The relative stability of the seven most common crystal structures of the $\mathrm{pd}$-bonded $\mathrm{AB}$ compounds is examined within a tight-binding model which allows the influence of atomic size, $p$ and $d$ energy-level separation, and band filling to be studied directly. The simple theory, which neglects the valence $s$ electrons, accounts qualitatively for the observed domains of NaCl, CsCl, NiAs, MnP, and boride stability, only the narrow FeSi domain remaining unaccounted for.

Field emission microscopy studies and very high-resolution Auger electron spectroscopy analyses of platinum field-emitter surfaces show that P, Si, and S impurities strongly segregate to the {100} areas, and that Si stabilizes the nonequilibrium {012} planes. Auger spectra demonstrate the difficulty of detecting Si and S impurities on Pt because of peak-overlap problems at 92 and 152 eV, respectively. Evidence is presented which suggests that these impurities have been largely overlooked in Pt{100} reconstruction studies.

Self-avoiding walks may be constructed through a progressive exclusion of walks with loops. A study of the process leads to critical exponents $\nu \simeq \frac{\mathrm{}(4+D)\mathrm{}}{4D}$ and $\gamma \simeq \frac{8}{\mathrm{}(4+D)\mathrm{}}$ for dimension $4>~D>~\frac{4}{3}$. The equations agree with the $\epsilon$ expansion to first order, fit the (known) values for $D=3,2\mathrm{}$, and also those (suggested) for $D<\mathrm{}2\mathrm{}$. The probability of an exclusion due to a loop of length $j$ appears to be asymptotically equal to $(\gamma -1)j^{-2\mathrm{}}$, for $4>D>\mathrm{}\frac{4}{3}$ ("strong universality").

By rapid decompression of 55% polarized solid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$, we have measured a depression of the liquid-solid melting curve as large as 1 bar at 100 mK. It is found that the lowering $\Delta P$ depends on the global magnetization $m$. We explain this by a "dendritic melting" which ensures the homogeneity of the magnetization in each phase. $\Delta P$ has the expected $m^2$ dependence for small $m$. However, the slope $\frac{d\Delta P}{d{m}^2}$ is three times the expected value. A possible explanation is a rotation of the magnetization on melting.

It is proposed that the nucleation of the $B$ phase of liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ from the metastable $A$ phase is a consequence of the passage of a cosmic ray through the cell and the resultant anomaly in the effective temperature distribution in the liquid.

The proximity effect in weak localization offers new applications. As an example sandwiches of thin disordered films of a normal metal (Mg) and a strong-coupling superconductor such as amorphous Bi allow the determination of the inelastic lifetime and the pair-breaking parameter of the strong-coupling superconductor.

The spin dynamics of the classical Heisenberg model on the bcc lattice is computed with a Monte Carlo molecular-dynamics approach in the paramagnetic phase at $T=1.025\mathrm{}{T}_c$ and $1.275T_c$. The resulting scattering function $S(q,w)\mathrm{}$ and its integral over restricted energy windows are computed and compared with the recent neutron-scattering experiments on iron. Reasonable overall agreement with much of the experimental data is found.

We report on low-frequency ac susceptibility measurements on Pd doped with 2.2, 6.8, 11, and 100 at. ppm Fe at temperatures between 79 μK and 24 mK and in fields of less than 1 mG at 3.8 G. The samples show typical spin-glass behavior with a ratio of freezing temperature to Fe concentration $\frac{T_f}{x}\simeq 83$ μK/at. ppm Fe. The effective moment determined from the Curie constant at $T\gtrsim 2T_f$ is 10${\mathrm{\mu }}_{\mathrm{B}}$ per Fe atom.

We present a fully quantum-mechanical theory of the inelastic scattering of low-energy atoms from surfaces, based on the perturbation series and an expansion in numbers of phonons exchanged. Numerical calculations are carried out with a simple potential model and good agreement is obtained for the thermal attenuation of a helium beam by a close-packed surface of copper.

A solar neutrino experiment utilizing the interaction of ${}_{}{}^{81}{}_{}{}^{}\mathrm{Br}(\nu ,e^{-}){}_{}{}^{81}{}_{}{}^{}\mathrm{Kr}$ to study the ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$ neutrino source in the interior of the sun is shown to be feasible. Resonance ionization spectroscopy was used to count less than 1000 atoms of 2×${10}^5$-yr ${}_{}{}^{81}{}_{}{}^{}\mathrm{Kr}$, making the bromine experiment possible. Except for the method of counting product atoms, the bromine experiment would be very similar to the successful chlorine detector ${}_{}{}^{37}{}_{}{}^{}\mathrm{Cl}(\nu ,e^{-}){}_{}{}^{37}{}_{}{}^{}\mathrm{Ar}$, and thus it is a natural sequel to the only solar neutrino experiment to date.

Vibrational excitation of chemisorbed benzene on Pd(100) by low-energy electron impact exhibits strong energy-dependent structure and mode selectivity. These results can be consistently understood in terms of resonance electron scattering, analogous to low-energy shape resonances in the gas phase.

The kinetics of polaron recombination into bipolarons in polypyrrole has been studied by optical-absorption spectroscopy on films doped in situ in an electrochemical cell. ESR studies confirm that the metastable states possess spin, while the stable states do not. The data reveal a slow evolution, consistent with polaron-diffusion rates limited by the mobility of the accompanying counterion.

We report measurements of the ultrasonic absorption in UP${\mathrm{t}}_3$ through the superconducting transition. The attenuation varies as $T^2$ at low temperature and is inconsistent with the identification of UP${\mathrm{t}}_3$ as a singlet superconductor. Our results can be well explained by assuming that UP${\mathrm{t}}_3$ is an anisotropic (triplet) superconductor in a polarlike state, where the gap vanishes along a line on the Fermi surface.

A model for the transient behavior of photoconductivity and induced photoabsorption under bias illumination is derived for the saturated band-tail regime. For weak bias and strong pulse excitation, the usual dispersive transport decay is obtained, while at strong biases and weak excitation, the transport becomes nondispersive resulting in steep decay slopes. The model explains some puzzling experimental results on photoconductivity and photoabsorption in presence of bias illumination.

The evolution of a universe with $\Omega =1\mathrm{}$ which becomes dominated by relatively light, nonintercommuting strings at red shift $z_s$ is similar to that of a matter-dominated universe with $\Omega \sim {(2+z_s)}^{-1\mathrm{}}<1\mathrm{}$. The existence of such strings can resolve the conflict between the $\Omega =1\mathrm{}$ prediction of inflationary cosmology and observations.

An optical field produced by intracavity four-wave mixing is shown to exhibit the following nonclassical features: photon antibunching, squeezing, and violation of Cauchy-Schwarz and Bell's inequalities. These intrinsic quantum mechanical effects are shown to be associated with the nonexistence of a positive normalizable Glauber-Sudarshan $P$ function.

A class of models for relaxation in strongly interacting glassy materials is suggested. Degrees of freedom are divided into a sequence of levels such that those in level $n+1\mathrm{}$ are locked except when some of those in level $n$ find the right combination to release them, this representing the hierarchy of constraints in real systems. The Kohlrausch anomalous relaxation law, $\exp [-{\left(\frac{t}{\tau }\right)}^{\beta }]$, emerges naturally, and a maximum time scale is found which exhibits a Vogel-Fulcher-type temperature dependence.

Measurements of chaotic vibrations of a forced nonlinear oscillator with a two-well potential suggest that the frequency-amplitude boundary between periodic and chaotic motions may be fractal. The fractal dimension of this curve is 1.26. The experiment consisted of an elastic beam and magnets which were used to create two stable equilibrium positions. Analysis has shown that this system possesses strange-attractor solutions for a single-mode model. However, a fractal boundary suggests that the role of higher modes may be important.

For asymptotically free theories, ultraviolet divergences computed in the $\frac{1}{N}$ expansion with dimensional regularization reduce to simple poles plus powers of $\ln \epsilon$ or finite terms. The theories are effectively superrenormalizable since all divergences are determined by the one- and two-loop perturbative renormalization-group functions.

We present new measurements of parity conservation in the 293-nm transition in atomic ${}_{81}{}^{205}{}_{}{}^{}\mathrm{Tl}$. Linearly polarized 293-nm photons, polarization $\hat{\epsilon }$, are absorbed by $6{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ atoms in crossed electric and magnetic fields. The transition probability for each Zeeman component contains a term proportional to $\hat{\epsilon }·\overrightarrow{\mathrm{B}}\hat{\epsilon }·\overrightarrow{\mathrm{E}}\times \overrightarrow{\mathrm{B}}$ arising from interference between the Stark $E1$ amplitude $\beta E$ and the parity-nonconserving $E1$ amplitude ${\mathcal{E}}_p$. Our result, ${\left[\mathrm{Im}\frac{{\mathcal{E}}_p}{\beta }\right]}_{\mathrm{expt}}=-1.73\mathrm{}\pm 0.33$ mV/cm, is compared with estimates based on the standard electroweak model.