[1] Xi An Jiao Tong Univ, Sch Math & Stat, Xian 710049, Shaanxi, Peoples R China
[2] Shaanxi Univ Sci & Technol, Sch Arts & Sci, Xian 710021, Shaanxi, Peoples R China
[3] Baoji Univ Arts & Sci, Dept Math, Baoji 721007, Peoples R China
[4] Univ Calgary, Schulich Sch Engn, Dept Chem & Petr Engn, 2500 Univ Dr NW, Calgary, AB T2N 1N4, Canada