Neutron diffraction studies of ${\mathrm{O}}_2$ thin films physisorbed on the basal plane of graphite show three distinct two-dimensional crystalline phases, all incommensurate with the substrate lattice. The low-temperature monolayer phase has a distorted triangular structure analogous to the closest-packed plane of bulk $\alpha$-${\mathrm{O}}_2$. As in $\alpha$-${\mathrm{O}}_2$, a magnetic superlattice reflection persisting up to $T=10\mathrm{}$ K indicates a well-developed antiferromagnetic order. Above $T=10\mathrm{}$ K the structure is similar to the closest-packed plane of $\beta$-${\mathrm{O}}_2$.

Following suitable preparation the intensity of zero sound propagated through ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$A$ in zero magnetic field varies periodically with time. This implies an oscillatory motion of the field of the orbital axis $\hat{l}$, which is probably driven by a residual heat flow.

We report the suppression by electric fields of longitudinal resistivity anomalies at 145 and 59 K in the compound Nb${\mathrm{Se}}_3$. Sample resistance was determined by conventional four-probe dc measurement as well as with short current pulses. We attribute the observed suppression to Zener breakdown across extremely small gaps introduced by the presence of charge density waves.

New results of He and Ne atomic beams scattered from the (001) face of LiF are presented. The angular distribution of the inelastically scattered intensity shows pronounced minima that are identified with the occurrence of bound-state resonances for inelastic processes. The extent to which the effect can be used to determine the phonon spectrum at the surface is discussed.

A novel variational procedure for the partition function based on a generalization of the "coherent state" representation is presented. As an example of its use, I apply it to a simple model of a disordered system. It is shown to yield results which are exact in both the high and low temperature limits, the latter being particularly difficult to obtain by conventional methods.

A new type of wave propagation in pure metals in a magnetic field is reported. This mode is analogous to cyclotron waves but is carried by the spin of conduction electrons. Oscillations in the microwave transmission spectra of copper and gold foils with ferromagnetic layers deposited onto them are attributed to these waves.

In an extension of its capabilities, ion-neutralization spectroscopy is used to determine transition density functions corresponding to ion neutralization at different ion positions. This provides the first direct measurement of the relative variation in the local density of states outside a solid surface. It is shown that the $d$ orbitals of Hg adsorbed on Si are a minor component of the total wave function at the ion position and decay more rapidly with distance outside the solid than does the $\mathrm{Si}p$ component.

The low-temperature anomaly in the lattice dynamics of SrTi${\mathrm{O}}_3$ and KTa${\mathrm{O}}_3$ is described as resulting from an anharmonic coupling between an optical and an acoustic branch. The numerical calculations performed for ${\omega }_{\mathrm{TO}}$ at the center of the Brillouin zone give an excellent fit to the available data from 4 to 300 K. It is shown that the ferroelectric phase transition in SrTi${\mathrm{O}}_3$ is prevented by the zero-point fluctuations of the acoustic mode.

In studying resonant Raman scattering around the $C$ exciton of the wurtzite semiconductor CdSe we have observed a Raman mode with an unusual dependence on the incident photon frequency. As the incident photon is tuned across the $C$ exciton, this Raman mode gradually broadens and shifts in frequency until it becomes a photoluminescence peak centered at the $C$ exciton frequency. A phenomenological theory is proposed to explain the behavior of this mode by the presence of a "bottleneck" in the decay of resonant intermediate states involved in the scattering of this mode.

The first far-infrared measurements on metallic particles with diameters < 10 nm are reported. The absorptivity is well approximated by ${\alpha }_{\exp }\approx C_{\exp }{\tilde{\nu }}^2$, where $3<\mathrm{}\tilde{\nu }<150\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$. The results are compared with the Gor'kov-Eliashberg (GE) theory of particles with quantized electronic levels as well as with the classical Drude theory. When a size distribution is included, ${\alpha }_{\mathrm{GE}}=C_{\mathrm{GE}}{\tilde{\nu }}^2$ irrespective of level statistics. However, $C_{\exp }\gg C_{\mathrm{GE}}$ and the observed dependence on the diameter is directly contrary to predictions of the GE theory. Neither can the data be reconciled with the classical theory.

For all complex space-times in which the self-dual part of the Weyl tensor is algebraically degenerate, Einstein's vacuum equations are reduced to a single differential equation of the second order and second degree.

From in-beam $\gamma$-ray spectroscopy in ${}_{}{}^{74}{}_{}{}^{}\mathrm{Se}$, a negative-parity band to (${11}^{-}$) with rotational properties built on a $3^{-}$ collective octupole state is established along with the positive-parity (Barrette et al.) yrast band to (${14}^{+}$). The negative-parity band has essentially a constant moment of inertia in sharp contrast to the positive-parity band. This is the first negative-parity band outside those in deformed nuclei with such pure rotational behavior.

We present temporally and spectrally resolved x-ray emission data from a laser-irradiated target. The temporal dependence is interpreted in terms of a laser heating phase, a plateau period in which the glass-shell pusher propagates radially inward, a secondary x-ray burst corresponding to stagnation of the pusher at the target center, and a rapid decay of emission in the post-compression target disassembly period.

We report on the quasi-linear evolution of the electron-beam-plasma instability in a two-dimensional system. The numerical solutions of the basic equations show that a two-dimensional system evolves in a different way as compared with a one-dimensional system. After saturation the wave energy monotonically decreases with time while the width of its spectral distribution in $k$ space narrows rapidly. In some cases, the system reaches a state which is modulationally unstable, and consequently cannot be described by the weak-turbulence theory.

We have measured the dispersion of the sidebands of a large-amplitude plasma wave. The large wave causes a beamlike perturbation in the electron velocity distribution, which significantly affects the sideband dispersion. We measure a beam-plasma dispersion which is correctly predicted by a linear dispersion theory which includes only the time average of the perturbation in the distribution.

Fast-ion generation in a laser target plasma is investigated including the effect of a strong magnetic field. Laser-heated electrons generate both an electric field parallel to the laser beam and a magnetic field in an azimuthal direction. In this field configuration, ions are accelerated by the electric field along the magnetic null line, and the sign of the azimuthal magnetic field dictates whether ions converge or diverge.

We have found that the mobility of negative ions increases rapidly below $T_c$ in both superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ phases. The ratio $\frac{\mu }{{\mu }_N}$ of superfluid to normal mobility is larger in the $B$ phase than in the $A$ phase. A critical velocity consistent in magnitude with the Landau limit for pair breaking has also been observed. In the normal fluid we find a temperature-independent mobility between 30 mK and $T_c$ for all pressures between 0 and 28 bars.

The ESR relaxation of a weakly aligned spin probe dissolved in N-[$p$-methoxybenzylidine]-$p$-butylaniline has been studied near $T_c$, the isotropic-nematic transition. Spin relaxation due to critical orientational fluctuations is observed on either side of $T_c$ and is characterized by a symmetry about $T_c$ that is rather well explained by simple Landaude Gennes mean-field theory for the weak first-order transition.

Inelastic neutron scattering experiments on an ordered Invar alloy ${\mathrm{Fe}}_3$Pt show large softening of the [100]TA and [110]T${\mathrm{A}}_1$ acoustic shear modes below the Curie temperature. In addition, a central peak is observed below 100 K, which, however, behaves noncritically. The phonon softening is discussed in terms of the magnetoelastic coupling caused by the electron-phonon interaction.

The $I\left(V\right)\mathrm{}$ characteristic of a superconductor-insulator-superconductor tunneling junction in which both of the superconductors are driven out of equilibrium is investigated. We show that the steady-state quasiparticle distribution function is related to the $I\left(V\right)\mathrm{}$ characteristic by a linear integral equation. Modifications of the $I\left(V\right)\mathrm{}$ characteristic due to nonequilibrium distributions produced by phonon and microwave irradiations are discussed.