Cu(100)films of average thicknesses from 3 to 7 Å have been grown on a Ni(100) substrate and capped with Ni(100) films of varying thickness. Electron transmission through the films was measured as a function of incident electron energy. Features observed above 9.5 eV above the Fermi energy show a strong dependence on the thickness of the Ni outer layer, characteristic of the quantum size effect. A feature below 9.5 eV shows only a weak dependence on the Ni thickness. This feature is suggested to result from resonant transmission through a bound state. The position of the feature as a function of the thickness of the Cu layer is in good agreement with the position for the bound state in a quantum well formed by the offset ${\mathrm{X}}_1$ points of the bulk Ni and Cu band structures.

We report preliminary results from a search for galactic axions in the frequency range 1.09<$f_a$<1.22 GHz. For an axion linewidth ${\Gamma }_a$≤200 Hz we obtain the experimental limit ($g_{a\gamma \gamma }$/$m_a$${)}^2$${\rho }_a$<1.4×${10}^{-41}$. The theoretical prediction is ($g_{a\gamma \gamma }$/$m_a$${)}^2$${\rho }_a$=3.9×${10}^{-44}$ with ${\rho }_a$=300 MeV/${\mathrm{cm}}^3$. We have also searched for the presence of a continuous spectrum of light pseudoscalar particles; if we assume that the above ${\rho }_a$ is contained between the upper and lower frequencies of our search, then we find that $g_{a\gamma \gamma }$<2×${10}^{\mathrm{-}30}$ ${\mathrm{MeV}}^{1/2}$ ${\mathrm{cm}}^{3/2}$≃${10}^{\mathrm{-}11}$ ${\mathrm{GeV}}^{\mathrm{-}1}$.

We have carried out a direct free-fall experiment to measure the differential acceleration between two different materials (copper and uranium) falling in the Earth’s gravitational field. The differential acceleration was measured to be less than 5 parts in ${10}^{10}$ of the normal gravitational acceleration. This null result puts new limits on the strength and range of the proposed fifth force.

We report that dc-excited discharges in gases that display current oscillations which develop into deterministically chaotic behavior. A period-doubling route to chaos characteristic of 1D maps is established for sealed discharges in Plücker’s tubes containing helium. Besides this we report the observation of a scenario showing properties analogous to those of the 2D map of Hénon. Clear sequences of period doublings are also reported for flowing discharges.

We present a numerical study of lattice (compact) QED with dynamical fermions using hybrid stochastic differential equations. Working with an $8^4$ lattice and fermions of mass 0.10 (lattice units), we have found an unexpected first-order transition separating the strong- and weak-coupling regions.

We propose a coherent explanation of the puzzle associated with J/ψ (ψ’) decays into vector plus pseudoscalar exclusive final states by assuming the general validity of the perturbative QCD hadron-helicity theorem, but supplemented by violation of this theorem when J/ψ decay to hadrons is mediated by an intermediate gluonium state scrO. The mass of the scrO must be within 100 MeV of the mass of the J/ψ, and its total width must be less than 160 MeV. Comments are made about vector-scalar decays of J/ψ to φ$S^{\mathrm{*}}$ and ρδ. .AE

The E2/M1 ratio of electromagnetic N(939)→Δ(1232) transitions is calculated in a relativistic three-quark model for the nucleon and Δ(1232). Relativistic kinematics in the three-quark N and Δ wave functions yields an E2/M1 contribution of about -0.2% without any tensor forces in the dynamics.

We demonstrate, using two different quark models of hadrons, that there should be isodoublets of dibaryons with strangeness -3 and J=1,2, which are stable with respect to strong decay.

Transverse-momentum measurements of collective flow are analyzed in terms of scale-invariant quantities. Deviation from the fluid-dynamical scaling behavior, at energies below $E_{\mathrm{lab}=200\mathrm{}}$ MeV/nucleon, indicates a drastic change in the reaction mechanism. This might be due to a liquid-gas phase transition and nuclear mean-field effects.

We introduce an expression for the deformed nuclear density in gauge space in terms of the pairing deformation parameter ${\mathrm{\beta }}_{\mathrm{P}}$. The Fourier components of this quantity as functions of the ordinary space variables can be used to define macroscopic form factors for multiparticle transfer processes in superfluid nuclei. Experimental ΔN-particle transfer cross sections for ΔN=±2, ±4, etc., analyzed within this framework yield the relative magnitudes of the Fourier amplitudes. This procedure therefore allows for the reconstruction of density contours in the abstract space.

The formation of ${\mathrm{O}}^{\mathrm{-}}$ ions via dissociative attachment in electron-stimulated desorption from condensed ${\mathrm{O}}_2$ on a polycrystalline platinum surface is reported. The energy dependence of the ${\mathrm{O}}^{\mathrm{-}}$ yield exhibits two peaks at 7 and 13 eV. The 7-eV peak arises from the ${}_{}{}^2{}_{}{}^{}\mathrm{\Pi }_{\mathrm{u}}^{}{}_{}{}^{}$ state of ${\mathrm{O}}_2$${\mathrm{}}^{\mathrm{-}}$, whereas the 13-eV peak is ascribed to two distinct resonance states, the ${}_{}{}^2{}_{}{}^{}\mathrm{\Pi }_{\mathrm{u}}^{}{}_{}{}^{}$ and the ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{g}}^{+}{}_{}{}^{}$ ${\mathrm{O}}_2$${\mathrm{}}^{\mathrm{-}}$ states, from ion kinetic energy measurements. The ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{g}{}^{+}}^{}{}_{}{}^{}$ ${\mathrm{O}}_2$${\mathrm{}}^{\mathrm{-}}$ state is then accessible by attachment of an electron to the X ${}^3$${\Sigma }_{g^{\mathrm{-}}}$ ${\mathrm{O}}_2$ target via a violation of the selection rule ${\Sigma }^{\mathrm{-}}$⇆${\Sigma }^{+}$. .AE

We have calculated cross sections for elastic and spin-flip scattering processes of electrons on positronium atoms in the para and ortho states in the energy region scrE≤0.05 eV; elastic and symmetric charge-exchange cross sections for the same system were calculated without spin interactions for the scattering energies scrE≤4 eV. This energy region has been treated for the first time. The calculations have been done by the adiabatic method, where this three-body problem reduces to the multichannel-scattering problem. Very high scattering cross sections were obtained, expecially near the threshold for spin-flip processes.

Electron-scattering cross sections for intramolecular and intermolecular vibrational excitation in amorphous solid ${\mathrm{H}}_2$O are reported for the incident energy range 1–18 eV. The origin of the feature for the stretching modes is ascribed to resonant scattering similar to the gas phase. Those in the translational and librational modes are shown to arise mainly from the interaction of a long-lived transient anion with the dipoles of the surrounding molecules.

The standard picture of Kadomtsev reconnection process predicts sawtooth crash times that are longer than those observed in the present day large tokamaks. Ideal kink modes are investigated as a possible mechanism for these fast crashes, by use of fully toroidal, compressible, full magnetohydrodynamic equations. In systems with low shear, parallel-current and pressure-driven modes are identified well below the previously accepted poloidal beta limits. Linear and nonlinear calculations show good agreement with experiments and indicate that such modes may explain fast collapse times reported in the recent literature.

It is revealed in microwave-plasma interaction experiments that a large-amplitude electrostatic wave propagating obliquely to a magnetic field accelerates electrons strongly almost along the magnetic field lines via the process of ${\mathrm{V}}_{\mathrm{p}}$×B acceleration. The experimental results are in reasonable agreement with the theoretical prediction of Sugihara et al.

We calculate the low-frequency phonon spectrum of the π-bonded–chain model of the Si(111)2×1 surface, and find an explanation for the surprising observation, in He-atom scattering experiments, of a low-energy dispersionless surface phonon. This feature results from strong electron polarization effects, which arise from the quasi one-dimensional nature of the π-bonded–chain model. The assignment of this mode as an Einstein oscillator is incorrect. Our calculations are based on Chadi’s tight-binding theory for structural energies, with the addition of a Hubbard interaction.

A neutron-diffraction experiment (λ=0.704 Å) has been performed for the first time on liquid arsenic above the triple point. The coordination number (Z=3) does not change through the semimetal-to-semiconductor transition on melting. This is in sharp contrast to the elemental semiconductors (Si,Ge) that undergo a semiconductor-to-metal transition upon melting, accompanied by an increase (4→6.4) of the coordination number. The nonmetallic behavior of As, which has a half-filled p band, can be understood as a Peierls distortion in the p-bonding mechanism (three p-p bonds are reinforced; the others are considerably weakened).

We describe a channeling analysis of the strain associated with ultrathin (2–6 monolayers) epitaxial films of Ge embedded in Si. Measured strains are at the level of 3–4%, exceeding that accessible in bulk materials. These values, in both single-layer films and Ge-Si superlattices, are in approximate agreement with bulk elastic properties suggesting that Poisson’s ratio is applicable at the few-monolayer level.

We have examined the kinetics of phase separation in ${\mathrm{Mn}}_{0.67}$${\mathrm{Cu}}_{0.33}$ using time-resolved neutron-scattering techniques. In an early-time regime, the kinetics follows the Cahn-Hilliard-Cook linear theory of spinodal decomposition. There is an intermediate stage. Then, at a late time, dynamic scaling is obeyed. The time dependence of the wave vector at maximum scattering intensity (which is inversely proportional to the average linear domain size) can be well described over the entire late-time regime and much of the intermediate-time regime by arguments recently put forward for earlier-time corrections to the limitingly late-time stages of phase separation.

We have confined over 5×${10}^{12}$ atoms of hydrogen in a static magnetic trap. The atoms are loaded into the trap by precooling with a dilution refrigerator. At operating densities near 1×${10}^{13}$ ${\mathrm{cm}}^{\mathrm{-}3}$ the gas is observed to be electron and nuclear polarized in the uppermost hyperfine state. The long lifetime of the trapped gas (over 20 min) suggests that it is thermally decoupled from the wall and has evaporatively cooled to a temperature of about 40 mK. The residual decay of the gas density is consistent with spin relaxation induced by dipolar interactions between atoms.