  Collisions involving 112Sn and 124Sn nuclei have been simulated with the
improved Quantum Molecular Dynamics transport model. The results of the
calculations reproduce isospin diffusion data from two different observables
and the ratios of neutron and proton spectra. By comparing these data to
calculations performed over a range of symmetry energies at saturation density
and different representations of the density dependence of the symmetry energy,
constraints on the density dependence of the symmetry energy at sub-normal
density are obtained. Results from present work are compared to constraints put
forward in other recent analysis.
