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Dissertations / Theses on the topic 'Reaction equations'
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1
Fei, Ning Fei. "Studies in reaction-diffusion equations." Thesis, Heriot-Watt University, 2003. http://hdl.handle.net/10399/310.
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Grant, Koryn. "Symmetries and reaction-diffusion equations." Thesis, University of Kent, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264601.
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Knaub, Karl R. "On the asymptotic behavior of internal layer solutions of advection-diffusion-reaction equations /." Thesis, Connect to this title online; UW restricted, 2001. http://hdl.handle.net/1773/6772.
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Coville, Jerome. "Equations de reaction diffusion non-locale." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2003. http://tel.archives-ouvertes.fr/tel-00004313.
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Cette thèse est consacrée à l'étude des équations de réaction diffusion non-locale du type $u_(t)-(\int_(\R)J(x-y)[u(y)-u(x)]dy)=f(u)$. Ces équations non-linéaires apparaissent naturellement en physique et en biologie. On s'intéresse plus particulièrement aux propriétés (existence, unicité, monotonie) des solutions du type front progressif. Trois classes de non-linéarités $f$ (bistable, ignition, monostable) sont étudiées. L'existence dans les cas bistable et ignition est obtenue via une technique d'homotopie. Le cas monostable nécessite une autre approche. L'existence est obtenue via une approximation des équations sur des semi-intervales infinis $(-r,+\infty)$. L'unicité et la monotonie des solutions sont quand elles obtenues par méthode de glissement. Le comportement asymptotique ainsi que des formules pour les vitesses sont aussi établis.
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Lunney, Michael E. "Numerical dynamics of reaction-diffusion equations." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ61659.pdf.
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Bradshaw-Hajek, Bronwyn. "Reaction-diffusion equations for population genetics." Access electronically, 2004. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20041221.160902/index.html.
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Sun, Xiaodi. "Metastable dynamics of convection-diffusion-reaction equations." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape15/PQDD_0002/NQ34630.pdf.
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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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Freitas, Pedro S. C. de. "Some problems in nonlocal reaction-diffusion equations." Thesis, Heriot-Watt University, 1994. http://hdl.handle.net/10399/1401.
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Yu, Weiming. "Identification of Coefficients in Reaction-Diffusion Equations." University of Cincinnati / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1076186036.
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Al-Ofl, Abdalaziz Saleem. "Analysis of complex nonlinear reaction-diffusion equations." Thesis, Durham University, 2008. http://etheses.dur.ac.uk/2422/.
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A mathematical analysis has been carried out for some nonlinear reaction- diffusion equations on open bounded convex domains Ω C R(^d)(d < 3) with Robin boundary conditions- Existence, uniqueness and continuous dependence on initial data of weak and strong solutions are proved. A numerical analysis has also been undertaken for these nonlinear reaction- diffusion equations on the above domains. A fully practical piecewise linear finite element approximation is proposed for which existence and uniqueness of the numerical solution are proved. Semi-discrete and fully discrete error estimates are given. A practical algorithm for computing the numerical solution is given and its convergence is proved. Finally, some numerical simulations in one-dimensional space are exhibited.
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Hagberg, Aric Arild. "Fronts and patterns in reaction-diffusion equations." Diss., The University of Arizona, 1994. http://hdl.handle.net/10150/186901.
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This is a study of fronts and patterns formed in reaction-diffusion systems. A doubly-diffusive version of the two component FitzHugh-Nagumo equations with bistable reaction dynamics is investigated as an abstract model for the study of pattern phenomenologies found in many different physical systems. Front solutions connecting the two stable uniform states are found to be key building blocks for understanding extended patterns such as stationary domains and traveling pulses in one dimension, and labyrinthine structures, splitting spots, and spiral wave turbulence in two dimensions. The number and type of front solutions is controlled by a bifurcation that we derive both analytically and numerically. At this bifurcation, called the nonequilibrium Ising-Bloch (NIB) bifurcation, a single stationary Ising front loses stability to a pair of counterpropagating Bloch fronts. In two dimensions, we derive a boundary where extended fronts become unstable to transverse perturbations. In addition, near the NIB bifurcation, we discover a multivalued relation between the front speed and general perturbations such as curvature or an external convective field. This multivalued form allows perturbations to induce transitions that reverse the direction of front propagation. When occurring locally along an extended front, these transitions nucleate spiral-vortex pairs. The NIB bifurcation and transverse instability boundaries divide parameter space into regions of different pattern behaviors. Before the bifurcation, the system may form transient patterns or stationary domains consisting of pairs of Ising fronts. Above the transverse instability boundary, two-dimensional planar fronts destabilize, grow, and finger to form a space-filling labyrinthine, or lamellar, pattern. Beyond the bifurcation the multiplicity of Bloch front solutions allows for the formation of persistent traveling pulses and spiral waves. Near the NIB bifurcation there is an intermediate region where new unexpected patterns are found. One-dimensional stationary domains become unstable to oscillating or breathing domains. In two dimensions, the transverse instability and local front transitions are the mechanisms behind spot splitting and the development of spiral wave turbulence. Similar patterns have been observed recently in the ferrocyanide-iodate-sulfite reaction.
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Burke, Meghan A. "Suicide substrates : an analysis of the enzyme reaction and reaction-diffusion equations." Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305420.
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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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Coulon, Anne-Charline. "Propagation in reaction-diffusion equations with fractional diffusion." Doctoral thesis, Universitat Politècnica de Catalunya, 2014. http://hdl.handle.net/10803/277576.
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This thesis focuses on the long time behaviour of solutions to Fisher-KPP reaction-diffusion equations involving fractional diffusion. This type of equation arises, for example, in spatial propagation or spreading of biological species (rats, insects,...). In population dynamics,
the quantity under study stands for the density of the population.
It is well-known that, under some specific assumptions, the solution tends to a stable state of the evolution problem, as time goes to infinity. In other words, the population invades the medium, which corresponds to the survival of the species, and we want to understand at which speed this invasion takes place. To answer this question, we set up a new method to study the speed of propagation when fractional diffusion is at stake and apply it on three different problems.
Part I of the thesis is devoted to an analysis of the asymptotic location of the level sets of the solution to two different problems : Fisher-KPP models in periodic media and cooperative systems, both including fractional diffusion. On the first model, we prove that, under some assumptions on the periodic medium, the solution spreads exponentially fast in time and we find the precise exponent that appears in this exponential speed of propagation. We also carry out numerical simulations to investigate the dependence of the speed of propagation on the initial condition. On the second model, we prove that the speed of propagation is once again exponential in time, with an exponent depending on the smallest index of the fractional Laplacians at stake and on the reaction term.
Part II of the thesis deals with a two dimensional environment, where reproduction of Fisher-KPP type and usual diffusion occur, except on a line of the plane, on which fractional diffusion takes place. The plane is referred to as 'the field' and the line to 'the road', as a reference to the biological situations we have in mind. Indeed, it has long been known that fast diffusion on roads can have a driving effect on the spread of epidemics. We prove that the speed of propagation is exponential in time on the road, whereas it depends linearly on time in the field. Contrary to the precise asymptotics obtained in Part I, for this model, we are not able to give a sharp location of the level sets on the road and in the field. The expansion shape of the level sets in the field is investigated through numerical simulations.<br>Esta tesis se centra en el comportamiento en tiempos grandes de las soluciones de la ecuación de Fisher- KPP de reacción-difusión con difusión fraccionaria. Este tipo de ecuación surge, por ejemplo, en la propagación espacial o en la propagación de especies biológicas (ratas, insectos,...). En la dinámica de poblaciones, la cantidad que se estudia representa la densidad de la población. Es conocido que, bajo algunas hipótesis específicas, la solución tiende a un estado estable del problema de evolución, cuando el tiempo tiende a infinito. En otras palabras, la población invade el medio, lo que corresponde a la supervivencia de la especie, y nosotros queremos entender con qué velocidad se lleva a cabo esta invasión. Para responder a esta pregunta, hemos creado un nuevo método para estudiar la velocidad de propagación cuando se consideran difusiones fraccionarias, además hemos aplicado este método en tres problemas diferentes. La Parte I de la tesis está dedicada al análisis de la ubicación asintótica de los conjuntos de nivel de la solución de dos problemas diferentes: modelos de Fisher- KPP en medios periódicos y sistemas cooperativos, ambos consideran difusión fraccionaria. En el primer modelo, se prueba que, bajo ciertas hipótesis sobre el medio periódico, la solución se propaga exponencialmente rápido en el tiempo, además encontramos el exponente exacto que aparece en esta velocidad de propagación exponencial. También llevamos a cabo simulaciones numéricas para investigar la dependencia de la velocidad de propagación con la condición inicial. En el segundo modelo, se prueba que la velocidad de propagación es nuevamente exponencial en el tiempo, con un exponente que depende del índice más pequeño de los Laplacianos fraccionarios y también del término de reacción. La Parte II de la tesis ocurre en un entorno de dos dimensiones, donde se reproduce un tipo ecuación de Fisher- KPP con difusión estándar, excepto en una línea del plano, en el que la difusión fraccionada aparece. El plano será llamado "campo" y la línea "camino", como una referencia a las situaciones biológicas que tenemos en mente. De hecho, desde hace tiempo se sabe que la difusión rápida en los caminos puede causar un efecto en la propagación de epidemias. Probamos que la velocidad de propagación es exponencial en el tiempo en el camino, mientras que depende linealmente del tiempo en el campo. Contrariamente a los precisos exponentes obtenidos en la Parte I, para este modelo, no fuimos capaces de dar una localización exacta de los conjuntos de nivel en la carretera y en el campo. La forma de propagación de los conjuntos de nivel en el campo se investiga a través de simulaciones numéricas
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Xu, Lu. "Large deviations technique on stochastic reaction-diffusion equations." Thesis, University of Warwick, 2008. http://wrap.warwick.ac.uk/2736/.
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There are two different problems studied in this thesis. The first one is a travelling wave problem. We will improve the result proved in [4] to derive the ergodic property of the travelling wave behind the wavefront. The second problem is a large deviation problem concerning solutions to certain kind stochastic partial differential equations. We will first briefly introduce some basics about SPDE in chapter 2. In chapter 3, we will prove a large deviation principle for super-Brownian motion when it is considered as a solution to an SPDE, using the LDP for super-Brownian motion when it is considered as a measure-valued branching process as solution to a martingale problem. In chapter 4, we will prove another LDP result for solutions of a stochastic reaction-diffusion equation with degenerate noise term. Finally in chapter 5, we will explore some applications of those LDP results proved previously.
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Ding, Weiwei. "Propagation phenomena of integro-difference equations and bistable reaction-diffusion equations in periodic habitats." Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4737.
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Cette thèse concerne les phénomènes de propagation de certaines équations d'évolution dans des habitats périodiques. Dans la première partie, nous étudions les phénomènes d'expansion de certaines équations d'intégro-différence spatialement périodiques. Tout d'abord, nous établissons une théorie générale sur l'existence des vitesses de propagation pour des systèmes d'évolution noncompacts, sous l'hypothèse que les systèmes linéarisés ont des valeurs propres principales. Ensuite, nous introduisons la notion d'irréductibilité uniforme des mesures de Radon finies sur le cercle. On démontre que tout opérateur de convolution généré par une telle mesure admet une valeur propre principale. Enfin, nous prouvons l'existence de vitesses de propagation pour certains équations d'intégro-différence avec des noyaux de dispersion uniformément irréductibles. Dans la deuxième partie, nous étudions les phénomènes de propagation de front pour des équations de réaction-diffusion spatialement périodiques avec des non-linéarités bistables. Nous nous concentrons d'abord sur les solutions de type fronts pulsatoires. Sous diverses hypothèses, il est prouvé que les fronts pulsatoires existent lorsque la période spatiale est petite ou grande. Nous caractérisons aussi le signe des vitesses et nous montrons la stabilité exponentielle globale des fronts pulsatoires de vitesse non nulle. Nous étudions ensuite les solutions de type fronts de transition. Sous des hypothèses convenables, on prouve que les fronts de transition se ramènent aux fronts pulsatoires avec une vitesse non nulle. Mais nous montrons aussi l'existence de nouveaux types de fronts de transition qui ne sont pas des fronts pulsatoires<br>This dissertation is concerned with propagation phenomena of some evolution equations in periodic habitats. The main results consist of the following two parts. In the first part, we investigate the spatial spreading phenomena of some spatially periodic integro-difference equations. Firstly, we establish a general theory on the existence of spreading speeds for noncompact evolution systems, under the hypothesis that the linearized systems have principal eigenvalues. Secondly, we introduce the notion of uniform irreducibility for finite Radon measures on the circle. It is shown that, any generalized convolution operator generated by such a measure admits a principal eigenvalue. Finally, applying the above general theories, we prove the existence of spreading speeds for some integro-difference equations with uniformly irreducible dispersal kernels. In the second part, we study the front propagation phenomena of spatially periodic reaction-diffusion equations with bistable nonlinearities. Firstly, we focus on the propagation solutions in the class of pulsating fronts. It is proved that, under various assumptions on the reaction terms, pulsating fronts exist when the spatial period is small or large. We also characterize the sign of the front speeds and we show the global exponential stability of the pulsating fronts with nonzero speed. Secondly, we investigate the propagation solutions in the larger class of transition fronts. It is shown that, under suitable assumptions, transition fronts are reduced to pulsating fronts with nonzero speed. But we also prove the existence of new types of transition fronts which are not pulsating fronts
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Qu, Lei, and 瞿磊. "Multiplicity and stability of two-dimensional reaction-diffusion equations." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2001. http://hub.hku.hk/bib/B31226656.
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Meral, Gulnihal. "Numerical Solution Of Nonlinear Reaction-diffusion And Wave Equations." Phd thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/3/12610568/index.pdf.
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In this thesis, the two-dimensional initial and boundary value problems (IBVPs)
and the one-dimensional Cauchy problems defined by the nonlinear reaction-
diffusion and wave equations are numerically solved. The dual reciprocity boundary
element method (DRBEM) is used to discretize the IBVPs defined by single
and system of nonlinear reaction-diffusion equations and nonlinear wave equation,
spatially. The advantage of DRBEM for the exterior regions is made use
of for the latter problem. The differential quadrature method (DQM) is used
for the spatial discretization of IBVPs and Cauchy problems defined by the
nonlinear reaction-diffusion and wave equations.
The DRBEM and DQM applications result in first and second order system
of ordinary differential equations in time. These systems are solved with three
different time integration methods, the finite difference method (FDM), the least
squares method (LSM) and the finite element method (FEM) and comparisons
among the methods are made. In the FDM a relaxation parameter is used to
smooth the solution between the consecutive time levels.
It is found that DRBEM+FEM procedure gives better accuracy for the IBVPs
defined by nonlinear reaction-diffusion equation. The DRBEM+LSM procedure
with exponential and rational radial basis functions is found suitable for exterior wave problem.
The same result is also valid when DQM is used for space
discretization instead of DRBEM for Cauchy and IBVPs defined by nonlinear
reaction-diffusion and wave equations.
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Ryan, John Maurice-Car. "Global existence of reaction-diffusion equations over multiple domains." Texas A&M University, 2004. http://hdl.handle.net/1969.1/3312.
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Systems of semilinear parabolic differential equations arise in the modelling of many chemical and biological systems. We consider m component systems of the form
ut = DΔu + f (t, x, u)
∂uk/∂η =0 k =1, ...m
where u(t, x)=(uk(t, x))mk=1 is an unknown vector valued function and each u0k is zero outside Ωσ(k), D = diag(dk)is an m à m positive definite diagonal matrix,
f : R à Rnà Rm → Rm, u0 is a componentwise nonnegative function, and each Ωi is a bounded domain in Rn where ∂Ωi is a C2+αmanifold such that Ωi lies locally on one side of ∂Ωi and has unit outward normal η. Most physical processes give rise to systems for which f =(fk) is locally Lipschitz in u uniformly for (x, t) ∈ Ω Ã [0,T ] and f (·, ·, ·) ∈ L∞(Ω Ã [0,T ) à U ) for bounded U and the initial data u0 is continuous and nonnegative on Ω.
The primary results of this dissertation are three-fold. The work began with a proof of the well posedness for the system . Then we obtained a global existence result if f is polynomially bounded, quaipositive and satisfies a linearly intermediate sums condition. Finally, we show that systems of reaction-diffusion equations with large diffusion coeffcients exist globally with relatively weak assumptions on the vector field f.
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Wang, Shuyu. "Reaction-diffusion equations and the Laplacian in Hilbert space." Thesis, University of Ottawa (Canada), 1990. http://hdl.handle.net/10393/5772.
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This dissertation consists of two parts. First, we study some problems associated with reaction-diffusion equations with variables in finite-dimensional space. We investigate the positivity of solutions, the existence of positive invariant regions, and we also make some stability analysis. In part II, we study the Levy-Laplacian in infinite-dimensional space. We explore some properties of this Laplacian and solve some boundary value problems.
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Baugh, James Emory. "Group analysis of a system of reaction-diffusion equations." Thesis, Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/28554.
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Fullwood, Timothy Brent. "Pattern formation and travelling waves in reaction-diffusion equations." Thesis, University of Warwick, 1995. http://wrap.warwick.ac.uk/4251/.
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This thesis is about pattern formation in reaction - diffusion equations, particularly Turing patterns and travelling waves. In chapter one we concentrate on Turing patterns. We give the classical approach to proving the existence of these patterns, and then our own, which uses the reversibility of the associated travelling wave equations when the wave speed is zero. We use a Lyapunov - Schmidt reduction to prove the existence of periodic solutions when there is a purely imaginary eigenvalue. We pay particular attention to the bifurcation point where these patterns arise, the 1: 1 resonance. We prove the existence of steady patterns near a Hopf bifurcation and then include a similar result for dynamics close to a Takens - Bogdanov point. Chapter two concentrates on travelling waves and looks for the existence of such in three different ways. Firstly we prove the conditions that are needed for the travelling wave equations to go through a Hopf bifurcation. Secondly, we look for the existence of travelling waves as the wave speed is perturbed from zero and prove when this occurs, again, using a Lyapunov - Schmidt reduction. Thirdly we describe a result proving the existence of periodic travelling waves when the wave speed is perturbed from infinity. In the last part of chapter two we prove the stability of such waves for A-w systems. In chapter three we discuss computer simulations of the work done in the earlier chapters. We present the mappings used and prove that their behaviour is similar to the original partial differential equations. The two specific examples we give are a predator prey model and the complex Ginzburg - Landau equations.
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Kay, Alison Lindsey. "Travelling fronts and wave-trains in reaction-diffusion equations." Thesis, University of Warwick, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342513.
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Coulon, Chalmin Anne-Charline. "Fast propagation in reaction-diffusion equations with fractional diffusion." Toulouse 3, 2014. http://thesesups.ups-tlse.fr/2427/.
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Cette thèse est consacrée à l'étude du comportement en temps long, et plus précisément de phénomènes de propagation rapide, des équations de réaction-diffusion de type Kisher-KPP avec diffusion fractionnaire. Ces équations modélisent, par exemple, la propagation d'espèces biologiques. Sous certaines hypothèses, la population envahit le milieu et nous voulons comprendre à quelle vitesse cette invasion a lieu. Pour répondre à cette question, nous avons mis en place une nouvelle méthode et nous l'appliquons à différents modèles. Dans une première partie, nous étudions deux problèmes d'évolution comprenant une diffusion fractionnaire : un modèle de type Fisher-KPP en milieu périodique et un système coopératif. Dans les deux cas, nous montrons, sous certaines conditions, que la vitesse de propagation est exponentielle en temps, et nous donnons une expression précise de l'exposant de propagation. Nous menons des simulations numériques pour étudier la dépendance de cette vitesse de propagation en la donnée initiale. Dans une seconde partie, nous traitons un environnement bidimensionnel, dans lequel le terme de reproduction est de type Fisher-KPP et le terme diffusif est donné par un laplacien standard, excepté sur une ligne du plan où une diffusion fractionnaire intervient. Le plan est nommé "le champ" et la ligne "la route", en référence aux situations biologiques que nous voulons modéliser. Nous prouvons que la vitesse de propagation est exponentielle en temps sur la route, alors qu'elle dépend linéairement du temps dans le champ. La forme des lignes de niveau dans le champ est étudiée au travers de simulations numériques<br>This thesis focuses on the long time behaviour, and more precisely on fast propagation, in Fisher-KPP reaction diffusion equations involving fractional diffusion. This type of equation arises, for example, in spreading of biological species. Under some specific assumptions, the population invades the medium and we want to understand at which speed this invasion takes place when fractional diffusion is at stake. To answer this question, we set up a new method and apply it on different models. In a first part, we study two different problems, both including fractional diffusion : Fisher-KPP models in periodic media and cooperative systems. In both cases, we prove, under additional assumptions, that the solution spreads exponentially fast in time and we find the precise exponent of propagation. We also carry out numerical simulations to investigate the dependence of the speed of propagation on the initial condition. In a second part, we deal with a two dimensional environment, where reproduction of Fisher-KPP type and usual diffusion occur, except on a line of the plane, on which fractional diffusion takes place. The plane is referred to as "the field" and the line to "the road", as a reference to the biological situations we have in mind. We prove that the speed of propagation is exponential in time on the road, whereas it depends linearly on time in the field. The expansion shape of the level sets in the field is investigated through numerical simulations
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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<sub>c</sub> , 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<sub>c</sub>. 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<sub>c</sub>. 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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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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Dunne, Peter C. "Properties of solutions to some systems of reaction-diffusion equations." Thesis, Heriot-Watt University, 1985. http://hdl.handle.net/10399/1657.
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Craciun, Gheorghe. "Systems of nonlinear equations deriving from complex chemical reaction networks /." The Ohio State University, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=osu1486463321624709.
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Montecinos, Gino Ignacio. "Numerical methods for advection-diffusion-reaction equations and medical applications." Doctoral thesis, Università degli studi di Trento, 2014. https://hdl.handle.net/11572/368529.
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The purpose of this thesis is twofold, firstly, the study of a relaxation procedure for numerically solving advection-diffusion-reaction equations, and secondly, a medical application. Concerning the first topic, we extend the applicability of the Cattaneo relaxation approach to reformulate time-dependent advection-diffusion-reaction equations, that may include stiff reactive terms, as hyperbolic balance laws with stiff source terms. The resulting systems of hyperbolic balance laws are solved by extending the applicability of existing high-order ADER schemes, including well-balanced and non-conservative schemes. Moreover, we also present a new locally implicit version of the ADER method to solve general hyperbolic balance laws with stiff source terms. The relaxation procedure depends on the choice of a relaxation parameter $\epsilon$. Here we propose a criterion for selecting $\epsilon$ in an optimal manner, relating the order of accuracy $r$ of the numerical scheme used, the mesh size $\Delta x$ and the chosen $\epsilon$. This results in considerably more efficient schemes than some methods with the parabolic restriction reported in the current literature. The resulting present methodology is validated by applying it to a blood flow model for a network of viscoelastic vessels, for which experimental and numerical results are available. Convergence-rates assessment for some selected second-order model equations, is carried out, which also validates the applicability of the criterion to choose the relaxation parameter. The second topic of this thesis concerns the numerical study of the haemodynamics impact of stenoses in the internal jugular veins. This is motivated by the recent discovery of a range of extra cranial venous anomalies, termed Chronic CerbroSpinal Venous Insufficiency (CCSVI) syndrome, and its potential link to neurodegenerative diseases, such as Multiple Sclerosis. The study considers patient specific anatomical configurations obtained from MRI data. Computational results are compared with measured data.
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Montecinos, Gino Ignacio. "Numerical methods for advection-diffusion-reaction equations and medical applications." Doctoral thesis, University of Trento, 2014. http://eprints-phd.biblio.unitn.it/1200/1/PhDthesisMontecinos.pdf.
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The purpose of this thesis is twofold, firstly, the study of a relaxation procedure for numerically solving advection-diffusion-reaction equations, and secondly, a medical application. Concerning the first topic, we extend the applicability of the Cattaneo relaxation approach to reformulate time-dependent advection-diffusion-reaction equations, that may include stiff reactive terms, as hyperbolic balance laws with stiff source terms. The resulting systems of hyperbolic balance laws are solved by extending the applicability of existing high-order ADER schemes, including well-balanced and non-conservative schemes. Moreover, we also present a new locally implicit version of the ADER method to solve general hyperbolic balance laws with stiff source terms. The relaxation procedure depends on the choice of a relaxation parameter $\epsilon$. Here we propose a criterion for selecting $\epsilon$ in an optimal manner, relating the order of accuracy $r$ of the numerical scheme used, the mesh size $\Delta x$ and the chosen $\epsilon$. This results in considerably more efficient schemes than some methods with the parabolic restriction reported in the current literature. The resulting present methodology is validated by applying it to a blood flow model for a network of viscoelastic vessels, for which experimental and numerical results are available. Convergence-rates assessment for some selected second-order model equations, is carried out, which also validates the applicability of the criterion to choose the relaxation parameter. The second topic of this thesis concerns the numerical study of the haemodynamics impact of stenoses in the internal jugular veins. This is motivated by the recent discovery of a range of extra cranial venous anomalies, termed Chronic CerbroSpinal Venous Insufficiency (CCSVI) syndrome, and its potential link to neurodegenerative diseases, such as Multiple Sclerosis. The study considers patient specific anatomical configurations obtained from MRI data. Computational results are compared with measured data.
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De, Zan Cecilia. "Some new results on reaction-diffusion equations and geometric flows." Doctoral thesis, Università degli studi di Padova, 2012. http://hdl.handle.net/11577/3422529.
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In this thesis we discuss the asymptotic behavior of the solutions of scaled reaction-diffusion equations in the unbounded domain Rn × (0 + ∞), in the cases when such a behavior is described in terms of moving interfaces.
As first class of asymptotic problems we consider the singular limit of bistable reaction-diffusion equations in the case when the velocity of the traveling wave equation depends on the space variable, i.e. cε = cε(x), and it satisfies, in some suitable sense, cε/ετ → α, as ε → 0+, where α is a discontinuous function and τ is an integer that can be equal to 0 or 1. The second part of the thesis concerns semilinear reaction-diffusion equations with diffusion term of type tr(Aε(x)D2uε), where tr denotes the trace operator, Aε = σεσtε for some matrix map σε : Rn → Rn×(m+n) and Aε converges to a degenerate matrix.
In order to establish such results rigorously, we modify and adapt to our problems the ”geometric approach” introduced by G. Barles and P. E. Souganidis for solving problems in Rn, and then partially revisited by G. Barles and F. Da Lio for reaction-diffusion equations in bounded domains. When it is possible we always consider the question of the well posedness of the Cauchy problems governing the motion of the fronts that describe the asymptotics we consider<br>In questa tesi discutiamo il comportamento asintotico delle soluzioni di equazioni di reazione-diffusione nel dominio illimitato Rn × (0,+∞) nei casi in cui tale comportamento sia descritto da un’interfaccia in movimento. Come primo tipo di problemi asintotici consideriamo il limite singolare di equazioni di reazione-diffusione bistabili nel caso in cui la velocità dell’onda viaggiante dipenda dalla variabile di stato, cioè cε = cε(x), e sia soddisfatto, al tendere di ε a zero e in qualche modo opportuno, cε/ετ → α, laddove α è una funzione discontinua e τ è un intero che può essere uguale a 0 o a 1.
La seconda parte della tesi riguarda equazioni di reazione-diffusione semilineari e aventi termini di diffusione del tipo tr(Aε(x)D2uε), laddove tr denota l’operatore traccia, Aε = σεσtε per qualche funzione σε : Rn → Rn×(m+n) e Aε converge ad una matrice degenere.
Al fine di provare tali risultati in modo rigoroso, abbiamo modificato e adattato "l’approccio geometrico" introdotto da G. Barles e P. E. Souganidis per risolvere problemi in Rn e in seguito parzialmente rivisto dallo stesso G. Barles assieme a F. Da Lio per equazioni di reazione-diffusione in domini limitati. Laddove possibile abbiamo sempre considerato la questione della buona posizione dei problemi di Cauchy che governano il moto dei fronti che descrivono le asintotiche da
noi considerate
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Lei, Peng. "The Cauchy problem for the Diffusive-Vlasov-Enskog equations." Diss., This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-05042006-164524/.
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Garvie, Marcus Roland. "Analysis of a reaction-diffusion system of λ-w type". Thesis, Durham University, 2003. http://etheses.dur.ac.uk/4105/.
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The author studies two coupled reaction-diffusion equations of 'λ-w' type, on an open, bounded, convex domain Ω C R(^d) (d ≤ 3), with a boundary of class C², and homogeneous Neumann boundary conditions. The equations are close to a supercritical Hopf bifurcation in the reaction kinetics, and are model equations for oscillatory reaction-diffusion equations. Global existence, uniqueness and continuous dependence on initial data of strong and weak solutions are proved using the classical Faedo-Galerkin method of Lions and compactness arguments. The work provides a complete case study for the application of this method to systems of nonlinear reaction-diffusion equations. The author also undertook the numerical analysis of the reaction-diffusion system. Results are presented for a fully-practical piecewise linear finite element method by mimicking results in the continuous case. Semi-discrete and fully-discrete error estimates are proved after establishing a priori bounds for various norms of the approximate solutions. Finally, the theoretical results are illustrated and verified via the numerical simulation of periodic plane waves in one space dimension, and preliminary results representing target patterns and spiral solutions presented in two space dimensions.
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Yang, Yuanjie. "Reaction-diffusion equations with time delay, theory, application, and numerical simulation." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq23095.pdf.
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SaÌnchez, Garduño Faustino. "Travelling waves in one-dimensional degenerate non-linear reaction-diffussion equations." Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334929.
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Mulholland, Anthony J. "The Eikonal approach to reaction-diffusion equations in multiply-connected domains." Thesis, Glasgow Caledonian University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359146.
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Allen, Nicholas Alexander. "Computational Software for Building Biochemical Reaction Network Models with Differential Equations." Diss., Virginia Tech, 2003. http://hdl.handle.net/10919/30059.
Full textAbstract:
The cell is a highly ordered and intricate machine within which a wide variety of chemical processes take place. The full scientific understanding of cellular physiology requires accurate mathematical models that depict the temporal dynamics of these chemical processes. Modelers build mathematical models of chemical processes primarily from systems of differential equations. Although developing new biological ideas is more of an art than a science, constructing a mathematical model from a biological idea is largely mechanical and automatable.
This dissertation describes the practices and processes that biological modelers use for modeling and simulation. Computational biologists struggle with existing tools for creating models of complex eukaryotic cells. This dissertation develops new processes for biological modeling that make model creation, verification, validation, and testing less of a struggle. This dissertation introduces computational software that automates parts of the biological modeling process, including model building, transformation, execution, analysis, and evaluation. User and methodological requirements heavily affect the suitability of software for biological modeling. This dissertation examines the modeling software in terms of these requirements.
Intelligent, automated model evaluation shows a tremendous potential to enable the rapid, repeatable, and cost-effective development of accurate models. This dissertation presents a case study that indicates that automated model evaluation can reduce the evaluation time for a budding yeast model from several hours to a few seconds, representing a more than 1000-fold improvement. Although constructing an automated model evaluation procedure requires considerable domain expertise and skill in modeling and simulation, applying an existing automated model evaluation procedure does not. With this automated model evaluation procedure, the computer can then search for and potentially discover models superior to those that the biological modelers developed previously.<br>Ph. D.
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Allen, Nicholas A. "Computational Software for Building Biochemical Reaction Network Models with Differential Equations." Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/30059.
Full textAbstract:
The cell is a highly ordered and intricate machine within which a wide variety of chemical processes take place. The full scientific understanding of cellular physiology requires accurate mathematical models that depict the temporal dynamics of these chemical processes. Modelers build mathematical models of chemical processes primarily from systems of differential equations. Although developing new biological ideas is more of an art than a science, constructing a mathematical model from a biological idea is largely mechanical and automatable.
This dissertation describes the practices and processes that biological modelers use for modeling and simulation. Computational biologists struggle with existing tools for creating models of complex eukaryotic cells. This dissertation develops new processes for biological modeling that make model creation, verification, validation, and testing less of a struggle. This dissertation introduces computational software that automates parts of the biological modeling process, including model building, transformation, execution, analysis, and evaluation. User and methodological requirements heavily affect the suitability of software for biological modeling. This dissertation examines the modeling software in terms of these requirements.
Intelligent, automated model evaluation shows a tremendous potential to enable the rapid, repeatable, and cost-effective development of accurate models. This dissertation presents a case study that indicates that automated model evaluation can reduce the evaluation time for a budding yeast model from several hours to a few seconds, representing a more than 1000-fold improvement. Although constructing an automated model evaluation procedure requires considerable domain expertise and skill in modeling and simulation, applying an existing automated model evaluation procedure does not. With this automated model evaluation procedure, the computer can then search for and potentially discover models superior to those that the biological modelers developed previously.<br>Ph. D.
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Rodrigues, Maria Manuela Fernandes. "Exact and numerical solutions for diffusio-reaction equations with convection term." Doctoral thesis, Universidade de Aveiro, 2009. http://hdl.handle.net/10773/2944.
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Doutoramento em Matemática<br>Esta dissertação estuda essencialmente dois problemas: (A) uma classe de equações unidimensionais de reacção-difusão-convecção em meios não uniformes (dependentes do espaço), e (B) um problema elíptico não-linear e paramétrico ligado a fenómenos de capilaridade.
A Análise de Perturbação Singular e a dinâmica de Hamilton-Jacobi são utilizadas na obtenção de expressões assimptóticas para a solução (com
comportamento de frente) e para a sua velocidade de propagação. Os seguintes três métodos de decomposição, Adomian Decomposition Method
(ADM), Decomposition Method based on Infinite Products (DIP), e New Iterative Method (NIM), são apresentados e brevemente comparados.
Adicionalmente, condições suficientes para a convergência da solução em série, obtida pelo ADM, e uma aplicação a um problema da Telecomunicações por Fibras Ópticas, envolvendo EDOs não-lineares designadas equações de
Raman, são discutidas. Um ponto de vista mais abrangente que unifica os métodos de decomposição referidos é também apresentado. Para subclasses desta EDP são obtidas soluções numa forma explícita, para diferentes tipos de
dados e usando uma variante do método de simetrias de Bluman-Cole.
Usando Teoria de Pontos Críticos (o teorema usualmente designado mountain pass) e técnicas de truncatura, prova-se a existência de duas soluções não triviais (uma positiva e uma negativa) para o problema elíptico não-linear e paramétrico (B). A existência de uma terceira solução não trivial é demonstrada usando Grupos Críticos e Teoria de Morse.<br>This thesis studies mainly two problems: (A) a one-dimensional reactiondiffusion- convection equation in a nonuniform media (i.e. with space dependent coefficients), and (B) a nonlinear parametric elliptic problem related with capillary phenomena.
Regarding problem (A), Singular Perturbation Analysis and Hamilton-Jacobi dynamics are used to compute asymptotic expressions for a solution (behaving as a travelling wave) and for its wavefront speed. The three decomposition methods, Adomian Decomposition Method (ADM), Decomposition Method based on Infinite Products (DIP) and New Iterative Method (NIM), are
presented and briefly compared for this class of PDEs. Additionally, sufficient conditions for the convergence of the ADM series solution and an application to Fiber Optics Communication, involving the nonlinear ODEs known as Raman
equations, are given. A general point of view, generalizing the aforementioned decomposition methods, is discussed. The same class of PDEs are studied, from the Lie symmetry point of view, by considering a variant of Bluman-Cole method obtaining explicit solutions for subclasses of such differential equations under several types of data.
Using Critical Point Theory (mountain pass theorem) and truncation techniques, the existence of two nontrivial solutions (one positive and one negative) are proved for the nonlinear parametric elliptic problem (B). A nontrivial third solution is also proven by using Critical Groups and Morse Theory.
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Vo, Hoang Hung. "Reaction-diffusion equations and dynamics of population facing a climate change." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066219/document.
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Cette thèse traite de différents modèles issus de l'étude de la dynamique des populations devant faire face à un changement climatique. Notre but est d’atteindre deux objectifs ; le premier est d'étendre les travaux initiaux de Berestycki, Diekmann, Nagelkerke, Zegeling [5], ainsi que leurs développements ultérieurs (Berestycki et Rossi [18, 19]) ; le second est de dévoiler les aspects mathématiques profonds de ce modèle, en considérant de nouveaux problèmes, faisant intervenir une diffusion non-locale et non-linéaire. Le Chapitre 1 traite du cas d’un domaine cylindrique infini, dans l'espace entier, lorsque le terme de réaction est indépendant (resp. périodiquement dépendant) du temps. La nouveauté de ce travail est d’exprimer une condition globale dans le cadre de la théorie spectrale, afin de pouvoir supposer que l'environnement de la population est globalement défavorable à l'infini (au lieu de ponctuellement défavorable au voisinage de l'infini) comme dans [5, 18, 19]. Nous poursuivons l’étude de la concentration des espèces dans le domaine cylindrique lorsque le domaine extérieur est rendu extrêmement défavorable. Dans le Chapitre 2, nous nous concentrons sur les hypothèses permettant d’établir l'existence (vs l'inexistence) et l'unicité de la solution positive de l'équation elliptique semi-linéaire complète. Lorsque la divergence du terme de dérive est nulle, l'existence d'une solution positive peut être caractérisée à partir de l'amplitude du terme de dérive (sous des hypothèses adéquates de vitesse d’accroissement). L’étude du comportement pour des temps longs de l'équation parabolique nous amène à traiter le cas de coefficients éventuellement non bornés. Le Chapitre 3 étend les critères d'existence, d'inexistence et d'unicité explicités dans le deuxième chapitre aux équations quasi-linéaires impliquant un opérateur p-Laplacien. La principale difficulté rencontrée est que le principe du maximum fort semble difficile à appliquer ; nous devons alors utiliser une approche variationnelle pour obtenir un important principe de comparaison. Dans le Chapitre 4, nous étudions trois notions de valeurs propres principales généralisées pour les opérateurs non locaux sur des domaines bornés et non bornés (éventuellement ). Si le noyau est à support compact, nous pouvons également démontrer l'équivalence de ces valeurs propres sur domaine non borné. Nous étudions les limites des valeurs propres de l'opérateur de mise à l'échelle induit par la diffusion. Les résultats sont très dépendants du taux de mise à l'échelle. Dans le Chapitre 5, à la lumière des résultats obtenus dans le Chapitre 4, nous considérons l'équation d'évolution non locale et démontrons que la solution de l'équation d'évolution converge vers l’unique solution stationnaire, dont l'existence est directement conditionnée par le signe de la valeur propre principale généralisée. Cette convergence a lieu dans L1 (RN) et Lp (RN), p> 0. Dans la deuxième partie de ce chapitre, nous examinons les limites singulières de l'unique solution positive des équations de remise à l’échelle. Nous montrons que l'unique solution de l'équation non locale approche – soit l'unique solution de l'équation locale de type KPP, soit une solution (qui peut ne pas être unique) de l’équation de réaction<br>The thesis is concerned with various models arising from the study of the dynamics of the population facing a climate change. We aim at achieving two following goals: The first one is to extend original work of Berestycki, Diekmann, Nagelkerke, Zegeling [5] and later developments of Berestycki and Rossi [18,19] the second one is to investigate the deeper mathematical aspects of this model and deal with the new problems where nonlocal and nonlinear diffusion are considered. The Chapter 1 deals with the problem in an infinite cylindrical domain and in the whole space where the reaction term is (resp.) independent or periodically dependent on time. The novelty of this work is that we consider a global condition in term of the spectral theory to assume that the environment of the population is globally unfavorable at infinity instead of pointwise unfavorable near infinity as in [5,18,19]. We further study the concentration of the species in the cylindrical domain when the exterior domain is changed to be extremely unfavorable. In the Chapter 2, we focus on conditioning the a sharp criterion for the existence, nonexistence and uniqueness of positive solution of fully semilinear elliptic equation. When the divergence of the drift term is zero, the existence of positive solution can be characterized by the amplitude of the drift term under some fair assumptions on the growth rate. The large time behavior of associated parabolic equation is considered, where we have to deal with the case of possibly unbounded coefficients. The Chapter 3 extends the existence, nonexistence and uniqueness in the second chapter for a quasilinear equation involving p-laplacian operator. The main difficulty is that it seems hard to apply the strong maximum principle and thus we make use a variational approach to attain an important comparison principle. In Chapter 4, we investigate three notion of generalized principal eigenvalues for nonlocal operators in bounded and unbounded domains (eventually $\R^N$). If the kernel is compactly supported, we can also prove the equivalence of these eigenvalues in unbounded domain. We consider the limits of the eigenvalues of the rescaling operator with respect to the diffusion. The results are very different depending on the rate of rescaling. In Chapter 5, by the help of the results in Chapter 4, we consider the nonlocal evolution equation and prove that the solution of evolution equation converges to the unique stationary solution, whose existence is directly conditioned by the sign of the generalized principal eigenvalue. The convergences holds in $L^\infty(\R^N)$ and $L^p(\R^N)$, $p>0$. In the second part of this chapter, we further investigate the singular limits of the unique positive solution of the rescaling equations. We show that the unique solution of nonlocal equation either approximates the unique solution of local KPP type equation or approximates a solution of reaction-equation, which may not be unique
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Duncan, Kirsteen. "Pseudo-spectral and path-following techniques with applications to problems in biology and the gasification of coal." Thesis, Heriot-Watt University, 1988. http://hdl.handle.net/10399/962.
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Mahmoud, Mostafa Maher Sayed. "Predator-prey, competition and co-operation systems with mixed boundary conditions." Thesis, Heriot-Watt University, 1989. http://hdl.handle.net/10399/944.
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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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Lee, Isobel Micheline. "The existance of multiple steady-state solutions of a reaction-diffusion equation." Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329934.
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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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Gurevich, Svetlana V. "Lateral self-organization in nonlinear transport systems described by reaction diffusion equations." [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=983706921.
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Zou, Xingfu. "Traveling wave solutions of delayed reaction-diffusion systems and lattice differential equations." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq22936.pdf.
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Choi, Chi-Ho Francis. "Numerical methods for solving some non-linear reaction-diffusion equations in chemistry." Thesis, Brunel University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341555.
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McGowan, Robert. "Eikonal analysis of excitable reaction-diffusion equations in anisotropic and inhomogeneous media." Thesis, Glasgow Caledonian University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309345.
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