A two-dimensional Fermi gas with an attractive s-wave interaction is shown to display a finite number of bound fermion pairs at all densities and temperatures. We study the chemical equilibrium between bound and ionized fermion pairs by including single-pair fluctuations in the free energy. While this turns out to be sufficient to drive the critical temperature for the onset of long-range order to zero, higher-order processes must be invoked to describe correctly the low-temperature regime.

Systematic studies have been performed on the layer-thickness dependence of magnetization and anisotropy for amorphous rare-earth–transition-metal compositionally modulated films with characteristic bilayer thicknesses (λ) in the 0.6–3-nm (6–30 Å) range. The results permit for the first time the development of a detailed model for the magnetization and perpendicular magnetic anisotropy as a function of λ. Single-ion anisotropy is shown to be the major contributor to the perpendicular anisotropy for Dy/Co and similar systems.

The temperature-dependent and magnetic-field-dependent ultrasonic-attenuation data of Ho-rich ${\mathrm{Er}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Ho}}_{\mathrm{x}}$${\mathrm{Rh}}_4$${\mathrm{B}}_4$ polycrystalline samples indicate that the attenuation increase observed throughout the superconducting state of this system is associated with the onset and existence of superconductivity. This attenuation behavior is different from any other which has been previously associated with superconductivity, where the attenuation either starts to decrease immediately below ${\mathrm{T}}_{\mathrm{c}}$ or decreases after exhibiting a peak. We suggest that interaction with spin fluctuations or that perhaps a different BCS coherence factor may cause this anomalous behavior.

A scaling relationship between switching fields, of which remanent coercivity is a prominent example, and measurement time is derived. The energy barrier to thermal fluctuations is found to exhibit a (3/2-power dependence on the difference between the applied field and the nonthermally assisted switching field. This (3/2-power dependence contrasts with the 2-power dependence which has been widely assumed in the literature. Implications for magnetic viscosity and the orientational dependence of the time-dependent switching field in certain small, isolated particles are also discussed.

We discuss possible quantum disordered states of the O(3) nonlinear σ model in which time-reversal invariance (T) and parity (P) are spontaneously broken. We show that there is spin-charge separation in these T- and P-broken disordered states. In one of the disordered states the quasiparticles are half-fermions, or semions, as in the Kalmeyer-Laughlin approach to the resonating-valence-bond state. We also write down the effective Lagrangian for the quasiparticles in these disordered phases.

A globally coupled map lattice is investigated. A simple coding of many attractors with clustering is shown. Through the coding, the attractors are organized so that their change exhibits the period-doubling bifurcation. By a simple input on a site, we can switch among attractors and tune the strength of chaos. A threshold on the cluster size is found beyond which a peculiar ‘‘posi-nega’’ switch occurs.

We investigate measurable gravitational and cosmological effects in four dimensions that can arise from the compactification of higher-dimensional theories incorporating gravity. We identify the nature of effects due to massless scalar components of the compactified higher-dimensional metric and due to modifications of cosmological dynamics. Current experimental data impose constraints on the viability of many higher-dimensional theories, including Kaluza-Klein, supergravity, and string theories. The phenomenological problems can be avoided if the components of the metric in the higher dimensions acquire an effective mass. We survey some possible mechanisms for mass generation.

We propose a simple extension of the standard model by adding an SU(2${)}_{\mathrm{H}}$ horizontal gauge symmetry in the leptonic sector, which leads to a large transition magnetic moment of the electron neutrino while keeping the neutrino mass naturally small. This model can provide a solution, to the solar neutrino puzzle while at the same time avoiding the SN 1987A bound on the neutrino magnetic moment.

We report on the observation of a light-pressure-induced asymmetry of the well-known absorption dip occurring in optical saturation spectroscopy. This asymmetry is due to the small modification of the atomic velocity distribution that is caused by the spontaneous scattering force of the saturating light field. Our measurements were performed on the λ=555.65 nm ${}_{}{}^1{}_{}{}^{}\mathrm{S}_0^{}{}_{}{}^{}$${\mathrm{-}}^3$${\mathrm{P}}_1$ transition in atomic ytterbium vapor by the use of a frequency-modulated test field propagating collinearly with the scattering field. The experimental results clearly confirm theoretical predictions and demonstrate the significance of the phenomenon for high-resolution laser spectroscopy.

Near-optimum conditions for lasing in Ni-like W are calculated for a 90-μg/${\mathrm{cm}}^2$ foil irradiated by a 2ω (λ=0.53 μm), 2.3×${10}^{14}$-W/${\mathrm{cm}}^2$, 550-ps trapezoidal pulse. The gain coefficient for the J=0–1, 4d-4p Ni-like transition at 43.1 Å is predicted to be 5.5 ${\mathrm{cm}}^{\mathrm{-}1}$. The electron density and temperature are 2.5×${10}^{21}$ ${\mathrm{cm}}^{\mathrm{-}3}$ and 860 eV at x-ray laser time.

An investigation of the radiative processes for a collection of N two-state atoms strongly coupled to the field of a high-finesse optical cavity is presented. Observations of the spectral response of the composite system to weak external modulation reveal a coupling-induced normal-mode splitting. Linewidth averaging leads to linewidths below the free-space atomic width.

Diverse problems lead to groups of states with wave functions localized into different regions of space. This result is shown to be characteristic of a large number of problems in physics (atomic and nuclear examples are given) where states of highly degenerate manifolds are mixed by an interaction, which may be one or two particle in nature. Common analytical structures are derived and their origin traced. Random distributions and statistical arguments have often been used for the form of the localization which we derive, however, as a consequence of specific structures in the interaction Hamiltonians.

We report the first results of a fully ab initio treatment of the scattering of low-energy electrons by formaldehyde. The calculations are carried out using the complex Kohn variational method, which is an anomaly-free algebraic variational procedure, and are implemented by a combination of analytic and adaptive, three-dimensional quadrature techniques. The calculations reveal a low-energy shape resonance of ${}_{}{}^2{}_{}{}^{}\mathrm{B}_1^{}{}_{}{}^{}$ symmetry, which is prominent in the elastic differential cross section only at large scattering angles, and which has been observed experimentally. Its position is sensitive to target distortion effects which are accurately handled by inclusion of an optical potential calculated from first principles.

For the first time triple differential cross sections of the electron impact ionization of atomic hydrogen close to threshold have been measured. The angular correlation of the outgoing electrons have been determined at 4 eV excess energy and are compared with results obtained with helium. A method is proposed allowing to measure the range of the threshold law. The data are analyzed using a partial-wave method. Although the asymptotic states of the two processes are the same—the charge of the ion is Z=1 in both cases—the triple differential cross sections are drastically different.

The line shape of the plasma resonance in both neutral and charged small sodium clusters is calculated. The overall properties of the multipeak structure observed in the photoabsorption cross section of spherical ${\mathrm{Na}}_8$ and ${\mathrm{Na}}_{20}$ neutral clusters can be understood in terms of Landau damping. Quantal configurations are shown to play an important role. In the case of charged ${\mathrm{Na}}_9^{+}$ and ${\mathrm{Na}}_{21}^{+}$ clusters a single peak is predicted that carries most of the oscillator strength.

The optical diffusion coefficient D and photon absorption time ${\mathrm{\tau }}_{\mathrm{a}}$ in a sample of titania spheres in air are determined from measurements of picosecond pulse transmission over the wavelength range 514–650 nm. At 514 nm, D=1.45×${10}^4$ ${\mathrm{cm}}^2$/s. This corresponds to an anomalously small value of the effective mean free path l̃==3D/v=250 Å, where v is the velocity of light in the medium. Throughout the wavelength range measured, l̃≤0.15λ. Assuming that D is reduced by coherent backscattering and that the optical mobility edge is given by the Ioffe-Regel criterion, the renormalization factor at 514.5 nm is 2.8.

Inverted micelles are found to exhibit marked viscoelasticity with a pronounced dependence on volume fraction. The frequency dependence, measured using both ultrasonic and Brillouin techniques, reflects the dynamics of the interactions between the micelles. At low frequencies they behave as isolated spheres, while at high frequencies they behave as an instantaneous connected network. The rigidity of this network exhibits power-law scaling with volume fraction, consistent with rigidity percolation.

We report on the analysis of time-resolved x-ray spectra from direct-drive, Ar-filled polymer shell implosion experiments in which we trace the time evolution of the electron density through stagnation. Very high electron densities in the range 2–8×${10}^{24}$ ${\mathrm{cm}}^{\mathrm{-}3}$ are inferred. We also discuss several novel spectral features, including large Stark broadening of satellite line emission, optical thicknesses for resonant transitions lower than expected, and the onset of density-dependent ‘‘blue satellites’’ on the high-energy wing of the ${\mathrm{He}}_{\mathrm{\alpha }}$ line.

Large-scale density modification was optimally achieved by electromagnetic waves whose frequency matched the plasma frequency at a height where the ionospheric density profile was flat. The density in this region was dramatically clamped during the morning when it normally increases from solar ionization. Electromagnetic wave propagation in the polar magnetic field geometry and strongly resonantly enhanced electrostatic fields over a large region of constant density account for the observation.

We examine a planar wetting model which exhibits a sessile drop and microscopic droplets. The contact angle of the sessile drop obeys the modified Young equation. The microscopic droplets diverge in size and the contact angle vanishes at a single wetting temperature.