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The Role of Hydrodynamics in the Behavior of Active Matter

流体动力学在活性物质行为中的作用

基本信息

批准号：
1803662
负责人：
John Brady
金额：
$ 33.5万
依托单位：
California Institute of Technology
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2018
资助国家：
美国
起止时间：
2018-09-01 至 2021-08-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1803662&HistoricalAwards=false
关键词：
Role Hydrodynamics Behavior Active Matter

项目摘要

A distinguishing feature of many living organisms is their ability to move, to self-propel, to be active. Constituents of "active matter" systems are capable of independent self-propulsion by converting fuel into mechanical motion. Examples of active matter include both microscopic entities like microorganisms and motor proteins within our cells and large bodies like fishes and birds. Inanimate, nonliving bodies can also achieve self-propulsion using mechanisms that are different than living organisms. The outcome of the collective behavior of these nonliving active systems is not necessarily different from living active systems. Indeed, active matter systems of all scales have the tendency to associate together and move collectively, from colonies of bacteria, swarms of insects, flocks of birds, schools of fish, to herds of cattle. The question addressed in this research is the micromechanical, hydrodynamic, origin for living (and nonliving) organisms to exhibit collective and coherent motion and how it can be explained and modeled using simple physical principles. Such insight will enable the prediction, design, and control of active soft matter systems and their exploitation in nature and in industry.The intrinsic activity imparts new behaviors to active matter that distinguish it from equilibrium condensed matter systems. Active matter systems generate their own internal stress, which drives them far from equilibrium and thus frees them from conventional thermodynamic constraints, and by so doing can control and direct their own behavior and that of their surrounding environment. Active matter is always at least a two-component system - the active body and the embedding medium off of which the active body self-propels. In this research fluid-mediated hydrodynamic interactions among self-propelled bodies are incorporated for the first time. Hydrodynamics significantly affect the forces active particles exert on boundaries or other objects and can profoundly affect the phase separation in active systems by modifying the mechanical "swim pressure." The swim pressure provides a pressure-concentration relation for active matter that can quantitatively predict condensation and phase separation in active systems and provides a route for determining the amount of work that can be harvested from the often random motion of active systems. We also show that, in general, the swim stress has off-diagonal or deviatoric contributions, especially when an active system is subject to shearing motion. The swim stress predicts that, under very general conditions, active particles can reduce the suspension effective viscosity to zero, enabling spontaneous flow of active matter. The mechanical swim stress perspective allows one to understand, analyze and exploit a wide class of active soft matter systems, from swimming bacteria to catalytic nanobots to molecular motors that activate the cellular cytoskeleton.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

许多活着的有机体的一个显著特征是它们能够移动、自我推进和活跃。“活性物质”系统的组成部分能够通过将燃料转化为机械运动来独立地自我推进。活性物质的例子既包括我们细胞中的微生物和马达蛋白等微观实体，也包括鱼类和鸟类等大型实体。无生命、无生命的身体也可以使用不同于生物的机制来实现自我推进。这些无生命的主动系统的集体行为的结果不一定与有生命的主动系统不同。事实上，所有尺度的活动物质系统都有相互联系和集体移动的趋势，从细菌群体、昆虫群体、鸟类群体、鱼群到牛群。这项研究涉及的问题是微机械、流体动力学、生物(和非生物)的起源以及如何用简单的物理原理来解释和模拟这种集体和连贯的运动。这种洞察力将使活性软物质系统的预测、设计和控制及其在自然界和工业上的开发成为可能。本征活性赋予活性物质新的行为，使其有别于平衡凝聚态物质系统。活性物质系统产生自己的内应力，使它们远离平衡，从而使它们从传统的热力学约束中解放出来，通过这样做，可以控制和指导自己和周围环境的行为。活性物质总是至少是一个双组分系统--活性物质和嵌入介质，活性物质通过它自动推进。在这项研究中，首次将流体介导的自行体之间的水动力相互作用纳入其中。流体动力学显著影响活性粒子施加在边界或其他物体上的力，并通过改变机械“游泳压力”来深刻影响活性体系中的相分离。游泳压力提供了活性物质的压力-浓度关系，可以定量地预测活性体系中的凝结和相分离，并提供了一种确定从活性体系经常随机运动中获得的功量的途径。我们还表明，一般来说，游泳应力具有非对角线或偏角的贡献，特别是当一个活跃的系统受到剪切运动的影响时。游泳压力预测，在非常一般的条件下，活性颗粒可以将悬浮液的有效粘度降低到零，从而使活性物质能够自发流动。机械游泳压力视角使人们能够了解、分析和开发一大类活跃的软物质系统，从游泳细菌到催化纳米机器人，再到激活细胞骨架的分子马达。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。