Diffusion of a passive scalar in a random velocity field v(x,t) is considered. An exact, closed form of the limiting (t→∞) probability distribution of the normalized scalar is derived. The predictions of the theory are compared with the results of numerical simulations.

A theory of probability distributions of temperature in high-Rayleigh-number turbulent Bénard convection is presented.

We present experiments on the effect of a transverse magnetic field (0 to 12 T) on surface discharges (Lichtenberg figures) in different dense gases (${\mathrm{N}}_2$, air, ${\mathrm{CO}}_2$, and ${\mathrm{SF}}_6$). The formation of circular shaped current filaments can be explained by a simple model. The particular dependence of the radius of curvature on the magnetic field observed (R∝${\mathrm{B}}^{\mathrm{-}1.5}$) is thought to be due to local Hall fields. The structure of the discharge pattern can be tuned gradually with increasing magnetic field from a nonbranched, open morphology towards a dense, highly branched structure.

Diabatic potential-energy curves for ${\mathrm{Ar}}^{+}$ and ${\mathrm{Kr}}^{+}$ interacting with a metal surface are reported. At intermediate distances, the attractive force is considerably smaller than the classical result for an ion attracted to its image charge. This has a substantial impact on the dynamics of electronically stimulated desorption, and on the Franck-Condon broadening of photoemission lines. Quantum effects on ion motion are considered, and the validity of a classical treatment is discussed.

High-resolution 4f photoemission spectra from clean W(110) show that the natural lifetime width and the (electron-hole)-pair singularity index are both larger in the first atomic layer than in the bulk. Phonon broadening for the surface and bulk components are smaller than theoretical estimates, and little excess broadening is detected in the surface layer. These findings are very different from the conventional picture of surface-atom core-level line shapes and have implications extending to other systems.

New results of parallel transport effects in a GaAs/AlGaAs superlattice are reported. The observations show a positive magnetoconductivity and a linear variation of the conductivity with temperature. The results are best explained by a recent weak-localization theory which explicitly accounts for the superlattice periodic structure. In contrast, neither the standard three-dimensional anisotropic weak-localization theory nor the two-dimensional one is found to be adequate. This analysis demonstrates the influence of the superlattice structure on parallel charge conduction.

We report a Hall effect and magnetoresistance study of sin- gle crystals of the organic superconductor tetramethyl-tetraselenafulvalinium hexafluorophosphate, (TMTSF${)}_2$${\mathrm{PF}}_6$, under hydrostatic pressure at temperatures down to 0.5 K in magnetic fields up to 25 T. There is clear evidence for a quantized Hall effect, with plateaus labeled by the integers n=5 to 1, up to 17 T. A new field-induced phase transition to a very resistive state occurs at 18 T. We believe that this is the ‘‘n=0’’ spin-density-wave state predicted by the quantized nesting theory.

We have observed remarkably flat Hall plateaus (step ratios . . .5:4:3:2:1) with correspondingly sharp peaks in the magnetoresistance in the Bechgaard salt (TMTSF${)}_2$${\mathrm{PF}}_6$. This highly anisotropic conductor exhibits magnetic-field-induced spin-density-wave (FISDW) states at low temperatures and pressures above about 6 kbar. Unlike previous measurements on similar materials we find almost complete confirmation of the theoretical model for the FISDW transitions, their quantum Hall effects, and the predicted high-field semiconducting state.

We report NMR measurements of the nuclear relaxation rate at all copper and oxygen sites in magnetically aligned powder samples of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$. Comparison of the oxygen and copper relaxation reveals a characteristic temperature greater than $T_c$. The copper relaxation rate is enhanced by antiferromagnetic copper spin fluctuations which are undiminished in the superconducting state. The absence of a coherence peak indicates that the superconductive pairing is not of the conventional BCS type.

The universal anomalies in the normal state of Cu-O high-temperature superconductors follow from a single hypothesis: There exist charge- and spin-density excitations with the absorptive part of the polarizability at low frequencies ω proportional to ω/T, where T is the temperature, and constant otherwise. The behavior in such a situation may be characterized as that of a marginal Fermi liquid. The consequences of this hypothesis are worked out for a variety of physical properties including superconductivity.

We define fractal shot noise, which is a stationary continuous-time process that is fundamentally different from fractional Brownian motion. Two applications in physics are considered: the mass distribution of collections of solid-particle aggregates and the electric field at the growing edge of a doped semiconductor quantum wire. For a broad range of parameters, the amplitude probability density function of this process is a Lévy-stable random variable with dimension less than unity; it therefore does not converge to Gaussian form.

Ising models with correlated or uncorrelated random horizontal bonds are studied for square lattices in zero field. The partition sum is expressed in terms of a one-component field. Griffiths singularities in the free energy as function of temperature are derived. They are log-transforms of certain Lifshitz band tails. Griffiths singularities occur above as well as below the critical temperature.

The string tension is calculated using magnetic monopoles in three-dimensional U(1) lattice gauge theory. The monopoles are identified in configurations of link angles generated in a simulation on a ${32}^3$ lattice. Wilson-loop values are determined by the monopoles’ flux through the loop. The string-tension results are in excellent agreement with a semiclassical analytic formula.

The nature of the finite-temperature deconfining phase transition is studied by Monte Carlo simulation on lattices ranging over $8^3$×4 to ${36}^3$×4. The spatial-volume dependence of the susceptibility and the mass gap strongly support a first-order transition. This is corroborated by an explicit construction of the effective Z(3) spin system whose dominant two-spin couplings are found to be all positive.

Three-jet events produced in $e^{+}$$e^{\mathrm{-}}$ annihilations are used to provide comparisons between quark and gluon jets. Differences between quark-induced and gluon-induced jets are observed. Quark jets tend to have a more tightly collimated structure than gluon jets, which is reflected in the concentration of a larger fraction of the jet’s energy near the jet axis.

A search for a new charge -(1/3 quark has been carried out at the KEK $e^{+}$$e^{\mathrm{-}}$Collider TRISTAN under the assumption of its photonic decay through a flavor-changing neutral current (FCNC). The observed number of multihadronic events with isolated photons is consistent with that expected from the known five quark flavors. Including the usual charged-current decays, limits on the absolute photonic branching ratio and FCNC processes were obtained.

We study effects of instanton-induced quark-quark interactions in baryon spectroscopy and in the baryon-baryon interaction. The quark-cluster model is applied to calculating baryon-baryon interactions. Results are compared with those of the one-gluon-exchange interaction. We propose a new phenomenological model which contains both the instanton-induced interaction and the one-gluon-exchange potential.

We present the first measurements of spin effects in ${\pi }^{+}$ elastic and inelastic scattering from complex nuclei, ${}_{}{}^{15}{}_{}{}^{}$N→${\left(\right(1/2\mathrm{}}^{\mathrm{-}}$) and ${}_{}{}^6{}_{}{}^{}$Li→${(1\mathrm{}}^{+}$). For the case of ${}_{}{}^{15}{}_{}{}^{}$N→, the analyzing power $A_y$ was measured at $T_{\pi }$=164 MeV between 60° and 100°. Although large values of $A_y$ are predicted by theory, the data are consistent with zero. For the case of ${}_{}{}^6{}_{}{}^{}$Li→, the analyzing power ${\mathrm{iT}}_{11}$ was measured at $T_{\pi }$=134 and 164 MeV, between 50° and 110°. Large values of ${\mathrm{iT}}_{11}$ were found at some angles, but the measured angular distributions differ considerably from theoretical predictions.

Using the one-boson-exchange model a relativistic covariant analysis is carried out of the elastic electromagnetic form factors of the deuteron including the ρπγ and ωεγ mesonic-exchange-current contributions. The theoretical predictions are compared with the recent experimental data at high momentum transfer.

We have measured analyzing powers in d(p→,${\pi }^{\mathrm{-}}$pp)p at a beam energy of 400 MeV and laboratory pion detector angles of 35° and 43°. The ${\pi }^{\mathrm{-}}$ and two of the outgoing protons were detected in coincidence in a geometry which selected the quasifree two-body reaction pn→${\pi }^{\mathrm{-}}$pp${(}^1$$S_0$). The analyzing-power data combined with ${}_{}{}^3{}_{}{}^{}\mathrm{He}$(${\pi }^{\mathrm{-}}$,pn)n differential cross sections allow determination of the transition amplitudes. The results indicate a significant contribution from a very short-range part of the nucleon-nucleon interaction.