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 depend on 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 the bacteria front. We find that the bacteria front behave diffusive at short times, whereas at long times decays linearly. The sedimentation speed of passive particles decays at a constant speed and decreases as bacteria concentration ($\phi_b$) is increased. As $\phi_b$ is increased further, the sedimentation speed becomes independent of $\phi_b$. The timescales of the bacteria front is associated with the particle settling speeds. Remarkably, all experiments collapse onto a single master line by using the bacteria front timescale. A phenomenological model is proposed that captures the sedimentation of passive particles in active fluids. Show Chinese abstract

Abstract: 许多自然系统依赖于游泳微生物存在下的被动粒子沉降。 在这里，我们研究了在稀释范围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和一个由细菌形成的前沿。 我们发现细菌前沿在短时间表现出扩散行为，而在长时间时呈线性衰减。 被动粒子的沉降速度以恒定速度衰减，并随着细菌浓度（$\phi_b$）的增加而减小。 当$\phi_b$进一步增加时，沉降速度变得与$\phi_b$无关。 细菌前沿的时间尺度与粒子沉降速度有关。 值得注意的是，通过使用细菌前沿的时间尺度，所有实验都叠加到一条单一的主线上。 提出了一种现象学模型，用于描述活性流体中被动粒子的沉降。