Dynamics of Slow Granular Flow

这个实验凝聚态物理学项目将研究颗粒流的动力学，表现出开/关不稳定性。这种行为非常常见，但传统的测量技术没有足够的分辨率和动态范围来捕获非常快速的颗粒-颗粒碰撞和流动的缓慢开/关切换。将采用一种新的方法，在该信息中提取的第二和第四阶强度相关函数的时间波动的光的强度的样品的多重散射。将获得间歇性表面流（雪崩）、库埃特流（粘滑）和振动流（周期性）的数据。特别感兴趣的是在平滑和间歇流之间的交叉作为强迫率的函数。这应该有助于测试和发展理论，目前仅限于准静态或完全流化状态。这在各种各样的工业中应该是有用的，在这些工业中，颗粒材料的运输和加工现在只能以极低的效率完成。还可以深入了解密切相关的地球物理事件，如滑坡、侵蚀和地震。该项目为研究生提供了最先进的实验方法方面的优秀培训，并向他们介绍了现代凝聚态物理学前沿的材料和主题。这个实验凝聚态物理学项目研究颗粒流的微观动力学，这些颗粒流是缓慢的，因此是间歇的。这种行为对任何一个从桶里慢慢倒出少量沙子，从袋子里慢慢倒出大米，或者试图从瓶子里摇出一粒药丸的人来说都很熟悉。这些流动都是平滑的，就像液体一样，只有在非常快的时候;如果很慢，它们通过一系列雪崩间歇性地流动。这一特性在许多行业中都很重要，例如食品、医药和陶瓷粉末、建筑材料、原矿石等需要（但通常无法）高效加工和运输而不会发生堵塞。这种行为在诸如滑坡、侵蚀和地震等地球物理事件中也很重要。尽管它们的普遍性和重要性，慢流和平滑快流的交叉尚未被理解。目前的工程理论只适用于光滑流动，而目前的物理理论只适用于非常罕见的流动;没有一个理论可以捕捉到全部的行为。通常的实验方法也不能同时捕捉颗粒在流动过程中的快速运动沿着流动本身的缓慢开关。该项目将首次通过最先进的技术来实现这一点，该技术涉及从样品反射的激光的光子相关性。除了对工业和物理学的实际影响外，该项目还将为学生提供新实验方法的优秀培训，并将向他们介绍现代凝聚态物理学前沿的材料和主题。

This experimental condensed matter physics project will investigate the dynamics of granular flows that exhibit on/off intermittency. Such behavior is very common, but traditional measurement techniques do not have sufficient resolution and dynamic range to capture the very rapid grain-grain collisions and the slow on/off switching of the flows. A new approach will be employed in which this information is extracted from the second- and fourth-order intensity correlation functions for temporal fluctuations in the intensity of light multiply-scattered by the sample. Data will be obtained for intermittent surface flows (avalanches), Couette flows (stick-slip), and vibrated flows (periodic). Particular interest is in the crossover between smooth and intermittent flows as a function of forcing rate. This should aid in testing and developing theories, which are currently limited to either quasi-static or fully-fluidized regimes. This should be useful in a wide variety of industries, where transport and processing of granular materials is now accomplished only with great inefficiency. Insight may also be gained into closely related geophysical events such as landslides, erosion, and earthquakes. The project provides excellent training for graduate students in state-of-the art experimental methods and for introducing them to materials and topics at the forefront of modern condensed matter physics.%%%This experimental condensed matter physics project investigates the microscopic dynamics of granular flows that are slow and, hence, intermittent. Such behavior is familiar to anyone who has slowly poured a small amount of sand from a bucket, or rice from a bag, or tried to shake out one pill from a bottle. These flows are all smooth, like a liquid, only if very fast; if slow, they are intermittent via a series of avalanches. This behavior is important in a wide variety of industries, where foods, pharmaceutical and ceramic powders, building materials, raw ores, etc. need to be -but are often not- processed and transported efficiently without jamming. This behavior is also important in geophysical events such as landslides, erosion, and earthquakes. In spite of their ubiquity and importance, slow flows and the crossover to smooth fast flows are not yet understood. Current engineering theories are applicable only to smooth flows, and current physics theories are applicable only to very infrequent flows; none can capture the full range of behavior. The usual experimental methods are also incapable of simultaneously capturing the rapid grain motion during flow along with the slow on-off switching of the flow itself. This project will do so, for the first time, by state-of-the-art techniques involving photon correlations from laser light bounced off a sample. In addition to practical impact on industry and geophysics, this project will provide excellent training for students in new experimental methods and will introduce them to materials and topics at the forefront of modern condensed matter physics.