Acknowledgement

• All gratitude is due to “ALLAH ” almighty who have guided and aided me to fulfill this work and who supported me in all my life. To Him I extend my heartfelt gratitude. • I am grateful to my parents, who have supported me through not only my education but also my entire life, my sisters and my brother for their love and support. I am also grateful to my beloved wife, for her patience with me especially during the past few years, for her unwavering love, support and giving me the strength and comfortable atmosphere to finish this study, to my nice children Yara, Sara, Mohamed and Eman who will always be in my heart. I would like to dedicate this thesis to all my family. • I am grateful to my promoter Prof. Dr. Peter Köchel for welcoming me as his student, for his kind supervision, continuous encouragement, valuable enthusiastic discussion and unfailing advice throughout the present work and for giving me the opportunity to study in an intellectually rich environment. He supported and helped me during my learning period in Germany. I am very lucky being one of his students. • I would like to express my deep thanks to the members of my examining committe