Oscillon
Encyclopedia
In physics
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...

, an oscillon is a soliton
Soliton
In mathematics and physics, a soliton is a self-reinforcing solitary wave that maintains its shape while it travels at constant speed. Solitons are caused by a cancellation of nonlinear and dispersive effects in the medium...

-like phenomenon that occurs in granular and other dissipative
Dissipative system
A dissipative system is a thermodynamically open system which is operating out of, and often far from, thermodynamic equilibrium in an environment with which it exchanges energy and matter....

 media. Oscillons in granular media result from vertically vibrating a plate with a layer of uniform particles placed freely on top. When the sinusoidal vibrations are of the correct amplitude and frequency and the layer of sufficient thickness, a localized wave, referred to as an oscillon, can be formed by locally disturbing the particles. This meta-stable
Phase (matter)
In the physical sciences, a phase is a region of space , throughout which all physical properties of a material are essentially uniform. Examples of physical properties include density, index of refraction, and chemical composition...

 state will remain for a long time (many hundreds of thousands of oscillations) in the absence of further perturbation. An oscillon changes form with each collision of the grain layer and the plate, switching between a peak that projects above the grain layer to a crater like depression with a small rim. This self-sustaining state was named by analogy with the soliton
Soliton
In mathematics and physics, a soliton is a self-reinforcing solitary wave that maintains its shape while it travels at constant speed. Solitons are caused by a cancellation of nonlinear and dispersive effects in the medium...

, 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
Waveguide
A waveguide is a structure which guides waves, such as electromagnetic waves or sound waves. There are different types of waveguides for each type of wave...

 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. In comparison, solitons do not form bound states.

Stable interacting localized waves with subharmonic response were discovered and baptized oscillons at The University of Texas at Austin. Solitary bursts had been reported earlier in a quasi two-dimensional grain layer at the University of Paris, but these transient events were unstable and no bonding interaction or subharmonic response was reported.

The cause of this phenomenon is currently under debate; the most likely connection is with the mathematical theory of chaos
Chaos theory
Chaos theory is a field of study in mathematics, with applications in several disciplines including physics, economics, biology, and philosophy. Chaos theory studies the behavior of dynamical systems that are highly sensitive to initial conditions, an effect which is popularly referred to as the...

 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 vibrational modes of the plate than the response of the sand and created an experimental set-up that minimized outside effects, using a shallow layer of brass balls in a vacuum and a rigid plate . When they vibrated the plate at critical amplitude, they found that the balls formed a localized vibrating structure when perturbed which lasted indefinitely.

Oscillons have also been experimentally observed in thin parametrically vibrated layers of viscous fluid and colloidal suspensions. Oscillons have been associated with Faraday wave
Faraday wave
Faraday waves, also known as Faraday ripples, named after Michael Faraday, are nonlinear standing waves that appear on liquids enclosed by a vibrating receptacle. When the vibration frequency exceeds a critical value, the flat hydrostatic surface becomes unstable. This is known as the Faraday...

s 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.

Further reading

  • Philip Ball (1999), The Self-Made Tapestry: Pattern Formation in Nature, Oxford University Press.
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