Table of contents

We discuss a Weyl-type theory which was considered by Utiyama and Nishioka. We point out that the vanishing of the trace of the energy-momentum tensor in the space-time with _μν = η_μν is not an inevitable outcome of the theory, but follows from an incorrect treatment.

It is pointed out that the existence of similar collective band structure fostered on the excited J = 1/2 states is a systematic feature of the nonstrange and strange baryon resonances.

We have measured the temperature of cesium atoms released from optical molasses. For a wide range of laser intensity and detuning from resonance, the temperature depends only on the intensity-to-detuning ratio. The lowest temperature achieved is (2.5 ± 0.6) μK, which corresponds to an r.m.s. velocity of 12.5 mm/s or 3.6 times the single-photon recoil velocity. This is, to our knowledge, the coldest kinetic temperature ever measured for three-dimensional (3D) cooling.

Parameter-free model calculations are presented to describe positron scattering by polyatomic targets and the results are analysed within a density functional description of correlation forces. It is shown that the absence of exchange interaction for positron projectiles needs to be correctly considered when using the correlation potentials (CP) obtained from that description. Results are presented for integral cross-sections and, for the first time, for the differential cross-sections of positron-H₂O scattering.

We examine theoretically the effect of electrostatics on the self-assembly of charged, cylindrical micelles. The growth of micelles as a function of increasing surfactant and/or electrolyte concentration exhibits three distinct regimes. The most striking feature of the growth law is the existence of a dilute regime, i), in which the average micelle size varies slowly with concentration. At higher concentrations, regimes ii) and iii) are characterized by more rapid growth than for neutral micelles. This may be responsible, in part, for the anomalous scaling of rheological properties, as observed in recent experiments.

We report experimental results from IR-reflectivity between 4.2 K and 300 K for substituted 123-ceramics with different T_c and different approach to the dirty-limit condition. The results show a scaling of the reflectivity increase with T_c and with approaching the dirty limit on cooling through T_c. Phonon hardening and softening at T_c agreed with theoretical predictions if a symmetry-dependent response to the gap is assumed. The BCS-ratio for the c-axis gap is deduced to be 1.7K_BT_c.

The melting of small lead particles embedded in a silicon monoxide matrix has been studied by dark-field electron microscopy. Thomson's idea from 1888, that the melting temperature depends on the size of the particles and Faraday's idea from 1860, that melting of the surface occurs below the bulk melting temperature, are demonstrated here straight-forwardly. The electron microscope pictures give the most direct observation on the existence of a molten surface layer in equilibrium with a solid core at temperatures below the melting point. The width of the molten layer is demonstrated to depend on the particle curvature as well as on temperature indicating a continuous transition. Quantitatively, it was found that for the small lead particles, the width of the molten layer is wider than the reported one for bulk lead.

Monolayers of amphiphilic molecules spread at the air-water interface have been intensively studied using x-ray reflectivity in both the liquid-expanded and the liquid-condensed phase, below and above the triple-point temperature. The phase diagrams of hexadecanoic acid and of the phospholipid L-α DPPC have been investigated. Evidence for the transition is given by an abrupt increase of the aliphatic medium thickness. The results are discussed through recent experimental data and calculations.

We have applied newly numerical schemes to study the ground-state properties of the 1D Hubbard model. Through finite-size scaling, we determine the singularity of the momentum distribution at k_F and the power law decay of the spin and charge correlations in real space. Our results confirm the non-Fermi-liquid nature of the system. The model is shown to scale to the Tomonaga-Luttinger model even in the large-U regime where perturbative results are invalid.

We report the first detailed measurements on the critical current of periodic superconducting wire networks as a function of an external magnetic field. Sharp spikes are observed at integer and fractional reduced magnetic fluxes ϕ/ϕ₀, where ϕ is the magnetic flux per unit cell of the network. The experimental results are discussed in terms of the depairing current for the 2D array. An approach based upon the band properties of the paired Electrons on the underlying lattice is proposed. This model explains the main features of the field and temperature dependence of the critical current without referring to pinning effects of the vortex lattice.

The well-known Dirichlet problem defining the ellipsoidal equilibrium configuration for a self-gravitating homogeneous fluid mass endowed with internal motion linear functions of the coordinates is here generalized. In the present work using the second-order virial equations we provide the conditions necessary to solve the Dirichlet problem in a more general case of heterogeneous masses having nonlinear internal motions. The equations for the stability are presented with the general algorithms for their solution. The generalization to these new solutions of Dedekind's theorem is also proved. These models may lead to a direct explanation of some basic features of galactic morphology.

Erratum of Europhys. Lett.12 (6) pp 523