At a collision energy E=0.1 eV we see a large polarization effect ${\mathit{Q}}_{\mathrm{ion}}^{\mathrm{*}{\mathit{M}}_{\mathit{j}}\mathrm{*}=0,1\mathrm{}}$/${\mathit{Q}}_{\mathrm{ion}}^{{\mathit{M}}_{\mathit{j}}\mathrm{*}=3\mathrm{}}$=2.5, decreasing to 1.4 for E≥1 eV. A two-state basis is used for the autoionization width of the π and σ orientations of the (2p${)}^{\mathrm{-}1}$ core hole, resulting in a preference for the Ω=0,1 molecular states as seen at 0.1 eV. The energy dependence is due to the decrease of ‘‘locking’’ of J to the internuclear axis with increasing angular velocity φ̇, leading to the semiclassical criterion ${\omega }_{\mathrm{prec}=4\mathrm{}\mathrm{\phi }\mathrm{̇}}$ for the transition from a space-fixed to a body-fixed description of J.

The electron emission yield from the doubly excited {(2${\mathrm{p}}^1$${)}^2$D+(2s2p${)}^1$P} states in He excited by impact of fast equivelocity electrons, protons, and carbon ions (charge state 4–6) has been measured at the reduced energy of 1.84 MeV/amu. The data constitute a challenge to the recently proposed models that incorporate electron-correlation effects in atomic collisions.

The Susskind-Glogower (SG) phase operator is shown to be the maximum-likelihood (ML) quantum measurement of optical phase for all input states. The ML performance of the SG measurement is optimized, at average photon number N, by an input state with number-ket representation of the form ${\mathrm{\psi }}_{\mathrm{n}}$=A/(1+n), for 0≤n≤M<∞. The optimum phase-error behavior, measured by the reciprocal peak-likelihood, is proportional to 1/${\mathrm{N}}^2$, as opposed to the 1/ √N and 1/N dependences of coherent-state and optimum squeezed-state interferometers.

Collisions of electron and positron bunches at the interaction point of the linear collider at SLAC have led to the first detected emission of beamstrahlung. This radiation, caused by the collective electromagnetic fields of one beam deflecting particles of the other, is a potential tool for optimizing collisions in linear colliders.

The problem of determining a scattering potential from measurements of the far-field intensity distribution obtained in a set of scattering experiments is addressed within the Born approximation. It is shown that this problem admits a conceptually and computationally simple approximate solution if the incident and scattered radiation are mutually coherent in the far field and if the spatial resolution at which the far-field distribution of total intensity is measured is sufficiently high. The resolution of the inversion procedure is discussed and a computer simulation illustrating the proposed method is presented.

An experimental demonstration of a strong enhancement of the interaction efficiency in a high-power relativistic backward-wave oscillator when plasma is injected is presented. Controlled plasma injection enhances the interaction efficiency over the vacuum case by a factor of up to 8 to a value of about 40%. The enhanced interaction is attributed to induced scattering of the electromagnetic radiation of electrons in an electrostatic field produced by the background plasma and a beam space-charge wave in the corrugated interaction region.

A brief, deliberate, perturbation of hot tokamak electrons produces a transient, synchrotron radiation signal, in frequency-time space, with impressive informative potential on plasma parameters; for example, the dc toroidal electric field, not available by other means, may be measurable. Very fast algorithms have been developed, making tractable a statistical analysis that compares essentially all parameter sets that might possibly explain the transient signal. By simulating data numerically, we can estimate the informative worth of data prior to obtaining it.

We apply a new model equation of state, based on realistic interparticle potentials and a self-consistent treatment of the internal levels, to fluid hydrogen at high density. This model shows a strong connection between molecular dissociation and pressure ionization. We consider the possibility of a first-order plasma phase transition for which we give both the evolution in temperature and the critical point.

A two-dimensional melting transition has been observed in a freely expanding colloidal monolayer lattice formed of 1.01-μm polystyrene microspheres in an aqueous suspension between two parallel optical flats. The correlation functions computed from digitized images of the particle distribution within a fixed sampling area are consistent with a continuous two-step melting transition. However, direct observations of defect creation and evolution reveal that the system may melt via a first-order process.

Recent heat-capacity measurements of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ adsorbed on graphite by Greywall and Busch are interpreted in terms of a triangular second-layer solid having √7 × √7 registry with respect to the first adsorbed layer. The observed entropy change in the millikelvin region is well accounted for by an antiferromagnetic Heisenberg spin Hamiltonian in which only a subset of second-layer spins forming a Kagomé net are strongly coupled.

We present high-resolution x-ray diffraction mesaurements of the recently discovered face-centered icosahedral phase of ${\mathrm{Al}}_{65}$${\mathrm{Cu}}_{20}$${\mathrm{Ru}}_{15}$. Analysis of the diffraction-peak profiles shows that this alloy is better ordered than the simple-icosahedral alloys previously studied. In particular, the peak broadening is well accounted for by simple lattice strain, with no measurable dependence of the peak widths on phason momentum. This implies a significantly diminished role for phason disorder in this system relative to the simple-icosahedral alloys.

We show that thermal positron reemission and positronium formation at clean Cu(111) and Al(110) surfaces are strongly reduced at low temperatures. This is explained by quantum mechanical reflection of the positron wave function from the surface potential. Analysis of the data yields first estimates of the different transition rates for positrons at the surface. Information on the nature of the positron-surface interaction can be obtained. We discuss the implications of our findings to other surface emission and sticking processes.

The possibility of formulating a time-dependent current-functionsl theory which describes the linear responses of systems of inhomogeneous, interacting electron gas to an arbitrary form of time-dependent electromagnetic field is studied. A Kohn-Sham–type theory for the dynamical electronic conductivity tensor is derived and a local-density type of approximation for the resulting exchange-correlation electric field is constructed.

The simplest random evolution is the motion of particle on a straight line with constant velocity suffering random collisions, which reverses the velocity. The position x(t) of the particle at time t is the stochastic process that defines Kac’s path-integral solution of the telegrapher equation. We view Kac’s prescription as a path-dependent time reparametrization, which associates to the time t spent by the particle in going from ${\mathrm{x}}_0$ to x along a path ω, the time r(ω) the particle would have taken to go from ${\mathrm{x}}_0$ to x without reversal. We compute explicitly the probability distribution of the random variable r. It is then possible to compute by simple quadrature any path integral with an integrand function of r(ω).

The quantum-mechanical uncertainty in the position of a particle or the time of its emission is shown to produce observable effects that are inconsistent with any local hidden-variable theory. A new experimental test of local hidden-variable theories based on optical interference is proposed.

An exposition is given of the fundamental ideas of the recently opened field of two-particle interferometry, which employs spatially separated, quantum mechanically entangled two-particle states. These ideas are illustrated by a realizable arrangement, in which four beams are selected from the output of a laser-pumped down-converting crystal, with two beams interferometrically combined at one locus and two at another. When phase shifters are placed in these beams, the coincident count rates at the two loci will oscillate as the phases are varied, but the single count rates will not.

Diffusion is explored in a two-dimensional phase space in which a connected separatrix layer (web) of intrinsic stochasticity bounds regions of regular motion (tiles). In the presence of weak extrinsic noise, if the web diffusion dominates, the noise slows the web diffusion rate; if the extrinsic diffusion dominates, the diffusion is enhanced. The diffusion is characterized by two space and time scales. For a local-equilibrium model analytic calculations agree well with numerical results.

We show that in the semiclassical theory of gravity, flat spacetime with quantum fields in the Minkowski vacuum is unstable to a certain type of infinitesimal perturbation. Moreover, these perturbations evolve into a catastrophic collapse in an arbitrarily short time scale. However, our universe is safe against these perturbations until some time far in the future.

Using only the equation of motion and the canonical commutator of anomalous gauge theories, we show clearly the relation between the Schwinger-Jackiw-Johnson (SJJ) term, the anomalous Jacobian, and the current-divergence anomaly by obtaining both the SJJ term and the anomalous Jacobian from the current-divergence anomaly.

Proton decay in three-generation superstring models with intermediate scale is investigated. It is shown that matter-parity ($M_2$) invariance alone does not stabilize the proton. However, models with $M_2$ invariance and Calabi-Yau manifolds such that the exotic C-odd quarks and leptons are superheavy will generally lead to proton lifetimes consistent with existing data.