Ulrich Dobramysl

Spatial Variability Enhances Species Fitness in Stochastic Predator-Prey Interactions

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.

Environmental versus demographic variability in two-species predator-prey models.

We investigate the competing effects and relative importance of intrinsic demographic and environmental variability on the evolutionary dynamics of a stochastic two-species Lotka-Volterra model by means of Monte Carlo simulations on a two-dimensional lattice. Individuals are assigned inheritable predation efficiencies; quenched randomness in the spatially varying reaction rates serves as environmental noise. We find that environmental variability enhances the population densities of both predators and prey while demographic variability leads to essentially neutral optimization.

Relaxation dynamics in type-II superconductors with point-like and correlated disorder

We employ an elastic line model to investigate the steady-state properties and non-equilibrium relaxation kinetics of magnetic vortex lines in disordered type-II superconductors using Langevin molecular dynamics (LMD). We extract the dependence of the mean vortex line velocity and gyration radius as well as the mean-square displacement in the steady state on the driving current, and measure the vortex density and height autocorrelations in the aging regime. We study samples with either randomly distributed point-like or columnar attractive pinning centers, which allows us to distinguish the complex relaxation features of interacting flux lines subject to extended vs. uncorrelated disorder. Additionally, we find that our new LMD findings match earlier Monte Carlo (MC) simulation data well, verifying that these two microscopically quite distinct simulation methods lead to macroscopically very similar results for non-equilibrium vortex matter.

Particle-Based Multiscale Modeling of Calcium Puff Dynamics

Intracellular calcium is regulated in part by the release of Ca

Relaxation dynamics of vortex lines in disordered type-II superconductors following magnetic field and temperature quenches.

^{2+}

Disordered vortex matter out of equilibrium: a Langevin molecular dynamics study

ions from the endoplasmic reticulum via inositol-4,5-triphosphate receptor (IP

Environmental versus demographic variability in stochastic predator–prey models

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Particle-based Multiscale Modeling of Intracellular Calcium Dynamics

R) channels (among other possibilities such as RyR and L-type calcium channels). The resulting dynamics are highly diverse and lead to local calcium “puffs” as well as global waves propagating through cells, as observed in Xenopus oocytes, neurons, and other cell types. Local fluctuations in the number of calcium ions play a crucial role in the onset of these features. Previous modeling studies of calcium puff dynamics stemming from IP

Dynamical regimes of vortex flow in type-II superconductors with parallel twin boundaries

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Flux line relaxation kinetics following current quenches in disordered type-II superconductors

R channels have predominantly focused on stochastic channel models coupled to deterministic diffusion of ions, thereby neglecting local fluctuations of the ion number. Tracking of individual ions is computationally difficult due to the scale separation in the Ca