Ion diffusion coefficient measurements in nanochannels at various concentrations
Wang, Junrong; Zhang, Li; Xue, Jianming; Hu, Guoqing
2014-01-01
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
Comparison of ICRF-Induced Ion Diffusion Coefficients Calculated with the DC and AORSA Codes
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
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.
Ion diffusion coefficients model and molar conductivities of ionic salts in aprotic solvents.
Garrido, Leoncio; Mejía, Alberto; García, Nuria; Tiemblo, Pilar; Guzmán, Julio
2015-02-19
In the study of the electric properties of electrolytes, the determination of the diffusion coefficients of the species that intervene in the charge transport process is of great importance, particularly that of the free ions (D(+) and D(-)), the only species that contribute to the conductivity. In this work we propose a model that allows, with reasonable assumptions, determination of D(+) and D(-), and the degree of dissociation of the salt, ?, at different concentrations, using the diffusion coefficients experimentally obtained with NMR. Also, it is shown that the NMR data suffice to estimate the conductivity of the electrolytes. The model was checked by means of experimental results of conductivity and NMR diffusion coefficients obtained with solutions of lithium triflate in ethylene and propylene carbonates, as well as with other results taken from the literature. PMID:25603311
Influence of diffusion coefficient on chloride ion penetration of concrete structure
Sang-Hun Han
2007-01-01
This paper proposes a modified diffusion coefficient that considers the effect of chloride binding and evaporable water on the diffusion coefficient. A finite element method (FEM) program based on the modified diffusion coefficient estimates chloride concentration according to concrete depth, and external and internal conditions. The predicted chloride concentrations were compared with experimental values.The modified diffusion coefficient, which is a
Bodor, Sándor; Zook, Justin M; Lindner, Erno; Tóth, Klára; Gyurcsányi, Róbert E
2008-05-01
The diffusion coefficients of active components in ion-selective membranes have a decisive influence on the life-time and detection limit of the respective ion-selective electrodes, as well as influencing the rate of polarization and relaxation processes of electrically perturbed ion sensors. Therefore, the rational design of mass transport controlled ion-selective electrodes with sub-nanomolar detection limits requires reliable data on the diffusion coefficients. We have implemented electrochemical methods for the quantitative assessment of both the diffusion coefficients of free ionophores and ion-ionophore complexes. The diffusion coefficients of the pH-sensitive chromoionophore ETH 5294 and the calcium-selective ionophore ETH 5234 were determined in plasticized PVC membranes with different PVC to plasticizer ratios. The diffusion coefficient of the free chromoionophore determined by a chronoamperometric method was validated with optical methods for a variety of membrane compositions. The calcium-selective ionophore ETH 5234 was used as a model compound to assess the diffusion coefficient of the ion-ionophore complex calculated from the time required for the complexes to cross a freshly prepared membrane during potentiometric ion-breakthrough experiments. The difference between the diffusion coefficients of the free ionophore ETH 5234 and the ion-ionophore complex was found to be significant and correlated well with the geometry of the respective species. PMID:18427685
Diffusion Coefficients in White Dwarfs
NASA Astrophysics Data System (ADS)
Saumon, D.; Starrett, C. E.; Daligault, J.
2015-06-01
Models of diffusion in white dwarfs universally rely on the coefficients calculated by Paquette et al. (1986). We present new calculations of diffusion coefficients based on an advanced microscopic theory of dense plasmas and a numerical simulation approach that intrinsically accounts for multiple collisions. Our method is validated against a state-of-the-art method and we present results for the diffusion of carbon ions in a helium plasma.
Diffusion coefficient of yttrium ion in YCrO{sub 3}
Kawamura, Kenichi; Saiki, Atushi; Maruyama, Toshio; Nagata, Kazuhiro [Tokyo Inst. of Tech., Tokyo (Japan)
1995-09-01
The solid-state reaction; 1/2 Y{sub 2}O{sub 3} + 1/2 Cr{sub 2}O{sub 3} = YCrO{sub 3} was conducted between 1,458 and 1,719 K in air (P{sub O{sub 2}} = 0.21 atm). The reaction obeyed the parabolic rate law and the diffusion of yttrium ion controlled the reaction. According to Wagner`s theory, the diffusion coefficient of yttrium ion Y{sup 3+} in YCrO{sub 3} was evaluated using the Gibbs free energy change of the reaction and the parabolic rate constant. The defect reaction, Cr{sub 2}O{sub 3} + 3/2 O{sub 2} in the presence of YCrO{sub 3} yields 2 V{prime}{double_prime}{sub Y} + 2Cr{sub Cr}{sup x} + 6O{sub O}{sup X} + 6h{sup {sm_bullet}}, is predominant in the formation of yttrium vacancy. The diffusion coefficient of yttrium ion is given D{sub Y{sup 3+}}/m{sup 2} s{sup {minus}1} = [8.36 {times} 10{sup {minus}9} exp ({minus} 272/kJ/mol/RT)] P{sub O{sub 2}}{sup 3/16}a{sub Cr{sub 2}O{sub 3}}{sup 1/8} where a{sub Cr{sub 2}O{sub 3}} is activity of Cr{sub 2}O{sub 3} and P{sub O{sub 2}} is oxygen pressure.
Portable vapor diffusion coefficient meter
Ho, Clifford K. (Albuquerque, NM)
2007-06-12
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.
Determination of diffusion coefficient for unsaturated soils
Sood, Eeshani
2005-08-29
resulting in failure of slopes of embankments constructed with these soils. Therefore, it is very important to study the diffusion properties of unsaturated soils. Study of the diffusion properties requires the determination of the diffusion coefficient...
Subramaniam, Shankar
which are usually ex pressed as functions of the binary diffusion coefficients of each species pair of components with identical binary diffusivities. While these minimum error effective diffusion coefficients binary diffusion coefficients, thereby reducing computational expense. The necessary background for mass
Search for selective ion diffusion through membranes
NASA Technical Reports Server (NTRS)
May, C. E.; Philipp, W. H.
1983-01-01
The diffusion rates of several ions through some membranes developed as battery separators were measured. The ions investigated were Li(+), Rb(+), Cl(-), and So4. The members were crosslinked polyvinyl alcohol, crosslinked polyacrylic acid, a copolymer of the two, crosslinked calcium polyacrylate, cellulose, and several microporous polyphenylene oxide based films. No true specificity for diffusion of any of these ions was found for any of the membranes. But the calcium polyacrylate membrane was found to exhibit ion exchange with the diffusing ions giving rise to the leaching of the calcium ion and low reproducibility. These findings contrast earlier work where the calcium polyacrylate membrane did show specificity to the diffusion of the copper ion. In general, Fick's law appeared to be obeyed. Except for the microporous membranes, the coefficients for ion diffusion through the membranes were comparable with their values in water. For the microporous membranes, the values found for the coefficients were much less, due to the tortuosity of the micropores.
Composition dependence of ion-transport coefficients in gas mixtures
NASA Technical Reports Server (NTRS)
Whealton, J. H.; Mason, E. A.; Robson, R. E.
1974-01-01
Simple momentum-transfer theory for the composition dependence of ion mobilities and diffusion coefficients in gas mixtures at arbitrary field strengths is corrected and extended, and compared with a similar theory based on momentum and energy transfer, and with results based on direct solution of the Boltzmann equation by Kihara's method. Final equations are recommended for predicting composition dependences, given only results on ion mobilities and diffusion coefficients in the pure component gases.
Composition dependence of ion transport coefficients in gas mixtures
NASA Technical Reports Server (NTRS)
Whealton, J. H.; Mason, E. A.; Robson, R. E.
1973-01-01
A simple momentum-transfer theory for the composition dependence of ion mobilities and diffusion coefficients in gas mixtures at arbitrary field strengths is corrected, extended, and compared with a similar theory based on momentum and energy transfer, and with results based on direct solution of the Boltzmann equation by Kihara's method. Final equations are recommended for predicting composition dependences, given only results on ion mobilities and diffusion coefficients in the pure component gases.
Molecular Diffusion Coefficients: Experimental Determination and Demonstration.
ERIC Educational Resources Information Center
Fate, Gwendolyn; Lynn, David G.
1990-01-01
Presented are laboratory methods which allow the demonstration and determination of the diffusion coefficients of compounds ranging in size from water to small proteins. Included are the procedures involving the use of a spectrometer, UV cell, triterated agar, and oxygen diffusion. Results including quantification are described. (CW)
Fractal diffusion coefficient from dynamical zeta functions
G. Cristadoro
2005-09-28
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.
Notes on Updated Diffusion Coefficients* University of Delaware
Wang, Hai
these diffusion coefficients in flame modeling, the temperature dependence of binary diffusion coefficients at 1 9, pp. 353-363 (2005). #12;Table 1 Summary of polynomial coefficients for updated binary diffusionNotes on Updated Diffusion Coefficients* Hai Wang University of Delaware December 10, 2003 The need
Toshitaka Funazukuri; Chang Yi Kong; Seiichiro Kagei
2006-01-01
Dr. Aydin Akgerman greatly contributed to studies on diffusion in liquids and supercritical fluids, in particular, measurements by the Taylor dispersion method. Based on his work, this article describes recent progress in measurements for binary diffusion coefficients in supercritical fluids by using the chromatographic impulse response technique as well as the Taylor dispersion method, and in the predictive empirical correlations.
Precision of diffusion coefficients by the isotope exchange technique
Masao Nanba; Y. Oishi; Ken Ando
1981-01-01
The precision of diffusion coefficients determined by the gas–solid isotope exchange technique was analyzed for planar sheet diffusion, rate controlled by the isotope exhange reaction. An objective function was employed to estimate the degree of fit of a theoretical calculation to the experimental diffusion profile as a function of the sample size (l), the diffusion coefficient (D), the surface exchange
An Ion Diffusion Model in Semi-Permeable Clay Materials
Liu, Chongxuan
2007-08-01
Ion diffusion in semi-impermeable clay materials dynamically interacts with electrostatic fields (or diffuse double layers) associated with clay particles. Current theory of ion transport in porous media containing fixed charges on solid materials, however, cannot explicitly account for the dynamic interactions. Here we proposed a model by coupling electrodynamics and nonequilibrium thermodynamics to describe ion diffusion in the clay materials. The developed model was validated by comparing the calculated and measured apparent ion diffusion coefficients in clay materials as a function of ionic strength, which affects the overlap extent of the electrostatic double layers associated with adjacent clay particles. The model shows that ion diffusion in clay materials is a complex function of factors including surface charge density, tortuosity, porosity, chemico-osmotic coefficient, and ion self-diffusivity. At transitional states, ion diffusive fluxes are dynamically related to the electrostatic fields, which shrink or expand as ion diffusion. At steady states, the electrostatic fields are time-invariant and ion diffusive fluxes conform to flux and concentration gradient relationships; and apparent diffusivity can be expressed by the ion diffusivity in bulk electrolytes corrected by a tortuosity factor and concentration gradient variations at the interfaces between clay materials and bulk solutions.
Continuum estimate of the heavy quark momentum diffusion coefficient $?$
Olaf Kaczmarek
2014-09-12
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.
Annunziata, Onofrio
(Lij)0 for each composition at pH 4.5 and 6.0. Binary diffusion coefficients of aqueous lysozyme not be the case. For example, binary diffusion coefficient measurements in dilute solutions have long been usedExtraction of Thermodynamic Data from Ternary Diffusion Coefficients. Use of Precision Diffusion
Diffusion coefficient measurements of transparent liquid solutions using Moiré deflectometry
Kazem Jamshidi-Ghaleh; Mohammad Taghi Tavassoly; Nastaran Mansour
2004-01-01
In this study the Moiré deflectometry technique is applied to the investigation of diffusion dynamics in transparent liquid mixtures. We describe the experimental details and present theoretical analysis for obtaining the magnitude of diffusion coefficient using the Moiré fringe patterns. The theoretical aspects of the method are presented and the relationship between the Moiré fringes shift and the diffusion coefficient
On measurement of thermal diffusion coefficients in multicomponent mixtures
Firoozabadi, Abbas
for measuring thermal diffusion coefficients analogous to the existing equations for a binary mixture for the thermal diffusion coefficient of binary liquids in a thermogravitational column is from the work of Furry parameter positive thermal diffusion ratio in a binary and one for the negative parameter. In this work
Binary Diffusion Coefficients for Aqueous Solutions of Lactic Acid
Ana C. F. Ribeiro; Victor M. M. Lobo; Derek G. Leaist; Joaquim J. S. Natividade; Luís P. Veríssimo; Marisa C. F. Barros; Ana M. T. D. P. V. Cabral
2005-01-01
Taylor dispersion equipment installed at the University of Coimbra for the measurement of diffusion in liquids has been tested to ensure adequate accuracy and precision by measuring mutual diffusion coefficients for binary aqueous solutions of sucrose, glycine, lithium chloride, potassium chloride, and hydrochloric acid at 298.15 K. In addition, binary mutual diffusion coefficients for aqueous solutions of lactic acid (not
Aggregate influence on chloride ion diffusion into concrete
Hobbs, D.W.
1999-12-01
An attempt is made to predict the probable effect of the aggregate on chloride ion diffusion into saturated concrete. It is shown that if the chloride ion diffusion coefficient of an aggregate ranges from 0.2 to 10 times that of the cement past matrix, then this could result in variations in the concrete chloride ion diffusion coefficient of up to 10:1. Such a variation is equivalent to a change in free water-cement ration from 0.77 to 0.45.
Diffusion coefficient of three-dimensional Yukawa liquids
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
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.
Determination of the zincate diffusion coefficient and its application to alkaline battery problems
NASA Technical Reports Server (NTRS)
May, C. E.; Kautz, Harold E.
1978-01-01
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.
Determination of the zincate diffusion coefficient and its application to alkaline battery problems
NASA Technical Reports Server (NTRS)
May, C. E.; Kautz, H. E.
1978-01-01
The diffusion coefficient for the zincate ion at 24 C was found to be 9.9 x 10 to the -7th power sq cm/sec + or - 30% in 45% potassium hydroxide and 1.4 x 10 to the -7th power sq cm/sec + or - 25% in 40% 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.
Binary mutual diffusion coefficients of aqueous ammonium and potassium sulfates at 25°C
Derek G. Leaist; Ling Hao
1992-01-01
The diffusion coefficients of aqueous ammonium and potassium ions at infinite dilution differ by only 0.01% at 25C, so, according\\u000a to Nernst's law, the binary mutual diffusion coefficients D of pairs of dilute aqueous ammonium and potassium salts should\\u000a be nearly identical. Yet precise optical interferometric data for ammonium and potassium sulfates contradict this rule: the\\u000a value of D reported
Comparative study of methods used to estimate ionic diffusion coefficients using migration tests
Narsilio, G.A. [Department of Civil and Environmental Engineering, School of Engineering, University of Melbourne, Victoria 3010 (Australia)], E-mail: narsilio@unimelb.edu.au; Li, R. [Department of Civil and Environmental Engineering, School of Engineering, University of Melbourne, Victoria 3010 (Australia); Institute of Geotechnical Engineering, Southeast University (SEU), Nanjing, Jiangsu (China)], E-mail: lirenmin@seu.edu.cn; Pivonka, P. [Department of Civil and Environmental Engineering, School of Engineering, University of Melbourne, Victoria 3010 (Australia)], E-mail: ppivonka@unimelb.edu.au; Smith, D.W. [Department of Civil and Environmental Engineering, School of Engineering, University of Melbourne, Victoria 3010 (Australia)], E-mail: david.smith@unimelb.edu.au
2007-08-15
Ionic diffusion coefficients are estimated rapidly using electromigration tests. In this paper, electromigration tests are accurately simulated by numerically solving the Nernst-Planck (NP) equation (coupled with the electroneutrality condition (EN)) using the finite element method. Numerical simulations are validated against experimental data obtained elsewhere [E. Samson, J. Marchand, K.A. Snyder, Calculation of ionic diffusion coefficients on the basis of migration test results, Materials and Structures/Materiaux et Constructions 36 (257) (2003) 156-165., H. Friedmann, O. Amiri, A. Ait-Mokhtar, A direct method for determining chloride diffusion coefficient by using migration test, Cement and Concrete Research 34 (11) (2004) 1967-1973.]. It is shown that migration due to the non-linear electric potential completely overwhelms diffusion due to concentration gradients. The effects of different applied voltage differences and chloride source concentrations on estimations of chloride diffusion coefficients are explored. We show that the pore fluid within concrete and mortar specimens generally differs from the curing solution, lowering the apparent diffusion coefficient, primarily due to interactions of chloride ions with other ions in the pore fluid. We show that the variation of source chloride concentration strongly affects the estimation of diffusion coefficients in non-steady-state tests; however this effect vanishes under steady-state conditions. Most importantly, a comparison of diffusion coefficients obtained from sophisticated analyses (i.e., NP-EN) and a variety of commonly used simplifying methods to estimate chloride diffusion coefficients allows us to identify those methods and experimental conditions where both approaches deliver good estimates for chloride diffusion coefficients. Finally, we demonstrate why simultaneous use and monitoring of current density and fluxes are recommended for both the non-steady and steady-state migration tests.
Velocity-Space Diffusion Coefficients Due to Full-Wave ICRF Fields in Toroidal Geometry
Harvey, R.W. [CompX, P.O. Box 2672, Del Mar, CA 92014-5672 (United States); Jaeger, F.; Berry, L.A.; Batchelor, D.B.; D'Azevedo, E.; Carter, M.D. [ORNL, Oak Ridge, TN (United States); Ershov, N.M.; Smirnov, A.P. [Moscow State Univ. (Russian Federation); Bonoli, P.; Wright, J.C. [PSFC, MIT, Boston, MA (United States); Smithe, D.N. [ATK-Mission Research (United States)
2005-09-26
Jaeger et al. have calculated bounce-averaged QL diffusion coefficients from AORSA full-wave fields, based on non-Maxwellian distributions from CQL3D Fokker-Planck code. A zero banana-width approximation is employed. Complementing this calculation, a fully numerical calculation of ion velocity diffusion coefficients using the full-wave fields in numerical tokamak equilibria has been implemented to determine the finite orbit width effects. The un-approximated Lorentz equation of motion is integrated to obtain the change in velocity after one complete poloidal transit of the tokamak. Averaging velocity changes over initial starting gyro-phase and toroidal angle gives bounce-averaged diffusion coefficients. The coefficients from the full-wave and Lorentz orbit methods are compared for an ITER DT second harmonic tritium ICRF heating case: the diffusion coefficients are similar in magnitude but reveal substantial finite orbit effects.
Optical determination of molecule diffusion coefficients in polymer films
R. P. Podgorsek; H. Franke
1998-01-01
We present a method using surface-plasmon leaky mode spectroscopy for the analysis of the vapor-molecule diffusion process in polymer films leading to the diffusion coefficients of the molecules. The solution of the diffusion differential equation in the case of thin films yields a molecule concentration profile. Linearity between refractive index increase and molecule concentration gives the same variation for the
Ion Diffusion in polyelectrolyte solution
NASA Astrophysics Data System (ADS)
Jia, Pengxiang; Zhao, Jiang
2010-03-01
We use fluorescence correlation spectroscopy to study diffusion of sparse charged fluorescent molecules as probes of ions in the solution of polystyrene sulfonate (PSS-Na+). The diffusion of the probe was found to depend strongly on its charged state. More importantly, the diffusion of positively charged probes depends strongly the concentration and molecular weight of PSS- Na+. The results show that the fraction of free ``counterions'' in the solution decreases sharply with the increase of the polymer concentration and the molecular weight, showing the role of entropy and electrostatic interaction in the distribution of counterions around the polyelectrolyte chains.
Apparent Diffusion Coefficients from High Angular Resolution Diffusion Imaging: Estimation and
Chen, Yiling
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
Analytic expressions for ULF wave radiation belt radial diffusion coefficients
Ozeke, Louis G; Mann, Ian R; Murphy, Kyle R; Jonathan Rae, I; Milling, David K
2014-01-01
We present analytic expressions for ULF wave-derived radiation belt radial diffusion coefficients, as a function of L and Kp, which can easily be incorporated into global radiation belt transport models. The diffusion coefficients are derived from statistical representations of ULF wave power, electric field power mapped from ground magnetometer data, and compressional magnetic field power from in situ measurements. We show that the overall electric and magnetic diffusion coefficients are to a good approximation both independent of energy. We present example 1-D radial diffusion results from simulations driven by CRRES-observed time-dependent energy spectra at the outer boundary, under the action of radial diffusion driven by the new ULF wave radial diffusion coefficients and with empirical chorus wave loss terms (as a function of energy, Kp and L). There is excellent agreement between the differential flux produced by the 1-D, Kp-driven, radial diffusion model and CRRES observations of differential electron flux at 0.976 MeV—even though the model does not include the effects of local internal acceleration sources. Our results highlight not only the importance of correct specification of radial diffusion coefficients for developing accurate models but also show significant promise for belt specification based on relatively simple models driven by solar wind parameters such as solar wind speed or geomagnetic indices such as Kp. Key Points Analytic expressions for the radial diffusion coefficients are presented The coefficients do not dependent on energy or wave m value The electric field diffusion coefficient dominates over the magnetic
Improved diffusion coefficients generated from Monte Carlo codes
Herman, B. R.; Forget, B.; Smith, K. [Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States); Aviles, B. N. [Knolls Atomic Power Laboratory, Bechtel Marine Propulsion Corporation, P.O. Box 1072, Schenectady, NY 12301-1072 (United States)
2013-07-01
Monte Carlo codes are becoming more widely used for reactor analysis. Some of these applications involve the generation of diffusion theory parameters including macroscopic cross sections and diffusion coefficients. Two approximations used to generate diffusion coefficients are assessed using the Monte Carlo code MC21. The first is the method of homogenization; whether to weight either fine-group transport cross sections or fine-group diffusion coefficients when collapsing to few-group diffusion coefficients. The second is a fundamental approximation made to the energy-dependent P1 equations to derive the energy-dependent diffusion equations. Standard Monte Carlo codes usually generate a flux-weighted transport cross section with no correction to the diffusion approximation. Results indicate that this causes noticeable tilting in reconstructed pin powers in simple test lattices with L2 norm error of 3.6%. This error is reduced significantly to 0.27% when weighting fine-group diffusion coefficients by the flux and applying a correction to the diffusion approximation. Noticeable tilting in reconstructed fluxes and pin powers was reduced when applying these corrections. (authors)
Heavy Quark Momentum Diffusion Coefficient from Lattice QCD
Debasish Banerjee; Saumen Datta; Rajiv Gavai; Pushan Majumdar
2011-12-13
The momentum diffusion coefficient for heavy quarks is studied in a deconfined gluon plasma in the static approximation by investigating a correlation function of the color electric field using Monte Carlo techniques. The diffusion coefficient is extracted from the long distance behavior of such a correlator. For temperatures Tc < T <~ 2 Tc, our nonperturbative estimate of the diffusion coefficient is found to be very different from the leading order perturbation theory, and is in the right ballpark to explain the heavy quark flow seen by PHENIX at RHIC.
Study of diffusion coefficients of glasses under zero-G
NASA Technical Reports Server (NTRS)
Kinser, D. L.
1975-01-01
Diffusion studies of the glass forming ion are examined in zero-g environments and diffusion data obtained from these experiments are unique because of earth based experimental problems. The choice of system for diffusion studies is discussed along with the lab processing. The space processing is described consisting of a heating cycle designed to maximize time exposed to the diffusion temperature without exposing the low viscosity melt to gravitational forces.
Morgan, Benjamin J; Madden, Paul A
2014-04-11
Ionic transport in conventional ionic solids is generally considered to proceed via independent diffusion events or "hops." This assumption leads to well-known Arrhenius expressions for transport coefficients, and is equivalent to assuming diffusion is a Poisson process. Using molecular dynamics simulations of the low-temperature B1, B3, and B4 AgI polymorphs, we have compared rates of ion hopping with corresponding Poisson distributions to test the assumption of independent hopping in these common structure types. In all cases diffusion is a non-Poisson process, and hopping is strongly correlated in time. In B1 the diffusion coefficient can be approximated by an Arrhenius expression, though the physical significance of the parameters differs from that commonly assumed. In low temperature B3 and B4, diffusion is characterized by concerted motion of multiple ions in short closed loops. Diffusion coefficients cannot be expressed in a simple Arrhenius form dependent on single-ion free energies, and intrinsic diffusion must be considered a many-body process. PMID:24765989
Estimation of effective diffusion coefficients in porous catalysts
Kulkarni, Shrikant Ulhas
1991-01-01
OF SCIENCE August 1991 Major Subject: Chemical Engineering ESTIMATION OF EFFECTIVE DIFFUSION COEFFICIENTS IN POROUS CATALYSTS A Thesis by SHRIKANT ULHAS KLLKARXI Approved as to style and content by: R. HL Anthony (Chair ot' Conrmit tee) M.... Nikolaou (Member) M. R osynek (Member) R. %. Plumer elt (Head of Department) August 1991 ABSTRACT Estimation of Effective Diffusion Coefficients in Porous Catalysts. (August 1991) Shrikant Ulhas Kulkarni, B. Chem. Engg. , University of Bombay...
Upscaling matrix diffusion coefficients for heterogeneous fractured rocks
Zhenxue Dai; Andrew Wolfsberg; Zhiming Lu; Paul Reimus
2007-01-01
The scale dependence of the matrix diffusion coefficient (Dm) for fractured media has been observed at variable scales from column experiments to field tracer tests. In this paper, we derive an effective Dm for multimodal heterogeneous fractured rocks using characteristic distributions of matrix properties and volume averaging of the mass transfer coefficient. The effective field-scale Dm is dependent on the
Annunziata, Onofrio
determination of diffusion coefficients for binary and ternary liquid mixtures. For ternary mixtures, the 2 × 2Effect of Macromolecular Polydispersity on Diffusion Coefficients Measured by Rayleigh matrix of multicomponent diffusion coefficients is obtained. Polydispersity adds complexity
Onsager coefficients for binary mixture diffusion in nanopores
R. Krishna; J. M. van Baten
2008-01-01
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
Determination of effective water vapor diffusion coefficient in pemfc gas diffusion layers
Kandlikar, Satish
at higher temperature operation. Diffusion in porous media results in a reduction in the free stream binary used in fuel cell literature is the Bruggeman equation [4] which adjusts the binary diffusionDetermination of effective water vapor diffusion coefficient in pemfc gas diffusion layers Jacob M
Toshitaka Funazukuri; Chang Yi Kong; Seiichiro Kagei
2008-01-01
The hydrodynamic equation D\\/T=???, where D is the infinite dilution binary diffusion or self-diffusion coefficient, T is the temperature, ? is the fluid viscosity, and ? and ? are constants, were demonstrated to be effective for predicting both binary diffusion and self-diffusion coefficients in high density fluids, i.e. liquid and supercritical states. When a solute was specified, the correlation well
Exploring non-linear cosmological matter diffusion coefficients
Hermano Velten; Simone Calogero
2014-07-16
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.
Golmohamadi, Mahmood; Wilkinson, Kevin J
2013-04-15
The diffusion of solutes has been evaluated in an alginate hydrogel as a function of its structure. The role of solute and gel charge on the diffusion measurements were of particular interest. Diffusion coefficients were measured using fluorescence correlation spectroscopy as a function of solute charge and size, bulk solution ionic strength and pH, and gel density. Diffusion coefficients of fluorescent dextrans with hydrodynamic radii up to 6 nm were reduced by 30% in a 1.8% (w/w) hydrogel whereas they were reduced by only 2% in a 0.2% (w/w) hydrogel. The role of ionic strength was examined for various concentrations (0.1-100 mM) and compositions of ions (Na(+), Ca(2+) or mixtures thereof). The diffusion coefficient of a small charged probe (rhodamine 6G, R6G(+)) did not change significantly with increasing ionic strength when sodium was used as the counter ion. The diffusion coefficient was only moderately influenced by the charge of solutes (from +1 to -2). Similarly, pH variations from 3 to 9 had little impact on the diffusion coefficients of R6G(+) in the gel. On the other hand, the addition of Ca(2+) had a significant impact on gel compactness, which led to a significant reduction in solute diffusion. For the calcium alginate hydrogels, structural modifications resulting from Ca binding were much more important than electrostatic effects due to modifications of the gel Donnan potential. PMID:23544513
Calculation of self-diffusion coefficients in iron
Zhang, Baohua, E-mail: zhangbh148@qq.com [Laboratory for High Temperature and High Pressure Study of the Earth's Interior, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, Guizhou 550002, China and Institute for Study of the Earth's Interior, Okayama University, Misasa, Tottori-ken 682-0193 (Japan)] [Laboratory for High Temperature and High Pressure Study of the Earth's Interior, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, Guizhou 550002, China and Institute for Study of the Earth's Interior, Okayama University, Misasa, Tottori-ken 682-0193 (Japan)
2014-01-15
On the basis of available P-V-T equation of state of iron, the temperature and pressure dependence of self-diffusion coefficients in iron polymorphs (?, ?, ? and ? phases) have been successfully reproduced in terms of the bulk elastic and expansivity data by means of a thermodynamical model that interconnects point defects parameters with bulk properties. The calculated diffusion parameters, such as self-diffusion coefficient, activation energy and activation volume over a broad temperature range (500-2500 K) and pressure range (0-100 GPa), compare favorably well with experimental or theoretical ones when the uncertainties are considered.
Diffusion coefficient and shear viscosity of rigid water models
NASA Astrophysics Data System (ADS)
Tazi, Sami; Bo?an, Alexandru; Salanne, Mathieu; Marry, Virginie; Turq, Pierre; Rotenberg, Benjamin
2012-07-01
We report the diffusion coefficient and viscosity of popular rigid water models: two non-polarizable ones (SPC/E with three sites, and TIP4P/2005 with four sites) and a polarizable one (Dang-Chang, four sites). We exploit the dependence of the diffusion coefficient on the system size (Yeh and Hummer 2004 J. Phys. Chem. B 108 15873) to obtain the size-independent value. This also provides an estimate of the viscosity of all water models, which we compare to the Green-Kubo result. In all cases, a good agreement is found. The TIP4P/2005 model is in better agreement with the experimental data for both diffusion and viscosity. The SPC/E and Dang-Chang models overestimate the diffusion coefficient and underestimate the viscosity.
Diffusion coefficient and shear viscosity of rigid water models.
Tazi, Sami; Bo?an, Alexandru; Salanne, Mathieu; Marry, Virginie; Turq, Pierre; Rotenberg, Benjamin
2012-07-18
We report the diffusion coefficient and viscosity of popular rigid water models: two non-polarizable ones (SPC/E with three sites, and TIP4P/2005 with four sites) and a polarizable one (Dang-Chang, four sites). We exploit the dependence of the diffusion coefficient on the system size (Yeh and Hummer 2004 J. Phys. Chem. B 108 15873) to obtain the size-independent value. This also provides an estimate of the viscosity of all water models, which we compare to the Green-Kubo result. In all cases, a good agreement is found. The TIP4P/2005 model is in better agreement with the experimental data for both diffusion and viscosity. The SPC/E and Dang-Chang models overestimate the diffusion coefficient and underestimate the viscosity. PMID:22739097
Diffusion of ions in sea water and in deep-sea sediments
Yuan-Hui Li; Sandra Gregory
1974-01-01
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
The diffusion of ions in unconsolidated sediments
Manheim, F. T.
1970-01-01
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.
THE DETERMINATION OF DIFFUSION COEFFICIENT OF INVERT MATERIALS
P. Heller and J. Wright
2000-01-11
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.
A pumping system for measuring coastal diffusion coefficients
Bolen, Zane Kevin
1980-01-01
) Tsung om Su, Eng. Sc. D. , P. E, (Member) Thomas N. Spen e, P'n. D. ( Mer. . b e r) Donald McDonald, Ph. D. , P. E. (Head of Department) May 19SO ASST. RACT A Pumping System for Neasuring Coastal Diffusion Coefficients. (Nay 1980) Zane Kevin... horizontal diffusion coefficients is described, De- sign calculations are discussed which were used to select the compatible equipmeut consisting of a suction hose, hose reel, pump, and flow board. The pumping system was designed to collect continuous...
Exact curvilinear diffusion coefficients in the repton model.
Buhot, A
2005-10-01
The Rubinstein-Duke or repton model is one of the simplest lattice model of reptation for the diffusion of a polymer in a gel or a melt. Recently, a slightly modified model with hardcore interactions between the reptons has been introduced. The curvilinear diffusion coefficients of both models are exactly determined for all chain lengths. The case of periodic boundary conditions is also considered. PMID:16235000
Measurement of the local particle diffusion coefficient in a magnetized plasma
Meyerhofer, D.D.; Levinton, F.M.
1987-02-01
Local impurity particle diffusion coefficients have been measured in a low temperature plasma by the injection of test particles at the center of the plasma. The injection is accomplished by a high voltage discharge between two small graphite electrodes on a probe. The probe can be located anywhere in the plasma. The diffusion is observed spectroscopically. An analysis of the spatial and temporal evolution of the CII radiation from the carbon discharge can determine the parallel and perpendicular diffusion of the impurity ions. Results with the diagnostic have been obtained in the Proto S-1/C spheromak. The measured value of the diffusion coefficient in the afterglow plasma is in good agreement with classical predictions.
Diffusion coefficients and particle transport in synthetic membrane channels
NASA Astrophysics Data System (ADS)
Pagliara, S.; Dettmer, S. L.; Misiunas, K.; Lea, L.; Tan, Y.; Keyser, U. F.
2014-12-01
Diffusion in constrained geometries is paramount to transport across biological membranes and in mesoporous materials. Although the transported species vary from system to system, the underlying physical mechanisms are universal. However, there is an imbalance between theory and quantitative experimental model systems. We have recently introduced a new synthetic approach to mimic molecular diffusion based on colloidal particles, digital video microscopy, particle tracking, microfluidics and holographic optical tweezers. In this paper we report useful guidelines for the fabrication, handling and characterisation of the microfluidic chips and a study of diffusion coefficients, particle attempt and translocation rates through microfluidic channels with cross sections of different dimensions.
Asymptotic diffusion coefficient of particles in a random medium
NASA Astrophysics Data System (ADS)
Ambaye, Hailemariam; Kehr, Klaus W.
1995-05-01
Avramov, Milchev, and Argyrakis [Phys. Rev. E 47, 2303 (1993)] have investigated the mean-square displacements of particles that perform random walks in two- and three-dimensional lattices with random barriers with uniform distributions of activation energies. They discussed the crossover between anomalous and normal diffusion, but they did not analyze the behavior of the mean-square displacements at long times where normal diffusion occurs. We point out that the asymptotic diffusion coefficients are well described by the effective-medium theory in the range of parameters investigated; they are in disagreement with the predictions of critical-path arguments in dimension d=3.
Wo?nica, Emilia; Mieczkowski, Józef; Michalska, Agata
2011-11-21
The origin and effect of surface accumulation of primary ions within the ion-selective poly(n-butyl acrylate)-based membrane, obtained by thermal polymerization, is discussed. Using a new method, based on the relation between the shape of a potentiometric plot and preconditioning time, the diffusion of copper ions in the membrane was found to be slow (the diffusion coefficient estimated to be close to 10(-11) cm(2) s(-1)), especially when compared to ion-exchanger counter ions--sodium cations diffusion (a diffusion coefficient above 10(-9) cm(2) s(-1)). The higher mobility of sodium ions than those of the copper-ionophore complex results in exposed ion-exchanger role leading to undesirably exposed sensitivity to sodium or potassium ions. PMID:21957488
Zhu, Qingyu; Moggridge, Geoff D.; D’Agostino, Carmine
2015-04-29
. However, in general, it is more correct to state that the diffusion flux originates from the deviation from equilibrium between molecular friction and thermodynamic interactions (Taylor and Krishna, 1993). Thus, from a thermodynamic perspective... and frictional coefficients for the systems benzene–chlorobenzene, benzene–n-hexane and benzene n-heptane at 25 oC. J. Phys. Chem 74 (19), 3518–3529. Hartley, G.S., J. Crank, J., 1949. Some fundamental definitions and concepts in diffusion processes. Trans...
Does the photon-diffusion coefficient depend on absorption?
Boas, David
Does the photon-diffusion coefficient depend on absorption? T. Durduran and A. G. Yodh Department independent of absorption, i.e., D0 v/3 s . After presentation of the general theoretical arguments underlying this assertion, Monte Carlo simulations are performed and explicitly reveal that the absorption- independent
On the Diffusion Coefficient: The Einstein Relation and Beyond
Goran Peskir
2003-01-01
We present a detailed derivation of the closed-form expression for the diffusion coefficient that was initially obtained by Einstein.[4] The present derivation does not make use of a fictitious force as did the original Einstein derivation, but instead concentrates directly on establishing a dynamic equilibrium between the forces of pressure and friction acting on a Brownian particle. This approach makes
Comparison of field-measured radon diffusion coefficients with laboratory-measured coefficients
Lepel, E.A.; Silker, W.B.; Thomas, V.W.; Kalkwarf, D.R.
1983-04-01
Experiments were conducted to compare radon diffusion coefficients determined for 0.1-m depths of soils by a steady-state method in the laboratory and diffusion coefficients evaluated from radon fluxes through several-fold greater depths of the same soils covering uranium-mill tailings. The coefficients referred to diffusion in the total pore volume of the soils and are equivalent to values for the quantity, D/P, in the Generic Environmental Impact Statement on Uranium Milling prepared by the US Nuclear Regulatory Commission. Two soils were tested: a well-graded sand and an inorganic clay of low plasticity. For the flux evaluations, radon was collected by adsorption on charcoal following passive diffusion from the soil surface and also from air recirculating through an aluminum tent over the soil surface. An analysis of variance in the flux evaluations showed no significant difference between these two collection methods. Radon diffusion coefficients evaluated from field data were statistically indistinguishable, at the 95% confidence level, from those measured in the laboratory; however, the low precision of the field data prevented a sensitive validation of the laboratory measurements. From the field data, the coefficients were calculated to be 0.03 +- 0.03 cm/sup 2//s for the sand cover and 0.0036 +- 0.0004 cm/sup 2//s for the clay cover. The low precision in the coefficients evaluated from field data was attributed to high variation in radon flux with time and surface location at the field site.
The effects of deionization processes on meteor radar diffusion coefficients below 90 km
NASA Astrophysics Data System (ADS)
Younger, J. P.; Lee, C. S.; Reid, I. M.; Vincent, R. A.; Kim, Y. H.; Murphy, D. J.
2014-08-01
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.
Secondary Ion Mass Spectrometry for Mg Tracer Diffusion: Issues and Solutions
Tuggle, Jay [Virginia Polytechnic Institute and State University; Giordani, Andrew [Virginia Polytechnic Institute and State University; Kulkarni, Nagraj S [ORNL; Warmack, Robert J Bruce [ORNL; Coffey, Kevin [University of Central Florida; Sohn, Yong Ho [University of Central Florida; HunterJr., Jerry [Virginia Polytechnic Institute and State University
2014-01-01
A Secondary Ion Mass Spectrometry (SIMS) method has been developed to measure stable Mg isotope tracer diffusion. This SIMS method was then used to calculate Mg self- diffusivities and the data was verified against historical data measured using radio tracers. The SIMS method has been validated as a reliable alternative to the radio-tracer technique for the measurement of Mg self-diffusion coefficients and can be used as a routine method for determining diffusion coefficients.
Do thermal diffusion and Dufour coefficients satisfy Onsager's reciprocity relation?
Würger, Alois
2014-10-01
It is commonly admitted that in liquids the thermal diffusion and Dufour coefficients D(T) and D(F) 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 D(T) arises from chemical reactions or viscous effects but is not related to the Dufour coefficient D(F). The situation is less clear for binary molecular mixtures; available experimental and simulation data do not settle the question whether D(T) and DF are reciprocal coefficients. PMID:25341414
NASA Astrophysics Data System (ADS)
Kowsari, M. H.; Alavi, Saman; Ashrafizaadeh, Mahmud; Najafi, Bijan
2008-12-01
Molecular dynamics simulations are used to study the dynamics and transport properties of 12 room-temperature ionic liquids of the 1-alkyl-3-methylimidazolium [amim]+ (alkyl=methyl, ethyl, propyl, and butyl) family with PF6-, NO3-, and Cl- counterions. The explicit atom transferable force field of Canongia Lopes et al. [J. Phys. Chem. B 108, 2038 (2004)] is used in the simulations. In this first part, the dynamics of the ionic liquids are characterized by studying the mean-square displacement (MSD) and the velocity autocorrelation function (VACF) for the centers of mass of the ions at 400 K. Trajectory averaging was employed to evaluate the diffusion coefficients at two temperatures from the linear slope of MSD(t) functions in the range of 150-300 ps and from the integration of the VACF(t) functions at 400 K. Detailed comparisons are made between the diffusion results from the MSD and VACF methods. The diffusion coefficients from the integration of the VACFs are closer to experimental values than the diffusion coefficients calculated from the slope of MSDs. Both methods can show good agreement with experiment in predicting relative trends in the diffusion coefficients and determining the role of the cation and anion structures on the dynamical behavior of this family of ionic liquids. The MSD and self-diffusion of relatively heavier imidazolium cations are larger than those of the lighter anions from the Einstein results, except for the case of [bmim][Cl]. The cationic transference number generally decreases with temperature, in good agreement with experiments. For the same anion, the cationic transference numbers decrease with increasing length of the alkyl chain, and for the same cation, the trends in the cationic transference numbers are [NO3]-<[Cl]-<[PF6]-. The trends in the diffusion coefficient in the series of cations with identical anions are [emim]+>[pmim]+>[bmim]+ and those for anions with identical cations are [NO3]->[PF6]->[Cl]-. The [dmim]+ has a relatively low diffusion coefficient due to its symmetric structure and good packing in the liquid phase. The major factor for determining the magnitude of the self-diffusion is the geometric shape of the anion of the ionic liquid. Other important factors are the ion size and the charge delocalization in the anion.
Zhou, Quanlin
rock Yingqi Zhang,1 Hui-hai Liu,1 Quanlin Zhou,1 and Stefan Finsterle1 Received 16 August 2005; revised diffusion coefficient for fractured rock, Water Resour. Res., 42, W04405, doi:10.1029/2005WR004513. 1 in fractured rock. Understand- ing the diffusion of contaminants from fractures into the matrix is essential
Chowdhury, Mohammed Tareque, E-mail: mtareque@mail.tagen.tohoku.ac.jp; Takekawa, Reiji; Iwai, Yoshiki; Kuwata, Naoaki; Kawamura, Junichi [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1, Katahira, Aoba-ku Sendai 980-8577 (Japan)] [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1, Katahira, Aoba-ku Sendai 980-8577 (Japan)
2014-03-28
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{sup ?11} m{sup 2}/s in the direction perpendicular to the c axis at room temperature. The Li ion diffusion coefficient along the c axis direction was found to be very small (6.4 × 10{sup ?13} m{sup 2}/s at 333 K), which suggests that the macroscopic diffusion of the Li ion in the ?-alumina crystal is mainly two-dimensional. The diffusion coefficient for the same sample was also estimated using NMR line narrowing data and impedance measurements. The impedance data show reasonable agreement with PFG-NMR data, while the line narrowing measurements provided a lower value for the diffusion coefficient. Line narrowing measurements also provided a relatively low value for the activation energy and pre-exponential factor. The temperature dependent diffusion coefficient was obtained in the temperature range 297–333 K by PFG-NMR, from which the activation energy for diffusion of the Li ion was estimated. The activation energy obtained by PFG-NMR was smaller than that obtained by impedance measurements, which suggests that thermally activated defect formation energy exists for 93% Li ?-alumina single crystals. The diffusion time dependence of the diffusion coefficient was observed for the Li ion in the 93% Li ?-alumina single crystal by means of PFG-NMR experiments. Motion of Li ion in fractal dimension might be a possible explanation for the observed diffusion time dependence of the diffusion coefficient in the 93% Li ?–alumina system.
Diffusion of ion implanted aluminum in silicon carbide
Tajima, Y.; Kijima, K.; Kingery, W.D.
1982-09-01
Diffusion of aluminum in silicon carbide was studied by Al implantation into single crystal SiC and subsequent profile analyses by secondary ion mass spectrometry (SIMS). The bulk diffusion coefficient of Al at temperatures between 1350 and 1800 /sup 0/C was determined to be D(cm/sup 2//s) = 1.3 x 10/sup -8/ exp (-231 kJ/mol/RT). The results were characterized by a low activation energy and a low pre-exponential constant compared with previously reported results. Dislocation enhanced diffusion was suggested from the appearance of the tails observed in the annealed concentration profiles.
Vertical eddy diffusion coefficient from the LANDSAT imagery
NASA Technical Reports Server (NTRS)
Viswanadham, Y. (principal investigator); Torsani, J. A.
1982-01-01
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.
Takeda, M.; Hiratsuka, T.; Ito, K.; Finsterle, S.
2011-02-01
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.
T. Stefansson; T. Berge; R. Lausund; H. R. Skullerud
1988-01-01
A drift-tube mass spectrometer for precision measurements of transport coefficients for ions in gases is described. The apparatus has been used to determine the ratio DT\\/ mu between the transverse diffusion coefficient and the mobility for He+ ions in the helium at 294 K and 15
Lead diffusion in apatite and zircon using ion implantation and Rutherford Backscattering techniques
D. J. Cherniak; W. A. Lanford; F. J. Ryerson
1991-01-01
Ion implantation was used to introduce Pb into the minerals zircon and apatite. Diffusion profiles were obtained using Rutherford Backscattering, and the results were fitted with a model to determine the diffusion coefficients. This approach is both simple and useful in studying diffusion over a temperature range of geologic interest without inordinate annealing times. Results for apatite over the temperature
Dix, J A; Diamond, J M; Kivelson, D
1974-02-01
The translational diffusion coefficient and the partition coefficient of a spin-labeled solute, di-t-butyl nitroxide, in an aqueous suspension of dipalmitoyl lecithin vesicles have been studied by electron spin resonance spectroscopy. When the lecithin is cooled through its phase transition temperature near 41 degrees C, some solute is "frozen out" of the bilayer, and the standard partial molar enthalpy and entropy of partition go more positive by a factor of 8 and 6, respectively. However, the apparent diffusion constant in the lecithin phase is only slightly smaller than that in water, both above and below the transition temperature. The fraction of bilayer volume within which solute is distributed may increase with temperature, contributing to the positive enthalpy of partition. Comparison of time constants suggests that there is a permeability barrier to this solute in the periphery of the bilayer. PMID:4360944
Response of radiation belt simulations to different radial diffusion coefficients
NASA Astrophysics Data System (ADS)
Drozdov, A.; Shprits, Y.; Subbotin, D.; Kellerman, A. C.
2013-12-01
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.
John C. Slattery; R. Byron Bird
1958-01-01
A corresponding-states correlation of low-density binary- and self-diffusion coefficients is presented. The equations are simple to use, are sdciently accurate for most calculations, and correlate those data used in their derivation somewhat better than calculations based on the Lennard-Jones potential if potential parameters have to be estimated from the critical properties. The Enskog kinetic theory of dense gases is used
Network modeling of diffusion coefficients for porous media: II. Simulations
Steele, D.D. [North Dakota State Univ., Fargo, ND (United States); Nieber, J.L. [Univ. of Minnesota, St. Paul, MN (United States)
1994-09-01
Gas diffusion often dominates constituent in porous media (PM) and it dependent on pore geometry, water content, and water distribution in PM. Network models of PM offer the ability to investigate the influence and interaction of pore-scale PM properties and fluid properties on macroscopic properties of the system. This study was conducted to investigate the macroscopic relative gas diffusion coefficient vs. air-filled porosity relationship or diffusion characteristic (DC) of PM using a network model. The network model was used to simulate DCs in wetting and drying PM containing air and water. A network size of nine by nine spheres was used; increasing the network size to 19 by 19 by 19 produced essentially no change in the DC. The DC was independent of Henry`s law gas-liquid partition coefficient (H) for H values of 0.1, 1.0, and 5.0. The product HR{sub W}, where R{sub W} is the ratio between the bulk gas- and liquid-phase diffusion coefficients, strongly influences the DC when H values of 1000 to 10 000 are considered; this indicates that certain organic compounds have DCs independent of air-filled porosity. Hysteresis in DCs was found in selected network cases, with the wetting DCs being greater than the drying DCs for most air-filled porosities, in accord with some experimental results reported in the literature. Spatial correlation of network pore space was shown to bring the simulated DCs into better agreement with some experimental DCs. 23 refs., 10 figs., 3 tabs.
Simulations of anomalous ion diffusion in experimentally measured turbulent potential
NASA Astrophysics Data System (ADS)
Seidl, J.; Krlín, L.; Pánek, R.; Pavlo, P.; Stöckel, J.; Svoboda, V.
2009-08-01
The diffusion of plasma impurities in tokamak-edge-plasma turbulence is investigated numerically. The time-dependent potential governing particle motion was measured by 2D array of 8×8 Langmuir probes in edge region of CASTOR tokamak. The diffusion of particles is found to be classical in the radial direction, but it can be of an anomalous Lévy-walk type in the poloidal direction. The diffusion is found to be dependent on the ratio of particles’ mass and charge. When this ratio grows, the diffusion coefficient in radial direction grows as well, whereas poloidal diffusion coefficient drops down. Moreover, movement of particles in the time-frozen snapshot of this potential is investigated showing that also the time-independent potential is much more favorable for the particle diffusion in poloidal direction than in radial one. In the case of single ionized carbon ions the poloidal diffusion in time-independent potential transits to the Lévy-walk type for temperatures greater than 25 eV, for radial diffusion Lévy-walk was not observed even for 500 eV.
Kalwarf, D.R.; Nielson, K.K.; Rich, D.C.; Rogers, V.C.
1982-11-01
A method was developed and used to determine radon diffusion coefficients in compacted soils by transient-diffusion measurements. A relative standard deviation of 12% was observed in repeated measurements with a dry soil by the transient-diffusion method, and a 40% uncertainty was determined for moistures exceeding 50% of saturation. Excellent agreement was also obtained between values of the diffusion coefficient for radon in air, as measured by the transient-diffusion method, and those in the published literature. Good agreement was also obtained with diffusion coefficients measured by a steady-state method on the same soils. The agreement was best at low moistures, averaging less than ten percent difference, but differences of up to a factor of two were observed at high moistures. The comparison of the transient-diffusion and steady-state methods at low moistures provides an excellent verification of the theoretical validity and technical accuracy of these approaches, which are based on completely independent experimental conditions, measurement methods and mathematical interpretations.
Distribution coefficients of rare earth ions in cubic zirconium dioxide
NASA Astrophysics Data System (ADS)
Romer, H.; Luther, K.-D.; Assmus, W.
1994-08-01
Cubic zirconium dioxide crystals are grown with the skull melting technique. The effective distribution coefficients for Nd(exp 3+), Sm(exp 3+) and Er(sup 3+) as dopants are determined experimentally as a function of the crystal growth velocity. With the Burton-Prim-Slichter theory, the equilibrium distribution coefficients can be calculated. The distribution coefficients of all other trivalent rare earth ions can be estimated by applying the correlation towards the ionic radii.
Estimation of diffusion coefficients for electrolytes in hot water. Final report. [PWR
W. T. Jr
1981-01-01
Diffusion coefficients are calculated for electrolytes dissolved in water at temperatures 25 to 300Â°C and saturation pressures. Plots and tables are given of estimated diffusion coefficients for NaCl at concentrations from infinite dilution to 4 molal, limiting diffusion coefficients for divalent metal chlorides and for sodium phosphates of several compositions, and tracer diffusion coefficients for hydrochloric acid in sodium chloride
Diffusion behavior of chloride ions in concrete
Zhang, T.; Gjoerv, O.E. [Norwegian Univ. of Science and Technology, Trondheim (Norway). Div. of Building Materials] [Norwegian Univ. of Science and Technology, Trondheim (Norway). Div. of Building Materials
1996-06-01
In the present paper, an analysis of the diffusion behavior of chloride ions in concrete is presented. In concentrated electrolytic aqueous solutions such as seawater or that typically used in laboratory experiments, the effect of ionic interaction may significantly reduce the chemical potential and thus the driving force of the diffusing species. Because of different drift velocities of the cations and chloride ions in the solution, the lagging motion of the cations will also retard the drift velocity of the chlorides. In addition, both the electrical double layer forming on the solid surface and the chemical binding may significantly interfere with the transport of the chloride ions. As a result, the diffusion behavior of the chloride ions in concrete is a more complex and complicated transport process than what can be described by Fick`s law of diffusion.
Firoozabadi, Abbas
New Thermal Diffusion Coefficient Measurements for Hydrocarbon Binary Mixtures: ViscosityVised Manuscript ReceiVed: February 22, 2008 New thermal diffusion coefficients of binary mixtures are measured the recently observed nonmonotonic behavior of thermal diffusion coefficients with molecular weight for binary
Form of multicomponent Fickian diffusion coefficients matrix J. Wambui Mutoru, Abbas Firoozabadi
Firoozabadi, Abbas
. Further, Cullinan argues that these eigenvalues are pseudo-binary diffusion coefficients; thus, they are analogous to diffusion coefficients in binary mixtures which are real positive numbers that are equivalentForm of multicomponent Fickian diffusion coefficients matrix J. Wambui Mutoru, Abbas Firoozabadi
Modeling Infinite Dilution and Fickian Diffusion Coefficients of Carbon Dioxide in Water
Firoozabadi, Abbas
also accurately predicts infinite dilution diffusion coefficients for other binary water mixtures whereModeling 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
Calculation of combined diffusion coefficients in SF{sub 6}-Cu mixtures
Zhong, Linlin; Wang, Xiaohua, E-mail: xhw@mail.xjtu.edu.cn; Rong, Mingzhe, E-mail: mzrong@mail.xjtu.edu.cn; Wu, Yi [State Key Laboratory of Electrical Insulation and Power Equipment, School of Electrical Engineering, Xi'an Jiaotong University, Xi'an 710049 (China); Murphy, Anthony B. [CSIRO Manufacturing Flagship, P.O. Box 218, Lindfield, NSW 2070 (Australia)
2014-10-15
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 SF{sub 6}-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.
Radon diffusion coefficients in soils of varying moisture content
NASA Astrophysics Data System (ADS)
Papachristodoulou, C.; Ioannides, K.; Pavlides, S.
2009-04-01
Radon is a naturally occurring radioactive gas that is generated in the Earth's crust and is free to migrate through soil and be released to the atmosphere. Due to its unique properties, soil gas radon has been established as a powerful tracer used for a variety of purposes, such as exploring uranium ores, locating geothermal resources and hydrocarbon deposits, mapping geological faults, predicting seismic activity or volcanic eruptions and testing atmospheric transport models. Much attention has also been given to the radiological health hazard posed by increased radon concentrations in the living and working environment. In order to exploit radon profiles for geophysical purposes and also to predict its entry indoors, it is necessary to study its transport through soils. Among other factors, the importance of soil moisture in such studies has been largely highlighted and it is widely accepted that any measurement of radon transport parameters should be accompanied by a measurement of the soil moisture content. In principle, validation of transport models in the field is encountered by a large number of uncontrollable and varying parameters; laboratory methods are therefore preferred, allowing for experiments to be conducted under well-specified and uniform conditions. In this work, a laboratory technique has been applied for studying the effect of soil moisture content on radon diffusion. A vertical diffusion chamber was employed, in which radon was produced from a 226Ra source, was allowed to diffuse through a soil column and was finally monitored using a silicon surface barrier detector. By solving the steady-state radon diffusion equation, diffusion coefficients (D) were determined for soil samples of varying moisture content (m), from null (m=0) to saturation (m=1). For dry soil, a D value of 4.1×10-7 m2s-1 was determined, which increased moderately by a factor of ~3 for soil with low moisture content, i.e. up to m ~0.2. At higher water fractions, a decrease in D was initiated and became particularly pronounced approaching complete saturation; at m =0.9, D was as low as 2×10-9 m2s-1. A series of field experiments has also been conducted using alpha-track CR-39 detectors to follow the moisture-dependence of radon diffusion through soil under natural conditions. Diffusion coefficients were determined as a function of surface soil moisture assuming a one-dimensional diffusive radon transport model. Comparison between results obtained by the two methods showed that laboratory studies may provide a good indication of radon diffusion coefficients to be expected in the field. However, values determined in the field were systematically lower than those assessed in the laboratory. This finding could be attributed to soil-dependent parameters, such as differences in pore space geometry between the soil used in laboratory experiments and the undisturbed soil. In the latter case, the higher degree of compaction imposes a more tortuous pathway to soil gas, while at the same time the diffusive gas flux is hindered by local-scale zones of higher bulk density or water content.
Diffusion behavior of chloride ions in concrete
Tiewei Zhang; Odd E. Gjørv
1996-01-01
In the present paper, an analysis of the diffusion behavior of chloride ions in concrete is presented. In concentrated electrolytic aqueous solutions such as seawater or that typically used in laboratory experiments, the effect of ionic interaction may significantly reduce the chemical potential and thus the driving force of the diffusing species. Because of different drift velocities of the cations
Examination of three methods for studying ion diffusion in cement pastes, mortars and concrete
N. R. Buenfeld; J. B. Newman
1987-01-01
Three laboratory techniques for studying ion diffusion in hydrated cement pastes, mortars and concrete are described and compared.\\u000a In the first method, concentration profiles are produced by analysing material sampled at various distances from the surface\\u000a exposed to the selected ion, after various periods of exposure. The second technique employs a diffusion cell and calculation\\u000a of an effective diffusion coefficient
Noel, James Michael
1994-01-01
is the molecular diffusivity of the organic in the supercritical fluid. However, data for diffusivities in supercritical fluids are scarce. Because diffusion coefficients cannot be determined a priofi, it is necessary to measure them. We have utilized the Taylor...
Vicente Garzó; J. Aaron Murray; Francisco Vega Reyes
2013-03-26
The mass flux of a low-density granular binary mixture obtained previously by solving the Boltzmann equation by means of the Chapman-Enskog method is considered further. As in the elastic case, the associated transport coefficients $D$, $D_p$ and $D'$ are given in terms of the solutions of a set of coupled linear integral equations which are approximately solved by considering the first and second Sonine approximations. The diffusion coefficients are explicitly obtained as functions of the coefficients of restitution and the parameters of the mixture (masses, diameters and concentration) and their expressions hold for an arbitrary number of dimensions. In order to check the accuracy of the second Sonine correction for highly inelastic collisions, the Boltzmann equation is also numerically solved by means of the direct simulation Monte Carlo (DSMC) method to determine the mutual diffusion coefficient $D$ in some special situations (self-diffusion problem and tracer limit). The comparison with DSMC results reveals that the second Sonine approximation to $D$ improves the predictions made from the first Sonine approximation. We also study the granular segregation driven by a uni-directional thermal gradient. The segregation criterion is obtained from the so-called thermal diffusion factor $\\Lambda$, which measures the amount of segregation parallel to the temperature gradient. The factor $\\Lambda$ is determined here by considering the second-order Sonine forms of the diffusion coefficients and its dependence on the coefficients of restitution is widely analyzed across the parameter space of the system. The results obtained in this paper extend previous works carried out in the tracer limit (vanishing mole fraction of one of the species) by some of the authors of the present paper.
Salgado-García, R
2014-09-01
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. PMID:25314393
Computing quasi-linear diffusion coefficients using the delta-f particle-in-cell method
Austin, T. M.; Smithe, D. N.; Ranjbar, V. [Tech-X Corporation, 5621 Arapahoe Ave., Suite A, Boulder, CO 80303 (United States)
2009-11-26
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.
Ion radial diffusion in an electrostatic impulse model for stormtime ring current formation
NASA Technical Reports Server (NTRS)
Chen, Margaret W.; Schulz, Michael; Lyons, Larry R.; Gorney, David J.
1992-01-01
Two refinements to the quasi-linear theory of ion radial diffusion are proposed and examined analytically with simulations of particle trajectories. The resonance-broadening correction by Dungey (1965) is applied to the quasi-linear diffusion theory by Faelthammar (1965) for an individual model storm. Quasi-linear theory is then applied to the mean diffusion coefficients resulting from simulations of particle trajectories in 20 model storms. The correction for drift-resonance broadening results in quasi-linear diffusion coefficients with discrepancies from the corresponding simulated values that are reduced by a factor of about 3. Further reductions in the discrepancies are noted following the averaging of the quasi-linear diffusion coefficients, the simulated coefficients, and the resonance-broadened coefficients for the 20 storms. Quasi-linear theory provides good descriptions of particle transport for a single storm but performs even better in conjunction with the present ensemble-averaging.
Measurement of diffusion coefficient of propylene glycol in skin tissue
NASA Astrophysics Data System (ADS)
Genin, Vadim D.; Bashkatov, Alexey N.; Genina, Elina A.; Tuchin, Valery V.
2015-03-01
Optical clearing of the rat skin under the action of propylene glycol was studied ex vivo. It was found that collimated transmittance of skin samples increased, whereas weight and thickness of the samples decreased during propylene glycol penetration in skin tissue. A mechanism of the optical clearing under the action of propylene glycol is discussed. Diffusion coefficient of propylene glycol in skin tissue ex vivo has been estimated as (1.35±0.95)×10-7 cm2/s with the taking into account of kinetics of both weight and thickness of skin samples. The presented results can be useful for enhancement of many methods of laser therapy and optical diagnostics of skin diseases and localization of subcutaneous neoplasms.
Paris-Sud XI, Université de
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
Y. Adda; J. Philibert
1958-01-01
The concentration-penetration curves were established for the Ti--U ; diffusion couple between 950 and 1075 d C. The coefficient of ; chemical diffusion was determined as a function of the concentration. The ; Kirkendall effect was studied quantitatively, and the coefficients of intrinsic ; diffusion were calculated for uranium and titaniuun. (tr-auth);
Meyers, Steven D.
sensing MODIS SeaWiFS Bio-optical algorithm Diffuse attenuation coefficient Euphotic depth Optical data to MODIS/Aqua, MODIS/Terra, and SeaWiFS satellite observations. The products included the diffuse attenuAuthor's personal copy Assessment of satellite-derived diffuse attenuation coefficients
-resolved Raman scattering measurements to determine composition-dependent binary diffusion coefficientsEffective Diffusion Coefficients for Methanol in Sulfuric Acid Solutions Measured by Raman 17, 2008; ReVised Manuscript ReceiVed: August 17, 2008 The diffusion of methanol into 0-96.5 wt
Annunziata, Onofrio
Precision Measurements of Binary and Multicomponent Diffusion Coefficients in Protein Solutions binary diffusion coefficients Dv for lysozyme chloride/water at concentrations from 0.43 to 3.08 mM (6 Naples, Italy ReceiVed October 1, 1998 Abstract: Accurate models of protein diffusion are important
The solid-phase diffusion coefficient (Dm) and material-air partition coefficient (Kma) are key parameters for characterizing the sources and transport of semivolatile organic compounds (SVOCs) in the indoor environment. In this work, a new experimental method was developed to es...
H. S. Harned; J. A. Shropshire
1958-01-01
The diffusion coefficients of lithium and cesium nitrates have been ; measured at 25 deg over a concentration range from 0.003 to 0.015 molar. From ; these data, the activity coefficients of these electrolytes have been compated at ; low concentrations. Similar calculations have been carried cat for lithium and ; potassium perchlorates and potassium nitrate solutions and the results
Prediction of Self-Diffusion Coefficients of Fluids Based on Friction and Free Volume Theories
NASA Astrophysics Data System (ADS)
Zhong, Qiu; Yang, Liping; Tao, Ye; Luo, Caiyun; Xu, Zijun; Xi, Tonggeng
2015-05-01
With a combination of friction and free volume theories, a new equation for calculating the self-diffusion coefficient is presented based on molecular dynamics simulation data in the literature. The equation could be applied to calculate the self-diffusion coefficient of real fluids in the gas or liquid phase. The equation was used to calculate the self-diffusion coefficients of 18 substances. The absolute average relative deviation was 13.79 %.
Controlling chloride ions diffusion in concrete
Zeng, Lunwu; Song, Runxia
2013-01-01
The corrosion of steel in concrete is mainly due to the chemical reaction between the chloride ions and iron ions. Indeed, this is a serious threaten for reinforced concrete structure, especially for the reinforced concrete structure in the sea. So it is urgent and important to protect concrete against chloride ions corrosion. In this work, we report multilayer concrete can cloak chloride ions. We formulated five kinds of concrete A, B, C, D and E, which are made of different proportion of cement, sand and glue, and fabricated six-layer (ABACAD) cylinder diffusion cloak and background media E. The simulation results show that the six-layer mass diffusion cloak can protect concrete against chloride ions penetration, while the experiment results show that the concentration gradients are parallel and equal outside the outer circle in the diffusion flux lines, the iso-concentration lines are parallel outside the outer circle, and the concentration gradients in the inner circle are smaller than those outside the outer circle. PMID:24285220
Controlling chloride ions diffusion in concrete
NASA Astrophysics Data System (ADS)
Zeng, Lunwu; Song, Runxia
2013-11-01
The corrosion of steel in concrete is mainly due to the chemical reaction between the chloride ions and iron ions. Indeed, this is a serious threaten for reinforced concrete structure, especially for the reinforced concrete structure in the sea. So it is urgent and important to protect concrete against chloride ions corrosion. In this work, we report multilayer concrete can cloak chloride ions. We formulated five kinds of concrete A, B, C, D and E, which are made of different proportion of cement, sand and glue, and fabricated six-layer (ABACAD) cylinder diffusion cloak and background media E. The simulation results show that the six-layer mass diffusion cloak can protect concrete against chloride ions penetration, while the experiment results show that the concentration gradients are parallel and equal outside the outer circle in the diffusion flux lines, the iso-concentration lines are parallel outside the outer circle, and the concentration gradients in the inner circle are smaller than those outside the outer circle.
Controlling chloride ions diffusion in concrete.
Zeng, Lunwu; Song, Runxia
2013-01-01
The corrosion of steel in concrete is mainly due to the chemical reaction between the chloride ions and iron ions. Indeed, this is a serious threaten for reinforced concrete structure, especially for the reinforced concrete structure in the sea. So it is urgent and important to protect concrete against chloride ions corrosion. In this work, we report multilayer concrete can cloak chloride ions. We formulated five kinds of concrete A, B, C, D and E, which are made of different proportion of cement, sand and glue, and fabricated six-layer (ABACAD) cylinder diffusion cloak and background media E. The simulation results show that the six-layer mass diffusion cloak can protect concrete against chloride ions penetration, while the experiment results show that the concentration gradients are parallel and equal outside the outer circle in the diffusion flux lines, the iso-concentration lines are parallel outside the outer circle, and the concentration gradients in the inner circle are smaller than those outside the outer circle. PMID:24285220
Diffusion coefficient using pausing time of hydrogen in a-Si:H with exponential energy distribution
NASA Astrophysics Data System (ADS)
Hikita, Harumi; Morigaki, Kazuo
2015-03-01
The diffusion coefficient of hydrogen is obtained for exponential energy distribution in hydrogenated amorphous silicon (a-Si:H). It is shown that the diffusion coefficient follows the form of ??-1 (?: diffusion time) in the case of ? < 1 and a larger ?, in which ? is the ratio of hydrogen temperature to width for energy distribution function. In the case of ? ? 1, as ? reaches infinity at the limit, the hydrogen diffusion approaches Brownian motion.
Shalchi, A., E-mail: andreasm4@yahoo.com [Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2 (Canada)
2013-09-01
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.
Author's personal copy Quaternary diffusion coefficients for the sucroseNaClKClwater system at 25 C
Annunziata, Onofrio
to describe solute diffusion transport in terms of only N solute pseudo-binary diffusion coefficientsAuthor's personal copy Quaternary diffusion coefficients for the sucroseNaClKClwater system: Diffusion electrolyte carbohydrates cross diffusion coupled diffusion Transport properties of saccharide
Collisional-rate coefficients for sodiumlike Ar VIII ions.
NASA Technical Reports Server (NTRS)
Datla, R. U.; Kunze, H.-J.; Petrini, D.
1972-01-01
Determination of collisional-excitation-rate coefficients for sodium-like Ar VIII ions theoretically using the Coulomb-Born approximation as well as experimentally from the absolute intensities of lines emitted by these ions in well-diagnosed plasmas whose parameters were obtained from the analysis of scattered laser light. These plasmas were produced in a theta-pinch device. The agreement between theory and experiment is within the estimated accuracy of plus or minus 50% for excitation from the ground state to the n = 3 and n = 4 levels, whereas some deviations are observed for two transitions to the n = 5 levels at lower temperatures. A rate coefficient for ionization was obtained from the time dependence of the ionization.
Technology Transfer Automated Retrieval System (TEKTRAN)
Knowledge of the diffusion coefficient is necessary for modeling gas transport in soils and other porous media. This study was conducted to determine the relationship between the diffusion coefficient and pore structure parameters, such as the fractal dimension of pores (Dmp), the shortest path leng...
Abstract In this study, we measure effective diffusion coefficients for trichloroethene in undisturbed soil samples taken from Picatinny Arsenal, New Jersey. The measured effective diffusion coefficients ranged from 0.0053 to 0.0609 cm2/s over a range of air...
The remote sensing algorithm of spectral diffuse attenuation coefficient of ocean
Qiankun Zhu; Xianqiang He; Zhihua Mao; Fang Gong
2008-01-01
Diffuse attenuation coefficient is an apparent optical property (AOP) which directly links to the inherent optical properties in ocean color remote sensing. So far, the study on the satellite retrieve algorithm of water diffuse attenuation coefficient has not been deeply-going, which is mainly discussed using the bands-ratio methods based on the in situ data. Only a few scientists apply the
H. J. ARNIKAR; H. M. GHULE
1969-01-01
It has been recently shown that an electrodeless discharge can servo as a detector of high sensitivity in the chromatography of gases and vapours. The technique has also been used for the determination of inter-diffusion coefficients of gases. This procedure, however, being found lengthy, has been modified in the present work to permit a rapid determination of the diffusion coefficients.
Impulse response techniques to measure binary diffusion coefficients under supercritical conditions
Toshitaka Funazukuri; Chang Yi Kong; Seiichiro Kagei
2004-01-01
This review describes impulse response techniques with a curve-fitting method to measure thermodynamic properties, such as binary diffusion coefficient, retention factor, and partial molar volume, under supercritical conditions. Theoretical background, parameter sensitivity, sources of experimental error, noise elimination technique, and the correction of apparent binary diffusion coefficients due to column coiling are discussed based on recent studies, together with data
Liquid-phase Mutual Diffusion Coefficients for Heavy Oil + Light Hydrocarbon Mixtures
X. Zhang; J. M. Shaw
2007-01-01
Liquid-phase mutual diffusion coefficients are a key parameter in reservoir simulation models related to both primary production and envisioned secondary recovery processes for heavy oil and bitumen. The measurement of liquid-phase mutual diffusion coefficients in bitumen and heavy oil + light hydrocarbon or gas mixtures present numerous experimental and data analysis challenges due to the viscosity and opacity of the
G. A. Fernández; Jadran Vrabec; Hans Hasse
2005-01-01
Self- and binary Maxwell–Stefan (MS) diffusion coefficients were determined by equilibrium molecular dynamics simulations with the Green–Kubo method. This study covers self-diffusion coefficients at liquid states for eight pure fluids, i.e., F2, N2, CO2, CS2, C2H6, C2H4, C2H2, and SF6 as well as MS diffusion coefficients for three binary mixtures N2+CO2, N2+C2H6, and CO2+C2H6. The fluids were modeled by the
NASA Astrophysics Data System (ADS)
Ilia Anisa, Nor; Azian, Noor; Sharizan, Mohd; Iwai, Yoshio
2014-04-01
6-gingerol and 6-shogaol are the main constituents as anti-inflammatory or bioactive compounds from zingiber officinale Roscoe. These bioactive compounds have been proven for inflammatory disease, antioxidatives and anticancer. The effect of temperature on diffusion coefficient for 6-gingerol and 6-shogaol were studied in subcritical water extraction. The diffusion coefficient was determined by Fick's second law. By neglecting external mass transfer and solid particle in spherical form, a linear portion of Ln (1-(Ct/Co)) versus time was plotted in determining the diffusion coefficient. 6-gingerol obtained the higher yield at 130°C with diffusion coefficient of 8.582x10-11 m2/s whilst for 6-shogaol, the higher yield and diffusion coefficient at 170°C and 19.417 × 10-11 m2/s.
Kazuhiko Seki; Sanoop Ramachandran; Shigeyuki Komura
2011-07-22
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.
Deinert, Mark
Methodology for using prompt gamma activation analysis to measure the binary diffusion coefficient to determine the binary diffusion coefficients of a gas in a porous system. Argon diffusion experiments were- suring the binary diffusion coefficient of a gas in a geological med- ium using prompt gamma activation
Measurements of molecular and thermal diffusion coefficients in ternary mixtures
Firoozabadi, Abbas
the estimation of thermal diffusion factors in binary and ternary mixtures. However, in the ternaries one also of the binary and ternary thermal diffusion factors for the mixtures comprised of octane-decane-1-methylnaphthalene reveals a remarkable difference in the thermal diffusion behavior in binary and ternary mixtures
Correlation of high-pressure diffusion and viscosity coefficients for n-alkanes
J. H. Dymond; M. A. Awan
1989-01-01
Self-diffusion coefficient and viscosity coefficient data for liquid n-alkanes over the whole pressure range at different temperatures are satisfactorily correlated simultaneously by a method which is just an extension of that previously used to apply the smooth hard-sphere theory of transport properties to individual transport coefficients. Universal curves are developed for reduced quantities D * and eta * as a
J. Baranski; E. Bich; E. Vogel; J. K. Lehmann
2003-01-01
A measuring system for the determination of binary diffusion coefficients of gases has been developed. The lower and upper half cells of the Loschmidt diffusion cell are fixed, one upon the other, contrary to the usual shearing cells. A sliding component between the half cells is moved to connect them and to start the diffusion. The concentration changes due to
Technology Transfer Automated Retrieval System (TEKTRAN)
The diffusion coefficient of water in biobased hydrogels were measured utilizing a simple NMR method. This method tracks the migration of deuterium oxide through imaging data that is fit to a diffusion equation. The results show that a 5 wt% soybean oil based hydrogel gives aqueous diffusion of 1.37...
Xiaoju Pan; Richard C. Zimmerman
2010-01-01
The diffuse attenuation coefficient (Kd) is critical to understand the vertical distribution of underwater downwelling irradiance (Ed). Theoretically Ed is composed of the direct solar beam and the diffuse sky irradiance. Applying the statistical results from Hydrolight radiative transfer simulations, Kd is expressed into a mathematical equation (named as PZ06) integrated from the contribution of direct solar beam and diffuse
Moteki, T; Ishizaka, H
2000-12-01
Diffusion-weighted echoplanar imaging (EPI) was performed to evaluate the contents of cystic ovarian lesions [33 endometrial cysts, 16 ovarian cysts, 5 serous cystadenomas, 6 mucinous cystadenomas, 13 malignant cystic ovarian tumors, and 3 benign cystic lesions mimicking malignant cystic ovarian tumor (BMMs)]. Apparent diffusion coefficient (ADC) values were calculated for the cystic contents. Many lesions showed unrealistically high ADC greater than water at body temperature (0.00324 mm(2)/sec), especially in lesions more than 12 cm in diameter. The higher ADC values were attributed to the sloshing effect: intermittent compression of large ovarian lesions by abdominal breathing before the breath-hold scan. When limited to lesions with ADC less than 0. 00324 mm(2)/sec, endometrial cysts and malignant cystic ovarian tumors showed lower ADC values than ovarian cysts and serous cystadenomas (P < 0.03). When further limited to lesions less than 12 cm in axial diameter, an additional ADC difference between malignant cystic ovarian BMMs was demonstrated (P < 0.03). Diffusion-weighted EPI showed the possibility that calculated ADC values might be useful in evaluating small to medium cystic ovarian lesions. J. Magn. Reson. Imaging 2000;12:1014-1019. PMID:11105044
Impurity Diffusion Coefficients of Al and Zn in Mg Determined from Solid-to-Solid Diffusion Couples
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
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.
Ha, Jiyeon; Engler, Cady R; Lee, Seung Jae
2008-07-01
Diffusion characteristics of chlorferon and diethylthiophosphate (DETP) in Ca-alginate gel beads were studied to assist in designing and operating bioreactor systems. Diffusion coefficients for chlorferon and DETP in Ca-alginate gel beads determined at conditions suitable for biodegradation studies were 2.70 x 10(-11) m(2)/s and 4.28 x 10(-11) m(2)/s, respectively. Diffusivities of chlorferon and DETP were influenced by several factors, including viscosity of the bulk solution, agitation speed, and the concentrations of diffusing substrate and immobilized cells. Diffusion coefficients increased with increasing agitation speed, probably due to poor mixing at low speed and some attrition of beads at high speeds. Diffusion coefficients also increased with decreasing substrate concentration. Increased cell concentration in the gel beads caused lower diffusivity. Theoretical models to predict diffusivities as a function of cell weight fraction overestimated the effective diffusivities for both chlorferon and DETP, but linear relations between effective diffusivity and cell weight fraction were derived from experimental data. Calcium-alginate gel beads with radii of 1.65-1.70 mm used in this study were not subject to diffusional limitations: external mass transfer resistances were negligible based on Biot number calculations and effectiveness factors indicated that internal mass transfer resistance was negligible. Therefore, the degradation rates of chlorferon and DETP inside Ca-alginate gel beads were reaction-limited. PMID:18080347
Measurement of gas diffusion coefficient using photonic crystal fiber
Y. L. Hoo; W. Jin; H. L. Ho; D. N. Wang
2003-01-01
We report the use of photonic crystal fiber (PCF) for the measurement of gas diffusion constant. PCF has uniform airhole columns along the fiber length that provide the basis for the study of gas diffusion based on the capillary method. The gas concentration within the airhole columns is monitored by measuring the attenuation of light through the PCF caused by
Lober, Robert M; Cho, Yoon-Jae; Tang, Yujie; Barnes, Patrick D; Edwards, Michael S; Vogel, Hannes; Fisher, Paul G; Monje, Michelle; Yeom, Kristen W
2014-03-01
While pediatric diffuse intrinsic pontine gliomas (DIPG) remain fatal, recent data have shown subgroups with distinct molecular biology and clinical behavior. We hypothesized that diffusion-weighted MRI can be used as a prognostic marker to stratify DIPG subsets with distinct clinical behavior. Apparent diffusion coefficient (ADC) values derived from diffusion-weighted MRI were computed in 20 consecutive children with treatment-naïve DIPG tumors. The median ADC for the cohort was used to stratify the tumors into low and high ADC groups. Survival, gender, therapy, and potential steroid effects were compared between the ADC groups. Median age at diagnosis was 6.6 (range 2.3-13.2) years, with median follow-up seven (range 1-36) months. There were 14 boys and six girls. Seventeen patients received radiotherapy, five received chemotherapy, and six underwent cerebrospinal fluid diversion. The median ADC of 1,295 × 10(-6) mm(2)/s for the cohort partitioned tumors into low or high diffusion groups, which had distinct median survivals of 3 and 13 months, respectively (log-rank p < 0.001). Low ADC tumors were found only in boys, whereas high ADC tumors were found in both boys and girls. Available tissue specimens in three low ADC tumors demonstrated high-grade histology, whereas one high ADC tumor demonstrated low-grade histology with a histone H3.1 K27M mutation and high-grade metastatic lesion at autopsy. ADC derived from diffusion-weighted MRI may identify prognostically distinct subgroups of pediatric DIPG. PMID:24522717
Scale Dependence of Effective Matrix Diffusion Coefficient Evidence and Preliminary Interpertation
H.H. Liu; Y. Zhang
2006-06-20
The exchange of solute mass (through molecular diffusion) between fluid in fractures and fluid in the rock matrix is called matrix diffusion. Owing to the orders-of-magnitude slower flow velocity in the matrix compared to fractures, matrix diffusion can significantly retard solute transport in fractured rock, and therefore is an important process for a variety of problems, including remediation of subsurface contamination and geological disposal of nuclear waste. The effective matrix diffusion coefficient (molecular diffusion coefficient in free water multiplied by matrix tortuosity) is an important parameter for describing matrix diffusion, and in many cases largely determines overall solute transport behavior. While matrix diffusion coefficient values measured from small rock samples in the laboratory are generally used for modeling field-scale solute transport in fractured rock (Boving and Grathwohl, 2001), several research groups recently have independently found that effective matrix diffusion coefficients much larger than laboratory measurements are needed to match field-scale tracer-test data (Neretnieks, 2002; Becker and Shapiro, 2000; Shapiro, 2001; Liu et al., 2003,2004a). In addition to the observed enhancement, Liu et al. (2004b), based on a relatively small number of field-test results, reported that the effective matrix diffusion coefficient might be scale dependent, and, like permeability and dispersivity, it seems to increases with test scale. This scale-dependence has important implications for large-scale solute transport in fractured rock. Although a number of mechanisms have been proposed to explain the enhancement of the effective matrix diffusion coefficient, the potential scale dependence and its mechanisms are not fully investigated at this stage. The major objective of this study is to again demonstrate (based on more data published in the literature than those used in Liu et al. [2004b]) the potential scale dependence of the effective matrix-diffusion coefficient, and to -develop a preliminary explanation for this scale-dependent behavior.
Liu, Hui-Hai; Zhang, Yingqi; Molz, Fred J.
2006-04-30
The exchange of solute mass (through molecular diffusion) between fluid in fractures and fluid in the rock matrix is called matrix diffusion. Owing to the orders-of-magnitude slower flow velocity in the matrix compared to fractures, matrix diffusion can significantly retard solute transport in fractured rock, and therefore is an important process for a variety of problems, including remediation of subsurface contamination and geological disposal of nuclear waste. The effective matrix diffusion coefficient (molecular diffusion coefficient in free water multiplied by matrix tortuosity) is an important parameter for describing matrix diffusion, and in many cases largely determines overall solute transport behavior. While matrix diffusion coefficient values measured from small rock samples in the laboratory are generally used for modeling field-scale solute transport in fractured rock (Boving and Grathwohl, 2001), several research groups recently have independently found that effective matrix diffusion coefficients much larger than laboratory measurements are needed to match field-scale tracer-test data (Neretnieks, 2002; Becker and Shapiro, 2000; Shapiro, 2001; Liu et al., 2003, 2004a). In addition to the observed enhancement, Liu et al. (2004b), based on a relatively small number of field-test results, reported that the effective matrix diffusion coefficient might be scale dependent, and, like permeability and dispersivity, it seems to increases with test scale. This scale-dependence has important implications for large-scale solute transport in fractured rock. Although a number of mechanisms have been proposed to explain the enhancement of the effective matrix diffusion coefficient, the potential scale dependence and its mechanisms are not fully investigated at this stage. The major objective of this study is to again demonstrate (based on more data published in the literature than those used in Liu et al. [2004b]) the potential scale dependence of the effective matrix-diffusion coefficient, and to develop a preliminary explanation for this scale-dependent behavior.
Effective diffusion coefficient of a Brownian particle in a periodically expanded conical tube.
Antipov, Anatoly E; Barzykin, Alexander V; Berezhkovskii, Alexander M; Makhnovskii, Yurii A; Zitserman, Vladimir Yu; Aldoshin, Sergei M
2013-11-01
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. PMID:24329385
Diffusion coefficient anisotropy near the liquid-vapour interface for simple fluid
NASA Astrophysics Data System (ADS)
Lebovka, N. I.; Mank, V. V.
1990-07-01
The estimation of the translation diffusion-coefficient profiles D(z) near the liquid-vapour interface of a simple Lennard-Jones (LJ) fluid is done. The calculations are based on the Kirkwood-Rice model for the diffusion in fluids. The diffusion process is shown to reveal the anisotropic behaviour in the vicinity of the interface. In the liquid phase, the diffusion coefficient normal to the interface exceeds the parallel one, and the situation is vice versa in the vapour phase.
NASA Astrophysics Data System (ADS)
Jafari Raad, Seyed Mostafa; Azin, Reza; Osfouri, Shahriar
2015-03-01
Storage and disposal of CO2 as the main component of greenhouse gases in saline aquifers require careful measurement of diffusivity for predicting rate of transfer and cumulative amount of trapped gas. Little information is available on diffusion of CO2 in highly concentrated saline aquifers at reservoir conditions. In this study, diffusivity of CO2 was measured into different solutions, including saline aquifer taken from oil field, distilled water and synthetic solutions prepared from four most common ions, Mg2+, Ca2+, K+, Na+. The roles of salvation effect and hydration phenomenon were studied on diffusivity of dissolved CO2. Synthetic solutions were prepared at concentration ranges of 83-200 g/l. Experimental measurements were reported at temperature and pressure ranges of 30-40 °C and 5,880-6,265 kPa, respectively. Results show that both type and concentration of ion affect CO2 diffusivity. Diffusion coefficient was found dependent on effective radius of hydrated ions. Also, CO2 diffusivity increase by increasing strength of bonds between ion and neighbor water molecules. Also, presence of ions in water solution creates hydration competition between solution metal ions and aqua ions from diffusive gas. The Mg2+ cation, which has strongest hydration competition among other ions, has an increasing effect on gas diffusivity into saline aquifer. However, increasing ion concentration in solution decreases diffusivity of CO2 due to growth in fraction of contact ion pairs. Results of this study provide unique measures of CO2 diffusion coefficient in saline aquifer at high pressure and temperature conditions and conceptual information about effect of each common saline formation ion on gas diffusivity.
NASA Astrophysics Data System (ADS)
Wu, Yan; Duan, Guosheng; Zhao, Xiang
2015-03-01
Effects of magnetic field intensity on carbon diffusion coefficient in pure iron in the ?-Fe temperature region were investigated using carburizing technology. The carbon penetration profiles from the iron surface to interior were measured by field emission electron probe microanalyzer. The carbon diffusion coefficient in pure iron carburized with different magnetic field intensities was calculated according to the Fick's second law. It was found that the magnetic field intensity could obviously affect the carbon diffusion coefficient in pure iron in the ?-Fe temperature region, and the carbon diffusion coefficient decreased obviously with the enhancement of magnetic field intensity, when the magnetic field intensity was higher than 1 T, the carbon diffusion coefficient in field annealed specimen was less than half of that of the nonfield annealed specimen, further enhancing the magnetic field intensity, the carbon diffusion coefficient basically remains unchanged. The stiffening of lattice due to field-induced magnetic ordering was responsible for an increase in activation barrier for jumping carbon atoms. The greater the magnetic field intensity, the stronger the inhibiting effect of magnetic field on carbon diffusion.
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
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.
Parthasarathy, Ranganathan; Misra, Anil; Park, Jonggu; Ye, Qiang; Spencer, Paulette
2012-01-01
The diffusion of water into dentin adhesive polymers and leaching of unpolymerized monomer from the adhesive are linked to their mechanical softening and hydrolytic degradation. Therefore, diffusion coefficient data are critical for the mechanical design of these polymeric adhesives. In this study, diffusion coefficients of water and leachables were obtained for sixteen methacrylate-based crosslinked polymers using absorption experiments. The experimental mass change data was interpreted using numerical solution of the two-dimensional diffusion equations. The calculated diffusion coefficients varied from 1.05 × 10?8 cm2/sec (co-monomer TMTMA) to 3.15 × 10?8 cm2/sec (co-monomer T4EGDMA). Correlation of the diffusion coefficients with crosslink density and hydrophilicity showed an inverse trend (R2 = 0.41). The correlation of diffusion coefficient with crosslink density and hydrophilicity are closer for molecules differing by simple repeat units (R2 = 0.95). These differences in the trends reveal mechanisms of interaction of the diffusing water with the polymer structure. PMID:22430592
From free to effective diffusion coefficients in fluorescence correlation spectroscopy experiments.
Ipiña, Emiliano Pérez; Dawson, Silvina Ponce
2013-02-01
Diffusion is one of the main transport processes that occur inside cells determining the spatial and time distribution of relevant action molecules. In most cases these molecules not only diffuse but also interact with others as they get transported. When these interactions occur faster than diffusion the resulting transport can be characterized by "effective diffusion coefficients" that depend on both the reaction rates and the "free" diffusion coefficients. Fluorescence correlation spectroscopy (FCS) gives information on effective rather than free diffusion coefficients under this condition. In the present paper we investigate what coefficients can be drawn from FCS experiments for a wide range of values of the ratio of reaction to diffusion time scales, using different fitting functions. We find that the effective coefficients can be inferred with relatively small errors even when the condition of fast reactions does not exactly hold. Since the diffusion time scale depends on the size of the observation volume and the reaction time scale depends on concentrations, we also discuss how by changing either one or the other property one can switch between the two limits and extract more information on the system under study. PMID:23496547
Application of the Poisson-Nernst-Planck Theory with Space-Dependent Diffusion Coefficients to KcsA
Furini, Simone; Zerbetto, Francesco; Cavalcanti, Silvio
2006-01-01
The Poisson-Nernst-Planck electrodiffusion theory serves to compute charge fluxes and is here applied to the ion current through a protein channel. KcsA was selected as an example because of the abundance of experimental and theoretical data. The potassium channels MthK and KvAP were used as templates to define two open channel models for KcsA. Channel boundary surfaces and protein charge distributions were defined according to atomic radii and partial atomic charges. To establish the sensitivity of the results to these parameters, two different sets were used. Assigning the potassium diffusion coefficients equal to the value for free-diffusion in water (1.96 × 10?9 m2/s), the computed currents overestimated the experimental data. Ion distributions inside the channel suggest that the overestimate is not due to an excess of charge shielding. A good agreement with the experimental data was achieved by reducing the potassium diffusion coefficient inside the channel to 1.96 × 10?10 m2/s, a value of substantial motility but nonetheless in accord with the intuitive notion that the channel has a high affinity for the ions and therefore slows them down. These results are independent of the open channel model and the parameterization adopted for atomic radii and partial atomic charges. The method offers a reliable estimate of the channel current with low computational effort. PMID:16877513
On the determinatino of high-pressure mass-diffusion coefficients for binary mixtures
NASA Technical Reports Server (NTRS)
Bellan, J.; Harstad, K.
2003-01-01
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.
Manzini, Gianmarco [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Cangiani, Andrea [University of Leicester, Leicester (United Kingdom); Sutton, Oliver [University of Leicester, Leicester (United Kingdom)
2014-10-02
This document presents the results of a set of preliminary numerical experiments using several possible conforming virtual element approximations of the convection-reaction-diffusion equation with variable coefficients.
NASA Astrophysics Data System (ADS)
Delgado, J. M. P. Q.
2013-06-01
The aim of this work is to present a mathematical and experimental formulation of a new simple procedure for the measurement of effective molecular diffusion coefficients of a salt solution in a water-saturated building material. This innovate experimental procedure and mathematical formulation is presented in detail and experimental values of "effective" molecular diffusion coefficient of sodium chloride in a concrete sample ( w/ c = 0.45), at five different temperatures (between 10 and 30 °C) and four different initial NaCl concentrations (between 0.1 and 0.5 M), are reported. The experimental results obtained are in good agreement with the theoretical and experimental values of molecular diffusion coefficient presented in literature. An empirical correlation is presented for the prediction of "effective" molecular diffusion coefficient over the entire range of temperatures and initial salt concentrations studied.
Lai, C.C.; Tan, C.S. (National Tsing Hua Univ., Hsinchu (Taiwan, Province of China). Dept. of Chemical Engineering)
1995-02-01
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.
Orejuela, Mauricio
1994-01-01
LIMITING DIFFUSION COEFFICIENTS OF HEAVY MOLECULAR WEIGHT ORGANIC CONTAMINANTS IN SUPERCRITICAL CARBON DIOXIDE A Thesis by MAURICIO OREJUELA Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment... of the requirements for the degree of MASTER OF SCIENCE August 1994 Major Subject: Chemical Engineering LIMITING DIFFUSION COEFFICIENTS OF HEAVY MOLECULAR WEIGHT ORGANIC CONTAMINANTS IN SUPERCRITICAL CARBON DIOXIDE A Thesis by MAURICIO OREJUELA Submitted...
Note on coefficient matrices from stochastic Galerkin methods for random diffusion equations
Zhou Tao, E-mail: tzhou@lsec.cc.ac.c [Institute of Computational Mathematics, The Chinese Academy of Sciences, Beijing 100190 (China); Tang Tao, E-mail: ttang@hkbu.edu.h [Department of Mathematics, Hong Kong Baptist University, Kowloon Tong (Hong Kong)
2010-11-01
In a recent work by Xiu and Shen [D. Xiu, J. Shen, Efficient stochastic Galerkin methods for random diffusion equations, J. Comput. Phys. 228 (2009) 266-281], the Galerkin methods are used to solve stochastic diffusion equations in random media, where some properties for the coefficient matrix of the resulting system are provided. They also posed an open question on the properties of the coefficient matrix. In this work, we will provide some results related to the open question.
An estimate of heavy quark momentum diffusion coefficient in gluon plasma
Debasish Banerjee; Saumen Datta; Rajiv V. Gavai; Pushan Majumdar
2012-11-11
We calculate the momentum diffusion coefficient for heavy quarks in SU(3) gluon plasma at temperatures 1-2 times the deconfinement temperature. The momentum diffusion coefficient is extracted from a Monte Carlo calculation of the correlation function of color electric fields, in the leading order of expansion in heavy quark mass. Systematics of the calculation are examined, and compared with perturbtion theory and other estimates.
Doru Constantin; Patrick Oswald
2015-04-09
We measure diffusion coefficients in the lamellar phase of the nonionic binary system C$_{12}$EO$_6$/H$_2$O using fluorescence recovery after photobleaching. The diffusion coefficient across the lamellae shows an abrupt increase upon approaching the lamellar-isotropic phase transition. We interpret this feature in terms of defects connecting the surfactant structure. An estimation of the defect density and of the variation in defect energy close to the transition is given in terms of a simple model.
Effect of particle size on the diffuse reflection coefficient of titanium dioxide powder
NASA Astrophysics Data System (ADS)
Vlasov, V. A.; Astafyev, A. L.; Zarubin, A. N.
2015-04-01
In the present work a model of light scattering is shown which explains the result about effect of particle size on the diffuse reflection coefficient of initial titanium dioxide powders. The diffuse reflection coefficient depending on particle size for TiO2 pigment varies on the curve with maximum. The experimental results and the model can be used for technology development of manufacturing pigment for light-reflecting temperature-control coatings of spacecraft
The Diffusion Coefficient For Piecewise Expanding Maps Of The Interval With Metastable States
Dmitry Dolgopyat; Paul Wright
2010-11-24
Consider a piecewise smooth expanding map of the interval possessing several invariant subintervals and the same number of ergodic absolutely continuous invariant probability measures (ACIMs). After this system is perturbed to make the subintervals lose their invariance in such a way that there is a unique ACIM, we show how to approximate the diffusion coefficient for an observable of bounded variation by the diffusion coefficient of a related continuous time Markov chain.
Binary mutual diffusion coefficients of aqueous alcohols. Methanol to 1-heptanol
Ling Hao; Derek G. Leaist
1996-01-01
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 (DÂ°) for the 1-alkanols are found to decrease with alcohol molar volume V approximately as Vâ»Â¹Â². Although values of DÂ° for aqueous 1-propanol and 2-propanol are nearly identical within experimental
Binary mutual diffusion coefficient of aqueous solutions of propylene glycol and dipropylene glycol
Ming-Hung Wang; Allan N. Soriano; Alvin R. Caparanga; Meng-Hui Li
2010-01-01
Binary mutual diffusion coefficient data for aqueous solutions of propylene and dipropylene glycols were measured using the Taylor dispersion technique for each aqueous binary system at different concentrations (x1=0.2–0.80) and temperatures (303.2–323.2K). The measured data were fit to different empirical and semi-theoretical models and compared with the values predicted from such models. The measured mutual diffusion coefficient data are well
Sumit Chakraborty; Jibamitra Ganguly
1992-01-01
We present new experimental data on diffusion of divalent cations in almandine-spessartine diffusion couples in graphite capsules in the P-T range of 14–35 kb, 1100–1200° C. The tracer diffusion coefficients of the major divalent cations, viz. Fe, Mg and Mn, retrieved from the multicomponent diffusion profiles, have been combined with earlier data from our laboratory at 29–43 kb, 1300–1480° C
Ong, Shyue Ping
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 ...
Diffusion and Coulomb separation of ions in dense matter.
Beznogov, M V; Yakovlev, D G
2013-10-18
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
Faguang Leng; Naiqian Feng; Xinying Lu
2000-01-01
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
Diffusion coefficient in a semi-dilute solution measured by concentration gradient technique
Boyer, Edmond
L-435 Diffusion coefficient in a semi-dilute solution measured by concentration gradient technique coefficient of a coil without hydrodynamic interactions between its elements. LE JOURNAL DE PHYSIQUE - LETTRES-dilute solution is characterized by an inter- penetration of the coils, when the monomer concen- tration c
NASA Astrophysics Data System (ADS)
Imel, Adam; Miller, Brad; Holley, Wade; Baskaran, Durairaj; Mays, Jimmy; Dadmun, Mark
2015-03-01
The diffusion properties of nanoparticles in polymer nanocomposites are largely unknown and depend intimately on the dispersion of the nanoparticles. We examine the diffusion of soft, organic nanoparticles, which disperse in a polymer matrix due to the interpenetration of polymer chains and particles and the reduction in the depletion of entropy in the system. The impact of the presence of soft nanoparticles on the diffusion coefficient of polystyrene chains has recently been determined with neutron reflectivity. This was completed by monitoring the interdiffusion of deuterated and protonated polystyrene nanocomposite bilayers with and without the soft nanoparticles dispersed throughout both layers and extracting the diffusion coefficient from the one-dimensional solution to Fick's second law of diffusion. In this work, we extend this method to bilayer systems with only the soft nanoparticles as one of the layers and a linear deuterated polystyrene as an adjacent layer. The development of this method allows us to determine the tracer diffusion coefficient of the soft polystyrene nanoparticles for the first time by analyzing the mutual diffusion coefficient from Fick's second law and the fast and slow modes theories for diffusion.
Spreading Waves of a Reduced Diffusion Coefficient of Water in Normal and Ischemic Rat Brain
Yasuhiro Hasegawa; Lawrence L. Latour; James E. Formato; Christopher H. Sotak; Marc Fisher
1995-01-01
Summary: Using echo planar diffusion-weighted magnetic resonance imaging, we measured three-dimensional changes in the apparent diffusion coefficient (ADC) of water in eight contiguous coronal slices, encompassing the entire rat brain, before and after local cortical stimulation. We applied chemical (potassium chloride application; n = 6) and mechanical (needle stab; n = 4) stimulations to the right posterior parietal rat cortex.
Propagator for the Fokker-Planck equation with an arbitrary diffusion coefficient.
Lee, Chern; Zhu, Ka-Di; Chen, Ji-Gen
2013-11-01
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
Propagator for the Fokker-Planck equation with an arbitrary diffusion coefficient
NASA Astrophysics Data System (ADS)
Lee, Chern; Zhu, Ka-Di; Chen, Ji-Gen
2013-11-01
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.
Velocity and diffusion coefficient of a random asymmetric one-dimensional hopping model
Paris-Sud XI, UniversitÃ© de
899 Velocity and diffusion coefficient of a random asymmetric one-dimensional hopping model C hopping rates are calculated in a simple way through a recursion relation method, which allows of drift and diffusion on one-dimensional lattices with random asymmetric hopping rates has recently
An alternative model for estimating liquid diffusion coefficients requiring no viscosity data
NASA Technical Reports Server (NTRS)
Morales, Wilfredo
1993-01-01
An equation, based on the free volume of a liquid solvent, was derived via dimensional analysis, to predict binary diffusion coefficients. The equation assumed that interaction between the solute and liquid solvent molecules followed a Lennard-Jones potential. The equation was compared to other diffusivity equations and was found to give good results over the temperature range examined.
NASA Astrophysics Data System (ADS)
Wu, Qiong; Li, Shu-Suo; Ma, Yue; Gong, Sheng-Kai
2012-10-01
The diffusion coefficients of several alloying elements (Al, Mo, Co, Ta, Ru, W, Cr, Re) in Ni are directly calculated using the five-frequency model and the first principles density functional theory. The correlation factors provided by the five-frequency model are explicitly calculated. The calculated diffusion coefficients show their excellent agreement with the available experimental data. Both the diffusion pre-factor (D0) and the activation energy (Q) of impurity diffusion are obtained. The diffusion coefficients above 700 K are sorted in the following order: DAl > DCr > DCo > DTa > DMo > DRu > DW > DRe. It is found that there is a positive correlation between the atomic radius of the solute and the jump energy of Ni that results in the rotation of the solute-vacancy pair (E1). The value of E2-E1 (E2 is the solute diffusion energy) and the correlation factor each also show a positive correlation. The larger atoms in the same series have lower diffusion activation energies and faster diffusion coefficients.
Correlation of high-pressure diffusion and viscosity coefficients for n -alkanes
J. H. Dymond; M. A. Awan
1989-01-01
Self-diffusion coefficient and viscosity coefficient data for liquid n-alkanes over the whole pressure range at different temperatures are satisfactorily correlated simultaneously by a method which is just an extension of that previously used to apply the smooth hard-sphere theory of transport properties to individual transport coefficients. Universal curves are developed for reduced quantities D* and ?* as a function of
Lead diffusion in apatite and zircon using ion implantation and Rutherford Backscattering techniques
Cherniak, D.J.; Lanford, W.A. (State Univ. of New York, Albany (United States)); Ryerson, F.J. (Lawrence Livermore National Lab., CA (United States))
1991-06-01
Ion implantation was used to introduce Pb into the minerals zircon and apatite. Diffusion profiles were obtained using Rutherford Backscattering, and the results were fitted with a model to determine the diffusion coefficients. This approach is both simple and useful in studying diffusion over a temperature range of geologic interest without inordinate annealing times. Results for apatite over the temperature range 600-900C are in good agreement with earlier results obtained for higher temperatures (Watson et al., 1985) and are described. This suggests that radiation damage induced by ion implantation has little effect on Pb diffusion in this case due to rapid annealing of induced damage at low temperatures. The activation energy stated above is somewhat smaller than that previously determined (70 kcal mol{sup {minus}1}), reflecting the larger range in 1/T sampled by the present results. Closure temperatures calculated with these diffusion parameters are in good agreement with those inferred from geochronologic data. Diffusion coefficients for Pb in zircon determined in this study are greater than those obtained from a single experimental measurement and estimates of Pb diffusion based on geochronologic data and U/Pb zoning in natural zircons. The differing results for zircon and apatite obtained in this study appear to be related to each mineral's ability to anneal the radiation damage induced by ion implantation.
Determination of binary diffusion coefficients of gases using photothermal deflection technique
J. H. Rohling; J. Shen; C. Wang; J. Zhou; C. E. Gu
2007-01-01
A photothermal deflection (PD) technique was applied to measure the binary diffusion coefficients of various gases (CO2–N2, CO2–O2, N2–He, O2–He, and CO2–He). With an in-house-made Loschmidt diffusion cell, a transverse PD system was employed to measure the time-resolved PD\\u000a signal associated with the variation of the thermal diffusivity and the temperature coefficient of the refractive index of\\u000a the gas mixture
Measurement of the Diffusion Coefficient of Radium A
Otto G. Raabe
1968-01-01
THE potential hazard in mines from the inhalation of the progeny of radon gas has become increasingly interesting in recent years. This hazard involves radon daughters in two forms: (a) attached to aerosol particles or condensation nuclei; and (b) unattached atoms or ions. The form of the unattached daughters is not fully known, but one of their important and basic
NITRIC ACID-AIR DIFFUSION COEFFICIENT: EXPERIMENTAL DETERMINATION
Trace gaseous HNO3 in air is removed in a laminar flow nylon tube. The HNO3 deposition pattern was obtained by sectioning the tube, extracting with an aqueous solution, and measuring the concentration by ion chromatography. Mass transport analysis of the deposition pattern demons...
Entropy-scaling laws for diffusion coefficients in liquid metals under high pressures
NASA Astrophysics Data System (ADS)
Cao, Qi-Long; Shao, Ju-Xiang; Wang, Pan-Pan; Wang, Fan-Hou
2015-04-01
Molecular dynamic simulations on the liquid copper and tungsten are used to investigate the empirical entropy-scaling laws D*=A exp(B Se x) , proposed independently by Rosenfeld and Dzugutov for diffusion coefficient, under high pressure conditions. We show that the scaling laws hold rather well for them under high pressure conditions. Furthermore, both the original diffusion coefficients and the reduced diffusion coefficients exhibit an Arrhenius relationship DM=DM0 exp(-EM/KBT ) , ( M =u n ,R ,D ) and the activation energy EM increases with increasing pressure, the diffusion pre-exponential factors ( DR0 and DD0 ) are nearly independent of the pressure and element. The pair correlation entropy, S2, depends linearly on the reciprocal temperature S2=-ES/T , and the activation energy, ES, increases with increasing pressure. In particular, the ratios of the activation energies (Eun, ER, and ED) obtained from diffusion coefficients to the activation energy, ES, obtained from the entropy keep constants in the whole pressure range. Therefore, the entropy-scaling laws for the diffusion coefficients and the Arrhenius law are linked via the temperature dependence of entropy.
NASA Astrophysics Data System (ADS)
Yang, Linlin; Sun, Hai; Fu, Xudong; Wang, Suli; Jiang, Luhua; Sun, Gongquan
2014-07-01
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.
NASA Astrophysics Data System (ADS)
Öncan, N.; Player, M. A.; Macdonald, A. G.
2004-10-01
A series of liposomes has been studied by the Fluorescence Recovery after Photobleaching technique using confocal scanning laser microscopy. Both mobile and immobile specimens of lipid membranes have been examined. The specimens consisted of liposomal suspensions incorporating mixtures of the phospholipids dioleoyl phosphatidylcholine (DOPC) and distearoyl phosphatidylcholine (DSPC) with the aminolipid dihexadecanol glycerophospho-ethanolamine (DHPE). The measurements reported provide information about the effective diffusion coefficients, which vary from 0.2 · 10-10 cm2s-1 to 3.2 · 10-10 cm2s-1. They were highly dependent on the ratio DSPC:DOPC. A simple theoretical model of 1-D diffusion was applied for the calculation of the effective diffusion coefficients. The measurements show that it is possible to use straightforward procedures with an unmodified commercial confocal microscope to determine diffusion coefficients of biological specimens.
Solvable Examples of Drift and Diffusion of Ions in Non-uniform Electric Fields
Cahn, Robert; Cahn, Robert N.; Jackson, John David
2008-05-30
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.
Balch, J; Guéguen, C
2015-01-01
In situ measurements of labile metal species using diffusive gradients in thin films (DGT) passive samplers are based on the diffusion rates of individual species. Although most studies have dealt with chemically isolated humic substances, the diffusion of dissolved organic matter (DOM) across the hydrogel is not well understood. In this study, the diffusion coefficient (D) and molecular weight (MW) of 11 aquatic DOM and 4 humic substances (HS) were determined. Natural, unaltered aquatic DOM was capable of diffusing across the diffusive gel membrane with D values ranging from 2.48×10(-6) to 5.31×10(-6) cm(2) s(-1). Humic substances had diffusion coefficient values ranging from 3.48×10(-6) to 6.05×10(-6) cm(2) s(-1), congruent with previous studies. Molecular weight of aquatic DOM and HS samples (?500-1750 Da) measured using asymmetrical flow field-flow fractionation (AF4) strongly influenced D, with larger molecular weight DOM having lower D values. No noticeable changes in DOM size properties were observed during the diffusion process, suggesting that DOM remains intact following diffusion across the diffusive gel. The influence of molecular weight on DOM mobility will assist in further understanding and development of the DGT technique and the uptake and mobility of contaminants associated with DOM in aquatic environments. PMID:25112575
Electro-diffusion in a plasma with two ion species
Kagan, Grigory; Tang Xianzhu [Theoretical Division Los Alamos National Laboratory Los Alamos, New Mexico 87545 (United States)
2012-08-15
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.
On The Anomalous Fast Ion Energy Diffusion in Toroidal Plasmas Due to Cavity Modes
N.N. Gorelenkov, N.J. Fisch and E. Fredrickson
2010-03-09
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.
He, M G; Zhang, S; Zhang, Y; Peng, S G
2015-05-01
As for the measurement of diffusion coefficient in transparent liquids by digital holographic interferometry, there are many kinds depending on the mathematical model and experimental setup. The method of using the distance of the peaks in concentration difference profile to determine diffusion coefficient by Mach-Zehnder interferometric experimental setup, is easy to handle. In order to improve the accuracy and convenience of measurement in this method, we combine procedures of hologram analysis used by Mialdun et al (2011) and those by He et al (2009). By using polynomial to fit the continuous phase difference (interference phase) of object beam, it can be more convenient and accurate to determine the distance between the two peaks. Besides, the shift of initial time has been discussed as a separated topic at the first time and two functions for minimization have been given for determination of the initial time in this paper. With the development, diffusion coefficient of KCl in water at 0.33mol/L and 25 °C has been measured. The diffusion coefficient is 1.844 × 10^{-9} m^{2}/s with the uncertainty of ± 0.012 × 10^{-9} m^{2}/s. Our measurement has more similar result with other methods than holographic interferometry. The relative uncertainty of diffusion coefficient in our experiment is less than 1% and total uncertainty of temperature is within ± 0.04 K. PMID:25969184
Sublimation kinetics and diffusion coefficients of TNT, PETN, and RDX in air by thermogravimetry.
Hikal, Walid M; Weeks, Brandon L
2014-07-01
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
Kinetic theory of point vortices: diffusion coefficient and systematic drift
P. H. Chavanis
2001-07-11
We develop a kinetic theory for point vortices in two-dimensional hydrodynamics. Using standard projection operator technics, we derive a Fokker-Planck equation describing the relaxation of a ``test'' vortex in a bath of ``field'' vortices at statistical equilibrium. The relaxation is due to the combined effect of a diffusion and a drift. The drift is shown to be responsible for the organization of point vortices at negative temperatures. A description that goes beyond the thermal bath approximation is attempted. A new kinetic equation is obtained which respects all conservation laws of the point vortex system and satisfies a H-theorem. Close to equilibrium this equation reduces to the ordinary Fokker-Planck equation.
A first-principles methodology for diffusion coefficients in metals and dilute alloys
NASA Astrophysics Data System (ADS)
Mantina, Manjeera
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
Solar wind bulk velocity fluctuations acting as velocity space diffusion on comoving ions
NASA Astrophysics Data System (ADS)
Fahr, H.-J.; Chashei, I. V.; Siewert, M.
2012-01-01
From most in-situ plasma observations made in the outer heliosphere it became evident that above the injection border of pick-up ions (?1 keV), an extended suprathermal ion tail is found which in most cases can be fitted by a power law with velocity power indices of (-6) ? ?v ? (-4). As has been shown by theory such energetic ion tails cannot be explained by Fermi-2 type velocity diffusion, since in the outer heliosphere both Alfvenic and magnetoacoustic turbulences become too weak. Here we come to a new solution of this unsolved problem by studying the action of solar wind bulk velocity fluctuations on ions co-moving with the wind. As we show the passage of such fluctuations results in energization of each individual ion and systematic evolution of the ion distribution function towards suprathermal tails. From the basic knowledge that we can obtain on this process we can calculate the velocity divergence of the ion phasespace flow and thus can derive a velocity diffusion operator. As we can show here this operator leads to a velocity diffusion coefficient proportional to the square of the ion velocity and, when employed in the phasespace transport equation, together with terms for convective changes, cooling processes and pick-up ion injection, interestingly enough, permits to find solutions for suprathermal power law tails with power indices of ?v ? -5 as very often observed.
Electron loss coefficients at 80 km from a simplified positive ion model
B. S. N. Prasad; S. Mohanty
1980-01-01
Experimental electron densities for a mid-latitude station and a simplified positive ion model consisting of O2(+), NO(+) and their respective cluster ions are used in analyzing the normal day ion production and loss processes at 80 km for solar zenith angles 45 to 75 deg. Effective recombination coefficient and positive ion relative composition are calculated and compared with the experimental
Importance of diffuse metal ion binding to RNA.
Tan, Zhi-Jie; Chen, Shi-Jie
2011-01-01
RNAs are highly charged polyanionic molecules. RNA structure and function are strongly correlated with the ionic condition of the solution. The primary focus of this article is on the role of diffusive ions in RNA folding. Due to the long-range nature of electrostatic interactions, the diffuse ions can contribute significantly to RNA structural stability and folding kinetics. We present an overview of the experimental findings as well as the theoretical developments on the diffuse ion effects in RNA folding. This review places heavy emphasis on the effect of magnesium ions. Magnesium ions play a highly efficient role in stabilizing RNA tertiary structures and promoting tertiary structural folding. The highly efficient role goes beyond the mean-field effect such as the ionic strength. In addition to the effects of specific ion binding and ion dehydration, ion-ion correlation for the diffuse ions can contribute to the efficient role of the multivalent ions such as the magnesium ions in RNA folding. PMID:22010269
Effective molecular diffusion coefficient in a two-phase gel medium
NASA Astrophysics Data System (ADS)
Hickey, Owen A.; Mercier, Jean-François; Gauthier, Michel G.; Tessier, Frédéric; Bekhechi, Smaine; Slater, Gary W.
2006-05-01
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.
Safe positive temperature coefficient composite cathode for lithium ion battery
NASA Astrophysics Data System (ADS)
Zhong, Hai; Kong, Chan; Zhan, Hui; Zhan, Caimao; Zhou, Yunhong
2012-10-01
Ethylene vinyl acetate (EVA) based positive temperature coefficient (PTC) material with a transition temperature (Tc) of 90 °C is proposed and successfully fabricated in this study. It is further introduced into LiFePO4 cathode by directly mixing it with LiFePO4 powder, binder and conductive carbon or sandwiching it between the current collector and LiFePO4 electrode membrane. Thus obtained LiFePO4/PTC composite electrodes both show a self-current-limiting effect at 90 °C. The electrochemical properties of the LiFePO4/PTC composite electrodes are determined in terms of galvanostatic charging/discharging, cyclic voltammograms and electrochemical impedance spectroscopy measurements. Comparing with bare LiFePO4 electrode, both LiFePO4/PTC composite electrodes show no degradation in cycling stability, rate capability and electrochemical kinetic property at room temperature. The results indicate that the proposed LiFePO4/PTC composite electrode with the suitable Tc of 90 °C can effectively prevent thermal runaway before the occurrence of side reactions and better protect lithium ion battery during the abnormal temperature increasing.
Freeform determination of a nonlinear diffusion coefficient by a reduced adjoint system
NASA Astrophysics Data System (ADS)
Malengier, B.; Houbaert, Y.
2008-07-01
In this article we deal with the determination of a diffusion coefficient function in a quasi-linear parabolic system. The motivation comes from a metallurgy setting. The solution method is based on the output least-squares approach (OLS) with minimization applying the adjoint equation. As the diffusion coefficient has an a-priori unknown form, we apply freeform determination in which the coefficient is defined by a linear interpolation. To avoid higher order of interpolation of the coefficient, as well as to enable the use of an adjoint system which is of the same complexity as the original partial differential equation, a reduced adjoint equation is used, applying a mapping strategy. This method is compared with a standard Levenberg-Marquardt approach.
NASA Astrophysics Data System (ADS)
Nagai, Shingo
2013-11-01
We report estimation of the effective diffusion coefficient of moisture through a barrier coating to develop an encapsulation technology for the thin-film electronics industry. This investigation targeted a silicon oxide (SiOx) film that was deposited on a plastic substrate by a large-process-area web coater. Using the finite difference method based on diffusion theory, our estimation of the effective diffusion coefficient of a SiOx film corresponded to that of bulk glass that was previously reported. This result suggested that the low diffusivities of barrier films can be obtained on a mass-production level in the factory. In this investigation, experimental observations and mathematical confirmation revealed the limit of the water vapor transmission rate on the single barrier coating.
A New Method for the Calculation of Diffusion Coefficients with Monte Carlo
NASA Astrophysics Data System (ADS)
Dorval, Eric
2014-06-01
This paper presents a new Monte Carlo-based method for the calculation of diffusion coefficients. One distinctive feature of this method is that it does not resort to the computation of transport cross sections directly, although their functional form is retained. Instead, a special type of tally derived from a deterministic estimate of Fick's Law is used for tallying the total cross section, which is then combined with a set of other standard Monte Carlo tallies. Some properties of this method are presented by means of numerical examples for a multi-group 1-D implementation. Calculated diffusion coefficients are in general good agreement with values obtained by other methods.
NASA Technical Reports Server (NTRS)
Penner, Reginald M.; Vandyke, Leon S.; Martin, Charles R.
1987-01-01
The current pulse E sub oc relaxation method and its application to the determination of diffusion coefficients in electrochemically synthesized polypyrrole thin films is described. Diffusion coefficients for such films in Et4NBF4 and MeCN are determined for a series of submicron film thicknesses. Measurement of the double-layer capacitance, C sub dl, and the resistance, R sub u, of polypyrrole thin films as a function of potential obtained with the galvanostatic pulse method is reported. Measurements of the electrolyte concentration in reduced polypyrrole films are also presented to aid in the interpretation of the data.
Kruk, D; Meier, R; Rachocki, A; Korpa?a, A; Singh, R K; Rössler, E A
2014-06-28
Field Cycling Nuclear Magnetic Resonance (FC NMR) relaxation studies are reported for three ionic liquids: 1-ethyl-3- methylimidazolium thiocyanate (EMIM-SCN, 220-258 K), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4, 243-318 K), and 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6, 258-323 K). The dispersion of (1)H spin-lattice relaxation rate R1(?) is measured in the frequency range of 10 kHz-20 MHz, and the studies are complemented by (19)F spin-lattice relaxation measurements on BMIM-PF6 in the corresponding frequency range. From the (1)H relaxation results self-diffusion coefficients for the cation in EMIM-SCN, BMIM-BF4, and BMIM-PF6 are determined. This is done by performing an analysis considering all relevant intra- and intermolecular relaxation contributions to the (1)H spin-lattice relaxation as well as by benefiting from the universal low-frequency dispersion law characteristic of Fickian diffusion which yields, at low frequencies, a linear dependence of R1 on square root of frequency. From the (19)F relaxation both anion and cation diffusion coefficients are determined for BMIM-PF6. The diffusion coefficients obtained from FC NMR relaxometry are in good agreement with results reported from pulsed- field-gradient NMR. This shows that NMR relaxometry can be considered as an alternative route of determining diffusion coefficients of both cations and anions in ionic liquids. PMID:24985656
Suárez, Inmaculada; Coto, Baudilio
2015-08-14
Average molecular weights and polydispersity indexes are some of the most important parameters considered in the polymer characterization. Usually, gel permeation chromatography (GPC) and multi angle light scattering (MALS) are used for this determination, but GPC values are overestimated due to the dispersion introduced by the column separation. Several procedures were proposed to correct such effect usually involving more complex calibration processes. In this work, a new method of calculation has been considered including diffusion effects. An equation for the concentration profile due to diffusion effects along the GPC column was considered to be a Fickian function and polystyrene narrow standards were used to determine effective diffusion coefficients. The molecular weight distribution function of mono and poly disperse polymers was interpreted as a sum of several Fickian functions representing a sample formed by only few kind of polymer chains with specific molecular weight and diffusion coefficient. Proposed model accurately fit the concentration profile along the whole elution time range as checked by the computed standard deviation. Molecular weights obtained by this new method are similar to those obtained by MALS or traditional GPC while polydispersity index values are intermediate between those obtained by the traditional GPC combined to Universal Calibration method and the MALS method. Values for Pearson and Lin coefficients shows improvement in the correlation of polydispersity index values determined by GPC and MALS methods when diffusion coefficients and new methods are used. PMID:26163929
Saripalli, Kanaka P.; Serne, R. Jeffrey; Meyer, Philip D.; McGrail, B. Peter
2002-08-01
Determination of aqueous phase diffusion coefficients of solutes through porous media is essential for understanding and modeling contaminant transport. Prediction of diffusion coefficients in both saturated and unsaturated zones requires knowledge of tortuosity and constrictivity factors. No methods are available for the direct measurement of these factors, which are empirical in their definition. In this paper, a new definition for the tortuosity factor is proposed, as the real to ideal interfacial area ratio. We define the tortuosity factor for saturated porous media (ts) as the ratio S/So (specific surface of real porous medium to that of an idealized capillary bundle). For unsaturated media, tortuosity factor (ta) is defined as aaw/aaw,o (ratio of the specific air-water interfacial area of real and the corresponding idealized porous medium). This tortuosity factor is suitably measured using sorptive tracers (e.g., nitrogen adsorption method) for saturated media and interfacial tracers for unsaturated media. A model based on this new definition of tortuosity factors, termed the Interfacial Area Ratio (IAR) model, is presented for the prediction of diffusion coefficients as a function of the degree of water saturation. Diffusion coefficients and diffusive resistances measured in a number of saturated and unsaturated granular porous media, for solutes in dilute aqueous solutions, agree well with the predictions of the IAR model. A comparison of permeability of saturated sands estimated based on ts and the same based on the Kozeny-Carman equation confirm the usefulness of the ts parameter as a measure of tortuosity.
IBRAHIM DINCER
1998-01-01
This study deals with the development of an analytical technique for determining the moisture diffusivities and moisture transfer coefficients for wood products subjected to drying. The wood products are idealized in the modeling as either infinite plates or long cylinders. The analysis of transient moisture diffusion is carried out on the basis of two important practical criteria: 0.1
Application of the clustering method in molecular dynamics simulation of the diffusion coefficient
Qingzhi Liu; Yangdong Hu
2008-01-01
Using molecular dynamics (MD) simulation, the diffusion of oxygen, methane, ammonia and carbon dioxide in water was simulated\\u000a in the canonical NVT ensemble, and the diffusion coefficient was analyzed by the clustering method. By comparing to the conventional\\u000a method (using the Einstein model) and the differentiation-interval variation method, we found that the results obtained by\\u000a the clustering method used in
NASA Astrophysics Data System (ADS)
Rengel, R.; Martín, M. J.
2013-10-01
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.
Reorientational angle distribution and diffusion coefficient for nodal and cylindrical surfaces
NASA Astrophysics Data System (ADS)
Plewczy?ski, D.; Ho?yst, R.
2000-12-01
We present a catalogue of diffusion coefficients and reorientational angle distribution (RAD) for various periodic surfaces, such as I-WP, F-RD, S, and S1 nodal surfaces; cylindrical structures like simple, undulated, and spiral cylinders, and a three-dimensional interconnected-rod structures. The results are obtained on the basis of a simulation algorithm for a diffusion on a surface given by the general equation ?(r)=0 [Ho?yst et al., Phys Rev. E 60, 302 (1999)]. I-WP, S, and S1 surfaces have a spherelike RAD, while F-RD has a cubelike RAD. The average of the second Legendre polynomial with RAD function for all nodal surfaces, except the F-RD nodal surface, decays exponentially with time for short times. The decay time is related to the Euler characteristic and the area per unit cell of a surface. This analytical formula, first proposed by B. Halle, S. Ljunggren, and S. Lidin in J. Chem. Phys. 97, 1401 (1992), is checked here on nodal surfaces, and its range of validity is determined. RAD function approaches its stationary limit exponentially with time. We determine the time to reach stationary state for all surfaces. In the case of the value of the effective diffusion coefficient the mean curvature and a connectivity between parts of surfaces have the main influence on it. The surfaces with low mean curvature at every point of the surface are characterized by high-diffusion coefficient. However if a surface has globally low mean curvature with large regions of nonzero mean curvature (negative and positive) the effective diffusion coefficient is low, as for example, in the case of undulated cylinders. Increasing the connectivity, at fixed curvatures, increases the diffusion coefficient.
Tatistcheff, H.B.; Fritsch-Faules, I.; Wrighton, M.S. (Massachusetts Inst. of Technology, Cambridge (United States))
1993-03-18
The authors report electrochemical measurement of diffusion coefficients and operation of electrochemical devices in aqueous polyacrylate gels formed by neutralization of poly(acrylic acid), MW = 4 [times] 10[sup 6]. Upon neutralization, dilute aqueous solutions become gels with viscosities as high as 5 [times] 10[sup 4] cP at low shear rates. Diffusivity was measured using potential step generation-collection on arrays of closely spaced microelectrodes. The diffusion coefficient, D, of 1,1[prime]-bis(hydroxymethyl)ferrocenium was found to be (5.8 [+-] 0.4) [times] 10[sup [minus]6] cm[sup 2]/s in the gel electrolyte (aqueous 0.5% poly(acrylic acid) at pH 7) and (8.8 [+-] 0.8) [times] 10[sup [minus]6] cm[sup 2]/s in the aqueous fluid electrolyte 0.1 M NaCH[sub 3]CO[sub 2] (pH 7). The small decrease observed in D for the gel vs the fluid with such a large increase in viscosity is contrary to the Stokes-Einstein mode for diffusion in viscous solutions but is in accord with the structure of polyacrylate gels which consists of two phases. The continuous, aqueous phase allows for high diffusivity. Electrochemical transistors based on ruthenium oxide exhibit similar operating characteristics in both polyacrylate gel and aqueous fluid electrolytes. Response times of electrochromic polymer films made from N,N[prime]-bis[p-(trimethoxysilyl)benzyl]-4,4[prime]-bipyridinium are slower in gel by about a factor of 10 compared to aqueous fluid electrolytes. The slow electrochromic switching is likely due to sluggish ion motion, owing to the effects of charge compensation by the polyacrylate. 30 refs., 11 figs., 2 tabs.
Measurement and modeling of CO2 diffusion coefficient in Saline Aquifer at reservoir conditions
NASA Astrophysics Data System (ADS)
Azin, Reza; Mahmoudy, Mohamad; Raad, Seyed; Osfouri, Shahriar
2013-12-01
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.
An analytic approximation to the Diffusion Coefficient for the periodic Lorentz Gas
C. Angstmann; G. P. Morriss
2012-02-14
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.
Michalet, Xavier
Fit Algorithm Performance Comparison (Supporting Information for "Optimal Diffusion Coefficient but are best used as follows: q Fig. S1 shows a comparison of execution time for the MLE and OLSF algorithms of "Success Maps" for D, 2 or D and 2 obtained by either the OLSF or MLE algorithm, as described
The measurement of the diffusion coefficient and the sorption isotherm of water in paint films
A. J. J. van der Zanden; E. L. J. Goossens
2003-01-01
An experimental technique together with a numerical model is proposed with which the diffusion coefficient and the sorption isotherm of water in paint can be measured. Inside a closed vessel, paint films are on stainless-steel plates. Water is present as water vapour in the air and in the paint. After blowing dry or wet air through the vessel for some
Plasma loss and associated diffusion coefficients to an isolated internal octupole ring
A. J. Cavallo
1976-01-01
Measurement of particle transport is made in the magnetohydrodynamically stable region near a completely isolated internal ring in a levitated octupole by telemetering the collected plasma signal. With a toroidal field of 10% of the poloidal field and with the parameters of a specified gun-injected plasma a derived diffusion coefficient of D = 60 sq cm per sec results. With
Although detailed thermodynamic analyses of the 2-pK diffuse layer surface complexation model generally specify bound site activity coefficients for the purpose of accounting for those non-ideal excess free energies contributing to bound site electrochemical potentials, in applic...
M. J. Assael; J. H. Dymond; V. Tselekidou
1990-01-01
Thermal conductivity, viscosity, and self-diffusion coefficient data for liquid n-alkanes are satisfactorily correlated simultaneously by a method based on the hard-sphere theory of transport properties. Universal curves are developed for the reduced transport properties lambda *, eta *, and D * as a function of the reduced volume. A consistent set of equations is derived for the characteristic volume and
M. J. Assael; J. H. Dymond; V. Tselekidou
1990-01-01
Thermal conductivity, viscosity, and self-diffusion coefficient data for liquid n-alkanes are satisfactorily correlated simultaneously by a method based on the hard-sphere theory of transport properties. Universal curves are developed for the reduced transport properties ?*, ?*, and D* as a function of the reduced volume. A consistent set of equations is derived for the characteristic volume and for the parameters
Relaxation Time Constants and Apparent Diffusion Coefficients of Rat Retina at 7 Tesla
Duong, Timothy Q.
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
Annunziata, Onofrio
2001-01-01
Journal of Crystal Growth 232 (2001) 273284 Precision measurement of ternary diffusion coefficients and implications for protein crystal growth: lysozyme chloride in aqueous ammonium chloride at 258 the driving force for nucleation and crystal growth of lysozyme chloride. # 2001 Elsevier Science B.V. All
THE DIFFUSION COEFFICIENT FOR PIECEWISE EXPANDING MAPS OF THE INTERVAL WITH METASTABLE STATES
Dolgopyat, Dmitry
THE DIFFUSION COEFFICIENT FOR PIECEWISE EXPANDING MAPS OF THE INTERVAL WITH METASTABLE STATES. Introduction Metastable dynamics arise in a number of physical systems. In such systems, the phase space can be divided into a finite number of components, called metastable states, that are nearly invariant under
Kiyoaki TAKETANI; Katsuichi IKAWA
1965-01-01
In connection with a program to study the behavior of punctured fuel elements for the Tokai Atomic Power Reactor, the diffusion coefficient of fission gas in uranium oxide powder formed by CO2 oxidation of U was determined by post-irradiation experiment, in which the fractional release of fission gas during isothermal heating of the powder was measured. The U was oxidized
Water diffusion coefficients during copper electropolishing and IAN IVAR SUNI2*
Suni, Ian Ivar
Water diffusion coefficients during copper electropolishing BING DU1 and IAN IVAR SUNI2* 1, including several with ethanol and other species added as diluents. Diluents allow a wider range of water in the mass transfer limited regime are shown to depend on both the number of water acceptor molecules
Unsteady-state evaporation and the measurement of a binary diffusion coefficient
John C. Slattery; Vijay R. Mhetar
1997-01-01
A solution for the isothermal evaporation of a pure volatile liquid that accounts for the moving liquid-vapor interface is presented. This solution is compared with new experimental data for the evaporation of methanol and methyl formate into air at 25.4°C. The resulting diffusion coefficients for these systems are in excellent agreement with reported values (corrected for temperature and pressure).
Ching-Chih Lai; Chung-Sung Tan
1995-01-01
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
Solubilities and diffusion coefficients of high boiling compounds in supercritical carbon dioxide
Hidenori Higashi; Yoshio Iwai; Yasuhiko Arai
2001-01-01
A brief introduction of the data sources and the applications of correlation methods for the solubilities and diffusion coefficients of high-boiling compounds (mainly in solid state) in supercritical carbon dioxide are reviewed. Empirical equations, equations of state, solution models, and the Monte Carlo simulation for the calculation of solubilities in supercritical carbon dioxide are discussed. The application of empirical equation
Richard W. Gould; Robert A. Arnone
1994-01-01
An iterative technique has been developed to improve coastal zone color scanner (CZCS) estimates of upwelled subsurface water radiances (Lu) in Case II waters. Regional relationships between the diffuse attenuation coefficient measured at 490 nm (K490) and Lu measured at 443, 520, and 550 nm were developed using data collected in the northern Gulf of Mexico in April 1993. These
NASA Astrophysics Data System (ADS)
Chenyakin, Y.; Kamal, S.; Bertram, A. K.
2014-12-01
Secondary organic aerosol (SOA) particles are formed in the atmosphere via gas-to-particle conversion of low and semi volatile organic compounds. They are abundant in the atmosphere and can directly contribute to climate change by scattering solar radiation or indirectly by acting as cloud condensation nuclei or ice nuclei. There is also a health concern associated with SOA particles because they can make up a large fraction of suspended submicron particulate mass. In addition, a reduction in visibility in both polluted and rural areas can be due to SOA particles. Knowledge of diffusion coefficients of organic species within SOA particles is needed to predict the atmospheric behaviour and environmental impacts of these particles. Here we introduce a new method to determine diffusion coefficients of organic probes in particles made up of organic species as a function of relative humidity (RH). Our method involves using fluorescence recovery after photobleaching (FRAP) to measure the diffusion coefficients of organic fluorescent dyes in organic particles with dimensions of approximately 25 ?m. We validated this method by measuring diffusion coefficients of organic dyes of varied size in sucrose-water solutions as a function of RH and comparing these results with data from the literature. In the future this method will be applied to SOA particles.
Scaling of the diffusion coefficient on the normal form remainder in doubly resonant domains
C. Efthymiopoulos
2008-12-04
An outline of theoretical estimates is given regarding the dependence of the value of the diffusion coefficient $D$ on the size $R$ of the remainder of the normal form in doubly or simply resonant domains of the action space of 3dof Hamiltonian systems.
Kovalishin, A. A., E-mail: kaa@adis.vver.kiae.ru; Laletin, N. I. [Russian Research Centre Kurchatov Institute (Russian Federation)
2011-12-15
The preference of even approximations of the surface pseudo source method for calculation of the diffusion coefficient is substantiated. The homogenization limit for the G{sub 0} approximation in the case of the cell size tending to zero is analytically proved.
Rare earth ion diffusion in AgBr crystals
L. Nagli; A German; A Katzir
1999-01-01
The luminescence of silver bromide crystals doped with rare earth ions (Nd3+ and Er3+) was investigated in the visible and near infrared spectral ranges. Crystal doping was produced by growing in the melt and by a diffusion method. The diffusion profile of rare earth ions in AgBr crystals was measured by the luminescence method. The luminescence parameters of AgBr crystals
Albert Jambon; Michel P. Semet
1978-01-01
Tracer diffusion coefficients for Li in glasses of albite, orthoclase, and obsidian composition have been determined by a method involving deposition of a thin source on polished glass wafers, anneal under controlled temperature conditions (300-900°C), and ion-microprobe determination of the concentration profile. All results conform to an Arrhenius-type relationship, D = D0 exp(-Q\\/RT), where Q is 23, 17, and 22
Transport diffusion coefficient for a Knudsen gas in a random tube
Francis Comets; Serguei Popov; Gunter M. Schütz; Marina Vachkovskaia
2010-04-10
We consider transport diffusion in a stochastic billiard in a random tube which is elongated in the direction of the first coordinate (the tube axis). Inside the random tube, which is stationary and ergodic, non-interacting particles move straight with constant speed. Upon hitting the tube walls, they are reflected randomly, according to the cosine law: the density of the outgoing direction is proportional to the cosine of the angle between this direction and the normal vector. Steady state transport is studied by introducing an open tube segment as follows: We cut out a large finite segment of the tube with segment boundaries perpendicular to the tube axis. Particles which leave this piece through the segment boundaries disappear from the system. Through stationary injection of particles at one boundary of the segment a steady state with non-vanishing stationary particle current is maintained. We prove (i) that in the thermodynamic limit of an infinite open piece the coarse-grained density profile inside the segment is linear, and (ii) that the transport diffusion coefficient obtained from the ratio of stationary current and effective boundary density gradient equals the diffusion coefficient of a tagged particle in an infinite tube. Thus we prove Fick's law and equality of transport diffusion and self-diffusion coefficients for quite generic rough (random) tubes.
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
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.
Ion beam analysis of diffusion in heterogeneous materials
A. S. Clough; P. M. Jenneson
1998-01-01
Ion-beam analysis has been applied to a variety of problems involving diffusion in heterogeneous materials. An energy loss technique has been used to study both the diffusion of water and the surface segregation of fluoropolymers in polymeric matrices. A scanning micro-beam technique has been developed to allow water concentrations in hydrophilic polymers and cements to be measured together with associated
Estimation of the radial diffusion coefficient using REE-associated ground Pc 5 pulsations
NASA Astrophysics Data System (ADS)
Fujimoto, A.; Yumoto, K.
2010-12-01
Pc 5 pulsations with frequencies between 1.67 and 6.67 mHz are believed to contribute to the REE in the outer radiation belt during magnetic storms, by means of the observations [Baker et al., 1998; Rostoker et al., 1998; Mathie and Mann, 2000; O'Brien et al., 2001, 2003] and several theoretical studies. The latter studies are roughly categorized into two themes: in-situ acceleration at L lower than 6.6 by wave-particle interactions [Liu et al., 199 9; Summers et al., 1999; Summers and Ma, 2000] and acceleration by radial diffusion from the outer to the inner magnetosphere [Elkington et al., 1999, 2003; Hudson et al., 2000; Kim et al., 2001]. One possible acceleration mechanism is the resonant interaction with Pc 5 toroidal and poloidal pulsations, referred as the radial diffusion mechanism. One of unsolved problems is where and which Pc 5 pulsation mode (toroidal and/or poloidal) play effective role in the radial diffusion process. In order to verify Pc 5 pulsation as the major roles for REEs, we have to examine the time variation of electron phase space density (cf. Green et al., 2004). Electron phase space density is not directly measured, but we can estimate radial diffusion coefficients which determine the electron transportation efficiency, using ground-based magnetic field data. We estimated the radial diffusion coefficient of ground Pc 5 pulsations associated with the Relativistic Electron Enhancement (REE) in the geosynchronous orbit. In order to estimate the radial diffusion coefficient D_LL, we need the value of in-situ Pc 5 electric field power spectral density. In this paper, however, we estimated the equatorial electric field mapped from Pc 5 pulsations power spectral density on the ground. Reciprocal of radial diffusion coefficient describes the timescale T_LL for an electron to diffuse 1 Re. Applying a superposed epoch analysis about timescales T_LL of the radial diffusion for 12 REE events in 2008, we found that when the relativistic electron enhancements occur, T_LL at higher latitude (L larger than 5) is predominantly diffusional, whereas T_LL at lower latitude (L less than 4) is mainly convectional. We concluded that higher-latitude Pc 5 pulsations play more effective roles than lower latitude Pc 5 pulsations in the radial diffusion process.
Diffusivity measurement of heavy ions in Wyoming montmorillonite gels by X-ray computed tomography
NASA Astrophysics Data System (ADS)
Nakashima, Yoshito
2003-03-01
Medical X-ray computed tomography (CT) was applied to the measurement of the diffusion coefficients of heavy ions in an artificial barrier material for the disposal of nuclear wastes. Cs +, Sr 2+, I -, and Br - are the heavy ions measured and the barrier used is the water-rich gel of Wyoming montmorillonite (86.5-100 wt.% H 2O). X-ray CT yields an inevitable artifact (beam-hardening) in the obtained images. Before the diffusion experiments, the polychromatic primary X-ray spectrum of the CT scanner was measured by a CdZnTe detector, and the effects of the artifact were examined for an aqueous CsCl solution sample. The results show that the beam-hardening artifact derived from the polychromatic photon energy distribution can be suppressed by applying a special image reconstruction method assuming the chemical composition of samples. The transient one-dimensional diffusion of heavy ions in a plastic container filled with the gel was imaged nondestructively by the X-ray CT scanner with an in-plane resolution of 0.31 mm and slice thickness of 2 mm. The results show that diffusivities decrease with increasing clay weight fraction. The degree of the diffusivity decrease was high for cations (Cs + and Sr 2+) and low for anions (I - and Br -). The quantitative decomposition of the contribution of the geometrical tortuosity and of the sorption to the diffusivity was performed by subtracting the diffusivity of nonsorbing I - from the measured diffusivities. The results show that the contribution of the sorption is large for Cs +, Sr 2+ and small for Br -. Because X-ray CT allows nondestructive and quick measurements of diffusivities, the technique would be useful particularly for measuring the diffusive migration of harmful radioactive elements.
Hermes, Helen E; Sitta, Christoph E; Schillinger, Burkhard; Löwen, Hartmut; Egelhaaf, Stefan U
2015-06-28
The dissolution of polyethylene oxide (PEO) tablets in water has been followed in situ by neutron radiography. When in contact with water, the crystalline phase of semi-crystalline PEO melts once a certain water content is attained. Polymer concentration profiles obtained from the neutron transmission images exhibited a pronounced kink which corresponds to a sharp front in the images and which is related to the melting transition. Sharp diffusion fronts and phase transitions are often linked to non-Fickian behaviour. However, by considering the time evolution of the complete concentration profiles in detail it is shown that the dissolution process can be explained using Fickian diffusion equations with a concentration-dependent diffusion coefficient. PMID:26018995
T. Kraska; S. E. Quiñones-Cisneros; U. K. Deiters
2007-01-01
An easy applicable and accurate method for the correlation of the infinite dilution diffusion coefficient of organic solutes in supercritical fluids is proposed. The method is applicable to all supercritical fluids; in this work, however, only supercritical carbon dioxide is considered. The infinite dilution diffusion coefficient is calculated from the solvent viscosity by means of a modified Stokes–Einstein relation. The
Bond lifetime and diffusion coefficient in colloids with short-range interactions.
Ndong Mintsa, E; Germain, Ph; Amokrane, S
2015-03-01
We use molecular dynamics simulations to study the influence of short-range structures in the interaction potential between hard-sphere-like colloidal particles. Starting from model potentials and effective potentials in binary mixtures computed from the Ornstein-Zernike equations, we investigate the influence of the range and strength of a possible tail beyond the usual core repulsion or the presence of repulsive barriers. The diffusion coefficient and mean "bond" lifetimes are used as indicators of the effect of this structure on the dynamics. The existence of correlations between the variations of these quantities with the physical parameters is discussed to assess the interpretation of dynamics slowing down in terms of long-lived bonds. We also discuss the question of a universal behaviour determined by the second virial coefficient B ((2)) and the interplay of attraction and repulsion. While the diffusion coefficient follows the B ((2)) law for purely attractive tails, this is no longer true in the presence of repulsive barriers. Furthermore, the bond lifetime shows a dependence on the physical parameters that differs from that of the diffusion coefficient. This raises the question of the precise role of bonds on the dynamics slowing down in colloidal gels. PMID:25813606
An interpretation of potential scale dependence of the effectivematrix diffusion coefficient
Liu, H.H.; Zhang, Y.Q.; Zhou, Q.; Molz, F.J.
2005-11-30
Matrix diffusion is an important process for solutetransport in fractured rock, and the matrix diffusion coefficient is akey parameter for describing this process. Previous studies indicatedthat the effective matrix diffusion coefficient values, obtained from alarge number of field tracer tests, are enhanced in comparison with localvalues and may increase with test scale. In this study, we have performednumerical experiments to investigate potential mechanisms behind possiblescale-dependent behavior. The focus of the experiments is on solutetransport in flow paths having geometries consistent with percolationtheories and characterized by local flow loops formed mainly bysmall-scale fractures. The water velocity distribution through a flowpath was determined using discrete fracture network flow simulations, andsolute transport was calculated using a previously derivedimpulse-response function and a particle-tracking scheme. Values foreffective (or up-scaled) transport parameters were obtained by matchingbreakthrough curves from numerical experiments with an analyticalsolution for solute transport along a single fracture. Results indicatethat a combination of local flow loops and the associated matrixdiffusion process, together with scaling properties in flow pathgeometry, seems to be the dominant mechanism causing the observed scaledependence of theeffective matrix diffusion coefficient (at a range ofscales).
Kruk, D. [Faculty of Mathematics and Computer Science, University of Warmia and Mazury in Olsztyn, S?oneczna 54, PL-10710 Olsztyn (Poland); Universität Bayreuth, Experimentalphysik II, 95440 Bayreuth (Germany); Meier, R.; Rössler, E. A. [Universität Bayreuth, Experimentalphysik II, 95440 Bayreuth (Germany); Rachocki, A. [Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60-179 Pozna? (Poland); Korpa?a, A. [Department of Biophysics, Jagiellonian University Medical College, ?azarza 16, 31-530 Kraków, Poland and Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Kraków (Poland); Singh, R. K. [Ionic Liquid and Solid State Ionics Laboratory, Department of Physics, Banaras Hindu University, Varanasi 221 005 (India)
2014-06-28
Field Cycling Nuclear Magnetic Resonance (FC NMR) relaxation studies are reported for three ionic liquids: 1-ethyl-3- methylimidazolium thiocyanate (EMIM-SCN, 220–258 K), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF{sub 4}, 243–318 K), and 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF{sub 6}, 258–323 K). The dispersion of {sup 1}H spin-lattice relaxation rate R{sub 1}(?) is measured in the frequency range of 10 kHz–20 MHz, and the studies are complemented by {sup 19}F spin-lattice relaxation measurements on BMIM-PF{sub 6} in the corresponding frequency range. From the {sup 1}H relaxation results self-diffusion coefficients for the cation in EMIM-SCN, BMIM-BF{sub 4}, and BMIM-PF{sub 6} are determined. This is done by performing an analysis considering all relevant intra- and intermolecular relaxation contributions to the {sup 1}H spin-lattice relaxation as well as by benefiting from the universal low-frequency dispersion law characteristic of Fickian diffusion which yields, at low frequencies, a linear dependence of R{sub 1} on square root of frequency. From the {sup 19}F relaxation both anion and cation diffusion coefficients are determined for BMIM-PF{sub 6}. The diffusion coefficients obtained from FC NMR relaxometry are in good agreement with results reported from pulsed- field-gradient NMR. This shows that NMR relaxometry can be considered as an alternative route of determining diffusion coefficients of both cations and anions in ionic liquids.
Stress enhanced diffusion of krypton ions in polycrystalline titanium
Nsengiyumva, S., E-mail: s.nsengiyumva@ru.ac.za [Department of Physics and Electronics, Rhodes University, Grahamstown 6140 (South Africa); Raji, A. T. [School of Interdisciplinary Research and Graduate Studies, University of South Africa, Mucklenuek Campus, P O Box 392, UNISA 0003, Pretoria (South Africa); Rivière, J. P. [Laboratoire de Métallurgie Physique, UMR 6630 CNRS- Université de Poitiers, Bd M. et P. Curie, BP30179, 86962 Chasseneuil Futuroscope, Cedex (France); Britton, D. T.; Härting, M. [NanoSciences Innovation Center, Department of Physics, University of Cape Town, Rondebosch 7701 (South Africa)
2014-07-14
An experimental investigation on the mutual influence of pre-existing residual stress and point defect following ion implantation is presented. The study has been carried out using polycrystalline titanium samples energetically implanted with krypton ions at different fluences. Ion beam analysis was used to determine the concentration profile of the injected krypton ions, while synchrotron X-ray diffraction has been used for stress determination. Ion beam analysis and synchrotron X-ray diffraction stress profile measurements of the implanted titanium samples show a clear evidence of stress-enhanced diffusion of krypton ions in titanium. It is further observed that for the titanium samples implanted at low fluence, ion implantation modifies the pre-existing residual stress through the introduction of point and open volume defects. The stress fields resulting from the ion implantation act to drift the krypton inclusions towards the surface of titanium.
A new in-situ method to determine the apparent gas diffusion coefficient of soils
NASA Astrophysics Data System (ADS)
Laemmel, Thomas; Paulus, Sinikka; Schack-Kirchner, Helmer; Maier, Martin
2015-04-01
Soil aeration is an important factor for the biological activity in the soil and soil respiration. Generally, gas exchange between soil and atmosphere is assumed to be governed by diffusion and Fick's Law is used to describe the fluxes in the soil. The "apparent soil gas diffusion coefficient" represents the proportional factor between the flux and the gas concentration gradient in the soil and reflects the ability of the soil to "transport passively" gases through the soil. One common way to determine this coefficient is to take core samples in the field and determine it in the lab. Unfortunately this method is destructive and needs laborious field work and can only reflect a small fraction of the whole soil. As a consequence insecurity about the resulting effective diffusivity on the profile scale must remain. We developed a new in-situ method using new gas sampling device, tracer gas and inverse soil gas modelling. The gas sampling device contains several sampling depths and can be easily installed into vertical holes of an auger, which allows for fast installation of the system. At the lower end of the device inert tracer gas is injected continuously. The tracer gas diffuses into the surrounding soil. The resulting distribution of the tracer gas concentrations is used to deduce the diffusivity profile of the soil. For Finite Element Modeling of the gas sampling device/soil system the program COMSOL is used. We will present the results of a field campaign comparing the new in-situ method with lab measurements on soil cores. The new sampling pole has several interesting advantages: it can be used in-situ and over a long time; so it allows following modifications of diffusion coefficients in interaction with rain but also vegetation cycle and wind.
Drag and diffusion coefficients of $B$ mesons in hot hadronic matter
Santosh K Das; Sabyasachi Ghosh; Sourav Sarkar; Jan-e Alam
2012-04-27
The drag and diffusion coefficients of a hot hadronic medium consisting of pions, kaons and eta using open beauty mesons as a probe have been evaluated. The interaction of the probe with the hadronic matter has been treated in the framework of chiral perturbation theory. It is observed that the magnitude of both the transport coefficients are significant, indicating substantial amount of interaction of the heavy mesons with the thermal bath. The results may have significant impact on the experimental observables like the suppression of single electron spectra originating from the decays of heavy mesons produced in nuclear collisions at RHIC and LHC energies
Firoozabadi, Abbas
Molecular and Thermal Diffusion Coefficients of Alkane-Alkane and Alkane-Aromatic Binary Mixtures Form: October 27, 2006 New molecular and thermal diffusion coefficients of binary mixtures of normal-molecular diffusion coefficient for nC10 from binary data. I. Introduction Molecular and thermal diffusion processes
R. N. Sener
2001-01-01
Diffusion-weighted imaging, dependent on motion of water molecules, provides information regarding tissue integrity. Apparent diffusion coefficient (ADC) values in the normal brain parenchyma, and those in a variety of lesions were studied by echo-planar diffusion MRI in 310 cases. Brain disorders were classified based on their ADC values, taking the ADC values of the normal brain white matter as the
Renslow, Ryan S.; Majors, Paul D.; McLean, Jeffrey S.; Fredrickson, Jim K.; Ahmed, B.; Beyenal, Haluk
2010-08-15
Diffusive mass transfer in biofilms is characterized by the effective diffusion coefficient. It is well-documented that the effective diffusion coefficient can vary by location in a biofilm. The current literature is dominated by effective diffusion coefficient measurements for distinct cell clusters and stratified biofilms showing this spatial variation. Regardless of whether distinct cell clusters or surface-averaging methods are used, position-dependent measurements of the effective diffusion coefficient are currently: 1) invasive to the biofilm, 2) performed under unnatural conditions, 3) lethal to cells, and/or 4) spatially restricted to only certain regions of the biofilm. Invasive measurements can lead to inaccurate results and prohibit further (time dependent) measurements which are important for the mathematical modeling of biofilms. In this study our goals were to: 1) measure the effective diffusion coefficient for water in live biofilms, 2) monitor how the effective diffusion coefficient changes over time under growth conditions, and 3) correlate the effective diffusion coefficient with depth in the biofilm. We measured in situ two-dimensional effective diffusion coefficient maps within Shewanella oneidensis MR-1biofilms using pulsed-field gradient nuclear magnetic resonance methods, and used them to calculate surface-averaged relative effective diffusion coefficient (Drs) profiles. We found that 1) Drs decreased from the top of the biofilm to the bottom, 2) Drs profiles differed for biofilms of different ages, 3) Drs profiles changed over time and generally decreased with time, 4) all the biofilms showed very similar Drs profiles near the top of the biofilm, and 5) the Drs profile near the bottom of the biofilm was different for each biofilm. Practically, our results demonstrate that advanced biofilm models should use a variable effective diffusivity which changes with time and location in the biofilm.
Renslow, Ryan S; Majors, Paul D; McLean, Jeffrey S; Fredrickson, Jim K; Ahmed, Bulbul; Beyenal, Haluk
2010-08-15
Diffusive mass transfer in biofilms is characterized by the effective diffusion coefficient. It is well documented that the effective diffusion coefficient can vary by location in a biofilm. The current literature is dominated by effective diffusion coefficient measurements for distinct cell clusters and stratified biofilms showing this spatial variation. Regardless of whether distinct cell clusters or surface-averaging methods are used, position-dependent measurements of the effective diffusion coefficient are currently: (1) invasive to the biofilm, (2) performed under unnatural conditions, (3) lethal to cells, and/or (4) spatially restricted to only certain regions of the biofilm. Invasive measurements can lead to inaccurate results and prohibit further (time-dependent) measurements which are important for the mathematical modeling of biofilms. In this study our goals were to: (1) measure the effective diffusion coefficient for water in live biofilms, (2) monitor how the effective diffusion coefficient changes over time under growth conditions, and (3) correlate the effective diffusion coefficient with depth in the biofilm. We measured in situ two-dimensional effective diffusion coefficient maps within Shewanella oneidensis MR-1 biofilms using pulsed-field gradient nuclear magnetic resonance methods, and used them to calculate surface-averaged relative effective diffusion coefficient (D(rs)) profiles. We found that (1) D(rs) decreased from the top of the biofilm to the bottom, (2) D(rs) profiles differed for biofilms of different ages, (3) D(rs) profiles changed over time and generally decreased with time, (4) all the biofilms showed very similar D(rs) profiles near the top of the biofilm, and (5) the D(rs) profile near the bottom of the biofilm was different for each biofilm. Practically, our results demonstrate that advanced biofilm models should use a variable effective diffusivity which changes with time and location in the biofilm. PMID:20589671
Choi, Choong Gon; Kim, Jeong Kon; Yun, Sung-Cheol; Jahng, Geon-Ho; Jeong, Ha-Kyu; Kim, Eun Ju
2015-01-01
Objective To validate the usefulness of a diffusional anisotropic capillary array phantom and to investigate the effects of diffusion tensor imaging (DTI) parameter changes on diffusion fractional anisotropy (FA) and apparent diffusion coefficient (ADC) using the phantom. Materials and Methods Diffusion tensor imaging of a capillary array phantom was performed with imaging parameter changes, including voxel size, number of sensitivity encoding (SENSE) factor, echo time (TE), number of signal acquisitions, b-value, and number of diffusion gradient directions (NDGD), one-at-a-time in a stepwise-incremental fashion. We repeated the entire series of DTI scans thrice. The coefficients of variation (CoV) were evaluated for FA and ADC, and the correlation between each MR imaging parameter and the corresponding FA and ADC was evaluated using Spearman's correlation analysis. Results The capillary array phantom CoVs of FA and ADC were 7.1% and 2.4%, respectively. There were significant correlations between FA and SENSE factor, TE, b-value, and NDGD, as well as significant correlations between ADC and SENSE factor, TE, and b-value. Conclusion A capillary array phantom enables repeated measurements of FA and ADC. Both FA and ADC can vary when certain parameters are changed during diffusion experiments. We suggest that the capillary array phantom can be used for quality control in longitudinal or multicenter clinical studies. PMID:25741191
Oxygen diffusion coefficient and solubility in a new proton exchange membrane
Haug, A.T.; White, R.E.
2000-03-01
The electrochemical monitoring technique is used to measure the solubility and the diffusion coefficient of oxygen in a new proton exchange membrane that is being developed by Cape Cod Research, Inc., Using the method of least squares, the data were fit to an analytical solution of Fick's second law to determine D and c{sub 0}. Values of 0.40 x 10{sup {minus}6}cm{sup 2}/s and 4.98 x 10{sup {minus}6} mol/cm{sup 3} were obtained for the diffusion coefficient and solubility, respectively, of the Cape Cod membrane. These values are significantly less than those of Nafion 117 tested under identical conditions.
Guo, Zijian; Favazza, Christopher; Garcia-Uribe, Alejandro; Wang, Lihong V.
2012-01-01
Abstract. Photoacoustic (PA) microscopy (PAM) can image optical absorption contrast with ultrasonic spatial resolution in the optical diffusive regime. Conventionally, accurate quantification in PAM requires knowledge of the optical fluence attenuation, acoustic pressure attenuation, and detection bandwidth. We circumvent this requirement by quantifying the optical absorption coefficients from the acoustic spectra of PA signals acquired at multiple optical wavelengths. With the acoustic spectral method, the absorption coefficients of an oxygenated bovine blood phantom at 560, 565, 570, and 575 nm were quantified with errors of <3%. We also quantified the total hemoglobin concentration and hemoglobin oxygen saturation in a live mouse. Compared with the conventional amplitude method, the acoustic spectral method provides greater quantification accuracy in the optical diffusive regime. The limitations of the acoustic spectral method was also discussed. PMID:22734767
Mialdun, A; Yasnou, V; Shevtsova, V; Königer, A; Köhler, W; Alonso de Mezquia, D; Bou-Ali, M M
2012-06-28
We report on the measurement of diffusion (D), thermodiffusion (D(T)), and Soret (S(T)) coefficients in water-isopropanol mixtures by three different instrumental techniques: thermogravitational column in combination with sliding symmetric tubes, optical beam deflection, and optical digital interferometry. All the coefficients have been measured over the full concentration range. Results from different instruments are in excellent agreement over a broad overlapping composition (water mass fraction) range 0.2 < c < 0.7, providing new reliable benchmark data. Comparison with microgravity measurements (SODI/IVIDIL (Selected Optical Diagnostic Instrument/Influence of VIbration on DIffusion in Liquids)) onboard the International Space Station and with literature data (where available) generally gives a good agreement. Contrary to theoretical predictions and previous experimental expectations we have not observed a second sign change of S(T) at low water concentrations. PMID:22755592
Thermal diffusivity coefficient of glycerin determined on an acoustically levitated drop.
Ohsaka, K; Rednikov, A; Sadhal, S S
2002-10-01
We present a technique that can be used to determine the thermal diffusivity coefficient of undercooled liquids that exist at temperatures below their freezing points. The technique involves levitation of a small amount of liquid in the shape of a flattened drop using an acoustic levitator and heating it with a CO2 laser. The heated drop is then allowed to cool naturally by heat loss from the surface. Due to acoustic streaming, heat loss is highly non-uniform and appears to mainly occur at the drop circumference (equatorial region). This fact allows us to relate the heat loss rate with a heat transfer model to determine the thermal diffusion coefficient. We demonstrate the feasibility of the technique using glycerin drops as a model liquid. PMID:12446319
A Monte Carlo model for determination of binary diffusion coefficients in gases
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
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.
Eddy diffusion coefficient for the atmosphere of Venus from radio scintillation measurements
NASA Astrophysics Data System (ADS)
Woo, R.; Ishimaru, A.
1981-01-01
Estimates are obtained of the vertical mass eddy diffusion coefficient of the Venus atmosphere in the region of turbulence near 60 km on the basis of radio scintillations observed during radio occultation by the atmosphere. The structure constant estimated from Pioneer Venus orbit 18 entrance radio occultation measurements is used, under the assumption that the turbulence is generated by wind-shear, to derive a value of 40,000 sq cm/sec for the vertical mass eddy diffusion coefficient, together with an energy dissipation rate of 20 sq cm/sec and a temperature fluctuation dissipation rate of 0.001 K-squared/sec. Results are noted to fall within the range measured for the earth's troposphere, however, indicate that small-scale turbulence is probably the dominant mechanism for vertical transport near the tropopause in the Venus atmosphere.
Determination of the Solute Diffusion Coefficient by the Droplet Migration Method
Shan Liu; Jing Teng; Jeongyun Choi
2007-07-01
Further analysis of droplet migration in a temperature gradient field indicates that different terms can be used to evaluate the solute diffusion coefficient in liquid (D{sub L}) and that there exists a characteristic curve that can describe the motion of all the droplets for a given composition and temperature gradient. Critical experiments are subsequently conducted in succinonitrile (SCN)-salol and SCN-camphor transparent alloys in order to observe dynamic migration processes of a number of droplets. The derived diffusion coefficients from different terms are the same within experimental error. For SCN-salol alloys, D{sub L} = (0.69 {+-} 0.05) x 10{sup -3} mm{sup 2}/s, and for SCN-camphor alloys, D{sub L} = (0.24 {+-} 0.02) x 10{sup -3} mm{sup 2}/s.
Yaxiong Gu; Seiichi Washio
2010-01-01
In this paper it is reported that the diffusion coefficient of N2 gas in a rubber sheet is derived based on combination of measurement using U-tube and laser heterodyne interferometry and one dimension diffusion theory successfully. Experiments were carried out under different pressure and temperature conditions to investigate the dependency of diffusion of gas in rubber. A conclusion has been
Effective Diffusion Coefficients of CO2 and HCFC22 in Polyurethane and Polyisocyanurate Foams
D. Bhattacharjee; J. R. Booth
1995-01-01
Thin-slice accelerated desorption of gases using a gravimetric methodology has been used to determine effective diffusion coefficients of both carbon dioxide and HCFC-22 in thermoset foam structures. Foam samples consisting of a polyurethane appliance foam and a polyisocyanurate boardstock foam both blown with CFC-11, and polyurethane foams blown with HCFC-22 and carbondioxide have been employed as polymer substrates for the
Temperature-dependent diffusion coefficient of soluble substances during ethanol extraction of clove
San Myint; Wan Ramli Wan Daud; Abu Bakar Mohamad; Abdul Amir H. Kadhum
1996-01-01
The temperature dependence of the diffusion coefficient of ethanol-soluble substances from ground cloves (particle size 250\\u000a ?m) during extraction was estimated by fitting batch extraction data at several temperatures (27.8, 40, 50, and 60C) to a\\u000a previously developed mass transfer model. The model was based on spherical geometry of particles. Nonlinear regression analysis\\u000a was used to develop an equation that
THE PARALLEL DIFFUSION COEFFICIENT AND ADIABATIC FOCUSING OF COSMIC-RAY PARTICLES
Litvinenko, Yuri E. [Department of Mathematics, University of Waikato, P.B. 3105, Hamilton (New Zealand)
2012-01-20
In this paper, the problem of focused particle transport is revisited. A description in terms of a system of stochastic differential equations, completely equivalent to the Fokker-Planck equation, is suggested. The coefficient for spatial diffusion parallel to the mean magnetic field is calculated. The case of isotropic pitch angle scattering and weak focusing is analyzed in detail. The disagreement between a recent analysis by Shalchi and other treatments of the same problem is discussed.
Measurement of the diffusion coefficient of acetone in succinonitrile at its melting point
NASA Technical Reports Server (NTRS)
Chopra, M. A.; Glicksman, M. E.; Singh, N. B.
1988-01-01
The diffusion coefficient of acetone in liquid succinonitrile at 331.1 K was determined using the method of McBain and Dawson (1935). Only dilute mixtures of SCN-acetone were studied. The interdiffusion constant was determined to be 0.0000127 sq cm/s and was essentially independent of the acetone concentration over the range investigated (0.5 to 18 mol pct acetone).
Wang, Junmei; Hou, Tingjun
2011-01-01
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
Arnab Mukherjee; Sarika Bhattacharyya; Biman Bagchi
2002-01-01
Extensive isothermal-isobaric (NPT) molecular dynamics simulations at many different temperatures and pressures have been carried out in the well-known Kob-Andersen binary mixture model to monitor the effect of pressure (P) and temperature (T) on the dynamic properties such as the viscosity (?) and the self-diffusion (Di) coefficients of the binary system. The following results have been obtained: (i) Compared to
Diffuse attenuation coefficient of downwelling irradiance: An evaluation of remote sensing methods
Zhong-Ping Lee; Miroslaw Darecki; Kendall L. Carder; Curtiss O. Davis; Dariusz Stramski; W. Joseph Rhea
2005-01-01
The propagation of downwelling irradiance at wavelength ? from surface to a depth (z) in the ocean is governed by the diffuse attenuation coefficient, $\\\\bar{K}_{d}$(?). There are two standard methods for the derivation of $\\\\bar{K}_{d}$(?) in remote sensing, which both are based on empirical relationships involving the blue-to-green ratio of ocean color. Recently, a semianalytical method to derive $\\\\bar{K}_{d}$(?) from
Binary diffusion coefficients of ?-pinene and ?-pinene in supercritical carbon dioxide
Carlos M. Silva; Cláudio A. Filho; Marintho B. Quadri; Eugénia A. Macedo
2004-01-01
?-Pinene and ?-pinene are two important structural isomers, which appear as major components of the pine tree essential oil. In this work, their binary diffusion coefficients at infinite dilution in supercritical CO2 were measured at 313.15, 323.15 and 333.15K and pressures ranging from 12 to 20MPa using the Capillary Peak Broadening technique. The experimental errors found for ? and ?
A new method for determining binary diffusion coefficients in dilute condensable vapors
C. C. M. Luijten; K. J. Bosschaart; M. E. H. Van Dongen
1997-01-01
A new method for determining binary diffusion coefficients in dilute condensable vapors is outlined. The method is based on condensational droplet growth. It can be used in a large range of pressures and temperatures, even below the freezing point of the condensing vapor. Results are obtained for the mixtures water-nitrogen and water-helium in the pressure range 11–44 bar. The product
Influence of voltage on chloride diffusion coefficients from chloride migration tests
McGrath, P.F.; Hooton, R.D. [Univ. of Toronto, Ontario (Canada). Dept. of Civil Engineering] [Univ. of Toronto, Ontario (Canada). Dept. of Civil Engineering
1996-08-01
A chloride migration test method is described and test results are given for concrete subjected to a range of potential gradients. A method for setting the potential across the sample length using reference electrodes and Luggin capillaries is described. Apparent and effective diffusion coefficients were calculated from chloride break-through time and steady state chloride flux respectively at each potential. Accounting for polarization and IR drop losses is significant particularly at lower applied potentials.
Measurement of mass diffusion coefficients using nonexponential forced Rayleigh scattering signals
NASA Astrophysics Data System (ADS)
Spiegel, D. R.; Marshall, A. H.; Jukam, N. T.; Park, H. S.; Chang, T.
1998-07-01
Recent reports on mass-diffusion forced Rayleigh scattering (FRS) experiments have emphasized that the detected signal arises as a difference between two exponentially decaying fields diffracted from "complementary" ground-state and photoproduct population gratings. A mass-diffusion coefficient has nevertheless often been extracted by forcing a single-exponential fit to the data, especially in cases where the decay appears to be monotonic. In this paper, we use simulations and experiments to evaluate the accuracy of single-exponential fits for FRS profiles, and we propose a useful alternative method for obtaining a meaningful rate constant in cases in which the error in the single-exponential analysis is large. We begin by noting from the complementary grating model that (1) severe deviations from single-exponential decay can occur for an arbitrarily small (but nonzero) difference in the ground-state/photoproduct rate constants, and (2) the first cumulant of a FRS decay—in contrast to that of a dynamic light scattering profile—does not (in general) represent a physically useful decay rate. These statements apply to both monotonic and nonmonotonic decays. We then show that a combination of the first two FRS cumulants provides a physically useful mean rate constant. Finally, to address these issues experimentally, we have reexamined the diffusion of methyl red (MR) through 2-propanol at room temperature, a system previously analyzed using single-exponential fits. The new experiments, carried out at higher sensitivity than the previous studies, show that the MR/2-propanol signal is nonmonotonic. The geometric-mean diffusion coefficient obtained from the curvature of the local maximum is compared to the diffusion coefficient inferred from single-exponential fits, and it is found that the latter is larger by nearly a factor of 2. The results reported here should prove important in improving the accuracy of the FRS technique.
NASA Astrophysics Data System (ADS)
Fujii, Z.; McDonald, F. B.
When cosmic ray streaming in the heliosphere is negligible, the basic transport equation gives a simple approximation for the diffusion coefficient of cosmic ray particles, Krr = CVSW/ gr, where C is the Compton-Getting factor, VSW is the solar wind velocity and gr is the radial intensity gradients. Using this equation we calculated the particle diffusion coefficients from 1974 to 1995 out to heliocentric distances of ˜70 AU, using the measured gr for galactic 180-450 MeV/n He, 130-220 MeV H and anomalous 30-57 MeV/n He and 10-20 MeV/n He. Further we made first order estimates of the distance to the modulation boundary, using these diffusion coefficients and the modulation function for galactic 180-450 MeV/n He. It was shown that the distance is from about 65 AU to 110 AU varying inversely proportional to the solar activity for the period from 1978 to 1990. After 1990 these estimation were not significant because of the very small gradients in the outer heliosphere.
Diffusion coefficients in CO2/n-alkane binary liquid mixtures by molecular simulation.
Zabala, Damelys; Nieto-Draghi, Carlos; de Hemptinne, Jean Charles; López de Ramos, Aura L
2008-12-25
The objective of this work was to determine Fick diffusion coefficients in CO2/n-alkane binary mixtures without experimental test. For doing so, Maxwell-Stefan (MS) diffusivity was calculated by molecular simulation. Simultaneously, a thermodynamic factor was estimated using the PC-SAFT (perturbed chain statistical associating fluid theory) equation of state (eos). The binary Fick diffusivities are calculated as the product of both quantities. The binary mixtures investigated contain CO2 and various n-alkanes (nC10, nC16, nC22, nC28, nC44), at their bubble pressure at varying temperatures between 298 and 373 K. The calculated values of Fick diffusivities were compared against the experimental ones for the systems where literature data exist. An average deviation of 26% was found for the CO2/n-decane and 15% for CO2/n-hexadecane mixtures. These results support that molecular simulation can be employed as a tool for the determination of Fick diffusivities in high pressure systems, like in oil reservoirs, without the need to construct a complicated and expensive experimental setup. This method only requires the phase behavior of the desired system, and it can be used for multicomponent mixtures. As an example, predictions of Fick diffusivities were done for CO2 binary mixtures with heavy n-alkanes (nC22, nC28, nC44). PMID:19367942
Aguilar-Mendez, M A; Martin-Martinez, E San; Morales, J E; Cruz-Orea, A; Jaime-Fonseca, M R
2007-04-01
Water vapor diffusion coefficient (WVDC) and thermal diffusivity (alpha) were determined in gelatin-starch films through photothermal techniques. The effect of different variables in the elaboration of these films, such as starch and glycerol concentrations and pH, were evaluated through the response surface methodology. The results indicated that an increase in the glycerol concentration and pH favored the WVDC of the films. On the other hand, alpha was influenced principally by the starch content and pH of the film-forming solution. The minimum alpha value was 4.5 x 10(-4) cm2/s, which is compared with alpha values reported for commercial synthetic polymers. PMID:17420552
Ion-beam-induced topography and surface diffusion
NASA Technical Reports Server (NTRS)
Robinson, R. S.; Rossnagel, S. M.
1982-01-01
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.
Molecular dynamics calculation of rotational diffusion coefficient of a carbon nanotube in fluid
NASA Astrophysics Data System (ADS)
Cao, Bing-Yang; Dong, Ruo-Yu
2014-01-01
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.
Molecular dynamics calculation of rotational diffusion coefficient of a carbon nanotube in fluid.
Cao, Bing-Yang; Dong, Ruo-Yu
2014-01-21
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. PMID:25669403
Lienhard, Daniel M; Huisman, Andrew J; Bones, David L; Te, Yiea-Funk; Luo, Bei P; Krieger, Ulrich K; Reid, Jonathan P
2014-08-21
The time-dependent growth and shrinkage of aqueous aerosol particles trapped in an electrodynamic balance exposed to changes in relative humidity (RH) depend on the translational diffusion coefficient of water (DH2O). Resonances in the Mie scattering patterns of the illuminated micrometre-sized droplets are used to follow the compositional evolution through stepwise changes in RH. Under conditions where the diffusion of water molecules becomes sufficiently slow, e.g. in the highly viscous or even glassy regime, the concentration and temperature dependent values of DH2O can be determined iteratively by comparing the observed shifts in the Mie resonant wavelengths with predicted shifts from a diffusion model of a multi-layered sphere. It is shown that condensation and evaporation of water vapour from or to highly viscous or glassy droplets follow different kinetic regimes, a result that is consistent with previous studies of adsorption and desorption on glassy surfaces. PMID:24998384
Causal Baryon Diffusion and Colored Noise for Heavy Ion Collisions
J. I. Kapusta; C. Young
2014-09-05
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.
Relativistic diffusion and heavy-ion collisions
Rajeev S. Bhalerao; Sourendu Gupta
2009-02-24
We study first and second order theories of relativistic diffusion coupled to hydrodynamics under the approximation, valid at mid-rapidity in the RHIC and LHC, that conserved number densities are much smaller than the entropy density. We identify experimentally accessible quantities of interest, and show that the first and second order theories may lead to radically different evolutions of these quantities. In the first order theory the memory of the initial state is almost completely washed out, whereas in the second order theory it is possible that freezeout occurs at a time when transient dynamics is still on, and the memory of the initial state remains. There are observational consequences which we touch upon. In the first order theory, and for initial conditions when the second order theory mimics the first order, one may be able to put a bound on the diffusion constant.
NASA Technical Reports Server (NTRS)
Goldstein, M. L.
1977-01-01
In a study of cosmic ray propagation in interstellar and interplanetary space, a perturbed orbit resonant scattering theory for pitch angle diffusion in a slab model of magnetostatic turbulence is slightly generalized and used to compute the diffusion coefficient for spatial propagation parallel to the mean magnetic field. This diffusion coefficient has been useful for describing the solar modulation of the galactic cosmic rays, and for explaining the diffusive phase in solar flares in which the initial anisotropy of the particle distribution decays to isotropy.
Turchenkov, D A; Boronovski?, S E; Nartsissov, Ia R
2013-01-01
Changes in the state of the central nervous system, leading to the development of pathological processes, are directly associated with a state of neurons, particularly with their conductivity in synaptic cleft region. The synaptic flexibility plays a key role in environmental adaptation, which manifests in dynamic changes of synaptic properties. However more attention was paid rather to their functional, than physical-chemical properties. We present the results of simulation of potential determining ions in synaptic contact area using Langevin dynamics. Diffusion and self-diffusion coefficients were calculated. It is shown that the range of variability of the diffusion coefficient of ions in perimembrane space, caused by variable viscosity and dielectric conductivity of electrolyte can reach 20%. These physical-chemical synaptic parameters can be considered as relevant for synaptic flexibility. PMID:25486759
2013-01-01
Changes in the state of the central nervous system, leading to the development of pathological processes, are directly associated with a state of neurons, particularly with their conductivity in synaptic cleft region. The synaptic flexibility plays a key role in environmental adaptation, which manifests in dynamic changes of synaptic properties. However more attention was paid rather to their functional, than physical-chemical properties. We present the results of simulation of potential determining ions in synaptic contact area using Langevin dynamics. Diffusion and self-diffusion coefficients were calculated. It is shown that the range of variability of the diffusion coefficient of ions in perimembrane space, caused by variable viscosity and dielectric conductivity of electrolyte can reach 20%. These physical-chemical synaptic parameters can be considered as relevant for synaptic flexibility. PMID:25508890
Sanford, R.F.
1982-01-01
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.
Fokin, Vladimir M; Schmelzer, Jürn W P; Nascimento, Marcio L F; Zanotto, Edgar D
2007-06-21
We calculate, employing the classical theory of nucleation and growth, the effective diffusion coefficients controlling crystal nucleation of nanosize clusters and the subsequent growth of micron-size crystals at very deep undercoolings, below and above Tg, using experimental nucleation and growth data obtained for stoichiometric Li2O.2SiO2 and Na2O.2CaO.3SiO2 glasses. The results show significant differences in the magnitude and temperature dependence of these kinetic coefficients. We explain this difference showing that the composition and/or structure of the nucleating critical clusters deviate from those of the stable crystalline phase. These results for diffusion coefficients corroborate our previous conclusion for the same glasses, based on different experiments, and support the view that, even for the so-called case of stoichiometric (polymorphic) crystallization, the nucleating phase may have a different composition and/or structure as compared to the parent glass and the evolving macroscopic crystalline phase. This finding gives a key to explain the discrepancies between calculated (by classical nucleation theory) and experimentally observed nucleation rates in these systems, in particular, and in deeply undercooled glass-forming liquids, in general. PMID:17600425
Bounce-averaged diffusion coefficients in the Tsyganenko field model for oblique chorus waves
NASA Astrophysics Data System (ADS)
Orlova, Ksenia; Shprits, Yuri
We present the results of computations of bounce-averaged quasi-linear momentum Dpp, pitch-angle D?? and mixed D?p diffusion coefficients in the Tsyganenko magnetic field model. We assume that electrons are scattered by oblique whistler mode chorus waves of Gaussian spread of wave power spectral density and wave normal angle outside the plasmasphere. The scat-tering rates are computed using the full electromagnetic dispersion relation and up to 5-order resonance condition including Landau resonance. The diffusion coefficients are calculated for quiet conditions and storm-time conditions for the day and night sides. We compare scattering rates bounce-averaged in the Tsyganenko field model with those in the dipole field and discuss the differences. The results are followed by a physical explanation of how the magnetic field model can change the bounce-averaged scattering rates. The calculations show that, during active conditions, the pitch-angle scattering by chorus waves in the realistic magnetic field can diffuse relativistic electrons to the loss cone not only on the day side, but also on the night side. Our study shows that while there are still a number of unknown parameters that determine scattering rates, inclusion of bounce-averaging in the realistic field will be crucially important for future radiation belt modeling.
Measurement of Retinalamin diffusion coefficient in human sclera by optical spectroscopy
NASA Astrophysics Data System (ADS)
Genina, Elina A.; Bashkatov, Alexey N.; Zubkova, Elena A.; Kamenskikh, Tatiana G.; Tuchin, Valery V.
2008-12-01
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.
The measurement of self-diffusion coefficients in liquid metals with quasielastic neutron scattering
NASA Astrophysics Data System (ADS)
Meyer, Andreas
2015-01-01
Quasielastic incoherent neutron scattering (QENS) has proven to be a versatile tool to study self diffusion of atoms in liquid metals. Here it is shown, that coherent contributions to the signal in the small q limit appear as a flat and energy independent constant to the QENS signal in single-component liquid metals even for systems with a small incoherent scattering cross section, like aluminum. Container-less processing via electromagnetic or electrostatic levitation devices, especially designed for QENS, enables the in-situ measurement on liquid metallic droplets of sizes between 5 mm to 10 mm in diameter. This gives access to the study of chemically reactive, refractory metallic melts and extends the accessible temperature range to undercoolings of several hundred Kelvin below the respective melting point. Compared to experiments using a thin-walled crucible giving hollow-cylindrical sample geometry it is shown that multiple scattering on levitated droplets is negligible for the analysis of the self-diffusion coefficient. QENS results of liquid germanium and 73germanium isotope mixtures, titanium, nickel, copper and aluminum are reviewed. The self-diffusion coefficients of these systems are best described by an Arrhenius-type temperature dependence around their respective melting points.
Measuring diffusion coefficients via two-photon fluorescence recovery after photobleaching.
Sullivan, Kelley D; Brown, Edward B
2010-01-01
Multi-fluorescence recovery after photobleaching is a microscopy technique used to measure the diffusion coefficient (or analogous transport parameters) of macromolecules, and can be applied to both in vitro and in vivo biological systems. Multi-fluorescence recovery after photobleaching is performed by photobleaching a region of interest within a fluorescent sample using an intense laser flash, then attenuating the beam and monitoring the fluorescence as still-fluorescent molecules from outside the region of interest diffuse in to replace the photobleached molecules. We will begin our demonstration by aligning the laser beam through the Pockels Cell (laser modulator) and along the optical path through the laser scan box and objective lens to the sample. For simplicity, we will use a sample of aqueous fluorescent dye. We will then determine the proper experimental parameters for our sample including, monitor and bleaching powers, bleach duration, bin widths (for photon counting), and fluorescence recovery time. Next, we will describe the procedure for taking recovery curves, a process that can be largely automated via LabVIEW (National Instruments, Austin, TX) for enhanced throughput. Finally, the diffusion coefficient is determined by fitting the recovery data to the appropriate mathematical model using a least-squares fitting algorithm, readily programmable using software such as MATLAB (The Mathworks, Natick, MA). PMID:20190730
NASA Technical Reports Server (NTRS)
Nesbitt, J. A.; Heckel, R. W.
1987-01-01
Interdiffusion in Ni-rich Ni-Cr-Al alloys is investigated experimentally after annealing at 1100 and 1200 C using gamma/gamma, gamma/gamma+beta, gamma/gamma+gamma prime, and gamma/gamma+alpha diffusion couples. The amount and location of Kirkendall porosity suggests that Al diffuses more rapidly than Cr which diffuses more rapidly than Ni in the gamma phase of Ni-Cr-Al alloys. The location and extent of maxima and minima in the concentration profiles of the diffusion couples indicate that both cross-term diffusion coefficients are positive. Measurements are also presented of the ternary interdiffusion coefficients of the gamma phase in the Ni-Cr-Al system. It is shown that the interdiffusion coefficients can be accurately predicted by using a ternary finite-difference interdiffusion model.
Pierce, Theodore Thomas; Provenzale, James M
2014-02-01
We assess a diffusion-weighted imaging (DWI) analysis technique as a potential basis for computer-aided diagnosis (CAD) of pediatric posterior fossa tumors. A retrospective medical record search identified 103 children (mean age: 87 months) with posterior fossa tumors having a total of 126 preoperative MR scans with DWI. The minimum ADC (ADCmin) and normalized ADC (nADC) values [ratio of ADCmin values in tumor compared to normal tissue] were measured by a single observer blinded to diagnosis. Receiver operating characteristic (ROC) curves were generated to determine the optimal threshold for which the nADC and ADCmin values would predict tumor histology. Inter-rater reliability for predicting tumor type was evaluated using values measured by two additional observers. At histology, ten tumor types were identified, with astrocytoma (n=50), medulloblastoma (n=33), and ependymoma (n=9) accounting for 89%. Mean ADCmin (0.54 × 10(-3) mm(2)/s) and nADC (0.70) were lowest for medulloblastoma. Mean ADCmin (1.28 × 10(-3) mm(2)/s) and nADC (1.64) were highest for astrocytoma. For the ROC analysis, the area under the curve when discriminating medulloblastoma from other tumors using nADC was 0.939 and 0.965 when using ADCmin. The optimal ADCmin threshold was 0.66 × 10(-3) mm(2)/s, which yielded an 86% positive predictive value, 97% negative predictive value, and 93% accuracy. Inter-observer variability was very low, with near perfect agreement among all observers in predicting medulloblastoma. Our data indicate that both ADCmin and nADC could serve as the basis for a CAD program to distinguish medulloblastoma from other posterior fossa tumors with a high degree of accuracy. PMID:24571835
Alonso de Mezquia, David; Wang, Zilin; Lapeira, Estela; Klein, Michael; Wiegand, Simone; Mounir Bou-Ali, M
2014-11-01
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
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). A dynamic dual-chamber test meth...
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). A dynamic dual-chamber test meth...
New type of metal ion source: Surface diffusion Li{sup +} ion source
Medvedev, V.K.; Suchorski, Y.; Block, J.H. [Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin (Germany)] [Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin (Germany)
1995-03-01
A surface diffusion metal ion source, a new type of metal ion source, is explored. In this device a field desorption process is used to achieve an almost monoenergetic continuous flux of Li{sup +} ions from a [111]-oriented W field emitter. Earlier difficulties with the continuous supply of adatoms, required to produce measurable desorption rates, were overcome by making use of solid state surface diffusion from the Li multilayer reservoir at the shank of the field emitter. The high density of the ion beam (an ion current of 10{sup {minus}12} A was achieved from a W trimer), the extremely narrow energy distribution (full width at half-maximum of 0.25 eV) and the stable geometric form of the emitter itself during the operation are advantages of the new ion source which may be important in different areas of nanotechnology. {copyright} {ital 1995} {ital American} {ital Vacuum} {ital Society}
NASA Astrophysics Data System (ADS)
Wu, Dan; Lu, Wanjun
2015-04-01
Injecting CO2 into lean-oil reservoirs is not only a way to geological storage but also enhanced oil recovery. In the secondary displacements of oil reservoir by CO2-injection, diffusion coefficients and solubility of CO2 are key parameters to calculate the volume of CO2 injected and the time to achieve the desired viscosity in the numerical simulation. Unfortunately, the experimental data on the CO2 diffusion coefficient and solubility in liquid hydrocarbons under high pressure conditions are scarce. Hexadecane has properties similar to the average properties of Brazilian heavy oil. Experimental data on the diffusion coefficients and solubility of CO2 in hexadecane were reviewed by Nieuwoudt and Rand (2002), Rincon and Trejo (2001) and Breman et al (1994), indicating that the data in the literature were limited at relatively low temperatures and/or low pressures. In this paper, the diffusion coefficients of carbon dioxide in hexadecane at different temperature and pressure were determined with in situ Raman spectroscopy. A model was established to describe relationship among diffusion coefficients, temperature, and pressure. The solubility of CO2 in hexadecane was obtained from 298.15 to 473.15 K and 10 to 45 MPa. The experimental results show that:(1) Solubility of CO2 decreases with increasing temperature.(2) Increasing pressure increases the CO2 solubility. in terms of the degree of influence,100K is similar with 10MPa.(3) Diffusion coefficients of CO2 increases with increasing temperature. (4) Increasing pressure decreases the CO2 diffusion coefficients, whereas the pressure effect on CO2 diffusion coefficients is very weak. Compared with traditional sampling and analytical methods, the advantages of our method include: (1) the use of in situ Raman signals for solubility measurements eliminates possible uncertainty caused by sampling and ex situ analysis. (2) it is simple and efficient, and (3) high-pressure data can be obtained safely.
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
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.
2014-01-01
Background Diffusion tensor cardiac magnetic resonance (DT-CMR) enables probing of the microarchitecture of the myocardium, but the apparent diffusion coefficient (ADC) and fractional anisotropy (FA) reported in healthy volunteers have been inconsistent. The aim of this study was to validate a stimulated-echo diffusion sequence using phantoms, and to assess the intercentre reproducibility of in-vivo diffusion measures using the sequence. Methods and results A stimulated-echo, cardiac-gated DT-CMR sequence with a reduced-field-of-view, single-shot EPI readout was used at two centres with 3 T MRI scanners. Four alkane phantoms with known diffusivities were scanned at a single centre using a stimulated echo sequence and a spin-echo Stejskal-Tanner diffusion sequence. The median (maximum, minimum) difference between the DT-CMR sequence and Stejskal-Tanner sequence was 0.01 (0.04, 0.0006) × 10-3 mm2/s (2%), and between the DT-CMR sequence and literature diffusivities was 0.02 (0.05, 0.006) × 10-3 mm2/s (4%). The same ten healthy volunteers were scanned using the DT-CMR sequence at the two centres less than seven days apart. Average ADC and FA were calculated in a single mid-ventricular, short axis slice. Intercentre differences were tested for statistical significance at the p??0.05), and only the diastolic ADC showed a statistically significant, but numerically small, difference of 0.07 × 10-3 mm2/s (p?=?0.047). The intercentre, intrasubject coefficients of variance were: systolic ADC 7%, FA 6%; diastolic ADC 7%, FA 3%. Conclusions This is the first study to demonstrate the accuracy of a stimulated-echo DT-CMR sequence in phantoms, and demonstrates the feasibility of obtaining reproducible ADC and FA in healthy volunteers at separate centres with well-matched sequences and processing. PMID:24886285
The Determination of the `Diffusion Coefficients' and the Stellar Wind Velocities for X-Ray Binaries
V. M. Lipunov; S. B. Popov
1995-04-20
The distribution of neutron stars (NS's) is determined by stationary solution of the Fokker-Planck equation. In this work using the observed period changes for four systems: Vela X-1, GX 301-2, Her X-1 and Cen X-3 we determined D, the 'diffusion coefficient',-parameter from the Fokker-Planck equation. Using strong dependence of D on the velocity for Vela X-1 and GX 301-2, systems accreting from a stellar wind, we determined the stellar wind velocity. For different assumptions for a turbulent velocity we obtained $V=(660-1440) km s ^{-1}$. It is in good agreement with the stellar wind velocity determined by other methods. We also determined the specific characteristic time scales for the 'diffusion processes' in X-ray pulsars. It is of order of 200 sec for wind-fed pulsars and 1000-10000 sec for the disk accreting systems.
Measurements of the diffusion coefficient of silver 110-m in a nuclear grade graphite
McMillan, Thad Calhoun
1980-01-01
Ag. B DESCRIPTION OF GRAPHITES. 87 89 92 94 B. 1 Graphite Structure. B. 2 Manufacture of Graphite. 8. 3 Nuclear Grade Graphites. 94 94 97 C DATA FOR THE CYLINDRICAL EXPERIMENTS. . 99 TABLE OF CONTENTS (Continued) Appendix D SOLUTIONS... 7710 data. 20. Fitted profile of FRIZCCC and IZIRCCC through trial I/ll data. 75 21, Arrhenius plot of diffusion coefficients. . . . . . 110 m A. 1. Gamma spectra of Ag using 3 x 3 in. Nal 78 detector. 93 0. 1. Concentration profile of trial /71...
Rathapon A-sasutjarit; Anuvat Sirivat; Panida Vayumhasuwan
2005-01-01
\\u000a Purpose This study was conducted to determine the effect of formula compositions on viscoelastic properties of piroxicam gels using\\u000a Carbopol 940 as a gelling agent and to determine the relationships between viscoelastic properties of Carbopol 940 gel bases\\u000a and diffusion coefficients of piroxicam in gel bases.\\u000a \\u000a \\u000a \\u000a Methods Piroxicam gels (1.0% w\\/w) were prepared by using Carbopol 940 as a gelling agent and
NASA Technical Reports Server (NTRS)
Kozyra, J. U.; Rasmussen, C. E.; Miller, R. H.; Lyons, L. R.
1994-01-01
Protons that are convected into the inner magnetosphere in response to enhanced magnetic activity can resonate with ducted plasmaspheric hiss in the outer plasmasphere via an anomalous Doppler-shifted cyclotron resonance. Plasmaspheric hiss is a right-hand-polarized electromagnetic emission that is observed to fill the plasmasphere on a routine basis. When plasmaspheric hiss is confined within field-aligned ducts or guided along density gradients, wave normal angles remain largely below 45 deg. This allows resonant interactions with ions at typical ring current and radiation belt energies to take place. Such field-aligned ducts have been observed both within the plasmasphere and in regions outside of the plasmasphere. Wave intensities are estimated using statistical information from studies of detached plasma regions. Diffusion coefficients are presented for a range of L shells and proton energies for a fixed wave distribution. Harmonic resonances in the range N = +/-100 are considered in order to include interactions between hiss at 100 Hz to 2 kHz frequencies, and protons in the energy range between approximately 10 keV and 1000 keV. Diffusion timescales are estimated to be of the order of tens of days and comparable to or shorter than lifetimes for Coulomb decay and charge exchange losses over most of the energy and spatial ranges of interest.
Yu, Xin; Schmidt, Arthur R; Bello-Perez, Luis A; Schmidt, Shelly J
2008-01-01
The bulk moisture diffusion coefficient (Db) is an important physical parameter of food ingredients and systems. However, the traditional method of measuring Db using saturated salt solutions is very time-consuming and cumbersome. New automated water sorption instruments, which can be used to conveniently and precisely control both relative humidity and temperature, provide a faster, more robust method for collecting the data needed for determining Db. Thus, the objectives of this study were to (1) investigate the use of the DVS instrument for collecting the data needed for determining the adsorption (Dba) and desorption (Dbd) bulk moisture diffusion coefficients for dent corn starch as a function of relative humidity and (2) determine the effect of temperature on Dba for dent corn starch at a constant relative humidity. Kinetic water sorption profiles of dent corn starch were obtained at eight relative humidity values ranging from 10 to 80% at 10% intervals at 25 degrees C and at five temperatures, 15, 20, 25, 30, and 35 degrees C, at 50% relative humidity using a DVS instrument. Db was calculated from the kinetic water sorption profiles using the full solution of Fick's second law for the thin slab model, as well as the slope method, a simplification of the full model. The Dba of dent corn starch at 25 degrees C reached a maximum at intermediate relative humidity values, after which Dba decreased due to a change in the moisture diffusion mechanism from vapor to liquid diffusion. The Dbd of dent corn starch at 25 degrees C remained nearly constant as a function of relative humidity. The Dba for dent corn starch increased as temperature increased from 15 to 35 degrees C, with an activation energy of 38.85 +/- 0.433 kJ/mol. PMID:18078318
Radon (222Rn) in ground water of fractured rocks: A diffusion/ion exchange model
Wood, W.W.; Kraemer, T.F.; Shapiro, A.
2004-01-01
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.
Ab initio transport coefficients of Ar? ions in Ar for cold plasma jet modeling.
Chicheportiche, A; Lepetit, B; Gadéa, F X; Benhenni, M; Yousfi, M; Kalus, R
2014-06-01
Collision cross sections and transport coefficients are calculated for Ar{+} ions, in the ground state {2}P_{3/2} and in the metastable state {2}P_{1/2}, 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. PMID:25019899
About the single-stage separation coefficient of lithium isotopes by the ion-exchange method
G. M. Panchenkov; E. M. Kuznetsova; O. N. Kaznadzei
1961-01-01
authors, oscillates from 1.016 to 1.021, and the solution is always enriched in the light isotope. In our work, we have considered the problem of determining the coefficient of single-stage separation of lithium isotopes for the ion-exchange reaction on domestic eationite, and also of clarifying the dependence of this coefficient upon the nature of the salts and of the cationites,
Diffusion coefficients of humic substances in agarose gel and in water.
Lead, J R; Starchev, K; Wilkinson, K J
2003-02-01
Measurements of the diffusion coefficients of five different humic substances (HS) have been performed in water and in agarose hydrogels at several pH values (in the range of 3-10) and gel concentrations (in the range of 0.7-3% w/w). Fluorescence correlation spectroscopy (FCS) and classical diffusion cells were used in parallel to probe diffusion over both microscopic and mesoscopic distance scales. In general, agreement between the techniques was reasonable, which indicated that local nonhomogenities in the gel did not play an important role. Diffusion coefficients (D) in the gel were generally in the range of 0.9-2.5 x 10(-10) m2 s(-1) but were generally only 10-20% lower than in solution. At low pH values, one of the studied humic substances (a peat humic acid, PPHA) formed large aggregates that could not penetrate into the gel and therefore could not be defined by a single D value. The observed decreases of D in the gel for other HS were too large to be explained by the tortuousity and obstructive effects of the gel alone. D decreased slightly with increasing gel concentration and increased slightly with pH. Because modifications of D due to pH were similar in both the gel and the free solution, it is unlikely that complexation with the gel was greatly influenced by the pH. Rather, the main effect that appeared to decrease the diffusive flux in gels was likely small increases in the hydrodynamic radii of the humic macromolecules. An anomalous diffusion model was used to describe the FCS data in the gel. The characteristic exponent determined by fitting the autocorrelation functions with this model decreased only slightly (from 0.96 to 0.90) with increasing gel concentration providing support that HS complexation with the gel fibers was not very important. The results have important implications for our understanding of the fate and behavior of the HS and their associated pollutants and for interpreting metal speciation data obtained using gel-covered analytical sensors. PMID:12630462
NASA Astrophysics Data System (ADS)
Tulipano, P. Karina; Millar, William S.; Imielinska, Celina; Liu, Xin; Rosiene, Joel; D'Ambrosio, Anthony L.
2006-03-01
Magnetic resonance (MR) imaging is an imaging modality that is used in the management and diagnosis of acute stroke. Common MR imaging techniques such as diffusion weighted imaging (DWI) and apparent diffusion coefficient maps (ADC) are used routinely in the diagnosis of acute infarcts. However, advances in radiology information systems and imaging protocols have led to an overload of image information that can be difficult to manage and time consuming. Automated techniques to assist in the identification of acute ischemic stroke can prove beneficial to 1) the physician by providing a mechanism for early detection and 2) the patient by providing effective stroke therapy at an early stage. We have processed DW images and ADC maps using a novel automated Relative Difference Map (RDM) method that was tailored to the identification and delineation of the stroke region. Results indicate that the technique can delineate regions of acute infarctions on DW images and ADC maps. A formal evaluation of the RDM algorithm was performed by comparing accuracy measurements between 1) expert generated ground truths with the RDM delineated DWI infarcts and 2) RDM delineated DWI infarcts with RDM delineated ADC infarcts. The accuracy measurements indicate that the RDM delineated DWI infarcts are comparable to the expert generated ground truths. The true positive volume fraction value (TPVF), between RDM delineated DWI and ADC infarcts, is nonzero for all cases with an acute infarct while the value for non-acute cases remains zero.
Effect of cation on diffusion coefficient of ionic liquids at onion-like carbon electrodes
NASA Astrophysics Data System (ADS)
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
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.
Group Analysis of Variable Coefficient Diffusion--Convection Equations. III. Conservation Laws
N. M. Ivanova; R. O. Popovych; C. Sophocleous
2007-10-16
The notions of generating sets of conservation laws of systems of differential equations with respect to symmetry groups and equivalence groups are introduced and applied. This allows us to generalize essentially the procedure of finding potential symmetries for the systems with multidimensional spaces of conservation laws. A class of variable coefficient (1+1)-dimensional nonlinear diffusion-convection equations of general form $f(x)u_t=(g(x)A(u)u_x)_x+h(x)B(u)u_x$ is investigated. Using the most direct method, we carry out two classifications of local conservation laws up to equivalence relations generated by both usual and enhanced equivalence groups. Equivalence with respect to $\\hat G^{\\sim}$ and correct choice of gauge coefficients of equations play the major role for simple and clear formulation of the final results. The notion of contractions of conservation laws and one of characteristics of conservation laws are introduced and contractions of conservation laws of diffusion-convection equations are found.
NASA Astrophysics Data System (ADS)
Hennad, A.; Yousfi, M.
2011-01-01
The ion swarm transport coefficients such as reduced mobility, diffusion coefficients and reaction rates of the following systems Ar+/Cl2, Ar+/N2, N_2^+/Cl_{2} and N_2^+/Ar have been determined from a Monte Carlo simulation using calculated elastic and experimentally estimated inelastic collision cross sections. The elastic momentum transfer cross sections have been determined from a semi-classical JWKB approximation based on a rigid core interaction potential model. The inelastic cross sections have been fitted using the measured reaction coefficients as for instance ion conversion reaction coefficients. Then, the cross section sets are fitted using either the measured reduced mobility when available in the literature or the zero-field mobility calculated from Satoh's relation. From the sets of elastic and inelastic collision cross sections thus obtained in Ar+/Cl2, Ar+/N2, N_2^+/Cl_{2} and N_2^+/Ar systems, the ion transport and reaction coefficients are then calculated in pure gases and also in binary and ternary mixtures involving Cl2, Ar and N2 over a wide range of reduced electric field. These ion data are very useful for modelling and simulation of non-equilibrium low pressure electrical discharges used more particularly for etching of the III-V compounds in the case of crystal photonic applications.
Theoretical calculations of the self-reflection coefficients for some species of ions
NASA Astrophysics Data System (ADS)
Luo, Z. M.; Gou, C.; Hou, Q.
2002-06-01
The bipartition model of ion transport has been applied to study the self-reflection coefficients of some species of ion beams which are normally incident to a surface. The computational results has been compared with the results taken from Eckstein and Biersack and the compilation data given by Thomas, Janev and Smith. It was found that there are in reasonable agreement between the results given by the bipartition model and the results given by Monte Carlo method.
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
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.
University of California, Berkeley; Lawrence Berkeley National Laboratory; Raymond, Kenneth; Pluth, Michael D.; Tiedemann, Bryan E.F.; van Halbeek, Herman; Nunlist, Rudi; Raymond, Kenneth N.
2007-10-22
Understanding the solution behavior of supramolecular assemblies is essential for a full understanding of the formation and chemistry of synthetic host-guest systems. While the interaction between host and guest molecules is generally the focus of mechanistic studies of host-guest complexes, the interaction of the host-guest complex with other species in solution remains largely unknown, although in principle accessible by diffusion studies. Several NMR techniques are available to monitor diffusion and have recently been reviewed. Pulsed gradient spin-echo (PGSE) NMR methods have attracted increasing interest, since they allow diffusion coefficients to be measured with high accuracy; they have been successfully used with observation of {sup 7}Li and {sup 31}P nuclei as well as with {sup 1}H NMR. We report here the direct measurement of diffusion coefficients to observe ion-association interactions by counter cations with a highly-charged supramolecular assembly. Raymond and coworkers have described the design and chemistry of a class of metal-ligand supramolecular assemblies over the past decade. The [Ga{sub 4}L{sub 6}]{sup 12-} (L = 1,5-bis(2,3-dihydroxybenzamido)naphthalene) (1) (Figure 1) assembly has garnered the most attention, with the exploration of the dynamics and mechanism of guest exchange as well as the ability of 1 to achieve either stoichiometric or catalytic reactions inside its interior cavity. Recent studies have revealed the importance of counter cations in solution on the chemistry of 1. During the mechanistic study of the C-H bond activation of aldehydes by [Cp*Ir(PMe{sub 3})(olefin){sup +} {contained_in} 1]{sup 11-} a stepwise guest dissociation mechanism with an ion-paired intermediate was proposed. Similarly, in the mechanism for the hydrolysis of iminium cations generated from the 3-aza Cope rearrangement of enammonium cations in 1, the presence of an exterior ion association was part of the kinetic model. To further substantiate the indirect kinetic evidence for such ion-paired species, we sought to explore the solution behavior of 1 by studying the diffusion of 1 with varying alkali and tetraalkyl ammonium cations. For large molecules in solution, such as synthetic supramolecular assemblies, the diffusion behavior of host and guest molecules can provide valuable information on host-guest interaction. One characteristic feature of a stable host-guest complex is that the host and guest molecules diffuse at the same rate in solution; this has been observed in a number of supramolecular systems. In order to confirm that this system was suitable for study by diffusion NMR spectroscopy, a PGSE-DOSY spectrum was acquired of [NEt{sub 4} {contained_in} 1]{sup 11-} (Figure 2), which shows that the host and guest molecules diffuse at the same rate. Quantitative analysis of the data, from monitoring the integral of host and guest resonances as a function of applied gradient strength, gave identical diffusion coefficients, confirming that the host and guest molecules diffuse together.
Hadjiev, Nicholas A; Amsden, Brian G
2015-02-10
The ability to estimate the diffusion coefficient of a solute within hydrogels has important application in the design and analysis of hydrogels used in drug delivery, tissue engineering, and regenerative medicine. A number of mathematical models have been derived for this purpose; however, they often rely on fitted parameters and so have limited predictive capability. Herein we assess the ability of the obstruction-scaling model to provide reasonable estimates of solute diffusion coefficients within hydrogels, as well as the assumption that a hydrogel can be represented as an entangled polymer solution of an equivalent concentration. Fluorescein isothiocyanate dextran solutes were loaded into sodium alginate solutions as well as hydrogels of different polymer volume fractions formed from photoinitiated cross-linking of methacrylate sodium alginate. The tracer diffusion coefficients of these solutes were measured using fluorescence recovery after photobleaching (FRAP). The measured diffusion coefficients were then compared to the values predicted by the obstruction-scaling model. The model predictions were within ±15% of the measured values, suggesting that the model can provide useful estimates of solute diffusion coefficients within hydrogels and solutions. Moreover, solutes diffusing in both sodium alginate solutions and hydrogels were demonstrated to experience the same degree of solute mobility restriction given the same effective polymer concentration, supporting the assumption that a hydrogel can be represented as an entangled polymer solution of equivalent concentration. PMID:25499554
Khan, Javaid Shahbaz; Imamoto, Yasushi; Harigai, Miki; Kataoka, Mikio; Terazima, Masahide
2006-05-15
Conformational changes in the light illuminated intermediate (pB) of photoactive yellow protein (PYP) were studied from a viewpoint of the diffusion coefficient (D) change of several N-truncated PYPs, which lacked the N-terminal 6, 15, or 23 amino acid residues (T6, T15, and T23, respectively). For intact PYP (i-PYP), D of pB (D(pB)) was approximately 11% lower than that (D(pG)) of the ground state (pG) species. The difference in D (D(pG) - D(pB)) decreased upon cleavage of the N-terminal region in the order of i-PYP>T6>T15>T23. This trend clearly showed that conformational change in the N-terminal group is the main reason for the slower diffusion of pB. This slower diffusion was interpreted in terms of the unfolding of the two alpha-helices in the N-terminal region, increasing the intermolecular interactions due to hydrogen bonding with water molecules. The increase in friction per one residue by the unfolding of the alpha-helix was estimated to be 0.3 x 10(-12) kg/s. The conformational change in the N-terminal group upon photoillumination is discussed. PMID:16500975
Conformational Changes of PYP Monitored by Diffusion Coefficient: Effect of N-Terminal ?-Helices
Khan, Javaid Shahbaz; Imamoto, Yasushi; Harigai, Miki; Kataoka, Mikio; Terazima, Masahide
2006-01-01
Conformational changes in the light illuminated intermediate (pB) of photoactive yellow protein (PYP) were studied from a viewpoint of the diffusion coefficient (D) change of several N-truncated PYPs, which lacked the N-terminal 6, 15, or 23 amino acid residues (T6, T15, and T23, respectively). For intact PYP (i-PYP), D of pB (DpB) was ?11% lower than that (DpG) of the ground state (pG) species. The difference in D (DpG ? DpB) decreased upon cleavage of the N-terminal region in the order of i-PYP>T6>T15>T23. This trend clearly showed that conformational change in the N-terminal group is the main reason for the slower diffusion of pB. This slower diffusion was interpreted in terms of the unfolding of the two ?-helices in the N-terminal region, increasing the intermolecular interactions due to hydrogen bonding with water molecules. The increase in friction per one residue by the unfolding of the ?-helix was estimated to be 0.3 × 10?12 kg/s. The conformational change in the N-terminal group upon photoillumination is discussed. PMID:16500975
NASA Astrophysics Data System (ADS)
Pan, Xiaoju; Zimmerman, Richard C.
2010-08-01
The diffuse attenuation coefficient (Kd) is critical to understand the vertical distribution of underwater downwelling irradiance (Ed). Theoretically Ed is composed of the direct solar beam and the diffuse sky irradiance. Applying the statistical results from Hydrolight radiative transfer simulations, Kd is expressed into a mathematical equation (named as PZ06) integrated from the contribution of direct solar beam and diffuse sky irradiance with the knowledge of sky and water conditions. The percent root mean square errors (RMSE) for the vertical distribution of Ed(z) under various sky and water conditions between PZ06 and Hydrolight results are typically less than 4%. Field observations from the southern Middle Atlantic Bight (SMAB) and global in situ data set (NOMAD) also confirmed the validity of PZ06 in reproducing Kd. PZ06 provides an alternative and improvement to the simpler models (e.g., Gordon, 1989; and Kirk, 1991) and an operational ocean color algorithm, while the latter two kinds of models are valid to limited sky and water conditions. PZ06 can be applied to study Kd from satellite remotely sensed images and seems to improve Kd derivation over current operational ocean color algorithm.
Demir, Senay; Altinkaya, Naime; Kocer, Nazim Emrah; Erbay, Ayse; Oguzkurt, Pelin
2015-01-01
PURPOSE In children the assessment of solid tumors’ response to chemotherapy is based primarily on size reduction, which can be unreliable and a late marker, in the presence of necrosis. We aimed to establish whether apparent diffusion coefficient (ADC) values of childhood neuroblastomas show proportional changes in relation to chemotherapy response. METHODS We evaluated 15 pediatric patients with abdominopelvic neuroblastomas, who had undergone MRI before and after chemotherapy. Two radiologists retrospectively analyzed all images by drawing a round uniform region-of-interest in the solid/contrast-enhancing portion of the lesions in consensus. The ADC values from pre- and postchemotherapy images were compared. RESULTS Postchemotherapy ADC values were significantly higher than those obtained before treatment (P < 0.05, for minimum, maximum, and median ADC values). CONCLUSION Our results support diffusion-weighted MRI as a promising noninvasive biomarker of therapeutic responses. To the best of our knowledge, this is the first report to compare diffusion-weighted imaging findings before and after chemotherapy in childhood neuroblastic tumors. PMID:25519453
Neurite beading is sufficient to decrease the apparent diffusion coefficient after ischemic stroke
Budde, Matthew D.; Frank, Joseph A.
2010-01-01
Diffusion-weighted MRI (DWI) is a sensitive and reliable marker of cerebral ischemia. Within minutes of an ischemic event in the brain, the microscopic motion of water molecules measured with DWI, termed the apparent diffusion coefficient (ADC), decreases within the infarcted region. However, although the change is related to cell swelling, the precise pathological mechanism remains elusive. We show that focal enlargement and constriction, or beading, in axons and dendrites are sufficient to substantially decrease ADC. We first derived a biophysical model of neurite beading, and we show that the beaded morphology allows a larger volume to be encompassed within an equivalent surface area and is, therefore, a consequence of osmotic imbalance after ischemia. The DWI experiment simulated within the model revealed that intracellular ADC decreased by 79% in beaded neurites compared with the unbeaded form. To validate the model experimentally, excised rat sciatic nerves were subjected to stretching, which induced beading but did not cause a bulk shift of water into the axon (i.e., swelling). Beading-induced changes in cell-membrane morphology were sufficient to significantly hinder water mobility and thereby decrease ADC, and the experimental measurements were in excellent agreement with the simulated values. This is a demonstration that neurite beading accurately captures the diffusion changes measured in vivo. The results significantly advance the specificity of DWI in ischemia and other acute neurological injuries and will greatly aid the development of treatment strategies to monitor and repair damaged brain in both clinical and experimental settings. PMID:20660718
In vivo measurement of apparent diffusion coefficients of hyperpolarized ¹³C-labeled metabolites.
Søgaard, Lise Vejby; Schilling, Franz; Janich, Martin A; Menzel, Marion I; Ardenkjaer-Larsen, Jan Henrik
2014-05-01
The combination of hyperpolarized MRS with diffusion weighting (dw) allows for determination of the apparent diffusion coefficient (ADC), which is indicative of the intra- or extracellular localization of the metabolite. Here, a slice-selective pulsed-gradient spin echo sequence was implemented to acquire a series of dw spectra from rat muscle in vivo to determine the ADCs of multiple metabolites after a single injection of hyperpolarized [1- ¹³C]pyruvate. An optimal control optimized universal-rotation pulse was used for refocusing to minimize signal loss caused by B1 imperfections. Non-dw spectra were acquired interleaved with the dw spectra and these were used to correct for signal decay during the acquisition as a result of T1 decay, pulse imperfections, flow etc. The data showed that the ADC values for [1- ¹³C]lactate (0.4-0.7?µm² /ms) and [1- ¹³C]alanine (0.4-0.9 µm² /ms) were about a factor of two lower than the ADC of [1- ¹³C]pyruvate (1.1-1.5 µm²/ms). This indicates a more restricted diffusion space for the former two metabolites consistent with lactate and alanine being intracellular. The higher ADC for pyruvate (similar to the proton ADC) reflected that the injected substance was not confined inside the muscle cells but also present extracellular. PMID:24664927
Blackness coefficients, effective diffusion parameters, and control rod worths for thermal reactors
Bretscher, M.M.
1984-09-01
Simple diffusion theory cannot be used to evaluate control rod worths in thermal reactors because of the strongly absorbing character of the control material. However, good results can be obtained from a diffusion calculation by representing the absorber slab by means of a suitable pair of internal boundary conditions, ..cap alpha.. and ..beta.., which are ratios of neutron flux to neutron current. Methods for calculating ..cap alpha.. and ..beta.. in the P/sub 1/, P/sub 3/, and P/sub 5/ approximations, with and without scattering, are presented. By appropriately weighting the fine-group blackness coefficients, broad group values, <..cap alpha..> and <..beta..>, are obtained. The technique is applied to the calculation of control rod worths of Cd, Ag-In-Cd, and Hf control elements. Results are found to compare very favorably with detailed Monte Carlo calculations. For control elements whose geometry does not permit a thin slab treatment, other methods are needed for determining the effective diffusion parameters. One such method is briefly discussed and applied to the calculation of control rod worths in the Ford Nuclear Reactor at the University of Michigan. Calculated and measured worths are found to be in good agreement.
Diffusion coefficients of endogenous cytosolic proteins from rabbit skinned muscle fibers.
Carlson, Brian E; Vigoreaux, Jim O; Maughan, David W
2014-02-18
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
?erifo?lu, ?smail; Oz, ?brahim ?lker; Damar, Murat; Tokgöz, Özlem; Yazgan, Ömer; Erdem, Zuhal
2015-01-01
PURPOSE We aimed to evaluate the role of apparent diffusion coefficient (ADC) values calculated from diffusion-weighted imaging for head and neck lesion characterization in daily routine, in comparison with histopathological results. METHODS Ninety consecutive patients who underwent magnetic resonance imaging (MRI) at a university hospital for diagnosis of neck lesions were included in this prospective study. Diffusion-weighted echo-planar MRI was performed on a 1.5 T unit with b factor of 0 and 1000 s/mm2 and ADC maps were generated. ADC values were measured for benign and malignant whole lesions seen in daily practice. RESULTS The median ADC value of the malignant tumors and benign lesions were 0.72×10?3 mm2/s, (range, 0.39–1.51×10?3 mm2/s) and 1.17×10?3 mm2/s, (range, 0.52–2.38×10?3 mm2/s), respectively, with a significant difference between them (P < 0.001). A cutoff ADC value of 0.98×10?3 mm2/s was used to distinguish between benign and malignant lesions, yielding 85.3% sensitivity and 78.6% specificity. The median ADC value of lymphomas (0.44×10?3 mm2/s; range, 0.39–0.58×10?3 mm2/s) was significantly smaller (P < 0.001) than that of squamous cell carcinomas (median ADC value 0.72×10?3 mm2/s; range, 0.65–1.06×10?3 mm2/s). There was no significant difference between median ADC values of inflammatory (1.13×10?3 mm2/s; range, 0.85–2.38×10?3 mm2/s) and noninflammatory benign lesions (1.26×10?3 mm2/s; range, 0.52–2.33×10?3 mm2/s). CONCLUSION Diffusion-weighted imaging and the ADC values can be used to differentiate and characterize benign and malignant head and neck lesions. PMID:25910284
Measurements of the coefficient of combination of small ions with aerosol particles
V. P. V. Flanagan
1966-01-01
The equilibrium small ion concentration ( n) was measured in aerosols for various ionization rates ( q) and particle concentrations ( Z). The results agree with the formula q=bZn+alphan 2. These experiments were carried out with different particle sizes and the results provided a series of values of the combination coefficient b. The size of the particles was determined by
Ion implantation and diffusion of Zn in GaAs
G. J. van Gurp; A. H. van Ommen; P. R. Boudewijn; D. P. Oosthoek; M. F. C. Willemsen
1984-01-01
Zn implantation (dose 5×1015 cm?2) and subsequent diffusion were carried out on GaAs wafers and on liquid-phase epitaxial GaAs layers. A silicon nitride cap was deposited by chemical vapor deposition (CVD) or by sputtering either before or after implantation. Profiles were determined with Secondary Ion Mass Spectrometry and Differential Hall Effect measurements and damage was studied with Rutherford Backscattering Spectrometry.
Kimura, Y; Kida, Y; Matsushita, Y; Yasaka, Y; Ueno, M; Takahashi, K
2015-06-25
Translational diffusion coefficients of diphenylcyclopropenone (DPCP), diphenylacetylene (DPA), and carbon monoxide (CO) in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([BMIm][NTf2]) and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([EMIm][NTf2]) were determined by the transient grating (TG) spectroscopy under pressure from 0.1 to 200 MPa at 298 K and from 298 to 373 K under 0.1 MPa. Diffusion coefficients of these molecules at high temperatures in tributylmethylphosphonium bis(trifluoromethanesulfonyl)imide ([P4441][NTf2]), and tetraoctylphosphonium bis(trifluoromethanesulfonyl)imide ([P8888][NTf2]), and also in the mixtures of [BMIm][NTf2], N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide ([Pp13][NTf2]), and trihexyltetradecylphosphonium bis(trifluoromethanesulfonyl)imide ([P66614][NTf2]) with ethanol or chloroform have been determined. Diffusion coefficients except in ILs of phosphonium cations were well scaled by the power law of T/?, i.e., (T/?)(P), where T and ? are the absolute temperature and the viscosity, irrespective of the solvent species, pressure and temperature, and the compositions of mixtures. The values of the exponent P were smaller for the smaller size of the molecules. On the other hand, the diffusion coefficients in ILs of phosphonium cations with longer alkyl chains were larger than the values expected from the correlation obtained by other ILs and conventional liquids. The deviation becomes larger with increasing the number of carbon atoms of alkyl-chain of cation, and with decreasing the molecular size of diffusing molecules. The molecular size dependence of the diffusion coefficient was correlated by the ratio of the volume of the solute to that of the solvent as demonstrated by the preceding work (Kaintz et al., J. Phys. Chem. B 2013 , 117 , 11697 ). Diffusion coefficients have been well correlated with the power laws of both T/? and the relative volume of the solute to the solvent. PMID:26061826
Effect of the transition of networks from floppy to rigid on the diffusion coefficient.
Tsakiris, N; Argyrakis, P; Avramov, I
2010-02-01
We investigate a tracer particle moving on a two-dimensional square lattice created by network formers (NF). The positions of all network formers are randomly displaced by a small amount from the nodes of the network. Each NF can be in a "floppy" or "rigid" state, depending on the number of bonds connecting it to neighboring network formers. The NF that have more than a specified number of m bonds are in rigid state, the remaining ones are in a floppy state. The energy of the tracer particle depends on its distance from those of the four nearest NF that are in "rigid" state. The NF in floppy state do not contribute to the energy. We here demonstrate that the a priori increase in the diffusion coefficient with the concentration of the floppy states goes through a crossover point, after which the increase is much sharper. PMID:20365613
Surface diffusion coefficient of Au atoms on single layer graphene grown on Cu
Ruffino, F., E-mail: francesco.ruffino@ct.infn.it; Cacciato, G.; Grimaldi, M. G. [Dipartimento di Fisica ed Astronomia-Universitá di Catania, via S. Sofia 64, 95123 Catania, Italy and MATIS IMM-CNR, via S. Sofia 64, 95123 Catania (Italy)
2014-02-28
A 5?nm thick Au film was deposited on single layer graphene sheets grown on Cu. By thermal processes, the dewetting phenomenon of the Au film on the graphene was induced so to form Au nanoparticles. The mean radius, surface-to-surface distance, and surface density evolution of the nanoparticles on the graphene sheets as a function of the annealing temperature were quantified by scanning electron microscopy analyses. These quantitative data were analyzed within the classical mean-field nucleation theory so to obtain the temperature-dependent Au atoms surface diffusion coefficient on graphene: D{sub S}(T)=[(8.2±0.6)×10{sup ?8}]exp[?(0.31±0.02(eV)/(at) )/kT]?cm{sup 2}/s.
A comparative study on temperature dependent diffusion coefficient of liquid Fe
NASA Astrophysics Data System (ADS)
Gosh, R. C.; Syed, Ishtiaque M.; Amin, Zahurul; Bhuiyan, G. M.
2013-10-01
The self-diffusion coefficients, D, of liquid Fe at different temperatures have been investigated using hard sphere (HS) theory and universal scaling laws (USLs). Inter-ionic interaction is derived from both pseudopotential proposed by Brettonet-Silbert (BS) and many body potential obtained from embedded atom method (EAM). Temperature dependent effective HS diameter, ?(T), and excess entropy, Sex, are the premier ingredients of the study. The former ingredient is calculated using both variational modified hypernetted chain, VMHNC, integral equation theory and Linearized Weeks-Chandler-Andersen, LWCA, thermodynamic perturbation theory together with an empirical relation of Protopapas et al. (1973) [2] whereas the later one is calculated using VMHNC theory alone, with BS and EAM potentials. We observe that D increases with increasing temperatures. The obtained results are compared with those predicted by Protopapas et al. The comparison suggests that USL of Dzugutov and HS theory with BS potential are better choices to predict D(T) of liquid Fe.
Energetic particle diffusion coefficients upstream of quasi-parallel interplanetary shocks
NASA Technical Reports Server (NTRS)
Tan, L. C.; Mason, G. M.; Gloeckler, G.; Ipavich, F. M.
1989-01-01
The properties of about 30 to 130-keV/e protons and alpha particles upstream of six quasi-parallel interplanetary shocks that passed by the ISEE 3 spacecraft during 1978-1979 were analyzed, and the values for the upstream energegic particle diffusion coefficient, kappa, in these six events were deduced for a number of energies and upstream positions. These observations were compared with predictions of Lee's (1983) theory of shock acceleration. It was found that the observations verified the prediction of the A/Q dependence (where A and Q are the particle atomic mass and ionization state, respectively) of kappa for alpha and proton particles upstream of the quasi-parallel shocks.
The role of diffusion in ISOL targets for the production of radioactive ion beams
NASA Astrophysics Data System (ADS)
Beyer, G. J.; Hagebø, E.; Novgorodov, A. F.; Ravn, H. L.; Isolde Collaboration
2003-05-01
On-line isotope separation techniques (ISOL) for production of ion beams of short-lived radionuclides require fast separation of nuclear reaction products from irradiated target materials followed by a transfer into an ion source. As a first step in this transport chain the release of nuclear reaction products from refractory metals has been studied systematically and will be reviewed. High-energy protons (500-1000 MeV) produce a large number of radionuclides in irradiated materials via the nuclear reactions spallation, fission and fragmentation. Foils and powders of Re, W, Ta, Hf, Mo, Nb, Zr, Y, Ti and C were irradiated with protons (600-1000 MeV) at the Dubna synchrocyclotron, the CERN synchrocyclotron and at the CERN PS-booster to produce different nuclear reaction products. The main topic of the paper is the determination of diffusion coefficients of the nuclear reaction products in the target matrix, data evaluation and a systematic interpretation of the data. The influence of the ionic radius of the diffusing species and the lattice type of the host material used as matrix or target on the diffusion will be evaluated from these systematics. Special attention was directed to the release of group I-, II- and III-elements. Arrhenius plots lead to activation energies of the diffusion process. Results:A strong radius determined diffusion behaviour was found: DIIIB> DIIA> DIA> DVIIIA, ( DY> DSr> DRb> DKr). Rare earth elements diffuse as Me 3+-species. Within the host elements of one period of the periodic table the diffusion of the trace elements changes in the following order: DIIIB> DIVB? DVB> DVIB. In a given target trace elements of group I and II of a lower period diffuse faster than the corresponding elements of the higher period of the periodic table. D2ndperiod> D5thperiod> D6thperiod, ( DBe? DSr> DBa). The diffusion determined transport rate of nuclear reaction products in solid target materials is often satisfactory, and consequently several refractory metals are suited as targets for fast on-line separation of short-lived nuclear reaction products. The delay times measured in on-line mode at ISOLDE, however, are significantly shorter. An enhancement of the diffusion under radiation condition is considered, subject for further systematic studies. The results obtained in this systematic study may also be applied in the development of alternative separation technologies in medical radionuclide production.
Ion radial diffusion in an electrostatic impulse model for stormtime ring current formation
NASA Technical Reports Server (NTRS)
Chen, Margaret W.; Schulz, Michael; Lyons, Larry R.; Gorney, David J.
1992-01-01
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.
NASA Astrophysics Data System (ADS)
Noah, Martin A.; Flötotto, David; Wang, Zumin; Mittemeijer, Eric J.
2015-04-01
Self-diffusion coefficients of Si and Ge in amorphous Si1-xGex (a-Si1-xGex) solid solutions were determined quantitatively in the temperature range of 440 °C - 460 °C by the investigation of interdiffusion in amorphous Si/Si0.52Ge0.48 multilayers using Auger electron spectroscopy sputter-depth profiling. The determined concentration dependent self-diffusion coefficients of Si and Ge in a-Si1-xGex with 0 ? x ? 0.48 at. % Ge are about ten orders of magnitude larger than in the corresponding crystalline phases, due to the inherent, excess free volume in the amorphous phase. The self-diffusion coefficient of Si (or Ge) in a-Si1-xGex increases in association with a decreasing activation enthalpy with increasing Ge concentration. This concentration dependence has been related to an overall decrease of the average bond strength with increasing Ge concentration.
Golebiewska, Urszula; Nyako, Marian; Woturski, William; Zaitseva, Irina
2008-01-01
Phosphatidylinositol 4,5-bisphosphate (PIP2) controls a surprisingly large number of processes in cells. Thus, many investigators have suggested that there might be different pools of PIP2 on the inner leaflet of the plasma membrane. If a significant fraction of PIP2 is bound electrostatically to unstructured clusters of basic residues on membrane proteins, the PIP2 diffusion constant, D, should be reduced. We microinjected micelles of Bodipy TMR-PIP2 into cells, and we measured D on the inner leaflet of fibroblasts and epithelial cells by using fluorescence correlation spectroscopy. The average ± SD value from all cell types was D = 0.8 ± 0.2 ?m2/s (n = 218; 25°C). This is threefold lower than the D in blebs formed on Rat1 cells, D = 2.5 ± 0.8 ?m2/s (n = 26). It is also significantly lower than the D in the outer leaflet or in giant unilamellar vesicles and the diffusion coefficient for other lipids on the inner leaflet of these cell membranes. The simplest interpretation is that approximately two thirds of the PIP2 on inner leaflet of these plasma membranes is bound reversibly. PMID:18256277
A uniqueness result for the identification of a time-dependent diffusion coefficient
NASA Astrophysics Data System (ADS)
Fraguela, A.; Infante, J. A.; Ramos, A. M.; Rey, J. M.
2013-12-01
This paper deals with the problem of determining the time-dependent thermal diffusivity coefficient of a medium, when the evolution of the temperature in a part of it is known. Such situations arise in the context of food technology, when thermal processes at high pressures are used for extending the shelf life of the food, in order to preserve its nutritional and organoleptic properties (Infante et al 2009 On the Modelling and Simulation of High Pressure Processes and Inactivation of Enzymes in Food Engineering pp 2203-29 and Otero et al 2007 J. Food Eng. 78 1463-70). The phenomenon is modeled by the heat equation involving a term which depends on the source temperature and pressure increase, and appropriate initial and boundary conditions. We study the inverse problem of determining time-dependent thermal diffusivities k, when some temperature measurements at the border and inside the medium are known. We prove the uniqueness of the inverse problem solution under suitable a priori assumptions on regularity, size and growth of k.
The Course of Apparent Diffusion Coefficient Values following Perinatal Arterial Ischemic Stroke
van der Aa, Niek E.; Benders, Manon J. N. L.; Vincken, Koen L.; Groenendaal, Floris; de Vries, Linda S.
2013-01-01
Background Diffusion weighted MR imaging (DWI) plays an important role in the diagnosis of perinatal arterial ischemic stroke (PAIS) during the acute phase. Its derived apparent diffusion coefficient (ADC) can be used to quantify the diffusion restriction. Aim of the current study was to identify the changes in ADC values in the acute phase following PAIS. Methods A cohort of 36 infants with a confirmed PAIS who were examined once during the first ten days of life was studied. ADC values in the core of the ischemic tissue (iADC) were determined and correlated with postnatal age. ADC ratios (rADC) were calculated by dividing the iADC value by the ADC value of the corresponding area in the contralateral ‘healthy’ hemisphere. Results Infants were scanned between days two and ten. A non-linear increase in iADC and rADC values was observed over time and large middle cerebral artery strokes resulted in lower iADC and rADC values. Normalisation of rADC values was observed after day seven. rADC values were lower when compared to previously published rADC values of infants with hypoxic ischemic encephalopathy, suggesting more severe injury. Conclusions Following PAIS, DWI showed decreased ADC values with a non-linear increase during the first week, and pseudonormalization after day 7, which limits the use of DWI to assess PAIS to the first week. Compared to previous studies, ADC values were lower when compared to infants with hypoxic ischemic encephalopathy, most likely due to more severe injury. PMID:23457613
Danel, J-F; Kazandjian, L; Zérah, G
2012-06-01
Computations of the self-diffusion coefficient and viscosity in warm dense matter are presented with an emphasis on obtaining numerical convergence and a careful evaluation of the standard deviation. The transport coefficients are computed with the Green-Kubo relation and orbital-free molecular dynamics at the Thomas-Fermi-Dirac level. The numerical parameters are varied until the Green-Kubo integral is equal to a constant in the t?+? limit; the transport coefficients are deduced from this constant and not by extrapolation of the Green-Kubo integral. The latter method, which gives rise to an unknown error, is tested for the computation of viscosity; it appears that it should be used with caution. In the large domain of coupling constant considered, both the self-diffusion coefficient and viscosity turn out to be well approximated by simple analytical laws using a single effective atomic number calculated in the average-atom model. PMID:23005237
NASA Astrophysics Data System (ADS)
Danel, J.-F.; Kazandjian, L.; Zérah, G.
2012-06-01
Computations of the self-diffusion coefficient and viscosity in warm dense matter are presented with an emphasis on obtaining numerical convergence and a careful evaluation of the standard deviation. The transport coefficients are computed with the Green-Kubo relation and orbital-free molecular dynamics at the Thomas-Fermi-Dirac level. The numerical parameters are varied until the Green-Kubo integral is equal to a constant in the t?+? limit; the transport coefficients are deduced from this constant and not by extrapolation of the Green-Kubo integral. The latter method, which gives rise to an unknown error, is tested for the computation of viscosity; it appears that it should be used with caution. In the large domain of coupling constant considered, both the self-diffusion coefficient and viscosity turn out to be well approximated by simple analytical laws using a single effective atomic number calculated in the average-atom model.
First-principles binary diffusion coefficients for H, H2, and four normal alkanes + N2
NASA Astrophysics Data System (ADS)
Jasper, Ahren W.; Kamarchik, Eugene; Miller, James A.; Klippenstein, Stephen J.
2014-09-01
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%.
First-principles binary diffusion coefficients for H, H?, and four normal alkanes + N?.
Jasper, Ahren W; Kamarchik, Eugene; Miller, James A; Klippenstein, Stephen J
2014-09-28
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 CnH(2n+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
NASA Astrophysics Data System (ADS)
Shimada, Kayori; Kato, Haruhisa; Saito, Takeshi; Matsuyama, Shigetomo; Kinugasa, Shinichi
2005-06-01
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 (D2O) at 30 ° 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 H2O 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.
Jiránek, Martin; Rovenská, Kate?ina
2012-04-01
Paper presents the principles for unified test methods for determining the radon diffusion coefficient in waterproof materials in order to increase the accuracy, repeatability and reproducibility of the results. We consider this very important, because an assessment of the radon diffusion coefficient is required by several national technical standards when waterproofing acts as a radon-proof membrane. The requirements for key parameters for one test method performed under non-stationary conditions and for two methods performed under stationary conditions are described in this paper. PMID:22245288
Preferential interaction coefficient for nucleic acids and other cylindrical poly-ions
E. Trizac; G. Tellez
2007-04-04
The thermodynamics of nucleic acid processes is heavily affected by the electric double-layer of micro-ions around the polyions. We focus here on the Coulombic contribution to the salt-polyelectrolyte preferential interaction (Donnan) coefficient and we report extremely accurate analytical expressions valid in the range of low salt concentration (when polyion radius is smaller than the Debye length). The analysis is performed at Poisson-Boltzmann level, in cylindrical geometry, with emphasis on highly charged poly-ions (beyond ``counter-ion condensation''). The results hold for any electrolyte of the form $z_-$:$z_+$. We also obtain a remarkably accurate expression for the electric potential in the vicinity of the poly-ion.
M. Zistler; C. Schreiner; P. Wachter; P. Wasserscheid; D. Gerhard; H. J. Gores
According to literature, binary mixtures of ionic liquids (ILs) such as 1-methyl-3-propylimidazolium iodide (MPII) as an iodide source and another IL of low viscosity such as 1-ethyl-3- methylimidazolium thiocyanate (EMISCN) may be used to increase the diffusion coefficients of redox-active species (I-\\/I3 - ). As dye-sensitized solar cells (DSCs) are diffusion limited a better performance may result with blends when
Apparent electrostatic ion cyclotron waves in the diffuse aurora
Bering, E.A.
1983-08-01
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/sup +/ and O/sup +/ 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 ..mu..A/m/sup 2/. 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.
NASA Astrophysics Data System (ADS)
Kienle, Alwin; Lilge, Lothar; Patterson, Michael S.; Hibst, Raimund; Steiner, Rudolf; Wilson, Brian C.
1996-05-01
The absorption and transport scattering coefficients of biological tissues determine the radial dependence of the diffuse reflectance that is due to a point source. A system is described for making remote measurements of spatially resolved absolute diffuse reflectance and hence noninvasive, noncontact estimates of the tissue optical properties. The system incorporated a laser source and a CCD camera. Deflection of the incident beam into the camera allowed characterization of the source for absolute reflectance measurements. It is shown that an often used solution of the diffusion equation cannot be applied for these measurements. Instead, a neural network, trained on the results of Monte Carlo simulations, was used to estimate the absorption and scattering coefficients from the reflectance data. Tests on tissue-simulating phantoms with transport scattering coefficients between 0.5 and 2.0 mm-1 and absorption coefficients between 0.002 and 0.1 mm -1 showed the rms errors of this technique to be 2.6% for the transport scattering coefficient and 14% for the absorption coefficients. The optical properties of bovine muscle, adipose, and liver tissue, as well as chicken muscle (breast), were also measured ex vivo at 633 and 751 nm. For muscle tissue it was found that the Monte Carlo simulation did not agree with experimental measurements of reflectance at distances less than 2 mm from the incident beam. Carlo, neural network.
Fusion product measurements of the local ion thermal diffusivity in the PLT tokamak
Heidbrink, W.W.; Lovberg, J.; Strachan, J.D.; Bell, R.E.
1986-03-01
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.
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
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.
Electron-Ion Recombination Rate Coefficient Measurements in a Flowing Afterglow Plasma
NASA Technical Reports Server (NTRS)
Gougousi, Theodosia; Golde, Michael F.; Johnsen, Rainer
1996-01-01
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.
NASA Astrophysics Data System (ADS)
Song, Weixin; Ji, Xiaobo; Wu, Zhengping; Yang, Yingchang; Zhou, Zhou; Li, Fangqian; Chen, Qiyuan; Banks, Craig E.
2014-06-01
NASICON-type Na3V2(PO4)2F3 is employed as a promising cathode for sodium-ion batteries in order to explore the ion-migration mechanism and diffusion capability. Two kinds of Na sites, namely Na(1) site and Na(2) site exist in the crystal structure per formula unit to accommodate a total of three sodium ions. The ion at Na(2) site with half occupation extracts first and inserts the last due to its high chemical potential, while the whole extraction/insertion of two ions between 1.6 and 4.6 V vs. Na+/Na can produce three plateaus in charge/discharge processes because of the reorganization of ions. The first discharge capacity of 111.6 mAh g-1 with retention of 97.6% after 50 cycles could be obtained by electrochemical testing at 0.091C. Electrochemical activation and/or structural reorganization of the system by cycling could improve the diffusion coefficient of sodium with a comparatively large magnitude of 10-12 cm2 s-1, though many influences on the resistance factors also can be attributed to the cycling process. Such work is of fundamental importance to the progression of sodium-based batteries to be fully realized and be implemented over existing Li-ion based batteries.
NASA Astrophysics Data System (ADS)
Ya?a, F.; Anli, F.; Güngör, S.
2007-04-01
We present analytical calculations of spherically symmetric radioactive transfer and neutron transport using a hypothesis of P1 and T1 low order polynomial approximation for diffusion coefficient D. Transport equation in spherical geometry is considered as the pseudo slab equation. The validity of polynomial expansionion in transport theory is investigated through a comparison with classic diffusion theory. It is found that for causes when the fluctuation of the scattering cross section dominates, the quantitative difference between the polynomial approximation and diffusion results was physically acceptable in general.
Yasa, F.; Anli, F. [Department of Physics, Faculty of Science and Art, KSUe 46100 K.Maras (Turkey); Guengoer, S. [Department of Physics, Faculty of Science and Art, CUe Balcali-Adana (Turkey)
2007-04-23
We present analytical calculations of spherically symmetric radioactive transfer and neutron transport using a hypothesis of P1 and T1 low order polynomial approximation for diffusion coefficient D. Transport equation in spherical geometry is considered as the pseudo slab equation. The validity of polynomial expansionion in transport theory is investigated through a comparison with classic diffusion theory. It is found that for causes when the fluctuation of the scattering cross section dominates, the quantitative difference between the polynomial approximation and diffusion results was physically acceptable in general.
Karim, K.R.; Bhalla, C.P.
1989-04-01
Dielectronic recombination (DR) rate coefficients are calculated for selected heliumlike ions with atomic number Z = 10, 14, 18, 22, 24, 26, and 28 at plasma temperatures 0.1--10 keV. The total DR rate coefficient has been obtained by summing over partial DR rates of recombination processes that proceed via intermediate lithiumlike resonance states chemically bond1s2lnl'LSJ>. The effects of configuration interaction and spin-orbit coupling have been included for all states with nless than or equal to8; for higher-lying autoionizing states, the 1/n/sup 3/ scaling was employed. The results from the present calculation are compared with available theoretical and experimental values of DR rate coefficients.
Karim, K.R.; Bhalla, C.P.
1988-04-01
Dielectronic-recombination rate coefficients of selected hydrogenlike ions (Z = 10, 14, 18, 20, 22, 26, and 28) have been calculated at various plasma temperatures (kT/sub e/ = 0.6--10 keV) using the Hartree-Fock-Slater atomic model and assuming a Maxwellian velocity distribution for the free electrons. The effects of configuration interaction and spin-orbit coupling are included in all intermediate resonance states )vertreverse arrowbar)2lnl'SLJ> for nless than or equal to4. Configuration average rates have been used to calculate dielectronic-recombination rate coefficients for n = 5--8, and 1/n/sup 3/ scaling law for all higher-lying states. The results from the present calculations are compared with available theoretical and experimental values of dielectronic-recombination rate coefficients.
Measurements of the coefficient of combination of small ions with aerosol particles
V. P. V. Flanagan
1966-01-01
The equilibrium small ion concentration (n) was measured in aerosols for various ionization rates (q) and particle concentrations (Z). The results agree with the formulaq=bZn+an2. These experiments were carried out with different particle sizes and the results provided a series of values of the combination coefficientb. The size of the particles was determined by the diffusion box method and the
NASA Astrophysics Data System (ADS)
Drozdov, Alexander; Mann, Ian; Baker, Daniel N.; Subbotin, Dmitriy; Ozeke, Louis; Shprits, Yuri; Kellerman, Adam
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.
Zhao, Yi-lei; Guo, Qing-qu; Yang, Gen-ren; Wang, Qi-dong
2014-01-01
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
Resorlu, Mustafa; Gokmen, Ferhat; Resorlu, Hatice; Adam, Gurhan; Akbal, Ayla; Cevizci, Sibel; Sariyildirim, Abdullah; Savas, Yilmaz; Guven, Mustafa; Aras, Adem Bozkurt
2015-01-01
Purpose: To assess the relation between ankylosing spondylitis (AS) and degenerative disc disease emerging in association with various intrinsic and extrinsic factors and to evaluate the correlation between degree of degeneration in intervertebral discs and apparent diffusion coefficient (ADC) values. Methods: Thirty-five patients with AS and a control group of 35 patients were included in the study. Three hundred fifty intervertebral discs were assessed in terms of degeneration by analyzing signal intensities and morphologies on T2 weighted series of a 1.5 Tesla magnetic resonance scanner. ADC values were determined in diffusion weighted images (DWI) using a “b value of 500 s/mm2”. Patients in the AS and control groups were compared in terms of intervertebral disc degeneration, and association between degree of degeneration and ADC values was analyzed. Results: The mean of total degeneration degrees for five lumbar intervertebral discs was significantly higher in the patients with AS compared to the control group (16.77±4.67 vs 13.00±4.08, respectively; P=0.001). When intervertebral discs were analyzed separately, disc degeneration was again significantly higher in patients with AS compared to the control group, with the exception of L5-S1. Age, cholesterol level, triglyceride level, duration of disease and BASFI index were significantly associated with degree of degeneration in patients with AS. A negative correlation was determined between disc degeneration and ADC value. Conclusion: AS is a risk factor for degenerative disc disease due to its systemic effects, the fact it leads to posture impairment and its inflammatory effects on the vertebrae. A decrease in ADC values is observed as degeneration worsens in degenerative disc disease. PMID:25785119
Cui, Yong; Ma, Li; Chen, Xuzhu; Zhang, Zhe; Jiang, Haihui; Lin, Song
2014-09-01
Tumor grade and molecular variants influence the survival of patients with glioma. The apparent diffusion coefficient (ADC) map is a non-invasive tool for evaluating the outcomes and response to therapy in glioma. In this study, we investigated the correlation between the tumor grade and prognostic biomarkers with the ADC in glioma patients. Eighty-two patients with supratentorial glioma were identified via analysis of surgical specimens and neuroradiological data. Using the World Health Organization grade, histological subtype, and molecular variants (1p/19q codeletion, isocitrate dehydrogenase 1/2 mutation, Ki-67 index, O6-methylguanine DNA methyltransferase, P53, and vascular endothelial growth factor immunoactivity) as prognostic biomarkers, we performed receiver operating characteristic analysis and multiple linear regression to assess the association between the magnetic resonance diffusion parameter and mean ADC and the prognostic factors of glioma pathology. Univariate analysis and multiple linear regression revealed inverse correlations between the ADC values and the tumor grade, oligodendrocytoma histology, and 1p/19q codeletion. A threshold mean ADC value could predict the 1p/19q chromosomal status in WHO II gliomas with 72 % sensitivity and 88 % specificity (area under the curve 0.82, 95 % confidence interval 0.68-0.97) and could distinguish low-grade glioma with low-risk factors from the high-risk group (P < 0.01). The mean ADC value could be used as a non-invasive tool to evaluate the prognosis of supratentorial glioma patients. A threshold mean ADC value could be used to predict the 1p/19q codeletion and to identify low-risk low-grade gliomas (LGGs). Lower ADC values are indicative of a favorable prognosis in LGGs. PMID:24874469
Kido, A; Kataoka, M; Koyama, T; Yamamoto, A; Saga, T; Togashi, K
2010-01-01
This study investigated the apparent diffusion coefficients (ADCs) of the uterine zonal structures (myometrium, endometrium and junctional zone) among reproductive women, and their changes during the menstrual cycle. Magnetic resonance (MR) images of seven healthy females (aged 24–31 years) were obtained during the periovulatory, luteal and menstrual phases. Diffusion-weighted imaging (DWI) was performed with a single-shot echo-planar imaging (EPI) sequence in the midsagittal plane of the uterus using three b-values (b = 0, 500 or 1000 s mm?2). The ADC values of the three uterine zonal structures were measured on an ADC map by placing two regions of interest (ROI) on the corresponding zonal structures. The average changes of ADC values (intra-individual ADC value variation) over three menstrual phases were 0.41 × 10?3 mm2 s?1 (range, 0.08–0.91) for myometrium, 0.55 × 10?3 mm2 s?1 (0.35–0.84) for endometrium, and 0.40 × 10?3 mm2 s?1 (0.18–0.59) for the junctional zone. The ADC values for myometrium and endometrium were lower in the menstrual phase, although there was some overlap of individual values. Interindividual variation in ADC value for a given zone or phase ranged from 0.48 × 10?3 mm2 s?1 to 0.85 × 10?3 mm2 s?1. Intermeasurement variation between the two ROIs ranged from 0 to 0.48 × 10?3 mm2 s?1 per measurement. The magnitude of these variations was comparable to reported differences between malignant and non-malignant tissues. These preliminary results, from a small number of subjects, suggest that the menstrual cycle and individual variation in pre-menopausal women should be considered when interpreting the ADC values of uterine structures. PMID:20505034
Kido, A; Kataoka, M; Koyama, T; Yamamoto, A; Saga, T; Togashi, K
2010-06-01
This study investigated the apparent diffusion coefficients (ADCs) of the uterine zonal structures (myometrium, endometrium and junctional zone) among reproductive women, and their changes during the menstrual cycle. Magnetic resonance (MR) images of seven healthy females (aged 24-31 years) were obtained during the periovulatory, luteal and menstrual phases. Diffusion-weighted imaging (DWI) was performed with a single-shot echo-planar imaging (EPI) sequence in the midsagittal plane of the uterus using three b-values (b = 0, 500 or 1000 s mm(-2)). The ADC values of the three uterine zonal structures were measured on an ADC map by placing two regions of interest (ROI) on the corresponding zonal structures. The average changes of ADC values (intra-individual ADC value variation) over three menstrual phases were 0.41 x 10(-3) mm(2) s(-1) (range, 0.08-0.91) for myometrium, 0.55 x 10(-3) mm(2) s(-1) (0.35-0.84) for endometrium, and 0.40 x 10(-3) mm(2) s(-1) (0.18-0.59) for the junctional zone. The ADC values for myometrium and endometrium were lower in the menstrual phase, although there was some overlap of individual values. Interindividual variation in ADC value for a given zone or phase ranged from 0.48 x 10(-3) mm(2) s(-1) to 0.85 x 10(-3) mm(2) s(-1). Intermeasurement variation between the two ROIs ranged from 0 to 0.48 x 10(-3) mm(2) s(-1) per measurement. The magnitude of these variations was comparable to reported differences between malignant and non-malignant tissues. These preliminary results, from a small number of subjects, suggest that the menstrual cycle and individual variation in pre-menopausal women should be considered when interpreting the ADC values of uterine structures. PMID:20505034
Diffusion length damage coefficient and annealing studies in proton-irradiated InP
NASA Technical Reports Server (NTRS)
Hakimzadeh, Roshanak; Vargas-Aburto, Carlos; Bailey, Sheila G.; Williams, Wendell
1993-01-01
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.
Mónika Valiskó; Dezs? Boda
2014-09-15
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.
Thakur, Anshuman Bramhanand
2005-11-01
of soils exert a critical influence on the depth to which seasonal variations of moisture and suction at the ground surface extend into the soil mass. Hence, a study of moisture diffusion coefficient is pivotal. In this research the drying test originally...
E. L. J. Goossens; A. J. J. van der Zanden; H. L. M. Wijen; W. H. van der Spoel
2003-01-01
An interferometric technique has been used to measure the swelling of a paint film caused by its absorption of water vapour. The diffusion coefficient of water in paint is obtained from the time evolution of the thickness of the paint film, when the paint film is subjected to an almost stepwise change in the relative humidity of the surrounding air.
Marchal, D; Boireau, W; Laval, J M; Moiroux, J; Bourdillon, C
1998-01-01
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
Estimation of CO2 diffusion coefficient at 0-10 cm depth in undisturbed and tilled soils
Technology Transfer Automated Retrieval System (TEKTRAN)
Diffusion coefficients (D) of CO2 at 0 – 10 cm layers in undisturbed and tilled soil conditions were estimated using Penman, Millington-Quirk, Ridgwell et al. (1999), Troeh et al., and Moldrup et al. models. Soil bulk density and volumetric soil water content ('v) at 0 – 10 cm were measured on April...
Majer, G., E-mail: majer@is.mpg.de [Max Planck Institute for Intelligent Systems, Heisenbergstr. 3, 70569 Stuttgart (Germany); Melchior, J. P. [Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569 Stuttgart (Germany)] [Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569 Stuttgart (Germany)
2014-03-07
Precise diffusion measurements of rhodamine 6G (Rh6G) dissolved in D{sub 2}O 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 {sup 1}H NMR spectrum. To analyze the differences due to the isotope effect of the solvent (D{sub 2}O vs. H{sub 2}O), the correlation time ?{sub D} of Rh6G was measured by FCS in both D{sub 2}O and H{sub 2}O. The obtained isotopic correction factor, ?{sub D}(D{sub 2}O)/?{sub D}(H{sub 2}O) = 1.24, reflects the isotope effect of the solvent´s self-diffusion coefficients as determined previously by PFG-NMR.
Gebrekristos, R.A.; Shapiro, A.M.; Usher, B.H.
2008-01-01
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.
Nonneutral and quasi-neutral diffusion of weakly ionized multiconstituent plasma
R. J. Hill
1978-01-01
A theory is developed for ambipolar diffusion in a multiconstituent weakly ionized plasma. The implications of the presence of negative ions and of differing positive ion and negative ion diffusion coefficients are found. In particular, the presence of numerous negative ions is found to enhance the diffusion of the electrons. Furthermore, this theory of multiconstituent ambipolar diffusion is extended to
Selectivity coefficient for Ca/Na ion exchange in highly compacted bentonite
NASA Astrophysics Data System (ADS)
Karnland, Ola; Birgersson, Martin; Hedström, Magnus
Bentonite clay is proposed as buffer material around the waste canisters and as tunnel backfill material in several concepts for disposal of radioactive waste. The distribution of charge compensating cations in the bentonite is of interest for several reasons, one being possible release of colloid particles from the bentonite to groundwater with very low ionic strength. The cation distribution at equilibrium may be calculated for various relevant groundwater compositions by use of selectivity coefficients. However, present literature data generally concerns coefficients measured in batch experiments with high water-to-solid ratios. The basic aim with the present work was therefore to determine selectivity coefficients for sodium/calcium exchange in bentonite with low water-to-solid ratios, and thereby give a reliable base for calculating the cation distribution in a confined bentonite buffer with a relatively high density. In total, six tests with homo-ionic Na- and Ca-montmorillonite, prepared to three material densities, were equilibrated with test solutions of successively increasing concentration. The distribution of cations at equilibrium was measured by use of ion selective electrodes and ICP/AES, and selectivity coefficients were calculated according to the Gaines-Thomas convention. The obtained selectivity coefficient was found to be in the range of 3.8-7.8, which is similar to those previously reported for high water-to-solid ratios.
NASA Astrophysics Data System (ADS)
Bologna, Mauro; Svenkeson, Adam; West, Bruce J.; Grigolini, Paolo
2015-07-01
Diffusion processes in heterogeneous media, and biological systems in particular, are riddled with the difficult theoretical issue of whether the true origin of anomalous behavior is renewal or memory, or a special combination of the two. Accounting for the possible mixture of renewal and memory sources of subdiffusion is challenging from a computational point of view as well. This problem is exacerbated by the limited number of techniques available for solving fractional diffusion equations with time-dependent coefficients. We propose an iterative scheme for solving fractional differential equations with time-dependent coefficients that is based on a parametric expansion in the fractional index. We demonstrate how this method can be used to predict the long-time behavior of nonautonomous fractional differential equations by studying the anomalous diffusion process arising from a mixture of renewal and memory sources.
NASA Astrophysics Data System (ADS)
Silva, Antonio
2005-03-01
It is well-known that the mathematical theory of Brownian motion was first developed in the Ph. D. thesis of Louis Bachelier for the French stock market before Einstein [1]. In Ref. [2] we studied the so-called Heston model, where the stock-price dynamics is governed by multiplicative Brownian motion with stochastic diffusion coefficient. We solved the corresponding Fokker-Planck equation exactly and found an analytic formula for the time-dependent probability distribution of stock price changes (returns). The formula interpolates between the exponential (tent-shaped) distribution for short time lags and the Gaussian (parabolic) distribution for long time lags. The theoretical formula agrees very well with the actual stock-market data ranging from the Dow-Jones index [2] to individual companies [3], such as Microsoft, Intel, etc. [] [1] Louis Bachelier, ``Th'eorie de la sp'eculation,'' Annales Scientifiques de l''Ecole Normale Sup'erieure, III-17:21-86 (1900).[] [2] A. A. Dragulescu and V. M. Yakovenko, ``Probability distribution of returns in the Heston model with stochastic volatility,'' Quantitative Finance 2, 443--453 (2002); Erratum 3, C15 (2003). [cond-mat/0203046] [] [3] A. C. Silva, R. E. Prange, and V. M. Yakovenko, ``Exponential distribution of financial returns at mesoscopic time lags: a new stylized fact,'' Physica A 344, 227--235 (2004). [cond-mat/0401225
Analysis of ligand-protein exchange by Clustering of Ligand Diffusion Coefficient Pairs (CoLD-CoP)
NASA Astrophysics Data System (ADS)
Snyder, David A.; Chantova, Mihaela; Chaudhry, Saadia
2015-06-01
NMR spectroscopy is a powerful tool in describing protein structures and protein activity for pharmaceutical and biochemical development. This study describes a method to determine weak binding ligands in biological systems by using hierarchic diffusion coefficient clustering of multidimensional data obtained with a 400 MHz Bruker NMR. Comparison of DOSY spectrums of ligands of the chemical library in the presence and absence of target proteins show translational diffusion rates for small molecules upon interaction with macromolecules. For weak binders such as compounds found in fragment libraries, changes in diffusion rates upon macromolecular binding are on the order of the precision of DOSY diffusion measurements, and identifying such subtle shifts in diffusion requires careful statistical analysis. The "CoLD-CoP" (Clustering of Ligand Diffusion Coefficient Pairs) method presented here uses SAHN clustering to identify protein-binders in a chemical library or even a not fully characterized metabolite mixture. We will show how DOSY NMR and the "CoLD-CoP" method complement each other in identifying the most suitable candidates for lysozyme and wheat germ acid phosphatase.
Nd3+ ion diffusion during sintering of Nd:YAG transparent ceramics
Hollingsworth, J P; Kuntz, J D; Soules, T F
2008-10-24
Using an electron microprobe, we measured and characterized the Nd{sup 3+} ion diffusion across a boundary between Nd doped and undoped ceramic yttrium aluminum garnet (YAG) for different temperature ramps and hold times and temperatures. The results show significant Nd ion diffusion on the order of micrometers to tens of micrometers depending on the time and temperature of sintering. The data fit well a model including bulk diffusion, grain boundary diffusion and grain growth. Grain boundary diffusion dominates and grain growth limits grain boundary diffusion by reducing the total cross sectional area of grain boundaries.
Marco J. W. Frank; Johannes A. M. Kuipers; Swaaij van W. P. M
1996-01-01
To evaluate quantitatively the results of gas-liquid absorption experiments, accurate liquid-phase diffusion coefficients and viscosities are needed. In this paper experimental values of these quantities will be reported for the binary systems carbon dioxide + water, carbon dioxide + methanol, ammonia + water, and ammonia + methanol. The diffusion coefficients have been measured using the Taylor-Aris dispersion method, and the
M. J. W. Frank; J. A. M. Kuipers; W. P. M. van Swaaij
1996-01-01
To evaluate quantitatively the results of gas-liquid absorption experiments, accurate liquid-phase diffusion coefficients and viscosities are needed. In this paper experimental values of these quantities will be reported for the binary systems carbon dioxide + water, carbon dioxide + methanol, ammonia + water, and ammonia + methanol. The diffusion coefficients have been measured using the Taylor-Aris dispersion method, and the
P. Y. Pennarun; P. Dole; A. Feigenbaum
2004-01-01
SUMMARY This paper defines parameters which can be used to predict worst case migration from recycled PET bottles, with and without a functional barrier. Starting with a set of diffusion coefficients determined in well defined experimental conditions (temperature, presence or not of a solvent, with and without swelling effect), empirical equations for the diffusion coefficient of a migrant or a
Excitation-autoionization cross sections and rate coefficients for Ga-like ions
NASA Astrophysics Data System (ADS)
Mandelbaum, P.; Schwob, J. L.
2008-09-01
Detailed level-by-level calculations of cross sections and rate coefficients for electron impact direct and indirect ionization of ions belonging to the GaI isoelectronic sequence (ground 3 d 104 s 24 p) have been performed. The cross sections are presented in the energy range near the threshold for the five ions Kr5+, Mo11+, Xe23+, Pr28+ and Dy35+. The rate coefficients are given for ions from Kr5+ to U61+ in the GaI sequence at seven electron temperatures ( kT e = 0.1 E I , 0.3 E I , 0.5 E I , 0.7 E I , E I , 2 E I and 10 E I , where E I is the first ionization energy). The calculations include the contribution of direct ionization ( DI) calculated using the Lotz formula approximation and the contributions of excitation-autoionization (EA) computed in the framework of the distorted wave ( DW) approximation for the 4 s-nl, 3 d-nl and 3 p-nl resonant inner-shell excitations. The ionization enhancement due to the EA channels is presented as a function of Z along the GaI isoelectronic sequence. The present results show the great importance of the EA processes; an ionization enhancement factor of up to 10 is predicted for instance for La26+ ( Z = 57) at electron temperature of coronal equilibrium maximum abundance.
Garnet/high-silica rhyolite trace element partition coefficients measured by ion microprobe
Sisson, T.W.; Bacon, C.R.
1992-01-01
Garnet/liquid trace element partition coefficients have been measured in situ by ion microprobe in a rhyolite from Monache Mountain, California. Partition coefficients are reported for La, Ce, Nd, Sm, Dy, Er, Yb, Sc, Ti, V, Cr, Sr, Y, and Zr. The in situ analyses avoid the problem of contamination of the garnet phase by trace element-rich accessory minerals encountered in traditional bulk phenocryst/matrix partitioning studies. The partitioning pattern for the rare earth elements (REEs, excluding Eu) is smooth and rises steeply from the light to the heavy REEs with no sharp kinks or changes in slope, unlike patterns for garnet /silicic liquid REE partitioning determined by bulk methods. This difference suggests that the previous determinations by bulk methods are in error, having suffered from contamination of the phenocryst separates. ?? 1992.
Use of apparent diffusion coefficient values for diagnosis of pediatric posterior fossa tumors.
Pierce, Theodore; Kranz, Peter G; Roth, Christopher; Leong, Dalun; Wei, Peter; Provenzale, James M
2014-04-01
We prospectively compared the ability of neuroradiologists to diagnose medulloblastoma with novice raters using only apparent diffusion coefficient (ADC) values measured on ADC maps. One hundred and three pediatric patients with pre-operative magnetic resonance imaging scans showing a posterior fossa tumor with histological verification were retrospectively identified from a ten-year period at a tertiary care medical center. A single observer measured the lowest ADC values in all tumors to determine the mean minimum ADC (ADCmin) value that provided greatest accuracy in distinguishing medulloblastomas from other tumors, which was determined to be 0.66×10(-3) mm(2)/s. Imaging studies, including ADC maps, from 90 patients were provided to two neuroradiologists, who provided a diagnosis, which was later dichotomized as medulloblastoma or other. Two medical students measured ADCmin within tumors and those with ADCmin < 0.66×10(-3) mm(2)/s were recorded as medulloblastoma; any other value was recorded as other. Diagnostic accuracy was measured. ADCmin values allowed a correct identification of lesions as either medulloblastoma or other in 91% of cases. After diagnoses by the two neuroradiologists were categorized as either medulloblastoma or other, their diagnoses were correct in 90% and 84% of cases, respectively. In 19 cases, at least one neuroradiologist was incorrect; the addition of ADC values to clinical interpretation would have allowed a correct diagnosis in 63% of such cases. Diagnostic accuracy based on ADC values by medical students was comparable to that of subspecialty-trained neuroradiologists. Our findings suggest that the addition of ADC values to standard film interpretation may improve the diagnostic rate for these tumors. PMID:24750714
Torgersen, T.; Mathieu, G.; Hesslein, R.H.; Broecker, W.S.
1982-01-20
A direct field comparison was conducted to determine the dependency of gas exchange coefficient (k/sub x/) on the diffusion coefficient (D/sub x/). The study also sought to confirm the enhanced vertical exchange properties of limnocorrals and similar enclosures. Gas exchange coefficients for /sup 222/Rn and /sup 3/He were determined in a small northern Ontario lake, using a /sup 226/Ra and /sup 3/H spike to gain the necessary precision. The results indicate that the gas exchange coefficient is functionally dependent on the diffusion coefficient raised to the 1.22/sub -35//sup + > 12/ power (k/sub x/ = f(D/sub x//sup 1.22)), clearly supporting the stagnant film model of gas exchange. Limnocorrals were found to have gas exchange rates up to 1.7 times higher than the whole lake in spite of the observation of more calm surface conditions in the corral than in the open lake. 33 references, 6 figures, 8 tables.
Elkomoss, S G; Bernhardt, I; Pape, A
2008-08-01
Quantum mechanical calculations of elastic scattering cross sections for some permeant ions crossing the human red blood cell and resting axolemma squid axon membranes have been carried out using the three-dimensional spherically symmetric square potential well. Making the assumption that the permeability coefficient is inversely proportional to scattering cross section, we obtain the order of membrane selectivity for the ions as well as values for the permeability coefficients. Despite the relatively simple method used, good agreement between calculated permeability coefficients and data available in the literature is obtained. We suggest that elastic scattering cross section measurements for ions in various membranes would be valuable not only because they give a precise idea about the permeability ratios between ions but they also determine the form of the potential the ions are moving in. PMID:18420467
Correlation of diffusion coefficients with the electronic structure of interacting atoms
G. V. Samsonov; I. S. Kiva; N. G. Kaidash; E. G. Borisenko
1976-01-01
spect to the electron-phonon structure of solids, the interaction between the diffusion parameters and the electronic structure of atoms interecting during the diffusion was followed. An analysis of diagrams constructed from experimental data on the activation energy A and the preexponential factor D o of elements diffusing into the matrix shows that both quantities are very sensitive to the electronic
An evaluation of energy-independent heavy ion transport coefficient approximations
NASA Technical Reports Server (NTRS)
Townsend, L. W.; Wilson, J. W.
1988-01-01
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.
Croccolo, F; Bataller, H; Scheffold, F
2012-12-21
We use dynamic near field scattering to measure the dynamics of concentration non equilibrium fluctuations at the steady-state of Soret separation. The analysis reveals that above a threshold wave vector q(c), the dynamics is governed by diffusion while at smaller wave vectors, gravity dominates. From the measurements, we extract both the mass diffusion and the Soret coefficients. Comparing our results with literature data, we find good agreement confirming that the proposed experimental technique can be considered a sound approach for the study of thermodiffusion processes. PMID:23267479
Okuda, H.; Cheng, C.Z.; Lee, W.W.
1980-11-01
One- and two-dimensional simulations have been carried out to study electrostatic ion cyclotron instabilities for a hydrogen plasma in a strong magnetic field. It is found that strong ion heating and anomalous cross-field diffusion comparable to Bohm diffusion take place associated with the instability. Implications of the instability to the recent observations in fusion devices and space plasmas are discussed.
Juan Bisquert; Vyacheslav S Vikhrenko
2002-01-01
This paper analyses the mechanisms of ion transport and storage in insertion materials such as metal-oxide electrochromics, Li ion batteries and conducting polymers. We generalize the normal description of intercalation kinetics, based on diffusion of a lattice gas with mean field interactions, using an intercalation model system composed of different types of intercalation sites: a shallow site that allows diffusion
Toshitaka Funazukuri; Chang Yi Kong; Seiichiro Kagei
2002-01-01
Binary diffusion coefficients (D12) for low volatile compounds such as Vitamin K3, ubiquinone (UQ-10), ?-tocopherol, ?-carotene, and phenol in supercritical carbon dioxide were measured by the Taylor dispersion method with two columns connected in series: a poly(ethylene glycol) (PEG) coated capillary column followed by a stainless steel uncoated capillary column, at 313.15K and pressures from 9 to 30MPa. The tracer
Broddak, R.; Voloshchuk, A.M.; Gorlov, V.A.; Dubinin, M.M.; Kochirzhik, M.
1987-01-10
An analytical description has been given of the kinetic adsorption curves with account of the influence of the change in adsorbent temperature due to the evolution of heat and adsorption on the coefficient of intracrystalline diffusion of the adsorbate. The deviation of the experimental kinetic curves for the adsorption of trans-2-butene by finely crystalline NaA zeolite from those calculated from the equation of isothermal diffusion is due to the influence of temperature on the coefficient of intracrystalline diffusion.
Jacobsen, M K; Liu, W; Li, B
2012-09-01
In this paper, a high pressure setup is presented for performing simultaneous measurements of Seebeck coefficient and thermal diffusivity in multianvil apparatus for the purpose of enhancing the study of transport phenomena. Procedures for the derivation of Seebeck coefficient and thermal diffusivity/conductivity, as well as their associated sources of errors, are presented in detail, using results obtained on the filled skutterudite, Ce(0.8)Fe(3)CoSb(12,) up to 12 GPa at ambient temperature. Together with recent resistivity and sound velocity measurements in the same apparatus, these developments not only provide the necessary data for a self-consistent and complete characterization of the figure of merit of thermoelectric materials under pressure, but also serve as an important tool for furthering our knowledge of the dynamics and interplay between these transport phenomena. PMID:23020390
Yemloul, Mehdi; Castola, Vincent; Leclerc, Sébastien; Canet, Daniel
2009-08-01
In the limit of sufficient sensitivity, natural abundance 13C offers a much better spectral resolution than proton NMR. This is due to an important chemical shift range and to proton-decoupling conditions that yield one peak per carbon with practically no overlap. However, pulsed gradient spin echo experiments, which lead to the diffusion coefficient associated with each peak, have scarcely been employed. In this article, we present and compare different ways to access this quantity and we have effectively verified that, without any precaution, diffusion coefficients cannot be properly determined from standard procedures. The cause of such a failure is decoupling during the gradient pulses. We have used a very simple remedy that proved to be very successful on a model mixture of three monoterpenes and that appears as being of general applicability. PMID:19431152
Kuppel, S.; Matsushita, D.; Hatayama, A. [Graduate School of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522 (Japan); Bacal, M. [Laboratoire de Physique des Plasmas, UMR 7648 du CNRS, Ecole Polytechnique, 91128 Palaiseau (France)
2010-02-15
The physical mechanisms involved in the extraction of H{sup -} 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{sup -} current. However, the value of this coefficient does not affect qualitatively the mechanism leading to the peak of extracted H{sup -} ion current observed for an optimum value of the PE bias.
Transient enhanced diffusion after laser thermal processing of ion implanted silicon
Florida, University of
Transient enhanced diffusion after laser thermal processing of ion implanted silicon Kevin S. Jones and transient enhanced diffusion TED of boron was investigated. A 270-Å-thick amorphous layer formed by 10 ke atoms during annealing can considerably broaden the profile shape through transient enhanced diffusion
NASA Astrophysics Data System (ADS)
Raymundo-Ortiz, A. I.; Ramos-Ramirez, E. G.; Cruz-Orea, A.; Salazar-Montoya, J. A.
2013-09-01
The main objective of this work is to determine the effect of different sodium alginate concentrations in hydrogels on their water-vapor diffusion coefficient (WVDC) and thermal effusivity (. These physical parameters were measured by photoacoustic and pyroelectric techniques, respectively. The results indicate that the higher values for the WVDC are presented at a concentration of 2 % sodium alginate. At lower concentrations of sodium alginate, the sample thermal effusivity increases, with a value close to the water thermal effusivity.
NASA Astrophysics Data System (ADS)
Rafiee, Hamid Reza; Rastgar, Mina; Heidari, Neda
2011-08-01
The accurate reduced potential energies for two binary gas mixtures including benzene-methanol and methane-tetrafluoromethane at low density have been obtained by direct inversion of the viscosity collision integral equations. The kinetic theory along with the extended principle of corresponding-states has been used to calculate the viscosity and diffusion coefficients over a wide range of temperature and composition. Good agreements between calculated and experimental data are obtained.
Mendez, J H; Martinez, R C
The technique of constant-potential electrolysis at a stationary spherical electrode (hanging mercury drop) was investigated for the determination of the diffusion coefficient of Tl(I) in sodium citrate-sodium hydroxide medium and of Tl in mercury. Current-time curves, at controlled potential, were obtained, covering periods from 1 to 25 sec after the start of the electrolysis. The influence of applied potential, time of electrolysis, convection and shielding of the electrode was studied. PMID:18962006
Tatsiana P. Rusina; Foppe Smedes; Jana Klanova
2010-01-01
Diffusion coefficients (D) of polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) were determined by film-stacking technique in low-density polyethylene (LDPE) and two types of polydimethylsiloxane (PDMS) (also known as silicone rubber, SR) with the trade names AlteSil (TM) and Silastic. The estimated values of D for PCBs and PAHs over a wide range of hydrophobicity were 2-2.5 orders of
Masaki Amaya; Viktors Grismanovs; Terje Tverberg
2010-01-01
Short-lived fission gas release from fuel pellets during irradiation was investigated based on the experimental results of the gas-flow rigs irradiated in the Halden Heavy Water Reactor (HBWR).The release-to-birth (R\\/B) rates of short-lived fission gas were measured by means of gas-flow measurement during the irradiation experiments. Surface-to-volume (S\\/V) ratios of fuel pellets and diffusion coefficients of short-lived fission gas release
T. Funazukuri; C. Y. Kong; S. Kagei
2004-01-01
Infinite dilution binary diffusion coefficients and retention factors for the oleic acid family such as oleic acid, methyl- and ethyl esters, and mono-, di-, and triglycerides at 313.21K and 8–30MPa, and for other 13 lipids consisting of C18–C22 unsaturated fatty acid constituents at 313.21K and 11MPa were measured in carbon dioxide by a chromatographic impulse response method with a polymer
Chang Yi Kong; Toshitaka Funazukuri; Seiichiro Kagei
2006-01-01
The chromatographic impulse response (CIR) method with curve fitting was employed for measuring binary diffusion coefficients D12 at infinite dilution for polar compounds such as benzoic acid and C1 to C3 mono-alcohols in supercritical (SC) carbon dioxide at 313.2K and pressures higher than 9.5MPa. The measured D12 values for the polar compounds were expressed with two correlations which well represent
Chang Yi Kong; Nirosha R. W. Withanage; Toshitaka Funazukuri; Seiichiro Kagei
2006-01-01
Infinite dilution binary diffusion coefficients D12 and retention factors k for ?-linolenic acid were measured by chromatographic impulse response technique in supercritical carbon dioxide over the ranges of temperature from 308 to 343K and pressure from 9 to 30MPa, together with those for the methyl and ethyl esters at 313 and 343K and pressures from 8 to 16MPa. In comparison
Toshitaka Funazukuri; Chang Yi Kong; Seiichiro Kagei
2003-01-01
Binary diffusion coefficients D12 and partition ratios k at infinite dilution for ?-carotene and ?-tocopherol in supercritical carbon dioxide were measured at temperatures from 308.15 to 333.15 K and pressures from 9 to 30 MPa by a tracer response technique with a poly(ethylene glycol) coated capillary column. Both parameters, simultaneously determined by fitting the calculated response curve to that measured
NASA Astrophysics Data System (ADS)
Lin, Binhua; Cui, Bianxiao; Xu, Xinliang; Zangi, Ronen; Diamant, Haim; Rice, Stuart A.
2015-03-01
We report the results of experimental studies of the short time-long wavelength behavior of collective particle displacements in q1D and q2D colloid suspensions. Our results are reported via the q->0 behavior of the hydrodynamic function H (q) that relates the effective collective diffusion coefficient, De (q) , with the static structure factor S (q) and the self-diffusion coefficient of isolated particles Do: H (q) De (q) S (q) /Do. We find an apparent divergence of H (q) as q->0 with the form H(q)q-(1.7 < ?<1.9), for both q1D and q2D colloid suspensions. Given that S (q) does not diverge as we infer that De (q) does. This behavior is qualitatively different from that of the three-dimensional H (q) and De (q) as q->0, and the divergence is of a different functional form from that predicted for the diffusion coefficient in one component 1D and 2D fluids not subject to boundary conditions that define the dimensionality of the system. The research was supported by the NSF MRSEC at the U of Chicago (NSF/DMR-MRSEC 0820054), NSF/CHE 0822838 (ChemMatCARS), and Israel Science Foundation (Grant No. 8/10).
Shuvam Sen
2012-01-16
In this paper, a new family of implicit compact finite difference schemes for computation of unsteady convection-diffusion equation with variable convection coefficient is proposed. The schemes are fourth order accurate in space and second or lower order accurate in time depending on the choice of weighted time average parameter. The proposed schemes, where transport variable and its first derivatives are carried as the unknowns, combine virtues of compact discretization and Pad\\'{e} scheme for spatial derivative. These schemes which are based on five point stencil with constant coefficients, named as \\emph{(5,5) Constant Coefficient 4th Order Compact} [(5,5)CC-4OC], give rise to a diagonally dominant system of equations and shows higher accuracy and better phase and amplitude error characteristics than some of the standard methods. These schemes are capable of using a grid aspect ratio other than unity and are unconditionally stable. They efficiently capture both transient and steady solutions of linear and nonlinear convection-diffusion equations with Dirichlet as well as Neumann boundary condition. The proposed schemes can be easily implemented and are applied to problems governed by incompressible Navier-Stokes equations apart from linear convection-diffusion equation. Results obtained are in excellent agreement with analytical and available numerical results in all cases, establishing efficiency and accuracy of the proposed scheme.
Yao, Shenggen; Weber, Daniel K; Separovic, Frances; Keizer, David W
2014-07-01
Molecular translational self-diffusion, a measure of diffusive motion, provides information on the effective molecular hydrodynamic radius, as well as information on the properties of media or solution through which the molecule diffuses. Protein translational diffusion measured by pulsed-field gradient nuclear magnetic resonance (PFG-NMR) has seen increased application in structure and interaction studies, as structural changes or protein-protein interactions are often accompanied by alteration of their effective hydrodynamic radii. Unlike the analysis of complex mixtures by PFG-NMR, for monitoring changes of protein translational diffusion under various conditions, such as different stages of folding/unfolding, a partial region of the spectrum or even a single resonance is sufficient. We report translational diffusion coefficients measured by PFG-NMR with a modified stimulated echo (STE) sequence where band-selective pulses are employed for all three (1)H RF pulses. Compared with conventional non-selective sequence, e.g. the BPP-LED sequence, the advantage of this modified band-selective excitation short transient (BEST) version of STE (BEST-STE) sequence is multi-fold, namely: (1) potential sensitivity gain as in generalized BEST-based sequences, (2) water suppression is no longer required as the magnetization of solvent water is not perturbed during the measurement, and (3) dynamic range problems due to the presence of intense resonances from molecules other than the protein or peptide of interest, such as non-deuterated detergent micelles, are avoided. PMID:24824112
Strong Pitch-Angle Diffusion of Ring Current Ions in Geomagnetic Storm-Associated Conditions
NASA Technical Reports Server (NTRS)
Khazanov, G. V.; Gamayunov, K. V.; Gallagher, D. L.; Spann, J. F.
2005-01-01
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.
NASA Technical Reports Server (NTRS)
Cao, Fang; Fichot, Cedric G.; Hooker, Stanford B.; Miller, William L.
2014-01-01
Photochemical processes driven by high-energy ultraviolet radiation (UVR) in inshore, estuarine, and coastal waters play an important role in global bio geochemical cycles and biological systems. A key to modeling photochemical processes in these optically complex waters is an accurate description of the vertical distribution of UVR in the water column which can be obtained using the diffuse attenuation coefficients of down welling irradiance (Kd()). The Sea UV Sea UVc algorithms (Fichot et al., 2008) can accurately retrieve Kd ( 320, 340, 380,412, 443 and 490 nm) in oceanic and coastal waters using multispectral remote sensing reflectances (Rrs(), Sea WiFS bands). However, SeaUVSeaUVc algorithms are currently not optimized for use in optically complex, inshore waters, where they tend to severely underestimate Kd(). Here, a new training data set of optical properties collected in optically complex, inshore waters was used to re-parameterize the published SeaUVSeaUVc algorithms, resulting in improved Kd() retrievals for turbid, estuarine waters. Although the updated SeaUVSeaUVc algorithms perform best in optically complex waters, the published SeaUVSeaUVc models still perform well in most coastal and oceanic waters. Therefore, we propose a composite set of SeaUVSeaUVc algorithms, optimized for Kd() retrieval in almost all marine systems, ranging from oceanic to inshore waters. The composite algorithm set can retrieve Kd from ocean color with good accuracy across this wide range of water types (e.g., within 13 mean relative error for Kd(340)). A validation step using three independent, in situ data sets indicates that the composite SeaUVSeaUVc can generate accurate Kd values from 320 490 nm using satellite imagery on a global scale. Taking advantage of the inherent benefits of our statistical methods, we pooled the validation data with the training set, obtaining an optimized composite model for estimating Kd() in UV wavelengths for almost all marine waters. This optimized composite set of SeaUVSeaUVc algorithms will provide the optical community with improved ability to quantify the role of solar UV radiation in photochemical and photobiological processes in the ocean.
Determination of the diffusion coefficient of proton in CVD gamma aluminum oxide thin films
George T. Yu; S. K. Yen
2003-01-01
Proton diffusion in aluminum oxide thin films is of significant interest because of its importance in barrier, sensor and catalytic coating applications. In this study, a novel method based on potential-pH response measurement was used to determine proton diffusivity in CVD produced gamma aluminum oxide thin films. This technique based on the model of diffusion-controlled transport at the oxide surface,
Malyarenko, Dariya; Galbán, Craig J.; Londy, Frank J.; Meyer, Charles R.; Johnson, Timothy D.; Rehemtulla, Alnawaz; Ross, Brian D.; Chenevert, Thomas L.
2012-01-01
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
NASA Astrophysics Data System (ADS)
Oderji, Hassan Yousefi; Ding, Hongbin; Behnejad, Hassan
2011-06-01
The second self-diffusion and viscosity virial coefficients of the Lennard-Jones (LJ) fluid were calculated by a detailed evaluation of the velocity and shear-stress autocorrelation functions using equilibrium molecular dynamics simulations at low and moderate densities. Accurate calculation of these coefficients requires corresponding transport coefficient values with low degrees of uncertainty. These were obtained via very long simulations by increasing the number of particles and by using the knowledge of correlation functions in the Green-Kubo method in conjunction with their corresponding generalized Einstein relations. The values of the self-diffusion and shear viscosity coefficients have been evaluated for systems with reduced densities between 0.0005 and 0.05 and reduced temperatures from 0.7 to 30.0. This provides a new insight into the transport coefficients beyond what can be offered by the Rainwater-Friend theory, which has not been developed for the self-diffusion coefficient.
Oderji, Hassan Yousefi; Ding, Hongbin; Behnejad, Hassan
2011-06-01
The second self-diffusion and viscosity virial coefficients of the Lennard-Jones (LJ) fluid were calculated by a detailed evaluation of the velocity and shear-stress autocorrelation functions using equilibrium molecular dynamics simulations at low and moderate densities. Accurate calculation of these coefficients requires corresponding transport coefficient values with low degrees of uncertainty. These were obtained via very long simulations by increasing the number of particles and by using the knowledge of correlation functions in the Green-Kubo method in conjunction with their corresponding generalized Einstein relations. The values of the self-diffusion and shear viscosity coefficients have been evaluated for systems with reduced densities between 0.0005 and 0.05 and reduced temperatures from 0.7 to 30.0. This provides a new insight into the transport coefficients beyond what can be offered by the Rainwater-Friend theory, which has not been developed for the self-diffusion coefficient. PMID:21797351
Use of NMR Imaging to Determine the Diffusion Coefficient of Water in Bio-based Hydrogels
Technology Transfer Automated Retrieval System (TEKTRAN)
The diffusion of liquid in a hydrogel material is a fundamental property which must be controlled in order to create effective delivery systems for the agricultural and pharmaceutical industries. NMR spectroscopy has been used to determine the diffusion of water and deuterium oxide in a bio-based h...
Tarek M. Madkour; Rasha Azzam
The efficiency of polyurethane foams as thermal insulators depends to a great deal on the permeability of various gas molecules through the urethane polymer with higher temperatures enhancing the diffusion of gas molecules through the polymer. In order to increase the efficiency of these insulators, the design of new urethane polymers with low affinity for diffusing gas molecules such as
EFFECT OF GRAIN BOUNDARIES ON DIFFUSION-CONTROLLED PROCESSES IN ALUMINUM OXIDE
A. E. Paladino; R. L. Coble
1963-01-01
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
NASA Astrophysics Data System (ADS)
Agarwal, Neeraj; Sharma, Rashmi; Agarwal, Vijay K.
2006-12-01
The realism of the impact of penetrative solar radiation, an effect we refer to as biological heating, on the upper ocean thermodynamics has been studied using an Ocean General Circulation Model (OGCM). Daily fields of winds, air temperature, specific humidity, net long-wave and shortwave radiation from NCEP were used to force the model. In the control run (cntl-R), diffuse attenuation coefficient (K d) which signifies the visible radiation penetration is parameterized for clear water condition. In the experimental run (exp-R), attenuation coefficient for blue-green wavelength (K d_490) obtained from SeaWiFS sensor was used to determine the penetrative depth of solar radiation. Use of satellite derived K d_490 alters the upper ocean thermodynamics quite significantly. Model simulated parameters sea surface temperature (SST), current and mixed layer depth (MLD) were found to be sensitive to the choice of diffuse attenuation coefficients that limit the penetration of solar radiation into the ocean. The SST cools and MLD deepens in clear water regions (large attenuation depths) due to heat penetration in deeper layers, while the surface gets heated and MLD shoals in regions of high turbidity (low attenuation depths) due to heat trapping.
Giuseppe Ferrara; Monica Bertoldo; Marco Scoponi; Francesco Ciardelli
2001-01-01
The diffusion of a thermal stabiliser, Irganox 1010, has been studied both in a commercially available polypropylene homopolymer (HomoQ) and in a poly(propylene-co-ethylene) copolymer (RacoS). The diffusion experiments were carried out by using the Roe method formed by a stack of several polymer films having 60–70 ?m as thickness under nitrogen atmosphere. The concentration profile of stabiliser in every film
Tsai, Jang-Zern; Peng, Syu-Jyun; Chen, Yu-Wei; Wang, Kuo-Wei; Wu, Hsiao-Kuang; Lin, Yun-Yu; Lee, Ying-Ying; Chen, Chi-Jen; Lin, Huey-Juan; Smith, Eric Edward; Yeh, Poh-Shiow; Hsin, Yue-Loong
2014-01-01
Determination of the volumes of acute cerebral infarct in the magnetic resonance imaging harbors prognostic values. However, semiautomatic method of segmentation is time-consuming and with high interrater variability. Using diffusion weighted imaging and apparent diffusion coefficient map from patients with acute infarction in 10 days, we aimed to develop a fully automatic algorithm to measure infarct volume. It includes an unsupervised classification with fuzzy C-means clustering determination of the histographic distribution, defining self-adjusted intensity thresholds. The proposed method attained high agreement with the semiautomatic method, with similarity index 89.9 ± 6.5%, in detecting cerebral infarct lesions from 22 acute stroke patients. We demonstrated the accuracy of the proposed computer-assisted prompt segmentation method, which appeared promising to replace the laborious, time-consuming, and operator-dependent semiautomatic segmentation. PMID:24738080
Hishida, Yukihiro; Nishi, Minako; Baba, Yukie; Ikeuchi, Haruko
2006-07-01
The diffusion coefficients of C(60) in dichloromethane and benzonitrile solutions containing 0.1 M tetrabutylammonium perchlorate were determined by single potential-step chronoamperometry at small disk electrodes. The diffusion coefficients of C(60) were obtained by curve fitting of the chronoamperograms to a theoretical equation by Shoup and Szabo. The values were (1.4 +/- 0.3) x 10(-9) and (4.1 +/- 0.3) x 10(-10) m(2) s(-1), respectively (the errors are 95% confidence limits). The diffusion coefficients of C(60)(-) in these solutions were measured by double potential-step chronoamperometry. The ratios of the diffusion coefficients of C(60) to those of C(60)(-) were obtained from theoretical curves of the ratios of the current at the second potential step to the current at the first one. The values of the ratios were 1.2 +/- 0.2 and 1.0 +/- 0.3, respectively. PMID:16837741
Combined energy and pitch angle diffusion of pickup ions at Comet Halley
NASA Technical Reports Server (NTRS)
Ye, Gang; Cravens, T. E.
1991-01-01
It is well known that cometary pickup ions, e.g., H2O(+), OH(+), O(+), CO(+), H(+), initially form a ring-beam distribution in the solar wind reference frame, which is highly unstable to the growth of MHD waves (such as ion-cyclotron waves). The low-frequency magnetic fluctuations (or waves), which were observed upstream of Comet Halley, cannot only pitch-angle-scatter the pickup ions so that the distribution becomes at least partially isotropized, but also stochastically accelerate the ions, resulting in the energetic ion populations observed in the vicinity of Comet Halley. Here, numerical solutions of the quasi-linear diffusion equation were used to investigate the cometary ion pickup process at Comet Halley. Both pitch angle and energy diffusion are taken into account. Many quasi-linear models of cometary pickup ions exist which involve one type of diffusion or the other but not both types at once. It is found that the pitch angle scattering occurs faster than the energy diffusion, as expected. Moreover, the results demonstrate that the distribution of accelerated energetic ions is more isotropic than that of ions which have just been picked up. In fact, the ion distribution function on the initial pickup shell is quite anisotropic, even close to the Comet-Halley bow shock.
NASA Astrophysics Data System (ADS)
Suzuki, Takuji; Iida, Simpei; Yamashita, Takashi; Nagashima, Yasuyuki
2015-06-01
We have measured the positron diffusion constants in polycrystalline molybdenum by the observation of positronium negative ions (Ps-). The Ps- ions emitted from the sample surface coated with Na were accelerated. The ?-rays from the accelerated Ps- ions were Doppler- shifted and thus the signals of self-annihilation of the Ps- ions were isolated from those of self-annihilation of para-positronium (p-Ps) or pair-annihilation of positrons in the bulk. Clear and reliable values of the diffusion constants have been obtained.
Effects of ion dynamics on kinetic structures of the diffusion region during magnetic reconnection
NASA Astrophysics Data System (ADS)
Chen, L. J.; Shuster, J. R.; Bessho, N.; Li, G.; Torbert, R. B.; Daughton, W. S.
2014-12-01
Based on results from Particle-in-cell (PIC) simulations, we report how ion dynamics influencethe Hall electric field and electron velocity distributions in the diffusion region of magnetic reconnection.The Hall electric field is due to charge imbalance in the diffusion region. At early times, within a few ion cyclotron oscillations from the peak reconnection,electron orbit dynamics dominate, and the Hall electric field layer assumes the width of the electron current layer.As the pre-existing current sheet ions are accelerated and jetted away, inflowing ions form an ion phase space hole structure.The ion hole structure is self-consistently supported by the Hall electric field. The ion meandering orbit width increasesover the course of about 10 ion cyclotron oscillations from several to approximately 40 electron skin depths (two ion skin depths,where the skin depth is based on the initial current sheet density), and theHall electric field layer widens in the same manner to become much broader than the electron diffusion region.The electron velocity distributions upstream of the electron diffusion region and within the regionof counter streaming ions become fragmented as the ion hole establishes itself.The fragmentation is carried into the electron diffusion region, and through the electron outflow jet, leading to a multitude of arcs in the electron distributions at the end of the jet. The broadening of the Hall electric field layer resolves a longstanding discrepancy concerning whether the narrowest width of the layer is of the electron [Chen et al., 2008] or ion [Mozer et al., 2002] scale. The fragmentation of the electron distributions may be due to an electron-ion instability, and is underinvestigation.
Chun-Li Wong; Allan N. Soriano; Meng-Hui Li
2008-01-01
Here, we presented new experimental data of diffusion coefficients of five [Emim, (1-ethyl-3-methylimidazolium)]-based ionic liquids in water at infinite dilution for temperatures ranging from 303.2 to 323.2K using Taylor dispersion method. The investigated ILs were [Emim][C2N3 (dicyanamide)], [Emim][BF4 (tetrafluoroborate)], [Emim][C2H5SO4 (ethylsulfate)], [Emim][CF3SO3 (trifluoromethanesulfonate)], and [Emim][MDEGSO4 (2-(2-methoxyethoxy) ethylsulfate)]. The molar conductivities of these ionic liquids were also measured and the infinite
Li ion diffusion mechanisms in LiFePO4: an ab initio molecular dynamics study.
Yang, Jianjun; Tse, John S
2011-11-17
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
Skarpalezos, Loukas; Argyrakis, Panos; Vikhrenko, Vyacheslav S
2014-05-01
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. PMID:25353925
Use of the Stokes-Einstein equation to estimate the diffusion coefficient in metallic melts
Eremenko, V.N.; Natanzon, Ya.V.
1987-06-01
The Stokes-Einstein equation is often used to estimate the effective radius of a diffusing particle. The values of the interatomic distances in liquid metals, determined by x-ray diffraction, are evidence that the atomic radii should be assumed as the characteristic dimension of the particles in metallic metals. The effective radius of the diffusing particle as a rule differs from the atomic radius, and this difference is considerably greater than the experimental error. The goal of this paper was to determine the conditions under which the effective radius of the diffusing particle has the least deviation from the atomic radius of the metal under consideration. Determinations were made for Ti, V, Cr, Fe, Co, Ni, Cu, Ga, Zr, Nb, Mo, Ag, In, Sn, Sb, Ta, W, Re, Li, Na, K, Rb, Zn, Cd, and Pb.
NASA Astrophysics Data System (ADS)
Petrishcheva, E.; Abart, R.
2012-04-01
We address mathematical modeling and computer simulations of phase decomposition in a multicomponent system. As opposed to binary alloys with one common diffusion parameter, our main concern is phase decomposition in real geological systems under influence of strongly different interdiffusion coefficients, as it is frequently encountered in mineral solid solutions with coupled diffusion on different sub-lattices. Our goal is to explain deviations from equilibrium element partitioning which are often observed in nature, e.g., in a cooled ternary feldspar. To this end we first adopt the standard Cahn-Hilliard model to the multicomponent diffusion problem and account for arbitrary diffusion coefficients. This is done by using Onsager's approach such that flux of each component results from the combined action of chemical potentials of all components. In a second step the generalized Cahn-Hilliard equation is solved numerically using finite-elements approach. We introduce and investigate several decomposition scenarios that may produce systematic deviations from the equilibrium element partitioning. Both ideal solutions and ternary feldspar are considered. Typically, the slowest component is initially "frozen" and the decomposition effectively takes place only for two "fast" components. At this stage the deviations from the equilibrium element partitioning are indeed observed. These deviations may became "frozen" under conditions of cooling. The final equilibration of the system occurs on a considerably slower time scale. Therefore the system may indeed remain unaccomplished at the observation point. Our approach reveals the intrinsic reasons for the specific phase separation path and rigorously describes it by direct numerical solution of the generalized Cahn-Hilliard equation.
Yu, Yang-Xin; Tian, Ai-Wei; Gao, Guang-Hua
2005-06-21
A new method to predict concentration dependence of collective diffusion coefficient of bovine serum albumin (BSA) in aqueous electrolyte solution is developed based on the generalized Stokes-Einstein equation which relates the diffusion coefficient to the osmotic pressure. The concentration dependence of osmotic pressure is evaluated using the solution of the mean spherical approximation for the two-Yukawa model fluid. The two empirical correlations of sedimentation coefficient are tested in this work. One is for a disordered suspension of hard spheres, and another is for an ordered suspension of hard spheres. The concentration dependence of the collective diffusion coefficient of BSA under different solution conditions, such as pH and ionic strength is predicted. From the comparison between the predicted and experimental values we found that the sedimentation coefficient for the disordered suspension of hard spheres is more suitable for the prediction of the collective diffusion coefficients of charged BSA in aqueous electrolyte solution. The theoretical predictions from the hard-core two-Yukawa model coupled with the sedimentation coefficient for a suspension of hard spheres are in good agreement with available experimental data, while the hard sphere model is unable to describe the behavior of diffusion due to its neglect of the double-layer repulsive charge-charge interaction between BSA molecules. PMID:15962025
Forrey, Christopher; Saylor, David M; Silverstein, Joshua S; Douglas, Jack F; Davis, Eric M; Elabd, Yossef A
2014-10-14
Diffusion of small to medium sized molecules in polymeric medical device materials underlies a broad range of public health concerns related to unintended leaching from or uptake into implantable medical devices. However, obtaining accurate diffusion coefficients for such systems at physiological temperature represents a formidable challenge, both experimentally and computationally. While molecular dynamics simulation has been used to accurately predict the diffusion coefficients, D, of a handful of gases in various polymers, this success has not been extended to molecules larger than gases, e.g., condensable vapours, liquids, and drugs. We present atomistic molecular dynamics simulation predictions of diffusion in a model drug eluting system that represent a dramatic improvement in accuracy compared to previous simulation predictions for comparable systems. We find that, for simulations of insufficient duration, sub-diffusive dynamics can lead to dramatic over-prediction of D. We present useful metrics for monitoring the extent of sub-diffusive dynamics and explore how these metrics correlate to error in D. We also identify a relationship between diffusion and fast dynamics in our system, which may serve as a means to more rapidly predict diffusion in slowly diffusing systems. Our work provides important precedent and essential insights for utilizing atomistic molecular dynamics simulations to predict diffusion coefficients of small to medium sized molecules in condensed soft matter systems. PMID:25115846
NASA Astrophysics Data System (ADS)
Petrov, Yu. V.; Inogamov, N. A.; Migdal, K. P.
2013-03-01
The two-temperature ( T e > T i ) thermal conductivity coefficient ?2 T and electron-ion heat transfer coefficient ?, which are necessary for the quantitative description of the processes initiated by ultrashort laser pulse, have been calculated using a kinetic equation, the matrix element for the scattering probability, and a screened Coulomb potential describing the interaction between charged particles. Quantitative information has been obtained for coefficients ?2 T and ? values for noble and transition metals, where the d-band electrons play a significant role.
Tuula Kaukola; Marja Perhomaa; Leena Vainionpää; Uolevi Tolonen; Jukka Jauhiainen; Eija Pääkkö; Mikko Hallman
2010-01-01
Background: New imaging techniques allow a detailed visualization of the brain and the findings possibly correlate with neurophysiologic measurements and neurosensory and motor outcomes. Postnatal clinical factors known to associate with neurologic disabilities may contribute to brain abnormalities not visible to the naked eye. Objectives: We evaluated whether quantitative measurement of organized water diffusion on MR imaging, apparent diffusion coefficient
Paul W. Reimus; Timothy J. Callahan; S. Doug Ware; Marc J. Haga; Dale A. Counce
2007-01-01
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
M. Aslam Siddiqi; Burak Atakan
2007-01-01
Vapor pressures and sublimation pressures of organometallic (metalorganic) compounds are needed in several processes like chemical vapor deposition (CVD). Thermobalances at ambient pressures are often used to study the evaporation of such compounds. At least three strategies are found in the literature to evaluate the results using different theoretical approaches. In some of the frequently used approaches the diffusion out
Stochastic diffusion of ions due to a finite set of lower hybrid waves
Lucio M. Tozawa; Luiz F. Ziebell
2002-01-01
In this paper we generalize the discussion on stochastic diffusion of energetic ions by lower hybrid waves by considering a case where a set of waves with similar frequencies is present in the system. In the particular case of a finite number of coherent waves, we show that the threshold for stochastic diffusion is reduced in comparison with the threshold
Negative Ion Drift Velocity and Longitudinal Diffusion in Mixtures of Carbon Disulfide and Methane
NASA Technical Reports Server (NTRS)
Dion, Michael P.; Son, S.; Hunter, S. D.; deNolfo, G. A.
2011-01-01
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.
OXYGEN DIFFUSION IN FORSTERITE
K. P. R. Reddy; S. M. Oh; L. D. Major; A. R. Cooper
1980-01-01
Oxygen self-diffusion coefficients for forsteritc single crystals were determined in different orientations by the single-spectrum proton activation technique. In the temperature range 1275ø-1625C chdiffusion coefficients in b direction can be represented by D b = 3.5 x 10 '3 exp ((-89 _ 3 kcal\\/mol)\\/RT) cm2\\/s. Int roduct ion
Werts, Martinus H V; Raimbault, Vincent; Texier-Picard, Rozenn; Poizat, Rémi; Français, Olivier; Griscom, Laurent; Navarro, Julien R G
2012-02-21
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
Ion diffusion mechanisms in the cross-linked poly(ether) doped with LiN(CF 3SO 2) 2
NASA Astrophysics Data System (ADS)
Aihara, Y.; Hayamizu, K.; Sugimoto, K.; Bando, T.; Iguchi, T.; Kuratomi, J.; Ono, T.; Kuwana, K.
The cross-linked poly(ether) electrolytes were prepared by the polymerization of a macro-monomer (tri-acryroyl terminated ethyleneoxide- co-propyleneoxide (EO-PO)) containing LiN(CF 3SO 2) 2 for the three different salt concentrations (O/Li=10/1, 20/1 and 30/1). The self-diffusion coefficients ( D) of the anions ( 19F NMR) measured by the pulsed gradient spin-echo (PGSE) NMR method showed the time dependency. The short-range anion diffusion is faster than the long-range diffusion. The accurate measurement of the diffusion for lithium ( 7Li NMR) was difficult but the lithium diffusion seems slower than that of the anion. The fast hopping motion of lithium ions is correlated to the segment motion of the polymer. The ion conduction is closely related to the anion diffusion in the longer range. The transport number of the lithium ion can also be estimated from the electrochemical measurements.
Albedo and flux extinction coefficient of impure snow for diffuse shortwave radiation
NASA Technical Reports Server (NTRS)
Choudhury, B. J.; Mo, T.; Wang, J. R.; Chang, A. T. C.
1981-01-01
Impurities enter a snowpack as a result of fallout of scavenging by falling snow crystals. Albedo and flux extinction coefficient of soot contaminated snowcovers were studied using a two stream approximation of the radiative transfer equation. The effect of soot was calculated by two methods: independent scattering by ice grains and impurities and average refractive index for ice grains. Both methods predict a qualitatively similar effect of soot; the albedo is decreased and the extinction coefficient is increased compared to that for pure snow in the visible region; the infrared properties are largely unaffected. Quantitatively, however, the effect of soot is more pronounced in the average refractive index method. Soot contamination provides a qualitative explanation for several snow observations.
Diffusion model in ion channel gating. Extension to agonist-activated ion channels.
Oswald, R E; Millhauser, G L; Carter, A A
1991-01-01
Previously, we described a model which treats ion channel gating as a discrete diffusion problem. In the case of agonist-activated channels at high agonist concentration, the model predicts that the closed lifetime probability density function from single channel recording approximates a power law with an exponent of -3/2 (Millhauser, G. L., E. E. Salpeter, and R. E. Oswald. 1988a. Proc. Natl. Acad. Sci. USA. 85: 1503-1507). This prediction is consistent with distributions derived from a number of ligand-gated channels at high agonist concentration (Millhauser, G. L., E. E. Salpeter, and R. E. Oswald. 1988b. Biophys. J. 54: 1165-1168.) but does not describe the behavior of ion channels at low activator concentrations. We examine here an extension of this model to include an agonist binding step. This extended model is consistent with the closed time distributions generated from the BC3H-1 nicotinic acetylcholine receptor for agonist concentrations varying over three orders of magnitude. PMID:1714303
ANALYSIS OF NITRITE IN NO2 DIFFUSION TUBES USING ION CHROMATOGRAPHY
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...
Optimal estimates of the diffusion coefficient of a single Brownian trajectory
Denis Boyer; David S. Dean; Carlos Mejía-Monasterio; Gleb Oshanin
2012-03-22
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.
NASA Astrophysics Data System (ADS)
Wang, Jinyang; Zhong, Haimin; Feng, Huajie; Qiu, Wenda; Chen, Liuping
2014-03-01
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; Qiu, Wenda; Chen, Liuping, E-mail: cesclp@mail.sysu.edu.cn [KLGHEI of Environment and Energy Chemistry, School of Chemistry and Chemical Engineering, Sun Yat-sen University, Guangzhou 510275 (China)] [KLGHEI of Environment and Energy Chemistry, School of Chemistry and Chemical Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Feng, Huajie [School of Chemistry and Chemical Engineering, Hainan Normal University, Haikou 571158 (China)] [School of Chemistry and Chemical Engineering, Hainan Normal University, Haikou 571158 (China)
2014-03-14
The binary infinite dilute diffusion coefficients, D{sub 12}{sup ?}, of some alkylbenzenes (Ph-C{sub n}, from Ph-H to Ph-C{sub 12}) from 313 K to 333 K at 15 MPa in supercritical carbon dioxide (scCO{sub 2}) 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{sub n}/CO{sub 2} fluids are further investigated by calculating radial distribution functions and coordination numbers. It qualitatively convinces that the first solvation shell of Ph-C{sub n} in scCO{sub 2} is significantly influenced by the structure of Ph-C{sub 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{sub n} in scCO{sub 2}. 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{sub n} is the result of internal rotation of C-C single bond (?{sub 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{sub 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{sub n} (n ? 4) in scCO{sub 2} are different.
Takahara, Shuichi; Sumiyama, Naoya; Kittaka, Shigeharu; Yamaguchi, Toshio; Bellissent-Funel, Marie-Claire
2005-06-01
Quasielastic neutron scattering (QENS) spectra of water-filled MCM-41 samples (pore diameters: 21.4 and 28.4 Angstrom) were measured over the temperature range 238-298 K and the momentum transfer range 0.31-0.99 A(-1) to investigate the dynamics of confined water molecules. The spectra, which consist mainly of contributions from the translational diffusion of water molecules, were analyzed by using the Lorentzian and the stretched exponential functions. Comparison of the fits indicated that the latter analysis is more reliable than the former one. The fraction of immobile water molecules located in the vicinity of the pore walls, which give an elastic component, was found to be 0.044-0.061 in both pores. The stretch exponent beta was determined as 0.66-0.80. It was shown that the translational diffusion of water molecules in the pores is decelerated by confinement and that the deceleration becomes marked with a decrease in pore size. The ratios of the translational diffusion coefficient D(T) of confined water to that of bulk water at room temperature were within a range of 0.47-0.63. PMID:16852371
Ion beam mixing and radiation enhanced diffusion in metal\\/ceramic interfaces
K. Neubeck; C.-E. Lefaucheur; H. Hahn; A. G. Balogh; H. Baumann; K. Bethge; D. M. Rück
1995-01-01
Ion beam techniques are frequently used to modify the physical properties of materials. It is the aim of this contribution to obtain information on ion beam effects on irradiated metal\\/ceramic interfaces with bilayer geometry. Ion beam mixing and radiation enhanced diffusion have been investigated in CuAl2O3, AuAl2O3 and AuZrO2 samples. Specimen, with thicknesses of the metallic film in the range
Blackledge, Matthew D; Collins, David J; Tunariu, Nina; Orton, Matthew R; Padhani, Anwar R; Leach, Martin O; Koh, Dow-Mu
2014-01-01
We describe our semi-automatic segmentation of whole-body diffusion-weighted MRI (WBDWI) using a Markov random field (MRF) model to derive tumor total diffusion volume (tDV) and associated global apparent diffusion coefficient (gADC); and demonstrate the feasibility of using these indices for assessing tumor burden and response to treatment in patients with bone metastases. WBDWI was performed on eleven patients diagnosed with bone metastases from breast and prostate cancers before and after anti-cancer therapies. Semi-automatic segmentation incorporating a MRF model was performed in all patients below the C4 vertebra by an experienced radiologist with over eight years of clinical experience in body DWI. Changes in tDV and gADC distributions were compared with overall response determined by all imaging, tumor markers and clinical findings at serial follow up. The segmentation technique was possible in all patients although erroneous volumes of interest were generated in one patient because of poor fat suppression in the pelvis, requiring manual correction. Responding patients showed a larger increase in gADC (median change = +0.18, range = -0.07 to +0.78 × 10(-3) mm2/s) after treatment compared to non-responding patients (median change = -0.02, range = -0.10 to +0.05 × 10(-3) mm2/s, p = 0.05, Mann-Whitney test), whereas non-responding patients showed a significantly larger increase in tDV (median change = +26%, range = +3 to +284%) compared to responding patients (median change = -50%, range = -85 to +27%, p = 0.02, Mann-Whitney test). Semi-automatic segmentation of WBDWI is feasible for metastatic bone disease in this pilot cohort of 11 patients, and could be used to quantify tumor total diffusion volume and median global ADC for assessing response to treatment. PMID:24710083
Blackledge, Matthew D.; Collins, David J.; Tunariu, Nina; Orton, Matthew R.; Padhani, Anwar R.; Leach, Martin O.; Koh, Dow-Mu
2014-01-01
We describe our semi-automatic segmentation of whole-body diffusion-weighted MRI (WBDWI) using a Markov random field (MRF) model to derive tumor total diffusion volume (tDV) and associated global apparent diffusion coefficient (gADC); and demonstrate the feasibility of using these indices for assessing tumor burden and response to treatment in patients with bone metastases. WBDWI was performed on eleven patients diagnosed with bone metastases from breast and prostate cancers before and after anti-cancer therapies. Semi-automatic segmentation incorporating a MRF model was performed in all patients below the C4 vertebra by an experienced radiologist with over eight years of clinical experience in body DWI. Changes in tDV and gADC distributions were compared with overall response determined by all imaging, tumor markers and clinical findings at serial follow up. The segmentation technique was possible in all patients although erroneous volumes of interest were generated in one patient because of poor fat suppression in the pelvis, requiring manual correction. Responding patients showed a larger increase in gADC (median change?=?+0.18, range?=??0.07 to +0.78×10?3 mm2/s) after treatment compared to non-responding patients (median change?=??0.02, range?=??0.10 to +0.05×10?3 mm2/s, p?=?0.05, Mann-Whitney test), whereas non-responding patients showed a significantly larger increase in tDV (median change?=?+26%, range?=?+3 to +284%) compared to responding patients (median change?=??50%, range?=??85 to +27%, p?=?0.02, Mann-Whitney test). Semi-automatic segmentation of WBDWI is feasible for metastatic bone disease in this pilot cohort of 11 patients, and could be used to quantify tumor total diffusion volume and median global ADC for assessing response to treatment. PMID:24710083
Na and Li ion diffusion in modified ASTM C 1260 test by Magnetic Resonance Imaging (MRI)
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
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.
Effective segregation coefficient of Er3+ ions in ErF3-doped CaF2 crystals
NASA Astrophysics Data System (ADS)
Munteanu, M.; Stef, M.; Bunoiu, O.; Nicoara, I.
2010-03-01
ErF3-doped CaF2 crystals were grown using the vertical Bridgman method. The optical absorption spectra reveal the characteristic peaks of the Er3+ ions. The dopant distribution along two crystals has been investigated using the optical absorption method. The effective segregation coefficient of the Er3+ ions has been calculated using the classical Scheil relationship between the impurity concentration and the crystal growth conditions. The effective segregation coefficient of the Er3+ions in the CaF2 host depends slightly on the doping concentration, and varies between 0.99 and 1.03, for 0.8 mol % ErF3 and 2 mol % ErF3-doped CaF2 crystals, respectively.
NASA Astrophysics Data System (ADS)
Fahr, H. J.; Fichtner, H.
2011-09-01
Context. The phase space transport of pick-up ions (PUIs) in the heliosphere has been studied for the cases that these particles are experiencing a second-order Fermi process, i.e. velocity diffusion, a convection with the solar wind, and adiabatic or "magnetic" cooling, i.e. cooling connected with the conservation of the magnetic moment. Aims: The study aims at a quantification of the process of "magnetic cooling" that has recently been introduced as a modification of adiabatic cooling in the presence of frozen-in magnetic fields. Methods: The isotropic PUI velocity distributions are obtained as numerical solutions of a Fokker-Planck phase space transport equation. Results: It is demonstrated that this newly discussed process is, like adiabatic energy changes, not limited to cooling but can also, depending on the shape of the distribution function, result in heating. For pure cooling with negligible velocity diffusion a v-5 velocity power law is found for magnetic cooling, thus confirming earlier analytical results. For non-negligible second-order Fermi acceleration, the tails of the distribution functions exhibit different shapes, which in special cases are also close to the prominent v-5 behaviour, which is often found in observations. Conclusions: The existence of an exact v-5 power law of PUI distribution functions can be confirmed for insignificant velocity diffusion and its approximate validity for specific choices of the velocity dependence of the diffusion coefficient.
Kinetics Tuning of Li-Ion Diffusion in Layered Li(NixMnyCoz)O2.
Wei, Yi; Zheng, Jiaxin; Cui, Suihan; Song, Xiaohe; Su, Yantao; Deng, Wenjun; Wu, Zhongzhen; Wang, Xinwei; Wang, Weidong; Rao, Mumin; Lin, Yuan; Wang, Chongmin; Amine, Khalil; Pan, Feng
2015-07-01
Using ab initio calculations combined with experiments, we clarified how the kinetics of Li-ion diffusion can be tuned in LiNixMnyCozO2 (NMC, x + y + z = 1) materials. It is found that Li-ions tend to choose oxygen dumbbell hopping (ODH) at the early stage of charging (delithiation), and tetrahedral site hopping (TSH) begins to dominate when more than 1/3 Li-ions are extracted. In both ODH and TSH, the Li-ions surrounded by nickel (especially with low valence state) are more likely to diffuse with low activation energy and form an advantageous path. The Li slab space, which also contributes to the effective diffusion barriers, is found to be closely associated with the delithiation process (Ni oxidation) and the contents of Ni, Co, and Mn. PMID:26098282
2010-01-01
Background The goal of physiologically based pharmacokinetics (PBPK) is to predict drug kinetics from an understanding of the organ/blood exchange. The standard approach is to assume that the organ is "flow limited" which means that the venous blood leaving the organ equilibrates with the well-stirred tissue compartment. Although this assumption is valid for most solutes, it has been shown to be incorrect for several very highly fat soluble compounds which appear to be "diffusion limited". This paper describes the physical basis of this adipose diffusion limitation and its quantitative dependence on the blood/water (Kbld-wat) and octanol/water (Kow) partition coefficient. Methods Experimental measurements of the time dependent rat blood and adipose concentration following either intravenous or oral input were used to estimate the "apparent" adipose perfusion rate (FA) assuming that the tissue is flow limited. It is shown that the ratio of FA to the anatomic perfusion rate (F) provides a measure of the diffusion limitation. A quantitative relationship between this diffusion limitation and Kbld-wat and Kow is derived. This analysis was applied to previously published data, including the Oberg et. al. measurements of the rat plasma and adipose tissue concentration following an oral dose of a mixture of 13 different polychlorinated biphenyls. Results Solutes become diffusion limited at values of log Kow greater than about 5.6, with the adipose-blood exchange rate reduced by a factor of about 30 for a solute with a log Kow of 7.36. Quantitatively, a plot of FA/F versus Kow is well described assuming an adipose permeability-surface area product (PS) of 750/min. This PS corresponds to a 0.14 micron aqueous layer separating the well-stirred blood from the adipose lipid. This is approximately equal to the thickness of the rat adipose capillary endothelium. Conclusions These results can be used to quantitate the adipose-blood diffusion limitation as a function of Kow. This is especially important for the highly fat soluble persistent organic chemicals (e.g. polychlorinated biphenyls, dioxins) whose pharmacokinetics are primarily determined by the adipose-blood exchange kinetics. PMID:20055995
Particle Diffusion in Dust Grains
NASA Astrophysics Data System (ADS)
Pavlu, Jiri; Richterova, Ivana; Nemecek, Zdenek; Safrankova, Jana; Pechal, Radim
Energetic ions/neutrals interacting with dust grains are implanted into dust grains and, consequently, the density gradient induces their diffusion back towards the grain surface. The diffusion coefficient strongly depends on temperature, thus, neutrals can be transported over large distances or across boundaries. In our laboratory experiment, measurements of the diffusion coefficient of the particles implanted into the dust grain are carried out in an electrodynamic quadrupole trap. The experimental setup is not capable of an assessment of the dust grain temperature, however, the temperature can be modified via a change of the ambient radiation. We present measurements of diffusion coefficients and discuss several implications for the space dust.
Mg in plagioclase: Experimental calibration of a new geothermometer and diffusion coefficients
NASA Astrophysics Data System (ADS)
Faak, Kathrin; Chakraborty, Sumit; Coogan, Laurence A.
2013-12-01
The temperature-sensitive exchange of Mg between plagioclase (Pl) and clinopyroxene (Cpx) has been studied experimentally, accounting for different anorthite-contents in plagioclase (XAn) and various silica activities (aSiO2) in the system. The partitioning of Mg between plagioclase and clinopyroxene was determined over a temperature range of 1100-1200 °C, using plagioclase single crystals of different compositions (XAn = 0.5-0.8), surrounded by different clinopyroxene-bearing matrix powders to account for different silica activities from 0.55 to 1.0. The experimental design also allows the diffusivity (DMgPl) of Mg in plagioclase under these conditions to be determined. Both KMgPl/Cpx (defined as KMgPl/Cpx=CMgPl/CMgCpx) and DMgPl decrease with temperature and increase with aSiO2. Isothermal data for different XAn in plagioclase show a linear increase of ln KMgPl/Cpx with increasing XAn, but DMgPl appears to be insensitive to XAn. The partitioning data allow a new geothermometer to be calibrated, which may be widely applicable to terrestrial and extraterrestrial rocks where plagioclase and clinopyroxene coexist: T[K]=(-9219+2034XAn)/(ln KMgPl/Cpx-1.6-ln aSiO2). Application of this geothermometer to experimental data from this study reproduces the experimental temperatures within ±20 °C. Diffusion of Mg in plagioclase is described by DMgPl[m s]=1.25×10-4[ms]·exp(-320,924[J mol]/(RT))·(.
Oxygen diffusion and oxide phase formation in iron under swift heavy ion irradiation
Roller, Tobias; Bolse, Wolfgang [Institut fuer Strahlenphysik, Universitaet Stuttgart, Allmandring 3, 70569 Stuttgart (Germany)
2007-02-01
While irradiating thin iron films deposited on silicon wafers with swift heavy ions in the energy range of a few MeV/amu, we have observed that the iron surface oxidizes due to the residual oxygen in the irradiation chamber, induced by the energy deposition by the ion. We have investigated these processes in detail using Rutherford backscattering spectrometry and conversion electron Moessbauer spectroscopy. We found that two different types of oxidation processes were active, depending on the electronic energy loss of the incident ions. Irradiations above the track formation threshold S{sub ec}{sup Fe} of iron resulted in diffusion-controlled dissolution of oxygen in the iron bulk. Below S{sub ec}{sup Fe}, but above the track formation threshold of iron oxide, chemical reaction and homogeneous oxide phase formation took place in a surface layer, while almost no oxygen diffusion into the iron bulk could be observed anymore. These phenomena are discussed in terms of the oxygen mobility in the excited ion tracks in iron and iron oxide. The effective diffusion constant estimated for swift heavy ion induced oxygen diffusion in iron is larger by a factor of 100-1000 than the one reported for thermally activated oxygen diffusion in molten iron.
?uczy?ska, El?bieta; Heinze-Paluchowska, Sylwia; Domalik, Agnieszka; ?wierz, Anna; Kasperkiewicz, Hanna; Blecharz, Pawe?; Jereczek-Fossa, Barbara
2014-01-01
Summary Background The aim of this study was to investigate the utility of diffusion weighted imaging (DWI) using Apparent Diffusion Coefficient (ADC) values in discriminating between patients with tumors and normal prostate tissue before the initial systematic core biopsy. The relationship between histological grade of prostate cancer and ADC values in the peripheral zone was also investigated. Material/Methods Our study included 62 patients who underwent magnetic resonance imaging (MRI) of the pelvis. The examinations were performed in T1-, T2-weighted, DWI and T1 after dynamic contrast administration sequences. In all patients there were abnormal foci within the peripheral zone determined in DWI/ADC. ADC values were compared with the Gleason score (GS) after core needle biopsy (CNB) in patients with low, medium and high stage tumors. Results Within the examined group of patients, ADC was statistically higher for normal tissue than for cancerous tissue (p=0.00). Mean ADC values for patients with low, intermediate and high GS were 0.85±0.03, 0.72±0.03, and 0.61±0.04, respectively. Conclusions DWI/ADC is useful in differentiating high-risk patients from those at low and intermediate risk, since there is a significant correlation between ADC values determined in patients included in three different groups according to their Gleason score. This information may be helpful in the assessment of prostate cancer aggressiveness. PMID:25484999
Nazarlou, Ali Kiani; Abdolmohammadi, Jamil
2015-01-01
Background: Diffusion-weighted magnetic resonance imaging (DWI) systems are very effective in detecting strokes, and they also have shown significant promise in the detection of fibrosis and cirrhosis of the liver. However, such systems have the disadvantages of poor reproducibility and noise, which can diminish the accuracy of the apparent diffusion coefficients (ADCs) provided by the DWI process. The main aim of this study was to determine the relationship between the age and gender of healthy adults in terms of the ADC values of the spleen measured by DWI. Methods: Sixty-nine subjects selected for this study from people who were referred to the Tabesh Medical Imaging Center in Tabriz, Iran, in 2013. Each subject underwent echo-planar DWI for her or his ADC values of the spleen with b-values of 50, 400, and 800 s/mm2, and the resulting ADC values were evaluated. Results: No significant differences were observed in ADC values of the spleen among the female and male participants or those from various ages (P>0.05). Conclusions: Based on the findings of this study, it was concluded that the effect of age and gender on the spleen’s ADC values can be omitted from the spleen-diagnosis procedure. In other words, the spleen’s ADC values are not related to the age or the gender of healthy adults.
NASA Astrophysics Data System (ADS)
Bekstein, A.; Benhenni, M.; Yousfi, M.
2011-01-01
The ion swarm transport coefficients such as reduced mobility, diffusion coefficients and reaction rates of three water vapour ion clusters (H2O) n H+ (with n = 1, 2 and 3) in N2 and O2 have been determined from a Monte Carlo simulation using calculated and measured elastic and inelastic collision cross sections. The elastic momentum transfer cross sections have been determined from a semi-classical JWKB approximation based on a rigid core interaction potential model. The inelastic cross sections have been deduced from the measured ones in the case of similar ion cluster. Then, the cross sections sets are fitted using either the measured reduced mobility at low electric field in the case of (H2O) n H+ in N2 or the zero-field mobility calculated from the Satoh's relation and the measured ones in N2. From the sets of elastic and inelastic collision cross sections thus obtained in pure N2 and O2, the ion transport and reaction coefficients for (H2O) n H+ are then calculated in dry air and also extended over a wide range of reduced electric field in N2 and O2. These ion data are very useful for modelling and simulation of non-equilibrium electrical discharges more particularly in humid gases at atmospheric pressure.
Morelli, John N.; Michaely, Henrik J.; Meyer, Mathias M.; Rustemeyer, Thassilo; Schoenberg, Stefan O.; Attenberger, Ulrike I.
2013-01-01
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
Nogueira, Luísa; Brandão, Sofia; Matos, Eduarda; Nunes, Rita Gouveia; Ferreira, Hugo Alexandre; Loureiro, Joana; Ramos, Isabel
2015-01-01
PURPOSE We aimed to compare two different methods of region of interest (ROI) demarcation and determine interobserver variability on apparent diffusion coefficient (ADC) in breast lesions. METHODS Thirty-two patients with 39 lesions were evaluated with a 3.0 Tesla scanner using a diffusion-weighted sequence with several b-values. Two observers independently performed the ADC measurements using: 1) a small fixed area of 10 mm2 ROI within the area with highest restriction; 2) a large ROI so as to include the whole lesion. Differences were assessed using the Wilcoxon-rank test. Bland-Altman method and Spearman coefficient were applied for interobserver variability and correlation analysis. RESULTS ADC values measured using the two ROI demarcation methods were significantly different for both observers (P = 0.026; P = 0.033). There was no interobserver variability in ADC values using either method (large ROI, P = 0.21; small ROI, P = 0.64). ADC values of malignant lesions were significantly different between the two methods (P < 0.001). Variability in ADC was ?0.008×10?3 mm2/s for both methods. When using the same method, ADC values were significantly correlated between the observers (small ROI: r=0.990, P < 0.001; large ROI: r=0.985, P < 0.001). CONCLUSION The choice of ROI demarcation method influences ADC measurements. Small ROIs show less overlap in ADC values and higher ADC reproducibility, suggesting that this method may improve lesion discrimination. Interobserver variability was low for both methods. PMID:25698095
Rohr, Uwe D; Saeger-Lorenz, Katrin
2002-03-01
The pharmacokinetic performance of a matrix system for transdermal beta-estradiol (E(2)) delivery after multiple consecutive dosing in postmenopausal women undergoing hormone replacement therapy was investigated. The E(2) plasma profiles determined during the third application in 16 postmenopausal women were compared with results obtained in a published clinical study using the same patch in 24 postmenopausal women without E(2) pretreatment; they were compared with a theoretical diffusion/pharmacokinetic model. A conventional theoretical model with constant model parameter (CPM) obtained from in vitro mass balance experiments in a Franz cell type set up described successfully the transdermal E(2) bioavailability parameter AUC(0-96h) (4341.9 +/- 1513.1; calculated 4250.8) and C(average) (45.0 +/- 13.2; calculated 41.2). Also, experimentally, there was no significant drop in E(2) plasma values after patch removal and reapplication; this was corroborated by calculations. Accumulation of E(2) did not occur when several patches were applied consecutively over a period of 3 weeks. Steady state was achieved following application of the first patch. However, the differences between recorded E(2) plasma profiles and theoretical results detected at specific measurement points cannot be explained by the CPM model. Experimentally obtained plasma profiles were always lower in the morning and higher in the evening than predicted on the basis of the model. Measurements of in vivo skin temperature in the postmenopausal women showed oscillating temperature profiles in the form of a cosinor function: The temperature mesor of untreated postmenopausal women was 34.8 degrees C with an acrophase at 17.0 o'clock (95% CI: 14.30-19.30) and an amplitude of +/- 0.4 degrees C (p = 0.1). During the application of the patch the average temperature next to a patch rose 0.3 degrees C, which was statistically significant (p = 0.1). In the skin under the application of the matrix patch a mesor temperature was detected as 35.6 degrees C with an amplitude of +/- 0.5 degrees C with an acrophase at 17.51 o'clock (95% CI: 14.30-21.00) (p = 0.05). The temperature period was 24 h for all measurements and the maximum temperature was observed at about 16.30 h, and a minimum at about 5.00 h. A linear dependency was detected in in vitro experiments between the log of E(2) permeability and the temperature for stripped skin, epidermis/dermis layer, as well as for the matrix. Modeling of E(2) plasma profiles with oscillating diffusion coefficients (ODM1) with a sine wave function results in this equation: D(1) = D(0x) + Da(x).sin(k.t). D(0x) is the diffusion coefficient determined at 35.6 degrees C, k is 1/24 h, D(a) is the diffusion coefficient of the temperature amplitude, h is hour, and x stands for the respective diffusion layer. It was shown that the experimental E(2) plasma profile variations are more pronounced than can simply be explained by skin temperature variations alone (ODM1 model). A simplex fit with an oscillating diffusion coefficient in the form of a sine wave function for the stratum corneum (ODM2 model) resulted in a temperature amplitude of 1.1 degrees C, about twice as high as was determined in the in vivo measurements (ODM2 model). Therefore, other circadian parameterlike blood flow might superimpose the temperature profile. The improvement in data analysis by incorporating oscillating diffusion coefficients (ODM1 and 2) over CPM was judged from a comparison of experimental data with the calculated plasma profiles with the AIC, Akaikes model selection criterion, which allows ranking between models because it is independent of the scaling of the data points. ODM1 and ODM2 improved the data analysis over CPM by allowing better calculation of experimental C(max), t(max), the time to reach to C(max), and the fluctuation, f. No difference between CPM, ODM1, or ODM2 was found for the bioavailability parameter C(average) and AUC(0-96h). PMID:11920768
Moteki, T; Ishizaka, H; Horikoshi, H; Matsumoto, M
1995-01-01
Serial turboFLASH (fast low-angle shot) images with and without diffusion-perfusion (DP) gradients were used for the evaluation of and differentiation between hemangiomas and hepatocellular carcinomas (HCCs) of the liver. Twenty-six patients with 27 hemangiomas, and 19 patients with 21 HCCs were studied. T1- and T2-weighted spin-echo images, serial turboFLASH images with and without DP gradients (b = 294.8 and 0 sec/mm2, respectively) were obtained, and the apparent diffusion coefficient (ADC) was calculated for all lesions. Hemangiomas were detected as well-defined areas of decreased signal intensity on turboFLASH images obtained with DP gradients; HCCs showed slight or no obvious decrease in signal intensity on serial turboFLASH images obtained with DP gradients compared with turboFLASH images obtained without DP gradients, while a considerable percentage (76.5%) of nodular HCCs showed an obvious decrease in signal intensity at the margins. Hemangiomas had large ADC values compared with HCCs. Both ADC and T2 values were significantly different between hemangiomas and HCCs (P < .01). However, there was no obvious correlation between ADC and T2 values for either hemangiomas or HCCs (r = .18 and .48, respectively). On the basis of these results, the calculated ADC should be helpful for distinguishing hemangiomas from HCCs, and the ADC values may be useful even when T2 values are not helpful for making the distinction. PMID:7766981
Zhang, Yuan; Liu, Xu; Zhang, Yun; Li, Wen-Fei; Chen, Lei; Mao, Yan-Ping; Shen, Jing-Xian; Zhang, Fan; Peng, Hao; Liu, Qing; Sun, Ying; Ma, Jun
2015-01-01
The prognostic value of the primary lesion pretreatment apparent diffusion coefficient (ADC), which is obtained by diffusion-weighted magnetic resonance imaging (MR-DWI), remains unknown in nasopharyngeal carcinoma (NPC). Thus, to investigate whether the pretreatment ADC value as measured from the primary site on MR-DWI is an independent prognostic factor in NPC, we retrospectively reviewed a cohort of 541 patients with histologically-proven stage I-IVB NPC. All patients underwent MRI using a 3-Tesla system (Trio Tim; Siemens, Erlangen Germany). To calculate ADC, the primary lesion was designated on the ADC map at the level of the largest tumor diameter to cover most of the lesion, avoiding cystic or necrotic components. Median and mean (±SD) pretreatment ADC were 0.713 and 0.716?±?0.079?×?10(-3)?mm(2)/s, respectively. Univariate and multivariate analysis confirmed high pretreatment ADC was a good prognostic factor for poor local relapse-free survival and disease-free survival. Furthermore, the area under the ROC curve for prediction of local failure significantly increased when pretreatment ADC was combined with T classification (P?=?0.004). Thus, pretreatment ADC might provide useful information for predicting outcome and selecting high-risk patients appropriate for more aggressive therapy. Further studies are warranted to investigate the biological basis of this observation. PMID:26184509
Zhang, Yuan; Liu, Xu; Zhang, Yun; Li, Wen-Fei; Chen, Lei; Mao, Yan-Ping; Shen, Jing-Xian; Zhang, Fan; Peng, Hao; Liu, Qing; Sun, Ying; Ma, Jun
2015-01-01
The prognostic value of the primary lesion pretreatment apparent diffusion coefficient (ADC), which is obtained by diffusion-weighted magnetic resonance imaging (MR-DWI), remains unknown in nasopharyngeal carcinoma (NPC). Thus, to investigate whether the pretreatment ADC value as measured from the primary site on MR-DWI is an independent prognostic factor in NPC, we retrospectively reviewed a cohort of 541 patients with histologically-proven stage I-IVB NPC. All patients underwent MRI using a 3-Tesla system (Trio Tim; Siemens, Erlangen Germany). To calculate ADC, the primary lesion was designated on the ADC map at the level of the largest tumor diameter to cover most of the lesion, avoiding cystic or necrotic components. Median and mean (±SD) pretreatment ADC were 0.713 and 0.716?±?0.079?×?10?3?mm2/s, respectively. Univariate and multivariate analysis confirmed high pretreatment ADC was a good prognostic factor for poor local relapse-free survival and disease-free survival. Furthermore, the area under the ROC curve for prediction of local failure significantly increased when pretreatment ADC was combined with T classification (P?=?0.004). Thus, pretreatment ADC might provide useful information for predicting outcome and selecting high-risk patients appropriate for more aggressive therapy. Further studies are warranted to investigate the biological basis of this observation. PMID:26184509
Er, Hale Çolako?lu; Erden, Ay?e; Özlem Küçük, N.; Geçim, Ethem
2014-01-01
PURPOSE The aim of this study was to retrospectively assess the correlation between minimum apparent diffusion coefficient (ADCmin) values obtained from diffusion-weighted magnetic resonance imaging (MRI) and maximum standardized uptake values (SUVmax) obtained from positron emission tomography-computed tomography (PET-CT) in rectal cancer. MATERIALS AND METHODS Forty-one patients with pathologically confirmed rectal adenocarcinoma were included in this study. For preoperative staging, PET-CT and pelvic MRI with diffusion-weighted imaging were performed within one week (mean time interval, 3±1 day). For ADC measurements, the region of interest (ROI) was manually drawn along the border of each hyperintense tumor on b=1000 s/mm2 images. After repeating this procedure on each consecutive tumor-containing slice to cover the entire tumoral area, ROIs were copied to ADC maps. ADCmin was determined as the lowest ADC value among all ROIs in each tumor. For SUVmax measurements, whole-body images were assessed visually on transaxial, sagittal, and coronal images. ROIs were determined from the lesions observed on each slice, and SUVmax values were calculated automatically. The mean values of ADCmin and SUVmax were compared using Spearman’s test. RESULTS The mean ADCmin was 0.62±0.19×10?3 mm2/s (range, 0.368–1.227×10?3 mm2/s), the mean SUVmax was 20.07±9.3 (range, 4.3–49.5). A significant negative correlation was found between ADCmin and SUVmax (r=?0.347; P = 0.026). CONCLUSION There was a significant negative correlation between the ADCmin and SUVmax values in rectal adenocarcinomas. PMID:24100063
Göya, Cemil; Hamidi, Cihad; Bozkurt, Ya?ar; Yavuz, Alpaslan; Kuday, Suzan; Gümü?, Hatice; Türkçü, Gül; Hattapo?lu, Salih; Bilici, Aslan
2015-01-01
Background: Diffusion-weighted magnetic resonance imaging (DWI) is a widely-accepted diagnostic modality whose efficacy has been investigated by numerous past studies in the differentiation of malignant lesions from benign entities. Aims: The aim of this study was to evaluate the efficiency of diffusion-weighted magnetic resonance imaging in the characterization of renal lesions. Study Design: Diagnostic accuracy study. Methods: A total of 137 patients with renal lesions were included in this study. The median apparent diffusion coefficient (ADC) values as well as the b 800 and b 1600 signal intensities of normal kidneys, solid components of mixed renal masses, and total cystic lesions were evaluated. Results: There were significant differences between the ADC values of lesions and normal renal parenchyma, and between the ADC values of benign and malignant renal lesions on DWIs at b values of 800 and 1600 s/mm2 (p<0.001 and p<0.001, respectively). There were significant differences between the ADC values of Bosniak Category 1 and 2 cysts and the ADC values of Bosniak Category 1 and 3 cysts on DWIs at b values of 800 s/mm2 (p<0.001) and 1600 s/mm2 (p<0.001). A cutoff value of 1.902 × 10?3 mm2/s for the ADC with a b value of 800 s/mm2 provided 88% sensitivity and 96% specificity for differentiation between benign and malignant renal lesions. A cutoff value of 1.623 × 10?3 mm2/s for the ADC with a b value of 1600 s/mm2 provided 79% sensitivity and 96% specificity (p<0.001) for the differentiation between benign and malignant renal lesions. Conclusion: Accurate assessment of renal masses is important for determining the necessity for surgical intervention. DWI provides additional value by differentiating benign from malignant renal tumors and can be added to routine kidney MRI protocols. PMID:26185715
Distribution coefficient of Pr3+ ions in crystals of solid solutions LiF-LuF3-YF3-PrF3
NASA Astrophysics Data System (ADS)
Shavelev, A. A.; Nizamutdinov, A. S.; Semashko, V. V.; Korableva, S. L.; Gorieva, V. G.
2014-11-01
Aim of this work was to investigate the possibility of increasing the distribution coefficient of Pr3+ ions in fluoride crystals with scheelite structure. As a result of investigations by XRF and optical absorption spectroscopy the absorption cross section for 3H0 ? 3P0 transitions Pr3+ ions was clarified and segregation coefficient of Pr3+ ions in LiY0,3Lu0,7F4 mixed crystals was estimated.
Diffusion or bounce back in relativistic heavy-ion collisions?
Georg Wolschin; Minoru Biyajima; Takuya Mizoguchi
2008-03-12
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.
First-principles binary diffusion coefficients for H, H{sub 2}, and four normal alkanes + N{sub 2}
Jasper, Ahren W., E-mail: ajasper@sandia.gov; Kamarchik, Eugene [Combustion Research Facility, Sandia National Laboratories, Livermore, California 94551 (United States); Miller, James A.; Klippenstein, Stephen J. [Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)
2014-09-28
Collision integrals related to binary (dilute gas) diffusion are calculated classically for six species colliding with N{sub 2}. 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 + N{sub 2} and H{sub 2} + N{sub 2} and with recent experimental results for C{sub n}H{sub 2n+2} + N{sub 2}, 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{sup ?12} repulsive interactions. The effect of anisotropy is found to be negligible for H + N{sub 2} and H{sub 2} + N{sub 2} (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 + N{sub 2} by 15% at 300 K. The neglect of inelasticity, in contrast, introduces only very small errors. Approximating the repulsive wall as an unphysical R{sup ?12} interaction is a significant source of error at all temperatures for the weakly interacting systems H + N{sub 2} and H{sub 2} + N{sub 2}, with errors as large as 40%. For the normal alkanes in N{sub 2}, 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 + N{sub 2}. 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 + N{sub 2} is presented and is estimated to have a 2-sigma error bar of only 0.7%.
NASA Astrophysics Data System (ADS)
Fang, Tilden T.; Fang, Wingra T. C.; Griffin, Peter B.; Plummer, James D.
1996-02-01
Investigation of boron diffusion in strained silicon germanium buried layers reveals a fractional interstitial component of boron diffusion (fBI) in Se0.8Ge0.2 approximately equal to the fBI value in silicon. In conjunction with computer-simulated boron profiles, the results yield an absolute lower-bound of fBI in Si0.8Ge0.2 of ˜0.8. In addition, the experimental methodology provides a unique vehicle for measuring the segregation coefficient; oxidation-enhanced diffusion is used instead of an extended, inert anneal to rapidly diffuse the dopant to equilibrium levels across the interface, allowing the segregation coefficient to be measured more quickly.
D. Boulanger; R. Parrot
1987-01-01
A molecular orbital model has been elaborated to determine the orbit–lattice coupling coefficients to strains of symmetry E of the orbital triplet states of d5 ions in tetrahedral symmetry. The wave functions and energies of the monoelectronic molecular orbitals have been determined for a tetrahedral molecule MnX4 in a crystal and for a slightly distorted molecule of symmetry D2d corresponding
Consuelo Pizarro; Octavio Suárez-Iglesias; Ignacio Medina; Julio L. Bueno
2009-01-01
The measurement and correlation of the experimental binary diffusion coefficients of 2,3-dimethylaniline, 2,6-dimethylaniline, 2-methylanisole, 4-methylanisole and 3-nitrotoluene in supercritical carbon dioxide is reported. Results were obtained using the Taylor-Aris dispersion technique, at 313, 323, and 333K, and in a pressure range from 15.0 to 35.0MPa. The diffusivity experimental data were correlated with temperature, pressure and carbon dioxide density and viscosity.
Simulations of Li ion diffusion in the electrolyte material -- Li3PO4
N. A. W. Holzwarth
2007-01-01
Solid-state lithium ion electrolytes are becoming increasingly important in batteries and in related technologies. We have used first-principles modeling techniques based on density functional theory and the nudged elastic band method to examine possible Li ion diffusion mechanisms in terms of their migration energies Em. Simulations were performed in idealized crystals of the electrolyte material Li3PO4, considering both vacancy and
Rundle-Thiele, Dayle; Day, Bryan; Stringer, Brett; Fay, Michael; Martin, Jennifer; Jeffree, Rosalind L; Thomas, Paul; Bell, Christopher; Salvado, Olivier; Gal, Yaniv; Coulthard, Alan; Crozier, Stuart; Rose, Stephen
2015-01-01
Introduction Accurate knowledge of O6-methylguanine methyltransferase (MGMT) gene promoter subtype in patients with glioblastoma (GBM) is important for treatment. However, this test is not always available. Pre-operative diffusion MRI (dMRI) can be used to probe tumour biology using the apparent diffusion coefficient (ADC); however, its ability to act as a surrogate to predict MGMT status has shown mixed results. We investigated whether this was due to variations in the method used to analyse ADC. Methods We undertook a retrospective study of 32 patients with GBM who had MGMT status measured. Matching pre-operative MRI data were used to calculate the ADC within contrast enhancing regions of tumour. The relationship between ADC and MGMT was examined using two published ADC methods. Results A strong trend between a measure of ‘minimum ADC’ and methylation status was seen. An elevated minimum ADC was more likely in the methylated compared to the unmethylated MGMT group (U = 56, P = 0.0561). In contrast, utilising a two-mixture model histogram approach, a significant reduction in mean measure of the ‘low ADC’ component within the histogram was associated with an MGMT promoter methylation subtype (P < 0.0246). Conclusion This study shows that within the same patient cohort, the method selected to analyse ADC measures has a significant bearing on the use of that metric as a surrogate marker of MGMT status. Thus for dMRI data to be clinically useful, consistent methods of data analysis need to be established prior to establishing any relationship with genetic or epigenetic profiling.
Rahman, Rifaquat; Hamdan, Alhafidz; Zweifler, Rebecca; Jiang, Han; Norden, Andrew D; Reardon, David A; Mukundan, Srinivasan; Wen, Patrick Y; Huang, Raymond Y
2014-08-01
While patients with recurrent glioblastoma receiving anti-angiogenic therapy demonstrate significant response rates, the benefit on patient survival is less clear. We assessed whether histogram analysis of diffusion weighted MRI can stratify for progression-free and overall survival. Baseline and 3-6 week post-treatment MRI exams of 91 patients with recurrent glioblastoma treated with bevacizumab were retrospectively evaluated. Histograms of apparent diffusion coefficient (ADC) within the volume of contrast enhancing and nonenhancing T2/FLAIR lesions were analyzed using curve-fit analysis. Overall survival (OS) and progression-free survival (PFS) were assessed using ADC parameters in a Cox proportional hazards model adjusted for clinical variables. Baseline ADC(L)/ADC(M) within nonenhancing T2/FLAIR volume (> or ?0.64) can stratify OS (HR = 2.24, p = 0.002) and PFS (HR = 1.90, p = 0.005). %ADC(H) within enhancing T1+C volume (> or ?25 %) can also stratify OS (HR = 0.59, p = 0.034) and PFS (HR = 0.56, p = 0.01). Stratification of patient survival can be improved by merging these two ADC parameters into a single combined ADC factor (HR = 0.17, p < 0.0001). The median OS ratio of patient groups stratified by this combined factor was 2.03, larger than median OS ratio when stratifying by either %ADC(H) within T1+C volume alone (1.3) or ADC(L)/ADC(M) within T2/FLAIR alone (1.86). ADC histogram analysis within both enhancing and nonenhancing components of tumor can be used to stratify for PFS and OS in patients with recurrent glioblastoma. PMID:24805151
P. G. Wahlbeck; D. L. Myers; V. V. Truong
1985-01-01
The Ruff–MKW boiling point method is used to determine equilibrium vapor pressures greater than 660 Pa (5 Torr). Samples are vaporized from a Ruff cell, which has a capillary exit, in the presence of an inert gas. Viscosity coefficients and gaseous interdiffusion coefficients may be determined also. This is a second study of the method using Cd(l) and Zn(l) as
Chang Yi Kong; Toshitaka Funazukuri; Seiichiro Kagei
2004-01-01
The theoretical basis of a Gaussian-like approximate solution was applied to a chromatographic impulse response technique with curve fitting for measuring binary diffusion coefficients and retention factors using a polymer-coated capillary column. The formulae were derived for evaluating both the accuracy of the approximate solution and the sensitivity of the parameters. The validity of the solution also was confirmed experimentally
J. L. Bueno; J. J. Suárez; I. Medina
2001-01-01
Experimental data for diffusion coefficients obtained by supercritical fluid chromatography (SFC) according to the Taylor–Aris dispersion method are compared with results from predictive equations for dense fluids. The goodness of fit and the bias of the correlation only suggest a slight empirical correction in these equations not specifically formulated for supercritical fluids (SCFs) and justify a persevering effort in experimentation
Investigation of Inter-Ion Species Diffusion in Inertial Confinement Fusion Implosions
NASA Astrophysics Data System (ADS)
Herrmann, Hans W.; Kim, Yongho; Hoffman, Nelson M.; Schmitt, Mark J.; Kagan, Grigory; Batha, Steven H.; Garbett, Warren J.; Horsfield, Colin J.; Rubery, Michael S.; Gales, Steven
2014-10-01
Anomalous fusion yield degradation has been observed for gas fill mixtures in inertial confinement fusion (ICF) implosions. These mixtures have included D/3He [Rygg et al., Phys Plasmas 13, 052702 (2006)], D/T/3He [Herrmann et al., Phys Plasmas 16, 056312 (2009)], D/Ar [Lindl et al., Phys Plasmas 11, 339 (2004)] and even D/T [Casey et al., PRL 108, 075005 (2012)]. Fuel ion segregation has been suggested as a possible cause [Amendt et al., PRL 18, 056308 (2011); Kagan et al., Phys Lett. A 10.1016 (2014)]. Segregation may be caused by inter-ion species diffusion driven by gradients in plasma pressure, temperature and electric field, either across a relatively narrow shock boundary or across the entire interior of the compressed capsule. It is expected that lower Z &/or A ions will diffuse outward while higher Z &/or A diffuse inward. In the case of D/T/3He, the 3He diffuses inward to the hotter core, reducing the DT reactivity. A D/T/H mixture should result in H diffusing outward, leaving the hotter core D & T rich and hence enhance reactivity over the simulated expectation. Past results will be reviewed and plans for a hydro-equivalent comparison D/T/3He and D/T/H will be presented. Research conducted under the auspices of the U.S. Department of Energy under Contract DE-AC52-06NA25396.
Solvent Diffusion Model for Aging of Lithium-Ion Battery Cells Harry J. Ploehn,z
model of solvent diffusion describing the growth of solid-electrolyte inter- faces SEIs in Li-ion cells the ingress of electrolyte, anode passivation by the SEI, and cell perfor- mance during initial cycling film over the negative electrode,7-14 known as the solid-electrolyte interface SEI . Formation
A Novel Detector Design for Imaging Low-Intensity Diffuse Ion Beams
de Souza, Romualdo T.
A Novel Detector Design for Imaging Low- Intensity Diffuse Ion Beams J. Schmidt, R. de Souza, S interval over which they will be taken are selected. Detector Operation Materials · Saint-Gobain BCF-10 Scintillating Fibers · Bicron BC-630 Optical Grease · CPTA 151-30 Metal-Resistor-Semiconductor Avalanche
Using the thermal diffusion cloud chamber to study the ion-induced nucleation by radon decay
Yefei
1991-01-01
Thermal diffusion cloud chamber is steady-state device and has been extensively used for nucleation research. In order to study the ion-induced nucleation by radon decay, a new chamber was designed with improved both upper and bottom plates, the system of circulating fluid, the gasketting, the temperature measurement and the insulation. An alternative method of using oxygen as carrier gas was
Transport process of ions in insulating media in the hyperbolic diffusion regime G. Barbero1
Macdonald, James Ross
of mobile charge carriers, com- pletely blocked at the electrodes, on the properties of dielectric materials The fundamental equations describing the redistribution of ions in a dielectric material upon the application that the diffusion current is given by Fick's law, relating the current density with the gradient of concentration
NASA Astrophysics Data System (ADS)
Spandler, Carl; O'Neill, Hugh St. C.
2009-11-01
Lattice diffusion coefficients have been determined for 19 elements (Li, Be, Na, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Eu, Gd, Lu and Hf) in a single crystal of San Carlos olivine as a function of crystallographic orientation, at 1,300°C, 1 bar and fO2 = 10-8.3 bars, by equilibration with a synthetic silicate melt. Results for Li, Na, V, Cr, Fe and Zn are from diffusion of these elements out of the olivine, starting from their indigenous concentrations; those for all other elements are from diffusion into the olivine, from the silicate melt reservoir. Our 25-day experiment produced diffusion profiles 50 to > 700 ?m in length, which are sufficiently long that precise analyses could be achieved by scanning laser ablation inductively coupled plasma mass spectrometry, even at concentration levels well below 1 ?g g-1. For the divalent cations Ca, Mn, Fe and Ni, profiles were also obtained by electron microprobe analysis. The results of the two methods agree well with each other, and are consistent with divalent cation diffusion coefficients previously determined using different experimental methodologies. Olivine/melt partition coefficients retrieved from the data are also consistent with other published partitioning data, indicating that element incorporation and transport in olivine in our experiment occurred via mechanisms appropriate to natural conditions. Most of the examined trace elements diffuse through olivine at similar rates to the major octahedral cations Fe and Mg, showing that cation charge and radius have little direct influence on diffusion rates. Aluminium and P remain low and constant in the olivine, implying negligible transport at our analytical scale, hence Al and P diffusion rates that are at least two orders of magnitude slower than the other cations studied here. All determined element diffusivities are anisotropic, with diffusion fastest along the [001] axis, except Y and the REEs, which diffuse isotropically. The results suggest that element diffusivity in olivine is largely controlled by cation site preference, charge balance mechanisms and point-defect concentrations. Elements that are present on multiple cation sites in olivine (e.g. Be and Ti) and trivalent elements that are charge-balanced by octahedral site vacancies tend to diffuse at relatively fast rates.
NASA Technical Reports Server (NTRS)
Blais, R. N.; Copeland, G. E.; Lerner, T. H.
1975-01-01
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.
Ahn, Sung Jun; Shin, Hyun Joo; Chang, Jong-Hee; Lee, Seung-Koo
2014-01-01
Objective Apparent diffusion coefficients (ADC) can help differentiate between central nervous system (CNS) lymphoma and Glioblastoma (GBM). However, overlap between ADCs for GBM and lymphoma have been reported because of various region of interest (ROI) methods. Our aim is to explore ROI method to provide the most reproducible results for differentiation. Materials and Methods We studied 25 CNS lymphomas and 62 GBMs with three ROI methods: (1) ROI1, whole tumor volume; (2) ROI2, multiple ROIs; and (3) ROI3, a single ROI. Interobserver variability of two readers for each method was analyzed by intraclass correlation(ICC). ADCs were compared between GBM and lymphoma, using two-sample t-test. The discriminative ability was determined by ROC analysis. Results ADCs from ROI1 showed most reproducible results (ICC >0.9). For ROI1, ADCmean for lymphoma showed significantly lower values than GBM (p?=?0.03). The optimal cut-off value was 0.98×10?3 mm2/s with 85% sensitivity and 90% specificity. For ROI2, ADCmin for lymphoma was significantly lower than GBM (p?=?0.02). The cut-off value was 0.69×10?3 mm2/s with 87% sensitivity and 88% specificity. Conclusion ADC values were significantly dependent on ROI method. ADCs from the whole tumor volume had the most reproducible results. ADCmean from the whole tumor volume may aid in differentiating between lymphoma and GBM. However, multi-modal imaging approaches are recommended than ADC alone for differentiation. PMID:25393543
NASA Astrophysics Data System (ADS)
Dorian, Matthew; Seitaridou, Effrosyni
2014-03-01
Understanding the rate of biofilm growth is essential for studying genes and preventing unwanted biofilms. In this study, the diffusion coefficient (D) of polystyrene microspheres was used to quantify biofilm growth rates of Sinorhizobia meliloti, a nitrogen fixing bacteria that forms a symbiotic relationship with alfalfa plants. Five strains were studied, two wild types (8530 expR+ and 1021) and three mutants in the exopolysaccharide (EPS I, EPS II) synthesis (8530 exoY , 9034 expG , and 9030-2 expA 1); 1021 and 9030-2 expA 1 are known to be unable to form biofilms. Each strain was inserted into a microfluidic channel with the microspheres. As the cultures grew, the spheres' D values were obtained every 24 hours for 4 days using fluorescence microscopy. Although the D values for 9030-2 expA 1 were inconclusive, 8530 expR+ , 8530 exoY , and 9034 expG showed significant decreases in D between 3 days of growth (| z | > 2 . 25 , p < 0 . 025). The data also indicated that 8530 expR+ and 8530 exoY grew at similar rates. There was no significant change in D for 1021 (?2(2) = 5 . 76 , p > 0 . 05), which shows the lack of a structured biofilm community. Thus, D can be used as an indicator of the presence of a biofilm and its development.
Sevcenco, Sabina; Haitel, Andrea; Ponhold, Lothar; Susani, Martin; Fajkovic, Harun; Shariat, Shahrokh F.; Hiess, Manuela; Spick, Claudio; Szarvas, Tibor; Baltzer, Pascal A. T.
2014-01-01
Purpose To investigate the association between Apparent Diffusion Coefficient (ADC) values and cell cycle and proliferative biomarkers (p53, p21, Ki67,) in order to establish its potential role as a noninvasive biomarker for prediction of cell cycle, proliferative activity and biological aggressiveness in bladder cancer. Materials and Methods Patients with bladder cancer who underwent 3,0 Tesla DW-MRI of the bladder before TUR-B or radical cystectomy were eligible for this prospective IRB-approved study. Histological specimen were immunohistochemically stained for the following markers: p53, p21 and ki67. Two board-certified uropathologists reviewed the specimens blinded to DW-MRI results. Histological grade and T-stage were classified according to the WHO 2004 and the 2009 TNM classification, respectively. Nonparametric univariate and multivariate statistics including correlation, logistic regression and ROC analysis were applied. Results Muscle invasive bladder cancer was histologically confirmed in 10 out of 41 patients. All examined tissue biomarkers were significantly correlated with ADC values (p<0.05, respectively). Based on multivariate analysis, p53 and ADC are both independent prognostic factors for muscle invasiveness of bladder cancer (>/?=?T2). (p?=?0.013 and p?=?0.018). Conclusion ADC values are associated with cell cycle and proliferative biomarkers and do thereby reflect invasive and proliferative potential in bladder cancer. ADC and p53 are both independent prognostic factors for muscle invasiveness in bladder cancer. PMID:25202965
Pitch angle diffusion of newborn ions due to intrinsic turbulence in the solar wind
NASA Astrophysics Data System (ADS)
Ziebell, L. F.; Yoon, Peter H.; Wu, C. S.; Winske, D.
1990-10-01
The objective of the present study is to understand the interaction of the solar wind with newborn ions in far upstream regions of a comet where the level of intrinsic turbulence is moderately low. Based on the assumption that quasi-linear theory is adequate and applicable, the pitch angle diffusion process and the time evolution of the newborn ion distribution function are investigated. Numerical solutions to the quasi-linear diffusion equation, including the effect of resonance broadening and that of continuous creation of newborn ions due to the ionization process, are obtained under several assumptions and approximations. It is found that theoretical results are consistent with the Giotto observations recently reported by Neugebauer et al. (1989).
NASA Astrophysics Data System (ADS)
Cao, J. B.; Mazelle, C.; Zhou, G. C.
2000-02-01
The phase angle diffusion, pitch angle diffusion, and energy diffusion of newborn ions in the self-consistently generated fields in solar wind plasmas are studied by means of a one-dimensional electromagnetic hybrid code. For newborn ions, the time for phase angle diffusing to 2? is a little shorter than the time for pitch angle scattering to a relatively thin complete shell, and it is much shorter than the energy scattering time for broadening of the shell toward a thermal distribution. The speed of phase angle diffusion increases monotonously with the injection velocity, but it does not change in the same way with the injection rate. The phase angle diffusion of heavier injected ions is slower than that of lighter injected ions. The complete pickup process of newborn ions should consist of four stages: (1) the creation of the newborn ions and macroperpendicular pickup due to the motional electric field; (2) phase angle diffusion; (3) pitch angle diffusion; and (4) energy diffusion.
C Y Ouyang; S Q Shi; Z X Wang; H Li; X J Huang; L Q Chen
2004-01-01
Using the adiabatic trajectory method, the migration energy barriers for the migration of Li ions and Cr ions along the one-dimensional diffusion pathway in pure and Cr doped LiFePO4 are obtained from first principles calculations. The results show that while Li ions can diffuse along the diffusion pathway easily, Cr ions do not easily diffuse away from their initial positions.
NASA Astrophysics Data System (ADS)
Chrobak, ?.; Mali?ski, M.; Pawlak, M.
2014-11-01
This paper presents a method of the measurement of the optical absorption coefficient of the Ar8+ ions implanted layers in the p-type silicon substrate. The absorption coefficient is calculated using a value of the attenuation of amplitudes of a photothermal radiometry (PTR) and/or a modulation free carrier absorption (MFCA) signals and the implanted layer thickness calculated by means of the TRIM program. The proposed method can be used to indicate the amorphization of the ions implanted layers.
NASA Astrophysics Data System (ADS)
Zheng, Wen-Chen
1990-11-01
It is shown that our simple and uniform method of calculating the spin-lattice coupling coefficients Gc11 and Gc44 for d n ions in cubic symmetry can also be applied for the approximate calculation of coefficients Gij in some low symmetry cases by using an appropriate coordinate transformation. As an example, the six coefficients Gtij for the Cr 3+ ion in the trigonal site of a Ca 3 Ga 2Ge 3O 12 crystal have been calculated by expressing these coefficients in terms of the coefficients Gc11 and Gc44. The results are clos e to the observed values. Thus, the optical spectra, the EPR g-factor and zero-field splitting D, as well as the six spin-lattice coupling coefficients Gtij for Ca 3Ga 2Ge 3O 12:Cr 3+ crystal can be explained satisfactorily in a unified way from our method b y using only two adjustable parameters.
Diffusion coefficients for Tl, Pb, Cd, In, Zn, Bi, As, Mo and Sb in hydrous rhyolite at 100-200 MPa
NASA Astrophysics Data System (ADS)
Berlo, Kim; Brooker, Richard; Wilke, Max
2014-05-01
A series of experiments have been conducted to determine the diffusivities of Tl, Pb, Cd, In, Zn, Bi, As, Mo and Sb in hydrous rhyolitic melt. Diffusion experiments used two adjoining glass cylinder of the same hydrous composition, one doped with the elements of interest at ~ 100 ppm. These couples were rapidly heated to 850, 1000 and 1150°C at 100-200 MPa for a few hours. After quenching the sectioned charges were analyzed by both synchrotron XRF (The Diamond Light Source) and LA-ICP-MS (University of Oxford). The data shows excellent correlation between these two techniques. The diffusion profiles were fitted to a 1-D diffusion couple equation to determine the diffusivities and fitting to the different temperature runs defined the Arrhenius parameters. We find that for 850°C the diffusion coefficients follow the trend Tl>Pb>Cd>Zn>In>Bi>As>Sb>Mo. Additional experiments were performed with either S or Cl added (to both sides of the diffusion couple). In general S increases the diffusion rate of all metals except Mo and Sb, which diffuse slower in the presence of S. Chlorine also speeds up the diffusion of metals with the exception of In, Mo and Sb. The systematic change in diffusivities of these metals and their different behaviour in the presence of the ligands that are also observed to be significant in volcanic gases, are important in determining the distribution of these metals during degassing (e.g. MacKenzie and Canil, 2008). This is particularly important in a dynamic environment such as a volcanic conduit. There are also implications for economic exploration and well as hazard mitigation.
Heo, Suk Hee; Kim, Jin Woong; Lim, Hyo Soon; Jeong, Yong Yeon; Kang, Woo Dae; Kim, Seok Mo; Kang, Heoung Keun
2013-01-01
Objective To evaluate the value of apparent diffusion coefficient (ADC) histogram analysis for predicting tumor recurrence in patients with uterine cervical cancer treated with chemoradiation therapy (CRT). Materials and Methods Our institutional review board approved this retrospective study and waived informed consent from each patient. Forty-two patients (mean age, 56 ± 14 years) with biopsy-proven uterine cervical squamous cell carcinoma who underwent both pre-treatment pelvic magnetic resonance imaging with a 3.0 T magnetic resonance scanner and concurrent CRT were included. All patients were followed-up for more than 6 months (mean, 36.4 ± 11.9 months; range 9.0-52.8 months) after completion of CRT. Baseline ADC parameters (mean ADC, 25th percentile, 50th percentile, and 75th percentile ADC values) of tumors were calculated and compared between the recurrence and no recurrence groups. Results In the recurrence group, the mean ADC and 75th percentile ADC values of tumors were significantly higher than those of the no recurrence group (p = 0.043 and p = 0.008, respectively). In multivariate analysis, the 75th percentile ADC value of tumors was a significant predictor for tumor recurrence (p = 0.009; hazard ratio, 1.319). When the cut-off value of the 75th percentile ADC (0.936 × 10-3 mm2/sec) was used, the overall recurrence free survival rate above the cut-off value was significantly lower than that below the cut-off value (51.9% vs. 91.7%, p = 0.003, log-rank test). Conclusion Pre-CRT ADC histogram analysis may serve as a biomarker for predicting tumor recurrence in patients with uterine cervical cancer treated with CRT. PMID:23901319
That Bound-Free Absorption Coefficient of the Hydrogen Negative Ion
S. Geltman
1962-01-01
The bound-free absorption coefficient of Hâ» is evaluated by using ; a set of successively improved bound- and freestate wave functions. Better ; agreement with experiment and greater theoretical consistency are shown to result. ; The best theoretical result is tabulated for use in astrophysical applications. ; (auth);
P. R. Bueno; E. R. Leite
2003-01-01
This paper describes the mechanisms of ion and electron transport in nanostructured insertion electrode materials such as metal oxide electrochromics and\\/or Li ion batteries. A general description is given of cases of insertion into a short path region predicted by the geometric disposition of insertion materials in nanostructural electrodes, designed mainly by connected spherical-like particles and nanofibers, both protruding from
Electroreduction of oxygen on metal (Au, Cu)-ion exchanger nanocomposites in the diffusion mode
NASA Astrophysics Data System (ADS)
Gorshkov, V. S.; Polyanskii, L. N.; Kravchenko, T. A.
2014-02-01
The kinetics of the electroreduction of oxygen in the diffusion mode on single granules of nanocomposites consisting of dispersed particles of the metal (Au, Cu) of the nanometer size and macroporous sulfonic cation-exchanger matrix KU-23 is studied. No noticeable effect of the factors of size of the metal component and ion exchange over the matrix on the external diffusion current of oxygen reduction is observed. The drop in current observed in a number of cases is due to a transition to the mixed external and internal kinetics as a result of the macroporous structure of the matrix and the chemical activity of nanoparticles of the metal component.
Xu, Guigui, E-mail: xuguigui082@126.com, E-mail: zghuang@fjnu.edu.cn [Concord University College Fujian Normal University, Fuzhou 350117 (China); College of Physics and Energy, Fujian Normal University, Fuzhou 350117 (China); Fujian Provincial Key Laboratory of Quantum Manipulation and New Energy Materials, Fuzhou 350117 (China); Zhong, Kehua; Zhang, Jian-Min; Huang, Zhigao, E-mail: xuguigui082@126.com, E-mail: zghuang@fjnu.edu.cn [College of Physics and Energy, Fujian Normal University, Fuzhou 350117 (China); Fujian Provincial Key Laboratory of Quantum Manipulation and New Energy Materials, Fuzhou 350117 (China)
2014-08-14
We present a first-principles calculation for the electronic and Li-ion diffusion properties of the LiFePO{sub 4} (010) surface modified by sulfur. The calculated formation energy indicates that the sulfur adsorption on the (010) surface of the LiFePO{sub 4} is energetically favored. Sulfur is found to form Fe-S bond with iron. A much narrower band gap (0.67?eV) of the sulfur surface-modified LiFePO{sub 4} [S-LiFePO{sub 4} (010)] is obtained, indicating the better electronic conductive properties. By the nudged elastic band method, our calculations show that the activation energy of Li ions diffusion along the one-dimensional channel on the surface can be effectively reduced by sulfur surface modification. In addition, the surface diffusion coefficient of S-LiFePO{sub 4} (010) is estimated to be about 10{sup ?11} (cm{sup 2}/s) at room temperature, which implies that sulfur modification will give rise to a higher Li ion carrier mobility and enhanced electrochemical performance.
NASA Astrophysics Data System (ADS)
Liao, J. B.; Lu, M. Z.; Chu, Y. Q.; Wang, J. L.
2015-05-01
An amphoteric ion-exchange membrane (AIEM) from fluoro-methyl sulfonated poly(arylene ether ketone) bearing content-controlled benzimidazole moiety, was firstly fabricated for vanadium redox flow battery (VRB). The AIEM and its covalently cross-linked membrane (AIEM-c) behave the highly suppressed vanadium-ion crossover and their tested VO2+ permeability are about 638 and 1117 times lower than that of Nafion117, respectively. This is further typically verified by the lower VO2+ concentration inside AIEM that is less than half of that inside Nafion117 detected by energy dispersive X-ray spectrometry, in addition of the nearly 3 times longer battery self-discharge time. The ultra-low vanadium ion diffusion could be ascribed to the narrower ion transporting channel originated from the acid-base interactions and the rebelling effect between the positively-charged benzimidazole structure and VO2+ ions. It is found that, VRB assembled with AIEM exhibits the equal or higher Coulombic efficiency (99.0% vs. 96.4%), voltage efficiency (90.7% vs. 90.7%) and energy efficiency (89.8% vs. 87.4%) than that with Nafion117 and keeps continuous 220 charge-discharge cycles for over 25 days, confirming that the AIEM of this type is a potentially suitable separator for VRB application.
NASA Astrophysics Data System (ADS)
Heitjans, P.; Tobschall, E.; Wilkening, M.
2008-07-01
In the present paper we review experimental studies on ion transport and diffusion in nanocrystalline and glassy ceramics of LiNbO3 and LiAlSi2O6 and report on new ones on LiBO2 using the measurement of dc conductivities and 7Li nuclear magnetic resonance spin-lattice relaxation rates. Nanocrystalline ceramics, with an average particle size of 50 nm and less, often show an enhanced diffusivity compared to their microcrystalline (?m-sized) counterparts. This increase is due to the large fraction of atoms or ions located in the interfacial regions. A key for understanding the structure-mobility relations in nanocrystalline ceramics is to clarify the microscopic structure of the grain boundaries and also the morphology of the grain boundary network. In this context it is useful to study not only the ion transport properties of the nano- and microcrystalline materials but also those of the corresponding glassy forms. Such comparative studies gave strong evidence that in some cases the interfacial regions are of amorphous structure. For example, this was recently shown for nanocrystalline lithium niobate which was prepared by high-energy ball milling.
Lianshun Zhang
2008-01-01
When a light beam is incident normally upon a tissue, the spatial distribution of diffuse reflectance on the tissue surface is affected by the optical properties of the tissue. The purpose of this paper is to find the relationship between the spatial distribution of diffuse reflectance on the tissue surface and optical properties of the tissue. The diffuse reflected light
Ion association in aqueous and non-aqueous solutions probed by diffusion and electrophoretic NMR.
Giesecke, Marianne; Mériguet, Guillaume; Hallberg, Fredrik; Fang, Yuan; Stilbs, Peter; Furó, István
2015-02-01
The results of diffusion and electrophoretic NMR (eNMR) measurements are reported for a series of tetramethylammonium (TMA) electrolytes (with sulphate, fluoride, acetate, chloride, bromide, nitrate, iodide and perchlorate as anions) in deuterated solvents such as water, dimethylsulphoxide (DMSO), acetonitrile, methanol and ethanol. In addition, similar data are presented for aqueous solutions of tetraalkylammonium salts with increasing alkyl chain length. The combination of diffusion NMR and eNMR yields the effective charge for the TMA cation. Relative to the nominal charge of znom = 1 of TMA, the effective charge in the different solvents is found to be progressively smaller in the order water > DMSO > methanol > acetonitrile > ethanol. A part of this observed trend is ascribed to regular ion-ion interactions incorporated in the Onsager limiting law. Indeed, in solvents with high dielectric constants such as water, DMSO and methanol, the Onsager limiting law describes well the observations for all tetraalkylammonium ions. For ethanol and acetonitrile, there is a significant difference between the experimental data and the expected limiting-law behavior that is attributed to ion association (ion pairing) not taken into consideration by the Onsager limiting law. PMID:25529069
NASA Astrophysics Data System (ADS)
Bogatko, Stuart A.
2013-04-01
We present a simple separation of ion diffusion into solvent-berg and non-solvent-berg components. The non-solvent-berg component is shown to contain relevant information concerning solvent structure and dynamics and correlates reasonably well with 1st shell water residence times for 2+ and 3+ charged cations; no such dependence is detected for -1 and +1 charged ions. An empirical equation is proposed for estimating 1st shell water residence times of +2 and +3 cations. We suggest the non-solvent-berg component as a proxy for the formation of an extended solvation region. This work thus provides a new approach to investigate solvent dynamics.
Phan, T. D.; Mozer, F. S.; Eastwood, J. P. [Space Sciences Laboratory, University of California, Berkeley, California 94720 (United States); Drake, J. F. [Space Sciences Laboratory, University of California, Berkeley, California 94720 (United States); University of Maryland, College Park, Maryland, 20742 (United States); Shay, M. A. [Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716 (United States)
2007-12-21
Observations of an extremely elongated electron diffusion region occurring during fast reconnection are presented. Cluster spacecraft in situ observations of an expanding reconnection exhaust reveal a broad current layer ({approx}10 ion skin depths thick) supporting the reversal of the reconnecting magnetic field together with an intense current embedded at the center that is due to a super-Alfvenic electron outflow jet with transverse scale of {approx}9 electron skin depths. The electron jet extends at least 60 ion skin depths downstream from the X-line.
Nahar, Sultana Nurun
cross sections PI and RC are computed using an identical wave function expansion for both processes%15%. The comprehensive data sets are applicable for ionization balance and recombination-cascade models for UVand X and electron-ion recombination rates for the He-like ionization stage and adja- cent Li-like and H-like stages
Non-diffusive suprathermal ion transport associated with blobs in TORPEX plasmas
NASA Astrophysics Data System (ADS)
Bovet, Alexandre; Avino, Fabio; Fasoli, Ambrogio; Furno, Ivo; Gustafson, Kyle; Ricci, Paolo
2014-10-01
We present unprecedented space and time-resolved measurements of the transport of a suprathermal ion beam injected in the toroidal device TORPEX. Experiments are performed in turbulence dominated by an ideal-interchange mode using a Li6+ ion source and a set of energy analyzers. Depending on the suprathermal ion energy, the transport exhibits subdiffusive or superdiffusive behaviors. The fast ion current fluctuations are quasi-Gaussian in the former regime and strongly intermittent in the latter. In the superdiffusive case, using conditional sampling, we show that the transport is associated with intermittent field-aligned blobs. In the subdiffusive case, supra-thermal ions average the turbulent structures during their gyro-motion and their vertical drift. These results complement our investigations of the supra-thermal ion transport using 3D time-averaged measurements, which are in agreement with numerical simulations. Numerical modeling is performed by computing the trajectories of tracers in a turbulent electrostatic field generated by a 2D global fluid model. Gyro- and drift-averaging reduce the transport. The evolution of the radial distribution of fast ions can be modeled by a fractional diffusion equation describing fractional Lévy motion. This work was supported in part by the Swiss National Science Foundation and European Union's Horizon 2020 program (Grant Number 633053).
Theory of dust and dust-void structures in the presence of the ion diffusion.
Tsytovich, V N; Vladimirov, S V; Morfill, G E
2004-12-01
A dust void is a dust-free region inside the dust cloud that often develops for conditions relevant to plasma processing discharges and complex plasma experiments. A distinctive feature of the void is a sharp boundary between the dust and dust-free regions; this is manifested especially clear when dissipation in the plasma is small and discontinuity of the dust number density appear. Here, the structure of the dust void boundary and the distribution of the dust and plasma parameters in the dust structure bordering the void is analyzed taking into account effects of dissipation due to the ion diffusion on plasma neutrals. The sharp boundary between the dust and void regions exists also in the presence of the ion diffusion; however, only derivatives of the dust density, dust charge, electron density and electric field are discontinuous at the void boundaries, while the functions themselves as well as derivatives of the ion drift velocity and the ion density are continuous. Numerical calculations demonstrate various sorts of diffusive dust void structures; the possibility of singularities in the balance equations caused by the diffusion process inside the dust structures is investigated. These singularities can be responsible for a new type of shocklike structures. Other structures are typically self-organized to eliminate the singularities. Numerical computations in this case demonstrate a set of thin dust layers separated by high density thin dust clouds similar to the multiple-layer dust structures observed in the laboratory and in the upper ionosphere. The possibility for existence of a few equilibrium positions of the void boundary is discussed. PMID:15697515
Philipp Wachter; Markus Zistler; Christian Schreiner; Marko Berginc; Urša Opara Krašovec; Dirk Gerhard; Peter Wasserscheid; Andreas Hinsch; Heiner J. Gores
2008-01-01
A comprehensive characterisation of an ionic liquid based electrolyte for dye-sensitised solar cells (DSSC) was performed by determination of triiodide diffusion coefficients, viscosities and photovoltaic performances. The electrolyte, consisting of 1-ethyl-3-methylimidazolium dicyanamide, 1-methyl-3-propylimidazolium iodide (MPII), and iodine, was examined at varying ionic liquid molar ratio and fixed iodine concentration, as well as at fixed ionic liquid molar ratio and varying
C. Alonso; R. C. Salvarezza; J. M. Vara; A. J. Arvia; L. Vazquez; A. Bartolome; A. M. Baro
1990-01-01
A simple method is presented for measuring the surface diffusion coefficients of Au and Pt atoms at electrodispersed electrodes of the same metals in contact with 0.5{ital M} HâSOâ. The technique is based upon the time dependence of the surface roughness factor of electrodispersed metal overlayers. The method requires a model for the surface roughness of the metal structure. The
Toshitaka Funazukuri; Chang Yi Kong; Seiichiro Kagei
2003-01-01
A tracer response technique with a poly(ethylene glycol) coated capillary column was employed to measure binary diffusion coefficient and partition ratio for the ?3 group of long chain unsaturated fatty acids such as docosahexaenoic acid, eicosapentaenoic acid and ?-linolenic acid at infinite dilution in supercritical (SC) carbon dioxide at temperatures from 308.15 to 343.15K and pressures from 9 to 30MPa.
T. Funazukuri; C. Y. Kong; S. Kagei
2000-01-01
Binary diffusion coefficients of acetone in carbon dioxide were measured by the Taylor dispersion method at 308.2 K and 7.9 to 40 MPa and at 313.2 K and 8.0 to 37 MPa. The D12 values obtained from the response curves by the method of fitting in the time domain were more accurate than those obtained by the moment method. At