Mathematical modeling of spreading processes have been largely studied in the literature, and its presented a boom in the past few years. This is a fundamental task on the understanding and prediction of real spreading processes on top of a population and are subject to many structural and dynamical constraints. Aiming at a better understanding of this processes, we focused in two task: the modeling and the analysis of both dynamical and structural aspects of these processes. Initially, we proposed a new and general model that unifies epidemic and rumor spreading. Besides, regarding the analysis of these processes, we extended the classical formalism to multilayer networks, in which the theory was lacking. Interestingly, this study opened up new challenges concerning the understanding of multilayer networks. More specifically, regarding their spectral properties. In this thesis, we analyzed such processes on top of single and multilayer networks. Thus, throughout our analysis, we followed three complementary approaches: (i) analytical, (ii) numerical and (iii) simulations, mainly Monte Carlo simulations. Our main results are: (i) a new unifying model, enabling us to model and understand spreading processes on large systems, (ii) characterization of new phenomena on multilayer networks, such as layer-wise localization and the barrier effect and (iii) an spectral analysis of multilayer systems, suggesting a universal parameter and proposing a new analytical tool for its analysis. Our contributions enable further research on modeling of spreading processes, also emphasizing the importance of considering the complete multilayer structure instead of any coarse-graining. Additionally, it can be directly applied on the prediction and modeling real processes. Thus, aside from the theoretical interest and its mathematical implications, it also presents important social impact. / A modelagem matemática dos processos de disseminação tem sido amplamente estudada na literatura, sendo que o seu estudo apresentou um boom nos últimos anos. Esta é uma tarefa fundamental na compreensão e previsão de epidemias reais e propagação de rumores numa população, ademais, estas estão sujeitas a muitas restrições estruturais e dinâmicas. Com o objetivo de entender melhor esses processos, nos concentramos em duas tarefas: a de modelagem e a de análise de aspectos dinâmicos e estruturais. No primeiro, propomos um modelo novo e geral que une a epidemia e propagação de rumores. Também, no que diz respeito à análise desses processos, estendemos o formalismo clássico às redes multicamadas, onde tal teoria era inexistente. Curiosamente, este estudo abriu novos desafios relacionados à compreensão de redes multicamadas, mais especificamente em relação às suas propriedades espectrais. Nessa tese, analisamos esses processos em redes de uma e múltiplas camadas. Ao longo de nossas análises seguimos três abordagens complementares: (i) análises analíticas, (ii) experimentos numéricos e (iii) simulações de Monte Carlo. Assim, nossos principais resultados são: (i) um novo modelo que unifica as dinâmicas de rumor e epidemias, nos permitindo modelar e entender tais processos em grandes sistemas, (ii) caracterização de novos fenômenos em redes multicamadas, como a localização em camadas e o efeito barreira e (iii) uma análise espectral de sistemas multicamadas, sugerindo um parâmetro de escala universal e propondo uma nova ferramenta analítica para sua análise. Nossas contribuições permitem que novas pesquisas sobre modelagem de processos de propagação, enfatizando também a importância de se considerar a estrutura multicamada. Dessa forma, as nossas contribuições podem ser diretamente aplicadas à predição e modelagem de processos reais. Além do interesse teórico e matemático, nosso trabalho também apresenta implicações sociais importantes.

Submitted by (ana.araujo@ufrpe.br) on 2016-08-12T14:04:00Z No. of bitstreams: 1 Rosangela Silveira do Nascimento.pdf: 1012353 bytes, checksum: b5f0d139481ab0bfdd6a1f689175c1f6 (MD5) / Made available in DSpace on 2016-08-12T14:04:00Z (GMT). No. of bitstreams: 1 Rosangela Silveira do Nascimento.pdf: 1012353 bytes, checksum: b5f0d139481ab0bfdd6a1f689175c1f6 (MD5) Previous issue date: 2008-02-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In the present work we analyze the dynamics of electrical cortical activity during the phenomenon of spreading depression (DA) and during the periods before and after this phenomenon. The characteristic of DA is reduced amplitude of spontaneous electrical activity that occurs in neural tissue after the application of stimulus that can be electrical, chemical, mechanical, luminous etc. In order to study properties of time series of electrical cortical activity recorded by ECoG (electrocortiogram) before,during and after DA, we apply Detrended Fluctuation Analysis(DFA). This method is designed to quantify long term correlations (memory) in temporal series such ECoG register. The method was successfully applied in studies of DNA sequences and non-stationary time series as heart rate variability, stride intervals, financial time series etc. The application of DFA results in scaling exponentα that quantifies correlation properties of nonlinear dynamical systems. This experiment indicates if temporal series posses long term correlations. In this work we calculate exponent α for different intervals: control (before the stimulus), after the stimulus, during the avalanche, during DA and after DA for two experimental groups of rats, nourished and malnourished. For both experimental groups the values of exponent α indicates persistent behavior for all intervals except during the avalanche in which correlations degrade. The presence of long term correlations in physiological time series observed in healthy organisms represents complexity that guaranties the organism’s adaptability to stress and disease. The absence of correlations during the avalanche indicates the loss of this complexity. Non-parametric Wilcoxon test was used to compare mean values of exponents α for all intervals of analyzed time series. In cases of nourished rats, the mean values ofα are significantly different for control, stimulus, avalanche, DA and after-DA intervals. Wilcoxon test was also used to compare mean values of α for corresponding intervals for the two experimental groups. The result is significant difference in mean values of α for control, stimulus avalanche, DA and after DA intervals between two experimental groups. The hypothesis that α =0.5 for avalanche intervals was not rejected by test, confirming the loss of correlations in this phase. Comparison of mean values of α for different intervals (control, stimulus, DA and after DA) with avalanche using the Wilcoxon test results in significant difference between two groups. / O presente estudo se propõe a analisar a dinâmica da atividade elétrica cortical durante o fenômeno da depressão alastrante (DA) e nos períodos que antecede e sucede o fenomêno. A DA é caracterizada pela redução da amplitude da atividade elétrica espontânea que ocorre no tecido neural, após a aplicação de um estímulo de natureza elétrica, química, mecânica, luminosa e outros. Visando estudar o comportamento da série temporal da atividade elétrica cortical, registrada no ECoG (eletrocorticograma), durante a DA e nos períodos que precede e sucede o fenômeno, foi aplicado o método do DFA (Detrended Fluctuation Analysis). Este método permite quantificar a existência de correlação de longo alcance (memória) numa série temporal, como é o caso do registro do ECoG. Anteriormente, o método foi aplicado em seqüências de DNA e no estudo de séries temporais não estacionárias, tais como, dinâmica da variabilidade cardíaca, flutuações de eletroencefalograma de humanos, intervalos entre passos sucessivos de humanos, séries econômicas e outros. A aplicação do DFA numa série temporal permite a determinação de um expoente de escalonamento α, que pode contribuir para a compreensão das propriedades dos sistemas dinâmicos não lineares. Este expoenteα revela se a série temporal apresenta correlação de longo alcance ou não. Neste trabalho os expoentes α foram calculados nas fases de controle, estímulo, avalanche, DA e após a DA para o ECoG, em dois grupos experimentais, ratos nutridos e ratos desnutridos. Em ambos os grupos experimentais, os valores obtidos para o expoente de escalonamento α denotam que a série temporal do ECoG apresenta correlação persistente (comportamento da série no presente se mantém no futuro) em todas as fases do processo com exceção da avalanche, período no qual ocorre perda de correlação. A presença de correlação de longo alcance numa série temporal biológica é uma resposta sempre observada em organismos saudáveis cuja complexidade do sinal registrado garante a adaptabilidade do organismo a situações de estresse e/ou distúrbios. Enquanto a ausência de correlação, observada na avalanche, indica a perda de propriedades fractais nos sistemas fisiológicos. O uso do método não-paramétrico de Wilcoxon, para comparar os valores médios dos expoentes α obtidos para o grupo de animais nutrido, durante as fases de controle, estimulação, DA, após DA, revelou que essas diferentes fasesdiferem significativamente. Os valores médios dos expoentes α obtidos para o grupo de animais desnutrido, durante as fases de controle, estimulação, DA, após DA, também não foram significativamente diferentes, quando comparados pelo método de Wilcoxon. Na comparação dos valores médios de α nas fases de controle, estimulação, DA, após DA entre os dois grupos de animais (nutrido e desnutrido) o teste de Wilcoxon revelou que as médias dos expoentes α em cada fase para os animais nutridos diferem significativamente daquelas obtidas para os animais desnutridos. Na avalanche a hipótese de que o expoente α é igual a 0,5, não foi rejeitada pelo teste de Wilcoxon, ou seja, o teste confirmou a perda de correlação nessa fase. Na comparação entre as médias dos expoentes α nos diferentes intervalos (controle, estimulação, DA, após DA) com o valor do expoente α na avalanche, o teste de Wilcoxon acusou diferença significativa tanto no grupo dos nutridos como no grupo dos desnutridos.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2016-12-01T12:26:58Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Tese Mariana Barros.pdf: 1911747 bytes, checksum: f5c0832d347da9436db27522938984b9 (MD5) / Made available in DSpace on 2016-12-01T12:26:59Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Tese Mariana Barros.pdf: 1911747 bytes, checksum: f5c0832d347da9436db27522938984b9 (MD5) Previous issue date: 2016-02-26 / CAPES / A nutrição no início da vida e o exercício físico podem alterar a excitabilidade cerebral, interferindo em processos de desenvolvimento e em parâmetros eletrofisiológicos. A depressão alastrante cortical (DAC) é um fenômeno relacionado com a excitabilidade cerebral. Em estudos anteriores, demonstramos potenciação da atividade elétrica cortical espontânea (ECoG) após a DAC. Nesta tese investigou-se a influência das condições de lactação e do exercício de natação, no início da vida e na idade adulta, sobre essa potenciação. Ratos Wistar machos foram amamentados em ninhadas com 6 ou 12 filhotes (grupos L6 e L12). A natação, precoce e tardia, foi realizada entre 8-23 e 60-75 dias de vida, respectivamente. O ECoG foi registrado aos 90-120 dias. Com um algoritmo específico (software Matlab™), determinou-se a amplitude do ECoG. Diferenças intergrupos de peso corporal e encefálico (L12<L6) confirmaram a deficiência nutricional do grupo L12. Diferenças, no mesmo animal, entre as amplitudes do ECoG antes e depois da DAC confirmaram a potenciação pós-DAC. Um grupo que não sofreu DAC não apresentou potenciação do ECoG. A natação precoce reduziu, e a tardia aumentou, essa potenciação do ECoG. A deficiência nutricional (condição L12) atenuou esse efeito. Estes dados sugerem que “condição de lactação”, “exercício de natação” e “idade ao exercício” modulam a potenciação do ECoG. A relevância desses resultados na fisiopatologia de doenças neurológicas dependentes da excitabilidade cerebral, como enxaqueca com aura e epilepsia, merecem futura investigação. / Nutrition in early life and physical exercise can alter brain excitability, interfering with development processes and electrophysiological parameters. Cortical spreading depression (CSD) is a phenomenon related to brain excitability. In previous studies, we demonstrated spontaneous brain electrical activity (ECoG) potentiation after CSD. In this thesis investigated the influence of the lactation conditions and swimming exercise in early life and adulthood, on this potentiation. Male Wistar rats were suckled in litters with 6 or 12 pups (L6 and L12 groups). The swimming, early and late, was carried out between 8-23 and 60-75 days of age, respectively. The ECoG was recorded at 90-120 days. With a specific algorithm (software Matlab ™), we determined the amplitude of the ECoG. Intergroup differences in body- and brain- weight (L12 <L6) confirmed the nutritional deficiency of the L12 group. Differences, in the same animal, between ECoG amplitudes before and after the CSD confirmed the post-CSD potentiation. A group that did not suffer CSD displayed no ECoG potentiation. Early swimming reduced, and later increased, this ECoG potentiation. The nutritional deficiency (L12 condition) attenuated this effect. These data suggest that "lactation condition", "swimming exercise" and "age to exercise" modulate ECoG potentiation. The relevance of these findings in the pathophysiology of brain excitability-dependent neurological diseases, such as migraine with aura and epilepsy, deserve further investigation.

Orientador: Celso de Almeida / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-12T06:34:19Z (GMT). No. of bitstreams: 1 Mataveli_LuisOtavio_M.pdf: 877476 bytes, checksum: afc5fb9153e7311af03669d45d798a73 (MD5) Previous issue date: 2008 / Resumo: O desempenho dos sistemas de comunicação sem fio que utilizam a técnica de múltiplo acesso CDMA é limitado pela interferência. A proposição de um algoritmo de escolha de seqüências de espalhamento foi feita para buscar uma diminuição na interferência média do sistema. Nos padrões atuais, como CDMA2000 e WCDMA, não são definidos nenhum critério para escolha das seqüências. Por isso, nesta dissertação será analisado o desempenho do algoritmo de escolha de seqüências de espalhamento proposto anteriormente juntamente com o uso de códigos corretores de erro em canais com desvanecimento seletivo em freqüência. Será analisado o comportamento das seqüências Walsh, Gold e m-deslocadas. O algoritmo analisado apresenta bons resultados sem o uso de codificação, mas, como maneira de analisar um sistema mais próximo do real, serão utilizados os códigos convolucionais e turbo. Palavras-chave: Algoritmo de busca, sistemas CDMA, espalhamento espectral, códigos convolucionais, códigos turbo. / Abstract: The performance of wireless communication systems that use the multiple access code division technique, CDMA, is interference-limited. A sequence selection algorithm allows a reduction in the mean interference of the system. In the standards like CDMA2000 and WCDMA no algorithm is defined for choosing the sequences. For this reason, in this dissertation we evaluate the performance of the proposed spread sequences selection algorithm together with error correcting codes over frequency selective fading channels. It is analyzed the behavior of Walsh, Gold, and shifted-m sequences. The algorithm had shown good results without channel coding, but to analyze a system similar to a real one, convolutional and turbo codes are going to be used. Key words: Selection algorithm, CDMA systems, spread spectrum, convolutional codes, turbo codes. / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica

Orientador: Mónica Graciela Zoppi-Fontana / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Estudos da Linguagem / Made available in DSpace on 2018-08-22T16:31:21Z (GMT). No. of bitstreams: 1 Ormaneze_Fabiano_M.pdf: 2478633 bytes, checksum: 725c51fb16584ed0535fd3043aa7377d (MD5) Previous issue date: 2013 / Resumo: Este trabalho analisa a coleção "Grandes Cientistas Brasileiros", produzida pela revista Caros Amigos, entre dezembro de 2009 e novembro de 2010. A partir de Pêcheux (1969; 1975), Orlandi (1993, 1998, 2001, 2008 e 2009) e Foucault (1969, 1970), o objetivo é identificar a imagem de Ciência e de cientista presente nos textos, as condições de produção que lhe permitiram emergir e o modo como o interdiscurso se faz presente, com base nos efeitos de pré-construído. O estudo também teve como propósito verificar como a função-autor (ORLANDI, 1998) é exercida pela revista Caros Amigos e de que forma o projeto científico do Brasil (uma vez que a coletânea foi produzida com patrocínio do Ministério da Ciência e Tecnologia), a linha editorial da revista e as tradicionais práticas jornalísticas, como a ideia de objetividade, atuam como interdiscurso, ainda que num gênero que se estrutura a partir do Jornalismo Literário. Também foram estudadas as diferenças entre os discursos relativos às áreas de Ciências Humanas e de Ciências Naturais, como produtos da constituição de cada campo do conhecimento, bem como do já-dito sobre cada área, além da presença de imagens cristalizadas de cientistas, que se constituem como estereótipos em cada campo e nas diferenças entre homens e mulheres na Ciência. Esta análise se faz importante, uma vez que as biografias representam um gênero crescente no País e, embora haja diversos estudos sobre Jornalismo Científico, não foi encontrado nenhum trabalho que analisa a biografia como estratégia de divulgação científica. Ademais, textos biográficos costumam gerar identificação nos leitores e, por essa razão, também exercem o papel de serem modelos de Ciência e de cientista e, no caso da presente coleção, esse caráter modelar fica mais evidente, uma vez que a coletânea tinha como um de seus objetivos servir de material didático para escolas. A análise de dez das 24 biografias publicadas pela coletânea demonstrou não só a presença da percepção pública sobre ciência, do projeto científico nacional, dos paradigmas positivistas de Ciência e Jornalismo atuando como interdiscurso, além de lugares distintos e ideologicamente marcados para homens e mulheres na Ciência, mas também imagens diferenciadas sobre cientistas e o fazer Ciência nas áreas de Humanas e de Naturais / Abstract: This work analyzes the collection "Grandes Cientistas Brasileiros", a magazine Caros Amigos' production from December 2009 to November 2010. From Pêcheux (1969, 1975), Orlandi (1993, 1998, 2001, 2008) and Foucault (1969, 1970), the general objective is to identify science and scientists' images in the texts, the conditions of production and the forms of interdiscourse manifestation. The study has also verified how Caros Amigos exertes the author function (ORLANDI, 1998), how the scientific project in Brazil, the magazine's editorial line and the traditional journalistic practices have influenced the discourse. The ideas of objectivity and truth are given as examples of traditional journalistic practice. The idea of objectivity acts as interdiscourse, even in a genre like in biographies, from Literary Journalism. The work has also studied the differences between the interdiscourse used about the areas of Humanities and Natural Sciences, as products of each field of knowledge, and the presence of stereotype of scientist. The differences between men and women in the discourse about science are also studied. This analysis is important, since biographies represent a genre that is growing in numbers of publications in Brazil and there are not works about biographies as a strategy for science communication. Biographical texts usually generate the identification of readers and, therefore, also play the role Science and scientist models. In case of collection, this model has become more evident, because the collection is used in schools. The study out of ten of the 24 biographies published by the collection has revealed the presence of the public perception of science, the national scientific project, the positivist paradigm of Science and Journalism as interdiscourse, different positions and ideologically marked for men and women in Science and different images of scientists and Science in Humanities ans Natural areas / Mestrado / Divulgação Científica e Cultural / Mestre em Divulgação Científica e Cultural

This thesis is concerned with studying the behavior of a gossiping protocol in the specific sense meant by Ericsson; in the following pages I’ll introduce a Markov process which models the spread of information in such systems. The results will be verified by means of a discreet-event simulation. / Gossiping Protocols, are inherently random in behavior.Nonetheless, they are not structure-less. Their asymptotic behavior when implemented in large scales is the matter of focus in this thesis. / Tel: +46709700505 Address: Pinnharvsgatan 3 E lgh 1202 43147 Mölndal Sweden

Since decades, drop impact has been a popular topic of investigation for the importance that such a phenomenology has in many different application domains.<p><p>So far, the effect of micro-particles on the drop impact morphology has been studied for a limited number of configurations and often modelled as a change in the viscosity of the carrier fluid. However, this approach has been found sometimes questionable. The aim of the thesis is to better understand the phenomenology associated with particle-laden drop impact such as the distribution of particles in splats and to extend the number of experimental configurations for particle-laden drop impact to occur.<p><p>The impact of millimetre-size particle-laden drops was investigated for hydrophilic and hydrophobic substrates. The drops were dispersions of water and round, spherical and nearly iso-dense hydrophobic particles with diameters around 200 µm and 500 µm. The substrates were transparent glass and polycarbonate plates. The impact was studied by side, bottom and angle view images in the range 148≤We≤744 and 7092≤Re≤16368.<p><p>The particles were found to suppress the appearance of singular jetting and drop partial rebound, and also cause early splashing, receding break-up and rupture. The occurrences of these phenomena depend on the impact velocity, particles’ diameter and volume fraction. The drops with 200 µm particles spread in two phases: fast and slow, caused by inertial and capillary forces, respectively. Also, the increase of volume fraction of 200 µm particle leads to a linear decrease of the maximum spreading factor caused by the inertia force on the hydrophilic and hydrophobic substrates. The comparison of our data and the existing ones for splashing led to the formulation of а new splashing criterion for particle-laden drops. The novel criterion improves upon current models in predicting the splashing threshold by introducing effect of particle volume fraction and particle wettability. The analysis of particle distribution showed that 200 µm particles formed atypical distributions in splats after the impact in contrast to 500 µm particles with random pattern. The 200 µm particles formed rings/disks and a crown-like structure on hydrophilic and hydrophobic substrates, respectively. These patterns were described by correlations.<p> / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

L’objectif de cette thèse de doctorat était de concevoir et développer un système permettant de caractériser les épandeurs et de prédire la répartition d’engrais au sol. Nous avons proposé deux approches basées respectivement sur l’imagerie 2D et 3D.Le système 2D a permis de déterminer les déplacements dans les images avec une très haute précision où 90% des estimations ont uniquement moins de 0,2 pixels d’erreur. Cependant cette précision n’était applicable que dans le cas d’un épandeur équipé de disques plats pour lequel la plupart des engrais est éjectée dans le plan horizontal parallèle au plan d’image de la camera. Par conséquent nous avons proposé un système d’imagerie 3D qui a permis de déterminer le mouvement 3D des engrais. Ainsi il peut être appliqué sur des épandeurs équipés de disque concave.Ce nouveau système peut : Caractériser les épandeurs dans un hall avec des conditions contrôlées ;Evaluer les effets de différents réglages des épandeurs ;Etudier le comportement des granulés et améliorer le modèle de vol balistique.Un tel système, moyennant quelques modifications, est envisagé à long terme sur un épandeur, permettant une gestion en temps réel de l’épandage et une rétroaction potentielle sur le fonctionnement de l’épandeur. [extrait du résumé] / The characterization of the fertilizer centrifugal spreading has become an important agriculture scientific issue in order to help farmers having a higher fertilization precision hence higher production efficiency. The ejected fertilizer grains are comparable to projectiles; hence, by using a ballistic flight model, predicting the spread pattern on the ground relies on an estimation of the trajectories and velocities of ejected grains. To estimate those parameters two approaches were proposed. First a two-steps zero mean normalized cross-correlation based algorithm for motion estimation was used to determine the displacement of the grains in the 2D images. The efficiency of this algorithm was evaluated by the mean of a grain images’ simulator. The results showed a high accuracy with an error of less than 0.2 pixels for 90% of the estimated velocities. However, the vertical ejection angle cannot be determined. This limits the use of the technique to spreaders equipped with flat disks where the trajectories of the grains will mostly be in a horizontal plane. This restriction was handled by the second approach. It is based on a 3D stereovision imaging system. A region based stereo matching algorithm with uniqueness and ordering constraints was introduced. It was validated using a grains’ stereo images simulator. 90% of the disparities were estimated with errors less than 2 pixels (around 1%). Moreover a 3D motion estimation algorithm was developed. It is based on an improvement of the previous 2D motion estimation algorithm combined with the estimated 3D coordinates. The efficiency of the whole system was approved via a comparison of its results and a real distribution obtained from a developed cylindrical collector.

La physique statistique, développée à l'origine pour décrire les systèmes thermodynamiques, a joué pendant les dernières décennies un rôle central dans la modélisation d'un ensemble incroyablement vaste et hétérogène de différents phénomènes qui ont lieu par exemple dans des systèmes sociaux, économiques ou biologiques. Un champ d'applications possibles aussi vaste a été trouvé aussi pour les réseaux, comme une grande variété de systèmes peut être décrite en termes d'éléments interconnectés. Après une partie introductive sur les thèmes abordés ainsi que sur le rôle de la modélisation abstraite dans la science, dans ce manuscrit seront décrites les nouvelles perspectives auxquelles on peut arriver en approchant d'une façon physico-statistique trois problèmes d'intérêt dans la théorie des réseaux: comment une certaine quantité peut se répandre de façon optimale sur un graphique, comment explorer un réseau et comment le reconstruire à partir d'un jeu d'informations partielles. Quelques remarques finales sur l'importance que ces thèmes préserveront dans les années à venir conclut le travail. / Statistical physics, originally developed to describe thermodynamic systems, has been playing for the last decades a central role in modelling an incredibly large and heterogeneous set of different phenomena taking for instance place on social, economical or biological systems. Such a vast field of possible applications has been found also for networks, as a huge variety of systems can be described in terms of interconnected elements. After an introductory part introducing these themes as well as the role of abstract modelling in science, in this dissertation it will be discussed how a statistical physics approach can lead to new insights as regards three problems of interest in network theory: how some quantity can be optimally spread on a graph, how to explore it and how to reconstruct it from partial information. Some final remarks on the importance such themes will likely preserve in the coming years conclude the work.

Cette thèse s’intéresse à l’exploitation de la sémantique de données pour la recherche exploratoire. La recherche exploratoire se réfère à des tâches de recherche qui sont très ouvertes, avec de multiples facettes, et itératives. Les données sémantiques et les données liées en particulier, offrent de nouvelles possibilités pour répondre à des requêtes de recherche et des besoins d’information complexes. Dans ce contexte, le nuage de données ouvertes liées (LOD) joue un rôle important en permettant des traitements de données avancés et des interactions innovantes. Nous détaillons un état de l’art de la recherche exploratoire sur les données liées. Puis nous proposons un algorithme de recherche exploratoire à base de données liées basé sur une recherche associative. A partir d’un algorithme de propagation d’activation nous proposons une nouvelle formule de diffusion optimisée pour les graphes typés. Nous proposons ensuite des formalisations supplémentaires de plusieurs modes d’interrogation avancée. Nous présentons également une architecture logicielle innovante basée sur deux choix de conception paradigmatiques. D’abord, les résultats doivent être calculés à la demande. Deuxièmement, les données sont consommées à distance à partir de services SPARQL distribués. Cela nous permet d’atteindre un niveau élevé de flexibilité en termes d’interrogation et de sélection des données. L’application Discovery Hub implémente ces résultats et les présente dans une interface optimisée pour l’exploration. Nous évaluons notre approche grâce à plusieurs campagnes avec des utilisateurs et nous ouvrons le débat sur de nouvelles façons d’évaluer les moteurs de recherche exploratoires. / The general topic of the thesis is web search. It focused on how to leverage the data semantics for exploratory search. Exploratory search refers to cognitive consuming search tasks that are open-ended, multi-faceted, and iterative like learning or topic investigation. Semantic data and linked data in particular offer new possibilities to solve complex search queries and information needs including exploratory search ones. In this context the linked open data cloud plays an important role by allowing advanced data processing and innovative interactions model elaboration. First, we detail a state-of-the-art review of linked data based exploratory search approaches and systems. Then we propose a linked data based exploratory search solution which is mainly based on an associative retrieval algorithm. We started from a spreading activation algorithm and proposed new diffusion formula optimized for typed graph. Starting from this formalization we proposed additional formalizations of several advanced querying modes in order to solve complex exploratory search needs. We also propose an innovative software architecture based on two paradigmatic design choices. First the results have to be computed at query-time. Second the data are consumed remotely from distant SPARQL endpoints. This allows us to reach a high level of flexibility in terms of querying and data selection. We specified, designed and evaluated the Discovery Hub web application that retrieves the results and present them in an interface optimized for exploration. We evaluate our approach thanks to several human evaluations and we open the discussion about new ways to evaluate exploratory search engines.