Personne : Dupont, Pierre
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Faculté des sciences et de génie, Université Laval
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- PublicationRestreintIsotopic evidence of passive mineral carbonation in mine wastes from the Dumont Nickel Project (Abitibi, Quebec)(Elsevier, 2017-03-17) Beaudoin, Georges; Dupont, Pierre; Gras, Antoine; Bussière, Bruno; Lemieux, Jean-Michel; Plante, Benoît; Molson, John W. H.Natural weathering of ultramafic rocks in mine tailings captures atmospheric CO2 through the formation of magnesium carbonates. The Dumont Nickel Project (DNP) is of particular interest as it will generate 1.7 Gt of ultramafic residues. A field experiment has been conducted at the DNP site in order to understand the process of natural CO2 sequestration. Two experimental cells were built using waste rock and mineral processing tailings and were instrumented with gas sampling ports and probes to monitor water saturation and suction. A decrease of the interstitial gas-phase CO2 concentration in both cells, from atmospheric values (∼390 ppmv) near the surface to ∼100 ppmv near the bottom, reflects active CO2 consumption by the residues. The total carbon content of the weathered DNP mine waste ranges from 0.2 wt% to 6.5 wt% C. Hydrotalcites supergroup minerals (pyroaurite-3R, brugnatellite, pyroaurite 2-H), aragonite, nesquehonite, dypingite and hydromagnesite were absent from the unweathered residues and precipitated in the cells during passive mineral carbonation. In situ measurements using Wavelength-Scanned Cavity Ring Down Spectroscopy reveal an increase of δ13C(air) from −8‰ near the surface of the cells to ∼2‰ near the bottom that is correlated with the decrease in CO2 concentration. This trend is explained by kinetic carbon isotope fractionation during dissolution of atmospheric CO2 in interstitial water (ΔDIC-CO2 = −11.2‰). Secondary carbonates, precipitated from the interstitial water, are characterized by a moderately high δ18O and low δ13C. These isotopic compositions of the carbonates are consistent with precipitation in an evaporative environment where the kinetic carbon fractionation during atmospheric CO2 dissolution produces interstitial water depleted in 13C. Moreover, isotopic compositions of hydrotalcite supergroup minerals and other carbonate minerals are consistent with modern precipitation from the weathering of mining residue. These observations demonstrate the atmospheric source for the sequestered CO2 and help constrain a conceptual model of the carbonation reaction in the residues.
- PublicationAccès libreExpression and activity of 20alpha-hydroxysteroid dehydrogenase (AKR1C1) in abdominal subcutaneous and omental adipose tissue in women(Charles C. Thomas, 2005-01-15) Blanchette, Sophie; Blouin, Karine; Dupont, Pierre; Richard, Christian; Luu-The, Van; Tchernof, AndréWe examined the expression and activity of 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD) in abdominal adipose tissue in women. This recently characterized enzyme from the aldoketoreductase 1C family is responsible for the conversion of progesterone into 20alpha-hydroxyprogesterone. Abdominal sc (SC) and omental (OM) adipose tissue biopsies were obtained from a sample of 32 women aged 47.7 +/- 5.9 yr (body mass index 27.6 +/- 5.0 kg/m(2)) undergoing abdominal hysterectomies. Body composition and body fat distribution measurements were performed before the surgery by dual-energy x-ray absorptiometry and computed tomography, respectively. The expression of 20alpha-HSD was determined by real-time RT-PCR, and its activity was measured in whole-tissue homogenates. mRNA and activity of the enzyme were detected in both the SC and OM fat depots, the two measures being significantly higher in the SC compartment. Women characterized by a visceral adipose tissue area of 100 cm(2) or greater had an increased 20alpha-HSD conversion rate in their OM adipose tissue, compared with women without visceral obesity (13.99 +/- 2.07 vs. 7.92 +/- 0.83 fmol/microg protein per 24 h, P < 0.05). Accordingly, a positive correlation was found between OM adipose tissue 20alpha-HSD activity and computed tomography-measured visceral adipose tissue area (r = 0.36, P < 0.05). Significant positive correlations were also found between OM 20alpha-HSD activity and OM adipocyte diameter (r = 0.49, P < 0.05) and OM adipose tissue LPL activity (r = 0.36, P = 0.06). In conclusion, 20alpha-HSD activity and mRNA were detected in SC and OM adipose tissue in women, and OM 20alpha-hydroxylation of progesterone was highest in women with visceral obesity. Additional studies are required to establish whether local conversion of progesterone may impact on the metabolism and function of adipocytes located within the abdominal cavity.
- PublicationAccès libreExpression and activity of aldoketoreductases 1C in omental adipose tissue are positive correlates of adiposity in women(American Physiological Society, 2005-02-01) Blouin, Karine; Blanchette, Sophie; Dupont, Pierre; Richard, Christian; Luu-The, Van; Tchernof, AndréWe examined the expression and activity of steroid aldoketoreductase (AKR) 1C enzymes in abdominal subcutaneous and omental adipose tissue in women. AKR1C1 (20-hydroxysteroid dehydrogenase), AKR1C2 (3-hydroxysteroid dehydrogenase type 3), and AKR1C3 (17-hydroxysteroid dehydrogenase type 5) are involved mainly in the conversion of progesterone to 20-hydroxyprogesterone and in the inactivation of dihydrotestosterone to 5-androstane3,17-diol. Abdominal subcutaneous (Sc) and omental (Om) adipose tissue biopsies were obtained during abdominal hysterectomies in 7 women with low visceral adipose tissue area and 7 age- and total body fat mass-matched women with visceral obesity. Body composition and body fat distribution were assessed before surgery by dual energy x-ray absorptiometry and computed tomography. Women with elevated visceral adipose tissue areas were characterized by significantly higher Om adipose tissue 20-HSD and 3-HSD-3 mRNA abundance compared to women with low visceral adipose tissue accumulations (1.4 and 1.6 fold differences respectively, p<0.05). Om and Sc adipose tissue 3-HSD activities were significantly higher in women with high vs. low visceral adipose tissue areas (p<0.05 for both comparisons). Total and visceral adiposity measures were positively associated with Om 20-HSD mRNA level (r=0.75, p<0.003 for fat mass and r=0.57, p<0.04 for visceral adipose tissue area) and Om 3-HSD-3 mRNA level (r=0.68, p<0.01 for fat mass and r=0.74, p<0.003 for visceral adipose tissue area). Enzyme activities in both the Sc and Om depots were also positively and significantly correlated with total and abdominal adiposity measures, respectively. Omental adipose tissue enzyme expression and activity were positively associated with omental adipocyte size and LPL activity. In conclusion, mRNA abundance and activity of AKR1C enzymes in abdominal adipose tissue compartments are positive correlates of adiposity measures in women. Further studies are required to elucidate whether increased inactivation of progesterone and/or dihydrotestosterone in abdominal adipose tissue impacts locally on fat metabolism in abdominally obese women.
- PublicationAccès libreDynamique de population du doré jaune (Sander vitreus) du Lac Mistassini : structure de population, dispersion et distribution spatiale(2007) Dupont, Pierre; Bernatchez, LouisLa compréhension de la dynamique des populations sauvages est un enjeu majeur au niveau de la gestion et de la conservation des espèces. Il est dorénavant largement accepté dans la littérature que certains plans d'eau douce abritent plusieurs populations de poissons plutôt qu'une simple population panmictique. Étant le plus grand lac naturel au Québec, le Lac Mistassini nous offre, par son éloignement et son intégrité écologique, un site exceptionnel pour l'étude des processus comportementaux et écologiques influençant la trajectoire évolutive des espèces aquatiques y habitant. Ayant pour sujet le doré jaune (Sander vitreus), ce mémoire de maîtrise porte plus spécifiquement sur l'étude de la structure génétique, des processus de dispersion et de migration ainsi que sur la distribution spatiale et temporelle des populations de cette espèce au Lac Mistassini. Les résultats de cette étude mettent en évidence l'importance et la pertinence de l'utilisation des méthodes génétiques d'assignations populationnelles afin d'élucider certains éléments composants la dynamique des populations sauvages. Parmi ces éléments, les processus comportementaux tels que la dispersion asymétrique et le partage de l'espace entre les populations ont été identifiés comme étant partiellement responsables de l'apparition et du maintient de la structuration génétique chez cette espèce.