Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session AE: Biofluids I: General I - Biological Systems |
Hide Abstracts |
Chair: Silas Alben, Georgia Institute of Technology Room: 101E |
Sunday, November 22, 2009 8:00AM - 8:13AM |
AE.00001: Fluid Friction and Fungal Spore Ejection Joerg Fritz, Agnese Seminara, Marcus Roper, Anne Pringle, Michael Brenner A wide range of fungal species in the phylum Ascomycota uses the forcible ejection of microscopic spores to disperse and to cover new territory, triggered by the breakdown of osmolytes in the sack containing the spores (the ascus). The spores experience very high aerodynamic drag due to their small size and need to attain high velocities to leave the boundary layer of still air around the fruiting body. Here we address the efficiency of conversion of osmotic pressure to the kinetic energy of the spore, and in particular its dependence on the design of the ascus and the hole (the so-called apical ring) from where the spores leave the ascus. We present a fluid mechanical model of the ejection process, which predicts that the hole the apical ring should have specific properties, in order to minimize frictional and pressure losses and maximize the ejection velocity. We compare these predictions to measurements of apical ring properties across the phylum. [Preview Abstract] |
Sunday, November 22, 2009 8:13AM - 8:26AM |
AE.00002: Dynamics of a nuclear invasion Marcus Roper, Anna Simonin, N. Louise Glass Filamentous fungi grow as a network of continuous interconnected tubes, containing nuclei that move freely through a shared cytoplasm. Wild fungi are frequently chimerical: two nuclei from the same physiological individual may be genetically different. Such internal diversity can arise either from spontaneous mutations during nuclear division, or by nuclear exchange when two individuals fuse, sharing their resources and organelles to become a single individual. This diversity is thought to be essential to adaptation in plant pathogens, allowing, for instance, an invading fungus to present many different genetic identities against its host's immune response. However, it is clear that the presence of multiple genetic lineages within the same physiological individual can also pose challenges - lineages that are present in growing hyphal tips will multiply preferentially. Nuclei must therefore be kept well mixed across a growing front. By applying models developed to describe mixing of fluids in microfluidic reactors to experimental observations of lineage mixing in a growing \emph{Neurospora crassa} colony, we show how this mixing is achieved. In particular we analyze the individual contributions from interdigitation of hyphae and from nuclear transport. [Preview Abstract] |
Sunday, November 22, 2009 8:26AM - 8:39AM |
AE.00003: A model for wetting and evaporation of a post-blink precorneal tear film Daniel Anderson, Katlyn Winter, Richard Braun We examine a one-dimensional hydrodynamic model derived using lubrication theory for the evolution of a post-blink precorneal tear film that includes evaporation of the aqueous layer and a wetting corneal surface. The evaporation model includes the effects of conjoining pressure and predicts the existence of an equilibrium adsorbed fluid layer that serves as a model for a wetting corneal surface/mucin layer. The dewetting rates predicted by the model are in qualitative agreement with experimental measurements. [Preview Abstract] |
Sunday, November 22, 2009 8:39AM - 8:52AM |
AE.00004: The ant raft Nathan Mlot, David Hu, Solomon Equabai To survive floods, fire ants link their arms together to assemble a raft with their own bodies. Because ants are nearly as dense as water, this cooperative behavior requires that a portion of the ant colony must sacrifice itself by remaining underwater to support the colony's weight. Surprisingly, few ants drown during this process due to a striking metamorphosis of the raft: as we show using time-lapse photography, the raft morphs from a spherical to a pancake shape. This pancake configuration--a monolayer of floating ants supporting their dry counterparts--allows all ants to both breathe and remain united as a colony. Data is presented in the form of the dimensions and the rates of formation of the ant raft. We use the statics of small floating bodies to account for the equilibrium raft size as a function of the initial mass and density of the ants. [Preview Abstract] |
Sunday, November 22, 2009 8:52AM - 9:05AM |
AE.00005: Flight of the smallest insects Laura Miller, Arvind Santhanakrishnan, Tyson Hedrick, Alice Robinson A vast body of research has described the complexity of flight in insects ranging from the fruit fly, \textit{Drosophila melanogaster}, to the hawk moth, \textit{Manduca sexta}. Over this range of scales, flight aerodynamics as well as the relative lift and drag forces generated are surprisingly similar. The smallest flying insects (Re$\sim $10) have received far less attention, although previous work has shown that flight kinematics and aerodynamics can be significantly different. In this presentation, we have used a three-pronged approach that consists of measurements of flight kinematics in the tiny insect \textit{Thysanoptera} (thrips), measurements of flow velocities using physical models, and direct numerical simulations to compute lift and drag forces. We find that drag forces can be an order of magnitude larger than lift forces, particularly during the clap and fling motion used by all tiny insects recorded to date. [Preview Abstract] |
Sunday, November 22, 2009 9:05AM - 9:18AM |
AE.00006: Legged locomotion on sand Chen Li, Paul Umbanhowar, Haldun Komsuoglu, Daniel Koditschek, Daniel Goldman To understand how and why animals modulate foot kinematics to achieve effective locomotion on granular media, we study the speed of a six-legged robot with c-shaped legs, SandBot, moving on granular media for varying volume fraction, $\phi$, limb frequency, $f$, and gait timing parameters\footnote{Li et. al, PNAS, \textbf{106}, 3029, 2009}. Speed is determined by step length which in turn depends on limb penetration. At low $f$ and high $\phi$ penetration is small, step length is large, and SandBot advances with a rotary walking gait in which c-legs rotate about their centers by slipping relative to stationary grains. In the opposite extreme, grains cannot support the robot; its underside always contacts the ground and it advances slowly via thrust generated as the c-legs translate through the grains. For varied gait parameters, high speeds are only observed in a small area of parameter space. A yield stress based model predicts the speed and reveals that performance is maximized when gait parameters minimize limb acceleration and interference, and limbs utilize the solidification properties of the media. [Preview Abstract] |
Sunday, November 22, 2009 9:18AM - 9:31AM |
AE.00007: Aquatic mapping using hydrodynamic pressure sensing Roland Bouffanais, Dick K.P. Yue Pressure sensing is instrumental to most animals and organisms living in an aquatic environment: for instance fish at human scale through their lateral line and amoeba at microscale through mechanodetection at their surface. It also represents for underwater vehicles an alternative way of sensing the fluid environment when visual and acoustic sensing are limited. To assess the effectiveness of hydrodynamic sensing we propose a framework applicable to both high- and low-Reynolds number flows corresponding to typical fluid environment encountered by macro- and micro-swimmers respectively. In this framework both the forward and inverse problem corresponding to the object shape detection are presented. The forward mapping relies on a general solution of the pressure field expanded as an infinite series. The detection problem corresponds to the inverse problem which consists in determining some of the necessary coefficient of the expansion based on a noisy pressure signal over the limited length of the mechanosensing device. [Preview Abstract] |
Sunday, November 22, 2009 9:31AM - 9:44AM |
AE.00008: The hummingbird's tongue: a self-assembling syphon John Bush, Francois Peaudecerf, David Quere We present the results of a combined experimental and theoretical investigation of the drinking technique of the hummingbird. Its long, thin tongue is dipped into nectar approximately 20 times per second. With each insertion, fluid rises along the length of the tongue through capillary action. While the tongue is open in cross-section, resembling a sliced straw, experiments demonstrate that surface tension serves to close it, with the tongue's zipping front corresponding to the rising meniscus. Supporting theoretical and analogue experimental models of this novel, natural example of capillary origami are developed and explored. [Preview Abstract] |
Sunday, November 22, 2009 9:44AM - 9:57AM |
AE.00009: Why Do Elephants Flap Their Ears? Moise Koffi, Latif Jiji, Yiannis Andreopoulos It is estimated that a 4200 kg elephant generates as much as 5.12 kW of heat. How the elephant dissipates its metabolic heat and regulates its body temperature has been investigated during the past seven decades. Findings and conclusions differ sharply. The high rate of metabolic heat coupled with low surface area to volume ratio and the absence of sweat glands eliminate surface convection as the primary mechanism for heat removal. Noting that the elephant ears have high surface area to volume ratio and an extensive vascular network, ear flapping is thought to be the principal thermoregulatory mechanism. A computational and experimental program is carried out to examine flow and heat transfer characteristics. The ear is modeled as a uniformly heated oscillating rectangular plate. Our computational work involves a three-dimensional time dependent CFD code with heat transfer capabilities to obtain predictions of the flow field and surface temperature distributions. This information was used to design an experimental setup with a uniformly heated plate of size 0.2m x 0.3m oscillating at 1.6 cycles per second. Results show that surface temperature increases and reaches a steady periodic oscillation after a period of transient oscillation. The role of the vortices shed off the plate in heat transfer enhancement will be discussed. [Preview Abstract] |
Sunday, November 22, 2009 9:57AM - 10:10AM |
AE.00010: The effect of shear and flow separation on out of plane growth in biological films Derek Rinderknecht, Mory Gharib Shear stress and flow separation are important physical cues initiating biofouling in many biological systems examples are the formation of plaques in the cardiovascular system and the accumulation of algae or other contaminants on the hulls of ships. To examine the effect of unsteady flow on the local shear profile and flow separation location and their relationship to the growth of thin biofilms, an experiment was constructed consisting of an open ended box with two opposing cylindrical half rounds located along the midline of the top and bottom faces. This chamber when mounted on a traverse is capable of creating steady, oscillatory and pulsatile flow profiles. A parametric study consisting of LIF dye experiments and PIV was conducted to examine the affect of unsteady flow amplitude and frequency on flow separation. Empirical velocity fields were analyzed using Lagrangian Coherent Structures to determine the impact of the unsteady flow profile on boundaries to transport within the flow. Results show the existence of three distinct flow regimes where the size and number of recirculations present depend on the frequency and amplitude of the oscillation. The flow was also seeded with algae and the apparent effects of flow separation and time periodic shear on out-of-plane biological growth will be discussed. [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