A thesis was completed due to the special kindness, patience, guidance, and contribution from my advisor, Dr.Illian Assenov. i wish to think the members of my committee, Professor Dr.Taweep Sirirassamee, Association Professor Dr.Dr. Ranee Esichaikul, Professor Dr.Anek Hirunraks who gave me very excellent suggestions and examined the thesis. I would also like to thank Ajarn Pratrick Jory who gave me the recommendation on thesis writing, and all staffs at the Faculty of Service Industries, for their various assistance.