ACKNOWLEDGEMENTS

Foremost, praise and thanks be to Almighty Allah, Most Gracious, Most Merciful, Who enabled me to reach my goal. I would like to express my sincere thanks and deep appreciation to my supervisor Dr. Tahsin Ghazal for his help and continuous encouragement throughout this work. Thanks and appreciation are also due, to my parents, my brothers and my sisters for their help, encouragement and their moral support. I would like to express my thanks to King Saud University for pro-viding the necessary support and facilities. Also I wish to extend my thanks to all my teachers and colleagues in Mathematics Department, King Saud University for their cooperation and kind help