g-factor anisotropy for donor-bound electrons at all magnetic fields

Summary A theory of theg-factor for electrons bound to donors in zincblende semiconductors is presented for all magnetic fields. Simple analytical expressions are obtained for weak, intermediate and high magnetic-field intensities. A comparison between theory and the experimental result in the case of InSb is made.     

Anomalous thermopower in the metalliclike phase of a 2D hole system

We report very low temperature ( T) thermopower and resistivity ( rho) measurements on variable-density, two-dimensional hole systems confined to GaAs quantum wells. As the hole density is lowered from 1.49x10(11) cm(-2) to 0.14x10(11) cm(-2), the system crosses from an insulating ( drho / dT less, similar0) to a metallic regime ( drho / dT>0) and finally displays insulating behavior ( drho / dT<0). Diffusion thermopower shows a striking sign reversal in a narrow range of density in the metallic regime, suggesting a qualitative change in the conduction or the scattering mechanism.     

A monopole mass filter with a hyperbolic V-shaped electrode

In this article we compare the classical monopole mass filter of von Zahn and the monopole mass filter with a hyperbolic V-shaped electrode. The experimental results and those of computer simulation for both mass spectrometers are presented. We show that the replacement of a conventional 90 degrees V-shaped electrode by an electrode with a hyperbolic profile substantially improves the peak shape of any given mass, and increases the mass resolution by a factor of 3-4 and the abundance sensitivity by a factor of 100. The potential of high analytical performance combined with electroforming techniques for electrode manufacture indicate future practical uses of such instruments. Copyright 1999 John Wiley & Sons, Ltd.     

Energy levels of bound polarons

A new variational wave function to describe the ground state and the excited states of a bound polaron is proposed. It is of the form

$\text{|Ψ〉 = c|O〉|ø}{}_{\mathrm{n}}\text{〉 +}\text{∑}\text{g}{}_{\mathrm{k}}{}^1\text{V}{}_{\mathrm{k}}{}^1\text{(e}{}^{\mathrm{<mtext>i</mtext><mtext>k·r</mtext>}}\text{? ρ}{}_{\mathrm{k}}{}^1\text{)a}{}_{\mathrm{k}}{}^{\mathrm{+}}\text{|O〉|ø}{}_{\mathrm{n}}$

. It is argued that this form is reasonable for all electron—phonon coupling α and all strengths β of the Coulomb potential. Numerical and analytical results are derived for the energy of the ground state and compared to existing results. Results for the energy of the lowest p-type excited state of the bound polaron are obtained.     

Shape resonances in slow electron scattering by aromatic molecules. I. Anthraquinone derivatives

A series of anthraquinone (C(14)O(2)H(8)) derivatives has been studied by means of electron capture negative ion mass spectrometry (ECNI-MS), photoelectron spectroscopy (PES), and AM1 quantum chemical calculations. Mean lifetimes of molecular negative ions M(-.) (MNI) have been measured. The mechanism of long-lived MNI formation in the epithermal energy region of incident electrons has been investigated. A simple model of a molecule (a spherical potential well with the repulsive centrifugal term) has been applied for the analysis of the energy dependence of cross sections at the first stage of the electron capture process. It has been shown that a temporary resonance of MNI at the energy approximately 0.5 eV corresponds to a shape resonance with lifetime 1-2.10(-13) s in the f-partial wave (l = 3) of the incident electron. The next resonant state of MNI at the energy approximately 1.7 eV has been associated with the electron excited Feshbach resonance (whose parent state is a triplet npi* transition). In all cases the initial electron state of the MNI relaxes into the ground state by means of a radiationless transition, and the final state of the MNI is a nuclear excited resonance with a lifetime measurable on the mass spectrometry timescale. Copyright 1999 John Wiley & Sons, Ltd.     

Shallow center in AgBr: Theoretical investigation by sum rules

In AgBr, an absorption band at 168 cm^?1 can be attributed to absorption by an electron bound in an electrostatic potential. The comparison between the experimental values of the moments of the absorption coefficient and their theoretical expressions gives the ground state mean radius, mean kinetic energy and mean charge density seen by the electron. The ionization energy and electron charge distribution of this center are also obtained.     

Domain decomposition algorithms for indefinite weakly singular integral equations: the h and p versions

We extend the approach of Cai and Widlund (Domain decompositionalgorithms for indefinite elliptic problems, SIAM J. Sci. Stat.Comput. 13 (1992), 243-258), which was designed for finite elementdiscretizations, to boundary element discretizations of indefiniteweakly singular integral equations. Both the h and p versionsof the Galerkin approximation are considered. We prove thatthe additive Schwarz method suggested by Cai and Widlund canbe used for this equation as an efficient preconditioner forGMRES, an iterative method of conjugate gradient type. For bothversions, the rates of convergence of this iterative methodare shown to approach 1 only logarithmically as the degreesof freedom tend to infinity.