  Polymer translocation through a nanopore in a membrane investigated
theoretically. Recent experiments on voltage-driven DNA and RNA translocations
through a nanopore indicate that the size and geometry of the pore are
important factors in polymer dynamics. A theoretical approach is presented
which explicitly takes into account the effect of the nanopore length and
diameter for polymer motion across the membrane. It is shown that the length of
the pore is crucial for polymer translocation dynamics. The present model
predicts that for realistic conditions (long nanopores and large external
fields) there are two regimes of translocation depending on polymer size: for
polymer chains larger than the pore length, the velocity of translocation is
nearly constant, while for polymer chains smaller than the pore length the
velocity increases with decreasing polymer size. These results agree with
experimental data.
