2025-03-18 東京科学大学
<関連情報>
- https://www.isct.ac.jp/ja/news/8zsohegkxf8b
- https://www.isct.ac.jp/plugins/cms/component_download_file.php?type=2&pageId=&contentsId=1&contentsDataId=946&prevId=&key=09fbe40d795490c52734b08b4323ade8.pdf
- https://www.pnas.org/doi/10.1073/pnas.2414446122
渦の反転はバクテリアの閉じ込め乱流の前兆である Vortex reversal is a precursor of confined bacterial turbulence
Daiki Nishiguchi, Sora Shiratani, Kazumasa A. Takeuchi, and Igor S. Aranson
Proceedings of the National Academy of Sciences Published:March 14, 2025
DOI:https://doi.org/10.1073/pnas.2414446122
Significance
Biological and synthetic self-propelled entities, such as cultured cells, swimming bacteria, and active colloids, often exhibit complex collective motion. Controlling and rectifying such motion is crucial for developing microscopic active devices and sensors composed of swarming self-propelled particles. This study reveals how geometrical confinement transforms chaotic motion into a stabilized vortex and converts it into unsteady reversing configurations. The underlying mechanism is generic and thus applicable to various active systems. This work paves the way for design strategies for active devices grounded in robust theoretical insights.
Abstract
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.
