O objetivo deste trabalho é caracterizar os polinômios cujas raízes têm todas parte real negativa, chamados de polinômios estáveis ou de Hurwitz. Para este fim, apresentaremos e provaremos o critério de Routh-Hurwitz. Também estenderemos este resultado para obter uma caracterização da estabilidade para uma família de polinômios com seus coeficientes variando independentemente num intervalo limitado. Aplicaremos os resultados para obter um critério de estabilidade robusta para um sistema de equações diferenciais que descreve um sistema mecânico. / The objective of this work is to determine when all of zeros of a given polynomial have negative real parts, called stable or Hurwitz polynomials. We will present and prove the Routh-Hurwitz criterion. Furthermore we will extend the result for classes of polynomials defined by letting their coeficients vary independently in an arbitrary finite interval. Then we will apply them to derive a robust stability condition for a mechanical system.

O objetivo deste trabalho é caracterizar os polinômios cujas raízes têm todas parte real negativa, chamados de polinômios estáveis ou de Hurwitz. Para este fim, apresentaremos e provaremos o critério de Routh-Hurwitz. Também estenderemos este resultado para obter uma caracterização da estabilidade para uma família de polinômios com seus coeficientes variando independentemente num intervalo limitado. Aplicaremos os resultados para obter um critério de estabilidade robusta para um sistema de equações diferenciais que descreve um sistema mecânico. / The objective of this work is to determine when all of zeros of a given polynomial have negative real parts, called stable or Hurwitz polynomials. We will present and prove the Routh-Hurwitz criterion. Furthermore we will extend the result for classes of polynomials defined by letting their coeficients vary independently in an arbitrary finite interval. Then we will apply them to derive a robust stability condition for a mechanical system.

No description available.

We explore the geometry of certain special subvarieties of spaces of branched covers which we call the Maroni and Casnati-Ekedahl loci. Our goal is to understand the divisor theory on compactifications of Hurwitz space, with the aim of providing upper bounds for slopes of sweeping families of d-gonal curves. / Mathematics

The goal of this paper is to explain the mathematics involved in modeling biochemical oscillations. We first discuss several important biochemical concepts fundamental to the construction of descriptive mathematical models. We review the basic theory of differential equations and stability analysis as it relates to two-variable models exhibiting oscillatory behavior. The importance of the Hopf Bifurcation will be discussed in detail for the central role it plays in limit cycle behavior and instability. Once we have exposed the necessary mathematical framework, we consider several specific models of biochemical oscillators in three or more variables. This will include a detailed analysis of Goodwin's equations and their modification first studied by Painter. Additionally, we consider the consequences of introducing both distributed and discrete time delay into Goodwin's model. We will show that the presence of distributed time lag modifies Goodwin's model in no significant way. The final section of the paper will discuss discrete time lag in the context of a minimal model of the circadian rhythm. In the main, this paper will address mathematical, as opposed to biochemical, issues. Nevertheless, the significance of the mathematics to the biochemistry will be considered throughout. / Master of Science

No description available.

In attempting to solve the regular inverse Galois problem for arbitrary subfields K of C (particularly for K=Q), a very important result by Fried and Völklein reduces the existence of regular Galois extensions F|K(t) with Galois group G to the existence of K-rational points on components of certain moduli spaces for families of covers of the projective line, known as Hurwitz spaces. In some cases, the existence of rational points on Hurwitz spaces has been proven by theoretical criteria. In general, however, the question whether a given Hurwitz space has any rational point remains a very difficult problem. In concrete cases, it may be tackled by an explicit computation of a Hurwitz space and the corresponding family of covers. The aim of this work is to collect and expand on the various techniques that may be used to solve such computational problems and apply them to tackle several families of Galois theoretic interest. In particular, in Chapter 5, we compute explicit curve equations for Hurwitz spaces for certain families of \(M_{24}\) and \(M_{23}\). These are (to my knowledge) the first examples of explicitly computed Hurwitz spaces of such high genus. They might be used to realize \(M_{23}\) as a regular Galois group over Q if one manages to find suitable points on them. Apart from the calculation of explicit algebraic equations, we produce complex approximations for polynomials with genus zero ramification of several different ramification types in \(M_{24}\) and \(M_{23}\). These may be used as starting points for similar computations. The main motivation for these computations is the fact that \(M_{23}\) is currently the only remaining sporadic group that is not known to occur as a Galois group over Q. We also compute the first explicit polynomials with Galois groups \(G=P\Gamma L_3(4), PGL_3(4), PSL_3(4)\) and \(PSL_5(2)\) over Q(t). Special attention will be given to reality questions. As an application we compute the first examples of totally real polynomials with Galois groups \(PGL_2(11)\) and \(PSL_3(3)\) over Q. As a suggestion for further research, we describe an explicit algorithmic version of "Algebraic Patching", following the theory described e.g. by M. Jarden. This could be used to conquer some problems regarding families of covers of genus g>0. Finally, we present explicit Magma implementations for several of the most important algorithms involved in our computations. / Das Umkehrproblem der Galoistheorie und explizite Berechnung von Familien von Überlagerungen des \(\mathbb{P}^1\mathbb{C}\) mit vorgegebener Verzweigung

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We construct several modular compactifications of the Hurwitz space \(H^d_{g/h}\) of genus g curves expressed as d-sheeted, simply branched covers of genus h curves. They are obtained by allowing the branch points of the cover to collide to a variable extent, generalizing the spaces of twisted admissible covers of Abramovich, Corti, and Vistoli. The resulting spaces are very well-behaved if d is small or if relatively few collisions are allowed. In particular, for d = 2 and 3, they are always well-behaved. For d = 2, we recover the spaces of hyperelliptic curves of Fedorchuk. For d = 3, we obtain new birational models of the space of triple covers. We describe in detail the birational geometry of the spaces of triple covers of \(P^1\) with a marked fiber. In this case, we obtain a sequence of birational models that begins with the space of marked (twisted) admissible covers and proceeds through the following transformations: (1) sequential contractions of the boundary divisors, (2) contraction of the hyperelliptic divisor, (3) sequential flips of the higher Maroni loci, (4) contraction of the Maroni divisor (for even g). The sequence culminates in a Fano variety in the case of even g, which we describe explicitly, and a variety fibered over \(P^1\) with Fano fibers in the case of odd g. / Mathematics

Tugul s - kompleksinis kintamasis ir a yra periodinė kompleksinių skaičių seka. Periodinė Hurvico zeta-funkcija yra apibrėžta, kai sigma > 1 ir analiziškai pratęsiama. Įrodyta, kad funkcija yra universali. Tegul K yra kompaktinė juosta su papildiniu, ir tegul funkciją f(s) pratęsiama ant K ir analizinė K viduje. Su kiekvienu epsilion > 1. / Let s be a complex variable, and a be a periodic sequence of complex numbers. The periodic Hurwitz zeta-function is defined, for sigma > 1 and by analytic continuation elsewhere. We prove that the function is universal in the following sense. Let K be a compact subset of the strip with connected complement, and let the function f(s) be continuous on K and analytic in the interior of K. Than, for every epsilion > 0.