The flow between two horizontal coaxial cylinders with a partially filled gap, the Taylor-Dean system, is investigated for the case in which the outer cylinder rotates while the inner cylinder remains at rest. The initial instability is to a mixed state of both traveling inclined rolls and laminar base flow. At a larger rotation rate, the entire flow becomes time dependent. At a still larger rotation rate, the flow undergoes a subcritical transition to a stationary roll pattern, a process previously observed only in binary fluid mixtures.

Precise undercooling measurements at the cell tips of solid-liquid cellular interfaces in directional solidification of a dilute succinonitrile alloy in a rectangular channel are made in a metastable regime that is unstable relative to a longer-wavelength pattern seen at larger undercooling. As the pattern coarsens, its wavenumber scales with undercooling. The data are consistent with an unstable cellular pattern predicted for the Saffman-Taylor analogy of directional solidification.

Dynamical critical behavior for a nonionic micellar solution of tetraethylene glycol n-decylether in water has been examined by the time-dependent correlation function measurements of scattered light close to its critical point of mixing. The asymptotic behavior in the decay rate is compared with the current prediction associated with a dynamic universal function proposed recently for a fluid system.

We use Monte Carlo simulations to investigate the ground state of electrorheological (ER) fluids in a strong electric field. Our results suggest a body-centered tetragonal (bct) lattice with conventional Bravais vectors ${\mathbf{a}}_1$= √6 ax^, ${\mathbf{a}}_2$= √6 ay^, and ${\mathbf{a}}_3$=2az^ where a is the radius of dielectric spheres and the z axis is the direction of the applied electric field. This bct lattice can be regarded as a compound of chains of class A and class B where chains of class B are obtained from chains of class A by shifting a distance of a in the z direction. For typical ER systems, this bct structure can be formed at room temperature.

We propose an extension of the diffusion-limited-aggregation model for fractal growth. In our model, the Poisson equation is statistically simulated through the use of diffusive particles generated everywhere outside the aggregate. We relate the model to our experiments on viscous fingering in a Hele-Shaw cell in which flow is forced by separating the plates. Our simulations yield nonstationary fractal patterns which exhibit multiscaling and look much like the experimental patterns. We discuss features of the growth measure.

A regime of the plasma wave-field accelerator (PWFA) is proposed, in which a high-intensity electron beam is used to excite extremely nonlinear, transverse motion-dominated plasma oscillations. Through computational analysis of the plasma electron motion and the associated wake fields, it is shown that if the beam is dense enough to eject nearly all of the plasma electrons from the beam channel, then the short-range wake fields are of excellent quality for acceleration and focusing of electron beams. These results clear up many conceptual difficulties with the practical realization of a PWFA.

We demonstrate that the generating functionals for two-dimensional models with two real scalar fields, one interacting with an external electromagnetic field and the other with coupling terms but without external fields, can be reduced to the case of the free-particle propagator when quasistatic solutions for this theory are used.

‘‘Dynamical driving’’ means driving a system by another dynamical system, in contrast to driving by an external force (which acts on the system but is not acted upon by the system). The model consists of a localized spin driven by a polarized beam of spins. A remarkably complex variety of behaviors is possible as a result of the competition between the aligning effect of interaction with the beam and the precession due to the external magnetic field. The state of the localized spin can evolve from pure to mixed, or from mixed to pure, and its motion is characterized by an attractor. The final state of the driven spin is usually independent of its initial state, so the model provides an example of quantum-state preparation. These effects cannot be produced by a prescribed external force.

A classical spin, dynamically driven by a polarized beam, is shown to exhibit a complex variety of behaviors, incuding stable fixed points, bifurcations, limit cycles, and chaos. In the classical (large-spin) limit of the corresponding quantum model, the probability distributions for the spin components converge to their classical counterparts, even though the classical motions are qualitatively different for different ranges of parameters. However, the nature of the quantum-to-classical limit has some unexpected features, which are discussed.

The shifted 1/N expansion method has been extended to solve the Klein-Gordon equation with both scalar and vector potentials. The calculations are carried out to the third-order correction in the energy series. The analytical results are applied to a linear scalar potential to obtain the relativistic energy eigenvalues. Our numerical results are compared with those obtained by Gunion and Li [Phys. Rev. D 12, 3583 (1975)].

We have calculated quadrupole moments, ${\mathit{Q}}_{\mathit{z}\mathit{z}}$, of helium in several of its doubly excited states and in two of its singly excited Rydberg states, and of the alkaline-earth atoms Be, Mg, Ca, Sr, and Ba in their ground and low-lying excited states. The calculations use well-converged, frozen-core configuration-interaction (CI) wave functions and, for interpretive purposes, Hartree-Fock (HF) atomic wave functions and single-term, optimized, molecular rotor-vibrator (RV) wave functions. The quadrupole moments calculated using RV wave functions serve as a test of the validity of the correlated, moleculelike model, which has been used to describe the effects of electron correlation in these two-electron and pseudo-two-electron atoms. Likewise, the quadrupole moments calculated with HF wave functions test the validity of the independent-particle model. In addition to their predictive use and their application to testing simple models, the quadrupole moments calculated with CI wave functions reveal previously unavailable information about the electronic structure of these atoms. Experimental methods by which these quadrupole moments might be measured are also discussed. The quadrupole moments computed from CI wave functions are presented as predictions; measurements of ${\mathit{Q}}_{\mathit{z}\mathit{z}}$ have been made for only two singly excited Rydberg states of He, and a value of ${\mathit{Q}}_{\mathit{z}\mathit{z}}$ has been computed previously for only one of the states reported here. We present these results in the hope of stimulating others to measure some of these quadrupole moments.

Doubly excited ${}_{}{}^1{}_{}{}^{}$${\mathit{P}}^{\mathit{o}}$ autoionizing states in He between the N=2 and 3 thresholds of ${\mathrm{He}}^{+}$ ions are calculated by use of a method of complex-coordinate rotation. Hylleraas-type wave functions are used to calculate resonance parameters for the lowest ten resonances, and products of Slater orbitals are used for higher-lying resonances. In the KTNn notation, the states reported in the present work include six members in (113n) series with (3≤n≤8), four members in the (-113n) series (3≤n≤6), four members in the (203n) series (4≤n≤7), four members in the (003n) series (4≤n≤7), and three members in the (-203n) series with (4≤n≤6). Comparisons are made with other theoretical calculations and with experimental observations.

Nonadiabatic calculations have been performed for the g, h, i, and j states of ${\mathrm{H}}_2$, HD, and ${\mathrm{D}}_2$, yielding the lowest rovibrational levels (ν,N=0,1,2,3). Born-Oppenheimer potential-energy curves were taken from literature. Irregularly shaped rotational and vibrational couplings were significantly reduced by an appropriate electronic basis transformation. In the diabatic electronic basis introduced here the rotational matrix elements were fixed to their united-atom-limit values, and the vibrational matrix elements were adjusted to reproduce experimental data. Apart from the hydrogen ${}_{}{}^3{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{g}}^{+}{}_{}{}^{}$ state ν=2 and 3 series that we suspect are misassigned, we obtained agreement with experiment down to a wave number for all calculated energy levels. Calculated branching ratios for radiative decay, which are very sensitive to the excited-state electronic composition, are found to agree with experimental data [following paper, Phys. Rev. A 44, 4171 (1991)]. The confusion in the nomenclature of the adiabatic electronic ${}_{}{}^3{}_{}{}^{}\mathrm{\Sigma }_{\mathit{g}}^{+}{}_{}{}^{}$ states is addressed.

A systematic study has been performed on the singly excited n=3 triplet gerade states of molecular hydrogen using fast-neutral-beam photofragment spectroscopy. These states fluoresce to the triplet 2p states and are analyzed according to the energy released in the subsequent dissociation process. The resulting spectra are compared with theoretical results obtained by solving the coupled nuclear Schrödinger equation. Good overall agreement is reported for both the shape of the spectra and the branching ratios for fluorescence to either one of the triplet 2p states. Rotational and vibrational couplings that affect the n=3 triplet gerade complex are well described by theory.

A detailed cascade-corrected energy-level lifetime analysis of the 3${\mathit{p}}^4$ ${\mathit{D}}_{3/2,5/2,7/2}$ energy levels in N iii was undertaken by studying the 3p ${}_{}{}^4{}_{}{}^{}$${\mathit{D}}_{\mathit{J}}$–3s ${}_{}{}^4{}_{}{}^{}$${\mathit{P}}_{\mathit{J}}^{\mathrm{°}}$ transitions, as well as incorporating cascading from the higher-lying 3d ${}_{}{}^4{}_{}{}^{}$${\mathit{P}}_{\mathit{J}}^{\mathrm{°}}$, 3d ${}_{}{}^4{}_{}{}^{}$${\mathit{D}}_{\mathit{J}}^{\mathrm{°}}$, and 3d ${}_{}{}^4{}_{}{}^{}$${\mathit{F}}_{\mathit{J}}^{\mathrm{°}}$ energy levels. The present paper therefore describes beam-foil measurements of the decay times of a number of 2${\mathit{s}}^1$2${\mathit{p}}^1$${(}^3$${\mathit{P}}^{\mathrm{°}}$)3p and 3d levels in N iii. These 3d levels were found to have a very marked influence of approximately 15% on the lifetimes of the 3p ${}_{}{}^4{}_{}{}^{}$${\mathit{D}}_{\mathit{J}}$ energy levels. This influence was studied using a multiexponential curve-fitting technique, as well as the now well-proved (arbitrarily normalized decay curve) technique. The beam-foil method using these techniques is expected to provide a reliable and consistent experimental check on lifetime calculations.

The 6pnf series of barium converging to both 6${\mathit{p}}_{1/2}$ and 6${\mathit{p}}_{3/2}$ limits were investigated in a two-step pulsed-laser experiment. From 6s5d ${}_{}{}^3{}_{}{}^{}$${\mathit{D}}_{1,2,3}$ metastable atoms, discharge populated in an atomic beam, 11 out of the full manifold of 12 autoionizing 6${\mathit{p}}_{1/2,3/2}$nf J=1–5 Rydberg series were excited via selected 5d6p J=0–4 doubly excited intermediate states. For each value of the total angular momentum J, the data were analyzed using R-shifted multichannel-quantum-defect theory. The autoionization rates of the different series compare well with a model for autoionization based upon only a direct Coulomb interaction mechanism with neglect of exchange effects. The multiplet level structure of the 6pnf configuration for a particular n Rydberg manifold was analyzed in terms of Slater integrals. The level ordering of 6pnf J substates could only be explained by including a large exchange parameter. Some 6pnp series were also observed, in particular 6${\mathit{p}}_{3/2}$${\mathit{np}}_{3/2}$ J=3.

Regge-pole positions and residues associated with real and complex optical potentials of the Lennard-Jones type are calculated by phase-integral formulas. Two relevant transition zeros are taken into account; they may lie at an arbitrary distance from each other, while the origin and the other transition points are assumed to lie far away from the two relevant transition zeros. The calculations are performed up to the 13th order of the phase-integral approximation. The results obtained are much more accurate than results published earlier.

Experimental and theoretical investigations of resonant transfer excitation (RTE) for ${\mathrm{F}}^{6+}$+${\mathrm{H}}_2$ and ${\mathrm{Mg}}^{9+}$+${\mathrm{H}}_2$ collisions have been made. For both collision systems good agreement is obtained between the measured cross sections for K-shell x-ray emission coincident with electron-capture and theoretical RTE calculations. For ${\mathrm{F}}^{6+}$ the present calculations are about 10% lower than previous results of Bhalla and Karim [Phys. Rev. A 39, 6060 (1989); 41, 4097(E) (1990]; the measured cross sections are a factor of 2.3 larger than earlier measurements of Schulz et al. [Phys. Rev. A 38, 5454 (1988)]. The previous disagreement between experiment and theory for ${\mathrm{F}}^{6+}$ is removed.

Total dielectronic-recombination rate coefficients for 11 ions with 6≤Z≤54 in the Li isoelectronic sequence have been calculated using the distorted-wave technique and the multiconfiguration Dirac-Fock model. The total rate coefficients for the fine-structure states for ions with Z≥24 can differ by as much as one order of magnitude at low temperatures due to the effects of relativity and intermediate coupling. Effects of Coster-Kronig transitions on rate coefficients are examined. Results from the present work are compared with previous nonrelativistic Hartree-Fock calculations.

Polarization of scattered electrons is enhanced up to 1 near p- and d-wave resonances or weakly bound negative-ion energy levels (‖E‖≲0.1 eV, ${\mathit{v}}^2$/${\mathit{c}}^2$≲${10}^{\mathrm{-}6}$). We consider as examples Ra and Ba. We also note that the cross section for Ra is very large (>${10}^{11}$ b at electron energy ∼${10}^{\mathrm{-}2}$ eV).