acase@tulane.edu / Modular-type transformation formulas are the identities that are invariant under the transformation α → 1/α, and they can be represented as F (α) = F (β) where α β = 1. We derive a new transformation formula of the form F (α, z, w) = F (β, z, iw) that is a one-variable generalization of the well-known Ramanujan-Guinand identity of the form F (α, z) = F (β, z) and a two-variable generalization of Koshliakov’s formula of the form F (α) = F (β) where α β = 1. The formula is generated by first finding an integral J that is comprised of an invariance function Z and evaluating the integral to give F (α, z, w) mentioned above. The modified Bessel function K z (x) appearing in Ramanujan-Guinand identity is generalized to a new function, denoted as K z,w (x), that yields a pair of functions reciprocal in the Koshliakov kernel, which in turn yields the invariance function Z and hence the integral J and the new formula. The special function K z,w (x), first defined as the inverse Mellin transform of a product of two gamma functions and two confluent hypergeometric functions, is shown to exhibit a rich theory as evidenced by a number of integral and series representations as well as a differential-difference equation. The second topic of the thesis is 2-adic valuations of integer sequences associated with quadratic polynomials of the form x 2 +a. The sequence {n 2 +a : n ∈ Z} contains numbers divisible by any power of 2 if and only if a is of the form 4 m (8l+7). Applying this result to the sequences derived from the sums of four or fewer squares when one or more of the squares are kept constant leads to interesting results, that also points to an inherent connection with the functions r k (n) that count the number of ways to represent n as sums of k integer squares. Another class of sequences studied is the shifted sequences of the polygonal numbers given by the quadratic formula, for which the most common examples are the triangular numbers and the squares. / 1 / Aashita Kesarwani

(please take a look at the pdf)

In the thesis, the error and stability analysis is made for the 2D Helmholtz equation by the method of fundamental solutions (MFS) using both Bessel and Neumann functions. The bounds of errors in bounded simply-connected domains are derived, while the bounds of condition number are derived only for disk domains. The MFS using Bessel functions is more efficient than the MFS using Neumann functions. Interestingly, for the MFS using Bessel functions, the radius R of the source points is not necessarily larger than the maximal radius r_max of the solution domain. This is against the traditional condition: r_max < R for MFS. Numerical experiments are carried out to support the analysis and conclusions made.

Στην παρούσα διατριβή μελετώνται οι ρίζες της συνάρτησης Mν(z), στην περίπτωση όπου οι συναρτήσεις F(z) και G(z) είναι της μορφής: y(z) = Σ ynzn-1 αναλυτικές στον μοναδιαίο δίσκο και πληρούν τη συνθήκη: Σ |yn|2 < ∞, δηλ. ανήκουν στον χώρο Hardy-Lebesgue Η2 (Δ). / --

Οι γενικευμένες συναρτήσεις Bessel (συναρτήσεις Bessel πολλών μεταβλητών και δεικτών) χρησιμοποιούνται ως το βασικό μαθηματικό υπόβαθρο για την απλούστευση πολύπλοκων υπολογισμών σε φαινόμενα όπως της σκέδασης όπου η προσέγγιση του διπόλου δεν μπορεί να εφαρμοσθεί. Επίσης εμφανίζονται σε προβλήματα αλληλεπίδρασης ισχυρών δεσμών laser με ηλεκτρόνια, αλληλεπίδρασης φωτός με ασθενώς δεσμευμένο ηλεκτρόνιο, σε προβλήματα ιονισμού κτλ. Οι συναρτήσεις αυτές ικανοποιούν αντίστοιχες ιδιότητες (όσον αφορά στη γεννή- τρια συνάρτηση και τις αναδρομικές σχέσεις ) με τις συναρτήσεις Bessel μιας πραγ- ματικής μεταβλητής και η απόδειξη αυτών των σχέσεων βασίζεται στον ορισμό των γενικευμένων συναρτήσεων Bessel και στις ιδιότητες των συνήθων συναρτήσεων Bessel. Συγκεκριμένα παρουσιάζονται οι διάφορες γενικεύσεις των συναρτήσεων Bessel ξεκινώντας με αυτές των δύο μεταβλητών και του ενός ακέραιου δείκτη της μορφής για τις οποίες παραθέτονται η γεννήτρια συνάρτηση, οι αναδρομικές σχέσεις, παράγωγοι ως προς τις 2 μεταβλητές κάθε τάξης, αναπτύγματα τύπου Jacobi – Anger καθώς και σχέσεις σημαντικές για τους αριθμητικούς υπολογισμούς. Η ίδια μελέτη γίνεται και για τις διάφορες τροποποιημένες μορφές των συναρτήσεων καθώς και για τις γενικευμένες συναρτήσεις τριών αλλά και γενικά Μ μεταβλητών. Επίσης δίνονται αποτελέσματα για τις συναρτήσεις Bessel με περισσότερους από έναν δείκτες όπως οι συναρτήσεις , στην μονοδιάστατη περίπτω- ση και οι , και στην πολυδιά-στατη. Γίνεται καταγραφή των γενικευμένων μορφών των πολυωνύμων Hermite στις δύο διαστάσεις, των πολυωνύμων Gould – Hopper, των ιδιοτήτων τους καθώς και του τρόπου με τον οποίο συνδέονται με τις γενικευμένες συναρτήσεις Bessel. Τέλος, στην εργασία, που έχει τον χαρακτήρα της ανασκόπησης παρουσιάζονται και κάποια αποτελέσματα τα οποία αφορούν σε ιδιότητες πολυωνύμων Legendre και Laguerre δύο μεταβλητών. / The Generalized Bessel Functions (GBF) are multivariable extensions of the ordinary Bessel functions and their modified versions. Functions of this type encountered in a large number of fields, especially in physics, and used as a very important mathematical tool for simplifying the complicated computations. Problems, like the phenomenon of ionization and scattering, the interaction of intense laser beams with electrons, the effect of an intense electromagnetic field on a weakly bound system, are some examples of GBF’s applications in physics. In this work we gather and write down all the information related to the generalized Bessel functions and their modified versions, regarding their recurrence properties, generating functions ,integral representations, Jacobi – Anger expansions etc. Also we study the way that the generalized Bessel functions are linked with some multidimensional orthogonal polynomials such as Hermite, Laguerre, Legendre and Gould – Hopper polynomials.

Στη παρούσα εργασία ασχοληθήκαμε με ιδιότητες μονοτονίας των Τροποποιημένων συναρτήσεων Bessel 1ου και 2ου είδους. Συγκεκριμένα ομαδοποιήσαμε ήδη υπάρχοντα φράγματα για τα κλάσματα των συναρτήσεων αυτών. Η εύρεση φραγμάτων για τα κλάσματα των Τροποποιημένων Συναρτήσεων Bessel είναι σημαντική, λόγω της χρησιμότητάς τους σε διάφορους κλάδους των Μαθηματικών και όχι μόνο, όπως ενδεικτικά, στην Πεπερασμένη Ελαστικότητα, στην Στατιστική και στις Πιθανότητες, στην Ειδική Θεωρία Σχετικότητας, στην Μηχανική των Ρευστών, στην Ηλεκτρομηχανική, στη Βιοφυσική, στη Μαθηματική Φυσική και αλλού. Αρχικά, στο Κεφάλαιο 1, παρατέθηκαν κάποια βασικά στοιχεία, όπως ορισμοί των συναρτήσεων Bessel 1ου και 2ου είδους (Τροποποιημένων και μη) και αναδρομικές σχέσεις που ικανοποιούν. Στο Κεφάλαιο 2, γίνεται η καταγραφή και σύγκριση άνω και κάτω φραγμάτων για τα διάφορα κλάσματα των Τροποποιημένων συναρτήσεων Bessel 1ου είδους, καθώς και αναφορά σε ανισότητες τύπου Turán για τις συναρτήσεις αυτές. Επίσης, αναφέρεται η μεθοδολογία στην οποία στηρίχθηκε ο κάθε ερευνητής για να πάρει τα αντίστοιχα αποτελέσματα. Στο Κεφάλαιο 3, γίνεται η αντίστοιχη διαδικασία για τα κλάσματα και εκ νέου αναφορά σε ανισότητες τύπου Turán για αυτές τις συναρτήσεις. / In this project we described properties of Modified Bessel functions of the 1st and 2nd kind. Specifically we have grouped existing bounds for the quotients of these functions. These bounds of the Modified Bessel functions is very importand and could be found in different branches of Mathematics and other sciences, such as in Finite Elasticity, in Statistics and Probability Theory, in Relativity Theory, in Fluid Mechanics, in Engineering, in Biophysics, in Mathematical Physics and so on. Firsty, in Chapter 1, we cited some basic data, such as definitions of definitions of Bessel fynctions of the 1st and 2nd kind (both simple and Modified) and recurrence relations that they satisfy. In Chapter 2, we describe upper and lower bounds of different quotients of Modified Bessel functions of the 1st kind and reference to Turán type Inequalities of those functions. Moreover, we refer to the method that each recearcher based on in order to prove the required results. In Chapter 3, we have the same process but for Modified Bessel functons of the 2nd kind as well as reference to Turán type Inequalities for the corresponding functions.

Orientador: Edmundo Capelas de Oliveira / Dissertação (mestrado profissional) - Universidade Estadual de Campinas, Instituto de Matematica, Estatistica e Computação Cientifica / Made available in DSpace on 2018-08-11T05:13:17Z (GMT). No. of bitstreams: 1 Coelho_JoaoBosco_M.pdf: 1003588 bytes, checksum: c8b5b0bbc0f7fe49adbeacc39f398bcf (MD5) Previous issue date: 2008 / Resumo: Efetua-se um estudo sistemático das equações diferenciais parciais, lineares, de segunda ordem e do tipo hiperbólico, isto é, aquelas equações que estão associadas com o problema envolvendo a propagação de ondas. Como uma aplicação, discute-se o problema de ondas de corrente e ondas de tensão, através da chamada equação do telégrafo, também conhecida como equação dos telegrafistas. Casos particulares são discutidos tanto do ponto de vista matemático quanto do ponto de vista físico. Apresenta-se o método de Riemann como ferramenta para discutir a solução geral / Abstract: We perform a systematic way to study the linear, second order partial differential equation of the hyperbolic type, that is, those equations which are associated with the problem involving wave propagation. As an application, we discuss the problem associated with the current waves and tension waves by means of the so-called telegraph equation, also known as telephone equation. Particular cases are discussed in both sense, Mathematic and Physical point of view. We also present the Riemann¿s method as a powerful tool to discuss the general solution / Mestrado / Mestre em Matemática

Orientador: Edmundo Capelas de Oliveira / Dissertação (mestrado profissional) - Universidade Estadual de Campinas, Instituto de Matemática, Estatística e Computação Científica / Made available in DSpace on 2018-08-17T12:38:24Z (GMT). No. of bitstreams: 1 Nakamura_MarciaMayumi_M.pdf: 683963 bytes, checksum: 0fbcfd687c511e4845ba13501415f91e (MD5) Previous issue date: 2011 / Resumo: Efetuamos um estudo sistemático envolvendo o caso geral de uma equação diferencial parcial, linear, de segunda ordem, com n variáveis independentes. Particularizamos para o caso bidimensional, n = 2, duas variáveis independentes. Utilizamos o método de separação de variáveis para conduzir esta equação diferencial parcial a um conjunto de duas equações diferenciais ordinárias. Introduzimos o método de Frobenius a partir de uma particular equação diferencial ordinária, a chamada equação de Bessel. Como aplicação, apresentamos e discutimos o chamado problema de forcas centrais, em particular, estudamos o problema de Kepler de onde emerge naturalmente o problema de classificação de uma cônica, onde a elipse merece tratamento destacado / Abstract: We develop a systematic study involving the general case of a second order linear partial differential equation with n independent variables. We particularize to the bidimensional case, n = 2, involving two independent variables. In this case, we present the method of separating variables to develop the partial differential equation into a set of two differential ordinary equations. We introduce the Frobenius method using a particular ordinary di1'l'erential equation, the so-called Bessel equation. As an application, we present and discuss the so-called central forces and as particular case, we study the Kepler problem from which naturally emerges the problem of the classification of a conic, where ellipse deserves special treatment / Mestrado / Equação Diferenciais / Mestre em Matemática

The existence and -if exists- the nature of the solutions of the scalar wave equation in spacetimes with closed timelike curves are investigated. The general properties of the solutions on some class of spacetimes are obtained. Global monochromatic solutions of the scalar wave equation are obtained in flat wormholes of dimensions 2+1 and 3+1. The solutions are in the form of infinite series involving cylindirical and spherical wave functions and they are elucidated by the multiple scattering method. Explicit solutions for some limiting cases are illustrated as well. The results of 2+1 dimensions are verified by using numerical methods.

Ce travail s’inscrit dans l’étude des symétries d’espaces de dimension infinie. Il répond à des questions algébriques en suivant des méthodes analytiques. Plus précisément, nous étudions certaines représentations du groupe symplectique complexe dans des espaces fonctionnels. Elles sont caractérisées par leurs décompositions isotypiques relativement à un sous-groupe compact maximal. Ce travail décrit ces décompositions dans deux modèles : un modèle classique (dit compact) et un autre plus récent (dit non-standard). Nous montrons que cela établit un lien entre deux familles de fonctions spéciales (fonctions hypergéométriques et fonctions de Bessel) ; ces familles sont associées à des équations différentielles ordinaires d’ordre 2, fuchsiennes dans un cas et non fuchsiennes dans l’autre. Nous mettons aussi en évidence, dans le modèle non-standard, un lien avec certaines équations d'Emden-Fowler, ainsi qu’un opérateur différentiel simple qui agit sur les décompositions isotypiques. / The general setting of this work is the study of symmetry groups of infinite-dimensional spaces. We answer algebraic questions, using analytical methods. To be more specific, we study certain representations of the complex symplectic group in functional spaces. These representations are characterised by their isotypic decompositions with respect to a maximal compact subgroup. In this work, we describe these decompositions in two different models: a classical model (compact picture) and a more recent one (non-standard picture). We show that this establishes a connection between two families of special functions (hypergeometric functions and Bessel functions); these families correspond to second order differential equations, which are Fuchsian in one case and non-Fuchsian in the other. We also establish a link with certain Emden-Fowler equations and exhibit a simple differential operator that acts on the isotypic decompositions.