  The translocation of a short DNA fragment through a nanopore is addressed
when the perforated membrane contains an embedded electrode. Accurate numerical
solutions of the coupled Poisson, Nernst-Planck, and Stokes equations for a
realistic, fully three-dimensional setup as well as analytical approximations
for a simplified model are worked out. By applying a suitable voltage to the
membrane electrode, the DNA can be forced to preferably traverse the pore
either along the pore axis or at a small but finite distance from the pore
wall.
