It is shown that for a translationally invariant solution to string theory, spacetime duality interchanges the momentum in the symmetry direction and the axion charge per unit length. As one application, we show explicitly that charged black strings are equivalent to boosted (uncharged) black strings. The extremal black strings (which correspond to the field outside of a fundamental macroscopic string) are equivalent to plane-fronted waves describing strings moving at the speed of light.

The transverse polarization in a plane perpendicular to the nuclear spin has been measured for electrons emitted in the beta decay of polarized ${\mathrm{Li}}^8$ nuclei. The amplitude R of the time-reversal-violating triple correlation between nuclear spin, momentum, and spin of the electron has been determined. Our result, R=0.004±0.014, is consistent with time-reversal invariance and provides a first direct limit on the imaginary charged weak tensor interaction -0.03${\mathrm{C}}_{\mathrm{T}}$+${\mathrm{C}}_{\mathrm{T}}^{\prime }$)/${\mathrm{C}}_{\mathrm{A}}$<0.05.

Cross sections for the electron-impact ionization of helium atoms in a coplanar symmetric geometry are computed by including in the Coulomb-Born approximation a normalization factor which approximately incorporates electron-electron interactions in the final-state wave function. This approximation yields excellent agreement with recent experimental observations at impact energies between 0.5 and 5 eV above the ionization threshold. It is shown that the angular distributions given by the present theory are in agreement with Wannier’s threshold theory.

A novel treatment of dissipation of energy from a ‘‘small’’ quantum system to a reservoir is presented. We replace the usual master equation for the small-system density matrix by a wave-function evolution including a stochastic element. This wave-function approach provides new insight and it allows calculations on problems which would otherwise be exceedingly complicated. The approach is applied here to a two- or three-level atom coupled to a laser field and to the vacuum modes of the quantized electromagnetic field.

We present the first experimental results on the electric-field dependence of the threshold for ion-pair formation in a molecular system. The results were obtained for the process ${\mathrm{H}}_2$+hν→${\mathrm{H}}^{+}$+${\mathrm{H}}^{\mathrm{-}}$ by using a double-resonance excitation scheme via the E, ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{g}}^{+}{}_{}{}^{}$, v=6 level. The similarity of the long-range interaction in the ion-pair system with that of the electron-ion system leads to analogies between the field-induced process and the processes of field ionization and forced autoionization of Rydberg states of atoms.

The spatial coherence of a neonlike selenium x-ray laser operating at 206 and 210 Å has been measured using a technique based on partially coherent x-ray diffraction. The time-integrated spatial coherence of the selenium x-ray laser was determined to be equivalent to that of a quasimonochromatic spatially incoherent disk source whose diameter is comparable to the line focus of the visible-light laser pumping the x-ray laser. The spatial coherence was improved by narrowing the line focus width.

An analytical theory of toroidicity-induced shear-Alfvén eigenmodes (TAE) is presented. The full two-dimensional problem is treated using a variational approach and the radial eigenmode structure is analyzed. We show that TAE suffer a significant damping due to the strong absorption occurring at the resonances with the shear-Alfvén continouus spectrum. The resonant damping is shown to be larger than the electron Landau damping and therefore constitutes an important dissipation mechanism in determining the threshold for TAE instabilities driven by alpha and energetic particles in tokamak experiments.

An asymptotic theory is developed to determine the continuum damping of short-wavelength toroidal Alfvén eigenmodes, which is essential for ascertaining thresholds for alpha-particle-driven instability in ignited tokamaks.

We report the first experimental observation of the internal precession of the normal and superfluid magnetizations around the molecular Landau field in ${}_{}{}^3{}_{}{}^{}\mathit{B}$. This mode is excited by cross relaxation with the conventional NMR precession of the total magnetization around an external field when the two fields have similar values. From NMR measurements down to 0.12${\mathit{T}}_{\mathit{c}}$ we conclude that the catastrophic relaxation phenomenon can be explained as a capture of the internal-precession mode by the Larmor precession.

Although there is a growing consensus as to the universality of domain growth kinetics in quenced systems, discrepancies remain among theory, experiments, and simulations. We identify a major discrepancy between the three—the time dependence of mass transfer kinetics. We show that this discrepancy can be resolved in Monte Carlo simulations of domain growth. Our results strengthen the emerging consensus that systems having a nonconserved order parameter obey Lifshitz-Allen-Cahn growth kinetics in the asymptotic scaling limit.

We argue that there exist universal fixed points (FPs) that classify the universality classes of fracture processes in disordered media. As a system approaches its macroscopic failure point, the ratio of its elastic moduli appears to approach a universal value, independent of microscopic features of the system. We suggest that there are two such FPs: one describes systems that are under a uniform external load and in which fracture does not take place at random, but depends on the stress field in the system, while the other describes systems in which fracture accumulates at random and is identical with the FPs of elastic percolation networks. Experimental data on fractured rocks appear to support this.

A simple dynamical generalization of the electrical random fuse model for rupture in random media is introduced in which fuses are heated locally by a generalized Joule effect. When their temperature reaches a given threshold, the fuses burn out irreversibly and become insulators. In one limit, the rupture dynamics is spontaneously attracted to the critical state of the bond percolation model. In another limit, it recovers the ‘‘static’’ random fuse model previously studied in the literature. In between these two extremes, the existence of a novel dynamical memory effect produces a rich phenomenology of fractal rupture patterns, which are sensitively dependent upon the input current.

Phason-strained octagonal quasicrystal phases of Mo-Cr-Ni have been studied by electron diffraction and dark-field imaging. The shifting of some of the diffraction spots lowers the symmetry from eightfold to fourfold. Diffraction patterns of the orthogonal twofold axes show that the shifted spots are split along the fourfold axis. Discommensurations (DC’s) observed in dark-field images of split reflections are aligned perpendicular to the fourfold axis. We have found that the density of the DC’s in widely separated and adjacent regions may vary by more than 1 order of magnitude. The density of the DC’s is directly related to the separation of the splitting. The large difference in the density of DC’s in adjacent regions supports the interpretation that the DC’s in the Mo-Cr-Ni phases are due to the ordering of atomic species in the quasilattice. Our observations are consistent with some of the results of the two-dimensional octagonal random tiling model of Li, Park, and Widom.

The growth of diamondlike films and overlayers by the depsotion of energetic carbon atoms has been investigated by molecular-dynamics simulations. The interatomic many-atom potential suggested by Tersoff is used. The structurel analysis of the grown films shows that there is an energy window between 40 and 70 eV for the deposited atoms where the growth most closely results in dense diamondlike structure. This observation supports earlier experimental suggestions for optimal deposition conditions.

Scanning-tunneling-microscopy observations on an Al(111) surface reveal that O adatoms at 300 K are practically immobile. Low-coverage overlayers formed by dissociative chemisorption of ${\mathrm{O}}_2$ consist essentially only of single isolated atoms rather than of pairs of adjacent atoms. Hence, upon dissociation, at least part of the chemisorption energy must be transformed into translational energy parallel to the surface which causes the two O atoms formed to separate from each other by at least 80 Å before the excess energy is dissipated. The lifetime of these ‘‘hot’’ adatoms is estimated to be on the order of ≥1 ps.

We report the first observation of reconstructions on semiconductor surfaces in atmospheric pressure (AP) environments. Using reflectance-difference spectroscopy we show that the primary reconstructions that occur on (001) GaAs in ultrahigh vacuum (UHV) also occur under AP, ${\mathrm{H}}_2$, He, and ${\mathrm{N}}_2$. These results demonstrate that dimer formation is not restrited to surfaces in UHV and justify the use of UHV studies to determine (001) GaAs chemistry during AP organometaliic chemical vapor deposition (OMCVD). Reconstructions observed during OMCVD growth are inconsistent with previous models and provide new insights concerning growth.

We have calculated the electronic structure of a fullerene tubule using a first-principles, self-consistent, all-electron Gaussian-orbital based local-density-functional approach. Extending these results to a model containing an electron-lattice interaction, we estimate that the mean-field transition temperature from a Peierls-distorted regime to a high-temperature metallic regime should be well below room temperature. Such fullerene tubules should have the advantages (compared to the other conjugated carbon systems) of a carrier density similar to that of metals and zero band gap at room temperature.

We have studied resonance Raman scattering of the self-trapped exciton (STE) in NaCl tuned to the ${\mathrm{\sigma }}_{\mathrm{g}}$→${\mathrm{\sigma }}_{\mathrm{u}}$ hole transition and to the 1s→2p electron transition. The former spectrum is characterized by a sharp line at 366 ${\mathrm{cm}}^{\mathrm{-}1}$, which coincides with the stretching-vibration frequency of the H center, while the latter is characterized by broad bands, similar to that of the F center, situated below the LO phonon frequency. The result provides evidence that the STE is essentially an interacting F-H pair.

Using the diffusion quantum Monte Carlo method, we calculte the ground-state density and energy, and the quasiparticle band gap, of a model semiconductor. The exchange-correlation potential of density-functional theory (DFT), ${\mathit{V}}_{\mathrm{xc}}$(r), is obtained using optimization techniques. From this we calculate the DFT functionals ${\mathit{E}}_{\mathrm{sc}}$ and ${\mathit{T}}_{\mathit{s}}$ and the DFT band gap for various external potentials and compare the results with the local-density approximation (LDA). Whereas energies are found to be very accurate in the LDA, and the density reasonably good, we find large differences in the shape of ${\mathit{V}}_{\mathrm{xc}}$(r).

We present a new expression of the dissipative conductance and study under which conditions it is equal to the Thouless conductance defined as the curvature of the energy levels for a change of the boundary conditions. This equality is related to the transition between different classes of universality of random matrices.