The topological properties of many materials are central to their behavior. In intrinsically out-of-equilibrium active materials, the dynamics of topological defects can be particularly important. In this paper, local manipulation of the order, dynamics, and topological properties of microtubule-based active nematic films is demonstrated in a joint experimental and simulation study. Hydrodynamic stresses created by magnetically actuated rotation of disk-shaped colloids in proximity to the films compete with internal stresses in the active nematic, influencing the local motion of +1/2 charge topological defects that are intrinsic to the nematic order in the spontaneously turbulent active films. Sufficiently large applied stresses drive the formation of +1 charge topological vortices through the merger of two +1/2 defects. The directed motion of the defects is accompanied by ordering of the vorticity and velocity of the active flows within the film that is qualitatively unlike the response of passive viscous films. Many features of the film's response to the stress are captured by lattice Boltzmann simulations, providing insight into the anomalous viscoelastic nature of the active nematic. The topological vortex formation is accompanied by a rheological instability in the film that leads to significant increase in the flow velocities. Comparison of the velocity profile in vicinity of the vortex with fluid-dynamics calculations provides an estimate of the film viscosity.

中文翻译：

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主动向列型膜的驱动拓扑转变。

许多材料的拓扑特性对其行为至关重要。在本质上不平衡的活性材料中，拓扑缺陷的动力学尤其重要。在本文中，在联合实验和模拟研究中证明了对基于微管的主动向列膜的顺序，动力学和拓扑特性的局部操纵。膜附近的盘状胶体的磁驱动旋转产生的水动力应力与活性向列相中的内应力竞争，影响了自发湍流活性中向列相序固有的+1/2电荷拓扑缺陷的局部运动电影。足够大的外加应力通过合并两个+1/2缺陷来驱动+1电荷拓扑漩涡的形成。缺陷的定向运动伴随着膜内活性流的涡度和速度排序，这在质量上与无源粘性膜的响应不同。晶格Boltzmann模拟可捕获薄膜对应力的反应的许多特征，从而洞悉活性向列的异常粘弹性。拓扑涡流的形成伴随着膜中的流变不稳定性，从而导致流速显着增加。涡旋附近的速度分布与流体动力学计算的比较提供了膜粘度的估计。晶格Boltzmann模拟可以捕获薄膜对应力的响应的许多特征，从而洞悉活性向列的异常粘弹性。拓扑漩涡的形成伴随着膜中的流变不稳定性，从而导致流速显着增加。涡旋附近的速度分布与流体动力学计算的比较提供了膜粘度的估计。晶格Boltzmann模拟捕捉了薄膜对应力的响应的许多特征，从而洞察了活性向列的异常粘弹性。拓扑漩涡的形成伴随着膜中的流变不稳定性，从而导致流速显着增加。涡旋附近的速度分布与流体动力学计算的比较提供了膜粘度的估计。