An asymptotic solution to interacting walks in one dimension is presented. For repulsive and attractive interactions, respectively, the model describes aspects of uncorrelated diffusion on a lattice with sources or with randomly distributed traps. In the latter case, the average number of sites visited varies with the number of steps in the walk as $N^{\frac{1}{3}}$, while the survival probability decays as $N^{-\frac{1}{3}}\exp (-b{N}^{\frac{1}{3}})$, improving on previous predictions for diffusion with traps.

Three recent Letters have presented Dirac-equation optical-model calculations for intermediate-energy nucleon-nucleus scattering based upon a relativistic impulse approximation. In these works the relativistic impulse approximation is shown to be capable of explaining certain features of the experimental data that resist all attempts at a nonrelativistic impulse-approximation description. The reasons for the success of these relativistic impulse-approximation calculations are analyzed in the present work.

It is shown that the fact that there are six flavor-color degrees of freedom (two flavors in each generation, three colors, and lepton number) implies, under plausible assumptions, that there are three generations of light quarks and leptons. The assumptions include (a) supersymmetry for the preon theory, (b) validity of the chiral group $\mathrm{SU}{\mathrm{}\left(4\right)\mathrm{}}_L\otimes \mathrm{SU}{\mathrm{}\left(2\right)\mathrm{}}_L\otimes \mathrm{SU}{\mathrm{}\left(4\right)\mathrm{}}_R\otimes \mathrm{SU}{\mathrm{}\left(2\right)\mathrm{}}_R$ at the stage prior to the generation of the quark and lepton masses, and (c) chiral symmetry and the supersymmetric Nambu-Goldstone mechanism to protect quarks and leptons from getting large masses.

The ground-state band up to the $4^{+}$ state in the even ${}_{}{}^{74-82}{}_{}{}^{}\mathrm{Se}$ isotopes was studied by inelastic scattering of polarized protons at 65 MeV. Both the cross-section $\sigma \left(\theta \right)$ and the analyzing-power $A\left(\theta \right)$ measurements leading to the $4^{+}$ state in the light ${}_{}{}^{74,76,78}{}_{}{}^{}\mathrm{Se}$ isotopes show quite different shapes from those in the heavy ${}_{}{}^{80,82}{}_{}{}^{}\mathrm{Se}$ isotopes. Coupled-channels analyses show that both the $\sigma \left(\theta \right)$ and $A\left(\theta \right)$ distributions are well reproduced with a positive deformation parameter ${\beta }_4$ in ${}_{}{}^{74,76,78}{}_{}{}^{}\mathrm{Se}$, but with a negative ${\beta }_4$ in ${}_{}{}^{80,82}{}_{}{}^{}\mathrm{Se}$, indicating a hexadecapole-shape transition between ${}_{}{}^{78}{}_{}{}^{}\mathrm{Se}$ and ${}_{}{}^{80}{}_{}{}^{}\mathrm{Se}$.

Lifetimes for $3R_{\mathrm{g}}$ Rydberg states of benzene and perdeuterobenzene, and for $4d$ Rydberg states of toluene and perdeuterotoluene, have been measured by time-resolved ionization following two-photon excitation with 0.19-ps laser pulses. For benzene, this lifetime is 70±20 fs. This is the shortest molecular process ever resolved by direct measurement. For toluene, the lifetime is 170±20 fs. The decay mechanism is not established, but could involve internal conversion to high vibrational levels of the ground state.

A novel technique combining the advantages of the laser-rf double-resonance scheme and fast-beam collinear laser spectroscopy has been applied to a detailed study of the hyperfine structure of ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$ I I. The experimental results are analyzed with use of ab initio Dirac-Fock calculations of the reduced radial parameters of relativistic hyperfine-structure theory. The analysis results in a new value for the nuclear dipole moment $\mu \left({}_{}{}^{235}{}_{}{}^{}\mathrm{U}\right)=-0.38\mathrm{}\left(3\right)\mathrm{}{\mu }_N$ and a determination of the spin density $a^{10}\mathrm{}\left(7s\right)=-2880\mathrm{}\left(75\right)\mathrm{}$ MHz of the $7s$ electron.

A method is described for two-photon excitation of autoionizing states by use of two different-frequency photons in which the first photon reaches an energy which is near a maximum in the one-photon cross section but where the one-photon cross section is very nearly zero. This provides a large two-photon amplitude while suppressing the single-photon excitation. The application of the technique to study the Ba $6snd-7snd$ transitions by detecting the total ionization produced is described. No discrimination between ionization from one- and two-photon processes was required.

Measurements of the absolute neutron yield and the time dependence of the appearance of neutrons resulting from muon-catalyzed fusion have been carried out in high-density deuterium-tritium mixtures. The temperature dependence of the resonant $\mathrm{dt}\mu$-molecular formation process has been determined in the range 100 to 540 K. Mesomolecular formation is found to be resonant for DT as well as ${\mathrm{D}}_2$ target molecules. The sticking probability and other fundamental parameters have been measured for the first time.

Experiments on pressure-induced extra resonances in degenerate four-wave mixing involving Zeeman coherence have been performed on Ba atoms in an argon atmosphere under conditions of large detunings from the Ba resonance line. The dependence on the detuning gives evidence for a breakdown of the impact approximation, when the laser is detuned by more than 5×${10}^{11}$ rad ${\sec }^{-1\mathrm{}}$; the behavior can be interpreted semiquantitatively by a model based on optical collisions.

A theory of the structure, energetics, and modes of a film formed from a non-self-bound fluid is developed and applied to spin-polarized hydrogen at zero temperature. A hydrogen film is found to saturate at areal density ${n_s}^{\mathrm{sat}}=1.1\mathrm{}\times {10}^{14}$ ${\mathrm{cm}}^{-2\mathrm{}}$ and to support a third-sound mode with velocity that varies strongly with areal density.

The gel-sol transition for the polydiacetylene 4-butoxycarbonylmethylurethane in toluene is studied. For gelation to occur, the polymer must be in its fully extended rodlike conformation. Specific evidence that the gelation is due to the percolation of rods is presented.

The effect of a bulk triple point between phases $\alpha$, $\beta$, and $\gamma$ on the wetting, by films of $\beta$ or $\gamma$, of an $\alpha |\omega$ interface (between a wall $\omega$ and bulk $\alpha$) is discussed phenomenologically. Various additional wetting and surface transitions are induced by the triple point and may be pinned by it, and a compound ($\beta \gamma$) film may appear. The results are relevant to recent adsorption experiments and simulations.

Theory predicts that in two dimensions, the Navier-Stokes transport coefficients diverge. The results of molecular-dynamics simulations of viscous flow for a two-dimensional fluid are reported. The results suggest that, at low shear rate, instabilities in the flow screen the predicted logarithmic divergence of viscosity with respect to strain rate. When a Maxwell demon is used to suppress these instabilities, the computed viscosity is consistent with the divergent behavior predicted theoretically.

A simple model for the kinetics of two interacting interfaces moving at a prescribed rate is proposed. It is a kinetic generalization for problems like wetting, pinning, surface segregation, or surface reordering during solidification. Various types of non-equilibrium phase transitions are predicted.

Fermi-level pinning by misfit dislocations at GaAs interfaces has been investigated. $n^{+}$-GaInAs was used to control the misfit dislocation density by varying of composition and epilayer thickness. Interfaces with zero or low dislocation densities are Ohmic to current flow, and become rectifying with increasing dislocation density. The "Schottky barrier height" increases with dislocation density in accordance with a simple physical model which assumes Fermi-level pinning at the dislocation.

The dynamics of an incommensurate pinned charge-density wave in an external electric field is described by a kinetic three-dimensional discrete Gaussian model. Current oscillations are obtained as a consequence of a flat interface and a broken symmetry of this model.

The authors report on susceptibility ($\chi$) measurements of insulating spin-glasses ${\mathrm{Eu}}_x{\mathrm{Sr}}_{1-x}\mathrm{S}$ in the high-frequency region 0.1 to 12 GHz. For $x=0.43\mathrm{}$ an anomalous dependence of $\chi$ on temperature is found with a dip instead of a $\chi$ maximum at 8 and 12 GHz. A study at 12 GHz over the ${\mathrm{Eu}}_x{\mathrm{Sr}}_{1-x}\mathrm{S}$ series shows that the dip is more pronounced near the ferromagnetic phase boundary. The behavior can be understood as arising from a competition between $\chi (T,\nu )$ of spin-glass and ferromagnetic short-range order.

It is suggested that resonant tunneling via defect-related states is an important mechanism for high-field carrier injection into thin Si${\mathrm{O}}_2$ films of metal-oxide-semiconductor structures. A model is also proposed for high-field insulator breakdown which cannot be explained by available theories.

Conclusive evidence is provided for the first time that through adsorbate-induced surface-structure changes, effective channels open for hydrogen to move from the surface to the interior of metals. In Pd(110), all available subsurface sites between the first and the second metal layers can be selectively populated by thermal activation from a specific type of chemisorption place, which is associated with a substrate reconstruction at high hydrogen surface coverage.

The influence of coadsorbed potassium atoms on the electronic structure of CO adsorbed on Ni(111) was studied by use of surface metastable quenching spectroscopy. An enhancement of electron emission from the partially filled $2{\pi }^{*}$ antibonding orbital of CO is observed, and the result is interpreted in terms of increased electron back-donation from the metal to the $2{\pi }^{*}$ orbital, caused by potassium atoms.