The Penning ionization interaction He(12$s^3$S)+K(3$p^6$4s) and the atomic autoionizing state interaction He(1$s^2$)+K(3$p^5$4$s^2$) have been determined in a configuration-interaction calculation utilizing a basis set designed to treat these two states equitably. In contrast to an earlier calculation, the corresponding two potential curves are found not to cross. This finding puts in question the original speculation that the observed large ${\mathrm{He}}^{\mathrm{*}}$+K ionization cross section is due partially to collisional excitation of atomic states that subsequently autoionize. However, the calculated Penning ionization cross section is still in agreement with the experimental measurement.

A new theoretical technique is developed for a charged particle in an external potential. All dipole-coupled counter-rotating terms are removed from the Hamiltonian by a canonical transformation. The transformation renormalizes the wave functions and introduces intensity-dependent energy-level shifts. These correspond to the classical ponderomotive potential in the ionization limit. The predicted level shifts directly explain the increased ionization potentials observed in intense-field multiphoton ionization. A refractive-index shift occurs as well.

We study the decay of an unstable state in the presence of colored noise by calculating the moment generating function of the passage-time distribution. The problems of the independence of the initial condition in this non-Markovian process and that of nonlinear effects are addressed. Our results are compared with recent analog simulations.

A method for minimizing the unphysical oscillations in simple lattice-gas hydrodynamic models is presented. Numerical simulations of two types of shear flows are reported that illustrate the usefulness of this method.

A computational method, which explicitly employs a streamline coordinate as an independent variable, is proposed for analyzing steady flows of non-Newtonian matter.

By molecular dynamics for a Lennard-Jones fluid at $n^{\mathrm{*}}$=0.55 and $T^{\mathrm{*}}$=3.2 we determine both the Fourier-transformed velocity autocorrelation function z(ω) and the incoherent neutron scattering functions $S_s$(k,ω). $z( omega )— (including the ‘‘long-time-tail’’ singularity near ω=0) can be obtained from $S_s$(k,ω) by extrapolation to k=0, only when data for $S_s$(k,ω) are included with k smaller than (ω/2D${)}^{1/2}$, with D the self-diffusion coefficient.

Quadratic maps are used to study the spectrum of singularities of the period-doubling attractor close to and at the onset of chaos. Finite approximations of the critical orbit have observable effects on the determination of f(α) which can be predicted by using the scaling properties of the attractor.

We describe the problem of impurity diffusion in a semi-infinite region in the context of a model that caricatures the Fokker-Planck equation. The solution obtained for the surface flux is an improvement over that found using the diffusion equation in two important respects: The short-time behavior is better and additional information is found regarding the physical process at the substrate-reactant interface.

Two needles growing from a single point compete for material. If the angle between them is less than about 0.920 154 rad, spontaneous symmetry breaking occurs and one of them ‘‘wins.’’ The stable equilibrium in this case corresponds to a fixed length ratio different from unity. For larger angles the stable equilibrium is for equal lengths. The critical exponent at the symmetry-breaking transition is 1/2.

We apply the smoothed-density approximation to study the nematic–smectic-A transition for the system of perfectly aligned hard spherocylinders. We find that the transition occurs for all length-to-width ratios L/D of a spherocylinder and is always continuous. The bifurcation analysis is applied to locate the transition. Our results are in reasonable agreement with those obtained in computer simulations.

It is suggested that the viscoelastic coupling between a DNA molecule and its hydration shell, used by VanZandt [Phys. Rev. Lett. 57, 2085 (1986)] and VanZandt and Davis [J. Biomol. Struct. Dyn. 3, 1045 (1986)] in their treatment of this problem, is an essential element of their work. Other interactions lead to results inconsistent with recent data by Tao, Lindsay, and Rupprecht [Phys. Rev. Lett. 59, 518 (1987)].

In a recent paper, Peacock-López, West, and Lindenberg [Phys. Rev. A 37, 3530 (1988)], starting from a formal path-integral expression, show that the differences between effective Fokker-Planck equations arise as a consequence of different approximations. In this Comment we show that a closed formula for the effective diffusion coefficient may be used to derive the different approximate expressions.

In a recent paper [K. Życzkowski, Phys. Rev. A 35, 3546 (1987)] the generalized Husimi distribution was used to investigate the quantum kicked rotator. It was shown that in the classically chaotic region the Husimi distribution displayed a ‘‘rippled irregular shape.’’ It was suggested that such behavior could be considered as a qualitative criterion for quantum chaos. In this Comment it is suggested that such behavior is not necessarily associated with quantum chaos. The rippled irregular features may be due to quantum interference effects between superposed states.

The interpretation of Milburn in the preceding Comment [Phys. Rev A 39, 2749 (1989)] is confirmed in further numerical study.

The spectrum of light emitted out the sides of a confocal mode-degenerate optical cavity by Ba atoms driven by a strong, resonant, excitation field has been studied. The cavity is found to induce asymmetries in the classic three-peaked Mollow spectrum. These asymmetries are explained primarily in terms of a spectral structure introduced into the electromagnetic vacuum reservoir by the cavity.

A neon atomic beam in the metastable state 1$s_5$ has been decelerated and trapped by the spontaneous light force of a resonant laser in a quadrupole magnetic field. Trapping has been achieved on all isotopes ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$, ${}_{}{}^{21}{}_{}{}^{}\mathrm{Ne}$, and ${}_{}{}^{22}{}_{}{}^{}\mathrm{Ne}$ using a sample with natural abundance. For ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$, approximately 4×${10}^7$ atoms are trapped.

A Rayleigh-Bénard experiment in a moderate-aspect-ratio cell (7×4×1) filled with mercury reveals for the first time the spatiotemporal dynamics of the oscillatory regime. The oscillatory instability, first step on the route to turbulence at low Prandtl number, generates propagating waves, which interfere spatially and involves very rich dynamics of topological defects.

We report experimental observations of confined and temporally modulated states produced by the oscillatory instability of straight convective rolls. For this system we have measured all the critical parameters characterizing the instability. We are thus able to confirm the interpretation of such phenomena proposed by Cross [Phys. Rev. A 38, 3593 (1988)] based on the combination of propagative effects and finite geometry.