The dissociative recombination of vibrationally cold ${\mathrm{CD}}^{+}$ with electrons in the energy range of 0.01 eV to 60 eV has been measured using the Test Storage Ring in a merged beam arrangement. New resonance structures are observed with prominent peaks at 0.8 eV, 8.6 eV, and 11.7 eV. While the second and third resonance are readily attributed to direct recombination processes through Rydberg levels with dissociating molecular ion cores, the origin of the first resonance structure is not well understood, however, its small width of 0.45 eV is an indication of an indirect recombination process.

We discuss how contributions to the order O(m${\mathrm{\alpha }}^8$) orthopositronium decay rate can be separated into two categories, one due to relativistic momenta and calculable in terms of quantum electrodynamics scattering amplitudes, the other due to low momenta and calculable in the simpler framework of a low-energy effective theory. We report new results for all low-momentum contributions, and give a formula relating the remaining contributions to conventional (on-shell) quantum electrodynamics scattering amplitudes.

We report the observation of synchronization of the chaotic intensity fluctuations of two Nd:YAG lasers when one or both the lasers are driven chaotic by periodic modulation of their pump beams.

General properties of nonlinear wave interactions in systems with periodic boundary conditions (so-called resonators) are studied. The wave field evolution in resonators displays striking, peculiar characteristics because only a small number of waves dominate the energy transfer processes. Indeed, the very fact of setting up boundary conditions is more important than the specific form of the nonlinear evolution equation. Results are presented for a number of wave fields whose evolution is governed by different nonlinear equations: planetary waves, gravity waves, capillary waves, and drift waves in plasmas.

A new kind of instability, induced by a uniform differential flow, is predicted. It affects dynamical systems of three or more variables that do not contain an unstable subsystem (activator). This is in contrast to the Turing instability and to the differential flow induced chemical instability which destabilize the homogeneous state of activator-inhibitor systems by releasing the inherent tendency of the activator to grow. A chemical example is given. Arguments are presented that interpret the mechanism of the instability as arising from a resonant excitation of a subsystem due to the differential flow.

The enhancement of acoustic caviation at a liquid-solid interface following laser-induced bubble formation is studied. The experiment results indicate that metastable ultramicroscopic bubbles formed on the solid surface cause a long-term ‘‘memory effect’’ on acoustic cavitation. By performing a double-pulse experiment using two excimer lasers, the temporal decay of this memory effect is determined for two different liquids on a chromium surface. An explanation of the observed decay mode by a diffusion model is presented.

We investigate the beam-beam interaction in a synchrotron collider, specifically studying slow particle diffusion in phase space away from tune resonances. Using the tune and tune shift of contemporary large hadron colliders as reference parameters, our computation shows all particles diffusive after ${10}^5$ rotations in contrast to previous single particle tracking results. The diffusion coefficients are several orders of magnitude higher than the tracking code and increase exponentially with the action, caused by the collision induced variation of the second moment of the beams 〈${\mathit{x}}^2$〉.

We present the results of an experimental investigation of the parametric dependence of the geometry factor g associated with line-charge perturbations in space-charge dominated beams. The experiment consists of a novel method of launching localized space-charge waves and measuring simultaneously the wave velocity and the radius a of an electron beam propagating through a periodic focusing channel with pipe radius b. We find that the g factor obeys the relation g=2 ln(b/a). This result is supported by theoretical analysis, and is also in agreement with previous theoretical work. The experimental technique can be used for any type of beam, whether space charge dominates over emittance or not.

The nonlinear evolution of the Kelvin-Helmholtz instability in an inhomogeneous plasma is studied using a two-dimensional magnetohydrodynamic (MHD) simulation code which includes the Hall term. This term is important when the thickness of the boundary layer is less than an ion inertial length. In comparison to the evolution of the instability based upon ideal MHD, the Hall term generates short wavelength turbulence which inhibits vortex formation, and introduces an asymmetry into the nonlinear evolution of the instability depending upon the sign of the vorticity.

The concentration fluctuations induced in a semidilute polymer solution by shear flow are directly visualized for the first time. The spatial structure of the ‘‘butterfly pattern’’ observed by light scattering is elucidated, being the result of hydrodynamic rippling waves which have a distribution of tilt angles. The minimal tilt angle depends on shear rate in a power law fashion, causing the butterfly to almost close upon itself at high shear rates. The concentration waves have a time scale related to a shear rate γ̇∼1 ${\sec }^{\mathrm{-}1}$ and periodicity λ∼10 μm, indicating a link to reptation processes.

We generalize the Kardar-Parisi-Zhang (KPZ) equation to an O(3)N=2j+1 component model. In the limit N→∞ we show that the mode coupling equations become exact. Solving these approximately we find that the dynamic exponent z increases from 3/2 for d=1 to 2 at the dimension d≊3.6. For d=1 it can be shown analytically that z=3/2 for all j. The case j=2 for d=2 is investigated by numerical integration of the KPZ equation.

The crystal structure of AlAs has been studied in a diamond anvil cell using energy-dispersive x-ray diffraction to 46 GPa. AlAs undergoes a first order phase transformation from zinc blende to NiAs structure. This is the first experimental observation of a III-V compound transforming to the NiAs structure. The decrease in volume on transformation is 17±1% at 7 GPa. The transformation is reversible but has large hysteresis. The equilibrium transformation pressure is 7±5 GPa. Equations of state were obtained for both phases. The bulk modulus at zero pressure, ${\mathit{B}}_0$, of zinc blende AlAs was measured to be 74±4 GPa. These results are in good agreement with theoretical calculations.

The infrared transmittance of the quasi-one-dimensional charge-density-wave (CDW) material blue bronze (${\mathrm{K}}_{0.3}$${\mathrm{MoO}}_3$) is observed to be affected by an applied electric field. The effect is interpreted in terms of changes in free carrier absorption resulting from surprisingly large changes in the density of quasiparticles which screen the CDW polarization at electrical contacts. The magnitude of the screening charge has a maximum at 110 K, and is thermally activated below this temperature.

We have measured the low temperature resistivity of AuFe wires in the dilute magnetic impurity limit as a function of wire width, temperature, and magnetic field. When the width dependence of the electron-electron interaction contribution to the resistivity is taken into account, the temperature dependence of the remaining Kondo contribution to the resistivity of all samples with the same impurity concentration is identical. Similar behavior is observed for the magnetic field dependent resistivity. Thus, the Kondo contribution to the resistivity is independent of width down to 38 nm, much smaller than the Kondo length ${\xi }_{\mathit{K}}$=ħ${\mathit{v}}_{\mathit{F}}$/${\mathit{k}}_{\mathit{B}}$${\mathit{T}}_{\mathit{K}}$≊10 μm.

We present an interpretation of recent cyclotron resonance experiments on the two-dimensional electron gas in GaAs/AlGaAs heterostructures. We show that the observed dependence of the resonance spectrum on Landau level occupancy and temperature arises from the interplay of three factors: spin splitting of the cyclotron frequency, thermal population of the two spin states, and coupling of the resonances for each spin orientation by Coulomb interactions. In addition, we derive an f-sum rule which allows spin polarization to be determined directly from resonance spectra.

We have observed a Fermi-edge singularity in the tunneling current between a two-dimensional electron gas (2DEG) and a zero-dimensional localized state. A sharp peak in the tunnel current is observed when the energy of the localized state matches the Fermi energy of the 2DEG. The peak grows and becomes sharper as the temperature is decreased to our lowest temperature of 70 mK. We attribute the singularity to the Coulomb interaction between the tunneling electron on the localized site and the Fermi sea.

We report on transverse magnetic focusing experiments in two-dimensional electron systems in the vicinity of Landau level filling factor ν=1/2. We observe quasiperiodic magnetic focusing peaks for ν<1/2 and no periodic structure for ν>1/2 in several double-constriction GaAs heterojunction samples. The quasiperiod and the direction of focusing in all of these samples are in good quantitative agreement with that expected from semiclassical transport by composite fermions of charge -‖e‖.

We have introduced a controllable artificial impurity or ‘‘antidot’’ into a quantum wire and report on the novel phenomena observed as this system evolves from classical behavior at low magnetic fields to the quantum Hall regime. In the transition, conductance resonances due to magnetically bound impurity states are detected. The resonant oscillations exhibit beating and sharp period changes. A theoretical model based on an interedge state coupling mechanism and a new nonlocal effect of edge state formation at local potential energy maxima account for the principal experimental features.

The single-chain dynamics of a typical soluble conducting polymer, poly(3-hexylthiophene), has been studied in solutions by frequency-domain electric birefringence spectroscopy. From the results, we have obtained information on the intrachain conduction mechanism exclusively without the interference from the interchain one as well as information on a close correlation between the conduction mechanism and the main-chain conformation. It is clearly revealed that there exist two kinds of transport of carriers along the polymer chain with different diffusion distances and diffusion constants.

In this paper, a multiorbital generalization of standard spin fluctuation theory is considered within an on-site approximation. For f electrons, this theory leads to an instability for a superconducting pair state which obeys Hund’s rules, with L=5, S=1, and J=4. The degeneracy of this state is broken by crystalline effects, and realistic calculations for ${\mathrm{UPt}}_3$ find a pair state with ${\mathrm{\Gamma }}_6^{\mathrm{-}}$ (${\mathit{E}}_{2\mathit{u}}$) symmetry, consistent with current experimental constraints.