Universiẗat, Diss., 1999--Regensburg. / Erscheinungsjahr an der Haupttitelstelle: 1998.

University, Diss., 2004--Jena.

University, Diss., 2004--Tübingen.

Thesis (Ph. D.)--University of Oregon, 1999. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 95-97). Also available for download via the World Wide Web; free to University of Oregon users. Address:http://wwwlib.umi.com/cr/uoregon/fullcit?p9957570.

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In this thesis, we study the soft gluon corrections to hard wide-angle scattering processes due to a virtual gluon exchange (one-loop order) and the emission of up to two gluons. Our primary aim is to determine the ordering condition that should be used to dress a hard scattering process with corrections due to gluon emissions and a Coulomb (Glauber) gluon exchange. We find that, due to an elegant cancellation of many Feynman diagrams, a specific ordering variable should be used to order the transverse momentum of the exchanged Coulomb gluon with respect to the real emissions. Furthermore, in the case of the scattering process accompanied with a single emission, we find that the radiative part of the loop correction satisfies the same ordering condition as the Coulomb gluon contribution. Based upon the assumption that the ordering condition continues at higher orders, we conjecture an expression for the soft corrections to a general hard scattering process due to one-loop and any number of gluon emissions.

Orientador: Antonio José Accioly / Mestre

We use Monte Carlo simulations in order to investigate the density of states and the two-time density autocorrelation function for the two- and three-dimensional Coulomb glass as well as the Bose glass phase of flux lines in type-II superconductors. We find a very fast forming gap in the density of states and explore the dependence of temperature and filling fraction. By studying two scaling methods, we find that the nonequilibrium relaxation properties can be described sufficiently by a full-aging scaling analysis. The scaling exponents depend on both temperature and filling fraction, and are thus non-universal. We look at the trends of these exponents and found that as either the temperature decreases or the filling fraction deviates more from half-filling, the exponents reflect slower relaxation kinetics. With two separate interaction potentials, a comparison of relaxation rates and the gap in the density of states is made. / Ph. D.

This work treats dual-plane automatic ball balancing of elastically-mounted cylindrical rotors. The application is primarily to systems with a vertically-oriented single-bearing support, but extension is also made to horizontally-oriented single-bearing support as typically found in a vehicle wheel. The rotor elastic mounting includes three translational degrees of freedom for the body geometric center and three rotational degrees of freedom. Damping is included for each of these six degrees of freedom. The model for the automatic ball balancer consists of up to two arbitrarily-located hollow circumferential races, each of which contains up to two sliding particles. The friction model for the particles includes both viscous and Coulomb friction forces. Of considerable complexity is the logic path for the individual particles being either in motion or stationary relative to the rotor. The exact equations of motion for the overall system are derived via a Newtonian approach. Numerical-integration results show that the balancer performance depends strongly on the friction levels as well as the operating speed of the body. Simulations conducted with a pure static imbalance show that ideal automatic balancing is possible only for vertical-axis rotors that have zero Coulomb friction levels between the balancing particles and the races. Simulations with a horizontal-axis statically-imbalanced rotor show that an automatic balancer can improve performance for certain operating speeds and non-zero Coulomb friction levels in the presence of gravitational forces. Simulations conducted with a pure dynamic imbalance show that there is no inherent mechanism to counteract rotational displacements of the rotor about its geometric center. As a result, the balancing particles exhibit several phenomena described in previous works such as synchronous motion and oscillatory behaviors within their respective races. Simulations for an arbitrarily located imbalance show that rotor performance can be improved using dual-plane balancing techniques for certain operating speeds and Coulomb friction levels. Due to the inherent complexity in eliminating an arbitrarily located mass imbalance, the system is generally unable to reach a perfectly balanced configuration, but performance can be improved for carefully-selected initial conditions. / Ph. D.

Coulomb propulsion has been proposed for spacecraft cluster applications with separation distances on the order of dozens of meters. This thesis presents an investigation of analytic charge solutions for a planar and three dimensional four satellite formations. The solutions are formulated in terms of the formation geometry. In contrast to the two and three spacecraft Coulomb formations, a four spacecraft formation has additional constraints that need to be satisfied for the individual charges on the spacecraft to be unique and real. A spacecraft must not only satisfy the previously developed inequality constraints to yield a real charge solution, but it must also satisfy three additional equality constraints to ensure the spacecraft charge is unique. Further, a method is presented to reduce the number of equality constraints arising due the dynamics of a four spacecraft formation. Formation geometries are explored to determine the feasibility of orienting a square formation arbitrarily in any given plane. The unique and real spacecraft charges are determined as functions of the orientation of the square formation in a given principal orbit plane. For a three-dimensional tetrahedron formation, the charge products obtained are a unique set of solution. The full three-dimensional rotation of a tetrahedron is reduced to a two angle rotation for simpler analysis. The number of equality constraints for unique spacecraft charges can not be reduced for a three-dimensional formation. The two angle rotation results are presented for different values of the third angle. The thesis also presents the set up for a co-linear four-craft problem. The solution for the co-linear formation is not developed. The discussion of co-linear formations serves as an open question on how to determine analytic solutions for system with null-space dimension greater than 1. The thesis also presents a numerical tool for determining potential shapes of a static Coulomb formation as a support to the analytical solutions. The numerical strategy presented here uses a distributed Genetic Algorithm (GA) as an optimization tool. The GA offers several advantages over traditional gradient based optimization methods. Distributing the work of the GA over several processors reduces the computation time to arrive at a solution. The thesis discusses the implementation of a distributed GA used in the analysis of a static Coulomb formation. The thesis also addresses the challenges of implementation of a distributed GA on a computing cluster and presents candidate solutions. / Master of Science