A.E. Assie, M.A. Eltaher and F.F. Mahmoud
Applied Mathematical Modelling 34 ( 9 ): 2336 - 2352 , 2010
Amal E. Alshorbagy, M.A. Eltaher and F.F. Mahmoud
Applied Mathematical Modelling 35 ( 1 ): 412 - 425 , 2011