Experiments on Fluctuations in Nonthermal Systems

这个软凝聚态物理项目将研究两种统计大小的非热系统，其中单个元素足够大，热波动在动力学中不起作用。在这样的系统中，热力学参数（如温度）的定义和含义可能需要新的方法。这两种系统在物理上是完全不同的：流化颗粒介质与皱巴巴的弹性片。在这两个系统中，实验探索了由各种动力学和运动学量的波动所定义的温度的等价性。此外，将测量频率相关的机械敏感性，以检查波动的时间相关性是否也通过波动耗散定理的推广决定了整体机械线性响应。其中一个实验还设计用于研究波动中的空间相关性，因为有迹象表明，即使在粒状介质的流动状态下，被称为力链的自发形成的线性结构也可能在应力传递中发挥重要作用。研究生将接触到各种技术，如高速视频成像、漫射波光散射、应力测量、荧光显微镜和声学测量。有些项目是为本科生保留的，这些本科生在之前的NSF支持下已经参与了研究工作。新的研究成果通过网站发布，并被纳入与麻省理工大学同事共同教授的软凝聚态物理研究生课程。提出了研究具有大量大粒子的系统的统计行为的实验，这是传统的热力学和统计力学技术不适用的。所研究的两种物理系统是流化颗粒介质和皱化弹性片。出现类似问题的其他系统是泡沫、悬浮液、乳液，所有这些系统在技术上都很重要。这些实验将探索诸如温度和熵之类的概念是否可以扩展到诸如此类的非平衡系统。此外，该项目将研究温度与材料对外力响应的关系是否可以扩展到远离平衡的地方。研究生将接触到各种技术，如高速视频成像、漫射波光散射、应力测量、荧光显微镜和声学测量。有些项目是为本科生保留的，这些本科生在之前的NSF支持下已经参与了研究工作。新的研究成果通过网站发布，并被纳入与麻省理工大学同事共同教授的软凝聚态物理研究生课程。

\This soft condensed matter physics project will investigate two types of statistically sized, non-thermal systems, in which individual elements are large enough that thermal fluctuations play no role in the dynamics. In such systems, definitions and meanings of thermodynamic parameters such as temperature can require new approaches. The two systems are physically quite different: Fluidized granular media versus crumpled elastic sheets. In both systems, experiments probe the equivalence of temperatures defined by fluctuations of various dynamical and kinematic quantities. Further, frequency-dependent mechanical susceptibilities will be measured to examine whether the time-dependence of the fluctuations also determine bulk mechanical linear response via generalizations of the fluctuation-dissipation theorem. One of the experiments is also designed to study spatial correlations in the fluctuations, since there are indications that spontaneously formed linear structures known as force-chains may play an important role in stress transmission even in the flowing state of granular media. Graduate students will be exposed to a variety of techniques such as high-speed video imaging, diffusing-wave light scattering, stress measurements, fluorescence microscopy, and acoustic measurements. Some projects are reserved for undergraduate students who have been integral to research efforts under prior NSF support. The new research results are disseminated via a website and are incorporated in a new graduate course in soft condensed matter physics that is co-taught with UMass colleagues.Experiments are proposed to study the statistical behaviors of systems with large numbers of large particles, to which conventional techniques of thermodynamics and statistical mechanics do not apply. The two physical systems studied are fluidized granular media and crumpled elastic sheets. Other systems in which similar issues arise are foams, suspensions, emulsions, all of which are technologically important. The experiments will probe whether concepts such as temperature and entropy can be extended to out-of-equilibrium systems such as these. Further, the project will study whether the relationship of temperature to the response of a material to external forces can be extended far away from equilibrium. Graduate students will be exposed to a variety of techniques such as high-speed video imaging, diffusing-wave light scattering, stress measurements, fluorescence microscopy, and acoustic measurements. Some projects are reserved for undergraduate students who have been integral to research efforts under prior NSF support. The new research results are disseminated via a website and are incorporated in a new graduate course in soft condensed matter physics that is co-taught with UMass colleagues.