Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session A18: Biofluids: General |
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Chair: Luca Brandt, KTH, Stockholm Room: 28D |
Sunday, November 18, 2012 8:00AM - 8:13AM |
A18.00001: Fluid fragmentation and disease transmission Lydia Bourouiba, John W.M. Bush The transfer of pathogens from infected to non-infected members of a population is critical in determining the outcome of an epidemic. However, fundamental mechanisms of pathogen spreading remain poorly understood. We here present the results of combined experimental and theoretical studies of the~role of fluid fragmentation in the transmission of a number of common pathogens, with a particular focus on those causing respiratory infections. [Preview Abstract] |
Sunday, November 18, 2012 8:13AM - 8:26AM |
A18.00002: The fluid dynamics of human birth Andrea Lehn, Megan C. Leftwich This study investigates the fluid dynamics associated with the human birth process. Specifically, we investigate the role of the viscosity of the amniotic fluid in transferring force from the contracting uterus to the fetus during delivery. This experimental work uses an approximate uterus and dilated cervix--fabricated with liquid latex--filled with a fluid of known viscosity and an oblong solid fetus. The force required to extract the fetus is recorded for several values of amniotic viscosity. The study looks at both pull-out force values (where the fetus is pulled from outside the uterus) and push-out force values (where pressure in the experimental uterus is used to remove the fetus). In addition to the viscosity study, we also investigate the increased force required to deliver an offset fetus by tilting the major axis of the oblong fetus and repeating the pull-and push-out experiments. This study will provide knowledge about the fundamental fluid dynamic processes involved in human birth. [Preview Abstract] |
Sunday, November 18, 2012 8:26AM - 8:39AM |
A18.00003: Evolution of a pre and post lens tear film with a contact lens Matthew Gerhart, Daniel Anderson The work is the development, implementation, and analysis of a two-dimensional tear film model including a porous contact lens. The geometry of the problem is: a pre-lens layer that is a thin tear film between the outside air and contact lens, a contact lens that is a rigid but movable porous substrate, and a post-lens layer that is a thin film layer between the contact lens and the cornea. We are looking at short and long term behavior of the evolution of the thin film in the pre-lens layer coupled with the porous layer and the thin squeeze film in the post-lens layer. We model the different behaviors that arise as the Darcy number, evaporation effects, and boundary flux conditions change. [Preview Abstract] |
Sunday, November 18, 2012 8:39AM - 8:52AM |
A18.00004: A Model Problem for Tear Film Distribution on a Moving Rectangular Domain Quan Deng, Tobin Driscoll, Richard Braun We consider a model problem for the pre-corneal tear film on a moving 2D rectangular domain. The problem considers a thin Newtonian layer covered by an insoluble surfactant representing the effect of polar lipids. A non-linear PDE for film thickness from the lubrication approximation, together with a nonlinear PDE for the surfactant concentration is solved using the method of lines with spectral methods in space. The Marangoni effect couples the variables together. Numerical experiments using different end motions (realistic or sinusoidal) and perturbations to the surfactant distributions (to imitate observe lipid distributions \textit{in vivo}) were performed. The results indicate that some \textit{in vivo} elements of the tear film distribution with relatively long length scales are captured by the model, but some fine-scale phenomena are not captured. If time permits, results from a two layer model will presented. [Preview Abstract] |
Sunday, November 18, 2012 8:52AM - 9:05AM |
A18.00005: Modeling Tear Film Dynamics on a 2-D Eye-shaped Domain Longfei Li, Richard Braun, Kara Maki, William Henshaw We study tear film dynamics on a 2-D eye-shaped domain using a lubrication model. Time dependent flux boundary conditions that model the lacrimal gland tear supply and punctal drainage are imposed. We solved the model equations with Overture computational framework. Results reveals our model captures the hydraulic connectivity and other key physics of human tear film observed {\it in vivo}. Comparisons are made with existing models and experiments. Should time permit, osmolarity dynamics (salt ion concentration) will be included. [Preview Abstract] |
Sunday, November 18, 2012 9:05AM - 9:18AM |
A18.00006: Two Layer Model for Local Tear Film Dynamics Nicholas Gewecke, Rich Braun, Chris Breward, Ewen King-Smith Many tear film models utilize a single-layer approach that represents only the aqueous layer, which constitutes the majority of the tear film. In such models, the layer is dominated by shear stresses. Some recent models have incorporated surfactant effects at the liquid-air interface to model the effects of polar lipids there. Clinical observations of the lipid layer indicate more complicated dynamics of the lipid layer than demonstrated by these previous models. The model presented in this talk includes a thin lipid layer between the aqueous layer and the air, which is treated as an extensional flow. Our results demonstrate formation of lipid drops, with the number of drops dependent upon the parameters of the system, especially the thickness ratio between the lipid and aqueous layers. [Preview Abstract] |
Sunday, November 18, 2012 9:18AM - 9:31AM |
A18.00007: On conjoining pressures in the tear film Javed Siddique, Nicholas Gewecke, Rich Braun We study the local tear film dynamics in a two-layer model with a Newtonian extensional layer over a Newtonian shear layer with a surfactant between. The upper layer represents the lipid layer and the underlying layer the aqueous layer in the tear film. We study the effect of the ions on the conjoining pressure in the aqueous layer using a Debye-Huckel approximation. If time permits, we will treat the evaporation of the water from the underlying aqueous layer and the effect of increasing osmolarity of the aqueous and the interaction with the conjoining pressure. More complicated conjoining pressure contributions are added as needed. [Preview Abstract] |
Sunday, November 18, 2012 9:31AM - 9:44AM |
A18.00008: Convective transport resistance in the vitreous humor Anita Penkova, Satwindar Sadhal, Komsan Ratanakijsuntorn, Rex Moats, Yang Tang, Patrick Hughes, Michael Robinson, Susan Lee It has been established by MRI visualization experiments that the convection of nanoparticles and large molecules with high rate of water flow in the vitreous humor will experience resistance, depending on the respective permeabilities of the injected solute. A set of experiments conducted with Gd-DTPA (Magnevist, Bayer AG, Leverkusen, Germany) and 30 nm gadolinium-based particles (Gado CELLTrack$^{TM}$, Biopal, Worcester, MA) as MRI contrast agents showed that the degree of convective transport in this Darcy-type porous medium varies between the two solutes. These experiments consisted of injecting a mixture of the two (a 30 $\mu $l solution of 2{\%} Magnevist and 1{\%} nanoparticles) at the middle of the vitreous of an ex vivo whole bovine eye and subjecting the vitreous to water flow rate of 100 $\mu $l/min. The water (0.9{\%} saline solution) was injected at the top of the eye, and was allowed to drain through small slits cut at the bottom of the eyeball. After 50 minutes of pumping, MRI images showed that the water flow carried the Gd-DTPA farther than the nanoparticles, even though the two solutes, being mixed, were subjected to the same convective flow conditions. We find that the convected solute lags the water flow, depending on the solute permeability. The usual convection term needs to be adjusted to allow for the filtration effect on the larger particles in the form (1-$\sigma )$\textbf{\textit{u}}$\cdot $\textbf{$\nabla $}$c$ with important implications for the modeling of such systems. [Preview Abstract] |
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