Random flows in an active fluid become directional under confinement There are few sights more spectacular than the swarming of a school of fish or a flock of birds that suddenly gives way to a directional motion. Arguably, our admiration is rooted in the surprise that individual organisms, capable of self-propulsion on their own, organize to move en masse in a coherent fashion. Coherent motion is common in a large class of biological and synthetic materials that are often referred to as active matter. Such materials consist of particles immersed in a fluid that can extract energy from their surroundings (or internal fuel) and convert it into directed motion. Living organisms, biological tissues, rods on a vibrated plate, and self-phoretic colloids are just a few examples (1). Similar to schools of fish and flocks of birds, active matter often exhibits random swarming motion (2–5) that until now was impossible to control or use. On page 1284 of this issue, Wu et al. (6) demonstrate that an active fluid can be manipulated to flow in a particular direction without any external stimuli by confining it in microchannels.

中文翻译：

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活性流体中从混沌到有序

活动流体中的随机流动在限制条件下变为定向 几乎没有比成群结队的鱼或一群鸟突然让位于定向运动更壮观的景象了。可以说，我们的钦佩源于对能够自行推进的个体生物体以一致的方式组织起来集体移动的惊讶。相干运动在一大类生物和合成材料中很常见，这些材料通常被称为活性物质。这种材料由浸入流体中的粒子组成，这些粒子可以从周围环境（或内部燃料）中提取能量并将其转化为定向运动。生物体、生物组织、振动板上的棒和自泳胶体只是几个例子 (1)。类似于鱼群和鸟群，活性物质经常表现出随机的蜂群运动（2-5），直到现在还无法控制或使用。在本期第 1284 页，Wu 等人。(6) 证明活性流体可以通过将其限制在微通道中而被操纵以在没有任何外部刺激的情况下沿特定方向流动。