CAREER: Flow, Failure, and Migration in Glassy Materials

技术总结：这个职业奖项支持理论和计算研究以及教育，以调查无序的材料和生物组织如何流动和失败。理解这些流动具有直接的实际意义。例如，块体金属玻璃显示出作为结构材料的巨大前景，但由于它们通过鲜为人知的局部剪切带而失效，因此尚未被广泛采用。同样，细胞迁移率有助于控制胚胎发生和癌症发生，但这些速率如何受到单细胞机械特性的影响尚不清楚。尽管非生物无序和玻璃状固体在边界上施加力时会流动，生物组织在单个细胞向相邻细胞施加力时会流动，但这些“材料”流动和变形的方式有一个令人惊讶的普遍性。PI将使用统计和软物质物理的工具来利用这种普遍性，并对流动、故障和细胞迁移做出可验证的预测。为了实现这一目标，PI将专注于三个方法：(1)开发一种新的普适性类的随机矩阵系综来对支配受塞固体塑性的振动模式和局域缺陷进行第一性原理预测。(2)识别无序固体中的流动缺陷或软点，并检验三个著名的塑性流动连续介质模型所作的假设。这将确定正确描述缺陷的模型(如果有的话)。这将允许测试剪切反转下缺陷的行为，它们的统计数据作为结构无序程度的函数，以及它们在导致灾难性破坏的剪切带内的演变。然后，将仅使用来自模拟的微观信息来对连续介质模型进行参数化。(3)开发一种新的理论来预测融合组织中的细胞迁移率，解决堆积拓扑、两种组织类型之间的边界和异常细胞力学如何影响迁移率的问题；预测将直接在实验中得到验证。这项研究将与几项以高中最后几年和大学一年级学生为重点的教育计划相结合。具体地说，PI将与一个高中项目合作，在高中开发和部署模块，这些模块(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，(C)与经济学教育教授合作，对学生进行每周自我评估，以帮助他们将班级期望和社会规范内在化；(D)与物理教育和科学教学教授合作，在新制定的“助教”计划中改进对研究生助理的培训。PI还将使用在线和课堂技术来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：这个职业奖支持理论研究和教育，目的是了解无序固体是如何变形和失败的。对这些材料进行预测是具有挑战性的，因为当施加小的力时，它们的反应就像固体一样，但组成它们的原子、粒子或细胞的排列方式却像液体中的原子、粒子或细胞一样。当施加更大的力时，这些材料会显示出有趣的流动模式，这在自然界和工业中都很重要。例如，块体金属玻璃显示出作为结构材料的巨大前景，但由于它们通过鲜为人知的局部剪切带而失效，因此尚未被广泛采用。最近，研究人员还发现，生物组织的行为就像无序的固体，因此胚胎发育和癌症转移过程中的细胞迁移也可以被认为是在这些“材料”中流动。这项拟议工作的目标是为无序固体中的流动开发可预测的、可验证的理论。为了实现这一目标，PI建议分析支配流程的缺陷的动态，并表征它们的属性。尽管识别这些固体中的“缺陷”不是一件容易的事情，因为这些系统是无序的，但PI基于统计和软物质物理的想法开发了几个工具来做到这一点。有了这些新技术，PI旨在回答以下问题：缺陷是如何自组织导致灾难性故障的？一种给定的材料应该有多少缺陷？像癌细胞这样的机械异常细胞有没有可能充当生物组织内的缺陷，从而更快地迁移？提案的第二部分旨在提高科学、技术、工程和数学(STEM)学科的留存率。它关注的是高中最后几年和大学一年级的学生，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，部署在线免费提供的教学模块，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.