No abstract available

[en] Models for hadron-nucleus scattering at intermediate and high energies are shown to depend sensitively on the mutual compatibility of the basic approximations such as non-local interactions, fixed scatterers, and eikonal amplitudes

[en] In this note we want to remedy the situation by providing a simple and systematic generalization of the eikonal equation as a general means to study high-energy scattering. (Author)

[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.)

No abstract available

[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.