The finite-temperature commensurability problem is formulated and reduced to the solution of a transfer-integral problem. Numerical solutions for the free energy, equation of state, one- and two-particle densities,..., provide a detailed description of the behavior of epitaxial systems at $T\ne 0$.

The gap exponent for the isotropic-nematic phase transition in MBBA (N-[$p$-methoxybenzylidine]-$p$-butylaniline) has been determined from measurements of the induced birefringence in very strong magnetic fields. The experimental value, $\Delta =1.26\mathrm{}\pm 0.10$, is consistent with the tricritical exponent, $\Delta =\frac{5}{4}$, but is clearly inconsistent with the exponent $\Delta =2\mathrm{}$ predicted by the mean-field theory. It is also shown that some of the observed effects are more than two orders of magnitude larger than the values predicted by the mean-field theory.

We propose a "competing barrier model" for nucleation of quantized vortices in small channels. The results are compared to experiments on decay of persistent currents, critical velocities, onset temperatures, and the effective superfluid density at onset.

Fully automatic computer simulation of random-network structures in amorphous Si and Ge has been achieved using a generalization of Keating's potential. The local potential for one-atom displacements shows many multiple minima with broad distributions of the energy difference and tunneling matrix element. These distributions lead to reasonable estimates for the specific heat, which behaves as $T\ln T$. One-atom tunneling states appear to be appropriate for amorphous Si/Ge.

The diffusion coefficient of a mobile C${\mathrm{H}}_4$ submonolayer adsorbed on graphite (0001) is systematically measured by quasielastic neutron scattering. Its behavior with coverage is used to distinguish clearly two kinds of adsorbed fluids; a two-dimensional liquid and a two-dimensional liquid an a two-dimensional hypercritical fluid.

Disorder such as defects or phonons causes interband scattering and renormalization effects. When these are included in a generalization of Boltzmann transport theory, an interband conduction channel opens up which might account for the "parallel-resistor" effect seen in "saturation" of dc resistance of metals.

Using SQUID (superconducting quantum interference device) detection, the field and temperature dependence of the magnetization $m$ has been measured close to the critical point of this uniaxial dipolar-coupled ferromagnet. It is shown for the first time that the Landau expansion of the field $h$ holds if $m$ is scaled by ${\left[\frac{\ln \left(\frac{\partial m}{\partial h}\right)}{{\chi }_0}\right]}^{\frac{1}{3}}$, while other equations (of Ising, mean field) yield less agreement and unrealistic parameters. The expansion coefficients of the present analysis can explain in detail formerly measured zero-field properties.

I present the first strong evidence for the observation of $D^{-}$ centers in a semiconductor with a simple conduction band minimum at $k=0\mathrm{}$. The identification is based primarily upon agreement between the predicted and observed curve of photodetachment threshold frequency vs magnetic field in CdS. New, relatively simple and physically motivated variation trail functions are employed which give eigenvalues of sufficient accuracy for critical comparison with experiment.

The edge of the gap in the distribution of the Yang-Lee zeros is concluded to be a singular point of square-root type in all hierarchical models, in distinction to expectations based on renormalization-group arguments for short-range models in dimensions $d<\mathrm{}6\mathrm{}$.

Dimuon production is studied in 217-GeV/c ${\pi }^{-}$-hydrogen and ${\pi }^{-}$-beryllium collisions with a lead-glass array to detect photons associated with the $\psi$. The $\psi -\gamma$ mass spectrum shows a 2.6-standard-deviation excess of events above background at ∼3.5 GeV. This excess, if attributed to the decay $\chi (\sim 3.5)\to \psi \gamma$, implies that 0.70±0.28 of the $\psi$'s are produced via radiative decay of one of the $\chi$ states.

The yrast line in ${}_{}{}^{22}{}_{}{}^{}\mathrm{Ne}$ has been investigated by the reaction ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}$+${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ up to the ${10}^{+}$ state which is found at 15.46-MeV excitation energy. A backbending in ${}_{}{}^{22}{}_{}{}^{}\mathrm{Ne}$ shows up around spin 8. The Strutinsky method is applied to interpret the ${}_{}{}^{22}{}_{}{}^{}\mathrm{Ne}$ rotational motion.

The ($t_{\mathrm{pol}}$, $d$) reaction at 16 MeV has been used to determine the total angular momentum of levels in ${}_{}{}^{59}{}_{}{}^{}\mathrm{Ni}$ and ${}_{}{}^{65}{}_{}{}^{}\mathrm{Ni}$. This represents the first reported results of this reaction using a polarized triton beam. The data indicate distinct differences and advantages over ($d_{\mathrm{pol}}$,$p$) data at similar bombarding energies. The ($t_{\mathrm{pol}}$,$d$) reaction is used on ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ to compare data with distorted-wave Bron-approximation predictions for known spin states and on ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$ to resolve an important controversy over spin values in ${}_{}{}^{65}{}_{}{}^{}\mathrm{Ni}$.

Solutions applicable for all interaction strengths are obtained for a schematic Hamiltonian with pairing forces and particle-hole octupole-octupole forces. The method is applied to the light U isotopes. Adjusting the particle-hole interaction strength to the measured $K^{\pi }=0^{-}$ excitation energies leads to an immediate explanation for the low-lying $0^{+}$ excited states in this region.

A strong, isolated pole gives rise to periodic structure in backward-angle excitation functions. A moderate pole interfering with a nonresonant diffraction amplitude produces similar structure. The ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ backward-angle elastic excitation function is analyzed from these points of view.

States of ${}_{}{}^{154}{}_{}{}^{}\mathrm{Er}$ were studied by means of the (${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$,$4n$) and (${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$,$4n$) reactions. Beginning with a 40-nsec isomeric state [$J^{\pi }=({10}^{-},{11}^{-})$], an intensely populated unusual cascade of $\Delta J=2\mathrm{}$ and $\Delta J=1\mathrm{}$ transitions was established up to spin (35,36) and 12.5 MeV excitation. On an $E$ vs $I(I+1\mathrm{})\mathrm{}$ plot the yrast levels form a series of straight-line segments with side feeding occurring primarily at the ends of segments. A second cascade of even-spin, even-parity levels from the ground state to $J^{\pi }={18}^{+}$ (quasi-ground-state band) does not exhibit these properties.

We have identified two new infrared absorption bands in potassium vapor. The band between 1.1 and 1.6 μm is attributed to the ${\mathrm{K}}_2$ (${{}_{}{}^3{}_{}{}^{}\Sigma _{\mathrm{u}}^{}{}_{}{}^{}}^{+}\to {{}_{}{}^3{}_{}{}^{}\Sigma _{\mathrm{g}}^{}{}_{}{}^{}}^{+}$) transition, the absorption analog of the intense emission continuum of ${\mathrm{H}}_2$. The absorption at wavelengths longer than 1.6 μm is probably due to trimers.

For the Raman instability in nonuniform plasma, the linear space-time asymptotic response consists of two parts, convectively growing wave packets and temporally growing localized side-scattered eigenmodes. Eigenmodes dominate the response only after the growth of the side-scattered wave packets is terminated by refraction from their resonance zones. A finite pump-beam diameter typically ends all growth before eigenmodes appear, except near quarter-critical density. These considerations may reconcile simulations, previous theories, and experiments.

In a sheared magnetic field, turbulent diffusion of electrons in the vicinity of a mode rational surface can eliminate the stabilizing influence of nonresonant electrons and lead to an absolute instability at small but nonzero wave amplitudes. As the turbulence grows, the inverse electron Landau resonance is broadened in both velocity and configuration space, and the convective shear damping due to ions is enhanced by turbulent spatial broadening of the mode until saturation occurs.

Measurements of the energy confinement time ${\tau }_E$ in the ISX-$A$ (Impurity Study Experiment) tokamak are interpreted theoretically using a one-dimensional time-dependent transport code. The maximum ${\tau }_E$ observed as the plasma density is varied over a wide range occurs at that density above which anomalous electron thermal conductivity leads to a smaller energy flux than neoclassical ion thermal conductivity.

Gross-energy-confinement times (${\tau }_E$) in the ISX-$A$ (Impurity Study Experiment) tokamak exceeded predictions of the usual empirical scaling relations. We attribute this performance to reductions of impurity radiation and magnetohydrodynamically driven loss channels. The value of ${\tau }_E$ reached a limit as a function of plasma density. We suggest that this limit is due to a transition from electron- to ion-dominated loss regimes. Maximum attainable values of ${\tau }_E$ increased with discharge current, in agreement with this interpretation.