Through a thermodynamic perturbation expansion, a new sphericalization procedure has been obtained for anisotropic molecular potentials. For ${\mathrm{N}}_2$ the resulting fluid pressures and internal energies for the effective spherical potential differ at high densities by at most 1.5% from exact molecular-dynamics calculations for the anisotropic ${\mathrm{N}}_2$ potential. Results at lower densities are comparably good. Preliminary results for C${\mathrm{O}}_2$, an even more anisotropic molecule, are also excellent.

The method of glancing-incidence x-ray diffraction has been applied to the Au(110) reconstructed surface. The long-range structure is incommensurate with the bulk in one direction, comprising locally 2 × 1 regions separated by domain walls. The atomic positions in the 2 × 1 cell are determined independently of any models, and their alignment with respect to the bulk is deduced; the result is a missing-row structure with lateral pairing displacements in the second layer of 0.122± 0.017 Å.

Vibrational excitations of carbon monoxide on Ni(100) have been observed for the first time in the energy-loss spectrum of reemitted positrons. For $\mathrm{Ni}\mathrm{}\left(100\right)c(2\mathrm{}\times 2)\mathrm{CO}$ at room temperature, energy-loss peaks are found at ∼ 57 and ∼ 248 meV, corresponding to Ni-C and C-O stretching vibrations, respectively. These peak positions are in good agreement with previously reported results for electron energy-loss spectroscopy. Anticipated improvements in resolution promise to make reemitted-positron energy-loss spectroscopy competitive with high-resolution electron energy-loss spectroscopy.

The continuum field theory describing the low-energy dynamics of the large-spin one-dimensional Heisenberg antiferromagnet is found to be the O(3) nonlinear sigma model. When weak easy-axis anisotropy is present, soliton solutions of the equations of motion are obtained and semiclassically quantized. Integer and half-integer spin systems are distinguished.

The temperature dependence of the impurity susceptibility and specific heat for the Anderson model is investigated on the basis of the exact solution already obtained for this model.

Recent ESR measurements on the spin-glass $\mathrm{Ag}\mathrm{Mn}$ in the paramagnetic phase reveal an increase in the linewidth over the expected linear temperature dependence for $\frac{T}{T_g}\lesssim 3$. The Mori-Kawasaki formalism was used to calculate quantitatively the linewidth due to the broadening by the Dzyaloshinsky-Moriya anisotropy interaction of an exchange-narrowed line. With no adjustable parameters the authors explain the increase in linewidth, and they also relate the shift in the resonance to the imaginary part of the frequency-dependent self-energy.

A theoretical analysis of velocity fluctuations in semiconductors is presented, and results obtained from a Monte Carlo procedure are shown for Si. It has been found in particular that (i) off-diagonal contributions to the velocity autocorrelation function must be taken into account; (ii) the convective contribution is positive; and (iii) a long tail in the autocorrelation function, due to intervalley fluctuations, may be present.

Charge- and spin-density response functions in the one-dimensional ¼-filled extended Hubbard model have been studied by use of a Monte Carlo technique. The results show that Coulomb interactions suppress the $2p_{\mathrm{F}}$ charge-density singularity, while they enhance the $2p_{\mathrm{F}}$ spin-density singularity. The $4p_{\mathrm{F}}$ response is only appreciable if, in addition to on-site repulsion, longer-range interactions exist. The present results are compared with weak-coupling renormalization-group predictions.

Sensitivity of a nonequilibrium chemical system to small symmetry-breaking influences is analyzed in the context of chiral-symmetry breaking. For a hypothetical model system, with realistic kinetic constants, a reaction energy barrier difference of $\frac{\Delta E}{\mathrm{kt}}={10}^{-17\mathrm{}}-{10}^{-15\mathrm{}}$ is shown to be sufficient to have a strong chiral selectivity. This is in the range of the estimated energy differences between right- and left-handed molecules due to weak neutral currents.

The metric is presented, in terms of six determinants of degree $N$, in a concise closed form, describing $N$ collinear isolated Kerr masses ($N=1, 2, 3, \dots$) balanced by their gravitational spin-spin interaction. Two hitherto unnoticed potentials $L$ and $M$ are introduced to evaluate the metric function $\omega$. The conditions for regularity of the metric on the symmetrical axis are presented.

Recent efforts to estimate the number of modes sufficient for the approximate solutions of Navier-Stokes equations in two dimensions are summarized. Several such estimates have been obtained, and their relations to one another are discussed. The physical significance of the results is noted and used to infer the possible nature of similar estimates in three dimensions.

This paper presents an exact solution of the Dirac equation for an $I=\frac{1}{2}$ fermion in the field of a 't Hooft-Polyakov magnetic monopole (in the Prasad-Sommerfield limit), which is analytic at $\mathcal{r}=0\mathrm{}$. Helicity conservation restricts the $J=0\mathrm{}$ $S$ matrix to be pure charge exchange. Because of the long-range interaction, the scattering amplitude is enhanced at long wavelengths $\lambda \gg \frac{1}{M}$ (the monopole structure size). The relevance of the present results for the question of proton decay catalysis is briefly discussed.

Soft-x-ray excitation involving C $1s$ electrons in CO and acetone, ${\left(\mathrm{C}{\mathrm{H}}_3\right)}_2$CO, is found to result in ionic fragmentation of the original molecule. The fragmentation pattern changes whether the C $1s$ electron gets ionized or excited into a Rydberg-line orbital or into an antibonding ${\pi }^{*}$ molecular orbital. Moreover, the fragmentation occurs specifically around the site of the carbon atom where the optical excitation takes place. Based on these observations one might consider the use of tunable soft x rays to stimulate chemical reactions or to selectively break large organic molecules.

The authors have observed the ionization of Na Rydberg states by strong microwave fields and have found that the field required for ionization is $\frac{1}{\left(3.7\mathrm{}{n}^5\right)}$ (in atomic units) for $n=20-37\mathrm{}$. This field is close to the field $\frac{1}{\left(3\mathrm{}{n}^5\right)}$ at which the Stark manifolds of principal quantum numbers $n$ and $n+1\mathrm{}$ intersect. The ionization can be shown to arise from transitions occurring near these intersections.

Transitions between excited states of molecular nitrogen, which are generated in a hollow-cathode discharge, have been studied by use of optogalvanic double-resonance spectroscopy as a state-selective method. By pumping of the known (0, 0) band of the $c_4{}_{}{}^1{}_{}{}^{}\Pi _{\mathrm{u}}^{}{}_{}{}^{}-a^{\prime \prime }{}_{}{}^1{}_{}{}^{}{\Sigma }_{\mathrm{g}}_{}^{+}{}_{}{}^{}$ system in ${\mathrm{N}}_2$ the (16, 0) and (17, 0) bands of the $b^{\prime }{{}_{}{}^1{}_{}{}^{}\Sigma _{\mathrm{u}}^{}{}_{}{}^{}}^{+}-a^{\prime \prime }{{}_{}{}^1{}_{}{}^{}\Sigma _{\mathrm{g}}^{}{}_{}{}^{}}^{+}$ system have been identified for the first time, and the recent assignment for the (0, 0) band of the ${c_5}^{\prime }{{}_{}{}^1{}_{}{}^{}\Sigma _{\mathrm{u}}^{}{}_{}{}^{}}^{+}-a^{\prime \prime }{{}_{}{}^1{}_{}{}^{}\Sigma _{\mathrm{g}}^{}{}_{}{}^{}}^{+}$ system has been verified.

The nonlinear self-consistent theory of short-pulse free-electron laser oscillators can now be extended to include transverse diffraction within the optical resonator mode. The theory provides efficient solutions to the three-dimensional parabolic-wave equation coupled to the Lorentz force equation. The method is general enough to include arbitrary magnet designs, optical mirror arrangements, and driving currents. New mode structures are predicted which should be observed in future experiments at Stanford University.

Hard-x-ray continuum spectra from high-$Z$ tracers are used to obtain lateral and axial energy-deposition profiles by hot electrons in C${\mathrm{O}}_2$-laser-irradiated slab targets. The interpretation of the results emphasizes a local direction of incidence of the hot electrons on the target and an energy-deposition pattern which are consistent with self-generated magnetic fields.

The authors report measurements of the density and temperature gradients in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ mixtures near their liquid-vapor critical point, as induced by a heat flux. From these they deduce the thermal diffusion ratio $k_T$ and the conductivity $\kappa$. They find that $k_T$ and $\kappa$ diverge with respective effective exponents $\varphi \approx 1.2$ and $\psi \approx 0.6$. Both of these results are in contradiction with the asymptotic predictions for binary mixtures and are discussed in the light of the hydrodynamic transport equations.

Nucleation and growth are studied in the metastable region of the Glauber-kinetic Ising model with medium-range interactions. Monte Carlo data indicate that the nucleating droplets are not in general compact but quickly become so during the initial phase of growth and then grow as compact droplets. This two-stage growth process is also predicted by a qualitative theory.

The field splitting of the real squashing, $J=2\mathrm{}$, mode in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$B$ is shown to become highly nonlinear at large fields as a result of the ellipsoidal deformation of the energy gap. This leads to crossings of the $J_z=+1\mathrm{}$ and $J_z=0\mathrm{}$ levels with the $J_z=+2\mathrm{}$ level. The crossing points depend sensitively on the couplings between the $J=2, 1, \mathrm{and} 0$ modes. The theory is in good agreement with the observed field evolution and level crossing as measured recently by Shivaram et al.