Acknowledgment
First and foremost, I would like to thank my academic advisor, Professor
Nguyen Dong Yen, for his guidance and constant encouragement.
The wonderful research environment of the Institute of Mathematics, Viet-
nam Academy of Science and Technology, and the excellence of its staff have
helped me to complete this work within the schedule. I would like to express
my special appreciation to Prof. Hoang Xuan Phu, Assoc. Prof. Ta Duy
Phuong, Assoc. Prof. Phan Thanh An, and other members of the weekly
seminar at Department of Numerical Analysis and Scientific Computing, In-
stitute of Mathematics, as well as all the members of Prof. Nguyen Dong
Yen’s research group for their valuable comments and suggestions on my re-
search results. In particular, I would like to express my sincere thanks to
Dr. Thai Doan Chuong for his significant comments and suggestions con-
cerning the research related to Chapters 1 and 5 of this dissertation.
I would like to thank the Assoc. Prof. Truong Xuan Duc Ha, Prof. Le
Dung Muu, Assoc. Prof. Pham Ngoc Anh, Assoc. Prof. Tran Dinh Ke,
Assoc. Prof. Nguyen Thi Thu Thuy, and Dr. Le Hai Yen, and the two
anonymous referees, for their careful readings of this dissertation and valuable
comments.
I am sincerely grateful to Prof. Jen-Chih Yao from China Medical Uni-
versity and National Sun Yat-sen University, Taiwan, for granting several
short-termed scholarships for my PhD studies.
Furthermore, I would like to thank my colleagues at Department of Math-
ematics and Informatics, Hanoi National University of Education for their
efficient help during the years of my Master and PhD studies.
Finally, I would like to thank my family for their endless love and uncon-
ditional support.
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