Elastic scattering of relativistic electrons and positrons by atoms is considered in the framework of the static field approximation. The scattering field is expressed as a sum of Yukawa terms to allow the use of various approximations. Accurate phase shifts have been computed by combining Bühring’s power-series method with the WKB and Born approximations. This combined procedure allows the evaluation of differential cross sections for kinetic energies up to several tens of MeV. Numerical results are used to analyze the validity of several approximate methods, namely the first- and second-order Born approximations and the screened Mott formula, which are frequently adopted as the basis of multiple scattering theories and Monte Carlo simulations of electron and positron transport.

It is argued that a set of manifestly normalizable solutions of the two-dimensional Coulomb diamagnetic problem generated by the fine-tuning of the external magnetic field is unphysical. An implication of this for the Hill determinant method is pointed out.

Momentum transfer to atoms by a standing light wave is measured in the presence of spontaneous decay. As the number of spontaneous decays is increased, the well-known Kapitza-Dirac diffractive structure observed in the absence of spontaneous decay evolves into a smooth diffusive pattern. Theoretical treatments based on a diffusive model adequately describe the rms momentum transfers and the envelopes of the momentum distributions. However, we observe significant persistence of diffractive structure at our long interaction times and find that details of the deflection profiles are accurately predicted only when several spontaneous decays occur during the interaction.

Laser systems can be used to detect very weak optical signals. The physical mechanism is the dynamical process of the relaxation of a laser from an unstable state to a steady stable state. We present an analysis of this process based on the study of the nonlinear relaxation time. Our analytical results are compared with numerical integration of the stochastic differential equations that model this process.

Spontaneous excitation of an atom near a phase conjugator should be amenable to experimental verification through a measurement of the atomic probe absorption profile. It is shown that the absorption decreases quickly with increasing reflectivity, due to a population of the excited state. The responsible physical process is a three-photon event.

We prove the stability of the ground state of an ensemble of charged particles interacting with a quantized electromagnetic field. We show that recently predicted instabilities of such a system do not occur.

Recently, De Brito and Baseia [Phys. Rev. A 40, 4097 (1989)] have studied the appearance of squeezed states for the Bateman Hamiltonian. Although the final results obtained in that report are correct, it is our intention to use an alternative point of view, based on a density matrix defined according to the maximum entropy principle, which allows us to reobtain those results in a more general way.

The capture of convoy muons by fusion α particles is reexamined following the theory of Müller, Rafelski, and Rafelski [Phys. Rev. A 40, 2839 (1989)] but including an appropriate treatment of collisionless muon transport in three space dimensions. As a first estimate we find that the initial convoy-muon capture probability increases with at least the second power of the density in the medium. The convoy-muon effect hence provides no immediate explanation for the observed density dependence of the muon sticking probability following deuterium-tritium muon-catalyzed fusion.

We consider the forces acting on the muon following the d-t fusion and show that it is improper to neglect the α-μ Coulomb interaction. We further show that the muon separation from the α particle is large at the time both interact with matter. This invalidates the assumption of pointlike source for transport studies of the muon evolution. We conclude, therefore, that the comment made by Jändel is physically incorrect.

A factorization of the dynamical Z function of the periodic-orbit expansion is presented for a Hamiltonian system displaying discrete symmetries. It is shown that the periodic orbits that are pointwise invariant under a symmetry operation require special treatment.

We have made the first determination of relative cross sections for the population of individual ${\mathit{M}}_{\mathit{L}}$ substates in a double-electron capture collision by measuring the angular distribution of electrons emitted in the Auger decay of doubly excited 1s2l2l${\mathcal{’}}^2$L states of ${\mathrm{C}}^{3+}$ formed in ${\mathrm{C}}^{5+}$+He collisions. Large anisotropies were observed for the 1s2${\mathit{p}}^2$ ${}_{}{}^2{}_{}{}^{}$D and 1s(2s2p ${}_{}{}^1{}_{}{}^{}$P${)}^2$${\mathit{P}}^{\mathit{o}}$ terms which varied markedly with projectile velocity in the range 0.29–0.50 a.u. A strong velocity variation was also observed for the total L-subshell relative cross sections.

We present data on atom-triatomic state-to-state collisional transfer that shows an exponential drop in rate as a function of transferred angular momentum. Earlier data on diatomic molecules may also be interpreted in these terms and we outline an alternative model for rotational transfer based solely on angular momentum. In this model, the exponential drop in probability of transfer as a function of transferred angular momentum results from the convolution of the speed distribution with the radial function for the repulsive intermolecular potential. This interpretation offers the opportunity to obtain parameters of the intermolecular potential directly from spectroscopic experiments. An illustration of this angular-momentum-inversion method is given, yielding the first potential inverted from scattering data.

Satellite intensity factors ${\mathit{F}}_2^{\mathrm{*}}$(s-f) have been calculated for the 1${\mathit{s}}^2$εl→1s2pnl→1${\mathit{s}}^2$nl dielectronic-recombination processes of heliumlike Ne, Si, Ar, Ti, Cr, and Ni. The relevant atomic parameters have been calculated explicitly for all intermediate resonance states ‖s〉=‖1s2pnlSLJ〉 with n=2–8 and l=0–6 in the intermediate-coupling scheme. The 1/${\mathit{n}}^3$ scaling, which has often been used in extrapolating ${\mathit{F}}_2^{\mathrm{*}}$(s-f) for n≥4, is tested against these values of ${\mathit{F}}_2^{\mathrm{*}}$(s-f).

Self-induced wandering among local attractors, that is, chaotic itinerancy, and the chaotic search of coexisting periodic or chaotic local orbits have been discovered in a nonequilibrium optical system with distributed nonlinear elements (Otsuka-Ikeda model system). It is shown on the basis of numerical simulations that spatiotemporal chaos in this system is interpreted as unstable motions which dynamically connect destabilized spatial structures via a chaotic itinerancy process.

The distribution of seismic moment or energy of earthquakes is well described by the universal Gutenberg-Richter power law, N(s)≊${\mathit{s}}^{\mathrm{-}1\mathrm{-}\mathit{b}}$, where b≊0.5–0.6. We have constructed a simple dynamical model of crack propagation; when driven by slowly increasing shear stress, the model evolves into a self-organized critical state. A power-law distribution for earthquakes with b≊0.4 in two dimensions and b≊0.6 in three dimensions is found. The critical state is ‘‘at the edge of chaos,’’ with algebraic growth in time of a small initial perturbation.

The random sequential adsorption of parallel (aligned) squares is studied by computer simulation. A new precise value of the maximum (jamming) coverage is found: ${\mathrm{\theta }}_{\mathit{J}}$=0.562 009±0.000 004. The dynamics for times t≳6000 agree with Swendsen’s prediction ${\mathrm{\theta }}_{\mathit{J}}$-θ(t)∼c(lnt)/t. Various two-point correlation functions are measured, and the effects of the finite size and the discretization of the adsorbing surface are also investigated.

The quantum kicked rotator is linearly coupled to a heat bath via its momentum coordinate. A momentum-space formulation of the Feynman-Vernon formalism is introduced to find the reduced propagator. The Wigner picture of the dynamics is adopted. It is found that it is a good approximation to ignore the ‘‘friction’’ effect and to replace the bath by a correlated noise source. For certain values of the friction coefficient, this replacement is exact. Destruction of coherence at zero temperature is qualitatively different for an undriven rotator.

Matrix elements for fermion and boson operators describing the creation or annihilation of particles with multiple angular-momentum quantum numbers can be factored into products of matrix elements of generalized operators, one for each quantum number. The generalized operators have nonzero matrix elements between states of arbitrary permutational symmetry. This factorization greatly increases the efficiency of shell-model calculations. We provide a physical interpretation for these generalized operators and introduce a simple operator-reordering procedure.

The behavior of the periodically kicked pendulum is determined classically and quantum mechanically. Our earlier analytic study [Phys. Rev. A 41, 2952 (1990)] is confirmed and extended by the numerical results presented here. We are able to construct minimum uncertainty, Gaussian wave packets that maintain their form, and shadow the corresponding classical motion for long times when the classical motion is nonchaotic or only weakly chaotic. However, when the classical motion is robustly chaotic, the quantum-mechanical probability distribution grows macroscopically broad exponentially fast and the quantum-classical correspondence breaks down.

Exact and asymptotic solutions to a linear rate equation for fragmentation with mass loss are presented. Solutions for spatially discrete random bond annihilation illustrate the mutual exclusiveness of the fragmentation and recession terms in the rate equation. Exact solutions for deterministic equal fragment recession show that continuous mass loss between fragmentation events can be approximated by discrete mass loss during fragmentation events when this mass loss is small. Evidence that continuous and discrete mass loss preclude shattering mass loss, the loss of mass to zero-mass particles due to runaway fragmentation, is presented. General asymptotic scaling forms, general solutions reflecting arbitrary initial conditions, and explicit scaling solutions are derived.