  Deformation of single stranded DNA in translocation process before reaching
the pore is investigated. By solving the Laplace equation in a suitable
coordinate system and with appropriate boundary conditions, an approximate
solution for the electric field inside and outside of a narrow pore is
obtained. With an analysis based on "electrohydrodynamic equivalence" we
determine the possibility of extension of a charged polymer due to the presence
of an electric field gradient in the vicinity of the pore entrance. With a
multi-scale hybrid simulation (LB-MD), it is shown that an effective
deformation before reaching the pore occurs which facilitates the process of
finding the entrance for the end monomers. We also highlight the role of long
range hydrodynamic interactions via comparison of the LB-MD results with those
obtained using a Langevin thermostat instead of the LB solver.
