for their important comments and suggestions for improving the text.To all my family, especially my mother Lucilene Leal Mota, and my brothers Marcos André, Daniel Renato, Maria Eliene and Antônio Neto, who, with great affection and support, spared no effort for me to reach this stage of my life.To all my friends and colleagues of PIPGES for the partnership, help, and moments of relaxation during the course. Special thanks go to