Rank-6 symmetry in energy transfer collisions is observed. A Ca(4s4f${,}^1$${\mathit{F}}_3$) state is prepared by three-photon excitation. The angular wave function of the Ca${(}^1$${\mathit{F}}_3$) state depends on the angles of the three laser polarizations with respect to each other. The alignment effect for energy transfer, Ca(4s4f${,}^1$${\mathit{F}}_3$)+He→Ca(4${\mathit{p}}^2$${,}^1$${\mathit{S}}_0$)+He, is determined for two different initial angular wave functions. Each alignment curve can be analyzed in terms of the same set of relative cross sections for the individual Ca${(}^1$${\mathit{F}}_3$) magnetic sublevels, providing an independent verification of the data.

Additional superpromotion S series successively connecting an infinite number of ‖N,l,m〉-‖N+1,l,m〉 adiabatic states of a one-electron–two-Coulomb-center system (${\mathit{Z}}_1$,e,${\mathit{Z}}_2$) have been discovered in the complex plane of internuclear distance. The structure of the 5gσ series for the ${\mathit{Z}}_1$=${\mathit{Z}}_2$ system has been investigated in more detail. The additional superpromotion S series provide additional ionization channels in the (${\mathit{Z}}_1$,e,${\mathit{Z}}_2$) collision system, with a significant contribution to the total cross section for energies above -5 keV/u.

The isotopic shift of the 6${\mathit{p}}^2$ ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_0$→6${\mathit{p}}^2$ ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_1$ (1.28 μm) magnetic-dipole transition in Pb, which had been previously estimated incorrectly in the literature, has been measured, together with the magnetic hyperfine constant of the ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_1$ level in ${}_{}{}^{207}{}_{}{}^{}\mathrm{Pb}$. The shifts of the ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$ and ${}_{}{}^{207}{}_{}{}^{}\mathrm{Pb}$ lines from the ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ position are δ(206–208)=220.4(15) MHz and δ(207–208)=138.0(17) MHz, and the hyperfine constant A(6${\mathit{p}}^2$ ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_1$)=-2388.2(45) MHz. Inclusion of the shifts in calculated optical rotation line shapes removes long-standing discrepancies between theory and experiment, which have limited the precision of parity-nonconservation measurements in Pb.

Laser-induced fluorescence spectroscopy in a collimated atomic beam has been applied to determine isotope shifts and the hyperfine structure of an isotopic chain of the radioactive element polonium ${(}^{200}$Po, ${}_{}{}^{202}{}_{}{}^{}\mathrm{Po}$, ${}_{}{}^{204–210}{}_{}{}^{}\mathrm{Po}$). The relative isotope shifts show a striking similarity with results for other elements in the vicinity of Pb, even reproducing details of the odd-even staggering.

We prove the existence of anti-dark-solitons, i.e., dark solitons of the reverse sign of the amplitude, near the zero-group-dispersion wavelength of normally dispersive optical fibers using direct numerical simulations of the nonlinear Schrödinger equation which includes the third-order dispersion. These solitons were predicted earlier in the small-amplitude limit [Yu. S. Kivshar, Phys. Rev. A 43, 1677 (1991)] and they may exist only for a certain propagation direction, so that the interaction of dark and anti-dark-solitons propagating in opposite directions is possible; this is probably the only possibility to observe direct collisions of dark and bright solitons. We investigate the collision numerically and demonstrate that it looks elastic at least for small-amplitude solitons.

We present measurements of absolute rates for multiphoton ionization of the ground state of atomic hydrogen by a linearly polarized, subpicosecond KrF laser at a wavelength of 248 nm. The irradiance was varied from 3×${10}^{12}$ to 2×${10}^{14}$ W/${\mathrm{cm}}^2$, and three above-threshold-ionization peaks were observed. The measured rate for total electron production was less than that predicted by Floquet theory [S.-I. Chu and J. Cooper, Phys. Rev. A 32, 2769 (1985)] and perturbation calculations [S. V. Khristenko and S. I. Vetchinkin, Opt. Specktrosk. 40, 417 (1976)], but significantly higher than calculated by the Reiss [Phys. Rev. A 22, 1786 (1980)] and Keldysh [Sov. Phys.—JETP 20, 1307 (1965)] methods using Volkov final states.

We present nonperturbative calculations of ionizing and trapping probabilities for a one-dimensional model and a three-dimensional hydrogen atom in an intense high-frequency Gaussian-pulsed laser field. Investigating the dynamics of the ionization process (for one- and two-photon ionization), we find that only for extremely short pulses, especially for hydrogen, does the system have a significant probability of surviving at the end of the pulse, leading to the phenomenon of atomic stabilization with respect to ionization. We also find that a one-dimensional model has a higher survival probability at the end of a Gaussian pulse, as compared to the three-dimensional hydrogen atom.

We report on the multiphoton ionization and dissociation of hydrogen and deuterium molecules in intense (8×${10}^{11–}$4×${10}^{13}$ W/${\mathrm{cm}}^2$) laser fields. The investigations were performed with the second harmonics of two different laser systems, a 50-ps neodymium-doped yttrium lithium fluoride and a 10-ns neodymium-doped yttrium aluminum garnet laser. Measurements included energy-resolved photoelectron and mass spectroscopy. In addition, we report on a measurement of the dynamics of different above-threshold dissociation branching ratios for ${\mathrm{H}}_2^{+}$ and ${\mathrm{D}}_2^{+}$ over a wide range of laser intensities. Our results support the dressed-molecule picture at least qualitatively, but differences do exist with the quantitative predictions.

We consider the scattering of atoms off a standing electromagnetic wave in a given quantum state and show that the photon statistics can directly manifest itself in the momentum distribution of scattered atoms. Revival-like structures in the distribution function, resulting from quantization, appear as well.

An exact solution is reported for the kinetics of random sequential adsorption of mixtures of monomers and k-mers on a one-dimensional lattice. The limit k→∞can then be appropriately defined, yielding the solution for the continuum deposition of a mixture of fixed-size and pointlike particles. The addition of the pointlike particles is found to modify in a nonuniversal way the form of the large-time convergence law of the approach to the jamming coverage.

There exists a class of maps that possesses nonchaotic orbits with either finite or infinite periods. However, these maps have computationally determined periods that are dependent on the precision of the arithmetic. Such maps are said to have relative, apparently real periods.$-— We give analytical proof that a special case of the logistic map with a discontinuity belongs to this class and support this proof with some numerical illustrations.

We report an experimental study of polymerized membranes using graphite oxide (GO) suspension. Dry samples of GO are analyzed using electron microscopy and electron diffraction. They are found to be composed of thin solid membranes. The conformation of these membranes in solution is investigated using light scattering and is found to be fractal.

We present numerical studies of the effect of long-range correlated noise on (i) the nonlinear Kardar, Parisi, and Zhang (KPZ) stochastic differential equation and the related problem of directed-polymer (DP) growth, and (ii) the ballistic-deposition (BD) model. The results for the KPZ and DP models are consistent with each other, and agree better with one recent theoretical prediction of Hentschel and Family [Phys. Rev. Lett. 66, 1982 (1991)] than with other theoretical predictions. Contrary to the general belief that BD is described by the KPZ equation, we find the surprising result that BD with correlated noise belongs to a different universality class than the KPZ equation.

We consider interacting rotating spiral waves (vortices) under conditions when the asymptotic wave number is small and apply consistent approximations near the vortex core and in the outer region and asymptotic matching to derive a mobility relationship that connects the propagation velocity of a vortex with relevant characteristics of the extrinsic phase field in its vicinity. The results are applied to the problem of the existence of bound states of a pair of interacting vortices of the opposite charge. It is found that interaction decays exponentially with separation and remains attractive at all distances.

By carrying out a Monte Carlo simulation we compute the lifetime of thermodynamically unstable bilayers of a specific initial conformation in the Widom model of microemulsions. For identical initial conformations of these model bilayers, we study the dependence of the lifetime on (a) the initial concentration of the amphiphilic molecules, (b) the temperature, and (c) the strengths of the curvature elasticity of the amphiphilic membrane. We also discuss the similarities and differences between our computer experiment and the laboratory experiment on the rupture of the Newton black films.

Exact, periodic multipolaron solutions are constructed for the Gross-Neveu (GN) field theory in one dimension for particles with N flavors. First we connect the appropriate GN equations with continuum models of Peierls distorted polymer chains. Then we utilize a relationship between the cnoidal wave solutions of the Toda lattice and the potential of a polaron lattice in polymers.

In this work we analyze how amplitude modulations of the laser field affect the plasma-wave amplification in the beat-wave accelerator. It is shown that under certain resonance conditions, modulated lasers may cause the plasma wave to grow beyond the limits calculated from homogeneous models with the same initial-energy content.

We study a randomly diluted higher-order network of spinlike neurons that interact via Hebbian-type connections and derive and solve exact dynamical equations for a general block-sequential updating algorithm. The system has a variety of static and oscillatory solutions. The bifurcation parameters in the present model include neuronal interaction coefficients, the synchronicity parameter, and a rescaled noise level, which represents the combined effects of the random synaptic dilution, interference between stored patterns, and additional background noise.

The localization factor (inverse of the localization length) is derived as a function of the transmission matrix τ for multichannel disordered systems using a multiplicative ergodic theorem of Oseledets [Trans. Mosc. Math. Soc. 19, 197 (1968)]. The wave-transfer-matrix formalism is used in which the transfer matrices are symplectic and elements of the special unitary group SU(d,d). Modeling the disordered multichannel system via a product of random-wave-transfer matrices and applying the theorem of Oseledets as a starting point, it is shown that the multichannel localization factor (the smallest Lyapunov exponent of the random matrix product) can be expressed asymptotically as a function of any one of three matrix norms of the transmission matrix τ. As a by-product of this analysis, we also develop expressions for the remaining Lyapunov exponents as a function of τ. The localization factor result is compared with two others appearing in the literature.

We study the effects of the reaction field on the spin relaxation. We find that they are not only responsible for a nonlinear friction process, as recently pointed out by several authors, but, in the case of sufficiently strong coupling, they also result in a bistable precession process. This implies that at weak temperatures the rate of the spin relaxation is expected to exhibit an Arrhenius-like dependence on temperature.