We consider the full set of equations ruling the interaction of an electromagnetic field with matter in a laser, without assuming that the direction of the transverse electric field is fixed. Near the lasing threshold, we reduce the dynamics to its normal form equation, and show that the electromagnetic field can be described by a Ginzburg-Landau equation in a vector form. Then by using topological arguments we show the possibility of vectorial topological defects which are not predictable by the scalar theory.

We discuss the relation between predictability and the sensitive dependence on initial conditions in turblent flows. We find that the maxium Lyapunov exponent λ and the variance of the effective Lyapunov exponent diverge as a power of the Reynolds number with scaling exponents which can be calculated from the eddy turnover time at the Kolmogorov length using the multifractal approach. The intermittency leads to long tails in the distribution of the predictability time. The typical predictability time T is related to the value of ${\lambda }^{\mathrm{-}1}$. We provide numerical evidence of this picture within the framework of a cascade model for three-dimensional fully developed turbulence.

The quasiperiodic transition to chaos in an undriven discharge plasma has been investigated. Results from the power spectrum and Lyapunov exponents quantitatively confirm the transition to chaos through quasiperiodicity. A low-dimension strange attractor has been found for this kind of plasma chaos.

Molecular dynamics calculations revealed that a pressure-induced ‘‘amorphized’’ solid is disordered and anisotropic but not structurally related to an isotropic quenched melt. The results explain the anomalous elastic behavior observed via Brillouin scattering on α-quartz [L. E. McNeil and M. Grimsditch, Phys. Rev. Lett. 68, 83 (1991)]. The reversal in frequency shifts for sound propagation in the perpendicular and parallel directions is due to the unequal densification in the a and c directions. The helical chains are found to recover upon depressurizing. Anisotropy of pressure amorphized solids is thus a general property, and pressure-induced amorphization is not related to melting.

The binary phase diagram of He-Ne mixtures has been measured at 296 K in a diamond anvil cell. It is of the eutectic type with no fluid-fluid separation of phases. A homogeneous solid mixture is shown to be stable for a mole fraction of He equal to 2/3. Single-crystal synchrotron x-ray measurements indicate that this solid is ordered with 12 atoms in the unit cell. Gibbs free energy calculations support the attribution to the ${\mathrm{MgZn}}_2$ type structure. It is the first Laves phase observed in a van der Waals molecular compound,

The soft potential model (an extension of the tunneling model to include soft localized vibrations) is shown to describe the anomalous features of the specific heat ${\mathit{C}}_{\mathit{P}}$ and the thermal conductivity of glasses over the entire low-temperature range, up to an including the peak in ${\mathit{C}}_{\mathit{P}}$/${\mathit{T}}^3$ and the second rise of the thermal conductivity above the plateau.

A quest for microcanonical functionals describing near-critical behavior has led to an exact local variational functional for square lattice Ising models in zero field with varying bond strengths along the z axis. In the continuum limit near ${\mathit{T}}_{\mathit{C}}$ this yields a second-order differential equation for the transverse Fourier coefficients of the energy density. Applications to a ‘‘grain boundary’’ between differing regions and to a wall with a surface field ${\mathit{h}}_1$ give bulk and surface exponents and scaling-limit energy-density profiles which exhibit rich crossovers and nonmonotonic variation.

We measured the coarsening exponent φ and the nontrivial scaling exponent λ, which characterize how the two-time correlation function C(t,t’) scales with the correlation length L(t), C(t,t’)∝L(t${)}^{\mathrm{-}\lambda }$ when t≫t’, for a twisted nematic liquid-crystal system quenched from the isotropic phase to the nematic phase. This system is expected to be Ising-like with φ=0.5 and λ=1.25. Our values, φ=0.515±0.026, measured over two decades in time, and λ=1.246±0.079, measured over the late time period, 30 to 150 s, are in good agreement with theory.

Stable nematic director fields of liquid crystals confined to cylindrical cavities which enforce homogeneous concentric anchoring depend on the competition between azimuthal and polar molecular anchoring strengths and the surface elastic constant ${\mathit{K}}_{24}$. Deuterium nuclear-magnetic-resonance line shapes of such systems reveal a structural transition from an escaped-twisted to a newly discovered planar-bipolar configuration as the curvature is varied. This observation allows for the first determination of the polar and azimuthal anchoring energies and ${\mathit{K}}_{24}$, by a single experimental method.

We report the first direct measurement of Δ${\mathit{C}}_{\mathrm{mix}}$, the excess specific heat due to mixing of a binary system, a liquid crystal (LC)/matrix mixture. Both LC concentration and matrix cross-linking (cure) affect mixing. In uncured systems we observe a steplike decrease in specific heat due to a negative value of Δ${\mathit{C}}_{\mathrm{mix}}$. A plot of Δ${\mathit{C}}_{\mathrm{mix}}$ vs LC content shows a minimum, consistent with Flory-Huggin theory; the theory also gives the upper critical solution temperature phase diagram and sign of Δ${\mathit{C}}_{\mathrm{mix}}$. Partially cured samples also exhibit Δ${\mathit{C}}_{\mathrm{mix}}$ transitions which persist until cure is almost complete and demixing is essentially irreversible.

We demonstrate by ${\mathit{D}}_2$ nozzle beam experiments on cold Cu(111), Cu(100), and Cu(110) surfaces that the substrate surface structure profoundly influences the sticking and trapping of particles in the physisorption well. Comparison with theoretical calculations reveals that this is caused by structure-specific differences in the particle-phonon coupling and the collision processes that control the lateral propagation of particles trapped in quasibound states.

We present time-resolved elastic light scattering results of structure determination in phase-separating mixtures of guaiacol and glycerol-water constrained to lie between plates 0.5 mm apart. The structure functions show two peaks with different kinetics: a slow mode with L(t)∼${\mathit{t}}^{1/3}$ and a ‘‘fast mode’’ with L(t)∼${\mathit{t}}^{\mathit{b}}$, where b ranges from 1.1 for a quench of depth ΔT=0.01°C to 1.5 when ΔT≥0.15°C. A similar fast mode was observed in a polymer system [A. Cumming, P. Wiltzius, F. S. Bates, and J.H. Rosedale, Phys. Rev. A 45, 885 (1992)]. The observation of the fast mode in a low-molecular-weight, Ising-like system establishes it as generic to phase-separating fluids, and not peculiar to polymers.

Action of an external high-frequency electromagnetic field on free electrons in normal-metal mesoscopic rings threaded by a static magnetic flux is shown to lead to a direct current proportional to the electromagnetic field intensity. The disorder-averaged value of the current is a periodic function of the static magnetic flux and may considerably exceed the corresponding value of equilibrium persistent current.

Pronounced structure at large biases in the ballistic-electron-emission-microscopy (BEEM) current for Cr/GaP(110) is attributed to density-of-states effects in GaP. Quasielastic scattering at the Cr-GaP interface appears vital for the effect. Impact ionization in the GaP is invoked to explain the unusually large collector currents that can exceed the injected STM tip current.

Current density-voltage characteristics are presented for a molecular structure of the form metal/organic-multilayer/metal for which the rectifierlike forward bias current density dependence is unequivocally associated with zwitterionic molecules. By placing passive organic barriers between the metal layers and the active molecules we prove that Schottky barrier effects are not important. This is the clearest evidence so far for molecularly controlled rectification, the basis for molecular electronics.

A study of the phase diagram and magnetic susceptibility χ(x,δ,T) of the title system is reported. For δ≃0.03, macroscopic phase separation, below ≃300 K into ${\mathrm{superconductingLa}}_{2\mathrm{-}\mathrm{x}}$${\mathrm{Sr}}_{\mathrm{x}}$${\mathrm{CuO}}_{4+\mathrm{\delta }}$(δ≃0.08) and ${\mathrm{nonsuperconductingLa}}_{2\mathrm{-}\mathrm{x}}$${\mathrm{Sr}}_{\mathrm{x}}$${\mathrm{CuO}}_{4+{\mathrm{\delta }}^{\mathrm{″}}}$(δ″≃0.00) phases, known to occur forx=0, disappears by x≃0.03. The behaviors of the Néel temperature ${\mathrm{T}}_{\mathrm{N}}$(x) and χ(x,T) of the antiferromagnetic phase (0≃x≲0.02,δ″≃0.00) reveal a novel microscopic segregation of the doped holes in this phase into walls of hole-rich material separating undoped domains. © 1993 The American Physical Society

A model of interacting electrons living on two chains coupled by a transverse hopping ${\mathit{t}}_{\mathrm{\perp }}$ is solved exactly by a bosonization technique. It is shown that ${\mathit{t}}_{\mathrm{\perp }}$ does modify the shape of the Fermi surface also in the presence of interaction, although charge and spin excitations keep different velocities ${\mathit{u}}_{\mathrm{\rho }}$, ${\mathit{u}}_{\mathrm{\sigma }}$. Two different regimes occur: At short distances, x≪ξ=(${\mathit{u}}_{\mathrm{\rho }}$-${\mathit{u}}_{\mathrm{\sigma }}$)/4${\mathit{t}}_{\mathrm{\perp }}$, the two chain model is not sensitive to ${\mathit{t}}_{\mathrm{\perp }}$, while for larger separation x≫ξ interchain hopping is relevant and generates further singularities in the electron Green function besides those due to spin-charge decoupling.

The magneto-optical Kerr rotation was measured in Co/U-As multilayers and compared with calculations of the Kerr response of such multilayered structures. From the thickness dependence of the Kerr rotation it is concluded that the U-As layers have an exchange-induced magnetic moment at room temperature reaching 20% of the low-temperature value.

We present direct experimental observations of collective transport in two-dimensional magnetic bubble arrays in thin garnet films. Shear flow is produced by forcing the array to move past a flat interface; the array is strongly pinned on the other side of the interface. Time-resolved images of the dislocation dynamics that produce shear flow are obtained via Voroni constructions.

We investigate the excitation energy dependence of the boron K soft-x-ray emission of ${\mathrm{B}}_2$${\mathrm{O}}_3$ and hexagonal-BN using synchrotron radiation. When exciting into the core exciton state the spectra are shifted to lower energy by 1.5 and 1.8 eV, respectively. This shift is found to be a result of phonon relaxation and differences in initial-and final-state electronic screening.