@article{may_golick_phillips_shearer_daniels_2010, title={Shear-driven size segregation of granular materials: Modeling and experiment}, volume={81}, ISSN={["1550-2376"]}, DOI={10.1103/physreve.81.051301}, abstractNote={Granular materials segregate by size under shear, and the ability to quantitatively predict the time required to achieve complete segregation is a key test of our understanding of the segregation process. In this paper, we apply the Gray-Thornton model of segregation (developed for linear shear profiles) to a granular flow with an exponential shear profile, and evaluate its ability to describe the observed segregation dynamics. Our experiment is conducted in an annular Couette cell with a moving lower boundary. The granular material is initially prepared in an unstable configuration with a layer of small particles above a layer of large particles. Under shear, the sample mixes and then resegregates so that the large particles are located in the top half of the system in the final state. During this segregation process, we measure the velocity profile and use the resulting exponential fit as input parameters to the model. To make a direct comparison between the continuum model and the observed segregation dynamics, we map the local concentration (from the model) to changes in packing fraction; this provides a way to make a semiquantitative comparison with the measured global dilation. We observe that the resulting model successfully captures the presence of a fast mixing process and relatively slower resegregation process, but the model predicts a finite resegregation time, while in the experiment resegregation occurs only exponentially in time.}, number={5}, journal={PHYSICAL REVIEW E}, publisher={American Physical Society (APS)}, author={May, Lindsay B. H. and Golick, Laura A. and Phillips, Katherine C. and Shearer, Michael and Daniels, Karen E.}, year={2010}, month={May} }
 @article{golick_daniels_2009, title={Mixing and segregation rates in sheared granular materials}, volume={80}, ISSN={["1550-2376"]}, DOI={10.1103/PhysRevE.80.042301}, abstractNote={The vertical size segregation of granular materials, a process commonly associated with the Brazil-nut effect, has generally been thought to proceed faster the greater the size difference of the particles. We experimentally investigate sheared dense bidisperse granular materials as a function of the size ratio of the two species and find that the mixing rate at low confining pressure behaves as expected from percolation-based arguments. However, we also observe an anomalous effect for the resegregation rates, wherein the segregation rate is a nonmonotonic function of the particle size ratio with a maximum for intermediate particle size ratio. Combined with the fact that increasing the confining pressure significantly suppresses both mixing and segregation rates of particles of sufficiently dissimilar size, we propose that the anomalous behavior may be attributed to a species-dependent distribution of forces within the system.}, number={4}, journal={PHYSICAL REVIEW E}, author={Golick, Laura A. and Daniels, Karen E.}, year={2009}, month={Oct} }