The growth rate for an ion-ion two-streaming instability in a freely expanding two-ion two-temperature noncollisional plasma is derived on the basis of linear perturbation model. The local growth rate Γ is determined by four independent parameters, viz., α, the relative charge to mass ratio of the two ion species; ${\mathit{N}}_{10}$, the initial concentration of the main ion; τ, the temperature ratio of the hot and cold electrons; and ρ, the initial concentration ratio of the cold and hot electrons. For a single-temperature plasma, the total instability growth over a period of time needed for the complete separation of the two ion species is found to be maximum for an optimum value of α. The high-frequency modulation over the usual ion-velocity distribution in a multi-ion plasma system exhibits an accumulated instability effect of various ion-species pairs participating in the flow process. This oscillatory modulation tends to be smoothed out with the increasing effects of the hot electrons (high τ or lower ρ). For higher values α (say α>5), the accumulated instability growth is very small and is least affected by the presence of hot electrons.

Electron distribution functions have been calculated from a powerful numerical solution of the Boltzmann equation in the case of a positive column of low-pressure Hg–rare-gas discharge. The most important electron-atom collisional processes occurring in the plasma have been taken into account (elastic collisions, inelastic collisions including excitation, direct and stepwise ionizations, and also superelastic collisions). Coulomb interactions as well as atom-atom collisions leading to the creation of new electrons in the discharge (Penning reactions and Hg metastable-metastable ionizing collisions) are also considered. Then a comparative study of numerous methods of electron-distribution-function determination available in the literature has been carried out in the case of a Hg-Ar mixture followed by a discussion on the influence of several collisional processes on the electron-distribution-function calculation. The influence on the distribution-function calculation of the rare gas (He, Ne, Ar, Kr, or Xe) mixed with Hg has also been discussed in the case of a low-pressure positive-column fluorescent lamp discharge.

We have observed experimentally that during electron-cyclotron heating the electron longitudinal temperature drops as the perpendicular temperature increases. The experiment was carried out in a linear mirror machine with a low-density (${10}^{10}$ ${\mathrm{cm}}^{\mathrm{-}3}$) weakly ionized (≤1.0%) plasma.

It has been found, very generally, that there is a critical volume of the diffusion space, ${\mathrm{\Omega }}_{\mathit{c}}$, for a class of diffusions in random media, characterized by V(r) with a zero mean. If the size of the diffusion space is bigger than ${\mathrm{\Omega }}_{\mathit{c}}$, the total population increases with time. Otherwise, the total population decreases with time and will eventually vanish. An estimation of ${\mathrm{\Omega }}_{\mathit{c}}$ is obtained by a variation method.

We study the surface effect on the change in a helical structure induced by an external electric field near the isotropic-cholesteric transition in cholesteric liquid crystals. We show that in the presence of an ac electric field, a homogeneously anchored sample cooled from the isotropic phase produces a mono-domain in which the helix lies in the plane of the substrate. The angle between the aligned helix axis and the buffing axis b^ increases with the field up to the critical strength for helix dilation. The direction of the helix axis with respect to b^ depends on the sense of the cholesteric helicity and the nature of the substrate. A simple model is presented to account for the observed experimental results.

The formalism of bilocal field theory was applied to the calculation of the ground-state energy and the effective mass of the large polaron. This calculation illustrates the bilocal field method using a relatively realistic model of a physical system. In bilocal theory the fermion field is dependent on two spatial points (nonrelativistically). Fermi particles can then be described in terms of a center of mass and internal wave function, and field operators can be expanded in functions related to the exact one-fermion Green’s function, thereby eliminating self-energy terms from the S matrix and related operators. Similarities and differences between calculated large-polaron properties using the bilocal treatment and the customary local treatment are discussed. In particular, it is found that, within the approximations made, the bilocal and local methods give the same leading term in powers of the coupling constant for the ground-state energy and effective mass in the strong-coupling limit. For weak coupling, the bilocal energy is larger (more positive) and the effective mass smaller than in the local case due to an additional kinetic energy of internal motion.

The motion of charged particles in a standing electromagnetic wave is considered. For amplitudes that are not too high, the wave causes an effect of attraction of particles to the nodal points, resembling the channeling effect reported by Salomon, Dalibard, Aspect, Metcalf, and Cohen-Tannoudji [Phys. Rev. Lett. 59, 1659 (1987)] consistent with the ‘‘high-frequency potential’’ of Kapitza [Zh. Eksp. Teor. Fiz. 21, 588 (1951)]. For high-field intensities, however, the nodal points undergo a qualitative metamorphosis, converting themselves from particle attractors into resonant centers. Some chaotic phenomena arise and the description of the oscillating field in terms of an ‘‘effective potential’’ becomes inappropriate. The question of a correct Floquet Hamiltonian that could describe the standing wave within this amplitude and frequency regime is open.

The wave-packet reduction in quantum measurements is investigated for quantum-mechanical treatments except for the macroscopic limit in the final step. We show that the internal trace represented by the integrations over the internal variables of detectors, which are independent of the measured physical quantity, leads to the disappearance of the interference in the density matrix and then a reduction of the wave packet. Through the evaluations of two simple examples we clarify the role of the internal trace in quantum measurements and point out the difference between our idea and the others.

We present a variational method, based on direct minimization of energy, for the calculation of eigenvalues and eigenfunctions of a hydrogen atom in a strong uniform magnetic field in the framework of the nonrelativistic theory (quadratic Zeeman effect). Using semiparabolic coordinates and a harmonic-oscillator basis, we show that it is possible to give rigorous error estimates for both eigenvalues and eigenfunctions by applying some results of Kato [Proc. Phys. Soc. Jpn. 4, 334 (1949)]. The method can be applied in this simple form only to the lowest level of given angular momentum and parity, but it is also possible to apply it to any excited state by using the standard Rayleigh-Ritz diagonalization method. However, due to the particular basis, the method is expected to be more effective, the weaker the field and the smaller the excitation energy, while the results of Kato we have employed lead to good estimates only when the level spacing is not too small. We present a numerical application to the ${\mathit{m}}^{\mathit{p}}$=$0^{+}$ ground state and the lowest ${\mathit{m}}^{\mathit{p}}$=$1^{\mathrm{-}}$ excited state, giving results that are among the most accurate in the literature for magnetic fields up to about ${10}^{10}$ G.

The Feynman path-integral representation for memory superoperators is investigated. A physical interpretation of evolution superoperators in a Liouville space is given and shown to be closely related to the Feynman representation of quantum mechanics. From a general Huygens-like principle it is possible to obtain the Feynman path-integral representation for field operators. An application of the present formalism to a noninteracting many-boson system is provided.

It is suggested that the rate of the muon-catalyzed fusion cycle can be increased by powerful electromagnetic fields. The fraction of muons reaching the deuterium ground state ${\mathit{Q}}_{1\mathit{S}}$ can be decreased (thus increasing the fusion cycle) by changing the route of the muon-deexcitation cascade under laser irradiation. The muon cascade is determined by a competition between radiative transitions, external Auger transitions, quenching of the muon levels, and transfer processes. The muon-transfer cross section from the 2S level of deuterium is larger by a factor of about 5 than the transfer cross section from the 2P level. Therefore the following two-step process is proposed in order to enhance the rate of the muon transfer (1): (a) a laser-induced transition between the levels 2P and 2S of the deuterium (b) muon transfer by collisions to the tritium 2S level. The results show that a 0.2-eV laser (the Lamb shift in deuterium) with an intensity of about ${10}^9$ W/${\mathrm{cm}}^2$ can decrease the value of ${\mathit{Q}}_{1\mathit{S}}$ by a factor of 3.

A variational-perturbation method and explicitly correlated wave functions have been used to calculate the frequency-dependent polarizability α(ω,R) for the ${\mathit{B}}^1$${\mathrm{\Sigma }}_{\mathit{u}}^{+}$ state of the hydrogen molecule. The polarizability was calculated for the range 0.8${\mathit{a}}_0$≤R≤12.0${\mathit{a}}_0$ and for a wide range of electric-field frequencies ω. The behavior of this property is discussed in terms of the internal structure of the molecule and the electron density. The vibrational and rotational averaging of α(ω,R) was performed. A comparison with earlier Hartree-Fock and configuration-interaction calculations is presented.

An experiment was performed at TRIUMF to study the formation of pionic hydrogen atoms and molecules in solids, particularly in groups of organic molecules of slightly different structure in order to help further clarify the problem. The nuclear capture of pions by hydrogen was measured using the charge exchange of stopped pions. The coincident photons emitted by the decaying ${\mathrm{\pi }}^0$ mesons were detected by TRIUMF’s two large NaI spectrometers. Experimental results were obtained for the capture probability of stopped ${\mathrm{\pi }}^{\mathrm{-}}$ mesons in the nuclei of hydrogen atoms, chemically bound in molecules of some simple hydrides, acid anhydrides, and sugar isomers. A possible correlation was found between pion capture in hydrogen and the melting point of sugar isomers. The pion-capture probability in acid anhydrides is fairly well described by a simple atomic-capture model in which the capture probability on the hydrogen dramatically increases as the hydrogen atom is separated from the strongly electronegative ${\mathrm{C}}_2$${\mathrm{O}}_3$ group. Both effects are consistent with a correlation between pion capture and electron density on hydrogen atoms.

The saddle-point complex-rotation method is used to compute the energies and autoionization widths of the 1s3s3p ${}_{}{}^4{}_{}{}^{}$P° and 1s3p3p ${}_{}{}^4{}_{}{}^{}$P Feshbach resonances for the lithiumlike ions with nuclear charges from Z=2 to 6. These doubly core-excited quartet states rapidly autoionize, emitting low-energy electrons via the continua associated with the 1s2s ${}_{}{}^3{}_{}{}^{}$S and 1s2p ${}_{}{}^3{}_{}{}^{}$P° states of the residual ion. The radiative decay rates of these initial states are shown to be small relative to their autoionization rates, so that the lifetimes of these resonances are essentially determined by their widths due to autoionization. A detailed study of the closed-channel component of the 1s3p3p ${}_{}{}^4{}_{}{}^{}$P resonance is made in order to investigate the degree to which the saddle-point solution approximates this component of the resonance wave function.

Electron-impact-ionization cross sections are measured for GaCl, GeCl, and SnCl. In all three cases, the metal fragment ion has the largest cross section, and the parent-ion cross sections are somewhat smaller. A significant fraction of the metal fragment ion results from ion-pair formation. The parent-ion ionization energies are 10.1±0.3 eV for GaCl, 7.2±0.5 eV for GeCl, and 6.8±0.3 eV for SnCl.

Electron-impact-ionization cross sections to form the parent ions of ${\mathrm{N}}_2$, CO, ${\mathrm{CO}}_2$, CS, ${\mathrm{S}}_2$, and ${\mathrm{CS}}_2$ have been measured with the same apparatus used recently to measure ionization cross sections of 27 atoms with an absolute accuracy of ±10%. The ionization cross sections for CS, ${\mathrm{S}}_2$, and ${\mathrm{CS}}_2$ are measured here for the first time to our knowledge. The results for ${\mathrm{N}}_2$, CO, and ${\mathrm{CO}}_2$ generally agree with previous measurements. A remeasurement of the ionization cross sections of metastable ${\mathrm{N}}_2$ improves upon our previous measurement.

Results for the atomic elastic scattering of photons of 59.54 keV lying in the vicinity of K-absorption edges of rare earths ${(}_{68}$Er and ${}_{70}{}^{}{}_{}{}^{}\mathrm{Yb}$) are presented. An assessment of all existing experimental results published in the last few years has been made in terms of some of the most important calculations on photon–bound-electron collisions as a function of photon energy and momentum transfer that have been developed in the 1980s. The analysis presents the trend of behavior of the theoretical cross section as the incident photon energy crosses the K-shell photoionization thresholds of the scattering atomic system.

Ionization in H(1s)+${\mathrm{H}}^{+}$ collisions is studied in the relative collision energy range 4.0–25.0 keV by classical trajectory simulations. Improved total ionization cross sections are reported for the collision energies 2.0–10.0 keV. A thorough study of the qualitative dynamics of ionization has been carried out, with emphasis placed on the distinction between ‘‘direct-impact’’ and ‘‘saddle-point’’ mechanisms. A precise criterion for classifying trajectories according to these mechanisms is given, and by analyzing the trajectories in a quasistatic molecular frame it is shown that the distinction is established early in the collision. The development of position and velocity-space correlations in ensembles of trajectories of each type is studied.

We have measured and calculated state-resolved angular distributions of one- and two-electron-capture processes in 0.5–20 eV/u ${\mathrm{Ar}}^{4+}$-Ar collisions. The experimental energy-gain spectra show single-electron capture to six unresolved 4p LS terms, while no trace of a 4s population was found for laboratory collision energies below 200 eV. Semiclassical trajectory calculations, using a seven-channel Landau-Zener model for the probability flux on the multivalued deflection functions, show that the oscillations in the experimental 4p angular differential cross section are due to multiple rainbow scattering and that interference effects play a limited role. Experimental and calculated 4p angular distributions compare nicely over the whole energy range. For energies above 150 eV, true double-capture and transfer ionization with angular distributions consistent with a two-step electron-transfer process appear within the ±9° experimental acceptance.

A quantum theory of atom-molecule collisions is developed for potentials with a hard core. It is assumed that the potential is spherically symmetric in the medium- and the long-range parts. The scattering amplitude is given as a solution of algebraic equations.