Anomalously high values of the superconductive transition temperature $T_c$ are correlated with anomalies in bond lengths in intermetallic compounds. The bond length anomalies arise from anharmonic stabilization of harmonic lattice instabilities, and confirm this interpretation of recent neutron studies of short-wavelength vibrational anomalies.

The possibility of making a new form of hydrogen in the metallic state through preparation of the compound Li${\mathrm{H}}_2$F is discussed. A proposed structure is specified which is believed to be nearly stable under ambient conditions. The pressures needed to stabilize this compound and to convert it to a metal are estimated. It may have an exceptionally high hydrogen density, high electrical conductivity, high Debye temperatures in the hydrogen sublattice, and perhaps a high superconducting transition temperature.

Modulation of photoemission from $n$-type GaSb by additional light leads to the conclusion that the surface dipole (i.e., the electron affinity and the ionization energy) of semiconductors is influenced by the electric field of the space charge. Comparison of calculated with observed modulation yields an escape depth of 100 Å for photoelectrons from clean surfaces.

Experimental current-voltage characteristics and potential distributions are presented for a $p-n$ junction in high-resistivity GaAs, whose dielectric relaxation time ${\tau }_D$ exceeds carrier lifetime ${\tau }_0$. The condition ${\tau }_D>{\tau }_0$ defines the new "relaxation regime" for which theory predicts behavior entirely different from that of the familiar ideal rectifier of conventional semiconductor physics with ${\tau }_D\ll {\tau }_0$. The predicted field distributions and the linear and sublinear current-voltage relationships are observed. These results confirm the theory in detail.

The upper branch of an exciton-polariton curve is measured directly for the first time. The two-photon spectrum of the first exciton line of CuCl shows a strong dependence on the total $K$ vector of the two beams. The resulting dispersion curve can be quantitatively explained using one-photon data.

Using a very pure single crystal of magnesium we have observed large-amplitude oscillations in the transverse magnetoresistance which result from the direct interference of normal-state electron waves. The amplitudes of these interference oscillations appear to be independent of the $\mathrm{kT}$ broadening of the Fermi distribution. The primary result of our experiment shows that these waves are phase coherent at 1.2°K over macroscopic distances of at least 0.01 mm; this corresponds to a quasiparticle lifetime of at least 2 ×${10}^{-11\mathrm{}}$ sec.

Measurements of the linear growth rate and the first two nonlinear saturation coefficients are reported for magnetothermal pinch oscillations, instability oscillations that spontaneously grow to a saturated amplitude in nonequilibrium electron-hole plasmas in InSb. Also shown is the suppression and, to a lesser degree, enhancement of the instability oscillations by feedback.

The nuclear quadrupole moment $Q$ of ${\mathrm{Fe}}^{57m}$ has been determined from the calculated electric field gradients (including all the metal-ion-ligand overlaps) and the quadrupole splitting data in ${\mathrm{Fe}}_2$${\mathrm{O}}_3$ and ${\mathrm{Al}}_2$${\mathrm{O}}_3$:${\mathrm{Fe}}^{3+}$. The values of $Q\left({\mathrm{Fe}}^{57m}\right)$ obtained in the two cases are 0.180 ± 0.015 and 0.204 ± 0.018 b which are consistent with the values reported in ferrous compounds, thus disposing of the well-known ferrous-ferric anomaly.

The asymptotic decay of the two-point correlation function $G_{\mathrm{AB}}\left(\overrightarrow{\mathrm{R}}\right)$ at and near a phase-separation point is discussed for $d$-dimensional, spin-½ Ising models at low temperature. The general behavior, even on the phase boundary ($H=0\mathrm{}$), is in agreement with extended Ornstein-Zernike predictions. It is shown why the nearest-neighbor two-dimensional model in zero field is an exception. The decay of $G_{\mathrm{AB}}({\overrightarrow{\mathrm{R}}}_1,{\overrightarrow{\mathrm{R}}}_2)$ near a free surface at high temperatures agrees with phenomenological predictions using a vanishing boundary condition. At low temperature, however, the decay of correlation near a surface is exponentially slower than in the bulk.

It is shown that, contrary to popular belief, diffraction scattering in nuclear and particle physics is not always of Fraunhofer type. By establishing a simple physical connection between scattering in a Coulomb field and Fresnel diffraction we show that diffractive collisions of heavy charged particles are predominantly of Fresnel type. We derive quantitative criteria for Fraunhofer and Fresnel scattering which lead to a new classification of all scattering processes.

The reaction ${}_{}{}^{92}{}_{}{}^{}\mathrm{Mo}({}_{}{}^3{}_{}{}^{}\mathrm{He},d){}_{}{}^{93}{}_{}{}^{}\mathrm{Tc}$ leading to unbound isobaric analog states (IAS) has been studied. A distorted-wave Born-approximation analysis of the IAS using unbound single-particle form factors is shown to provide good fits and reasonable spectroscopic factors for (${}_{}{}^3{}_{}{}^{}\mathrm{He},d$) data from this and other work in the $A=90\mathrm{}$ region. Calculations for available ($d,n$) reaction data result in spectroscopic factors which are lower than the (${}_{}{}^3{}_{}{}^{}\mathrm{He},d$) values.

It is shown that a precise account of the nonlocal aspects of the low-energy nucleon-nucleus interaction can be made by means of a simple effective-mass approximation provided that one invokes the correct effective mass of the problem. Unlike conventional descriptions with energy-dependent local potentials, the effective-mass description is seen to involve the true geometric parameters of the interaction.

The differential scattering cross sections have been measured for electron scattering from randomly oriented and aligned ${\mathrm{Ho}}^{165}$ nuclei. The alignment axis was parallel to the direction of the momentum transferred to the nucleus. Incident electron energies from 160.6 to 462.2 MeV were used at a fixed polar scattering angle of 36°. Available theories are unable to explain the measured difference between the aligned and nonaligned cross sections.

A cloud chamber of horizontal area 0.2 ${\mathrm{m}}^2$ is being used to observe the ionization by the particles in the vicinity of the center of air showers in the manner of McCusker. No particle tracks with ionization typical of charge $\frac{2}{3}e$ or $\frac{1}{3}e$ have been found in 3200 shower photographs taken with a trigger rate of about one per hour.

An attractive $K^{-}$-nuclear strong interaction as favored by a recent measurement weakens the atomic binding. The repulsion is due to the absorption in the nucleus and starts to dominate over the strong attraction. It is also against normal perturbation calculational experience that a smaller absorptive potential may produce a higher absorption rate. These highly nonlinear phenomena are displayed. The gradient potential has little influence for kaonic atoms.

With the use of a dispersion relation and a high-energy cutoff, the model involving $\pi$, $\rho$, $\omega$, ${\eta }_V$, $f$, and $\sigma$ ($0^{+}$, $I=0,416\mathrm{}$ MeV) is studied for nucleon-nucleon interactions below 3 GeV. All nucleon-nucleon elastic-scattering data and those for $p-p$ collisions at 0.67, 0.97, and 1.4 GeV are in qualitative agreement with the calculations.

A symmetry argument is presented that gives a relation between the small-momentum limits of the reactions $\gamma +\gamma \to$ odd number of pions, as calculated explicitly from a single nucleon (or quark) loop in a theory with a formally conserved axial-vector current. These limits are nonvanishing as a consequence of the Adler anomalies in the divergence of the axial-vector current. It is argued that the relationship derived should be true in any chiral model. The cross section for $\gamma +\gamma \to {\pi }^{+}+{\pi }^{-}+{\pi }^0$ is calculated in terms of the measured ${\pi }^0\to 2\gamma$ decay rate.

Using the $\pi N$ phase shifts and fixed-$t$ dispersion relations we have calculated (to first order in symmetry breaking) the nucleon matrix element of the current algebra "sigma" term, and found a value of about 110 MeV. This is an order of magnitude larger than the prediction of the ${(3,3^{*})}^{\oplus }(3^{*},3)$ model for chiral symmetry breaking and it indicates that $\mathrm{SU}\mathrm{}\left(2\right)\mathrm{}\otimes \mathrm{SU}\mathrm{}\left(2\right)\mathrm{}$ breaking is comparable to SU(3) breaking.

The ratios of x-ray yields from the irradiation of Ti, Cu, and Au targets with $\alpha$ particles and deuterons of identical velocities have been determined between 6.25 and 20 MeV/amu. At the lowest velocities the data for $K$ x rays from Ti and Cu indicate deviations as large as 12% from the theoretical ratios calculated according to the Born approximation. No significant deviation is observed for $L$ x rays from Au.

Formulas are derived, in the two-state approximation, for the cross sections for ion-atom atom excitation and excited-state ion capture for the case when the exctied states are nearly degenerate. Under certain conditions the theory predicts oscillations in the total excitation and capture cross sections resulting from interference between the two degenerate final channels, in qualitative agreement with the measurements of van den Bos on ${\mathrm{H}}^{+}$-He excitation collisions and of Hughes et al. on capture into excited states of H.