In the past three years, a number of different interpretatons of the optical properties of LiF have appeared in the physics literature. We present new evidence which shows that most of these interpretations are incorrect in the soft-x-ray region, and for the first time we present measurements of anisotropies in the excitations in the ultraviolet region as a function of momentum transfer in single-crystal samples.

Surface resonances on Mo(100) have been confirmed and studied in detail experimentally by field-emission energy distributions and theoretically by a linear-combination-of-atomic-orbitals calculation of the ${\overrightarrow{\mathrm{k}}}_{\parallel }$-resolved surface local density of states. The experimental results in conjunction with the calculations have provided evidence of band-structure effects in field-emission energy distributions. The calculated results have also explained the angle-resolved photoemission results on W(100) and provided a clear picture as to the origin of these resonances.

We comment on the feasibility of a recent suggestion by Carneiro that the Kohn anomaly in tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) occurs in the C-H stretch molecular modes.

The two-dimensional anisotropic, nearest-neighbor Heisenberg model on a square lattice, both quantum and classical, has been shown regorously to have a phase transition in the sense that the spontaneous magnetization is positive at low temperatures. This is so for all anisotropies. An analogous result (staggered polarization) holds for the antiferromagnet in the classical case; in the quantum case it holds if the anisotropy is large enough (depending on the single-site spin).

The $K$ x-ray emission spectrum of Li has been measured with 0.1-eV resolution for temperatures between 85 and 490 K. A prominent shoulder is observed on the emission edge that is strongly broadened and shifted in energy as the temperature is raised. The peak in the emission spectrum lies about 0.6 eV below this shoulder. The steep high-energy edge of the spectrum is interpreted as a Fermi edge centered at 54.8 eV and having a width of 0.2 eV. The results are compared with similar structure observed in the absorption spectrum of Li.

Films of sodium and ammonia have been formed on substrates held at 5 K. The electrical resistivity of the films has been measured and a metal-nonmetal transition has been observed, but the transition was found to be anomalous in that the resistivity was not a monotonic function of the sodium concentration. No evidence was found for the anomalously high electrical conductivity reported for bulk sodium-ammonia solids which were quick-frozen from liquid solutions.

The magnetic susceptibility of an electron gas at high density is found to be $\chi ={\chi }_{\mathrm{P}}{\{1-(\frac{\alpha r_s}{\pi })+\frac{1}{2}{\left(\frac{\alpha r_s}{\pi }\right)}^2[0.306-\ln \left(\frac{\alpha r_s}{\pi }\right)]+O({r_s}^3\left)\right\}}^{-1\mathrm{}}$.

The implications of the weak equivalence principles are investigated in detail for electromagnetic systems in a general framework. In particular, I show that the universality of free-fall trajectories {Galileo weak equivalence principle (WEP[I])} does not imply the validity of the Einstein equivalence principle (EEP). However, WEP[I] plus the universality of free-fall rotation states (WEP[II]) does imply EEP. To test WEP[II] and EEP, I suggest that Eötvös-type experiments on polarized bodies be performed.

The newly discovered mesons with mass near 1.87 GeV are speculatively identified with diquark states of integrally charged Han-Nambu quarks. The weak decays of diquarks are found to be similar but not identical to the decays of charmed mesons.

Lipatov's estimates for large orders of perturbation theory are extended to scalar electrodynamics.

A sensitive frequency-shift technique is employed to monitor the magnetic quantum state of a single electron stored in a compensated Penning trap. The electron sees a weak parabolic magnetic pseudopotential in addition to the electric well, which causes the axial oscillation frequency to have a slight magnetic quantum state dependence. Transitions at both the spin-cyclotron-beat (anomaly) frequency and the cyclotron frequency have been measured in the same environment to yield a magnetic anomaly $a_e=(1\mathrm{}159652410\pm 200)\times {10}^{-12\mathrm{}}$.

We have analyzed differential distributions for a sample of high-energy $\nu$ and $\overline{\nu }$ interactions. The antineutrino data require more antiquark component than expected from low-energy results. Also, some hints of energy-dependent effects have been observed in these distributions.

Recent data compel us to interpret several peaks in the cross section of $e^{-}{e}^{+}$ annihilation into hadrons as being due to the production of four-quark molecules, i.e., resonances between two charmed mesons. A rich spectroscopy of such states is predicted and may be studied in $e^{-}{e}^{+}$ annihilation.

We show that effective nuclear second-class axial-vector currents provide a consistent description of the available $\beta$-decay data and probe the fundamental structure of weak currents.

We have performed a thick-target particle-$\gamma$ coincidence experiment to measure $q\left(2^{+\prime }\right)$, the quadrupole moment of the second $2^{+}$ state, of ${}_{}{}^{184,186}{}_{}{}^{}\mathrm{W}$. We have also determined $q\left(2^{+\prime }\right)$ of ${}_{}{}^{186}{}_{}{}^{}\mathrm{W}$ by an independent method involving particle spectroscopy. Neither the rotation-vibration nor the asymmetric rotor model can explain the results. Kumar-Baranger calculations agree with the trend.

High-spin levels of the rotation-aligned bands built on the $h_{\frac{9}{2}}$ subshell in ${}_{}{}^{183}{}_{}{}^{}\mathrm{Ir}$ and ${}_{}{}^{185}{}_{}{}^{}\mathrm{Ir}$ have been populated by ($\alpha , 6n\gamma$) and ($\alpha , 4n\gamma$) reactions. In ${}_{}{}^{183}{}_{}{}^{}\mathrm{Ir}$ a rapid increase in the apparent moment of inertia has been observed at high spins. The implication of this result for the interpretation of backbending phenomena in even nuclei in this mass region is discussed.

$\gamma$-ray multiplicities have been measured as a function of fragment $Z$ both for the relaxed and quasielastic component in the reaction of 175-MeV ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ on ${}_{}{}^{\mathrm{nat}}{}_{}{}^{}\mathrm{Ag}$. Evidence for maximum transfer of orbital angular momentum to rotation of the fragments is seen at 90° for the relaxed component, indicating a rigid rotation of the intermediate complex. Possible evidence for angular-momentum transfer via mass transfer and other mechanisms are discussed for the quasielastic component.

Yields of discrete $\gamma$ transitions in coincidence with deep-inelastic fragments identified in a particle telescope have been measured as a function of $Q$ value and $Z$ from the scattering of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ with ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ at 100 MeV. The anisotropies in the $\gamma$-particle angular correlations indicate a high degree of spin alignment in the fragments. This, as well as the deduced value of the internal angular momentum, is consistent with sticking of the fragments prior to scission.

The reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ has been studied at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=2.5\mathrm{} \mathrm{to} 6.2$ MeV by $\gamma$-ray spectroscopy. New resonances were found below 4 MeV. When the influence of the Coulomb barrier is removed, these resonances are superimposed on a flat background, which does not show a strong increase at low energies, in contrast to previous work.

On the basis of a Faddeev calculation, an Efimov state is predicted to exist in ${}_{}{}^4{}_{}{}^{}\mathrm{He}_3^{}{}_{}{}^{}$. This discovery represents the first manifestation of the Efimov effect and may have farreaching consequences in the statistical mechanics of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ gas at low temperatures.