for dedicating their precious time to the evaluation of this PhD thesis. The feedback provided by them was very valuable to me and to this thesis. I would like to thank my beloved wife, Julia, who supported me during the conduction of this work. There is no words to describe her love, patience and kindness. My deepest gratitude goes to my whole family, who always supported me. A special thank goes to my aunt, Leticia, who was responsible for raising and educating me. Without her I would not have come this far. I also thank my friends Roberto, Givanilde, Carlos, Frank, and Hélio and my former students Flávio, Navarro, Lucas, Angélica, and Henrique.