  Reptation governs motion of long polymers through a confining environment.
Slack enters at the ends and diffuses along the polymer as stored length. The
rate at which stored length diffuses limits the speed at which the chain can
drift. This paper relates the rate of stored length diffusion to the
conformation of the tube within which the polymer is confined. In the scaling
limit of long polymer chains and weak applied electric fields, holding the
product of polymer length times field finite, the tube length and stored length
density take on their zero-field values. The drift velocity then depends only
on the the polymer's end-to-end separation in the direction of the field.
