We suggest a mechanism allowing the introduction of a small violation of the Pauli exclusion principle. Within this framework, we compute the grand partition function for a free-electron gas in a metal. We discuss the physical implications of our results and infer an upper bound on the violation parameter.

A quantum partitioning theory is given for extracting dynamic information from the high-resolution spectra of highly excited atoms and molecules that is relatively simple to apply. The presented approach is applicable whenever the classical counterpart of the system studied is chaotic. The theory allows a picture of the underlying non-statistically-describable part of the dynamics to be obtained from the spectra. The theory presented effectively uses and unifies many aspects of classical trajectory approaches, Feshbach resonant-scattering partitioning theory, semiclassical periodic-orbit theory, ‘‘scars’’ theory, bright- and dark-state concepts, and Fourier transforms of the spectra. The power of the theory is demonstrated quantitatively by interpreting the dynamics underlying the absorption spectra of the hydrogen atom in a strong uniform magnetic field.

The projection-operator method is used to find a Fokker-Planck equation with a time-dependent diffusion coefficient. It is shown that this equation is correct under a precise condition of small noise intensity and can be used successfully to study the problem of escape over the potential barrier of a bistable system. An exact expression for the first-passage time for τ→∞ is found, where τ is the noise correlation time. It is then shown with a numerical method that the Fokker-Planck equation relying on the assumption of local linearization bridges the exact limit for τ→∞ and the standard one for τ=0. Some intriguing aspects of the short-τ region are discussed.

A colloidal dispersion consisting of optically matched host particles and a small amount of strongly scattering tracer particles has been studied with dynamic light scattering. Analysis of the self-dynamic structure factor $F_s$(q,t) obtained from these measurements demonstrates that the displacement statistics of the interacting colloidal particles shows considerable non-Gaussian behavior.

We use results from a scaling variational approach to screened Coulomb problems to calculate bound-bound transition matrix elements for atomic inner shells. We use wave functions which are just radial Sturmian functions scaled by the variational parameter. Our results are compared with numerical results and those of analytic perturbation theory.

The ground-state hyperfine structure of atomic states is shown to exhibit interesting new aspects of the topological phase discovered by M. V. Berry [Proc. R. Soc. London, Ser. A 392, 45 (1984)]. In particular, although a nontrivial topological phase exists, monopoles are absent. A possible experiment to probe these aspects is discussed.

Electron capture in fast-proton–${\mathrm{H}}_2$ collisions has been reexamined in the Brinkman-Kramers approximation. The interference, first noted by T. F. Tuan and E. Gerjuoy [Phys. Rev. 117, 756 (1960)], between two capture amplitudes associated with two centers in the molecule is found to be more pronounced at fixed orientations of the molecular axis as compared to the results obtained by averaging over all orientations. This interference effect varies significantly with the orientations of the molecule. For example, in a certain angular range the number of oscillations in the differential cross sections (DCS) is maximum at ${\theta }_{\rho }$=90°, ${\phi }_{\rho }$=0°, where ${\theta }_{\rho }$ and ${\phi }_{\rho }$ are the polar and azimuthal angles, respectively, of the molecular axis with respect to the incident-beam direction. The number of oscillations of the DCS decreases (i) as impact energy decreases at a fixed value of orientation and (ii) as the orientation changes from the perpendicular position (${\theta }_{\rho }$=90°, ${\phi }_{\rho }$=0°) to other orientations for a fixed proton energy. This interference effect has not yet been observed experimentally.

Twenty-four unknown U ii energy levels are classified according to configuration using pattern-recognition methods. The energy level, Landé g factor, quantum number J, and ${}_{}{}^{234}{}_{}{}^{}\mathrm{U}$ isotope shift are used to describe each level. Preliminary results of the prediction of the extent of configuration mixing for low-energy odd levels are presented.

Electron shake processes are shown to be time independent, in contrast to collision processes, implying the existence of distinct levels of nonseparability (connection). The higher level of nonseparability, which occurs in the $e^{\mathrm{-}}$-p interaction, is capable of preventing time development of the electron system.

We present data on the temperature dependence of the polarization ratios of redistributed fluorescence in the Ba-Ar and Ba-Xe systems. The temperature dependence is observed to be less than 1% per 100 K, which is significantly below predicted levels.

In this Brief Report, the linearized Balescu-Lenard-Poisson equations are solved in the weakly collisional limit to show that ion-acoustic waves in a current-free plasma, which are Landau damped in the absence of collisions, can become marginally stable due to the undamping effect of electron-ion (e-i) collisions. For (${\mathit{T}}_{\mathit{e}0}$/${\mathit{T}}_{\mathit{i}0}$${)}^{1/2}$≪(5/16(2${\mathit{m}}_{\mathit{i}/\mathit{me}}$${)}^{1/2}$ the e-i collisional undamping effect dominates the i-i, e-e, and i-e collisional effects, and marginal stability occurs when the collisional undamping rate balances the electron and ion Landau damping rates.

We investigate a bistable Fokker-Planck equation describing the overdamped motion of particles in a Landau potential driven by weakly colored Gaussian noise. Our focus is on the noise-intensity dependence of the decay rates in the limit of small correlation times of the noise. In linear order of the external-noise correlation time τ the decay rates can be expressed in terms of the eigenvalues of a white-noise Fokker-Planck equation. Numerical results for the first nonvanishing eigenvalue, i.e., the inverse mean first-passage time, are presented for arbitrary noise intensity. In the limit of very low noise intensity an analytical expression is derived and in the strong-noise limit an asymptotic form is given for this eigenvalue.

A stirred percolating superconducting-insulating system is examined as a model for the transport properties of micelles. A scaling assumption is proposed which relates the merging frequency of the transient clusters of superconducting sites with the number of sites on the effective external perimeters. The conductivity exponent s for the divergence of the conductivity Σ≊($p_c$-p${)}^{\mathrm{-}s}$ is consistent with the relation s=D+$D_e$-β in two dimensions, where s≊4.2, which is compatible with the high value of s observed in a recent computer simulation.

We show how to generalize supersymmetric quantum mechanics to coupled two-body channels. For the case with different thresholds for each channel we obtain simple relations between $S$-matrix elements of the original problem and its supersymmetric partner in a given partial wave. We find corresponding relations among reflection and transmission coefficients for one-dimensional scattering. These relations are obtained without a knowledge of the dynamical details.

We discuss low-energy antiproton ($\overline{p}$) collisions with H and He on the basis of adiabatic potentials and with the use of a molecular-orbital expansion method. Every electronic state for the $\overline{p}-\mathrm{H}$ system merges into the continuum at a certain internuclear separation, and this separation is farther and farther out for higher and higher excited states. (This fact was first pointed out by E. Fermi and E. Teller [Phys. Rev. 72, 399 (1947)], who specifically considered the ground state of a system consisting of a meson and a hydrogen atom.) For the $\overline{p}-\mathrm{H}\mathrm{e}$ system, as for to the $\overline{p}-\mathrm{H}$ system, all electronic states cross over into the continuum of the ${\mathrm{He}}^{+}+{\mathrm{le}}^{-}$ state at a finite separation. These findings lead us to suggest that a close encounter of $\overline{p}$ with an atom should result, at a high probability, in ionization with near-zero electron energy and a wide range of ejected-electron angle. This mechanism of ionization is absent for collisions of protons ($p$), and may account in part for the greater double-ionization cross section of He for $\overline{p}$ than for $p$ at the same energy, which was found in a recent experiment.

Iodine atoms have been produced by laser-induced dissociation of molecular iodine and photoionized in the $4d$ shell with synchrotron radiation. The photoelectron spectrum originating from the ${4d}^9{5s}^2{5p}^5$ configuration shows a broad multiplet structure. We have also performed ab initio calculations of the spectrum in an intermediate coupling scheme. The energy spread as well as branching ratios are found to be in excellent agreement with experimental results.

In inner-shell photoionization of an atom followed by Auger decay, the Auger electron initially screens the ionic Coulomb field experienced by the photoelectron. A sudden change in screening occurs when the Auger electron overtakes the photoelectron, causing energy transfer from the latter to the former. According to both semiclassical and quantum theories of post-collision interaction, the photoelectron can thus be recaptured by the atom from which it was emitted. This phenomenon has been measured directly with synchrotron radiation, as a function of incident-photon energy, and is found to be in accord with predictions.

Stimulated resonance Raman spectroscopy is presented as an alternative to laser-rf double resonance for obtaining high-precision measurements in ion beams. By use of a single-phase modulated laser beam to derive the two required fields, the laser-ion-beam alignment is significantly simplified. In addition, this method is especially useful in the low-frequency regime where the laser-rf double-resonance method encounters difficulties due to modifications of the ion-beam velocity distribution. These modifications, which result from interaction with the traveling rf wave used to induce magnetic dipole transitions, are observed and quantitatively modeled.