  We investigate the chain conformation of ring polymers confined to a
cylindrical nanochannel using both theoretical analysis and three dimensional
Langevin dynamics simulations. We predict that the longitudinal size of a ring
polymer scales with the chain length and the diameter of the channel in the
same manner as that for linear chains based on scaling analysis and Flory-type
theory. Moreover, Flory-type theory also gives the ratio of the longitudinal
sizes for a ring polymer and a linear chain with identical chain length. These
theoretical predictions are confirmed by numerical simulations. Finally, our
simulation results show that this ratio first decreases and then saturates with
increasing the chain stiffness, which has interpreted the discrepancy in
experiments. Our results have biological significance.
