Velocity distributions of desorbing molecules have been measured as a function of both desorption angle, $\theta$, and surface temperature, $T_s$. The mean energy, $\overline{E}$, of ${\mathrm{D}}_2$ desorbing from a half-sulfur-covered nickel surface at $T_s=1143\mathrm{}$ K decreases from $3.35k{T}_s$ at $\theta =0\mathrm{}°$ to $2k{T}_s$ at glancing desorption, whereas the speed ratio increases from values < 1 to values ≥ 1. Over the range $940 \mathrm{K}<T_s<1040\mathrm{} \mathrm{K}$, $\overline{E}$ was proportional to $T_s$. No differences in mean energy and speed ratio for ${\mathrm{H}}_2$, HD, or ${\mathrm{D}}_2$ were observed.

The existence of solitons in two or more dimensions is discussed. Solitary-wave solutions are found for a system of discrete chains with a derivative of a periodic coupling between the chains. Relevance of the model to phase solitons in the Peierls condensate and in spin systems is discussed.

A discussion of some of the difficulties with previous analyses of the resistivity of $A-15\mathrm{}$ compounds is given. Precise high-temperature data on $\alpha$-particle- and electron-damaged ${\mathrm{Nb}}_3$Ge and ${\mathrm{Nb}}_3$Sn samples with different defect concentrations are presented here and analyzed in a simple way with use of a phenomenological model based on the idea that the ideal resistivity must approach some limiting value in the regime where the mean free path becomes comparable to the interatomic spacing.

A high-temperature series expansion for the Edwards and Anderson spin-glass order-parameter susceptibility is computed for Ising spins on hypercubic lattices with nearest-neighbor interactions. The series is analyzed by Padé approximants with Rudnick-Nelson-type corrections to scaling. The results agree with the first-order $\epsilon$ expansion of Harris, Lubensky, and Chen. The critical exponent ${\gamma }_Q$ increases monotonically with decreasing dimension, $d$, for $d<\mathrm{}6\mathrm{}$, and apparently tends to infinity at $d=4\mathrm{}$; however, the critical temperature does not appear to go to zero at $d=4\mathrm{}$.

A simple explanation is suggested for the recently discovered universal behavior of defected $A-15\mathrm{}$ superconductors. Qualitatively and quantitatively, this behavior can be understood as being the direct result of an extremely large anisotropy of the superconducting energy gap.

Failure to detect parity-nonconserving effects in atomic transitions coupled with the available neutrino neutral-current data would appear to rule out all SU(2) ⊗ U(1) gauge theories which respect "natural" conservation laws for charm and strangeness and quark-lepton symmetry. We analyze a left-right symmetric "natural" (in the above sense) and quark-lepton symmetric $\mathrm{SU}{\mathrm{}\left(2\right)\mathrm{}}_L\otimes \mathrm{SU}{\mathrm{}\left(2\right)\mathrm{}}_R\otimes \mathrm{U}\mathrm{}\left(1\right)\mathrm{}$ gauge theory and find that it accommodates all the features of neutral-current phenomena.

We have measured at Fermilab the production of hadrons at ∼90° in the c.m. system as a function of incident proton energy, atomic number $A$ of the production target, and the transverse momentum $p_{\perp }$ of the produced hadron. The $A$ dependence of the production cross section of the hadrons can be described by a function $A^{\propto \left(p_{\perp }\right)}$, where the power $\alpha$ rises with $p_{\perp }$. At $p_{\perp } \sim 5$ GeV/c, $\alpha$ is ∼1.1 for ${\pi }^{\pm }$ and $K^{+}$, and ∼1.3 for $p$, $\overline{p}$, and $K^{-}$. The energy dependence of the power is also measured.

The representation mixing induced by the spontaneous breaking of chiral symmetry is a spatially varying phenomenon. A model for this effect predicts the form of the spin-dependent structure functions of deep inelastic lepton scattering and leads to the relation $1-{\alpha }_{A_1}\mathrm{}\left(0\right)=2[1-{\alpha }_{\rho }\mathrm{}(0\left)\right]$.

Inelastic $\alpha$ scattering experiments at 120 MeV on ${}_{}{}^{206,208}{}_{}{}^{}\mathrm{Pb}$, ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$, and ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$ reveal the existence of a new isoscalar resonance located at $\sim 80A^{-\frac{1}{3}}$ MeV in addition to the well-known resonance at $\sim 63A^{-\frac{1}{3}}$ MeV. The angular distribution of this new resonance, though not inconsistent with an $E4\mathrm{}$ assignment, is better described by $E0\mathrm{}$ or $E2\mathrm{}$. It would exhaust approximately 100%, 50%, or 17% of the corresponding isoscalar $E0\mathrm{}$, $E2\mathrm{}$, or $E4\mathrm{}$ energy-weighted sum rules, respectively.

Differential cross sections for the rotational excitation from $j=0\mathrm{}$ to $j=1\mathrm{}$ of HD molecules in collisions with Ne atoms have been measured in a crossed molecular beam experiment. The inelasticity is obtained by time-of-flight analysis of the scattered particles using the pseudorandom chopper method. The measured cross sections of 0.31 to 0.45 ${\mathrm{\AA }}^2$/sr at energies of about 30 meV and angles between 40° and 80° prove very sensitive to the angle-dependent part of the interaction potential as shown by a comparison with calculated data.

A rigorous evaluation of the time evolution amplitude $G\left(t\right)\mathrm{}$ for an isolated autoionizing state has yielded the result ${{\mathrm{}\left|G\right(t\left)\right|}^2}_{t\to \infty }=e^{-\frac{\Gamma t}{\hslash }+\frac{{\hslash }^2}{{\pi }^2(4\mathrm{}{E}^2+{\Gamma }^2)t^2}}$ where $E$ is the energy above the ionization threshold and $\Gamma$ the width. For states with lifetimes in the region ${10}^{-8\mathrm{}}$-${10}^{-11\mathrm{}}$ sec near the ionization threshold, the nonexponential decay corrections are sufficiently large to suggest that perhaps it is possible to test the validity of the fundamental exponential "law" within the realm of atomic physics.

The long-range parts of the $A$, $C{{}_{}{}^1{}_{}{}^{}\Sigma _{\mathrm{u},\mathrm{g}}^{}{}_{}{}^{}}^{+}$ excimer potentials of the ${\mathrm{He}}_2$ molecule have been accurately dtermined from high-resolution differential-cross-section measurements at the relative kinetic energy range from 18 to 140 meV. The barrier height of the intermediate maximum of the $A{{}_{}{}^1{}_{}{}^{}\Sigma _{\mathrm{u}}^{}{}_{}{}^{}}^{+}$ potentials is ${47}_{-1\mathrm{}}^{+2\mathrm{}}$ meV at an internuclear distance of 3.14 ± 0.05 Å. The long-range parts of the potential from the recent ab initio calculation by Guberman and Goddard is always 5 to 20 meV higher than the potential determined from our experiments.

Very narrow (∼2 meV) ${}_{}{}^1{}_{}{}^{}D$ and ${}_{}{}^1{}_{}{}^{}P$ shape resonances above the ground state of atomic fluorine lead to electron and photon near-threshold ${\mathrm{F}}^{-}$ detachment cross sections of approximately (2-3)×${10}^{-15\mathrm{}}$ and 4×${10}^{-14\mathrm{}}$ ${\mathrm{cm}}^2$, respectively, and could affect the F-atom production rates in the relativistic-electron-beam ${\mathrm{H}}_2$/${\mathrm{F}}_2$ lasers.

Optical sum-frequency generation, due to either noncollinear excitation, or magnetic-field mixing, or to their combined effect, is observed in atomic sodium vapor. Novel interference effects are observed and explained.

The several magnetic-source terms affecting laser-produced plasmas are presented and their importance discussed. The thermal force is shown to greatly modify the magnetic-field distribution in numerical simulations. Experimental implications are also discussed.

We study a nonlinear effect on ion motion of an electrostatic wave propagating perpendicularly to a uniform magnetic field. When the wave near the ion cyclotron harmonics has sufficiently large amplitude, the trapped motions of hot ions ($v_{\perp }>\frac{\omega }{k_{\perp }}$) become stochastic in the region of appreciable width near the separatrix. Numerical calculations show the tail formation in a $v_1$ distribution and theoretically predicted upper bound conditioned by the amplitude.

A dynamical model is developed to infer the energy content of a relativistic-electronbeam-heated plasma column from global or local magnetic field measurements. Under this model, magnetic signals are interpreted in terms of the propagation of macroscopic magnetosonic waves, and differences in characteristics such as beam duration, probe position, and pulse shape, etc., can be distinguished. This model applies to experimental regimes where the commonly used static model becomes invalid.

Large-scale, fully three-dimensional particle simulations have been carried out for the collisionless drift instabilities in a cylindrical geometry. It is found that nonlinear excitation of convective cells ($\omega =0, k_{\parallel }=0\mathrm{}$) due to drift instabilities gives rise to enhanced turbulence and anomalous plasma diffusion. The observed power spectra have resemblance with the recent measurements in toroidal devices.

We explain the absorption line and resonant Raman lines splittings together with the selection rules at low temperatures in polydiacetylene polymer crystals in terms of a chain-pairing mechanism arising from side-group interactions between the conjugated carbon chains. The symmetry of the pairing configuration has drastic effects on the one- and two-photon absorption spectra.

We have measured the heat capacity of TTF-TCNQ in the vicinity of the low-temperature transitions. High-resolution measurements, realized by the improvement of standard relaxation techniques, lead to the observation of four phase transitions at 52.6, ∼ 49-48, 46, and 37 K. The new transition observed at 46 K is tentatively attributed to the softening of $0.59b^{*}$ mode in TTF-TCNQ.