Emergent Phenomena in the Macroworld: Jamming and Flow of Particulate Systems

宏观世界中的新兴现象：颗粒系统的干扰和流动

• 批准号: 1409093
• 负责人: Bulbul Chakraborty
• 金额: $ 32.89万
• 依托单位: Brandeis University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-09-01 至 2018-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1409093&HistoricalAwards=false
• 关键词: Emergent; Phenomena; Macroworld; Jamming; Flow

NONTECHNICAL SUMMARYThis award supports theoretical research and educational activities focused on emergence in the macroworld. Diversity in the natural world emerges from the collective behaviors of large numbers of interacting objects. The origin of collectively organized structures at atomic and molecular scales is the competition between energy and entropy, with thermal motion providing the mechanism for organization by allowing particles to explore the space of configurations. This well-established paradigm of temperature-assisted emergent behavior breaks down for collections of macroscopic objects ranging from grains of sand to asteroids. Sand dunes are created by shearing forces, and asteroid belts self-assemble under gravity. Even in this granular world, however, there are structures that resemble gases, liquids and solids. But without the regularizing influence of thermal motion, the changes can be abrupt and often catastrophic. Avalanches and earthquakes are examples of such catastrophic failures. The overarching goal of this research project is to establish the unifying principles of emergence in systems where friction and dissipation are important, thermal motion is absent and the dynamics is dominated by large, rare fluctuations. To achieve this, the grand challenge is to construct a predictive theoretical framework analogous to thermodynamics and statistical mechanics. This research will impact the understanding of a broad range of materials, which do not necessarily belong to the macro world, but whose structures and collective properties are shaped by internal and external stresses, and not by temperature. These include active materials such as assemblies of biopolymers and motors, and carbon nanotube suspensions.In terms of broader impacts, sand is the quintessential playground of children and an ideal platform to awaken their scientific curiosity. The education part of this project builds on the idea to create hands-on-activities for Elementary School children. Sparking interest in Physics and Materials Science in children at this age has the potential to sustain excitement in these subjects through the Middle and High School years, a time when many minorities and women lose interest in science. The activities will be showcased at the Acton Discovery Museum in Massachusetts, which is participating in a program called "Portal to the Public". The museum-related activities will be designed at Brandeis with the help of graduate students and postdoctoral associates. This training of early-career scientist in conducting informal science education will enhance the broader impact of the scientific community as a whole.TECHNICAL SUMMARYThis award supports theoretical research and educational activities with focus on the collective properties and emergent behavior of athermal systems. The PI's group will study materials that epitomize non-thermal matter, which stay in a single configuration unless driven externally. Examples of such systems include granular materials, and dense, non-Brownian suspensions. At the atomic and molecular levels, thermal motion allows the system to organize into structures that are determined by a competition between energy and entropy. This well-established paradigm of temperature-assisted emergent behavior breaks down, however, for collections of macroscopic objects ranging from grains of sand to asteroids. In this world of macroscopic objects, mechanical forces are all important and the ambient temperature is completely ineffective at exploring phase space. Without the regularizing influence of thermal fluctuations, failures are often catastrophic, and there are no established relations between fluctuations and response. Using a judicious combination of modeling and data analysis, the PI's group will address fundamental questions such as (i) what characteristics can be used to distinguish fluids from solids in the macroworld where thermal fluctuations are irrelevant, (ii) are there universal features of transitions between these phases, (iii) the nature of large scale fluctuations such as failures and flow of solids. These explorations are intended to establish a theoretical framework, analogous to that of equilibrium statistical mechanics, which can predict the collective behavior of athermal systems.This research would impact our understanding of a broad range of materials including those that do not belong to the macro world, but where internal and external stresses, not temperature, shape structures and collective properties. These could include active materials such as assemblies of microtubules and motors, tissues undergoing morphogenesis or wound healing.

非技术性总结该奖项支持理论研究和教育活动，重点是在宏观世界的出现。 自然界的多样性来自于大量相互作用的物体的集体行为。在原子和分子尺度上集体组织结构的起源是能量和熵之间的竞争，热运动通过允许粒子探索配置空间提供了组织机制。这种温度辅助的涌现行为的成熟范例在从沙粒到小行星的宏观物体的集合中被打破。沙丘是由剪切力产生的，小行星带在重力作用下自我组装。然而，即使在这个颗粒状的世界里，也有类似于气体、液体和固体的结构。但是，如果没有热运动的规则化影响，变化可能是突然的，往往是灾难性的。雪崩和地震就是这种灾难性故障的例子。该研究项目的总体目标是建立系统中出现的统一原则，其中摩擦和耗散很重要，没有热运动，动力学主要是由大的，罕见的波动。为了实现这一目标，最大的挑战是构建一个类似于热力学和统计力学的预测理论框架。这项研究将影响对广泛材料的理解，这些材料不一定属于宏观世界，但其结构和集体性质是由内部和外部应力而不是温度形成的。其中包括活性材料，如生物聚合物和发动机的组装，以及碳纳米管悬浮液。就更广泛的影响而言，沙子是儿童的典型游乐场，也是唤醒他们科学好奇心的理想平台。 这个项目的教育部分建立在为小学生创造动手活动的想法之上。在这个年龄段的孩子对物理学和材料科学的兴趣有可能在初中和高中期间保持对这些学科的兴奋，这是许多少数民族和妇女对科学失去兴趣的时候。这些活动将在马萨诸塞州的阿克顿发现博物馆展出，该博物馆正在参与一个名为“公众门户”的项目。博物馆相关活动将在研究生和博士后的帮助下在布兰代斯设计。这种培训的早期职业科学家进行非正式的科学教育将提高科学界作为一个整体的更广泛的影响。技术总结这个奖项支持理论研究和教育活动，重点是集体属性和紧急行为的无热系统。 PI的团队将研究非热物质的缩影材料，这些材料除非受到外部驱动，否则会保持单一配置。 这种系统的实例包括颗粒材料和致密的非布朗悬浮液。在原子和分子水平上，热运动允许系统组织成由能量和熵之间的竞争决定的结构。然而，对于从沙粒到小行星的宏观物体的集合来说，这种温度辅助的涌现行为的良好范例是不成立的。 在这个宏观物体的世界里，机械力都很重要，环境温度在探索相空间时完全无效。 如果没有热涨落的正则化影响，故障往往是灾难性的，并且在涨落和响应之间没有建立的关系。 使用建模和数据分析的明智组合，PI小组将解决基本问题，例如（i）在热波动不相关的宏观世界中，哪些特征可用于区分流体和固体，（ii）这些阶段之间的转变是否存在普遍特征，（iii）大规模波动的本质，例如固体的故障和流动。 这些探索旨在建立一个理论框架，类似于平衡统计力学，它可以预测非热系统的集体行为。这项研究将影响我们对广泛材料的理解，包括那些不属于宏观世界，但内部和外部应力，而不是温度，形状结构和集体属性。这些可能包括活性材料，如微管和马达的组件，经历形态发生或伤口愈合的组织。