After over 1000 days of PhD research, around 500 pages of thesis, paper and report writing, I can finally add the final and the most enjoyable part: it is these lines in which I can thank the many people that have enabled me to produce this work by providing the fruitful environment that I have had in the last three years.
First of all, I have to thank Isabel, my wife, for her endless patience and support and for cheering me up when things did not run as smoothly as my cabeza cuadrada would have wished. Furthermore I would like thank my parents and my sister, not only for their financial support during these years but also for confiding in me and my abilities, especially at times when I was not so sure about them. Then, there are the many friends that I have met during that time and who have made this period so pleasant, fruitful and so rich in experience. To mention a few: Cristina Boeres (my second sister) and Vinod Rebello, Ana Goldenberg and Luis Araujo ("love is beautiful"), Beate and Thomas Kleymann ("squash is beautiful"), Olga Savasta and Victor Varela ("los padrinos"), Nils Knafla and Frank Yang (my officemates), Martin Reddy, Rob Payne, Marcus Marr, Mike Galloway, Alistair Ewing and so many more who would deserve to be mentioned. You all contributed in one or the other way, through technical discussions, sharing experience or `simply' by your company and your friendship. To that list I would like to add Ulf Schwitzke, my best man in many ways.
My special thanks go to Peter Thanisch who not only contributed so many things in the numerous discussions that we had about this work but who also convinced me to start with the PhD in the first place. Supervising a PhD student is not always an easy and pleasant job and there are thousands of other things that one has to pursue. Although things not always went as Peter or I would have wished, I always knew that he tried his best. I also enjoyed playing in the many football matches.