G.A. Ebong, H.S. Etuk and J.P. Essien
Journal of Applied Sciences 7 ( 20 ): 3045 - 3050 , 2007
G.A. Ebong, H.S. Etuk and A.S. Johnson
Journal of Applied Sciences 7 ( 10 ): 1404 - 1409 , 2007