Structure and dynamics of flexible and active packings

非技术摘要材料的性质通常取决于一组固定的成分是如何排列的，并通过分子间力相互作用。在这项研究中，我们研究了两种不符合这种范式的材料。第一种材料是纤维物质，由长而有弹性的细丝组成。堆积或编织在一起的限制可能会导致单独的细丝弯曲和扭曲，从而改变单独的细丝与其他细丝相互作用的方式。纤维材料是植物物质的主要成分，也是从纸到织物和绝缘材料等人类产品的主要成分，因此对这一无处不在的材料类别的基本了解是重要的。第二种类型的材料是由所谓的活性粒子组成的，当这些活性粒子被激发时，它们会倾向于沿着身体的某个方向移动。在某种程度上，这是为了阐明生物系统中的行为，如成群、成群和群体运动。另一方面，我们希望使用其中的一些行为来创建具有新功能的材质。这项拟议的工作让研究生和本科生接触到各种技术，并有机会在新兴的物理领域工作。PI是马萨诸塞州大学阿默斯特分校为软物质和统计物理专业的早期研究生举办的一年一度暑期学校的组织者。在该项目期间，PI还将为以小组为基础的形式教授的入门物理课程创建和分发教案。技术摘要由不经历热涨落的宏观实体组成的非平衡系统是我们技术、物理和生物世界的重要组成部分。这里提出的实验研究了两大类模型非热系统。(I)柔性细丝系统，其中除了刚性非热包装的丰富物理学之外，我们还获得了新的几何元素，例如细丝之间纠缠的可能性。一个特别的焦点将是摩擦和弹性在决定纤维垫的强度方面的作用。(2)主动粒子系统，由外部噪声驱动，在单个粒子的水平上提供推进。核心的科学问题将是确定粒子迁移率和相互作用对称性的不同作用，这在以前的研究中被选择为重合的。PI将研究散装，要么自发组装，要么模板化。这些将通过直接成像和3D成像、激光薄片或X射线成像来研究2D。这项拟议的工作让研究生和本科生接触到各种技术，并有机会在新兴的物理领域工作。国际和平研究所也是马萨诸塞州大学阿默斯特分校为软物质物理早期就业研究生举办的一年一度暑期学校的组织者。在该项目期间，PI还将为以小组为基础的形式教授的入门物理课程创建和分发教案。

Non-technical AbstractThe properties of a material typically depend on how a fixed set of constituents are arranged and interact via intermolecular forces. In this research we study two types of materials that do not fit this paradigm. This first type of material is fibrous matter, made up of long, flexible filaments. The constraints of packing or weaving together can cause individual filaments to bend and twist thus modifying the way in which an individual filament interacts with other filaments. Fibrous materials are the main constituent of plant matter, as well as human products ranging from paper to fabrics and insulants, so a basic understanding of this ubiquitous class of materials is important. The second type of material is composed of assemblies of so-called active particles, which when energized have a tendency to move in some direction along their body. At one level, this is intended to illuminate behaviors seen in living systems such as flocking, swarming and group locomotion. On the other hand, we hope to use some of these behaviors to create materials with new functionalities. The proposed work gives graduate and undergraduate students exposure to a variety of techniques and the opportunity to work in emerging areas of physics. The PI is an organizer of an annual summer school hosted at UMass Amherst for early-career graduate students in soft matter and statistical physics. During the project, the PI will also create and disseminate lesson plans for introductory physics courses taught in a team-based format. Technical AbstractNonequilibrium systems made up of macroscopic entities that do not undergo thermal fluctuations are an important part of our technological, physical and biological world. The experiments proposed here study two broad classes of model nonthermal systems. (i) Systems of flexible filaments, where in addition to the rich physics of rigid nonthermal packing, we gain new geometrical elements, such as the possibility of entanglements between filaments. A particular focus will be the roles of friction and elasticity in determining the strength of a mat of fibres. (ii) Systems of active particles, driven by external noise that provide propulsion at the level of individual particles. The central scientific question will be to identify the separate roles of the symmetry of the particle mobility and interaction, which in previous studies have been chosen to coincide. The PI will study bulk packings, assembled either spontaneously, or templated. These will be studied in 2D by imaging directly and in 3D, by laser-sheet or x-ray imaging. The proposed work gives graduate and undergraduate students exposure to a variety of techniques and the opportunity to work in newly-emerging areas of physics. The PI is also an organizer of an annual summer school hosted at UMass Amherst for early-career graduate students in soft matter physics. During the project, the PI will also create and disseminate lesson plans for introductory physics courses taught in a team-based format.