Changes in flow stress, which occur in indium at the transition from the normal to the superconducting states, have been studied in a series of experiments in which strain rate, state, and temperature are changed independently. The results are consistent with a simple theory which associates the changes in flow stress with changes in activation volume and thus with the nature of the interaction between moving dislocations and obstacles.

We propose as a model of some amorphous semiconductors a system with undulations in composition or structure on a scale within the range of validity of the graded bandgap concept. Electronic states well within allowed bands are determined by perturbative analysis; states near band edges, by a modification of an effective-mass analysis. Localized states are obtained and the band edge identified as the locus of classical turning points of the effective mass functions.

The absorption spectrum of solid thin films of neon has been recorded at 4.2 K in the photon energy range from 15 to 25 eV. The first three terms of the hydrogenic series, corresponding to the resonance doublet of the free atom, have been identified and the energy gap at the $\Gamma$ point is calculated to be 21.42 eV.

The reflection and transmission spectra of solid Ne films have been measured at 6°K for photon energies between 10 and 35 eV where transitions from the valence band occur. The use of the continuous spectrum of synchrotron radiation of DESY enabled us to resolve an exciton series with sharp maxima beginning at 17.8 eV and converging to 21.4 eV. At higher energies solid Ne exhibits additional weak structures in the conduction-band continuum.

Anamalous temperature-dependent photoemission has been measured from the silver halides. Structure in the photoelectron energy distributions sharpens dramatically as samples are cooled from 295 to 80°K. We believe this is due to a lattice vibrationally dependent hybridization of the halogen $p$ and silver $d$ valence states. Using this effect, we have experimentally located the Ag states with almost pure $4d$ symmetry at 3.7 and 3.3 eV below the highest valence states in AgBr and AgCl, respectively.

The importance of orbital paramagnetism in a weakly exchange-enhanced dilute solution of transition-metal impurities in a nonmagnetic host metal is demonstrated both theoretically and experimentally. It is shown that the orbital and spin contributions to the nuclear resonance shift and relaxation rate separately satisfy a Korringa-like relation. These relations may be used to determine uniquely the individual contributions. The sensitivity of the analysis to crystal-field effects is discussed.

Measurements of the electrical and thermal resistivity in longitudinally saturated $〈111〉$ iron crystals provide evidence that the temperature-dependent transport is dominated by electron-electron scattering from 0.28 to 20°K. The ideal Lorenz number is nearly constant below 40°K and has a value of 1.09 × ${10}^{-8\mathrm{}}$ W Ω/${\mathrm{deg}}^2$ from 40 to 6°K and a value of 1.16 × ${10}^{-8\mathrm{}}$ W Ω/${\mathrm{deg}}^2$ below 6°K.

The negative magnetoresistance in ${\mathrm{Fe}}_3$${\mathrm{O}}_4$ crystals at 77°K was found to saturate at about 9 kG and to increase with increasing electric field. The magnetoresistance data are explained in terms of spin disorder scattering. In the presence of a magnetic field the switching in this material can be advanced if voltage pulses are applied, and delayed if current pulses are applied. These findings are shown to be in quantitative agreement with the magnetoresistance data and the expectations from Joule self-heating.

The absorption of SrTi${\mathrm{O}}_3$ below the fundamental edge shows, near liquid-nitrogen temperature, an oscillatory behavior, for which an explanation is proposed in terms of indirect transitions ${\Gamma }_{15}\to X_3$, centered around 3.27 eV and involving a 51-meV LO phonon. There is no evidence of excitonic effects. The first direct transition is probably $X_{5^{\prime }}\to X_3$ and is located at ∼3.46 eV. Broadening effects mask the indirect structure at higher temperatures where the absorption curves gradually evolve into normal Urbach tailing.

From threshold photoneutron cross-section and angular-distribution measurements on ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$, seven $1^{+}$ states have been detected, which have a total $M1\mathrm{}$ strength of 51 eV. This $M1\mathrm{}$ strength, centered at an excitation energy of 7.9 MeV and spread over a range of 700 keV, constitutes at least half and perhaps all of the total $M1\mathrm{}$ strength obtained from shell-model calculations.

The process $\gamma p\to {\rho }^{0}p\to {\pi }^{+}{\pi }^{-}p$ has been studied with linearly polarized photons between 1.4 and 3.3 GeV. We observe almost pure diffractionlike behavior in the whole energy region.

It is shown that the hadronic decay modes of the weak intermediate boson $W$ produced by high-energy neutrinos provide a unique and unambiguous experimental signal of the production and decay of the $W$, even in the absence of any information about the number, the configuration, or the momenta of the decay products. This method of detecting the hadronic decay modes of the $W$, in conjunction with previously utilized methods for detecting the leptonic decay modes, should allow a search for the $W$ to be made which is independent of any assumptions about the hadronic-to-leptonic branching ratio of the $W$.

An experiment on photoproduction of muon pairs with invariant masses between 930 and 1770 MeV is reported. The measured invariant-mass spectrum is in good agreement with theoretical quantum electrodynamics predictions plus a contribution from $\varphi \to {\mu }^{+}+{\mu }^{-}$ at invariant masses near 1020 MeV. A quantum electrodynamics cutoff $\Lambda >~1.9$ BeV (2 standard deviations) and a $\varphi \to {\mu }^{+}+{\mu }^{-}$ branching ratio equal to (2.17 ± 0.06) × ${10}^{-4\mathrm{}}$ are obtained. For masses above the $\varphi$, limits which are approximately 100 times smaller than the rho are placed on resonance production.

Results valid for arbitrarily high intensity of electromagnetic field are presented for induced emission from an excited state of an atom. Comparison with perturbation theory shows that perturbative calculations fail quantitatively and qualitatively at lower intensity than had been expected. Distinctive intense-field features are discussed such as vanishing of the transition probability for certain intensities and photon multiplicities, and appearance of two extrema of the transition amplitude for multiphoton processes at very high intensities.

The time-dependent variation of the photoelectric counting probability has been measured for a $Q$-switched single-mode laser, whose steady state is in the neighborhood of the threshold of oscillation. The mean and the variance of the instantaneous light intensity, at various times and for various pump parameters, are derived and found to be in very good agreement with the values predicted by Risken and Vollmer.

We give an analytical consideration of the relaxation of the distribution function for systems of particles with Coulomb interaction. It takes into account two-particle correlations which correspond to formation of some macroparticles, i.e., coherently moving regions. It is argued that such relaxation leads to the Lynden-Bell distribution with an additional high-energy tail.

We have accurately measured the Brillouin spectrum of pure xenon along the critical isochore using two high-resolution spherical Fabry-Perot interferometers in tandem. The spectrum, which contained an extra diffusive mode, is analyzed in terms of a hydrodynamic model employing a relaxing bulk viscosity. We obtain the temperature dependence of the relaxation time, the bulk viscosity, the specific heat ratio $\frac{C_p}{C_v}$ at finite $k$ and $\omega$, the correlation range, and the $k=0\mathrm{}$, $\omega =0\mathrm{}$ values for the compressibility and $C_p-C_v$.

Ultrasonic attenuation in Xe has been measured along a near-critical isochore at frequencies in the range 0.4-5 MHz and at temperatures above $T_c$. Hypersonic attenuation values obtained from Brillouin linewidths are also cited. It is shown that the critical attenuation per wavelength depends on temperature and frequency through a single reduced variable ${\omega }^{*}=\frac{\omega }{{\omega }_{\mathrm{D}}}$, where the characteristic frequency ${\omega }_{\mathrm{D}}=\left(\frac{2\Lambda }{\rho C_p}\right){\xi }^{-2\mathrm{}}$. The experimental results are compared with numerical calculations based on a recent theoretical formulation by Kawasaki.

The sound velocity in xenon on the critical isochore was determined in Brillouin scattering measurements at scattering angles of 40° and 90°. The sound dispersion calculated from our data, ultrasonic data, and other Brillouin data agrees with the Kawasaki theory for a particular choice of parameters, but the dispersion in the Brillouin velocities is 2 to 3 times smaller than the theory predicts when values obtained for the parameters from other experiments are used.

The Rayleigh linewidth $\Gamma$ of xenon was measured on the critical isochore between 0.003 and 5.0°C above $T_c$. In the hydrodynamic region ($q\xi <~0.2$) we find $\Gamma =q^2{\chi }_0{\left[\frac{(T-T_c)}{T_c}\right]}^{\gamma -\psi }$ with ${\chi }_0=(6.94\mathrm{}\pm 0.21)\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^2$/sec, and $\gamma -\psi =0.751\mathrm{}\pm 0.004$. Our data over the entire region $0.009<~q\xi <~6.7$ agree quite well with the recent Kawasaki extended mode-mode coupling theory. However, the Kadanoff-Swift-Kawasaki result $\gamma -\psi =\nu$ does not appear to be valid.