Table of contents

By assuming a homogeneous and isotropic (D + 1) dimensional metric and a matter content described by ultrarelativistic particles with bulk viscosity represented by a coefficient that depends on the square root of the curvature, we find that the positive curvature topology leads to a slowly varying linear expansion which may preceed the usual period of inflation commonly discussed in cosmological scenarios. The flat spatial topology leads to a cosmology expanding to an infinite radius in an inverse power law fashion.

The calculation of weak intercombination line strengths sometimes requires an especially careful treatment of a combination of factors, including configuration mixing, spin-orbit interactions and relativistic effects. Fully relativistic ab initio MCDF calculations, when available, can provide an excellent guide to the Z-dependence of these transition probabilities for the upper portion of an isoelectronic sequence. For low to moderate ionization stages, good results may sometimes be obtained using an LS-coupled basis, MCHF or CI wavefunctions, and a treatment of the spin-mixing interactions which is guided by empirical data. These ideas are illustrated by examples from the configurations 2s3p in the Be isoelectronic sequence, 3s4p in the Mg sequence, and 3s3p³ in the Si sequence. Revised wavelength predictions for the 3s²3p²³P_1,2-3s3p³⁵S₂ lines in the Si sequence are also presented.

This paper presents a comparison between experimental and theoretical transition probabilities for resonance lines in the Cu, Na, Mg and Al isoelectronic sequences. Particular emphasis is placed on modern beam-foil studies where detailed cascade corrections have been made. In general, good agreement is observed between theoretical calculations with an extensive treatment of correlation effects and the beam-foil results with an equally extensive treatment of cascades. Some cases where the experimental situation is less complicated will also be mentioned. In particular we discuss the recently observed discrepancy between the experimental and theoretical intensity ratios for the two fine-structure components of the 3s²3p²P-3s3p²²S resonance transition in the Al-sequence.

MCHF calculations recently predicted a positive binding energy for the 4p electron in the 4s²4p²P state of Ca⁻, in good agreement with experiment. These calculations were extended to other ns²np systems and, in cases where the (n - 1)d shell of the atom was unfilled, theoretical calculations predict the existence of stable, negative ions. These calculations modeled the atom as (Core)ns² and the ion as (Core)ns²np and included correlation only among the outer electrons. Similar calculations have been performed for Rb and Cs where the neutral atom can be modeled as (Core)ns. In this case, the interesting question is whether (Core)nsnp³P is a bound state, but because of fewer electrons outside the core, the calculations were able to include core polarization or correlations with the core. A survey of some of these results is presented.

Optical studies of multiply-excited states are reviewed with emphasis on emission spectroscopy. From optical measurements, properties such as excitation energies, lifetimes and autoionization widths can be determined with high accuracy, which constitutes a challenge for modern computational methods. This article mainly covers work on two-, three- and four-electron systems, but also sodium-like quartet systems. Furthermore, some comments are given on bound multiply-excited states in negative ions. Fine structure effects on transition wavelengths and lifetimes (autoionization) are discussed. In particular, the most recent experimental and theoretical studies of multiply-excited states are covered. Some remaining problems, which require further attention, are discussed in more detail.

The R-matrix method is used to calculate electron impact collision strengths for various transitions in Ti XIV from its ground state (²P°). Extensive configuration interaction wavefunctions are used to represent the lowest twelve target states which are included in the calculations. Finally effective collision strengths have been calculated for electron temperature in the range (5 × 10⁴-10⁶K) by assuming a Maxwellian electron velocity distribution of the incident electrons.

The dispersion relation for a magnetoactive waveguide filled with semiconductor plasma is derived using Maxwell's equations and MHD plasma description. This relation is analysed numerically. The existence of a single family of EH-waves and two families of HE-waves – high frequency (HF) and low frequency (LF) types, and also typical plasma waves is demonstrated. A new hybrid HE-mode is found to exist, connected with the anisotropy of the semiconductor plasma, filling the waveguide. The numerical results indicate at the occurrence of backward LF waves and anisotropic HE-modes for certain values of the external magnetic field and the waveguide radius.

The Langevin equation is used to describe dispersion of pollutants in the atmosphere. It is shown that the Langevin equation can describe dispersion in complex circumstances. In particular, the equation is applied to dispersion in a convective boundary layer where it reproduced the measurements accurately.

Two forms of the Langevin equation, which have both been used in practical applications, are compared and it is concluded that in terms of their theoretical properties they are not very different in spite of important differences in practical application.

We report on results of the first measurements made on the interaction of a magnetized relativistic electron annular beam (V_b = 2.3 mV, I_b ≃ 70 kA) with a cold (T_e < 1 eV) dense (n_io ~ 10¹⁸ cm⁻³) CO₂-laser-produced carbon annular plasma. We also report on results from a computational model which is used to interpret the experimental data. We find that at peak electron temperature (T_e ~ 107 eV), beam energy deposition into electron thermal energy due to the two-stream instability is approximately 8% per cm.

An investigation is made of nonlinear interaction of waves in a narrow inhomogeneous magnetoactive plasma layer at the boundary of a semibounded magnetoactive plasma in the case of simultaneous incidence of S and P-polarized waves onto the plasma. The amplitudes of waves radiated at combination frequencies are calculated. It is found that the effect of the external magnetic field is to increase the amplitudes of the generated waves in the case when the width of the plasma-vacuum transition layer is much less than the wavelength.

The interaction between electron beams and plasmas containing several species of heavy particles (i.e., atomic particles possessing polarisable electronic envelopes) is analysed. It is established that the longitudinal beam instability at ω = ω_pe ≈ k_zu is possible not only in the resonant case (i.e., when the electron plasma frequency is very close to the frequency of radiation emitted in transitions between the two working energy levels), but also in the non-resonant situations. The characteristics of the instability in this latter case are discussed in detail. It is found that, generally, the trends of the amplitude increments are opposite to those in the equivalent resonant cases.

Equations for particle distribution functions of a multicomponent, nonuniform plasma describing the response to a very strong and strongly oscillating electromagnetic field are developed. Both "collisionless" and "collisional" phenomena are encompassed by the theory as well as "interaction" between such phenomena.

To explain discrepancies between experiments and standard theories of stimulated Brillouin scattering Zozulya, Silin, and Tikhonchuk [Sov. Phys. JETP 59, 756 (1984)] have suggested a parametric process called Double Stimulated Brillouin Scattering (DSBS). In DSBS the incident pump wave is reflected from the critical surface and the two waves scatter from a common ion wave. In this paper some of the properties of DSBS are reviewed. Complete formulary for calculating the stationary eigensolutions of the fields and the eigenvalues of the reflection coefficients and oscillation frequencies is presented. The approach allows inhomogeneous plasma density and temperature. Temperature gradient effects are studied in detail. Numerical solutions including the temporal variation of the ion wave show that the fields start to pulsate above a critical intensity. The backscattering and specular reflections in DSBS develop into regular pulse trains.

By assuming an anomalous heat conduction of the form 1/T and a power law for the total dissipation, it is possible to show the existence of bifurcated universal profiles for current density and temperature. This is done without a priori imposing an abstract relaxation procedure through a variational approach having less transparent constrains attached to it. The exact solutions are a simple demonstration showing that Kadomtsev's arguments [1] for ruling out the heat conduction dependence on the inverse temperature (κ ∝ T^–1), do not hold, although his reasoning for a non-local dependence in the κ still holds. The H and L bifurcated branches also exist for pure ohmic heated tokamaks and they coincide with the canonical profiles for 1/T heat conduction.

The branching occurs for q(edge)/q(axis) = 2 in the circular symmetric case with a power law for the total dissipation. The current profiles are labelled universal in the sense of being the same no matter what exponent one has in the power law approximation, and they resemble the observed profiles in most tokamaks. The general consideration in the first part may suggest that the results from the special model are qualitatively correct in a more general physical setting.

The dispersion equation for parallel whistler-mode propagation in a weakly relativistic anisotropic plasma is presented and investigated in some limiting cases. It is pointed out that the nonrelativistic approach to the problem is justified when the wave refractive index is well above unity. This is not always valid in magnetospheric conditions.

In this work we simulated the growth of amorphous silicon on a substrate of a two-layer-slab of crystalline silicon with various surface indices. We used the Lennard-Jones form for the pair potentials and the Axilrod-Teller form for the three-body potentials. The growth is realized by means of a continuum Monte-Carlo method and the radial distribution functions are compared for various cases.

We present a simple cluster calculation which strongly suggests that the one band Hubbard model is not sufficient for a complete description of the CuO₂ layers in high T_c superconductors.

This paper reviews different topics concerning the Kelvin-Helmholtz instability at the terrestrial magnetopause: role in the magnetopause transfers, experimental observations, linear theory, and numerical simulations. Two main questions are raised from this review: (i) is the role of the Kelvin-Helmholtz instability to be opposed to the one of reconnection, or are both phenomena to be considered as complementary? (ii) why are the measured surface wavelengths much longer than predicted by the linear theory? We present new results of numerical simulations which may allow to answer these two questions.