Browsing by Author "Dobramysl, U."

Now showing 1 - 12 of 12
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    Disordered vortex matter out of equilibrium: a Langevin molecular dynamics study
    Assi, H.; Chaturvedi, H.; Dobramysl, U.; Pleimling, Michel J.; Täuber, Uwe C. (2015-11-04)
    We discuss the use of Langevin molecular dynamics in the investigation of the non-equilibrium properties of disordered vortex matter. Our special focus is set on values of system parameters that are realistic for disordered high-$T_c$ superconductors such as YBCO. Using a discretized elastic line model, we study different aspects of vortices far from thermal equilibrium. On the one hand we investigate steady-state properties of driven magnetic flux lines in a disordered environment, namely the current-voltage characteristics, the gyration radius, and the pinning time statistics. On the other hand we study the complex relaxation processes and glassy-like dynamics that emerge in type-II superconductors due to the intricate competition between the long-range vortex-vortex repulsion and flux pinning due to randomly placed point defects. To this end we consider different types of sudden perturbations: temperature, magnetic field, and external current quenches.
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    Dynamical regimes of vortex flow in type-II superconductors with parallel twin boundaries
    Chaturvedi, H.; Galliher, N.; Dobramysl, U.; Pleimling, Michel J.; Täuber, Uwe C. (2017-10-11)
    We explore the dynamics of driven magnetic flux lines in disordered type-II superconductors in the presence of twin boundaries oriented parallel to the direction of the applied magnetic field, using a three-dimensional elastic line model simulated with Langevin molecular dynamics. The lines are driven perpendicular to the planes to model the effect of an electric current applied parallel to the planes and perpendicular to the magnetic field. A study of the long-time non-equilibrium steady states for several sample thicknesses L and drive strengths F_d reveals a rich collection of dynamical regimes spanning a remarkably broad depinning transition region that separates the pinned and moving-lattice states of vortex matter. We perform novel direct measurements of flux line excitations such as half-loops and double kinks, and quantitatively analyze their excitation occurrence distributions to characterize the topologically rich flux flow profile and generate a boundary curve separating the regions of linear and non-linear transport in the (L, F_d) plane. Rich static and dynamic visualizations of the vortex matter in different drive regimes supplement the quantitative results obtained.
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    Environmental versus demographic variability in stochastic predator prey models
    Dobramysl, U.; Täuber, Uwe C. (IOP, 2013-10-01)
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    Environmental Versus Demographic Variability in Two-Species Predator-Prey Models
    Dobramysl, U.; Täuber, Uwe C. (American Physical Society, 2013-01-24)
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    Evolutionary dynamics and competition stabilize three-species predator-prey communities
    Chen, S.; Dobramysl, U.; Täuber, Uwe C. (2017-11-15)
    We perform individual-based Monte Carlo simulations in a community consisting of two predator species competing for a single prey species, with the purpose of studying biodiversity stabilization in this simple model system. Predators are characterized with predation efficiency and death rates, to which Darwinian evolutionary adaptation is introduced. Competition for limited prey abundance drives the populations' optimization with respect to predation efficiency and death rates. We study the influence of various ecological elements on the final state, finding that both indirect competition and evolutionary adaptation are insufficient to yield a stable ecosystem. However, stable three-species coexistence is observed when direct interaction between the two predator species is implemented.
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    Flux line relaxation kinetics following current quenches in disordered type-II superconductors
    Chaturvedi, H.; Assi, H.; Dobramysl, U.; Pleimling, Michel J.; Täuber, Uwe C. (2016-06)
    We investigate the relaxation dynamics of magnetic vortex lines in type-II superconductors following rapid changes of the external driving current by means of an elastic line model simulated with Langevin molecular dynamics. A system of flux vortices in a sample with randomly distributed point-like defects is subjected to an external current of appropriate strength for a sufficient period of time so as to be in a moving non-equilibrium steady state. The current is then instantaneously lowered to a value that pertains to either the moving or pinned regime. The ensuing relaxation of the flux lines is studied via one-time observables such as their mean velocity and radius of gyration. We have in addition measured the two-time flux line height autocorrelation function to investigate dynamical scaling and aging behavior in the system, which in particular emerge after quenches into the glassy pinned state.
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    Pinning time statistics for vortex lines in disordered environments
    Dobramysl, U.; Pleimling, Michel J.; Täuber, Uwe C. (American Physical Society, 2014-12-02)
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    Relaxation dynamics in type-II superconductors with point-like and correlated disorder
    Dobramysl, U.; Assi, H.; Pleimling, Michel J.; Täuber, Uwe C. (Springer, 2013-05-01)
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    Relaxation dynamics of vortex lines in disordered type-II superconductors following magnetic field and temperature quenches
    Assi, H.; Chaturvedi, H.; Dobramysl, U.; Pleimling, Michel J.; Täuber, Uwe C. (American Physical Society, 2015-11-17)
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    Spatial Variability Enhances Species Fitness in Stochastic Predator-Prey Interactions
    Dobramysl, U.; Täuber, Uwe C. (American Physical Society, 2008-12-19)
    We study the influence of spatially varying reaction rates on a spatial stochastic two-species Lotka-Volterra lattice model for predator-prey interactions using two-dimensional Monte Carlo simulations. The effects of this quenched randomness on population densities, transient oscillations, spatial correlations, and invasion fronts are investigated. We find that spatial variability in the predation rate results in more localized activity patches, which in turn causes a remarkable increase in the asymptotic population densities of both predators and prey and accelerated front propagation.
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    Spatial Variability Enhances Species Fitness in Stochastic Predator-Prey Interactions
    Dobramysl, U.; Täuber, Uwe C. (American Physical Society, 2008-12-19)
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    Stochastic population dynamics in spatially extended predator-prey systems
    Dobramysl, U.; Mobilia, M.; Pleimling, Michel J.; Täuber, Uwe C. (2017-12-26)
    Spatially extended population dynamics models that incorporate intrinsic noise serve as case studies for the role of fluctuations and correlations in biological systems. Including spatial structure and stochastic noise in predator-prey competition invalidates the deterministic Lotka-Volterra picture of neutral population cycles. Stochastic models yield long-lived erratic population oscillations stemming from a resonant amplification mechanism. In spatially extended predator-prey systems, one observes noise-stabilized activity and persistent correlations. Fluctuation-induced renormalizations of the oscillation parameters can be analyzed perturbatively. The critical dynamics and the non-equilibrium relaxation kinetics at the predator extinction threshold are characterized by the directed percolation universality class. Spatial or environmental variability results in more localized patches which enhances both species densities. Affixing variable rates to individual particles and allowing for trait inheritance subject to mutations induces fast evolutionary dynamics for the rate distributions. Stochastic spatial variants of cyclic competition with rock-paper-scissors interactions illustrate connections between population dynamics and evolutionary game theory, and demonstrate how space can help maintain diversity. In two dimensions, three-species cyclic competition models of the May-Leonard type are characterized by the emergence of spiral patterns whose properties are elucidated by a mapping onto a complex Ginzburg-Landau equation. Extensions to general food networks can be classified on the mean-field level, which provides both a fundamental understanding of ensuing cooperativity and emergence of alliances. Novel space-time patterns emerge as a result of the formation of competing alliances, such as coarsening domains that each incorporate rock-paper-scissors competition games.