Table of contents

In this paper we make a Painlevé analysis of the Zakharov-Kuznetsov equation (which governs nonlinear ion-acoustic waves in a magnetized plasma) and show that it possesses the Painlevé property though there is no other evidence that this equation is integrable.

Research in recent years shows that a number of physically significant problems can be modelled by coupled nonlinear wave equations. It is observed that most of such equations exhibit solitary wave solutions which reveal the important properties of the system concerned. In this work, we consider a coupled system which describes the propagation of dispersive water waves. By an explicit analytical method we demonstrate several solutions of the equation. It is worth remarking that under certain conditions solitary wave solutions can be obtained. Finally, some interesting results are also found by introducing cubic nonlinearity in the basic system.

An unexpected new method of high speed narrow-banded filtration and separation of electromagnetic signals in the range (1-10⁴) Hz is proposed. This method, based on thermic transformation of LF electromagnetic waves to second sound waves in a cavity, filled in by superfluid helium, may be utilized for processing of carrying and beating frequencies in the LF range. Superfluidity phenomena, hitherto useless in instrumentation, proved to be valid for quick spectral measurements in the LF range important for geophysics and cosmic radiophysics.

Dielectronic recombination rates and cross sections for the metastable C V and O VII ions are calculated and found to be extremely large, with cross sections of the order of 10⁻¹⁵ cm² and rates of the order of 10⁻⁹ cm³ s⁻¹ for individual resonances. Electric field enhancement and composition of the metastable 1s2s ion beams in terms of (¹S) and (³S) are used to reproduce the recent experimental data of Andersen et al. [Phys. Rev. Lett. 62, 2656 (1989)] for O VII and unpublished data for C V. The overall features are well explained in the case of carbon, while the features for oxygen are well explained except for the broad prominent peaks at 2.5 and 6.8 eV, which are only partially explained.

We present a model of dense sodium vapour ionization induced by nanosecond resonant laser pulses exciting the 3S → 4P transition. The results of calculations are compared with those obtained by means of a similar model for the case of 3S → 3P excitation. The possibility of population inversion formation between excited sodium levels is also discussed.

A simple numerical method of constructing orthogonal fine structure parameters is suggested. The possibility of estimating the parameters from experimental energy levels is discussed. Parametric fitting to the 2p⁵3d configuration in A1 IV is carried out as a numerical example.

An experimental investigation is conducted to enhance the output energy of a N₂ laser using a flow enhanced corona discharge phenomena (Corona Torch). The results show that the output energy increases using that type of corona by more than three-fold. Moreover, the corona polarity shows a significant effect on the output energy of the N₂ laser.

The spectrum of singly ionized oxygen, O II, emitted by a spark-generated, electrodeless discharge light source, has been investigated in the wavelength range 2100-11 700 Å. About 740 lines, 359 of which have not been reported earlier, were measured. As a result the energies of about 50 new levels have been determined, and the O II term system now presented includes 254 levels. The quartet system is firmly connected to the doublet system by 56 identified intersystem lines. The ionization limits have been determined by applying the polarization formula to the 4f, 5f, 5g and 6g levels. The experimentally determined value for the lowest limit, 2s²2p²³P₀, is 283 270.9 ± 0.5 cm⁻¹ above the 2s²2p³⁴S_3/2 ground state.

Conventional three level probe spectroscopy is used to investigate magnetically induced level crossings. Pump laser induced signals in the probe laser response are investigated when the atomic systems are tuned magnetically. This has been carried out in both a co-propagating and a counter-propagating configuration. The level scheme considered is a simplified J = 1 → J = 2 → J = 1 system. The theoretical calculations are based on the semiclassical laser theory and the equations obtained are solved numerically. Experimental verification of the theoretical lineshapes is carried out in a neon gas absorber. The agreement between the calculated results and the measurements is good.

Radiative lifetimes of some levels belonging to 2p⁵ 4p configuration of Ne I have been determined using electron excitation followed by selective laser excitation. The experimental results of this work are 123.8 ± 3.6 ns, 120.3 ± 2.8 ns and 135.9 ± 4.5 ns for the 4p'(3/2)₁, 4p'(1/2)₁ and 4p(5/2)₂ levels respectively.

The finite element method (FEM) is now developed to solve two-dimensional Hartree-Fock (HF) equations for atoms and diatomic molecules. The method and its implementation is described and results are presented for the atoms Be, Ne and Ar as well as the diatomic molecules LiH, BH, N₂ and CO as examples. Total energies and eigenvalues calculated with the FEM on the HF-level are compared with results obtained with the numerical standard methods used for the solution of the one dimensional HF equations for atoms and for diatomic molecules with the traditional LCAO quantum chemical methods and the newly developed finite difference method on the HF-level. In general the accuracy increases from the LCAO - to the finite difference - to the finite element method.

We show that configuration mixing coefficients can be evaluated from the fine structure level data under some circumstances. Specifically, these values are found for the 3snf series as perturbed by the 3p3d³F° levels in Al II and in Si III. Comparisons are made with results from configurational interaction calculations.

The lifetime of the 4s level in Al I-like ions, from Cl to Mn, has been measured by beam-foil spectroscopy in order to check on the validity of calculations which predict irregularities of the oscillator strength of the 3p-4s transition. The experimental data do not confirm the presence of notable irregularities. More complex theoretical calculations reported elsewhere corroborate these findings. The measured lifetimes are close to the predicted ones.

The eventual reordering along the isoelectronic sequences of the atomic shells of ions with 61 to 64 electrons (Pm I- to Gd I-like) into systems with one to four electrons outside the closed 4f¹⁴ electronic shell has been predicted by theory. However, this prediction provides a formidable challenge for an experimental proof, since very line-rich spectra are associated with ions with so many electrons. The possibilities and problems of a beam-foil spectroscopic approach which combines wavelength and lifetime measurements are discussed, and the results of a search for the intercombination lines expected in such few-electron spectra are presented for ions of Os, Pt and Au. Tentative identifications are given for intercombination lines in the Sm I- and Eu I-like spectra.

Explosive growth of self-forming structures of a "bell-shaped" form occurs in media, such as hot plasmas, as a result of simultaneous reaction-diffusion processes. The problem of interaction of two such structures is studied analytically for cases where the overlap between them is nearly complete. The change in explosive growth-rate from the optimum one is determined as a function of the separation between the centres of the two structures. The case where an asymmetry exists between the central values of the interacting structures is found to be of particular interest. It is discovered that, under certain conditions, run-away in amplitude of one structure from the other may occur.

Computer simulations of the expansion of a plasma cloud into vacuum in an external electric field is performed. The features of motion at different stages are studied. Particle currents to the electrodes are calculated. A comparison of the numerical solution with simple analytic models is made.

The toroidal ion temperature gradient electrostatic drift waves are investigated including the effect of ion dynamics parallel to the ambient magnetic fields. By using the transport equations of Braginskii, the mode equations are derived. The local as well as nonlocal dispersion relations are obtained and various limiting cases are discussed. Also addressed is the issue of the anomalous ion energy transport that is caused by the nonthermal ion temperature gradient drift waves. A possible stationary solution of the nonlinear mode coupling equations is presented. The relevance of our investigation to the ion energy confinement in tokamaks is pointed out.

A model based on the continual deformation of mass distribution by sputtering of thin films is formed. Presented theory shows that due to mass deformation acoustical phonons are eliminated which causes a higher critical superconductive temperatures. The theory and experimental data for ceramic oxides are in good agreement. Presented theory should serve the synthesis of new superconductive materials. Some general considerations concerning specificity of phonon spectra in thin films are also exposed.

The experimental work presented in this paper is associated with the impact ionization phenomena which may occur during the surface discharge process of solid organic dielectrics. According to the experimental results, it may be stated that, surface discharges are closely related to negative differential resistance and impact ionization. It is also shown that the electromagnetic spectrum of the radiation which is emitted during gliding discharge occurrence may be varied between acoustic waves and soft X-rays.

Giant polarition dispersions by Frenkel excitons are derived and compared within three approaches: the boson representation, the effective Hamiltonian formalism and that based on the exact commutation relations for non-boson exciton operators. The latter approach resulted in a situation which could serve as a possible method of determining the effective dynamical exciton-exciton coupling constant by measuring dispersion curves of the polariton energy lower-branches under different levels of excitation.

Within the Random Phase Approximation and by using the exact trilinear commutation relations for Frenkel exciton operators an effective Hamiltonian is constructed for a coupled exciton-photon system in highly excited molecular crystals. The polariton dispersion relations derived from the Hamiltonian is explicitly dependent on the excitation level.

We investigate here how the CDW and the distribution of non-magnetic impurities affect each other. The former is assumed to induce a distortion of the latter having the same wave vector. This CDW-induced distortion yields an enhancement of CDW which competes to the usual destructive effect via electronic life-time. The behaviour of relevant quantities changes in a non-trivial manner as compared to the case of perfectly random inpurity distribution. Depending on the values of the various coupling strengths of the problem, a reentrant CDW can be obtained by increasing the impurity concentration. The conditions for occurrence of the gapless CDW state are also modified. Thermal hysteresis effects are suggested for the doped quasi-1D conductors. Data reported for a variety of compounds ((CH)_x, NbSe₃, deuterated thiourea, (TMTSF)₂X) are interpreted within the present model.