To my family, my brother-in-law Paolo, and to Valerio with infinite gratitude for reasons they know well
ACKNOWLEDGMENTSNow that I am at the end of the path of my PhD program, it is a pleasure to contemplate this important and meaningful experience. At the same time, I would like to show my gratitude for the great care and the support that I received from numerous people at different periods of time. It has been both an exacting and educational journey, and I was lucky to have had the pleasure of meeting and interacting with so many eminent professors, some of whom were members of the dissertation committee. They have made essential and precious contributions to my growth. To those people, I would like to express my deepest gratitude.First and foremost, I would like to thank Professor Fontana, an outstanding figure and my point of reference even before I began the doctorate program. During the degree course and under his guidance, I was able to approach and accomplish my first thesis experiences; without him, I would never have started my PhD program. Since he encouraged me to pursue my present research path, he played a decisive role in my choice. I had the opportunity to benefit from his experience and reassuring guidance.The fulfillment of this work was made possible thanks to my very good interaction with the members of my dissertation committee.I am particularly grateful to Professor Boccardelli for several important reasons. He helped me to achieve a crucial breakthrough in my studies, and it is in large part due to him that I have achieved results. As Director of the Doctoral Program, he undertook a leading role in the orientation process. I would like to thank him for his psychological support and firm encouragement: he always expressed faith in my abilities when sometimes I was in doubt. During some crucial steps in the execution of my work, his valid intervention helped me to find solutions and persevere. His essential contributions induced me to find alternatives to some points in a lasting and fruitful exchange of ideas. He played a decisive role during the difficult starting steps when I was identifying and defining my research problem and he made the difference when suggesting how to direct my ideas towards goals. Furthermore, he helped me to define the model by turning my attention to key matters combining a pragmatic approach with the capability of seizing shades. During the final stage, he provided advice about data processing. On several occasions, he made time to answer to my questions. I also owe a debt of thanks to him for my wonderful opportunity to conduct my research for this thesis at the University of Michigan for a year. It has been an absorbing and educational experience. Professor Boccardelli has been and will remain an important point of reference.I will never be able to fully thank Professor Ahuja for having assisted me during this long period at his university. It is an honor that he agreed to be part of my dissertation committee. I owe a great debt to him for all of the opportuni...