Force renormalization for probes immersed in an active bath

Shea, Jeanine; Jung, Gerhard; Schmid, Friederike

doi:10.1039/d3sm01387a

Cited by 5 publications

(9 citation statements)

References 113 publications

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“…We consider a three dimensional system of a passive probe immersed in a bath of ALPs of mass m and radius R, which propel themselves with a constant force F 0 subject to rotational diffusion with a diffusion constant D R [19,[36][37][38][39][40][41][42][43][44]. The ALPs are coupled to a thermal bath with temperature k B T via a Markovian, Langevin thermostat, and they interact with each other and with the immersed probe by repulsive hard core interactions of the Weeks-Chandler-Anderson (WCA) type [45].…”

Section: Model and Simulation Detailsmentioning

confidence: 99%

“…Specifically, we follow references [19,37,39,44] and set the rotational inertia of ALPs to zero for simplicity. The equations of motion for an ALP, n, in the bath, are thus given by…”

Section: Model and Simulation Detailsmentioning

confidence: 99%

“…In the following, for consistency with previous work [19,44], we will often also use dimensionless quantities…”

Section: Model and Simulation Detailsmentioning

confidence: 99%

“…The memory kernel K(t) is determined from the VACF by Volterra inversion, as suggested by the Mori-Zwanzig projection operator formalism [53,[60][61][62][63][64]. We emphasize that the GLE is a coarse-grained model equation, not the true dynamical equation of motion for the probe in the explicit active fluid [19,44].…”

Section: Vacf and Memory Kernelmentioning

confidence: 99%

“…We examine the angle-dependent density distribution ρ(r) of ALPs around the probe in a comoving and corotating frame with origin at the probe center, R(t), and z axis always aligned in the direction of the instantaneous probe velocity V(t). This method has already been used to study the properties of an ALP fluid surrounding a probe of radius R p = 3.0σ in [44].…”

Section: Properties In the Probe Vicinitymentioning

confidence: 99%

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How boundary interactions dominate emergent driving of inertial passive probes in active matter

Shea,

Jung,

Schmid

2024

J. Phys. A: Math. Theor.

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Colloidal probes immersed in an active bath have been found to behave like active particles themselves. Here, we use coarse-grained simulations to investigate the mechanisms behind this behavior. We find that the active motion of the colloid cannot be simply attributed to the convective motion in the bath. Instead, the boundary of the probe contributes significantly to these adopted dynamics by causing active bath particles to spontaneously accumulate at the probe. This gathering of active bath particles then pushes the probe, thus promoting its emergent active-particle-like behavior. Furthermore, we find that the dynamic properties of the probe depend on its size in a non-monotonic way, which further highlights the non-trivial interplay between probe and bath.

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Section: Model and Simulation Detailsmentioning

confidence: 99%

“…Specifically, we follow references [19,37,39,44] and set the rotational inertia of ALPs to zero for simplicity. The equations of motion for an ALP, n, in the bath, are thus given by…”

Section: Model and Simulation Detailsmentioning

confidence: 99%

“…In the following, for consistency with previous work [19,44], we will often also use dimensionless quantities…”

Section: Model and Simulation Detailsmentioning

confidence: 99%

Section: Vacf and Memory Kernelmentioning

confidence: 99%

Section: Properties In the Probe Vicinitymentioning

confidence: 99%

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How boundary interactions dominate emergent driving of inertial passive probes in active matter

Shea,

Jung,

Schmid

2024

J. Phys. A: Math. Theor.

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How to define temperature in active systems?

Hecht,

Caprini,

Löwen

et al. 2024

The Journal of Chemical Physics

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We are used to measuring temperature with a thermometer, and we know from everyday life that different types of thermometers measure the same temperature. This experience can be based on equilibrium thermodynamics, which explains the equivalence of different possibilities to define temperature. In contrast, for systems out of equilibrium such as active matter, measurements performed with different thermometers can generally lead to different temperature values. In the present work, we systematically compare different possibilities to define temperature for active systems. Based on simulations and theory for inertial active Brownian particles, we find that different temperatures generally lead to different temperature values, as expected. Remarkably, however, we find that different temperatures not only lead to the same values near equilibrium (low Péclet number or high particle mass) but also even far from equilibrium, several different temperatures approximately coincide. In particular, we find that the kinetic temperature, the configurational temperature, and temperatures based on higher moments of the velocity distribution constitute a class of temperatures that all assume very similar values over a wide parameter range. Notably, the effective temperature and temperatures exploiting the virial theorem, the Stokes–Einstein relation, or a harmonic confinement form a second class of temperatures whose values approximately coincide with each other but which strongly differ from those of the first class. Finally, we identify advantages and disadvantages of the different possibilities to define temperature and discuss their relevance for measuring the temperature of active systems.

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Memory effects in colloidal motion under confinement and driving

Straube,

Höfling

2024

J. Phys. A: Math. Theor.

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The transport of individual particles in inhomogeneous environments is complex and exhibits non-Markovian responses. The latter may be quantified by a memory function within the framework of the linear generalised Langevin equation (GLE). Here, we exemplify the implications of steady driving on the memory function of a colloidal model system for Brownian motion in a corrugated potential landscape, specifically, for one-dimensional motion in a sinusoidal potential. To this end, we consider the overdamped limit of the GLE, which is facilitated by separating the memory function into a singular (Markovian) and a regular (non-Markovian) part. Relying on exact solutions for the investigated model, we show that the random force entering the GLE must display a bias far from equilibrium, which corroborates a recent general prediction. Based on data for the mean-square displacement (MSD) obtained from Brownian dynamics simulations, we estimate the memory function for different driving strengths and show that already moderate driving accelerates the decay of the memory function by several orders of magnitude in time. We find that the memory may persist on much longer timescales than expected from the convergence of the MSD to its long-time asymptote. Furthermore, the functional form of the memory function changes from a monotonic decay to a non-monotonic, damped oscillatory behaviour, which can be understood from a competition of confined motion and depinning. Our analysis of the simulation data further reveals a pronounced non-Gaussianity, which questions the Gaussian approximation of the random force entering the GLE.

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Force renormalization for probes immersed in an active bath

Abstract: Modelling the dynamics of a passive particle suspended in an active fluid by a generalized Langevin description, we find that dynamical consistency not only requires renormalization of the effective temperature, but also of the effective force.

Cited by 5 publications

References 113 publications

How boundary interactions dominate emergent driving of inertial passive probes in active matter

How boundary interactions dominate emergent driving of inertial passive probes in active matter

How to define temperature in active systems?

Memory effects in colloidal motion under confinement and driving

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