Le rôle et la nature du mouvement parmi les genres de l'être chez Plotin

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Analyse et classification des sols pour une étude écologique intégrée d’un secteur de l’Abitibi, Québec

Dans le cadre d'une étude écologique intégrée, nous avons effectué une analyse et une classification des sols, dans la région du lac Abitibi, Québec. Soixante-neuf paramètres, provenant des analyses physico-chimiques de même que de la description du sol et du site d'échantillonnage, ont servi au calcul des similarités entre chacun des profils de sol. L'analyse en coordonnées principales a permis de dégager les relations entre les différents profils de sols. Ceux-ci varient principalement en fonction de la roche-mère pédologique, du drainage et de la richesse relative en bases. L'analyse par agglomération hiérarchique nous a permis de classifier chacun des sous-ensembles définis par la roche-mère pédologique. Cette classification a montré, a posteriori, une bonne corrélation avec le système canadien de classification des sols, bien qu'elle ne coïncide pas parfaitement avec les unités taxonomiques de celui-ci.Sixty-nine parameters, ranging from physical and chemical analyses to soil and sampling site description, were used for the computation of the similarity index between each soil profile. The principal coordinate analysis revealed the relationships between the soil profiles. These vary mainly according to parent material, drainage and relative richness in bases. The hierarchic agglomeration cluster analysis gave groupings well defined within each subset of the parent material. This classification showed good correlation with the Canadian soil classification although it did not overlap exactly.Im Rahmen einer Umfassenden okologischen Forschungsarbeit haben wir eine Bodenanalyse und Klassifikation in der Gegend des Abitibi Sees (Québec) unternommen. Neunundsechzig Parameter, die physische und chemische Analysen umfassen, auch Beschreibungen des Bodens und der Probenplâtze, wurden fur die Errechnung des Gleichheitsindexes unter den verschiedenen Bodenprofilen benutzt. Die Analyse der Hauptkomponenten erlaubte es die Beziehungen unter den verschiedenen Bodenprofilen festzustellen. Diese unterscheiden sich hauptsachlich nach dem Muttergestein, der Entwàsserung und des Basen Reichtums. Die Analyse der hierarschischen Anhâufung ergab klare Untergruppen die sich je nach dem verschiedenen Muttergestein deutlich unterscheiden. Diese Klassifikation zeigte eine gute Korrelation mit der Kana-dischen Bodenklassifikation, wenn sie auch nicht ganz genau mit dieser ubereinstimmt

Accounting for spatial autocorrelation improves the estimation of climate, physical environment and vegetation’s effects on boreal forest’s burn rates

Context: Wildfires play a crucial role in maintaining ecological and societal functions of North American boreal forests. Because of their contagious way of spreading, using statistical methods dealing with spatial autocorrelation has become a major challenge in fire studies analyzing how environmental factors affect their spatial variability. Objectives: We aimed to demonstrate the performance of a spatially explicit method accounting for spatial autocorrelation in burn rates modelling, and to use this method to determine the relative contribution of climate, physical environment and vegetation to the spatial variability of burn rates between 1972 and 2015. Methods: Using a 482,000 km2 territory located in the coniferous boreal forest of eastern Canada, we built and compared burn rates models with and without accounting for spatial autocorrelation. The relative contribution of climate, physical environment and vegetation to the burn rates variability was identified with variance partitioning. Results: Accounting for spatial autocorrelation improved the models’ performance by a factor of 1.5. Our method allowed the unadulterated extraction of the contribution of climate, physical environment and vegetation to the spatial variability of burn rates. This contribution was similar for the three groups of factors. The spatial autocorrelation extent was linked to the fire size distribution. Conclusions: Accounting for spatial autocorrelation can highly improve models and avoids biased results and misinterpretation. Considering climate, physical environment and vegetation altogether is essential, especially when attempting to predict future area burned. In addition to the direct effect of climate, changes in vegetation could have important impacts on future burn rates

Proposition d’une méthodologie d’inventaire et de cartographie écologique; le cas de la MRC du Haut-Saint-Laurent

Au Québec, les rapports entre écologie et aménagement sont encore ténus. La législation, après avoir privilégié la notion de conservation des sites, ne s'est dotée que récemment de lois d'aménagement impliquant des principes de planification écologique. Quant aux grands projets d'aménagement, ils n'ont généralement pas tiré profit des études écologiques qu'ils avaient pourtant suscitées. Un projet du Centre de recherches écologiques de Montréal (CREM) envisage une approche interactive où la cartographie des écosystèmes permet d'identifier les aptitudes du territoire ainsi que les zones de contraintes, mais ne saurait, seule, commander automatiquement les affectations et les types d'aménagement.In Québec, the relationship between ecology and land use is still tenuous. Government legislation, after an initial conservationist approach, has only recently incorporated some elements of ecological planning. Large development projects, in Québec, have generally not profited from ecological studies that they had sponsored. A project of the Centre de recherches écologiques de Montréal (CREM) is developing an interactive approach where ecosystem mapping permits to identify the land capabilities and suitabilities in addition to the constraints, although this approach will not, by itself, establish resource allocations

Supercharacters, symmetric functions in noncommuting variables (extended abstract)

International audienceWe identify two seemingly disparate structures: supercharacters, a useful way of doing Fourier analysis on the group of unipotent uppertriangular matrices with coefficients in a finite field, and the ring of symmetric functions in noncommuting variables. Each is a Hopf algebra and the two are isomorphic as such. This allows developments in each to be transferred. The identification suggests a rich class of examples for the emerging field of combinatorial Hopf algebras.Nous montrons que deux structures en apparence bien différentes peuvent être identifiées: les super-caractères, qui sont un outil commode pour faire de l'analyse de Fourier sur le groupe des matrices unipotentes triangulaires supérieures à coefficients dans un corps fini, et l'anneau des fonctions symétriques en variables non-commutatives. Ces deux structures sont des algèbres de Hopf isomorphes. Cette identification permet de traduire dans une structure les dévelopements conçus pour l'autre, et suggère de nombreux exemples dans le domaine nouveau des algèbres de Hopf combinatoires

Increasing fire and the decline of fire adapted black spruce in the boreal forest

Intensifying wildfire activity and climate change can drive rapid forest compositional shifts. In boreal North America, black spruce shapes forest flammability and depends on fire for regeneration. This relationship has helped black spruce maintain its dominance through much of the Holocene. However, with climate change and more frequent and severe fires, shifts away from black spruce dominance to broadleaf or pine species are emerging, with implications for ecosystem functions including carbon sequestration, water and energy fluxes, and wildlife habitat. Here, we predict that such reductions in black spruce after fire may already be widespread given current trends in climate and fire. To test this, we synthesize data from 1,538 field sites across boreal North America to evaluate compositional changes in tree species following 58 recent fires (1989 to 2014). While black spruce was resilient following most fires (62%), loss of resilience was common, and spruce regeneration failed completely in 18% of 1,140 black spruce sites. In contrast, postfire regeneration never failed in forests dominated by jack pine, which also possesses an aerial seed bank, or broad-leaved trees. More complete combustion of the soil organic layer, which often occurs in better-drained landscape positions and in dryer duff, promoted compositional changes throughout boreal North America. Forests in western North America, however, were more vulnerable to change due to greater long-term climate moisture deficits. While we find considerable remaining resilience in black spruce forests, predicted increases in climate moisture deficits and fire activity will erode this resilience, pushing the system toward a tipping point that has not been crossed in several thousand years

The North American tree-ring fire-scar network

Fire regimes in North American forests are diverse and modern fire records are often too short to capture important patterns, trends, feedbacks, and drivers of variability. Tree-ring fire scars provide valuable perspectives on fire regimes, including centuries-long records of fire year, season, frequency, severity, and size. Here, we introduce the newly compiled North American tree-ring fire-scar network (NAFSN), which contains 2562 sites, >37,000 fire-scarred trees, and covers large parts of North America. We investigate the NAFSN in terms of geography, sample depth, vegetation, topography, climate, and human land use. Fire scars are found in most ecoregions, from boreal forests in northern Alaska and Canada to subtropical forests in southern Florida and Mexico. The network includes 91 tree species, but is dominated by gymnosperms in the genus Pinus. Fire scars are found from sea level to >4000-m elevation and across a range of topographic settings that vary by ecoregion. Multiple regions are densely sampled (e.g., >1000 fire-scarred trees), enabling new spatial analyses such as reconstructions of area burned. To demonstrate the potential of the network, we compared the climate space of the NAFSN to those of modern fires and forests; the NAFSN spans a climate space largely representative of the forested areas in North America, with notable gaps in warmer tropical climates. Modern fires are burning in similar climate spaces as historical fires, but disproportionately in warmer regions compared to the historical record, possibly related to under-sampling of warm subtropical forests or supporting observations of changing fire regimes. The historical influence of Indigenous and non-Indigenous human land use on fire regimes varies in space and time. A 20th century fire deficit associated with human activities is evident in many regions, yet fire regimes characterized by frequent surface fires are still active in some areas (e.g., Mexico and the southeastern United States). These analyses provide a foundation and framework for future studies using the hundreds of thousands of annually- to sub-annually-resolved tree-ring records of fire spanning centuries, which will further advance our understanding of the interactions among fire, climate, topography, vegetation, and humans across North America

CD47 fusion protein targets CD172a+ cells in Crohn’s disease and dampens the production of IL-1β and TNF

In mice, the transfer of CD172a(+) (SIRP-α) dendritic cells (DCs) elicits T cell–driven colitis, whereas treatment with CD47-Fc protein, a CD172a-binding agent, confers protection. The aim of this study was to elucidate the nature and functional properties of human CD172a(+) DCs in chronic intestinal inflammation. Here, we show that CD172a(+)CD11c(+) cells accumulate in the mesenteric lymph nodes (mLNs) and inflamed intestinal mucosa in patients with Crohn’s disease (CD). These cells are distinct from resident DCs and may coexpress markers typically associated with monocyte-derived inflammatory DCs such as CD14 and/or DC-SIGN, E-Cadherin, and/or CX(3)CR1. Spontaneous IL-1β and TNF production by HLA-DR(+) cells in CD tissues is restricted to those expressing CD172a. An avidity-improved CD47 fusion protein (CD47-Var1) suppresses the release of a wide array of inflammatory cytokines by CD172a(+) cells, which may include HLA-DR(−)CD172a(+) neutrophils, in inflamed colonic explant cultures and impairs the ability of HLA-DR(+)CD172a(+) cells to activate memory Th17 but not Th1 responses in mLNs. In conclusion, targeting CD172a(+) cells may represent novel therapeutic perspectives for patients with CD

Le contact visuel à la traversée d’une intersection par les piétons à Montréal et à Toronto

Le contact visuel est un des signes de l’interaction entre un piéton et un automobiliste. C’est une fonction importante de l’attention lorsque le piéton se prépare à traverser la voie publique à une intersection.Cette recherche présente les résultats d’une enquête menée au printemps 2001 sur le comportement des piétons à Montréal et à Toronto. Les résultats montrent que le contact visuel est plus fréquent à Montréal par rapport à Toronto selon le genre et les groupes d’âge et il y a aussi des différences significatives, entre les deux villes, du comportement du piéton au départ et durant la traversée d’une intersection. La variable dépendante, dans les modèles de régression logistique, est contact/non contact visuel. Au regard du modèle comportemental, il y a 1,63 fois plus de chance à Montréal et 2,12 fois plus à Toronto d’observer un contact visuel lorsque le piéton a un comportement non respectueux des règles de sécurité routière. De plus, la probabilité est plus faible d’observer un contact visuel lorsque le piéton montréalais ne traverse pas à un passage piétonnier. Par contre, la probabilité d’un contact visuel est plus élevée lorsque le piéton torontois n’observe pas un respect strict des règles pour traverser à une intersection.Pour le modèle environnemental, les résultats indiquent que le piéton montréalais a plus de chance d’effectuer un contact visuel lorsqu’il traverse une intersection dans une zone résidentielle, dans une rue de trois voies et plus, en présence d’un feu standard et à une intersection située à la périphérie du centre-ville. À Toronto, le modèle extrait les deux dernières variables du modèle montréalais et, en plus, les flux de véhicules. La discussion souligne l’importance du concept d’attention pour expliquer le contact visuel du piéton dans un contexte environnemental.Visual contact is one of the indications of interaction between a pedestrian and a motorist. It is also an important fonction with respect to cognitive information when a visual attention pedestrian prepares to enter a public crosswalk at an urban intersection.This research presents the results of field data collected in Montreal and Toronto in the spring of 2001, which analyzed the behaviour of pedestrians at signalized crosswalks. The results showed that visual contact is more frequent in Montreal than in Toronto having regard to gender and age groups. There were also significant differences in behaviour of pedestrians as they began to cross and during the crossing of intersection. Logistic regression analysis was used with visual contact/no contact as the dependent variable. With regard to the behavioural model there was 1,63 times greater chance in Montreal and 2,12 in Toronto of observing visual contact when the pedestrian did not respect the rules of crossing an intersection. It is significant, however, that in Montreal there is lower probability of observing visual contact when the pedestrian do not cross at a pedestrian crossing. In Toronto there is a higher probability of visual contact if the pedestrian is not strictly observing the rules for crossing the intersection.With regarded to the environmental model a pedestrian in Montreal has more chances of making visual contact when he/she crosses intersections in residential areas, streets with three or more lanes, in the presence of a standard stoplight, and at intersection located on the periphery of the city center. In Toronto, we found the last two environmental variables included in the Montreal model. In addition, the automobile flow appeared in the Toronto model. The discussion underlines the importance of the notion of attention with regard to visual contact between pedestrian and driver in an environmental context