N. Nirmal Thyagu, an alumnus of IIT Madras, now at the University of Rutgers, and coworkers Troy Shinbrot and Nam H. Kim, found that packing granular powders in a rotating cylinder gives rise to avalanche events, a fact which is well known to those who study granular media.
The bursts originate from tiny flaws in the structure of the densely packed powder which propagate towards the surface as the cylinder revolves, eventually resulting in a crack that shears off a portion of the powder from the main body. However, the new discovery came when they stuck a voltage probe inside the powder, (Tylenol, in case anyone is giving themselves a headache identifying the powder), having first cleared the cylinder of static electricity. The probe recorded a voltage spike as considerable as 100 volts, about five seconds before the actual avalanche, or slip event occurs. These five seconds, by which the precursor event (the voltage spike) precedes the actual event (the avalanche), should be compared with the time scale of the avalanche itself, which lasts about 19 seconds. Troy Shinbrot, who led the group, got this idea from earthquake folklore, which has always told stories of lightning and other electrical disturbances preceding earthquakes. The table top experiment set up at Rutgers confirmed this. Similar prediction is possible for events that involve the impending failure of granular materials, as in cascades in silos, concrete bridge collapses, and perhaps even earthquakes.
Journal reference: Proceedings of the Natural Academy of sciences, DOI: 10.1073/pnas.1121596109
Popular articles: Science News, New Scientist, Phys. Org.
This blog post is by Neelima Gupte and Sumathi Rao.