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 CT: Biolocomotion II: Slithering, Crawling and Undulatory Swimming |
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Chair: Amy Lang, University of Alabama Room: Long Beach Convention Center Grand Ballroom B |
Sunday, November 21, 2010 1:00PM - 1:13PM |
CT.00001: Locomotion of C elegans in structured environments Trushant Majmudar, Eric Keaveny, Michael Shelley, Jun Zhang Undulatory locomotion of microorganisms like soil-dwelling worms and sperm, in structured environments, is ubiquitous in nature. They navigate complex environments consisting of fluids and obstacles, negotiating hydrodynamic effects and geometrical constraints. Here we report experimental observations on the locomotion of C elegans swimming in arrays of micro-pillars in square lattices, with different lattice spacing. We observe that the worm employs a number of different locomotion strategies depending on the lattice spacing. As observed previously in the literature, we uncover regimes of enhanced locomotion, where the velocity is much higher than the free-swimming velocity. In addition, we also observe changes in frequency, velocity, and the gait of the worm as a function of lattice spacing. We also track the worm over time and find that it exhibits super-diffusive behavior and covers a larger area by utilizing the obstacles. These results may have significant impact on the foraging behavior of the worm in its natural environment. Our experimental approach, in conjunction with modeling and simulations, allows us to disentangle the effects of structure and hydrodynamics for an undulating microorganism. [Preview Abstract] |
Sunday, November 21, 2010 1:13PM - 1:26PM |
CT.00002: Simulations of \emph{C. elegans} locomotion through a structured medium Eric Keaveny, Trushant Majmudar, Jun Zhang, Michael Shelley The small nematode \emph{C. elegans} serves as a model system with which to study low Reynolds number undulatory locomotion, particularly in fluids with an embedded microstructure that is comparable in size to the swimmer. Recent experimental observations of \emph{C. Elegans} locomotion in a lattice of obstacles indicate that the worm can achieve speeds as much as an order of magnitude greater than its free-swimming value. In addition to a series of experimental studies of this phenomenon, we perform numerical simulations of a self-locomoting chain of beads in a lattice of spherical obstacles. We explore the dependence of the worm's speed on the frequency of undulation and lattice spacing and quantify the necessary conditions for enhanced locomotion. We also use the simulations to characterize the forces experienced by the worm in this regime. Further, by comparing the simulation results with our experimental data, we identify changes in worm locomotive behavior in response to imposed geometric conditions. [Preview Abstract] |
Sunday, November 21, 2010 1:26PM - 1:39PM |
CT.00003: Locomotion and Body Shape Changes of Metabolically Different \textit{C.elegans} in Fluids with Varying Viscosities Rachel Wong, Noah Brenowitz, Amy Shen \textit{Caenorhabditis elegans} (\textit{C.elegans}) are soil dwelling roundworms that have served as model organisms for studying a multitude of biological and engineering phenomena. On agar, the locomotion of the worm is sinusoidal, while in water, the swimming motion of the worm appears more episodic. The efficiency of the worm locomotion is tested by placing the worm in four fluids with varying viscosities. We quantify the locomotion pattern variations by categorizing the swimming kinematics and shapes of the \textit{C.elegans}. The locomotion of two mutants \textit{C.elegans }and a control\textit{ C.elegans} was tested: \textit{daf2}, \textit{nhr49}, and $N2$ \textit{Wildtype}. The metabolic effects of the worms are evaluated by focusing on the forward swimming velocity, wavelength, amplitude and swimming frequency were compared. Using these measured values, we were able to quantify the efficiency, the speed of propagation of the wave along the body resulting in forward movement (wave velocity), and transverse velocity, defined as the amplitude times the frequency, of the worm locomotion. It was shown that \textit{C.elegans} has a preferential swimming shape that adapts as the environment changes regardless of its efficiency. [Preview Abstract] |
Sunday, November 21, 2010 1:39PM - 1:52PM |
CT.00004: Motility of small nematodes in disordered wet granular media Gabriel Juarez, Kevin Lu, Josue Sznitman, Paulo E. Arratia Organisms that evolve within complex fluidic environments often develop unique methods of locomotion that allow them to exploit the properties of the media. In this talk, we present an investigation on the motility of the worm nematode \textit{Caenorhabditis elegans} in shallow, wet granular media as a function of particle size dispersity and area density ($\phi )$ using both particle- and nematode-tracking methods. Surprisingly, the nematode's propulsion speed is enhanced by the presence of particles in a fluid and is nearly independent of local area density. The undulation speed, often used to differentiate locomotion gaits, is significantly affected by particle size dispersity for area densities above $\phi >$ 0.55, and is characterized by a change in the nematode's waveform from swimming to crawling. This change occurs for dense polydisperse media \textit{only} and highlights the organism's adaptability to subtle differences in local structure between monodisperse and polydisperse media. [Preview Abstract] |
Sunday, November 21, 2010 1:52PM - 2:05PM |
CT.00005: Collective behavior of nematodes in a thin fluid Sean Gart, Sunghwan Jung Many organisms live in a confined fluidic environment such as in a thin fluid layer on dermal tissues, in saturated soil, and others. In this study, we investigate collective behaviors of nematodes in a thin fluid layer. The actively moving nematodes feel various hydrodynamic forces such as surface tension from the top air-liquid interface, viscous stress from the bottom surface, and more. Two or more nematodes in close proximity can be drawn together by the capillary force between bodies. This capillary force also makes it difficult for nematodes to separate. The Strouhal number and a ratio of amplitude to wavelength are measured before and after nematode aggregation and separation. Grouped and separate nematodes have no significant changes of the Strouhal number and the ratio of amplitude to wavelength, which shows that body stroke and kinematic performance do not change while grouped together. This result implies that nematodes gain no mechanical advantage during locomotion when grouped but that the capillary force draws and keeps nematodes joined together. [Preview Abstract] |
Sunday, November 21, 2010 2:05PM - 2:18PM |
CT.00006: The Effect of Electric Field Magnitude and Frequency on \textit{Caenorhabditis} Elegans Han-Sheng Chuang, David Raizen, Nooreen Dabbish, Annesai Lamb, Haim Bau Low magnitude, DC electric fields have been used to guide the motion of the wild-type nematode (worm) Caenorhabditis elegans. Low intensity AC fields ($<$100 Hz) can even be utilized to localize the worm. However, the worm appears oblivious to the electric field as the frequency is higher than several hundreds of Hz. In contrast, in the presence of nonuniform, moderate AC fields ($\sim $15--50 kV/m) at higher frequencies ($>$10 kHz), the worm is restrained by the field's maximum. This is the first demonstration of dielectrophoretic trapping of an animal. With certain electrode arrangements, only the worm's tail is immobilized, and the worm's swimming motion does not appear to be affected by the trapping force. Similar trapping conditions with transitional frequencies ($\sim $10--100 kHz) can cause paralysis. The worm is (irreversibly) paralyzed with lower frequencies (e.g. 45 kV/m, 2 kHz) or electrified with higher electric field intensities (e.g. 10 Hz, 70 kV/m). We report on the results of a parametric study that delineates the effect of the electric field on the worm as a function of the worm's stage and the electric field intensity and frequency. Worm-dielectrophoresis can be used, among other things, to sort worms by size, to temporarily immobilize worms to enable their characterization and study, and to use worms to induce fluid motion and mixing. [Preview Abstract] |
Sunday, November 21, 2010 2:18PM - 2:31PM |
CT.00007: Could gastropods crawl using Newtonian mucus? Janice Lai, Maria Vazquez-Torres, Juan C. del Alamo, Javier Rodriguez-Rodriguez, Juan C. Lasheras The locomotion of terrestrial gastropods is driven by a train of periodic muscle contractions (pedal waves) and relaxations (interwaves) that propagate from their tail to their head (direct waves). We study the locomotion of these animals on smooth flat surfaces by measuring the three-dimensional displacements of the ventral foot surface induced by the passage of the waves. A simple model based on lubrication theory is proposed in accordance with the experimental observations. This model uncovers a new mode of locomotion that works even when the lubricant between the foot and the animal is Newtonian. The model can also be adapted to situations where the animal's foot is in contact with the ground only at discrete points, as is the case when it crawls on a wire mesh or on rough soil surfaces. Furthermore, comparison between the stress exerted by the animal on the substrate and the model predictions allows us to clarify the role of the complex rheology observed in the mucus of terrestrial gastropods. [Preview Abstract] |
Sunday, November 21, 2010 2:31PM - 2:44PM |
CT.00008: Concertina locomotion of snakes Hamidreza Marvi, David Hu Snake-like modes of locomotion may easily traverse water as well as land. In this combined experimental and theoretical investigation, we investigate the accordion-like motion of snakes, in which snakes move by a series of extensions and contractions of their bodies. Snakes are filmed performing concertina locomotion on flat cloth surfaces arranged at various angles of inclination. Using the body kinematics of the snakes and friction properties of their skin, we model snake locomotion using a three-mass model propelled by sliding friction. Particular attention is paid to maximizing propulsive efficiency using optimum rates of contraction and snake scales as brakes for ascending inclines. [Preview Abstract] |
Sunday, November 21, 2010 2:44PM - 2:57PM |
CT.00009: Comparison of physical, numerical and resistive force models of undulatory locomotion within granular media Daniel I. Goldman, Ryan D. Maladen, Yang Ding, Paul Umbanhowar We integrate biological experiments, empirical theory, numerical simulation, and a physical robot model to reveal principles of undulatory locomotion in granular media. High speed x-ray imaging of the sandfish, {\em Scincus scincus,} in $3$~mm glass particles reveals that it swims within the medium without limb use by propagating a single period traveling sinusoidal wave down its body, resulting in a wave efficiency, $\eta$, the ratio of its average forward speed to wave speed, of $0.54\,\pm\,0.13$. A resistive force theory (RFT) which balances granular thrust and drag forces along the body predicts $\eta$ close to the observed value. We test this prediction against two other modeling approaches: a numerical model of the sandfish coupled to a Molecular Dynamics (MD) simulation of the granular medium, and an undulatory robot which swims within granular media. We use these models and analytic solutions of the RFT to vary the ratio of undulation amplitude to wavelength ($A/\lambda$) and demonstrate an optimal condition for sand-swimming that results from competition between $\eta$ and $\lambda$. The RFT, in agreement with simulation and robot models, predicts that for a single period sinusoidal wave, maximal speed occurs for $A/\lambda \approx 0.2,$ the same kinematics used by the sandfish. [Preview Abstract] |
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