Low-frequency measurements of the shear modulus and internal friction of pure and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-doped crystals of hcp ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ are reported. Previously unobserved features are seen in both quantities. With use of the parameters obtained from our measurements, it is shown for the first time that all the existing dissipation measurements spanning five decades in frequency are consistent with each other and the Granato-Lücke model of overdamped dislocation motion.

Pressure decay measurements are used to study adsorption and recombination of atomic hydrogen on liquid helium surfaces below 1 K. Recombination is suppressed by five orders of magnitude by applying a 10-T magnetic field. The surface-recombination-rate constant ($K_s$) and the adsorption energy (${\epsilon }_a$) of H↓ on ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ are $\frac{K_s{B}^2}{T^{\frac{1}{2}}}=(2.6\mathrm{}\pm 0.8)\times {10}^{-7\mathrm{}}$ ${\mathrm{cm}}^2$ ${\mathrm{T}}^2$ ${\mathrm{K}}^{-1/2\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ and $\frac{{\epsilon }_a}{k_{\mathrm{B}}}=0.89\mathrm{}\pm 0.07$ K. An estimate of $\frac{{\epsilon }_a}{k_{\mathrm{B}}}=0.59\mathrm{}$ K is obtained for H↓ on a dilute ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ mixture.

A thin-crystal channeling experiment has been devised to locate preferential sites of monolayers of Ni atoms deposited onto Si crystalline substrates. The Ni scattering yield shows dips or peaks in the angular scan measurements when channeled along the major crystallographic axes and planes of Si. The results can be explained by a dispersed Ni-Si interface with 2.1×${10}^{15}$ Ni atoms/${\mathrm{cm}}^2$ occupying the tetrahedral interstitial voids of Si.

The residual resistance $R$ of thin (compared to a mean free path $l$) wires is strongly affected by the nature of their surfaces. In perfectly cylindrical wires $\ln R\propto \left(\frac{L}{l}\right)\ln \left(\frac{S}{a^2}\right)$, where $R$ is dimensionless, $S$ and $L$ are the wire cross-sectional area and length, and $a$ is an interelectron distance. Certain cross sections and external magnetic fields provide $\ln R\propto \frac{\mathrm{LS}}{l{a}^2}\gg \frac{L}{l}$.

Detailed experimental results for the phase diagrams, ground states, and critical points for electron-hole liquid condensation in unstressed Si and in Si stressed along the $〈111〉$, $〈110〉$, and $〈100〉$ directions are given and are shown to be in good agreement with microscopic calculations. These results for a set of systems with widely varying band structure provide, for the first time, a quantitative test for, and a verification of systematic scaling relations between the ground state and the critical properties for electron-hole liquid condensation.

A new approach to quantum gravity is proposed. The framework is sufficiently general to handle nontrivial space-time topologies required, e.g., in the black-hole formation and evaporation processes, and yet it incorporates notions such as energy-momentum, angular momentum, spin, mass, and discrete symmetries, normally associated with the Poincaré group.

The masses and widths of $S=0\mathrm{}$ resonances in the (70, $1^{-}$) and (56, $1^{-}$) multiplets have been fitted with use of a quark model with hyperfine interactions. Three models for the decay of these and other states have been examined, and it is concluded that the usual spectator model for the decays must be modified. No positive evidence is found for a tensor force, while conflicting evidence is found for a three-body spin-orbit force, and the (56, $1^{-}$) mass is lower than expected.

Results are presented from an isobar-model partial-wave analysis of a high-statistics sample of the neutral $3\pi$ system produced in forward charge exchange. Large forward phase motions relative to an exotic reference wave are seen for partial waves with the quantum numbers of the $A_1$ and of the previously unobserved isoscalar companion ($``H\text{'}\text{'}$) of the $B\left(1235\right)\mathrm{}$.

A breakdown of the selection rules of the supersymmetry model is observed for the population of the $0_2^{+}$ and $2_2^{+}$ levels of ${}_{}{}^{194}{}_{}{}^{}\mathrm{Pt}$ in the ${}_{}{}^{193}{}_{}{}^{}\mathrm{Ir}$→ ${}_{}{}^{194}{}_{}{}^{}\mathrm{Pt}$ proton-stripping reactions performed with use of the Orsay and McMaster University tandem accelerators. The existence of other violations in the neighboring nuclei leads one to believe that the limitations of the supersymmetry scheme itself are being seen, at least for particle-transfer reactions.

The version of the interacting-boson model (IBM) which treats neutrons and protons symmetrically can be converted into a Bohr Hamiltonian description in three steps: (1) Mapping the IBM pairing bosons onto a quadrupole particle-hole-type boson under a generalized Holstein-Primakoff transformation; (2) introduction of pseudocanonical coordinates and momenta; (3) expansion in powers of the pseudomomenta, valid for large particle numbers. The limiting symmetries of the IBM emerge directly from a study of the potential-energy surface.

The inclusion of the quadrupole moment of ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ and ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ in coupled-channels calculations removes the need to renormalize the real double-folded potential, obtained from an effective nucleon-nucleon interaction, for ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$+${}_{}{}^{54}{}_{}{}^{}\mathrm{Fe}$, ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ and ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$+${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ elastic scattering.

The interplay between the bulk properties of the plasma and the nonlinear particle heating due to resonance absorption is analyzed. It is shown that the dependence of the heating on the initial energy with which particles enter the heating region provides a key to understanding the formation of the time-averaged distribution.

The static structure factor $S\left(q\right)\mathrm{}$ for ${\mathrm{H}}_2$O was measured by x-ray scattering for $0.15{\AA }^{-1\mathrm{}}<q<\mathrm{}1\mathrm{}{\AA }^{-1\mathrm{}}$ and for $253 \mathrm{K}<T<\mathrm{}348\mathrm{} \mathrm{K}$. The low-temperature data show a surprising increase of $S\left(q\right)\mathrm{}$ with decreasing $q$, which can be fitted with a Lorentzian whose width corresponds to density fluctuations with a length scale that increases to about 8 Å as $T$ is decreased to 253 K. The anomaly is more pronounced in ${\mathrm{D}}_2$O, while small amounts of the hydrogen-bonding impurity ethanol decrease the anomaly.

Angle-integrated photoemission and low-energy electron-diffraction studies of laser-annealed Si(111) surfaces show that a buckled reconstruction takes place upon laser quenching. No long-range order exists but a short-range 2×1 reconstruction is present.

Elementary edge dislocations in a lyotropic smectic liquid crystal have been observed with use of a new technique. Their annealing dynamics are related to the permeation coefficient ${\lambda }_p$, which appears in the viscoelastic equations for a smectic, yielding ${\lambda }_p=1\mathrm{}\times {10}^{-30\mathrm{}}$ ${\mathrm{cm}}^2$ / poise in hydrated dimyristoyl phosphatidylcholine. The associated self-diffusion coefficient anisotropy $\frac{D_{\perp }}{D_{\parallel }}=2\mathrm{}\times {10}^{12}$ is many orders of magnitude larger than that found in earlier attempts where the effect of structural defects may have prevailed.

A microscopic calculation of localized electron states of an intrinsic, real, threedimensional disordered solid has been attempted by applying a first-principles method to a structurally relaxed large network of amorphous silicon dioxide. A valence-band mobility edge of 0.15-0.30 eV is estimated. No localized states are found near the conduction-band edge. The nature and the microscopic origin of these localized states are analyzed in terms of local structural disorder.

With use of perturbed electron density, calculated self-consistently in the density-functional theory, and a new form for the strain tensor, quantitative agreement has been achieved for the first time with experiment for the electric field gradient and asymmetry parameter at various near-neighbor sites in Al containing vacancies. The implication of this theory in understanding lattice displacement around a point defect is discussed.

The mean-field theory of an antiferromagnetic superconductor is solved and some fluctuation effects are discussed. In contrast to claims of other authors, it is found that the pairing is of the usual BCS type, $\Delta =〈{C_{\overrightarrow{\mathrm{k}},\uparrow }}^{†}{C_{-\overrightarrow{\mathrm{k}},\downarrow }}^{†}〉$. Results for the gap parameter $\Delta \mathrm{}\left(T\right)\mathrm{}$ and $H_c\mathrm{}\left(T\right)\mathrm{}$ are presented. The latter is similar to the measured $H_{c2\mathrm{}}\mathrm{}\left(T\right)\mathrm{}$. The ratio $\frac{\Delta \mathrm{}\left(0\right)\mathrm{}}{T_c}$ and the (nonmonotonic) temperature $T$ dependence of $H_c$ and $\Delta \mathrm{}\left(T\right)\mathrm{}$ are shown to deviate markedly from BCS theory.

It is shown that the Ohmic dc conductance of a one-dimensional system equals to either $G_p=\left(\frac{e^2}{\pi \hslash }\right)T$ or $G_c=\frac{\left(\frac{e^2}{\pi \hslash }\right)T}{\mathrm{}(1-T)\mathrm{}}$, depending on whether the system is connected to a perfect one-dimensional conductor or to a classical wire (behaving as a current source), respectively. The parameter $\beta \equiv \frac{d〈\ln g^{\prime }〉}{d\ln L}$, where $L$ is the length of the system, depends only on $〈\ln g^{\prime }〉$, so that $\beta =〈\ln g^{\prime }〉$, with $g^{\prime }=\left(\frac{\pi \hslash }{e^2}\right)G_p$.

A method is presented for carrying out Monte Carlo calculations for field theories with fermion degrees of freedom. As an example of this technique, results are given for a simple one-dimensional model.