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Its has been a rewarding experience to be a student at Iowa State University. I am greatful to my teachers, advisor, colleagues and fiiends who supported my educational endeavour and helped me achieve my personal and professional goals. Fond appreciation and special thanks must go to my parents. To my Father for his encouragement, advice and support to pursue knowledge and education over the last many years, during my MS at Iowa State and this research project, and to my mother for her support prayers and Jove in my life and during the past two years as well. An enormous debt of gratitude is owed to Dr. Helen Jensen, my advisor and mentor. I am obliged to her for her continued support, cooperation , guidance patience and invaluable advice throughout the different stages of my MS program and my thesis research. I am also thankful to Jacinto Fabiosa, my assistantship supervisor from day one. He first encouraged me to work on this topic and guided me through the preliminary stages of my research. During my association with him, I learned a great deal about the research process and this research topic. Thanks are due to my good fiiends Muhammed Iqbal and Yaya Takahashi, for their encouragement, help and support. Many thanks are also due to Liyu Yang, a very good fiiend for her continued and close support during my days in Ames and for her invaluable assistance during this research project. Special thanks are also due to my colleagues and good fiiends Chun-Fu Chen and Gerry Parise for their help and support in statistical analysis and computer programming. These acknowledgements are not complete without specially thanking my dear brother and fiiend, Aqeel and his dear wife Maliha for their support and encouragement during the different stages of my thesis research and for their patience with reading and editing my work inspite of their engagements. * indicate significance level of 5 percent Chi-sq (df) = 50.868 (42). * indicate signifi cance level of 5 percent Chi-sq (df) = 66.260 (56).

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