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.

非技术摘要该奖项支持专注于宏观世界出现的理论研究和教育活动。 自然界的多样性源于大量相互作用物体的集体行为。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构型空间来提供组织机制。对于从沙粒到小行星等宏观物体的集合，这种成熟的温度辅助紧急行为范式被打破。沙丘是由剪切力形成的，小行星带在重力作用下自组装。然而，即使在这个粒状世界中，也存在类似气体、液体和固体的结构。但如果没有热运动的规律性影响，变化可能是突然的，而且往往是灾难性的。雪崩和地震就是此类灾难性故障的例子。该研究项目的总体目标是建立摩擦和耗散很重要、不存在热运动且动力学由大的、罕见的波动主导的系统中出现的统一原理。为了实现这一目标，巨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，但其结构和集体特性是由内部和外部应力而不是温度决定的。其中包括生物聚合物和电机组件以及碳纳米管悬浮液等活性材料。就更广泛的影响而言，沙子是儿童典型的游乐场，也是唤醒他们的科学好奇心的理想平台。 该项目的教育部分建立在为小学生创造实践活动的理念之上。激发这个年龄段的儿童对物理和材料科学的兴趣有可能在整个初中和高中阶段维持对这些科目的兴奋，而在这个时期，许多少数族裔和女性对科学失去了兴趣。这些活动将在马萨诸塞州的阿克顿探索博物馆展出，该博物馆正在参与一个名为“公众门户”的计划。与博物馆相关的活动将在布兰迪斯大学研究生和博士后的帮助下设计。这种对早期职业科学家进行非正式科学教育的培训将增强整个科学界的更广泛影响。技术摘要该奖项支持理论研究和教育活动，重点关注非热系统的集体属性和紧急行为。 PI 的小组将研究体现非热物质的材料，除非外部驱动，否则这些材料将保持单一配置。 此类系统的示例包括粒状材料和致密的非布朗悬浮液。在原子和分子水平上，热运动使系统能够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等宏观物体的集合，这种由温度辅助的紧急行为的完善范例就失效了。 在这个宏观物体的世界中，机械力非常重要，而环境温度对于探索相空间完全无效。 如果没有热波动的规律性影响，故障通常是灾难性的，并且波动和响应之间没有既定的关系。 通过明智地结合建模和数据分析，PI 团队将解决一些基本问题，例如 (i) 在与热波动无关的宏观世界中，可以使用哪些特征来区分流体和固体，(ii) 是否存在过渡的普遍特征在这些阶段之间，（iii）大规模波动的性质，例如故障和固体流动。 这些探索旨在建立一个类似于平衡统计力学的理论框架，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的材料，但其中存在内部和外部应力，而不是温度、形状结构和集体属性。这些可能包括活性材料，例如微管和马达的组件、正在进行形态发生或伤口愈合的组织。