Memarian Fereshteh L, Hammar Derek, Sabbir Md Mainul Hasan, Elias Mark, Mitchell Kevin A, Hirst Linda S
Department of Physics, University of California, Merced, 5200 North Lake Road, Merced, California 95343, USA.
Phys Rev Lett. 2024 May 31;132(22):228301. doi: 10.1103/PhysRevLett.132.228301.
This work examines self-mixing in active nematics, a class of fluids in which mobile topological defects drive chaotic flows in a system comprised of biological filaments and molecular motors. We present experiments that demonstrate how geometrical confinement can influence the braiding dynamics of the defects. Notably, we show that confinement in cardioid-shaped wells leads to realization of the golden braid, a maximally efficient mixing state of exactly three defects with no defect creation or annihilation. We characterize the golden braid state using different measures of topological entropy and the Lyapunov exponent. In particular, topological entropy measured from the stretching rate of material lines agrees well with an analytical computation from braid theory. Increasing the size of the confining cardioid produces a transition from the golden braid, to the fully chaotic active turbulent state.
这项工作研究了活性向列相中的自混合现象，活性向列相是一类流体，在由生物细丝和分子马达组成的系统中，移动拓扑缺陷会驱动混沌流动。我们展示了一些实验，这些实验证明了几何限制如何影响缺陷的编织动力学。值得注意的是，我们表明，在心形阱中的限制会导致实现金色辫子，这是一种恰好三个缺陷的最大效率混合状态，且没有缺陷的产生或湮灭。我们使用不同的拓扑熵和李雅普诺夫指数度量来表征金色辫子状态。特别是，从物质线的拉伸率测量得到的拓扑熵与辫子理论的解析计算结果非常吻合。增加限制心形的尺寸会导致从金色辫子状态转变为完全混沌的活性湍流状态。
