Angular differential cross sections for the process ${\mathrm{H}}^{+}+\mathrm{H}\mathrm{}\left(1s\right)\mathrm{}\to {\mathrm{H}}^{+}\left(\theta \right)+\mathrm{H}\mathrm{}(n=2\mathrm{})\mathrm{}$ are presented for 25-, 50-, and 100-keV protons incident on atomic hydrogen. The experimental results are in fair agreement with Glauber-approximation calculations.

A new approach to prevent the influx of high-$Z$ impurities into the core of a tokamak discharge by using rf power to modify the edge plasma temperature profile is discussed. This concept is based on spectroscopic measurements on PLT (Princeton Large Torus) during ohmic heating and ATC (Adiabatic Toroidal Compressor) during rf heating.

Comparisons of observed ion velocity maxima with predictions of theoretical models suggest that departures from ideal isothermal expansion behavior are caused by nonequilibrium critical-surface electron distributions.

The stability of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$A$ with uniform superflow is examined in the hydrodynamic limit. Below the threshold found by Bhattacharyya, Ho, and Mermin, any reasonable choice of hydrodynamic parameters renders the uniform texture stable with respect to general three-dimensional perturbations. Beyond threshold, the texture undergoes a transition to a static helix, whose broken translational symmetry complicates the general stability analysis. In a truncated variational approximation, this structure is stable near threshold with respect to perturbations proportional to $\exp \left(i\overrightarrow{\mathrm{k}}·\overrightarrow{\mathrm{r}}\right)$.

Density- and current-fluctuation spectra of a dense, classical one-component plasma are discussed within a simple model based on the mode-coupling theory of liquid dynamics. The appearance of a second high-frequency shear mode at intermediate wave numbers is explained in terms of a level repulsion effect between the bare transverse current mode and the two-mode excitation spectrum. The same interaction with the longitudinal current mode is responsible for a small additional high-frequency peak in the densityfluctuation spectrum.

Experimental evidence is presented which supports the prediction of de Gennes of anomalous extended boundary layers accompanying the permeative steady-state flow of a single-domain smectic-$A$ around an obstacle.

We have found new minigaps in inversion layers on Si surfaces tilted at $\theta$ from (100) at $k_{\mathrm{F}}=0.85\left(\frac{2\pi }{a}\right)sin\theta , \left(\frac{2\pi }{a}\right)sin\theta , \mathrm{and} 1.15\left(\frac{2\pi }{a}\right)sin\theta$. Our results confirm the surface band-structure model of Sham et al., demonstrate that both intervalley and intravalley minigaps exist, and show that the minibands, expected for two-dimensional electron gas with a one-dimensional superlattice, have been realized in inversion layers with $\theta \lesssim 3°$.

We consider a new kind of percolation model in which sites can be occupied by two kinds of "atoms," $A$ or $B$, or by "molecules" formed from $A$ and $B$. Introducing plausible models for conductivity we find numerically that the total sample resistivity $\rho$ can be a nonmonotonic function of the total concentration of free and bound $A$. These results are qualitatively consistent with recent experiments on solid mixtures of sodium and ammonia. We discuss other features of the model qualitatively.

Photoelectrons from the (111) face of single-crystalline Fe show a high positive spin polarization of + 60% at threshold at $T=200\mathrm{}$ K and $H=11\mathrm{}$ kG. The results exclude an interpretation based on a localized model for the $3d$ states.

Angular momentum excitations of six quarks in a bag give a rich resonance structure in the $\mathrm{NN}$ channel above $P_{\mathrm{lab}}\simeq 1.3$ GeV/c. Some states occur with quantum numbers foreign to $\mathrm{NN}$, which we refer to as extraneous states. The lowest negative-parity states are an $\mathrm{}\left(\mathrm{NN}\right)\mathrm{}{}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}$ resonance and two extraneous $I=0\mathrm{}$ states with $J^P=0^{-} \mathrm{and} 2^{-}$, all around 2.2 GeV. The latter two states mainly decay in $\mathrm{NN}\pi$. The lowest $\mathrm{}\left(\mathrm{NN}\right)\mathrm{}{}_{}{}^3{}_{}{}^{}F_3^{}{}_{}{}^{}$ resonance lies at $M=2.34\mathrm{}$ GeV.

We present an analysis of new data for 0.8-GeV inelastic proton scattering to the $2^{+}$ (4.4 MeV) and $4^{+}$ (14.1 MeV) states of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, using both distorted-wave Born-approximation and coupled-channels calculations with empirical, spherical, and deformed optical potentials. Both the deformation of the optical potential and the two-step transition via the $2^{+}$ state are shown to influence strongly the shape and magnitude of the calculated $4^{+}$ inelastic angular distribution.

Recently measured gross structure in the 180° excitation function of ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ + ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ elastic scattering is fitted very well by including a small parity-dependent term in an energy-dependent and surface-transparent optical potential. This interpretation is in contrast to a previous proposal suggesting that the structure is due to potential shape resonances of varying principal quantum numbers $n$ and angular momenta $L$.

The analyzing power of the reaction $p_{\mathrm{pol}}d\to \mathrm{dp}$ has been measured over the angular range $100°<{\theta }_p<~170°$. It is found to be larger than that for the corresponding $p_{\mathrm{pol}}p\to d\pi$ reaction which is interpreted as an indication of $N-N$ rescattering and nucleon-exchange contributions along with the presumably dominant nucleon-pion triangle diagram.

In the approximation in which the nuclei are fixed in space, the electric current density induced in a molecule or solid by a uniform external magnetic field $\overrightarrow{\mathrm{B}}$ is shown to have the form $\overrightarrow{\mathrm{J}}=\nabla \times \overrightarrow{\mathrm{k}}$ where, to first order in $\overrightarrow{\mathrm{B}}$, $\overrightarrow{\mathrm{k}}=\left(\frac{e^2\overrightarrow{\mathrm{B}}}{2mc}\right)\Sigma i^{}{g}_i\left(\overrightarrow{\mathrm{r}}\right)$. There is one function $g_i$ for each electron. These functions are independent of the gauge of the vector potential, and they are determined by the zero-field configuration-space probability density.

The unexpected crossing of molecular-orbital energy curves recently observed by Fortner et al. for slightly asymmetric multiply charged collision systems is explained in the framework of a Hartree-Fock theory with a constraint enforcing unequal charge sharing between the subsystems.

Spontaneous emission of radiation with frequencies near the electron plasma frequency is studied for a plasma which consists of both thermal and runaway electrons. It is found that a substantial enhancement of the spontaneous radiation intensity can occur in this frequency regime via a Cherenkov resonance with the runaway electrons. Numerical analysis indicates that, for reasonable estimates of densities and energies, the plasma-frequency radiation can attain levels greater than the peak thermal emission at the second gyroharmonic.

We report the results of a linear radial-eigenmode analysis of dissipative drift waves in a plasma with magnetic shear and spatially varying density gradient. The results of the analysis are shown to be consistent with a recent experiment concerned with dissipative drift-wave instabilities in a toroidal stellarator.

DT-filled glass microspheres have been imploded at power levels exceeding 4 TW using the Lawrence Livermore Laboratory 1.06-μm Argus laser. Thermonuclear neutron yields in excess of 1.5 × ${10}^9$ have been observed implying a DT burn efficiency of 1.6 × ${10}^{-5\mathrm{}}$. Neutron and $\alpha$ time-of-flight measurements indicate DT burn temperatures of 4-8 keV, implying that a DT gain of approximately ${10}^{-2\mathrm{}}$ and a $n\tau$ of ${10}^{12}$ were obtained.

A contribution to the heat capacity that is linear in $T$ has been measured for solid argon and for two solid isotopic methanes in the region $0.25<T<\mathrm{}4\mathrm{}$ K. The effect is observed because of exceptional circumstances where a small specimen is contained in a relatively large calorimeter vessel. It is suggested that the same effect may account for some unexplained observations on solid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ and solid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$.

An unusual minimum in the optical birefringence has been observed at the smectic-$A$ to smectic-$C$ transition temperature of 4-$n$-pentylphenylthiol-4-$n^{\prime }$-octyloxybenzoate. The results are interpreted in terms of the reduction of the birefringence by short-range smectic-$C$ order in the smectic-$A$ phase. Data analysis yields a specific-heat critical exponent $\alpha$ of 0.32± 0.12.