Results 1 - 10 of 64575
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[en] A model for multilevel superfluorescence is presented. By using a parametric solution of this model we explain basic features in the two-color solid-state superfluorescence experiments of Florian, Schwan and Schmid. (author). 23 refs
[en] The simplified P2 (SP2) angular approximation typically produces more accurate reaction rates and eigenvalues than the P1 (diffusion) approximation for problems in which the P1 approximation is reasonably accurate. The SP2 scalar flux spatial distributions are also often more accurate than the P1 distributions away from material interfaces and source discontinuities. However, the SP2 scalar flux is spatially discontinuous at material interfaces and source discontinuities. These spatial discontinuities are unphysical, aesthetically displeasing, and can lead to large inaccuracies near interfaces. The scalar flux discontinuities in the planar geometry P2 approximation have recently been eliminated by combining the P2 approximation with the P1 approximation. In essence, the P1 angular approximation is used at material interfaces and source discontinuities to obtain spatially continuous scalar flux distributions; the P2 angular approximation is utilized elsewhere to take advantage of its improved accuracy. In this paper, we generalize this planar geometry approach to the multidimensional SP2 approximation. Numerical results from two-dimensional fixed-source and eigenvalue problems demonstrate the effectiveness of the technique. (authors)
[en] Theoretical calculations for excitation of hydrogen-like atoms by ion impact at high and intermediate energies, are presented. Impulsive and eikonal wave functions are employed, both normalized. It is studied the dependence on energy and projectil charge (saturation) of cross sections, compared to experimental results. (A.C.A.S.)
[pt]Apresentam-se os calculos teoricos da excitacao de atomos hidrogenados por impacto de ions em energia alta e intermediaria. As funcoes de onda empregadas sao uma funcao de onda impulsiva e eiconal, ambas normalizadas. Estuda-se a dependencia da energia e a carga do projetil nas secoes de choques comparando com os resultados experimentais. (C.G.C.)
[en] We investigate the origin of quantum geometric phases, gauge fields and forces beyond the adiabatic regime. In particular, we extend the notions of geometric magnetic and electric forces discovered in studies of the Born-Oppenheimer approximation to arbitrary quantum systems described by matrix-valued quantum Hamiltonians. The results are illustrated by several physical relevant examples.
[en] Penetrability through a three-humped barrier has been calculated in quasi-classical approximation and a plausible explanation of sub-barrier fission characteristics of thorium is suggested. (Auth.)
[en] We consider the use of quasi-diabatic bases to improve upon the Born-Oppenheimer approximation in molecular systems. In a nonrigorous, but still suggestive, manner, it is shown that, when the quasi-diabatic approximation is a good one, the use of 'frozen' electronic states will often be equally good, or nearly so.