摘要:

A closed, macroscopic description of the dynamics of an assembly of electrons under the influence of space-time varying fields is presented. It is attained by considering the kinetic distribution function, f, to be a vector in a space whose coordinates are the infinite set of moments, {mj; j = 1, …, ∞}. A distribution, f(k)M, is then defined by approximating the contribution from all but a finite set of coordinates (moments), {mj; j = 1, …, k}. In the scale of resolution of the k moments, f(k)Mis equivalent to f and can be used to describe the dynamics of the assembly. Expressions for the f(k)Mand the transport parameters are obtained for scales of resolution corresponding to density transport, energy relaxation, and momentum relaxation. Comparisons are presented between results obtained with this formulation and those obtained from a kinetic model.

ISSN:0041-1450    

DOI:10.1080/00411459108203899

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

This paper describes radiative transfer through a single cloud layer that is horizontally uniform but statistically distributed in the vertical and compares the radiative transfer in such a statistical cloud to its deterministic counterpart. Specific examples of the derivation of the probability density functions of cloud reflection and transmission by single cloud layers are described for given observed statistical distributions of cloud optical depth and single scattering albedo. Numerical results of the probability density functions for cloud albedo, transmission and absorption are presented, as are the moments of these distributions. Although the computations apply to a hypothetical statistical medium that only approximate clouds in the atmosphere to a limited extent, results of this study demonstrate that radiative transfer in the statistical cloud is substantially different from that of its deterministic counterpart having the same ensemble mean properties. It is also demonstrated that the rate at which the moments of the distributions decay with order, differs for reflection and transmission in a way that is influenced by the absorption of cloud droplets and the asymmetry of droplet scattering. This result suggests that it may be difficult to infer information about the variability of transmitted solar radiation from reflection measurements.

ISSN:0041-1450    

DOI:10.1080/00411459108203900

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

In this article we demonstrate that Colombeau's theory of generalized functions is suitable for studying the Carleman system with singular initial data. We obtain existence, unïqueness, and continuous dependence of a generalized solution, given arbitrary positive measures as initial data. The results are based on the theory of nonnegative, locally bounded solutions to the Carleman system. An explicit solution with initial data Dirac masses is discussed.

ISSN:0041-1450    

DOI:10.1080/00411459108203901

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We discuss exact positive solutions of some boundary value problems for a family of the Broadwell models of the Boltzmann equation in various spatial geometries (slab, Couette flow) with general boundary data which admit recombination and sources on the boundaries. We also investigate dependence of the solutions on the parameters characterizing the boundaries and on the collision cross sections.

ISSN:0041-1450    

DOI:10.1080/00411459108203902

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A method is proposed for calculating appoximate values of those integral quantities used in nuclear reactor calculations which require' a transport-theoretical formulation. A priori error estimates are given in the form of lower and upper bounds. The method is compared with the multiple collision approach. The numerical calculations of the absorption blackness in a slab shows that the present method leads to the reduction of the computing time needed to achieve a prescribed accuracy. We present the method in its one-velocity version, mainly for simplicity. It can be extended to multi-group, or even continuous energy dependent case at the cost of the considerable complication in the procedure algebra.

ISSN:0041-1450    

DOI:10.1080/00411459108203903

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The problem of planar condensation/evaporation of a monatomic vapor is solved based on the linearized Boltzmann equation. Accurate numerical results for the pressure and temperature jumps, and the macroscopic profiles for the density and temperature are reported for rigid sphere molecular interaction. Variational expressions for the jumps for several different molecular force laws are evaluated. For rigid spheres, these agree well with the numerical results but are otherwise found to be relatively insensitive to the intermolecular force laws.

ISSN:0041-1450    

DOI:10.1080/00411459108203904

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The Euromech colloquium bearing the number 267 convened at Figueira da Foz (Portugal) on Wednesday, September 19, 1990. The topic (Discrete Models of Fluid Dynamics) was new to Euromech colloquia, but the meeting was, in a sense, a continuation of previous meetings under slightly different titles held in Santa Fe' (New Mexico, 1986) and Torino (Italy, 1988).

ISSN:0041-1450    

DOI:10.1080/00411459108203905

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor