Firstly I want to thank Prof. Dr. Stefan Bräse for giving me the opportunity to write and to defend this doctoral thesis at his department. I thank Dr. Ute Schepers for her expert guidance in the realization of this work and who assisted me by words and deeds. I thank in particular the Dr. U. Schepers team who willingly provided information at any time. I would also like to thank all people who supported me realizing this thesis.
