  Using simulations and a virtual-spring-based approach, we measure the
segregation force, Fseg, over a range of size-bidisperse mixture
concentrations, particle size ratios, and shear rates to develop a model for
Fseg that extends its applicability from the well-studied non-interacting
intruders regime to finite-concentration mixtures where cooperative phenomena
occur. The model predicts the concentration below which the single intruder
assumption applies and provides an accurate description of the pressure
partitioning between species.
