The Stability of Branonium

We analyse the orbital motion of a light anti D6-brane in the presence of a stack of heavy, distant D6-branes in ten dimensions, taking account of possible time-variations in the background moduli fields. The Coulomb-like central potential arising through brane-antibrane interactions is then modified to include time-dependent prefactors, which generally preclude the existence of stable elliptical orbits.Comment: 13 pages, Latex, 3 eps figure

Some physical and thermodynamic properties of organic melts

Imperial Users onl

Advanced Medical Imaging in Privately Insured Patients Recent Trends in Utilization and Payments

Boston University Health Policy Institut

Vanishing Voices: The Impact of Life Behind the Barbed Wire on World War II Prisoners of War

This dissertation is an exploration into the lived experiences and interconnectedness of World War II prisoners of war (POWs). It is driven by the personal accounts of four men who experienced life on the wrong side of the barbed wire: my father, the late William Austin Burgess, formerly of Hinesville, Georgia; C. Neill Baylor, of Vidalia, Georgia; Herman Cranman, of Savannah, Georgia; and Robert Waldrop, of Beaufort, South Carolina. The impetus for this exploration began with the stories I received as a child when my father would share his wartime military experiences with me and continues with the learning of pre-war, wartime, and post-war experiences. The story purposefully has no end. The experiences of these men are meant to live on, not vanish with them

Computational and numerical aspects of full waveform seismic inversion

Full-waveform inversion (FWI) is a nonlinear optimisation procedure, seeking to match synthetically-generated seismograms with those observed in field data by iteratively updating a model of the subsurface seismic parameters, typically compressional wave (P-wave) velocity. Advances in high-performance computing have made FWI of 3-dimensional models feasible, but the low sensitivity of the objective function to deeper, low-wavenumber components of velocity makes these difficult to recover using FWI relative to more traditional, less automated, techniques. While the use of inadequate physics during the synthetic modelling stage is a contributing factor, I propose that this weakness is substantially one of ill-conditioning, and that efforts to remedy it should focus on the development of both more efficient seismic modelling techniques, and more sophisticated preconditioners for the optimisation iterations. I demonstrate that the problem of poor low-wavenumber velocity recovery can be reproduced in an analogous one-dimensional inversion problem, and that in this case it can be remedied by making full use of the available curvature information, in the form of the Hessian matrix. In two or three dimensions, this curvature information is prohibitively expensive to obtain and store as part of an inversion procedure. I obtain the complete Hessian matrices for a realistically-sized, two-dimensional, towed-streamer inversion problem at several stages during the inversion and link properties of these matrices to the behaviour of the inversion. Based on these observations, I propose a method for approximating the action of the Hessian and suggest it as a path forward for more sophisticated preconditioning of the inversion process.Open Acces

Aspects of brane-antibrane inflation

I describe a dynamical mechanism for solving the fine-tuning problem of brane-antibrane inflation. By inflating with stacks of branes and antibranes, the branes can naturally be trapped at a metastable minimum of the potential. As branes tunnel out of this minimum, the shape of the potential changes to make the minimum shallower. Eventually the minimum disappears and the remaining branes roll slowly because the potential is nearly flat. I show that even with a small number of branes, there is a good chance of getting enough inflation. Running of the spectral index is correlated with the tilt in such a way as to provide a test of the model by future CMB experiments.Comment: 6 pages, 5 figures; proceedings of Theory Canada 1 conference, 2-5 June 2005, UBC, Vancouve