We have analyzed data recorded by the Haverah Park extensive air-shower array above 5×${10}^{17}$ eV to search for a neutral particle signal from Cygnus X-3 as reported by the Fly’s Eye Group. For the period 1974 to 1987 we obtained a 95% upper limit of 4×${10}^{\mathrm{-}18}$ particles ${\mathrm{cm}}^{\mathrm{-}2}$ ${\mathrm{s}}^{\mathrm{-}1}$, in significant disagreement with the Fly’s Eye signal of (2.0±0.6)×${10}^{\mathrm{-}17}$ particles ${\mathrm{cm}}^{\mathrm{-}2}$ ${\mathrm{s}}^{\mathrm{-}1}$. The limit assumes that the neutral particles are hadronlike. For γ-ray primaries the limit is weakened to 8×${10}^{\mathrm{-}18}$ photons ${\mathrm{cm}}^{\mathrm{-}2}$ $s^{\mathrm{-}1}$ because of the reduced sensitivity of the Haverah Park array to photon primaries.

We present an exploratory computation of the electric dipole moment of the neutron induced by a CP-violating θ term in the QCD Lagrangian in the framework of quenched lattice QCD. We find $d_N$≊-4×${10}^{\mathrm{-}14}$θe cm.

A consistent method for the perturbative calculation of scattering amplitudes in hot gauge theories is developed. It involves the resummation of a subset of thermal fluctuations, termed hard thermal loops, into effective propagators and vertices. The damping rate of a heavy fermion is computed as an example.

We have observed orderly structure in the spectrum of lithium in the range -1≤E≤+8 ${\mathrm{cm}}^{\mathrm{-}1}$, in magnetic fields of approximately 6 T. The structure resembles series of Rydberg levels converging on Landau levels. Interactions between levels are evident, but the underlying orderly structure raises hopes that a quantum solution to the problem may be feasible. The structure occurs in a regime where the classical motion is believed to be chaotic.

We studied the Gγ=2 imperfection depolarizing resonance at 108 MeV, both with and without a Siberian snake, by varying the resonance strength while storing beams of 104- and 120-MeV polarized protons at the Indiana University Cooler Ring. We used a cylindrically symmetric polarimeter to simultaneously study the effect of a depolarizing resonance on both the vertical and radial components of the polarization. AT 104 MeV we found that the Siberian snake eliminated the effect of the nearby Gγ=2 depolarizing resonance.

With the use of a standard model, beam breakup growths in all types of linacs are shown to be classified by only two dimensionless parameters which depend on the beam current, beam energy, pulse length, machine length, breakup mode frequency, focal strength, and transverse shunt impedance. This classification suggests that rf cure plays a more important role in the control of beam breakup than focusing in a long pulse beam. The converse holds for a short pulse beam.

Observations of electromagnetic emission stimulated by a high-frequency radio wave injected into the ionosphere from a ground-based powerful transmitter operated near harmonics of the iono- spheric electron cyclotron frequency are reported. Significant changes in the spectrum of the stimulated electromagnetic radiation were obtained as the injected frequency was varied in small steps around these harmonics. The experimental results are attributed to nonlinear wave interactions involving electrostatic wave modes perpendicular to the local geomagnetic field.

It is observed that fast waves launched into an electron cyclotron heated plasma from a phased four-strip-line antenna array couple effectively with core electrons. This coupling produces enhanced electron cyclotron emission and a drop in the loop voltage. These effects depend on the phase difference between adjacent strip lines and on the electron density. An absorption efficiency of 20% is deduced under the conditions $v_{\mathrm{ph}}$/$v_{e0}$∼3 and $f_0$/$f_{\mathrm{LH}\mathrm{}\left(0\right)\mathrm{}\mathrm{\sim }0.38}$. The experimental results agree well with predictions based on electron Landau damping of fast waves.

We report what we believe to be the first direct visual observations of order-parameter fluctuations near a critical point. The observation has been made in a number of binary fluids which belong to the same universality class as the 3D Ising model. New properties can be investigated, in particular, the morphology of the flucutations when they are considered as clusters. This analysis has demonstrated the self-similarity of the clusters and provided a measurement of a fractal exponent ${\mathrm{D}}_{\mathrm{f}}$=2.8±0.1. .AE

A simple theory for melting, freezing, and phase coexistence is presented with special reference to small clusters and spinodal curves. This theory, which neglects fluctuations, coupled with the results of computer simulations, suggests a reevaluation of our interpretation of spinodals and first-order phase changes. We find sufficient, physically plausible conditions for a system of mutually attracting quasiparticles to give rise to stable, coexisting solidlike and liquidlike ‘‘isomers’’ of small clusters. These isomers are identifiable as the small-particle counterparts of metastable solids and liquids whose existences are bounded by spinodals; the theory implies the sharp termination of the spinodals.

We present a model of insulating glasses in which defects interact strongly via the elastic strain field. The interactions are oscillatory at short range and cross over to 1/$r^3$ interactions at longer length scales. This crossover is marked by a strong renormalization of the density of states and is consistent with the long phonon mean free path found at low temperatures.

We study surface and bulk equilibrium in Si-Ge alloys by direct simulation. The composition at a reconstructed (100) surface varies with depth in a complex oscillatory way. Lateral ordering occurs even in the fourth layer, driven by the local stress field. The bulk phase diagram is well described by regular solution theory.

The electronic structures of ${\mathrm{NiSi}}_2$/Si(111) A- and B-type interfaces are calculated within the local density approximation (LDA) using large supercells and the LMTO full-potential and ASA methods. The Schottky-barrier heights for the two interfaces differ by 0.14 eV, in agreement with experiment. The difference is caused by a partly filled interface band present in both structures. The LDA barrier heights $E_F$-$E_v$ are both 0.4 eV too low, and insensitive to interface relaxations and to external potentials. The correct density-functional expression for the barrier height is $E_F$-$E_v$+Δ$v_{\mathrm{xc}}$, where Δ$v_{\mathrm{xc}}$ is a nonlocal correction.

The angular distribution of the photoelectron yield excited by two coherently related photon beams has been calculated and measured. Dynamical Bragg diffraction from a Ge(111) single crystal was used to generate the two beams, and L-shell photoelectron yields from an I overlayer were measured with a variable-angular-acceptance detector. The use of two-beam photoelectric excitation to understand final-state angular momentum symmetry is demonstrated.

The local susceptibility of isolated Mo ions in Na is observed to be consistent with a localized, magnetic 4$d^5$ state of ${\mathrm{Mo}}^{1+}$. Size, valence, and bonds of such ${\mathrm{Mo}}^{1+}$ cells are similar to the host ${\mathrm{Na}}^{1+}$ cells. These features allow a study of 4d magnetism by local-spin-density calculations under the premise of substitutional Mo ions in Na. The calculations yield an effective moment of more than 5${\mu }_B$ for Mo in Na. In the larger hosts, K, Rb, and Cs, we propose unusual large lattice contractions around d ions with localized d states, up to 22% for the extreme case of ${\mathrm{Fe}}^{2+}$ in Cs. This results from impurity-host bond strengths larger than those between host atoms along with the very large compressibilities of K, Rb, and Cs.

Single-electron tunneling in Al/${\mathrm{AlO}}_{\mathrm{x}}$/Al junctions with areas below 0.01 μ${\mathrm{m}}^2$ was studied at temperatures close to 1 K. The junctions, placed in different high-frequency environments but similar in all other aspects, exhibited different dc I-V curves, in accordance with the theory of correlated single-electron tunneling. Our results imply that a tunneling electron can effectively probe its electrodynamic environment at distances much larger than c${\mathrm{\tau }}_{\mathrm{t}}$, where ${\mathrm{\tau }}_{\mathrm{t}}$ is the ‘‘traversal’’ time of its passage through the energy barrier.

The upper critical field of percolating lead films above and below the percolation threshold has been measured by monitoring the sample’s electrical resistance as a function of an applied magnetic field. We find that it remains constant across the threshold, as predicted by theory based on the fractal nature of the infinite clusters and of large finite clusters.

A hyperfine transition in the ground state of ${}_{}{}^9{}_{}{}^{}\mathrm{Be}_{}^{+}{}_{}{}^{}$ was used to test a nonlinear generalization of quantum mechanics recently formulated by Weinberg. We searched for a dependence of the frequency of a coherent superposition of two hyperfine states on the populations of the states. We are able to set a limit of 4×${10}^{\mathrm{-}27}$ on the fraction of binding energy per nucleon of the ${}_{}{}^9{}_{}{}^{}\mathrm{Be}_{}^{+}{}_{}{}^{}$ nucleus that could be due to nonlinear corrections to quantum mechanics.

The JANZOS Collaboration has reported a 2-day burst of TeV γ rays from SN 1987 A 11 months after the explosion. At this supernova epoch TeV γ rays can only be produced by inelastic proton interactions and secondary ${\pi }^0$ decay. The proton luminosity during the burst has to be 2×${10}^{39}$ ergs/s, in contradiction with the most recent estimates of the total power of an internal energy source. We suggest a burst model where the TeV γ-ray burst is produced by a previously accumulated proton beam, which is in agreement with the observed energetics of SN 1987A in all observation bands.

Astrophysical lower bounds on the neutrino mass require assumptions about the phase-space distribution in dark-matter halos. Even with perfect spherical symmetry, a collisionless dark-matter halo can have an anisotropic phase-space distribution from angular momentum conservation. An example gives much less restrictive condition on the neutrino mass, showing that bounds such as that of Tremaine and Gunn are model dependent. I conclude that current mass bounds on neutrinos derived from dwarf galaxy rotation curves are overly restrictive, so that neutrinos in the mass range of 10–100 eV remain a viable candidate for galactic dark matter.