THEORETICAL AND EXPERIMENTAL STUDIES IN TRANSIENT MEMBRANE-FLUID FILM INTERACTIONS FOR SINGLE CELLS AND ASSEMBLAGES.
Item
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Title
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THEORETICAL AND EXPERIMENTAL STUDIES IN TRANSIENT MEMBRANE-FLUID FILM INTERACTIONS FOR SINGLE CELLS AND ASSEMBLAGES.
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Identifier
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AAI8112748
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identifier
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8112748
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Creator
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WU, RANDALL.
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Contributor
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Sheldon Weinbaum
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Date
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1981
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Language
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English
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Publisher
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City University of New York.
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Subject
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Engineering, Mechanical
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Abstract
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In vitro experiments performed on excised artery segments have shown that the artery wall possesses non-linear filtration properties. The high deformability of the smooth muscle cells in the artery's media region might be a major factor contributing to this non-linear behavior. Since it is not possible to measure the local excess pore pressure in the interstitial space of the media region a laboratory model of the cellular component of the artery wall is used to obtain the draining behavior of a two phase system, with the particulate phase composed of membrane bound fluid filled cells, under a consolidating load. The experiments are performed for various values of initial porosity.;A comparison is made between Terzaghi's one-dimensional consolidation theory and the experimental results for excess pore pressure. This comparison shows that at an initial matrix porosity of 0.25 the assemblage consolidates according to classical theory. As initial porosity is decreased a departure from classical theory is evident. At a physiologically significant initial porosity of 0.10 all similarities with the classical linear theory are absent. The time dependent draining of the interstitial fluid is seen to be on a longer time scale as initial porosity is decreased.;A quantitative theoretical model is developed to describe the draining of a fluid film between a membrane bound fluid filled cell and a planar surface in an effort to understand the local mechanisms involved in the consolidating specimen. Order of magnitude analysis performed on the non-linear equations shows two characteristics times are required to describe the draining behavior of the fluid film. The two time scales are called the characteristic time for fluid trapping and the characteristic time for draining the fluid film. During the early period following the loading of the cell the fluid film exhibits a behavior unique to the membrane squeeze film theory. A bidirectional flow is set up in the lubricating layer due to an off axis pressure peak. This dual flow condition is not seen in elastohydrodynamic squeeze film theory, where the maximum pressure is always located at the point of maximum deformation and the flow is directed radially outward everywhere. The bidirectional flow causes a gradual thickening of the film in the central region and the formulation of a narrow gap region of high curvature near the edge of the near contact area where the flow is directed radially outward. On the longer time scale, after the fluid trapping has been achieved, the off axis pressure peak is replaced by a characteristic pressure plateau in the inner region of the near contact area. The membrane descends monotonically from this time on and the flow rate is positive at every location. The characteristic time for draining is typically several orders of magnitude larger than the trapping time. During this larger time period changes in the flow behavior are characterized by a nearly constant edge region and greatly diminished velocities in the lubricating film.;For the case of a rigid disc replacing the membrane bound cell the characteristic time for draining the fluid film is equal to the trapping time of the membrane problem. This comparison shows that the membrane boundary increases draining time by several orders of magnitude when the initial film thickness is two or more orders of magnitude smaller than the typical cell size. At an initial porosity of 0.10 the typical channel dimensions in the consolidation experiment have reached the point where the membrane squeeze film theory is valid.;A simple experiment has been constructed to confirm the existance of the bidirectional flow and the fluid trapping phenomena. Experimental photographs graphically illustrate the gradual thickening of the lubricating layer near the origin and the formation and draining of the edge region as predicted by the membrane squeeze film theory.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
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Program
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Engineering
