The cross sections for electron-impact double ionization of ${\mathrm{I}}^{1+}$ and ${\mathrm{Xe}}^{1+}$ ions (and to a lesser extent also of ${\mathrm{Xe}}^{2+}$, ${\mathrm{Xe}}^{3+}$, and ${\mathrm{Xe}}^{4+}$ ions) show a dominant resonancelike contribution which, both in shape and size, almost coincides with the partial $4d$-photoionization cross section of Xe atoms.

The photoemission cross section for the $1{\pi }_{\mathrm{u}}$ level in acetylene is calculated including electronic correlations using a time-dependent local-density approximation. Structure in the cross section from 12 to 17 eV is identified as arising from a Fano autoionization resonance ($2{\sigma }_{\mathrm{u}}\to 1{\pi }_{\mathrm{g}}$) and a redistribution of oscillator strength from a bound-to-bound transition ($1{\pi }_{\mathrm{u}}\to 1{\pi }_{\mathrm{g}}$) to the continuum. A minimum in the observed photoemission asymmetry parameter and the optical frequency polarizability are also accounted for with electronic correlations.

A reduced Fokker-Planck theory of Coulomb collisional electrons in high-$Z$ laser-fusion plasmas is found to give self-consistent results of lower than classical absorption and heat transport in numerical calculations characterized by laboratory parameters. These results are determined by non-Maxwell-Boltzmann distributions which are established when laser absorption is balanced by heat transport.

An intensity dependence of the absorption of 10-μ m laser light on C${\mathrm{O}}_2$-laser-fusion targets has been observed. Absorption on gold spheres increases from 25%-30% at ${10}^{14}$ W/${\mathrm{cm}}^2$ to 50%-60% at ${10}^{16}$ W/${\mathrm{cm}}^2$, with most of the variation occurring above ${10}^{15}$ W/${\mathrm{cm}}^2$. Concurrently, hot-electron temperature scales as $T_{\mathrm{hot}}\propto I^{0.43}$ over the entire range. The absorption variation is interpreted as enhanced resonant absorption. It is suggested that as intensity is increased, the critical surface in the irradiated region becomes increasingly unstable, thereby permitting greater surface distortion and more favorable coupling conditions for resonant absorption.

This Letter reports investigations by molecular dynamics of the melting transition of a two-dimensional one-component plasma consisting of 511 particles with logarithmic interactions confined to a disk. Evidence is presented for a weak first-order transition occurring at $T_m=\frac{e^2}{k{\Gamma }_m}$ with ${\Gamma }_m\simeq 142$ and with a melting entropy ≃ 0.17 K. This small entropy is attributed to important premelting phenomena which are cooperative, cyclic permutations of six and more particles as revealed by labeling experiments.

Asymptotic long-range properties of the triplet distribution function of a fluid near its critical point are inferred from known properties of the pair distribution function and the second equation in the Bogoliubov-Born-Green-Kirkwood-Yvon hierarchy. The inverse correlation range $\kappa$ and the critical exponent $\eta$ are related to coefficients in this asymptotic form. This structural information can be used, in some cases, to test whether a proposed functional relationship between the distribution functions is consistent with realistic critical behavior.

The planar diffusive motion of alkali-metal atoms in the disordered phases of the compounds Rb${\mathrm{C}}_{24}$ and Cs${\mathrm{C}}_{24}$ has been studied for the first time by quasielastic neutron scattering. All neutron spectra show Lorentzian line profiles arising from liquidlike alkalimetal diffusion within graphite planes. The widths increase with temperature and show de Gennes narrowing at the peak of the intercalant structure factor. The results also show that Cs atoms diffuse faster than Rb atoms.

Anti-level-crossing of Landau and the electric subband levels is observed in the high-mobility two-dimensional electron gas at the GaAs/(GaAl)As interface. Coupling between the electron motion parallel and perpendicular to the interface is due to a small parallel component of magnetic field. This novel subband spectroscopic technique determines the electric subband transition energy in this two-dimensional electron system.

New effects are predicted to occur in the resistance of a one-dimensional system when the inelastic scattering time becomes longer than the transit time of a carrier through the system. While the mean behavior of $R\left(T\right)\mathrm{}$ is the same as in the multiple-hopping regime, the fluctuations in $R\left(T\right)\mathrm{}$ change dramatically, depending logarithmically on the length. The behavior of $R\left(T\right)\mathrm{}$ can give a detailed reconstruction of the microscopic eigenstates of the system.

The first-order Stark effect is observed for CO adsorbed on Ni(110). The Stark tuning rate is (1.1 ± 0.4) × ${10}^{-6\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$/(V/cm). The present measurement agrees with a model calculation. By electric field modulation of the resonant vibrational frequency of adsorbed molecules, the derivative vibrational spectrum can be measured. The spectra of CO on Ni(110) obtained are consistent with published electron-energy-loss spectra. The new technique is zero background, surface selective, and can be used in UHV or atmospheric pressure.

A series or burst of 32 extensive air showers of estimated mean energy 3×${10}^{15}$ eV was observed within a 5-min time interval beginning at 9:55 A.M. (CST) on 20 January 1981 in Winnipeg, Canada. This observation was the only one of its kind during an experiment which recorded 150 000 such showers in a period of 18 months between October 1980 and April 1982.

Self-diffusion in a Lorentz gas on a triangular lattice is studied both analytically and numerically. A simple estimate for the diffusion coefficient, based on the idea of a random walk between traps, is found to be in good agreement with the numerical results.

In a neutrino bubble-chamber experiment with a mean event energy of 90 GeV, clear evidence is observed for muon inner bremsstrahlung. The corrected rate, for gamma rays with $E_{\gamma }>1\mathrm{}$ GeV and within 32 mrad of the muon direction, is 0.027±0.005 per charged-current event. Comparison with QED calculations is discussed.

The glow model of broken QCD allows for free, low-mass, fractionally charged, glow-singlet, color 6 diquarks $Q$. Apparently the $Q\text{'}\mathrm{s}$ are nearly confined at present $e^{+}{e}^{-}$ and hadronic energies. The situation can be quite different in heavy-ion collisons. In contrast to other models, the glow model allows for parameters which could lead to fractional charge production at Bevalac energies. A search at the Bevalac is proposed that is sensitive to the production of ∼ ${10}^{-11\mathrm{}}$ diquark/collision.

Transverse momenta and rapidities of $\Lambda \text{'}\mathrm{s}$ produced in central nucleus-nucleus collisions at 4.5 GeV/c·u (C-C,...,O-Pb) were studied and compared with those from inelastic He-Li interactions at the same incident momentum. Polarization of the $\Lambda$ hyperons was found to be consistent with zero ($\alpha P=-0.06=0.11\mathrm{}$ for $\Lambda \text{'}\mathrm{s}$ from central collisions). An upper limit of the $\frac{\overline{\Lambda }}{\Lambda }$ production ratio was estimated to be less than 4.5×${10}^{-3\mathrm{}}$. The experiment was performed in a triggered streamer chamber.

A new and model-independent way of analyzing the data on magnetic moments and $\beta$ decays of mirror nuclei gives firm evidence for a quenching of the axial-vector coupling constant in nuclei. Specifically, $R=\left|\frac{C_A}{C_V}\right|=1.00\mathrm{}\pm 0.02$ is found, compared with the bare nucleon value $R=1.25\mathrm{}\pm 0.01$. The same analysis yields effective orbital $g$ factors ${\tilde{g}}_p=0.94\mathrm{}\pm 0.05$ and ${\tilde{g}}_n=0.10\mathrm{}\pm 0.04$ for proton and neutron, values which deviate from the bare values $g_p=1\mathrm{}$ and $g_n=0\mathrm{}$ in a direction opposite to that generally accepted.

This work reports the first application of the many-body optical potential of Bell and Squires beyond second order for electron-molecule scattering. The optical potential is calculated in the two-particle-hole Tamm-Dancoff approximation and the scattering problem solved by use of the Schwinger variational principle. The method is applied to the well-known ${}_{}{}^2{}_{}{}^{}\Pi _{\mathrm{g}}^{}{}_{}{}^{}$ shape resonance of ${\mathrm{N}}_2$ near 2.3 eV, with highly satisfactory results. The importance of including target correlation and polarization in a balanced way is stressed.

The influence of coherence terms on the differential cross section for $\mathrm{K}\left(4\mathrm{}{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}\right)$ interacting with Ar has been measured. The excitation with circularly polarized light directed perpendicularly to the scattering plane induces oscillations in the cross section for ${\sigma }^{+}$ light in contrast to ${\sigma }^{-}$. This asymmetry is verified by the measurement of the corresponding left-right asymmetry with respect to the scattering angle.

The first observation of enhanced optical second-harmonic generation due to excitation of the long-range surface plasmon is reported. When the fundamental mode of this plasmon is excited on both surfaces of a thin silver film bounded by a nonlinear quartz crystal and an index-matched liquid, the harmonic generation is over 2 orders of magnitude larger than that due to a single-boundary surface plasmon. Nonlinear excitation of the harmonic long-range surface-plasmon mode is also observed.

It is shown by theory and computer simulations that streaming electrons confined by a surface picket-fence magnetic field (periodic array of magnetic cusps) are subject to a two-stream instability between the electrons trapped by the surface cusp fields and the streaming electrons. This phenomenon is discussed, and its relationship to the toroidal cusp experiment is given.