Affiliation: | aInstitute for Mathematics and its Applications, University of Minnesota, 357 Lind Hall, 207 Church Street S.E., Minneapolis, MN 55455-0436, USA bLaboratoire LIMOS, CNRS UMR 6158, Université de Clermont-Ferrand II, Complexe Scientifique des Cézeaux, 63177 Aubière, France |