Deterministic chaos in the intensity of the beam produced by a barium titanate self-pumped phase-conjugate mirror has been observed. The correlation exponent of the strange attractor is found to depend on the crystal orientation and to lie within the range 1.2 to 2.4, and the order-two Renyi entropy is found to increase with increasing laser intensity and to be as large as 22 bits/sec. A standard model of self-pumped phase conjugation due to four-wave mixing has been generalized to include time dependence. This model predicts frequency shifts and chaotic behavior for the reflectivity.

Temporally and spectrally resolved, large-angle Thomson scattering was used to measure the frequency of thermal ion acoustic waves in a plasma in the presence of a high-frequency (${\mathrm{\omega }}_0$>${\mathrm{\omega }}_{\mathrm{pe}}$) laser beam. At high laser intensities (${\mathrm{v}}_{\mathrm{osc}/{\mathrm{v}}_{\mathrm{e}}\mathrm{\gtrsim }4}$), the frequency of the short-wavelength ion acoustic waves (k${\lambda }_{\mathrm{D}\mathit{e}=0.3\mathrm{}\mathrm{-}1.2}$) which propagated parallel to the electric field of the laser (i.e., parallel to the oscillation velocity of the quivering electrons) was observed to be larger than the frequency of those waves which propagated perpendicular to the electric field (anisotropic sound). The measured frequency ratios are found to be in good agreement with the predictions of theory.

The exchange frequency in crystal ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ is calculated from first principles with a combination of path-integral Monte Carlo method and a method used in classical statistical mechanics to determine free-energy differences. The frequency of nearest-neighbor exchange at melting density is 0.46 mK, that of triple exchange is 0.19 mK, and that of four-particle planar exchange is 0.27 mK. These exchange frequencies are within 30% of the values obtained from the empirical multiple-exchange model and agree with measurements. Many other types of high-order cyclic exchanges make significant contributions to thermodynamic properties, showing that ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ is more complex than previously thought.

The growth of dendritic crystals of ${\mathrm{NH}}_4$Br from supersaturated solution has been studied in a way that allows high-resolution measurements of the early stages of side branching. The branches are found to be nonperiodic at any distance from the tip, with apparently random variations in both phase and amplitude. Side branches on opposite sides of the dendrite are imperfectly correlated. The rms side-branch amplitude is an exponential function of distance from the tip, with no apparent onset. The implications of these results for several theories of the stability of growing dendrites are discussed.

We propose a semimicroscopic model for the glass transformation. The long-lived nonequlibrium fluctuations are represented by quenched disorder in an equilibrium ensemble. The model predicts a sharp transition without latent heat. The liquid cannot be supercooled below the glass transition temperature, even though by adjustment of the cooling rate the glassy phase can be obtained at various temperatures. The glass is characterized by local static density fluctuations and a finite zero-frequency shear modulus.

Nonconvex interparticle interactions are proposed as a mechanism for the occurrence of modulated order in condensed matter. This is examined by application of a recent numerical algorithm to two microscopic models in which frustration is present only if the interparticle interactions are nonconvex. A devil’s staircase is found when the particles, in the ground state, make use only of the convex part of the interaction potential, whereas both first- and second-order transitions are found when the region of nonconvexity is felt by some of the particles.

Accurate solutions of the Ginzburg-Landau equations describing the A-B phase boundary for a planar interface between ${}_{}{}^3{}_{}{}^{}\mathit{A}$ and ${}_{}{}^3{}_{}{}^{}\mathit{B}$ are calculated near the tricritical pressure and classified in terms of simple discrete symmetries. The order-parameter components of the A-B phase boundary and the interfacial energy ${\mathrm{\sigma }}_{\mathrm{AB}\left(\mathrm{T}\right)}$ deviate considerably from previous variational calculations.

We report scanning tunneling microscope images of isolated oxygen atoms adsorbed on the GaAs(110) surface. The images display a dramatic voltage dependence, which arises from the energy dependence of the local state density, and provides a signature of an adsorbed electronegative atoms. At low oxygen coverages, a long-range screening of the adsorbed atoms is observed in the surrounding bare surface region, with a characteristic screening length scale of ∼50 Å. .AE

Using molecular-dynamics calculations, we show that at 80 K, ice Ih undergoes a transition to a high-density amorphous (hda) form at about 13 kbar. At higher pressures, the calculated oxygen atom radial distribution function shows strong resemblance to that of ice VIII. The most characteristic feature of hda ice, namely the peak observed around 3.5 Å in the oxygen radial distribution function, is ascribed to molecules occupying interstitial-like sites. On warming of a sample of hda ice recovered at zero pressure, the structure evolves to a lower-density form. These observations are in good accord with available experimental data.

We have prepared and identified as a single phase the high-temperature superconducting compound in the chemical system Y-Ba-Cu-O, an orthorhombic, distorted oxygen-deficient perovskite of stoichiometry ${\mathrm{Ba}}_2$${\mathrm{YCu}}_3$${\mathrm{O}}_{9\mathrm{-}\mathrm{\delta }}$ (δ≃2.1). Samples exhibit zero resistance at 91 K, with a transition width of 1.5 K. The Meissner effect attains a value of 76% of the independently measured diamagnetic susceptibility. We estimate parameters that characterize this superconductor, e.g., γ≃3–5 mJ (mole Cu${)}^{\mathrm{-}1}$ ${\mathrm{K}}^{\mathrm{-}2}$. The critical current density at 77 K and H=0 exceeds 1100 A/${\mathrm{cm}}^2$.

High-intensity femtosecond laser pulses are used to induce non- equilibrium electron heating in gold metal. The thermal relaxation of the electronic distribution is studied through pump and continuum probe measurements of transient reflectivity. Measurements are performed for different heating-pulse fluences and probe-photon energies. The observed reflectivity line shape demonstrates the generation of nonequilibrium electron temperatures which cool to the lattice on a 2–3 ps time scale.

Gas adsorption to particles 7 nm in radius and free from contact with any substrate is measured for the first time. The particles are suspended in He doped with an adsorbing gas of concentration c and the photothreshold change is measured as a function of c. The He does not interfere with adsorption kinetics. For ${\mathrm{O}}_2$ on Ag at 300 K the sticking coefficient α is determined as a function of the coverage θ. In contrast to findings on macroscopic surfaces, the small-particle result is α=${\alpha }_0$(1-θ${)}^2$, indicating simple dissociative adsorption, and ${\alpha }_0$ is very small compared to flat-surface data.

We have measured the emission and capture time of individual electron traps residing within the tunneling barrier of very small-area (<0.05 μ${\mathrm{m}}^2$) Josephson junctions. The voltage-bias dependence of the times is consistent with a simple nonequilibrium model in which the bias enhances the rate for electrons to tunnel into the trap from one side of the barrier and exit out the other. Some junctions show clear evidence of interactions between traps, and for certain bias conditions the noise displays predominantly series kinetics.

The reaction of oxygen on Si(100) surfaces from 700 to 950°C has been studied in real time with about 10-μs resolution, by use of pulsed molecular-beam reactive scattering. The oxygen reaction probability is roughly proportional to the normal component of the incident ve- locity of the ${\mathrm{O}}_2$ molecule. An intermediate step between the initial adsorption of oxygen and the desorption of SiO was observed.

If an accelerator of energetic ions turns on inside a new type II supernova while the shell is sufficiently thick, energetic secondary mesons will be produced by collisions in the expanding shell. These will decay to give rise to neutrinos of energies much larger than the deleptonization and thermal neutrinos emitted during the collapse itself. If the power in accelerated protons is comparable to the optical luminosity, there may be enough neutrinos to be detectable in existing underground detectors within the next few months.

It was recently predicted that nondiffracting beams, with beam spots as small as a few wavelengths, can exist and propagate in free space. We report the first experimental investigation of these beams.

A new functional equation satisfied by the commuting row-to-row transfer matrices is derived for the eight-vertex model. Functional equations of the same form are satisfied by hard hexagons, magnetic hard squares, the self-dual Potts models, the Andrews-Baxter-Forrester models, and others. These new functional equations are called inversion identities because they generalize the inversion relation for local transfer matrices. It is conjectured that all solvable models satisfying Yang-Baxter equations possess such inversion identities and that, in general, these functional equations can be solved for the transfer-matrix eigenvalues.

We study the general class of superpotentials on Kähler manifolds that give rise to vanishing chiral potential at the tree level. We study properties of these potentials in the presence of gaugino condensation and show that it can lead to reasonable hierarchies in the scalar sector.

Cascade-model calculations are extended to study the pion energy spectra in high-energy heavy-ion collisions of heavy systems. It is found that pion reabsorption (π+N→Δ) is essential in explaining the difference between the energy slopes for pions and protons. This pion-reabsorption effect becomes more and more important as the mass number increases and reproduces even the observed falloff of the energy slopes (temperatures) for pions in the collisions of heavier nuclei. We show also the average pion multiplicities with mass number.

Synthetic small-angle excitation functions and angular distributions are calculated for the reaction ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$,${\alpha }_0$)${}^{28}$Si by use of a compound-nucleus decay model which includes angular momentum conservation. Fluctuations in the synthesized cross sections are shown to exhibit all the general characteristics of measured ${\alpha }_0$ cross sections, including features usually attributed to resonances.