Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session L24: Biofluids: General I |
Hide Abstracts |
Chair: Michael Brenner, Harvard University Room: 327 |
Monday, November 21, 2011 3:35PM - 3:48PM |
L24.00001: Meshfree Computations for Flow Pumping in a Microchannel Inspired by Insect Physiological Systems Yasser Aboelkassem, Anne Staples The present study is inspired by pumping mechanisms observed in physiological systems in insects that use multiple contractions to transport fluid. A meshfree computational method is used to solve for the 2D viscous flow in a microchannel at low Reynolds number. The channel is assumed to have a large aspect ratio and localized multiple contractions from the upper wall. These contractions are allowed to move with or without time (phase) lags with respect to each other. The flow development and structures induced by these wall contractions are obtained at various snapshots in the collapse cycle. The effect of the contraction amplitudes and time-lags between its individual prescribed motion protocols on the flow variables and on the time-averaged net flow over a complete cycle of wall motions is studied. The meshfree computational approach presented here is based on the method of fundamental solutions (MFS) which is considered to be an efficient numerical technique for solving elliptic boundary value problems (BVP) such as the Stokes equations. This class of numerical methods uses a set of singularized force elements (Stokeslets) which are distributed according to the method of collocations with unknown strengths. The Stokeslets' strengths are then calculated by imposing the appropriate boundary conditions and solving the resulting system of equations. The flow motions induced by these point forces are then computed by the principle of superposition. [Preview Abstract] |
Monday, November 21, 2011 3:48PM - 4:01PM |
L24.00002: Butterfly proboscis: natural combination of a drinking straw with a nanosponge Kostya Kornev, Daria Monaenkova, Peter Adler, Wah-Keat Lee, Matthew Lehnert, Taras Andrukh, Charles Beard, Binyamin Rubin, Alexander Tokarev The ability of Lepidoptera, or butterflies and moths, to drink liquids from rotting fruit and wet soil, as well as nectar from floral tubes, raises the question of whether the conventional view of the proboscis as a drinking straw can account for the withdrawal of fluids from porous substrates or of films and droplets from floral tubes. We discovered that the proboscis promotes capillary pull of liquids from diverse sources due to a hierarchical pore structure spanning nano- and microscales. X-ray phase-contrast imaging reveals that Plateau instability causes liquid bridges to form in the food canal, which are transported to the gut by the muscular sucking pump in the head. The dual functionality of the proboscis represents a key innovation for exploiting a vast range of nutritional sources. A transformative two-step model of capillary intake and suctioning can be applied not only to butterflies and moths but also potentially to vast numbers of other insects such as bees and flies. [Preview Abstract] |
Monday, November 21, 2011 4:01PM - 4:14PM |
L24.00003: Bubbles of Metamorphosis Manu Prakash Metamorphosis presents a puzzling challenge where, triggered by a signal, an organism abruptly transforms its entire shape and form. Here I describe the role of physical fluid dynamic processes during pupal metamorphosis in flies. During early stages of pupation of third instar larvae into adult flies, a physical gas bubble nucleates at a precise temporal and spatial location, as part of the normal developmental program in Diptera. Although its existence has been known for the last 100 years, the origin and control of this ``cavitation'' event has remained completely mysterious. Where does the driving negative pressure for bubble nucleation come from? How is the location of the bubble nucleation site encoded in the pupae? How do molecular processes control such a physical event? What is the role of this bubble during development? Via developing in-vivo imaging techniques, direct bio-physical measurements in live insect pupal structures and physical modeling, here I elucidate the physical mechanism for appearance and disappearance of this bubble and predict the site of nucleation and its exact timing. This new physical insight into the process of metamorphosis also allows us to understand the inherent design of pupal shell architectures in various species of insects. [Preview Abstract] |
Monday, November 21, 2011 4:14PM - 4:27PM |
L24.00004: Contraction driven flow in the extended vein networks of \textit{Physarum polycephalum} Karen Alim, Gabriel Amselem, Francois Peaudecerf, Anne Pringle, Michael P. Brenner The true slime mold \textit{Physarum polycephalum} is a basal organism that forms an extended network of veins to forage for food. \textit{P. polycephalum} is renown for its adaptive changes of vein structure and morphology in response to food sources. These rearrangements presumably occur to establish an efficient transport and mixing of resources throughout the networks thus presenting a prototype to design transport networks under the constraints of laminar flow. The physical flows of cytoplasmic fluid enclosed by the veins exhibit an oscillatory flow termed ``shuttle streaming.'' The flow exceed by far the volume required for growth at the margins suggesting that the additional energy cost for generating the flow is spent for efficient and/or targeted redistribution of resources. We show that the viscous shuttle flow is driven by the radial contractions of the veins that accompany the streaming. We present a model for the fluid flow and resource dispersion arising due to radial contractions. The transport and mixing properties of the flow are discussed. [Preview Abstract] |
Monday, November 21, 2011 4:27PM - 4:40PM |
L24.00005: Fluid Flow of Vitrectomy Pooria Sharif-Kashani, Tingting Juan, Jean-Pierre Hubschman, Jeff D. Eldredge, H. Pirouz Kavehpour Vitrectomy is a microsurgical technique to remove the vitreous gel from the vitreous cavity. Due to the viscoelastic nature of the vitreous gel, its complex fluidic behavior during vitrectomy affects the outcome of the procedure. Therefore, the knowledge of such behavior is essential for better designing the vitrectomy devices, such as vitreous cutters, and tuning the system settings such as port and shaft diameters, infusion, vacuum, and cutting rate. We studied the viscoelastic properties of porcine vitreous humor using a stressed-control shear rheometer and obtained its relaxation time, retardation time, and shear-zero viscosity. We performed a computational study of the flow in a vitreous cutter using the viscoelastic parameters obtained from the rheology experiments. We found significant differences between the modeled vitreous gel and a Newtonian surrogate fluid in the flow behavior and performance of the vitreous cutter. Our results will help in understanding of the vitreous behavior during vitrectomy and providing guidelines for new vitreous cutter design. [Preview Abstract] |
Monday, November 21, 2011 4:40PM - 4:53PM |
L24.00006: Leonardo's branching rule in trees: How self-similar structures resist wind Christophe Eloy In his notebooks, Leonardo da Vinci observed that ``\emph{all the branches of a tree at every stage of its height when put together are equal in thickness to the trunk},'' which means that the total cross-sectional area of branches is conserved across branching nodes. The usual explanation for this rule involves vascular transport of sap, but this argument is questionable because the portion of wood devoted to transport varies across species and can be as low as 5\%. It is proposed here that Leonardo's rule is a consequence of the tree skeleton having a self-similar structure and the branch diameters being adjusted to resist wind-induced loads. To address this problem, a continuous model is first considered by neglecting the geometrical details of branching and wind incident angles. The robustness of this analytical model is then assessed with numerical simulations on tree skeletons generated with a simple branching rule producing self-similar structures. [Preview Abstract] |
Monday, November 21, 2011 4:53PM - 5:06PM |
L24.00007: Aquatic vegetation in flow: To buoy or not to buoy Mitul Luhar, Heidi Nepf Previous studies show that the flexural stiffness and buoyancy of many species of aquatic vegetation change in response to hydrodynamic conditions. We present a theoretical and experimental study that describes the flow-induced reconfiguration of aquatic vegetation across the natural range of vegetation buoyancy and stiffness. We show how posture and drag depend on two dimensionless parameters that represent the relative magnitudes of the hydrodynamic forcing, and the restoring forces due to stiffness and buoyancy. Reconfiguration leads to a transition away from the classical quadratic drag law. We present scaling laws that describe the relationship between drag and velocity for both stiffness- and buoyancy-dominated reconfiguration. Our results may explain the morphological plasticity observed for aquatic vegetation. [Preview Abstract] |
Monday, November 21, 2011 5:06PM - 5:19PM |
L24.00008: Modeling tumor growth in a complex evolving confinement using a diffuse domain approach Yao-li Chuang, John Lowengrub, Ying Chen, Xiangrong Li, Hermann Frieboes, Vittorio Cristini Understanding the spatiotemporal evolution of tumor growth represents an essential step towards engineering effective treatment for cancer patients. At the macroscopic scale, various biophysical models describing tumors as continuum fluids have been constructed, particularly on a Cartesian grid, where efficient numerical schemes are available to analyze the model for general tumor behaviors in a relatively unconfined space. For practical problems, however, tumors are often found in a confined sub-domain, which can even be dilated and distorted by the growing tumor within. To study such tumors, we adopt a novel diffuse domain approach that enables us to adapt a model to an evolving sub-domain and formulate the modified problem on a Cartesian grid to utilize existing numerical schemes. To demonstrate this approach, we adapt a diffuse-interface model presented in Wise et al. [2008, Three-dimensional multispecies nonlinear tumor growth - I Model and numerical method, J. Theor. Biol. 253, 524-543] to simulate lymphoma growth in a lymph node structure. [Preview Abstract] |
Monday, November 21, 2011 5:19PM - 5:32PM |
L24.00009: The mechanics of pollination by wind: is anemophily aeroelastically optimized for reproduction? David Timerman, David F. Greene, Josef D. Ackerman, Javier Urzay Approximately 10 percent of plant species rely on wind for pollination (anemophily). These include many taxa of economic importance: e.g. cultigens such as wheat and maize; species like grasses and ragweed that trigger allergies; and the conifers, our most important species for the forest industry in the mid- latitudes. It has often been assumed that anemophily is an inefficient mechanism compared to animal pollination (zoophily), but very little is known about the forces and micromechanics that deliver pollen grains into wind streams. Here we ask a fundamental question: is anemophily optimized for pollen shedding? In this talk, we focus on an as-yet rudimentary theory of turbulence- initiated pollen shed that models the pollen-bearing stamen as an aeroelastic oscillator. Ongoing experiments with anemophilous and zoophilous flowers excited by shakers are analyzed to extract values of damping ratios, adhesion forces and flexural rigidities. Finally, the anatomical differences between anemophilous and zoophilous species are evaluated using a dimensionless number that measures the ratio of adhesion to aeroleastic forces. [Preview Abstract] |
Monday, November 21, 2011 5:32PM - 5:45PM |
L24.00010: Universality of osmotically driven sap-flow in plants Tomas Bohr, K{\AA}re Hartvig Jensen, Kirstine Berg S{\O}rensen, S{\O}ren M{\O}rch Friis, Johannes Liesche, Alexander Schulz Since Ernst M\"{u}nch in the 1920s proposed that sugar transport in the phloem vascular system of plants is driven by passive osmotic pressure gradients, it has been strongly debated whether this hypothesis can account even for long distance translocation. Recently, it was shown that theoretical optimization of the M\"{u}nch mechanism leads to surprisingly simple predictions for the dimensions of the phloem sieve elements in relation to those of the plants [Jensen et. al., J. Roy. Soc. Interface \textbf{8}, pp. 1155--1165 (2011)]. We show that the theoretical results are very insensitive to the details of the sugar-loading (in leaves) and unloading (in shoots or roots) and can even be obtained from a simple coupled resistor model. We have compiled anatomical data for a wide group of plants and find good agreement with theory, even for conifer trees, in which the sugar translocation is substantially slower than hardwood trees. [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