1. E.T.S.I. Aeronáutica y del Espacio, Universidad Politécnica de Madrid, P. Cardenal Cisneros 3, E-28040, Madrid, Spain
2. CEA, DAM, DIF, 91297 Arpajon Cedex, France
3. Centre de Mathématiques et de Leurs Applications, ENS Cachan and CNRS, 61 Av. du President Wilson, 94235 Cachan Cedex, France
4. AWE plc, Aldermaston, Reading, Berkshire RG7 4PR, United Kingdom