This thesis deals with the existence and properties of certain types of covering spaces. It contains the discussion of a generalization of the notion of simple connectedness and several well-known theorems depending on this. / Thesis / Master of Science (MS)

In this thesis we build on the theory concerning the metric geometry of relatively hyperbolic and mapping class groups, especially with respect to the difficulty of embedding such groups into Banach spaces. In Chapter 3 (joint with Alessandro Sisto) we construct simple embeddings of closed graph manifold groups into a product of three metric trees, answering positively a conjecture of Smirnov concerning the Assouad-Nagata dimension of such spaces. Consequently, we obtain optimal embeddings of such spaces into certain Banach spaces. The ideas here have been extended to other closed three-manifolds and to higher dimensional analogues of graph manifolds. In Chapter 4 we give an explicit method of embedding relatively hyperbolic groups into certain Banach spaces, which yields optimal bounds on the compression exponent of such groups relative to their peripheral subgroups. From this we deduce that the fundamental group of every closed three-manifold has Hilbert compression exponent one. In Chapter 5 we prove that relatively hyperbolic spaces with a tree-graded quasi-isometry representative can be characterised by a relative version of Manning's bottleneck property. This applies to the Bestvina-Bromberg-Fujiwara quasi-trees of spaces, yielding an embedding of each mapping class group of a closed surface into a finite product of simplicial trees. From this we obtain explicit embeddings of mapping class groups into certain Banach spaces and deduce that these groups have finite Assouad-Nagata dimension. It also applies to relatively hyperbolic groups, proving that such groups have finite Assouad-Nagata dimension if and only if each peripheral subgroup does.

Cette thèse travaille sur l'agir collectif des encadrantes de la petite enfance dans les établissements d'accueil collectif du jeune enfant. Elle élabore une intelligibilité du processus du "travailler ensemble, à partir des conditions du surgissement et de sa mise en visibilité. L'enjeu de notre recherche est d'établir un dialogue entre l'éducation et le travail questionnant la créativité du travail collectif par le jeu des Sciences de l’Éducation et des concepts de l'approche ergologique et de la psychodynamique du travail. L'accent est mis sur la création de nouvelles manières de faire en situation d'activités festives. A partir de questionnaires et d'entretiens, il a été montré que lors de ces activités, les encadrantes nouent des liens de coopération avec l'équipe et avec d'autres acteurs. Dans ces moments-là, les nouvelles manières deviennent visibles et se traduisent entre autre, par un changement de regard sur l'autorité. Ces encadrantes reçoivent divers signes de reconnaissance. La convocation du concept d'"entité collective relativement pertinente" nous permet de mieux appréhender le passage de l'équipe à des collectifs à géométrie variable. Cette recherche met l'accent sur le rôle joué par l'encadrement intermédiaire et questionne la construction d'une nouvelle identité professionnelle qui pourrait être celle d'"accueillante éducative". / This thesis works on collective action framing early chilldhood in institutions care of young children.It develops an intelligible process of "working together", from the conditions of the emergence and development of its visibility.The aim of our research is to establish a dialogue between educatin and workby questioning the creativity of the collective work by the play of Educational Sciences and concepts of the approach ergologic and the psychodynamics of work.The emphasis is on creating new ways of doing in a situation of festive activities.From questionnaires and interwiews, it was shown that during these activities, flanking establish ties of cooperation with the team and with other actors.in these times, new ways to besome visible and result in another, for a change of outlook on authority.These boxes are various signs of recognition.The convening of the concept of "collective entity relatively relevant" allows us to better understand the transition team to collective variable geometry.This research focuses on the role played by middle management and questions the construction of a new professional identity to be that of "welcoming educational".

abstract: Before 1990s, the relationship between money supply and inflation was positively correlated, however, from 1990 onwards, the US and other major developed countries entered into a new financial era with a typical belief that hyper money supply coexisted with lower inflation. This phenomenon is called “the paradox of inflation”. Traditional theories cannot provide reasonable explanations of this new phenomenon. In my study, I have taken the linear filtering techniques which Lucas developed in 1980, and the recursive estimation method, as well as the chow test and F-test, and choose the data of the US, Britain, Japan, Germany, Euro area, BRICKs and some members of ASEAN, from 1960 to 2012, to study the relationship between annual rate of M2 growth and CPI inflation. The results show that in most sample developed and developing countries the positive correlation relationship between money supply and inflation began to weaken since the 1990s, and “the paradox of inflation” is now a common phenomenon. In my paper, I attempt to provide a new explanation of “the paradox of inflation”. I conjecture that, in the past two decades, some advanced countries were becoming a “relatively wealthy society”, which means that commodity supply as well as money supply is abundant. I state that the US is a “relatively wealthy society” and try to determine what features could mark a “relatively wealthy society”. I choose the credit growth rate of nonfinancial sectors and the ratio of dividends to investment to represent the production inclination of the business sector, and choose the income per capita and the GINI index to represent the consumption inclination of the resident sector. Then, through a semi parametric varying-coefficient regression model, I found that, in the US, when the credit growth of the business sector is under 5%, the ratio of dividends to investment is over 0.20, the per capita income is more than $30,000, and the GINI index is over 0.45, the country becomes a “relatively wealthy society”. Base on this new explanation, I can conclude “in the relatively wealthy society, inflation is no longer a monetary phenomenon; it is a wealth allocation phenomenon”. / Dissertation/Thesis / Doctoral Dissertation Business Administration 2015

Atualmente, faz-se necessário pensar em uma nova forma de tutela de direitos supraindividuais, tão em evidência na denominada sociedade de risco. Isto pois o Direito Penal vem sendo utilizado de forma desarrazoada e desproporcional, como principal instrumento para a coibição de condutas que, nem sempre, mostram adequação e necessidade de sua intervenção. Um dos maiores exemplos deste equívoco é encontrado no Direito do Consumidor, em que muitas condutas que sequer protegem bem jurídico com dignidade e carência penais são tuteladas por meio da via penal. É certo que este modo de atuar do Direito Penal somente o transforma em instrumento meramente simbólico e sem poder coercitivo real, o que faz com que, na realidade, os consumidores restem desprotegidos. Além disso, a utilização do Direito Penal como vala comum de todas as condutas que se pretende proteger, mas não se sabe de que modo, culmina por desconfigurá-lo e enfraquecê-lo. Não se deve dar à via penal mais encargos do que aqueles para os quais ela fora criada. Neste sentido, ao invés de utilizar o Direito Penal, modo mais gravoso de atuação social, como prima ratio na proteção dos direitos consumeristas, mostra-se mais razoável e inteligente a reestruturação do Direito Administrativo Sancionador, inserido no sistema de atuação denominado Terceira Via. As deficiências da via administrativa devem ser sanadas, de modo a torná-la suficiente para a proteção de grande parte dos bens jurídicos consumeristas. Assim, o Direito Administrativo Sancionador, fortalecido e marcado por sua independência, em variadas vertentes, passaria a ser a prima ratio na proteção dos direitos do consumidor, sendo que a via penal, como tradicionalmente foi concebida, seria a ultima ratio, sendo utilizada de forma fragmentária e subsidiária. Neste sentido, haveria o funcionamento relativamente independente, entre os dois instrumentos de atuação. Somente lançar-se-ia mão da via penal em situações em que o bem jurídico atingido demonstrasse ser digno da tutela penal, bem como demonstrasse haver a carência de sanção penal, como nos casos de fraude a medicamentos e a alimentos. Deste modo, as relações de consumo restariam mais e melhor protegidas, bem como haveria a mantença da função e do papel do Direito Penal, bem como de seus princípios constitucionais basilares. / Currently, it is necessary to consider a new form of guardianship rights supraindividuais, so evident in so-called \"risk society\". This is because the criminal law has been used so unreasonable and disproportionately, as the main instrument for the deterrence of conduct that do not always show the appropriateness and need for its intervention. One of the greatest examples of this mistake is found in Consumer Law, in which even many behaviors that protect the legal rights of consumers without criminal dignity and lack are tutored through the criminal route. It is true that this way of doing make the criminal law becomes an instrument merely symbolic and not real coercive power, which means that, in fact, a lot of consumers become unprotected. In addition, the use of criminal law as a common grave of all ducts to be protected, but do not know how, culminates by unconfigure and weaken it. Should not be given to the criminal case over charges than those for which it was created. In this sense, instead of using the criminal Law, that is the more serious way of social action, as prima ratio in protecting the consumers rights, seems more reasonable and intelligent restructuring of Administrative Law sanctioned, inserted in the actuation system called the Third Way. The deficiencies must be remedied administratively in order to make it sufficient for the protection of consumers interests. Thus, the Administrative Law sanctioned, marked by strengthened and its independence in various aspects, would be the best instrument to the protection of consumer rights, and the criminal case, as has traditionally been conceived, would be a last resort and is used in a fragmentary and subsidiary way. In this sense, there would be relatively independent operation between the two instruments of action. Only release would hand the means of criminal law in situations where the legal reached proved to be worthy of criminal protection, as well as having demonstrated a lack of criminal sanction, as in cases of fraud of medicines and food. In this way, consumer relations would remain more and better protected, and there would be a maintenance function and the role of criminal law, as well as their basic constitutional principles

Atualmente, faz-se necessário pensar em uma nova forma de tutela de direitos supraindividuais, tão em evidência na denominada sociedade de risco. Isto pois o Direito Penal vem sendo utilizado de forma desarrazoada e desproporcional, como principal instrumento para a coibição de condutas que, nem sempre, mostram adequação e necessidade de sua intervenção. Um dos maiores exemplos deste equívoco é encontrado no Direito do Consumidor, em que muitas condutas que sequer protegem bem jurídico com dignidade e carência penais são tuteladas por meio da via penal. É certo que este modo de atuar do Direito Penal somente o transforma em instrumento meramente simbólico e sem poder coercitivo real, o que faz com que, na realidade, os consumidores restem desprotegidos. Além disso, a utilização do Direito Penal como vala comum de todas as condutas que se pretende proteger, mas não se sabe de que modo, culmina por desconfigurá-lo e enfraquecê-lo. Não se deve dar à via penal mais encargos do que aqueles para os quais ela fora criada. Neste sentido, ao invés de utilizar o Direito Penal, modo mais gravoso de atuação social, como prima ratio na proteção dos direitos consumeristas, mostra-se mais razoável e inteligente a reestruturação do Direito Administrativo Sancionador, inserido no sistema de atuação denominado Terceira Via. As deficiências da via administrativa devem ser sanadas, de modo a torná-la suficiente para a proteção de grande parte dos bens jurídicos consumeristas. Assim, o Direito Administrativo Sancionador, fortalecido e marcado por sua independência, em variadas vertentes, passaria a ser a prima ratio na proteção dos direitos do consumidor, sendo que a via penal, como tradicionalmente foi concebida, seria a ultima ratio, sendo utilizada de forma fragmentária e subsidiária. Neste sentido, haveria o funcionamento relativamente independente, entre os dois instrumentos de atuação. Somente lançar-se-ia mão da via penal em situações em que o bem jurídico atingido demonstrasse ser digno da tutela penal, bem como demonstrasse haver a carência de sanção penal, como nos casos de fraude a medicamentos e a alimentos. Deste modo, as relações de consumo restariam mais e melhor protegidas, bem como haveria a mantença da função e do papel do Direito Penal, bem como de seus princípios constitucionais basilares. / Currently, it is necessary to consider a new form of guardianship rights supraindividuais, so evident in so-called \"risk society\". This is because the criminal law has been used so unreasonable and disproportionately, as the main instrument for the deterrence of conduct that do not always show the appropriateness and need for its intervention. One of the greatest examples of this mistake is found in Consumer Law, in which even many behaviors that protect the legal rights of consumers without criminal dignity and lack are tutored through the criminal route. It is true that this way of doing make the criminal law becomes an instrument merely symbolic and not real coercive power, which means that, in fact, a lot of consumers become unprotected. In addition, the use of criminal law as a common grave of all ducts to be protected, but do not know how, culminates by unconfigure and weaken it. Should not be given to the criminal case over charges than those for which it was created. In this sense, instead of using the criminal Law, that is the more serious way of social action, as prima ratio in protecting the consumers rights, seems more reasonable and intelligent restructuring of Administrative Law sanctioned, inserted in the actuation system called the Third Way. The deficiencies must be remedied administratively in order to make it sufficient for the protection of consumers interests. Thus, the Administrative Law sanctioned, marked by strengthened and its independence in various aspects, would be the best instrument to the protection of consumer rights, and the criminal case, as has traditionally been conceived, would be a last resort and is used in a fragmentary and subsidiary way. In this sense, there would be relatively independent operation between the two instruments of action. Only release would hand the means of criminal law in situations where the legal reached proved to be worthy of criminal protection, as well as having demonstrated a lack of criminal sanction, as in cases of fraud of medicines and food. In this way, consumer relations would remain more and better protected, and there would be a maintenance function and the role of criminal law, as well as their basic constitutional principles

Diferentes estratégias foram projetadas e desenvolvidas para sistemas de análises em fluxo envolvendo reações químicas relativamente lentas. O aprisionamento da zona da amostra na bobina de reação permite melhorias de sensibilidade em métodos espectrofotométricos em fluxo envolvendo reações catalíticas. Uma característica inerente a esta estratégia é que, de acordo com as baixas concentrações do analito de interesse esperadas nas amostras, pode-se explorar tanto a variação do tempo quanto da temperatura de aquecimento para o desenvolvimento reacional. Esta estratégia evita a geração de bolhas de ar quando temperaturas elevadas são empregadas. O aprisionamento da zona da amostra na bobina de reação em sistema de análises por injeção em fluxo foi aplicado à reação de oxidação do reagente Tiron por peróxido de hidrogênio catalisada por Co(II) para determinação espectrofotométrica de cobalto em gramíneas. O sistema apresentou boas figuras de mérito, tais como repetibilidade [d.p.r. = 0,8% para 0,6 ?g L-1 Co(II), (n = 5)], limite de detecção [0,046 ?g L-1 Co(II)], frequência de amostragem (19 h-1) e consumo de reagente (330 ?g de Tiron por determinação). Os dados de recuperação nas amostras de gramíneas digeridas variaram entre 97% e 113%. O aquecimento explorando o aprisionamento da zona da amostra na cubeta de detecção mostrou-se promissor para implementação de reações relativamente lentas sem a geração de bolhas de ar, e não houve liberação de bolhas mesmo sob a temperatura de 95ºC. Esta estratégia foi aplicada à determinação espectrofotométrica de vanádio em águas minerais envolvendo a oxidação de p-anisidina por bromato catalisada por V(V) e ativada por Tiron. Sob temperatura de 95ºC, boas figuras de mérito foram obtidas, tais como limite de detecção (0,1 ?g L-1), repetibilidade [d.p.r. = 2,1 % para 5,0 ?g L-1 (n = 10)], frequência analítica [25 h-1] e consumo de reagente (3,0 mg de p-anisidina por determinação). Adicionalmente, foi desenvolvido um procedimento analítico em fluxo para monitoramento dos resíduos de ametrina e atrazina potencialmente lixiviáveis em solos, envolvendo também um processo relativamente lento. Um sistema de análises por injeção sequencial foi utilizado para as etapas de dessorção dos herbicidas com solução 0,01 mol L-1 CaCl2 e concentração em fase sólida em linha, seguida da eluição dessas espécies para a separação em uma coluna monolítica C18 conectada a um cromatógrafo líquido por meio de uma válvula de seis vias. Os eluatos eram injetados no cromatógrafo por meio de uma alça de amostragem de 300 ?L conectada à válvula. Boas figuras de mérito foram obtidas, tais como fatores de enriquecimento de 10,2 e 18,8 e limites de detecção de 0,016 e 0,015 mg L-1 para ametrina e atrazina, respectivamente, limite de quantificação de 0,05 mg L-1 para ambos os herbicidas e repetibilidade estimada como 6,3% e 5,1% para 0,05 mg L-1 (n = 10) para ametrina e atrazina, respecivamente. Os dados de adição e recuperação dos herbicidas nos extratos de solos em condições de equilíbrio se situaram na faixa de 85 a 99% / Different approaches to analytical flow systems involving relatively slow chemical reactions were developed. Zone trapping inside the reaction coil enables sensitivity improvements in flow-based spectrophotometric procedures relying on catalytic reactions. The reaction time and/or temperature can be increased for the determination of analytes present in the samples at low concentrations. Exploitation of the strategy avoids the liberation of air bubbles in the analytical path when high temperatures are involved. A flow injection system with zone trapping in the main reactor was developed for the spectrophotometric determination of cobalt in grass samples exploiting the oxidation of Tiron by bromate catalised by Co(II). Good figures of merit such as repeatability [r.s.d. = 0.8% for 0.6 ?g L-1 Co(II), (n = 5)], detection limit [0.046 ?g L-1 Co(II)], sampling frequency [19 h-1] and reagent consumption (330 ?g of Tiron for determination) were attained. Recovery data in grass sample digests varied within 97% e 113%. Zone trapping inside the flow-through cuvette for exploiting high temperatures was also promising for relatively slow reactions, as no liberation of air bubbles was noted even for temperatures as high as 95oC. The approach was applied to the spectrophotometric determination of vanadium in mineral water samples relying on the oxidation of p-anisidine by bromate catalised by V(V) at 95ºC. Good analytical figures of merit such as repeatability [r.s.d. = 2.1% for 5.0 µg L-1 V(V), n = 10], detection limit [0.1 µg L-1 V(V), sample frequency (25 h-1) and reagent consumption (3.0 mg of p-anisidine per determination) were attained. Additionally, an analytical procedure to monitor the potentially leachable ametryn and atrazine residues in soil samples was proposed. As leaching is relatively slow, a sequential injection system was used to perform the herbicide extractions with 0.01 mol L-1 CaCl2 and in-line solid phase extraction followed by elution towards a C18 monolithic column connected to a liquid chomatograph. To this end, the outlet of the column was connected to a 300-µL six-port valve. Regarding analytical performance, enrichment factors and detection limits were 10.2 and 18.8 and 0.016 e 0.015 mg L-1 for ametryn and atrazine, respectively, quantification limits were 0.05 mg L-1 for both herbicides and good repeatability (r.s.d. = 6.3 and 5.1 % for 0.05 mg L-1 of ametryn and atrazine, n = 10) were attained. Recovery data in the soil extracts under equilibrium conditions were within 85 and 99%

Diferentes estratégias foram projetadas e desenvolvidas para sistemas de análises em fluxo envolvendo reações químicas relativamente lentas. O aprisionamento da zona da amostra na bobina de reação permite melhorias de sensibilidade em métodos espectrofotométricos em fluxo envolvendo reações catalíticas. Uma característica inerente a esta estratégia é que, de acordo com as baixas concentrações do analito de interesse esperadas nas amostras, pode-se explorar tanto a variação do tempo quanto da temperatura de aquecimento para o desenvolvimento reacional. Esta estratégia evita a geração de bolhas de ar quando temperaturas elevadas são empregadas. O aprisionamento da zona da amostra na bobina de reação em sistema de análises por injeção em fluxo foi aplicado à reação de oxidação do reagente Tiron por peróxido de hidrogênio catalisada por Co(II) para determinação espectrofotométrica de cobalto em gramíneas. O sistema apresentou boas figuras de mérito, tais como repetibilidade [d.p.r. = 0,8% para 0,6 ?g L-1 Co(II), (n = 5)], limite de detecção [0,046 ?g L-1 Co(II)], frequência de amostragem (19 h-1) e consumo de reagente (330 ?g de Tiron por determinação). Os dados de recuperação nas amostras de gramíneas digeridas variaram entre 97% e 113%. O aquecimento explorando o aprisionamento da zona da amostra na cubeta de detecção mostrou-se promissor para implementação de reações relativamente lentas sem a geração de bolhas de ar, e não houve liberação de bolhas mesmo sob a temperatura de 95ºC. Esta estratégia foi aplicada à determinação espectrofotométrica de vanádio em águas minerais envolvendo a oxidação de p-anisidina por bromato catalisada por V(V) e ativada por Tiron. Sob temperatura de 95ºC, boas figuras de mérito foram obtidas, tais como limite de detecção (0,1 ?g L-1), repetibilidade [d.p.r. = 2,1 % para 5,0 ?g L-1 (n = 10)], frequência analítica [25 h-1] e consumo de reagente (3,0 mg de p-anisidina por determinação). Adicionalmente, foi desenvolvido um procedimento analítico em fluxo para monitoramento dos resíduos de ametrina e atrazina potencialmente lixiviáveis em solos, envolvendo também um processo relativamente lento. Um sistema de análises por injeção sequencial foi utilizado para as etapas de dessorção dos herbicidas com solução 0,01 mol L-1 CaCl2 e concentração em fase sólida em linha, seguida da eluição dessas espécies para a separação em uma coluna monolítica C18 conectada a um cromatógrafo líquido por meio de uma válvula de seis vias. Os eluatos eram injetados no cromatógrafo por meio de uma alça de amostragem de 300 ?L conectada à válvula. Boas figuras de mérito foram obtidas, tais como fatores de enriquecimento de 10,2 e 18,8 e limites de detecção de 0,016 e 0,015 mg L-1 para ametrina e atrazina, respectivamente, limite de quantificação de 0,05 mg L-1 para ambos os herbicidas e repetibilidade estimada como 6,3% e 5,1% para 0,05 mg L-1 (n = 10) para ametrina e atrazina, respecivamente. Os dados de adição e recuperação dos herbicidas nos extratos de solos em condições de equilíbrio se situaram na faixa de 85 a 99% / Different approaches to analytical flow systems involving relatively slow chemical reactions were developed. Zone trapping inside the reaction coil enables sensitivity improvements in flow-based spectrophotometric procedures relying on catalytic reactions. The reaction time and/or temperature can be increased for the determination of analytes present in the samples at low concentrations. Exploitation of the strategy avoids the liberation of air bubbles in the analytical path when high temperatures are involved. A flow injection system with zone trapping in the main reactor was developed for the spectrophotometric determination of cobalt in grass samples exploiting the oxidation of Tiron by bromate catalised by Co(II). Good figures of merit such as repeatability [r.s.d. = 0.8% for 0.6 ?g L-1 Co(II), (n = 5)], detection limit [0.046 ?g L-1 Co(II)], sampling frequency [19 h-1] and reagent consumption (330 ?g of Tiron for determination) were attained. Recovery data in grass sample digests varied within 97% e 113%. Zone trapping inside the flow-through cuvette for exploiting high temperatures was also promising for relatively slow reactions, as no liberation of air bubbles was noted even for temperatures as high as 95oC. The approach was applied to the spectrophotometric determination of vanadium in mineral water samples relying on the oxidation of p-anisidine by bromate catalised by V(V) at 95ºC. Good analytical figures of merit such as repeatability [r.s.d. = 2.1% for 5.0 µg L-1 V(V), n = 10], detection limit [0.1 µg L-1 V(V), sample frequency (25 h-1) and reagent consumption (3.0 mg of p-anisidine per determination) were attained. Additionally, an analytical procedure to monitor the potentially leachable ametryn and atrazine residues in soil samples was proposed. As leaching is relatively slow, a sequential injection system was used to perform the herbicide extractions with 0.01 mol L-1 CaCl2 and in-line solid phase extraction followed by elution towards a C18 monolithic column connected to a liquid chomatograph. To this end, the outlet of the column was connected to a 300-µL six-port valve. Regarding analytical performance, enrichment factors and detection limits were 10.2 and 18.8 and 0.016 e 0.015 mg L-1 for ametryn and atrazine, respectively, quantification limits were 0.05 mg L-1 for both herbicides and good repeatability (r.s.d. = 6.3 and 5.1 % for 0.05 mg L-1 of ametryn and atrazine, n = 10) were attained. Recovery data in the soil extracts under equilibrium conditions were within 85 and 99%

In this master thesis we investigate completeness theorems in the framework of abstract algebraic logic. Our main interest lies in the completeness with respect to the so called relatively (finitely) subdirectly irreducible models. Notable part of the presented theory concerns the difference between finitary and infinitary logical systems. We focus on the well-known fact that the completeness theorem with respect to relatively (finitely) subdirectly irreducible models can be proven in general for all finitary logics and we discuss the possible of generalizing this theorem even to infinitary logics. We show that there are two interesting inter- mediate properties between this completeness and finitarity, namely (completely) intersection-prime extension properties. Based on these notions we define five classes of logics and propose a new hierarchy of finitary and infinitary logics. As a main contribution of this dissertation we present an example of a logic separat- ing some of these classes. Keywords: Abstract algebraic logic, completeness, relatively (finitely) sub- directly irreducible models, RSI-completeness, RFSI-completeness, (completely) intersection-prime extension property, IPEP, CIPEP.

La classe des graphes quasi-médians est une généralisation des graphes médians, ou de manière équivalente, des complexes cubiques CAT(0). L'objectif de cette thèse est d'introduire ces graphes dans le monde de la théorie géométrique des groupes. Dans un premier temps, nous étendons la notion d'hyperplan définie dans les complexes cubiques CAT(0), et nous montrons que la géométrie d'un graphe quasi-médian se réduit essentiellement à la combinatoire de ses hyperplans. Dans la deuxième partie de notre texte, qui est le cœur de la thèse, nous exploitons la structure particulière des hyperplans pour démontrer des résultats de combinaison. L'idée principale est que si un groupe agit d'une bonne manière sur un graphe quasi-médian de sorte que les stabilisateurs de cliques satisfont une certaine propriété P de courbure négative ou nulle, alors le groupe tout entier doit satisfaire P également. Les propriétés que nous considérons incluent : l'hyperbolicité (éventuellement relative), les compressions lp (équivariantes), la géométrie CAT(0) et la géométrie cubique. Finalement, la troisième et dernière partie de la thèse est consacrée à l'application des critères généraux démontrés précédemment à certaines classes de groupes particulières, incluant les produits graphés, les groupes de diagrammes introduits par Guba et Sapir, certains produits en couronne, et certains graphes de groupes. Les produits graphés constituent notre application la plus naturelle, où le lien entre le groupe et son graphe quasi-médian associé est particulièrement fort et explicite; en particulier, nous sommes capables de déterminer précisément quand un produit graphé est relativement hyperbolique. / The class of quasi-median graphs is a generalisation of median graphs, or equivalently of CAT(0) cube complexes. The purpose of this thesis is to introduce these graphs in geometric group theory. In the first part of our work, we extend the definition of hyperplanes from CAT(0) cube complexes, and we show that the geometry of a quasi-median graph essentially reduces to the combinatorics of its hyperplanes. In the second part, we exploit the specific structure of the hyperplanes to state combination results. The main idea is that if a group acts in a suitable way on a quasi-median graph so that clique-stabilisers satisfy some non-positively curved property P, then the whole group must satisfy P as well. The properties we are interested in are mainly (relative) hyperbolicity, (equivariant) lp-compressions, CAT(0)-ness and cubicality. In the third part, we apply our general criteria to several classes of groups, including graph products, Guba and Sapir's diagram products, some wreath products, and some graphs of groups. Graph products are our most natural examples, where the link between the group and its quasi-median graph is particularly strong and explicit; in particular, we are able to determine precisely when a graph product is relatively hyperbolic.