An eight-loop superconducting magnetic monopole detector has been in continuous operation for 547 days, starting 4 March 1987. Its sensing area is 1.1 ${\mathrm{m}}^2$ for double-coincident events. The data, which contain no candidate events, set an upper limit of 7.2×${10}^{\mathrm{-}13}$ ${\mathrm{cm}}^{\mathrm{-}2}$ ${\mathrm{s}}^{\mathrm{-}1}$ ${\mathrm{sr}}^{\mathrm{-}1}$ (90% confidence level) on the flux of monopoles of any mass and at any velocity passing through the Earth’s surface.

A search for cosmic-ray magnetic monopoles has been conducted using a fully coincident superconducting induction detector consisting of six independent high-order gradiometer coils forming the surfaces of a rectangular parallelepiped. The detector had an effective area for isotropic flux averaged over 4π sr of 1.0 ${\mathrm{m}}^2$. Data have been collected from October 1986 to January 1989 with an accumulated live time of 13 410 h. No monopole candidate events were seen, setting a new lower monopole flux limit for induction detectors of 3.8×${10}^{\mathrm{-}13}$ ${\mathrm{cm}}^{\mathrm{-}2}$ ${\mathrm{s}}^{\mathrm{-}1}$ ${\mathrm{sr}}^{\mathrm{-}1}$ at the 90% confidence level.

We have measured the branching ratio Γ(${\mathrm{\Xi }}^0$→Λγ)/Γ(${\mathrm{\Xi }}^0$→Λ${\mathrm{\pi }}^0$) to be [1.06±0.12(stat)±0.11(syst)]×${10}^{\mathrm{-}3}$. In 670 000 Λγ candidates we found 116±13 ${\Xi }^0$→Λγ decays (background subtracted). These compare with 29 510 ${\Xi }^0$→Λ${\pi }^0$ events reconstructed from the Λγγ sample. Monte Carlo studies gave the relative acceptances for the two processes. The helicity of the Λ yielded the product of asymmetry parameters α(Λ→p${\mathrm{\pi }}^{\mathrm{-}}$)α(${\mathrm{\Xi }}^0$→Λγ)=0.27±0.28, which implies α(${\mathrm{\Xi }}^0$→Λγ)=0.43±0.44, where the uncertainty is all statistical.

Semi-inclusive spectra of ${\pi }^{\pm }$, $K^{\pm }$, and p have been measured near midrapidity for central collisions of 14.6A-GeV/c ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ with ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ nuclei. The invariant cross sections are all well fit by exponential distributions in transverse mass, within the measured ranges. The π and K cross sections can also be fit by Boltzmann distributions. From integrated yields, at midrapidity, the kaon/pion yield ratios are (19.2±3)% for $K^{+}$/${\pi }^{+}$ and (3.6±0.8)% for $K^{\mathrm{-}}$/${\pi }^{\mathrm{-}}$; the ${\pi }^{+}$/${\pi }^{\mathrm{-}}$ ratio is 1.00±0.04.

Beams of fully stripped nitrogen ions have been used to investigate the behavior of the double-to-single ionization cross-section ratio of helium in the 10–30-MeV/amu velocity region. The measured ratio was found to remain nearly constant over this velocity range at a value of 0.01, which is about 4.5 times higher than the high-velocity limit established previously for q=1 projectiles.

The occurrence of quantum beats for an extended exciton state in a solid is demonstrated for the first time. They are observed as oscillations in the two-phonon resonance fluorescence decay of the indirect free exciton states in AgBr split in magnetic fields up to 1 T after excitation by picosecond laser pulses. The results are in agreement with calculations by a density-matrix formalism. From the beating frequencies the splitting of the exciton states can be obtained with high accuracy. Quantum dephasing times of several hundred picosecond are determined comparable to the energy relaxation time.

We report a new cooling scheme used to actively collimate an atomic beam of ${}_{}{}^{85}{}_{}{}^{}\mathrm{Rb}$ with one-dimensional optical molasses. The atoms’ transverse velocity is damped by a standing wave of circularly polarized light in a magnetic field of ∼20 μT to 2 cm/s (rms), well below the Doppler velocity $v_D$=(7ħγ/20M${)}^{1/2}$∼10 cm/s for one-dimensional optical molasses. The minimum measured velocity is limited only by the experimental geometry. We have developed a model in which the mixing by the field and optical pumping combine to form a cycle that cools below the Doppler limit, in agreement with our measurements.

We present the results of high-frequency intense-laser numerical multiphoton experiments on a model atom. These results indicate both suppression of ionization and localization of the atomic electron even after a smooth laser turn on.

Symmetry arguments are used to classify the various modes of instabilities of one-dimensional periodic patterns. An important feature of this theory is to point out the coupling between these modes and the phase of the cellular structure. A number of results presented allow to interpret recent observations in hydrodynamical flows, directional solidification, and fingering experiments.

Two-dimensional numerical simulations of compressible, spatially evolving, unforced planar shear flows are used to investigate the role of feedback in the reinitiation of vortex roll up. The calculated pattern of coherent structures shows global self-sustaining instabilities in which new vortex roll ups are triggered in the initial shear layer by pressure disturbances originating in the fluid accelerations downstream. This reinitiation mechanism, absent in the linear treatments of stability, is demonstrated conclusively here.

Experiments show that the addition of small amounts of polymer to a Newtonian fluid undergoing chaotic advection decreases the amount of chaos; regular or unmixed regions increase in size and squeeze out the regions of chaotic behavior while preserving underlying symmetries. The size of the islands increases with increasing elasticity and rate of stirring. Large effects are present at relatively low Deborah numbers (relaxation time of the fluid to the time scale of the flow).

We derive equations of motion for a diluted gas of spiral defects in the two-dimensional complex Ginzburg-Landau equation. The interaction of two defects is treated and our predictions agree with a recent numerical experiment.

Through first-principles hydrodynamic calculations, the macroscopic behavior of the displacement of immiscible fluids in a capillary tube is linked to the microscopic parameters governing the dynamics of the moving contact line. Comparison with experimental data reveals that the contact line is dragged by a frictional force varying as $U^x$, where U is the mean flow velocity and x≃(1/2. Consideration of capillary-wave excitation at the fluid-fluid interface as the source mechanism of this frictional force yields predictions in excellent agreement with experimental data.

When a positive potential is applied to a spherical electrode in the presence of a low-pressure gas in a uniform magnetic field, a stable toroidal plasma can form around the anode. This plasma is produced by electrons which are trapped in the combined electric and magnetic fields. We present observations of some of the basic properties of this plasma as measured using electrostatic probes and a low-light-level camera. We interpret these measurements in terms of an extended treatment of electromagnetic ‘‘bottles’’ which have been predicted to exist in this system.

The nonlinear evolution of the modulational instability of whistler waves coupled to fast magnetosonic waves is investigated in two spatial dimensions by numerical simulations. The long time evolution of the modulational instability shows a quasirecurrent behavior with a slow spreading of the energy, originally confined to the lowest wave numbers, to larger and larger wave numbers resulting in an apparently chaotic or random wave field.

We report results of an investigation of the growth of the ${}_{}{}^3{}_{}{}^{}\mathit{B}$ phase into the hypercooled ${}_{}{}^3{}_{}{}^{}\mathit{A}$ phase. The form of the magnetization signal associated with the interface evolved radically with increased hypercooling, suggesting a transition to a new mode of growth. We propose a model based on magnetization transport by a spin supercurrent which accounts for many features of the data.

Experiments carried out at high pressures show that the transition of completely ordered solid ε-${\mathrm{N}}_2$ to orientationally disordered δ-${\mathrm{N}}_2$ is shifted over a factor of 2 in temperature or pressure due to the admixture of fluid helium. Between 5.4 and 11.0 mole % helium can be dissolved in ε-${\mathrm{N}}_2$, favoring the occurrence of this ordered phase. In contrast, the transition from disordered δ-${\mathrm{N}}_2$ to disordered β-${\mathrm{N}}_2$ is not shifted at all.

Mobile interacting quantum-mechanical kinks of very low mass explain the roton contribution to the growth resistance and the thermal phonon transmission coefficient of the rough surface of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ crystals.

An optical study of the smectic-O films which float on the free surface of droplets of racemate MHTAC [1(methyl)-heptyl-terephtalidene-bis-amino cinnamate] in the isotropic phase, is presented. It allows us to elucidate the herringbone structure of the molecules in this original liquid-crystal phase, and to estimate the dipole moment (∼5×${10}^{\mathrm{-}3}$ D) that the molecules bear in the first smectic layer in contact with the air.

A nematic liquid-crystal cylinder may exhibit metastable cholesteric-type twisted states in which the director uniformly rotates along the sample in the plane orthogonal to the cylinder axis. If a constant torque is maintained by strongly anchoring end plates, thermal fluctuations can produce rotation, leading to torsionally viscous behavior. We present a theory for the fluctuation-induced intrinsic torsional viscosity of narrow cylinders of nematic, based on the Frank free energy and constructed by analogy with the work of Langer and Ambegaokar on the resistance of superconducting channels.