Author Description

All praises and thanks are due to Almighty and majesty Allah and Peace be upon all His prophets. May Allah make this effort solely for His sake and accept it. What is the recompense for someone who put his great knowledge, keen advices and patience before a student!?!. With deep respect and sincerity I express my appreciation and gratitude to the compassionate and concerned Professor Salih Ahmed Babiker for his wise and kind supervision rather than encouragement and guidance throughout the PhD course. The far above the ground skies will by no means be reached or replaced. Prayers and wishes that, at all times he stays well and sound. With pleasure and good cheer I admire Professor Hamid Sulieman Abdalla for his excellent and brilliant assistances, understanding and sound judgments. Thanks to him for his patience, kindness plus full of pity and great help. I cannot offer enough thanks or remuneration to Dr. Adil Elkhidir Bala for his constant and continuous support, except praying humbly and earnestly, for Allah to attain him full health and success. Professor Amir Mohammed Salih the scientific father of all, I admire his unlimited support throughout the PhD course.