Nga T. T. Pham, Hao T. P. Nguyen, Cong T. Nguyen, Vietnam Academy of Science and Technology, Viet Nam; Hang T. Vu, Ha T. Pham, Vietnam National University, Viet Nam; Hoa V. Pham, Hong V. Pham, Vietnam Academy of Science and Technology, Viet Nam; Kenji Nakamura, Dokkyo University, Japan