Affiliation: | Department of Mathematics, Nanjing University of Aeronautics and Astronautics, Nanjing 211106, People''s Republic of China,Department of Mathematics, Nanjing University of Aeronautics and Astronautics, Nanjing 211106, People''s Republic of China and Department of Mathematics, Nanjing University of Aeronautics and Astronautics, Nanjing 211106, People''s Republic of China |