Electron-photon angular correlations between electrons which have excited the $2{}_{}{}^1{}_{}{}^{}P$ state of He and photons from the $2{}_{}{}^1{}_{}{}^{}P\to 1{}_{}{}^1{}_{}{}^{}S$ transition have been studied for 27-, 30-, 35-, and 40-eV incident electrons. Values of $\lambda$ and $\left|\chi \right|$ obtained from these measurements are compared to values obtained in distorted-wave and $R$-matrix calculations. The values of $\lambda$ and $\left|\chi \right|$ have been combined to examine the behavior of $\left|O_{1-}^{\mathrm{col}}\right|$ [$\lambda (1-\lambda )sin\left|\chi \right|$], the nonvanishing component of orientation. At 27 eV, a substantial decrease was observed in the values of $\lambda$ and $\left|O_{1-}^{\mathrm{col}}\right|$, compared with their values for $E>~30$ eV.

The relative cross sections for 6-, (6 + 1)-, and (6 + 2)-photon above-threshold ionization of xenon at 0.53 μm are experimentally determined. The influence of these transitions on the total ion yield is discussed for different intensity regimes, at 0.53 and 1.06 μm.

In this Brief Report we comment on the use of the relativistic form factor to estimate the contribution of the coherent scattering of photons, and its subsequent use for the evaluation of the incoherent-scattering cross sections from the measured total photon attenuation cross sections.

We present experimental data showing destruction of degenerate four-wave-mixing signals by collisions at extremely low pressures of added buffer gases (∼100 mtorr). These experiments are performed on the $3s{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}\mathrm{}(F=2\mathrm{})-3p{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}\mathrm{}(F=3\mathrm{})\mathrm{}$ transition of the $D_2$ line in atomic sodium for which, in the absence of buffer gases, the lower state is not optically pumped to the $3s{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}\mathrm{}(F=1\mathrm{})\mathrm{}$ ground state. However, using a simple rate equation model we are able to qualitatively explain the observed behavior by showing that state-changing collisions have the effect of generating a collision-induced optical pumping. This transfers the $F=2\mathrm{}$ ground-state population to the $F=1\mathrm{}$ ground state, thus reducing the density of atoms available for generating a signal.

Using correlated complex functions with Gamow orbitals and a recently developed variational procedure, we have calculated the autoionizing widths of the $\mathrm{He}2s2p{}_{}{}^1{}_{}{}^{}P_{}^{\circ }{}_{}{}^{}$, $2p^2{}_{}{}^1{}_{}{}^{}D$, and $2s^2{}_{}{}^1{}_{}{}^{}S$ resonances. They are found to be in good agreement with previous accurate calculations which employed the golden-rule formula with real scattering functions.

Wave propagation in free space is considered without invoking the paraxial approximation. An explanation is provided for the discrepancy which arises when the general formalism is applied to the case of a Gaussian beam.

Recent neutron inelastic scattering experiments on dense krypton gases are analyzed using a dynamical theory of simple fluids which includes the correct static susceptibilities but approximates the generalized wave-number- and frequency-dependent transport coefficients by the hard-sphere Enskog-theory values. The full width at half maximum of the dynamical structure factor is found to depend strongly on the thermal pressure coefficient, which is evaluated and discussed for a Lennard-Jones pair potential using the Kirkwood superposition approximation.

Recently, Holmes found that the behavior of Duffing's equation with negative stiffness can be studied profitably via its approximate Poincaré section which takes the form of a two-dimensional antisymmetric cubic map. We have pursued the study of its universal metric properties. A renormalization-group calculation shows that its bifurcation ratio is the same as that for the Hénon map. We have also studied the one-dimensional cubic map and found that its bifurcation ratio is the same as the quadratic map, thus answering in the affirmative a recent question raised by May.

A finite-amplitude long- (short-) wavelength kinetic Alfvén wave is found to be modulationally stable (unstable) in a plasma with $\beta$ (ratio of particle pressure to magnetic pressure) much smaller than electron-to-ion mass ratio.

The optimized Kohn method proposed by Takatsuka and Fueno [Phys. Rev. A 19, 1011 (1979)] is reexamined. The approach is clarified and, in particular, it is shown that the "unavoidable" singularities appearing in their treatment can also be eliminated and, therefore, have nothing to do with true resonances. The strong points of the optimized procedure are discussed and reemphasized in the light of the present formulation.

We have completed a new calculation of the ground-state doublet separation of the boron and fluorine isoelectronic sequences. This calculation is based on a variational formulation which leads to transition energies which are stationary with respect to small variations in the atomic orbitals.

States behaving like autoionizing states can be selectively induced by laser radiation into one of the continuum spin channels in the photoionization of polarized excited alkaki atoms. As a result of destructive or constructive interference between the direct ionization channel and those introduced by the dressing laser radiation, the cross section of this specific spin component is completely suppressed or enhanced, while leaving the other spin channel unaffected. The $q$ parameter which determines the line shape of the Fano-type resonance can be resonantly tuned as a function of the dressing laser frequency.

We describe the energy and angular distributions of electrons ejected from the $\mathrm{Ba} {\left(6\mathrm{}{p}_{j}n{s}_{\frac{1}{2}}\right)}_1$ states in their autoionization to the ${\mathrm{Ba}}^{+} 6s$, $5d$, and $6p$ states. The atoms are excited by a three-step laser approach which enables us to excite to the autoionizing state from the spherically symmetric $6sns {}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ states. Since we excite to the discrete part of an autoionizing state, the angular distributions are different from those expected for continuum excitation. Both the angular distributions of the ejected electrons and branching ratios to the available ion states exhibit much more variation than would have been anticipated on the basis of the $n^{-3\mathrm{}}$ dependence of the total autoionization rates.

The Texas Experimental Tokamak (TEXT) was used to observe magnetic-dipole radiation arising from transitions within the $3s^{2}3p^n$ ground-state configurations of highly stripped ions heavier than Ni. This device generates a plasma of 3 × ${10}^{13}$${-\mathrm{c}\mathrm{m}}^{-3\mathrm{}}$ electron density and ∼1.5-keV temperature, ideally suited for ionization of these atoms to the $n=3\mathrm{}$ shell. Wavelength and transition-rate predictions were made with Scaled Hartree-Fock radial energy integrals.

The dynamics of phase separation has been investigated by light scattering measurements with a critical liquid mixture of polydimethylsiloxane in diethyl carbonate. It is found that the structure factor has a scaling form predicted by recent theories. The experimental result suggests that the negative diffusivity is dependent on the wave number in the unstable region of the phase diagram.

We present a proof that the entropy density production for a fluid obeying the nonlinear revised Enskog equation is positive provided $f_1$, the one-particle distribution function, is slowly varying in space.

A scaling analysis is performed on Monte Carlo simulations of random walks on percolation clusters both above and below the threshold $p_c$. The average diffusion constant is described by a single scaling function in which the crossover from an algebraic decay (in time) near $p_c$ to the asymptotic behavior above or below it occurs at time $t_{\mathrm{cross}}\propto {|p-p_c|}^{-(2\mathrm{}\nu -\beta +\mu )}$. The value of the percolation conductivity exponent $\mu$ is found to be 1.05 ±0.05 for two-dimensional systems and 1.5 ±0.1 for three dimensions.

Microscopic structures of supercooled one-component plasma fluids below the crystallization temperature are investigated through a solution to the improved hypernetted-chain equations with proven accuracy. The result shows that the plasma fluid may form a metastable glassy state in the supercooled domain, with a sufficiently large lifetime to be of astrophysical interest. The transport coefficients of a glassy plasma appropriate to a crustal matter in a neutron star are found to differ significantly from those of the corresponding crystalline plasma.

C${\mathrm{O}}_2$-laser scattering experiments were performed to measure collective fluctuations in a thermal plasma containing two ion components of different mass. Coherent detection was used to obtain the necessary sensitivity and spectral resolution. Ion temperatures, ion composition, and effective charge numbers $\overline{Z}$ were determined for mass numbers ranging from 1 to 40.