First Author:   Serge Blondel GRANEM, University of Angers serge.blondel@univ-angers.fr   13 allée Mitterrand Angers, 49000   0650773695(Phone) 0650773695(Fax) Second Author: Ngoc-thao Noet GRANEM, University of Angers ngoc-thao.noet@etud.univ-angers.fr   13 allée Mitterrand Angers, 49000, France