Collective dynamics in suspensions of swimming particles

摘要-0522386威斯康星州麦迪逊大学项目描述：拟议的工作将使用直接模拟大量的流体动力学相互作用的游泳粒子在低雷诺数，以获得集体动力学的理解，已经实验观察到这些系统中出现。提出了一种适用于大规模模拟的游动粒子最小模型。 在该模型中，每个游泳者由施加流体阻力的珠棒哑铃组成，沿着具有对流体和哑铃施加相等且相反的力的幻影鞭毛。 这个模型的初步结果是有希望的，这些游泳者的悬浮液产生大规模的运动和制度的异常扩散与实验观察是一致的。拟议的工作将开始，通过表征集体动力学的这种简单的模型在散装解决方案，特别是解决所产生的流体运动的连贯性，以及这些运动如何改变运输的悬浮液。开放的问题包括长度和时间尺度上的议案保持连贯性，和依赖的大规模运动的形状和模式的细节推进的游泳者。此外，还将探讨对游泳者的溶液施加剪切力和限制在狭缝或薄膜中等影响。除了拟议的研究外，还将为中学和高中教师和学生编制教育材料。这些材料的主题将是游泳微生物的力学，并将有两个主要组成部分：一个简短的视频，说明低雷诺数推进的基础知识和一个工具包，其中将包含视频的许多元素，并将提供给科学和教师。该项目将被整合到UW MRSEC的教育工作中，UW MRSEC拥有优秀的资源，可以将这些材料分发给教师和学生。智力价值：最近的实验表明，在生物体之间相互作用的主要模式仅仅是每个微生物在游泳时驱动的流体运动的情况下，游泳微生物群体中存在各种迷人的集体运动。集体游泳导致时空相干流体运动的规模远远大于生物体本身，以及增强运输的微生物和被动示踪剂粒子移动的流动。事实上，游泳微生物最近已被探索作为一种手段，提高微流体装置中的运输。有没有以前的模拟这种现象在文献中：以前的工作低雷诺数游泳集中在一对游泳运动员之间的相互作用的运动的详细分析。这项工作的最终结果将是对游泳粒子群的低雷诺数动力学的基本理解。更广泛的影响：拟议的工作将通过提供对生物群体集体运动的洞察力，加强流体力学和生物学之间的智力联系。多体系统的集体动力学也是非平衡统计物理学的一个重要方面，所提出的工作提供了一个模型系统的集体运动的“代理人”，其中代理人之间的多体相互作用是已知的第一原则。这项工作还可能提供与医学和纳米技术的联系：例如，自主游泳的微型或纳米机器长期以来一直被设想为诊断甚至治疗疾病的潜在方法。拟议工作的教育影响也将有几个方面。研究生教育将部分提供给两名研究生，他们将学习和开发最先进的计算方法以及生物推进和一些结构生物学的基本机制。这些学生，沿着PI和一名本科生，还将开发令人兴奋的教育材料，分发给K-12学生和教师。

ABSTRACT - 0522386University of Wisconsin MadisonProject description: The proposed work will use direct simulations of large populations of hydrodynamically interacting swimming particles at low-Reynolds number to gain understanding of the collective dynamics that have been experimentally observed to arise in these systems. A minimal model of swimming particles, which can be efficiently used in large-scale simulations, is proposed. In this model each swimmer consists of a bead-rod dumbbell where the fluid drag is exerted, along with a phantom flagellum that exerts equal and opposite forces on the fluid and the dumbbell. Preliminary results with this model are promising; suspensions of these swimmers produce largescale motions and regimes of anomalous diffusion that are consistent with experimental observations. The proposed work will begin by characterizing the collective dynamics of this simple model in bulk solutions, specifically addressing the coherence of the fluid motions that are generated and how these motions alter transport in the suspension. Open questions include the length and time scales over which the motions remain coherent, and the dependence of the large scale motion on the details of the shape and mode of propulsion of the swimmers. Other phenomena that will be explored include effects such as imposed shear and confinement of the solution of swimmers to a slit or thin film.In addition to the proposed research, educational materials will be developed for secondary and high school teachers and students. The theme of these materials will be the mechanics of swimming microorganisms and will have two main components: a brief video that illustrates the basics of low Reynolds number propulsion and a kit that will contain many of the elements of the video and will be accessible to science and teachers. The project will be integrated into the educational efforts of the UW MRSEC, which has outstanding resources for distributing these materials to teachers and students.Intellectual merit: Recent experiments show a variety of fascinating collective motions in populations of swimming microorganisms, in situations where the primary mode of interaction between the organisms is simply the fluid motion driven by each of the microorganisms as it swims. The collective swimming leads to spatiotemporally coherent fluid motions on scales much larger than the organisms themselves, as well as to enhanced transport of the microorganisms and passive tracer particles moving with the flow. Indeed, swimming microorganisms have recently been explored as a means of enhancing transport in microfluidic devices. There are no previous simulations of this phenomenon in the literature: prior work on low Reynolds number swimming has focused on detailed analyses of the motion of individual swimmers of on the interaction between a pair of swimmers. The end result of the work will be a basic understanding of the low-Reynolds number dynamics of groups of swimming particles.Broader impacts: The proposed work will strengthen the intellectual connections between fluid mechanics and biology by providing insight into the collective motion of groups of organisms. Collective dynamics of many-body systems is also an important aspect of nonequilibrium statistical physics, and the proposed work provides a model system for collective motion of groups o f"agents" in which the many-body interactions between agents are known from first principles. The work also potentially provides links to medicine and nanotechnology: for example, autonomous swimming micro- or nanomachines have long been envisioned as potential ways to diagnose or even treat diseases. The educational impact of the proposed work will also have several facets. Graduate education will be provided in part for two graduate students, who will learn and develop state-of-the-art computational methods as well as the fundamental mechanisms of biopropulsion and some structural biology as well. These students, along with the PI and an undergraduate student, will also develop exciting educational materials that will be distributed to K-12 students and teachers.