CAREER: Anomalous Thermal Relaxations of Physical Systems

非技术描述自然界中的大多数过程都是不平衡的。这样的例子在我们身边随处可见——飞机机翼侧面形成的涡流，水龙头流出的水，一杯茶冷却到室温。系统与环境的耦合，茶叶与周围空气的耦合，导致两者之间的能量交换，并松弛到一个新的联合状态。如果孤立，这个关节系统就会达到我们所说的热平衡。这意味着能量交换不再是平均方向的，从一杯热茶到更冷的环境空气。相反，能量的流动开始波动，没有任何漂移或偏差，平均而言，在茶和空气之间均匀地来回流动。这种联合稳定状态的方法被称为热松弛或平衡——这是大多数耦合系统长期的共同命运。了解弛豫过程与冶金和材料科学特别相关，其中退火是产生具有理想硬度和应力性能的金属或玻璃的热处理。热松弛也用于优化问题，以找到最适合环境的配置，例如，最小化里程的最优交通计划路线，或具有最小能量的聚合物配置，因此在低温下普遍存在。我们的大多数直觉和理论理解都源于对处于或接近平衡状态的物理系统的观察。这也是动力学不再重要的地方，物理系统的性质可以通过一些可测量的量来捕获，例如温度、平均能量和磁化（在磁性系统中）。然而，通常在自然界和实验室中，物理系统甚至不接近平衡。那么松弛是如何发生的呢？显然，它充满了“惊喜”，而我们的直觉经常失败。其中一个非常不寻常的放松现象是姆潘巴效应。当“热的冷却速度比冷的更快”时就会发生这种情况，也就是说，在高温下制备的系统比在较低温度下启动的相同系统需要更少的冷却时间。姆潘巴是第一个在水中观察到这种现象的人；后来，其他人在水、塑料、磁铁和其他系统中看到了这种效果。PI的目标是将这些不同的观测结果放在一个共同的“保护伞”下——一个关注异常弛豫所必需的显著特征的一般理论框架。也就是说，这项活动的目的是研究异常热松弛，并建立一个描述不同物理系统的热平衡方法的理论框架。概述研究的应用包括适当的样品制备，具有特定性能的材料设计，最佳加热和冷却方案。PI的长期教育目标是向不同教育背景和年龄的受众有效地传播科学。该项目的教育目标是向初高中学生介绍一系列迷你互动科学讲座，让他们了解前沿研究，促进科学家和学生之间的联系。高中生在选择理科必修学分时往往会忽略物理。PI旨在弥补这一差距，通过她的“测试科学家”系列，使物理学和其他自然科学更容易接近。技术描述本活动的研究目的是研究物理系统的异常热松弛，从而加深对非平衡物理的基本理解。不寻常松弛现象的一个主要例子是热松弛中的“捷径”，称为姆潘巴效应。当在高温下制备的系统比在较低温度下启动的相同系统需要更少的冷却时间，而两者都耦合到更冷的环境时，就会发生这种情况。在水、笼形水合物、聚合物、碳纳米管谐振器、磁性合金、驱动颗粒气体和自旋玻璃的冷却中都观察到这种现象。这些在不同系统中观察到的效应表明，这些现象背后可能有一个普遍的理论。作为一种非平衡动力学现象，Mpemba效应不能通过观察线性响应机制来捕捉。因此，PI引入了一个基于随机热力学的框架来研究异常弛豫效应。概述的理论框架将作为一些宏观系统的分析和数值研究的起点，通常也很难处理，介观系统。作为模型系统，动力学约束晶格气体，随机能量模型，以及一些自旋和磁系统将被探索。观察到Mpemba效应的体系具有相变。因此，PI将探索相变与姆潘巴效应之间的联系，以及衰老、记忆、再生和效应之间的关系。一个微扰方法将用于研究马尔可夫链蒙特卡罗算法的反常松弛。从活动中产生的结果的应用将导致控制理论，优化和数值算法的进步。特别是PI设想了更有效的模拟退火和马尔可夫链蒙特卡罗算法，这将对有效的采样和蛋白质折叠非常有用。另一个应用是优化冷却和加热协议，通过这些，研究产品将影响具有特定热性能的材料的设计。姆潘巴效应在教育界受到的关注要多于在研究领域。对反常松弛过程所知不多。大多数的直觉和理论框架来自于热平衡的静态性质。然而，大多数生物和物理系统都是不平衡的，在这种情况下，动力学是必不可少的。未来的研究成果将对物理领域产生广泛的影响。概述的理论工作也将影响实验，因为强姆潘巴效应应该很容易观察到。随着这项工作的加深，教育计划将使尖端的研究课题更接近高中生和中学生。PI将组织一系列小型的科学讲座和学生主导的与演讲者的讨论。更广泛的影响包括几个年龄组的STEM教育的改善，公众科学素养的提高以及年轻人对STEM兴趣的保持。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical descriptionMost processes in nature are out of equilibrium. Examples are everywhere around us – turbulence of vortexes forming on the sides of airplane wings, water flows from a tap, cooling of a cup of tea to room temperature. Coupling of a system to its environment, the tea to the surrounding air, leads to energy exchange between the two, and relaxation to a new joint state. If isolated, this joint system settles to what we call a thermal equilibrium. It means that the energy exchange stops being on average directional, from the hot cup of tea to the colder ambient air. Instead, the flow of energy starts to fluctuate, without any drift or bias, on average, equally back and forth, between the tea and the air. This approach to a joint steady state is called thermal relaxation or equilibration – it is the long-time collective fate of most coupled systems.Understanding relaxation processes is particularly relevant for metallurgy and materials science, where annealing is the heat treatment that yields metals or glasses with desirable hardness and stress properties. Thermal relaxation is also used in optimization problems to find configurations that are optimal for an environment, for example, optimal traffic schedule routes that minimize the mileage or polymer configurations that have the minimal energy and thus are prevalent at low temperatures.Most of our intuition and theoretical understanding stems from observing physical systems in or close to equilibrium. It is also where the dynamics stop to be important, and the properties of the physical systems can be captured by a few measurable quantities, such as temperature, average energy, and magnetization (in a magnetic system). However, often in nature and in the laboratory, physical systems are not even close to an equilibrium. How does the relaxation occur then? Apparently, it is full of ”surprises,” and our intuition often fails. One such highly unusual relaxation phenomenon is the Mpemba effect. It occurs when ”hot can cool faster than cold,” that is, when a system prepared at high temperature takes less time for cooling than an identical system starting at a lower temperature. Mpemba was the first to observe it in water; later, others saw the effect in the water, plastics, magnets, and other systems. The PI aims to put many of these diverse observations under a common ”umbrella” – a general theoretical framework that focuses on salient features necessary for the anomalous relaxation. That is, the goal of this activity is to study anomalous thermal relaxations and build a theoretical framework describing the approach to thermal equilibrium of different physical systems. Applications of the outlined research include proper sample preparation, design of materials with specific properties, optimal heating, and cooling protocols.The PI’s long-term education goal is to effectively communicate science to audiences of diverse educational backgrounds and ages. The educational objective of this project is to introduce a mini-series of interactive science lectures to middle and high school students, exposing them to cutting-edge research and facilitating networking between scientists and students. High school students selecting their science requirement credits often overlook physics. The PI aims to remedy this gap by making physics, as well as other natural sciences, more approachable by her "quiz the scientist" series. Technical descriptionThe research objective of this activity is to study the anomalous thermal relaxation of physical systems and thus deepen the fundamental understanding of nonequilibrium physics. A prime example of unusual relaxation phenomena is a ”shortcut” in thermal relaxation called the Mpemba effect. It occurs when a system prepared at high temperature takes less time for cooling than an identical system starting at a lower temperature while both are coupled to an even colder environment. It was observed in the cooling of water, clathrate-hydrates, polymers, carbon nano- tube resonators, magnetic alloys, driven granular gasses, and spin glasses. These observations of the effect in very different systems suggest that there might be a general theory behind the phenomena.As a nonequilibrium dynamics phenomenon, the Mpemba effect cannot be captured by looking at the linear-response regime. Therefore, the PI introduces a framework based on stochastic thermodynamics to study anomalous relaxation effects. The outlined theoretical framework will serve as the starting point for analytical and numerical studies of several macroscopic, and also typically much harder to treat, mesoscopic systems. As model systems, kinetically constrained lattice gases, random energy models, and several spin and magnetic systems will be explored. The systems where the Mpemba effect was observed have phase transitions. Hence the PI will explore the connections between phase transitions and the Mpemba effect as well as the relationships between aging, memory, rejuvenation, and the effect. A perturbative approach will be used to study the anomalous relaxation of Markov chain Monte Carlo algorithms.Applications of results emanating from the activity will lead to advancements in control theory, optimization, and numerical algorithms. Particularly the PI envisions more efficient simulated annealing and Markov chain Monte Carlo algorithms, which would be extremely useful for efficient sampling and protein folding. Another application is optimal cooling and heating protocols, and through those, the research products will impact the design of materials with specific thermal properties.The Mpemba effect has received more attention in education than in research. Not much is known about anomalous relaxation processes. Most of the intuition and theoretical framework come from static properties of thermal equilibrium. Yet most of biology and physical systems are out-of-equilibrium, where dynamics is essential. The prospective research results will have an impact on a wide range of physics fields. The outlined theoretical work will impact experiments as well, as the strong Mpemba effect should be readily observable. With improved understanding from this work, the educational plan will bring cutting-edge research topics closer to high school and middle school students. The PI will organize a mini-series of scientific talks and student led discussions with the speaker. The broader impacts include improvements in the STEM education of several age groups, an increase in public scientific literacy and retention of STEM interest among the younger population.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.