Table of contents

We introduce a simple multi-scale algorithm for connected component labeling on parallel computers, which we apply to the problem of labeling clusters in spin and percolation models. We give numerical evidence that it is only logarithmically slowed down in the critical limit. We also discuss, in light of the proposed Teraflop computers optimized for lattice gauge theories and other lattice problems, the minimum requirements for computer switchboard architectures for which one can efficiently implement such multi-scale algorithms.

The direct measurement of the Van der Waals interaction between a tungsten tip and a mica surface down to the molecular contact has been performed. The original apparatus used allows a continuous measurement without jump contrary to the previous tentatives. The experimental result is fitted with a Lennard-Jones potential.

The rotational dynamics of NH₄⁺ ions in dilute solutions in potassium halides (I, Br, Cl) have been investigated at temperatures below 20 K by inelastic neutron scattering. Tunnel splitting in the (NH₄)_xK_1-xCl mixed crystal is reported for the first time. An almost free uniaxial quantum rotation of the NH₄ is observed in all the halides. An increase in NH₄ concentration in all mixed salts produces a collapse of the free-rotor line into a broad intense feature to lower energies. The onset of this collapse occurs at different NH₄ concentrations x in the different halides, with x(Cl) < x(Br) < x(I). The tunnel splittings of the different halides exhibit a systematic relationship to the nearest-neighbour distance of the respective matrices. The remarkable similarity to the methane-rare-gas systems is discussed.

We investigate the effects of the spatial structure of a single field mode on the internal dynamics of a two-level atom. The atom is supposed to cross a cylindrical cavity along its axis with a speed high enough to allow neglect of any effect of the interaction with the field on the atomic translational degrees of freedom. A finite detuning is supposed to exist between the atom and the field and its effects on the state of the atom at the exit from the cavity is considered. We show that if the detuning is modulated synchronously with the field mode structure the dynamics is again exactly soluble. A perturbative solution is given for the case of fixed detuning.

We demonstrate that some mirrors using four-wave mixing processes can transform phase variations of the incident beam into amplitude variations of the reflected beam. The property of these mirrors arises from the interference between phase-conjugate and distributed feedback emissions. We present the results of experiments done with a rubidium cell and show how wave front deformations may be studied by such a mirror.

We have achieved high-spin polarizations in concentrated mixtures of ³He in ⁴He using the rapid-melting method originally suggested by Castaing and Nozières for pure ³He. Polarizations well above the equilibrium value (greater than 10%) were obtained at T ≈ 350 mK. The observed relaxation time T₁ = 4000 s was of the same order as the theoretical predictions of the bulk relaxation time, and was long enough to suggest that it should be possible to study the properties of these strongly polarized mixtures.

We study the adsorption of long, linear polymer chains from a melt or a semi-dilute solution onto a solid wall, the adsorption of a monomer on a surface site being irreversible. Using scaling arguments, we derive the concentration profile and the extension of the polymer layer, which has been washed out with pure solvent. Let us consider, Φ the volume fraction of the initial semi-dilute solution (Φ = 1 in the case of the melt), a the monomer size and N the degree of polymerization of the chains. Our main result is that the extension h of the profile scales as: aΦ^7/24N^5/6 and that the concentration profile ϕ(z) varies as: Φ^7/10(a/z)^2/5 for aΦ^−3/4 < z < h.

A real-space renormalization group (RSRG) scheme is developed to calculate the local Green's functions for electrons in two-dimensional quasi-crystals. The RSRG transformations are derived in terms of the inflation rule of the quasi-crystals. The local electronic densities of states at some key sites are presented, which match the numerical results obtained by other groups for the global electronic energy spectra of the quasi-crystals.

1S and 2P excitons in ZnTe are studied by two-photon absorption with uniaxial stress up to 350 MPa. The energy shift and splitting which is caused by the stress-induced valence band splitting and the envelope-hole coupling allows the determination of deformation potentials.

The statistical distribution of the voltage drop along a mesoscopic conductor is calculated in a soluble model: a 3-terminal device consisting of 1D wires. In general, one finds appreciable voltage fluctuations. For instance, the voltage measured at the midpoint of a strongly disordered conductor of a given length falls, with large probability, in the vicinity of the voltage of either terminal! Consequences for a 4-probe measurement are analysed.

We have designed and operated a device consisting of three nanoscale tunnel junctions biased below the Coulomb gap. Phase shifted r.f. voltages of frequency f applied to two gates "pump" one electron per cycle through the device. This is shown experimentally by plateaus in the current-voltage characteristic at I = ± ef, the sign of the current depending on the relative phase of the r.f. voltages and not on the sign of the bias voltage.

Results of infrared reflectivity measurements of Tl₂Ba₂CaCu₂O₈ crystals for the electric-field vector parallel to the (a, b)-plane suggest that the TlO layers are almost nonconducting. This follows from the similarity of the observed reflectivity with that of YBa₂Cu₃O_7-δ for the electric-field vector perpendicular to the chain direction. The conductivity in the CuO₂ layers is analysed using Eliashberg's strong electron-phonon coupling theory.

We analyse quantitatively the low-temperature magnetotransport properties of a series of spin-valve structures of composition NiFe t Å/Cu 22 Å/NiFe 50 Å/FeMn 80 Å/Cu 15 Å. We adopt the approach of Camley and Barnas which is based on the classical Boltzmann equation and assume spin-dependent scattering in the bulk of the ferromagnetic layers. We show that by introducing an anisotropy in the mean-free paths of conduction electrons (of the order of 30%) we can fit with the same set of parameters the variation of the sheet conductance and magnetoresistance with the thicknesses of the Cu and NiFe layers. This anisotropy is ascribed to grain boundaries scattering in these sputtered polycrystalline samples. We also compare our results with others obtained on (Fe/Cr)-type spin-valve multilayers. We emphasise the very important role of the number of periods of the multilayered structure on the magnetotransport properties of these systems.

Time spectra of nuclear resonant diffraction of synchrotron radiation in nearly perfect single crystals of ⁵⁷FeBO₃ and ⁵⁷Fe₃BO₆ have been measured in Laue geometry. Characteristic shifts of the quantum beat pattern proportional to the crystal thickness were observed. This shifts originate from the thickness dependence of the relative phases of the interfering hyperfine components of the scattered radiation. The phase velocities of the components are different because of a complicated dispersion law where all 14.4 keV nuclear hyperfine transitions of ⁵⁷Fe contribute to the scattering amplitudes. A kind of interferometry employing beam splitting in energy was demonstrated in the experiment.

The elliptic-type motion in a Schwarzschild-de Sitter gravitational field is being studied by a classic method, considering separately the contribution of the Schwarzschild space-time local deformation and that of the cosmological background as perturbing forces. The first-order variations of the orbital elements over one nodal period (and the second-order changes only for the Schwarzschild "force") as well as those of the nodal period itself are determined. The domain in which the used methods are applicable (estimated for a black hole of 10 solar masses) results to be large enough to allow investigations in realistic astronomical situations.

Addendum to Europhys. Lett.13 (6) pp 481