This abstract was rather severely mangled by UMI, including getting the year wrong (the thesis was submitted in Spring 1999), having sentences truncated in the middle and sometimes having sentences merged with other sentences. The relevant information that you should take from the abstract is the following: The thesis as submitted to the University of Arizona is available on astro-ph as submission number 9908158. Chapter 2 is published as Astrophysical Journal volume 502 page 342. (1998) Chapter 4 is the submitted (to ApJ) version of the paper published as Astrophysical Journal volume 529 page 357 (2000) Chapter 6 is published as Astrophysical Journal volume 500 page 940 (1998) The rest is not very useful to the average reader, but might be amusing to some. --Andy Nelson Author comment submitted 13-Mar-2000 by Andy Nelson (andy@mpia-hd.mpg.de).