Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session H25: Biofluids: Biflagellates and Synchronization |
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Chair: Kyriacos Leptos, University of Cambridge Room: 304 |
Monday, November 23, 2015 10:35AM - 10:48AM |
H25.00001: High-fidelity phototaxis in biflagellate algae Kyriacos Leptos, Maurizio Chioccioli, Silvano Furlan, Adriana Pesci, Raymond Goldstein The single-cell alga {\it Chlamydomonas reinhardtii} is a motile biflagellate that can swim towards light for its photosynthetic requirements, a behavior referred to as phototaxis. The cell responds upon light stimulation through its rudimentary eye -- the eyespot -- by changing the beating amplitude of its two flagella accordingly -- a process called the photoresponse. All this occurs in a coordinated fashion as {\it Chlamydomonas} spins about its body axis while swimming, thus experiencing oscillating intensities of light. We use high-speed video microscopy to measure the flagellar dynamics of the photoresponse on immobilized cells and interpret the results with a mathematical model of adaptation similar to that used previously for {\it Volvox}. These results are incorporated into a model of phototactic steering to yield trajectories that are compared to those obtained by three-dimensional tracking. Implications of these results for the evolution of multicellularity in the Volvocales are discussed. [Preview Abstract] |
Monday, November 23, 2015 10:48AM - 11:01AM |
H25.00002: Synchronization of Eukaryotic Flagella with an Imposed Periodic Flow Greta Quaranta, Marie-Eve Aubin-Tam, Daniel Tam The eukaryotic cilia and flagella are subcellular structures able to beat in synchrony for long periods of time. Recent studies have characterized the dynamics of flagellar locomotion and have focused on the physical mechanisms driving synchronous beating and especially on the importance of hydrodynamic interactions. We explored the possibility to control the beating of the two flagella of a single \textit{C. reinhardtii} cell by imposing an external periodic hydrodynamic force. We do so by generating an oscillatory background flow around a single cell. Our study shows that flagellar beating can be phase locked to an external hydrodynamic forcing of non-biological origin and the synchronization transition is well represented by a low-order stochastic model. Remarkably, the hydrodynamic forces needed to synchronize the flagella and the background flow are considerably larger than the forces typically experienced in physiological conditions. Our results suggest that the importance of hydrodynamics in flagellar synchronization may be limited. [Preview Abstract] |
Monday, November 23, 2015 11:01AM - 11:14AM |
H25.00003: Quiet swimming at low Reynolds number Anders Andersen, Navish Wadhwa, Thomas Kiorboe Planktonic organisms that inhabit the water masses of the oceans are faced with a dilemma: They need to swim to find food and mates, but by swimming they inevitably create flow disturbances that attract predators. We discuss that planktonic swimmers can reduce the flow disturbances due to their swimming, simply by appropriately arranging their propulsion apparatus. Motivated by recent experiments, we demonstrate that a three-Stokeslet model of a breast stroke swimmer is an example of a quiet swimmer. We show that the flow disturbances around the organism in both the near field and the far field are small in comparison with simple pullers and pushers, and we find that the far field power laws are valid surprisingly close to the organism. Breast stroke swimming may thus be advantageous, and this might explain why it is very common in the world of the plankton. [Preview Abstract] |
Monday, November 23, 2015 11:14AM - 11:27AM |
H25.00004: Feeding and swimming of flagellates Julia Doelger, Lasse Tor Nielsen, Thomas Kiorboe, Tomas Bohr, Anders Andersen Hydrodynamics plays a dominant role for small planktonic flagellates and shapes their survival strategies. The high diversity of beat patterns and arrangements of appendages indicates different strategies balancing the trade-offs between the general goals, i.e., energy-efficient swimming, feeding, and predator avoidance. One type of flagellated algae that we observe, are haptophytes, which possess two flagella for flow creation and one so-called haptonema, a long, rigid structure fixed on the cell body, which is used for prey capture. We present videos and flow fields obtained using velocimetry methods around freely swimming haptophytes and other flagellates, which we compare to analytical results obtained from point force models. The observed and modelled flows are used to analyse how different morphologies and beat patterns relate to different feeding or swimming strategies, such as the capture mechanism in haptophytes. [Preview Abstract] |
Monday, November 23, 2015 11:27AM - 11:40AM |
H25.00005: Fluid transport by an unsteady microswimmer Peter Mueller, Jean-Luc Thiffeault We study the drift caused by the microscopic algae \emph{Chlamydomonas reinhardtii}, which swims by rapidly beating two frontal flagella. Previous studies of transport by microswimmers have neglected the ubiquitous time-dependence of their swimming. We model the organism by a time-dependent dumbbell consisting of a solid body and a regularized Stokeslet. We then analyze individual particle paths and their displacements in a region around the swimmer. Of particular interest are particles near the swimmer, which have complex trajectories due to the unsteady model. Particles directly in front of the swimmer contribute large, but rare, displacements. We use this to determine the tails of the distribution of particle displacements. Finally we compare the effective diffusivity of varying particle sizes to gauge the importance of time-dependence on overall fluid transport and mixing. [Preview Abstract] |
Monday, November 23, 2015 11:40AM - 11:53AM |
H25.00006: Propulsion of micro-structures in Oscillatory Stokes Flow Ikhee Jo, Yangyang Huang, Walter Zimmerman, Eva Kanso Drug delivery often necessitates specific site-targeting within the human body. The use of micro and/or nano devices swimming through the bloodstream provides an attractive mechanism for targeted drug targeting, however the design and practical implementation of such devices remain very challenging. Inspired by flapping wings, we construct a two-dimensional wedge-like device, consisting of two links connected by a linear torsional spring and released in an oscillatory Stokes flow. We vary the stiffness and rest angle of the linear spring and the oscillation amplitude and frequency of the background flow to explore the behavior of the device. We find that the device achieves a net displacement, or propulsion, in oscillatory flows even when no elastic energy is stored initially, thus breaking Purcell’s scallop's theorem. More importantly, the vehicle tends to align with the background flow under perturbations. We conclude by commenting on how to control the parameters of the device and the fluid to achieve desired behavior of the device. These findings may have significant implications on the design of micro devices in viscous fluids. [Preview Abstract] |
Monday, November 23, 2015 11:53AM - 12:06PM |
H25.00007: Narrower bottlenecks could be more efficient for concentrating choanoflagellates G. Mi\~no, J. Sparacino, M.A.R. Koehl, N. King, R. Stocker, A.J. Banchio, V.I. Marconi In evolutionary biology choanoflagellates are broadly investigated as the closest living relatives of the animal ancestors. Under diverse environmental cues, choanoflagellate \textit{Salpingoeca rosetta} can differentiate in two types of solitary swimming cells: slow and fast microswimmers. Here we present a first phenomenological 2D--model for the choanoflagellates dynamics confined into a flat device divided by a wall of asymmetric microconstrictions. The model allow us to optimize the geometry of the microchannels for directing and concentrating cell populations under strict control. We solve our set of dynamical equations using Langevin dynamics. Experimental parameters for the motility of the slow and fast cells were measured and used for our numerical estimations of the directed transport efficiency, otherwise we have no adjustable parameters. We find remarkable differences in the rectification results for slow and fast choanoflagellates, which give us a strategy to develop a suitable microfluidic sorting device. For a given population velocity, narrower bottlenecks, of similar size to the cell dimension, show to be more efficient as concentrator of populations. Experiments and simulations are in good agreement. [Preview Abstract] |
Monday, November 23, 2015 12:06PM - 12:19PM |
H25.00008: Data-driven, low-order modeling of interflagella synchronization Jonathan H. Tu, Murat Arcak, Michel M. Maharbiz Synchrony is a common feature in the locomotive strategies employed by microswimmers. At the level of individual organisms, it can manifest as flagellar bundling or metachronal coordination of cilia. In large populations of microswimmers, interorganism coordination can result in collective behavior. This study focuses on the hydrodynamic interactions between two nearby flagella, looking to develop low-order models that accurately capture the dynamics of flagellar synchronization. Rather than build up a model based on simplified geometries and asymptotic expansions, we take a data-driven, top-down approach. For a single, isolated flagellum, our low-order model exactly reproduces the dynamics of a high-fidelity simulation of the full equations of motion. To extend the model to two flagella, we use insight gleaned from high-fidelity simulations, along with symmetry arguments, to eliminate terms in the equations of motion that are unrelated to synchronization effects. The resulting model accurately predicts synchronization rates at a greatly reduced computational cost. In future work, we hope to extend this approach to model larger numbers of interacting flagella, for which high-fidelity simulations become impractical. [Preview Abstract] |
Monday, November 23, 2015 12:19PM - 12:32PM |
H25.00009: Hydrodynamic interactions of cilia on a spherical body Babak Nasouri, Gwynn J. Elfring The emergence of metachronal waves in ciliated microorganisms can arise solely from the hydrodynamic interactions between the cilia. For a chain of cilia attached to a flat ciliate, it was observed that fluid forces can lead the system to form a metachronal wave. However, several microorganisms such as paramecium and volvox possess a curved shaped ciliate body. To understand the effect of this geometry on the formation of metachronal waves, we evaluate the hydrodynamic interactions of cilia near a large spherical body. Using a minimal model, we show that for a chain of cilia around the sphere, the embedded periodicity in the geometry leads the system to synchronize. We also report an emergent wave-like behavior when an asymmetry is introduced to the system. [Preview Abstract] |
Monday, November 23, 2015 12:32PM - 12:45PM |
H25.00010: Integration of hydrodynamic interactions between filaments Yi Man, Eric Lauga In many biological situations, slender filaments interact through a viscous fluid, and these hydrodynamic interactions play a crucial cellular role. Examples include the ability of peritrichous bacteria to bundle their flagella or the generation of metachronal waves in cilia arrays. In most cases of interest, three distinct length scales characterize the filaments, their typical thickness $a$, relative distance $h$, and length $L$, which are asymptotically separated as $a\ll h \ll L$. In this talk, we demonstrate how to analytically develop a long-wavelength integration of hydrodynamic singularities in this biologically-relevant limit. [Preview Abstract] |
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