We present an analysis of the phenomena occurring whenever a level crossing is encountered. Besides Landau-Zener transitions and the quantum nonintegrable phase, fractionalization of quantum numbers and chaotic behavior emerge as intrinsically intertwined phenomena.

We report the first measurement of the ratio of double-to-single photoionization of helium well above the double-ionization threshold. Using a time-of-flight technique, we find ${\mathrm{He}}^{++}$/${\mathrm{He}}^{+}$=1.6±0.3% at hν=2.8 keV. This value lies between calculations by Amusia (2.3%) and by Samson, who predicts 1.2% by analogy with electron-impact ionization cross sections of singly charged ions. Good agreement is obtained with older shake calculations of Byron and Joachain, and of Åberg, who predict 1.7%.

We have studied the resonant optical response of a dense atomic potassium vapor under conditions such that the response is strongly influenced by local-field effects. Our experimental results are in good agreement with the predictions of theory. We have also discovered a collision-induced shift of the potassium resonance lines given by Δ${\mathrm{\omega }}_{\mathrm{c}\mathrm{o}\mathrm{l}=}$βN, where β=-5.0×${10}^{\mathrm{-}8}$ ${\sec }^{\mathrm{-}1}$ ${\mathrm{cm}}^3$ for the 4 ${}_{}{}^2{}_{}{}^{}$${\mathit{S}}_{1/2}$⇆4 ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}_{1/2}$ transition and where β=-3.0×${10}^{\mathrm{-}8}$ ${\sec }^{\mathrm{-}1}$ ${\mathrm{cm}}^3$ for the 4 ${}_{}{}^2{}_{}{}^{}$${\mathit{S}}_{1/2}$⇆4 ${}_{}{}^2{}_{}{}^{}$${\mathit{S}}_{1/2}$⇆4 ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}_{3/2}$ transition.

When a rapidly decaying, autoionizing Rydberg series is excited with a short pulse, it may decay in a series of discrete ‘‘stair steps,’’ separated in time by the classical Rydberg orbit period. A rapid core transition can generate a Rydberg shock front which itself produces stair-step changes in the core dipole moment each time the shock front passes. These core excitations significantly reduce the laser power and bandwidth requirements compared to those used in one-electron-like-atom wave-packet studies, while many of the same effects may be observed.

I demonstrate a very large degree of quenching of spontaneous emission noise in different laser systems that work on mechanisms other than the population inversion between the bare states of the atom. Such laser systems have much narrower linewidths. I give explicit results for phase diffusion for four different model systems.

Cavitation in a liquid seeded with bubbles is used as a new visualization technique to single out the regions of very low pressure of a fully developed turbulent flow. By this means, the sudden appearance of high vorticity filaments is observed. These structures are very thin and short lived and display a high degree of temporal as well as spatial intermittency. They contribute to the flow organization: In particular their disintegration corresponds to the formation of large eddies.

Electron accelerators on sounding rockets have injected 8–40-keV electrons on closed magnetospheric tail field lines near 250 km altitude in the northern auroral zone. These beams mirrored at the southern conjugate point and returned as ‘‘echoes’’ which were detected on the rocket system. The 20% of the beam that returned was sufficient to measure field line lengths and verify magnetospheric magnetic models, to measure fluctuating electric fields and electron pitch angle scattering (6–10)${\mathit{R}}_{\mathit{E}}$ distant, and to identify 10–100 V field-aligned potentials above the rocket. The experiment gives new insight into the motion of natural electrons in the outer Van Allen radiation belt.

A relativistic electron beam propagating through an ummagnetized, underdense plasma exhibits a transverse instability due to the coupling of the beam centroid to plasma electrons at the ‘‘ion-channel’’ edge. The transverse wake field corresponding to this ‘‘electron-hose’’ effect is calculated in the ‘‘frozen-field’’ approximation for a low-current, cylindrical beam in a radially infinite plasma. The asymptotic growth of beam-centroid oscillations is computed, and the growth length is found to be very rapid, indeed much less than the betatron period of the beam. Results for a radially finite plasma and for a slab beam are noted. Damping and saturation mechanisms are discussed.

We have investigated the finite-temperature behavior of the Frenkel-Kontorova model, and have found it unable to reach the ground state when cooled at a finite rate, freezing instead into some metastable configuration. The correlation length of the final state grows as the logarithm of the logarithm of the cooling time. By adding ‘‘numerical enzymes,’’ or long-range Monte Carlo moves which precisely eliminate certain barriers to relaxation, we can equilibrate to significantly lower temperatures. Our numerical method for developing these enzymes is motivated by Darwinian evolution.

By measuring the complex dielectric susceptibility over 15 decades in frequency we compare the α relaxation in low-molecular-weight glass-forming liquids and polymers. To describe the scaling behavior of the α relaxation, a minimal set of four parameters is necessary, the mean relaxation time, the dielectric strength, and two shape parameters, describing the low- and high-frequency wings of the relaxation function, in pronounced contrast to a recently published scaling function.

Novel solutions of the Yang-Baxter relation for a series of multistate vertex models are presented in the braid-group limit. The obtained family of solutions gives a sequence of ‘‘colored’’-braid-group representations. Possible generalizations of the multivariable Alexander polynomial are discussed.

We present a new formulation of Feynman’s path integral, based on Voronin’s theorems on the universality of the Riemann zeta function. The result is a discrete sum over ‘‘paths,’’ each given by a zeta function. A new measure which leads to the correct quantum mechanics is explicitly given.

The wave functions of Sinai-billiard-shaped microwave cavities are experimentally studied. Some of the general features observed are parity breaking in the lowest eigenstates, ‘‘bouncing-ball’’ states, and states with quasirectangular or quasicircular symmetry. The above features are associated with nonisolated periodic orbits. Some states are observed which can be associated with isolated periodic orbits, leading to scars. This work represents the first direct experimental observation of scarred eigenfunctions. At high frequencies the eigenfunctions are very complex, and are yet to be classified in a general scheme.

Recently, Poisson and Israel have shown how, when an electrically charged black hole is perturbed, its inner horizon becomes a singularity of infinite spacetime curvature—the mass-inflation singularity. In this paper we construct an exact mass-inflation solution of the Einstein-Maxwell equations, and use it to analyze the mass-inflation singularity. We find that this singularity is weak enough that its tidal gravitational forces do not necessarily destroy physical objects which attempt to cross it. The possible continuation of the spacetime through this weak singularity is discussed.

Finite-temperature field theory is used for a self-consistent and manifestly gauge-invariant derivation of the effective field equations governing the evolution of adiabatic perturbations of a homogeneous, isotropic cosmological model dominated by an ultrarelativistic plasma of weakly interacting particles in thermal equilibrium. Solutions are obtained in the form of rapidly converging power-series expansions.

A survey is made of the known Becchi-Rouet-Stora (BRS) cohomology and potential anomalies in ‘‘nonrenormalizable’’ effective gauge theories with and without supersymmetry. The probable existence of higher-dimension Abelian anomalies is mentioned. Supersymmetric theories have complicated BRS cohomology, but at least for N=1 and D=4, it appears that this does not give rise to corresponding anomalies so long as the gauge anomalies are eliminated.

A 17-keV particle tentatively observed in β decays is assumed to be a new Dirac-type neutrino. Coupling to the Higgs sector of the Dine-Fischter-Srednicki-Zhitnitsky (DFSZ) axion model provides a mass for this particle, its mixing with the electron neutrino, and a channel for a reasonably fast decay into an electron neutrino and the light DFSZ axion. Results are consistent with most laboratory, astrophysical, and cosmological limits on the properties of this particle and of the axion.

A sample of 24 700 ${\mathrm{\Omega }}^{\mathrm{-}}$ hyperons was produced by a prolarized neutral beam in a spin-transfer reaction. The ${\mathrm{\Omega }}^{\mathrm{-}}$ polarizations are found to be -0.054±0.019 and -0.149±0.055 at mean ${\mathrm{\Omega }}^{\mathrm{-}}$ momenta of 322 and 398 GeV/c, respectively. The directions of these polarizations give an ${\mathrm{\Omega }}^{\mathrm{-}}$ magnetic moment of -(1.94±0.17±0.14)${\mathrm{\mu }}_{\mathit{N}}$

The cross section for the astrophysically important ${}_{}{}^{13}{}_{}{}^{}\mathrm{N}$(p,γ${)}^{14}$O reaction has been measured directly with an intense (3×${10}^8$ particles/s) and pure (>99%) 8.2-MeV ${}_{}{}^{13}{}_{}{}^{}\mathrm{N}$ radioactive ion beam. The average value, for the 5.8–8.2-MeV ${}_{}{}^{13}{}_{}{}^{}\mathrm{N}$ energy range, is 106(30) μb. The partial γ width of the resonance which occurs in this reaction at a center-of-mass energy of 0.545 MeV has been deduced to be 3.8(1.2) eV. It is compared with theoretical predictions and indirect determinations.

We report the first on-line measurements of quadrupole-interaction-resolved nuclear magnetic resonance on oriented nuclei. The 10-min ${}_{}{}^{186}{}_{}{}^{}\mathrm{Au}$ activity was obtained as daughter after cold implantation of mass-separated ${}_{}{}^{186}{}_{}{}^{}\mathrm{Hg}$ into a hcp Co single crystal at the NICOLE facility at ISOLDE-3 (CERN). The quadrupole interaction of ${}_{}{}^{186}{}_{}{}^{}\mathit{Co}$(hcp) was fully resolved, and the spectroscopic quadrupole moment of ${}_{}{}^{186}{}_{}{}^{}\mathrm{Au}$ was determined to be Q=+3.12(20) b. This implies ${\mathrm{\beta }}_2$=+0.246(16), proving the large prolate deformation of the ${}_{}{}^{186}{}_{}{}^{}\mathrm{Au}$ ground state.