A new form of the stimulated Brillouin scattering (SBS) instability in laser-produced plasmas is analyzed in the context of recent advances in thermal transport theory. Inverse-bremsstrahlung heating rather than the usual ponderomotive force provides the driving force for the instability. It is found that in low-temperature, high-density, high-Z plasmas this form of the instability dominates and can lead to significantly higher growth rates for SBS.

Energy dispersive x-ray diffraction measurements show that the T phase of ${\mathrm{Nb}}_2$${\mathrm{O}}_5$ becomes x-ray amorphous at a pressure of 19.2 GPa at 300 K. This pressure-induced amorphization is novel since the oxide is simultaneously reduced as it becomes amorphous. The amorphization occurs because the pressure-induced reduction T-${\mathrm{Nb}}_2$${\mathrm{O}}_5$→crystalline ${\mathrm{Nb}}_{12}$${\mathrm{O}}_{29}$ is kinetically impeded. A consideration of the ambient pressure atomic mechanism of the oxidation of ${\mathrm{NbO}}_{\mathit{x}}$ compounds (x<2.5) suggests that the pressure-induced amorphous state is formed by oxygen defects in the T-${\mathrm{Nb}}_2$${\mathrm{O}}_5$ lattice.

Based on the manner in which large Coulomb terms with opposite signs cancel each other at long range, it is proposed that most ionic-crystal surfaces undergo a simple zero-temperature reconstruction, a prediction validated by computer simulation of surfaces in rocksalt-structured materials.

We have made fully ab initio calculations on the energetics of defects in the oxide materials MgO and ${\mathrm{Li}}_2$O using a parallel computing methodology. The calculations, based on density functional and pseudopotential theory, yield results for the formation and migration energies of Schottky defects in MgO and Frenkel defects in ${\mathrm{Li}}_2$O which are in excellent accord with experiment. The work gives new insight into the defect-induced redistribution of valence electrons.

Atomic-force-microscope measurements of the forces on a sharp tungsten tip sliding across silicon substrates coated with perfluoropolyether polymers provide insight into how lubricants function at the molecular level. In particular, hydrodynamic lubrication is observed for tip-substrate separation distances as small as a few polymer chain diameters and a relatively small change in the composition of the polymer, namely, the addition of alcohol end groups, greatly increases the load required to compress and squeeze out the polymers from between the sliding surfaces.

The aggregation of dense colloidal solutions has been investigated by means of low-angle static light scattering. We show that the scattered pattern exhibits a finite-q-vector peak, whose intensity and position ${\mathit{q}}_{\mathit{m}}$ change with time. We find that the intensity distributions scale according to S(q/${\mathit{q}}_{\mathit{m}}$,t)=${\mathit{q}}_{\mathit{m}}$(t${)}^{\mathrm{-}\mathit{d}}$F(q/${\mathit{q}}_{\mathit{m}}$), in agreement with the scaling law for spinodal decomposition. While d=3 for spinodal decomposition, here scaling requires that d=${\mathit{d}}_{\mathit{f}}$, the fractal dimension of the clusters.

We have observed spin-mass vortices (SMV) in superfluid ${}_{}{}^3{}_{}{}^{}\mathit{B}$. The SMV is a combined topological object made up of a vortex line with mass current and a disclination line with spin current. It is also a termination line of a planar defect, the so-called θ soliton. The SMVs are bound either as pairs or to the container wall by the soliton. They are nucleated when a rotating ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ sample cools slowly through the A→B phase transition. The identification of the SMV is based on the NMR signatures of the soliton.

We have investigated the epitaxial growth of Ag(111) by x-ray reflectivity experiments. In the temperature range from 175 to 575 K the growth mode changes gradually from three-dimensional to step flow, but at no temperature was layer-by-layer growth observed. Submonolayer deposits of Sb on the starting surface dramatically alter the growth behavior. With Sb the Ag grows layer by layer over the entire temperature range investigated (225–375 K), resulting in smoother surfaces at the lowest growth temperatures. We propose that Sb decreases the barrier for interlayer diffusion.

Ag-Au(111) superlattices are examined with angle-resolved photoemission. A Shockley-type surface state is observed within a superlattice gap. Varying the location of the terminating (surface) plane within a superlattice period causes this surface state to move across the gap for one half of the period and to disappear for the other half of the period. These observations are in good agreement with theoretical predictions.

A vortex lattice consisting of a pinstripe pattern of vortex chains has been observed in untwinned ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ crystals. This state is present when the field is tilted away from the c^ axis, and is oriented with the chains confined to the plane defined by B and c^. The chains arise from the attractive part of the vortex-vortex interaction in this geometry as described within the ansiotropic London equations. For B>${\mathrm{\Phi }}_0$/2πλ̃ ${}_{}{}^2{}_{}{}^{}$ the chains merge into an oriented vortex lattice. From the fitted value of λ̃, we can conclude that the microscopic irreversibility temperature is T/${\mathit{T}}_{\mathit{c}}$∼0.92 for B∼20 G.

Current-voltage ($I-V$) characteristics were measured for $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ thin films in high magnetic fields and at temperatures well below the superconducting transition temperature. The functional form of the $I-V$ curves is described by $\frac{E}{J\propto \exp }[-{\left(\frac{J_0}{J}\right)}^{\mu }]$, with $E$ the electric field and $J$ the current density. The exponent $\mu$ is 0.19 ± 0.05 for low values of current density and $\mu =0.94\mathrm{}\pm 0.1$ at high values. The results at low current density are characteristic of a vortex glass and constitute the first direct evidence that the low-temperature phase of a disordered superconductor is a vortex glass.

The spin glass susceptibility of ‘‘infinite-range’’ ±J Ising spin glass samples has been measured as a function of sample size and temperature using numerical simulations. A slow-cooling annealing schedule was used. The data indicate that spin glass order appears to set in only at a temperature well below T=1, the accepted theoretical ordering temperature ${\mathit{T}}_{\mathit{g}}$ for the infinite-range Ising spin glass model.

Magneto-optical polar Keer effects in ultrathin bcc Fe(100) films sandwiched by Au layers were investigated in the 1.6–5.3 eV photon energy range at room temperature. A new peak appeared in the off-diagonal conductivity spectrum at around 3.5–4.5 eV for the Fe films thinner than 10 Å. The peak energy is lower for thinner Fe films. The absolute value of ${\mathrm{\epsilon }}_{\mathit{x}\mathit{y}}$ at 3.7 eV in the 3 Å thick Fe film is 2 times as large as that in the bulk Fe.

A surprisingly large isotope effect is observed in nonthermal uv photodesorption of ammonia from GaAs(100). The cross section for ${\mathrm{NH}}_3$ photodesorption is 4 times larger than for ${\mathrm{ND}}_3$, a fact which cannot be explained using existing photodesorption models, e.g., the conventional Menzel-Gomer-Redhead model. We take this as the first evidence for uv-driven photodesorption from electronically quenched, vibrationally excited ground-state adsorbates.

We prove the existence of a first-order, entropy-driven demixing transition in a simple lattice model for a hard-core mixture. The existence of this transition follows from the fact that this lattice model can be mapped onto an Ising model with nearest-neighbor interactions for which the phase behavior is known. The same mapping leads to a very simple interpretation of the entropic contribution of the solvent to the interaction parameter χ in the Flory-Huggins theory of polymer solutions.

The solution of the initial-boundary-value problem of integrabale nonlinear evolution equations, with the spatial variable on a half-infinite line, can be reduced to the solution of a linear intregral equation. The asymptotic analysis of this equation for large t shows how the boundary conditions can generate solitons.

Quantum techniques for key distribution—the classically impossible task of distributing secret information over an insecure channel whose transmissions are subject to inspection by an eavesdropper, between parties who share no secret initially—have been proposed using (a) four nonorthogonally polarized single-photon states or low-intensity light pulses, and (b) polarization-entangled or spacetime-entangled two-photon states. Here we show that in principle any two nonorthogonal quantum states suffice, and describe a practical interferometric realization using low-intensity coherent light pulses.

We show that a large class of Fokker-Planck equations, like the Schrödinger equation, can exhibit a transition in their spectral statistics as a coupling parameter is varied. We assert that this transition is connected to the transition to nonintegrability in a particular set of Hamilton’s equations. In the case of the Schrödinger equation, this transition is known to be a fingerprint of the underlying classical dynamics. However, the Hamilton’s equations describing the transition in the Fokker-Planck spectrum have no direct physical relation to the underlying dynamics of the Fokker-Planck equation, and consequently have no such simple physical interpretation.

General conditions are developed for the formation of naked precursory (‘‘shell-focusing’’) singularities in spherical gravitational collapse. These singularities owe their nakedness to the fact that the gravitational potential fails to be single valued prior to the onset of a true gravitational singularity. It is argued that they do not violate the spirit of cosmic censorship. Rather, they may well be an essentially generic feature of relativistic gravitational collapse.

We emphasize that it is the Pauli metric, not the Jordan metric, which describes the massless spin-two graviton in the Brans-Dicke theory. Similarly in the ‘‘Jordan-Brans-Dicke theory’’ based on Kaluza-Klein unification, only the Pauli metric can correctly describe Einstein’s theory of gravitation. This necessitates a completely new reinterpretation of the ‘‘old’’ Kaluza-Klein cosmology as well as the Brans-Dicke theory. More significantly our analysis shows that the Kaluza-Klein dilaton must generate a fifth force which could violate the equivalence principle.