The hadronic spectra of 200A GeV S+S collisions are analyzed assuming thermal emission of particles including resonance decays. While the rapidity distributions suggest a longitudinal flow almost independent of the temperature, the transverse momentum spectra exhibit an ambiguity between transverse flow and temperature, which cannot be resolved by the spectra of the heavier particles. However, in a theoretical model for the global hydrodynamic expansion with a dynamical freeze-out criteron, we find that almost inevitably a sizable transverse flow develops, which is in quantitative agreement with the data.

Absolute helium (e,2e) differential cross sections have been measured over a more general range of directions of the outgoing electrons than has previously been attempted and at an incident energy for which all the complexities of exchange and capture processes, incoming and outgoing channel distortions, and short- and long-range correlations are present.

We report, for the first time, the experimental observation of solitary waves in an axisymmetric Taylor-Couette flow. The solitary waves result from a parity-breaking bifurcation which occurs near the onset of Eckhaus instability for Taylor vortex flow in a wide-gap, counterrotating system (radius ratio η=0.5 and speed ratio μ=-0.2). Our results agree quantitatively with a recent theoretical calculation by Riecke and Paap.

Measured impurity temperature profiles from linewidths in the TJ-I tokamak are shown to be higher than proton temperature profiles. The difference between both apparent temperatures, which is attributed to the presence of anisotropic nonthermal velocities, tends to decrease as the density increases. Whereas electrostatic drifts due to E${\mathrm{̃}}_{\mathit{I}}$×B might be responsible for the poloidal turbulence velocities, radial velocities might be dominated by magnetic turbulence. These conclusions are supported by criteria based on the radial dependence and typical strengths of electric and magnetic fluctuations.

A Kolmogorov-type analysis of the energy- and enstrophy-cascading ranges of a forced Hasegawa-Mima equation allows one to derive a criterion for the threshold of the transition between the weak-turbulence and the strong-turbulence regimes. Contrary to general belief, it is found that due to the inverse energy cascade the large-scale portion of the inertial range is in the strong-turbulence regime in the limit of infinite Reynolds-like numbers for any finite amount of forcing.

The weakly bound hydrogen dimer has been detected in diffraction from LiF(001) along the 〈100〉 direction. The incident dimer energy is 48 meV and the crystal surface temperature is 150 K. The data are analyzed with a simple eikonal elastic scattering calculation and inelastic phonon scattering attenuation is estimated with a measured Debye-Waller factor. These calculations suggest that at least 5% of the dimers survive fragmentation. The well-defined first-order diffraction peak has an intensity of order 5×${10}^{14}$ dimers/sec str which could be useful for further beam studies.

A few eV hot electron is found to stimulate the motion of a gold atom, leading to adatom generation at the surfaces of a Au film. This is detected through ballistic electron emission microscopy (BEEM) observations of the resulting growth of an atomic layer terrace on the interfacial Au surface of AU passivation-layer Si samples. We deduce the presence of concurrently produced vacancies in the film from their (time-dependent) effect on the BEEM current. The phenomenon has similarities to electron stimulated desorption.

A side chain mesomorphic co-oligomer possesses a large blue-phase temperature domain. Upon cooling down from blue phase I colored crystallites are quenched below the glass transition of this material. The microtome cut of these crystallities and their observation by transmission electron microsocopy reveal the presence of biperiodic textures different from the cholesteric ones. Image analysis of these textures, associated with an original model of diffraction confirms the presence of the ${\mathit{O}}^{8\mathrm{-}}$ symmetry and suggests that the transmission electron microscopy contrast obtained here has to be associated with changes of the molecular orientations in the bulk of the sample.

Reflection high-energy electron diffraction oscillations during pulsed laser ablation of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ on ${\mathrm{SrTiO}}_3$(100) substrates were measured. We have found for the first time that the oscillations are modulated by the laser-pulse repetition frequency. Each laser pulse deposits 0.14 nm of material. This causes the specularly reflected intensity to decrease instantaneously, but then it increases exponentially due to crystallization. An activation energy of 0.7±0.1 eV and a diffusion constant of 1.4×${10}^{\mathrm{-}12}$ ${\mathrm{cm}}^2$/sec at 720°C for the formation of c-axis oriented films was determined.

Synchrotron x-ray Bragg intensities from a ${\mathrm{C}}_{60}$ single crystal were used to evaluate the nonuniform atomic density distribution on a ${\mathrm{C}}_{60}$ sphere at 300 K. Coefficients of the symmetry-adapted spherical harmonics up to l=18 are required with a resulting density deficiency of ∼16% in 〈111〉 directions and four lobes of ∼10% excess about 〈110〉. The results are discussed in terms of an effective potential which a single ${\mathrm{C}}_{60}$ sees in the cubic field of its neighbors. Initial calculations give a maximum rotational potential barrier height of about 2kT or ∼600 K.

The (2×1) reconstruction of the (111) surface of diamond has been characterized via a series of first principles molecular dynamics calculations. The reconstructed clean surface is found to consist of dimerized π-bonded chains with no buckling and to be stable against thermal fluctuations up to about 2500 K. Our results for the atomic and electronic structure agree well with the experimental information available.

Inelastic helium-atom scattering from epitaxial films (2–20 monolayers) of sodium on Cu(001) reveals a large number of nearly dispersionless phonon modes whose frequencies depend on the thickness and scale as the lower harmonics of an open-ended organ pipe. These data provide evidence for confined acoustic resonances, corresponding to longitudinal standing waves normal to the surface with frequencies about 20% larger than in the bulk.

We study core-valence interactions in several technologically important semiconductors. We compute band structures treating many-body effects in Hedin’s GW approximation. The core-valence correlation and core polarization are treated using a core-polarization potential formulation instead of standard, less reliable, mean-field approaches. This is critical for materials with shallow cores (Ge, GaAs), where mean-field treatments of core-valence interactions bias certain band gaps by up to 0.4 eV. The core-polarization potential formulation may be used in either frozen-core all-electron or pseudopotential calculations, since it deals only with core-valence many-body effects.

We study the expansion of an exciton gas against lattice drag, describe the transition between the diffusive and low-drag hydrodynamic regimes, and compare with experimental data obtained at exciton densities and temperatures near the Bose-Einstein phase boundary. As we show through numerical simulation, the rapid expansion of the exciton cloud seen experimentally at high exciton densities can be explained as drag-free hydrodynamic flow. Such a reduction in drag strongly suggests that Bose-Einstein condensation has occurred and that excitonic superfluidity is being observed.

Magnetophotoluminescence spectra of GaAs quantum wires with lateral and vertical dimensions of 20 and 10 nm, respectively, were measured up to 40 T with three orthogonal magnetic field configurations. The observed photoluminescence peak shift with increase of applied magnetic field was strongly dependent on the direction of magnetic field, which directly demonstrates the existence of two-dimensional confinement in the quantum wires. It was found that the excitons were anisotropically shrunk in the quantum wires, and that the observed anisotropic energy shift was consistent with the size of the quantum wire structure.

We report the results of scanning tunneling microscopy (STM) and spectroscopy (STS) studies on high-quality single crystals of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ (YBCO) which were cleaved in situ at 20 K prior to measurement. STS reveals an energy gap with 2Δ/${\mathit{kT}}_{\mathit{c}}$=6–8 and conductance curves with small zero bias conductance. STM images show for the first time the complex atomic structure of the YBCO surface; atomic resolution disappears after heating to 70 K. Large features may be due to the electronic effects of oxygen disorder, and YBCO is shown to cleave between the BaO and CuO chain layers.

We have studied phase transitions in fabricated 2D arrays of Josephson junctions where the charging and Josephson coupling energies are about equal. We find a crossover from superconducting behavior in low fields to insulating behavior for fields above a critical value of 0.1–0.2 flux quanta per unit cell. The quantitative aspects agree well with predictions from a recent theory for quantum vortex motion by M. P. A. Fisher and with measurements on films. Similar transitions are found around values f=n/m, where f is the flux per cell and n,m=1,2,3. The field dependence is periodic in f with period 1.

The in-plane resistivity (${\mathrm{\rho }}_{\mathit{a}\mathit{b}}$) of ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_4$ has been studied over a wide temperature (4–1000 K) and composition range (0<x<0.35). The much discussed T-linear resistivity is observed only in the narrow composition region associated with optimal superconductivity. In the underdoped range (x<0.1), we observe first indications of resistivity saturation and analyze the resistivity as indicative of a ‘‘small’’ Fermi surface. In the overdoped range (x>0.2), ${\mathrm{\rho }}_{\mathit{a}\mathit{b}}$ follows a novel power-law dependence, ρ∞${\mathit{T}}^{1.5}$, over the entire temperature range up to 1000 K.

The problem of phase coherence of a fermion in a spin liquid state of a quantum magnet is reduced to the problem of phase coherence of a fermion moving in a random magnetic field. The latter problem is solved for the fermions moving with large velocity, i.e., close to the Fermi surface. The motion of such fermions turns out to be classical in the direction perpendicular to the classical trajectory, but it remains quantum in the direction along the trajectory.

The D NMR spectra of HD and ortho-${\mathrm{D}}_2$ are sensitive to the crystal fields from the MgO surface sites. At fractional coverages 0.6<x<0.9, beyond the limit of island growth, rapid motion among inequivalent sites occurs, even at 4.2 K. For 1<x<2, broad and narrow lines arise from the first and second layers, respectively. Isotopic bilayer mixtures show nearly complete separation, with the more massive specie in the first layer.