This Letter reports the first experimental study of the spatial structure of spontaneous thermal fluctuations for $\mathrm{ka}\gtrsim 1$ in a physical system maintained in a nonequilibrium steady state. In particular, the shear-flow-induced distortion of the static structure factor, $\mathcal{S}\left(\overrightarrow{\mathrm{k}}\right)$, is observed for a colloidal suspension of strongly interacting spherical particles of interparticle separation $a$.

The distribution function of the distance between a mobile and an immobile atom on a single-crystal surface has been measured for various temperatures, resulting in the first experimental demonstration of nonmonotonic long-range interactions. With W as the immobile atom and Pd as the mobile atom, at least two well-defined bond distances, 3.2 and 11 Å, are observed; with Re replacing W, at least one well-defined bond distance, 5.0 Å, and a strong anisotropy are seen. Additional bound states are indicated at larger distances.

The $\overrightarrow{\mathrm{k}}$ dependence of the conduction-electron-rare-earth-moment exchange interaction is directly measured for the first time and found to be opposite in sense for Gd and Yb impurities in Au. Atomic exchange dominates for Au(Gd), while a phase-shift analysis indicates that covalent mixing of conduction $p$ waves accounts for the observed $\overrightarrow{\mathrm{k}}$ dependence in Au(Yb).

Cerium and light actinide monopnictides of NaCl structure have extraordinarily strong magnetic anisotropy, with unusual magnetic structures and transitions. We show that this behavior can be understood on the basis of a Coqblin-Schrieffer-type interaction, effectively treating mixing of $f$ and conduction electrons.

Optical measurements of phosphorus-doped silicon yield a donor susceptibility which can be fitted with a critical form that extrapolates to a polarization catastrophe at the insulator-metal transition. The exponent is about twice classical predictions and demonstrates the quantum nature of the transition.

A simple model of eutectic solidification is used to illustrate the marginal-stability theory of pattern selection in nonequilibrium processes. The nonlinear equation of motion which describes this model suggests a mechanism for noise amplification at the marginally stable operating point of the system.

Inelastic-electron-scattering cross sections for ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$ have been measured in the continuum region. The longitudinal and transverse inelastic response functions have been determined for vector momentum transfers, $q$, from 210-410 MeV/c and for energy losses $0<\mathrm{}\omega <~220$ MeV.

The widths of states of $\Sigma$-hypernuclei have been estimated in two models. Widths as small as one to a few megaelectronvolts are found, a result which should hold for some isolated simple $\Sigma$-hypernuclear states. The standard procedure by use of the two-body absorptive cross section is shown to overestimate the width by one or more orders of magnitude.

Ratios of cross sections for ${}_{}{}^7{}_{}{}^{}\mathrm{Li}(p, n){}_{}{}^7{}_{}{}^{}\mathrm{Be}$ leading to the ground and first excited states of ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$ have been measured at 24.8, 35, and 45 MeV. An analysis of these ratios yields the ratio of spin-flip to spin-nonflip strength, ${\left|\frac{V_{\sigma \tau }}{V_{\tau }}\right|}^2$, free of many of the uncertainties usually associated with distorted wave analyses for such light nuclei. The ratio increases by about 60% in the observed energy range. A comparison with known values of $V_{\tau }$ yields $V_{\sigma \tau }$. The isovector tensor force is also obtained.

The influence on atomic motion of quantum-mechanical fluctuations of the resonance-radiation force is investigated theoretically. Fluctuations due to both induced and spontaneous absorption-emission processes give rise to diffusion of atomic momentum, here described by a Fokker-Planck equation. It is shown that quantum-mechanical fluctuations of the radiation force place a lower bound on the temperature achievable by radiation cooling, inhibit cooling in a strong standing wave, and lead to finite, often short, confinement times for atoms in radiation traps.

$l$-changing collisions were observed in a crossed ${\mathrm{He}}^{+}$-ion/Na-Rydberg-atom beam experiment. Transitions $\mathrm{nd}\to n(l>~3)$ induced in Na by ion impact at 450 and 600 eV were studied for $n=20-34\mathrm{}$. Cross sections vary approximately as $n^5$ and have magnitudes of order ${10}^8$ ${\mathrm{\AA }}^2$, a few hundred times the geometric cross section of the Rydberg atoms.

The excitation probability of the $1s\sigma$-molecular orbital has been measured as a function of the impact parameter $b$ for several collision systems in the region $129<~Z_1+Z_2<~178$ at the UNILAC. All published impact-parameter data agree with a simple scaling law except those for impact parameters $b<~40$ fm in the Pb+Cm system ($Z_1+Z_2=178\mathrm{}$).

Experimental evidence is presented which shows that couette flow has several transitions at quite low Reynolds numbers compared to the Taylor transition ($\frac{R}{R_c}\approx 1$) which exhibit increased degrees of freedom, line broadening, extra broad-band noise, loss of spatial coherence, and hysteresis. The visual signature of these transitions has been identified as dislocations in the cell structure.

At finite ratios of the kinetic plasma pressure to the magnetic pressure, the magnetic confinement configurations of axisymmetric plasma columns tend to acquire characteristics that hinder the onset of instabilities driven by the combined effects of magnetic curvature and pressure gradient. A simple analytical dispersion relation that contains the main physical factors affecting an important class of these modes is given.

Microtearing (high-$m$) modes driven by the electron temperature gradient are found to be unstable for present tokamak parameters. A self-consistent calculation of the nonlinear saturation of this instability yields magnetic fluctuations $\frac{\left|\tilde{B}\right|}{B}\simeq \frac{{\rho }_e}{L_T}$. The associated crossfield electron thermal conductivity is shown to be inversely proportional to density, consistent with Alcator scaling, and comparable in magnitude with that inferred from experiments.

This paper reports calculation of the mobility tensor of negative ions, in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$A$ for temperatures close to $T_c$ in terms of normal-state properties from an exact solution for the anisotropic quasiparticle-rigid-ion elastic scattering amplitude in the Anderson-Brinkman-Morel state.

It is shown that in parity nonconservation experiments currently underway on hydrogen and deuterium, the limits on the proton and deuteron electric dipole moments may be improved by as much as two and nine orders of magnitude, respectively. The situation for heavier atoms is briefly examined.

The results of a search for narrow $\overline{p}p$ states produced in the baryon-exchange reaction ${\pi }^{+}p\to {{\Delta }_f}^{++}\overline{p}p$ at 9.8 GeV/c are reported. This channel provides an enhanced sensitivity to such states compared with the reaction ${\pi }^{-}p\to {{\Delta }_f}^0\overline{p}p$. We find no evidence for such states at the 20-30-nb level in the mass range 1.9-2.3 GeV/${\mathit{c}}^2$. Assuming a nucleon-exchange production mechanism, the states which have been reported in ${\pi }^{-}p$ interactions at 2.02 and 2.20 GeV/${\mathit{c}}^2$ would appear as > 5-standard-deviation peaks in this data.

In weak-interaction models with spontaneous parity nonconservation, based on the gauge group $\mathrm{SU}{\mathrm{}\left(2\right)\mathrm{}}_L\otimes \mathrm{SU}{\mathrm{}\left(2\right)\mathrm{}}_R\otimes \mathrm{U}\mathrm{}\left(1\right)\mathrm{}$, we obtain the following formula for the neutrino mass: $m_{{\nu }_e}\simeq \frac{{m_e}^2}{g{m}_{W_R}}$, where $W_R$ is the gauge boson which mediates right-handed weak interactions. This formula, valid for each lepton generation, relates the maximality of observed parity nonconservation at low energies to the smallness of neutrino masses.

This Letter compares neutral-current and charged-current scaling-variable distributions in neutrino-nucleon interactions induced by a narrow-band beam at Brookhaven National Laboratory; the $x$ distribution of neutral-current events has been reported previously. The first measurement of flux-normalized neutrino cross sections from a narrow-band beam in the energy range $E_{\nu }=3-9\mathrm{}$ GeV is also presented.