  We present molecular dynamics study of a generic (coarse-grained) model for
single-polymer diffusion confined in a corrugated cylinder. For a narrow tube,
i.e., diameter of the cylinder $\delta < 2.3$, the axial diffusion coefficient
$D_{||}$ scales as $D_{||} \propto N^{-3/2}$, with chain length $N$, up to $N
\approx 100$ then crosses over to Rouse scaling for the larger $N$ values. The
$N^{-3/2}$ scaling is due to the large fluctuation of the polymer chain along
its fully stretched equilibrium conformation. The stronger scaling, namely
$N^{-3/2}$, is not observed for an atomistically smooth tube and/or for a
cylinder with larger diameter.
