The contribution of virtual pions to the total ${\mathit{K}}^{+}$-nucleus cross section in the ${\mathit{p}}_{\mathit{L}}$=450–1000 MeV/c region is found to be about 10%. With this contribution, the data can be explained without the assumption of nucleons ‘‘swelling’’ in the nucleus.

Spectra of energetic protons and deuterons emitted following negative muon capture from rest in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ have been measured for the first time. Significant capture strength is observed at high energy transfers (${\mathit{m}}_{\mathrm{\mu }}$-${\mathit{E}}_{\nu }$>60 MeV) for the two-body and three-body breakup channels, indicative of the importance of nucleon-nucleon correlations and meson exchange currents in the capture process. A simple plane wave impulse approximation calculation reproduces the proton spectrum reasonably well, but underpredicts the deuteron rate at the highest energies by a large factor.

The multiconfiguration Dirac-Fock program grasp has been modified for large-scale, relativistic correlation studies requiring wave-function expansions with several thousand configuration state functions. As a test case, the program was used to study the effects of relativistic correlation on the levels of ${\mathrm{Pr}}^{+3\mathrm{}}$. Our results are in reasonable agreement with experimental data, the lower ${}_{}{}^3{}_{}{}^{}$H and ${}_{}{}^3{}_{}{}^{}$F levels being in good agreement. The previously controversial ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}_0$ term is confirmed by theory for the first time.

Localized traveling-wave trains (LTW) have been observed in various experiments on binary mixture convection. I show that the commonly used complex Ginzburg-Landau equations, which fail to describe a characteristic feature of LTW—their extremely slow drift—break down in these systems and I derive a new set of coupled equations which takes into account the slow dynamics of the concentration field. It possesses slow LTW over a wide range of parameters. In addition, it supports LTW even if it has only real coefficients and is therefore far from the nonlinear Schrödinger limit.

It is now apparent that the two principal models of turbulence (the ‘‘beta’’ and ‘‘lognormal’’ models) and the extremes of a continuous family of (stable, attractive, hence ‘‘universal’’) multifractals characterized by Levy indices α=0 and 2, respectively. Using a technique called double trace moment analysis, and turbulent velocity data, we empirically obtain α≊1.3±0.1: As has long been suspected, turbulence really is ‘‘in between’’ the β and lognormal models. This describes the entire hierarchy of singularities of the Navier-Stokes equations.

A method for conditioning electron beams is proposed to enhance gain in resonant electron-beam devices by introducing a correlation between betatron amplitude and energy. This correlation reduces the axial-velocity spread within the beam, and thereby eliminates an often severe constraint on beam emittance. Free-electron-laser performance with a conditioned beam is examined and analysis is performed of a conditioner consisting of a periodic arry of ‘‘FODO’’ channels and idealized microwave cavitites excited in the ${\mathrm{TM}}_{210}$ mode. Numerical examples are discussed.

A theory is presented for the transport of dust particles in glow-discharge plasmas. The forces which act on the negatively charged dust particles are examined and estimated. The dominant force is shown to be dependent upon the particle size and location within the discharge.

The rate at which the temperatures parallel and perpendicular to a magnetic field relax to a common value has been measured in a pure electron plasma. This rate was measured over the temperature range 28 to ${10}^4$ K and for magnetic fields in the range 30 to 60 kG. When the cyclotron radius ${\mathit{r}}_{\mathit{c}}$ is large compared to the classical distance of closest approach b, the measured rates are described by conventional scattering theory. When ${\mathit{r}}_{\mathit{c}}$/b<1, the measured rate drops precipitously as ${\mathit{r}}_{\mathit{c}}$/b is decreased, in agreement with the adiabatic-invariant theory of O’Neil and Hjorth.

Tunnel-ionized plasmas have been studied through experiments and particle simulations. Experimentally, x-ray measurements show that the plasma temperature is higher for a circularly polarized laser-produced plasma compared to when linear polarization is used. A higher parallel temperature than expected from the single-particle tunneling model was observed through Compton scattering fluctuation spectra. Simulations indicate that stochastic heating and the Weibel instability play an important role in plasma heating in all directions and isotropization.

Fast excited H atoms produced in collisions of fast H atoms with ${\mathrm{H}}_2$ and observed by Doppler spectroscopy and quantitative radiometry are the dominant Hα source in low-current, low-pressure ${\mathrm{H}}_2$ dc discharges. For heavy-metal cathodes, backscattered fast H atoms from incident H and ${\mathrm{H}}^{+}$ atoms and ${\mathrm{H}}_2$ and ${\mathrm{H}}_2^{+}$ molecules excite most of the Hα. For graphite cathodes, backscattering is small and Hα is produced by electrons and by approaching fast H atoms produced by charge transfer in ${\mathrm{H}}^{+}$-${\mathrm{H}}_2$ collisions and dissociation in ${\mathrm{H}}_2^{+}$-${\mathrm{H}}_2$ and ${\mathrm{H}}_2$-${\mathrm{H}}_2$ collisions. Excitation of Hα by ion collisions with ${\mathrm{H}}_2$ and the cathoode is small.

The tunneling microscope is used to excite electron standing waves at the ${\mathrm{NiSi}}_2$Si(111) metal-semiconductor interface. Conductivity mappings show contrast between type-A and type-B domains of nickel disilicide, as well as contrast between domains of type-B disilicide of varying thicknesses. We demonstrate the presence of buried steps, and that these steps can act as diffusion barriers in the reaction that leads to the formation of the nickel disilicide overlayer.

A microscopic model of liquid crystals, with frustrated dipolar, van der Waals, and benzene-ring steric hindrance interactions, yields reentrant phase diagrams with the sequence nematic–smectic-${\mathit{A}}_{\mathit{d}–}$nematic–smectic-${\mathit{A}}_{1–}$smectic-C. The Lindemann criterion of melting is adapted to liquid crystals and Monte Carlo simulation is used. The smectic-${\mathit{A}}_1$ and -C phases occur in two versions, one pointing to in-plane domain formation. Layer tilting is found to be due to permeation-rotation lock-in. The model yields three types of smectic-C phases distinguished by tilt saturation.

Long-wavelength density fluctuations are monitored by small-angle light scattering during the crystallization of hard colloidal spheres. These measurements demonstrate the coupling of the density, a conserved parameter, to the previously measured nonconserved crystal order parameter.

The x-ray standing-wave technique through detection of surface-sensitive Auger electrons has determined the surface reconstruction of clean InP(110). Using the back-reflection diffraction geometry from (220) planes, we find the perpendicular displacements of the surface P and In atoms to be +0.18±0.1 and -0.48±0.08 Å, respectively, from their unrelaxed bulk positions. The use of low-energy x rays combined with a novel method of data analysis opens the general problem of surface reconstruction to study by this technique.

A full-potential version of a recently proposed generalization of the local-density method (LDA+U) is used to study the influence of impurities, lattice, and magnetic relaxation in ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_4$. The carriers form mean-field analogs of Zhang-Rice singlets, which are only slightly affected by impurity and in-plane lattice relaxation effects. On the other hand, an ‘‘anti-Jahn-Teller’’ polaron, characterized by a 0.26 Å shorter Cu to apical-oxygen bond length and triplet spin, is nearly stable. Although the impurity potentials are similar, the self-localization effects are much stronger in ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{NiO}}_4$.

We report the experimental observation of exciton spin relaxation in GaAs quantum wells in moderate magnetic fields. We resolve the electron and hole contributions and discuss the large sensitivity of the spin-relaxation time to exciton localization and quantum well width. We use the long duration of spin orientation to demonstrate deep transient oscillations, resulting from biexcitonic effects.

A direct comparison of quantum Monte Carlo results with experimental values for the charge-transfer gap leads to a set of parameters for the three-band Hubbard model that consistently describes salient features of high-${\mathit{T}}_{\mathit{c}}$ superconductors. The temperature and doping dependence of the normal-state magnetic susceptibility agrees qualitatively with experiments. Furthermore, the interaction vortex for the pairing correlation function in the extended s channel shows a maximum for δ∼20%, resembling the dependence of ${\mathit{T}}_{\mathit{c}}$ on doping.

The weak-localization correction to the conductivity for a strongly anisotropic 2D electron gas is studied in the presence of a magnetic field. We find that the low-field regime with usual negative magnetoresistance is followed by an increase in the localization with a crossover to a 1D regime. In a 3D anisotropic conductor, the magnetic field will induce a transition from a diffusive 3D regine to a localized 2D or 1D regime.

We study the eigensolution statistics of large N×N real and symmetric sparse random matrices as a function of the average number p of nonzero matrix elements per row. In the very sparse matrix limit (small p) the averaged density of states deviates from the Wigner semicircle law with the appearance of a singularity 〈ρ(E)〉∝1/‖E‖ as E→0. A localization threshold is identified at ${\mathit{p}}_{\mathit{q}}$≃1.4 via a simple criterion based on the density fluctuations, and the nearest-level-spacing function P(S) is shown to obey the Wigner surmise law in the delocalized phase (p>${\mathit{p}}_{\mathit{q}}$). Our findings are in agreement with previous supersymmetric and replica theories and studies of the Anderson transition in dilute Bethe lattices.

The ferromagnetically ordered state in the nuclear spin system of silver has been reached at negative absolute temperatures by adiabatic nuclear demagnetization at entropies below 0.82 ln2. The ordering, caused by the antiferromagnetic Ruderman-Kittel interaction, was observed below -1.9 nK as a saturation of susceptibility close to -1 and as an increase of the NMR frequencies. Comparison with recent mean-field calculations by Viertiö and Oja suggests a domain configuration. The phase diagram of silver nuclei at T<0 is outlined in the magnetic field versus entropy plane.