Jamming transitions and kinetic phenomena

* 技术摘要 * 的主要目标是通过测量堵塞前沿和跨越前沿的颗粒尺度动力学，了解颗粒系统中堵塞的动力学。 最简单的情况是在沉积沉积过程中堵塞前沿的静止向上传播，其中颗粒浓度分布将通过医学X射线成像测量，颗粒温度分布（Tg）将通过斑点可见度光谱（SVS）测量。 主要的兴趣是在偏离阶跃函数配置文件，消失的Tg，时空相关的波动的动力学类似的动态异质性，但现在存在的梯度和时间演化。 另一种情况是从高料斗排出的各种颗粒类型的堵塞行为。 从宏观上，通过平均流量随孔径增大的发散性来研究堵塞的转变。 在微观上，它将被研究的空间相关的波动的Tg周围的流体动力学时间平均流场;不稳定的Tg被假设为增加的方法堵塞过渡。 这将通过颗粒跟踪和SVS通过侧壁进行研究。 一个单独的推力计划为二维空气流化颗粒的动力学钉扎颗粒阵列内。 这些项目将把现代物理学和测量技术带入研究生和本科生的教育体验中。 要创建的知识将有助于理解和控制工业和自然环境中的干扰现象，在这些环境中，干扰和非干扰区域之间通常存在移动边界。非技术摘要 * 除了流体之外，几乎任何东西的流动都具有令人讨厌的“堵塞”倾向，并且不管施加的力如何都会停止。 我们熟悉的例子包括高速公路上的车辆、溜槽里的煤和沙漏里的沙子。 这些问题使食品、种子、矿物、矿石、建筑材料和药丸粉末等各种颗粒材料的加工变得混乱。 在自然界中，干扰现象是泥石流和地震等可怕事件的基础。 在所有这些情况下，行为都不能真正得到控制。 但由于最近的理论和实验科学，现在对均匀系统的干扰过渡有了合理的理解，所有的颗粒都受到相同的条件，并且都被卡住或未被卡住。 该奖项将支持突破性的研究，即在有一个界面或“干扰前沿”的情况下，干扰是如何发展的，该界面或“干扰前沿”将干扰区域和非干扰区域分开，并随时间而变化。 想想当沙漏的出口堵塞时会发生什么，或者当颗粒从流体中沉淀出来时会发生什么。 虽然材料看起来很普通，但科学和实验方法是复杂的。 这将是理想的研究生和本科生的教育经验。 将要创建的知识将引起物理学家、工程师和地质学家的兴趣，并将帮助工业避免由于干扰而导致的效率低下和过程故障。 它甚至可能最终通过控制泥石流和侵蚀来帮助拯救生命和财产。

****Technical Abstract****The main goal is to develop an understanding of the kinetics of jamming in granular systems, through measurement of jamming fronts and of grain-scale dynamics across the fronts. The simplest situation is the stationary upward propagation of a jamming front during sedimentary deposition, where the grain concentration profile will be measured by medical x-ray imaging, and the granular temperature profile (Tg) will be measured by Speckle-Visibility Spectroscopy (SVS). Key interest is in the deviations from step-function profiles, the vanishing of Tg, and spatiotemporally correlated fluctuations of dynamics akin to dynamical heterogeneities but now in presence of gradients and time evolution. Another situation is the clogging behavior for various grain types discharged from tall hoppers. Macroscopically, the clogging transition will be studied by the divergence of average discharge mass as hole size increases. Microscopically, it will be studied by spatially-correlated fluctuations of Tg around the hydrodynamic time-average flow field; unsteadiness of Tg is hypothesized to increase on approach to the clogging transition. This will be studied by particle tracking and by SVS through the sidewall. A separate thrust is planned for the dynamics of 2d air-fluidized grains within an array of pinned grains. These projects will bring modern physics and measurement techniques into the educational experience of graduate and undergraduate students. And the knowledge to be created will be helpful for understanding and controlling jamming phenomena in industrial and natural settings, where there is often a moving boundary between jammed and unjammed regions.****Non-Technical Abstract****The flow of almost anything other than a fluid has an annoying tendency to "jam" and come to rest in spite of applied forces. Familiar examples include traffic on a highway, coal in a chute, and sand in an hourglass. Such problems confound the processing of diverse granular materials like foods, seeds, minerals, ores, building materials, and pharmaceutical pills & powders. In the natural world, jamming phenomena underlie horrific events such as mudslides and earthquakes. In none of these cases can the behavior yet be truly controlled. But thanks to recent theoretical and experimental science, there is now a reasonable understanding of the jamming transition for uniform systems, where all the grains are subjected to the same conditions and are all either jammed or unjammed. This award will support groundbreaking research on how jams develop in situations where there is an interface or "jamming front" that separates jammed and unjammed regions and that changes with time. Think of what happens when a clog forms over the outlet of an hourglass, or when grains settle out of from a fluid. Though the materials may seem mundane, the science and the experimental methods are sophisticated. This will be ideal for the educational experience of graduate and undergraduate students. The knowledge to be created will be of interest to physicists, engineers, and geologists, and will help industry avoid inefficiencies and process failures due to jamming. It may ultimately even help save lives and property through control of mudslides and erosion.