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 R9: Biofluids: General |
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Chair: David Hu, Georgia Institute of Technology Room: 3014/3016 |
Tuesday, November 25, 2014 1:05PM - 1:18PM |
R9.00001: An experimental and theoretical approach to a simplified model of human birth Alexa Baumer, Andrea Lehn, James Grotberg, Megan C. Leftwich his study investigates the effects of amniotic fluid and vernix caseosa, as well as the uterine contraction wave dynamics, on the forces associated with human birth. An experimental model of the fetus passing through the birth canal is represented as concentric cylinders with a fluid filled gap. The rigid inner cylinder moves through the highly flexible outer cylinder while stabilized on a track. The inner cylinder is pulled through the system with constant velocity. As it moves, the rigid cylinder's position is recorded with a high-speed camera and the force is simultaneously measured. A perturbation solution considers the upper boundary as the uterine wall with a peristaltic wave. The lower boundary is the fetus traveling at constant velocity. Assuming lubrication theory and a small Reynolds number, the Navier-Stokes Equations and conservation of mass are solved for an expression for shear stress at the wall. This solution, and the experimental results, are compared to the exact Couette flow solution for constant gap width. This model can be used as the foundation for predicting the force needed to deliver a fetus in the final stages of parturition. From the concentric cylinders representation of human delivery, more complex and geometrically accurate models can be generated. [Preview Abstract] |
Tuesday, November 25, 2014 1:18PM - 1:31PM |
R9.00002: ABSTRACT WITHDRAWN |
Tuesday, November 25, 2014 1:31PM - 1:44PM |
R9.00003: Behavioral Response of Atlantic Mud Crab Megalopae to Coherent Shear Flows D.R. Webster, A.C. True, M.J. Weissburg, J. Yen Behavioral assays with megalopae of the Atlantic mud crab (\textit{Panopeus herbstii}) were performed in a laboratory mimic of hydrodynamic structure associated with fronts and clines. A laminar, planar free jet was used to create fine-scale upwelling, downwelling, and horizontal shear flows. Analyses of digitized trajectories established orientation-specific behavioral shear strain rate thresholds in the range 0.04 -- 0.1 s$^{-1}$. Changes in average kinematics revealed area-restricted searching in the vicinity of horizontal shear flows and excited area-restricted searching in the vicinity of both vertical shear flows, although not in the layers themselves. These responses could produce aggregations in the vicinity of coherent shear flows, although there is avoidance of vertical flow regions. Reduction in the net-to-gross displacement ratio (NGDR) and the vertical-net-to-gross displacement ratio (VNGDR) with respect to stagnant conditions indicate that trajectories become more sinuous and that larvae enhance depth-keeping in all shear flows. Collectively, this is consistent with foraging and sampling behaviors in which shear flow cues larvae to restrict search volume in hopes of exploiting some coincident cue or resource patch, typical in fronts and clines. Area-restricted searching along with depth-keeping seen here reveals that larvae may utilize the information contained in coherent shear flows to optimize needs operating on disparate space and time scales (e.g. foraging and site selection for settlement). [Preview Abstract] |
Tuesday, November 25, 2014 1:44PM - 1:57PM |
R9.00004: Flow inside an eye under vitreous surgery Daiki Kono, Shun Sakamoto, Jun Sakakibara Vitreous is a clear gel filling the space between crystalline lens and retina in human eye. Under circumstances where the vitreous becomes opaque due to bleeding or other disease, ophthalmologist removes the vitreous from eye by cutting and sucking through a pipe named vitreous cutter, and meanwhile replaces fluid in the eye with a balanced salt solution by injecting it through the infusion port. Jet flow from the infusion port may cause intense flow. Consequently, this may generate a pressure and a shear stress on the retinal wall and possibly lead to the damage of retinal cell. In this study, we visualized the flow inside eye and estimated the shear stress on the retinal wall under the vitreous surgery. Instead of using human eye, we used a spherical shell model simulating human eyeball, and measured the two dimensional distribution of two-component velocity by PIV. Under the condition of Re=66 to 99, which meet in the actual operation, the maximum shear stress reaches 0.4 Pa. This value is insufficient to cause retinal detachment, while any physiological effect on the retinal endothelial cells is still unclear. Flow field under higher Re will be presented in the talk. [Preview Abstract] |
Tuesday, November 25, 2014 1:57PM - 2:10PM |
R9.00005: 3D simulation of floral oil storage in the scopa of South American insects Alexander Ruettgers, Michael Griebel, Lars Pastrik, Heiko Schmied, Dieter Wittmann, Andreas Scherrieble, Albrecht Dinkelmann, Thomas Stegmaier Several species of bees in South America possess structures to store and transport floral oils. By using closely spaced hairs at their back legs, the so called scopa, these bees can absorb and release oil droplets without loss. The high efficiency of this process is a matter of ongoing research. Basing on recent x-ray microtomography scans from the scopa of these bees at the Institute of Textile Technology and Process Engineering Denkendorf, we build a three-dimensional computer model. Using NaSt3DGPF, a two-phase flow solver developed at the Institute for Numerical Simulation of the University of Bonn, we perform massively parallel flow simulations with the complex micro-CT data. In this talk, we discuss the results of our simulations and the transfer of the x-ray measurement into a computer model. [Preview Abstract] |
Tuesday, November 25, 2014 2:10PM - 2:23PM |
R9.00006: Physics of Weightlifting Caroline Cohen In the footsteps of J.B. Keller who determined the optimal strategy to run a race [1], we investigate weightlifting records. We measure the dynamics of lifting barbells of different masses at Bench Press for different athletes. To understand the shape of experimental results, we need both a macroscopic mechanic model and microscopic description of muscle contraction. We dive into muscle in order to understand the relation between force generated by the muscle and its contraction velocity [2,3] and draw a capillary analogy of muscle contraction. Finally we use the Deshcherevskii kinetik model [4] and derive the dynamics of the barbell. From the fit between data and predictions, we extract microscopic characteristics of muscles. We consider to apply this protocole to diagnose muscle aging or dysfunctions. \\[4pt] [1] Keller, J. B. (1973). iA theory of competitive running. Physics today, 43.\\[0pt] [2] Hill, A. V. (1938). The heat of shortening and the dynamic constants of muscle. Proceedings of the Royal Society of London. Series B, Biological Sciences, 136-195.\\[0pt] [3] Huxley, H. E. (1990). Sliding filaments and molecular motile systems. J. Biol. Chem, 265(15), 8347-8350.\\[0pt] [4] Deshcherevskii, V. I. (1971). A kinetic theory of striated muscle contraction. Biorheology, 7(3), 147-170. [Preview Abstract] |
Tuesday, November 25, 2014 2:23PM - 2:36PM |
R9.00007: Shape-assisted body reorientation enhances trafficability through cluttered terrain Chen Li, Andrew Pullin, Duncan Haldane, Ronald Fearing, Robert Full Many birds and fishes have slender, streamlined bodies that reduce fluid dynamic drag and allow fast and efficient locomotion. Similarly, numerous terrestrial animals run through cluttered terrain where 3-D, multi-component obstacles like grass, bushes, trees, walls, doors, and pillars also resist motion, but it is unknown whether their body shape plays a major role. Here, we challenged discoid cockroaches that possess a rounded, thin, nearly ellipsoidal body to run through tall, narrowly spaced, grass-like beams. The animals primarily rolled their body to the side to maneuver through the obstacle gaps. Reduction of body roundness by artificial shells inhibited this side roll maneuver, resulting in a lower traversal probability and a longer traversal time ($P$ \textless 0.001, ANOVA). Inspired by this discovery, we added a cockroach-like, rounded exoskeleton shell to a legged robot of a nearly cuboidal body. The rounded shell enabled the robot to use passive side rolling to maneuver through beams. To explain the mechanism, we developed a simple physics model to construct an energy landscape of the body-terrain interaction, which allowed estimation of body forces and torques exerted by the beams. Our model revealed that, by passive interaction with the terrain, a rounded body (ellipsoid) rolled more easily than an angular body (cuboid) to access energy valleys between energy barriers caused by obstacles. Our study is the first to demonstrate that a terradynamically ``streamlined'' shape can reduce terrain resistance and enhance trafficability by assisting body reorientation. [Preview Abstract] |
Tuesday, November 25, 2014 2:36PM - 2:49PM |
R9.00008: Mathematical Modeling of Tear Film Break up Modes and Fluorescent Intensity Javed Siddique, Richard Braun, C.G. Begley, P.E. King-Smith We develop a mathematical model for variables of interest in tear film break up (TBU) to compare with experimental images of TBU to better predict local values of tear film (TF) osmolarity and fluorescence during and following the TBU. Models are developed for local changes in TF thickness, osmolarity and fluorescein concentration. Fluorescence concentration was converted to fluorescent intensity using the expression involving film thickness and the full range of fluorescence (Nichols et al (IOVS 2012). The fluorescent intensity response is a primary tool for visualizing the TF thickness, and it is qualitatively different in the dilute vs concentrated regimes. Computed results over a wide range of fluorescein concentrations show that evaporation rate led to thinner regions where TBU first occurs. The computed results will be closely compared with experimential fluorescence and other imaging techniques to help determine relevant parameters. The model predicts locally elevated concentration of osmolarity within areas of TBU and predicts osmolarity in these regions which can't be measured experimental results to date. The osmolarity may increase from 50\% to 1300\% of the isosmolar value, depending sensitively on the corneal permeability and diffusivity of solutes in tear film. [Preview Abstract] |
Tuesday, November 25, 2014 2:49PM - 3:02PM |
R9.00009: The hydrodynamics of defecation Patricia Yang, Duc Dao, Richard Lehner, Mike Tennenbaum, Alberto Fernandez-Nieves, David Hu According to the U.S. Department of Health and Human Services, digestive disease affects 60 to 70 million people and costs over 140 billion annually. Despite the significance of the gastrointestinal tract to human health, the physics of both digestion and defecation remain poorly understood. In this combined experimental and theoretical study, we investigate the defecation of mammals, from mice to elephants. We film defecation events at Zoo Atlanta and apply plate-on-plate rheometry to measure the viscosity of mammalian feces. Among animals heavier than 3 kg, we find herbivores defecate for only 10 seconds (N = 13), while carnivores do so for 19 seconds (N = 8). We rationalize this surprising trend on the basis of the higher viscosity of carnivore feces. We compare defecation times to theoretical predictions based on a Poiseuille flow model of the rectum and parallel experiments with a synthetic defecator that extrudes pizza dough upon applied pressure. Our findings may help to diagnose digestive problems in animals. [Preview Abstract] |
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