Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session H18: Biofluids: General IV - Plant Biomechanics |
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Chair: Laura Miller, University of North Carolina Room: 306/307 |
Monday, November 25, 2013 10:30AM - 10:43AM |
H18.00001: Reconfiguration of broad leaves into cones Laura Miller Flexible plants, fungi, and sessile animals are thought to reconfigure in the wind and water to reduce the drag forces that act upon them. Simple mathematical models of a flexible beam immersed in a two-dimensional flow will also exhibit this behavior. What is less understood is how the mechanical properties of a leaf in a three-dimensional flow will passively allow roll up and reduce drag. This presentation will begin by examining how leaves roll up into drag reducing shapes in strong flow. The dynamics of the flow around the leaf of the wild ginger \textit{Hexastylis arifolia} are described using particle image velocimetry. The flows around the leaves are compared with those of simplified sheets using 3D numerical simulations and physical models. For some reconfiguration shapes, large forces and oscillations due to strong vortex shedding are produced. In the actual leaf, a stable recirculation zone is formed within the wake of the reconfigured cone. In physical and numerical models that reconfigure into cones, a similar recirculation zone is observed with both rigid and flexible tethers. These results suggest that the three-dimensional cone structure in addition to flexibility is significant to both the reduction of vortex-induced vibrations and the forces experienced by the leaf. [Preview Abstract] |
Monday, November 25, 2013 10:43AM - 10:56AM |
H18.00002: Physical Limits to Leaf Size in Tall Trees Kaare Jensen, N. Michele Holbrook, Maciej Zwieniecki Leaf size in angiosperm trees vary by more than three orders of magnitude, from a few mm to over 1 m. This large morphological freedom is, however, only expressed in small trees and the observed leaf size range declines with tree height, forming well-defined upper and lower boundaries. We recently showed (Phys. Rev. Lett. \textbf{110}, 018104 (2013)) that the limits to leaf size can be understood by physical constraints imposed by the microfluidic sugar transport network. The lower boundary is set by a minimum P\'eclet number, the upper boundary by a diminishing gain in transport efficiency. [Preview Abstract] |
Monday, November 25, 2013 10:56AM - 11:09AM |
H18.00003: Nuclear traffic and peloton formation in fungal networks Marcus Roper, Patrick Hickey, Stephanie Lewkiewicz, Emilie Dressaire, Nick Read Hyphae, the network of microfluidic pipes that make up a growing fungal cell, must balance their function as conduits for the transport of nuclei with other cellular functions including secretion and growth. Constant flow of nuclei may interfere with the protein traffic that enables other functions to be performed. Live-cell imaging reveals that nuclear flows are anti-congestive; that groups of nuclei flow faster than single nuclei, and that nuclei sweep through the colony in dense clumps. We call these clumps pelotons, after the term used to describe groups of cycle racers slip-streaming off each other. Because of the pelotons, individual hyphae transport nuclei only intermittently, producing long intervals in which hyphae can perform their other functions. Modeling reveals how pelotons are created by interactions between nuclei and the hyphal cytoskeleton, and reveal the control that the fungus enjoys over peloton assembly and timing. [Preview Abstract] |
Monday, November 25, 2013 11:09AM - 11:22AM |
H18.00004: Moss hair water transport Zhao Pan, Nan Wu, Randy Hurd, Scott Thomson, William Pitt, Tadd Truscott We present an investigation of water transportation on a moss ({\it Syntrichia caninervis}) indigenous to temperate deserts. The moss typically appears to be in a dry, brown state, but is rehydrated by water during the wet season, making the desert green. Small hairs (500-2000 $\mu$m in length, and 40 $\mu$m in diameter, {\it d}) growing out from the tip of the moss leaves transport water back to the leaves. Through high speed observations and mathematical modeling it appears that this transportation is driven by two different mechanisms. 1) Droplet transport is achieved in three ways: i) A large (10{\it d}) droplet attached between two intersecting fibers will move toward the bases of the leaves by the changing angle between the two hairs. ii) The shape of the moss hair is conical, thicker at the base, producing a gradient that moves fluid (5{\it d}) toward the leaf similar to cactus spines. iii) We also observe that in some cases a Plateau-Rayleigh instability trigger a series of droplets moving toward the base. 2) Micro-grooves on the moss hair transport a film of water along the moss hair when larger droplets are not available. These various water transportation strategies combine to help the moss to survive in the desert and provide valuable insight. [Preview Abstract] |
Monday, November 25, 2013 11:22AM - 11:35AM |
H18.00005: Control of fluidic environments by mushrooms Emilie Dressaire, Junius Santoso, Lisa Yamada, Marcus Roper Thousands of fungal species rely on mushrooms for spore release and dispersal. Long distance spore dispersal by wind is instrumental to maintain genetic diversity and to the spread of pathogenic species. The conventional view is that fungi enjoy little control over the mechanism of dispersal. A spore falling from the mushroom cap can only hope to be picked up by a favorable airflow and carried away from the gap between the mushroom cap and the ground. We show that fungi actively manipulate their local fluidic environment by altering the buoyancy of the air surrounding the mushroom using a combination of water vapor and active cooling. This manipulation allows spore escape and dispersal from caps that may be spaced a few millimeters above the ground, or apart from each other. Through high speed videography, scaling analysis and indirect measurements, we reveal the fluid mechanics of spore escape, and how they are controlled by the biophysical properties of the mushroom. [Preview Abstract] |
Monday, November 25, 2013 11:35AM - 11:48AM |
H18.00006: Self-burial mechanics of hygroscopically active awns Wonjong Jung, Wonjung Kim, Ho-Young Kim We present the results of a combined experimental and theoretical investigation of the mechanics of self-burial of some plant seeds whose morphologies respond to humidity change of the surroundings. The seeds of Pelargonium species have hygroscopically active awns that play a critical role in the dispersal from the parent plant and burial in soil. While the awn uncoils to a linear shape in a highly humid condition, it recoils to a helical shape when dry. The rotation is driven by the structure of the cell walls that are comprised of cellulose microfibers aligned in a tilted helix. During uncoiling of the awn, the revolving tail generates thrust to burrow into soil, so that the seed is self-buried. We present the direct observation of the self-burial of the seed with the thrust into a soft substrate being measured at the same time. The elastica theory allows us to rationalize this botanical digging mechanics using the structural deformations of the hygroexpansive tissues. [Preview Abstract] |
Monday, November 25, 2013 11:48AM - 12:01PM |
H18.00007: Physicochemical hydrodynamics of porous structures in vascular plants Jeongeun Ryu, Sungsook Ahn, Seung-Gon Kim, Taejoo Kim, Sang Joon Lee Transport of sap flow through xylem conduits of vascular plants has been considered as a passive process, because the xylem conduits are regarded as inert, dead wood. However, plants can actively regulate water transport using ion-mediated response for adapting to environmental changes. In order to understand the active regulation mechanism of physicochemical hydrodynamics of porous structures in vascular plants, the effects of specific ion types and their ionic ratios on the water transport were experimentally investigated under \textit{in vivo }condition. Based on the experimental results, the principle of ionic effects will be explained through \textit{in-vitro} comparative experiments and theoretical considerations. [Preview Abstract] |
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