相互作用的主动流体中的物体：单个物体的远场影响和两个物体之间的相互作用
Bodies in an Interacting Active Fluid: Far-Field Influence of a Single Body and Interaction Between Two Bodies
摘要：
由于活性粒子打破了时间反演对称性，即使没有外部驱动，活性流体也可以维持电流。我们表明，当被动体被放置在成对相互作用的活性粒子的流体中时，它会产生长程电流，对应于密度和压力梯度。通过使用多极展开和远场本构关系，我们表明，所有三个的领导阶行为对应于源偶极子。然后，当两个或更多实体放置在活动流体中时，实体之间会发生一般的远程交互作用。我们发现这些是从其他流体介导的相互作用，如流体动力学或热卡西米尔定性不同。相互作用可以通过在单独的实验中测量一些单体性质来预测。此外，它们是各向异性的，不满足作用-反应原理。这些结果扩展了以前关于非相互作用活性粒子的结果。我们的框架可能指向一条通往自我组装的道路。
英文摘要：
Because active particles break time-reversal symmetry, an active fluid can sustain currents even without an external drive. We show that when a passive body is placed in a fluid of pairwise interacting active particles, it generates long-range currents, corresponding to density and pressure gradients. By using a multipole expansion and a far-field constitutive relation, we show that the leading-order behavior of all three corresponds to a source dipole. Then, when two bodies or more are placed in the active fluid, generic long-range interactions between the bodies occur. We find these to be qualitatively different from other fluid mediated interactions, such as hydrodynamic or thermal Casimir. The interactions can be predicted by measuring a few single-body properties in separate experiments. Moreover, they are anisotropic and do not satisfy an action-reaction principle. These results extend previous results on non-interacting active particles. Our framework may point to a path towards self-assembly.
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