Dissertations / Theses: 'Reaction systems'

1

Fromell, Karin. "Nanoscale Reaction Systems." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8249.

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2

Steele, Aaron J. "Collective behavior in chemical systems." Morgantown, W. Va. : [West Virginia University Libraries], 2007. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=5386.

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Thesis (Ph. D.)--West Virginia University, 2007.
Title from document title page. Document formatted into pages; contains vii, 126 p. : ill. (some col.) + video files. Includes supplementary video files in a zip file. Includes abstract. Includes bibliographical references.

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3

He, Taiping. "Reaction-Diffusion Systems with Discontinuous Reaction Functions." NCSU, 2005. http://www.lib.ncsu.edu/theses/available/etd-03192005-101102/.

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This dissertation studies coupled reaction diffusion systems with discontinuous reaction functions. It includes three parts: The first part is concerned with the existence of solutions for a coupled system of two parabolic equations and the second part is devoted to the monotone iterative methods for monotone and mixed quasimonotone functions. Various monotone iterative schemes are presented and each of these schemes leads to an existence-comparison theorem and the monotone convergence of the maximal and minimal sequences. In the third part, the monotone iterative schemes are applied to compute numerical solutions of the system. These numerical solutions are based on the finite element method which gives a finite approximation of the coupled system. Numerical results for some scalar parabolic bounday problems and a coupled system of parabolic equations are also given.

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4

Newton, Elizabeth Lynn. "Sustainable Reaction and Separation Systems." Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7463.

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With increasing environmental awareness and natural resource limitations, researchers must begin to incorporate sustainability into their process and product designs. One target for green engineering is in reaction and separation design. This is typically done in a wasteful and often toxic manner with organic solvents and lack of recycle. The following thesis discusses alternatives to these costly separations by means of ionic liquids, benign extraction, separation with carbon dioxide, and near critical water. Ionic liquids are combined with carbon dioxide to induce melting point depressions of up to 124 degrees Celsius. Using this system as a reaction medium will offer control over the reaction phases while utilizing green solvents. Benign extractions are performed on both ferulic acid and on proteins from biomass by replacing alkaline solvents and costly protein separation techniques with simple liquid-liquid extraction. This means simpler systems and less waste than from previous methods. This thesis also discusses an opportunity for more efficient separation and recycle of a pharmaceutical catalyst, Mn-Salen. Using carbon dioxide with the organic aqueous tunable solvent system, the reaction can be run homogeneously and the product and catalyst separated heterogeneously, thus creating an extremely efficient process. Lastly, near critical water is used as an extraction and reaction medium by extracting ferulic acid from Brewers Spent Grain and then catalyzing its transformation to 4-vinylguaiacol. In this manner a simple, benign process is used to turn waste into valuable chemicals. Although somewhat different, each of the studied processes strives to eliminate waste and toxicity of many commonly used reaction and separation techniques, thus creating safe and sustainable processes.

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5

Hemming, Christopher John. "Resonantly forced inhomogeneous reaction-diffusion systems." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0022/MQ50344.pdf.

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6

Brendel, Marc Levin. "Incremental identification of complex reaction systems /." Düsseldorf : VDI-Verl, 2006. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=015009980&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.

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7

Smith, Mark. "Spatial reaction systems on parallel supercomputers." Thesis, University of Edinburgh, 1994. http://hdl.handle.net/1842/12985.

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A wide variety of physical, chemical and biological systems can be represented as a collection of discrete spatial locations within which some interaction proceeds, and between which reactants diffuse or migrate. Many such real-world spatial reaction systems are known to be both non-linear and stochastic in nature, and thus studies of these systems have generally relied upon analytic approximation and computer simulation. However, this later approach can become impractical for large, complex systems which require massive computational resources. In this work we analyse a general spatial reaction system in both the deterministic and stochastic scenarios. A study of the deterministic parameter space reveals a new categorisation for system development in terms of its criticality. This result is then coupled with a complete analysis of the linearised stochastic system, in order to provide an understanding of the spatial-temporal covariance structures within reactant distributions. In addition to an analysis, and empirical confirmation, of the various criticality behaviours in both deterministic and stochastic cases, we use our theoretical results to enable efficient implementation of spatial reaction system simulations on parallel supercomputers. Such novel computing resources are necessary to enable the study of realistic-scale, long-term stochastic activity, however they are notoriously difficult to exploit. We have therefore developed advanced programming and implementation techniques, concentrating mainly on dynamic load-balancing methodologies, to enable such studies. These techniques make direct use of our analytic results in order to achieve the most efficient exploitation of supercomputing resources, given the particular attributes of the system under study. These new techniques have allowed us to investigate complex individual-based systems on a previously untried scale. In addition, they are of general applicability to a wide range of real-world simulations.

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8

Vaughan, Asa Dee Byrne Mark E. "Reaction analysis of templated polymer systems." Auburn, Ala., 2008. http://hdl.handle.net/10415/1538.

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9

Memon, Muhammad Hanif. "Microemulsions as analytical reaction media." Thesis, University of Hull, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235839.

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10

Nagaiah, Chamakuri. "Adaptive numerical simulation of reaction-diffusion systems." [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=985277882.

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11

Smith, Mathew D. "Reaction of hydroxyl radical with aromatic systems." Virtual Press, 2008. http://liblink.bsu.edu/uhtbin/catkey/1399191.

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The regioselectivity of the reaction of hydroxyl radical addition to toluene and naphthalene are examined in this study over the temperature range of 25°C-45°C. Also, the relative rates of reactivity as compared to benzene are determined for toluene, naphthalene, mesitylene, and p-xylene over the same temperature range. 2-(t-Butylazo)prop-2-yl hydroperoxide was used as the hydroxyl radical source and 1,1,3,3-tetramethylisoindolin-2-yloxyl was used as radical trap. For toluene the relative rates of addition were found to be 4 times greater for the ortho position versus the meta postion and 2 times greater for the para position versus the meta position, when the number of meta and para sites are taken into account.
Department of Chemistry

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12

Davidson, Fordyce A. "Bifurcation in systems of reaction-diffusion equations." Thesis, Heriot-Watt University, 1993. http://hdl.handle.net/10399/1444.

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13

Howard, Martin. "Non-equilibrium dynamics of reaction-diffusion systems." Thesis, University of Oxford, 1996. http://ora.ox.ac.uk/objects/uuid:4485a178-6262-4487-b40f-7c7ec790d687.

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Fluctuations are known to radically alter the behaviour of reaction-diffusion systems. Below a certain upper critical dimension d_c , this effect results in the breakdown of traditional approaches, such as mean field rate equations. In this thesis we tackle this fluctuation problem by employing systematic field theoretic/renormalisation group methods, which enable perturbative calculations to be made below d_c. We first consider a steady state reaction front formed in the two species irreversible reaction A + B → Ø. In one dimension we demonstrate that there are two components to the front - one an intrinsic width, and one caused by the ability of the centre of the front to wander. We make theoretical predictions for the shapes of these components, which are found to be in good agreement with our one dimensional simulations. In higher dimensions, where the intrinsic component dominates, we also make calculations for its asymptotic profile. Furthermore, fluctuation effects lead to a prediction of asymptotic power law tails in the intrinsic front in all dimensions. This effect causes high enough order spatial moments of a time dependent reaction front to exhibit multiscaling. The second system we consider is a time dependent multispecies reaction-diffusion system with three competing reactions A+A → Ø, B + B → Ø, and A + B → Ø, starting with homogeneous initial conditions. Using our field theoretic formalism we calculate the asymptotic density decay rates for the two species for d ≤ d_c. These calculations are compared with other approximate methods, such as the Smoluchowski approach, and also with previous simulations and exact results.

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14

Turpin, Kevin. "Patterns and fronts in reaction-diffusion systems." Thesis, University of Nottingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287233.

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15

Aldurayhim, Abdullah Mohammed. "Propagating waves in reaction cross-diffusion systems." Thesis, University of Exeter, 2017. http://hdl.handle.net/10871/31129.

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This research focuses on the reaction diffusion systems where the matrix of diffusion co- efficients is not diagonal. We call these systems reaction cross-diffusion systems. These systems possess interesting solutions that do not appear in the reaction self-diffusion systems that have a diagonal diffusion matrix. Compared to research conducted on re- action self-diffusion systems, the reaction cross-diffusion systems have received little attentions. The aim of this research is to extend existing literature on these systems. In this thesis we considered two-components reaction cross-diffusion systems. We find an ana- lytical solution of reaction diffusion system with replacing FitzHugh-Nagumo kinetics by quartic polynomial. Finding the analytical solution is extends analytical results pre- sented in [9]. This analytical solution is presented in a wave front profile. We study the possibility of imitating Fisher-KPP and ZFK-Nagumo front waves by our analytical solution which we have introduced. The existence of a quartic polynomial yields four different cases with respect to the positions of the roots of the quartic polynomial and the resting states of the wave front. We solve the problem numerically and compare the numerical solution to the analytical solution for those four cases. Finally, we extend the analysis of the different wave regimes in reaction cross- diffusion system with FitzHugh-Nagumo kinetics by varying parameters in the system using numerical continuation. We compute the speed of propagating waves in this sys- tem and show the corresponding eigenvalues of equilibrium which gives an indication about the profile of the propagating waves. We find a stable propagating wave that is not obtained by direct numerical simulation in [55]. We investigate the stability of prop- agating waves by using direct numerical simulation.

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16

Fernandez, Fonseca Andrea. "Sharp interface models from homogeneous reaction systems." Thesis, University of Bath, 2013. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.607473.

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This thesis investigates the fast-reaction limit for a one dimensional reaction-diffusion system describing the penetration of the carbonation reaction in concrete. Three conceptually different scaling regimes of the effective diffusivities of the driving chemical species are explored using matched asymptotics. The limiting models include one-phase and two-phase generalised Stefan moving boundary problems as well as a nonstandard two-scale (micro-macro) moving boundary problem. These sharp interface models are studied to uncover the mechanisms at the free boundary. A power law for the concentration of the chemical species at the interface is derived, as well as the large and small time asymptotic behaviour of the free boundary and the concentration profiles. Numerical results, supporting the analytical results, are presented throughout this thesis, including the application of the method of lines to solve the limiting Stefan problems. To conclude, numerical illustrations of different two-dimensional geometries are included.

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17

Kammogne, Kamgaing Rodrigue. "Domain decomposition methods for reaction-diffusion systems." Thesis, University of Birmingham, 2014. http://etheses.bham.ac.uk//id/eprint/4599/.

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Domain Decomposition (DD) methods have been successfully used to solve elliptic problems, as they deal with them in a more elegant and efficient way than other existing numerical methods. This is achieved through the division of the domain into subdomains, followed by the solving of smaller problems within these subdomains which leads to the solution. Furthermore DD-techniques can incorporate in their implementation not only the physics of the different phenomena associated with the modeling, but also the enhancement of parallel computing. They can be divided into two major categories: with and without overlapping. The most important factor in both cases is the ability to solve the interface problem referred to as the Steklov-Poincaré problem. There are two existing approaches to solving the interface problem. The first approach consists of approximating the interface problem by solving a sequence of subproblems within the subdomains, while the second approach aims to tackle the interface problem directly. The solution method presented in this thesis falls into the latter category. This thesis presents a non-overlapping domain decomposition (DD) method for solving reaction-diffusion systems. This approach addresses the problem directly on the interface which allows for the presentation and analysis of a new type of interface preconditioner for the arising Schur complement problem. This thesis will demonstrate that the new interface preconditioner leads to a solution technique independent of the mesh parameter. More precisely, the technique, when used effectively, exploits the fact that the Steklov-Poincaré operators arising from a non-overlapping DD-algorithm are coercive and continuous, with respect to Sobolev norms of index 1/2, in order to derive a convergence analysis for a DD-preconditioned GMRES algorithm. This technique is the first of its kind that presents a class of substructuring methods for solving reaction diffusion systems and analyzes their behaviour using fractional Sobolev norms.

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18

Zhang, Wenling. "Model building methodology for complex reaction systems." Thesis, University of Manchester, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.503069.

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The complexity of chemical reaction processes and the short market window of some chemical products mean that detailed model building can often not be justified. With little knowledge of chemistry, this work aims to provide a new methodology for model building of chemical reaction systems with minimum experimental measurements, for the purpose of reactor design and optimisation. Most often reactor designs are scaled from experimental measurements, especially for the manufacture of fine and speciality chemicals. Yet, without a model of the reaction system, major opportunities can be missed in the design and optimisation of the reactor. When models are developed for a reaction system in the laboratory, they are often inappropriate for reactor design and optimisation. In the first part of this thesis, the reaction scheme that best describes the production of a given chemical and suitable kinetic equations are obtained simultaneously using optimisation. A hybrid optimisation method is used to deal with this large problem where more than one model fits the same experimental data within a certain confidence level. Stochastic optimisation methods provide multiple solutions that are rival models for model discrimination. An NLP method improves model precision from the stochastic optimisation in the narrowed search space. A strategy for reaction scheme construction is used to generate all reactions from the reacting species and to provide plausible reaction schemes during optimisation. These reaction schemes are screened simultaneously with kinetic models to fit the most appropriate reaction scheme and kinetic model from the rival models. Optimal experiments then need to be designed to discriminate among rival models. The experimental design exploits the potential for mixing, as well as temperature and concentration effects to discriminate between models through the reactor superstructure. The oleic acid epoxidation reaction is used to demonstrate the methodology. For refinery heterogeneous catalytic reactions, due to the complex nature of catalysis, a large number of rival models pose difficulties for model building and discrimination. In the rest of the thesis, three-level kinetic study method is developed for model building to reduce the model complexity by separating diffusion effects from kinetic equations. In addition, catalyst characterisation is used to assist model discrimination. There are a large number of techniques available to connect catalyst properties, catalyst activities with model performance with different capabilities and limitations. However, not all of these will be useful in a given application. A classification of those techniques specified for hydrodesulphurisation (HDS) processes provides guidance for selecting suitable techniques to yield the most information with accuracy, speed, and economy. Furthermore, plausible ways for model discrimination and model improvement for thiophene and diesel HDS are explored, including operating condition, feedstock and catalyst effects.

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19

Hiwale, Rameshwar. "Model Building Methodology for Multiphase Reaction Systems." Thesis, University of Manchester, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.521567.

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20

Alves, Jessica. "Advanced photochemical reaction systems for molecular design." Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/227734/1/Jessica_Alves_Thesis.pdf.

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Direct laser writing is a technique for printing complex 3D structures with high resolution by irradiating a photoresist in a two-photon process. Improved resolution and dynamic material properties of the printed structures is critical. Herein, advanced photochemical systems were investigated, potentially enabling dual-wavelength direct laser writing. Such systems consisting of organic photoswitches enable the formation of a single product only when irradiated with two wavelengths. A well-known class of photoswitches was investigated for this purpose and its chemistry was carefully explored. Further, photocatalysis combined with a photoswitch was identified as a possible strategy for the two-colour activated photoresist development.

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21

Keller, Tobias [Verfasser]. "Reactive Distillation for Multiple-reaction Systems: Experimental Investigation, Modelling and Optimisation / Tobias Keller." München : Verlag Dr. Hut, 2013. http://d-nb.info/103728948X/34.

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22

Rolland, Guillaume. "Global existence and fast-reaction limit in reaction-diffusion systems with cross effects." Phd thesis, École normale supérieure de Cachan - ENS Cachan, 2012. http://tel.archives-ouvertes.fr/tel-00785757.

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This thesis is devoted to the study of parabolic systems of partial differential equations arising in mass action kinetics chemistry, population dynamics and electromigration theory. We are interested in the existence of global solutions, uniqueness of weak solutions, and in the fast-reaction limit in a reaction-diffusion system. In the first chapter, we study two cross-diffusion systems. We are first interested in a population dynamics model, where cross effects in the interactions between the different species are modeled by non-local operators. We prove the well-posedness of the corresponding system for any space dimension. We are then interested in a cross-diffusion system which arises as the fast-reaction limit system in a classical system for the chemical reaction C1+C2=C3. We prove the convergence when k goes to infinity of the solution of the system with finite reaction speed k to a global solution of the limit system. The second chapter contains new global existence results for some reaction-diffusion systems. For networks of elementary chemical reactions of the type Ci+Cj=Ck and under Mass Action Kinetics assumption, we prove the existence and uniqueness of global strong solutions, for space dimensions N<6 in the semi-linear case, and N<4 in the quasi-linear case. We also prove the existence of global weak solutions for a class of parabolic quasi-linear systems with at most quadratic non-linearities and with initial data that are only assumed to be nonnegative and integrable. In the last chapter, we generalize a global well-posedness result for reaction-diffusion systems whose nonlinearities have a "triangular" structure, for which we now take into account advection terms and time and space dependent diffusion coefficients. The latter result is then used in a Leray-Schauder fixed point argument to prove the existence of global solutions in a diffusion-electromigration system.

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23

Balding, D. J. "Some annihilating particle systems." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236110.

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24

Sinclair, E. C. "Geometric reaction forces in billiards." Thesis, University of Bristol, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294868.

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25

Picciani, Massimiliano. "Rare events in many-body systems : reactive paths and reaction constants for structural transitions." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2012. http://tel.archives-ouvertes.fr/tel-00706510.

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Cette thèse aborde l'étude de phénomènes physiques fondamentaux, avec des applications aux matériaux d'intérêt nucléaire. Nous avons développé des méthodes pour l'étude d'évènements rares concernant des transitions structurales thermiquement activées dans des systèmes à N-corps. La première méthode consiste en la simulation numérique du courant de probabilité associé aux chemins réactifs. Après avoir dérivé les équations d'évolution du courant de probabilité, on échantillonne ce courant grâce à un algorithme de type Monte Carlo Diffusif. Cette technique, dénommée Transition Current Sampling, a été appliquée pour étudier les transitions structurales d'un agrégat de 38 atomes liés par un potentiel Lennard-Jones (LJ-38). Un deuxième algorithme, dénommée Transition Path Sampling avec bias de Lyapunov local (LyTPS), a ensuite été développé. LyTPS permet de calculer des taux de réaction à température finie en suivant la théorie des états de transition. Un biais statistique dérivant du maximum des exposantes de Lyapunov locaux est introduit pour accélérer l'échantillonnage de trajectoires réactives. Afin d'extraire la valeur des constantes de réaction d'équilibre depuis celle obtenues par LyTPS, on utilise le Multistate Bennett Acceptance Ratio. Nous avons à nouveau validé cette méthode sur l'agrégat LJ-38. LyTPS est ensuite utilisé pour calculer les constantes de migration des lacunes et di-lacunes dans le Fer-α, ainsi que l'entropie de migration associée. Ces constantes de réaction servent de paramètre d'input dans des codes de modélisation cinétique (First Passage Kinetic Monte Carlo) pour reproduire numériquement des recuits de résistivité de Fer-α après irradiation.

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26

Barkat, Omar. "Rheology of flowing, reacting systems the crosslinking reaction of hydroxypropyl guar with titanium chelates /." Access abstract and link to full text, 1987. http://0-wwwlib.umi.com.library.utulsa.edu/dissertations/fullcit/8712850.

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27

Howarth, J. N. "Microelectrode studies of Electroplating systems." Thesis, University of Southampton, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380601.

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28

Büger, Matthias. "Systems of reaction-diffusion equations and their attractors." Giessen : Selbstverlag des Mathematischen Instituts, 2005. http://catalog.hathitrust.org/api/volumes/oclc/62216537.html.

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29

Stich, Michael. "Target patterns and pacemakers in reaction-diffusion systems." [S.l.] : [s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=967163943.

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30

Filho, Sergio Muniz Oliva. "Reaction-diffusion systems on domains with thin channels." Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/28837.

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Lamb, David R. "New reaction systems for environmentally conscious chemical processes." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/30075.

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Provatas, Nikolas. "Kinetic roughening and bifurcations in reaction-diffusion systems." Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=28886.

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We study the dynamics of two reaction-diffusion phenomena driven by chemical activation and thermal dissipation and evolving, respectively, on a randomly distributed or continuous medium. The first system describes the process of slow combustion of a randomly distributed reactant. It is studied by a phase-field model built up from first principles and describes the evolution of thermal and reactant concentration fields. Our combustion model incorporates thermal diffusion, activation and dissipation. We examine it in a manner which makes a connection between the propagation of combustion fronts, their kinetic roughening and the percolation transition. In so doing, we examine slow combustion in the context phase transitions. The second system describes propagation of reaction fronts arising in transformations obeying the Arrhenius law of chemical reactions. It too is modelled by a set of phase-field equations describing the dynamics of both thermal and concentration fields. A typical example of this transformation is the crystallization of an amorphous material. In addition to the features of our combustion model, this model also incorporated a realistic treatment of mass diffusion. Front propagation of our model is shown to undergo period doubling bifurcations as one varies the background temperature at which the system is maintained. The signature of these bifurcations is the same as those of the logistics map. We study how the bifurcation structure changes as a function mass diffusion, focusing on changes of the background temperature for which period doubling first emerges. This temperature is the most easily obtained experimentally.

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Lesutis, Heather Patrick. "Reaction kinetics in environmentally benign novel solvent systems." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/11865.

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34

Menon, Shakti Narayana. "Bifurcation problems in chaotically stirred reaction-diffusion systems." Thesis, The University of Sydney, 2008. http://hdl.handle.net/2123/3685.

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A detailed theoretical and numerical investigation of the behaviour of reactive systems under the influence of chaotic stirring is presented. These systems exhibit stationary solutions arising from the balance between chaotic advection and diffusion. Excessive stirring of such systems results in the termination of the reaction via a saddle-node bifurcation. The solution behaviour of these systems is analytically described using a recently developed nonperturbative, non-asymptotic variational method. This method involves fitting appropriate parameterised test functions to the solution, and also allows us to describe the bifurcations of these systems. This method is tested against numerical results obtained using a reduced one-dimensional reaction-advection-diffusion model. Four one- and two-component reactive systems with multiple homogeneous steady-states are analysed, namely autocatalytic, bistable, excitable and combustion systems. In addition to the generic stirring-induced saddle-node bifurcation, a rich and complex bifurcation scenario is observed in the excitable system. This includes a previously unreported region of bistability characterised by a hysteresis loop, a supercritical Hopf bifurcation and a saddle-node bifurcation arising from propagation failure. Results obtained with the nonperturbative method provide a good description of the bifurcations and solution behaviour in the various regimes of these chaotically stirred reaction-diffusion systems.

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Menon, Shakti Narayana. "Bifurcation problems in chaotically stirred reaction-diffusion systems." University of Sydney, 2008. http://hdl.handle.net/2123/3685.

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Doctor of Philosophy
A detailed theoretical and numerical investigation of the behaviour of reactive systems under the influence of chaotic stirring is presented. These systems exhibit stationary solutions arising from the balance between chaotic advection and diffusion. Excessive stirring of such systems results in the termination of the reaction via a saddle-node bifurcation. The solution behaviour of these systems is analytically described using a recently developed nonperturbative, non-asymptotic variational method. This method involves fitting appropriate parameterised test functions to the solution, and also allows us to describe the bifurcations of these systems. This method is tested against numerical results obtained using a reduced one-dimensional reaction-advection-diffusion model. Four one- and two-component reactive systems with multiple homogeneous steady-states are analysed, namely autocatalytic, bistable, excitable and combustion systems. In addition to the generic stirring-induced saddle-node bifurcation, a rich and complex bifurcation scenario is observed in the excitable system. This includes a previously unreported region of bistability characterised by a hysteresis loop, a supercritical Hopf bifurcation and a saddle-node bifurcation arising from propagation failure. Results obtained with the nonperturbative method provide a good description of the bifurcations and solution behaviour in the various regimes of these chaotically stirred reaction-diffusion systems.

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36

Kamm, Philipp Willi. "Understanding of lambda-orthogonal photo-induced reaction systems." Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/234293/1/Philipp%20Willi_Kamm_Thesis.pdf.

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Using light as an energy source allows chemical reactions to be carried out with high precision in time and space. In time, because light can be switched on and off, in space, because light can be highly focussed. Further, different colours of light can be used to activate different reactants individually, even when they are present in the same reaction mixture. Herein, a system of two light-sensitive molecules was developed, which react completely sequence-independently with UV or visible light. The wavelength-dependence as well as the influence of chemical-physical parameters on such reactions were investigated in-depth.

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37

Asar, Isik. "Model Predictive Control (mpc) Performance For Controlling Reaction Systems." Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/12605001/index.pdf.

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In this study, the performance of the Model Predictive Controller (MPC) algorithm is investigated in two different reaction systems. The first case is a saponification reaction system where ethyl acetate reacts with sodium hydroxide to produce sodium acetate and ethanol in a CSTR. In the reactor, temperature and sodium acetate concentration are controlled by manipulating the flow rates of ethyl acetate and cooling water. The model of the reactor is developed considering first principal models. The experiments are done to obtain steady state data from the reaction system and these are compared with the model outputs to find the unknown parameters of the model. Then, the developed model is used for designing SISO and MIMO-MPC considering Singular Value Decomposition (SVD) technique for coupling. The second case is the reaction system used for the production of boric acid by the reaction of colemanite and sulfuric acid in four CSTR&rsquo
s connected in series. In the reactor, the boric acid concentration in the fourth reactor is controlled by manipulating the sulfuric acid flow rate fed to the reactor. The transfer functions of the process and disturbance (colemanite flow rate) are obtained experimentally by giving step changes to the manipulated variable and to the disturbance. A model-based and constrained SISO-MPC is designed utilizing linear step response coefficients. The designed controllers are tested for performance in set point tracking, disturbance rejection and robustness issues for the two case studies. It is found that, they are satisfactory except in robustness issues for disturbance rejection in boric acid system.

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38

Joglekar, Saurabh Gajanan. "Numerical Study of Reaction-Diffusion Systems using Front Tracking." Thesis, State University of New York at Stony Brook, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10622549.

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We study the three component Reaction-Diffusion systems with and without precipitation and crystal growth. Focus is on the generic chemical reaction represented by nA + mB → C, where n,m are the stoichiometric coefficients. In case of the reaction-diffusion system without precipitation, we investigate the movement of the center of reaction zone in for equal and unequal diffusivities. We compare the analytical and numerical solutions for equal diffusivities to establish the accuracy of the numerical method. Then we apply the numerical method to provide numerical evidence in support of a conjecture in the case of unequal diffusivities.

Next, we apply the Front Tracking method to study the reaction-diffusion systems with crystal growth in higher spatial dimensions. The effects of different parameters on the crystal growth are investigated.

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39

Geffen, Dara. "Parameter identifiability of biochemical reaction networks in systems biology." Thesis, Kingston, Ont. : [s.n.], 2008. http://hdl.handle.net/1974/1347.

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Crews, Steven R. II. "Increasing slew performance of reaction wheel attitude control systems." Thesis, Monterey, California: Naval Postgraduate School, 2013. http://hdl.handle.net/10945/37606.

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Approved for public release; distribution is unlimited
This thesis explores the physical and mathematical limitations of two common attitude control systems: one based on reaction wheels and another based on control moment gyroscopes (CMGs). The dynamics are derived from first principles and control algorithms for achieving maximum reaction wheel potential are discussed. The shaped eigenaxis input is utilized to establish baseline maneuver performance. A time-optimal shaped input is introduced and implemented in a feedback setting, subject to the limitations of the Moore-Penrose pseudo-inverse control allocation. Finally, a feed-forward plus feedback controller is introduced to implement the time-optimal torque inputs directly to the reaction wheels. This obviates the need for the pseudo-inverse control allocation, and therefore exploits the total capacities of both the reaction wheel momentum envelope and torque envelope. These reaction wheel control approaches are compared with CMG performance to establish spacecraft size and slew parameters that make the use of reaction wheels a reasonable choice

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Parker, Duncan J. "Uncovering features of chemical reaction networks in complex systems." Thesis, University of Southampton, 2018. https://eprints.soton.ac.uk/422229/.

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This thesis introduces a comprehensive atlas of behaviour in the iron-catalysed Belousov-Zhabotinsky reaction across a wide parameter space, under both stirred and unstirred conditions, encompassing variations in the concentrations of sulfuric acid, malonic acid and sodium bromate. All stirred reactions were monitored by UV-vis spectroscopy enabling the definition of concentration-dependent transitions in behaviour including those to chaotic oscillation. A programme was generated to quantify spirals observed in the unstirred reaction. This expanded on the work of Müller et al. by increasing the length of time that such spirals had been monitored. There was good agreement between their experimental results and those set out in this thesis, which shows the transition from normal spiral wave behaviour to a final steady state. The work on spiral waves also includes the first use of a statistical image-based method for identifying changes in chemical wave behaviour with time. Attempts were made at producing a model for the iron-catalysed Belousov-Zhabotinsky reaction using a swarm intelligence algorithm having identified key reactions involved in modifying the reaction behaviour based upon the Marburg-Budapest-Missoula model. A further comparison between this model for the cerium-catalysed reaction and the chemical component of the Kyoto Encyclopaedia of Genes and Genomes database demonstrated that study of such small scale systems is applicable to a larger scale biochemical network.

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Taylor, Benjamin Luke. "Reaction systems and phase development for investment casting ceramics." Thesis, University of Birmingham, 2015. http://etheses.bham.ac.uk//id/eprint/5932/.

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Aero engine turbine blades are commonly produced via investment casting methods utilising sacrificial ceramic cores during casting to provide internal features such as cooling channels. During the firing process the conversion of the main ingredient (amorphous silica) to β-cristobalite plays a significant role, as it directly affects the dimensional stability, shrinkage, and leachability of the core after casting. Dilatometry, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were utilised to evaluate common additives such as zirconium silicate and aluminosilicate. Zircon was found to act as a nucleation site with high temperature stability while aluminosilicate acts as a flux enhancing cristobalite formation rates. This understanding was utilised to mimic the performance of the formulation using both a novel engineered material and alternative naturally sourced silica. An innovative method was also developed utilising confocal Raman spectroscopy (CRM) and polarised light microscopy (PLM) for analysis of ceramic systems studied with a hot stage up to 1500 °C. Polarised light microscopy was shown to be favourable for analysis of crystal growth mechanisms and low temperature (≈250 °C) α-β cristobalite phase transitions. Developments in Raman spectroscopic technique enabled the location and crystallinity of devitrified amorphous silica (cristobalite) to be observed via a quasi-real time method, providing insight to the source, direction and corresponding crystal growth rates. The combination of analytical techniques has provided sufficient understanding to explain the role of key components in ceramic core formulations, which can be used to improve control and the predictability of the system during development and manufacture.

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Losey, Matthew W. "Novel multiphase chemical reaction systems enabled by microfabrication technology." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/8634.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2001.
Includes bibliographical references (p. 237-251).
Advances in MEMS (micro-electromechanical systems) have enabled some of the "Lab-on-a-Chip" technologies and microfluidics that are pervasive in many of the current developments in analytical chemistry and molecular biology. Coinciding with this effort in micro-analytics has been research in chemical process miniaturization -- reducing the characteristic length scale of the unit operation to improve heat and mass transfer, and ultimately process performance. My research has involved the design and fabrication of novel chemical reaction systems using MEMS and microfabrication methods (photolithography, deep-reactive-ion etching, thin-film growth and deposition, and multiple wafer bonding). Miniature chemical systems provide the opportunity for distributed, on-demand manufacturing, which would eliminate the hazards of transportation and storage of toxic or hazardous chemical intermediates. Reactions that are particularly suitable for miniaturized chemical systems are those that are fast and involve toxic intermediates: the controlled synthesis of phosgene is such a reaction and has been demonstrated in a microfabricated packed bed reactor. Owing to the high surface-to-volume ratios, micro chemical systems also have the potential to make improvements in process performance through enhanced heat and mass transfer.
(cont.) Heterogeneously catalyzed gas-liquid reactions have been performed in the microfabricated reactors and have been shown to have mass transfer coefficients several orders of magnitude larger than their industrial-scale counterparts. Multiphase reactions are often hindered by mass-transfer limitations owing to the difficulty in transporting the gaseous reactant through the liquid to the catalytic surface. The microchemical device has been designed to increase the interfacial gas-liquid contacting area by promoting dispersion and preventing coalescence. Microfabrication allows the design of reactors with complicated fluidic distribution networks, staggered arrays of microstructural features to promote mixing, and the integration of sensing and temperature control. Other uses of microfabrication include the incorporation of porous silicon as a high surface area catalyst support. In all, performing multiphase chemistry on a chip has been demonstrated to have inherent advantages, particularly for those fast reactions that can benefit from improved mixing and mass transfer.
by Matthew W. Losey.
Ph.D.

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Li, Fei. "Stochastic Modeling and Simulation of Reaction-Diffusion Biochemical Systems." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/64913.

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Reaction Diffusion Master Equation (RDME) framework, characterized by the discretization of the spatial domain, is one of the most widely used methods in the stochastic simulation of reaction-diffusion systems. Discretization sizes for RDME have to be appropriately chosen such that each discrete compartment is "well-stirred" and the computational cost is not too expensive. An efficient discretization size based on the reaction-diffusion dynamics of each species is derived in this dissertation. Usually, the species with larger diffusion rate yields a larger discretization size. Partitioning with an efficient discretization size for each species, a multiple grid discretization (MGD) method is proposed. MGD avoids unnecessary molecular jumping and achieves great simulation efficiency improvement. Moreover, reaction-diffusion systems with reaction dynamics modeled by highly nonlinear functions, show large simulation error when discretization sizes are too small in RDME systems. The switch-like Hill function reduces into a simple bimolecular mass reaction when the discretization size is smaller than a critical value in RDME framework. Convergent Hill function dynamics in RDME framework that maintains the switch behavior of Hill functions with fine discretization is proposed. Furthermore, the application of stochastic modeling and simulation techniques to the spatiotemporal regulatory network in Caulobacter crescentus is included. A stochastic model based on Turing pattern is exploited to demonstrate the bipolarization of a scaffold protein, PopZ, during Caulobacter cell cycle. In addition, the stochastic simulation of the spatiotemporal histidine kinase switch model captures the increased variability of cycle time in cells depleted of the divJ genes.
Ph. D.

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Tu, Junyi. "Global Attractors and Random Attractors of Reaction-Diffusion Systems." Scholar Commons, 2016. http://scholarcommons.usf.edu/etd/6418.

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The dissertation studies about the existence of three different types of attractors of three multi-component reaction-diffusion systems. These reaction-diffusion systems play important role in both chemical kinetics and biological pattern formation in the fast-growing area of mathematical biology. In Chapter 2, we prove the existence of a global attractor and an exponential attractor for the solution semiflow of a reaction-diffusion system called Boissonade equations in the L2 phase space. We show that the global attractor is an (H, E) global attractor with the L∞ and H2 regularity and that the Hausdorff dimension and the fractal dimension of the global attractor are finite. The existence of exponential attractor is also shown. The upper-semicontinuity of the global attractors with respect to the reverse reaction rate coefficient is proved. In Chapter 3, the existence of a pullback attractor for non-autonomous reversible Selkov equations in the product L2 phase space is proved. The method of grouping and rescaling estimation is used to prove that the L4-norm and L6-norm of solution trajectories are asymptotic bounded. The new feature of pinpointing a middle time in the process turns out to be crucial to deal with the challenge in proving pullback asymptotic compactness of this typical non-autonomous reaction-diffusion system. In Chapter 4, asymptotical dynamics of stochastic Brusselator equations with multiplicative noise is investigated. The existence of a random attractor is proved via the exponential transformation of Ornstein-Uhlenbeck process and some challenging estimates. The proof of pullback asymptotic compactness here is more rigorous through the bootstrap pullback estimation than a non-dynamical substitution of Brownian motion by its backward translation. It is also shown that the random attractor has the L2 to H1 attracting regularity by the flattening method.

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Crooks, Elaine Craig Mackay. "Travelling-wave solutions for parabolic systems." Thesis, University of Bath, 1996. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319218.

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Ma, Jinyu, and 马金余. "Phloretin and phloridzin as modulators in maillard reaction model systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B47146977.

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Haffenden, Luke John William. "Investigation into the role of redox reactions in Maillard model systems : generation of aroma, colour and other non-volatiles." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=111850.

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The role of redox reactions in the formation of aroma volatiles, colour and other non-volatiles in the Maillard Reaction was investigated. The electrochemical properties of individual reactants and Maillard model mixtures were monitored via ORP (oxidation-reduction potential) and oxygen electrodes. All models exhibited unique electrochemical activities represented by their corresponding ORP profiles. Investigation into the redox potentials of several model systems demonstrated that the increased negative value of a redox potential is not necessarily correlated with its browning potential. An optimal redox potential range, where browning is favoured, was found to represent a balance between carbonyl and hydroxyl moieties in the structure. Adjustment of this redox potential by introducing reducing or oxidizing species can shift this balance resulting in modifications in browning capacities. However, it was concluded that there is a clear relationship between browning ability and reducing capacity of the model systems. Furthermore, a novel oxidative pyrolysis technique was developed to study the role of oxidative environment on the product distribution during pyrolysis and to investigate the mechanism of formation of non-volatiles through 13C and 15N-label incorporation. Application of this technique to glucoselglycine model system have indicated that most non-volatile Maillard reaction products can arise from glucose oxidation intermediates such as glucosone, gluconic acid and deoxyglucosones. To study the specific role of redox reactions in the formation of non-volatiles, a post-pyrolytic derivatization technique was developed and optimized. Several non-volatile end products were identified and mechanistically confirmed to involve oxidation and reduction reactions for their formation, such as lactones, hydroxylated benzenes and hydroxylated pyrazine. The latter was identified and confirmed to be generated via the dimerization of glycine and subsequent oxidation. In addition, the formation of different volatiles such as pyrazole, imidazole and oxazole was mechanistically confirmed to depend on redox reactions.

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Thul, Rüdiger. "Analysis of intracellular reaction diffusion systems the stochastic medium Calcium /." [S.l.] : [s.n.], 2004. http://www.diss.fu-berlin.de/2005/97/index.html.

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Gerisch, Alf. "Numerical methods for the simulation of taxis-diffusion-reaction-systems." [S.l. : s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=963208098.

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Dissertations / Theses on the topic 'Reaction systems'

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