“Homotopy Perturbation Method With Modified Riemann –Liouville Derivative for Solving Fractional- Time Partial Differential Equations ”. University of Thi-Qar Journal of Science, vol. 3, no. 2, Feb. 2012, pp. 163-7, http://mail.jsci.utq.edu.iq/index.php/main/article/view/395.