We investigate the effect that a current flowing on a superconducting string has on its motion, and demonstrate that for a wide class of models the current can build up so that the tension vanishes, leaving the string behaving more like a ‘‘spring.’’ Possible conflicts with both nucleosynthesis and constraints on gravitational radiation are briefly discussed.

Assuming that the chaotic time history of a single variable in a differential equation possessing a strange attractor can be represented as a random superposition of deterministic ‘‘structures,’’ we predict the power spectral density. We justify the assumption for perturbations of nonlinear Hamiltonian oscillators ans compare our predictions with computations on versions of Duffing’s equation.

Combinatorial optimization problems such as the determination of the ground-state energy of Ising spin-glasses, the construction of low-autocorrelation binary sequences, and the traveling salesman problem are analyzed with use of zero-temperature scaling concepts. The difficulty of obtaining good ground states with most heuristic algorithms is influenced by the number of local minima. It is shown that the number of such minima is related to the thermal eigenvalue at the zero-temperature fixed point.

Certain four-dimensional gauge models which can arise from a compactification of the ${\mathrm{E}}_8$×${\mathrm{E}}_8$ superstring theory predict the existence of ’t Hooft–Polyakov monopoles. Although typically superheavy, the primordial monopoles first appear when the temperature of the universe reaches the TeV scale. One phenomenologically attractive model with three fermion families predicts the existence of monopoles with mass ∼${10}^{16}$ GeV carrying three quanta of Dirac charge. They may occur in the galaxy at the level of the Parker bound.

This Letter reports results of a search for radiative production, by $e^{+}$$e^{\mathrm{-}}$ annihilation of particles that interact only weakly in matter. The search has been made in the total data set of 115 ${\mathrm{pb}}^{\mathrm{-}1}$ acquired with the ASP detector at the SLAC storage ring PEP (s=29 GeV). No anomalous signal was observed. The number of generations of light neutrinos has been limited to $N_{\nu }$<7.5 (90% confidence level). Limits are also placed on the masses of particles predicted to exist by models of supersymmetry.

We report the results of a search at the Brookhaven National Laboratory’s Alternating-Gradient Synchrotron for the ξ(2.2) observed by the Mark III group at the SLAC $e^{+}$$e^{\mathrm{-}}$ storage ring SPEAR. 37 000 p¯p→$K^{+}$$K^{\mathrm{-}}$ events and 200 000 p¯p→${\pi }^{+}$${\pi }^{\mathrm{-}}$ events were studied in the incident-momentum interval from 1.25 to 1.56 GeV/c, corresponding to a mass interval of 110 MeV/$c^2$ about the reported ξ mass. The mass resolution was 3 MeV/$c^2$. We find no evidence for ξ formation and determine that the product B(ξ→p¯p)B(ξ→$K^{+}$$K^{\mathrm{-}}$) is <2×${10}^{\mathrm{-}4}$ for $J^{\mathrm{PC}}$${=2\mathrm{}}^{++}$ and Γ=35 MeV/$c^2$.

The K¯N S-wave interaction is investigated with a coupled-channels potential model. The importance of using relativistic kinematics and of requiring a subthreshold resonance while fitting to low-energy scattering data is explored. A model reproducing the above-threshold data, and agreeing with the kaonic-hydrogen energy shift, is found.

The deuteron magnetic form factor B($Q^2$) has been measured at momentum transfers $Q^2$=1.21, 1.49, 1.61, 1.74, 1.98, 2.23, 2.48, 2.53, and 2.77 (GeV/c${)}^2$ at the Stanford Linear Accelerator Center by detection of electrons backscattered at 180° in coincidence with recoiling deuterons at 0°. The data for B($Q^2$) are found to decrease rapidly from $Q^2$=1.2 to 2 (GeV/c${)}^2$, then rise to a secondary maximum around $Q^2$=2.5 (GeV/c${)}^2$, in qualitative agreement with impulse-approximation calculations.

A quasielastic (e,e’p) experiment has been performed on ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ for both backward- (transverse) and forward-angle (longitudinal) electron kinematics. Cross sections for knockout of protons from two different orbits (1s and 1p) have been measured simultaneously. The densities probed by the (e,e’p) reaction differ by a factor of 4 between these orbits. In both cases the backward/forward cross-section ratio deviates by the same amount from the impulse approximation.

Measurements of the absorption spectrum near the ionization threshold for an atom in a strong magnetic field showed that the spectrum is a superposition of many oscillatory terms (‘‘quasi-Landau oscillations’’). We have developed a quantitative theory which shows that each classical closed electron orbit which begins and ends near the nucleus contributes an oscillatory term to the average oscillator strength. The theory gives new understanding of the behavior under combined Coulomb and Lorentz forces, and it elucidates the roles of isolated closed orbits in chaotic systems. The first results of this theory are shown to be in good agreement with experimental results.

We have measured cross sections for the correlated emission of two K x rays following the collision of hydrogenlike sulfur ions with ${\mathrm{H}}_2$ in the energy range between 70 and 160 MeV. The observation of the two correlated x rays is interpreted as a resonant capture of a target electron accompanied by simultaneous excitation of the projectile in the collision (RTE). By our distinguishing between Kα and Kβ lines, contributions from KLL and KLn (n≥M) resonances could be determined independently.

We have observed the resonance line shape for a very weak atomic transition excited when an atomic beam intersects a strong standing-wave laser field. The line shape has a dramatic intensity-dependent distortion which is Doppler free and independent of the excitation rate. We have calculated the line shape predicted by optical Bloch equations that include a spatially varying ac Stark shift, and find good agreement with our experimental results.

High-accuracy numerical results are shown which go against current conjecture that dimensionless finger width λ in the Saffman-Taylor problem is a monotonically increasing function of dimensionless surface tension τ, asymptotically approaching 1/2 as τ→0. Specifically, quasi steady-state fingers are shown for finite τ with λ significantly below 0.5. These solutions are consistent with published experimental results obtained in a Hele-Shaw cell, indicating that the Saffman-Taylor equations are sufficient to explain this phenomenon.

The distribution function for ripple-trapped particles has been found in a series form valid for all low collision frequencies, for standard and transport-optimized stellarators. The diffusion coefficient obtained with this distribution function shows excellent agreement with the results of Monte Carlo and Fokker-Planck computer codes, in the cases studied.

We present the results of the first molecular-dynamics simulations of a molecular liquid, namely a system of prolate hard ellipsoids of revolution, near the isotropic-nematic liquid-crystal phase transition. Collective rotational motion in the isotropic phase slows down on approach to the transition. It is found that the most important contribution to the rotational slowing down is due to static correlations as measured by the Kirkwood factor ${\mathrm{g}}_2$. The results suggest that the dynamics factor ${\mathrm{j}}_2$, which occurs in the hydrodynamical theory of collective reorientation, is small and negative.

We have measured the mobility of electrons above ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ films condensed on a solid hydrogen substrate. Oscillations in the mobility as a function of film thickness indicate substantial layerwise adsorption of the films up to nine atomic layers. Superfluid and normal films show similar behavior.

Series of sharp optical-absorption lines around 2000 ${\mathrm{cm}}^{\mathrm{-}1}$ in GaAs, 2300 ${\mathrm{cm}}^{\mathrm{-}1}$ in InP, and 2200 ${\mathrm{cm}}^{\mathrm{-}1}$ in GaP are reported. They are shown to be due to the vibration of As—H or P—H bonds, the hydrogen sitting near a transition-metal impurity or other defect. The ‘‘chemical shift’’ of the line is characteristic of the impurity or defect. A model of these centers is proposed.

Analysis of Monte Carlo enumerations for diffusion on the fractal structure generated by the random walk on a two-dimensional lattice allows us to predict a behavior 〈r〉∼${\mathrm{n}}^{\nu }$(lnn${)}^{\mathrm{\alpha }}$ with ν=0.325±0.01 and α=0.35±0.03. This leads to the conjecture that ν=α=(1/3). This value of ν, and the presence of logarithmic corrections, are strongly supported by heuristic arguments based on Flory theory and on plausible assumptions. Evidence for the validity of these assumptions and the Flory approach is coming from remarkably successful applications in related problems.

Raman scattering from acoustic phonons in Si-${\mathrm{Ge}}_{\mathrm{x}}$${\mathrm{Si}}_{1\mathrm{-}\mathrm{x}}$ Fibonacci superlattices is reported. The main features of the experimental results are determined by the Fourier components of the dependence on position along the growth direction of the photoelastic coefficient. An analytic expression for the Fourier transform of any function of position in a Fibonacci lattice is used to interpret the experimental results.

An ab initio total-energy approach to molecular dynamics and simulated quenching is applied for the first time and used to study the structure of the Ge(100) surface. The geometry of the lowest-energy c(4×2)-symmetry dimer model is predicted. A soft energy surface for displacement of dimers in the [11¯0] direction is discovered which could lead to a new type of symmetry breaking.