1,720,960 research outputs found
Three-dimensional computational simulation of multiscale multiphysics cellular/particulate processes in microcirculatory blood flow
No full textComputational modeling and simulation is considered to study the concurrent multiscale/multiphysics phenomena associated with cellular/particulate transport in microcirculatory blood flow. The model integrates microhydrodynamics of different blood cells, complexity of vascular geometry, and nanoscale adhesive interactions. A finite element method (FEM) is used to model the cell membrane deformation with high accuracy, and is coupled to the bulk flow motion via a front-tracking method. The geometric complexities are simulated using a sharp-interface immersed boundary method, and the molecular adhesion is coarse-grained via a Monte Carlo method. The following sequence of problems is addressed: (a) Hydrodynamic interaction between a platelet and a red blood cell (RBC) in a dilute suspension: 3D simulations of pairwise hydrodynamic interaction between a platelet and an RBC in a wall-bounded shear flow are conducted. The effects of different dynamics of the RBC, namely tank-treading and tumbling, and the proximity to the wall on platelet trajectories are quantified. Based on the numerical results, a mechanism of continual platelet drift towards the vessel wall is proposed. (b) Platelet transport and dynamics in blood flow: 3D simulations are considered to study the transport of platelets in semi-dense suspension of flowing RBCs. It is found that the local microstructure of RBC suspension provides a fast margination mechanism for platelets to drift towards the blood vessel wall. It is also shown that the anisotropic diffusion of platelets contributes to the formation of platelet clusters, and may act as a hydrodynamic precursor to blood clot formation. (c) Microparticle shape effects on their transport and dynamics in blood flow: The shape effect of microscale targeting drug carriers modeled as platelet-sized microparticles on their margination, near-wall dynamics, and adhesion is quantified and explained by individual particle dynamics and interaction with RBCs. It is shown that the particle shape has entirely different effects on different stages of margination/adhesion cascade. It is suggested that the local hemorheological conditions of the targeted site should be taken into account while selecting the optimum shape for microvascular drug carriers. (d) Blood flow in stenosed microvessels: 3D simulations of cellular motion through stenosed microvessels are considered. The Fahraeus-Lindqvist effect is shown to be significantly enhanced, due to the asymmetric distribution of the RBCs caused by the stenosis geometry. Such asymmetry together with the discrete motion of cells are demonstrated to cause an asymmetry in the average as well as the time-dependent flow characteristics along the length of stenosis. It is concluded that the flow physics and its physiological consequences are significantly different in micro- versus macrovascular stenosis. (e) Adhesion of microparticles in microvessels – role of RBCs and microparticle deformability: 3D simulations of the adhesion of deformable drug carrier particles in the flow of semi-dense RBC suspension through microvessels are conducted. It is shown that both the presence of RBCs and the particle deformability have a dual role in microparticle adhesion. During the initial formation of adhesive bonds, the RBCs have an enhancing effect while the effect of particle deformation is adverse. In contrast, during the subsequent adhesive rolling of microparticles, the RBCs have an adverse effect while the particle deformation improves stable adhesive rolling motion. It is concluded that to efficiently benefit from the advantages of deformable particles in biomedical targeting, the local blood flow characteristics of the targeted site must be taken into account.Ph.D.Includes bibliographical referencesby Koohyar Vahidkha
Particle Dynamics in Inhomogeneous Flow at Moderate to High Reynolds Number
No full textIn order to obtain an accurate parameterization of the hydrodynamic force acting on a spherical particle in complex inhomogeneous flows at moderate particle Reynolds numbers (Re = 10--600), we develop a DNS technique that resolves the smallest scales in the ambient flow and in the particle wake, and provides detailed microscale information on flow-particle interaction. We address the following sequence of problems. (a) Irrotational flow: We perform DNS of stationary and freely moving particles in straining flows. We show that the spatial nonuniformity in the ambient flow can substantially enhance drag and lift. We explore the mechanism of these forces and relate them to the structure of the wake. A universal description of the added-mass force, and a generalized invariant representation of the viscous force are presented. An improved parameterization, comprising of the generalized viscous and added-mass forces, is shown to predict the DNS results very accurately. (b) Particle rotation: We perform DNS of a freely rotating particle in linear shear flow. We observe that under the torque-free condition, the rotation-rate of the particle decreases rapidly with Re following a power law. The effect of rotation on the drag is negligible, while that on the lift is to generate the Magnus force. DNS of a freely translating and rotating particle shows that free rotation has little effect on the unsteady motion. (c) Shear- vs. vortex-induced lift force: We perform DNS of a particle in a shear flow and in a pure rotational flow. We observe that the lift force in a pure rotational flow is two orders of magnitude higher than that in a shear flow. We explore the mechanism of the difference, and its implication on the particle/bubble migration in a vortex. (d) Particle-turbulence interaction: We perform DNS of a particle subjected to an isotropic turbulent flow. We explore different estimates of the mean and instantaneous drag and compare them with the DNS results. The mean and instantaneous wake structure, wake oscillation and vortex shedding in turbulent flow are studied to understand the mechanism of turbulence modulation in the wake.Made available in DSpace on 2015-09-28T16:23:34Z (GMT). No. of bitstreams: 2
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Previous issue date: 2002Embargo set by: Seth Robbins for item 88988
Lift date: Forever
Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDsRestricted to the U of I community idenfinitely during batch ingest of legacy ETDsU of I Only317 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2002
Particle Dynamics in Inhomogeneous Flow at Moderate to High Reynolds Number
No full text317 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2002.In order to obtain an accurate parameterization of the hydrodynamic force acting on a spherical particle in complex inhomogeneous flows at moderate particle Reynolds numbers (Re = 10--600), we develop a DNS technique that resolves the smallest scales in the ambient flow and in the particle wake, and provides detailed microscale information on flow-particle interaction. We address the following sequence of problems. (a) Irrotational flow: We perform DNS of stationary and freely moving particles in straining flows. We show that the spatial nonuniformity in the ambient flow can substantially enhance drag and lift. We explore the mechanism of these forces and relate them to the structure of the wake. A universal description of the added-mass force, and a generalized invariant representation of the viscous force are presented. An improved parameterization, comprising of the generalized viscous and added-mass forces, is shown to predict the DNS results very accurately. (b) Particle rotation: We perform DNS of a freely rotating particle in linear shear flow. We observe that under the torque-free condition, the rotation-rate of the particle decreases rapidly with Re following a power law. The effect of rotation on the drag is negligible, while that on the lift is to generate the Magnus force. DNS of a freely translating and rotating particle shows that free rotation has little effect on the unsteady motion. (c) Shear- vs. vortex-induced lift force: We perform DNS of a particle in a shear flow and in a pure rotational flow. We observe that the lift force in a pure rotational flow is two orders of magnitude higher than that in a shear flow. We explore the mechanism of the difference, and its implication on the particle/bubble migration in a vortex. (d) Particle-turbulence interaction: We perform DNS of a particle subjected to an isotropic turbulent flow. We explore different estimates of the mean and instantaneous drag and compare them with the DNS results. The mean and instantaneous wake structure, wake oscillation and vortex shedding in turbulent flow are studied to understand the mechanism of turbulence modulation in the wake.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD
Mesoscale Simulation of Blood Flow in Small Vessels
No full textAbstractComputational modeling of blood flow in microvessels with internal diameter 20–500μm is a major challenge. It is because blood in such vessels behaves as a multiphase suspension of deformable particles. A continuum model of blood is not adequate if the motion of individual red blood cells in the suspension is of interest. At the same time, multiple cells, often a few thousands in number, must also be considered to account for cell-cell hydrodynamic interaction. Moreover, the red blood cells (RBCs) are highly deformable. Deformation of the cells must also be considered in the model, as it is a major determinant of many physiologically significant phenomena, such as formation of a cell-free layer, and the Fahraeus-Lindqvist effect. In this article, we present two-dimensional computational simulation of blood flow in vessels of size 20–300μm at discharge hematocrit of 10–60%, taking into consideration the particulate nature of blood and cell deformation. The numerical model is based on the immersed boundary method, and the red blood cells are modeled as liquid capsules. A large RBC population comprising of as many as 2500 cells are simulated. Migration of the cells normal to the wall of the vessel and the formation of the cell-free layer are studied. Results on the trajectory and velocity traces of the RBCs, and their fluctuations are presented. Also presented are the results on the plug-flow velocity profile of blood, the apparent viscosity, and the Fahraeus-Lindqvist effect. The numerical results also allow us to investigate the variation of apparent blood viscosity along the cross-section of a vessel. The computational results are compared with the experimental results. To the best of our knowledge, this article presents the first simulation to simultaneously consider a large ensemble of red blood cells and the cell deformation
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Three-dimensional computational modeling and simulation of cell rolling and deformation on an adhesive surface in shear flow
No full textThree-dimensional computational modeling and simulations are presented on the rolling motion of a deformable cell on an adhesive surface in shear flow. The problem is motivated primarily by the adhesive rolling motion of white blood cells or leukocytes in response to inflammation in the body. The methodology is based on an immersed boundary method to predict cell deformation, and a Monte Carlo simulation to model the random formation and breakage of the adhesion bonds formed between a ligand-bearing cell and a receptor-coated surface. The multiscale and multiphysics modeling developed in this study allows us to resolve the complex coupling between the hydrodynamics, the deformation dynamics of the cell, and the biophysics of the adhesion bonds. In the thesis, we address the sequence of events that are encountered in the multistep process of cell rolling, namely, the initial arrest of the cell, followed by its deformation and spreading on the substrate, and the subsequent quasi-steady rolling motion. We provide phase diagrams for cell adhesion/escape, and showed that the hydrodynamic lift, that exists on a deformable cell in the wall-bounded motion, plays a major role in the process. The experimentally observed 'stop-and-go' motion of the cells is predicted in our simulations. After providing results on the general adhesive rolling motion, we focus specifically on the rolling dynamics of the leukocytes, and study the effect of cell deformability, shear rate and cell concentration on the instantaneous and time-averaged rolling characteristics. We also study the biophysical characteristics of the adhesion bonds during the rolling process. Finally, we consider the effect of the adherent leukocytes on the surrounding flow in terms of the changes in tracer dispersion and the vascular flow resistance. Comparison with experimental measurements (in vitro and in vivo) is presented throughout the thesis.M.S.Includes bibliographical references (p. 125-131)
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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