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31.
The production and use of nanomaterials will inevitably lead to their disposal in the natural environment. To assess the risk that these materials pose to human and ecosystem health an understanding of their mobility and ultimate fate is essential. To date, however, relatively little research has been conducted on the fate of nanoparticles in subsurface systems. In this study the subsurface mobility of two carbon nanoparticles: nano-fullerenes (nC60) and multi-walled carbon nanotubes (MWCNTs) is assessed. A two-dimensional finite element model was used to simulate the movement of these nanoparticles under a range of hydrologic and geological conditions, including a heterogeneous permeability field. The numerical model is based on colloid filtration theory (CFT) with a maximum retention capacity term. For the conditions evaluated the carbon nanotubes are much more mobile than nC60 due to the smaller collector efficiency associated with carbon nanotubes. However, the mobility of nC60 increased significantly when a maximum retention capacity term was included in the model. Model results also demonstrate that, for the systems examined, nanoparticles were predicted to be less mobile in heterogeneous systems compared to the homogeneous systems with the same average hydraulic properties. 相似文献
32.
P. Par Mercier 《Aquatic Sciences - Research Across Boundaries》1957,19(2):613-623
Conclusion Par ce qui précède, on se rend compte que chaque lac constitue un cas particulier qui doit être étudié pour lui-même et que
l'aération artificielle d'un lac de grandes dimensions est susceptible d'être réalisée.
A notre époque les lacs prennent de plus en plus d'importance comme réservoirs pouvant servir à l'alimentation en eau potable.
Pour remplir ce r?le il est indispensable que la qualité de l'eau soit satisfaisante afin d'éviter des traitements co?teux.
On peut dire que l'aération artificielle, malgré le co?t initial des installations et la consommation annuelle d'énergie électrique,
est le procédé le plus économique pour améliorer l'eau d'un lac eutrophe.
Actuellement la consommation de l'eau augmente partout et dépasse parfois dans certaines agglomérations 1000l/habitant/par
jour. Dans ces conditions les frais d'exploitation d'une station d'aération conjuguée avec un service important de distribution
d'eau ne grèvent le prix de revient du mètre cube que d'un supplément minime. Il est évident que l'emploi de l'aération artificielle
pour assainir un lac ne dispense pas de combattre les causes originelles de la pollution des eaux. C'est un procédé auxiliaire
précieux qui peut aider un lac à rétablir son équilibre biologique compromis par les conséquences de l'eutrophie.
Cet article résume les idées exposées par l'auteur à l'occasion d'un colloque organisé à Zurich le 22 février 1957 par le
Prof.Jaag, président de la Commission hydrobiologique de la Société helvétique des sciences naturelles. 相似文献
33.
Low-frequency current fluctuations in the deep central equatorial Atlantic are analyzed using current meter measurements recorded
from November 1992 to November 1994. Current meters were located at about 14°W of longitude and 1° of latitude on both sides
of the equator between 1,700 m depth and the ocean bottom. At all sampling depths, the velocity fluctuations are dominantly
zonal and symmetrical with respect to the equator. At 1,700 and 2,000 m, the flow is dominated by annual period fluctuations,
at 3,000 m, the velocity field amplitude presents a minimum, and at 3,750 and 3,950 m, the flow is modulated by annual and
semiannual period variability. The annual signal exhibits an apparent upward phase propagation. When considering the phase
and the amplitude of the seasonal fluctuations, the data compare well with the outputs of a realistic numerical simulation
of the Atlantic Ocean. Together with a previous analysis of the model simulations, this supports the idea that the observed
annual fluctuations are due to wind-forced vertically propagating Kelvin and Rossby waves. Data and model do not provide deciding
evidences of the presence of semiannual equatorial waves deeper than 3,500 m depth in the central equatorial Atlantic Ocean. 相似文献
34.
Denis J. Dean 《Transactions in GIS》2013,17(2):159-181
Geospatial data analysis techniques are widely used to find optimal routes from specified starting points to specified destinations. Optimality is defined in terms of minimizing some impedance value over the length of the route – the value to be minimized might be distance, travel time, financial cost, or any other metric. Conventional analysis procedures assume that impedance values of all possible travel routes are known a priori, and when this assumption holds, efficient solution strategies exist that allow truly optimal solutions to be found for even very large problems. When impedance values are not known with certainty a priori, exact solution strategies do not exist and heuristics must be employed. This study evaluated how the quality of the solutions generated by one such heuristic were impacted by the nature of the uncertainty in the cost database, the nature of the costs themselves, and the parameters used in the heuristic algorithm. It was found that all of these factors influenced the qualities of the solutions produced by the heuristic, but encouragingly, an easily controlled parameter of the heuristic algorithm itself played the most important role in controlling solution quality. 相似文献
35.
N. Peyraube R. Lastennet A. Denis P. Malaurent J. D. Villanueva 《Environmental Earth Sciences》2014,72(10):4207-4215
Saturation index with respect to calcite (SIc) and equilibrium CO2 partial pressure are important parameters to study groundwater in limestone aquifers. Aside from their use in time series, CO2 and SIc are used to estimate the baseline of CO2 in the vadose zone. The objective of this paper is to present conceptual examples on the use of the CO2–SIc relationship to have new information from usual parameters. Case study was considered as an example of use from Cussac site, a limestone aquifer in southwest of France. The result showed that CO2 baseline in unsaturated zone is found close to 25,000 ± 1,000 ppm. 相似文献
36.
The Ereendavaa Range (north-eastern Mongolia): an additional argument for Mesozoic extension throughout eastern Asia 总被引:3,自引:0,他引:3
Yannick Daoudene Denis Gapais Patrick Ledru Alain Cocherie Sébastien Hocquet Tatiana V. Donskaya 《International Journal of Earth Sciences》2009,98(6):1381-1393
Mesozoic rift basins locally bounding metamorphic core complexes have been recognized in Transbaikalia and northern China.
Numerous basement outcrops located between these two regions, in eastern Mongolia, are considered as pre-Palaeozoic in age.
One of these, the Ereendavaa Range, appears as a gneissic core marked by amphibolite-facies metamorphic conditions. The range
is overlain to the NW by the unmetamorphosed Mesozoic Onon Basin. Below the basin, the upper part of the range consists of
a gently NW-dipping shear zone associated with top-to-the-NW motion. The structural pattern is consistent with syn-extensional
exhumation of the range. Preliminary geochronological data indicate that the shear zone is late Jurassic to early Cretaceous
in age, coeval with the Onon Basin. These new data from eastern Mongolia constitute a link between Transbaikalia and northern
China, indicating that NW–SE extensional Mesozoic tectonics occurred throughout the entire region. 相似文献
37.
38.
Jean Delteil Jean-François Stéphan Bernard Mercier de Lépinay Étienne Ruellan 《Comptes Rendus Geoscience》2003,335(9):743-750
In eastern North Island New Zealand, oblique subduction of the Pacific Plate beneath the Australian Plate is associated with strain partitioning. Dextral along-strike component of displacement occurred first at Early Miocene major faults within the eastern fore-arc domain. These faults were active from Early Miocene to Pliocene times. Since Pliocene times, most of the movement occurs at western faults such as the Wellington Fault. The latter joins the back-arc domain to the north. The jump of wrench faulting is related to the oblique opening of the back-arc domain. Both phenomena are impeded southwards by the Hikurangi oceanic plateau entering the subduction zone. To cite this article: J. Delteil et al., C. R. Geoscience 335 (2003). 相似文献
39.
40.
Luke Daly Phil A. Bland Svetlana Tessalina David W. Saxey Steven M. Reddy Denis Fougerouse William D.A. Rickard Lucy V. Forman Alexandre La Fontaine Julie M. Cairney Simon P. Ringer Bruce F. Schaefer Daniel Schwander 《Geostandards and Geoanalytical Research》2018,42(3):279-299
Atom probe microscopy (APM) is a relatively new in situ tool for measuring isotope fractions from nanoscale volumes (< 0.01 μm3). We calculate the theoretical detectable difference of an isotope ratio measurement result from APM using counting statistics of a hypothetical data set to be ± 4δ or 0.4% (2s). However, challenges associated with APM measurements (e.g., peak ranging, hydride formation and isobaric interferences), result in larger uncertainties if not properly accounted for. We evaluate these factors for Re‐Os isotope ratio measurements by comparing APM and negative thermal ionisation mass spectrometry (N‐TIMS) measurement results of pure Os, pure Re, and two synthetic Re‐Os‐bearing alloys from Schwander et al. (2015, Meteoritics and Planetary Science, 50, 893) [the original metal alloy (HSE) and alloys produced by heating HSE within silicate liquid (SYN)]. From this, we propose a current best practice for APM Re‐Os isotope ratio measurements. Using this refined approach, mean APM and N‐TIMS 187Os/189Os measurement results agree within 0.05% and 2s (pure Os), 0.6–2% and 2s (SYN) and 5–10% (HSE). The good agreement of N‐TIMS and APM 187Os/189Os measurements confirms that APM can extract robust isotope ratios. Therefore, this approach permits nanoscale isotope measurements of Os‐bearing alloys using the Re‐Os geochronometer that could not be measured by conventional measurement principles. 相似文献