2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/180245The semiclassical approximation for electron wave-packets in crystals leads to equations which can be derived from a Lagrangian or, under suitable regularity conditions, in a Hamiltonian framework. In the plane, these issues are studied %in presence of external fields using the method of the coadjoint orbit applied to the ``enlarged'' Galilei group.15 pages, Talk given at Nonlinear Physics. Theory and Experiment. IV,Gallipoli (Lecce), Italy - June 22 - July 1, 2006Mesoscale and Nanoscale PhysicsHigh Energy Physics - Theorytext