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Acknowledgments This dissertation owes itself to help and support from several people. It is a great pleasure to first thank my advisor, P. Sundar, for his constant guidance, advice and encourage-ment. I also would like to thank Professor H.H. Kuo for teaching me Stochastic Analysis. I am so grateful to Professors G. Cochran, J. Lawson, R. Perlis and A. Sengupta for serving in my thesis committee. I would like to thank the Department of Mathematics and the Graduate School of Louisiana State University for providing me with a pleasant working environment and generous financial support. Finally it is a pleasure to thank Dr. L. Richardson for his support. This dissertation is dedicated to my wife Ling and my son Jing