Table of contents

Collision strengths for all transitions up to and including the n = 5 levels of Al XIII have been computed in the LS coupling scheme using the R-matrix code. All partial waves with angular momentum L ≤ 45 have been included, and resonances have been resolved in a fine energy grid in the threshold region. Collision strengths are tabulated at energies above thresholds in the range 162.30 ≤ E ≤ 220.0 Ry, and results for the 1s–2s and 1s–2p transitions are compared with those of previous authors. Additionally, effective collision strengths, obtained after integrating the collision strengths over a Maxwellian distribution of electron velocities, are tabulated over a wide temperature range of 4.40 ≤ log T_e ≤ 6.40 K.

Recent studies of the Si and Ge isoelectronic sequences have shown that branching fractions within the ns²np²–ns²np(n + 1)s supermultiplets are accurately described by a semiempirical model that uses spectroscopic energy level data to characterize intermediate coupling. It was also recently shown that a similar model applied to alkaline-earthlike ns²–nsnp transitions can be advantageously generalized to include the effects of spin-other-orbit interaction and differences between the singlet and triplet radial wave functions. These two formalisms are combined, extended, and applied here to obtain a predictive systematization of branching fractions for the 5s²5p²–5s²5p6s supermultiplet of the ions Sn I–Cs VI in the Sn sequence.

The spectrum of antimony was recorded in the 300-2080 Å region on a 3-m normal incidence vacuum spectrograph. Earlier analyses of Sb IV were revised. Two electrons excited configurations, viz 5p5d and 5p6s, and 5s8s, configurations were established. One hundred and twelve lines have now been classified in this spectrum. Multi-configuration Hartree-Fock calculations with relativistic corrections (HFR) and least squares-fitting calculations (LSF) were carried out to interpret the spectrum satisfactorily. The ionization limit of Sb IV has been estimated to be 353300 cm^-1.

The spectrum of Yb IV has been reinvestigated and its analysis has been extended. The present work is supported by the comparison of line intensities with transition probabilities derived from the Cowan (1981) codes. Starting from the first analysis by Sugar, Kaufman and Spector (1978), the number of established levels has been increased from 111 to 193, including high excitation levels of the new 4f¹²7s + 4f¹²6d even configurations. Of the 1023 classified lines about one half are new. Computed transition probabilities are given for selected lines.

New radiative lifetimes of 18 levels (energy range between 30 000 cm^-1 and 39 000 cm^-1) in Ce II have been measured using the time-resolved laser-induced fluorescence method. A tunable frequency-doubled dye laser with 1 ns pulse duration was used to excite selectively singly ionized cerium in a laser-produced plasma. The experimental results are compared with theoretical data and the agreement is found to be very good.

We investigate the quantum statistics of three harmonic oscillators mutually interacting with each other determining quadratures squeezing, second-order correlation function and phase space distributions. We assume that the modes are initially prepared in coherent states. We show that the initial coherent states can evolve into squeezed states which are not minimum uncertainty states governed by the interaction parameters. Moreover, we demonstrate that the interaction is able to produce squeezing of different types, i.e. single-mode, two-mode and three-mode squeezing. Further, we show for specific modes and under certain conditions the oscillatory behaviour in the photon-number distribution and the bifurcation phenomenon in the phase distribution for squeezed light.

A new channel of nonlinear ionization of quantum system in a strong laser field is discussed. The probability of spontaneous radiation decay from the ground state in a short-range potential to the final Volkov wave function, is calculated by the first order of the perturbation theory. It is shown that this process at high intensities of the laser field will be comparable with the high harmonic generation.

The three dimensional stability of ion-acoustic double layers in a magnetized plasma consisting of warm ions and non-thermal electrons is investigated by the multiple-scale perturbation expansion method of Allen and Rowlands (1993 J. Plasma Phys.50 413). It is found that the double layer solutions obtained from the combined MKdV-KdV-ZK equation are stable.

Instability of a stratified shear layer in a gravitational field is studied by using the compressional magnetohydrodynamic (MHD) equations. The equations describing a fully nonlinear, two-dimensional travelling solution are derived and solved in the small amplitude limit for an arbitrary steep velocity profile. The Boussinesq instability criterion is recovered as the existence condition of linearly unstable surface waves, and a second unstable configuration is found, which has a large velocity jump of more than double the sound speed.

The contribution due to the turbulence to the shear layer formation has been evaluated by measuring the off-diagonal part of the Reynolds stress tensor in the magnetised plasma Thorello. Measurements have been performed through a four pin electrostatic probe along the plasma radius and in different discharge conditions.

The evolution of large metal clusters is considered when the cluster is irradiated by a super-intense ultra-short laser pulse. The cluster excitation results from the interaction of the electron subsystem with the laser field. The electron temperature and the charge of the produced cluster ion are derived for this process. The optical density of the cluster plasma is found to be relatively low for resonant radiative transitions of multicharged atomic ions inside the cluster. Thus, the reabsorption of photons is inefficient in the cluster plasma. The optimal conditions are analyzed for the effective absorption of laser radiation by the metal cluster. It was found that a maximum of absorption was achieved for large sizes of the clusters.

Using the effective field theory, we investigate the phase diagrams of the multilayer Ising model under a layered magnetic field. With varying the number of layers "n", several phases are observed. Moreover, we distinguish two different features with varying magnetic field, corresponding to odd or even number "n". The phase diagram of the system with infinite "n" presents the ferromagnetic and the layered phases which are separated by a first order transition line, at low temperatures. However, at high temperatures, this line is found to be of second order with a tricritical end-point.

We investigated the effect of photo quenching on the galvanomagnetic properties in Te doped n-type GaAs grown by Liquid Encapsulated Czochralski (LEC) process. Although magnetoresistance coefficient and carrier concentration do not change as a function of photo-quenching time at 55 K, the Hall mobility increases with increasing photoquenching illumination time. This results from the photo-quenching of the EL2 centres. On the other hand, the Hall mobility and carrier concentration increase with increasing photoquenching time at 10 K. These are expected because of the acceptor behaviour of reverse contrast (RC) centres. The magnetoresistance coefficients are constant at this temperature. Two different kinds of photo-quenching are once again observed in lightly n-type GaAs at sample temperature of below 65 K and 40 K from a different aspect using galvanomagnetic effects.

The conclusions made in a paper published recently (M Hashmi and G Staudenmaier 2000 Physica Scripta62 268) are crucially based on the statements that reabsorption of the cyclotron radiation emitted by gyrating plasma electrons is highly improbable and that Kirchhoff's law has been applied erroneously in the literature to derive the absorption coefficient. We would like to contradict these statements from an experimentalist's point of view.