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Pudipeddi, Sridevi Iaia Joseph A. "Localized radial solutions for nonlinear p-laplacian equation in R[superscript N]." [Denton, Tex.] : University of North Texas, 2008. http://digital.library.unt.edu/permalink/meta-dc-6059.
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Adhikari, Dhruba R. "Applications of degree theories to nonlinear operator equations in Banach spaces." [Tampa, Fla.] : University of South Florida, 2007. http://purl.fcla.edu/usf/dc/et/SFE0002158.
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Pudipeddi, Sridevi. "Localized Radial Solutions for Nonlinear p-Laplacian Equation in RN." Thesis, University of North Texas, 2008. https://digital.library.unt.edu/ark:/67531/metadc6059/.
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We establish the existence of radial solutions to the p-Laplacian equation ∆p u + f(u)=0 in RN, where f behaves like |u|q-1 u when u is large and f(u) < 0 for small positive u. We show that for each nonnegative integer n, there is a localized solution u which has exactly n zeros. Also, we look for radial solutions of a superlinear Dirichlet problem in a ball. We show that for each nonnegative integer n, there is a solution u which has exactly n zeros. Here we give an alternate proof to that which was given by Castro and Kurepa.
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Abdeljabbar, Alrazi. "Wronskian, Grammian and Pfaffian Solutions to Nonlinear Partial Differential Equations." Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/3939.
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It is significantly important to search for exact soliton solutions to nonlinear partial differential equations (PDEs) of mathematical physics. Transforming nonlinear PDEs into bilinear forms using the Hirota differential operators enables us to apply the Wronskian and Pfaffian techniques to search for exact solutions for a (3+1)-dimensional generalized Kadomtsev-Petviashvili (KP) equation with not only constant coefficients but also variable coefficients under a certain constraint
(ut + α 1(t)uxxy + 3α 2(t)uxuy)x +α 3 (t)uty -α 4(t)uzz + α 5(t)(ux + α 3(t)uy) = 0.
However, bilinear equations are the nearest neighbors to linear equations, and expected to have some properties similar to those of linear equations. We have explored a key feature of the linear superposition principle, which linear differential equations have, for Hirota bilinear equations, while intending to construct a particular sub-class of N-soliton solutions formed by linear combinations
of exponential traveling waves. Applications are given for the (3+1) dimensional KP, Jimbo-Miwa (JM) and BKP equations, thereby presenting their particular N-wave solutions. An opposite question
is also raised and discussed about generating Hirota bilinear equations possessing the indicated N-wave solutions, and two illustrative examples are presented.
Using the Pfaffianization procedure, we have extended the generalized KP equation to a generalized KP system of nonlinear PDEs. Wronskian-type Pfaffian and Gramm-type Pfaffian solutions of the resulting Pfaffianized system have been presented. Our results and computations basically depend on Pfaffian identities given by Hirota and Ohta. The Pl̈ucker relation and the Jaccobi identity for determinants have also been employed.
A (3+1)-dimensional JM equation has been considered as another important example in soliton theory,
uyt - uxxxy - 3(uxuy)x + 3uxz = 0.
Three kinds of exact soliton solutions have been given: Wronskian, Grammian and Pfaffian solutions. The Pfaffianization procedure has been used to extend this equation as well.
Within Wronskian and Pfaffian formulations, soliton solutions and rational solutions are usually expressed as some kind of logarithmic derivatives of Wronskian and Pfaffian type determinants and the determinants involved are made of functions satisfying linear systems of differential equations. This connection between nonlinear problems and linear ones utilizes linear theories in solving soliton equations.
B̈acklund transformations are another powerful approach to exact solutions of nonlinear equations. We have computed different classes of solutions for a (3+1)-dimensional generalized KP equation based on a bilinear B̈acklund transformation consisting of six bilinear equations and containing nine free parameters.
A variable coefficient Boussinesq (vcB) model in the long gravity water waves is one of the
examples that we are investigating,
ut + α 1 (t)uxy + α 2(t)(uw)x + α 3(t)vx = 0;
vt + β1(t)(wvx + 2vuy + uvy) + β2(t)(uxwy - (uy)2) + β3(t)vxy + β4(t)uxyy = 0,
where wx = uy. Double Wronskian type solutions have been constructed for this (2+1)-dimensional vcB model.
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Ali, Jaffar. "Multiple positive solutions for classes of elliptic systems with combined nonlinear effects." Diss., Mississippi State : Mississippi State University, 2008. http://library.msstate.edu/etd/show.asp?etd=etd-07082008-153843.
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Asaad, Magdy. "Pfaffian and Wronskian solutions to generalized integrable nonlinear partial differential equations." Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/3956.
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The aim of this work is to use the Pfaffian technique, along with the Hirota bilinear method to construct different classes of exact solutions to various of generalized integrable nonlinear partial differential equations. Solitons are among the most beneficial solutions for science and technology, from ocean waves to transmission of information through optical fibers or energy transport along protein molecules. The existence of multi-solitons, especially three-soliton solutions, is essential for information technology: it makes possible undisturbed simultaneous propagation of many pulses in both directions.
The derivation and solutions of integrable nonlinear partial differential equations in two spatial dimensions have been the holy grail in the field of nonlinear science since the late 1960s. The prestigious Korteweg-de Vries (KdV) and nonlinear Schrödinger (NLS) equations, as well as the ,Kadomtsev-Petviashvili (KP) and Davey-Stewartson (DS) equations, are prototypical examples of integrable nonlinear partial differential equations in (1+1) and (2+1) dimensions, respectively. Do there exist Pfaffian and soliton solutions to generalized integrable nonlinear partial differential equations in (3+1) dimensions? In this dissertation, I obtained a set of explicit exact Wronskian, Grammian, Pfaffian and N-soliton solutions to the (3+1)-dimensional generalized integrable nonlinear partial differential equations, including a generalized KP equation, a generalized B-type KP equation, a generalized modified B-type KP equation, soliton equations of Jimbo-Miwa type, the nonlinear Ma-Fan equation, and the Jimbo-Miwa equation. A set of sufficient conditions consisting of systems of linear partial differential equations involving free parameters and continuous functions is generated to guarantee that the Wronskian determinant or the Pfaffian solves these generalized equations.
On the other hand, as part of this dissertation, bilinear Bäcklund transformations are formally derived for the (3+1)-dimensional generalized integrable nonlinear partial differential equations: a generalized B-type KP equation, the nonlinear Ma-Fan equation, and the Jimbo-Miwa equation. As an application of the obtained Bäcklund transformations, a few classes of traveling wave solutions, rational solutions and Pfaffian solutions to the corresponding equations are explicitly computed.
Also, as part of this dissertation, I would like to apply the Pfaffianization mechanism of Hirota and Ohta to extend the (3+1)-dimensional variable-coefficient soliton equation of Jimbo-Miwa type to coupled systems of nonlinear soliton equations, called Pfaffianized systems.
Examples of the Wronskian, Grammian, Pfaffian and soliton solutions are explicitly computed. The numerical simulations of the obtained solutions are illustrated and plotted for different parameters involved in the solutions.
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López, Ríos Luis Fernando. "Two problems in nonlinear PDEs : existence in supercritical elliptic equations and symmetry for a hypo-elliptic operator." Tesis, Universidad de Chile, 2014. http://www.repositorio.uchile.cl/handle/2250/115530.
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Doctor en Ciencias de la Ingeniería, Mención Modelación MatemáticaEn este trabajo se aborda el problema de encontrar soluciones regulares para algunas EDPs elípticas e hipo-elípticas no lineales y estudiar sus propiedades cualitativas. En una primera etapa, se considera la ecuación $$ -\Delta u = \lambda e^u, $$ $\lambda > 0$, en un dominio exterior con condición de Dirichlet nula. Un esquema de reducción finito-dimensional permite encontrar infinitas soluciones regulares cuando $\lambda$ es suficientemente pequeño. En la segunda parte se estudia la existencia de soluciones de la ecuación no local $$ (-\Delta)^s u = u^{p \pm \epsilon}, u > 0, $$ en un dominio acotado y suave, con condición de Dirichlet nula; donde $s > 0$ y $p:=(N+2s)/(N-2s) \pm \epsilon$ es cercano al exponente crítico ($\epsilon > 0$ pequeño). Para hallar soluciones, se utiliza un esquema de reducción finito-dimensional en espacios de funciones adecuados, donde el término principal de la función reducida se expresa a partir de las funciones de Green y de Robin del dominio. La existencia de soluciones dependerá de la existencia de puntos críticos de este término principal y de una condición de no degeneración. Por último, se considera un problema no local en el grupo de Heisenberg $H$. En particular, se buscan propiedades de rigidez para soluciones estables de $$ (-\Delta_H)^s v = f(v) en H, $$ $s \in (0,1)$. Como paso fundamental, se prueba una desigualdad del tipo Poincaré en conexión con un problema elíptico degenerado en $R^4_+$. Esta desigualdad se usará en un procedimiento de extensión para dar un criterio bajo el cual los conjuntos de nivel de las soluciones del problema anterior son superficies mínimas en $H$, es decir, tienen $H$-curvatura media nula.
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Lopez, Rios Luis Fernando. "Two problems in nonlinear PDEs : existence in supercritical elliptic equations and symmetry for a hypo-elliptic operator." Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4701/document.
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Le travail présenté est dédié à des problèmes d'EDP non linéaires. L'idée principale est de construire des solutions régulières á certaines EDPs elliptiques et hypo-elliptiques et étudier leur propriétés qualitatives. Dans une première partie, on considère un problème sur-critique du type $$-Delta u = lambda e^u$$ avec $lambda > 0$ posé dans un domaine extérieur avec conditions de Dirichlet homogènes. Une réduction en dimension finie permet de prouver l'existence d'un nombre infini de solutions régulières quand $lambda$ est assez petit. Dans une deuxième partie, on étudie la concentration de solutions d'un problème non local $$(-Delta)^s u = u^{p pm epsilon}, u>0, epsilon > 0$$ dans un domaine borné, régulier sous conditions de Dirichlet homogènes. Ici, on prend $0 < s < 1$ et $p:=(N+2s)/(N-2s)$, l'exposant de Sobolev critique. Une réduction en dimension finie dans des espaces fonctionnels bien choisis est utilisée. La partie principale de la fonction réduite est donnée en termes des fonctions de Green et Robin sur le domaine. On prouve que l'existence de solutions dépend des points critiques de la fonction susmentionnée augmentée d'une condition de non-dégénérescence. Enfin, on considère un problème non local dans le groupe de Heisenberg $H$. On s'intéresse à des propriétés de rigidité des solutions stables de $(-Delta_H)^s v = f(v)$ sur $H$, $s in (0,1)$. Une inégalité de type Poincaré connectée à un problème dégénéré dans $R^4_+$ est prouvée. Au travers d'une procédure d'extension, cette inégalité est utilisée pour donner un critère sous lequel les lignes de niveaux de la solution de l'EDP sont des surfaces minimales dans $H$This work is devoted to nonlinear PDEs. The aim is to find regular solutions to some elliptic and hypo-elliptic PDEs and study their qualitative properties. The first part deals with the supercritical problem $$ -Delta u = lambda e^u,$$ $lambda > 0$, in an exterior domain under zero Dirichlet condition. A finite-dimensional reduction scheme provides the existence of infinitely many regular solutions whenever $lambda$ is sufficiently small.The second part is focused on the existence of bubbling solutions for the non-local equation $$ (-Delta)^s u =u^p, ,u>0,$$in a bounded, smooth domain under zero Dirichlet condition; where $0 0$ small). To this end, a finite-dimensional reduction scheme in suitable functional spaces is used, where the main part of the reduced function is given in terms of the Green's and Robin's functions of the domain. The existence of solutions depends on the existence of critical points of such a main term together with a non-degeneracy condition.In the third part, a non-local entire problem in the Heisenberg group $H$ is studied. The main interests are rigidity properties for stable solutions of $$(-Delta_H)^s v = f(v) in H,$$ $s in (0,1)$. A Poincaré-type inequality in connection with a degenerate elliptic equation in $R^4_+$ is provided. Through an extension (or ``lifting") procedure, this inequality will be then used to give a criterion under which the level sets of the above solutions are minimal surfaces in $H$, i.e. they have vanishing mean $H$-curvature
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Hofmann, B., and O. Scherzer. "Local Ill-Posedness and Source Conditions of Operator Equations in Hilbert Spaces." Universitätsbibliothek Chemnitz, 1998. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-199800957.
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The characterization of the local ill-posedness and the local degree of nonlinearity are of particular importance for the stable solution of nonlinear ill-posed problems. We present assertions concerning the interdependence between the ill-posedness of the nonlinear problem and its linearization. Moreover, we show that the concept of the degree of nonlinearity com bined with source conditions can be used to characterize the local ill-posedness and to derive a posteriori estimates for nonlinear ill-posed problems. A posteriori estimates are widely used in finite element and multigrid methods for the solution of nonlinear partial differential equations, but these techniques are in general not applicable to inverse an ill-posed problems. Additionally we show for the well-known Landweber method and the iteratively regularized Gauss-Newton method that they satisfy a posteriori estimates under source conditions; this can be used to prove convergence rates results.
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Ye, Jinglong. "Infinite semipositone systems." Diss., Mississippi State : Mississippi State University, 2009. http://library.msstate.edu/etd/show.asp?etd=etd-07072009-132254.
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Hofmann, B. "On Ill-Posedness and Local Ill-Posedness of Operator Equations in Hilbert Spaces." Universitätsbibliothek Chemnitz, 1998. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-199801185.
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In this paper, we study ill-posedness concepts of nonlinear and linear inverse problems
in a Hilbert space setting. We define local ill-posedness of a nonlinear operator
equation $F(x) = y_0$ in a solution point $x_0$ and the interplay between the nonlinear
problem and its linearization using the Frechet derivative $F\acent(x_0)$ . To find an
appropriate ill-posedness concept for the linarized equation we define intrinsic
ill-posedness for linear operator equations $Ax = y$ and compare this approach with
the ill-posedness definitions due to Hadamard and Nashed.
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Monteiro, Evandro 1982. "Multiplicidade de soluções para equação de quarta ordem." [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/306960.
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Orientador: Djairo Guedes de FigueiredoTese (doutorado) - Universidade Estadual de Campinas, Instituto de Matemática, Estatística e Computação Científica
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Doutorado
Matematica
Doutor em Matemática
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Angoshtari, Arzhang. "Geometric discretization schemes and differential complexes for elasticity." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/49026.
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In this research, we study two different geometric approaches, namely, the discrete exterior calculus and differential complexes, for developing numerical schemes for linear and nonlinear elasticity. Using some ideas from discrete exterior calculus (DEC), we present a geometric discretization scheme for incompressible linearized
elasticity. After characterizing the configuration manifold of volume- preserving discrete deformations, we use Hamilton’s principle on this configuration manifold. The discrete Euler-Lagrange equations are obtained without using Lagrange multipliers.
The main difference between our approach and the mixed finite element formulations is that we simultaneously use three different discrete spaces for the displacement field. We test the efficiency and robustness of this geometric scheme using some numerical examples. In particular, we do not see any volume locking and/or checkerboarding of pressure in our numerical examples. This suggests that our choice of discrete solution
spaces is compatible. On the other hand, it has been observed that the linear elastostatics complex can be used to find very efficient numerical schemes. We use some geometric techniques to obtain differential complexes for nonlinear elastostatics.
In particular, by introducing stress functions for the Cauchy and the second Piola-Kirchhoff stress tensors, we show that 2D and 3D nonlinear elastostatics admit separate kinematic and kinetic complexes. We show that stress functions corresponding to the first Piola-Kirchhoff stress tensor allow us to write a complex for 3D nonlinear
elastostatics that similar to the complex of 3D linear elastostatics contains both the kinematics an kinetics of motion. We study linear and nonlinear compatibility equations
for curved ambient spaces and motions of surfaces in R3. We also study the relationship between the linear elastostatics complex and the de Rham complex. The geometric approach presented in this research is crucial for understanding connections
between linear and nonlinear elastostatics and the Hodge Laplacian, which can enable one to convert numerical schemes of the Hodge Laplacian to those for linear and possibly nonlinear elastostatics.
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Childers, Kristen Snyder. "Generalizations of a Laplacian-Type Equation in the Heisenberg Group and a Class of Grushin-Type Spaces." Scholar Commons, 2011. http://scholarcommons.usf.edu/etd/3042.
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In [2], Beals, Gaveau and Greiner find the fundamental solution to a 2-Laplace-type equation in a class of sub-Riemannian spaces. This fundamental solution is based on the well-known fundamental solution to the p-Laplace equation in Grushin-type spaces [4] and the Heisenberg group [6]. In this thesis, we look to generalize the work in [2] for a p-Laplace-type equation. After discovering that the "natural" generalization fails, we find two generalizations whose solutions are based on the fundamental solution to the p-Laplace equation.
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Howard, Timothy G. "Predicting the asymptotic behavior for differential equations with a quadratic nonlinearity." Diss., Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/28823.
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Uhliarik, Marek. "Operator Splitting Methods and Artificial Boundary Conditions for a nonlinear Black-Scholes equation." Thesis, Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-6111.
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There are some nonlinear models for pricing financial derivatives which can improve the linear Black-Scholes model introduced by Black, Scholes and Merton. In these models volatility is not constant anymore, but depends on some extra variables. It can be, for example, transaction costs, a risk from a portfolio, preferences of a large trader, etc. In this thesis we focus on these models. In the first chapter we introduce some important theory of financial derivatives. The second chapter is devoted to the volatility models. We derive three models concerning transaction costs (RAPM, Leland's and Barles-Soner's model) and Frey's model which assumes a large (dominant) trader on the market. In the third and in the forth chapter we derive portfolio and make numerical experiments with a free boundary. We use the first order additive and the second order Strang splitting methods. We also use approximations of Barles-Soner's model using the identity function and introduce an approximation with the logarithm function of Barles-Soner's model. These models we finally compare with models where the volatility includes constant transaction costs.
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McCoy, James A. (James Alexander) 1976. "The surface area preserving mean curvature flow." Monash University, Dept. of Mathematics, 2002. http://arrow.monash.edu.au/hdl/1959.1/8291.
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Huth, Robert. "On a Fokker–Planck equation coupled with a constraint." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät II, 2012. http://dx.doi.org/10.18452/16557.
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In dieser Arbeit untersuchen wir zwei Modelle, die das Laden und Entladen einer Lithium-Ionen Batterie beschreiben. Beide Modelle spiegeln eine Hysterese in dem Spannungs-Ladungs-Verlauf wider. Wir skizzieren den Modellierungsprozess von einem diskreten vielteilchen Modell sowie einem kontinuierlichen vielteilchen Modell. Das erste führt zu einer axiomatischen Beschreibung der Evolution makroskopischer Größen, während das zweite in eine nichtlineare Fokker-Planck Gleichung mündet. Wir zeigen die Existenz und Eindeutigkeit von Lösungen der nichtlinearen Fokker-Planck Gleichung und untersuchen deren qualitative Eigenschaften. Wir benutzen Interpolationsräume und Halbgruppen sektorieller Operatoren um den semilinearen Charakter der partiellen Differentialgleichung auszunutzen. Um globale Existenz zu erhalten, schätzen wir die Dissipation einer mit dem Modell verknüpften Energie ab. Diese Energie ist verwandt mit der L-log-L Norm, welche wir mithilfe einer Gagliardo-Nirenberg Ungleichung zu der L^2 Norm in Verbindung setzen können. Die notwendigen und hinreichenden Bedingungen zur globalen Existenz von Lösungen sind aus physikalischer Sicht plausibel. Der Ladezustand der Batterie muss innerhalb der Werte Voll und Leer sein. In numerischen Experimenten untersuchen wir das qualitative Verhalten von Lösungen. Wir zeigen die Konvergenz der numerischen Lösungen zu den exakten Lösungen. Dafür nutzen wir ähnliche Techniken wie bei der lokalen Existenztheorie. Wir beobachten die Tendenz von Lösungen sich um bestimmte Punkte zu konzentrieren. Unterstützt durch die formale Asymptotik zeigt dies für eine bestimmte Wahl von Parameter-Skalierungen, dass Lösungen gegen Dirac-Maße konvergieren. In diesem Grenzverhalten wird das System durch die Evolution von makroskopischen Größen beschrieben, welche wir auch in dem diskreten vielteilchen Modell wiederfinden. In diesen makroskopischen Größen lässt sich eine Hysterese beobachten.We discuss two models which describe the charging and discharging of a lithium-ion battery and especially the hysteretical behaviour therein. We give an overview on the modelling process for a discrete many particle model and a continuous many particle model. The former results in an axiomatic description of macroscopic quantities while the latter gives a nonlinear Fokker-Planck equation. The nonlinear Fokker-Planck equation is analysed with respect to existence and uniqueness of solutions as well as qualitative behaviour of solutions. The nonlinearity in this partial differential equation stems from a coefficient which depends on the solution first non-local and second in a higher order. We use interpolation spaces and semigroups generated from sectorial operators to show the existence and uniqueness of solutions locally in time. The global existence in time relies on estimates for the dissipation of an energy. The suitable energy is related to the L-log-L norm and so a Gagliardo-Nirenberg inequality is needed to connect this back to L^2 estimates. It turns out that the conditions for global in time existence of solutions are physical reasonable. One needs that the loading state of the battery shall stay between totally empty and totally full. In numerical experiments we investigate the qualitative behaviour of solutions to the nonlinear Fokker-Planck equation. We are able to show convergence of the numerical solutions to the exact solution. We observe that solutions tend to concentrate at certain points. Supported by results from formal asymptotic expansions, we document the limiting behaviour in a certain scaling of the appearing parameters, which is the formation of Dirac measures. The evolution of the global quantities, which we observe in numerical simulations, is the same as what results from the discrete many particle model and one observes hysteretic behaviour in macroscopic quantities.
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Siegfanz, Monika. "Die eindimensionale Wellengleichung mit Hysterese." Doctoral thesis, [S.l. : s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=961880511.
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Neji, Ali. "Existence unicité et régularité de solutions de problèmes non linéaires et complètement non linéaires elliptiques singuliers." Thesis, Cergy-Pontoise, 2019. http://www.theses.fr/2019CERG1017.
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Dans cette thèse on s'intéresse à l'existence, et la régularité pour des équations aux dérivées partielles non linéaires relatives au p-Laplacien , avec des termes d'ordre critiques ou sous critique, utilisant dans un cas le lemme du col d'Ambrozetti Rabinowitz, dans l'autre la concentration compacité de P L Lions. On considère ensuite un problème qui présente un terme d'ordre zéro qui "explose " près du bord, sur le modèle d'un article de Lazer mackenna, la différence essentielle étant ici que l'on a aussi un terme d'ordre 0 linéaire, qui demande donc l'utilisation de certaines fonctions propres. Une généralisation de ce problème à des cas complètement non linéaires et donc à des solutions de viscosité est étudiée dans la dernière partie de la thèseWe studied in this thesis the properties of existence and regularity for various nonlinear partial differential equations of elliptic type. We proved the existence of weak solutions to certain problems involving the p-Laplacian operator using critical point theory and the mountain pass theorem . We have also showed the existence of viscosity solutions for singular equations involving fully nonlinear operators
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Ben, slimene Byrame. "Comportement asymptotique des solutions globales pour quelques problèmes paraboliques non linéaires singuliers." Thesis, Sorbonne Paris Cité, 2017. http://www.theses.fr/2017USPCD059/document.
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Dans cette thèse, nous étudions l’équation parabolique non linéaire ∂ t u = ∆u + a |x|⎺⥾ |u|ᵅ u, t > 0, x ∈ Rᴺ \ {0}, N ≥ 1, ⍺ ∈ R, α > 0, 0 < Ƴ < min(2,N) et avec une donnée initiale u(0) = φ. On établit l’existence et l’unicité locale dans Lq(Rᴺ) et dans Cₒ(Rᴺ). En particulier, la valeur q = N ⍺/(2 − γ) joue un rôle critique. Pour ⍺ > (2 − γ)/N, on montre l’existence de solutions auto-similaires globales avec données initiales φ(x) = ω(x) |x|−(2−γ)/⍺, où ω ∈ L∞(Rᴺ) homogène de degré 0 et ||ω||∞ est suffisamment petite. Nous montrons ainsi que si φ(x)∼ω(x) |x| ⎺(²⎺⥾)/⍺ pour |x| grande, alors la solution est globale et asymptotique dans L∞(Rᴺ) à une solution auto-similaire de l’équation non linéaire. Tandis que si φ(x)∼ω(x) |x| (x)|x|−σ pour des |x| grandes avec (2 − γ)/⍺ < σ < N, alors la solution est globale, mais elle est asymptotique dans L∞(Rᴺ) à eᵗ∆(ω(x) |x|−σ). L’équation avec un potentiel plus général, ∂ t u = ∆u + V(x) |u|ᵅ u, V(x) |x |⥾ ∈ L∞(Rᴺ), est également étudiée. En particulier, pour des données initiales φ(x)∼ω(x) |x| ⎺(²⎺⥾)/⍺, |x| grande, nous montrons que le comportement à grand temps est linéaire si V est à support compact au voisinage de l’origine, alors qu’il est non linéaire si V est à support compact au voisinage de l’infini. Nous étudions également le système non linéaire ∂ t u = ∆u + a |x|⎺⥾ |v|ᴾ⎺¹v, ∂ t v = ∆v + b |x|⎺ ᴾ |u|q⎺¹ u, t > 0, x ∈ Rᴺ \ {0}, N ≥ 1, a,b ∈ R, 0 < y < min(2,N)? 0 < p < min(2,N), p,q > 1. Sous des conditions sur les paramètres p, q, γ et ρ nous montrons l’existence et l’unicité de solutions globales avec données initiales petites par rapport à certaines normes. En particulier, on montre l’existence de solutions auto-similaires avec donnée initiale Φ = (φ₁, φ₂), où φ₁, φ₂ sont des données initiales homogènes. Nous montrons également que certaines solutions globales sont asymptotiquement auto-similaires. Comme deuxième objectif, nous considérons l’équation de la chaleur non linéaire ut = ∆u + |u|ᴾ⎺¹u - |u| q⎺¹u, avec t ≥ 0 et x ∈ Ω, la boule unité de Rᴺ, N ≥ 3, avec des conditions aux limites de Dirichlet. Soit h une solution stationnaire à symétrie radiale avec changement de signe de (E). On montre que la solution de (E) avec donnée initiale λh explose en temps fini si |λ − 1| > 0 est suffisamment petit et si 1 < q < p < Ps = N+2/N−2 et p suffisamment proche de Ps. Ceci prouve que l’ensemble des données initiales pour lesquelles la solution est globale n’est pas étoilé au voisinage de 0In this thesis, we study the nonlinear parabolic equation ∂ t u = ∆u + a |x|⎺⥾ |u|ᵅ u, t > 0, x ∈ Rᴺ \ {0}, N ≥ 1, ⍺ ∈ R, α > 0, 0 < Ƴ < min(2,N) and with initial value u(0) = φ. We establish local well-posedness in Lq(Rᴺ) and in Cₒ(Rᴺ). In particular, the value q = N ⍺/(2 − γ) plays a critical role.For ⍺ > (2 − γ)/N, we show the existence of global self-similar solutions with initial values φ(x) = ω(x) |x|−(2−γ)/⍺, where ω ∈ L∞(Rᴺ) is homogeneous of degree 0 and ||ω||∞ is sufficiently small. We then prove that if φ(x)∼ω(x) |x| ⎺(²⎺⥾)/⍺ for |x| large, then the solution is global and is asymptotic in the L∞-norm to a self-similar solution of the nonlinear equation. While if φ(x)∼ω(x) |x| (x)|x|−σ for |x| large with (2 − γ)/α < σ < N, then the solution is global but is asymptotic in the L∞-norm toe t(ω(x) |x|−σ). The equation with more general potential, ∂ t u = ∆u + V(x) |u|ᵅ u, V(x) |x |⥾ ∈ L∞(Rᴺ), is also studied. In particular, for initial data φ(x)∼ω(x) |x| ⎺(²⎺⥾)/⍺, |x| large , we show that the large time behavior is linear if V is compactly supported near the origin, while it is nonlinear if V is compactly supported near infinity. we study also the nonlinear parabolic system ∂ t u = ∆u + a |x|⎺⥾ |v|ᴾ⎺¹v, ∂ t v = ∆v + b |x|⎺ ᴾ |u|q⎺¹ u, t > 0, x ∈ Rᴺ \ {0}, N ≥ 1, a,b ∈ R, 0 < y < min(2,N)? 0 < p < min(2,N), p,q > 1. Under conditions on the parameters p, q, γ and ρ we show the existence and uniqueness of global solutions for initial values small with respect of some norms. In particular, we show the existence of self-similar solutions with initial value Φ = (φ₁, φ₂), where φ₁, φ₂ are homogeneous initial data. We also prove that some global solutions are asymptotic for large time to self-similar solutions. As a second objective we consider the nonlinear heat equation ut = ∆u + |u|ᴾ⎺¹u - |u| q⎺¹u, where t ≥ 0 and x ∈ Ω, the unit ball of Rᴺ, N ≥ 3, with Dirichlet boundary conditions. Let h be a radially symmetric, sign-changing stationary solution of (E). We prove that the solution of (E) with initial value λ h blows up in finite time if |λ − 1| > 0 is sufficiently small and if 1 < q < p < Ps = N+2/N−2 and p sufficiently close to Ps. This proves that the set of initial data for which the solution is global is not star-shaped around 0
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Lepule, Seipati. "Invariances, conservation laws and conserved quantities of the two-dimensional nonlinear Schrodinger-type equation." Thesis, 2014. http://hdl.handle.net/10539/18573.
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A dissertation submitted to the Faculty of Science, University of the Witwatersrand, in fulfilment of the requirements for the degree of Master of Science.
Johannesburg, 2014.Symmetries and conservation laws of partial di erential equations (pdes) have been instrumental in giving new approaches for reducing pdes. In this dissertation, we study the symmetries and conservation laws of the two-dimensional Schr odingertype equation and the Benney-Luke equation, we use these quantities in the Double Reduction method which is used as a way to reduce the equations into a workable pdes or even an ordinary di erential equations. The symmetries, conservation laws and multipliers will be determined though di erent approaches. Some of the reductions of the Schr odinger equation produced some famous di erential equations that have been dealt with in detail in many texts.
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Gehre, Nico. "Lösungsoperatoren für Delaysysteme und Nutzung zur Stabilitätsanalyse." 2017. https://monarch.qucosa.de/id/qucosa%3A21053.
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In diese Dissertation werden lineare retardierte Differentialgleichungen (DDEs) und deren Lösungsoperatoren untersucht. Wir stellen eine neue Methode vor, mit der die Lösungsoperatoren für autonome und nicht-autonome DDEs bestimmt werden. Die neue Methode basiert auf dem Pfadintegralformalismus, der aus der Quantenmechanik und von der Analyse stochastischer Differentialgleichungen bekannt ist. Es zeigt sich, dass die Lösung eines Delaysystems zum Zeitpunkt t durch die Integration aller möglicher Pfade von der Anfangsbedingung bis zur Zeit t gebildet werden kann. Die Pfade bestehen dabei aus verschiedenen Schritten unterschiedlicher Längen und Gewichte. Für skalare autonome DDEs können analytische Ausdrücke des Lösungsoperators in der Literatur gefunden werden, allerdings existieren keine für nicht-autonome oder höherdimensionale DDEs. Mithilfe der neuen Methode werden wir die Lösungsoperatoren der genannten DDEs aufstellen und zusätzlich auf Delaysysteme mit mehreren Delaytermen erweitern. Dabei bestätigen wir unsere Ergebnisse sowohl analytisch wie auch numerisch.
Die gewonnenen Lösungsoperatoren verwenden wir anschließend zur Stabilitätsanalyse periodischer Delaysysteme. Es werden zwei neue Verfahren präsentiert, die mithilfe des Lösungsoperators den transformierten Monodromieoperator des Delaysystems nähern und daraus die Stabilität bestimmen können. Beide neue Verfahren sind spektrale Methoden für autonome sowie nicht-autonome Delaysysteme und haben keine Einschränkungen wie bei der bekannten Chebyshev-Kollokationsmethode oder der Chebyshev-Polynomentwicklung. Die beiden bisherigen Verfahren beschränken sich auf Delaysysteme mit rationalem Verhältnis zwischen Periode und Delay. Außerdem werden wir eine bereits bekannte Methode erweitern und zu einer spektralen Methode für periodische nicht-autonome Delaysysteme entwickeln. Wir bestätigen alle drei neue Verfahren numerisch. Damit werden in dieser Dissertation drei neue spektrale Verfahren zur Stabilitätsanalyse periodischer Delaysysteme vorgestellt.In this thesis linear delay differential equations (DDEs) and its solutions operators are studied. We present a new method to calculate the solution operators for autonomous and non-autonomous DDEs. The new method is related to the path integral formalism, which is known from quantum mechanics and the analysis of stochastic differential equations. It will be shown that the solution of a time delay system at time t can be constructed by integrating over all paths from the initial condition to time t. The paths consist of several steps with different lengths and weights. Analytic expressions for the solution operator for scalar autonomous DDEs can be found in the literature but no results exist for non-autonomous or high dimensional DDEs. With the help of the new method we can calculate the solution operators for such DDEs and for time delay systems with several delay terms. We verify our results analytically and numerically. We use the obtained solution operators for the stability analysis of periodic time delay systems. Two new methods will be presented to approximate the transformed monodromy operator with the help of the solution operator and to get the stability. Both new methods are spectral methods for autonomous and non-autonomous delay systems and have no limitations like the known Chebyshev collocation method or Chebyshev polynomial expansion. Both previously known methods are limited to time delay systems with a rational relation between period and delay. Furthermore we will extend a known method to a spectral method for non-autonomous time delay systems. We verify all three new methods numerically. Hence, in this thesis three new spectral methods for the stability analysis of periodic time delay systems are presented.
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Jain, Rahul. "Regularity And Propagation Phenomena In Some Linear And Non-Linear Partial Differential Equations With Particular Reference To Microlocal Analysis." Thesis, 2005. http://etd.iisc.ernet.in/handle/2005/1447.
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Müller, Boris. "Brownian Particles in Nonequilibrium Solvents." Doctoral thesis, 2019. http://hdl.handle.net/21.11130/00-1735-0000-0005-12E6-3.
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Langer, Stefan. "Preconditioned Newton methods for ill-posed problems." Doctoral thesis, 2007. http://hdl.handle.net/11858/00-1735-0000-0006-B396-D.
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