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.     

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.     

New possibilities and prospects for the development of quadrupole transit time mass spectrometers (monopole,tripole, mass filter)

Potentials of a new operating mode of quadrupole transit time mass spectrometers (monopole, tripole, mass filter) are considered. This new mode was named the three-dimensional focusing mode. The results of numerical simulations of the shape of mass peaks of quadrupole transit time mass spectrometers are presented. The prospects for the drastic improvement of the resolution and sensitivity of these devices in the new mode are shown and substantiated.     

Simulation of Separating Flows over a Backward-Facing Step

Simulation results are reported for plane two-dimensional viscous incompressible flow in a channel with an abrupt expansion. The mathematical model is provided by the quasi-hydrodynamic equations in the incompressible fluid approximation. The computations are carried out in a range of Reynolds numbers including both laminar and turbulent flow. As the Reynolds number increases, the solution bifurcates and the steady laminar flow changes to time-dependent flow. The computation results are consistent with known experimental data. Turbulence models were not used for large Reynolds number computations.     

Anisotropic magnetoresistance of two-dimensional holes in GaAs

Experiments on high-quality GaAs (311)A two-dimensional holes at low temperatures reveal a remarkable dependence of the magnetoresistance, measured with an in-plane magnetic field ( B), on the direction of B relative to both the crystal axes and the current direction. The magnetoresistance features, and in particular the value of B above which the resistivity exhibits an insulating behavior, depend on the orientation of B. To explain the data, the anisotropic band structure of the holes and a repopulation of the spin subbands in the presence of B, as well as the coupling of the orbital motion to B, need to be taken into account.     

Anomalous magneto-oscillations in two-dimensional systems

The frequencies of Shubnikov-de Haas oscillations have long been used to measure the unequal population of spin-split two-dimensional subbands in inversion asymmetric systems. We report self-consistent numerical calculations and experimental results which indicate that these oscillations are not simply related to the zero-magnetic-field spin-subband densities.     

Highly anisotropic g-factor of two-dimensional hole systems

Coupling the spin degree of freedom to the anisotropic orbital motion of two-dimensional (2D) hole systems gives rise to a highly anisotropic Zeeman splitting with respect to different orientations of an in-plane magnetic field B relative to the crystal axes. This mechanism has no analog in the bulk band structure. We obtain good, qualitative agreement between theory and experimental data, taken in GaAs 2D hole systems grown on (113) substrates, showing the anisotropic depopulation of the upper spin subband as a function of in-plane B.     

Quasiconformal extremals of smooth functionals and of the energy integral on Riemann surfaces

Krasnodar. Translated from Sibirskii Matematicheskii Zhurnal, Vol. 29, No. 3, pp. 163–174, May–June, 1988.     

Uniqueness of extremal quasiconformal mappings of Teichmüller type

We prove a theorem concerning the uniqueness of extremal quasiconformal mappings, generalizing thereby a well-known theorem of Teichmüller.