Table of contents

Parametric correlations of the energy spectra of quantum chaotic systems are presented in the presence of time-reversal symmetry-breaking perturbations. The spectra disperse as a function of two external perturbations, one of which preserves time-reversal symmetry, while the other violates it. Exact analytical expressions for the parametric two-point autocorrelation function of the density of states are derived in the crossover region by means of the supermatrix method. For the orthogonal-unitary crossover, the velocity distribution is determined and shown to deviate from Gaussian.

Differential ionization cross-sections for 40 MeV H⁺ + He collisions were measured as a function of electron energy, electron ejection angle and final recoil ion charge state. Coincidences between recoil ions and emitted electrons were taken for electron ejection angles of 55° and 125° and energies between 3 and 500 eV. Good agreement is found between measured energy distributions of ejected electrons and results of standard first-order perturbation theory in the case of single ionization. The experimental double-ionization cross-sections, however, are found to exceed independent-electron model predictions by more than an order of magnitude. Furthermore, evidence is provided that this deviation is mainly due to initial-state correlation.

The fractal dimension δ_g⁽¹⁾ of turbulent passive scalar signals is calculated from the fluid dynamical equation. δ_g⁽¹⁾ depends on the scale. For small Prandtl (or Schmidt) number Pr < 10^-2 one gets two ranges, δ_g⁽¹⁾ = 1 for small-scale r and δ_g⁽¹⁾ = 5/3 for large r, both as expected. But for large Pr > 1 one gets a third, intermediate range in which the signal is extremely wrinkled and has δ_g⁽¹⁾ = 2. In that range the passive scalar structure function D_θ(r) has a plateau. We calculate the Pr-dependence of the crossovers. The plateau regime can be observed in a numerical solution of the fluid dynamical equation, employing a reduced wave vector set approximation introduced by us recently.

In a magnetofluid, magnetic and velocity fluctuations B' and ν' can generate a mean electromotive force along the mean magnetic field, which has been termed the alpha-effect. In the present paper the mathematical relationship between the alpha-effect and the mean current helicity of the fluctuations, ⟨B' · curl B'⟩, hitherto proven for the case that i) either the magnetic or the velocity fluctuations are statistically homogeneous and stationary, ii) the first-order smoothing approximation (FOSA) is valid, and iii) the mean flow, ⟨ν⟩, vanishes, is rederived, assuming the magnetic fluctuations to be stationary and the coupled magnetic-electric fluctuations to be homogeneous, but without using FOSA and allowing for a non-vanishing mean flow.

The room temperature structure of the hexagonal family of modifications of pure C₇₀ has been studied by single-crystal X-ray diffraction. The experimental evidence indicates rotational symmetry of the molecular electron density and supports the previously published assumptions that the molecules are freely rotating tops arranged in a hexagonal close packing, space group P6₃/mmc. The tops librate about axes perpendicular to the rotation axis with a r.m.s. amplitude of 7.33(3)°. The distances between the atomic planes perpendicular to the molecular axis agree well with earlier work.

Annealed organic monolayers of dodecanethiol (CH₃(CH₂)₁₁SH) self-assembled on Au(111) have been investigated by scanning tunnelling microscopy. By using very high tunnelling resistances (TΩ) we find evidence of well-ordered molecular domains at room temperature and observe two different types of c(4 × 2) superlattice structures with the same rectangular unit cell. In contrast to theoretical calculations each unit cell contains four inequivalent molecules. Possible reasons for this discrepancy are discussed.

The microphase separation in a symmetric diblock copolymer consisting of polystyrene and polyparamethylstyrene has been studied by small-angle neutron scattering. The observed peak changes with temperature in intensity, shape and position. The peak position shifts at the microphase separation transition temperature T_MST by approximately 7%. Also from a peak intensity analysis we determine T_MST at approximately 180 °C. The shape of the peak change at T_MST and the indication of a second-order peak is observed, characteristic of a lamellar phase in the ordered regime. Intensity does not vanish for q → 0, but has a temperature-dependent level. Results are discussed with respect to recent computer simulations and theoretical approaches. A simple mean-field picture is not consistent with the data.

In a superfluid at finite temperature, thermal fluctuations yield the normal, viscous component of the two-fluid theory. At T = 0 K, the zero-point fluctuations give a non-vanishing amplitude to the phonon mode. The scattering of these phonons by an obstacle could yield a non-vanishing drag proportional to the speed at low speed. Arguments show that this Casimir drag on a sphere grows like the square root of the radius.

Constant-altitude AFM images of the NaCl(100) surface are calculated from a fully relaxed molecular-mechanic approach using a diamond tip apex. Three different ranges of the z tip-apex-to-surface distance have been found. For 2.5 Å < z < 5 Å, the apparent corrupgation is recorded from the normal force component. For intermediate z (1.4 Å < z < 2.5 Å), a surface image can be formed by measuring the lateral force because the normal corrugation decreases due to surface deformation. At even smaller distances (z < 1.4 Å), a contrast reversal phenomenon occurs just before the surface destruction.

The Anderson transition in three-dimensional disordered systems in the presence of a magnetic field is investigated using a tight-binding Hamiltonian, where the magnetic field is incorporated via Peierls phase factors. Disorder is introduced via independent random diagonal elements distributed according to a box function. The localization lengths of the quasi-one-dimensional systems are calculated by using the transfer matrix method with periodic boundary conditions applied across the finite cross-section. The critical exponent is determined by exploiting the existence of a one-parameter scaling law. The result, ν = 1.35 ± 0.15, is, within the errors, the same as that obtained without a magnetic field.

Using the Dyson-equation approach to spin-spin correlation functions we derive self-consistent mean-field equations for the antiferromagnetic spin-(1/2) Heisenberg model. An analytic expression for the one-magnon dispersion valid in D = 1, 2, 3 is obtained. For the linear chain it gives the exact result ω_k = (π/2) |sin k| known from the Bethe ansatz. For the square lattice the same procedure leads to ω_k = 1.188 × 2 √1 - ((cos k_x + cos k_y)/2)² in agreement with recent Monte Carlo results. Values for the simple cubic lattice in three dimensions are also given.

Far-IR static-electric-field experiments on KI:Ag⁺ reveal that the field-induced frequency shifts for the "pocket" vibrational gap modes are nearly two orders of magnitude smaller than the corresponding shifts measured for the low-frequency resonant modes. When combined with previously measured stress shifts and a quasi-harmonic perturbed shell-model calculation, these results firmly establish that the silver ion has a significant quadrupolar deformability, which has been proposed to play an important role in the dynamics of the silver ion in other systems.

An investigation on the local structure of liquid and supercooled pure gallium at several temperatures is presented. Accurate EXAFS (Extended X-ray Absorption Fine Structure) spectra have been analysed by means of ab initio calculations of the multiple-scattering signals associated with two-atom and three-atom configurations. The extracted g₂ (r) first-neighbour distribution of the liquid phase was found to be in excellent agreement with diffraction measurements. Clear evidence of nearly covalent bonds has been found in highly supercooled gallium where the asymmetric first-neighbour distribution is split into two resolved peaks. Analysis of the three-atom g₃ (r₁, r₂, θ) distribution has shown evidence for nearly-equilateral and nearly-orthogonal configurations.