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.
