By monitoring the characteristic fluorescent radiation excited by x-ray standing waves we have been able to distinguish the two different kinds of lattice sites in a heteropolar crystal of GaAs. The strong extinction effects that mask the position-dependent fluorescent signal were minimized by adopting a suitable detector geometry.

Secondary Bragg scattering of neutrons which have already undergone inelastic scattering from a phonon will give rise to sharp changes in inelastic neutron scattering intensity near a Bragg peak. The effect should be observable, and the energy and momentum of the phonon can be found by a suitable experimental setup. Special attention is given to acoustic phonons and questions of resolution are discussed.

A correlated study of the structural, optical, magnetic, and transport properties of polyacetylene, doped with iodine to nearly the metallic doping levels, shows that essentially all charges go into solitonlike states. The measurements are in quantitative agreement with charge transport via variable-range hopping among solitonlike levels.

A one-dimensional Schrödinger equation in a discontinuous quasiperiodic potential is reduced to a recursion relation for transfer matrices and then to one for traces of these matrices. When the potential is periodic, the bandwidth goes to zero as an algebraic function of the period with a critical index which depends upon the potential strength. This critical index is also evaluated as the solution to an escape-rate problem for the recursion relations.

Recent theories of scaling in quasiperiodic dynamical systems are applied to the behavior of a particle in an almost periodic potential. A special tight-binding model is solved exactly by a renormalization group whose fixed points determine the scaling properties of both the energy spectrum and certain features of the eigenstates. Similar results are found empirically for Harper's equation. In addition to ordinary extended and localized states, "critical" states are found which are neither extended nor localized according to conventional criteria.

The authors investigate possible candidates of configuration spaces for the description of the rotational degrees of freedom of quantum spinning particles (including half-integer spin states), and point out their connections in relation to the set of physical observables and superselecting sectors present in the theory.

In the two-dimensional Liouville quantum field theory a perturbation theory may be defined for which space-translation invariance is spontaneously broken and space-time (semi)compactifies spontaneously.

A new method of solution is proposed for a Boltzmann equation describing the slowing down of charged particles in solids. It seems as if it would be more generally applicable. It can be considered as a multigroup method with the energy groups varying from point to point in a natural way dictated by the local spectrum. The energy moments of the density of moving particles are calculated at each point in the target, and at each point an extremal (in energy) density of particles is constructed. The extremal density allows for particles being stopped, and, hence, removed from the beam.

The general scale-invariant Lagrangian, $-\frac{1}{4}\int d^{4}x{\mathrm{}(-g)\mathrm{}}^{\frac{1}{2}}[\alpha c^{\mu \nu \lambda \sigma }{c}_{\mu \nu \lambda \sigma }+\beta R^2]$, with $\alpha \beta >~0$, is considered. Although this theory admits linearized solutions with negative energy, it is shown that all exact solutions representing isolated systems have precisely zero energy. This result also holds in the presence of arbitrary matter. It can be understood as resulting from a confinement of energy. The implications of this result for quantum gravity are discussed.

The general relativistic interaction of the electric field with the gravitational field may be observable in a charged-particle interferometer containing a suitable arrangement of fields. Observation of the effect in the earth's field would constitute a new laboratory test of the equivalence principle, involving $e$, $h$, $c$, and $g$. The magnitude of the phase shift induced can be comparable to the Colella-Overhauser-Werner phase shift, for electrons.

If heavy magnetic monopoles exist, then extreme magnetically charged black holes ($P^2=M^2$) with masses as small as 150${\left[\right({10}^{17}\mathrm{G}\mathrm{e}\mathrm{V})/\mathrm{\mu }]}^2$ g will be stable against evaporation over periods of ${10}^{10}$ yr or longer, where $\mu$ is the mass of the lightest monopole. It appears unlikely that such black holes exist in the present universe, but this conclusion depends strongly on the details of the first ${10}^{-24\mathrm{}}$ sec of the universe. Such long-lived small holes will exist in the late universe if there is at least 1 monopole per ${10}^{50}$${\left[\right({10}^{17}\mathrm{G}\mathrm{e}\mathrm{V})/\mathrm{\mu }]}^6$ baryons in the universe.

The possibility that both the mass and the width of the $W$ boson can be measured by the Jacobian peak in the transverse mass distribution is proposed and examined.

The reaction ${}_{}{}^3{}_{}{}^{}\mathrm{He}(p, 2p)pn$ has been studied at 250 and 400 MeV in a quasifree scattering arrangement characterized by $\overrightarrow{\mathrm{P}}\left(\mathrm{recoil}\right)=0\mathrm{}$ and various excitation or total energies $E\left(\mathrm{recoil}\right)$ of the unobserved $p-n$ pair. The ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ spectral function deduced in the framework of the plane-wave impulse approximation is compared to the predictions of Faddeev and variational calculations. Comparisons are also made with $p-n$ relative-motion momentum distributions calculated as the overlap between plane waves for the $p-n$ pair and Irving, Irving-Gunn, and Khanna wave functions for ${}_{}{}^3{}_{}{}^{}\mathrm{He}$.

Data are presented for the (${}_{}{}^3{}_{}{}^{}\mathrm{He}$, $t$) reaction at energies of 600 MeV, 1.2 GeV, and 2 GeV on targets ${}_{}{}^{\mathrm{nat}}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{54}{}_{}{}^{}\mathrm{Fe}$, and ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}$. The low-excitation-energy regions of the spectra are dominated by isospin-spin excitations. Cross-section calculations in distorted-wave impulse approximation with parameters from $\mathrm{NN}$ data account reasonably well for the data. At 2-GeV bombarding energy a strong excitation of the $\Delta$ resonance is observed for all targets.

Analysis of the second differences of the level energies, ${\Delta }^2{E}_{\mathrm{rot}}\mathrm{}\left(I\right)\mathrm{}$, for the negative-parity bands with only odd spins in ${}_{}{}^{236,238}{}_{}{}^{}\mathrm{U}$, ${}_{}{}^{218}{}_{}{}^{}\mathrm{Ra}$, and ${}_{}{}^{156}{}_{}{}^{}\mathrm{Er}$ shows, at least for $I>~7$, a $\Delta I=4\mathrm{}$ alternating energy-shift term. Such an unusual signature term is not expected in the framework of the quadrupole deformation model.

The ground-band levels of ${}_{}{}^{152}{}_{}{}^{}\mathrm{Dy}$ have been established up to ${18}^{+}$ at 5.8 MeV by ${}_{}{}^{152}{}_{}{}^{}\mathrm{Gd}(\alpha , 4n)$ in-beam experiments with 60-MeV α particles. The band members with $I>~8$ lie above the known ${}_{}{}^{152}{}_{}{}^{}\mathrm{Dy}$ yrast states which are formed by aligned multiparticle configurations typical for a spherical nucleus. An analysis of the ground-band energies in a guage-backbending plot suggests that the ground-band levels with $I>\mathrm{}8\mathrm{}$ are deformed.

The classical equations of motion for elastically coupled, elastic proton and neutron fluids allow two $T=0\mathrm{}$ and two $T=1\mathrm{}$ propagating modes. The Lamé coefficients evaluated empirically are seen to be very different from each other, yielding the large Poisson ratio of 0.485 for nuclear matter and the $T=0\mathrm{}$ and $T=1\mathrm{}$ giant-resonance energies, many of which have been seen experimentally.

A compact source which produces atomic alkali-metal beams in individual hyperfine sublevels has been developed. The methods are demonstrated with ${}_{}{}^{23}{}_{}{}^{}\mathrm{Na}$ atoms. Initially nearly all atoms are transferred into one hyperfine sublevel ($|F, m_F〉=|2, 2〉$) by a double-resonance technique using laser optical pumping and rf transitions. Subsequently the other hyperfine sublevels can be populated selectively by an adiabatic high-frequency transition. The hyperfine sublevel populations are determined by laser-induced fluorescence spectroscopy in a magnetic field.

The observation of radiative collisions in the strong-field regime is reported, specifically the multiphoton-microwave-assisted resonant collisional energy-transfer process $\mathrm{Na}\mathrm{}\left(\mathrm{ns}\right)+\mathrm{Na}\mathrm{}\left(\mathrm{ns}\right)\mathrm{}\to \mathrm{Na}\mathrm{}\left(\mathrm{np}\right)+\mathrm{Na}\mathrm{}\left(\right(n-1\mathrm{}\left)p\right)+mh\nu$, where $m$ is as high as 4. By use of a "dressed-atom" approach in a low-frequency (or adiabatic) approximation, a theoretical interpretation valid for the strong-field regime is given which is in good agreement with the present experimental results.

Experimental results on fine-structure transitions occurring in collisional redistribution of far—off-resonant radiation are presented. Measurements on Na-Ar atomic collisions illustrate that electronically nonadiabatic transitions occurring in the final state, following absorption, are important for describing the redistribution process. The results also provide details of the fine-structure transition process that are not obtainable from the usual resonant scattering experiments.