Partial cross sections for electron capture in 1–50-keV collisions of ${\mathrm{Ar}}^{6+}$ and ${\mathrm{Ar}}^{8+}$ with atomic hydrogen have been calculated using an atomic expansion including two complete principal shells of final states (n=4,5 for ${\mathrm{Ar}}^{6+}$ and n=5,6 for ${\mathrm{Ar}}^{8+}$). The qualitative structure of the results is in good accord with a reaction window picture. The results for ${\mathrm{Ar}}^{6+}$ ions are in agreement with published experimental data when precaution is taken with respect to uncertainties in absolute normalization of the data and with respect to a proper analysis of translation energy spectra at lower impact energies. The limited experimental data for ${\mathrm{Ar}}^{8+}$ do not agree with the present results.

The predicted charge-state dependence of dielectronic-recombination cross sections involving Δn>=1 L-shell excitation has been tested by measurements of resonant transfer and excitation (RTE) for ${}_{41}{}^{}{}_{}{}^{}\mathrm{Nb}_{}^{\mathrm{q}+}{}_{}{}^{}$+${\mathrm{H}}_2$ (q=28 to 32) collisions at 3.7 and 4.0 MeV/u. The measured RTE cross sections increase significantly with increasing charge state and thus disagree substantially with theoretical calculations that predict essentially equal cross sections for ${\mathrm{Nb}}^{29+}$, ${\mathrm{Nb}}^{30+}$, and ${\mathrm{Nb}}^{31+}$. This disagreement is contrary to the good agreement previously found between theory and experiment for K-shell RTE.

We present measurements of the relative electron-impact-excitation cross sections for the 1$s^2$ ${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$–1s2p ${}_{}{}^1{}_{}{}^{}\mathrm{P}_1^{}{}_{}{}^{}$, 1$s^2$ ${}_{}{}^1{}_{}{}^{}\mathrm{S}_0^{}{}_{}{}^{}$–1s2p ${}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}$, 1$s^2$ ${}_{}{}^1{}_{}{}^{}\mathrm{S}_0^{}{}_{}{}^{}$–1s2p ${}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$, and ${1s}^2$ ${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$–1s2s ${}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ transitions for the He-like ion, ${\mathrm{Fe}}^{24+}$. The measurements were made at two electron energies: 6.86 and 9.94 keV. The cross-section measurements are compared with theoretical calculations.

The Kβ-to-Kα x-ray intensity ratio was measured for the following elements: Mn, Cu, Zn, Ag, Cd, In, and Sn. The vacancies in the K shell were created by 59.54-keV γ rays from an ${}_{}{}^{241}{}_{}{}^{}\mathrm{Am}$ source and the x rays were measured using a hyperpure germanium detector. Our results agree with previous published experimental results.

We show in this report that the Bateman Hamiltonian belongs to the class of quadratic Hamiltonians, in terms of â and a${^}^{\mathrm{°}}$, that generates squeezed states of the electromagnetic field.

We consider the spontaneous emission by an atom near a phase-conjugating mirror (PCM). The effect of the PCM on the decay rate may be understood equivalently in terms of vacuum-field modes reflected and conjugated by the PCM, or in terms of vacuum modes transmitted and amplified without conjugation by the PCM.

A molecular-dynamics simulation of liquid Bi at 578 K using a system of 16 384 particles, supported by neutron-scattering measurements, shows that the side peaks of its dynamical structure factor S(Qω), attributed to the collective density excitations, are unobservable beyond wave vector Q=0.6 A${̊}^{\mathrm{-}1}$. Being in contrast to what has so far been observed in liquid metals, the strong damping of the longitudinal modes we found is concluded to result from the anomalies in the liquid-Bi structure, typical for molten semimetals.

Plasmon scattering by electrons in the simultaneous presence of two laser fields is considered. A kinetic equation for the plasmon population is derived, and the rate of change of the plasmon population is calculated. We found that plasma waves propagating parallel to the direction of polarization of the radiation fields may be amplified over a relatively narrow range of plasmon wave numbers.

We investigate properties of a recently proposed [Denton and Ashcroft, Phys. Rev. A 39, 426 (1989)] modification of the weighted density approximation. We apply the method to the low-density properties of several fluids and compare the results with those of other methods.

The Wigner-Seitz model for nonpolar fluids is used to calculate the conduction-band energy $V_0$ (relative to vacuum) of excess electrons in liquid argon as a function of number density n. The results are compared with those previously obtained in the framework of Lekner’s theory of the motion of electrons in nonpolar liquids.

We measured the spectral profiles of the Δn=0, n=2 transitions of C v in laser produced plasmas using both polyethylene and graphite targets. The line profiles were measured using an optical multichannel analyzer (OMA), with 5 ns gate time, yielding line profiles in a single shot with improved accuracy. The line widths measured at about 3 mm from the target surface indicate a high effective ion temperature over 1 keV. This result may be explained by hydrodynamic turbulence in addition to the radial expansion in the laser produced plasma. We also found that linewidths do not vary with time at 3 mm from the target surface, which indicates that the turbulence develops closer to the target surface. An imaging system was constructed to obtain spatially resolved spectra in a single shot. The spatially resolved profiles indicated that the line widths do not vary with position, except perhaps within 2 mm of the target surface.

A natural embedding for most time-continuous systems is presented. A set of nonlinear transformations is shown to split the whole family of dynamical systems into equivalence classes. The degree of nonlinearity is not a relevant characteristic of these classes of ordinary differential equations (ODE’s). In each class there exist two particular simple canonical forms into which any such ODE can be cast. We show on an example how to use these canonical forms to find nontrivial integrability conditions.

Collisionally induced four-wave mixing (FWM) signals have been observed in Na vapor broadened by He buffer gas at large detunings from resonance. Analytical expressions are developed which do not use the collisional impact approximation and which accurately describe the dependence of the FWM intensity on laser detuning and incident laser intensity. The measurements and the theory are used to calculate the nonimpact collisional lineshape for the Na-He system for detunings of 40 to 200 ${\mathrm{cm}}^{\mathrm{-}1}$ from the D line resonances.

We develop a technique for solving the time-dependent three-dimensional Schrödinger equation by expanding in terms of a set of Volkov functions and converting to a system of first-order temporal equations. Solutions are obtained through standard multivalue propagation schemes. We apply the method to several cases including the interaction of an intense, oscillating electric field with a model three-dimensional atomic system, observing the above-threshold ionization structure.

We present a quantitative study of radiation amplification without population inversion based on models recently proposed by Harris [Phys. Rev. Lett. 62, 1033 (1989)]. We discuss both two-level and three-level arrangements in terms of the density matrix. Our calculations, which are fully time dependent, incorporate an incoherent pumping mechanism that is essential for amplification. We discuss in detail the range of and conditions on atomic parameters for which amplification is possible. Its feasibility is demonstrated through the direct calculation of the change of the intensity of a probe beam interacting with the atom.

We discuss the effect of the transient response on the dynamics of lifetime broadened lasers that operate without the need for population inversion. A relationship between the steady-state absorptive transition probability rate and the transient gain and loss is given.

A theoretical model for studying the effects of optical gain and the cavity-mode squeezing on the spectrum of radiation produced by coherently driven two-level atoms is developed. The squeezing of the cavity mode dramatically affects the central component leading to a spike in the spectrum which becomes more pronounced with the increase in optical gain and squeezing. The squeezing can also affect the three photon Rabi sideband and can facilitate laser oscillation at such frequencies.

Time-resolved extreme-ultraviolet emission from sixteen 3p-3s transitions, some of the type in which lasing has been demonstrated in heavire elements, is measured for neonlike ${\mathrm{Ar}}^{8+}$ and ${\mathrm{Cl}}^{7+}$. These observations are made on a hydrogen θ-pinch plasma with a 5% admixture of argon or freon (for Cl). Fourteen 3d-3p spectral lines are also detected. The measured intensities are compared to theoretical predictions. All major lines agree within ±30%. Hence, there is no evidence of anomalously intense lines originating on 2$p^5$3p J=2 upper levels compared to J=0, as observed in gain experiments.

A neural network with excitatory neurons for associative storage and inhibitory neurons for control of firing rates is proposed. In distinction to attractor neural networks which are endowed with fixed-point dynamics, the basic recall mode of the network consists of a relaxation to a limit cycle originating from an inhibitory feedback loop. Nonlocal synaptic connections between excitatory neurons store all the information and yield robust associative abilities of the network. Inhibitory neutrons with short-range connections and nonlinear interaction (shunting) are introduced to stabilize low levels of neural activity. The mean firing rate per neuron ranges between 0.1 and 0.5 impulses per Monte Carlo step (MCS). The average activity of excitatory and inhibitory neurons oscillates with frequency of 0.5/MCS. The model generalizes the attractor concept for associative memory and brings logical neural networks closer to biological reality.

We have calculated the largest Lyapunov exponent near a crisis in spin-wave excitations in the ferrimagnetic material yttrium iron garnet. When the rf driving power is above the crisis, we observe chaotic transients. When the driving power is below the crisis, the largest Lyapunov exponent follows a scaling law as power is varied. We compare our observations in this high-dimensional system to the period-doubling cascade in one-dimensional maps, and suggest that the scaling law for the Lyapunov exponent might be caused by a high-dimensional inverse cascade.