Values Of Transport Coefficients Research Articles

Comment on “Thermodynamic and transport properties of dense hydrogen plasmas”

In a recent paper H. Reinholz, R. Redmer, and S. Nagel [Phys. Rev. E. 52, 5368 (1995)] developed a model of thermodynamic and transport properties of dense hydrogen plasmas, based on the Debye screening potential with the characteristic length interpolating between Debye and Thomas-Fermi radii. It is shown that under the thermodynamic conditions considered this model potential is inapplicable, and the electrical conductivity values predicted are inconsistent with available experimental data. I conclude that the results of Reinholz, Redmer, and Nagel on the plasma composition and the transport coefficient values are thus dubious.

Time‐resolved laser‐induced thermal grating experiments induced by short pulse CO2‐laser radiation

AbstractUsing a high pressure carbon dioxide laser with pulse lengths of 80 ns laser‐induced thermal grating spectroscopy (LITGS) experiments have been carried out in gas mixtures consisting of an absorbing species (ethylene) and buffer gases (nitrogen/helium) at various temperatures and pressures. The grating structure is written into the medium by absorption and subsequent collisional relaxation of CO2‐laser radiation. Transport properties in these mixtures such as thermal conductivity and the speed of sound have been determined from the time‐resolved signal generated by Bragg scattering of a continuous wave HeNe‐laser beam off the grating structure. Accurate numerical values for transport coefficients are obtained from fitting analytical expressions to the measured oscillating signal traces and are compared with literature values.

Cosmic ray momentum diffusion in the presence of nonlinear Alfvén waves

Abstract. The relation between the spatial diffusion coefficient along the magnetic field, kII, and the momentum diffusion coefficient, Dp, for relativistic cosmic ray particles is modelled using Monte Carlo simulations. Wave fields with vanishing wave helicity and cross-helicity, constructed by superposing 'Alfvén-like' waves are considered. As the result, particle trajectories in high amplitude wave fields and then - by averaging over these trajectories - the values of transport coefficients are derived. The modelling is performed at various wave amplitudes, from δ B/B0 = 0.15 to 2.0, and for a number of wave field types. At our small amplitudes approximately the quasi-linear theory (QLT) estimates for kII and Dp are reproduced. However, with growing wave amplitude the simulated results show a small divergence from the QLT ones, with kII decreasing slower than theoretical prediction and the opposite being true for Dp. The wave field form gives only a slight influence on the wave-particle interactions at large wave amplitudes δ B/B0 ~ 1. The parameter characterizing the relative efficiency of the second-order to the first-order acceleration at shock waves, Dp κII is given in the QLT approximation by the Skilling formula V2A p2 / 9. In simulations together with increasing δ B it increases above this scale in all the cases under our study. Consequences of the present results for the second-order Fermi acceleration at shock waves are briefly addressed.

Prediction of Phase Separation During the Drying of Polymer Shells

During the drying of polymer shells formed by microencapsulation, vacuole formation is believed to occur as a result of phase separation. To better understand and control this process, we have used a multicomponent diffusion formalism to predict compositional changes in the layer as organic solvents diffuse out and water diffuses into the layer. Formation of thermodynamically unstable compositions can lead to phase separation by condensation of water on submicron foreign particles present in the shell wall. We used statistical mechanics, the UNIFAP methodology, and empirical data to deduce the required values of transport coefficients and equilibrium phase compositions. The results suggest that vacuole formation can be eliminated or reduced by removing submicron and larger particles from the shell wall and by using solvents with lower intrinsic water solubilities. 21 refs., 7 figs.

Water channels in plants: do basic concepts of water transport change?

A review and re-examination of literature data shows that highly selective water channels (aquaporins) have marked effects on the overall transport properties of the plasma membrane of plant cells. The application of the channel blocker HgCl2 (50 μM) or of high external concentrations of permeating solutes reduced the water permeability (hydraulic conductivity, Lp) of Chara internodes down to 25% of the control. In treated cells, reflection coefficients (σs) of permeating low molecular weight organic test solutes (alcohols, amides, ketones) were markedly reduced as well, but solute permeability (permeability coefficient, Ps) remained constant. A similar relation between Lp and σs was found with untreated cells of isolated epidermis of Tradescantia virginiana. The results can not be interpreted in terms of conventional membrane models (pore or solubility membrane); for instance, the classical frictional pore model (Dainty and Ginzburg, 1963) fails to explain low σs of rapidly permeating solutes. The results fit into a model which treats the membrane as a composite structure with proteinaceous arrays (containing water channels) in parallel with lipid arrays (‘composite transport model’). Test solutes predominantly pass across the lipid array which was not affected by treatments. Water, however, largely uses the water channel array which was affected. When using heavy water (HDO) as an osmotic solute, the transport pattern changed as predicted by the model. As indicated by low channel reflection coefficients of test solutes, water channels did not completely exclude small uncharged molecules and do show some permeability for the test solutes used. Low σs values of water channels are interpreted by a single-file mechanism of water and solute flow. Absolute values of transport coefficients (Lp, Ps, σs) represent mixed values to which the different membrane arrays contribute according to concepts available from irreversible thermodynamics. The patchy structure of the cell membrane results in a circulation flow of water in the membrane. The fact that water channels can be triggered by factors such as heavy metals and high concentration suggests that water transport can be regulated by opening or closing water channels. The results have consequences for our basic understanding of osmosis and water transport in plants.

Influence of departures from complete thermodynamic equilibrium on transport coefficient values: application to an oxygen plasma

The main transport coefficients (thermal and electrical conductivities, viscosity) of an oxygen plasma at atmospheric pressure and at lower pressures are calculated by a classical formalism described by Hirchfelder et al, using a plasma composition obtained from a collisional radiative model which allows the authors to take into account the influence of the radiation escape. Results show that the viscosity is not affected by departures from complete thermodynamic equilibrium but that electrical and thermal conductivities are appreciably affected, which has an effect on energy balance equations.

Stability of Computational Algorithm Used in Molecular Dynamics Simulations. 1st Report. For Velocity Verlet Algorithm.

The present study focuses attention on a three-dimensional Lennard-Jones system in a thermodynamic equilibrium to discuss the divergence processes, the relationships between time intervals and divergence times, and the influences of the time intervals on transport coefficients, under various conditions of number densities and temperatures. The main results obtained here are as follows : the velocities of molecules in the system increase gradually with time, and then the system diverges exponentially suddenly at a specific time ; the time interval-divergence time relationships can be expressed approximately as linear functions if the log-log scale is used, and the system diverges more easily as the temperature or the number density increases ; as long as such sufficiently small time intervals that the system does not diverge are used, the values of transport coefficients and thermodynamical quantities are approximately independent of the values of time intervals.

Effects of bound pairs on the low-density transport properties of gases

In some derivations of the Boltzmann equation, the equation which describes the time evolution of the distribution function in the phase space of the atoms of a low-density gas, it has been assumed that all of the trajectories in the phase space of the pairs of atoms are such that transforming back sufficiently far in time leads to separated atoms. In a recent development, it has been shown that if this is not true the ‘‘bound-state’’ trajectories lead to an addition to the collision integral which, in turn, leads to corrections to the values of the low-density transport coefficients. In the present alternate development, it is shown that the ‘‘bound-state’’ trajectories may be joined to trajectories in the ‘‘unbound region’’ through the introduction of a complex time and analytic continuation. With this generalization of the concept of trajectories, one may introduce the ‘‘molecular chaos assumption’’ in the usual manner, and the ‘‘collision integral’’ may be generalized to include the bound-state region of the phase space. This leads to ‘‘corrections’’ to the low-density limiting values of the transport coefficients. These effects of the bound pairs of atoms on the low-density transport coefficients of a gas of atoms which interact according to a Lennard-Jones potential are investigated numerically. It is found that the effects become important at temperatures, scaled in the usual manner by ε/k, below about unity. Specifically, it is found that at a scaled temperature of unity, corresponding to a temperature in the range of about 100–200 K, the effect is to lower the self-diffusion coefficient by about 3.7% and the viscosity and thermal conductivity by about 0.7%. The effects become significantly greater at lower temperatures.

Bi2 Te3 Crystals Heavily Doped with Tin Atoms

AbstractThe values of transport coefficients (Hall constant and Seebeck coefficient) of Bi2Te3 crystals strongly doped with Sn atoms are determined at room temperature. From reflectivity measurements in the IR region, the plasma resonance frequency ωp, relaxation time τ, and high frequency permittivity are found. The interpretation of the results obtained in the concentration interval, 0 < x < 3 × 1020 Sn atoms per cm3, leads to the conclusion that one part of the Sn atoms incorporated enters into the bismuth sublattice giving rise to negatively charged substitutional defects Sn'Bi, the other part forms uncharged defects. The formation of uncharged defects produced by the incorporation of Sn‐atoms into the Bi2Te3 crystal lattice is explained in the following way: Sn‐atoms form seven‐layer‐lamellae of the composition Te‐Bi‐Te‐Sn‐Te‐Bi‐Te which corresponds to the structure of the SnBi2Te4 compound; this seven‐layer‐lamella is uncharged. The formation of such a seven‐layer‐lamella can easily explain the experimental results: Sn‐atoms incorporated into the seven‐layer‐lamella are electrically inactive.

Bi2-xInxSe3 crystals; optical properties and transport coefficients

Single crystals of Bi2-xInxSe3 (x = 0.0-0.66) were prepared from the elements of 5N purity using the modified Bridgman method. On the samples with a various content of incorporated In-atoms the reflectivity in IR-region and the transport coefficients (electrical conductivity σ⊥, Hall coefficient RH (B ∥ c), Seebeck coefficient S⊥) were measured. The results showed that the In-atoms incorporation to the crystal lattice of Bi2Se3 in the region of small concentrations of In-atoms increases the free carriers concentration, in the region of higher concentrations of In-atoms the free carriers concentration is suppressed. On the ground of measured changes in the values of transport coefficients and optical parameters (determined from the interpretation of infrared reflectivity) a model of point defects in the Bi2-x Inx Se3 crystal lattice has been suggested. This model takes into account the existence of antisite defects Bi'Se in the Bi2Se3 crystal lattice the concentration of which is suppressed by incorporated In-atoms. The built-in In-atoms form uncharged defects InxBi which are positively polarized.

Numerical modelling of three-dimensional plasma cloud evolution in crossed E × B fields

A numerical solution of the complete three-dimensional equation system for plasma inhomogeneity evolution in crossed E × B fields is presented. The approximation of homogeneous infinite ambient plasma is considered. The model values of transport coefficients were used. The physical pattern of processes is discussed. The simple analytical formulae for plasma evolution at various stages are derived. These formulae are in good agreement with numerical results.

Translocation in the staminal hairs ofSetcreasea purpurea

Previously reported studies of cell ultrastructure and molecular probe passage in immature staminal hairs were extended to kinetic studies. The rate of transport of carboxyfluorescein into the cytoplasm in individual cells was monitored with a video analyzer and transport coefficients were determined. Carboxyfluorescein was found to traverse 5 cells in less than 5 minutes. The values of transport coefficients differed between cells and this was taken to mean that some cells are more closely coupled than others.

The Calculation of Transport Coefficients of Phosphate and Calcium Fluxes Across the Sediment-Water Interface, from Experiments with Undisturbed Sediment Cores

Fluxes of phosphate and calcium across the sediment-water interface of six undisturbed cores are investigated. Attention is paid to the accuracy of porewater extraction and the influence of this sampling upon the experiments. From this, it is concluded that sampling time should at least be one day. Continuous and batch experiments resulted in a rapid release of phosphorus and calcium from the sediment. The influence of induced seepage could not be shown. On a theoretical base, it is concluded that the benthic fluxes are fed by desorption at or just below the interface, rather than by diffusion from deeper layers. Hence, data of interstitial water could not directly be used for calculating the driving forces of these fluxes. Instead, endconcentrations in the overlaying water of the batch experiments are used, which resulted in values of transportcoefficients of 3–10.10−7 m.s−1, being in good agreement with theoretical as well as field data.

Correlation of the transport properties of simple fluids at low temperatures and high pressures based on the generalized Eucken relation and the molecular dynamics of hard sphere fluid

A generalized correlation is developed for the viscosity and thermal conductivity of isotropic fluids under high pressures (up to 200 MPa) and low temperatures (down to 85 K). Two known observations have been taken into consideration in the development of the correlation. First, the Alder correction factors for the Enskog theory values of transport coefficients obtained from molecular dynamics simulations for hard sphere fluids are incorporated. The inclusion of these corrections in the theory makes it possible to describe correctly the density dependence of the hard sphere viscosity and thermal conductivity at high pressures. The hydrodynamic “cage” effect, which is manifested in the molecular motions of dense fluid systems, is thus correctly accounted for. Second, the generalized Eucken relation, which relates the thermal conductivity to the viscosity, is incorporated. As a consequence, an internally consistent correlation is obtained, which can adequately predict the behavior of the thermal conductivity from given values of viscosity. Tests on simple fluids, such as argon, krypton, etc., show that the correlation is valid within a few percent for the entire fluid range where experimental data are available for comparison, and also along the vapor-liquid saturation line, with the exclusion of the critical region. Furthermore, since the variables appearing in the theory are in reduced form, a corresponding states correlation is established for isotropic fluids.

Evaluation of the performance of thermal diffusion column separating binary gas mixtures with continuous draw-off.

Advanced transport relations involving three column constants, Hσ, Kσc and Kσd are developed to describe the separation performance of a thermal diffusion column with continuous draw-off. These constants were related to some integral functions of velocity profile, temperature distribution, density of gas mixture and characteristic values of transport coefficients. The separation of binary gas mixture by this technique was so effective that three reasonable factors had to be introduced into the column constants in the theory. They are a circulation constant of natural convection, a definition of characteristic mean temperature and a definition of mean composition over the column. The separation performance and the column constants also varied with the distortion of velocity profile due to continuous draw-off from the top or the bottom of column. However, its effect was not large, compared with the other factors mentioned above. The theory presented here makes possible to estimate the separation performance of hot-wire type thermal diffusion column with high accuracy.

The interpretation of transport coefficients on the basis of the Van der Waals model

Abstract The Van der Waals model for transport properties which forms a very satisfactory basis for the interpretation of dense-gas transport-coefficient data, is applied to dilute gases to determine the effect of attractive forces between real molecules on the values of transport coefficients. It is found that experimental viscosity coefficient and thermal-conductivity coefficient data are lower than the values calculated by up to 40%. For the rare gases these differences are found to be related simply to the temperature and molar volume and expressions are given which reproduce the available experimental data generally to better than 2% over the whole density range.

Dynamic structure factor of liquid sodium: a generalized hydrodynamic approach

The dynamic structure factor, S(q, omega ), for liquid sodium is investigated by means of a generalized hydrodynamic approach, using a computed fourth moment, measured values of transport coefficients (as far as possible) and the experimentally determined specific heat ratio CP/CV. This ratio has characteristically a value of 1.1 to 1.3 for liquid metals, near their melting points, and the importance of its proximity to unity in determining the shape of the dynamic structure factor is stressed, as is the need for accurate experimental results for S(q, omega ) in liquid metals.

Unified Transport Theory of Partially Ionized Nonisothermal Plasmas

The unified charged-particle interaction operators of Kihara and Aono have been used in the system of kinetic equations for a partially ionized, nonisothermal gas in a magnetic field. It has been assumed that the coupling between the kinetic equation of the electrons and those of the heavy species is weak, as it is always the case in MHD-generator plasmas. It has been demonstrated that the new theory introduces essential corrections to the values of transport coefficients calculated by other theories of nonisothermal plasmas. Simplified calculation methods for electron transport coefficients have been proposed, which are based on the exact results given by this theory.

Transport coefficients from molecular dynamics for a very small system

Values of transport coefficients calculated in a computer experiment on a system of only 64 particles are given and are compared with values obtained from other methods.

Elastic and Inelastic Collision Cross Sections in Hydrogen and Deuterium from Transport Coefficients

By means of a numerical solution of the Boltzmann equation, elastic and inelastic collision cross sections have been derived for electrons in ${\mathrm{H}}_{2}$ and ${\mathrm{D}}_{2}$ subjected to a dc electric field. The cross sections for momentum transfer, rotational excitation, vibrational excitation, electronic excitation, and ionization are investigated by comparing experimental and theoretical values of transport coefficient. The same momentum transfer cross section previously obtained for ${\mathrm{H}}_{2}$ by Frost and Phelps has been found to be valid for ${\mathrm{D}}_{2}$. Good agreement is secured between experiment and theory by multiplying the theoretical rotational cross sections of Gerjuoy and Stein by approximately 1.5, provided the polarization factor of Dalgarno and Moffett is used. The final cross section for vibrational excitation of ${\mathrm{H}}_{2}$ has a threshold at 0.52 eV and a peak of 7.7\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}17}$ ${\mathrm{cm}}^{2}$ at 4.5 eV, whereas that of ${\mathrm{D}}_{2}$ has a threshold at 0.36 eV and a peak of 6.6\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}17}$ ${\mathrm{cm}}^{2}$ at 4.7 eV. The derived electronic excitation cross sections are the same for both ${\mathrm{H}}_{2}$ and ${\mathrm{D}}_{2}$. The ionization cross section was taken from the experimental results of Tate and Smith. Calculated transport coefficients for electrons subjected to crossed electric and magnetic fields, and high-frequency ac electric fields are in agreement with recent experimental and theoretical results.