The accuracy of the distorted-wave approximation for inelastic scattering is studied in a solvable model. By formulating the scattering problem as an integral equation, the inhomogeneity can be identified as the distorted-wave approximation, and the norm of the kernel as the convergence parameter of the multistep series. The convergence parameter is studied as a function of dimensionless control parameters in order to extract what governs the convergence of the series.

The first observation of optical Stark splitting of a molecular Raman transition is reported. The splitting is observed in inverse Raman rotational spectra of diatomic nitrogen, measured in the presence of a pulsed 1.06-μm laser field. The line positions and intensities of the Stark-split multiplets are in good agreement with calculations of the quadratic Stark effect associated with the optical polarizability anisotropy.

The Lamb-shift splitting in hydrogenic chlorine is measured to be 31.19(22) THz. The experiment was performed on a relativistic beam of chlorine ions using a C${\mathrm{O}}_2$ laser resonance method. The result agrees with one of the two existing calculations and is the most sensitive test to date of QED in high-$Z$ systems.

Discovery of a new phenomenon is reported for submicron spheres undergoing a fall in nitrogen in the density range of 1 to 22 atm at 293 K. The measured fall rate of a single test particle increases with density if the particle is sufficiently small that its Brownian diffusion velocity becomes comparable to its velocity of fall, in contradiction to the Millikan law of fall embodying the concept of slip. The trend appears to reverse smoothly to that of Millikan's in the limit of large particle radius.

It is shown that self-consistent calculations of the electronic charge density in large periodic cells containing a single displaced atom provide all the information needed for ab initio determination of force constants, phonon dispersion curves, effective charges, and the static dielectric constant. Results are presented for GaAs.

A simple but realistic model for the condensed phases of S${\mathrm{F}}_6$ gives a plastic phase at 80 K in a molecular-dynamics simulation. Equilibration of a sample of 4096 molecules at 25 K and at zero pressure results in a transition to a polycrystal. The crystal structure found is triclinic $P\overline{1}$, $Z=3\mathrm{}$, but is pseudo-orthorhombic, a result not inconsistent with recent spectroscopic measurements. It is suggested that, to avoid bias, a large size is necessary for modeling the plastic-to-crystalline phase transition.

With use of the "rigid-pseudoion" model, the first calculation of the electron-phonon and hole-phonon scattering matrix elements for the TO, LO, TA, and LA phonon-assisted indirect transitions ($\Gamma -\Delta$) in Si has been performed. Excellent agreement with experimental values for the TO phonon is found. Based on the present results, the intensities of the entire $\Gamma -\Delta$ indirect spectrum of this material can be accurately described, thereby rigorously testing the model.

The effects of momentum and energy transport across the fluid-solid interfaces on the dynamic structure factor of a fluid layer have been studied. New spectral features have been found; their positions and line shapes are sensitive to the boundary conditions. This theory suggests that experiments that probe the dynamic structure factor (such as light scattering) may be important for studying the nature of interfacial transport.

The observation of a metastable field-induced doping effect which occurs in the bulk of $n$-type hydrogenated amorphous silicon films at temperatures above 150°C is reported. This effect produces a reversible tenfold change in the net shallow donor concentration and thus is intimately related to the overall doping mechanism of these films.

The transient response of a grain boundary to a voltage pulse is discussed in terms of the basic capture and emission processes at the boundary states. This model is used to interpret the deep-level transient spectroscopy spectrum of a low-angle tilt boundary with a known dislocation structure in a germanium bicrystal. A characteristic level is found at 0.42 eV below the bottom of the conduction band; the number of states at this level is about ${10}^9$ ${\mathrm{cm}}^{-2\mathrm{}}$ and their capture cross section for electrons is 5×${10}^{-12\mathrm{}}$ ${\mathrm{cm}}^2$.

The first direct measurements are reported of the velocity distributions of sputtered atoms in excited states with electronic configurations completely different from the ground state. In contrast to previous work, the measured distributions for both the singlet and triplet metastable $D$ states of Ba atoms showed no energy thresholds and had most probable energies similar to those of sputtered ground-state atoms.

From nuclear relaxation-time measurements, experimental evidence is given that the magnetic solitons behave diffusively in the chains of ${\left(\mathrm{C}{\mathrm{D}}_3\right)}_4$NMn${\mathrm{Cl}}_3$ doped with copper. Some neutron inelastic-scattering results are also presented, which support this analysis.

Inhomogeneous dissipative states found in a current-driven superconducting filament have been investigated with explicit allowance for depairing and coupling between pairs and quasiparticles off equilibrium. The resulting charge imbalance is insensitive to the gapless approximation used over a wide range of parameters; it can induce additional synchronized phase-slip centers, and leads to novel effects related to a mismatch between the core and the wings of each phase-slip center if local equilibrium cannot be maintained.

Neutron scattering experiments have been performed in the diluted antiferromagnets ${\mathrm{Rb}}_2$${\mathrm{Co}}_{0.7}$${\mathrm{Mg}}_{0.3}$${\mathrm{F}}_4$ and ${\mathrm{Co}}_{0.3}$${\mathrm{Zn}}_{0.7}$${\mathrm{F}}_2$ in a uniform magnetic field. These systems are isomorphous to, respectively, two- and three-dimensional Ising ferromagnets in a site-random magnetic field. It is shown that small random magnetic fields destroy the long-range order at all temperatures, consistent with three as the lower marginal dimensionality; the structure factor in the disordered state is predominantly a squared Lorentzian.

An experimental observation of anomalies in the dielectric susceptibility of thiourea under field is reported. Four anomaly lines $T_{\pm }$ are determined; they follow the laws ${(T_{\pm }-198.1)}^2=\alpha E$ and ${(T_{\pm }-198.8)}^2=\alpha E$, with $\alpha =0.11\mathrm{}\pm 0.01$ ${\mathrm{K}}^2$ ${\mathrm{V}}^{-1\mathrm{}}$ mm (for $E<\mathrm{}100\mathrm{}$ V/mm). A theoretical discussion, based on a Landau-Ginzburg formulation of the free energy, suggests that a pinned commensurate phase, of commensurability order $p=8\mathrm{}$, exists under field at temperatures $T_{-}<T<\mathrm{}{T}_{+}$. This clarifies the nature of the phase diagram of SC${\left(\mathrm{N}{\mathrm{D}}_2\right)}_2$.

It is shown that the following statements about a quantum correlation experiment are mutually equivalent. (1) There is a deterministic hidden-variables model for the experiment. (2) There is a factorizable, stochastic model. (3) There is one joint distribution for all observables of the experiment, returning the experimental probabilities. (4) There are well-defined, compatible joint distributions for all pairs and triples of commuting and noncommuting observables. (5) The Bell inequalities hold.

Newton's gravitational constant $G$ is calculated in a class of scale-invariant gauge theories with an infrared fixed point. The sign of $G$ depends on the coefficients in the renormalization-group $\beta$ function.

In a sample of approximately 17500 charged-current neutrino-deuterium interactions from an exposure of the Fermilab 15-ft bubble chamber to a high-energy wide-band neutrino beam, the charmed baryon ${{\Lambda }_c}^{+}$ is observed in a new decay mode, ${{\Lambda }_c}^{+}\to {\Sigma }^0{\pi }^{+}$. The product of branching ratio and production rate is estimated to be (3.2±2.1)×${10}^{-3\mathrm{}}$ for this ${\Sigma }^0{\pi }^{+}$ channel.

Measurements of $\mathrm{pp}\to {\mu }^{+}{\mu }^{-}+X$ at $\sqrt{s}=44\mathrm{} \mathrm{and} 62$ GeV are compared. The data are taken under identical conditions utilizing clean proton-proton collisions from the CERN intersecting storage rings and confirm scaling to 5%. The observed ${\mu }^{+}{\mu }^{-}$ yield is a factor of 1.6±0.2 larger than estimated from a simple parton model but is consistent with QCD. The $p_T$ dependence of the muon pairs agrees well with expectations from QCD.

The interaction mean free paths in nuclear emulsion of relativistic projectile fragments, $3<~Z<~26$, emitted from heavy-ion beams of ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ and ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$ at an energy of ∼2 GeV/nucleon have been measured, and they gave evidence for anomalously shorter mean free paths in the first 2-3 cm after their production than at larger distances. Some characteristics of the primary and the secondary interactions connected with the anomaly are presented.