Optical turbulence and periodic oscillations are easily seen with a hybrid optically bistable device with a delay in the feedback. The behavior of these instabilities is in good agreement with the recent work of Ikeda, Daido, and Akimoto, who predicted them for both ring-cavity and delay-line hybrid devices.

Nonlinear two-dimensional interchange modes, excited in a nonuniform magnetized plasma, are found as analytical stationary solutions of the ion vortex equation. The effects of deviation from charge neutrality and nonuniform gravity have been included in these solutions. For an exponential type of density and enstrophy functions it is possible to reduce the equation governing the electric potential to the Liouville equation ($\Delta \Phi =\exp \lambda \Phi$).

The high-frequency conductivity tensor of a plasma in a magnetic field has been evaluated. An anomalous perpendicular conductivity is obtained for a strongly magnetized plasma. Contrary to the previous prediction, the effective shielding length is found to be the Debye length even when the Debye length is larger than the electron gyroradius. The effective shielding length is further discussed by presenting the generalized Balescu-Lenard equation.

A recently observed second collective-mode peak in the sound absorption in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$B$ is shown to arise from weak excitation of a known order-parameter mode with weak-coupling frequency $\omega =\left(\sqrt{\frac{8}{5}}\right)\Delta \mathrm{}\left(T\right)\mathrm{}$ due to particle-hole-symmetry-violating terms. The somewhat lower value of the observed frequency might be caused by strong-coupling effects or admixture of $l=3\mathrm{}$ pair fluctuations.

An exact mapping is constructed of the site-diagonally disordered electron system onto a renormalizable field theory of interacting matrices. The matrix model that emerges is the same as for off-diagonal disorder, and it is therefore concluded that for diagonal disorder also there is a kind of local gauge invariance near the mobility edge.

Nonlinear renormalization-group recursion relations are used to show that the thermal conductivity of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ has a crossover between a weak-coupling regime for $t_c\ll t<\mathrm{}1\mathrm{}$ and a scaling regime for $t\ll t_c$, where $t=\frac{(T-T_{\lambda })}{T_{\lambda }}$ and $t_c\approx {10}^{-3\mathrm{}}$. The smallness of $t_c$—an essential feature—is explained by a small bare dynamic coupling constant. The asymmetric spin model ($F$) provides a quantitative fit to experiment, whereas the symmetric model ($E$) is only semiquantitative. The border-line dimension $d^{*}$, below which dynamic scaling breaks down, is shown to satisfy $d^{*}\lesssim 2.54$.

Sound propagation and damping are studied near the spin-glass transition for a time-dependent Landau-Ginzburg model coupled to phonons. The sound speed decreases linearly with $T-T_g$, and the sound damping diverges as ${(T-T_g)}^{-1\mathrm{}}$, when the spin-glass transition, $T_g$, is approached from high temperatures. At the spin-glass transition, the sound speed has a term proportional to ${\omega }^{\frac{1}{2}}$, and the sound damping is proportional to ${\omega }^{-\frac{1}{2}}$.

Apart from Fuchs-Kliewer surface phonons, conduction-band surface plasmons and probably intraband single-particle scattering contribute to the electron-energy-loss spectra (primary energy ∼5 eV, resolution <10 meV) measured on clean, UHV-cleaved, $n$-type GaAs(110) surfaces. Coupling between surface phonons and plasmons derives from frequency shifts which depend on surface carrier concentration.

The first measurements of Fermi-surface properties in a mixed-valence metal with use of the de Haas-van Alphen effect are presented. At least nine separate frequency branches in Ce${\mathrm{Sn}}_3$ are seen and effective masses as large as 9.2 have been measured. The experiments show that hybridization between the conduction states and local $f$ states occurs coherently in the mixed-valence compound Ce${\mathrm{Sn}}_3$, resulting in Bloch states with well-defined wave vector and energy.

Neutron-inelastic-scattering techniques have been used to study the spin dynamics of EuO. High-quality single crystals were used so that temperature-dependent line shapes could be obtained at all momentum values. It was found that the magnetic excitations above $T_c$ changed from Lorentzian-like peaks centered at zero energy near the zone center to rather well-defined spin-wave-like excitations at the zone boundary.

A simple model for the depinning and dynamics of a sliding charge-density wave is presented. The model consists of viscously damped motion in a periodic potential and accounts for the main features of the nonlinear conductivity, noise, and ac-dc coupling in the charge-density-wave state of Nb${\mathrm{Se}}_3$ at low temperature. Comparison with experimental data suggests that the depinning process is associated with the displacement of the charge-density wave by approximately one period $\lambda$.

The notion of self-duality is extended to self-triality. One example from spin systems is given and completely solved by use of fermion variables. It is then shown that the O(8) Gross-Neveu model has self-triality: The Lagrangian $\mathcal{L}\left(\psi \right)=\mathcal{L}\mathrm{}\left(R\right)=\mathcal{L}\mathrm{}\left(L\right)\mathrm{}$, where $\psi$ is the original fermion while $R$ and $L$ are two types of kinks that occur dynamically. The anatomy of self-duality (triality) in the Ising and present examples is exposed as is the origin of the fermionic solutions.

A careful consideration of the propagation of null geodesics in a black-hole geometry modified by Hawking-radiation back reaction shows that the event horizon is stable and shifted only very slightly in radius from what is expected in a vacuum background, contrary to a recent claim in the literature.

At some special temperature $T_0$, the distribution functions of a two-dimensional one-component plasma are explicitly computed up to the four-body one. The correlations have a Gaussian falloff. The distribution functions at $T_0$ are used for building a temperature expansion around $T_0$.

Consider a system rendered unstable by both quantum tunneling and thermodynamic fluctuation. The tunneling rate $\Gamma$, at temperature ${\beta }^{-1\mathrm{}}$, is related to the free energy $F$ by $\Gamma =\left(\frac{2}{\hslash }\right)\mathrm{Im}F$. However, the classical escape rate is $\Gamma =\left(\frac{\omega \beta }{\pi }\right)\mathrm{Im}F$, $-{\omega }^2$ being the negative eigenvalue at the saddle point. A general theory of metastability is constructed in which these formulas are true for temperatures, respectively, below and above $\frac{\omega \hslash }{2\pi }$ with a narrow transition region of $O\left({\hslash }^{\frac{3}{2}}\right)$.

A finite-action self-dual solution of SU(2) gauge theory with topological charge $\frac{3}{2}$ is given.

A search for narrow $\overline{p}p$ states (width ≲ 20 MeV/${\mathit{c}}^2$) has been conducted in the Brookhaven National Laboratory multiparticle spectrometer. No significant structure has been observed in events where the $\overline{p}p$ system has been produced forward in the laboratory. Upper limit cross sections (95% confidence level) for $\overline{p}p$ masses below 2.2 ${\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c}}^2$ are ≤0.12 μb and ≤0.22 μb for the final states $\overline{p}p{\pi }^0$ and $\overline{p}p{\rho }^0$, respectively.

Forward particle production in $\mathrm{pp}$ interactions triggered by a 30° pion of momentum exceeding 5 GeV/c has been studied at c.m. energy of 63 GeV. Quantum-chromodynamic model calculations show that in a majority of such interactions the incident proton loses a valence quark. Results indicate that hadronization of diquarks is primarily a recombination process leading to the formation of a high-$x$ baryon.

Electroexcitation of the singlet $S$ state of the deuteron has been measured for the range of momentum transfer $q^2=6-19\mathrm{}$ ${\mathrm{fm}}^{-2\mathrm{}}$, where meson-exchange current contributions dominate the cross section.

The multiplicity ${\overline{M}}_S$ of the statistical $\gamma$ rays following several (${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$,$\mathrm{xn}$) reactions has been measured. A correlation between the total $\gamma$ multiplicity ${\overline{M}}_T$ and ${\overline{M}}_S$ was found. This effect is attributed to an increase in the mean excitation energy above the yrast line with increasing angular momentum input.