Cross-field transport of test ions is investigated in a linear Q-machine plasma. Test particles are created and followed in their motion by an optical tagging diagnostic scheme. Diffusion is demonstrated to be supported by classical mechanisms. When different noble buffer gases are injected, the plasma reacts in such a way that the diffusivity remains classical but its magnitude is considerably reduced.

We have developed a microscopic theory which describes the orientational dynamics of ${\mathrm{C}}_{60}$ molecules in the face-centered-cubic phase of ${\mathrm{C}}_{60}$ fullerite. The molecular interaction potential and the crystal-field potential are formulated in terms of symmetry-adapted rotator functions. The phase transition to the Pα3¯ structure is driven by an active multipolar of ${\mathit{T}}_{2\mathit{g}}$ symmetry belonging to the l=10 manifold. The Birman criterion is satisfied. The transition is found to be of first order.

We present here direct calorimetric evidence for a new transition at ${\mathit{T}}^{\mathrm{*}}$=22.25 K in the metallic state of quasi-2D organic superconductor β-(BEDT-TTF${)}_2$${\mathrm{I}}_3$ at ambient pressure, as suggested by our previous measurement of the temperature-dependent Hall coefficient ${\mathit{R}}_{\mathit{H}}$(T). The apparent reduction in the effective electronic density of states at ${\mathit{T}}^{\mathrm{*}}$ quantitatively explains for the first time the suppression of ${\mathit{T}}_{\mathit{c}}$ from the pressure-stabilized ‘‘high-${\mathit{T}}_{\mathit{c}}$’’ value of 8 K to the ambient-pressure cooled ‘‘low-${\mathit{T}}_{\mathit{c}}$’’ value of 1.5 K.

Electrical conductivities were measured for liquid ${\mathrm{D}}_2$ and ${\mathrm{H}}_2$ shock compressed to pressures of 10–20 GPa (100–200 kbar), molar volumes near 8 ${\mathrm{cm}}^3$/mol, and calculated temperatures of 2900–4600 K. The semiconducting energy gap derived from the conductivities is 12 eV in good agreement with recent quasiparticle calculations and with oscillator frequencies measured in diamond-anvil cells.

A simple acceleration algorithm for Ising systems with conserved magnetization (model B) is presented. The dynamical critical exponent and the domain growth exponent in spinodal decomposition are found to be equal to those observed for model A systems with no conservation law. Our results demonstrate that systems with global conservation laws are in the same dynamical universality class as systems with no conservation laws.

A system for simultaneously measuring the heat capacity and in-plane density of free-standing liquid-crystal films as a function of temperature has been developed. Measurements of two-layer films of the compound 3(10)OBC near the smectic-A–hexatic-B transition have been completed. The results do not support the existing 2D-XY theoretical model that supposedly describes this transition.

We study a two-dimensional nonlinear evolution equation which describes the three-dimensional spatiotemporal behavior of the air-liquid interface of a thin liquid film lying on the underside of a cooled horizontal plate. We show that the equation has a Liapunov functional and exploit this fact to demonstrate that the Marangoni effect can stabilize the destabilizing effect of gravity (the Rayleigh-Taylor instability) allowing for the existence of stable localized axisymmetric solutions for a wide range of parameter values. Various properties of these structures are discussed.

Laser-induced surface disordering of Pb(110) is studied using reflection high-energy electron diffraction with 180-ps time resolution. By monitoring the time-dependent modulation of the diffraction streak intensity, information is obtained on the time scales for the disordering of the first few atomic layers and the regrowth of crystalline order at the surface. These are determined to be reversible within the time resolution of our experiment.

We present a dynamical-stochastic scheme to determine from first principles the structure of low-symmetry atomic systems. The method is based on Langevin molecular-dynamics and quantum-mechanical interactions derived from self-consistent local-density-functional calculations. It can be used for insulating as well as metallic and charged systems. Here we examine small neutral and charged Si clusters, and show that the ground-state structures can be efficiently obtained with this approach.

We present a new model describing strongly correlated electrons on a general d-dimensional lattice. It is an extended Hubbard model and it contains the t-J model as a special case. The model naturally describes local electron pairs, which can move coherently at arbitrary momentum. By using an η-pairing mechanism we can construct eigenstates of the Hamiltonian with off-diagonal long-range order. In the attractive case the exact ground state is superconducting in any number of dimensions. On a one-dimensional lattice, the model is exactly solvable by Bethe ansatz.

We show that the effects of spin-orbit interaction in disordered conductors are manifestations of the Aharonov-Casher effect in the same sense as the effects of weak magnetic fields are manifestations of the Aharonov-Bohm effect. We propose that, in semiconducting samples, conductance oscillations should occur due to the Aharonov-Casher effect, whose observation would constitute a thousandfold improvement in its measurement. As in the disordered Aharonov-Bohm effect, these oscillations have half the period expected from the conventional Aharonov-Casher effect.

We show that the dynamics of both switching and nonswitching charge-density waves can be described by the classical Fukuyama-Lee-Rice model when the effects of normal carriers (present for T>0) are properly taken into account. We have constructed a circuit representation of the model and have performed numerical simulations in one dimension. We find switching in the limits of strong pinning or large normal-carrier resistance, consistent with experiment.

We show that thermal modulation of the spin density is determined primarily by the defect correlation energy in intrinsic amorphous semiconductors, and is fairly insensitive to Fermi level position. We present temperature-dependent electron-spin-resonance (ESR) measurements for intrinsic hydrogenated amorphous silicon indicating a correlation energy of about 0.3 eV in low-defect-density material. We discuss the previous interpretation of depletion-width-modulated ESR in intrinsic a-Si:H as indicating a correlation energy of 0.0 eV.

We consider the overdamped ac-driven dynamics of an incommensurate one-dimensional array of coupled oscillators in a spatially periodic substrate potential (Frenkel-Kontorova model) by means of molecular-dynamics simulations. The ac steady-state trajectories are described by a two-dimensional hull function which, as the strength of the substrate potential varies, undergoes a transition by the breaking of analyticity. This critical behavior is macroscopically observed as the appearance of Shapiro steps in the response function.

A prehistory problem is formulated for large occasional fluctuations in noise-driven systems. It has been studied theoretically and experimentally, thereby illuminating the concept of optimal paths and making it possible to visualize and investigate them. The prehistory probability distribution measured for a white-noise-driven system, taken as an example, is shown to be in agreement with the theory.

We report a numerical study of near-integrable Hamiltonian systems with many degrees of freedom. Recently reported transition phenomena for a coarse discrete sine-Gordon system are reexamined in the near-integrable limit and with the aid of statistical and integrable diagnostics. We show that the critical energy of transition from recurrence to chaotic transport of energy coincides with the onset, in the initial data, of integrable exponential instabilities and associated homoclinic orbits. This Letter aims to tie together classical and recent numerical experiments and theory of lattice instabilities and integrable systems.

We consider polynomials of high degree with random coefficients which appear in the context of ‘‘quantum chaotic’’ dynamics and investigate various conditions under which their roots tend to concentrate near the unit circle in the complex plane. Correlation functions of roots are computed analytically. We also investigate a certain class of random polynomials whose roots cover, in a uniform way, the Riemann sphere. Special emphasis is devoted to the influence of symmmetries.

We analyze a model of globally coupled nonlinear oscillators with randomly distributed frequencies. Twenty-five years ago it was conjectured that, for coupling strengths below a certain threshold, this system would always relax to an incoherent state. We prove this conjecture for the system linearized about the incoherent state, for frequency distributions with compact support. The relaxation is exponentially fast at intermediate times but slower than exponential at long times. The decay mechanism is remarkably similar to Landau damping in plasmas, even though the model was originally inspired by biological rhythms.

We present a measurement of the cross section for production of isolated prompt photons in p¯p collisions at √s =1.8 TeV. The cross section, measured as a function of transverse momentum (${\mathit{P}}_{\mathit{T}}$), agrees qualitatively with QCD calculations but has a steeper slope at low ${\mathit{P}}_{\mathit{T}}$.

Using $4\pi$ data from the Bevalac streamer chamber, we study azimuthal correlations for fragment pairs and higher-order multiplets. We point out that previous studies of sideward flow have not ruled out the possibility that the effect is dominated by a small number of correlated fragments in each event, as opposed to being a collective motion to which most or all fragments contribute. Based on a simulation, we infer that more than 70% of the forward-going fragments from collisions of Ar on Pb at 0.4A GeV carry a component of the collective motion.