• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 75
  • 16
  • 15
  • 6
  • 4
  • 4
  • 3
  • 2
  • 2
  • 1
  • 1
  • 1
  • Tagged with
  • 149
  • 149
  • 29
  • 22
  • 18
  • 16
  • 16
  • 15
  • 15
  • 15
  • 14
  • 14
  • 12
  • 11
  • 11
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
71

Structural Studies and Modelling of Oxygen Transport in Barrier Materials for Food Packaging

Nyflött, Åsa January 2014 (has links)
The requirements of food packages are to ensure food safety and quality, to minimize spoilage, and to provide an easy way to store and handle food. To meet these demands for fibre-based food packages, barrier coatings are generally used to regulate the amount of gases entering a package, as some gases are detrimental to food quality. Oxygen, for example, initiates lipid oxidation in fatty foods. Bakery products may also be sensitive to oxygen. This thesis focused on mass transport of oxygen in order to gain deeper knowledge in the performance of barrier coatings and to develop means to optimize the performance of barrier coatings. This experimental study along with computer modelling characterized the structure of barrier materials with respect to the mass transport process.This project was performed as part of the multidisciplinary industrial graduate school VIPP (www.kau.se/en/vipp) - Values Created in Fibre Based Processes and Products – at Karlstad University, with the financial support from the Knowledge Foundation, Sweden, and Stora Enso. / <p>Artikel 2 "The influence of clay orientation..." ingick som manuskript i avhandlingen, då med titeln: "Influence of clay orientation in dispersion barrier coatings on oxygen permeation". Nu publicerad.</p>
72

Simulação de transporte de massa de um soluto em meio poroso com auxílio do CFD (Computer Fluid Dynamics). / Solute mass transport simulation in a porous media with CFD\'s support (Computer Fluid Dynamics).

Frankfurt, Ricardo 23 October 2008 (has links)
Com o avanço dos computadores pessoais, problemas técnicos complexos, antes restritos aos grandes centros de pesquisas internacionais, passam a ser acessíveis pelas mais diversas áreas do conhecimento, como as engenharias e em particular a Engenharia Química. Fenômenos físicos são representados matematicamente por equações diferenciais, que na maioria das vezes não possuem solução analítica possível. O CFD ( Computer Fluid Dynamics) é uma técnica numérica iterativa, que busca a solução destas equações diferenciais através da discretização do domínio estudado e das equações que governam o fenômeno envolvido. Neste trabalho, através de um software especialista de CFD, o ANSYS CFX 11.0, foi simulado o transporte de massa e momento de um soluto traçador, o Cloreto, presente no sal Cloreto de Sódio, em um meio poroso. Em seguida, os resultados desta simulação foram comparados e validados por um experimento de transporte de massa numa caixa de areia. / With the advance of the personal computers, complex technical problems, before restricted to the huge centers of international researches, have become more accessible by many areas of the knowledge, like the engineering and in particular the Chemical Engineering. Physical phenomena are represented mathematically by differentials equations, which most of the time do not have possible analytical solution. CFD (Computer Fluid Dynamics) is an iterative numeric technique, which search the solution of these differentials equations through both discretization of the studied domain and the equations that govern the involved phenomenon. In this work, through a CFD\'s specialist software, ANSYS CFX 11.0, it was simulated the mass and momentum transport of a solute tracer, Chloride, present in Sodium Chloride, in a porous media. After this, the simulations results were compared and validated in a mass transport experiment in a sand box.
73

Simulação de transporte de massa de um soluto em meio poroso com auxílio do CFD (Computer Fluid Dynamics). / Solute mass transport simulation in a porous media with CFD\'s support (Computer Fluid Dynamics).

Ricardo Frankfurt 23 October 2008 (has links)
Com o avanço dos computadores pessoais, problemas técnicos complexos, antes restritos aos grandes centros de pesquisas internacionais, passam a ser acessíveis pelas mais diversas áreas do conhecimento, como as engenharias e em particular a Engenharia Química. Fenômenos físicos são representados matematicamente por equações diferenciais, que na maioria das vezes não possuem solução analítica possível. O CFD ( Computer Fluid Dynamics) é uma técnica numérica iterativa, que busca a solução destas equações diferenciais através da discretização do domínio estudado e das equações que governam o fenômeno envolvido. Neste trabalho, através de um software especialista de CFD, o ANSYS CFX 11.0, foi simulado o transporte de massa e momento de um soluto traçador, o Cloreto, presente no sal Cloreto de Sódio, em um meio poroso. Em seguida, os resultados desta simulação foram comparados e validados por um experimento de transporte de massa numa caixa de areia. / With the advance of the personal computers, complex technical problems, before restricted to the huge centers of international researches, have become more accessible by many areas of the knowledge, like the engineering and in particular the Chemical Engineering. Physical phenomena are represented mathematically by differentials equations, which most of the time do not have possible analytical solution. CFD (Computer Fluid Dynamics) is an iterative numeric technique, which search the solution of these differentials equations through both discretization of the studied domain and the equations that govern the involved phenomenon. In this work, through a CFD\'s specialist software, ANSYS CFX 11.0, it was simulated the mass and momentum transport of a solute tracer, Chloride, present in Sodium Chloride, in a porous media. After this, the simulations results were compared and validated in a mass transport experiment in a sand box.
74

Movimentos sociais contemporâneos: o Tarifa Zero Goiânia / Contemporary social movements: the Tarifa Zero Goiânia

Morais , Lays Bárbara Vieira 25 November 2016 (has links)
Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2017-01-05T10:16:19Z No. of bitstreams: 2 Dissertação - Lays Bárbara Vieira Morais - 2016.pdf: 1806586 bytes, checksum: 617b70dff25f70679826980be77e632a (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2017-01-05T10:16:41Z (GMT) No. of bitstreams: 2 Dissertação - Lays Bárbara Vieira Morais - 2016.pdf: 1806586 bytes, checksum: 617b70dff25f70679826980be77e632a (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2017-01-05T10:16:41Z (GMT). No. of bitstreams: 2 Dissertação - Lays Bárbara Vieira Morais - 2016.pdf: 1806586 bytes, checksum: 617b70dff25f70679826980be77e632a (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2016-11-25 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / This research aims to understand the dynamics and the action of Zero Rate Goiânia, regional arm of the Movement Free Pass to then produce data and interpretations that allows to understand the discourse used by the group is carried out in their practices. The methodology techniques were used discourse analysis, based on interviews and literature review. To understand this phenomenon we start from a Marxist theoretical basis. Social movements were treated as a social conflictive nature of collectivity, a pressure group, whose development involves changes or conservation privileges, values, rules, standards, etc. It was concluded that a first threshold that can be pointed out is the very clash of ideas within the movement and the personal life of every activist. Also noteworthy is that very progressive agendas, such as the end of the tariff, collides with its own structural and historical limits of capitalism in the context where the fight is inserted. There is also the fact that the Zero Rate Goiania seek to promote dialogue and awareness of the population, but the very limited financial resources and members just preventing this is done properly. Finally, we have the organizational, aspect that struck MPL as a whole. The movement turned its principles in his doctrine, which resulted some contradictions. / A presente pesquisa visa entender a dinâmica e a atuação do coletivo Tarifa Zero Goiânia, braço regional do Movimento Passe Livre, para então produzir dados e interpretações que possibilite entender se o discurso usado pelo grupo se realiza nas suas práticas. As técnicas de metodologia utilizadas foram a análise de discurso, com base em entrevistas, e revisão bibliográfica. Para entender esse fenômeno partimos de uma base teórica marxista. Os movimentos sociais foram tratados como uma coletividade de caráter conflitivo, um grupo de pressão, cujo desenvolvimento implica mudanças ou conservação de privilégios, valores, regras, normas, etc. Concluiu-se que um primeiro limite que pode ser apontado é o próprio embate de ideias no interior do movimento e a vida pessoal de cada ativista. Destaca-se também, que pautas muito progressistas, como o fim da tarifa, se choca com os próprios limites estruturais e históricos do capitalismo no contexto onde a luta está inserida. Existe também o fato do Tarifa Zero Goiânia buscar promover o diálogo e a conscientização da população, mas a própria limitação de recursos financeiros e de membros acaba impedindo que isso seja feito de forma adequada. Por fim, temos as questões organizativas, aspecto que atingiu o MPL como um todo. O movimento transformou seus princípios em sua doutrina, o que acarretou algumas contradições.
75

Influence of the electrolyte on the electrode reactions in the chlorate process

Nylén, Linda January 2008 (has links)
The chlorate process is very energy intensive and a major part of the production costs are for electrical energy. Since the electricity prices are constantly increasing and may also vary periodically, the chlorate plants may be forced to adjust their production rate to the price at each moment in order to minimise their costs. Variation of current load requires increased knowledge regarding the electrode behaviour in a wide current range. In this thesis, the aim was to study the impact of the electrolyte on the electrode reactions in order to reduce the energy consumption. The work has mainly been experimental and additionally mathematical modelling has been carried out. A wide current range has been investigated in order to increase the understanding of the phenomena and to obtain results useful for low-load operation during the periods of high electricity cost. To operate the anode as energy efficiently as possible, the anode potential should not exceed the critical potential (Ecr), where the slope of the anodic polarisation curve increases, most likely due to ruthenium(VIII)-formation, and where the side reaction of oxygen evolution increases. In this work, the influence of different electrolyte parameters on Ecr has been studied. It was shown that a higher chloride concentration and an increased temperature lowered Ecr, which was expected to increase the risk of exceeding Ecr. However, this was not observed due to a simultaneous favouring of the chloride oxidation. Hence it was concluded that the electrolyte parameters should be optimised so that the lowest possible anode potential is obtained, which would enable higher current densities without exceeding Ecr. A further conclusion is that the increased slope of the polarisation curve at Ecr was possibly related to the lower activity for chloride oxidation on ruthenium oxidised to ruthenium(VIII). At full-load operation, the cathode potential was shown to be rather independent of the electrolyte composition despite a large variation of electrolyte parameters. The cathode composition appears to be more critical than the electrolyte composition when aiming at reducing the energy consumption. A strategy to increase the cathode activity could be to in situ apply a catalytic film onto the electrode surface. Therefore, Y(III) was added to a chloride electrolyte in order to form a yttrium hydroxide film on the alkaline cathode surface during hydrogen evolution. The yttrium-hydroxide film activated reduction of water (hydrogen evolution) and hindered hypochlorite reduction, proton reduction and nitrate reduction. The inhibiting properties are important for the prevention of side reactions, which currently are avoided by reducing Cr(VI) of the electrolyte on the cathode, producing an inhibiting chromium-hydroxide film. The studies on Y(III) increase the expectations for finding alternatives to the toxic Cr(VI). The addition of chromate to the chlorate electrolyte gives a high cathodic current efficiency and chromate has buffering properties in the electrolyte. The role of the buffer has been investigated for the oxygen evolution from water (one possible anodic side reaction), as well as cathodic hydrogen evolution. Models have been developed for these systems to increase the understanding of the interaction between buffer, electrode reactions and mass transport; the results have been verified experimentally. The chromate buffer increased the limiting current significantly for the cathodic H+ reduction and the cathodic overpotential was reduced drastically at currents lower than the limited current. A too low overpotential could result in the cathodic protection being lost. The presence of chromate buffer increased the limiting current for the oxygen evolution from OH-. The modelling of these systems revealed that the homogeneous reactions connected to the electrode reactions were not in equilibrium at the electrode surface. Further, a good resolution of the interface at the electrode surface was crucial since the, for the electrode reactions, important buffering takes place in an nm-thick reaction layer. / Framställning av klorat är mycket energiintensiv och kräver stora mängder elenergi. Stigande elpriser, som dessutom ofta varierar under dygnet eller säsongsvis, gör att man vill reducera onödiga förluster samt ibland försöka anpassa produktionen så att man när elpriset är högt minskar den, för att sedan öka produktionen igen då elpriset sjunker. Denna flexibla drift kräver ny kunskap om hur elektroderna beter sig i ett större strömintervall än vad som tidigare varit av intresse. Målet med detta arbete var att, med fokus på elektrolytens betydelse, identifiera möjliga förbättringar för kloratprocessen och därmed minska energiförbrukningen. Studierna har i huvudsak varit experimentella men även matematisk modellering har använts. Ett brett strömintervall har undersökts för att bättre förstå fenomenen och för att även kunna använda resultaten då höga elpriser gör att man vill köra processen vid lägre laster än normalt. För att driften av anoden ska vara så energieffektiv som möjligt bör anodpotentialen inte överskrida den kritiska potentialen (Ecr), där den anodiska polarisationskurvan får en högre lutning (troligtvis pga Ru(VIII)-bildning) och bireaktionen syrgasutveckling ökar. I detta arbete har påverkan av olika elektrolytparametrar på Ecr undersökts. Det visade sig att en ökad kloridkoncentration och ökad temperatur sänkte Ecr. Trots att detta borde göra att Ecr lättare överskrids, blev inte detta fallet eftersom kloridoxidationen samtidigt gynnades. Slutsatsen blir därför att elektrolytparametrarna bör optimeras så att lägsta möjliga anodpotential uppnås, vilket då även gör att strömtätheten kan ökas utan att Ecr överskrids. Slutsatsen är vidare att polarisationskurvans högre lutning vid Ecr kan ha att göra med att rutenium oxiderat till rutenium(VIII) har lägre aktivitet för kloridoxidation. Vid full last visade sig katodens potential vara relativt oberoende av elektrolytsammansättningen trots att denna varierades kraftigt. Katodens sammansättning verkar vara viktigare att ta hänsyn till än elektrolytens för kunna åstadkomma en större energibesparing. Ett alternativ till att öka katodens aktivitet skulle vara att in-situ belägga elektrodytan med en katalytisk film. Försök gjordes att sätta till Y(III) till kloridelektrolyt för att under vätgasutveckling fälla ut en yttriumhydroxidfilm på den alkaliska katodytan. Yttriumhydroxidfilmen aktiverade vattenreduktion (vätgasutveckling) och inhiberade hypokloritreduktion, protonreduktion och nitratreduktion. De inhiberande egenskaperna är viktiga för att förhindra bireaktioner, vilka idag hindras av att Cr(VI) i elektrolyten reduceras på katoden och bildar en hindrande kromhydroxidfilm. Försöken med Y(III) visar att det finns goda möjligheter att hitta alternativ till det miljöfarliga Cr(VI). Kromattillsatsen i kloratelektrolyt ger förutom ett högt katodiskt strömutbyte även en buffrande effekt till elektrolyten. Effekten av buffert har undersökts för en av de anodiska bireaktionerna, syrgasutveckling ur vatten, samt för vätgasutvecklingen på katoden. Dessa system har modellerats för att bättre förstå samspelet mellan buffert, elektrodreaktioner och materietransport och resultaten har verifierats experimentellt. Kromatbufferten ökade gränsströmmen för katodisk H+-reduktion betydligt och katodöverpotentialen sjönk kraftigt vid lägre strömmar än gränsströmmen. Detta kan vara ett problem om överpotentialen sjunker så lågt att elektroden inte är katodiskt skyddad. För syrgasutvecklingen ökade närvaron av kromatbuffert gränsströmmen för syrgasutveckling ur OH-. Modellering av dessa system visar att de homogena reaktioner som var kopplade till elektrodreaktionerna inte var i jämvikt vid elektrodytan. Vidare visade det sig vara mycket viktigt med en bra upplösning av gränsskiktet vid elektrodytan, då den buffring som är viktig för elektrodreaktionerna sker i ett mycket tunt reaktionsskikt (nanometertjockt). / <p>QC 20100901</p>
76

Oxidative Dissolution of Spent Fuel and Release of Nuclides from a Copper/Iron Canister : Model Developments and Applications

Liu, Longcheng January 2001 (has links)
Three models have been developed and applied in the performance assessment of a final repository. They are based on accepted theories and experimental results for known and possible mechanisms that may dominate in the oxidative dissolution of spent fuel and the release of nuclides from a canister. Assuming that the canister is breached at an early stage after disposal, the three models describe three sub-systems in the near field of the repository, in which the governing processes and mechanisms are quite different. In the model for the oxidative dissolution of the fuel matrix, a set of kinetic descriptions is provided that describes the oxidative dissolution of the fuel matrix and the release of the embedded nuclides. In particular, the effect of autocatalytic reduction of hexavalent uranium by dissolved H2, using UO2 (s) on the fuel pellets as a catalyst, is taken into account. The simulation results suggest that most of the radiolytic oxidants will be consumed by the oxidation of the fuel matrix, and that much less will be depleted by dissolved ferrous iron. Most of the radiolytically produced hexavalent uranium will be reduced by the autocatalytic reaction with H2 on the fuel surface. It will reprecipitate as UO2 (s) on the fuel surface, and thus very little net oxidation of the fuel will take place. In the reactive transport model, the interactions of multiple processes within a defective canister are described, in which numerous redox reactions take place as multiple species diffuse. The effect of corrosion of the cast iron insert of the canister and the reduction of dissolved hexavalent uranium by ferrous iron sorbed onto iron corrosion products and by dissolved H2 are particularly included. Scoping calculations suggest that corrosion of the iron insert will occur primarily under anaerobic conditions. The escaping oxidants from the fuel rods will migrate toward the iron insert. Much of these oxidants will, however, be consumed by ferrous iron that comes from the corrosion of iron. The nonscavenged hexavalent uranium will be reduced by ferrous iron sorbed onto the iron corrosion products and by dissolved hydrogen. In the transport resistance network model, the transport of reactive actinides in the near field is simulated. The model describes the transport resistance in terms of coupled resistors by a coarse compartmentalisation of the repository, based on the concept that various ligands first come into the canister and then diffuse out to the surroundings in the form of nuclide complexes. The simulation results suggest that carbonate accelerates the oxidative dissolution of the fuel matrix by stabilizing uranyl ions, and that phosphate and silicate tend to limit the dissolution by the formation of insoluble secondary phases. The three models provide powerful tools to evaluate "what if" situations and alternative scenarios involving various interpretations of the repository system. They can be used to predict the rate of release of actinides from the fuel, to test alternative hypotheses and to study the response of the system to various parameters and conditions imposed upon it. / QC 20100521
77

Experimental Measurement of Effective Diffusion Coefficient in Gas Diffusion Layer/Microporous Layer in PEM Fuel Cells

Chan, Carl 25 August 2011 (has links)
Accuracy in the effective diffusion coefficient of the gas diffusion layer (GDL)/microporous layer (MPL) is important to accurately predict the mass transport limitations for high current density operation of polymer electrolyte membrane (PEM) fuel cells. All the previous studies regarding mass transport limitations were limited to pure GDLs, and experimental analysis of the impact of the MPL on the overall diffusion in the porous GDL is still lacking. The MPL is known to provide beneficial water management properties at high current operating conditions of PEM fuel cells but its small pore sizes become a resistance in the diffusion path for mass transport to the catalyst layer. A modified Loschmidt cell with an oxygen-nitrogen mixture is used in this work to determine the effect of MPL on the effective diffusion coefficients. It is found that Knudsen effects play a dominant role in the diffusion through the MPL where pore diameters are less than 1 μm. Experimental results show that the effective diffusion coefficient of the MPL is only about 21% that of its GDL substrate and Knudsen diffusion accounts for 80% of the effective diffusion coefficient of the GDL with MPL measured in this study. No existing correlations can correlate the effective diffusion coefficient with significant Knudsen contribution.
78

The development and implementation of high-throughput tools for discovery and characterization of proton exchange membranes

Reed, Keith Gregory 13 November 2009 (has links)
The need for sustainable energy use has motivated the exploration of renewable alternative fuels and fuel conversion technology on a global scale. Fuel cells, which convert chemical energy directly into electrical energy with high efficiency and low emissions, provide a promising strategy for achieving energy sustainability. The current progress in fuel cell commercialization is mainly in portable and stationary applications, but fuel cell technology for transportation applications, which make up a substantial portion of the global energy market, have seen little commercial success. Proton exchange membrane fuel cells (PEMFCs) have high potential for addressing the future energy needs of the transportation energy sector. However, one of the prevailing limitations of the PEMFC is the availability of high-performance, cost-effective electrolyte materials. These materials may be realized in the near future by developing multi-functional polymer blends targeted at specific performance capabilities. Due to the near-infinite possibilities of polymer combinations and processing techniques high-throughput polymer characterization techniques are necessary to effectively and systematically screen for optimal materials and relevant structure-property relationships. In this work, a high-throughput mass transport assay (HT-MTA) has been developed to characterize water flux and permeability at multiple sample locations in parallel. The functionality of HT-MTA was evaluated using standard Nafion® films and a model semi-interpenetrated polymer network with commercial polyvinylidine fluoride as the host matrix for a proprietary polyelectrolyte supplied by Arkema, Inc. To further demonstrate the utility of HT-MTA, the instrument was incorporated into the lab's current high-throughput characterization toolset and used to investigate the mechanisms and effects of rapid free radical degradation of Nafion® membranes based on various concentrations of hydrogen peroxide and iron(II) sulfate in solution. The results have been used suggest the effects of these regent components on preferential degradation pathways and will prove to be useful in later simulating the membrane performance during in-situ fuel cell lifetime which is both time-intensive and costly. The high-throughput toolset was also used to develop a novel optimized blend consisting of polyetherimide (PEI), a low-cost high performance resin, and sulfonated PEI (S-PEI) made using a relatively mild post sulfonation reaction with trimethylsilyl chlorosulfonate. The effects of blend composition and thermal annealing on film performance were evaluated and the polymer system was shown to have optimal performance properties that should prove to be useful in other high-performance applications where mechanical strength is critical. In general, this work shows promising results for efficiently developing advanced polymer materials using high-throughput screening techniques.
79

Efficient numerical method for solution of L² optimal mass transport problem

Rehman, Tauseef ur 11 January 2010 (has links)
In this thesis, a novel and efficient numerical method is presented for the computation of the L² optimal mass transport mapping in two and three dimensions. The method uses a direct variational approach. A new projection to the constraint technique has been formulated that can yield a good starting point for the method as well as a second order accurate discretization to the problem. The numerical experiments demonstrate that the algorithm yields accurate results in a relatively small number of iterations that are mesh independent. In the first part of the thesis, the theory and implementation details of the proposed method are presented. These include the reformulation of the Monge-Kantorovich problem using a variational approach and then using a consistent discretization in conjunction with the "discretize-then-optimize" approach to solve the resulting discrete system of differential equations. Advanced numerical methods such as multigrid and adaptive mesh refinement have been employed to solve the linear systems in practical time for even 3D applications. In the second part, the methods efficacy is shown via application to various image processing tasks. These include image registration and morphing. Application of (OMT) to registration is presented in the context of medical imaging and in particular image guided therapy where registration is used to align multiple data sets with each other and with the patient. It is shown that an elastic warping methodology based on the notion of mass transport is quite natural for several medical imaging applications where density can be a key measure of similarity between different data sets e.g. proton density based imagery provided by MR. An application is also presented of the two dimensional optimal mass transport algorithm to compute diffeomorphic correspondence maps between curves for geometric interpolation in an active contour based visual tracking application.
80

COMPUTER SIMULATION OF A HOLLOW-FIBER BIOREACTOR: HEPARAN REGULATED GROWTH FACTORS-RECEPTORS BINDING AND DISSOCIATION ANALYSIS

Zhang, Changjiang 01 January 2011 (has links)
This thesis demonstrates the use of numerical simulation in predicting the behavior of proteins in a flow environment. A novel convection-diffusion-reaction computational model is first introduced to simulate fibroblast growth factor (FGF-2) binding to its receptor (FGFR) on cell surfaces and regulated by heparan sulfate proteoglycan (HSPG) under flow in a bioreactor. The model includes three parts: (1) the flow of medium using incompressible Navier-Stokes equations; (2) the mass transport of FGF-2 using convection-diffusion equations; and (3) the cell surface binding using chemical kinetics. The model consists of a set of coupled nonlinear partial differential equations (PDEs) for flow and mass transport, and a set of coupled nonlinear ordinary differential equations (ODEs) for binding kinetics. To handle pulsatile flow, several assumptions are made including neglecting the entrance effects and an approximate analytical solution for axial velocity within the fibers is obtained. To solve the time-dependent mass transport PDEs, the second order implicit Euler method by finite volume discretization is used. The binding kinetics ODEs are stiff and solved by an ODE solver (CVODE) using Newton’s backward differencing formula. To obtain a reasonable accuracy of the biochemical reactions on cell surfaces, a uniform mesh is used. This basic model can be used to simulate any growth factor-receptor binding on cell surfaces on the wall of fibers in a bioreactor, simply by replacing binding kinetics ODEs. Circulation is an important delivery method for natural and synthetic molecules, but microenvironment interactions, regulated by endothelial cells and critical to the molecule’s fate, are difficult to interpret using traditional approaches. Growth factor capture under flow is analyzed and predicted using computer modeling mentioned above and a three-dimensional experimental approach that includes pertinent circulation characteristics such as pulsatile flow, competing binding interactions, and limited bioavailability. An understanding of the controlling features of this process is desired. The experimental module consists of a bioreactor with synthetic endotheliallined hollow fibers under flow. The physical design of the system is incorporated into the model parameters. FGF-2 is used for both the experiments and simulations. The computational model is based on the flow and reactions within a single hollow fiber and is scaled linearly by the total number of fibers for comparison with experimental results. The model predicts, and experiments confirm, that removal of heparan sulfate (HS) from the system will result in a dramatic loss of binding by heparin-binding proteins, but not by proteins that do not bind heparin. The model further predicts a significant loss of bound protein at flow rates only slightly higher than average capillary flow rates, corroborated experimentally, suggesting that the probability of capture in a single pass at high flow rates is extremely low. Several other key parameters are investigated with the coupling between receptors and proteoglycans shown to have a critical impact on successful capture. The combined system offers opportunities to examine circulation capture in a straightforward quantitative manner that should prove advantageous for biological or drug delivery investigations. For some complicated binding systems, where there are more growth factors or proteins with competing binding among them moving through hollow fibers of a bioreactor coupled with biochemical reactions on cell surfaces on the wall of fibers, a complex model is deduced from the basic model mentioned above. The fluid flow is also modeled by incompressible Navier-Stokes equations as mentioned in the basic model, the biochemical reactions in the fluid and on the cell surfaces are modeled by two distinctive sets of coupled nonlinear ordinary differential equations, and the mass transports of different growth factors or complexes are modeled separately by different sets of coupled nonlinear partial differential equations. To solve this computationally intensive system, parallel algorithms are devised, in which all the numerical computations are solved in parallel, including the discretization of mass transport equations and the linear system solver Stone’s Implicit Procedure (SIP). A parallel SIP solver is designed, in which pipeline technique is used for LU factorization and an overlapped Jacobi iteration technique is chosen for forward and backward substitutions. For solving binding equations ODEs in the fluid and on cell surfaces, a parallel scheme combined with a sequential CVODE solver is used. The simulation results are obtained to demonstrate the computational efficiency of the algorithms and further experiments need to be conducted to verify the predictions.

Page generated in 0.0229 seconds