It would not have been possible to write this thesis without the help and support of some people that are part of my life.
Above all, I would like to thank José Nilberto Gondim Lima, my brother whose life has been so intricately part of mine that it is hard to put into words my gratitude to him, and his unconditional love, which has always been a source of hope and cheerfulness when the struggles became overwhelming. I am proudly grateful to L***** and C*****, my children, who have been proudly supporting the writing of this thesis, and whose understanding of it brighten up my days. Zilda Gondim Lima, my mother, from whom I inherited the love for learning, to whom I cannot express appreciation to suffice what she represents in my academic and personal life. I am grateful to Hildeni, Hilzeni, and Hildeberto, my siblings, whose support has been fundamental. I want to thank my friend Umberto for his golden loving heart which embraces not only me, but José, throughout our lives since our childhood. [read more]