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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.

许多生物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而独立地自我推进。活性物质的例子包括微观实体，如微生物和我们细胞内的运动蛋白质，以及鱼类和鸟类等大型物体。无生命的非生命体也可以使用与生物体不同的机制实现自我推进。这些无生命的主动系统的集体行为的结果不一定不同于有生命的主动系统。事实上，所有尺度的活性物质系统都倾向于联合在一起并集体运动，从细菌群落，昆虫群，鸟群，鱼群，到牛群。在这项研究中解决的问题是微观力学，流体动力学，生物（和非生物）的起源表现出集体和连贯的运动，以及如何可以解释和建模使用简单的物理原理。这种洞察力将使预测，设计和控制活跃的软物质系统及其在自然界和工业中的开发成为可能。内在活动赋予活跃物质新的行为，使其区别于平衡态凝聚态系统。活跃的物质系统产生它们自己的内部应力，这使它们远离平衡，从而使它们摆脱传统的热力学约束，并且通过这样做可以控制和指导它们自己的行为及其周围环境。活性物质总是至少是一个双组分系统-活性体和活性体自推进离开的包埋介质。在这项研究中，流体介导的流体动力相互作用之间的自推进机构首次纳入。流体动力学显著地影响活性颗粒施加在边界或其他物体上的力，并且可以通过改变机械“游动压力”而深刻地影响活性系统中的相分离。“游泳压力为活性物质提供了一种压力-浓度关系，可以定量预测活性系统中的冷凝和相分离，并提供了一种确定可以从活性系统的随机运动中收获的工作量的途径。我们还表明，在一般情况下，游泳应力有非对角或偏的贡献，特别是当一个积极的系统是剪切运动。游泳应力预测，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。从机械游泳压力的角度，人们可以理解、分析和利用广泛的活性软物质系统，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。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。