Bulletin of the American Physical Society
2006 59th Annual Meeting of the APS Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2006; Tampa Bay, Florida
Session OA: Biofluid Dynamics XIII: Micro-Environment |
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Chair: Howard Hu, University of Pennsylvania Room: Tampa Marriott Waterside Hotel and Marina Grand Salon E |
Tuesday, November 21, 2006 12:15PM - 12:28PM |
OA.00001: Three-Dimensional Concentration Measurements around Actively Tracking Blue Crabs B.D. Dickman, J.L. Jackson, M.J. Weissburg, D.R. Webster Many aquatic arthropods locate food, suitable habitats, and mates solely through information extracted by chemical signals in their environment. Chemical plumes detected by larger animals are influenced by turbulence that creates an intermittent and unpredictable chemical stimulus environment. To link the stimulus pattern to behavior, we have developed a measurement system to quantify the instantaneous odor concentration surrounding a freely tracking blue crab through three-dimensional laser-induced fluorescence (3DLIF). A blue crab receives chemical stimulus at several locations, including the antennules near the mouth region and the distal tips of the legs and claws. Hence, three-dimensional measurements of the concentration field are required to link behavior to plume structure. During trials, crabs began their search 150 cm downstream of a source, and walking kinematics were recording simultaneously. The crabs were reversibly ``blindfolded'' during tracking to prevent aversive reactions to the intense laser light. Our experiments allow us to examine how hypothesized navigational cues, such as concentration bursts at the antennules and spatial asymmetry in concentration at the distributed chemosensory organs on the legs and claws, results in particular decisions during navigation. [Preview Abstract] |
Tuesday, November 21, 2006 12:28PM - 12:41PM |
OA.00002: Behavioral Response of Zooplankton to Environmental Cues Associated with Structure in the Ocean D.R. Webster, C.B. Woodson, M.J. Weissburg, J. Yen Recent observations of zooplankton aggregations in the ocean raise questions about the importance of copepod behavioral responses to layers of velocity gradient, density gradient, and dissolved chemicals and the influence of environmental structure in predator-prey dynamics. The current study uses controlled laboratory experiments to examine the response of several species of copepods to these layers and to identify and define the physical and chemical cues that these organisms exploit to improve foraging efficiency. Copepod response to horizontal layers of strain rate, density jump, and phytoplankton chemical exudates are observed in a laminar plane jet in order to isolate specific cues and combinations of cues. Particle image velocimetry (PIV) and laser induced fluorescence (LIF) quantify the environmental cues, and video-based observation quantifies path kinematics and swimming behavior. Behaviors elicited by the velocity gradient and chemical exudate layers include increased swimming speed and turn frequency consistent with excited area-restricted search behavior, which leads to increased proportional residence time in the layers. In contrast, the density gradient layer acts as a barrier to vertical movement and not as a positive cue for area-restricted search behavior. [Preview Abstract] |
Tuesday, November 21, 2006 12:41PM - 12:54PM |
OA.00003: Signal Structure in Bivalve Excurrent Flow S.K. Delavan, D.R. Webster Chemical cues provide information to organisms about potential mates, food, or predators and are subject to hydrodynamic processes as they are transported by the fluid flow. Recent studies show that the characteristics of the chemical release greatly influence the signal structure in a chemical plume. To fully characterize and quantify the nature of a chemical plume (metabolites from the excurrent siphon of a bivalve mollusk) several source characteristics, such as excurrent flux, flow unsteadiness, siphon diameter, and siphon height, must be examined. The resulting signal structure may be used by predators to distinguish unique characteristics of desired prey (for instance, small versus large bivalves). Alternatively, the signal structure may be manipulated by the bivalve to create a hydrodynamic refuge from predation. In the current study we used Laser Doppler Velicometry (LDV) to quantify the temporal pattern of the excurrent velocity of the benthic bivalve clam, \textit{Mercenaria mercenaria}. Time records of excurrent velocity were analyzed to reveal that pumping rates remain within a narrow range for a period of minutes followed by intermittent large decreases in velocity. Preliminary results suggest that clams have a ``resting period'' in which they retract then re-extend their siphons, possibly to control flux rates or to flush the filter. [Preview Abstract] |
Tuesday, November 21, 2006 12:54PM - 1:07PM |
OA.00004: Near-wall aerodynamics of idealized model foot motion Yoshi Kubota, Joseph Hall, Hiroshi Higuchi, Ritesh Sheth, Mark Glauser, Ezzat Khalifa The air quality is affected by amounts and types of contaminant particles suspended in the air. The particulate matter reaches the respiratory system in an indoor environment by fist becoming detached, resupended and then entrained in the human micro-environment. The resuspension phenomena from the floor occur through either a ballistic mechanism, where kinetic energy is transferred to dust particles through direct contact, or an aerodynamic mechanism, where dust particles are resuspended by the flow generated by the body. In this study we focus on the aerodynamic resuspension of particles caused by walking. The foot motion is idealized and is either towards or away from a floor. A circular disk and an elongated plate having the equivalent area to that of a human foot are used. The foot motion is driven vertically by a linear servo motor that controls the velocity, acceleration, stroke and deceleration. The model velocity is based on the real foot motion. In addition to flow visualization, flowfield measurements were conducted with PIV. In the downstroke, results show a vortex impacting the wall creating the strong wall jet. In upstroke, the vortex generated behind the idealized foot exhibits the large magnitude of velocity. Experiment is continuing with a model more closely to simulating shoe geometry as well as incorporating the real foot kinetics. The results will be compared with the numerical simulation and analytical results. [Preview Abstract] |
Tuesday, November 21, 2006 1:07PM - 1:20PM |
OA.00005: CFD Modeling of Particle Resuspension Jason DeGraw, John Cimbala, James Freihaut The phenomenon of resuspension plays a role in everyday life and is an important factor in indoor air quality. There are several models available for particle detachment, but the mechanisms by which particles are induced to lift off of a surface are not well explained in the literature. The lifting forces on a particle are generally too small to resuspend it, especially in the air flows generated by human activity (e.g., walking). We model the interaction of the aerodynamic disturbances and a thin layer of particles deposited on the surface. A standard CFD solver is used to compute the flow, and the particle transport model is one-way-coupled with the flow solution. Several time-dependent flows are considered, including an idealized footstep. The foot is represented using an immersed boundary technique, and is modeled as a disk that moves up and down with a trajectory patterned after experimental gait data. A jet and a radially moving vortex are generated as the foot approaches the floor. The strength of the jet is determined by the details of the foot movement near the surface. If the foot is slowed as it nears the floor, we find maximum velocities around 3 m/s, while the maximum velocity is more than doubled by a sudden stop. We have also computed a ``vacuum cleaner'' case to model the airflow generated by cleaning activities. In either case, the wall shear along the floor and the near-wall flow structure are used to examine the resuspension of particles. [Preview Abstract] |
Tuesday, November 21, 2006 1:20PM - 1:33PM |
OA.00006: Turbulent Anisotropy and Dissipation/Production in the Indoor Environment David Marr, Mark Glauser In the effort towards CFD validation and turbulent model calibration, various numerical terms are determined using various data sources such as DNS or experimental results. The presented research includes a series of PIV experiments and corresponding turbulent analysis in order to quantify these terms in the indoor environment. A variety of configurations are given to determine common values in such flow regimes as well as information critical to the CFD community for specific ventilation situations. Using a displacement ventilation design, where the heated body of the indoor occupant drives the flow, three components of velocity are presented around a breathing thermal manikin in various positions for a multi- faceted view of experimentally determined turbulence in the indoor environment. Specifically, an integrated length scale analysis in conjunction with the turbulent anisotropy and dissipation/production information is presented. [Preview Abstract] |
Tuesday, November 21, 2006 1:33PM - 1:46PM |
OA.00007: Bio-Fluid Dynamics in a Centimeter-Scale Diagnostics Incubator with Integrated Perfusion J. Vukasinovic, D.K. Cullen, A. Glezer, M.C. Laplaca Growing demands for long-term incubation of biologically faithful, three-dimensional neuronal and other cultures during extended physiological studies require efficient perfusion platforms with functional vasculatures that mimic the \textit{in vivo }condition in a thermally regulated environment. While thermostatically controlled incubation baths with capillary action perfusion are available, their use is confined to specific experimental conditions. The interstitial nutrient and gas delivery remains diffusion limited over the long term and cultures decay metabolically. To overcome these problems, we describe simple fabrication and experimental characterization of a compact, diagnostics incubator that allows \textit{in situ }monitoring of culture activity with a superior control of critical biological functions using convectively enhanced heat and mass transport. To overcome intercellular diffusion barriers culture is exposed to a direct flow of media issuing from an array of micro-nozzles that are directed normal to the substrate upholding the culture, and further improved by 3-D convection induced by jet interactions and biased, peripheral perfusate extraction through an array of microchannels as demonstrated by microPIV measurements. [Preview Abstract] |
Tuesday, November 21, 2006 1:46PM - 1:59PM |
OA.00008: Microfluidic device for rapid solution exchange to study kinetics of cell physiology Howard Hu, Meghana Honnatti, Kevin Gillis Exchanging the extracellular solution of the cell rapidly (less than 10ms) is an important requirement in study the kinetics of cell physiology. A microfluidic device is developed to exchange the solution around the cells as they flow through a junction at the intersection of two microfluidic channels. The solution exchange time is measured experimentally by fluorescently labeling the cell surface membranes with a styryl dye, FM1-43 or FM 2-10, and then observing the time course of cell fluorescence decay following the rapid drop in the extracellular concentration of the FM dye that occurs as the cell flows past the fluidic junction. A numerical model is developed to guide the experimental design of microfluidic device. In the model, the motion of a single cell through a fluid junction is simulated and the mixing process of the solutions is solved. The model also includes the kinetics of departitioning of FM dyes from the cell membrane. The departitioning time constants for the FM dyes are determined from fitting the measured data of the cell fluorescence decay. This departitioning kinetics is important as FM dyes are commonly used to label cell membranes for the purpose of measuring the release of neurotransmitter from synaptic vesicles via exocytosis and the subsequent reuptake of vesicular membrane by endocytosis. [Preview Abstract] |
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