studies challenging, enriching, and enjoyable. I would like to especially thank Dr. David K. Roe. His guidance, patience, and knowledge were the stimulus for this work. I would like to thank Dr. Bruce Brown and his wife Barbara for their encouragement and friendship. Dr. Brown and I endured many long miles and tall tales. The camaraderie I shared with my fellow graduate students was supportive. Mario Aparicio was always ready to answer my questions, give advice or challenge me to run that last mile.