The spectrum of bremsstrahlung radiation emitted by the scattering of protons by ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ near the 461-keV resonance has been studied at bombarding energies 130, 235, and 335 keV above the resonance. The measured spectra were analyzed and compared with the theoretical predictions calculated from the soft-photon approximation and the Feshbach-Yennie approximation.

The angular distribution of the tensor polarization $t_{20}$ in $\pi -d_{\mathrm{pol}}$ elastic scattering has been measured in the backward angular region at an incident pion energy of 138 MeV. Large oscillations have been found which are in disagreement with all theoretical calculations even when effects of the presently suggested dibaryon resonances with the assumed standard parameters are explicitly included.

Relativistic excitation energies and transition rates from the ${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ ground states to the first ${}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ and ${}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}$ excited states of berylliumlike ions are determined by using the newly developed multiconfiguration relativistic random-phase approximation (MCRRPA). Results from the MCRRPA theory are compared with those from other theories and experiments. The large discrepancies between the single-configuration RRPA predictions of excitation energies and the precise experimental values are resolved.

The enhanced electric fields and suprathermal electron production due to resonance absorption of a microwave beam in an inhomogeneous plasma are investigated. At unexpectedly low driver-field amplitudes, the enhanced field amplitude and associated electron acceleration are apparently limited by wave breaking rather than convection. In the wave-breaking regime, a simple cold-plasma model accurately predicts many of the results, including the observed increase in wave-breaking time, and decrease in hot-electron energy obtained upon use of a finite-bandwidth driver.

A class of model stellarator fields has been found in which the transport is reduced by an order of magnitude from transport in conventional stellarators, by localizing the helical ripple to the inside of the torus. The reduction is observed in numerical experiments, and explained theoretically. Realizations of this class are achievable with use of modular coils.

Calculations have been performed which demonstrate the possibility of operating poloidal divertors at high densities and low temperatures. Ionization of recycling neutral gas near the divertor neutralizer plate amplifies the input particle flux thereby raising the plasma density and lowering the plasma temperature. Low-temperature, high-density operation should reduce the erosion rate of the divertor walls and plate, and ease the pumping requirements in future large tokamaks.

High-precision $P_v\mathrm{}\left(T\right)\mathrm{}$ measurements have been made on liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ at low temperatures; the results yield values for the derivative of the heat capacity, $\frac{\partial C_v}{\partial v}$, which can be compared with those from actual heat-capacity measurements. The comparison shows agreement between the present data and $\frac{\partial C_v}{\partial v}$ from heat capacities of Wheatley but disagreement with $\frac{\partial C_v}{\partial v}$ from recent heat capacities of Haavasoja.

Dielectric relaxation studies in nematic liquid crystals with $\overrightarrow{\mathrm{E}}\parallel \overrightarrow{\mathrm{n}}$ give the unique opportunity to study a microscopically well-defined kinetic process in a temperature interval extending below $T_g$. Relaxation is nearly exponential at all temperatures and obeys the Vogel-Fulcher law even below $T_g$.

Time-resolved x-ray diffraction measurements of lattice strain in silicon during pulsed-laser annealing have been made with nanosecond resolution by using synchrotron radiation. Analyses of the strain in pure and boron-implanted silicon in terms of temperature indicate high temperatures and evidence for near-surface melting, in qualitative agreement with the melting model of laser annealing.

Anomalous slowing down of fluorescence decay at high excitation density has been observed in pyrene and $\alpha$-perylene crystals, and attributed to nonlinear fluorescence reabsorption by electronically excited molecules. This phenomenon may have various implications in studies of condensed phases at high levels of optical exciation.

A numerical method is developed to study the scaling of distribution of couplings of highly random antiferromagnetic Ising and quantum Heisenberg spin-½ systems. The method shows how freezing into inert local singlets prevents ordering down to temperatures well below the median nearest-neighbor coupling or bare exchange percolation threshold in positionally disordered systems with Heisenberg exchange varying exponentially with distance (e.g., doped semiconductors, quasi one-dimensional salts). This is contrasted with the Ising system.

High-resolution angle-resolved photoemission spectra for Fe(100) are reported which identify and characterize surface states near the Fermi energy extending from $\overline{\Gamma }$ to $\overline{X}$ of the two-dimensional Brillouin zone. These results provide an experimental test of recent transition-metal surface electronic structure calculations and yield predictions relevant to spin-polarized photoemission from Fe(100).

With use of Monte Carlo simulation techniques, it is shown that an exponential energy distribution of hopping sites gives rise to dispersive transport which is not experimentally distinguishable from multiple trapping. At low temperatures, the dispersive parameter $\alpha$ is equal to $\frac{T}{T_0}$. At high temperatures, the power-law approximation fails exactly as found for multiple trapping. These results show conclusively that hopping does give rise to dispersion and depending upon the hopping distribution function can be observed in a macroscopic system.

Thermal properties of large magnetic polarons localized on donors in a magnetic semiconductor are studied theoretically with the effect of thermodynamic fluctuations of magnetization taken into account. The model quantitatively describes recent spin-flip Raman scattering data for ${\mathrm{Cd}}_{0.95}$${\mathrm{Mn}}_{0.05}$Se.

The average positions of different bands in a solid are shown to be equal to the symmetry centers of the space group of the solid. These positions turn out to be eigenvalues of a band-center operator which is a conserved quantity for translationally invariant systems.

The Friedel sum rule for impurities is related to the Luttinger requirement that the volume of the Fermi surface of a crystal is independent of interactions. As a consequence important results derived by use of the Friedel sum rule, e.g., the $T\to 0$ properties of the Kondo problem, can be extended to periodic cases. Considered explicitly are the remarkable consequences for Fermi surfaces and Fermi-liquid properties of periodic Kondo and mixed-valence systems.

The entropy of a Robertson-Walker universe ($k=1\mathrm{}$, $\Lambda >0\mathrm{}$) in statistical thermodynamic stable equilibrium with conformal bosons is calculated with use of a new self-consistent method. Its value is similar to but higher than the entropy of an alternative empty de Sitter solution, which may help in interpretation of Hawking thermal states.

If one assumes a spontaneously broken local supersymmetry, big-bang cosmology implies that the universe is filled with a gravitino ($g_{\frac{3}{2}}$) gas—possibly its dominant constituent. From the observational bound on the cosmological mass density it follows that $m_{g_{\frac{3}{2}}}\lesssim 1$ keV. Correspondingly, the supersymmetry breaking parameter $F$ satisfies $\sqrt{F}\lesssim 2\times {10}^3$ TeV, requiring new supersymmetric physics in the teraelectronvolt energy region. An exact sum rule is derived and used to estimate the threshold and cross section for the production of the new states.

A measurement has been made of the neutron polarization, $P$, from 800-MeV $p-n$ quasielastic scattering at 133° c.m. This together with previous measurements of the analyzing power, $A$, at the same angle in free $n-p$ scattering at 775 MeV constitutes a $P-A$ check of time-reversal invariance. No evidence is found for time-reversal invariance violation in $n-p$ scattering at medium energies, a clear-cut disagreement with the model predictions of Bryan and Gersten.

The Lagrangian path integral for the hydrogen atom is calculated exactly by rescaling paths and performing the Kustaanheimo-Stiefel transformation in each short-time integral.