Dynamic and static light scattering results are reported for isobutyric acid and water in a 4 wt. % silica network with a crossover length of 300 Å. In the one-phase region, well away from the critical point, the decay rate for order parameter fluctuations is unaffected by the network. Near the critical point, the order-parameter correlation function is well fitted by the sum of an exponential with decay rate ${\mathrm{\Gamma }}_1$ and a term of the form exp[ln(τ/${\mathit{t}}_0$)/ln(${\mathrm{\Gamma }}_2$${\mathit{t}}_0$)${]}^3$, with ${\mathrm{\Gamma }}_2$≃${\mathrm{\Gamma }}_1$. When the system reaches conditions where the correlation length of the pure system is ∼100 Å, it spontaneously orders.

Time-domain light scattering experiments on ps-μs time scales have been conducted on a concentrated aqueous LiCl solution. Analysis of mechanical and electrical modulus spectra confirms some results of mode-coupling theory: Simple scaling for α peaks and property-independent power laws. This is made without any assumptions about the data which are not derived from theory. A new characteristic time scale, reflecting the short- and intermediate-range ordering dynamics, is also observed.

A three-dimensional model for particle-size segregation by shaking has been developed and used to study the upward motion of a large sphere in a random packing of smaller spheres. In this model segregation occurs only for values of the diameter ratio (Φ) above a critical value ${\mathrm{\Phi }}_{\mathit{c}}$≃2.8. The ratio of the upward velocity of the large particles to their diameter is greatest for values of Φ just larger than ${\mathrm{\Phi }}_{\mathit{c}}$. The simulation results can be understood in terms of a simple theoretical model that becomes exact in the limit Φ→∞.

We consider a dilute hard-sphere Bose gas in random external potentials at low temperatures, in D=3, using the technique of pseudopotentials and the Bogoliubov transformation. At absolute zero, the random potentials can deplete the Bose condensate, though not completely. On the other hand, they generate an amount of normal fluid equal to 4/3 the condensate depletion. This is a localization effect that can destroy superfluidity at absolute zero. General features of the superfluid density in the neighborhood of this transition point agree qualitatively with experimental results on helium in porous media.

We present the first ab initio determination of the surface structure and electronic properties of Ge(111)c(2×8). New features emerge, in addition to the basic adatom–rest-atom architecture. In agreement with LEED, which shows weak but nonvanishing quarter-order reflections, we find that an asymmetry is present in the surface unit cell, related to a small buckling between the two rest atoms, as well as to in-plane asymmetries of the rest atoms, adatoms, and first bilayer atoms. This inequivalance also produces a splitting of both the rest-atom and the adatom dangling-bond states, which explains the difference in their apparent heights as seen recently with scanning tunneling microscopy.

The melting of butane and hexane monolayers adsorbed on a graphite basal-plane surface has been studied by molecular-dynamics simulations and experimentally by neutron diffraction. The simulation results are qualitatively consistent with the observed diffraction patterns and suggest a general mechanism for melting in monolayers of flexible rod-shaped molecules. Melting requires the formation of vacancies in the monolayer by molecular motion perpendicular to the surface. This ‘‘footprint reduction’’ mechanism implies that strictly two-dimensional theories of melting are inapplicable to these systems.

A model for the surface reaction A+B→AB with B desorption exhibits a continuous irreversible phase transition from an A-poisoned state to a reactive regime. At criticality, an empty patch embedded in the poisoned state spreads on the sample following a random-walk diffusion behavior. So, a relationship between dynamic exponents of the reaction process, the random-walk exponent, and the fractal dimension of the substrate is conjectured and tested.

Electrical resistivities of heavily doped polyacetylene and polypyrrole exhibit a wide range of temperature variation as a function of the degree of disorder. Thermal activation behavior is found for the strongly disordered state, while a weak temperature dependence down to the mK region is found for the weakly disordered state. In the intermediate region we found the resistivity represented by a logT dependence, in a manner similar to amorphous metals. As a cause of the logT dependence, the possibility of scattering via interaction with molecular configurations possessing low-energy internal degrees of freedom is considered.

We have measured recovery of the optical absorption of the EL2 defect under [100] and [111] uniaxial stress during heating of the crystal. The recovery step, occurring at 45 K in n-type GaAs and at 125 K in semi-insulating GaAs, splits into two components under [111] stress, and no splitting is observed under [100] stress. A fraction of centers recovering at lower temperature can be altered by excitation of metastability with polarized light or by excitation under stress. These results indicate that EL2 in the metastable state is trigonally distorted from the tetrahedral symmetry of the ground state.

The modulus and phase of the complex third-order nonlinear optical (NLO) susceptibility χ${\mathrm{̃}}^{\mathrm{}\left(3\right)\mathrm{}}$(-3ω;ω,ω,ω) have been measured on an all-trans silicon polymer, poly(dihexylsilane), over a wide photon energy range. Several distinct structures observed in the χ${\mathrm{̃}}^{\mathrm{}\left(3\right)\mathrm{}}$ spectra are in excellent agreement with the theoretical results of a one-dimensional (1D) exciton model. Important aspects of the 1D Wannier-like exciton structure in polysilanes are elucidated in relation to the NLO processes.

We investigate the edge-state spectra of two-dimensional quantum dot arrays (QDA’s) in transverse magnetic fields, and the manifestation of the edge states in lateral quantum transport. We show the edge states to be superpositions of normal and counterrotating currents. A Büttiker-Landauer transport analysis of this physical picture predicts positive and negative Hall conductances, quantized in integer and fractional multiples of ${\mathit{e}}^2$/h, for QDA’s connected to ideal reservoirs. The predicted fractions differ in value and origin from the usual fractional quantum Hall effect.

The phase diagram of superconducting ${\mathrm{UPt}}_3$ is investigated within a Ginzburg-Landau theory that uses a complex two-component vector order parameter. For fields both along the c axis and in the basal plane, the theory allows for a kink in ${\mathit{H}}_{\mathit{c}2}$(T), but the inner lines may not be true phase boundaries. For basal plane fields, an additional transition is predicted at which a magnetization transverse to the field develops. For otherwise-oriented fields, there is no kink in ${\mathit{H}}_{\mathit{c}2}$. The nature of the order parameter in the various phases is determined.

The superconducting critical temperature ${\mathit{T}}_{\mathit{c}}$ of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{\mathit{x}}$ single crystals (6.35≲x≲7) has been measured resistively as a function of pressure P (0≤P≲20 kbar). The initial rate ${\mathit{dT}}_{\mathit{c}}$/dP exhibits three distinct regimes, a narrow plateau near x≊7 with ${\mathit{dT}}_{\mathit{c}}$/dP≊0.04 K/kbar, a plateau in the range 6.4≲x≲6.8, where ${\mathit{dT}}_{\mathit{c}}$/dP≊0.43 K/kbar, and a maximum value ∼0.8 K/kbar at x≊6.35. An analysis of the ${\mathit{T}}_{\mathit{c}}$(x,P) data using a phenomenological model yields a pronounced peak near x=6.8 in dΔ${\mathit{n}}_{\mathit{h}}$(x)/dP, where Δ${\mathit{n}}_{\mathit{h}}$(x) is the change in the hole density in the ${\mathrm{CuO}}_2$ planes relative to the value corresponding to the fully oxygenated sample.

The zero-field free induction decay of solid ammonium perchlorate at 1.5 K has been directly detected with a dc superconducting quantum interference device. The Fourier-transform spectrum consists of three sharp lines at 17.4, 38.8, and 56.2 kHz arising from pure ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ nuclear quadrupole resonance transitions. The absence of splittings and resonance transitions from dipolar-coupled proton spins is attributed to reorientation of the ammonium groups by quantum tunneling in combination with motional averaging in the three proton levels characterized by the irreducible representation T. The measured ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ spin-spin relaxation time is 22±2 ms and the spin-lattice relaxation time is 63±6 ms.

Small angle neutron scattering experiments were carried out on a charged stabilized dense colloidal suspension to observe changes in lattice structure as a function of shear rate. It is shown that (1) the lattice will evolve from a crystalline state in equilibrium to a polycrystalline state if subjected to a very low shear; and (2) as the shear is increased, partial order is reestablished with the apparent appearance of sliding layer flow. The transitions are reversible. The first transition occurs when the dynamic yield stress is exceeded; the second is discontinuous and is associated with an anomalous flow region in which the stress decreases with increasing shear rate.

In the linear regime close to equilibrium macroscopic transport coefficients can be calculated from the well-known Green-Kubo relations. Recently it has been shown, by Evans, Cohen, and Morriss that even far from equilibrium, bulk thermal transport coefficients can be calculated from the maximal, phase-space, Lyapunov exponents. In the present paper we point out that the Lyapunov exponents themselves can be expressed in terms of time correlation functions that are reminiscent of the Green-Kubo relations for Navier-Stokes transport coefficients.

A set of exactly solvable one-dimensional quantum-mechanical potentials is described. It is defined by a finite-difference-differential equation generating in the limiting cases the Rosen-Morse, harmonic, and Pöschl-Teller potentials. A general solution includes Shabat’s infinite number soliton system and leads to raising and lowering operators satisfying a q-deformed harmonic-oscillator algebra. In the latter case the energy spectrum is purely exponential and physical states form a reducible representation of the quantum conformal algebra ${\mathrm{su}}_{\mathit{q}}$(1,1).

The Van Vleck–Gutzwiller propagator is a fundamental quantity in semiclassical theory whose validity was recently demonstrated to extend beyond the time previously thought feasible, i.e., well past the time after which classical chaos has mixed the phase space on a scale smaller than Plancks’s constant. Little justification was given for this seeming contradiction of the usual vision of semiclassical errors. Though perhaps nonintuitive, we find that standard arguments, properly applied to chaotic dynamics, do explain the long time accuracy.

An interesting two-dimensional model theory has been proposed that allows one to consider black-hole evaporation in the semiclassical approximation. The semiclassical equations will give a singularity where the dilaton field reaches a certain critical value. This singularity will be hidden behind a horizon. As the evaporation proceeds, the dilaton field on the horizon will approach the critical value but the temperature and rate of emission will remain finite. These results indicate either that there is a naked singularity, or (more likely) that the semiclassical approximation breaks down.

We show that measurement of the difference in the transverse energy distribution of leptons and antileptons from tt¯ events at hadron colliders provides an interesting probe of CP violation in the Higgs sector. We predict a CP-violating asymmetry at the ${10}^{\mathrm{-}3}$ level.