The plasma-broadened ${\mathrm{H}}_{\alpha }$ and ${\mathrm{H}}_{\beta }$ spectral-line profiles of hydrogen were calculated retaining the time ordering in the $S$ matrices of the width-shift operator by diagonalizing with the O(4) group. Significant changes occur: The ${\mathrm{H}}_{\alpha }$ peak is decreased 15%, the half-width is increased 25%, and the ${\mathrm{H}}_{\beta }$ relative dip is decreased 23% without significant alteration of the maximum intensity of half-width. Agreement with experiment is improved appreciably.

An extended universality hypothesis is proposed for critical phenomena in simple systems. The hypothesis implies the invariance of $V_X=\frac{n_X{q}_X{K_C}^X}{g_X{l}_X}$, where $q_X$ is the coordination number, ${K_C}^X$ is the dimensionless inverse critical temperature, and $n_X$, $g_X$, and $l_X$ are the universality scale factors. $V_X$ is an exact invariant for the two-dimensional $S=\frac{1}{2}$ Ising model and invariant to high precision for several three-dimensional models. For the spherical model, however, $\frac{V_X}{l_X}$ is an exact invariant.

The linearized hydrodynamics of spin motion in $A$-${}_{}{}^3{}_{}{}^{}\mathrm{He}$ is derived from the broken symmetries and thermodynamics alone. Spin and diffusion modes are obtained without and with spin-orbit coupling and an external magnetic field.

Simultaneous measurements of the thickness at two locations of a He II film adsorbed on a rotating substrate have been made. From the thickness difference we deduce that for $T>\mathrm{}2.1\mathrm{}$ K the film has a solid-body velocity field, whereas for $T=1.23\mathrm{}$ K the velocity is zero until the linear velocity of the substrate exceeds the translational critical velocity of the film.

It is experimentally shown that specular second-harmonic emission from a dense, inhomogeneous plasma produced by laser irradiation of plane solid targets occurs on oblique reflection of a $p$-polarized light wave, in agreement with theoretical predictions.

We have carried out an investigation of coherent nonlinear envelope solutions for a spectrum of interacting random-phase electron plasma waves. Making a distinction between plasmons which are trapped or untrapped in density fluctuations associated with the envelope waves, it is shown that one can construct envelope solutions of arbitrary shape.

A theoretical study of a monolayer of H chemisorbed on the (111) surface of Si is described. The length and force constant of the chemisorptive bond are determined and are consistent with molecular data. The calculated electronic spectrum of the surface is consistent with recent photoemission results.

Blue electroluminescence has been observed in GaN when the energy supplied to each electron is more than $48kT$ below the energy of the emitted photons. The emission increases with the cube of the current. An external power efficiency of 3 × ${10}^{-4\mathrm{}}$ was obtained. Several excitation mechanisms by two hot electrons are considered.

Hartree-Fock calculations using the exact-exchange operator are reported for molecular and metallic solid hydrogen. Both calculations used the same basis set and the same crystal formalism. The calculations indicate a transition to the metallic phase at a pressure of 2.1 Mbar, in agreement with recent experiments.

The internal friction and dynamic modulus of W single crystals were measured after neutron irradiation near liquid-helium temperature. The results on dislocation pinning and the associated relaxation peaks suggest that in W the $〈110〉$ split interstitials perform a free migration at ∼ 15 K (substage ${\mathrm{I}}_1$) and the ∼ 30-K stage (substage ${\mathrm{I}}_2$) is associated with detrapping of the $〈110〉$ split interstitials from impurity atoms.

Low-energy electron-loss spectroscopy on Ge and GaAs surfaces reveals opticlike selection-rule behavior for transitions involving $d$-core states and empty dangling-bond surface states. From the observed breakdown of these rules at low incident primary electron energies the symmetry of the dangling-bond states may be estimated. The Ga dangling bond is found to be largely $s$ like on all surfaces, whereas the Ge dangling bond exhibits $p$-like character on the (111)-(8×8) surface, and mixed $s-p$ character on the (100)-(2×2) surface.

The excitation functions for the reactions ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({\pi }^{\pm }, \pi N){}_{}{}^{11}{}_{}{}^{}\mathrm{C}$ have been measured by activation over the energy ranges 50 to 470 MeV for ${\pi }^{+}$ and 40 to 550 MeV for ${\pi }^{-}$. These excitation functions, clearly reflecting the (3,3) pion-nucleon resonance, show an upward energy shift in the resonance peak for ${\pi }^{-}$ and a downward shift for ${\pi }^{+}$. The $\frac{{\sigma }_{{\pi }^{-}}}{{\sigma }_{{\pi }^{+}}}$ ratio at 180 MeV is 1.55 ± 0.10.

Charge-exchange interactions of the nucleons within the nucleus are shown to account for the observed differences in the ratios of neutron-knockout cross sections for ${\pi }^{\pm }$ from the impulse-approximation predictions. Also, the energy dependence of the knockout cross sections is obtained from the measured total pion reaction cross sections with a simple model for the threshold behavior.

The (${}_{}{}^3{}_{}{}^{}\mathrm{He}$, $\mathrm{df}$) and (${}_{}{}^3{}_{}{}^{}\mathrm{He}$, $\mathrm{tf}$) reactions were used to measure fission probabilities from threshold up to ∼ 12 MeV of excitation energy for a series of actinide nuclei. The data were fitted over the whole range of nuclei and excitation energies with a microscopic model which does not contain an arbitrary normalization for $\frac{{\Gamma }_n}{{\Gamma }_f}$. The fits indicate that for most actinide nuclei fission proceeds through a first saddle point that is not axially symmetric.

From a study of experimental phase shifts for $p$ + ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ elastic scattering at proton energies below 50 MeV we conclude that small $D$-state admixtures to the dominant $S$-state configuration exist in the ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ ground state. This result is obtained by evaluating a forward dispersion relation for the $p$ + ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ spin-flip scattering amplitude.

For ${\epsilon }^2<4\mathrm{}\pi$ the $\lambda sin(\epsilon \Phi +\theta )$ quantum field model corresponding to the "sine-Gordon" equation with a nonvanishing mass term in two space-time dimensions exists and yields a field theory satisfying the Wightman axioms. For $\left|\lambda \right|$ small enough, the Euclidean Green's functions of this model have a convergent Feynman perturbation series. For $\lambda$ large enough and positive, $\epsilon$ positive, and $\theta =0\mathrm{}$, the $\Phi \to -\Phi$ symmetry is presumably dynamically broken.

The space-time evolution of particle production at high energies was investigated by measuring the charged multiplicity in ${\pi }^{-}$-nucleus collisions at 100 and 175 GeV/c. We find that (a) the forward multiplicity (in the $\pi p$ center-of-mass system) is independent of the target nucleus; (b) the backward multiplicity is approximately proportional to the nuclear thickness; and (c) the data are consistent with the assumption that the absorption cross section of the incident particle characterizes the multiplication process.

At the six lowest-lying levels, the quark model predicts a sequence $L=0, 1, 2, \dots$ of meson states with specific $J^{\mathrm{PC}}$ coupling to two and three pions. The symmetric-group model gives exactly the coincident prediction for the $J^{\mathrm{PC}}$ sequence. The Neveu-Schwarz model is missing two states at these levels; the new states, predicted by both dual and quark models, are the $J^{\mathrm{PC}}=0^{++}$, ${}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$ isoscalar daughter of $f\left(1250\right)\mathrm{}$, and the $J^{\mathrm{PC}}=1^{+-}$, ${}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}$ isoscalar partner of $B\left(1235\right)\mathrm{}$.

The equations characterizing the orthogonal gauge do not restrict the spatial degrees of freedom. This observation leads to Poincaré invariance in $s+1\mathrm{}$ dimensional space for any $s$. The absence of a tachyonic ground state and of ghosts is derived from algebraic consistency.

We report studies of 20-MHz sound propagation in the $A$ and $B$ phases above the polycritical point, and in the $B$ phase below the polycritical point. Some striking features are observed which were not seen heretofore.