Life, as we know it, represents a complex, robust and, at the same time, an extremely fine-tuned organization of molecules and molecular processes that make use of stored and/or ambient free energy (and, as such, they are often referred to as ‘active’ processes), driving themselves into a hierarchy of nonequilibrium spatiotemporal forms known as the living matter. While the most basic questions concerning the origin of life and the emergence of its more complex forms still remain unanswered, contemporary advances have amassed into a substantial body of knowledge on the nature of the living matter, attracting interest also from other disciplines, including applied mathematics, computer science, chemistry, and physics. In this talk, we first provide a brief introduction on some of the basic notions that underlie our current understanding of active motion on the cellular level (including, for instance, the self-propelling motion, or swim, of E. coli and sperm cells in fluid media) from a physicist's point of view. We then review some of the results obtained from our recent studies in the field. These include computational modeling of the rheotactic and chemotactic responses of model swimmers in imposed shear flow in planar channels, in which case, swimmers are shown to exhibit intriguing behaviors such as population splitting and net upstream flux, paving the way for potential shear-induced separation strategies to be discussed in the end.
Ali Naji is an associate professor of physics at the Institute for Research in Fundamental Sciences (IPM) in Tehran, Iran. He received his PhD in Physics from the Ludwig-Maximilian University of Munich, Germany, in 2005 on the theory and simulation of charged polymers. He carried out his postdoctoral work at the University of California, Santa Barbara (2006-2009) and, as a Royal Society Newton Fellow (2009-2011), at the University of Sheffield and at the Department of Applied Mathematics and Theoretical Physics of the University of Cambridge, UK. His research interests include physics of Coulomb fluids and strongly charged macromolecules (such as colloids, polymers and membranes), nano-particle/DNA complexes, electrostatic stability of virus-like nano-capsids, Casimir effect, electrostatics of soft disordered media and, more recently, fluctuating hydrodynamics of strongly confined fluids, and active self-propulsion in fluid media.