Table of contents

A WKB formalism is presented to describe the quantum dynamics, including tunnelling, of a single spin with large spin quantum number. This is of particular relevance to the treatment of Hamiltonians with a large anisotropy. For a wide class of Hamiltonians we obtain the eigenstates and tunnelling rates and show the universal dependence of the latter upon the spin quantum number, anisotropy and transverse fields.

We present here the results of a direct calculation of the properties of polymer chains near the θ-tricritical point, i.e. in a poor solvent, a problem which has been the subject of contradictory studies. We have devised for this (to all orders) a direct renormalization method. We find, for space dimensions d < 3 and d = 3, new results, and confirm, when they exist, those previously obtained from field theory. Other recent studies, claiming differences between the polymer θ-point, and the field-theoretic tricritical point, are thus refuted.

A small implanted monolithic silicon calorimeter has been bombarded with alphaparticles at low temperatures in order to determine its thermal properties. From the temperature dependence of the pulse height and the time structure, we have obtained values for the lattice contribution to the heat capacity in excellent agreement with theory, while the contributions from the implanted zone are about an order of magnitude larger than expected from data on diffusion-doped semiconductor. This and other thermal properties are discussed.

Poly-4BCMU solutions in toluene have been studied as a function of temperature by differential scanning calorimetry and resonance Raman scattering. On cooling, two transitions occur around 65 and 55 °C, independent of polymer concentration. The corresponding enthalpy changes are ≈ 2.3 and ⩾ 0.6 kcal per mole of monomer repeat unit, respectively. The colour change is associated to the upper transition, but RRS shows that the polymer electronic structure changes at both transitions. A large hysteresis is observed and on heating the two transitions occur almost simultaneously around 75 °C. Thermal degradation influences the transition temperatures and enthalpies, and the properties of the intermediate phase.

We present the first microscopic calculation of nonlocal effects on the optical-response properties of a jellium surface in an applied electric field of the order of 1 V/Å, which is based on a self-consistent density functional calculation of electron density and effective potential. We find drastic field effects on the optical spectra and discuss them in terms of a plasmon excitation in diffuse surfaces. Experiments on nearly-free-electron metals in nonaqueous electrolytes can check our predictions.

Using the results of a previous analysis, we demonstrate a recently advanced hypothesis. Under some conditions which we state explicitly, during melting of polarized ³He, the mean measured magnetization is also that of the liquid at the interface. It allows us to use the data of a previous experiment to obtain the susceptibility of the liquid dm/dH vs. the field. The results suggest the existence of a metamagnetic transition, at round 40 Tesla.

Isothermal magnetization measurements on a CuMn spin glass show that the memory behaviour of time relaxations in spin glasses is governed by the principle of superposition, which yields fundamental links between the time relaxations of the field-cooled, zero-field-cooled, isothermal-remanent and remanent magnetizations. The principle of superposition applies in spite of a continuous change of the response function at constant temperature, due to aging of the spin glass state.

One characteristic behaviour of the Hopfield model of neural networks, namely the catastrophic deterioration of the memory due to overloading, is interpreted in simple physical terms. A general formulation allows for an exploration of some basic issues in learning theory. Two learning schemes are constructed, which avoid the overloading deterioration and keep learning and forgetting, with a stationary capacity.

Erratum for Europhys. Lett.1 (3) 135-140 (1986)