New experimental and theoretical results are presented which, in conjunction with previous experiments, allow us to determine cross sections for each of the ionization pathways leading to ${\mathrm{Ne}}^{+}$ and ${\mathrm{Ne}}^{+2\mathrm{}}$ formation in ${\mathrm{H}}^{+}$+ Ne collisions in the 0.5-4 MeV range. It is found that multiple outer-shell ionization is far more probable than inner-shell ionization.

The ionization of $6sns{}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ Rydberg states of ${}_{}{}^{138}{}_{}{}^{}\mathrm{Ba}$ has been investigated by high-resolution electron spectroscopy. The Rydberg states were excited by two cw dye lasers via the $6s6p{}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}$ level. The electron spectra show rich structure between 0.025 and 3 eV, largely attributable to collisional (Penning) ionization, photoionization, and autoionizing transitions. The first process might be interpreted as superelastic scattering of the Rydberg electron by optically pumped $\mathrm{Ba}\left(6s6p{}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}\right)$ or $\mathrm{Ba}\left(6s5d{}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}\right)$ atoms.

This paper reports the observation of optical bistability due to a radiation-pressure-induced change of the length of a Fabry-Perot resonator. In addition, for higher laser powers, a purely optical mechanism leading to the stabilization of the resonator has been observed.

Nonlinear equations are solved which describe the competition between two decay modes for laser light energy. When they are applied to the competition between Brillouin forward- and backward-scattered light, multivalued solutions occur for plasmas between two limiting sizes. Application to particular experiments may explain appearance of either red- or blue-shifted peaks or both in time-integrated spectra.

Spatially resolved measurements of the magnetic field of a spheromak have been analyzed and compared with expectations for the ratio of $\frac{j_{\parallel }}{B}$ from the pressure-gradient-free Taylor model and a model with pressure due to Morikawa. Better agreement is found with the model containing finite pressure.

Anode-plasma expansion in pinch-reflex diodes is investigated with use of a one-dimensional magnetohydrodynamic model. Early in time, the plasma undergoes thermal expansion and its front is slowed down as a result of $\overrightarrow{\mathrm{j}}\times \overrightarrow{\mathrm{B}}$.. After the current has reached its maximum and for small radius where $j$ and $B$ are larger, $\overrightarrow{\mathrm{j}}\times \overrightarrow{\mathrm{B}}$ may accelerate the bulk of the anode plasma to large velocities. Good qualitative agreement is obtained with observations of the time dependence of the plasma velocity as well as its radial profile. The maximum expansion velocities reach tens of centimeters per microsecond.

The thermal conductivity of freestanding films of $a$-Ge has been measured in the temperature range 0.03-5 K. The results indicate scattering of phonons from tunneling systems, cylindrical voids, and boundaries. The first two mechanisms are correlated with density, the strongest scattering occurring in the samples of lowest density.

The low-energy electron-diffraction patterns of the oxygen structures on the (001) pole of spherical Cu and Ni surfaces show characteristic differences: For Cu the (½ ½) and the (10) spots are elongated along $〈11〉$, while only the half-order spots are broadened for Ni. These unusual spot profiles are caused by antiphase scattering from neighboring domains, with the oxygen in the bridge position for Cu and in the fourfold hollow site for Ni.

Nuclear magnetic ordering in bcc ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ has been studied by a static magnetization measurement from 10 down to 0.3 mK for a molar volume region of $V=24.14\mathrm{}$ to $V=22.46\mathrm{}$ ${\mathrm{cm}}^3$/mole. The results show that the ordering temperature $T_{\mathrm{N}}$ varies in proportion to $V^{16.5\pm 1}$ and that the magnetization in the ordered state is constant. The magnetization reduced by its maximum value is found to be represented by a universal function of the reduced temperature $\frac{T}{T_{\mathrm{N}}}$.

The dynamics of ordering of $\mathrm{W}\mathrm{}\left(110\right)p(2\mathrm{}\times 1)-\mathrm{O}$ has been studied at two coverages with use of low-energy electron diffraction. Island coarsening and diffusion-limited island growth mechanisms are identified at the coverage corresponding to two-phase coexistence, while in the one-phase region, domain growth is observed. In all cases, the increase in the average size of ordered regions follows a $t^{\frac{1}{2}}$ dependence. Activation energies and frequency factors are extracted.

Volterra edge dislocations were introduced in an amorphous Lennard-Jones model. By application of suitable boundary conditions, equivalent to a shear stress, a recognizable step with a shape of a double-headed asymptote was formed on the other side of the amorphous solid. This suggests that atomic transport via dislocation motion can occur and could be the mechanism of shear-band formation in real amorphous materials.

By combining low-temperature ($T<\mathrm{}10\mathrm{}$ K) heavy-ion bombardment (275-keV ${\mathrm{Ar}}^{+}$, 250-keV ${\mathrm{Ne}}^{+}$) with an in situ low-temperature electron-diffraction technique, for the first time direct evidence could be provided that ion irradiation can result in a complete amorphization of gallium, i.e., of a pure metal without a second component stabilizing the amorphous phase. The results can be interpreted in terms of a spike model and are in close analogy to those found by vapor quenching onto a liquid-helium-cooled substrate.

Picosecond luminescence experiments on $\mathrm{GaAs}/{\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ quantum well structures reveal a significant influence of localization on the transition probabilities of photoexcited carriers. The spontaneous lifetime of electrons and holes within the quantum well decreases with well thickness $L_z$ from 1 ns for $L_z=14\mathrm{}$ nm to 350 ps for $L_z=5\mathrm{}$ nm because of the enhanced recombination due to localization of the carriers.

The charge-density-wave contribution to ac and dc conductivity, rectification, and harmonic mixing has been measured on a single crystal of orthorhombic Ta${\mathrm{S}}_3$. A modified tunneling theory based on the Zener model of charge-density-wave conduction provides a detailed and quantitative account of these experiments. This evidence strongly supports the hypothesis that macroscopic quantum effects are observed in the megahertz frequency region at temperatures as high as 200 K.

It is shown that if $n\left(r\right)\mathrm{}$ is the discrete density on a lattice (enclosed in a finite box) associated with a nondegenerate ground state in an external potential $v\left(r\right)\mathrm{}$ (i.e., is "$v$-representable"), then the density $n\left(r\right)+\mu m\left(r\right)\mathrm{}$, with $m\left(r\right)\mathrm{}$ arbitrary (apart from trivial constraints) and $\mu$ small enough, is also associated with a nondegenerate ground state in an external potential $v^{\prime }\mathrm{}\left(r\right)\mathrm{}$ near $v\left(r\right)\mathrm{}$; i.e., $n\left(r\right)+\mu m\left(r\right)\mathrm{}$ is also $v$-representable. Implications for the Hohenberg-Kohn variational principle and the Kohn-Sham equations are discussed.

Upper and lower bounds are obtained for the potential energy of two-dimensional classical systems consisting of particles interacting via a short-range potential that has a hard-disk core. The bounds coincide in the close-packing limit, implying that first-order thermodynamic perturbation theory becomes exact in this limit.

Neutron interferometry has been performed on an accelerated interferometer under conditions where gravitational effects on the interfering beams very nearly compensate each other. The observed neutron phase shift is found to be in excellent agreement with that calculated from Schrödinger's equation transformed to the accelerated frame where it is found essential to include the spherical wave aspect. The present experiment thus verifies the validity of the classical transformation laws for noninertial frames also in the quantum limit.

A solution is given to the problem of finding the continuous quantum nondemolition observables of a given system which has a classical analog. It is found that there are a nondenumerably infinite number of such observables which are generated by an arbitrary function. As an example the "mass on a negative spring" case is solved for a particular choice of the function.

The authors show how to construct a normalizable resonance wave function produced by a sharp-cutoff two-body potential using analyticity and basic quantum mechanical requirements. To this end they propose a saturation scheme, and estimate the duration of validity of the exponential decay law. The viability of the model is tested in a deuteron stripping to unbound-state calculation.

Recent data are presented on spin-spin correlation parameters $C_{\mathrm{LL}}=(L,L;0,0)$ and $C_{\mathrm{SL}}=(S,L;0,0)$ at forward angles from 1.18 to 2.47 GeV/c incident momenta in proton-proton elastic scattering. Values for $\Delta {\sigma }_L$ (inelastic) are derived and are shown to disagree with predictions of theoretical models attempting to describe $p-p$ scattering without dibaryon resonances. Finally, the $C_{\mathrm{LL}}$ and $C_{\mathrm{SL}}$ data discriminate among various phase-shift solutions, and will lead to a clarification of the $p-p$ phase shifts.