Université de Fribourg

Linear response approach to active Brownian particles in time-varying activity fields

Merlitz, Holger ; Vuijk, Hidde D. ; Brader, Joseph M. ; Sharma, Abhinav ; Sommer, Jens-Uwe

In: The Journal of Chemical Physics, 2018, vol. 148, no. 19, p. 194116

In a theoretical and simulation study, active Brownian particles (ABPs) in three- dimensional bulk systems are exposed to time-varying sinusoidal activity waves that are running through the system. A linear response (Green-Kubo) formalism is applied to derive fully analytical expressions for the torque-free polarization profiles of non- interacting particles. The activity waves induce fluxes...

Université de Fribourg

Isotropic-nematic transition of self-propelled rods in three dimensions

Bott, Matthias Christian ; Winterhalter, F. ; Marechal, Matthieu ; Sharma, Abhinav ; Brader, Joseph M. ; Wittmann, René

In: Physical Review E, 2018, vol. 98, no. 1, p. 012601

Using overdamped Brownian dynamics simulations we investigate the isotropic- nematic (IN) transition of self-propelled rods in three spatial dimensions. For two well- known model systems (Gay-Berne potential and hard spherocylinders) we find that turning on activity moves to higher densities the phase boundary separating an isotropic phase from a (nonpolar) nematic phase. This active IN phase...

Université de Fribourg

Mean first passage time of active Brownian particle in one dimension

Scacchi, Alberto ; Sharma, Abhinav

In: Molecular Physics, 2018, vol. 116, no. 4, p. 460–464

We investigate the mean first passage time of an active Brownian particle in one dimension using numerical simulations. The activity in one dimension is modelled as a two state model; the particle moves with a constant propulsion strength but its orientation switches from one state to other as in a random telegraphic process. We study the influence of a finite resetting rate r on the mean...

Université de Fribourg

Effective equilibrium states in mixtures of active particles driven by colored noise

Wittmann, René ; Brader, Joseph M. ; Sharma, Abhinav ; Marconi, U. Marini Bettolo

In: Physical Review E, 2018, vol. 97, no. 1, p. 012601

We consider the steady-state behavior of pairs of active particles having different persistence times and diffusivities. To this purpose we employ the active Ornstein- Uhlenbeck model, where the particles are driven by colored noises with exponential correlation functions whose intensities and correlation times vary from species to species. By extending Fox's theory to many components, we...

Université de Fribourg

Effective equilibrium states in the colored-noise model for active matter I. Pairwise forces in the Fox and unified colored noise approximations

Wittmann, René ; Maggi, C ; Sharma, Abhinav ; Scacchi, A ; Brader, Joseph M. ; Marconi, U Marini Bettolo

In: Journal of Statistical Mechanics: Theory and Experiment, 2017, vol. 2017, no. 11, p. 113207

The equations of motion of active systems can be modeled in terms of Ornstein– Uhlenbeck processes (OUPs) with appropriate correlators. For further theoretical studies, these should be approximated to yield a Markovian picture for the dynamics and a simplified steady-state condition. We perform a comparative study of the unified colored noise approximation (UCNA) and the approximation scheme...

Université de Fribourg

Brownian systems with spatially inhomogeneous activity

Sharma, Abhinav ; Brader, Joseph M.

In: Physical Review E, 2017, vol. 96, no. 3, p. 032604

We generalize the Green-Kubo approach, previously applied to bulk systems of spherically symmetric active particles [J. Chem. Phys. 145, 161101 (2016)], to include spatially inhomogeneous activity. The method is applied to predict the spatial dependence of the average orientation per particle and the density. The average orientation is given by an integral over the self part of the Van Hove...

Université de Fribourg

Escape rate of active particles in the effective equilibrium approach

Sharma, Abhinav ; Wittmann, René ; Brader, Joseph M.

In: Physical Review E, 2017, vol. 95, no. 1, p. 012115

The escape rate of a Brownian particle over a potential barrier is accurately described by the Kramers theory. A quantitative theory explicitly taking the activity of Brownian particles into account has been lacking due to the inherently out-of-equilibrium nature of these particles. Using an effective equilibrium approach [Farage et al., Phys. Rev. E 91, 042310 (2015)] we study the escape...

Université de Fribourg

Strain-driven criticality underlies nonlinear mechanics of fibrous networks

Sharma, Abhinav ; Licup, A. J. ; Rens, R. ; Vahabi, M. ; Jansen, K. A. ; Koenderink, G. H. ; MacKintosh, F. C.

In: Physical Review E, 2016, vol. 94, no. 4, p. 042407

Networks with only central force interactions are floppy when their average connectivity is below an isostatic threshold. Although such networks are mechanically unstable, they can become rigid when strained. It was recently shown that the transition from floppy to rigid states as a function of simple shear strain is continuous, with hallmark signatures of criticality [Sharma et al., Nature...

Université de Fribourg

Green-Kubo approach to the average swim speed in active Brownian systems

Sharma, Abhinav ; Brader, Joseph M.

In: The Journal of Chemical Physics, 2016, vol. 145, no. 16, p. 161101