Table of contents

Sea waves interacting with a surface current whose undisturbed velocity profile is linear form a physical system that is practically important and moreover easy to treat mathematically since the dispersion equation becomes an algebraic equation. The present paper emphasizes which information about fundamental wave modes that can be obtained from graphical solutions of the dispersion equation. Use of Taylor's nondimensional variables Y = U/c and Z = hg/U² makes it possible to show in a very clear way how the flow becomes unstable within a certain wave number band. The instability is reminiscent of the Kelvin-Helmholtz instability, but occurs even for a homogeneous fluid.

A new family of P-stable two-step high-order methods with minimal phaselag are developed for the numerical integration of the special second-order initial value problem. An application to the one-dimensional Schrödinger equation, indicates that these new methods are generally more accurate than other previously developed finite difference methods.

A plasma x-ray source is generated using a 10 mJ, 450 fs KrF excimer laser pulse focused onto a copper target at intensities up to 1.6 × 10¹⁵ W/cm². The energy conversion efficiency from 248 nm laser light to x-rays in the range from 1 keV to 1.4 keV is measured as a function of the laser energy onto the target. The maximum observed efficiency is 0.5% for 5 mJ incident laser energy. The obtained results are compared with efficiencies observed using longer laser pulses of the same wavelength and intensity onto the target.

A new investigation of the Ne V spectrum is reported. The beam-foil method has been used to produce spectra at two different energies (1.2 MeV and 2.5 MeV) between 450 and 1100 Å. Sixty-five lines of Ne V have been newly identified. Fifty levels have been determined for the first time and energies have been revised for seven levels.

Two methods, the Method of Effective Trajectories and the Method of Distorted Particle Flux, are suggested for calculation of cross-sections of n-n' transitions between Rydberg states of multicharged ions induced by electron impact. These methods are based on rectilinear trajectories with effective impact parameter and effective velocity. The difference between direct calculations of Coulomb-Born cross-sections and these methods for transitions with principal quantum numbers n,n' ⩽ 6 is about 10-20%. Calculations of cross-sections 20 → 20 + Δn are given.

Changes of the moments of atomic spectrum due to configuration interaction (CI), the CI strength, the average shift of the energy of a level due to its interaction with all levels of distant configuration and other global characteritics of CI effects in atoms are systematised and their expressions presented. The results of the calculation of these characteristics for the energy level spectra of the 3s3p³ + 3s²3p3d configurations in Si isoelectronic series, 3p⁵3d^N + 3p⁶3d^N−24p + 3p⁶3d^N−24f (N = 5, 6, 7, 8) in Cr, Mn, Fe and Co isoelectronic series, ns²np^N + np^N+2 at n = 2 – 5 and N = 2 – 4 in neutral atoms as well as for the characteristic emission spectra corresponding to the 3p⁵3d⁹ + 3d⁷4p → 3d⁸ transitions as well as for the Auger M_4,5N₁N_2,3 spectra in Kr and N_4,5O₁O_2,3 in Xe are given and compared with the same characteristics of the more complete experimental spectra.

The optogalvanic spectrum of neon in the spectral region 410-545 nm has been studied using a FeNe hollow cathode lamp and an excimer laser pumped dye laser. Nearly 440 lines of Ne have been assigned in this region. Several series of lines are identified to involve one photon Rydberg transitions from 2p_m (where m = 1–10) to various ns and nd levels. A number of lines involving transitions from the 1s_n levels (n = 2–5) to various s, p and d levels have also been observed.

We have measured the differential elastic scattering cross sections in the atomic region 13 ⩽ Z ⩽ 82 using nearly monoenergetic unpolarised Cs Kα (30.85 keV) radiation at a scattering angle of 90°. Experimental elastic scattering cross sections are compared with the theoretical estimates based on form factor formalisms (relativistic, non-relativistic and relativistic modified form factors). Good agreement is observed between the experimental results and the theoretical estimates. Form factors were deduced using experimental elastic scattering cross sections. Real (f') and imaginary (if") parts of the anomalous dispersion correction components have been calculated relativistically. Experimental nonanomalous form factors were corrected for anomalous dispersion. Experimental results were compared with the theoretical estimates and discussed in order to reflect the data on the current knowledge. Deviation of the experimental form factors above and below the absorption edges, and also nearer to the edges clearly indicates the need of dispersion corrections.

Spectra of gold, emitted from a hollow-cathode discharge, have been recorded with the Lund Fourier transform spectrometer in the region 1800-8000 Å. Complementary photographic spectrograms in the region 800-1900 Å have been obtained using the 10.7 m normal incidence spectrograph at Observatoire de Paris, Meudon. The term analysis has yielded 75 new energy levels of Au II, and improved values are given for the previously known levels of the 5d¹⁰, 5d⁹6s, 5d⁸6s², 5d⁹7s, 5d⁹6d, 5d⁹6p, 5d⁸6s6p and 5d⁹7p configurations. The new levels belong to the 5d⁸6s², 5d⁹6d, 5d⁹8s, 5d⁸6s6p, 5d⁹7p and 5d⁷6s²6p configurations. About 450 identified Au II lines with a wavelength uncertainty of about 1 mÅ are reported. The energy level structure has been studied by using the Slater-Condon parametric method. The ionization limit has been determined to 162950 ± 200 cm⁻¹.

This paper reports an investigation of the spectrum and term system of Li-like carbon, C IV. Between 200 and 7750 Å a total of 105 C IV lines have been identified by combining previously known data with new spectra recorded by the beam-foil technique and from observations at the JET tokamak. A comprehensive term system, with accurate energies for all levels up to n = 12, is constructed from the identified transitions. Semiempirical series formulae are also given, allowing reliable extrapolations to still higher n values. The ionization energy is determined to (520 175.3 ± 1.5) cm⁻¹, which confirms recent theoretical predictions that include quantum electrodynamical (QED) corrections.

A differential absorption (DIAL) lidar system based on a Raman shifted KrF excimer laser was constructed and employed for vertically sounding measurements of tropospheric ozone. This system is described, including a presentation of measurements of Raman shifting efficiencies in hydrogen and deuterium. The performance of the new system was evaluated in measurement campaigns involving two further optical remote-sensing systems: A Nd:YAG/dye laser based lidar and a long-path differential optical absorption spectroscopy (DOAS) system, utilising a high-pressure xenon lamp.

We introduce an intermediate state of the light field which is alternative to the binomial state introduced by Stoler et al, thus interpolating between the number state | n ⟩ and the coherent state | α ⟩. A comparison between their properties shows that the amount of nonclassical effects obtained in the present state can be greater than that obtained in the binomial state, depending on the values of the interpolating parameters and the excitations n and _α. Quantum coherence effect exhibited by the present state is also discussed.

Correlation measurements on the states of two-level atoms having passed through a micromaser at different times can be used to infer properties of the quantum state of the radiation field in the cavity. Long(short) correlation length in time is to some extent associated with super(sub)-Poissonian photon statistics. The correlation length is also an indicator of a phase structure much richer than what is revealed by the usual single-time observables, like the atomic inversion or the Mandel quality factor. In realistic experimental situations the correlations may extend over many times the decay time of the cavity. Our assertions are verified by comparing theoretical calculations with a high-precision Monte-Carlo simulation of the micromaser system.

A new method for taking into account rigid boundary conditions is developed. Two types of constant-heat-flow boundary conditions are used in two-dimensional calculations. It is discussed whether conditions of heat transfer occurring on the boundaries are vital to origination of hard turbulence at high Rayleigh number. The results of calculations are analysed and compared with two types of experimental data.

The properties of a monochromatic x-ray backlighting system based on a spherically bent crystal were investigated. Simulations of spatial resolution for spherically bent crystals with different radius of curvature and for several wavelengths of incidence radiation were done using the ray-tracing method. Test experiments were carried out to demonstrate the high spatial resolution using the incoherent soft x-ray radiation produced by laser- and x-pinch plasmas. Both experimental and theoretical results show that a spatial resolution of at least 4 μm can be obtained in a field of view ranging from a few mm to cm. The narrow spectral band of the diffracted beam (Δλ/λ ∼ 3 × 10⁻⁴), the high efficiency of the presented scheme and the possibility of significantly reducing the self radiation of the studied object make it one of the most promising backlighting systems. This scheme permits the essential reduction of requirements of the source of radiation and could be a less costly alternative to using x-ray lasers for such purposes.

A description of nonstationary simple waves and Riemann invariants in a relativistically hot electron-positron magnetoplasma is presented. It is noted that at relativistic temperatures the photon energy far exceeds the internal kinetic energy and that the particle effective mass depends strongly on the temperature. Starting from a set of relativistic radiation magnetohydrodynamic equations, the nonlinear characteristics and velocities of simple waves are obtained. The equations are further employed to examine the Riemann invariants in the presence of isentropic flow. It is found that at ultra-relativistic temperatures the photon pressure and the relativistic mass variation play a very important role.

The real part of the relative permittivity ε'_r as well as the dielectric loss as represented by ε''_r for the compounds (CH₂)_n(NH₃)₂MCl_4−xBr_x (where x = 0, 2, n = 2, 3 and M = Cu, Co) have been measured. The measurements were carried out as a function of temperature and frequency. Both ε'_r and ε''_r show the same relaxation phenomena which involves large reorientable dipoles in the total polarization. The phase transition observed at ~312K for ε'_r and ε''_r is expected from the variation in the spacing between the adjacent metallic layers arising from the increase in the number of carbon atoms and/or introducing the Br⁻ ions in the out of plane position.

The real and imaginary parts of the relative permittivity (ε'_r and ε''_r) as well as the a.c. resistivity of the mixed ferrite Co_xZn_1−xFe₂O₄ (x = 0.1 → 1.0) were measured as a function of temperature and frequency. The calculated values of the activation energy indicate that the conductivity of the system increased with increasing Zn concentration. The Curie temperature of the system as determined from a.c. conductivity measurements agree well with that of the relative permittivity. The calculation of the relaxation time (τ) from Cole-Cole plots indicates that its maximum value occurs at the critical concentration (x = 0.6). The grain size was calculated at different Co concentration with values ranged from 0.995 × 10⁻⁷ to 0.617 × 10⁻⁷ mm.

In this paper we address the problem of monitoring the amorphous silicon intrinsic material inside p-i-n thin film structures. Most of the techniques adopted for characterisation of single thick films cannot be used in this case; available techniques indeed lack precision, mainly due to spatial and energy distributions of defects. We achieve information on material properties by comparison of several different measurements performed on the samples. Capacitance measurement under forward bias is included in this set, together with I-V measurements in light and dark conditions, quantum yield, and temperature dependence of the dark current. A theoretical analysis of the different measurements shows how each result can be combined with the others to obtain a unified picture. Measurements were performed on samples with different p-i interface obtained by changing the structure of the amorphous silicon-carbide buffer layer. We show that intrinsic amorphous silicon grown at the interface is subject to an increase of quasi-shallow defects levels and to a decrease of deep defects with increasing buffer deposition time. This behaviour configures a balance effect between deep defects and quasi-shallow defects, ruled by the interface status.

The third author's name and affiliation were omitted from the article published in Physica ScriptaT69 (1997) 52–59.