In random solid solutions of ${\mathrm{Ga}}_{1-x}{\mathrm{In}}_x\mathrm{As}$, the Ga-As and In-As near-neighbor distances change by only 0.04 Å as $x$ varies from 0.01 to 0.99, despite the fact that this alloy accurately follows Vegard's law, with a change in average near-neighbor spacing of 0.17 Å. This result contradicts the underlying assumption of the virtual-crystal approximation. Nonetheless, the cation sublattice approaches a virtual crystal with a broadened single distribution of second-neighbor distances, whereas the anion sublattice exhibits a bimodal anion-anion second-neighbor distribution.

It has been determined that the nearest-neighbor distance around tin atoms dissolved in a Cu lattice is 2.63 Å, ∼0.07 Å larger than given by the average lattice constant. The determination was made by the extended x-ray-absorption fine-structure technique. The observed distortion agrees with that calculated from an anisotropic lattice model.

It is illustrated how an interplay between theoretical predictions and experimental measurements of binding energies or enthalpies and the corresponding equilibrium positions of hydrogen isotopes at defects in metals can lead to a new understanding of the microscopic structure of the observed hydrogen traps. Binding to vacancies and bubbles or voids is found to be strong, and a weaker trap is tentatively associated with self-interstitials. An extremely simple picture of the trapping process has evolved.

Low-temperature specific-heat measurements (0.06-2 K) on a superconducting polycrystalline Nb${\mathrm{Ti}}_{0.05}$ alloy show an anomaly in the presence of interstitial H and D (up to 3 at.%). The excess specific heat is roughly linear in temperature, indicating the existence of a glasslike low-energy excitation spectrum. The results raise the question as to what extent previously observed low-temperature anomalies in metallic glasses may be due to H contamination.

An x-ray scattering study is reported of the commensurate-incommensurate transition (CIT) in single-crystal ${\mathrm{C}}_{28}$${\mathrm{Br}}_2$ in which the ${\mathrm{Br}}_2$ stage-4 intercalant has an in-plane $\sqrt{3}\times 7$ superlattice structure. The CIT, which occurs only in the sevenfold direction, is a solid-to-solid transition with incommensurability $\epsilon \sim {\mathrm{}(T-342.20\mathrm{})\mathrm{}}^{0.50\pm 0.02}$. The relative displacements of successive harmonics are accurately predicted by a sharp domain-wall model with $\frac{4\pi }{7}$ phase shifts. The in-plane coherent ${\mathrm{Br}}_2$ regions exceed 10 000 Å in both commensurate and incommensurate phases.

Experimentally it is found that the energy loss of 620- and 942-keV electrons in barium titanate, as well as that of 942-keV electrons in triglycine sulphate, is anomalously high at the Curie temperature. The energy loss is also noticeably smaller in the ferroelectric state than in the paraelectric state.

A new theory is presented to determine the structure of the intrinsic density profile of the liquid-gas interface near the critical point. A nonlinear integral equation for this profile is derived and it is shown that a nontrivial solution branches off at the critical temperature. The scaling form and the asymptotic behavior of this solution are derived exactly: The wings of the intrinsic density profile decay exponentially with an exponent proportional to the inverse correlation length, confirming the conjectures of Widom.

The effects of high pressure on the valence-electron density in silicon and indium antimonide are investigated by x-ray diffraction. It is found that near the transition to the metallic $\beta$-tin structure the scattering from the valence electrons sharply decreases, indicating either smearing of the bonding charges or increased anharmonicity in the thermal vibrations.

Transmission electron micrographs of thin evaporated gold films were analyzed by computer. For length scales above 10 nm, the irregular connected clusters show a perimeter linearly proportional to area. Near the percolation threshold the large-scale power-law correlations and area distributions are consistent with the scaling theory of second-order phase transitions. Geometrically, the boundary of all clusters is a fractal of dimension $D=2\mathrm{}$ while individual boundaries are of fractal dimension $D_C\approx 1.9$.

The geometrical features of discontinuous Pb films are analyzed in terms of the scaling theory of percolation. Above the percolation threshold it is shown that the infinite cluster as well as the backbone has an anomalous mass distribution up to a length of the order of the percolation correlation length (${\xi }_p$), corresponding to that of self-similar objects. Above ${\xi }_p$, the mass distribution is homogeneous. Below the percolation threshold, the cluster statistics agrees with scaling theory.

Measurements are reported of the lower and upper critical fields, $B_{c1\mathrm{}}\mathrm{}\left(T\right)\mathrm{}$ and $B_{c2\mathrm{}}\mathrm{}\left(T\right)\mathrm{}$, of Ce${\mathrm{Cu}}_2$${\mathrm{Si}}_2$. The observed, extremely high values of the slope ${(-\frac{d{B}_{c2\mathrm{}}}{\mathrm{dT}})}_{T_{c0\mathrm{}}}$ lend strong support to the formation of Cooper pairs by the heavy fermions which exist in the normal state of Ce${\mathrm{Cu}}_2$${\mathrm{Si}}_2$. Characteristic parameters of the system of heavy fermions are derived.

An experimental and theoretical analysis of the Compton profile of beryllium is presented. The measurements on single-crystal beryllium are performed with use of synchrotron radiation (10-keV x rays). The theoretical calculation employs local density-functional pseudopotentials. The agreement between the one-electron calculation and the measured spectra is distinctly superior to previous attempts. A small directionally independent difference remains. This difference is substantially reduced by incorporating correlation effects within the homogeneous approximation.

The low-lying particlelike excitations of a model linearly conjugated diatomic polymer, ${(A=B)}_x$, are found to be pairs of either spin-0 or spin-½ solitons with irrational charge values. The charge values and excitation energies are calculated as functions of the difference of the energy levels of the atomic $p$ orbitals of the two atomic constitutents of the unit cell. The phonon spectrum of the uniform polymer is also calculated.

Introduced here is a model of the early universe based on the possibility of a first-order phase transition involving gravity, and arrived at by a consideration of instabilities in the semiclassical theory. The evolution of the system is very different from the standard Friedmann-Robertson-Walker big-bang scenario, indicating the potential importance of semiclassical finite-temperature gravitational effects. Baryosynthesis and monopole production in this scenario are also outlined.

A search for small-scale anisotropy in the cosmic microwave background has been conducted with the 140-ft telescope at Green Bank, West Virginia, operating at a frequency of 19.5 GHz. The half-power beamwidth was 1.5 arc minutes. A 95%-confidence upper limit of $\frac{\Delta T}{T}<1.1\mathrm{}\times {10}^{-4\mathrm{}}$ was set on fluctuations on this scale.

A model of a simple nonlinear physical system, the driven diode resonator comprised of an oscillator, resistor, inductor, and diode in series, is shown to reduce exactly to a one-dimensional, noninvertible map. With use of a model of the diode which includes the forward bias voltage, reverse recovery time, and junction capacitance, the response of the system is calculated exactly. The solution exhibits the period-doubling route to chaos with universal scaling.

The nucleation rate in a supersaturated Glauber-kinetic lattice gas of size ${168}^3$ is measured as a function of supersaturation (magnetic field). Results at $\frac{T}{T_c}=0.59\mathrm{}$ are roughly compatible with classical nucleation theory. The droplet surface tension for the critical nuclei, determined from the observed cluster numbers, shows no sharp spinodal point and is nearly independent of the field.

The $d=2\mathrm{}$ $\mathrm{XY}$ model is generalized to include an operator that couples directly to the vortex core energy, while maintaining the full symmetry of the original model. In addition to the usual Kosterlitz-Thouless transition, the model exhibits a true first-order transition and a pseudo first-order transition. The excitations of the model include fractionally charged vortices. Implications for the $d=2\mathrm{}$ melting problem are discussed.

The muon momentum spectrum in $K_{\mu 2}$ decay has been measured by using a high-resolution magnetic spectrograph to look for a discrete muon peak associated with heavy-neutrino emission. The spectrum revealed no distinct peak, and the upper bound of the mixing ratio between the muon neutrino and a massive neutrino has been determined to be ${10}^{-4\mathrm{}}$-${10}^{-6\mathrm{}}$ in the mass range of 70-300 MeV/${\mathit{c}}^2$.

Supersymmetric grand unified models with fractionally charged color singlets ("fractons") are considered. It is shown that the minimal supersymmetrized fracton model, which occurs in SU(7), gives a value of ${sin}^2\theta \left(m_W\right)$ that is naturally lower than the minimal SU(5) supersymmetric grand unified theory prediction, and can be in agreement with experiment for fracton charge $q=\frac{e}{3}$.