Add to ORKG. ^ \- ACKNOWLEDGEMENTS ^ At ' S/^, /JO. h^ c- /-"̂ I I would like to express my sincere gratitude to my advisor. Dr. Roland E. Menzel, for his guidance, patience and encouragement on my study and research in these three and half years. Without his consistent help, I could not finish my Ph.D. research in such a short time. I appreciate other committee members for their teaching, help and kindness. I want to thank my colleagues: Dean Stubbs, Russell Murdock and Dr. Digala Kualawansa, for their consistent help. I would also like to thank all the faculty members, staff members and graduate students who helped me during my staying at Texas Tech University. I am grateful to the Department of Physics, TTU, t