Long-time pulsations of stimulated Brillouin backscatter may occur in plasmas with sufficiently strong ion-acoustic damping in the presence of a negative feedback of the scattered wave.

The development of noninductive current drive is of great importance in establishing the tokamak as a long-pulse or steady-state fusion reactor. Lower hybrid waves, carrying 200 kW of power at 800 MHz, have been launched into the Princeton Large Torus tokamak to initiate and drive the discharge current to a level in excess of 100 kA.

Equilibrium crystals of Pb in the temperature range 200- 300°C exhibit facets and curved surfaces which are joined at "smooth" edges (no slope discontinuity). Recent theoretical interpretation has suggested that the crystal shape near such edges should show interfacial critical anomalies. Observation via scanning electron microscopy of 2-10-μm Pb crystals reveals a critical exponent which is consistent with theoretical identification as belonging to the Pokrovsky-Talapov universality class.

The "density functional" theory of freezing predicts that in the one-component plasma, (i) the density change on freezing is exactly zero, (ii) the liquid freezes to a bcc solid with an entropy change $\Delta S\approx -0.9\mathrm{Nk}$, and (iii) there exists a metastable fcc solid phase which has everywhere a slightly greater free energy than the bcc phase.

This paper presents the results of experimental measurements and a mean-field-theory analysis of the behavior of the average tilt angle near the smectic-$C^{*}$ to smectic-$A$ transition in thin films of two through ten molecular layers. These films provide one of the few physical realizations of systems where the surface layers remain ordered to a higher temperature than the bulk. The mean-field theory provides excellent quantitative fits to the critical-temperature spectrum and good qualitative fits to the order-parameter behavior.

Numerical techniques are used to obtain the value $\lambda =0.33\mathrm{}\pm 0.03$ for the exponent characterizing the energy dependence $\rho \propto E^{-\lambda }$ of the total density of spin-wave states in the diluted two-dimensional Heisenberg ferromagnet at the percolation threshold. The result supports a crossover relationship to static exponents. It is also consistent with a recently calculated dynamic exponent, with current fractal viewpoints and analyses, and with the Alexander-Orbach conjecture.

Brillouin scattering spectra in water both in the normal and in the metastable (supercooled) regions are investigated. The experimenal data are extended for the first time in a bulk sample down to -27.0°C. A refined analysis method allows the authors to obtain hypersonic absorption and velocity. The data are briefly analyzed in the frame of both a relaxation process and a heterophase-fluctuation hypothesis.

A theory for the low-voltage impedance of a superconductor-insulator-normal metal tunnel junction is developed that includes the effects of charge imbalance and of quasiparticle fluctuations. A novel, inelastic, charge-imbalance relaxation process is identified that is associated with the junction itself. This new process leads to the surprising result that the charge-imbalance component of the dc resistance of a junction becomes independent of the electron-phonon scattering rate as the insulator resistance decreases.

It is shown that the simplest nontrivial stochastic model for dielectric breakdown naturally leads to fractal structures for the discharge pattern. Planar discharges are studied in detail and the results are compared with properly designed experiments.

Spontaneous current oscillations which develop chaotic behavior are reported for an electron-hole plasma in a crystal of Ge at 77 K in parallel electric and magnetic fields. The observed behavior includes a period-doubling route to chaos with increasing applied electric field, regions of broadband noise which contain noise-free periodic windows, and bifurcations from quasiperiodic states to turbulence. A rate-equation model, which includes nonlinear coupling between unstable and damped plasma density waves, is presented.

The resonance frequency of an electric dipole placed near a conducting surface is shifted by the dipole-surface interaction. This Letter reports the observation and measurement of these shifts at optical frequencies for an experimental system that consists of a metal island film spaced a distance $d$ from a continuous Ag film. The dependence of the shift in the frequency of the island resonance on $d$ shows good agreement with that predicted by a classical theory of the dipole-surface interaction.

This paper reports the results of an experimental high-pressure study of solid oxygen at low temperature up to 60 kbar. Librons and vibron were observed with Raman light scattering. Evidence is presented for a low-temperature phase transition at about 9 kbar. Very recently a phase transition was predicted in this temperature and pressure regime. However, the overall agreement with theory is modest.

This paper reports a study of the dynamics of highly concurrent computing structures capable of learning and storing several input patterns. The existence of attractors in their dynamical behavior leads to a novel self-repairing mechanism. Quantitative experiments on adaptive processor arrays demonstrate the existence of attractive fixed points in their adaptation and recognition properties, as well as the immunity of these collective computation machines to random errors.

A scaling theory is developed to describe the time evolution of the irreversible diffusive recombination process $A+B\to \mathrm{inert}$. Fluctuations are shown to alter radically the decay laws predicted from the rate-equation approach. For unequal initial densities, the minority species is predicted to decay as $t^{-\alpha }$ for short times, crossing over to an $\exp (-A{t}^{\alpha })$ decay for long times, with $\alpha =\frac{d}{4}$ and $\alpha =\frac{\mathrm{}(d+1\mathrm{})\mathrm{}}{4}$ for unbiased and biased diffusion, respectively.

A Nambu—Jona-Lasinio type model is proposed as an effective Lagrangian for quantum chromodynamics at intermediate length scales. It is shown that the $\mathrm{SU}\mathrm{}\left(n\right)\mathrm{}\otimes \mathrm{SU}\mathrm{}\left(n\right)\mathrm{}$ non-linear $\sigma$ model, including the Wess-Zumino term, can be derived from it in the low-energy limit. Also presented is the effective nonminimal action whose minima correspond to baryons in the many-color limit.

It is pointed out that if heavy $\left[O\right(\mathrm{TeV}\left)\right]$ fermion generations exist and if the source of their masses is the single doublet of the Glashow-Weinberg-Salam model {with a light $[<~O(\frac{1}{2}\mathrm{TeV}\left)\right]$ physical Higgs} then very tightly bound exotic $\mathrm{LQ}$, $L\overline{Q}$, $\mathrm{QQ}$, $\mathrm{LL}$, etc., states may arise marking a dramatic appearance of new physics. In passing there is recalled the phenomenological observation that a discovery of a top quark via its semileptonic decay will practically exclude charged Higgs particles in the mass range $m_t-m_b>~m_{H^{+}}$.

By use of variational arguments and flavor independence, mass inequalities are derived between ground-state mesons, $m_{x\overline{y}}>~\frac{1}{2}(m_{x\overline{x}}+m_{y\overline{y}})$, and baryons, $m_{\mathrm{xyy}}>~\frac{1}{2}(m_{\mathrm{xxy}}+m_{\mathrm{yyy}})$.

Inclusive electrons have been studied in hadronic events from $e^{+}{e}^{-}$ annihilation at 29 GeV. The cross section is measured as $\sigma (e^{+}{e}^{-}\to e^{\pm }X)=35.8\mathrm{}\pm 4.6$ pb in the momentum range $0.5<p<\mathrm{}5.5\mathrm{}$ GeV/c. The semielectronic branching ratios of $b$ and $c$ quarks are found to be (14.6 ± 2.8)% and (9.1 ± 1.3)%, respectively. Hard fragmentation functions are found for both $b$ and $c$, with $〈Z_b〉=0.78\mathrm{}\pm 0.05$ and $〈Z_c〉=0.69\mathrm{}\pm 0.06$. No evidence of anomalous electron production is observed.

First results for ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}({\pi }^{\pm },{\pi }^{\pm }p){}_{}{}^{15}{}_{}{}^{}\mathrm{N}_{\mathrm{g}.\mathrm{s}.\mathrm{}}^{}{}_{}{}^{}$ at 240 MeV for ${\theta }_{\pi }=35\mathrm{}°, 60°, \mathrm{and} 130°$ in quasifree kinematics are reported. $\frac{{\pi }^{+}}{{\pi }^{-}}$ cross-section ratios much greater than for scattering by free protons are interpreted as due to a $\Delta -N$ interaction interfering with the quasifree process.

Nonrelativistic nucleon-nucleus first-order multiple-scattering calculations are extended to include virtual (Dirac) negative energy states of just the projectile. This effect may be thought of as virtual $N\overline{N}$ pair production and annihilation in the field of the nucleus. This extension leads to a parameter-free Dirac description of the projectile in elastic proton scattering which produces a characteristic effect in spin observables over a wide range of energies which is in agreement with experiment. This Dirac signature is extremely stable with respect to uncertainties in the microscopic input.