This thesis would not have been realized without the substantial support and contribution of many people, to whom I cannot but feel deeply grateful. First of all, I thank Professor Demetrios Sampson, initial supervisor yet continuous mentor of my doctoral thesis, for his trust, insights and patience during the last 4 years; his continuous guidance to my research; and his high investment towards helping me improve myself in many ways. For all these, I am indeed thankful. I would also like to thank my very good friend Panagiotis Zervas for supporting me throughout this process, especially during the difficult start. His advice greatly helped me to carry on. A special thank you goes out to my close friends that were always there when I needed them. Most of all, Helen, I thank you for your everlasting care and support; you are my hero. Last, but surely not least, I would like to express my absolute love and gratitude to my family for their everlasting love, their encouragement, and their belief to my capabilities. You made it all possible.