A note on shell models for MHD Turbulence
  We investigate the time evolution of two different (GOY-like) shell models which have been recently proposed to describe the gross features of MHD turbulence. We see that, even if they are formally of the same type sharing with MHD equations quadratic couplings and similar conserved quantities, fundamental differences exist which are related to the ideal invariants. 
P. Giuliani (University of Calabria), V. Carbone (University of   Calabria)