[1] Zhejiang Univ, Dept Math, Hangzhou 310027, Peoples R China
[2] King Saud Univ, Coll Sci, Dept Math, Riyadh 11451, Saudi Arabia
[3] Wayne State Univ, Dept Math, Detroit, MI 48202 USA
[4] King Fahd Univ Petr & Minerals, Dept Math & Stat, Dhahran 31261, Saudi Arabia
[5] Zhejiang Univ Technol, Dept Math, Hangzhou 310032, Zhejiang, Peoples R China
[6] Kaohsiung Med Univ, Ctr Gen Educ, Kaohsiung 80702, Taiwan