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 HA: Biofluid Dynamics IX |
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Chair: Anubhav Tripathi, Brown University Room: Tampa Marriott Waterside Hotel and Marina Grand Salon E |
Monday, November 20, 2006 2:00PM - 2:13PM |
HA.00001: Assessing Chaos in Sickle Cell Anemia Crises Wesley Harris, Francois Le Floch Recent developments in sickle cell research and blood flow modeling allow for new interpretations of the sickle cell crises. With an appropriate set of theoretical and empirical equations describing the dynamics of the red cells in their environment, and the response of the capillaries to major changes in the rheology, a complete mathematical system has been derived. This system of equations is believed to be of major importance to provide new and significant insight into the causes of the disease and related crises. With simulations, it has been proven that the system transition from a periodic solution to a chaotic one, which illustrates the onset of crises from a regular blood flow synchronized with the heart beat. Moreover, the analysis of the effects of various physiological parameters exposes the potential to control chaotic solutions, which, in turn, could lead to the creation of new and more effective treatments for sickle cell anemia. . [Preview Abstract] |
Monday, November 20, 2006 2:13PM - 2:26PM |
HA.00002: Harmonically driven oscillating flexible flat plates behind a bluff body Jeremy Pena, David Latortue, James Allen, Paulo de Sousa This experimental study details the oscillations of the flexible plate, mounted behind a bluff body. Plates of different stiffness were individually tested. Each plate was oscillated a range of frequencies 0.1 Hz to 2.0 Hz to produce a range of Strouhal numbers based on the bluff body width of 0.01-0.6. The natural frequency produced from the bluff body excites the oscillating plates. Similar to a fish behind a rock, the most energy efficient oscillating frequency is when the Strouhal number from the oscillating plates matches the shedding frequency of the bluff body. Efficiency is determined by the work input to the system via torque transducers. Experiments were used to determine an optimal stiffness material that couples most efficiently with the shedding of the structures from the bluff body. Torque sensors and Particle Image Velocimetry (PIV) were used to measure coupling effects. [Preview Abstract] |
Monday, November 20, 2006 2:26PM - 2:39PM |
HA.00003: Models for the Dynamics of the Human Tear Film R.J. Braun, L.P. Cook, P.E. King-Smith Every time one blinks, a tear film is left on the front of the eye to protect the cornea and to help provide a smooth optical surface, as well as other functions. We adopt the accepted view that the tear film layer contains a primarily aqueous layer, and we develop models for the formation and evolution of the aqueous layer over one or more blink cycles using lubrication theory. The models incorporate surface tension, viscosity, surfactant transport, Marangoni effects and slip on the cornea. A comparison with in vivo interferometry is made for a half blink and it is favorable. In two models and one set of conditions, the amount of lid closure required for the tear film to be completely restarted is found to be about 7/8 from considerations due solely to fluid dynamics; that is, if the eyelids close to about 1/8 of the fully open width, that is enough to fully refresh the tear film. [Preview Abstract] |
Monday, November 20, 2006 2:39PM - 2:52PM |
HA.00004: Eyelids Bertrand Selva, Virginie Duclaux, christophe clanet While blinking, the eyelids move up and down: 1) During their upward motion, they deposit the thin tear film in charge of the protectyion of the cornea. We first study the thikness of this film, modeling the eyelid as an elastic sheet and the tear as a newtonian liquid. 2) During the downward motion, the eyelid moves upon the tear film and in some case gets stuck and reverses, leading to the so called Entropion desease. We come back on this irregular motion and show how it can be physically understood. [Preview Abstract] |
Monday, November 20, 2006 2:52PM - 3:05PM |
HA.00005: Taylor Dispersion in PCR in a microchannel Anubhav Tripathi, Anuj Chauhan While amplifying DNA strands via polymerease chain reaction (PCR) in a microfluidic device, the sample is subjected to cyclic changes in temperature.~ We investigate the dispersion of molecules in a microchannel as these undergo a contraction-expansion flow that is driven by temporally changing temperatures. We use method of multiple time scales with regular expansions to obtain the effective dispersivity.~ Due to the thermal expansion of the carrier fluid, the cyclic temperature variations lead to both axial and lateral velocities. These periodic velocity profiles lead to an increase in axial dispersion.~The dispersion coefficient increases as the square of the channel position from the center of the microchannel. Due to the quadratic variation of the dispersion coefficient in the axial direction, the concentration profile is non-Gaussian and a complex function of frequency and magnitude of the temporal oscillations and the dimensions of the microchannel. We derive analytical expressions for dispersion coefficient for cyclic profiles of any shape. We report the results for the mean velocity and the dispersion coefficients for three cases: (i) sinusoidal temperature variations with no reaction; (ii) arbitrary temporal temperature changes without reaction; and (iii) sinusoidal temperature changes with reaction. [Preview Abstract] |
Monday, November 20, 2006 3:05PM - 3:18PM |
HA.00006: Modeling High Gradient Magnetic Separation in Biological Fluids D. Bockenfeld, H. Chen, D. Rempfer, M. Kaminski, A. Rosengart A portable magnetic filter capable of separating magnetic nanospheres from arterial blood flow for detoxification of human blood is under design. In the separator design, an array of biocompatible capillary tubing and magnetizable wires is immersed into an externally applied homogeneous magnetic field. While subject to the magnetic field, the wires create high magnetic field gradients, which aid in the collection of blood- borne magnetic nanospheres from blood flow. In this study, a numerical model was created to determine the configuration of the wire-tubing array from two possible configurations. To determine which configuration was better suited for the separator design, the numerical capture efficiencies of the separator for the different configurations were compared over a range of mean blood flow velocities using subsets of the full configurations and compared with experimental results. For the configuration that showed higher capture efficiencies, the effects of blood velocity, magnetic field strength, wire and particle materials, and the length of the separator is also studied. [Preview Abstract] |
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