title: Crystallization and melting of bacteria colonies and Brownian bugs.
abstract: Motivated by the existence of remarkably ordered cluster arrays of bacteria colonies growing in Petri dishes and related problems, we study the spontaneous emergence of clustering and patterns in a simple nonequilibrium system: the individual-based interacting Brownian bug model. We map this discrete model into a continuous Langevin equation which is the starting point for our extensive numerical analyses. For the two-dimensional case we report on the spontaneous generation of localized clusters of activity as well as a melting-freezing transition from a disordered or isotropic phase to an ordered one characterized by hexagonal patterns. We study in detail the analogies and differences with the well-established Kosterlitz-Thouless-Halperin-Nelson-Young theory of equilibrium melting, as well as with another competing theory. For that, we study translational and orientational correlations and perform a careful defect analysis. We find a nonstandard one-stage, defect-mediated transition whose nature is only partially elucidated.
authors: Departamento de Electromagnetismo y Física de la Materia and Instituto de Física Teórica y Computacional Carlos I, Facultad de Ciencias, Universidad de Granada, Granada, Spain.
authors: Francisco
authors: F
authors: Ramos
authors: Cristóbal
authors: C
authors: López
authors: Emilio
authors: E
authors: Hernández-García
authors: Miguel A
authors: MA
authors: Muñoz
mesh_terms: D018407:Bacterial Physiological Phenomena; D018441:Biofilms / Q000254:growth & development*; D049109:Cell Proliferation; D003198:Computer Simulation; D008954:Models, Biological; D015233:Models, Statistical