Acknowledgment:

I want to sincerely express my gratitude to the following people: I would like to thank to Dr. Cecilio López for his expert suggestions, patience and guidance and for making my achievements possible during this research project. I am very thankful. Also, I would like to show gratitude to Miss Pilar Balbuena for her great support and for enriching this research project and more importantly for being my teacher, thank you for your lessons. I would like to express my thankfulness to Professor José Fernando Alarcón for his dedication, commitment, kindness, and contribution to my dissertation work, and last but not least for being my teacher, thank you. Another person who I am very grateful to is my mother, who I would like to dedicate the following words in Spanish