  Efficiency of generation of net unidirectional current in an adiabatically
driven symmetric periodic potential system is studied.
  The efficiency shows a maximum, in the case of an inhomogeneous system with
spatially varying periodic friction coefficient, as a function of temperature.
The ratchet is not most efficient when it gives maximum current. The direction
of current may also be reversed as a function of noise strength when, instead,
an asymmetric periodic potential is considered.
