SOURCES AND STRUCTURES OF COMMONLY OCCURRING HIGHLY BRANCHED ISOPRENOID ALKENES

Highly branched isoprenoid (HBI) alkenes are ubiquitous lipids which have been identified in numerous geochemical samples, ranging from recent sediments to ancient oils. At the outset of the current investigation, the diatomaceous algae Haslea ostrearia (C25 alkenes) and Rhizosolenia setigera (C25 or C30 alkenes) were the only reported biological sources of these compounds. However, there remained a poor correlation between isomers found in diatoms and those commonly reported in sediments and water column particles. In the present study, the structures of fourteen novel C25 HBI trienes, tetraenes and pentaenes, and four C30 HBI pentaenes and hexaenes have been rigorously characterised via gas chromatography-mass spectrometry (GC-MS) and nuclear magnetic resonance (NMR) spectroscopy following isolation from diatoms. The GC-MS characteristics of the four novel C30 HBIs and eight of the novel C25 HBIs characterised herein show an excellent correlation with those of the HBIs commonly reported in sediments and water column particles. In contrast to the HBIs characterised previously, which all possess a saturated branch point and fixed double bond stereochemistry, the common isomers (C25 and C30) possess an unsaturated branch point and exhibit E/Z isomerism about a trisubstituted double bond. Three diatoms belonging to the Pleurosigma genus have been identified as HBI producers. Of these, the benthic species P. intermedium and the planktonic species Pleurosigma sp. have been found to biosynthesise the common C25 HBI isomers. P. planktonicum has also been identified as a producer of C25 HBIs possessing a novel structural type. The HBI distributions in five distinct strains of R. setigera have been investigated, and these were found to be highly variable. Two strains isolated from the northwest Atlantic were found to produce a single, uncommon C25 HBI pentaene, which has also been reported in H. ostrearia. In contrast, R. setigera isolated from the Arabian Sea was found to produce C30 HBIs only, whilst two strains isolated from southern Brittany were found to co-produce the common C25 and C30 HBI isomers. Four diatom species belonging to the Haslea genus have also been newly identified as producers of C25 HBI alkenes. The HBI distributions in H. salstonica, H. crucigera, H. pseudostrearia and Haslea sp. were examined, and HBI production appears to be widespread within the Haslea genus. All of the HBIs identified in these Haslea spp. were of the structural type previously observed in H. ostrearia, and thus do not correspond to the HBI isomers most commonly reported in sediments and particles. Hydrocarbon extracts isolated from sediments and particulates from the Arabian Sea, Cariaco Trench, Peru upwelling region and the Black Sea were examined by GC-MS, and the HBI isomers in these samples were identifie

Isolation of Lacustrine Basins and Marine Regression in the Kuujjuaq Area, Northern Québec, as Inferred from Diatom Analysis

The Holocene sediment records of two lakes, located 50 km south of the Ungava Bay coast near Kuujjuaq have been examined using diatom analysis in order to trace basin isolation from marine influence. The succession of diatom zones clearly documents paleoenvironmental changes induced by glacio-isostatic uplift and regression of postglacial D'lberville Sea through consecutive periods of marine occupation, isolation from the sea and subsequent lacustrine conditions. Diatom analysis proved to be an effective tool in identifying the position of the isolation contact in the sediment columns and in defining the related changes in paleosalinity and isolation dynamics. Based on the Sedated isolation contacts and the threshold elevations of both lakes, a tentative emergence curve has been reconstructed which is in agreement with curves from adjacent areas. This allowed, for the first time, to infer trends in glacio-isostatic rebound and duration of marine submergence for an area from which paleogeographical data are almost entirely lacking. The curve shows that, following déglaciation about 7000 years ago, the Kuujjuaq area experienced continuous and rapid emergence in the order of 5.7-5.8 m/century until 4800-4300 years BP. Thereafter, emergence slowed to a rate of approximately 0.9 m/century. This study provides further evidence for the usefulness of diatom analysis in reconstructing sea-level changes and land uplift of formerly glaciated regions.Le contenu diatomifère de carottes provenant du fond de deux lacs situés près de Kuujjuaq à 50 km au sud du rivage de la baie d'Ungava, a été examiné en vue de retracer les phases d'isolement de ces lacs de la mer postglaciaire d'lberville. La succession stratigraphique des zones de diatomées démontre clairement les changements paléoenvironnementaux provoqués par le relèvement isostatique postglaciaire et la régression marine; on reconnaît en effet dans les séquences diatomologiques une phase d'occupation marine, une phase d'isolement de la mer et une phase lacustre subséquente. L'analyse des diatomées s'est révélée un outil utile pour identifier la phase et les modalités d'isolement des bassins devenus lacustres et pour retracer les changements de paléosalinités associés. En tenant compte des dates au 14C sur les unités d'isolement, de l'altitude du seuil de ces lacs et de la forme des courbes d'émersion des régions adjacentes, une courbe d'émersion préliminaire de la région de Kuujjuaq a pu être construite. Cette courbe montre qu'après la déglaciation, datée à 7000 BP, !'emersion fut rapide et continue à un taux moyen de l'ordre de 5,7-5,8 m/siècle jusqu'à environ 4800-4300 BP. Par après, !'emersion fut plus lente, à un taux d'environ 0,9 m/siècle. Cette étude s'ajoute à d'autres pour mettre en évidence le grand potentiel de l'analyse des diatomées pour la reconstruction précise de courbes de variation du niveau marin et de relèvement isostatique des régions englaciées.Um die Abtrennung (Isolation) zweier kùstennaher Seen von marinem Einflup rekonstruieren zu konnen, wurden deren holozane Sedimente auf ihren Gehalt an fossilen Diatomeen untersucht. Die beiden Seen befinden sich etwa 50 km sùdlich der Ungava Bay in der Nâhe Kuujjuaqs. Die Abfolge der Diatomeenassoziationen dokumentiert eindeutig durch isostatische Landhebung bewirkte palàogeographische Verânderungen, wie z.B. das Zurùckweichen des post-glazialen d'lberville Meeres mit aufeinander folgenden Phasen mariner Ùberschwemmung, Isolation vom Meer und Ùbergang zu Sùpwasserbedingungen. Die Diatomeenanalyse erlaubte die Festlegung der exakten Lage des Isolationshorizontes, der Sedimente marinen Ursprungs von SGp-wassersedimenten trennt. Darùber hinaus erlaubte sie die Rekonstruktion der im Verlaufe der Heraushebung erfolgten Isolations-prozesse und Salzgehaltsschwankungen. Durch radiometrische Altersbestimmung (14C) der Isolationshorizonte und Ermittlung der Hôhenlage der randlichen Strandterrasse beider Seen konnte eine Landhebungskurve erstellt werden, die generell mit denen benachbarter Regionen im Gebiet der Ungava Bay ùbereinstimmt. Anhand dieser Landhebungskurve kann festgehalten werden, dap das Gebiet um Kuujjuaq in der Zeitspanne von letztem Eisrùckzug vor etwa 7000 Jahren bis 4800-4300 BP kontinuierliche und schnelle Heraushebung in der Grôpenordnung von 5,7-5,8 m/Jahrhundert erfuhr. Danach hat sich die Heraushebungsgeschwindigkeit bis auf etwa 0,9 m/Jahrhundert verlangsamt.

Effets d’un programme éducatif muséal comprenant des activités de prolongement en classe

Depuis 1980, le Groupe de recherche sur l’éducation et les musées (GREM) a conduit, en collaboration avec plusieurs écoles et quelques musées, des travaux ayant pour objet l’élaboration d’un modèle didactique d’utilisation des musées à des fins éducatives. Après avoir mené plusieurs expérimentations, un premier modèle inspiré de théories propres au curriculum des sciences humaines a été construit. Il comporte une visite au musée précédée et suivie d’activités se déroulant en salle de classe. La présente étude a pour objet l’étude des effets, au double plan cognitif et affectif, d’activités de prolongement considérées comme faisant partie intégrante d’une démarche globale d’apprentissage. Un plan de recherche de type quasi-expérimental a été utilisé. Since 1980, the Research Group on Education and Museums has collaborated with schools and museums to construct a pedagogical model for education in museums. Its researches led the Group to adopt a model drawn from the social studies curriculum. The model calls for museum visits preceded and followed by classroom activities. The present quasi-experimental study considers the affective and cognitive effects of follow-up activities that form an integral part of an overall teaching plan.

Increased Sugar Concentration with PM-Cutting and Wide Swathing Improves Alfalfa Silage Fermentation

Extensive protein degradation during silage fermentation reduces the efficiency of N utilization by ruminants and excess N is excreted in the environment. Forage nonstructural carbohydrates (NSC) represent the main source of readily fermentable energy for lactic bacteria during silage fermentation. Increasing forage NSC concentration can enhance silage fermentation, lactic acid production, and the decline in pH with an overall reduction in the extent of protein degradation. The NSC concentration increases during the day in alfalfa (Medicago sativa L.) to reach a maximum by the end of the afternoon. Under good wilting conditions, PM-cut alfalfa wilted in wide swaths had a greater NSC concentration than AM-cut alfalfa (Morin et al. 2012). Our objective was to study the effect of PM cutting and wide swathing on alfalfa silage quality attributes

Ultrafast quantitative ultrasound and shear wave elastography imaging of in vivo duck fatty livers

Multi-parametric ultrasound imaging is a promising tool for quantification of nonalcoholic fatty liver disease. In this work, a protocol of plane wave quantitative ultrasound (QUS) and shear wave elastography imaging (SWEI), quasi-simultaneously acquired, dedicated to quantification of liver steatosis on in vivo fatty duck liver is presented. Shear wave velocity was estimated to classify stiffness in duck liver tissue. QUS consisted of local attenuation coefficient slope estimated with Spectral Log Difference method, and coherent-to-diffuse signal ratio computed from homodyned-K parametric maps. After 9 days of feeding, US attenuation reached a maximum and coherent-todiffuse signal ratio reached a minimum. Coupled together, QUS and SWEI promise a strong potential in steatosis monitoring of fatty liver tissue, in ducks or humans