Total cross sections are reported for electron transfer and ionization in collisions between protons and the hydrogenic ions ${\mathrm{Be}}^{3+}$, ${\mathrm{B}}^{4+}$, and ${\mathrm{C}}^{5+}$, and results are presented for ${\mathrm{He}}^{+}$ and ${\mathrm{Li}}^{2+}$ in addition to those previously reported. Proton energies relative to the target ion are in the range 17.5–150 keV for ${\mathrm{He}}^{+}$ targets, increasing with the target’s nuclear charge to 150–600 keV for ${\mathrm{C}}^{5+}$ targets. Within these energy ranges the electron-transfer cross sections reach their peak values, and the ionization cross sections approach peak values from below. A coupled-Sturmian-pseudostate approach has been taken, and the largest-basis results are estimated to be converged to within 10% at energies where the electron-transfer cross sections peak. With sufficiently large bases, the cross-section curves vary smoothly and regularly with energy and the target’s nuclear charge. Scaling rules for these curves are examined and compared with the simple scaling laws in the Born approximations.

A model based on the heat diffusion equation is used to describe the switching dynamics in thermally induced optical bistable devices. In this model, energy is brought to the device by a cw holding light beam and by a light pulse. In this case, it is shown that switching times can be much faster than the thermal relaxation constant of the material. This model, applied to nonlinear ZnSe interference filters, explains the switching behavior recently observed.

A perturbative theoretical analysis of the operation of a long-pulse free-electron laser (FEL) is presented. This analysis was prompted by the remarkable property of the FEL at the University of California at Santa Barbara of generating radiation with a very small fractional bandwidth of the order of ${10}^{\mathrm{-}8}$. To third order in the radiation field, the transverse current driving the FEL contains large crossed-saturation terms between resonator modes. Through the strong crossed saturation the dominant mode depresses the effective gain of other modes to the point of extinction, resulting in single-mode operation. These conclusions hold as long as the long-pulse FEL is operating in a low-gain, homogeneously broadened regime, outside the deep saturation region. The perturbation expansion, nonlinear single-mode, and two-mode problems are discussed in detail.

We have rigorously included hyperfine interactions during electron-spin-exchange collisions between ground-state hydrogen atoms and find additional frequency shifts which are significant for low-temperature atomic hydrogen maser oscillators.

An extension of the quantum theory of the atom-field interaction within a high-finesse resonator is made to include spatial variations of the field mode in the limit of small cavity decay rate. The two particular examples of a Gaussian mode field in a ring cavity and a plane-wave field in a standing-wave interferometer are presented to illustrate the method. Analytic expressions are obtained for the incoherent intensity and photon correlations of the transmitted field. In qualitative terms, effects such as sub-Poissonian photon statistics predicted by the plane-wave theory in a ring cavity are preserved. In either the weak-field or dispersive limit the results of the plane-wave theory in a ring cavity are recovered independent of the form of the spatial dependence of the cavity mode.

A simple theory of the splitting of an atomic beam by monochromatic light is presented. It is argued that the components of an atomic beam split by the optical Stern-Gerlach effect do not correspond to the dressed states of the atom-field system.

The absolute intensities of Ti x spectral lines emitted from a θ-pinch plasma are measured with a 2.2-m grazing-incidence monochromator which is calibrated in situ by using the branching-ratio technique. An electron temperature of 50 eV and an electron density of 2.2×${10}^{16}$ ${\mathrm{cm}}^{\mathrm{-}3}$ of the plasma are determined from the laser scattering. The measured ratios of line intensities are compared with predictions based on the corona model using the excitation rates calculated by a distorted-wave method. It is shown that such a comparison is possible even for line intensities affected by self-absorption provided their optical depth corrections cancel in the ratio. The experimental uncertainty in the measured ratios is estimated to be ±30%. The results show good agreement between experiment and predictions.

A laterally infinite liquid layer is heated from below in a time-periodic fashion with dimensionless frequency ω and amplitude δ. A Lorenz-like truncation of the hydrodynamic equations is derived and used to study the pattern competition between hexagons and rolls near threshold. This approximation yields a realistic estimate, valid for arbitrary ω and δ, of the jump in convection amplitude at the subcritical bifurcation from conduction to hexagonal convection, and of the range of stability of hexagons near threshold. The jump is predicted to be unobservably small for typical parameter values, and the stability range of hexagons turns out to be small but potentially observable for suitable choices of parameters. An earlier calculation by Roppo, Davis, and Rosenblat [Phys. Fluids 27, 796 (1984)], which is limited to the range δ${\pi }^2$) but predicts observable hexagon effects in that range, is shown to overestimate those effects considerably. The present model is suitable for studying the dynamics of pattern competition by straightforward numerical techniques.

Measurements of the x-ray conversion efficiency (hν≥100 eV) for a KrF-laser–produced plasma are reported. Planar targets with atomic numbers varying from 4 to 82 were irradiated by moderate intensities (${<10\mathrm{}}^{13}$ W/${\mathrm{cm}}^2$) of 0.25-μm KrF-laser light and the resulting emission was observed by several detectors sensitive to x-ray photon energies from 100 eV to 15 keV. Most of the radiation appeared as xuv and was measured by x-ray diodes to obtain the conversion efficiency as well as the angular distribution of the emission. The x-ray emission both above and below 1 keV was found to display marked variation with atomic number, as successive atomic shells are ionized. These measurements are supplemented by spatial and temporal observations of the keV x-ray emission which also show variations with target atomic number.

We present here a study of the behavior of fluid systems under external constraints by molecular dynamics with stochastic boundary conditions. We investigate the validity of the local-equilibrium hypothesis. The agreement between measured local physical properties and those predicted by a first-order Chapman-Enskog theory is remarkable. We also discuss the difficulty of the measurement of local time-correlation functions.

A theory of Bayesian estimation of the behavior of a nonlinear stochastic system through observing a part of the system (partial observation) is developed. A new method to solve the evolution equation for the a posteriori probability density of the unobserved variable is studied with the extended use of the system-size expansion method. The resultant equations are of a computationally feasible form and enable us to estimate the unobserved variable with the use of the data on the observed variable. The method is shown to be effectively applied to the Lotka-Volterra population system with fluctuating forces to estimate the population of predators upon knowing that of the prey.

Using computer algebraic symbolic manipulation techniques, we rearrange the ideal-gas-based low-density expansions for the ground-state energy of a many-fermion and a many-boson system interacting via arbitrary pair central forces, into a repulsive-core-fluid-based perturbation expansion. Applications through second order are reported for liquid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ and liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$.

We have determined three maps (truncated at quadratic terms) that are fixed under the renormalization operator of pitchfork period doubling in symmetric four-dimensional volume-preserving maps. Each of these contains the previously known two-dimensional area-preserving map that is fixed under the period-doubling operator. One of these three fixed maps consists of two uncoupled two-dimensional (nonlinear) area-preserving fixed maps. The other two contain also the two-dimensional area-preserving fixed map coupled (in general) with a linear two-dimensional map. The renormalization calculation recovers all numerical results for the pitchfork period doubling in the symmetric four-dimensional volume-preserving maps, reported by Mao and Helleman [Phys. Rev. A 35, 1847 (1987)]. For a large class of nonsymmetric four-dimensional volume-preserving maps, we found that the fixed maps are the same as those for the symmetric maps.

The stochastic-trajectory-analysis technique is applied to the calculation of the mean–first-passage-time statistics for processes driven by external shot noise. Explicit analytical expressions are obtained for free and bound processes.

Far-infrared measurements (40–500 ${\mathrm{cm}}^{\mathrm{-}1}$) of vacuum-dried, free-standing, unoriented films of the polynucleotides poly(dA)⋅poly(dT), poly(dA-dT)⋅poly(dA-dT), and poly(dG)⋅poly(dC) and the ribonucleotide poly(rA)⋅poly(rU) under various salting conditions are reported. Spectral features that depend on temperature, crystallinity, and salting conditions have been observed. Of most interest are four sharp bands near 63, 83, 100, and 110 ${\mathrm{cm}}^{\mathrm{-}1}$ in polycrystalline poly(dA)⋅poly(dT). These low-frequency (<240 ${\mathrm{cm}}^{\mathrm{-}1}$) observations are discussed in terms of a lattice-dynamical model of homopolymer DNA.

Recent calculations of three-body systems have obtained correct dissociating states in a hyperspherical adiabatic framework. The hyperradius scrR, a measure of the size of the system, commutes with the kinematic rotations connecting united-atom and dissociation limits. This result has general significance. The widely discussed translation factors were included in the Born-Oppenheimer basis to compensate an intrinsic shortcoming rooted in the separation of nuclear and electronic kinetic energies. The treatment of kinetic energy in the adiabatic hyperspherical procedure eliminates the need for translation factors entirely, even though this procedure departs from the Born-Oppenheimer model only slightly in other respects.

The parity-nonconserving electric-dipole-transition amplitudes for the 6$s_{1/2}$→7$s_{1/2}$ transition in cesium and the 6$p_{1/2}$→7$p_{1/2}$ transition in thallium have been calculated by the Dirac-Hartree-Fock method. The effects of using different Dirac-Hartree-Fock atomic core potentials are examined and the transition amplitudes for both the length and velocity gauges are given. It is found that the parity-nonconserving transition amplitudes exhibit a greater dependence on the starting potential for thallium than for cesium.

We derive an expansion of the scattering matrix for any reasonable atomic potential V(r) by using the Sturmian expansion of the Coulomb Green’s function. We demonstrate the method for the case where V(r) is a Coulomb potential plus a Yukawa potential.

We have searched for long-lived (≳${10}^{\mathrm{-}5}$ s) doubly charged negative atomic ions produced in a high-current cesium sputter source with a tandem-accelerator-based charge spectrometer. The results of these ultrasensitive searches for doubly charged negative atomic ions of group VI B and VIII B elements, and hydrogen that can survive the acceleration to the tandem terminal, are reported. No evidence of doubly charged negative atomic ions was observed, and upper limits for the ratio of production (and survival) of doubly charged to singly charged negative atomic ions were obtained for the cesium sputter source.

The stability of a thin electron beam in a uniform magnetic field is studied. It is found that if the conducting wall is close to the beam, the cyclotron-maser action occurs in a fast wave structure. For given geometrical parameters, there is a critical current density below which the beam is stable to perturbations.