  Transport properties of a gated nanostructure depend crucially on the
coupling of its states to the states of electrodes. In the case of a single
quantum dot the coupling, for a given quantum state, is constant or can be
slightly modified by additional gating. In this paper we consider a concentric
dot-ring nanostructure (DRN) and show that its transport properties can be
drastically modified due to the unique geometry. We calculate the dc current
through a DRN in the Coulomb blockade regime and show that it can efficiently
work as a single electron transistor or a current rectifier. In both cases the
transport characteristics strongly depends on the details of the confinement
potential. The calculations are carried out for low and high bias regime, the
latter being especially interesting in the context of current rectification due
to fast relaxation processes.
