Table of contents

We introduce an approximate density function for the distribution of zeros of Bessel functions. This illuminates the discussion of some results on density and sum rules due to Arriola and Dehesa, Nuovo Cimento B, 103 (1989) 611.

We report a numerical study of the velocity autocorrelation function (VACF) in a lattice model of a Lorentz gas with scatterers that have a finite excluded volume. We observe that, at scatterer densities below the percolation threshold, the VACF decays as t⁻². As the percolation density is approached, the onset of the asymptotic t⁻²-decay shifts to increasingly longer times but the asymptotic exponent itself remains unaffected. Such behaviour appears to contrast with that of off-lattice Lorentz-gas simulations, where the asymptotic exponent was found to vary strongly with scatterer density. Our findings are, however, consistent with percolation-related crossover scenarios proposed by Götze et al. (Phys. Rev. A, 23 (1981) 2634) and van Velzen et al. (Physica A, 154 (1988) 34).

The Chemical Density Functional Theory (CDFT) is proposed as a new model for nonideal plasmas of nuclei and electrons in thermodynamical equilibrium. It is based on a DFT-like treating on the microscopic level assuming the existence of chemical species (chemical picture). This is embedded in a thermodynamical level which is spanned up by the large-distance limits of the distribution functions. The effects of inhomogeneity are taken into account which are important for the pressure ionization. Both levels of description are coupled via certain quantities.

We derive a systematic density expansion of the equation of state for a quantum Coulomb fluid. Our formalism is based on the Feynman-Kac path integral representation, and allows a coherent and simultaneous treatment of screening, diffraction, bound states and statistics. The calculations have been explicitly carried out up to the order ρ^5/2 in the density ρ. At the order ρ², we retrieve the results obtained via an effective-potential method.

We present results of numerical simulations of kinetic roughening for three variants of a growth model with surface diffusion in 2 + 1 dimensions. The variants differ by the rules of relaxation of a freshly arrived particle giving different effective roughness and dynamical exponents. In particular we have found that the model, studied by Wolf and Villain and by Das Sarma and Tamborenea in 1 + 1 dimensions, has in 2 + 1 dimensions exponents corresponding to a nonlinear differential equations.

A simple optical-model description of the width of heavy-quarkonium states is proposed. It is based on the string fragmentation picture. Experimentally known widths are fairly well reproduced. Predictions are made for other states.

Four very-high-multiplicity events from cosmic-ray data have been analysed in the light of scaled factorial moments as suggested by Białas and Peschanski with emphasis on the rapidity scale dependence of the moments. The investigation reveals a prominent rising in intermittency pattern which is an interesting information and can play an important role in understanding the phenomenon.

The T_c of superconducting Y₂Ba₄Cu₇O_15.32 is measured up to a pressure of 33.7 GPa. After an initial increase from 95 K to 101.7 K a decrease down to 26.6 K is found, with a clear kink at 22 GPa. We demonstrate that Y₂Ba₄Cu₇O_15.32 behaves as a multilayer of YBa₂Cu₃O₇ and YBa₂Cu₄O₈ building blocks coupled via the proximity effect. These data are not consistent with the idea that the coupling of two adjacent CuO₂ planes is necessary for superconductivity.

Itinerant-Electron Metamagnetism (IEM) is characterized by a first-order transition occurring, under the effect of varying external parameters such as temperature, magnetic field or pressure, between a nonmagnetic or low-induced-moment state and a ferromagnetic large-moment state. It is usually ascribed to peculiar features in the band structure of the considered systems. A new approach is proposed in the present paper in which this phenomenon results simply from the interplay between the magnetic energy and the elastic energy.

In this paper we calculate the regions of stability of the ferromagnetic and antiferromagnetic phases in the Hubbard model using the Kotliar-Ruckenstein slave-boson mean-field theory. The results for strong ferromagnetism in a 2d square lattice are seen to be in reasonable agreement with exact results.

We describe a new method for analysing the relaxational dynamics of glassy systems, and apply it to the Ising spin glass in three and four dimensions with nearest-neighbor interactions, as well as to the infinite-range Sherrington-Kirkpatrick model. We recover previously known results with considerably less computer effort, and find new results for both the dynamic exponent (z = 4.8 ± 0.4) and the critical dynamic correlation function for the four-dimensional case.

Epitaxial Fe(110) films on W(110) with smooth surfaces were covered by some additional Fe at lowered temperatures, to create a rough surface, showing roughly periodic arrays of atomic steps along [001], the density of which could be determined from Spot Profile Analysis Low-Energy Electron Diffraction. Annealing to a resmoothened surface was connected with a loss of magnetic moment by (1.1 ± 0.4) μ_B per step atom as measured by magnetometry in situ before and after annealing. The magnetic moment of a real step atom was estimated to be (3.4 ± 0.5) μ_B, definitely enhanced by roughly 0.5 μ_B with respect to the atomic moment in a smooth surface. Using the theory of local moments in metals, a model of the enhanced moment is given, providing a quantitative connection between atomic moment and coordination, in good agreement with the experiments. The model assumes the weak-coupling value of six resonances below the Fermi energy, rather than five assumed by local spin density theory.

The magnetic and structural dynamics in liquid oxygen are studied by means of high-resolution inelastic neutron scattering and computer molecular-dynamics simulations. The former technique enables an approximate separation between nuclear and magnetic responses from the total, unpolarized neutron double differential cross-sections. The magnetic scattering spectra are then shown to reproduce the wave vector dependence of the inelastic intensities associated with the magnetic excitations measured in a previous study. Finally, the magnetic spectral functions are shown to be well reproduced by a model of exchange-coupled paramagnet and estimates of the exchange parameter and correlation length are obtained from the analysis of the frequency moments.

We present a phenomenological Landau–de Gennes-type theory of strain effects on concentration fluctuations in "soft" elastic two-component solids. Introducing concentration-dependent elastic moduli and a coupling between the strain and concentration fields we find that, for systems which exhibit nearly linear elastic response to large, uniaxially applied strain, there is strong enhancement of thermal fluctuations with wave vectors along the elongation axis. We calculate the structure factor and find that the equal intensity lines produce "butterfly" patterns akin to those observed in neutron scattering from deformed rubbers, gels and mixtures of molten polymers.

Bulk properties like binding energies, proton separation energies, r.m.s. radii and quadrupole deformation parameters of Z = 31 ÷ 40 nuclei are calculated in the deformed relativistic mean-field model of nucleons and mesons. The calculation is extended to nuclei near the proton drip line. A path for the synthesis of nuclei in the rapid-proton (r.p.) capture is suggested.