Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 55, Number 16
Sunday–Tuesday, November 21–23, 2010; Long Beach, California
Session EQ: Biolocomotion III: Micro-swimming II |
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Chair: Paulo Arratia, University of Pennsylvania Room: Long Beach Convention Center 203B |
Sunday, November 21, 2010 4:10PM - 4:23PM |
EQ.00001: The random walk of a low-Reynolds-number swimmer Salima Rafa\"{I}, Micha\"{e}l Garcia, Stefano Berti, Philippe Peyla Swimming at a micrometer scale demands particular strategies. Indeed when inertia is negligible as compared to viscous forces (\textit{i.e.} Reynolds number $Re$ is lower than unity), hydrodynamics equations are reversible in time. To achieve propulsion a low Reynolds number, swimmers must then deform in a way that is not invariant under time reversal. Here we investigate the dispersal properties of self propelled organisms by means of microscopy and cell tracking. Our system of interest is the microalga Chlamydomonas Reinhardtii, a motile single celled green alga about 10 micrometers in diameter that swims with two flagellae. In the case of dilute suspensions, we show that tracked trajectories are well modelled by a correlated random walk. This process is based on short time correlations in the direction of movement called persistence. At longer times, correlations are lost and a standard random walk caracterizes the trajectories. Moreover, high speed imaging enables us to show how speed fluctuations at very short times affect the statistical description of the dynamics. Finally we show how drag forces modify the characteristics of this particular random walk. [Preview Abstract] |
Sunday, November 21, 2010 4:23PM - 4:36PM |
EQ.00002: Jump if you can't take the heat: three escape gaits of Paramecium swimming Charles N. Baroud, Amandine Hamel, Cathy Fisch, Laurent Combettes, Pascale Dupuys-Williams Paramecium is able to swim at velocities reaching several times its body size per second, by beating its thousands of cilia in an organized fashion. Here we show that Paramecium has in fact three distinct swimming gaits to escape from an aggression in the form of localized heating, depending on the magnitude of the aggression: For a weak agression, normal swimming is sufficient and produces a steady swimming velocity through cilia beating. As the heating amplitude is increased, a higher acceleration and faster swimming are achieved through synchronized beating of the cilia, which later give way to the usual metachronal waves. The synchronized beating yields high initial accelerations but requires the cell to coast through the synchrnized recovery. Finally, escape from a life-threatening agression is achieved by a ``jumping'' gait which does not rely on the cilia but is achieved from the explosive release of a rod-like organelles in the direction of the hot spot. Measurements through high-speed video explain the role of these rods in defending Paramecium. They also show that the zero-Reynolds number assumption is unverified in most cases. [Preview Abstract] |
Sunday, November 21, 2010 4:36PM - 4:49PM |
EQ.00003: Ciliary locomotion in presence of boundaries Saikat Jana, Soong Ho Um, Sunghwan Jung Micro-organisms in nature navigate through a variety of fluidic geometries and chemical conditions. We investigate the effect of confined spaces in nature by introducing \textit{Paramecium Multimicronucleatum} in two different configurations: a capillary tube {\&} a wavy PDMS channel. \textit{Paramecium} swims by creating the metachronal waves due to ciliary beating. The influence of the walls on \textit{Paramecia} is characterized by measuring the velocity and observing the ciliary beating pattern. Theoretically, we also model the system by solving the stream-function with a pressure gradient. The theoretical and experimental observations are compared and conclusions are drawn about the change in the swimming characteristics as compared to free swimming without the boundaries. [Preview Abstract] |
Sunday, November 21, 2010 4:49PM - 5:02PM |
EQ.00004: Collective beating of artificial microcilia arrays Denis Bartolo, Nais Coq, Olivia Du Roure, Marc Fermigier, Sandrine Ngo We report on the collective beating of artificial magnetic cilia. First, we show how to combine soft-lithography and colloidal-self assembly to achieve patterning of PDMS surfaces with soft magnetic micro-cilia. Second, we investigate the collective hydrodynamics of regular cilia arrays actuated by a precessing magnetic field. Whereas an isolated cilium follows a circular trajectory, the synchronous beating of thousands of micro-cilia results in symmetry breaking of the precession pattern. The trajectory of the cilia becomes elliptical, with an orientation and an asymmetry ratio, which increase with the actuation frequency. Interestingly, we show that the average orientation of the anisotropic trajectories is chiefly ruled by the large scale geometry of the ciliated array. Eventually we present a minimal model to account for our experimental findings and demonstrate how the hydrodynamic interactions between the beating cilia shape their trajectories. [Preview Abstract] |
Sunday, November 21, 2010 5:02PM - 5:15PM |
EQ.00005: Optimal swimming of model ciliates Sebastien Michelin, Eric Lauga In order to swim at low Reynolds numbers, microorganisms must undergo non-time-reversible shape changes. In ciliary locomotion, this symmetry breaking is achieved through the actuation of many flexible cilia distributed on the surface of the organism. Experimental studies have demonstrated the collective synchronization of neighboring cilia (metachronal waves), whose exact origin is still debated. Here we consider the hydrodynamic energetic cost of ciliary locomotion and consider an axisymmetric envelope model with prescribed tangential surface displacements. We show that the periodic strokes of this model ciliated swimmer that minimize the energy dissipation in the surrounding fluid achieve symmetry-breaking at the organism level through the propagation of wave patterns similar to metachronal waves. We analyze the properties of the optimal strokes, in particular the impact on the swimming performance introduced by a restriction on maximum cilia tip displacement due to the finite cilia length. [Preview Abstract] |
Sunday, November 21, 2010 5:15PM - 5:28PM |
EQ.00006: Digital Holographic Study of the Swimming Characteristics of \textit{Prorocnetrum minimum} (Dinophyceae) Myong Sohn, Kyung Seo, Sang Lee The present study investigated the swimming characteristics of dinoflagellate\textit{ Prorocentrum minimum,} which is one of the cosmopolitan harmful algae species. A digital holographic PTV technique was employed to get the swimming trajectories of hundreds of\textit{ P. minimum} cells and to extract the kinematics of the flagella beating motion. The swimming speeds of \textit{P. minimum} cells in a helical motion ranged from 20 to 140 $\mu$m $\cdot$ s$^{-1}$ and the average value of them was about 90$\pm$60 $\mu$m $\cdot$ s$^{-1}$. The mean value of the helix radius and pitch of the swimming trajectories were 3.8$\pm$1.6 $\mu $m and 34$\pm$15 $\mu $m, respectively. The longitudinal flagellum beaten with a planar wave at the frequency of about 100 Hz. The transverse flagellum beaten with a helical wave at the frequency of about 42 Hz. Effect of sea water viscosity was also analyzed. The increase of sea water viscosity reduced the flagella beating frequency and the swimming speed of \textit{P. minimum.} [Preview Abstract] |
Sunday, November 21, 2010 5:28PM - 5:41PM |
EQ.00007: Oscillatory Flows Induced by Swimming Microorganisms in Two-dimensions Jeffrey S. Guasto, Karl A. Johnson, J.P. Gollub We present the first time-resolved measurements of the oscillatory velocity field induced by swimming unicellular microorganisms. Confinement of the green alga \textit{Chlamydomonas reinhardtii} in stabilized thin liquid films allows simultaneous tracking of cells and tracer particles. The phase-resolved velocity field reveals complex time-dependent flow structures, which evolve throughout the beat cycle of the organism, and the fluid velocity scales inversely with distance. The instantaneous mechanical power generated by the cells is measured from the velocity fields via the viscous dissipation and scales with the square of the swimmer speed. The peak power is about 15 fW, and the dissipation per cycle is more than four times what steady swimming would require. These observations carry important implications for the interpretation and modeling of transport processes, locomotion, and flagellar mechanics. [Preview Abstract] |
Sunday, November 21, 2010 5:41PM - 5:54PM |
EQ.00008: Swimming of a Microrobot Actuated by a Clinical Magnetic Resonance Imaging Apparatus Frederck P. Gosselin, David Zhou, Viviane Lalande, Manuel Vonthron, Sylvain Martel A miniature robot was designed to achieve fish-like locomotion when actuated by the imaging coils of a clinical Magnetic Resonance Imaging (MRI) system. The wireless fish robot is composed of a ferromagnetic head, a flexible tail and a float. In an aquarium placed in the MRI, the robot is set into a swimming motion by an alternating transverse linear magnetic gradient. The influence of tail length, forcing frequency and forcing magnitude on the swimming velocity and flapping amplitude are investigated. Moreover, by using a combination of simultaneous magnetic gradients, the fish can reach superior swimming speeds than can be achieved by simply ``pulling'' on the fish with a magnetic field. Upon further miniaturization, the propulsion principle devised here could be used to navigate a micro surgical robot or a drug delivery system. A great advantage of this system is that no energy storage, motor or control system need to be carried by the robot, allowing great miniaturization possibilities. [Preview Abstract] |
Sunday, November 21, 2010 5:54PM - 6:07PM |
EQ.00009: Numerical simulation of a rotating elastic rod in a viscous fluid using the immersed boundary method Ranjith Maniyeri, Yong Kweon Suh, Sangmo Kang, MinJun Kim Immersed boundary method has proved its efficacy in handling complex fluid structure interaction problems in the field of biological fluid dynamics. Inspired by the bacterial propulsion, we are interested to study the interaction of a rotating elastic cylindrical rod in a viscous fluid, where the flow is induced by the rotation of the rod. We developed a three dimensional computational model based on the immersed boundary method (IBM) in which Eulerian variables are used for the fluid flow and Lagrangian variables are used for the elastic rod motion. The Navier-Stokes equations governing the fluid flow are solved based on finite volume method on a staggered Cartesian grid system. The elastic rod is modeled by a number of circular rings with immersed boundary points on each ring. The motor part is modeled by a single circular ring at the base. We simulated for two cases- a straight and slightly bent rod and for an inclined rod. We found that for low rotational frequencies of the motor, the elastic rod undergoes simple axial rotation known as twirling motion and for high rotational frequencies it undergoes whirling motion with a discontinuous shape transition from straight to helical shape resulting into overwhirling. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2010-0147). [Preview Abstract] |
Sunday, November 21, 2010 6:07PM - 6:20PM |
EQ.00010: Is paramecium swimming autonomic? Promode R. Bandyopadhyay, Norman Toplosky, Joshua Hansen We seek to explore if the swimming of paramecium has an underlying autonomic mechanism. Such robotic elements may be useful in capturing the disturbance field in an environment in real time. Experimental evidence is emerging that motion control neurons of other animals may be present in paramecium as well. The limit cycle determined using analog simulation of the coupled nonlinear oscillators of olivo-cerebellar dynamics (ieee joe \textbf{33}, 563-578, 2008) agrees with the tracks of the cilium of a biological paramecium. A 4-motor apparatus has been built that reproduces the kinematics of the cilium motion. The motion of the biological cilium has been analyzed and compared with the results of the finite element modeling of forces on a cilium. The modeling equates applied torque at the base of the cilium with drag, the cilium stiffness being phase dependent. A low friction pendulum apparatus with a multiplicity of electromagnetic actuators is being built for verifying the maps of the attractor basin computed using the olivo-cerebellar dynamics for different initial conditions. Sponsored by ONR 33. [Preview Abstract] |
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