Table of contents

We consider an infinite chain of atoms, where the bond lengths between neighbouring sites take two values, according to a quasi-periodic rule, associated to a circle map with an irrational rotation angle. In a particular case, this construction is related to the projection method used to describe quasi-crystals. The structure factor (Fourier spectrum) of the structure is shown, through a combined analytical and numerical analysis, to be "singular continuous", with nontrivial scaling properties. It does not contain any Dirac peak (discrete spectrum), nor a smooth component (absolutely continuous spectrum). This structure, therefore, exhibits a new kind of order, intermediate between quasi-periodicity and randomness.

We extend our previous solution of a network with deterministic parallel dynamics to stochastic dynamics. Stochasticity is controlled by a "temperature" variable. An exact solution for the dynamics of the network at any temperature is presented. A region of good recall is found, separated from a region of no recall by a first-order line terminating at a critical point. The exact time-evolution of mixtures of patterns is given as well.

By means of noise reduction we investigate the scaling behaviour of the surface width w of d-dimensional Eden clusters growing on flat substrates of linear extent L. We find that w scales for small average deposit height h as h^β, and in the steady state as L^α. Our results for d = 3 (α = 0.33 ± 0.01, β = 0.22 ± 0.02) and for d = 4 (α = 0.24 ± 0.02, β = 0.146 ± 0.015) support the scaling relation α(1 + 1/β) = 2. They suggest that α instead of being superuniversal might be equal to 1/d.

We study the time evolution of the distance between two configurations submitted to the same thermal noise for the 3d ± J Ising spin glass. We observe three temperature regimes: a high-temperature regime where the distances vanishes in the long-time limit. An intermediate-temperature regime where the distance has a nonzero limit independent of the initial distance. A low-temperature regime where the distance in the long time limit seems to depend upon the initial distance. For the sake of comparison, we have repeated our simulations for the ferromagnetic case.

We construct the kink sector of the ϕ₂⁴ quantum field theory, in the broken-symmetry phase, using Euclidean methods. The construction exhibits relations with differential geometry and statistical mechanics. In particular we prove that the Euclidean Green's functions of kinks are obtained by integration over section distributions of nontrivial bundles and are well defined as Jaffe ultradistributions.

The missing-mass spectra for the ³He(p, d)X reaction (B_x = 2, T_x = 1) have been measured at T_p = 1.2 GeV for θ_d = 33°. Narrow structures have been observed at M_x = 2.122, 2.198 and possibly 2.233 GeV with FWHM, respectively, equal to 5.2, 8.1 and 13 MeV. These results, obtained under new kinematical conditions, confirm previous data.

X-ray absorption of Ce, obtained by partial secondary yield, is compared with previously obtained electron-energy loss measurements in reflection mode. The absence of a strong feature below 4p_3/2 threshold in photon absorption provides confirmation that the peak in EELS is nondipole in character. Theoretical analysis supports interpretation in terms of a p-f giant quadrupole resonance, a result which broadens the analogy between giant resonances in atomic and nuclear physics.

In an experiment of Rayleigh-Benard convection the dependence of fractal dimension and metric entropy on the point of measurement has been studied. The phase space of the system has been reconstructed using either an embedding technique or 64 time series taken at different points. Furthermore, the use of spatial averaged variables is discussed.

The effect of thermal annealing in air at 350 °C on the photoconductive behaviour of chemically deposited PbSe thin films is investigated. A model of small crystallites embedded in an amorphous PbSe matrix is proposed for the discussion of the sharp drop in resistance in the first minutes of heating and for the shift in photoconduction maximum. The developing of photoconductive and resistance maximums due to thermal annealing is evidenced.

Phospholipid monolayers at the air-water interface have been studied by synchrotron x-ray reflection methods. The range of momentum transfers (perpendicular to the surface) exceeded 2π/(layer thickness) thus yielding information about the density distribution across the layer. Data for a monolayer of L-α-dipalmitoylphosphatidylcholine (DPPC) in the solid phase (surface pressure 40 mN/m) are interpreted in terms of a simple model of the density with adjustable values for the densities and the projected lengths of the aliphatic tail and the polar head as well as an overall Gaussian smearing of the densities. We find that the tails are close-packed but uniformly tilted 30° relative to the interface normal.

Local order in liquid tellurium has been investigated in both liquid and supercooled state. The nearest-neighbours number has been determined, and its variation vs. temperature is discussed in terms of theoretical predictions. The semiconductor-to-metal transition is shown to occur in a narrow temperature range, mainly in the supercooled-state region.

Semi-infinite O(n) systems are considered at a bulk tricritical point. A continuum model with a |ϕ|⁶ bulk nonlinearity and a |ϕ|⁴ surface nonlinearity is used to analyse the critical behaviour at the special transition in d = 3 and d = 3−ε dimensions. For n = 0 the model describes the statistics of polymers at the θ-point, in the presence of a wall. It is shown that the surface critical exponents have a systematic expansion in powers of ε^1/2. For d = 3, logarithmic corrections of an unusual form are found for surface quantities. In the special case of vanishing bulk nonlinearity the surface exponents can be expressed in terms of known bulk exponents for systems with long-range interactions.

The results of recent measurements of gas adsorption on a series of porous glass substrates with very narrow distributions of pore radii are analysed on the basis of a density functional theory of capillary condensation of a confined fluid. Assuming that hysteresis of the isotherms is associated with metastability of the gaslike configuration in a single pore, the calculated adsorption isotherms are in good agreement with experiment for the series of glasses. Our analysis indicates that for porous substrates of this type the collective effects of the pore network are less important for hysteresis than metastability in individual pores.

The growth of Ag monolayers on (111) Cu, studied by Auger electron spectroscopy and surface reflectance spectroscopy, follows the layer-by-layer mode. The Ag monolayer in contact with Cu displays a narrow absorption band at 3 eV, which is interpreted as due to transitions from d states in the Ag monolayer, the shift being caused by the interaction with the Cu substrate. The electronic properties of thicker Ag films gradually tend to those of bulk Ag.

We present a continuum model for the growth of solid epitaxial films which takes account of both surface tension and lattice mismatch. Layer-by-layer film growth is found to be unstable for fixed particle number. We show that the conventional nucleation and growth scenario for film decay is in error above the roughening temperature. Films decay to epitaxial solid "droplets" in coexistence with a microscopically thin, strained film through a barrierless mechanism which is closely related to spinodal decomposition. The decay of the film is triggered when the layer height exceeds the critical height beyond which misfit dislocations appear at the interface.

We have measured x-ray diffraction (XRD), high-resolution electron microscopy (HREM), resistivity and susceptibility for a series of differently prepared YBa₂Cu₃O_7-δ samples. The high-temperature superconductivity was studied as a function of variable quench temperature. Quenching above 820 °C leaves the sample in the tetragonal phase and destroys the superconductivity. We suggest that the supercondutivity is located in the CuO chains which are extremely sensitive to oxygen loss.

The YBa₂Cu₃O₇ compound has been prepared as a single-phase material. It exhibits a sharp superconducting transition around 93 K which is observed consistently by resistance and magnetic-susceptibility experiments. Upper critical fields H_c2 have been measured just below T_c up to 42 T, using a high-pulsed magnetic field. We conclude that the H_c2 value at 77 K is about 80 T and that the extrapolated value at 0.0 K could exceed 250 T.

¹⁷⁰Yb Mössbauer measurements show that magnetic ordering occurs within the Yb sublattices of YbCo₂Si₂ and YbFe₂Si₂ at 1.7 and 0.75 K, respectively. The saturated magnetic moments are 1.4 and 2.0μ_B and are directed near directions perpendicular to the local tetragonal symmetry axis. These moments and the observed 4f-shell electric-field gradients can be accounted for in terms of Yb³⁺ charge states experiencing crystalline electric fields.

Measured and computed 3d core level photoemission spectra for Yb in YbP are presented. The theoretical line shapes and satellite structures are obtained from a combination of standard atomic calculations in intermediate coupling, and many-body techniques due to Gunnarsson and Schoenhammer.

We investigate high-temperature quantum effects in multidimensional Mixmaster models. We show the universal character of such effects. A conclusion is drawn about the chaotic behaviour in these models.