Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session A9: Biofluids: Ciliary Flows |
Hide Abstracts |
Chair: Javier Urzay, Stanford University Room: 3014/3016 |
Sunday, November 23, 2014 8:00AM - 8:13AM |
A9.00001: Asynchronous beating of cilia enhances particle capture rate Yang Ding, Eva Kanso Many aquatic micro-organisms use beating cilia to generate feeding currents and capture particles in surrounding fluids. One of the capture strategies is to ``catch up'' with particles when a cilium is beating towards the overall flow direction (effective stroke) and intercept particles on the downstream side of the cilium. Here, we developed a 3D computational model of a cilia band with prescribed motion in a viscous fluid and calculated the trajectories of the particles with different sizes in the fluid. We found an optimal particle diameter that maximizes the capture rate. The flow field and particle motion indicate that the low capture rate of smaller particles is due to the laminar flow in the neighbor of the cilia, whereas larger particles have to move above the cilia tips to get advected downstream which decreases their capture rate. We then analyzed the effect of beating coordination between neighboring cilia on the capture rate. Interestingly, we found that asynchrony of the beating of the cilia can enhance the relative motion between a cilium and the particles near it and hence increase the capture rate. [Preview Abstract] |
Sunday, November 23, 2014 8:13AM - 8:26AM |
A9.00002: Mixing it up: Corals take an active role in mass transport Vicente Fernandez, Orr Shapiro, Douglas Brumley, Melissa Garren, Jeffrey Guasto, Esti Kramarski-Winter, Assaf Vardi, Roman Stocker The growth and health of reef-building corals are limited by corals' ability to exchange nutrients and oxygen with the surrounding, sometimes quiescent, seawater. Mass transport in coral systems has long been considered to occur passively as a result of molecular diffusion and the ambient fluid flow over the coral. Through a combination of microscale visualization experiments and numerical modeling, we demonstrate instead that motile cilia densely covering the coral surface -- previously thought to serve cleaning and feeding purposes-- actively stir the coral boundary layer by generating persistent vortices above the coral surface. This active mixing was observed over a variety of corals with differing surface geometries. We have quantified the contribution of ciliary surface vortices to mass transport, finding oxygen flux enhancements of 2 to 3 orders of magnitude under environmentally relevant ambient flow conditions. These results reveal a new, active role of the coral animal in regulating its mass transport by engineering its local hydrodynamic environment, an ability that may have an important role in the evolutionary success of reef corals. [Preview Abstract] |
Sunday, November 23, 2014 8:26AM - 8:39AM |
A9.00003: How a bacterial pathogen swims in the storm stirred up by its coral host Douglas Brumley, Melissa Garren, Vicente Fernandez, Roman Stocker One important cause of the worldwide demise of coral reefs is the infection of corals by pathogenic bacteria. These bacteria are always motile, yet how they land on the coral surface remains unclear. In particular, the recently discovered vortical flows produced by the coral with its epidermal cilia create a hostile hydrodynamic environment for motility and the pursuit of chemical cues. We used high-speed imaging coupled with dual-wavelength epifluorescent microscopy to track individual Vibrio coralliilyticus bacteria - known for causing coral disease - in the immediate vicinity of its host, the coral Pocillopora damicornis. By simultaneously determining the fluid velocity and bacterial trajectories, we quantified the ability of the bacteria to target the coral surface. We show that the cilia-driven flows considerably but not entirely disrupt bacterial navigation towards the coral, as a result of (i) the stirring of the chemical cues guiding the cells and (ii) the shear-induced alignment of bacteria within the flow. By enabling the direct visualization of microbial motility in ciliary flows, this system can not only provide insights into coral disease, but also serve as a model system for bacterial disease in other ciliated environments, including the human respiratory system. [Preview Abstract] |
Sunday, November 23, 2014 8:39AM - 8:52AM |
A9.00004: Cilia beating patterns are not hydrodynamically optimal Hanliang Guo, Janna Nawroth, Yang Ding, Eva Kanso We examine the hydrodynamic performance of two cilia beating patterns reconstructed from experimental data. In their respective natural systems, the two beating patterns correspond to: (A) pumping-specialized cilia, and (B) swimming-specialized cilia. We compare the performance of these two cilia beating patterns as a function of the metachronal coordination in the context of two model systems: the swimming of a ciliated cylinder and the fluid pumping by a ciliated carpet. Three performance measures are used for this comparison: (i) average swimming speed/pumping flow rate; (ii) maximum internal moments generated by the cilia; and (iii) swimming/pumping efficiencies. We found that, in both models, pattern (B) outperforms pattern (A) in almost all three measures, including hydrodynamic efficiency. These results challenge the notion that hydrodynamic efficiency dictates the cilia beating kinematics, and suggest that other biological functions and constraints play a role in explaining the wide variety of cilia beating patterns observed in biological systems. [Preview Abstract] |
Sunday, November 23, 2014 8:52AM - 9:05AM |
A9.00005: Hydrodynamic interactions of bacteria and particles with ciliated surfaces Janna Nawroth, John Dabiri Cilia are microscopic, hair-like structures on the surface of cells that enable animals to interact with bacteria and fluid boundary layers. Here we present experimental data showing that, in addition to transporting fluids and particles along the surface, the coordinated movement of cilia ensembles generates 3-dimensional, rotational flow fields extending far beyond the length scale of individual cilia. Further, our results suggest that combining such vortices with adhesive stagnation zones creates particle traps that can be tuned to preferentially retaining particles with particular surface properties, and size, on the ciliated surface. [Preview Abstract] |
Sunday, November 23, 2014 9:05AM - 9:18AM |
A9.00006: The effects of translation and rotation on flagellar synchronization Jonathan H. Tu, Murat Arcak, Michel Maharbiz Synchrony is often observed in studies of swimming microorganisms. Examples include collective behavior in large populations of microswimmers, metachronal waves passing through arrays of cilia, and flagellar bundling. In this work, we focus on the hydrodynamic interactions that occur between flagella in close proximity. Specifically, we use the method of regularized Stokeslets to numerically investigate the precise mechanisms through which phase synchrony occurs in a pair of side-by-side rigid helices. Because our ``end-pinned'' model enforces restoring forces at a single end of each helix, we are able to isolate and compare the respective effects of translational and rotational motions. We find that while certain degrees of freedom promote synchrony, others promote anti-synchrony or have little effect. [Preview Abstract] |
Sunday, November 23, 2014 9:18AM - 9:31AM |
A9.00007: Squirmers with swirl: a model for \textit{Volvox} swimming Timothy Pedley, Douglas Brumley, Takuji Ishikawa A \textit{Volvox }colony takes the form of a perfect sphere that swims because each cell on its surface has a pair of beating flagella. The flagella of the different cells are coordinated, almost certainly hydrodynamically [1], to beat approximately in a meridional plane, with axis of symmetry in the swimming direction, but with a roughly 10 degree azimuthal offset which means that the colonies rotate about their axes as they swim. Experiments on colonies held stationary on a micropipette show that the beating pattern takes the form of a symplectic metachronal wave [1]. Here we extend the Lighthill/Blake axisymmetric, Stokes-flow model of a free-swimming spherical squirmer to include azimuthal swirl. The kinematics of the metachronal wave are used to calculate the coefficients in the eigenfunction expansion and hence calculate the swimming speed and rotation rate (proportional to the square of the beating amplitude); measuring these provides a simple means of assessment of the flagellar beating parameters of individual colonies. Extension of the model to include colony interactions, with each other and a plane boundary, leads to simulations of Volvox ``dancing'': the observed bound states of ref [2]. \\[4pt] [1] D.R. Brumley et al, Phys. Rev. Lett., 109:268102,2012\\[0pt] [2] K. Drescher et al, Phys. Rev. Lett., 102:168101,2009 [Preview Abstract] |
Sunday, November 23, 2014 9:31AM - 9:44AM |
A9.00008: Buckling and relaxation of an elastic filament in a viscous fluid under compression Moumita Dasgupta, Julien Chopin, Arshad Kudrolli We discuss an experimental investigation of buckling of an elastic filament in a viscous fluid under compressive loading in which an interplay of elastic and viscous forces are important to the structure observed dynamically. Buckling of an elastic filament in a viscous medium is a common phenomenon in soft matter and biological systems, examples of which include buckling instability during uniflagellated bacteria locomotion and formation of short wavelength curvature of microtubule in surrounding cytoskeleton. The experimental system consists of an elastic PDMS filament with clamped boundary condition immersed in a viscous fluid. One end of the filament is then compressed through a prescribed speed and distance. It buckles with a wavelength which decreases with increasing speed. The amplitude of the buckled mode is observed to decrease from the end which is moved. Over long times, the filament is observed to relax to the fundamental Euler buckling mode. Focusing on the initial buckling, we measure the shapes of filament and the fluid flow, in response to the compression, using PIV and high speed imaging. We thus estimate and discuss the relative viscous and elastic stresses experienced by the filament during the growth of the various modes as a function of compression speed. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700