A new technique for the measurement of frequency differences in NMR spectra to very high accuracy is presented. The technique has been used to measure frequency differences to a relative accuracy of 0.2 mHz and an estimated absolute accuracy of <1.0 mHz.

The drag force on an ion moving through liquid helium II at finite velocities is discussed in terms of localized roton states near the ion. These ideas are compared with experiments on positive and negative ions below 1°K.

A lattice model with short-range interactions is proved to condense and have a singular coexistence-curve diameter at the critical point.

The real part of the shear mechanical impedance has been measured for three smectic liquid crystals using a shear-wave reflection technique. Results at 30 and 450 MHz are considerably lower than those expected for an isotropic, Newtonian fluid, suggesting the existence of viscoelastic relaxation.

The speculations of Chester, Andreev and Lifshitz, and Leggett concerning the possibility of Bose-Einstein condensation and/or superfluidity in quantum crystals are examined. The existing body of experimental data on these systems places extremely strong constraints on the experimental realization of these speculations.

We have observed an exponential temperature dependence of the quantity $\frac{d{\rho }_f}{\mathrm{dH}}$, where ${\rho }_f$ is the flux-flow resistivity, in thin-film superconductors in the reduced temperature interval $0.7\lesssim \frac{T}{T_c}\lesssim 1.0$. The results can be explained qualitatively if it is assumed that the dominant contribution to the flux-flow viscosity is power dissipation resulting from the presence of thermodynamic fluctuations.

The frequency spectrum of the phonons generated by a superconducting SnO-Sn tunnel junction has been determined through the observation of resonance absorption by Sb donor levels in Ge. These measurements show that one can use such junctions to generate and detect milliwatts of phonon power at energies of $2\Delta$ (1.2 meV).

The dielectric theory of the chemical bond has been extended to calculate pressure coefficients of interband energy differences in acceptable agreement with experiment. Some improvements in Van Vechten's prescriptions are suggested by these new, more stringent tests. An approximate empirical rule for pressure coefficients is confirmed, and deviations from it predicted.

Intensity-energy low-energy electron-diffraction spectra of a clean xenon single-crystal surface have been measured for the first time, and show almost no secondary structure. A theoretical explanation is given based on the large atomic volume of xenon, and the short extinction distance (of about 5 Å) at 100 eV.

Tunneling measurements on junctions between very thin superconducting aluminum films and ferromagnetic nickel films in a high magnetic field show that the tunneling current is spin dependent. The effective tunneling density of states in Ni determined by this means implies a polarization of the magnetic moments of the Ni current carriers parallel to the applied field. The technique offers a new method for investigating spin-dependent states in magnetic materials.

The electroexcitation cross section for the second-order magnetic monopole transition $0^{+}\to 0^{-}$ has been calculated in ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$. It is assumed that the spectrum of intermediate excited states is complete and that energy loss may be neglected. If these approximations are valid, it should be possible to observe this transition.

Arguments are advanced in favor of the existence of an upper cutoff in the spectrum of solar protons. In the case of the event of 28 January 1967, on the basis of the recordings made by the worldwide network of neutron monitors, this cutoff is found to be 4.3 ± 0.5 GeV.

The differential cross sections for ${\pi }^{-}+p\to \gamma +n$ at ${40}^{\circ }<{\tilde{\theta }}_{\gamma }<{150}^{\circ }$ at c.m. total energies 1245 and 1337 MeV are presented. The results do not agree with predictions based on the $\Delta I<~1$ rule for the electromagnetic current and fixed-$t$ dispersion relations. Our data can be fitted with the Sanda-Shaw model, in which the electromagnetic current contains an isotensor component. Our angular distribution at 1337 MeV agrees with the inverse reaction as deduced from $\gamma d$ work; however, there is some disagreement at 1245 MeV.

Angular distribution for the reaction ${\pi }^{-}p\to \gamma n$ are analyzed. Existing sets of multipoles do not agree with the data. An acceptable fit is obtained with the Sanda-Shaw model of an electromagnetic current with an isotensor component of $-0.1>x>-0.4\mathrm{}$. The model of Christ and Lee is used to estimate the magnitude of a possible $T$-invariance violation implied by the difference between the data at $\tilde{E}=1245\mathrm{}$ MeV and the inverse reaction deduced from $\gamma d$ work. A strong violation in the isovector or isotensor amplitude is excluded, but a maximum violation in the isoscalar amplitude is possible.

We have determined the single-variable analyticity of the inelastic electron-scattering structure functions in the complex $x$ plane, with $s$ kept fixed and real, to all orders of Feynman perturbation theory. We find that its Landau singularities, which move as a function of $s$, rapidly approach their asymptotic $s$-independent position once $s$ is large. We discuss how this observation offers a possible explanation for a rapid approach to "universality" of the inelastic electron-scattering structure functions and shows that $s{W}_2(s,\frac{q^2}{s})$ should "scale" faster than $\nu W_2\mathrm{}(s,x)\mathrm{}$.

Direct electromagnetic generation of ultrasound has been observed in liquid mercury and cesium near room temperature. The observations are well accounted for by a local theory.

The simultaneous determination of the two spectra of entropy and concentration fluctuations in a binary solution yields the Rayleigh ratio related to the concentration fluctuations. The results are in good agreement with the theoretical predictions. The departure from ideality of the solution is given by the evaluation of the term $\frac{\partial \mu }{\partial c}$.

Pressure-gradient—driven drift waves have been identified in a collisionless ($n_0={10}^{10}$ ${\mathrm{cm}}^{-3\mathrm{}}$, $T_e=10\mathrm{}$ eV), 5.4-m-long, hydrogen plasma. Measurements show large but finite parallel wavelengths and short transverse wavelengths as predicted by the theory. For these wavelengths, computations give the maximum linear theoretical growth rate.

New Raman spectra obtained in large oriented crystals of paradeuterium and orthohydrogen give an unambiguous identification of the single-libron modes and remove all former reservations in assigning the $\mathrm{Pa}3\mathrm{}$ structure to the orientationally ordered phase.

Experimental data are interpreted as evidence that with increasing irradiation temperature above Stage I in metals there is an increasing probability that close pairs will dissociate. The dissociated partners contribute to the damage produced during elevated-temperature irradiations in the same way as free defects produced otherwise.