A dynamical theory for the structure functions in convective turbulence at high Rayleigh numbers is presented. A range of scales is identified in which buoyancy forces dominate and the scaling exponents differ significantly from isotropic turbulence. A crossover to Kolmogorov-type scaling is predicted as a function of the Rayleigh number.

A simple model is constructed for the electric fields in the collapsing wave packets found in 3D simulations of driven and damped isotropic strong Langmuir turbulence. This model, based on a spherical-harmonic decomposition of the electrostatic potential, accounts for the distribution of wave-packet shapes observed in the simulations, particularly the predominance of oblate wave packets. In contrast with predictions for undamped and undriven subsonic collapse of scalar fields, oblate vector-field wave packets do not flatten during collapse but, instead, remain approximately self-similar and rigid.

New phenomenology of the chiral nematic (N), smectic-A (A), ferroelectric smectic-C (C) point (NAC) is reported in a binary mixture of two chiral components. We find a tricritical point on the AC phase-transition line which is displaced from the NAC point, and an NA line which is first order. At the NAC point all three transitions (NA,AC,NC) are first order, making it a triple point. The results suggest ways to generate a variety of additional new NAC behavior.

We have studied the dynamic self- and pair-correlation function on appropriately labeled polydimethylsiloxane melts. For small decays of the scattering function or for small values of the Rouse scaling variable both the results for self and pair correlations are in very good agreement with the Rouse model. For larger values, strong deviations from Rouse dynamics are found indicating the importance of topological constraints. However, no indication for the existence of an intermediate length scale corresponding to the tube diameter of the reptation concept is observed.

A computer simulation has been carried out to illuminate atomic processes in the fluorination of a dimerized Si(100) surface. The molecular dynamics utilizes a combination of two-atom interactions to represent the overall system potential energy. Distinctly different outcomes arise from a pair of 130-ps simulations that employ identical initial and boundary conditions. For one of these energy is conserved, the heat released by reaction causes substrate melting, and volatile ${\mathrm{SiF}}_3$ and ${\mathrm{SiF}}_4$ products emerge. The other is nonconservative due to periodic reduction of Si momenta to approximate thermal conduction into a bulk substrate; it just avoids melting, yields a passivated surface with all dangling bonds fluorinated, and fails to produce volatile products.

Using high-resolution low-energy electron diffraction techniques we have observed an increase in step density near 550 K in a stepped Pb(111) surface. At room temperature the Pb(111) surface contained steps with an average terrace width of 63 Å. At 580 K, after the surface reached its maximum roughness, the steps suddenly collapsed and the surface appeared to be extremely flat. A possible explanation of the observed phenomenon is the occurrence of a surface melting phase transition which is induced by the thermally excited high density of steps.

The adsorption probability for NO/Pt(111) is highest for an initial orientation with the N end of the molecule towards the surface. This steric effect in the adsorption brings about a large averaged steric effect in the direct scattering, which is amplified by the fact that the adsorption probability is very high. In case of direct scattering an N-end collision results in a smaller reflection angle than an O-end collision.

We have calculated the stress splitting of the ${\mathrm{A}}_1$→${\mathrm{T}}_2$ optical transition of the neutral ${\mathrm{As}}_{\mathrm{Ga}}$ in the presence of two perturbations, each of which is small compared to the Jahn-Teller relaxation energy. These are (i) a nearby ${\mathrm{As}}_{\mathrm{i}}$ such as has been postulated to be a component of EL2, and (ii) the kinetic energy of the ${\mathrm{As}}_{\mathrm{Ga}}$. The presence of the ${\mathrm{As}}_{\mathrm{i}}$ causes the calculated splitting to be incompatible with what has been observed by Kaminska, Skowronski, and Kuszko. The the extent that those observations have been linked to EL2 by other experiments, this calculation rules out the ${\mathrm{As}}_{\mathrm{i}}$ as a component of EL2.

A model self-energy correction to the local-density approximation is derived from the GW approximation of the self-energy operator. Excitation energies calculated in diamond, Si, Ge, GaAs, and AlAs compare favorably with those obtained with the full GW approximation. Results for GaP are close to experimental data. It is shown that the model consists of a ‘‘scissor’’ operator and additional nonrigid corrections.

We have realized arrays of quantum dots on InSb and observe intraband transitions between their discrete (zero-dimensional) electronic states with far-infrared magnetospectroscopy. In our devices, the number of electrons can be adjusted by a gate voltage and less than 5 electrons per dot are detectable.

We observe the magnetic-field-induced bifurcation of quantum levels into surface states and bulklike Landau States. The disruption of the electric field quantization by a magnetic field is most dramatic for electrons bound in two dimensions perpendicular to the magnetic field. The interplay between competing spatial and magnetic quantization mechanisms results in a pronounced and complex level splitting. The observed splitting of zero-dimensional energy levels depends critically on the size of the quantum dots, and can be explained with a calculated single-particle energy spectrum.

We measured the spatial variation of the probability densities in the first few electron states of a GaAs/${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As quantum well. This result was obtained from the optical determination of the energies of the bound states as a function of the position of a highly localized perturbation, consisting of one isoelectronic substituted cation plane containing either indium (attractive potential) or aluminum (repulsive potential). A series of samples was prepared, each with the probe plane in a different position, scanning thus the whole width of the quantum wells.

A simple analysis is given to ultrathin-film systems. Based on the physical picture proposed that the superconducting-insulating phase transition at T-0 is a combined effect of the pairing and localization in two-dimensional systems, the normal-state sheet resistance is evaluated in the vicinity of the transition. It is found to be universal and equal to h/(2e${)}^2$, independent of the details of different samples as observed in experiments. A similar formulation can be also used to explain the quantized conductance in narrow channels.

The onset of superconductivity in homogeneous ultrathin films is found to occur when their normal-state sheet resistance falls below a value close to h/4$e^2$, the quantum resistance for pairs. The data further suggest that in the T→0 limit such films are either superconducting or insulating. The existence of a threshold in systems which are not granular implies that its explanation involves more general arguments than those which follow from the modeling of films by Josephson-coupled arrays.

We report Bitter-pattern observations of the vortices for flux trapped in crystals of the orthorhombic high-${\mathrm{T}}_{\mathrm{c}}$ superconductor ${\mathrm{Y}}_1$${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$. For B∥c axis, the slight distortion of the vortex lattice yields a penetration-depth anisotropy ranging from 1.11 to 1.15 for different crystals. For B⊥c, the case of strong anisotropy, we observe chains of oval vortices. When they are not aligned by defects, the chains appear to undulate rather than adopt a crystalline habit. From the vortex spacing we deduce an anisotropy of 5.5±1.

We present the first detailed study of a mechanism for high-$T_c$ superconductivity where oxygen-hole pairing is mediated via the exchange of virtual fluctuations of copper electric quadrupole moments. The excitation scale Δ≃0.1–0.5 eV is large enough for high $T_c$, but the interaction is still significantly retarded. This mechanism explains the absence of superconductivity in doped ${\mathrm{La}}_2$${\mathrm{NiO}}_4$, the pressure dependence of $T_c$, and the different character of 60-K and 90-K phases of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ (through filling-dependent gap nodes). Experimental tests of the model are proposed.

We study static vacancies on a 2D Heisenberg spin-(1/2 lattice at T=0, using linear spin-wave theory (LSW) and exact diagonalizaton. Unexpectedly, quantum fluctuations are reduced on neighbors of an isolated vacancy. Two vacancies are attractive, with lowest energy as nearest neighbors. We find LSW to be surprisingly accurate relative to exact diagonalization, both done on a 4×4 lattice. However, LSW on larger systems gives substantial modification of the 4×4 results for binding and ground-state energies, suggesting the need for larger lattices than previously suspected for reliable numerical estimates.

We present a method to study the existence of effective Hamiltonians for lattice, Ising-type model systems with competing dynamics, and find explicit expressions for some relevant nonequilibrium situations. We also define dynamical versions of the random-field and spin-glass models.

We consider intermittency in inverted-pitchfork bifurcation of a 1D dissipative map and of a 2D conservative map. Exact solutions to respective renormalization-group equations are constructed and scaling ratios obtained. The effect of noise is considered and scaling laws in the presence of noise are deduced. Results for the saddle-node bifurcation in 2D area-preserving maps are presented.

We discover a low-energy equivalence between two apparently unrelated Lagrangians with fractional statistics. Exploiting this equivalence, we are able to study the quantum disordered phase of the nonlinear σ model with Hopf term. We find that the quasiparticles in the disordered phase also have fractional statistics. There appears to be a dual relationship between the ordered and disordered phases.