Experiments on Fluctuations in Nonthermal Systems

这个软凝聚态物理项目将研究两种类型的统计大小的非热系统，在这些系统中，单个元素足够大，热涨落在动力学中不起作用。在这样的系统中，温度等热力学参数的定义和含义可能需要新的方法。这两个系统在物理上有很大的不同：流态化的颗粒介质和皱缩的弹性薄片。在这两个系统中，实验探索由各种动力学和运动量的波动定义的温度的等价性。此外，还将测量与频率相关的机械极化率，以检验涨落的时间相关性是否也通过涨落耗散定理的推广来决定整体机械线性响应。其中一个实验也是为了研究波动中的空间相关性，因为有迹象表明，即使在颗粒介质的流动状态下，自发形成的称为力链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、扩散波光散射、应力测量、荧光显微镜和声学测量。一些项目是为本科生保留的，他们在之前的NSF资助下一直是研究工作的组成部分。这些新的研究成果通过一个网站传播，并被纳入一门新的软凝聚态物理研究生课程，该课程与加州大学质量分校的同事共同讲授。该课程提议用实验来研究含有大量大粒子的系统的统计行为，而传统的热力学和统计力学技术不适用于这些实验。所研究的两个物理系统是流态化的颗粒介质和皱缩的弹性薄片。出现类似问题的其他系统是泡沫、悬浮剂、乳状液，所有这些都具有重要的技术意义。这些实验将探索温度和熵等概念是否可以扩展到像这样的非平衡系统。此外，该项目将研究温度与材料对外力的响应之间的关系是否可以延伸到远离平衡的地方。研究生将接触到各种技术，如高速视频成像、扩散波光散射、应力测量、荧光显微镜和声学测量。一些项目是为本科生保留的，他们在之前的NSF资助下一直是研究工作的组成部分。新的研究成果通过一个网站传播，并被纳入与马萨诸塞州大学同事共同教授的一门新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.