Cheng Ke, Liu Peng, Yang Mingcheng, Hou Meiying
Beijing National Laboratory for Condensed Matter Physics and Laboratory of Soft Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China.
Soft Matter. 2022 Mar 30;18(13):2541-2548. doi: 10.1039/d1sm01798e.
In an active bath, besides thermal noise, immersed passive objects also persistently experience collisions from active particles, which are often coarse-grained into a colored active noise with an assumed exponential time correlation. The exponentially correlated active noise extremely simplifies the theoretical description of immersed passive objects but so far lacks direct experimental verification. Here, we experimentally investigate the active noise subjected by a passive rotor confined in an active granular bath. On the basis of Langevin dynamics, we extract the characteristic of the active noise by analyzing the power spectrum of the rotor trajectory. Our experimental results find that the active noise experienced by the granular rotor does show an exponential time correlation to a good extent, even though due to the small experimental system and low collision frequency, the profile of the active noise in our system is non-Gaussian. Our findings give direct experimental evidence, which supports the widely-used active Ornstein-Uhlenbeck particle model in our dry active system.
在一个活跃的浴槽中，除了热噪声外，浸入其中的被动物体还会持续受到来自活跃粒子的碰撞，这些活跃粒子通常被粗粒化为具有假定指数时间相关性的有色活跃噪声。指数相关的活跃噪声极大地简化了浸入式被动物体的理论描述，但迄今为止缺乏直接的实验验证。在这里，我们通过实验研究了限制在活跃颗粒浴槽中的被动转子所受到的活跃噪声。基于朗之万动力学，我们通过分析转子轨迹的功率谱来提取活跃噪声的特征。我们的实验结果发现，尽管由于实验系统较小且碰撞频率较低，我们系统中的活跃噪声分布是非高斯的，但颗粒转子所经历的活跃噪声在很大程度上确实呈现出指数时间相关性。我们的发现提供了直接的实验证据，支持了在我们的干式活跃系统中广泛使用的活跃奥恩斯坦 - 乌伦贝克粒子模型。
