A high-resolution Raman investigation is presented of the linewidth of the $J=2\mathrm{}$ rotons in solid $p-{\mathrm{H}}_2$ measured by means of a tandem interferometer-monochromator. The magnitude of the linewidths (≅ 0.08 ${\mathrm{cm}}^{-1\mathrm{}}$) at extremely low $o-{\mathrm{H}}_2$ concentration is in good agreement with a recent microscopic calculation, but a variation of the experimental widths by a factor of 2 was observed for different $\left|M_J\right|$. The dependence of the roton linewidth on the concentration of $o-{\mathrm{H}}_2$ impurities is found to be linear, indicating that the $o-{\mathrm{H}}_2$ act as noninteracting random scattering centers.

Magnetization measurements have been made on an insulating random mixture, ${\mathrm{Fe}}_{0.5}$${\mathrm{Mn}}_{0.5}$Ti${\mathrm{O}}_3$. An Ising spin-glass behavior has been observed below $T_g=21.1\mathrm{}$ K. It is shown that the time-dependent phenomena are well characterized by an algebraic function with the exponent described by an exponential function of temperature. The results are compared with the computer-simulation results obtained by Ogielski. In addition, we suggest the existence of a thermodynamic equilibrium state in magnetic fields.

We report the first study of optical-emission properties associated with interface-state formation for metals on III-V semiconductor surfaces. Cathodoluminescence spectroscopy reveals discrete levels distributed over a wide energy range and localized at the microscopic interface. Our results demonstrate the influence of the metal, the semiconductor, and its surface morphology on the energy distributions. Evolution of spectral features with interface formation, particularly above monolayer metal coverage, is correlated with Fermi-level movements and Schottky-barrier heights.

A simple model is used to calculate the phase behavior of microemulsions. The surfactant film at the oil-water interface is treated as an incompressible layer whose bending constant is renormalized by thermal fluctuations. Two- and three-phase equilibria involving upper-, lower-, and middle-phase microemulsions are found. The structure of the middle phase is characterized by the persistence length of the film, beyond which the bending constant is renormalized to smaller values.

Spacecraft observations of the interplanetary magnetic field at 1 AU (astronomical unit) are shown to have frequency spectra with a $\frac{1}{f}$ dependence in the range 2.7 × ${10}^{-6\mathrm{}}$ to 8.0 × ${10}^{-5\mathrm{}}$ Hz. We suggest that the $\frac{1}{f}$ spectrum results from the superposition of uncorrelated samples of solar surface turbulence that have log-normal distributions of correlation lengths corresponding to a scale-invariant distribution of correlation times over an appropriate range of parameters.

Many precipitation patterns are associated with the formation of a sparingly soluble product at a moving reaction front. This paper describes a model which describes the transport, reaction, nucleation, and droplet-growth kinetics of the processes involved. It is established that the rapid change in the nucleation rate as a function of the supersaturation is essential for pattern formation. The model allows us to correlate details of the patterns with the various kinetic processes.

We present theoretical arguments (using mean fields and strong-coupling graphs) for a line of first-order phase transitions in the three-dimensional $\mathrm{XY}$ model with the mixed action $\beta cos\left({\nabla }_i\theta \right)+\gamma cos\left(2\mathrm{}{\nabla }_i\theta \right)$, where $\gamma \in \mathrm{}(0.35,0.40)\mathrm{}$, and verify its existence by a Monte Carlo simulation.

We show that Witten's open-bosonic-string field-theory action and a closed-string analog can be written as a purely cubic interaction term. The conventional form of the action arises by expansion around particular solutions of the classical equations of motion. The explicit background dependence of the convential action via the Becchi-Rouet-Stora-Tyutin operator is eliminated in the cubic formulation. A closed-form expression is found for the full nonlinear gauge-transformation law.

The low-energy limit of superstring theory admits certain new quarks and scalar bosons. Their interaction with the known quarks may lead to a significant enhancement of the $\Delta I=\frac{1}{2}$ amplitude in weak decays.

A modification in the (harmonic) kernel of a QCD-oriented Bethe-Salpeter equation known for good fits to $q\overline{q}$ and $\mathrm{qqq}$ spectroscopy gives a comprehensive description of $q\overline{q}$, $Q\overline{q}$, and $Q\overline{Q}$ systems. The new assumptions are (i) proportionality of the "reduced" spring constant ${\tilde{\omega }}^2$ to ${\alpha }_s$ (${\tilde{\omega }}^2={\omega }_0^2{\alpha }_s$) and (ii) the replacement $r^2\to \frac{r^2}{{(1+A_0{m}_1{m}_2{r}^2)}^{\frac{1}{2}}}-\frac{c_0}{{\omega }_0^2}$. These provide a more direct QCD motivation for confinement and effect a smooth transition from harmonic ($q\overline{q}$) to linear ($Q\overline{Q}$) confinement.

We show that the hadronic decays of the $W$ gaugino ($\tilde{W}$) and $Z$ gaugino ($\tilde{Z}$) produced via each of the processes $W\to \tilde{W}\tilde{\gamma }$, $W\to \tilde{W}\tilde{Z}$, and $Z^0\to \tilde{W}\tilde{W}$ lead to a substantial rate for monojet and dijet + missing $p_T$ at the CERN collider. If the latter two decays are kinematically allowed, one should expect a comparable number of spectacular dilepton and trilepton events with little hadronic activity. In addition, there would also be jet + lepton + missing-$p_T$ signals. Absence of such signals could lead to the most stringent direct experimental limits on $\tilde{W}$ and $\tilde{Z}$ masses currently possible.

The ratio $R_{\nu }$ of the neutral- to charged-current cross sections of neutrinos in iron has been measured in an exposure of the CERN-Dortmund-Heidelberg-Saclay neutrino detector to a 160-GeV/c neutrino narrow-band beam at the CERN Super Proton Synchrotron. The result is $R_{\nu }=0.3072\mathrm{}\pm 0.0025\left(\mathrm{stat}\right)\pm 0.0020\left(\mathrm{syst}\right)$, for hadronic energy greater than 10 GeV. The electroweak mixing parameter is ${sin}^2{\theta }_W=0.225\mathrm{}\pm 0.005\left(\mathrm{expt}\right)\pm 0.003\left(\mathrm{theor}\right)+0.013(m_c-1.5\mathrm{} \frac{\mathrm{GeV}}{c^2})$, where $m_c$ is the charm-quark mass.

The dependence of collective nuclear flow on multiplicity and beam energy for Ca+Ca, Nb+Nb, and Au+Au collisions has been measured with the Plastic Ball detector at the Bevalac. Event by event the data are analyzed with the transverse-momentum method and a new quantitative measure of the flow effect is extracted. It is expected that comparison of the present systematic results with model calculations will lead to a more precise determination of the nuclear-matter equation of state.

We report the measured and calculated photoionization cross section of the excited $5d$ electron in neutral barium. The measurement and a local-density-based random-phase-approximation calculation show resonance enhancement of the $5d$ cross section when the $4d$ ionization channel opens. There is good agreement between the theory and experiment over a broad energy range.

We show that the optical Earnshaw theorem does not always apply to atoms and that it is possible to confine atoms by spontaneous light forces produced by static laser beams. A necessary condition for such traps is that the atomic transition rate cannot depend only on the light intensity. We give several general approaches by which this condition can be met and present a number of specific trap designs illustrating these approaches. These traps have depths on the order of a kelvin and volumes of several cubic centimeters.

We report the first observation of optically trapped atoms. Sodium atoms cooled below ${10}^{-3\mathrm{}}$ K in "optical molasses" are captured by a dipole-force optical trap created by a single, strongly focused, Gaussian laser beam tuned several hundred gigahertz below the $D_1$ resonance transition. We estimate that about 500 atoms are confined in a volume of about ${10}^3$ μ${\mathrm{m}}^3$ at a density of ${10}^{11}$-${10}^{12}$ ${\mathrm{cm}}^{-3\mathrm{}}$. Trap lifetimes are limited by background pressure to several seconds. The observed trapping behavior is in good quantitative agreement with theoretical expectations.

Energy-loss straggling values have been measured for low-velocity ($\frac{E}{M}=16\mathrm{}$ keV/u) ions, $9<~Z_1<~21$, transmitted through carbon foils. A comparison of these data with ion-induced Auger-electron yields for the same collision systems suggests a contribution to electronic-energy straggling arising from electron promotion.

The ultrafast relaxation in solution of two large organic molecules, malachite green and nile blue 690, has been investigated with the equal-pulse correlation technique. In addition to previously known picosecond processes, we have observed fast initial exponential decays (less than 100 fs) and damped sinusoidal oscillation over intermediate time delays. We believe that the latter behavior, the first such decay observed on a femtosecond time scale for any material, represents quantum beats.

Phase turbulence—a phenomenon associated with the time evolution of extended spatial patterns—is investigated on the basis of the Kuramoto-Sivashinsky equation. The turbulent behavior may be thought of as disorder of a primary cellular pattern and described by hydrodynamic analysis of slow modes. Such an approach explains qualitatively the spatial fluctuation spectrum. It also suggests that the ordering of the system into a linearly stable cellular state is inhibited and the lifetime of the turbulent state grows exponentially with the size of the system. This anomalous glasslike relaxation was observed in a numerical simulation.

The $\mathbf{E}\times \mathbf{B}$ rotation and associated collisional ion heating of noble-gas magnetized plasmas are investigated with high resolution by means of laser-induced fluorescence and electrical probes. Plasma rotation results from a radial potential gradient which can be controlled by biasing of the discharge electrodes. The time and space evolution of the potential, the rotation velocity $v_{\theta }$, and the ion perpendicular temperature indicate that heating is due to the randomization of $v_{\theta }$ by ionneutral collisions, and leads to temperature increases as high as a factor fo 50 over initial values.