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981.
Hlne Pauwels Irina Gaus Yves Michel le Nindre Jonathan Pearce Isabelle Czernichowski-Lauriol 《Applied Geochemistry》2007,22(12):2817-2833
Chemical and isotope studies of natural CO2 accumulations aid in assessing the chemical effects of CO2 on rock and thus provide a potential for understanding the long-term geochemical processes involved in CO2 geological storage. Several natural CO2 accumulations were discovered during gas and oil exploration in France’s carbogaseous peri-Alpine province (south-eastern France) in the 1960s. One of these, the Montmiral accumulation at a depth of more than 2400 m, is currently being exploited. The chemical composition of the water collected at the wellhead has changed in time and the final salinity exceeds 75 g/L. These changes in time can be explained by assuming that the fraction of the reservoir brine in the recovered brine–CO2–H2O mixture varies, resulting in variable proportions of H2O and brine in the sampled water. The proportions can be estimated in selected samples due to the availability of gas and water flowrate data. These data enabled the reconstruction of the chemical and isotope composition of the brine. The proportions of H2O and brine can also be estimated from isotope (δ2H, δ18O) composition of collected water and δ18O of the sulfates or CO2. The reconstituted brine has a salinity of more than 85 g/L and, according to its Br− content and isotope (δ2H, δ18O, δ34S) composition, originates from an evaporated Triassic seawater that underwent dilution by meteoric water. The reconstitution of the brine’s chemical composition enabled an evaluation of the CO2–water–rock interactions based on: (1) mineral saturation indices; and (2) comparison with initial evaporated Triassic seawater. Dissolution of K- and SO4-containing minerals such as K-feldspar and anhydrite, and precipitation of Ca and Mg containing minerals that are able to trap CO2 (carbonates) are highlighted. The changes in concentration of these elements in the brine, which are attributed to CO2 interactions, illustrate the relevance of monitoring the water quality at future industrial CO2 storage sites. 相似文献
982.
Kinetic Study of the Reactions of Ozone with Polycyclic Aromatic Hydrocarbons Adsorbed on Atmospheric Model Particles 总被引:1,自引:0,他引:1
In this experimental study, rate constants were measured for the reactions of ozone with 13 polycyclic aromatic hydrocarbons (PAHs) adsorbed on different types of particles. Graphite and silica were chosen to model, respectively, carbonaceous and mineral atmospheric particles. The pseudo-first order rate constants were obtained from the fit of the experimental decay of particulate PAH concentrations versus time. Second order rate constants were calculated considering the ozone gaseous concentration. At room temperature, rate constants varied, in the case of graphite particles, between (1.5 ± 0.5) × 10−17 and (1.3 ± 0.7) × 10−16 cm3 molecule−1 s−1 for chrysene and dibenzo[a,l]pyrene, respectively, and, in the case of silica particles, between (1.5 ± 0.3) × 10−17 and (1.4 ± 0.3) × 10−16 cm3 molecule−1 s−1 for fluoranthene and benzo[a]pyrene, respectively. Different granulometric parameters (particle size, pore size) and different PAH concentrations were tested in the case of silica particles. Heterogeneous reactions of ozone with particulate PAHs are shown to be more rapid than those occurring in the gas-phase, and may be competitive with atmospheric photodegradation. 相似文献
983.
984.
Hennie Henriët van der Veen Suzanne Jacqueline Marie Hélène Hulscher Michiel Adrianus Frederik Knaapen 《Ocean Dynamics》2006,56(3-4):228-234
Sandy shallow seas, like the North Sea, are very dynamic. Several morphological features are present on the bed, from small ripples to sand waves and large tidal sandbanks. The larger patterns induce significant depth variations that have an impact on human activities taking place in this area. Therefore, it is important to know where these large-scale features occur, what their natural behaviour is and how they interact with human activities. Here, we extend earlier research that compares the results of an idealized model of large-scale seabed patterns with data of seabed patterns in the North Sea. The idealized model is extended with a grain size dependency. The adaptations lead to more accurate predictions of the occurrence of large-scale bed forms in the North Sea. Therefore, grain size dependency and, in particular, critical shear stress are important to explain the occurrence of sand waves and sandbanks in the North Sea.
Responsible Editor: Alejandro Souza 相似文献
985.
The infiltration cube method presented in this paper allows concurrent field measurement of fine sediment content and embryo survival in an incubating environment reproducing, as closely as possible, the morphology and grain size composition of a natural salmonid redd. An infiltration cube is made up of a rectangular (30 cm square and 20 cm high) steel frame with no walls, which has a folded plastic bag attached to its base. Each infiltration cube is buried in the substrate using a procedure aimed at reproducing, as closely as possible, the construction and morpho‐sedimentological structure of a natural salmonid redd. Using a tripod installed on the river bed or at the surface of the ice, the infiltration cube method provides a quick, easy and robust way to pull relatively large samples (approximately 65 kg) out of underwater substrate even during tough winter field conditions. The absence of walls on the cube also precludes bias in infiltration rates by both allowing lateral sediment transport within substrate and preventing loss of fine particles during retrieval from underwater. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
986.
Om Prakash Tripathi Sophie Godin-Beekmann Franck Lefèvre Marion Marchand Andrea Pazmiño Alain Hauchecorne Florence Goutail Hans Schlager C. Michael Volk B. Johnson G. König-Langlo Stefano Balestri Fred Stroh T. P. Bui H. J. Jost T. Deshler Peter von der Gathen 《Journal of Atmospheric Chemistry》2006,55(3):205-226
Simulations of polar ozone losses were performed using the three-dimensional high-resolution (1∘ × 1∘) chemical transport model MIMOSA-CHIM. Three Arctic winters 1999–2000, 2001–2002, 2002–2003 and three Antarctic winters 2001, 2002, and 2003 were considered for the study. The cumulative ozone loss in the Arctic winter 2002–2003 reached around 35% at 475 K inside the vortex, as compared to more than 60% in 1999–2000. During 1999–2000, denitrification induces a maximum of about 23% extra ozone loss at 475 K as compared to 17% in 2002–2003. Unlike these two colder Arctic winters, the 2001–2002 Arctic was warmer and did not experience much ozone loss. Sensitivity tests showed that the chosen resolution of 1∘ × 1∘ provides a better evaluation of ozone loss at the edge of the polar vortex in high solar zenith angle conditions. The simulation results for ozone, ClO, HNO3, N2O, and NO
y
for winters 1999–2000 and 2002–2003 were compared with measurements on board ER-2 and Geophysica aircraft respectively. Sensitivity tests showed that increasing heating rates calculated by the model by 50% and doubling the PSC (Polar Stratospheric Clouds) particle density (from 5 × 10−3 to 10−2 cm−3) refines the agreement with in situ ozone, N2O and NO
y
levels. In this configuration, simulated ClO levels are increased and are in better agreement with observations in January but are overestimated by about 20% in March. The use of the Burkholder et al. (1990) Cl2O2 absorption cross-sections slightly increases further ClO levels especially in high solar zenith angle conditions. Comparisons of the modelled ozone values with ozonesonde measurement in the Antarctic winter 2003 and with Polar Ozone and Aerosol Measurement III (POAM III) measurements in the Antarctic winters 2001 and 2002, shows that the simulations underestimate the ozone loss rate at the end of the ozone destruction period. A slightly better agreement is obtained with the use of Burkholder et al. (1990) Cl2O2 absorption cross-sections. 相似文献
987.
The nucleation of H2O bubbles in magmas has been proposed as a trigger for volcanic eruptions. To determine how bubbles nucleate heterogeneously in silicate melts, experiments were carried out in which high-silica rhyolitic melts were hydrated at 740-800°C and 50-175 MPa, decompressed by 20-70 MPa, and held at the lower pressures for ≥10 s before being quenched. The hydration conditions were subliquidus, and all samples contain blocky magnetite + needle-shaped hematite ± plagioclase. Magnetite is abundant at 800°C and high pressures, whereas hematite becomes more abundant at lower temperatures and pressures. Bubbles nucleated in a single event in all samples, with the number density (NT) of bubbles varying between 2 × 107 and 1 × 109 cm−3. At low degrees of supersaturation, one to a few bubbles nucleate on faces of magnetite, but at medium to high degrees of supersaturation, multiple bubbles nucleate on single magnetite grains. On hematite, one to a few bubbles nucleated at the ends of the needle-shaped crystals at medium supersaturations, but formed along their entire lengths at high supersaturations. NT increases as water diffusivity decreases, indicating that the number of bubbles nucleated is influenced by their growth, which depletes the melt with respect to H2O and lowers supersaturation. If volcanic eruptions are triggered by bubble formation in magmas stored in shallow-level magma chambers, then the supersaturations needed for heterogeneous nucleation suggest that only small amounts of crystallization are needed, whereas homogeneous nucleation is unlikely to trigger eruptions. 相似文献
988.
Marie‐Hlne Vandersmissen Paul Villeneuve Marius Thriault 《The Professional geographer》2003,55(4):446-463
Urban work trips have changed in important ways during the last decades. In Québec City, a medium‐sized Canadian metropolitan area, commuting distances increased for both male and female workers between 1977 and 1996, while durations increased for male workers and decreased for female workers. This article seeks to identify spatial and social factors responsible for these changes. We develop a disaggregate model of trip duration estimated on the basis of large samples derived from travel surveys comparable through time. Using categorical variables to specify change, we are able to separate change effects from level effects attributable to various dimensions of urban form. Our analysis clearly indicates that, once travel mode and key social factors are controlled for, the shift from a monocentric to a dispersed city form is responsible, in the Québec metropolitan area, for increasing commuting time. This is contrary to findings in larger metropolitan areas, where, it has been argued, the suburbanization of jobs maintains stability in commuting duration. 相似文献
989.
Bernard Peybernès Richard Ciszak Marie-José Fondecave-Wallez Pierre-Jean Combes Hubert Camus Michel Séranne 《Comptes Rendus Geoscience》2003,335(8):681-689
In the Grands Causses, incised valleys, lapies, fissures and sinkholes inherited from successive polyphase karstifications were filled by Palaeocene marine sediments overall assigned to the P1c–P3 interval (Upper Danian–Lower Selandian). These sediments are distributed into three detritic facies, generated by extensional tectonics controlling karstic and erosional processes. Upper Cretaceous marine fossils known within these facies are interpreted as reworked from hypothetically pellicular deposits. The probable palaeogeographic connection with the Pyrenean Palaeocene ‘Breccia trough’ supposes the presence of a SE–NW ‘ria’ running across the continental areas of Lower Languedoc and draining towards the northwest the marine waters of the Palaeocene transgression as far as the Rodez region. To cite this article: B. Peybernès et al., C. R. Geoscience 335 (2003). 相似文献
990.
Neupert W.M. Newmark J. Delaboudinière J.-P. Thompson B.J. Catura R.C. Moses J.D. Gurman J.B. Portier-Fozzani F. Maucherat A.J. Defise J.M. Jamar C. Rochus P. Dere K.P. Howard R.A. Michels D.J. Freeland S. Lemen J.R. Stern R.A. 《Solar physics》1998,183(2):305-321
Solar EUV images recorded by the EUV Imaging Telescope (EIT) on SOHO have been used to evaluate temperature and density as a function of position in two largescale features in the corona observed in the temperature range of 1.0–2.0 MK. Such observations permit estimates of longitudinal temperature gradients (if present) in the corona and, consequently, estimates of thermal conduction and radiative losses as a function of position in the features. We examine two relatively cool features as recorded in EIT's Feix/x (171 Å) and Fexii (195 Å) bands in a decaying active region. The first is a long-lived loop-like feature with one leg, ending in the active region, much more prominent than one or more distant footpoints assumed to be rooted in regions of weakly enhanced field. The other is a near-radial feature, observed at the West limb, which may be either the base of a very high loop or the base of a helmet streamer. We evaluate energy requirements to support a steady-state energy balance in these features and find in both instances that downward thermal conductive losses (at heights above the transition region) are inadequate to support local radiative losses, which are the predominant loss mechanism. The requirement that a coronal energy deposition rate proportional to the square of the ambient electron density (or pressure) is present in these cool coronal features provides an additional constraint on coronal heating mechanisms. 相似文献