We show that a layer rigidity model which includes the effects of elastic deformations of the host layers can account for the composition dependence of the c-axis lattice expansion of a variety of layered intercalation compounds. Rigidity parameters deduced from this model for each of the three classes of layered solids are reflective of structurally derived rigidity as are the healing lengths computed on the basis of discrete and continuum analyses. The layer rigidity model provides the first quantitative explanation for the 1D non–Vegard’s-law behavior of a 2D solid solution.

We present a bond-charge-model, slab calculation of the 2×1 reconstructed Si(111) surface dynamics, which enlightens long-unexplained experimental features and provides general guidelines for the dynamical study of deeply reconstructed surfaces. This analysis is based on the concepts of geometrical folding in the surface Brillouin zone, reconstructed-to-ideal interface, and structural interpretation of the gaps that appear in the folded branches.

In a simple model based on the Schottky-Mott theory of metal-semiconductor contacts, a metallic precipitate in a semiconducting matrix has the properties of a multicarrier, amphoteric trap. A use is made of this model to analyze the trapping effects of copper-decorated twinned boundaries in silicon bicrystals. The model gives in particular a simple explanation for the emission properties of the boundary traps, as determined by deep-level-transient-spectroscopy experiments on the bicrystals.

Photoconductivity measurements revealing two-photon absorption in GaAs/AlGaAs multiple quantum wells are presented. It is shown that both the forbidden 1S and the allowed 2P excitons can be observed. The energy separation between 1S and 2P excitons is determined directly from the absorption spectra to high accuracy. The data give evidence for two different absorption mechanisms: One is the two-photon absorption and the other one is the absorption of the second-harmonic wave which is generated inside the sample by nonlinear optical processes. By means of this additional absorption mechanism, the observation of the 1S excitions in two-phonon absorption spectra can be explained qualitatively.

We study the Chern numbers associated with the adiabatic conductances of mesoscopic systems with leads. We describe the results of exact calculations of all the Chern numbers of several model networks. For a network with one lead we find the integer conductances 0,±1. For a network with three leads we find noninteger conductances bounded by 1.

Diffraction has been observed in the scattering of Ar from a 2H-W(100) surface. Results are found to be consistent with an effective surface corrugation amplitude of about 0.05 Å, which is similar to values obtained for He and Ne diffraction from this surface. The temperature dependence yields a surface Debye temperature of ∼400 K. We also find that the shape and behavior of surface scattering rainbows observed in this system are best accounted for by a quantum mechanical treatment of the Ar-surface interaction.

Scanning-tunneling-microscope measurements by Hess et al. of the tunneling conductance into a superconducting vortex core show a pronounced peak at small bias. We show that this peak is due to the quasiparticle bound states in the core. A numerical (and approximately self-consistent) solution of the Bogoliubov–de Gennes equations yields the local density of states in the core, which resembles the tunneling conductance once we account for thermal broadening effects. We find additional structure in the local density of states which should be observable at lower temperatures.

We report two novel flux-creep-related phenomena in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ films at elevated currents in presence of magnetic fields: a sharp onset of nonequilibrium optical response and a current-dependent thermally activated electrical resistivity. In this regime the activation energy of the resistivity scales uniquely with current density as log(${\mathrm{J}}_0$/J) with ${\mathrm{J}}_0$≊3×${10}^6$ A/${\mathrm{Cm}}^2$. This nonlinear current dependence is significantly different from the predictions of the standard flux-creep model. At currents ≲7×${10}^3$ A/${\mathrm{cm}}^2$ the resistivity is current independent and the optical response is purely bolometric.

A theorem which connects exact thermal averages in a quantum system (fermions or bosons) with microcanonical averages in the presence of only one extra classical variable is proven. The theorem is a nontrivial extension of that introduced by Nosé for a classical system. It provides the basis for new canonical algorithms based on solving the time-dependent Schrödinger equation with a parametric dependence upon the extra variable. One such algorithm is constructed, and the canonical distribution is demonstrated for fermions in a harmonic potential.

The quantum signature of chaos in dissipative systems is cubic repulsion of their generalized energies (eigenvalues of the generators of the dynamics) in the complex plane. As in the Hamiltonian case the degree of repulsion is the same under temporally homogeneous conditions and periodic driving. Somewhat surprisingly, however, cubic repulsion prevails irrespective of whether or not the Hamiltonian embedding of the dissipative system obeys time-reversal invariance. More-over, even antiunitary symmetries of the dissipative generator itself cannot modify the repulsion exponent. In establishing the universality in question we find, as a useful byproduct, the generalization of detailed balance for periodically driven systems with damping.

It is shown that a loop of idealized cosmic string deforms the background geometry in its vicinity so that its path and shape become geodesics of this background. For angular deficits smaller than π, this deformation causes the background curvature to grow without bound near an infinitely thin string. However, the rate of growth is so weak that the tidal forces are not yet appreciable at the surface of a grand-unification string. Although equations of motion for the string in a ‘‘background’’ geometry cannot be defined in a clear-cut fashion, they are not inconsistent with the conventional dynamics derived from the Nambu action.

A differential accelerometer consisting of a solid sphere floating freely inside a stratified saline solution has been used to search for a composition-dependent force, originated by a mountain relief. No evidence of such a force has been obtained. From the upper limit to the velocity of the sphere, ν<10 μm/h, the differential acceleration field between solid and liquid comes out to be less than 2.4 nGal.

We discuss the recent formulation of conformal gravity as a first-order Chern-Simons gauge theory and show that N superconformal gravity can be treated analogously for arbitrary N. This formulation unifies the gravitational and O(N) Yang-Mills Chern-Simons actions.

We have succeeded in constructing a two-dimensional gauge model with both vector U(1) and axial-vector U(1) symmetries. This model is exactly solvable. The Schwinger term vanishes in this model as a consequence of the above symmetries, and negative-norm states appear. However, the norms of physical states are always positive semidefinite due to the gauge symmetries.

The Υ(3S) is much closer than lower Υ(nS) states to BB¯ and $B^{\mathrm{*}}$B¯ thresholds. These ‘‘s-channel singularities’’ may dominate Υ(3S) decay amplitudes, while ‘‘t-channel gluonic states’’ dominant in conventional models are more important for other decays. An ‘‘s-channel’’ decay mechanism of sequential pion emission via a heavy intermediate state such as BB¯ or $B^{\mathrm{*}}$B¯ predicts a qualitatively different pion spectrum from that predicted by conventional ‘‘t-channel’’ models for Υ(3S)→Υ(nS)ππ decays and the yet unobserved Υ(3S)→Υ${(}^1$$P_1$)ππ decay and may explain the observed disagreement between experiment and previous predictions as well as the difference between the Υ(3S) and other states.

The nonstrange and strange baryon resonances have been studied in the framework of the nonrelativistic constituent-quark model involving a SU(6)⊗O(3) oscillator basis spanned by six major shells. It turns out that the inclusion of the orbit-orbit component of the Fermi-Breit interaction obviates to a large extent the necessity of the usual ad hoc parametrization of empirical anharmonic effects.

We argue that four-quark ($Q^2$Q${¯}^2$) intermediate-state resonances containing a sizable ss¯ admixture produce selective enhancements in particular NN¯ annihilation channels with φ mesons. The pattern of enhanced φ production induced by NN¯ coupling to $Q^2$Q${¯}^2$ resonances is compared to that due to ss¯ admixtures in the N and N¯.

A new mechanism for producing J/ψ’s in a quark-gluon plasma is explored. A cc¯ pair created in the hard part of a hadronic collision need not be initially formed as a color singlet to result in a charmonium state if a plasma is also present. Instead, a color-octet pair can subsequently scatter off of the plasma to lose its color. It is shown that if a hot plasma is formed in a relativistic heavy-ion collider, then a substantial enhancement of the J/ψ production rate might be expected from this mechanism. Thus this production mechanism acts to counteract the decrease in cross section arising from Debye screening of the color-binding force in the plasma.

The ${}_{}{}^6{}_{}{}^{}\to \mathit{p}+(\mathit{n}\mathit{\alpha }$) spectral function for the proton-knockout reaction ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$(e,e’p) has been measured in parallel kinematics in the missing-momentum range -100<$p_m$<200 MeV/c. The data below α breakup are well described by a three-body (αnp) model of ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$. The shell model with discrete energy eigenstates cannot describe the data. The experimental spectroscopic strength below α breakup amounts to 0.79(10), compared to 0.87 as predicted by the three-body model and 1.33 as calculated from a schematic harmonic-oscillator shell model. The discrepancy between the predictions of the two models is discussed.

Recently, two scientific papers have reported positive detection of nuclear radiation from similar electrochemical cells operating with deuterated water. We have experimented with similar electrolytic cells and have looked for energetic charged particles which are characteristic of nuclear fusion reactions. We report on six variations of the cell, with an upper limit of 0.005 detected particles/${\mathrm{cm}}^3$ sec. Within background statistics, we observe no nuclear fusions.