SchoolofSciences;
NorthChinaUniversityofTechnology;
Beijing100041;
China;
SchoolofMathematicsandStatistics;
HebeiUniversityofEconornyandTrade;
Shijiazhuang050063;
China;
DepartmentofBasicCourses;
ShijiazhuangVocationalTechnologyInstitute;
Shijiazhuang050081;
China;