen parameter in the estimation of self-diffusion coefficients in alkaline earth oxides  

NASA Astrophysics Data System (ADS)

In a previous publication [J. Appl. Phys. 110, 036103 (2011)], we have shown that the bulk expansivity and elastic data can reproduce the self-diffusion coefficients in MgO over a wide range of values, i.e., 20 orders of magnitude. This publication was crossed with recent studies supporting the view that the Anderson-Gruneisen parameter ? is independent of the temperature in alkaline earth oxides. Here, we take this view and using the resulting elastic and expansivity parameters, we repeat the calculation for the diffusion coefficient of O in MgO. The results obtained agree with the experimental data.

Dologlou, Elizabeth

2012-11-01

395

Basic principles for the development of a common standardised method for determining the radon diffusion coefficient in waterproofing materials.  

PubMed

Paper presents the principles for unified test methods for determining the radon diffusion coefficient in waterproof materials in order to increase the accuracy, repeatability and reproducibility of the results. We consider this very important, because an assessment of the radon diffusion coefficient is required by several national technical standards when waterproofing acts as a radon-proof membrane. The requirements for key parameters for one test method performed under non-stationary conditions and for two methods performed under stationary conditions are described in this paper. PMID:22245288

Jiránek, Martin; Rovenská, Kate?ina

2012-04-01

396

New experimental method to measure pure and cross diffusion coefficients of transparent ternary mixtures using Mach–Zehnder interferometry  

NASA Astrophysics Data System (ADS)

In this study, a Mach–Zehnder interferometer that is equipped with two lasers of different wavelengths was used to conduct high resolution measurements of concentration profiles of a ternary mixture inside a diffusion cell. Windowed Fourier transform along with an advanced unwrapping procedure was employed to extract the phase image from fringe images. Then the phase difference was obtained for a spatial resolution of 1920×1240. According to the measured refractive index profile, concentration contours of two components (out of three) were measured. Consequently, the concentration profile of the third components was calculated. Previously, the analytical solution for binary mixtures was used to estimate only the pure diffusion coefficients. In this study, for the first time, the refractive indices measured by two lasers along with the analytical solution for the ternary system, based on Fick?s law, and an evolutionary algorithm (EA) known as a genetic algorithm (GA) were employed to measure the pure and cross diffusion coefficients of a transparent ternary mixture simultaneously. The optimization method to estimate diffusion coefficients was tested against various objective functions, and the best approach was that which was proposed herein. In order to validate the proposed measurement method, the experimental results of the Selectable Optical Diagnostics Instrument-Diffusion Coefficients in Mixtures (SODI-DCMIX1 project) on board the International Space Station (ISS) were analyzed using this technique and the obtained results were compared with previous techniques.

Ahadi, Amirhossein; Saghir, M. Ziad

2014-08-01

397

Diffusion coefficients in the lateral intercellular spaces of Madin-Darby canine kidney cell epithelium determined with caged compounds.  

PubMed Central

The diffusion coefficients of two caged fluorescent dyes were measured in free solution and in the lateral intercellular spaces (LIS) of cultured Madin-Darby canine kidney (MDCK) cells after photoactivation by illumination with a continuous or pulsed UV laser. Both quantitative video imaging and a new photometric method were utilized to determine the rates of diffusion of the caged fluorescent dyes: 8-((4,5-dimethoxy-2-nitrobenzyl)oxy)pyrene-1,3,6-trisulfonic acid (DMNB-HPTS) and (4,5-dimethoxy-2-nitrobenzyl) fluorescein dextran (10,000 MW) (DMNB-caged fluorescein dextran). The diffusion coefficients at 37 degrees C in free solution were 3.3 x 10(-6) cm2/s (HPTS) and 0.98 x 10(-6) cm2/s (10,000 MW dextran). Diffusion of HPTS within nominally linear stretches of the LIS of MDCK cells grown on glass coverslips was indistinguishable from that in free solution, whereas dextran showed a 1.6 +/- 0.5-fold reduction in diffusivity. Measurements of HPTS diffusion within the LIS of multicellular regions also exhibited a diffusivity comparable to the free solution value. The restriction to diffusion of the dextran within the LIS may be due to molecular hindrance.

Xia, P; Bungay, P M; Gibson, C C; Kovbasnjuk, O N; Spring, K R

1998-01-01

398

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

399

Relationship between apparent diffusion coefficients at 3.0-T MR imaging and Gleason grade in peripheral zone prostate cancer  

Microsoft Academic Search

PURPOSE: To retrospectively determine the relationship between apparent diffusion coefficients (ADCs) obtained with 3.0-T diffusion-weighted (DW) magnetic resonance (MR) imaging and Gleason grades in peripheral zone prostate cancer. MATERIALS AND METHODS: The requirement to obtain institutional review board approval was waived. Fifty-one patients with prostate cancer underwent MR imaging before prostatectomy, including DW MR imaging with b values of 0,

T. Hambrock; D. M. Somford; H. J. Huisman; I. M. van Oort; J. A. Witjes; C. A. Hulsbergen-van de Kaa; T. W. J. Scheenen; J. O. Barentsz

2011-01-01

400

Ion implantation and diffusion of Zn in GaAs  

Microsoft Academic Search

Zn implantation (dose 5×1015 cm?2) and subsequent diffusion were carried out on GaAs wafers and on liquid-phase epitaxial GaAs layers. A silicon nitride cap was deposited by chemical vapor deposition (CVD) or by sputtering either before or after implantation. Profiles were determined with Secondary Ion Mass Spectrometry and Differential Hall Effect measurements and damage was studied with Rutherford Backscattering Spectrometry.

G. J. van Gurp; A. H. van Ommen; P. R. Boudewijn; D. P. Oosthoek; M. F. C. Willemsen

1984-01-01

401

Mechanism of Ion Diffusion in Coarse-Grained Ionomer Melts  

NASA Astrophysics Data System (ADS)

Ionomers (polymers with a small amount of charged groups) have been identified as possible single ion conducting battery electrolytes. A barrier their use in such applications is that the strong electrostatic interactions lead to ionic aggregation and can make ion diffusion very slow. In order to understand the physics underlying ionomer dynamics and especially how charge transport occurs, we perform molecular dynamics simulations. Our model has polymers with charged groups either in the backbone or pendant to it, explicit counterions, and long-range Coulomb interactions. Depending on placement, amount, and spacing of the ionic groups, various morphologies of ionic aggregates are formed. We find for all systems, ions can rearrange locally within the ionic aggregates on a relatively short timescale. Ions can move a longer distance when they rearrange collectively on a longer timescale, that is especially long for systems with discrete ionic aggregates. Because of this, a typical ion trajectory shows mostly small movements and rare large, sudden movements. However, these features are not due to `hopping' as typically understood. Instead, nearby aggregates of ions join together, rearrange, and later break apart, during which time some ions are exchanged and appear to have `hopped'.

Hall, Lisa M.; Stevens, Mark J.; Frischknecht, Amalie L.

2013-03-01

402

Transport of magnetic flux and the vertical structure of accretion discs - I. Uniform diffusion coefficients  

NASA Astrophysics Data System (ADS)

Standard models of accretion discs study the transport of mass on a viscous time-scale but do not consider the transport of magnetic flux. The evolution of a large-scale poloidal magnetic field is, however, an important problem because of its role in the launching of jets and winds and in determining the intensity of turbulence. As a consequence, the transport of poloidal magnetic flux should be considered on an equal basis to the transport of mass. In this paper, we develop a formalism to study such a transport of mass and magnetic flux in a thin accretion disc. The governing equations are derived by performing an asymptotic expansion in the limit of a thin disc, in the regime where the magnetic field is dominated by its vertical component. Turbulent viscosity and resistivity are included, with an arbitrary vertical profile that can be adjusted to mimic the vertical structure of the turbulence. At a given radius and time, the rates of transport of mass and magnetic flux are determined by a one-dimensional problem in the vertical direction, in which the radial gradients of various quantities appear as source terms. We solve this problem to obtain the transport rates and the vertical structure of the disc. This paper is then restricted to the idealized case of uniform diffusion coefficients, while a companion paper will study more realistic vertical profiles of these coefficients. We show the advection of weak magnetic fields to be significantly faster than the advection of mass, contrary to what a crude vertical averaging might suggest. This results from the larger radial velocities away from the mid-plane, which barely affect the mass accretion owing to the low density in these regions but do affect the advection of magnetic flux. Possible consequences of this larger accretion velocity include a potentially interesting time dependence with the magnetic flux distribution evolving faster than the mass distribution. If the disc is not too thin, this fast advection may also partially solve the long-standing problem of too efficient diffusion of an inclined magnetic field.

Guilet, Jérôme; Ogilvie, Gordon I.

2012-08-01

403

Diffusion length damage coefficient and annealing studies in proton-irradiated InP  

NASA Technical Reports Server (NTRS)

We report on the measurement of the diffusion length damage coefficient (K(sub L)) and the annealing characteristics of the minority carrier diffusion length (L(sub n)) in Czochralski-grown zinc-doped indium phosphide (InP), with a carrier concentration of 1 x 10(exp l8) cm(exp -3). In measuring K(sub L) irradiations were made with 0.5 MeV protons with fluences ranging from 1 x 10(exp 11) to 3 x 10(exp 13) cm(exp -2). Pre- and post-irradiation electron-beam induced current (EBIC) measurements allowed for the extraction of L(sub n) from which K(sub L) was determined. In studying the annealing characteristics of L(sub n) irradiations were made with 2 MeV protons with fluence of 5 x 10(exp 13) cm(exp -2). Post-irradiation studies of L(sub n) with time at room temperature, and with minority carrier photoinjection and forward-bias injection were carried out. The results showed that recovery under Air Mass Zero (AMO) photoinjection was complete. L(sub n) was also found to recover under forward-bias injection, where recovery was found to depend on the value of the injection current. However, no recovery of L(sub n) after proton irradiation was observed with time at room temperature, in contrast to the behavior of 1 MeV electron-irradiated InP solar cells reported previously.

Hakimzadeh, Roshanak; Vargas-Aburto, Carlos; Bailey, Sheila G.; Williams, Wendell

1993-01-01

404

Relationship between Apparent Diffusion Coefficient and Tumour Cellularity in Lung Cancer  

PubMed Central

Background and objective To prospectively investigate the relationship between the apparent diffusion coefficient (ADC) and cellularity in lung cancer. Methods Sixty patients histopathologically confirmed with lung cancer (41 men, 19 women) underwent diffusion-weighted magnetic resonance imaging of the chest (with b values of 50 and 1000 s/mm2). The median mean ADC (ADCmean) value and median minimum ADC (ADCmin) value within each primary tumour were calculated and compared with the median nucleo-cytoplasmic ratio (NCR), which was selected to represent the cellularity. The correlation between the NCR and ADCmean/ADCmin was calculated with SPSS 18.0 software. Results The mean ADCmean values, ADCmin values and median NCR were (1.07±0.12)×10?3 mm2/s, (0.86±0.14)×10?3 mm2/s, and (14.9±2.6) %, respectively, in adenocarcinoma; (0.88±0.10)×10?3 mm2/s, (0.73±0.12)×10?3 mm2/s, and (20.6±4.4) %, respectively, in squamous cell carcinoma; and (0.89±0.13)×10?3 mm2/s, (0.67±0.13)×10?3 mm2/s, and (18.3±3.5) %, respectively in small cell lung cancer. The NCR of squamous cell carcinoma and small cell lung cancer is greater than that of adenocarcinoma (P<0.01 and P?=?0.002, respectively). There was an inverse relationship between ADCmean/NCR and ADCmin/NCR (r?=??0.60, P?=?0.001 and r?=??0.47, P<0.001, respectively). Conclusion There is a significant inverse relationship between tumour cellularity and ADC in lung cancer. However, tumour cellularity most likely is not the sole determinant of the ADC.

Chen, Yongfeng; Wang, Wenwei; Zhou, Xiangdong; Yan, Xiaochu; Wang, Jian

2014-01-01

405

Synapse models for neural networks: from ion channel kinetics to multiplicative coefficient wij  

Microsoft Academic Search

This paper relates different levels at which the modeling of synaptic transmission can be grounded in neural networks: the level of ion channel kinetics, the level of synaptic conductance dynamics, and the level of a scalar synaptic coefficient. The important assumptions to reduce a synapse model from one level to the next are explicitly exhibited. This coherent progression provides control

François Chapeau-blondeau; Nicolas Chambet

1995-01-01

406

The Free-Free Absorption Coefficient of the Negative Ion of Molecular Hydrogen.  

National Technical Information Service (NTIS)

The free-free absorption coefficient of the negative ion of molecular hydrogen is calculated in the dipole length formulation using wavefunctions which take account of exchange and polarization effects on the free electron. The results are found to be app...

K. L. Bell A. E. Kingston W. A. McIlveen

1974-01-01

407

Distribution coefficients and ion exchange behaviour of some elements with Purolite S-950 in hydrochloric acid.  

PubMed

Equilibrium distribution coefficients, K(d), are presented for some elements in hydrochloric acid using the phosphonated polystyrene ion exchange resin Purolite S-950. A few possible separations using this resin are demonstrated by elution curves and separations of synthetic mixtures of some elements (Ru, Rh, Mo, I, Li, Te, Si, Y). PMID:15045222

Van Der Walt, T N; Coetzee, P P

1996-12-01

408

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

2013-02-01

409

Doping-Enhanced Lithium Diffusion in Lithium-Ion Batteries  

NASA Astrophysics Data System (ADS)

We disclose a distortion-assisted diffusion mechanism in Li3N and Li2.5Co0.5N by first-principles simulations. A B2g soft mode at the ? point is found in ?-Li3N, and a more stable ?'-Li3N (P3¯m1) structure, which is 0.71 meV lower in energy, is further derived. The same soft mode is inherited into Li2.5Co0.5N and is enhanced due to Co doping. Consequently, unlike the usual Peierls spin instability along Co-N chains, large lithium-ion displacements on the Li-N plane are induced by a set of soft modes. Such a distortion is expected to offer Li atoms a route to bypass the high diffusion barrier and promote Li-ion conductivity. In addition, we further illustrate abnormal Born effective charges along Co-N chains which result from the competition between the motions of electrons and ion cores. Our results provide future opportunities in both fundamental understanding and structural modifications of Li-ion battery materials.

Wu, Gang; Wu, Shunnian; Wu, Ping

2011-09-01

410

Probability distribution of financial returns in a model of multiplicative Brownian motion with stochastic diffusion coefficient  

NASA Astrophysics Data System (ADS)

It is well-known that the mathematical theory of Brownian motion was first developed in the Ph. D. thesis of Louis Bachelier for the French stock market before Einstein [1]. In Ref. [2] we studied the so-called Heston model, where the stock-price dynamics is governed by multiplicative Brownian motion with stochastic diffusion coefficient. We solved the corresponding Fokker-Planck equation exactly and found an analytic formula for the time-dependent probability distribution of stock price changes (returns). The formula interpolates between the exponential (tent-shaped) distribution for short time lags and the Gaussian (parabolic) distribution for long time lags. The theoretical formula agrees very well with the actual stock-market data ranging from the Dow-Jones index [2] to individual companies [3], such as Microsoft, Intel, etc. [] [1] Louis Bachelier, ``Th'eorie de la sp'eculation,'' Annales Scientifiques de l''Ecole Normale Sup'erieure, III-17:21-86 (1900).[] [2] A. A. Dragulescu and V. M. Yakovenko, ``Probability distribution of returns in the Heston model with stochastic volatility,'' Quantitative Finance 2, 443--453 (2002); Erratum 3, C15 (2003). [cond-mat/0203046] [] [3] A. C. Silva, R. E. Prange, and V. M. Yakovenko, ``Exponential distribution of financial returns at mesoscopic time lags: a new stylized fact,'' Physica A 344, 227--235 (2004). [cond-mat/0401225

Silva, Antonio

2005-03-01

411