With resonance $R_2$ laser light pumping, the observation of stimulated emission of the 29-${\mathrm{cm}}^{-1\mathrm{}}$ phonon in ruby is reported. The transverse phonons propagate along the $C_3$ axis and have some nonlinear gain.

Extensive experimental evidence indicates that the Schottky-barrier formation on III-V semiconductors is due to defects formed near the interface by deposition of the metal (or of oxygen). Detailed level positions are established and assigned to either missing column III or V atoms. This model also applies to formation of states at III-V oxide interface states.

An explanation is given for the unusual enhancement in the Rutherford backscattering yield at 180° found by Pronko and co-workers. It involves a nonstochastic dependence between inward and outward trajectories of backscattering projectiles. Results are presented of Monte Carlo simulations in random solids which show excellent agreement with experiment without need of considering electronic disturbances induced by the projectiles.

Measurements of electrical resistivity as a function of temperature reveal that deviations from Matthiessen's rule (DMR) in aluminum can, under suitable conditions, be made to vanish in a strong magnetic field. Theories explaining DMR on the basis of anisotropic and inelastic scattering predict such behavior suggesting that such scattering is the source of DMR in dilute aluminum alloys at low temperatures.

The success of Miedema's empirical theory of transition-metal compound formation has given credence to the physical picture used in its construction. Self-consistently calculated electron densities, state densities, and heats of formation reveal this picture to be inappropriate. Miedema's success is shown to result from the implicit incorporation of a dominant chemical trend, which is well described by Pettifor's $d$-bond model.

If black-hole formation and evaporation can be described by a superscattering operator which is $\mathrm{CPT}$ invariant, then it can be described by an $S$ matrix which maps pure initial states into pure final states. Thus black holes may be in principle no more unpredictable than other quantum phenomena.

The unique ability of heavy-quark leptoproduction to probe constituent gluons is exploited. From recent ${\gamma }^{*}N\to \psi N$ data, the gluon distribution ${\eta }^{-1\mathrm{}}{(1-\eta )}^p$, $p={5.6}_{-1.2\mathrm{}}^{+0.8\mathrm{}}$, is extracted and $\frac{{\alpha }_s}{\pi }$ is inferred. It is shown that measurement of $\frac{{\sigma }_L}{{\sigma }_T}$ as a function of $Q^2$ for charm production can determine the gluon spin and parity.

Systematic properties of dissipation and exchange mechanisms associated with damped nuclear reactions are obtained from available data, yielding results that cannot be consistently described in a classical approach. However, correlations between energy loss and the variances of the fragment $A$ and $Z$ distributions are understood on the basis of an exchanged-induced dissipation mechanism, if account is taken of the Pauli exclusion principle.

The explicit incorporation of the Breit interaction in relativistic many-body perturbation theory provides an explanation of the recent experimental value of 1.27±0.10 Hz for the nuclear quadrupole interaction constant in the spherical ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ atom. The theoretical value including the Breit and other mechanisms is 1.7 Hz.

The molecular-beam laser-rf double-resonance technique has been used to make high-precision measurements of the spin-rotation and hyperfine interactions in the $v^{\prime \prime }=0\mathrm{}$ vibrational level of the ${{}_{}{}^2{}_{}{}^{}\Sigma _{\frac{1}{2}}^{}{}_{}{}^{}}^{+}$ ground state of CaF. Both interactions exhibit a strong dependence on $N$, the rotational quantum number. The details of this $N$ dependence, neither observed nor explicitly predicted previously, are in accord with theory.

A method is presented for obtaining explicit bounds for the total cross section (including scattering into several final charged fragments) for the scattering of two bound clusters of nuclei and electrons so long as either both clusters are neutral or one is neutral and without an electric dipole moment.

In the presence of a random spectrum of lower hybrid waves, the $m=1\mathrm{}$ resistive tearing instability becomes an oscillating instability with a significantly enhanced growth rate. For typical tokamak parameters, the growth time can become comparable to plasma disruption times for rather moderate levels of fluctuations.

Polished aluminum targets were irradiated with 1.06-μm laser pulses of 60-psec and 2.5-nsec duration and of $\pi$ and $\sigma$ polarization. The peak focused intensity was varied over the range ${10}^{14}$-${10}^{16}$W/${\mathrm{cm}}^2$. Clear evidence of resonant absorption for 60-psec pulses was obtained from target momentum measurements made with a torsion pendulum. No resonant absorption effects dependent on light polarization or angle of incidence were detected for long-pulse irradiations.

The assumption is explored that the equilibrium order parameter of a superfluid rotates with a rotating container. Since rotations and changes of phase are then intimately related in inhomogeneous configurations, effects like the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$A$ "gauge wheel" of Liu and Cross should arise in any superfluid. Such effects may be difficult to observe, but it is shown that their existence in superfluid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ is directly implied by nothing more than the conventional equations of two-fluid hydrodynamics.

Third-sound velocity and onset measurements have been made for ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ adsorbed on Grafoil foam. The third-sound velocity has a dependence on film thickness and temperature similar to that of third sound on glass substrates, with some distinguishing features. The film vapor pressure at onset has, to some degree, the universal temperature dependence found for other substrates. The superfluid areal density divided by the onset temperature agrees with the universal constant predicted by the Kosterlitz-Thouless-Nelson theory to within 11%.

Muon spin-rotation studies on the purest available samples of Al and Cu and on $\mathrm{Al}{\mathrm{Mn}}_x$ ($x=1300, 57, \mathrm{and} 42$ ppm) down to temperatures around 50 mK show that the muons are delocalized in pure Al but increasingly localized with increasing Mn content. The temperature variations are discussed in terms of strain localization and trapping in the vicinity of the impurities. For Cu, partial delocalization is observed below 2 K, which is probably limited by elastic strains from remaining impurities.

We report the first observation of magnetophonon resonances in the two-dimensional electronic system in single interface GaAs-${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ heterojunctions and heterojunction superlattices. They result from inelastic scattering between Landau levels with resonant absorption of LO phonons of GaAs and yield a polaron mass ${m_p}^{*}=(0.077\mathrm{}\pm 0.004)m_e$.

Photoemission indicates that the surface resonances on Mo(100) are not removed entirely by the adsorption of ${\mathrm{H}}_2$. It also shows two H-induced states below the bulk $d$-band edge with the binding energies independent of coverage and in good agreement with a calculation. The results indicate that H on Mo(100) is bridge bonded with the local bonding configuration relatively unchanged by reconstruction. A significant correlation between the surface resonances and the surface reconstruction is suggested.

Anomalously large ${}_{}{}^{195}{}_{}{}^{}\mathrm{Pt}$ NMR linewidths have been observed in platinum particles with diameters ranging from 33 Å to 200 Å. Spin-echo measurements revealed the presence of nuclear spin-exchange diffusion in large magnetic field gradients attributable to the large indirect exchange interaction in platinum. These data indicate that there are electron spin-density oscillations near the platinum surface consistent with a simple model ascribing free-electron behavior to the $s$-like conduction electrons.

The magnetic susceptibility of a Ag-3-at.%-Mn spin-glass has been measured under hydrostatic pressure to 15 kbar. The spin-glass freezing temperature $T_0$ increases with pressure at the rate $\frac{d{T}_0}{\mathrm{dP}}\simeq +42\mathrm{}\pm 4$ mK/kbar. This pressure dependence is clear evidence that the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, and not the magnetic dipole interaction, is responsible for spin-glass freezing at $T_0$. The present results thus support those models of spin-glass freezing which are based solely on RKKY interactions between spins.