Motile and driven particles confined in microfluidic channels exhibit interesting emergent behavior from propagating density bands to density shock waves. A deeper understanding of the physical mechanisms responsible for these emergent structures is relevant to a number of physical and biomedical applications. Here, we study the formation of density shock waves in the context of an idealized model of microswimmers confined in a narrow channel and subject to a uniform external flow. Interestingly, these density shock waves exhibit a transition from `subsonic' with compression at the back to `supersonic' with compression at the front of the population as the intensity of the external flow increases. This behavior is the result of a non-trivial interplay between hydrodynamic interactions and geometric confinement, and is confirmed by a novel quasilinear wave model that properly captures the dependence of the shock formation on the external flow. These findings can be used to guide the development of novel mechanisms for controlling the emergent density distribution and average population speed, with potentially profound implications on various processes in industry and biotechnology such as the transport and sorting of cells in flow channels.
Mixing induced by microswimmers as probed by mutual information
Max Planck Institute for Dynamics and Self-Organization（马克斯·普朗克动力学与自组织研究所）；Institute of Science and Technology Austria（奥地利科学技术研究所）；Department of Mathematics, Kyoto University（京都大学数学系）；Jožef Stefan Institute（约瑟夫·斯特凡研究所）；Rudolf Peierls Centre for Theoretical Physics, University of Oxford（牛津大学鲁道夫·皮尔斯理论物理中心）
Shocking a Shock Wave for Nonlinear Summation of GPa Pressures
Massachusetts Institute of Technology（麻省理工学院）；Institute for Soldier Nanotechnologies, Massachusetts Institute of Technology（麻省理工学院士兵纳米技术研究所）；Institut de Physique de Rennes, UMR CNRS 6251, Université de Rennes（雷恩大学物理研究所，CNRS 6251联合实验室）
