Motion of two micro-wedges in a turbulent bacterial bath

Kaiser, Andreas; Sokolov, Andrey; Aranson, Igor S.; Löwen, Hartmut

doi:10.1140/epjst/e2015-02459-x

Cited by 28 publications

(24 citation statements)

References 83 publications

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“…there is no equation of state for self-propelled rods Another consequence is the nontrivial influence of boundary conditions or spatial inhomogeneities (disordered environments) on the macroscopic emergent patterns. The tendency of rods to form clusters and accumulate at walls enables the construction of traps [75,79] use them to propel micro-gears [80,81]. The self-propelled rod concept has been extended in several regards:…”

Section: B Emergent Patterns In Ensembles Of Dry Self-propelled Rodsmentioning

confidence: 99%

Self-Propelled Rods: Insights and Perspectives for Active Matter

Bär

Großmann

Heidenreich

et al. 2020

Annu. Rev. Condens. Matter Phys.

255

182

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A wide range of experimental systems including gliding, swarming and swimming bacteria, in-vitro motility assays as well as shaken granular media are commonly described as self-propelled rods. Large ensembles of those entities display a large variety of self-organized, collective phenomena, including formation of moving polar clusters, polar and nematic dynamic bands, mobility-induced phase separation, topological defects and mesoscale turbulence, among others. Here, we give a brief survey of experimental observations and review the theoretical description of selfpropelled rods. Our focus is on the emergent pattern formation of ensembles of dry self-propelled rods governed by short-ranged, contact mediated interactions and their wet counterparts that are also subject to long-ranged hydrodynamic flows. Altogether, self-propelled rods provide an overarching theme covering many aspects of active matter containing well-explored limiting cases. Their collective behavior not only bridges the well-studied regimes of polar self-propelled particles and active nematics, and includes active phase separation, but also reveals a rich variety of new patterns. arXiv:1907.00360v1 [cond-mat.stat-mech]

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Section: B Emergent Patterns In Ensembles Of Dry Self-propelled Rodsmentioning

confidence: 99%

Self-Propelled Rods: Insights and Perspectives for Active Matter

Bär

Großmann

Heidenreich

et al. 2020

Annu. Rev. Condens. Matter Phys.

255

182

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“…They have attracted much attention [2,3] due to a host of interesting physical phenomena [4][5][6][7][8][9], their relevance to many biological systems [10][11][12][13], and their potential use for self-assembly applications [14]. They have also been suggested as tools for novel engineering applications -for example, active fluids have been used to power microscopic gears [15][16][17][18][19][20][21]. This results from the fact that, when an asymmetric body is immersed in a fluid with broken time-reversal symmetry, it experiences a net force [22][23][24] which is coupled to the generation of ratchet-like currents [25,26].…”

mentioning

confidence: 99%

Generic Long-Range Interactions Between Passive Bodies in an Active Fluid

Baek

Solon

et al. 2018

Phys. Rev. Lett.

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Because active particles break time-reversal symmetry, a single non-spherical body placed in an active fluid generates currents. We show that when two or more passive bodies are placed in an active fluid these currents lead to long-range interactions. Using a multipole expansion we characterize their leading-order behaviors in terms of single-body properties and show that they decay as a power law with the distance between the bodies, are anisotropic, and do not obey an action-reaction principle. The interactions lead to rich dynamics of the bodies, illustrated by the spontaneous synchronized rotation of pinned non-chiral bodies and the formation of traveling bound pairs. The occurrence of these phenomena depends on tunable properties of the bodies, thus opening new possibilities for self-assembly mediated by active fluids.Active matter is a class of nonequilibrium systems in which energy is converted into systematic motion on a microscopic scale [1]. They have attracted much attention [2,3] due to a host of interesting physical phenomena [4][5][6][7][8][9], their relevance to many biological systems [10][11][12][13], and their potential use for self-assembly applications [14]. They have also been suggested as tools for novel engineering applications -for example, active fluids have been used to power microscopic gears [15][16][17][18][19][20][21]. This results from the fact that, when an asymmetric body is immersed in a fluid with broken time-reversal symmetry, it experiences a net force [22][23][24] which is coupled to the generation of ratchet-like currents [25,26].In this Letter we study passive bodies immersed in an active fluid. We show that the ratchet-like currents generated by each body give rise to forces and torques which decay as a power law with distance, are anisotropic, and do not obey an action-reaction principle. Using a multipole expansion, the leading-order behavior of the interactions can be expressed in terms of single-body quantities that can be measured independently in experiments or numerical simulations. Moreover, by designing the two bodies one can control the amplitude and polarity of the interactions between them. This leads to a host of interesting dynamical phenomena of which we illustrate two: the spontaneous synchronized rotations of pinned rotors and the formation of traveling bound pairs. Our results suggest a new method for self-assembly by embedding passive bodies in an active fluid.We stress that the interactions studied here exist even between non-moving bodies and are therefore distinct from usual hydrodynamic interactions [27]. They are also different from thermal Casimir interactions [28,29], because they do not rely on correlations between the fluid particles and are present even in a dilute active fluid.Model. -We base our study on a common model of an active fluid consisting of N point-like particles, which * y.baek@damtp.cam.ac.uk do not interact among themselves and self-propel at a constant speed v in two dimensions. The position r i and the orientation θ i of acti...

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“…Still, it represents the moving passive particles driven by the (tangential) external force defined in Eq. (75). The latter is the main source of the fluid flows induced by particles of species B.…”

Section: Shear Cellmentioning

confidence: 99%

Multi-species dynamical density functional theory for microswimmers: Derivation, orientational ordering, trapping potentials, and shear cells

Hoell

Löwen

Menzel

2019

The Journal of Chemical Physics

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Microswimmers typically operate in complex environments. In biological systems, often diverse species are simultaneously present and interact with each other. Here, we derive a (time-dependent) particle-scale statistical description, namely a dynamical density functional theory, for such multi-species systems, extending existing works on one-component microswimmer suspensions. In particular, our theory incorporates the effect of external potentials, but also steric and hydrodynamic interactions between swimmers. For the latter, a previously introduced force-dipole-based minimal (pusher or puller) microswimmer model is used. As a limiting case of our theory, mixtures of hydrodynamically interacting active and passive particles are captured as well. After deriving the theory, we apply it to different planar swimmer configurations. First, these are binary pusher-puller mixtures in external traps. In the considered situations, we find that the majority species imposes its behavior on the minority species. Second, for unconfined binary pusher-puller mixtures, the linear stability of an orientationally disordered state against the emergence of global polar orientational order (and thus emergent collective motion) is tested analytically. Our statistical approach predicts, qualitatively in line with previous particle-based computer simulations, a threshold for the fraction of pullers and for their propulsion strength that lets overall collective motion arise. Third, we let driven passive colloidal particles form the boundaries of a shear cell, with confined active microswimmers on their inside. Driving the passive particles then effectively imposes shear flows, which persistently acts on the inside microswimmers. Their resulting behavior reminds of the one of circle swimmers, though with varying swimming radii. arXiv:1904.07277v2 [cond-mat.soft]

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Motion of two micro-wedges in a turbulent bacterial bath

Cited by 28 publications

References 83 publications

Self-Propelled Rods: Insights and Perspectives for Active Matter

Self-Propelled Rods: Insights and Perspectives for Active Matter

Generic Long-Range Interactions Between Passive Bodies in an Active Fluid

Multi-species dynamical density functional theory for microswimmers: Derivation, orientational ordering, trapping potentials, and shear cells

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