Active materials are capable of converting free energy into directional motion, giving rise to notable dynamical phenomena. Developing a general understanding of their structure in relation to the underlying nonequilibrium physics would provide a route toward control of their dynamic behavior and pave the way for potential applications. The active system considered here consists of a quasi-two-dimensional sheet of short (≈1 μm) actin filaments driven by myosin II motors. By adopting a concerted theoretical and experimental strategy, new insights are gained into the nonequilibrium properties of active nematics over a wide range of internal activity levels. In particular, it is shown that topological defect interactions can be led to transition from attractive to repulsive as a function of initial defect separation and relative orientation. Furthermore, by examining the +1/2 defect morphology as a function of activity, we found that the apparent elastic properties of the system (the ratio of bend-to-splay elastic moduli) are altered considerably by increased activity, leading to an effectively lower bend elasticity. At high levels of activity, the topological defects that decorate the material exhibit a liquid-like structure and adopt preferred orientations depending on their topological charge. Together, these results suggest that it should be possible to tune internal stresses in active nematic systems with the goal of designing out-of-equilibrium structures with engineered dynamic responses.

中文翻译：

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活性液晶的可调谐结构和动力学。

活性材料能够将自由能转化为定向运动，从而产生显着的动力学现象。对其结构与潜在非平衡物理的关系有一个总体的了解，将为控制其动态行为提供一条途径，并为潜在应用铺平道路。这里考虑的主动系统由由肌球蛋白 II 电机驱动的准二维短肌动蛋白丝（约 1 μm）组成。通过采用协调一致的理论和实验策略，对活性向列相在广泛的内部活性水平上的非平衡特性有了新的认识。特别是，它表明拓扑缺陷相互作用可以作为初始缺陷分离和相对方向的函数从吸引转变为排斥。此外，通过检查 +1/2 缺陷形态作为活性的函数，我们发现系统的表观弹性特性（弯曲与张开弹性模量的比率）随着活性的增加而显着改变，从而有效地较低的弯曲弹性。在高活性水平下，装饰材料的拓扑缺陷表现出类似液体的结构，并根据其拓扑电荷采取优选方向。总之，这些结果表明，应该可以调整主动向列系统中的内应力，以设计具有工程动态响应的非平衡结构。