Controlling diffusive transport in confined geometries

We analyze the diffusive transport of Brownian particles in narrow channels with periodically varying cross-section. The geometrical confinements lead to entropic barriers, the particle has to overcome in order to proceed in transport direction. The transport characteristics exhibit peculiar behaviors which are in contrast to what is observed for the transport in potentials with purely energetic barriers. By adjusting the geometric parameters of the channel one can effectively tune the transport and diffusion properties. A prominent example is the maximized enhancement of diffusion for particular channel parameters. The understanding of the role of channel-shape provides the possibility for a design of stylized channels wherein the quality of the transport can be efficiently optimized.Comment: accepted for publication in Acta Physica Polonica

Spin Transport in a Quantum Wire

We study the effect of electron-electron backscattering interactions on spin transport in a quantum wire. Even if these interactions have no significant effect on charge transport, they strongly influence the transport of spin. We use the quantum Boltzmann equation in the collision approximation to derive equations of motion for spin current and magnetization. In the limit of small perturbations from equilibrium, we explain the existence of `precessional' and `diffusive' behaviors. We also discuss the low-temperature non-linear decay of an uniform spin current outside the hydrodynamic regime.Comment: 10 pages, 5 figures, REVTE

Nest and Prey of \u3ci\u3eAgeniella (Leucophrus) Fulgifrons\u3c/i\u3e (Hymenoptera: Pompilidae)

Information on the habitat, nest-site, hunting, prey transport, closure, burrow structure, and prey of Ageniella (Leucophrus) fulgifrons is presented. Components of the nesting behaviors of other species of Ageniella are examined and compared with those of A. fulgifrons