Aida Fadzliana Abdul Kadir, Azah Mohamed, Hussein Shareef, Ahmad Asrul Ibrahim, Tamer Khatib, Wilfried Elmenreich.  (2014).  An Improved Gravitational Search Algorithm for Optimal Placement and Sizing of Distributed Generation Units in a Distribution System for Power Quality Enhancement.  - Journal of Renewable and Sustainable Energy.  6(2014):033112. 

Hussain Shareef, Azah Mohamed, Ahmad Asrul Ibrahim.  (2013).  Identification of voltage sag source location using S and TT transformed disturbance power.  - Journal of Central South University.  20(1):83-97. 

Ahmad Asrul Ibrahim, Azah Mohamed, Hussain Shareef, Sakti Prasad Ghoshal.  (2012).  A new approach for optimal power quality monitor placement in power system considering system topology.  - Prezglad Elektrotechniczy (Electrical Review).  88(9a):272-276.