Oscillon
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In physics, an oscillon is a soliton-like phenomenon that results from vibrating a plate with a large number of small uniform particles placed freely on top. When the sinusoidal vibrations are of the correct amplitude and frequency a small peak, referred to as an oscillon, can be formed by locally disturbing the particles. This meta-stable state will remain for a long time (many hundreds of thousands of oscillations) given no outside interference. The disturbance will transform from a peak to a dish on the next period and back to a peak on the next. This self-sustaining state was named by analogy with the soliton, which is a localized wave that maintains its integrity as it moves. Whereas solitons occur as travelling waves in a fluid or as electromagnetic waves in a waveguide oscillons may be stationary.
Astonishingly, oscillons of opposite phase will attract over short distances and form 'bonded' pairs. Oscillons of like phase repel. Oscillons have been observed forming 'molecule' like structures and long chains.
The apparently new phenomenon was reported initially as a solitary burst at University of Paris and subsequently studied in detail and baptized oscillons at University of Texas at Austin. The cause of these phenomena is currently under debate; the most likely connection is with the mathematical theory of chaos and may give insights into the way patterns in sand form.
The experimental procedure is similar to that used to form Chladni figures of sand on a vibrating plate. Researchers realized that these figures say more about the vibrations in the plate than in the sand and created an experimental set-up that minimized outside effects, using a shallow layer of brass balls in a vacuum. When they vibrated the plate at critical amplitude, they found that the balls spontaneously formed a localized vibrating column which lasted indefinitely.
Oscillons have been experimentally observed in thin parametrically vibrated layers of viscous fluid. Oscillons have been associated with Faraday waves because they require similar resonance conditions.
Nonlinear electrostatic oscillations on a plasma boundary can also appear in the form of oscillons. This was discovered in 1989.
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[edit] References
- E. Clément, L. Vanel, J. Rajchenbach & J. Duran (1996). "Pattern formation in a vibrated granular layer". Physical Review E 53 (March 1996): 2972. doi:.
- Paul B. Umbanhowar, Francisco Melo & Harry L. Swinney (1996). "Localized excitations in a vertically vibrated granular layer". Nature 382 (29 August 1996): 793 - 796. doi:.
- L. Stenflo and M. Y. Yu. "Origin of oscillons". Nature 384 (21 November 1996): 224.
