Let V( ) denote a local system of weight on X = A2;n(C), where X is the moduli space of principle polarized abelian varieties of genus 2 over C with xed n-level structure. The inner cohomology of X with coe cients in V( ), H3 ! (X;V( )), has a Hodge ltration of weight 3. Each term of this Hodge ltration can be presented as space of cuspidal automorphic representations of genus 2. We consider the purely non-holomorphic part of H3 ! (X;V( )) denoted by H3 Ends(X;V( )). First of all we show that there is a non-zero subspace of H3 Ends(X;V( )) denoted by V (K), where K is an open compact subgroup of GSp(4;A), such that elements of V (K) are obtained by the global theta lifting of cuspidal automorphic representations of GL(2) GL(2)=Gm. This means that there is a non-zero part of H3 Ends(X;V( )) which is endoscopic. Secondly, we consider the local theta correspondence and nd an explicit answer for the level of lifted cuspidal automorphic representations to GSp(4; F) over a non-archimedean local eld F. Therefore, we can present an explicit way for nding a basis for V (K) for a xed level structure K. ii There is a part of the Hodge structure that only contributes in H(3;0) ! (X;V( )) H(0;3) ! (X;V( )). This part is endoscopic and coming from the Yoshida lift from O(4). Finally, in the case X = A2, if eendo(A2;V( )) denotes the motive corresponded to the strict endoscopic part (the part that contributes only in non-holomorphic terms of the Hodge ltration), then we have eendo(A2;V( )) = s 1+ 2+4S[ 1 2 + 2]L 2+1; (1) where = ( 1; 2) and is far from walls. Here S[k] denotes the motive corresponded to Sk, the space of cuspidal automorphic forms of weight k and trivial level, and sk = dim(Sk). ii

The main results of this thesis describe a relationship between two families of arithmetic divisors on an integral model of a Shimura curve. The first family, studied by Kudla, Rapoport and Yang, parametrizes abelian surfaces with specified endomorphism structure. The second family is comprised of pullbacks of arithmetic cycles on integral models of Shimura varieties associated to unitary groups of signature (1,1). In the thesis, we construct these families of cycles, and describe their relationship, which is expressed in terms of the ``Shimura lift", a classical tool in the theory of modular forms of half-integral weight. This relations can be viewed as further evidence for the modularity of generating series of arithmetic "special cycles" for U(1,1), and fits broadly into Kudla's programme for unitary groups.

Let V( ) denote a local system of weight on X = A2;n(C), where X is the moduli space of principle polarized abelian varieties of genus 2 over C with xed n-level structure. The inner cohomology of X with coe cients in V( ), H3 ! (X;V( )), has a Hodge ltration of weight 3. Each term of this Hodge ltration can be presented as space of cuspidal automorphic representations of genus 2. We consider the purely non-holomorphic part of H3 ! (X;V( )) denoted by H3 Ends(X;V( )). First of all we show that there is a non-zero subspace of H3 Ends(X;V( )) denoted by V (K), where K is an open compact subgroup of GSp(4;A), such that elements of V (K) are obtained by the global theta lifting of cuspidal automorphic representations of GL(2) GL(2)=Gm. This means that there is a non-zero part of H3 Ends(X;V( )) which is endoscopic. Secondly, we consider the local theta correspondence and nd an explicit answer for the level of lifted cuspidal automorphic representations to GSp(4; F) over a non-archimedean local eld F. Therefore, we can present an explicit way for nding a basis for V (K) for a xed level structure K. ii There is a part of the Hodge structure that only contributes in H(3;0) ! (X;V( )) H(0;3) ! (X;V( )). This part is endoscopic and coming from the Yoshida lift from O(4). Finally, in the case X = A2, if eendo(A2;V( )) denotes the motive corresponded to the strict endoscopic part (the part that contributes only in non-holomorphic terms of the Hodge ltration), then we have eendo(A2;V( )) = s 1+ 2+4S[ 1 2 + 2]L 2+1; (1) where = ( 1; 2) and is far from walls. Here S[k] denotes the motive corresponded to Sk, the space of cuspidal automorphic forms of weight k and trivial level, and sk = dim(Sk). ii

This thesis is devoted to a problem in the representation theory of the symmetric group over C (the field of the complex numbers). Let d be a positive integer, and let S_d denote the symmetric group on d letters. Given a partition k of d, the Specht module V_k is a finite dimensional vector space over C which admits a natural basis indexed by all standard tableaux of shape k with entries in {1, 2, ..., d}. It affords an irreducible representation of the symmetric group S_d, and conversely every irreducible representation of S_d is isomorphic to V_k for some partition k. Given two Specht modules V_k, V_t their tensor product representation is in general reducible, and hence it splits into a direct sum of irreducibles. This raises the problem of describing the S_d equivariant projection morphisms (alternately called S_d-homomorphisms) in terms of the standard tableaux basis. In this work we give explicit formulae describing this morphism in the following cases: k=(d-1, 1), (d-2, 1,1), (2, 1,... ,1). Finally, we present a conjecture formula for the q-morphism in the case k=(d-r, 1, ..., 1).

The Poincaré series, Py(f) of a polynomial f was first introduced by Borevich and Shafarevich in [BS66], where they conjectured, that the series is always rational. Denef and Igusa independently proved this conjecture. However it is still of interest to explicitly compute the Poincaré series in special cases. In this direction several people looked at diagonal polynomials with restrictions on the coefficients or the exponents and computed its Poincaré series. However in this dissertation we consider a general diagonal polynomial without any restrictions and explicitly compute its Poincaré series, thus extending results of Goldman, Wang and Han. In a separate chapter some new results are also presented that give a criterion for an element to be an mth power in a complete discrete valuation ring.

This thesis is devoted to a problem in the representation theory of the symmetric group over C (the field of the complex numbers). Let d be a positive integer, and let S_d denote the symmetric group on d letters. Given a partition k of d, the Specht module V_k is a finite dimensional vector space over C which admits a natural basis indexed by all standard tableaux of shape k with entries in {1, 2, ..., d}. It affords an irreducible representation of the symmetric group S_d, and conversely every irreducible representation of S_d is isomorphic to V_k for some partition k. Given two Specht modules V_k, V_t their tensor product representation is in general reducible, and hence it splits into a direct sum of irreducibles. This raises the problem of describing the S_d equivariant projection morphisms (alternately called S_d-homomorphisms) in terms of the standard tableaux basis. In this work we give explicit formulae describing this morphism in the following cases: k=(d-1, 1), (d-2, 1,1), (2, 1,... ,1). Finally, we present a conjecture formula for the q-morphism in the case k=(d-r, 1, ..., 1).

Den här studien undersöker för- och nackdelar med att migrera existerande mobilaapplikationer till Xamarins crossplatform ramverk Xamarin Forms. Metoden somanvänts för att samla in data är inom ramen för forskningsparadigmet Design Science.En prototyp har utvecklats med syftet att undersöka vad som är möjligt att migrera tillXamarin Forms. Prototyputvecklingen har dokumenterats i loggböcker som sedananalyserats som kvalitativ data. Två intervjuer har även genomförts med andraxamarinutvecklare med syftet att nå en djupare förståelse för ämnet. Studien harproducerat ett flödesschema för när ett beslut om att migrera en existerande applikationtill Xamarin Forms bör tas. Vid beslut om migration har vi även formulerat ett antalriktlinjer som bör efterföljas för att uppnå bra resultat. Flödesschemat och riktlinjerna ärbaserade på resultaten från analysen av loggböckerna och intervjuerna. / This study investigates the pros and cons of migraiting existing mobile applications toXamarins crossplatform framework Xamarin Forms. The method that is being used tocollect data is within the scope of the research paradigm Design Science. A prototype ofan existing mobile application has been developed in order to research the possibilitiesof migraiting existing applications to Xamarin Forms. The development process of theprototype has been documented in journals which later were to be analyzed asqualitative data. Two interviews have been done with other Xamarin developers in orderto get a deeper understanding of the subject. This study produced a flowchart that is tobe used when deciding about a migration of an existing mobile application aswell asguidelines for the migration itself. The flowchart and guidelines are based on analyzingthe data from our journals aswell as our interviews with other developers.

Lehmer's conjecture asserts that $\tau(p) \neq 0$, where $\tau$ is the Ramanujan $\tau$-function. This is equivalent to the assertion that $\tau(n) \neq 0$ for any $n$. A related problem is to find the distribution of primes $p$ for which $\tau(p) \equiv 0 \text{ } (\text{mod } p)$. These are open problems. However, the variant of estimating the number of integers $n$ for which $n$ and $\tau(n)$ do not have a non-trivial common factor is more amenable to study. More generally, let $f$ be a normalized eigenform for the Hecke operators of weight $k \geq 2$ and having rational integer Fourier coefficients $\{a(n)\}$. It is interesting to study the quantity $(n,a(n))$. It was proved by S. Gun and V. K. Murty (2009) that for Hecke eigenforms $f$ of weight $2$ with CM and integer coefficients $a(n)$ \begin{equation} \{ n \leq x \text { } | \text{ } (n,a(n))=1\} = \displaystyle\frac{(1+o(1)) U_f x}{\sqrt{\log x \log \log \log x}} \end{equation} for some constant $U_f$. We extend this result to higher weight forms. \\ We also show that \begin{equation} \{ n \leq x \ | (n,a(n)) \text{ \emph{is a prime}}\} \ll \displaystyle\frac{ x \log \log \log \log x}{\sqrt{\log x \log \log \log x}}. \end{equation}

Lehmer's conjecture asserts that $\tau(p) \neq 0$, where $\tau$ is the Ramanujan $\tau$-function. This is equivalent to the assertion that $\tau(n) \neq 0$ for any $n$. A related problem is to find the distribution of primes $p$ for which $\tau(p) \equiv 0 \text{ } (\text{mod } p)$. These are open problems. However, the variant of estimating the number of integers $n$ for which $n$ and $\tau(n)$ do not have a non-trivial common factor is more amenable to study. More generally, let $f$ be a normalized eigenform for the Hecke operators of weight $k \geq 2$ and having rational integer Fourier coefficients $\{a(n)\}$. It is interesting to study the quantity $(n,a(n))$. It was proved by S. Gun and V. K. Murty (2009) that for Hecke eigenforms $f$ of weight $2$ with CM and integer coefficients $a(n)$ \begin{equation} \{ n \leq x \text { } | \text{ } (n,a(n))=1\} = \displaystyle\frac{(1+o(1)) U_f x}{\sqrt{\log x \log \log \log x}} \end{equation} for some constant $U_f$. We extend this result to higher weight forms. \\ We also show that \begin{equation} \{ n \leq x \ | (n,a(n)) \text{ \emph{is a prime}}\} \ll \displaystyle\frac{ x \log \log \log \log x}{\sqrt{\log x \log \log \log x}}. \end{equation}

This thesis presents a new algorithm for computing the Hermite form of a polynomial matrix. Given a nonsingular n by n matrix A filled with degree d polynomials with coefficients from a field, the algorithm computes the Hermite form of A in expected number of field operations similar to that of matrix multiplication. The algorithm is randomized of the Las Vegas type.