| 07/2022 Stress anisotropy in confined populations of growing rods Jonas Isensee et al. Order and alignment are ubiquitous in growing colonies of rod-shaped bacteria due to the nematic properties of the constituent particles. These effects are the result of the active stresses generated by growth, passive mechanical interactions between cells, and flow-induced effects due to the shape of the confining container. However, how these contributing factors interact to give rise to the obs … |
| 07/2022 From a microscopic solution to a continuum description of active particles with a recoil interaction in one dimension Matthew J Metson et al. We consider a model system of persistent random walkers that can jam, pass through each other or jump apart (recoil) on contact. In a continuum limit, where particle motion between stochastic changes in direction becomes deterministic, we find that the stationary inter-particle distribution functions are governed by an inhomogeneous fourth-order differential equation. Our main focus is on determin … |
| 07/2022 Tuning attraction and repulsion between active particles through persistence Matthew J Metson et al. We consider the interplay between persistent motion, which is a generic property of active particles, and a recoil interaction which causes particles to jump apart on contact. The recoil interaction exemplifies an active contact interaction between particles, which is inelastic and is generated by the active nature of the constituents. It is inspired by the `shock' dynamics of certain microor … |
| 02/2021 Coarse graining of biochemical systems described by discrete stochastic dynamics David Seiferth et al. Many biological systems can be described by finite Markov models. A general method for simplifying master equations is presented that is based on merging adjacent states. The approach preserves the steady-state probability distribution and all steady-state fluxes except the one between the merged states. Different levels of coarse graining of the underlying microscopic dynamics can be obtained by … |
| 09/2020 Inter-particle ratchet effect determines global current of heterogeneous particles diffusing in confinement Emil Mallmin et al. In a model of $N$ volume-excluding spheres in a $d$-dimensional tube, we consider how differences between particles in their drift velocities, diffusivities, and sizes influence the steady state distribution and axial particle current. We show that the model is exactly solvable when the geometrical constraints prevent any particle from overtaking every other — a notion we term quasi-one-dimension … |
| 03/2020 Stochastic effects on the dynamics of an epidemic due to population subdivision Philip Bittihn et al. Using a stochastic Susceptible-Infected-Removed (SIR) meta-population model of disease transmission, we present analytical calculations and numerical simulations dissecting the interplay between stochasticity and the division of a population into mutually independent sub-populations. We show that subdivision activates two stochastic effects—extinction and desynchronization—diminishing the over … |
| 01/2020 Swimming suppresses correlations in dilute suspensions of pusher microorganisms Viktor Škultéty et al. Active matter exhibits various forms of non-equilibrium states in the absence of external forcing, including macroscopic steady-state currents. Such states are often too complex to be modelled from first principles and our understanding of their physics relies heavily on minimal models. These have mostly been studied in the case of "dry" active matter, where particle dynamics are dominat … |
| 12/2019 Debye-Hückel potential at an interface between two media Alexander Morozov et al. Electrostatic interactions between point charges embedded into interfaces separating dielectric media are omnipresent in soft matter systems and often control their stability. Such interactions are typically complicated and do not resemble their bulk counterparts. For instance, the electrostatic potential of a point charge at an air-water interface falls off as $r^{-3}$, where $r$ is the distance … |
| 10/2018 Exact spectral solution of two interacting run-and-tumble particles on a ring lattice Emil Mallmin et al. Exact solutions of interacting random walk models, such as 1D lattice gases, offer precise insight into the origin of nonequilibrium phenomena. Here, we study a model of run-and-tumble particles on a ring lattice interacting via hardcore exclusion. We present the exact solution for one and two particles using a generating function technique. For two particles, the eigenvectors and eigenvalues are … |
| 08/2018 Minimal stochastic field equations for one-dimensional flocking Eoin Ó Laighléis et al. We consider the collective behaviour of active particles that locally align with their neighbours. Agent-based simulation models have previously shown that in one dimension, these particles can form into a flock that maintains its stability by stochastically alternating its direction. Until now, this behaviour has been seen in models based on continuum field equations only by appealing to long-ran … |