Scale-dependent colocalization in a population of gyrotactic swimmers

Borgnino, Matteo; Lillo, F. De; Boffetta, G.

doi:10.1103/physreve.95.023108

Cited by 3 publications

(11 citation statements)

References 32 publications

(59 reference statements)

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“…A similar argument can be done for swimmers with the same stability parameter and different swimming velocities where one finds R * ηΨ∆Φ [92]. For R < R * the separation dynamics is dominated by the parameter mismatch and one expect poor correlation between the swimmers, i.e.…”

Section: Clustering Of Polydisperse Populationssupporting

confidence: 52%

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Gyrotactic phytoplankton in laminar and turbulent flows: A dynamical systems approach

et al. 2019

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Gyrotactic algae are bottom heavy, motile cells whose swimming direction is determined by a balance between a buoyancy torque directing them upwards and fluid velocity gradients. Gyrotaxis has, in recent years, become a paradigmatic model for phytoplankton motility in flows. The essential attractiveness of this peculiar form of motility is the availability of a mechanistic description which, despite its simplicity, revealed predictive, rich in phenomenology, easily complemented to include the effects of shape, feed-back on the fluid and stochasticity (e.g. in cell orientation). In this review we consider recent theoretical, numerical and experimental results to discuss how, depending on flow properties, gyrotaxis can produce inhomogeneous phytoplankton distributions on a wide range of scales, from millimeters to kilometers, in both laminar and turbulent flows. In particular, we focus on the phenomenon of gyrotactic trapping in nonlinear shear flows and in fractal clustering in turbulent flows. We shall demonstrate the usefulness of ideas and tools borrowed from dynamical systems theory in explaining and interpreting these phenomena.

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Section: Clustering Of Polydisperse Populationssupporting

confidence: 52%

“…below the Kolmogorov length η, the velocity field is smooth and we can write ∆u(R) ∼ u η (R/η). Thus from the balance of the two terms in the above equation a characteristic scale emerges [92]:…”

Section: Clustering Of Polydisperse Populationsmentioning

confidence: 99%

Gyrotactic phytoplankton in laminar and turbulent flows: A dynamical systems approach

et al. 2019

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“…Additionally, the condition v eff < v max defines a region in the {v s , α} parameter space for which swimmers are trapped. For the Lamb-Oseen vortex we numerically obtain v max ≈ 0.726 as the maximum of (16). Hence, by taking into account the role of shape, microswimmers with much lower swimming velocity v s than the maximum fluid velocity u 0 can escape the vortex.…”

Section: Fixed-point Analysismentioning

confidence: 79%

“…To elucidate this, we begin by considering spherical swimmers (α = 0). It is well known that, in general, equations for spherical swimmers following (1) and (2) conserve phasespace volume [11,16,21] ∇ x ·ẋ + ∇p ·ṗ = 0.…”

Section: Distributionsmentioning

confidence: 99%

“…in the context of phytoplankton in the ocean [1] or artificial swimmers in the laboratory [2], the investigation of microswimmers in complex flows has gained considerable momentum over the past years. In such flows, inertial effects [3][4][5][6][7], gyrotactic swimming [8][9][10][11][12][13][14][15][16][17][18][19], fluid-cell [20,21] and cell-cell interaction [22,23], and active motility and morphological changes [24,25] can give rise to complex swimmer spatial distributions and enable migration strategies.…”

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confidence: 99%

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Microswimmers in an axisymmetric vortex flow

Arguedas-Leiva

Wilczek

2020

New J. Phys.

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Microswimmers are encountered in a wide variety of biophysical settings. When interacting with flow fields, they show interesting dynamical features such as hydrodynamical trapping, clustering, and preferential orientation. One important step towards the understanding of such features is to clarify the interplay of hydrodynamic flow with microswimmer motility and shape. Here, we study the dynamics of ellipsoidal microswimmers in a two-dimensional axisymmetric vortex flow. Despite this simple setting, we find surprisingly rich dynamics, which can be comprehensively characterized in the framework of dynamical systems theory. By classifying the fixed point structure of the underlying phase space as a function of motility and swimmer shape, we uncover the topology of the phase space and determine the conditions under which swimmers are trapped in the vortex. For spherical swimmers, we identify Hamiltonian dynamics, which are broken for swimmers of a different shape. We find that prolate ellipsoidal shaped microswimmers tend to align parallel to the velocity field, while oblate microswimmers tend to remain perpendicular to it. Additionally, we find that rotational noise allows microswimmers to escape the vortex with an enhanced escape rate close to the system's saddle point. Our results clarify the role of shape and motility on the occurrence of preferential concentration and clustering and provide a starting point to understand the dynamics in more complex flows.

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Physical modeling of motile and sedimenting plankton: from simple flows to turbulence

Leiva¹

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Planktonic microorganisms play a fundamental role in oceanic ecology and chemical cycles. Different planktonic species are found at various levels of the oceanic trophic chain, ranging from photosynthetic organisms to grazing species higher in the food chain. Many planktonic species have developed migration strategies to aid their survival. This includes motility and density regulation. Physical aspects, such as transport and collision rates, have a direct impact on planktonic survival and are influenced by the planktonic migration strategies. Furthermore, collision rates between planktonic organisms also play an important role in the formation of macroscopic plankton blooms. These have a direct effect on the ecology of oceans and lakes. In this dissertation we use physical modeling to study motile and sedimenting microorganisms in a fluid flow. We aim at shedding light on the key features of microorganism dynamics in fluid flows as a function of their key parameters: shape, motility, and density offset.In chapter 1 we introduce the biological setting of plankton, and give a very brief overview of the physical modeling approaches for plankton in fluid flows. Subsequently in chapter 2 we introduce the theoretical framework of turbulence and the methodology of our numerical simulations.In chapter 3 we start by examining microswimmers in a simple two-dimensional toy-model. We use methods from dynamical systems theory to uncover the role played by shape and motility in determining the microorganism dynamics in this simple setting. We explicitly identify the Hamiltonian dynamics followed by spherical microswimmers. Additionally, we find that elongated microswimmers more easily escape simple vortex structures than other shapes. In chapter 4 we then move on to ellipsoidal microswimmers in realistic mild turbulent flows. We analyze transport and rotation rates of motile ellipsoids. We find that elongated microswimmers have an advantage in transport, which is in part due to shape-dependent rotation rates. We also investigated the collision rates of motile spheres, and we were able to extract a master curve interpolating between the passive and motile limits for different sized spheres. We quantified the effect of motility and found that even very small motility greatly enhances collision rates.In chapter 5 we study of sedimentation of elongated microorganisms in mild turbulence. We measure the collision rates of elongated microorganisms in terms of size, energy dissipation rate, and aspect ratio. We then find a master curve interpolating between a passive particle and a sedimentation dominated limit. We characterize the role played by shape, which increases collision rates of elongated microorganisms in comparison with equal-volume spheres. This shape-induced enhancement helps to explain the timescales for formation of blooms of elongated planktonic species. In summary, in this dissertation we study the effect of shape, motility, and density regulation on physical models of planktonic microorganisms. Our findings help to ...

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Scale-dependent colocalization in a population of gyrotactic swimmers

Cited by 3 publications

References 32 publications

Gyrotactic phytoplankton in laminar and turbulent flows: A dynamical systems approach

Gyrotactic phytoplankton in laminar and turbulent flows: A dynamical systems approach

Microswimmers in an axisymmetric vortex flow

Physical modeling of motile and sedimenting plankton: from simple flows to turbulence

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