In this thesis I investigate the effects of positive and negative connections on social and organization networks, and the presence and role of homophily in networks of scientific collaborations and citations through the combination of methodologies borrowed from complexity science, statistics, and organizational sciences. In the first part of the thesis, I study the differences between patterns of positive and negative connections among individuals in two online signed social networks. Findings suggest that the sign of links in a social network shapes differently the network's topology: there is a positive correlation between the degrees of two nodes, when they share a positive connection, and a negative correlation when they share a negative connection. I then move my focus to the study of a dataset on start-ups from which I construct and analyse the competition and mobility networks among companies. Results show that the presence of competition has negative effects on the mobility of people among companies and on the success of the start-up ecosystem of a nation. Competitive behaviours may also emerge in science. Therefore, in the second part of this thesis, I focus on a database of all papers and authors who have published in the American Physical Society (APS) journals. Through the analysis of the citation network of the APS, I propose a method that aims to statistically validate the presence (or absence) of a citation between any two articles. Results show that homophily is an important mechanism behind the citation between articles: the more two articles share similar bibliographies, i.e., deal with similar arguments, the more likely there is a citation between them. In the last chapter, I investigate the presence of homophily in the APS data set, this time at the level of the collaboration network among sci- entists. Results show that homophily can be responsible in fostering collaboration, but above a given point the effect of similarity decreases the probability of a collaboration. Additionally, I propose a model that successfully reproduces the empirical findings.

Dans les sources de la période médiobyzantine, tous les moines n’apparaissaient pas en marge de la société. Certains se distinguaient très clairement par leurs incursions dans le monde ou dans les affaires terrestres. Ils pouvaient voyager, changer de monastère et surtout fréquenter des laïcs. Ils tissaient des liens avec le monde que les autorités avaient pourtant cherché à rompre, et pouvaient jouir d’une liberté que les lois et canons visaient à contrôler. Partant de ce constat, nous avons donc étudié précisément l’insertion des moines dans les réseaux de pouvoir. La première étape de ce travail de recherche fut de recenser les moines qui se distinguaient dans les sources par une intervention dans le monde terrestre. À partir de cette prosopographie, nous avons pu définir les contours de l’élite des moines, groupe qui se caractérisait par ses nombreuses interactions avec la haute aristocratie. La deuxième étape fut d’étudier les réseaux sociaux de ces moines. Nous avons décrit les modalités de leur insertion dans ces réseaux pour mettre en évidence les différentes logiques de construction et de transmission de leurs liens avec l’aristocratie. Nous avons surtout souligné l’importance des relations construites personnellement. Puis, nous avons analysé leur rôle dans ces réseaux pour démontrer qu’ils étaient sollicités et agissaient moins en tant que moines qu’en tant que membres de clans puissants. Ainsi, le rôle politique et social joué par les moines dans l’Empire byzantin ne pouvait s’expliquer que par leur intégration dans des réseaux sociaux puissants composés de membres de la haute aristocratie constantinopolitaine. / It is evident from Medieval Byzantine sources that not all monks lived on society’s margins. Some of them were highly implicated in worldly affairs. They could travel, move into other monasteries and visit lay people. They built up ties with people that the authorities had sought to break and could even enjoy freedoms that the laws and cannons aimed to control. Based on such observations, I have studied closely how monks could be embedded in political networks. Firstly, I have made a census of the Byzantine monks that distinguished themselves by their intervention in the lay world. Based on this prosopographical study, I have defined the contours of a monastic elite and shown that this was a group who interacted frequently with members of the high aristocracy. Consequently, I have studied in detail the social networks in which such monks belonged. I have attempted to describe and to underline the complexity of how monks build up their networks as well as inherit and possibly transmit them. I also have tried to distinguish their institutional bonds from their personal ones. In doing so, I have demonstrated that they acted and were solicited less often as monks and more often as members of powerful clans. Thus, I have concluded that the political and social role played by monks in the Byzantine Empire can only be explained by their integration in very powerful social networks.

Há anos, os estudos e avaliações de uso de produtos e/ou serviços disponibilizados em ambientes digitais ganharam importância, objetivando produtos e/ou serviços que ofereçam facilidade de uso e experiências agradáveis aos usuários destes. Ocorre, entretanto, que os usuários compreendem o mundo de maneira diferente e, consequentemente, suas necessidades de informação também são diferentes. Assim, partindo desta premissa, o principal objetivo desta pesquisa foi buscar a identificação e caracterização de princípios norteadores para análise do uso de sistemas de informação em ambientes digitais. A pesquisa foi conduzida com base nos estudos de redes de relacionamentos conceituais. Para tanto, utilizou-se uma infraestrutura (framework) conceitual e, partir das formas e comportamentos apresentados pelas conexões conceituais, foram observados e extraídos princípios para análise de uso dos sistemas informação. Trata-se, portanto, de uma pesquisa qualitativa, baseada no Método Bibliográfico e Levantamento (survey) em fóruns eletrônicos de discussão e, de modo complementar nas análises, foram utilizados métodos, técnicas e medidas dos estudos de redes, para identificação e caracterização dos princípios para avaliação de sistemas de informação. Como resultado, destaca-se que os princípios identificados representam elementos norteadores para a composição de parâmetros e criação de procedimentos que auxiliam na análise dos usos de sistemas de informação em geral. Não se trata de substituição dos métodos e técnicas amplamente utilizados nas áreas de Interface Humano Computador (IHC), Usabilidade, Análise de Sistemas e/ou Engenharia de Requisitos, contudo, os referidos princípios representam contribuições ao estudo das interações entre pessoas e sistemas de informação, considerando-se os relacionamentos entre os conceitos que estas pessoas ativam e/ou mobilizam para interpretar estes contextos de uso. / For years, studies and evaluations of the use of products and / or services made available in digital environments have gained importance, aiming products and / or services that offer ease of use and pleasant experiences to users of these. It occurs, however, that users understand the world differently and therefore their information needs are also different. Thus, based on this premise, the main objective of this research was to identify and characterize guiding principles for the analysis of the use of information systems in digital environments. The research was conducted based on the studies of networks of conceptual relationships. For that, a conceptual framework was used and, from the forms and behaviors presented by the conceptual connections, principles were observed and extracted for analysis of the use of information systems. It is therefore a qualitative research, based on the Bibliographic Method and Survey in electronic discussion forums and, in a complementary way in the analyzes, were used methods, techniques and measures of the networks studies, for identification and characterization of the Principles for evaluation of information systems. As a result, it is highlighted that the identified principles represent guiding elements for the composition of parameters and creation of procedures that help in the analysis of the uses of information systems in general. It is not a question of replacing the widely used methods and techniques in the areas of Computer Human Interface (IHC), Usability, Systems Analysis and / or Requirements Engineering, however, these principles represent contributions to the study of the interactions between people and information systems , Considering the relationships between the concepts that these people activate and / or mobilize to interpret these contexts of use.

Há anos, os estudos e avaliações de uso de produtos e/ou serviços disponibilizados em ambientes digitais ganharam importância, objetivando produtos e/ou serviços que ofereçam facilidade de uso e experiências agradáveis aos usuários destes. Ocorre, entretanto, que os usuários compreendem o mundo de maneira diferente e, consequentemente, suas necessidades de informação também são diferentes. Assim, partindo desta premissa, o principal objetivo desta pesquisa foi buscar a identificação e caracterização de princípios norteadores para análise do uso de sistemas de informação em ambientes digitais. A pesquisa foi conduzida com base nos estudos de redes de relacionamentos conceituais. Para tanto, utilizou-se uma infraestrutura (framework) conceitual e, partir das formas e comportamentos apresentados pelas conexões conceituais, foram observados e extraídos princípios para análise de uso dos sistemas informação. Trata-se, portanto, de uma pesquisa qualitativa, baseada no Método Bibliográfico e Levantamento (survey) em fóruns eletrônicos de discussão e, de modo complementar nas análises, foram utilizados métodos, técnicas e medidas dos estudos de redes, para identificação e caracterização dos princípios para avaliação de sistemas de informação. Como resultado, destaca-se que os princípios identificados representam elementos norteadores para a composição de parâmetros e criação de procedimentos que auxiliam na análise dos usos de sistemas de informação em geral. Não se trata de substituição dos métodos e técnicas amplamente utilizados nas áreas de Interface Humano Computador (IHC), Usabilidade, Análise de Sistemas e/ou Engenharia de Requisitos, contudo, os referidos princípios representam contribuições ao estudo das interações entre pessoas e sistemas de informação, considerando-se os relacionamentos entre os conceitos que estas pessoas ativam e/ou mobilizam para interpretar estes contextos de uso. / For years, studies and evaluations of the use of products and / or services made available in digital environments have gained importance, aiming products and / or services that offer ease of use and pleasant experiences to users of these. It occurs, however, that users understand the world differently and therefore their information needs are also different. Thus, based on this premise, the main objective of this research was to identify and characterize guiding principles for the analysis of the use of information systems in digital environments. The research was conducted based on the studies of networks of conceptual relationships. For that, a conceptual framework was used and, from the forms and behaviors presented by the conceptual connections, principles were observed and extracted for analysis of the use of information systems. It is therefore a qualitative research, based on the Bibliographic Method and Survey in electronic discussion forums and, in a complementary way in the analyzes, were used methods, techniques and measures of the networks studies, for identification and characterization of the Principles for evaluation of information systems. As a result, it is highlighted that the identified principles represent guiding elements for the composition of parameters and creation of procedures that help in the analysis of the uses of information systems in general. It is not a question of replacing the widely used methods and techniques in the areas of Computer Human Interface (IHC), Usability, Systems Analysis and / or Requirements Engineering, however, these principles represent contributions to the study of the interactions between people and information systems , Considering the relationships between the concepts that these people activate and / or mobilize to interpret these contexts of use.

Uppsala University Library owns eight volumes of manuscripts attributed to the academy equerry Johan Leven Ekelund (c.1701−1775). In this thesis, I apply methods from the field of material culture studies in order to establish which of the volumes that formed the donation from Leven to the library mentioned in his will. By mapping certain markers such as places, names and dates I am able to identify to some extent where Leven gained his practical skills and which writers influenced him. By analysing the texts, I draw the conclusion that the manuscripts can be divided into groups aimed for different audiences. Some of them fit in an utilitarian context, some of them aim to give riding and horsemanship scientific legitimacy. Some are aimed for a narrow circle of peers, connaisseurs of the art of riding. By examining Leven’s networks, I seek to shed light on whether he wrote in order to further his career. My conclusion is that in that case, Leven’s main focus was probably to help his son, who had a remarkably successful career as a physician after the death of his father. / <p>Orcid nr: 0000-0002-8791-4109</p>