https://www.sciencedirect.com/science/article/pii/S1364032113002256

https://www.sciencedirect.com/science/article/pii/S093936251400003X

https://www.sciencedirect.com/science/article/pii/S1364032114006790

https://www.sciencedirect.com/science/article/pii/S0360544215014589

https://www.sciencedirect.com/science/article/pii/S1364032115014069

https://www.sciencedirect.com/science/article/pii/S0967070X16304322

https://www.sciencedirect.com/science/article/pii/S1364032116311704

https://www.sciencedirect.com/science/article/pii/S1369847818300147

http://www.alshargahlia.edu.sd/journal/pdf/ver_6/sub6.pdf#cont