  Polymer transport is investigated for two paradigmatic laminar flows having
open and closed streamlines, respectively. For both types of flows we find
transport depletion owing to the action of the polymers elastic degree of
freedom. For flows with closed streamlines the leading mechanism for the
observed transport reduction is the (dynamical) formation of barriers. For
flows with open streamlines the reduction of transport is induced by the
renormalization of the bare diffusion coefficient. Results have been obtained
by means of Lagrangian simulations.
