Table of contents

Three-body and higher forces in dense noble gases are represented either through a many-body virial expansion or as a mean field applied to a fluid of atoms interacting with the true pair potential. Some predictions of this model are shown to agree with bulk data for krypton. It is concluded that noble gases find it easy to develop mean-field behaviour with increasing density, and that bulk data do not contain enough information to test many-body potential models in detail.

The fractal geometry of fracture patterns in materials is explored by means of a simple model which incorporates the equations of elasticity and simple rules for fracture propagation. Different isotropic media and boundary conditions are considered. Self-similar patterns with fractal dimensions nearly independent of the elastic constants are obtained.

We present arguments which weaken the proposition of Pisarki and Appelquist et al. that mass is dynamically generated in a (parity-doubled) version of three-dimensional electrodynamics.

Configuration-space propagators are defined which are turned on and off covariantly with respect to the proper times of the interacting bosons. The resulting products of a δ-function and step functions are defined in turn by their transforms into auxiliary state variables, yielding oscillatory integrals similar to those that describe diffraction catastrophes. These or related propagators should enable theoretical and experimental tests of the pair hypothesis.

A shielded Ge(Li) surrounded by natural tellurium and located in an underground laboratory has been used to search for double beta decay of ¹²⁸Te and ¹³⁰Te leading to the first 2⁺ excited state of the corresponding Xenon isotopes. No evidence for such decays is found and it is proved experimentally that the geologically measured rate for double beta decay of ¹³⁰Te is dominated by the 0⁺-0⁺ mechanism. Upper limits on the presence of right-handed currents are obtained which are independent of the value for the neutrino mass.

Two new α emitters were observed in heavy-ion fusion reactions leading to the compound nuclei ^210-212Ra. They are assigned to decays of an isomeric state in ²⁰⁷Ra and of ²⁰⁵Ra. The measured decay properties of ^207mRa are E_α = (7320 ± 10) keV, T_1/2 = (55 ± 10) ms. For ²⁰⁵Ra and α energy of E_α = (7360 ± 20) keV and a half-life of T_1/2 = (220 ± 60) ms were obtained. The data show evidence, that the latter α emitter might be due to a mixture of α decay from the ground state of ²⁰⁵Ra and from an isomeric state ^205mRa.

In this paper we analyse the influence of laser power intensity fluctuations in multiphoton ionization processes. In particular, we have carried out the analysis for the specific case of four-photon ionization of benzene molecules, which we have recently investigated both experimentally and theoretically. We have calculated the total ion yield for the above process by taking into account the experimentally observed energy fluctuations of our pulsed laser system and compared it to the value obtained in the hypothesis of perfect pulse-to-pulse reproducibility. Finally, we also report the results obtained by using different Gaussian distributions for the laser energies, thus testing the sensitivity of the ion yield to the laser intensity spread in more general conditions.

We investigate some stability properties of different curved fronts, such as the Davies-Taylor bubble and the needle crystal, by analogy with the flame problem studied previously by Zel'dovich et al. Some useful insights on the limitation of the WKB analysis are first presented by using as an example the Saffman-Taylor finger recently considered by Bensimon et al. The analysis of these different fronts shows that, as a general rule, the stability criterion relates nondimensional numbers (characterizing the steady-state solutions) to the amplitude of the initial perturbation at the tip.

We study experimentally the influence of a horizontal flow upon a unidimensional Rayleigh-Bénard roll chain. We show that it produces a roll diameter gradient proportional to the flow rate. Very small flow rates are sufficient to induce big changes in the roll diameters. This effect provides a way of locally obtaining roll diameters which are very different from the critical value, and even of observing a localized instability related to the Eckhaus instability. We can well describe those results by including an advection term in the phase diffusion equation.

The superconducting transition temperature T_c of mechanically alloyed Ni_xZr_1-x alloys with 0.10 ⩽ x ⩽ 0.45 has been determined by a.c. susceptibility measurements. Similar to melt-spun amorphous samples T_c decreases linearly with increasing Ni content for x ⩾ 0.3. T_c is about 0.5 K lower than for melt-spun samples which is attributed to the different measuring technique (susceptibility vs. resistivity measurements) and to a probably relaxed amorphous structure of the mechanically alloyed samples. For x ⩽ 0.25, T_c is almost constant which demonstrates in accordance with X-ray diffraction and crystallization temperature results that a two-phase region exists, where the amorphous phase with a terminal Ni concentration of about 27 at.% is in metastable equilibrium with the ω-Zr phase with a residual Ni content of about 7 at.%.

Direct implantation into interstitial sites has been found for Fe in Al at temperatures below 200 K. This result was obtained from an in-beam Mössbauer experiment, which assures that each Fe atom comes to rest in its own isolated defect cascade.

A testing-stand is described which allowed us to measure noises on a fractal lattice built with resistors and capacitors. Flicker noise measures of resistors taken one by one show a great dispersion. In this lattice, for size dependence, the exponent measured value is in keeping with calculations and included between theoretical bounds.

Magnetic susceptibility and inelastic neutron scattering experiments have been performed in the nearly ideal one-dimensional Heisenberg antiferromagnet with spin one, Ni(C₂H₈N₂)₂NO₂ClO₄. The experimental results are consistent with the recent theoretical predictions for a quantum energy gap between the ground state and the first excited states.

It is shown that the addition of a "three-spin" exchange interaction term to one-dimensional easy-plane Heisenberg ferromagnet leads to the same effective Hamiltonian as the addition of biquadratic exchange, thus leading to the same soliton properties.

We present the results of measurements of the inelastic scattering of X-rays with very high-energy resolution. Optical phonons in pyrolytic graphite with an energy transfer of ΔE = (171 ± 10) meV as well as an optical phonon in a Be single crystal with ΔE = (79 ± 10) meV were detected.