[1] OFFIS, Escherweg 2, D-26121 Oldenburg, Germany
[2] Carl von Ossietzky Univ Oldenburg, Escherweg 2, D-26121 Oldenburg, Germany
[3] Ecole Polytech, CNRS, 1 Rue Honor Estienne dOrves, F-91120 Palaiseau, France
[4] Ecole Polytech, LIX, 1 Rue Honore dEstienne dOrves, F-91120 Palaiseau, France