CAREER: Flow, Failure, and Migration in Glassy Materials

技术概述：该职业奖支持理论和计算研究和教育，以调查无序材料和生物组织如何流动和失效。理解这些流程具有直接的实际重要性。例如，大块金属玻璃作为结构材料显示出巨大的前景，但由于对局部剪切带的理解不足，它们无法被广泛采用。同样，细胞迁移速率有助于控制胚胎发生和癌症肿瘤发生，但尚不清楚这些速率如何受到单细胞力学特性的影响。尽管非生物的无序和玻璃状固体在边界处受力时会流动，而生物组织在单个细胞对其相邻细胞施力时会流动，但这些“材料”流动和变形的方式具有令人惊讶的普遍性。PI将使用统计学和软物质物理学的工具来开发这种普遍性，并对流动、失效和细胞迁移做出可验证的预测。为了实现这一目标，PI将专注于三种方法：(1)利用一种新的通用类随机矩阵系综来对控制堵塞固体塑性的振动模式和局部缺陷进行第一性原理预测。(2)在无序固体中识别流动缺陷或软点，并验证三种众所周知的塑性流动连续介质模型所做的假设。这将决定哪个模型（如果有的话）正确地描述了缺陷。这将允许测试剪切逆转下缺陷的行为，它们的统计数据作为结构紊乱程度的函数，以及它们在导致灾难性破坏的剪切带内的演变。然后，连续体模型将仅使用模拟的微观信息进行参数化。(3)发展一种新的理论，预测融合组织中的细胞迁移速率，解决包装拓扑结构、两种组织类型之间的边界和异常细胞力学如何影响迁移速率；预测将直接在实验中得到验证。这项研究将与几项教育计划相结合，重点关注高中最后几年和大学第一年的学生。具体来说，PI将与一个高中项目合作，在高中开发和部署模块，以(a)“调整”边缘学生的数学技能，(b)将入门物理概念与材料科学前沿的研究联系起来。在大学入门阶段，PI将(c)与经济学教育教授合作，为学生实施每周一次的自我评估，以帮助他们将课堂期望和社会规范内化；(d)与物理教育和科学教学教授合作，在新开发的“教学研究员”计划中改进对研究生助理的培训。PI还将(e)利用在线和课堂技术开发社交网络和讨论平台，帮助学生建立社区意识。非技术总结：该职业奖支持理论研究和教育，旨在了解无序固体如何变形和失效。对这些材料进行预测是具有挑战性的，因为当施加很小的力时，它们会像固体一样反应，而组成它们的原子、粒子或细胞却像液体一样排列。当施加更大的力时，这些材料表现出有趣的流动模式，这在自然界和工业中都很重要。例如，大块金属玻璃作为结构材料显示出巨大的前景，但由于对局部剪切带的理解不足，它们无法被广泛采用。最近，研究人员还发现，生物组织的行为就像一个无序的固体，因此胚胎发育和癌症转移中的细胞迁移也可以被认为是这些“材料”中的流动。提出的工作的目标是发展预测，可验证的理论在无序固体流动。为了实现这一目标，PI建议分析控制流的缺陷的动力学，并描述它们的特性。尽管识别这些固体中的“缺陷”并非易事，因为这些系统是无序的，但PI已经基于统计和软物质物理学的思想开发了几种工具来做到这一点。有了这些新技术，PI的目标是回答以下问题：缺陷是如何自组织导致灾难性失败的？在给定的材料中应该有多少缺陷？一个机械异常的细胞，如癌细胞，是否可能作为生物组织中的缺陷，从而更快地迁移？该提案的第二部分旨在提高科学、技术、工程和数学（STEM）学科的留校率。它关注的是高中最后几年和大学第一年的学生，因为许多学生在这段时间离开了科学领域。PI将与纽约州锡拉丘兹的一个高中项目合作，部署免费在线提供的教学模块，将入门物理概念与材料科学前沿的研究联系起来，突出它们在现实世界中的相关性。额外的模块将“调整”边缘学生的数学技能，让他们有机会在物理课上取得成功。PI还将在大学入门课程中实施几项举措，包括每周自我评估、研究生助教培训和奖学金，以及帮助学生建立社区意识的在线和社交网络技术。

Technical Summary:This CAREER award supports theoretical and computational research and education to investigate how disordered materials and biological tissues flow and fail. Understanding these flows is of immediate practical importance. For example, bulk metallic glasses show great promise as structural materials but have not been widely adopted because they fail via poorly understood localized shear bands. Similarly, rates of cell migration help govern embryogenesis and cancer tumorigenesis, yet it is unclear how these rates are influenced by single cell mechanical properties. Although non-biological disordered and glassy solids flow when forces are applied at a boundary, and biological tissues flow when individual cells apply forces to their neighbors, there is a surprising universality in the way that these "materials" flow and deform. The PI will use tools from statistical and soft matter physics to exploit this universality and make verifiable predictions about flow, failure, and cell migration. To achieve this goal, the PI will focus on three approaches: (1) Exploit a new universality class of random matrix ensembles to make first-principles predictions about the vibrational modes and localized defects that govern plasticity in jammed solids. (2) Identify flow defects, or soft spots, in disordered solids and test the assumptions made by three well-known continuum models for plastic flow. This will determine which model, if any, correctly describes the defects. This will allow testing the behavior of defects under shear reversal, their statistics as a function of the degree of structural disorder, and their evolution inside the shear bands leading to catastrophic failure. The continuum model will then be parameterized using only microscopic information from simulations. (3) Develop a new theory that makes predictions for the rates of cell migration in confluent tissues, addressing how packing topology, boundaries between two tissue types, and abnormal cell mechanics affect migration rates; predictions will be directly tested in experiments.This research will be integrated with several education initiatives that focus on students in the last years of high school and the first years of college. Specifically, the PI will partner with a high school program to develop and deploy modules in high schools that (a) "tune-up" the math skills of marginal students, and (b) connect introductory physics concepts to research at the frontier of materials science. At the introductory college level, the PI will (c) work with an economics education professor to implement a weekly self-assessment for students to help them internalize class expectations and social norms, and (d) collaborate with physics education and science teaching professors to improve training for graduate assistants in a newly developed "Teaching Fellows" program. The PI will also (e) use online and classroom technologies to develop social networking and discussion platforms that help students build a sense of community.Nontechnical Summary: This CAREER award supports theoretical research and education with the aim of understanding how disordered solids deform and fail. Making predictions about these materials is challenging because they respond like a solid when a small force is applied, and yet the atoms, particles, or cells that comprise them are arranged like those in a liquid. When larger forces are applied, these materials exhibit interesting flow patterns that are important in both nature and industry. For example, bulk metallic glasses show great promise as structural materials but have not been widely adopted because they fail via poorly understood localized shear bands. Recently, researchers have also discovered that biological tissues behave like a disordered solid, and therefore cell migration in embryonic development and cancer metastasis can also be thought of as flow within these "materials". The goal of the proposed work is to develop predictive, verifiable theories for flow in disordered solids. To achieve this goal, the PI proposes to analyze the dynamics of the defects that govern flow, and characterize their properties. Although identifying a "defect" in these solids is non-trivial because the systems are disordered, the PI has developed several tools based on ideas from statistical and soft matter physics to do so. Armed with these new techniques, the PI aims to answer questions such as: how do defects self-organize to cause catastrophic failure? How many defects should one expect in a given material? Is it possible for a mechanically abnormal cell, such as a cancer cell, to act as a defect inside a biological tissue and thereby migrate more quickly?A second part of the proposal aims to increase retention in Science, Technology, Engineering and Math (STEM) disciplines. It focuses on students in the last years of high school and the first years of college, because many students leave the science fields during this time period. The PI will partner with a high school program in Syracuse, NY to deploy teaching modules, made freely available online, that connect introductory physics concepts to research at the frontier of materials science, highlighting their relevance in the real world. Additional modules will "tune-up" the math skills of marginal students, giving them a chance to succeed in physics classes. The PI will also implement several initiatives in an introductory college course, including a weekly self-assessment, training and fellowships for graduate teaching assistants, and online and social networking technologies to help students build a sense of community.