Les altérités du bouclier canadien : premier bilan d’une campagne de reconnaissance

Une campagne de reconnaissance des altérites du bouclier Laurentidien dans deux régions, les Laurentides au nord de Montréal et Charlevoix, a permis de dégager, entre autres, une logique de distribution des altérites, tributaire de plusieurs paramètres clés. Une cinquantaine de coupes ont été étudiées, étude certes descriptive et sommaire, qui sera complétée sous peu par les résultats d'une série d'analyses. Parmi ces paramètres figure, d'une part, la lithologie. Les calcaires silicates et les marbres comptent parmi les ensembles le plus souvent altérés, puis les paragneiss et métagabbro riches en grenats, les gneiss charnockitiques et les mangérites. À l'autre extrémité de l'échelle d'altérabilité, signalons les pegmatites. Entre ces deux extrêmes se situent les migmatites et granitogneiss, les granites, les monzonites à quartz, les gabbros gneissiques. Un autre paramètre doit être considéré; la situation morphologique de la coupe et sa position sur le versant, en situant ces dernières relativement au cheminement des glaciers pleistocenes. Parmi les sites les plus favorables à la conservation des altérites, on trouve les cols placés à l'écart des courants principaux de glace, les positions d'abri, le tiers inférieur des pentes ou position d'angle mort, etc. Enfin, on ne peut négliger, en changeant d'échelle, le rôle des microsites: il faut considérer la position des altérites à l'intérieur même des coupes, dans le détail du dispositif structural et morpho-structural.Field investigation of saprolites on the Canadian Shield in two areas, the Laurentides north of Montréal and the Charlevoix area, Québec, allowed us to define a logic of distribution of saprolites, dependent of several key-parameters. Some fifty roadcuts have been studied, indeed a descriptive study which will soon be completed by analytical and laboratory results. Among these key-parameters, is the lithology. Calc-silicate rocks and marbles are the most frequently weathered, followed by paragneisses and metagabbros rich in garnet, charnockitic gneisses and mangerites. At the other end of the weathering scale are the pegmatites. Between these two extremes, migmatites and granitic gneisses, granites, quartz-rich monzonites, gneissic gabbros are moderately weathered. Another parameter which must be considered is the morphologic situation of the saprolite and its position on the slope, relative to the advancing glacier. Among the most favourable sites for the preservation of saprolites are the cols out of range of the main ice currents, sheltered positions, the lower parts of the slopes (dead angle position), etc. Lastly, at a different scale, the role of the microsites cannot be ignored : the position of the saprolites inside the exposures and the details of the structural and morphostructural characteristics are very important.Eine Erkennungsstudie der Verwitterungsprodukte des Laurentischen Schilds in zwei Gebieten, den Laurentides im Norden von Montréal und Charlevoix, lieB u.a. eine Logik in der Verteilung der Verwitterungsprodukte erkennen, die von mehreren Schlussel-Parametern abhàngt. Etwa 50 Schnitte wurden studiert in einer sicherlich deskriptiven und summarischen Studie, die binnen kurzem durch die Ergebnisse einer Série von Analysen ergànzt werden wird. Unter diesen Parametern befindet sich einerseits die Gesteinskunde. KaIk-Silikat-Steine und Marmor zàhlen zu den Ansammlungen, die am hàufigsten verwittert sind, dann die Paragneise und Metagabbro, die reich an Granaten sind, die Charnock-Gneise und die Mangerite. Am anderen Ende der Skala der Verànderlichkeit sind die Pegmatite. Zwischen diesen beiden Extremen befinden sich die Migmatite und Granitgneise, die Granite, die Quarz-Monzonite, die Gabbro-Gneise. Ein Parameter muB berucksichtigt werden: der morphologische Zustand des Schnitts und seine Lage am Abhang, wobei letztere in Bezug zur Bewegung der Gletscher des Pleistozân gebracht werden. Unter den fur die Konservierung der Verwitterungsprodukte gùnstigsten Plâtzen findet man die Passe, die abseits der wichtigsten Eisbewegungen liegen, die geschutzten Stellen, das untere Drittel der Abhânge oder tote Winkel usw. Schliesslich dart man die RoIIe der Mikro-Plâtze nicht vernachlàssigen, wenn man den Massstab wechselt: die Lage der Verwitterungsprodukte innerhalb der Schnitte muss berucksichtigt werden bis ins Detail des strukturellen und morphostrukturellen Aufbaus

Biodiversity in salt marshes: from the patrimonial value to the ecosystem functioning. The case study of the Mont Saint-Michel bay.

Until 1979, European salt marshes were known only through the inventories of fauna and especially of flora. On such criteria, the salt marshes of the Mont-Saint-Michel bay (France) were regarded as most significant of the French coasts. However, it took 20 years of research on the role of these wetlands of the estuaries-salt marsh systems to highlight the ecological, social and economic interest of this ecotone, between continental and marine systems, a long time considered as territory “without value”, except for stock breeders or hunters

Les collégiens et la bioéthique: valeurs, attitudes et perceptions

Titre de l'écran-titre (visionné le 22 août 2006)"La présente recherche a été subventionnée par l'Association des collèges privés du Québec dans le cadre du Programme de recherche et d'expérimentation

Les collégiens et la bioéthique valeurs, attitudes et perceptions : rapport de recherche ACPQ /

Titre de l'écran-titre (visionné le 22 août 2006)"La présente recherche a été subventionnée par l'Association des collèges privés du Québec dans le cadre du Programme de recherche et d'expérimentation

European salt marshes diversity and functioning: the case study of the Mont Saint-Michel bay, France

The macrotidal Mont Saint-Michel bay has been studied intensively since 1990. The objectives of this study, supported by the European Union, was to understand various processes underlying the functioning of this hydrosystem with a special focus on organic matter and nutrient fluxes between saltmarshes and marine waters. This paper presents a synopsis of these studies. The tidal flats are unvegetated and primary production is exclusively due to microphytobenthos communities dominated by diatoms. Halophile plant communities colonize the top parts of the tidal flats. Their composition and production vary according to a maturity gradient and sheep grazing. In ungrazed saltmashes, production ranged from 1080 gDW m−2yr−1 in the lower marsh to 1990 gDW m−2yr−1 in the upper marsh whereas it was only 200 to 500 gDW m−2yr−1 in Salicornia spp. dominated pioneer zones and sheep grazed areas. Most of this organic matter (OM) was trapped in situ, processed by fungi and bacteria, and then released seaward via tidal fluxes, groundwater and runoff as particulate OM and nutrients: –497 kg N, –1200/–1000 kg P-PO4 and –9900/–4200 kg inorganic carbon). A small amount of OM was exported to the bay as macrodetritus. Fatty acids and stable isotopes, used as markers, showed that OM produced by the marsh halophytes contributed to the diet of all the tidal flats invertebrates that were studied. Transient fish species were shown to colonize the saltmarshes to forage or graze, exporting about 50 tons POM (DW)y−1. Therefore, it is assumed that the saltmarsh production enhances the production of the whole bay. But the functioning is still poorly known because the nutrient sinks have not all been identified. Part of the nutrients input was provided by precipitation (+327 kg y−1), but the contribution of the catchments was not quantified despite the fact that their influence was shown by the presence of lindane in all the compartments of the system. Dynamics of saltmarshes are mainly influenced by natural sedimentation (1.5 million m3y−1 in the bay), plant community succession, and management (i.e., reclamation and agricultural activities)

About equivalent interval colorings of weighted graphs

AbstractGiven a graph G=(V,E) with strictly positive integer weights ωi on the vertices i∈V, a k-interval coloring of G is a function I that assigns an interval I(i)⊆{1,…,k} of ωi consecutive integers (called colors) to each vertex i∈V. If two adjacent vertices x and y have common colors, i.e. I(i)∩I(j)≠0̸ for an edge [i,j] in G, then the edge [i,j] is said conflicting. A k-interval coloring without conflicting edges is said legal. The interval coloring problem (ICP) is to determine the smallest integer k, called interval chromatic number of G and denoted χint(G), such that there exists a legal k-interval coloring of G. For a fixed integer k, the k-interval graph coloring problem (k-ICP) is to determine a k-interval coloring of G with a minimum number of conflicting edges. The ICP and k-ICP generalize classical vertex coloring problems where a single color has to be assigned to each vertex (i.e., ωi=1 for all vertices i∈V).Two k-interval colorings I1 and I2 are said equivalent if there is a permutation π of the integers 1,…,k such that ℓ∈I1(i) if and only if π(ℓ)∈I2(i) for all vertices i∈V. As for classical vertex coloring, the efficiency of algorithms that solve the ICP or the k-ICP can be increased by avoiding considering equivalent k-interval colorings, assuming that they can be identified very quickly. To this purpose, we define and prove a necessary and sufficient condition for the equivalence of two k-interval colorings. We then show how a simple tabu search algorithm for the k-ICP can possibly be improved by forbidding the visit of equivalent solutions

A theoretical framework for trading experiments

A general framework is suggested to describe human decision making in a certain class of experiments performed in a trading laboratory. We are in particular interested in discerning between two different moods, or states of the investors, corresponding to investors using fundamental investment strategies, technical analysis investment strategies respectively. Our framework accounts for two opposite situations already encountered in experimental setups: i) the rational expectations case, and ii) the case of pure speculation. We consider new experimental conditions which allow both elements to be present in the decision making process of the traders, thereby creating a dilemma in terms of investment strategy. Our theoretical framework allows us to predict the outcome of this type of trading experiments, depending on such variables as the number of people trading, the liquidity of the market, the amount of information used in technical analysis strategies, as well as the dividends attributed to an asset. We find that it is possible to give a qualitative prediction of trading behavior depending on a ratio that quantifies the fluctuations in the model

Choix éthiques et valeurs des collégiens: influence de l'environnement culturel

"La présente recherche a été subventionnée par l'Association des collèges privés du Québec dans le cadre du Programme de recherche et d'expérimentation"Titre de l'écran-titre (visionné le 8 mars 2007)Également disponible en format papierBibliogr

Edge effects on vegetation in rights-of-way

Ce texte est issu d’un symposium: International Symposium on Environmental Concerns in Rights-of-Way Management (6e : 1997 : La Nouvelle-Orléans, Louisiane)©ElsevierAs a result of an increasing use of ecological methods for the control of vegetation in rights-of-way, it has become necessary to understand the natural processes that are likely to facilitate or hinder management objectives. Several factors may influence species composition within corridors, but edge effects ofthe vegetation immediately adjacent to the right-of-way is one ofthe mostimportant. To better measure and understand edge effects, we studied the spatial distribution of vegetation types on test right-of-way sites located in southern Quebec. Sampling was done along 133 transects located perpendicular to the right-of-way, with a distance of50 m between transects. Each transect consisted ofseven quadrats covering the vegetation within the corridor and two quadrats outside of the corridor. The results show that there is a strong edge effect on plant composition in the right-of-way corridor, especially when it is bordered by a forest. The edge effects result in a greater dominance of tree species and to a lesser extent a greater number of shrubs. Besides species richness, the species composition is also different at the edge of the right-of-way, with several species more likely to be found at the edge, while others occur more often in the central zone. There was little significant difference between north-facing and south-facing edges. Seed dispersal is assumed to be the main factor responsible for edge effects on plant composition. These results have implications on vegetation management in right-of-way corridors