Showing papers by "Fraunhofer Society published in 1974"

Computer simulation of transferred electron devices using the displaced Maxwellian approach

Abstract: Computer simulations of GaAs transferred electron devices have been performed by solving the time- and space-dependent Boltzmann equation and assuming displaced Maxwellian distributions for the two conduction band valleys. Since this model includes particle, momentum, and energy relaxation (as distinct from models using instantaneous velocity field dependence) and retains the spatial dependence (as distinct from uniform field models) it is particularly well suited for studying cases that are characterized by a strong x-dependence of electron temperature. Short devices as well as long ones operating at very high frequencies have been studied extensively, since these devices were thought and, in fact, have been found to be strongly affected by nonuniform energy relaxation due to contacts, domains, and other types of space charge. The results have been compared with experimental findings and with theoretical results computed by others.

Type II radio bursts and particle acceleration

Abstract: 328 particle events recorded during 30 months from January 1, 1966 to June 30, 1968 (taken from the new Catalog of Solar Particle Events, 1955–1969) are compared with the occurrence of 166 type II radio bursts during the same period. The results of this comparison give a convincing evidence that proton acceleration to higher energies in flares (the ‘second acceleration step’) is closely connected with the type II burst occurrence. The shock wave appears to originate near the time when the impulsive burst occurs, and the second acceleration step follows immediately the first one; in some cases the second step sets in while the first step is still in progress.

On the energy distribution in wavenumber spectra of the granular velocity field

Abstract: Wavenummer spectra of spatial velocity fluctuations measured in selected high resolution solar photospheric spectrograms are presented. The statistical stability of the power estimates of particular ‘peaks’ in these spectra is discussed.