title: Biased diffusion in tubes of alternating diameter: Numerical study over a wide range of biasing force.
abstract: This paper is devoted to particle transport in a tube formed by alternating wide and narrow sections, in the presence of an external biasing force. The focus is on the effective transport coefficients--mobility and diffusivity, as functions of the biasing force and the geometric parameters of the tube. Dependences of the effective mobility and diffusivity on the tube geometric parameters are known in the limiting cases of no bias and strong bias. The approximations used to obtain these results are inapplicable at intermediate values of the biasing force. To bridge the two limits Brownian dynamics simulations were run to determine the transport coefficients at intermediate values of the force. The simulations were performed for a representative set of tube geometries over a wide range of the biasing force. They revealed that there is a range of the narrow section length, where the force dependence of the mobility has a maximum. In contrast, the diffusivity is a monotonically increasing function of the force. A simple formula is proposed, which reduces to the known dependences of the diffusivity on the tube geometric parameters in both limits of zero and strong bias. At intermediate values of the biasing force, the formula catches the diffusivity dependence on the narrow section length, if the radius of these sections is not too small.
authors.affiliation: Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Leninsky Prospect 29, Moscow 119991, Russia.
authors.forename: Yurii A
authors.initials: YA
authors.lastname: Makhnovskii
authors.affiliation: Mathematical and Statistical Computing Laboratory, Division of Computational Bioscience, Center for Information Technology, National Institutes of Health, Bethesda, Maryland 20819, USA.
authors.forename: Alexander M
authors.initials: AM
authors.lastname: Berezhkovskii
authors.affiliation: Faculty of Fundamental Physics and Chemical Engineering, Moscow State University, GSP-1, 1-51 Leninskie Gory, Moscow 119991, Russia.
authors.forename: Anatoly E
authors.initials: AE
authors.lastname: Antipov
authors.affiliation: Joint Institute for High Temperatures, Russian Academy of Sciences, Izhorskaya 13, Bldg. 2, Moscow 125412, Russia.
authors.forename: Vladimir Yu
authors.initials: VY
authors.lastname: Zitserman