Professor Carlsson's work, in biophysical modeling, treats the molecular-scale processes which allow cells to move and divide. These processes involve the formation of branched polymer networks, or parallel bundles, of the protein actin. These phenomena are being modeled by a combination of Brownian dynamics and stochastic growth simulation, and analytic theory. The main aims of the modeling are to understand the extraordinary responsiveness of the supramolecular actin structures to external stimuli, to explain how the interior of a cell acts as an excitable medium, and to predict the phase diagram of the supramolecular structures in terms of the parameters that characterize their growth, cross-linking, and depolymerization. This work is being carried out in collaboration with Professor John Cooper's group at the Washigton University School of Medicine.