Two new trends associated with spin-orbit effects in a non-central-force field are evident in recent data for $F$ centers: (1) an inverse power-law dependence of spin-orbit splitting on the lattice parameter of the host crystal and (2) a direct dependence of the splitting on the size of the host-lattice ions. These features may be summarized by a simple semiempirical formula closely related to the Mollwo-Ivey relation for the absorption energy.

The effects of both random chemical and bond-length variations on the electronic structure of zinc-blende pseudobinary alloys are treated within a realistic self-consistent effective-medium theory. Calculations for ${\mathrm{In}}_{1-x}{\mathrm{Ga}}_x\mathrm{As}$ indicate that the effects of structural disorder are comparable in magnitude to those of chemical disorder and together they can either enhance or diminish the total scattering in a particular energy region.

The first measurement of the far-infrared absorption spectrum of a bound exciton is reported. This spectrum reveals the odd-parity excited states of the exciton, which cannot be observed by other means. The excited-state spectrum is found to be in excellent agreement with those of acceptors in Si, verifying earlier predictions of the level structure for isoelectronic bound excitons.

It is shown that the existence of a potential is not a generic property of a continuous nonlinear dissipative system but requires the complete integrability of an associated Hamiltonian system.

Numerical evidence of a percolation phase transition on infinitely ramified exact fractals is presented. The percolation transition is studied by a real-space renormalization-group technique on a family of exact fractal lattices with fractal dimensionality $\overline{d}$ between 1 and 2. The critical exponents for percolation depend strongly on the geometry of the fractals.

Some rigorous inequalities governing hadron masses in QCD are proved. One states that the electromagnetic mass shift of the pion is positive. The other states that if $m_{A\overline{B}}$ is the mass of the lightest meson made from a quark of type $A$ and an antiquark of type $B$, then—under conditions such that annihilation into gluons can be ignored—$2m_{A\overline{B}}>~m_{A\overline{A}}+m_{B\overline{B}}$. These inequalities agree with experimental data and have analogs for arbitrary vectorlike gauge theories. The first inequality has applications to the vacuum alignment problem in vectorlike technicolor theories.

A solution is found for the vector-particle equation with Yang-Mills coupling to an electromagnetic plane-wave potential. The local gauge and Poincaré transformation structure of such generalized Volkov solutions of single-particle equations (spin ≤1) leads to a decoupling theorem for the scattering of a system of particles immersed in an external plane wave.

The analyzing power $A$ in 28-GeV/c proton-proton elastic scattering was measured with a polarized proton target and a high-intensity unpolarized proton beam at the Brook-haven National Laboratory alternating-gradient synchrotron. The ${P_{\perp }}^2$ range of 2.85 to 5.95 ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ was covered with good precision. A small dip of about -3.5% was found near ${P_{\perp }}^2=3.5\mathrm{}$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ where a 24-GeV/c CERN experiment had reported a deep dip of about -16% with large errors. In the previously unexplored large-${P_{\perp }}^2$ region near 6 ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ these new large-error points suggest that $A$ may be rising.

In an experiment measuring charmed-particle lifetimes with use of a hybrid-emulsion spectrometer in the wide-band neutrino beam at the Fermi National Accelerator Laboratory, 1248 neutrino and antineutrino interactions have been located. Twenty-three charged charm decay candidates have been reconstructed, from which we determine the lifetime of the $D^{\pm }$ to be ${11.5}_{-3.5\mathrm{}}^{+7.5}$ × ${10}^{-3\mathrm{}}$ s, that of the $F^{\pm }$ to be ${1.9}_{-0.7}^{+1.3}$ × ${10}^{-13\mathrm{}}$ s, and that of the ${{\Lambda }_c}^{+}$ to be ${2.3}_{-0.6}^{+1.0}$ × ${10}^{-13\mathrm{}}$ s.

Simple total-energy considerations allow an explanation for the nuclear surface transparency in heavy-ion elastic scattering and hence a prediction of the reactions that present a strong backward rise in the angular distributions.

The authors present the first simultaneous studies of fragment ion production and electron emission of a molecule following deep core-level excitation. Using synchrotron radiation they tune in to various absorption resonances and correlate certain electron-hole states in the decay of the x-ray excitation with the appearance of specific ionic fragments. For ${\mathrm{N}}_2$ specifically they observe a 1:1 correspondence between single valence hole states and undissociated ${\mathrm{N}}_2^{+}$ after N $1s\to {\pi }^{*}$ excitation and relate the production of ${\mathrm{N}}^{++}$ ions to the generation of holes in the $2{\sigma }_{\mathrm{u}}$ orbital.

Positive and negative ground-state spin densities are obtained exactly for regular Pariser-Parr-Pople radicals up to eleven carbons and Heisenberg antiferromagnetic chains up to fifteen spins. Molecular Pariser-Parr-Pople parameters for the ratio $\left|\frac{{\rho }_{-}}{{\rho }_{+}}\right|$ of total negative and positive spin densities extrapolate to ∼ 0.43 for fifty sites, slightly above the ENDOR value for polyacetylene. Correlations in interacting Heisenberg systems lead to long-range interactions between spin solitons and a shifted midgap state.

Experimental vibration spectra for ordered overlayers of O and S on Ni(100) are analyzed in terms of surface-lattice dynamics in relation to rigid-lattice calculations. It is shown how spectral differences for the consecutive $p(2\mathrm{}\times 2)$ and $c(2\mathrm{}\times 2)$ structures are primarily due to differences in the coupling to the substrate phonon modes.

Diffusion-controlled deposition in dimension $d=2\mathrm{}$ is studied by Monte Carlo simulation, and the number of clusters of size $s$ is found to scale as $n_s\sim s^{-\tau }$ with $\tau \approx 1.35$. The inequality $\tau <2\mathrm{}$ is shown to imply for a deposit of $N$ particles per nucleation site that the exponents in the scaling Ansatz $n_s\mathrm{}\left(N\right)\mathrm{}\sim s^{-\tau }f\left(\frac{s^{\sigma }}{N}\right)$ satisfy the scaling law $\sigma =2-\tau$. If the scaling properties of deposits on a surface are related to those of an aggregate grown on a seed particle, $\tau =1+\frac{\mathrm{}(d-1\mathrm{})\mathrm{}}{D}$ is obtained, where $D$ is the fractal dimension of the aggregate.

The results of a dislocation-loop theory of the nematic-smectic $A$-smectic $C$ multicritical point are presented. A new, biaxial nematic phase is found to intervene between the nematic and smectic-$C$ phases. These four phases meet at a decoupled tetracritical point.

The existence of several new field-induced regions of stability is shown for the wave number $q$ corresponding to the high commensurability orders $\frac{2}{15}$, $\frac{4}{29}$, and $\frac{6}{43}$. It is suggested that this result can be accounted for intrinsically by sequences of antiphase domains of the type ${〈7〉}^n〈8〉(n=1,3, \mathrm{and} 5)$ where $〈m〉$ represents a domain of $m$ consecutive ferroelectrically aligned layers. A high-field hysteresis effect is also observed.

The authors analyze the wetting behavior at interfaces of three-phase equilibria exhibited by a fluid with two independent densities when described in mean field. The calculation treats nonuniformities exactly and regions are identified in interaction space where first- or second-order transitions or no transitions occur. Sullivan's model of the fluid-solid interface is obtained as a limiting case, but the global phase diagram is qualitatively different from that pertaining to a system described by one bulk order parameter plus two surface fields.

Raman-scattering measurements are reported for liquid Te near the melting point. The spectra, which indicate three distinct bands, one of which is strongly polarized, exhibit a number of qualitative similarities to those of amorphous As and P. The results thus indicate similar pyramidal short-range order in liquid Te and confirm the Cabane-Friedel bonding model of the liquid. A comparison with theoretical calculations for amorphous As implies a continuous random-network model with backbonding interactions for liquid Te. No direct evidence for twofold-coordinated chainlike structures is observed.

Based on the direct structure determination of the silicide formed at room temperature from <1 monolayer of Ni deposited on Si(111) and from Ni coverages up to 5 monolayers, a model for silicide growth and interface formation is presented. The model forms a basis for understanding many of the photoemission, ion scattering, and microscopy results from this system.

A new high-frequency cutoff for phonon propagation which lies beyond the well-known low-frequency cutoff due to anomalous dispersion is observed in phonon propagation experiments in liquid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ using superconducting Sn and A1 tunnel-junction generators and detectors. The cutoff depends strongly on pressure and is interpreted as arising from a strong increase in phase space for phonon-roton scattering as normal dispersion in the phonon branch sets in.