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 KB: Biofluid Dynamics XI |
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Chair: Petia Vlahovska, Dartmouth College Room: Tampa Marriott Waterside Hotel and Marina Grand Salon F |
Monday, November 20, 2006 5:15PM - 5:28PM |
KB.00001: Macromolecules and deformable drops in linear flows with vorticity: a second conformation transition Jerzy Blawzdziewicz Polymer or DNA macromolecules in an external straining flow undergo a rapid transition between a coiled state and a much more elongated stretched state. This change is due to the interplay between the entropic spring forces driving relaxation of the molecule towards equilibrium and the hydrodynamic forces causing deformation. The coil--stretch transition has a close analogy in the instability of a drop shape when the flow strength is slowly increased to the critical value above which the capillary forces cannot balance hydrodynamic forces. For highly viscous drops in flows with nonzero vorticity there also exists a less known additional transition occurring between two stationary states stabilized either by capillary forces or by rotation. We predict that macromolecules also undergo an additional transformation between a rotationally stabilized nearly undeformed state and a moderately deformed state. Using small-deformation equations for both the drop shape and the conformation tensor of a macromolecule we quantitatively explore the analogy between the dynamics of drops and macromolecules in flows with rotation. [Preview Abstract] |
Monday, November 20, 2006 5:28PM - 5:41PM |
KB.00002: Fluid vesicle dynamics and interaction in shear flow. Vasiliy Kantsler, Enrico Serge, Victor Steinberg We present experimental results on single vesicle behavior subjected to shear flow, as well as the hydrodynamic interaction between neighboring vesicles. Moreover the dynamics of a vesicle in many-vesicle field is also studied. Tank treading, trembling and tumbling regimes of the motion are described in terms of the dimensionless variables, such as viscosity contrast, excess area and the dimensionless shear. It should be emphasized that vesicle interaction considerably increases tank treading angle fluctuations, though suppressing the transition to tumbling motion. [Preview Abstract] |
Monday, November 20, 2006 5:41PM - 5:54PM |
KB.00003: Transport of cardiovascular microbubbles in gas embolotherapy Joseph L. Bull, Andres J. Calderon, Brijesh Eshpuniyani, Doug Valassis, J. Brian Fowlkes This work is motivated by our ongoing development of a novel gas embolotherapy technique to occlude blood flow to tumors using gas bubbles that are selectively formed by the in vivo acoustic vaporization of liquid perfluorocarbon droplets. The droplets are small enough to pass through the microcirculation, but the subsequent bubbles are large enough to lodge in vessels. The uniformity of tumor infarction depends on the transport the blood-borne bubbles before they stick. We theoretically and experimentally investigate the transport of gas bubbles through bifurcating blood vessels. More homogenous bubble splitting is observed for higher values of capillary numbers and lower values of Bond numbers. The dependence of bubble lodging on flow parameters is also investigated, and several modes of bubble lodging and sticking are identified. These findings indicate the ability of gas bubbles to occlude flow and suggest the potential for development of treatment strategies that uniformly occlude the tumor circulation while minimizing collateral infarction. This work is supported by NSF grant BES-0301278 and NIH grant EB003541. [Preview Abstract] |
Monday, November 20, 2006 5:54PM - 6:07PM |
KB.00004: Three dimensional numerical simulation of a suspension of multiple deformable liquid capsules in pressure-driven flow Sai Doddi, Prosenjit Bagchi Capsules are liquid drops surrounded by hyper-elastic membranes, and are representative of biological cells. We present 3D numerical simulations of a large ensemble of capsules (up to 350 in numbers) flowing through a rectangular channel at low Reynolds numbers. The numerical method is based on the front tracking method, and the capsule membranes are assumed to follow neo-Hookean law. First we will discuss the lateral migration of an isolated capsule in the channel. The numerical results will be compared with the analytical results in the limit of small deformation. Then we will present results on how the lateral migration is affected in presence of a pairwise interaction between two neighboring capsules. We will show that the deformation-induced lateral migration is strongly hindered by the dispersion effect of the pairwise interaction. Finally, we will present simulations of the flow of suspension of multiple capsules up to 350 in numbers. The focus here will be on the multi-particle interaction, formation of the particle-free region near the wall, and the microstructure evolution. [Preview Abstract] |
Monday, November 20, 2006 6:07PM - 6:20PM |
KB.00005: Vesicle dynamics in linear viscous flows Petia Vlahovska, Ruben Serral-Gracia A vesicle is a capsule made of phospholipid bilayer membrane; it is widely employed as a cell paradigm. A vesicle in shear flow represents a simple model system to study cell dynamics in the microcirculation. We develop an analytical theory for the dynamics of a quasi--spherical vesicle in a linear viscous flow. The analysis includes the effects of the viscosity contrast between the inner and suspending fluids and the membranes bending stresses on the flow--induced vesicle deformation. We obtain that in simple shear flow the leading order stationary vesicle shape and orientation angle with respect to the flow are independent of the membrane bending rigidity. If the viscosity contrast exceeds a critical value, which depends on the vesicle excess area, no stationary solution exist and the vesicle tumbles with frequency which increases with viscosity contrast and approaches the rotation rate of the external flow. Non-Newtonian rheology with both shear thinning viscosity and normal stresses is predicted for a dilute suspension of vesicles. The results agree well with published experimental data for vesicle behavior in shear flows. [Preview Abstract] |
Monday, November 20, 2006 6:20PM - 6:33PM |
KB.00006: Non-equilibrium All-atoms Molecular Dynamics Simulations of Free and Tethered DNAs in Nano-channel Shear Flows Guan Wang, William Sandberg The CHARMM equilibrium biomolecular dynamics software has been extended to handle non-equilibrium molecular dynamics (NEMD) problems. Biomolecules, both free and wall-tethered, have been simulated in the all-atom style in a water-filled nanochannel shear flow. The new methods and computational codes were demonstrated by carrying out NEMD simulations of tethered dsDNAs on gold surfaces. We investigated the diffusion coefficient and the velocity auto-correlation function in selected regions in the direction of shear. The fluidic forces on tethered ss/ds-DNAs and the tilting angles were also calculated. The tethering of the linker molecule (6-mercapto-1-hexanol) to perfect Au(111) surfaces was parameterized based on density functional theory calculations. Force field parameters were incorporated into the CHARMM database. Gold surfaces are simulated in a Lennard-Jones style model that was fitted to the Morse potential model of bulk gold. [Preview Abstract] |
Monday, November 20, 2006 6:33PM - 6:46PM |
KB.00007: Protein crystallization induced and enhanced via hydrodynamics: Forced crystallization. Ali Azadani, Amir Hirsa The ability to describe and utilize protein structure has made possible the rational design of new drugs and pharmacological agents. Proteins must be first crystallized in order to utilize the techniques that yield a precise description of their structure. Two-dimensional protein crystallization at the air-water interface entails the specific binding of a protein to a lipid monolayer containing a ligand. There are several classic crystallization strategies such as varying the ionic strength, pH, and temperature of the protein solution; in all of these, fluid motion is reported to be detrimental. However, we have discovered that fluid dynamics can be used to advantage. The flow system utilized consists of a stationary open cylinder driven by the constant rotation of the floor, in the axisymmetric flow regime with inertia. We show that by applying shear stress to the protein-ligand complexes at the interface, it is possible not only to control the protein-protein interaction and induce crystallization, but also, by varying the Reynolds number, regulate the rate of nucleation and growth separately which were always a challenge for crystallographers. [Preview Abstract] |
Monday, November 20, 2006 6:46PM - 6:59PM |
KB.00008: ABSTRACT WITHDRAWN |
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