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Shuai Yuan
1School of Mathematics and Statistics
HNP-LAMA, Central South University,
2.Department of Mathematics,
University of Craiova,
3.China-Romania Research Center in Applied Mathematics
Craiova,Craiova
Yuning Gao
Department of Material Enginering,
Hebei Vocational University of Industry and Technology,
Ovidius University of Constanta
P.R.China