Localized excitations in a vertically vibrated granular layer

• Published in: Nature (London) 1996-08, Vol.382 (6594), p.793-796
• Main Authors: Umbanhowar, Paul B, Melo, Francisco, Swinney, Harry L
• Format: Article
• Language: English
• Subjects: Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Granular solids; Humanities and Social Sciences; Kinetics; letter; Material form; multidisciplinary; Physics; Rheology; Sand & gravel; Science; Science (multidisciplinary)
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/382793a0

THE formation of two-dimensional patterns in biological, chemical and physical systems is often described by the nonlinear interaction of plane waves 1 . An alternative approach views patterns as ensembles of interacting localized objects, analogous to the assembly of crystals from atoms. For macroscopic pattern-forming systems, one objection to the latter approach is that no 'atoms' exist; however spatially localized excitations can play an analogous role. One-dimensional localized states are observed in many systems—for example, solitary waves in water 2–4 and optical fibres 5 —and can organize into simple patterns 6,7 . But few examples of two-dimensional localized states are known, and these tend to be unstable and/or do not show simple pattern-forming interactions 8–11 . Here we report the observation of stable, two-dimensional localized excitations zin a vibrating layer of sand. These excitations, which we term 'oscillons', have a propensity to assemble into 'molecular' and 'crystalline' structures. Our experimental results, together with the observation of similar localized excitations in model differential equations 12–14 , indicate a crucial, cooperative role for hysteresis and dissipation in the formation of oscillons, and suggest that similar behaviour may occur in continuous media.