We have performed high-resolution energy analysis of the near-band-gap photoemission of a p-type InP/Ag Schottky diode under electrical bias. This original technique brings direct information on high-electric-field electron transport in semiconductors. From our experimental data, using simple models, we estimate characteristic phonon emission times in an energy range which spans the whole first conduction band, and we evidence an efficient ${\mathrm{\Gamma }}_6$-${\mathit{X}}_6$ intervalley transfer.

We analyze the distribution of bond lifetimes in simulations of liquid water using a novel bond definition. We find that the characteristic lifetimes of the bonds and of the ‘‘gel’’ network itself both increase strongly when temperature is decreased–and even appear to diverge at a temperature well below the freezing temperature–thereby providing an appealing physical picture of the anomalous behavior of water in the supercooled region.

Dynamical quasidegeneracies may arise in the spectrum of systems having discrete symmetries. They are semiclassically interpreted as quantized congruent but distinct tori in phase space. With them the separation of regular and irregular states in the quantum spectrum of some mixed phase-space systems may be performed in a simple yet clear fashion. At finite energies (h finite), the frontier between regular and irregular states is not sharp. This is illustrated by the study of two coupled quartic oscillators.

We carry out Monte Carlo simulations of the two-dimensional classical neutral Coulomb gas of integer charges on a square lattice, as a function of temperature and chemical potential, and find new critical behavior. At low temperature, as density increases, the system has a first-order transition to an ordered-charge lattice. As temperature increases, this dense phase has a Kosterlitz-Thouless transition followed by an Ising transition. The first-order line joins the line of Ising transitions at a new tricritical point.

We show that by coupling a three-dimensional Chern-Simons theory to (2+1)-dimensional gravity through an arbitrarily small ${\mathit{F}}^2$ term, one can obtain integrals of conformal-field-theory amplitudes over moduli space. The conformal anomaly appears as an induced gravitational Chern-Simons term. String-theory amplitudes can thus be obtained from three dimensions.

The E731 experiment at Fermilab has searched for direct CP violation in ${\mathit{K}}^0$→ππ, which is parametrized by ɛ’/ɛ. For the first time all four of the ${\mathit{K}}_{\mathit{L},}$S→ππ modes were collected simultaneously, which greatly facilitated studies of systematic uncertainty. We find Re(ɛ’/ɛ)=-0.0004±0.0014(stat)±0.0006(syst). The result provides no evidence for direct CP violation.

A generalization of the Goldberger-Trieman relation for the singlet channel is obtained. This gives a new relation between the total quark contribution to the proton spin (ΔΣ) and the η′-meson couplign constants (${\mathrm{g}}_{\mathrm{\eta }\prime \mathrm{NN}}$ and ${\mathrm{f}}_{\mathrm{\eta }\prime }$). Using these we find ΔΣ≈1, precisely as in the naive quark model. © >1990 The American Physical Society

We discuss a class of flavor-changing two-photon rare decays, such as b→sγγ. Both dimension-six and dimension-eight operators are shown to contribute to these decays. For a heavy top, contributions from dimension-six operators become sizable and even dominant. They can be simply related to a single-photon decay like b→sγ. Implications for ${\mathit{B}}_{\mathit{s}}$→γγ are discussed, especially with regard to the spin orientations of the photons.

We calculate the pion spectrum and its electromagnetic annihilation vertex in nuclear matter taking into account the strong πNΔ interaction. For nuclear densities the pion kinetic energy is approximately compensated by the interaction, but also the free-pion annihilation matrix element is almost canceled by the contribution from the interaction with the medium. Consequently, the enhancement of the dilepton production rate due to the softening of the pion spectrum is strongly reduced.

In the presence of output coupling the longitudinal eigenmodes of a laser are not orthogonal. This may affect the quantum limit to the laser linewidth, in particular, if the outcoupling is high. We present experimental evidence of this effect, using single-mode semiconductor lasers with various coatings.

Cross sections and asymmetry (${\mathrm{\beta }}_{\mathit{n}\mathit{l}}$) parameters for the photodetachment of 2s and 2p electrons from ${\mathrm{He}}^{\mathrm{-}}$(1s2s2p${)}^4$${\mathit{P}}^0$ are calculated using the multiconfiguration Hartree-Fock method which includes the effects of dynamical core polarization and electron correlation. The excellent agreement with limited experimental data suggests its accuracy over the energy range from 0 to 4 eV. The photodetachment cross sections are used to calculate the inverse radiative attachment cross sections.

The anisotropy of the photodissociation cross section of metastable ${\mathrm{H}}_2$ for excitation around the resonance due to the ${}_{}{}^3{}_{}{}^{}\mathrm{\Delta }_{\mathrm{g}}^{\mathrm{-}}{}_{}{}^{}$(v=5,N+2) level is investigated. The ${\mathit{j}}^3$${\mathrm{\Delta }}_{\mathit{g}}^{\mathrm{-}}$(v=5,N=2) state is coupled to the continuum of the ${\mathit{i}}^3$${\mathrm{\Pi }}_{\mathit{g}}^{\mathrm{-}}$ state by the nuclear rotation. Since both states carry oscillator strength, the cross section shows interference effects. The interference is difficult to detect on the total cross section, but is clearly seen in the angular distribution of the photofragments.

When a long channel of shallow liquid is driven parametrically, there can occur a 180° kink in the phase of the fundamental cross mode of the surface. The kink is stable and localized, and is nonpropagating in the limit where the system is uniform. The weakly nonlinear theoretical description is a damped driven nonlinear Schrödinger equation supplemented with second harmonics. The kink is a robust state even at amplitudes where the perturbation expansion leading to this equation is unjustified.

We derive formulas which describe the interaction of laser beams with electron beams. Specializing to the case of 1-TeV electron beams from the future generation of electron linear accelerators, we calculate the production rate of backscattered 1-TeV photons, and using these photons, we show that it is possible to organize the photoproduction of beauty particles so as to measure ${10}^9$ bb¯ pairs per year. This should be adequate to study rare decays and CP violation in B meson decay.

Dynamic light scattering at the crystal-melt interface of solidifying salol was followed for 14 days. The hydrodynamic radius deduced from intensity correlation data increased continuously from ∼1 to ∼100 μm. When the scattering layer was trapped by the advancing crystal front, microscopic observation revealed bubbles as inclusions whose size agreed with the light-scattering value. Scattering was also observed to disappear after prolonged pumping on the sample.

Quantum freezing of the Bose hard-sphere liquid is described by an extension of the classical modified weighted-density approximation to nonuniform quantum liquids at zero temperature. The theory requires structural and thermodynamic information for the corresponding uniform quantum liquid, which we have chosen to take, for the purpose of illustration, from the paired phonon analysis. Predictions for solid-phase energies and for freezing parameters are in generally good agreement with available simulation data.

Using simple thermodynamic arguements, it is shown that sharp concentration gradients occurring during diffusive mixing of multilayer composites facilitate amorphization by solid-state reaction by reducing or suppressing the driving force for crystallization Δ${\mathit{G}}_{\mathit{a}\mathit{c}}$. As the concentration gradients diminish during diffusive layer growth, the driving force for crystalline phase formation is restored and the energetic barrier to their nucleation to the classical expression. This evolution yields a critical maximum amorphous-layer thickness as observed experimentally.

The yield and final-state distributions in translational and internal degrees of freedom have been established for NO molecules desorbed from a Pd(111) surface by 200-fs pulses of 2.0-eV photons. Among the significant characteristics of the desorption process are the large cross section and the high vibrational energy content (${\mathit{T}}_{\mathit{v}}$>2000 K) of the desorbed molecules. A comparison with the behavior for nanosecond laser pulses indicates that a new desorption mechanism, distinct from either conventional thermal or photochemical processes, is operative in this regime.

We report the first quantitative study of the size-dependent suprefluid transition in ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ films adsorbed on porous glasses with pore diameters d from 50 to 10 000 Å. ${\mathit{T}}_{\mathit{c}}$ for the submonolayer films decreases as d increases up to d=2900 Å, whereas ${\mathit{T}}_{\mathit{c}}$ for the full-pore liquid increases with d. The d dependence of ${\mathit{T}}_{\mathit{c}}$ and the dissipation at the transition for the films reveal that the vortex-pair unbinding on length scales smaller than the pore sizes determines the superfluid transition. We obtain the diameter of vortex core ${\mathit{a}}_0$=25±12 Å from the fit by letting the 2D coherence length ${\xi }_2^{+}$(${\mathit{T}}_{\mathit{c}}$)=πd/2. .AE

High-resolution x-ray and optical studies were peformed on oriented samples of the recently discovered smectic-${\mathit{A}}^{\mathrm{*}}$ phase. We confirm that this phase exhibits smectic-A layers as well as a macroscopic helical strcucture with the helical axis parallel to the layer planes. Furthermore, we demonstrate that the observed scattering can be explained by a cylindrical structure factor that is, within our instrumental resolution, a δ function in the radial direction and a Gaussian in the transverse direction as predicted by Renn and Lubensky for the ‘‘twist grain boundary’’ phase.