Collaborative Research: The Analysis and Simulation of Biologically Active Suspensions

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。生物活性悬浮液，其中游泳细菌浴是一个典型的例子，是其微观结构是活的和能动的流体系统。当系统的“活性粒子”推动自己穿过周围的流体时，它们会产生扰动流，将它们的运动传递给其他游泳者，从而改变他们的游泳方向和速度。这种相互作用可以导致相关的、大规模的和复杂的流体流动，其在长度和时间尺度上的移动远远大于任何单个游泳者的移动。这些游泳者驱动的流动对微生物菌落的进化和生存具有重要意义，因为它们通过颗粒运输和流体混合来影响营养物的输送，并且还可能在其他重要现象中发挥作用，例如群体感应和生物膜形成。它们也是非平衡模式形成系统的基本例子。在这个项目中，我们建议使用分析模型和数值模拟相结合，进一步加深我们对生物活性悬浮液的理解。研究将集中在这些系统中出现的相干结构的建模和分析，以及它们与流体混合的关系。具体地说，边界和边界条件，禁闭和系统规模的影响将被检查。新的多尺度的方法，使成千上万的相互作用的游泳者被模拟也将被开发，从而接近生物reality.As这项研究的结果，一个改进的理论理解的主动悬浮液将实现，并将揭示核心的生物物理机制的营养物质的运输和混合的运动微生物菌落。它也可能揭示运动策略的进化，特别是对于合作生活和繁荣的微生物，如生物膜。这项研究的更广泛影响在于主动悬浮液对几个关键科学领域的重要性，包括生物学，人类健康和医学，软凝聚态物理学和工程学。了解主动悬浮液以及是什么驱动（或停止）它们的大规模混合可能会导致控制感染的新方法。它为物理学提供了生物学中出现的非平衡模式形成的一个很好的例子，在工程中，这种理解可能会导致利用生物材料进行混合和泵送等任务的新设备。该项目的影响还在于应用和计算数学的新的和重要的调查领域的发展，并在其添加到理论和计算工具包，应用数学家和理论工程师可以带来生物和复杂的流体动力学问题。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Biologically active suspensions, of which a bath of swimming bacteria is a paradigmatic example, are fluid systems whose microstructure is alive and motile. As the system's "active particles" propel themselves through the surrounding fluid, they produce disturbance flows that communicate their motions to other swimmers, thereby altering their swimming direction and speed. This reciprocal interaction can result in correlated, large-scale, and complex fluid flows that move on length- and time-scales much larger than those of any single swimmer. These swimmer-driven flows have important implications for the evolution and survival of micro-organismal colonies, as they impact nutrient delivery through both particle transport and fluid mixing, and may also play a role in other important phenomena such as quorum sensing and biofilm formation. They are also fundamental examples of non-equilibrium pattern-forming systems. In this project, we propose to further deepen our understanding of biologically active suspensions using a combination of analytical models and numerical simulations. The research will focus on the modeling and analysis of the coherent structures that arise in these systems and on their relation to fluid mixing. Specifically the effect of boundaries and boundary conditions, confinement, and system scale will be examined. New multiscale approaches allowing hundreds of thousands of interacting swimmers to be simulated will also be developed, thus approaching biological realism.As a result of this study, an improved theoretical understanding of active suspensions will be achieved and will reveal the core biophysical mechanisms underlying nutrient transport and mixing in colonies of motile microorganisms. It may also shed light on the evolution of locomotory strategies, particularly for microorganisms that live and thrive cooperatively, as in biofilms. The broader impacts of this research lie in the importance of active suspensions to several key areas of science, including biology, human health and medicine, soft-condensed matter physics, and engineering. An understanding of active suspensions and what drives (or stops) their large-scale mixing could lead to new ways of controlling infection. It provides to physics a well-characterized example of nonequilibrium pattern formation arising in biology, and in engineering this understanding could lead to new devices that exploit biological materials for tasks such as mixing and pumping. This project's impact also lies in the development of new and important areas of inquiry for applied and computational mathematics, and in its adding to the theoretical and computational tool-kit that applied mathematicians and theoretical engineers can bring to problems in biological and complex fluid dynamics.