With use of relativistic many-body perturbation theory, $E_1=(1.51\mathrm{}\pm 0.07)\left(i{\mu }_{\mathrm{B}}{Q}_W\right)\times {10}^{-10\mathrm{}}$ has been obtained for the $6P_{\frac{1}{2}}\to 7P_{\frac{1}{2}}$ dipole transition matrix element in the presence of parity-nonconserving weak electron-nucleon interaction effects explicitly, which on combination with the available experimental $M_1$ leads, for ${{sin}^2\theta }_{\mathrm{W}}=0.23\mathrm{}$, to $\delta =(1.65\mathrm{}\pm 0.24)\times {10}^{-3\mathrm{}} \mathrm{and} (1.68\mathrm{}\pm 0.25)\times {10}^{-3\mathrm{}}$ respectively, for ${}_{}{}^{203}{}_{}{}^{}\mathrm{Tl}$ and ${}_{}{}^{205}{}_{}{}^{}\mathrm{Tl}$ in good agreement with the most recent experimental result for $\delta$.

Sufficiently long population decay times and sufficiently short dipole decay times in a single-mode model for a laser with saturable absorber permit coexistence of soft-excited oscillations and $Q$ switching (hard-mode sustained relaxation oscillations).

The Alfvén surface waves propagating along a viscous conducting fluid-vacuum interface have been studied. It is found that besides the "ordinary" Alfvén surface waves, modified by viscosity effects, the interface can support a second mode which is the over-damped solution of the dispersion equation. The possibility of observation of a two-mode structure of Alfvén surface waves in the laboratory and in the solar coronal plasmas is discussed.

Studies of He diffraction from Ni(110) with energies between 17 and 270 meV and different scattering geometries yield for the first time quantitative data on the energy dependence of both corrugation and softness. The results are discussed in connection with recent surface electron-density calculations for Ni(110).

Solid adsorption isotherms and crystal growth rates for ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ epitaxially adsorbed on graphite have been determined from measurements of fourth sound in Grafoil. The results suggest first-order transitions in each layer below a critical temperature and continuous growth with a decreasing nucleation barrier above the critical temperature.

The nonlinear coupling between the velocity field and the layer-displacement field leads to a radical breakdown of the conventional hydrodynamical theory for smectic-$A$ liquid crystals. Three of the five viscosities are found to diverge as $\frac{1}{\omega }$ for small frequencies $\omega$ with the result that the sound attenuation scales as $\omega$ (not ${\omega }^2$ as predicted by conventional hydrodynamics). It is also found that there is a simple relationship between the three diverging viscosities. Reanalysis of existing data appears to confirm the present prediction for the sound attenuation.

It has been found that high-frequency acoustic phonons with certain polarizations can propagate ballistically through a highly deformed LiF crystal. With use of the method of phonon imaging, a large anisotropy has been observed in the phonon-dislocation interaction—the crystal acts as a phonon polarizer. The data are consistent with the fluttering dislocation model. Phonon-focusing and anisotropic-scattering processes profoundly affect the transport of heat through a dislocated crystal.

Surface microscopy using vacuum tunneling is demonstrated for the first time. Topographic pictures of surfaces on an atomic scale have been obtained. Examples of resolved monoatomic steps and surface reconstructions are shown for (110) surfaces of ${\mathrm{CaIrSn}}_4$ and Au.

Based on a set of nonlinear rate equations with phonon-mediated transition rates calculated from mean field theory, the coverage-dependent isothermal desorption time for ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ on graphite up to a coverage of 1.5 adlayers is determined. Prefactors in the Arrhenius parametrization drop by 2 orders of magnitude as the heat of adsorption decreases for increasing coverage, establishing a compensation effect in physisorption kinetics.

The interconfigurational mixing and excitation energies, $\Gamma$ and $E_x$, of the Eu ions in ${\mathrm{EuCu}}_2$${\mathrm{Si}}_2$ are determined experimentally as functions of pressure and temperature. $\Gamma$ seems to depend only on $E_x$, and the strongly nonlinear $\Gamma \left(E_x\right)$ reflects the intra-ionic multiplet splittings and degeneracies of $4f^6$. The observed pressure and temperature dependence of $E_x$ is analyzed self-consistently in terms of contributions from mixing, elastic, and conduction-electron energies, which arise from the temperature and pressure dependence of the valence.

Photoluminescence spectra from ${\mathrm{CdCr}}_2$${\mathrm{Se}}_4$ have been measured at low temperatures. When the temperature was lowered below 70 K, an extra peak was observed on the higher-energy side of the band-to-band luminescence transition. The energy difference between the two peaks was measured to be 3.5 meV. The emission was attributed to the transitions from the split $s$-conduction bands.

Within the framework of an $\mathrm{SU}{\mathrm{}\left(2\right)\mathrm{}}_L\otimes \mathrm{U}\mathrm{}\left(1\right)\mathrm{}\otimes \mathrm{SU}{\mathrm{}\left(3\right)\mathrm{}}_c$ gauge model with suitably extended Higgs sector, the possibility of oscillations between neutral matter and antimatter, such as neutron-antineutron and hydrogen-antihydrogen systems, is discussed. This model incorporates the spontaneous breakdown of global $B-L$ symmetry associated with a Majoron, and as a result, a relation between $n-\overline{n}$ mixing, $\mathrm{H}-\overline{H}$ mixing, and the mass of the electron neutrino is obtained. With present limits on ${\tau }_{n-\overline{n}}$, ${\tau }_{\mathrm{H}-\overline{H}}\gtrsim {10}^{13}$ yr is predicted.

Measurements are presented of the energy dependence of the spin polarization of low-energy (0.5-25 eV) secondary electrons when a 500-eV primary beam is incident on an iron-based ferromagnetic glass. The polarization of the lowest-energy electrons is found to correspond to the net valence-band spin density. Possible causes for the observed decrease in polarization with increasing secondary energy are discussed. The results demonstrate a mechanism for measuring surface magnetic structure with the very high spatial resolution of scanning electron microscopy.

The vibrational and rotational state distributions of a supersonic nitric oxide beam, scattered from a Pt(111) single crystal surface, were investigated. A two-photon ionization technique was applied to monitor the internal energy content of the scattered molecules. Vibrational distributions were found to be colder than that corresponding to the crystal temperature between 450-1100 K. Rotational temperatures were also found to be colder than expected for thermal equilibrium with the platinum surface.

It is shown, in an experiment, that the spin polarization $P_0$ of a primary electron beam causes a spin polarization $P_{\mathrm{ex}}$ of the secondary electrons produced in a single collision from the conduction bands of a metal. The results of $\frac{P_{\mathrm{ex}}}{P_0}$ obtained with gold suggest that this type of experiment might provide a critical test of the electron-electron interactions in solids.

It is proven that when correlations in an equilibrium classical system in $\nu$ dimensions, $\nu >~2$, containing charges decay faster than ${\left(\mathrm{distance}\right)}^{-(l+\nu )}$ then the charge cloud surrounding particles has no multipole moments of order $k<~l$. This yields $l+1\mathrm{}$ sum rules with $l=\infty$ when the decay is exponential. This extends previous results for $l<~2$ sum rules and also generalizes them to systems containing fixed dipoles (or higher multipoles). Some consequences are described.

A simple mathematical model is given which shows how phase locking, bistability, period-doubling bifurcations, and chaos may result from periodic stimulation of nonlinear oscillators. A new fixed-point theorem, which extends the classic results of Arnold, is used in the analysis.

Globally supersymmetric theories often have several degenerate supersymmetric vacua. Gravitation splits this degeneracy in such a way that at most one of these vacuum solutions has energy density and cosmological constant equal to zero, while all the rest have negative energy density. Nevertheless, the vacuum with vanishing energy density is stable against decay into the others.

Cross sections for negative pion production in 183-MeV/nucleon Ne + NaF and Ne + Pb collisions have been measured at laboratory angles from 20° to 90°. Almost isotropic angular distributions in the nucleon-nucleon c.m. frame are observed. The energy spectra in this frame are of an exponential type with an inverse slope of 25 MeV for NaF and 26 MeV for Pb. No evidence of a bump predicted to result from pionic instability is observed. Possible mechanisms for producing high-energy pions are discussed.

A comparison of distorted-wave impulse-approximation calculations with recent ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({\pi }^{+}, {\pi }^{+}p){}_{}{}^{11}{}_{}{}^{}\mathrm{B}$ data shows excellent agreement and demonstrates the applicability of the quasifree knockout reaction model. Both the shape and the magnitude of the energy-sharing distributions are well described by the calculations.