\title{Acknowledgements} This thesis and the research it presents is not the result of just my own work. I have received a lot of ideas, inspiration and comments from other people, who I would like to mention here. First of all, I would like to thank Christiaan Baaij, which has been my partner in crime during this research. Together we have started a new area of research at the University of Twente, in which I would not have progressed so far on my own. Then there is my first supervisor, Jan Kuper, whose visions and ideas have sparked this research and who always managed to place my practical views into the proper theoretical background. The rest of the graduation committee has been a great help, providing feedback, comments and challenging questions, each from their own unique point of view. Finally, I would like to thank Brenda, who has been suffering my working late and general lack of time for just over a year now.