Hoang Van Viet - Master of Engineering, researcher, Le Quy Don Technical University E-mail: viethv76@gmail.com Bui The Truyen - Dr.Sc., teacher, Le Quy Don Technical University E-mail: buithetruyen@gmail.com Tong Minh Duc - Dr.Sc., teacher, Le Quy Don Technical University E-mail: tmduc08@gmail.com Luu Hong Dung - Dr.Sc., teacher, Le Quy Don Technical University E-mail: luuhongdung@gmail.com