Dynamics of Slow Granular Flow

这个实验凝聚态物理项目将研究具有开/关间歇性的颗粒流的动力学。这种行为很常见，但传统的测量技术没有足够的分辨率和动态范围来捕捉非常快速的颗粒-颗粒碰撞和缓慢的流动开关。本文将采用一种新的方法，从样品乘散光强度的时间波动的二阶和四阶强度相关函数中提取该信息。将获得间歇性地表流动（雪崩）、库埃特流（粘滑）和振动流（周期性）的数据。特别感兴趣的是平滑流和间歇流之间的交叉作为强迫率的函数。这将有助于测试和发展理论，这些理论目前仅限于准静态或完全流化的制度。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和向他们介绍现代凝聚态物理前沿的材料和主题的优秀培训。这个实验凝聚态物理项目研究了缓慢的、因此是间歇性的颗粒流动的微观动力学。这种行为对于任何一个从桶里慢慢倒出少量沙子，从袋子里慢慢倒出少量大米，或者试图从瓶子里摇出一粒药丸的人来说都是熟悉的。这些流动都很平滑，就像液体一样，只是速度很快；如果速度缓慢，则会通过一系列雪崩断断续续地发生。这种行为在各种各样的行业中都很重要，在这些行业中，食品、制药和陶瓷粉末、建筑材料、原材料等需要——但通常不是——有效地加工和运输而不会堵塞。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。尽管慢流无处不在，也很重要，但人们还没有理解慢流和平稳快流的交叉。目前的工程理论只适用于平稳流动，而目前的物理理论只适用于非常不频繁的流动；没有一个能捕捉到行为的全部范围。通常的实验方法也无法同时捕捉流动过程中颗粒的快速运动和流动本身的缓慢开关。这个项目将首次通过最先进的技术来实现这一目标，该技术涉及从样品反射的激光中产生的光子相关性。除了对工业和地球物理学的实际影响外，该项目将为学生提供新的实验方法的优秀培训，并将向他们介绍现代凝聚态物理前沿的材料和主题。

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.