Neutron scattering experiments on liquid argon show evidence for the existence of well defined though strongly damped sound waves with wavelengths comparable to the size of the atoms. The dynamic structure factor can be described in terms of Rayleigh and Brillouin lines. The sound oscillation frequency shows an anomaly consistent with the mode-coupling theory. The shape of the dispersion curve resembles that of solid argon except for a wave-length region where the oscillation frequency vanished as predicted by kinetic theory.

Xenon films on graphite are simulated with a molecular-dynamics technique. Because of exchange of atoms between the first and second layers, there is a very small temperature window where the first layer melts and freezes continuously in time with a period of nanoseconds. Two-phase coexistence is prevalent during the transitions. The first-layer melting transition is first order, but would appear to be continuous if temporally averaged. These features are in quantitative agreement with recent x-ray scattering experiments.

Supercooled liquids and metallic glasses can be viewed as defected states of bond orientational order. Surfaces of constant negative curvature contain an irreducible density of point disclinations in a hexatic order parameter. Analogous defect lines in an icosahedral order parameter appear in three-dimensional flat space. The Frank-Kasper phases are ordered networks of these lines, which, when disordered, provide an appealing model for structure in metallic glasses.

Angular distributions of neutral CO desorbed by electron impact from chemisorbed CO on Ru(001), and of neutral ${\mathrm{N}}_2$O and ${\mathrm{N}}_2$ from chemisorbed and physisorbed ${\mathrm{N}}_2$O on Ru(001), have been measured and compared to angular distributions of desorbing ions. All distributions are peaked around the surface normal. Angular widths of neutrals are generally broader than those of ions, but are much narrower than for thermal desorption, and show large differences. The results are discussed in terms of mechanisms of ionic and neutral desorption.

Measurements of the scattering of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ atoms grazing the surface of liquid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ show that the reflectivity approaches unity as the perpendicular wave vector tends to zero, in agreement with theoretical predictions.

An optical heterodyne technique based on the coherent Raman effect is demonstrated for detecting nuclear magnetic resonances (NMR) and coherent spin transients in normal and optically excited impurity-ion solids at low temperature. Initial measurements on ${\mathrm{Pr}}^{3+}$: La${\mathrm{F}}_3$ provide the first spin-echo studies of an electronically excited state, and cw resonances yield NMR line centers and shapes with kilohertz precision.

Electrodynamic calculations of the electric field on the surface of large Ag prolate spheroids indicate that the field enhancement decreases rapidly, the resonance shifts to longer wavelengths and broadens, and a new set of higher-order resonances appears at shorter wavelengths. These results form the basis for comparison with surface-enhanced Raman scattering measurements from lithographically produced Ag microstructures.

The $S$-matrix scheme allows a straightforward formalization of the Einstein-Podolsky-Rosen nonseparability either of distant measurements issuing from a common preparation, or of distant preparations converging into a common measurement. This implies Lorentz and $\mathrm{CPT}$ invariance of the causality concept at the elementary level, which is a quantal and relativistic extension of the 1876 Loschmidt reversibility statement.

A nonlinear oscillator externally driven by an impulsive periodic force is investigated. An exact analytical expression is obtained for the stoboscopic or Poincaré map for all values of parameters. The model displays period-doubling sequences and chaotic behavior. The convergence rate of these cascades is in very good agreement with Feingenbaum theory.

Both bound and scattering states of the Pöschl-Teller potential are shown to be connected with unitary representations of certain groups. A family of periodic potentials, and their associated transfer matrices and band structure, can also be obtained from group theory and reduce to the above potential when the real period approaches infinity. These results suggest that the algebraic approach used for treating bound-state problems can be extended to scattering and band-structure problems.

The branching fraction for the decay of the $\Upsilon \mathrm{}\left(1S\right)\mathrm{}$ into $\tau$ paris has been measured to be (3.4±0.4±0.4)%. This result agrees with the previously measured branching ratio of the decay into muon pairs.

$B$-meson decays to final states consisting of a $D^0$ or $D^{*\pm }$ and one or two charged pions have been observed. The charged-$B$ mass is 5270.8 ± 2.3 ± 2.0 MeV and the neutral-$B$ mass is 5274.2 ± 1.9 ± 2.0 MeV.

It is shown that the standard SU(2) lattice gauge theory is in a confining phase for all values of the coupling, $0<\mathrm{}\beta <\infty$, and $d<~4$. The main idea is to show that the electricflux free energy is bounded by expressions resulting from approximate (Migdal-Kadanoff) renormalization-group transformations.

Light shifts of a Rb Rydberg level, induced by an intense nonresonant electromagnetic field, have been measured for the first time. Agreement between experimental results and theory is satisfactory.

Strong magnetohydrodynamic activity has been observed in PDX neutral-beam-heated discharges. It occurs for ${\beta }_{T}q>~0.045$ and is associated with a significant loss of fast ions and a drop in neutron emission. As much as 20%-40% of the beam heating power may be lost. The instability occurs in repetitive bursts of oscillations of ≤ 1 msec duration at 1-6-msec intervals. The magnetohydrodynamic activity has been dubbed the "fishbone instability" from its characteristic signature on the Mirnov coils.

Direct experimental measurements of the melt-in, resolidification, and amorphization velocities for pulsed (2.5 to 10 ns) uv and ruby-laser irradiation have been made on $〈100〉$ silicon on sapphire. An experimental value for the critical amorphization velocity in $〈100〉$ Si has been measured as 15 m/s. Epitaxial resolidification was observed from 5 to 15 m/s. Additionally, melt-in velocities in excess of 200 m/s were observed for 2.5-ns ruby irradiation.

Colloidal crystals, made of large polystyrene particles (1.1 μm in diameter), are confined into a thin layer between two glass boundaries. When the thickness $h$ of the layer is increased progressively from zero, a sequence of structures $S\left(h\right)\mathrm{}$ is detected from direct observations in an optical microscope. These structures are stacks of $n$ square (□)—or triangular $\left(\Delta \right)$—ordered layers. For $n<~7$, the sequence $S\left(h\right)\mathrm{}$ is $\dots n\Delta \to \mathrm{}(n+1\mathrm{})\mathrm{}\square \to \mathrm{}(n+1\mathrm{})\mathrm{}\Delta \to \dots$.

The first low-energy electron-diffraction intensity analysis of the structure of molecules adsorbed at several different surface sites yields, for the compact Rh(111)-(2×2)-3CO structure, symmetric bridge sites and nonsymmetric near-top sites, which are separated by only ∼ 2.85 Å. CO molecules in near-top sites are shifted sideways by ∼ 0.5 Å from ideal top sites, but are tilted by less than 15° from the surface normal. These results support an antiphase domain model of high-coverage CO structures on metal surfaces in general.

New measurements of the anomalous magnetic field dependence in the amplitude of the oscillatory magnetoresistance (Shubnikov-de Haas effect) of $n$-type HgSe and ${\mathrm{Hg}}_{1-x}{\mathrm{Mn}}_x\mathrm{Se}$ are presented. These data are interpreted with use of a closed-orbit magnetic breakdown model which permits Fermi-surface parameters of interest to be determined. It is found that the addition of 0.1-at.% Mn to HgSe results in a Fermi surface whose shape is temperature dependent.

Measurements of the La $3d$ binding energies as studied by x-ray photoelectron and x-ray absorption spectroscopies are reported. Apparent discrepancies of ∼ 2-3 eV in the observed peak energies are shown to be due to the $d^9{f}^n$ multiplet splittings and the different selection rules in the different spectroscopies. It is argued that these effects have a wider relevance to solid systems with strongly localized, open-shell electrons, such as rare earths and transition-metal compounds.