In order to check theoretical results obtained recently in the treatment of the superradiant emission of atoms when taking the level degeneracy into account explicitly, an experiment has been performed using a special "multiple beam" of Rb atoms. A careful study of the polarization characteristics of the emitted light has shown us several features which appear to be quite different in the superradiant emission and in the ordinary spontaneous one. An analysis is given for the few typical cases which have been observed and reported.

It is argued that resonant magnetic fluctuations are the mechanism of anomalous electron heat loss in tokamaks. The experimental and theoretical support for this assertion are given.

We propose a new empirical criterion using the pair distribution function for specifying the supercooled-liquid/amorphous phase boundary.

Cu-implanted Si crystals were irradiated with $Q$-switched ruby-laser single pulses. After irradiation with energy density in excess of 1.0 J/${\mathrm{cm}}^2$, the Cu atoms accumulate at the sample surface. Thermal annealing in the 500-800°C range casues a migration of Cu inside the specimen, in agreement with diffusion coefficient and solid solubility values. The results indicate the formation of a liquid layer induced by laser irradiation. The solid-liquid interface movement during freezing qualitatively justifies the observed surface accumulation.

The broad line shape for absorption due to transitions between heavy-hole and spin-orbit bands in electron-hole droplets in Ge is explained. The calculation uses multiple-scattering concepts to remove the divergences of ordinary perturbation expansions in the dynamical Coulomb interaction. The absorption resembles the free-hole theory at low frequencies, is sensitive to both band anisotropy and screening approximations at intermediate frequencies, and is independent of screening at high frequencies.

The first observation of magnetic resonance field shifts proportional to an applied electric field in a magnetically ordered material is reported. It involves ferromagnetic resonance experiments on lithium ferrite crystals in an applied electric field at temperatures between 4.2 and 77°K. The observed shifts are predicted by using statically measured values of the electric field derivative of the uniaxial anisotropy energy existing in the "skin" region of these crystals.

There exist functions $F\left(x\right)\mathrm{}$ whose asymptotic expansions, when computed at fixed $x$ and optimal order, seem to converge to a numerical value which deviates significantly from $F\left(x\right)\mathrm{}$ itself. Several examples are given, showing that this phenomenon is not exceptional, and should occur in quantum theory. In particular, the semiclassical expansion, at large quantum numbers, of levels of the quartic oscillator $V=x^4$ presents such discrepancies, which we explain quantitatively as contributions from classical trajectories for which space and time coordinates become complex.

We present a renormalization-group approach for treating the percolation properties of the nearest-neighbor triangular Ising model. We obtain exponents for the line of percolation transitions $T_c<~T<~\infty$. In particular, we find a possibly exact result for the connectedness-length exponent ${\nu }_p=\frac{\ln \sqrt{3}}{\ln \left(\frac{3}{2}\right)}$ in the "pure" percolation ($T=\infty$) limit, which holds for $T_c<T<~\infty$. At $T=T_c$ we find the connectedness-length exponents of the percolation problem to be identical to the correlation-length exponents for the thermal problem.

We have measured charged multiplicities, inclusive branching ratios to states containing kaons, and average energy fractions in charged and neutral particles for decays of $D$ mesons produced at the $\psi \mathrm{}\left(3772\right)\mathrm{}$ resonance. The average charged multiplicity is 2.3±0.3 for both the neutral and the charged $D$. We find inclusive branching ratios $B(D^0\to K^{\pm }X)=0.35\mathrm{}\pm 0.10$ and $B(D^{+}\to K^{-}X)=0.10\mathrm{}\pm 0.07$ for decays into charged kaons.

Light-charged-particle emission in the reaction ${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}$+${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ has been studied by simultaneously measuring the atomic numbers of both deep-inelastic fragments. The results seem consistent with an evaporative process and indicate that the entrance-channel kinetic energy is essentially thermalized over a broad range of bombarding energies.

The large-$q^2$ behavior of new elastic electron-scattering measurements from ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ is compared with the dimensional-scaling quark model. The slope change in $\frac{F_{{}_{}{}^3{}_{}{}^{}\mathrm{He}}}{F_{\mathrm{quark}}}$ for $q^2>2\mathrm{}$ Ge${\mathrm{V}}^2$ when compared to ${}_{}{}^2{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ is conjectured to be evidence for scaling permitting the further synthesis of nucleon-nucleon and quark-gluon physical ideas.

The application of the distorted-wave Born approximation (DWBA) to inelastic scattering is examined. Particular attention is given to the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ system. The one-channel optical-potential wave function is found to be an adequate representation of the entrance-channel relative motion. The choice of exit-channel distorting potential DWBA is found to be crucial and a procedure to choose it correctly is discussed.

We describe a new type of molecular electronic state in which all vibrational levels occur entirely at internuclear distances large compared to ordinary chemical-bond lengths. We present explicit calculations for two such electronic states of $0_{\mathrm{g}}^{-}$ and $1_{\mathrm{u}}$ symmetry in the ${\mathrm{Na}}_2$ molecule which are near the $\mathrm{Na}\left(3\mathrm{}{P}_{\frac{3}{2}}\right)+\mathrm{Na}\left(3\mathrm{}{S}_{\frac{1}{2}}\right)$ dissociation asymptote. We feel experimental observation of such levels is possible.

$K$- and $L$-shell ionization of ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ with Xe and U projectiles is investigated. Internal conversion following nuclear Coulomb excitation which is particularly important for deformed heavy nuclei is compared with direct ionization of inner-shell electrons in superheavy quasimolecules. Both processes exhibit different impact-parameter dependences. As a result of internal conversion, about 0.1-0.3 $K$ holes per central collision are created.

The quasielastic central peak of paraelectric potassium dihydrogen phosphate is suppressed by annealing. The solf-branch Brillouin spectra are then fitted with a classical coupled-mode expression without any deviation that could suggest additional contributions, and with parameters in good agreement with the available data.

A stochastic theory of heterogeneous bimolecular reactions catalyzed by active sites is formulated using a defect-renormalized propagator method. Reaction between adsorbed migrating species occurs upon their coincidence on active sites and may demand proper internal-state configurations. Effects due to spatial heterogeneity, lattice structure, and internal states on the reaction evolution are analyzed.

The theory of two-dimensional superfluidity by Nelson and Kosterlitz is examined in the context of ideal interacting ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ films. It is shown that superfluid onset in a film on a uniform surface would have a critical-temperature gap due to phase condensation. No experiments on uniform or heterogeneous substrates have disclosed any gap, indicating that superfluid onset in experimental films may have another origin.

The adsorption of nitric oxide and its dissociation on the Ru(001) surface have been studied through the vibrational energies of the adsorbed layer. The inelastic electron scattering measurements show that two distinct states of molecular NO are adsorbed at 130 K. The dissociation of a bridged NO is complete at 316 K, whereas a linear form remains on the surface until 500 K. This is explained by a difference in activation energies for dissociation of NO and by the blocking of sites by nitrogen and oxygen adatoms.

We have measured photoemission from the valence band and outer core levels of rare-earth (Ce, Gd, La) pentaphosphates. Varying the photon energy through the region of the giant resonance of the $4d$ cross section ($h\nu =100-200\mathrm{}$ eV), we find a dramatic enhancement of the rare-earth-derived states ($4f, 5p, 5s$) in the energy distribution curves. This enhancement is explained as due to a strong interaction of the $4d^{9}4f^{n+1\mathrm{}}$ configuration with such other configurations as, e.g., $4d^{10}4f^{n-1\mathrm{}}\epsilon l$ (autoionization).

Measurements of the electric quadrupole interaction at ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$ impurities in paramagnetic Ho metal using time-differential perturbed angular correlations show marked deviation from the usual $T^{\frac{3}{2}}$ behavior. A phenomenological theory applied to this and other cases of closed-shell probes in rare-earth metals indicates that the deviation is due to the aspherical charge distribution of the host ion arising from the influence of the crystalline electric field on their unfilled $4f$ shells.