Dissertations / Theses on the topic 'Singular integral'

Los problemas que estudiamos en esta tesis se encuentran en el área de Análisis Armónico y Teoría de la Medida Geométrica. En particular, consideramos la conexión entre las propiedades analíticas de operadores integrales singulares definidos en $L^2(\mu)$ y asociados con algunos núcleos de Calderón-Zygmund y las propiedades geométricas de la medida $\mu$. Seamos más precisos. Sea $E$ un conjunto de Borel en el plano complejo con la medida lineal de Hausdorff $H^1$ finita y distinta de cero, es decir, $00$ es una pequeña constante absoluta. Es importante que, para algunos de los $t$ que acabamos de mencionar, el llamado método de curvatura comúnmente utilizado para relacionar $L^2$-acotación y rectificabilidad no está disponible, pero todavía es posible establecer la propiedad mencionada. Hasta donde sabemos, es el primer ejemplo de este tipo en el plano complejo. También vale la pena mencionar que ampliamos nuestros resultados a una clase aún más general de núcleos y, además, consideramos problemas análogos para conjuntos $E$ Ahlfors-David-regulares.
The problems that we study in this thesis lie in the area of Harmonic Analysis and Geometric Measure Theory. Namely, we consider the connection between the analytic properties of singular integral operators defined in $L^2(\mu)$ and associated with some Calderón-Zygmund kernels and the geometric properties of the measure $\mu$. Let us be more precise. Let $E$ be a Borel set in the complex plane with non-vanishing and finite linear Hausdorff measure $H^1$, i.e. such that $00$ is a small absolute constant. It is important that for some of the $t$ just mentioned the so called curvature method commonly used to relate $L^2$-boundedness and rectifiability is not available but it is still possible to establish the above-mentioned property. To the best of our knowledge, it is the first example of this type in the plane. It is also worth mentioning that we extend our results to even more general class of kernels and additionally consider analogous problems for Ahlfors-David regular sets $E$.

Els principals objectes d'estudi d'aquesta memòria són les integrals singulars. Per l'elaboració d'aquesta memòria, trobem una especial motivació en tres articles originats a partir de la idea d'acotar la norma de l'operador maximal d'una integral singular per la norma de la integral singular. En el primer article, de J. Mateu i J. Verdera del 2006, [MV], s'hi proven desigualtats puntuals pels casos particulars de la j-èssima transformada de Riesz i de la transformada de Beurling. Es fa notar per primer cop que les acotacions són diferents degut a la paritat del nucli de les respectives transformades. A posteriori, en els articles de J. Mateu, J. Orobitg i J. Verdera de 2011, [MOV], i en [MOPV] de 2010 dels mateixos autors més C. Pérez, s'han provat acotacions puntuals com les esmentades per transformades de Riesz d'ordre superior. En el primer treball es tracta el cas d'operadors amb el nucli parell i en el segon es fa el mateix pels de nucli senar. Aquí, la desigualtat de Cotlar pren protagonisme, ja que es fa notar que la desigualtat puntual pel cas parell és una millora d'aquesta. En [MOV] es demostra que, per les integrals singulars de Calderón-Zygmund de grau parell i amb nucli prou regular, l'acotació puntual de l'operador maximal pel mateix operador és equivalent a l'acotació en L^2 i al mateix temps a una condició algebraica sobre el nucli de la integral singular. En el cas de les integrals de grau senar, en [MOPV], es veu que succeeix el mateix però en la desigualtat puntual necessitem la segona iterada de l'operador maximal de Hardy-Littlewood. Ja s'havia vist en [MV] que l'acotació sense iteració no funcionava en el cas de la transformada de Riesz. A partir d'aquí, en el treball que ens ocupa, ens hem dedicat a estendre aquestes acotacions. En el primer capítol es resol una pregunta oberta que es planteja a [MOV]. Es demostra que l'acotació en L^p (i en L^p amb pesos) és també equivalent a la desigualtat puntual, no només amb p=2. Aquests resultats estan reflectits en [BMO1]. En el segon capítol es treballa una altra pregunta plantejada al mateix article. Es tracta de veure si es pot relaxar la regularitat del nucli i que segueixi passant el mateix. Quan ens trobem al pla, donem una bona resposta fixant una diferenciabilitat inicial que ha de tenir el nucli. En el cas de que la dimensió és més gran que 2, tenim una resposta parcial, en el sentit de que aquesta regularitat inicial depèn del grau d'un cert polinomi que depèn del nucli. Això podria fer que s'hagués de demanar una diferenciabilitat molt gran. Però, això sí, finita. En el tercer capítol donem un exemple pel qual no tenim acotació de la norma L^1 feble de la funció maximal en termes de la norma L^1 de l'operador. Presentem el cas d'un polinomi harmònic de grau 3 en el pla i expliquem com es pot generalitzar al cas d'operadors de qualsevol grau senar en el pla. Tot i això, degut a la difícil caracterització dels polinomis harmònics en dimensions superiors, ens ha quedat obert el problema a R^n, per n>2. En l'últim capítol considerem el mateix problema d'acotar puntualment l'operador maximal d'una integral singular pel mateix operador, però en aquest cas definim una nova maximal on trunquem amb cubs en lloc de boles. Treballem el cas de la transformada de Beurling i veiem que per poder acotar ho hem de fer utilitzant la segona iterada del maximal de Hardy-Littlewood, i que no ho podem reemplaçar per la primera iteració. Aquests resultats estan reflectits en [BMO2]. Bibliografia [BMO1] A. Bosch-Camós, J. Mateu, J. Orobitg, «L^p estimates for the maximal singular integral in terms of the singular integral», J. Analyse Math. 126 (2015), 287-306. [BMO2] A. Bosch-Camós, J. Mateu, J. Orobitg, «The maximal Beurling transform associated with squares», Ann. Acad. Sci. Fenn. 40 (2015), 215-226. [MOPV] J. Mateu, J. Orobitg, C. Perez, J. Verdera, «New estimates for the maximal singular integral», Int. Math. Res. Not. 19 (2010), 3658-3722. [MOV] J. Mateu, J. Orobitg, J. Verdera, «Estimates for the maximal singular integral in terms of the singular integral: the case of even kernels», Ann. of Math. 174 (2011), 1429-1483. [MV] J. Mateu, J. Verdera, «L^p and weak L^1 estimates for the maximal Riesz transform and the maximal Beurling transform, Math. Res. Lett. 13 (2006), 957-966.
The main objects of study of this dissertation are the singular integrals. We find an special motivation in three papers originated from the idea of bounding the norm of maximal operator of a singular integral by the norm of the singular integral itself. In the first one, of J. Mateu and J. Verdera from 2006, [MV], they prove pointwise inequalities for the particular cases of the j-th Riesz transform and the Beurling transform. For the first time, one notice that we obtain different bounds depending on the parity of the kernel of each operator. A posteriori, in the papers of J. Mateu, J. Orobitg and J. Verdera from 2011, [MOV], and in [MOPV] from 2010 from same authors plus C. Pérez, they prove pointwise inequalities as the aforementioned for higher order Riesz transforms. In the first work they treat the case of operators with even kernel, and in the second one, they do the same but for odd kernels. Here is when Cotlar inequality takes shows of, because we can notice that the inequality for the even case is an improvement of this one In [MOV] they prove that, for even Calderón-Zygmund singular integrals with smooth kernel, the pointwise inequality of the maximal operator bounded by the operator itself is equivalent to the L^2 estimate and also to an algebraic condition on the kernel of the singular integral. For the odd operators, in [MOPV], it's proved the same result, but in the pointwise inequality we need the second iteration of the Hardy-Littlewood maximal operator. It was proved before, in [MV], that one cannot bound without this iteration in the case of the Riesz trasnform. From here on, in this dissertation we have been working on this kind of estimates. In the first chapter we give a positive answer to one open question in [MOV]. We prove that the L^p estimate (and the weighted L^p) is also equivalent to the pointwise inequality, not only with p=2. This results are reflected in [BMO1]. In the second chapter we work on another open question from the same paper. We deal with the same estimates but relaxing the regularity of the kernel. When we are in the plane, we give a good answer, setting an initial differenciability for the kernel. For higher dimensions, with n bigger than 2, we have a partial answer, in the sense that the initial regularity depends on the degree of a polynomial depending on the kernel. This means that we may should ask for a very big differentiability, but a finite one. In the third chapter, we give an example for which we can't bound de weak L^1 norm of the maximal function in terms of the L^1 norm of the operator. We give the case of a harmonic polynomial of degree 3 in the plane and we explain how we can generalize to all polynomials with odd degree in the plane. However, because of the difficult caracterization of the harmonic polynomials en higher dimensions, the problem in R^n, for n>2, is open. In the last chapter, we consider the same problem of pointwise estimating the maximal operator of a singular integral by the same operator, but in this case we define a new maximal where we truncate by cubes instead of balls. We work with the Beurling transform and we prove that we need the second iteration of the Hardy-Littlewood maximal operator, and that we can't replace it for the first iteration. This results are reflected in [BMO2]. Bibliography [BMO1] A. Bosch-Camós, J. Mateu, J. Orobitg, «L^p estimates for the maximal singular integral in terms of the singular integral», J. Analyse Math. 126 (2015), 287-306. [BMO2] A. Bosch-Camós, J. Mateu, J. Orobitg, «The maximal Beurling transform associated with squares», Ann. Acad. Sci. Fenn. 40 (2015), 215-226. [MOPV] J. Mateu, J. Orobitg, C. Perez, J. Verdera, «New estimates for the maximal singular integral», Int. Math. Res. Not. 19 (2010), 3658-3722. [MOV] J. Mateu, J. Orobitg, J. Verdera, «Estimates for the maximal singular integral in terms of the singular integral: the case of even kernels», Ann. of Math. 174 (2011), 1429-1483. [MV] J. Mateu, J. Verdera, «L^p and weak L^1 estimates for the maximal Riesz transform and the maximal Beurling transform, Math. Res. Lett. 13 (2006), 957-966.

This work is a numerical study of a class of weakly singular neutral equations. The motivation for this study is an aeroelastic system. Numerical techniques are developed to approximate the singular integral equation component appearing in the complete dynamical model for the elastic motions of a three degree of freedom structure, an airfoil with trailing edge flap, in a two dimensional unsteady flow. The flap can be viewed as an active control surface to dampen vibrations that contribute to flutter. The goal of this work is to provide accurate approximations for weakly singular neutral equations using finite elements as basis functions for the initial function space. Several examples are presented in order to validate the numerical scheme.
Master of Science

The thesis provides answers, in one case partial and in the other final, to two conjectures in the area of weighted inequalities for Singular Integral Operators. We study the mapping properties of these operators in weighted Lebesgue spaces with weight w. The novelty of this thesis resides in proving sharp dependence of the operator norm on the Muckenhoupt constant associated to the weigth w for a rich class of Singular Integral operators. The thesis also addresses the end point case p=1, providing counterexamples for the dyadic and continuous settings.

Doutoramento em Matemática
Nesta tese, consideram-se operadores integrais singulares com a acção extra de um operador de deslocacamento de Carleman e com coeficientes em diferentes classes de funções essencialmente limitadas. Nomeadamente, funções contínuas por troços, funções quase-periódicas e funções possuíndo factorização generalizada. Nos casos dos operadores integrais singulares com deslocamento dado pelo operador de reflexão ou pelo operador de salto no círculo unitário complexo, obtêm-se critérios para a propriedade de Fredholm. Para os coeficientes contínuos, uma fórmula do índice de Fredholm é apresentada. Estes resultados são consequência das relações de equivalência explícitas entre aqueles operadores e alguns operadores adicionais, tais como o operador integral singular, operadores de Toeplitz e operadores de Toeplitz mais Hankel. Além disso, as relações de equivalência permitem-nos obter um critério de invertibilidade e fórmulas para os inversos laterais dos operadores iniciais com coeficientes factorizáveis. Adicionalmente, aplicamos técnicas de análise numérica, tais como métodos de colocação de polinómios, para o estudo da dimensão do núcleo dos dois tipos de operadores integrais singulares com coeficientes contínuos por troços. Esta abordagem permite também a computação do inverso no sentido Moore-Penrose dos operadores principais. Para operadores integrais singulares com operadores de deslocamento do tipo Carleman preservando a orientação e com funções contínuas como coeficientes, são obtidos limites superiores da dimensão do núcleo. Tal é implementado utilizando algumas estimativas e com a ajuda de relações (explícitas) de equivalência entre operadores. Focamos ainda a nossa atenção na resolução e nas soluções de uma classe de equações integrais singulares com deslocamento que não pode ser reduzida a um problema de valor de fronteira binomial. De forma a atingir os objectivos propostos, foram utilizadas projecções complementares e identidades entre operadores. Desta forma, as equações em estudo são associadas a sistemas de equações integrais singulares. Estes sistemas são depois analisados utilizando um problema de valor de fronteira de Riemann. Este procedimento tem como consequência a construção das soluções das equações iniciais a partir das soluções de problemas de valor de fronteira de Riemann. Motivados por uma grande diversidade de aplicações, estendemos a definição de operador integral de Cauchy para espaços de Lebesgue sobre grupos topológicos. Assim, são investigadas as condições de invertibilidade dos operadores integrais neste contexto.
In this thesis we consider singular integral operators with the extra action of a Carleman shift operator and having coefficients on different classes of essentially bounded functions. Namely, continuous, piecewise continuous, semi-almost periodic and generalized factorable functions. In the cases of the singular integral with shift action given by the reflection or the flip operator on the complex unit circle, we obtain a Fredholm criteria and, for the continuous coefficients case, an index formula is also provided. These results are consequence of explicit equivalence operator relations between those operators and some extra operators such as pure singular integral, Toeplitz and Toeplitz plus Hankel operators. Furthermore, the equivalence relations allow us to give an invertibility criterion and formulas for the left-sided and right-sided inverses of the initial operators with generalized factorable coefficients. In addition, we apply numerical analysis techniques, as polynomial collocation methods, for the study of the kernel dimension of these two kinds of singular integral operators with piecewise continuous coefficients. This approach also permits us to compute the Moore-Penrose inverse of the main operators. For singular integral operators with generic preserving-orientation Carleman shift operators and continuous functions as coefficients, upper bounds for the kernel dimensions are obtained. This is implemented by using some estimations which are derived with the help of certain explicit operator relations. We also focus our attention to the solvability, and the solutions, of a class of singular integral equations with shift which cannot be reduced to a binomial boundary value problem. To attain our goals, some complementary projections and operator identities are used. In this way, the equations under study are associated with systems of pure singular integral equations. These systems will be then analyzed by means of a corresponding Riemann boundary value problem. As a consequence of such a procedure, the solutions of the initial equations are constructed from the solutions of Riemann boundary value problems. Motivated by a large diversity of applications, we extend the definition of Cauchy integral operator to the framework of Lebesgue spaces on topological groups. Thus, invertibility conditions for paired operators in this setting are investigated.
FCT - SFRH/BD/30679/2006

The dissertation consists of two parts. In the first part approximate methods for multidimensional weakly singular integral operators with operator-valued kernels are investigated. Convergence results and error estimates are given. There is considered an application of these methods to solving radiation transfer problems. Numerical results are presented, too. In the second part we consider a polynomial collocation method for the numerical solution of a singular integral equation over the interval. More precisely, the operator of our integral equation is supposed to be of the form \ $aI + b \mu^{-1} S \mu I $\ with \ $S$\ the Cauchy singular integral operator, with piecewise continuous coefficients \ $a$\ and \ $b,$\ and with a Jacobi weight \ $\mu.$\ To the equation we apply a collocation method, where the collocation points are the Chebyshev nodes of the first kind and where the trial space is the space of polynomials multiplied by another Jacobi weight. For the stability and convergence of this collocation method in weighted \ $L^2$\ spaces, we derive necessary and sufficient conditions. Moreover, the extension of these results to an algebra generated by the sequences of the collocation method applied to the mentioned singular integral operators is discussed and the behaviour of the singular values of the discretized operators is investigated
Die Dissertation beschäftigt sich insgesamt mit der numerischen Analysis singulärer Integralgleichungen, besteht aber aus zwei voneinander unabhängigen Teilen. Der este Teil behandelt Diskretisierungsverfahren für mehrdimensionale schwach singuläre Integralgleichungen mit operatorwertigen Kernen. Darüber hinaus wird hier die Anwendung dieser allgemeinen Resultate auf ein Strahlungstransportproblem diskutiert, und numerische Ergebnisse werden präsentiert. Im zweiten Teil betrachten wir ein Kollokationsverfahren zur numerischen Lösung Cauchyscher singulärer Integralgleichungen auf Intervallen. Der Operator der Integralgleichung hat die Form \ $aI + b \mu^{-1} S \mu I $\ mit dem Cauchyschen singulären Integraloperator \ $S,$\ mit stückweise stetigen Koeffizienten \ $a$\ und \ $b,$\ und mit einem klassischen Jacobigewicht \ $\mu.$\ Als Kollokationspunkte dienen die Nullstellen des n-ten Tschebyscheff-Polynoms erster Art und Ansatzfunktionen sind ein in einem geeigneten Hilbertraum orthonormales System gewichteter Tschebyscheff-Polynome zweiter Art. Wir erhalten notwendige und hinreichende Bedingungen für die Stabilität und Konvergenz dieses Kollokationsverfahrens. Außerdem wird das Stabilitätskriterium auf alle Folgen aus der durch die Folgen des Kollokationsverfahrens erzeugten Algebra erweitert. Diese Resultate liefern uns Aussagen über das asymptotische Verhalten der Singulärwerte der Folge der diskreten Operatoren

Given a doman $\Omega$ in $C^n$, it is a classical problem to study the boundary behavior of functions which are holomorphic on $\Omega$. The boundary values of a given function are often expressed by means of singular integral operators. In this thesis we study this problem in two different settings with different motivations. In the first part we deal with a non-smooth version of the so-called worm domain in order to understand the role played by the pathological geometry of this domain. In the second part we study the problem in the case of a product Lipschitz surface and some boundedness results for biparameter singular integral operators are proved.

The paper is devoted to the foundation of approximation methods for integral equations of the form (aI+SbI+K)f=g, where S is the Cauchy singular integral operator on (-1,1) and K is a weakly singular integral operator. Here a,b,g are given functions on (-1,1) and the unknown function f on (-1,1) is looked for. It is assumed that a and b are real-valued and Hölder continuous functions on [-1,1] without common zeros and that g belongs to some weighted space of Hölder continuous functions. In particular, g may have a finite number of singularities. Based on known spectral properties of Cauchy singular integral operators approximation methods for the numerical solution of the above equation are constructed, where both aspects the theoretical convergence and the numerical practicability are taken into account. The weighted uniform convergence of these methods is studied using a general approach based on the theory of approximation spaces. With the help of this approach it is possible to prove simultaneously the stability, the convergence and results on the order of convergence of the approximation methods under consideration.

En aquesta tesi s’obtenen nous resultats sobre l’acotació d’operadors de Calderón-Zygmund en espais de Sobolev en dominis de Rd. En primer lloc es demostra un teorema de tipus T(P) vàlid per a Wn,p(U), a on U és un domini uniforme acotat de Rd, n és un nombre natural arbitrari, i p>d. Essencialment, el resultat obtingut afirma que un operador de Calderón-Zygmund de convolució és acotat en aquest espai si i solament si per a tot polinomi P de grau menor que n restringit al domini, T(P) pertany a Wn,p(U). Per a índexs p menors o iguals que d, es demostra una condició suficient per a l'acotació en termes de mesures de Carleson. En el cas n=1 i p<=d, es comprova que aquesta caracterització en termes de mesures de Carleson és també una condició necessària. El cas en què n és no enter i 02. La darrera aportació de la tesi és l'aplicació dels resultats anteriorment descrits a l'estudi de la regularitat de l'equació de Beltrami que satisfan les aplicacions quasiconformes. Essencialment, es demostra que si el coeficient de Beltrami pertany a l'espai Wn,p(U), essent U un domini Lipschitz del pla complex amb parametritzacions de la frontera en un cert espai de Besov i p>2, llavors l'aplicació quasiconforme associada està en l'espai Wn,p(U).
In this dissertation some new results on the boundedness of Calderón-Zygmund operators on Sobolev spaces on domains in Rd. First a T(P)-theorem is obtained which is valid for Wn,p (U), where U is a bounded uniform domain of Rd, n is a given natural number and p>d. Essentially, the result obtained states that a convolution Calderón-Zygmund operator is bounded on this function space if and only if T(P) belongs to Wn,p (U) for every polynomial P of degree smaller than n restricted to the domain. For indices p less or equal than d, a sufficient condition for the boundedness in terms of Carleson measures is obtained. In the particular case of n=1 and p<=d, this Carleson condition is shown to be necessary in fact. The case where n is not integer and 02. Finally, an application of the aforementioned results is given for quasiconformal mappings in the complex plane. In particular, it is checked that the regularity Wn,p(U) of the Beltrami coefficient of a quasiconformal mapping for a bounded Lipschitz domain U with boundary parameterizations in a certain Besov space and p>2, implies that the mapping itself is in Wn+1,p(U).

Cette thèse traite de trois sujets en trois parties. Dans la première partie, nous étudions les points S-entiers de la courbe modulaire X0(p). Yuri Bilu a montré qu’en utilisant la méthode de Baker, on peut donner une borne effective de la hauteur de ces points en fonction de p, du corps de base et de l’ensemble de places S. Min Sha a rendu ce résultat explicite. avec une borne doublement exponentielle en dans p. Nous améliorons considérablement dans cette thèse le résultat de Sha, en obtenant une borne simplement exponentielle. Cela se fait en utilisant une version très explicite du principe de Chevalley-Weil basée sur des travaux de Qing Liu et Dino Lorenzini. Notre borne est non seulement plus nette que celle de Sha, mais également explicite en tous les paramètres. Dans la deuxième partie, nous considérons des modules singuliers de courbes elliptiques. Pour un module singulier fixe a, nous donnons une borne supérieure effective de la norme de x - a pour un autre module singulier x avec un grand discriminant. Dans la troisième partie, nous donnons une relation entre les conducteurs d’Artin d’un modèle Werestrass Y et ceux de deux modèles de Weierstrass donnés Y1,Y2. Avec cette relation, nous déduisons que l’inégalité conducteur-discriminant est valable pour Y si elle est valable pour Y1 et Y2
This thesis discusses three topics, so it includes three parts. In the first part, we study S-integral points on the modular curve X0(p). Bilushowed that, using Baker’s method, they can be effectively bounded in terms of p, the base field and the set of places S. Sha made this result explicit, but the bound he obtained is double exponential in p. We drastically improve upon the result of Sha, obtaining a simple exponential bound. This is done using a very explicit version of the Chevalley-Weil principle based on the work of Liu and Lorenzini. Our bound is not only sharper than that of Sha, but is also explicit in all parameters. In the second part, we consider singular moduli. For a fixed singular modulus a, we give an effective upper bound of norm of x - a for another singular modulus x with large discriminant. In the third part, we give a relation between Artin conductors of a Weierstrass model Y and the ones of two given Weierstrass models Y1,Y2. With this relation, we know that the conductor-discriminant inequality holds for Y if it holds for Y1 and Y2

A força hidrodinâmica em termos dos coeficientes de massa adicional e amortecimento, para obstáculos aproximadamente circulares, finos e submersos sob uma superfície livre aquática, é calculada numericamente usando um método espectral. Primeiramente, é apresentado um modelo matemático para ondas aquáticas de superfície e em seguida, o problema de difração de ondas devido à presença de um obstáculo é descrito. Quando o obstáculo é submerso e fino, o problema pode ser formulado em termos de uma equação integral hipersingular. Usando um mapeamento conforme sobre um disco circular, é mostrado que a solução pode ser obtida através de um método espectral onde a hipersingularidade é avaliada analiticamente em termos de polinômios ortogonais. Os coeficientes da força hidrodinâmica, em função do número de onda, são obtidos para obstáculos quase circulares. A ocorrência de frequências ressoantes ´e observada para submersões suficientemente pequenas e subpicos de ressonância aparecem para valores moderados da submersão, em comparação com o caso do disco circular.
The hydrodynamic force, in terms of the added mass and damping coefficients, for thin and submerged nearly circular obstacles below a water free surface is computed by a spectral method. Firstly, a mathematical model for surface water waves is presented. Next, the diffraction problem of waves due to the presence of an obstacle is described. When the body is thin and submerged, the problem can be formulated in terms of a hypersingular integral equation. Using a conformal mapping over a circular disc, it is shown that the solution can be obtained by means of a spectral method where the hipersingularity is analytically evaluated in terms of orthogonal polynomials. The hydrodynamics coefficients, in function of the wavenumber, are computed and shown for nearly circular obstacles. The occurrence of resonant frequencies is observed for sufficiently small submergences and subpeaks of resonances appear for moderate values of the submergence, in comparison with the case of a circular disc.

We consider a finite section (Galerkin) and a collocation method for Cauchy singular integral equations on the interval based on weighted Chebyshev polymoninals, where the coefficients of the operator are piecewise continuous. Stability conditions are derived using Banach algebra techniques, where also the system case is mentioned. With the help of appropriate Sobolev spaces a result on convergence rates is proved. Computational aspects are discussed in order to develop an effective algorithm. Numerical results, also for a class of nonlinear singular integral equations, are presented.

Mathematics
Ph.D.
Many boundary value problems of mathematical physics are modelled by elliptic differential operators L in a given domain Ω . An effective method for treating such problems is the method of layer potentials, whose essence resides in reducing matters to solving a boundary integral equation. This, in turn, requires inverting a singular integral operator, naturally associated with L and Ω, on appropriate function spaces on ƌΩ. When the operator L is of second order and the domain Ω is Lipschitz (i.e., Ω is locally the upper-graph of a Lipschitz function) the fundamental work of B. Dahlberg, C. Kenig, D. Jerison, E. Fabes, N. Rivière, G. Verchota, R. Brown, and many others, has opened the door for the development of a far-reaching theory in this setting, even though several very difficult questions still remain unanswered. In this dissertation, the goal is to solve a number of open questions regarding spectral properties of singular integral operators associated with second and higher-order elliptic boundary value problems in non-smooth domains. Among other spectral results, we establish symmetry properties of harmonic classical double layer potentials associated with the Laplacian in the class of Lipschitz domains in R2. An array of useful tools and techniques from Harmonic Analysis, Partial Differential Equations play a key role in our approach, and these are discussed as preliminary material in the thesis: --Mellin Transforms and Fourier Analysis; --Calderón-Zygmund Theory in Uniformly Rectifiable Domains; -- Boundary Integral Methods. Chapter four deals with proving invertibility properties of singular integral operators naturally associated with the mixed (Zaremba) problem for the Laplacian and the Lamé system in infinite sectors in two dimensions, when considering their action on the Lebesgue scale of p integrable functions, for 1 < p < ∞. Concretely, we consider the case in which a Dirichlet boundary condition is imposed on one ray of the sector, and a Neumann boundary condition is imposed on the other ray. In this geometric context, using Mellin transform techniques, we identify the set of critical integrability indexes p for which the invertibility of these operators fails. Furthermore, for the case of the Laplacian we establish an explicit characterization of the Lp spectrum of these operators for each p є (1,∞), as well as well-posedness results for the mixed problem. In chapter five, we study spectral properties of layer potentials associated with the biharmonic equation in infinite quadrants in two dimensions. A number of difficulties have to be dealt with, the most significant being the more complex nature of the singular integrals arising in this 4-th order setting (manifesting itself on the Mellin side by integral kernels exhibiting Mellin symbols involving hyper-geometric functions). Finally, chapter six, deals with spectral issues in Lipschitz domains in two dimensions. Here we are able to prove the symmetry of the spectra of the double layer potentials associated with the Laplacian. This is in essence a two-dimensional phenomenon, as known examples show the failure of symmetry in higher dimensions.
Temple University--Theses

Master of Science
Mathematics
Nathan Albin
Pietro Poggi-Corradini
This report explores singular integration, both real and complex, focusing on the the Cauchy type integral, culminating in the proof of generalized Sokhotski-Plemelj formulae and the applications of such to a Riemann-Hilbert problem.

The solutions for a class of Neutral Functional Di erential Equations (NFDE) with weakly singular kernels are studied. Using singular expansion techniques, a representation of the solution of the NFDE is obtained by studing an associated Volterra Integral Equation. We study the Collocation Method as a projection method for the approximation of solutions for Volterra Integral Equations. Particulary, the possibility of achieving higher order ap- proximations is discussed. Special attention is given to the choice of the projection space and its relation to the smoothness of the approximated solution. Finally, we study the identification problem for a parameter appearing in the weakly singular operator of the NFDE.
Ph. D.

We consider a collocation method for Cauchy singular integral equations on the interval based on weighted Chebyshev polynomials , where the coefficients of the operator are piecewise continuous. Stability conditions are derived using Banach algebra methods, and numerical results are given.

This thesis considers the problem of semi-infinite hydraulic fractures driven by shear-thinning power-law fluids through a permeable elastic medium. In the recent work by Dontsov and Peirce [Journal of Fluid Mechanics, 784:R1 (2015)], the authors reformulated the governing equations in a way that avoids singular integrals for the case of a Newtonian fluid. Moreover, the authors constructed an approximating ordinary differential equation (ODE) whose solutions accurately describe the fracture opening at little to no computational cost. The present thesis aims to extend their work to the more general case where the fracture is driven by a shear-thinning power-law fluid. In the first two chapters of this thesis we outline the relevant physical modelling and discuss the asymptotic propagation regimes typically encountered in hydraulic fracturing problems. This is followed by Chapters 4 and 5 where we reformulate the governing equations as a non-singular integral equation, and then proceed to construct an approximating ODE. In the final chapter we construct a numerical scheme for solving the non-singular integral equation. Solutions obtained in this way are then used to gauge the accuracy of solution obtained by solving the approximating ODE. The most important results of this thesis center on the accuracy of using the approximating ODE. In the final chapter we find that when the fluid's power-law index is in the range of 0.4 ≤ n ≤ 1, an appropriate method of solving the approximating ODE yields solutions whose relative errors are less than 1%. However, this relative error increases with decreasing values of n so that in the range 0 ≤ n < 0.4 it reaches a maximum value of approximately 6%. Thus, at least for values of 0.4 ≤ n ≤ 1 the approximating ODE presents an accurate and computationally fast alternative to solving the semi-infinite problem. The same can't be said for values of 0 ≤ n < 0.4, but the methods presented in this thesis may be used as a starting point for future work in this direction.
Science, Faculty of
Mathematics, Department of
Graduate

A Teoria das equações integrais, desde a segunda metade do século XX, tem assumido um papel cada vez maior no âmbito de problemas aplicados. Com isso, surge a necessidade do desenvolvimento de métodos numéricos cada vez mais eficazes para a resolução deste tipo de equação. Isso tem como consequência a possibilidade de resolução de uma gama cada vez maior de problemas. Nesse sentido, outros tipos de equações integrais estão sendo objeto de estudos, dentre elas as chamadas equações integro-diferenciais. O presente trabalho tem como objetivo o estudo das equações integro-diferenciais singulares lineares e não-lineares. Mais especificamente, no caso linear, apresentamos os principais resultados necessários para a obtenção de um método numérico e a formulação de suas propriedades de convergência. O caso não-linear é apresentado através de um modelo matemático para tubulações em um tipo específico de reator nuclear (LMFBR) no qual origina-se a equação integro-diferencial. A partir da equação integro-diferencial um modelo numérico é proposto com base nas condições físicas do problema
The theory of the integral equations, since the second half of the 20th century, has been assuming an ever more important role in the modelling of applied problems. Consequently, the development of new numerical methods for integral equations is called for and a larger range of problems has been possible to be solved by these new techniques. In this sense, many types of integral equations have been derived from applications and been the object of studies, among them the so called singular integro-differential equation. The present work has, as its main objective, the study of singular integrodifferential equations, both linear and non-linear. More specifically, in the linear case, we present our main results regarding the derivation of a numerical method and its uniform convergence properties. The non-linear case is introduced through the mathematical model of boiler tubes in a specific type of nuclear reactor (LMFBR) from which the integro-differential equation originates. For this integro-differential equation a numerical method is proposed based on the physical conditions of the problem

We consider the Dirichlet, Neumann and Zaremba problems for harmonic functions in a bounded plane domain with nonsmooth boundary. The boundary curve belongs to one of the following three classes: sectorial curves, logarithmic spirals and spirals of power type. To study the problem we apply a familiar method of Vekua-Muskhelishvili which consists in using a conformal mapping of the unit disk onto the domain to pull back the problem to a boundary problem for harmonic functions in the disk. This latter is reduced in turn to a Toeplitz operator equation on the unit circle with symbol bearing discontinuities of second kind. We develop a constructive invertibility theory for Toeplitz operators and thus derive solvability conditions as well as explicit formulas for solutions.

Introdução: O Projeto Terapêutico Singular (PTS) é um conjunto de condutas e propostas terapêuticas que orientam o trabalho direcionado a um sujeito singular e coletivo, que resulta da discussão coletiva interdisciplinar de profissionais de determinado serviço de saúde e se consolida em cenário histórico e de Políticas Públicas, orientado em âmbito nacional pelo Sistema Único de Saúde. Objetivos: Realizar uma Revisão Integrativa da Literatura sobre o tema PTS. Identificar, na literatura, se a construção do PTS no campo psicossocial atende a seus pressupostos teóricos e conceituais e, indicar a re-organização do trabalho com vistas à construção compartilhada do PTS junto ao usuário, no campo psicossocial, a partir das normativas e diretrizes do Ministério da Saúde, na vigência da RAPS. Método: Trata-se de um estudo de Revisão Integrativa da Literatura. Utilizou-se dois descritores de assuntos combinados: Assistência Integral à Saúde e Serviços de Saúde Mental. A palavra-chave Projeto Terapêutico Singular foi utilizada em algumas bases de dados com o intuito de refinar buscas que se mostraram muito amplas. Os dados foram coletados no Banco de Teses e Dissertações da CAPES e da USP, Biblioteca Virtual em Saúde e, nas bases de dados, Cinahl, Pubmed e Web of Science. O período de publicação das referências localizadas não foi limitado. Resultados: Foram selecionados 14 estudos, produzidos no período de 1997 a 2014, sendo que 13 deles realizados em âmbito nacional e, apenas um foi produzido em âmbito internacional. Para análise dos estudos, buscou-se a categorização dos achados em cinco grupos: 1) conceitos e bases teóricas do campo psicossocial e da reabilitação como cidadania; 2) estrutura, forma e o como-fazer dos projetos terapêuticos singulares; 3) vantagens do emprego do projeto terapêutico singular nas práticas assistenciais; 4) os desafios, obstáculos e dificuldades nos quais o PTS esbarra; 5) as propostas para superação dos desafios relacionados ao PTS. Conclusões: A presente revisão integrativa valeu-se da combinação do uso de descritores de assunto e palavra-chave, o que permitiu a recuperação de maior número de estudos, pertinentes ao objetivo estabelecido. O PTS é ferramenta potente de cuidado, porém enfrenta muitos desafios para seu desenvolvimento o que pode restringir suas potencialidades. Foi recomendado que estudos futuros proponham um registro norteador de ações, que corresponda aos saberes teóricos e conceituais do campo psicossocial e da reabilitação como cidadania, de modo a contribuir com a elaboração do PTS. Esse norteador de ações deve apontar para a possibilidade de guiar a construção coletiva do PTS para atingir de forma efetiva a reabilitação psicossocial, a qualidade de vida, a dignidade, o poder de troca de mercadorias, de apoio social e familiar e de direito de pertencimento, ou seja, do verdadeiro direito à cidadania e a vida.
Introduction: The Singular Therapeutic Project (known as PTS in Brazil) is an arrangement of therapeuct actions that is due to guide the work process directed towards a singular person or a collective subjects, that results in an interdisciplinary collective discussion of employees of health services and has its bases in a historical setting and Public Policies, oriented at the national level by the National Health System. Objective: Identify if the development of the PTS in the psychosocial field meets its theoretical and conceptual assumptions, as well as propose the rearrangement of the work processes, aiming the shared development of the PTS with the user of the health services, in the psychosocial field, through the regulations and guidelines of the Ministry of Health, in the presence of the governement program Attention Networks to Psychosocial Health (known as RAPS). Method: Its an Integrative Literature Review. Were combined in this review two index-terms: Comprehensive Health Care and Mental Health Services. The keyword Therapeutic Project was used in same databases in order to refine searches that were very broad. Data were collected at the Bank of Theses and Dissertations of CAPES and USP, Virtual Health Library and, in the databases, Cinahl, Pubmed and Web of Science. The period of publication of localized references was not limited. Results: A total of fourteen (14) studies, producted from 1997 to 2014. Thirteen (13) of them were performed at the national level and only one of them was produced internationally. For analysis of the studies, we sought to categorize the findings into five groups: 1) concepts and theoretical bases of the psychosocial field and the rehabilitation as citizenship; 2) structure, shape and the how-to of the PTS; 3) advantages of using the PTS in the health care practices; 4) the challenges, obstacles and difficulties that the PTS faces; 5) proposals for overcoming the challenges related to PTS. Conclusion: This Integrative Review drew on the combination of the index-terms and keyword, which allowed the recovery of the greatest number of relevant studies to the proposed goal. The PTS is a powerful tool care, but it faces many challenges to its development which may restrict its potentialities. It is recommended that future studies could propose a registration that guides actions, which corresponds to the theoretical and conceptual knowledge of the psychosocial field and the rehabilitation as citizenship, in order to contribute to the development of the PTS. This guide for the actions should point the possibility of guiding the collective construction of the PTS to achieve effectively the psychosocial rehabilitation, the quality of life, the dignity, the social exchanges, the labor, the social and family support and the right of belonging, in other words, the true right to citizenship and life.

On s'interesse a des conditions necessaires et suffisantes de continuite-l**(2) (resp. Continuite - besov b**(s)::(p,q)), des commutateurs entre les operateurs pseudo-differentiels o. P. D. De type s**(11,a); a1 (resp. S**(11,0)), et les fonctions dont les gradients sont bornes (resp. Des multiplicateurs de besov m(b**(s)::(p,q))). La continuite - besov du commutateur a l'aide du critere de lemarie, mene a etudier la continuite des o. P. D. De type s**(01,0) sur m(b**(sp,q)): les o. P. D. D'ordre 0 sont bornes sur les versions "localisees l**(e") de b**(s)::(p,q), par consequent sur m(b**(s)::(p,p)) pour s>n/p. Si s