  The centrality dependence of directed and elliptic flow in light and heavy
systems of colliding nuclei is studied within two microscopic transport models
at energies from 1 AGeV to 160 A GeV. The pion directed flow has negative slope
in the midrapidity range irrespective of bombarding energy and mass number of
the colliding ions. In contrast, the directed flow of nucleons vanishes and
even develops antiflow in the midrapidity range in (semi)peripheral collisions
at energies around 11.6 A GeV and higher. The origin of the disappearance of
flow is linked to nuclear shadowing. Since the effect is stronger for a light
system, it can be distinguished from the similar phenomenon caused by the
quark-gluon plasma formation. In the latter case the disappearance of the flow
due to the softening of the equation of state should be most pronounced in
collisions of heavy ions. The centrality dependence of the elliptic flow shows
that the maximum in the <v_2(b)> distribution is shifted to very peripheral
events with rising incident energy, in accord with experimental data. This is
an indication of the transition from baryonic to mesonic degrees of freedom in
hot hadronic matter.
