A search for the electron electric dipole moment ${\mathit{d}}_{\mathit{e}}$ is carried out with two counterpropagating beams of ground-state ${}_{}{}^{205}{}_{}{}^{}\mathrm{Tl}$. The experiment employs atomic-beam magnetic resonance with separated oscillatory fields combined with laser state selection and fluorescence detection. Extensive tests were made for possible systematic effects. The result for the atomic electric dipole moment is ${\mathit{d}}_{\mathit{a}}$=(1.6 ±5.0)×${10}^{\mathrm{-}24}$ e cm, where the uncertainty includes equal statistical and systematic contributions. This yields ${\mathit{d}}_{\mathit{e}}$=(-2.7±8.3) ×${10}^{\mathrm{-}27}$ e cm, assuming the ratio ${\mathit{d}}_{\mathit{a}}$/${\mathit{d}}_{\mathit{e}}$=-600.

We report results of ${\mathrm{Ba}}^{\mathrm{*}\mathrm{*}}$-Na Penning ionization experiments in which the reactivity of pure Rydberg states is compared with that of mixed Rydberg-valence states. Pure states having energy near the ionization threshold of Na are highly reactive, σ≊2500 Å ${}_{}{}^2{}_{}{}^{}$ for Ba(17d ${}_{}{}^1{}_{}{}^{}$${\mathit{D}}_2$), but mixed states are unreactive. These results are explained using a model that includes an ion-induced dipole ${\mathrm{Ba}}^{+}$-Na interaction and a modified Coulomb interaction resulting from fractional charge accumulation around the Na.

Dissociation probabilities and populations of excited vibrational states are calculated numerically for interaction of a Morse oscillator with a chirped, ultrashort (${\mathit{t}}_{\mathit{p}}$<${10}^{\mathrm{-}11}$ sec), intense laser pulse. It is shown that if the pulse frequency ω(t) decreases at a specific rate adapted to the molecular anharmonicity, the dissociation probability is many orders of magnitude higher than for a monochromatic pulse of the same intensity. Such pulses should be useful for more efficient multiphoton dissociation of molecular bonds.

Collisions of low-energy (5–20 eV), ground-state oxygen atoms with ${\mathrm{H}}_2$O and ${\mathrm{CO}}_2$ in a crossed-beams geometry lead to chemical reaction in the case of ${\mathrm{H}}_2$O to produce OH (${\mathit{A}}^2$${\mathrm{\Sigma }}^{+}$→${\mathit{X}}^2$Π) emissions; and to inelastic electronic excitation in the case of ${\mathrm{CO}}_2$ to produce the ${\mathrm{CO}}_2$ (Ã ${}_{}{}^1{}_{}{}^{}$${\mathit{B}}_2$→X̃ ${}_{}{}^1{}_{}{}^{}$${\mathit{A}}_1$) flame bands. Species identifications are made through known wavelengths and emission intensities in the range 300–400 nm. The measured difference in threshold energies for the two processes confirms the channels involved. These are the first measurements in this energy range of optical emissions through collisions of fast neutral species.

We present the first quantitative results for the ionization of hydrogen at relatively high frequencies, from low intensities to superintensities in excess of the atomic unit ${\mathit{I}}_0$=3.51×${10}^{16}$ W/${\mathrm{cm}}^2$. We find that at superintensities the atom has a tendency to stabilize against multiphoton ionization, even at low frequencies. We show, however, the existence of very short lifetimes for the ground state, at intensities just below those needed for stabilization.

We present a simple model of time-resolved absorption spectra of molecules that are in the process of dissociating. Within an ‘‘impact approximation,’’ the spectra are shown to be superpositions of Lorentzian and dispersion profiles with relative weights determined by a net phase shift. New methods are proposed for obtaining molecular transition frequencies and relative transition dipole moments as functions of internuclear separation. Experimental data on TlI are compared to theoretical predictions, with good overall agreement.

The defects of a system where hexagons and rolls are both stable solutions are considered. On the basis of topological arguments we show that the unstable phase is present in the core of the defects. This means that a roll is present in the penta-hepta defect of hexagons and that a hexagon is found in the core of a grain boundary connecting rolls with different orientations. These results are verified in an experiment of thermal convection under non-Boussinesq conditions.

A transition analogous to the strongest 4d-4p nickel-like x-ray laser transition has been observed in cobaltlike ions within the same plasma. Amplified spontaneous emission from Co-like ions has been identified in laser-produced exploding-foil plasmas of Yb and Ta. The Co-like line exhibits similar time history to the Ni-like laser line and has a gain coefficient consistent with a significant Co-like population. The observation of this transition is of interest as fluorinelike analogs to neonlike 3p-3s x-ray lasers have never been seen although they are predicted to have gain.

We have observed convective flow in a thin freely suspended film of smectic-A liquid crystal when a sufficiently large electric field is applied in the plane of the film. The convective flow neither reorients the director nor deforms the free surfaces of the film. Thus the film behaves as a two-dimensional isotropic fluid. We have studied the onset of this flow in two film holders, one which allows injection of charges from the electrodes into the film and one which does not. We present measurements of the threshold voltage and of the wavelength of the vortex pattern as a function of the frequency of the applied field, and briefly discuss the nature of the mechanisms driving the flow.

The first encouraging experiments demonstrating direct, explicit control of the ${\mathrm{He}}^{2+}$ density in a tokamak plasma have been performed in the TEXTOR tokamak with the Advanced Limiter Test-II pump limiter. Helium is injected in a short gas puff from the outside of the plasma, is observed to reach the plasma core, and then is readily removed from the plasma. An exhaust efficiency of ∼8% is obtained. Active charge-exchange spectroscopy is used to study the exhaust and transport of ${\mathrm{He}}^{2+}$ within the plasma, and the density evolution is modeled with a diffusive-convective transport code.

Experimental investigations on the resonant wave-particle interaction in the framework of both a ${\mathbf{v}}_{\mathit{p}}$×B acceleration and a conventional resonance-absorption scheme have been performed by injecting electron beams into the wave-particle interaction region. In the ${\mathbf{v}}_{\mathit{p}}$×B acceleration scheme, the particles can interact with the wave for a longer duration and the final particle energy reaches larger values (about 1.5 times) than those observed in the resonance absorption. A simple model based on the ${\mathbf{v}}_{\mathit{p}}$×B acceleration scheme can be used to interpret the results.

Dimensionally similar tokamak discharges with all dimensionless parameters the same except the relative gyroradius can be scaled to ignition-regime discharges of larger size and/or field in analogy to the principles of wind-tunnel design. This Letter describes the first controlled experiment to determine whether the scaling with relative gyroradius corresponds to short- or long-wavelength turbulence.

We have investigated the dynamic structure factor of room-temperature ${}_{}{}^{36}{}_{}{}^{}\mathrm{Ar}$ at two densities (0.25 and 0.63 times the critical) and at very low momentum transfer (0.3<κ<1.3 ${\mathrm{nm}}^{\mathrm{-}1}$). Linearized hydrodynamics agrees with the experimental data only at the higher density and κ<1 ${\mathrm{nm}}^{\mathrm{-}1}$. However, the description in terms of three extended hydrodynamic modes is fully satisfactory at both densities over the whole κ range. We provide the first experimental evidence that the concept of extended hydrodynamic modes is valid for the whole range from hydrodynamics up into the kinetic regime.

In this Letter we investigate a symmetry-breaking transition in the Frenkel-Kontorova model for finite chains with free-end boundary conditions. We present a detailed study of the behavior in the vicinity of the transition. It is shown that the gap in the phonon spectrum, the disorder parameter, and the reflection-symmetry parameter display scaling properties close to the transition. Their associated critical exponents are discussed and related to the displacements of the particles in the chains.

At a critical end point a critical phase coexists with a noncritical phase α and singularities arise beyond those on the associated critical line. New universal amplitude ratios are defined for the shape of the α-phase boundary and for the noncritical surface tensions near end points. A postulated correspondence with wall/surface criticality leads to predictions for general dimension d that are exact at (and near) d=2 and for d≥4 (where mean-field theory applies) and yield experimentally testable estimates for d=3.

The connection between the growth of a wetting layer and bulk phase separation is investigated in a liquid system undergoing spinodal decomposition. The wetting phase, which grows at the walls of the container, is found to be rippled and connected to the bulk, and layering of spatially anisotropic domains of the nonwetting phase is observed near the wall. Growth laws are determined and compared with a dimensional analysis of the Navier-Stokes equations.

We have observed sharp cusplike heat-capacity singularities, coincident with the superfluid transition, in two ${}_{}{}^4{}_{}{}^{}\mathrm{filled}$ aerogel glasses. These features are interpreted as conclusive evidence of genuine critical behavior at the superfluid transition in these systems. The cusplike heat-capacity singularities confirm that ${}_{}{}^4{}_{}{}^{}\mathrm{filled}$ aerogels are not in the same universality class as bulk helium.

Solid hydrogen in the atomic bcc structure is studied using a variational quantum Monte Carlo approach. Various magnetic phases are investigated at densities between Wigner-Seitz radius of ${\mathit{r}}_{\mathit{s}}$=1.6 and 3.0 a.u. Correlated wave functions of Jastrow-Slater form are used with their antisymmetric part constructed from the Kohn-Sham self-consistent orbitals. A transition from paramagnetic to antiferromagnetic phase at lower density is found at ${\mathit{r}}_{\mathit{s}}$=2.4. There is, however, no evidence for metastable partial ferromagnetic structure.

We have demonstrated that a gold scanning-tunneling-microscope tip can be used as a miniature solid-state emission source for directly depositing nanometer-size gold structures. The emission mechanism is believed to be field evaporation of tip atoms, which is enhanced by the close proximity of the substrate. The technique has been used in air on Ag(111) surfaces to write several thousand features with no apparent degradation of the tip’s ability to emit atoms.

Extended scaling forms are usually required to account for the complex behavior near a multicritical point. We explore their role in understanding kinetic phase transitions described by the Kardar-Parisi-Zhang equation for interface growth. For a surface of dimension d=2, an exponentially slow logarithmic-to-power-law crossover is predicted from a renormalization-group analysis and compared with numerical simulations of a deposition and evaporation model. Derivation of scaling forms associated with the kinetic roughening transition at d>2 is presented.