Low-energy—electron-loss spectroscopy is used to study collective surface excitations on accumulation layers on ZnO. A prominent loss peak is observed which shifts in energy with electron concentration. The results are well accounted for theoretically and provide direct evidence for the existence of two-dimensional plasmons.

By means of high-resolution electron-energy-loss spectroscopy (resolution ∼ 7 meV) atomic H and D are shown to adsorb on GaAs(110) on Ga and on As sites. From a comparison of the H and D vibration frequencies Morse adsorption potential curves for hydrogen on Ga and on As sites are constructed. The results are compared with thermal desorption data.

A path-integral method is developed for the calculation of the statistical properties of a class of dissipative mappings which exhibit strange attractors. Exact analytic results are derived for the low-order statistical moments. These nontrivial results are verified numerically.

Using a two-slit neutron interferometer, we have measured the shift of the interference pattern induced by the motion of a quartz rod. The measured shift is found to be in agreement with the quantum mechanical prediction derived from a relativity argument. Some peculiarities of the case of massive particles as compared with the classic Fizeau photon case are discussed.

We report on the observation of twelve like-sign (${\mu }^{-}{\mu }^{-}$) neutrino-induced dimuon events with muon momenta greater than 9 GeV. The background from $\pi$ and $K$ decay is 1.3 events so that we conclude that this prompt signal is real with a significance greater than 1 in ${10}^7$. Although the overall rate is higher than present theoretical estimates, the kinematic distributions of these events are qualitatively consistent with a picture of charm-anticharm production. The ratio of $\frac{{\mu }^{-}{\mu }^{-}}{{\mu }^{-}}$ shows a strong energy dependence and rises to (2.5±1.0) × ${10}^{-3\mathrm{}}$ at $E_{\nu }=250\mathrm{}$ GeV.

An excited $K^{\pi }=0^{+}$ band in ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ which can be associated with the prolate Hartree-Fock solution has been observed in the reactions ${}_{}{}^{25}{}_{}{}^{}\mathrm{Mg}$($\alpha$,$n\gamma$) and ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$($p$,$\gamma$). The $I^{\pi }=0^{+}$ through $6^{+}$ band members have been located at $E_x=6691, 7381, 9164, \mathrm{and} 11509$ keV, respectively. Strong distortion is indicated from $B\left(E2\mathrm{}\right)\mathrm{}$ values, resulting in $\left|Q_0\right|={876}_{-85\mathrm{}}^{+110\mathrm{}}$ mb.

The cross sections of ${}_{}{}^{3,4}{}_{}{}^{}\mathrm{He}$(${\pi }^{-}$,$n$)${}_{}{}^{2,3}{}_{}{}^{}\mathrm{H}$ have been measured at 285, 428, 525, and 575 MeV, extending the information on the energy dependence beyond the region previously known (50-300 MeV). The cross sections beyond the region of the $\Delta$ resonance are found to decrease less rapidly than that of the elementary $\pi d\to \mathrm{pp}$ process. This energy dependence suggests that pion absorption in a nucleus is associated with $\pi +N$ (off-shell) scattering which includes $I=\frac{1}{2} \pi N$ resonances that are strongly suppressed in $\pi d\to \mathrm{pp}$.

Selective population of high-$j$ and high-$K$ states in ${}_{}{}^{167,169,171}{}_{}{}^{}\mathrm{Er}$ nuclei has been observed in heavy-ion-induced single-neutron-transfer reactions. $\gamma$ rays in coincidence with outgoing particles have been used to aid in level assignments and several previously unobserved high-$j$ states have been identified.

We report the first observation of zero-field quantum beats in the electron-impact excitation of an atomic state. The effect has been observed in electron-photon coincidence experiments on the $3{}_{}{}^2{}_{}{}^{}P$ state in sodium. The beats arise from the influence of the hyperfine structure in the $J=\frac{3}{2}$ level of the excited state.

We describe a unique indicator for the effect of second—Born-approximation terms in the secondary-electron spectra of continuum-electron capture by positive ions. Specifically, a discontinuity in the function $f(v_e,v_p,{\theta }_e)$, where $d^3\sigma \propto \left[\frac{f(v_e,v_p,{\theta }_e)}{|{\overrightarrow{\mathrm{v}}}_e-{\overrightarrow{\mathrm{v}}}_p|}\right]d{E}_{e}d{\Omega }_e$, indicates second—Born-approximation contributions. Three different experiments are analyzed with respect to this indicator. In all cases we find strong evidence for the discontinuity and hence the presence of second—Born-approximation terms.

We derive a differential equation governing the evolution of the turbulent energy during the course of the ion-acoustic instability. It is shown that the modification of the electron distribution function constitutes an efficient mechanism of saturation. The saturated energy is found to be lower than that obtained in any theory of saturation by ions.

It is found that appreciable multibeam effects are observable even when the Ewald sphere is quite far from any extra node in reciprocal space. It is proposed to use these effects for phase identification in mosaic crystals.

The domain-coarsening kinetics of ordering systems with $p$-fold—degenerate equilibrium states, quenched from high temperatures, is analyzed. For long times ($t$) and low temperatures, the domain sizes equilibrate as a power law in $t$ for $p<d+1\mathrm{}$ and as a logarithmic function of $t$ for $p>~d+1\mathrm{}$, where $d$ is the spatial dimensionality of the system. The relation of these slowly equilibrating, kinetically disordered systems to glasses and suggestions for simulations and experiments are discussed.

A low-symmetry low-energy—electron-diffraction pattern observed at a fractional nitrogen-adatom coverage of 0.4 monolayer on W{001} is attributed to a structure composed of islands in which the surface-layer tungsten atoms are displaced to produce a contracted interatomic spacing. The model correlates well with other published data for this system.

We report observations of nonlinear phenomena in the propagation of zero-sound pulses near a collective-mode attenuation peak in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$B$. These include saturation of the sound absorption, amplitude dependence of the group velocity, and pulse breakup. Our data show effects similar to those observed in nonlinear optical systems. We suggest that above a threshold input level, the sound pulse propagates as a soliton.

A model of a disordered planar model is introduced and solved with use of the replica method. The model is designed to mimic the inhomogeneities known to exist in helium and granular superconducting films. The results indicate that at onset, the universal results, predicted on the basis of renormalization-group analysis, hold to lowest order in the parameter measuring the disorder. The disorder has the important effect of increasing the vortex pairs couplings, resulting in an initial increase of the critical temperature. Possible consequences of the results to related experiments are also presented.

The equilibrium thermodynamics of the $s-d$ exchange model with arbitrary impurity spin has been investigated on the basis of the exact solution.

From the critical-field data on the strongly Pauli limited superconductor ${\mathrm{V}}_3$Ga it is shown that large electron-electron interactions (and their associated spin fluctuations) may play an important role in the superconductivity of the $A15\mathrm{}$ superconductors. This possibility is shown to be consistent with existing $T_c$, heat-capacity, and spin-susceptibility data on several $A15\mathrm{}$ superconductors.

We discuss the properties of an ideal relativistic Bose gas with nonzero chemical potential $\mu$ (i.e., with net charge) but differ from all previous discussions by including the effects of antiparticles. We obtain for the first time the relevant high-temperature expansion, emphasizing the constraint $\left|\mu \right|<~m$, and show that a box of massless particles can have a net charge even though $\mu =0\mathrm{}$. Finally, we discuss the properties of Bose-Einstein condensation for both massless and massive bosons in $d$ space dimensions.

We construct a natural SU(2) ⊗ U(1) ⊗ [SU(2)]′ gauge model in which the lightest weak bosons can be heavier than those of the standard model. At energies below the $Z$ boson, the model could be distinguished from the standard model by precision measurements of $e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-}$.