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Au-delà de l'adoption des marchés électroniques de la part des consommateurs et des offreurs, ces marchés ont fait l'objet de plusieurs recherches académiques. Ils ont posé plusieurs questions relatives à leur structure, à leur fonctionnement et à leur degré d'efficience. Ce dernier élément nous parait crucial pour prévoir le développement futur de ces marchés. Avec les marchés électroniques, un système économique plus concurrentiel permettant caractérisé par un grand nombre d’offreurs et de demandeurs où l’information est quasi parfaite devrait prendre place. Si de nombreuses études ont été effectuées pour comparer les prix des offreurs opérant sur les marchés traditionnels et les prix des offreurs opérant sur les marchés électroniques, rares sont les études qui ont analysé les stratégies-prix entre les offreurs purement électroniques et les offreurs hybrides. Nous présentons dans le cadre de notre travail une analyse, à la fois théorique et empirique, de la concurrence sur les marchés électroniques, ayant pour but de déterminer si ces marchés sont plus efficients que les marchés traditionnels. Afin de trancher les questions relatives à la nature de la concurrence et aux stratégies-prix sur ces marchés, nous avons suivi l'évolution des prix de 70 livres vendus par 6 offreurs sur une période de 6 mois. Nos résultats montrent que contrairement aux attentes théoriques, la concurrence par les prix entre les offreurs n’est pas la règle et les prix sur ces marchés ne convergent pas vers la loi du prix unique. D’autres facteurs encouragent les offreurs à ne pas s’engager dans une concurrence par les prix (la discrimination, l'image de marque, les stratégies de lock-in). Nous pouvons conclure que ces marchés ne sont pas des marchés parfaitement efficients et les stratégies-prix adoptées par les offreurs sont complexes. Même s’ils ne sont pas des marchés parfaitement efficients, les marchés électroniques sont sans doute plus efficients que les marchés traditionnels. / Price levels and price dispersion on the Internet have attracted a lot of economic and managerial research. Contrary to initial predictions that the Internet would lead to the emergence of frictionless economy, empirical research shows price dispersion persist in electronic market. There have been a few studies comparing prices levels at online and offline retailers, but not much is known about how prices compare among two types of retailers, pure play and bricks-and-clicks retailers. We address this important issue in this thesis through an empirical analysis of price levels, price dispersion and menu cost in the book industry among the two types of retailers in electronic market. This thesis responds to this need by exploring how the Internet reduces the market friction common in physical commerce. Our objective is to address the question of online price and dispersion empirically and theoretically. We seek to determine whether the pricing policies of these two types of online retailers differ, possibly because of the different competitive environments in which each operates.Using data collected an 6 month period, we investigate our hypotheses using a data set of book prices for 70 titles sold by 6 retailers in electronic market. One common prediction is that the reduction in search costs on the Internet relative to the traditional market would cause both price and price dispersion to fall. We present evidence for the persistence of price dispersion in electronic market books. We show that prices do not converge to the “law of one price”. Price changes by both types of retailers do not change their price frequently despite the claim that menu cost might be negligible in electronic market. Our findings suggest the online markets are still inefficient and online price strategy is complex, offering opportunities for different types of retailers in electronic market to differentiate themselves from another.

The current research seeks to develop a computational model that accurately describes particle dispersion in turbulent ow. Current particle dispersion models do not accurately predict the small-scale clumping of particles in turbulent ow that occurs due to interaction with turbulent eddies. A new stochastic vortex structure (SVS) model was developed and compared with current stochastic Lagrangian models (SLM) for turbulent ows. To examine what characteristics of the uid ow eld that lead to dispersion of particles, a number of non trivial measures were used. A discrete-element model is used to transport particle locations for cases with and without adhesive forces. Direct numerical simulations (DNS) are used as a baseline for comparison between the two models. Initial results show that the SVS model matches the spatial structure of the ow eld of DNS reasonably well, while the SLMs do not. Investigation of particle collision rate suggest that while SVS matches the large length scales of ow, it omits the smaller scales of the ow.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Freshwater invertebrates especially species from temporary ponds are suitable model organisms for studying of dispersal mechanisms in their discontinous habitats. Tadpole shrimp Lepidurus apus (Notostraca) is restricted to vernal temporary waters in floodplain areas of big rivers. This Master's thesis is concentrated on survey of genetic variability and structure of L. apus population from Central Europe. Mitochondrial COI analysis of 45 specimens mostly from the Czech Republic indicates that all Central European specimens falls into the subspecies L. apus apus and also indicates low level of genetic variability and structure (on average 0,2 %). These results are confronted with other notostracan species, additionally with czech populations of coldstenothermal brine shrimp Eubranchipus grubii (Anostraca) and possible reasons of the low values are discussed.