Flow phenomena in the $A$ phase of superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ have been studied by observing the transverse NMR signal. Marked changes occur in the presence of flow, including structure and satellite signals, step changes in signal amplitude at particular velocities, and rapid attenuation of the signal beyond some critical velocity. Little, if any, change of frequency of the signal is produced by flow.

The coefficients in the Callan-Symanzik equations for a three-dimensional, continuous spin Ising model with an $\exp (-A{s}^4+B{s}^2)$ spin-weight factor are expanded in the dimensionless, renormalized coupling constant. These series are summed by the Padé-Borel method to yield the critical indices $\gamma =1.241\mathrm{}\pm 0.002$, $\eta =0.02\mathrm{}\pm 0.02$, $\nu =0.63\mathrm{}\pm 0.01$, and ${\Delta }_1=0.49\mathrm{}\pm 0.01$.

In a simple search for muon pairs directly produced in proton-nucleon collisions at 300 GeV performed with two range telescopes looking at a beam dump, we observe the $\psi \left(3.1\mathrm{} \mathrm{GeV}\right)$ and have an indication for a structure around ${m_{\mu \mu }}^2=36\mathrm{}$ Ge${\mathrm{V}}^2$.

The effects of isospin mixing observed by isospin-forbidden resonant proton scattering from the stable, self-conjugate, even-even nuclei exhibit a simple dependence on target mass number $A$. Furthermore, for $A=8n+4\mathrm{}$, $n$ integral, the mixing is systematically a factor of 5 larger than for $A=8n$ The relation between this behavior and the trends of other relevant nuclear properties is discussed.

We report the first observation of photon echoes in an organic mixed crystal. The echo was observed after excitation with a nitrogen-laser-pumped dye laser in the ${}_{}{}^1{}_{}{}^{}B_{2\mathrm{u}}^{}{}_{}{}^{}\leftarrow {}_{}{}^1{}_{}{}^{}A_g^{}{}_{}{}^{}$ electronic transition at 3739.9 Å of pyrene in biphenyl at 2 K. The photon-echo excitation spectrum of the origin (zero-phonon line) region shows that drastic variations occur in the coherence lifetime of sites which, qua incoherent (fluorescent) decay, are indistinguishable.

Because of its electrostatic properties, the rate of the parametric growth of the kinetic Alfvén wave [Alfvén wave with $\lambda \equiv \frac{{k_{\perp }}^2{c_s}^2}{{{\omega }_{\mathrm{ci}}}^2}\sim O\left(1\right)\mathrm{}$] is shown to be larger than that of the classic result by a factor of $\frac{\lambda {\omega }_{\mathrm{ci}}}{{\omega }_{\mathrm{A}}}$, where ${\omega }_{\mathrm{ci}}$ and ${\omega }_{\mathrm{A}}$ are the ion-cyclotron and the Alfvén frequencies, $k_{\perp }$ is the perpendicular wave number, and $c_s$ is the ion sound speed. This fact can be utilized to heat a plasma with typical tokamak parameters.

A theoretical and experimental investigation of the time evolution of instabilities in counterpenetrating, low-density, nonrelativistic electron beams is reported. The dominant nonlinear effect is the dispersion in energy of the beam electrons by wave-particle interactions. A large change in the frequency of the fastest growing mode is predicted at moderate values of beam temperature (corresponding to $k_{\perp }{\lambda }_D\sim 1$). An experiment designed to detect the new mode is performed. The observations confirm the theoretical model.

An inhomogeneous plasma layer is unstable under intense laser irradiation as applied in laser fusion experiments. Experimental observations support the results of recent two-dimensional computer simulations.

Using a very sophisticated light-beating spectrometer and a new correlation technique, we have measured the relaxation time of entropy fluctuations in a critical binary mixture in the reduced temperature range of $4\times {10}^{-6\mathrm{}}<~t<~{10}^{-1\mathrm{}}$. In the hydrodynamic regime this relaxation time, which is proportional to the specific heat at constant pressure and critical concentration, is found to behave as $t^{-\alpha }(1+{\mathrm{Bt}}^{+\mathrm{x}})$ with a critical exponent $\alpha =0.059\mathrm{}\pm 0.003$ and $x=1.05\mathrm{}\pm 0.15$.

From light scattered by director modes in the smectic-$A$ phase of cyanobenzylidene octyloxyaniline (CBOOA) and octyloxy cyanobiphenyl (80CB) we deduce that the restoring force for phase fluctuations in the smectic order parameter vanishes as ${(T_c-T)}^{0.33}$ as the nematic phase is approached. In CBOOA the force maintaining the molecules normal to the layers vanishes as ${(T_c-T)}^{0.50}$. We conclude that de Gennes's analogy between charged superfluids and the smectic-$A$ phase is not entirely correct.

We present a phenomenological theory, valid for $\hslash \omega \ll \Delta \mathrm{}\left(T\right)\mathrm{}$, which incorporates the ideas of Cross on normal-superfluid locking but uses quite different kinematics. Our results agree with his in the "overdamped" region, while we also predict a low-temperature "flapping" mode, orbital effects on the NMR, and a linear orbit-wave spectrum at $T=0\mathrm{}$.

Effects of electron-electron interactions on cyclotron resonance are studied in a model two-dimensional system. The position of the subharmonic structure is mainly determined by the dressed mass $m^{*}$, while that of the main peak is given by the bare mass $m$. This explains the fair agreement of the effective mass obtained by Smith and Stiles and that deduced from the position of observed subharmonic structure of the cyclotron resonance in inversion layers.

We consider the influence of a periodic lattice upon the plasmon energy in a metal, by means of the equation of motion proposed by March and Tosi. The solution, within the random-phase approximation and for a weak periodic potential, shows the existence of two plasmon bands separated by a complex energy gap near the Brillouin zone border. This gap, due to plasmon Bragg diffraction, is rapidly quenched in presence of damping in simple metals. Group-IV metals and semiconductors should offer better chances for the observation of these "nearly-free-plasmon" bands near the Brillouin zone border.

The mobility ${\mu }_{+}$ of positrons in Ge has been measured. Energetic positrons from a radioactive source enter an intrinsic planar Ge detector where they annihilate in the presence of the detector bias field. The motion of the positrons is detected by observing the Doppler shift of the annihilation $\gamma \text{'}\mathrm{s}$ as a function of the voltage across the detector. We obtain ${\mu }_{+}=(124\mathrm{}\pm 10)$ ${\mathrm{cm}}^2$ ${\mathrm{V}}^{-1\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ at (93±5) K and ${\mu }_{+}=(350\mathrm{}\pm 17)$ ${\mathrm{cm}}^2$ ${\mathrm{V}}^{-1\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ at (36±5) K.

Inelastic neutron scattering measurements on single crystals of cubic ${\mathrm{Na}}_x\mathrm{W}{\mathrm{O}}_3$ reveal a large concentration-dependent Kohn anomaly in the [100] longitudinal acoustic-phonon dispersion curve. The results demonstrate the two-dimensional character of the Fermi surface, support the rigid-band model for $0.56<x<\mathrm{}0.83\mathrm{}$, and conflict with the percolation model which has just recently been proposed to explain the transport properties of the tungsten bronzes.

We find strong polarization effects in the angular-resolved energy distribution of photoelectrons emitted from a Cu(111) surface using plane polarized light at normal incidence with $\omega =10.2\mathrm{}$ eV. This polarization dependence reveals the symmetry and $\overrightarrow{\mathrm{k}}$ vector of the states involved, in particular for excitation from $d$ states. The spectra can be interpreted assuming direct transitions between bulk states and subsequent elastic emission. No evidence for many-body effects or modification of the states at the surface is observed.

Photoluminescence data for $\mathrm{Ga}{\mathrm{As}}_{1-x}{\mathrm{P}}_x$ alloys implanted with nitrogen are reported for $0.28\lesssim x\lesssim 1.0$ and for N concentrations from ${10}^{16}\lesssim N_{\mathrm{N}}\lesssim {10}^{20}$ ${\mathrm{cm}}^{-3\mathrm{}}$. Evidence is presented of a new excited shallow bound state (${\mathrm{N}}_{\Gamma }$) of the isolated N impurity, coexisting with the tightly bound ground state (${\mathrm{N}}_X$) of this center. The two levels are associated primarily with nonequivalent conduction-band minima.

All effects of target and constituent masses on the $Q^2$ dependence of lepton-hadron scattering are computable in an expansion in $g\left(Q^2\right)$, the effective coupling of asymptotic freedom. To leading order, these are summarized by a "best" scaling variable, $\xi$, which depends on the particular process. The results relevant to low $Q^2$ and charm threshold are discussed.

We have measured the ratio, $\frac{Y^{+}}{Y^{-}}$, of positron to electron inelastic scattering yields from hydrogen and deuterium at $Q^2$ the square of the four-momentum transfer, between 2.4 and 14.9 ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$. The ratios are consistent with $\frac{Y^{+}}{Y^{-}}=1\mathrm{}$ to within errors of a few percent.

A simple dynamical model is used to calculate the partial rates for various decay modes of charmed pseudoscalar and vector mesons. Our results together with the presently available data lend support to the hypothesis that the lowest-lying charmed particles are vector mesons. It is suggested that the multiparticle state $K^{-}{\pi }^{+}{\pi }^{-}{\pi }^{+}$ should be produced fairly copiously in charmed-vector-meson decays, which could offer a fruitful way of identifying charm.