Steady-state current drive in tokamak plasmas during the parametric heating at frequencies higher than the lower-hybrid frequency is considered. The new effect of parametric generation of the steady-state current formed by suprathermal electrons and directed opposite to the main toroidal current is predicted. This effect can significantly affect the stability of tokamak plasma in the case of lower-hybrid heating.

A mechanism is proposed whereby high-phase-velocity lower-hybrid waves can interact with lower-parallel-velocity electrons through nonlinearly excited plasma waves. Significant steady-state current can be sustained by the rf after the Ohmic field is turned off in a tokamak provided the initial electron distribution is in the runaway regime with density below a critical value.

The growth of ion waves at a wave number of $2k_{\mathrm{pump}}$ has been studied in a C${\mathrm{O}}_2$-laser-plasma interaction, by use of Thomson scattering. Time- and wave-number-resolved spectra have been obtained. Harmonic generation has been observed in the ion-wave spectrum. Saturation of the reflectivity is also observed. These results are consistent with nonlinearities in the ion wave affecting both the damping and the interaction length.

Dynamical theory yields a simple expression for the integrated intensity $I_{0H}$ of a symmetric two-beam Bragg reflection versus azimuthal angle around $\overrightarrow{\mathrm{H}}$, perturbed to first order as another reciprocal lattice point $\overrightarrow{\mathrm{L}}$ approaches the Ewald sphere. Around the three-beam point $I_{0H}$ shows pronounced asymmetry sensitive to the magnitude and phase of the product of all three structure factors. The fully quantitative description allows optimization of the conditions for determination of that phase. It applies regardless of inversion symmetry.

High-resolution neutron-diffraction measurements have been performed on a single crystal of ${\mathrm{Eu}}_x{\mathrm{Sr}}_{1-x}\mathrm{S}$ for $x=0.52\mathrm{}$, an insulating spin system with competing exchange interactions. No detectable long-range magnetic order is observed at any temperature. However, intense magnetic diffuse scattering, well described by a Lorentzian, is present. As the temperatre is reduced from 6 to 0.4 K, the magnetic correlation length $\xi$ increases to a resolution-limited maximum (> 400 Å) at 2.5 K, and subsequently decreases.

Dielectric relaxation measurements are reported in KTa${\mathrm{O}}_3$: Li and interpreted in terms of a Gaussian distribution of logarithmic relaxation times. The center and width of this distribution depend continuously on temperature, and reveal no signs of critical effects at the freezing temperature. It is suggested that the same mechanism governs freezing in KTa${\mathrm{O}}_3$: Li, spin-glasses, the quadrupole glass KBr: CN, and the tunneling-dipole glass KCl: OH.

The upper critical field $H_{c2\mathrm{}}$ of the random percolating superconductor InGe has been measured as a function of the metal volume fraction $x$. Near the percolation threshold $x_c$, $H_{c2\mathrm{}}$ diverges with a critical exponent which is significantly smaller than that of the normal-state resistivity. An interpretation of this behavior is proposed in terms of the properties of the infinite cluster.

A linear-response theory leads to a generalized additional boundary condition (ABC) which includes as special cases all the well-known ABC's. Calculations for the reflectivity are compared with an experimental spectrum of CdS. Strong evidence is found in favor of the Pekar ABC and against other ABC's. Comparison with an attenuated total reflectivity spectrum of ZnO suggests that a more sophisticated surface response is necessary for semiconductors with a small exciton-free surface layer.

A force-measuring system composed of a macroscopic harmonic oscillator, mechanical-electrical transducer, and linear amplifier is described and the sensitivity is calculated for a "back-action evasion" mode of operation. It is shown that it is possible to surpass the standard amplifier limit with this device, and the specific requirements to do so are given. These results may also apply to a quantum-limited amplifier and thus give the requirements to perform quantum-nondemolition measurements.

Molecular dynamics simulations have been used to compute the thermal conductivity of the strongly coupled, nearly classical hydrogen plasma. The relaxation of a suitably defined heat current is significantly faster than the decay of the microscopic electric current. Electrical and thermal conductivities are not related by a simple Wiedemann-Franz law in the dense plasma.

A velocity- and mass-independent search for moving magnetic monopoles is being performed by continuously monitoring the current in a 20-${\mathrm{cm}}^2$-area superconducting loop. A single candidate event, consistent with one Dirac unit of magnetic charge, has been detected during five runs totaling 151 days. These data set an upper limit of 6.1×${10}^{-10\mathrm{}}$ ${\mathrm{cm}}^{-2\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ ${\mathrm{sr}}^{-1\mathrm{}}$ for magnetically charged particles moving through the earth's surface.

Fast-neutron emission from the giant quadrupole resonance in ${}_{}{}^{119}{}_{}{}^{}\mathrm{Sn}$ was studied for the first time by measuring the deexciting neutrons in coincidence with the inelastic ${\alpha }^{\prime }$ from the reaction ${}_{}{}^{119}{}_{}{}^{}\mathrm{Sn}(\alpha , {\alpha }^{\prime })$. The neutron time-of-flight spectrum shows both the slow evaporation component corresponding to the spreading process and the fast component corresponding to the direct escape leading to single-hole states in the residual nucleus ${}_{}{}^{118}{}_{}{}^{}\mathrm{Sn}$.

Previous interacting-boson-approximation studies of deformed nuclei have used different forms of the quadrupole operator in the Hamiltonian and $E2\mathrm{}$ operators. A revised formalism is proposed which employs consistent operators and embodies a simpler Hamiltonian. It yields improved agreement with the data for deformed nuclei, a number of parameter-free predictions for transition regions, a specific form of the O(6) limit which agrees with that found empirically, and a closer relation to the neutron-proton version of the model, IBA-2.

Angular distributions for the electronic to vibrational-rotational and translational energy transfer process ${\mathrm{Na}}^{*}\mathrm{}\left(3p\right)+{\mathrm{H}}_2, {\mathrm{D}}_2\to \mathrm{Na}\mathrm{}\left(3s\right)+{\mathrm{H}}_2(v^{\prime }, j^{\prime })$ with product energy analysis have been measured for the first time. The differential cross sections are forward peaked, constant but small between 35° and 160°, and very slightly increasing at 180°. The observations can be qualitatively understood by a simple model for the particle motion on the attractive $\tilde{A}{}_{}{}^2{}_{}{}^{}B_2^{}{}_{}{}^{}$ excited-state surface with a hop to the repulsive $\tilde{X}{}_{}{}^2{}_{}{}^{}A_1^{}{}_{}{}^{}$ ground state.

The intensity of the pure rotational spectrum of gaseous HD is measured as a function of density to determine the dipole moment in the ground vibrational state. $J$-dependent values are found in the range (8.0-9.8) × ${10}^{-4\mathrm{}}$ D which, contrary to previous determinations of Trefler and Gush, agree reasonably with ab initio calculations. Intracollisional interference is taken into account and its $J$ dependence determined.

Recent experimental results of Kaminishi et al. on the photon statistics of a dye laser are compared with the exact solution of a laser model with fluctuating pump parameter.

The steady-state saturated-evaporation theory of a cold cloud in a hot tenuous atmosphere developed by Cowie and McKee is applied to the evaporation of pellets injected into tokamak plasmas. The agreement with limited experimental results is found to be quite good, and extrapolation of the theory to a reactor-size tokamak indicates a required pellet injection velocity of 5×${10}^6$ cm/sec. Finally, the experimental evaporation times can be viewed as a measurement of the classical flux-limit parameter, which is found to be $f=0.6\mathrm{}$.

By use of a director representation, it is proved that the disordered phase in cholesterics becomes thermodynamically unstable with respect to a localized mode. It is argued that this instability provides a basis for understanding the experimentally observed "fog" or "gray" phase.

Observations of stable, freely suspended liquid-crystal strands are reported. Liquid crystals of triphenylene hexa-$n$-dodecanoate can be stretched into strands of diameter ≳1 μm, with the disk-shaped molecules arranged into columns along the strand axis. In the $D1\mathrm{}$ phase ($T<\mathrm{}110\mathrm{}°$ C) the molecules are tilted with respect to the strand axis, the tilt orientation behaving as a one-dimensional nematiclike field, interrupted by jumps in orientation between degenerate stable positions relative to the column lattice.

With use of a delayed-field technique, the unusual observation has been made that the quantum efficiency in poly(N-vinyl carbazole), for a given field, is the same whether the pulse photoexcitation occurs with the field applied or delayed up to many seconds. A possible explanation is that the geminate recombination rate is sufficiently slow that it allows the photogeneration process to be time resolved.