Affiliation: | 1. School of Mathematics and Statistics, Chongqing Technology and Business University, Chongqing 400067, PR China;2. College of Mathematics and System Sciences, Xinjiang University, Urumqi, Xinjiang 830046, PR China;3. Department of Mathematics, West Virginia University, Morgantown, WV 26506, USA;4. Department of Mathematics, Millersville University, Millersville University of Pennsylvania, Millersville, PA 17551, USA |