Proton-proton correlations were measured in ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$-induced reactions on ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ at 400 MeV. Measurements at both small and large proton relative momenta indicate that a significant fraction of the correlated protons are emitted from a spatially localized region of high excitation.

Major-shell effects are seen in the unresolved $\gamma$-ray spectra coming from high-spin states in the transition region: ${}_{}{}^{154}{}_{}{}^{}\mathrm{Er}$ to ${}_{}{}^{160}{}_{}{}^{}\mathrm{Er}$. The angular momentum alignments in the valence shell, which are spread in frequency in the heavier nuclei, are compressed into the low-frequency region in the lighter nuclei and separate almost completely from the angular momentum contributions due to the next higher major (proton) shell.

Neutron spectra as a function of spin and the neutron multiplicity distribution have been measured for the reaction 233-MeV ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$ + ${}_{}{}^{92}{}_{}{}^{}\mathrm{Zr}$. The emission of two neutrons constitutes the strongest decay channel, in contrast to statistical-model calculations which predict the emission of three neutrons to be the strongest by more than one order of magnitude. This is possibly due to trapping in a superdeformed potential well, similar to that giving rise to fission isomers, as the compound nucleus relaxes from the highly distorted initial shape.

Unexpectedly large cross sections have been observed for the collision-induced excitation of ${\mathrm{H}}_3^{+}$ with subsequent decay to the three-particle state ${\mathrm{H}}^{+}$ + ${\mathrm{H}}^{-}$ + ${\mathrm{H}}^{+}$. The differential (in laboratory angle) cross sections for ${\mathrm{H}}^{-}$ were found to be comparable to that for the final-state formation of ${\mathrm{H}}_2^{+}$ + $\mathrm{H}\mathrm{}\left(2p\right)\mathrm{}$, as determined by a separate coincidence experiment, indicating a strong ionic component to the excited-state wave function.

The radio-frequency-wave heating of ions in a tokamak plasma employing the second-harmonic ion-cyclotron resonance interaction has been demonstrated in recent high-power (3-MW) experiments on the Princeton Large Torus tokamak.

A mechanism of long-scale magnetic field generation from rippled surface irregularities is given and compared with the thermoelectric effect. Criteria are given for the former dominating over the latter. These criteria are accessible in present-day experiments. An experiment is done to show an implication of the above mechanism.

Total-energy calculations based on microscopic electronic structure are combined with position-space renormalization-group calculations to predict the structural phase transitions of the Si(100) surface as a function of temperature. It is found that two distinct families of reconstructed geometries can exist on the surface, with independent phase transitions occurring within each. Two critical temperatures representing order-disorder transitions are calculated.

Ion shadowing and blocking measurements show that the first interlayer spacing of Ni(001) is contracted if the surface is clean, but expanded if it is covered by half a monolayer of oxygen. The thermal vibration amplitude of surface atoms is strongly enhanced. A simple tight-binding model relates the change in first interlayer spacing to a change in surface force constants, and explains the recently measured surface phonon dispersion curves.

A mean-field theory for spin-glasses is constructed in terms of coexisting spontaneous symmetry breaking in a whole spectrum of localized eigenstates of the exchange interaction. The spectrum moves with time as the smallest frozen modes begin to disorder, providing a simple physical picture of the universally observed features of the time dependence of the susceptibility. Similar dynamics are expected in disordered ferromagnets.

The local-density approximation for the exchange-correlation potential understimates the fundamental band gaps of semiconductors and insulators by about 40%. It is argued here that underestimation of the gap width is also to be expected from the unknown exact potential of Kohn-Sham density-functional theory, because of derivative discontinuities of the exchange-correlation energy. The need for an energy-dependent potential in band theory is emphasized. The center of the gap, however, is predicted exactly by the Kohn-Sham band structure.

The energy-band gap of an insulator is obtained from the eigenvalues of the one-particle density-functional equation for the ground state and a finite correction due to the discontinuity of the functional derivative of the exchange and correlation energy. This correction is expressed in terms of the improper self-energy and the density-functional exchange-correlation potential. It is evaluated for a two-plane-wave model including exchange only.

Electrical relaxation measurements at high pressures have been carried out on lead fluoride doped with lanthanum and cerium. A single, strong relaxation peak is observed and the relaxation time decreases with increasing pressure. This is contrary to the behavior exhibited by all known relaxations and can be explained by attributing the relaxation to a substitutional trivalent rare-earth ion compensated either by an interstitial fluorine ion with a soft attempt mode or by an electron.

A critical scaling of the real and imaginary parts of the low-frequency ac conductance of insulating phosphorus-doped silicon near the metal-insulator transition has been observed. The results are interpreted as evidence of an electron glass, i.e., glasslike behavior, intimately connected with the scaling description of the transition, in which Coulomb interactions play a significant role.

A two-dimensional model of interacting electrons on a lattice, the Hubbard model, has been studied by means of a numerical simulation technique. Results for the half-filled-band sector are presented for lattices of up to 6×6 spatial sites, as a function of temperature and electron-electron repulsion $U$. In the ground state, the system is found to exhibit antiferromagnetic long-range order for all values of $U$, although greatly reduced from the mean-field-theory predictions.

Asymmetric heat generation is detected by Seebeck-voltage measurements in currentcarrying microcontacts, produced by adjoining two wedges of $n$-type silicon in ultrahigh vacuum. Decreasing the contact dimensions increases this asymmetry, which arises in the Knudsen regime of ballistic electron transport when the geometric dimensions of the contacts are sufficiently reduced to become comparable to the electron mean free path.

The random-phase-approximation integral equation for the density response function of the electron gas in a metal film is solved (in a cosine representation) for all wave vectors and frequencies. The Kohn-Sham-Lang ground-state wave functions are used in the computation of the noninteracting electron response. Numerical results are presented for the dynamic structure factor and for the screening field at the position of an oscillating point dipole placed in the surface region.

Rietveld structural refinement of neutron powder diffraction data for Chevrel-phase samples in both the Sn-Mo-S-O and Pb-Mo-S-O systems has led to a model for an oxygen-containing point defect. The oxygen substitutes for the sulfur located in the special position along the $\overline{3}$ axis and the metal ion is displaced ≃ 0.8 Å toward the oxygen impurity, presumably forming a covalent bond. This defect is responsible for the wide variation reported for $T_c$ and $\frac{c}{a}$ (hexagonal, lattice-constant ratio).

The problem of two-dimensional localization in the presence of a magnetic field is reconsidered. The existence of extended electronic states is demonstrated by use of the replica formalism and duality arguments. These states are analogs of $\theta =\pi$ vacua in four-dimensional Yang-Mills theories, and occur at the center of each Landau band. The present results complete the explanation of the integrally quantized Hall effect.

Chaotic intermittency between soliton dynamic states has been found in a perturbed sine-Gordon system in the absence of an external ac driving term. The system is a model of a long Josephson oscillator with constant loss and bias current in an external magnetic field. The results predict the existence of a current step between the first two Fiske steps in the current-voltage characteristic. A simple probability model demonstrates an asymmetry in the statistical nature of the switching in the two directions.

The Hamiltonian of a system containing decaying states is subjected to a nonunitary similarity transformation which introduces the wave functions of these decaying states as well as those of the "antidecaying" dual states explicitly into the representation. The dependence of the Green's-function pole on these wave functions is used to formulate a variational principle for their determination, yielding a non-Hermitian, nonlinear wave equation including self-energy contributions. Explicit solutions are given in a simple example.