for their guidance and support throughout the course of this research. In addition, I would also like to thank my parents, my wife, my friends and my siblings for their unfailing support during my studies, and my colleagues, the department faculty and staff for making my time at Iowa State University a wonderful experience. I want to also offer my appreciation to those who were willing to participate in my research, without whom, this thesis would not have been possible. Finally, I would like to express my gratitude to the Government of Saudi Arabia for sponsoring me to conduct my studies in the United States.