Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session R20: Bio: General Topics III |
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Chair: Laura Miller, University of North Carolina, Chapel Hill Room: D137-138 |
Tuesday, November 22, 2016 1:30PM - 1:43PM |
R20.00001: Passive aerial dispersal of insects and other arthropods Laura Miller One of the defining features of the aerial dispersal of tiny organisms is the ability to overcome negative buoyancy. This can be accomplished by dispersing in the right wind conditions (e.g. an updraft) or by active flight or active release. Once in the air, draggy structures, such as the draglines of spiders or bristled wings of tiny insects, can reduce the settling velocity and extend the time of transport. Purely passive mechanisms allow spiders and other arthropods to drift on strands of silk to heights of 14,000 m and distances of hundreds of miles. Similarly, tiny insects like thrips and parasitoid wasps can travel distances of thousands to tens of thousands of meters, possibly using a combination of periods of active and passive flight. In this presentation, we used the immersed boundary method to quantify settling velocities and transport dynamics of parachuting insects and other arthropods within a quiescent fluid, a uniform updraft, and eddies. [Preview Abstract] |
Tuesday, November 22, 2016 1:43PM - 1:56PM |
R20.00002: ABSTRACT WITHDRAWN |
Tuesday, November 22, 2016 1:56PM - 2:09PM |
R20.00003: Radial fingering at an active interface Amarender Nagilla, Ranganathan Prabhakar, Sameer jadhav It has been suggested that the shapes of single cells crawling on surfaces [Callan-Jones et al., Phys. Rev. Lett., 100:258106, 2008] and those of the fronts of thin layers of cells collectively expanding to close a wound [Mark et al., Biophys. J., 98:361-370, 2010] are the results of fingering instabilities. Motivated by these studies, we investigate the conditions under which an actively forced interface between a pair of immiscible viscous fluids will destabilize under Hele-Shaw confinement. The case of a circular active interface with surface tension and bending resistance is considered. Active forces exerted by the inner fluid at the interfacial region can be either completely internal or due to interactions with the confining substrate. In addition, the effects of cell growth or actin depolymerization or external injection of cell suspensions are modeled by including a distributed source and a point source of arbitrary strengths. Linear stability analysis reveals that at any given mean radius of the interface, its stability is dictated by two key dimensionless parameters. We discuss the different regions in a state space of these parameters. [Preview Abstract] |
Tuesday, November 22, 2016 2:09PM - 2:22PM |
R20.00004: The Importance of Seed Characteristics in the Dispersal of Splash-Cup Plants Joel Eklof, Rachel Pepper Pepper, Juliana Echternach Splash-cup plants disperse their seeds by exploiting the kinetic energy of raindrops. When raindrops impact the splash-cup, a 3-5 mm vessel that holds seeds, the seeds are projected up to 1 m away from the parent plant. It has been established, using 3D printed models, that a 40\textdegree cone angle maximizes dispersal distance when seeds are not present in the cup. We therefore use 40\textdegree cups with the addition of different types of seeds to determine the effect that seeds of varying characteristics have on the dispersal and splash dynamics of splash-cup plants. Splash characteristics and dispersal distances of seeds with differing characteristics such as size, shape, texture, density, and hydrophobicity were compared to one another, as well as to the case of having no seeds present. We found that the presence of seeds dramatically decreased dispersal distance and changed splash characteristics (are measured by the angle and velocity of the resulting splash). In addition, different types of seeds yielded splashes with differing dispersal distance and splash characteristics. Splash characteristics and dispersal distances of glass beads of differing hydrophobicity were compared to determine the effect hydrophobicity has on dispersal and splash dynamics. These beads yielded some differences in dispersal distance, but no notable difference in splash dynamics. Models of the conical fruit bodies of the splash-cups were 3D printed and high-speed video was used to find splash characteristics, and dispersal distance was calculated by measuring the distance from the model to the final resting position of the seeds and droplets. [Preview Abstract] |
Tuesday, November 22, 2016 2:22PM - 2:35PM |
R20.00005: Dynamic self-organization of confined autophoretic particles Anthony Medrano, Sébastien Michelin, Eva Kanso We study the behavior of chemically-active Janus particles in microfluidic \textit{Hele}-\textit{Shaw}-type confinement. These micron-scale chemical motors, when immersed in a fuel-laden fluid, produce an ionic chemical field which leads to motility and consequently a local fluid flow. In unconfined settings, experimental and computational studies have shown these particles to spontaneously self-organize into crystal structures, and form into asters of two or more particles. Here, we show that geometric confinement alters both the chemical and hydrodynamic signature of the particles in such a way that their far-field effects can be modeled as source dipoles. Each particle moves according to its own self-propelled motion and in response to the chemical and hydrodynamic field created by other particles. Two interaction modes are observed: self-assembly into quasi-static crystals and into dynamically-evolving chains. We discuss the conditions that lead to these modes of interactions and the phase transitions between them for various Janus particle concentrations. [Preview Abstract] |
Tuesday, November 22, 2016 2:35PM - 2:48PM |
R20.00006: Feedback between intracellular flow, signaling and active stresses in Physarum plasmodial fragments Shun Zhang, Robert Guy, Juan Carlos del Alamo Physarum polycephalum is a multinucleated slime mold whose endoplasm flows periodically driven by the contraction of its ectoplasm, a dense shell of F-actin cross-linked by myosin molecular motors and attached to the cell membrane. Ectoplasm contractions are regulated by calcium ions whose propagation is in turn governed by the flow. We study experimentally how this feedback leads to auto-oscillation by simultaneously measuring endoplasmic flow speed and rheological properties, the traction stresses between the ectoplasm and its substratum and the distribution of endoplasmic free calcium ions. We find that physarum fragments smaller than 100 microns remain round and stay in place. However, larger fragments break symmetry leading to sustained forward locomotion, in process that is reminiscent of an interfacial instability that seems to settle around two different limit cycles (traveling waves and standing waves). By using different adhesive coatings in the substratum we investigate the role of substratum friction in the emergence of coherent endoplasmic flow patterns and overall physarum fragment locomotion. [Preview Abstract] |
Tuesday, November 22, 2016 2:48PM - 3:01PM |
R20.00007: ABSTRACT WITHDRAWN |
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