gen for providing a comfortable and genial work environment. My esteemed colleagues Sebastian Bücking and Patrick Grosz deserve additional thanks for finding time in their busy schedules to discuss data and theoretical issues with me. This work profited considerably from their expertise.I'm also indepted to my advisors Magdalena Kaufmann, Cleo Condoravdi, and Regine Eckardt for their continued advice and support.Further thanks go to people who continued to provide technical and moral support, as well as great friendship over the years. Jerra Busch, Dirk Buschbon, Eva Csipak, and Dolf Rami-you are the best! Big thanks also go to Thomas Weskott, who again excelled at the hard task of the spontaneous proof-reader. In my most impartial opinion, however, Thomas, you deserve the biggest thanks and a cornucopia of everything that is good just for being the way you are! And lastly, of course, I want to thank my brother and my parents-especially for not caring that it took nearly two more years until this thing was done.