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 M9: Biofluids: Plant Physiology |
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Chair: Tomas Bohr, Technical University of Denmark Room: 3014/3016 |
Tuesday, November 25, 2014 8:00AM - 8:13AM |
M9.00001: Morphological characteristics of motile plants for dynamic motion Kahye Song, Eunseop Yeom, Kiwoong Kim, Sang Joon Lee Most plants have been considered as non-motile organisms. However, plants move in response to environmental changes for survival. In addition, some species drive dynamic motions in a short period of time. Mimosa pudica is a plant that rapidly shrinks its body in response to external stimuli. It has specialized organs that are omnidirectionally activated due to morphological features. In addition, scales of pinecone open or close up depending on humidity for efficient seed release. A number of previous studies on the dynamic motion of plants have been investigated in a biochemical point of view. In this study, the morphological characteristics of those motile organs were investigated by using X-ray CT and micro-imaging techniques. The results show that the dynamic motions of motile plants are supported by structural features related with water transport. These studies would provide new insight for better understanding the moving mechanism of motile plant in morphological point of view. [Preview Abstract] |
Tuesday, November 25, 2014 8:13AM - 8:26AM |
M9.00002: Dynamic analysis on cavitation and embolization in vascular plants under tension Jeongeun Ryu, Bae Geun Hwang, Yangmin Kim, Sang Joon Lee Plants can transport sap water from the soil to the tip of their leaves using the tensile forces created by leaf transpiration without any mechanical pumps. However, the high tension adversely induces a thermodynamically metastable state in sap water with negative pressure and gas bubbles are prone to be formed in xylem vessels. Cavitation easily breaks down continuous water columns and grows into embolization, which limits water transport through xylem vessels. Meanwhile, the repair process of embolization is closely related to water management and regulation of sap flow in plants. In this study, the cavitation and embolization phenomena of liquid water in vascular plants and a physical model system are experimentally and theoretically investigated in detail under in vivo and in vitro conditions. This study will not only shed light on the understanding of these multiphase flows under tension but also provide a clue to solve cavitation problems in micro-scale conduits and microfluidic network systems. [Preview Abstract] |
Tuesday, November 25, 2014 8:26AM - 8:39AM |
M9.00003: Taking the Pulse of Plants Kaare H. Jensen, Sierra Beecher, N. Michele Holbrook, Michael Knoblauch Many biological systems use complex networks of vascular conduits to distribute energy over great distances. Examples include sugar transport in the phloem tissue of vascular plants and cytoplasmic streaming in some slime molds. Detailed knowledge of transport patterns in these systems is important for our fundamental understanding of energy distribution during development and for engineering of more efficient crops. Current techniques for quantifying transport in these microfluidic systems, however, only allow for the determination of either the flow speed or the concentration of material. Here we demonstrate a new method, based on confocal microscopy, which allows us to simultaneously determine velocity and solute concentration by tracking the dispersion of a tracer dye. We attempt to rationalize the observed transport patterns through consideration of constrained optimization problems. [Preview Abstract] |
Tuesday, November 25, 2014 8:39AM - 8:52AM |
M9.00004: Hydraulic pulse induced by bending in synthetic and natural branches: role in plant mechano-perception Jean-Francois Louf, Geoffroy Guena, Yoel Forterre, Eric Badel Plants can detect mechanical stimuli such as wind or touch and respond to these stimuli by modifying their development and growth. A fascinating feature of this mechanical-induced-growth response is that it is not only local, but also non-local: bending locally a stem or a branch can induce a very rapid ($\sim$ min) modification of the growth far away from the stimulated area. The nature and mechanism of this long distance signal is not well understood, but it has been suggested that it could result from a purely hydraulic pressure signal, in response to the mechanical bending of the hydrated wood tissue. To address this issue, we investigate the poroelastic response to sudden bending of both natural tree branches and synthetic branches made of PDMS elastomer perforated with longitudinal micro-channels and filled with a viscous fluid. In both systems, we observe that the bending of the branch generates a sudden increase of the mean pore pressure, which scales with the beam elasticity and increases quadratically with the bending amplitude. We propose a simple non-linear model to explain the generation of this hydraulic pulse and discuss our results in the context of plant mechano-perception. [Preview Abstract] |
Tuesday, November 25, 2014 8:52AM - 9:05AM |
M9.00005: Tree-on-a-chip: a microfluidic osmotic pump mimicking passive phloem loaders Jean Comtet, Kaare H. Jensen, Abraham D. Stroock, Anette (Peko) Hosoi According to the M\"unch mechanism, vascular plants rely on osmotic pressure gradients to export sugars from regions of synthesis (mature leaves) to regions of consumption (roots, fruits). A crucial step in this process is the loading of sugars from photosynthetic cells (known as mesophylls) to the export conduit (the phloem). In some plants, known as passive loaders, sugars are thought to simply diffuse from mesophylls to the phloem. In this case, we show that a single nondimensional ``flushing number,'' characterizing the relative balance of diffusive sugar loading and convective phloem transport, accurately describes the state of the system (phloem hydrostatic pressure, sugar export rates...). We build a synthetic microfluidic osmotic pump mimicking this biological transport mechanism. In particular, our pump can work in a diffusion-limited regime, for which the flow rate scales weakly with the resistance of the hydraulic circuit. This bio-inspired device provides insight into the biophysical mechanism of passive phloem loading, and could be relevant for microfluidic or micro-robotic applications, where high actuation pressures and steady-state flow rates are necessary. [Preview Abstract] |
Tuesday, November 25, 2014 9:05AM - 9:18AM |
M9.00006: Fluid dynamics of hydrophilous pollination in Ruppia (widgeon grass) Naga Musunuri, Daniel Bunker, Susan Pell, Ian Fischer, Pushpendra Singh The aim of this work is to understand the physics underlying the mechanisms of two-dimensional aquatic pollen dispersal, known as hydrophily, that have evolved in several genera of aquatic plants, including Halodule, Halophila, Lepilaena, and Ruppia. We selected Ruppia, which grows in the wetlands of the New Jersey/New York metropolitan area, for this study. Our experiments show that the pollen grains from an anther suddenly disperse and form a monolayer when they come in contact with a water surface. This is a crucial first step in the formation of floating porous pollen structures called ``pollen rafts,'' which often contain pollen grains from several anthers. The formation of porous pollen rafts increases the probability of pollination by increasing the two-dimensional reach of the pollen from each individual anther. [Preview Abstract] |
Tuesday, November 25, 2014 9:18AM - 9:31AM |
M9.00007: Experimental investigation of the flow field and pollen trajectories/deposition around ovulate pine cones Neta-lee Jacobson, Ren\'e van Hout Particle deposition on bluff bodies is important both in industrial applications as well as in furthering our understanding of ecological networks. It has been hypothesized that plant structural morphology manipulates the flow field in order to enhance capturing of species-specific pollen and thereby increase fertilization chances. Here, the deposition mechanism of different pine pollen on freshly harvested ovulate pine cones (\textit{Pinus Halepensis}/\textit{Brutia}) was investigated using high speed, planar particle image velocimetry and holographic 3D technique enabling measurement of both Lagrangian particle tracks and instantaneous flow fields. Measurements were performed in a small blow--through windtunnel at Reynolds numbers ranging from Re $=$ 174 to 767. The roughness on a pine cone is characterized by ``scales'' organized as Fibonacci spirals. Effects of this roughness on the flow field are compared to results for a smooth sphere at similar Re. Particle deposition results indicate that inertial deposition on the windward side of the cone is the main mechanism. However, at the lowest Reynolds numbers pollen with Stokes numbers less than one were entrained into the cone's near wake and advected towards the leeward side of the cone. [Preview Abstract] |
Tuesday, November 25, 2014 9:31AM - 9:44AM |
M9.00008: Modeling of wind-initiated liberation of fungal propagules from host plant leaves Trevor Gonzalinajec Successful airborne propagule dispersal must begin with liberation into the air. The physical shedding mechanism of airborne propagules in the 100-250$\mu$m size range are not well understood. Many fungal plant pathogens have propagules in this size range that are shed from the bottom of infected leaves. If turbulent air flow is sufficient to liberate the sporocarps of fungi from leaves then the aerodynamic forces exerted must be sufficient to overcome adhesive forces. In this study I have sought to quantify the magnitude and direction of these aerodynamic forces and their causal flow fields with dynamically scaled physical models. I chose a genus of powdery mildew because maturation of the sporocarp entails morphological changes that lever the sporocarp further away from the leaf surface and out of the viscous boundary layer. Consequently I varied the sporocarp morphology, the boundary layer thickness, and the flow velocity as forces on models were measured with a transducer. Additionally I analyzed the fluid velocity around the models using PIV, which allowed for quantification of the relative importance of shear forces and pressure-gradient forces. The results suggest that forces from steady and unsteady wind alike are insufficient to explain liberation. [Preview Abstract] |
Tuesday, November 25, 2014 9:44AM - 9:57AM |
M9.00009: The efficient flight of \textit{Ruellia ciliatiflora} seeds Dwight Whitaker, Franklin Marsh, Peter Chen, David Vejar, Patrick Babb, Josue Castillo, Sabrina Cordero, Maharani Lumban-Gaol, Irlanda Mora, Tania Partida, Julian Pineda, Aaron Rodriguez The seeds of {\em Ruellia ciliatiflora} are small disks measuring approximately 3 mm in diameter and 0.3 mm in height, which are launched from exploding fruits at speeds exceeding 10 m/s. The seeds fly with backspin such that the axis of symmetry is parallel to the ground. With rotation rates that exceed 1 kHz they keep an aerodynamic profile and move through the air with a extremely low drag. Using high-speed video we have learned that the drag coefficients for these flying seeds can measure less than 0.01 for those launched with the least wobble. To understand the role of seed morphology and rotation rate on the flight of the seeds, we will also present work using 3D printed models of the seeds for studies in wind tunnels. Three-dimensional models are created by photographing seeds from many angles and inferring a shape using commercial software, which also creates a printable model. These studies should help guide work that compares explosions from fruits within the Acanthaceae family to which {\em R. ciliatiflora} belongs. This family consists of over 2000 species with exploding fruit with diverse habitats and morphologies. [Preview Abstract] |
Tuesday, November 25, 2014 9:57AM - 10:10AM |
M9.00010: Make a wish: coins falling in water Lionel Vincent, Luke Heisinger, Eva Kanso Accurate prediction of the flight range and landing site of an object descending under the influence of gravitational and aerodynamic forces is relevant to many engineering and science applications. Examples range from forecasting the touchdown locations of re-entry space vehicles to understanding the settlement patterns of seeds. While the descent motion follows the laws of classical mechanics, the delicate interplay between the fluid medium and the physical properties of the descending object makes the exact landing site difficult to predict a priori and thus best treated probabilistically. Indeed, objects falling in a fluid medium rarely descend in a straight line. The descent motion is generally complex, even for regularly shaped objects such as coins and cards. For such objects, four types of descent regimes have been identified: steady, fluttering, chaotic, or tumbling. Here, we assess the dependence of landing sites on the type of descent motion through controlled experiments of coins falling in water where we quantify the spread in the landing sites and probability of landing heads up. Interestingly, we find that, in certain descent regimes, the fluid medium acts as a randomization device, while other regimes only cause small uncertainties in the landing sites. [Preview Abstract] |
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