We present an analysis of the electron-energy-loss spectra produced by dipole scattering from lattice vibrations of the $p(2\mathrm{}\times 2)$ and $c(2\mathrm{}\times 2)$ oxygen overlayer on the Ni(100) surface. We conclude that the distance between the oxygen layer and the Ni surface is very much smaller for the $c(2\mathrm{}\times 2)$ overlayer than for the $p(2\mathrm{}\times 2)$, in accord with a recent suggestion by Upton and Goddard.

The cluster compounds ${\mathrm{Nb}}_6$${\mathrm{I}}_{11}$ and H${\mathrm{Nb}}_6$${\mathrm{I}}_{11}$ exhibit a coupled structural and electronic phase transition. The structural deformation is accompanied by a crossing of electronic levels which leads to a reduction of the spin degeneracy. We expect such level-crossing transitions to occur in other compounds containing transition-metal clusters.

Measurements of angular correlation of $\gamma$ rays from positron annihilation in Cu-Ge alloys have been used to reconstruct the momentum density in these alloys in the (110) plane. The densities show, for the first time in a copper alloy, details beyond fermiology which are linked to the detailed character of the electron wave functions and thus to $s-d$ hybridization. This hybridization undergoes large and anisotropic changes upon the alloying of Cu with Ge.

We have studied the "$5f$, $6d$" electron states of the system $\mathrm{U}{\mathrm{Sb}}_x{\mathrm{Te}}_{1-x}$ (100) using photoemission spectroscopy with synchrotron radiation. In contrast with the generally accepted picture of uranium chalcogenides and pnictides, we find for UTe that the main $5f$ level lies 0.75 eV below $E_{\mathrm{F}}$ rather than at $E_{\mathrm{F}}$ and that $6d$ states exist at $E_{\mathrm{F}}$. Our results may be explained with a model having a correlated quasilocalized $5f^{3-\delta }(\delta =0-0.5\mathrm{}$) level resonant with broader $6d$ bands rather than bandlike $5f$ levels.

The magnetizations and Curie temperatures of amorphous particles produced by spark erosion are found to be greatly reduced from the values for amorphous ribbons of the same compositions. The differences increase as particle size decreases. This behavior is interpreted as a decrease of chemical short-range order in the particles as a result of their faster quenching rate. Anomalous low-field behavior in the critical region also supports this conclusion.

A computer simulation of an isotopically disordered harmonic crystal with positive and negative masses is presented. This system may be related to a Heisenberg-Mattis random magnet, for which our results give the elementary excitations. Ideas of percolation theory are employed to explain the existence of a mobility edge in two and three dimensions whenever the positive or negative masses, but not both, percolate. For the corresponding random magnet this implies a new kind of magnon spectrum in which localized and extended states coexist.

High-temperature treatment in a reducing atmosphere of Ni-doped MgO crystals resulted in the formation of colloids with an average size of about 50 nm. The colloids are coherent nickel precipitates having a fcc structure ($a=0.352\mathrm{}$ nm), and occasionally a bcc structure ($a=0.288\mathrm{}$ nm). The ratio of magnetic to nuclear scattering amplitudes for the (111) precipitate reflection was about 17% below the value for nickel. Optical absorption measurements indicate that a broad optical band centered at ∼ 2.2 eV is associated with the colloidal precipitates.

It is shown that the same arguments which lead to black-hole evaporation also predict that a thermal spectrum of sound waves should be given out from the sonic horizon in transsonic fluid flow.

We study the $K_L-K_S$ mass difference and the $K_L\to {\mu }^{+}{\mu }^{-}$ decay rate in the Kobayashi-Maskawa model. If the matrix element $〈{\overline{K}}^0\left|{\left[\overline{s}{\gamma }_{\mu }\right(1-{\gamma }_5\left)d\right]}^2\right|{\overline{K}}^0〉$ is sufficiently small (e.g., as estimated in the Massachusetts Institute of Technology bag model), then a stringent upper bound on the top-quark mass can be obtained.

We present cross-section measurements for inclusive kaon charge exchange, $(K^{-},p)\to ({\overline{K}}^0,X)$, at 68, 116, and 176 GeV/c in the kinematic region $x>\mathrm{}0.7\mathrm{}$ and $-t<\mathrm{}1.3\mathrm{}$ (GeV/${\mathit{c})}^2$. The results are in excellent agreement with the predictions of triple-Regge theory and for the first time confirm the dominance of the Regge-Regge-Pomeron terms.

We discuss coherent conversion of hypothetical very light pseudoscalar bosons into a photon in the Coulomb and vector meson fields of a nucleus. The process provides a way to look for such bosons independently of whether their mass and lifetime allow for detection of the two-photon decay.

A proof of confinement in quantum chromodynamics is presented that relies only upon general properties of the theory, such as asymptotic freedom and analyticity.

Massive neutrinos may dominate the universe's rest mass and compose galactic halos. By requiring that the photoionization of the high-velocity clouds of neutral hydrogen near our galaxy not exceed observational limits, we find that the radiative decay lifetime for ionizing photon production by neutrinos ($m_{\nu }>27.2\mathrm{}$ eV) composing our galactic halo must exceed ${10}^{24}$ sec.

The isoscalar giant quadrupole resonance in ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, studied by ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ ($\alpha$, ${\alpha }^{\prime }c$) angular correlation experiments (in which the charged particle $c={\alpha }_0, {\alpha }_1, p_0, p_{1,2}$), constitutes the first obvious case of a dominant direct nucleon decay of a giant quadrupole resonance.

Deep-inelastic electron scattering from ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ at momentum transfers $1<~Q^2<~4$ (GeV/${\mathit{c})}^2$ is successfully described in a quark-cluster model of the nucleus. The quark-cluster probabilities and Fermi motion are obtained from a nuclear wave function consistent with low-energy data. A nucleon-bag (three-quark-cluster) radius of 0.45 fm provides an optimal description of the data. It fixes the geometrical probabilities at 0.83, 0.16, and 0.01 for three-, six-, and nine-quark clusters, respectively.

We remark that resonances in the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^8{}_{}{}^{}\mathrm{Be}$)${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ reaction are due to the "exit doorway state," that is ready for decay to the exit channel. We find a parameter-free formula that relates the resonance energy and angular momentum of the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ system to those of the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ system. If we use the experimental resonance energies of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, this formula yields more than a dozen one-to-one correspondences to the resonance energies of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^8{}_{}{}^{}\mathrm{Be}$)${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$. We also find a parameter-free formula for ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^4{}_{}{}^{}\mathrm{He}$)${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$.

Spectra of $\gamma$ rays in the 2-30-MeV range have been observed following ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$-induced reactions leading to the ${}_{}{}^{122}{}_{}{}^{}\mathrm{Te}$, ${}_{}{}^{150}{}_{}{}^{}\mathrm{Gd}$, and ${}_{}{}^{164}{}_{}{}^{}\mathrm{Er}$ systems. Shoulders in the spectra for $E_{\gamma }>10\mathrm{}$ MeV are interpreted as arising from the giant dipole resonance and are consistent with statistical-model calculations that use the giant-dipole-resonance strength function. Their observation offers the possibility of studying nuclear shapes and dynamics as functions of temperature and spin.

First observations of the photogeneration of spin-polarized hydrogen atoms and electrons are reported. A mixture of cesium vapor and helium and hydrogen buffer gases is optically pumped with a circularly polarized tunable—dye-laser beam (4593 Å). The paramagnetic species (H atoms, $e^{-}$) generated by the laser-induced processes are detected with use of spin-exchange-magnetic-resonance spectroscopy.

High-$\beta$, collisionless, toroidal multipole equilibria with parameters $n=5\mathrm{}\times {10}^{13}$ ${\mathrm{cm}}^{-3\mathrm{}}$, $T_i=200\mathrm{}$ eV, $T_e=25\mathrm{}$ eV, and bridge $\beta =8\mathrm{}$% have been obtained in the University of California at Los Angeles dodecapole. The equilibrium is characterized by perturbed vacuum magnetic fields, flat internal pressure profile with sharp edge, and a steep hoop bridge profile 2 ion-gyroradii wide centered on the separatrix. The transition from diffuse profiles at low $\beta <1\mathrm{}$% to sharp profiles at high $\beta >~5$% is observed. A stable equilibrium is observed in excess of 400 Alfvén times.

A wide range of magnetohydrodynamically stable high-$\beta$ plasmas is produced in the University of Wisconsin Levitated Toroidal Octupole. Near the single-fluid regime we obtain, in the bad-curvature region, $\beta =nk(T_e+T_i)\frac{8\pi }{B^2}\approx 8$%, twice the theoretical single-fluid ballooning instability limit of 4%. We also obtain stable plasmas at $\beta =35\mathrm{}$%, nine times the theoretical limit, in a regime in which finite-ion-gyroradius (e.g., gyroviscosity) effects are important. Experimental spatial profiles of the equilibrium diamagnetism are compared with theory.