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1
Rabodzey, Aleksandr. "Flow-induced mechanotransduction in cell-cell junctions of endothelial cells." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/41586.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Biological Engineering Division, 2006.<br>Includes bibliographical references (leaves 86-92).<br>Endothelial cells show an unexpected behavior shortly after the onset of laminar flow: their crawling speed decreases ~40% within the first 30 min, but only in a confluent monolayer of endothelial cells, not in subconfluent cultures, where cell-cell interactions are limited. This led us to study early shear effects on cell-cell adherens junctions. We found a 30±6% increase in the number of VE-cadherin molecules in the junctions. The strength of interactions of endothelial cells with surfaces coated with recombinant VE-cadherin protein also increased after laminar flow. These observations suggest that endothelial cell junction proteins respond to flow onset. The process of clustering may induce diffusion of monomers to the junction area, resulting in an overall increase in VE-cadherins in the junctions. To directly confirm the role of adherens junctions in the decrease in cell crawling speed, we used siRNA-knockdown technique to produce cells lacking VE-cadherin. These cells showed no decline in crawling speed under flow. Our interpretation is consistent with previous data on junction disassembly 8 hr after flow onset. The speed of endothelial cell crawling returns to the original level by that time, and junctional disassembly may explain that phenomenon. In order to understand better the change in VE-cadherin distribution under flow and during junction formation and remodelling, we developed a mathematical model of VE-cadherin redistribution in endothelial cells. This model allowed us to develop a quantitative framework for analysis of VE-cadherin redistribution and estimate the amount of protein in the junctions and on the apical surface. In addition to that, the model explains rapid junction disassembly in the leukocyte transmigration and junction formation in subconfluent cells.<br>(cont.) These studies show that intercellular adhesion molecules are important in the force transmission and shear stress response. Their role, however, is not limited to flow mechanotransduction. Intercellular force transmission has an important application - organ development and, specifically, angiogenesis. We studied the role of VE-cadherin in vessel development in HUVECs and showed that VE-cadherin-null cells do not form vessels in the in vitro assay. This observation confirms the important role of intercellular force transmission in response to external force caused by flow or exerted by other cells.<br>by Aleksandr Rabodzey.<br>Ph.D.
2
LASAGNA, DAVIDE. "Flow physics and control of trapped vortex cell flows." Doctoral thesis, Politecnico di Torino, 2013. http://hdl.handle.net/11583/2518621.
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The main objective of this work is to investigate on the physics and on the control of the flow in a Trapped Vortex Cell, often referred to as TVC in the following. A TVC is a cavity with a particular geometry, which is optimised to trap a vortical structure. This configuration has recently gained interest has a device to control the flow past thick airfoils, but fundamental research is still required to make this technique effective.
Specifically, a first goal of this work is to investigate on the fundamental physics of this flow, by studying the basic elements and the dominant phenomena. In fact, this flow field is the result of the complex interaction of several flows, such as the upstream boundary layer, the shear layer detaching from the cavity leading edge, the vortex core, and the boundary layer developing downstream. A further issue of interest addressed in this work is that related to the role of unsteadiness of the cell flow, and in particular of the shear layer, whose self-sustained oscillations are a common feature of open-cavity flows.
The understanding of the driving physical mechanisms of the base flow is required to successfully proceed in developing a control strategy aiming at the control of the flow, because it is necessary to manipulate this flow in order to make the TVC an effective control device. Therefore, a second goal is to study and compare two different control techniques targeting the cavity flow. The first of the two is steady suction of the flow in the cell and has been already applied in past researches, but some additional insight into its effects on the base flow is required. The second proposed control technique is open-loop control with a synthetic jet actuator, a more efficient device whose unsteady action can couple to or drive the relevant mechanisms of the flow. Furthermore, open-loop control studies with a synthetic jet are propaedeutic for closed-loop control of the flow, briefly investigated in the last part of research.
3
Kucukal, Erdem. "BIOMIMETIC MICROFLUIDIC PLATFORMS FOR MONITORING CELLULAR INTERACTIONS IN MICROSCALE FLOW." Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1576231265150031.
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4
Ofsthun, Norma Jean. "Cross-flow membrane filtration of cell suspensions." Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/1721.1/14481.
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Han, Tian. "Flow cell separation in fluctuating g-field." Thesis, Brunel University, 2015. http://bura.brunel.ac.uk/handle/2438/11105.
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Field flow fractionation of particles in rotating coiled column has been investigated in recent year. In contrast to the classical mode of field flow fractionation in narrow channels, the use of rotating coiled columns offers the possibility of large sample loading. In this thesis, the potential for new cell separation methods based on the use of flow fractionation in fluctuating g-fields generated in rotating coil columns is examined. The effects of operational conditions (flow rate and rotational speed – Chapter 3 and Chapter 5); cell properties (cell flexibility – Chapter 4); and column shapes (different inner diameters and coil geometries – Chapter 6) on the flow behaviour of a model system of red blood cells (RBCs) from different species, which differ markedly in size, shape & density, flowing in a single phase of buffered saline have been characterised. Operational Conditions: For a particular rotational speed, there was a minimum flow rate which caused all the cells to be retained in the column and a maximum flow rate at which all cells were eluted. Both the minimum and maximum flow rate were increased when a higher rotational speed was applied. Differences in the behaviour of sheep & hen RBCs have been used to develop a separation method using a continuously increasing flow gradient. This separation could be speeded up by using a step flow gradient. The effects of cell load and rotational direction on the behaviour of RBCs in the column was also studied in this thesis. Cell Properties: The minimum flow rate was found to correlate with cell diameter/cell volume of the RBCs as expected for a sedimentation related process and was partially described by a theoretic equation developed for particles by Fedotov and colleagues (Fedotov et al. 2005). However cell dependent departures from this equation were found which appear to indicate that cell specific surface properties may also be involved for cells (Chapter 3). By contrast the maximum flow rate showed no correlation with cell diameter/cell volume. An effect of cell deformability on the flow separation behaviour of the cells has been demonstrated. Chemical fixation of sheep RBCs with glutaraldehyde rendered the normally deformable RBCs rigid and non-deformable and resulted in the fixed sheep RBCs eluting significantly earlier than unfixed sheep RBCs. This difference was great enough that a mixture of deformable (unfixed) and non-deformable (fixed) sheep RBCs could be separated. Fixed cells tended to show cell aggregation, which could be reduced by the addition of surfactant. Column Geometry: An effect of column shapes on the flow separation behaviour of cells has been demonstrated showing that the optimisation of column design is an important feature of this mode of cell separation. For columns with the same cross sectional area, a “horizontal” rectangular column provided better separation than a circular column and a “vertical” rectangular column gave the least efficient separation. A possible explanation for this behaviour is suggested the thinner sedimentation layer and less secondary flow. Differences in the behaviour of various species of RBCs in the “horizontal” rectangular column have been used to study the efficiency of separation of a mixture of sheep and hen RBCs, and a mixture of rabbit and hen RBCs. This work shows similarities and differences with other reports on cell/particle separations in rotating coiled columns in single phases and also in aqueous two phases systems (ATPS) and these are discussed. Fedotov P.S., Kronrod V.A. & Kasatonova O.N. (2005). Simulation of the motion of solid particles in the carries liquid flow in a rotating coiled column. J. Anal. Chem., 60, 4, 310-316.
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Choe, Juno. "Genomic analysis by single cell flow sorting /." Thesis, Connect to this title online; UW restricted, 2003. http://hdl.handle.net/1773/10850.
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Dive, C. "Flow cytoenzymology with special reference to cancer chemotherapy." Thesis, Open University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384585.
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Camplejohn, Richard Stephen. "Cell kinetics and cancer." Thesis, University of Newcastle Upon Tyne, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327272.
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Korn, Christian. "Stochastic dynamics of cell adhesion in hydrodynamic flow." Phd thesis, Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2007/1299/.
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10
Allen, R. J. "Modelling the endothelial cell response to fluid flow." Thesis, University College London (University of London), 2009. http://discovery.ucl.ac.uk/16119/.
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In vitro endothelial cells respond to fluid flow by elongating in the direction of flow. How the mechanical signal is transformed into an organised and directed response is poorly understood. The most studied and crucial aspects to this response are; actin filament alignment, mechano-transduction, signal transduction, Rho GTPase localised activation and lamellipodium formation. The goal of this project is to understand how these separate facets interact and lead to a coordinated response. The flow is modelled over a 3D virtual cell, which naturally gives the force the flow exerts on the cell surface via a boundary integral representation. This force is coupled to a Kelvin-body model of mechano-transduction which links, via a focal adhesion associated protein, Src, to a partial differential equation model (PDE) of the Rho GTPases Rac and Rho. The PDEs are integrated over a 2D projection of the 3D cell giving a time course for protein concentration at any point in the cell. It is demonstrated that a mechano-transducer that can respond to the normal component of the force is likely to be a necessary (though perhaps not sufficient) component of the signalling network. In some processes cross talk between the GTPases is thought to be important in forming spatially segregated zones of activation, for example in the front and back of migratory cells. This research shows that local signalling in endothelial cells could be initiated by the force normal to the surface of the cell and maintained by limited diffusion. Modelling indicates the EC signalling response to fluid flow may be attenuated by a change in morphology. Rac and Rho activation and deactivation are validated against experimentally reported time courses that have been taken for whole cell averages. However it will be demonstrated that these time courses do not characterise the process and therefore there is a need for more quantitative local measure of protein activation.
11
Polacheck, William J. (William Joseph). "Effects of interstitial flow on tumor cell migration." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/61917.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 80-84).<br>Interstitial flow is the convective transport of fluid through tissue extracellular matrix. This creeping fluid flow has been shown to affect the morphology and migration of cells such as fibroblasts, cancer cells, endothelial cells, and mesenchymal stem cells. However, due to limitations in experimental procedures and apparatuses, the mechanism by which cells detect flow and the details and dynamics of the cellular response remain largely unknown. We developed a microfluidic cell culture system in which we can apply stable pressure gradients and fluid flow, and in which we can observe transient responses of breast cancer cells seeded in a 3D collagen type I scaffold. We employed this system to examine cell migration in the presence of interstitial flow to address the hypothesis that interstitial flow increases the metastatic potential of breast cancer cells. By varying the concentration of chemoattractants, we decoupled the mechanisms that provide the migratory stimulus and the directional stimulus to migrating breast cancer cells in the presence of a flow field. We found that cells migrated along streamlines in the presence of flow and that the strength of the flow field determined directional bias of migration along the streamline. We provide evidence that CCR7-dependent autologous chemotaxis is the mechanism by which cells migrate with the flow, while a competing CCR7-independent mechanism leads to migration against the flow. Furthermore, we demonstrate these competing mechanisms are a powerful migrational stimulus, which likely play an important role in development of metastatic disease.<br>by William J. Polacheck.<br>S.M.
12
Bose, Suman. "Affinity Flow Fractionation for label-free cell sorting." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/87961.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages [107]-118).<br>Capture and isolation of flowing cells from body fluids such as peripheral blood, bone marrow or pleural effusion has enormous implications in diagnosis, disease monitoring, and drug testing. However, in many situations the conventional methods of cell sorting are of limited use due to complex sample preparation steps, high costs, or low sensitivity. Drawing inspiration from nature, a novel platform technology for cell separation known as Affinity Flow Fractionation (AFF) was developed. AFF relies on interaction of cells with asymmetric patterns of weak adhesive molecules allowing for continuous sorting of cells with high purity without irreversible capture of cells. Cells are sorted in a single step, which is a significant advance over conventional immunocapture methods, especially for point-of-care and point-of-use applications. In this work, first, the interaction of cells under shear flow with asymmetric patterns of weak adhesive molecules was studied systematically to highlight the underlying mechanism of AFF at a phenomenological level. Next, an optimized separation device was fabricated and its performance was characterized using model cell lines. A detailed predictive mathematical model, which accounts for the major transport processes involved in cell separation by AFF, was developed and the results validated using experiments. Finally, AFF was applied for rapid isolation of neutrophils from blood, which is important for several applications where conventional procedures involve multiple steps and time-intense manual skills. It was demonstrated that asymmetric patterns of Pselectin, a weak adhesive molecule involved in cell trafficking, can directly draw neutrophils out of a continuously flowing stream of blood, with high purity (92%). As cells exhibiting non-specific adhesion are not drawn out of the flowing stream, an ultrahigh 400,000-fold enrichment of leukocytes over erythrocytes is achieved. Moreover, the sorted neutrophils remain viable, unaltered, and functionally intact. The lack of background erythrocytes enabled direct enumeration of neutrophils by a downstream detector, which could distinguish the activation state of neutrophils in blood. This method is compatible with capillary microfluidics and may find use in isolation of neutrophils for diagnosis of sepsis, genetic analysis, HLA typing, assessment of chemoreadiness, and other applications. Weak molecular interactions govern a large number of important physiological processes such as stem cell homing, inflammation, immune modulation and cancer metastasis. Yet, currently there are no effective technologies that can separate cells based on weak interactions alone. We believe, AFF would fulfill this un-met need in the area of cell sorting and enabling new discoveries. Keywords: Microfluidics, Cell sorting, cell rolling, selectin, blood, point-of-care, neutrophils.<br>by Suman Bose.<br>Ph. D.
13
Kimpton, Laura Saranne. "On two-phase flow models for cell motility." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:93c3cc12-4aac-424d-83bf-3e695efb49fe.
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The ability of cells to move through their environment and spread on surfaces is fundamental to a host of biological processes; including wound healing, growth and immune surveillance. Controlling cell motion has wide-ranging potential for medical applications; including prevention of cancer metastasis and improved colonisation of clinical implants. The relevance of the topic coupled with the naturally arising interplay of biomechanical and biochemical mechanisms that control cell motility make it an exciting problem for mathematical modellers. Two-phase flow models have been widely used in the literature to model cell motility; however, little is known about the mathematical properties of this framework. The majority of this thesis is dedicated to improving our understanding of the two-phase flow framework. We first present the simplest biologically plausible two-phase model for a cell crawling on a flat surface. Stability analyses and a numerical study reveal a number of features relevant to modelling cell motility. That these features are present in such a stripped-down two-phase flow model is notable. We then proceed to investigate how these features are altered in a series of generalisations to the minimal model. We consider the effect of membrane-regulated polymerization of the cell's actin network, the effect of describing the network as viscoelastic, and the effect of explicitly modelling myosin, which drives contraction of the actin network. Validation of hydrodynamical models for cell crawling and spreading requires data on cell shape. The latter part of the thesis develops an image processing routine for extracting the three-dimensional shape of cells settling on a flat surface from confocal microscopy data. Models for cell and droplet settling available in the literature are reviewed and we demonstrate how these could be compared to our cell data. Finally, we summarise the key results and highlight directions for future work.
14
Brown, Jason Britton. "An experimental facility for the investigation of the flow in a circular-couette flow bioreactor." Thesis, Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/18174.
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Lähdesmäki, Ilkka Johannes. "Flow injection methods for drug-receptor interaction studies, based on probing cell metabolism /." Thesis, Connect to this title online; UW restricted, 1999. http://hdl.handle.net/1773/8590.
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Silva, Michael Santos. "Flow cytometric of c-FLIPl-mediated regulation of cell cycle and cell population size." Master's thesis, Universidade de Aveiro, 2017. http://hdl.handle.net/10773/22487.
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Mestrado em Bioquímica - Bioquímica Clínica<br>c-FLIP é uma proteína conhecida pela sua capacidade de se ligar ao DISC, onde compete com a procaspase-8 pela interação com FADD. No entanto, existem evidências que a sua isoforma longa consegue regular também o ciclo celular e mecanismos de proliferação. Para além disso, a atividade de c-FLIPL pode ser controlada por fosforilação. Assim, o objetivo deste estudo é perceber como a fosforilação no resíduo de serina 227 nesta proteína afeta a proliferação e ciclo celular. Neste estudo, observamos que a sobre-expressão de c-FLIPL com uma mutação de serina para alanina no resíduo 227 levou a uma diminuição da capacidade proliferativa dessas células. O uso de citometria de fluxo permitiu verificar este decréscimo na capacidade proliferativa, assim como uma acumulação de células na fase G1 do ciclo celular aquando da sobre-expressão de S227A c-FLIPL. Os resultados obtidos sugerem que a sobre-expressão de c-FLIPL controla a população celular através da transição G1/S, através da sua fosforilação no resíduo 227. No entanto, mais estudos são necessários para se perceber a partir de qual mecanismo esta transição é afetada<br>c-FLIP is a protein known for its capacity to bind to the DISC and compete with procaspase-8 for FADD interaction. However, published studies have shown that c-FLIPL can regulate cell cycle and proliferation. Similarly to many other proteins, c-FLIP can be regulated by phosphorylation. Therefore, the aim of this work was to understand how the phosphorylation of S227 residue on c-FLIPL affects cell cycle and cell proliferation. We observed that overexpression of phosphodeficient mutant c-FLIPL lead to a decrease in cell proliferation. Flow cytometric analysis confirmed this decrease, as well as an accumulation of cell at G1 phase of cell cycle, when overexpressing S227A c-FLIPL. Our results suggest that c-FLIPL overexpression controls cell population size by controlling the G1/S transition, via its phosphorylation. Nonetheless, further studies need to be done to understand which mechanism affects this transition.
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Shaffer, Christian Edward. "Flow system modeling with applications to fuel cell systems." Morgantown, W. Va. : [West Virginia University Libraries], 2005. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4198.
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Thesis (M.S.)--West Virginia University, 2005.<br>Title from document title page. Document formatted into pages; contains xii, 111 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 100-102).
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Tamaresis, John S. "Mathematical modeling of arterial endothelial cell responsiveness to flow /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2004. http://uclibs.org/PID/11984.
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Raina, Rajeev. "Development of a cell-based stream flow routing model." Thesis, Texas A&M University, 2003. http://hdl.handle.net/1969.1/2219.
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This study presents the development of a cell-based routing model. The model developed is a two parameter hydrological routing model that uses a coarse resolution stream network to route runoff from each cell in the watershed to the outlet. The watershed is divided into a number of equal cells, which are approximated as cascade of linear reservoirs or tanks. Water is routed from a cell downstream, depending on the flow direction of the cell, using the cascade of tanks. The routing model consists of two phases, first is the overland flow routing, which is followed by the channel flow routing. In this study, the cell-to-cell stream flow routing model is applied to the Brazos River Basin to demonstrate the impact of the cascade of tanks on the flow over a simple linear reservoir method. This watershed was tested with a uniform runoff depth in absence of observed runoff data. A case study on Waller Creek in Austin, Texas with observed runoff depths and stream flow is used to demonstrate the calibration and validation of model parameters.
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Hasson, Ali Thuriya A. Razzak. "A flow cell to study formation potential of pulps." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ29377.pdf.
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Yamamoto, Miharu. "Coupling of Arterial Wall Cell Dynamics and Blood Flow." Thesis, University of Canterbury. Centre for Bioengineering, 2011. http://hdl.handle.net/10092/6288.
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The objective of this research is to investigate both mathematically and numerically the effects of vascular geometry upon the cellular dynamics in the endothelium and its consequence in the localisation of atherosclerosis. It is widely accepted that the formation of atherosclerotic plaques preferentially occurs at specific locations in the vasculature, such as arterial branches and bends. It has also been observed that, at the sites of plaque formation, the physiological functions of the vascular endothelium are impaired due to a defect in the production mechanisms of or diminished activities of endothelial nitric oxide (NO). From these observations, a correlation between the vascular geometry, which is effected via local haemodynamic forces, and local bioavailability of endothelial NO has been postulated. The research areas that have been involved in the investigation of atherosclerosis's localisation in the past, haemodynamics, medicine, calcium dynamics, NO kinetics and endothelial cell biology, have been studied individually, and there appears to be no integrated model to date that allows investigation of coupled haemodynamic and cellular mechanism applied in physiologically realistic model geometries. An integrated numerical model that includes these mechanisms will be developed in this research, which will lead to a further, more comprehensive understanding of the pathogenesis of atherosclerosis.
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Alexander, R. G. "Flow cytometry and cell sorting in plant genetic manipulations." Thesis, University of Nottingham, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356016.
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Sayer, Robert Michael. "Atir flow cell developments and studies in atmospheric chemistry." Thesis, University of York, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.250623.
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Madden, Jacqueline. "Flow cytometric assessment of T cell activation in asthma." Thesis, University of Southampton, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245048.
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Bremner, Sherry. "A granular flow model of an annular shear cell." Doctoral thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/20304.
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Machinery such as an IsaMillTM used in communition to produce fine particle sizes that allow minerals to be extracted are best modelled using granular flows. A single rheological description that captures all the features of granular flows has not yet been realised, although considerable progress towards a complete theory has been made. Existing models of such horizontally stirred mills are empirical, tend to be extremely dependent on boundary conditions and do not allow for confident extrapolation beyond their window of design. As a first step to understanding the dynamics inside the IsaMillTM,a constitutive stress model of a horizontal annular shear cell is developed. This shear stress model was used in an athermal energy balance to develop a description of the power dissipation, which drives the communition purpose of the IsaMillTM. The key ingredients (velocity, shear rate and volume fraction distributions) to the granular ow model are extracted from experiments using Positron Emission Particle Tracking (PEPT), as well as Discrete Element Method (DEM) simulations. 5mm glass beads were used to fill an annulus 51mm wide. In the PEPT experiments, two different surfaces of the driving wall (the inner cylinder of the shear cell) were used, over two shearing velocities. The effect of two friction coefficients over a range of shearing wall velocities were examined in the DEM simulations. The data were examined over 3 selected radial lines and utilised to calculate the shear stress distribution and the power dissipation from the developed models. It was found that even the usually simple relations describing the dynamics within a vertical shear cell are greatly modified by changing the orientation of the rotation axis.
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Reyes, Eduardo Alberto. "Flow chamber for studying cell attachment to opaque substrates." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0008971.
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Melane, Xolani. "Visualisation of electrolyte flow fields in an electrolysis cell." Diss., University of Pretoria, 2015. http://hdl.handle.net/2263/57492.
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The performance and efficiency of an electrochemical system with gas evolution can be related to the mass transfer effects which are influenced by the resulting two-phase flow. The aim of this investigation was to develop a better understanding in the effects of current density, anode height and inter-electrode spacing on the electrolyte flow patterns and to validate Computational Fluid Dynamic (CFD) model predictions of the electrolyte flow patterns. The CFD model was developed in a previous study and was applied to the experimental rig developed for this study, in which the electrolysis of copper sulphate was studied.
A direct flow visualisation technique was used as the method of investigation in the experimental work. To facilitate the visual observation of the electrolyte flow patterns, O2 gas bubbles evolved on the anode surface were used as the flow followers to track the electrolyte flow patterns. At the bottom of the anode where there was no gas evolution, polyamide seeding particles (PSP) were used as the flow followers. A Photron FASTCAM SA4 high speed camera with a capability of recording up to 5000 fps was used to record the electrolyte flow patterns and circulation. The Photron FASTCAM Viewer (PFV) camera software was used for the post analysis of the recordings and for measuring bubble size, bubble speed and the speed of the PSP tracking particles.
The experimental results were then compared with the results obtained from the CFD model simulation in order to validate the CFD model. The electrolysis cell was approximated by a simplified planar two-dimensional domain. The fluid flow patterns were assumed to be affected only by the change in momentum of the two fluids. To simplify the model, other physical, chemical and electro-magnetic phenomena were not modelled in the simulation. The Eulerian multiphase flow model was used to model the multiphase flow problem investigated.
The flow fields observed in the experiments and predicted by the model were similar in some of the positions of interest. The gas bubble flow field patterns obtained in the experiment and model were similar to each other in Position A (the top front of the anode), C (the area at the bottom of the cell below the anode), and D (the gap between the anode and the diaphragm), with the only exception being Position B (slightly above the anode top back). The experimental results showed an accumulation of the smaller gas bubbles in Position B with a resulting circulation loop across that region. On the other hand, the model predictions did not show this gas bubble accumulation and circulation in Position B.
All the flow patterns predicted for the electrolyte flow illustrated similar flow patterns to the ones observed in the experimental results, including the circulation loop in Position B. The bubble speeds measured at Position A in the experimental work had a reasonable agreement with the bubble speeds predicted by the model. The error between the two results ranged from 6% to 29% for the various cases which were tested.
An increase in the current density generated more gas bubbles which resulted in an increase in the bubble speed. Increasing the anode height increased the amount of gas bubbles generated as well as bubble speed while the bubble speed was decreased with an increasing inter-electrode distance.<br>Dissertation (MEng)--University of Pretoria, 2015.<br>tm2016<br>Chemical Engineering<br>MEng<br>Unrestricted
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McIlvenna, David. "Raman activated cell sorting and counting in continuous flow." Thesis, University of Glasgow, 2015. http://theses.gla.ac.uk/6333/.
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Bacteria play a key role in the natural maintenance of our ecosystem and are also used extensively in agriculture, environmental engineering and in the manufacturing of food products and medicines. However, it is estimated that up to 99% of all micro- organisms are currently unculturable. As a result, it is likely that a vast range of potentially useful phenotypes remain unknown. Current techniques to investigate unculturable cells, such as metagenomics, lack the ability to link a specific piece of genetic information to an originating cell. As heterogeneity of phenotypes exists in populations of genetically identical bacteria, single cell studies are becoming more popular to characterize individual microorganisms. In this thesis a continuous flow, Raman activated single cell sorting system has been developed for the first time. Single cell Raman spectroscopy provides the biochemical information of a cell, enabling the label-free and non-destructive characterisation of different cell types and physiological and phenotypic changes to living cells. The system was based on a novel microfluidic pressure divider platform, where the effects of pressure fluctuations upon the cell detection region are minimised, thereby allowing mechanical switching. With this integrated platform, sorting carbon fixing Synechocystis sp. PCC6803 bacteria containing 12C and 13C isotopes at over 96% accuracy was successfully achieved. Also presented in this thesis is a novel technique for Raman based cell counting in continuous flow. By characterising the likely errors resulting from weak Raman signals, the algorithm used allows accurate analysis of the proportions of known cell types in a mixture, at the fastest acquisition rates achievable on the Raman spectrometer used. The results, obtained in real-time, had an r2 correlation value of 0.996 to the independently measured input proportions. The control of cells at low flow rates offered by the pressure divider microfluidic platform would allow significant increases in Raman signal integration times. The combination of the algorithm with this microfluidic platform could allow real-time Raman based sample analysis and diagnostics to be realised.
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Duqi, Enri. "Continuos Flow Single Cell Separation into Open Microwell Arrays." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amsdottorato.unibo.it/4778/1/duqi_enri_tesi.pdf.
Texte intégralRésumé :
A novel design based on electric field-free open microwell arrays for the automated continuous-flow sorting of single or small clusters of cells is presented. The main feature of the proposed device is the parallel analysis of cell-cell and cell-particle interactions in each microwell of the array. High throughput sample recovery with a fast and separate transfer from the microsites to standard microtiter plates is also possible thanks to the flexible printed circuit board technology which permits to produce cost effective large area arrays featuring geometries compatible with laboratory equipment. The particle isolation is performed via negative dielectrophoretic forces which convey the particles’ into the microwells. Particles such as cells and beads flow in electrically active microchannels on whose substrate the electrodes are patterned. The introduction of particles within the microwells is automatically performed by generating the required feedback signal by a microscope-based optical counting and detection routine.
In order to isolate a controlled number of particles we created two particular configurations of the electric field within the structure. The first one permits their isolation whereas the second one creates a net force which repels the particles from the microwell entrance. To increase the parallelism at which the cell-isolation function is implemented, a new technique based on coplanar electrodes to detect particle presence was implemented. A lock-in amplifying scheme was used to monitor the impedance of the channel perturbed by flowing particles in high-conductivity suspension mediums. The impedance measurement module was also combined with the dielectrophoretic focusing stage situated upstream of the measurement stage, to limit the measured signal amplitude dispersion due to the particles position variation within the microchannel.
In conclusion, the designed system complies with the initial specifications making it suitable for cellomics and biotechnology applications.
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Duqi, Enri. "Continuos Flow Single Cell Separation into Open Microwell Arrays." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amsdottorato.unibo.it/4778/.
Texte intégralRésumé :
A novel design based on electric field-free open microwell arrays for the automated continuous-flow sorting of single or small clusters of cells is presented. The main feature of the proposed device is the parallel analysis of cell-cell and cell-particle interactions in each microwell of the array. High throughput sample recovery with a fast and separate transfer from the microsites to standard microtiter plates is also possible thanks to the flexible printed circuit board technology which permits to produce cost effective large area arrays featuring geometries compatible with laboratory equipment. The particle isolation is performed via negative dielectrophoretic forces which convey the particles’ into the microwells. Particles such as cells and beads flow in electrically active microchannels on whose substrate the electrodes are patterned. The introduction of particles within the microwells is automatically performed by generating the required feedback signal by a microscope-based optical counting and detection routine.
In order to isolate a controlled number of particles we created two particular configurations of the electric field within the structure. The first one permits their isolation whereas the second one creates a net force which repels the particles from the microwell entrance. To increase the parallelism at which the cell-isolation function is implemented, a new technique based on coplanar electrodes to detect particle presence was implemented. A lock-in amplifying scheme was used to monitor the impedance of the channel perturbed by flowing particles in high-conductivity suspension mediums. The impedance measurement module was also combined with the dielectrophoretic focusing stage situated upstream of the measurement stage, to limit the measured signal amplitude dispersion due to the particles position variation within the microchannel.
In conclusion, the designed system complies with the initial specifications making it suitable for cellomics and biotechnology applications.
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Poles, Richard R. "Free-surface flow in a shallow laterally heated cavity." Thesis, City University London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363313.
Texte intégral
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Pinto, Preston Albert. "Novel Bio-inspired Aquatic Flow Sensors." Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/33807.
Texte intégralRésumé :
Inspired by the roles of hair cells in nature, this study aims to develop and characterize two new sets of novel flow sensors. One set of sensors developed and studied in this work are flow sensors fabricated using carbon nanomaterials. These sensors are made by embedding carbon nanotubes (CNT) and carbon nanohorns (CNH) into a polymeric substrate and then tested by flowing a conductive aqueous solution over the surface of the exposed CNT and CNH. In response, a flow-dependent voltage is generated. The surface coverage and the electrical relationship between the sensor and water is investigated and the voltage measurements of sensors with different levels of resistance were tested in varying fluid velocities. In response to these fluid velocities, the least resistive sensor showed small, but detectable changes in voltages, while higher resistance sensors showed less response. In addition, plasma treatment of the carbon nanomaterial/PDMS films were conducted in order to render the PDMS on the surface hydrophilic and in turn to pull more fluid towards the carbon material. This showed to improve the sensitivity of the flow sensors. This work also builds on previous research by investigating the flow dependent electrical response of a â skinâ -encapsulated artificial hair cell in an aqueous flow. An artificial cell membrane is housed in a flexible polyurethane substrate and serves as the transduction element for the artificial hair cell. Flow experiments are conducted by placing the bio-inspired sensor in a flow chamber and subjecting it to pulse-like flows. This study demonstrates that the encapsulated artificial hair cell flow sensor is capable of sensing changes in flow through a mechanoelectrical response and that its sensing capabilities may be altered by varying its surface morphology. Furthermore, the sensorâ s response and dynamics as a function of its surface morphology and structural properties are investigated through synchronized motion tracking of the hair with a laser vibrometer and current measurements across the artificial cell membrane.<br>Master of Science
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Zheng, Hong. "Efficient Algorithms for the Cell Based Single Destination System Optimal Dynamic Traffic Assignment Problem." Diss., The University of Arizona, 2009. http://hdl.handle.net/10150/195304.
Texte intégralRésumé :
The cell transmission model (CTM) based single destination system optimal dynamic traffic assignment (SD-SO-DTA) model has been widely applied to situations such as mass evacuations on a transportation network. Although formulated as a linear programming (LP) model, embedded multi-period cell network representation yields an extremely large model for real-size networks. As a result, most of these models are not solvable using existing LP solvers. Solutions obtained by LP also involve holding vehicles at certain locations, violating CTM flow dynamics. This doctoral research is aimed at developing innovative algorithms that overcome both computational efficiency and solution realism issues. We first prove that the LP formulation of the SD-SO-DTA problem is equivalent to the earliest arrival flow (EAF), and then develop efficient algorithms to solve EAF. Two variants of the algorithm are developed under different model assumptions and network operating conditions. For the case of time-varying network parameters, we develop a network flow algorithm on a time-expanded network. The main challenge in this approach is to address the issue of having backward wave speed lower than forward wave speed. This situation leads to non-typical constraints involving coefficients with value of less than 1. In this dissertation we develop a new network algorithm to solve this problem in optimal, even with coefficients of value less than 1. Additionally, the developed approach solves for optimal flows that exhibit non-vehicle-holding properties, which is a major breakthrough compared to all existing solution techniques for SD-SODTA. For the case of time-invariant network parameters, we reduce the SD-SO-DTA to a standard EAF problem on a dynamic network, which is constructed on the original roadway network without dividing it into cells. We prove that the EAF under free flow status is one of the optimal solutions of SD-SO-DTA, if cell properties follow a trapezoidal/triangular fundamental diagram. We use chain flows obtained on a static network to induce dynamic flows, an approach applicable to large-scale networks. Another contribution of this research is to provide a simple and practical algorithm solving the EAF with multiple sources, which has been an active research area for many years. Most existing studies involve submodular function optimization as subroutines, and thus are not practical for real-life implementation. This study’s contribution in this regard is the development of a practical algorithm that avoids submodular function optimization. The main body of the given method is comprised of |S⁺| iterations of earliest arrival s - t flow computations, where |S⁺| is the number of sources. Numerical results show that our multi-source EAF algorithm solves the SD-SO-DTA problem with time-invariant parameters to optimum.
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Trotter, Martin James. "Intermittent blood flow in the murine SCCVII squamous cell carcinoma." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/31344.
Texte intégralRésumé :
Intermittent blood flow in tumour microvasculature is believed to contribute to heterogeneity in tumour oxygen delivery; transient vessel nonperfusion is thought to result in acutely hypoxic cells resistant to conventional radiotherapy. This thesis describes three main areas of work: (1) the development of a histologic method capable of detecting intermittent blood flow in experimental tumours at the single vessel level; (2) the quantification and characterization of tumour blood flow fluctuations in the murine SCCVII carcinoma; and (3) the modification of tumour blood flow and the reduction of flow heterogeneity using vasoactive drugs.
A double staining technique involving the sequential intravenous injection of two fluorescent vascular markers was used to detect transient episodes of tumour vessel nonperfusion. The stains employed were Hoechst 33342 and the carbocyanine dye, DiOC₇(3), both of which have short (< 3 minutes) circulation half-lives and preferentially stain cells adjacent to perfused blood vessels. When injections of the vascular markers are separated by some interval, each stain defines only those tumour vessels which were perfused during the few minutes immediately post-injection; thus, two "pictures" of tumour microvascular flow are obtained and tumour vessels subject to periods of nonperfusion can be easily visualized in frozen sections since they are outlined by one stain but not the other.
Using the double staining technique, in which Hoechst 33342 and then DiOC₇(3) are administered intravenously 20 minutes apart to unrestrained C3H/He mice, staining mismatch (indicative of transient vessel nonperfusion) is regularly observed in subcutaneous SCCVII carcinoma. Vessels stained with DiOC₇(3) only (reperfusion of previously nonperfused vessels) or with H33342 only (nonperfusion of previously perfused vessels) are observed in approximately equal numbers. The percentage of tumour vessels subject to intermittent flow is a function of SCCVII tumour size: tumours ≤100 mg do not exhibit statistically significant amounts of mismatch. At sizes > 100 mg, overall staining mismatch is significantly increased over background levels and maximum mismatch is observed at tumour sizes >400 mg (8.6 ±2.9%). In most tumours, transient vessel nonperfusion is more pronounced in central tumour regions. In addition to mismatch observed in individual vessels, large "patches" of unequal staining are also seen. Anaesthesia or restraint do not significantly influence intermittent blood flow.
The above information suggests that transient episodes of tumour vessel nonperfusion occur as a consequence of flow reduction in a feeding vessel; vessels in central regions of large tumours may be susceptible to collapse as a result of elevated tumour interstitial pressure. In the SCCVII tumour, a small number of peripheral vessels possess vascular smooth muscle and thus may be capable of vasomotor activity.
The importance of perfusion pressure in the control of tumour microcirculatory flow was examined using vasoactive drugs. Hydralazine, a vasodilator which lowers blood pressure, causes a profound reduction in tumour RBC flow to 8.7 + 6.4% of pretreatment values in unanaesthetized mice. The drug causes collapse of central tumour vessels: following a dose of 10mg/kg intravenously, 36±16% of vessels are completely nonperfused, as detected using the double staining technique. Conversely, elevation of blood pressure using the vasoconstrictor angiotensin II results in a 2-3x increase in tumour blood flow. In addition, angiotensin II infusion significantly reduces the number of tumour vessels subject to transient nonperfusion from 8.1 % to 2.0%. However, intermittent blood flow in the SCCVII carcinoma can also be influenced by nonvasoactive drugs: nicotinamide, the amide form of vitamin B3, reduces episodes of transient nonperfusion.
In summary, intermittent blood flow has been characterized in a transplanted murine squamous cell carcinoma using a novel fluorescent double staining method which allows the detection of flow fluctuations in solid tumours at the microvascular level. If transient episodes of nonperfusion occur in human tumours and result in impaired oxygen or drug delivery, then such flow fluctuations may be an important factor limiting tumour cure or local control by radiotherapy or chemotherapy.<br>Medicine, Faculty of<br>Pathology and Laboratory Medicine, Department of<br>Graduate
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Chu, Chun-sing, and 朱振聲. "Flow cytometric analysis of cell-cycle regulatory proteins during apoptosis." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2000. http://hub.hku.hk/bib/B31240070.
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Chu, Chun-sing. "Flow cytometric analysis of cell-cycle regulatory proteins during apoptosis /." Hong Kong : University of Hong Kong, 2000. http://sunzi.lib.hku.hk/hkuto/record.jsp?B21490144.
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Martin, Ashley Diane. "Modulation of endothelial cell characteristics by pericytes." Thesis, University of Ulster, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287133.
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Piri, Hossein. "Flow visualization in 3D printed PEM fuel cell bipolar plates." Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/62259.
Texte intégralRésumé :
In recent years, due to the public concern on global warming, both increasing energy efficiency and developing green energy become crucially important. Fuel cells can be one of the most suitable clean energy solutions for the environment because of its high energy conversion efficiency and near zero emissions of criteria air pollutants at the use stage. To increase the energy efficiency of fuel cells, effectively utilize the Pt catalyst and increase the fuel cell durability, the uniform distribution of the reactants over the fuel cell active area is of great importance. Over the last decade, many researchers have focused on developing flow field design to homogenously distribute the reactant and to decrease the pressure drop in the bipolar plates. However, most of the previous studies are in the stage of numerical simulation, and the few experimental studies have used very simple flow field geometries. Not to mention that complex transport phenomena inside a fuel cell make even the numerical simulation challenging and time consuming, which hinders the quick screening of proposed modifications and new designs.
While the conventional fabrication techniques are expensive and time consuming, 3D printing is a very good rapid prototyping method that can be used both to validate the simulation results and to supplement the tedious simulation work. The question is whether the results from 3D printed flow fields could be as accurate and reliable as flow fields fabricated with conventional methods.
In the present research, we investigated the applicability of 3D printing in validating the simulation results and as a fast screening method. State of the art designs for anode, cathode and water cooling BPPs proposed and fabricated using Polyjet 3D printing, SLA 3D printing and laser-cutter technologies and the pressure drop and velocity profiles were measured for each plate. The results demonstrated that SLA 3D printing has great promises to serve as a screening tool in modifying the flow field design, as well as in validating the simulation results.<br>Applied Science, Faculty of<br>Chemical and Biological Engineering, Department of<br>Graduate
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Godoy, Ramirez Karina. "Flow cytometric methods for assessment of cell-mediated immune responses /." Stockholm, 2005. http://diss.kib.ki.se/2005/91-7140-409-0/.
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O'Connell, Gregory Raymond. "Detector cell hydrodynamics and electrode selectivity in flow-injection potentiometry." Thesis, Brunel University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.290935.
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Bae, C. H. "Cell design and electrolytes of a Novel Redox flow battery." Thesis, University of Manchester, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.509374.
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Bessaih, Nabil. "Erosion of sediment from a cell under high velocity flow." Thesis, University of Salford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386404.
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Medina, Jose L. "Work-cell Centric Satellite Pulse Flow Production System Integration Test." Digital Commons at Loyola Marymount University and Loyola Law School, 2012. https://digitalcommons.lmu.edu/etd/419.
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Moshaei, Mohammad Hossein. "Adhesion of Rolling Cell to Deformable Substrates in Shear Flow." Ohio University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou153373230467728.
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Kim, Jungtae. "Development of continuos flow micro cell sorter using immune magnetophoresis." Aachen Shaker, 2008. http://d-nb.info/992481430/04.
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Karp-Boss, Lee. "Phytoplankton-flow interactions in relation to cell size and morphology /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/11004.
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Poon, Grace Chemical Sciences & Engineering Faculty of Engineering UNSW. "Bromine complexing agents for use in vanadium bromide (V/Br) redox flow cell." Publisher:University of New South Wales. Chemical Sciences & Engineering, 2008. http://handle.unsw.edu.au/1959.4/41210.
Texte intégralRésumé :
The Vanadium bromide (V/Br) flow cell employs the Br3-/Br- couple in the positive and the V(II)/V(III) couple in the negative half cell. One major issue of this flow cell is bromine gas formation in the positive half cell during charging which results from the low solubility of bromine in aqueous solutions. Bromine complexing agents previously used in the zinc-bromine fuel cell were evaluated for their applicability in V/Br flow cell electrolytes. Three quaternary ammonium bromides: N-ethyl-N-methyl-morpholinium bromide (MEM), N-ethyl-N-methyl-pyrrolidinium bromide (MEP) and Tetra-butyl ammonium bromide (TBA) were studied. It is known that aqueous bromine reacts with quaternary ammonium bromides to form an immiscible organic phase. Depending on the number of quaternary ammonium bromides used and the environmental temperature, the second phase formed will either be solid or liquid. As any solid formation would interrupt the flow cell operation, potential formation of such kind has to be eliminated. Stability tests of simulated V/Br electrolyte with added quaternary ammonium bromides were carried out at 11, 25 and 40 oC. In the absence of bromine, the addition of MEM, MEP and TBA were found to be stable in V/Br electrolytes. However, in the presence of bromine, solid formation was observed in the bromine rich organic phase when the V/Br electrolyte contained a single quaternary ammonium bromide (QBr) compound. For V/Br electrolytes with binary or ternary QBr mixtures containing TBA, the presence of bromine caused a viscous polybromide phase to form at room temperature and the release of bromine gas at higher temperature. Only a binary mixture of MEM and MEP formed a stable liquid organic phase between 11 ?? 40 oC. In this study it was found that V/Br electrolytes containing a binary QBr mixture (0.75M) of MEM and MEP gave the best combination that formed an orange oily layer in the presence of bromine without solidification between 11 ?? 40oC. Furthermore, it was found that samples of V/Br electrolytes containing a ternary QBr mixture, are less effective in bromine capturing if the total QBr concentration was less than 1 M at 40oC, where bromine gas evolution was observed. From electrochemical studies of V3+/V2+, it was found that the addition of MEM and MEP had a minimal effect on the formal potential of the V3+/V2+ couple, the V2+/V3+ transfer coefficient and the diffusion coefficient of V3+. Therefore, MEM and MEP can be added to the negative half-cell of a V/Br flow cell without major interference From linear sweep voltammetry, the kinetics of the Br-/Br3- redox couple was found to be mass transfer controlled. After the addition of MEM and MEP mixture, the exchange current density was found to decrease from 0.013 Acm-2 to 0.01 Acm-2. On the other hand the transfer coefficient before and after MEM and MEP addition was found to be 0.5 and 0.44 respectively. Since the kinetic parameters were not significantly affected by the addition of MEM and MEP mixture, they can be added to the positive half-cell of the V/Br flow cell as bromine complexing agents. The electrochemical studies of both V3+/V2+ and Br-/Br3- showed the addition of MEM and MEP has minimal interference with the redox reactions of the vanadium bromide flow cell. This thesis also investigated the effect of MEM and MEP addition on the cell performance of a lab scale V/Br flow cell using two different membranes (ChiNaf and VF11). Flow cell performance for 2 M V3.7+ + 0.19 M MEM + 0.56 M MEP electrolytes utilising ChiNaf membrane at 10 mAcm-2 produced an energy efficiency of 59%, and this decreased to 43% after 15 cycles. For the static cell utilising VF11 membrane, the addition of MEM and MEP reduced the energy efficiency from 59.7% to 43.4%. It is believed that this is caused by the mass transfer controlled Br-/Br3- couple in the complexed positive half-cell solution. Therefore, uniformity between the organic and aqueous phase is important for flow cells utilising electrolytes with MEM and MEP. Finally, the polarization resistance of a lab scale V/Br flow cell utilising ChiNaf membrane and 2 M V3.7+ electrolytes was found to be slightly higher during cell charging (3.9 cm2) than during the discharge process (3.6 cm2), which is opposed to that in the all-vanadium redox cell.
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Pomalis, Richard. "A fundamental study of Starling flow and protein redistribution within a cell-free rectilinear membrane flow device." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq20982.pdf.
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Sawyer, Frederick Emile. "Coupled mixing-cell and mass balance flow path models of the White River Flow System, Nevada, USA." abstract and full text PDF (UNR users only), 2009. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1467765.
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FACCHINETTI, IRENE. "Thermally Regenerable Redox-Flow Batteries." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2021. http://hdl.handle.net/10281/308694.
Texte intégralRésumé :
Il calore a bassa temperatura (LTH), inferiore a 100°C, è una forma di energia largamente disponibile che viene dispersa nell’ambiente, senza alcun utilizzo. La conversione di questo tipo di energia in elettricità aprirebbe le porte allo sfruttamento di fonti energetiche come il calore solare, geotermico e di scarto industriale.
La conversione di LTH in elettricità non è però un processo efficiente a causa dei limiti posti dalla termodinamica, con la cosiddetta legge di Carnot, oltre che ai limiti tecnologici che riducono ulteriormente la conversione di questa forma di energia.
I dispositivi preposti per convertire LTH in elettricità devono poter operare con alte efficienze e potenze, e devono essere facilmente scalabili ed economici. Purtroppo, attualmente nessun dispositivo è in grado di effettuare questa conversione con potenze ed efficienze abbastanza elevate da giustificare gli alti costi (materiali, operazionali e manutenzione) e la complessità dei dispositivi stessi ed è per questo motivo che LTH non trova tutt’ora alcuna applicazione
Questo progetto di ricerca si è focalizzato sullo sviluppo di un dispositivo in grado di convertire LTH in maniera efficiente e con alte potenze. Tale dispositivo, chiamato Thermally Regnerable Redox-Flow Battery, TRB, è una batteria a flusso ricaricabile termicamente. Il dispositivo conta due diverse processi: la produzione energetica, che avviene in una cella elettrochimica in grado di produrre elettricità alle spese dell’energia libera di mescolamento di due soluzioni acquose dello stesso sale ma a diversa concentrazione. Quando le due soluzioni raggiungono la stessa concentrazione, la soluzione esausta viene mandata al secondo processo: un distillatore sottovuoto che rigenera il gradiente di concentrazione tra le due soluzioni sfruttando risorse di LTH. L’efficienza totale del dispositivo è quindi data dal prodotto tra l’efficienza della cella elettrochimica e l’efficienza del distillatore.
Studi termodinamici dimostrano che per incrementare tale efficienza è fondamentale lavorare sull’efficienza del distillatore, il cui valore dipende dalla scelta del soluto e del solvente. In particolare, per questo lavoro di ricerca si è scelto di operare con soluzioni acquose di NaI/I2 e LiBr/Br2.
I risultati raggiunti e le principali attività di ricerca vengono riportate brevemente in questo abstract:
Con la determinazione dei coefficienti di attività, si è calcolato l’energia libera di mescolamento e il potenziale a circuito aperto per entrambi i set di soluzioni (NaI e LiBr).
Le celle elettrochimiche sono state sviluppate specificamente per entrambi I sistemi studiati e test elettrochimici hanno permesso di valutare le performance dei due dispositivi, come potenza ed efficienza elettrochimica. La distillazione è stata modellizzata in modo da definire le condizioni ottimali di lavoro e determinare l’efficienza del processo.<br>Low-Temperature Heat (LTH), below of 100°C, has elicited great interest among the scientific community, as a source of energy since it does not see any form of utilization as it is currently simply released into the environment. Its conversion would open the doors to the exploitation of a huge amount of energy as well, such as geothermal, solar, and industrial waste heat.
The conversion efficiencies of LTH are low because of the limitations imposed by Carnot law, as well as the existence of technological limits which further reduce the efficiency of the conversion of LTH.
In order to be suitable for extensive industrial production, LTH converters should show high power densities, scalable and efficient whilst being cost-effective; to this point, the devices proposed for this afore mentioned application all failed to achieve suitable efficiencies and power density, making the LTH conversion unfeasible.
This PhD project was focused on the design of a device called Thermally Regenerable Redox-Flow Battery (TRB) consisting of a redox-flow battery that can be recharged by a thermal process.
The device is based upon a two-stages technology composed by a “power production” stage and a “thermal” stage: power production happens in an electrochemical cell which release electricity at the expenses of the mixing free energy of two water solutions of the same salt at different concentrations, referred to as a concentration cell. When the two solutions reach the same concentration, the exhausted fluid is sent to the second stage, the thermal process, which regenerates the initial mixing free energy, by exploiting LTH sources, through vacuum distillation. The efficiency of the technology is the product between the efficiencies of the units in the device where both stages happen: the electrochemical cell, engineered for power production, and a distillation unit, designed to be responsible for thermal conversion.
NaI/I2 and LiBr/Br2 water solutions will be the most discussed redox couple in this thesis, as result of thermodynamic analysis that have shown the importance related to the solvent and salt choice to ensure high energy conversion efficiencies.
The achieved results, as well as the main research activities, are briefly reported here:
starting from the determination of the activity coefficients, mixing free energy of the initial solutions, and the open circuit voltage of the electrochemical are calculated.
Electrochemical cells are specifically designed for both systems while electrochemical tests are performed to evaluate the main performances of the devices, such as power density and electrochemical efficiency.
Modeling of the operational conditions of the thermal stage allows to determine the distillation efficiency for both the solutions.
The initial experiments prove an unprecedented heat-to-electricity efficiency for both the systems: 3% for TRB-NaI and 4-5% for TRB based on LiBr, depending on the thickness of the membrane with a power density output of almost 10 W m-2 for both technologies, which opens various possibilities to implement further improvements into this new class of energy storage/converter devices.