A chain of aerosol-initiated, C${\mathrm{O}}_2$-laser-produced, air-breakdown plasmas has been used to guide electrical discharges over distances ≲ 2 m in laboratory air in a direction almost perpendicular to the strongest electric field. The guiding effect existed at average electric fields ≳ 1 kV/cm and the discharge propagation velocity (${10}^9$ cm/sec at 360 kV) depended on the applied potential. Such laser-initiated current-carrying channels appear to be capable of efficiently transporting relativistic electron beams in pellet-fusion reactors.

High-precision measurements of the constant-volume specific heat of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ solutions with up to 1% ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ are presented for the temperature range $70 \mathrm{mK}<T<\mathrm{}1\mathrm{} \mathrm{K}$. The data are inconsistent with three previously proposed ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-quasiparticle excitation spectra: (1) a spectrum which is purely quadratic in wave number $\mathcal{k}$, (2) a spectrum which is quadratic for small $\mathcal{k}$ and possesses a "roton" minimum at larger $\mathcal{k}$, and (3) a spectrum which as a ${\mathcal{k}}^4$ term in addition to the ${\mathcal{k}}^2$ term at all values of $\mathcal{k}$.

The electronic band structure of ${\mathrm{Nb}}_3$Sn has been calculated by means of the augmented—plane-wave method. Comparison with a variety of experimental data suggest that the band model is highly accurate.

Classical diffusion of localized excitations is investigated on a one-dimensional chain with (energy-independent) nearest-neighbor transfer rates $W_{n,n+1\mathrm{}}=W_{n+1,n}$ that are independently distributed according to a probability density $\rho \mathrm{}\left(W\right)\mathrm{}$. An exact formal solution is derived for $〈P_0\mathrm{}\left(t\right)\mathrm{}〉$, the time development of the initial excitation. The long-time decay of $〈P_0\mathrm{}\left(t\right)\mathrm{}〉$, determined by the behavior of $\rho \mathrm{}\left(W\right)\mathrm{}$ near $W=0\mathrm{}$, is analyzed in detail for arbitrary probability densities $\rho \mathrm{}\left(W\right)\mathrm{}$.

Ultraviolet photoemission spectra of nickel atoms vapor deposited on an amorphous carbon substrate show a characteristic energy-loss peak 6 eV below $E_{\mathrm{f}}$ for the full range of coverages from adsorbed nickel adatoms to bulk nickel. The quasiatomic excitation responsible for this energy-loss peak is the promotion of a nickel valence-shell electron to a $4p$ level in the ionic final state.

The ability of a local pseudopotential to describe accurately core effects in energy calculations is demonstrated. If the pseudopotential is properly chosen, excitation energies of the silicon atom and binding-energy curves of the ${\mathrm{Si}}_2$ dimer agree well with calculations using the full density functional and the pseudo charge density is virtually identical to the real charge density outside the core region.

Reduction of the photothreshold in degenerately doped EuO below the Curie temperature is shown to arise from a magnetically induced space charge layer at the surface. A good fit to the measured shift versus temperature for EuO-2% La is obtained within a simple model, yielding new information about the magnetic nature of the semiconductor surface.

We compare the charge densities of the orbitals of ${\mathrm{Si}}_2$ calculated from Hartree-Fock-Slater self-consistent-field wave functions and pseudo charge densities from a local pseudopotential and found considerable differences. Given that the former are correct, this means that physically misleading conclusions could be drawn from the pseudo charge density. While pseudopotential methods have added much insight, current pseudocharge calculations for molecules and surfaces could be unreliable indicators of the true charge density.

We identify two different processes by which free atoms are ionized in a static electric field. The first process is by tunneling and is described accurately by theory developed for hydrogen. The second process, important for all atoms except hydrogen, is similar to autoionization and arises from the effect of level mixing. Data are presented on field ionization in lithium which display behavior due to each of these ionization mechanisms.

Iron is injected into a well-diagnosed $\theta$-pinch plasma. The intensities of lines from various ionization stages are measured as functions of time and interpreted by means of a time-dependent corona ionization-recombination model. Effective coefficients for dielectronic recombination at electron densities $N_e\approx 3\times {10}^{16}$ ${\mathrm{cm}}^{-3\mathrm{}}$ are equal to or smaller than presently accepted theoretical values for low-density plasmas. Rate coefficients for ionization tend to be smaller than theoretical values.

Ionization and recombination rate coefficients have been estimated using the effect of saw-tooth electron-temperature relaxations in a tokamak plasma on the emission of impurity ions. The ionization rate coefficient of highly ionized (of the order of 30) molybdenum has been found to be between 1 and 1.5 times Lotz's semiempirical coefficient. For the first time, we have also estimated the recombination (mainly dielectronic) rate coefficient for the same ions, and have found it to be between 0.5 and 1 times the value given by Burgess's formula.

Density fluctuations in the ion-cyclotron frequency range have been observed in the TFR tokamak by microwave scattering. The geometry was such that the selected fluctuation wave vector was aligned across the confining magnetic field in the outside region of the torus. A threshold for the onset of the instability as a function of the discharge current has been observed. A plausible explanation of this instability in terms of current-driven ion-cyclotron electrostatic wave is discussed.

For oxygen adsorbed on a Cu(001) surface, the O $1s$ x-ray photoelectron intensity is found to exhibit a complex azimuthal anisotropy with an overall amplitude of ∼ 26% for a grazing 10° angle of emission. No significant anisotropy is observed at 45°. Several reasons for expecting a direct relationship between such final-state scattering effects and atomic geometry are discussed, and the data are found to be suggestive of a surface-chemisorbed $c(2\mathrm{}\times 2)$ oxygen overlayer in fourfold coordination.

The consequences of a theory of dislocation-mediated two-dimensional melting are worked out for triangular lattices. Dissociation of dislocation pairs first drives a transition into a "liquid crystal" phase with exponential decay of translational order, but power-law decay of sixfold orientational order. A subsequent dissociation of disclination pairs at a higher temperature then produces an isotropic fluid. The critical behavior, as well as the effect of a periodic substrate, is discussed.

The dominant mechanism of methyl-group rotation in MDBP (4-methyl-2, 6-ditertiary-butylphenol) between 4 and 15 K is a Raman process involving the scattering of optical phonons, rather than the usually assumed two-step process of methyl torsional excitation with phonon absorption and subsequent emission. The Raman process is positively identified for the first time by combining magnetic resonance measurements of tunnel splittings with inelastic neutron scattering spectra for both normal and partially deuterated MDBP.

We propose a real-space renormalization-group technique to treat dynamic critical phenomena in two-dimensional Glauber-Ising models. The invariant form of the time-dependent probability distribution is found within linear response theory and an estimate of the dynamic exponent $z$ is given.

Energy transport in molecular solids is investigated using a picosecond transient-grating technique. A model is presented which directly relates the rate of energy transport to the experimental observable. The diffusion coefficient for singlet electronic excitation transport is reported for pentacene in $p$-terphenyl. Acoustically induced optical absorption effects are also observed.

Faraday rotation is very small (<0.5 rad) in most compact, extragalactic radio sources. The usual explanation has been a severe depletion of low-energy particles and absence of cold plasma. I propose instead that the radiating particles are an equal mixture of electrons and positrons. Such a plasma can still produce, by propagation effects, circular polarization that varies rapidly, and with a non-${\nu }^{-\frac{1}{2}}$ dependence, but it produces no Faraday rotation. I discuss production and show that the pairs, once produced, will survive quite well in an expanding source.

We extend the rigorous theory of complex scaling to atoms in constant electric field. This allows one to give a precise mathematical definition of resonance and leads to several results about the perturbation series: Borel summability at nonreal field and a relation between the asymptotics of the perturbation coefficients for large $n$ and the width of the resonance for small field.

We report new measurements of the asymmetry in the deep-inelastic scattering of longitudinally polarized electrons by longitudinally polarized protons in the kinematic range $2<~\omega <~10$, $1<~Q^2<~4$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$, and $2<~W<~4$ GeV. We compare our results with the Bjorken sum rule and with several theoretical models of the internal spin structure of the proton.