NSF-BSF: Fluctuation phenomena out of equilibrium

NSF-BSF：不平衡的波动现象

• 批准号: 2218849
• 负责人: Mehran Kardar
• 金额: $ 44.1万
• 依托单位: Massachusetts Institute of Technology
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-03-01 至 2026-02-28
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2218849&HistoricalAwards=false
• 关键词: NSF; BSF; Fluctuation; phenomena; out

NONTECHNICAL SUMMARYThis award supports basic research and education aimed at characterizing emergence of collective behaviors in large assemblies of interacting entities. While actions of individual components of a system may be difficult to chart (due to chaotic classical motion or inherent quantum uncertainty), the collective behavior of a large number can be easier to predict, for example the dispersion of sound waves despite random movements of gas molecules. This is made possible by the tools of statistical physics that enable systematic averaging over stochastic motions of molecules, to describe effective field theories for evolution of relevant densities. The extensive utility of this approach, averaging from uncertain motions of particles to near deterministic collective behavior, in describing physical systems in equilibrium, suggests its applicability to broader class of entities. Some examples of collective behaviors of complex entities, especially in systems out of equilibrium, are explored in this research. (i) The emerging field of active matter is concerned with collective motions of entities, such as bacteria, artificial self-powered nanobots, of even flocks of birds or school of fish, that individually consume and dissipate energy. Despite stochasticity at the individual level, interactions lead to fascinating coordinated motions of the collective. We have found that such long-range coordination can be disrupted by obstacles within the medium, or even disorder at its edges. The research team will explore the roles of disorder and boundaries on phases of active matter. Phenomena to be studied include the long-reach of disruptions caused by impurities, and the wanderings of passive bystanders caught in the flow of active matter.(ii) At a basic level, a key difference between elements of active matter and atoms in “equilibrium matter,” is that consumption of energy sets up a natural arrow of time. In contrast, one cannot distinguish between movies of equilibrium gas particles running forward or backward. Interestingly, insights gained from behavior of “active matter” can be explored in other domains of physics, such as in the context of photons and radiation, for example, heat transfer. The team is investigating the feasibility of heat engines based on radiation, with similarity to non-equilibrium forces exerted in active matter through the ratchet effect arising from asymmetric boundaries.(iii) Living systems, the epitome of non-equilibrium, consume energy not only to move, but to grow and reproduce, presenting other phenomena to explore. For example, as a bacterial film, or a tumor expands into new space, its composition is dominated by successful ancestors at the expansion front. This sets up a connection between the shape of the front, and the competing bacterial variants. The research team will classify possible shapes of films that may appear during growth and expansion of competing variants. This research activity is closely incorporated in seminars and courses of the PI which through his published textbooks and web-pages reach a broad scientific community. This research crosses disciplinary boundaries and has potential impact in diverse areas from applied mathematics to immunology.TECHNICAL SUMMARYFluctuations, whether of quantum, thermal, or non-equilibrium origin, are cause or signature of various physical phenomena. Generalizing concepts and mathematical tools characterizing equilibrium fluctuations to the realm of non-equilibrium phenomena has been a long-running endeavor. This research aims at quantifying out of equilibrium fluctuations in diverse contexts. Specific goals include:(i) The emerging field of active matter is concerned with collective behaviors of entities that consume energy to move. The current of energy through the system yields novel collective phases and fluctuations, not always describable with field theories of equilibrium matter. The research projects will explore the roles of disorder and boundaries (static or mobile) on active matter. Phenomena to be explored include long-ranged correlations and force, and anomalous dynamics of inclusions.(ii) Quantum electrodynamic phenomena in setups without time reversal symmetry share common features with active matter. In particular, we shall explore the feasibility of a radiative heat engine that utilizes a ratchet effect to generate force, and forces that violate Newton’s third law in setups that break electromagnetic reciprocity.(iii) Growing populations provide yet another venue for exploration of emergent phenomena. One set of research projects pertain to classifying morphologies of films arising during growth and expansion of competing species. Another set deals with dynamics of populations with time-varying reproduction rate due to mutations or external conditions.The projects in this research will be studied through a combination of numerical and analytical methods. The typical starting point would be a simplified model of elements following simplified but refine-able rules. On the analytic front, the goal would be to coarse-grain the model to the level of a continuum description, and to then apply methods of field theory to characterize phases and fluctuations. The numerical task would be to implement the simplified rules and characterize the emergent behaviors, in contrast or support to the theory.Characterizing probability distributions underlying fluctuations in nonequilibrium settings has been a long-standing quest in statistical physics, with notable recent progress on several fronts. Yet, puzzles of force in active matter, and fixation in growing bacterial fronts are but two examples amongst several projects pointing to complexity of the underlying phenomena, which this research aims to unravel.Education and development of human resources are an essential broader impact: The research activity is closely incorporated in seminars and courses of the PI which through textbooks and web-pages reach a broad scientific community. Past students and postdocs of the group are productive members of academic and research communities. This research crosses disciplinary boundaries and has potential impact in diverse areas from applied mathematics to immunology.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

非技术摘要该奖项支持基础研究和教育，旨在表征大型相互作用实体中集体行为的出现。虽然系统中各个组件的行为可能很难绘制图表（由于混沌经典运动或固有的量子不确定性），但大量的集体行为可以更容易预测，例如尽管气体分子随机运动，但声波的色散。这是通过统计物理学工具实现的，这些工具能够对分子的随机运动进行系统平均，以描述相关密度演化的有效场论。这种方法的广泛实用性，从粒子的不确定运动到近乎确定性的集体行为的平均，在描述平衡的物理系统时，表明它适用于更广泛的实体类别。本研究探讨了复杂实体集体行为的一些例子，特别是在不平衡的系统中。 （i）新兴的活性物质领域涉及实体的集体运动，例如细菌、人造自供电纳米机器人，甚至是鸟群或鱼群，它们各自消耗和耗散能量。尽管个体层面存在随机性，但相互作用会导致集体的令人着迷的协调运动。我们发现，这种远程协调可能会被介质内的障碍物甚至边缘的无序所破坏。研究小组将探索无序和边界对活性物质相的作用。要研究的现象包括由杂质引起的远距离破坏，以及陷入活跃物质流动中的被动旁观者的徘徊。（ii）在基本层面上，活跃物质元素与“平衡物质”中的原子之间的一个关键区别在于，能量的消耗建立了一个自然的时间箭头。相比之下，人们无法区分向前或向后运行的平衡气体粒子的电影。有趣的是，从“活性物质”的行为中获得的见解可以在物理学的其他领域进行探索，例如在光子和辐射的背景下，例如传热。该团队正在研究基于辐射的热机的可行性，这与通过不对称边界产生的棘轮效应在活性物质中施加的非平衡力相似。（iii）生命系统是非平衡的缩影，它不仅消耗能量来移动，还消耗能量来生长和繁殖，提出了其他值得探索的现象。例如，当细菌膜或肿瘤扩展到新空间时，其组成由扩展前沿的成功祖先主导。这在前端的形状和竞争的细菌变体之间建立了联系。研究小组将对竞争变体生长和扩张过程中可能出现的薄膜形状进行分类。这项研究活动与 PI 的研讨会和课程紧密结合，通过他出版的教科书和网页传播到广泛的科学界。这项研究跨越了学科界限，对从应用数学到免疫学的各个领域都具有潜在影响。技术摘要波动，无论是量子、热还是非平衡起源，都是各种物理现象的原因或特征。将平衡波动的概念和数学工具推广到非平衡现象领域一直是一项长期的努力。这项研究旨在量化不同背景下的均衡波动。具体目标包括：（i）新兴的活性物质领域涉及消耗能量移动的实体的集体行为。通过系统的能量流产生新的集体相和波动，并不总是可以用平衡物质场论来描述。这些研究项目将探索无序和边界（静态或移动）对活性物质的作用。待探索的现象包括长程相关性和力，以及包裹体的异常动力学。(ii)没有时间反转对称性的设置中的量子电动力学现象与活性物质具有共同的特征。特别是，我们将探索利用棘轮效应产生力的辐射热机的可行性，以及在打破电磁互易性的设置中违反牛顿第三定律的力。（iii）不断增长的人口为探索新兴现象提供了另一个场所。一组研究项目涉及对竞争物种生长和扩张过程中产生的薄膜形态进行分类。另一组涉及由于突变或外部条件而导致繁殖率随时间变化的种群动态。本研究中的项目将通过数值和分析方法相结合进行研究。典型的起点是遵循简化但可细化规则的元素的简化模型。在分析方面，目标是将模型粗粒度到连续描述的水平，然后应用场论方法来表征相位和波动。数值任务是实施简化的规则并表征涌现的行为，与理论形成对比或支持。表征非平衡环境中波动的概率分布一直是统计物理学领域的长期探索，最近在几个方面取得了显着进展。然而，活性物质中的力之谜和生长中的细菌前沿的固定只是指向潜在现象复杂性的几个项目中的两个例子，本研究旨在解开这些现象。人力资源的教育和发展具有重要的更广泛的影响：研究活动与PI的研讨会和课程紧密结合，通过教科书和网页到达广泛的科学界。该小组过去的学生和博士后都是学术和研究界富有成效的成员。这项研究跨越了学科界限，在从应用数学到免疫学的各个领域都具有潜在影响。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Specialization at an expanding front

不断扩大的专业化

• DOI: 10.1103/physreve.108.l032402
• 发表时间: 2023
• 期刊: Physical Review E
• 影响因子: 2.4
• 作者: Li, Lauren H.;Kardar, Mehran
• 通讯作者: Kardar, Mehran

Interplay between morphology and competition in two-dimensional colony expansion

二维菌落扩张中形态与竞争之间的相互作用

• DOI: 10.1103/physreve.108.l032301
• 发表时间: 2023
• 期刊: Physical Review E
• 影响因子: 2.4
• 作者: Swartz, Daniel W.;Lee, Hyunseok;Kardar, Mehran;Korolev, Kirill S.
• 通讯作者: Korolev, Kirill S.