We show that the criticality of integrable lattice models based on the Lie algebras ${\mathit{A}}_{\mathit{n}}$,${\mathit{D}}_{\mathit{n}}$,${\mathit{E}}_{\mathit{n}}$ can be understood as the product of certain numbers of bosonic fields and a generalized parafermionic (fractional spin) theory (GPT). We compute the central charge of the GPT using the thermodynamic Bethe-ansatz approach. For the model associated with the ${\mathit{A}}_2$ Lie algebra, we propose that the associated GPT can be described by a composition of Ising and tricritical-Ising conformal field theories.

In the analysis of background events from a counter-technique experiment to study cosmic-ray nuclei above 8-GV rigidity two events were observed which are consistent with the assumption of Z∼14, A∼350, and 450 MeV/nucleon, and which cannot be acocunted for by more conventional background. Such events may be explained by the hypothesis of strange-quark matter (SQM). It is concluded that the existence of SQM has not been excluded by experiment at a flux level of ∼6×${10}^{\mathrm{-}9}$ ${\mathrm{cm}}^{\mathrm{-}2}$ ${\mathrm{s}}^{\mathrm{-}1}$ ${\mathrm{sr}}^{\mathrm{-}1}$.

Models of a single real symmetric matrix are exactly solved in the scaling limit where the size of the matrix is taken to infinity and a physical cosmological constant is kept fixed. This limit represents the quantization of unoriented surfaces with various kinds of matter content but without surfacelike extrinsic properties.

Neutral excitations present in the repulsive regime of the sine-Gordon or massive Thirring model are studied in the massless limit by extending the thermodynamic Bethe-ansatz analysis to a class of nonreflectionless points. At ${\mathrm{\beta }}^2$/8π=1-1/(p+1) the solitons become infinitely heavy, forcing truncation to the neutral excitations alone. The central change in this limit is calculated to be c=1-6/p(p+1); the mass and S matrices of the truncated theories are identified as those of the minimal conformal theory ${\mathit{M}}_{\mathit{p}}$ perturbed by the ${\mathrm{\phi }}_{\mathrm{}(1,3)\mathrm{}}$ operator, realized in a topological phase of confined kinks.

We have carried out a simulation of quantum chromodynamics using the hybrid-molecular-dynamics algorithm with two flavors of Kogut-Susskind quarks. We have used Kogut-Susskind and Wilson valence quarks to calculate the hadron mass spectrum. Among our extensive results we discuss baryon hyperfine splitting, the nucleon-to-ρ mass ratio, the sclar-to-tensor-glueball mass ratio, and the quantization and susceptibility of the topological charge. We have used a gauge coupling of 6/${\mathit{g}}^2$=5.60, and quark masses ${\mathit{am}}_{\mathit{q}}$=0.025 and 0.01, in generating gauge configurations on ${12}^4$, ${12}^3$×24, and ${16}^4$ lattices.

A measurement of the ${\mathit{K}}^{+}$ total cross sections on carbon and deuterium and their ratios from 450 to 740 MeV/c has been carried out at the Brookhaven Alternating Gradient Synchrotron. The observed ratios depart significantly from those expected from conventional nuclear physics calculations. The data are compared to models of nucleon ‘‘swelling,’’ which ascribe the effect to quark deconfinement or, alternatively, to vector-meson exchange with density-dependent masses.

Two-proton correlation functions measured for the ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$${+}^{27}$Al reaction at E/A=75 MeV are compared to correlation functions predicted for collision geometries obtained from numerical solutions of the Boltzmann-Uehling-Uhlenbeck (BUU) equation. The calculations are in rather good agreement with the experimental correlation function, indicating that the BUU equation gives a reasonable description of the space-time evolution of the reaction.

The first correlation functions from a neutron–light-charged-particle small-angle coincidence measurement are reported for the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$${+}^{27}$Al reaction at E${(}^{16}$O)=215 MeV. Clear evidence for singlet-deuteron and ${}_{}{}^5{}_{}{}^{}\mathrm{He}$ production, and an anticorrelation of low-relative-momentum neutron-dueteron pairs, is observed. The nuclear temperature of 1.6±0.3 MeV, calculated from the ratio of excited-state to ground-state deuteron emission and corrected for sequential emission, is considerably lower than expected.

The intensities of γ transitions from neutron-resonance states in ${}_{}{}^{169}{}_{}{}^{}\mathrm{Er}$ and ${}_{}{}^{178}{}_{}{}^{}\mathrm{Hf}$ to low-lying states with spin 2–5 are shown to depend on the K values of the final states. This K dependence favors a conclusion that the resonance states can also be associated with good K quantum numbers. The results contradicts the hypothesis that K is completely mixed in this energy region, as expected for a chaotic structure.

Infrared fluorescence has been observed from a monolayer of ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}_{}^{16}{}_{}{}^{}$O on NaCl(100) following vibrational excitation of its fundamental absorption band with a pulsed CO gas laser. Direct time-domain measurements of the fluorescence reveal a lifetime of 4.3 ms. Since fluorescence occurs in the overtone region from high vibrational states, these results demonstrate that energy can be stored in the adsorbate long enough to allow vibrational up-pumping between neighboring molecules. It is suggested that the primary channel for CO vibrational relaxation is Δv=-1 transfer to phonons of the NaCl substrate.

Measurements of the spatial and spectral intensity correlation of microwave radiation allow us to identify the leading terms in a perturbation expansion of the correlation function. This function is shown to depend upon two average properties of damped eigenstates of the random medium. These are the average level width δν and the number of eigenstates within the level width δ, whose inverse is the expansion parameter for the correlation function.

The evolution of a magnetic field in a chaotic web is studied. The model flow possessing the web is closely related to the nearly integrable ABC flow with A=B and C≪1. The magnetic diffusivity is taken to be zero and the field is followed using the Cauchy solution. It is found that the flow folds the magnetic field constructively, in the sense that the average magnetic field in a chaotic region grows exponentially in time. This is suggestive of fast dynamo action, although the effect of diffusion of the strong streamwise magnetic field remains to be assessed.

We formulate the statistical mechanics of a two-dimensional inviscid incompressible fluid in a manner which, for the first time, respects all conservation laws. For a special case, we demonstrate that a mean-field theory is exact. A consequence of our arguments is that, in an inviscid fluid evolving from initial conditions to statistical equilibrium, only the energy and certain one-body integrals appear to be conserved. Our methods may be applied to a variety of Hamiltonian systems possessing an infinite number of conservation laws.

We report the observation of saturation with chain length of the second hyperpolarizability of a series of long, well-defined, conjugated oligothiophenes. This saturation occurs at the same length as that of the band gap and of the polarizability, and is attributed to a saturation of the effective conjugation length. Solvatochromic and thermochromic measurements indicate that conformational effects play a role.

The classical theory of laser thermal filamentation in a homogeneous plasma has been extended to include the effects of nonlocal electron heat transport. The new theory reduces the instability threshold and predicts an optimum perturbation wavelength that maximizes the spatial growth. Theoretical predictions suggest that the thermal mechanism, rather than the ponderomotive one, may explain the experimental observation of filaments by Young et al. [Phys. Rev. Lett. 61, 2336 (1988)]. In general, for conditions typical of inertial-confinement fusion, the thermal filamentation instability is expected to dominate.

We have used pulsed NMR to investigate longitudinal spin diffusion and nonlinear spin dynamics in a dilute (350 ppm) spin-polarized (∼60%) solution of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ in ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ at temperatures between 4 and 400 mK. Our results for the spin diffusion are in good agreement with recent theoretical calculations. In addition, we have observed new, extremely long-lived modes in this system that appear to be driven by a nonlinear instability.

The smectic layer displacement fluctuation profile, σ(r)=〈${\mathit{u}}^2$(r)${\mathrm{〉}}^{1/2}$, has been calculated for thin smectic-A films. In thin smectic-A films the calculated fluctuation amplitudes are only σ≊4 Å, compared to σ≊8 Å in a macroscopic sample. The fluctuations are suppressed at the two free surfaces by the surface tension, grow rapidly away from each surface, and have a parabolic profile near the center of the film. These results are in quantitative agreement (±0.1 Å) with recent x-ray measurements.

X-ray diffraction has been used to study the interlayer structure of fluid freely suspended liquid-crystal films versus film thickness. The observed scattering is described extremely well by a simple interlayer density model based on predicted layer fluctuation ${\mathrm{\sigma }}_{\mathit{i}}$ and tilt angle ${\mathrm{\phi }}_{\mathit{i}}$ profiles. The diffraction data determine the individual ${\mathrm{\sigma }}_{\mathit{i}}$’s to about ±0.1 Å, and the layer-fluctuation profiles calculated for the hydrodynamic fluctuations agree to this precision. The tilt profiles calculated using a simple elastic theory are also in excellent agreement with the data.

Atomistic calculations using the Stillinger-Weber interatomic potential show that stress relaxation can lower the energy of a Si(100) stepped surface below that of the flat surface. Two types of elastic interactions are identified: One is due to stress anisotropy which occurs only on single-stepped surfaces and has a logarithmic dependence on ledge separation l; the other is associated with ledge rebonding, present in both single- and double-stepped surfaces, and has a variation of ${\mathit{l}}^{\mathrm{-}2}$. On the vicinal Si(001), single-layer ledges are predicted to be favored over double-layer ledges at low miscut angles with the crossover occurring at about 1° at zero temperature, and at 3° at 500 K, in agreement with experiment.

We have used the tunneling microscope to excite electron standing waves over clean and adsorbate-covered surfaces. For smooth, continuous overlayers we observe a resonance in the conductivity spectra that is absent on the clean surface, over film defects, and over film areas that are rough on a length scale of the electron’s de Broglie wavelength. By making reasonable assumptions of the adlayer thickness and interface scattering strength, the resonance can be modeled by a quantum-size effect in electron transmission through the adlayer.