A lower bound for the photino mass $m_{\tilde{\gamma }}$ as a function of the spin-0 fermion superpartner mass $m_{\tilde{f}}$ is derived as an extension of the calculation of Lee and Weinberg. The Majorana nature of the photino induces a $p$-wave threshold for annihilation $\tilde{\gamma }\tilde{\gamma }\to f\overline{f}$ into light fermions, and leads to a rather unexpected form for the bound: for $25 \mathrm{GeV}\lesssim m_{\tilde{f}}\lesssim 45 \mathrm{GeV}$, ${\left(m_{\tilde{\gamma }}\right)}_{min}\simeq m_{\tau }=1.8\mathrm{}$ GeV; for $m_{\tilde{f}}>45\mathrm{}$ GeV, ${\left(m_{\tilde{\gamma }}\right)}_{min}$ increases approximately linearly with $m_{\tilde{f}}$ to a value of 20 GeV when $m_{\tilde{f}}=100\mathrm{}$ GeV.

Some problems encountered in describing the $\Delta S=1\mathrm{}$ semileptonic hyperon decays in terms of the Cabibbo model are considered, and these decays are studied in an $\mathrm{SU}{\mathrm{}\left(2\right)\mathrm{}}_L\otimes \mathrm{SU}{\mathrm{}\left(2\right)\mathrm{}}_R\otimes \mathrm{U}\mathrm{}\left(1\right)\mathrm{}$ gauge theory. It is found that a reported discrepancy between the Cabibbo model and experiment in $\Lambda \to \mathrm{pe}{\overline{\nu }}_e$ can be accounted for if right-handed currents exist. The only obstacle to this interpretation is the experimental sign of the electron asymmetry in $\Sigma \to \mathrm{ne}{\overline{\nu }}_e$ which, as in the Cabibbo model, is predicted to be negative.

A possibility of a very clean signature for the production of ${W_R}^{\pm }$ is pointed out. If the right-handed neutrino is lighter than ${W_R}^{\pm }$, left-right symmetric gauge theory predicts the decay ${W_R}^{+}\to {\mu }^{+}{\mu }^{+}+2\mathrm{}$ hadronic jets, with the branching ratio ∼3%. The lack of neutrinos in the final state and the absence of a sizable background make ${W_R}^{\pm }$ rather easy to detect (if it exists). Detailed predictions regarding the production and decay rates of ${W_R}^{+}$ are presented.

The deep-inelastic electromagnetic structure functions of steel, deuterium, and hydrogen nuclei have been measured with use of the high-energy electron beam at the Stanford Linear Accelerator Center. The ratio of the structure functions of steel and deuterium cannot be understood simply by corrections due to Fermi-motion effects. The data indicate that the quark momentum distributions in the nucleon become distorted in the nucleus. The present results are consistent with recent measurements with high-energy muon beams.

Within a modified barrier penetration model the fusion cross section for ${}_8{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{74}{}^{184}{}_{}{}^{}\mathrm{W}$ is calculated at subbarrier energies. It is shown that nuclei with positive quadrupole moments and large negative hexadecapole moments have enhanced fusion cross sections over elongated systems only. Fusion measurements with such systems will provide a definitive answer to the question of deformation effects on subbarrier fusion.

The impulse approximation to the Dirac optical potential for proton-nucleus elastic scattering is deduced from elementary considerations and found to be in remarkably good agreement with phenomenological parameters. The large difference between the real parts of scalar and vector optical potentials is explained by the impulse approximation.

First calculations based on an impulse-approximation Dirac optical potential are presented. All input parameters are constrained by other experimentally determined quantities. Excellent agreement with $T_p=500\mathrm{}$ MeV $p_{\mathrm{pol}}$+${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ elastic scattering data is demonstrated. The differences between the relativistic and nonrelativistic results are explored in detail.

Gamma-gamma coincidence studies of ${}_{}{}^{150-152}{}_{}{}^{}\mathrm{Dy}$ have been performed with use of Compton-suppressed Ge(Li) detectors to resolve ambiguities in the high-spin structure of these nuclei. On the basis of $I^{\pi }$ assignments, transition rates, and level systematics for ${}_{}{}^{148-152}{}_{}{}^{}\mathrm{Dy}$, the observed levels are interpreted as proton particle-hole excitations coupled to aligned valence neutron configurations. The proposed single-particle configurations are confirmed by shell-model calculations.

Bonding and dissociation properties of multiply bonded ${\mathrm{Mo}}_2$ and ${\mathrm{Cr}}_2$ molecules are examined with use of the local spin-density theory and ab initio pseudopotentials. The equilibrium properties are in good agreement with experimental data. The core-polarization shifts are large; pseudopotentials give accurate results for multiply bonded systems only if outer-core $p$ electrons are included in the calculations. The results confirm the applicability of pseudopotential techniques to these systems.

Computer simulations of magnetosonic waves, velocity-shell instabilities, and upper-hybrid heating show evidence of a general damping mechanism for large-amplitude electrostatic waves propagating perpendicular to a magnetic field: Particles trapped by a wave of frequency $\omega$ and phase velocity $V_{\mathrm{ph}}$ see an electric field $V_{\mathrm{ph}}\times B$, which accelerates them parallel to the wave front until the $v\times B$ force is large enough for detrapping. For $\omega \gg {\omega }_c$, velocities as large as $\left(\frac{\omega }{4{\omega }_c}\right)V_{\mathrm{ph}}$ can be attained, within a time ${\omega }_{c}t\approx \frac{\omega }{4{\omega }_c}$.

The local translational structure of a two-dimensional colloidal liquid is observed by use of cross correlation of the intensity fluctuations of light scattered by the liquid through two different wave vectors. The utility of multidetector scattering in probing multipoint correlations in disordered phases is thereby demonstrated unambiguously.

The observation of polygonated thin films of fcc ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ in contact with the fluid is described. Partial melting of the polygonated structure allows the observation of the dihedral angle of fluid helium at a grain boundary. The fluid is shown to wet the grain boundaries almost completely.

Single-crystal metastable ${\left(\mathrm{GaAs}\right)}_{1-x}{\left({\mathrm{Ge}}_2\right)}_x$ alloys with $0<x<\mathrm{}1\mathrm{}$ have been grown on (100) GaAs substrates by use of ultrahigh-vacuum ion-beam sputter deposition. Optical-absorption measurements showed that the direct gap $E_0$ exhibited a large negative $V$-shaped bowing as a function of $x$ with a minimum $E_0\simeq 0.5$ eV near $x=0.3\mathrm{}$. A zinc-blende to diamond-lattice order-disorder transition model is proposed as a possible explanation for these results.

An ideal ternary heterostructure graphite intercalation compound, KCs${\mathrm{C}}_{16}$, which exhibits a stage-1 $c$-axis stacking sequence,...CKCCsCKCCs..., has been prepared. The stage, stacking sequence, and $(2\mathrm{}\times 2)R0°$ in-plane structure have been confirmed by high-resolution x-ray diffraction studies which reveal a $c$-axis correlation range of ∼350 Å. The structure factor and widths of the ($00l$) reflections calculated on the basis of the proposed stacking sequence are in excellent agreement with experimental observations.

A strong case is made to show that the $F$-type color centers in oxide crystals are qualitatively different from the color centers of alkali halides. A semiquantitative discussion is followed by the results of an $X\alpha$ self-consistent-field calculation for the $\alpha$-${\mathrm{Al}}_2$${\mathrm{O}}_3$ crystal. An oxygen-ion vacancy in $\alpha$-alumina is a deep electron trap, the ground state of which lies between the two valence bands, unlike the $F$ center of alkali halides whose ground state lies between the valence and conduction bands. The two electrons in the trap are stabilized by a hole.

Computer simulations of ion-bombardment events which recrystallize the target demonstrate pit formation at 1.0 keV. Atoms are ejected from the first two target layers in the pit region. The remainder of the pit is created by replacement-collision sequences. Linear-cascade and spike-regime events are dynamically indistinguishable.

Calculations of the densities of states associated with a particular local configuration of atoms in a substitutionally disordered alloy are reported. An application to ${\mathrm{Ag}}_c{\mathrm{Pd}}_{1-c}$ alloys yields detailed information about charge transfer and short-range order in these alloys.

A time-dependent mean-field theory of the nonlinear electric field response of a charge-density wave pinned by impurities is implemented. It is found that above a threshold electric field $E_T$, the charge-density wave moves with velocity $v\propto {(E-E_T)}^{\frac{3}{2}}$. Some general discussion of the behavior as a function of dimension is included.

With use of an ultrafast Ge photodiode and a high-power picosecond laser system, the fastest radiative processes in plasma-deposited $a$-Si: H have been resolved. Spectrally integrated measurements on a 250-ps time scale provide a simple picture that for the first time isolates single rates in the recombination dynamics, permitting quantitative physical modeling. Spectral shifts are observed on time scales faster than the radiative decay, providing clear evidence of slow relaxation processes.

The one-dimensional Ising model in a random field is studied with use of a functional recursion relation. For temperatures exceeding a given value, the fixed function of the relation is found and shown to be a devil's staircase. From this result it is possible to evaluate the free energy to arbitrary precision. In the field-strength-temperature plane, a crossover line corresponding to the onset of frustration is found.