I would like to convey my deepest gratitude to my thesis supervisor, Dr. Antar Jutla. I am grateful to him for inspiring me through the path of my journey in acquiring knowledge and supporting me to develop the thirst for research. I thank him for his immense guidance and support. I am thankful to my committee members, Dr. Radhey S. Sharma and Dr. Lian-Shin Lin for their encouragement and knowledge that has guided me in improving my research. Their course works helped me incalculably during my research period. My deepest gratitude to my father, Nurul Anwar and my mother, Parveen Fatema, for whom I have achieved every success in my life. Their unconditional love and support has been by biggest strength. I would like to thank my beloved husband, Musfique Ahmed, for his unconditional support and love and for always being by my side. I would like to express my gratitude to him, for without his support I would not be able to achieve any success. I would like to thank my father in law, Md Jasim Uddin Ahmed and mother in law, Maksuda Begum, for their immense love and support. I would like to express my gratitude to my sisters and sister in law, for always being there for me. I express my greatest gratitude to my creator, Allah, for giving me the strength and being the best planner of my life.