Table of contents

It is shown how to correctly implement the linear chiral boson constraint in the Lagrangian formalism in order to be consistent with the Hamiltonian counterpart.

Indistinguishable particles are classified according to extremality properties (with respect to the set of all states) of the extreme points of the convex set of symmetric states.

The dispersion relations of scalar and pseudoscalar mesonic excitations of the Nambu and Jona-Lasinio model are studied in the framework of the time-dependent Hartree-Fock method in the semi-classical limit of the model. A Fock-space approach, including a three-dimensional regularizing cut-off, is used. We show that a consistent semi-classical treatment, including an appropriate definition of the generators, leads to dispersion relations in agreement with the requisites of relativistic covariance.

The charge distribution of projectile fragments emerging from events of ⁸⁴Kr at 1.52A GeV in nuclear emulsion is fitted with a power law. The method of scaled factorial moments is employed to study fluctuations in the nuclear fragmentations. An intermittent behavior is observed in the data and this may be due to the mixing of events produced under different excitation energies.

A new type of trap for ground-state atoms is proposed. It is based on the balancing of gravity and the electric-dipole attraction between the polarisable atom and a slowly oscillating electric charge. The stability of this dynamic trap is predicted for a narrow range of operating conditions. However, practical considerations result in a trap depth only comparable to the lowest temperatures routinely obtained with laser-cooled atoms.

We discuss the collective resonances of the C₆₀ molecule described by a spherical shell. Detailed results are given for the π and π + σ plasmons of C₆₀, the polarisability and the dielectric function. We present results in good quantitative agreement with recent experiments. Some new features in the spectrum, like a monopole mode of oscillation, are predicted for a doped C₆₀ molecule.

The angular distribution (AD) of the II-component of SR (ADIISR) of a pulsed synchrotron LIS-2 with an electron orbit radius of 6 cm has been investigated experimentally and theoretically. It has been shown that the asymmetry in relation to the plane of the electron orbit, observed in ADIISR in experiments, can be explained by interference of the radiation components produced by the orbiting charge and an additional magnetic moment polarized along the acceleration vector.

We report the first observation of Faraday rotation of light in multiple-scattering media. Speckle patterns generated by diffusive transport of laser light through turbid granular samples are strongly modified by high magnetic fields (B). The speckle intensity correlation function, measured at various sample thicknesses and Verdet constants, decays with increasing B in agreement with the simple model discussed. In addition the coherent backscattering cone is partially suppressed by the field, again consistent with the model. This effect provides a unique way to destroy interferences between time-reversed scattering paths and may be expected to affect light localization.

Effective-medium approximation and computer simulations were employed to study the fracture of a two-dimensional fibre network of random topology at densities well above the percolation threshold. As strain is increased adiabatically, the fracture process changes from a two-dimensional "percolationlike" process to a one-dimensional uncorrelated process. The stress-strain curve has a discontinuous size-dependent drop at the transition and a non-universal tail at high strain.

It is shown that isocurrent density surfaces in MHD turbulence have fractal dimension D = 11/4 (D = 7/4 in 2D) instead of D = 8/3 in Navier-Stokes turbulence, which is due to the Alfvén effect. The results is in good agreement with numerical simulations of 2D MHD turbulence.

We describe dynamic measurements of the stress obtained during a sand flow. The data show a large noise component as seen in power spectra for these data which satisfy P = P₀ω^-α over at least three decades. Values of α span 1.3 ⩽ α ⩽ 2.3. A calculation of the Hurst parameter of fractional Brownian motion yields values of H which satisfy α = 2H + 1 within statistical errors. A time scale predicted from continuum models of sand flow may be present, but the inherent noise makes this scale difficult to determine.

Brushes of liquid crystalline polymers swollen by nematic solvents are described by an extended Alexander model. Long-main-chain LCP with hairpins are considered. For the case of homogeneous anchoring a second-order tilting phase transition is expected as the grafting density is increased. When the grafting density is subcritical the transition can be triggered by very weak electrical or magnetic fields.

First investigation of the pressure dependence of the pretransitional optical activity in the isotropic liquid of highly chiral liquid crystal CE2 in isothermal regime is reported. The inversion of sign of the solpe of the dependence of the optical rotation on pressure in the isotropic liquid is observed. The experimental data agree well with the theory of the effect, developed in terms of the Landau-de Gennes approach to the description of flucturational phenomena in liquid crystals. Theoretical parameters, describing the process of orientational correlations in the isotropic liquid, are determined.

We report measurements of a heat pulse diffusion in a glass substrate coated by 2.5 atomic layers of ⁴He. By comparison with data obtained on the bare glass substrate, we get values of the Kapitza resistance between the glass and the helium film. The value of the Kapitza resistance between a solid and a helium film has recently been the subject of a controversy. From our determinations, the values for thin films are comparable to that reported for bulk helium.

Results for the optical conductivity and resistivity of the Hubbard model in infinite spatial dimensions are presented. At half-filling we observe a gradual crossover from a metal with a Drude peak at ω = 0 in the optical conductivity to an insulator as a function of U for temperatures above the antiferromagnetic phase transition. When doped, the "insulator" becomes a Fermi liquid with a corresponding temperature dependence of the optical conductivity and resistivity. We find a T²-coefficient in the low-temperature resistivity which suggests that the carriers in the system acquire a considerable mass-enhancement due to the strong local correlations. At high temperatures, a crossover into a semi-metallic regime takes place.

Self-consistent spin-polarized relativistic calculations of the electronic structure and magnetic characteristics of U, Np, Pu impurities in thorium have been carried out. It is shown that all these metals in thorium reveal well-defined magnetic behavior. The values of magnetic moment at the impurities are defined by the partial cancellation of spin and orbital contributions. For Pu the total moment is large and of orbital nature, the magnetic moments of U and Np are small and have spin origin.

A system of two serially coupled normal-metal tunnel junctions driven by an external voltage is investigated in a high-impedance environment. It can be shown that with respect to the mean current the classical Coulomb blockade of first-order perturbation theory is suppressed by contributions of the next order. Because of the presence of the environment a new "quantum" blockade is produced which is less than the usual one but of the same order of magnitude.

The energy of a pointlike vortex is calculated for a layered superconductor with very weak interlayer Josephson coupling. An energy barrier existing near the sample surface is found. Magnetization relaxation due to thermally activated penetration of pointlike vortices and quantum tunnelling of pointlike vortices are considered. An initial avalanche-type decay of magnetization is predicted.

We report a non-Ohmic excess conductivity measured in an YBa₂Cu₃O_7-x single crystal in the absence of an applied magnetic field. Mean-field paraconductivity data are in agreement with a recent theory (1992) of a clean layered superconductor in an electric field. In a strong enough electric field, a continuous dimensional crossover from three-dimensional to two-dimensional (2D) behaviour takes place at the superconducting transition point. A broadening of the temperature dependence of the resistive transition is attributed to large 2D out-of-plane non-linear fluctuations.

The magnetic susceptibility of the spin-(S = 3/2) Heisenberg chain AgCrP₂S₆ follows in a wide temperature range the recent quantum Monte Carlo result (Sandvik and Kurkijärvi, 1991) with a nearest-neighbour exchange (JS_iS_{i + 1}) J/k_B = 100 K. Inelastic neutron scattering in the quasi-one-dimensional phase indicates a spin-wave velocity C = 4.6J, well in excess of the classical value 3J. The results emphasize the strong quantum character of the S = 3/2 Heisenberg chain. The extrapolated zero-temperature susceptibility and the observed spin-wave velocity are compared with the theoretical predictions for half-integer spins and are compatible with universal critical properties for S = 1/2 and S = 3/2.

We present a new method for a systematic spin-wave expansion for the quantum fluctuations of a generic spin Hamiltonian in a finite lattice, where the inverse spin magnitude 1/S is a well-defined expansion parameter. The first two leading contributions of the spin-spin correlation function are evaluated for the J₁-J₂ Heisenberg model. Very good agreement between our finite-size predictions and the exact diagonalization and Monte Carlo results is found for J₂/J₁ < 0.2 and S = 1/2, thus confirming the existence of antiferromagnetic long-range order in this J region. For J₂/J₁ > 0.3 the expansion is poorly converging, suggesting a possible breakdown of the spin-wave approximation. Here our calculation seems consistent with a possible spin liquid ground state.