Laborima, Ecole Polytechnique B.P 8390 Yaounde, Cameroon. g_koum@yahoo.fr|Laborima, Ecole Polytechnique B.P 8390 Yaounde, Cameroon. g_koum@yahoo.fr|Laborima, Ecole Polytechnique B.P 8390 Yaounde, Cameroon. g_koum@yahoo.fr|Laborima, Ecole Polytechnique B.P 8390 Yaounde, Cameroon. g_koum@yahoo.fr