  We study the scattering of a moving discrete breather (DB) on a junction in a
Fermi-Pasta-Ulam (FPU) chain consisting of two segments with different masses
of the particles. We consider four distinct cases: (i) a light-heavy (abrupt)
junction in which the DB impinges on the junction from the segment with lighter
mass, (ii) a heavy-light junction, (iii) an up mass-ramp in which the mass in
the heavier segment increases continuously as one moves away from the junction
point, and (iv) a down mass-ramp. Depending on the mass difference and DB
characteristics (frequency and velocity), the DB can either reflect from, or
transmit through, or get trapped at the junction or on the ramp. For the
heavy-light junction, the DB can even split at the junction into a reflected
and a transmitted DB. The latter is found to subsequently split into two or
more DBs. For the down mass-ramp the DB gets accelerated in several stages,
with accompanying radiation (phonons). These results are rationalized by
calculating the Peierls-Nabarro barrier for the various cases. We also point
out implications of our results in realistic situations such as electron-phonon
coupled chains.
