Showing papers on "Transport phenomena published in 1974"

Electron transport phenomena in small-gap semiconductors

Abstract: Electron transport phenomena in small-gap III–V, II–VI and IV–VI semiconducting compounds are reviewed. We emphasize peculiarities due to nonparabolic energy-momentum dependence in the conduction band and the structure of Bloch wavefunctions, when electron energy becomes comparable to that of the gap. General theoretical framework is compared with real conduction bands in the materials of interest. Thermodynamic properties of electron gas are derived for arbitrary nonparabolic and nonspherical energy bands. We develop a theory of d.c. transport phenomena and free-carrier optics based on a linear Boltzmann equation solved for an ellipsoidal band of arbitrary nonparabolicity. Elastic electron scattering is considered taking into account true Bloch eigenstates of the conduction electrons. We give a unified description of electron mobility, thermoelectric power, thermomagnetic phenomena and free-carrier optical effects illustrating the theoretical methods with experimental results of various authors....

Constitutive equations for heat conduction in general relativity

Abstract: A heat flux constitutive equation is derived in three approximations from a general functional constitutive equation which describes heat conduction in so-called 'simple' thermodeformable media in general relativity. The three approximations correspond to materials having a so-called 'fading memory', and infinitely short memory, and materials of the 'rate-type', respectively. The third approximation may contain the other two as particular cases. Within the frame of the approximations made for isotropic materials, it is shown that interactions between the different transport phenomena, eg, heat flow and viscosity, cannot be accounted for.

Quantum theory of photon-drag transport phenomena in solids and its application to tellurium crystal

Abstract: Starting with the density-matrix equation, we obtain the transport equation for the photon-drag effect arising from an optical interband transition. Using this transport equation, the current induced by the photon-drag effect is derived. The temperature dependence of the photon-drag current predicted by the theory agrees quite well with the experimental result in tellurium crystal.

Current transport in MSM devices

Abstract: A theoretical treatment of the current transport in MSM devices is presented. It is based upon the application of the thermionic diffusion theory to both junctions and makes it possible to relate the current density to the total voltage applied to the device by a single expression valid for any voltage above reach through. So doing, the contributions of the different transport mechanisms, i.e., thermionic injection over the energy barriers at the junctions and drift diffusion within the semiconductor, may be evaluated both for majority and minority carriers. It turns out that before the flat‐band condition the current is limited by transport phenomena in the semiconductor, while above flat band neither mechanism definitely prevails. However, in spite of the different physical models, numerical results are of the same order of magnitude as those obtained by Sze et al.

Steady State Transport Phenomena in Non-Ideal Permeant-Polymer Systems

Abstract: The so generally used Fick’s first law of diffusion with the material current density proportional to concentration gradient of the penetrant is inapplicable to even the simplest uniform homogeneous polymer membranes which as a rule are not ideal. The nonideality shows up in a nonlinear increase of sorbed penetrant with applied pressure of gas or concentration of liquid. That modifies the concentration gradient in the membrane. The same effect can obtain as a consequence of the finite compressibility of swollen membrane under the applied pressure gradient in the hydraulic experiment. In both cases the membrane becomes nonuniform under the influence of concentration or pressure gradient in spite of the fact that it is uniform in a gradient free environment. But the true driving force is in all cases the gradient of the chemical potential of the penetrant and not that of concentration. The deviations of sorption, partition and diffusion coefficients from ideality in highly swollen and in plastically deformed polymer films can be to some extent described by the change of fractional free volume as a consequence of the finite amount of sorbate present. A new effect may occur in the hydraulic experiment. With increasing swelling the membranes exhibit a substantial viscous flow permeability which may be orders of magnitude larger than the diffusive permeability. It cannot be described in terms of diffusive transport.

Transport phenomena in a capillary-porous medium I. The model of a capillary-porous body and a series of balance equations

Abstract: The reality of a capillary-porous body is substituted by the model of a continuous viscoelastic, isotropic two-component medium (component 1 is the solid phase, component 2 is a liquid). It has been proved that if a polymolecular adsorbent layer is created, this model is physically adequate to the reality. In this paper, the balance equation of mass, the momentum, the moment of momentum, the kinetic energy, the total energy, and the internal energy are derived for this model. Since it is characteristic of an arbitrarily chosen volume of the investigated system to change its mass, the derivation of these equations is based on Mescerski's instead of on Newtonian mechanics as is usual. The binding energy, which characterizes the energy interaction in sorbent processes, is considered. Tensors are found that describe the swelling of the investigated body and the friction between the fluid and the solid phase. The results are generalized for systems confined within diathermic, soft, unscreening and semipermeable walls.

NMR Experimental Test for the Existence of the Kondo Resonance

Abstract: A major part of the information about the behavior of impurities in a metal is contained in the conduction electron scattering on the impurities described, e.g., by a t-matrix. Theories are more or less primarily directly concerned with the t-matrix; experimentally, however, this quantity is not directly accessible. Investigation of the transport properties (mainly resistivity) is the usual way to obtain information about impurity scattering, in which case we are actually concerned with some integrals containing the t-matrix and confined to a narrow energy range around the Fermi energy, characterized by a width scaling with kT. As we will show, the charge density oscillation (Friedel oscillation1) around the impurity is also generally related to some integral containing the t-matrix and having its most important contributions from the vicinity of the Fermi energy. This integral is different from those involved in transport phenomena; in particular, it is essentially temperature independent (except for a possible temperature dependence of the t-matrix itself). We will find that the additional information one can obtain from the investigation of the charge density oscillation, combined with the readily available data about the effect of the impurity on the bulk transport properties, yields a powerful tool to study the energy dependence of the t-matrix. It is particularly important to note that this method works at a given temperature; it therefore offers the new possibility of direct separation of the energy and the temperature dependence of the scattering, which is not present in the usual scheme based on transport property studies.

Transport phenomena in a nonequilibrium, partially ionized gas in a magnetic field

Abstract: A small-parameter method in which the gas and electron temperatures can be different is used to solve the Boltzmann equation. The zeroth-approximation solutions are Maxwellian with different temperatures Te and Ts. Transition to the BGK formalism on the basis of an extremely crude estimate of the frequency of electron collisions leads to numerical results which agree well with the available data. Then an extension of the Eucken method leads to analytic expressions for the nonequilibrium quasi-Lorentz transport coefficients.

Fundamentals of electrochemical engineering: the role of transport phenomena

Abstract: Mass transfer limits the rate at which an electrochemical process can be carried out under given hydrodynamic conditions It thus determines the minimum size of an electrochemical reactor Acceleration of the mass transport is of decisive importance for the decrease of the investment and for making the electrochemical route more competitive The possibilities to achieve larger transport rates are reviewed Usually, an additional cost for the stirring or for the cell design is involved: Its optimization is an important target of electrochemical engineering The energy necessary for the stirring increases in general rapidly when the mass transport rate to be attained becomes larger The actual figures for various hydrodynamic models are compared As an illustration the savings which can be achieved by stirring are shown for a typical case

Theoretical Aspects of Transport Phenomena

Abstract: In this paper the structure of the time correlation functions which determine the transport coefficients in a simple liquid are discussed. It is pointed out that the success of the rigid sphere model requires a modification of the usual memory function approach based on Mori’s continued fraction method. The role of binary collisions is treated in some detail and it is shown that their effect can be represented by a function of time which scales with a parameter representing the ‘hardness’ of the interaction, but which gives a contribution to the transport coefficient approximately independent of ‘hardness’.

Transport Phenomena in Polyelectrolyte-Salt Solutions

Abstract: The interpretation of sedimentation and diffusion velocity data for non-electrolytes in binary macromolecular component systems as well as in solutions of more than two components is based on well-tried and familiar equations. Whether the same principles can be extended to multicomponent polyelectrolyte solutions has been the subject of several controversies.

Transport phenomena in a capillary-porous medium II. Entropy production and phenomenological equations

Abstract: By means of the balance equation of internal energy and the assumption of local equilibrium there is derived the balance equation of entropy. In the entropy production such terms that have connection with the work of reactive forces, with the energy of change of mass, and with the work of binding forces also appear in addition to the usual expressions. It is shown that entropy production can be written in two equivalent ways by means of tensors of different orders. Every form of entropy production in linear area leads to a different system of phenomenological equations. Transfer relations between the two systems are found. Also an expression is found for mass flux which depends explicitly neither on the temperature gradient nor on the gradient of chemical potentials. A relationship is found between viscosity tensor and the tensor which describes the swelling of a body, and friction between a fluid and the solid phase. Dependence of dispersion coefficient on concentration is derived.

Sedimentation and Diffusion of Polyelectrolytes in the Presence of Added Salt

Abstract: The purpose of the study on transport phenomena of polyelectrolytes may be to discuss the response of both the polymeric ion and the counter-ions in solutions to externally applied fields: those considered include the electric field, centrifugal field, shearing force and the chemical potential gradient. That is, sedimentation, diffusion, viscosity, electrophoresis, electric conductivity, etc. may be included in the transport phenomena of linear polyelectrolytes. Among them, here we shall discuss sedimentation and diffusion which both are closely related. Just as in all other phenomena, it is convenient to divide our discussion into two problems; the concentration dependence of transport coefficients, which is mainly concerned with the interaction between two polymeric ions, and the limiting magnitudes of sedimentation and diffusion coefficients, which are determined mainly by the radius of gyration of polymeric ion in an infinitely large volume of solvent.