A new class of polarization echoes is reported in which the frequencies of the input pulses are harmonically related. The previously reported echo phenomenon in piezoelectric semiconductors is shown to be a special case in which all frequencies are the same.

Neutron-scattering studies of $2H$-Nb${\mathrm{Se}}_2$ and $2H$-Ta${\mathrm{Se}}_2$ reveal the strong Kohn anomalies and incommensurate superlattice characteristic of charge-density-wave instabilities. Whereas the Nb${\mathrm{Se}}_2$ superlattice ($T_0=33.5\mathrm{}$ K) remains incommensurate to 5 K, Ta${\mathrm{Se}}_2$ ($T_0=122.3\mathrm{}$ K) locks to a commensurate $3a$ superlattice at 90 K. The temperature dependence of the superlattice wave vector and the lockin behavior are understood using a free energy involving terms third order in atomic displacement. A secondary lattice distortion required by this model is observed.

X-ray photoemission spectra of W core levels in metallic sodium tungsten bronzes, ${\mathrm{Na}}_x\mathrm{W}{\mathrm{O}}_3$, clearly show asymmetries due to many-body effects. Na and O core levels show only the expected plasmon satellite, demonstrating the importance of the local density of states in the screening of the core hole.

The tetracyano-$p$-quinodimethane salts of tetrathiafulvalene and its newly synthesized selenium analogs tetraselenafulvalene and cis/trans-diselenadithiafulvalene form an "isostructural" series of highly conducting organic salts. The electrical conductivity is remarkably similar and peaks at 59, 40, and 64°K, respectively. It is concluded that the conduction mechanism is of the same origin in spite of their varying molecular properties.

We measure the lifetimes of excited states in ${}_{}{}^{81}{}_{}{}^{}\mathrm{Rb}$ and in the core nucleus ${}_{}{}^{80}{}_{}{}^{}\mathrm{Kr}$. Ratios of reduced transition probabilities in ${}_{}{}^{80}{}_{}{}^{}\mathrm{Kr}$ are consistent with those given by the rotational model. The $B\left(E2\mathrm{}\right)\mathrm{}$ of the ${\frac{13}{2}}^{+}$ state in ${}_{}{}^{81}{}_{}{}^{}\mathrm{Rb}$ is in agreement with the particle-plus-rotor value and inconsistent with the weak-coupling prediction. The $B\left(E2\mathrm{}\right)\mathrm{}$ values of the ${\frac{17}{2}}^{+}$ and ${\frac{21}{2}}^{+}$ states lie much higher than predicted by several models.

The giant-resonance region was studied for ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$, ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$, ${}_{}{}^{36}{}_{}{}^{}\mathrm{Ar}$, ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$, ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$, ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$, and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ by inelastic scattering of 96.6-MeV $\alpha$ particles. A systematic broadening of the isoscalar giant resonance at $E_{\mathrm{exc}}\simeq \frac{63}{A^{\frac{1}{3}}}$ MeV occurs as $A$ decreases. The width for ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ is 3.5±0.3 MeV, for ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$ it is 7.1±0.5 MeV, and for nuclei below $A=32\mathrm{}$ the resonance is too diffuse to be observed.

Coincident $\gamma$ rays of total energy 2.22 MeV, the deuteron binding energy, were observed following the capture of subthermal neutrons by an ${\mathrm{H}}_2$O target. The differential cross section, assuming a $\frac{1}{v}$ neutron energy dependence, increases from about 0.2 μb/keV at equal $\gamma$ energies to about 1.0μb/keV for a $\gamma$ energy of 1600 keV. The branching ratio for emission of two $\gamma$ rays, both in the $\gamma$-ray energy range from 600 to 1620 keV, to single 2.22-MeV $\gamma$ rays was found to be (1.05±0.16)×${10}^{-3\mathrm{}}$.

Direct observation of the excess brightness from photospheric faculae are presented. This excess brightness is, at times, large enough to produce an apparent oblateness that exceeds that reported by Dicke and Goldenberg. These results support the Chapman-Ingersoll facular explanation for the excess solar oblateness and support the findings of Hill et al. by offering a possible source for their excess equatorial brightness which, they showed, can produce an apparent, nongeometrical oblateness.

We report new measurements of inclusive pion electroproduction. Data were taken with deuterium and hydrogen targets at the $W$ and $Q^2$ points (2.15 GeV, 1.2 Ge${\mathrm{V}}^2$), (2.15, 4.0) and (3.11, 1.2) and with only hydrogen at (2.15, 2.0), (2.67, 0.6), (2.67, 1.2), (2.67, 2.0), (2.67, 3.3), and (3.11, 1.7). The invariant structure function and the $\frac{{\pi }^{+}}{{\pi }^{-}}$ ratio are studied as a function of $Q^2$, $W$, and $\omega$.

We have searched the mass region 3.2 to 5.9 GeV for evidence of narrow resonances in $e^{+}{e}^{-}\to \mathrm{hadrons}$. We find no evidence for any such resonances other than the $\psi \mathrm{}\left(3695\right)\mathrm{}$ in this region with a sensitivity ranging from about 12 to 45% of the integrated cross section of the $\psi \mathrm{}\left(3695\right)\mathrm{}$. The more stringent bounds apply to resonances of a few MeV width, while the looser bounds apply to resonances of up to 20 MeV width.

The total cross section for hadron production by $e^{+}{e}^{-}$ annihilation has been measured at center-of-mass energies between 2.4 and 5.0 GeV. Aside from the very narrow resonances $\psi \mathrm{}\left(3105\right)\mathrm{}$ and $\psi \mathrm{}\left(3695\right)\mathrm{}$, the cross section varies between 32 and 17 nb over this region with structure in the vicinity of 4.1 GeV.

Charmed-quark models of the new narrow resonances at 3.1 and 3.7 GeV suggest that a virtual $S$ state lies slightly above the charmed-hadron threshold. This state causes a large enhancement of $R=\frac{\sigma (e^{+}{e}^{-}\to \mathrm{hadrons})}{(e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-})}$ just above the threshold, followed by a dip and several broad but smaller enhancements at higher energy. Estimates of this intriguing structure in $R$ are presented.

We propose assignment of the new $\psi$ particles in an SU(4) symmetry scheme, incorporating SU(3) and a new additive quantum number, paracharge $Z$. Anomalous currents are introduced to account for the production and decays of these particles. Two more rather broad resonances at around 4.3 and 5.0 (±0.2) GeV are expected in the $e^{+}{e}^{-}$ annihilation, one of which has recently been reported (at 4.15 GeV).

The relative intensities of the argon $\mathrm{KLL}$ Auger transitions, measured with an accuracy of better than 10%, are found to agree well with recent theoretical predictions based on a theory that uses intermediate coupling, configuration interaction, and good wave functions and level energies. Large widths for $K{L}_1{L}_{1,2,3}$ lines suggest high Coster-Kronig transition rates for double-hole configurations $L_1{L}_1$ and $L_1{L}_{2,3}$.

It is shown that even for optical frequencies the dipole approximation is not always valid in multiphoton ionization. For certain photon frequencies, we find quadrupole-dipole contributions which are several orders of magnitude larger than the usual dipole-dipole contribution to two-photon ionization.

We have observed supercooling in liquid C${\mathrm{O}}_2$ near the critical temperature greatly exceeding that allowed by existing theories of homogeneous nucleation.

We calculate the viscosity $\eta$ and diffusive thermal conductivity ${\kappa }_D$ of the Balian-Wert-hamer state of a $p$-wave superfluid for $T\ll T_c$. The nature of the excitations in the superfluid state is fully taken into account, and realistic effective interactions are used. $\eta$ tends to a constant, $\sim \frac{1}{4}\eta \left(T_c\right)$ for liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$, and ${\kappa }_D\sim T^{-1\mathrm{}}$. Mean free paths are also calculated.

The wave number of an electron plasma wave propagating on a collisionless plasma column is found to differ from that of a small-amplitude wave at the same frequency. The nonlinear wave-number shift oscillates in space. The magnitude of its first maximum, when normalized to the initial (nonlinear) damping coefficient, is found to be proportional to the square root of the initial wave amplitude.

Anomalous resistivity and intense ion heating are observed in isothermal plasmas where ion sound is damped, concomitant with onset of resonant discrete and nonresonant continuous spectra of ion-cyclotron drift waves. These results are explained by a theory based on statistically averaged instability amplitudes and frequencies.

Elastic- and inelastic-neutron-scattering methods have been used to study the low-temperature properties of argon films adsorbed on graphite. At $T=5\mathrm{}$ K the film forms a two-dimensional triangular lattice incommensurate with the substrate. The spectrum of neutrons inelastically scattered in the plane of the film is found to be consistent with calculations based on a simple two-dimensional phonon model in which interactions with the substrate are neglected.