Nishiguchi Daiki, Shiratani Sora, Takeuchi Kazumasa A, Aranson Igor S
Department of Physics, School of Science, Institute of Science Tokyo, Meguro-ku, Tokyo 152-8551, Japan.
Department of Physics, School of Science, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan.
Proc Natl Acad Sci U S A. 2025 Mar 18;122(11):e2414446122. doi: 10.1073/pnas.2414446122. Epub 2025 Mar 14.
Active turbulence, or chaotic self-organized collective motion, is often observed in concentrated suspensions of motile bacteria and other systems of self-propelled interacting agents. To date, there is no fundamental understanding of how geometrical confinement orchestrates active turbulence and alters its physical properties. Here, by combining large-scale experiments, computer modeling, and analytical theory, we have identified a generic sequence of transitions occurring in bacterial suspensions confined in cylindrical wells of varying radii. With increasing the well's radius, we observed that persistent vortex motion gives way to periodic vortex reversals, four-vortex pulsations, and then well-developed active turbulence. Using computational modeling and analytical theory, we have shown that vortex reversal results from the nonlinear interaction of the first three azimuthal modes that become unstable with the radius increase. The analytical results account for our key experimental findings. To further validate our approach, we reconstructed equations of motion from experimental data. Our findings shed light on the universal properties of confined bacterial active matter and can be applied to various biological and synthetic active systems.
在运动细菌的浓缩悬浮液以及其他自推进相互作用粒子系统中，常常会观察到主动湍流，即混沌自组织集体运动。迄今为止，对于几何约束如何调控主动湍流并改变其物理性质，尚无基本的认识。在此，通过结合大规模实验、计算机建模和解析理论，我们确定了在不同半径的圆柱形孔中受限的细菌悬浮液中发生的一系列通用转变。随着孔半径的增加，我们观察到持续的涡旋运动让位于周期性的涡旋反转、四涡旋脉动，然后是充分发展的主动湍流。通过计算建模和解析理论，我们表明涡旋反转是由随着半径增加而变得不稳定的前三个方位模式的非线性相互作用引起的。解析结果解释了我们的关键实验发现。为了进一步验证我们的方法，我们从实验数据重建了运动方程。我们的发现揭示了受限细菌活性物质的普遍性质，并可应用于各种生物和合成活性系统。
