We show that lowest-order predictions for large-angle Compton scattering and photoproduction are not sensitive to Sudakov corrections. As a result, the asymptotic amplitudes for these processes, including their absolute normalizations and phases, should be given by lowest-order calculations, without a resummation of perturbation theory.

We have measured $B^0$B${¯}^0$ mixing by observing like-sign dilepton events in Υ(4S) decay. Assuming that the semileptonic branching fractions of the charged and neutral B mesons are equal and that the Υ(4S) decays to $B^{+}$$B^{\mathrm{-}}$ 55% of the time and to $B^0$B${¯}^0$ 45% of the time, we measure the mixing parameter r to be 0.19±0.06±0.06, where the first error is statistical and the second is systematic.

We present the results of a search for neutrino oscillations conducted at Brookhaven National Laboratory. The experiment searched for the appearance of ${\nu }_e$ 1 km from the source of a 1.4-GeV (mean energy) narrow-band ${\nu }_{\mu }$ beam. With 3×${10}^{19}$ protons on target from the Alternating Gradient Synchrotron, no excess of ${\nu }_e$ was detected. The 90% confidence limits obtained are Δ$m^2$≤0.10 ${\mathrm{eV}}^2$ for maximal mixing, and ${\sin }^2$2θ≤0.016 for large Δ$m^2$.

Angular distributions of the analyzing powers ${}_{}{}^{\mathrm{T}}{}_{}{}^{}\mathrm{T}_{\mathrm{k}0}^{}{}_{}{}^{}$ (k=1,2,3), $T_{20}$, and $T_{21}$ for elastic and quasielastic scattering of 110-MeV polarized ${}_{}{}^{23}{}_{}{}^{}\mathrm{Na}$ from ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$ and the cross section for quasielastic scattering have been measured. Vanishing odd-rank tensor analyzing powers and the validity of the shape-effect relations indicate the importance of the projectile deformation for the interaction potential. The data are well explained by coupled-channel calculations using realistic double-folding potentials and taking into account projectile deformation and excitation.

It is shown that a schematic three-body force in addition to a general two-body force leads to a strongly improved description of the energies of A=4–16 nuclei. The values of the two strength parameters of the proposed three-body force, which are obtained empirically from energies and static moments of p-shell nuclei, are found to be similar to those of a realistic three-nucleon force.

Calculations have been made to explore the effect of configuration mixing in a large basis on the fragmentation of the ‘‘stretched’’ M6 strength in ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$. Our work extends a previous calculation, which allowed a single particle in the $f_{7/2}$ orbit and the remainder in the (unrestricted) 1$d_{5/2}$ and 2$s_{1/2}$ orbits, by also allowing up to four particles in the 1$d_{3/2}$ orbit. It is found that configuration mixing within this expanded basis gives an improved description of the spectrum and several other properties of the observed states.

Absolute apparent cross sections for electron-impact excitation out of the $2^3$S metastable level of He to the $3^3$S, $4^3$S, $3^3$P, $3^3$D, $4^3$D, $5^3$D, and $6^3$D levels have been measured by a novel method. A beam of metastable atoms from a hollow-cathode discharge is crossed by an electron beam of energy from 3 to 16 eV, and the emission from the excited states is detected. Absolute calibration is made by measuring the ratio of electron excitation cross section to the known optical-absorption cross section and using knowledge of the pertinent branching ratios. Direct electron-impact excitation cross sections for the $3^3$P, $3^3$S, and $3^3$D levels are obtained.

Self-induced transparency in a resonant two-level system creates a 2π-soliton pulse, which produces large optical nonlinearities with a very fast response time and an extremely small loss. The self-phase modulation of a 2π soliton and the mutual-phase modulation by the collision of two 2π solitons in the excitonic range of the spectrum in CdS can achieve the effective ${\chi }^{\mathrm{}\left(3\right)\mathrm{}}$ coefficient of ${10}^{\mathrm{-}6}$ to ${10}^{\mathrm{-}4.5}$ esu for a pulse duration of 1 to 3 ps. The quantum theory of 2π solitons predicts this new nonlinear process can realize squeezed states and quantum nondemolition measurement 20 dB below the standard quantum limit.

Evidence is presented of an excitation process in ion-atom collisions analogous to electron-impact excitation in free-electron-ion collisions. The production of (1s2s2p${)}^4$P projectile states excited in collisions of (1${\mathrm{s}}^2$2s) ${\mathrm{O}}^{5+}$ and ${\mathrm{F}}^{6+}$ with He and ${\mathrm{H}}_2$ targets was found to increase with projectile energy above ∼0.75 MeV/u, in agreement with an impulse-approximation treatment of 1s→2p electron-impact excitation of ions in collisions with ‘‘quasifree’’ target electrons. Such ion-atom excitations could provide presently unavailable information about inner-shell electron-impact excitation.

A method of describing turbulence in terms of dynamical connectivity in the wave-number space is proposed. The connectivity is quantified by the information theoretical quantities, i.e., mutual information and cross information flow rate. This method is applied to the analysis of two simple examples of turbulence in one spatial dimension. Although the examples have quite different physical origins, the information structures of the wave-number space turn out to be quite similar: The wave-number space consists of several regions generating information in different ways, and how information flows between these regions reflects the dynamical structure of turbulence.

In this Letter an exact solution for nonlinear cold-electron plasma oscillations against a periodic ion background is found. The main difference with respect to the known solution corresponding to a uniform ion background is that, after a while, electron density peaks will appear. This phenomenon, which was forseen in general terms by Dawson, has possible practical implications which are indicated briefly. A thermal limitation on the peaks is given.

We show that the temporal evolution of a highly excited classical plasma can be strongly modified due to the collective nature of the plasma. We show this to be particularly pronounced when the plasma frequency matches the transition energy from the continuum free-electron levels to the core states. The three-body collisions are then strongly resonant enhanced by the collective nature of the plasma. Our self-consistent calculations for an Al plasma show a dramatic enhancement of core repopulation in regions of plasma temperature and density of experimental interest.

An automaton is described in which growth is regulated by connectivity and a simple self screening constraint. With increased screening, the pattern evolves from compact to one dimensional, passing through a ‘‘critical’’ state which resembles diffusion-limited aggregation. A finite-size scaling analysis is performed. We propose that this is true critical behavior with the effective temperature determined by the strength of screening. We suggest an order parameter and extract critical exponents. Hyperscaling is discussed.

The analogy between polymer and binary critical fluid dynamics in simple shear flow is used to construct a renormalization-group analysis of the scaling exponent ν for the end-to-end distance of an isolated long polymer chain in a good solvent undergoing strong shear flow. The shear flow induces a crossover from the usual fixed point with the good solvent Flory exponent ν to a new, strong shear fixed point with the classical exponent ν=(1/2. Based on the blob picture we argue that the dynamic exponent z is not affected by the flow and remains at its zero shear, z=3 value. Experimentally observable consequences of this result are also discussed.

A new method of scanning tunneling microscopy is proposed that should allow atomic resolution imaging on insulators. A nonlinear ac technique is used that is shown to allow stable control of a microscope tip above insulating surfaces where dc tunneling is not possible, including aluminum oxide and liquid-crystal layers. Images of copper oxide and ${\mathrm{WSe}}_2$ have been obtained using this technique. Nanometer features have been observed.

Extensive simulations of growth in a stochastic ballistic deposition model on a (d-1)-dimensional substrate with a constraint on neighboring interface heights are described. The interface width obeys scaling even for small systems and grows as $t^{\beta }$ with β=1/(d+1). Generalizations to include irrevelant effects such as noise reduction are discussed as are possible reasons for the discrepancies in earlier results.

We report the first observation of layered structures in the computer-simulated Coulomb glasses produced by rapid quenching of one-component plasmas in the absence of an external force field. Degrees of polycrystalline nucleation and the nature of local order developed in the glasses are elucidated through analyses of the intralayer and interlayer particle correlations and by means of the Laue patterns formed by scattering of plane waves. Stages of evolution for the glass transition in Coulombic systems are conjectured.

The binding sites for adsorption of a single iridium atom on a close-packed iridium (111) plane have been mapped out in the field ion microscope by observing the location of one iridium atom after diffusion over the surface at T∼100 K. Both surface (hcp) and bulk (fcc) sites are found occupied, but the former are favored, with the free energy for adatoms ∼370 cal/mol lower on surface sites. This free-energy difference is small compared to the barrier of 6.2 kcal/mol which separates equivalent sites in surface diffusion.

The optical spectra of small isolated sodium clusters adsorbed on a boron nitride surface have been measured from 3000 to 7500 Å over a range of average cluster size 〈N〉=10 to 300 atoms by change in reflectivity spectroscopy. The spectra are dominated by the dipole resonance of the surface collective mode of the sodium valence electrons, and the resonance frequency shifts from 2.4 eV to near the bulk value of 3.4 eV as cluster size increases. A quantitative comparison of experimental results with the jellium model of sodium clusters is presented.

We study processes in which excited electrons in semiconductor quantum wells lose energy by emitting slab LO phonons of the quantum well, namely, bulklike confined phonons and interface phonons. We consider both intrasubband and intersubband relaxation and show that, consistent with a recent experimental finding, phonon selection rules are responsible for a large reduction of intersubband relaxation rates.