Active matter

Active matter is composed of a large number of self-locomoting constituents, which are capable of converting the energy into motion, thereby driving the system out of thermodynamical equilibrium. If the interaction between constituents is nematic in symmetry, these systems are termed active nematics, and material examples include bacteria colonies, tissue, microtubule-kinesin mixtures and cytoskeleton. We study analytically and numerically the source of the active contribution to macroscopic stress tensor in nematodynamics and the near-field flow profiles of micro-swimmers in anisotropic nematic fluid, offering analytical insight into the source of the activity in biological active matter. Using a mesoscopic approach, we model the non-equilibrium dynamics of 3D active nematics and focus specifically on the dynamics of topological defects, that form spontaneously under sufficient activity or under geometrical constraints. We characterise the topology in active nematic turbulence confined to droplets and in cylindrical capillaries.

Selected papers

  • J. Binysh, Z. Kos, S. Copar, M. Ravnik, and G. P. Alexander, Three-Dimensional Active Defect Loops, Phys. Rev. Lett. 124, 088001 (2020) [abstract] [PDF].

  • S. Čopar, J. Aplinc, Ž. Kos, S. Žumer and M. Ravnik Topology of three-dimensional active nematic turbulence confined to droplets, Phys. Rev. X, 9, 031051 (2019). [Link] [PDF].

  • P. Guillamat, Ž Kos, J. Hardoüin, J. I. Ignés-Mullol, M. Ravnik and F. Sagués Active nematic emulsions, Sci. Adv. 4, eaao1470 (2018). [Link] [PDF].

  • Ž. Kos and M. Ravnik Elementary Flow Field Profiles of Micro-Swimmers in Weakly Anisotropic Nematic Fluids: Stokeslet, Stresslet, Rotlet and Source Flows, Fluids 3, 15 (2018). [Link]

  • M. Ravnik and J. M. Yeomans Confined active nematic flow in cylindrical capillaries, Phys. Rev. Lett., 110, 026001 (2013). [Link] [PDF].

  • D. Svenšek, H. Pleiner and H. R. Brand Collective Stop-and-Go Dynamics of Active Bacteria Swarms, Phys. Rev. Lett 111, 228101 (2013). [Link] [PDF]