Discoveries in recent years have disclosed the importance of marine cyano-bacteria in the context of primary production and global nitrogen cycling. It is hypothesized here that microbial mats in tropical coastal habitats harbour a rich diversity of previously uncharacterized cyanobacteria and that benthic marine nitrogen fixation in coastal zones is substantial. A polyphasic approach was used to investigate cyanobacterial diversity in three tropical benthic marine habitats of different characters; an intertidal sand flat and a mangrove forest floor in the Indian Ocean, and a beach rock in the Pacific Ocean. In addition, nitrogenase activity was measured over diel cycles at all sites. The results revealed high cyanobacterial diversity, both morphologically and genetically. Substantial nitrogenase activity was observed, with highest rates at daytime where heterocystous species were present. However, the three habitats were dominated by non-heterocystous and unicellular genera such as Microcoleus, Lyngbya, Cyanothece and a large group of thin filamentous species, identified as members of the Pseudanabaenaceae family. In these consortia nocturnal nitrogenase activities were highest and nifH sequencing also revealed presence of non-cyanobacterial potential diazotrophs. A conclusive phylogenetic analysis of partial nifH sequences from the three sites and sequences from geographi-cally distant microbial mats revealed new clusters of benthic potentially ni-trogen-fixing cyanobacteria. Further, the non-heterocystous cyanobacterium Lyngbya majuscula was subjected to a physiological characterization to gain insights into regulatory aspects of its nitrogen fixation. The data demon-strated that nitrogenase activity is restricted to darkness, which called upon a re-evaluation of its diazotrophic behaviour.

Summer blooms of filamentous, diazotrophic cyanobacteria are typical of the Baltic Sea Proper, and are dominated by Aphanizomenon sp. and the toxic Nodularia spumigena. Although occurring every summer, the blooms vary greatly in timing and spatial distribution, making monitoring difficult and imprecise. This thesis studies how the spatial variability of Baltic cyanobacterial blooms influences estimates of abundance, vertical and horizontal distribution and N2-fixation. Implications for sampling and monitoring of cyanobacterial blooms are also discussed. The results of the thesis confirm the importance of diazotrophic cyanobacteria in providing N for summer production in the Baltic Proper. It also highlights the large spatial and temporal variation in these blooms and argues that improved spatial coverage and replication could make monitoring data more useful for demonstrating time trends, and for identifying the factors regulating the blooms. The vertical distribution of Aphanizomenon and Nodularia was found to be spatially variable, probably as a combination of species-specific adaptations and ambient weather conditions. Vertical migration in Aphanizomenon was more important towards the end of summer, and is probably regulated by a trade-off between P-availability and light and temperature.

Polyethylene wear and micromotion of the implant play an important role in multifactorial etiology of osteolysis leading to aseptic loosening of the acetabular components. Despite excellent results in primary total hip arthoplasty in a 10-15 year perspective there are still unsolved problems. The weakest link is the longevity of the actabular component. Young and active patients have a clearly worse outcome than older patients. Consequences of polyehtylene wear and ways to reduce wear have therefore been in focus during recent years. Radiostereometry (RSA) is the golden standard in measuring in vivo micromotions. In 4 clinical studies including 332 patients we used therefore RSA to record the efficacy of fixation of cemented and uncemented cups. The amount of wear of old and newly designed polyethylenes (PE) was related to cup stability and radiological and clinical measures of outcome. This study showed that cementless cups inserted with pressfit technique do not need additional augmentation. Screws and pegs increase the risk for radiolucencies and osteolystic lesions but are helpful tools in cases where primary stability is jeopardized. In the second decade clinically silent osteolysis is common for the porous coated Harris Galante cup with unsealed screw holes. The locking mechanism of the PE liner in this cup is unsatisfactory and an increase of liner dissociations is expected. EtO sterilized PE displayed high in vivo wear and we do not recommend its continued use but close monitoring of patients with earlier inserted EtO sterilized implants. The substantially reduced wear in cemented highly cross-linked PE cups without any negative in vivo tradeoffs might have a substantial impact on choice of material and operating technique in the near future. However, we still recommend its restrained use in controlled series until longer follow-up data is available. Nevertheless, the short term in vivo results of modern highly cross-linked PE look promising and ight improve the outcome of cemented and uncemented hip arthroplasties by reducing complication and revisions.

There is a demand for new recommendations for pulse seeding rates that will meet the needs of organic farmers. This study was conducted to determine the impact of seeding rate on N2 fixation and N accumulation in lentil and pea and to examine the impact of different seeding rates of lentil and pea on the productivity and N-uptake (i.e., N benefit) in a subsequent wheat crop.<p> The study was performed between 2005 and 2007. Two sites were selected each year of the two-year experiment on certified organic farms in central Saskatchewan. At each location, lentil (<i>Lens culinaris</i> L.) cultivar CDC Sovereign and field pea (<i>Pisum sativum</i> L.) cultivar CDC Mozart were each seeded at five different rates. Wheat (<i>Triticum aestivum</i> L.) cultivar AC Elsa was sown as a non-fixing reference crop at a plant population density of 250 seeds m-2. In the following year, wheat was sown to assess the effect of the pulse seeding rate treatments on the succeeding crop.<p> The pulse crop seeding rates significantly affected the quantity of N2 fixed of lentil and field pea, although %Ndfa (80 to 88% and 79 to 85% for lentil and pea, respectively) typically was unaffected by seeding rate. Yield parameters of following wheat crop were not affected by the seeding rates of the previous pulses. Typically, N contributions increased with increasing seeding rates of both lentil and pea, but there was no detectable difference in N uptake by the following wheat grown on the both pulse stubble. The different seeding rates of organically grown lentil and field pea have impacts on the amount of N2 fixed and N contribution to the soil. However, the differences in N remaining in the soil at different seeding rates of the pulse crops were not detectable in the following wheat crop and the soil N in the following year.

On the Canadian prairies, organic production generally includes the use of annual green manure (GrM) crops, which are terminated using tillage to add nutrients and organic matter to the soil. However, in a GrM plough-down year, farmers face loss of income. As an alternative to growing traditional GrM crops, legumes can be grown alone or intercropped with cereals and harvested as green feed forage (GF) for use on-farm or for sale to other producers without depleting soil nitrogen (N) for the subsequent crop. We hypothesized that the GF system would have similar biomass, and N yield, and ultimately would return N into the soil. Furthermore, by intercropping a legume with a cereal, biological N2-fixation will be enhanced in the legume.<p> Field experiments, conducted over two years, were established at Vonda and Delisle, Saskatchewan, Canada. The experiment was conducted using a randomized complete block design (RCBD) with 16 treatments and four replicates in which field pea (<i>Pisum sativum</i> cv 40-10 silage pea), oat (<i>Avena sativa</i> L.cv AC Morgan), and triticale (X <i>Triticosecale</i> Wittmack cv Pika) were grown alone or in combination and managed as GrM or GF. Wheat and tillage fallow served as cropped and uncropped controls, respectively. The tillage fallow-control system was tilled twice in the growing season using a small tractor disc. The intercropped oat was seeded at three densities (50, 100, and 150 plants m-2) to determine whether increasing cereal density stimulated N2-fixation in the field pea.<p> The GrM system was sampled and incorporated (when the field pea was at full bloom) two weeks earlier than the GF system. Consequently, at both sites, all treatments in the GF system consistently yielded more dry matter and accumulated more N than treatments in the GrM system. At the Delisle site, where percent nitrogen derived from the atmosphere (%Ndfa) was compared, increasing cereal density did not increase N2-fixation in both management systems. However, pea in the GF system accumulated more than twice the amount of N (kg ha-1) from fixation as compared to pea in the GrM system, presumably because of the longer growth period.<p> Wheat grown following the GrM treatments produced more biomass and accumulated more N than wheat following the GF treatments. Wheat grown after the monoculture field pea as a GrM had greater yield than all treatments. As well, the GrM system returned more N to the soil than did the GF system. The extra two weeks of growth in the GF system resulted in the extraction of significant amounts of nutrients and probably moisture from the soil, which adversely affected yield and nutrient composition of the following wheat crop.<p> Although organic farmers may lose income in the plough-down year, on a longterm soil sustainability basis, the GrM system is a better option than the GF system as it returns nutrients to the soil, thus providing improved plant biomass, and N accumulation of subsequent crops. However, organic farmers growing GF for hay may benefit from the increased productivity of this system on a short-term basis. Thus, farmers pursuing GF options may need to adopt other means of sustaining soil productivity on a longer term. The tilled fallow-control system resulted in high amounts of biomass and N accumulation by the subsequent wheat crop, probably due to the fact that there were no nutrients taken up in the previous year and moisture was conserved in these treatments. However, this system may have less long-term benefits compared to the GrM regime, as no nutrients are returned through ploughing down a crop.

Nitrogen (N) is an essential plant nutrient, widely applied as N-fertilizer to improve yields of agriculturally important crops. An alternative to fertilizer use could be the exploitation of plant growth-promoting bacteria, capable of enhancing growth and yield of many plant species. Azospirillum and Gluconacetobacter are root colonizing, free-living, N2-fixing bacteria (diazotrophs) with the potential to transfer fixed N to associated plants. The purpose of this study was to evaluate the agronomic efficiency of two diazotrophs, Azospirillum lipoferum and Gluconacetobacter azotocaptans, inoculated onto wheat. Physiological parameters and yield components were evaluated. The objectives of this study were to: 1) determine the survival of each diazotroph species on wheat seeds over time; 2) determine the survival of A. lipoferum and G. azotocaptans inoculated on wheat seed treated with a fungicide seed treatment, Dividend® XL RTA®; 3) determine if inoculation of wheat with the diazotrophs under controlled conditions causes an increase in dry matter, N2-fixation and N uptake; 4) determine if fertilizer N applied at three levels influences atmospheric N2-fixation by A. lipoferum or G. azotocaptans; 5) determine if inoculation of wheat with A. lipoferum or G. azotocaptans under field conditions causes any increase in dry matter, N2-fixation and N uptake; 6) determine if N-fertilization levels under field conditions influenced N2-fixation by A. lipoferum or G. azotocaptans. In order to meet these objectives lab, growth chamber, and field studies were completed. Laboratory investigations revealed that the decline in recovery of colony forming units (CFU) of G. azotocaptans was not significantly different (P<0.05) for any seed treatment. There was a general decrease in CFU over time regardless of seed treatment. Analysis of the recovered CFU of A. lipoferum over time showed that there was a significant difference (P<0.05) between both the non-sterilized seed and the Dividend® XL RTA® treated seed when compared sterilized seed. Recovery of CFU on sterilized seed declined at a more rapid rate compared to the other two seed treatments. Gluconacetobacter azotocaptans and A. lipoferum were not negatively influenced by the Dividend® XL RTA® seed treatment. Also, both diazotrophs were able to compete with other microorganisms that may have been on the seed coat of unsterilized seeds. Azospirillum lipoferum and G. azotocaptans were able to fix atmospheric N, but, there were no significant (P<0.05) differences between the diazotroph species. Additions of fertilizer N enhanced N2-fixation, in both the growth chamber and field studies. As the amount of fertilizer N increased, so did the %Ndfa and N uptake. In the growth chamber study, inoculated wheat, and fertilized with 12.2 and 24.5 µg N g-1 had the highest %Ndfa of 25.5%, and wheat fertilized with 24 µg N g-1 had the highest N uptake (1.3 g pot-1) at maturity. In the field study, inoculated wheat fertilized with of 80 kg N ha-1 had significantly higher (P<0.05) %Ndfa (10.5%) compared to wheat grown with the other fertilizer levels, which also corresponded to the highest N uptake in wheat plants (47 kg ha-1). The diazotrophs also affected the partitioning of N in the wheat plants differently. Wheat inoculated with A. lipoferum had significantly higher (P<0.05) amounts of N accumulated in heads of plants, and wheat inoculated with G. azotocaptans had significantly higher (P<0.05) amounts of N accumulated in stems of plants. However, this trend was not evident in the field study.

Ce mémoire vise à déterminer comment devraient être fixées les composantes de la tarification de l'électricité de la société d'État responsable de la fourniture de ce produit au Québec, Hydro-Québec, et vérifier si la tarification présentement utilisée par la société d'État est souhaitable comparativement à une tarification uniforme. Cette question est importante et d'actualité, car au Québec, la tarification de l'électricité a donné lieu à plusieurs débats. Entre autres, de récents rapports concernant l'équilibre budgétaire du gouvernement québécois et ses perspectives pour les prochaines décennies identifiaient l'augmentation des tarifs d'électricité (les profits qui en découlent) comme un levier à considérer pour le financement de l'État. En effet, les tarifs d'électricité sont relativement faibles au Québec. Par exemple, la facture de la clientèle résidentielle de Montréal était, au 1er avril 2006, la troisième plus basse parmi les principales villes nord-américaines. Une des raisons pour lesquelles les tarifs d'électricité sont faibles au Québec est justement liée à la grille tarifaire utilisée par Hydro-Québec (tarification par tranche). Celle-ci est composée d'une redevance et de deux tranches de tarification. La première tranche de consommation est tarifiée à un niveau relativement bas et la deuxième tranche à un niveau plus élevé. Pour répondre à cette problématique, nous modélisons trois types de tarification ce qui nous permettra d'établir les tarifs optimaux dans chacun des cas. Nous trouvons ainsi que la structure tarifaire présentement utilisée par Hydro-Québec ne serait pas liée aux conditions du marché, mais se justifierait plutôt par une contrainte politique imposant un tarif plus faible pour la consommation correspondant à des besoins de base. De plus, notre modèle montre que cette structure n'est pas socialement optimale. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Tarif d'électricité, Tarification par tranche, Tarification uniforme, Tarification en deux parties, Bien public.

Les entreprises actuelles connaissent de nos jours un ensemble de mutations quotidiennes dues en partie à l'environnement dans lequel elles évoluent, mais également dans le but d'atteindre des sommets, d'aller toujours plus haut, ou même parfois de survivre. Pour cela, des changements se décident et s'opèrent constamment. Ces derniers peuvent se matérialiser de différentes façons. Alors que certaines entreprises réajustent leur processus de production, d'autres mises sur des investissements en recherche et développement. Certaines entreprises décident de développer leurs systèmes d'informations ou encore de déployer des nouvelles mesures tarifaires. Air Canada a connu ces dernières années un grand nombre de changements, mais celui qui nous a le plus interpellé est le lancement d'une nouvelle stratégie commerciale incluant des changements dans son modèle tarifaire. De par son secteur (le secteur des services) et de ses activités, nous avons jugé intéressant d'analyser ces changements en profondeur. Cette étude porte donc sur l'analyse de l'impact des changements tarifaires d'Air Canada. Nous incluons donc une revue des nombreux éléments qui interviennent autour de ces décisions de modification tarifaire, spécifiquement dans le domaine du transport aérien. Pour mieux comprendre le cas d'Air Canada, nous présentons également en détail quels sont les changements opérés par Air Canada. En se basant sur l'ensemble de ces informations, nous procéderons à l'analyse de ces changements tarifaires et de ses résultats pour Air Canada, mais aussi pour ses usagers. Nous tenterons aussi d'établir un lien entre les résultats de ces changements pour les usagers et la façon dont ces derniers peuvent contribuer aux résultats pour Air Canada. Nous nous sommes par contre fixés certaines limites pour ce qui a trait aux résultats de ces changements tarifaires. Nous traiterons essentiellement certains aspects comme la détermination des tarifs effectuée par Air Canada, les résultats sur l'avis des usagers, mais aussi sur la propension à l'achat de ces derniers, ou encore sur les économies réalisables pour Air Canada grâce au modèle tarifaire proposé.

Subjects viewed steadily two luminous dots with various instructions as ta where ta fixate and attend, and what disappearances ta report. An analysis of the results showed that the frequency and duration of disappearances was significantly influenced by fixation,attention, and report. A control indicated that the attention effect was not simply due ta missing unattended events. It was suggested that these uncontrol led factors might have confounded some of the visual disappearance research results and that attention might be the primary determinant of the meaningful perceptual unit effect.

There is a demand for new recommendations for pulse seeding rates that will meet the needs of organic farmers. This study was conducted to determine the impact of seeding rate on N2 fixation and N accumulation in lentil and pea and to examine the impact of different seeding rates of lentil and pea on the productivity and N-uptake (i.e., N benefit) in a subsequent wheat crop.<p> The study was performed between 2005 and 2007. Two sites were selected each year of the two-year experiment on certified organic farms in central Saskatchewan. At each location, lentil (<i>Lens culinaris</i> L.) cultivar CDC Sovereign and field pea (<i>Pisum sativum</i> L.) cultivar CDC Mozart were each seeded at five different rates. Wheat (<i>Triticum aestivum</i> L.) cultivar AC Elsa was sown as a non-fixing reference crop at a plant population density of 250 seeds m-2. In the following year, wheat was sown to assess the effect of the pulse seeding rate treatments on the succeeding crop.<p> The pulse crop seeding rates significantly affected the quantity of N2 fixed of lentil and field pea, although %Ndfa (80 to 88% and 79 to 85% for lentil and pea, respectively) typically was unaffected by seeding rate. Yield parameters of following wheat crop were not affected by the seeding rates of the previous pulses. Typically, N contributions increased with increasing seeding rates of both lentil and pea, but there was no detectable difference in N uptake by the following wheat grown on the both pulse stubble. The different seeding rates of organically grown lentil and field pea have impacts on the amount of N2 fixed and N contribution to the soil. However, the differences in N remaining in the soil at different seeding rates of the pulse crops were not detectable in the following wheat crop and the soil N in the following year.