I would firstly like to thank God-Almighty for not only the ability, but also the constant strength and perseverance that kept me going through this thesis.Further, I would like to express my deepest gratitude to my supervisor, Professor Volker Gruhn, who has been a steady guide through the course of my research and has always been supportive of my academic endeavours -no matter which corner of the Earth they led me to -thereby allowing me to interact with and learn from excellent researchers in my field from around the globe. I am thankful for dedicating his time and effort and for always making me feel welcome at his office. I would also like to express my appreciation for Professor Matthias Book, who not only offered deep critical insights through his review of my thesis, but also went out of his way to make available to me certain academic opportunities that I found to be extremely valuable.I would also like to extend my thanks to all my colleagues in Paluno. It has been a great experience working with and exchanging ideas with them. All the talks, discussions and dissertation seminars have been invaluable experiences for me.Last but not least, I would like to give thanks to my family, particularly my mother, who has always been a pillar of support for me, and without whom I would not be where I stand today. I thank her for her prayers, her emotional support and for always giving me advice when I hit a rough patch in life and don't know what to do. My wife too, has been a constant source of strength for me, a companion, a friend and both a mother and father for my children in my absence. I thank her for all of this and for not killing me when I told her I would be living in a different country for the next three years. I'd like to thank my daughter Eshal and my son Shaheer for bearing with me patiently and not holding against me the time I could not give them in pursuit of my doctoral studies.