SUPA, School of Physics & Astronomy, The University of Edinburgh, Mayfield Road, Edinburgh EH9 3JZ, UK.
Soft Matter. 2020 May 21;16(19):4682-4691. doi: 10.1039/d0sm00166j.
Systems combining rod-shaped objects with self-generated motion such as suspensions of microtubules or growing bacterial colonies are commonly modeled as active nematics - nematic liquid crystals with an additional active stress term. Confining a 2D active nematic to the surface of a sphere generates novel behaviour as the four +1/2 nematic defects which are produced by the spherical geometry move round each other in an intricate dance. Here, these defects are modeled as point particles experiencing elastic forces from defect position and orientation, and self-propulsion due to activity. This model exhibits four qualitatively distinct types of trajectory state: two which are consistent with previous experimental and simulated trajectories; and two others, which are apparently novel and in regions of parameter space that may not yet have been explored. This work also explains a discrepancy between some previous point-particle models and the trajectories seen in experiments and simulations: this was due to a failure to fully account for the spherical geometry in the point-particle models.
将棒状物体与自生成运动（如微管悬浮液或生长的细菌菌落）相结合的系统通常被建模为活性向列型 - 具有附加活性应力项的向列型液晶。将二维活性向列体限制在球体表面会产生新颖的行为，因为由球体几何形状产生的四个+1/2 向列型缺陷会以复杂的舞蹈方式相互绕转。在这里，这些缺陷被建模为点粒子，它们经历来自缺陷位置和取向的弹性力以及由于活性而产生的自推进力。该模型表现出四种定性不同的轨迹状态：两种与先前的实验和模拟轨迹一致；另外两种则是明显新颖的，并且处于可能尚未探索的参数空间区域。这项工作还解释了一些先前的点粒子模型与实验和模拟中观察到的轨迹之间的差异：这是由于在点粒子模型中未能完全考虑到球体几何形状。
