title: Targets, ripples and spirals in a precipitation system with anomalous dispersion.
abstract: We present a novel reaction-diffusion system that exhibits three-dimensional superdiffusive traveling waves without utilizing any external forces. These waves include single circular targets, spirals, and ripples as well as phase-like waves. The system is based on the interplay of the precipitation reaction of mercuric iodide in a gel medium, its polymorphic transformation to a different crystalline form, and its redissolution in excess iodide. A phase diagram is constructed as a function of the initial concentrations of the reagents. The spatiotemporal evolution of these waves is thoroughly analyzed and seems to be a consequence of an anomalous dispersion relationship. Pattern selection and wavelengths of propagating waves are found to depend on initial concentrations of the reactants. The breakup of the waves is also investigated. While the breakdown of ripples and spirals is shown to be a consequence of a Doppler-like instability in conjunction with anomalous dispersion, the targets undergo a boundary defect-mediated breakup.
authors.affiliation: Department of Chemistry, American University of Beirut, P.O. Box 11-0236, Riad El-Solh 1107 2020, Beirut, Lebanon. mazen.ghoul@aub.edu.lb.
authors.forename: Mahmoud M
authors.initials: MM
authors.lastname: Ayass
authors.forename: Istvan
authors.initials: I
authors.lastname: Lagzi
authors.forename: Mazen
authors.initials: M
authors.lastname: Al-Ghoul
mesh_terms: D004058:Diffusion; D005782:Gels / Q000737:chemistry; D007454:Iodides / Q000737:chemistry*; D017669:Mercury Compounds / Q000737:chemistry; D011193:Potassium Iodide / Q000737:chemistry; D013696:Temperature
chemical_list: D005782:Gels; D007454:Iodides; D017669:Mercury Compounds; D011193:Potassium Iodide; C025718:mercuric iodide, red