A calculation of the electronic energy and optimum atomic spacing for an equally spaced linear array of hydrogen atoms is combined with other information to yield an improved analysis of the existence and stability of metallic hydrogen. A filamentary structure postulated by others is predicted not to be stable or metastable at any pressure; previous predictions of a transition under pressure to a metallic cubic (or hcp) phase are reaffirmed. The energies and interatom spacings in ${\mathrm{H}}_2$, linear chains, and cubic crystals are in good accord with chemical expectations.

Longitudinal magnetic relaxation in superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ as described by the theory of Leggett and Takagi is observed for particular geometries within a very limited range of $H_0$ and $1-\frac{T}{T_c}$. Other observations demonstrate that, under certain conditions, the longitudinal magnetization in superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$A$ does not relax monotonically in time.

We present direct measurements of the layer rigidity in a smectic-$A$ liquid crystal, 4′-$n$-octyloxy-4-cyanobiphenyl. For low normal to the layers, the instantaneous induced stress is elastic and gives $B=0.8\mathrm{}\times {10}^7$ cgs units at 60°C. In response to a steplike strain, the stress relaxes almost completely, with a time constant ∼50 ms. The relaxation stops for a residual strain smaller than ½ layer over the total thickness of the smectic sample.

We have compared the electron velocity distributions observed at 180° when helium ions of 0.8-2 MeV are incident on both helium gas and carbon foils. These distributions are characteristic of electron loss from the atomic $1s$ state of the ion and not from a wake-bound state even for the case when a ${}_{}{}^3{}_{}{}^{}\mathrm{He}_{}^{++}{}_{}{}^{}$ ion first captures an electron from the solid and subsequently ejects it when inside the solid.

The use of a double tunnel junction to investigate the nonequilibrium quasiparticle distribution due to tunnel injection has been studied. I give quantitative explanations of the sharp structures and the asymmetric effects observed by Kaplan, Kirtley, and Langenberg in the second derivative of the $I\left(V\right)\mathrm{}$ characteristics of the driven detector junction. It is suggested that the energy- and temperature-dependent inelastic quasiparticle relaxation time, as well as the elastic-scattering branch-mixing time, can be extracted from these sharp structures and the asymmetric effects.

The electron-hole gas, in equilibrium with the electron-hole liquid, has been directly observed in Ge by observation of a luminescence feature. Parameters of the coexistence curve between the two phases are determined to be $T_c=7.0\mathrm{}\pm 0.1$ K and $n_c=(8.9\mathrm{}\pm 0.5)\times {10}^{16}$ Information concerning the transition between the electron-hole-gas phase and bound excitons is also obtained.

We demonstrate that dimerized organic linear-chain conductors afford an unambiguous experimental determination of symmetry-allowed electron-molecular-vibration coupling constant.

By a careful analysis of the pyroelectric effect in LiTa${\mathrm{O}}_3$ between 10 and 200°K, we have demonstrated for the first time the dominance of the lowest-order (polar-mode) contributions to the primary pyroelectric effect over a wide temperature range in a strongly pyroelectric material. In doing so we confirm, as an excellent approximation for the effect, a simple analytic form the theoretical origins of which go back to a paper by Boguslawski in 1914.

We discuss a phenomenological theory of the onset of an inhomogeneous state in a nonequilibrium superconducting film. The length scale of the initial instability is given by the geometric mean of the coherence length and an effective quasiparticle diffusion length.

The hydrodynamic relaxation rate for water inhomogeneities in aligned lipid-water smectics is measured for the first time using an improved version of the "forced Rayleigh" technique. Variation of the relaxation rate with water concentration yields a distinction between "bound" and "free" water.

We propose a simple alternative to the sphericity as a measure of jet structure in $e^{+}{e}^{-}$ annihilation. Our variable has the property that it can be reliably calculated in perturbation theory in quantum chromodynamics (QCD) for large $Q^2$. It is not sensitive to the details of quark and gluon decay into color-singlet hadrons. We discuss the nonperturbative effects which are important at moderate $Q^2$.

The properties of the dimuon enhancement seen in 400-GeV proton-nucleus collisions have been clarified by a threefold increase in data. We find two peaks whose widths are consistent with our resolution: $M_1=9.4\mathrm{}$ GeV with $B{\frac{d\sigma }{\mathrm{dy}}|}_{y=0\mathrm{}}=1.8\mathrm{}\times {10}^{-37\mathrm{}}$ ${\mathrm{cm}}^2$/nucleon and $M_2=10.0\mathrm{}$ GeV with $B{\frac{d\sigma }{\mathrm{dy}}|}_{y=0\mathrm{}}=0.7\mathrm{}\times {10}^{-37\mathrm{}}$ ${\mathrm{cm}}^2$/nucleon. Evidence for the possible existence of a third peak near 10.4 GeV is discussed as are the comparisons with the properties of a $q\overline{q}$ system, where $q$ is a new heavy quark.

Differential cross sections and density-matrix elements in ${\rho }^{-}$ decay have been measured at 6 GeV/c for $\overline{p}p\to {\pi }^{+}{\rho }^{-}$ and its line-reversed partner ${\pi }^{-}p\to p{\rho }^{-}$ in the range $t_{min}>t>-1.5\mathrm{}$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$. The reactions satisfy line-reversal symmetry and the ${\rho }^{-}$ decay is consistent with isotropy for $-t\lesssim 0.5$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$. For $-t\gtrsim 0.5$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$, the differential cross sections show a weaker $t$ dependence, and the decays become anisotropic.

Mass and total-kinetic-energy (TKE) distributions of fission fragments from the spontaneous fission of ${}_{}{}^{262}{}_{}{}^{}\mathrm{}\left[105\right]\mathrm{}$ and ${}_{}{}^{256}{}_{}{}^{}\mathrm{Fm}$ have been obtained. No events with anomalously high TKE were observed, contrary to theoretical expectations. The mass distribution from the fission of ${}_{}{}^{262}{}_{}{}^{}\mathrm{}\left[105\right]\mathrm{}$ is very probably asymmetric and similar to distributions obtained from all spontaneously fissioning systems with the exception of ${}_{}{}^{257}{}_{}{}^{}\mathrm{Fm}$ and ${}_{}{}^{259}{}_{}{}^{}\mathrm{Fm}$.

Angular and energy distributions of $\alpha$ particles and neutrons resulting from the decay of a hot spot are calculated using a diffusion model for the internal decay of the hot spot and a final-state interaction of the emitted particles with the residual nuclei. The particle spectra are highly disturbed. Consequences for the interpretation of light-particle emission accompanying deep-inelastic collisions in terms of the hot-spot model are pointed out.

We have measured the cross section for neutron-deuteron elastic scattering over the incident energy range 200-800 MeV. Preliminary results for the extreme back angles (${{\theta }_n}^{*}>~175°$) show a striking shoulder in the excitation function for neutron energies 300-600 MeV. Comparison is made with calculations using the Craigie-Wilkin triangle-diagram technique.

Absolute cross sections have been measured for excitation of the $2s{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}-2p{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2},\frac{3}{2}}^{}{}_{}{}^{}$ resonance doublet in Li-like ${\mathrm{C}}^{3+}$ by electron impact for energies ranging from below threshold (8.0 eV) to 530 eV. The measurements agree with recent unpublished Coulomb-Born and close-coupling calculations over the entire range of electron energies.

A novel pulsed-molecular-beam technique has been used to measure differential cross sections for state-resolved rotational transitions in HD + HD collisions. Inelastic transition probabilities are reported for the rotation-energy-level transitions $J_A{J}_B=00\mathrm{}\to {J_A}^{\prime }{J_B}^{\prime }=(10, 01), 11, \mathrm{and} (20, 02)$ at a center-of-mass scattering angle at 90° and at several collision energies. A brief description of the apparatus is provided.

Greatly enhanced stopping powers result from the interaction of sufficiently dense charged particle beams with matter. Stopping power is proportional to a well-defined number of beam particles that interact coherently. The effect is not due to turbulence, but relies on a phase mixing of the polarization wakes produced by the beam particles. The beam-density effect can drive a self-dissipative instability.

Peak plasma densities in excess of ${10}^{15}$ ${\mathrm{cm}}^{-3\mathrm{}}$ have been obtained in the Alcator tokamak with $60<~B_T<85\mathrm{}$ kG. The highest average density so far achieved is ${\overline{n}}_e=6\mathrm{}\times {10}^{14}$ ${\mathrm{cm}}^{-3\mathrm{}}$; the corresponding $n_0{\tau }_E=2\mathrm{}\times {10}^{13}$ ${\mathrm{cm}}^{-3\mathrm{}}$ s. These ultrahigh-density discharges exhibit (i) nearly complete energy equilibration between electrons and ions, (ii) severe attenuation of energetic-neutral-particle fluxes, (iii) a minor role of impurities, and (iv) energy-confinement properties consistent with neoclassical estimates.