Circular dichroism in photoemission can be described by an atomic approach and a comparison is made with an itinerant-electron model. The latter cannot describe the multiplet effects arising from the many-particle Coulomb and exchange interactions. The atomic model predicts a strong dichroic effect in localized transition-metal, rare-earth, and actinide compounds; for Cu p core-hole emission an asymmetry ratio of 45% is calculated. In contrast to x-ray absorption, the angular-dependent part of the electrostatic interaction between the core hole and localized valence holes is essential for circular dichroism.

Vortex motion has been studied for the first time in high-quality, highly underdamped, two-dimensional Josephson-junction arrays, with normal-state junction resistances ranging from 43 Ω to 48 kΩ. Strong similarity is found with the dynamics of the phase in single junctions, e.g., vortices with mass moving in the spatially periodic washboard potential of the 2D array. High-resistance arrays show resistance below 35 mK due to either thermally activated depinning or quantum fluctuations.

We present a lattice-gas automaton approach to coupled reaction-diffusion equations. This approach provides a microscopic bases for exploring systems which exhibit such interesting features as oscillatory behavior and pattern formation. Two-species systems are analyzed in detail. As an application of the formalism, we construct the microscopic dynamics for a system described by the Maginu equations; simulation results show excellent agreement with the phenomenological predictions. Most important is the result showing that we obtain Turing-type structures by a purely microscopic approach.

A lattice-gas automaton model is constructed for multispecies, chemically reacting, spatially distributed systems and applied to a two-species reaction. The automaton simulations show monotone and oscillatory decay to the steady state as well as excitability and limit cycles. Chemical waves, such as rings and spiral waves, and Turing patterns that arise from the bifurcation of the homogeneous state are found. The model allows the exploration of nonequilibrium spatial sructures at the mesoscopic level and goes beyond the usual reaction-diffusion equation descriptions.

We establish that in the functional-integral expression for the grand partition function, the thermodynamic properties of a charged, rotating black hole are derived from a complex geometry. The corresponding real ‘‘thermodynamical’’ action is constructed explicitly.

The yields of the 1S and the sum of the 2S and 3S Υ resonances have been measured for 800-GeV protons incident on targets of ${}_{}{}^2{}_{}{}^{}\mathrm{H}$, C, Ca, Fe, and W. A significant nuclear dependence is seen in the yield per nucleon which, within errors, is the same for the Υ(1S) and Υ(2S+3D) states. A large decrease in the relative yield from heavy nuclei is found for the range ${\mathit{x}}_{\mathit{F}}$<0. Significant nuclear dependence is also observed in the ${\mathit{p}}_{\mathit{t}}$ distribution. Differential cross sections for the Υ(1S) for ${}_{}{}^2{}_{}{}^{}\mathrm{H}$ are presented over the ranges 0.24≤${\mathit{p}}_{\mathit{t}}$≤3.4 GeV/c and -0.15≤${\mathit{x}}_{\mathit{F}}$≤0.5.

It is explained that a large cross section and an increase with energy of diffractive production of nucleons (${\mathit{N}}^{\mathrm{*}}$, . . .) (${\mathit{E}}_{\mathit{N}}$,${\mathit{E}}_{\mathit{N}}^{\mathrm{*}}$≥${\mathit{E}}_{\mathit{A}}$/A) in central collisions of light (A) and heavy (B) nuclei would signal the color-screening phenomenon and large fluctuations of size in the nucleon wave function. In particular, we find that for ${\mathit{E}}_{\mathit{A}}$/A≥200 GeV and B∼240, the probability of diffractive nucleon production should increase by a factor >5 as compared to that observed at BNL energies.

We report a first measurement of the spin-correlation parameter ${\mathit{A}}_{\mathit{z}\mathit{z}}$ in neutron-proton scattering at 67.5 MeV. The results, obtained in the angular range 105°≤${\mathrm{\theta }}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$≤170° with typical accuracies of 0.008, are highly sensitive to the ${}_{}{}^3{}_{}{}^{}$${\mathit{S}}_1$${\mathrm{-}}^3$${\mathit{D}}_1$ mixing parameter ${\mathrm{\epsilon }}_1$. A phase-shift analysis based on the current world data yields a value of ${\mathrm{\epsilon }}_1$ significantly higher than predicted by modern potential models.

Stimulated Raman transitions between the ground-level hyperfine states of atoms have been used to manipulate slowly moving atoms in an atomic fountain. An ensemble of sodium atoms with an inferred velocity spread along one dimension of 270 μm/sec has been prepared by this technique. We also show that this velocity-selection method is effective in measuring ultracold temperatures of laser-cooled atoms in a regime where traditional ballistic methods fail.

As a result of transient atomic behavior, the achievements of laser cooling in pulsed fields are very different from those in continuous fields. Semiclassical and quantal treatments are used to identify the conditions for optimal cooling. For light atoms and narrow lines, energies below the one-photon recoil limit are obtained.

The validity of time-dependent Hartree-Fock (TDHF) theory is explored for the multiphoton ionization of atoms. The 3D electrostatic interaction is replaced by a 1D soft-core interaction which allows the construction of an N-electron atom in only N dimensions. For multiphoton ionization of a two-electron ‘‘He’’ atom in its ground state, we solve the time-dependent Schrödinger equation directly on a 2D lattice and solve a 1D formulation of the TDHF equations. The 2D lattice solution compares favorably with the frozen-core TDHF results, but not with the full nonlinear TDHF results.

Stimulated Raman and Brillouin scattering in the quasi-steady-state (QSS) regime are analyzed by the inverse-scattering transform (IST) with nonoverlapping square wave packets and second-order Zakharov-Shabat scattering problem. It is shown that the important QSS characteristics, namely, the number of pulses required for establishing the QSS condition, the Stokes growth, and the development of polarization are readily calculated using IST. These results are usually obtained by extensive numerical computations which, however, do not lead to their fundamental determinations. The IST results are found to be in excellent agreement with experimental observations and numerical computations.

It is shown that stimulated synchrotron emission and absorption can act simultaneously on a relativistic electron beam with a narrow energy spread to reduce the spread significantly. This beam ‘‘cooling’’ mechanism acts most effectively for beam energies belonging to a sequence of discrete values, one for each synchrotron harmonic. The discrete energy values are absolute, and are not influenced by external parameters such as magnetic field strength. Application of this mechanism to cool beams for free-electron lasers, synchrotron-radiation lasers, and slow-wave cyclotron amplifiers is suggested.

We preent numerically obtained bounded solutions of the one-dimensional complex Ginzburg-Landau equation with a destabilizing cubic term and no stabilizing higher-order contributions. The boundedness results from competition between dispersion and nonlinear frequency renormalization. We find chaotic and also stationary and time-periodic states with spatial structure corresponding to a periodic array of pulses. An analytical description is presented. Possibly experimental results connected with the dispersive chaos found in binary-fluid mixtures can be explained.

A numerical simulation of a complex turbulent shear flow using large-eddy simulation techniques is carried out. The filtered Navier-Stokes equations are solved with a finite-volume method. The subgrid model is a local adaptation to the physical space of isotropic spectral eddy-viscosity models. The statistics of the mean field are in good agreement with the experimental data available, corresponding to low step. Calculations in a high-step case show that the eddy structure of the flow presents striking analogies with the plane shear layers, with large billows shed behind the step, and longitudinal hairpin vortices strained between these billows.

Measurement of the intensity scaling of stimulated Raman forward scattering (SRFS) at one observation angle is presented. A single, high-intensity 527-nm laser beam excited the instability in a preformed plasma whose properties are such that the predicted gain for SRFS spans the range anticipated for high-gain laser-fusion experiments. At low intensities, the gain of the instability was consistent with convective theory. At intensities greater than 1×${10}^{15}$ W/${\mathrm{cm}}^2$, the instability saturated at a level of less than ${10}^{11}$ W/sr nm ${\mathrm{cm}}^2$.

Plasma wake fields in the ion-wave regime have been excited by injecting ion bunches with a variety of shapes. An excited-wave amplitude (δn/${\mathit{n}}_0$) of up to 17% has been observed for a bunch falloff time less than the wake-field period. The large-amplitude wake wave damps out, along with oscillations of the wave envelope. A simple linear theoretical model is developed, which can explain most of the observed phenomena, except for the large-amplitude oscillations.

The statistical properties of anisotropic diffusion-limited aggregates (DLA) grown in a strip are investigated. The mean shape of these aggregates being related to the corresponding smooth Saffman-Taylor solutions, a finite-size scaling analysis is applied. This scaling description shows that the anisotropy-induced crossover from isotropic DLA clusters (${\mathit{D}}_{\mathit{F}}$=5/3) to dendritic fractals (${\mathit{D}}_{\mathit{F}}$=3/2) is actually contained in the continuous shape transition of the stable solution, from isotropic fingers of relative width λ=0.5 to λ=0 needlelike fingers.

We use the fixed scale transformation method, developed for fractal growth, to investigate analytically the nature of clusters in self-organized criticality (SOC). In two dimensions the clusters of sites involved in a relaxation process turn out to be compact (D=2) because of the absence of effective screening. Therefore they are more similar to Eden-type clusters (possibly with a rough surface) than to those of the usual fractal growth models. This result is in good agreement with the computer simulations and one can conjecture that it should hold for any dimensions. The critical state corresponding to SOC dynamics is therefore of much simpler nature with respect to those of the usual fractal growth models.

The coexistence of sharp and broad features in the electronic spectrum of a chromophore embedded in a rare-gas cluster has been interpreted as a signature of solid-liquid phase coexistence in the melting transition. We peform molecular-dynamics simulations of benzene-${\mathrm{Ar}}_{\mathit{N}}$ clusters which show that the observed spectra features are instead dominated by inhomogeneous broadening due to various cluster configurations.