Angle- and velocity-resolved inelastic He scattering has been used to study how the surface dynamics of thin rare-gas films evolves on a layer-by-layer basis. Surface-phonon dispersion relations for ordered 1-, 2-, 3-, and 25-layer Kr films physisorbed on Ag(111) are presented along $\overline{\Gamma }\overline{M}$ across the entire Brillouin zone. The monolayer data are dispersionless, indicative of an Einstein oscillator mode. In comparison, the 25-layer film has a well-developed Rayleigh wave, typical of a thick crystal surface. Excitation linewidths for monolayer Kr, which vary across the zone, are also briefly discussed.

uv-photoemission spectra of the $\alpha$ and $\gamma$ phases of Ce have been measured with an unprecedented resolution (20 meV). A detailed many-body calculation based on the Anderson impurity model and including the $4f^1$ spin-orbit splitting has been performed. It accounts perfectly for the fine structures observed in the spectra. Within the energy range corresponding to the ground-state lowering by the $f-d$ hybridization, the $f$ contribution to the spectra reveals the density of low-energy excitations culminating at $E_{\mathrm{F}}$.

We describe superconducting-quasiparticle interface states which are produced by a certain class of local potentials at interfaces involving superconductors. These states penetrate at least a coherence distance into the superconductor and arise even when the pair potential is uniform throughout the superconductor. We specifically predict such a state at the interface between an insulating ferromagnet below its Curie temperature and a thin superconductor.

The energy loss and differential probability of energy losses is calculated to all multipole orders for a charged particle moved uniformly past a sphere. The sphere's response is characterized by use of a local dielectric function.

The Hopfield model for a neural network is studied in the limit when the number $p$ of stored patterns increases with the size $N$ of the network, as $p=\alpha N$. It is shown that, despite its spin-glass features, the model exhibits associative memory for $\alpha <{\alpha }_c$, ${\alpha }_c\gtrsim 0.14$. This is a result of the existence at low temperature of $2p$ dynamically stable degenerate states, each of which is almost fully correlated with one of the patterns. These states become ground states at $\alpha <0.05\mathrm{}$. The phase diagram of this rich spin-glass is described.

A direct approach to resolve the solar-neutrino problem would be to observe neutrinos by use of both neutral-current and charged-current reactions. Then, the total neutrino flux and the electron-neutrino flux would be separately determined to provide independent tests of the neutrino-oscillation hypothesis and the standard solar model. A large heavy-water Cherenkov detector, sensitive to neutrinos from ${}_{}{}^8{}_{}{}^{}\mathrm{B}$ decay via the neutral-curent reaction $\nu +d\to \nu +p+n$ and the charged-current reaction ${\nu }_e+d\to e^{-}+p+p$, is suggested for this purpose.

A recent theory of two-dimensional percolation predicts critical singularities identical to those appropriate for the associated dilute Ising model. This implies the absence of a separate universality class for two-dimensional percolation processes. Novel numerical and series-expansion studies are presented in support of this unexpected result.

New covariant actions for both the Green-Schwarz superstrings and the heterotic strings are presented. The construction of these new actions is based on a simple, intuitive, physical picture. The connection to the Green-Schwarz light-cone quantization is discussed.

A new Lagrangean formulation for supersymmetric particles is given. With the inclusion of a Wess-Zumino term one can obtain any irreducible representation of supersymmetry upon quantization. The quantization is carried out in a gauge-invariant manner. A possible generalization of this Lagrangean to superstrings is given.

Conformal invariance allows a complete classification of critical theories in two-dimensional systems with continuous symmetries. We study the spin-½ chain by non-Abelian bosonization to show how it fits into this classification.

Recent ideas in the geometrical model of multiparticle production in hadron-hadron collisions are applied to two-jet events in $e^{+}{e}^{-}$ annihilation. A coherent picture emerges which is compared with experimental data. A number of predictions are made, including the prediction that Koba-Nielsen-Olesen scaling does not obtain for such events. The relationship with QCD models remains unexplored.

Deuteron electrodisintegration at threshold has been measured between $Q^2=7\mathrm{} \mathrm{and} 28$ ${\mathrm{fm}}^{-2\mathrm{}}$. Nonnucleonic degrees of freedom are essential for the interpretation of the data. In particular, beyond 20 ${\mathrm{fm}}^{-2\mathrm{}}$ the data provide evidence for processes beyond the conventional one-pion exchange.

We report the first experimental observation of nuclear deexcitation via an electronic-bridge mechanism. We have studied the deexcitation of the 30.7-keV ($T_{\frac{1}{2}}\sim 13.6$ yr) isomeric level of ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$ with the electronic bridge involving initial-state $L$ electrons and final-state $N$ or higher electrons. The relative probability for the inelastic-electronic-bridge effect deexcitation, as compared to direct $\gamma$-ray decay of the isomeric level, is 0.070±0.018. This result is within an order of magnitude of our theoretical prediction of 0.19.

Gamow-Teller transition probabilities are extracted for eight nuclei with masses between $A=13\mathrm{} \mathrm{and} 39$ from medium-energy ($p, n$) reactions via the distorted-wave impulse approximation, and compared with experimental $\beta$-decay and with free-nucleon transition probabilities. These comparisons indicate strongly that the renormalization of the Gamow-Teller operator needed for ($p, n$) reactions on finite nuclei is different from that needed for $\beta$ decay.

The coherence recently observed in heavy-ion collisions is attributed to the decay of a collective state of $\Delta +N$ baryons. A simple model for this phenomenon is formulated and several new experimental implications are discussed.

Systematic measurements of linear-momentum-transfer distributions have been performed for ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$-, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$-, and ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$-induced reactions on ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ at energies up to $\frac{E}{A}=45\mathrm{}$ MeV. The data establish a limitation in linear momentum transfer at 200 MeV/c per projectile nucleon, which occurs near a beam energy of $\frac{E}{A}\approx 35$ MeV. This limitation is interpreted in terms of precompound particle emission, and calculations based on this concept reproduce the global energy dependence of the data.

The lifetimes of the $\gamma$ rays in the collective rotational bands observed in the $\gamma$-ray continuum at very high spin in ${}_{}{}^{152}{}_{}{}^{}\mathrm{Dy}$ are shown to be less than 100 fs for energies above 0.90±0.05 MeV. The corresponding $B\left(E2\mathrm{}\right)\mathrm{}$ values are very enhanced and provide definite evidence that the rotational bands are associated with a superdeformed prolate structure in ${}_{}{}^{152}{}_{}{}^{}\mathrm{Dy}$.

The decay of the $T=\frac{5}{2}$ isobaric analog state in ${}_{}{}^{35}{}_{}{}^{}\mathrm{K}$ at 9053 ± 45 keV, fed by the superallowed $\beta$ decay of 50 ± 30-ms ${}_{}{}^{35}{}_{}{}^{}\mathrm{Ca}$, results in two-proton emission to both the ground and the first excited states of ${}_{}{}^{33}{}_{}{}^{}\mathrm{Cl}$. The measured energy correlations between the two decay protons indicate a sequential-decay mechanism. From the isobaric-multiplet mass equation, a mass excess of 4453 ± 60 keV can be predicted for the ground state of ${}_{}{}^{35}{}_{}{}^{}\mathrm{Ca}$.

The $\beta$-decay energy spectrum which results from the decay of one of the nuclei in the ${\mathrm{T}}_2$ molecule has been computed. An accurate, explicitly correlated basis set was used to describe electronic states of both the parent and the daughter molecules, and effects of nuclear motion have been taken into account. All the channels which meaningfully affect the spectrum have been incorporated, including resonance and scattering channels. The spectra are presented for several neutrino masses. It is shown that the molecular effects are crucial for accurately determining the neutrino mass from a tritium $\beta$-decay experiment.

New experimental data are presented for the scattering of 35-keV electrons by He, Ne, and Ar in the limit of vanishing momentum transfer. Previous data of Geiger and Morón-León show a strong forward peak with structures similar to a Fraunhofer diffraction pattern (shadow scattering) for elastic scattering of 15-25-keV electrons. No recent theory can explain this effect; therefore we repeated the experiment. The new data agree well with partial-wave calculations utilizing configuration interaction and Hartree-Fock potentials. The results are compared with the previous unexpected findings.