A model is developed for a superconductor under an external dynamic pair-breaking influence such as a flux of optical photons. The recombination time for quasiparticles to form pairs is much greater than the characteristic time for their thermalization to the lattice temperature $T$. For this reason the model treats the unpaired electrons as a Fermi gas at temperature $T$, but more numerous than in the complete equilibrium situation.

Two-electron transitions are observed in Si at liquid-He temperature for high excitation levels. A broad emission line appears at an energy of $h\nu =2.28\mathrm{}$ eV with a linewidth of about 20 meV. The experimental line shape agrees well with a theoretical calculation obtained from the model of electron-hole drops proposed by Pokrovsky, Kaminsky, and Svistunova.

The sharp edge of the phonon "bremsstrahlung" spectrum of a superconducting tunnel junction was isolated by modulation. This yielded a monochromatic, voltage-tunable phonon source which was applied for phonon spectroscopy on ${\mathrm{V}}^{3+}$ ions in ${\mathrm{Al}}_2$${\mathrm{O}}_3$. At a frequency corresponding to the ground-state splitting of ${\mathrm{V}}^{3+}$ an absorption dip was obtained due to resonant scattering. A frequency resolution of about 3% of the energy gap was achieved.

It is shown that the exciton spectra in Pb${\mathrm{I}}_2$ can only be described in terms of a single Wannier series with a large ground-state anomaly. This anomaly is explained by a repulsive central-cell correction due to the cationic character of the exciton.

As a model of an amorphous system we consider a collection of atoms with one atomic orbital per site, in terms of which the one-electron Green's function is expanded. We apply multiple-scattering techniques to this system, and obtain the quasicrystalline approximation of Lax and the self-consistent approximation of Schwartz and Ehrenreich. Results are given for the electronic density of states using pair distribution functions for random and hard-sphere liquids.

We observed in LiNb${\mathrm{O}}_3$ a collinear triply phase-matched interaction between two input infrared waves and two input ultrasonic shear waves that yielded an output visible wave near the optical second-harmonic frequency. The five-wave-interaction output was 35% of that from a related three-wave interaction under comparable conditions.

The dielectric matrix $\epsilon (\overrightarrow{\mathrm{q}}+\overrightarrow{\mathrm{G}}, \overrightarrow{\mathrm{q}}+{\overrightarrow{\mathrm{G}}}^{\prime })$ of a semiconductor is computed in the pseudopotential scheme. The result is applied to the calculation of the phonon frequencies in the [100] direction of Si. The presence of off-diagonal dielectric terms introduces long-range forces and leads to real TA frequencies, thus avoiding the necessity of introducing explicitly a bond-charge model.

The optical absorptivity of dilute CuNi alloys at 4°K has been measured for photon energies between 0.1 and 3 eV and Ni concentrations between 0.5 and 4 at.%. The data are interpreted in terms of the Anderson model of magnetic impurities. A virtual bound state is found 0.75±0.02 eV below the Fermi energy with a half-width of 0.27±0.02 eV. The extra absorptivity of the alloy is found to arise predominantly from the scattering of the host conduction electrons in the presence of the virtual bound state.

We studied the second derivative of the magnetization with respect to the magnetic field, $\frac{d^{2}M}{d{H}^2}$, for polycrystalline materials having uniaxial anisotropy. Evidence is given of a singular point located at $H=H_A$, the anisotropy field. The observed sharp peak is associated with the infinity at $H=H_A$ of the $\frac{d^{2}M}{d{H}^2}$ curve for the single crystal in the hard direction. The detection of singularities is proposed as a new, and sometimes unique, method of measuring magnetic anisotropy using polycrystalline samples.

The analyzing power $A$ of the reaction $\mathrm{T}(p, n){}_{}{}^3{}_{}{}^{}\mathrm{He}$ has been measured at 45° c.m. from 1.5 to 12 MeV with a polarized proton beam. A comparison with existing data for the neutron polarization $P$ shows that $P$ and $A$ have similar excitation functions at this angle, but that the magnitude of $P$ is generally less than that of $A$. While the $R$-matrix formalism does not require exact equality between $P$ and $A$, we do not have at present a successful explanation of the observed differences.

A strong resonancelike structure (∼400 keV wide) has been observed in elastic ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ scattering. Inelastic scattering excitation functions with ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ in the unresolved $0^{+}$, $3^{-}$ states at 6.1 MeV show structure correlated with the elastic channel. An analysis of the angular distribution measured on the resonance indicates a spin $I=14\mathrm{}$.

Measurements of echo delays of radar signals transmitted from Earth to Mercury have yielded an accurate value for the advance of the latter's perihelion position. Given that the Sun's gravitational quadrupole moment is negligible, the result in terms of the Eddington-Robertson parameters is $\frac{(2+2\mathrm{}\gamma -\beta )}{3}\simeq 1.005\pm 0.007$, where $\gamma =\beta =1\mathrm{}$ in general relativity, and where 0.007 represents the statistical standard error. Inclusion of the probable contribution of systematic errors raises the uncertainty to about 0.02.

We have measured the quantity $\frac{\left|{\eta }_{00}\right|}{\left|{\eta }_{+-}\right|}$ which is defined in terms of $K_L$ and $K_S$ decay rates by the ratio ${\left[\frac{\Gamma (K_L\to {\pi }^0{\pi }^0)\Gamma (K_S\to {\pi }^{+}{\pi }^{-})}{\Gamma (K_L\to {\pi }^{+}{\pi }^{-})\Gamma (K_S\to {\pi }^0{\pi }^0)}\right]}^{\frac{1}{2}}$. We find $\frac{\left|{\eta }_{00}\right|}{\left|{\eta }_{+-}\right|}=1.03\mathrm{}\pm 0.07$.

We have measured the cross section for production of events in the $A_1$ mass region for two reactions: (1) ${\pi }^{+}p\to {\pi }^{+}{\rho }^{0}p$ and (2) ${\pi }^{-}n\to {\pi }^{-}{\rho }^{-}p$. The results of these experiments, both conducted at an incident pion momentum of ∼7 GeV/c, are interpreted within the framework of dual models of inelastic hadron collisions.

Assuming that hadrons are bound states of large numbers of partons and antipartons, we argue that the hadronic medium is characterized by a tension which is independent of the amount by which it has been stretched. The dynamically stable configurations of such a medium are spinning loops, where the tension is balanced against the centrifugal force. The corresponding Regge trajectories are in excellent agreement with experiment, but rise only like $s^{\frac{2}{3}}$ for large $s$.

We examine the quasilinear time evolution of a spin-flip maser system, the radiative corrections to the theory of spin-flip resonance, and saturation in spin-flip resonance spectroscopy.

It is shown that the nonlinear Boltzmann equation, as opposed to its linearized version, predicts time correlation functions with asymptotic tails $\simeq c{t}^{-\frac{3}{2}}$, and with coefficients $c$ in agreement with recently obtained results. The appropriate specialization of the mode-mode formula is also shown to follow from the nonlinear Boltzmann equation.

We have measured the mobility of negative carriers in liquid and gaseous neon. The results suggest that an electron injected in the liquid is localized in a bubble.

A localized collisionless instability that occurs in a nonuniform or skin current flowing along an external magnetic field is shown to produce an anomalous viscosity giving cross-field diffusion of the current. The instability can occur under conditions where the ion-sound wave is stable and is then the dominant process for penetration.

The Rayleigh linewidth $\Gamma$ of isobutyric acid in water has been measured by means of signal correlation at the critical solution concentration between 0.003 and 30°C above the critical mixing temperature $T_c$ over a range of scattering angles $\theta$ varying from 20° to 140°. The results are analyzed according to the mode-mode coupling theory of Kawasaki in the $K\to 0$ limit, and at $K\xi \gg 1$.