Well, it has been a long journey since the beginning of this dissertation. I have learned so much and experienced so many things throughout this process that I am afraid I have no words to express my gratitude to all the people involved in it. But here is an honest and brief attempt. Firstly, I would like to thank FCT for the financial support which made the accomplishment of this dissertation possible. Secondly, but most important, I would like to thank both my advisors. Teresa, thank you for teaching me all you know. Thank you for putting so much effort and vision on this dissertation. Thank you for standing by me even when the times were rough and for giving me all the "frustrations" that I needed to become a stronger researcher. I am sure that, without your dedication, this dissertation would not have the quality it has. Jim, thank you for teaching me all you know. Thank you for the way you receive me at UCSB. It is not easy to leave your country and go to the other side of the planet, but you sure made it easier. I learned a lot in your labmeetings. I am sure I am a more complete researcher because of your advices and teachings. For all the emotional support, I also would like to thank my parents, my big brother, my sister and my aunt. And Carlos. And Ricardo. It was surely important to lie on your shoulders when the times got tough. Words are not enough to express my gratitude for your love. I also would like to thank my colleagues for their inputs and friendship. Mariana, Ana,