受限诱导的活性流体中涨落诱导力的优化
Confinement-Induced Optimization of Fluctuation-Induced Forces in Active Fluids
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中文总结 AI 辅助
该研究通过朗之万动力学模拟发现，活性流体中涨落诱导力随侵入体间距呈非单调依赖，最佳间隙处力最大，源于粒子输运与拥挤的受限平衡，确定受限几何为关键控制参数。
中文摘要 AI 辅助
活性物质会产生非平衡涨落，这些涨落介导浸没物体之间的有效相互作用。活性流体中的涨落诱导（FI）力取决于活性、密度和几何形状，但它们对受限的依赖关系仍知之甚少。我们使用朗之万动力学模拟，研究了由自驱圆形或棒状粒子组成的二维活性流体中，固定侵入体之间的FI力。我们发现，FI力对侵入体间距呈现出明显的非单调依赖关系，在远超出耗尽区的最佳间隙尺寸处达到最大值，这与通常假设的单调衰减形成对比。这种最佳受限在不同参数下均具有鲁棒性，且对于细长粒子更为明显。该效应源于粒子输运与拥挤之间由受限控制的平衡：窄间隙阻碍内部与外部区域之间的交换，而大间距则使侵入体有效解耦。在中间距离下，侵入体周围增强的拥挤产生最大的碰撞率不对称性，从而导致最强的有效相互作用。这些结果确定了受限几何是活性物质中FI力的关键控制参数。
英文摘要
Active matter generates nonequilibrium fluctuations that mediate effective interactions between immersed objects. While fluctuation-induced (FI) forces in active fluids depend on activity, density, and geometry, their dependence on confinement remains poorly understood. We study FI forces between fixed intruders in two-dimensional active fluids composed of self-propelled circular or rodlike particles using Langevin dynamics simulations. We find that the FI force exhibits a pronounced nonmonotonic dependence on intruder separation, reaching a maximum at an optimal gap size well beyond the depletion regime, in contrast to the commonly assumed monotonic decay. This optimal confinement is robust across parameters and is more pronounced for elongated particles. The effect arises from a confinement-controlled balance between particle transport and crowding: narrow gaps hinder exchange between inner and outer regions, whereas large separations effectively decouple the intruders. At intermediate distances, enhanced crowding around the intruders generates maximal collision-rate asymmetries, leading to the strongest effective interactions. These results identify confinement geometry as a key control parameter for FI forces in active matter.
