We report the first observations of collision-induced infrared absorption of the fundamental vibrational band of molecular hydrogen incorporated in microvoids in heavily hydrogenated amorphous silicon. These results provide the first direct evidence of high-pressure gas (∼ 2000 atm) occluded in $a$-Si: H. We also report the observation of the overtone absorption spectrum of the Si-H bond in $a$-Si: H, thus providing useful information regarding anharmonic potential well describing the Si-H bond in bulk amorphous silicon.

The Ablowitz-Ramani-Segur conjecture relates the Painlevé property, i.e., polelike local singularity structure, to integrability. As such this conjecture cannot be applied, as integrability detector, to nonlocal integrodifferential equations. We show, however, that, for the physically interesting cases of the Benjamin-Ono and intermediate long-wave equations, the Painlevé property can be recovered despite the apparent nonlocality.

We show that the calculation of the Bohm-Aharonov effect in disordered systems by Al'tshuler, Aronov, and Spivak can be simply explained in terms of first-order degenerate perturbation theory. We find that the conductivity varies periodically with half a flux quantum in both one- and two-dimensional geometries.

We derive an equation of motion for a fully observed classical system which is coupled to a quantum companion whose degrees of freedom are only partially observed. Our purpose is to discuss the nature of the quantum noise by using a generalization of the Langevin equation.

A purely algebraic procedure is presented for calculating recursion relations for $S$ matrices belonging to problems associated with the group SU(1,1). The procedure involves supplementing a recently introduced group-theoretic approach to scattering by an algebraic framework that characterizes asymptotic behavior. Our formulation makes use of the Euclidean group, which contains the symmetry transformations for a free particle. The Coulomb and Pöschl-Teller potentials are discussed to illustrate our methods.

Associated with the local Lorentz symmetry of gravitational interactions of fermions there are chiral anomalies in ($4n+2$)-dimensional space-times. We present chiral Lorentz anomalies in two and six dimensions. Existence of chiral Lorentz anomalies implies that quantum effects induce a breakdown of local Lorentz symmetry in $4n+2$ dimensions, in general, in theories containing chiral Weyl fermions.

We report measurements from the CLEO detector of the rate of $\Xi$ and $\Lambda$ production in $e^{+}{e}^{-}$ interactions in the upsilon region. Hyperon production from the decay of the $\Upsilon \mathrm{}\left(1s\right)\mathrm{}$ is compared with continuum $e^{+}{e}^{-}$ data. The ratio of the production rates of $\Lambda$ (and $\bar{\Lambda }$) to $K^0$ (and ${\bar{K}}^0$) on the $\Upsilon \mathrm{}\left(1s\right)\mathrm{}$ is 0.21 ± 0.03, much larger than in the continuum, 0.07 ± 0.01. The ratios of the production rates of the $\Xi$ and $\Lambda$ are comparable, $0.10\pm 0.02 \left[\Upsilon \mathrm{}\right(1S\left)\right]$ and 0.07 ± 0.02 (continuum). We discuss some implications of the data for gluon and quark fragmentation models.

Relations among high-$p_t$ exclusive cross sections, particularly for $\gamma \gamma \to \mathrm{baryon}$-antibaryon and for meson-nucleon scattering, test the applicability of perturbative QCD in the kinematic regime of the experiments. This permits assessment of the importance of higher-order corrections and non-leading-twist contributions to the Born approximation, the extent of the "Sudakov suppression," and the validity of the asymptotic approximation to the wave functions.

We have measured the atomic-mass dependence of the $P_T$ distribution of massive muon pairs produced in 225-GeV/c ${\pi }^{-}$-nucleus collisions at Fermilab. We find that $〈P_T^2〉$ is consistent with being independent of the atomic mass $A$, with the value of 1.69±0.10 ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ for muon pairs of mass between 4.0 and 8.5 GeV/${\mathit{c}}^2$. When the dependence of $〈P_T^2〉$ on $A$ is parametrized as $〈P_T^2〉=a+b{A}^{\frac{1}{3}}$, we find that $b=-0.079\mathrm{}\pm 0.073$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ which corresponds to an upper limit of 0.015 ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ at the 90% confidence level.

Intermediate structure has been observed in the photofission cross section of ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$ measured with a photon energy resolution <500 eV. The gamma rays, variable in energy, were obtained from the ($p$, $\gamma$) reaction on several nuclei. The average spacing of the observed photofission resonances at an excitation energy of 6.16 MeV is 1.6±0.4 keV. The average areas of the resonances are compared with theoretical expectations for a double-humped and a triple-humped barrier.

A statistical scission model is applied to heavy-ion-induced fission. Comparison of model calculations to experimental data on fission-fragment angular distributions shows excellent agreement for systems in a large range of fissility parameter, excitation energy, and spin value. For many of these reactions, the traditional transition-state model and its extensions are inapplicable or fail to reproduce the data.

A new technique has been developed for evaluating second-order distorted-wave amplitudes for atomic excitation without making any approximations. By this technique, second-order amplitudes with arbitrary distorted waves and arbitrary Green's functions in the interaction can be evaluated with comparable difficulty. The utility of the method is demonstrated through a practical calculation of the second-order distorted-wave approximation for electron excitation of the $2p$ state of hydrogen.

A new double-minimum state, $\mathrm{}\left(2\right)\mathrm{}{}_{}{}^1{}_{}{}^{}{\Sigma }_{\mathrm{u}}_{}^{+}{}_{}{}^{}$, of ${\mathrm{Na}}_2$ has been characterized by infrared fluorescence recorded at high resolution by Fourier-transform spectrometry. A ring dye laser populates ${}_{}{}^1{}_{}{}^{}{\Sigma }_{\mathrm{g}}_{}^{+}{}_{}{}^{}$ Rydberg levels in the two-photon process ${}_{}{}^1{}_{}{}^{}{\Sigma }_{\mathrm{g}}_{}^{+}{}_{}{}^{}\leftarrow A{}_{}{}^1{}_{}{}^{}{\Sigma }_{\mathrm{u}}_{}^{+}{}_{}{}^{}\leftarrow X{}_{}{}^1{}_{}{}^{}{\Sigma }_{\mathrm{g}}_{}^{+}{}_{}{}^{}$, and ${}_{}{}^1{}_{}{}^{}{\Sigma }_{\mathrm{g}}_{}^{+}{}_{}{}^{}\to \mathrm{}\left(2\right)\mathrm{}{}_{}{}^1{}_{}{}^{}{\Sigma }_{\mathrm{u}}_{}^{+}{}_{}{}^{}$ fluorescence is analyzed. The two potential minima lie at 28 454.6 ${\mathrm{cm}}^{-1\mathrm{}}$, 3.688 Å, and 27 870.4 ${\mathrm{cm}}^{-1\mathrm{}}$, 6.739 Å, respectively, and the energy at the top of the barrier is about 29 150 ${\mathrm{cm}}^{-1\mathrm{}}$ (relative to the minimum in $X{}_{}{}^1{}_{}{}^{}{\Sigma }_{\mathrm{g}}_{}^{+}{}_{}{}^{}$).

Quantitative experimental results are presented on the response of a convecting fluid to periodic modulation of the imposed heat current. A theoretical model which is a generalization of the Lorenz equations is proposed to describe the results. It yields semiquantitative agreement with experiment in both linear and nonlinear regimes.

An $\mathrm{XY}$ model of classical spins, on a two-dimensional square lattice, with nearest-neighbor interaction $V\left(\theta \right)=2J[1-{\left(\frac{{cos}^2\theta }{2}\right)}^{p^2}]$ is studied by a Monte Carlo simulation that also monitors the vortex excitations. Both continuous and first-order transitions are found. In the latter the density of vortices sharply increases at the transition point. The transition turns first order, because the shape of $V$ is such that vortex-antivortex pair formation is suppressed at low temperatures for $p\gtrsim 3$.

A Thomas-Fermi density-functional theory is developed for structural energies in stage-one alkali-graphite intercalation compounds. Correct trends for lattice constants and elastic moduli are obtained. We compute corrugation energies $\Delta E$ and alkali-alkali spring constants $k$, which determine in-plane intercalant diffusion and domain-wall structure. $k$ is determined by electrostatic effects, and is mainly independent of intercalant. $\Delta E$ depends strongly on intercalant size; thus Li differs substantially from K, Rb, and Cs.

By means of inelastic neutron scattering, the dispersion of the longitudinal [$00q$] phonon modes has been measured for the first time in the mixed layered compound ${\mathrm{K}}_{1-x}{\mathrm{Rb}}_x{\mathrm{C}}_8$ over the whole composition range $0<~x<~1$. From the optic and acoustic phonon branches interlayer force constants are derived which are strongly composition dependent. At $x=0.65\mathrm{}$ the elastic constant $C_{33}$ shows an anomalous softening of more than 20%, which may be due to a composition-dependent charge transfer between the intercalant and graphite layers.

Polyacrylamide, agarose, and silica gels have been prepared with solvents which are nearcritical binary liquid mixtures. Near the critical temperature of the free liquid mixtures, the binary-liquid gel exhibits a broad region wherein light-scattering intensity is large and varies monotonically with temperature. Some features of this scattering suggest that the gel matrix acts like a random field. Only very weak temporal fluctuations are observed throughout this broad transition region.

The (heretofore unknown) crystal structure of lithium at low temperature is identified to be close-packed rhombohedral $9R$. The stacking order of the hexagonal layers is $ABCBCA-CAB$, a nine-layer repeat sequence. There are three atoms per primitive rhombohedral cell, and nine in the (nonprimitive) hexagonal cell. The only other element with this structure is samarium.

This study of Na on Ru(001) at 80 K provides the first detailed examination of orientational ordering in a strongly chemisorbed monolayer. The relative orientation of a Na layer on Ru(001) varies with the Na-Ru lattice misfit in a way consistent with predictions from theoretical models that have been used to explain orientational ordering of rare gases physisorbed on graphite. The similarity between physisorbed systems and the chemisorbed Na on Ru system suggests a universal behavior of rigid overlayers on hexagonal substrates.