Definitive evidence for strong density dependence in the two-nucleon effective interaction is noted in inelastic ($p$,$p^{\prime }$) differential cross section and polarization data for $E_p\sim 150$ MeV. These effects are quite sensitive to variations in the nuclear medium and are well described, for inelastic scattering, by the local-density approximation with use of density-dependent effective interactions from nuclear matter.

The proton spectra from pion- and photon-induced reactions on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ at the $\Delta (\frac{3}{2},\frac{3}{2})$ resonance are found to be very similar in shape, and in their variation with angle. It seems reasonable to assume that these protons arise from a common reaction mechanism ($\Delta$ production) for the two projectiles. The absolute cross sections for producing protons with pions and with photons are in roughly the same ratio as the total inelastic pion yield to the total photopion yield.

Excitation cross sections for positrons of energies up to 10 eV above threshold scattered in the forward direction by helium atoms have been measured directly by use of time-of-flight spectrometry. The results indicate that the scattering is dominated by excitation of the $2{}_{}{}^1{}_{}{}^{}S$ state and that there exists a strong small-angle lobe in the angular distribution of the scattered positrons.

Monte Carlo calculations are presented of the ion-ion recombination rate coefficient for the ${\mathrm{Kr}}^{+}$ + ${\mathrm{F}}^{-}$ + Ar reaction. The effect of other ions on the recombination rate is taken into account by use of the Debye screened potential rather than the Coulomb potential. This potential should be valid for ion densities between ${10}^{13}$ and ${10}^{15}$ ${\mathrm{cm}}^{-3\mathrm{}}$. Results are presented for ion densities in this range and for neutral pressures of 0.5 to 8.0 atm. It is found that screening effects significantly decrease the ion-ion recombination rate.

Results of injected-impurity transport studies on the Alcator-$A$ tokamak are presented. It is found that injected silicon diffuses throughout the plasma and is then observed, contrary to the predictions of neoclassical theory, to leave the discharge, having confinement times much shorter than the discharge length. There is no observed buildup of silicon on the axis of the device. The impurity confinement is found to increase with plasma current and background-ion mass. Scalings with electron density and toroidal field are also discussed.

The velocity and attenuation of second sound in the $A_1$ phase of superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ are measured. The present observations strongly support the theory of Liu. With use of NMR, a magnetic disturbance associated with the wave is observed, and from its polarity it is concluded that the most probable orientation of the magnetic moment of the paired spins in the $A_1$ phase is along the field $H$.

A surface molecular-dynamics method is described and employed to investigate the epitaxial crystallization of a supercooled melt. The procedure allows for thermal dissipation via a dynamic bulk reservoir, thus enabling the study of the approach to equilibrium. The early stages of the crystallization involve layering in the fluid, followed by intralayer ordering. The system evolution is described via layer profiles of particle number, temperature, potential energy, and orientational- and translational-order parameter versus time.

Amorphous Si layers have been melted by pulsed electron irradiation. Implanted As has been used as a marker for determining melt duration. Systematic differences between As diffusion in initially amorphous or crystalline Si are interpreted in terms of different enthalpies of melting between amorphous (1220 J/g) and crystalline (1790 J/g) Si. The implanted amorphous layers melt and crystallize at significantly lower electron energies than those required to melt and recrystallize crystalline Si, indicating that amorphous Si melts at 1170 K compared to 1685 K for crystalline Si.

Time-of-flight measurements have been performed on the inelastic scattering of room-temperature beams of ${\mathrm{H}}_2$ and ${\mathrm{D}}_2$ molecules from a LiF (100) surface. The results show discrete inelastic peaks corresponding to energy losses approximately equal to the molecular rotational excitation energy but shifting with scattering angle. This indicates that rotationally inelastic scattering is dissipative rather than diffractive; i.e., it includes phonon excitations in the solid. The phonons involved can be identified as single Ray-leigh surface phonons.

The parallel and perpendicular displacements of atoms in the first few layers of Si(111)-(7×7) have been determined with use of ion scattering. It was directly observed that the major reconstruction of this surface involves ∼0.4 Å displacements perpendicular to the surface.

Disks of diffuse scattering are observed at $\overrightarrow{\mathrm{q}}=〈\sim 0.6,0,0〉$ around the bcc Bragg reflections implying correlations of the Ag ions in the [100] directions. The average correlation length and the inverse Haven's ratio both decrease with increasing temperature. The x-ray measurements provide structural evidence for strongly correlated ionic transport in $\beta$-${\mathrm{Ag}}_2$S.

By using a thermodynamic analysis, it is shown that a horizontal layer of the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ superfluid mixture heated from below is unstable with respect to oscillatory convection. The neutral oscillations of this overstability are undamped standing second-sound waves. Estimates show the possibility to observe the predicted effect experimentally in the vicinity of the tricritical point of the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ mixture.

We have measured for the first time the electron spin polarization $P$ of photoelectrons emitted from a transversely magnetized sample in the absence of an externally applied magnetic field. With this photoemission geometry, use has been made of optical selection rules for selectively exciting spin-polarized electron states of different symmetry as illustrated for emission from the ${\Sigma }_3$ and ${\Sigma }_4$ bands of Ni(110), where values of $P$ up to —100% have been observed.

Spin-dependent electron mean free paths as a function of the hot electron energy are calculated for Fe, Co, and Ni. The difference in mean free paths of electrons for spin parallel and antiparallel to the majority spin direction of the ferromagnet is found to change sign and decrease rapidly in magnitude with increasing electron energy. Results for the mean free path with and without exchange included are also presented.

Small-angle neutron experiments show that near the transition from superconductor to ferromagnet in Er${\mathrm{Rh}}_4$${\mathrm{B}}_4$ scattering peaks occur at a wave vector $\left|{\overrightarrow{\mathrm{q}}}_s\right|=0.06\mathrm{}$ ${\mathrm{\AA }}^{-1\mathrm{}}$. The temperature and wave-vector dependence suggest this signal is due to oscillatory magnetization fluctuations caused by the electromagnetic coupling of magnetic and superconducting order parameters. The ferromagnetic Bragg scattering shows a 5% hysteresis and transition-temperature-smearing effects which are also due to magnetic-superconducting interactions.

Magneto-far-infrared studies of the hole cyclotron resonance and its associated subband exciton have been made for frequencies in the vicinity of the LO frequency. Just below ${\omega }_{\mathrm{LO}}$ a resonant exciton lifetime process is observed in which the hole-pocket subband exciton decays into the electron-pocket cyclotron resonance continuum via a virtual LO phonon. The experiments also give evidence for other phonon-mediated many-body processes.

The first optical detection of microwave cyclotron resonance via band-gap luminescence is reported. The method is based on the measurement of resonant heating of the carriers by monitoring shapes and intensities of low-temperature photoluminescence lines. As an example, electron and hole resonances in GaAs and CdTe are studied. Mobilities of up to 1.9×${10}^6$ ${\mathrm{cm}}^2$ ${\mathrm{V}}^{-1\mathrm{}}$ ${\mathrm{s}}^{-1\mathrm{}}$ have been observed. The method should be applicable to a wide range of compounds and alloys.

A superconducting spin-glass is studied as an example of how magnetic ordering is reflected in the superconducting density of states $N_s\left(\omega \right)$. Of particular interest is the prediction of a large "magnon" associated peak in $\frac{d{N}_s}{d\omega }$ for $\omega$ near the magnetic ordering temperature. This effect may have been observed in (gapless) superconducting spin-glasses. It is expected that this effect will also be present in antiferromagnetic superconductors.

The hierarchy of baryon generation by multiple species of both gauge and Higgs bosons whose interactions do not conserve baryon number are considered. A procedure for computing the final baryon asymmetry in terms of the masses and coupling strengths of all the various species is presented. If the lightest gauge boson has a mass below ${10}^{15}$ GeV, then the final asymmetry depends only upon this boson and any lighter Higgs bosons.

The ray description in the WKB (or eikonal) limit is extended to all orders in the expansion in powers of wavelength/characteristic length. The equations for the ray trajectories are given by a Hamiltonian system, and the intensity is given by a conservation law with flow along the rays, just as in the eikonal limit. The generalization requires that the Hamiltonian depends weakly on the solution, in a way which can be solved iteratively.