The dynamical form factor $S(Q,\omega )$ of liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$, including both the coherent and the incoherent contributions, is calculated within the random-phase approximation. At low temperature a sharp zero-sound mode is obtained. At higher temperature this mode becomes a broad resonance in the particle-hole spectrum. This temperature effect may help account for the difference in $S(Q,\omega )$ observed in two recent neutron-scattering experiments.

Elastic diffraction of neutrons from helium adsorbed on Grafoil shows that the surface monolayer forms as a highly compressed, ordered triangular lattice incommensurate with the structure of the underlying graphite basal planes. Inelastic scattering from thin superfluid films on top of the surface monolayers reveals the existence of bulklike rotons in films containing on average as few as three layers of atoms.

The observation of an ac photoconductivity ${\sigma }_{\mathrm{Ph}}\sim {\omega }^n$ is reported in the organic charge-transfer complex trinitrofluorenone:polyvinylcarbazole (TNF:PVK). The exponent $n$ is found to increase with decreasing temperature from 0.25 at 300 K to 0.8 at 100 K and saturates at lower temperatures. This result is viewed as a strong indication for a hopping conduction mechanism for photocarriers. The temperature dependence of the exponent $n$ suggests an increasing degree of localization of electron hopping with decreasing temperature.

We report the observation of enhancement in the Raman cross section for photon energies near electronic resonance in $\mathrm{GaAs}{\mathrm{Ga}}_{1-x}{\mathrm{Al}}_x\mathrm{As}$ superlattices of a variety of configurations. Both the energy positions and the general shape of the resonant curves agree with those derived theoretically based on the two-dimensionality of the quantum states in such superlattices. Polarization studies indicate a major contribution to the scattering from forbidden processes.

The temperature dependence of the $g$ values measured for the series of alloys ${\mathrm{}\left(\mathrm{TSeF}\right)\mathrm{}}_x{\mathrm{}\left(\mathrm{TTF}\right)\mathrm{}}_{1-x}\mathrm{}\left(\mathrm{TCNQ}\right)\mathrm{}$ (where TSeF is tetraselenafulvalene, TTF is tetrathiafulvalene, and TCNQ is tetracyanoquinodimethane), $0<~x<~0.68$, in the temperature range $60\mathrm{K}<T<\mathrm{}300\mathrm{}\mathrm{K}$ is presented. It is shown that the experimentally observed temperature dependence does not agree with the expected behavior based on significant effects of Peierls fluctuations on the magnetic susceptibility.

A new emission line, observed in strongly excited AgBr near the free-excition edge, is attributed to the recombination of excitonic molecules. From the analysis of the emission line shape the following parameters of the excitonic molecule are deduced: binding energy $E_B=6.7\mathrm{}$ meV; radius $a_M\simeq 20$ ÅA.

The Lax equation of nonlinear wave theory is described in a purely Lie-algebraic context. A realization—independent of linear operator theory—which leads to the Kortewegde Vries equation is described in terms of the Poisson-Moyal Lie algebra of quantum mechanics. This approach leads to a generalization of the Euler rigid-body equations.

We report on direct production of positron-electron pairs by 360-GeV/c pions incident on the Fermilab 30-in. hydrogen bubble chamber. These high-energy data are the first with liquid hydrogen, and are shown to be in agreement with quantum-electrodynamic calculations. For the region of four-momentum transfer considered, quantum electrodynamics predicts essentially equal contributions from production in the Coulomb field of the nucleus and the atomic electron.

We present the inclusive photon spectra observed in $\psi \mathrm{}\left(3095\right)\mathrm{}$ and $\psi \mathrm{}\left(3684\right)\mathrm{}$ decays. The decay $\psi \mathrm{}\left(3684\right)\mathrm{}\to \gamma \chi \mathrm{}\left(3415\right)\mathrm{}$ is observed with a branching fraction of 0.075 ± 0.026. Evidence is presented for three intermediate states in the decay sequence $\psi \mathrm{}\left(3684\right)\mathrm{}\to \gamma \gamma \psi \mathrm{}\left(3095\right)\mathrm{}$ with masses of 3504, 3543, and 3455 or 3340 MeV.

Jacob, Maris, Schneider, and Teodoro have suggested that spin-orbit coupling in nuclei, combined with absorption in ($p,2p$) reactions, will select nuclear protons with a given polarization resulting in $j$-dependent ($\overrightarrow{\mathrm{p}},2p$) cross sections. Using a 200-MeV polarized proton beam at TRIUMF we have observed an asymmetry which has the expected $j$ dependence and agrees with the predictions of a distorted-wave impulse-approximation calculation.

An exact four-body model of heavy-ion two-nucleon transfer reactions is described that includes all orders of interaction between the exchanged nucleons. The relative importance of the $Q$ value of the reaction and of the nature of the nucleon-nucleon interaction in governing the magnitude of the transfer cross section is studied.

In an effort to help determine the distribution of magnetic dipole radiation strength in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$, we have measured the distributions of de-excitation $\gamma$ rays following excitation by deuteron and proton inelastic scattering. A level at 7.061 MeV with a radiative strength of ≅ 23 eV is a good candidate for $J^{\pi }=1^{+}$; several other levels with large radiative widths are assigned $J^{\pi }=1^{-}$.

We observe that the Raman excitation profile in matrix-isolated ${\mathrm{Br}}_2$ is significantly red-shifted from the absorption maximum and show that a straightforward relationship between the two can in general not be expected. A simple theory considering only the resonant contributions describes our data reasonably well. In addition, we discuss the effect on our results of interference between the $B$ and ${}_{}{}^1{}_{}{}^{}\Pi _{1\mathrm{u}}^{}{}_{}{}^{}$ states.

The effect of collective interactions between an intense ion beam and a background plasma is found to increase the plasma return current above that necessary for current neutralization, which eventually contributes to defocusing of the beam.

Tokamak and Ohmically heated stellarator plasmas have been compared in the CLEO apparatus, using gas current in the range 10-25 kA at a toroidal field of 12.7 kG. It is found that the vacuum poloidal field due to the helical winding has a considerable influence on the containment properties. In particular, for the same current the electron energy per unit length is a factor of 2 greater in the stellarator than in the tokamak.

Two beams of waves of finite diameters intersecting within a magnetized plasma emit a secondary beam of waves, provided a resonance condition is satisfied. The field of the secondary beam and the total power emitted are determined for arbitary directions and polarizations of the incident beams. This process could be used as a means of time- and space-resolved diagnostics since it yields two relations between the density, the temperatures, and the magnetic field. Explicit formulas are given for the case of two beams in the ordinary mode producing a lower hybrid wave.

An impurity-stabilized Si{111} 1×1 structure has been obtained by depositing minute amounts of Te on a clean Si{111} 7×7 surface. A low-energy electron diffraction structure analysis of this 1×1 structure reveals that the atomic arrangement is essentially bulklike, but involves a slight contraction of the first interlayer spacing by about 15% with respect to the bulk value.

We treat the Kapitza thermal boundary resistance $R_K$ between a Debye solid and liquid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ in the temperature range 0.1 to 1 K, where the phonon transmission coefficient is known to be highly anomalous. Using a continuum model, we consider the consequences of a solid van der Waals layer of helium which is acoustically absorbing. Using values of acoustic wave attenuation in the layer based on experiment, we are able to predict the correct order of magnitude and temperature dependence of $R_K$ for copper.

Spin-aligned hydrogen (H ↑) and deuterium (D ↑) are generally predicted to be stable for $\frac{\mathcal{H}}{T}\gtrsim {10}^6$ G/K. Magnetic-field-dependent resonances (inverse to field-induced predissociations of high vibrational-rotational levels of HD and ${\mathrm{D}}_2$) provide exceptions to this general rule. Their existence suggests 50 kG (H ↑ + D ↑) and 19 kG (D ↑ + D ↑) should be avoided for stable H ↑ and D ↑. Induced predissociation observations should yield ultraprecise resonance information and dissociation limits.

The chemisorption-site geometries for chlorine on cleaved Si(111) 2×1 and Ge(111) 2×1 surfaces have been determined by comparing detailed pseudopotential calculations with energy distribution spectra and polarization selection rules of photoemission spectroscopy. Strong $p$-symmetry polarization effects observed in photoemission allow us to determine that on Si(111) the correct geometry is a onefold covalent site while on Ge(111) the Cl is in a threefold coordinated ionic site.