Title: Phase-separation during sedimentation of dilute bacterial suspensions Show Chinese title

Title: 稀释细菌悬浮液沉降过程中的相分离

Abstract: Numerous natural systems showcase the sedimentation of passive particles in presence of swimming microorganisms. Here, we investigate the dynamics of the sedimentation of spherical colloids at various E. coli concentration within the dilute regime. Results show the appearance of two sedimentation fronts, a spherical particle front and a bacteria front. We find that the sedimentation speed of passive particles decreases as bacteria concentration ($\phi_b$) is increased. As $\phi_b$ is increased further, the sedimentation speed becomes independent of $\phi_b$. The timescale of the second front captures the behavior of both regimes, and a simple model based on particle-bacteria interactions is proposed that can describe this timescale for a range of $\phi_b$. Remarkably, all experiments collapse onto a single master line by using the second front timescale. A phenomenological model is proposed that captures the sedimentation of passive particles in active fluids. Show Chinese abstract

Abstract: 许多自然系统展示了在游泳微生物存在下的被动粒子沉降。 在这里，我们研究了在稀释区域内不同大肠杆菌浓度下球形胶体的沉降动力学。 结果表明出现了两个沉降前沿，一个是由球形粒子形成的前沿，另一个是由细菌形成的前沿。 我们发现，随着细菌浓度（$\phi_b$）的增加，被动粒子的沉降速度会降低。 当$\phi_b$进一步增加时，沉降速度变得与$\phi_b$无关。 第二个前沿的时间尺度捕捉了两种情况的行为，并提出了一种基于粒子-细菌相互作用的简单模型，该模型可以描述一系列$\phi_b$的时间尺度。 值得注意的是，通过使用第二个前沿的时间尺度，所有实验都落在一条单一的主线上。 提出了一种现象学模型，可以描述主动流体中被动粒子的沉降。