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Abstract

This work would not have been possible without the understanding of my friends, the encouragement of my parents and the support of all the colleagues with whom I worked together. I have to thank them all and I am especially indebted to the following people. I would like to sincerely thank my advisor Friedhelm Meyer auf der Heide for giving me the opportunity to choose the direction of my research, for his optimism and his encouragement. I am also grateful to my co-advisor Christian Schindelhauer for the good cooperation in research and teaching, for having patience with me in numerous discussions and for his invaluable help. I also thank Inés Bebea González for burning the midnight oil when working on our research project and the good cooperation despite the thousand miles between Paderborn and Madrid. ¡Muchas gracias! Special thanks to Silke Geisen and Peter Birkner who didn’t shrink away from reading parts of this work in a preliminary state. Their comments helped a lot in improving its readability. Paderborn, July 2006 Stefan Rühru