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arXiv 2008.03207cond-mat.softcond-mat.stat-mech
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活性浴中极性示踪剂的有效朗之万方程

Effective Langevin equations for a polar tracer in an active bath

Milos Knezevic, Holger Stark

摘要:

我们研究了一个极性示踪剂,有一个凹面,沉浸在一个二维的活性粒子悬浮液。使用布朗动力学模拟,我们测量的分布和自关联函数的力和扭矩施加在示踪剂上的活性粒子。示踪剂沿其极轴经受有限的平均力,而所有的关联函数随时间呈指数衰减。使用这些见解,我们构建了完整的粗粒度朗之万描述示踪剂的位置和方向,其中的活性粒子被归入一个有效的自推进力和指数相关的噪声。随后的介观动力学可以用五个无量纲参数来描述。我们进行了彻底的参数研究的均方位移,这说明了不同的参数如何影响示踪剂的动态,跨越从弹道扩散运动。我们还表明,示踪剂位移的分布演变从一个非高斯形状在早期阶段的高斯行为足够长的时间。

英文摘要:

We study a polar tracer, having a concave surface, immersed in a two-dimensional suspension of active particles. Using Brownian dynamics simulations, we measure the distributions and auto-correlation functions of forces and torque exerted by active particles on the tracer. The tracer experiences a finite average force along its polar axis, while all the correlation functions show exponential decay in time. Using these insights we construct the full coarse-grained Langevin description for tracer position and orientation, where the active particles are subsumed into an effective self-propulsion force and exponentially correlated noise. The ensuing mesoscopic dynamics can be described in terms of five dimensionless parameters. We perform a thorough parameter study of the mean squared displacement, which illustrates how the different parameters influence the tracer dynamics, which crosses over from a ballistic to diffusive motion. We also demonstrate that the distribution of tracer displacements evolves from a non-Gaussian shape at early stages to a Gaussian behavior for sufficiently long times.

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