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When the researchers shake the container at a certain amplitude and frequency, the energy put into the system manifests itself as small isolated clumps of particles (about thirty bronze balls in diameter) which also bob up and down. These clumps, which the researchers call "oscillons," are stable, holding together for thousands of shakings and able to slowly drift across the bed.
Oscillons can be seen in the image on the lower right of the photographs shown above. They resemble a splash of water in a puddle, but with one important difference: instead of spreading,
they slosh back and forth between a state that resembles a crater and a state that resembles a peak. When one oscillon in a crater state collides
with an oscillon in the peak state, they can form a bound system, as shown in the image on the lower right.
The team believes that oscillons may exist not only in granular materials but in other "dissipative
systems," those which lose energy over time.
Special thanks to Paul Umbanhowar (University of Texas at Austin) for supplying the image and some of the caption text.
This research was reported by Paul B. Umbanhowar, Francisco Melo, and Harry L. Swinney in Nature 382, 793 (1996).