Stabilization, the exotic process by which an atom in a superintense laser field, of the order of the atomic unit, reacts to the increase in intensity or decrease in frequency by increasing its lifetime, has been recognized as elusive for atomic ground states. We now show that the stabilization regime can be effectively attained at present laser performances (intensities, frequencies, pulse shapes) when starting with atoms prepared initially in Rydberg states of high magnetic quantum number with respect to the axis of linear polarization.

Optical pumping of potassium atoms followed by spin-exchange scattering with deuterium atoms in a high magnetic field was found to produce an intense, highly spin-polarized beam of atomic deuterium. In particular, the atomic polarization of deuterium was determined to be (73±3)% at an intensity of 2.1×${10}^{17}$ atoms/s.

An analytical model based on the WKB approximation is developed to describe the suppression of the short-wavelength Rayleigh-Taylor instability by convective flow. The boundary-value problem for the instability growth rate is reduced to the solution of a system of algebraic equations with the coefficients depending upon the unperturbed variables. The method, which is applicable for perturbation with wavelengths small compared with the density scale length, is applied to analyze the instability, in stationary, ablating plasmas with convection and strong inhomogeneity.

A significant particle pinch and reduction of the effective thermal diffusivity are observed after switching the neutral beam direction from coinjection to counterinjection in the JFT-2M tokamak. The particle pinch measured in the counterinjection phase shows good agreement with the prediction of the inward pinch model related to the electric fields.

The effect of shear on phase separation in a binary fluid mixture has been studied by monitoring the steady-state transmitted intensity of a laser beam through a continuously stirred mixture of isobutyric acid and water. Measurements were made on samples with five different off-critical compositions and one at the critical composition of the binary mixture, for three different stirring frequencies in each case. The data for the onset of phase separation in the stirred samples that are as far away as 500 mK from the critical point compare favorably with the theory of Onuki and Takasue and with similar measurements on very off-critical mixtures of 2-6 lutidine plus water reported by K. Y. Min et al.$-— However, as the composition gets closer to the critical composition significant differences arise. The main feature is that the measured suppression in temperature peaks at an off-critical composition which is dependent on the stirring frequency. A simple, analytical calculation is also found to show the same feature.

Multiscaling of the free energy is obtained by generalizing the classification of phase transitions proposed by Ehrenfest. The free energy is found to obey a new generalized scaling form which contains as special cases standard and multiscaling forms. The results are obtained by analytic continuation from the classification scheme of Ehrenfest.

We report an extensive Monte Carlo study of the density and energy fluctuations in a 2D Lennard-Jones fluid, within the grand-canonical ensemble. The results are analyzed within a finite-size-scaling theory incorporating the mixed character of the scaling fields that manifests particle-hole asymmetry. The limiting critical distribution of the density matches that of the magnetization in the 2D Ising model, illuminating the configurational basis of universality; the corrections to the limiting behavior contain an antisymmetric component which reflects the critical Ising energy operator, corroborating the anticipated structure of the scaling fields.

The spinodal decomposition in a critical mixture of polydimethylsiloxane and diethyl carbonate was investigated by a time-resolved light-scattering technique focusing especially on the early and intermediate stages of phase separation. A second peak in addition to the main peak was found in the higher-scattering-angle region of the spectrum characteristic of the intermediate stage.

We report studies of the anomalous wetting of a cesium substrate by a liquid-helium film by means of the technique of third sound. In an apparatus which incorporates both glass and cesium substrates, we observe third sound to propagate across cesium for helium films such that the film thickness on glass is ${\mathit{d}}_{\mathit{g}}$≥11.5 layers. For ${\mathit{d}}_{\mathit{g}}$≤9 layers, third sound does not propagate across the cesium substrate. The transition region is hysteretic as a function of the amount of helium in the experimental cell.

Why does a sheet of water flowing over an initially featureless surface spontaneously form a river network? To address this question, we construct a simple model which enables us to examine the shape and stability of individual river channels. We compare predictions for the geometry of fluvial channels with experimental data. In addition, we construct a lattice model which allows us to look at large-scale features of river networks and calculate their scaling relations.

It is shown that screening greatly diversifies the type of patterns that can grow in an electrostatic field. Screening introduces a new length scale and a nontrivial dependence on the boundary conditions. Growing patterns can either have a fractal character (diffusion-limited-aggregation–like) at scales shorter than the screening length, be similar to the Eden model, or even be dense. A transition from dense to multibranched growth occurs at a point which depends on the potentials at the boundaries, the distance between them, and the screening length.

We record the height of the crack surface as a function of position along one-dimensional cuts orthogonal to the crack for six different brittle materials. We find that the width w of this one-dimensional trace as a function of its length L behaves as w∼${\mathit{L}}^{\mathrm{\zeta }}$, where ζ=0.87(7). This result is in agreement with recent conjectures of a universal roughness exponent ζ for these materials.

We have studied the localization of deformation in a 2D packing model. The samples consist of regular packings of equal parallel cylinders (drinking straws). The local stress-strain characteristics, at the contact between two straws, shows a softening part, responsible for the localization of the deformation. We have analyzed the roughness of localization band, i.e., the width W of the localized zone versus its length L. Our results demonstrate the self-affine character of the localized zone: We find a power law, W∼${\mathit{L}}^{\mathrm{\zeta }}$ with ζ=0.73±0.07, which is consistent with recent work on the ‘‘weak’’ disorder model.

The elasticity and hardness of a-C and a-C:H are related to their mean network coordinations. It is shown that ${\mathit{sp}}^2$ sites contribute no rigidity if they form graphitic clusters, as suggested by experiment and electronic structure calculations, despite their having coordinations above the critical value 2.4. Hence both ${\mathit{sp}}^2$ sites and polymeric =${\mathrm{CH}}_2$ groups can severely lower the hardness of amorphous carbons.

Fluctuation of a step of a crystal in the vapor growth condition, where surface diffusion of adsorbed atoms is essential, is studied with a linear stochastic theory. With an asymmetry in step kinetics, the step becomes smooth when it recedes, whereas it becomes very rough when it grows near the Mullins-Sekerka instability point. These effects are confirmed by Monte Carlo simulations.

It is shown that local-field effects in simple metals and semiconductors couple the plasmon into the large-wave-vector q particle-hole excitation spectrum, leading to a plasmon antiresonance (plasmon-Fano resonance). The resulting structure is observed in inelastic x-ray scattering spectroscopy (IXSS) of single-crystal Si for scattering vectors q along the 〈111〉 direction. The inclusion of exchange and correlation effects is important to obtain good agreement between theory and experiment. Previously unexplained structures in the IXSS of single-crystal Li for q along the 〈110〉 direction and of single-crystal Be for q along 〈100〉 and 〈001〉 are also identified as plasmon-Fano resonances.

In the present paper, dielectric, polarization, and Raman results have been combined to identify the existence of a ferroelectric phase transition in the substitutionally disordered dipolar system, ${\mathrm{KTa}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Nb}}_{\mathit{x}}$${\mathrm{O}}_3$, for low Nb concentrations (x=1.2%). A detailed study of the first-order ${\mathrm{TO}}_2$ and ${\mathrm{TO}}_3$ Raman lines reveals (1) the existence of polar microregions well above ${\mathit{T}}_{\mathit{c}}$ and (2) the structural transition at ${\mathit{T}}_{\mathit{c}}$ with the appearance of ferroelectric macroregions. Similar results are obtained in ${\mathrm{K}}_{1\mathrm{-}\mathit{y}}$${\mathrm{Li}}_{\mathit{y}}$${\mathrm{TaO}}_3$ with a quantitative difference due to the slow reorientation of Li. These results can be explained by a random-field model which predicts the coexistence of both dipolar glass and ferroelectric behavior.

4f levels in Ce heavy-fermion compounds are examined using resonant photoemission. We find the following inconsistencies with the predictions of the Kondo model: (a) All temperature dependence can be accounted for simply by phonon broadening and the Fermi function; (b) the spectral weights of the features near ${\mathit{E}}_{\mathit{F}}$ do not scale with ${\mathit{T}}_{\mathit{K}}$; and (c) the line shape of the feature previously identified as the Kondo resonance is Lorentzian and about an order of magnitude broader than predictions. Instrument resolution is not a limiting factor.

Since the discovery of the high-${\mathit{T}}_{\mathit{c}}$ superconductors there has been a revival of interest in frustrated magnetic systems. In this work, we compare predictions of frustrated and doped Hamiltonians by studying the t-J model with one hole and the frustrated Heisenberg J-J’ model. In particular, we compare for both systems the dynamic spin-spin structure factor S(q,ω), and the ${\mathit{B}}_{1\mathit{g}}$ Raman scattering spectrum R(ω) at zero temperature. We observe that, for the t-J model, both quantities are in qualitative agreement with experimental measurements while the corresponding ones for the J-J’ model are not. These results indicate that doped systems cannot be accurately modeled by a purely spin model and that the latter, including the chiral spin states, might not be relevant to describe measurable quantities of the high-${\mathit{T}}_{\mathit{c}}$ materials.

We give the exact spectrum and thermodynamics for a long-range hopping Hubbard chain with linear dispersion. This model exhibits a Mott-Hubbard metal-insulator transition at half filling when the interaction strength U equals the bandwidth W. The solution for U≫W also covers the corresponding t-J model, which reduces to the spin model of Haldane and Shastry at half filling. We mention possible extensions of the model in one and higher dimensions.