title: Geometrical interpretation of long-time tails of first-passage time distributions in porous media with stagnant parts.
abstract: Using a combined experimental-numerical approach, we study the first-passage time distributions (FPTD) of small particles in two-dimensional porous materials. The distributions in low-porosity structures show persistent long-time tails, which are independent of the Péclet number and therefore cannot be explained by the advection-diffusion equation. Instead, our results suggest that these tails are caused by stagnant, i.e., quiescent areas where particles are trapped for some time. Comparison of measured FPTD with an analytical expression for the residence time of particles, which diffuse in confined regions and are able to escape through a small pore, yields good agreement with our data.
authors.affiliation: 2. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Wirner
authors.affiliation: 2. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Scholz
authors.affiliation: 2. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany and Max-Planck-Institut für Intelligente Systeme, Heisenbergstraße 3, 70569 Stuttgart, Germany.
authors.forename: Clemens
authors.initials: C
authors.lastname: Bechinger
mesh_terms: D057446:Hydrodynamics; D008962:Models, Theoretical; D009038:Motion; D010316:Particle Size; D016062:Porosity; D013997:Time Factors