Active transport in a channel: stabilisation by flow or thermodynamics

Chandragiri, Santhan; Doostmohammadi, Amin; Yeomans, J. M.; Thampi, Sumesh P.

doi:10.1039/c8sm02103a

Cited by 39 publications

(40 citation statements)

References 45 publications

(67 reference statements)

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“…A complex interface with a persistent saptio-temporal structure (panel C) is observed for a range of activities beyond the instability. At even higher activities the interface cannot be sustained, as the isotropic phase in the channel becomes unstable, and complex flow states, danc-ing D and active turbulence E, are observed in line with earlier reports 4,48 .…”

Section: Flow States and Interfacial Instabilitysupporting

confidence: 91%

Active nematic–isotropic interfaces in channels

2019

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We use numerical simulations to investigate the hydrodynamic behavior of the interface between nematic (N) and isotropic (I) phases of a confined active liquid crystal. At low activities, a stable interface with constant shape and velocity is observed separating the two phases. For nematics in homeotropic channels, the velocity of the interface at the NI transition increases from zero (i) linearly with the activity for contractile systems and (ii) quadratically for extensile ones. Interestingly, the nematic phase expands for contractile systems while it contracts for extensile ones, as a result of the active forces at the interface. Since both activity and temperature affect the stability of the nematic, for active nematics in the stable regime the temperature can be tuned to observe static interfaces, providing an operational definition for the coexistence of active nematic and isotropic phases. At higher activities, beyond the stable regime, an interfacial instability is observed for extensile nematics. In this regime defects are nucleated at the interface and move away from it. The dynamics of these defects is regular and persists asymptotically for a finite range of activities. We used an improved hybrid model of finite differences and lattice Boltzmann method with multirelaxation-time collision operator, the accuracy of which allowed us to characterize the dynamics of the distinct interfacial regimes.

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Section: Flow States and Interfacial Instabilitysupporting

confidence: 91%

Active nematic–isotropic interfaces in channels

2019

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“…First, we consider the case of a positive flow-aligning parameter in the flow-aligning regime with λ = 0.7 (ν = 1.2). Since most of the numerical studies so far have only focused on extensile activities [16,23,25,30,[58][59][60][61][62], we begin by exploring the effect of contractile activity to shed light on possible different patterns. At low contractile activities, splay instabilities are followed by the unbinding of ±1/2 defect pairs, and active turbulence is established, a process that is consistent with both previous theoretical predictions [17,25] and numerical simulations [63,64].…”

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confidence: 99%

Binding self-propelled topological defects in active turbulence

Thijssen¹,

Doostmohammadi

2020

Phys. Rev. Research

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We report on the emergence of stable self-propelled bound defects in monolayers of active nematics, which form virtual full-integer topological defects in the form of vortices and asters. Through numerical simulations and analytical arguments, we identify the phase space of the bound defect formation in active nematic monolayers. It is shown that an intricate synergy between the nature of active stresses and the flow-aligning behavior of active particles can stabilize the motion of self-propelled positive half-integer defects into specific bound structures. Our findings therefore, uncover conditions for the formation of full integer topological defects in active nematics with the potential for triggering further experiments and theories.

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“…Finally, a logical next step towards predictive modeling of the biomechanical and biophysical aspects of swarming will be to combine agent-based microscopic models as in this paper with mesoscale models for active liquid crystals [32][33][34][35][36] .…”

Section: Discussionmentioning

confidence: 99%

“…Recent numerical and theoretical studies have focused on the collective flows and identified dynamical exponents characterizing the energy spectrum and spatiotemporal features as well as variations near interfaces 24,28 . To explain these features, theoretical models for swarming systems based on adaptations of classical nematic hydrodynamic theories and hydrodynamic multiphase models have been used to characterize the phase-separating active nematic and passive phases and propagation of interfaces of active nematics on substrates [33][34][35][36] . Understanding the role of swarming in enabling bacterial collective motility and rapid propagation is both important and timely; this will require combination of experimental, analytical and computational approaches.…”

Section: Introductionmentioning

confidence: 99%

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Swarming bacterial fronts: Dynamics and morphology of active swarm interfaces propagating through passive frictional domains

Gopinath

Tamayo

Zhang³

et al. 2020

Preprint

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Swarming, a multicellular mode of flagella-based motility observed in many bacteria species, enables coordinated and rapid surface translocation, expansion and colonization. In the swarming state, bacterial films display several characteristics of active matter including intense and persistent long-ranged flocks and strong fluctuating velocity fields with significant vorticity. Additionally, swarm fronts are typically dynamically evolving interfaces. Many of these fronts separate motile active domains from passive frictional regions comprised of dead or non-motile bacteria. Here, we study the dynamics and structural features of a model active-passive interface in swarming Serratia marcescens. We expose localized regions of the swarm to high intensity wide-spectrum light thereby creating large domains of tightly packed immotile bacteria. When the light source is turned off, swarming bacteria outside this passivated region advance into this highly frictional domain and continuously reshape the interphase boundary. Combining results from Particle Image Velocimetry (PIV) and intensity based image analysis, we find that the evolving interface has both a width and a characterizable roughness. Correlations between spatially separated surface fluctuations and damping of the same are influenced by the interaction of the interphase region with adjacently located and emergent collective flows. Dynamical growth exponents characterizing the spatiotemporal features of the surface are extracted and are found to differ from classically expected values for passive growth or erosion. To isolate the effects of hydrodynamic interactions generated by collective flows and that arising from steric interactions, we propose and analyze agent-based simulations with full hydrodynamics of rod-shaped, self-propelled particles. Our computations capture qualitative features of the swarm and predict correlation lengths consistent with experiments. Combining experiments with simulations, we conclude that hydrodynamic and steric interactions enable different modes of surface dynamics, morphology and thus front invasion. like biofilms, however, the motile swarms feature long-range collective motions 7,9,[17][18][19][20][21][22][23][24][25] featuring structures with defined length scales and persistence times.

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Active transport in a channel: stabilisation by flow or thermodynamics

Cited by 39 publications

References 45 publications

Active nematic–isotropic interfaces in channels

Active nematic–isotropic interfaces in channels

Binding self-propelled topological defects in active turbulence

Swarming bacterial fronts: Dynamics and morphology of active swarm interfaces propagating through passive frictional domains

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