It is shown that the time component of axial currents in nuclei can be given a simple description in terms of a one-pion exchange diagram with its structure constrained by a soft-pion theorem. We suggest the directional correlation measurements in nuclear $\beta$ decay as a possible means to test the theory.

Observed transitions in the reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({\pi }^{+}, p){}_{}{}^{11}{}_{}{}^{}\mathrm{C}$ at 49.3 MeV confirm the importance of multistep processes in the reaction mechanism. The relative intensity of the transitions is nearly the same as in the reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}(p, d){\mathrm{C}}^{11}$ at 700 MeV, except for an apparent isospin selection rule. Transitions to low-lying states in ${}_{}{}^{10}{}_{}{}^{}\mathrm{C}$ via the reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({\pi }^{+}, d)$ have also been observed.

A classical, linear theory is given for the gain of a short-wavelength free-electron laser. Waves propagating along the relativistic beam are unamplified when the beam is cold. Two of the six geometric optics modes have phase velocities $<c$. When thermal effects are included, the theory predicts the possibility of substantial amplification of these two modes for asymmetric electron distribution functions, due to wave-particle resonance.

A hollow, rotating 2.3-MeV electron beam, moving with axial velocity of ∼0.25c after injection through a magnetic-field cusp, is slowed down and trapped in a small magnetic mirror well by interaction with a 30-60-Ω/square resistive wall. The trapped-electron ring containing ∼ ${10}^{12}$ particles performs a damped oscillation about the well minimum and settles down into an equilibrium state.

The Rayleigh-Taylor instability is generated in a plasma flowing along a curved magnetic field. The instability, which appears only in the bad-curvature region of the magnetic field, is controlled by changing the flow speed and Larmor radius of the ions. A drastic suppression of the instability is observed in the presence of weak magnetic shear.

A hot ion plasma (${\overline{E}}_{i\perp }\simeq 400$ eV, $n\simeq {10}^{13}$ ${\mathrm{cm}}^{-3\mathrm{}}$) is trapped in a minimum-$B$ mirror system. A strong instability at ${\omega }_{\mathrm{ci}}$ is observed for neutral densities <${10}^{11}$ ${\mathrm{cm}}^{-3\mathrm{}}$. We have observed the suppression of this instability when an electron beam (≥42 kW) is injected into the plasma. We believe the suppression is due to a population of hot electrons produced and trapped in the mirror by the beam-plasma interaction.

The dispersion relations for molecular-orientation fluctuations in a freely suspended ferroelectric smectic-$C$ liquid-crystal film have been determined by inelastic light scattering. The smectic-$C$ film geometry appears to be ideal for the experimental study of the space-time behavior of a two-dimensional orientational field.

We report careful measurements of the Rayleigh linewidth of light scattered from a critical binary fluid. Laser heating and multiple-scattering effects are accounted for. With use of independent data for $\xi$ and the shear viscosity, a parameter-free fit is obtained with theory in the region $55>k\xi >0.32\mathrm{}$. The renormalization-group-modified mode theory is shown to be necessary; however, we find a value of the dynamical exponent $z=2.992\mathrm{}\pm 0.014$ instead of 3.065.

We show that in a nonequilibrium, two-dimensional superfluid near the critical point, the energy for dissipative fluctuations is greatly reduced as a result of screening by the gas of bound vortex pairs, leading to an enhanced decay of the superfluid velocity. We also show that the superfluid density is reduced by a velocity-dependent amount as $T_c$ is approached from below.

Dissipation of energy by a thin film of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ on an oscillating planar substrate arises both from motion of free vortices and from polarization of bound pairs. Starting from a Langevin equation for vortex diffusion, and taking into account production of free vortices from bound pairs, we estimate this dissipation in various regimes of frequency, amplitude of vibration, and temperature.

Phonons incident on an Al-PbBi tunnel junction were found to be detectable only if their frequency exceeds a voltage-tunable threshold. Modulating this threshold yielded a phonon spectrometer with a resolution of 10 GHz at a phonon power of ${10}^{-6\mathrm{}}$ W and a frequency range from 100 GHz up to several hundred GHz.

The critical behavior of magnetic resonance linewidths has been measured at fixed frequencies between 0.7 and 9.6 GHz. At sufficiently low frequencies, the derived Onsager coefficient of the spin-relaxation rate "speeds up" with ${\chi }^{\frac{7}{4}}$ in the exchange critical region ($\chi \ll 1$) and flattens around $\chi =1\mathrm{}$ when reaching the crossover to the dipolar region. These results turn out to be quantitative confirmations of current mode-coupling calculations.

In two recent moleuclar-dynamics experiments on two-component ionic fluids it was observed that the plasma frequency was shifted with respect to its mean-field value. This effect is explained here on the basis of a microscopic theory. The shift is shown to exhibit a strong plasma parameter dependence.

Nuclear acoustic-resonance absorption and dispersion of both isotopes ${\mathrm{Mo}}^{95}$ and ${\mathrm{Mo}}^{97}$ have been observed for the first time in molybdenum. From quantitative evaluation of the nuclear-acoustic-resonance results in the conduction-electron contribution to the tensor $\overleftrightarrow{\mathrm{S}}$ connecting the electric field gradient to elastic strains have been determined at high magnetic fields. Comparison of the electronic contributions to the diagonal and offdiagonal elements of the electric-field gradient in Mo, Ta, and Nb show a disparity in the dependence on the density of states.

We have determined the magnetic structure of neodymium metal by combining the results of neutron diffraction studies on single crystals of neodymium with the results of Landau symmetry arguments and renormalization-group theory. The spins form a unique, two-dimensional, incommensurably modulated structure accompanied by a similarly modulated lattice distortion. The experimental value of the critical exponent $\beta =0.36\mathrm{}\pm 0.02$ is in agreement with the theoretical prediction of $\beta \sim 0.38$.

It is suggested that the suppression of normal photoemission from surface states on a W(100) surface near the plasma frequency is due to refraction effects. Two model calculations are presented which are expected to bracket the real situation, and they both exhibit this property. Possible additional effects of refraction on the photoemission cross section are discussed.

Auger-electron spectroscopy is shown to measure something quite different from photoemission: the distribution of atomic (as opposed to overlap) charge populations across the valence bands. While matrix-element effects must be considered in $s-p$ band materials, their inclusion in calculations still lead to poor agreement with experiment. Good agreement may be obtained, however, if one divides the electronic charge into atomic and overlap (bonding) LCAO components and notes that the latter does not contribute to the Auger current.

First measurements of the time for the recovery of the critical current at a phaseslip site have been made by studying the frequency dependence of the hysteretic rf current-voltage characteristics in the low-power limit. The data are incompatible with recent hot-spot models but can be expalined by a model relating a nonequilibrium length to the critical current.

It is shown that the first atomic layer of trivalent metallic samarium has a large divalent component. The valence transition is attributed to a narrowing of the $5d$ band which populates the low-lying $4f^6$ state.

The frequency dependence of the relaxation parameter which determines the line shape of the Mössbauer spectrum in spin-spin relaxation is derived directly from the experimental spectrum for the case of the 84-keV resonance of ${}_{}{}^{170}{}_{}{}^{}\mathrm{Yb}$ in ${\mathrm{Cs}}_2$NaYb${\mathrm{Cl}}_6$. The scale of the frequency variation of its relaxation parameter is in agreement with a theoretical estimate.