Results of ab initio molecular-dynamics simulations of the properties of solid ${\mathrm{C}}_{60}$ are reported. The soccerball structure of molecular ${\mathrm{C}}_{60}$ is well preserved in the solid. The T=0 structure consists of alternating single and double bonds, but this distinction becomes blurred at relatively low temperatures. The intermolecular interactions are so weak that the individual ${\mathrm{C}}_{60}$ can rotate at relatively low temperatures. At high temperatures vibrations cause large distortions, but the case structure is still preserved. The present results are in excellent agreement with photoemission and NMR data.

We present microscopic total-energy calculations which provide a cohesive property and electronic structures of a new form of solid carbon, the face-centered-cubic ${\mathrm{C}}_{60}$ crystal (fcc ${\mathrm{C}}_{60}$). We find that ${\mathrm{C}}_{60}$ clusters are condensed by van der Waals force, and that the resulting fcc ${\mathrm{O}}_{60}$ is a novel semiconductor with direct energy gap of 1.5 eV at the Brillouin-zone boundary (X point). We also find that an ‘‘impurity’’ ${\mathrm{C}}_{60}$K cluster induces a shallow donor state in fcc ${\mathrm{C}}_{60}$.

The noise-rise phenomenon is a long-standing problem that was first observed in Josephson-junction-parametric amplifiers over ten years ago. We present here a case where noise-rise data from a Josephson junction is successfully explained, using a theory based on the universal properties of a dynamical system operated near a bifurcation point. The experiment and theory presented here is for a bifurcation of the Hopf type, a case not discussed previously. The predicted behavior is qualitatively different from that of previously studied bifurcations.

Photoelectrons ejected by normally incident linearly polarized He i radiation and emitted normal to epitaxial Au layers on Pt(111) are strongly spin polarized for both emission from the Pt substrate and the Au adsorbate up to 2.2 layers coverage. Relativistic Green’s-function calculations reproduce the measured data and reveal the physical origin of the polarization for a monolayer Au coverage to be a Au-induced surface state. The spin polarization is significantly influenced by the underlying Pt bulk and is thus a sensitive measure of the Au adsorption site.

Multiple-quantum-well structures based on two crystalline organic semiconductors, namely, 3,4,9,10 perylenetetracarboxylic dianhydride and 3,4,7,8 naphthalenetetracarboxylic dianhydride, have been grown by organic molecular-beam deposition. Both optical-absorption and time-resolved photoluminescence measurements reveal a significant effect on the binding energy and the radiative recombination probability of excitons due to localization of carriers. Variational calculations of the ground-state exciton energy in quantum wells have been done, and the results agree with the experimental data. This provides evidence for exciton confinement in organic quantum-well structures.

We argue that in a degenerate planar semiconductor, where the low-energy dynamics of electrons can be modeled by a relativistic Dirac theory, it is important to include the Zeeman interaction of the physical spin of the electron with magnetic fields. We show that including this interaction leads to a quantization of the high-field magnetic suceptibility.

Quasi-one-dimensional electronic systems have been realized in deep-mesa-etched AlGaAs/GaAs quantum wires. By means of a metallic grating coupler oriented perpendicularly to the wires, we could couple far-infrared radiation to one-dimensional plasmons propagating along the wires. The most prominent feature of the one-dimensional plasmon is a wire-width-dependent negative dispersion in a magnetic field, which is a unique property of edge-plasmon-type oscillations. In addition, we observe a rich spectrum of further modes which arise from the mixing between the one-dimensional plasmon and a charge oscillation perpendicular to the wires.

We have measured the ac impedance of Y-Ba-Cu-O thin films in a magnetic field of 0.55 T and in the frequency range from 100 kHz to 500 MHz. At the temperature of the dc vortex-glass transition but in the ac linear regime, we find scaling behavior of the impedance amplitude, ‖Z‖∞${\mathrm{\omega }}^{0.83}$, and a frequency-independent phase φ=74°. At higher temperatures, we find a crossover from a frequency-independent to a frequency-dependent impedance. This crossover frequency Ω varies with temperature like Ω∼(T-${\mathit{T}}_{\mathit{g}}$${)}^{5,8}$. Within experimental error, all of these results are in excellent agreement with predictions for the ac impedance of the vortex-glass phase of a superconductor in a large magnetic field.

Muon-spin-relaxation and bulk measurements of the magnetic-field penetration depth suggest that the cuprate high-${\mathit{T}}_{\mathit{c}}$, bismuthate, organic Chevrel-phase, and heavy-fermion systems possibly belong to a unique group of superconductors characterized by high transition temperatures ${\mathit{T}}_{\mathit{c}}$ relative to the values of ${\mathit{n}}_{\mathit{s}}$/${\mathit{m}}^{\mathrm{*}}$ (carrier density/effective mass). This feature distinguishes these exotic superconductors from ordinary BCS superconductors.

The force required to pull sandpaper across a carpet fluctuates. Slips (sudden drops of magnitude M of the force) are observed to have a probability N(M>m)∼${\mathit{m}}^{\mathrm{-}\mathit{b}}$ with b≃0.8. The power spectrum of force fluctuations has a low-frequency 1/f behavior. Thus our system reaches a self-organized critical state with fractal scaling in both the spatial and the time domain. We introduce a new nonconservative cellular automaton that exhibits self-organized criticality and describes these observations well.

Transient infrared absorbance changes of photolyzed carbon monoxide are used to probe internal dynamics in myoglobin over the time range 50 ns to 10 μs and the temperature range 100 to 240 K. The infrared absorbance of the photolyzed carbon monoxide at temperatures above 170 K disappears long before the CO recombines with the iron, indicating that the carbon monoxide experiences substantial time-dependent heterogenous line broadening. We argue that this broadening occurs as the carbon monoxide diffuses a substantial distance from the heme iron binding site.

The generalization error of the Bayes optimal classification algorithm when learning a perceptron from noise-free random training examples is calculated exactly using methods of statistical mechanics. It is shown that if an assumption of replica symmetry is made, then, in the thermodynamic limit, the error of the Bayes optimal algorithm is less than the error of a canonical stochastic learning algorithm, by a factor approaching √2 as the ratio of the number of training examples to perceptron weights grows. In addition, it is shown that approximations to the generalization error of the Bayes optimal algorithm can be achieved by learning algorithms that use a two-layer neutral net to learn a perceptron.

We present new results on the scaling of the ground-state energy ${\mathit{E}}_0$∝-${\mathit{N}}^{\mathrm{\beta }}$ for a neutral system with a large number (N) of locally interacting ‘‘charged’’ bosons in one dimension (1D). Variational methods provide an upper bound on β (β≤3) and lower bounds depending on the ratio of attraction to repulsion: β≥3, 5/3, and 1 when the ratio is >1, 1, and <1. It is argued that the lower bounds to β give the actual scaling laws. Connections to the 3D charged-boson gas and to 2D directed random paths in disordered media are discussed.

Sequences of nonsingular, asymptotically flat initial data for general relativity (GR) in vacuo, called critical sequences, are defined which approach the strong-field limit of GR in a precise sense. It is proven that critical sequences contain trapped surfaces for large values of the argument. Thus, by a theorem due to Penrose, the spacetimes evolving from all such configurations must develop singularities. In the course of the proof a new and conceptually simple proof of the positivity of the Arnowitt-Deser-Misner mass in the strong-field regime is obtained.

The cooling history of a strange star surrounded by a thin crust of ordinary matter is followed by solving analytically the general-relativistic equation of heat transfer across the crust. The surface temperature of the strange star is found to be lower than that of a neutron star (ordinary with core condensates) of the same age. This provides a definite observational signature for these exotic objects, so far the first quantitative one to be proposed.

We study the strong-coupling expansion of a Euclidean lattice formulation of the two-dimensional O(3) σ-model at nonzero topological angle θ, mapping it onto a solid-on-solid model with well-known critical behavior. The results are consistent with those predicted by the mapping of the Hamiltonian formulation of the σ model onto quantum spin chains. The model has a gapless phase at θ=π and weak coupling in which a condensate of Coleman’s ‘‘half-asymptotic’’ particles exists.

Associated production of Higgs bosons with top-antitop pairs at hadron colliders, pp→Htt¯X, is examined. By tagging on an isolated secondary lepton, e or μ, from the t or t¯ decay, discovery of an intermediate-mass Higgs boson, ${\mathit{m}}_{\mathit{H}}$≃80–150 GeV, via H→γγ is rendered feasible at the Superconducting Super Collider (SSC) (√s =40 TeV). Allowing a factor-of-0.4 signal reduction for isolation cuts and selection efficiencies leaves about 21 events per SSC year for ${\mathit{m}}_{\mathit{H}}$≃80–130 GeV, and somewhat less for 130–150 GeV, above an anticipated small background. At the CERN Large Hadron Collider (√s =16 TeV), the cross section is reduced by about a factor of 1/8.

B-meson semileptonic decay spectra have been obtained at the Υ(4S) and at the Υ(5S) at the Cornell Electron Storage Ring with the Columbia University–Stony Brook detector. The branching ratio for B→eνX at the Υ(4S) is found to be (10.0±0.5)%. The electron spectrum of B→eνX at the Υ(5S) is observed for the first time and the average branching ratio of B,${\mathit{B}}_{\mathit{s}}$→eνX is consistent with that for B’s from Υ(4S) decays. The shape of the electron spectrum at the Υ(5S) indicates production of B mesons which are heavier than nonstrange B’s, presumably strange B’s.

We have searched for orthoposition decay into γ plus a feebly interacting boson ${\mathit{X}}^0$, by looking for a narrow peak in the energy spectrum of single γ taken under the condition of no additional γ detected in a hermetic photon detector. No evidence of such decay is observed, resulting in a new upper limit on the branching ratio of 1.1×${10}^{\mathrm{-}6}$, which is a factor of 60 more stringent than previous limits in the ${\mathit{m}}_{\mathit{x}}$ region below 30 keV. This experiment rules out the existence of light (${\mathit{m}}_{\mathit{X}}$<800 GeV) Goldstone-like bosons having electron-coupling constants ${\mathrm{\alpha }}_{\mathit{X}\mathit{e}\mathit{e}}$ larger than 1.1×${10}^{\mathrm{-}11}$.

We have studied the β spectrum of ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ using a germanium detector containing a crystal with ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ dissolved in it. We find a feature in the β spectrum 17 keV below the end point which can be explained by the hypothesis that there is a heavy neutrino emitted in the β decay of ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ with a mass of 17±2 keV and an emission probability of (1.40±0.45±0.14)%.