We present an analytic wave function describing a spin-singlet incompressible fluid of electrons confined to a single Landau level, which exhibits a half-integral quantum Hall effect. Our numerical studies suggest that this state may be responsible for the recently observed effect with ν=(5/2. .AE

Photon-stimulated desorption of ${\mathrm{F}}^{+}$ from Si(111) was studied with use of photon energies in the region of the Si 2p core level. Fluorinated surfaces with variable amounts of ${\mathrm{SiF}}_{\mathrm{x}}$ groups were prepared, and distinct photon-stimulated–desorption thresholds in the Si 2p region were observed for ${\mathrm{F}}^{+}$ desorption from SiF vs ${\mathrm{SiF}}_3$ surface groups. In addition, the angular distributions of the ejected ${\mathrm{F}}^{+}$ showed variations with respect to the Si(111) surface normal dependent on the bonding configuration, which were used to obtain local 2p absorption spectra for the individual ${\mathrm{SiF}}_{\mathrm{x}}$ groups.

We point out that the nondiffracting ${\mathrm{J}}_0$ beams of Durnin, Miceli, and Eberly are subgroup-reduced basis functions for the group of paraxial (symplectic, linear) transformations of optical phase space. This allows the action of the group on such and similar beams to be computed through 2×2 matrix algebra.

Examples of time-dependent kinematic magnetic dynamos arising from chaotic flows in the zero-resistivity limit are presented. These examples suggest that typically (1) the flux concentrates on a fractal, and (2) the magnetic field exhibits arbitrarily fine-scaled oscillations between parallel and antiparallel directions. Results quantitatively relating these effects to the dynamo growth rate are presented.

We have demonstrated 42% squeezing of 4.2-K thermal noise using a Josephson-parametric amplifier operated at 19.4 GHz. The amplifier has been operated at 0.1 K with an excess noise of 0.28 K referred to the input port. This is less than the vacuum fluctuation noise hν/2k=0.47 K at 19.4 GHz. The amplifier thus is less noise than a linear phase-insensitive amplifier such as a maser could in principle be.

Solar or supernova neutrinos incident on an iodine-bearing liquid will produce the noble gas ${}_{}{}^{127}{}_{}{}^{}\mathrm{Xe}$ (${\tau }_{1/2}$=36.4 d), which can be recovered and counted as in the present ${}_{}{}^{37}{}_{}{}^{}\mathrm{Cl}$ experiment. The rate of neutrino reactions per unit volume of detector could be more than an order of magnitude greater than in perchloroethylene. I discuss the new physics that might be learned from such an experiment.

Finite-size studies of noncompact quantum electrodynamics with four species of almost massless fermions suggest that there is an ultraviolet-stable, nonperturbative fixed point in four dimensions which describes an interacting field theory of bound states. This theory may be relevant to grand unification schemes, technicolor, and recent anomalous heavy-ion experiments.

Longitudinal and transverse structure functions for the quasielastic reaction ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$(e,e’p${)}^{39}$${\mathrm{K}}^{\mathrm{*}}$ have been obtained. Their q dependences appear like those for free nucleons. However, the ratio of the longitudinal to transverse structure functions is found reduced by 30% relative to theoretical calculations.

The intensity interferometry method has been used to measure pion-source parameters in the reaction 1.70A-GeV ${}_{}{}^{56}{}_{}{}^{}$Fe+Fe→2${\pi }^{\mathrm{-}}$+X. The parameters show an oblate source for a narrow-acceptance spectrometer near either 0° or 90° with respect to the beam axis in the center-of-mass frame. Intranuclear-cascade–model predictions show similar behavior and are compared to the experimental results.

Shallow imaginary potentials ($W_0$≊18–25 MeV) are found to be essential to describe various sets of elastic-scattering data for ${}_{}{}^{12}{}_{}{}^{}\mathrm{-}_{}^{12}{}_{}{}^{}$C and ${}_{}{}^{16}{}_{}{}^{}\mathrm{-}_{}^{12}{}_{}{}^{}$C at intermediate energies. This result does not show a continuous ambiguity. An energy-dependent Woods-Saxon–shaped optical-model potential is presented for 60 MeV≲$E_{\mathrm{c}.\mathrm{m}.\mathrm{}\lesssim 650}$ MeV.

We have observed associative ionization of laser-cooled and -trapped sodium atoms. The measured rate coefficient for the process at a temperature of 0.75±0.25 mK is (1.1${\pm }_{0.5}^{1.3}$)×${10}^{\mathrm{-}11}$ ${\mathrm{cm}}^3$ ${\mathrm{s}}^{\mathrm{-}1}$, which implies a cross section of 8.6×${10}^{\mathrm{-}14}$ ${\mathrm{cm}}^2$. This is 3 orders of magnitude larger than the cross section measured in previous experiments at higher temperatures. The measurement involves the use of a new kind of laser trap.

A constant-current–driven semiconductor laser produced a field with amplitude noise reduced to below the standard quantum limit by -1.7 dB (32%) over an entire frequency range from near dc to 1.1 GHz. The amplitude squeezing dependence on laser pump rate and optical loss was in good agreement with theoretical prediction. The new squeezed-state generation principle of high impedance suppression for pump-amplitude fluctuation was thus confirmed experimentally.

The energy balance of the picosecond photoelectric effect is compared with that of the subpicosecond photoelectric effect. A full accounting of the energy must include the phase modulation (blue shift) induced on the laser beam by the ionization event itself.

The wake of an oscillating cylinder at low Reynolds numbers is a nonlinear system in which a limit cycle due to natural vortex shedding is modulated, generating in phase space a flow on a torus. We experimentally show that the system displays Arnol’d tongues for rational frequency ratios, and approximates the devil’s staircase along the critical line. The ‘‘singularity spectrum’’ as well as spectral peaks at various Fibonacci sequences accompanying quasiperiodic transition to chaos shows that the system belongs to the same universality class as the sine circle map.

The nonlocal Vlasov-Maxwell dielectric response kernel, K(r,r’), is constructed by integration along particle orbits in a nonuniform magnetic field. The phase integrals comprising the usual plasma dispersion function are altered, and contain a parameter characterizing the parallel field gradient. We numerically solve a 1D integral wave equation, including a parallel field gradient, describing the propagation, mode conversion, and absorption physics. Significant changes in absorption are found for the small-${\mathit{k}}_{\mathrm{\parallel }}$ regime.

Kinetics of poly(methylmethacrylate) adsorption onto a single surface from dilute carbon tetrachloride solution is reported. From stagnant solution the well-known steady-state plateau level of mass adsorbed is approached at long times. However, the mass adsorbed resumes its rise when moderate shear flow is initiated. For adsorption onto an initially bare surface, at a shear rate of 3 ${\sec }^{\mathrm{-}1}$, there is no sign of plateau on the logarithmic time scale.

A general off-lattice microscopic theory of the equilibrium properties of polymer mixtures is developed based on reference interaction site model integral equation methods. A derivation of a random-phase-approximation–like scattering function is presented along with a fully microscopic, general formula for the effective χ parameter measured in small-angle neutron-scattering experiments. Numerical results for χ of an athermal, Gaussian-chain–polymer binary blend are presented as a function of concentration, packing fraction, molecular weight, and structural asymmetry.

We report x-ray measurements on well aligned, freely suspended films of stacked bilayer membranes of the phospholipid dimyristoyl-phosphatidylcholine in a continuously variable humidity- and temperature-controlled environment. Remarkably, the most commonly observed ${\mathrm{L}}_{\mathrm{\beta }\mathcal{’}}$ phase is in fact three distinct 2D phases where the phase transitions are driven by hydration forces and the phases are distinguished by the relation between the molecular tilt direction and the 2D bond direction.

We have applied the potential-induced breathing model, a nonempirical ionic model, to ${\mathrm{La}}_2$${\mathrm{CuO}}_4$. The ionic model predicts the observed tetragonal-to-orthorhombic distortion, predicts a lower-symmetry ground state, and predicts a stable oxygen breathing mode. We find unstable phonon branches that we relate to phase transitions. Harmonically unstable double-well modes will couple to the charge density in the copper-oxide planes and possibly contribute to high-$T_c$ superconductivity. This ionic coupling is not included in recent calculations.

The supersymmetrical gauge theory of strongly correlated electronic systems, based on a geometrical approach to the quantization of the Hubbard model, is presented. It is shown that topological magnetic excitations induce the long-distance interaction between the charged particles. This interaction, depending on the statistics of the magnetic excitations, leads to the confinement or statistical transmutation phenomenon and finally to the superconductivity. The long-wave theory of the short-range-order antiferromagnetic insulator state is proposed.