an analytical treatment of the electron screening effect within an active-electron model is given for positronium formation from helium atoms. a first-order distorted wave approximation with correct boundary conditions is applied to evaluate the transition amplitude. in the range of impact energy for which the introduced perturbative approach is valid, both the total and differential cross sect...

a detailed analysis of the electron-impact-induced fragmentation of 5,8dithiaspiro (3.1) octane and s,9-dithiaspiro 6.5) nonane is presented. the tetradeuteri6-analog of the cyclic dithioketals is prepared as an aid in analysing the fragmentation patterns. it was readily seen that the nature of the fragmentation pathway was governed by the size of the ring containing the two sulfur atoms and th...

In this paper we describe the formation of fingers from ionization fronts for a hydrodynamic plasma model. The fingers result from a balance between the destabilizing effect of impact ionization and the stabilizing effect of electron diffusion on ionization fronts. We show that electron diffusion acts as an effective surface tension on moving fronts and estimate analytically the size of the fin...

When biased on the negative differential resistance regime, electroluminescence (EL) is emitted from planar GaAs heterostructure Gunn diodes due to the recombination of electrons in the device channel with holes that are generated by impact ionisation when the Gunn domains reach the anode edge. This EL forms non-uniform patterns whose intensity shows short-range intensity variations in the dire...

A fully relativistic time-dependent close-coupling method is developed based on Dirac’s covariant formulation of quantum mechanics. The expansion of a one-electron wave function in spin-orbit eigenfunctions yields the well-known coupled Dirac equations in two radial wave functions, while the expansion of a twoelectron wave function in coupled spin-orbit eigenfunctions yields close-coupled Dirac...

We have measured electron and hole multiplication factors and impact ionization coefficients in 550 A GaAs/SOO A AbX3G%,,As quantum wells with an intermediate A&,.45Ga0.55As barrier (50 and 100 %L) inserted in the well region. It is seen that while the measured value of a(E) is insensitive to the position of the intermediate barrier in the well, the value of P(E) is very sensitive. The value of...

Simulation of dynamic phosphor space charge in alternating-current thin-film electroluminescent (ACTFEL) devices is performed using SPICE equivalent circuit models. Two SPICE equivalent circuits are developed; one for the case of space charge creation via impact ionization and another for field emission. Both SPICE equivalent circuits are based on modeling the space charge distribution as a sin...

The electron-impact widths for 30 Zr III lines were calculated using the modified semi-empirical (MSE) method. For two Zr II and four Zr III astrophysically important UV lines, only electron-impact widths are given, since for their calculation the experimental oscillator strengths were used and consequently the accuracy of the parameters is lower than in the case of other lines. The influence o...

In this work we present fully differential cross sections (FDCSs) calculations using post and prior version of CDW–EIS theory for helium single ionization by 100 MeV C 6+ amu −1 and 3.6 MeV amu −1 Au 24+ and Au 53+ ions. We performed our calculations for different momentum transfer and ejected electron energies. The influence of internuclear potential on the ejected electron spectra is taken in...