College of Agronomy, Gansu Agricultural University, Lanzhou, Gansu, China.|Department of Mathematics, Middle Tennessee State University, Murfreesboro, Tennessee, United States of America.|Department of Medicine, Pulmonary Vascular Research Institute, Vanderbilt University Medical Center, Nashville, Tennessee, United States of America.|College of Agronomy, Gansu Agricultural University, Lanzhou, Gansu, China.