Propulsive matrix of a helical flagellum

We study the propulsion matrix of bacterial flagella numerically using slender body theory and the regularized Stokeslet method in a biologically relevant parameter regime. All three independent elements of the matrix are measured by computing propulsive force and torque generated by a rotating flagellum, and the drag force on a translating flagellum. Nu- merical results are compared with the predictions of resistive force theory, which is often used to interpret micro-organism propulsion. Neglecting hydrodynamic interactions between different parts of a flagellum in resistive force theory leads to both qualitative and quantitative discrepancies between the theoretical prediction of resistive force theory and the numerical results. We improve the original theory by empirically incorporating the effects of hydrodynamic interactions and propose new expressions for propulsive matrix elements that are accurate over the parameter regime explored.     

涌现于交叉科学的新方向——活性物质

活性物质是一类由自驱动个体组成的非平衡系统,存在于从宏观到微观的各个尺度,典型例子包括动物群落、细胞组织、微纳米机器、分子马达等。活性物质的组成个体可以通过消耗局域存储的自由能打破细致平衡、实现自驱动运动,同时通过相互作用形成众多的集体行为,比如自发流动、无序—有序相变、运动的拓扑缺陷等。文章聚焦活性物质的集体行为,从理论和实验的角度揭示这些行为的形成机制和非平衡特征,并讨论活性物质研究在生物、数学和工程等学科中的影响和可能应用。