Les simulations numériques représentent un outil fondamental pour la conception et l'optimisation de procédés industriels de fabrication tels que le soudage. Malgré le développement impressionnant des méthodes numériques et des moyens de calcul utilisables, la complexité des procédés de fabrication et les nouvelles exigences des industries les plus avancées obligent à repenser les méthodes, les stratégies et les algorithmes de simulation disponibles. Dans cette thèse, de nouvelles méthodes numériques avec une approche de Réduction des Modèles sont proposées, une discipline consolidée qui a fourni des solutions étonnantes dans différentes applications, comme les procédés de fabrication avancés. Tout d'abord, différentes stratégies sont proposées pour la simulation efficace des procédés de soudage conventionnel, à cet effet, l'utilisation de Computational Vademecums est introduite. L’introduction de ces abaques numériques améliorent des méthodes telles que : les Éléments Finis Généralisés pour le calcul thermique, l'approche local-global pour le calcul mécanique et enfin, la construction directe des abaques numériques utiles pour la phase de pré-design. En second lieu, un solveur PGD efficace est présenté pour les simulations thermo-mécaniques de soudage par friction-malaxage. Cette thèse montre comment la réduction des modèles,en plus d'être une fin en soi, peut être un excellent ingrédient pour améliorer l'efficacité des méthodes numériques traditionnelles. Cela représente un grand intérêt pour l'industrie. / Numerical simulations represent a fundamental tool for the design and optimization of industrial manufacturing processes such as welding. Despite the impressive development of the numerical methods and the means of calculation, the complexity of these processes and the new demands of the more advanced industries make it necessary to rethink the available methods, strategies and simulation algorithms. In this thesis, we propose new numerical methods with a Model Order Reduction approach, a consolidated discipline that has provided surprising solutions indifferent applications, such as advanced manufacturing processes. First, different strategies for the efficient simulation of conventional welding processes are proposed. To this end, the use of Computational Vademecums is introduced for the improvement of methods such as the Generalized Finite Element for thermal calculation, the local-global approach for the mechanical calculation or the direct construction of vademecums useful for predesign phases. Then, an efficient PGD solver for thermomechanical simulations for friction stir welding is presented. This thesis shows how Model Reduction, besides being an end, it can be an excellent ingredient to improve the efficiency of traditional numerical methods, with great interest for the industry.

Frequentist model averaging has started to grow in popularity, and it is considered a good alternative to model selection. It has recently been applied favourably to gen- eralized linear models, where it has mainly been purposed to aid the prediction of probabilities. The performance of averaging estimators has largely been compared to that of models selected using AIC or BIC, without much discussion of model screening. In this paper, we study the performance of model averaging in classification problems, and evaluate performances with reference to a single prediction model tuned using cross-validation. We discuss the concept of model screening and suggest two methods of constructing a candidate model set; averaging over the models that make up the LASSO regularization path, and the so called LASSO-GLM hybrid. By means of a Monte Carlo simulation study, we conclude that model averaging does not necessarily offer any improvement in classification rates. In terms of risk, however, we see that both methods of model screening are efficient, and their errors are more stable than those achieved by the cross-validated model of comparison.

Soit $G$ un groupe connexe quasi-déployé défini sur un corps non-Archimédien de caractéristique nulle. On suppose que l'on se donne un sous-groupe parabolique standard de décomposition de Levi $P=MU$ ainsi qu'une représentation irréductible tempérée $\tau$ de $M$. Soit $\nu$ un élement dans le dual de l'algèbre de Lie de la composante déployée de $M$; on le choisit dans la chambre de Weyl positive. La représentation induite $I_P^G(\tau_{\nu})$ est appelée module standard. Quand la représentation $\tau$ est générique (pour un caractère non-dégénéré de $U$), i.e a un modèle de Whittaker, le module standard $I_P^G(\tau_{\nu})$ est également générique.Casselman et Shahidi ont conjecturé que l'unique sous-quotient générique apparaissait nécessairement comme sous-représentation dans le module standard $I_P^G(\tau_{\nu})$. Ceci a été démontrée dans le cas des groupes classiques $SO(2n+1), Sp(2n)$, et $SO(2n)$ quand $P$ est un sous-groupe parabolique maximal de $G$, par Hanzer en 2010.Dans notre travail, nous formulons et étudions ce problème dans le contexte plus général d'un groupe connexe quasi-déployé tel que les composantes irréductibles de $\Sigma_{\sigma}$ sont de type $A,B,C$ ou $D$.Dans la deuxième partie de cette thèse (en commun avec D.Prasad), nous prouvons d'abord qu'il n'existe pas de representation cuspidale du groupe quasi-déployé $\U_{2n}(F)$ qui soit distinguée par son sous-groupe $\Sp_{2n}(F)$ pour $F$ un corps local non-Archimédien. Nous prouvons ensuite le théorème équivalent pour un corps global: il n'existe pas de représentation cuspidale de $\U_{2n}(\A_k)$ qui ait une période symplectique non nulle pour $k$ un corps de nombres ou corps de fonctions. / Let $G$ be a quasi-split connected reductive group over a non-Archimedean local field $F$ of characteristic zero. We assume we are given a standard parabolic subgroup $P$ with Levi decomposition $P=MU$ as well as an irreducible, tempered representation $\tau$ of $M$. Let now $\nu$ be an element in the dual of the real Lie algebra of the split component of $M$; we take it in the positive Weyl chamber. The induced representation $I_P^G(\tau_{\nu})$ is called a standard module. When the representation $\tau$ is generic (for a non-degenerate character of $U$), i.e. has a Whittaker model, the standard module $I_P^G(\tau_{\nu})$ is also generic. Casselman and Shahidi have conjectured that the unique irreducible generic subquotient of a standard module $I_P^G(\tau_{\nu})$ is necessarily a subrepresentation. This conjecture known as the Generalized Injectivity Conjecture was proved for the classical groups $SO(2n+1), Sp(2n)$, and $SO(2n)$ for $P$ a maximal parabolic subgroup, by Hanzer in 2010.In our work, we formulate and study this problem for any quasi-split connected reductive group such that the irreducible components of $\Sigma_{\sigma}$ are of type $A,B,C$ or $D$. In the second part of this thesis (joint work with D.Prasad), we prove that there are no cuspidal representations of the quasi-split unitary groups $\U_{2n}(F)$ distinguished by $\Sp_{2n}(F)$ for $F$ a non-archimedean local field. We also prove the corresponding global theorem that there are no cuspidal representations of $\U_{2n}(\A_k)$ with nonzero period integral on $\Sp_{2n}(k) \backslash \Sp_{2n}(\A_k)$ for $k$ any number field or a function field.

Dynamische Programmierung (DP) ist eine Methode um Optimisierungsprobleme zu lösen. Hierbei wird das Problem in sich überlappende Teilprobleme unterteilt und eine optimale Lösung zu jedem der Teilprobleme berechnet. Diese werden dann wiederrum zur Gesamtlösung zusammengesetzt. Teillösungen werden in einer Tabelle gespeichert, sodass jede Teillösung nur einmal berechnet werden muss. So kann ein Suchraum exponentieller Größe in polynomieller Zeit durchsucht und eine optimale Lösung gefunden werden. Die dynamische Programmierung wurde 1952 von Bellman entwickelt und eine der ersten Anwendung war die Detektion von Tippfehlern beim Programmieren. DP Algorithmen werden oft und sehr vielschichtig in der Bioinformatik angewendet wie zum Beispiel beim Vergleich von Gensequenzen, Sequenzalignment genannt, oder der Vorhersage von Molekülstrukturen. Die Menge an Daten und somit auch deren Analyse steigt stetig an, weshalb neue und komplexere Datenstrukturen immer wichtiger werden. Ein Ziel ist es deswegen, DP Algorithmen zu entwickeln, die auf komplexeren Daten- strukturen als Strings angewendet werden können. Durch das Prinzip der algebraischen dynamischen Programmierung (ADP) können DP Algorithmen in kleinere Bestandteile zerlegt werden, die dann unabhängig voneinander weiterentwickelt und abgeändert werden können. Die Arbeit ist in zwei Teile gegliedert, wobei der erste Teil die theoretische Arbeit zur Entwicklung von Algorithmen der dynamischen Programmierung beinhaltet. Hierbei werden zuerst Prinzipien und Definitionen zur dynamischen Programmierung vorgestellt (Kapitel 2), um ein besseres Verständnis der darauffolgenden Kapitel zu gewährleisten. Der zweite Teil der Arbeit zeigt unterschiedliche bioinformatische Anwendungen von DP Algorithmen auf biologische Daten. In einem ersten Kapitel (Kapitel 5) werden Grundsätze biologischer Daten und Algorithmen vorgestellt, die dann in den weiteren Kapiteln benutzt werden.

Barrier trees are a convenient way of representing the structure of complex combinatorial landscapes over graphs. Here we generalize the concept of barrier trees to landscapes defined over general multi-parent search operators based on a suitable notion of topological connectedness that depends explicitly on the search operator. We show that in the case of recombination spaces, path-connectedness coincides with connectedness as defined by the mutation operator alone. In contrast, topological connectedness is more general and depends on the details of the recombination operators as well. Barrier trees can be meaningfully defined for both concepts of connectedness.

This study used content analysis to investigate the development of the concept of variables in middle grades mathematics textbooks during four eras of mathematics education in the United States (New Math, Back to Basics, Problem Solving, and the NCTM Standards era: 1957 – 2009). It also examined the nature of support that the curricula provide for teachers to enact variables ideas in the classroom. Findings revealed that each of the middle grades mathematics curricula examined used variables, but in varied proportions and levels of complexity. Formal definitions for variables were found in 11 of the 12 students’ editions examined. The characteristics of the definitions for variables found in the different curricula were, however, different from one another. The uses of variables as placeholders and as labels dominated the uses of variables in the mathematics curricula. The least used category of variables was as an abstract symbol. When examined in terms of the content areas, the use of variables as placeholders dominated Number and Operations, and Algebra contents. In Geometry, Measurement, and Data Analysis and Probability content areas, the use of variables as labels was predominant. Overall, the data did not reveal any systematic or drastic change in the treatment of variable ideas during the 50 year period within which this study is situated. There was however, a steady increase in the use of variables as varying quantities across grade levels, and the four eras of mathematics education in the United States. There were also some noticeable changes in the treatment of variable ideas found in Math Connects curriculum when compared to the treatment in the other three curricula. The data collected also supported the evidence of guidance provided to teachers in the respective curricula to enact variable ideas in the classroom. However, the amount of guidance identified was limited in the majority of the curricula. Limitations of the study, implications for curriculum and teacher development, as well as recommendations for future research are also presented.

Several models for predicting future customer profitability early into customer life-cycles in the property and casualty business are constructed and studied. The objective is to model risk at a customer level with input data available early into a private consumer’s lifespan. Two retained models, one using Generalized Linear Model another using a multilayer perceptron, a special form of Artificial Neural Network are evaluated using actual data. Numerical results show that differentiation on estimated future risk is most effective for customers with highest claim frequencies.

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Thesis advisor: Uzi Segal / The dissertation studies the property of transitivity in the social choice theory. I explain why we should care about transitivity in decision theory. I propose two social decision theories: redistribution regret and ranking regret, study their properties of transitivity, and discuss the possibility to find a best choice for the social planner. Additionally, in the joint work, we propose a general method to construct a consistent estimator given two parametric models, one of which could be incorrectly specified. In “Why Transitivity”, to explain behaviors violating transitivity, e.g., preference reversals, some models, like regret theory, salience theory were developed. However, these models naturally violate transitivity, which may not lead to a best choice for the decision maker. This paper discusses the consequences and the possible extensions to deal with it. In “Redistribution Regret and Transitivity”, a social planner wants to allocate resources, e.g., the government allocates fiscal revenue or parents distribute toys to children. The social planner cares about individuals' feelings, which depend both on their assigned resources, and on the alternatives they might have been assigned. As a result, there could be intransitive cycles. This paper shows that the preference orders are generally non-transitive but there are two exceptions: fixed total resource and one extremely sensitive individual, or only two individuals with the same non-linear individual regret function. In “Ranking Regret”, a social planner wants to rank people, e.g., assign airline passengers a boarding order. A natural ranking is to order people from most to least sensitive to their rank. But people's feelings can depend both on their assigned rank, and on the alternatives they might have been assigned. As a result, there may be no best ranking, due to intransitive cycles. This paper shows how to tell when a best ranking exists, and that when it exists, it is indeed the natural ranking. When this best does not exist, an alternative second-best group ranking strategy is proposed, which resembles actual airline boarding policies. In “Over-Identified Doubly Robust Identification and Estimation”, joint with Arthur Lewbel and Jinyoung Choi, we consider two parametric models. At least one is correctly specified, but we don't know which. Both models include a common vector of parameters. An estimator for this common parameter vector is called Doubly Robust (DR) if it's consistent no matter which model is correct. We provide a general technique for constructing DR estimators (assuming the models are over identified). Our Over-identified Doubly Robust (ODR) technique is a simple extension of the Generalized Method of Moments. We illustrate our ODR with a variety of models. Our empirical application is instrumental variables estimation, where either one of two instrument vectors might be invalid. / Thesis (PhD) — Boston College, 2021. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Economics.

Bakgrund: Psykisk ohälsa är idag ett vanligt hälsoproblem hos unga svenska kvinnor. Ett växande intresse finns även för den psykiska hälsan hos elitidrottare eftersom forskning har identifierat en rad idrottsspecifika stressorer som ökar risken för psykisk ohälsa. Self-efficacy är en annan faktor som har visats kunna påverka elitidrottarens idrottsliga prestation och är tillsammans med ett gott psykiskt mående viktigt för att elitidrottaren ska lyckas. Syfte: Att undersöka förekomst och grad av generaliserat ångestsyndrom (GAD) och self-efficacy (SE) till att nå idrottsspecifika mål hos unga svenska kvinnliga elitgymnaster samt dess korrelation. Metod: Studien är en tvärsnittsstudie med en kvantitativ ansats. Generaliserat ångestsyndrom mättes med en elektronisk version av GAD-7 och SE med General Self-Efficacy Scale (GSES). Deltagarna rekryterades genom ett icke slumpmässigt bekvämlighetsurval och datan analyserades i det statistiska dataprogrammet SPSS. Resultat: 48 deltagare rekryterades till studien och av dessa rapporterade 54,3 % någon grad av GAD. Deltagarna hade ett medianvärde på 29 poäng för SE till att nå idrottsspecifika mål. Det fanns en signifikant, svag och negativ korrelation mellan GAD och SE till att nå idrottsspecifika mål. Konklusion: Studiens resultat går i linje med tidigare forskning som visar att GAD är vanligt förekommande hos kvinnliga elitidrottare. Ett svagt negativt samband kunde visas mellan GAD och SE till att nå idrottsspecifika mål hos de unga, kvinnliga svenska elitgymnasterna. Dock behövs mer forskning på en större population rekryterade från ett slumpmässigt urval för att resultatet ska kunna generaliseras. / Background: Mental illness is a common health problem among young Swedish women. There is also a growing interest for the mental health of elite athletes as previous research has identified several sport-specific stressors that can increase the risk of mental illness. Self-efficacy is another factor that has been shown to affect athletic performance and is, as well as a good mental state, important for an elite athlete to succeed.  Aim: To investigate the prevalence and severity of generalized anxiety disorder (GAD) and self-efficacy (SE) to achieve sport-specific goals in young Swedish female elite gymnasts and its correlation. Methods: The study is a cross-sectional, non-randomized study with a quantitative approach. GAD was measured using an electronic version of GAD-7 Scale and SE with the General Self-Efficacy Scale (GSES). Results: 48 participants were recruited and out of these, 54,3% reported some degree of GAD. The participants had a median value of 29 points for SE to achieve sport-specific goals. There was a significant, weak and inverse correlation between GAD and SE to achieve sport-specific goals. Conclusion: The results of the study are in line with previous research that identifies GAD as a common health problem among female elite athletes. A significant, weak and inverse correlation could be shown between GAD and SE to achieve sport-specific goals. However, more research is needed on a larger population recruited from a randomized sample for the results to be generalized.