People choose to spend a large amount of their time on the internet these days, which has led to an increase in search engine marketing. It is a form of online marketing that displays the ads as organic and sponsored links and is considered less intrusive by internet users. However, internet users' low perceived credibility towards online marketing, in general, seems to be affecting their perception of the two links as well. There is currently a gap in knowledge regarding what factors affect internet users' perceived credibility towards organic and sponsored links. This was explored in this study to see what affects the users' perception and how it could be raised. The trustworthiness, expertise, and attractiveness factors in the source credibility theory were utilized and explored to see if they affected the internet users' perceived credibility towards the links. This was achieved through a quantitative study and by conducting two questionnaires with sample sizes of 140 respondents each. The findings of this study indicate that the three factors positively affect internet users' perceived credibility. By performing a t-test on the combined results from the two questionnaires, it was also evident that which type of link it is, organic or sponsored, plays a significant role in how the users perceive the link’s credibility. The organic links have a more positive effect on the users' perceived credibility and are viewed as more credible than the sponsored links, suggesting a bias towards the sponsored links.

Advances in structural systems that resist extreme loading such as earthquake forces are important in their ability to reduce damages, improve performance, increase resilience, and improve the reliability of structures. Buckling resistant shear panels can be used to form new structural systems, which have been shown in preliminary analysis to have improved hysteretic behavior including increased stiffness and energy dissipating ability. Both of these characteristics lead to reduced drifts during earthquakes, which in turn leads to a reduction of drift related structural and nonstructural damage. Shear links are being used for seismic energy dissipation in some structures. A promising type of fuse implemented in structures for seismic energy dissipation, and seismic load resistance consists of a steel plate with cutouts leaving various shaped shear links. During a severe earthquake, inelastic deformation and damage would be concentrated in the shear links that are part of replaceable structural fuses, while the other elements of the building remain in the elastic state. In this study, by identifying the issues associated with general fuses previously used in structures, the behavior of the links is investigated and procedures to improve the behavior of the links are explained. In this study, a promising type of hysteretic damper used for seismic energy dissipation of a steel plate with cutouts leaving butterfly-shaped links subjected to shear deformations. These links have been proposed more recently to better align bending capacity with the shape of the moment diagram by using a linearly varying width between larger ends and a smaller middle section. Butterfly-shaped links have been shown in previous tests to be capable of substantial ductility and energy dissipation, but can also be prone to lateral torsional buckling. The mathematical investigations are conducted to predict, explain and analyze the butterfly-shaped shear links behavior for use in seismic structural fuses. The ductile and brittle limit states identified based on the previous studies, are mathematically explained and prediction equations are proposed accordingly. Design methodologies are subsequently conceptualized for structural shear links to address shear yielding, flexural yielding and buckling limit states for a typical link subjected to shear loading to promote ductile deformation modes. The buckling resistant design of the links is described with the aid of differential equations governing the links' buckling behavior. The differential equations solution procedures are developed for a useful range of link geometries and the statistical analysis is conducted to propose an equation for critical buckling moment. Computational studies on the fuses are conducted with finite element analysis software. The computational modeling methodology is initially verified with laboratory tests. Two parametric computational studies were completed on butterfly-shaped links to study the effect of varying geometries on the shear yielding and flexural yielding limit states as well as the buckling behavior of the different butterfly-shaped link geometries. It is shown that the proposed critical moment for brittle limit state has 98% accuracy, while the prediction equations for ductile limit states have more than 97% accuracy as well. Strategies for controlling lateral torsional buckling in butterfly links are recommended and are validated through comparison with finite element models. The backbone behavior of the seismic butterfly-shaped link is formulized and compared with computational models. In the second parametric study, the geometrical properties effects on a set of output parameters are investigated for a 112 computational models considering initial imperfection, and it is indicated that the narrower mid-width would reach to their limit states in lower displacement as compared to wider mid-width ones. The work culminates in a system-level validation of the proposed structural fuses with the design and analysis of shear link structural fuses for application in three buildings with different seismic force resisting systems. Six options for shear link geometry are designed for each building application using the design methodologies and predictive equations developed in this work and as guided by the results of the parametric studies. Subsequently, the results obtained for each group is compared to the conventional systems. The effect of implementation of the seismic links in multi-story structures is investigated by analyzing two prototype structures, with butterfly-shaped links and simple conventional beam. The results of the nonlinear response history analysis are summarized for 44 ground motions under Maximum Considered Event (MCE) and Design Basic Earthquake (DBE) ground motion hazard levels. It is shown that implementation of the butterfly-shaped links will lead to higher dissipated energy compared to conventional Eccentrically Braced Frame (EBF) systems. It is concluded that implementation of the seismic shear links significantly improves the energy dissipation capability of the systems compared to conventional systems, while the stiffness and strength are close in these two systems. / Ph. D. / Structural fuses are replaceable elements of a structure that are designed to yield and protect the surrounding members from damages, and then be accessible and replaceable after a major event. Several studies have indicated that steel plates with cutouts would have advantages for use in structural fuses. Having cutouts in a steel plate would make different shapes inside of the plate, which are called structural links. To have the same yielding condition all over the links, it is tried to better align the capacity of the links with the shape of the demand diagram caused by loading, which would be leading to the efficient implementation of the steel. In general, links are implemented to substantially increase the energy dissipation capacity of a structure and significantly reduce the energy dissipation demand on the framing members of a structure. For these purposes, various shapes have been proposed in this research study. The main feature of a replaceable link system is that the inelasticity is concentrated at the steel link while the beams and columns remain almost elastic. This study investigated the general behavior of the fuses, the applicability of them for space-constrained applications, the flexure, shear and buckling limit states affecting the behavior of the links. The computational analysis methodologies to model the links are explained and confirmed with the behavior of the different experiment tests as well as the proposed brittle limit state prediction equations. Subsequently, the two parametric studies are done to investigate the effect of geometrical properties on the links output results and establish prediction equations. The results from the analytical and computational studies for the seismic links are incorporated for seismic investigation of multi-story buildings. The results of seismic analysis of the two buildings are summarized for 44 ground motions.

The purpose of this thesis is to develop a PC implemented kinematic synthesis system for four-bar and six-bar planar linkages using Turbo Pascal. CYPRUS is an interactive program that calculates and displays graphically the designed four-bar and six-bar linkages. This package can be used for three and four position synthesis of path generation, path generation with input timing, body guidance, and body guidance with input timing linkages. The package can also be used for function generation linkages where the user may enter a set of angle pairs or choose one of the following functions: tangent, cosine, sine, exponential, logarithmic, and natural logarithmic. The above syntheses can be combined to design linkages that produce more complex motion. For each kinematic synthesis case the code calculates a certain number of solutions. Then the designer chooses the most suitable solution for the particular application at hand. After a mechanism is synthesized, it can be animated for a check of the mechanical action. Watching this animation allows the designer to judge criteria such as clearances, forces, velocities and acceleration of the moving links. The software operates on an IBM PC or any other PC compatible. The language used is Turbo Pascal, an extremely effective tool and one of the fastest high level languages in compilation and execution time. / M.S.

No description available.

A predição de links em redes é uma tarefa com aplicações em diversos cenários. Com a automatização de processos, as redes sociais, redes tecnológicas e outras cresceram muito em número de vértices e arestas. Portanto, a utilização de preditores de links em redes com alta complexidade estrutural não é trivial, mesmo considerando algoritmos de baixa complexidade computacional. A grande quantidade de operações necessárias para que os preditores possam escolher quais arestas são promissoras torna o processo de considerar a rede toda inviável na maioria dos casos. As abordagens existentes enfrentam essa característica de diversas formas, sendo que as mais populares são as que limitam o conjunto de pares de vértices que serão considerados para existência de arestas promissoras. Este projeto aborda a criação de uma estratégia que utiliza otimização multinível para contrair as redes, executar os algoritmos de predição de links nas redes contraídas e projetar os resultados de predição para a rede original, para reduzir o número de operações necessárias à predição de links. Os resultados mostram que a abordagem consegue reduzir o tempo necessário para predição, apesar de perdas esperadas na qualidade na predição. / Link prediction in networks is a task with applications in several scenarios. With the automation of processes, social networks, technological networks, and others have grown considerably in the number of vertices and edges. Therefore, the creation of systems for link prediction in networks of high structural complexity is not a trivial process, even considering low-complexity algorithms. The large number of operations required for predicting which edges are promising makes the considering of the whole network impracticable in many cases. The existing approaches face this characteristic in several ways, and the most popular are those that limit the set of vertex pairs that will be considered for the existence of promising edges. This project addresses a strategy that uses multilevel optimization to coarse networks, execute prediction algorithms on coarsened networks and project the results back to the original network, in order to reduce the number of operations for link prediction. The experiments show that the approach can reduce the time despite some expected losses of accuracy.

A partir de um grupo H e um elemento h em H, nós definimos uma representação : \'B IND. n\' Aut(\'H POT. n\' ), onde \'B IND. n\' denota o grupo de trança de n cordas, e \'H POT. n\' denota o produto livre de n cópias de H. Chamamos a a representação de tipo Artin associada ao par (H, h). Nós também estudamos varios aspectos de tal representação. Primeiramente, associamos a cada trança um grupo \' IND. (H,h)\' () e provamos que o operador \' IND. (H,h)\' determina um grupo invariante de enlaçamentos orientados. Então damos uma construção topológica da representação de tipo Artin e do invariante de enlaçamentos \' IND.(H,h)\' , e provamos que a representação é fiel se, e somente se, h é não trivial / From a group H and a element h H, we define a representation : \' B IND. n\' Aut(\'H POT. n\'), where \'B IND. n\' denotes the braid group on n strands, and \'H POT. n\' denotes the free product of n copies of H. We call the Artin type representation associated to the pair (H, h). Here we study various aspects of such representations. Firstly, we associate to each braid a group \' IND. (H,h)\' () and prove that the operator \' IND. (H,h)\' determines a group invariant of oriented links. We then give a topological construction of the Artin type representations and of the link invariant \' iND. (H,h)\' , and we prove that the Artin type representations are faithful if and only if h is nontrivial

Orientador: Mário Alexandre Coelho Sinhoreti / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba / Made available in DSpace on 2018-09-11T21:15:34Z (GMT). No. of bitstreams: 1 Brandt_WilliamCunha_D.pdf: 1998947 bytes, checksum: 914e15da8572efd8f5e7f4b69beb9370 (MD5) Previous issue date: 2010 / Resumo: O objetivo neste estudo foi analisar diferentes fontes de luz e fotoiniciadores e sua influência nas propriedades físicas e térmicas e na resistência da união (RU) de compósitos odontológicos experimentais contendo diferentes fotoiniciadores. Um compósito experimental contendo uma mistura de BisGMA, UDMA, BisEMA, TEGDMA e 65% em peso de partículas de carga silanizadas foi preparado com o uso dos fotoiniciadores CQ (Canforoquinona) e PPD (1-Fenil-1,2-Propanodiona). O co-iniciador usado foi a amina terciária dimetil amino etil metacrilato (DMAEMA). As fontes de luz utilizadas foram uma lâmpada halógena (XL 2500-3M/ESPE) e duas de diodo emissor de luz - LED (UltraBlue ISDMC e UltraLume LED 5-UltraDent). A mensuração da irradiância e do espectro de luz emitido pelos aparelhos foi realizada por meio de medidor de potência e espectrômetro (USB 2000), respectivamente. A curva de absorção dos fotoiniciadores foi aferida por um espectrofotômetro (Varian Cary 5G). As propriedades físicas e térmicas do material foram analisadas em Espectroscopia de Infravermelho Transformada de Fourier (FTIR), análise Termogravimétrica (TGA), análise Termo-Dinâmica-Mecânica (DMA), resistência à compressão (RC), resistência à compressão diametral (RCD) e módulo diametral (MD). Para o teste de RU, push-out foi realizado em cavidades cônicas preparadas em noventa incisivos bovinos. Porém, antes da realização do teste push-out, a dureza Knoop (DK) foi mensurada no topo e na base das restaurações. O monitoramento (tempo real) da reação de polimerização foi realizado utilizando FTIR (Prestige21) e o grau de conversão (GC) para cada segundo foi calculado e curvas GC x tempo obtidas. A taxa de conversão (TC) foi avaliada por meio de ajuste das curvas, utilizando regressão não-linear (Hill - 3 parâmetros). Todos os resultados (GC, TGA, DMA, RC, RCD, MD, DK e RU) foram submetidos à análise de variância dois fatores e as médias comparadas pelo teste de Tukey (5%). De acordo com os resultados de FTIR, que avaliou o DC (%), quando os compósitos foram fotoativados pelos LEDs, não existiu diferença nos valores de GC. Porém, quando o XL 2500 foi usado, o compósito com PPD mostrou valores de GC menores que os com CQ. Não existiram diferenças nas propriedades mecânicas (RC, RCD e MD) entre os compósitos quando fotoativados por qualquer fonte de luz. A análise termogravimétrica (TGA), usada para confirmar a quantidade de partículas de carga e a porcentagem de monômero residual, não mostrou nenhuma diferença estatisticamente significante desses dois fatores, independentemente do fotoiniciador ou fonte de luz utilizada. A análise Termo-Dinâmica-Mecânica (DMA) analisou a temperatura de transição vítrea (Tg) e a rigidez do material a 37°C. De acordo com os resultados, o fotoiniciador PPD e a fonte de luz UltraLume LED 5 produziram polímeros com maior densidade de ligações cruzadas, pois apresentaram os maiores valores de Tg. Nenhuma diferença foi encontrada na rigidez a 37°C. A avaliação da cinética e taxa de polimerização mostrou que o PPD produz reação de polimerização mais lenta, levando a maiores valores de RU. Os valores de DK mostraram que XL 2500 produziu os maiores valores tanto no topo como na base das restaurações, exceto para a fotoativação do PPD, que mostrou resultados de DK inferiores no topo das restaurações. Em geral, UltraBlue IS e UltraLume 5 não apresentaram diferenças entre si. Dessa forma, pode-se concluir que o PPD mostrou potencial para a iniciação da reação de polimerização, pois apresentou propriedades semelhantes às da CQ, aumentando a RU entre dente/restauração. Os LEDs, principalmente o UltraLume 5, produziram valores de GC semelhantes para todos os compósitos, enquanto o QTH produziu maior conversão para a CQ, comparado ao PPD. / Abstract: The aim of this study was to analyze the spectrum of different lightcuring units (LCUs) and photo-initiators and yours influence in the physical and thermal properties and bond strength (BS) of experimental resin composites with different photo-initiators. A blend with BisGMA, UDMA, BisEMA, TEGDMA and 65 wt% of silanated filler particles was prepared with CQ (Camphorquinone) and PPD (1-phenyl-1,2-propanedione) photo-initiator. Dimethylaminoethyl methacrylate (DMAEMA) was used as co-initiator. One quartz-tungsten-halogen - QTH (XL 2500, 3M/ESPE) and two light-emitting diode (LED) LCUs (UltraBlue IS, DMC and UltraLume LED 5, Ultradent) were used for photo-activation procedures. Irradiance (mW/cm²) was calculated by the ratio of the output power by the area of the tip, and spectral distribution with a spectrometer (USB 2000). The absorption curve of each photo-initiator was determined using a spectrophotometer (Varian Cary 5G). The physical and thermal properties were analyzed through of Fourier transformed infra-red spectroscopy (FTIR), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), compression strength (CS), diametral tensile strength (DTS) and diametral modulus (DM). For BS, push-out test was accomplished in prepared conical cavities in ninety incisive bovine. However, before the accomplishment push-out test, Knoop hardness (KH) was made in the top and botton of the restorations. The real-time polymerization of the experimental resins was evaluated by Fourier transform infrared spectroscopy (Prestige21) and the degree of conversion (DC) for each second was calculated and a curve DC x time obtained. The rate of polymerization (RP) was calculated considering data fitting and Hill's 3 parameter non-linear regressions were used. The all results obtained (DC, TGA, DMA, CS, DTS, DM, KH and BS) were evaluated using a two-way analysis of variance (ANOVA) and Tukey's test (5%). The FTIR results, which analyzed the DC (%), when the resin composites were photo-activated with the LEDs LCUs, there aren't differences in the DC values. However, when XL 2500 was used for photo-activation, the PPD-containing resins showed lower DC values that CQ-containing resins. There are not differences in the mechanical properties (CS, DTS and DM) among the composite resins, regardless LCU used. The TGA, used to confirm the weight percent filler and the lost residual monomer (%) in each composite resin, didn't show any difference, regardless photo-initiator or LCU used. The DMA analyzed the glass transition temperature - Tg (°C) and the storage modulus (E' - MPa) in 37°C. In agreement with the results, the photo-initiator PPD and the UltraLume LED 5 LCU produced polymers with higher cross-link density, because they presented the highest Tg values. No difference was found in the E' in 37°C. The evaluation of the kinetics and rate of polymerization showed that PPD produces a slower reaction of polymerization, taking to highest BS values. The KH values showed that XL 2500 produced the highest values in the top and botton of the restorations, except for PPD, that showed lower KH values in the top of the restorations. In general, UltraBlue IS and UltraLume 5 didn't present differences amongst themselves. In that way, it can be concluded that PPD showed potential for the initiation of the polymerization reaction, because it presented similar properties to CQ; however it increased the BS between tooth/restoration. The LEDs, mainly the UltraLume 5, produced similar DC values for all composite resins, while QTH produced higher conversion for CQ, compared to PPD. / Doutorado / Materiais Dentarios / Doutor em Materiais Dentários

Muitos links entre páginas na Web podem ser vistos como indicadores de qualidade e importância para as páginas que eles apontam. A partir desta ideia, vários estudos propuseram métricas baseadas na estrutura de links para inferir qualidade de conteúdo em páginas da web. Contudo, até onde sabemos, o único trabalho que examinou a correlação entre tais métricas e qualidade de conteúdo consistiu de um estudo limitado que deixou várias questões em aberto. Embora tais métricas sejam muito bem sucedidas na tarefa de ranquear páginas que foram fornecidas como respostas para consultas submetidas para máquinas de busca, não é possível determinar a contribuição específica de fatores como qualidade, popularidade e importância para os resultados. Esta dificuldade se deve em parte ao fato de que a informação sobre qualidade, popularidade e importância é difícil de obter para páginas da web em geral. Ao contrário de páginas da web, estas informações podem ser obtidas para artigos da Wikipédia, uma vez que qualidade e importância são avaliadas por especialistas humanos, enquanto a popularidade pode ser estimada com base nas visualizações dos artigos. Isso torna possível a verificação da relação existente entre estes fatores e métricas de análise de links, nosso objetivo neste trabalho. Para fazer isto, nós implementamos vários algoritmos de análise de links e comparamos os rankings obtidos com eles com os obtidos considerando a avaliação humana feita na Wikipédia com relação aos fatores qualidade, popularidade e importância. Nós observamos que métricas de análise de links são mais relacionadas com qualidade e popularidade que com importância e a correlação é moderada / Many links between Web pages can be viewed as indicative of the quality and importance of the pages pointed to. Accordingly, several studies have proposed metrics based on links to infer web page content quality. However, as far as we know, the only work that has examined the correlation between such metrics and content quality consisted of a limited study that left many open questions. In spite of these metrics having been shown successful in the task of ranking pages which were provided as answers to queries submitted to search machines, it is not possible to determine the specific contribution of factors such as quality, popularity, and importance to the results. This difficulty is partially due to the fact that such information is hard to obtain for Web pages in general. Unlike ordinary Web pages, the content quality of Wikipedia articles is evaluated by human experts, which makes it feasible to verify the relation between such link analysis metrics and the quality of Wikipedia articles, our goal in this work. To accomplish that, we implemented several link analysis algorithms and compared their resulting rankings with the ones created by human evaluators regarding factors such as quality, popularity and importance. We found that the metrics are more correlated to quality and popularity than to importance, and the correlation is moderate

The British Isles have been invaded by 12 alien cynipid gallwasps over the past 150 years. The first 4 of these species have been studied in depth and represent a model system in phytophagous insect community structure. In this thesis, I extend this research programme to incorporate 8 further invaders. I examine recent changes in the distribution of invading oak gallwasps in Britain and spatial patterns in the composition of the associated communities of phytophagous cynipid inquilines and parasitoids. I use fully quantitative webs to assess the diversity and strength of trophic interactions between native and invading species and assess the potential for apparent competition between gallwasps mediated by shared natural enemies. Of the first 4 invaders to be studied, 3 have expanded their range since 1991/2. Three of these 4 species are now well established in Scotland, while Andricus corruptrix remains confined to England. Four new invaders (A. aries, A. lucidus, A. grossulariae, Aphelonyx cerricola) are established in southern England and are spreading. Rates of range expansion vary across species (between means of 3.3 and 24.4 km per year), and may be correlated with variation in lifecycles and abundance. The four newest invaders (Neuroterus saliens, Plagiotrochus australis, P. coriaceus, P. quercusilicis) are currently restricted to their sites of first record. Previous studies on one of the early invaders, Andricus quercuscalicis, identified south to north and east to west declines in community species richness and in the abundance of specific parasitoid species. I find that: 1) Parasitoid associations with the asexual galls of A. quercuscalicis track inquiline recruitment to this host. 2) The longitudinal and latitudinal gradients in parasitoid species richness demonstrated in previous work are no longer apparent, suggesting that younger northern communities may be converging on their older southern counterparts. 3) Inquilines show increasing survivorship with distance from the original centre of their distribution in south east England, suggesting at least temporary exploitation of enemy-free space. 4) The recently invading Andricus and Aphelonyx species have all rapidly recruited parasitoids and inquilines. Fully quantitative webs were constructed for 4 sites in England and Scotland incorporating both native and invading cynipids. I tested the hypothesis that newly arriving gallwasp generations would fall within food web compartments based on their host oaks and location on the tree as demonstrated in previous work. Counter to this hypothesis, parasitoids attacking one of the newest invaders (A. grossulariae) break down host tree-associated compartmentalisation. Where A. grossulariae has yet to become established, host-based compartmentalisation remains pronounced. Despite extensive sharing of parasitoid species, I found only one strong indirect interaction between species (both aliens) and no evidence for widespread apparent competition. Spatial density dependent predation on an appropriate scale can stabilise population dynamics. I quantified predation by blue tits (Parus caeruleus) of spring generation bud galls on Turkey oak (Q. cerris) at three spatial scales (shoots within branches, branches within trees, trees within sites). I found significant levels of bird predation, with most variation occurring between trees rather than between shoots within branches. Spatial density dependence was detected at sites in southern England, primarily at the level of trees within a site. Relationships at finer spatial scales were far more variable in magnitude and sign. My results suggest that blue tits forage primarily at the level of trees. This thesis presents comprehensive new data on the establishment and spread of 12 invading cynipid species and on their interactions with native communities. The results further understanding of both spatial and temporal aspects of natural enemy recruitment to invading species. In particular, it is clear that individual invading species can significantly modify trophic linkage between established food web compartments. Finally, my data emphasise the significant (but often unstudied) contribution of highly mobile vertebrate predators to otherwise closed ecological microcosms.

Cette thèse est partie d'une interrogation sur les modalités de transmission en milieu urbain de l’ethnicité sereer, associée par excellence à la ruralité dans le paradigme ethnique sénégalais et réputée menacée de disparition. L’approche déconstructiviste de l’ethnicité, essentielle en particulier dans l’étude des « ethnies » africaines, s’est avérée insuffisante pour une compréhension adéquate de l’expérience d’appartenance vécue par les enquêtés. Il a donc semblé pertinent de remobiliser la notion weberienne de croyance en une origine commune, qui ouvre la possibilité de réintégrer la dimension subjective de l’ethnicité vécue comme lien de filiation entre les membres du groupe et, dans un mouvement complémentaire inspiré par la théorie des liens sociaux et des régimes d’attachement, d’envisager ce lien de filiation dans sa relation avec d’autres liens caractéristiques de la vie sociale. Ainsi repositionnée, l’ethnicité peut être analysée à travers les cadres sociaux de sa formation, de sa mise en œuvre et de sa transmission, et apparaît comme un fait social à part entière s’imposant au regard du sociologue. L'enquête, menée de manière inductive auprès de personnes se disant sereer installées à Dakar et à Paris, a mené au constat d'une forte diversité dans les rapports revendiqués par les intéressés à l’ethnicité sereer. Il est apparu que ces rapports s’organisent sur le fond de la représentation idéale dominante d’une modernisation linéaire, opposant schématiquement tradition et modernité, à laquelle l'approche théorique de l'ethnicité elle-même est encore partiellement soumise. L'analyse du matériau d’enquête a ainsi conduit à la construction d'une typologie des rapports idéalisés aux origines et des modalités de transmission associées. Il en ressort qu’au niveau du groupe, l’ethnicité sereer, réinterprétée selon le cadre relationnel, international ou national, mobilise différemment les personnes s’en réclamant. A un niveau plus individuel et familial, la confrontation des discours et pratiques des enquêtés à la typologie a permis d’éclairer la manière dont les rapports aux origines, travaillés par des réalités de socialisation et de positionnement social différentes pour les membres du groupe, influencent leurs pratiques familiales de transmission et le sentiment d’appartenance ethnique des descendants. Il apparaît finalement que loin de les soustraire à la machine sociale, l’expérience ethnique met le groupe et son projet de reproduction à l’épreuve des facteurs sociaux, dans le temps et l’espace, et pose en réalité la question de ce qu’est faire société. / This thesis is part of a query on the modes of transmission in urban environment of Sereer ethnicity, associated par excellence with rurality in the Senegalese ethnic paradigm and deemed threatened of disappearance. The deconstructivist approach to ethnicity, essential in particular in the study of African "ethnic groups", proved to be insufficient for an adequate understanding of the experience of belonging lived by the respondents. It therefore seemed appropriate to remobilize the Weber notion of belief in a common origin, which opens up the possibility of reintegrating the subjective dimension of ethnicity experienced as a link of filiation between the members of the group and, in a complementary move inspired by the theory of social links and attachment regimes, of considering this link of filiation in its relation with other characteristic links of social life. Thus repositioned, ethnicity can be analyzed through the social frameworks of its formation, performance and transmission, and appears as a social fact in its own right which imposes itself to the sociologist. The field survey, conducted using the inductive method among people considering themselves as Sereer and living in Dakar and Paris, led to the finding of a strong diversity in the relation of those concerned to Sereer ethnicity. It appears that this relation is organized on the basis of the dominant ideal representation of a linear modernization, schematically opposing tradition and modernity, to which the theoretical approach of ethnicity itself is still partially subject. The analysis of the field survey material thus led to the construction of a typology of idealized relations with the origins and associated transmission modes. It appears that at the level of the group, Sereer ethnicity, reinterpreted according to the relational framework, at the international or national level, mobilizes differently the people claiming it. At a more individual and family level, the comparison of the words and the practices of the respondents with the typology made it possible to enlighten the way in which the relations with the origins, reshaped by social realities and a social positioning that are different for the members of the group, influence their family practices of transmission and the feeling of ethnic belonging of the descendants. Finally, it appears that, far from removing them from the social machine, ethnic experience puts the group and its reproduction plan to the test of various social factors in time and space, and poses in fact the question of what the social construct is about.