127,281 research outputs found
Hole tunneling times in GaAs/AlAs double-barrier structures
We have calculated hole tunneling times in GaAs/AlAs double-barrier structures taking quantum well band-mixing effects into account. Our results indicate that for sufficiently high hole temperatures and concentrations, band-mixing effects reduce average hole tunneling times from the pure heavy hole value to values comparable to electron tunneling times in the same structure. For very low hole temperatures and concentrations, band mixing is less important and average hole tunneling times should approach the pure heavy hole value. These results provide an explanation for previously reported experimental results in which electrons and holes were found to be characterized by very similar tunneling times
Bethe-Salpeter study of radially excited vector quarkonia
We solve the Bethe-Salpeter equation (BSE) for a system of a heavy
quark-antiquark pair interacting with a Poincare invariant generalization of
screened linear confining potential. In order to get reliable description the
Lorentz scalar confining interaction is complemented by the effective one gluon
exchange. Within presented model we reasonably reproduce all known radial
excitations of the vector charmonia. We have found that is the only
charmonium left bellow naive quark-antiquark threshold , while the all
excited states are situated above this threshold. We develop a method which is
enable to provide solution of full four dimensional BSE for the all excited
states. We discuss the consequences of the use of the free propagators for
calculation of excited states above the threshold. The Bethe-Salpeter string
breaking scale appears to be relatively larger then the one
defined in various potential models .Comment: typos and grammar correcte
Evaluation of aerothermal modeling computer programs
Various computer programs based upon the SIMPLE or SIMPLER algorithm were studied and compared for numerical accuracy, efficiency, and grid dependency. Four two-dimensional and one three-dimensional code originally developed by a number of research groups were considered. In general, the accuracy and computational efficieny of these TEACH type programs were improved by modifying the differencing schemes and their solvers. A brief description of each program is given. Error reduction, spline flux and second upwind differencing programs are covered
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