Table of contents

The planar symmetrical (n+1)-body problem in a Manev-type field (featured by a potential of the form α/r + β/r²) is being tackled. One proves that, if n equal masses are initially situated at the vertices of a regular polygon centered in the (n+1)-th mass (Maxwell's model for the rings of Saturn), and if the initial velocities form a vector field symmetrical with respect to the central mass, then the polygonal configuration is preserved all along the motion, but with variable side and with variable rotation around the centre. The motion of every mass relative to the centre is given by the solution of the Manev-type two-body problem. All possible behaviours of the polygonal solution are surveyed, and the equilibria of the problem are pointed out. One associates a restricted problem to them, for which the Jacobi integral is proved to exist.

An extended concept of the Morse oscillator is presented, where the potential is constructed from several smoothly joined Morse-type (ordinary, reversed or pseudo-Morse) components. The analytic procedures of calculating the complete spectrum of the bound states of the modified Morse oscillator are described. The validity of the asymptotic normalization of the continuum wavefunctions is discussed and a correction method suggested, which takes account of the rigorous sum rules for the complete set of the energy eigenfunctions. All the analytic procedures are illustrated on Xe₂ molecule in its 0_g⁺ and 0_u⁺ electronic states.

Macroscopic adiabatic invariants are found for plasmas with equilibrium electric fields, and nonlinear constraints on energy transfer between particles and turbulent electric fields are analyzed. The fluid convective-cell model is considered, as well as a general quasi-particle theory, which takes into account kinetic effects. The role of temperature gradients is investigated within the context of the latter.

The spectra of iridium were photographed on 3-m and 6.65-m normal incidence spectrographs in the region 300–2100 Å using a triggered spark source. The (5d³ + 5d²6s) – 5d²6p transitions were investigated. The configurations 5d³ and 5d²6p had been previously studied which resulted in establishing all 19 levels of the 5d³ configuration and 44 out of 45 levels of the 5d²6p configuration. In this analysis 15 out of 16 theoretically possible levels of the 5d²6s configuration have been found which are based on 106 classified lines as being the transitions from the 5d²6p configuration. All previously found levels in Ir VII have been confirmed. One missing level in the odd configuration has been established and 46 additional spectral lines have been identified as the 5d³ – 5d²6p transitions in the ion. Calculated energy values and LS-compositions, obtained from the fitted parameter values using the orthogonal operator approach, are given for all levels of the three configurations.

A field theoretic study of the simultaneous electron – photon excitation (SEPE) and direct electron excitation (DEE) is done for He 1¹S → 2³S transition by spin polarized electrons in a field of soft photons. The ratio of SEPE to DEE is found to lie around 3 × 10^-3 for 0.117 eV photons and incident electrons of energy E_i between 19.817 eV and 20 eV. The present result is compared with the existing experimental data.

The lifetimes of 11 levels in the 2s6d, 6f and 6g configurations in O V have been determined using the beam-foil technique. The new CCD detection system is described and its advantages for atomic lifetime measurements are discussed. The experimental results are compared with ab initio theoretical and semiempirical values calculated by the superposition-of-configurations method. Configuration interactions between 2s6f and 2p4d and between 2s6g and 2p4f are found to have a significant influence on the lifetimes and an accurate treatment of this level mixing is necessary to bring theory and experiment into agreement.

Spectra of Rb XIII and Sr XIV have been studied in the region from 80 to 110Å by means of a triggered spark and a 3m-grazing incidence spectrograph equipped with a 3600 lines/mm holographic grating. Sixty-two lines in Sr XIV and 105 lines in Rb XIII are used to derive energy levels of the ground configuration 3p⁶3d⁷ and of the first excited odd parity configuration 3p⁵3d⁸. A parametric study by means of the chain of Cowan codes stresses the importance of configuration interactions (C.I.) within the Layzer complexes (3)¹⁵. Both the effective electrostatic C.I. parameters and the full complex treatment lead to a reduction of the large residual deviations noticed in earlier studies of 3p⁵3d⁸ configurations of the sequence Y XV–Mo XVIII. Theoretical transition probabilities are reported for all classified lines.

We analyze how the frequency dependence of the electric permittivity ε affects the electromagnetic field radiated by a point charge uniformly moving in a medium. Various limiting cases are studied analytically and confirmed numerically. It turns out that a moving charge radiates at every velocity when the standard parametrization of ε is chosen. The space distribution of this radiation exhibits rapid oscillations behind the moving charge. They differ drastically for charge velocities below and above some critical velocity ν_c defined by the medium properties and independent of frequency. It turns out that for ν < ν_c the radiation flux is maximal at the same place where in the absence of ω dispersion lies in the Cherenkov radiation singular cone. For ν < ν_c the radiation flux is maximal behind the moving charge on a sufficiently remote distance. This consideration is applied to the interpretation of experiments recently discussed in physical literature.

In the present paper cavitation processes induced by laser pulses are studied. Some applications of cavitation processes are also discussed.

A theory of electromagnetic fluctuations in dusty plasmas is developed with regard for the dynamics of charging processes associated with electron and ion absorption by grains. Dielectric response functions and correlation functions of the Langevin sources are calculated in terms of the transition probability matrix of a system with no self-consistent electric fields. General relations for the correlation functions of electron density fluctuations are derived and detailed numerical analysis of their spectral distributions is performed. The fluctuation spectra are shown to be considerably modified by the self-consistent grain charging dynamics.

A model of filamentation in azimuthal direction for cylindrical microwave discharges is presented. Instability is shown to be driven by particle diffusion, caused by electron pressure gradients. A "window" for the azimuthal mode numbers, where the azimuthally asymmetric modes are unstable, is shown to open if the electron density in the discharge is sufficiently high. The presented model is in reasonable agreement with experimental observations of filamentation in surface-wave-sustained discharges.

A rippled metal surface with periodicity wave vector qz acts like a ftee electron density modulation n_q. A high power laser incident on it produces an oscillatory velocity of electrons in the ripple region and exerts a second harmonic ponderomotive force on them, giving rise to a second harmonic velocity, ν₂. The beating of ν₂ with the density ripple nq, produces a nonlinear current that generates a resonant second harmonic surface plasma wave, when q = (2ω/c) ((ε₂/(1 + ε₂))^1/2 – sin θ), where w is the frequency of the incident laser, θ is its angle of incidence and ε₂ is the effective permittivity of the metal at 2 ω frequency.

The character and role of finite correlations between potential and magnetic low-frequency plasma excitations are investigated. Caused by the Lorentz force, they are significantly inherent to the nonlinear plasma behaviour. The cross-field correlations are found to narrow the renormalized width of the potential fluctuation spectrum and broaden that of the magnetic one. So the anomalous diffusion relevant to the long-wave perturbations, is increased. The anomalous heat conductivity associated with the short-wave motions, is not essentially influenced.

The angular force model of Clark, Gazis and Wallis (CGW) have been applied to calculate the phonon frequencies of antiferromagnetic Fe-30%Mn alloy. Furthermore, the second order elastic constants of the alloy have been computed using a new empirical many body potential (MBP), which has been developed by Akgün and Uğur. The parameters defining the MBP for the alloy have been computed following a procedure given by Akgün and Uğur. The computed elastic constants have been used to calculate the phonon frequencies of the alloy. Finally the theoretical results have been compared with the corresponding experimental values.

A nonequilibrium distribution function for electrons in metals excited by ultrashort laser pulses and its relaxation dynamics is analyzed. This distribution function is based on a kinetic differential equation for the nonequilibrium population of excited electrons. The deviation of the distribution function from the equilibrium one can be monitored by femtosecond broadband pump-probe spectroscopy. Transient changes of the dielectric function Δε and the relaxation of nonequilibrium charge carriers in a thin gold film are discussed for different excitation energies ℏω_pump that corresponds to intra- or interband excitation or to photoemission of the excited electrons.

The investigation of ultrafast processes in copper films by femtosecond pump-supercontinuum probe laser spectroscopy is presented. The energy dependence of electron-electron and electron-phonon scattering rates in wide spectral region of probing 1.6 < ℏω_probe < 3.2 eV is clearly observed. It is shown that the relaxation rates sharply slow down in the spectral area, related to the optical transitions into the vicinity of the Fermi level. The position of rate minimum gives the location of the Fermi level. The rate energy dependence around minimum gives unique information on the quasiparticle damping rate near the Fermi surface and thus on the Fermi liquid vs non-Fermi liquid behavior.

p-TlGaSe₂ and Tl_(1-x), GaPr_xSe₂ single crystals were grown by the modified Bridgman-Stockbarger method. The absorption measurements were carried out in p-TlGaSe₂ and TI_(1-x)GaPr_xSe₂ samples in temperature range 10–320 K with a step of 10 K. The phonon energies calculated for p-TlGaSe₂, p-TI_0.999GaPr_0.001 Se₂ and p-Tl_0.995GaPr_0.005Se₂ are 34.0 meV, 30.0 meV and 35.0 meV, respectively. At 300 K, the direct band gaps of p-TlGaSe₂, p-Tl_0.999GaPr_0.001Se₂ and p-Tl_0.995GaPr_0.005Se₂ are 2.165 eV, 2.164 eV and 2.155 eV and the indirect band gaps are 2.110 eV, 2.122 eV and 2.128 eV, respectively. There is an abrupt change in the direct energy peak for p-TlGaSe₂ in the temperature ranges 230–250 K, for p-Tl_0.999GaPr_0.001Se₂ and p-Tl_0.995GaPr_0.005Se₂ in the temperature ranges 195–215 K. On the other hand, indirect energy peaks for p-Tl_0.999GaPr_0.001Se₂ and Tl_0.995GaPr_0.005Se₂ are in the temperature ranges 215–235 K.

Large photoinduced transmission and reflection is observed in porous silicon (PS) films in the spectral region 1.6–3.2 eV by using a femtosecond pump-supercontinuum. probe technique. The measured nonlinear transmission and reflectivity spectra have a fast component ~500 fs. The spectral structure and relaxation dynamics of the short-lived component with slowing down of relaxation rate at ~1.95 eV and ~2.5 eV are suggestive that relaxation processes correspond to nanocrystallites defects scattering. Observed coherent phonons vibrations at 518 cm^-1 and 480 cm^-1 may be attributed to the size of crystallites ~5 nm and due to presence of a disordered phase, respectively.

The evolution of atmospheric gravity waves (AGW) in unbounded horizontal winds with constant shear is developed for the three-dimensional case. The atmosphere is considered to be isothermally stratified and the wind shear lies in the horizontal plane. Time varying frequencies of the AGW, which for large times tends to the isothermal Brunt-Väisälä frequency is obtained. The excitation of vortical perturbations located in the horizontal plane – shear waves, is shown. The time variation of AGW frequencies, the existence of shear wave and their amplitudes amplification/damping are due to the presence of the horizontal shear flow. The horizontal shear flow as a possible source of formation of large scale travelling ionospheric disturbances (TIDs) with small period (16–19 min) is considered. The different pictures of evolution of the AGW like initial perturbation are obtained in vertical, horizontal winds and its shear directions. The importance of coupling between the gravity and shear waves in the horizontal shear flow is shown. The possibility of transformation of shear waves into AGWs is demonstrated.

A new plasma mechanism for the magnetic field generation in the Crab Nebula is put forward. The mechanism is based upon the development of a two-stream instability resulting from the supernova explosion which took place in 1054 and led to the formation of the Crab Nebula.