The size and distribution of built-in electric fields in $a-\mathrm{Si}:\mathrm{H}/a-\mathrm{Si}{\mathrm{N}}_x:\mathrm{H}$ layered amorphous semiconductor materials have been determined by use of electroabsorption spectroscopy. Strong asymmetries are present between the interfaces, leading to internal fields as large as 4 × ${10}^5$ V/cm in material with thin (12 Å) layers. These fields are due to an interface charge present when amorphous silicon is deposited onto silicon nitride, which we attribute to strain-relieving defects caused by structural mismatch.

Measurements of the total energy reflected from crystalline and amorphous silicon illuminated by a femtosecond laser pulse are reported, for wavelengths of 0.62 and 0.31 μm. The results are interpreted by use of a highly nonlinear regime of light propagation in the dense plasma of electrons and holes ($e-h$). Densities higher than ${10}^{22}$ ${\mathrm{cm}}^{-3\mathrm{}}$ are reached. We demonstrate that free-carrier absorption is dominated by $e-h$ collisions.

Density-functional calculations have been performed for low-lying states of ozone (${\mathrm{O}}_3$) with use of a local-density approximation for exchange and correlation. The energy surfaces are qualitatively better than Hartree-Fock results and in generally good agreement with experiment and configuration-interaction calculations where available. As in $\mathrm{sp}$-bonded solids and diatomic molecules, there is a substantial overestimate of the dissociation energy. This suggests caution in interpreting local-density calculations of bonding energies in general, particularly if local bonding effects are important.

In the context of Einstein-Cartan-Sciama-Kibble theory, modified to include a time-dependent gravitational coupling $G\mathrm{}\left(t\right)\mathrm{}$, torsion is shown to be proportional to the variation $\frac{\dot{G}}{G}$. The magnitude of this effect based on recent experimental evidence is substantially greater than the usual spin-dependent torsion effects predicted by standard Einstein-Cartan-Sciama-Kibble theory. It is suggested that the detection of a time-varying $G$ could provide evidence for the existence of torsion.

The survival probability of a particle that performs a random walk on a linear chain with randomly distributed traps is considered. An asymptotically exact solution was found, valid for large step numbers $n$ and all trap concentrations $c$. The survival probability depends upon the combination $x={[-\pi \ln \mathrm{}(1-c\left)\right]}^{\frac{2}{3}}{n}^{\frac{1}{3}}$ of the variables $n$ and $c$ only and is in leading order equal to $\left(\frac{8}{\pi }\right){\left(\frac{2}{3}\pi \right)}^{\frac{1}{2}}{x}^{\frac{3}{2}}\exp (-\frac{3x}{2})$. The analytical result includes correction terms and is confirmed by Monte Carlo simulations.

We investigate stability of Freund-Rubin—type solutions of eleven-dimensional supergravity in which extra spaces are direct products of compact spaces of constant curvature. It is shown that the solutions of the form $\mathrm{Ad}{\mathrm{S}}_4\times B_7$ with $B_7=S^5\times S^2,S^4\times S^3,S^3\times C{P}^2,S^3\times S^2\times S^2$, etc., are unstable against relative dilatations between the subspaces.

We investigate nonrandom, half-random, and random variants of clusters generated by the "squig" process, using renormalization or Monte Carlo methods. Each variant is compared to two-dimensional percolation clusters at criticality from the viewpoints of the fractal dimensionalities of the whole, the backbone, the multiconnected parts, the ring hulls, the backbone links, the shortest paths, and the recurrences of diffusion, hence the fracton dimensionality. The random variant fits very well when its only parameter $s$ is a bit above 0.4.

We have performed Monte Carlo random-walk experiments on a one-dimensional periodic lattice with a trapping site using the logistic map as a generator of pseudorandom numbers. Comparison with analytical results indicates that, when it has sensitive dependence to the initial conditions, this map provides a true pseudorandom generator.

By numerically computing orbits for a chaotic, one-dimensional, many-body system placed between two thermal reservoirs, we verify directly that its energy transport obeys the Fourier heat law and we determine its thermal conductivity $K$. The same value of $K$ is independently obtained by use of the Green-Kubo formalism. These numerical studies verify that chaos is the essential ingredient of diffusive energy transport, and they validate the Green-Kubo formalism.

In a tungsten beam-dump experiment performed at Fermilab, 1480 neutrino-induced muonless events were observed. The prompt ${\nu }_e$ flux was determined both by subtraction of residual ${\nu }_{\mu }$ and nonprompt ${\nu }_e$ interactions and by use of the difference between the longitudinal energy deposition of electromagnetic and hadronic showers. The ratio of the prompt ${\nu }_e$ flux to the ${\nu }_{\mu }$ flux was measured to be 0.95 ±0.12 ±0.08 for $E_{\nu }>20\mathrm{}$ GeV and was consistent with unity throughout the range of energy and transverse momentum accessible to the experiment.

We have set an upper limit on the ${\nu }_{\tau }$ mass from a study of the four-pion invariant-mass distribution in the decay $\tau \to 3{\pi }^{\pm }{\pi }^0{\nu }_{\tau }$. We obtain the limit ${m_{\nu }}_{\tau }<164\mathrm{}$ MeV/${\mathit{c}}^2$ at 95% confidence level.

The wide-angle spectra of the 134-MeV ($p$, $n$) reaction on ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$, ${}_{}{}^{54}{}_{}{}^{}\mathrm{Fe}$, ${}_{}{}^{88}{}_{}{}^{}\mathrm{Sr}$, and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ are each dominated by the excitation of a single state at low excitation energy. These excitations correspond to the $``0\mathrm{}\hslash \omega "$ stretched states and are seen to be fragmented much less than $``1\mathrm{}\hslash \omega "$ stretched states in medium- and heavy-mass nuclei. The normalization factors required for comparison with distorted-wave impulse-approximation calculations are >0.50 and indicate that these are the purest particle-hole states known in these nuclei.

Measurement of the alpha inelastic-scattering cross sections for the first two $2^{+}$ states in ${}_{}{}^{34}{}_{}{}^{}\mathrm{S}$ shows unambiguously that the relative sign of the neutron and proton transition matrix elements for both $2^{+}$ states are positive, just as in the cases of ${}_{}{}^{26}{}_{}{}^{}\mathrm{Mg}$ and ${}_{}{}^{30}{}_{}{}^{}\mathrm{Si}$. Consideration of coupled-channel effects in inelastic scattering do not change this overall result. The present results are in contradiction with the predictions of recent shell-model calculations.

Xenon atoms are excited to $5p^{5}6p{\left[\frac{1}{2}\right]}_0$ during a collision using two-photon laser excitation. The probability for subsequent fluorescence is measured as a function of laser detuning into the line wing of the transition. This probability is found to decrease significantly for large detunings corresponding to excitation of collision pairs at smaller internuclear separations. We interpret the decrease in fluorescence as inelastic quenching to dissociative channels encountered during the first half-collision.

The velocity of strong shock waves, induced by 0.26-μm-wavelength laser pulses, is measured in aluminum, copper, and gold targets. The results lead to an ablation pressure of 3 TPa at 4.5×${10}^{14}$ W/${\mathrm{cm}}^2$ incident intensity for 450-ps full width at half maximum pulses focused on a 50-μm-diam spot. These first shock-pressure results at 0.26 μm wavelength outline the great interest in short wavelengths for producing ultrahigh pressure in a laser-matter interaction experiment.

Stimulated Brillouin scattering is analyzed in finite systems which have a boundary reflective to light. The linear instability is considerably altered from that for the usual transmitting boundaries. In the nonlinear regime the scattered light intensity may behave chaotically in time and exhibit rich frequency spectra including shifts corresponding to fractional harmonics of the fundamental acoustic wave. Simulation results compare favorably with data from laser-plasma-interaction experiments.

We study the macroscopic elastic moduli of an elastic percolating network in the critical region. A microscopic elastic Hamiltonian is used, which contains a bending energy term. We find that the rigidity threshold of this system is identical to the percolation threshold $p_c$. By considering the elastic properties of elements of the infinite percolation cluster we calculate the critical exponent $\tau$ which describes the behavior of the elastic stiffness near $p_c$ for $d=6\mathrm{}$ and obtain a lower bound on $\tau$ for $d<\mathrm{}6\mathrm{}$. $\tau$ is considerably higher than the conductivity exponent $t$, suggesting that the elastic problem belongs to a different universality class.

Composition and light scattering results in a three-phase equilibrium of a microemulsion system provide evidence for the existence of an apparent field variable related to composition. This variable, the water-over-surfactant ratio ($X$), takes the same value in the three coexisting phases. This three-phase equilibrium disappears by a critical end point which is approached by varying $X$. The dependences of the scattered intensity and the correlation length as a function of $X$ are described by power laws with Ising exponents.

We present a Monte Carlo study on a square lattice of a model classical Hamiltonian which has molecular dimerized phases as well as atomic phases. The phase diagram is discussed in detail and the main analogies with and differences from that of three-dimensional hydrogen are pointed out.

Field-induced reorientations of liquid crystals, far from equilibrium, produce spatially periodic responses. The wavelength selected maximizes response speed. A detailed analysis of the effect in a novel geometry is presented, along with a discussion of its general importance in polymerlike liquid crystals.