The convection mode and its relation with the lower-hybrid waves are investigated. It is demonstrated that the convection mode can be unstable in the presence of a drift or beam, and that it can also be driven parametrically.

A structural analysis of matrix elements is used to interpret fa- miliar propensity rules.

The eigenvalue problem for two particles interacting through the attractive truncated Coulomb potential, V(r)=-${\mathrm{Ze}}^2$/($r^p$+${\beta }^p$${)}^{1/p}$, for p=1 and 2 is solved numerically. Energy eigenvalues accurate to within eight to six significant figures for the states 1s to 4f are calculated as a function of the truncation parameter β. It is found that the level ordering satisfies $E_{\mathrm{nl}}$>$E_{\mathrm{nl}\mathcal{’}}$ for l’. Systematics of the eigenvalues are studied and it is found that for each l value the energies are well represented by a Ritz type of formula.

Electromagnetic radiation in a cavity is used to investigate the question of the photon mass. Bounds on this quantity are calculated from the spectrum and the radiance obtained under the assumption of a nonzero mass for light, and they turn out to be several orders of magnitude worse than the limits from nonthermal measurements. Considering the correction to the Planck formula due to the size and shape of the cavity, one is led to the conclusion that thermal methods cannot improve on already existing bounds: This would either require enormous cavities or unreasonably small errors in measurements of the cosmic background radiation.

We consider the problem of identification and characterization of (Hamiltonian operators of) quantum systems which have a uniform-level-energy behavior (i.e., the level distribution follows a rectangular law) and a regular-level-energy behavior (i.e., the level energies are distributed according to an inverted semicircle law). Here we find a large class of Hamiltonians with these level-energy behaviors in terms of the matrix elements of their associated Lanczos matrix forms.

Cross sections for the excitation of a core electron, which leads to autoionization, in lithium (Li) atomic system by electron impact have been calculated with use of the single-configuration Hartree-Fock wave function within the asymptotic Green’s-function approximation (AGFA) in the low-bombarding-energy region. Comparison is made with available results. Our investigation demonstrates that the AGFA supports the R-matrix as well as the distorted-wave Born-approximation behavior.

The proton stopping cross section of liquid water for the energy range from 40 keV to 10 MeV is calculated by applying the modified local-plasma model and employing a simple model of liquid water. The calculated stopping cross section of liquid water is about 5.6% to 14% lower than the calculated vapor-state results for the range of 80 to 500 keV and is about 8.5% to 13.4% lower than measured vapor-state results. The present results agree well with the measurements for ice crystals. The mechanism of this physical-state effect is also presented.

A model-potential method due to Khan et al. [Phys. Rev. A 29, 3129 (1984)] is used to investigate elastic $e^{\pm }$-Ar scattering at low incident energy, up to 18 eV. The effect of short-range correlation has been included via an adjustable parameter. Same polarization potentials have been used for both the electron and positron cases, and scattering parameters are presented. The results are found to be in good agreement with the existing theoretical predictions and measured values.

A relationship between the low-energy antiproton-atom scattering parameters and Coulomb level shifts is derived. The corresponding scattering lengths are calculated for the p¯-${\mathrm{He}}^{+}$ system on the basis of energy level shifts evaluated earlier by means of the Born-Oppenheimer approximation.

The aerothermodynamic studies of proposed space missions require atmospheric charge-transfer data. ${\mathrm{N}}_2$${\mathrm{}}^{+}$ eigenstate energies are calculated with use of the complete-active-space self-consistent-field method with an extended Gaussian basis set. The ${\mathrm{N}}^{+}$-N charge-exchange cross section, determined from these energies, agrees with merged-beam measurements. This contradicts the previous theoretical conclusion. A simple physical description of the long-range interaction is presented and should expedite future charge transfer studies.

The counterterm F(ɛ) needed for an upper-bound variational principle, to compensate for the additional binding which occurs when a singular repulsion is truncated, is shown to be exponentially small. The proof of this result is based on a coupled-wave expansion of the many-body wave function in products of wave functions for one pair of particles and the A-2 other particles. A simple manipulation of the properties of a second-order linear differential equation in a region of positive potential shows that F(ɛ) is of order A(A-1) exp{0.65[V(ɛ${\left)\right]}^{3/2}$ [V’(ɛ${\left)\right]}^{\mathrm{-}1}$} or less, where V(ɛ) is the value at which the singular potential is truncated and V’(ɛ) is the corresponding derivative. This result is incorporated in a generalized variational principle which is based on Padé approximants and defines an optimal effective force.

The lifetimes of the 7 ${\mathrm{}}^2$$P_{1/2}^o$ and 7 ${\mathrm{}}^2$$P_{3/2}^o$ states of thallium have been measured for the first time by observing the fluorescence decay following two-photon resonant excitation in an atomic beam. The values obtained for these states are 61.9 and 48.4 ns, respectively, with an uncertainty of 2%. These results are in good quantitative agreement with the calculations of Bardsley and Norcross, which include the effect of core polarizability.

From published potential-energy curves and transition dipole moments we obtain by numerical integration of the equations of nuclear motion the vibrational eigenfunctions of the X ${\mathrm{}}^1$${\Sigma }_g^{+}$ and B’ ${\mathrm{}}^1$${\Sigma }_u^{+}$ states of ${\mathrm{H}}_2$ and we calculate the probabilities of radiative transitions from the discrete vibrational levels of the excited B’ ${\mathrm{}}^1$${\Sigma }_u^{+}$ electronic state of ${\mathrm{H}}_2$ to the discrete and continuum vibrational levels of the ground X ${\mathrm{}}^1$${\Sigma }_g^{+}$ electronic state. The Franck-Condon factors are also presented.

It is shown that Kohn’s finite-volume variational method [H. Le Rouzo and G. Raşeev, Phys. Rev. A 29, 1214 (1984)] is able to provide ab initio continuum wave functions that are properly orthogonalized, in a generalized sense, to the bound eigenstates having a significant amplitude within the finite volume. These necessary orthogonality conditions are automatically accounted for during the variational process, provided the relevant bound states are included in the basis set used to expand the continuum wave functions. The rate of convergence of these expansions is greatly enhanced in this way, even when approximate bound wave functions are used.

For a three-level atom excited by two laser fields whose amplitudes are sinusoidally modulated with a phase difference of π/2, we show that, rather surprisingly, a second (independent) linear constant of motion may be obtained even more directly by the coherence vector method than by the recent density-matrix formulation of Hioe. As a consequence it is found that the two corresponding eigenvectors of the time-independent time-evolution matrix in the degenerate subspace with two zero eigenvalues are orthogonal if a certain relation holds between the laser modulation and Rabi frequencies.

Spiraling vortices observed in instabilities of annular flows are found as propagating-wave solutions of nonsymmetric amplitude equation. The damping of the wave near the ends of the vortex system results in a selection of the wave number through a new mechanism. The distance of the wave number q to the critical one $q_c$ is shown to be q-$q_c$=O(ε), where ε is the small relative distance to threshold. This result is supported by theoretical and numerical arguments, and confirmed by experiment.

The hydrodynamic modification of an expanding plasma by the ponderomotive force of the laser radiation is calculated without introducing the assumption of the density profile being locally linear from the sonic point to the critical density. Intensity dependence of various parameters which characterize the density profile modification are presented. Our results can reflect the density jump occurring in the critical region more completely and accurately. In addition, the field structure and the density profile for all regions of coronal plasma are also studied.

The dependence of EPR line shape on molecular motion is carefully studied both in an ordered and in an isotropic fluid in the slow-motion regime. It is shown that spectroscopy can successfully follow the onset of orientational order and measure the $D_{\perp }$ component of the diffusion tensor for a stearic spin probe. The weak dependence of the absorption upon $D_{\mathrm{para}}$ component is interpreted.

The relaxation of an isotropic approximately monoenergetic system of like particles through small-angle Coulomb collisions is followed numerically. It is found that when energy conservation is ensured, the results are qualitatively different from that of an earlier study [W. M. MacDonald, M. N. Rosenbluth, and Wong Chuck, Phys. Rev. 107, 350 (1957)], and show a smaller, global relaxation time. A new interpretation is advanced for the earlier results.

The large-time solutions to this equation for the coagulation kernel K(i,j)=$i^{\lambda }$+$j^{\lambda }$ (with 0<λ<1) are obtained under the scaling hypothesis. It is shown why the results on this problem, derived previously, are incorrect.