The $Q$-machine "edge oscillation" is identified as a Kelvin-Helmholtz instability by a comparison of theory with experiment. Specifically, measurements of frequency and of radial variation in wave phase and amplitude agree with numerical integrations of the radial wave equation, including finite parallel wavelength. The computations show that the instability is caused principally by velocity shear.

Previous experimental results on the feedback stabilization of a "drift-type" instability are interpreted in terms of a nonlinear theory of the Van der Pol type. This theory predicts a variation of the instability amplitude and its frequency as a function of the gain and the phase angle in the feedback loop. Comparison between these predictions and the experimental results shows remarkably good agreement.

Novel resonances in the acoustoelectric gain have been observed in pure $n$-InSb at longitudinal magnetic fields corresponding to the well-known Gurevich-Firsov magnetophonon resonances. The magnetoacoustoelectric resonances were obtained at 77 and at ${4.2}^{\mathrm{°}}$K, with acoustic phonons internally amplified from the thermal background. The resonant peaks in the gain are attributed to resonant cooling of hot carriers by the resonant enhancement of optical-phonon induced transitions between Landau levels.

In narrow-gap semiconductors, the energy of conduction-electron plasma oscillations can be made equal to the band gap by doping. When such a crystal is pumped with an electron beam or light wave, stimulated emission of plasma waves takes place. Estimates of growth rate suggest that, in ${\mathrm{Pb}}_{1-X}{\mathrm{Sn}}_X\mathrm{Se}$ and ${\mathrm{Pb}}_{1-X}{\mathrm{Sn}}_X\mathrm{Te}$ alloys, collisional losses can be overcome and the plasma waves excited to high amplitude.

Experimental data on the Hall effect and the resistivity anomaly are analyzed using the two-current conduction model; information is obtained on the Fermi surfaces of Ni.

All of the normalization factors used in the zero-range distorted-wave Born-approximation analysis of single-nucleon stripping reactions with projectiles of $A<~4$ can be calculated by use of Hulthén potentials with a common short-range parameter $\beta =1.36\mathrm{}$ ${\mathrm{fm}}^{-1\mathrm{}}$ and long-range parameters $\alpha$ obtained from the nucleon-separation energy from the projectile. The values obtained are in close agreement with previous determinations.

Electroexcitation of ${\mathrm{C}}^{12}$ in and above the giant resonance has been measured at several angles and incident electron energies in order to obtain transverse and longitudinal reduced matrix elements. Results are presented for a $q$ range of from 0.35 to 0.84 ${\mathrm{fm}}^{-1\mathrm{}}$ and for excitation of 22-37 MeV. Comparison is made with the recent calculation by deForest of quasielastic scattering, as well as with earlier particle-hole and liquid-drop-model calculations.

A summary is given of the statistics and coincidences of the Argonne-Maryland gravitational-radiation-detector array. New experiments have been carried out. These include a parallel coincidence experiment in which one coincidence detector had a time delay in one channel and a second coincidence detector operated with no time delays. Other experiments involve observations to rule out the possibility that the detectors are being excited electromagnetically. These results are evidence supporting an earlier claim that gravitational radiation is being observed.

McCusker and Cairns have published data on cloud-chamber tracks which they claim to be less ionizing than would be possible for singly charged particles, thus giving positive evidence for the existence of quarks of charge $\frac{2}{3}$. They neglected the effects of the relativistic rise of ionization in the gas of their cloud chamber and we believe they underestimated the errors of their drop count. Considering the fluxes of known particles in the cosmic rays it is concluded that their results can be explained as due to statistical fluctuations.

Accelerated protons and ions are observed when an intense relativistic electron stream is propagated through a gas-filled region. Several proton momentum peaks are observed for each stream pulse with a spread of ≤10%, consistent with our resolution. Proton energies are independent of the filling gas for ${\mathrm{H}}_2$, ${\mathrm{N}}_2$, and air. Total ion fluxes are ${10}^{13}$ to ${10}^{15}$ particles/stream pulse. Nitrogen-ion tracks were too short to determine the charge state and hence the energy, but estimated upper limits suggest +4 or +5, consistent with the energy-to-change ratio observed for protons.

A model for high-energy hadron reactions is proposed, incorporating ideas borrowed from the duality scheme of strong interactions and from the quark version of the parton model for inelastic electron-hadron scattering. Experimental tests of the model are discussed.

A quantitative explanation is given, using Regge poles and cuts, for unexpected features of total cross sections in the newly accessible range 25-65 GeV/c. Negative contributions from the leading vacuum cuts explain the leveling out of ${\sigma }_T\left(K^{-}N\right)$ and ${\sigma }_T\left({\pi }^{-}N\right)$ above 25 GeV/c; they also reconcile the apparently nonconverging $K^{\pm }N$ results with a common asymptotic limit, in accord with the Pomeranchuk theorem.

We consider a model for the pion electromagnetic form factor based on duality and Regge asymptotic behavior for strong interactions. We find that $F_{\pi }\mathrm{}\left(t\right)\mathrm{}\underset{t\to \infty }{\to }{t}^{-\frac{1}{2}}$ and that vector dominance is expressed through second-order poles as $t$ approaches the masses of vector mesons.

The zero-field hyperfine frequencies in the ground state of atomic ${\mathrm{N}}^{14}$ have been measured in a hydrogen maser with sufficient accuracy to resolve the quadrupole coupling constant $B$. The result is $B=+1.32\mathrm{}\pm 0.20$ Hz.

The zero-field level-crossing signal of even isotopes of natural Hg excited by resonant collisions from directly excited ${\mathrm{Hg}}^{198}$ atoms has been observed with circularly polarized light. The signal is proportional to the atomic "orientation" (mean value of the angular momentum of the excited atoms). The sense of this orientation is reversed when the excitation is transferred by collisions from ${\mathrm{Hg}}^{198}$ to other isotopes, as predicted by the theory.

It is proposed that the temperature of mesomorphic-isotropic phase changes and of transitions between mesophases may be markedly shifted by manageable electric fields. First experiments demonstrating such a shift in the nematic-isotropic transition of $p$-ethoxybenzylidene-$p^{\prime }$-aminobenzonitrile are reported.

We show that the low-temperature specific-heat anomaly in bcc solid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ can be explained in terms of an indirect interaction among pairs of spins brought about by virtual absorption and emission of phonons in the exchange process.

Large-amplitude ion-acoustic waves ($\frac{e\varphi }{k{T}_e}\lesssim 0.3$) are excited in the University of California, Los Angeles double-plasma device by the interpenetration of two plasmas with high electron-to-ion temperature ratios ($6<\mathrm{}\frac{T_e}{T_i}<20\mathrm{}$). A compressional wave with a ramp shape is found to steepen in a fashion consistent with the classical overtaking predicted by the usual Riemann invariants. This steepening continues until dispersive short scale ($k\approx \frac{1}{2}{k}_{\mathrm{D}}$) oscillations develop at the front. Ions streaming in front of the shock are also observed.

A new electric-field-induced color range, in which colors change from blue to red with increasing field, has been observed in cholesteric liquid crystals. Observations of this new color range quantitatively confirm the theories of Meyer and de Gennes and enable identification of the specific nature of the electric-field-induced cholesteric-nematic phase transitions previously observed by other workers.

It is shown that low-energy electrons (<40 eV) excite luminescence in CdS at ∼80°K by direct electron-hole pair production. Momentum in pair production is conserved without phonon participation.