This thesis advances the theory of network specialization by characterizing the effect of network specialization on the eigenvectors of a network. We prove and provide explicit formulas for the eigenvectors of specialized graphs based on the eigenvectors of their parent graphs. The second portion of this thesis applies network specialization to learning problems. Our work focuses on training reservoir computers to mimic the Lorentz equations. We experiment with random graph, preferential attachment and small world topologies and demonstrate that the random removal of directed edges increases predictive capability of a reservoir topology. We then create a new network model by growing networks via targeted application of the specialization model. This is accomplished iteratively by selecting top preforming nodes within the reservoir computer and specializing them. Our generated topology out-preforms all other topologies on average.

Sustainable agriculture is one of the greatest challenges of our time. The pathways to sustainable agriculture consist of successive decisions for optimization that are often a matter of negotiation as resources are shared at all levels. This work essentially comprises three research projects with novel inter- and transdisciplinary methods to better understand and optimize agricultural water management under water scarcity conditions. In the first project, climate variability in the US Corn Belt was analyzed with a focus on deficit irrigation to find the optimal irrigation strategies for possible future changes. Two optimization methods for deficit irrigation showed positive water savings and yield increases in the predicted water scarcity scenarios. In the second project, a serious board game was developed and game sessions were carried out to simulate the complex decision space of actors in irrigated agriculture under climate and groundwater variability. The aim of the game was to understand how decisions are made by actors by observing the course of the game and linking these results to common behavioral theories implemented in socio-ecological models. In the third project, two frameworks based on innovation theories and agro-social-hydrological networks were developed and tested using agent-based models. In the first framework, centralized and decentralized irrigation management in Kansas US was compared to observe the development of collective action and the innovation diffusion of sustainable irrigation strategies. The second framework analyzed different decision processes to perform a sensitivity analysis of innovation implementation, groundwater abstraction and saline water intrusion in the Al Batinah region in Oman. Both frameworks allowed the evaluation of diverse behavior theories and decision-making parameters to find the optimal irrigation management and the impact of diverse socio-ecological policies. Inter- and Trans-disciplinary simulations of the interactions between human decisions and water systems, like the ones presented in here, improve the understanding of irrigation systems as anthropogenic landscapes in socio-economic and ecological contexts. The joint application of statistical and participatory approaches enables different but complementary perspectives that allow for a multidimensional analysis of irrigation strategies and water resources management.:Contents Declaration of Independent Work i Declaration of Conformity iii List of Publications v Acknowledgments ix Abstract xi Zusammenfassung xiii Contents xv List of Figures xvii List of Tables xix List of Abbreviations xxi 1. Introduction 3 1.1 Complex Networks Approach 3 1.2 Research Objectives 4 1.3 Thesis Outline 5 2. Literature Review 9 2.1 Agro-Hydrological Systems 9 2.1.1 Necessary Disciplinary Convergence 9 2.1.2 Multi-Objective Optimization Approaches 10 2.2 Optimization of Crop-Water Productivity 11 2.2.1 Irrigation Strategies 11 2.3 Sustainable Management of A-S-H Networks 12 2.3.1 Socio-Hydrology 13 2.3.2 Representation of Decision-Making Processes 14 2.3.3 Influence of Social Network 16 2.4 Socio-Hydrological Modeling Approaches 17 2.4.1 Game Theory Approach 17 2.4.2 Agent-Based Modeling 18 2.4.3 Participatory Modeling 20 2.5 Education for Sustainability 21 2.5.1 Experiential Learning 21 2.5.2 Serious Games 22 2.6 Summary of Research Gaps 24 3. Irrigation Optimization in The US Corn Belt 27 3.1 Agriculture in The Corn Belt 27 3.2 Historical and Prospective Climatic Variability 29 3.3 Simulated Irrigation Strategies 29 3.4 Optimal Irrigation Strategies Throughout the Corn Belt 30 3.5 Summary 31 4. Participatory Analysis of A-S-H Dynamics 35 4.1 Decision-Making Processes in A-S-H Networks 36 4.1.1 Collaborative and Participatory Data Collection Approaches 37 4.2 MAHIZ 38 4.2.1 Serious Game Development 38 4.2.2 Implementation of Serious Game Sessions 39 4.4 Evaluation of The Learning Process in Serious Games 40 4.5 Evaluation of Behavior Theories and Social Parameters 42 4.6 Summary 43 5 Robust Evaluation of Decision-Making Processes In A-S-H Networks 47 5.1 Innovation in A-S-H Networks 47 5.1.1 Multilevel Social Networks 48 5.1.2 Theoretical Framework of Developed ABMs 49 5.2 DInKA Model: Irrigation Expansion in Kansas, US 50 5.2.1 Robust Analysis of Innovation Diffusion 53 5.3 SAHIO Implementation: Coastal Agriculture in Oman 54 5.3.1 SAHIO Sensitivity analysis 58 5.4 Summary 60 6 Conclusions and Outlook 63 6.1 Limitations 64 6.2 Outlook 64 Bibliography 69 Appendix A. Implementation Code 79 A.1 DInKA 79 A.2 SAHIO 82 Appendix B. SAHIO’s Decision-Making Process for Each MoHuB Theory 91 Appendix C. SAHIO A-S-H Innovation Results 97 Appendix D. Selected Publications 101 D.1 Evaluation of Hydroclimatic Variability and Prospective Irrigation Strategies in the U.S. Corn Belt. 103 D.2 A Serious Board Game to Analyze Socio-Ecological Dynamics towards Collaboration in Agriculture. 121 D.2.1 MAHIZ Rulebook 140 D.2.2 MAHIZ Feedback Form 156

In geometry, various tools have been developed to explore the topology and other features of a manifold from its geometrical structure. Among the two most powerful ones are the analysis of the critical points of a function, or more generally, the closed orbits of a dynamical system defined on the manifold, and the evaluation of curvature inequalities. When any (nondegenerate) function has to have many critical points and with different indices, then the topology must be rich, and when certain curvature inequalities hold throughout the manifold, that constrains the topology. It has been observed that these principles also hold for metric spaces more general than Riemannian manifolds, and for instance also for graphs. This thesis represents a contribution to this program. We study the relation between the closed orbits of a dynamical system and the topology of a manifold or a simplicial complex via the approach of Floer. And we develop notions of Ricci curvature not only for graphs, but more generally for, possibly directed, hypergraphs, and we draw structural consequences from curvature inequalities. It includes methods that besides their theoretical importance can be used as powerful tools for data analysis. This thesis has two main parts; in the first part we have developed topological methods based on the dynamic of vector fields defined on smooth as well as discrete structures. In the second part, we concentrate on some curvature notions which already proved themselves as powerful measures for determining the local (and global) structures of smooth objects. Our main motivation here is to develop methods that are helpful for the analysis of complex networks. Many empirical networks incorporate higher-order relations between elements and therefore are naturally modeled as, possibly directed and/or weighted, hypergraphs, rather than merely as graphs. In order to develop a systematic tool for the statistical analysis of such hypergraphs, we propose a general definition of Ricci curvature on directed hypergraphs and explore the consequences of that definition. The definition generalizes Ollivier’s definition for graphs. It involves a carefully designed optimal transport problem between sets of vertices. We can then characterize various classes of hypergraphs by their curvature. In the last chapter, we show that our curvature notion is a powerful tool for determining complex local structures in a variety of real and random networks modeled as (directed) hypergraphs. Furthermore, it can nicely detect hyperloop structures; hyperloops are fundamental in some real networks such as chemical reactions as catalysts in such reactions are faithfully modeled as vertices of directed hyperloops. We see that the distribution of our curvature notion in real networks deviates from random models.

El uso de las redes para modelar sistemas complejos es creciente en multitud de ambitos. Son extremadamente utiles para representar interacciones entre genes, relaciones sociales, intercambio de informaci on en Internet o correlaciones entre precios de acciones burs atiles, por nombrar s olo algunos ejemplos. Analizando la estructura de estas redes, comprendiendo c omo interaccionan sus distintos elementos, podremos entender mejor c omo se comporta el sistema en su conjunto. A menudo, los nodos que conforman estas redes tienden a formar grupos altamente conectados. Esta propiedad es conocida como estructura de comunidades y esta tesis doctoral se ha centrado en el problema de c omo mejorar su detecci on y caracterizaci on. Como primer objetivo de este trabajo, se encuentra la generaci on de m etodos e cientes que permitan caracterizar las comunidades de una red y comprender su estructura. Segundo, pretendemos plantear una serie de pruebas donde testar dichos m etodos. Por ultimo, sugeriremos una medida estad stica que pretende ser capaz de evaluar correctamente la calidad de la estructura de comunidades de una red. Para llevar a cabo dichos objetivos, en primer lugar, se generan una serie de algoritmos capaces de transformar una red en un arbol jer arquico y, a partir de ah , determinar las comunidades que aparecen en ella. Por otro lado, se ha dise~nado un nuevo tipo de benchmarks para testar estos y otros algoritmos de detecci on de comunidades de forma e ciente. Por ultimo, y como parte m as importante de este trabajo, se demuestra que la estructura de comunidades de una red puede ser correctamente evaluada utilizando una medida basada en una distribuci on hipergeom etrica. Por tanto, la maximizaci on de este ndice, llamado Surprise, aparece como la estrategia id onea para obtener la partici on en comunidades optima de una red. Surprise ha mostrado un comportamiento excelente en todos los casos analizados, superando cualitativamente a cualquier otro m etodo anterior. De esta manera, aparece como la mejor medida propuesta para este n y los datos sugieren que podr a ser una estrategia optima para determinar la calidad de la estructura de comunidades en redes complejas. / Aldecoa García, R. (2013). Detección de comunidades en redes complejas [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/31638 / TESIS / Premios Extraordinarios de tesis doctorales

Die große Menge an Datensätzen, die in den letzten Jahren verfügbar wurden, hat es ermöglicht, sowohl menschlich-getriebene als auch biologische komplexe Systeme in einem beispiellosen Ausmaß empirisch zu untersuchen. Parallel dazu ist die Vorhersage und Kontrolle epidemischer Ausbrüche für Fragen der öffentlichen Gesundheit sehr wichtig geworden. In dieser Arbeit untersuchen wir einige wichtige Aspekte von Diffusionsphänomenen und Ausbreitungsprozeßen auf Netzwerken. Wir untersuchen drei verschiedene Probleme im Zusammenhang mit Ausbreitungsprozeßen im überkritischen Regime. Zunächst untersuchen wir die Reaktionsdiffusion auf Ensembles zufälliger Netzwerke, die durch die beobachteten Levy-Flugeigenschaften der menschlichen Mobilität charakterisiert sind. Das zweite Problem ist die Schätzung der Ankunftszeiten globaler Pandemien. Zu diesem Zweck leiten wir geeignete verborgene Geometrien netzgetriebener Streuprozeße, unter Nutzung der Random-Walk-Theorie, her und identifizieren diese. Durch die Definition von effective distances wird das Problem komplexer raumzeitlicher Muster auf einfache, homogene Wellenausbreitungsmuster reduziert. Drittens führen wir durch die Einbettung von Knoten in den verborgenen Raum, der durch effective distances im Netzwerk definiert ist, eine neuartige Netzwerkzentralität ein, die ViralRank genannt wird und quantifiziert, wie nahe ein Knoten, im Durchschnitt, den anderen Knoten im Netzwerk ist. Diese drei Studien bilden einen einheitlichen Rahmen zur Charakterisierung von Diffusions- und Ausbreitungsprozeßen, die sich auf komplexen Netzwerken allgemein abzeichnen, und bieten neue Ansätze für herausfordernde theoretische Probleme, die für die Bewertung künftiger Modelle verwendet werden können. / The large amount of datasets that became available in recent years has made it possible to empirically study humanly-driven, as well as biological complex systems to an unprecedented extent. In parallel, the prediction and control of epidemic outbreaks have become very important for public health issues. In this thesis, we investigate some important aspects of diffusion phenomena and spreading processes unfolding on networks. We study three different problems related to spreading processes in the supercritical regime. First, we study reaction-diffusion on ensembles of random networks characterized by the observed Levy-flight properties of human mobility. The second problem is the estimation of the arrival times of global pandemics. To this end, we derive and identify suitable hidden geometries of network-driven spreading processes, leveraging on random-walk theory. Through the definition of network effective distances, the problem of complex spatiotemporal patterns is reduced to simple, homogeneous wave propagation patterns. Third, by embedding nodes in the hidden space defined by network effective distances, we introduce a novel network centrality, called ViralRank, which quantifies how close a node is, on average, to the other nodes. These three studies constitute a unified framework to characterize diffusion and spreading processes unfolding on complex networks in very general settings, and provide new approaches to challenging theoretical problems that can be used to benchmark future models.

Die Methoden der Netzwerktheorie erfreuen sich wachsender Beliebtheit, da sie die Darstellung von komplexen Systemen durch Netzwerke erlauben. Diese werden nur mit einer Menge von Knoten erfasst, die durch Kanten verbunden werden. Derzeit verfügbare Methoden beschränken sich hauptsächlich auf die deskriptive Analyse der Netzwerkstruktur. In der hier vorliegenden Arbeit werden verschiedene Ansätze für die Inferenz über Prozessen in komplexen Netzwerken vorgestellt. Diese Prozesse beeinflussen messbare Größen in Netzwerkknoten und werden durch eine Menge von Zufallszahlen beschrieben. Alle vorgestellten Methoden sind durch praktische Anwendungen motiviert, wie die Übertragung von Lebensmittelinfektionen, die Verbreitung von Zugverspätungen, oder auch die Regulierung von genetischen Effekten. Zunächst wird ein allgemeines dynamisches Metapopulationsmodell für die Verbreitung von Lebensmittelinfektionen vorgestellt, welches die lokalen Infektionsdynamiken mit den netzwerkbasierten Transportwegen von kontaminierten Lebensmitteln zusammenführt. Dieses Modell ermöglicht die effiziente Simulationen verschiedener realistischer Lebensmittelinfektionsepidemien. Zweitens wird ein explorativer Ansatz zur Ursprungsbestimmung von Verbreitungsprozessen entwickelt. Auf Grundlage einer netzwerkbasierten Redefinition der geodätischen Distanz können komplexe Verbreitungsmuster in ein systematisches, kreisrundes Ausbreitungsschema projiziert werden. Dies gilt genau dann, wenn der Ursprungsnetzwerkknoten als Bezugspunkt gewählt wird. Die Methode wird erfolgreich auf den EHEC/HUS Epidemie 2011 in Deutschland angewandt. Die Ergebnisse legen nahe, dass die Methode die aufwändigen Standarduntersuchungen bei Lebensmittelinfektionsepidemien sinnvoll ergänzen kann. Zudem kann dieser explorative Ansatz zur Identifikation von Ursprungsverspätungen in Transportnetzwerken angewandt werden. Die Ergebnisse von umfangreichen Simulationsstudien mit verschiedenstensten Übertragungsmechanismen lassen auf eine allgemeine Anwendbarkeit des Ansatzes bei der Ursprungsbestimmung von Verbreitungsprozessen in vielfältigen Bereichen hoffen. Schließlich wird gezeigt, dass kernelbasierte Methoden eine Alternative für die statistische Analyse von Prozessen in Netzwerken darstellen können. Es wurde ein netzwerkbasierter Kern für den logistischen Kernel Machine Test entwickelt, welcher die nahtlose Integration von biologischem Wissen in die Analyse von Daten aus genomweiten Assoziationsstudien erlaubt. Die Methode wird erfolgreich bei der Analyse genetischer Ursachen für rheumatische Arthritis und Lungenkrebs getestet. Zusammenfassend machen die Ergebnisse der vorgestellten Methoden deutlich, dass die Netzwerk-theoretische Analyse von Verbreitungsprozessen einen wesentlichen Beitrag zur Beantwortung verschiedenster Fragestellungen in unterschiedlichen Anwendungen liefern kann.

Alors que les réseaux sociaux s'attachent à représenter des entités et les relations existant entre elles, les réseaux d'information intègrent également des attributs décrivant ces entités ; ce qui conduit à revisiter les méthodes d'analyse et de fouille de ces réseaux. Dans ces travaux, nous proposons des méthodes de classification des entités du réseau d'information qui exploitent d'une part les relations entre celles-ci et d'autre part les attributs les caractérisant. Nous nous penchons sur le cas des réseaux à vecteurs d'attributs, où les entités du réseau sont décrites par des vecteurs numériques. Ainsi nous proposons des approches basées sur des techniques reconnues pour chaque type d'information, faisant appel notamment à l'inertie pour la classification automatique et à la modularité de Newman et Girvan pour la détection de communautés. Nous évaluons nos propositions sur des réseaux issus de données bibliographiques, faisant usage en particulier d'information textuelle. Nous évaluons également nos approches face à diverses évolutions du réseau, notamment au regard d'une détérioration des informations des liens et des attributs, et nous caractérisons la robustesse de nos méthodes à celle-ci / While social networks use to represent entities and relationships between them, information networks also include attributes describing these entities, leading to review the analysis and mining methods for these networks. In this work, we discuss classification of the entities in an information network. Classification operate simultaneously on the relationships and on the attributes characterizing the entities. We look at the case of attributed graphs where entities are described by numerical feature vectors. We propose approaches based on proven classification techniques for each type of information, including the inertia for machine learning and Newman and Girvan's modularity for community detection. We evaluate our proposals on networks from bibliographic data, using textual information. We also evaluate our methods against various changes in the network, such as a deterioration of the relational or vector data, mesuring the robustness of our methods to them

Orientador: Andriana Susana Lopes de Oliveira Campanharo / Resumo: O Alzheimer é uma doença degenerativa do cérebro, incurável, que se agrava ao longo do tempo e atinge sobretudo pessoas entre 65 e 90 anos. A doença de Alzheimer (DA) é a principal demência entre os idosos e caracteriza-se por perda de funções cognitivas (memória, orientação, comportamento e linguagem), causada pela morte de células cerebrais. Atualmente, o diagnóstico definitivo da DA é feito por meio de um exame do tecido cerebral obtido por biopsia ou necropsia. Como somente após a morte do paciente pode-se ter a certeza que o mesmo tinha a DA, seu diagnóstico é feito utilizando exames, avaliações e excluindo-se outras causas de demência do seu histórico clínico. Em paralelo, estudos têm sido desenvolvidos para o estudo da DA com base de dados de EletroEncefaloGrama (EEG), e nesse sentido, diversos métodos de análise de dados de EEG têm sido propostos. Contudo, o estudo da DA por meio de dados de EEG é ainda um desafio, e consequentemente, faz-se necessária a preposição de novos métodos com o intuito de capturar informações adicionais da doença. Nesse sentido, utilizamos o mapeamento de uma série temporal em uma rede complexa no estudo da dinâmica de séries temporais de EEG de pacientes com a DA. Mais especificamente, na distinção entre envelhecimento e a DA e na identificação, dos estágios da DA em pacientes doentes a partir, das ondas cerebrais, alfa, beta, teta e delta. / Abstract: Alzheimer’s is a degerative brain disease, incurable, which aggravates over time and mainly affects people between 65 and 90 years. Alzheimer’s disease (AD) is the leading dementia among the elderly and is characterized by cognitive functions loss (memory, orientation, behavior and language) caused by the death of brain cells. Currently, confirmatory diagnosis of AD can only be made through the examination the brain tissue obtained by biopsy or necropsy. Considering that only after the patient’s death it is possible to be sure that he or she had AD, the approximate diagnosis is made excluding other causes of dementia. In parallel, studies have been developed for the study of AD with the use of Electroencephalography (EEG), and in this sense, several methods of EEG data analysis have been proposed. However, the study of AD with the use of EEG data is still a challenge, and consequently, it is necessary the proposal of new methods to capture additional information about the disease. In this sense, we used the map from a time series to a network, recently proposed by Campanharo, in a novel application, that is, in the study of EEG time series of patients with AD. More specifically, to distinguish aging and AD and to identify the stages of AD in unhealthy patients based on alpha, beta, theta and delta brain waves information. / Mestre

Ces dernières années, la puissance croissante des ordinateurs a permis à la fois de rassembler une quantité sans précédent de données décrivant la société moderne et d'envisager des outils numériques capables de s'attaquer à l'analyse et la modélisation les processus dynamiques qui se déroulent dans cette réalité complexe. Dans cette perspective, l'approche quantitative de la physique est un des catalyseurs de la croissance de nouveaux domaines interdisciplinaires visant à la compréhension des systèmes complexes techno-sociaux. Dans cette thèse, nous présentons dans cette thèse un cadre théorique et numérique pour simuler des épidémies de maladies infectieuses émergentes dans des contextes réalistes. Dans ce but, nous utilisons le rôle crucial de la mobilité des agents dans la diffusion des maladies infectieuses et nous nous appuyons sur l'étude des réseaux complexes pour gérer les ensembles de données à grande échelle décrivant les interconnexions de la population mondiale. En particulier, nous abordons deux différents problèmes de santé publique. Tout d'abord, nous considérons la propagation d’une épidémie au niveau mondial, et présentons un modèle de mobilité (GLEAM) conçu pour simuler la propagation d'une maladie de type grippal à l'échelle globale, en intégrant des données réelles de mobilité dans le monde entier. La dernière pandémie de grippe H1N1 2009 a démontré la nécessité de modèles mathématiques pour fournir des prévisions épidémiques et évaluer l'efficacité des politiques d'interventions. Dans cette perspective, nous présentons les résultats obtenus en temps réel pendant le déroulement de l'épidémie, ainsi qu'une analyse a posteriori portant sur les stratégies de lutte et sur la validation du modèle. Le deuxième problème que nous abordons est lié à la propagation de l'épidémie sur des systèmes en réseau dépendant du temps. En particulier, nous analysons des données décrivant les mouvements du bétail en Italie afin de caractériser les corrélations temporelles et les propriétés statistiques qui régissent ce système. Nous étudions ensuite la propagation d'une maladie infectieuse, en vue de caractériser la vulnérabilité du système et de concevoir des stratégies de contrôle. Ce travail est une approche interdisciplinaire qui combine les techniques de la physique statistique et de l'analyse des systèmes complexes dans le contexte de la mobilité des agents et de l'épidémiologie numérique. / In recent years, the increasing availability of computer power has enabled both to gather an unprecedented amount of data depicting the global interconnections of the modern society and to envision computational tools able to tackle the analysis and the modeling of dynamical processes unfolding on such a complex reality. In this perspective, the quantitative approach of Physics is catalyzing the growth of new interdisciplinary fields aimed at the understanding of complex techno-socio-ecological systems. By recognizing the crucial role of host mobility in the dissemination of infectious diseases and by leveraging on a network science approach to handle the large scale datasets describing the global interconnectivity, in this thesis we present a theoretical and computational framework to simulate epidemics of emerging infectious diseases in real settings. In particular we will tackle two different public health related issues. First, we present a Global Epidemic and Mobility model (GLEaM) that is designed to simulate the spreading of an influenza-like illness at the global scale integrating real world-wide mobility data. The 2009 H1N1 pandemic demonstrated the need of mathematical models to provide epidemic forecasts and to assess the effectiveness of different intervention policies. In this perspective we present the results achieved in real time during the unfolding of the epidemic and a posteriori analysis on travel related mitigation strategies and model validation. The second problem that we address is related to the epidemic spreading on evolving networked systems. In particular we analyze a detailed dataset of livestock movements in order to characterize the temporal correlations and the statistical properties governing the system. We then study an infectious disease spreading, in order to characterize the vulnerability of the system and to design novel control strategies. This work is an interdisciplinary approach that merges statistical physics techniques, complex and multiscale system analysis in the context of hosts mobility and computational epidemiology.

Les contacts face-à-face entre individus permettent de caractériser les réseaux sociaux et jouent un rôle prépondérant dans la compréhension des mécanismes de propagation des épidémies dans une population. De récentes avancées technologiques ont rendu possible l'acquisition de données précises sur les interactions humaines. Cette thèse présente, dans un premier temps, l'analyse de données de contacts collectées trois années de suite (2011, 2012 et 2013) dans un lycée français entre des étudiants de classes préparatoires. L'analyse a montré que la plupart des contacts se produisent entre étudiants de même classe et que les structures des contacts sont très similaires d'un jour sur l'autre. Dans un second temps, on compare différentes méthodes de collecte de données qui permettent d'obtenir des informations de nature différente (par exemple existence d'un contact face-à-face vs existence d'une amitié).L'utilisation de données rapportant les amitiés entre les étudiants ne permet pas d'obtenir une bonne estimation du réseau de contact (i.e., les amitiés ne correspondent pas forcément à des contacts face-à-face et vice versa) résultant en une sous-estimation du risque épidémique dans cette population.Dans la dernière partie, nous essayons de reproduire les biais provenant du réseau d'amitié en échantillonnant le réseau de contact. Ceci pourrait nous donner des indications sur comment compenser ces biais et comment utiliser des données incomplètes pour obtenir des prédictions fiables sur le risque épidémique. / Face-to-face contacts between individuals contribute to shape social networks and play an important role in determining how infectious diseases can spread within a population. Recently, technological advances have made it possible to obtain accurate data on human interactions.This thesis first presents the analysis of contact data collected three years in a row (2011, 2012 and 2013) in a French high school among students of "classes préparatoires" (i.e., studies taking place after high school and preparing for admission to higher education colleges). The analysis showed that most contacts occur within students of same classes and that contact patterns are very similar from one day to the next.Then, we compare different methods of data collection which allow to gather information of different nature (for instance existence of a face-to-face contact vs existence of a friendship).The use of data reporting friendships does not allow to obtain a good estimation of the contact network (i.e., friendships do not correspond necessarily to face-to-face contacts and vice versa) resulting in an underestimation of the epidemic risk in that population.Finally, we try to reproduce the biases coming from the friendship network by sampling the contact network. This might give hints on how to compensate these biases and how to use the information contained in incomplete data sets to obtain accurate predictions of the epidemic risk.