A dynamic reaction zone is produced in the A+B→C reaction-diffusion system with initially separated components. Our perturbation analysis results predict a rich behavior for the kinetics of the reaction front in the short-time limit, with variety of universality classes. In particular, we show that the center of the front can change its direction of motion. Our experimental data support this prediction and demonstrate that this behavior is measurable over a time scale of hours in bimolecular reactions at room temperature.

A quantum R-matrix structure is presented for a family of exactly integrable multidimensional rational mappings related to lattice versions of the Korteweg–de Vries equation. It is shown that these mappings possess a commuting family of invariants.

The structural and dynamical properties of liquid alkali metals near melting are investigated by realistic computer simulations, which support the idea that several important features follow from suitable scaling criteria. The data are found to be in excellent agreement with the recent theories of single-particle dynamics in simple liquids.

In this paper we report the dc Kerr constant and the pretransitional temperature of a polar nematic liquid crystal 4-(trans-4’-4’-n-pentylcyclohexy)-benzonitrile (PCH-5). The observed second-order pretransitional temperature ${\mathit{T}}^{\mathrm{*}}$ from our measurements is found to be 1.2 °C below the first-order nematic to isotropic transition temperature. The dependence of the Kerr constant on (T-${\mathit{T}}^{\mathrm{*}}$${)}^{\mathrm{-}1}$ is found to be in good agreement with the predictions of the Landau–de Gennes model. The highest value of the Kerr constant observed at 632.8 nm is found to be 9.737×${10}^{\mathrm{-}11}$ m ${\mathrm{V}}^{\mathrm{-}2}$, corresponding to a temperature of 55.3 °C.

Several important phenomenological relations dealing with thermophysical properties of liquids are collected. It is shown that the Laplace ratio between the surface energy and the latent heat improves substantially if we add a volume-expansion term to the surface energy.

Using a Gaussian stochastic model for configurational size fluctuations, we show that diffusion-limited aggregates asymptotically attain monodispersity (variance→0) in their radii of gyration (${\mathit{R}}_{\mathit{g}}$) in three dimensions and above. The decay of the variance in ${\mathit{R}}_{\mathit{g}}$ as function of the cluster mass is found to be the fastest in Euclidean dimension ${\mathit{d}}_{\mathit{c}}$=2+ √7 . However, in two dimensions, the variance is found to diverge with the mass. These results are a consequence of relating ${\mathit{R}}_{\mathit{g}}$ fluctuations to the width of the active zone of growth.

This paper extends an investigation of the stability of intense optical slab beams in infinite plasmas [E. Infeld and G. Rowlands, Phys. Rev. A 42, 1005 (1990)]. These beams can be profiled in the shape of nonlinear waves or else solitons. In contradistinction to the earlier, purely theoretical investigation, perturbations of arbitrary wavelength are considered numerically. The results still imply radial stability, but also azimuthal instability of the soliton pulse. The wave structures, however, are unstable in both directions. In the long-wavelength perturbation limit, agreement with previous theoretical results is obtained. This gives a check on the lengthy calculations involved.

We show that the experimental enhancing of negative-ion production in pulsed discharges recently obtained in different laboratories can be rationalized on the basis of a theoretical model we developed.

In a recent paper, Adair [Phys. Rev. A 43, 1039 (1991)] concludes that weak extremely-low-frequency (ELF) electromagnetic fields cannot affect biology on the cell level. However, Adair’s assertion that few cells of higher organisms contain magnetite (${\mathrm{Fe}}_3$${\mathrm{O}}_4$) and his blanket denial of reproducible ELF effects on animals are both wrong. Large numbers of single-domain magnetite particles are present in a variety of animal tissues, including up to a hundred million per gram in human brain tissues, organized in clusters of tens to hundreds of thousand per gram. This is far more than a ‘‘few cells.’’ Similarly, a series of reproducible behavioral experiments on honeybees, Apis mellifera, have shown that they are capable of responding to weak ELF magnetic fields that are well within the bounds of Adair’s criteria. A biologically plausible model of the interaction of single-domain magnetosomes with a mechanically activated transmembrane ion channel shows that ELF fields on the order of 0.1 to 1 mT are capable of perturbing the open-closed state by an energy of kT. As up to several hundred thousand such structures could fit within a eukaryotic cell, and the noise should go as the square root of the number of independent channels, much smaller ELF sensitivities at the cellular level are possible. Hence, the credibility of weak ELF magnetic effects on living systems must stand or fall mainly on the merits and reproducibility of the biological or epidemiological experiments that suggest them, rather than on dogma about physical implausibility.

Kirschvink [preceding Comment, Phys. Rev. A 46, 2178 (1992)] objects to my conclusions [Phys. Rev. A 43, 1039 (1991)] that weak extremely-low-frequency (ELF) electromagnetic fields cannot affect biology on the cell level. He argues that I did not properly consider the interaction of such fields with magnetite (${\mathrm{Fe}}_3$${\mathrm{O}}_4$) grains in cells and that such interactions can induce biological effects. However, his model, designed as a proof of principle that the interaction of weak 60-Hz ELF fields with magnetite domains in a cell can affect cell biology, requires, by his account, a magnetic field of 0.14 mT (1400 mG) to operate, while my paper purported to demonstrate only that fields smaller than 0.05 mT (500 mG) must be ineffective. I then discuss ELF interactions with magnetite generally and show that the failure of Kirschvink’s model to respond to weak fields must be general and that no plausible interaction with biological magnetite of 60-Hz magnetic fields with a strength less than 0.05 mT can affect biology on the cell level.

A direct numerical solution of the Schrödinger equation for quantum scattering problems is presented. The wave function for each partial wave is expanded in coupled spherical harmonics and the corresponding radial functions are expanded in a local basis set using finite-element analysis, with the appropriate scattering boundary conditions. The method is shown to give very accurate results for elastic phase shifts (S,P,D, and F) and resonance positions for electron-hydrogen scattering.

Differential cross sections for positronium formation into 1s, 2s, and 2p states are calculated exactly by the second Born approximation. Destructive interference of the two second-order amplitudes related to the Thomas double scattering is identified as the vanishing of the imaginary part of the second-order amplitudes. When the collision velocity is high, two sharp dips appear at 26° and 39°. These dips are produced by the mutual cancellation of the first- and the second-order terms rather than the destructive interference of the two second-order terms.

The energy levels and wave functions of the electrons confined on the surface of a sphere in uniform magnetic fields H are obtained from both the exact solution in terms of the spheroidal function and numerical study. The crossover points between the weak-H (orbital Zeeman splitting) and strong-H (landau quantization) regimes are shown to delineate a series of envelopes, which, together with peculiar bunch of Landau levels, form a series of overlapping bands. The result is compared with the Landau quantization of tight-binding electrons on ${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{240}$ fullerene structures. These spectra are shown to imply an interesting orbital magnetism.

We study conditions necessary for the observation of Bose-Einstein condensation in a magnetically trapped sample of atomic Cs gas. These conditions are associated with the value of the elastic scattering length, the rate of elastic scattering events, and the lifetime for decay of the density due to both magnetic dipole relaxation in two-body collisions, as well as recombination to ${\mathrm{Cs}}_2$ in three-body collisions. We find that, on the basis of these conditions, the prospects for observing Bose-Einstein condensation are favorable for a gas of ground-state Cs atoms in the highest state of the lowest hyperfine manifold. In all calculated elastic and inelastic two-body rates we find a pronounced resonance structure, which can be understood in terms of the interplay between the singlet-triplet interaction and the hyperfine, Zeeman, and magnetic dipole interactions. The experimental observation of these resonances may help to eliminate present uncertainties about interaction potentials.

Laser-induced autoionization of transient molecules is investigated. The peculiarity of the process is that three different kinds of interaction (collisional, radiative, and Coulombic) are simultaneously present. The results show that laser-induced quantum interferences occurring in the continuum of the ionization of atoms can play an important role also in processes dominated by strong collisions.

It is shown that the quantum form of the nonlinear Schrödinger equation does not call, in general, for the introduction of a finite relaxation time of the Kerr medium and of the concomitant quantum noise sources.

An alternative technique to obtain neutral-atom beams for multiphoton-ionization studies, via wavelength-selective photodetachment of negative ions, is described. This approach is illustrated by multiphoton ionization of Al(3${\mathit{s}}^2$3p ${}_{}{}^2{}_{}{}^{}$P) atoms with selected visible and uv laser pulses of ≤300 ps duration, and with intensities ∼${10}^9$–6×${10}^{10}$ W/${\mathrm{cm}}^2$. For visible wavelengths, single-electron ionization dominates, while excitation of doubly excited states over the ionization limit is observed under uv irradiation. Possible future experiments and the general perspectives of the technique are briefly discussed.

We report observation of up to 18% (50% inferred) squeezing in a near-bistable cavity-atom system. The squeezing is found in a new regime which produces a squeezed beam of significant (0.17 mW) power. This allows the shape and orientation of the squeezing ellipse to be experimentally determined. These results, in conjunction with other work, demonstrate that the type of squeezing produced by the cavity-atom system can be altered by changing experimentally accessible parameters, a versatility not found in other systems.

We consider a system of globally coupled bistable systems under the influence of noise and periodic modulations. The hopping process between the stable states is described by a nonlinear master equation. We observe an unusually large amplification of the periodic modulations for certain values of the noise strength due to collective dynamics of the coupled bistable elements.