Table of contents

A manifestly dissipative dynamical system which is measure preserving and non-reversible is found to exhibit Hamiltonian type of chaos for certain values of the parameters. The onset of chaos is studied through a computation of the Lyapunov exponent and the analysis of the Kolmogorov-Arnold-Moser regions. The critical values of the parameters are obtained in course of our analysis.

We have analyzed the positive and negative energy solutions of the Schrödinger equation, with derivatives of δ functions as potentials. It is found that these potentials act as localized, infinite barriers and the wave functions outside the barrier may be obtained by requiring that they vanish at the barrier. We have also obtained the Green's functions for these potentials.

We are investigating a large number of Rydberg series of neutral calcium, with the help of the recently introduced Spline-Galerkin method. Perturbers belonging to the 4p², 3d², 3d5s and 3d4p configurations are investigated and their influence on different Rydberg series is discussed. Results are reported for members of different Rydberg series, with n up to 20-30, and compared with experiment and other theories.

Using a semiclassical approach, we have calculated electron-, proton-, and ionized-argon-impact line widths and shifts for 24 Rb I multiplets. The resulting data have been compared with existing experimental and theoretical values.

Semiempirical calculations of probabilities of the radiative transitions 5d⁹6p-5d⁹6s, 5d⁹6p-5d¹⁰ in Pt-like spectra of Tl IV-Bi VI were carried out. Effective magnetic interactions were introduced when fitting the 5d⁹6p, 5d⁹6s levels. A situation when it is possible to neutralize consequences of the error of particular level identification is discussed.

The R-matrix method is used to calculate the photoionization cross-section of Ti XIII from its ground and first three excited states. The results are obtained for photon energies ranging from the first ionization threshold to just above the second ionization threshold of the residual ion Ti XIV. Configuration interaction wavefunctions are used to describe the initial Ti XII and final Ti XIV states. The positions and effective quantum numbers for the Rydberg series converging to the excited state 2s2p⁶²S^e of the residual ion, are predicted.

Electron impact excitation rates for the Be-like ion Si XI, Ca XVII and Fe XXIII, calculated with the R-matrix code, are used to interpolate or extrapolate data for the ions between Sc XVIII and Zn XXVII. Results for all 45 transitions among the 2s^{2 1}S; 2s2p³P, ¹P; 2p^{2 3}P, ¹D and ¹S levels are presented in the form of polynomial fits in log T_e to the effective collision strengths (γ) for each transition. These fits lead to results accurate to an estimated ± 10%, and are applicable over a temperature range of log T_max ± 0.8 dex, where T_max is the temperature of maximum fractional abundance in ionization equilibrium of the relevant species. Significant differences between the present results and the earlier distorted-wave calculations of Bhatia et al. for Ti XIX and Ni XXV are found for some transitions.

The spectrum of thallium was photographed in the 700-1500 Å region on 6.65 m and 3 m normal incidence spectrographs, using a sliding spark and a triggered spark as excitation source. On the basis of these new measurements we have established 29 levels of the 38 theoretically possible levels of the 5d⁷6s configuration of TI VI. Of the 70 levels of the 5d⁷6p configuration, given before, 68 levels have been confirmed, two levels have been revised and 21 new levels were established. 289 lines have been classified in the 5d⁷6s-5d⁷6p transition array of TI VI. Additional lines in the 5d⁸-5d⁷6p transition array are presented. The ¹S₀ level of the 5d⁸ configuration has been established. Least-squares fitted parametric calculations were carried out and they describe the spectrum adequately.

The excitation cross-sections of DyI spectral lines in the 262-363 nm spectrum region have been measured by the extended crossing beams method, recording optical signals from the intersection region. Measurements have been made of 21 optical excitation functions at electron energies varying from the excitation threshold to 200eV. For 59 lines of DyI earlier unclassified a classification is proposed within the known term system. The experimental conditions are discussed in detail.

We present a set of concise formulas for dielectronic recombination rate coefficients of the He-like isoelectronic sequence for ions from B³⁺ to Xe⁵²⁺ in the electron temperature range from 0.1 keV to 70keV. These formulas are obtained by fitting the directly computed dielectronic recombination rate coefficients on the basis of the relativistic intermediate-coupling MCDF model made by M. H. Chen and J. Nilsen. The reproduced dielectronic recombination rate coefficients are in close agreement with the original results of Chen. The errors are generally less than 5%. Our formulas may be used easily to obtain dielectronic recombination rate coefficients for other members of the He-like isoelectronic sequence between B³⁺ and Xe⁵²⁺ in which explicit calculation are unavailable. The detailed results are tabulated and discussed.

The results of experimental and theoretical studies of hole distribution function and cyclotron resonance (CR) laser emission processes in uniaxially stressed p-Ge in strong crossed E ⊥ H fields are presented. The CR emission spectra were studied for various orientations of E and H fields with respect to the crystallographic axes of the p-Ge crystal. A complicated structure of CR emission spectra (instead of a single line without stress) was found to arise in stressed crystals, corresponding to transitions between different pairs of light hole Landau levels. A considerable effect of quantum deformation of the lower light hole Landau levels due to interaction and mixing of light and heavy hole states on emission spectra was found, resulting in strong broadening and shift with the stress of an emission line, corresponding to (n = 2) → (n = 1) transitions. The transitions were shown to dominate in CR emission spectra for stress larger than 400 bar. Numerical calculations of hole lifetimes and distribution function in uniaxially stressed Ge based on the quantum model of carrier dynamics in strong crossed E and H fields were carried out, taking into account the optical phonon and ionized impurity scattering processes. The results of the calculations allowed us to identify the observed CR transitions.

It is shown that the relativistic ponderomotive force exerted by an ultra intense laser pulse launched in a plasma could generate a very strong low frequency (with index 1f hereafter) magnetic field B_1f with a maximum value of the order of B_1f/B₁ = ω_pe/ω, where ω_pe is the electron plasma frequency and ω the laser one, and B₁ the high frequency magnetic field of the laser pulse. We derive the mechanism for this B_1f-field creation in an underdense plasma and show how to diagnose its presence and propose an experimental set-up to achieve the measurement. We also stress the universality of this detection as far as picosecond pulses and the far infrared radiation range (FIR) are concerned. The great influence of this B_1f-field on related important phenomena, such as relativistic self-focusing and wakefield generation by short laser pulses, is briefly underlined.

We propose a new method to determine reflection coefficients for nonsinusodial electromagnetic waveforms containing only a few oscillations. This method is suitable for studies of wideband pulses which cannot be treated by the traditional Fourier techniques. The incident waveform is described by means of Hermitian functions in order to illustrate how the reflection is influenced by the pulse shape and duration.

The dynamic response of a burning fusion plasma to periodic particle source fluctuations as well as to self-induced or externally induced fluctuations in the transport coefficients is studied. Simple coupled reaction-diffusion equations are deduced for the dynamic description of the time variation of the temperature and density in the central part of the plasma. As a result of the form of the alpha particle heating term such a system of equations exhibits free oscillations in temperature and density in approaching an equilibrium state from any given initial state. When the particle sources or the transport coefficients are asumed to have driven periodic parts the plasma responds dynamically by exhibiting a mixture of free and forced oscillations. Since, due to heat conduction and particle diffusion, the free oscillations will be damped, only the forced oscillations remain after some time. The plasma dynamic response to the driven variations in the source and transport coefficients contains information about the plasma transport parameters, e.g. the power of the temperature dependence of the heat conductivity as well as of the particle diffusion. It might therefore be used for diagnostics for a burning fusion plasma.

In this paper we report an application of forward bias, low frequency capacitance measurements in order to relate the electrical properties of the intrinsic material to the solar cell performance after photodegradation and thermal recovery. The capacitance vs. frequency technique (C-v-f) is based on the measurement of the variation of the total charge trapped in the gap defect states of the intrinsic layer during a low frequency voltage perturbation. As expected, after illumination the efficiencies of the tested devices decreased. These variations were found to be only weakly related to the initial electrical performance, but strongly dependent on the initial density of states of the intrinsic layers. Efficiency degradation of the investigated solar cells has been quantitatively related to a reduced mobility-lifetime product and, lesser, to a variation of the density of defects. The defects detected by the C-v-f technique are positioned around 0.55 eV from the band-edge and do not act as recombination centers but, rather, as free carrier traps. Thus, due to their energy position they do not interfere with steady-state current-voltage (I-V) measurements and with recombination mechanisms. Employing either the I-V or the C-v-f technique, a more complete picture of the defect distribution in the gap of a-Si : H has been drawn and the defects behaviour, after light soaking and annealing, has been investigated.