  We investigate a Bose-Einstein condensate held in a quasi-one-dimensional
Wannier-Stark lattice which is a combination of linear potential with an
accelerated optical lattice. It is demonstrated that the system can be reduced
to a periodically driven Gross-Pitaevskii one, in which we find the first exact
analytical solution and the regular and chaotic numerical solutions with
accelerated atomic flow densities. The results suggest an experimental scheme
for generating and controlling the accelerating regular and chaotic
matter-waves.
