The elastic electron-neutron cross section has been measured at four-momentum transfers squared ($Q^2$) of 2.5, 4.0, 6.0, 8.0, and 10.0 ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ with use of a deuterium target and detection of the scattered electrons at 10°. The ratio of neutron to proton elastic cross sections decreases with $Q^2$. At high $Q^2$ this trend is inconsistent with the dipole law, form-factor scaling, and many vector dominance models, although it is consistent with some parton models.

The structure of single-particle states in spherical nuclei is analyzed within the shell model by use of a representation which consists of a correlated basis.

The first observation of the rotational Zeeman effect in a van der Waals molecule is presented. The spectrometer used in this study is a Fourier-transform microwave spectrometer employing an evacuated Fabry-Perot cavity and a pulsed gas nozzle, both of which are placed inside the bore of a superconducting solenoid. The rotational Zeeman parameters for ArHF are $g_{\perp }=-0.005\mathrm{}03\left(12\right)\mathrm{}$ and $({\chi }_{\parallel }-{\chi }_{\perp })=-1.7\mathrm{}\left(11\right)\mathrm{}\times {10}^{-30\mathrm{}}$ ${\mathrm{cm}}^3$. The molecular quadrupole moment is $Q_{\parallel }=2.79\mathrm{}\left(77\right)\mathrm{}\times {10}^{-26\mathrm{}}$ statcoulomb ${\mathrm{cm}}^2$.

With use of a resonant, counterpropagating laser beam the velocity of atoms in a neutral, thermal-sodium beam has been reduced to 40 m/s, or 4% of their initial velocity. These atoms have a kinetic energy comparable to the well depth of proposed optical traps. The "temperature" characterizing the atoms' relative motion was reduced to 70 mK.

Double ionization of helium at high projectile velocities, $v$, is considered in terms of two mechanisms. In the shakeoff mechanism the ratio of double- to single-ionization cross sections, $\frac{{\sigma }^{\mathrm{ii}}}{{\sigma }^i}$, is independent of $v$. In the two-step mechanism it is shown that $\frac{{\sigma }^{\mathrm{ii}}}{{\sigma }^i}\sim {\left(v^2\ln v\right)}^{-1\mathrm{}}$. Combining amplitudes gives a reasonable fit to the observed velocity dependence as well as an explanation of the observed factor-of-2 differences between double ionization of helium by protons and electrons near $v\simeq 10v_{\mathrm{Bohr}}$.

A relation is proposed between fluid turbulence in $d$ dimensions and branched polymer physics in $d-1\mathrm{}$ dimensions. The argument leads to a formula for the intermittency exponent $\mu$, $\mu =\frac{\mathrm{}(3d-7)\mathrm{}}{5}$, and thus $\mu =0.4\mathrm{}$ in three dimensions.

NMR spectra from $2H$-Ta${\mathrm{Se}}_2$ are analyzed to obtain charge-density-wave parameters versus temperature. It is shown that there is a major orthorhombic distortion within each Se-Ta-Se layer, implying unexpectedly strong interlayer coupling. Evidence is also given for the existence of a significant interaction between discommensurations and the bulk charge-density wave, and an estimate of the width of a discommensuration is derived.

A model system is introduced that is meant to simulate classically the saturation of chemical forces in species that form binary molecules. It is given in the form of a lattice-gas Ising-type Hamiltonian with suitable many-body forces. The existence and the properties of two molecular phases, one solid and one fluid, are made evident with a transfer-matrix study of the one-dimensional case.

This x-ray scattering study of the melting of a monolayer of Pb on the Cu(110) surface reveals an irreversible commensurate-to-incommensurate transition and an anisotropic reversible incommensurate melting transition. This study demonstrates the impressive capabilities of surface x-ray diffraction techniques since (1) kinematic theory can be used to interpret the results, (2) correlation lengths of >1000 Å are easily measured, and (3) high counting rates (>5000 cps) were measured from a monolayer of Pb.

The melting curve $P\left(T\right)\mathrm{}$ of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ has been measured from 220 to 360 K (8 to 16 GPa); it is found to exhibit a well-defined cusp point at 299 K and 11.65 GPa. The cusp, together with estimates of the relative volume change, points to the existence of a triple point and a new high-pressure phase in solid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$. The melting curve below this point is accurately fitted by theory on the basis of a modified Aziz interatomic potential.

For most glassy materials at temperatures below ≈ 1 K, the magnitudes and temperature dependences of specific heat, thermal conductivity, and ultrasonic dispersion are qualitatively similar, independent of chemical composition. It has been suggested that thermal expansion also exhibits this universal behavior. However, from measurements made on amorphous Si${\mathrm{O}}_2$, ${\mathrm{As}}_2$${\mathrm{S}}_3$, and two glassy polymers at $T<\mathrm{}1\mathrm{}$ K, it is found that the linear expansion coefficient can be positive, negative, large, or small.

Exact elliptic-function solutions are presented for intense light waves in cholesteric liquid crystals. Light-induced changes in the pitch of the cholesteric helix lead to a bistable reflection characteristic even in the absence of external reflectors.

Exact calculations of the $B$-phase collective-mode frequencies in a magnetic field are presented, and they provide new information about the effective mass, the pairing interaction, and the Landau parameters. The calculation of the Zeeman splitting for the 2+ mode (real squashing mode) is consistent with the zero-field frequency and agrees quantitatively with the measurements of Avenel et al., for a range of values of $m^{*}$ which includes some, but not all, of the differing experimental results for this important parameter.

The doping of hydrogenated amorphous silicon is discussed within the context of Mott's $8-N$ rule, and found to have properties distinctly different from dopants in crystalline silicon. A unifying description of dopant and defect states based on the position of the Fermi energy is given. Some possible consequences of the $8-N$ rule for the deposition and structure of $a$-Si: H are also discussed.

A Heisenberg spin-glass with local uniaxial anisotropy is studied within replica meanfield theory, including consideration of replica-symmetry breaking. It is shown that it represents a very rich model with much to offer as a test bed for comparison of theory and experiment. The explanation of recent experiments on $\mathrm{Zn}\mathrm{Mn}$, $\mathrm{Mg}\mathrm{Mn}$, and $\mathrm{Cd}\mathrm{Mn}$ is one of its consequences.

The spectrum of the Schrödinger equation, with magnetic field, on a model self-similar structure is considered. Nesting properties are formulated. Low-field behavior of the spectrum edge (of interest for superconductive diamagnetism) is discussed. Comparison between self-similar structures and regular lattices is emphasized.

Self-consistent augmented-plane-wave calculations are reported which predict that nickel should transform from a metal to an insulator at a pressure of 34 TPa (∼340 × ${10}^6$ atm), and then revert back to a metal at 51 TPa. These transitions follow from general trends in the evolution of electronic structure under compression and indicate that the richness found in the electronic structure of most solids can persist throughout, and well beyond, the pressure range of current experimental and geophysical interest.

Shape magnetostriction measurements along the [001] direction were carried out for all the magnetic rare-earth ions, $R$, in $R_x{\mathrm{La}}_{1-x}\mathrm{Sb}$. At low temperatures the magnetostriction of both Ce and Sm are "reversed" with respect to the high temperatures. A crystal-field model can explain this phenomenon by the sign reversal of the expectation value of the quadrupole operator $〈{{\hat{O}}_2}^0〉$. The data are consistent with a negative second-order magnetoelastic coupling constant, ${V_2}^3$, for all the rare-earth ions.

A pair theory of the Hubbard Hamiltonian is presented for the case of a half-filled band. The original Hamiltonian is reformulated exactly in terms of pair operators which satisfy boson commutation relations. The pair energies and wave functions are obtained explicitly. In the one-dimensional case, these reduce to the results derived by Lieb and Wu for $M=1\mathrm{}$. The pair Hamiltonian offers a better starting point for perturbation treatments or variational calculations.

Coherent transient effects in Mössbauer spectroscopy due to phase modulation of recoilless $\gamma$ radiation are considered both theoretically and experimentally. Absolute calibration of the source motion in the angstrom range and separation of the source and absorber contributions to the experimental linewidth were obtained from a single transient Mössbauer spectrum. A new phase-modulation method for generating short enhanced recoilless $\gamma$ pulses is introduced.