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Sample records for ion diffusion coefficient

  1. Limits on ion radial diffusion coefficients in Saturn's inner magnetosphere

    NASA Technical Reports Server (NTRS)

    Paonessa, M.; Cheng, A. F.

    1986-01-01

    The development of upper and lower limits for the rate of radial diffusion of energetic ions in Saturn's inner magnetosphere is discussed. Improved calculations of the satellite-sweeping rate and phase space density profiles for a wide range of ion invariants are utilized to determine the limits. The lower limit for the radial diffusion coefficient is established by requiring the rate of inward diffusion to be large enough to balance satellite sweeping losses; the upper limit is obtained by requiring the rate of inward diffusion to be less than the observable ultraviolet aurora on plasma torus L shell. It is concluded that the radial diffusion coefficient for ions in Saturn's inner magnetosphere is calculated to about two orders of magnitude.

  2. Ion diffusion coefficient measurements in nanochannels at various concentrations

    PubMed Central

    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

  3. Mutual diffusion coefficients in systems containing the nickel ion

    NASA Astrophysics Data System (ADS)

    Ribeiro, Ana C. F.; Veríssimo, Luis V. M. M.; Gomes, Joselaine C. S.; Santos, Cecilia I. A. V.; Barros, Marisa C. F.; Lobo, Victor M. M.; Sobral, Abílio J. F. N.; Esteso, Miguel A.; Leaist, Derek G.

    2013-04-01

    Mutual diffusion coefficients of nickel chloride in water have been measured at 293.15 K and 303.15 K and at concentrations between 0.020 mol dm-3 and 0.100 mol dm-3, using a conductimetric cell. The experimental mutual diffusion coefficients are discussed on the basis of the Onsager-Fuoss model. The equivalent conductances at infinitesimal concentration of the nickel ion in these solutions at those temperatures have been estimated using these results. In addition, from these data, we have estimated some transport and structural parameters, such as limiting diffusion coefficient, ionic conductance at infinitesimal concentration, hydrodynamic radii and activation energy, contributing this way to a better understanding of the structure of these systems and of their thermodynamic behavior in aqueous solution at different concentrations.

  4. Fluoride-ion-conducting Polymers: Ionic Conductivity and Fluoride Ion Diffusion Coefficient in Quaternized Polysulfones.

    PubMed

    Pasquini, Luca; Ziarelli, Fabio; Viel, Stéphane; Di Vona, Maria Luisa; Knauth, Philippe

    2015-12-01

    We describe the three-step synthesis of a new polymeric fluoride ion conductor based on the fully aromatic polymer polysulfone (PSU). In the first step, PSU is chloromethylated (CM-PSU) using reagents (i.e., stannic chloride, paraformaldehyde, and trimethylchlorosilane) that are less toxic than those used in the standard procedure. In the second step, CM-PSU reacts with a tertiary amine (trimethylamine or 1,4-diazabicyclo[2.2.2]octane) to form quaternary ammonium groups fixed on the PSU backbone and mobile chloride counter-anions. The chloride ions can, in a third step, be exchanged with fluoride ions by immersion of the ionomer in NaF solution. The fluoride ion conductivity reaches 3-5 mS cm(-1) at 25 °C and 5-10 mS cm(-1) at 40 °C. We determined the F(-) diffusion coefficient in these ionomers by pulsed gradient spin-echo (PGSE) high-resolution magic angle spinning (HRMAS) nuclear magnetic resonance (NMR) spectroscopy and by impedance spectroscopy using the Nernst-Einstein relation. The diffusion coefficients determined by the two methods are in good agreement, ranging from 2 to 4×10(-10)  m(2)  s(-1) . The porosity and tortuosity of the ionomer membranes can be estimated. PMID:26373407

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

    SciTech Connect

    Harvey, R. W.; Petrov, Yu.; Jaeger, E. F.; Berry, L. A.; Batchelor, D. B.; Bonoli, P. T.; Wright, J. C.

    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.

  6. Effects of ions on the diffusion coefficient of water in carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Gao, Xiang; Zhao, Tianshou; Li, Zhigang

    2014-08-01

    In this work, we investigate the ion effects on the diffusion of water in carbon nanotubes through molecular dynamics simulations. The diffusion coefficient of water molecules Dw in the presence of cations (Na+ and K+) and anions (F-, Cl-, and Br-) are calculated by changing the ion concentration. The dependence of Dw on the ion concentration is found highly nonlinear and distinct for different ions. For positively charged systems, as the ion concentration is varied, Dw assumes a maximum under the competition between the number and orientation changes of free OH bonds and the effects of ionic hydration. For negatively charged systems, however, Dw decreases monotonously with increasing ion concentration for F-. For Cl- and Br-, Dw reaches the minima at certain ion concentrations and then gently increases. The different behaviors of Dw in the presence of different anions are caused by the stability change of water hydrogen bonds due to ionic hydration.

  7. Ion diffusion coefficients model and molar conductivities of ionic salts in aprotic solvents.

    PubMed

    Garrido, Leoncio; Meja, Alberto; Garca, Nuria; Tiemblo, Pilar; Guzmn, 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

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

    NASA Astrophysics Data System (ADS)

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

    1993-03-01

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

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

    PubMed

    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

  10. Electrochemical Effect of Different Modified Glassy Carbon Electrodes on the Values of Diffusion Coefficient for Some Heavy Metal Ions

    NASA Astrophysics Data System (ADS)

    Radhi, M. M.; Amir, Y. K. A.; Alwan, S. H.; Tee, T. W.

    2013-04-01

    Glassy carbon electrode (GCE) was modified with carbon nanotubes (CNT), C60 and activated carbon (AC) by mechanical attachment method and solution evaporation technique to preparation CNT/GCE, C60/GCE and AC/GCE, these electrodes were modified in Li+ solution via cyclic voltammetry (CV) potential cycling to preparing CNT/Li+/GCE, C60/Li+/GCE and AC/Li+/GCE. The sensing characteristics of the modified film electrodes, demonstrated in the application study for different heavy metal ions such as Hg2+, Cd2+, and Mn2+. Cyclic voltammetric effect by chronoamperometry (CA) technique was investigated to determination the diffusion coefficient (Df) values from Cottrell equation at these ions. Based on Cottrell equation (diffusion coefficient) of the redox current peaks of different heavy metal ions at different modified electrodes were studied to evaluate the sensing of these electrodes by the diffusion coefficient values. The modification of GCE with nano materials and Li+ act an enhancement for the redox current peaks to observe that the diffusion process are high at CNT/Li+/GCE, C60/Li+/GCE and AC/Li+/GCE, but it has low values at unmodified GCE.

  11. Diffusion coefficients of actinide and lanthanide ions in molten Li[sub 2]BeF[sub 4

    SciTech Connect

    Moriyama, Hirotake; Moritani, Kimikazu; Ito, Yasuhiko . Dept. of Nuclear Engineering)

    1994-01-01

    In the conceptual design of molten salt breeder reactors (MSBR) developed at ORNL, molten fluoride mixtures are used as the fuel carrier and coolant. The fuel salt must be reprocessed continuously in order to meet a high breeding ratio. The main function of the reprocessing are to isolate [sup 233]Pa from the neutron flux and to remove the fission product lanthanides having high neutron absorption cross sections. The processing method involves the reductive extraction of these components from the fuel salt into liquid bismuth solutions in a two phase contacting system. Diffusion coefficients of actinide and lanthanide ions in molten Li[sub 2]BeF[sub 4] were measured in the temperature range from 813 to 1,023 K by a capillary method. The diffusion coefficients of both ions are unusually high, considering the high viscosity of the liquids. The dependence of the diffusion coefficients on temperature and ionic charge are discussed in terms of the theories of Stokes and Einstein.

  12. Portable vapor diffusion coefficient meter

    DOEpatents

    Ho, Clifford K.

    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.

  13. 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.

  14. 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)

  15. Diffusion and transport coefficients in synthetic opals

    SciTech Connect

    Sofo, J. O.; Mahan, G. D.; Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee 37996-1200

    2000-07-15

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

  16. Correlation and prediction of gaseous diffusion coefficients.

    NASA Technical Reports Server (NTRS)

    Marrero, T. R.; Mason, E. A.

    1973-01-01

    A new correlation method for binary gaseous diffusion coefficients from very low temperatures to 10,000 K is proposed based on an extended principle of corresponding states, and having greater range and accuracy than previous correlations. There are two correlation parameters that are related to other physical quantities and that are predictable in the absence of diffusion measurements. Quantum effects and composition dependence are included, but high-pressure effects are not. The results are directly applicable to multicomponent mixtures.

  17. The electron diffusion coefficient in Jupiter's magnetosphere

    NASA Technical Reports Server (NTRS)

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

    1974-01-01

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

  18. Intrinsic Diffusion Coefficient of Interstitial Copper in Silicon

    SciTech Connect

    Istratov, A.A.; Flink, C.; Hieslmair, H.; Weber, E.R.; Heiser, T.

    1998-08-01

    Transient ion drift experiments designed to obtain reliable values for the intrinsic copper diffusivity in silicon are reported. From these measurements, the diffusion barrier of Cu in Si is determined to be 0.18{plus_minus}0.01 eV . It is shown that the commonly used expression of Hall and Racette [J.thinspthinspAppl.thinspthinspPhys.thinspthinsp{bold 35}, 379 (1964)] actually gives an effective diffusion coefficient for heavily boron-doped silicon and can neither be used for other doping levels nor extrapolated to lower temperatures. A model is developed which predicts the effective diffusion coefficient as a function of temperature, doping level, and the type of dopant. {copyright} {ital 1998} {ital The American Physical Society}

  19. Micro-Fluidic Diffusion Coefficient Measurement

    SciTech Connect

    Forster, F.K.; Galambos, P.

    1998-10-06

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

  20. ANALYTIC FORMS OF THE PERPENDICULAR DIFFUSION COEFFICIENT IN NRMHD TURBULENCE

    SciTech Connect

    Shalchi, A.

    2015-02-01

    In the past different analytic limits for the perpendicular diffusion coefficient of energetic particles interacting with magnetic turbulence were discussed. These different limits or cases correspond to different transport modes describing how the particles are diffusing across the large-scale magnetic field. In the current paper we describe a new transport regime by considering the model of noisy reduced magnetohydrodynamic turbulence. We derive different analytic forms of the perpendicular diffusion coefficient, and while we do this, we focus on the aforementioned new transport mode. We show that for this turbulence model a small perpendicular diffusion coefficient can be obtained so that the latter diffusion coefficient is more than hundred times smaller than the parallel diffusion coefficient. This result is relevant to explain observations in the solar system where such small perpendicular diffusion coefficients have been reported.

  1. Calculation and application of combined diffusion coefficients in thermal plasmas

    PubMed Central

    Murphy, Anthony B.

    2014-01-01

    The combined diffusion coefficient method is widely used to treat the mixing and demixing of different plasma gases and vapours in thermal plasmas, such as welding arcs and plasma jets. It greatly simplifies the treatment of diffusion for many gas mixtures without sacrificing accuracy. Here, three subjects that are important in the implementation of the combined diffusion coefficient method are considered. First, it is shown that different expressions for the combined diffusion coefficients, arising from different definitions for the stoichiometric coefficients that assign the electrons to the two gases, are equivalent. Second, an approach is presented for calculating certain partial differential terms in the combined temperature and pressure diffusion coefficients that can cause difficulties. Finally, a method for applying the combined diffusion coefficients in computational models, which typically require diffusion to be expressed in terms of mass fraction gradients, is given. PMID:24603457

  2. Calculation and application of combined diffusion coefficients in thermal plasmas.

    PubMed

    Murphy, Anthony B

    2014-01-01

    The combined diffusion coefficient method is widely used to treat the mixing and demixing of different plasma gases and vapours in thermal plasmas, such as welding arcs and plasma jets. It greatly simplifies the treatment of diffusion for many gas mixtures without sacrificing accuracy. Here, three subjects that are important in the implementation of the combined diffusion coefficient method are considered. First, it is shown that different expressions for the combined diffusion coefficients, arising from different definitions for the stoichiometric coefficients that assign the electrons to the two gases, are equivalent. Second, an approach is presented for calculating certain partial differential terms in the combined temperature and pressure diffusion coefficients that can cause difficulties. Finally, a method for applying the combined diffusion coefficients in computational models, which typically require diffusion to be expressed in terms of mass fraction gradients, is given. PMID:24603457

  3. The mobility and diffusion of ions in gases

    NASA Technical Reports Server (NTRS)

    Mcdaniel, E. W.; Mason, E. A.

    1973-01-01

    Experimental and theoretical aspects of the mobility and diffusion of ions in gases are studied in detail. Some of the subjects discussed include ion-ion interaction, boundary condition and ion and electron behavior. Also discussed in separate chapters are the problems of the diffusion coefficients and the afterglow techniques. Finally, a special chapter studies the kinetic theory of diffusion and mobility, stressing the low-, medium- and high-field theory.

  4. An Ion Diffusion Model in Semi-Permeable Clay Materials

    SciTech Connect

    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.

  5. 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.

  6. 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.

  7. Comparative study of methods used to estimate ionic diffusion coefficients using migration tests

    SciTech Connect

    Narsilio, G.A. Li, R. Pivonka, P. Smith, D.W.

    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.

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

    SciTech Connect

    Harvey, R.W.; Jaeger, F.; Berry, L.A.; Batchelor, D.B.; D'Azevedo, E.; Carter, M.D.; Ershov, N.M.; Smirnov, A.P.; Bonoli, P.; Wright, J.C.; Smithe, D.N.

    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.

  9. Quantitative diffusion coefficient maps using fast spin-echo MRI.

    PubMed

    Brockstedt, S; Thomsen, C; Wirestam, R; Holts, S; Sthlberg, F

    1998-10-01

    In this work, we have evaluated the performance of a diffusion-sensitive fast spin-echo (FSE) pulse sequence. The proposed pulse sequence utilises velocity-compensating diffusion-encoding gradients and includes the collection of navigator echoes. Spoiler gradients were inserted in the slice-selecting direction to minimise effects from stimulated echoes. Calculations of the b values showed that cross-terms between imaging gradients and diffusion gradients only led to a marginal increase of b values. Pixel-wise calculation of apparent diffusion coefficient (ADC) maps was performed numerically, considering cross-terms between diffusion-encoding and imaging gradients. The sequences investigated used echo train lengths of 16, 8 and 4 echoes and were encoded in either the slice-, frequency- or phase-encoding direction. In order to allow for higher b values a pulse-sequence version using non-motion compensating diffusion-encoding gradients was written. Phantom measurements were performed and the diffusion coefficients of water and acetone were reasonable. Seven healthy volunteers (age 28-50 years) were examined and apparent diffusion coefficient values agreed well with expected values. Diffusion-weighted images, apparent diffusion coefficient maps and images corresponding to the trace of the diffusion tensor of good quality were retrieved in vivo. PMID:9814769

  10. Analytic expressions for ULF wave radiation belt radial diffusion coefficients

    PubMed Central

    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 PMID:26167440

  11. Improved diffusion coefficients generated from Monte Carlo codes

    SciTech Connect

    Herman, B. R.; Forget, B.; Smith, K.; Aviles, B. N.

    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)

  12. Local carbon diffusion coefficient measurement in the S-1 spheromak

    SciTech Connect

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

    1988-10-01

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

  13. Observations of Ag diffusion in ion implanted SiC

    NASA Astrophysics Data System (ADS)

    Gerczak, Tyler J.; Leng, Bin; Sridharan, Kumar; Hunter, Jerry L.; Giordani, Andrew J.; Allen, Todd R.

    2015-06-01

    The nature and magnitude of Ag diffusion in SiC has been a topic of interest in connection with the performance of tristructural isotropic (TRISO) coated particle fuel for high temperature gas-cooled nuclear reactors. Ion implantation diffusion couples have been revisited to continue developing a more complete understanding of Ag fission product diffusion in SiC. Ion implantation diffusion couples fabricated from single crystal 4H-SiC and polycrystalline 3C-SiC substrates and exposed to 1500-1625 °C, were investigated by transmission electron microscopy and secondary ion mass spectrometry (SIMS). The high dynamic range of SIMS allowed for multiple diffusion régimes to be investigated, including enhanced diffusion by implantation-induced defects and grain boundary (GB) diffusion in undamaged SiC. Estimated diffusion coefficients suggest GB diffusion in bulk SiC does not properly describe the release observed from TRISO fuel.

  14. The temperature variation of hydrogen diffusion coefficients in metal alloys

    NASA Technical Reports Server (NTRS)

    Danford, M. D.

    1990-01-01

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

  15. Calculation of self-diffusion coefficients in iron

    SciTech Connect

    Zhang, Baohua

    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 (α, δ, γ and ε 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.

  16. Diffusion and viscosity coefficients for helium. [in astrophysical gas mixtures

    NASA Technical Reports Server (NTRS)

    Roussel-Dupre, R.

    1982-01-01

    The first order Boltzmann-Fokker-Planck equation is solved numerically to obtain diffusion and viscosity coefficients for a ternary gas mixture composed of electron, protons, and helium. The coefficients are tabulated for five He/H abundances ranging from 0.01 to 10 and for both He II and He III. Comparison with Burgers's thermal diffusion coefficients reveals a maximum difference of 9-10% for both He II and He III throughout the range of helium abundances considered. The viscosity coefficients are compared to those of Chapman and Cowling and show a maximum difference of only 5-6% for He II but 15-16% for He III. For the astrophysically important gas mixtures, it is concluded that the results of existing studies which employed Burgers's or Chapman and Cowling's coefficients will remain substantially unaltered.

  17. Transport coefficients of He+ ions in helium

    NASA Astrophysics Data System (ADS)

    Viehland, Larry A.; Johnsen, Rainer; Gray, Benjamin R.; Wright, Timothy G.

    2016-02-01

    This paper demonstrates that the transport coefficients of 4He+ in 4He can be calculated over wide ranges of E/N, the ratio of the electrostatic field strength to the gas number density, with the same level of precision as can be obtained experimentally if sufficiently accurate potential energy curves are available for the X2Σu+ and A2Σg+ states and one takes into account resonant charge transfer. We start by computing new potential energy curves for these states and testing their accuracy by calculating spectroscopic values for the separate states. It is established that the potentials obtained by extrapolation of results from d-aug-cc-pVXZ (X = 6, 7) basis sets using the CASSCF+MRCISD approach are each in exceptionally close agreement with the best potentials available and with experiment. The potentials are then used in a new computer program to determine the semi-classical phase shifts and the transport cross sections, and from these the gaseous ion transport coefficients are determined. In addition, new experimental values are reported for the mobilities of 4He+ in 4He at 298.7 K, as a function of E/N, where careful consideration is given to minimizing various sources of uncertainty. Comparison with previously measured values establishes that only one set of previous data is reliable. Finally, the experimental and theoretical ion transport coefficients are shown to be in very good to excellent agreement, once corrections are applied to account for quantum-mechanical effects.

  18. Transport coefficients of He(+) ions in helium.

    PubMed

    Viehland, Larry A; Johnsen, Rainer; Gray, Benjamin R; Wright, Timothy G

    2016-02-21

    This paper demonstrates that the transport coefficients of (4)He(+) in (4)He can be calculated over wide ranges of E/N, the ratio of the electrostatic field strength to the gas number density, with the same level of precision as can be obtained experimentally if sufficiently accurate potential energy curves are available for the X(2)Σu (+) and A(2)Σg (+) states and one takes into account resonant charge transfer. We start by computing new potential energy curves for these states and testing their accuracy by calculating spectroscopic values for the separate states. It is established that the potentials obtained by extrapolation of results from d-aug-cc-pVXZ (X = 6, 7) basis sets using the CASSCF+MRCISD approach are each in exceptionally close agreement with the best potentials available and with experiment. The potentials are then used in a new computer program to determine the semi-classical phase shifts and the transport cross sections, and from these the gaseous ion transport coefficients are determined. In addition, new experimental values are reported for the mobilities of (4)He(+) in (4)He at 298.7 K, as a function of E/N, where careful consideration is given to minimizing various sources of uncertainty. Comparison with previously measured values establishes that only one set of previous data is reliable. Finally, the experimental and theoretical ion transport coefficients are shown to be in very good to excellent agreement, once corrections are applied to account for quantum-mechanical effects. PMID:26896985

  19. Study of diffusion coefficients of glasses under Zero-G

    NASA Technical Reports Server (NTRS)

    Kinser, D. L.

    1977-01-01

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

  20. ULF wave derived radiation belt radial diffusion coefficients

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  1. Exact curvilinear diffusion coefficients in the repton model.

    PubMed

    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

  2. Scale dependency of the effective matrix diffusion coefficient

    SciTech Connect

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

    2003-05-30

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

  3. Diffusion of cold magnetospheric ions

    NASA Technical Reports Server (NTRS)

    Birmingham, T. J.; Northrop, T. G.

    1981-01-01

    The paper investigates conditions under which a diffusion equation is a valid description of the transport across magnetic field lines of low energy magnetospheric plasma. The case in which the guiding center drift and its fluctuating component are comparable in size to the particle thermal speed is considered. It is concluded that a two-dimensional diffusion equation is valid in the alpha-beta space of the Euler potentials, provided that the fluctuations have a short enough correlation time so that the guiding center drifts remain negligible, and ions in Jupiter's Io plasma torus can thus be described by a diffusion equation if the correlation time is no more than a few rotation periods of the planet.

  4. Diffusion coefficients of sodium fluoride in aqueous solutions at 298.15 k and 310.15 k.

    PubMed

    Ribeiro, Ana C F; Lobo, Victor M M; Sobral, Abilio J F N; Soares, Helder T F C; Esteso, Ana R J; Esteso, Miguel A

    2010-06-01

    Mutual diffusion coefficients (interdiffusion coefficients) have been measured for sodium fluoride in water at 298.15 K and 310.15 K at concentrations between 0.003 mol dm-3 and 0.05 mol dm-3. The diffusion coefficients were measured using a conductimetric cell. The experimental mutual diffusion coefficients are discussed on the basis of the Onsager-Fuoss model. The limiting molar conductivity of the fluoride ion in these solutions at 310.15 K has been estimated using these results. PMID:24061738

  5. Experimental system to evaluate the effective diffusion coefficient of radon

    NASA Astrophysics Data System (ADS)

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

    2009-01-01

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

  6. Evaluation of the vertical turbulent diffusion coefficient of industrial emissions

    NASA Astrophysics Data System (ADS)

    Ryzhakova, N. K.; Pokrovskaya, E. A.; Babicheva, V. O.

    2015-07-01

    A method for determining the vertical turbulent diffusion coefficients of industrial emissions in complex terrain and with long exposure times has been considered. The method is based on the usage of the distribution of the polluting impurity measured along a certain direction from a point source. The measurements are carried out with moss-biomonitors for a CHP in Novosibirsk.

  7. Minimum Error Fickian Diffusion Coefficients for Mass Diffusion in Multicomponent Gas Mixtures

    NASA Astrophysics Data System (ADS)

    Subramaniam, S.

    1999-04-01

    Mass diffusion in multicomponent gas mixtures is governed by a coupled system of linear equations for the diffusive mass fluxes in terms of thermodynamic driving forces, known as the generalized Stefan-Maxwell equation. In computations of mass diffusion in multicomponent gas mixtures, this coupling between the different components results in considerable computational overhead. Consequently, simplified diffusion models for the diffusive mass fluxes as explicit functions of the driving forces are an attractive alternative. These models can be interpreted as an approximate solution to the Stefan-Maxwell equation. Simplified diffusion models require the specification of “effective” diffusion coefficients which are usually expressed as functions of the binary diffusion coefficients of each species pair in the mixture. Current models for the effective diffusion coefficients are incapable of providing a priori control over the error incurred in the approximate solution. In this paper a general form for diagonal approximations is derived, which accounts for the requirement imposed by the special structure of the Stefan-Maxwell equation that such approximations be constructed in a reduced-dimensional subspace. In addition, it is shown that current models can be expressed as particular cases of two general forms, but not all these models correspond to the general form for diagonal approximations. A new minimum error diagonal approximation (MEDA) model is proposed, based on the criterion that the diagonal approximation minimize the error in the species velocities. Analytic expressions are derived for the MEDA model's effective diffusion coefficients based on this criterion. These effective diffusion coefficients automatically give the correct solution in two important limiting cases: for that of a binary mixture, and for the case of arbitrary number of components with identical binary diffusivities. Although these minimum error effective diffusion coefficients are more expensive to compute than existing ones, the approximation will still be cheaper than computing the exact Stefan-Maxwell solution, while at the same time being more accurate than any other diagonal approximation. Furthermore, while the minimum error effective diffusion coefficients in this work are derived for bulk diffusion in homogeneous media, the minimization procedure can in principle be used to derive similar coefficients for diffusion problems in heterogeneous media which can be represented by similar forms of the Stefan-Maxwell equation. These problems include diffusion in macro- and microporous catalysts, adsorbents, and membranes.

  8. Application of anomalous diffusion in production of negative ions

    SciTech Connect

    Jimbo, K.

    1984-11-01

    The production of negative hydrogen ions is investigated in the reflex-type negative ion sources. When anomalous diffusion in the positive column was found by Hoh and Lehnert (Phys. Fluids 3, 600 (1960)), it was pointed out that the large particle loss produced by anomalous diffusion is compensated for by the larger particle production inside the plasma. In the present experiments anomalous diffusion was artificially encouraged by changing the radial electric field inside the reflex discharge. Apparent encouragement of negative ion current by the increase of the density fluctuation amplitude is observed. Twice as much negative ion current was obtained with the artificial encouragement as without. On the other hand, the larger extracted negative ion current was observed with a lower electron temperature, which is calculated from the anomalous diffusion coefficient derived from a simple nonlinear theory. This result is consistent with Wadehra's calculated results (Appl. Phys. Lett. 35, 917 (1979)).

  9. Optimal estimation of diffusion coefficients from single-particle trajectories

    NASA Astrophysics Data System (ADS)

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

    2014-02-01

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

  10. The diffusion of ions in unconsolidated sediments

    USGS Publications Warehouse

    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.

  11. Measurement of the local particle diffusion coefficient in a magnetized plasma

    SciTech Connect

    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.

  12. Role of the Molar Volume on Estimated Diffusion Coefficients

    NASA Astrophysics Data System (ADS)

    Santra, Sangeeta; Paul, Aloke

    2015-09-01

    The role of the molar volume on the estimated diffusion parameters has been speculated for decades. The Matano-Boltzmann method was the first to be developed for the estimation of the variation of the interdiffusion coefficients with composition. However, this could be used only when the molar volume varies ideally or remains constant. Although there are no such systems, this method is still being used to consider the ideal variation. More efficient methods were developed by Sauer-Freise, Den Broeder, and Wagner to tackle this problem. However, there is a lack of research indicating the most efficient method. We have shown that Wagner's method is the most suitable one when the molar volume deviates from the ideal value. Similarly, there are two methods for the estimation of the ratio of intrinsic diffusion coefficients at the Kirkendall marker plane proposed by Heumann and van Loo. The Heumann method, like the Matano-Boltzmann method, is suitable to use only when the molar volume varies more or less ideally or remains constant. In most of the real systems, where molar volume deviates from the ideality, it is safe to use the van Loo method. We have shown that the Heumann method introduces large errors even for a very small deviation of the molar volume from the ideal value. On the other hand, the van Loo method is relatively less sensitive to it. Overall, the estimation of the intrinsic diffusion coefficient is more sensitive than the interdiffusion coefficient.

  13. Determination of diffusion coefficient in disordered organic semiconductors

    NASA Astrophysics Data System (ADS)

    Rani, Varsha; Sharma, Akanksha; Ghosh, Subhasis

    2016-05-01

    Charge carrier transport in organic semiconductors is dominated by positional and energetic disorder in Gaussian density of states (GDOS) and is characterized by hopping through localized states. Due to the immobilization of charge carriers in these localized states, significant non-uniform carrier distribution exists, resulting diffusive transport. A simple, nevertheless powerful technique to determine diffusion coefficient D in disordered organic semiconductors has been presented. Diffusion coefficients of charge carriers in two technologically important organic molecular semiconductors, Pentacene and copper phthalocyanine (CuPc) have been measured from current-voltage (J-V) characteristics of Al/Pentacene/Au and Al/CuPc/Au based Schottky diodes. Ideality factor g and carrier mobility μ have been calculated from the exponential and space charge limited region respectively of J-V characteristics. Classical Einstein relation is not valid in organic semiconductors due to energetic disorders in DOS. Using generalized Einstein relation, diffusion coefficients have been obtained to be 1.31×10-6 and 1.73×10-7 cm2/s for Pentacene and CuPc respectively.

  14. Validation of drift and diffusion coefficients from experimental data

    NASA Astrophysics Data System (ADS)

    Riera, R.; Anteneodo, C.

    2010-04-01

    Many fluctuation phenomena, in physics and other fields, can be modeled by Fokker-Planck or stochastic differential equations whose coefficients, associated with drift and diffusion components, may be estimated directly from the observed time series. Its correct characterization is crucial to determine the system quantifiers. However, due to the finite sampling rates of real data, the empirical estimates may significantly differ from their true functional forms. In the literature, low-order corrections, or even no corrections, have been applied to the finite-time estimates. A frequent outcome consists of linear drift and quadratic diffusion coefficients. For this case, exact corrections have been recently found, from It-Taylor expansions. Nevertheless, model validation constitutes a necessary step before determining and applying the appropriate corrections. Here, we exploit the consequences of the exact theoretical results obtained for the linear-quadratic model. In particular, we discuss whether the observed finite-time estimates are actually a manifestation of that model. The relevance of this analysis is put into evidence by its application to two contrasting real data examples in which finite-time linear drift and quadratic diffusion coefficients are observed. In one case the linear-quadratic model is readily rejected while in the other, although the model constitutes a very good approximation, low-order corrections are inappropriate. These examples give warning signs about the proper interpretation of finite-time analysis even in more general diffusion processes.

  15. Diffusion coefficients from signal fluctuations: influence of molecular shape and rotational diffusion.

    PubMed

    Hahne, Susanne; Maass, Philipp

    2014-03-27

    Analysis of signal fluctuations of a locally fixed probe, caused by molecules diffusing under the probe, can be used to determine diffusion coefficients. Theoretical treatments so far have been limited to point-like particles or to molecules with circle-like shapes. Here we extend these treatments to molecules with rectangle-like shapes, for which also rotational diffusion needs to be taken into account. Focusing on the distribution of peak widths in the signal, we show how translational as well as rotational diffusion coefficients can be determined. We address also the question, how the distribution of interpeak time intervals and autocorrelation function can be employed for determining diffusion coefficients. Our approach is validated against kinetic Monte Carlo simulations. PMID:24640969

  16. 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.

  17. Diffusion of solvents in coals: 2. Measurement of diffusion coefficients of pyridine in Cayirhan lignite

    SciTech Connect

    Meryem Seferinolu; Yuda Yurum

    2006-05-15

    The aim of this study is to measure the diffusion coefficients of pyridine in Turkish Cayirhan lignite (C: 57.1 wt%, dmmf) at temperatures about 20-27{sup o}C and determine the type of transport mechanism of diffusion. The raw coal sample was demineralized with HCl and HF by standard methods, and the raw and demineralized coal samples were extracted with pyridine. To investigate the diffusion of pyridine vapor in coal samples, the mass of pyridine uptake per mass of coal sample (M{sub t}/M{sub {infinity}}) was calculated as a function of time. The diffusion coefficients were measured from the slope of graphs of M{sub t}/M{sub {infinity}} versus t{sup 1/2}. The diffusion coefficient of pyridine in the raw coal increased from 10.0 x 10{sup -15} to 11.9 x 10{sup -15} m{sup 2}/s when the temperature was elevated from 21.1 to 26.9{sup o}C, respectively. The diffusion coefficients of pyridine raw coal and of those treated with HCl and HF were 11.9 x 10{sup -15}, 4.3 x 10{sup -15}, and 4.8 x 10{sup -15} m{sup 2}/s at 26.9{sup o}C, respectively. The studies in the present work on pyridine vapor diffusion in raw coals have generally indicated that the diffusion obeyed the Fickian diffusion mechanism the temperatures 20.0-27.0{sup o}C. Generally, the diffusion exponent values increased when the temperature elevated from 20.0 to 27.0{sup o}C, but this rise placed the diffusion of pyridine between the Fickian diffusion and Case II diffusion mechanisms. 29 refs., 6 figs., 4 tabs.

  18. Measurement of cesium diffusion coefficients in graphite IG-110

    NASA Astrophysics Data System (ADS)

    Carter, L. M.; Brockman, J. D.; Loyalka, S. K.; Robertson, J. D.

    2015-05-01

    An understanding of the transport of fission products in High Temperature Gas-Cooled Reactors (HTGRs) is needed for operational safety as well as source term estimations. We have measured diffusion coefficients of Cs in IG-110 by using the release method, wherein we infused small graphite spheres with Cs and measured the release rates using ICP-MS. Diffusion behavior was investigated in the temperature range of 1100-1300 K. We have obtained: DCs = (1.0 ×10-7m2 /s) exp(-1.1×105J/mol/RT) and, compared our results with those available in the literature.

  19. Hydrodynamic correlations and diffusion coefficient of star polymers in solution.

    PubMed

    Singh, Sunil P; Huang, Chien-Cheng; Westphal, Elmar; Gompper, Gerhard; Winkler, Roland G

    2014-08-28

    The center-of-mass dynamics of star polymers in dilute solution is analyzed by hybrid mesoscale simulations. The fluid is modeled by the multiparticle collision dynamics approach, a particle-based hydrodynamic simulation technique, which is combined with molecular dynamics simulations for the polymers. Star polymers of various functionalities are considered. We determine the center-of-mass velocity correlation functions, the corresponding mean square displacements, and diffusion coefficients. The velocity correlation functions exhibit a functionality-dependent and structure-specific intermediate time regime, with a slow decay. It is followed by the long-time tail t(-3/2), which is solely determined by the fluid. Infinite-system-size diffusion coefficients are determined from the velocity correlation function by a combination of simulation and analytical results, as well as from the center-of-mass mean square displacement for various systems sizes and extrapolation. In terms of the hydrodynamic radius, the star polymer hydrodynamic diffusion coefficient exhibits the same universal system-size dependence as a spherical colloid. The functionality dependence of the ratio of hydrodynamic radii and the radii of gyration agrees well with experimental predictions. PMID:25173039

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

    SciTech Connect

    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.

  1. 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.

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

    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.

  3. Effect of gamma irradiation on the structural properties and diffusion coefficient in Co-Zn ferrite

    NASA Astrophysics Data System (ADS)

    Hemeda, O. M.; El-Saadawy, M.

    2003-01-01

    A series of samples of Co 1- xZn xFe 2O 4 were prepared by the usual ceramic technique where x=0.3,0.5,0.6, and 0.8. The samples were irradiated by Co 60 gamma source with a high dose equal to 10 6 rad/h. The diffusion coefficient of oxygen vacancies was estimated from DC conductivity measurements. It was noticed that the diffusion coefficient increased after gamma irradiation for all Zn 2+ concentrations. This could be explained on the basis of displacement of metal ions from its original sites under the effect of irradiation leaving behind it lattice vacancies which increase the diffusion coefficient. The concentration of lattice vacancies increased, whereas the activation energy of diffusion process decreased after irradiation. The lattice parameter of the studied samples increased due to the formation of ferrous ions under the ionizing effect of gamma radiation. These changes in some physical properties of the studied samples are useful for the detection of nuclear contamination of environmental atmosphere.

  4. Diffusion coefficients of Fokker-Planck equation for rotating dust grains in a fusion plasma

    SciTech Connect

    Bakhtiyari-Ramezani, M. Alinejad, N.; Mahmoodi, J.

    2015-11-15

    In the fusion devices, ions, H atoms, and H{sub 2} molecules collide with dust grains and exert stochastic torques which lead to small variations in angular momentum of the grain. By considering adsorption of the colliding particles, thermal desorption of H atoms and normal H{sub 2} molecules, and desorption of the recombined H{sub 2} molecules from the surface of an oblate spheroidal grain, we obtain diffusion coefficients of the Fokker-Planck equation for the distribution function of fluctuating angular momentum. Torque coefficients corresponding to the recombination mechanism show that the nonspherical dust grains may rotate with a suprathermal angular velocity.

  5. Diffusion coefficients of Fokker-Planck equation for rotating dust grains in a fusion plasma

    NASA Astrophysics Data System (ADS)

    Bakhtiyari-Ramezani, M.; Mahmoodi, J.; Alinejad, N.

    2015-11-01

    In the fusion devices, ions, H atoms, and H2 molecules collide with dust grains and exert stochastic torques which lead to small variations in angular momentum of the grain. By considering adsorption of the colliding particles, thermal desorption of H atoms and normal H2 molecules, and desorption of the recombined H2 molecules from the surface of an oblate spheroidal grain, we obtain diffusion coefficients of the Fokker-Planck equation for the distribution function of fluctuating angular momentum. Torque coefficients corresponding to the recombination mechanism show that the nonspherical dust grains may rotate with a suprathermal angular velocity.

  6. 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.

  7. M558 radioactive tracer diffusion. [diffusion coefficients of Zn-65 in liquid zinc under weightlessness conditions

    NASA Technical Reports Server (NTRS)

    Ukanwa, A. O.

    1974-01-01

    This experiment was performed in Skylab 3 with two objectives in mind. First, the experimental self-diffusion coefficients for liquid zinc were to be determined in a convection-free environment. Secondly the reduction in convective mixing in earth gravity by going into the zero-gravity environment of space was to be estimated. The experiment was designed to utilize high temperatures and linear thermal gradients provided by the M518 Multipurpose Electric Furnace, and the radioactivity of zinc-65 of 245-day half-life to investigate self-diffusion in liquid zinc. The distribution of zinc-65 tracer, after melting, maintaining at soak temperature for 1 hour of soak time and then resolidifying, was obtained by sample sectioning. The concentration of activity of each section (microcurie-gram) was plotted against positions along the sample axial and radial position. Experimental data and theoretical results from solution of Fick's law of diffusion in one dimensional were compared. Samples tested on earth showed very rapid diffusion. Diffusion coefficient in unit gravity was 50 times the zero-gravity diffusion coefficient of Skylab.

  8. Comparison Actin- and Glass-Supported Phospholipid Bilayer Diffusion Coefficients

    PubMed Central

    Sterling, Sarah M.; Dawes, Ryan; Allgeyer, Edward S.; Ashworth, Sharon L.; Neivandt, David J.

    2015-01-01

    The formation of biomimetic lipid membranes has the potential to provide insights into cellular lipid membrane dynamics. The construction of such membranes necessitates not only the utilization of appropriate lipids, but also physiologically relevant substrate/support materials. The substrate materials employed have been shown to have demonstrable effects on the behavior of the overlying lipid membrane, and thus must be studied before use as a model cushion support. To our knowledge, we report the formation and investigation of a novel actin protein-supported lipid membrane. Specifically, inner leaflet lateral mobility of globular actin-supported DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) bilayers, deposited via the Langmuir-Blodgett/Langmuir Schaefer methodology, was investigated by z-scan fluorescence correlation spectroscopy across a temperature range of 20–44°C. The actin substrate was found to decrease the diffusion coefficient when compared to an identical membrane supported on glass. The depression of the diffusion coefficient occurred across all measured temperatures. These results indicated that the actin substrate exerted a direct effect on the fluidity of the lipid membrane and highlighted the fact that the choice of substrate/support is critical in studies of model lipid membranes. PMID:25902434

  9. Secondary Ion Mass Spectrometry for Mg Tracer Diffusion: Issues and Solutions

    SciTech Connect

    Tuggle, Jay; Giordani, Andrew; Kulkarni, Nagraj S; Warmack, Robert J Bruce; Coffey, Kevin; Sohn, Yong Ho; HunterJr., Jerry

    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.

  10. Li + ion diffusion in nanoscale alumina coatings

    NASA Astrophysics Data System (ADS)

    Johannes, Michelle; Bernstein, Noam

    Nanoscale coatings of alumina are used to stabilize surfaces for a variety of technologies. Diffusion of ions through these coatings is of primary importance: in some cases, diffusion is unwanted (e.g. corrosion) and in others (e.g. electrode materials), it is necessary. In this work DFT and AIMD calculations are used to investigate Li+ ion diffusion through a nano-layer of alumina, examining the phase (alpha, gamma, and amorphous), ion concentration, and electron count dependence. We look at the role of the surface itself in promoting diffusion. One of our main findings is that as the number of ions or charge increases, the diffusivity rises. We show how our data can explain electrochemical data from coated LiCoO2 cathodes and may point toward better and more efficient coatings for stabilizing electrodes.

  11. A New Relationship Among Self- and Impurity Diffusion Coefficients in Binary Solution Phases

    NASA Astrophysics Data System (ADS)

    Xin, Jinghua; Du, Yong; Shang, Shunli; Cui, Senlin; Wang, Jianchuan; Huang, Baiyun; Liu, Zikui

    2016-05-01

    A new relationship among self- and impurity diffusion coefficients has been proposed for binary solution phases and verified via 30 solid solutions. In terms of this model, one impurity diffusion coefficient in a binary phase can be predicted once the other three diffusion coefficients are available. The application of the present model is exemplified in the Al-Mg system.

  12. Calculation of combined diffusion coefficients in SF{sub 6}-Cu mixtures

    SciTech Connect

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

    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.

  13. Nonperturbative estimate of the heavy quark momentum diffusion coefficient

    NASA Astrophysics Data System (ADS)

    Francis, A.; Kaczmarek, O.; Laine, M.; Neuhaus, T.; Ohno, H.

    2015-12-01

    We estimate the momentum diffusion coefficient of a heavy quark within a pure SU(3) plasma at a temperature of about 1.5 Tc . Large-scale Monte Carlo simulations on a series of lattices extending up to 1923×48 permit us to carry out a continuum extrapolation of the so-called color-electric imaginary-time correlator. The extrapolated correlator is analyzed with the help of theoretically motivated models for the corresponding spectral function. Evidence for a nonzero transport coefficient is found and, incorporating systematic uncertainties reflecting model assumptions, we obtain κ =(1.8 - 3.4 )T3 . This implies that the "drag coefficient," characterizing the time scale at which heavy quarks adjust to hydrodynamic flow, is ηD-1=(1.8 - 3.4 )(Tc/T )2(M /1.5 GeV ) fm /c , where M is the heavy quark kinetic mass. The results apply to bottom and, with somewhat larger systematic uncertainties, to charm quarks.

  14. C-Depth Method to Determine Diffusion Coefficient and Partition Coefficient of PCB in Building Materials.

    PubMed

    Liu, Cong; Kolarik, Barbara; Gunnarsen, Lars; Zhang, Yinping

    2015-10-20

    Polychlorinated biphenyls (PCBs) have been found to be persistent in the environment and possibly harmful. Many buildings are characterized with high PCB concentrations. Knowledge about partitioning between primary sources and building materials is critical for exposure assessment and practical remediation of PCB contamination. This study develops a C-depth method to determine diffusion coefficient (D) and partition coefficient (K), two key parameters governing the partitioning process. For concrete, a primary material studied here, relative standard deviations of results among five data sets are 5%-22% for K and 42-66% for D. Compared with existing methods, C-depth method overcomes the inability to obtain unique estimation for nonlinear regression and does not require assumed correlations for D and K among congeners. Comparison with a more sophisticated two-term approach implies significant uncertainty for D, and smaller uncertainty for K. However, considering uncertainties associated with sampling and chemical analysis, and impact of environmental factors, the results are acceptable for engineering applications. This was supported by good agreement between model prediction and measurement. Sensitivity analysis indicated that effective diffusion distance, contacting time of materials with primary sources, and depth of measured concentrations are critical for determining D, and PCB concentration in primary sources is critical for K. PMID:26347992

  15. Efficient approximations of quasi-linear diffusion coefficients in the radiation belts

    NASA Astrophysics Data System (ADS)

    Albert, J. M.

    2008-06-01

    Combined pitch angle and energy diffusion are key ingredients in current models of radiation belt electron dynamics. Bounce-averaged quasi-linear diffusion coefficients can be approximated with a recently developed approach based on the ranges of wave normal angle compatible with cyclotron and Landau resonance within a prescribed wave frequency band, as has been demonstrated for a model of chorus waves. The method casts nested, multiple integrals over wave normal angle as a single weighted average, which is further approximated by evaluation at only a few, carefully chosen points. Here, the method is shown to agree well with results for more recent models of chorus, electromagnetic ion cyclotron waves, and whistler mode hiss. Highly oblique magnetosonic waves are also considered, and a related approach is developed which is shown to give a good approximation for their diffusion rates.

  16. 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.

  17. Continuum Absorption Coefficient of Atoms and Ions

    NASA Technical Reports Server (NTRS)

    Armaly, B. F.

    1979-01-01

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

  18. SNR dependence of optimal parameters for apparent diffusion coefficient measurements.

    PubMed

    Saritas, Emine U; Lee, Jin H; Nishimura, Dwight G

    2011-02-01

    Optimizing the diffusion-weighted imaging (DWI) parameters (i.e., the b-value and the number of image averages) to the tissue of interest is essential for producing high-quality apparent diffusion coefficient (ADC) maps. Previous investigation of this optimization was performed assuming Gaussian noise statistics for the ADC map, which is only valid for high signal-to-noise ratio (SNR) imaging. In this work, the true statistics of the noise in ADC maps are derived, followed by an optimization of the DWI parameters as a function of the imaging SNR. Specifically, it is demonstrated that the optimum b-value is a monotonically increasing function of the imaging SNR, which converges to the optimum b-value from previously proposed approaches for high-SNR cases, while exhibiting a significant deviation from this asymptote for low-SNR situations. Incorporating the effects of T(2) weighting further increases the SNR dependence of the optimal parameters. The proposed optimization scheme is particularly important for high-resolution DWI, which intrinsically suffers from low SNR and therefore cannot afford the use of the conventional high b-values. Comparison scans were performed for high-resolution DWI of the spinal cord, demonstrating the improvements in the resulting images and the ADC maps achieved by this method. PMID:20934948

  19. Measurement of the diffusion coefficient of sulfur hexafluoride in water

    SciTech Connect

    King. D.B.; Saltzman, E.S.

    1995-04-15

    Sulfur hexafluoride has been widely used in field studies and laboratory experiments to develop a relationship between gas transfer and wind speed. The interpretation of the data from such studies requires the diffusion coefficient of SF{sub 6} (D{sub SF6}), which has not previously been measured. In this study, D{sub SF6} has been determined in pure water and in 35%NaCl over a temperature range of 5-25{degrees}C. The measurements were made using a continuous-flow diffusion cell where SF{sub 6} flows beneath an agar gel membrane while helium flows above the gel. The experimental data for pure water yielded the following equation: D{sub SF6}=0.029 exp ({minus}19.3/RT, where R is the gas constant and T is temperature in kelvins). Measurements of D{sub SF6} in 35% NaCl were not significantly different from the pure water values. On the basis of this data, the authors estimate the Schmidt numbers for seawater over the temperature range 5-25{degrees}C to be Sc=3016.1{minus}172.00t+4.4996t{sup 2}{minus}0.047965t{sup 3}, where t is temperature in degrees Celsius. 31 refs., 3 figs., 2 tabs.

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

    SciTech Connect

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

    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.

  1. Evaluation of diffusion coefficient of thiocholine in enzyme-loaded polypyrrole composite film through different methods and electrode polarization.

    PubMed

    Gogoi, Sudarshan; Borah, Himadri; Dutta, Rekha R; Puzari, Panchanan

    2015-04-01

    In this work, the diffusion of thiocholine ion into an enzyme-loaded polypyrrole film was evaluated by different methods, and the results were compared to identify the most suitable method. The enzyme-loaded polypyrrole film was coated with a thin layer of gelatin and gluteraldehyde so as to prevent enzyme leaching. Diffusion coefficients under normal and prepolarized conditions were calculated by five different methods, namely, the Cottrell method, the method of Peerce and Bard, the theoretical impedance model, the electrochemically stimulated conformational relaxation (ESCR) method, and the direct impedance measurement method. The theoretical model of Vortynstev was used to calculate the parameters from the impedance spectra using simplex technique in MATLAB. The results indicate that under normal unpolarized condition the ESCR method gives a diffusion coefficient close to that given by Vortynstev method, but under polarized conditions the Cottrell method can provide a better value of diffusion coefficient than ESCR. The diffusion coefficient of thiocholine in PPy composite film from an electrolytic background of phosphate buffer of pH 7.4 was found to be 1.00 × 10(-8) cm(2) s(-1) based on Vortynstev method. The mechanism of thiocholine diffusion into the positively charged/polarized matrix is attributed to be through the formation of a dinegative ion between thiocholine and phosphate anion via electrostatic attraction. PMID:25782026

  2. Protein diffusion coefficient measurements by laminar flow analysis: method and applications.

    PubMed

    Walters, R R; Graham, J F; Moore, R M; Anderson, D J

    1984-07-01

    Laminar flow in an open tube leads to solute band spreading. This process is opposed by radial diffusion. The translational diffusion coefficient of a solute can be calculated from the band dispersion, tube length, and flow rate. No calibration is necessary. A simple apparatus was used to measure the diffusion coefficients of several small solutes and 18 proteins. Most results were within +/- 10% of literature values. Each determination required 7-90 min, depending on the magnitude of the diffusion coefficient. The amount of protein needed was approximately 25 micrograms. The diffusion coefficient data were useful for the estimation of molecular weights. PMID:6486405

  3. Experimental Method Development for Estimating Solid-phase Diffusion Coefficients and Material/Air Partition Coefficients of SVOCs

    EPA Science Inventory

    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...

  4. Diffusion studies with radioactive ions

    NASA Astrophysics Data System (ADS)

    Räisänen, J.; Whitlow, H. J.

    2014-01-01

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

  5. High silicon self-diffusion coefficient in dry forsterite

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  6. Reproducibility of Apparent Diffusion Coefficient Measurements in Malignant Breast Masses.

    PubMed

    Jang, Mijung; Kim, Sun Mi; Yun, Bo La; Ahn, Hye Shin; Kim, Soo Yeon; Kang, Eunyoung; Kim, Sung-Won

    2015-11-01

    This study aimed to evaluate the reproducibility of apparent diffusion coefficient (ADC) measurements in malignant breast masses, and to determine the influence of mammographic parenchymal density on this reproducibility. Sixty-six patients with magnetic resonance findings of the mass were included. Two breast radiologists measured the ADC of the malignant breast mass and the same area on the contralateral normal breast in each patient twice. The effects of mammographic parenchymal density, histology, and lesion size on reproducibility were also assessed. There was no significant difference in the mean ADC between repeated measurements in malignant breast masses and normal breast tissue. The overall reproducibility of ADC measurements was good in both. The 95% limits of agreement for repeated ADCs were approximately 30.2%-33.4% of the mean. ADC measurements in malignant breast masses were highly reproducible irrespective of mass size, histologic subtype, or coexistence of microcalcifications; however, the measurements tended to be less reproducible in malignant breast masses with extremely dense parenchymal backgrounds. ADC measurements in malignant breast masses are highly reproducible; however, mammographic parenchymal density can potentially influence this reproducibility. PMID:26539016

  7. Sodium ion diffusion in Al2O3: a distinct perspective compared with lithium ion diffusion.

    PubMed

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

    2014-11-12

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

  8. 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 τα-1 (τ: diffusion time) in the case of α < 1 and a larger τ, in which α is the ratio of hydrogen temperature to width for energy distribution function. In the case of α ≥ 1, as α reaches infinity at the limit, the hydrogen diffusion approaches Brownian motion.

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

    SciTech Connect

    Shalchi, A.

    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.

  10. Chemical diffusion coefficient of lithium in carbon fiber

    SciTech Connect

    Uchida, Takashi; Morikawa, Yasuyuki; Ikuta, Hiromasa; Wakihara, Masataka; Suzuki, Kimihito

    1996-08-01

    In order to obtain safer and more reversible negative electrodes for lithium secondary batteries, intensive research on various carbon materials, such as pyrolytic carbon, polyacrylonitrile- (PAN) based carbon, petroleum coke-based carbon, pitch-based carbon, etc., has been carried out in recent years. Electrochemical investigations on coal pitch-based carbon fiber (heat-treated at 2,800 C) were carried out. The open-circuit voltages of the Li{vert_bar}Li{sub x}C{sub 6} cell were lower than 0.15 V vs. Li/Li{sup +} in the range of 0.15 < x < 0.65. The open-circuit voltage profile vs x showed no distinct two-phase region in the present Li-carbon system in 0 < x < 0.65. Almost constant capacity of 220 mAh/g was observed until the 140th cycle in the cycling tests of the Li{vert_bar}carbon fiber cell (current density 25 mA/g). The compositional variation of the chemical diffusion coefficient of lithium {tilde D}{sub Li} at ambient temperature was measured by two different methods, i.e., the current pulse relaxation method and the potential step chronoamperometric method. Excellent agreement within one order of magnitude was observed between the two sets of {tilde D}{sub Li} values obtained from these two methods. The values were around 10{sup {minus}9.5} cm{sup 2}/s at x = 0 and decreased with increasing x. The {tilde D}{sub Li} values lay between 10{sup {minus}11} and 10{sup {minus}12} c/{sup 2}/s in x > 0.2.

  11. Film-pore diffusion modeling for the sorption of metal ions from aqueous effluents onto peat.

    PubMed

    Chen, B; Hui, C W; McKay, G

    2001-10-01

    The sorption of three metal ions, namely, copper, nickel and lead onto sphagnum peat moss has been studied using an agitated batch sorber system. The equilibrium isotherms were determined and kinetic runs were performed over a range of concentrations for each metal ion. A film-pore diffusion mass transfer model has been developed based on a single effective diffusion coefficient for each system. Error analysis of the experimental and theoretical data indicated relatively large errors at low initial metal ion concentrations. Therefore the model was modified to introduce a surface coverage concentration dependent effective diffusivity to account for a contribution from surface diffusion. PMID:11547855

  12. 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.

  13. Controlling chloride ions diffusion in concrete

    PubMed Central

    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

  14. 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.

  15. Controlling chloride ions diffusion in concrete.

    PubMed

    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

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

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

    EPA Science Inventory

    Abstract

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

  18. Data set for diffusion coefficients of alloying elements in dilute Mg alloys from first-principles

    PubMed Central

    Zhou, Bi-Cheng; Shang, Shun-Li; Wang, Yi; Liu, Zi-Kui

    2015-01-01

    Diffusion coefficients of alloying elements in Mg are critical for the development of new Mg alloys for lightweight applications. Here we present the data set of the temperature-dependent dilute tracer diffusion coefficients for 47 substitutional alloying elements in hexagonal closed packed (hcp) Mg calculated from first-principles calculations based on density functional theory (DFT) by combining transition state theory and an 8-frequency model. Benchmark for the DFT calculations and systematic comparison with experimental diffusion data are also presented. The data set refers to “Diffusion coefficients of alloying elements in dilute Mg alloys: A comprehensive first-principles study” by Zhou et al. [1]. PMID:26702419

  19. Estimate eddy diffusion coefficients from gravity wave vertical momentum and heat fluxes

    NASA Astrophysics Data System (ADS)

    Liu, Alan Z.

    2009-04-01

    A method was presented to estimate the eddy momentum and thermal diffusion coefficients from the gravity wave momentum and heat fluxes based on linear saturation theory. This method was applied using the fluxes between 85-100 km altitude measured by a Na wind/temperature lidar at Starfire Optical Range, NM (35N, 106.5W). The seasonal and altitude variations of the diffusion coefficients and Prandtl number were estimated. It is found that both diffusion coefficients are small in spring and fall and large in winter and summer. The annual mean momentum diffusion coefficient is about 400 m2/s between 85-100 km; the thermal diffusion coefficient decreases from 400 m2/s at 85 km to 100 m2/s at 100 km, resulting in a Prandtl number that increases with altitude from 1 to over 3.

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

    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.

  1. Simulation of Ion Diffusion in Kinetic Alfven Waves

    NASA Astrophysics Data System (ADS)

    Lin, Yu; Wang, Xueyi; Johnson, Jay

    2013-10-01

    Kinetic Alfven waves (KAWs) have been suggested to play an important role in the plasma transport. Previously, we carried out a three-dimensional (3-D) hybrid simulation for mode conversion from a fast wave to KAWs at the magnetopause, in which the magnetic field is in the ẑ direction perpendicular to the density gradient (◯). KAWs with kxρi ~ 1 generated by linear mode conversion were found to nonlinearly decay to modes with kyρi ~ 1 . The transfer of energy to large perpendicular and azimuthal ky modes has been suggested to provide large transport across plasma boundaries. In order to understand the ion diffusion in these KAWs, we now show a further 3-D hybrid simulation combined with test particle calculations for ion cross-field line diffusion in KAWs. A system of uniform plasma is driven by a steady KAW with k⊥ =kx . A turbulence spectrum is obtained. Dependence of the ion diffusion coefficient D⊥ on the driver amplitude, frequency, wave vector, ion beta, Te /Ti , and the particle energy is obtained. The results are also compared with those based on the quasilinear theory. The 3-D results are compared with the 2-D runs (ky = 0) to show the importance of 3-D physics.

  2. Ion diffusion at interfaces in hot plasmas

    SciTech Connect

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

    1986-04-01

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

  3. NMR measurements of solvent self-diffusion coefficients in polymer solutions

    NASA Astrophysics Data System (ADS)

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

    1989-11-01

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

  4. Diffusion coefficients of water in biobased hydrogel polymer matrices by nuclear magnetic resonance imaging

    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...

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

    SciTech Connect

    Kammerer, Catherine; Kulkarni, Nagraj S; Warmack, Robert J Bruce; Perry, Kelly A; Belova, Irina; Murch, Prof. Graeme; Sohn, Yong Ho

    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.

  6. Proton diffusion in nickel hydroxide films. Measurement of the diffusion coefficient as a function of state of charge

    SciTech Connect

    Motupally, S.; Streinz, C.C.; Weidner, J.W.

    1995-05-01

    Electrochemical impedance spectroscopy (ETS) was used to measure the solid-state diffusion coefficient of protons in nickel hydroxide films at room temperature as a function of state of charge (SOC). A model for the complex faradaic impedance of the nickel hydroxide active material is presented and used to extract the diffusion coefficient of protons from the EIS data. Impedance data over a range of frequencies can be used to extract a constant diffusion coefficient without the knowledge of the initial mobile proton concentration or the form of the charge-transfer kinetic expression. The proton diffusion coefficient is a strong function of SOC and decreases approximately three orders of magnitude from 3.4 {times} 10{sup {minus}8} to 6.4 {times} 10{sup {minus}11} cm{sup 2}/s as the electrode discharges from the completely charged to the completely discharged state. The measurements were performed on well-conditioned nickel hydroxide films and therefore it is likely that the diffusion coefficients measured correspond to the {beta}-phase of the active material. The diffusion coefficient of protons was measured for three different film thicknesses, 1.5, 1.2, and 1.0 {mu}m. The diffusion coefficient is independent of the thickness of the film is predicted by theory. The three orders of magnitude decrease in the diffusion coefficient of protons can be explained on the assumption that the protons move predominantly through the oxidized phase [NIOOH] which is interdispersed along with the reduced phase [Ni(OH){sub 2}] in the active material.

  7. Low coefficient of thermal expansion polyimides containing metal ion additives

    SciTech Connect

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

    1992-07-01

    Polyimides have become widely used as high performance polymers as a result of their excellent thermal stability and toughness. However, lowering their coefficient of thermal expansion (CTE) would increase their usefulness for aerospace and electronic applications where dimensional stability is a requirement. The CTE's of conventional polyimides range from 30 to 60 ppm/C. Approaches that have been reported to lower their CTE's include linearizing the polymer molecular structure and orienting the polyimide film. This current study involves the incorporation of metal ion-containing additives into polyimides and has resulted in significantly lowered CTE's. Various metal ion additives have been added to both polyamic acid resins and soluble polyimide solutions in the concentration range of 4-23 weight percent. The incorporation of these metal ions has resulted in reductions in the CTE's of the control polyimides of 12% to over 100% depending on the choice of additive and its concentration.

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

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

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

  9. A liquid state least-squares procedure for obtaining solid state multicomponent diffusion coefficients from diffusion couples

    SciTech Connect

    Miller, D.G.

    1998-11-02

    A procedure is developed for analyzing combined concentration profiles from multicomponent solid-state diffusion data obtained with free-diffusion boundary conditions. This procedure is exactly analogous to the analysis of liquid-state diffusion data obtained from free-diffusion refractive-index profiles (e.g. from Rayleigh interferometry). All data from all couples are least-squared together to characterize the diffusion coefficient matrix. Different profile weightings provide interesting alternatives, as well as diagnostics. Symmetric averagings are shown to eliminate or reduce effects of concentration dependence.

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

    NASA Astrophysics Data System (ADS)

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

    2002-06-01

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

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

    PubMed

    Bartelt-Hunt, Shannon L; Smith, James A

    2002-06-01

    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-filled porosity of 0.23-0.49. The experimental data were compared to several previously published relations that predict diffusion coefficients as a function of air-filled porosity and porosity. A multiple linear regression analysis was developed to determine if a modification of the exponents in Millington's [Science 130 (1959) 100] relation would better fit the experimental data. The literature relations appeared to generally underpredict the effective diffusion coefficient for the soil cores studied in this work. Inclusion of a particle-size distribution parameter, d10, did not significantly improve the fit of the linear regression equation. The effective diffusion coefficient and porosity data were used to recalculate estimates of diffusive flux through the subsurface made in a previous study performed at the field site. It was determined that the method of calculation used in the previous study resulted in an underprediction of diffusive flux from the subsurface. We conclude that although Millington's [Science 130 (1959) 100] relation works well to predict effective diffusion coefficients in homogeneous soils with relatively uniform particle-size distributions, it may be inaccurate for many natural soils with heterogeneous structure and/or non-uniform particle-size distributions. PMID:12102318

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

    PubMed

    Zhang, S; Splendiani, A; dos Santos, L M; Livingston, A G

    1998-07-01

    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. The TCE diffusion coefficients in the GJ10 biofilms were apparently constant at about the water value. The change in the diffusion coefficient for the JS150 biofilms is attributed to the influence of eddy diffusion and convective flow on transport in the thinner (<1-mm thick) biofilms. PMID:10099317

  13. An analytical estimate of the coefficient for radial charged particle diffusion in Jupiter's magnetosphere using plasma radial distribution

    NASA Astrophysics Data System (ADS)

    Gubar, Yu. I.

    2015-11-01

    A radial profile of the plasma mass distribution in Jupiter's magnetosphere in the region beyond Io's orbit up to ˜15 Jupiter radii R J constructed according to the results of measurements on the Voyager 1 and Galileo spacecraft is used to determine the radial dependence and radial diffusion coefficient D LL . The initial profile is approximated by a function decreasing as L -5 ± 1. For this radial mass distribution, radial ion diffusion outside of Io's orbit caused by centrifugal forces is possible. An estimate of (1.2-6.7)10-11 L 6 ± 1 for D LL was obtained.

  14. Scale Dependence of Effective Matrix Diffusion Coefficient Evidence and Preliminary Interpertation

    SciTech Connect

    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.

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

    SciTech Connect

    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.

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

    SciTech Connect

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

    2014-03-28

    The lithium ion diffusion coefficient of a 93% Li β-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 β-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 β-alumina single crystals. The diffusion time dependence of the diffusion coefficient was observed for the Li ion in the 93% Li β-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 β–alumina system.

  17. Banded structures in electron pitch angle diffusion coefficients from resonant wave-particle interactions

    NASA Astrophysics Data System (ADS)

    Tripathi, A. K.; Singhal, R. P.; Khazanov, G. V.; Avanov, L. A.

    2016-04-01

    Electron pitch angle (Dαα) and momentum (Dpp) diffusion coefficients have been calculated due to resonant interactions with electrostatic electron cyclotron harmonic (ECH) and whistler mode chorus waves. Calculations have been performed at two spatial locations L = 4.6 and 6.8 for electron energies ≤10 keV. Landau (n = 0) resonance and cyclotron harmonic resonances n = ±1, ±2, … ±5 have been included in the calculations. It is found that diffusion coefficient versus pitch angle (α) profiles show large dips and oscillations or banded structures. The structures are more pronounced for ECH and lower band chorus (LBC) and particularly at location 4.6. Calculations of diffusion coefficients have also been performed for individual resonances. It is noticed that the main contribution of ECH waves in pitch angle diffusion coefficient is due to resonances n = +1 and n = +2. A major contribution to momentum diffusion coefficients appears from n = +2. However, the banded structures in Dαα and Dpp coefficients appear only in the profile of diffusion coefficients for n = +2. The contribution of other resonances to diffusion coefficients is found to be, in general, quite small or even negligible. For LBC and upper band chorus waves, the banded structures appear only in Landau resonance. The Dpp diffusion coefficient for ECH waves is one to two orders smaller than Dαα coefficients. For chorus waves, Dpp coefficients are about an order of magnitude smaller than Dαα coefficients for the case n ≠ 0. In case of Landau resonance, the values of Dpp coefficient are generally larger than the values of Dαα coefficients particularly at lower energies. As an aid to the interpretation of results, we have also determined the resonant frequencies. For ECH waves, resonant frequencies have been estimated for wave normal angle 89° and harmonic resonances n = +1, +2, and +3, whereas for whistler mode waves, the frequencies have been calculated for angle 10° and Landau resonance. Further, in ECH waves, the banded structures appear for electron energies ≥1 keV, and for whistler mode chorus waves, structures appear for energies >2 keV at L = 4.6 and above 200 eV for L = 6.8. The results obtained in the present work will be helpful in the study of diffusion curves and will have important consequences for diffuse aurora and pancake distributions.

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

    NASA Astrophysics Data System (ADS)

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

    2007-10-01

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

  19. Molecular modeling of diffusion coefficient and ionic conductivity of CO2 in aqueous ionic solutions.

    PubMed

    Garcia-Ratés, Miquel; de Hemptinne, Jean-Charles; Bonet Avalos, Josep; Nieto-Draghi, Carlos

    2012-03-01

    Mass diffusion coefficients of CO(2)/brine mixtures under thermodynamic conditions of deep saline aquifers have been investigated by molecular simulation. The objective of this work is to provide estimates of the diffusion coefficient of CO(2) in salty water to compensate the lack of experimental data on this property. We analyzed the influence of temperature, CO(2) concentration,and salinity on the diffusion coefficient, the rotational diffusion, as well as the electrical conductivity. We observe an increase of the mass diffusion coefficient with the temperature, but no clear dependence is identified with the salinity or with the CO(2) mole fraction, if the system is overall dilute. In this case, we notice an important dispersion on the values of the diffusion coefficient which impairs any conclusive statement about the effect of the gas concentration on the mobility of CO(2) molecules. Rotational relaxation times for water and CO(2) increase by decreasing temperature or increasing the salt concentration. We propose a correlation for the self-diffusion coefficient of CO(2) in terms of the rotational relaxation time which can ultimately be used to estimate the mutual diffusion coefficient of CO(2) in brine. The electrical conductivity of the CO(2)-brine mixtures was also calculated under different thermodynamic conditions. Electrical conductivity tends to increase with the temperature and salt concentration. However, we do not observe any influence of this property with the CO(2) concentration at the studied regimes. Our results give a first evaluation of the variation of the CO(2)-brine mass diffusion coefficient, rotational relaxation times, and electrical conductivity under the thermodynamic conditions typically encountered in deep saline aquifers. PMID:22292779

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

    SciTech Connect

    Zhang, S.F.; Splendiani, A.; Freitas dos Santos, L.M.; Livingston, A.G.

    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.

  1. Diffusion Coefficients of Water and Leachables in Methacrylate-based Crosslinked Polymers using Absorption Experiments

    PubMed Central

    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

  2. NITRIC ACID-AIR DIFFUSION COEFFICIENT: EXPERIMENTAL DETERMINATION

    EPA Science Inventory

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

  3. Numerical results using the conforming VEM for the convection-diffusion-reaction equation with variable coefficients.

    SciTech Connect

    Manzini, Gianmarco; Cangiani, Andrea; Sutton, Oliver

    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.

  4. 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.

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

    SciTech Connect

    Lai, C.C.; Tan, C.S. . 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.

  6. A new procedure to measure effective molecular diffusion coefficients of salts solutions in building materials

    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.

  7. Diffusion Coefficient when fine Aerosol Media Propagate in a Confined Volume

    NASA Astrophysics Data System (ADS)

    Korovina, N. V.; Zharova, I. K.; Kudryashova, O. B.; Titov, S. S.

    2016-02-01

    An experimental estimation is reported of the value of the effective diffusion coefficient during aerosol deposition in a confined volume. Aerosol propagation regularities have experimentally been studied in a chamber of a complex configuration with different placement of aerosol generators.

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

    PubMed Central

    Meulemans, A

    1992-01-01

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

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

    SciTech Connect

    Fan, Y.; Qian, R.; Shi, M.; Shi, J.

    1995-09-01

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

  10. 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.

  11. Diffusion of ion-implanted Sn and Sb in heavily doped n-type silicon

    NASA Astrophysics Data System (ADS)

    Andersen, P. E.; Larsen, A. Nylandsted; Tidemand-Petersson, P.; Weyer, G.

    1988-08-01

    The diffusion of ion-implanted Sn and Sb in silicon single crystals during rapid thermal annealing at 1000 and 1050 °C has been studied as a function of P donor concentration. For extrinsic/intrinsic carrier concentration ratios (n/ni )≥20, almost identical, extremely large diffusion coefficients are found for both impurities. The diffusion coefficients exhibit approximately an (n/ni )4 dependence. The onset of this dependence is accompanied by the appearance of a new defect-complex type containing Sb or Sn, respectively.

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

    SciTech Connect

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

    2006-03-16

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

  13. Implications of observed PBDE diffusion coefficients in low density polyethylene and silicone rubber.

    PubMed

    Narváez Valderrama, Jhon F; Baek, Kine; Molina, Francisco J; Allan, Ian J

    2016-01-01

    A film-stacking technique was used to estimate diffusion coefficients of polybrominated diphenyl ethers (PBDEs) in low density polyethylene (LDPE) and silicone rubber. Substantially higher PBDE diffusion coefficients were observed for silicone rubber (AlteSil™) than for LDPE. A much steeper decrease in LDPE diffusion coefficients was found with increasing PBDE molecular weight than that for silicone rubber. From a passive sampling point-of-view, this means that for equivalent polymer-water partition coefficients for these two materials, the mass transfer resistance for these substances in the LDPE will be significantly higher than that for silicone rubber. Boundary layer control of the uptake process for silicone rubber can be expected for PBDEs. With a microplastic perspective, the low diffusion coefficients of PBDEs and in particular of decabromo diphenyl ether (BDE 209) in LDPE imply that the polymer diffusion coefficients for these plastic additives used as flame retardants need to be taken into account when considering the risk posed by microplastic particle ingestion by marine organisms. PMID:26678428

  14. Entropy-scaling laws for diffusion coefficients in liquid metals under high pressures

    SciTech Connect

    Cao, Qi-Long Shao, Ju-Xiang; Wang, Fan-Hou; Wang, Pan-Pan

    2015-04-07

    Molecular dynamic simulations on the liquid copper and tungsten are used to investigate the empirical entropy-scaling laws D{sup *}=A exp(BS{sub ex}), 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 D{sub M}=D{sub M}{sup 0} exp(−E{sub M}/K{sub B}T), (M=un,R,D) and the activation energy E{sub M} increases with increasing pressure, the diffusion pre-exponential factors (D{sub R}{sup 0} and D{sub D}{sup 0}) are nearly independent of the pressure and element. The pair correlation entropy, S{sub 2}, depends linearly on the reciprocal temperature S{sub 2}=−E{sub S}/T, and the activation energy, E{sub S}, increases with increasing pressure. In particular, the ratios of the activation energies (E{sub un}, E{sub R}, and E{sub D}) obtained from diffusion coefficients to the activation energy, E{sub S}, 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.

  15. Bounce averaged diffusion coefficients in a physics based magnetic field geometry from RAM-SCB

    NASA Astrophysics Data System (ADS)

    Zhao, Lei; Yu, Yiqun; Delzanno, Gian Luca; Jordanova, Vania K.

    2014-10-01

    In this work we explore wave-particle interaction in the radiation belt. By applying quasilinear theory, we obtain the particle diffusion coefficients in both pitch angle and energy for different configurations of the Earth's magnetic field. We consider the Earth's magnetic dipole field as a reference, and compare the results against non-dipole field configurations corresponding to quiet and stormy conditions. The latter are obtained with RAM-SCB, a code that models the Earth's ring current and provide a realistic modeling of the Earth's magnetic field. The bounce averaged electron pitch angle diffusion coefficients are calculated for each magnetic field configuration. The equatorial pitch angle, wave frequency and spectral distribution of whistler waves are shown to affect the bounce averaged diffusion coefficients. In addition, wave-particle resonance is significantly influenced by the magnetic field configuration: in storm conditions, diffusion is strongly reduced for some equatorial pitch angles.

  16. Maps of self-diffusion coefficients by radiofrequency field gradient NMR microscopy

    PubMed

    Valtier; Humbert; Canet

    1999-11-01

    The methods of measurement of spatially resolved diffusion coefficients using radiofrequency field gradient (E. Mischler et al., J. Magn. Reson. B 106, 32, 1995; R. Kimmich et al., J. Magn. Reson. A 112, 7, 1995) produce 1D profiles whose amplitude is not only a function of the local self-diffusion coefficient but also is modulated by cosine functions of spatial coordinates. Due to this modulation diffusion-weighted images cannot be obtained unless cumbersome data processing is used. Here, we present a new sequence which avoids this modulation and yields in a straightforward manner true self-diffusion coefficient maps; this is in contrast with conventional methods which use static field gradients and which are therefore altered by background gradients. The feasibility and the reliability of the method are demonstrated with phantoms; it is also applied to different systems of interest such as solvent swelled rubber, membranes, and plants. Copyright 1999 Academic Press. PMID:10527738

  17. Eddy diffusion coefficients and their upper limits based on application of the similarity theory

    NASA Astrophysics Data System (ADS)

    Vlasov, M. N.; Kelley, M. C.

    2015-07-01

    The equation for the diffusion velocity in the mesosphere and the lower thermosphere (MLT) includes the terms for molecular and eddy diffusion. These terms are very similar. For the first time, we show that, by using the similarity theory, the same formula can be obtained for the eddy diffusion coefficient as the commonly used formula derived by Weinstock (1981). The latter was obtained by taking, as a basis, the integral function for diffusion derived by Taylor (1921) and the three-dimensional Kolmogorov kinetic energy spectrum. The exact identity of both formulas means that the eddy diffusion and heat transport coefficients used in the equations, both for diffusion and thermal conductivity, must meet a criterion that restricts the outer eddy scale to being much less than the scale height of the atmosphere. This requirement is the same as the requirement that the free path of molecules must be much smaller than the scale height of the atmosphere. A further result of this criterion is that the eddy diffusion coefficients Ked, inferred from measurements of energy dissipation rates, cannot exceed the maximum value of 3.2 × 106 cm2 s-1 for the maximum value of the energy dissipation rate of 2 W kg-1 measured in the mesosphere and the lower thermosphere (MLT). This means that eddy diffusion coefficients larger than the maximum value correspond to eddies with outer scales so large that it is impossible to use these coefficients in eddy diffusion and eddy heat transport equations. The application of this criterion to the different experimental data shows that some reported eddy diffusion coefficients do not meet this criterion. For example, the large values of these coefficients (1 × 107 cm2 s-1) estimated in the Turbulent Oxygen Mixing Experiment (TOMEX) do not correspond to this criterion. The Ked values inferred at high latitudes by Lübken (1997) meet this criterion for summer and winter polar data, but the Ked values for summer at low latitudes are larger than the Ked maximum value corresponding to the criterion. Analysis of the experimental data on meteor train observations shows that energy dissipation with a small rate of about 0.2 W kg-1 sometimes can induce turbulence with eddy scales very close to the scale height of the atmosphere. Our results also explain the discrepancy between the large cooling rates calculated by Vlasov and Kelley (2014) and the temperatures given by the MSIS-E-90 model because, in these cases, the measured eddy diffusion coefficients used in calculating the cooling rates are larger than the maximum value presented above.

  18. Effects of molecular weight on the diffusion coefficient of aquatic dissolved organic matter and humic substances.

    PubMed

    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

  19. Blackness coefficients, effective diffusion parameters, and control rod worths for thermal reactors - methods

    SciTech Connect

    Bretscher, M.M.

    1984-01-01

    Simple diffusion theory cannot be used to evaluate control rod worths in thermal neutron reactors because of the strongly absorbing character of the control material. However, reliable control rod worths can be obtained within the framework of diffusion theory if the control material is characterized by a set of mesh-dependent effective diffusion parameters. For thin slab absorbers the effective diffusion parameters can be expressed as functions of a suitably-defined pair of blackness coefficients. Methods for calculating these blackness coefficients in the P/sub 1/, P/sub 3/, and P/sub 5/ approximations, with and without scattering, are presented. 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, based on reaction rate ratios, is discussed.

  20. Quaternary diffusion coefficients in a protein-polymer-salt-water system determined by rayleigh interferometry.

    PubMed

    Annunziata, Onofrio; Vergara, Alessandro; Paduano, Luigi; Sartorio, Roberto; Miller, Donald G; Albright, John G

    2009-10-01

    We have experimentally investigated multicomponent diffusion in a protein-polymer-salt-water quaternary system. Specifically, we have measured the nine multicomponent diffusion coefficients, D(ij), for the lysozyme-poly(ethylene glycol)-NaCl-water system at pH 4.5 and 25 degrees C using precision Rayleigh interferometry. Lysozyme is a model protein for protein-crystallization and enzymology studies. We find that the protein diffusion coefficient, D(11), decreases as polymer concentration increases at a given salt concentration. This behavior can be quantitatively related to the corresponding increase in fluid viscosity only at low polymer concentration. However, at high polymer concentration (250 g/L), protein diffusion is enhanced compared to the corresponding viscosity prediction. We also find that a protein concentration gradient induces salt diffusion from high to low protein concentration. This effect increases in the presence of poly(ethylene glycol). Finally, we have evaluated systematic errors associated with measurements of protein diffusion coefficients by dynamic light scattering. This work overall helps characterize protein diffusion in crowded environments and may provide guidance for further theoretical developments in the field of protein crystallization and protein diffusion in such crowded systems, such as the cytoplasm of living cells. PMID:19746957

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

    PubMed Central

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

    2014-01-01

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

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

    PubMed Central

    2014-01-01

    Background Support vector regression (SVR) and Gaussian process regression (GPR) were used for the analysis of electroanalytical experimental data to estimate diffusion coefficients. Results For simulated cyclic voltammograms based on the EC, Eqr, and EqrC mechanisms these regression algorithms in combination with nonlinear kernel/covariance functions yielded diffusion coefficients with higher accuracy as compared to the standard approach of calculating diffusion coefficients relying on the Nicholson-Shain equation. The level of accuracy achieved by SVR and GPR is virtually independent of the rate constants governing the respective reaction steps. Further, the reduction of high-dimensional voltammetric signals by manual selection of typical voltammetric peak features decreased the performance of both regression algorithms compared to a reduction by downsampling or principal component analysis. After training on simulated data sets, diffusion coefficients were estimated by the regression algorithms for experimental data comprising voltammetric signals for three organometallic complexes. Conclusions Estimated diffusion coefficients closely matched the values determined by the parameter fitting method, but reduced the required computational time considerably for one of the reaction mechanisms. The automated processing of voltammograms according to the regression algorithms yields better results than the conventional analysis of peak-related data. PMID:24987463

  3. Development of measuring diffusion coefficients by digital holographic interferometry in transparent liquid mixtures.

    PubMed

    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) m2/s with the uncertainty of ± 0.012 × 10(-9) m2/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

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

    PubMed

    Jiránek, M; Kotrbatá, M

    2011-05-01

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

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

    NASA Astrophysics Data System (ADS)

    Chae, Kyungchan; Violi, Angela

    2011-01-01

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

  6. Measurement and clinical and pharmacokinetic implications of diffusion coefficients of antibiotics in tissues.

    PubMed

    Meulemans, A; Paycha, F; Hannoun, P; Vulpillat, M

    1989-08-01

    A method for determining diffusion coefficients of four antibiotics in extracellular tissue space according to Fick's law is described. This new method was applied to rat brain tissue and to agar. After diffusion of the antibiotic in one axis, the gradient concentration was determined with microvoltammetric electrodes. These microelectrodes (1 micron at the extreme tip) measured the free diffusible form of electroactive antibiotics in the extracellular brain space. Metronidazole, chloramphenicol succinate, cefsulodin, and piperacillin gave diffusion coefficients ranging from 0.1 x 10(-6) to 0.2 x 10(-6) cm2 . s-1 in tissue; chloramphenicol base, which is positively charged, gave a coefficient of 0.04 x 10(-6) cm2 . s-1. The coefficient ranged from 0.6 x 10(-6) to 1.2 x 10(-6) cm2 . s-1 in agar. These coefficients were used to simulate antibiotic concentrations in infectious sites and between capillaries by using a simple model of plane diffusion. PMID:2802555

  7. Measurement and clinical and pharmacokinetic implications of diffusion coefficients of antibiotics in tissues.

    PubMed Central

    Meulemans, A; Paycha, F; Hannoun, P; Vulpillat, M

    1989-01-01

    A method for determining diffusion coefficients of four antibiotics in extracellular tissue space according to Fick's law is described. This new method was applied to rat brain tissue and to agar. After diffusion of the antibiotic in one axis, the gradient concentration was determined with microvoltammetric electrodes. These microelectrodes (1 micron at the extreme tip) measured the free diffusible form of electroactive antibiotics in the extracellular brain space. Metronidazole, chloramphenicol succinate, cefsulodin, and piperacillin gave diffusion coefficients ranging from 0.1 x 10(-6) to 0.2 x 10(-6) cm2 . s-1 in tissue; chloramphenicol base, which is positively charged, gave a coefficient of 0.04 x 10(-6) cm2 . s-1. The coefficient ranged from 0.6 x 10(-6) to 1.2 x 10(-6) cm2 . s-1 in agar. These coefficients were used to simulate antibiotic concentrations in infectious sites and between capillaries by using a simple model of plane diffusion. PMID:2802555

  8. Confinement, Desolvation, And Electrosorption Effects on the Diffusion of Ions in Nanoporous Carbon Electrodes

    PubMed Central

    2015-01-01

    Supercapacitors are electrochemical devices which store energy by ion adsorption on the surface of a porous carbon. They are characterized by high power delivery. The use of nanoporous carbon to increase their energy density should not hinder their fast charging. However, the mechanisms for ion transport inside electrified nanopores remain largely unknown. Here we show that the diffusion is characterized by a hierarchy of time scales arising from ion confinement, solvation, and electrosorption effects. By combining electrochemistry experiments with molecular dynamics simulations, we determine the in-pore conductivities and diffusion coefficients and their variations with the applied potential. We show that the diffusion of the ions is slower by 1 order of magnitude compared to the bulk electrolyte. The desolvation of the ions occurs on much faster time scales than electrosorption. PMID:26369420

  9. Time of Flight Electrochemistry: Diffusion Coefficient Measurements Using Interdigitated Array (IDA) Electrodes

    SciTech Connect

    Liu, Fei; Kolesov, Grigory; Parkinson, Bruce A.

    2014-09-26

    A simple and straightforward method for measuring diffusion coefficients using interdigitated array (IDA) electrodes is reported. The method does not require that the exact electrode area be known but depends only the size of the gap between the IDA electrode pairs. Electroactive molecules produced at the generator electrode of the IDA by a voltage step or scan can diffuse to the collector electrode and the time delay before the current for the reverse electrochemical reaction is detected at the collector is used to calculate the diffusion coefficient. The measurement of the diffusion rate of Ru(NH3)6+2 in aqueous solution has been used as an example measuring diffusion coefficients using this method. Additionally, a digital simulation of the electrochemical response of the IDA electrodes was used to simulate the entire current/voltage/time behavior of the system and verify the experimentally measured diffusion coefficients. This work was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the Department of Energy, Office of Science, Office of Basic Energy Sciences.

  10. Combined refinement of diffusion coefficients applied on the Nb-C and Nb-N systems

    SciTech Connect

    Rafaja, D.; Lengauer, W.; Wiesenberger, H.; Joguet, M.

    1998-02-01

    A novel technique was used for the calculation of diffusion coefficients in the niobium carbides and nitrides prepared by reaction diffusion. The temperature ranges investigated were 1,500 C to 2,100 C for the Nb-C system and 1,400 C to 1,800 C for the Nb-N system. Three independent theoretical approaches were applied and their results are compared. In the metalloid-rich phases, the concentration-dependent diffusion coefficients were calculated from the concentration profiles; two models of layer growth were used to obtain the concentration-independent diffusion coefficients in all phases. It was found that the diffusion coefficient of carbon in {delta}-NbC{sub 1{minus}x} shows a decrease with increasing metalloid concentration, whereas the diffusivity of nitrogen in {delta}-NbN{sub 1{minus}x} is nearly independent of the nonmetal concentration. The concentration dependence of the carbon diffusion coefficients in {delta}-NbC{sub 1{minus}x} is a result of a lower activation energy of carbon diffusion in the substoichiometric {delta}-NbC{sub 1{minus}x} than in the {delta}-NbC. On the contrary, the activation energy of nitrogen in {delta}-NbN{sub 1{minus}x} does not change with the nitrogen concentration. This behavior could be explained by the different occupancies of metal sublattices, which remain constant in {delta}-NbC{sub 1{minus}x} but decrease with increasing nonmetal concentration in {delta}-NbN{sub 1{minus}x}.

  11. Tracer diffusion coefficients in sedimentary rocks: correlation to porosity and hydraulic conductivity.

    PubMed

    Boving, T B; Grathwohl, P

    2001-12-01

    Matrix diffusion is an important transport process in geologic materials of low hydraulic conductivity. For predicting the fate and transport of contaminants, a detailed understanding of the diffusion processes in natural porous media is essential. In this study, diffusive tracer transport (iodide) was investigated in a variety of geologically different limestone and sandstone rocks. Porosity, structural and mineralogical composition, hydraulic conductivity, and other rock properties were determined. The effective diffusion coefficients were measured using the time-lag method. The results of the diffusion experiments indicate that there is a close relationship between total porosity and the effective diffusion coefficient of a rock (analogous to Archie's Law). Consequently, the tortousity factor can be expressed as a function of total porosity. The relationship fits best for thicker samples (> 1.0 cm) with high porosities (> 20%), because of the reduced influence of heterogeneity in larger samples. In general, these correlations appear to be a simple way to determine tortuosity and the effective diffusion coefficient from easy to determine rock porosity values. PMID:11816996

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

    NASA Astrophysics Data System (ADS)

    Marquardt, Katharina; Dohmen, Ralf; Wagner, Johannes

    2014-05-01

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

  13. Diffusion and Coulomb separation of ions in dense matter.

    PubMed

    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

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

    PubMed

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

    2014-04-01

    The mathematical apparatus and the experimental installation for the rapid determination of radon diffusion coefficient in various materials are developed. The single test lasts not longer than 18h and allows testing numerous materials, such as gaseous and liquid media, as well as soil, concrete and radon-proof membranes, in which diffusion coefficient of radon may vary in an extremely wide range, from 110(-12) to 510(-5)m(2)/s. The uncertainty of radon diffusion coefficient estimation depends on the permeability of the sample and varies from about 5% (for the most permeable materials) to 40% (for less permeable materials, such as radon-proof membranes). PMID:24412813

  15. 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.

  16. Measurement of CO2 diffusivity in synthetic and saline aquifer solutions at reservoir conditions: the role of ion interactions

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2009-02-01

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

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

    SciTech Connect

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

    2005-03-28

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

  19. Approximation of effective moisture-diffusion coefficient to characterize performance of a barrier coating

    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.

  20. Nuclear magnetic resonance relaxometry as a method of measuring translational diffusion coefficients in liquids.

    PubMed

    Kruk, D; Meier, R; Rössler, E A

    2012-02-01

    By application of the field-cycling technique, we measure the dispersion of the (1)H nuclear magnetic resonance (NMR) spin-lattice relaxation time T(1)(ω) for a series of molecular liquids. We demonstrate that such NMR relaxometry studies can be used for determining diffusion coefficients. A broad frequency range of 10 kHz-20 MHz is covered. By scanning T(1)(ω) one directly probes the spectral density of the diffusion processes. The value of the diffusion coefficient D can be determined from a linear dependence of the (1)H spin-lattice relaxation rate on the square root of the frequency at which it is measured. The power of this method lies in its simplicity, which allows one to determine D(T) independently of the diffusive model. The results obtained are in very good agreement with those of field gradient NMR methods. PMID:22463139

  1. Minority carrier diffusion lengths and absorption coefficients in silicon sheet material

    SciTech Connect

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

    1980-01-01

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

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

    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.

  3. ICP-MS measurement of diffusion coefficients of Cs in NBG-18 graphite

    NASA Astrophysics Data System (ADS)

    Carter, L. M.; Brockman, J. D.; Robertson, J. D.; Loyalka, S. K.

    2015-11-01

    Graphite is used in the HGTR/VHTR as moderator and it also functions as a barrier to fission product release. Therefore, an elucidation of transport of fission products in reactor-grade graphite is required. We have measured diffusion coefficients of Cs in graphite NBG-18 using the release method, wherein we infused spheres of NBG-18 with Cs and measured the release rates in the temperature range of 1090-1395 K. We have obtained: These seem to be the first reported values of Cs diffusion coefficients in NBG-18. The values are lower than those reported for other graphites in the literature.

  4. Determining molecule diffusion coefficients on surfaces from a locally fixed probe: Analysis of signal fluctuations

    NASA Astrophysics Data System (ADS)

    Hahne, Susanne; Ikonomov, Julian; Sokolowski, Moritz; Maass, Philipp

    2013-02-01

    Methods of determining surface diffusion coefficients of molecules from signal fluctuations of a locally fixed probe are revisited and refined. Particular emphasis is put on the influence of the molecule's extent. In addition to the formerly introduced autocorrelation method and residence time method, we develop a further method based on the distribution of intervals between successive peaks in the signal. The theoretical findings are applied to scanning tunneling microscopy measurements of copper phthalocyanine (CuPc) molecules on the Ag(100) surface. We discuss advantages and disadvantages of each method and suggest a combination to obtain accurate results for diffusion coefficients.

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

    NASA Astrophysics Data System (ADS)

    Cristadoro, Giampaolo

    2006-03-01

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

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

    SciTech Connect

    Sarkar, Sreemoyee; Dutt-Mazumder, Abhee K.

    2011-11-01

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

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

    SciTech Connect

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

    2005-04-08

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

  8. Lithium Ion Solvation and Diffusion in Bulk Organic Battery Electrolytes from First Principles Molecular Dynamics

    NASA Astrophysics Data System (ADS)

    Ong, Mitchell; Lordi, Vincenzo; Draeger, Erik; Pask, John

    2014-03-01

    Lithium-ion batteries are commonly used to power many consumer devices. One of the key properties that influence the performance of lithium-ion batteries is the ionic conductivity of the electrolyte. This is dependent on the speed at which Li ions diffuse across the cell and related to the solvation structure of the Li ions. The choice of the electrolyte can greatly impact both solvation and diffusivity of Li ions. In this work, we use first principles molecular dynamics to examine the solvation and diffusion of Li ions in several bulk organic electrolytes. We find that differences in the local environment throughout the liquid can lead to solvation of Li ions by either carbonyl or ether oxygen atoms. In addition, we examine the differences in solvation of associated and dissociated Li(PF6) salts, showing that the bulky PF6 group blocks complete solvation of Li+ by solvent oxygen atoms. Finally, we calculate Li diffusion coefficients in each electrolyte, finding slightly larger diffusivities in a linear carbonate such as ethyl methyl carbonate (EMC) compared to a cyclic carbonate like ethylene carbonate (EC). Results from this work can be used to design new bulk electrolytes that will improve the performance of current Li-ion batteries.

  9. Correlation between the self-diffusion coefficient of lithium and the equation of state

    NASA Astrophysics Data System (ADS)

    Eftaxias, K.; Grammatikakis, J.; Varotsos, P.

    1985-10-01

    Anderson and Swenson [Phys. Rev. B 31, 668 (1985)] have recently presented new isothermal elastic data for lithium for temperatures up to 350 K. It is shown that these data are closely connected to the temperature variation of the self-diffusion coefficient D. Although the latter varies by six orders of magnitude (in the temperature region 195-350 K), however, the elastic data can successfully reproduce the self-diffusion curve without the use of any adjustable parameter.

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Martinavičius, A.; Abrasonis, G.; Möller, W.

    2011-10-01

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

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

    SciTech Connect

    Martinavicius, A.; Abrasonis, G.; Moeller, W.

    2011-10-01

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

  13. 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.

  14. Effect of surface modification, microstructure, and trapping on hydrogen diffusion coefficients in high strength alloys

    NASA Astrophysics Data System (ADS)

    Jebaraj Johnley Muthuraj, Josiah

    Cathodic protection is widely used for corrosion prevention. However, this process generates hydrogen at the protected metal surface, and diffusion of hydrogen through the metal may cause hydrogen embrittlement or hydrogen induced stress corrosion cracking. Thus the choice of a metal for use as fasteners depends upon its hydrogen uptake, permeation, diffusivity and trapping. The diffusivity of hydrogen through four high strength alloys (AISI 4340, alloy 718, alloy 686, and alloy 59) was analyzed by an electrochemical method developed by Devanathan and Stachurski. The effect of plasma nitriding and microstructure on hydrogen permeation through AISI 4340 was studied on six different specimens: as-received (AR) AISI 4340, nitrided samples with and without compound layer, samples quenched and tempered (Q&T) at 320° and 520°C, and nitrided samples Q&T 520°C. Studies on various nitrided specimens demonstrate that both the gamma'-Fe 4N rich compound surface layer and the deeper N diffusion layer that forms during plasma nitriding reduce the effective hydrogen diffusion coefficient, although the gamma'-Fe4N rich compound layer has a larger effect. Multiple permeation transients yield evidence for the presence of only reversible trap sites in as-received, Q&T 320 and 520 AISI 4340 specimens, and the presence of both reversible and irreversible trap sites in nitrided specimens. Moreover, the changes in microstructure during the quenching and tempering process result in a significant decrease in the diffusion coefficient of hydrogen compared to as-received specimens. In addition, density functional theory-based molecular dynamics simulations yield hydrogen diffusion coefficients through gamma'- Fe4N one order of magnitude lower than through α-Fe, which supports the experimental measurements of hydrogen permeation. The effect of microstructure and trapping was also studied in cold rolled, solutionized, and precipitation hardened Inconel 718 foils. The effective hydrogen diffusion coefficient is considerably higher for the solutionized Inconel 718 than for either the cold rolled or precipitation hardened specimens. Microstructural studies indicate that the reduced hydrogen diffusion coefficients in the latter specimens arise from hydrogen trapping at dislocations and precipitates that are present at much lower concentrations in the solutionized specimens. Repeated permeation transients provide evidence for irreversible hydrogen trapping in the cold rolled and precipitation hardened specimens, but such effects are insignificant in the solutionized specimens. The effect of trapping in determining the hydrogen diffusion coefficients was also studied in alloy 686 and 59 specimens. Microstructural studies indicate the presence of bcc-Mo rich inclusions concentrated along the grain boundaries in alloy 686 specimens, but randomly distributed in alloy 59 specimens. Multiple permeation transients show an increase in diffusion coefficient values for the decay transients compared to rise transients in alloy 686 specimens. On the other hand, the first rise transient had a lower diffusion coefficient compared to successive rise and decay transients in alloy 59 specimens. Effective diffusion coefficient (Deff) values of hydrogen in multiple permeation transients suggest that hydrogen trapping sites are predominantly reversible in alloy 686, but mixed reversible and irreversible in alloy 59.

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

    NASA Astrophysics Data System (ADS)

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

    1997-08-01

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

  16. Ion Implantation in ZnO: Defect Interaction and Impurity Diffusion

    NASA Astrophysics Data System (ADS)

    Yaqoob, Faisal

    In the first part of this research we studied the entropy changes in diffusion prefactor and its effects on diffusion mechanisms and activation energies. We demonstrate a method based on ion implantation and Rutherford backscattering spectroscopy combined with ion channeling (RBS/C) to experimentally determine the diffusion properties of substitutional and interstitial diffusing atoms. The activation energies for each diffusing species are found to be in good agreement with those calculated in previous theoretical studies. The exponential prefactors of the measured diffusion coefficients vary by ten orders of magnitude among substitutional and interstitial diffusing species, allowing us to assign a specific diffusion mechanism to each type of diffusant according to both its diffusion energetics and entropic changes. In addition, the diffusion activation energies and the diffusivity prefactor for the four diffusing species studied are found to follow the Meyer--Neldel relationship with a characteristic excitation energy of ~ 92 meV in ZnO. In another important problem related to the p-doping difficulty in ZnO materials, we studied the effects of ion-implanted hydrogen ions on defect formation and impurity redistribution in ZnO crystals implanted with silver ions. Following Ag ion implantation, the damage level in the ZnO lattice was higher in the sample without H ion implantation than the sample with the H. We found that the damage created to oxygen lattice by the Ag atoms during implantation was higher than the damaged caused to the zinc lattice. Moreover, the Zn lattice recovered faster than the O lattice during thermal annealing. The Ag atoms have higher substitutional fraction in samples without H and increases with annealing temperature. In H implanted samples Ag and H is passivated in defect-related cluster, resulting lower activation of Ag. The diffusion process is affected by H implantation, making it difficult to diffuse to substitutional sites. We discuss these findings in the context of the effects of nano-cavities on formation and annihilation of point defects as well as on impurity diffusion and trapping in ZnO crystals. In the last part of this research we implanted antimony in zinc oxide at higher substrate temperature to study the substitution on desired lattice location. The idea was to study the effect of thermal processes on defect creation and Sb substitution during ion implantation. RBS/C was combined with angular scans along two-crystal direction to study the lattice location and substitution of Sb in ZnO. Areal density measured at different substrate temperatures and a post annealing is compered for substitution on Zn and O lattice sites.

  17. The Influence of Spatial Variations of Diffusion Length on Charge Collected by Diffusion from Ion Tracks

    NASA Technical Reports Server (NTRS)

    Edmonds, L. D.

    1996-01-01

    Charge collected by diffusion from ion tracks in a semiconductor substrate may be influenced by the substrate diffusion length, which is related to recombination losses. A theoretical analysis shows that, excluding some extreme cases, charge collection is insensitive to spatial variations in the diffusion length funciton, so it is possible to define an effective diffusion length having the property that collected charge can be approximated by assuming a uniform diffusion length equal to this effective value.

  18. 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.

  19. Diffusion Coefficients from Molecular Dynamics Simulations in Binary and Ternary Mixtures

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

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

  20. VARYING COEFFICIENT MODEL FOR MODELING DIFFUSION TENSORS ALONG WHITE MATTER TRACTS

    PubMed Central

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

    2012-01-01

    Diffusion tensor imaging provides important information on tissue structure and orientation of fiber tracts in brain white matter in vivo. It results in diffusion tensors, which are 3×3 symmetric positive definite (SPD) matrices, along fiber bundles. This paper develops a functional data analysis framework to model diffusion tensors along fiber tracts as functional data in a Riemannian manifold with a set of covariates of interest, such as age and gender. We propose a statistical model with varying coefficient functions to characterize the dynamic association between functional SPD matrix-valued responses and covariates. We calculate weighted least squares estimators of the varying coefficient functions for the Log-Euclidean metric in the space of SPD matrices. We also develop a global test statistic to test specific hypotheses about these coefficient functions and construct their simultaneous confidence bands. Simulated data are further used to examine the finite sample performance of the estimated varying co-efficient functions. We apply our model to study potential gender differences and find a statistically significant aspect of the development of diffusion tensors along the right internal capsule tract in a clinical study of neurodevelopment. PMID:24533040

  1. Bounce averaged diffusion coefficients in a physics based magnetic field geometry from RAM-SCB

    NASA Astrophysics Data System (ADS)

    Zhao, L.; Yu, Y.; Delzanno, G. L.; Jordanova, V.

    2014-12-01

    Local acceleration via whistler wave and particle interaction plays an important role in particle dynamics in the radiation belt. In this work we explore wave-particle interaction in different magnetic field configurations related to the 17 March, 2013 storm. We consider the Earth's magnetic dipole field as a reference, and compare the results against non-dipole field configurations corresponding to quiet and stormy conditions. The latter are obtained with RAM-SCB, a code that models the Earth's ring current and provides a realistic modeling of the Earth's magnetic field. By applying quasi-linear theory, the bounce-averaged electron pitch angle, energy and mixed term diffusion coefficients are calculated for each magnetic field configuration. It is shown that the magnetic field can have a significant influence on the diffusion coefficients via the wave-particle resonance condition. In addition, the equatorial pitch angle, wave frequency and spectral distribution of whistler waves also affect the bounce-averaged diffusion coefficients in particle energy range from KeV to MeV. Part of the ongoing work will focus on the phase space density evolution based on the Fokker-Planck equation with the bounce-averaged diffusion coefficients previously calculated.

  2. Measuring arbitrary diffusion coefficient distributions of nano-objects by taylor dispersion analysis.

    PubMed

    Cipelletti, Luca; Biron, Jean-Philippe; Martin, Michel; Cottet, Hervé

    2015-08-18

    Taylor dispersion analysis is an absolute and straightforward characterization method that allows determining the diffusion coefficient, or equivalently the hydrodynamic radius, from angstroms to submicron size range. In this work, we investigated the use of the Constrained Regularized Linear Inversion approach as a new data processing method to extract the probability density functions of the diffusion coefficient (or hydrodynamic radius) from experimental taylorgrams. This new approach can be applied to arbitrary polydisperse samples and gives access to the whole diffusion coefficient distributions, thereby significantly enhancing the potentiality of Taylor dispersion analysis. The method was successfully applied to both simulated and real experimental data for solutions of moderately polydisperse polymers and their binary and ternary mixtures. Distributions of diffusion coefficients obtained by this method were favorably compared with those derived from size exclusion chromatography. The influence of the noise of the simulated taylorgrams on the data processing is discussed. Finally, we discuss the ability of the method to correctly resolve bimodal distributions as a function of the relative separation between the two constituent species. PMID:26243023

  3. Test liquids for quantitative MRI measurements of self-diffusion coefficient in vivo.

    PubMed

    Tofts, P S; Lloyd, D; Clark, C A; Barker, G J; Parker, G J; McConville, P; Baldock, C; Pope, J M

    2000-03-01

    A range of liquids suitable as quality control test objects for measuring the accuracy of clinical MRI diffusion sequences (both apparent diffusion coefficient and tensor) has been identified and characterized. The self-diffusion coefficients for 15 liquids (3 cyclic alkanes: cyclohexane to cyclooctane, 9 n-alkanes: n-octane to n-hexadecane, and 3 n-alcohols: ethanol to 1-propanol were measured at 15-30 degrees C using an NMR spectrometer. Values at 22 degrees C range from 0.36 to 2.2 10(-9) m(2)s(-1). Typical 95% confidence limits are +/-2%. Temperature coefficients are 1.7-3.2% degrees C. T1 and T2 values at 1.5 T and proton density are given. n-tridecane has a diffusion coefficient close to that of normal white matter. The longer n-alkanes may be useful T2 standards. Measurements from a spin-echo MRI sequence agreed to within 2%. PMID:10725879

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

    EPA Science Inventory

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

  5. Compact exponential scheme for the time fractional convection-diffusion reaction equation with variable coefficients

    NASA Astrophysics Data System (ADS)

    Cui, Mingrong

    2015-01-01

    High-order compact exponential finite difference scheme for solving the time fractional convection-diffusion reaction equation with variable coefficients is considered in this paper. The convection, diffusion and reaction coefficients can depend on both the spatial and temporal variables. We begin with the one dimensional problem, and after transforming the original equation to one with diffusion coefficient unity, the new equation is discretized by a compact exponential finite difference scheme, with a high-order approximation for the Caputo time derivative. We prove the solvability of this fully discrete implicit scheme, and analyze its local truncation error. For the fractional equation with constant coefficients, we use Fourier method to prove the stability and utilize matrix analysis as a tool for the error estimate. Then we discuss the two dimensional problem, give the compact ADI scheme with the restriction that besides the time variable, the convection coefficients can only depend on the corresponding spatial variables, respectively. Numerical results are provided to verify the accuracy and efficiency of the proposed algorithm.

  6. Electro-diffusion in a plasma with two ion species

    SciTech Connect

    Kagan, Grigory; Tang Xianzhu

    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.

  7. Heavy Ion Distribution Function in Magnetic Reconnection Diffusion Region

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  8. Fickian Diffusion Coefficient of Binary Liquid Mixtures in a Thermogravitational Column

    NASA Astrophysics Data System (ADS)

    Valencia, J. J.; Bou-Ali, M. M.; Platten, J. K.; Ecenarro, O.; Madariaga, J. M.; Santamara, C. M.

    2007-09-01

    By measuring the mass fraction difference between the top and the bottom of a thermogravitational column as a function of time, we show that this transient evolution of the separation toward its steady value gives the isothermal mass diffusion coefficient, at least in the validity limit of the Furry-Jones-Onsager theory, whereas the final steady separation produces the thermodiffusion coefficient. The following mixtures have been considered: water-ethanol (39.12 wt% ethanol), toluene-hexane (51.7 wt% toluene), and the three systems of the so-called benchmark of Fontainebleau, which are the three binaries composed of isobutylbenzene and/or dodecane and/or 1,2,3,4 tetrahydronaphthalene (50 wt% in each component for each case). The obtained results indicate that reliable values of the isothermal diffusion coefficient can be determined by using the thermogravitational method.

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

    SciTech Connect

    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.

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

    PubMed

    Perko, Janez; Patel, Ravi A

    2014-05-01

    The paper presents an approach that extends the flexibility of the standard lattice Boltzmann single relaxation time scheme in terms of spatial variation of dissipative terms (e.g., diffusion coefficient) and stability for high Péclet mass transfer problems. Spatial variability of diffusion coefficient in SRT is typically accommodated through the variation of relaxation time during the collision step. This method is effective but cannot deal with large diffusion coefficient variations, which can span over several orders of magnitude in some natural systems. The approach explores an alternative way of dealing with large diffusion coefficient variations in advection-diffusion transport systems by introducing so-called diffusion velocity. The diffusion velocity is essentially an additional convective term that replaces variations in diffusion coefficients vis-à-vis a chosen reference diffusion coefficient which defines the simulation time step. Special attention is paid to the main idea behind the diffusion velocity formulation and its implementation into the lattice Boltzmann framework. Finally, the performance, stability, and accuracy of the diffusion velocity formulation are discussed via several advection-diffusion transport benchmark examples. These examples demonstrate improved stability and flexibility of the proposed scheme with marginal consequences on the numerical performance. PMID:25353916

  11. A study of enhanced diffusion during high dose high flux pulsed metal ion implantation into steel and aluminium

    NASA Astrophysics Data System (ADS)

    Tonghe, Zhang; Chengzhou, Ji; Jinghua, Shen; Jun, Chen

    1992-04-01

    The depth profiles of metal ions implanted into steel and aluminium were measured by Rutherford backscattering (RBS). The ions of Mo, W and Y, produced by a metal vapour vacuum arc ion source (MEVVA) were implanted at an energy range from 25 to 50 keV for doses of (2-5)×10 17 cm -2 into H13 steel and aluminium. Beam currents were from 0.5 to 1.0 A. The beam flux is in the range of 25 to 75 μAcm -2. In order to simulate the profiles, a formula which includes the sputtering yield, diffusion coefficients and reaction rate was obtained. The results demonstrate that the penetration depth and retained dose increase with increasing beam flux for Mo implanted into aluminum. The peak concentration of Mo implanted H13 steel increases with increasing ion flux. In contrast to this for Y implantation into steel, the peak concentration of Y decreases with increasing ion flux. For an ion flux of 25 μA cm -2 for Mo, Y and W implantation into steel, the penetration depth and retained dose are 3-5 times greater than the theoretical values. The diffusion coefficients are about 10 -16 to 10 -15 s -1. If the ion flux is greater than 47 μA cm -2, the penetration depth and retained dose are 5 to 10 times greater than the theoretical values for Mo implanted aluminium. The diffusion coefficients increase with increasing ion flux for Mo implanted aluminium. The diffusion coefficients hardly change with increasing ion flux for Y and Mo implanted H13 steel. The retained dose increases 0.43 to 1.16 times for Y implanted steel for an ion flux of 25 μA cm -2. Finally, the influence of phases precipitates, reaction rate and diffusion on retained dose, diffusion coefficient and penetration depth are discussed.

  12. Calculations of Li Ion Diffusion in Olivine Phosphates

    SciTech Connect

    Dathar, Gopi Krishna Phani; Sheppard, Daniel; Stevenson, Keith J.; Henkelman, Graeme

    2011-09-13

    Kinetic pathways of Li-ion diffusion in olivine phosphates are calculated from density functional theory (DFT). Previously reported theoretical diffusion rates for Li ions and vacancies in defect-free crystalline FePO₄ and LiFePO₄ are six orders of magnitude faster than experimentally measured values. This discrepancy can be resolved by considering the different components of Li kinetics, including diffusion in the bulk, on the surface, in the presence of defects, and in varying local environments. Using DFT+U, we quantify each of these effects and determine that, while bulk diffusion is affected by strain and Li concentration, these are not significant enough to explain the slow diffusion observed in experiment. However, surface diffusion is observed to have have high barriers, which could contribute to slow kinetics in nanostructured cathodes. Anti-site defects also provide a possible explanation for slow diffusion, but only for vacancy diffusion in LiFePO₄, which has a barrier of 0.71 eV, compared to 0.29 eV in defect-free channels. In FePO₄, a concerted Li-ion diffusion mechanism around the anti-site defect is found to have a low barrier of 0.35 eV, allowing for facile cross-channel diffusion at room temperature. The difference between Li-ion and vacancy diffusion is understood in terms of a favorable coordination between Li ions and localized electrons on Fe centers at the transition states for Li-ion hopping in FePO₄. Greater distances between vacancies and holes at the transition states for vacancy diffusion lead to higher diffusion barriers.

  13. 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.

  14. Kinks in experimental diffusion profiles of a dissolving semi-crystalline polymer explained by a concentration-dependent diffusion coefficient.

    PubMed

    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

  15. Importance of diffuse metal ion binding to RNA.

    PubMed

    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

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

    NASA Astrophysics Data System (ADS)

    Newton, A. G.; Kozaki, T.

    2010-12-01

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

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

    SciTech Connect

    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.

  18. Bond lifetime and diffusion coefficient in colloids with short-range interactions.

    PubMed

    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

  19. [Characteristics of the diffuse attenuation coefficient and its impact on aquatic ecology environment].

    PubMed

    Huang, Chang-Chun; Li, Yun-Mei; Sun, De-Yong; Le, Cheng-Feng; Wu, Lan; Wang, Li-Zhen; Wang, Xing

    2009-02-15

    According to the optical property data measured in Taihu Lake at October and November 2006, the characteristics of the diffuse attenuation coeffcient (Kd), the contribution of each factor effecting on Kd and the effect of Kd on the aquatic ecology environment were analyzed. The results indicate that, the diffuse attenuation coefficient Kd of Taihu Lake has two main trends in the whole visible wavelength range (400-700 nm). The first type is that, Kd decreases with the wavelengths by exponential style in the range of less than 571 nm wavelengths, and the second type is that, Kd is in the form of fluctuations in the range of larger than 571 nm wavelengths. In the range of 400-700 nm wavelength, the absorption coefficient of pigment particles is the first contributors of diffuse attenuation coefficient. Non-pigment particles absorption and scattering coefficients is the second contributor, and the rate of contribution of yellow substance is the smallest. The Kd of Taihu Lake determines the light factor of the Taihu water ecosystem. The "water window" shaped by the Kd provides the light base for different kinds of ecosystem and the appearance of Microcystic aentginosa which is the preponderant algae in the "algal blooms" phenomenon. PMID:19402480

  20. An interpretation of potential scale dependence of the effectivematrix diffusion coefficient

    SciTech Connect

    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).

  1. Spectrophotometric Method for Differentiation of Human Skin Melanoma. I. Optical Diffuse Reflection Coefficient

    NASA Astrophysics Data System (ADS)

    Petruk, V. G.; Ivanov, A. P.; Kvaternyuk, S. M.; Barun, V. V.

    2016-03-01

    We have designed an experimental setup, based on two integrating spheres, that lets us measure the optical diffuse reflectance spectra (diffuse reflection coefficient vs. wavelength) of human skin quickly under clinical conditions in vivo. For the wavelength interval 520-1100 nm, we give the values of the diffuse reflection coefficient for healthy tissue, skin with a benign nevus, and skin with a malignant melanoma for a large group of test subjects. We experimentally established a number of wavelengths in the red-near IR region of the spectrum which can be used for early differential diagnosis of nevi and melanoma in patient cancer screening. According to the Kramer-Welch test, the probability of the diffuse reflection coefficient for skin with melanoma and a nevus having different distributions is >0.94, and at many wavelengths it is >0.999. By solving the inverse problem, we estimated the changes in a number of structural and biophysical parameters of the tissue on going from healthy skin to nevus and melanoma. The results obtained can provide a basis for developing a clinical approach to identifying the risk of malignant transformation of the skin before surgery and histological analysis of the tissue.

  2. Binary Diffusion Coefficient Data of Various Gas Systems Determined Using a Loschmidt Cell and Holographic Interferometry

    NASA Astrophysics Data System (ADS)

    Kugler, T.; Rausch, M. H.; Fröba, A. P.

    2015-11-01

    The paper reports on binary diffusion coefficient data for the gaseous systems argon-neon, krypton-helium, ammonia-helium, nitrous oxide-nitrogen, and propane-helium measured using a Loschmidt cell combined with holographic interferometry between (293.15 and 353.15) K as well as between (1 and 10) bar. The investigations on the noble gas systems aimed to validate the measurement apparatus by comparing the binary diffusion coefficients measured as a function of temperature and pressure with theoretical data. In previous studies, it was already shown that the raw concentration-dependent data measured with the applied setup are affected by systematic effects if pure gases are used prior to the diffusion process. Hence, the concentration-dependent measurement data were processed to obtain averaged binary diffusion coefficients at a mean mole fraction of 0.5. The data for the molecular gas systems complete literature data on little investigated systems of technical interest and point out the capabilities of the applied measurement apparatus. Further experimental data are reported for the systems argon-helium, krypton-argon, krypton-neon, xenon-helium, xenon-krypton, nitrous oxide-carbon dioxide, and propane-carbon dioxide at 293.15 K, 2 bar, and a mean mole fraction of 0.5.

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

    SciTech Connect

    Kruk, D.; Meier, R.; Rössler, E. A.; Rachocki, A.; Korpała, A.; Singh, R. K.

    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}(ω) 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.

  4. Determination of diffusion, reflection and deexcitation coefficients of metastable excited Ne(3P2) atom

    NASA Astrophysics Data System (ADS)

    Suzuki, S.; Itoh, H.

    2016-05-01

    The diffusion coefficient of the metastable excited Ne(3P2) atom in neon, the reflection coefficient of Ne(3P2) at the surface of an electrode and the rate coefficient of Ne(3P2) for collisional quenching by Ne(1S0) were determined from the gas pressure dependence of the effective lifetime of Ne(3P2). The effective lifetime of Ne(3P2) was measured from the transient current after turning off the Ultraviolet (UV) light in a Townsend discharge. The observed transient current waveform was analysed by solving the diffusion equation for the metastable excited Ne(3P2) atom using the third kind of boundary condition. The rate coefficient of Ne(3P2) for collisional quenching by Ne(1S0) and the reflection coefficient were determined by a nonspectroscopic method for the first time in neon to the best of our knowledge and were (3.2  ±  0.4)  ×  10‑16 cm3 s‑1 and 0.10  ±  0.04, respectively. The obtained diffusion coefficient at 1 Torr was 177  ±  17 cm2 s‑1, which is consistent with the value reported by Dixon and Grant. Moreover, the present results are compared with the results of Phelps and were found to be in good agreement. We also discuss the deexcitation rate of Ne(3P2) at pressures of up to 60 Torr in comparison with previously reported values.

  5. Effect of imaging parameters on the accuracy of apparent diffusion coefficient and optimization strategies

    PubMed Central

    Celik, Azim

    2016-01-01

    PURPOSE We aimed to investigate the effect of key imaging parameters on the accuracy of apparent diffusion coefficient (ADC) maps using a phantom model combined with ADC calculation simulation and propose strategies to improve the accuracy of ADC quantification. METHODS Diffusion-weighted imaging (DWI) sequences were acquired on a phantom model using single-shot echo-planar imaging DWI at 1.5 T scanner by varying key imaging parameters including number of averages (NEX), repetition time (TR), echo time (TE), and diffusion preparation pulses. DWI signal simulations were performed for varying TR and TE. RESULTS Magnetic resonance diffusion signal and ADC maps were dependent on TR and TE imaging parameters as well as number of diffusion preparation pulses, but not on the NEX. However, the choice of a long TR and short TE could be used to minimize their effects on the resulting DWI sequences and ADC maps. CONCLUSION This study shows that TR and TE imaging parameters affect the diffusion images and ADC maps, but their effect can be minimized by utilizing diffusion preparation pulses. Another key imaging parameter, NEX, is less relevant to DWI and ADC quantification as long as DWI signal-to-noise ratio is above a certain level. Based on the phantom results and data simulations, DWI acquisition protocol can be optimized to obtain accurate ADC maps in routine clinical application for whole body imaging. PMID:26573977

  6. Thermal Expansion and Diffusion Coefficients of Carbon Nanotube-Polymer Composites

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-02-01

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

  8. Determination of the Solute Diffusion Coefficient by the Droplet Migration Method

    SciTech Connect

    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.

  9. The influence of different turbulence models on the diffusion coefficients of energetic particles

    NASA Astrophysics Data System (ADS)

    Hussein, M.; Tautz, R. C.; Shalchi, A.

    2015-06-01

    We explore the influence of turbulence on the transport of energetic particles by using test particle simulations. We compute parallel and perpendicular diffusion coefficients for two-component turbulence, isotropic turbulence, a model based on Goldreich-Sridhar scaling, noisy reduced magnetohydrodynamic turbulence, and a noisy slab model. We show that diffusion coefficients have a similar rigidity dependence regardless which turbulence model is used, and thus, we conclude that the influence of turbulence on particle transport is not as strong as originally thought. Only fundamental quantities such as particle rigidity and the Kubo number are relevant. In the current paper we also confirm the unified nonlinear transport theory for noisy slab turbulence. To double check the validity and accuracy of our numerical results, we use a second test particle code. We show that both codes provide very similar results confirming the validity of our conclusions.

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

    NASA Astrophysics Data System (ADS)

    Gonçalves, Patrícia; Jara, Milton

    2008-09-01

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

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

    PubMed Central

    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

  12. 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).

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

    NASA Technical Reports Server (NTRS)

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

    1977-01-01

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

  14. Venus ionosphere: photochemical and thermal diffusion control of ion composition.

    PubMed

    Bauer, S J; Donahue, T M; Hartle, R E; Taylor, H A

    1979-07-01

    The major photochemical sources and sinks for ten of the ions measured by the ion mass spectrometer on the Pioneer Venus bus and orbiter spacecraft that are consistent with the neutral gas composition measured on the same spacecraft have been identified. The neutral gas temperature (Tn) as a function of solar zenith angle (chi) derived from measured ion distributions in photochemical equilibrium is given by Tn (K) = 323 cos(1/5)chi. Above 200 kilometers, the altitude behavior of ions is generally controlled by plasma diffusion, with important modifications for minor ions due to thermal diffusion resulting from the observed gradients of plasma temperatures. The dayside equilibrium distributions of ions are sometimes perturbed by plasma convection, while lateral transport of ions from the dayside seems to be a major source of the nightside ionosphere. PMID:17778920

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

    PubMed

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

    2008-09-15

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

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

    NASA Technical Reports Server (NTRS)

    Chow, M.; Houska, C. R.

    1980-01-01

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

  17. In Situ Effective Diffusion Coefficient Profiles in Live Biofilms Using Pulsed-Field Gradient Nuclear Magnetic Resonance

    SciTech Connect

    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.

  18. Empirical correlations between the arrhenius' parameters of impurities' diffusion coefficients in CdTe crystals

    SciTech Connect

    Shcherbak, L.; Kopach, O.; Fochuk, P.; James, R. B.; Bolotnikov, A. E.

    2015-01-21

    Understanding of self- and dopant-diffusion in semiconductor devices is essential to our being able to assure the formation of well-defined doped regions. In this paper, we compare obtained in the literature up to date the Arrhenius’ parameters (D=D0exp(–ΔEa/kT)) of point-defect diffusion coefficients and the I-VII groups impurities in CdTe crystals and films. We found that in the diffusion process there was a linear dependence between the pre-exponential factor, D0, and the activation energy, ΔEa, of different species: This was evident in the self-diffusivity and isovalent impurity Hg diffusivity as well as for the dominant IIIA and IVA groups impurities and Chlorine, except for the fast diffusing elements (e.g., Cu and Ag), chalcogens O, S, and Se, halogens I and Br as well as the transit impurities Mn, Co, Fe. As a result, reasons of the lack of correspondence of the data to compensative dependence are discussed.

  19. Empirical correlations between the arrhenius' parameters of impurities' diffusion coefficients in CdTe crystals

    DOE PAGESBeta

    Shcherbak, L.; Kopach, O.; Fochuk, P.; James, R. B.; Bolotnikov, A. E.

    2015-01-21

    Understanding of self- and dopant-diffusion in semiconductor devices is essential to our being able to assure the formation of well-defined doped regions. In this paper, we compare obtained in the literature up to date the Arrhenius’ parameters (D=D0exp(–ΔEa/kT)) of point-defect diffusion coefficients and the I-VII groups impurities in CdTe crystals and films. We found that in the diffusion process there was a linear dependence between the pre-exponential factor, D0, and the activation energy, ΔEa, of different species: This was evident in the self-diffusivity and isovalent impurity Hg diffusivity as well as for the dominant IIIA and IVA groups impurities andmore » Chlorine, except for the fast diffusing elements (e.g., Cu and Ag), chalcogens O, S, and Se, halogens I and Br as well as the transit impurities Mn, Co, Fe. As a result, reasons of the lack of correspondence of the data to compensative dependence are discussed.« less

  20. Diffusion coefficients in CO2/n-alkane binary liquid mixtures by molecular simulation.

    PubMed

    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

  1. Minority carrier diffusion lengths and absorption coefficients in silicon sheet material

    NASA Technical Reports Server (NTRS)

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

    1980-01-01

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

  2. Pressure-dependent diffusion coefficients and haven ratios in cation-conducting glasses.

    PubMed

    Imre, A W; Staesche, H; Voss, S; Ingram, M D; Funke, K; Mehrer, H

    2007-05-17

    The influence of hydrostatic pressure on diffusion and ionic conduction is providing deeper insights into the atomistic mechanisms of ionic motion in glasses. We have studied the tracer diffusion of 22Na in a sodium borate glass and of 86Rb in a rubidium borate glass as functions of hydrostatic pressures. The activation volumes of tracer diffusion are DeltaVD(Rb) = 33.5 cm3 mol-1 and DeltaVD(Na) = 6.1 cm3 mol-1. In comparison, the activation volumes of charge diffusion obtained recently from the pressure dependence of conductivity are smaller: DeltaVsigma(Rb) = 7.2 cm3 mol(-1) and DeltaVsigma(Na) = 2.8 cm3 mol(-1). These differences, where (DeltaVD - DeltaVsigma) > 0, imply that the Haven ratios decrease with pressure. This effect is particularly significant for the rubidium borate glass. Starting from basic equations of linear response theory for mass and charge transport, we develop a model that accounts for these experimental findings. The difference between the activation volumes, DeltaVD and DeltaVsigma, and the pressure-dependent Haven ratios are consequences of collective movements of ions in glass, implying a concerted motion of ions in a chain- or caterpillar-like fashion. In our treatment, it is a vacant site (with ions jumping into it successively) that moves along an extended pathway. Hence, we regard vacant sites as the carriers of charge and ions as the carriers of diffusing matter. The decrease of the Haven ratio with pressure is attributed to the influence of pressure on the topology of the conduction pathways, which are progressively straightened out with increasing pressure. PMID:17455973

  3. Quantification of sampling uncertainty for molecular dynamics simulation: Time-dependent diffusion coefficient in simple fluids

    NASA Astrophysics Data System (ADS)

    Kim, Changho; Borodin, Oleg; Karniadakis, George Em

    2015-12-01

    We analyze two standard methods to compute the diffusion coefficient of a tracer particle in a medium from molecular dynamics (MD) simulation, the velocity autocorrelation function (VACF) method, and the mean-squared displacement (MSD) method. We show that they are equivalent in the sense that they provide the same mean values with the same level of statistical errors. We obtain analytic expressions for the level of the statistical errors present in the time-dependent diffusion coefficient as well as the VACF and the MSD. Under the assumption that the velocity of the tracer particle is a Gaussian process, all results are expressed in terms of the VACF. Hence, the standard errors of all relevant quantities are computable once the VACF is obtained from MD simulation. By using analytic models described by the Langevin equations driven by Gaussian white noise and Poissonian white shot noise, we verify our theoretical error estimates and discuss the non-Gaussianity effect in the error estimates when the Gaussian process approximation does not hold exactly. For validation, we perform MD simulations for the self-diffusion of a Lennard-Jones fluid and the diffusion of a large and massive colloid particle suspended in the fluid. Our theoretical framework is also applicable to mesoscopic simulations, e.g., Langevin dynamics and dissipative particle dynamics.

  4. A novel grating-imaging method to measure carrier diffusion coefficient in graphene

    NASA Astrophysics Data System (ADS)

    Chen, Ke; Wang, Yaguo; Akinwande, Deji; Bank, Seth; Lin, Jung-Fu

    Similar to carrier mobility, carrier diffusion coefficient in graphene determines the response rate of future graphene-based electronics. Here we present a simple, sensitive and non-destructive technique integrated with ultrafast pump-probe spectroscopy to measure carrier diffusion in CVD-grown graphene. In the method, the pump and the probe beams pass through the same area of a photomask with metal strips i.e. a transmission amplitude grating, and get diffracted. The diffracted light is collected by an objective lens and focused onto the sample to generate carrier density grating. Relaxation of this carrier density grating is governed by both carrier recombination and carrier diffusion in the sample. Transient transmission change of the probe beams, which reflects this relaxation process, is recorded. The measured diffusion coefficients of multilayer and monolayer CVD-grown graphene are 2000cm2/s and 10000cm2/s, respectively, comparable with the reported values of epitaxial graphene and reduced graphene. This transmission grating technique can be used to measure carrier dynamics in versatile 2D materials.

  5. Temperature dependence of Soret and diffusion coefficients for toluene-cyclohexane mixture measured in convection-free environment

    NASA Astrophysics Data System (ADS)

    Mialdun, A.; Shevtsova, V.

    2015-12-01

    We report on the measurement of diffusion (D), Soret (ST), and thermodiffusion (DT) coefficients in toluene-cyclohexane mixture with mass fraction of toluene 0.40 onboard of the International Space Station. The coefficients were measured in the range of the mean temperatures between 20 °C and 34 °C. The Soret coefficient is negative within the investigated temperature range and its absolute value |ST| decreases with increasing temperature. The diffusion coefficient for this system increases with temperature rising. For comparison, the temperature dependence of diffusion coefficient was measured in ground laboratory using counter-flow cell technique and revealed a good agreement with microgravity results. A non-direct comparison of the measured onboard Soret coefficients with different systems indicated a similar trend for the temperature dependent behavior. Unexpected experimental finding is that for this system the thermodiffusion coefficient DT does not depend on temperature.

  6. Temperature dependence of Soret and diffusion coefficients for toluene-cyclohexane mixture measured in convection-free environment.

    PubMed

    Mialdun, A; Shevtsova, V

    2015-12-14

    We report on the measurement of diffusion (D), Soret (S(T)), and thermodiffusion (D(T)) coefficients in toluene-cyclohexane mixture with mass fraction of toluene 0.40 onboard of the International Space Station. The coefficients were measured in the range of the mean temperatures between 20 °C and 34 °C. The Soret coefficient is negative within the investigated temperature range and its absolute value |S(T)| decreases with increasing temperature. The diffusion coefficient for this system increases with temperature rising. For comparison, the temperature dependence of diffusion coefficient was measured in ground laboratory using counter-flow cell technique and revealed a good agreement with microgravity results. A non-direct comparison of the measured onboard Soret coefficients with different systems indicated a similar trend for the temperature dependent behavior. Unexpected experimental finding is that for this system the thermodiffusion coefficient D(T) does not depend on temperature. PMID:26671399

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

    NASA Astrophysics Data System (ADS)

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

    1996-08-01

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

  8. Ion beam microtexturing and enhanced surface diffusion

    NASA Technical Reports Server (NTRS)

    Robinson, R. S.

    1982-01-01

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

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

    PubMed

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

    2014-12-01

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

  10. Effect of carbon ion irradiation on Ag diffusion in SiC

    NASA Astrophysics Data System (ADS)

    Leng, Bin; Ko, Hyunseok; Gerczak, Tyler J.; Deng, Jie; Giordani, Andrew J.; Hunter, Jerry L.; Morgan, Dane; Szlufarska, Izabela; Sridharan, Kumar

    2016-04-01

    Transport of Ag fission product through the silicon-carbide (SiC) diffusion barrier layer in TRISO fuel particles is of considerable interest given the application of this fuel type in high temperature gas-cooled reactor (HTGR) and other future reactor concepts. The reactor experiments indicate that radiation may play an important role in release of Ag; however so far the isolated effect of radiation on Ag diffusion has not been investigated in controlled laboratory experiments. In this study, we investigate the diffusion couples of Ag and polycrystalline 3C-SiC, as well as Ag and single crystalline 4H-SiC samples before and after irradiation with C2+ ions. The diffusion couple samples were exposed to temperatures of 1500 °C, 1535 °C, and 1569 °C, and the ensuing diffusion profiles were analyzed by secondary ion mass spectrometry (SIMS). Diffusion coefficients calculated from these measurements indicate that Ag diffusion was greatly enhanced by carbon irradiation due to a combined effect of radiation damage on diffusion and the presence of grain boundaries in polycrystalline SiC samples.

  11. Layer-growth kinetics on gaseous nitriding of pure iron: Evaluation of diffusion coefficients for nitrogen in iron nitrides

    NASA Astrophysics Data System (ADS)

    Somers, Marcel A. J.; Mittemeijer, Eric J.

    1995-01-01

    Models were derived for monolayer and bilayer growth into a substrate in which diffusion of the solute governs the growth kinetics, as in gas-solid reactions, for example. In the models, the composition dependence of the solute diffusivity in the phases constituting the layers was accounted for by appropriate definition of an effective diffusion coefficient for a (sub)layer. This effective diffusion coefficient is the intrinsic diffusion coefficient weighted over the composition range of the (sub)layer. The models were applied for analyzing the growth kinetics of a γ'-Fe4N1-x monolayer on an α-Fe substrate and the growth kinetics of an ɛ-Fe2N1-z/γ'-Fe4N1-x bilayer on an α-Fe substrate, as observed by gaseous nitriding in an NH3/H2-gas mixture at 843 K. The kinetics of layer development and the evolution of the microstructure were investigated by means of thermogravimetry, layer-thickness measurements, light microscopy, and electron probe X-ray microanalysis (EPMA). The effective and self-diffusion coefficients were determined for each of the nitride layers. The composition dependence of the intrinsic (and effective) diffusion coefficients was established. Re-evaluating literature data for diffusion in γ'-Fe4N1-x on the basis of the present model, it followed that the previous and present data are consistent. The activation energy for diffusion of nitrogen in γ'-Fe4N1-x was determined from the temperature dependence of the self-diffusion coefficient. The self-diffusion coefficient for nitrogen in ɛ-Fe2N1-z was significantly larger than that for γ'-Fe4N1-x. This was explained qualitatively, considering the possible mechanisms for interstitial diffusion of nitrogen atoms in the close-packed iron lattices of the ɛ and γ' iron nitrides.

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

    PubMed Central

    Zhou, H X; Szabo, A

    1996-01-01

    A general formalism is developed for calculating the time-dependent rate coefficient k(t) of an irreversible diffusion-influenced reaction. This formalism allows one to treat most factors that affect k(t), including rotational Brownian motion and conformational gating of reactant molecules and orientation constraint for product formation. At long times k(t) is shown to have the asymptotic expansion k(infinity)[1 + k(infinity) (pie Dt)-1/2 /4 pie D + ...], where D is the relative translational diffusion constant. An approximate analytical method for calculating k(t) is presented. This is based on the approximation that the probability density of the reactant pair in the reactive region keeps the equilibrium distribution but with a decreasing amplitude. The rate coefficient then is determined by the Green function in the absence of chemical reaction. Within the framework of this approximation, two general relations are obtained. The first relation allows the rate coefficient for an arbitrary amplitude of the reactivity to be found if the rate coefficient for one amplitude of the reactivity is known. The second relation allows the rate coefficient in the presence of conformational gating to be found from that in the absence of conformational gating. The ratio k(t)/k(0) is shown to be the survival probability of the reactant pair at time t starting from an initial distribution that is localized in the reactive region. This relation forms the basis of the calculation of k(t) through Brownian dynamics simulations. Two simulation procedures involving the propagation of nonreactive trajectories initiated only from the reactive region are described and illustrated on a model system. Both analytical and simulation results demonstrate the accuracy of the equilibrium-distribution approximation method. PMID:8913584

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

    PubMed Central

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

    2013-01-01

    OBJECTIVE The purpose of our study was to correlate decrease in apparent diffusion coefficient (ADC) and increase in fractional anisotropy (FA) in various white matter (WM) regions using diffusion tenor imaging (DTI) within the first year of life. MATERIALS AND METHODS We performed DTI on 53 infants and measured FA and ADC within 10 WM regions important in brain development. For each region, we calculated the slope of ADC as a function of FA, the correlation coefficient (r) and correlation of determination (r2). We performed a group analysis of r values and r2 values for six WM regions primarily composed of crossing fibers and four regions primarily having parallel fibers. Upon finding that a strong correlation of FA with age existed, we adjusted for age and calculated partial correlation coefficients. RESULTS Slopes of FA versus ADC ranged from −1.00711 to −1.67592 (p < 0.05); r values ranged from −0.81 to −0.50 and r2 values from 0.25 to 0.66. The four greatest r2 values were within WM regions having large numbers of crossing fibers and the three lowest r2 values were in regions having predominantly parallel fibers. After adjusting for age, slopes ranged from −1.08095 to 0.09612 (p < 0.05 in five cases); partial correlation coefficients ranged from −0.49 to 0.03 and r2 values from 0.31 to 0.79. The highest partial correlation coefficients were then relatively equally distributed between the two types of WM regions. CONCLUSION In various regions, FA and ADC evolved with differing degrees of correlation. We found a strong influence of age on the relationship between FA and ADC. PMID:21098179

  14. Mechanisms of Stochastic Diffusion of Energetic Ions in Spherical Tori

    SciTech Connect

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

    2001-01-18

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

  15. Diffusion mechanism and the thermal stability of fluorine ions in GaN after ion implantation

    SciTech Connect

    Wang, M. J.; Yuan, L.; Chen, K. J.; Xu, F. J.; Shen, B.

    2009-04-15

    The diffusion mechanisms of fluorine ions in GaN are investigated by means of time-of-flight secondary ion mass spectrometry. Instead of incorporating fluorine ions close to the sample surface by fluorine plasma treatment, fluorine ion implantation with an energy of 180 keV is utilized to implant fluorine ions deep into the GaN bulk, preventing the surface effects from affecting the data analysis. It is found that the diffusion of fluorine ions in GaN is a dynamic process featuring an initial out-diffusion followed by in- diffusion and the final stabilization. A vacancy-assisted diffusion model is proposed to account for the experimental observations, which is also consistent with results on molecular dynamic simulation. Fluorine ions tend to occupy Ga vacancies induced by ion implantation and diffuse to vacancy rich regions. The number of continuous vacancy chains can be significantly reduced by a dynamic thermal annealing process. As a result, strong local confinement and stabilization of fluorine ions can be obtained in GaN crystal, suggesting excellent thermal stability of fluorine ions for device applications.

  16. Anisotropie des coefficients de diffusion dans des cristaux liquides discotiques hexagonaux

    NASA Astrophysics Data System (ADS)

    Daoud, M.; Gharbia, M.; Gharbi, A.

    1994-06-01

    The diffusion constants of dyes in several hexagonal discotic liquid crystals are measured and discussed. For all the liquid crystals studied, these constants are anisotropic : the diffusion in the direction parallel to the columns is faster than that in the perpendicular plane (frac{D_allel}{D_perp}>1). The effects of the length and shape of the chains bound to the triphenylene discs are shown. The effect of the dye molecular size is also described. The study of the diffusion coefficients of hexapentoxytriphenylene (C5HET) as a function of temperature has shown that the activation energies along the columns and perpendicular to the columns are comparable. The main features of dye diffusion in the hexagonal columnar liquid crystals studied are similar to those reported in nematic phases. Les mesures des constantes de diffusion de colorants dans plusieurs cristaux liquides discotiques hexagonaux sont présentées et discutées. Pour tous les cristaux liquides étudiés, ces constantes présentent une anisotropie, avec une diffusion plus rapide parallèlement aux colonnes que perpendiculairement à celles-ci (frac{D_allel}{D_perp}>1). Des effets de longueur et de forme des chaînes branchées sur les disques de triphénylène sont mis en évidence. Il en est de même pour la taille des molécules de colorants. L'étude en fonction de la température a montré que dans le cas de l'hexapentoxytriphénylène (C5HET), les énergies d'activation dans les directions parallèle et perpendiculaire aux colonnes sont comparables. Les caractéristiques de la diffusion de colorants dans les cristaux liquides colonnaires hexagonaux étudiés sont semblables à celles des nématiques.

  17. Stress enhanced diffusion of krypton ions in polycrystalline titanium

    SciTech Connect

    Nsengiyumva, S.; Raji, A. T.; Rivière, J. P.; Britton, D. T.; Härting, M.

    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.

  18. 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.

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

    PubMed

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

  20. Measuring diffusion coefficients via two-photon fluorescence recovery after photobleaching.

    PubMed

    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

  1. 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.

  2. 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 Dαα and mixed Dαp 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.

  3. Ab initio calculation of oxygen self-diffusion coefficient in uranium dioxide UO2

    NASA Astrophysics Data System (ADS)

    Dorado, Boris; Garcia, Philippe; Torrent, Marc

    Uranium dioxide UO2 is the most widely used nuclear fuel worldwide and its atomic transport properties are relevant to practically all engineering aspects of the material. Although transport properties have already been studied in UO2 by means of first-principles calculations, the ab initio determination of self-diffusion coefficients has up to now remained unreachable because the relevant computational tools were neither available or adapted. The present work reports our results related to the ab initio calculation of the oxygen self-diffusion coefficient in UO2. We first determine the Gibbs free energies of formation of oxygen charged defects by calculating both the electronic and vibrational (hence entropic) contributions. Then, we use the transition state theory in order to compute the effective jump frequency of the defects, which in turn provides us with the value of the pre-exponential factor. The results are compared to self-diffusion data obtained experimentally with a careful monitoring of the relevant thermodynamic conditions (oxygen partial pressure, temperature, impurity content).

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

    NASA Astrophysics Data System (ADS)

    Kristoffersen, Anders

    2007-08-01

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

  5. Lithium ion solvation and diffusion in bulk organic electrolytes from first-principles and classical reactive molecular dynamics.

    PubMed

    Ong, Mitchell T; Verners, Osvalds; Draeger, Erik W; van Duin, Adri C T; Lordi, Vincenzo; Pask, John E

    2015-01-29

    Lithium-ion battery performance is strongly influenced by the ionic conductivity of the electrolyte, which depends on the speed at which Li ions migrate across the cell and relates to their solvation structure. The choice of solvent can greatly impact both the solvation and diffusivity of Li ions. In this work, we used first-principles molecular dynamics to examine the solvation and diffusion of Li ions in the bulk organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC), and a mixture of EC and EMC. We found that Li ions are solvated by either carbonyl or ether oxygen atoms of the solvents and sometimes by the PF6(-) anion. Li(+) prefers a tetrahedrally coordinated first solvation shell regardless of which species are involved, with the specific preferred solvation structure dependent on the organic solvent. In addition, we calculated Li diffusion coefficients in each electrolyte, finding slightly larger diffusivities in the linear carbonate EMC compared to the cyclic carbonate EC. The magnitude of the diffusion coefficient correlates with the strength of Li(+) solvation. Corresponding analysis for the PF6(-) anion shows greater diffusivity associated with a weakly bound, poorly defined first solvation shell. These results can be used to aid in the design of new electrolytes to improve Li-ion battery performance. PMID:25523643

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

    NASA Astrophysics Data System (ADS)

    Deb Nath, S. K.

    2014-05-01

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

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

    PubMed Central

    Nicholson, C; Phillips, J M

    1981-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2002-05-01

    An NMR method is presented for measuring compartment-specific water diffusion coefficient (D) values. It uses relaxography, employing an extracellular contrast reagent (CR) to distinguish intracellular (IC) and extracellular (EC) 1H2O signals by differences in their respective longitudinal (T1) relaxation times. A diffusion-weighted inversion-recovery spin-echo (DW-IRSE) pulse sequence was used to acquire IR data sets with systematically and independently varying inversion time (TI) and diffusion-attenuation gradient amplitude (g) values. Implementation of the DW-IRSE technique was demonstrated and validated using yeast cells suspended in 3 mM Gd-DTPA2- with a wet/dry mass ratio of 3.25:1.0. Two-dimensional (2D) NMR data were acquired at 2.0 T and analyzed using numerical inverse Laplace transformation (2D- and sequential 1D-ILT) and sequential exponential fitting to yield T1 and water D values. All three methods gave substantial agreement. Exponential fitting, deemed the most accurate and time efficient, yielded T1:D (relative contribution) values of 304 ms:0.023×10-5 cm2/s (47%) and 65 ms:1.24×10-5 cm2/s (53%) for the IC and EC components, respectively. The compartment-specific D values derived from direct biexponential fitting of diffusion-attenuation data were also in good agreement. Extension of the DW-IRSE method to in vivo models should provide valuable insights into compartment-specific water D changes in response to injury or disease.

  9. Simulations of ion acceleration at non-relativistic shocks. III. Particle diffusion

    SciTech Connect

    Caprioli, D.; Spitkovsky, A.

    2014-10-10

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

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

    NASA Astrophysics Data System (ADS)

    Caprioli, D.; Spitkovsky, A.

    2014-10-01

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

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

    PubMed Central

    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 3T 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) 10-3mm2/s (2%), and between the DT-CMR sequence and literature diffusivities was 0.02 (0.05, 0.006) 10-3mm2/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 10-3mm2/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

  12. Diffusion coefficients and dissociation constants of enhanced green fluorescent protein binding to free standing membranes.

    PubMed

    Thomas, Franziska A; Visco, Ilaria; Petrášek, Zdeněk; Heinemann, Fabian; Schwille, Petra

    2015-12-01

    Recently, a new and versatile assay to determine the partitioning coefficient [Formula: see text] as a measure for the affinity of peripheral membrane proteins for lipid bilayers was presented in the research article entitled, "Introducing a fluorescence-based standard to quantify protein partitioning into membranes" [1]. Here, the well-characterized binding of hexahistidine-tag (His6) to NTA(Ni) was utilized. Complementarily, this data article reports the average diffusion coefficient [Formula: see text] of His6-tagged enhanced green fluorescent protein (eGFP-His6) and the fluorescent lipid analog ATTO-647N-DOPE in giant unilamellar vesicles (GUVs) containing different amounts of NTA(Ni) lipids. In addition, dissociation constants [Formula: see text] of the NTA(Ni)/eGFP-His6 system are reported. Further, a conversion between [Formula: see text] and [Formula: see text] is provided. PMID:26587560

  13. Consequences of using nonlinear particle trajectories to compute spatial diffusion coefficients. [for cosmic ray propagation in interstellar and interplanetary space

    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.

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

    NASA Astrophysics Data System (ADS)

    Tian, Hui; Reece, Charles E.

    2010-08-01

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

  15. The diffusive logistic equation with a free boundary and sign-changing coefficient

    NASA Astrophysics Data System (ADS)

    Wang, Mingxin

    2015-02-01

    This short paper concerns a diffusive logistic equation with a free boundary and sign-changing coefficient, which is formulated to study the spread of an invasive species, where the free boundary represents the expanding front. A spreading-vanishing dichotomy is derived, namely the species either successfully spreads to the right-half-space as time t → ∞ and survives (persists) in the new environment, or it fails to establish itself and will extinct in the long run. The sharp criteria for spreading and vanishing are also obtained. When spreading happens, we estimate the asymptotic spreading speed of the free boundary.

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

    USGS Publications Warehouse

    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.

  17. Asymmetric liquid-core cylindrical lens used to measure liquid diffusion coefficient.

    PubMed

    Sun, Licun; Du, Chao; Li, Qiang; Pu, Xiaoyun

    2016-03-10

    We design and fabricate an asymmetric liquid-core cylindrical lens (ALCL), which is used to measure the binary liquid diffusion coefficient (D). Acting as both diffusion cell and key imaging element, ALCL is of the function to measure the refractive index (RI) of liquid filled in its core in the way of spatial resolution. Comparing the ALCL with a symmetric liquid-core cylindrical lens (SLCL), the spherical aberration is reduced from about 300 μm (SLCL) to less than 5 μm (ALCL) when the RI of filled liquid is near 1.333, while the measurement accuracy of the RI of the ALCL is superior to 0.0002, which is much better than that of the SLCL. Equipped with the ALCL, the D value of triethylene glycol diffusing in water is measured at 25°C. The result is D=0.7515×10-5  cm2/s, a value very close to the literature value. The rational design of ALCL gives the optical method for measuring the D value good measurement precision and direct observation of the diffusive process as well as a simple experimental instrument. PMID:26974796

  18. Lateral diffusivity coefficients from the dynamics of a SF6 patch in a coastal environment

    NASA Astrophysics Data System (ADS)

    Kersalé, M.; Petrenko, A. A.; Doglioli, A. M.; Nencioli, F.; Bouffard, J.; Blain, S.; Diaz, F.; Labasque, T.; Quéguiner, B.; Dekeyser, I.

    2016-01-01

    The dispersion of a patch of the tracer sulfur hexafluoride (SF6) is used to assess the lateral diffusivity in the coastal waters of the western part of the Gulf of Lion (GoL), northwestern Mediterranean Sea, during the Latex10 experiment (September 2010). Immediately after the release, the spreading of the patch is associated with a strong decrease of the SF6 concentrations due to the gas exchange from the ocean to the atmosphere. This has been accurately quantified, evidencing the impact of the strong wind conditions during the first days of this campaign. Few days after the release, as the atmospheric loss of SF6 decreased, lateral diffusivity coefficient at spatial scales of 10 km has been computed using two approaches. First, the evolution of the patch with time was combined with a diffusion-strain model to obtain estimates of the strain rate (γ = 2.5 10- 6 s- 1) and of the lateral diffusivity coefficient (Kh = 23.2 m2 s- 1). Second, a steady state model was applied, showing Kh values similar to the previous method after a period of adjustment between 2 and 4.5 days. This implies that after such period, our computation of Kh becomes insensitive to the inclusion of further straining of the patch. Analysis of sea surface temperature satellite imagery shows the presence of a strong front in the study area. The front clearly affected the dynamics within the region and thus the temporal evolution of the patch. Our results are consistent with previous studies in open ocean and demonstrate the success and feasibility of those methods also under small-scale, rapidly-evolving dynamics typical of coastal environments.

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

    NASA Technical Reports Server (NTRS)

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    Diffusion of gas molecules to the surface is the first step for all gas-surface reactions. Gas phase diffusion can influence and sometimes even limit the overall rates of these reactions; however, there is no database of the gas phase diffusion coefficients of atmospheric reactive trace gases. Here we compile and evaluate, for the first time, the diffusivities (pressure-independent diffusion coefficients) of atmospheric inorganic reactive trace gases reported in the literature. The measured diffusivities are then compared with estimated values using a semi-empirical method developed by Fuller et al. (1966). The diffusivities estimated using Fuller's method are typically found to be in good agreement with the measured values within ±30%, and therefore Fuller's method can be used to estimate the diffusivities of trace gases for which experimental data are not available. The two experimental methods used in the atmospheric chemistry community to measure the gas phase diffusion coefficients are also discussed. A different version of this compilation/evaluation, which will be updated when new data become available, is uploaded online (diffusion"target="_blank">https://sites.google.com/site/mingjintang/home/diffusion).

  2. Determination of partition and diffusion coefficients of formaldehyde in selected building materials and impact of relative humidity (journal)

    EPA Science Inventory

    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...

  3. Bend stresses arising from ion-exchange diffusion in glasses

    SciTech Connect

    Babukova, M.V.; Glebov, L.B.; Nikonorov, N.V.; Petrovskii, G.T.

    1985-11-01

    This paper demonstrates experimental confirmation of the presence of gigastresses arising under ion exchange, for the purpose of providing data relating to the magnitudes of stress greater than 1 GPa in these ion-exchange layers. To determine the stresses, a bend method was used on a specimen under nonuniform load. Small values of bend were determined on an IT-70 inferometer. With larger values of bend the radius of curvature of the surface was determined by measuring the focal distance in the beam of a He-Ne laser reflected from the specimen. Bending is observed in silicate glass subjected to unilateral ion-exchange diffusion of K/sup +/. It is shown that the bending of the specimens is caused by compressive stresses arising in the diffusion layer and having a value of greater than 1.5 GPa. The changes in the refractive index (RI) in the diffusion layer are determined primarily by the photoelastic effect.

  4. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2000-05-01

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

  6. In Situ Raman Spectroscopic Study of the Diffusion Coefficients and Solubility:Indicates to Carbon Dioxide Injection into Hexadecane

    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.

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

    SciTech Connect

    Shalchi, A.; Danos, R. J.

    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.

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

    PubMed

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

    2008-06-01

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

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

    PubMed

    Pommois, P; Veltri, P; Zimbardo, G

    2001-06-01

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

  10. Drag and diffusion coefficients of a spherical particle attached to a fluid-fluid interface

    NASA Astrophysics Data System (ADS)

    Dörr, Aaron; Hardt, Steffen; Masoud, Hassan; Stone, Howard A.

    2016-03-01

    Explicit analytical expressions for the drag and diffusion coefficients of a spherical particle attached to the interface between two immiscible fluids are constructed for the case of a small viscosity ratio between the fluid phases. The model is designed to explicitly account for the dependence on the contact angle between the two fluids and the solid surface. The Lorentz reciprocal theorem is applied in the context of a geometric perturbation approach, which is based on the deviation of the contact angle from a 90{\\deg}-value. By testing the model against experimental and numerical data from the literature, good agreement is found within the entire range of contact angles below 90{\\deg}. As an advantage of the method reported, the drag and diffusion coefficients can be calculated up to second order in the perturbation parameter, while it is sufficient to know the velocity and pressure fields only up to first order. Extensions to other particle shapes with known velocity and pressure fields are straightforward.

  11. 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.

  12. Double obstacle phase field approach to an inverse problem for a discontinuous diffusion coefficient

    NASA Astrophysics Data System (ADS)

    Deckelnick, Klaus; Elliott, Charles M.; Styles, Vanessa

    2016-04-01

    We propose a double obstacle phase field approach to the recovery of piece-wise constant diffusion coefficients for elliptic partial differential equations. The approach to this inverse problem is that of optimal control in which we have a quadratic fidelity term to which we add a perimeter regularization weighted by a parameter σ. This yields a functional which is optimized over a set of diffusion coefficients subject to a state equation which is the underlying elliptic PDE. In order to derive a problem which is amenable to computation the perimeter functional is relaxed using a gradient energy functional together with an obstacle potential in which there is an interface parameter ɛ. This phase field approach is justified by proving {{Γ }}- convergence to the functional with perimeter regularization as ε \\to 0. The computational approach is based on a finite element approximation. This discretization is shown to converge in an appropriate way to the solution of the phase field problem. We derive an iterative method which is shown to yield an energy decreasing sequence converging to a discrete critical point. The efficacy of the approach is illustrated with numerical experiments.

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  14. Interaction of ring current and radiation belt protons with ducted plasmaspheric hiss. 1: Diffusion coefficients and timescales

    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.

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

    NASA Astrophysics Data System (ADS)

    Frazer, E. J.; Thonstad, J.

    2010-06-01

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

  16. Statistical analysis of diffuse ion events upstream of the Earth's bow shock

    NASA Technical Reports Server (NTRS)

    Trattner, K. J.; Mobius, E.; Scholer, M.; Klecker, B.; Hilchenbach, M.; Luehr, H.

    1994-01-01

    A statistical study of diffuse energetic ion events and their related waves upstream of the Earth's bow shock was performed using data from the Active Magnetospheric Particle Tracer Explorers/Ion Release Module (AMPTE/IRM) satellite over two 5-month periods in 1984 and 1985. The data set was used to test the assumption in the self-consistent model of the upstream wave and particle populations by Lee (1982) that the particle acceleration through hydromagnetic waves and the wave generation are directly coupled. The comparison between the observed wave power and the wave power predicted on the observed energetic particle energy density and solar wind parameters results in a high correlation coefficient of about 0.89. The intensity of diffuse ions falls off approximately exponentially with the distance upstream from the bow shock parallel to the magnetic field with e-folding distances which vary from approximately 3.3 R(sub E) to approximately 11.7 R(sub E) over the energy range from 10 keV/e to 67.3 keV/e for both protons and alpha particles. After normalizing the upstream particle densities to zero bow shock distance by using these exponential variations, a good correlation (0.7) of the density of the diffuse ions with the solar wind density was found. This supports the suggestion that the solar wind is the source of the diffuse ions. Furthermore, the spectral slope of the diffuse ions correlates well with the solar wind velocity component in the direction of the interplanetary magnetic field (0.68 and 0.66 for protons and alpha particles) which concurs with the notion that the solar wind plays an important role in the acceleration of the upstream particles.

  17. Self-diffusion coefficients for water and organic solvents at high temperatures along the coexistence curve

    NASA Astrophysics Data System (ADS)

    Yoshida, Ken; Matubayasi, Nobuyuki; Nakahara, Masaru

    2008-12-01

    The self-diffusion coefficients D for water, benzene, and cyclohexane are determined by using the pulsed-field-gradient spin echo method in high-temperature conditions along the liquid branch of the coexistence curve: 30-350 °C (1.0-0.58 g cm-3), 30-250 °C (0.87-0.56 g cm-3), and 30-250 °C (0.77-0.48 g cm-3) for water, benzene, and cyclohexane, respectively. The temperature and density effects are separated and their origins are discussed by examining the diffusion data over a wide range of thermodynamic states. The temperature dependence of the self-diffusion coefficient for water is larger than that for organic solvents due to the large contribution of the attractive hydrogen-bonding interaction in water. The density dependence is larger for organic solvents than for water. The difference is explained in terms of the van der Waals picture that the structure of nonpolar organic solvents is determined by the packing effect due to the repulsion or exclusion volumes. The dynamic solvation shell scheme [K. Yoshida et al., J. Chem. Phys. 127, 174509 (2007)] is applied for the molecular interpretation of the translational dynamics with the aid of molecular dynamics simulation. In water at high temperatures, the velocity relaxation is not completed before the relaxation of the solvation shell (mobile-shell type) as a result of the breakdown of the hydrogen-bonding network. In contrast, the velocity relaxation of benzene is rather confined within the solvation shell (in-shell type).

  18. Drag and diffusion coefficient of a spherical particle attached to a fluid interface

    NASA Astrophysics Data System (ADS)

    Hardt, Steffen; Doerr, Aaron; Masoud, Hassan; Stone, Howard

    2015-11-01

    We consider a spherical particle attached to the interface between two immiscible fluids of large viscosity contrast. The degree of immersion in the two fluids is determined by the contact angle. For small enough particles and significant contact-angle hysteresis, it can be assumed that the three-phase contact line is pinned at the particle surface. We study the movement of such particles along the fluid interface for the case of small Reynolds and capillary numbers. We solve the Stokes equation based on two geometric perturbation expansions around contact angles of 90 degrees and 180 degrees, the latter corresponding to a particle completely immersed in the less viscous phase. Based on the Lorentz Reciprocity Theorem we obtain expressions for the drag coefficient of an interfacial particle which are analogs of the well-known Stokes drag coefficient for a particle moving in an unbounded medium. Interpolation of the two results gives a relationship which approximates the drag coefficient quite accurately over the entire range of contact angles. A comparison with previously published numerical results for contact angles below 90 degrees shows good agreement. Using the fluctuation-dissipation theorem, we also obtain expressions for the diffusion constant of a small particle attached to a fluid interface.

  19. Apparent diffusion coefficient and fractional anisotropy of newly diagnosed grade II gliomas†

    PubMed Central

    Khayal, Inas S.; McKnight, Tracy R.; McGue, Colleen; Vandenberg, Scott; Lamborn, Kathleen R.; Chang, Susan M.; Cha, Soonmee; Nelson, Sarah J.

    2013-01-01

    Distinguishing between low-grade oligodendrogliomas (ODs) and astrocytomas (AC) is of interest for defining prognosis and stratifying patients to specific treatment regimens. The purpose of this study was to determine if the apparent diffusion coefficient (ADC) and fractional anisotropy (FA) from diffusion imaging can help to differentiate between newly diagnosed grade II OD and AC subtypes and to evaluate the ADC and FA values for the mixed population of oligoastrocytomas (OA). Fifty-three patients with newly diagnosed grade II gliomas were studied using a 1.5T whole body scanner (23 ODs, 16 ACs, and 14 OAs). The imaging protocol included post-gadolinium T1-weighted images, T2-weighted images, and either three and/or six directional diffusion imaging sequence with b = 1000 s/mm2. Diffusion-weighted images were analyzed using in-house software to calculate maps of ADC and for six directional acquisitions, FA. The intensity values were normalized by values from normal appearing white matter (NAWM) to generate maps of normalized apparent diffusion coefficient (nADC) and normalized fractional anisotropy (nFA). The hyperintense region in the T2 weighted image was defined as the T2All region. A Mann–Whitney rank-sum test was performed on the 25th, median, and 75th nADC and nFA among the three subtypes. Logistic regression was performed to determine how well the nADC and nFA predict subtype. Lesions diagnosed as being OD had significantly lower nADC and significantly higher nFA, compared to AC. The nADC and nFA values individually classified the data with an accuracy of 87%. Combining the two did not enhance the classification. The patients with OA had nADC and nFA values between those of OD and AC. This suggests that ADC and FA may be helpful in directing tissue sampling to the most appropriate regions for taking biopsies in order to make a definitive diagnosis. PMID:19125391

  20. Apparent diffusion coefficient and fractional anisotropy of newly diagnosed grade II gliomas.

    PubMed

    Khayal, Inas S; McKnight, Tracy R; McGue, Colleen; Vandenberg, Scott; Lamborn, Kathleen R; Chang, Susan M; Cha, Soonmee; Nelson, Sarah J

    2009-05-01

    Distinguishing between low-grade oligodendrogliomas (ODs) and astrocytomas (AC) is of interest for defining prognosis and stratifying patients to specific treatment regimens. The purpose of this study was to determine if the apparent diffusion coefficient (ADC) and fractional anisotropy (FA) from diffusion imaging can help to differentiate between newly diagnosed grade II OD and AC subtypes and to evaluate the ADC and FA values for the mixed population of oligoastrocytomas (OA). Fifty-three patients with newly diagnosed grade II gliomas were studied using a 1.5T whole body scanner (23 ODs, 16 ACs, and 14 OAs). The imaging protocol included post-gadolinium T1-weighted images, T2-weighted images, and either three and/or six directional diffusion imaging sequence with b = 1000 s/mm(2). Diffusion-weighted images were analyzed using in-house software to calculate maps of ADC and for six directional acquisitions, FA. The intensity values were normalized by values from normal appearing white matter (NAWM) to generate maps of normalized apparent diffusion coefficient (nADC) and normalized fractional anisotropy (nFA). The hyperintense region in the T2 weighted image was defined as the T2All region. A Mann-Whitney rank-sum test was performed on the 25th, median, and 75th nADC and nFA among the three subtypes. Logistic regression was performed to determine how well the nADC and nFA predict subtype. Lesions diagnosed as being OD had significantly lower nADC and significantly higher nFA, compared to AC. The nADC and nFA values individually classified the data with an accuracy of 87%. Combining the two did not enhance the classification. The patients with OA had nADC and nFA values between those of OD and AC. This suggests that ADC and FA may be helpful in directing tissue sampling to the most appropriate regions for taking biopsies in order to make a definitive diagnosis. PMID:19125391

  1. Neurite beading is sufficient to decrease the apparent diffusion coefficient after ischemic stroke.

    PubMed

    Budde, Matthew D; Frank, Joseph A

    2010-08-10

    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

  2. Variations in apparent diffusion coefficient values following chemotherapy in pediatric neuroblastoma

    PubMed Central

    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

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

    PubMed

    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

  4. Comparison of Quasi-linear and Exact Ion Cyclotron Resonant Diffusion

    NASA Astrophysics Data System (ADS)

    Harvey, R. W.; Petrov, Yu.; Jaeger, E. F.; Batchelor, D. B.; Berry, L. A.; Bonolil, P. T.

    2010-11-01

    These studies investigate the validity of ICRF quasilinear(QL) diffusion theory by comparison with coefficients calculated from Lorentz orbits in full-wave fields. We also compare power deposition and distribution functions obtained with the coupled CQL3D Fokker-Planck code[1], using the two RF diffusion sets. Results are obtained within the context of the Alcator C-Mod ICRF experiment. QL theory is examined using the new, parallelized, diffusion coefficient code, DC, which calculates RF diffusion by suitable average of results of 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. Resulting tail ion distributions with DC are substantailly smoothed in pitch angle compared to QL results. [1] R.W. Harvey and M. McCoy, The CQL3D Fokker Planck Code, www.compxco.com [2] E.F. Jaeger et al, Nucl. Fusion 46, (2006) S397-S408

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

    SciTech Connect

    Goemans, M.G.E.; Gloyna, E.F.; Buelow, S.J.

    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.

  6. Association between visual degeneration of intervertebral discs and the apparent diffusion coefficient.

    PubMed

    Niinimäki, Jaakko; Korkiakoski, Arto; Ojala, Outi; Karppinen, Jaro; Ruohonen, Jyrki; Haapea, Marianne; Korpelainen, Raija; Natri, Antero; Tervonen, Osmo

    2009-06-01

    The value of apparent diffusion coefficient (ADC) measurements in intervertebral disc has been studied because ADC provides an estimate of free diffusion of unbound water and could be used as a quantitative tool to estimate degenerative changes. However, the challenging nature of diffusion imaging of spine and limited numbers of subjects in earlier studies has produced contradictory findings. We aimed to determine the relation between ADC and visual degenerative changes in lumbar intervertebral discs in a sufficiently large homogeneous study group. Lumbar spines of 228 volunteer middle-aged men were MR imaged at 1.5 T including anatomic and diffusion-weighted imaging. ADC values, T2 signal intensity and height, and width of the three lowest lumbar intervertebral discs were measured and disc degeneration visually graded. The calculated average ADC of 530 measured discs was 2.01 x 10(-3) mm(2)/s+/-0.29 (+/-S.D.). The reduction in ADC between visually normal and moderately degenerated discs was 4%. Severely degenerated discs showed 5% larger ADC values than normal discs, presumably due to free water in cracks and fissures of those discs. T2 signal intensity of the disc was significantly correlated with the ADC values, whereas other measured parameters did not show correlation. There was no evident difference in ADC between the studied anatomic lumbar levels. Because there is considerable overlap between ADC values of normal and degenerated discs, we conclude that ADC measurements of intervertebral discs, at least with current technology, have limited clinical value. PMID:19106025

  7. Parallel Diffusion and the Energetic Ion Distributions in the Heliosheath

    NASA Astrophysics Data System (ADS)

    Czechowski, A.; Hilchenbach, M.; Hsieh, K.

    2012-12-01

    We calculate energetic ion distributions in the heliosheath in the energy range from 5 to 100 keV with particular attention to the effects of parallel diffusion in the heliospheric magnetic field. The model used for calculations is the Bonn model of the heliosphere with the magnetic field described in the kinematic approximation. The effects on the energetic neutral atoms observations are discussed.

  8. The Effect of a Fluorophore Photo-Physics on the Lipid Vesicle Diffusion Coefficient Studied by Fluorescence Correlation Spectroscopy.

    PubMed

    Drabik, Dominik; Przybyło, Magda; Sikorski, Aleksander; Langner, Marek

    2016-03-01

    Fluorescence Correlation Spectroscopy (FCS) is a technique, which allows determination of the diffusion coefficient and concentration of fluorescent objects suspended in the solution. The measured parameter is the fluctuation of the fluorescence signal emitted by diffusing molecules. When 100 nm DOPC vesicles labeled with various fluorescent dyes (Fluorescein-PE, NBD-PE, Atto488 DOPE or βBodipy FL) were measured, different values of diffusion coefficients have been obtained. These diffusion coefficients were different from the expected values measured using the dynamic light scattering method (DLS). The FCS was initially developed for solutions containing small fluorescent molecules therefore the observed inconsistency may result from the nature of vesicle suspension itself. The duration of the fluorescence signal may depend on the following factors: the exposure time of the labeled object to the excitation beam, the photo-physical properties (e.g., stability) of a fluorophore, the theoretical model used for the calculations of the diffusion coefficient and optical properties of the vesicle suspension. The diffusion coefficients determined for differently labeled liposomes show that its dependence on vesicle size and quantity of fluorescent probed used for labeling was significant demonstrating that the fluorescence properties of the fluorophore itself (bleaching and/or blinking) were critical factors for a correct outcome of FCS experiment. The new, based on combined FCS and DLS measurements, method for the determination of the focal volume prove itself to be useful for the evaluation of a fluorescence dye with respect to its applicability for FCS experiment. PMID:26695945

  9. Additional Value of Diffusion-Weighted Imaging to Evaluate Prognostic Factors of Breast Cancer: Correlation with the Apparent Diffusion Coefficient

    PubMed Central

    Park, Eun Kyung; Cho, Kyu Ran; Seo, Bo Kyoung; Woo, Ok Hee; Cho, Sung Bum; Bae, Jeoung Won

    2016-01-01

    Background: Breast cancer is a heterogeneous disease with diverse prognoses. The main prognostic determinants are lymph node status, tumor size, histological grade, and biological factors, such as hormone receptors, human epidermal growth factor receptor 2 (HER2), Ki-67 protein levels, and p53 expression. Diffusion-weighted imaging (DWI) can be used to measure the apparent diffusion coefficient (ADC) that provides information related to tumor cellularity and the integrity of the cell membranes. Objectives: The goal of this study was to evaluate whether ADC measurements could provide information on the prognostic factors of breast cancer. Patients and Methods: A total of 71 women with invasive breast cancer, treated consecutively, who underwent preoperative breast MRIs with DWI at 3.0 Tesla and subsequent surgery, were prospectively included in this study. Each DWI was acquired with b values of 0 and 1000 s/mm2. The mean ADC values of the lesions were measured, including the entire lesion on the three largest sections. We performed histopathological analyses for the tumor size, lymph node status, histological grade, hormone receptors, human epidermal growth factor receptor 2 (HER2), Ki-67, p53, and molecular subtypes. The associations with the ADC values and prognostic factors of breast cancer were evaluated using the independent-samples t test and the one-way analysis of variance (ANOVA). Results: A low ADC value was associated with lymph node metastasis (P < 0.01) and with high Ki-67 protein levels (P = 0.03). There were no significant differences in the ADC values among the histological grade (P = 0.48), molecular subtype (P = 0.51), tumor size (P = 0.46), and p53 protein level (P = 0.62). Conclusion: The pre-operative use of the 3.0 Tesla DWI could provide information about the lymph node status and tumor proliferation for breast cancer patients, and could help determine the optimal treatment plan.

  10. Preoperative Axillary Staging with 3.0-T Breast MRI: Clinical Value of Diffusion Imaging and Apparent Diffusion Coefficient

    PubMed Central

    Rautiainen, Suvi; Könönen, Mervi; Sironen, Reijo; Masarwah, Amro; Sudah, Mazen; Hakumäki, Juhana; Vanninen, Ritva; Sutela, Anna

    2015-01-01

    The axillary staging in newly diagnosed breast cancer is under major evolution. The aims of this study were to define the diagnostic performance of 3.0-T diffusion-weighted imaging (DWI) in the detection of axillary metastases in newly diagnosed breast cancer, to assess apparent diffusion coefficients (ADCs) for histopathologically confirmed metastatic lymph nodes in a clinical setting. Altogether 52 consecutive breast cancer patients underwent magnetic resonance imaging and DWI in addition to axillary ultrasound. ADCs of axillary lymph nodes were analysed by two breast radiologists and ultrasound-guided core biopsies were taken. In a separate reading by one radiologist two types of region of interests were used for a smaller group of patients. Altogether 56 axillae (121 lymph nodes) were included in the statistical analysis. Metastatic axillae (51.8%) had significantly lower ADCs (p<0.001). Mean ADCs were 0.663–0.676 x 10-3 mm2/s for the histologically confirmed metastatic LNs and 1.100–1.225 x 10-3 mm2/s for the benign. The sensitivity, specificity, and accuracy of DWI were 72.4%, 79.6%, and 75.9%, respectively with threshold ADC 0.812 x 10-3 mm2/s. Region of interest with information on the minimum value increased the diagnostic performance (area under the curve 0.794 vs. 0.619). Even though ADCs are significantly associated with histopathologically confirmed axillary metastases the diagnostic performance of axillary DWI remains moderate and ultrasound-guided core biopsies or sentinel lymph node biopsies cannot be omitted. PMID:25823016

  11. MRI apparent diffusion coefficient reflects histopathologic subtype, axonal disruption, and tumor fraction in diffuse-type grade II gliomas

    PubMed Central

    Khayal, Inas S.; VandenBerg, Scott R.; Smith, Kenneth J.; Cloyd, Colleen P.; Chang, Susan M.; Cha, Soonmee; Nelson, Sarah J.; McKnight, Tracy R.

    2011-01-01

    The apparent diffusion coefficient (ADC) determined from MR diffusion tensor imaging (DTI) has shown promise for distinguishing World Health Organization grade II astrocytoma (AS) from the more prognostically favorable grade II oligodendroglioma (OD). Since mixed oligoastrocytomas (OAs) with codeletions in chromosomes 1p and 19q confer prognoses similar to those of OD, we questioned whether a previously determined ADC-based criterion for distinguishing OD and AS would hold on an independent set of gliomas that included OA with codeleted or intact 1p/19q chromosomes. We also questioned whether the ADC is associated with the tumor microstructure. ADC colormaps generated from presurgical DTI scans were used to guide the collection of biopsies from each tumor. The median normalized ADC distinguished OD from AS with 91% sensitivity and 92% specificity. 1p/19q codeleted OAs were always classified as ODs, while 1p/19q intact OAs were always classified as ASs. There were positive associations between the ADC and both the SMI-31 score of axonal disruption and the fraction of tumor cells in the biopsies. The ADC of OD and 1p/19q codeleted OA was more associated with tumor fraction, while the ADC of AS and 1p/19q intact OA was more associated with SMI-31 score. We conclude that our previously determined threshold median ADC can distinguish grade II OD and AS on a new patient cohort and that the distinctions extend to OA with codeleted and intact 1p/19q chromosomes. Further, the ADC in grade II gliomas is associated with the fraction of tumor cells and degree of axonal disruption in tumor subregions. PMID:21865401

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

    PubMed

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

    2010-01-01

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

  13. Surface diffusion coefficient of Au atoms on single layer graphene grown on Cu

    SciTech Connect

    Ruffino, F. Cacciato, G.; Grimaldi, M. G.

    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.

  14. Gamma convolution models for self-diffusion coefficient distributions in PGSE NMR.

    PubMed

    Röding, Magnus; Williamson, Nathan H; Nydén, Magnus

    2015-12-01

    We introduce a closed-form signal attenuation model for pulsed-field gradient spin echo (PGSE) NMR based on self-diffusion coefficient distributions that are convolutions of n gamma distributions, n⩾1. Gamma convolutions provide a general class of uni-modal distributions that includes the gamma distribution as a special case for n=1 and the lognormal distribution among others as limit cases when n approaches infinity. We demonstrate the usefulness of the gamma convolution model by simulations and experimental data from samples of poly(vinyl alcohol) and polystyrene, showing that this model provides goodness of fit superior to both the gamma and lognormal distributions and comparable to the common inverse Laplace transform. PMID:26524648

  15. Optimal Experiment Design for Monoexponential Model Fitting: Application to Apparent Diffusion Coefficient Imaging

    PubMed Central

    Alipoor, Mohammad; Maier, Stephan E.; Gu, Irene Yu-Hua; Mehnert, Andrew; Kahl, Fredrik

    2015-01-01

    The monoexponential model is widely used in quantitative biomedical imaging. Notable applications include apparent diffusion coefficient (ADC) imaging and pharmacokinetics. The application of ADC imaging to the detection of malignant tissue has in turn prompted several studies concerning optimal experiment design for monoexponential model fitting. In this paper, we propose a new experiment design method that is based on minimizing the determinant of the covariance matrix of the estimated parameters (D-optimal design). In contrast to previous methods, D-optimal design is independent of the imaged quantities. Applying this method to ADC imaging, we demonstrate its steady performance for the whole range of input variables (imaged parameters, number of measurements, and range of b-values). Using Monte Carlo simulations we show that the D-optimal design outperforms existing experiment design methods in terms of accuracy and precision of the estimated parameters. PMID:26839880

  16. 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.

  17. Gamma convolution models for self-diffusion coefficient distributions in PGSE NMR

    NASA Astrophysics Data System (ADS)

    Röding, Magnus; Williamson, Nathan H.; Nydén, Magnus

    2015-12-01

    We introduce a closed-form signal attenuation model for pulsed-field gradient spin echo (PGSE) NMR based on self-diffusion coefficient distributions that are convolutions of n gamma distributions, n ⩾ 1 . Gamma convolutions provide a general class of uni-modal distributions that includes the gamma distribution as a special case for n = 1 and the lognormal distribution among others as limit cases when n approaches infinity. We demonstrate the usefulness of the gamma convolution model by simulations and experimental data from samples of poly(vinyl alcohol) and polystyrene, showing that this model provides goodness of fit superior to both the gamma and lognormal distributions and comparable to the common inverse Laplace transform.

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

    NASA Astrophysics Data System (ADS)

    Kingsburry, Christine; Slater, Gary W.

    2009-12-01

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

  19. Diffusion Coefficients of a Non-Linear Astrophysical Process: Luis Carrasco's Scientific (and other) Contributions

    NASA Astrophysics Data System (ADS)

    Aguilar, L. A.

    2009-11-01

    The Luis Carrasco phenomenon in Astrophysics is a widespread event that has appeared in many branches of theoretical and observational Astronomy, as well as in astronomical instrumentation. It is an ubiquitous and highly non-linear effect with multiple coupling constants. To understand it, it is necessary to dwell, not only into many areas of Astronomy, but of human culture and knowledge in general. Some authors believe that it is only through the ``many-worlds'' interpretation of Quantum Mechanics, that this effect can be understood. In this work, we will demonstrate its fractal nature, present a panoramic view of this global effect, and estimate its diffusion coefficients in the regular and irregular regimes. Connections with areas outside Astronomy will be shown.

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

    PubMed Central

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

    2012-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

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

    PubMed

    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

  3. The efficacy of diffusion weighted imaging and apparent diffusion coefficients mapping for liver metastasis of colonic adenocarcinomas

    PubMed Central

    Metin, Melike R.; Aydın, Hasan; Çetin, Hüseyin; Özmen, Evrim; Kayaçetin, Serra

    2016-01-01

    Objectives: To establish retrospectively the relation between the histopathologic grade of colorectal liver metastasis and apparent diffusion coefficient (ADC) values of hepatic metastases of colorectal adenocarcinomas. Methods: The diagnoses of liver metastases were confirmed with biopsy, surgery, and follow-up imaging findings. Twenty-six patients with 94 liver metastasis were included in the study. Of 94 masses, 59 were poorly-differentiated adenocarcinoma, 18 were moderately-differentiated adenocarcinoma, and 17 were well-differentiated regarding the diameters, ADC values, and ratio index (RI) values. Kolmogorov-smirnov normality test, Kruskal-wallis analysis of variance, Mann-Whitney U test with Bonferroni correction, Spearman correlation analysis, and receiver operating characteristics curve methods were applied to evaluate the statistical relations. Results: There was a statistically significant difference in terms of ADC values and RI between poorly-differentiated adenocarcinoma and moderately-differentiated adenocarcinoma plus well-differentiated adenocarcinomas. Poorly-differentiated adenocarcinomas have the lowest ADC values and highest RI values among other groups. Conclusion: Use of ADC values alone can be executed for the diagnosis of focal hepatic masses and also can aid in the differentiation of benign and malignant hepatic lesions. PMID:27052280

  4. 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.

  5. Relationship Between Choline and Apparent Diffusion Coefficient in Patients With Gliomas

    PubMed Central

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

    2011-01-01

    Purpose To examine the relationship between apparent diffusion coefficients (ADC) from diffusion weighted imaging (DWI) and choline levels from proton magnetic resonance spectroscopic imaging (MRSI) in newly diagnosed Grade II and IV gliomas within distinct anatomic regions. Materials and Methods A total of 37 patients with Grade II and 28 patients with Grade IV glioma were scanned on a 1.5T system with 3D MRSI and DWI. Region level analysis included Spearman rank correlation between median normalized ADC and choline for each patient per grade within each distinct abnormal anatomical region. Voxel level analysis calculated a Spearman rank correlation per region, per patient. Results Grade II lesions showed no evidence of a correlation between normalized ADC and choline using either the region or voxel level analysis. Region level analysis of Grade IV lesions did not appear to correlate in the contrast enhancement or necrotic core, but did suggest a significant negative correlation in the more heterogeneous nonenhancing and combined regions. Conclusion There appears to be differences in the relationship between ADC and choline levels in Grade II and Grade IV gliomas. Correlation within these regions in Grade IV lesions was strongest when all regions were included, suggesting heterogeneity may be driving the relationship. PMID:18383265

  6. Dynamics and absorption properties of stochastic equations with Hlder diffusion coefficients

    NASA Astrophysics Data System (ADS)

    Touboul, Jonathan; Wainrib, Gilles

    2015-07-01

    In this article, we characterize the dynamics and absorption properties of a class of stochastic differential equations around singular points where both the drift and diffusion functions vanish. According to the Hlder coefficient ? of the diffusion function around the singular point, we identify different regimes: a regime where the solutions almost surely reach the singular point in finite time, and regimes of exponential attraction or repulsion from the singular point. Stability of the absorbing state, large deviations for the absorption time, existence of stationary or quasi-stationary distributions are discussed. In particular, we show that quasi-stationary distributions only exist for ? < 3 / 4, and for ? ?(3 / 4 , 1) , no quasi-stationary distribution is found and numerical simulations tend to show that the process conditioned on not being absorbed initiates an almost sure exponential convergence towards the absorbing state (as is demonstrated to be true for ? = 1). These results have several implications in the understanding of stochastic bifurcations, and we completely unfold two generic situations: the pitchfork and saddle-node bifurcations, and discuss the Hopf bifurcation in the appendix.

  7. Absolute rate coefficients for photorecombination of beryllium-like and boron-like silicon ions

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    We report measured rate coefficients for electron-ion recombination of Si10+ forming Si9+ and of Si9+ forming Si8+, respectively. The measurements were performed using the electron-ion merged-beams technique at a heavy-ion storage ring. Electron-ion collision energies ranged from 0 to 50 eV for Si9+ and from 0 to 2000 eV for Si10+, thus, extending previous measurements for Si10+ (Orban et al 2010 Astrophys. J. 721 1603) to much higher energies. Experimentally derived rate coefficients for the recombination of Si9+ and Si10+ ions in a plasma are presented along with simple parameterizations. These rate coefficients are useful for the modeling of the charge balance of silicon in photoionized plasmas (Si9+ and Si10+) and in collisionally ionized plasmas (Si10+ only). In the corresponding temperature ranges, the experimentally derived rate coefficients agree with the latest corresponding theoretical results within the experimental uncertainties.

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

    PubMed

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

    2013-06-13

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

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

    PubMed Central

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

    2014-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

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

  11. Easy measurement of diffusion coefficients of EGFP-tagged plasma membrane proteins using k-Space Image Correlation Spectroscopy.

    PubMed

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

    2014-01-01

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

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

    DOE PAGESBeta

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

    2014-09-30

    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 C n H2n+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 structuremore » 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. Moreover, 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%.« less

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

    PubMed

    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

  14. 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%.

  15. Diffusion-weighted magnetic resonance imaging in cancer: Reported apparent diffusion coefficients, in-vitro and in-vivo reproducibility.

    PubMed

    Jafar, Maysam M; Parsai, Arman; Miquel, Marc E

    2016-01-28

    There is considerable disparity in the published apparent diffusion coefficient (ADC) values across different anatomies. Institutions are increasingly assessing repeatability and reproducibility of the derived ADC to determine its variation, which could potentially be used as an indicator in determining tumour aggressiveness or assessing tumour response. In this manuscript, a review of selected articles published to date in healthy extra-cranial body diffusion-weighted magnetic resonance imaging is presented, detailing reported ADC values and discussing their variation across different studies. In total 115 studies were selected including 28 for liver parenchyma, 15 for kidney (renal parenchyma), 14 for spleen, 13 for pancreatic body, 6 for gallbladder, 13 for prostate, 13 for uterus (endometrium, myometrium, cervix) and 13 for fibroglandular breast tissue. Median ADC values in selected studies were found to be 1.28 × 10(-3) mm(2)/s in liver, 1.94 × 10(-3) mm(2)/s in kidney, 1.60 × 10(-3) mm(2)/s in pancreatic body, 0.85 × 10(-3) mm(2)/s in spleen, 2.73 × 10(-3) mm(2)/s in gallbladder, 1.64 × 10(-3) mm(2)/s and 1.31 × 10(-3) mm(2)/s in prostate peripheral zone and central gland respectively (combined median value of 1.54×10(-3) mm(2)/s), 1.44 × 10(-3) mm(2)/s in endometrium, 1.53 × 10(-3) mm(2)/s in myometrium, 1.71 × 10(-3) mm(2)/s in cervix and 1.92 × 10(-3) mm(2)/s in breast. In addition, six phantom studies and thirteen in vivo studies were summarized to compare repeatability and reproducibility of the measured ADC. All selected phantom studies demonstrated lower intra-scanner and inter-scanner variation compared to in vivo studies. Based on the findings of this manuscript, it is recommended that protocols need to be optimised for the body part studied and that system-induced variability must be established using a standardized phantom in any clinical study. Reproducibility of the measured ADC must also be assessed in a volunteer population, as variations are far more significant in vivo compared with phantom studies. PMID:26834942

  16. Predicting liver metastasis of gastrointestinal tract cancer by diffusion-weighted imaging of apparent diffusion coefficient values

    PubMed Central

    Zheng, De-Xian; Meng, Shu-Chun; Liu, Qing-Jun; Li, Chuan-Ting; Shang, Xi-Dan; Zhu, Yu-Seng; Bai, Tian-Jun; Xu, Shi-Ming

    2016-01-01

    AIM: To determine if efficacy of chemotherapy on liver metastasis of gastrointestinal tract cancer can be predicted by apparent diffusion coefficient (ADC) values of diffusion-weighted imaging (DWI). METHODS: In total, 86 patients with liver metastasis of gastrointestinal tract cancer (156 metastatic lesions) diagnosed in our hospital were included in this study. The maximum diameters of these tumors were compared with each other before treatment, 2 wk after treatment, and 12 wk after treatment. Selected patients were classified as the effective group and the ineffective group, depending on the maximum diameter of the tumor after 12 wk of treatment; and the ADC values at different treatment times between the two groups were compared. Spearman rank correlation was used to analyze the relationship between ADC value and tumor diameter. Receiver operating characteristic curve (ROC curve) was used to analyze the ADC values before treatment to predict the patient’s sensitivity and specificity degree of efficacy to the chemotherapy. RESULTS: There was no difference in age between the two groups and in maximum tumor diameter before treatment and 2 wk after treatment. However, after 12 wk of treatment, maximum tumor diameter in the effective group was significantly lower than that in the ineffective group (P < 0.05). Before treatment, ADC values in the ineffective group were significantly higher than those in the effective group (P < 0.05). There was no difference in ADC values between the effective and ineffective groups after 2 and 12 wk of treatment. However, ADC values were significantly higher after 2 and 12 wk of treatment compared to before treatment in the effective group (P < 0.05). Spearman rank correlation analysis showed that ADC value before treatment and the reduced percentage of the maximum tumor diameter after 12 wk of treatment were negatively correlated, while the increase in the percentage of the ADC value 12 wk after treatment and the decrease in the percentage of the maximum tumor diameter were significantly positively correlated. The results of the ROC curve showed that ADC value with a chemotherapy ineffective threshold value of 1.14 × 10-3 mm2/s before treatment had a sensitivity and specificity of 94.3% and 76.7%, respectively. CONCLUSION: DWI ADC values can be used to predict the response of patients with liver metastasis of gastrointestinal tract cancer to chemotherapy with high sensitivity and relatively high specificity. PMID:26973399

  17. Diffusion-weighted magnetic resonance imaging in cancer: Reported apparent diffusion coefficients, in-vitro and in-vivo reproducibility

    PubMed Central

    Jafar, Maysam M; Parsai, Arman; Miquel, Marc E

    2016-01-01

    There is considerable disparity in the published apparent diffusion coefficient (ADC) values across different anatomies. Institutions are increasingly assessing repeatability and reproducibility of the derived ADC to determine its variation, which could potentially be used as an indicator in determining tumour aggressiveness or assessing tumour response. In this manuscript, a review of selected articles published to date in healthy extra-cranial body diffusion-weighted magnetic resonance imaging is presented, detailing reported ADC values and discussing their variation across different studies. In total 115 studies were selected including 28 for liver parenchyma, 15 for kidney (renal parenchyma), 14 for spleen, 13 for pancreatic body, 6 for gallbladder, 13 for prostate, 13 for uterus (endometrium, myometrium, cervix) and 13 for fibroglandular breast tissue. Median ADC values in selected studies were found to be 1.28 × 10-3 mm2/s in liver, 1.94 × 10-3 mm2/s in kidney, 1.60 × 10-3 mm2/s in pancreatic body, 0.85 × 10-3 mm2/s in spleen, 2.73 × 10-3 mm2/s in gallbladder, 1.64 × 10-3 mm2/s and 1.31 × 10-3 mm2/s in prostate peripheral zone and central gland respectively (combined median value of 1.54×10-3 mm2/s), 1.44 × 10-3 mm2/s in endometrium, 1.53 × 10-3 mm2/s in myometrium, 1.71 × 10-3 mm2/s in cervix and 1.92 × 10-3 mm2/s in breast. In addition, six phantom studies and thirteen in vivo studies were summarized to compare repeatability and reproducibility of the measured ADC. All selected phantom studies demonstrated lower intra-scanner and inter-scanner variation compared to in vivo studies. Based on the findings of this manuscript, it is recommended that protocols need to be optimised for the body part studied and that system-induced variability must be established using a standardized phantom in any clinical study. Reproducibility of the measured ADC must also be assessed in a volunteer population, as variations are far more significant in vivo compared with phantom studies. PMID:26834942

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

    PubMed Central

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

    2014-01-01

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

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

    USGS Publications Warehouse

    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.

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

    PubMed

    Wood, Warren W; Kraemer, Thomas F; Shapiro, Allen

    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 degrees 56'N, 71 degrees 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. PMID:15318778

  1. Modeling Diffusion Induced Stresses for Lithium-Ion Battery Materials

    NASA Astrophysics Data System (ADS)

    Chiu Huang, Cheng-Kai

    Advancing lithium-ion battery technology is of paramount importance for satisfying the energy storage needs in the U.S., especially for the application in the electric vehicle industry. To provide a better acceleration for electric vehicles, a fast and repeatable discharging rate is required. However, particle fractures and capacity loss have been reported under high current rate (C-rate) during charging/discharging and after a period of cycling. During charging and discharging, lithium ions extract from and intercalate into electrode materials accompanied with the volume change and phase transition between Li-rich phase and Li-poor phase. It is suggested that the diffusion-induced-stress is one of the main reasons causing capacity loss due to the mechanical degradation of electrode particles. Therefore, there is a fundamental need to provide a mechanistic understanding by considering the structure-mechanics-property interactions in lithium-ion battery materials. Among many cathode materials, the olivine-based lithium-iron-phosphate (LiFePO4) with an orthorhombic crystal structure is one of the promising cathode materials for the application in electric vehicles. In this research we first use a multiphysic approach to investigate the stress evolution, especially on the phase boundary during lithiation in single LiFePO4 particles. A diffusion-controlled finite element model accompanied with the experimentally observed phase boundary propagation is developed via a finite element package, ANSYS, in which lithium ion concentration-dependent anisotropic material properties and volume misfits are incorporated. The stress components on the phase boundary are used to explain the Mode I, Mode II, and Mode III fracture propensities in LiFePO4 particles. The elastic strain energy evolution is also discussed to explain why a layer-by-layer lithium insertion mechanism (i.e. first-order phase transformation) is energetically preferred. Another importation issue is how current rate (C-rate) during charging/discharging affects diffusion induced stresses inside electrode materials. For the experimental part we first conduct charging/discharging under different C-rates to observe the voltage responses for commercial LiFePO4 batteries. Then Time-of-Flight Secondary Ion Mass Spectrometry technique is applied to measure the lithium ion intensities in different C-rate charged/discharged samples. These experimental results could be used to support that a more significant voltage fluctuation under high C-rates is due to different lithium insertion mechanisms, rather than the amount of lithium ions intercalated into electrode materials. Thus the investigation of C-rate-dependent stress evolution is required for the development of a more durable lithium ion battery. In this dissertation, we extend the single particle finite element model to investigate the C-rate-dependent diffusion induced stresses in a multi-particle system. Concentration dependent anisotropic material properties, C-rate-dependent volume misfits and concentration dependent Li-ion diffusivity are incorporated in the model. The concentration gradients, diffusion induced stresses, and strain energies under different C-rates are discussed in this study. Particle fractures have been observed in many experimental results, in this study we further discuss the effect of the crack surface orientation on the lithium concentration profile and stress level in cathode materials. The results of this dissertation provide a better understanding of diffusion induced stresses in electrode materials and contribute to our fundamental knowledge of interplay between lithium intercalations, stress evolutions, particle fractures and the capacity fade in lithium-ion batteries.

  2. Temperature Activated Diffusion of Radicals through Ion Implanted Polymers.

    PubMed

    Wakelin, Edgar A; Davies, Michael J; Bilek, Marcela M M; McKenzie, David R

    2015-12-01

    Plasma immersion ion implantation (PIII) is a promising technique for immobilizing biomolecules on the surface of polymers. Radicals generated in a subsurface layer by PIII treatment diffuse throughout the substrate, forming covalent bonds to molecules when they reach the surface. Understanding and controlling the diffusion of radicals through this layer will enable efficient optimization of this technique. We develop a model based on site to site diffusion according to Fick's second law with temperature activation according to the Arrhenius relation. Using our model, the Arrhenius exponential prefactor (for barrierless diffusion), D0, and activation energy, EA, for a radical to diffuse from one position to another are found to be 3.11 × 10(-17) m(2) s(-1) and 0.31 eV, respectively. The model fits experimental data with a high degree of accuracy and allows for accurate prediction of radical diffusion to the surface. The model makes useful predictions for the lifetime over which the surface is sufficiently active to covalently immobilize biomolecules and it can be used to determine radical fluence during biomolecule incubation for a range of storage and incubation temperatures so facilitating selection of the most appropriate parameters. PMID:26562064

  3. A new approach to evaluating the effects of pharmacologic vitreolysis on vitreous diffusion coefficients using dynamic light scattering

    NASA Astrophysics Data System (ADS)

    Ansari, Rafat R.; Suh, Kwang I.; Sebag, J.

    2006-02-01

    PURPOSE: Pharmacologic vitreolysis is a new approach to improve vitreo-retinal surgery. Ultimately, the development of drugs to liquefy and detach vitreous from retina should prevent disease by mitigating the contribution of vitreous to retinopathy and eliminate the need for surgery. However, the mechanism of action of pharmacologic vitreolysis remains unclear. The technique of Dynamic light scattering (DLS) was used to evaluate the effects of microplasmin by following the diffusion coefficients of spherical polystyrene nano-particles injected with microplasmin into the vitreous. METHODS: Diffusion coefficients in dissected (n=9) porcine eyes were measured in vitro. DLS was performed on all specimens at 37°C as often as every 10 minutes for up to 6 hours following injections of human recombinant microplasmin at doses ranging from 0.125 mg to 0.8 mg, with 20 nm diameter tracer nanospheres. RESULTS: DLS findings in untreated porcine vitreous were similar to the previously described findings in bovine and human vitreous, demonstrating a fast (early) component, resulting from the flexible hyaluronan molecules, and a slow (late) component, resulting form the stiff collagen molecules. Microplasmin increased porcine vitreous diffusion coefficients. A new approach was developed to use DLS measurements of vitreous diffusion coefficients to evaluate the effects of microplasmin in intact eyes. CONCLUSIONS: Pharmacologic vitreolysis with human recombinant microplasmin increases vitreous diffusion coefficients in vitro. The results of these studies indicate that this new approach using DLS to measure vitreous diffusion coefficients can be used to study the effects of pharmacologic vitreolysis using microplasmin and other agents in intact eyes and ultimately in vivo.

  4. Numerical convergence of the self-diffusion coefficient and viscosity obtained with Thomas-Fermi-Dirac molecular dynamics

    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.

  5. Numerical convergence of the self-diffusion coefficient and viscosity obtained with Thomas-Fermi-Dirac molecular dynamics.

    PubMed

    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

  6. Discrimination of dimethyl sulphoxide diffusion coefficient in the process of optical clearing by confocal micro-Raman spectroscopy.

    PubMed

    Liu, Ping; Huang, Yanyue; Guo, Zhouyi; Wang, Jianping; Zhuang, Zhengfei; Liu, Songhao

    2013-02-01

    Confocal micro-Raman spectroscopy is employed to study the diffusion process of dimethyl sulfoxide (DMSO) in porcine skin optical clearing. The variation of DMSO concentration with time at different depths of the skin was obtained and then the DMSO diffusion coefficient with the passive diffusion model was calculated. Results show that it has a significant difference at different depths of the skin. Also, the DMSO concentration with the depth at different times was obtained and the same method was used to find the change law of the DMSO diffusion coefficient. Results indicate that it also changes with the treatment time. The experimental results are consistent with the theoretical model in a previous study. The current results demonstrate that Raman spectroscopy has the ability to quantitatively monitor the process of optical clearing. PMID:23416924

  7. Discrimination of dimethyl sulphoxide diffusion coefficient in the process of optical clearing by confocal micro-Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Liu, Ping; Huang, Yanyue; Guo, Zhouyi; Wang, Jianping; Zhuang, Zhengfei; Liu, Songhao

    2013-02-01

    Confocal micro-Raman spectroscopy is employed to study the diffusion process of dimethyl sulfoxide (DMSO) in porcine skin optical clearing. The variation of DMSO concentration with time at different depths of the skin was obtained and then the DMSO diffusion coefficient with the passive diffusion model was calculated. Results show that it has a significant difference at different depths of the skin. Also, the DMSO concentration with the depth at different times was obtained and the same method was used to find the change law of the DMSO diffusion coefficient. Results indicate that it also changes with the treatment time. The experimental results are consistent with the theoretical model in a previous study. The current results demonstrate that Raman spectroscopy has the ability to quantitatively monitor the process of optical clearing.

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

    NASA Astrophysics Data System (ADS)

    Ahadi, Amirhossein; Saghir, M. Ziad

    2014-08-01

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

  9. Diffusivity of ions in agarose gels and intervertebral disc: effect of porosity.

    PubMed

    Gu, Wei Yong; Yao, Hai; Vega, Adriana L; Flagler, Daniel

    2004-12-01

    The effect of tissue porosity on ion (sodium, potassium, and chloride) diffusivity in agarose gels and porcine intervertebral disc tissues was investigated using an electrical conductivity method. An empirical, constitutive model for diffusivity (D) of solutes in porous fibrous media was proposed: D/Do = exp[-alpha(r(s)/k(1/2))beta] where r(s) is the Stokes radius of a solute, kappa is the Darcy permeability of the porous medium, Do is the diffusivity in free solution, alpha and beta are two positive parameters whose values depend on material structure. It is found that alpha = 1.25 +/- 0.138, beta = 0.681 +/- 0.059 (95% confidence interval, R2 = 0.92, n = 72) for agarose gels and alpha = 1.29 +/- 0.171 and beta = 0.372 +/- 0.088 (95% confidence interval, R2 = 0.88, n = 86) for porcine annulus fibrosus. The functional relationship between solute diffusivity and tissue deformation was derived. Comparisons of our model prediction with experimental data on diffusion coefficients of macromolecules (proteins, dextrans, polymer beads) in agarose gels in the literature were made. Our results were also compared to the data on ion diffusivity in charged gels and in cartilaginous tissues reported in the literature. There was a good agreement between our model prediction and the data in the literature. The present study provides additional information on solute diffusivity in uncharged gels and charged tissues, and is important for understanding nutritional transport in avascular cartilaginous tissues under different mechanical loading conditions. PMID:15675682

  10. 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.

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

    SciTech Connect

    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.

  12. Parameterization of the Age-Dependent Whole Brain Apparent Diffusion Coefficient Histogram

    PubMed Central

    Klose, Uwe; Batra, Marion; Nägele, Thomas

    2015-01-01

    Purpose. The distribution of apparent diffusion coefficient (ADC) values in the brain can be used to characterize age effects and pathological changes of the brain tissue. The aim of this study was the parameterization of the whole brain ADC histogram by an advanced model with influence of age considered. Methods. Whole brain ADC histograms were calculated for all data and for seven age groups between 10 and 80 years. Modeling of the histograms was performed for two parts of the histogram separately: the brain tissue part was modeled by two Gaussian curves, while the remaining part was fitted by the sum of a Gaussian curve, a biexponential decay, and a straight line. Results. A consistent fitting of the histograms of all age groups was possible with the proposed model. Conclusions. This study confirms the strong dependence of the whole brain ADC histograms on the age of the examined subjects. The proposed model can be used to characterize changes of the whole brain ADC histogram in certain diseases under consideration of age effects. PMID:26609526

  13. Isotopic mass-dependence of metal cation diffusion coefficients in liquid water

    SciTech Connect

    Bourg, I.C.; Richter, F.M.; Christensen, J.N.; Sposito, G.

    2009-01-11

    Isotope distributions in natural systems can be highly sensitive to the mass (m) dependence of solute diffusion coefficients (D) in liquid water. Isotope geochemistry studies routinely have assumed that this mass dependence either is negligible (as predicted by hydrodynamic theories) or follows a kinetic-theory-like inverse square root relationship (D {proportional_to} m{sup -0.5}). However, our recent experimental results and molecular dynamics (MD) simulations showed that the mass dependence of D is intermediate between hydrodynamic and kinetic theory predictions (D {proportional_to} m{sup -{beta}} with 0 {<=} {beta} < 0.2 for Li{sup +}, Cl{sup -}, Mg{sup 2+}, and the noble gases). In this paper, we present new MD simulations and experimental results for Na{sup +}, K{sup +}, Cs{sup +}, and Ca{sup 2+} that confirm the generality of the inverse power-law relation D {proportional_to} m{sup -{beta}}. Our new findings allow us to develop a general description of the influence of solute valence and radius on the mass dependence of D for monatomic solutes in liquid water. This mass dependence decreases with solute radius and with the magnitude of solute valence. Molecular-scale analysis of our MD simulation results reveals that these trends derive from the exponent {beta} being smallest for those solutes whose motions are most strongly coupled to solvent hydrodynamic modes.

  14. [Optical properties and remote sensing retrieval model of diffuse attenuation coefficient of Taihu Lake water body].

    PubMed

    Le, Cheng-Feng; Li, Yun-Mei; Zha, Yong; Sun, De-Yong; Wang, Li-Zhen

    2009-02-01

    The spectral and chemical analytical data of Taihu Lake water quality in Nov. 8-22, 2007 were used to analyze the spectral characteristics of diffuse attenuation coefficient (Kd) of the water body in autumn and related affecting factors. On the basis of this analysis, the Kd at band 490 nm, Kd (490), was used as a variable to build the relationship between Kd and remote sensing reflectance. The results indicated that within the scope of visible band, the Kd of the water body at most locations of Taihu Lake presented an exponent decreasing trend with the increase of wave length. Due to the higher concentration of phytoplankton in some locations, a peak value of Kd was presented at band 675 nm. Non-organic suspended particles, because of their higher content in suspended sediment, had larger effects on Kd than organic suspended ones. There was a good correlation between Kd and remote sensing reflectance. Taking Rrs (550), Rrs (675) and Rrs (731) as independent variables and doing regression analysis with Kd (490), a good linear relationship was found between Kd (490) and Rrs (731), and multi-variate linear regression analysis using variables Rrs (550), Rrs (675) and Rrs (731) could get better effect (R2 > 0.96) than the regression analysis using variable Rrs (731). PMID:19459373

  15. Simple analytical forms of the perpendicular diffusion coefficient for two-component turbulence. II. Dynamical turbulence with constant correlation time

    SciTech Connect

    Shalchi, A.

    2014-01-10

    We explore perpendicular diffusion based on the unified nonlinear transport theory. In Paper I, we focused on magnetostatic turbulence, whereas in the present article we include dynamical turbulence effects. For simplicity, we assume a constant correlation time. We show that there is now a nonvanishing contribution of the slab modes. We explore the parameter regimes in which the turbulence dynamics becomes important for perpendicular diffusion. Analytical forms for the perpendicular diffusion coefficient are derived, which can be implemented easily in solar modulation or shock acceleration codes.

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

    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.

  17. 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...

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

    USGS Publications Warehouse

    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.

  19. Determination of hydrogen diffusion coefficients in F82H by hydrogen depth profiling with a tritium imaging plate technique

    SciTech Connect

    Higaki, M.; Otsuka, T.; Hashizume, K.; Tokunaga, K.; Ezato, K.; Suzuki, S.; Enoeda, M.; Akiba, M.

    2015-03-15

    Hydrogen diffusion coefficients in a reduced activation ferritic/martensitic steel (F82H) and an oxide dispersion strengthened F82H (ODS-F82H) have been determined from depth profiles of plasma-loaded hydrogen with a tritium imaging plate technique (TIPT) in the temperature range from 298 K to 523 K. Data on hydrogen diffusion coefficients, D, in F82H, are summarized as D [m{sup 2}*s{sup -1}] =1.1*10{sup -7}exp(-16[kJ mol{sup -1}]/RT). The present data indicate almost no trapping effect on hydrogen diffusion due to an excess entry of energetic hydrogen by the plasma loading, which results in saturation of the trapping sites at the surface and even in the bulk. In the case of ODS-F82H, data of hydrogen diffusion coefficients are summarized as D [m{sup 2}*s{sup -1}] =2.2*10{sup -7}exp(-30[kJ mol{sup -1}]/RT) indicating a remarkable trapping effect on hydrogen diffusion caused by tiny oxide particles (Y{sub 2}O{sub 3}) in the bulk of F82H. Such oxide particles introduced in the bulk may play an effective role not only on enhancement of mechanical strength but also on suppression of hydrogen penetration by plasma loading.

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

    SciTech Connect

    Majer, G.; Melchior, J. P.

    2014-03-07

    Precise diffusion measurements of rhodamine 6G (Rh6G) dissolved in D{sub 2}O at concentrations between 50 and 200 μM 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 τ{sub D} of Rh6G was measured by FCS in both D{sub 2}O and H{sub 2}O. The obtained isotopic correction factor, τ{sub D}(D{sub 2}O)/τ{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.

  1. Cyclic voltammetric technique for the determination of the critical micelle concentration of surfactants, self-diffusion coefficient of micelles, and partition coefficient of an electrochemical probe

    SciTech Connect

    Mandal, A.B.; Nair, B.U. )

    1991-10-31

    Critical micelle concentrations (cmc) of cetyltrimethylammonium bromide (CTAB) and cetylpyridinium chloride (CPC) surfactants in aqueous solution have been determined by using the cyclic voltammetric technique. (Co(en){sub 3})(ClO{sub 4}){sub 3} has been used as the redox-active electrochemical probe. The cmc values so obtained for the surfactants were found to be in good agreement with the literature values. The partition coefficient, K, of the electrochemical probe between water and surfactants in nonmicellar and micellar states was estimated using the peak current, i{sub p} and half-wave potential, E{sub 1/2} values. The self-diffusion coefficient, D{sub m}, interaction parameter, k{sub f}, and hydrodynamic radius of the micelles were also estimated. The results suggest that the probe is sensitive to the nature of surfactant as well as surfactant concentration.

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

    NASA Technical Reports Server (NTRS)

    Paillat, O.; Wasserburg, G. J.

    1993-01-01

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

  3. The mimetic finite difference method for elliptic and parabolic problems with a staggered discretization of diffusion coefficient

    NASA Astrophysics Data System (ADS)

    Lipnikov, Konstantin; Manzini, Gianmarco; Moulton, J. David; Shashkov, Mikhail

    2016-01-01

    Numerical schemes for nonlinear parabolic equations based on the harmonic averaging of cell-centered diffusion coefficients break down when some of these coefficients go to zero or their ratio grows. To tackle this problem, we propose new mimetic finite difference schemes that use a staggered discretization of the diffusion coefficient. The primary mimetic operator approximates div (k ṡ); the derived (dual) mimetic operator approximates - ∇ (ṡ). The new mimetic schemes preserve symmetry and positive-definiteness of the continuum problem which allows us to use algebraic solvers with optimal complexity. We perform detailed numerical analysis of the new schemes for linear elliptic problems and a specially designed linear parabolic problem that has solution dynamics typical for nonlinear problems. We show that the new schemes are competitive with the state-of-the-art schemes for steady-state problems but provide much more accurate solution dynamics for the transient problem.

  4. On the calculation of electric diffusion coefficient of radiation belt electrons with in situ electric field measurements by THEMIS

    NASA Astrophysics Data System (ADS)

    Liu, Wenlong; Tu, Weichao; Li, Xinlin; Sarris, Theodore; Khotyaintsev, Yuri; Fu, Huishan; Zhang, Hui; Shi, Quanqi

    2016-02-01

    Based on 7 years' observations from Time History of Events and Macroscale Interactions during Substorms (THEMIS), we investigate the statistical distribution of electric field Pc5 ULF wave power under different geomagnetic activities and calculate the radial diffusion coefficient due to electric field, , for outer radiation belt electrons. A simple empirical expression of is also derived. Subsequently, we compare to previous DLL models and find similar Kp dependence with the model, which is also based on in situ electric field measurements. The absolute value of is constantly higher than , probably due to the limited orbital coverage of CRRES. The differences between and the commonly used and models are significant, especially in Kp dependence and energy dependence. Possible reasons for these differences and their implications are discussed. The diffusion coefficient provided in this paper, which also has energy dependence, will be an important contributor to quantify the radial diffusion process of radiation belt electrons.

  5. Spatial dependence of the local diffusion coefficient measured upstream of the November 12, 1978 interplanetary traveling shock

    NASA Technical Reports Server (NTRS)

    Gloeckler, G.; Ipavich, F. M.; Klecker, B.; Hovestadt, D.; Scholer, M.

    1985-01-01

    Characteristics of wuprathermal particles accelerated by quasi-parallel interplanetary traveling shocks have been generally explained in terms of a first order Fermi mechanism. Such models require diffusive scattering of particles upstream of the shock. This scattering is characterized by a local diffusion coefficient, kappa, which is determined by the local power density of waves in the upstream region. The dependence of the diffusion coefficient of suprathermal upstream protons on distance from the November 12, 1978 interplanetary traveling shock using a different approach is studied. Unlike previous studies this method, which is based on measurements of particle streaming and intensity gradients, does not rely on predictions. The local spatial variations of Kappa upstream of the November 12, 1978 shock have been chosen for study because the characteristics of this quasi-parallel shock have been extensively studied, and also because of its favorable geometry (i.e. B field nearly radial).

  6. Diffusion in heterogeneous media: An iterative scheme for finding approximate solutions to fractional differential equations with time-dependent coefficients

    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.

  7. A feasibility study on monitoring the evolution of apparent diffusion coefficient decrease during thermal ablation

    PubMed Central

    Plata, Juan C.; Holbrook, Andrew B.; Marx, Michael; Salgaonkar, Vasant; Jones, Peter; Pascal-Tenorio, Aurea; Bouley, Donna; Diederich, Chris; Sommer, Graham; Pauly, Kim Butts

    2015-01-01

    Purpose: Evaluate whether a decrease in apparent diffusion coefficient (ADC), associated with loss of tissue viability (LOTV), can be observed during the course of thermal ablation of the prostate. Methods: Thermal ablation was performed in a healthy in vivo canine prostate model (N = 2, ages: 5 yr healthy, mixed breed, weights: 13–14 kg) using a transurethral high-intensity ultrasound catheter and was monitored using a strategy that interleaves diffusion weighted images and gradient-echo images. The two sequences were used to measure ADC and changes in temperature during the treatment. Changes in temperature were used to compute expected changes in ADC. The difference between expected and measured ADC, ADCDIFF, was analyzed in regions ranging from moderate hyperthermia to heat fixation. A receiver operator characteristic (ROC) curve analysis was used to select a threshold of detection of LOTV. Time of threshold activation, tLOTV, was compared with time to reach CEM43 = 240, tDOSE. Results: The observed relationship between temperature and ADC in vivo (2.2%/ °C, 1.94%–2.47%/ °C 95% confidence interval) was not significantly different than the previously reported value of 2.4%/ °C in phantom. ADCDIFF changes after correction for temperature showed a mean decrease of 25% in ADC 60 min post-treatment in regions where sufficient thermal dose (CEM43 > 240) was achieved. Following our ROC analysis, a threshold of 2.25% decrease in ADCDIFF for three consecutive time points was chosen as an indicator of LOTV. The ADCDIFF was found to decrease quickly (1–2 min) after reaching CEM43 = 240 in regions associated with heat fixation and more slowly (10–20 min) in regions that received slower heating. Conclusions: Simultaneous monitoring of ADC and temperature during treatment might allow for a more complete tissue viability assessment of ablative thermal treatments in the prostate. ADCDIFF decreases during the course of treatment may be interpreted as loss of tissue viability. PMID:26328964

  8. The predictive capacity of apparent diffusion coefficient (ADC) in response assessment of brain metastases following radiation.

    PubMed

    Jakubovic, Raphael; Zhou, Stephanie; Heyn, Chris; Soliman, Hany; Zhang, Liyang; Aviv, Richard; Sahgal, Arjun

    2016-03-01

    To investigate the predictive capacity of the apparent diffusion coefficient (ADC) as a biomarker of radiation response in brain metastases. Seventy brain metastases from 42 patients treated with either stereotactic radiosurgery or whole brain radiotherapy were imaged at baseline, 1 week, and 1 month post-treatment using diffusion-weighted MRI. Mean and median relative ADC for metastases was calculated by normalizing ADC measurements to baseline ADC. At 1 year post-treatment, or last available follow-up MRI, volume criteria determined final tumour response status. Uni- and multivariate analysis was used to account for factors associated with tumour response at 1 week and 1 month. A generalized estimating equations model took into consideration multiple tumours per subject. Optimal thresholds that distinguished responders from non-responders, as well as sensitivity and specificity were determined by receiver operator characteristic analysis and Youden's index. Lower relative ADC values distinguished responders from non-responders at 1 week and 1 month (P < 0.05). Optimal cut-off values for response were 1.060 at 1 week with a sensitivity and specificity of 75.0 and 56.3 %, respectively. At 1 month, the cut-off was 0.971 with a sensitivity and specificity of 70.0 and 68.8 %, respectively. A multivariate general estimating equations analysis identified no prior radiation [odds ratio (OR) 0.211 and 0.137, P = 0.033 and 0.0177], and a lower median relative ADC at 1 week and 1 month (OR 0.619 and 0.694, P = 0.0036 and 0.005), as predictors of tumour response. Lower relative ADC values at 1 week and 1 month following radiation distinguished responders from non-responders and may be a promising biomarker of early radiation response. PMID:26786978

  9. Coronal Diffusion-weighted Magnetic Resonance Imaging of the Kidney: Agreement with Axial Diffusion-weighted Magnetic Imaging in Terms of Apparent Diffusion Coefficient Values

    PubMed Central

    Wang, Hai-Yi; Wang, Jia; Tang, Ye-Huan; Ye, Hui-Yi; Ma, Lin

    2015-01-01

    Background: Coronal diffusion-weighted magnetic resonance imaging (DW-MRI) and apparent diffusion coefficient (ADC) values have gradually become applied (following conventional axial DW-MRI) in the renal analysis. To explore whether data obtained using coronal DW-MRI are comparable with those derived using axial DW-MRI, this preliminary study sought to assess the agreement in renal ADC values between coronal DW-MRI and axial DW-MRI. Methods: Thirty-four healthy volunteers were enrolled in the study; written consents were obtained. All subjects underwent respiratory-triggered axial and coronal DW-MRI using a 1.5-MR system with b values of 0 and 800 s/mm2. The signal-to-noise ratios (SNRs) of the two DW-MRI sequences were measured and statistically compared using the paired t-test. The extent of agreement of ADC values of the upper pole, mid-pole, and lower pole of the kidney; the mean ADC values of the left kidney and right kidney; and the mean ADC values of the bilateral kidneys were evaluated via calculation of intraclass correlation coefficients (ICCs) or Bland–Altman method between the two DW-MRI sequences. Results: The SNR of coronal DW-MR images was statistically inferior to that of axial DW-MR images (P < 0.001). The ICCs of the ADC values of each region of interest, and the mean ADC values of bilateral kidneys, between the two sequences, were greater than 0.5, and the mean ADCs of the bilateral kidneys demonstrated the highest ICC (0.869; 95% confidence interval: 0.739–0.935). In addition, 94.1% (32/34), 94.1% (32/34), and 97.1% (31/34) of the ADC bias was inside the limits of agreement in terms of the mean ADC values of the left kidneys, right kidneys, and bilateral kidneys when coronal and axial DWI-MRI were compared. Conclusions: ADC values derived using coronal DW-MRI exhibited moderate-to-good agreement to those of axial DW-MRI, rendering the former an additional useful DW-MRI method, and causing the ADC values derived using the two types of DW-MRI to be comparable. PMID:25673453

  10. 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.

  11. Apparent Diffusion Coefficient Predicts Pathology Complete Response of Rectal Cancer Treated with Neoadjuvant Chemoradiotherapy

    PubMed Central

    Chen, Yuan-Gui; Chen, Ming-Qiu; Guo, Yu-Yan; Li, Si-Cong; Wu, Jun-Xin; Xu, Ben-Hua

    2016-01-01

    Objective To evaluate the predictive value of the apparent diffusion coefficient (ADC) for pathologic complete response (pCR) to neoadjuvant chemoradiotherapy (NCRT) in locally advanced rectal cancer. Methods A total of 265 patients with rectal adenocarcinoma, whole Diffusion-Weighted MRI (DWI-MRI) images, clinically stage II to III (cT3-4 and/or cN+) and treated with NCRT followed by TME were screened. Fifty patients with pCR and another 50 patients without pCR with similar clinical charcacters and treatment regimens were selected for statistical analysis. All the patients’ pre-CRT and post-CRT average ADC values were calculated from the coefficient maps created by DWI-MRI and recorded independently. The difference in the ADC values between the pCR and non-pCR was analyzed by the Mann-Whitney U test. The cut-off ADC value of the receiver operating characteristic (ROC) curve with pCR was then established. Results The mean pre- and post-ADC values in all patients, and in pCR patients and non-pCR patients were 0.879±0.06 and 1.383±0.11, 0.859±0.04 and 1.440±0.10, 0.899±0.07 and 1.325±0.09 (×10-3mm2/s), respectively. The difference between the pre- and post-ADC values in all patients, pCR patients, and non-pCR patients were considered to be statistically significant. The pre-ADC value was significantly lower in the pCR patients than in the non-pCR patients (p = 0.003), whereas the post-ADC values were significantly higher in the pCR patients than in the non-pCR patients. The percentage increase of the ADC value (ΔADC%) in the pCR and non-pCR patients were 68% and 48% respectively (p<0.001). The ROC curves of the cut-off value of the pre-CRT patient ADC value was 0.866×10-3mm2/s. The AUC, sensitivity, specificity, PPV, NPV, and accuracy of diagnosing pCR were 0.670 (95% CI 0.563–0.777), 0.600, 0.640, 60%, 60%, and 60%, respectively. The cut-off value of ΔADC% was 58%. The corresponding AUC, sensitivity, specificity, PPV, NPV, and accuracy of diagnosing pCR were 0.856 (95% CI 0.783–0.930), 0.800, 0.760, 76.9%, 79.2%, and 78%, respectively. Conclusions DWI-MRI technology can be efficient for predicting pCR for LARC after NCRT. Although the mean pre-CRT ADC value and the ΔADC% are moderate predictors for pCR, the latter would be more accurate. PMID:27100991

  12. 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.

  13. 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.

  14. A method for estimating the diffuse attenuation coefficient (KdPAR)from paired temperature sensors

    USGS Publications Warehouse

    Read, Jordan S.; Rose, Kevin C.; Winslow, Luke A.; Read, Emily Kara

    2015-01-01

    A new method for estimating the diffuse attenuation coefficient for photosynthetically active radiation (KdPAR) from paired temperature sensors was derived. We show that during cases where the attenuation of penetrating shortwave solar radiation is the dominant source of temperature changes, time series measurements of water temperatures at multiple depths (z1 and z2) are related to one another by a linear scaling factor (a). KdPAR can then be estimated by the simple equation KdPAR ln(a)/(z2/z1). A suggested workflow is presented that outlines procedures for calculating KdPAR according to this paired temperature sensor (PTS) method. This method is best suited for conditions when radiative temperature gains are large relative to physical noise. These conditions occur frequently on water bodies with low wind and/or high KdPARs but can be used for other types of lakes during time periods of low wind and/or where spatially redundant measurements of temperatures are available. The optimal vertical placement of temperature sensors according to a priori knowledge of KdPAR is also described. This information can be used to inform the design of future sensor deployments using the PTS method or for campaigns where characterizing sub-daily changes in temperatures is important. The PTS method provides a novel method to characterize light attenuation in aquatic ecosystems without expensive radiometric equipment or the user subjectivity inherent in Secchi depth measurements. This method also can enable the estimation of KdPAR at higher frequencies than many manual monitoring programs allow.

  15. Computing translational diffusion and sedimentation coefficients: an evaluation of experimental data and programs.

    PubMed

    Rocco, Mattia; Byron, Olwyn

    2015-09-01

    Hydrodynamic characterisation of (bio)macromolecules is a well-established field. Observables linked to translational friction, such as the translational diffusion (Dt(0)(20,w)) and sedimentation (s(0)(20,w)) coefficients, are the most commonly used parameters. Both can be computed starting from high-resolution structures, with several methods available. We present here a comprehensive study of the performance of public-domain software, comparing the calculated Dt(0)(20,w) and s(0)(20,w) for a set of high-resolution structures (ranging in mass from 12,358 to 465,557 Da) with their critically appraised literature experimental counterparts. The methods/programs examined are AtoB, SoMo, BEST, Zeno (all implemented within the US-SOMO software suite) and HYDROPRO. Clear trends emerge: while all programs can reproduce Dt(0)(20,w) on average to within ±5% (range -8 to +7%), SoMo and AtoB slightly overestimate it (average +2 and +1%, range -2 to +7 and -4 to +5%, respectively), and BEST and HYDROPRO underestimate it slightly more (average -3 and -4%, range -7 to +2 and -8 to +2%, respectively). Similar trends are observed with s(0)(20,w), but the comparison is likely affected by the necessary inclusion of the partial specific volume in the computations. The somewhat less than ideal performances could result from the hydration treatment in BEST and HYDROPRO, and the bead overlap removal in SoMo and AtoB. Interestingly, a combination of SoMo overlapping bead models followed by Zeno computation produced better results, with a 0% average error (range -4 to +4%). Indeed, this might become the method of choice, once computational speed considerations now favouring the 5 Å-grid US-SOMO AtoB approach are overcome. PMID:26066679

  16. Mean apparent diffusion coefficient values in defining radiotherapy planning target volumes in glioblastoma

    PubMed Central

    Malalis, Christian; Arrington, John A.; Field, Aaron S.; Choi, Jung W.; Kocak, Mehmet

    2015-01-01

    Background To evaluate mean apparent diffusion coefficient (ADC) values on pre-radiotherapy magnetic resonance (MR) at sites that gave rise to glioblastoma (GBM) recurrence compared to similar surrounding background tissue that did not progress to tumor. Methods Twenty out of 110 consecutive patients with pathology proven GBM treated at our institution from 1/1/2009 to 5/31/2012 had definitive recurrence 6 months following radiotherapy. In this single-center retrospective cohort study, pre- and post-radiotherapy MR brain exams were evaluated. Sites of tumor recurrence on post-therapy exams were co-localized to pre-therapy exams and the background tissue type which gave rise to tumor was noted (i.e., T2 hyperintensity, normal appearing white or gray matter). Similar surrounding background tissue not progressing to tumor was also selected. Two radiologists compared mean ADC values on pre-radiotherapy MR for sites which gave rise to future tumor recurrence and sites of similar background tissue. Results Pre-radiotherapy mean ADC values were significantly lower in regions of future tumor recurrence than in regions of surrounding background tissue not progressing to tumor (P=0.003). There were no significant quantitative differences on T1-weighted pre contrast (P=0.50) or T2-weighted (P=0.10) sequences between sites. There was strong interobserver agreement with an intraclass correlation of 0.867 for ADC values at sites of future tumor recurrence and background tissue. Conclusions Mean ADC values may help predict sites of future gross tumor recurrence in GBM, which could be helpful in radiation therapy planning. PMID:26807366

  17. Effect of lithium-ion diffusibility on interfacial resistance of LiCoO2 thin film electrode modified with lithium tungsten oxides

    NASA Astrophysics Data System (ADS)

    Hayashi, Tetsutaro; Miyazaki, Takamichi; Matsuda, Yasutaka; Kuwata, Naoaki; Saruwatari, Motoaki; Furuichi, Yuki; Kurihara, Koji; Kuzuo, Ryuichi; Kawamura, Junichi

    2016-02-01

    To investigate the contribution of lithium-ion diffusibility of lithium tungsten oxides (LWOs) to low interfacial resistance, we fabricate thin-film electrodes of 6Li-enriched LiCoO2 (6LCO) modified with various structure-types of 6Li-enriched LWOs by pulsed laser deposition. The electrodes are subjected to X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and secondary-ion mass spectrometry (SIMS) analyses. XRD reveals that the LWO layers have Li2WO4 structure with rhombohedral and tetragonal symmetries and amorphous states. EIS shows that the lowest interfacial resistance of the positive electrodes is given by the amorphous state, followed in order by the tetragonal and the rhombohedral symmetry, and that the diffusion coefficients of lithium-ions in the electrodes increase in the same order. SIMS demonstrates that the fastest lithium-ion self-diffusibility into the LWOs is found in the amorphous state, followed in order by tetragonal and rhombohedral symmetry. Furthermore, the amorphous state LWO modification shows smooth lithium-ion diffusion between the LWO and LCO layers after the electrochemical test. Conversely, the rhombohedral LWO modification demonstrates congested lithium-ion diffusion between the LWO and LCO layers after the test. Thus, fast lithium-ion self-diffusibility into the LWO-modified LCO contributes to enhancing the diffusion of lithium-ions, resulting in the reduction of interfacial resistance.

  18. Heavy quark diffusion in the pre-equilibrium stage of heavy ion collisions

    NASA Astrophysics Data System (ADS)

    Das, Santosh K.; Ruggieri, Marco; Mazumder, Surasree; Greco, Vincenzo; Alam, Jan-e.

    2015-09-01

    The drag and diffusion coefficients of heavy quarks (HQs) have been evaluated in the pre-equilibrium phase of the evolving fireball produced in heavy ion collisions at relativistic heavy ion collider and Large Hadron Collider energies. KLN and classical Yang-Mills spectra have been used for describing the momentum distributions of the gluons produced just after the collisions but before they thermalize. The interaction of the HQs with these gluons has been treated within the framework of perturbative quantum chromodynamics. We have observed that the HQs are dragged almost equally by the kinetically equilibrated and out-of-equilibrium gluonic systems. We have also noticed that the HQ diffusion in the pre-equilibrium gluonic phase is as fast as in the kinetically equilibrated gluons. Moreover, the diffusion is faster in the pre-equilibrium phase than in the chemically equilibrated quark-gluon plasma. These findings may have significant impact on the analysis of experimental results on the elliptic flow and the high momentum suppression of the open charm and beauty hadrons.

  19. Simultaneous Rapid Determination of the Solubility and Diffusion Coefficients of a Poorly Water-Soluble Drug Based on a Novel UV Imaging System.

    PubMed

    Lu, Yan; Li, Mingzhong

    2016-01-01

    The solubility and diffusion coefficient are two of the most important physicochemical properties of a drug compound. In practice, both have been measured separately, which is time consuming. This work utilizes a novel technique of UV imaging to determine the solubility and diffusion coefficients of poorly water-soluble drugs simultaneously. A 2-step optimal method is proposed to determine the solubility and diffusion coefficients of a poorly water-soluble pharmaceutical substance based on the Fick's second law of diffusion and UV imaging measurements. Experimental results demonstrate that the proposed method can be used to determine the solubility and diffusion coefficients of a drug with reasonable accuracy, indicating that UV imaging may provide a new opportunity to accurately measure the solubility and diffusion coefficients of a poorly water-soluble drug simultaneously and rapidly. PMID:26852848

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

    PubMed Central

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

    2013-01-01

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

  1. Electrochemical measurements of diffusion coefficients of redox-labeled poly(ethylene glycol) dissolved in poly(ethylene glycol) melts

    SciTech Connect

    Haas, O.; Velazquez, C.S.; Porat, Z.; Murray, R.W.

    1995-10-12

    Ferrocene labeled monomethoxy-poly(ethylene glycol)s (MPEG) with molecular weights of 1900 and 750 were used as redox probe solutes in poly(ethylene glycol) melt solvents of molecular weight 750, 2000, and 20000. Cyclic voltammetry and chronoamperometry at microdisk electrodes were employed to measure the diffusion coefficients of the redox probes, which were independent of the probe concentration and varied between 10{sup -7} and 10{sup -10} cm{sup 2}/s. Diffusional activation barrier results also suggest that the ferrocene label does not significantly influence the diffusivity of the probe molecule in the host solvent. Activation barrier, viscosity, and ionic conductivity results show that the LiClO{sub 4} electrolyte does not influence the diffusion barrier or viscosity as long as the ether O/Li{sup +} ratio is >=250 (ca. 0.1 M) which is still a sufficient electrolyte concentration to allow quantitative electrochemical diffusion measurements. 21 refs., 7 figs., 2 tabs.

  2. Low temperature diffusion coefficients in the Fe-Ni and FeNiP systems: Application to meteorite cooling rates

    NASA Technical Reports Server (NTRS)

    Dean, D. C.; Goldstein, J. I.

    1984-01-01

    The interdiffusion coefficient of FeNi in fcc taenite (gamma) of Fe-Ni and Fe-Ni-0.2 P alloys was measured as a function of temperature between 600 and 900 C. This temperature range is directly applicable to the nucleation and growth of the Widmanstatten pattern in iron meteorites and metal regions of stony and stony-iron meteorites. Diffusion couples were made from FeNi or FeNiP alloys which ensured that the couples were in the taenite phase at the diffusion temperature. The presence or absence of grain boundary diffusion was determined by measuring the Ni profile normal to the existing grain boundaries with the AEM. Ignoring any variation of interdiffusion coefficient with composition, the measured data was plotted versus the reciprocal of the diffusion temperature. The FeNi data generally follow the extrapolated Goldstein, et al. (1965) data from high temperatures. The FeNiP data indicates that small additions of P (0.2 wt%) cause a 3 to 10 fold increase in the FeNi interdifussion coefficient increasing with decreasing temperature. This increase is about the same as that predicted by Narayan and Goldstein (1983) at the Widmanstatten growth temperature.

  3. Measurements of the Fe³⁺ diffusion coefficient in Fricke xylenol gel using optical density measurements.

    PubMed

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

    2014-08-01

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

  4. Rate Coefficients of Singly Ionized Triatomic Hydrogen Using An RF Ion Trap

    NASA Astrophysics Data System (ADS)

    Pope, Nick; Ronald, Sam; Mount, Emily; Daw, Adrian; Calamai, Anthony

    2009-05-01

    In order to better understand the interactions and composition of the universe, it is essential to know reaction rates between ions, neutral species, electrons, and photons. A significant reaction of interest is H2 + H2+ -> H3+ + H, a fundamental reaction that produces some of the most abundant ions in the interstellar medium and other areas of the universe. Due to its instrumental role in forming many different polyatomic molecules, rate coefficients for singly ionized triatomic hydrogen are needed in order to accurately model its interactions in the interstellar medium. Singly ionized triatomic hydrogen is studied using a quadrupole radio frequency ion trap coupled with a time of flight mass spectrometer. Singly ionized diatomic hydrogen is created by electron bombardment with diatomic hydrogen. H2+ and H3+ are then studied by ejecting the ions into an active-film electron multiplier. By variation of experimental parameters, systematic uncertainties are addressed and rate coefficients for the H2+ + H2 -> H3+ + H at electron-volt energies are determined.

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

    PubMed

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

    2014-10-01

    A method is presented to obtain ion chamber calibration coefficients relative to secondary standard reference chambers in electron beams using depth-ionization measurements. Results are obtained as a function of depth and average electron energy at depth in 4, 8, 12 and 18 MeV electron beams from the NRC Elekta Precise linac. The PTW Roos, Scanditronix NACP-02, PTW Advanced Markus and NE 2571 ion chambers are investigated. The challenges and limitations of the method are discussed. The proposed method produces useful data at shallow depths. At depths past the reference depth, small shifts in positioning or drifts in the incident beam energy affect the results, thereby providing a built-in test of incident electron energy drifts and/or chamber set-up. Polarity corrections for ion chambers as a function of average electron energy at depth agree with literature data. The proposed method produces results consistent with those obtained using the conventional calibration procedure while gaining much more information about the behavior of the ion chamber with similar data acquisition time. Measurement uncertainties in calibration coefficients obtained with this method are estimated to be less than 0.5%. These results open up the possibility of using depth-ionization measurements to yield chamber ratios which may be suitable for primary standards-level dissemination. PMID:25211012

  6. Simulation of diatomic gas-wall interaction and accommodation coefficients for negative ion sources and accelerators

    NASA Astrophysics Data System (ADS)

    Sartori, E.; Brescaccin, L.; Serianni, G.

    2016-02-01

    Particle-wall interactions determine in different ways the operating conditions of plasma sources, ion accelerators, and beams operating in vacuum. For instance, a contribution to gas heating is given by ion neutralization at walls; beam losses and stray particle production—detrimental for high current negative ion systems such as beam sources for fusion—are caused by collisional processes with residual gas, with the gas density profile that is determined by the scattering of neutral particles at the walls. This paper shows that Molecular Dynamics (MD) studies at the nano-scale can provide accommodation parameters for gas-wall interactions, such as the momentum accommodation coefficient and energy accommodation coefficient: in non-isothermal flows (such as the neutral gas in the accelerator, coming from the plasma source), these affect the gas density gradients and influence efficiency and losses in particular of negative ion accelerators. For ideal surfaces, the computation also provides the angular distribution of scattered particles. Classical MD method has been applied to the case of diatomic hydrogen molecules. Single collision events, against a frozen wall or a fully thermal lattice, have been simulated by using probe molecules. Different modelling approximations are compared.

  7. Simulation of diatomic gas-wall interaction and accommodation coefficients for negative ion sources and accelerators.

    PubMed

    Sartori, E; Brescaccin, L; Serianni, G

    2016-02-01

    Particle-wall interactions determine in different ways the operating conditions of plasma sources, ion accelerators, and beams operating in vacuum. For instance, a contribution to gas heating is given by ion neutralization at walls; beam losses and stray particle production-detrimental for high current negative ion systems such as beam sources for fusion-are caused by collisional processes with residual gas, with the gas density profile that is determined by the scattering of neutral particles at the walls. This paper shows that Molecular Dynamics (MD) studies at the nano-scale can provide accommodation parameters for gas-wall interactions, such as the momentum accommodation coefficient and energy accommodation coefficient: in non-isothermal flows (such as the neutral gas in the accelerator, coming from the plasma source), these affect the gas density gradients and influence efficiency and losses in particular of negative ion accelerators. For ideal surfaces, the computation also provides the angular distribution of scattered particles. Classical MD method has been applied to the case of diatomic hydrogen molecules. Single collision events, against a frozen wall or a fully thermal lattice, have been simulated by using probe molecules. Different modelling approximations are compared. PMID:26931910

  8. Gas exchange dependency on diffusion coefficient: direct /sup 222/Rn and /sup 3/He comparisons in a small lake

    SciTech Connect

    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.

  9. Determination of spatially-resolved porosity, tracer distributions and diffusion coefficients in porous media using MRI measurements and numerical simulations.

    PubMed

    Marica, Florea; Jofré, Sergio Andrés Bea; Mayer, K Ulrich; Balcom, Bruce J; Al, Tom A

    2011-07-01

    This work is focused on measuring the concentration distribution of a conservative tracer in a homogeneous synthetic porous material and in heterogeneous natural sandstone using MRI techniques, and on the use of spatially resolved porosity data to define spatially variable diffusion coefficients in heterogeneous media. The measurements are made by employing SPRITE, a fast MRI method that yields quantitative, spatially-resolved tracer concentrations in porous media. Diffusion experiments involving the migration of H(2)O into D(2)O-saturated porous media are conducted. One-dimensional spatial distributions of H(2)O-tracer concentrations acquired from experiments with the homogeneous synthetic calcium silicate are fitted with the one-dimensional analytical solution of Fick's second law to confirm that the experimental method provides results that are consistent with expectations for Fickian diffusion in porous media. The MRI-measured concentration profiles match well with the solution for Fick's second law and provide a pore-water diffusion coefficient of 1.75×10(-9)m(2)s(-1). The experimental approach was then extended to evaluate diffusion in a heterogeneous natural sandstone in three dimensions. The relatively high hydraulic conductivity of the sandstone, and the contrast in fluid density between the H(2)O tracer and the D(2)O pore fluid, lead to solute transport by a combination of diffusion and density-driven advection. The MRI measurements of spatially distributed tracer concentration, combined with numerical simulations allow for the identification of the respective influences of advection and diffusion. The experimental data are interpreted with the aid of MIN3P-D - a multicomponent reactive transport code that includes the coupled processes of diffusion and density-driven advection. The model defines local diffusion coefficients as a function of spatially resolved porosity measurements. The D(e) values calculated for the heterogeneous sandstone and used to simulate diffusive and advective transport range from 5.4×10(-12) to 1.0×10(-10)m(2)s(-1). These methods have broad applicability to studies of contaminant migration in geological materials. PMID:21669472

  10. Determination of spatially-resolved porosity, tracer distributions and diffusion coefficients in porous media using MRI measurements and numerical simulations

    NASA Astrophysics Data System (ADS)

    Marica, Florea; Jofr, Sergio Andrs Bea; Mayer, K. Ulrich; Balcom, Bruce J.; Al, Tom A.

    2011-07-01

    his work is focused on measuring the concentration distribution of a conservative tracer in a homogeneous synthetic porous material and in heterogeneous natural sandstone using MRI techniques, and on the use of spatially resolved porosity data to define spatially variable diffusion coefficients in heterogeneous media. The measurements are made by employing SPRITE, a fast MRI method that yields quantitative, spatially-resolved tracer concentrations in porous media. Diffusion experiments involving the migration of H 2O into D 2O-saturated porous media are conducted. One-dimensional spatial distributions of H 2O-tracer concentrations acquired from experiments with the homogeneous synthetic calcium silicate are fitted with the one-dimensional analytical solution of Fick's second law to confirm that the experimental method provides results that are consistent with expectations for Fickian diffusion in porous media. The MRI-measured concentration profiles match well with the solution for Fick's second law and provide a pore-water diffusion coefficient of 1.75 10 - 9 m 2 s - 1 . The experimental approach was then extended to evaluate diffusion in a heterogeneous natural sandstone in three dimensions. The relatively high hydraulic conductivity of the sandstone, and the contrast in fluid density between the H 2O tracer and the D 2O pore fluid, lead to solute transport by a combination of diffusion and density-driven advection. The MRI measurements of spatially distributed tracer concentration, combined with numerical simulations allow for the identification of the respective influences of advection and diffusion. The experimental data are interpreted with the aid of MIN3P-D a multicomponent reactive transport code that includes the coupled processes of diffusion and density-driven advection. The model defines local diffusion coefficients as a function of spatially resolved porosity measurements. The D e values calculated for the heterogeneous sandstone and used to simulate diffusive and advective transport range from 5.4 10 - 12 to 1.0 10 - 10 m 2 s - 1 . These methods have broad applicability to studies of contaminant migration in geological materials.

  11. Evaluation of Fourier transform coefficients for the diagnosis of rheumatoid arthritis from diffuse optical tomography images

    NASA Astrophysics Data System (ADS)

    Montejo, Ludguier D.; Jia, Jingfei; Kim, Hyun K.; Hielscher, Andreas H.

    2013-03-01

    We apply the Fourier Transform to absorption and scattering coefficient images of proximal interphalangeal (PIP) joints and evaluate the performance of these coefficients as classifiers using receiver operator characteristic (ROC) curve analysis. We find 25 features that yield a Youden index over 0.7, 3 features that yield a Youden index over 0.8, and 1 feature that yields a Youden index over 0.9 (90.0% sensitivity and 100% specificity). In general, scattering coefficient images yield better one-dimensional classifiers compared to absorption coefficient images. Using features derived from scattering coefficient images we obtain an average Youden index of 0.58 +/- 0.16, and an average Youden index of 0.45 +/- 0.15 when using features from absorption coefficient images.

  12. Analysis of monopolar ionized field as influenced by ion diffusion

    SciTech Connect

    Abdel-Salam, M.; Al-Hamouz, Z.

    1995-05-01

    High voltage dc has many advantages over conventional ac liens for long distance power transmission. Recently, the economic feasibility of dc transmission has increased with the development of the hv terminal equipment. One of the problems associated with the HVDC transmission is the corona occurring on the transmission lines and the power loss, audible noise, radio interference, and television interference. Many attempts were made to solve the ionized field problem using the finite-element technique (FET). None of them included the ion diffusion in the solution of the describing equations. A few attempts included ion diffusion but using other numerical techniques. Ghione and Graglia adopted the finite-boxes technique for the solution of ionized field in conductor-to-plane configurations and wire-duct precipitators. Levin and Hoburg used the donor cell-finite element technique for the solution of the ionized field in wire-duct precipitators. In the present paper, a new iterative FET is proposed as a numerical tool to solve Poisson`s equation while the current continuity condition is satisfied by applying Kirchoff`s current balance-law at each node of the FE grid. In addition, the constancy of the conductor surface field at the corona onset value is implemented directly into the proposed FE formulation.

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

    SciTech Connect

    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.

  14. Study of oxygen self-diffusion in oxides by ion beam techniques: comparison between nuclear reaction analysis and SIMS

    NASA Astrophysics Data System (ADS)

    Sabioni, A. C. S.; Freire, F. L.; Leite, C. V. Barros; Amami, B. A.; Dolin, C.; Monty, C.; Millot, F.

    1993-01-01

    Oxygen self-diffusion in Fe 1-xO single crystals has been studied by means of the isotope exchange method in H 2/H 218O atmospheres. The 18O concentration profiles were determined by using two different techniques based on ion beams: secondary ion mass spectrometry (SIMS) and nuclear reaction analysis (NRA); the latter by means of the narrow nuclear resonance reaction 18O(p, α) 15N at 629 keV, Γ = 2.1 keV. The diffusion coefficients obtained from the analysis of the measured profiles are in good agreement with those found in the literature. To compare the depth resolution and sensitivity of both techniques, the 18O profiles of implanted Cr 2O 3 single crystals ( E18O=50 keV, fluence=1.6 × 10 16 ions/cm 2 were also measured.

  15. Improved Algorithms for Accurate Retrieval of UV - Visible Diffuse Attenuation Coefficients in Optically Complex, Inshore Waters

    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.

  16. Behavior of rate coefficients for ion-ion mutual neutralization, 300-550 K

    SciTech Connect

    Miller, Thomas M.; Shuman, Nicholas S.; Viggiano, A. A.

    2012-05-28

    Rate coefficients k{sub MN} have been measured for a number of anion neutralization reactions with Ar{sup +} and Kr{sup +} over the temperature range 300-550 K. For the first time, the data set includes anions of radicals and other short-lived species. In the present paper, we review these results and make note of correlations with reduced mass, electron binding energy of the anion (equivalent to the electron affinity of the corresponding neutral), and temperature, and compare with expectations from absorbing sphere models. An intriguing result is that the data for diatomic anions neutralized by Ar{sup +} and Kr{sup +} have k{sub MN} values close to 3 x 10{sup -8} cm{sup 3} s{sup -1} at 300 K, a figure which is lower than those for all of the polyatomic anions at 300 K except for SF{sub 5}{sup -}+ Kr{sup +}. For the polyatomic anions studied here, neutralized by Ar{sup +} and Kr{sup +}, the reduced mass dependence agrees with theory, on average, but we find a stronger temperature dependence of T{sup -0.9} than expected from the theoretical E{sup -0.5} energy dependence of the rate coefficient at thermal energies. The k{sub MN} show a weak dependence on the electron binding energy of the anion for the polyatomic species studied.

  17. Coherent quantum transport in disordered systems: II. Temperature dependence of carrier diffusion coefficients from the time-dependent wavepacket diffusion method

    NASA Astrophysics Data System (ADS)

    Zhong, Xinxin; Zhao, Yi; Cao, Jianshu

    2014-04-01

    The time-dependent wavepacket diffusion method for carrier quantum dynamics (Zhong and Zhao 2013 J. Chem. Phys. 138 014111), a truncated version of the stochastic Schrödinger equation/wavefunction approach that approximately satisfies the detailed balance principle and scales well with the size of the system, is applied to investigate the carrier transport in one-dimensional systems including both the static and dynamic disorders on site energies. The predicted diffusion coefficients with respect to temperature successfully bridge from band-like to hopping-type transport. As demonstrated in paper I (Moix et al 2013 New J. Phys. 15 085010), the static disorder tends to localize the carrier, whereas the dynamic disorder induces carrier dynamics. For the weak dynamic disorder, the diffusion coefficients are temperature-independent (band-like property) at low temperatures, which is consistent with the prediction from the Redfield equation, and a linear dependence of the coefficient on temperature (hopping-type property) only appears at high temperatures. In the intermediate regime of dynamic disorder, the transition from band-like to hopping-type transport can be easily observed at relatively low temperatures as the static disorder increases. When the dynamic disorder becomes strong, the carrier motion can follow the hopping-type mechanism even without static disorder. Furthermore, it is found that the memory time of dynamic disorder is an important factor in controlling the transition from the band-like to hopping-type motions.

  18. The influence of mucus on the diffusion of chloride ions across the oesophagus of the minnow (Phoxinus phoxinus (L.].

    PubMed Central

    Shephard, K L

    1984-01-01

    Micro-electrodes sensitive to Cl- have been used to measure Cl- activities in the mucous layer on the mucosal surface of an isolated oesophageal preparation of the fresh-water teleost, Phoxinus phoxinus (L.). The technique has also been used to estimate the diffusion coefficient of Cl- in mucus in situ on the mucosal surface of this preparation. The mucous layer supports a linear gradient of Cl- which represents approximately 20% of the gradient of Cl- between mucosal and serosal solutions. The estimate of the diffusion coefficient of Cl- in mucus was 0.30 X 10(-5) +/- 0.029 X 10(-5) cm2 s-1 (mean +/- S.E. of mean, n = 13). This value is approximately 20% of published values of the diffusion coefficient in pure NaCl solutions or in teleost saline. It is suggested that the mucous layer acts to lower the permeability of the oesophagus in two ways. Its viscous and gel-forming nature encourages the formation of an unstirred layer, through which diffusion is the only means whereby salts can move. Also, it provides a layer through which Cl- and possibly other ions diffuse much more slowly than they would through a similar layer of mucosal solution without mucus. PMID:6699781

  19. Rotating-disk determination of the diffusion coefficients of cobalt(II) hydroxo complexes in KOH solutions

    SciTech Connect

    Stepanov, A.N.; Kazarinov, I.A.; Fetisova, T.A.

    1986-11-01

    Cobalt(II) hydroxide is added to the active mass of the nickel oxide electrodes in alkaline storage batteries as an activator. To eliminate the problem of self-discharge, the authors determined the diffusion coefficients of the cobalt(II) hydroxide complexes in 2, 5, 8.1, 10, and 12 N KOH solutions with the aid of a rotating disk electrode following the method of Hitchman and Albery. Polarization curves for the cathodic reduction and anodic oxidation of cobalt(II) hydroxo complexes in 5 N KOH solutions saturated in cobalt(II) hydroxide are shown. Data for the diffusion coefficients of cadmium and mercury hydroxo complexes obtained in KOH solutions of different concentrations are shown in comparison with that of the cobalt(II) hydroxo complexes.

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

    PubMed

    Navrátilová Rovenská, Katerina

    2014-07-01

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

  1. Temporal development of diffuse ion events upstream of the earth's bow shock - The October 31, 1977, event

    NASA Technical Reports Server (NTRS)

    Skadron, G.; Lee, M. A.

    1983-01-01

    The origin of the intensity-time profile characteristic of diffuse ion events upstream of the earth's bow shock is investigated. It is believed that the profile results from a rotation of the interplanetary magnetic field that produces as a systematic variation in the connection time of field lines with the bow shock. If the connection time exceeds the time needed to reach equilibrium between the shock acceleration and ion loss processes, a plateau in the ion intensity is formed. The upstream diffusion ion event of October 31, 1977, for which simultaneous magnetic field and ion intensity data have been published is used to test this scenario. This event is analyzed using a two-dimensional Gleeson-Axford equation to describe the shock acceleration process and a model bow shock whose nose serves as a uniform source of ions injected into the acceleration process. Intensity-time profiles are calculated for 30-keV and 120-keV protons for a range of diffusion coefficients using connection times that are based on the shock geometry and the magnetic field data.

  2. Nonlinear Diffusions and Stable-Like Processes with Coefficients Depending on the Median or VaR

    SciTech Connect

    Kolokoltsov, Vassili N.

    2013-08-01

    The paper is devoted to the well-posedness for nonlinear McKean-Vlasov type diffusions with coefficients depending on the median or, more generally, on the {alpha}-quantile of the underlying distribution. The median is not a continuous function on the space of probability measures equipped with the weak convergence. This is one reason why well-posedness of the SDE considered in the paper does not follow by standard arguments.

  3. Application of Photothermal Techniques in the Determination of the Water-Vapor Diffusion Coefficient and Thermal Effusivity of Hydrogels

    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.

  4. 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...

  5. Collective diffusion model for ion conduction through microscopic channels.

    PubMed

    Liu, Yingting; Zhu, Fangqiang

    2013-01-22

    Ion conduction through microscopic channels is of central importance in both biology and nanotechnology. To better understand the current-voltage (I-V) dependence of ion channels, here we describe and prove a collective diffusion model that quantitatively relates the spontaneous ion permeation at equilibrium to the stationary ionic fluxes driven by small voltages. The model makes it possible to determine the channel conductance in the linear I-V range from equilibrium simulations without the application of a voltage. To validate the theory, we perform molecular-dynamics simulations on two channels-a conical-shaped nanopore and the transmembrane pore of an ?-hemolysin-under both equilibrium and nonequilibrium conditions. The simulations reveal substantial couplings between the motions of cations and anions, which are effectively captured by the collective coordinate in the model. Although the two channels exhibit very different linear ranges in the I-V curves, in both cases the channel conductance at small voltages is in reasonable agreement with the prediction from the equilibrium simulation. The simulations also suggest that channel charges, rather than geometric asymmetry, play a more prominent role in current rectification. PMID:23442858

  6. Rate Coefficients for H3^+ Production Measured in an RF Ion Trap

    NASA Astrophysics Data System (ADS)

    Ronald, Sam; Mount, Emily; Pope, Nick; Daw, Adrian; Calamai, Anthony

    2008-10-01

    The reaction H2^+ + H2-> H3^+ + H is studied using a quadrupole radio frequency ion trap coupled with a time of flight mass spectrometer. Protonated molecular hydrogen is one of the most abundant ions in the universe, and is believed to be responsible for the formation of many molecular ions in, for example, the interstellar medium and the aurorae of Jupiter. Also, since this ion is the simplest polyatomic molecule, it can be used as a basis for comparison with other polyatomic molecules. H2^+ is created in a RF ion trap by electron bombardment of H2, and then allowed to react with H2 for varying time intervals before the H2^+ and H3^+ populations are ejected from the trap and detected with an active-film electron multiplier. A number of different experimental parameters (H2 pressure, trapping parameters and electron bombardment conditions) are explored and preliminary rate coefficients for the H2^+ + H2-> H3^+ + H reaction are presented.

  7. Plasma rate coefficients for electron-impact ionization of Xeq+ ions (q = 8, …, 17)

    NASA Astrophysics Data System (ADS)

    Borovik, A., Jr.; Gharaibeh, M. F.; Schippers, S.; Müller, A.

    2015-02-01

    Plasma rate coefficients (PRCs) for electron-impact single ionization of ground-state Xeq+ ions (q=8,\\ldots ,17) in the temperature range 2 × 105 - 2 × 107 K have been derived from a combination of experimental cross-section data and results of distorted-wave calculations. For Xe8+ and Xe9+ new measurements were performed and thoroughly analyzed with respect to the contributions from different ionization mechanisms and the effects of long-lived excited states in the parent ion beams that had been employed in the experiments. In the same manner, previously published experimental data for the higher charge states were analyzed to extract the ground-configuration ionization cross sections and to derive the associated PRCs. The resulting temperature-dependent PRC functions were parameterized and the associated parameters are provided in tabular form. With the exception of Xe8+ the absolute uncertainties of the inferred rate coefficients are estimated to be +/- 10%. For Xe8+ the uncertainties are +/- 25% due to the necessary correction for strong metastable-ion contributions to the measured cross sections.

  8. Divergence of the Long Wavelength Collective Diffusion Coefficient in Quasi-one and Quasi-two Dimensional Colloid Suspensions

    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 < γ<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).

  9. Exploration of ion migration mechanism and diffusion capability for Na3V2(PO4)2F3 cathode utilized in rechargeable sodium-ion batteries

    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.

  10. Optical absorption coefficient and minority carrier diffusion length measurements in low-cost silicon solar cell material

    SciTech Connect

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

    1982-11-01

    The optical absorption coefficient of silicon solar cell material grown by three low-cost growth methods was measured in the wavelength interval 0.8< or =lambda< or =1.0 ..mu..m, the wavelength region of interest in surface photovoltage measurements of the minority carrier diffusion length. The square root of the absorption coefficient was found to vary linearly with photon energy over the wavelengths studied, and the measured data agree with a linear empirical fit to within 0.5% RMS. The absorption coefficients obtained are slightly lower than those reported by Runyan, with the greatest disagreement at long wavelengths. Minority carrier diffusion lengths computed using the present absorption coefficients are approximately 16% greater than those calculated using Runyan's data. Excellent sample-to-sample agreement within and between lots indicates that for two of the growth methods studied, material quality as judged by optical properties has not been sacrificed by the use of low-cost growth methods. Samples grown by the third growth method studied showed measurably poorer optical quality.

  11. Garnet/high-silica rhyolite trace element partition coefficients measured by ion microprobe

    USGS Publications Warehouse

    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.

  12. Electron-impact excitation rate-coefficients and polarization of subsequent emission for Ar+ ion

    NASA Astrophysics Data System (ADS)

    Dipti; Srivastava, Rajesh

    2016-06-01

    Electron impact excitation in Ar+ ions has been studied by using fully relativistic distorted wave theory. Calculations are performed to obtain the excitation cross-sections and rate-coefficients for the transitions from the ground state 3p5 (J=3/2) to fine-structure levels of excited states 3p44s, 3p44p, 3p45s, 3p45p, 3p43d and 3p44d. Polarization of the radiation following the excitation has been calculated using the obtained magnetic sub-level cross-sections. Comparison of the present rate-coefficients is also done with the previously reported theoretical results for some unresolved fine structure transitions.

  13. The temperature-dependent diffusion coefficient of helium in zirconium carbide studied with first-principles calculations

    SciTech Connect

    Yang, Xiao-Yong; Lu, Yong; Zhang, Ping

    2015-04-28

    The temperature-dependent diffusion coefficient of interstitial helium in zirconium carbide (ZrC) matrix is calculated based on the transition state theory. The microscopic parameters in the activation energy and prefactor are obtained from first-principles total energy and phonon frequency calculations including the all atoms. The obtained activation energy is 0.78 eV, consistent with experimental value. Besides, we evaluated the influence of C and Zr vacancies as the perturbation on helium diffusion, and found the C vacancy seems to confine the mobility of helium and the Zr vacancy promotes helium diffusion in some extent. These results provide a good reference to understand the behavior of helium in ZrC matrix.

  14. Permeability and kinetic coefficients for mesoscale BCF surface step dynamics: Discrete two-dimensional deposition-diffusion equation analysis

    NASA Astrophysics Data System (ADS)

    Zhao, Renjie; Evans, James W.; Oliveira, Tiago J.

    2016-04-01

    A discrete version of deposition-diffusion equations appropriate for description of step flow on a vicinal surface is analyzed for a two-dimensional grid of adsorption sites representing the stepped surface and explicitly incorporating kinks along the step edges. Model energetics and kinetics appropriately account for binding of adatoms at steps and kinks, distinct terrace and edge diffusion rates, and possible additional barriers for attachment to steps. Analysis of adatom attachment fluxes as well as limiting values of adatom densities at step edges for nonuniform deposition scenarios allows determination of both permeability and kinetic coefficients. Behavior of these quantities is assessed as a function of key system parameters including kink density, step attachment barriers, and the step edge diffusion rate.

  15. Drag force, diffusion coefficient, and electric mobility of small particles. I. Theory applicable to the free-molecule regime.

    PubMed

    Li, Zhigang; Wang, Hai

    2003-12-01

    The transport of small particles in the free-molecule regime is investigated on the basis of gas kinetic theory. Drag force formulations were derived in two limiting collision models-namely, specular and diffuse scattering-by considering the potential force of interactions between the particle and fluid molecules. A parametrized drag coefficient equation is proposed and accounts for the transition from specular to diffuse scattering as particle size exceeds a critical value. The resulting formulations are shown to be consistent with the Chapman-Enskog theory of molecular diffusion. In the limit of rigid-body interactions, these formulations can be simplified also to Epstein's solutions [P. S. Epstein, Phys. Rev. 23, 710 (1924)]. PMID:14754191

  16. Permeability and kinetic coefficients for mesoscale BCF surface step dynamics: Discrete two-dimensional deposition-diffusion equation analysis

    DOE PAGESBeta

    Zhao, Renjie; Evans, James W.; Oliveira, Tiago J.

    2016-04-08

    Here, a discrete version of deposition-diffusion equations appropriate for description of step flow on a vicinal surface is analyzed for a two-dimensional grid of adsorption sites representing the stepped surface and explicitly incorporating kinks along the step edges. Model energetics and kinetics appropriately account for binding of adatoms at steps and kinks, distinct terrace and edge diffusion rates, and possible additional barriers for attachment to steps. Analysis of adatom attachment fluxes as well as limiting values of adatom densities at step edges for nonuniform deposition scenarios allows determination of both permeability and kinetic coefficients. Behavior of these quantities is assessedmore » as a function of key system parameters including kink density, step attachment barriers, and the step edge diffusion rate.« less

  17. 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.

  18. Nd3+ ion diffusion during sintering of Nd:YAG transparent ceramics

    SciTech Connect

    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.

  19. Evaluation of diffusion coefficients by means of an approximate steady-state condition in sedimentation velocity distributions.

    PubMed

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

    2015-12-01

    This investigation examined the feasibility of manipulating the rotor speed in sedimentation velocity experiments to spontaneously generate an approximate steady-state condition where the extent of diffusional spreading is matched exactly by the boundary sharpening arising from negative s-c dependence. Simulated sedimentation velocity distributions based on the sedimentation characteristics for a purified mucin preparation were used to illustrate a simple procedure for determining the diffusion coefficient from such steady-state distributions in situations where the concentration dependence of the sedimentation coefficient, s = s(0)/(1 + Kc), was quantified in terms of the limiting sedimentation coefficient as c → 0 (s(0)) and the concentration coefficient (K). Those simulations established that spontaneous generation of the approximate steady state could well be a feature of sedimentation velocity distributions for many unstructured polymer systems because the requirement that Kcoω(2)s(0)/D be between 46 and 183 cm(-2) is not unduly restrictive. Although spontaneous generation of the approximate steady state is also a theoretical prediction for structured macromolecular solutes exhibiting linear concentration dependence of the sedimentation coefficient, s = s(0)(1 - kc), the required value of k is far too large for any practical advantage to be taken of this approach with globular proteins. PMID:26321223

  20. Sensitivity of the interpretation of the experimental ion thermal diffusivity to the determination of the ion conductive heat flux

    SciTech Connect

    Stacey, W. M.

    2014-04-15

    A moments equation formalism for the interpretation of the experimental ion thermal diffusivity from experimental data is used to determine the radial ion thermal conduction flux that must be used to interpret the measured data. It is shown that the total ion energy flux must be corrected for thermal and rotational energy convection, for the work done by the flowing plasma against the pressure and viscosity, and for ion orbit loss of particles and energy, and expressions are presented for these corrections. Each of these factors is shown to have a significant effect on the interpreted ion thermal diffusivity in a representative DIII-D [J. Luxon, Nucl. Fusion 42, 614 (2002)] discharge.

  1. Polycyclic aromatic hydrocarbon ions and the diffuse interstellar bands

    NASA Technical Reports Server (NTRS)

    Salama, F.; Allamandola, L. J.

    1995-01-01

    Neutral naphthalene (C10H8), phenanthrene (C14H10), and pyrene (C16H10) absorb strongly in the ultraviolet and may contribute to the extinction curve. High abundances are required to produce detectable structures. The cations of these Polycyclic Aromatic Hydrocarbons (PAHs) absorb in the visible. C10H8(+) has 12 discrete absorption bands which fall between 6800 and 5000 A. The strongest band at 6741 A falls close to the weak 6742 A diffuse interstellar band (DIB). Five other weaker bands also match DIBs. The possibility that C10H8(+) is responsible for some of the DIBs can be tested by searching for new DIBS at 6520, 6151, and 5965 A, other moderately strong naphthalene cation band positions. If C10H8(+) is indeed responsible for the 6742 A feature, it accounts for 0.3% of the cosmic carbon. The spectrum of C16H10(+) is dominated by a strong band at 4435 A in an Ar matrix and 4395 A in a Ne matrix, a position which falls very close to the strongest DIB, that at 4430 A. If C16H10(+), or a closely related pyrene-like ion is indeed responsible for the 4430 A feature, it accounts for 0.2% of the cosmic carbon. We also report an intense, very broad UV-to-visible continuum which is associated with both ions and could explain how PAHs convert interstellar UV and visible radiation into IR.

  2. The heavy ion diffusion region in magnetic reconnection in the Earth's magnetotail

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    While the plasma in the Earth's magnetotail predominantly consists of protons and electrons, there are times when a significant amount of oxygen is present. When magnetic reconnection occurs, the behavior of these heavy ions can be significantly different from that of the protons, due to their larger gyroradius. In this study, we investigate the heavy ion distribution functions in the reconnection ion diffusion region from a 2.5D three-species particle-in-cell numerical simulation and compare those with Cluster observations from the near-Earth magnetotail. From the simulation results, we find that the heavy ions are demagnetized and accelerated in a larger diffusion region, the heavy ion diffusion region. The ion velocity distribution functions show that, inside the heavy ion diffusion region, heavy ions appear as counterstreaming beams along z in the GSM x-z plane, while drifting in y, carrying cross-tail current. We compare this result with Cluster observations in the vicinity of reconnection regions in the near-Earth magnetotail and find that the simulation predictions are consistent with the observed ion distribution functions in the ion diffusion region, as well as the inflow, exhaust, and separatrix regions. Based on the simulation and observation results, the presence of a multiscale diffusion region model, for O+ abundant reconnection events in the Earth's magnetotail, is demonstrated. A test particle simulation shows that in the diffusion region, the H+ gains energy mainly through Ex, while the O+ energy gain comes equally from Ex and Ey.

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

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

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

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

    PubMed

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

    2013-08-21

    We have developed a method to measure thermodiffusion and Fickian diffusion in transparent binary solutions. The measuring instrument consists of two orthogonally aligned phase-shifting interferometers coupled with a single rotating polarizer. This high-resolution interferometer, initially developed to measure isothermal diffusion coefficients in liquid systems [J. F. Torres, A. Komiya, E. Shoji, J. Okajima, and S. Maruyama, Opt. Lasers Eng. 50, 1287 (2012)], was modified to measure transient concentration profiles in binary solutions subject to a linear temperature gradient. A convectionless thermodiffusion field was created in a binary solution sample that is placed inside a Soret cell. This cell consists of a parallelepiped cavity with a horizontal cross-section area of 10 × 20 mm(2), a variable height of 1-2 mm, and transparent lateral walls. The small height of the cell reduces the volume of the sample, shortens the measurement time, and increases the hydrodynamic stability of the system. An additional free diffusion experiment with the same optical apparatus provides the so-called contrast factors that relate the unwrapped phase and concentration gradients, i.e., the measurement technique is independent and robust. The Soret coefficient is determined from the concentration and temperature differences between the upper and lower boundaries measured by the interferometer and thermocouples, respectively. The Fickian diffusion coefficient is obtained by fitting a numerical solution to the experimental concentration profile. The method is validated through the measurement of thermodiffusion in the well-known liquid pairs of ethanol-water (ethanol 39.12 wt.%) and isobutylbenzene-dodecane (50.0 wt.%). The obtained coefficients agree with the literature values within 5.0%. Finally, the developed technique is applied to visualize biomolecular thermophoresis. Two protein aqueous solutions at 3 mg∕ml were used as samples: aprotinin (6.5 kDa)-water and lysozyme (14.3 kDa)-water. It was found that the former protein molecules are thermophilic and the latter thermophobic. In contrast to previously reported methods, this technique is suitable for both short time and negative Soret coefficient measurements. PMID:23968083

  5. Anomalous and classical neutral beam fast ion diffusion on JET

    NASA Astrophysics Data System (ADS)

    Baranov, Yu F.; Jenkins, I.; Alper, B.; Challis, C. D.; Conroy, S.; Kiptily, V.; Ongena, J.; Popovichev, S.; Smeulders, P.; Surrey, E.; Zastrow, K.-D.; JET EFDA contributors

    2009-04-01

    Trace tritium experiments (TTE) on JET were analysed using Monte Carlo modelling of the neutron emission resulting from the neutral beam injection (NBI) of short (~300 ms) tritium (T) beam blips into reversed shear, hybrid ELMy H-mode and L-mode deuterium plasmas for a wide range of plasma parameters. The calculated neutron fluxes from deuterium-tritium (DT) reactions could only be made consistent with all plasmas by applying an artificial reduction of the T beam power in the modelling of between 20% and 40%. A similar discrepancy has previously been observed in both JET (Gorini et al 2004 Proc. 31st EPS Conf. on Plasma Physics (London, UK) vol 28G (ECA)) and TFTR (Ruskov et al 1999 Phys. Rev. Lett. 82 924), although no mechanism has yet been found that could explain such a difference in the measured T beam power. Applying this correction in the T beam power, good agreement between calculated and measured DT neutron emission profiles was obtained in low to moderate line averaged density (\\overline {n_\\rme} <4\\times 10^{19}\\,m^{-3}) ELMy H-Mode plasmas assuming that the fast beam ions experience no, or relatively small, anomalous diffusion (Dan Lt 0.5 m2 s-1). However, the modelled neutron profiles do not agree with measurements in higher density plasmas using the same assumption and the disagreement between the measured and calculated shape of the neutron profile increases with plasma density. In this paper it is demonstrated that large anomalous losses of fast ions have to be assumed in the simulations to improve agreement between experimental and simulated neutron profiles, characterized by the goodness of fit. Various types of fast ion losses are modelled to explain aspects of the data, though further investigation will be required in order to gain a more detailed understanding of the nature of those anomalous losses.

  6. Study of variation of thermal expansion coefficients diffuse by real-time interferometry of holographic

    NASA Astrophysics Data System (ADS)

    Karimi, M.; Moghadam Saraee, A. A.

    2005-12-01

    Using the real-time holographic interferometry, we have studied the way of variation of thermal expansion coefficient as a function of temperature. For this purpose we have used a particular set-up appropriate to in-situs developing process. In the reconstruction step, the observer will see-through the hologram ,a virtual image which is coincident with the wave diffracted by the object itself, and an interference pattern will appear. If then the temperature of the object is increased, this will cause the movement of fringe. Hype number of displaced fringes give measure to evaluatethe coefficient of the thermal expansion of the object. The corresponding curves is depicted.

  7. The radial diffusion coefficient of 1.3 - 2.3 MeV protons in recurrent proton streams

    NASA Technical Reports Server (NTRS)

    Mewaldt, R. A.; Stone, E. C.; Vogt, R. E.

    1978-01-01

    The paper presents anisotropy measurements of 1.3-2.3 MeV protons in the interplanetary space during recurrent events for which the radial intensity variation is measured within the radial range from about 0.3 to about 4 AU for the period from June, 1973 through April, 1976. The simultaneous measurements of the diffusive anisotropy and the radial gradient are used to make a direct estimate of the interplanetary radial diffusion coefficient, which is independent of any particular solution of the propagation equation. IMP 7 and 8 is required to be sunward of the earth and hence outside of the magnetosphere; if both spacecraft are sunward, measurements from the one farthest from the magnetosphere are used. The resulting values for the radial diffusivity coefficient near 1 AU lie in the range (3 to 9) x 10 to the 20th sq cm/sec, corresponding to scattering mean free paths between 0.03 and 0.1 AU with a mean of 0.06 AU.

  8. The interaction between apparent diffusion coefficients and transverse relaxation rates of human brain metabolites and water studied by diffusion-weighted spectroscopy at 7 T.

    PubMed

    Branzoli, Francesca; Ercan, Ece; Webb, Andrew; Ronen, Itamar

    2014-05-01

    The dependence of apparent diffusion coefficients (ADCs) of molecules in biological tissues on an acquisition-specific timescale is a powerful mechanism for studying tissue microstructure. Unlike water, metabolites are confined mainly to intracellular compartments, thus providing higher specificity to tissue microstructure. Compartment-specific structural and chemical properties may also affect molecule transverse relaxation times (T?). Here, we investigated the correlation between diffusion and relaxation for N-acetylaspartate, creatine and choline compounds in human brain white matter in vivo at 7 T, and compared them with those of water under the same experimental conditions. Data were acquired in a volume of interest in parietal white matter at two different diffusion times, ? = 44 and 246 ms, using a matrix of three echo times (T(E)) and five diffusion weighting values (up to 4575 s/mm). Significant differences in the dependence of the ADCs on T(E) were found between water and metabolites, as well as among the different metabolites. A significant decrease in water ADC as a function of TE was observed only at the longest diffusion time (p < 0.001), supporting the hypothesis that at least part of the restricted water pool can be associated with longer T?, as suggested by previous studies in vitro. Metabolite data showed an increase of creatine (p < 0.05) and N-acetylaspartate (p < 0.05) ADCs with TE at ? = 44 ms, and a decrease of creatine (p < 0.05) and N-acetylaspartate (p = 0.1) ADCs with TE at ? = 246 ms. No dependence of choline ADC on TE was observed. The metabolite results suggest that diffusion and relaxation properties are dictated not only by metabolite distribution in different cell types, but also by other mechanisms, such as interactions with membranes, exchange between "free" and "bound" states or interactions with microsusceptibility gradients. PMID:24706330

  9. On the Variation of Water Diffusion Coefficient in Stratum Corneum With Water Content.

    PubMed

    Li, Xin; Johnson, Robert; Kasting, Gerald B

    2016-03-01

    Water permeability and transient water sorption data in human and porcine stratum corneum (SC) are analyzed in conjunction with equilibrium water sorption data and a dynamic skin swelling model to develop a quantitative model for water diffusivity in the SC as a function of its water content. The recommended function (model 1) is phenomenological and treats the SC as a uniform, swellable slab. This approach yields satisfactory agreement with experimental data over a wide range of RH and associated equilibrium SC water content, Cw. It is supported by two alternative approaches. Model 2 considers the SC to be a multilaminate membrane consisting of alternating lipid and protein layers. Diffusivity in the protein phase is estimated from water diffusivity in other keratinized tissues, whereas diffusivity in the lipid phase is assumed to be linearly related to the swelling strain on intercellular lipids. Model 3 uses an analysis previously suggested by Stockdale to rationalize transepidermal water loss data in humans over a wide range of relative humidity. All models yield similar results for 0.20 ≤ Cw ≤ 0.78 g/cm(3), the usual range of SC water content in vivo. PMID:26886319

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

    NASA Technical Reports Server (NTRS)

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

    1997-01-01

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

  11. Recombination of W19 + ions with electrons: Absolute rate coefficients from a storage-ring experiment and from theoretical calculations

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    Experimentally measured and theoretically calculated rate coefficients for the recombination of W19 +([Kr ] 4 d10 4 f9 ) ions with free electrons (forming W18 +) are presented. At low electron-ion collision energies, the merged-beam rate coefficient is dominated by strong, mutually overlapping, recombination resonances as already found previously for the neighboring charge-state ions W18 + and W20 +. In the temperature range where W19 + is expected to form in a collisionally ionized plasma, the experimentally derived recombination rate coefficient deviates by up to a factor of about 20 from the theoretical rate coefficient obtained from the Atomic Data and Analysis Structure database. The present calculations, which employ a Breit-Wigner redistributive partitioning of autoionizing widths for dielectronic recombination via multi-electron resonances, reproduce the experimental findings over the entire temperature range.

  12. A precision physical model for three terminal diffused or ion-implanted resistors

    NASA Astrophysics Data System (ADS)

    Qian, MingRui; Wang, DeZhong

    2005-03-01

    In modern CMOS and BiCMOS technologies, the diffused or ion-implanted resistors are widely used devices. One important source of errors in the accurate analog circuit simulation is the variation of resistance respect to applied voltage for diffused or ion-implanted resistors. This paper analyzes the electrical properties of the diffused resistors, and derives a closed form precision physical model for three terminal diffused resistors or ion-implanted. The voltage dependency of the resistance can be described by the depletion layer spreading into the resistor body. The back bias effect is also included in the model. The temperature model is derived from the mobility and built-in potential temperature models. The extreme cases have been studied, which sets up the minimum resistor width and maximum applied voltage of diffused or ion-implanted resistors. Good match between the modeled and experimental results is observed in the diffused resistors with n- and p-type doping.

  13. Determination of the self-diffusion coefficient of intracellular water using PGSE NMR with variable gradient pulse length

    NASA Astrophysics Data System (ADS)

    Åslund, Ingrid; Topgaard, Daniel

    2009-12-01

    A new pulsed-gradient spin-echo NMR protocol for assessing the local self-diffusion coefficient D0 of water confined within living cells is proposed. Equations for the apparent mean-square displacement < Z2> as a function of the effective diffusion time td and the duration of the displacement-encoding gradient pulses δ are derived. The standard method of estimating D0 - reducing td until the influence of collisions between the water molecules and the plasma membrane can be neglected - often fails because of the small size of typical cells. As demonstrated here, the decrease of the apparent < Z2> with increasing δ at constant td can be utilized to measure D0.

  14. Experimental Study of Diffusion Coefficients of Water through the Collagen: Apatite Porosity in Human Trabecular Bone Tissue

    PubMed Central

    Bini, Fabiano; Marinozzi, Andrea

    2014-01-01

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

  15. Force-Clamp Experiments Reveal the Free-Energy Profile and Diffusion Coefficient of the Collapse of Protein Molecules

    NASA Astrophysics Data System (ADS)

    Lannon, H.; Haghpanah, J. S.; Montclare, J. K.; Vanden-Eijnden, E.; Brujic, J.

    2013-03-01

    We present force-clamp data on the collapse of ubiquitin polyproteins from a highly extended state to the folded length, in response to a quench in the force from 110 pN to 5 or 10 pN. Using a recent method for free-energy reconstruction from the observed nonequilibrium trajectories, we find that their statistics is captured by simple diffusion along the end-to-end length. The estimated diffusion coefficient of ˜100nm2s-1 is significantly slower than expected from viscous effects alone, possibly because of the internal degrees of freedom of the protein. The free-energy profiles give validity to a physical model in which the multiple protein domains collapse all at once and the role of the force is approximately captured by the Bell model.

  16. Monte Carlo calculation of diffusion coefficient, noise spectral density and noise temperature in HgCdTe

    NASA Astrophysics Data System (ADS)

    Palermo, C.; Varani, L.; Vaissière, J.-C.; Millithaler, J.-F.; Starikov, E.; Shiktorov, P.; Gružinskis, V.; Azaïs, B.

    2005-08-01

    Noise in optoelectronic devices is a critical parameter since it can affect dramatically the quality of target discrimination. In the domain of LWIR atmospherical window photodetection, used in the framework of night-vision applications, mercury-cadmium-telluride is a widely used material. We propose the first kinetic calculation of Hg0.8Cd0.2Te noise parameters, that is of diffusion coefficient, spectral density and noise temperature, and investigate the importance of the excess noise due to the presence of impact-ionization processes.

  17. Divergence of the long-wavelength collective diffusion coefficient in quasi-one- and quasi-two-dimensional colloidal suspensions.

    PubMed

    Lin, Binhua; Cui, Bianxiao; Xu, Xinliang; Zangi, Ronen; Diamant, Haim; Rice, Stuart A

    2014-02-01

    We report the results of experimental studies of the short-time-long-wavelength behavior of collective particle displacements in quasi-one-dimensional (q1D) and quasi-two-dimensional (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 D(e)(q), with the static structure factor S(q) and the self-diffusion coefficient of isolated particles D(0): H(q) ≡ D(e)(q)S(q)/D(0). We find an apparent divergence of H(q) as q → 0 with the form H(q) ∝ q(-γ) (1.7 < γ < 1.9) for both q1D and q2D colloid suspensions. Given that S(q) does not diverge as q → 0 we infer that D(e)(q) does. This behavior is qualitatively different from that of the three-dimensional H(q) and D(e)(q) as q → 0, and the divergence is of a different functional form from that predicted for the diffusion coefficient in one-component one-dimensional and two-dimensional fluids not subject to boundary conditions that define the dimensionality of the system. We provide support for the contention that the boundary conditions that define a confined system play a very important role in determining the long-wavelength behavior of the collective diffusion coefficient from two sources: (i) the results of simulations of H(q) and D(e)(q) in quasi-1D and quasi-2D systems and (ii) verification, using data from the work of Lin, Rice and Weitz [Phys. Rev. E 51, 423 (1995)], of the prediction by Bleibel et al., arXiv:1305.3715, that D(e)(q) for a monolayer of colloid particles constrained to lie in the interface between two fluids diverges as q(-1) as q → 0. PMID:25353468

  18. Direct evaluation of the position dependent diffusion coefficient and persistence time from the equilibrium density profile in anisotropic fluids.

    PubMed

    Olivares-Rivas, Wilmer; Colmenares, Pedro J; Lpez, Floralba

    2013-08-21

    We derive expressions for the transverse diffusion coefficient D(z) and the average persistence time ?(z; L) within a layer of width L, for particles of a non-homogeneous fluid enclosed in a planar nanopore. The method allows the direct evaluation of these position-dependent dynamical quantities from the equilibrium local particle density profile. We use results for the density and persistence time profiles from the virtual layer molecular dynamics method to numerically assess the significance of the Smoluchowski approximation. PMID:23968068

  19. The use of the experimentally deduced Brunt-Vaisala frequency and turbulent velocity fluctuations to estimate the eddy diffusion coefficient

    NASA Technical Reports Server (NTRS)

    Rottger, J.

    1986-01-01

    The determination of the turbulent energy dissipation rate or the eddy diffusion coefficient from radar observations can be done through the turbulence refractive index structure constant, deduced from calibrated echo power measurements, or through the turbulent velocity fluctuations, deduced from the echo spectrum width. Besides the radar parameters, power and spectrum width, the first approach needs knowledge of profiles of temperature and electron density in the mesosphere and the fraction of the radar volume filled with turbulence. The latter approach needs knowledge of the temperature profile, namely, the Brunt-Vaisala frequency. The use of this latter approach is demonstrated.

  20. 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.

  1. Evaluating the Diffusion Coefficient of Dopamine at the Cell Surface During Amperometric Detection: Disk vs. Ring Microelectrodes

    PubMed Central

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

    2013-01-01

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

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

    PubMed

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

    2013-07-01

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

  3. Generalized Cahn-Hilliard equation for solutions with drastically different diffusion coefficients. Application to exsolution in ternary feldspar

    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.

  4. Mass loading and velocity diffusion models for heavy pickup ions at comet Grigg-Skjellerup

    NASA Technical Reports Server (NTRS)

    Huddleston, D. E.; Coates, A. J.; Johnstone, A. D.; Neubauer, Fritz M.

    1993-01-01

    We compare model predictions of cometary water group ion densities and the solar wind slow down with measurements made by the Giotto Johnstone plasma analyzer implanted ion sensor at the encounter with comet Grigg-Skjellerup (G-S) on July 10, 1992. The observed slope of the ion density profile on approach to the comet is unexpectedly steep. Possible explanations for this are discussed. We present also a preliminary investigation of the quasilinear velocity-space diffusion of the implanted heavy ion population at G-S using a transport equation including souce, convection, adiabatic compression, and velocity diffusion terms. Resulting distributions are anisotropic, in agreement with observations. We consider theoretically the waves that may be generated by the diffusion process for the observed solar wind conditions. At initial ion injections, waves are generated at omega approximately Omega(sub i) the ion gyrofrequency, and lower frequencies are predicted for diffusion toward a bispherical shell.

  5. Method for the determination of oxygen consumption rates and diffusion coefficients in multicellular spheroids.

    PubMed Central

    Mueller-Klieser, W

    1984-01-01

    A method has been developed for the quantitative evaluation of oxygen tension (PO2) distributions in multicellular spheroids measured with O2-sensitive microelectrodes. The experimental data showed that multicellular tumor spheroids in stirred growth media were characterized by a diffusion-depleted zone surrounding the spheroids. This zone was elicited by an unstirred layer of medium next to the spheroid leading to a continuous decrease in the PO2 values from the bulk medium towards the spheroid surface. Theoretical considerations demonstrate that the volume-related O2 consumption rate, Q, in the spheroids can be assessed by measuring the PO2 gradient in the diffusion-depleted zone outside the spheroids. Accordingly, Krogh's diffusion constant, KS, in the spheroids can be determined through measuring the PO2 gradient within the spheroids. The results obtained suggest that multicellular spheroids represent useful in vitro tumor models for the experimental and theoretical analysis of the interrelationship among O2 supply to tumor cells, O2 metabolism in tumors tissue, and the responsiveness of cancer cells to treatment. PMID:6487734

  6. Dynamics of supercooled water in nanotubes: Cage correlation function and diffusion coefficient

    NASA Astrophysics Data System (ADS)

    Khademi, Mahdi; Kalia, Rajiv K.; Sahimi, Muhammad

    2015-09-01

    Dynamics of low-temperature water in nanostructured materials is important to a variety of phenomena, ranging from transport in cement and asphaltene, to conformational dynamics of proteins in "crowded" cellular environments, survival of microorganisms at very low temperatures, and diffusion in nanogeoscience. Using silicon-carbide nanotubes as a prototype of nanostructured materials, extensive molecular dynamics simulations were carried out to study the cage correlation function C (t ) and self-diffusivity D of supercooled water in the nanotubes. C (t ) , which measures changes in the atomic surroundings inside the nanotube, follows the Kohlrausch-Williams-Watts law, C (t ) ˜exp[-(t/τ ) β] , where τ is a relaxation time and β is a topological exponent. For the temperature range 220 Kdiffusivity manifests a transition around 230 K, very close to 228 K, the temperature at which a fragile-to-strong dynamic crossover is supposed to happen. Thus the results indicate that water does not freeze in the nanotube over the studied temperature range, and that the Stokes-Einstein relation breaks down.

  7. Comparison of Apparent Diffusion Coefficient and Intravoxel Incoherent Motion for Differentiating among Glioblastoma, Metastasis, and Lymphoma Focusing on Diffusion-Related Parameter

    PubMed Central

    Shim, Woo Hyun; Kim, Ho Sung; Choi, Choong-Gon; Kim, Sang Joon

    2015-01-01

    Background and Purpose Brain tumor cellularity has been assessed by using apparent diffusion coefficient (ADC). However, the ADC value might be influenced by both perfusion and true molecular diffusion, and the perfusion effect on ADC can limit the reliability of ADC in the characterization of tumor cellularity, especially, in hypervascular brain tumors. In contrast, the IVIM technique estimates parameter values for diffusion and perfusion effects separately. The purpose of our study was to compare ADC and IVIM for differentiating among glioblastoma, metastatic tumor, and primary CNS lymphoma (PCNSL) focusing on diffusion-related parameter. Materials and Methods We retrospectively reviewed the data of 128 patients with pathologically confirmed glioblastoma (n = 55), metastasis (n = 31), and PCNSL (n = 42) prior to any treatment. Two neuroradiologists independently calculated the maximum IVIM-f (fmax) and minimum IVIM-D (Dmin) by using 16 different b-values with a bi-exponential fitting of diffusion signal decay, minimum ADC (ADCmin) by using 0 and 1000 b-values with a mono-exponential fitting and maximum normalized cerebral blood volume (nCBVmax). The differences in fmax, Dmin, nCBVmax, and ADCmin among the three tumor pathologies were determined by one-way ANOVA with multiple comparisons. The fmax and Dmin were correlated to the corresponding nCBV and ADC using partial correlation analysis, respectively. Results Using a mono-exponential fitting of diffusion signal decay, the mean ADCmin was significantly lower in PCNSL than in glioblastoma and metastasis. However, using a bi-exponential fitting, the mean Dmin did not significantly differ in the three groups. The mean fmax significantly increased in the glioblastomas (reader 1, 0.103; reader 2, 0.109) and the metastasis (reader 1, 0.105; reader 2, 0.107), compared to the primary CNS lymphomas (reader 1, 0.025; reader 2, 0.023) (P < .001 for each). The correlation between fmax and the corresponding nCBV was highest in glioblastoma group, and the correlation between Dmin and the corresponding ADC was highest in primary CNS lymphomas group. Conclusion Unlike ADC value derived from a mono-exponential fitting of diffusion signal, diffusion-related parametric value derived from a bi-exponential fitting with separation of perfusion effect doesn’t differ among glioblastoma, metastasis, and PCNSL. PMID:26225937

  8. 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.

  9. Measurement of Secondary Electron Emission Coefficient of Plane Target in Plasma Immersion Ion Implantation

    NASA Astrophysics Data System (ADS)

    Nakamura, Keiji; Ando, Masaki; Sugai, Hideo

    This paper describes in-process measurements of secondary electron emission coefficient (SEEC) during plasma immersion ion implantation for a plane target. In the plane target, trajectories of secondary electrons (SEs) emitted from the target strongly depends on the plasma conditions as well as amplitude of pulse voltages applied to the target because of variation of a curvature radius of the sheath formed around the target. Therefore, absolute measurements of the SE current as well as of the SEEC were difficult to be performed. However calibration of a SE detector using a plane target with very high SEEC enabled the SEEC measurements. The measurements of the SE current revealed that the sheath curvature was affected by the plasma condition and the target shape. This calibration will be useful for SEEC measurements of arbitrary-shaped target.

  10. Apparent diffusion coefficient of breast cancer and normal fibroglandular tissue in diffusion-weighted imaging: the effects of menstrual cycle and menopausal status.

    PubMed

    Kim, Jin You; Suh, Hie Bum; Kang, Hyun Jung; Shin, Jong Ki; Choo, Ki Seok; Nam, Kyung Jin; Lee, Seok Won; Jung, Young Lae; Bae, Young Tae

    2016-05-01

    The purpose of this study was to investigate prospectively whether the apparent diffusion coefficients (ADCs) of both breast cancer and normal fibroglandular tissue vary with the menstrual cycle and menopausal status. Institutional review board approval was obtained, and informed consent was obtained from each participant. Fifty-seven women (29 premenopausal, 28 postmenopausal) with newly diagnosed breast cancer underwent diffusion-weighted imaging twice (interval 12-20 days) before surgery. Two radiologists independently measured ADC of breast cancer and normal contralateral breast tissue, and we quantified the differences according to the phases of menstrual cycle and menopausal status. With normal fibroglandular tissue, ADC was significantly lower in postmenopausal than in premenopausal women (P = 0.035). In premenopausal women, ADC did not differ significantly between proliferative and secretory phases in either breast cancer or normal fibroglandular tissue (P = 0.969 and P = 0.519, respectively). In postmenopausal women, no significant differences were found between ADCs measured at different time intervals in either breast cancer or normal fibroglandular tissue (P = 0.948 and P = 0.961, respectively). The within-subject variability of the ADC measurements was quantified using the coefficient of variation (CV) and was small: the mean CVs of tumor ADC were 2.90 % (premenopausal) and 3.43 % (postmenopausal), and those of fibroglandular tissue ADC were 4.37 % (premenopausal) and 2.55 % (postmenopausal). Both intra- and interobserver agreements were excellent for ADC measurements, with intraclass correlation coefficients in the range of 0.834-0.974. In conclusion, the measured ADCs of breast cancer and normal fibroglandular tissue were not affected significantly by menstrual cycle, and the measurements were highly reproducible both within and between observers. PMID:27091644

  11. Diffusion coefficient of the cyclic GMP analog 8-(fluoresceinyl)thioguanosine 3',5' cyclic monophosphate in the salamander rod outer segment.

    PubMed Central

    Koutalos, Y; Brown, R L; Karpen, J W; Yau, K W

    1995-01-01

    Cyclic GMP (cGMP) is the intracellular messenger mediating phototransduction in retinal rods, with its longitudinal diffusion in the rod outer segment (ROS) likely to be a factor in determining light sensitivity. From the kinetics of cGMP-activated currents in the truncated ROS of the salamander (Ambystoma tigrinum), the cGMP diffusion coefficient was previously estimated to be approximately 60 x 10(-8) cm2 s-1. On the other hand, fluorescence measurements in intact salamander ROS using 8-(fluoresceinyl)thioguanosine 3',5'-cyclic monophosphate (Fl-cGMP) led to a diffusion coefficient for this compound of 1 x 10(-8) cm2 s-1; after corrections for differences in size and in binding to cellular components between cGMP and Fl-cGMP, this gave an upper limit of 11 x 10(-8) cm2 s-1 for the cGMP diffusion coefficient. To properly compare the two sets of measurements, we have examined the diffusion of Fl-cGMP in the truncated ROS. From the kinetics of Fl-cGMP-activated currents, we have obtained a diffusion coefficient of 3 x 10(-8) cm2 s-1 for this analog; the cGMP diffusion coefficient measured from the same truncated ROSs was approximately 80 x 10(-8) cm2 s-1. Thus, a factor of 27 appears appropriate for correcting differences in size and intracellular binding between cGMP and Fl-cGMP. Application of this correction factor to the Fl-cGMP diffusion coefficient measurements by Olson and Pugh (1993) gives a cGMP diffusion coefficient of approximately 30 x 10(-8) cm2 s-1, in reasonable agreement with the value measured from the truncated ROS. PMID:8580360

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

    Rate coefficients for photorecombination (PR) and cross sections for electron-impact ionization (EII) of Fe14+, forming Fe13+ and Fe15+, respectively, have been measured by employing the electron-ion merged-beams technique at a heavy-ion storage ring. Rate coefficients for PR and EII of Fe14+ ions in a plasma are derived from the experimental measurements. Simple parametrizations of the experimentally derived plasma rate coefficients are provided for use in the modeling of photoionized and collisionally ionized plasmas. In the temperature ranges where Fe14+ is expected to form in such plasmas, the latest theoretical rate coefficients of Altun et al. [Astron. Astrophys. 474, 1051 (2007), 10.1051/0004-6361:20078238] for PR and of Dere [Astron. Astrophys. 466, 771 (2007), 10.1051/0004-6361:20066728] for EII agree with the experimental results to within the experimental uncertainties. Common features in the PR and EII resonance structures are identified and discussed.

  13. Drag force, diffusion coefficient, and electric mobility of small particles. II. Application.

    PubMed

    Li, Zhigang; Wang, Hai

    2003-12-01

    We propose a generalized treatment of the drag force of a spherical particle due to its motion in a laminar fluid media. The theory is equally applicable to analysis of particle diffusion and electric mobility. The focus of the current analysis is on the motion of spherical particles in low-density gases with Knudsen number Kn>1. The treatment is based on the gas-kinetic theory analysis of drag force in the specular and diffuse scattering limits obtained in a preceding paper [Z. Li and H. Wang, Phys. Rev. E., 68, 061206 (2003)]. Our analysis considers the influence of van der Waals interactions on the momentum transfer upon collision of a gas molecule with the particle and expresses this influence in terms of an effective, reduced collision integral. This influence is shown to be significant for nanosized particles. In the present paper, the reduced collision integral values are obtained for specular and diffuse scattering, using a Lennard-Jones-type potential energy function suitable for the interactions of a gas molecule with a particle. An empirical formula for the momentum accommodation function, used to determine the effective, reduced collision integral, is obtained from available experimental data. The resulting treatment is shown to be accurate for interpreting the mobility experiments for particles as small as approximately 1 nm in radius. The treatment is subsequently extended to the entire range of the Knudsen number, following a semiempirical, gas-kinetic theory analysis. We demonstrate that the proposed formula predicts very well Millikan's oil-droplet experiments [R. A. Millikan, Philos. Mag. 34, 1 (1917); Phys. Rev. 22, 1 (1923)]. The rigorous theoretical foundation of the proposed formula in the Kn>1 limit makes the current theory far more general than the semiempirical Stokes-Cunningham formula in terms of the particle size and condition of the fluid and, therefore, more attractive than the Stokes-Cunningham formula. PMID:14754192

  14. A dynamic subgrid-scale eddy diffusivity model with a global model coefficient for passive scalar transport in complex geometry

    NASA Astrophysics Data System (ADS)

    Lee, Jungil; Choi, Haecheon; Park, Noma

    2008-11-01

    In the present study, a dynamic subgrid-scale eddy diffusivity model is proposed for large eddy simulation of passive scalar transport in complex geometry. The eddy viscosity model proposed by Vreman [Phys. Fluids, 16, 3670 (2004)], which guarantees theoretically zero SGS dissipation for various laminar shear flows, is utilized as the base eddy diffusivity model. The model coefficient is determined by the dynamic procedure based on the method proposed by Park et al. [Phys. Fluids, 18, 125109 (2006)] such that the model coefficient is globally constant in space but varies only in time. The large eddy simulations of passive scalar transport in turbulent channel flow and turbulent boundary layer are conducted and the proposed model shows nearly the same performance as the dynamic Smagorinsky model does. Since the proposed model does not require any ad hoc clipping and averaging over the homogeneous direction, it can be readily applied to transport of passive scalar in complex flows. Some other examples such as heat transfer in a ribbed channel will be shown in the final presentation.

  15. Evaluation of Taylor dispersion injections: determining kinetic/affinity interaction constants and diffusion coefficients in label-free biosensing.

    PubMed

    Quinn, John G

    2012-02-15

    In label-free biomolecular interaction analysis, a standard injection provides an injection of uniform analyte concentration. An alternative approach exploiting Taylor dispersion produces a continuous analyte titration allowing a full analyte dose response to be recorded in a single injection. The enhanced biophysical characterization that is possible with this new technique is demonstrated using a commercially available surface plasmon resonance-based biosensor. A kinetic interaction model was fitted locally to Taylor dispersion curves for estimation of the analyte diffusion coefficient in addition to affinity/kinetic constants. Statistical confidence in the measured parameters from a single Taylor dispersion injection was comparable to that obtained for global analysis of multiple standard injections. The affinity constants for multisite interactions were resolved with acceptable confidence limits. Importantly, a single analyte injection could be treated as a high-resolution real-time affinity isotherm and was demonstrated using the complex two-site interaction of warfarin with human serum albumin. In all three model interactions tested, the kinetic/affinity constants compared favorably with those obtained from standard kinetic analysis and the estimates of analyte diffusion coefficients were in good agreement with the expected values. PMID:22197422

  16. Estimating the Underwater Diffuse Attenuation Coefficient with a Low-Cost Instrument: The KdUINO DIY Buoy.

    PubMed

    Bardaji, Raul; Sánchez, Albert-Miquel; Simon, Carine; Wernand, Marcel R; Piera, Jaume

    2016-01-01

    A critical parameter to assess the environmental status of water bodies is the transparency of the water, as it is strongly affected by different water quality related components (such as the presence of phytoplankton, organic matter and sediment concentrations). One parameter to assess the water transparency is the diffuse attenuation coefficient. However, the number of subsurface irradiance measurements obtained with conventional instrumentation is relatively low, due to instrument costs and the logistic requirements to provide regular and autonomous observations. In recent years, the citizen science concept has increased the number of environmental observations, both in time and space. The recent technological advances in embedded systems and sensors also enable volunteers (citizens) to create their own devices (known as Do-It-Yourself or DIY technologies). In this paper, a DIY instrument to measure irradiance at different depths and automatically calculate the diffuse attenuation Kd coefficient is presented. The instrument, named KdUINO, is based on an encapsulated low-cost photonic sensor and Arduino (an open-hardware platform for the data acquisition). The whole instrument has been successfully operated and the data validated comparing the KdUINO measurements with the commercial instruments. Workshops have been organized with high school students to validate its feasibility. PMID:26999132

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

    PubMed

    Werts, Martinus H V; Raimbault, Vincent; Texier-Picard, Rozenn; Poizat, Rmi; Franais, 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

  18. Use of microdevices to determine the diffusion coefficient of electrochemically generated species: application to binary solvent mixtures and micellar solutions.

    PubMed

    Ferreira, Tiago L; Paixo, Thiago R L C; Richter, Eduardo M; El Seoud, Omar A; Bertotti, Mauro

    2007-11-01

    A new approach for the determination of diffusion coefficient, D, of redox species is presented. It is based on the use of a home-constructed twin electrode within a thin-layered cell (TETLC) filled with a solution of electroactive species. Values of D are readily calculated, provided that the time required for the electrochemically generated species (produced at the generator electrode) to reach the collector electrode and the distance between both electrodes are known. Other parameters typically required to calculate D, e.g., concentration of the redox species, area of the electrode, and number of electrons transferred, are not needed. Diffusion coefficients of Fe(CN)(6)(3-), Ru(NH3)(6)(2+), and quinone were determined in water and, for Fe(CN)(6)(4-), in binary mixtures with glycerol. The results obtained were in good agreement with literature values. Aqueous glycerol solutions are microheterogeneous, as shown by the dependence on medium composition of the empirical solvent polarity scale, ET(30), determined by the solvatochromic probe RB. The responses of RB and the electrochemically generated species (Fe(CN)(6)(4-)) to the composition of aqueous glycerol mixtures were found to be remarkably similar. Measurements of D of ferrocene in micellar solutions of the cationic surfactant CTABr were also performed. Values of D for ferrocene and the ferrocenium cation are very different, in agreement with the chemical affinity of both species for the cationic micelle. PMID:17924691

  19. Estimating the Underwater Diffuse Attenuation Coefficient with a Low-Cost Instrument: The KdUINO DIY Buoy

    PubMed Central

    Bardaji, Raul; Sánchez, Albert-Miquel; Simon, Carine; Wernand, Marcel R.; Piera, Jaume

    2016-01-01

    A critical parameter to assess the environmental status of water bodies is the transparency of the water, as it is strongly affected by different water quality related components (such as the presence of phytoplankton, organic matter and sediment concentrations). One parameter to assess the water transparency is the diffuse attenuation coefficient. However, the number of subsurface irradiance measurements obtained with conventional instrumentation is relatively low, due to instrument costs and the logistic requirements to provide regular and autonomous observations. In recent years, the citizen science concept has increased the number of environmental observations, both in time and space. The recent technological advances in embedded systems and sensors also enable volunteers (citizens) to create their own devices (known as Do-It-Yourself or DIY technologies). In this paper, a DIY instrument to measure irradiance at different depths and automatically calculate the diffuse attenuation Kd coefficient is presented. The instrument, named KdUINO, is based on an encapsulated low-cost photonic sensor and Arduino (an open-hardware platform for the data acquisition). The whole instrument has been successfully operated and the data validated comparing the KdUINO measurements with the commercial instruments. Workshops have been organized with high school students to validate its feasibility. PMID:26999132

  20. Apparent Diffusion Coefficient Quantification in Determining the Histological Diagnosis of Malignant Liver Lesions

    PubMed Central

    Drevelegas, Konstantinos; Nikiforaki, Katerina; Constantinides, Manolis; Papanikolaou, Nickolas; Papalavrentios, Lavrentios; Stoikou, Ioanna; Zarogoulidis, Paul; Pitsiou, Georgia; Pataka, Athanasia; Organtzis, John; Papadaki, Eleni; Porpodis, Konstantinos; Kougioumtzi, Ioanna; Kioumis, Ioannis; Kouskouras, Constantinos; Akriviadis, Evaggelos; Drevelegas, Antonios

    2016-01-01

    Purpose: Diffusion Weighted Imaging is an established diagnostic tool for accurate differential diagnosis between benign and malignant liver lesions. The aim of our study was to evaluate the role of Histogram Analysis of ADC quantification in determining the histological diagnosis as well as the grade of malignant liver tumours. To our knowledge, there is no study evaluating the role of Histogram Analysis of ADC quantification in determining the histological diagnosis as well as the grade of malignant liver tumours. Methods: During five years, 115 patients with known liver lesions underwent Diffusion Weighted Imaging in 3Tesla MR scanner prior to core needle biopsy. Histogram analyses of ADC in regions of interest were drawn and were correlated with biopsy histological diagnosis and grading. Results: Histogram analysis of ADC values shows that 5th and 30th percentile parameters have statistically significant potency of discrimination between primary and secondary lesions groups (p values 0.0036 and 0.0125 respectively). Skewness of the histogram can help discriminate between good and poor differentiated (p value 0.17). Discrimination between primary malignancy site in metastases failed for the present number of patients in each subgroup. Conclusion: Statistical parameters reflecting the shape of the left side of the ADC histogram can be useful for discriminating between primary and secondary lesions and also between well differentiated versus moderate or poor. For the secondary malignancies, they failed to predict the original site of tumour. PMID:27076855

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

    SciTech Connect

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

    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 (σ{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.

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

    PubMed Central

    Xiong, Jianyin; Huang, Shaodan; Zhang, Yinping

    2012-01-01

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

  3. Effective diffusion coefficients in random packings of polydisperse hard spheres from two-point and three-point correlation functions

    NASA Astrophysics Data System (ADS)

    Hlushkou, D.; Liasneuski, H.; Tallarek, U.; Torquato, S.

    2015-09-01

    We evaluate the effective diffusion coefficient Deff in random packings of polydisperse hard spheres with an analytical formula involving the three-point microstructural parameter ζ2. Bulk packings with solid volume fraction between ϕ = 0.54 and ϕ = 0.634 were computer-generated using experimentally determined particle size distributions characterized by different mean particle diameter and associated standard deviation. The parameter ζ2 was calculated from two- and three-point correlation functions S2 and S3, respectively, via an approach based on sampling templates. Results of the asymptotic analysis for S2 and S3 compare favorably with theoretical predictions. Effective diffusivities calculated by the approximate analytical formula are close to those obtained from simulations using a random-walk particle-tracking technique. The values of Deff are affected by the packings' solid volume fraction, the spatial positions of the spheres, and to a far lesser extent by the particles' polydispersity. The proposed numerical approach can be applied to evaluate effective diffusive transport properties of general two-phase materials just from the geometrical information embodied in ϕ and ζ2.

  4. Magnetic resonance characterization of tissue engineered cartilage via changes in relaxation times, diffusion coefficient, and shear modulus.

    PubMed

    Yin, Ziying

    2014-01-01

    The primary goal of this paper is to describe a combined MR relaxation (T(2) and T(1ρ)), diffusion (apparent diffusion coefficient [ADC]), and elastography (shear stiffness) method of fully characterizing the development of tissue-engineered cartilage in terms of the changes in its composition, structure, and mechanical properties during tissue growth. Then, we may better use MR-based methodologies to noninvasively monitor and optimize the cartilage tissue engineering process without sacrificing the constructs. This process begins by demonstrating the potential capability of T(2), T(1ρ), ADC, and shear stiffness in characterizing a scaffold-free engineered cartilage. The results show that, in addition to the conventional T(2) and ADC, T(1ρ) and MRE can be used as potential biomarkers to assess the specific changes in proteoglycan content and mechanical properties of engineered cartilage during culture. Moreover, to increase the efficiency of MR characterization, two new methodologies for simultaneous acquisition of diffusion and MRE (dMRE), and T(1ρ) and MRE (T(1ρ)-MRE) are introduced that allow the simultaneous characterization of both biochemical and mechanical properties of engineered cartilage tissue. The feasibilities of dMRE and T(1ρ)-MRE approaches are validated on tissue-mimicking phantoms. The results show good correspondence between simultaneous acquisitions and conventional separate acquisition methods. PMID:25403876

  5. Ion Diffusion in the Mode Conversion Associated with Kinetic Alfvén Waves

    NASA Astrophysics Data System (ADS)

    Lin, Y.; Wang, X.; Johnson, J.

    2012-12-01

    A three-dimensional (3-D) hybrid simulation is carried out for the mode conversion from a fast mode compressional wave to kinetic Alfvén waves (KAWs) at the magnetopause, in which the magnetic field is oriented in the \\hat {z} direction perpendicular to the gradients in the background density and magnetic field (\\hat {x}). Following a stage dominated by linear physics in which KAWs with large wave numbers kx ρ i ˜ 1 (with ρ i being the ion Larmor radius) are generated near the Alfvén resonance surface, the growth of KAW modes with ky ρ i ˜ 1 is observed in the nonlinear stage when the amplitude of KAWs generated by linear mode conversion becomes large enough to drive a nonlinear parametric decay process. The transfer of energy to large perpendicular and azimuthal ky modes has been suggested to provide large transport across plasma boundaries. To understand the 3-D physics of transport in the mode conversion process, the ion cross-field line diffusion coefficient (D⊥) is calculated by following test particles of various energies in both 2-D and 3-D hybrid simulations. The results are discussed for cases with various wave amplitudes and magnetopause conditions.

  6. Solute diffusion in liquid metals

    NASA Technical Reports Server (NTRS)

    Bhat, B. N.

    1973-01-01

    A gas model of diffusion in liquid metals is presented. In this model, ions of liquid metals are assumed to behave like the molecules in a dense gas. Diffusion coefficient of solute is discussed with reference to its mass, ionic size, and pair potential. The model is applied to the case of solute diffusion in liquid silver. An attempt was made to predict diffusion coefficients of solutes with reasonable accuracy.

  7. Estimation of the Diffuse Attenuation Coefficient KdPAR Using MERIS Satellite Reflections for European Coastal Waters

    NASA Astrophysics Data System (ADS)

    Saulquin, Bertand; Hamdi, Anouar; Populus, Jacques; Loutier, Romain; Demaria, Julien; Mangin, Antoine; D'Andon, Odile Fanton

    2010-12-01

    Accurate estimations of the diffuse attenuation coefficient is critical to understand physical processes such as the heat transfer in the upper layer of the ocean and also biological processes such as phytoplankton photosynthesis in the ocean euphotic zone. Light availability in the water column and the seabed determine the euphotic zone and constraints the type and distribution of the algae species. The EuSeaMap project's aim is to characterize at a resolution of 250m the European infralitoral benthic zone, according to biology, physic and geology criteriums and using observations and models. Satellite observations of the diffuse attenuation coefficient of the downwelling spectral irradiance at wavelength 490 nm (Kd490) or the diffuse attenuation coefficient for the downwelling photosynthetically available radiation (KdPAR) is an effective method to provide large scale maps of these parameters at high spatial and temporal resolution. Several empirical and semi-analytical models are commonly used to derive the Kd490 and KdPAR maps from ocean colour satellite sensors such as the Medium Resolution Imaging Spectrometer Instrument (MERIS), the Sea- viewing Wide Field-of-view Sensor (SeaWiFS), and the Moderate Resolution Imaging Spectroradiometer (MODIS). Most of these existing empirical or semi- analytical models have been calibrated on open ocean waters and provide good results in these areas, but tend to underestimate the attenuation of light in coastal waters, our area of interest. We propose here a new estimation of the euphotic depth and the KdPAR for coastal European waters using MERIS reflectances at the resolution of 1km and 250 m. First, a semi-analytical model is used to estimate the Kd490, and in a second step, two relationships have been developed between the KdPAR and the Kd490 for respectively clear and turbid waters. Satellite-derived fields of Kd490 and the deduced KdPAR are validated using matchups collected over the world. Distribution maps of seabed algae are compared with the satellite-derived euphotic limit and the influence of the KdPAR on a hydrodynamic simulation is also illustrated.

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

    USGS Publications Warehouse

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

    2013-01-01

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

  9. Boron nitride nanotube as a delivery system for platinum drugs: Drug encapsulation and diffusion coefficient prediction.

    PubMed

    Khatti, Zahra; Hashemianzadeh, Seyed Majid

    2016-06-10

    Molecular dynamics (MD) simulation has been applied to investigate a drug delivery system based on boron nitride nanotubes, particularly the delivery of platinum-based anticancer drugs. For this propose, the behavior of carboplatin drugs inserted in boron nitride nanotubes (BNNT) as a carrier was studied. The diffusion rate of water molecules and carboplatin was investigated inside functionalized and pristine boron nitride nanotubes. The penetration rate of water and drug in functionalized BNNT was higher than that in pristine BNNT due to favorable water-mediated hydrogen bonding in hydroxyl edge-functionalized BNNT. Additionally, the encapsulation of multiple carboplatin drugs inside functionalized boron nitride nanotubes with one to five drug molecules confined inside the nanotube cavity was examined. At high drug loading, the hydrogen bond formation between adjacent drugs and the non-bonded van der Waals interaction between carboplatin and functionalized BNNT inner surface were found to be influential in drug displacement within the functionalized BNNT cavity for higher drug-loading capacity. PMID:27084121

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

    PubMed

    Omoto, Akira

    2013-01-01

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

  11. Surface diffusion activation energy determination using ion beam microtexturing

    NASA Technical Reports Server (NTRS)

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

    1982-01-01

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

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

    NASA Technical Reports Server (NTRS)

    James, W. P.

    1971-01-01

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

  13. 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.

  14. Ion transport and loss in the Earth's quiet ring current. 2: Diffusion and magnetosphere-ionosphere coupling

    NASA Technical Reports Server (NTRS)

    Sheldon, R. B.

    1994-01-01

    We have studied the transport and loss of H(+), He(+), and He(++) ions in the Earth's quiet time ring current (1 to 300 keV/e, 3 to 7 R(sub E), Kp less than 2+, absolute value of Dst less than 11, 70 to 110 degs pitchangles, all LT) comparing the standard radial diffusion model developed for the higher-energy radiation belt particles with measurements of the lower energy ring current ions in a previous paper. Large deviations of that model, which fit only 50% of the data to within a factor of 10, suggested that another transport mechanism is operating in the ring current. Here we derive a modified diffusion coefficient corrected for electric field effects on ring current energy ions that fit nearly 80% of the data to within a factor of 2. Thus we infer that electric field fluctuations from the low-latitude to midlatitude ionosphere (ionospheric dynamo) dominated the ring current transport, rather than high-latitude or solar wind fluctuations. Much of the remaining deviation may arise from convective electric field transport of the E less than 30 keV particles. Since convection effects cannot be correctly treated with this azimuthally symmetric model, we defer treatment of the lowest-energy ions to a another paper. We give chi(exp 2) contours for the best fit, showing the dependence of the fit upon the internal/external spectral power of the predicted electric and magnetic field fluctuations.

  15. MODIS-based retrieval of suspended sediment concentration and diffuse attenuation coefficient in Chinese estuarine and coastal waters

    NASA Astrophysics Data System (ADS)

    Sokoletsky, Leonid; Yang, Xianping; Shen, Fang

    2014-11-01

    Radiative transfer modelling in atmosphere, water, and on the air-water surface was used to create an algorithm and computer code for satellite monitoring Chinese estuarine and coastal waters. The atmospheric part of the algorithm is based on the Reference Evaluation of Solar Transmittance (REST) model for calculation of optical properties of the atmosphere from the top of the atmosphere to the target; for modelling optical properties from target towards satellite's sensor, an optical reciprocity principle has been used. An algorithm uses estimates derived from three different sources: 1) the MODIS-based software; 2) radiative transfer equations, and 3) well-known empirical relationships between measured parameters and optical depths and transmittances for such atmospheric components as molecules, aerosols, ozone, nitrogen dioxide, precipitable water vapor and uniformly mixed gases. Using this model allowed us to derive a reliable relationship relating an important parameter, the diffuse-to-global solar incoming irradiance ratio, to the aerosol optical thickness, solar zenith angle and wavelength. The surface and underwater parts of the algorithm contained theoretical and semi-empirical relationships between inherent (such as absorption, scattering and backscattering coefficients) and apparent (remote-sensing reflectance and diffuse attenuation coefficient, Kd) optical properties, and suspended sediment concentration (SSC) measured in the Yangtze River Estuary and its adjacent coastal area. The first false colour maps of SSC and Kd demonstrated a well accordance with the multi-year field observations in the region, and suggest promise for use of this algorithm for the regular monitoring of Chinese and worldwide natural waters.

  16. Effect of diffusion potential, osmosis and ion-exchange on transdermal drug delivery: theory and experiments.

    PubMed

    Hirvonen, J; Murtomäki, L; Kontturi, K

    1998-12-01

    Equations expressing the effect of the diffusion potential on the trace ion transfer across a porous charged membrane have been derived. These equations have been tested with experiments with human cadaver skin. The transfer of sotalol and salicylate was measured varying the salt (NaCl) concentration in the donor and receiver compartments. It appears that osmotic pressure and ion-exchange make a significant contribution to the flux enhancement by the diffusion potential. PMID:9801427

  17. Calculation of the convective heat transfer coefficient and thermal diffusivity of cucumbers using numerical simulation and the inverse method.

    PubMed

    da Silva, Wilton Pereira; E Silva, Cleide M D P S

    2014-09-01

    Cooling of fruits and vegetables, immediately after the harvest, has been a widely used method for maximizing post-harvest life. In this paper, an optimization algorithm and a numerical solution are used to determine simultaneously the convective heat transfer coefficient, hH, and the thermal diffusivity, α, for an individual solid with cylindrical shape, using experimental data obtained during its cooling. To this end, the one-dimensional diffusion equation in cylindrical coordinates is discretized and numerically solved through the finite volume method, with a fully implicit formulation. This solution is coupled to an optimizer based on the inverse method, in which the chi-square referring to the fit of the numerical simulation to the experimental data is used as objective function. The optimizer coupled to the numerical solution was applied to experimental data relative to the cooling of a cucumber. The obtained results for α and hH were coherent with the values available in the literature. With the results obtained in the optimization process, the cooling kinetics of cucumbers was described in details. PMID:25190830

  18. Simultaneous Measurement of Thermal Diffusivity and Optical Absorption Coefficient of Solids Using PTR and PPE: A Comparison

    NASA Astrophysics Data System (ADS)

    Fuente, R.; Mendioroz, A.; Apiñaniz, E.; Salazar, A.

    2012-11-01

    Modulated photothermal radiometry (PTR) and a modulated photopyroelectric (PPE) technique have been widely used to measure the thermal diffusivity of bulk materials. The method is based on illuminating the sample with a plane light beam and measuring the infrared emission with an infrared detector (PTR) or the electric voltage produced by a pyroelectric sensor in contact with the sample (PPE). The amplitude and phase of both photothermal signals are recorded as a function of the modulation frequency and then fitted to the theoretical model. In this work, we compare the ability of modulated PTR and PPE to retrieve simultaneously the thermal diffusivity and the optical absorption coefficient of homogeneous slabs. In order to eliminate the instrumental factor, self-normalization is used, i.e., the ratio of the photothermal signal recorded at the rear and front surfaces. The influence of the multiple reflections of the light beam and the transparency to infrared wavelengths are analyzed. Measurements performed on a wide variety of homogeneous materials, transparent and opaque, good and bad thermal conductors, confirm the validity of the method. The advantages and disadvantages of both techniques are discussed.

  19. On the relationship between the apparent diffusion coefficient and extravascular extracellular volume fraction in human breast cancer.

    PubMed

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

    2011-06-01

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

  20. A new phantom and empirical formula for apparent diffusion coefficient measurement by a 3 Tesla magnetic resonance imaging scanner

    PubMed Central

    HARA, MARINA; KURODA, MASAHIRO; OHMURA, YUICHI; MATSUZAKI, HIDENOBU; KOBAYASHI, TOMOKI; MURAKAMI, JUN; KATASHIMA, KAZUNORI; ASHIDA, MASAKAZU; OHNO, SEIICHIRO; ASAUMI, JUN-ICHI

    2014-01-01

    The aim of this study was to create a new phantom for a 3 Tesla (3T) magnetic resonance imaging (MRI) device for the calculation of the apparent diffusion coefficient (ADC) using diffusion-weighted imaging (DWI), and to mimic the ADC values of normal and tumor tissues at various temperatures, including the physiological body temperature of 37°C. The phantom was produced using several concentrations of sucrose from 0 to 1.2 M, and the DWI was performed using various phantom temperatures. The accurate ADC values were calculated using the DWIs of the phantoms, and an empirical formula was developed to calculate the ADC values of the phantoms from an arbitrary sucrose concentration and arbitrary phantom temperature. The empirical formula was able to produce ADC values ranging between 0.33 and 3.02×10−3 mm2/sec, which covered the range of ADC values of the human body that have been measured clinically by 3T MRI in previous studies. The phantom and empirical formula developed in this study may be available to mimic the ADC values of the clinical human lesion by 3T MRI. PMID:25013504

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

    NASA Astrophysics Data System (ADS)

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

    2009-10-01

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

  2. Decreased tumor apparent diffusion coefficient correlates with objective response of pediatric low-grade glioma to bevacizumab.

    PubMed

    Hsu, Christopher H; Lober, Robert M; Li, Matthew D; Partap, Sonia; Murphy, Patricia A; Barnes, Patrick D; Fisher, Paul G; Yeom, Kristen W

    2015-05-01

    Recent small, retrospective series suggest bevacizumab may be a therapeutic option for recurrent pediatric low-grade glioma (LGG). Assessment of therapeutic responses is complicated by the unpredictable natural history of these tumors. Because diffusion-weighted imaging quantifies microscopic water motion affected by cellular density and histologic features, we hypothesized that it may be helpful in monitoring therapeutic response of LGG to bevacizumab. We retrospectively reviewed eight consecutive patients, median age 4.8 (range 2.3-12.3) years at initiation of bevacizumab therapy for recurrent or refractory LGG. Patients received 10 mg/kg/dose every 2 weeks (median 16 doses/therapy course). Mean apparent diffusion coefficient (ADC) was measured and analyzed in respect to tumor volume. Following the first treatment course, seven of eight patients had reduced tumor volume (≥25 %) and ADC. The median decrease in tumor volume was 47% (range -6 to 78 %) and the median decrease in ADC was 14 % (range -5 to 30 %). The ADC was significantly decreased during therapy, whereas the decrease in volume was seen only after therapy completion. There was a positive correlation between percent change in tumor volume and ADC (p < 0.05). We report a decrease in tumor ADC during initial bevacizumab therapy that is accompanied by a decrease in volume following therapy. Imaging changes in microscopic water motion associated with histology may be useful in monitoring the therapeutic response of LGG to bevacizumab. PMID:25758812

  3. Effect of inflow density on ion diffusion region of magnetic reconnection: Particle-in-cell simulations

    SciTech Connect

    Wu, P.; Shay, M. A.; Phan, T. D.; Oieroset, M.; Oka, M.

    2011-11-15

    We perform a systematic study of the effect of inflow density on reconnection diffusion regions using a 2.5-D particle-in-cell code. The diffusion region structures are analyzed at times when all simulations have reconnected the same amount of magnetic flux. We find that reducing the inflow density from 1 to 1/100th of the current sheet density dramatically increases the diffusion region physical size and the reconnection rate. The width of the diffusion region scales with the upstream ion inertial length systematically. Consistent with the presence of counter-streaming inflowing ion beams near the x-line, the ion meandering width in the diffusion region also scales with the ion inertial length. The aspect ratio of the ion diffusion region remains a constant, independent of the inflow density. The quadrupole Hall magnetic field is reduced. The upstream magnetic field deviates from its asymptotic value by {approx}50% at the lowest simulated inflow density. The downstream ion outflow velocity scales linearly with the upstream Alfven speed with a multiplication factor {approx}0.4 < 1. When applied to magnetic reconnection in the Earth's magnetotail, this factor of 0.4 is a possible explanation as to why bulk flow velocities in the magnetotail are typically on the order of 500 km/s, while the Alfven speeds of inflowing plasmas can exceed 2000 km/s.

  4. Assessment of apparent diffusion coefficient values as predictor of aggressiveness in peripheral zone prostate cancer: comparison with Gleason score.

    PubMed

    Anwar, Shayan Sirat Maheen; Anwar Khan, Zahid; Shoaib Hamid, Rana; Haroon, Fahd; Sayani, Raza; Beg, Madiha; Khattak, Yasir Jamil

    2014-01-01

    Purpose. To determine association between apparent diffusion coefficient value on diffusion-weighted imaging and Gleason score in patients with prostate cancer. Methods. This retrospective case series was conducted at Radiology Department of Aga Khan University between June 2009 and June 2011. 28 patients with biopsy-proven prostate cancer were included who underwent ultrasound guided sextant prostate biopsy and MRI. MRI images were analyzed on diagnostic console and regions of interest were drawn. Data were entered and analyzed on SPSS 20.0. ADC values were compared with Gleason score using one-way ANOVA test. Results. In 28 patients, 168 quadrants were biopsied and 106 quadrants were positive for malignancy. 89 lesions with proven malignancy showed diffusion restriction. The mean ADC value for disease with a Gleason score of 6 was 935 mm(2)/s (SD = 248.4 mm(2)/s); Gleason score of 7 was 837 mm(2)/s (SD = 208.5 mm(2)/s); Gleason score of 8 was 614 mm(2)/s (SD = 108 mm(2)/s); and Gleason score of 9 was 571 mm(2)/s (SD = 82 mm(2)/s). Inverse relationship was observed between Gleason score and mean ADC values. Conclusion. DWI and specifically quantitative ADC values may help differentiate between low-risk (Gleason score, 6), intermediate-risk (Gleason score, 7), and high-risk (Gleason score 8 and 9) prostate cancers, indirectly determining the aggressiveness of the disease. PMID:24967293

  5. 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.

  6. First-principles binary diffusion coefficients for H, H{sub 2}, and four normal alkanes + N{sub 2}

    SciTech Connect

    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 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%.

  7. Radial diffusion of low-energy plasma ions in Saturn's magnetosphere

    NASA Technical Reports Server (NTRS)

    Barbosa, D. D.

    1990-01-01

    Radial diffusion of low-energy plasma ions in Saturn's magnetosphere is investigated using a comprehensive set of equations for radial diffusion that incorporate distributed sources and sinks of ions. The results of calculations indicate that the radial-diffusion transport of low-energy O(+) ions with a source in the neutral H2O cloud of the satellites Dione and Tethys can account for Voyager observations of thermal heavy ions in Saturn's magnetosphere. The source rate was calculated to be about 10 to the 26th O(+) ions/sec, in good agreement with the sputtering calculations of Johnson et al. (1989). It is estimated that, due to fast radial diffusion, the residence time of O(+) ions in the Dione-Tethys torus is about 30 days, sufficiently short to account for the plasma density observed there. The densities of hot H(+) and N(+) resulting from the ionization and pickup of Titan's neutral clouds in the outer magnetosphere can also be accounted for within the framework of diffusive ion transport.

  8. Diffusion-weighted imaging and the apparent diffusion coefficient on 3T MR imaging in the differentiation of craniopharyngiomas and germ cell tumors.

    PubMed

    Kinoshita, Yasuyuki; Yamasaki, Fumiyuki; Tominaga, Atsushi; Ohtaki, Megu; Usui, Satoshi; Arita, Kazunori; Sugiyama, Kazuhiko; Kurisu, Kaoru

    2016-04-01

    The apparent diffusion coefficient (ADC) on diffusion-weighted imaging (DWI) plays an important role in diagnosing intracranial tumors and predicting the histopathological grade of the tumor. However, the differences in the ADC values between craniopharyngiomas and germ cell tumors (GCTs) have not been clarified. We therefore evaluated the DWI and ADC values at b = 1000 and b = 4000 s/mm(2) on 3T magnetic resonance (MR) imaging and assessed the possibility of differentiating between craniopharyngiomas and GCTs. We retrospectively reviewed 19 patients with craniopharyngioma and 24 patients with GCT who underwent surgery and received a histopathological diagnosis. Thirty-four patients underwent DWI with b = 1000 and b = 4000 s/mm(2) and nine patients underwent periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) DWI with b = 1000 s/mm(2). The ADC was determined by manually placing regions of interests (ROIs) in the respective tumor regions on the ADC maps and is expressed as the minimum (ADCMIN), mean (ADCMEAN), and maximum (ADCMAX) absolute values. The craniopharyngiomas showed lower intensity on DWI at b = 1000 and b = 4000 s/mm(2) than the GCTs. Furthermore, the craniopharyngiomas demonstrated significantly high ADC values (ADCMIN, ADCMEAN, and ADCMAX) in comparison with the GCTs on DWI at b = 1000 and b = 4000 s/mm(2). The logistic discriminant analysis clarified the advantage of ADCMIN at b = 4000 s/mm(2) in differentiating between craniopharyngiomas and GCTs compared with the other ADC values. DWI and the ADC values may help clinicians to differentiate between craniopharyngiomas and GCTs. The ADCMIN at b = 4000 s/mm(2) is particularly useful for differentiation. PMID:26280640

  9. Ion chamber absorbed dose calibration coefficients, N{sub D,w}, measured at ADCLs: Distribution analysis and stability

    SciTech Connect

    Muir, B. R.

    2015-04-15

    Purpose: To analyze absorbed dose calibration coefficients, N{sub D,w}, measured at accredited dosimetry calibration laboratories (ADCLs) for client ionization chambers to study (i) variability among N{sub D,w} coefficients for chambers of the same type calibrated at each ADCL to investigate ion chamber volume fluctuations and chamber manufacturing tolerances; (ii) equivalency of ion chamber calibration coefficients measured at different ADCLs by intercomparing N{sub D,w} coefficients for chambers of the same type; and (iii) the long-term stability of N{sub D,w} coefficients for different chamber types by investigating repeated chamber calibrations. Methods: Large samples of N{sub D,w} coefficients for several chamber types measured over the time period between 1998 and 2014 were obtained from the three ADCLs operating in the United States. These are analyzed using various graphical and numerical statistical tests for the four chamber types with the largest samples of calibration coefficients to investigate (i) and (ii) above. Ratios of calibration coefficients for the same chamber, typically obtained two years apart, are calculated to investigate (iii) above and chambers with standard deviations of old/new ratios less than 0.3% meet stability requirements for accurate reference dosimetry recommended in dosimetry protocols. Results: It is found that N{sub D,w} coefficients for a given chamber type compared among different ADCLs may arise from differing probability distributions potentially due to slight differences in calibration procedures and/or the transfer of the primary standard. However, average N{sub D,w} coefficients from different ADCLs for given chamber types are very close with percent differences generally less than 0.2% for Farmer-type chambers and are well within reported uncertainties. Conclusions: The close agreement among calibrations performed at different ADCLs reaffirms the Calibration Laboratory Accreditation Subcommittee process of ensuring ADCL conformance with National Institute of Standards and Technology standards. This study shows that N{sub D,w} coefficients measured at different ADCLs are statistically equivalent, especially considering reasonable uncertainties. This analysis of N{sub D,w} coefficients also allows identification of chamber types that can be considered stable enough for accurate reference dosimetry.

  10. Calculation of the fractional interstitial component of boron diffusion and segregation coefficient of boron in Si0.8Ge0.2

    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.

  11. Using the apparent diffusion coefficient to identifying MGMT promoter methylation status early in glioblastoma: importance of analytical method

    SciTech Connect

    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

    2015-06-15

    Accurate knowledge of O{sup 6}-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. 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. 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). 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.

  12. Dust particle diffusion in ion beam transport region

    NASA Astrophysics Data System (ADS)

    Miyamoto, N.; Okajima, Y.; Romero, C. F.; Kuwata, Y.; Kasuya, T.; Wada, M.

    2016-02-01

    Dust particles of μm size produced by a monoplasmatron ion source are observed by a laser light scattering. The scattered light signal from an incident laser at 532 nm wavelength indicates when and where a particle passes through the ion beam transport region. As the result, dusts with the size more than 10 μm are found to be distributed in the center of the ion beam, while dusts with the size less than 10 μm size are distributed along the edge of the ion beam. Floating potential and electron temperature at beam transport region are measured by an electrostatic probe. This observation can be explained by a charge up model of the dust in the plasma boundary region.

  13. Contribution to the benchmark for ternary mixtures: Measurement of diffusion and Soret coefficients in 1,2,3,4-tetrahydronaphthalene, isobutylbenzene, and dodecane onboard the ISS.

    PubMed

    Khlybov, Oleg A; Ryzhkov, Ilya I; Lyubimova, Tatyana P

    2015-04-01

    The paper is devoted to processing the data of DCMIX 1 space experiment. In this experiment, the Optical digital interferometry was used to measure the diffusion and Soret coefficients in the ternary mixture of 1,2,3,4-tetrahydronaphthalene, isobutylbenzene and n-dodecane at mass fractions of 0.8/0.1/0.1 and at 25°C. The raw interferometric images were processed to obtain the temporal and spatial evolution of refractive indices for two laser beams of different wavelengths. The method for extracting the diffusion and thermal diffusion coefficients originally developed for optical beam deflection was extended to optical digital interferometry allowing for the spatial variation of refractive index along the diffusion path. The method was validated and applied to processing the data for Soret and diffusion steps in 5 experimental runs. The obtained results for the Soret coefficients and one of the eigenvalues of diffusion matrix showed acceptable agreement within each step. The second eigenvalue was not determined with sufficient accuracy. PMID:25916235

  14. Erbium diffusion in silicon dioxide

    SciTech Connect

    Lu Yingwei; Julsgaard, B.; Petersen, M. Christian; Jensen, R. V. Skougaard; Pedersen, T. Garm; Pedersen, K.; Larsen, A. Nylandsted

    2010-10-04

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

  15. Quantifying the rate of biofilm growth of S. meliloti strains in microfluidics via the diffusion coefficient of microspheres

    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 (χ2(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.

  16. Investigation of Relationships Between Transverse Relaxation Rate, Diffusion Coefficient, and Labeled Cell Concentration in Ischemic Rat Brain Using MRI

    PubMed Central

    Athiraman, Hemanthkumar; Jiang, Quan; Ding, Guang Liang; Zhang, Li; Zhang, Zheng Gang; Wang, Lei; Arbab, Ali S.; Li, Qingjiang; Panda, Swayam; Ledbetter, Karen; Rad, Ali M.; Chopp, Michael

    2009-01-01

    MRI has been used to evaluate labeled cell migration and distribution. However, quantitative determination of labeled cell concentration using MRI has not been systematically investigated. In the current study, we investigated the relationships between labeled cell concentration and MRI parameters of transverse relaxation rate, R2, and apparent diffusion coefficient (ADC), in vitro in phantoms and in vivo in rats after stroke. Significant correlations were detected between iron concentration or labeled cell concentration and MRI measurements of R2, ADC, and ADC×R2 in vitro. In contrast, in vivo labeled cell concentration did not significantly correlate with R2, ADC, and ADC×R2. A major factor for the absence of a significant correlation between labeled cell concentration and MRI measurements in vivo may be attributed to background effects of ischemic tissue. By correcting the background effects caused by ischemic damage, ΔR2 (difference in R2 values in the ischemic tissue with and without labeled cells) exhibited a significant correlation to labeled cell concentration. Our study suggests that MRI parameters have the potential to quantitatively determine labeled cell concentration in vivo. PMID:19107898

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

    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.

  18. Evaluation of extra- and intracellular apparent diffusion coefficient of sodium in rat skeletal muscle: effects of prolonged ischemia.

    PubMed

    Babsky, Andriy M; Topper, Stephen; Zhang, Hong; Gao, Yong; James, Judy R; Hekmatyar, Shahryar K; Bansal, Navin

    2008-03-01

    The mechanism of water and sodium apparent diffusion coefficient (ADC) changes in rat skeletal muscle during global ischemia was examined by in vivo 1H and 23Na magnetic resonance spectroscopy (MRS). The ADCs of Na+ and water are expected to have similar characteristics because sodium is present as an aqua-cation in tissue. The shift reagent, TmDOTP5(-), was used to separate intra- and extracellular sodium (Na+i and Na+e, respectively) signals. Water, total tissue sodium (Na+t), Na+i, and Na+e ADCs were measured before and 1, 2, 3, and 4 hr after ischemia. Contrary to the general perception, Na+i and Na+e ADCs were identical before ischemia. Thus, ischemia-induced changes in Na+e ADC cannot be explained by a simple change in the size of relative intracellular or extracellular space. Na+t and Na+e ADCs decreased after 2-4 hr of ischemia, while water and Na+i ADC remained unchanged. The correlation between Na+t and Na+e ADCs was observed because of high Na+e concentration. Similarly, the correlation between water and Na+i ADCs was observed because cells occupy 80% of the tissue space in the skeletal muscle. Ischemia also caused an increase in the Na+i and an equal decrease in Na+e signal intensity due to cessation of Na+/K+-ATPase function. PMID:18306401

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

    PubMed

    Quinn, John G

    2012-02-15

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

  20. Enhancing tumor apparent diffusion coefficient histogram skewness stratifies the postoperative survival in recurrent glioblastoma multiforme patients undergoing salvage surgery.

    PubMed

    Zolal, Amir; Juratli, Tareq A; Linn, Jennifer; Podlesek, Dino; Sitoci Ficici, Kerim Hakan; Kitzler, Hagen H; Schackert, Gabriele; Sobottka, Stephan B; Rieger, Bernhard; Krex, Dietmar

    2016-05-01

    Objective To determine the value of apparent diffusion coefficient (ADC) histogram parameters for the prediction of individual survival in patients undergoing surgery for recurrent glioblastoma (GBM) in a retrospective cohort study. Methods Thirty-one patients who underwent surgery for first recurrence of a known GBM between 2008 and 2012 were included. The following parameters were collected: age, sex, enhancing tumor size, mean ADC, median ADC, ADC skewness, ADC kurtosis and fifth percentile of the ADC histogram, initial progression free survival (PFS), extent of second resection and further adjuvant treatment. The association of these parameters with survival and PFS after second surgery was analyzed using log-rank test and Cox regression. Results Using log-rank test, ADC histogram skewness of the enhancing tumor was significantly associated with both survival (p = 0.001) and PFS after second surgery (p = 0.005). Further parameters associated with prolonged survival after second surgery were: gross total resection at second surgery (p = 0.026), tumor size (0.040) and third surgery (p = 0.003). In the multivariate Cox analysis, ADC histogram skewness was shown to be an independent prognostic factor for survival after second surgery. Conclusion ADC histogram skewness of the enhancing lesion, enhancing lesion size, third surgery, as well as gross total resection have been shown to be associated with survival following the second surgery. ADC histogram skewness was an independent prognostic factor for survival in the multivariate analysis. PMID:26830088

  1. The difference of apparent diffusion coefficient in the middle cerebellar peduncle among parkinsonian syndromes: Evidence from a meta-analysis.

    PubMed

    Sako, Wataru; Murakami, Nagahisa; Izumi, Yuishin; Kaji, Ryuji

    2016-04-15

    The measurement of middle cerebellar peduncle (MCP) width allows for differential diagnosis between Parkinson's disease (PD) and multiple system atrophy with predominant parkinsonian features (MSA-P). However, it remains controversial whether apparent diffusion coefficient (ADC) value in the MCP of MSA-P is elevated or not. In the present study, we aimed to assess the usefulness of ADC value in the MCP for differential diagnosis between PD and MSA-P. An on-line literature search yielded 5 eligible studies. We expressed between-group difference of ADC value as the standardized mean difference (SMD). The proportion of variation due to heterogeneity was computed and expressed as I(2). ADC in the MCP of MSA-P was significantly increased compared with PD with heterogeneous studies (P=0.0007, I(2)=81%). A meta-regression analysis of MSA-P was conducted for "UPDRS III", and revealed a significant correlation between UPDRS III and SMD (P=0.01). Our meta-regression analysis has clarified the contribution of severity of MSA-P to heterogeneity of the included studies for ADC in the MCP. This finding raised the possibility that ADC in the MCP depended on severity of MSA-P, and less severe patients with MSA-P should be mainly enrolled in future study to assess the ability for differential diagnostic tool. PMID:27000228

  2. The Heavy-Ion Approximation for Ambipolar Diffusion Calcuations for Weakly Ionized Plasmas

    SciTech Connect

    Li, P; McKee, C; Klein, R

    2006-07-27

    Ambipolar diffusion redistributes magnetic flux in weakly ionized plasmas and plays a critical role in star formation. Simulations of ambipolar diffusion using explicit MHD codes are prohibitively expensive for the level of ionization observed in molecular clouds ({approx}< 10{sup -6}) since an enormous number of time steps is required to represent the dynamics of the dominant neutral component with a time step determined by the trace ion component. Here we show that ambipolar diffusion calculations can be significantly accelerated by the 'heavy-ion approximation', in which the mass density of the ions is increased and the collisional coupling constant with the neutrals decreased such that the product remains constant. In this approximation, the ambipolar diffusion time and the ambipolar magnetic Reynolds number remain unchanged. We present three tests of the heavy-ion approximation: C-type shocks, the Wardle instability, and the 1D collapse of a magnetized slab. We show that this approximation is quite accurate provided that (1) the square of the Alfven Mach number is small compared to the ambipolar diffusion Reynolds number for dynamical problems, and that (2) the ion mass density is negligible for quasi-static problems; a specific criterion is given for the magnetized slab problem. The first condition can be very stringent for turbulent flows with large density fluctuations.

  3. Oxygen diffusion and oxide phase formation in iron under swift heavy ion irradiation

    SciTech Connect

    Roller, Tobias; Bolse, Wolfgang

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

  5. Ion diffusion at the bonding interface of undoped YAG/Yb:YAG composite ceramics

    NASA Astrophysics Data System (ADS)

    Fujioka, Kana; Sugiyama, Akira; Fujimoto, Yasushi; Kawanaka, Junji; Miyanaga, Noriaki

    2015-08-01

    Cation diffusion across a boundary between ytterbium (Yb)-doped and undoped yttrium aluminum garnet (YAG) ceramics was examined by electron microprobe analysis (EPMA). Polished Yb:YAG and undoped YAG ceramics were bonded by surface treatment with argon fast atom beam, and then heat-treated at 1400 or 1600 °C for 50 h or at 1400 °C for 10 h under vacuum. We obtained EPMA mapping images of the bonded samples that clearly showed the bulk and grain-boundary diffusion of Y and Yb ions. The number density profiles showed that the total diffusion distances of Yb and Y ions were almost equal and approximately 2 and 15 μm at 1400 and 1600 °C, respectively, and the dependence of diffusion distance on heating time was weak. The diffusion curves were well modeled by Harrison type B kinetics including bulk and grain-boundary diffusion. In addition, it was found that Si ions added to the samples as a sintering aid might be segregated at the grain boundary by heat treatment, and diffused only along grain boundaries.

  6. Ion collision cross sections and transport coefficients extended to intermediate energies and reduced electric fields for He(2)(+) ions colliding with He.

    PubMed

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

    2013-10-01

    This work is devoted to the calculation of transport coefficients for He(2)(+) ions in gaseous He at intermediate reduced electric fields. These swarm data are of great interest for a better understanding of the mechanisms of formation and propagation of the fast plasma bullets or ionization waves observed in dielectric barrier plasma jet devices. For transport data, the collision cross sections required are determined from several theoretical methods based on quantum, semiclassical, and hybrid approaches and a diatomics-in-molecules model for the potential energy surfaces of He(2)(+). The corresponding collision cross sections are then used in an optimized Monte Carlo code to calculate the ion transport coefficients over a wide range of reduced electric fields extending over the experimental range. Calculated transport coefficients are compared with available experimental data at low electric fields. Moreover, an extrapolation method is used in order to determine the reduced mobility for stronger fields. A critical discussion has been performed on the pertinence and the reliability of these different methods of determination of collision cross sections needed for the calculation of ion transport data. Such ion 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:24229290

  7. In-vivo method for determining and imaging temperature of an object/subject from diffusion coefficients obtained by nuclear magnetic resonance

    SciTech Connect

    LeBihan, D.; DeLannoy, J.; Levin, R.L.

    1988-08-19

    A method of determining and imaging the temperature or the temperature change of an object (human, animal, liquid, or solid) by nuclear magnetic resonance of molecular diffusion coefficients is presented. Because of the noninvasive, nondestructive and nonionizing properties of nuclear magnetic resonance, this invention may be employed in an object or an animal continuously.

  8. Evaluation of normal appearing spinal cord by diffusion tensor imaging, fiber tracking, fractional anisotropy, and apparent diffusion coefficient measurement in 13 dogs

    PubMed Central

    2013-01-01

    Background Functional magnetic resonance (fMR) imaging offers plenty of new opportunities in the diagnosis of central nervous system diseases. Diffusion tensor imaging (DTI) is a technique sensitive to the random motion of water providing information about tissue architecture. We applied DTI to normal appearing spinal cords of 13 dogs of different breeds and body weights in a 3.0 T magnetic resonance (MR) scanner. The aim was to study fiber tracking (FT) patterns by tractography and the variations of the fractional anisotropy (FA) and the apparent diffusion coefficient (ADC) observed in the spinal cords of dogs with different sizes and at different locations (cervical and thoracolumbar). For that reason we added a DTI sequence to the standard clinical MR protocol. The values of FA and ADC were calculated by means of three regions of interest defined on the cervical or the thoracolumbar spinal cord (ROI 1, 2, and 3). Results The shape of the spinal cord fiber tracts was well illustrated following tractogra