The dispersion of surface vibrational modes associated with the $c(2\mathrm{}\times 2)$ adsorbate layer of oxygen on Ni(100) is measured throughout the two-dimensional Brillouin zone along the [110] direction. Two oxygen modes and two nickel surface phonons are observed. A lattice-dynamical analysis gives good agreement with the data when the oxygen atom sits at ∼0.9Å above the nickel surface at the fourfold hollow site.

Angle-resolved photoemission extended fine structure from adsorbate core levels yields complete, accurate surface structures without resort to trial-and-error comparisons to theory. Scattering peaks from individual substrate atoms were observed with use of $\mathrm{S}\mathrm{}\left(1s\right)\mathrm{}$ photoemission from $c(2\mathrm{}\times 2)\mathrm{S}/\mathrm{Ni}\mathrm{}\left(001\right)\mathrm{}$ and $p(2\mathrm{}\times 2)\mathrm{S}/\mathrm{Cu}\mathrm{}\left(001\right)\mathrm{}$, along [011]. Fourfold-hollow site geometries were found for both systems, with interatomic distances of $R(\mathrm{S}-\mathrm{N}\mathrm{i})=2.24\mathrm{}\left(3\right)\mathrm{}$ Å and $R(\mathrm{S}-\mathrm{C}\mathrm{u})=2.28\mathrm{}\left(3\right)\mathrm{}$ Å.

A new structure has been observed in the phonon focusing pattern of a highly polished sapphire crystal with a metalized surface. It corresponds to a concentration of transverse phonons close to the critical cone for mode conversion between transverse and longitudinal waves. This wave-vector channeling effect is interpreted in terms of evanescent longitudinal waves at a weakly bonded sapphire-metal interface.

An electron-diffraction analysis is presented of the structure of amorphous hydrogenated carbon prepared from a dc magnetron glow discharge in argon-acetylene mixtures. On the basis of the evidence provided by the reduced intensity function, the atomic radial distribution function, and a reconstruction of the reduced intensity function based on a graphite layer model, it is concluded that such films exhibit a threefold coordinated structure with only slight correlation in the positions of two-dimensional layers.

Phonons emitted by superconducting tunneling junctions into insulator crystal substrates exhibit a sharp amplitude reduction above 85 GHz if the tunneling diodes are covered by ${}_{}{}^4{}_{}{}^{}\mathrm{He}$. This is attributed to the onset of an enhanced phonon transport into helium.

Neutron-scattering results on the decomposition in two AlZnMg alloys, after three different quenching procedures and for three annealing temperatures, can be represented by an unique curve if reduced variables for Guinier radius, $\rho =\frac{R_G\mathrm{}\left(t\right)\mathrm{}}{R_0}$, and the volume fraction of clusters, $v=\frac{V\left(t\right)\mathrm{}}{V_{\infty }}$, are used. The invariant curve $\rho$ vs $v$ reflects predominant nucleation at the beginning—i. e., increase of volume fraction connected with a small variation of $R_G$—and the coarsening regime when the equilibrium volume fraction is approached.

A novel approach to dimerization is developed, based on a many-body valence-bond approach, that predicts enhancement of the dimerization on inclusion of the on-site electron repulsion. Exact numerical calculations are presented to substantiate this conclusion.

The effect of electron-electron repulsion on the ground-state properties of one-dimensional electron-phonon systems is considered in the half-filled-band case. Two different electron-phonon models are studied, with use of a numerical simulation technique. For large phonon frequency, an on-site electron repulsion suppresses the Peierls distortion in both models, while for small phonon frequency, it enhances the dimerization in one model. The effect of a nearest-neighbor repulsion is always to enhance the ground-state dimerization.

The spectral distribution of the magnetic fluctuation scattering from metallic nickel has been studied above the Curie temperature with unpolarized and polarized neutrons. The present measurements confirm previous results of a spin-wave-like mode above $T_c$. It is shown however, that the main part of the magnetic scattering above $T_c$ does not come from the spin-wave ridge in ($\omega$, $\overrightarrow{\mathrm{q}}$) space but from a spectral part centered at zero energy with a broad energy distribution.

The infrared spectrum of acetanilide shows a new band that is red shifted from the main amide-I maximum by about 15 ${\mathrm{cm}}^{-1\mathrm{}}$, the intensity of which increases at low temperature. It is suggested that this band may arise from the creation of amide-I solitons that are similar (but not identical) to those proposed by Davydov for the alpha helix in proteins.

The exact thermodynamic equations of the Coqblin-Schrieffer model are solved in the scaling regime and the impurity susceptibility and specific-heat curves are obtained as a function of temperature for zero field and for the impurity spin $J=\frac{1}{2},\dots ,\frac{7}{2}$. The strong dependences of the numerical results on the impurity spin are discussed in terms of a noninteracting Fermi-liquid model.

Measurements of the temperature dependences of the upper critical field $H_{c2\mathrm{}}$ and heat capacity $C_P$ of ${\mathrm{U}}_6$Fe are reported. $H_{c2\mathrm{}}$ increases very rapidly for a low-transition-temperature ($T_c=3.8\mathrm{}$ K) superconductor, reaching $H_{c2\mathrm{}}=64\mathrm{}$ kOe at $T=1.95\mathrm{}$ K. $C_P$ data indicate that ${\mathrm{U}}_6$Fe is a strong-coupled bulk superconductor and an exchange-enhanced paramagnet with an electronic coefficient $\gamma =145\mathrm{}\pm 10$ mJ/mole.${\mathrm{K}}^2$. ${\mathrm{U}}_6$Fe constitutes a metallurgically clean and conclusive example of the occurrence of high-field superconductivity in a strongly interacting Fermi liquid.

The Josephson voltage-frequency relation has been compared between two quite different (and nonideal) types of Josephson junctions—an indium microbridge and a planar normal-metal barrier junction of niobium with a copper normal region. It is found that the constant of proportionality between voltage and frequency is the same in both the junctions to at least 2 parts in ${10}^{16}$.

A procedure has been developed for deriving functions which characterize the effect of geomagnetic cutoffs on the charged primary cosmic rays that give rise to neutrinos arriving in any given direction at specified points on or in the earth. These cutoff distribution functions, for use in atmospheric-neutrino flux calculations, have been determined for eight nucleon-decay-experiment sites, by use of a technique which employs the Stormer cutoff expression, and which assumes collinear motion of neutrino and parent primary.

Within a real-space renormalization-group framework, the spin-½ Heisenberg ferromagnet in the presence of an Ising-like anisotropy on a self-dual hierarchical lattice is discussed. The results are exact for this lattice but can also be considered as a quite satisfactory approximation for the simple square one. The controversial point on how $T_c$ vanishes in the isotropic Heisenberg limit is analyzed: Quite strong evidence is presented favoring a continuous function of anisotropy. The crossover from the isotropic Heisenberg model to the pure Ising one is exhibited.

It is shown that the Laplace transform of the diffusion-controlled bimolecular rate kernel can be directly obtained as the solution of a Riccati equation with the annihilation distance as the independent variable. This provides an efficient alternative to solving the Smoluchowski equation. The solution is expanded in powers of the square root of the Laplace variable; for the first time, the question of convergence is discussed and settled, and terms other than the first two are given explicitly and recursively by quadratures.

It is shown that quantum gravity with a cosmological constant in a purely affine picture is a power-counting-renormalizable (unitary) theory. The relevance of such a result is based on the equivalence, proved by Kijowski, of the affine formulation of gravity with the standard affine-metric picture.

Forty-seven charm events have been observed in an exposure of the SLAC Hybrid Facility bubble chamber to a 20-GeV backward-scattered laser beam. Thirty-seven events survive all the necessary cuts imposed. Based on this number the total charm cross section is calculated to be ${63}_{-28\mathrm{}}^{+33\mathrm{}}$ nb.

In a continuing study of the spectroscopy of the $b\overline{b}$ bound quark systems the discovery of the lowest $P$-wave bound states by observation of photons from the decays $2{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}\left(b\overline{b}\right)\to \gamma +1\mathrm{}{}_{}{}^3{}_{}{}^{}P_J^{}{}_{}{}^{}\left(b\overline{b}\right)$ and $1{}_{}{}^3{}_{}{}^{}P_J^{}{}_{}{}^{}\left(b\overline{b}\right)\to \gamma +1\mathrm{}{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}\left(b\overline{b}\right)$ is reported. The photons are observed as narrow enhancements in the inclusive photon spectrum from ${\Upsilon }^{\prime }$ decays. The center of gravity of the ${}_{}{}^3{}_{}{}^{}P_J^{}{}_{}{}^{}$ states (${\chi }_b$), the fine-structure splitting, and the branching ratios for the two transitions are given.

This Letter reports on a new search for the muon-number—nonconserving decay $\mu \to e\gamma \gamma$, using two large NaI(Tl) crystals. The new upper limit obtained is $R(\mu \to e\gamma \gamma )<\mathrm{}8.4\mathrm{}\times {10}^{-9\mathrm{}}$ (90% C.L.).