This monograph is the outgrowth of Stefan Axelson's PhD Dissertation at Chalmers University in G teborg, Sweden. The dissertation, in turn collects a number of research efforts performed over a period of six years or so into a coherent whole. It was my honor to serve as the "opponent" at Dr. Axelsson's examination. In the Swedish system, it is the job of the opponent to place the candidate's work into a broader perspective, demonstrating its significance...