A dynamic model for neural networks is proposed, which explicitly takes into account the existence of several time scales without discretizing the time. The dynamics is neither totally synchronous nor totally asynchronous, and may be regarded as more realistic. A simple but unphysical case of symmetric couplings has been analyzed to display desirable features similar to those of the Hopfield model. This supports the "universality" hypothesis that the properties are insensitive to the details of the model.

We present a new method for using the data from Monte Carlo simulations that can increase the efficiency by 2 or more orders of magnitude. A single Monte Carlo simulation is sufficient to obtain complete thermodynamic information over the entire scaling region near a phase transition. The accuracy of the method is demonstrated by comparison with exact results for the d=2 Ising model. New results for d=2 eight-state Potts model are also presented. The method is generally applicable to statistical models and lattice-gauge theories.

The physical basis for the description of phenomena by a rotating observer is investigated. A simple, yet tentative, extension of the hypothesis of locality is used to determine the interference phase shift induced by the rotation of a neutron interferometer. The result consists of the Sagnac term, which is due to the coupling of the orbital angular momentum of the neutron with the rotation of the frame, and a new term which arises from a similar coupling because of the neutron spin. The latter effect is generally smaller than the Sagnac phase shift by the ratio of de Broglie wavelength of the neutron to the dimension of the interferometer. The possibility of detecting the new effect is briefly discussed.

We analyzed lunar laser-ranging data, accumulated between 1970 and 1986, to estimate the deviation of the precession of the moon’s orbit from the predictions of general relativity. We found no deviation from this predicted de Sitter precession rate of nearly 2 angular sec per century (sec/cy), to within our estimated standard error of 0.04 sec/cy. This standard error, 2% of the predicted effect, incorporates our assessment of the likely contributions of systematic errors, and is about threefold larger than the statistical standard error.

The contribution of the ‘‘gravitomagnetic’’ interaction to a well-measured perturbation term in the orbits of Earth satellites is calculated. Laser-ranging determination of the Moon’s orbit and Lageos-satellite orbit require the precise participation of the gravitomagnetic interaction; otherwise anomalous orbital perturbations exist. For the Lageos-satellite orbit, the gravitomagnetic interaction’s contribution to the orbit is a 100-m altitude variation of frequency ω-Ω (ω and Ω are satellite and Earth orbital angular frequencies, respectively), but which is nullified by effects from other well established post-Newtonian gravitational potentials.

Solar flares have been suggested as the cause of occasional high counting rates in the ${}_{}{}^{37}{}_{}{}^{}\mathrm{Cl}$ solar-neutrino experiment. The sensitivity of neutrino detectors to flares is evaluated. Several neutrino detectors will show large signals when prominent flares are observed electromagnetically, if flares are detected in the chlorine experiment.

A search has been made for a correlation between large solar flares and neutrino events observed in Kamiokande for the period of July 1983–July 1988. No significant neutrino signal was found at the time of a solar flare, giving a limit on the time-integrated ‘‘solar-flare’’ ${\nu }_e$ flux <3.7×${10}^7$ (2.5×${10}^9$) /${\mathrm{cm}}^{\mathrm{-}2}$ per flare at 90% confidence level, for $E_{\nu }$=100 (50) MeV. These limits are 2000 (60) times smaller than the value required for neutrinos with those energies to account for the excess of signal in the ${}_{}{}^{37}{}_{}{}^{}\mathrm{Cl}$ solar-neutrino experiment of some of the corresponding solar-flare times.

We show that the mechanism which enhances ordinary fermion masses and raises the masses of pseudo Goldstone bosons in walking-technicolor models may also lead to an enhancement of weak-isospin–violating effects of extended-technicolor interactions. We discuss the constraints on these models due to limits on the deviation of the ρ parameter from 1.

Data taken in a Fermilab experiment designed to measure to CP-violation parameter ε’/ε from a study of K→2π decays were used to look for the as yet unseen decay modes $K_L$,S→${\mathrm{\pi }}^0$${\mathrm{e}}^{+}$${\mathrm{e}}^{\mathrm{-}}$. The detector was optimized for the detection of kaon decays with four electromagnetic showers in the final state. The results (90% confidence) are branching ratios <4.2×${10}^{\mathrm{-}8}$ and <4.5×${10}^{\mathrm{-}5}$ for $K_L$→${\pi }^0$$e^{+}$$e^{\mathrm{-}}$ and $K_S$→${\pi }^0$$e^{+}$$e^{\mathrm{-}}$, respectively.

Two-proton correlations were measured as a function of the total energy and relative momentum of the protons. The correlation is analyzed for different orientations of the relative momentum, which allows information on the size and lifetime of the emission source to be extracted. The most energetic particles are emitted from a short-lived source of compound-nucleus dimensions while the lower-energy protons appear to be emitted from a source considerably larger than the compound nucleus.

A new experimental approach for determining photoionization matrix elements which avoids the spin analysis of the photoelectron is presented for the case of 2p photoionization of atomic magnesium by 80-eV photons. Our experimental results clearly demonstrate the inadequacy of presently available theoretical calculations for this system.

Using a Sturmian function expansion we have computed the nth order coefficients ${\mathrm{E}}_{\mathrm{n}}$(ω), for 2≤n≤22, in the perturbation expansion of the ac Stark effect in the hydrogen 1s state. An ‘‘effective convergence’’ similar to that in the dc case is observed. A parametrization of these coefficients, based upon the analytic structure of the Coulomb Green’s function, separates the rapid oscillatory resonant behavior and the smooth background variation with respect to ω.

The angle and energy dependence of electron emission following the interaction of normal-incidence 70- to 170-MeV ${\mathrm{Ne}}^{\mathrm{q}+}$ (a=7,10) projectiles with thin carbon foils has been investigated experimentally. An enhancement of the target KLL Auger-electron emission was observed for forward ejection angles. Model calculations yield results in qualitative agreement with the observed Auger-electron anisotropies. The theoretical results predict a significant enhancement of target inner-shell ionization near the exit surface due to highly energetic secondary electrons.

In conventional heteroepitaxy, lattice mismatch is accommodated through biaxial strain and interfacial misfit dislocations. In studies of the heterophase boundaries appearing in semicoherent α-${\mathrm{Si}}_3$${\mathrm{N}}_4$ precipitates grown in situ in a silicon matrix, we have found that part of the lattice mismatch can be accommodated by formation of low-energy asymmetric tilt boundaries, which accommodate the lattice mismatch without producing a long-range stress field. This result suggests that growth of misfit-dislocation–free lattice-mismatched tilted structures should be possible.

We have performed the first measurements on surface-aligned samples of the blue phase III of chiral liquid crystals and have tested proposed icosahedral, cubic-domain, and double-twist structures for blue phase III. Angular-reflection studies on surface-aligned samples show no evidence of expected icosahedral structure; uv reflection measurements on unaligned samples show no evidence of expected cubic-domain structure; and attempts to observe Cano fringes show no evidence for any spatial periodicity.

It is shown via state-of-the-art theoretical calculations that self-diffusion in diamond is dominated by vacancies, independent of the position of the Fermi level. This is very different from self-diffusion in silicon and germanium, where vacancies, interstitials, and direct-exchange mechanisms all have comparable activation energies. The dominance of the vacancy mechanism is due to the stiffness of diamond bonds, which precludes bond twisting and large relaxations, and to the high electronic density and the large band gap in diamond, which result in a strongly repulsive potential-energy surface for self-interstitials.

Extensive first-principles calculations are presented for the formation energies and migration barriers of elementary defects in graphite, as well as for the activation energy of atomic exchange. The calculations show that the long-held view, that atomic diffusion in graphite occurs via the direct-exchange mechanism, is incorrect, although more complicated exchange processes have not been ruled out. We find that diffusion in graphite is most likely mediated by vacancies with an activation energy which is lower than that of the interstitial and the direct-exchange mechanisms, and is in reasonable agreement with experiment.

Temperature-dependent radiation-enhanced-diffusion rates for Ag in Ni have been found to decrease at elevated temperatures. The observed narrowing of interface interdiffusion regions with increasing temperature depends on both defect concentration and migration processes which occur in ion-bombarded solids. These findings can be interpreted in terms of a general model of radiation-enhanced diffusion that involves long-lived complex defects which can migrate for large distances and which are themselves subject to annealing.

Inelastic light scattering by inter-Landau-level excitations of the 2D electron gas in high-mobility GaAs structures in a perpendicular magnetic field was observed at the energies of the critical points in the mode dispersions. For Landau-level filling factors ν≥1, structure in the spectra indicates the excitonic binding and roton behavior predicted by the Hartree-Fock approximation. The large critical-point wave vectors, q≳(ħc/eB${)}^{\mathrm{-}1/2}$≳${10}^6$ ${\mathrm{cm}}^{\mathrm{-}1}$, are probably accessible in resonant light scattering through the residual disorder that broadens the Landau levels.

Inelastic scattering of ${\mathrm{He}}^{+}$ in the kinetic energy range 100–1000 eV from the surface of ionic compounds as well as metallic elements has been investigated. The inelastic ${\mathrm{He}}^{+}$ scattering at the surface of ionic crystals sometimes exceeds the elastic scattering even for kinetic energy below a few hundred eV. It can be ascribed to the excitation of surface valence electrons to the conduction band because of the interaction of the surface p-band with the He 1s orbital which is promoted in the quasimolecular state.