We calculate the optical response of silicon, ${\epsilon }_1$(ω), below the optical-absorption threshold and the static dielectric constant of germanium. The time-dependent local-density approximation (LDA) is modified by the addition of a self-energy term taken to be a ‘‘scissors operator,’’ $P_{c\mathrm{k}}$${\Delta }_{\mathrm{k}}$. This form leads to a Ward identity replacement p→(${\epsilon }_{n\mathrm{k}}$-$H_{\mathrm{k}}^{\mathrm{LDA}{)}^{-1}}$ (${\epsilon }_{n\mathrm{k}}$-$H_{\mathrm{k}}$)p. For silicon, we obtain 11.3 for ${\epsilon }_1$(ω=0), compared to 11.7 for experiment, 13.1 in our LDA calculation, and 8.4 in a naive self-energy corrected theory (i.e., simply modifying the eigenvalues without modifying the momentum operator). For germanium, the corresonding values as 16.5, 15.8, 21.3 and 10.4

We report the first comprehensive measurements of the lower critical field, &, for both orientations H∥a axis and H∥c axis, of the heavy electron superconductor ${\mathrm{UPt}}_3$. An accurate & is obtained in a LC oscillator whose resonance frequency changes on flux entry into the superconductor. The & values obtained with this technique indicate a ‘‘kink’’ for H∥a axis only. With this same technique we also measure the upper &. The results obtained are compared with & and & in anisotropic superconductors.

Solutions of the Ginzburg-Landau equations for a complex superconducting phase are presented for regions close to a domain wall and to the surface. The finite local magnetization found at these inhomogeneities yields a small magnetic response via a movement of domain walls in an external magnetic field. We examine line defects in the walls which are vortices enclosing a fraction of the universal flux quantum.

In ∼2-μm-wide Hall bars of high-mobility GaAs/AlGaAs heterostructure resistance fluctuations of quasiperiod ΔB≃0.016 T are observed near the diagonal resistance minima for Landau-level filling factors ν=1,2,3,4. This behavior is consistent with resonant reflection through magnetically bound states as a mechanism for the breakdown of dissipationless transport in narrow channels. In the ν=(1/3 minimum of the fractional quantum Hall effect we observe similar fluctuation structure, but with a period of ∼0.05 T≃3ΔB, indicative of transport by quasiparticles of fractional charge e/3.

A learning algorithm is developed to build a dynamical model from complex spatial data consisting of discrete values on a lattice evolving in time. The resulting dynamical system is a cellular automaton, and may be used for forecasting or for regenerating global spatial patterns. Part of the learning algorithm is a novel application of the genetic algorithm, originally developed in the field of machine learning. We outline extensions of this method to construct models for spatial dynamics that have continuous variables as well.

A class of neural networks is analyzed in which the interaction range grows sublinearly with the network diameter. This avoids wiring problems and leads to rapid formation of (pure or mixed) domains, which later coarsen and develop smooth domain walls that may be driven and finally pinned by weak, noisy data. Notably, the mixture states are destroyed by rapidly growing pure droplets, while the pinned pure domains can reconstruct exponentially many composite patterns, built from patches of ‘‘learned’’ basic textures or symbols.

The protein myoglobin is dried on the surface electrodes of a 5-MHz quartz crystal oscillator. As the humidity above the film increases, the protein absorbs water and develops a hydration shell. The oscillator frequency shift measures the mass of absorbed water. Incremental decreases in the amplitude of vibration are also observed, corresponding to a softening of the protein structure and subsequent energy dissipation (damping) of the oscillations. The transition of a protein from a dry, more rigid structure to a semifluid hydrated state is observed to occur in discrete steps.

On a short time scale, Brownian particles undergo a transtion from the initial ballistic trajectories to diffusive motion. Hydrodynamic interactions with the surrounding fluid lead to a complex time dependence of this transition. We directly probe this transition for colloidal particles by measuring the autocorrelation function of multiply scattered, transmitted light. We show that a quantitative interpretation is possible because the transport of the light is diffusive, resolving a conflict in previous measurements.

We have performed a test of Lorentz invariance by searching for a time-dependent quadrupole splitting of Zeeman levels in ${}_{}{}^{21}{}_{}{}^{}\mathrm{Ne}$. A component of the splitting at a twice the Earth’s sidereal frequency (${\mathrm{\Omega }}_{\mathrm{S}}$) would suggest a preferred direction which affects the local physics of the ${}_{}{}^{21}{}_{}{}^{}\mathrm{Ne}$ nucleus. The technique employs polarized ${}_{}{}^{21}{}_{}{}^{}\mathrm{Ne}$ and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ gases produced by spin exchange with laser optically pumped Rb. Both species are contained in the same glass cell, the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ providing magnetometry and a monitor of systematic effects. Data from two runs produce an upper limit at the 1σ confidence level of 2×${10}^{\mathrm{-}21}$ eV (0.45×${10}^{\mathrm{-}6}$ Hz) on the Lorentz-invariance violating contribution to the binding energy. This result is comparable to that of the most precise previous experiment.

We investigate some two- and three-dimensional Ising models with multispin interactions and a field, by means of Monte Carlo simulations. The phase diagram of these models contains a self-dual line, along which we have searched for the presence of a phase transition. Both in two and three dimensions we give examples exhibiting a first-order transition along a part of the self-dual line. These first-order lines end in critical points, which are classified as Ising-type in terms of universality. A lattice-gas interpretation of these models clearly shows their similarity with gas-liquid systems.

Fits of theoretical spectra from Monte Carlo radiation-transfer calculations to dips at ≊20 and 40 keV in a spectrum of the ‘‘classical’’ γ-ray burst GB 880 205 give best-fit values and 68%-confidence intervals B=(1.71±0.07)×${10}^{12}$ G, $N_e$=(1.2±0.6)×${10}^{21}$ electrons/${\mathrm{cm}}^2$, and μ=cosθ=0.31±0.05, where θ is the viewing angle relative to the field. Physical self-consistent fixes the temperature at $T_C$${=5.3\mathrm{}}_{\mathrm{-}0.2}^{+0.3\mathrm{}}$ keV. These results suggest that this γ-ray burst and many others which exhibit a low-energy dip originate from strong magnetic neutron stars and are galactic in origin.

We discuss the quantization of a four-dimensional model in which a massive Abelian vector field interacts with chiral massless fermions. We show that, by introducing extra scalar fields, a renormalizable unitary S matrix can be obtained in a suitably defined Hilbert space of physical states.

We have observed hadronic final states produced in the decays of Z bosons. In order to study the parton structure of these events, we compare the distributions in sphericity, thurst, aplanarity, and number of jets to the predictions of several QCD-based models and to data from lower energies. The data and models agree within the present statistical precision.

We show that the increase of bin-averaged factorial moments with decreasing size of the rapidity bin δy (the so-called ‘‘intermittency’’ phenomenon) can be understood on the basis of conventional short-range correlations and a simple linked-pair Ansatz for higher-order correlations.

The data on hadron production in nuclei exhibit two striking regularities which are not readily explained by conventional hadron dynamics: (1) The mass-number dependence ${\mathrm{A}}^{\mathrm{\alpha }\left({\mathrm{x}}_{\mathrm{F}}\right)}$ of inclusive production cross sections has a universal power α(${\mathrm{x}}_{\mathrm{F}}$), which is independent of the produced hadron. (2) The A dependence of J/ψ production in nuclei has two distinct components: an ${\mathrm{A}}^1$ contribution at low ${\mathrm{x}}_{\mathrm{F}}$ and an anomalous ${\mathrm{A}}^{2/3}$ contribution which dominates at large ${\mathrm{x}}_{\mathrm{F}}$. We show that both phenomena can be understood in QCD as a consequence of the nucleus filtering out small, color-singlet Fock-state components of the incident-hadron wave function.

We have made a good-resolution, high-sensitivity search for a $T=2\mathrm{}$ dibaryon in the missing-mass spectra for the reaction $d({\pi }^{-}, {\pi }^{+}){\pi }^{-}\mathrm{nn}$ at 292 MeV. Our results are consistent with there being no resonance peak due to such a state in the mass region 2001-2070 MeV. 95%-confidence upper limits for the integrated cross sections for such a state are presented. It is found that a quasifree model calculation, without final-state interactions, considerably underpredicts the continuum yield in the vicinity of the threshold.

We have measured the ${(}^3$H+p) and ${(}^3$He+n) breakup of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ by ${}_{}{}^4{}_{}{}^{}\mathrm{He}$(e,e’c) coincidence experiments at low momentum transfer (q≊0.39 ${\mathrm{fm}}^{\mathrm{-}1}$) in the excitation energy region 22≤$E_x$≤36 MeV. Both channels were studied simultaneously by detecting the charged fragments c=p, ${}_{}{}^3{}_{}{}^{}\mathrm{H}$, and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ in the same detector system. The measured ${}_{}{}^4{}_{}{}^{}\mathrm{He}$(e,e’p${)}^3$H and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$(e,e’n${)}^3$He angular correlations as well as the deduced total ${}_{}{}^4{}_{}{}^{}\mathrm{He}$(e,e’p${)}^3$H and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$(e,e’n${)}^3$He cross sections are reproduced by microscopic model calculations with a charge-symmetric nuclear Hamiltonian.

We have studied near-threshold single-photon detachment of a model negative ion, in the presence of a second, intense radiation field. We find a simple, continuous connection between detachment in strong static fields (dc limit) and the increased energy needed to detach an electron into an intense optical field (ac limit). Below this shifted threshold energy, net detachment is suppressed because parent systems reabsorb electrons that have been temporarily emitted. This fragile emission-absorption process is easily upset, leading to leakage detachment below the shifted threshold.

Angular correlations between the three outgoing electrons in the double ionization of argon by electron impact have been measured for the first time. Double and triple coincidence techniques are used to determine simultaneously all final electron energies and angles, and provide fourfold and fivefold differential cross sections, respectively. The angular distributions are consistent with a two-step model for the double ionization mechanism. The present results clearly show the feasibility and potentiality of (e,3e) experiments.

Temporal quantum fluctuations of the intensity of light pulses produced in the linear regime of stimulated Raman scattering are observed. A theoretical description based on the concept of coherent temporal modes is presented. The method makes use of a minimum number of random variables, which are the excitation amplitudes of the temporal modes, and allows an estimate of the probability for generating a Stokes pulse that is likely to form a soliton in the nonlinear propagation regime.