We propose and test a new molecular-dynamics method to study fragmentation of condensed matter under homogeneous adiabatic expansion. Our atomistic simulations give significant insight into the nature of fragment distributions. We also find that a simple continuum model based on energy balance gives a reasonably good estimate of the average fragment mass.

In periodically driven systems, the intersection of stable and unstable manifolds of saddle orbits forms two distinct (topological) horseshoes: The first horeshoe is associated with the destruction of a chaotic attractor, while the second horseshow creates a new chaotic attractor. A laser model is used to illustrate how sequential horseshoe formation controls the birth and death of chaotic attractors.

A supersymmetric gauge model based on $E_6$ particle content which conserves lepton number but not baryon number is derived from the requirement of a single, simple $Z_2$ discrete symmetry. The proton is stable because no physical final state having zero lepton number is available for its decay. Neutrinos are massless and left-handed as in the standard model or one is massless and left-handed while the other two are massive Dirac particles. Interesting experimental consequences of this model abound. Some are briefly discussed.

A Monte Carlo study is reported of pure SU(3) lattice gauge theory near the color-deconfining phase transition on lattices of size ${16}^3$×$N_T$ with $N_T$=6, 8, and 10. The critical coupling and latent heat per unit volume are deduced for this phase transition: ${\beta }_c$=5.889±0.008, 6.001±0.025, 6.16±0.007, and ΔscrE/$T_c^4$=3.61±0.28, 3.26±0.73, 3.54±1.14 for $N_T$=6, 8, 10, respectively. These errors are statistical only and do not reflect significant systematic uncertainty. For $N_T$=10 we demonstrate that the internal energy can be obtained from Wilson loops larger than the usual 1×1 plaquettes.

The mass of a doubly strange dibaryon called the H particle is calculated in lattice QCD on a ${16}^3$×48 lattice with a renormalization-group–improved gauge action and Wilson’s quark action. We find that the H is below the ΛΛ threshold for strong decay. Furthermore the case where the H is slightly below the NN threshold for weak decay is consistent with our numerical results and is not in conflict with the stability of the nuclei.

We report the results of a search for the leptonic decay ${\mathrm{D}}^{+}$→${\mathrm{\mu }}^{+}$${\nu }_{\mathrm{\mu }}$ using the Mark III detector at the SLAC ${\mathrm{e}}^{+}$${\mathrm{e}}^{\mathrm{-}}$ storage ring SPEAR. A data sample of 9.3 ${\mathrm{pb}}^{\mathrm{-}1}$ collected at the ψ(3770) resonance yields no signal events, corresponding to a 90%-confidence-level upper limit of 7.2×${10}^{\mathrm{-}4}$ on the branching ratio B(${\mathrm{D}}^{+}$→${\mathrm{\mu }}^{+}$${\nu }_{\mathrm{\mu }}$). This represents an upper limit on the pseudoscalar decay constant ${\mathrm{f}}_{\mathrm{D}}$ of 290 MeV/${\mathrm{c}}^2$.

We observe 97 decays of the charmed baryon, the ${\Lambda }_c^{+}$, into a ${\mathrm{pK}}^{\mathrm{-}}$${\pi }^{+}$ final state in a Fermilab photoproduction experiment. The mass is measured to be 2286.2±1.7±0.7 MeV/$c^2$. The positions of the production and decay vertices are reconstructed with the use of silicon microstrip vertex detector. From these measurements, we determine the lifetime of the ${\Lambda }_c$ to be (0.22±0.03 ±0.02)×${10}^{\mathrm{-}12}$ s.

The angular distribution parameter, β, has been measured for the resonant Auger spectra in Kr following 3d→5p excitation. Unusually low values, close to -1, were seen for two bands. From optical spectroscopy data these bands are assigned to the final states 4${\mathit{p}}^4$${(}^3$P)5p${(}^4$${\mathit{P}}_{5/2}$, ${}_{}{}^4{}_{}{}^{}$${\mathit{P}}_{3/2}$, and ${}_{}{}^4{}_{}{}^{}$${\mathit{D}}_{5/2}$). According to angular momentum transfer theory, some of the transitions could be parity unfavored, yielding β values of -1, but additional theory is required for a complete understanding. Implications for angular studies of highly resolved Auger spectra are discussed.

We report a variety of measurements on fluid interface motion through model porous media. The dynamics shares many features with other systems pinned by random fields. Over a range of pressures randomness pins the interface. In this range there are many metastable interface configurations and relaxation is extremely slow. The dc response outside the pinned region is markedly nonlinear. Oscillations in the pressure occur at constant velocity which reflect the pore geometry.

Experiments in the tandem mirror TMX-U reveal three significant sources of nonambipolar radial transport associated with resonant transport in the central cell and, in the end cells, with electron cyclotron heating and neutral beam heating. A simple model suggests that the electron-cyclotron-heating–induced transport is due to the asymmetric application of power. This transport mechanism is important because it applies even in axisymmetric magnetic geometries.

The atomic structure at the epitaxial ${\mathrm{CaF}}_2$/Si(111) interface has been determined by high-resolution electron microscopy. As-grown layers reveal only direct Ca-Si bonding at the interface, with eightfold coordinated Ca atoms. Fluorine is preferentially removed from the interface during a rapid thermal anneal leaving fivefold coordinated Ca atoms. Removal of F results in a dramatic improvement in the electrical properties of the interface. The measured interface state density is reduced from ≳${10}^{13}$ ${\mathrm{cm}}^{\mathrm{-}2}$ to ≲${10}^{11}$ ${\mathrm{cm}}^{\mathrm{-}2}$.

In a simple nonequilibrium statistical mechanics model (two coupled nonlinear stochastic reaction-diffusion equations), self-sustained oscillations appear as a symmetry-breaking effect for the associated probability density. Correlation and response functions are approximately calculated above and below the transition point. Renormalization-group theory yields the leading-order scaling of order parameter, relaxation time, correction to the collective frequency, and correlation length.

We study the low-temperature properties of glasses in a model consisting of elastic dipoles placed randomly in an elastic continuum. We use Monte Carlo annealing to find glassy minimum-energy states and then determine the density of states for small angular oscillations of the dipoles. The coupling of these modes to the phonon strain fields is shown to lead to a frequency-dependent velocity shift and lifetime for the phonons. We find a bump in C/${\mathrm{T}}^3$ and a plateau in the thermal conductivity, in quantitative agreement with experimental data for the orientational glass KBr:KCN.

A new technique for spectroscopic investigation of subsurface interface electronic structure has been developed. The method, ballistic electron emission microscopy (BEEM), is based on scanning tunneling microscopy. BEEM makes possible, for the first time, direct imaging of subsurface interface properties with nanometer spatial resolution. We report on the first application of BEEM to subsurface Schottky-barrier interfaces.

We report the first self-diffusion measurements of elongated micelles in the semidilute regime performed with fringe-pattern photobleaching-recovery techniques. These measurements give evidence for the power-law dependence of the self-diffusion coefficient ${\mathrm{D}}_{\mathrm{s}}$ versus concentration, but polymer models are not adequate. Suggestion is made that such micellar systems behave like ‘‘living polymers.’’

New shock compression data for Al, Cu, and Pb in the pressure range 0.3–1 TPa (3–10 Mbar) have been combined with first-principles theory and earlier equation-of-state data to give the first self-consistent description of the thermodynamic states of metals at ultrahigh pressures. No evidence is found for a break in the slope of the shock Hugoniot of Al near 0.5 TPa, as claimed by Al’tshuler.

A scanning tunneling microscopy (STM) study of the surface of a tetrathiafulvalene-tetracyanoquinodimethane) TTF-TCNQ crystal is described. The surface of this conducting organic molecular crystal is well ordered, with flat terraces separated by steps of a single molecular layer and with periodicity that agrees with the bulk crystal structure. Individual organic molecules at the surface are resolved in the STM images. The principal features of the experimental STM images are reproduced in simulations in which contours of constant electron density are calculated from the molecular orbitals that are involved in conduction.

The stable structures, vibrational modes, and passivation mechanisms of an interstitial hydrogen atom in boron- and phosphorus-doped crystalline silicon are determined by an ab initio pseudopotential method. Our calculated formation energies for passivated H-B and H-P complexes are 2.5 and 2.0 eV, respectively, as compared to a binding energy per H of 1.9 eV in an interstitial ${\mathrm{H}}_2$ molecule. The higher dissociation energy of H-B relative to H-P is consistent with recent experimental observations that show a more pronounced hydrogen passivation for shallow acceptors.

It is shown in Fe/Cu bilayered films that the magneto-optical polar Kerr rotation can be enhanced by an effect of the plasma resonance of the free charge carriers in Cu. The strong enhancement is observed around 560 nm which corresponds to the plasma edge of Cu metal. The magnitude of the Kerr rotation reaches up to above twice as large as that of Fe. This is the first example of substantial enhancement of Kerr rotation without use of the interference effect.

Flux-line-lattice flow has been studied in a novel superconducting device containing straight, nanometer-scale, weak-pinning channels in a strong-pinning environment. The shear strength of a two-dimensional, triangular lattice has been directly probed on length scales of order of the lattice parameter by variation of the magnetic field. Good agreement is found with a continuum-approximation model for shear flow. Unusual oscillations in shear strength and history effects were observed and explained by the (in)commensurability between flux-line lattice and channel.