Conrad Gregoire | Carleton University (original) (raw)
Papers by Conrad Gregoire
Journal of Geochemical Exploration, Mar 1, 1998
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Environmental Science & Technology, Oct 1, 1994
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New data on Ru/Ir abundance ratios are presented for nonmarine (Hell Creek, Montana; Frenchman Ri... more New data on Ru/Ir abundance ratios are presented for nonmarine (Hell Creek, Montana; Frenchman River, Saskatchewan) and marine Cretaceous-Tertiary boundary sites (Brazos River, Texas; Beloc, Haiti; DSDP 577 and DSDP 596). The Ru/Ir ratio varies from 0.5 to 1 within 4000 km of Chicxulub and increases to 2-3 at paleodistances (65 Ma) of up to 12,000 km from the impact site. For CI chondrites, Ru/Ir = 1.5. A ballistic model of ejecta cloud cooling and expansion, which employs the available vapor-pressure versus temperature data for Ru and It, predicts qualitatively similar global variation in the Ru/Ir ratio but by only a factor of 1.5. We infer that several other factors, such as remobilization of PGE during diagenesis, preferential oxidation of Ru, condensation kinetics and atmospheric chemical and circulation processes, may account for the observed larger Ru/Ir variation
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Spectrochimica Acta Part B: Atomic Spectroscopy, Jun 1, 1995
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Spectrochimica Acta Part B: Atomic Spectroscopy, 1982
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Analytical Chemistry, Nov 1, 1978
The peak and integrated absorbances of Mo, V, Al, Ni, Cu, Zn, and Cd as a function of the rate of... more The peak and integrated absorbances of Mo, V, Al, Ni, Cu, Zn, and Cd as a function of the rate of heating of the graphite tube in a modified HGA 2100 atomizer are reported. The increase in peak absorbance with heating rate is correlated with the activation energy of the rate-determining step in the atomization process. Integrated absorbances of relatively volatile elements decreased exponentially with increasing heating rates, whereas those of relatively involatile elements, such as Mo and V, increased exponentially with increasing heating rates. Characterization times (tau/sub 1/, tau/sub 2/, tau/sub 1//tau/sub 2/) of the absorption pulse are discussed and their applicability to analysis of real samples is assessed. 5 figs., 5 tables.
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Analytical Chemistry, Nov 1, 1977
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Analytical Chemistry, 1980
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Lake and Reservoir Management, 2022
Abstract Murphy MJJ, Sivarajah B, Grégoire DC, Vermaire JC. 2022. Assessing the ecological respon... more Abstract Murphy MJJ, Sivarajah B, Grégoire DC, Vermaire JC. 2022. Assessing the ecological responses of a shallow mesotrophic lake to multiple environmental stressors using paleolimnological techniques. Lake Reserv Manage. 38:67–79. White Lake, located in southeastern Ontario, Canada is a long, shallow, multibasin lake that supports recreational activities year-round and has 1538 private and commercial dwelling units. The construction of a dam at Waba Creek in 1845 resulted in the minimum water level at White Lake increasing by ∼1.5 m, and several water-level management strategies have been implemented since the mid 20th century. The lake has also been impacted by land-clearance activities and shoreline development along the eastern shores and is presently mesotrophic. More recently, White Lake was colonized by zebra mussels (Dreissena polymorpha) in 2015, and annual algal blooms have also been observed. In this paleolimnological study, diatom-based approaches and loss on ignition were used to track past changes in water quality and sediment characteristics, respectively, to inform the White Lake Property Owners Association’s ongoing lake monitoring program. The diatom-inferred total phosphorus (DI-TP) reconstruction suggests that White Lake has been mesotrophic (DI-TP range 11.5 − 17 µg/L) over the past ∼200 years. Notable changes in the diatom assemblages and declines in sedimentary organic content were recorded around the 1890s in the sediment core retrieved near Hardwood Island. The decrease in sedimentary organic content was likely a response to early land-clearance activities around the lake as erosion often leads to greater inorganic export from the catchment to the lake. The switch among benthic fragilarioid diatom taxa suggests that the light conditions at this shallow lake may have changed in response to higher allochthonous inputs. Continuous monitoring of White Lake is needed to ensure that the cumulative impacts from emerging environmental stressors (e.g., climate-mediated changes, invasion by dreissenids) are considered when making management decisions.
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Spectrochimica Acta Part B: Atomic Spectroscopy, 1982
Abstract The mechanism of atom formation of U, V, Mo, Ni, Mn, Cu and Mg atomized from pyrolytic g... more Abstract The mechanism of atom formation of U, V, Mo, Ni, Mn, Cu and Mg atomized from pyrolytic graphite and tantalum metal surfaces has been studied. The mechanism of atom formation for U from a graphite tube atomizer is reported for the first time. The peak absorbance for U and Cu is increased by factors of 59.7 and 2.0, respectively, whereas that of V, Mo and Ni is reduced by several orders of magnitude when they are atomized from a tantalum metal surface. The peak absorbance of Mn and Mg is not appreciably affected by the material of the atomization surface. Interaction of Mn and Mg with the graphite surface and formation of their refractory carbides was found to be negligible. Uranium forms a refractory carbide when heated from a graphite surface.
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Geostandards and Geoanalytical Research, Jun 1, 1999
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Canadian Mineralogist, Dec 1, 1993
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Cet essai décrit une étude préliminaire visant à précipiter l'ion vanadate par des sels d'... more Cet essai décrit une étude préliminaire visant à précipiter l'ion vanadate par des sels d'ammonium. Dépendant des conditions expérimentales et à partir d'une solution de lixiviation alcaline, le vanadium est récupéré sous la forme du métavanadate ou de l'hexavanadate d'ammonium. Les paramètres étudiés sont: le pH de précipitation, le temps et la vitesse d'agitation, le temps de cristallisation, l'effet du lavage, l'excès stoechiométrique et la concentration du V 2 O 5 . Dans ces études, des solutions synthétiques ont été utilisées et les résultats devraient servir de guide pour le traitement des solutions naturelles. Enfin, nous avons tenté de confirmer la nature d'un précipité obtenu après la lixiviation du concentré et de la scorie grillée en simulant certaines conditions
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J. Anal. At. Spectrom., 1996
... Materials* D. CONRAD GRkGOIRE Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario,... more ... Materials* D. CONRAD GRkGOIRE Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, Canada K1 A OE8 BARBARA M. ACHESON AND RICHARD P. TAYLOR Department of Earth Sciences, Carleton University, Col By Drive, Ottawa, Ontario, Canada K1 S 5B6 ...
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Journal of Geochemical Exploration, Mar 1, 1998
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Environmental Science & Technology, Oct 1, 1994
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New data on Ru/Ir abundance ratios are presented for nonmarine (Hell Creek, Montana; Frenchman Ri... more New data on Ru/Ir abundance ratios are presented for nonmarine (Hell Creek, Montana; Frenchman River, Saskatchewan) and marine Cretaceous-Tertiary boundary sites (Brazos River, Texas; Beloc, Haiti; DSDP 577 and DSDP 596). The Ru/Ir ratio varies from 0.5 to 1 within 4000 km of Chicxulub and increases to 2-3 at paleodistances (65 Ma) of up to 12,000 km from the impact site. For CI chondrites, Ru/Ir = 1.5. A ballistic model of ejecta cloud cooling and expansion, which employs the available vapor-pressure versus temperature data for Ru and It, predicts qualitatively similar global variation in the Ru/Ir ratio but by only a factor of 1.5. We infer that several other factors, such as remobilization of PGE during diagenesis, preferential oxidation of Ru, condensation kinetics and atmospheric chemical and circulation processes, may account for the observed larger Ru/Ir variation
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Spectrochimica Acta Part B: Atomic Spectroscopy, Jun 1, 1995
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Spectrochimica Acta Part B: Atomic Spectroscopy, 1982
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Analytical Chemistry, Nov 1, 1978
The peak and integrated absorbances of Mo, V, Al, Ni, Cu, Zn, and Cd as a function of the rate of... more The peak and integrated absorbances of Mo, V, Al, Ni, Cu, Zn, and Cd as a function of the rate of heating of the graphite tube in a modified HGA 2100 atomizer are reported. The increase in peak absorbance with heating rate is correlated with the activation energy of the rate-determining step in the atomization process. Integrated absorbances of relatively volatile elements decreased exponentially with increasing heating rates, whereas those of relatively involatile elements, such as Mo and V, increased exponentially with increasing heating rates. Characterization times (tau/sub 1/, tau/sub 2/, tau/sub 1//tau/sub 2/) of the absorption pulse are discussed and their applicability to analysis of real samples is assessed. 5 figs., 5 tables.
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Analytical Chemistry, Nov 1, 1977
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Analytical Chemistry, 1980
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Lake and Reservoir Management, 2022
Abstract Murphy MJJ, Sivarajah B, Grégoire DC, Vermaire JC. 2022. Assessing the ecological respon... more Abstract Murphy MJJ, Sivarajah B, Grégoire DC, Vermaire JC. 2022. Assessing the ecological responses of a shallow mesotrophic lake to multiple environmental stressors using paleolimnological techniques. Lake Reserv Manage. 38:67–79. White Lake, located in southeastern Ontario, Canada is a long, shallow, multibasin lake that supports recreational activities year-round and has 1538 private and commercial dwelling units. The construction of a dam at Waba Creek in 1845 resulted in the minimum water level at White Lake increasing by ∼1.5 m, and several water-level management strategies have been implemented since the mid 20th century. The lake has also been impacted by land-clearance activities and shoreline development along the eastern shores and is presently mesotrophic. More recently, White Lake was colonized by zebra mussels (Dreissena polymorpha) in 2015, and annual algal blooms have also been observed. In this paleolimnological study, diatom-based approaches and loss on ignition were used to track past changes in water quality and sediment characteristics, respectively, to inform the White Lake Property Owners Association’s ongoing lake monitoring program. The diatom-inferred total phosphorus (DI-TP) reconstruction suggests that White Lake has been mesotrophic (DI-TP range 11.5 − 17 µg/L) over the past ∼200 years. Notable changes in the diatom assemblages and declines in sedimentary organic content were recorded around the 1890s in the sediment core retrieved near Hardwood Island. The decrease in sedimentary organic content was likely a response to early land-clearance activities around the lake as erosion often leads to greater inorganic export from the catchment to the lake. The switch among benthic fragilarioid diatom taxa suggests that the light conditions at this shallow lake may have changed in response to higher allochthonous inputs. Continuous monitoring of White Lake is needed to ensure that the cumulative impacts from emerging environmental stressors (e.g., climate-mediated changes, invasion by dreissenids) are considered when making management decisions.
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Spectrochimica Acta Part B: Atomic Spectroscopy, 1982
Abstract The mechanism of atom formation of U, V, Mo, Ni, Mn, Cu and Mg atomized from pyrolytic g... more Abstract The mechanism of atom formation of U, V, Mo, Ni, Mn, Cu and Mg atomized from pyrolytic graphite and tantalum metal surfaces has been studied. The mechanism of atom formation for U from a graphite tube atomizer is reported for the first time. The peak absorbance for U and Cu is increased by factors of 59.7 and 2.0, respectively, whereas that of V, Mo and Ni is reduced by several orders of magnitude when they are atomized from a tantalum metal surface. The peak absorbance of Mn and Mg is not appreciably affected by the material of the atomization surface. Interaction of Mn and Mg with the graphite surface and formation of their refractory carbides was found to be negligible. Uranium forms a refractory carbide when heated from a graphite surface.
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Geostandards and Geoanalytical Research, Jun 1, 1999
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Canadian Mineralogist, Dec 1, 1993
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Cet essai décrit une étude préliminaire visant à précipiter l'ion vanadate par des sels d'... more Cet essai décrit une étude préliminaire visant à précipiter l'ion vanadate par des sels d'ammonium. Dépendant des conditions expérimentales et à partir d'une solution de lixiviation alcaline, le vanadium est récupéré sous la forme du métavanadate ou de l'hexavanadate d'ammonium. Les paramètres étudiés sont: le pH de précipitation, le temps et la vitesse d'agitation, le temps de cristallisation, l'effet du lavage, l'excès stoechiométrique et la concentration du V 2 O 5 . Dans ces études, des solutions synthétiques ont été utilisées et les résultats devraient servir de guide pour le traitement des solutions naturelles. Enfin, nous avons tenté de confirmer la nature d'un précipité obtenu après la lixiviation du concentré et de la scorie grillée en simulant certaines conditions
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J. Anal. At. Spectrom., 1996
... Materials* D. CONRAD GRkGOIRE Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario,... more ... Materials* D. CONRAD GRkGOIRE Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, Canada K1 A OE8 BARBARA M. ACHESON AND RICHARD P. TAYLOR Department of Earth Sciences, Carleton University, Col By Drive, Ottawa, Ontario, Canada K1 S 5B6 ...
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