The electron-photon delayed-coincidence technique was used to measure the coincident photon radiation for the $6{}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}\to 6{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}\to 6{}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ process of mercury by electron impact. This process, which is found to be partially coherent, has been analyzed with a new parametrization which takes into account spin-orbit coupling.

The spin polarization of photoelectrons emitted by an activated gallium arsenide photocathode excited with circularly polarized light has been measured by an optical method: A crossed-beam experiment has been performed in which polarized electrons transfer spin angular momentum to zinc atoms in inelastic exchange collisions. The polarized atoms emit circularly polarized light in the direction of the spin transfer. The degree of circular polarization is directly related to the electron polarization.

A relationship between the Lyapunov numbers of a map with a strange attractor and the dimension of the strange attractor has recently been conjectured. Here, the conjecture is numerically tested with use of several different maps, one of which results from a system of ordinary differential equations occurring in plasma physics. For the cases tested, the conjecture is verified to within the obtained accuracy.

Hot electron generation in a long-density-scale-length (∼300 μm) underdense plasma has been studied. For a plasma of maximum electron density of $\frac{1}{4}{n}_c$ the hot electron emission is localized in the plane of polarization of the incident C${\mathrm{O}}_2$ laser and peaked about 45° with respect to the $\overrightarrow{\mathrm{k}}$ vector of the laser beam, in both forward and backward directions. These observations suggest that the hot electrons are generated by the two-plasmon decay instability at quarter-critical density.

High-power microwaves are observed in two clear frequency bands when an intense relativistic electron beam passes through an unmagnetized plasma. The high-frequency band has frequency which scales with ${\omega }_p$ and resembles radiation from processes in type-III solar bursts. Theory indicates beam-plasma stabilization may arise from radiative losses. The lower-frequency band, with frequency independent of ${\omega }_p$, may represent conversion of electrostatic waves near the plasma boundary in inhomogeneities of size ∼0.3 cm. Experiments in a magnetic field qualitatively agree with our models.

The thermal density fluctuations in a typical tokamak plasma, for a wave vector perpendicular to the magnetic field and for a wavelength of the order of the ion gyroradius, are shown to be maximum at the frequency of the zero-group-velocity ion cyclotron waves. This frequency is sensitive to the ion- to electron-temperature ratio and the spectrum remains peaked despite a poor scattering-vector definition and destabilizing effects such as presence of a current. Possible applications to tokamak diagnosis are emphasized.

Efficient absorption of long-pulse C${\mathrm{O}}_2$-laser radiation is observed to follow a transient phase of stimulated Brillouin backscatter in critical density, laminar oxygen gas target irradiation experiments. Nearly complete energy absorption occurs for ≲ 10 nsec following stimulated Brillouin backscatter after which target burnthrough and refraction dominate. Inverse bremsstrahlung and resonance absorption cannot account for the general features observed. Anomalous collisions due to strong ion turbulence produced by the incident laser radiation are postulated to account for the efficient absorption.

An experimental study of electrostatically stabilized disclination walls is reported in the two-dimensional director field of freely suspended ferroelectric smectic-$C$ films. This Letter presents measurements of the dependence of the wall width on applied field and the collapse rate of walls forming closed circular loops. These are the first measurements of macroscopic orientation patterns in a physical $\mathrm{XY}$ system.

With use of a Lagrangian which allows for the variation of the shape and size of the periodically repeating molecular-dynamics cell, it is shown that different pair potentials lead to different crystal structures.

Direct observations of the effect of quasiparticle mean free path on the hydrodynamics of normal liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ are presented. Both the viscosity and the mean free path are found to vary as $T^{-2\mathrm{}}$ down to 1.5 mK. The relevance of these observations for other ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ experiments is mentioned.

Phonon-mediated and dynamically screened interactions between inversion-layer electrons in metal-oxide-semiconductor devices are studied. A numerical solution of the superconducting gap equation in the weak-coupling limit as a function of electron density for the Si(111)-Si${\mathrm{O}}_2$ system is given. Results are obtained for $T_c$ which demonstrate that at high densities (with $T_c\lesssim 10$ mK), pairing is dominated by intervalley phonon exchange, whereas at low densities it is essentially due to exchange of electronic (plasmon, electron-hole) excitations.

A high-resolution, electrostatic electron spectrometer combined with a Mössbauer spectrometer has been used to obtain depth-selective ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ Mössbauer spectra from the surface region of an iron scatterer by detecting emitted conversion electrons at selected electron energies. Clear experimental evidence of a sharp depth resolution in the Mössbauer spectra is demonstrated for the first time, in accordance with theoretical predictions.

A joint theoretical and experimental study of the effects of dilute doping on the optical absorption spectra of trans-polyacetylene, trans-${\left(\mathrm{CH}\right)}_x$, is presented. It is shown that the optical transition between a band state and the soliton level is considerably enhanced. However, the existence of a soliton kink strongly suppresses the interband transition. The agreement between theory and experiment supports the applicability of the soliton model to trans-${\left(\mathrm{CH}\right)}_x$.

The effect due to the tunneling of conduction electrons into the negative-$U$ centers at the disordered metal-semiconductor interfaces on the superconductivity of metal-semiconductor eutectic alloys is considered. Gorkov's formalism is used to calculate $T_c$ for (i) $n_I\ll 1$ and $\lambda \ne 0$, (ii) $\lambda =0\mathrm{}$. Where $n_I$ is the concentration of the pairing centers and $\lambda$ is the phonon-mediated electron-electron interaction in BCS theory. Our results can qualitatively explain the increase of $T_c$ in Al-Si, Al-Ge, and Be-Si eutectic alloys.

The static and dynamic critical properties of a nonionic amphiphile aqueous solution showing a lower consolution point are investigated by laser-light scattering. The osmotic isothermal compressibility and the correlation length of the concentration fluctuations diverge with mean-field-theory critical exponents. The behavior of the mass diffusion constant in the hydrodynamic region is in good agreement with the predictions of the mode-mode-coupling theory.

In an experiment measuring charmed-particle lifetimes with a hybrid emulsion spectrometer, 685 neutrino and antineutrino interactions produced by the wide-band beam at Fermi National Accelerator Laboratory have been located. These events have been carefully searched for visible decays. This Letter reports the seven neutral decays which are consistent with a $D^0$ hypothesis and determine a lifetime of ${1.00}_{-0.31\mathrm{}}^{+0.52\mathrm{}}$×${10}^{-13\mathrm{}}$ sec for this charmed state.

From the analysis of 685 neutrino and antineutrino interactions in an emulsion target, fifteen candidates for the multiprong decay of charged charmed particles are found. This Letter presents lifetimes for the $D^{\pm }$, $F^{\pm }$, and ${{\Lambda }_c}^{+}$ states based on the fitted events of the sample.

A generalization of the nonlinear $\sigma$ model is considered. The field takes values in a compact manifold $M$ and the coupling is determined by a Riemannian metric on $M$. The model is renormalizable in $2+\epsilon$ dimensions, the renormalization group acting on the infinite-dimensional space of Riemannian metrics. Topological properties of the $\beta$ function and solutions of the fixed-point equation $R_{\mathrm{ij}}-\alpha g_{\mathrm{ij}}={\nabla }_i{v}_j+{\nabla }_j{v}_i$, $\alpha =\pm 1 or 0$, are discussed.

In quark-quark scattering where a hard gluon is radiated, a charge-conjugation asymmetry is examined and found to be large. The perturbative quantum-chromodynamic prediction for this asymmetry is compared with that for an Abelian theory and an appreciable difference is found. The specific role of the trilinear coupling is significant. A program is set forth for three-jet experiments in hadron-hadron collisions in which the non-Abelian issue can be studied.

This Letter describes a calculation using superfield techniques, showing that the $\beta$ function is zero to three loops in $N=4\mathrm{}$ supersymmetric Yang-Mills theory. This result gives further indication that the theory is likely to be finite and conformally invariant order by order in perturbation theory.