Lenstra-Hurwitz Cliques In Real Quadratic Fields

Let $K$ be a number field and let \OO_K denote its ring of integers. We can define a graph whose vertices are the elements of \OO_K such that an edge exists between two algebraic integers if their difference is in the units \OO_K^{\times}. Lenstra showed that the existence of a sufficiently large clique (complete subgraph) will imply that the ring \OO_K is Euclidean with respect to the field norm. A recent generalization of this work tells us that if we draw more edges in the graph, then a sufficiently large clique will imply the weaker (but still very interesting) conclusion that $K$ has class number one. This thesis aims to understand this new result and produce further examples of cliques in rings of integers. Lenstra, Long, and Thistlethwaite analyzed cliques and gave us class number one through a prime element. We were able to extend and generalize their result to larger cliques through prime power elements while still preserving our desired property of class number one. Our generalization gave us that class number one is preserved if the number field $K$ contained a clique that is generated by a prime power

Pre-compact families of finite sets of integers and weakly null sequences in Banach spaces

Two applications of Nash-Williams' theory of barriers to sequences on Banach spaces are presented: The first one is the $c_0$-saturation of $C(K)$, $K$ countable compacta. The second one is the construction of weakly-null sequences generalizing the example of Maurey-Rosenthal

Fast and stable contour integration for high order divided differences via elliptic functions

In this paper, we will present a new method for evaluating high order divided differences for certain classes of analytic, possibly, operator valued functions. This is a classical problem in numerical mathematics but also arises in new applications such as, e.g., the use of generalized convolution quadrature to solve retarded potential integral equations. The functions which we will consider are allowed to grow exponentially to the left complex half plane, polynomially to the right half plane and have an oscillatory behaviour with increasing imaginary part. The interpolation points are scattered in a large real interval. Our approach is based on the representation of divided differences as contour integral and we will employ a subtle parameterization of the contour in combination with a quadrature approximation by the trapezoidal rule

Identification of large masses of citrus fruit and rice fields in eastern Spain

There are no author-identified significant results in this report