C P Sanjay, Joy Ashwin
Department of Physics, Indian Institute of Technology Madras, Chennai 600036, India.
Phys Rev E. 2022 Jun;105(6-2):065114. doi: 10.1103/PhysRevE.105.065114.
Active matter are a collection of units with intrinsic supply of energy that is utilized for self-propelled motion. Recent studies have confirmed that these active systems can exist in exotic phases, such as swarming, laning, jamming, and even turbulence, based on the size and density of the constituent units. An interesting question that naturally arises is whether one can identify an effective temperature for particles advected by such an active flow that is far from equilibrium. In this paper, we report using a continuum model of a dense bacterial suspension, an exact expression of the effective temperature for a distribution of interacting particles that are immersed in this suspension. We observe that this effective temperature is linear in particle diffusivity with the slope defining the particle mobility that is higher when the background fluid exhibits global polar ordering and lower when the fluid is in isotropic equilibrium. We believe our paper is a direct verification of the Einstein relation-the simplest fluctuation dissipation relation for interacting particles advected in an active matter flow.
活性物质是一组具有内在能量供应的单元，这些能量被用于自我推进运动。最近的研究证实，基于组成单元的大小和密度，这些活性系统可以存在于奇异相中，如群聚、列队、堵塞，甚至湍流。一个自然而然出现的有趣问题是，对于由这种远离平衡的活性流平流的粒子，是否能确定一个有效温度。在本文中，我们报告了使用一种稠密细菌悬浮液的连续介质模型，得到了浸没在该悬浮液中的相互作用粒子分布的有效温度的精确表达式。我们观察到，这个有效温度与粒子扩散率呈线性关系，其斜率定义了粒子迁移率，当背景流体呈现全局极性有序时迁移率较高，而当流体处于各向同性平衡时迁移率较低。我们相信我们的论文是对爱因斯坦关系的直接验证——这是活性物质流中平流的相互作用粒子最简单的涨落耗散关系。
