Finite difference computation of traveltimes in very contrasted velocity models: a massively parallel approach and its associated tools   总被引：14，自引：0，他引：14  

Pascal Podvin  Isabelle Lecomte 《Geophysical Journal International》1991,105(1):271-284

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A simple method for calculating growth rates of petroleum hydrocarbon plumes   总被引：3，自引：0，他引：3  

Bekins BA  Cozzarelli IM  Curtis GP 《Ground water》2005,43(6):817-826

Consumption of aquifer Fe(III) during biodegradation of ground water contaminants may result in expansion of a contaminant plume, changing the outlook for monitored natural attenuation. Data from two research sites contaminated with petroleum hydrocarbons show that toluene and xylenes degrade under methanogenic conditions, but the benzene and ethylbenzene plumes grow as aquifer Fe(III) supplies are depleted. By considering a one-dimensional reaction front in a constant unidirectional flow field, it is possible to derive a simple expression for the growth rate of a benzene plume. The method balances the mass flux of benzene with the Fe(III) content of the aquifer, assuming that the biodegradation reaction is instantaneous. The resulting expression shows that the benzene front migration is retarded relative to the ground water velocity by a factor that depends on the concentrations of hydrocarbon and bioavailable Fe(III). The method provides good agreement with benzene plumes at a crude oil study site in Minnesota and a gasoline site in South Carolina. Compared to the South Carolina site, the Minnesota site has 25% higher benzene flux but eight times the Fe(III), leading to about one-sixth the expansion rate. Although it was developed for benzene, toluene, ethylbenzene, and xylenes, the growth-rate estimation method may have applications to contaminant plumes from other persistent contaminant sources.  相似文献   

MINOR ELEMENTS IN MARJALAHTI OLIVINE     

Graham Ryder 《Meteoritics & planetary science》1984,19(2):79-83

Precise microprobe determinations of minor elements in olivine from Marjalahti show averages of 0.067% CaO; 0.0211% Cr₂O₃; less than 0.0045% TiO₂; 0.288% MnO; and 30 ppm Ni. The calcium is as high as in some terrestrial plutonic olivines (e.g. Stillwater) but lower than in terrestrial nodule (high-temperature mantle?) olivines, consistent with very slow cooling to low temperatures. The chromium is discrepant with some earlier determinations, and possibly chromium is zoned in most pallasitic olivines. The Ti, Mn, and Ni data are consistent with previous determinations.  相似文献   

Evidence for a warmer period during the 12th and 13th centuries AD from chironomid assemblages in Southampton Island, Nunavut, Canada     

Nicolas Rolland  Isabelle Larocque  Pierre Francus  Reinhard Pienitz 《Quaternary Research》2009,72(1):27-37

This study presents the Late-Holocene evolution of a northern Southampton Island (Nunavut, Canada) lake, using fossil chironomids supported by sedimentological evidences (XRF, grain size and CNS). All proxies revealed a relatively stable environment during the last millennium with short-lived events driving changes in the entire lake ecosystem. The chironomid-based paleotemperatures revealed variations of significant amplitude coincident with changes in the sediment density and chemical composition of the core. Higher temperature intervals were generally correlated to lower sediment density with higher chironomid concentration and diversity. Higher temperatures were recorded from cal yr AD 1160 to AD 1360, which may correspond to the Medieval Warm Period. Between cal yr AD 1360 and AD 1700, lower temperatures were probably related to a Little Ice Age event. This study presents new information on the timing of known climatic events which will refine our knowledge of the paleoclimate and climatic models of the Foxe Basin region. It also provides a new framework for the evolution of such freshwater ecosystems under the “Anthropocene” and underlines the importance of including sedimentological proxies when interpreting chironomid remains as this combined approach provides an extended overview of the past hydrological and geochemical changes and their impacts on lake biota.  相似文献   

Organic matter quality in reclaimed boreal forest soils following oil sands mining     

Isabelle Turcotte  Sylvie A. Quideau  Se-Woung Oh 《Organic Geochemistry》2009,40(4):510-519

Following surface mining of the Athabasca Oil Sands deposits in northeastern Alberta, Canada, land reclamation entails the reconstruction of soil-like profiles using salvaged soil materials such as peat and mining by-products. The overall objective of this research was to assess soil organic matter (SOM) quality in different reclamation practices as compared to undisturbed soils found in the region. Soil samples (0–10 cm) were taken from 45 plots selected to represent undisturbed reference ecosites and reclamation treatments. Soil OM pools were isolated using a combination of acid hydrolysis and physical separation techniques. Chemical composition of the low density fractions was characterized using ramped cross polarization (RAMP-CP) ¹³C nuclear magnetic resonance (NMR). Differences between disturbed and undisturbed sites reflected the influence of different botanical inputs (peat vs. forest litter) to SOM composition. Reconstructed soils were characterized by significantly lower alkyl over O-alkyl carbon (ALK/O-ALK) ratios (0.3) than undisturbed sites (0.5). For these reconstructed soils, a significantly higher proportion of soil carbon was present in the sand associated (Heavy sand) pool (49.2 vs. 37.3) and in the acid-unhydrolyzable residue (AUR) fraction (61.3 vs. 54.7). These SOM parameters were significantly related to time since reconstruction, with the AUR (p value = 0.012) and Heavy sand (p value = 0.05) fractions decreasing with time since reconstruction, while the ALK/O-ALK ratio increased (p value = 0.006). These findings suggest that the ALK/O-ALK, AUR, and Heavy sand parameters are suitable indicators for monitoring SOM quality in these reconstructed soils following oil sands mining.  相似文献   

Detection of early warning signals in paleoclimate data using a genetic time series segmentation algorithm     

Athanasia Nikolaou  Pedro Antonio Gutiérrez  Antonio Durán  Isabelle Dicaire  Francisco Fernández-Navarro  César Hervás-Martínez 《Climate Dynamics》2015,44(7-8):1919-1933

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Neogene upper‐crustal cooling of the Olympus range (northern Aegean): major role of Hellenic back‐arc extension over propagation of the North Anatolia Fault Zone     

Isabelle Coutand  Michael Walsh  Bertha Louis  Frank Chanier  Jacky Ferrière  Jean‐Yves Reynaud 《地学学报》2014,26(4):287-297

The North Anatolian Fault Zone (NAFZ) is one of the most hazardous active faults on Earth, yet its Pliocene space‐time propagation across the north Aegean domain remains poorly constrained. We use low‐temperature multi‐thermochronology and inverse thermal modelling to quantify the cooling history of the upper crust across the Olympus range. This range is located in the footwall of a system of normal faults traditionally interpreted as resulting from superposed Middle–Late Miocene N–S stretching, related to the back‐arc extension of the Hellenic subduction zone, and a Pliocene‐Quaternary transtensional field, attributed to the south‐westward propagation of the NAFZ. We find that accelerated exhumational cooling occurred between 12 and 6 Ma at rates of 15–35 °C Ma^?1 and decreased to <3 °C Ma^?1 by 8–6 Ma. The absence of significant Plio‐Pleistocene cooling across Olympus suggests that crustal exhumation there is driven by late Miocene back‐arc extension, while the impact of the NAFZ remains limited.  相似文献   

Geographic Patterns of Craft Breweries at the Intraurban Scale     

Isabelle Nilsson  Neil Reid  Matthew Lehnert 《The Professional geographer》2018,70(1):114-125

This article examines the intraurban geography of craft breweries in ten cities across the United States. First, through an exhaustive literature review, we outline both supply- and demand-side factors that might cause craft breweries to cluster. Second, we empirically test whether these establishments tend to cluster within cities using spatial statistical techniques. Many communities are attempting to support the establishment of more craft breweries as a way to boost tourism and economic development. The findings from this article aid in this discussion by providing insights into how craft brewers locate and the factors that could influence their location decision behavior. Our findings suggest that craft brewers do in fact cluster. There are both supply and demand factors responsible. On the supply side, the collaborative environment within the industry and the artisan nature of the industry's products allows for benefits of clustering to outweigh the costs associated with this behavior. On the demand side, the emergence of “brewery districts” allows individual brewers to enjoy the reputation benefits associated with the district in terms of increased foot traffic from locals and visitors looking to sample a variety of beers.  相似文献   

Cooling history of nested plutons from the Variscan Tichka plutonic complex (Morocco)     

Lécuyer  Christophe  Gasquet  Dominique  Allemand  Pascal  Martineau  François  Martinez  Isabelle 《International Journal of Earth Sciences》2017,106(8):2855-2872

International Journal of Earth Sciences - Four imbricated mafic to felsic plutons of Variscan age from Morocco have been investigated for their cooling history and geochemical interactions with...  相似文献   

Assessment of evaporation and water fluxes in a column of dry saline soil subject to different water table levels   总被引：1，自引：0，他引：1       下载免费PDF全文

María Fernanda Hernández‐López  Jorge Gironás  Isabelle Braud  Francisco Suárez  José Francisco Muñoz 《水文研究》2014,28(10):3655-3669

Dry saline soils are common in the arid and hyper‐arid basins located in the Chilean Altiplano, where evaporation from shallow groundwater is typically the major component of the water balance. Thus, a good understanding of evaporation processes is necessary for improving water resource planning and management in these regions. In this study, we conducted laboratory experiments with a natural saline soil column to estimate evaporation rates and assess the liquid and water vapor fluxes under different water table levels. Water content, electrical conductivity and temperature at different depths were utilized to assess the liquid and water vapor fluxes in the soil column. We observed movement of water that dissolves salts from the soil and transports them to areas in the column where they accumulate. Isothermal liquid flux was predominant, while thermal and isothermal liquid and thermal water vapor fluxes were negligible, except for deep water table levels where isothermal and thermal water vapor fluxes had similar magnitude but opposite directions. Differences observed in total fluxes for all water table levels were due to different upward and downward fluxes, which depend on changes in water content and temperature within the soil profile. Both the vapor flux magnitude and direction were found to be very sensitive to the choice of empirical parameters used in flux quantification, such as tortuosity and the enhancement factor for local temperature gradients in the air phase within the column. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献