The dynamics of island growth have been studied with Monte Carlo techniques for a simple lattice-gas model of O on W(110) when the system is suddenly quenched at a constant coverage $\rho =0.25\mathrm{}$ to a temperature well below its transition temperature. The structure functions for the local coverage and $p(2\mathrm{}\times 1)$ order parameter exhibit a simple scaling with respect to certain characteristic time-dependent lengths. This scaling is qualitatively similar to that found in other systems such as binary alloys.

A contribution to the magnetoresistance is observed at temperatures below 100 mK in bulk metallic Si: P that is unanticipated within theoretical analyses of localization. This contribution is positive, approximately independent of sample orientation, and varying roughly as the square root of the applied field. An analysis of Coulomb interactions including spin splitting is presented which, when combined with localization, describes the magnetoresistance.

The first observation of a first-order phase transition in the magnetization of Fe in an applied field is reported. The samples were epitaxially grown (110) Fe films on GaAs. Mean-field theory, with the inclusion of uniaxial anisotropy and the constraint that $\overrightarrow{\mathrm{M}}$ lie in the plane of the film, gives excellent agreement with the observed transition. The relationship of this transition to the predictions of the three-state Potts model for cubic ferromagnets is discussed.

In problems involving two-dimensional area-preserving maps, stochastic regions are separated by continuous curves called Kolmogorov-Arnold-Moser trajectories. As the mapping is changed continuously, these regions may fuse via the disappearance of the intervening trajectories. Scaling arguments are presented to describe the behavior of the curves near their disappearance.

The $L\to \infty$ asymptotic properties of ${\rho }_L\mathrm{}\left(g\right)\mathrm{}$, the probability distribution of the classical hopping conductivity $g_L$ corresponding to random one-dimensional systems of length $L$, are determined. These properties are nonuniversal, and become anomalous if the probability density $\rho \mathrm{}\left(w\right)\mathrm{}$ of the random near-neighbor hopping rates is such that $\int 0^{\infty }\mathrm{dw}\rho \mathrm{}\left(w\right)\mathrm{}{w}^{-1\mathrm{}}$ does not exist. The associated quasilocalization effects are discussed and their experimental observability is speculated upon.

A new gauge-invariant effective action is proposed for quantum gravity, based on older results that go beyond finite-order perturbation theory. Expressed in coordinate space rather than momentum space it should find important applications in theory of the early universe.

Results are presented from a search for fractional charges on mercury drops. About 1 00 000 drops have been measured, comprising 60 μg of refined mercury and 115 μg of native mercury. No fractionally charged drops were observed in this sample.

A microscopic model is presented for the complete fusion of two nuclei with the total excess energy being transferred to the pion field. The meson exchange between two nucleons, each of them belonging to one of the colliding fragments, leads naturally to a coupling of the initial relative motion to the final pion field. With use of this reaction mechanism an adequate description can be achieved for the process ${}_{}{}^3{}_{}{}^{}\mathrm{He}$(${}_{}{}^3{}_{}{}^{}\mathrm{He}$,${\pi }^{+}$)${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ around 280 MeV.

Direct measurements by time-resolved Thomson scattering of the saturation of the two-plasmon decay instability driven by a C${\mathrm{O}}_2$ laser in an underdense plasma are presented. A time-correlated growth in ion fluctuations is also seen, enabling the saturation mechanism to be identified with the ion motions driven by the ponderomotive force associated with the large-amplitude electrostatic waves.

The first measurements of high-energy x-ray emission ($h\nu \sim 30-300$ keV) by high-$Z$ microballoon targets irradiated at $5\times {10}^{14}<\varphi <2\mathrm{}\times {10}^{16}$ W/${\mathrm{cm}}^2$ by 10.6-μm laser light are reported. An exponential spectrum with a slope $k{T}_H\sim 250$ keV provides the best fit to spectrometer data at ${\varphi }_l={10}^{16}$ W/${\mathrm{cm}}^2$. The hard-x-ray yield indicates that a substantial fraction, probably between 10% and 100%, of the absorbed laser energy is converted to hot electrons. The slope $k{T}_H$ is proportional to the fastest ion energy.

A new technique is presented for investigating the normal modes of an amorphous solid with use of molecular-dynamics simulations. This method, based on the quench echo, can be used even in cases where the dynamical matrix is too large to be diagonalized. This technique has been applied to study the onset of localization in a Lennard-Jones frozen fluid.

The configurational relaxation time for the $F_{\mathrm{A}}\left(\mathrm{II}\right)$ center in KCl: Li has been measured with use of picosecond laser techniques. The saddle-point configuration of the electronically excited state is stabilized by means of multiphonon emission, and has a zero-temperature lifetime of 13 psec.

Experimental evidence for one-dimensional domain-wall relaxation above $T_c$ in the quasi one-dimensional ferromagnet [(C${\mathrm{H}}_3$)${}_4{}^{}{}_{}{}^{}\mathrm{N}$] Ni${\mathrm{Cl}}_3$ has been obtained from ac susceptibility measurements in the frequency range $10 \mathrm{Hz}<\nu <30\mathrm{} \mathrm{MHz}$. The field and temperature dependence of the absorption is well explained by the interaction of $\pi$ solitons with the oscillating magnetic field.

A modified droplet model is proposed that incorporates both compact fluctuations that give rise to weak singularities at the first-order transition, and ramified fluctuations that give rise to spinodals in high dimensions. Renormalization-group considerations and studies of the percolation problem allow the use of ramified fluctuations to calculate spinodal exponents for $d>\mathrm{}8\mathrm{}$. The problem in lower dimensions is also discussed together with possible interpretation of these exponents in light of the indeterminacy in locating spinodal points.

A very preliminary value $(-0.8\mathrm{}\pm 2.5){\left(\frac{\alpha }{\pi }\right)}^4$ is reported for the complete eighth-order QED contribution to the electron anomalous magnetic moment. The large error reflects the difficulty in evaluating the huge integrals involved and will be reduced in the future. Theory and experiment agree within 2 standard deviations. The current result enables us to determine, in a manner based solely upon elementary-particle physics, the fine-structure constant $\alpha$ to an accuracy of 0.08 ppm.

A search for neutrino oscillations in a wide-band neutrino beam at Fermilab with use of the 15-ft bubble chamber is reported. No evidence is found for neutrino oscillations and upper limits are set on the mixing angles and neutrino mass differences in the transitions ${\nu }_{\mu }\to {\nu }_e$, ${\nu }_{\mu }\to {\nu }_{\tau }$, and ${\nu }_e\to {\nu }_{{}_{}{}^{\sim }{}_{}{}^{}e}$, where $\sim e$ denotes "not $e$."

The forward-to-backward asymmetry of high-energy photons emitted in the radiative capture of neutrons with energies up to 20 MeV was measured for ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$. The asymmetry increases abruptly from small values to large ones near $E_{\gamma }\sim 23$ MeV supporting the location in that neighborhood of the $E2\mathrm{}$ giant isovector resonance.

Fine-structure transitions of alkali atoms induced by collisions with diatomic molecules are shown to be strongly influenced by a dynamical feature that is completely absent when the collision partner is a rare gas. The effect is a nonadiabatic coupling caused by the anisotropy of the molecule. Calculations for $\mathrm{Rb}\left(5\mathrm{}{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}\right)$ + ${\mathrm{H}}_2$ and for $\mathrm{Rb}\left(5\mathrm{}{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}\right)$ + He are in good agreement with recent experiments and explain the dramatic difference between these two systems.

This communication presents the first nonperturbative quantum-mechanical calculation for state-resolved angular differential cross sections for a chemical rearrangement for which experimental results are available. The reaction studied, F + ${\mathrm{H}}_2$ → H + HF, is an important prototype for understanding reaction dynamics and is one of the few for which comparisons of experiment and theory are possible. The significant features of the state-to-state angular distributions for this reaction observed experimentally are reproduced by this study.

A cutoff with wavelength is observed in the absorption of blackbody radiation by free atoms. The cutoff arises from a discontinuity in the density of modes between parallel conducting plates. Absorption at a wavelength of $\frac{2}{3}$ cm by atoms between planes $\frac{1}{3}$ cm apart is measured at a temperature of 180 K. The discontinuity in the absorption rate occurs when the absorption wavelength is varied across the cutoff of one of the parallel plate modes.