:DepartmentofAppliedMathematics;
ShanghaiJiaotongUniversity;
Shanghai200030;
China(permanentaddressisDepartmentofMathematics;
QuanzhouNormalCollege;
Quanzhou362000;
Fujian;
China).;
DepartmentofMathematics;
HuaQiaoUniversity;
Quanzhou362011;
Fujian;
China.;