I would like to offer my special thanks to every people who gave me the help to complete this thesis. I would like to express my deep gratitude to Assoc. Prof. Dr. Usa Humphries my research supervisor and Dr. Angkool Wangwongchai my research Co-supervisor, for them patience guidance, enthusiastic encouragement, advice and assistance of this research work. I also would like to the examination committee, Dr. Boonchai Phungpaingam from Department of Civil Engineering, Rajamangala University of Technology, Thanyaburi, Asst. Prof. Dr. Anirut Luadsong and Dr.Teerapol Saleewong from Department of Mathematics, Faculty of Science, King Mongkut’s University of Technology, Thonburi for acting as the member of the examination committees. Their valuable comments and suggestions are very much appreciated.
Also, I am deeply indebted to all lecturers who taught me in the graduate courses at the Mathematics Department of King Mongkut’s University of Technology Thonburi. I would like to thank my good friends for friendly helps whenever I need. Finally, I express my deep gratitude to my family who has always been my inspiration and my guiding light. They always support me with all their love.