Explicit saddle surfaces and return jump rates are calculated for model crystals; the results establish the validity of rate calculations for atomic jumps in solids. A nonphysical effect, in which isotopic substitution causes a "return jump catastrophe," is resolved by use of an exact momentum-dependent criterion to distinguish successful jumps.

The bare diamagnetic susceptibility $\chi$ of a composite superconductor below the percolation threshold $p_c$ has been numerically calculated. A novel fitting procedure gives $\chi \propto {\left(\Delta p\right)}^{-b}$ near $p_c$, with $b=1.29\mathrm{}$ in dimension $d=2\mathrm{}$, $b=0.35\mathrm{}$ in $d=3\mathrm{}$, the exponents agreeing between site and bond percolation to within 0.02 in both cases. Similar effects give a far-infrared absorption coefficient $\alpha$ in normal-metal-insulator composites varying as $\alpha \sim {\omega }^2{\left(\Delta p\right)}^{-\frac{\mathrm{}(s+b)\mathrm{}}{2}}$ where $s$ is the dielectric-constant exponent.

Persistent spectral antiholes, which correspond to increased absorption at the laser frequency, have been burned in an inhomogeneously broadened vibrational mode of Re${\mathrm{O}}_4^{-}$ embedded in alkali halide host lattices. A new model is proposed to explain nonphotochemical hole and antihole burning.

Nanosecond structural changes in a crystal lattice during pulsed laser annealing have been measured by use of time-resolved low-energy electron diffraction. Low-energy electron diffraction is both structure and surface (∼ 10 Å) sensitive and can yield lattice temperatures from Debye-Waller-like extinction coefficients. Combining these with nanosecond time resolution provides a surface probe for short-time dynamical processes. The results demonstrate rapid formation of a liquid layer and subsequent surface recrystallization and cooling on (111) Ge.

"Five-mode" massive aluminum gravitational radiation detectors cooled to millikelvin temperatures are considered for the purpose of approaching quantum sensitivity over a large bandwidth. A five-mode detector with a center frequency at 800 Hz would have a two-sided usable bandwidth of the order of 400 Hz. A five-mode detector with a center frequency at 1660 Hz would have a usable two-sided bandwidth of the order of 1000 Hz.

In a search for heavy charge-$\frac{4}{3}e$ particles produced in $e^{+}{e}^{-}$ collisions at a center-of-mass energy of 29 GeV, no candidate events were found in 22 ${\mathrm{pb}}^{-1\mathrm{}}$ of data collected by the time projection chamber at PEP. Upper limits are established on the inclusive cross section for the production of charge-$\frac{4}{3}e$ particles in the mass range of 1-10 GeV/${\mathit{c}}^2$.

It is suggested that an experimental verification of the relation $A_2=A_0$ ($A_i$ are the coefficients of the angular distribution of lepton pairs arising from decays of $Z^0$ produced at hadronic collisions) would be strong evidence for the vector nature of the spin of the gluon. The above relation $A_2=A_0$ is badly broken if the gluon coupling to quarks violates quark-helicity conservation.

The schematic model is extended to open-shell nuclei. The quasiparticle random-phase approximation plus core polarization are used to calculate multipole matrix elements $M_n$ and $M_p$. Calculated trends in the ratio of deformation parameters $\frac{{\beta }_n}{{\beta }_p}$ are compared with experimental ratios for several sets of isotopes and isotones. The systematics indicate a rather abrupt change toward equality of ${\beta }_n$ and ${\beta }_p$ when $N$ or $Z$ is changed from a closed-shell value.

Experimental cross sections at energies of 962 and 437 MeV/nucleon are reported for ${\mathrm{U}}^{92+}$ ⇄ ${\mathrm{U}}^{91+}$ and ${\mathrm{U}}^{91+}$ ⇄ ${\mathrm{U}}^{90+}$ in Mylar, Cu, and Ta, as well as equilibrium charge-state distributions in these materials. At 962 MeV/nucleon a beam containing over 85% bare ${\mathrm{U}}^{92+}$ nuclei is obtained.

Spectra of low-energy electrons ejected in the collisions of 2.5-keV ${\mathrm{H}}^{-}$ with ${\mathrm{O}}_2$ and NO have been studied. Charge transfer to the shape resonances, ${{\mathrm{O}}_2}^{-}({}_{}{}^2{}_{}{}^{}\Pi _g^{}{}_{}{}^{},v^{\prime \prime }>~4)$ and $\mathrm{N}{\mathrm{O}}^{-}({}_{}{}^3{}_{}{}^{}\Sigma _{}^{-}{}_{}{}^{},v^{\prime \prime }>~1)$, was found to be the predominant route for the electron detachment. It was also found that Wigner's threshold law was sensitively reflected in the vibrational structures of the spectra.

From the complete angular correlation between the $L$ x rays and scattered $\alpha$ particles after ionization of the Dy $L_{\mathrm{III}}$ subshell by 16-MeV $\alpha$ particles, the impact-parameter-dependent $A_{20}$, $A_{22}$, and $A_{21}$ alignment tensor components were determined. These alignment tensor components which characterize the magnetic substate ionization and the relative phases between the ionization amplitudes are in reasonable agreement with semiclassical-approximation predictions.

A short-pulse, high-intensity Nd-laser beam interacts with preformed plasmas of variable scale length. At the longest scale length, absorption is limited by backscatter, despite increased collisional absorption.

Space- and time-resolved Thomson scattering has been used to characterize strong nonthermal ion-acoustic fluctuations in C${\mathrm{O}}_2$-laser-heated plasmas in the density range $0.3<~\frac{n}{n_c}<~2.0$. The relative fluctuation amplitude scales as $\frac{\delta n}{n}\sim I^{0.6}$ with a level of $\frac{\delta n}{n}\simeq 15$% at a laser intensity $I=2.3\mathrm{}\times {10}^{14}$ W/${\mathrm{cm}}^2$. No saturation with intensity is observed. The wave-number spectrum peaks at a constant $k{\lambda }_{\mathrm{D}}\simeq 0.12$ over all densities.

The $p(2\mathrm{}\times 2)$ and $c(2\mathrm{}\times 2)$ coverages of O on Ni(100) are studied with a cluster model. The $p(2\mathrm{}\times 2)$ coverage is modeled by the addition of a single O at a fourfold site. The $c(2\mathrm{}\times 2)$ is modeled by the explicit inclusion of four additional O atoms. Consistent with electron energy-loss spectroscopy results, the O-Ni vibration is 85 ${\mathrm{cm}}^{-1\mathrm{}}$ lower for the $c(2\mathrm{}\times 2)$ cluster than for the $p(2\mathrm{}\times 2)$. The height of O above the surface is 0.11 Å smaller for the $c(2\mathrm{}\times 2)$ coverage. The nature of the O-to-Ni bonding is similar for both coverages.

From adiabatic-scanning calorimetric results it is demonstrated that in mixtures of 9CB and 10CB, two compounds of the alkylcyanobiphenyl ($n\mathrm{CB}$) series, the nematic ($N$) to smectic-$A$ ($A$) transition becomes first order for narrow $N$ ranges. From the latent heats a tricritical point is located in the phase diagram. Measurements for 7CB+ 8CB mixtures show that the specific-heat exponent $\alpha$ depends on the width of the $N$ range for continuous $\mathrm{AN}$ transitions.

High-resolution x-ray scattering measurements of the nematic to smectic-$A$ transitions in two different homologous series are reported; it is found that the correlation-length exponents ${\nu }_{\parallel }$ and ${\nu }_{\perp }$ and the susceptibility exponent $\gamma$ decrease continuously with decreasing nematic range; the transitions ultimately become first order. The exponents at the crossover point are close, but not identical, to mean-field tricritical values. For both series and all samples ${\nu }_{\parallel }\ne {\nu }_{\perp }$ while $\alpha +{\nu }_{\parallel }+2\mathrm{}{\nu }_{\perp }-2=0\mathrm{}$ to within the errors.

A Flory-type argument based on a branched-polymer topology is presented for the fractal tal dimension $D(d,d_w)$ of diffusion-limited aggregates formed by a random walk with fractal dimension $d_w$.

Bond percolation on elastic networks involving nearest-neighbor forces is studied by numerical simulations. With purely central forces, the bulk and shear moduli go to zero, with an exponent $f$, and at a threshold $p_{\mathrm{cen}}$, which are significantly higher than the exponent $t$ and threshold $p_c$ of the corresponding purely isotropic force or the equivalent electrical conduction problem. An interesting crossover is observed when both central and isotropic forces are included.

A study is presented of migration of optical or magnetic excitations on structures with fractal geometry, which terminates upon reaching a trapping site. The theory is based on the extension of results from the theory of random walks to systems without translational invariance, together with the use of scaling concepts. For the case of an excitation which resides on one type of atom in a randomly mixed crystal near the percolation threshold, new power laws for the time and concentration dependence of the number of distinct sites visited in time $t$ and of the number of excitations that are not yet trapped are obtained.

The conductance of metal-oxide-silicon field-effect transistors with ∼70-nm-wide inversion layers exhibits nonmonotonic variations with electron density below 15 K. The variations are largest at low electron concentrations and are the result of variations of the activation energy $E_A$. When $E_A$ is largest the current is found to be limited by spatial barriers which contain tunneling channels at discrete energies, as in the model of Azbel.