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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

Estimating The Sodium Ion Diffusion Coefficient in Rat Brain  

NASA Astrophysics Data System (ADS)

Quantifying sodium ion diffusion in the extra- and intracellular compartments will provide mechanistic insight into the as yet unexplained marked decrease in water diffusion resulting from central nervous system injury. As a first step, the apparent diffusion coefficient (ADC) of bulk brain Na+ has been determined in vivo in rat. A surface coil transmit/receive adiabatic-pulse scheme is used to provide two dimensions of volume localization, thus minimizing echo time. The third dimension is determined by slice selection gradients on the axis perpendicular to the coil plane. Signal decay in the presence of diffusion sensitizing pulsed field gradients was modeled by Bayesian Probability Theory. Preliminary findings indicate a bulk Na+ ADC of (1.16 ± .07) × 10-3 mm2/s.

Goodman, James A.; Bretthorst, G. Larry; Kroenke, Christopher D.; Ackerman, Joseph J. H.; Neil, Jeffrey J.

2004-04-01

3

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

4

The effect of copper, acid, and temperature on the diffusion coefficient of cupric ions in simulated electrorefining electrolytes  

Microsoft Academic Search

Deposition and dissolution processes involved in copper electrorefining are significantly affected by the diffusion coefficient of copper within an electrolyte. It is believed that the diffusion coefficient of cupric ions under conditions similar to those encountered in commercial electrolytes is not precisely known. The effects of copper, acid, and temperature on copper diffusivity were measured for simulated industrial electrolytes. Copper

Michael S Moats; J. Brent Hiskey; Dale W Collins

2000-01-01

5

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

6

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

7

Drift Tube Measurements of Mobilities and Longitudinal Diffusion Coefficients of Ions in Gases.  

NASA Astrophysics Data System (ADS)

The zero-field mobilities of Br('-) and NH(,4)('+) in O(,2) were determined as a function of gas temperature in a high pressure drift tube mass spectrometer. The mobilities and longitudinal diffusion coefficients of the ion-gas combinations Br('-) in Ne and Kr, Li('+) in Xe, and Tl('+) in Kr and Xe were determined as a function of E/N, where E is the electric field strength and N is the gas number density in a low pressure drift tube mass spectrometer. The measured longitudinal diffusion coefficients were used for a test and comparison of the generalized Einstein relations of Viehland-Mason and Waldman-Mason theories. The measured mobilities of Br('-) in Kr and Tl('+) in Kr were used in an iterative-inversion scheme from which the ion-neutral interaction potentials were determined. The zero-field reduced mobility of Br('-) in O(,2) ranged from 2.6 cm('2)/(V-sec) at 297(DEGREES)K to 3.0 cm('2)/(V-sec) at 600(DEGREES)K. The zero-field reduced mobility of NH(,4)('+) in O(,2) ranged from 3.4 cm('2)/(V -sec) at 418(DEGREES)K to 3.7 cm('2)/(V-sec) at 561(DEGREES)K. The zero-field values of the reduced mobilities measured as a function of E/N in units of cm('2)/(V-sec) are as follows: Br('-) in Kr (1.47 (+OR-) .03), Br('-) in Ne (6.94 (+OR -) .14), Li('+) in Xe (2.68 (+OR-) .05), Tl('+) in Kr (1.15 (+OR-) .03), and Tl('+) in Xe (.78 (+OR-) .02). The ion -gas combinations of Br('-) in Kr, Li('+) in Xe, and Tl('+) in Kr displayed the typical mobility peaks. The peak values in cm('2)/(V-sec) are for Br('-) in Kr, Li('+) in Xe, and Tl('+) in Kr respectively: (1.81 (+OR-) 0.4) at 130 Td, 4.47 (+OR-) .09 at 135 Td, and 1.42 (+OR-) .04 at 285 Td. The measured longitudinal diffusion coefficients were compared to the Einstein values in the low-field limit. Comparisons between the experimental values and the generalized Einstein relations (GER) of Viehland-Mason and Waldman-Mason were made at all E/N values. All comparisons were favorable within the error ranges. In general, the Waldman-Mason GER values were closer to the experimental data than the Viehland-Mason values. Interaction potentials for Br('-) in Kr and Tl('+) in Kr were determined. Initial potentials for the iterative -inversion scheme were of the 4-6-n type, the coefficients for the r('-4) term being the polarizability of Kr gas. The Tl('+) in Kr case represents the first time an ion-neutral interaction potential has been determined from a measured mobility in which the structure of the ion was not that of a rare gas.

Chelf, Roger Dale

8

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

9

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

E-print Network

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

Ishwar Dutt; Rajeev K. Puri

2010-04-04

10

Effect of carbon dioxide on chloride penetration and chloride ion diffusion coefficient of blended Portland cement mortar  

Microsoft Academic Search

This paper presents a study of the effects of carbon dioxide on chloride penetration and chloride ion diffusion coefficient of blended Portland cement mortar containing ground palm oil fuel ash (POA), ground rice husk ash (RHA) and classified fly ash (fine fly ash, FA). Ordinary Portland cement (OPC) is partially replaced with pozzolan and blends of pozzolans. Mortars with constant

Prinya Chindaprasirt; Sumrerng Rukzon; Vute Sirivivatnanon

2008-01-01

11

Computations of ion diffusion coefficients from the Boltzmann-Fokker-Planck equation  

NASA Technical Reports Server (NTRS)

The Boltzmann-Fokker-Planck equation is solved with the Chapman-Enskog method of analysis for the velocity distribution functions of helium, carbon, nitrogen, and oxygen. The analysis is a perturbation scheme based on the assumption of a collision-dominated gas, and the calculations are carried out to first order. The elements considered are treated as trace constituents in an electron-proton gas. From the resulting distribution functions, diffusion coefficients are computed which are found to be 20-30% less than those obtained by Chapman and Burgers. In addition, it is shown that the return current of cold electrons needed to maintain quasi-neutrality in a plasma with a temperature gradient contributes a term in the thermal diffusion coefficient omitted erroneously in previous works. This added term resolves the longstanding controversy over the discrepancy between the coefficients of Chapman and Burgers, which are seen to be completely equivalent in the light of this analysis. The viscosity coefficient for an electron-proton gas is also computed and found to be 7% less than that obtained by Braginskii.

Roussel-Dupre, R.

1981-01-01

12

Influence of the counterion and co-ion diffusion coefficient values on some dielectric and electrokinetic properties of colloidal suspensions.  

PubMed

The dependences of the conductivity increment, the electrophoretic mobility, and the permittivity increment on the counterion diffusion coefficient value were numerically determined. The use of the network simulation method made it possible to solve the governing equations for the whole range of counterion and co-ion diffusion coefficients and for very low frequencies, despite the far-reaching field-induced charge density outside the double layer. Calculations performed for different zeta potential and electrolyte concentration values show that increasing the counterion mobility, while keeping constant the electrolyte solution conductivity and the kappa a values, strongly increases the conductivity increment, barely affects the electrophoretic mobility, and strongly decreases the permittivity increment. The numerical results are discussed and compared to analytical predictions derived from the Shilov-Dukhin model, which generally leads to a good agreement, at least for high kappa a and moderate zeta. PMID:16852466

López-García, J J; Grosse, C; Horno, J

2005-06-23

13

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. PMID:24222910

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

2013-01-01

14

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

15

Diffusion coefficients in gravel under unsaturated conditions  

SciTech Connect

Diffusion coefficients were experimentally determined in unsaturated gravel to evaluate the effectiveness of gravel as a diffusion barrier to ionic transport in the vadose zone. Water contents were fixed by use of an ultracentrifuge with an ultralow constant rate flow pump supplying solution to the sample via a rotating seal. Once the gravel was at hydraulic steady state, the electrical conductivity was measured, and the diffusion coefficient calculated using the Nernst-Einstein equation. Diffusion coefficient values for potassium ion (D{sub e}) in four types of angular gravel ranged from 1.7 {times} 10{sup {minus}11} m{sup 2}/s (1.7 {times} 10{sup {minus}7} cm{sup 2}/s) for a 6.3-9.5 mm angular granitic gravel at a volumetric water content of 5.5% to 2.2 {times} 10{sup {minus}14} m{sup 2}/s (2.2 {times} 10{sup {minus}10} cm{sup 2}/s) in a 4.0-6.3 mm quartzite gravel at a volumetric water content of 0.47%. Variations in D{sub e} values resulted primarily from differences in water content which depends on gravel type and particle size.

Conca, J.L.; Wright, J. (Pacific Northwest Lab., Richland, WA (USA))

1990-05-01

16

Thermal Expansion and Diffusion Coefficients of Carbon  

E-print Network

Thermal Expansion and Diffusion Coefficients of Carbon Nanotube-Polymer Composites Chenyu Wei* NASA for polymer-nanotube interface are used to investigate the thermal expansion and diffusion characteristics to increase the glass transition temperature Tg, and thermal expansion and diffusion coefficients

Wei, Chenyu

17

Diffusion coefficients for fast reactor hexagonal assemblies  

SciTech Connect

A consistent model for the calculation of fast reactor assembly diffusion coefficients is presented. Allowance is made for the treatment of both sodiumfilled and sodium-voided lattices, with the same approximation applied, which is essential for the study of the sodium-voiding effect. The hexagonal steel tube is also taken into account. The formalism is implemented in the ASDIC (Assembly Diffusion Coefficients) program. Numerical results and comparisons with results of other models are given.

Benoist, P.; Duracz, T.

1984-05-01

18

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

19

Diffusion coefficients in leaflets of bilayer membranes  

E-print Network

We study diffusion coefficients of liquid domains by explicitly taking into account the two-layered structure called leaflets of the bilayer membrane. In general, the velocity fields associated with each leaflet are different and the layers sliding past each other cause frictional coupling. We obtain analytical results of diffusion coefficients for a circular liquid domain in a leaflet, and quantitatively study their dependence on the inter-leaflet friction. We also show that the diffusion coefficients diverge in the absence of coupling between the bilayer and solvents, even when the inter-leaflet friction is taken into account. In order to corroborate our theory, the effect of the inter-leaflet friction on the correlated diffusion is examined.

Kazuhiko Seki; Saurabh Mogre; Shigeyuki Komura

2014-02-05

20

Fractal diffusion coefficient from dynamical zeta functions  

E-print Network

Dynamical zeta functions provide a powerful method to analyze 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 observable 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.

G. Cristadoro

2005-09-28

21

Does the photon-diffusion coefficient depend on absorption?  

E-print Network

Does the photon-diffusion coefficient depend on absorption? T. Durduran and A. G. Yodh Department the controversy over the precise form of the photon diffusion coefficient and suggest that it is largely diffusion coefficient gives better agreement with theory than the traditionally accepted photon diffusion

Boas, David

22

Diffusion Coefficient of Electrons in Real Space  

NASA Astrophysics Data System (ADS)

A Monte-Carlo simulation of electron motion is carried out by a new method to obtain the exact values of swarm parameters. The elastic and total collision cross sections assumed here are proportional to various powers of the electron energy, and the mass ratio of an electron to a gas atom is taken as 10-2. Computation shows that the well-known expression for the diffusion doefficient Dv does not always give the exact values of the lateral diffusion coefficient DT. The differences between the values of Dv and DT are significant when the power value of the collision cross-section is large or the mass ratio is large. The disagreement is thought to be caused by the difference in the procedures for obtaining Dv and DT because of the difference in their definitions.

Ikuta, Nobuaki; Itoh, Hidenori; Toyota, Kazushige

1983-01-01

23

Calculation of combined diffusion coefficients in SF6-Cu mixtures  

NASA Astrophysics Data System (ADS)

Diffusion coefficients play an important role in the description of the transport of metal vapours in gas mixtures. This paper is devoted to the calculation of four combined diffusion coefficients, namely, the combined ordinary diffusion coefficient, combined electric field diffusion coefficient, combined temperature diffusion coefficient, and combined pressure diffusion coefficient in SF6-Cu mixtures at temperatures up to 30 000 K. These four coefficients describe diffusion due to composition gradients, applied electric fields, temperature gradients, and pressure gradients, respectively. The influence of copper fluoride and sulfide species on the diffusion coefficients is shown to be negligible. The effect of copper proportion and gas pressures on these diffusion coefficients is investigated. It is shown that increasing the proportion of copper generally increases the magnitude of the four diffusion coefficients, except for copper mole fractions of 90% or more. It is further found that increasing the pressure reduces the magnitude of the coefficients, except for the combined temperature diffusion coefficient, and shifts the maximum of all four coefficients towards higher temperatures. The results presented in this paper can be applied to the simulation of high-voltage circuit breaker arcs.

Zhong, Linlin; Wang, Xiaohua; Rong, Mingzhe; Wu, Yi; Murphy, Anthony B.

2014-10-01

24

Continuum estimate of the heavy quark momentum diffusion coefficient $?$  

E-print Network

Among quantities playing a central role in the theoretical interpretation of heavy ion collision experiments at RHIC and LHC are so-called transport coefficients. Out of those heavy quark diffusion coefficients play an important role e.g. for the analysis of the quenching of jets containing c or b quarks (D or B mesons) as observed at RHIC and LHC. We report on a lattice investigation of heavy quark momentum diffusion within pure SU(3) plasma above the deconfinement transition with the quarks treated to leading order in the heavy mass expansion. We measure the relevant colour-electric Euclidean correlator and based on several lattice spacings perform the continuum extrapolation. This extends our previous studies progressing towards a removal of lattice artifacts and a physical interpretation of the results. We find that the correlation function clearly exceeds its perturbative counterpart which suggests that at temperatures just above the critical one, non-perturbative interactions felt by the heavy quarks are stronger than within the weak-coupling expansion. Using an Ansatz for the spectral function which includes NNLO perturbative contributions we were able to determine, for the first time, a continuum estimate for the heavy quark momentum diffusion coefficient.

Olaf Kaczmarek

2014-09-12

25

Evaluation of diffusion coefficients from nonlinear impurity profiles  

Microsoft Academic Search

At high concentrations, impurity diffusion in semiconductors is governed by nonlinear diffusion processes. Using similarity analysis, a general expression for evaluation of the diffusion coefficient from experimental impurity profiles derived for the case of redistributive diffusion of implanted impurities. This expression corresponds to the Boltzmann-Matano analysis for the case of diffusion with constant surface concentration.

Dan Anderson; K. O. Jeppson

1985-01-01

26

Calculation and application of combined diffusion coefficients in thermal plasmas  

NASA Astrophysics Data System (ADS)

The combined diffusion coefficient method is widely used to treat the mixing and demixing of different plasma gases and vapours in thermal plasmas, such as welding arcs and plasma jets. It greatly simplifies the treatment of diffusion for many gas mixtures without sacrificing accuracy. Here, three subjects that are important in the implementation of the combined diffusion coefficient method are considered. First, it is shown that different expressions for the combined diffusion coefficients, arising from different definitions for the stoichiometric coefficients that assign the electrons to the two gases, are equivalent. Second, an approach is presented for calculating certain partial differential terms in the combined temperature and pressure diffusion coefficients that can cause difficulties. Finally, a method for applying the combined diffusion coefficients in computational models, which typically require diffusion to be expressed in terms of mass fraction gradients, is given.

Murphy, Anthony B.

2014-03-01

27

Water diffusion coefficients during copper electropolishing and IAN IVAR SUNI2*  

E-print Network

associated with each dissolving Cu ion and on the effective diffusion coefficient of water. Transient state behavior are the same, about one water molecule is associated with each dissolving Cu ion is also consistent with an assumption that six water molecules are associated with each dissolving Cu ion

Suni, Ian Ivar

28

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

29

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

30

Combined diffusion coefficients for a mixture of three ionized gases  

NASA Astrophysics Data System (ADS)

The combined diffusion coefficient method has been demonstrated to greatly simplify the treatment of diffusion in the modelling of thermal plasmas in gas mixtures without loss of accuracy. In this paper, an extension of this method to allow treatment of diffusion of a three-gas mixture has been achieved, provided that the gases are homonuclear and do not react with each other, and satisfy local chemical equilibrium. Formulas for the combined diffusion coefficients are presented, and combined diffusion coefficients for different mixtures of helium, argon and carbon at temperatures up to 30?000 K and at atmosphere pressure are calculated as an example.

Zhang, X. N.; Murphy, A. B.; Li, H. P.; Xia, W. D.

2014-12-01

31

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

32

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 rage 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.

2011-08-01

33

The solubility and diffusion coefficient of helium in uranium dioxide  

NASA Astrophysics Data System (ADS)

The solubility and diffusion coefficient of helium in the single-crystal UO 2 samples were determined by a Knudsen-effusion mass-spectrometric method. The measured helium solubilities were found to lie within the scatter of the available data, but to be much lower than those for the polycrystalline samples. The diffusion analysis was conducted based on a hypothetical equivalent sphere model and the simple Fick's law. The helium diffusion coefficient was determined by using the pre-exponential factor and activation energy as the fitting parameters for the measured and calculated fractional releases of helium. The optimized diffusion coefficients were in good agreement with those obtained by a nuclear reaction method reported in the past. It was also found that the pre-exponential factors of the determined diffusion coefficients were much lower than those analyzed in terms of a simple interstitial diffusion mechanism.

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

2011-12-01

34

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

35

Determination of diffusion coefficient for unsaturated soils  

E-print Network

. The laboratory procedure followed involves measuring the soil suction along the length of the sample and at different times using thermocouple psychrometers. The evaluation of the evaporation coefficient (he) has been made an integral part of the procedure...

Sood, Eeshani

2005-08-29

36

Apparent Diffusion Coefficients from High Angular Resolution Diffusion Imaging: Estimation and  

E-print Network

Apparent Diffusion Coefficients from High Angular Resolution Diffusion Imaging: Estimation resolution diffusion imaging has recently been of great interest in characterizing non-Gaussian diffusion pro- cesses. One important goal is to obtain more accurate fits of the apparent diffusion processes

Chen, Yiling

37

Effects of electrode properties and fabricated pressure on Li ion diffusion and diffusion-induced stresses in cylindrical Li-ion batteries  

NASA Astrophysics Data System (ADS)

The effects of electrode properties and fabricated pressure on Li ion diffusion and diffusion-induced stress in a cylindrical Li-ion battery are studied. It is found that hydrostatic pressure or elastic modulus variation in the active layer have little effect on the distribution of Li ions for a higher diffusivity coefficient, but both can facilitate Li ion diffusion for a lower diffusivity coefficient. The elastic modulus variation has a significant effect on the distribution of stress and hydrostatic pressure can reduce the surface stress for the lower diffusivity coefficient. A higher charging rate causes a more transient response in the stress history, but a linear charging history is observed for slow charging rates. A higher charging rate would not inflict extra damage on the electrode for the higher diffusivity coefficient and the stress history becomes highly transient and charging rate dependent for the lower diffusivity coefficient. The effect of fabricated pressure can be neglected.

Zhang, Tao; Guo, Zhansheng

2014-03-01

38

Single-particle tracking: the distribution of diffusion coefficients.  

PubMed Central

In single-particle tracking experiments, the diffusion coefficient D may be measured from the trajectory of an individual particle in the cell membrane. The statistical distribution of single-trajectory diffusion coefficients is examined by Monte Carlo calculations. The width of this distribution may be useful as a measure of the heterogeneity of the membrane and as a test of models of hindered diffusion in the membrane. For some models, the distribution of the short-range diffusion coefficient is much narrower than the observed distribution for proteins diffusing in cell membranes. To aid in the analysis of single-particle tracking measurements, the distribution of D is examined for various definitions of D and for various trajectory lengths. PMID:9083678

Saxton, M J

1997-01-01

39

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

40

Onsager coefficients for binary mixture diffusion in nanopores  

Microsoft Academic Search

This paper presents a critical appraisal of current estimation methods for the Onsager coefficients L11, L22, and L12 for binary mixture diffusion inside nanopores using pure component diffusivity data inputs. The appraisal is based on extensive sets of molecular dynamics (MD) simulation data on Lij for a variety of mixtures in zeolites (MFI, AFI, TON, FAU, CHA, DDR, MOR, and

R. Krishna; J. M. van Baten

2008-01-01

41

Empirical determination of diffusion coefficients and geospeedometry  

NASA Astrophysics Data System (ADS)

Geospeedometry allows to estimate the cooling rate (s init) of metamorphic rocks at the beginning of the cooling history using diffusion data. But the choice of a diffusion activation energy (E) and a preexponential factor (D 0) from experimental results can be difficult. We propose a method to obtain E directly from the rock itself by studying the variation of the average concentration of elements or isotopes () as a function of mineral grain size (d). An appropriate value of D 0 can then be estimated using an existing compensation rule, a linear relationship between log D 0 and E. Consequently, uncertainties on s init are markedly reduced. All parameters of this analytical model and their sensitivity on s init can be estimated from of the mineral grains under study. As a test we apply our model to a study by Edwards and Valley (1998)**** on 18O/ 16O fractionation between diopside and calcite in Adirondacks marbles, and find a cooling rate in agreement with previous works, without choosing experimental values for E and D 0.

Jaoul, Olivier; Béjina, Frédéric

2005-02-01

42

Exploring non-linear cosmological matter diffusion coefficients  

E-print Network

Since microscopic velocity diffusion can be incorporated into general relativity in a consistent way, we study cosmological background solutions when the diffusion phenomena takes place in an expanding universe. Our focus here relies on the nature of the diffusion coefficient $\\sigma$ which measures the magnitude of such transport phenomena. We test dynamics where $\\sigma$ has a phenomenological dependence on the scale factor, the matter density, the dark energy and the expansion rate.

Hermano Velten; Simone Calogero

2014-07-16

43

Impurity-concentration profile for an exponentially decaying diffusion coefficient in irradiation enhanced diffusion  

Microsoft Academic Search

The diffusion equation is solved for a semi-infinite region in the case of irradiation-enhanced diffusion produced by a diffusion coefficient falling off exponentially in the medium. Near the surface the concentration profile due to enhanced diffusion has a larger concentration than the profile due to thermal diffusion; conversely far from the surface the enhanced-diffusion profile has a lower concentration than

J. Kowall; D. Peak; J. W. Corbett

1976-01-01

44

Do thermal diffusion and Dufour coefficients satisfy Onsager's reciprocity relation?  

PubMed

It is commonly admitted that in liquids the thermal diffusion and Dufour coefficients DT and DF satisfy Onsager's reciprocity. From their relation to the cross-coefficients of the phenomenological equations, we are led to the conclusion that this is not the case in general. As illustrative and physically relevant examples, we discuss micellar solutions and colloidal suspensions, where DT arises from chemical reactions or viscous effects but is not related to the Dufour coefficient DF. The situation is less clear for binary molecular mixtures; available experimental and simulation data do not settle the question whether DT and DF are reciprocal coefficients. PMID:25341414

Würger, Alois

2014-10-01

45

ULF wave derived radiation belt radial diffusion coefficients  

NASA Astrophysics Data System (ADS)

Waves in the ultra-low-frequency (ULF) band have frequencies which can be drift resonant with electrons in the outer radiation belt, suggesting the potential for strong interactions and enhanced radial diffusion. Previous radial diffusion coefficient models such as those presented by Brautigam and Albert (2000) have typically used semiempirical representations for both the ULF wave's electric and magnetic field power spectral densities (PSD) in space in the magnetic equatorial plane. In contrast, here we use ground- and space-based observations of ULF wave power to characterize the electric and magnetic diffusion coefficients. Expressions for the electric field power spectral densities are derived from ground-based magnetometer measurements of the magnetic field PSD, and in situ AMPTE and GOES spacecraft measurements are used to derive expressions for the compressional magnetic field PSD as functions of Kp, solar wind speed, and L-shell. Magnetic PSD results measured on the ground are mapped along the field line to give the electric field PSD in the equatorial plane assuming a guided Alfvén wave solution and a thin sheet ionosphere. The ULF wave PSDs are then used to derive a set of new ULF-wave driven diffusion coefficients. These new diffusion coefficients are compared to estimates of the electric and magnetic field diffusion coefficients made by Brautigam and Albert (2000) and Brautigam et al. (2005). Significantly, our results, derived explicitly from ULF wave observations, indicate that electric field diffusion is much more important than magnetic field diffusion in the transport and energization of the radiation belt electrons.

Ozeke, Louis G.; Mann, Ian R.; Murphy, Kyle R.; Rae, I. Jonathan; Milling, David K.; Elkington, Scot R.; Chan, Anthony A.; Singer, Howard J.

2012-04-01

46

Diffusion coefficients of alkaline cations in Bure mudrock  

NASA Astrophysics Data System (ADS)

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

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

47

THE DETERMINATION OF DIFFUSION COEFFICIENT OF INVERT MATERIALS  

SciTech Connect

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

P. Heller and J. Wright

2000-01-11

48

Scale dependency of the effective matrix diffusion coefficient  

SciTech Connect

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

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

2003-05-30

49

The solubility and diffusion coefficient of helium in uranium dioxide  

Microsoft Academic Search

The solubility and diffusion coefficient of helium in the single-crystal UO2 samples were determined by a Knudsen-effusion mass-spectrometric method. The measured helium solubilities were found to lie within the scatter of the available data, but to be much lower than those for the polycrystalline samples. The diffusion analysis was conducted based on a hypothetical equivalent sphere model and the simple

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

2011-01-01

50

A review of chemical diffusion: Criticism and limits of simplified methods for diffusion coefficient calculation  

Microsoft Academic Search

A review of the physics and modelling of mass diffusion involving different gaseous chemical species is firstly proposed. Both accurate and simplified models for mass diffusion involve the calculation of individual species diffusion coefficients. Since these are computationally expensive, in CFD they are commonly estimated by assuming constant Lewis or Schmidt numbers for each chemical species. The constant Lewis number

E. Giacomazzi; F. R. Picchia; N. Arcidiacono

2008-01-01

51

A new method for measuring the diffusion coefficient in a gas phase.  

PubMed

A new and fast method for measuring the diffusion coefficients of binary gas mixtures using ion mobility spectrometry (IMS) has been developed. In this method, the sample is injected as a short pulse into the flowing drift gas, forming a Gaussian concentration profile inside the drift region. This Gaussian cloud is irradiated with a fast moving swarm of electrons to create negative ions. The flash of electrons is so short that the negative ions do not move much during the exposure time. The ions then drift toward the detector, where they are collected. The collected ion signal pattern reflects the spatial distribution of the sample inside the cloud at the time of exposure. This is repeated in intervals of 300-400 ms to monitor the spatial spreading of the molecules in the drift region. Consecutive IMS spectra show the evolution of the cloud over time. The collected spectra are fit to Gaussian functions to extract diffusion coefficients. Using this method, the diffusion coefficient of O(2), CHCl(3), and C(2)H(2)Cl(2) were measured, and the results are in good agreement with the previously reported experimental data. PMID:16986857

Rouholahnejad, Fereshteh; Tabrizchi, Mahmoud

2006-09-28

52

The diffusion of ions in unconsolidated sediments  

USGS Publications Warehouse

Diffusion in unconsolidated sediments generally proceeds at rates ranging from half to one twentieth of those applying to diffusion of ions and molecules in free solution. Diffusion rates are predictable with respect to porosity and path tortuosity in host sediments, and can be conveniently measured by determinations of electrical resistivity on bulk sediment samples. Net ion flux is further influenced by reactions of diffusing species with enclosing sediments, but such influences should not be confused with or lumped with diffusion processes. ?? 1970.

Manheim, F. T.

1970-01-01

53

Optimal estimation of diffusion coefficients from single-particle trajectories  

NASA Astrophysics Data System (ADS)

How does one optimally determine the diffusion coefficient of a diffusing particle from a single-time-lapse recorded trajectory of the particle? We answer this question with an explicit, unbiased, and practically optimal covariance-based estimator (CVE). This estimator is regression-free and is far superior to commonly used methods based on measured mean squared displacements. In experimentally relevant parameter ranges, it also outperforms the analytically intractable and computationally more demanding maximum likelihood estimator (MLE). For the case of diffusion on a flexible and fluctuating substrate, the CVE is biased by substrate motion. However, given some long time series and a substrate under some tension, an extended MLE can separate particle diffusion on the substrate from substrate motion in the laboratory frame. This provides benchmarks that allow removal of bias caused by substrate fluctuations in CVE. The resulting unbiased CVE is optimal also for short time series on a fluctuating substrate. We have applied our estimators to human 8-oxoguanine DNA glycolase proteins diffusing on flow-stretched DNA, a fluctuating substrate, and found that diffusion coefficients are severely overestimated if substrate fluctuations are not accounted for.

Vestergaard, Christian L.; Blainey, Paul C.; Flyvbjerg, Henrik

2014-02-01

54

Prediction of self-diffusion and heterodiffusion coefficients in zircon  

NASA Astrophysics Data System (ADS)

An empirical model interconnecting point defect parameters with bulk properties of solids has been employed to calculate the self-diffusion coefficients of O and Si in zircon. Meanwhile, the model is extended to heterodiffusions for the first time in this study, which are estimated for Pb, Ti, Li, trivalent cations (REEs: Sm, Dy, Yb), and tetravalent cations (Th, U, Hf) diffusing in zircon. For most cases, our empirically estimated diffusivities under anhydrous conditions agree well with the experimental measurements over the temperature ranges investigated in the laboratory, as compared to the estimates derived from the anion porosity, although the estimated activation energies of the diffusion have a little bit large uncertainties in some cases.

Zhang, Baohua; Wu, Xiaoping

2011-07-01

55

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

56

Vertical eddy diffusion coefficient from the LANDSAT imagery  

NASA Technical Reports Server (NTRS)

Analysis of five stable cases of the smoke plumes that originated in eastern Cabo Frio (22 deg 59'S; 42 deg 02'W), Brazil using LANDSAT imagery is presented for different months and years. From these images the lateral standard deviation (sigma sub y) and the lateral eddy diffusion coefficient (K sub y) are obtained from the formula based on Taylor's theory of diffusion by continuous moment. The rate of kinetic energy dissipation (e) is evaluated from the diffusion parameters sigma sub y and K sub y. Then, the vertical diffusion coefficient (K sub z) is estimated using Weinstock's formulation. These results agree well with the previous experimental values obtained over water surfaces by various workers. Values of e and K sub z show the weaker mixing processes in the marine stable boundary layer. The data sample is apparently to small to include representative active turbulent regions because such regions are so intermittent in time and in space. These results form a data base for use in the development and validation of mesoscale atmospheric diffusion models.

Viswanadham, Y. (principal investigator); Torsani, J. A.

1982-01-01

57

The effects of deionization processes on meteor radar diffusion coefficients below 90 km  

NASA Astrophysics Data System (ADS)

The decay times of VHF radar echoes from underdense meteor trails are reduced in the lower portions of the meteor region. This is a result of plasma neutralization initiated by the attachment of positive trail ions to neutral atmospheric molecules. Decreased echo decay times cause meteor radars to produce erroneously high estimates of the ambipolar diffusion coefficient at heights below 90 km, which affects temperature estimation techniques. Comparisons between colocated radars and satellite observations show that meteor radar estimates of diffusion coefficients are not consistent with estimates from the Aura Microwave Limb Sounder satellite instrument and that colocated radars operating at different frequencies estimate different values of the ambipolar diffusion coefficient for simultaneous detections of the same meteors. Loss of free electrons from meteor trails due to attachment to aerosols and chemical processes were numerically simulated and compared with observations to determine the specific mechanism responsible for low-altitude meteor trail plasma neutralization. It is shown that three-body attachment of positive metal ions significantly reduces meteor radar echo decay times at low altitudes compared to the case of diffusion only that atmospheric ozone plays little part in the evolution of low-altitude underdense meteor trails and that the effect of three-body attachment begins to exceed diffusion in echo decay times at a constant density surface.

Younger, J. P.; Lee, C. S.; Reid, I. M.; Vincent, R. A.; Kim, Y. H.; Murphy, D. J.

2014-08-01

58

Ischemic lesion volume determination on diffusion weighted images vs. apparent diffusion coefficient maps  

Microsoft Academic Search

Though diffusion weighted imaging (DWI) is frequently used for identifying the ischemic lesion in focal cerebral ischemia, the understanding of spatiotemporal evolution patterns observed with different analysis methods remains imprecise. DWI and calculated apparent diffusion coefficient (ADC) maps were serially obtained in rat stroke models (MCAO): permanent, 90 min, and 180 min temporary MCAO. Lesion volumes were analyzed in a blinded and

Birgul Bastan; Marc Fisher; James P. Bouley; Nils Henninger

2009-01-01

59

The thermal neutron diffusion cooling coefficient in polyethylene  

Microsoft Academic Search

The diffusion cooling coefficient C for thermal neutrons in polyethylene at 20°C has been determined theoretically. Granada's Synthetic Model of the scattering law has been applied to describe the interaction of neutrons with polyethylene. Two approximations of the neutron energy distribution in finite homogeneous systems have been used. The result of the calculation using a rough approximation is CB=2160cm4s?1. According

K. Drozdowi; V. H. Gillette

1999-01-01

60

The determination of molecular diffusion coefficients by the barometric method  

Microsoft Academic Search

The binary molecular diffusion coefficients D\\u000a AB of a vaporizing liquid in gases under atmospheric conditions were measured by the new simple barometric method. A change\\u000a in the pressure of a vapor-gas mixture in a closed cell was determined as a function of time. Under experimental conditions,\\u000a one can also find partial saturated vapor pressures of substances. The deviations of

O. A. Kashirskaya; V. A. Lotkhov; V. V. Dil’man

2008-01-01

61

Numerical solution of stochastic differential equations with constant diffusion coefficients  

SciTech Connect

We present Runge-Kutta methods of high accuracy for stochastic differential equations with constant diffusion coefficients. We analyze L/sub 2/ convergence of these methods and present convergence proofs. For scalar equations a second-order method is derived, and for systems a method of order one-and-one-half is derived. We further consider a variance reduction technique based on Hermite expansions for evaluating expectations of functions of sample solutions. Numerical examples in two dimensions are presented.

Chien-Cheng Chang

1987-10-01

62

Radial diffusion and ion partitioning in the Io torus  

NASA Technical Reports Server (NTRS)

A model is presented for radial diffusion and charge state partitioning of sulfur and oxygen ions in the Io torus, including effects of electron impact and charge exchange. When applied to Voyager 1 radial profiles of total ion flux tube content, the model shows that the ion residence time in the torus, tau(D), as defined in spectroscopic studies of ion partitioning, is related to the radial diffusion coefficient, D(LL), at L = 7 by tau(D) approximately 8/D(LL)(7). This result appears to bring spectroscopic estimates of the ion residence time (tau/D/ greater than about 60 to 100 days) into reasonable agreement with estimates of D(LL) from magnetospheric diffusion studies, D(LL) equals approximately 10 to the -6th/s.

Cheng, A. F.

1986-01-01

63

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

64

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

PubMed

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

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

2011-04-25

65

Concentration dependence of translational diffusion coefficients for globular proteins.  

PubMed

This investigation examines published results of traditional diffusion experiments on ovalbumin and bovine serum albumin to determine the extent to which assumed concentration independence of the translational diffusion coefficient is a reasonable approximation in the analysis of boundary spreading in sedimentation velocity experiments on proteins. Although significant positive concentration dependence of the diffusion coefficient (D) for both proteins is predicted by current theories, none has been detected in these experimental diffusion studies performed under the constraints of constant temperature and solvent chemical potential (those also pertinent to sedimentation velocity). Instead, the results are better described by the relatively minor concentration dependence predicted by considering solution viscosity to be an additional source of D-c dependence. Inasmuch as the predicted variation in D for solutions with concentrations below 10 mg mL(-1) is within the uncertainty of experimental estimates, these findings support use of the approximate solution of the Lamm equation developed by Fujita for the quantitative analysis of boundary spreading in sedimentation velocity experiments on proteins. PMID:25306977

Scott, David J; Harding, Stephen E; Winzor, Donald J

2014-10-27

66

Response of radiation belt simulations to different radial diffusion coefficients  

NASA Astrophysics Data System (ADS)

Resonant interactions between Ultra Low Frequency (ULF) waves and relativistic electrons may violate the third adiabatic invariant of motion, which produces radial diffusion in the electron radiation belts. This process plays an important role in the formation and structure of the outer electron radiation belt and is important for electron acceleration and losses in that region. Two parameterizations of the resonant wave-particle interaction of electrons with ULF waves in the magnetosphere by Brautigam and Albert [2000] and Ozeke et al. [2012] are evaluated using the Versatile Electron Radiation Belt (VERB) diffusion code to estimate their relative effect on the radiation belt simulation. The period of investigation includes quiet time and storm time geomagnetic activity and is compared to data based on satellite observations. Our calculations take into account wave-particle interactions represented by radial diffusion transport, local acceleration, losses due to pitch-angle diffusion, and mixed diffusion. We show that the results of the 3D diffusion simulations depend on the assumed parametrization of waves. The differences between the simulations and potential missing physical mechanisms are discussed. References Brautigam, D. H., and J. M. Albert (2000), Radial diffusion analysis of outer radiation belt electrons during the October 9, 1990, magnetic storm, J. Geophys. Res., 105(A1), 291-309, doi:10.1029/1999JA900344 Ozeke, L. G., I. R. Mann, K. R. Murphy, I. J. Rae, D. K. Milling, S. R. Elkington, A. A. Chan, and H. J. Singer (2012), ULF wave derived radiation belt radial diffusion coefficients, J. Geophys. Res., 117, A04222, doi:10.1029/2011JA017463.

Drozdov, A.; Shprits, Y.; Subbotin, D.; Kellerman, A. C.

2013-12-01

67

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

68

Effective diffusion coefficient in 2D periodic channels.  

PubMed

Calculation of the effective diffusion coefficient D(x), depending on the longitudinal coordinate x in 2D channels with periodically corrugated walls, is revisited. Instead of scaling the transverse lengths and applying the standard homogenization techniques, we propose an algorithm based on formulation of the problem in the complex plane. A simple model is solved to explain the behavior of D(x) in the channels with short periods L, observed by Brownian simulations of Dagdug et al. [J. Chem. Phys. 133, 034707 (2010)]. PMID:25318709

Kalinay, Pavol

2014-10-14

69

Effective diffusion coefficient in 2D periodic channels  

NASA Astrophysics Data System (ADS)

Calculation of the effective diffusion coefficient D(x), depending on the longitudinal coordinate x in 2D channels with periodically corrugated walls, is revisited. Instead of scaling the transverse lengths and applying the standard homogenization techniques, we propose an algorithm based on formulation of the problem in the complex plane. A simple model is solved to explain the behavior of D(x) in the channels with short periods L, observed by Brownian simulations of Dagdug et al. [J. Chem. Phys. 133, 034707 (2010)].

Kalinay, Pavol

2014-10-01

70

Modeling Infinite Dilution and Fickian Diffusion Coefficients of Carbon Dioxide in Water  

E-print Network

Modeling Infinite Dilution and Fickian Diffusion Coefficients of Carbon Dioxide in Water J. Wambui infinite dilution diffusion coefficients for carbon dioxide and water mixtures. The model takes, carbon dioxide, classical thermodynamics Introduction The increase in atmospheric concentrations of CO2

Firoozabadi, Abbas

71

Apparent diffusion coefficients and chemical species of neptunium (V) in compacted Na-montmorillonite.  

PubMed

Diffusion of neptunium (V) in compacted Na-montmorillonite was studied through the non-steady state diffusion method. In this study, two experimental attempts were carried out to understand the diffusion mechanism of neptunium. One was to establish the diffusion activation energy, which was then used to determine the diffusion process in the montmorillonite. The other was the measurement of the distribution of neptunium in the montmorillonite by a sequential batch extraction. The apparent diffusion coefficients of neptunium in the montmorillonite at a dry density of 1.0 Mg m-3 were from 3.7 x 10(-12) m2 s-1 at 288 K to 9.2 x 10(-12) m2 s-1 at 323 K. At a dry density of 1.6 Mg m-3, the apparent diffusion coefficients ranged between 1.5 x 10(-13) m2 s-1 at 288 K and 8.7 x 10(-13) m2 s-1 at 323 K. The activation energy for the diffusion of neptunium at a dry density of 1.0 Mg m-3 was 17.5 +/- 1.9 kJ mol-1. This value is similar to those reported for diffusion of other ions in free water, e.g., 18.4 and 17.4 kJ mol-1 for Na+ and Cl-, respectively. At a dry density of 1.6 Mg.m-3, the activation energy was 39.8 +/- 1.9 kJ mol-1. The change in the activation energy suggests that the diffusion process changes depending on the dry density of the compacted montmorillonite. A characteristic distribution profile was obtained by the sequential extraction procedure for neptunium diffused in compacted montmorillonite. The estimated fraction of neptunium in the pore water was between 3% and 11% at a dry density of 1.6 Mg m-3 and at a temperature of 313 K. The major fraction of the neptunium in the montmorillonite was identified as neptunyl ions sorbed on the outer surface of the montmorillonite. These findings suggested that the activation energy for diffusion and the distribution profile of the involved nuclides could become powerful parameters in understanding the diffusion mechanism. PMID:11288572

Kozai, N; Inada, K; Kozaki, T; Sato, S; Ohashi, H; Banba, T

2001-02-01

72

Diffusion coefficients of sulfate and methane in marine sediments: Influence of porosity  

Microsoft Academic Search

Tracer diffusion coefficients of sulfate and methane were determined in seawater ( D o ) and in sediments ( D s ). The diffusion coefficients in seawater (20 S) at 4°C were 0.56 ± 0.04 * 10 -5 cm 2 s -1 for sulfate and 0.87 ±0.10 * 10 -5 cm 2 s -1 for methane. The sediment diffusion coefficients

Niels Iversen; Bo Barker Jørgensen

1993-01-01

73

A rapid method for determining apparent diffusion coefficients in Chalk and other consolidated porous media  

NASA Astrophysics Data System (ADS)

SummaryThe development of a method for the determination of the apparent diffusion coefficient, DA, for chloride in saturated Chalk cores is described. The method is rapid compared with other approaches, taking typically less than 24 h for a single determination. Cylindrical Chalk cores approximately 25 mm high by 25 mm in diameter, which are routinely used in porosity and permeability measurements and which had been pre-equilibrated with a 200 mg/L chloride solution, were sealed at both ends and attached to a slowly rotating spindle suspended in a reservoir. A chloride ion-selective electrode (ISE) connected to a data logger was used to record chloride diffusion out of the core. DA was estimated by analysing the change in chloride concentration in the reservoir with time. Diffusion coefficients were estimated for six Chalk samples from a range of Chalk lithologies. Sample porosities for these Chalks ranged from 32% to 48% and gas permeabilities from 0.3 to 8.2 × 10 -9 m 2. The DA was found to vary from 3.1 to 8.7 × 10 -10 m 2/s, a similar range to that observed by others. A bromide ISE was also used on one sample and found to give a similar DA to that obtained for chloride. This approach, which combines a rigorous mathematical model of diffusion with a relatively simple practical method, could easily be adapted for other ions and for other consolidated porous media.

Gooddy, Daren C.; Kinniburgh, David G.; Barker, John A.

2007-09-01

74

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

75

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

76

Effective diffusion coefficient in tilted disordered potentials: Optimal relative diffusivity at a finite temperature  

NASA Astrophysics Data System (ADS)

In this work we study the transport properties of non-interacting overdamped particles, moving on tilted disordered potentials, subjected to Gaussian white noise. We give exact formulas for the drift and diffusion coefficients for the case of random potentials resulting from the interaction of a particle with a "random polymer". In our model the polymer is made up, by means of some stochastic process, of monomers that can be taken from a finite or countable infinite set of possible monomer types. For the case of uncorrelated random polymers we found that the diffusion coefficient exhibits a non-monotonous behavior as a function of the noise intensity. Particularly interesting is the fact that the relative diffusivity becomes optimal at a finite temperature, a behavior which is reminiscent of stochastic resonance. We explain this effect as an interplay between the deterministic and noisy dynamics of the system. We also show that this behavior of the diffusion coefficient at a finite temperature is more pronounced for the case of weakly disordered potentials. We test our findings by means of numerical simulations of the corresponding Langevin dynamics of an ensemble of noninteracting overdamped particles diffusing on uncorrelated random potentials.

Salgado-García, R.

2014-09-01

77

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

Microsoft Academic Search

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

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

2009-01-01

78

Evaluation of ligand-selector interaction from effective diffusion coefficient.  

PubMed

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

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

2010-07-01

79

Matrix diffusion coefficients for the NNWSI waste package environment  

SciTech Connect

The Nevada Nuclear Waste Storage Investigations (NNWSI) project is evaluating the tuffaceous rock units at Yucca Mountain, located on the western boundary of the Nevada Test Site, as a potential location for a high level radioactive waste repository. Within the NNWSI project, Lawrence Livermore National Laboratory (LLNL) has been assigned responsibility for the design and qualification of the waste package. This task includes the determination of the waste package environment, the characterization of waste package-repository material interactions and the analysis and testing of the waste package performance in the repository environment. This paper describes an ongoing analysis of experimental work to determine the matrix diffusion coefficient for the NNWSI waste package environment.

Eggert, K.G.; Revelli, M.A.

1985-04-01

80

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

81

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. PMID:24901638

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

2014-01-01

82

Position-dependent stochastic diffusion model of ion channel gating  

E-print Network

A position-dependent stochastic diffusion model of gating in ion channels is developed by considering the spatial variation of the diffusion coefficient between the closed and open states. It is assumed that a sensor which regulates the opening of the ion channel experiences Brownian motion in a closed region $R_{c}$ and a transition region $R_{m}$, where the dynamics is described by probability densities $p_{c}(x,t)$ and $p_{m}(x,t)$ which satisfy interacting Fokker-Planck equations with diffusion coefficient $D_{c}(x)=D_{c}\\exp(\\gamma_{c}x)$ and $D_{m}(x)=D_{m} \\exp(-\\gamma_{m}x)$. The analytical solution of the coupled equations may be approximated by the lowest frequency relaxation, a short time after the application of a depolarizing voltage clamp, when $D_{m} \\ll D_{c}$ or the diffusion parameter $\\gamma_{m}$ is sufficiently large. Thus, an empirical rate equation that describes gating transitions may be derived from a stochastic diffusion model if there is a large diffusion (or potential) barrier between open and closed states.

Samuel Robert Vaccaro

2014-06-30

83

Position-dependent stochastic diffusion model of ion channel gating  

E-print Network

A position-dependent stochastic diffusion model of gating in ion channels is developed by considering the spatial variation of the diffusion coefficient between the closed and open states. It is assumed that a sensor which regulates the opening of the ion channel experiences Brownian motion in a closed region $R_{c}$ and a transition region $R_{m}$, where the dynamics is described by probability densities $p_{c}(x,t)$ and $p_{m}(x,t)$ which satisfy interacting Fokker-Planck equations with diffusion coefficient $D_{c}(x)=D_{c}\\exp(\\gamma_{c}x)$ and $D_{m}(x)=D_{m} \\exp(-\\gamma_{m}x)$. The analytical solution of the coupled equations may be approximated by the lowest frequency relaxation, a short time after the application of a depolarizing voltage clamp, when $D_{m} \\ll D_{c}$ or the diffusion parameter $\\gamma_{m}$ is sufficiently large. Thus, an empirical rate equation that describes gating transitions may be derived from a stochastic diffusion model if there is a large diffusion (or potential) barrier betwe...

Vaccaro, Samuel Robert

2014-01-01

84

Diffusion coefficients of cerium and gadolinium in molten LiCl-KCl  

SciTech Connect

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

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

1998-01-01

85

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

86

Preferential Resonant Diffusion of Upgoing Auroral O+ Ions by Parallel Propagating Ion Acoustic Waves  

NASA Astrophysics Data System (ADS)

Resonant quasilinear diffusion time scales are examined for upgoing auroral O+ ions in resonance with ion acoustic waves. The waves are destabilized by simultaneous upgoing H+ and O+ ion beams and propagate in a mode parallel to the ambient magnetic field with phase velocity UO + CO, where UO is the oxygen streaming velocity and CO is the oxygen sound speed. Although the waves resonate with both ion species, the diffusion time scales for H+ are insignificant while those for O+ maximize in a narrow region in parallel velocity within the O+ beam distribution. Diffusion is primarily perpendicular to the background magnetic field, except at the edges of the beam perpendicular velocity distribution where it becomes more parallel. With typical values of the electric field energy density in the diffusion coefficients one sees diffusion time scales in the range 5 to 25 seconds in the narrow parallel velocity region. The narrow parallel velocity region sweeps through the O+ beam as it moves into weaker field regions, corresponding roughly to an altitude range of 5000 - 10000 km. The rate at which the maximum diffusion region sweeps through the beam is slow enough to allow O+ beam ions to significantly diffuse.

Ludlow, G. R.

2012-12-01

87

Diffusion coefficient of vegetation: measurements and Y. Smyrnova, J. Kang, C. Blackford and C. Cheal  

E-print Network

Diffusion coefficient of vegetation: measurements and simulation Y. Smyrnova, J. Kang, C. Blackford reports the initial results of an investigation of the diffuse sound reflection from two typical bedding at reducing noise from urban traffic. Directional diffusion coefficients of the plants have been measured

Paris-Sud XI, Université de

88

Variability of Renal Apparent Diffusion Coefficients: Limitations of the Monoexponential Model for Diffusion Quantification1  

PubMed Central

Purpose: To investigate whether variability in reported renal apparent diffusion coefficient (ADC) values in literature can be explained by the use of different diffusion weightings (b values) and the use of a monoexponential model to calculate ADC. Materials and Methods: This prospective study was approved by institutional review board and was HIPAA-compliant, and all subjects gave written informed consent. Diffusion-weighted (DW) imaging of the kidneys was performed in three healthy volunteers to generate reference diffusion decay curves. In a literature meta-analysis, the authors resampled the reference curves at the various b values used in 19 published studies of normal kidneys (reported ADC = [2.0–4.1] × 10?3 mm2 / sec for cortex and [1.9–5.1] × 10?3 mm2 / sec for medulla) and then fitted the resampled signals by monoexponential model to produce “predicted” ADC. Correlation plots were used to compare the predicted ADC values with the published values obtained with the same b values. Results: Significant correlation was found between the reported and predicted ADC values for whole renal parenchyma (R2 = 0.50, P = .002), cortex (R2 = 0.87, P = .0002), and medulla (R2 = 0.61, P = .0129), indicating that most of the variability in reported ADC values arises from limitations of a monoexponential model and use of different b values. Conclusion: The use of a monoexponential function for DW imaging analysis and variably sampled diffusion weighting plays a substantial role in causing the variability in ADC of healthy kidneys. For maximum reliability in renal apparent diffusion coefficient quantification, data for monoexponential analysis should be acquired at a fixed set of b values or a biexponential model should be used. © RSNA, 2010 PMID:20089719

Sigmund, Eric E.; Chandarana, Hersh; Rusinek, Henry; Chen, Qun; Vivier, Pierre-Hugues; Taouli, Bachir; Lee, Vivian S.

2010-01-01

89

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

90

HARDI Denoising: Variational Regularization of the Spherical Apparent Diffusion Coefficient  

E-print Network

in medical imaging. Diffusion imaging is a rel- atively new and powerful method to measure the 3D profile of attenuation can be used to measure the rate of water diffusion in any arbitrary 3D direction via the Stejskal of this diffusion anisotropy, initial approaches to assess fiber directions modeled the 3D diffusion Funded

Vese, Luminita A.

91

Water diffusion coefficient measurements in the finger by magnetic resonance imaging.  

PubMed

Diffusion coefficients of water have been measured in the fingers of humans by magnetic resonance imaging. It was found that the measured diffusion coefficients increased with subject age in certain regions of the finger but that these regions differed between males and females. The observation of an increased diffusion coefficient with age appears to be inconsistent with a direct-hydration model and possible explanations are given using other models. It is conjectured that the measured diffusion coefficient of water increases with age as a result of structural changes to proteins. PMID:7968287

Damion, R A; Vennart, W; Summers, I R; Ellis, R E

1994-01-01

92

Tracer diffusion coefficients of proteins by means of holographic relaxation spectroscopy: application to bovine serum albumin  

SciTech Connect

Holographic relaxation spectroscopy has been used to measure tracer diffusion coefficients for photochromically labeled bovine serum albumin in solutions having total bovine serum albumin concentrations in the range 3.25 to 257 g/liter. In the limit of zero concentration, the diffusion coefficient was found to be 5.9 X 10(-7) cm/sup 2//s and the initial slope was zero. The concentration dependence of the diffusion coefficient was not significantly affected by the fraction of protein molecules which were labeled. Holographic relaxation spectroscopy permits rapid, accurate determination of tracer diffusion coefficients for proteins in mixtures.

Arunyawongsakorn, U.; Johnson, C.S. Jr.; Gabriel, D.A.

1985-04-01

93

Sodium Ion Diffusion in Al2O3: A Distinct Perspective Compared with Lithium Ion Diffusion.  

PubMed

Surface coating of active materials has been one of the most effective strategies to mitigate undesirable side reactions and thereby improve the overall battery performance. In this direction, aluminum oxide (Al2O3) is one of the most widely adopted coating materials due to its easy synthesis and low material cost. Nevertheless, the effect of Al2O3 coating on carrier ion diffusion has been investigated mainly for Li ion batteries, and the corresponding understanding for emerging Na ion batteries is currently missing. Using ab initio molecular dynamics calculations, herein, we first find that, unlike lithiation, sodiation of Al2O3 is thermodynamically unfavorable. Nonetheless, there can still exist a threshold in the Na ion content in Al2O3 before further diffusion into the adjacent active material, delivering a new insight that both thermodynamics and kinetics should be taken into account to describe ionic diffusion in any material media. Furthermore, Na ion diffusivity in NaxAl2O3 turns out to be much higher than Li ion diffusivity in LixAl2O3, a result opposite to the conventional stereotype based on the atomic radius consideration. While hopping between the O-rich trapping sites via an Na-O bond breaking/making process is identified as the main Na ion diffusion mechanism, the weaker Na-O bond strength than the Li-O counterpart turns out to be the origin of the superior diffusivity of Na ions. PMID:25286155

Jung, Sung Chul; Kim, Hyung-Jin; Choi, Jang Wook; Han, Young-Kyu

2014-11-12

94

SIMPLE ANALYTICAL FORMS OF THE PERPENDICULAR DIFFUSION COEFFICIENT FOR TWO-COMPONENT TURBULENCE. I. MAGNETOSTATIC TURBULENCE  

SciTech Connect

We explore perpendicular diffusion based on the unified nonlinear transport theory. We derive simple analytical forms for the perpendicular mean free path and investigate the influence of different model spectra. We show that for cases where the field line random walk is normal diffusive, the perpendicular diffusion coefficient consists of only two transport regimes. Details of the spectral shape are less important, especially those of the inertial range. Only the macroscopic properties of the turbulence spectrum control the perpendicular diffusion coefficient. Simple formulae for the perpendicular diffusion coefficient are derived which can easily be implemented in solar modulation or shock acceleration codes.

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

2013-09-01

95

Quaternary Diffusion Coefficients in a Protein-Polymer-Salt-Water System Determined by Rayleigh Interferometry  

E-print Network

Quaternary Diffusion Coefficients in a Protein-Polymer-Salt-Water System Determined by Rayleigh in a protein-polymer-salt-water quaternary system. Specifically, we have measured the nine multicomponent diffusion coefficients, Dij, for the lysozyme-poly(ethylene glycol)-NaCl-water system at pH 4.5 and 25 °C

Annunziata, Onofrio

96

Diffusion coefficients for LMFBR cells calculated with MOC and Monte Carlo methods  

Microsoft Academic Search

The present work discusses the calculation of the diffusion coefficient of a lattice of hexagonal cells, with both “sodium present” and “sodium absent” conditions. Calculations are performed in the framework of lattice theory (also known as fundamental mode approximation). Unlike the classical approaches, our heterogeneous leakage model allows the calculation of diffusion coefficients under all conditions, even if planar voids

W. F. G. van Rooijen; G. Chiba

2011-01-01

97

Measurement of sound diffusion coefficients of scattering furnishing volumes present in workplaces  

E-print Network

Measurement of sound diffusion coefficients of scattering furnishing volumes present in workplaces of an initial database of the sound diffusion coefficient per octave of scattering furniture in workplaces. 1 software tools for mapping the sound pressure field in workplaces employ acoustic characteristics

Paris-Sud XI, Université de

98

3d Space-Varying Coefficient Models with Application to Diffusion Tensor Imaging  

E-print Network

3d Space-Varying Coefficient Models with Application to Diffusion Tensor Imaging S. Heim a,, L regressions is reformulated as a 3d space-varying coefficient model (SVCM) for the entire set of diffusion tensor images recorded on a 3d voxel grid. The SVCM unifies the three-step cascade of standard data

Marx, Brian D.

99

Correlation of Apparent Diffusion Coefficient and Computed Tomography Density in Acute Ischemic Stroke  

Microsoft Academic Search

Background and Purpose—Diffusion-weighted MR imaging is very sensitive for the detection of restricted molecular water diffusion in acute ischemic stroke. CT is sensitive to net water uptake in ischemic edema. We compared the decrease in the apparent diffusion coefficient (ADC) in diffusion-weighted MR imaging with CT density changes to study the correlation between diffusion restriction and water uptake in acute

Thomas Kucinski; Ole Väterlein; Volkmar Glauche; Jens Fiehler; Ernst Klotz; Bernd Eckert; Christoph Koch; Joachim Röther; Hermann Zeumer

100

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

E-print Network

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

Kazuhiko Seki; Sanoop Ramachandran; Shigeyuki Komura

2011-05-19

101

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

102

Single-Image Diffusion Coefficient Measurements of Proteins in Free Solution  

PubMed Central

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

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

2012-01-01

103

PITCH-ANGLE DIFFUSION COEFFICIENTS OF CHARGED PARTICLES FROM COMPUTER SIMULATIONS  

SciTech Connect

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

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

2009-12-10

104

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

105

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

106

Mass transfer in SCW extraction molecular diffusion and mass transfer coefficients of ketones and alkenes in sub- and supercritical water  

SciTech Connect

The potential of sub- and supercritical water as extraction solvents has been demonstrated for the (reactive) extraction of coals, used car tires, organic species from residual aqueous solutions, and class selective extraction of organic pollutants with different polarities from solids. In addition, the potential of extraction of coal with supercritical aqueous solutions has been studied. However, physical transport in water at elevated temperature and pressures- and their impact on heterogenous reactions and (reactive) extraction -are not adequately understood. This situation is largely due to the limited data that is available for diffusion in high temperature, high pressure water mixture. Only the molecular diffusion of Iodine ions and hydroquinone in near-critical subcritical water and the self diffusion of coefficient of compressed supercritical water have been reported. In this paper, we present molecular diffusion coefficients of benzophenone, acetone, naphthalene, and anthracene in water at infinite dilution. Pressures ranged from 250 to 500 bar at temperatures ranging from 50{degrees}C to 500{degrees}C resulting in water densities ranging from 1000 to 150 kg/m{sup 3}. Diffusion coefficients were determined by the Taylor-Aris dispersion technique. The effects of increased diffusion on the mass transfer coefficients for emulsions and packed beds were quantified. Molecular division coefficients were 10 to 20 times faster in supercritical water than in water at ambient conditions. Experimental results were correlated with hydrodynamic and kinetic theory. This study and results to be published elsewhere show that diffusion-limited conditions are much more likely to be encountered in supercritical water than is commonly acknowledged.

Goemans, M.G.E.; Gloyna, E.F. [Univ. of Texas, Austin, TN (United States)] [and others

1996-10-01

107

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

108

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

109

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

110

Chloride ion diffusivity of fly ash and silica fume concretes exposed to freeze–thaw cycles  

Microsoft Academic Search

This research focuses on investigating the durability of concretes containing fly ash and silica fume exposed to combined mode of deterioration. For this purpose, the chloride ion diffusivity of concrete was evaluated before and after 300 freeze–thaw (F–T) cycles. It was found that the coefficient of chloride ion diffusivity (CCID) increased as water to cementitious material ratio (w\\/cm) and air

Chul-Woo Chung; Chang-Seon Shon; Young-Su Kim

2010-01-01

111

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

SciTech Connect

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

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

1998-06-12

112

Spin waves and spin diffusion in Fermi liquids: Bounds on effective diffusion coefficients  

SciTech Connect

We investigate the accuracy of the usual relaxation-time approximations, involving the spin-diffusion lifetime tau/sub D/, which are generally made in analyses of spin waves and the Leggett-Rice effect in Fermi liquids. By employing the variational methods of Ah-Sam, Hojgaard-Jensen, and Smith and of Egilsson and Pethick, we are able to determine upper and lower bounds on the effective diffusion coefficient resulting from spin-wave phenomena which are accurate in the whole Fermi-liquid regime (T<

Bedell, K.S.; Meltzer, D.E.

1986-04-01

113

Effective diffusion coefficient of a Brownian particle in a periodically expanded conical tube  

NASA Astrophysics Data System (ADS)

Diffusion in a tube of periodically varying diameter occurs slower than that in a cylindrical tube because diffusing particles get trapped in wells of the periodic entropy potential which is due to variation of the tube cross-section area. To quantify the slowdown one has to establish a relation between the effective diffusion coefficient of the particle and the tube geometry, which is a very complicated problem. Here we show how to overcome the difficulties in the case of a periodically expanded conical tube, where we find an approximate solution for the effective diffusion coefficient as a function of the parameters determining the tube geometry.

Antipov, Anatoly E.; Barzykin, Alexander V.; Berezhkovskii, Alexander M.; Makhnovskii, Yurii A.; Zitserman, Vladimir Yu.; Aldoshin, Sergei M.

2013-11-01

114

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

SciTech Connect

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

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

1998-07-05

115

From free to effective diffusion coefficients in fluorescence correlation spectroscopy experiments  

NASA Astrophysics Data System (ADS)

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

Ipiña, Emiliano Pérez; Dawson, Silvina Ponce

2013-02-01

116

Binary mutual diffusion coefficients of aqueous alcohols. Methanol to 1-heptanol  

SciTech Connect

Mutual diffusion coefficients, measured by Taylor dispersion at 25 C, are reported for binary aqueous solutions of methanol, ethanol, isomeric propanols and butanols, 1-pentanol, 1-hexanol, and 1-heptanol. Limiting diffusion coefficients (D{sup 0}) for the 1-alkanols are found to decrease with alcohol molar volume V approximately as V{sup {minus}1/2}. Although values of D{sup 0} for aqueous 1-propanol and 2-propanol are nearly identical within experimental error, the limiting diffusion coefficients of the isomeric butanols differ by up to 10% and increase in the order D{sup 0}(2-methyl-2-propanol) < D{sup 0}(2-butanol) {approx} D{sup 0}(2-methyl-1-propanol) < D{sup 0}(1-butanol). The butanol results illustrate the difficulty of predicting accurate diffusion coefficients for aqueous solutions.

Hao, L.; Leaist, D.G. [Univ. of Western Ontario, London, Ontario (Canada). Dept. of Chemistry] [Univ. of Western Ontario, London, Ontario (Canada). Dept. of Chemistry

1996-03-01

117

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

SciTech Connect

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

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

1995-02-01

118

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

119

Diffusion coefficients of alkaline cations in Bure mudrock  

Microsoft Academic Search

In this work, the diffusivities of alkaline cations (Li+, Na+, K+, Rb+ and Cs+) were measured in a mudrock sample from Bure (ANDRA site, Meuse\\/Haute-Marne, France). The material is a natural rock, mainly composed of interstratified illite\\/smectite, quartz and calcite. It was saturated with a Na-Cl-dominated synthetic solution with an ionic strength of 57mM and a pH ?8.0. The effective

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

2007-01-01

120

Ischemic lesion volume determination on diffusion weighted images vs. apparent diffusion coefficient maps.  

PubMed

Though diffusion weighted imaging (DWI) is frequently used for identifying the ischemic lesion in focal cerebral ischemia, the understanding of spatiotemporal evolution patterns observed with different analysis methods remains imprecise. DWI and calculated apparent diffusion coefficient (ADC) maps were serially obtained in rat stroke models (MCAO): permanent, 90 min, and 180 min temporary MCAO. Lesion volumes were analyzed in a blinded and randomized manner by 2 investigators using (i) a previously validated ADC threshold, (ii) visual determination of hypointense regions on ADC maps, and (iii) visual determination of hyperintense regions on DWI. Lesion volumes were correlated with 24 hour 2,3,5-triphenyltetrazoliumchloride (TTC)-derived infarct volumes. TTC-derived infarct volumes were not significantly different from the ADC and DWI-derived lesion volumes at the last imaging time points except for significantly smaller DWI lesions in the pMCAO model (p=0.02). Volumetric calculation based on TTC-derived infarct also correlated significantly stronger to volumetric calculation based on last imaging time point derived lesions on ADC maps than DWI (p<0.05). Following reperfusion, lesion volumes on the ADC maps significantly reduced but no change was observed on DWI. Visually determined lesion volumes on ADC maps and DWI by both investigators correlated significantly with threshold-derived lesion volumes on ADC maps with the former method demonstrating a stronger correlation. There was also a better interrater agreement for ADC map analysis than for DWI analysis. Ischemic lesion determination by ADC was more accurate in final infarct prediction, rater independent, and provided exclusive information on ischemic lesion reversibility. PMID:19427841

Bråtane, Bernt Tore; Bastan, Birgul; Fisher, Marc; Bouley, James; Henninger, Nils

2009-07-01

121

A model of cefoperazone tissue penetration: diffusion coefficient and protein binding.  

PubMed Central

The apparent diffusion coefficient of a bound drug, cefoperazone, was studied. The protein binding of cefoperazone was studied by voltammetry, a technique which permitted instant measurements. The apparent diffusion coefficients were similar in agar and fibrin and lower in rat brain tissue. The influence of protein on the value of the apparent diffusion coefficient was negligible. The hypothesis that only the free drug diffuses was supported. The percentage of binding determined by voltammetry corresponded to the true concentration of drug which diffuses and is much lower than the percentage of binding determined by the ultrafiltration centrifugation method. This discrepancy could be explained by the rate of dissociation of the protein-drug complex. PMID:1605594

Meulemans, A

1992-01-01

122

Effective molecular diffusion coefficient in a two-phase gel medium  

Microsoft Academic Search

We derive a mean-field expression for the effective diffusion coefficient of a probe molecule in a two-phase medium consisting of a hydrogel with large gel-free solvent inclusions, in terms of the homogeneous diffusion coefficients in the gel and in the solvent. Upon comparing with exact numerical lattice calculations, we find that our expression provides a remarkably accurate prediction for the

Owen A. Hickey; Jean-François Mercier; Michel G. Gauthier; Fre´de´ric Tessier; Smaine Bekhechi; Gary W. Slater

2006-01-01

123

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

SciTech Connect

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

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

1995-09-01

124

The simulation of transport processes using the method of molecular dynamics. Self-diffusion coefficient  

Microsoft Academic Search

The possibility is investigated of using the method of molecular dynamics for calculating the self-diffusion coefficient of\\u000a liquids and gases. The exactness of calculation of the autocorrelation function of the velocity of molecules and of the self-diffusion\\u000a coefficient is systematically estimated. The characteristic errors of the method are analyzed. Correlations are constructed\\u000a which enable one to reduce the effect made

V. Ya. Rudyak; A. A. Belkin; D. A. Ivanov; V. V. Egorov

2008-01-01

125

Size and dimension dependent diffusion coefficients of SnO2 nanoparticles  

NASA Astrophysics Data System (ADS)

The size and dimension dependences of diffusion coefficient in SnO2 nanoparticles have been studied using Arrhenius relation and Lindemann's criteria. We have calculated diffusion coefficients of nitrogen doped SnO2 nanoparticles, with different sizes ranging from 1 nm to 20 nm. It is found that as the size of nanoparticles decreases, the diffusion activation energy of atoms decreases and results in the increase of diffusion coefficient. The dimension dependence has also been calculated for 0-, 1- and 2 dimensions. In the present paper, the size dependence of self diffusion coefficient is also reported for different dimensions in SnO2 nanoparticles. From calculated results, it can be observed that diffusion coefficient in the case of spherical SnO2 nanoparticles (0-d) is higher than the nanostructures of other dimensions such as cylindrical (1-d) and thin films (2-d) due to the fact that the activation energy for spherical particles is lower than the cylindrical wires and thin films. The size and dimension dependences in SnO2 nanoparticles show similar behavior for self diffusion as well as doped with nitrogen.

Bhatt, Purvi A.; Pratap, Arun; Jha, Prafulla K.

2013-06-01

126

Modeling spectral diffuse attenuation, absorption, and scattering coefficients in a turbid estuary  

Microsoft Academic Search

Spectral diffuse attenuation coefficients were measured in the Rhode River and Chesapeake Bay, Maryland, on 28 occasions in 1988 and 1989. The model of Kirk was used to extract scattering and absorption coefficients from the measurements in waters considerably more turbid than those in which the model was previously applied. Estimated scattering coefftcients were linearly related to mineral suspended solids.

CHARLES L. GALLEGOS; DAVID L. CORRELL; J. W. PIERCE

1990-01-01

127

Experimental measurement of the effective diffusion and thermodiffusion coefficients for binary gas mixture in porous media  

Microsoft Academic Search

Thermodiffusion or Soret effect, corresponding to a mass flux caused by a temperature gradient applied to fluid mixture, has been taken into account in many porous media applications, particularly in chemical engineering and geophysics. In the literature, the effective macro-scale diffusion coefficients are now well established, while uncertainty remains concerning the relationship between the effective thermodiffusion coefficient and micro-scale parameters

H. Davarzani; M. Marcoux; P. Costeseque; M. Quintard

2010-01-01

128

Measurements of the moisture diffusion coefficient of asphalt mixtures and its relationship to mixture composition  

Microsoft Academic Search

The presence of moisture in asphalt pavements detrimentally affects the bond between the aggregate and binder and the bond within the binder. The loss of these bonds leads to the deterioration of asphalt pavements. In regions with low rainfall, moisture diffusion is an important source of moisture transport in asphalt mixtures. The diffusion coefficient is a necessary input for models

Emad Kassem; Eyad Masad; Robert Lytton; Rifat Bulut

2009-01-01

129

Propagator for the Fokker-Planck equation with an arbitrary diffusion coefficient.  

PubMed

We consider a general diffusion process that is force-free and the corresponding Fokker-Planck equation with an arbitrary diffusion coefficient. A propagator for the Fokker-Planck equation of the Stratonovich form is obtained based on random walks. The characteristics of the solution are analyzed. PMID:24329387

Lee, Chern; Zhu, Ka-Di; Chen, Ji-Gen

2013-11-01

130

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

Microsoft Academic Search

Knowledge of the diffusion coefficient is necessary for modeling gas transport in soils and other porous media. This study was con- ducted to determine the relationship between the diffusion coeffi- cient and pore structure parameters, such as the fractal dimension of pores (Dmp), the shortest path length through the medium (lmin), and the fractal dimension of the shortest path (Dmin).

Gang Liu; Baoguo Li; Kelin Hu; M. Th. van Genuchten

2006-01-01

131

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

132

Molecular Simulations of Water and Ion Diffusion in Nanosized Mineral Fractures  

SciTech Connect

Molecular dynamics simulations were carried out to investigate the effects of confinement and of the presence of the mineral surface on the diffusion of water and electrolyte ions in nano-sized mineral fractures. Feldspar was used as a representative mineral because recent studies found that it is an important mineral that hosts contaminants within its intragrain fractures at US Department of Energy Hanford site (1, 2). Several properties of the mineral-water interface were varied, such as the fracture width, the ionic strength of the contacting solution, and the surface charge, to provide atomic-level insights into the diffusion of ions and contaminants within intragrain regions. In each case, the self-diffusion coefficient of water and that of the electrolyte ions were computed as a function of distance from the mineral surface. Our calculations reveal a 2.0 to 2.5 nm interfacial region within which the self-diffusion coefficient of water and that of the electrolyte ions decrease as the diffusing species approach the surface. As a result of the extent of the interfacial region, water and electrolyte ions are predicted to never reach bulk-like diffusion in fractures narrower than approximately 5 nm. A density weighted, averaged diffusion coefficient was computed as a function of fracture width and indicated that the surface effects only become negligible for fractures several tens of nanometers wide. The calculations also showed that, within 1.2 nm from the surface, the diffusion of electrolyte ions is affected by the presence of the mineral surface to a greater extent than that of water. The molecular dynamics results improve our conceptual models of ion transport in nano-scale pore regions surrounded by mineral surfaces in porous media.

Kerisit, Sebastien N.; Liu, Chongxuan

2009-02-01

133

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

PubMed

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

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

2010-07-14

134

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.

135

Prediction of diffusion coefficients in cement-based materials on the basis of migration experiments  

SciTech Connect

The chloride diffusion and migration coefficients of 15 different mortar mixtures were systematically compared. Test parameters included water/binder ratio (0.25 and 0.45), type of binder (ASTM type 1, ASTM type 3, and ASTM type 5), use of silica fume and sand volume fractions (0%, 30%, and 50%). Test results indicate the various ways of evaluating chloride transport coefficients generally yield much different values. Test results also show that the assumption of non interacting diffusing flows, used in the mathematical treatment of diffusion and migration equations, is most probably incorrect.

Delagrave, A.; Marchand, J.; Samson, E. [Univ. Laval, Ste-Foy, Quebec (Canada)] [Univ. Laval, Ste-Foy, Quebec (Canada)

1996-12-01

136

A novel method for effective diffusion coefficient measurement in gas diffusion media of polymer electrolyte fuel cells  

NASA Astrophysics Data System (ADS)

A novel method for measuring effective diffusion coefficient of porous materials is developed. The oxygen concentration gradient is established by an air-breathing proton exchange membrane fuel cell (PEMFC). The porous sample is set in a sample holder located in the cathode plate of the PEMFC. At a given oxygen flux, the effective diffusion coefficients are related to the difference of oxygen concentration across the samples, which can be correlated with the differences of the output voltage of the PEMFC with and without inserting the sample in the cathode plate. Compared to the conventional electrical conductivity method, this method is more reliable for measuring non-wetting samples.

Yang, Linlin; Sun, Hai; Fu, Xudong; Wang, Suli; Jiang, Luhua; Sun, Gongquan

2014-07-01

137

Quantifying radial diffusion coefficients of radiation belt electrons based on global MHD simulation and spacecraft measurements  

NASA Astrophysics Data System (ADS)

Radial diffusion is one of the most important acceleration mechanisms for radiation belt electrons, which can be enhanced from drift-resonant interactions with large-scale fluctuations of the magnetosphere's magnetic and electric fields (Pc5 range of ULF waves). In order to physically quantify the radial diffusion coefficient, DLL, we run the global Lyon-Fedder-Mobarry (LFM) MHD simulations to obtain the mode structure and power spectrum of the ULF waves and validate the simulation results with available satellite measurements. The calculated diffusion coefficients, directly from the MHD fields over a Corotating Interaction Region (CIR) storm in March 2008, are generally higher when solar wind dynamic pressure is enhanced or AE index is high. In contrary to the conventional understanding, our results show that inside geosynchronous orbit the total diffusion coefficient from MHD fields is dominated by the contribution from electric field perturbations, rather than the magnetic field perturbations. The calculated diffusion coefficient has a physical dependence on ? (or electron energy) and L, which is missing in the empirical diffusion coefficient, DLLKp as a function of Kp index, and DLLKp are generally greater than our calculated DLL during the storm event. Validation of the MHD ULF waves by spacecraft field data shows that for this event the LFM code reasonably well-reproduces the Bz wave power observed by GOES and THEMIS satellites, while the E? power observed by THEMIS probes are generally underestimated by LFM fields, on average by about a factor of ten.

Tu, Weichao; Elkington, Scot R.; Li, Xinlin; Liu, Wenlong; Bonnell, J.

2012-10-01

138

ULF Power Spectral Densities and Radial Diffusion Coefficients During High-Speed-Stream Storms  

NASA Astrophysics Data System (ADS)

Magnetospheric MHD waves in the mHz frequency range can strongly affect radiation belt electrons through radial transport, energization, and loss, and the power spectral density (PSD) of the MHD waves plays an important role in computing radial diffusion coefficients. In this paper power spectral densities are calculated using LFM global MHD simulations and then comparisons are made with measurements of MHD waves using GOES-8 and CRRES satellites. The PSD is also used to estimate radial diffusion coefficients, which are then compared with previous work, including Brautigam and Albert [2000], Fei et al. [2006], Huang et al. [2010], and recently-obtained radial diffusion coefficients from mapping ground-based magnetometer measurements to the equatorial magnetosphere. Finally, radial diffusion codes are run to compare simulated phase-space densities with observational data at GPS locations, for selected high-speed-stream storms. The radial diffusion coefficients show good consistency between LFM runs (simulation) and satellites (observation) when L<7. Based on these results, we seek to understand how to combine electric and magnetic radial diffusion coefficients to provide a more precise description of radial transport in the radiation belts.

Chen, Y.; Chan, A. A.; Elkington, S. R.; Mann, I. R.; Rae, J.; Ozeke, L.

2011-12-01

139

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

140

Phase transition and the Ag+-ion diffusion in AgI: Effect of homovalent Br--ion substitution  

Microsoft Academic Search

The incorporation of Br- ions in beta-AgI leads to an anomalously large increase in the ionic conductivity (sigmaAg+) and hence in the self-diffusion coefficient of Ag+ ions (DAg+) as well as a substantial decrease in the first-order (beta-alpha) phase-transition temperature (Tc). The effect of substitution is found to be qualitatively analogous to that of pressure (P), and is attributed to

K. Shahi; J. B. Wagner Jr.

1981-01-01

141

Parallel and perpendicular diffusion coefficients of energetic particles interacting with shear Alfvén waves  

NASA Astrophysics Data System (ADS)

We investigate the interaction of energetic particles with parallel propagating shear Alfvén waves. We use analytical tools as well as test-particle simulations. The analytical derivation of the parallel diffusion coefficient is done by employing quasi-linear theory, a well-known tool in diffusion theory. The perpendicular diffusion coefficient, however, is derived by employing the unifield non-linear transport theory. This is the first time we derive a simple analytical form of the perpendicular mean free path based on the latter theory. We perform the simulations and we show that quasi-linear theory works well for parallel diffusion in Alfvénic slab turbulence as expected. We also show that the unified non-linear transport theory perfectly describes perpendicular diffusion for the turbulence model used here.

Hussein, M.; Shalchi, A.

2014-11-01

142

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

143

Clinical applications and characteristics of apparent diffusion coefficient maps for the brain of two dogs  

PubMed Central

Diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) mapping are functional magnetic resonance imaging techniques for detecting water diffusion. DWI and the ADC map were performed for intracranial lesions in two dogs. In necrotizing leukoencephalitis, cavitated lesions contained a hypointense center with a hyperintense periphery on DWI, and hyperintense signals on the ADC maps. In metastatic sarcoma, masses including a necrotic region were hypointense with DWI, and hyperintense on the ADC map with hyperintense perilesional edema on DWI and ADC map. Since DWI and ADC data reflect the altered water diffusion, they can provide additional information at the molecular level. PMID:24675836

Kim, Boeun; Yi, Kangjae; Jung, Sunyoung; Ji, Seoyeon; Choi, Mincheol

2014-01-01

144

THEORETICAL EXPLANATION OF THE COSMIC-RAY PERPENDICULAR DIFFUSION COEFFICIENT IN THE NEARBY STARBURST GALAXY NGC 253  

SciTech Connect

Diffusion coefficients are usually used to describe the propagation of cosmic rays through the universe. Whereas such transport parameters can be obtained from experiments in the solar system, it is difficult to determine diffusion coefficients in the Milky Way or in external galaxies. Recently, a value for the perpendicular diffusion coefficient in the nearby starburst galaxy NGC 253 has been proposed. In the present paper, we reproduce this value theoretically by using an advanced analytical theory for perpendicular diffusion.

Buffie, K.; Shalchi, A. [Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2 (Canada)] [Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2 (Canada); Heesen, V., E-mail: shalchi@physics.umanitoba.ca, E-mail: v.heesen@soton.ac.uk [School for Physics and Astronomy, University of Southampton, Southampton SO17 1BJ (United Kingdom)

2013-02-10

145

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

146

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. PMID:24987463

2014-01-01

147

Diffusion and solubility coefficients determined by permeation and immersion experiments for organic solvents in HDPE geomembrane.  

PubMed

The chemical resistance of eight organic solvents in high density polyethylene (HDPE) geomembrane has been investigated using the ASTM F739 permeation method and the immersion test at different temperatures. The diffusion of the experimental organic solvents in HDPE geomembrane was non-Fickian kinetic, and the solubility coefficients can be consistent with the solubility parameter theory. The diffusion coefficients and solubility coefficients determined by the ASTM F739 method were significantly correlated to the immersion tests (p<0.001). The steady state permeation rates also showed a good agreement between ASTM F739 and immersion experiments (r(2)=0.973, p<0.001). Using a one-dimensional diffusion equation based on Fick's second law, the diffusion and solubility coefficients obtained by immersion test resulted in over estimates of the ASTM F739 permeation results. The modeling results indicated that the diffusion and solubility coefficients should be obtained using ASTM F739 method which closely simulates the practical application of HDPE as barriers in the field. PMID:17010510

Chao, Keh-Ping; Wang, Ping; Wang, Ya-Ting

2007-04-01

148

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

149

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

150

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

Microsoft Academic Search

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\\/Ld), where D*(0) is more than five orders of magnitude greater than thermal diffusion values, were measured in InSb\\/GaSb

A. H. Eltoukhy; J. E. Greene

1980-01-01

151

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

Microsoft Academic Search

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\\/Ld), where D*(0) is more than five orders of magnitude greater than thermal diffusion values, were measured in InSb\\/GaSb

A. H. Eltoukhy; J. E. Greene

1980-01-01

152

Estimation of the thermal diffusion coefficient in fusion plasmas taking frequency measurement uncertainties into account  

NASA Astrophysics Data System (ADS)

In this paper, the estimation of the thermal diffusivity from perturbative experiments in fusion plasmas is discussed. The measurements used to estimate the thermal diffusivity suffer from stochastic noise. Accurate estimation of the thermal diffusivity should take this into account. It will be shown that formulas found in the literature often result in a thermal diffusivity that has a bias (a difference between the estimated value and the actual value that remains even if more measurements are added) or have an unnecessarily large uncertainty. This will be shown by modeling a plasma using only diffusion as heat transport mechanism and measurement noise based on ASDEX Upgrade measurements. The Fourier coefficients of a temperature perturbation will exhibit noise from the circular complex normal distribution (CCND). Based on Fourier coefficients distributed according to a CCND, it is shown that the resulting probability density function of the thermal diffusivity is an inverse non-central chi-squared distribution. The thermal diffusivity that is found by sampling this distribution will always be biased, and averaging of multiple estimated diffusivities will not necessarily improve the estimation. Confidence bounds are constructed to illustrate the uncertainty in the diffusivity using several formulas that are equivalent in the noiseless case. Finally, a different method of averaging, that reduces the uncertainty significantly, is suggested. The methodology is also extended to the case where damping is included, and it is explained how to include the cylindrical geometry.

van Berkel, M.; Zwart, H. J.; Hogeweij, G. M. D.; Vandersteen, G.; van den Brand, H.; de Baar, M. R.; the ASDEX Upgrade Team

2014-10-01

153

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

154

Regulation of Nuclear NF-?B Oscillation by a Diffusion Coefficient and Its Biological Implications  

PubMed Central

The transcription factor NF-?B shuttles between the cytoplasm and the nucleus, and nuclear NF-?B is known to oscillate with a cycle of 1.5-2.5 h following the application of external stimuli. Oscillation pattern of NF-?B is implicated in regulation of the gene expression profile. In a previous report, we found that the oscillation pattern of nuclear NF-?B in a computational 3D spherical cell was regulated by spatial parameters such as nuclear to cytoplasmic volume ratio, nuclear transport, locus of protein synthesis, and diffusion coefficient. Here we report analyses and a biological implication for the regulation of oscillation pattern by diffusion coefficient. Our analyses show that the “reset” of nuclear NF-?B, defined as the return of nuclear NF-?B to the initial level or lower, was crucial for the oscillation; this was confirmed by the flux analysis. In addition, we found that the distant cytoplasmic location from the nucleus acted as a “reservoir” for storing newly synthesized I?B?. When the diffusion coefficient of proteins was large (?10?11 m2/s), a larger amount of I?B? was stored in the “reservoir” with a large flux by diffusion. Subsequently, stored I?B? diffused back to the nucleus, where nuclear NF-?B was “reset” to the initial state. This initiated the next oscillation cycle. When the diffusion coefficient was small (?10?13 m2/s), oscillation of nuclear NF-?B was not observed because a smaller amount of I?B? was stored in the “reservoir” and there was incomplete “reset” of nuclear NF-?B. If the diffusion coefficient for I?B? was increased to 10?11 m2/s keeping other proteins at 10?13 m2/s, the oscillation was rescued confirming the “reset” and “reservoir” hypothesis. Finally, we showed altered effective value of diffusion coefficient by diffusion obstacles. Thus, organelle crowding seen in stressed cells possibly changes the oscillation pattern by controlling the effective diffusion coefficient. PMID:25302804

Ohshima, Daisuke; Ichikawa, Kazuhisa

2014-01-01

155

Regulation of Nuclear NF-?B Oscillation by a Diffusion Coefficient and Its Biological Implications.  

PubMed

The transcription factor NF-?B shuttles between the cytoplasm and the nucleus, and nuclear NF-?B is known to oscillate with a cycle of 1.5-2.5 h following the application of external stimuli. Oscillation pattern of NF-?B is implicated in regulation of the gene expression profile. In a previous report, we found that the oscillation pattern of nuclear NF-?B in a computational 3D spherical cell was regulated by spatial parameters such as nuclear to cytoplasmic volume ratio, nuclear transport, locus of protein synthesis, and diffusion coefficient. Here we report analyses and a biological implication for the regulation of oscillation pattern by diffusion coefficient. Our analyses show that the "reset" of nuclear NF-?B, defined as the return of nuclear NF-?B to the initial level or lower, was crucial for the oscillation; this was confirmed by the flux analysis. In addition, we found that the distant cytoplasmic location from the nucleus acted as a "reservoir" for storing newly synthesized I?B?. When the diffusion coefficient of proteins was large (?10-11 m2/s), a larger amount of I?B? was stored in the "reservoir" with a large flux by diffusion. Subsequently, stored I?B? diffused back to the nucleus, where nuclear NF-?B was "reset" to the initial state. This initiated the next oscillation cycle. When the diffusion coefficient was small (?10-13 m2/s), oscillation of nuclear NF-?B was not observed because a smaller amount of I?B? was stored in the "reservoir" and there was incomplete "reset" of nuclear NF-?B. If the diffusion coefficient for I?B? was increased to 10-11 m2/s keeping other proteins at 10-13 m2/s, the oscillation was rescued confirming the "reset" and "reservoir" hypothesis. Finally, we showed altered effective value of diffusion coefficient by diffusion obstacles. Thus, organelle crowding seen in stressed cells possibly changes the oscillation pattern by controlling the effective diffusion coefficient. PMID:25302804

Ohshima, Daisuke; Ichikawa, Kazuhisa

2014-01-01

156

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

PubMed

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

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

2012-01-01

157

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

158

New method and installation for rapid determination of radon diffusion coefficient in various materials.  

PubMed

The mathematical apparatus and the experimental installation for the rapid determination of radon diffusion coefficient in various materials are developed. The single test lasts not longer than 18 h and allows testing numerous materials, such as gaseous and liquid media, as well as soil, concrete and radon-proof membranes, in which diffusion coefficient of radon may vary in an extremely wide range, from 1·10(-12) to 5·10(-5) m(2)/s. The uncertainty of radon diffusion coefficient estimation depends on the permeability of the sample and varies from about 5% (for the most permeable materials) to 40% (for less permeable materials, such as radon-proof membranes). PMID:24412813

Tsapalov, Andrey; Gulabyants, Loren; Livshits, Mihail; Kovler, Konstantin

2014-04-01

159

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

160

Effective molecular diffusion coefficient in a two-phase gel medium  

NASA Astrophysics Data System (ADS)

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

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

2006-05-01

161

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 Combining these results with data from the literature and fitting all data simultaneously to an Arrhenius relationship yielded the expression 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

2014-08-01

162

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

163

Cloride ion diffusion in low water-to-solid cement pastes  

SciTech Connect

Diffusion coefficients of 0.3 water to solids ratio (w/s) hydrated portland cement paste specimens were measured using a conventional diffusion cell. Specimens were made from both ASTM Type 1 and Type 2 portland cements and blends containing mineral admixtures (fly ash, granulated blastfurnace slag, or silica fume). The average diffusion coefficient for the portland cement paste specimens was 14 {times} 10{sup {minus}13} m{sup 2}/s. The diffusion coefficients for the specimens containing mineral admixtures were such more variable than those for the portland cement paste specimens. A probable cause of the variability in the test results was the presence of cracks observed in the test specimens. The effects of the depth of concrete cover over reinforcing steel and of the chloride ion diffusion coefficient on the service life of reinforced concrete exposed to chloride ions were predicted based on a diffusion model. Based on the model, the effect of the cover was shown to be proportional to the square of the cover depth. 18 refs., 5 figs., 6 tabs.

Clifton, J.R.; Knab, L.I.; Garboczi, E.J. (National Inst. of Standards and Technology, Gaithersburg, MD (USA)); Xiong, L.X. (Shanghai Research Inst., SH (China))

1991-06-01

164

Electronic/ionic conductivity and oxygen diffusion coefficient of Sr-Fe-Co-O system  

NASA Astrophysics Data System (ADS)

Oxides in the system Sr-Fe-Co-O exhibit both electronic and ionic conductivities. Recently, Sr-Fe-Co-O system attracted great attention because of the potential to be used for oxygen permeable membranes that can operate without the electrodes or external electrical circuitry. Electronic and ionic conductivities at various temperatures have been measured on two compositions in Sr-Fe-Co-O system named SFC-1 and SFC-2. The electronic transference number is much greater than the ionic transference number in SFC-1 sample, while the electronic and ionic transference numbers are very close in SFC-2 sample. At 800 C, the electronic conductivity and ionic conductivity are approximately 76 S/cm and approximately 4 S/cm, respectively, for SFC-1, while for SFC-2 the electronic and ionic conductivities are approximately 10 S/cm and approximately 7 S/cm, respectively. By a local fitting to sigma T = A exp(-E(sub alpha)/kappa Tau), we found that the oxide ion activation energies are 0.92 eV and 0.37 eV respectively for SFC-1 and SFC-2 samples. Oxygen diffusion coefficient of SFC-2 is approximately 9 x 10(exp -7) sq cm/sec at 900 C.

Ma, B.; Park, J. H.; Balachandran, U.; Segre, C. U.

1995-03-01

165

Rigorous Results on Surface Diffusion Coefficients Near a First-Order Phase Transition  

NASA Astrophysics Data System (ADS)

We present a microscopic statistical-mechanical approach from which the chemical surface diffusion coefficient can be obtained in the local equilibrium limit, assuming that the system of a finite size undergoes a first-order phase transition between two phases. We also show the behavior of the jump diffusion coefficient and thermodynamic factor near such a transition. Explicit formulas for the dependences of these quantities on the chemical potential, coverage, and size of the system are presented. The general results are applied to a simple two-dimensional lattice model on a regular triangular lattice.

Medved', Igor; Avsec, Jurij; Ková?, Jozef; Trník, Anton

2014-10-01

166

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

167

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

E-print Network

Fundamental thermodynamics and an earlier elastic solid-state point defect model [P. Varotsos and K. Alexopoulos, Phys. Rev B 15, 4111 (1977); 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 Gruneisen 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. B 112, 1329 (2008)].

A. N. Papathanassiou

2009-03-06

168

Diffusion of oxide ions in LaFeO3 single crystal  

Microsoft Academic Search

The tracer diffusion coefficient, D*O, of oxide ions in LaFeO3 single crystal was determined over the temperature range of 900-1100°C by the gas-solid isotopic exchange technique using 18O as a tracer. For the determination of D*O, the depth profile of 18O was measured by means of a secondary ion mass spectrometer (SIMS). The surface exchange reaction was found to be

Takamasa Ishigaki; Shigeru Yamauchi; Junichiro Mizusaki; Kazuo Fueki; Hiroyuki Naito; Tatsuya Adachi

1984-01-01

169

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

170

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

171

Diffusion coefficients of sodium dodecylsulfate in aqueous solutions of sucrose and in aqueous solutions  

Microsoft Academic Search

Differential diffusion coefficients of sodium dodecylsulfate (SDS) in aqueous solutions of sucrose and in aqueous solutions at 298.15 K, over the concentration range 0.0018 M to 0.0817 M, have been measured using a conductimetric cell and an automatic apparatus to follow the diffusion. The results are discussed on the basis of the Onsager-Fuoss model. The cell uses an open ended

Ana C. F. Ribeiro; Victor M. M. Lobo; Eduarda F. G. Azevedo; M. da G. Miguel; H. D. Burrows

2001-01-01

172

Voltage, Stability and Diffusion Barrier Differences between Sodium-ion and Lithium-ion Intercalation Materials  

E-print Network

To evaluate the potential of Na-ion batteries, we contrast in this work the difference between Na-ion and Li-ion based intercalation chemistries in terms of three key battery properties—voltage, phase stability and diffusion ...

Ong, Shyue Ping

173

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

174

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

NASA Astrophysics Data System (ADS)

Water has been considered to significantly affect the mantle dynamics. In particular, experimental deformation studies [1-4] claimed that even small amount of water enhanced the creep in olivine by orders of magnitude. However, we note that their results are experimental artifact due to a number of limitations: e.g., unavoidable grain boundary sliding when polycrystalline samples were used; limited ranges of water contents due to the limited pressures; several orders higher stress and strain rate than those in nature. High temperature creep of silicate minerals is controlled by silicon self-diffusion. Therefore, measurement of silicon self-diffusion coefficients (DSi) in minerals, which can be performed without these limitations, is an independent way to study the mantle rheology. In this study, we measured DSi in Mg end-member of olivine, namely, forsterite, as a function of water content (CH2O) across a wide range, and concluded that effect of water on upper mantle rheology is very small. Forsterite single crystals were doped with <1 to ~800 ?g/g of water at 1600 K, 8 GPa using talc+brucite water sources and graphite buffer. The CH2O in the samples were controlled by the ratio of water sources to graphite. The water doped samples were polished, deposited with 500 nm 29Si enriched Mg2SiO4 thin films, and annealed at 8 GPa, 1600 or 1800 K for diffusion with the same proportion of water sources, which successfully made constant values of CH2O during diffusion annealing. The diffusion profiles were obtained by SIMS. CH2O in the samples were determined by FT-IR before and after diffusion, and also examined by SIMS. Our results yield a relationship: DSi ? (CH2O)1/3. This is explained by defect chemistry, where DSi?[VSi????]×[VO??]?(CH2O)2/3×(CH2O)-1/3=(CH2O)1/3 under the charge neutrality condition of [(OH)O?]=2[VMg??] because both Si and O vacancies are needed for Si ions to diffuse. The water contents exponent (1/3) determined in this study is much smaller than 1.2 [5], which was estimated based on deformation experiments. The small water content exponent demonstrates that effect of water on upper mantle rheology is very small in comparing with other factors like temperature, or shear stress. The difference in viscosity of olivine between dry (e.g., ~1 ?g/g of water) and 1000 ?g/g (maximum in upper mantle [6]) is only by a factor of 10. The softening of oceanic lithosphere, which is required to explain the plate motion, cannot be caused by hydration. [1] Karato et al. (1986), JGR 91, 8151-8176. [2] Mei and Kohlstedt (2000a), JGR 105(B9), 21471-21481. [3] Mei and Kohlstedt (2000b), JGR 105(B9), 21457-21469. [4] Jung and Karato (2001), Science 293, 1460-1463. [5] Hirth and Kohlstedt (2003), Geophys. Monogr. Am. Geophys. Union. 138, 83-106. [6] Hirschmann (2006), An. Rev. Earth Planet. Sci. 34, 629-653.

Fei, H.; Wiedenbeck, M.; Yamazaki, D.; Katsura, T.

2012-12-01

175

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

176

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

177

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

178

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

179

Density, Viscosity, and Diffusion Coefficients in Hypoeutectic Al-Si Liquid Alloys: An Assessment of Available Data  

NASA Astrophysics Data System (ADS)

This article is a review of empirical and calculated data on density, viscosity, and diffusion coefficients in hypereutectic Al-Si liquid alloys. Many regressions of the data were effected in order to consolidate the data as functions, which can be used to calculate each property as a function of temperature and concentration of Si. The chemical diffusion coefficient in the alloys was derived based on the Sutherland model, which relates the diffusion coefficient to viscosity.

Poirier, David R.

2014-08-01

180

Author's personal copy Assessment of satellite-derived diffuse attenuation coefficients and euphotic depths  

E-print Network

form 16 October 2012 Accepted 4 December 2012 Available online xxxx Keywords: Ocean color Remote sensing MODIS SeaWiFS Bio-optical algorithm Diffuse attenuation coefficient Euphotic depth Optical data 2010 were used to evaluate products derived with three bio-optical inversion algorithms applied

Meyers, Steven D.

181

Diffusion coefficient of a passive contaminant in a local MHD model of a turbulent accretion disc  

Microsoft Academic Search

We calculate the radial diffusion coefficient for a passive contaminant in an accretion disc which is turbulent due to the action of the magnetorotational instability. Numerical magnetohydrodynamic (MHD) simulations are used to follow the evolution of a local patch of the disc using the shearing box formalism. A separate continuity equation for the mass fraction of contaminant is integrated along

Augusto Carballido; James M. Stone; James E. Pringle

2005-01-01

182

Self-Diffusion Coefficients of Methane or Ethane Mixtures with Hydrocarbons at High Pressure by NMR  

E-print Network

Self-Diffusion Coefficients of Methane or Ethane Mixtures with Hydrocarbons at High Pressure by NMR 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

Dysthe, Dag Kristian

183

An approximate formula for the diffusion coefficient for the periodic Lorentz gas  

NASA Astrophysics Data System (ADS)

An approximate stochastic model for the topological dynamics of the periodic triangular Lorentz gas is constructed. The model, together with an extremum principle, is used to find a closed form approximation to the diffusion coefficient as a function of the lattice spacing. This approximation is superior to the popular Machta and Zwanzig result and agrees well with a range of numerical estimates.

Angstmann, C.; Morriss, G. P.

2012-05-01

184

About Fokker-Planck equation with measurable coefficients: application to the fast diffusion equation  

E-print Network

About Fokker-Planck equation with measurable coefficients: application to the fast diffusion-dimensional Fokker-Planck type equation with non-homogeneous (possibly degenerated) measurable not necessarily with m (0, 1). Together with the mentioned Fokker-Planck equation, we make use of small time density

Paris-Sud XI, Université de

185

The Friction and Diffusion Coefficients of the Fokker-Planck Equation in a Plasma  

Microsoft Academic Search

In a recent paper (Thompson & Hubbard 1960) it was shown how the diffusion coefficients of the Fokker-Planck equation could be calculated in the case of a plasma in thermal equilibrium by a method which included automatically correlation effects and avoided the use of a cut-off procedure. In this paper the method is extended to plasmas not in thermal equilibrium

J. Hubbard

1961-01-01

186

Relaxation Time Constants and Apparent Diffusion Coefficients of Rat Retina at 7 Tesla  

E-print Network

Relaxation Time Constants and Apparent Diffusion Coefficients of Rat Retina at 7 Tesla Govind Nair* and ADC of the rat eyes were measured at 50 3 50 3 800 lm at 7 Tesla. Profiles of T1, T2, T2* and ADC

Duong, Timothy Q.

187

Self-diffusion of lithium, hydrogen, and oxygen ions in crystalline lithium hydroxide  

NASA Astrophysics Data System (ADS)

The self-diffusion coefficients of ions of the three chemical elements forming lithium hydroxide have been determined by the crystal-crystal and crystal-gas isotope exchange method in the temperature range 500-720 K. Crystal samples with different isotope compositions have been grown by the Bridgman method from melts. The melting temperature is 743 ± 2 K. Original methods have been developed for high-precision measurements of the isotope ratios of all three elements, i.e., lithium (6Li/7Li), hydrogen (H/D), and oxygen (16O/18O), and their changes after diffusion annealings with the use of the same sample. The self-diffusion coefficients of lithium and hydrogen ions differ but by a factor of no more than 3-5; however, their values exceed those for oxygen by several orders of magnitude. In particular, at 670 K, they are equal to 6.0 × 10-9, 3.2 × 10-9, and 2.0 × 10-12 cm2 s-1 for hydrogen, lithium, and oxygen, respectively. In the range 680-720 K, the self-diffusion coefficients of hydrogen and lithium increase sharply with increasing temperature to approximately 10-6 cm2 s-1. A probable mechanism of migration of protons and lithium ions in LiOH and the role played in this process by the oxygen ions with a lower mobility have been discussed.

Ba?kov, Yu. M.

2010-10-01

188

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

189

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

NASA Astrophysics Data System (ADS)

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

Bouazza, M. T.; Bouledroua, M.

190

Electro-diffusion in a plasma with two ion species  

SciTech Connect

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

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

2012-08-15

191

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

192

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

193

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

SciTech Connect

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

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

2013-01-01

194

An elemental mercury diffusion coefficient for natural waters determined by molecular dynamics simulation.  

PubMed

Mercury is a priority pollutant as its mobility between the hydrosphere and the atmosphere threatens the biosphere globally. The air-water gas transfer of elemental mercury (Hg0) is controlled by its diffusion through the water-side boundary layer and thus by its diffusion coefficient, D(Hg), the value of which, however, has not been established. Here, the diffusion of Hg0 in water was modeled by molecular dynamics (MD) simulation and the diffusion coefficient subsequently determined. Therefore the movement of either Hg(0) or xenon and 1000 model water molecules (TIP4P-Ew) were traced for time spans of 50 ns. The modeled D(Xe) of the monatomic noble gas agreed well with measured data; thus, MD simulation was assumed to be a reliable approach to determine D(Hg) for monatomic Hg(0) as well. Accordingly, Hg(0) diffusion was then simulated for freshwater and seawater, and the data were well-described by the equation of Eyring. The activation energies for the diffusion of Hg0 in freshwater was 17.0 kJ mol(-1) and in seawater 17.8 kJ mol(-1). The newly determined D(Hg) is clearly lower than the one previously used for an oceanic mercury budget. Thus, its incorporation into the model should lead to lower estimates of global ocean mercury emissions. PMID:19534132

Kuss, Joachim; Holzmann, Jörg; Ludwig, Ralf

2009-05-01

195

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

196

On The Anomalous Fast Ion Energy Diffusion in Toroidal Plasmas Due to Cavity Modes  

SciTech Connect

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

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

2010-03-09

197

Substrate concentration influences effective radial diffusion coefficient in canine cortical bone.  

PubMed

Transport of nutrients and waste across osseous tissue is dependent on the dynamic micro and macrostructure of the tissue; however little quantitative data exists examining how this transport occurs across the entire tissue. Here we investigate in vitro radial diffusion across a section of canine tissue, at dimensions of several hundred microns to millimeters, specifically between several osteons connected through a porous microstructure of Volkmann's canals and canaliculi. The effective diffusion coefficient is measured by a "sample immersion" technique presented here, in which the tissue sample was immersed in solution for 18-30 h, image analysis software was used to quantify the solute concentration profile in the tissue, and the data were fit to a mathematical model of diffusion in the tissue. Measurements of the effective diffusivity of sodium fluorescein using this technique were confirmed using a standard two-chamber diffusion system. As the solute concentration increased, the effective diffusivity decreased, ranging from 1.6 × 10(-7) ± 3.2 × 10(-8) cm(2)/s at 0.3 ?M to 1.4 × 10(-8) ± 1.9 × 10(-9) cm(2)/s at 300 ?M. The results show that there is no significant difference in mean diffusivity obtained using the two measurement techniques on the same sample, 3.3 × 10(-8) ± 3.3 × 10(-9) cm(2)/s (sample immersion), compared to 4.4 × 10(-8) ± 1.1 × 10(-8) cm(2)/s (diffusion chamber). PMID:25234132

Farrell, Kurt; O'Conor, Daniel; Gonzalez, Mariela; Androjna, Caroline; Midura, Ronald J; Tewari, Surendra N; Belovich, Joanne

2014-12-01

198

Effect of chain flexibility on master curve behavior for diffusion coefficient  

NASA Astrophysics Data System (ADS)

The diffusion coefficients of simple chain models are analyzed as a function of packing fraction, ?, and as a function of a parameter C that is the density raised to a power divided by temperature to look at scalar metrics to find master curves. The central feature in the analysis is the mapping onto an effective hard site diameter, d. For the molecular models lacking restrictions on dihedral angle (e.g., freely jointed), simple mappings of molecular potential to d work very well, and the reduced diffusion coefficient, D*, collapses into a single-valued function of ?. Although this does not work for the dihedral angle restriction case, assuming that d is inversely proportional to temperature to a power results in collapse behavior for an empirically selected value of the power. This is equivalent to D* being a single-valued function of C. The diffusion coefficient of a single-site penetrant in the chain systems also is found to be a scalar metric that can reduce the chain diffusion data for a given system to a single master curve.

Budzien, Joanne; Heffernan, Julieanne V.; McCoy, John D.

2013-12-01

199

Diffusion coefficient of a passive contaminant in a local MHD model of a turbulent accretion disc  

E-print Network

We calculate the radial diffusion coefficient for a passive contaminant in an accretion disc which is turbulent due to the action of the magnetorotational instability. Numerical MHD simulations are used to follow the evolution of a local patch of the disc using the shearing box formalism. A separate continuity equation for the mass fraction of contaminant is integrated along with the MHD system, and radial profiles of this fraction are obtained as a function of time. Solutions of a linear diffusion equation are fitted to the numerical measured profiles of the contaminant, treating the diffusion coefficient D as the fitting parameter. At early times, the value of D is found to vary, however once the contaminant is spread over scales comparable to the box size, it saturates at a steady value. The ratio of D to the transport coefficient of angular momentum due to shear stress is small. If D can be used as a proxy for the turbulent magnetic diffusivity, the effective magnetic Prandtl number P_eff=\

Augusto Carballido; James M. Stone; James E. Pringle

2005-01-21

200

Oxygen diffusion coefficients for Sr{sub 2}AlTaO{sub 6}: Ramifications on HTSC multilayer processing  

SciTech Connect

The authors have studied the rate of oxygen diffusion through Sr{sub 2}AlTaO{sub 6} (SAT), a buffer and dielectric layer used in high critical temperature superconducting (HTSC) structures. An epitaxial bilayer film of SAT on YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} (YBCO) was deposited onto an (001) oriented single crystal LaAlO{sub 3} substrate using the pulsed laser deposition technique. The rate of oxygen diffusion through the bilayer was investigated over the temperature range 415 to 675 C by post deposition annealing individual sections of the bilayer in 1/3 atm of {sup 18}O enriched molecular oxygen gas. Secondary ion mass spectroscopy was used to depth profile {sup 18}O and {sup 16}O in each sample. Oxygen diffusion coefficients for SAT at 418, 510, 570 and 673 C were determined to be roughly (0.93, 6.31, 26.6 and 75.3) {times} 10{sup {minus}16} cm{sup 2} s{sup {minus}1}, respectively. Since these diffusion rates can limit oxygen intake into underlying YBCO films, SAT may be an inappropriate choice as a dielectric candidate for use in an HTSC multilayer device technology and will at best require development of suitable post annealing schemes to oxygenate underlying YBCO layers.

Tidrow, S.C.; Lareau, R.T.; Eckart, D.W.; Tauber, A.; Wilber, W.D.; Pfeffer, R.L.; Finnegan, R.D. [Army Research Lab., Fort Monmouth, NJ (United States); King, L.L.H.; Neal, M. [Conductus, Inc., Sunnyvale, CA (United States)

1996-11-01

201

Measurements of Multicomponent Diffusion Coefficients for Lysozyme Chloride in Water and Aqueous Na$_2$SO$_4$  

E-print Network

This paper presents a diffusion experimental study for ternary lysozyme-Na$_2$SO$_4$-water system, from moderate precipitant concentrations into the supersaturated region and provides a complete set of four diffusion coefficients. These data are important in order to provide accurate models of protein diffusion with applications in growth of protein crystals for X-ray diffraction studies. All three-component mutual-diffusion experiments reported here were performed by Rayleigh interferometry at pH$=4.5$, T$=25^o$ C and at a mean lysozyme concentration (average of top and bottom solution concentrations) of 0.6 mM (8.6 mg/mL). Four experiments, with different combinations of protein and Na$_2$SO$_4$ concentration differences, were performed at each of five mean Na$_2$SO$_4$ concentrations (0.1, 0.25, 0.5, 0.65 and 0.8 M), for a total of 20 experiments. In addition, we have measured dynamic light-scattering diffusion coefficients of the ternary system lysozyme chloride-Na$_2$SO$_4$-water.

Buzatu, D; Buzatu, F D; Albright, J G

2004-01-01

202

The diffusion properties of ion implanted species in selected target materials  

SciTech Connect

Experiments important to the future success of the Holifield Radioactive Ion Beam Facility (HRIBF) are in progress at the Oak Ridge National Laboratory which are designed to select the most appropriate target material for generating a particular radioactive ion beam (RIB). The 25-MV HHIRF tandem accelerator is used to implant stable complements of interesting radioactive elements into refractory targets mounted in a high-temperature FEBIAD ion source which is {open_quotes}on-line{close_quotes} at the UNISOR facility. The intensity versus time of implanted species, which diffuse from the high-temperature target material ({approximately}1700{degrees}C) and are ionized in the FEBIAD ion source, is used to determine release times for a particular projectile/target material combination. From such release data, diffusion coefficients can be derived by fitting the theoretical results obtained by computational solution of Fick`s second equation to experimental data. The diffusion coefficient can be used subsequently to predict the release properties of the particular element from the same material in other target geometries and at other temperatures, provided that the activation energy is also known. Diffusion coefficients for Cl implanted into and diffused from CeS and Zr{sub 5}Si{sub 3} and As, Br, and Se implanted into and diffused from Zr{sub 5}Ge{sub 3} have been derived from the resulting intensity versus time profiles. Brief descriptions of the experimental apparatus and procedures utilized in the present experiments and plans for future related experiments are presented.

Alton, G.D. [Oak Ridge National Lab., TN (United States); Dellwo, J.; Carter, H.K.; Kormicki, J.; Bartolo, G. di; Batchelder, J.C.; Breitenbach, J.; Chediak, J.A.; Jentoff-Nilsen, K.; Ichikawa, S.

1995-02-01

203

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

204

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

205

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

206

Limiting diffusion coefficients of heavy molecular weight organic contaminants in supercritical carbon dioxide  

E-print Network

. Applications of this technology include decontamination of environmental solids, regeneration/cleaning of adsorbents and catalysts, selective removal/separation of organic components froin process streams among other applications. Supercritical fluid... is relatively low (Tc=304. 2 K and Pc=73. 8 bar) making a process less energy intensive. The diffusion coefficients in supercritical carbon dioxide, for even the most common species, are not available. The main objective of this research is to develop a...

Orejuela, Mauricio

2012-06-07

207

Diffusion coefficients estimated from turbulence data measured by the Metrac positioning system in Minneapolis field test  

NASA Technical Reports Server (NTRS)

An analysis is presented of the tropospheric turbulence data obtained by the Metrac positioning system, a radio location system which employs the Doppler principle to track inexpensive expendable balloon-borne transmitters. A Minneapolis field test of the Metrac system provided one-second samples of transmitter frequency from balloons tracked by four ground stations for more than an hour. The derivation of diffusion coefficients from the turbulence data was conducted by two methods, yielding highly consistent results.

Gage, K. S.; Jasperson, W. H.

1977-01-01

208

Diffusion coefficient of a passive contaminant in a local MHD model of a turbulent accretion disc  

Microsoft Academic Search

We calculate the radial diffusion coefficient for a passive contaminant in an\\u000aaccretion disc which is turbulent due to the action of the magnetorotational\\u000ainstability. Numerical MHD simulations are used to follow the evolution of a\\u000alocal patch of the disc using the shearing box formalism. A separate continuity\\u000aequation for the mass fraction of contaminant is integrated along with

Augusto Carballido; James M. Stone; James E. Pringle

2005-01-01

209

Application of Molecular Dynamics Simulations in Molecular Property Prediction II: Diffusion Coefficient  

PubMed Central

In this work, we have evaluated how well the General AMBER force field (GAFF) performs in studying the dynamic properties of liquids. Diffusion coefficients (D) have been predicted for 17 solvents, 5 organic compounds in aqueous solutions, 4 proteins in aqueous solutions, and 9 organic compounds in non-aqueous solutions. An efficient sampling strategy has been proposed and tested in the calculation of the diffusion coefficients of solutes in solutions. There are two major findings of this study. First of all, the diffusion coefficients of organic solutes in aqueous solution can be well predicted: the average unsigned error (AUE) and the root-mean-square error (RMSE) are 0.137 and 0.171 ×10?5 cm?2s?1, respectively. Second, although the absolute values of D cannot be predicted, good correlations have been achieved for 8 organic solvents with experimental data (R2 = 0.784), 4 proteins in aqueous solutions (R2 = 0.996) and 9 organic compounds in non-aqueous solutions (R2 = 0.834). The temperature dependent behaviors of three solvents, namely, TIP3P water, dimethyl sulfoxide (DMSO) and cyclohexane have been studied. The major MD settings, such as the sizes of simulation boxes and with/without wrapping the coordinates of MD snapshots into the primary simulation boxes have been explored. We have concluded that our sampling strategy that averaging the mean square displacement (MSD) collected in multiple short-MD simulations is efficient in predicting diffusion coefficients of solutes at infinite dilution. PMID:21953689

Wang, Junmei; Hou, Tingjun

2011-01-01

210

Iterative solutions for one-dimensional diffusion with time varying surface composition and composition-dependent diffusion coefficient  

NASA Technical Reports Server (NTRS)

Solutions are given for one-dimensional diffusion problems with a time varying surface composition and also a composition dependent diffusion coefficient. The most general solution does not require special mathematical functions to fit the variation in surface composition or D(C). In another solution, a series expansion may be used to fit the time dependent surface concentration. These solutions make use of iterative calculations that converge rapidly and are highly stable. Computer times are much shorter than that required for finite difference calculations and can efficiently make use of interactive graphics terminals. Existing gas carburization data were used to provide an illustration of an iterative approach with a time varying carbon composition at the free surface.

Chow, M.; Houska, C. R.

1980-01-01

211

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

212

Rapid simulation of the time-dependent diffusion coefficient in complex materials  

NASA Astrophysics Data System (ADS)

A finite-difference approach is presented for the analysis of the time-dependent diffusion coefficient for general heterogeneous materials that are either cavity-enclosed or periodic. In the bulk material, diffusivity and volume relaxivity are accounted for. The interaction of the diffusive medium with non-diffusive inclusions is modeled via a surface relaxivity. The time dependence is modeled using matrix exponentials that are shown to be efficiently evaluated using a Krylov-subspace approach. For a 3D model grid composed of M voxels of diffusive material (voxels containing non-diffusive material are not stored in the kernel matrix), the memory requirement is 15M and the computational time complexity for two large-scale example models is shown to be of order M1.39 and M1.10. Error estimate formulas are presented that can be used to guide the choice of domain grid resolution. Richardson extrapolation is shown to be effective in lowering simulation error. We apply this approach to modeling the nuclear magnetic resonance response of several subsurface rock pore geometries. They demonstrate the method to be simple and robust in both 2D and 3D complex geometries.

Prange, Michael D.; Druskin, Vladimir; Linton Johnson, David; Schwartz, Lawrence M.

2011-09-01

213

Ion implantation and diffusion of Al in a {SiO 2}/{Si} system  

NASA Astrophysics Data System (ADS)

The diffusion and segregation of ion implanted Al in SiO 2 and Si layers were studied for several experimental conditions. Al ions were implanted into SiO 2, Si and through a SiO 2 layer into Si substrates at several energies (80, 300, 650 and 6000 keV) and doses (3.4 × 10 14-1 × 10 15 cm -2). The Al diffusion coefficient in SiO 2 was measured at 1200°C for times up to 5 days, and it results five orders of magnitude lower than in Si. The experiments show that the Al atoms implanted into Si do not out-diffuse during thermal treatments from the SiO 2 capping layer, but segregate at the {SiO 2}/{Si} interface. The high segregation coefficient gives rise to a trapping of Al into the oxide layer comparable to the out-diffusion of Al from uncapped Si substrates. The determined parameters for Al diffusion and segregation in the {SiO 2}/{Si} system were introduced in a simulation code to calculate the Al diffusion profiles which result in agreement with the experimental data.

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

214

The difference in diffusion-weighted imaging with apparent diffusion coefficient between spontaneous and postoperative intracranial infection.  

PubMed

Abstract Background. Although the roles of diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) have been accepted as the initial or confirmatory diagnostic tool for spontaneous intracranial infections, the usefulness of these has rarely been investigated in intracranial infections after a craniotomy procedure. Through an analysis of the clinico-radiological characteristics of spontaneous and postoperative intracranial infections, the authors revealed the specific factors that affect the accuracy of DWI and ADC in diagnosing intracranial infections. Methods. The authors retrospectively analyzed 67 intracranial infections confirmed using preoperative MR imaging, including the DWI, ADC and gadolium-enhanced (Gd) images, and by peroperative pus drainage. Results. In 67 enrolled patients, no or uncertain diffusion restriction on DWI and ADC was found in 9 cases (13%). All the cases showed typical peripheral enhancement on Gd images. Among nine cases without diffusion restriction, postoperative infection was seen in five cases (62.5% [5/8 postoperative infection group] vs. 6.8% [4/59 spontaneous infection group], p = 0.001). On multivariate analysis, postoperative infection was the predictive factor for false-negative restriction on DWI and ADC (hazard ratio: 41.2, 95% confidential index: 2.39-710.25, p = 0.01). Conclusion. Despite the excellent availability of DWI and ADC for diagnosing spontaneous intracranial infections, negative restriction results of those images are not sufficient to exclude postoperative intracranial infection. PMID:24970588

Kim, Yeong-Jin; Moon, Kyung-Sub; Kim, Seul Kee; Kang, Seong-Ji; Lee, Kyung-Hwa; Jang, Woo-Yool; Jung, Tae-Young; Kim, In-Young; Jung, Shin

2014-12-01

215

Molecular dynamics calculation of rotational diffusion coefficient of a carbon nanotube in fluid  

NASA Astrophysics Data System (ADS)

Rotational diffusion processes are correlated with nanoparticle visualization and manipulation techniques, widely used in nanocomposites, nanofluids, bioscience, and so on. However, a systematical methodology of deriving this diffusivity is still lacking. In the current work, three molecular dynamics (MD) schemes, including equilibrium (Green-Kubo formula and Einstein relation) and nonequilibrium (Einstein-Smoluchowski relation) methods, are developed to calculate the rotational diffusion coefficient, taking a single rigid carbon nanotube in fluid argon as a case. We can conclude that the three methods produce same results on the basis of plenty of data with variation of the calculation parameters (tube length, diameter, fluid temperature, density, and viscosity), indicative of the validity and accuracy of the MD simulations. However, these results have a non-negligible deviation from the theoretical predictions of Tirado et al. [J. Chem. Phys. 81, 2047 (1984)], which may come from several unrevealed factors of the theory. The three MD methods proposed in this paper can also be applied to other situations of calculating rotational diffusion coefficient.

Cao, Bing-Yang; Dong, Ruo-Yu

2014-01-01

216

Decrystallization of glass-ceramics under ion exchange diffusion  

Microsoft Academic Search

Experimental results of studying ion exchange process in glass-ceramics are presented. For the first time, it is discovered that the process may result in the disappearance of the crystalline phase in the layers undergoing ion exchange diffusion. This new phenomenon has been called the effect of decrystallization. The effect has been observed in a ceramic material formed out of a

D. K Tagantsev

1999-01-01

217

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

NASA Astrophysics Data System (ADS)

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

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

2007-06-01

218

Copper diffusion in ion-exchanged soda-lime glass  

NASA Astrophysics Data System (ADS)

Cu-alkali ion exchange in silicate glasses gives rise to a peculiar copper distribution, with the presence of both the Cu2+ and Cu+ oxidation states. Grazing incidence X-ray absorption near-edge structure spectroscopy and secondary ion mass spectrometry were performed on different ion-exchanged samples. The results show that the Cu2+/Cu+ ratio is strongly depth-dependent. The relative presence of the two species throughout the exchanged region turns out to be governed by their different diffusion regimes, while the chemistry of the red-ox process is shown to play a minor role. A phenomenological model is proposed to describe the diffusion process.

Gonella, F.; Quaranta, A.; Padovani, S.; Sada, C.; D'Acapito, F.; Maurizio, C.; Battaglin, G.; Cattaruzza, E.

2005-10-01

219

Simulations of Ion Acceleration at Non-relativistic Shocks. III. Particle Diffusion  

E-print Network

We use large hybrid (kinetic protons-fluid electrons) simulations to investigate the transport of energetic particles in self-consistent electromagnetic configurations of collisionless shocks. In previous papers of this series, we showed that ion acceleration may be very efficient (up to $10-20\\%$ in energy), and outlined how the streaming of energetic particles amplifies the upstream magnetic field. Here, we measure particle diffusion around shocks with different strengths, finding that the mean free path for pitch-angle scattering of energetic ions is comparable with their gyroradii calculated in the self-generated turbulence. For moderately-strong shocks, magnetic field amplification proceeds in the quasi-linear regime, and particles diffuse according to the self-generated diffusion coefficient, i.e., the scattering rate depends only on the amount of energy in modes with wavelengths comparable with the particle gyroradius. For very strong shocks, instead, the magnetic field is amplified up to non-linear le...

Caprioli, Damiano

2014-01-01

220

Mechanisms of Stochastic Diffusion of Energetic Ions in Spherical Tori  

SciTech Connect

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

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

2001-01-18

221

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

SciTech Connect

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

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

2007-04-13

222

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

223

Measurement of Retinalamin diffusion coefficient in human sclera by optical spectroscopy  

NASA Astrophysics Data System (ADS)

The use of cytomedines (such as Retinalamin) in clinical practice has shown high effectiveness of the medicaments in ophthalmology. The study of diffusion of Retinalamin in scleral tissue is important for estimation of a drug dose delivered into inner tissue of eye, time of drug action, etc. In vitro measurements of spectral reflectance of sclera interacting with aqueous solution of Retinalamin have been carried out. Ten human sclera samples were included in the study. The results of the experiments have shown that penetration of Retinalamin into scleral tissue leads to the decrease of scleral reflectance due to optical immersion. Estimation of diffusion coefficient of studied solution has been made on the basis of analysis of optical reflectance dynamics of the sclera samples. The diffusion coefficient of Retinalamin in human scleral tissue was evaluated as (1.82±0.14)×10 -6 cm 2/s. The results are important for treatment of partial optic atrophy observed at primary open-angle glaucoma and others eye diseases.

Genina, Elina A.; Bashkatov, Alexey N.; Zubkova, Elena A.; Kamenskikh, Tatiana G.; Tuchin, Valery V.

2008-12-01

224

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

PubMed Central

1. The validity of the macroscopic laws of ion diffusion was critically examined within the microenvironment of the extracellular space in the rat cerebellum using ion-selective micropipettes and ionophoretic point sources. 2. The concepts of volume averaging, volume fraction (alpha) and tortuosity (lambda) were defined and shown to be theoretically appropriate for quantifying diffusion in a complex medium such as the brain. 3. Diffusion studies were made with the cations tetramethylammonium and tetraethylammonium and the anions alpha-naphthalene sulphonate and hexafluoro-arsenate, all of which remained essentially extracellular during the measurements. Diffusion parameters were measured for a period of 50s and over distances of the order of 0.1 mm. 4. Measurements of the diffusion coefficients of the ions in agar gel gave values that were very close to those derivable from the literature, thus confirming the validity of the method. 5. Measurements in the cerebellum did not reveal any systematic influences of ionophoretic current strength, electrode separation, anisotropy, inhomogeneity, charge discrimination or uptake, within the limits tested. 6. The pooled data from measurements with all the ions gave alpha = 0.21 +/- 0.02 (mean +/- S.E. of mean) and lambda = 1.55 +/- 0.05 (mean +/- S.E. of mean). 7. These results show that the extracellular space occupies about 20% of the rat cerebellum and that the diffusion coefficient for small monovalent extracellular ions is reduced by a factor of 2.4 (i.e. lambda 2) without regard to charge sign. The over-all effect of this is to increase the apparent strength of any ionic source in the cerebellum by a factor of lambda 2/alpha, about 12-fold in the present case, and to modify the time course of diffusion. 8. These conclusions confirm that the laws of macroscopic diffusion are closely obeyed in the cerebellum for small ions in the extracellular space, provided that volume fraction and tortuosity are explicitly taken into account. It is likely that these conclusions are generally applicable to other brain regions and other diffusing substances. PMID:7338810

Nicholson, C; Phillips, J M

1981-01-01

225

Simulations of Ion Acceleration at Non-relativistic Shocks. III. Particle Diffusion  

NASA Astrophysics Data System (ADS)

We use large hybrid (kinetic-protons-fluid-electrons) simulations to investigate the transport of energetic particles in self-consistent electromagnetic configurations of collisionless shocks. In previous papers of this series, we showed that ion acceleration may be very efficient (up to 10%-20% in energy), and outlined how the streaming of energetic particles amplifies the upstream magnetic field. Here, we measure particle diffusion around shocks with different strengths, finding that the mean free path for pitch-angle scattering of energetic ions is comparable with their gyroradii calculated in the self-generated turbulence. For moderately strong shocks, magnetic field amplification proceeds in the quasi-linear regime, and particles diffuse according to the self-generated diffusion coefficient, i.e., the scattering rate depends only on the amount of energy in modes with wavelengths comparable with the particle gyroradius. For very strong shocks, instead, the magnetic field is amplified up to non-linear levels, with most of the energy in modes with wavelengths comparable to the gyroradii of highest-energy ions, and energetic particles experience Bohm-like diffusion in the amplified field. We also show how enhanced diffusion facilitates the return of energetic particles to the shock, thereby determining the maximum energy that can be achieved in a given time via diffusive shock acceleration. The parameterization of the diffusion coefficient that we derive can be used to introduce self-consistent microphysics into large-scale models of cosmic ray acceleration in astrophysical sources, such as supernova remnants and clusters of galaxies.

Caprioli, D.; Spitkovsky, A.

2014-10-01

226

Time-dependent diffusion coefficient as a probe of the permeability of the pore wall  

NASA Astrophysics Data System (ADS)

The time dependence of the mean-square displacement (or equivalently of the diffusion coefficient) in the presence of a permeable barrier can be used as a probe of the surface-to-volume ratio and permeability of a membrane. An exact, universal, short-time asymptotics in a pack of cells, assuming that the surfaces are locally smooth, shows that the effects of nonzero permeability appear as a correction to the diffusion coefficient that is linear in time, whereas the surface-to-volume ratio enters as a square root in time. With ? as the permeability of the membrane, we find, for the particles released inside the cells, DR,eff(t)=DR[1-(SR/VR){4DRt/(9?)-?tDL(DL+DR)/(6DR)}]+... . Here DR and DL are free (i.e., bulk) diffusion coefficients inside and outside of the cell, respectively, and SR/VR is the total internal surface divided by the total internal cell volume. The other terms linear in t that add to the right side of above equation are DR(SR/VR)[(1/6)?t-(1/12)DRt<(1/R1+1/R2)>R], where ? is a surface relaxation, which is generally negligible in biological samples, and <(1/R1+1/R2)>R is the average of the principal radii of curvatures over the interior surface. An equivalent expression for the particles starting outside the cell is obtained by swapping L<-->R. The NMR data on erthrocytes show that the effect of permeability can be significant within the time scales of measurement and hence ? is deducible from the data. The long-time behavior given previously [Proc. Natl. Acad. Sci. USA 92, 1229 (1994)] is augmented by giving a nonuniversal form that includes the rate of approach to this limit.

Sen, Pabitra N.

2003-11-01

227

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

228

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

PubMed

The forward-reverse or FR method is an efficient bidirectional work method for determining the potential of mean force w(z) and also supposedly gives in principle the position-dependent diffusion coefficient D(z). Results from a variation called the OFR (oscillating FR) method suggest inconsistencies in the D(z) values when calculated as prescribed by the FR method. A new steering protocol has thus been developed and applied to the OFR method for the accurate determination of D(z) and also provides greater convergence for w(z) in molecular dynamics simulations. The bulk diffusion coefficient for water was found to be (6.03±0.16)×10(-5) cm2/s at 350 K with system size dependence within the statistical error bars. Using this steering protocol, D(z) and w(z) for water permeating a dipalmitoylphosphatidylcholine (DPPC) bilayer were determined. The potential of mean force is shown to have a barrier of peak height, wmax/(kBT)=8.4, with a width of about 10 Å on either side from the membrane center. The diffusion constant is shown to be highest in the core region of the membrane [peak value ?(8.0±0.8)×10(-5) cm2/s], lowest in the head-group region [minimum value ?(2.0±0.3)×10(-5) cm2/s], and to tend toward the bulk value as the water molecule leaves the membrane. The permeability coefficient P for H2O in DPPC was determined using the simulated D(z) and w(z) to give values of (0.129±0.075) cm/s at 323 K and (0.141±0.043) cm/s at 350 K. The results show more spatial detail than results presented in previous work while reducing the computational and user effort. PMID:23031053

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

2012-09-01

229

Three FORTRAN programs for finite-difference solutions to binary diffusion in one and two phases with composition-and time-dependent diffusion coefficients  

USGS Publications Warehouse

Geological examples of binary diffusion are numerous. They are potential indicators of the duration and rates of geological processes. Analytical solutions to the diffusion equations generally do not allow for variable diffusion coefficients, changing boundary conditions, and impingement of diffusion fields. The three programs presented here are based on Crank-Nicholson finite-difference approximations, which can take into account these complicating factors. Program 1 describes the diffusion of a component into an initially homogeneous phase that has a constant surface composition. Specifically it is written for Fe-Mg exchange in olivine at oxygen fugacities appropriate for the lunar crust, but other components, phases, or fugacities may be substituted by changing the values of the diffusion coefficient. Program 2 simulates the growth of exsolution lamellae. Program 3 describes the growth of reaction rims. These two programs are written for pseudobinary Ca-(Mg, Fe) exchange in pyroxenes. In all three programs, the diffusion coefficients and boundary conditions can be varied systematically with time. To enable users to employ widely different numerical values for diffusion coefficients and diffusion distance, the grid spacing in the space dimension and the increment by which the grid spacing in the time dimension is increased at each time step are input constants that can be varied each time the programs are run to yield a solution of the desired accuracy. ?? 1982.

Sanford, R. F.

1982-01-01

230

Determination of partition and diffusion coefficients of formaldehyde in selected building materials and impact of relative humidity.  

PubMed

The partition and effective diffusion coefficients of formaldehyde were measured for three materials (conventional gypsum wallboard, "green" gypsum wallboard, and "green" carpet) under three relative humidity (RH) conditions (20%, 50%, and 70% RH). The "green" materials contained recycled materials and were friendly to environment. A dynamic dual-chamber test method was used. Results showed that a higher relative humidity led to a larger effective diffusion coefficient for two kinds of wallboards and carpet. The carpet was also found to be very permeable resulting in an effective diffusion coefficient at the same order of magnitude with the formaldehyde diffusion coefficient in air. The partition coefficient (K(ma)) of formaldehyde in conventional wallboard was 1.52 times larger at 50% RH than at 20% RH, whereas it decreased slightly from 50% to 70% RH, presumably due to the combined effects of water solubility of formaldehyde and micro-pore blocking by condensed moisture at the high RH level. The partition coefficient of formaldehyde increased slightly with the increase of relative humidity in "green" wallboard and "green" carpet. At the same relative humidity level, the "green" wallboard had larger partition coefficient and effective diffusion coefficient than the conventional wallboard, presumably due to the micro-pore structure differences between the two materials. The data generated could be used to assess the sorption effects of formaldehyde on building materials and to evaluate its impact on the formaldehyde concentration in buildings. PMID:22788105

Xu, Jing; Zhang, Jianshun S; Liu, Xiaoyu; Gao, Zhi

2012-06-01

231

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

PubMed

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

Concannon, B M; Davis, J P

1999-08-20

232

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. PMID:23705855

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

2013-01-01

233

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

NASA Astrophysics Data System (ADS)

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.

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

2013-06-01

234

Compilation and evaluation of gas phase diffusion coefficients of reactive trace gases in the atmosphere: volume 1. Inorganic compounds  

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. A different version of this compilation/evaluation, which will be updated when new data become available, is uploaded online (diffusion"target="_blank">https://sites.google.com/site/mingjintang/home/diffusion).

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

2014-09-01

235

Thermodiffusion, molecular diffusion and Soret coefficient of binary and ternary mixtures of n-hexane, n-dodecane and toluene.  

PubMed

In this study, the thermodiffusion, molecular diffusion, and Soret coefficients of 12 binary mixtures composed of toluene, n-hexane and n-dodecane in the whole range of concentrations at atmospheric pressure and temperatures of 298.15 K and 308.15 K have been determined. The experimental measurements have been carried out using the Thermogravitational Column, the Sliding Symmetric Tubes and the Thermal Diffusion Forced Rayleigh Scattering techniques. The results obtained using the different techniques show a maximum deviation of 9% for the thermodiffusion coefficient, 8% for the molecular diffusion coefficient and 2% for the Soret coefficient. For the first time we report a decrease of the thermodiffusion coefficient with increasing ratio of the thermal expansion coefficient and viscosity for a binary mixture of an organic ring compound with a short n-alkane. This observation is discussed in terms of interactions between the different components. Additionally, the thermogravitational technique has been used to measure the thermodiffusion coefficients of four ternary mixtures consisting of toluene, n-hexane and n-dodecane at 298.15 K. In order to complete the study, the values obtained for the molecular diffusion coefficient in binary mixtures, and the thermodiffusion coefficient of binary and ternary mixtures have been compared with recently derived correlations. PMID:25376978

Alonso de Mezquia, David; Wang, Zilin; Lapeira, Estela; Klein, Michael; Wiegand, Simone; Mounir Bou-Ali, M

2014-11-01

236

Diffusion of Li + ion on graphene: A DFT study  

NASA Astrophysics Data System (ADS)

Density functional theory investigations show that the Li + ion is stabilized at the center of hexagonal carbon ring with the distance of 1.84 Å from graphene surface. The potential barrier of Li + ion diffusion on the graphene surface, about 0.32 eV, is much lower than that of Li + ion penetrating the carbon ring which is 10.68 eV. When a vacancy of graphene exists, potential barrier about 10.25 eV for Li + ion penetrating the defect is still high, and the ability of the vacancy to sizing the Li + ion is also observed. Electronic densities of states show that the formation of a localized bond between Li atom and edge carbon of vacancy is the main reason for high potential barrier when Li + ion penetrate a vacancy. While Coulomb repulsion is the control factor for high potential barrier in case of Li + ion penetrating a carbon ring.

Zheng, Jiming; Ren, Zhaoyu; Guo, Ping; Fang, Li; Fan, Jun

2011-12-01

237

Ion-beam-induced topography and surface diffusion  

NASA Technical Reports Server (NTRS)

It is pointed out that the development of surface topography along with enhanced surface and bulk diffusion processes accompanying ion bombardment have generated growing interest among users of ion beams and plasmas for thin film or material processing. Interest in these processes stems both from attempts to generate topographic changes for specific studies or applications and from the need to suppress or control undesirable changes. The present investigation provides a summary of the current status of impurity-induced texturing, with emphasis on recent developments. Particular attention is given to the texturing accompanying deposition of an impurity material onto a solid surface while simultaneously etching the surface with an ion beam. A description of experimental considerations is provided, and a thermal-diffusion model is discussed along with the development of sputter cones, and aspects of impact-enhanced surface diffusion.

Robinson, R. S.; Rossnagel, S. M.

1982-01-01

238

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

239

Causal Baryon Diffusion and Colored Noise for Heavy Ion Collisions  

E-print Network

We construct a model for baryon diffusion which has the desired properties of analyticity and causality. The model also has the desired property that the noise correlation function is not a Dirac delta function in space and time. The model depends on three time constants in addition to the diffusion constant. This description can be incorporated into 2nd order viscous hydrodynamical models of heavy ion collisions.

J. I. Kapusta; C. Young

2014-09-05

240

Diffusion studies using ion beam analysis  

Microsoft Academic Search

The combination of ion implantation with nuclear methods such as Rutherford Backscattering Spectrometry (RBS), Nuclear Reaction Spectroscopy (NRS) or Elastic Recoil Detection Analysis (ERDA) has shown to be well adapted to the study of impurity migration in solids induced by either thermal annealing or irradiation. This paper gives some typical examples studied in more detail in our laboratory. Among them,

N. Moncoffre; G. Barbier; E. Leblond; Ph. Martin; H. Jaffrezic

1998-01-01

241

Measurement of diffusion coefficients in supercritical carbon dioxide and correlation with the equation of Wilke and Chang  

SciTech Connect

Diffusion coefficients of acetone, benzene, naphthalene, 1,3,5-trimethylbenzene, phenanthrene, pyrene, and chrysene have been measured by a chromatographic broadening technique in an open capillary tube (950 x 0.103 cm) filled with pure supercritical carbon dioxide or, in the case of benzene, with CO/sub 2/-methanol mixtures ranging from 0 to 100% in methanol. In pure supercritical CO/sub 2/, diffusion coefficients decrease when density increases; they increase linearly vs. the reciprocal of the viscosity; a linear relationship exists between the logarithms of the diffusion coefficients and the molar volumes with a slope of 0.6. Finally, in the range 0.6-0.9 g cm/sup -3/, the Wilke and Chang equation for the calculation of diffusion coefficients is valid for supercritical CO/sub 2/. For methanol-CO/sub 2/ mixtures there is no discontinuity of the diffusion coefficient of benzene when the methanol content varies from 0 to 100%. In the usual supercritical chromatographic conditions with a methanol content less than 10%, diffusion coefficients are at least 4 times higher than in pure methanol.

Sassiat, P.R.; Mourier, P.; Caude, M.H.; Rosset, R.H.

1987-04-15

242

Measurement of the diffusion coefficients of metal vapors in graphite furnaces  

NASA Astrophysics Data System (ADS)

Atomic dissipation in a graphite furnace, heated at a rate of approximately 10 Kms -1, has been investigated. At such heating rates, atomic dissipation is separated by time from the atomization process, and the decay portion of the absorbance signal reflects the removal function. The diffusion coefficients of Ag, Au, Bi, Cd, Ga, In, Mn, Pb, Sb, Sn, Tl and Zn were determined by routine analytical signals obtained on commercial atomic absorption instrumentation, without any modification to the standard technique. The dynamic measurement of the effective gas temperature was carried out by the use of the two-line method, with Pb 368.3/280.2 nm, and Sn 286.3/284.0 nm line pairs. The agreement of the experimental data with the diffusion coefficients, calculated by the Chapman-Enskog theory, was obtained for all of the elements investigated; confirming the diffusional nature of atom removal for these elements, and as well the weak interaction of the atomic vapor with the graphite surface.

Sadagoff, Yuri M.

2000-07-01

243

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

244

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

245

Age-Dependent Changes in the Histogram of Apparent Diffusion Coefficients Values in Magnetic Resonance Imaging  

PubMed Central

The aim of this study was to develop a fast method for estimating whether a brain volume loss is within the normal range for the respective age of the patient. A readout-segmented diffusion-weighted echo-planar imaging sequence was performed as part of the routine examination at a 3-T scanner. Data without (b0-image) and with diffusion weighting (1000?s/mm2) from 492 patients were examined (in the age from 3 to 89?years). One hundred and seventy-three data-sets had to be excluded due to brain lesions or to pathological enlarged cerebrospinal fluid spaces. In the remaining 319 data-sets, apparent diffusion coefficients (ADCs) values were calculated for all pixels exceeding a combined threshold in the diffusion-weighted data and in the non-diffusion-weighted data. The first part of the histogram represents pixels containing mostly brain tissue. The percentage of number of pixels in this part of the ADC histograms was evaluated for all patients and was correlated with the age of the patients. In all the areas examined, a monotone change of relative pixel numbers with the age of the patients was found. The reduction of the contribution of pixels containing mostly brain tissue accelerated with age and was found to be 0.18%/year in the age of 20, 0.34%/year in the age of 50, and 0.50%/year in the age of 80. The observed decrease of the relative number of pixels from the brain tissue with increasing age corresponds to previously published results based on more time-consuming 3-D measurements. The presented technique uses a conventional clinical sequence and might be helpful in deciding whether an observed brain volume loss in a patient is within the normal range for the age of the patient. PMID:24312050

Klose, Uwe; Batra, Marion; Nagele, Thomas

2013-01-01

246

Apparent diffusion coefficient in glioblastoma with PNET-like components, a GBM variant.  

PubMed

Glioblastoma (GBM) with primitive neuroectodermal tumor (PNET)-like (GBM-PNET) components is a rare variant of GBM. Recent studies describe PNET-like clinical behavior in these patients-with significantly increased propensity for CSF dissemination and a benefit of "PNET-like" chemotherapy. The imaging appearance of GBM-PNET is not well-described and given areas of marked cellularity in the PNET components one might expect significantly reduced diffusion on MRI. The purpose of this study is to quantitatively evaluate the diffusion characteristics in GBM-PNET and compare them with conventional GBMs. Nine patients with surgical specimens yielding GBM-PNET were identified from the UCSF Pathology files. MR images of these patients were reviewed retrospectively. DWI (diffusion-weighted imaging) sequences were analyzed with multiple regions of interests placed within the tumor, and ADC (apparent diffusion coefficient) values were measured. Results were compared to previously published ADC values in pathology-proven conventional GBM cases from our institution. Reduced ADC was seen in GBM-PNET (mean 581 × 10(-6) mm(2)/s, range 338-817) compared to previously published mean of 1,030 × 10(-6) mm(2)/s in the enhancing components of conventional GBMs. We report substantially reduced ADC values in GBM-PNETs compared to conventional GBMs. If demonstrated in a larger sample, when areas of marked reduced diffusion are seen in a suspected GBM, MRI may appropriately direct tissue sampling and can advocate a thorough search for PNET-like components on histopathology. These patients may have a higher chance of developing CSF dissemination and may benefit from "PNET-like" platinum-based chemotherapy. PMID:24893732

Ali, Saad; Joseph, Nancy M; Perry, Arie; Barajas, Ramon F; Cha, Soonmee

2014-09-01

247

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

248

Secondary decline in apparent diffusion coefficient and neurological outcomes after a short period of focal brain ischemia in rats  

Microsoft Academic Search

This study was designed to characterize the initial and secondary changes of the apparent diffusion coefficient (ADC) of water with high temporal resolution measurements of ADC values and to correlate ADC changes with functional outcomes. Fourteen rats underwent 30 minutes of temporary middle cerebral artery occlusion (MCAO). Diffusion-, perfusion-, and T2-weighted imaging was performed during MCAO and every 30 minutes

Fuhai Li; Matthew D. Silva; Karl G. Helmer; Tsuyoshi Omae; Joseph D. Fenstermacher; Christopher H. Sotak; Marc Fisher

2000-01-01

249

Metabolic Counterpart of Decreased Apparent Diffusion Coefficient During Hyperacute Ischemic Stroke A Brain Proton Magnetic Resonance Spectroscopic Imaging Study  

Microsoft Academic Search

Background and Purpose—Recent studies have shown that the brain ischemic area defined by the map of decreased apparent diffusion coefficient (ADC) obtained by diffusion-weighted imaging (DWI) during the first hours of ischemic stroke includes a significant part of ischemic penumbra. We hypothesize that the misjudgment of the final infarct size by ADC mapping may be related to a restricted ability

F. Nicoli; Y. Lefur; B. Denis; J. P. Ranjeva; S. Confort-Gouny; P. J. Cozzone

2010-01-01

250

Method qualification and application of diffusion interaction parameter and virial coefficient.  

PubMed

This research focused on evaluation and application of two methods in studying weak protein-protein interactions, i.e. diffusion interaction parameter (KD) and second virial coefficient (B22), both of which are first-order coefficients of protein interactions. Although the plate-based KD method successfully distinguished KD values with relatively large difference in a pH ranging study, it failed to make a consistent statistical decision to determine close interactions as shown by the comprehensive ANOVA analysis. We also validated the DLS-based B22 method by using a model protein lysozyme. The dramatic change of solution appearance for lysozyme as a function of NaCl concentration highlighted the importance of B22 in understanding protein interactions. Moreover, B22 measurement for a MAb fragment suggested a more repulsive protein interaction in histidine buffer than in citrate buffer. The coefficient of variation was <10% when B22 was on an order of magnitude of 10(-4) L mmol/g(2) in contrast to >30% when it approached 10(-5) L mmol/g(2). In this research, we also made an attempt to study protein-protein interactions in concentrated MAb fragment solutions (e.g. >50 mg/mL). Our data suggested that such interactions could be empirically modeled by high-order virial expansions. PMID:24095715

Shi, Shuai; Uchida, Makiko; Cheung, Jason; Antochshuk, Valentyn; Shameem, Mohammed

2013-11-01

251

Diffusion coefficients of endogenous cytosolic proteins from rabbit skinned muscle fibers.  

PubMed

Efflux time courses of endogenous cytosolic proteins were obtained from rabbit psoas muscle fibers skinned in oil and transferred to physiological salt solution. Proteins were separated by gel electrophoresis and compared to load-matched standards for quantitative analysis. A radial diffusion model incorporating the dissociation and dissipation of supramolecular complexes accounts for an initial lag and subsequent efflux of glycolytic and glycogenolytic enzymes. The model includes terms representing protein crowding, myofilament lattice hindrance, and binding to the cytomatrix. Optimization algorithms returned estimates of the apparent diffusion coefficients, D(r,t), that were very low at the onset of diffusion (?10(-10) cm(2) s(-1)) but increased with time as cytosolic protein density, which was initially high, decreased. D(r,t) at later times ranged from 2.11 × 10(-7) cm(2) s(-1) (parvalbumin) to 0.20 × 10(-7) cm(2) s(-1) (phosphofructose kinase), values that are 3.6- to 12.3-fold lower than those predicted in bulk water. The low initial values are consistent with the presence of complexes in situ; the higher later values are consistent with molecular sieving and transient binding of dissociated proteins. Channeling of metabolic intermediates via enzyme complexes may enhance production of adenosine triphosphate at rates beyond that possible with randomly and/or sparsely distributed enzymes, thereby matching supply with demand. PMID:24559981

Carlson, Brian E; Vigoreaux, Jim O; Maughan, David W

2014-02-18

252

Mass transfer of SCWO processes: Molecular diffusion and mass transfer coefficients of inorganic nitrate species in sub- and supercritical water  

SciTech Connect

Molecular diffusion coefficients of lithium-, sodium-, potassium-, cesium-, calcium-, and strontium nitrate in subcritical water were determined by analysis of Taylor dispersion profiles. Pressures ranged from 300 to 500 bar at temperatures ranging from 25{degrees}C to 300{degrees}C. The reported diffusion values were determined at infinite dilution. Molecular diffusion coefficients were 10 to 20 times faster in near-critical subcritical water than in water at ambient temperature and pressure (ATP). These findings implied that the diffusion rates were more liquid like than they were gas like, hence experimental results were correlated with diffusion models for liquids. The subcritical diffusion data presented in this work, and supercritical diffusion results published elsewhere were correlated with hydrodynamic diffusion equations. Both the Wilke-Chang correlation and the Stokes-Einstein equation yielded predictions within 10% of the experimental results if the structure of the diffusing species could be estimated. The effect of the increased diffusion rates on mass transfer rates in supercritical water oxidation applications was quantified, with emphasis on heterogeneous oxidation processes. This study and results published elsewhere showed that diffusion limited conditions are much more likely to be encountered in SCWO processes than commonly acknowledged.

Goemans, M.G.E.; Gloyna, E.F. [Univ. of Texas, Austin, TX (United States). Dept. of Civil Engineering; Buelow, S.J. [Los Alamos National Lab., NM (United States)

1996-04-01

253

Isotropic diffusion weighting for measurement of a high-resolution apparent diffusion coefficient map using a single radial scan in MRI.  

PubMed

This work proposes an isotropic diffusion weighting method for a high-resolution diffusion-weighted image and for a high-resolution apparent diffusion coefficient (ADC) map using a single radial scan in MRI. By using a conventional radial imaging technique, a high-resolution diffusion-weighted (DW) image can be obtained at the cost of a long imaging time. To reduce the imaging time, the proposed method acquires a DW image by altering the diffusion gradient directions for each radial spoke. The acquisition order and directions of the diffusion gradients for an accurate DW image and an ADC map are also proposed by modifying the golden angle ratio in 3D space. In addition, an individual-direction diffusion-weighted (id-DW) image can also be obtained by a diffusion gradient direction, which is one of the multiple directions used in isotropic diffusion weighting. Computer simulations and experiment results show that the proposed method is more accurate and faster than the conventional radial diffusion-weighted imaging. This study suggests that the proposed isotropic diffusion-weighted imaging can be used to obtain a DW image and a high-resolution ADC map accurately in a single radial scan, while reducing the artifacts caused by the diffusion anisotropy, compared to the diffusion-weighted echo-planar-imaging. PMID:25256138

Seo, Hyunseok; Choi, Joonsung; Oh, Changheun; Han, Yeji; Park, HyunWook

2014-10-21

254

Isotropic diffusion weighting for measurement of a high-resolution apparent diffusion coefficient map using a single radial scan in MRI  

NASA Astrophysics Data System (ADS)

This work proposes an isotropic diffusion weighting method for a high-resolution diffusion-weighted image and for a high-resolution apparent diffusion coefficient (ADC) map using a single radial scan in MRI. By using a conventional radial imaging technique, a high-resolution diffusion-weighted (DW) image can be obtained at the cost of a long imaging time. To reduce the imaging time, the proposed method acquires a DW image by altering the diffusion gradient directions for each radial spoke. The acquisition order and directions of the diffusion gradients for an accurate DW image and an ADC map are also proposed by modifying the golden angle ratio in 3D space. In addition, an individual-direction diffusion-weighted (id-DW) image can also be obtained by a diffusion gradient direction, which is one of the multiple directions used in isotropic diffusion weighting. Computer simulations and experiment results show that the proposed method is more accurate and faster than the conventional radial diffusion-weighted imaging. This study suggests that the proposed isotropic diffusion-weighted imaging can be used to obtain a DW image and a high-resolution ADC map accurately in a single radial scan, while reducing the artifacts caused by the diffusion anisotropy, compared to the diffusion-weighted echo-planar-imaging.

Seo, Hyunseok; Choi, Joonsung; Oh, Changheun; Han, Yeji; Park, HyunWook

2014-10-01

255

Impact of the solute exclusion on the bed longitudinal diffusion coefficient and particle intra-tortuosity determined by ISEC.  

PubMed

The effective diffusion coefficient of non retained toluene and polystyrenes compounds was measured by the peak parking method for two columns packed with mesoporous silica. Different models used to predict the effective diffusion are compared. These models include the conventional Knox time-averaged model and some effective medium theory models such as Maxwell, Landauer, Garnett or Torquato models. In all these models the effective intraparticle diffusion coefficient is needed. It is derived here, in non-adsorbing conditions, from internal porosity, hindrance factor, which can be estimated with the Renkin correlation, and internal tortuosity, which can be considered as either constant or calculated by the Weissberg equation ?=1-pln?, where ? is the accessible particle porosity and p a parameter characteristic of the topology. The experimental effective diffusion coefficients of toluene and polystyrenes were found to be in good agreement with the values predicted by the Maxwell, or Torquato models, provided the internal tortuosity is calculated by using the Weissberg equation. PMID:24380650

Wernert, Véronique; Bouchet, Renaud; Denoyel, Renaud

2014-01-17

256

Diffusion study of plasma ion implanted H in silicon  

NASA Astrophysics Data System (ADS)

We report on thermal out-diffusion of hydrogen from p-type Si(100) samples prepared by hydrogen implantation using a low energy plasma ion implantation set-up. Samples have been annealed in vacuum in the temperature range 100-600°C. Hydrogen depth profiling of the as implanted and the vacuum annealed samples has been performed by elastic recoil detection analysis (ERDA) technique using 1.25 MeV He + ions. The activation energy for H out-diffusion has been calculated by fitting the amount of retained H at different temperatures. The out-diffusion phenomenon has been explained on the basis of depassivation of plasma implantation induced defects and/or dissociation of hydrogen molecules.

Som, T.; Rakshit, R.; Kulkarni, V. N.

2000-03-01

257

Charge collected by diffusion from an ion track under mixed boundary conditions  

NASA Technical Reports Server (NTRS)

Charge-carrier diffusion from an ion track in a silicon substrate at least a few hundred microns thick is analyzed. The substrate upper surface is treated as reflective except for a small section, intended to represent a reverse-biased junction, which is treated as a sink. Total charge collected by the sink is calculated by assuming transport to be governed by an ambipolar diffusion equation with temporally constant and spatially uniform carrier lifetime and diffusion coefficient. Present results apply to a normally incident track but could easily be generalized to arbitrary track direction. The collected charge is found to depend on track length and on the electrostatic capacitance, rather than the area, of the sink. Theoretical predictions are compared to the results of a numerical simulation called the Poisson and Continuity Equation Solver (PISCES) for three cases and are found to agree within a factor of two in the worst case.

Edmonds, Larry D.

1991-01-01

258

Correlation of the apparent diffusion coefficiency values on diffusion-weighted imaging with prognostic factors for breast cancer  

PubMed Central

Objective The aim of this study was to correlate the apparent diffusion coefficient (ADC) value of breast cancer with prognostic factors. Methods 335 patients with invasive ductal carcinoma not otherwise specified (IDC NOS) and ductal carcinoma in situ (DCIS) who underwent breast MRI with diffusion-weighted imaging were included in this study. ADC of breast cancer was calculated using two b factors (0 and 1000 s mm–2). Mean ADCs of IDC NOS and DCIS were compared and evaluated. Among cases of IDC NOS, mean ADCs were compared with lymph node status, size and immunochemical prognostic factors using Student's t-test. ADC was also correlated with histological grade using the Kruskal–Wallis test. Results Mean ADC of IDC NOS was significantly lower than that of DCIS (p<0.001). However, the mean ADC of histological grade of IDC NOS was not significantly different (p=0.564). Mean ADC of oestrogen receptor (ER)-positive or progesterone receptor (PR)-positive cancer was significantly lower than that of ER-negative or PR-negative cancer (p=0.003 vs p=0.032). Mean ADC of Ki-67 index-positive cancer was significantly lower than that of Ki-67 index-negative cancer (p=0.028). Mean ADC values of cancers with increased microvascular density (MVD) were significantly lower than those of cancer with no MVD increase (p=0.009). No correlations were observed between mean ADC value and human growth factor receptor 2 expression, tumour size and lymph node metastasis. Conclusion Low ADC value was correlated with positive expression of ER, PR, increased Ki-67 index, and increased MVD of breast cancer. PMID:22128125

Choi, S Y; Chang, Y-W; Park, H J; Kim, H J; Hong, S S; Seo, D Y

2012-01-01

259

Mutual diffusion coefficients and ionic transport coefficient l/sub ij/ of MgCl/sub 2/-H/sub 2/O at 25 /sup 0/C  

SciTech Connect

The volume-fixed mutual diffusion coefficients of aqueous MgCl/sub 2/ have been accurately measured at 25/sup 0/C from dilute solutions to near saturation, by free-diffusion Rayleigh interferometry. Density data for MgCl/sub 2/-H/sub 2/O have been measured with pycnometers. The generalized ionic transport coefficients of irreversible thermodynamics, l/sub ij/, have been calculated from our diffusion data and critically reviewed data for thermodynamic and other transport properties. These l/sub ij/ values are compared with those of other 2-1 chlorides. The diffusion data, l/sub ij/ values, and results reported elsewhere form part of the data base necessary for development of approximation procedures for binary and ternary solution transport properties. Mutual diffusion data are also reported for several sucrose-H/sub 2/O solutions. Realignment of the Beckman-Spinco Model-H electrophoresis apparatus to optimize Rayleigh interferometry is described in the supplementary material. 97 references, 8 figures, 7 tables.

Miller, D.G.; Rard, J.A.; Eppstein, L.B.; Albright, J.G.

1984-01-01

260

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

PubMed

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

Akköse, Ahmet; Akta?, Nesimi

2014-01-01

261

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

262

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

263

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

264

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

NASA Astrophysics Data System (ADS)

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

Wortmann, Ulrich G.; Chernyavsky, Boris M.

2011-06-01

265

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. PMID:24556745

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

2014-01-01

266

First-principles binary diffusion coefficients for H, H2, and four normal alkanes + N2  

NASA Astrophysics Data System (ADS)

Collision integrals related to binary (dilute gas) diffusion are calculated classically for six species colliding with N2. The most detailed calculations make no assumptions regarding the complexity of the potential energy surface, and the resulting classical collision integrals are in excellent agreement with previous semiclassical results for H + N2 and H2 + N2 and with recent experimental results for CnH2n+2 + N2, n = 2-4. The detailed classical results are used to test the accuracy of three simplifying assumptions typically made when calculating collision integrals: (1) approximating the intermolecular potential as isotropic, (2) neglecting the internal structure of the colliders (i.e., neglecting inelasticity), and (3) employing unphysical R-12 repulsive interactions. The effect of anisotropy is found to be negligible for H + N2 and H2 + N2 (in agreement with previous quantum mechanical and semiclassical results for systems involving atomic and diatomic species) but is more significant for larger species at low temperatures. For example, the neglect of anisotropy decreases the diffusion coefficient for butane + N2 by 15% at 300 K. The neglect of inelasticity, in contrast, introduces only very small errors. Approximating the repulsive wall as an unphysical R-12 interaction is a significant source of error at all temperatures for the weakly interacting systems H + N2 and H2 + N2, with errors as large as 40%. For the normal alkanes in N2, which feature stronger interactions, the 12/6 Lennard-Jones approximation is found to be accurate, particularly at temperatures above ˜700 K where it predicts the full-dimensional result to within 5% (although with somewhat different temperature dependence). Overall, the typical practical approach of assuming isotropic 12/6 Lennard-Jones interactions is confirmed to be suitable for combustion applications except for weakly interacting systems, such as H + N2. For these systems, anisotropy and inelasticity can safely be neglected but a more detailed description of the repulsive wall is required for quantitative predictions. A straightforward approach for calculating effective isotropic potentials with realistic repulsive walls is described. An analytic expression for the calculated diffusion coefficient for H + N2 is presented and is estimated to have a 2-sigma error bar of only 0.7%.

Jasper, Ahren W.; Kamarchik, Eugene; Miller, James A.; Klippenstein, Stephen J.

2014-09-01

267

First-principles binary diffusion coefficients for H, H2, and four normal alkanes + N2.  

PubMed

Collision integrals related to binary (dilute gas) diffusion are calculated classically for six species colliding with N2. The most detailed calculations make no assumptions regarding the complexity of the potential energy surface, and the resulting classical collision integrals are in excellent agreement with previous semiclassical results for H + N2 and H2 + N2 and with recent experimental results for CnH2n+2 + N2, n = 2-4. The detailed classical results are used to test the accuracy of three simplifying assumptions typically made when calculating collision integrals: (1) approximating the intermolecular potential as isotropic, (2) neglecting the internal structure of the colliders (i.e., neglecting inelasticity), and (3) employing unphysical R(-12) repulsive interactions. The effect of anisotropy is found to be negligible for H + N2 and H2 + N2 (in agreement with previous quantum mechanical and semiclassical results for systems involving atomic and diatomic species) but is more significant for larger species at low temperatures. For example, the neglect of anisotropy decreases the diffusion coefficient for butane + N2 by 15% at 300 K. The neglect of inelasticity, in contrast, introduces only very small errors. Approximating the repulsive wall as an unphysical R(-12) interaction is a significant source of error at all temperatures for the weakly interacting systems H + N2 and H2 + N2, with errors as large as 40%. For the normal alkanes in N2, which feature stronger interactions, the 12/6 Lennard-Jones approximation is found to be accurate, particularly at temperatures above ?700 K where it predicts the full-dimensional result to within 5% (although with somewhat different temperature dependence). Overall, the typical practical approach of assuming isotropic 12/6 Lennard-Jones interactions is confirmed to be suitable for combustion applications except for weakly interacting systems, such as H + N2. For these systems, anisotropy and inelasticity can safely be neglected but a more detailed description of the repulsive wall is required for quantitative predictions. A straightforward approach for calculating effective isotropic potentials with realistic repulsive walls is described. An analytic expression for the calculated diffusion coefficient for H + N2 is presented and is estimated to have a 2-sigma error bar of only 0.7%. PMID:25273443

Jasper, Ahren W; Kamarchik, Eugene; Miller, James A; Klippenstein, Stephen J

2014-09-28

268

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

269

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

USGS Publications Warehouse

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

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

2004-01-01

270

A New Coarse-Grained Model for E. coli Cytoplasm: Accurate Calculation of the Diffusion Coefficient of Proteins and Observation of Anomalous Diffusion  

PubMed Central

A new coarse-grained model of the E. coli cytoplasm is developed by describing the proteins of the cytoplasm as flexible units consisting of one or more spheres that follow Brownian dynamics (BD), with hydrodynamic interactions (HI) accounted for by a mean-field approach. Extensive BD simulations were performed to calculate the diffusion coefficients of three different proteins in the cellular environment. The results are in close agreement with experimental or previously simulated values, where available. Control simulations without HI showed that use of HI is essential to obtain accurate diffusion coefficients. Anomalous diffusion inside the crowded cellular medium was investigated with Fractional Brownian motion analysis, and found to be present in this model. By running a series of control simulations in which various forces were removed systematically, it was found that repulsive interactions (volume exclusion) are the main cause for anomalous diffusion, with a secondary contribution from HI. PMID:25180859

Hasnain, Sabeeha; McClendon, Christopher L.; Hsu, Monica T.; Jacobson, Matthew P.; Bandyopadhyay, Pradipta

2014-01-01

271

Diffuse plasma effects on the ion-hose instability  

NASA Astrophysics Data System (ADS)

The transverse stability of a relativistic electron beam focused by an ion channel in the presence of a diffuse background plasma is investigated. The linear behavior of the ion-hose and electron two-stream instabilities is treated analytically using a spread-mass model for the beam and ion channel and a cold-fluid model for the plasma. The electron two-stream instability is found to be quite weak. As the plasma neutralization radius approaches the beam radius, the ion-hose growth rate is reduced up to 50 percent before the model's assumptions break down. Particle-in-cell simulations confirm the linear analytic theory and show that the electron two-stream instability can saturate nonlinearly with little beam emittance growth.

Welch, Dale R.; Hughes, Thomas P.

1993-02-01

272

Helium diffusion coefficient measurements in R7T7 nuclear glass by 3He(d,?) 1H nuclear reaction analysis  

NASA Astrophysics Data System (ADS)

The immobilization of fission products and minor actinides by vitrification is the reference process for industrial management of high-level radioactive wastes generated by spent fuel reprocessing. Radiation damage and radiogenic helium accumulation must be specifically studied to evaluate the effects of minor actinide alpha decay on the glass long-term behavior under repository conditions. A specific experimental study was conducted for a comprehensive evaluation of the behavior of helium and its diffusion mechanisms in borosilicate nuclear waste glass. Helium production was simulated by external implantation with 3He ions at a concentration (?1 at.%) 30 times higher than obtained after 10,000 years of storage. Helium diffusion coefficients as a function of temperature were extracted from the depth profiles after annealing. The 3He(d,?) 1H nuclear reaction analysis (NRA) technique was successfully adopted for low-temperature in situ measurements of depth profiles. Its high depth resolution revealed helium mobility at temperatures as low as 253 K and the presence of a trapped helium fraction. The diffusion coefficients of un-trapped helium atoms follow an Arrhenius law between 253 K and 323 K. An activation energy of 0.55 ± 0.03 eV was determined, which is consistent with a process controlled by diffusion in the glass free volume.

Chamssedine, F.; Sauvage, T.; Peuget, S.; Fares, T.; Martin, G.

2010-05-01

273

Early Changes in Apparent Diffusion Coefficient From Diffusion-Weighted MR Imaging During Radiotherapy for Prostate Cancer  

SciTech Connect

Purpose: To investigate the feasibility of diffusion-weighted MRI (DWI) as an early and reproducible change indicator in patients receiving radiotherapy for prostate cancer (PC). Methods and Materials: Eight consecutive patients with biopsy-proven PC underwent DWI at 3T. All patients who received external-beam radiotherapy had four serial MR scans, as follows: before therapy (PreTx); after 1 week of therapy (PostT1); after 3 weeks of therapy (PostT2); and 1 month after the completion of therapy (PostT3). At each time, the apparent diffusion coefficient (ADC) was measured in tumors and normal tissues. For reproducibility of the ADC measurement, five patients also had two separate pretreatment DWI scans at an interval of <2 weeks. Serum prostate-specific antigen (PSA) levels were evaluated at the same time as MR scans. Results: Thirteen tumors (peripheral zone = 10; transition zone = 3) were found. The mean ADC values for the tumors from PreTx to PostT3 were 0.86, 1.03, 1.15, and 1.26 Multiplication-Sign 10{sup -3} mm{sup 2}/s in sequence, respectively. Compared with PreTx, PostT1 (p = 0.005), PostT2 (p = 0.003), and PostT3 (p < 0.001) showed a significant increase in ADC values. The mean ADC values of the benign tissues from PreTx to PostT3 were 1.60, 1.58, 1.47, and 1.46 Multiplication-Sign 10{sup -3} mm{sup 2}/s in sequence, respectively. Reproducibility of ADC measurements was confirmed with a mean difference in ADC of -0.04 in peripheral zone and -0.017 in transition zone between two separate pretreatment MR scans. The mean PSA levels from PreTx to PostT3 were 9.05, 9.18, 9.25, and 4.11 ng/mL in sequence, respectively. Conclusions: DWI, as a reproducible biomarker, has the potential to evaluate the early therapeutic changes of PC to radiotherapy.

Park, Sung Yoon [Department of Radiology and Center for Imaging Science, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul (Korea, Republic of); Kim, Chan Kyo, E-mail: chankyokim@skku.edu [Department of Radiology and Center for Imaging Science, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul (Korea, Republic of); Park, Byung Kwan [Department of Radiology and Center for Imaging Science, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul (Korea, Republic of); Park, Won; Park, Hee Chul [Department of Radiation Oncology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul (Korea, Republic of); Han, Deok Hyun [Department of Urology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul (Korea, Republic of); Kim, Bohyun [Department of Radiology, Mayo Clinic College of Medicine, Rochester, MN (United States)

2012-06-01

274

Activity coefficients of bicarbonate, carbonate and calcium ions in sea water  

Microsoft Academic Search

Measurements of pH of sea water samples equilibrated with known partial pressures of CO 2 and with calcite and aragonite have enabled the determination of molal activity coefficient for bicarbonate, carbonate, and calcium ions in two sea water samples at 25°C and 1 atm total pressure. Results are: For standard artificial sea water (chlorinity = 19.0 , titration alkalinity =

Robert A. Berner

1965-01-01

275

Apparent diffusion coefficients and chemical species of neptunium (V) in compacted Na-montmorillonite  

Microsoft Academic Search

Diffusion of neptunium (V) in compacted Na-montmorillonite was studied through the non-steady state diffusion method. In this study, two experimental attempts were carried out to understand the diffusion mechanism of neptunium. One was to establish the diffusion activation energy, which was then used to determine the diffusion process in the montmorillonite. The other was the measurement of the distribution of

Naofumi Kozai; Koichi Inada; Tamotsu Kozaki; Seichi Sato; Hiroshi Ohashi; Tsunetaka Banba

2001-01-01

276

Precise measurement of the self-diffusion coefficient for poly(ethylene glycol) in aqueous solution using uniform oligomers.  

PubMed

Uniform poly(ethylene glycol) (PEG) oligomers, with a degree of polymerization n=1-40, were separated by preparative supercritical fluid chromatography from commercial monodispersed samples. Diffusion coefficients, D, for separated uniform PEG oligomers were measured in dilute solutions of deuterium oxide (D(2)O) at 30 degrees C, using pulsed-field gradient nuclear magnetic resonance. The measured D for each molecular weight was extrapolated to infinite dilution. Diffusion coefficients obtained at infinite dilution follow the scaling behavior of Zimm-type diffusion, even in the lower molecular weight range. Molecular-dynamics simulations for PEG in H(2)O also showed this scaling behavior, and reproduced close hydrodynamic interactions between PEG and water. These findings suggest that diffusion of PEG in water is dominated by hydrodynamic interaction over a wide molecular weight range, including at low molecular weights around 1000. PMID:16035823

Shimada, Kayori; Kato, Haruhisa; Saito, Takeshi; Matsuyama, Shigetomo; Kinugasa, Shinichi

2005-06-22

277

Fe Mg diffusion in olivine II: point defect chemistry, change of diffusion mechanisms and a model for calculation of diffusion coefficients in natural olivine  

NASA Astrophysics Data System (ADS)

Analysis of existing data and models on point defects in pure (Fe,Mg)-olivine (Phys Chem Miner 10:27 37,1983; Phys Chem Miner 29:680 694, 2002) shows that it is necessary to consider thermodynamic non-ideality of mixing to adequately describe the concentration of point defects over the range of measurement. In spite of different sources of uncertainties, the concentrations of vacancies in octahedral sites in (Fe,Mg)-olivine are on the order of 10-4 per atomic formula unit at 1,000 1,200 °C according to both the studies. We provide the first explicit plots of vacancy concentrations in olivine as a function of temperature and oxygen fugacity according to the two models. It is found that in contrast to absolute concentrations at ˜1,100 °C and dependence on fO2, there is considerable uncertainty in our knowledge of temperature dependence of vacancy concentrations. This needs to be considered in discussing the transport properties such as diffusion coefficients. Moreover, these defect models in pure (Fe,Mg)-olivine need to be extended by considering aliovalent impurities such as Al, Cr to describe the behavior of natural olivine. We have developed such a formulation, and used it to analyze the considerable database of diffusion coefficients in olivine from Dohmen et al. (Phys Chem Miner this volume, 2007) (Part - I) and older data in the literature. The analysis documents unequivocally for the first time a change of diffusion mechanism in a silicate mineral—from the transition metal extrinsic (TaMED) to the purely extrinsic (PED) domain, at fO2 below 10-10 Pa, and consequently, temperatures below 900 °C. The change of diffusion mechanism manifests itself in a change in fO2 dependence of diffusivity and a slight change in activation energy of diffusion—the activation energy increases at lower temperatures. These are consistent with the predictions of Chakraborty (J Geophys Res 102(B6):12317 12331, 1997). Defect formation enthalpies in the TaMED regime (distinct from intrinsic defect formation) lie between -66 and + 15 kJ/mol and migration energies of octahedral cations in olivine are most likely ˜ 260 kJ/mol, consistent with previous inferences (Phys Chem 207:147 162, 1998). Plots are shown for diffusion at various constant fO2 as well as along fO2 buffers, to highlight the difference in behavior between the two. Considering all the diffusion data and constraints from the point defect models, (Fe Mg) diffusion in olivine along [001] is best described by the Master equations: (1) At oxygen fugacities greater than 10-10 Pa: log [D_{{{FeMg}}} (m2/s)] = - 9.21 - {201000 + (P - 105) × 7 × 10^{{- 6}}}/{2.303RT} + 1/6log (fO2 /10^{{- 7}}) + 3X_{{{Fe}}} where T is in Kelvin, P and fO2 is in Pascals, X Fe is the mole fraction of the fayalite component and R is the gas constant in J/mol/K. (2) At oxygen fugacities less than 10-10 Pa: log [D_{{{FeMg}}} (m2/s)] = - 8.91 - {220000 + (P - 105) × 7 × 10^{{- 6}}}/{2.303RT} + 3X_{{{Fe}}} These equations reproduce all of the 113 experimental data points within half an order of magnitude. (3) Alternately, a global equation averaging out the change of mechanism may be used, with somewhat larger errors in reproducing the measured diffusion data. It underestimates data at higher temperatures, and overestimates them at lower temperatures on the average. Note that fO2 is not explicitly considered here, leading to additional sources of error: log [D_{{{FeMg}}} (m2/s)] = - 8.27 - {226000 + (P - 105) × 7 × 10^{{- 6}}}/{2.303RT} + 3X_{{{Fe}}} To obtain diffusion coefficients along [100] and [010], log 6 needs to be subtracted from each of the above equations.

Dohmen, Ralf; Chakraborty, Sumit

2007-08-01

278

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

279

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

280

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. PMID:9635784

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

1998-01-01

281

A dependence of carbon impurity transport coefficients on fuel ions in hydrogen and helium plasmas of Large Helical Device  

NASA Astrophysics Data System (ADS)

Impurity transport of carbon has been studied using a new method combined carbon pellet injection with high-spatial resolution bremsstrahlung measurement on the Large Helical Device [A. Iiyoshi et al., Fusion Technol. 17, 169 (1990)]. The carbon pellets are injected into a steady phase in neutral beam heated discharges with a standard configuration of Rax=3.6m. The particle transport coefficients (diffusion coefficient D and convective velocity V ) are inferred using a diffusive/convective model. The results are compared between hydrogen and helium plasmas. As a result, it is found that the analyzed D has a constant radial profile with almost closed values of 0.2m2/s in both plasmas. On the other hand, the inward V is required only at the plasma outer region (? >0.6) where the electron density gradient exits, and the inward V in helium plasmas (-0.4m /s at ? =0.8 and ne˜4.0×1019m-3) is nearly half as much as that in hydrogen plasmas (-0.7m/s). This difference of the inward V between hydrogen and helium plasmas suggests a dependence on the charge state of fuel ions predicted from neoclassical theory.

Nozato, H.; Morita, S.; Goto, M.; Takase, Y.; Ejiri, A.; Amano, T.; Tanaka, K.; Inagaki, S.

2006-09-01

282

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

283

Evaluation of T2 values and apparent diffusion coefficient of the masseter muscle by clenching  

PubMed Central

Objective : The aim of this study was to evaluate the changes in T2 values and apparent diffusion coefficient (ADC) in the masseter muscle by clenching in healthy volunteers. Methods : 37 volunteers were enrolled in the study. We measured bite force using pressure-sensitive paper and a T2 map. The ADC map was obtained at rest, during clenching, immediately after and 5 min after clenching. The spin-echo sequence was used to calculate T2, and single-shot spin-echo echo planar imaging was used to calculate the ADC. The motion-probing gradients (MPGs) were applied separately along the posterior-to-anterior (PA), right-to-left (RL) and superior-to-inferior (SI) directions, with b values of 0, 300 and 600 s mm–2 in each direction. ADC-PA, ADC-RL, and ADC-SI values were obtained, and we calculated the ADC-iso for the mean diffusivity. Results : There were no significant differences between the stronger and weaker sides of bite force before, during or 5 min after clenching for T2 and ADC. The bite force had little effect on these parameters; thus, we used the average of the two sides for the following analyses. Time course analysis of ADC-iso, ADC-PA, ADC-RL and ADC-SI demonstrated a marked increase after clenching and a rapid decrease immediately after clenching, although they did not completely return to the initial values; however, the change in ADC-RL was significantly greater than those in ADC-PA or ADC-SI (P < 0.001 each). The changes in T2 were similar to those of ADC, although not as marked. Conclusions : ADC (especially ADC-RL) was altered by contraction of the masseter muscle. PMID:21159913

Shiraishi, T; Chikui, T; Yoshiura, K; Yuasa, K

2011-01-01

284

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

285

Early changes in apparent diffusion coefficient as an indicator of response to sorafenib in hepatocellular carcinoma*  

PubMed Central

Objective: The relationship between apparent diffusion coefficient (ADC) and chemotherapy has been established. However, whether ADC could be considered as a measure for monitoring response to sorafenib in hepatocellular carcinoma (HCC) has not been demonstrated. This study was to investigate the ADC changes of advanced HCC under sorafenib treatment. Methods: Athymic mice with HepG2 xenografts were allocated to two groups: control and sorafenib (40 mg/kg, bid). T2 and diffusion images were acquired at each time point (0, 10, 14, and 18 d post-therapy). Tumor volume and changes in ADC were calculated. Results: Tumor volumes on Days 10, 14, and 18 after treatment showed significant decreases in the sorafenib-treated group compared with the control. Pretreatment ADC values were not significantly different between the control and treated groups. A slow increase in ADC in the peripheral zone of tumors appeared in the treated group, which was significantly higher compared with the control group on Days 10, 14, and 18. In the central part of tumors on Day 10 after treatment, an increase in ADC appeared in the treated and control groups, the ADC of the control group being significantly lower compared with the treated tumors. From Day 10 to Day 14, the ADC map showed a progressive decrease in the central region of tumors in the treated and control groups. However, this change is more significant in the treated groups. Conclusions: Early changes in mean ADC correlated with sorafenib treatment in HCC, which are promising indicators for predicting sorafenib response in this carcinoma. PMID:25091989

Zhao, Yi-lei; Guo, Qing-qu; Yang, Gen-ren; Wang, Qi-dong

2014-01-01

286

Electron-Ion Recombination Rate Coefficients for C II Forming C I  

NASA Astrophysics Data System (ADS)

We have determined absolute dielectronic recombination rate coefficients for C II, using the CRYRING heavy-ions storage ring. The resonances due to 2s-2p (n = 0) core excitations are detected in the center-of-mass energy range of 0-15 eV. The experimental results are compared with intermediate coupling AUTOSTRUCTURE calculations. Plasma rate coefficients are obtained from the DR spectrum by convoluting it with a Maxwell-Boltzmann energy distribution for temperatures in the range of 103-106 K. The derived temperature-dependent plasma recombination rate coefficients are presented graphically and parameterized by using a fit formula for convenient use in plasma modeling codes. The experimental rate coefficients are also compared with the theoretical data available in literature. In the temperature range of 103-2 × 104 K, our experimental results show that previous calculations severely underestimate the plasma rate coefficients and also our AUTOSTRUCTURE calculation does not reproduce the experimental plasma rate coefficients well. Above 2 × 104 K, the agreement between the experimental and theoretical rate coefficients is much better, and the deviations are smaller than the estimated uncertainties.

Ali, S.; Orban, I.; Mahmood, S.; Altun, Z.; Glans, P.; Schuch, R.

2012-07-01

287

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

SciTech Connect

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

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

2009-08-15

288

Determining intrachain diffusion coefficients for biopolymer dynamics from single-molecule force spectroscopy measurements.  

PubMed

The conformational diffusion coefficient for intrachain motions in biopolymers, D, sets the timescale for structural dynamics. Recently, force spectroscopy has been applied to determine D both for unfolded proteins and for the folding transitions in proteins and nucleic acids. However, interpretation of the results remains unsettled. We investigated how instrumental effects arising from the force probes used in the measurement can affect the value of D recovered via force spectroscopy. We compared estimates of D for the folding of DNA hairpins found from measurements of rates and energy landscapes made using optical tweezers with estimates obtained from the same single-molecule trajectories via the transition path time. The apparent D obtained from the rates was much lower than the result found from the same data using transition time analysis, reflecting the effects of the mechanical properties of the force probe. Deconvolution of the finite compliance effects on the measurement allowed the intrinsic value to be recovered. These results were supported by Brownian dynamics simulations of the effects of force-probe compliance and bead size. PMID:25296317

Woodside, Michael T; Lambert, John; Beach, Kevin S D

2014-10-01

289

Apparent diffusion coefficient in normal and abnormal pattern of intervertebral lumbar discs: initial experience?  

PubMed Central

The aim of the present study was to compare the relationship of morphologically defined non-bulging/herniated, bulging and herniated intervertebral lumbar discs with quantitative apparent diffusion coefficient (ADC). Thirty-two healthy volunteers and 28 patients with back pain or sciatica were examined by MRI. All intervertebral lumbar discs from L1 to S1 were classified according to morphological abnormality and degenerated grades. The ADC values of nucleus pulposus (NP) were measured and recorded. The significant differences about mean ADC values of NP were found between non-bulging/herniated discs and bulging discs as well as herniated discs (P < 0.05), whereas there were no significant differences in ADC values between bulging and herniated discs (P > 0.05). Moreover, statistically significant relationship was found in the mean ADC values of NP between “non-bulging/herniated and non-degenerated discs” and “non-bulging/herniated degenerated discs” as well as herniated discs (P < 0.05). Linear regression analysis between ADC value and disc level revealed an inverse correlation (r = -0.18). The ADC map of the NP is a potentially useful tool for the quantitative assessment of componential and molecular alterations accompanied with lumbar disc abnormalities. PMID:23554690

Niu, Gang; Yu, Xuewen; Yang, Jian; Wang, Rong; Zhang, Shaojuan; Guo, Youmin

2011-01-01

290

Response of radiation belt simulations to different radial diffusion coefficients for relativistic and ultra-relativistic electrons  

NASA Astrophysics Data System (ADS)

Two parameterizations of the resonant wave-particle interactions of electrons with ULF waves in the magnetosphere by Brautigam and Albert [2000] and Ozeke et al. [2012] are evaluated using the Versatile Electron Radiation Belt (VERB) diffusion code to estimate the effect of changing a diffusion coefficient on the radiation belt simulation. The period of investigation includes geomagnetically quiet and active time. The simulations take into account wave-particle interactions represented by radial diffusion transport, local acceleration, losses due to pitch-angle diffusion, and mixed diffusion. 1. Brautigam, D. H., and J. M. Albert (2000), Radial diffusion analysis of outer radiation belt electrons during the October 9, 1990, magnetic storm, J. Geophys. Res., 105(A1), 291-309, doi:10.1029/1999JA900344 2. Ozeke, L. G., I. R. Mann, K. R. Murphy, I. J. Rae, D. K. Milling, S. R. Elkington, A. A. Chan, and H. J. Singer (2012), ULF wave derived radiation belt radial diffusion coefficients, J. Geophys. Res., 117, A04222, doi:10.1029/2011JA017463.

Drozdov, Alexander; Mann, Ian; Baker, Daniel N.; Subbotin, Dmitriy; Ozeke, Louis; Shprits, Yuri; Kellerman, Adam

291

Theoretical and experimental study of Differential Pulse Voltammetry at spherical electrodes: Measuring diffusion coefficients and formal potentials  

Microsoft Academic Search

Rigorous and approximate analytical expressions are deduced for Differential Pulse Voltammetry at spherical electrodes of any size, including microelectrodes, when the electrogenerated species is soluble in the electrolytic solution. From these, we examine the utility of DPV for the determination of diffusion coefficients and formal potentials, establishing the optimum conditions for this purpose. The experimental validation of the theoretical results

Ángela Molina; Eduardo Laborda; Emma I. Rogers; Francisco Martínez-Ortiz; Carmen Serna; Juan G. Limon-Petersen; Neil V. Rees; Richard G. Compton

2009-01-01

292

Electrochemical measurement of lateral diffusion coefficients of ubiquinones and plastoquinones of various isoprenoid chain lengths incorporated in model bilayers.  

PubMed Central

The long-range diffusion coefficients of isoprenoid quinones in a model of lipid bilayer were determined by a method avoiding fluorescent probe labeling of the molecules. The quinone electron carriers were incorporated in supported dimyristoylphosphatidylcholine layers at physiological molar fractions (<3 mol%). The elaborate bilayer template contained a built-in gold electrode at which the redox molecules solubilized in the bilayer were reduced or oxidized. The lateral diffusion coefficient of a natural quinone like UQ10 or PQ9 was 2.0 +/- 0.4 x 10(-8) cm2 s(-1) at 30 degrees C, two to three times smaller than the diffusion coefficient of a lipid analog in the same artificial bilayer. The lateral mobilities of the oxidized or reduced forms could be determined separately and were found to be identical in the 4-13 pH range. For a series of isoprenoid quinones, UQ2 or PQ2 to UQ10, the diffusion coefficient exhibited a marked dependence on the length of the isoprenoid chain. The data fit very well the quantitative behavior predicted by a continuum fluid model in which the isoprenoid chains are taken as rigid particles moving in the less viscous part of the bilayer and rubbing against the more viscous layers of lipid heads. The present study supports the concept of a homogeneous pool of quinone located in the less viscous region of the bilayer. PMID:9545054

Marchal, D; Boireau, W; Laval, J M; Moiroux, J; Bourdillon, C

1998-01-01

293

Characterization of the fluorescence correlation spectroscopy (FCS) standard rhodamine 6G and calibration of its diffusion coefficient in aqueous solutions.  

PubMed

Precise diffusion measurements of rhodamine 6G (Rh6G) dissolved in D2O at concentrations between 50 and 200 ?M were carried out in the temperature range from 280 to 320 K using pulsed field gradient nuclear magnetic resonance (PFG-NMR). The obtained diffusion coefficients can be used as a calibration reference in fluorescence correlation spectroscopy (FCS). Besides measuring the diffusivity of Rh6G, the diffusion coefficient of the solvent in the same system could be determined in parallel by PFG-NMR as the resonances of water and Rh6G are well separated in the (1)H NMR spectrum. To analyze the differences due to the isotope effect of the solvent (D2O vs. H2O), the correlation time ?D of Rh6G was measured by FCS in both D2O and H2O. The obtained isotopic correction factor, ?D(D2O)/?D(H2O) = 1.24, reflects the isotope effect of the solvent´s self-diffusion coefficients as determined previously by PFG-NMR. PMID:24606354

Majer, G; Melchior, J P

2014-03-01

294

In situ estimation of the effective chemical diffusion coefficient of a rock matrix in a fractured aquifer  

USGS Publications Warehouse

An in situ method of estimating the effective diffusion coefficient for a chemical constituent that diffuses into the primary porosity of a rock is developed by abruptly changing the concentration of the dissolved constituent in a borehole in contact with the rock matrix and monitoring the time-varying concentration. The experiment was conducted in a borehole completed in mudstone on the campus of the University of the Free State in Bloemfontein, South Africa. Numerous tracer tests were conducted at this site, which left a residual concentration of sodium chloride in boreholes that diffused into the rock matrix over a period of years. Fresh water was introduced into a borehole in contact with the mudstone, and the time-varying increase of chloride was observed by monitoring the electrical conductivity (EC) at various depths in the borehole. Estimates of the effective diffusion coefficient were obtained by interpreting measurements of EC over 34 d. The effective diffusion coefficient at a depth of 36 m was approximately 7.8??10-6 m2/d, but was sensitive to the assumed matrix porosity. The formation factor and mass flux for the mudstone were also estimated from the experiment. ?? Springer-Verlag 2007.

Gebrekristos, R. A.; Shapiro, A. M.; Usher, B. H.

2008-01-01

295

Self diffusion of alkaline-Earth in Ca-Mg-aluminosilicate melts: Experimental improvements on the determination of the self-diffusion coefficients  

NASA Technical Reports Server (NTRS)

Experimental studies of self-diffusion isotopes in silicate melts often have quite large uncertainties when comparing one study to another. We designed an experiment in order to improve the precision of the results by simultaneously studying several elements (Mg, Ca, Sr, Ba) during the same experiment thereby greatly reducing the relative experimental uncertainties. Results show that the uncertainties on the diffusion coefficients can be reduced to 10 percent, allowing a more reliable comparison of differences of self-diffusion coefficients of the elements. This type of experiment permits us to study precisely and simultaneously several elements with no restriction on any element. We also designed an experiment to investigate the possible effects of multicomponent diffusion during Mg self-diffusion experiments by comparing cases where the concentrations of the elements and the isotopic compositions are different. The results suggest that there are differences between the effective means of transport. This approach should allow us to investigate the importance of multicomponent diffusion in silicate melts.

Paillat, O.; Wasserburg, G. J.

1993-01-01

296

Rate coefficients of the reactions of ions with polar molecules at interstellar temperatures  

NASA Astrophysics Data System (ADS)

A theory has been developed recently which predicts that the rate coefficients, k, for the reactions of ions with polar molecules at low temperatures will be much greater than the canonical value of 10 to the -9th cu cm/s. The new theory indicates that k is greatest for low-lying rotational states and increases rapidly with decreasing temperature. Recent laboratory measurements which validate the theory, are examined, calculated values of k for the reactions of H3(+) ions with several polar molecules are presented, and their significance to interstellar chemistry is discussed. For the reactions of ions with molecules having large dipole moments, it is recommended that k values as large as 10 to the -7th cu cm/s should be used in ion-chemical models of low-temperature instellar clouds.

Adams, N. G.; Smith, D.; Clary, D. C.

1985-09-01

297

Ion radial diffusion in an electrostatic impulse model for stormtime ring current formation  

NASA Technical Reports Server (NTRS)

Guiding-center simulations of stormtime transport of ring-current and radiation-belt ions having first adiabatic invariants mu is approximately greater than 15 MeV/G (E is approximately greater than 165 keV at L is approximately 3) are surprisingly well described (typically within a factor of approximately less than 4) by the quasilinear theory of radial diffusion. This holds even for the case of an individual model storm characterized by substorm-associated impulses in the convection electric field, provided that the actual spectrum of the electric field is incorporated in the quasilinear theory. Correction of the quasilinear diffusion coefficient D(sub LL)(sup ql) for drift-resonance broadening (so as to define D(sub LL)(sup ql)) reduced the typical discrepancy with the diffusion coefficients D(sub LL)(sup sim) deduced from guiding-center simulations of representative-particle trajectories to a factor of approximately 3. The typical discrepancy was reduced to a factor of approximately 1.4 by averaging D(sub LL)(sup sim), D(sub LL)(sup ql), and D(sub LL)(sup rb) over an ensemble of model storms characterized by different (but statistically equivalent) sets of substorm-onset times.

Chen, Margaret W.; Schulz, Michael; Lyons, Larry R.; Gorney, David J.

1992-01-01

298

Nonlinear drift-diffusion model of gating in K and nACh ion channels  

NASA Astrophysics Data System (ADS)

The configuration of a sensor regulates the transition between the closed and open states of both voltage and ligand gated channels. The closed state dwell-time distribution f(t) derived from a Fokker Planck equation with a nonlinear diffusion coefficient is in good agreement with experimental data and can account for the power law approximation to f(t) for a delayed rectifier K channel and a nicotinic acetylcholine (nACh) ion channel. The solution of a master equation which approximates the Fokker Planck equation provides a better description of the small time behaviour of the dwell-time distribution and can account for the empirical rate-amplitude correlation for these ion channels.

Vaccaro, S. R.

2007-09-01

299

Apparent electrostatic ion cyclotron waves in the diffuse aurora  

NASA Technical Reports Server (NTRS)

Emissions that have properties consistent with electrostatic ion cyclotron (EIC) waves have been observed at low altitude in the diffuse aurora by a sounding rocket payload. Peaks were observed in the power spectrum of the electric field near the hydrogen and oxygen ion cyclotron frequencies. Doppler shift and polarization analyses have been performed using EIC wave parameters derived from linear theory. Both analyses indicated that these emissions had properties consistent with those expected for H(+) and O(+) EIC waves. The two analyses indicated that both emission bands were due to waves propagating eastward parallel to the poleward boundary of the diffuse aurora. The large local cold plasma density and resulting Landau damping require that the source be local. Magnetometer data indicated the presence of a downward parallel current density of 5 microamps/sq m. Sufficient free energy for the waves was available from this current, although the waves were observed frequently at altitudes where the ion-neutral collision frequency exceeded the oxygen cyclotron frequency.

Bering, E. A.

1983-01-01

300

Electron-Ion Recombination Rate Coefficient Measurements in a Flowing Afterglow Plasma  

NASA Technical Reports Server (NTRS)

The flowing-afterglow technique in conjunction with computer modeling of the flowing plasma has been used to determine accurate dissociative-recombination rate coefficients alpha for the ions O2(+), HCO(+), CH5(+), C2H5(+), H3O(+), CO2(+), HCO2(+), HN2O(+), and N2O(+) at 295 K. We find that the simple form of data analysis that was employed in earlier experiments was adequate and we largely confirm earlier results. In the case of HCO(+) ions, published coefficients range from 1.1 X 10(exp -7) to 2.8 x 10(exp -7) cu cm/S, while our measurements give a value of 1.9 x 10(exp -7) cu cm/S.

Gougousi, Theodosia; Golde, Michael F.; Johnsen, Rainer

1996-01-01

301

Evaluation of Moisture-Related Attenuation Coefficient and Water Diffusion Velocity in Human Skin Using Optical Coherence Tomography  

PubMed Central

In this study, time-resolved optical coherence tomography (OCT) scanning images of the process of water diffusion in the skin that illustrate the enhancement in the backscattered intensities due to the increased water concentration are presented. In our experiments, the water concentration in the skin was increased by soaking the hand in water, and the same region of the skin was scanned and measured with the OCT system and a commercial moisture monitor every three minutes. To quantitatively analyze the moisture-related optical properties and the velocity of water diffusion in human skin, the attenuation coefficients of the skin, including the epidermis and dermis layers, were evaluated. Furthermore, the evaluated attenuation coefficients were compared with the measurements made using the commercial moisture monitor. The results demonstrate that the attenuation coefficient increases as the water concentration increases. Furthermore, by evaluating the positions of center-of mass of the backscattered intensities from OCT images, the diffusion velocity can be estimated. In contrast to the commercial moisture monitor, OCT can provide three-dimensional structural images of the skin and characterize its optical property, which together can be used to observe morphological changes and quantitatively evaluate the moisture-related attenuation coefficients in different skin layers. PMID:23529149

Lee, Cheng-Kuang; Tsai, Meng-Tsan; Chang, Feng-Yu; Yang, Chih-Hsun; Shen, Su-Chin; Yuan, Ouyang; Yang, Chih-He

2013-01-01

302

Measuring the ratio of aqueous diffusion coefficients between 6Li +Cl - and 7Li +Cr - by osmometry  

NASA Astrophysics Data System (ADS)

Osmotic equilibrium is a singular occurrence in the evolution of an osmotic cell because at this event the net solution flux is zero such that -J w · V¯w = J s · V¯s. At this juncture, the diffusion coefficient of the solute through the membrane (?) equals the solute flux ( Js) divided by the osmotic pressure (??). Because the solute permeability coefficient (?) is related to the Fickian diffusion coefficient ( D) through the gas constant, temperature, and the membrane's thickness and tortuosity, the ratio of ? values for individual isotopic species equals the ratio of D values for the same isotopic components. A 0.9450 molal LiCl solution was placed within sealed dialysis tubing and osmoted against a kilogram of deionized water at 22°C. Osmotic equilibrium occurred at 164 ± 10 min. The ratio of ?6Li +Cl -/?7Li +Cl - was measured to be 1.011 ± 0.003 - a value close to the square root of the mass ratio between 7LiCl and 6LiCl (= 1.012) as calculated by Graham's Law. The measured diffusion coefficient ratio was used to predict the degree of hyperfiltration-induced fractionation of Li isotopes as a function of membrane ideality. When a membrane's ? exceeds 0.95 (as is likely for low-porosity shales) the 6Li /7Li ratio on the high-pressure side of the membrane can theoretically vary by more than 0.0017.

Fritz, Steven J.

1992-10-01

303

Determination of relative ion chamber calibration coefficients from depth-ionization measurements in clinical electron beams  

NASA Astrophysics Data System (ADS)

A method is presented to obtain ion chamber calibration coefficients relative to secondary standard reference chambers in electron beams using depth-ionization measurements. Results are obtained as a function of depth and average electron energy at depth in 4, 8, 12 and 18 MeV electron beams from the NRC Elekta Precise linac. The PTW Roos, Scanditronix NACP-02, PTW Advanced Markus and NE 2571 ion chambers are investigated. The challenges and limitations of the method are discussed. The proposed method produces useful data at shallow depths. At depths past the reference depth, small shifts in positioning or drifts in the incident beam energy affect the results, thereby providing a built-in test of incident electron energy drifts and/or chamber set-up. Polarity corrections for ion chambers as a function of average electron energy at depth agree with literature data. The proposed method produces results consistent with those obtained using the conventional calibration procedure while gaining much more information about the behavior of the ion chamber with similar data acquisition time. Measurement uncertainties in calibration coefficients obtained with this method are estimated to be less than 0.5%. These results open up the possibility of using depth-ionization measurements to yield chamber ratios which may be suitable for primary standards-level dissemination.

Muir, B. R.; McEwen, M. R.; Rogers, D. W. O.

2014-10-01

304

An evaluation of ferrihydrite- and Metsorb™-DGT techniques for measuring oxyanion species (As, Se, V, P): effective capacity, competition and diffusion coefficients.  

PubMed

This study investigated several knowledge gaps with respect to the diffusive gradients in thin films (DGT) technique for measurement of oxyanions (As(III), As(V), Se(IV), Se(VI), PO4(3-), and V(V)) using the ferrihydrite and Metsorb™ binding layers. Elution efficiencies for each binding layer were higher with 1:20 dilutions, as analytical interferences for ICP-MS were minimised. Diffusion coefficients measured by diffusion cell and by DGT time-series experiments were found to agree well and generally agreed with previously reported values, although a range of diffusion coefficients have been reported for inorganic As and Se species. The relative binding affinity for both ferrihydrite and Metsorb™ was PO4(3-) ? As(V)>V(V) ? As(III)>Se(IV) > Se(VI) and effective binding capacities were measured in single ion solutions, and spiked synthetic freshwater and seawater, advising practical decisions about DGT monitoring. Under the conditions tested the performance of both ferrihydrite and Metsorb™ binding layers was directly comparable for As(V), As(III) Se(IV), V(V) and PO4(3-) over a deployment spanning ? 2 days for both freshwater and seawater. In order to return quantitative data for several analytes we recommend that the DGT method using either ferrihydrite or Metsorb™ be deployed for a maximum of 2 days in marine waters likely to contain high levels of the most strongly adsorbing oxyanions contaminants. The high pH, the competitive ions present in seawater and the identity of co-adsorbing ions affect the capacity of each binding layer for the analytes of interest. In freshwaters, longer deployment times can be considered but the concentration and identity of co-adsorbing ions may impact on quantitative uptake of Se(IV). This study found ferrihydrite-DGT outperformed Metsorb-DGT while previous studies have found the opposite, with variation in binding materials masses used being a likely reason. Clearly, preparation of both binding layers should always be optimised to produce the highest capacity possible, especially for seawater deployments. PMID:24216197

Price, Helen L; Teasdale, Peter R; Jolley, Dianne F

2013-11-25

305

Measurement of Binary Diffusion Coefficients for Neon-Argon Gas Mixtures Using a Loschmidt Cell Combined with Holographic Interferometry  

NASA Astrophysics Data System (ADS)

The paper reports on experimental binary diffusion coefficient data of neon-argon gas mixtures. Measurements were performed in the temperature range between 293.15 K and 333.15 K and for pressures between 1 bar and 10 bar over almost the whole composition range using a Loschmidt diffusion cell combined with holographic interferometry. The thermostated Loschmidt cell is divided into two half-cells, which can be separated and connected by a sliding plate. Prior to the measurements, two different pure gases are filled into the two half-cells. After starting the diffusion process, the temporal change of the partial molar densities, or rather of the refractive index of the gases, is detected in both half-cells using two holographic interferometers. With this apparatus, the temperature, pressure, and concentration dependence of the binary diffusion coefficient can be determined. The relative uncertainty of a diffusion measurement is between 0.4 % and 1.4 % depending on the pressure. The experimental data are compared with data from the literature and with new theoretical data based on quantum-mechanical ab initio calculations combined with the kinetic theory of gases. Due to a systematic error, the concentration dependence determined in the upper half-cell shows deviations from the theoretical values and from most of the literature data. The concentration, temperature, and pressure dependence obtained from the data from the lower half-cell, however, are in very good agreement with available data. The product of the binary gas diffusion coefficient and the molar density of the gas mixture shows no significant dependence on pressure for the studied neon-argon noble gas system.

Kugler, T.; Jäger, B.; Bich, E.; Rausch, M. H.; Fröba, A. P.

2013-01-01

306

Fusion product measurements of the local ion thermal diffusivity in the PLT tokamak  

SciTech Connect

Measurement of the gradient of the d-d fusion rate profile in an ohmic PLT plasma is used to deduce the gradient of the ion temperature and, thus, the local ion thermal diffusivity through an energy balance analysis. The inferred ion diffusivity is consistent with neoclassical theory.

Heidbrink, W.W.; Lovberg, J.; Strachan, J.D.; Bell, R.E.

1986-03-01

307

Conductivity noise in transmembrane ion channels due to ion concentration fluctuations via diffusion.  

PubMed Central

A Green's function approach is developed from first principles to evaluate the power spectral density of conductance fluctuations caused by ion concentration fluctuations via diffusion in an electrolyte system. This is applied to simple geometric models of transmembrane ion channels to obtain an estimate of the magnitude of ion concentration fluctuation noise in the channel current. Pure polypeptide alamethicin forms stable ion channels with multiple conductance states in artificial phospholipid bilayers isolated onto tips of micropipettes with gigaohm seals. In the single-channel current recorded by voltage-clamp techniques, excess noise was found after the background instrumental noise and the intrinsic Johnson and shot noises were removed. The noise que to ion concentration fluctuations via diffusion was isolated by the dependence of the excess current noise on buffer ion concentration. The magnitude of the concentration fluctuation noise derived from experimental data lies within limits estimated using our simple geometric channel models. Variation of the noise magnitude for alamethicin channels in various conductance states agrees with theoretical prediction. PMID:9138563

Mak, D O; Webb, W W

1997-01-01

308

Molecular and Thermal Diffusion Coefficients of Alkane-Alkane and Alkane-Aromatic Binary Mixtures: Effect of Shape and Size of Molecules  

E-print Network

Molecular and Thermal Diffusion Coefficients of Alkane-Alkane and Alkane-Aromatic Binary Mixtures decane-normal alkanes and methylnaphthalene-normal alkanes are measured at atmospheric pressure and T ) 25 °C. The normal alkanes used in this work include nC5-nC20. Thermal diffusion coefficients were

Firoozabadi, Abbas

309

An Alternate Solution of Fluorescence Recovery Kinetics after Spot-Bleaching for Measuring Diffusion Coefficients. 2. Diffusion of Fluorescein in Aqueous Sucrose Solutions  

Microsoft Academic Search

The traditional analysis of the fluorescence recovery kinetics after spot bleaching yields expressions for the diffusion coefficient\\u000a of the probe that are not suitable for linear fittings. In a previous work we developed an improved recovery function that\\u000a is a better alternative for data analysis. To illustrate its application to real cases and compare it with the previous data\\u000a treatment,

H. R. Corti; G. A. Frank; M. C. Marconi

2008-01-01

310

Unraveling the behavior of the individual ionic activity coefficients on the basis of the balance of ion-ion and ion-water interactions  

E-print Network

We investigate the individual activity coefficients of pure 1:1 and 2:1 electrolytes using our theory that is based on the competition of ion-ion (II) and ion-water (IW) interactions (Vincze et al., J. Chem. Phys. 133, 154507, 2010). The II term is computed from Grand Canonical Monte Carlo simulations on the basis of the implicit solvent model of electrolytes using hard sphere ions with Pauling radii. The IW term is computed on the basis of Born's treatment of solvation using experimental hydration free energies. The two terms are coupled through the concentration-dependent dielectric constant of the electrolyte. With this approach we are able to reproduce the nonmonotonic concentration dependence of the mean activity coefficient of pure electrolytes qualitatively without using adjustable parameters. In this paper, we show that the theory can provide valuable insight into the behavior of individual activity coefficients too. We compare our theoretical predictions against experimental data measured by electrochemical cells containing ion-specific electrodes. As in the case of the mean activity coefficients, we find good agreement for 2:1 electrolytes, while the accuracy of our model is worse for 1:1 systems. This deviation in accuracy is explained by the fact that the two competing terms (II and IW) are much larger in the 2:1 case so errors in the two separate terms have less effects. The difference of the excess chemical potentials of cations and anions (the ratio of activity coefficients) is determined by asymmetries in the properties of the two ions: charge, radius, and hydration free energies.

Mónika Valiskó; Dezs? Boda

2014-09-15

311

Radiation Belt Radial Diffusion Coefficients Derived From Ground-based and In-situ ULF Wave Measurements  

NASA Astrophysics Data System (ADS)

Ultra Low Frequency (ULF) wave power in the Pc5 period band is thought to play an important role in the dynamics, acceleration and transport of energetic electrons in the outer radiation belt. Current estimates of radial diffusion coefficients are typically derived empirically and characterised in terms of Kp. Using the results from a statistical analysis of ground-based and in-situ electric- and magnetic field power spectral densities as a function of solar wind speed, MLT and L-shell we compile statistical representations for the transport under a diffusive approximation. Electric diffusion rates are calculated using ground-based data from the CARISMA magnetometer network and mapped into in-situ equatorial electric fields using the Ozeke et al. [2009] model. These diffusion rates are compared to those derived from the THEMIS satellites and from previously published CRRES estimates. We find an excellent comparison between the ground-based estimates and in-situ observations. Interestingly the ground-based Pc5 power spectra show evidence of mHz spectral power peaks consistent with those observed on CRRES, and consistent with a role for field line resonances in radial diffusion. We further calculate the magnetic diffusion coefficients using data from THEMIS and GOES, and compare with previous AMPTE estimates. Overall such analysis provides a wave power based method for calculating diffusive transport using observed wave fields. Future in-situ radiation belt missions such as the Canadian Space Agency Outer Radiation Belt Injection, Transport, Acceleration and Loss Satellite (ORBITALS) will enable these physics-based models to be tested and will provide an excellent complement to the single point measurements available from the satellites.

Mann, I. R.; Rae, J.; Ozeke, L.; Murphy, K. R.; Milling, D. K.; Chan, A. A.; Elkington, S. R.

2010-12-01

312

The effect on the radon diffusion coefficient of long-term exposure of waterproof membranes to various degradation agents.  

PubMed

Waterproofing, usually made of bitumen or polymers with various additives, is used to protect buildings mainly against dampness, but also against radon transported from the soil beneath the building. The radon diffusion coefficient is a material property which is considered to be strongly influenced by the inner structure (chemical composition, crystallinity) of a measured sample. We have used this parameter together with measurements of mechanical properties (hardness, tensile strength, elongation at break, etc.) and FTIR spectroscopy has been used in order to describe the changes in material properties induced by long-term degradation. This paper summarizes the results of radon diffusion coefficient measurements of waterproof materials exposed to radon, soil bacteria, high temperature and combinations of these factors. We have discovered changes as high as 83 % have been discovered compared to virgin samples. PMID:24748486

Navrátilová Rovenská, Katerina

2014-07-01

313

Ab initio screening of lithium diffusion rates in transition metal oxide cathodes for lithium ion batteries  

E-print Network

A screening metric for diffusion limitations in lithium ion battery cathodes is derived using transition state theory and common materials properties. The metric relies on net activation barrier for lithium diffusion. ...

Moore, Charles J. (Charles Jacob)

2012-01-01

314

Lateral diffusion coefficients of phospholipids in spherical bilayers on a solid support measured by 2resonance relaxation  

Microsoft Academic Search

An alternative nuclear-magnetic-resonance (NMR) method for the measurement of the lateral diffusion coefficient D of phospholipids along the plane of a spherical bilayer on a solid support is presented. D values are determined at various temperatures for palmitoyl-oleoyl-phosphatidylcholine (POPC) bilayer on a spherical silica support of 640 nm diameter. The method is based upon the measurement of the quadrupolar transverse

Thomas Köchy; Thomas M. Bayerl

1993-01-01

315

Effective Scattering Coefficient of the Cerebral Spinal Fluid in Adult Head Models for Diffuse Optical Imaging  

E-print Network

Optical Imaging Anna Custo1,2 , William M. Wells III1,3 , Alex H. Barnett2 , Elizabeth M.C. Hillman2 inversion for functional Diffuse Optical Imaging (DOI) of the brain. The diffusion approximation to photon this in detail using Monte Carlo simulation of the RTE in a three-dimensional head model based on clinical MRI

Barnett, Alex

316

Apparent Diffusion Coefficients in the Evaluation of High-grade Cerebral Gliomas  

Microsoft Academic Search

BACKGROUND AND PURPOSE: Preliminary data indicate that apparent diffusion coeffi- cient (ADC) values may be useful in identifying and grading primary cerebral tumors. We tested the hypothesis that ADC values can be used to differentiate tumor, edema, and normal brain tissue. METHODS: Fifteen patients with high-grade cerebral astrocytomas underwent conventional MR imaging, diffusion-weighted MR imaging, and proton MR spectroscopy. We

Mauricio Castillo; J. Keith Smith; Lester Kwock; Kathy Wilber

317

First-order virial expansion of short-time diffusion and sedimentation coefficients of permeable particles suspensions  

E-print Network

For suspensions of permeable particles, the short-time translational and rotational self-diffusion coefficients, and collective diffusion and sedimentation coefficients are evaluated theoretically. An individual particle is modeled as a uniformly permeable sphere of a given permeability, with the internal solvent flow described by the Debye-Bueche-Brinkman equation. The particles are assumed to interact non-hydrodynamically by their excluded volumes. The virial expansion of the transport properties in powers of the volume fraction is performed up to the two-particle level. The first-order virial coefficients corresponding to two-body hydrodynamic interactions are evaluated with very high accuracy by the series expansion in inverse powers of the inter-particle distance. Results are obtained and discussed for a wide range of the ratio, x, of the particle radius to the hydrodynamic screening length inside a permeable sphere. It is shown that for x >= 10, the virial coefficients of the transport properties are well-approximated by the hydrodynamic radius (annulus) model developed by us earlier for the effective viscosity of porous-particle suspensions.

Bogdan Cichocki; Maria L. Ekiel-Jezewska; G. Naegele; E. Wajnryb

2011-01-23

318

Multi-system repeatability and reproducibility of apparent diffusion coefficient measurement using an ice-water phantom  

PubMed Central

Purpose Quantitative quality control procedures were sought to evaluate technical variability in multi-center measurements of the diffusion coefficient of water as a prerequisite to use of the biomarker apparent diffusion coefficient (ADC) in multi-center clinical trials. Materials and Methods A uniform data acquisition protocol was developed and shared with 18 participating test sites along with a temperature-controlled diffusion phantom delivered to each site. Usable diffusion weighted imaging data of ice water at 5 b-values were collected on 35 clinical MRI systems from 3 vendors at 2 field strengths (1.5 and 3T) and analyzed at a central processing site. Results Standard deviation of bore-center ADCs measured across 35 scanners was <2%; error range: ?2% to +5% from literature value. Day-to-day repeatability of the measurements was within 4.5%. Intra-exam repeatability at the phantom center was within 1%. Excluding one outlier, inter-site reproducibility of ADC at magnet isocenter was within 3%, though variability increased for off-center measurements. Significant (>10%) vendor-specific and system-specific spatial non-uniformity ADC bias was detected for the off-center measurement that was consistent with gradient non-linearity. Conclusion Standardization of DWI protocol has improved reproducibility of ADC measurements and allowed identifying spatial ADC non-uniformity as a source of error in multi-site clinical studies. PMID:23023785

Malyarenko, Dariya; Galban, Craig J.; Londy, Frank J.; Meyer, Charles R.; Johnson, Timothy D.; Rehemtulla, Alnawaz; Ross, Brian D.; Chenevert, Thomas L.

2012-01-01

319

Diffusion coefficients and local structure in basic molten fluorides: in situ NMR measurements and molecular dynamics simulations.  

PubMed

The local structure and the dynamics of molten LiF-KF mixtures have been studied by nuclear magnetic resonance (NMR) and molecular dynamics simulations. We have measured and calculated the self-diffusion coefficients of fluorine, lithium and potassium across the full composition range around the liquidus temperature and at 1123 K. Close to the liquidus temperature, D(F), D(Li) and D(K) change with composition in a way that mimics the phase diagram shape. At 1123 K D(F), D(Li) and D(K) depend linearly on the LiF molar fraction. These results show that the composition affects the self-diffusion of anions and cations more weakly than the temperature. The activation energy for diffusion was also determined and its value can be correlated with the strength of the anion-cation interaction in molten fluoride salts. PMID:20024421

Sarou-Kanian, Vincent; Rollet, Anne-Laure; Salanne, Mathieu; Simon, Christian; Bessada, Catherine; Madden, Paul A

2009-12-28

320

An evaluation of energy-independent heavy ion transport coefficient approximations  

NASA Technical Reports Server (NTRS)

Utilizing a one-dimensional transport theory for heavy ion propagation, evaluations of typical energy-dependent transport coefficient approximations are made by comparing theoretical depth-dose predictions to published experimental values for incident 670 MeV/nucleon Ne-20 beams in water. Results are presented for cases where the input nuclear absorption cross sections, or input fragmentation parameters, or both, are fixed. The lack of fragment charge and mass concentration resulting from the use of Silberberg-Tsao fragmentation parameters continues to be the main source of disagreement between theory and experiment.

Townsend, L. W.; Wilson, J. W.

1988-01-01

321

Measurements of the diffusion coefficient of silver 110-m in a nuclear grade graphite  

E-print Network

in HTGRs. . . II. B Cesium Research. II. C Silver Research. 5 6 8 II. C. 1 Recognition of Importance of 110 m Ag II. C. 2 Current Work on 110 m Ag Diffusion in Structural Graphites. . . . . . . . . . . II. D Diffusion Theory. 10 10 II. D. 1... half life and temperature. I. B. 3 Genera' Atomics Silver Diffusion ~pro ram 110 m Cesium and Ag are considered to be the most important metallic fission products released from HTGRs. Core design calcula- tions have indicated that the largest...

McMillan, Thad Calhoun

2012-06-07

322

Diffusion-Weighted MRI: Influence of Intravoxel Fat Signal and Breast Density on Breast Tumor Conspicuity and Apparent Diffusion Coefficient Measurements  

PubMed Central

Promising recent investigations have shown that breast malignancies exhibit restricted diffusion on diffusion-weighted imaging (DWI) and may be distinguished from normal tissue and benign lesions in the breast based on differences in apparent diffusion coefficient (ADC) values. In this study, we assessed the influence of intravoxel fat signal on breast diffusion measures by comparing ADC values obtained using a diffusion-weighted single shot fast spin echo sequence with and without fat suppression. The influence of breast density on ADC measures was also evaluated. ADC values were calculated for both tumor and normal fibroglandular tissue in a group of twenty-one women with diagnosed breast cancer. There were systematic underestimations of ADC for both tumor and normal breast tissue due to intravoxel contribution from fat signal on non-fat-suppressed DWI. This ADC underestimation was more pronounced for normal tissue values (mean difference = 40%) than for tumors (mean difference = 27%, p<0.001) and was worse in women with low breast tissue density versus those with extremely dense breasts (p<0.05 for both tumor and normal tissue). Tumor conspicuity measured by contrast-to-noise ratio was significantly higher on ADC maps created with fat suppression and was not significantly associated with breast density. In summary, robust fat suppression is important for accurate breast ADC measures and optimal lesion conspicuity on DWI. PMID:21920686

Partridge, Savannah C.; Singer, Lisa; Sun, Ryan; Wilmes, Lisa J.; Klifa, Catherine; Lehman, Constance D.; Hylton, Nola M.

2011-01-01

323

Calculation of diffusion coefficients of water and alkanes through single-walled carbon nanotubes from simulations  

SciTech Connect

Recent experimental work has shown that membranes containing aligned carbon nanotubes exhibit transport rates for gases and liquids that are orders of magnitude larger than rates predicted from Knudsen or hydrodynamic no-slip flow. We present atomically detailed simulations of diffusion of water and alkanes through single-walled carbon nanotubes. The self, corrected, and transported diffusivities are calculated for liquid-like densities of water and alkanes in nanotubes using equilibrium molecular dynamics, with thermodynamic correction factors computed from Monte Carlo adsorption isotherm calculations. We also present the zero-coverage diffusivities for these fluids. We discuss the results in comparison with bulk fluid self-diffusivities and experimental data for flow through nanotubes membranes.

Johnson, J.K.; Wang, Y.; Liu, J.-C.; Sholl, D.S.

2007-08-01

324

Upscaling methods for a class of convection diffusion equations with highly oscillating coefficients  

NASA Astrophysics Data System (ADS)

This paper investigates the upscaling method to the following parabolic equation: ?tc+?·(uc)-?·(D?c)=f(x,t), which stems from the application of solute transport in porous media. Because of the highly oscillating permeability of the porous media, the Darcy velocity u hence the dispersion tensor D has many scales with high contrasts. Thus, how to calculate the macro-scale equivalent coefficients of the above equation becomes the target of this paper. A new upscaling method is proposed and studied via comparing with another upscaling method which was proposed in [Z. Chen, W. Deng, H. Ye, Discrete Contin. Dyn. Syst. 13 (2005), 941-960]. The two different equivalent coefficients computing formulations are based on the solutions of two different cell (local) problems, which one utilizes the elliptic operator with terms of all orders while the other only uses the second order term. Error estimates between the equivalent coefficients and the homogenized coefficients are given under the assumption that the oscillating coefficients are periodic (which is not required by the method). Numerical experiments are carried out for the periodic coefficients to demonstrate the accuracy of the proposed method. Moreover, the upscaling method is applied to solve the solute transport in a porous medium with a random log-normal relative permeability. The results show the efficiency and accuracy of the proposed method.

Deng, Weibing; Gu, Ji; Huang, Jianmin

2008-08-01

325

Water permeability and chloride ion diffusion in portland cement mortars: Relationship to sand content and critical pore diameter  

SciTech Connect

The pore structure of hydrated cement in mortar and concrete is quite different from that of neat cement paste. The porous transition zones formed at the aggregate-paste interfaces affect the pore size distribution. The effect of the sand content on the development of pore structure, the permeability to water, and the diffusivity of chloride ions was studied on portland cement mortars. Mortars of two water-to-cement ratios and three sand volume fractions were cast together with pastes and tested at degrees of hydration ranging from 45 to 70%. An electrically-accelerated concentration cell test was used to determine the coefficient of chloride ion diffusion while a high pressure permeability cell was employed to assess liquid permeability. The coefficient of chloride ion diffusion varied linearly with the critical pore radius as determined by mercury intrusion porosimetry while permeability was found to follow a power-law relationship vs. this critical radius. The data set provides an opportunity to directly examine the application of the Katz-Thompson relationship to cement-based materials.

Halamickova, P.; Detwiler, R.J. [Univ. of Toronto, Ontario (Canada). Dept. of Civil Engineering] [Univ. of Toronto, Ontario (Canada). Dept. of Civil Engineering; Bentz, D.P.; Garboczi, E.J. [National Inst. of Standards and Technology, Gaithersburg, MD (United States)] [National Inst. of Standards and Technology, Gaithersburg, MD (United States)

1995-05-01

326

Electron-Ion Recombination Rate Coefficients, Photoionization Cross Sections, and Ionization Fractions for Astrophysically Abundant Elements. II. Oxygen Ions  

NASA Astrophysics Data System (ADS)

A comprehensive and self-consistent set of new atomic data for photoionization cross sections, ?PI, and total unified recombination rate coefficients, ?R(T), of oxygen ions are obtained. The calculations are carried out in the close coupling approximation employing the R-matrix method. The unified treatment of total recombination includes both the radiative and dielectronic processes. The analysis of astrophysical spectra and ionization balance requires atomic data for all ionization stages of an element, and the accuracy depends on the self-consistency and completeness of data. In the present work the criterion of self-consistency between the rates for the inverse processes of photoionization and recombination is satisfied in an ab initio manner by employing an identical set of eigenfunction expansions in the calculations for both atomic processes. State-specific recombination rate coefficients are also presented for a large number of bound states. As a first application, the present ?R(T) are used to obtain ionization fractions of oxygen ions in plasmas in coronal equilibrium. Ionization fractions in photoionization equilibrium can be readily obtained by employing the present data for the total ?PI and for?R(T).

Nahar, Sultana N.

1999-01-01

327

Relationship Between Apparent Diffusion Coefficient and Subsequent Hemorrhagic Transformation Following Acute Ischemic Stroke  

Microsoft Academic Search

Background and Purpose—A method for identifying patients at increased risk for developing secondary hemorrhagic transformation (HT) after acute ischemic stroke could be of significant value, particularly in patients being considered for thrombolytic therapy. We hypothesized that diffusion-weighted MRI might aid in the identification of such patients. Methods—We retrospectively analyzed 17 patients with ischemic stroke who received diffusion-weighted MRI within 8

David C. Tong; Alessandro Adami; Michael E. Moseley; Michael P. Marks

2010-01-01

328

A comparision of laboratory and field based determinations of molecular diffusion coefficients in a low permeability geologic medium.  

PubMed

Molecular diffusion is the dominant transport mechanism for contaminants in many saturated clay-rich aquitards. The effective coefficient of diffusion (Da) is traditionally determined by conducting laboratory tests on cm-scale core samples that may not be representative of the bulk geologic formation. Here we conducted the first long-term field based in situ diffusion experimentto compare the effect of experimental scale (5 x 10(-5) m3 in the diffusion cells and (5-20) x 10(-2) m3 in the in situ experiments) on De values for clay-rich aquitards. Using a conservative tracer (deuterium), our testing shows De values estimated from in situ testing ((2.5-3.5) x 10(-10) m2 s(-1)) are similar but lower than the average De values measured in the laboratory (4 x 10(-10) m2 s(-1)). The difference was attributed to greater porosity values in the laboratory samples resulting from core barrel extrusion and sample swelling. With representative core sampling and care, laboratory-based diffusion testing remains a viable method to assess solute transport mechanisms in clay aquitards. PMID:19764242

Hendry, M Jim; Barbour, S Lee; Boldt-Leppin, Brigitte E J; Reifferscheid, Laura J; Wassenaar, Leonard I

2009-09-01

329

Effects of casein and fat content on water self-diffusion coefficients in casein systems: a pulsed field gradient nuclear magnetic resonance study.  

PubMed

The water self-diffusion coefficients in casein matrixes were measured using a pulsed field gradient spin-echo nuclear magnetic resonance technique (PFG-SE NMR). The dependence of the water self-diffusion coefficient on the casein concentration and the aqueous phase composition is reported in both a rehydrated native phosphocaseinate dispersion and a concentrated casein retentate. A model has been proposed to explain the different behavior of the water self-diffusion coefficient in the two casein systems. This model demonstrates that the water self-diffusion cannot be simply explained by the water content only. So, taking into account the specific effect of each constituent of the aqueous dispersing phase, the water self-diffusion reduction induced by the casein micelle can be modeled. The effect of fat on the water self-diffusion coefficients was investigated. Anhydrous milk fat-reconstituted retentate samples were used in order to estimate the obstruction effect of fat globules in the modeling process. The dependence of the self-diffusion coefficient of water on the fat and casein content is reported. A general model included the effect of the aqueous phase composition, and the obstruction effects of casein micelles and fat globules were proposed. This model was validated for water self-diffusion coefficients in industrial fatty retentates. PMID:15186127

Métais, Angélique; Cambert, Mireille; Riaublanc, Alain; Mariette, François

2004-06-16

330

Measurement of Soret and Fickian diffusion coefficients by orthogonal phase-shifting interferometry and its application to protein aqueous solutions  

NASA Astrophysics Data System (ADS)

We have developed a method to measure thermodiffusion and Fickian diffusion in transparent binary solutions. The measuring instrument consists of two orthogonally aligned phase-shifting interferometers coupled with a single rotating polarizer. This high-resolution interferometer, initially developed to measure isothermal diffusion coefficients in liquid systems [J. F. Torres, A. Komiya, E. Shoji, J. Okajima, and S. Maruyama, Opt. Lasers Eng. 50, 1287 (2012)], was modified to measure transient concentration profiles in binary solutions subject to a linear temperature gradient. A convectionless thermodiffusion field was created in a binary solution sample that is placed inside a Soret cell. This cell consists of a parallelepiped cavity with a horizontal cross-section area of 10 × 20 mm2, a variable height of 1-2 mm, and transparent lateral walls. The small height of the cell reduces the volume of the sample, shortens the measurement time, and increases the hydrodynamic stability of the system. An additional free diffusion experiment with the same optical apparatus provides the so-called contrast factors that relate the unwrapped phase and concentration gradients, i.e., the measurement technique is independent and robust. The Soret coefficient is determined from the concentration and temperature differences between the upper and lower boundaries measured by the interferometer and thermocouples, respectively. The Fickian diffusion coefficient is obtained by fitting a numerical solution to the experimental concentration profile. The method is validated through the measurement of thermodiffusion in the well-known liquid pairs of ethanol-water (ethanol 39.12 wt.%) and isobutylbenzene-dodecane (50.0 wt.%). The obtained coefficients agree with the literature values within 5.0%. Finally, the developed technique is applied to visualize biomolecular thermophoresis. Two protein aqueous solutions at 3 mg/ml were used as samples: aprotinin (6.5 kDa)-water and lysozyme (14.3 kDa)-water. It was found that the former protein molecules are thermophilic and the latter thermophobic. In contrast to previously reported methods, this technique is suitable for both short time and negative Soret coefficient measurements.

Torres, Juan F.; Komiya, Atsuki; Henry, Daniel; Maruyama, Shigenao

2013-08-01

331

Measuring the ratio of aqueous diffusion coefficients between [sup 6]Li[sup +]Cl[sup [minus  

SciTech Connect

Osmotic equilibrium is a singular occurrence in the evolution of an osmotic cell because at this event the net solution flux is zero such that [minus]J[sub w] [center dot] [bar V][sub w] = J[sub s] [center dot] [bar V][sub s]. At this juncture, the diffusion coefficient of the solute through the membrane ([omega]) equals the solute flux (J[sub s]) divided by the osmotic pressure ([delta]II). Because the solute permeability coefficient ([omega]) is related to the Fickian diffusion coefficient (D) through the gas constant, temperature, and the membrane's thickness and tortuosity, the ratio of [omega] values for individual isotopic species equals the ratio of D values for the same isotopic components. A 0.9450 molal LiCl solution was placed within sealed dialysis tubing and osmoted against a kilogram of deionized water at 22C. Osmotic equilibrium occurred at 164 [plus minus] 10 min. The ratio of [omega][sub [sup 6]Li[sup +]Cl[sup [minus

Fritz, S.J. (Purdue Univ., West Lafayette, IN (United States))

1992-10-01

332

On the air-filled effective porosity parameter of Rogers and Nielson's (1991) bulk radon diffusion coefficient in unsaturated soils.  

PubMed

The radon exhalation rate at the earth's surface from soil or rock with radium as its source is the main mechanism behind the radon activity concentrations observed in both indoor and outdoor environments. During the last two decades, many subsurface radon transport models have used Rogers and Nielson's formula for modeling the unsaturated soil bulk radon diffusion coefficient. This formula uses an "air-filled effective porosity" to account for radon adsorption and radon dissolution in the groundwater. This formula is reviewed here, and its hypotheses are examined for accuracy in dealing with subsurface radon transport problems. The author shows its limitations by comparing one dimensional steady-state analytical solutions of the two-phase (air/water) transport equation (Fick's law) with Rogers and Nielson's formula. For radon diffusion-dominated transport, the calculated Rogers and Nielson's radon exhalation rate is shown to be unrealistic as it is independent of the values of the radon adsorption and groundwater dissolution coefficients. For convective and diffusive transport, radon exhalation rates calculated using Fick's law and this formula agree only for high values of gas-phase velocity and groundwater saturation. However, these conditions are not usually met in most shallow subsurface environments where radon migration takes place under low gas phase velocities and low water saturation. PMID:24670909

Saâdi, Zakaria

2014-05-01

333

Inclusion compounds between ?-, ?- and ?-cyclodextrins: iron II lactate: a theoretical and experimental study using diffusion coefficients and molecular mechanics  

NASA Astrophysics Data System (ADS)

The inclusion compounds between iron II lactate and three different cyclodextrins (CDs) were studied by means of experimental and theoretical data. The importance of iron II in the human metabolism effort the necessity of a minimum concentration to the human life. Malnutrition is one great problem in social politics of many countries on the world. The possibility to the development of novel medicines with the iron II species stable look for an increase on the efficiency for this kind of aid. Kinetics measurements confirm the possibility to stop the oxidation reaction. It was the first indication of efficient molecular encapsulation. Diffusion coefficient measurements were carried out by Taylor-Aris diffusion technique. The decrease of diffusion coefficients measured for iron II lactate when alone and forming the inclusion complexes was obtained for all hosts molecules used. Molecular Mechanics calculations were performed to elucidate the perfect arrange of iron II lactate inside CDs cavity. No great differences were obtained to the binding energy for the different hosts. Using the software HyperChem6.03v MM+, AMBER94 and OPLS Forced Fields for iron atom in two chemical environments (a) vacuum and (b) with addition of 250 water molecules (MM+). The solvent treatment was decisive to the order of stability. This order was ?-CD>?-CD>?-CD, the same order of solubility in water. The results contained in this work confirm the possibility to protect iron II lactate against oxidation.

Leite, Rosiley A.; Lino, Antonio C. S.; Takahata, Yuji

2003-01-01

334

Average properties of the magnetic reconnection ion diffusion region in the Earth's magnetotail: The 20012005 Cluster  

E-print Network

Average properties of the magnetic reconnection ion diffusion region in the Earth's magnetotail (2010), Average properties of the magnetic reconnection ion diffusion region in the Earth's magnetotail; published 14 August 2010. [1] Magnetic reconnection plays a key role in the circulation of plasma through

California at Berkeley, University of

335

Measurement of Charge Transfer Rate Coefficient Between Ground-State N(2+) Ion and He at Electron-Volt Energies  

NASA Technical Reports Server (NTRS)

The charge transfer rate coefficient for the reaction N(2+)(2p(sup 2)P(sup 0)) + He yields products is measured by recording the time dependence of the N(2+) ions stored in an ion trap. A cylindrical radio-frequency ion trap was used to store N(2+) ions produced by laser ablation of a solid titanium nitride target. The decay of the ion signals was analyzed by single exponential least-squares fits to the data. The measured rate coefficient is 8.67(0.76) x 10(exp -11)sq cm/s. The N(2+) ions were at a mean energy of 2.7 eV while He gas was at room temperature, corresponding to an equivalent temperature of 3.9 x 10(exp 3) K. The measured value is in good agreement with a recent calculation.

Fang, Z.; Kwong, Victor H. S.

1997-01-01

336

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

E-print Network

by a negative power of the action and hence effectively uncorrelated for small actions, leading to a chaotic sea physics [8], while for = -1 a parti- cle bouncing on a vibrating plate [9] and closely related Chirikov, is effectively random, leading to strongly chaotic diffusion of J which can be described analyti- cally. Here we

Dettmann, Carl

337

Oxygen quantification methods and application to the determination of oxygen diffusion and solubility coefficients in food  

Microsoft Academic Search

Oxygen solubility and diffusivity in food are two key parameters to understand and quantify the impact of oxygen on food oxidation. A limiting step to the acquisition of these data is the availability and feasibility of methodologies to quantify oxygen content in food and especially in solid foods, even though some recent and significant progress has been made in this

C. Pénicaud; S. Peyron; N. Gontard; V. Guillard

2011-01-01

338

Oxygen Quantification Methods and Application to the Determination of Oxygen Diffusion and Solubility Coefficients in Food  

Microsoft Academic Search

Oxygen solubility and diffusivity in food are two key parameters to understand and quantify the impact of oxygen on food oxidation. A limiting step to the acquisition of these data is the availability and feasibility of methodologies to quantify oxygen content in food and especially in solid foods, even though some recent and significant progress has been made in this

C. Pénicaud; S. Peyron; N. Gontard; V. Guillard

2012-01-01

339

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

E-print Network

. It uses near-infrared light and has the advantage of low cost and portability. The success of DOI optical imaging Anna Custo, William M. Wells III, Alex H. Barnett, Elizabeth M. C. Hillman, and David A model is a key capability for performing accurate inversion for functional diffuse optical imaging

340

Experimental study of diffusion coefficients of water through the collagen: apatite porosity in human trabecular bone tissue.  

PubMed

We firstly measured the swelling of single trabeculae from human femur heads during water imbibition. Since the swelling is caused by water diffusing from external surfaces to the core of the sample, by measuring the sample swelling over time, we obtained direct information about the transport of fluids through the intimate constituents of bone, where the mineralization process takes place. We developed an apparatus to measure the free expansion of the tissue during the imbibition. In particular, we measured the swelling along three natural axes (length L, width W, and thickness T) of plate-like trabeculae. For this aim, we developed a 3D analytical model of the water uptake by the sample that was performed according to Fickian transport mechanism. The results were then utilized to predict the swelling over time along the three sample directions (L, W, T) and the apparent diffusion coefficients D T, D W, and D L. PMID:24967405

Marinozzi, Franco; Bini, Fabiano; Quintino, Alessandro; Corcione, Massimo; Marinozzi, Andrea

2014-01-01

341

Mass Transfer Modelling During Osmotic Dehydration of Jumbo Squid ( Dosidicus gigas ): Influence of Temperature on Diffusion Coefficients and Kinetic Parameters  

Microsoft Academic Search

Mathematical modelling was used to study the effect of process temperature on moisture and salt mass transfer during osmotic\\u000a dehydration (OD) of jumbo squid with 6% (w v\\u000a ?1) NaCl at 75, 85 and 95?°C. The diffusion coefficients for moisture and salt increased with temperature. Based on an Arrhenius-type\\u000a equation, activation energy values of 62.45 kJ mol?1 and 52.14 kJ mol?1 for moisture and

Elsa Uribe; Margarita Miranda; Antonio Vega-Gálvez; Issis Quispe; Rodrigo Clavería; Karina Di Scala

2011-01-01

342

Evaluating the diffusion coefficient of dopamine at the cell surface during amperometric detection: disk vs ring microelectrodes.  

PubMed

During exocytosis, small quantities of neurotransmitters are released by the cell. These neurotransmitters can be detected quantitatively using electrochemical methods, principally with disk carbon fiber microelectrode amperometry. An exocytotic event then results in the recording of a current peak whose characteristic features are directly related to the mechanisms of exocytosis. We have compared two exocytotic peak populations obtained from PC12 cells with a disk carbon fiber microelectrode and with a pyrolyzed carbon ring microelectrode array, with a 500 nm ring thickness. The specific shape of the ring electrode allows for precise analysis of diffusion processes at the vicinity of the cell membrane. Peaks obtained with a ring microelectrode array show a distorted average shape, owing to increased diffusion pathways. This result has been used to evaluate the diffusion coefficient of dopamine at the surface of a cell, which is up to an order of magnitude smaller than that measured in free buffer. The lower rate of diffusion is discussed as resulting from interactions with the glycocalyx. PMID:23706095

Trouillon, Raphaël; Lin, Yuqing; Mellander, Lisa J; Keighron, Jacqueline D; Ewing, Andrew G

2013-07-01

343

Estimation of the ion-stimulated desorption coefficient in the vacuum chamber of the U-70 proton synchrotron  

NASA Astrophysics Data System (ADS)

We propose a method for estimating the coefficient of ion-stimulated desorption in the vacuum chamber of the U-70 proton synchrotron by measuring the pressure difference for the main components of the residual gas in the chamber with and without a beam. The solutions to the equations describing the variation of hydrogen and nitrogen pressures are considered. The order of magnitude of the ion-stimulated desorption coefficient is determined for an accelerated carbon ion beam. The critical values of the coefficient are indicated. The experimental results are confirmed using various computational methods as well as by the graphs plotted in accordance with current measurements for magnetic-discharge (ion) pumps. The possible role of argon in desorption is considered.

Mirzoev, K. G.; Kiver, A. M.; Lapygin, V. G.; Larionov, A. V.

2014-02-01

344

A novel mathematical model considering change of diffusion coefficient for predicting dissolution behavior of acetaminophen from wax matrix dosage form.  

PubMed

From wax matrix dosage forms, drug and water-soluble polymer are released into the external solvent over time. As a consequence, the pore volume inside the wax matrix particles is increased and the diffusion coefficient of the drug is altered. In the present study, we attempted to derive a novel empirical mathematical model, namely, a time-dependent diffusivity (TDD) model, that assumes the change in the drug's diffusion coefficient can be used to predict the drug release from spherical wax matrix particles. Wax matrix particles were prepared by using acetaminophen (APAP), a model drug; glyceryl monostearate (GM), a wax base; and aminoalkyl methacrylate copolymer E (AMCE), a functional polymer that dissolves below pH 5.0 and swells over pH 5.0. A three-factor, three-level (3(3)) Box-Behnken design was used to evaluate the effects of several of the variables in the model formulation, and the release of APAP from wax matrix particles was evaluated by the paddle method at pH 4.0 and pH 6.5. When comparing the goodness of fit to the experimental data between the proposed TDD model and the conventional pure diffusion model, a better correspondence was observed for the TDD model in all cases. Multiple regression analysis revealed that an increase in AMCE loading enhanced the diffusion coefficient with time, and that this increase also had a significant effect on drug release behavior. Furthermore, from the results of the multiple regression analysis, a formulation with desired drug release behavior was found to satisfy the criteria of the bitter taste masking of APAP without lowering the bioavailability. That is to say, the amount of APAP released remains below 15% for 10 min at pH 6.5 and exceeds 90% within 30 min at pH 4.0. The predicted formulation was 15% APAP loading, 8.25% AMCE loading, and 400 ?m mean particle diameter. When wax matrix dosage forms were prepared accordingly, the predicted drug release behavior agreed well with experimental values at each pH level. Therefore, the proposed model is feasible as a useful tool for predicting drug release behavior, as well as for designing the formulation of wax matrix dosage forms. PMID:22405986

Nitanai, Yuta; Agata, Yasuyoshi; Iwao, Yasunori; Itai, Shigeru

2012-05-30

345

Optimal estimates of the diffusion coefficient of a single Brownian trajectory  

E-print Network

Modern developments in microscopy and image processing are revolutionizing areas of physics, chemistry and biology as nanoscale objects can be tracked with unprecedented accuracy. The goal of single particle tracking is to determine the interaction between the particle and its environment. The price paid for having a direct visualization of a single particle is a consequent lack of statistics. Here we address the optimal way of extracting diffusion constants from single trajectories for pure Brownian motion. It is shown that the maximum likelihood estimator is much more efficient than the commonly used least squares estimate. Furthermore we investigate the effect of disorder on the distribution of estimated diffusion constants and show that it increases the probability of observing estimates much smaller than the true (average) value.

Denis Boyer; David S. Dean; Carlos Mejía-Monasterio; Gleb Oshanin

2012-03-22

346

Strong Pitch-Angle Diffusion of Ring Current Ions in Geomagnetic Storm-Associated Conditions  

NASA Technical Reports Server (NTRS)

Do electromagnetic ion cyclotron (EMIC) waves cause strong pitch-angle diffusion of RC ions? This question is the primary motivation of this paper and has been affirmatively answered from the theoretical point of view. The materials that are presented in the Results section show clear evidence that strong pitch-angle diffusion takes place in the inner magnetosphere indicating an important role for the wave-particle interaction mechanism in the formation of RC ions and EMIC waves.

Khazanov, G. V.; Gamayunov, K. V.; Gallagher, D. L.; Spann, J. F.

2005-01-01

347

Diffusion Coefficients and Structure Properties in the Pluronic F127\\/n?C4H9OH\\/H2O System  

Microsoft Academic Search

Diffusion coefficients of different aggregates in aqueous solutions formed by an amphiphilic block copolymer, Pluronic F127 (F127), were determined by cyclic voltammetry, and the critical micelle concentration (CMC, 4.31 × 10 mol L) of F127 was obtained. The added n?butanol facilitates the formation of micelles from the monomers of F127 and makes the critical micelle temperature (CMT) of F127 solutions decrease. The diffusion coefficient

Yuanhua Ding; Ying Wang; Rong Guo

2003-01-01

348

Diffusion Coefficients and Structure Properties of Triton X-100\\/ nC6H13OH\\/H2O System  

Microsoft Academic Search

The diffusion coefficients of Triton X-100 micelles with different shape are determined by cyclic voltammetry without any probe. The first CMC (3.2 × 10 mol-L) and the second CMC (1.3 × 10 mol-L) of Triton X-100 micelles arc obtained, and the mechanism of electrochemical reaction for Triton X-100 is deduced, When n-hexanol is added, the diffusion coefficient of Triton X-100

Rong Guo; Yuanhua Ding; Tianqing Liu

2000-01-01

349

Influence of the electron cross-field diffusion in negative ion sources with the transverse magnetic field and the plasma-electrode bias.  

PubMed

The physical mechanisms involved in the extraction of H(-) ions from the negative ion source are studied with a PIC 2D3V code. The effect of a weak magnetic field transverse to the extraction direction is taken into account, along with a variable bias voltage applied on the plasma electrode (PE). In addition to previous modeling works, the electron diffusion across the magnetic field is taken into account as a simple one-dimensional random-walk process. The results show that without PE bias, the value of the diffusion coefficient has a significant influence upon the value of the extracted H(-) current. However, the value of this coefficient does not affect qualitatively the mechanism leading to the peak of extracted H(-) ion current observed for an optimum value of the PE bias. PMID:20192440

Kuppel, S; Matsushita, D; Hatayama, A; Bacal, M

2010-02-01

350

Absolute rate coefficients for photorecombination and electron-impact ionization of magnesium-like iron ions from measurements at a heavy-ion storage ring  

E-print Network

Rate coefficients for photorecombination (PR) and cross sections for electron-impact ionization (EII) of Fe$^{14+}$ forming Fe$^{13+}$ and Fe$^{15+}$, respectively, have been measured by employing the electron-ion merged-beams technique at a heavy-ion storage ring. Rate coefficients for PR and EII of Fe$^{14+}$ ions in a plasma are derived from the experimental measurements. Simple parametrizations of the experimentally derived plasma rate coefficients are provided for use in the modeling of photoionized and collisionally ionized plasmas. In the temperature ranges where Fe$^{14+}$ is expected to form in such plasmas the latest theoretical rate coefficients of Altun et al. [Astron. Astrophys. 474, 1051 (2007)] for PR and of Dere [Astron. Astrophys. 466, 771 (2007)] for EII agree with the experimental results to within the experimental uncertainties. Common features in the PR and EII resonance structures are identified and discussed.

Bernhardt, D; Grieser, M; Hahn, M; Krantz, C; Lestinsky, M; Novotný, O; Repnow, R; Savin, D W; Spruck, K; Wolf, A; Müller, A; Schippers, S

2014-01-01

351

Self-intermediate scattering function of strongly interacting three-dimensional lattice gases: Time- and wave-vector-dependent tracer diffusion coefficient  

NASA Astrophysics Data System (ADS)

We investigate the self-intermediate scattering function (SISF) in a three-dimensional (3D) cubic lattice fluid (interacting lattice gas) with attractive nearest-neighbor interparticle interactions at a temperature slightly above the critical one by means of Monte Carlo simulations. A special representation of SISF as an exponent of the mean tracer diffusion coefficient multiplied by the geometrical factor and time is considered to highlight memory effects that are included in time and wave-vector dependence of the diffusion coefficient. An analytical expression for the diffusion coefficient is suggested to reproduce the simulation data. It is shown that the particles' mean-square displacement is equal to the time integral of the diffusion coefficient. We make a comparison with the previously considered 2D system on a square lattice. The main difference with the two-dimensional case is that the time dependence of particular characteristics of the tracer diffusion coefficient in the 3D case cannot be described by exponentially decreasing functions, but requires using stretched exponentials with rather small values of exponents, of the order of 0.2. The hydrodynamic values of the tracer diffusion coefficient (in the limit of large times and small wave vectors) defined through SIFS simulation results agree well with the results of its direct determination by the mean-square displacement of the particles in the entire range of concentrations and temperatures.

Skarpalezos, Loukas; Argyrakis, Panos; Vikhrenko, Vyacheslav S.

2014-05-01

352

Extraction of Thermodynamic Data from Ternary Diffusion Coefficients of Lysozyme Chloride in Water and Aqueous Na$_2$SO$_4$  

E-print Network

This paper presents, for ternary lysozyme-Na$_2$SO$_4$-water system, the thermodynamic data extracted from the measured values of four ternary diffusion coefficients and the Onsager reciprocal relations. The calculation for derivatives of solute chemical potentials with respect to solute molar concentrations was made using the method presented in \\cite{1}. This method is applicable to systems in which the molar concentration of one solute is very small compared to that of the other, like in our case. The approach is illustrated for the lysozyme chloride-Na$_2$SO$_4$-water system at 25$^o$ C, pH 4.5 and at 0.6 mM (8.6 mg/mL) lysozyme chloride and 0.1, 0.25, 0.5, 0.65, and 0.8 M Na$_2$SO$_4$ concentrations. The calculated solute chemical potential derivatives were used to compute the protein cation charge approximately. We also compute the diffusion Onsager coefficients $(L_{ij})_o$ for each composition at pH 4.5.

Buzatu, D; Buzatu, F D; Albright, J G

2004-01-01

353

Quantitative full-colour transmitted light microscopy and dyes for concentration mapping and measurement of diffusion coefficients in microfluidic architectures.  

PubMed

A simple and versatile methodology has been developed for the simultaneous measurement of multiple concentration profiles of colourants in transparent microfluidic systems, using a conventional transmitted light microscope, a digital colour (RGB) camera and numerical image processing combined with multicomponent analysis. Rigorous application of the Beer-Lambert law would require monochromatic probe conditions, but in spite of the broad spectral bandwidths of the three colour channels of the camera, a linear relation between the measured optical density and dye concentration is established under certain conditions. An optimised collection of dye solutions for the quantitative optical microscopic characterisation of microfluidic devices is proposed. Using the methodology for optical concentration measurement we then implement and validate a simplified and robust method for the microfluidic measurement of diffusion coefficients using an H-filter architecture. It consists of measuring the ratio of the concentrations of the two output channels of the H-filter. It enables facile determination of the diffusion coefficient, even for non-fluorescent molecules and nanoparticles, and is compatible with non-optical detection of the analyte. PMID:22228225

Werts, Martinus H V; Raimbault, Vincent; Texier-Picard, Rozenn; Poizat, Rémi; Français, Olivier; Griscom, Laurent; Navarro, Julien R G

2012-02-21

354

Curious behaviour of the diffusion coefficient and friction force for the strongly inhomogeneous HMF model  

Microsoft Academic Search

.  We present first elements of kinetic theory appropriate\\u000a to the inhomogeneous phase of the Hamiltonian Mean Field (HMF)\\u000a model. In particular, we investigate the case of strongly\\u000a inhomogeneous distributions for T?0 and exhibit\\u000a curious behaviour of the force auto-correlation function and\\u000a friction coefficient. The temporal correlation function of the\\u000a force has an oscillatory behaviour which averages to zero over a

P. H. Chavanis

2006-01-01

355

Matrix diffusion coefficients in volcanic rocks at the Nevada test site: Influence of matrix porosity, matrix permeability, and fracture coating minerals  

NASA Astrophysics Data System (ADS)

Diffusion cell experiments were conducted to measure nonsorbing solute matrix diffusion coefficients in forty-seven different volcanic rock matrix samples from eight different locations (with multiple depth intervals represented at several locations) at the Nevada Test Site. The solutes used in the experiments included bromide, iodide, pentafluorobenzoate (PFBA), and tritiated water ( 3HHO). The porosity and saturated permeability of most of the diffusion cell samples were measured to evaluate the correlation of these two variables with tracer matrix diffusion coefficients divided by the free-water diffusion coefficient ( Dm/ D*). To investigate the influence of fracture coating minerals on matrix diffusion, ten of the diffusion cells represented paired samples from the same depth interval in which one sample contained a fracture surface with mineral coatings and the other sample consisted of only pure matrix. The log of ( Dm/ D*) was found to be positively correlated with both the matrix porosity and the log of matrix permeability. A multiple linear regression analysis indicated that both parameters contributed significantly to the regression at the 95% confidence level. However, the log of the matrix diffusion coefficient was more highly-correlated with the log of matrix permeability than with matrix porosity, which suggests that matrix diffusion coefficients, like matrix permeabilities, have a greater dependence on the interconnectedness of matrix porosity than on the matrix porosity itself. The regression equation for the volcanic rocks was found to provide satisfactory predictions of log( Dm/ D*) for other types of rocks with similar ranges of matrix porosity and permeability as the volcanic rocks, but it did a poorer job predicting log( Dm/ D*) for rocks with lower porosities and/or permeabilities. The presence of mineral coatings on fracture walls did not appear to have a significant effect on matrix diffusion in the ten paired diffusion cell experiments.

Reimus, Paul W.; Callahan, Timothy J.; Ware, S. Doug; Haga, Marc J.; Counce, Dale A.

2007-08-01

356

Molecular dynamics simulation of diffusion coefficients and structural properties of some alkylbenzenes in supercritical carbon dioxide at infinite dilution.  

PubMed

The binary infinite dilute diffusion coefficients, D??(?), of some alkylbenzenes (Ph-C(n), from Ph-H to Ph-C12) from 313 K to 333 K at 15 MPa in supercritical carbon dioxide (scCO2) have been studied by molecular dynamics (MD) simulation. The MD values agree well with the experimental ones, which indicate MD simulation technique is a powerful way to predict and obtain diffusion coefficients of solutes in supercritical fluids. Besides, the local structures of Ph-C(n)/CO2 fluids are further investigated by calculating radial distribution functions and coordination numbers. It qualitatively convinces that the first solvation shell of Ph-C(n) in scCO2 is significantly influenced by the structure of Ph-C(n) solute. Meanwhile, the mean end-to-end distance, the mean radius of gyration and dihedral angle distribution are calculated to gain an insight into the structural properties of Ph-C(n) in scCO2. The abnormal trends of radial distribution functions and coordination numbers can be reasonably explained in term of molecular flexibility. Moreover, the computed results of dihedral angle clarify that flexibility of long-chain Ph-C(n) is the result of internal rotation of C-C single bond (?(c-c)) in alkyl chain. It is interesting that compared with n-alkane, because of the existence of benzene ring, the flexibility of alkyl chain in Ph-C(n) with same carbon atom number is significantly reduced, as a result, the carbon chain dependence of diffusion behaviors for long-chain n-alkane (n ? 5) and long-chain Ph-C(n) (n ? 4) in scCO2 are different. PMID:24628176

Wang, Jinyang; Zhong, Haimin; Feng, Huajie; Qiu, Wenda; Chen, Liuping

2014-03-14

357

Molecular dynamics simulation of diffusion coefficients and structural properties of some alkylbenzenes in supercritical carbon dioxide at infinite dilution  

NASA Astrophysics Data System (ADS)

The binary infinite dilute diffusion coefficients, D_{12}^infty, of some alkylbenzenes (Ph-Cn, from Ph-H to Ph-C12) from 313 K to 333 K at 15 MPa in supercritical carbon dioxide (scCO2) have been studied by molecular dynamics (MD) simulation. The MD values agree well with the experimental ones, which indicate MD simulation technique is a powerful way to predict and obtain diffusion coefficients of solutes in supercritical fluids. Besides, the local structures of Ph-Cn/CO2 fluids are further investigated by calculating radial distribution functions and coordination numbers. It qualitatively convinces that the first solvation shell of Ph-Cn in scCO2 is significantly influenced by the structure of Ph-Cn solute. Meanwhile, the mean end-to-end distance, the mean radius of gyration and dihedral angle distribution are calculated to gain an insight into the structural properties of Ph-Cn in scCO2. The abnormal trends of radial distribution functions and coordination numbers can be reasonably explained in term of molecular flexibility. Moreover, the computed results of dihedral angle clarify that flexibility of long-chain Ph-Cn is the result of internal rotation of C-C single bond (?c-c) in alkyl chain. It is interesting that compared with n-alkane, because of the existence of benzene ring, the flexibility of alkyl chain in Ph-Cn with same carbon atom number is significantly reduced, as a result, the carbon chain dependence of diffusion behaviors for long-chain n-alkane (n ? 5) and long-chain Ph-Cn (n ? 4) in scCO2 are different.

Wang, Jinyang; Zhong, Haimin; Feng, Huajie; Qiu, Wenda; Chen, Liuping

2014-03-01

358

A Novel Method for Measuring the Diffusion, Partition and Convective Mass Transfer Coefficients of Formaldehyde and VOC in Building Materials  

PubMed Central

The diffusion coefficient (Dm) and material/air partition coefficient (K) are two key parameters characterizing the formaldehyde and volatile organic compounds (VOC) sorption behavior in building materials. By virtue of the sorption process in airtight chamber, this paper proposes a novel method to measure the two key parameters, as well as the convective mass transfer coefficient (hm). Compared to traditional methods, it has the following merits: (1) the K, Dm and hm can be simultaneously obtained, thus is convenient to use; (2) it is time-saving, just one sorption process in airtight chamber is required; (3) the determination of hm is based on the formaldehyde and VOC concentration data in the test chamber rather than the generally used empirical correlations obtained from the heat and mass transfer analogy, thus is more accurate and can be regarded as a significant improvement. The present method is applied to measure the three parameters by treating the experimental data in the literature, and good results are obtained, which validates the effectiveness of the method. Our new method also provides a potential pathway for measuring hm of semi-volatile organic compounds (SVOC) by using that of VOC. PMID:23145156

Xiong, Jianyin; Huang, Shaodan; Zhang, Yinping

2012-01-01

359

Statistics of velocity fluctuations arising from a random distribution of point vortices: The speed of fluctuations and the diffusion coefficient  

NASA Astrophysics Data System (ADS)

This paper is devoted to a statistical analysis of the fluctuations of velocity and acceleration produced by a random distribution of point vortices in two-dimensional turbulence. We show that the velocity probability density function PDF behaves in a manner which is intermediate between Gaussian and Lévy laws, while the distribution of accelerations is governed by a Cauchy law. Our study accounts properly for a spectrum of circulations among the vortices. In the case of real vortices (with a finite core), we show analytically that the distribution of accelerations makes a smooth transition from Cauchy (for small fluctuations) to Gaussian (for large fluctuations), probably passing through an exponential tail. We introduce a function T(V) which gives the typical duration of a velocity fluctuation V; we show that T(V) behaves like V and V-1 for weak and large velocities, respectively. These results have a simple physical interpretation in the nearest neighbor approximation, and in Smoluchowski theory concerning the persistence of fluctuations. We discuss the analogies with respect to the fluctuations of the gravitational field in stellar systems. As an application of these results, we determine an approximate expression for the diffusion coefficient of point vortices. When applied to the context of freely decaying two-dimensional turbulence, the diffusion becomes anomalous and we establish a relationship ?=1+(?/2) between the exponent of anomalous diffusion ? and the exponent ? which characterizes the decay of the vortex density.

Chavanis, Pierre-Henri; Sire, Clément

2000-07-01

360

Recombination of W18+ ions with electrons: Absolute rate coefficients from a storage-ring experiment and from theoretical calculations  

E-print Network

We present new experimentally measured and theoretically calculated rate coefficients for the electron-ion recombination of W$^{18+}$([Kr] $4d^{10}$ $4f^{10}$) forming W$^{17+}$. At low electron-ion collision energies, the merged-beam rate coefficient is dominated by strong, mutually overlapping, recombination resonances. In the temperature range where the fractional abundance of W$^{18+}$ is expected to peak in a fusion plasma, the experimentally derived Maxwellian recombination rate coefficient is 5 to 10 times larger than that which is currently recommended for plasma modeling. The complexity of the atomic structure of the open-$4f$-system under study makes the theoretical calculations extremely demanding. Nevertheless, the results of new Breit-Wigner partitioned dielectronic recombination calculations agree reasonably well with the experimental findings. This also gives confidence in the ability of the theory to generate sufficiently accurate atomic data for the plasma modeling of other complex ions.

Spruck, K; Krantz, C; Novotný, O; Becker, A; Bernhardt, D; Grieser, M; Hahn, M; Repnow, R; Savin, D W; Wolf, A; Müller, A; Schippers, S

2014-01-01

361

Recombination of W18+ ions with electrons: Absolute rate coefficients from a storage-ring experiment and from theoretical calculations  

NASA Astrophysics Data System (ADS)

We present experimentally measured and theoretically calculated rate coefficients for the electron-ion recombination of W18+([Kr ]4d104f10) forming W17+. At low electron-ion collision energies, the merged-beam rate coefficient is dominated by strong, mutually overlapping recombination resonances. In the temperature range where the fractional abundance of W18+ is expected to peak in a fusion plasma, the experimentally derived Maxwellian recombination rate coefficient is 5 to 10 times larger than that which is currently recommended for plasma modeling. The complexity of the atomic structure of the open-4f system under study makes the theoretical calculations extremely demanding. Nevertheless, the results of the present Breit-Wigner partitioned dielectronic recombination calculations agree reasonably well with the experimental findings. This also gives confidence in the ability of the theory to generate sufficiently accurate atomic data for the plasma modeling of other complex ions.

Spruck, K.; Badnell, N. R.; Krantz, C.; Novotný, O.; Becker, A.; Bernhardt, D.; Grieser, M.; Hahn, M.; Repnow, R.; Savin, D. W.; Wolf, A.; Müller, A.; Schippers, S.

2014-09-01

362

Modeling Self-Diffusion in Mixed-Solvent Electrolyte Solutions  

Microsoft Academic Search

A comprehensive model has been developed for calculating self-diffusion coefficients in mixed- solvent electrolyte solutions. The model includes methods for calculating the self-diffusion coefficients of ions and neutral species at infinite dilution and for predicting the effect of finite concentrations of electrolytes. For limiting diffusivities, a mixing rule has been developed for predicting the diffusivity in multicomponent mixed solvents using

Peiming Wang; Andrzej Anderko

2003-01-01

363

Ternary Solution Mutual Diffusion Coefficients and Densities of Aqueous Mixtures of Sucrose with NaCl and Sucrose with KCl at 25°C  

Microsoft Academic Search

Ternary solution isothermal mutual diffusion coefficients (interdiffusion coefficients) have been measured for aqueous mixtures of 0.250 mol-dm-3 sucrose (component 1) with 0.5 and 1.0 mol-dm-3 NaCl or with 0.5 and 1.0 mol-dm-3 KCl (salt = component 2) at 25.00°C using Rayleigh interferometry with computerized data acquisition. Densities were also measured. The volume-fixed diffusion coefficients (Dij)V show the following characteristics. At

Michelle C. Yang; John G. Albright; Joseph A. Rard; Donald G. Miller

1998-01-01

364

Determination of diffusion coefficients of carbon dioxide in water between 268 and 473 K in a high-pressure capillary optical cell with in situ Raman spectroscopic measurements  

USGS Publications Warehouse

Accurate values of diffusion coefficients for carbon dioxide in water and brine at reservoir conditions are essential to our understanding of transport behavior of carbon dioxide in subsurface pore space. However, the experimental data are limited to conditions at low temperatures and pressures. In this study, diffusive transfer of carbon dioxide in water at pressures up to 45 MPa and temperatures from 268 to 473 K was observed within an optical capillary cell via time-dependent Raman spectroscopy. Diffusion coefficients were estimated by the least-squares method for the measured variations in carbon dioxide concentration in the cell at various sample positions and time. At the constant pressure of 20 MPa, the measured diffusion coefficients of carbon dioxide in water increase with increasing temperature from 268 to 473 K. The relationship between diffusion coefficient of carbon dioxide in water [D(CO2) in m2/s] and temperature (T in K) was derived with Speedy–Angell power-law approach as: D(CO2)=D0[T/Ts-1]m where D0 = 13.942 × 10?9 m2/s, Ts = 227.0 K, and m = 1.7094. At constant temperature, diffusion coefficients of carbon dioxide in water decrease with pressure increase. However, this pressure effect is rather small (within a few percent).

Lu, Wanjun; Guo, Huirong; Chou, I. M.; Burruss, R. C.; Li, Lanlan

2013-01-01

365

Determination of molecular self-diffusion coefficient using multiple spin-echo NMR spectroscopy with removal of convection and background gradient artifacts.  

PubMed

A new approach is presented for the measurement of the self-diffusion coefficients of molecules in solution. It has been applied to metabolites in biofluids such as seminal and blood plasma at physiological temperature. The method is based on the double-gradient-spin-echo pulse sequence in which CPMG and bipolar gradient pulses have been implemented. The double-gradient spin-echo is shown to be useful in reducing the thermal convection that can cause over-estimation of the diffusion coefficients. The multiple spin-echoes in association with the CPMG approach is also insensitive to background gradient artifacts. In addition, the CPMG sequence enables longer diffusion periods (up to seconds) to be used without phase distortion; therefore, the proposed method is suitable for determining the diffusion coefficients of small metabolites in biofluids, where the resonances of large molecules, such as proteins, are suppressed during the spin-echo period as a result of their fast relaxation. PMID:11510814

Zhang, X; Li, C G; Ye, C H; Liu, M L

2001-08-01

366

Comment on "A theoretical framework for quantitatively characterizing sound field diffusion based on scattering coefficient and absorption coefficient of walls" [J. Acoust. Soc. Am. 128, 1140-1148 (2010)] (L).  

PubMed

The relationship between the acoustic scattering characteristics of materials and the degree of diffusion in enclosed acoustic spaces has recently attracted considerable research attention. Hanyu [J. Acoust. Soc. Am. 128(3), 1140-1148 (2010)] introduced a theoretical framework, in which the diffusion time in an enclosure is expressed as a function of a material's average scattering coefficient. In this letter, a modification of this theory is proposed. The decay process of the sound energy through scattering is divided into discrete sub-processes, specifically, a purely scattering process, and alternating scattering and specular reflections. The behavior of each process is examined for different scattering coefficients. PMID:23297877

Omoto, Akira

2013-01-01

367

A practical method of determining water current velocities and diffusion coefficients in coastal waters by remote sensing techniques  

NASA Technical Reports Server (NTRS)

A simplified procedure is presented for determining water current velocities and diffusion coefficients. Dye drops which form dye patches in the receiving water are made from an aircraft. The changes in position and size of the patches are recorded from two flights over the area. The simplified data processing procedure requires only that the ground coordinates about the dye patches be determined at the time of each flight. With an automatic recording coordinatograph for measuring coordinates and a computer for processing the data, this technique provides a practical method of determining circulation patterns and mixing characteristics of large aquatic systems. This information is useful in assessing the environmental impact of waste water discharges and for industrial plant siting.

James, W. P.

1971-01-01

368

Pressure dependence of diffusion coefficient and orientational relaxation time for acetonitrile and methanol in water: DRISM/mode-coupling study  

E-print Network

We present results of theoretical description and numerical calculation of the dynamics of molecular liquids based on the Reference Interaction Site Model / Mode-Coupling Theory. They include the temperature-pressure(density) dependence of the translational diffusion coefficients and orientational relaxation times for acetonitrile and methanol in water at infinite dilution. Anomalous behavior, i.e. the increase in mobility with density, is observed for the orientational relaxation time of methanol, while acetonitrile does not show any deviations from the usual. This effect is in qualitative agreement with the recent data of MD simulation and with experimental measurements, which tells us that presented theory is a good candidate to explain such kind of anomalies from the microscopical point of view and with the connection to the structure of the molecules.

Kobryn, A E; Hirata, F

2005-01-01

369

Dialectical multispectral classification of diffusion-weighted magnetic resonance images as an alternative to apparent diffusion coefficients maps to perform anatomical analysis.  

PubMed

Multispectral image analysis is a relatively promising field of research with applications in several areas, such as medical imaging and satellite monitoring. A considerable number of current methods of analysis are based on parametric statistics. Alternatively, some methods in computational intelligence are inspired by biology and other sciences. Here we claim that philosophy can be also considered as a source of inspiration. This work proposes the objective dialectical method (ODM): a method for classification based on the philosophy of praxis. ODM is instrumental in assembling evolvable mathematical tools to analyze multispectral images. In the case study described in this paper, multispectral images are composed of diffusion-weighted (DW) magnetic resonance (MR) images. The results are compared to ground-truth images produced by polynomial networks using a morphological similarity index. The classification results are used to improve the usual analysis of the apparent diffusion coefficient map. Such results proved that gray and white matter can be distinguished in DW-MR multispectral analysis and, consequently, DW-MR images can also be used to furnish anatomical information. PMID:19446434

Santos, W P; Assis, F M; Souza, R E; Santos Filho, P B; Lima Neto, F B

2009-09-01

370

Li ion diffusion mechanisms in LiFePO4: an ab initio molecular dynamics study.  

PubMed

The mechanisms for thermal (self) diffusion of Li ions in fully lithiated LiFePO(4) have been investigated with spin polarized ab initio molecular dynamics calculations. The effect of electron correlation is taken into account with the GGA+U formalism. It was found that Li ion diffusion is not a continuous process but through a series of jumps from one site to another. A dominant process is the hopping between neighboring Li sites around the PO(4) groups, which results in a zigzag pathway along the crystallographic b-axis. This observation is in agreement with a recent neutron diffraction experiment. A second process involves the collaborative movements of the Fe ions leading to the formation of antisite defects and promotes Li diffusion across the Li ion channels. The finding of the second mechanism demonstrates the benefit of ab initio molecular dynamics simulation in sampling diffusion pathways that may not be anticipated. PMID:21932862

Yang, Jianjun; Tse, John S

2011-11-17

371

Surface diffusion activation energy determination using ion beam microtexturing  

NASA Technical Reports Server (NTRS)

The activation energy for impurity atom (adatom) surface diffusion can be determined from the temperature dependence of the spacing of sputter cones. These cones are formed on the surface during sputtering while simultaneously adding impurities. The impurities form clusters by means of surface diffusion, and these clusters in turn initiate cone formation. Values are given for the surface diffusion activation energies for various materials on polycrystalline Cu, Al, Pb, Au, and Ni. The values for different impurity species on each of these substrates are approximately independent of impurity species within the experimental uncertainty, suggesting the absence of strong chemical bonding effects on the diffusion.

Rossnagel, S. M.; Robinson, R. S.

1982-01-01

372

Comparison of Dynamic and Liver-Specific Gadoxetic Acid Contrast-Enhanced MRI versus Apparent Diffusion Coefficients  

PubMed Central

Background Hepatic lesions often present diagnostic connundrums with conventional MR techniques. Hepatobiliary phase contrast-enhanced imaging with gadoxetic acid can aid in the characterization of such lesions. However, quantitative measures describing late-phase enhancement must be assessed relative to their accuracy of hepatic lesion classification. Purpose: To compare quantitative parameters in gadoxetic acid contrast-enhanced dynamic and hepatobiliary phase imaging versus apparent diffusion coefficients in hepatic lesion characterization. Material and Methods 57 patients with focal hepatic lesions on gadoxetic acid MR were included. Lesion enhancement at standard post-contrast time points and in the hepatobiliary phase (HB; 15 and 25 minutes post-contrast) was assessed via calculation of contrast (CR) and enhancement ratios (ER). Apparent diffusion coefficient (ADC) values were also obtained. Values for these parameters were compared among lesions and ROC analyses performed. Results: HB enhancement was greatest with FNH and adenomas. HB ER parameters but not HB CR could distinguish HCC from benign entities (0.9 ER ROC AUC versus 0.5 CR ROC AUC). There was no statistically significant difference found between the 15 and 25 minutes HB time points in detection of any lesion (p>0.4). ADC values were statistically significantly higher with hemangiomas (p<0.05) without greater accuracy in lesion detection relative to HB phase parameters. Conclusion Hepatobiliary phase gadoxetic acid contrast-enhanced MR characterizes focal hepatic lesions more accurately than ADC and conventional dynamic post-contrast time point enhancement parameters. ER values are generally superior to CR. No discernible benefit of 25 minute versus 15 minute delayed imaging is demonstrated. PMID:23805174

Morelli, John N.; Michaely, Henrik J.; Meyer, Mathias M.; Rustemeyer, Thassilo; Schoenberg, Stefan O.; Attenberger, Ulrike I.

2013-01-01

373

COMPARISON OF GKS CALCULATED CRITICAL ION TEMPERATURE GRADIENTS AND ITG GROWTH RATES TO DIII-D MEASURED GRADIENTS AND DIFFUSIVITIES  

SciTech Connect

OAK-B135 The gyrokinetic equations predict that various drift type waves or modes can be unstable in a tokamak. For some of these modes, such as the ion temperature gradient (ITG) mode and the electron temperature gradient mode, there exists a critical gradient, above which the mode is unstable. Since the existence of unstable modes can cause increased transport, plasmas which are centrally heated tend to increase in temperature gradient until the modes become unstable. Under some conditions the increased transport can fix the gradient at the critical value. here they present a comparison between the measured ion temperature gradients and the critical gradient as calculated by a gyrokinetic linear stability (GKS) code. They also present the maximum linear growth rate as calculated by this code for comparison to experimentally derived transport coefficients. The results show that for low confinement mode (L-mode) discharges, the measured ion temperature gradient is significantly greater than the GKS calculated critical gradient over a large region of the plasma. This is the same region of the plasma where the ion thermal diffusivity is large. For high confinement mode (H-mode) discharges the ion temperature gradient is closer to the critical gradient, but often still greater than the critical gradient over some region. For the best H-mode discharges, the ion temperature is less than or equal to the critical gradient over the whole plasma. In general they find that the position in the plasma where the ion thermal diffusivity starts to increase rapidly is where the maximum linear growth rate is greater than the E x B shearing rate.

BAKER,DR; STAEBLER,GM; PETTY,CC; GREENFIELD,CM; LUCE,TC

2003-04-01

374

EFFECT OF GRAIN BOUNDARIES ON DIFFUSION-CONTROLLED PROCESSES IN ALUMINUM OXIDE  

Microsoft Academic Search

Oxygen ion diffusion coefficients in single-crystal AlâOâ ; are several orders of magnitude less than aluminum ion diffusion coefficients in ; polycrystalline AlâOâ. In polycrystalline AlâOâ, oxygen ; ion diffusion is enhanced by the presence of grain boundaries as in the chloride ; ion diffusion in the alkali halides. Creep and sintering of polycrystalline Al\\/; sub 2\\/Oâ occur at a

A. E. Paladino; R. L. Coble

1963-01-01

375

Improved Diagnostic Accuracy of Breast MRI through Combined Apparent Diffusion Coefficients and Dynamic Contrast-Enhanced Kinetics  

PubMed Central

This study investigated the relationship between apparent diffusion coefficient (ADC) measures and dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) kinetics in breast lesions, and evaluated the relative diagnostic value of each quantitative parameter. Seventy-seven women with 100 breast lesions (27 malignant and 73 benign) underwent both DCE-MRI and diffusion weighted MRI (DWI). DCE-MRI kinetic parameters included peak initial enhancement, predominant delayed kinetic curve type (persistent, plateau or washout), and worst delayed kinetic curve type (washout>plateau>persistent). Associations between ADC and DCE-MRI kinetic parameters and predictions of malignancy were evaluated. Results showed that ADC was significantly associated with predominant curve type (ADC was higher for lesions exhibiting predominantly persistent enhancement compared to those exhibiting predominantly washout or plateau, p=0.006), but was not significantly associated with peak initial enhancement or worst curve type (p>0.05). Univariate analysis showed significant differences between benign and malignant lesions in both ADC (p<0.001) and worst curve (p =0.003). In multivariate analysis, worst curve type and ADC were significant independent predictors of benign versus malignant outcome and in combination produced the highest area under the ROC curve (AUC = 0.85, AUC=0.78 with 5-fold cross-validation). PMID:21254208

Partridge, SC; Rahbar, H; Murthy, R; Chai, X; Kurland, BF; DeMartini, WB; Lehman, CD

2011-01-01

376

Segmentation of infarct in acute ischemic stroke from MR apparent diffusion coefficient and trace-weighted images  

NASA Astrophysics Data System (ADS)

Evidence from several previous studies indicated that apparent diffusion coefficient (ADC) map was likely to reveal brain regions belonging to the ischemic penumbra, that is, areas that may be at risk of infarction in a few hours following stroke onset. Trace map overcomes the anisotropic diffusions of ADC map, so it is superior for evaluation of an infarct involving white matter. Mean shift (MS) approach has been successfully used for image segmentation, particularly in brain MR images. The aim of the study was to develop a tool for rapid and reliable segmentation of infarct in human acute ischemic stroke based on the ADC and trace maps using the MS approach. In addition, a novel method of 3-dimensional visualization was presented to provide useful insights into volume datasets for clinical diagnosis. We applied the presented method to clinical data. The results showed that it was consistent, fast (about 8-10 minutes per subject) and indistinguishable from an expert using manual segmentation when used our tool.

Li, Meng; Ai, Lin; He, Huiguang; Zheng, Zuofeng; Lv, Bin; Li, Wenjing; Yi, Jianhua; Chen, Xuejiao

2009-10-01

377

The realistic prediction of oxygen transport in a tissue-engineered scaffold by introducing time-varying effective diffusion coefficients.  

PubMed

An adequate oxygen supply is one of the most important factors needed in order to regenerate or engineer thick tissues or complex organs. To devise a method for maximizing the amount of oxygen available to cells, it is necessary to understand and to realistically predict oxygen transport within an engineered tissue. In this study, we focused on the fact that oxygen transport through a tissue-engineered scaffold may vary with time as cells proliferate. To confirm this viewpoint, effective oxygen diffusion coefficients (D(e)(,)(s)) of scaffolds were deduced from experimental measurements and simulations of oxygen-concentration profiles were performed using these D(e)(,)(s) values in a two-dimensional (2-D) perfusion model. The results of this study indicate that higher porosity, hydraulic permeability and interconnectivity of scaffolds with no cells are responsible for the prominent diffusion capability quantified using D(e)(,)(s). On the other hand, the D(e)(,)(s) of scaffolds with cells has a negative linear relationship with cell density. Cell proliferation with time leads to a significant decrease in oxygen concentration in the 2-D perfusion model. This result demonstrates the gradual restriction of oxygen transport in a porous scaffold during cell culture. Therefore, the realistic prediction of oxygen transport using a time-varying D(e)(,)(s) will provide an appropriate basis for designing optimal transport networks within a thick scaffold. PMID:21642022

Kang, Tae-Yun; Kang, Hyun-Wook; Hwang, Chang Mo; Lee, Sang Jin; Park, Jaesung; Yoo, James J; Cho, Dong-Woo

2011-09-01

378

On the Relationship Between the Apparent Diffusion Coefficient and Extravascular Extracellular Volume Fraction in Human Breast Cancer  

PubMed Central

MRI techniques have been developed that can noninvasively probe the apparent diffusion coefficient (ADC) of water via diffusion weighted MRI (DW-MRI). These methods have found much application in cancer where it is often found that the ADC within tumors is inversely correlated with tumor cell density, so that an increase in ADC in response to therapy can be interpreted as an imaging biomarker of positive treatment response. Dynamic contrast enhanced MRI (DCE-MRI) methods have also been developed and can noninvasively report on the extravascular extracellular volume fraction of tissues (denoted by ve). By conventional reasoning the ADC should therefore also be directly proportional to ve. Here we report measurements of both ADC and ve obtained from breast cancer patients at both 1.5T and 3.0T. The 1.5T data were acquired as part of normal standard-of-care, while the 3.0T data were obtained from a dedicated research protocol. We found no statistically significant correlation between ADC and ve for the 1.5T or 3.0T patient sets on either a voxel-by-voxel or ROI basis. These data, combined with similar results from other disease sites in the literature, may indicate that the conventional interpretation of either ADC, ve, or their relationship are not sufficient to explain experimental findings. PMID:21531106

Arlinghaus, Lori R.; Li, Xia; Rahman, A. Ridwan; Welch, E. Brian; Xu, Lei; Gore, John C.; Yankeelov, Thomas E.

2011-01-01

379

Negative Ion Drift Velocity and Longitudinal Diffusion in Mixtures of Carbon Disulfide and Methane  

NASA Technical Reports Server (NTRS)

Negative ion drift velocity and longitudinal diffusion has been measured for gas mixtures of carbon disulfide (CS2) and methane (CH4)' Measurements were made as a function of total pressure, CS2 partial pressure and electric field. Constant mobility and thermal-limit longitudinal diffusion is observed for all gas mixtures tested. Gas gain for some of the mixtures is also included.

Dion, Michael P.; Son, S.; Hunter, S. D.; deNolfo, G. A.

2011-01-01

380

Optimizing liquid waste treatment processing in PWRs: focus on modeling of the variation of ion-exchange resins selectivity coefficients  

Microsoft Academic Search

A bibliographic survey has highlighted the essential role of selectivity on resin efficiency, especially the variation of selectivity coefficients in function of the resin saturation state and the operating conditions. This phenomenon has been experimentally confirmed but is not yet implemented into an ion-exchange model specific for resins. This paper reviews the state of the art in predicting sorption capacity

Frederic Gressier; Jan Van der Lee; Helene Schneider; Martin Bachet; Hubert Catalette

2007-01-01

381

Generic van der Waals equation of state for polymers, modified free volume theory, and the self-diffusion coefficient of polymeric liquids  

NASA Astrophysics Data System (ADS)

In this paper, a molecular theory of self-diffusion coefficient is developed for polymeric liquids (melts) on the basis of the integral equation theory for site-site pair correlation functions, the generic van der Waals equation of state, and the modified free volume theory of diffusion. The integral equations supply the pair correlation functions necessary for the generic van der Waals equation of state, which in turn makes it possible to calculate the self-diffusion coefficient on the basis of the modified free volume theory of diffusion. A random distribution is assumed for minimum free volumes for monomers along the chain in the melt. More specifically, a stretched exponential is taken for the distribution function. If the exponents of the distribution function for minimum free volumes for monomers are chosen suitably for linear polymer melts of N monomers, the N dependence of the self-diffusion coefficient is N-1 for the small values of N, an exponent predicted by the Rouse theory, whereas in the range of 2.3?lnN?4.5 the N dependence smoothly crosses over to N-2, which is reminiscent of the exponent by the reptation theory. However, for lnN?4.5 the N dependence of the self-diffusion coefficient differs from N-2, but gives an N dependence, N(0diffusion becomes semiempirical, but once the parameters are chosen such that the N dependence of D can be successfully given for a polymer melt, the temperature dependence of the self-diffusion coefficient can be well predicted in comparison with experiment. The theory is satisfactorily tested against experimental and simulation data on the temperature dependence of D for polyethylene and polystyrene melts.

Sabbagh, Haidar; Eu, Byung Chan

2010-06-01

382

Ionic diffusion in naturally-occurring aqueous solutions: transition-state models that use either empirical expressions or statistically-derived relationships to predict mutual diffusion coefficients in the concentrated-solution regions of 8 binary systems  

NASA Astrophysics Data System (ADS)

Mutual diffusion coefficients for the systems NaCl-H 2O, KCl-H 2O, CaCl 2-H 2O, SrCl 2-H 2O, BaCl 2-H 2O, MgCl 2-H 2O, Na 2SO 4-H 2O, and MgSO 4-H 2O are computed using a model that postulates exchanges between ions and water molecules. Limiting ionic equivalent conductances, a solution-density function, and a mean ionic activity-coefficient function are required as input. A region of changing solution structure extends up to concentrations ranging from about 0.01 molar in MgCl 2-H 2O to about 0.2 molar in KCl-H 2O. In the remaining concentration range to saturation, a single expression in each system containing one variable parameter can be fitted empirically to reproduce selected sets of experimentally measured Dv12 with maximum errors for individual compositions ranging from about 0.25% in KCl-H 2O and Na 2SO 4-H 2O to about 4% in MgCl 2-H 2O. The experimentally measured Dv12 can be reproduced with errors comparable to those of the empirical fits by further postulating that individual ion-water molecule exchanges are coupled to yield hydrated neutral exchange complexes (the activated complexes), and defining probability expressions that describe the following exchanges: Ba2+ + 2 Cl- for 3H 2O, 2 Ca2+ + 4 Cl- for 6H 2O, 2 Sr2+ + 4 Cl- for 6H 2O, Na+ + Cl- for 3H 2O, 2 K+ + 2 Cl- for 5H 2O, NaSO-4 + Na+ for 5H 2O, Mg2+ + SO2-4 (+MgSO 04) for 4H 2O, and MgCl+ + Cl- for 2H 2O. This calculation also contains one variable parameter. Solute transport between exchange sites is by movement of ions, except for the ion-pair contribution indicated in parentheses.

Graf, Donald L.; Anderson, David E.; Woodhouse, John B.

1983-11-01

383

Efficient Reformulation of Solid-Phase Diffusion in Physics-Based Lithium-Ion Battery Models  

E-print Network

Efficient Reformulation of Solid-Phase Diffusion in Physics-Based Lithium-Ion Battery Models or approximation for the solid phase. One of the major difficulties in simulating Li-ion battery models is the need typically solve electrolyte con- centration, electrolyte potential, solid-state potential, and solid-state

Subramanian, Venkat

384

ANALYSIS OF NITRITE IN NO2 DIFFUSION TUBES USING ION CHROMATOGRAPHY  

EPA Science Inventory

An analytical method was developed for the analysis of the NO2 collected by a passive diffusion controlled atmospheric sampling device. The method measured the total amount of nitrite ion using ion chromatography. The precision obtained under field conditions, defined as twice th...

385

Erbium diffusion in silicon dioxide  

SciTech Connect

Erbium diffusion in silicon dioxide layers prepared by magnetron sputtering, chemical vapor deposition, and thermal growth has been investigated by secondary ion mass spectrometry, and diffusion coefficients have been extracted from simulations based on Fick's second law of diffusion. Erbium diffusion in magnetron sputtered silicon dioxide from buried erbium distributions has in particular been studied, and in this case a simple Arrhenius law can describe the diffusivity with an activation energy of 5.3{+-}0.1 eV. Within a factor of two, the erbium diffusion coefficients at a given temperature are identical for all investigated matrices.

Lu Yingwei; Julsgaard, B.; Petersen, M. Christian [Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C (Denmark); Jensen, R. V. Skougaard [Department of Physics and Nanotechnology, Aalborg University, DK-9220 Aalborg O (Denmark); Pedersen, T. Garm; Pedersen, K. [Department of Physics and Nanotechnology, Aalborg University, DK-9220 Aalborg O (Denmark); Interdisciplinary Nanoscience Center-iNANO, DK-8000 Aarhus C (Denmark); Larsen, A. Nylandsted [Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C (Denmark); Interdisciplinary Nanoscience Center-iNANO, DK-8000 Aarhus C (Denmark)

2010-10-04

386

Li Ion Diffusion Mechanisms in Bulk Monoclinic Li2CO3 Crystals from Density Functional Studies  

SciTech Connect

Density functional studies of Li+ ion diffusion mechanisms in bulk monoclinic lithium carbonate Li2CO3 crystals are performed to identify the stable Li+ interstitial positions and migration barriers. The migration barrier for Li+ diffusion between the planes defined by Li2CO3 units along the open channels [010] is found to be very small at 0.28 eV, while a higher migration barrier of 0.60 eV was found for the diffusion across the planes. These results show that diffusion of Li+ in Li2CO3 is favorable along the [010] channels. The implications for Li+ ion transport in solid electrolyte interphases (SEI) in Li ion batteries are discussed.

Iddir, Hakim; Curtiss, Larry A.

2010-12-09

387

Automated adjustment of display conditions in brain MR images: diffusion-weighted MRIs and apparent diffusion coefficient maps for hyperacute ischemic stroke.  

PubMed

We developed a new computerized scheme for proper display of brain diffusion-weighted magnetic resonance images (DWIs) and apparent diffusion coefficient (ADC) maps based on density histogram analysis. In our scheme, DWI volumes and b0 image volumes of 44 cases were first created, and brain regions on DWI volumes were segmented. ADC map volumes were then derived from both volumes. The density histogram was determined from the brain regions on these volumes, and the voxel value corresponding to the maximum in the density histogram was determined for each volume. The display gray level for each of the two volumes was adjusted by setting the determined voxel value as window conditions. In a comparison between the existing manual method and our automated method, the variation in the gray levels was evaluated quantitatively. The variation in the average of the cross-correlation values determined for pairs of density histograms in each of the DWIs and ADC maps was 57.3 and 27.1 % with the existing method, respectively, and 7.7 and 2.7 % with our scheme, respectively, which indicated a more consistent display of images with our scheme. The performance of the two-alternative-forced-choice method for visual comparison of pairs of images in each of the DWIs and ADC maps adjusted by our scheme was judged to be better than those of the existing method by 75.1 % and 92.7 %, respectively. Our computerized scheme would be a promising technique for an accurate, prompt automated adjustment of display conditions in brain DWIs and ADC maps. PMID:23184445

Nagashima, Hiroyuki; Doi, Kunio; Ogura, Toshihiro; Fujita, Hiroshi

2013-01-01

388

Na and Li ion diffusion in modified ASTM C 1260 test by Magnetic Resonance Imaging (MRI)  

SciTech Connect

In the current study, MRI was applied to investigate lithium and sodium ion diffusion in cement paste and mortars containing inert sand and borosilicate glass. Paste and mortars were treated by complying with ASTM C 1260. Lithium and sodium distribution profiles were collected at different ages after different treatments. Results revealed that sodium ions had a greater diffusion rate than lithium ions, suggesting that Na reaches the aggregate particle surface before Li. Results also showed that Na and Li ions had a competitive diffusion process in mortars; soaking in a solution with higher [Li] favored Li diffusion but hindered Na diffusion. In mortars containing glass, a substantial amount of Li was consumed by the formation of ASR products. When [Li] in soaking solution was reduced to 0.37 N, a distinctive Na distribution profile was observed, indicating the free-state Na ions were continuously transformed to solid reaction products by ASR. Hence, in the modified ASTM C 1260 test, [Li] in the storage solution should be controlled at 0.74 N, in order to completely prevent the consumption of Na ions and thus stop ASR.

Feng, X. [Department of Civil Engineering, University of New Brunswick, Fredericton, NB (Canada)], E-mail: XFeng@ctlgroup.com; Balcom, B.J. [MRI Center, Department of Physics, University of New Brunswick, Fredericton, NB (Canada); Thomas, M.D.A.; Bremner, T.W. [Department of Civil Engineering, University of New Brunswick, Fredericton, NB (Canada)

2008-12-15

389

The use of MR-detectable reporter molecules and ions to evaluate diffusion in normal and ischemic brain.  

PubMed

As a result of the technical challenges associated with distinguishing the MR signals arising from intracellular and extracellular water, a variety of endogenous and exogenous MR-detectable molecules and ions have been employed as compartment-specific reporters of water motion. Although these reporter molecules and ions do not have the same apparent diffusion coefficients (ADCs) as water, their ADCs are assumed to be directly related to the ADC of the water in which they are solvated. This approach has been used to probe motion in the intra- and extracellular space of cultured cells and intact tissue. Despite potential interpretative challenges with the use of reporter molecules or ions and the wide variety used, the following conclusions are consistent considering all studies: (i) the apparent free diffusive motion in the intracellular space is approximately one-half of that in dilute aqueous solution; (ii) ADCs for intracellular and extracellular water are similar; (iii) the intracellular ADC decreases in association with brain injury. These findings provide support for the hypothesis that the overall brain water ADC decrease that accompanies brain injury is driven primarily by a decrease in the ADC of intracellular water. We review the studies supporting these conclusions, and interpret them in the context of explaining the decrease in overall brain water ADC that accompanies brain injury. PMID:20669147

Ackerman, Joseph J H; Neil, Jeffrey J

2010-08-01

390

Kinetics of release of serotonin from isolated secretory granules. II. Ion exchange determines the diffusivity of serotonin.  

PubMed Central

We measured the efflux of 5-hydroxytryptamine (5-HT, serotonin) from an intact secretory granule extracted from the mast cell of the beige mouse. The efflux was measured with amperometry after rupture of the granule membrane was triggered by electroporation. We determined the diffusivity of 5-HT within the secretory granule to be 2.0 x 10(-8) cm2 s(-1) when the granule is in contact with a physiological saline and found that this diffusivity depends on the valence of the cation in the external electrolyte. There is a fivefold increase in the diffusion coefficient of 5-HT determined in CsCl (150 mM, pH 7.2) at 3.7 x 10(-8) cm2 s(-1) compared to that determined in histamine dihydrochloride (Hi, 100 mM at pH 4.5) at 0.7 x 10(-8) cm2 s(-1). We found that the rate of expansion of the granule matrix observed in physiological medium correlates with the efflux of 5-HT, and that the rate of swelling of the matrix and the efflux depend on the microviscosity within the granule matrix and not the bulk viscosity of the external solution. The low diffusivity of 5-HT (approximately 500-fold less than in the bulk), the observation that the valence of the counterion affects this diffusivity, and the relationship between the volume changes of the matrix and the efflux suggest that 5-HT is released from the granule by ion exchange. We discuss the implications of this result for exocytotic release in mast cells and propose that an ion exchange mechanism could control the rate of release in other secretory systems. Images FIGURE 1 PMID:9284284

Marszalek, P E; Farrell, B; Verdugo, P; Fernandez, J M

1997-01-01

391

Antiferromagnetic spin structure and lithium ion diffusion in Li2MnO3 probed by ?+SR  

NASA Astrophysics Data System (ADS)

In order to elucidate the antiferromagnetic (AF) spin structure below TN˜35 K and to clarify the diffusive behavior of Li+ ions in the layered compound Li2MnO3, we have performed a muon-spin rotation and relaxation (?+SR) experiment using a powder sample in the temperature range between 2 and 500 K. Below TN, the zero-field (ZF-) ?+SR spectrum showed a clear oscillation that consists of two muon-spin precession signals with different frequencies. Combining with the dipole field calculations, it was found that the most probable spin structure for Li2MnO3 is the Cx-type AF order in which Mn moments align parallel or antiparallel to the a axis in the [Li1/3Mn2/3]O2 layer, and a ferromagnetic chain along the a axis aligns antiferromagnetically along both the b and c axes. The ordered Mn moment was estimated as 2.62?B at 2 K. In the paramagnetic state, ZF- and longitudinal-field ?+SR spectra exhibited a dynamic nuclear field relaxation. From the temperature dependence of the field distribution width, the Li+ ions were found to diffuse mainly along the c axis through the Li ion in the [Li1/3Mn2/3]O2 layer. Also, based on the field fluctuation rate, a self-diffusion coefficient of Li+ ions (DLi) at 300 K was estimated as 4.7(4)×10-11 cm2/s with the thermal activation energy Ea=0.156(3) eV.

Sugiyama, Jun; Mukai, Kazuhiko; Nozaki, Hiroshi; Harada, Masashi; Månsson, Martin; Kamazawa, Kazuya; Andreica, Daniel; Amato, Alex; Hillier, Adrian D.

2013-01-01

392

Analysis of chemical reactions of ?-radiolysis, hydrolysis and complex formation in alkali solutions of the object ``Shelter". Investigations of transfer coefficients of UO22+, PuO22+ ions in aqueous solutions (in Ukrainian)  

NASA Astrophysics Data System (ADS)

Chemical reactions of ?-radiolysis, hydrolysis and complex formation as well as oxidizing-reducing processes in alkali solutions of ions UO^{2+}_2, PuO^{2+}_2, AmO^{2+}_2 have been analyzed. It has been established that polyuranites and superuranites, phosphate, carbonate and nitrate precipitates of uraninite and plutoninite may arise in aqueous solutions, which are characteristic of the object ``Shelter". Hydrodynamic-fluctuation theory for calculation of bimolecular reactions is presented. Calculation of mutual diffusion and viscosity transfer coefficients for ions UO^{2+}_2, PuO^{2+}_2 and atomic hydrohen in aqueous solutions is carried out.

Yukhnovskii, I. R.; Tokarchuk, M. V.; Kobryn, O. E.; Dmytriv, G. S.; Humenyuk, Y. A.

393

Evaluation of the normal-to-diseased apparent diffusion coefficient ratio as an indicator of prostate cancer aggressiveness  

PubMed Central

Background We tested the feasibility of a simple method for assessment of prostate cancer (PCa) aggressiveness using diffusion-weighted magnetic resonance imaging (MRI) to calculate apparent diffusion coefficient (ADC) ratios between prostate cancer and healthy prostatic tissue. Methods The requirement for institutional review board approval was waived. A set of 20 standardized core transperineal saturation biopsy specimens served as the reference standard for placement of regions of interest on ADC maps in tumorous and normal prostatic tissue of 22 men with PCa (median Gleason score: 7; range, 6–9). A total of 128 positive sectors were included for evaluation. Two diagnostic ratios were computed between tumor ADCs and normal sector ADCs: the ADC peripheral ratio (the ratio between tumor ADC and normal peripheral zone tissue, ADC-PR), and the ADC central ratio (the ratio between tumor ADC and normal central zone tissue, ADC-CR). The performance of the two ratios in detecting high-risk tumor foci (Gleason 8 and 9) was assessed using the area under the receiver operating characteristic curve (AUC). Results Both ADC ratios presented significantly lower values in high-risk tumors (0.48?±?0.13 for ADC-CR and 0.40?±?0.09 for ADC-PR) compared with low-risk tumors (0.66?±?0.17 for ADC-CR and 0.54?±?0.09 for ADC-PR) (p?

2014-01-01

394

Apparent Diffusion Coefficient (ADC) Value: A Potential Imaging Biomarker That Reflects the Biological Features of Rectal Cancer  

PubMed Central

Objective We elected to analyze the correlation between the pre-treatment apparent diffusion coefficient (ADC) and the clinical, histological, and immunohistochemical status of rectal cancers. Materials and Methods Forty-nine rectal cancer patients who received surgical resection without neoadjuvant therapy were selected that underwent primary MRI and diffusion-weighted imaging (DWI). Tumor ADC values were determined and analyzed to identify any correlations between these values and pre-treatment CEA or CA19-9 levels, and/or the histological and immunohistochemical properties of the tumor. Results Inter-observer agreement of confidence levels from two separate observers was suitable for ADC measurement (k ?=? 0.775). The pre-treatment ADC values of different T stage tumors were not equal (p ?=? 0.003). The overall trend was that higher T stage values correlated with lower ADC values. ADC values were also significantly lower for the following conditions: tumors with the presence of extranodal tumor deposits (p ?=? 0.006) and tumors with CA19-9 levels ? 35 g/ml (p ?=? 0.006). There was a negative correlation between Ki-67 LI and the ADC value (r ?=? ?0.318, p ?=? 0.026) and between the AgNOR count and the ADC value (r ?=? ?0.310, p ?=? 0.030). Conclusion Significant correlations were found between the pre-treatment ADC values and T stage, extranodal tumor deposits, CA19-9 levels, Ki-67 LI, and AgNOR counts in our study. Lower ADC values were associated with more aggressive tumor behavior. Therefore, the ADC value may represent a useful biomarker for assessing the biological features and possible relationship to the status of identified rectal cancers. PMID:25303288

Sun, Yiqun; Tong, Tong; Cai, Sanjun; Bi, Rui; Xin, Chao; Gu, Yajia

2014-01-01

395

Cross sections and rate coefficients for excitation of ?n = 1 transitions in Li-like ions with 6 < Z < 42.  

NASA Astrophysics Data System (ADS)

Excitation cross sections and rate coefficients by electron impact were calculated for the 1s22s - 1s2s2p, 1s22s - 1s2s2 and 1s22s - 1s2p2 transitions of the Li-like ions (C IV, N V, O VI, Ne VIII, Mg X, Al XI, Si XII, S XIV, Ar XVI, Ca XVIII, Ti XX, Fe XXIV, Ni XXVI, Zn XXVIII, Ge XXX, Se XXXII, Kr XXXIIV and Mo XXXX) by a Coulomb-Born approximation with exchange and including relativistic effects and configuration interactions. Level energies, mixing coefficients and transition wavelengths and probabilities were also computed.

Safronova, U. I.; Safronova, M. S.; Kato, T.

396

Diffusion or bounce back in relativistic heavy-ion collisions?  

E-print Network

The time evolution of pseudorapidity distributions of produced charged hadrons in d+Au collisions at sqrt(s_NN) = 200 GeV is investigated. Results of a nonequilibrium-statistical Relativistic Diffusion Model with three sources are compared with a macroscopic "bounce back" model that does not allow for statistical equilibration at large times, but instead leads to motion reversal. When compared to the data, the results of the diffusion approach are more precise, thus emphasizing that the system is observed to be on its way to thermal equilibrium.

Georg Wolschin; Minoru Biyajima; Takuya Mizoguchi

2008-03-12

397

Diffusion length variation and proton damage coefficients for InP/In(x)Ga(1-x)As/GaAs solar cells  

NASA Technical Reports Server (NTRS)

Indium phosphide solar cells are more radiation resistant than gallium arsenide and silicon solar cells, and their growth by heteroepitaxy offers additional advantages leading to the development of lighter, mechanically strong and cost-effective cells. Changes in heteroepitaxial InP cell efficiency under 0.5 and 3 MeV proton irradiations are explained by the variation in the minority-carrier diffusion length. The base diffusion length versus proton fluence is calculated by simulating the cell performance. The diffusion length damage coefficient K(L) is plotted as a function of proton fluence.

Jain, R. K.; Weinberg, I.; Flood, D. J.

1993-01-01

398

Use of LARS system for the quantitative determination of smoke plume lateral diffusion coefficients from ERTS images of Virginia  

NASA Technical Reports Server (NTRS)

A technique for measuring smoke plume of large industrial sources observed by satellite using LARSYS is proposed. A Gaussian plume model is described, integrated in the vertical, and inverted to yield a form for the lateral diffusion coefficient, Ky. Given u, wind speed; y sub l, the horizontal distance of a line of constant brightness from the plume symmetry axis a distance x sub l, downstream from reference point at x=x sub 2, y=0, then K sub y = u ((y sub 1) to the 2nd power)/2 x sub 1 1n (x sub 2/x sub 1). The technique is applied to a plume from a power plant at Chester, Virginia, imaged August 31, 1973 by LANDSAT I. The plume bends slightly to the left 4.3 km from the source and estimates yield Ky of 28 sq m/sec near the source, and 19 sq m/sec beyond the bend. Maximum ground concentrations are estimated between 32 and 64 ug/cu m. Existing meteorological data would not explain such concentrations.

Blais, R. N.; Copeland, G. E.; Lerner, T. H.

1975-01-01

399

Universal effects of collective interactions on long-time self-diffusion coefficients in hard-sphere systems  

NASA Astrophysics Data System (ADS)

We investigate how universal the collective behavior, due to the many-body interactions in polydisperse hard-sphere systems, is at higher volume fractions. We perform two types of computer simulations, a Brownian-dynamics simulation on colloidal suspensions of hard spheres, where the hydrodynamic interactions between particles are neglected, and a molecular-dynamic simulation on atomic systems of hard spheres. Thus, we show that the long-time self-diffusion coefficients DSL in both systems become singular as DSL( ?)?(1- ?/ ?c) 2 because of the collective interactions due to the many-body collision processes, where ? is a particle volume fraction and ?c?0.586 for 6% polydispersity. Although DSL exhibits the same singular behavior as that obtained theoretically for the monodisperse suspension with the hydrodynamic interactions, no liquid-glass transition is found because even the polydisperse hard-sphere systems crystallize without the hydrodynamic interactions for all ? above the melting volume fraction, which is lower than ?c.

Tokuyama, Michio; Yamazaki, Hiroyuki; Terada, Yayoi

2003-10-01

400

Modeling Taylor dispersion injections: determination of kinetic/affinity interaction constants and diffusion coefficients in label-free biosensing.  

PubMed

A new method based on Taylor dispersion has been developed that enables an analyte gradient to be titrated over a ligand-coated surface for kinetic/affinity analysis of interactions from a minimal number of injections. Taylor dispersion injections generate concentration ranges in excess of four orders of magnitude and enable the analyte diffusion coefficient to be reliably estimated as a fitted parameter when fitting binding interaction models. A numerical model based on finite element analysis, Monte Carlo simulations, and statistical profiling were used to compare the Taylor dispersion method with standard fixed concentration injections in terms of parameter correlation, linearity of parameter error space, and global versus local model fitting. A dramatic decrease in parameter correlations was observed for TDi curves relative to curves from standard fixed concentration injections when surface saturation was achieved. In FCI the binding progress is recorded with respect to injection time, whereas in TDi the second time dependency encoded in the analyte gradient increases resolving power. This greatly lowers the dependence of all parameters on each other and on experimental interferences. When model parameters were fitted locally, the performance of TDis remained comparable to global model fitting, whereas fixed concentration binding response curves yielded unreliable parameter estimates. PMID:22197421

Quinn, John G

2012-02-15