Table of contents

The anharmonic oscillator d²x/dt² + f₁(t)dx/dt + f₂(t)x + f₃(t)xⁿ = 0 (n ≠ 0, 1) is investigated applying the invertible point transformation, Lie symmetries and the Painlevé test.

A Melnikov type condition for the existence of homoclinic points in higher dimensional dynamical systems is discussed. An application to the homoclinic bifurcations in a parametrically driven Lorenz system is described. For selected parameters the theoretical predictions are checked by numerical experiments.

A sharp peak at 1150 MeV c⁻² in the π⁻π⁺π⁻π⁺ -system in the final state of ⁴He-reactions at 0.6 GeV c⁻¹ incident momentum is seen. This system probably has spin-parity = 0⁺ or 2⁺, which are possible spin-parity assignments of a glueball.

The influence of a quadrupole pair interaction on K^π = 1⁺ states in rare earth nuclei is investigated using the Quasiparticle Random Phase Approximation. Comparison of the obtained results with available experimental data indicates a rather weak quadrupole pair interaction in these nuclei. The calculation of the B(M1) strength is extended to higher energies to account for the recently observed higher lying M1-strength. The differential cross section of inelastic electron scattering is calculated within DWBA for lower lying K^π = 1⁺ states and is seen to be consistent with the interpretation that the observed states around 3 MeV are of isovector convection current character and have their main M1-strength coming from natural parity proton components.

Stark widths of many prominent 6s-6p and 5d-6p transitions have been measured and compared with theoretical results. A high current pinched discharge was used as a spectroscopic source. Electron density and temperature were estimated in 2.65 × 10²²m⁻³ and 1.45 × 10⁴ K respectively.

Experimental Stark widths agree well with previous theoretical results. Our data are compared with those of other authors concerning to the homologous ions Ne II, Ar II, Kr II and Xe II.

The photoabsorption spectrum of neutral chlorine has been photographed for the first time in the wavelength region 400-700 Å, the absorbing atomic vapour being produced by means of the flash-pyrolysis technique. Nine autoionizing resonances have been observed and identified as forming a series arising from the excitation of the inner 3s electron. The agreement with theoretical results is discussed.

This paper describes a new facility for accelerator-based atomic spectroscopy where three spectrometers, together covering the 40-8000 Å interval, simultaneously view the beam. The target chamber has been designed to give the monochromators the highest possible spatial resolution. In combination with a minimum foil transition of 0.5 μm, over a total length of 360mm, atomic lifetimes in the 1 ps to 100 ns range can be measured using ions with MeV energies. As a test of the set-up spectra and decay measurements in fluorine below 300 Å are reported.

With the new experimental set-up for beam-foil spectroscopy at the University of Lund atomic lifetimes down to about 10 ps are straight forward to measure at MeV energies. In this paper we discuss the modelling of the observed decay curves, including the effects of the finite spatial resolution of the monochromator and shadowing by the foil, that is necessary to obtain ps or even sub-ps lifetimes. The detailed model presented is based on measureable geometric quantities only and is found to accurately reproduce observed data. We conclude that the uncertainty in the shape of the foil surface is an important factor setting the low-lifetime limit for this method of analysis.

The transition 3d¹⁰4p²P^o-3d⁹4s²²D in Cu-like ions, the XUV laser transition proposed by Morley and Sugar, has now been identified in delayed spectra obtained with foil-excited ion beams of Nb, Mo and Ag. Calculations of the wavelengths agree closely with the observations, but the observed decay times are significantly larger than the theoretically expected lifetimes. We show that the lifetime is probably obscured by long-lived cascades from the lowest-lying quartet levels.

Experimental results concerning synchrotron radiation, particle losses and effects of initial plasma temperature on the relativistic plasma formation are given. The life time of a relativistic plasma in a simple mirror device coincides with the time of turbulent diffusion.

A numerical analysis of the three-wave decay interaction of oblique whistler mode waves with different types of ion waves is presented. It is shown that at altitudes h < 2000 km the most effective mechanism is the decay interaction of whistlers with quasielectrostatic ion-cyclotron waves (the increment is Γ ~ 25s⁻¹ for an initial whistler pump wave amplitude of ₁⁰ = 10 mVm^-1) as well as with Alfvén waves and ion-ion hybrid waves (Γ ~ 10s⁻¹ for the same pump amplitude ₁⁰). When taking into account the media inhomogeneity and the decay wave stabilization due to pump wave amplitude depletion, the magnitudes of excited ion waves are found to be E₃ ~ 50-120μV/(mHz^½) for ₁⁰ = 10 mVm^-1. At such amplitudes parametrically excited ion waves can provide transverse ion acceleration with a rate of 0.5eVs⁻¹ and longitudinal electron acceleration up to 5eV at a distance of the order of 2000 km, the flux reaching 3 × 10⁷ el/(cm²s sr eV).

Conditionally averaged random potential fluctuations are an important quantity for analyzing turbulent electrostatic plasma fluctuations. Experimentally, this averaging can be readily performed by sampling the fluctuations only when a certain condition is fulfilled at a reference position. Alternatively, for time stationary and homogeneous turbulence, analytical expressions, involving higher order correlation functions R_n(r, t) = ⟨ϕⁿ(ζ, τ)ϕ(r + ζ, t + τ)⟩, can be derived for the conditional averages. These expressions have the form of series expansions, which have to be truncated for practical applications. The convergence properties of these series are not known, except in the limit of Gaussian statistics. By applying the analysis to numerically simulated ion acoustic turbulence, we demonstrate that by keeping two or three terms in these series an acceptable approximation is obtained even in cases deviating significantly from Gaussian statistics.

Graphite collector probes were exposed in a time-resolved mode to several plasma discharges in TEXTOR under different configuration of poloidal and toroidal limiters as well as under different plasma densities. Fluxes of oxygen, metals and deuterium atoms in the scrape-off layer were collected on the probe surfaces and determined afterwards by means of Rutherford backscattering spectroscopy and nuclear reaction analysis. Similarities in the temporal and spatial behaviour of deterium and impurity fluxes were observed. For a given probe the ratios of collected fluxes, oxygen to metals and oxygen to deuterium, were almost constant. A distinct reduction of the collected fluxes was noticed when ALT II toroidal limiter was in operation since the characteristic decay lengths are shorter in the presence of the toroidal γ_T than of the poloidal γ_P limiter. The collected fluxes were observed to decrease with increasing electron density. The results are discussed in terms of processes responsible for the deposition of the plasma species onto surfaces exposed to the discharges.

The relative importance of the various contributions entering the energy of an electron gas in a quantum well is estimated on the basis of a very simple model in Hartree-Fock approximation. The situation here studied corresponds to an uncompensated electron gas inside the well. Kinetic and electrostatic energy may then cancel each other for some characteristic value of the well thickness, thus enhancing the importance of exchange. The roles of inter versus intrasubband terms, of subband population and of subband structure are discussed.

The normal-incidence monochromator beamline at the 550 MeV electron storage ring MAX in Lund has been utilized for VUV spectroscopy of solids at low temperatures. The experimental setup is described in some detail. The first results include reflectivity and luminescence excitation spectra for the high T_c superconductor Y-Ba-Cu-O and for solid LiH. The results agree with and extend previous optical data for these systems.

The magnetic susceptibility of the new compound (Glycine)₂MnCl₄ has been measured as a function of temperature and magnetic field. The dielectric permittivity and electric conductivity were measured as a function of temperature and frequency. The results indicate the existence of a structural phase transition at ≃ 345 K. Above that temperature the compound's conductivity becomes metallic-like and its magnetic susceptibility points to the formation of dimers.

Sm_1-xY_xSe solid solutions prepared as sintered pellets exhibit a miscibility gap in the composition range from x = 0.50 to x = 0.80. Lattice parameter and magnetic susceptibility determinations on alloys within the remaining composition regions indicate that the samarium cations remain essentially divalent throughout this series of solid solutions. An enhancement of the SmSe Van Vleck paramagnetism with increasing yttrium substitution is attributed to the conduction electrons introduced by chemical alloying.

The relaxation of solitions on lattice vibrations in the easy axis Heisenberg model was investigated. It was shown that the soliton dynamics is governed by the nonlinear Schrödinger equation with damping and fluctuation force. The presence of these terms is the consequence of the emission and absorption of real phonons when soliton velocity is greater then the speed of sound in the crystal.

As the result of these perturbations there arises the time dependence of soliton parameters.

Soliton amplitude decreases followed by the simultaneous increase of the soliton width while its propagation has the diffusion character since the soliton behaves like the classical Brownian particle.

We investigate the effects of the Earth's rotation upon nonresonant interactions of atmospheric waves. The wave perturbations in the atmosphere are represented by eigen modes which, when formulated in terms of a Hermitian operator by a judicious choice of state variables, called the F-system in this paper, becomes orthogonal to each other. The effects of geostrophic terms on the eigen vectors are simply represented by the parameter δ, also introduced in this paper. They are important when the wavenumber vector is nearly vertical. The general theory of nonresonant wave-wave interactions is then formulated. Two cases of nonresonant interactions where the Earth's rotation plays an important role are investigated in detail: the case of a gravity wave interacting with two vortical modes (GVI) and the case of elastic scattering (ES). It is found that the previously found threshold condition on GVI in the absence of rotation is weakened or disappears, depending on the scale of vortical modes, when atmospheric rotation is taken into account. As a consequence, GVI may be an important process in extracting energy and momentum from gravity waves. The Earth's rotation is also found to influence ES in important ways. Through nonresonant interactions with a vertical wind shear of circular polarization, the exchange of energy and momentum between a large scale, horizontally propagating gravity wave and a mesoscale, nearly vertical propagating gravity wave is found to proceed at a rapid rate.