A unique feature of Cygnus X-3 is that occasionally it has large radio outbursts that begin very abruptly and last for several days. Several experiments in the past have claimed to observe signals above 1 TeV correlated with these radio bursts; the most recent bursts occurred in June and July 1989. No significant signal was observed by the CYGNUS experiment over time scales longer than a day during this time; a 90%-confidence-level limit of 3.0×${10}^{\mathrm{-}13}$ ${\mathrm{cm}}^{\mathrm{-}2}$ ${\mathrm{s}}^{\mathrm{-}1}$ is placed on the flux above 50 TeV during the period from 15 May to 31 July 1989.

Data collected by the E731 experiment at Fermilab were used to search for CPT violation in ${\mathit{K}}^0$→ππ decays by measuring the difference Δφ between the phases of the CP-violating parameters ${\mathrm{\eta }}_{00}$ and ${\mathrm{\eta }}_{+\mathrm{-}}$. Our result, Δφ=-0.3°±2.4°±1.2°, where the first error is statistical and the second systematic, is consistent with CPT symmetry.

A search for pair production of stable charged particles from Z decay has been performed with the Mark II detector at the SLAC Linear Collider. Particle masses are determined from momentum, ionization energy loss, and time-of-flight measurements. A limit excluding pair production of stable fourth-generation charged leptons and stable mirror fermions with masses between the muon mass and 36.3 GeV/${\mathit{c}}^2$ is set at the 95% confidence level. Pair production of stable supersymmetric scalar leptons with masses between the muon mass and 32.6 GeV/${\mathit{c}}^2$ is also excluded.

We have searched for supersymmetric particles in 528 Z decays with the Mark II detector at the SLAC Linear Collider. We place 95%-confidence-level lower mass limits on degenerate squarks, nondegenerate up-type squarks, nondegenerate down-type squarks, charginos, pair-produced unstable neutralinos, and neutralinos from associated production.

We are searching for the coherent production of light pseudoscalar or scalar particles in a 12-m optical cavity placed in a 5-T transverse magnetic field. From the level of the observed optical rotation we have set a limit on the coupling of such particles to two photons, ${\mathit{g}}_{\mathit{a}\gamma \gamma }$<2.5×${10}^{\mathrm{-}6}$ ${\mathrm{GeV}}^{\mathrm{-}1}$, provided ${\mathit{m}}_{\mathit{a}}$≲7×${10}^{\mathrm{-}4}$ eV.

We derive the Ward identities that determine the gauge dependence of the QCD dispersion relations obtained from the ordinary gluon propagator in a certain class of gauges. These identities hold for complex structure functions at both zero and finite temperature. A direct consequence of our analysis is that the gauge dependence of the gluon-plasma damping constant obtained in recent one-loop calculations is due to an inconsistent approximation scheme.

We discuss the effect of “color transparency” on J/ψ, ψ′, and χ photoproduction off nuclear targets. We find (contrary to the conclusion of other authors) that it is not an important effect for J/ψ production at present energies, so that existing experimental extractions of${\mathrm{\sigma }}_{\mathrm{\psi }\mathrm{N}}$ should be reliable. It may, however, be important when determining ${\mathrm{\sigma }}_{\mathrm{\psi }\prime \mathrm{N}}$ and${\mathrm{\sigma }}_{\mathrm{\chi }\mathrm{N}}$. © 1990 The American Physical Society

By exploiting a narrow-linewidth dipole-laser source we measure the hyperfine structure of the ${}_{}{}^5{}_{}{}^{}$${\mathit{S}}_2$ state of ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$. Nuclear parameters can be calculated from the measured hyperfine structure. Recorded collision-free linewidths allow an estimate of the lifetime of levels involved in a new scheme proposed for the cooling of atomic oxygen.

We show that a semiconductor laser switched from below to above threshold by a gradual increase of the optical gain, which follows a stepwise change of the injected current (gain switching), exhibits, besides a random distribution of the turn-on times, peculiar features in the time-intensity evolution. In particular, we find that the switching trajectories in the time-intensity plane cluster under a line at a nonzero angle off the time axis. This new effect can be used to discriminate transient fluctuations due to spontaneous emission against those arising from other effects.

A new method of measuring a coherence length in weakly turbulent systems at the onset of spatiotemporal intermittency is suggested. Our method is based on direct measurement of the distributions of the velocity and its spatial derivatives. We consider a coupled circle-map lattice, identify a coherence length, and determine its scaling properties. We also connect the coherence length to the Lyapunov exponent. The second-order phase transition observed when a cutoff is introduced is described in terms of percolation theory.

We present a variational calculation of free-electron-laser gain the exponential regime before saturation using a dispersion relation incorporating the energy spread, emittance, and focusing of the electron beam, and the diffraction and guiding of the radiation. Rapid computation facilitates free-electron-laser design optimization. Results are expressed in a universal scaled form.

Marked changes in the edge radial electric field ${\mathit{E}}_{\mathit{r}}$ and in the edge poloidal rotation velocity ${\mathit{v}}_{\mathrm{\theta }}$ are important signatures of the L-H transition in the DIII-D tokamak. Shear exists in ${\mathit{E}}_{\mathit{r}}$ and ${\mathit{v}}_{\mathrm{\theta }}$ and increases from the L mode to the H mode. A comparison of experiment with theory shows that shear in ${\mathit{E}}_{\mathit{r}}$ and ${\mathit{v}}_{\mathrm{\theta }}$ is sufficient to suppress edge fluctuations, that ion-orbit loss is large enough to be the source of ${\mathit{v}}_{\mathrm{\theta }}$, and that ${\mathit{E}}_{\mathit{r}}$ and ${\mathit{v}}_{\mathrm{\theta }}$ may play a causal role in the L-H transition.

A closed set of fluid moment equations is developed which represents kinetic Landau damping physics and which takes a simple form in wave-number space. The linear-response function corresponds to a three-pole (or four-pole) approximation to the plasma dispersion function Z. Alternatively, the response is exact for a distribution function which is close to Maxwellian, but which decreases asymptotically as 1/${\mathit{v}}^4$ (or 1/${\mathit{v}}^6$). Among other applications, these equations should be useful for nonlinear studies of turbulence driven by the ion-temperature-gradient or other drift-wave microinstabilities.

Low-frequency, flute-type electrostatic fluctuations propagating across a strong homogeneous magnetic field are studied experimentally. The fluctuations are generated by the Kelvin-Helmholtz instability. The presence of relatively long-lived vortexlike structures in a background of wideband turbulent fluctuations is demonstrated by a conditional sampling technique. It is demonstrated that in spite of the large-scale convection patterns associated with these structures, they can in some cases contribute only modestly to the turbulent plasma flux across the magnetic-field lines.

The problems of existence and stability of drift vortices in plasmas with density and temperature inhomogeneities are studied analytically and numerically. It is shown that basically two space scales are involved: (i) the ion Larmor radius at the electron temperature, where dipolar vortices exist, and (ii) a longer space scale on which monopolar vortices are possible. The latter are shown to survive finite disturbances. A Liapunov functional for structural stability is presented. The analytical predictions are verified by a 2D numerical simulation.

The effect of charge transfer (CT) on the Young’s modulus of trans-polyacetylene was studied with a molecular-orbital cluster model incorporating a charged soliton and with an infinite-chain model using band theory. The results of both models agree with one another very well. The Young’s modulus (Y) of trans-polyacetylene changes up to 7% with CT of up to 0.25e per CH unit. The calculated changes of the geometry upon CT agree with experiments. The asymmetry of the variation of structure and Y with respect to the sign of the CT is due to second-neighbor antibonding interactions in both the soliton and and models.

The spectrum of the transfer matrix of a semi-infinite two-dimensional Isin model with marginally inhomogeneous couplings has been determined exactly in the finite-size-scaling limit at the bulk critical point. Depending on the local temperature at the boundary the surface phase transition of this system is either of first order or of second order with nonuniversal critical exponents. For a second-order transition, the excitation energies of the transfer matrix are inversely proportional to the linear size (N) of the system, but the levels are not equidistantly spaced. On the other hand, for a first-order transition the lowest gap vanishes algegraically, but faster than 1/N.

The response of a growing crystalline dendrite to a brief localized heat pulse applied near its tip was investigated in a directional solidification experiment on succinonitrile containing 1% acetone. The induced deformation was initially unobservably small, but grew rapidly into a sidebranchlike feature with time. This observation supports the proposed selective amplification of noise mechanism for sidebranching. A prelimimary fit to our data of the Gaussian wave-packet description of Pieters and Langer and of Barber, Barbieri, and Langer indicates exponential growth of the perturbation with the 1/4 power of distance.

We present a microscopic identification of a hydrogen-related-complex defect in electron-irradiated, hydrogenated, boron-doped, single-crystalline silicon, by optical detection of magnetic resonance. The symmetry of this defect has been deduced as ${\mathit{C}}_{2\mathit{v}}$, and from the observed hyperfine interactions the defect is identified as a di-hydrogen–vacancy complex, where the H atoms passivate two of the four dangling bonds in a monovacancy. A spin-triplet is the lowest electronic excited state of the defect, which exhibits a strong recombination channel for the free-carriers.

Fragmentation measurements on doubly charged Au clusters show that clusters smaller than 18 atoms decay by fission (i.e., two charged cluster fragments) and neutral-atom evaporation. The fission probability is found to increase relative to the evaporation probability with decreasing cluster size, roughly as an exponential function of ${\mathit{z}}^2$/n, where n is the number of atoms in the cluster. The results are found to be in good agreement with an adapted version of the nuclear liquid-drop model.