This paper reports on numerical studies of the generation of second-harmonic radiation by a $p$-polarized electromagnetic wave incident on an inhomogeneous overdense plasma. Maximum second-harmonic emission coincides with maximum absorption of the fundamental wave. The importance for second-harmonic emission of electromagnetic structure resonances due to density plateaus near the critical layer is demonstrated.

The collision of spherical ion-acoustic solitons having different centers of symmetry is studied. Unlike one-dimensional collisions, the solitons are significantly changed by the collision. A new two-dimensional nonlinear object is found to be created. Remnants of the solitons that survive are found to be shifted in phase and reduced in amplitude.

We have observed, by C${\mathrm{O}}_2$-laser-light scattering, large-amplitude electron-density fluctuations with $k{\lambda }_D\sim 0.1$ and a narrow angular spread in $\overrightarrow{\mathrm{k}}$ about the direction normal to a transient shocklike distance. This shock propagates radially inwards in a cylindrical plasma [$n_e=(1-6)\mathrm{}\times {10}^{13}$ ${\mathrm{cm}}^{-3\mathrm{}}$, $T_e\lesssim 1$ eV] having an axial magnetic bias field of 170 G. The observed fluctuations are seen in a narrow region in front of the shock where a stream of reflected ions passes through the background plasma, and are thought to be driven by this stream.

The Euler-Lagrange equation for an impurity interacting with an inhomogeneous fluid is derived and applied to a description of the polarized hydrogen system, ${\mathrm{H}}_{\mathrm{\uparrow }}$, ${\mathrm{D}}_{\mathrm{\uparrow }}$, and ${\mathrm{T}}_{\mathrm{\uparrow }}$ on the surface of liquid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$. We find well-defined, strongly bound physisorbed states for ${\mathrm{T}}_{\mathrm{\uparrow }}$, and ${\mathrm{D}}_{\mathrm{\uparrow }}$ and a weakly bound physisorbed state for ${\mathrm{H}}_{\mathrm{\uparrow }}$.

Results for the second-sound damping in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ solutions with ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ molar concentrations of 0.001, 0.003, and 0.005 are presented for frequencies of 2, 3, and 5 kHz and in the temperature range 40 mK to 1 K. The damping is nonhydrodynamic and shows a peak near $T=0\mathrm{} 4$ K, which increases with decreasing concentration and also with increasing pressure.

The dc magnetic susceptibility of CoO·${\mathrm{Al}}_2$${\mathrm{O}}_3$·Si${\mathrm{O}}_2$ (14.3 at.% Co) below $T_g=5.7\mathrm{}$ K decreases markedly with reduction in field for $H<\mathrm{}150\mathrm{}$ mOe. The observation of this field sensitivity, equilibrium behavior, and a sharp cusp at $T_g$ in this very weak field range is evidence for a cooperative transition at $T_g$ below which correlations extend over many spins. This state is characterized by an energy scale per spin comparable to that of magnetic dipolar coupling between nearest-neighbor spins.

The first observation of photoluminescence (PL) originating from intrinsic defects in annealed and neutron-irradiated amorphous ($a-$)Si${\mathrm{O}}_2$ is reported. The PL is compared with that for $a$-${\mathrm{As}}_2$${\mathrm{S}}_3$. The PL spectra scale with energy band gap and the temperature dependence of the PL quantum efficiencies scale with glass transition temperature. This strongly suggests that defects in $a$-Si${\mathrm{O}}_2$ and semiconducting chalcogenide glasses are similar.

Pure palladium films, evaporated between 4.2 and 300 K, can be transformed into superconductors by means of irradiation at low temperatures with ${\mathrm{He}}^{+}$ ions. The maximum transition temperature obtained is 3.2 K. It is shown that the presence of a special kind of defects produced during the irradiation is a necessary precondition for the occurrence of superconductivity.

Spin relaxation measurements on a color center in the conduction plane of $\beta$-${\mathrm{Al}}_2$${\mathrm{O}}_3$: Na reveal an exceptionally fast rate with an anomalous temperature and microwave frequency dependence. The data are quantitatively described by a mechanism involving the coupling of a color center to the phonon-induced relaxation of a nearby localized two-level tunneling state. The required density of such states is nearly the same as that used to explain the low-temperature properties of $\beta$-${\mathrm{Al}}_2$${\mathrm{O}}_3$: Na.

Recent precision measurements of the resistivity of potassium between 0.38 and 1.6 K revealed a surprising $T^{1.5}$ temperature dependence. We show that scattering of electrons by phasons—the collective excitations of an incommensurate charge-density wave—can provide an explanation.

Quantum kinetic equations for describing transport in submicron semiconducting devices in the finite collision duration regime are developed which are nonlocal in time and momentum. Utilizing a projected self-scattering formulation, a retarded path-integral equation is obtained. Quantum kinetic equations are usually exceedingly difficult to solve. The formulation found here presents a powerful technique to achieve these solutions even in the case where nonlocal effects are important.

A narrow peak (full width at half maximum about 60 meV) just above the top of the bulk $d$ bands has been observed in angle-resolved energy distribution curves of Cu(100). The peak is attributed to a $d$-like surface state in an energy gap of the projected bulk band structure near the symmetry point $\overline{M}$ of the two-dimensional Brillouin zone. A surface state near $\overline{M}$ was predicted in recent self-consistent calculations.

It is shown that a three-band, nonparabolic, model for zinc-blende semiconductors provides a universal curve for the frequency dependence of the two-photon coefficient, whose magnitude differs between semiconductors by the factor ${\left(E_g{{}_{}{}^3{}_{}{}^{}n_p^{}{}_{}{}^{}}^2\right)}^{-1\mathrm{}}$. Good agreement is obtained with reported coefficients at 300°K for InSb, ${\mathrm{Hg}}_{1-x}{\mathrm{Cd}}_x\mathrm{Te}$, GaAs, and CdTe.

The effect of a nontrivial conserved isotropic total angular momentum $M^2={m_x}^2+{m_y}^2+{m_z}^2$ on the equilibrium distribution of energy in a photon gas is examined. It is shown that the correspondingly modified Planck law takes the form $F\left(\nu \right)=\mathrm{const}\nu {\gamma }^{-1\mathrm{}}\ln \left[\frac{(1-e^{-\beta \nu -\gamma {\nu }^2})}{(1-e^{-\beta \nu })}\right],$ where $\beta$ and $\gamma$ are parameters determined by the energy and angular momentum. This law provides a good fit to the spectrum of the cosmic background radiation observed by Woody and Richards.

We study the temperature dependence of soft $\mathrm{CP}$-invariance violation in a class of gauge theories based on the gauge group $\mathrm{SU}{\mathrm{}\left(2\right)\mathrm{}}_L\times \mathrm{U}\mathrm{}\left(1\right)\mathrm{}$ and show that there exist physically acceptable domains of coupling parameters of the theory where $\mathrm{CP}$-invariance violation persists at high temperatures. Such models have the potential to explain matter-antimatter asymmetry in the universe while at the same time providing a cure for the strong $\mathrm{CP}$ problem.

We describe an extension of the Weinberg-Salam model to the group SU(2) ⊗ U(1) ⊗ U(1)' in which $\mathrm{CP}$ invariance is spontaneously broken and physical $\mathrm{CP}$-invariance violation is mediated by the new massive $Z^{\prime }$ boson.

The lowest-order perturbative expression for $\alpha \left(q^2\right)$, the quantum-chromodynamic running coupling constant, is inadequate for describing the moments of nucleon structure functions at present energies. I propose to determine $\alpha \left(q^2\right)$ with use of a new Borel-like summation technique described by Khuri. The $\alpha \left(q^2\right)$ which emerges from this procedure is free of the Landau ghost and it is consistent with experiments in both spacelike and timelike regions.

Pairs of odd-even nuclei with the wave functions of the valence nucleons different simply by an interchange of neutrons and protons (pseudo mirror pairs) have been identified and mirror symmetry in the subspace of valence nucleons conjectured. Isoscalar and isovector magnetic moments have been studied, for a given shell and for an increasing number of odd nucleons. Impressive regularities become evident.

A technique which employs heretofore unappreciated aspects of the optical stimulated echo was developed and used to measure the total scattering cross section for $\mathrm{Na}\left(3\mathrm{}{S}_{\frac{1}{2}}\right)$-He and $\mathrm{Na}\left(3\mathrm{}{P}_{\frac{1}{2}}\right)$-He collisions. The repulsive-core-dominated $\mathrm{Na}\left(3\mathrm{}{S}_{\frac{1}{2}}\right)$-He collision is found to be relatively soft. The cross section for degradation of the $3S_{\frac{1}{2}}-3\mathrm{}{P}_{\frac{1}{2}}$ superposition, determined from photon-echo-decay measurements, is anomalous in that it is smaller than the total elastic-scattering cross section with Na in either state separately.

The electronic conversion efficiency of a free-electron laser using an intense relativistic electron beam in a rippled magnetic field as its active medium is limited mainly by the destruction of the coherent slow space-charge wave through particle trapping and the depletion of the available beam energy. It is shown that by proper stepping up of the ripple magnetic field strength prior to electrostatic wave saturation, the efficiency can be substantially increased along with some bandwidth improvement and shortening of the device length.