Edge Current and Pairing Order Transition in Chiral Bacterial Vortex

Spontaneous ordering of a bacterial drop into a spiral vortex

In this fluid dynamics video we explore the nature and causes of the spontaneous ordering that emerges in a dense bacterial suspension under confinement. Recent experiments with B. Subtilis confined within small flattened drops show that the bacteria form a steady single-vortex state with a counterrotating cell boundary layer. Using simulations that capture oriented cell-cell and cell-fluid interactions, we show that hydrodynamics is crucial in reproducing and explaining the phenomenon. We give new insights into the microscopic arrangement of the bacteria, which are confirmed by new experiment…

Confinement Stabilizes a Bacterial Suspension into a Spiral Vortex

Confining surfaces play crucial roles in dynamics, transport and order in many physical systems, but their effects on active matter, a broad class of dynamically self-organizing systems, are poorly understood. We investigate here the influence of global confinement and surface curvature on collective motion by studying the flow and orientational order within small droplets of a dense bacterial suspension. The competition between radial confinement, self-propulsion, steric interactions and hydrodynamics robustly induces an intriguing steady single-vortex state, in which cells align in inwardly-…

Ferromagnetic and antiferromagnetic order in bacterial vortex lattices

Despite their inherent non-equilibrium nature, living systems can self-organize in highly ordered collective states that share striking similarities with the thermodynamic equilibrium phases of conventional condensed matter and fluid systems. Examples range from the liquid-crystal-like arrangements of bacterial colonies, microbial suspensions and tissues to the coherent macro-scale dynamics in schools of fish and flocks of birds. Yet, the generic mathematical principles that govern the emergence of structure in such artificial and biological systems are elusive. It is not clear when, or even w…

涡旋反转是受限细菌湍流的前兆

Vortex reversal is a precursor of confined bacterial turbulence

本文通过实验、建模与解析理论，发现圆柱约束下细菌悬浮液随半径增大经历涡旋反转、四涡旋脉动到主动湍流的转变序列，并揭示涡旋反转源于前三个方位角模态的非线性相互作用。

受限细菌涡旋中的几何阻挫与配对序转变

Geometric frustration and pairing order transition in confined bacterial vortices

本研究以受限细菌悬浮液为模型阻挫系统，发现三体涡旋相互作用存在随阻挫发生的反常配对序转变，基于弯曲能的理论可解释相关特征，且手性与阻挫的相互作用能产生集体旋转流，为微流控系统中调控活性湍流提供了几何方法。

Viscoelastic control of spatiotemporal order in bacterial active matter

Active matter consists of units that generate mechanical work by consuming energy. Examples include living systems, such as assemblies of bacteria and biological tissues, biopolymers driven by molecular motors, and suspensions of synthetic self-propelled particles. A central question in the field is to understand and control the self-organization of active assemblies in space and time. Most active systems exhibit either spatial order mediated by interactions that coordinate the spatial structure and the motion of active agents or the temporal synchronization of individual oscillatory dynamics.…