It is shown that a black hole of fixed mass can carry arbitrary axionic charge. The unique static black-hole solution is found to have vanishing axion field strength but nonvanishing potential. The axion charge cannot be detected by point particles, but can be detected by strings in a process analogous to the Aharonov-Bohm effect. It is argued that the existence of axion charge may play a significant role in the late stages of black-hole evaporation.

We consider the interacting ${\mathrm{CP}}^1$ nonlinear $\sigma$ model in 2 + 1 dimensions in the presence of an Abelian Chern-Simons term and quantize it canonically using the Dirac-Bergmann algorithm. There arises an anomalous term in the angular momentum in presence of the interaction, which in the long-range limit yields the fractional spin for the excitations.

We calculate angular correlations between coincident electron-positron pairs emitted in heavy-ion collisions with nuclear time delay. Special attention is directed to a comparison of supercritical and subcritical systems, where angular correlations of pairs produced in collisions of bare U nuclei are found to alter their sign for nuclear delay times of the order of 2 × ${10}^{-21\mathrm{}}$ s. This effect is shown to occur exclusively in supercritical systems, where spontaneous positron creation is active.

We propose a unified theory of nuclear level densities, encompassing both spherical and deformed nuclei, using the static-path approximation. The theory appears numerically tractable for a pairing-plus-quadrupole Hamiltonian.

The chaotic convection of passive scalars by an incompressible fluid is considered. (The convection is said to be chaotic if nearby fluid elements typically diverge from each other exponentially in time.) It is shown that during the time evolution the square of the gradient of chaotically convected passive scalars typically concentrates on a fractal set. Considerations of the local stretching properties of the flow lead to a partition function which yields the dimension spectra of the resulting fractal measure. Fractal structure is a result of the nonuniform stretching of typical chaotic flows.

We have demonstrated acceleration of magnetically confined plasma rings in a coaxial accelerator, with acceleration of 0.02-mg ring masses to 1.4×${10}^8$ cm/sec at ≥ 30% efficiency. In some cases low-mass rings have reached a velocity of 2.5×${10}^8$ cm/sec. When the accelerated rings translate into conical electrodes, we have observed focusing of rings by a factor of ∼3 in radius, with a factor of ≥ 4 magnetic field amplification. A reasonably complete accounting of ring mass, momentum, and energy confirms the basic concept of acceleration of stable, well-confined magnetized plasma rings.

Operation of the S-1 device in a high-current-density ($\frac{j}{n_e}\ge 2\times {10}^{-14\mathrm{}}$ A m) regime has created high-electron-temperature spheromaks ($50 \mathrm{eV}\le T_e\le 130 \mathrm{eV}$). The mechanisms and causes of the periodic relaxation events often observed in these hotter plasmas were made clear. A relationship between the MHD relaxation cycle and confinement was revealed for the first time. Resistive loss at the outer edge causes a departure from the initial force-free minimum-energy Taylor state to an MHD profile unstable to low-$n$ ideal MHD modes; a relaxation event then returns the configuration to a Taylor state.

Time-resolved electron temperature and line-intensity profiles in laser-produced plasmas have been measured for the first time with an x-ray framing camera. Temperature profiles measured from the slope of the free-bound recombination continuum in AlXIII ions are significantly lower than hydrodynamic model calculations. Simultaneous interferometric density measurements are in much closer agreement with computer simulations. Spectral-line-intensity profiles have also been measured and cannot be described by standard collisional radiative equilibrium models.

On the basis of a "spin-wave" analysis of coupled hexatic layers, we propose a form for the diffraction patterns from thin liquid-crystal films. We note that the deviations from "two-dimensional behavior" observed in recent experiments on films of a few layers can in fact be used to extract the effective hexatic Frank constant, and to probe its temperature dependence. Our predictions are found to be quite consistent with the experimental observations.

Chemisorption on solid surfaces is treated as a combination of a seeding process, whereby molecules adsorb directly onto vacant sites, and an island-growth mechanism initiated by physisorption over occupied sites followed by lateral migration towards vacant sites. It is argued that the islands are compact 2D (Eden) clusters, at marked variance with models which assume random distribution of the chemisorbed molecules. Simple general expressions are derived for the sticking probability and adsorption isotherms. Numerical results are presented for several cases of interest.

The equations which govern high-energy electron diffraction in a deformed crystal lattice are shown to be equivalent to a Schrödinger equation with a time-dependent Hamiltonian. If the lattice planes are not strongly distorted, as in the long-ranged strain field of a dislocation, this time variation is slow and adiabatic theory can be used. The effects of Berry's geometrical phase are then observed in the bending of two-beam diffraction fringes as a screw dislocation is crossed.

Real-space images of an incommensurate superlattice on a monolayer-gallium-covered silicon (111) surface have been obtained with the tunneling microscope. Large, internally ordered supercells which in turn form a lattice with discrete boundaries are observed. A graphitelike silicon-gallium top layer is suggested that is weakly bonded to the lattice below and stabilized by a periodic array of misfit dislocations. This model unifies reflection high-energy electron diffraction, x-ray standing-wave, and tunneling observations.

We consider the effects of textures on the collective-mode spectrum of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$. Our result for the frequency splitting of the real-squashing-mode doublet agrees well with the measurements of Shivaram et al. The smooth disappearance of the doublet and the nonlinear evolution of the real-squashing-mode frequencies at low magnetic fields are explained in terms of a crossover to the dispersion-dominated regime when $\frac{{\left(q{\upsilon }_f\right)}^2}{\Delta }>\gamma H$.

The digital electron-stimulated-desorption-ion-angular-distribution method has been used to observe the amplitude of the low-frequency "frustrated-translational" modes of chemisorbed CO on Pt(111) when the CO adsorbs on empty Pt sites present in a $p(2\mathrm{}\times 2)$-Se overlayer. Significant changes in the CO vibrational amplitudes are observed during a two-dimensional phase transition driven by repulsive forces in the overlayer. This work represents the first observation of the relationship between the vibrational amplitude of an adsorbed molecule and a phase transformation in an overlayer.

An empirical interatomic potential is introduced, which gives a convenient and relatively accurate description of the structural properties and energetics of carbon, including elastic properties, phonons, polytypes, and defects and migration barriers in diamond and graphite. The potential is applied to study amorphous carbon formed in three different ways. Two resulting structures are similar to experimental $a-\mathrm{C}$, but another more diamondlike form has essentially identical energy. The liquid is also found to have unexpected properties.

Diffraction of optical second-harmonic generation from a monolayer grating created by laser desorption of adsorbates can be used to study surface diffusion of molecules on substrates. Application of this novel technique to CO on Ni(111) yields a diffusion activation energy of 6.9 kcal/mol and a preexponential factor of ≃1.2 × ${10}^{-5\mathrm{}}$ ${\mathrm{cm}}^2$ ${\mathrm{s}}^{-1\mathrm{}}$.

Both electron thermal conductivity and thermal exchange with the lattice can cool an electron distribution initially heated on a metallic surface with an ultrashort laser pulse. The interplay between the two processes allows the electron-lattice coupling parameter to be determined. We report measurements of optical damage to molybdenum and copper. Damage caused by pulses have a duration ${\tau }_L\lesssim 1$ nsec can be understood only with a two-temperature model of metals.

A proof-of-principle experiment is presented demonstrating the generation of both direct and indirect spin echoes for ${\mu }^{+}$-spin spectroscopy. These two phenomena have direct bearing on several fundamental concerns, e.g., (i) muon diffusion and (ii) site determination in multinuclear systems. Also, in contrast to the case commonly found NMR, we conclude that the echo does not occur at $2t_{\pi }$ for a muon undergoing diffusive motion.

Discrete valence electron states are formed in adsorbed multilayers of Cs atoms on Cu(111) at energies within the Cu conduction-band gap at the $L$ point of the Brillouin zone. We measure the energies of these states by photoemission and obtain the wave vectors from the phase conditions satisfied by the states, and thereby determine the dispersion $E\left(k\right)\mathrm{}$ in the perpendicular direction for part of the filled Cs valence band.

We argue that extraction of unstable cycles and their eigenvalues is not only experimentally feasible, but is also a theoretically optimal measurement of the invariant properties of a dynamical system.