Statistical analysis of extremes currently assumes that data arise from a stationary process, although such an hypothesis is not easily assessable and should therefore be considered as an uncertainty. The aim of this paper is to describe a Bayesian framework for this purpose, considering several probabilistic models (stationary, step-change and linear trend models) and four extreme values distributions (exponential, generalized Pareto, Gumbel and GEV). Prior distributions are specified by using regional prior knowledge about quantiles. Posterior distributions are used to estimate parameters, quantify the probability of models and derive a realistic frequency analysis, which takes into account estimation, distribution and stationarity uncertainties. MCMC methods are needed for this purpose, and are described in the article. Finally, an application to a POT discharge series is presented, with an analysis of both occurrence process and peak distribution. 相似文献
A modified ceilometer has been used during the second Intensive Observation Period (IOP) of the “Expérience sur Site pour COntraindre les Modèles de Pollution atmosphériques et de Transport d'Émission” (ESCOMPTE) to perform continuous remote observations of aerosol accumulations in the first 3 km of the atmosphere. These observations encompassed an episode of intense particulate and photochemical pollution. The submicronic particles density, measured at an altitude of 600 m, went from a very low point of a few tens of particles per cubic centimeter (at the end of a Mistral episode in the free atmosphere) to a high point of more than 4500 particles per cubic centimeter (when pollutants were trapped by thermal inversions).The main result is that this instrument enables a fine documentation of the mixing layer height and of aerosol particles stratifications and circulation. Airborne aerosol measurements have been made above the mountainous region of Mérindol in order to validate in situ the remote sensing measurements. Ozone measurements near the summit of the mountains as well as in the valley were performed in order to correlate aerosol accumulation and ozone concentration. As a notable example, the two-layer aerosol stratification seen in the first 2 days of IOP 2b in that part of the ESCOMPTE domain confirms the results of another team which used backtrajectories. The low-altitude pollution for this timeframe had a local origin (the Fos industrial area), whereas above 500 m, the air masses had undergone regional-scale transport (from north-eastern Spain).The second major result is the highlighting of a pattern, in sea breeze conditions and in this part of the ESCOMPTE experiment zone, of nocturnal aerosol accumulation at an altitude of between 500 and 2000 m, followed by high ozone concentration the next day. 相似文献
The Dabieshan and its geological counterpart in the Sulu area represent the eastern part of the Qinling-Dabie orogenic belt in Eastern China. This Orogen corresponds to the collision zone between the North and South China blocks (denoted as NCB and SCB, respectively) during the Early Mesozoic. Since the discovery of ultra-high-pressure (UHP) metamor- phism[1?3], research of the Dabieshan has made great progress from petrological work (e.g. Cong and Wang, 1999 and enclosed references)[… 相似文献
Environmental parameters and gross sedimentation rates (GSR) were monitored at a fixed site located in the Bay of Banyuls-sur-Mer (NW Mediterranean), between March 1997 and April 1998, together with the main biochemical characteristics of both sedimenting and sedimented particulate organic matter (POM). Three storms which occurred during this time period resulted in natural sediment resuspension. This is indicated by the corresponding increase in GSR and a decrease in the enzymatically hydrolysable amino acids/totally hydrolysable amino acids ratio (EHAA/THAA), within the sedimenting POM. Only the strongest storm resulted in (1) a transitory increase in fine-grained particles, (2) concomitant increases in organic carbon, carbohydrates, lipids and THAA, and (3) a decrease in the EHAA/THAA ratio in surficial sediments. For most of the assayed parameters, the values recorded after the December 1997 storm corresponded to extremes for the whole period under study. This emphasises the role of storms in controlling the characteristics of sedimented and sedimenting POM.Ten sediment types, with contrasting biochemical characteristics, were selected for experiments; these were based on the results of the monitoring survey and were used during adsorption and absorption experiments involving 14C tetrachlorobiphenyl (TCB). Adsorption rates differed significantly between the sediment types, but did not correlate with any of the assayed biochemical parameters. Absorption efficiency by the mussel Mytilus galloprovincialis also differed between the sediment types; it correlated positively with all the assayed biochemical parameters, except lipids. Comparison between the magnitudes of the increase in GSR, together with the decrease in absorption efficiency during resuspension events, suggests that resuspension tends to enhance the transfer of organic pollutants in the benthic food chain. 相似文献
In the Pointe Géologie area (66°40 S; 140°00 E; Terre Adélie, East Antarctica), the Paleoproterozoic basement consists in a migmatitic complex of metasedimentary origin. Metasediments underwent a thermal event, leading to the high-grade amphibolite facies assemblages biotite–cordierite–sillimanite and to dehydration melting reactions at 4–6 kbar and 700±50 °C, followed by retrogression in greenschist facies.
In most of the archipelago, K-feldspar gneisses (KFG) are characterized by a Sil+Crd+Kfs+Bt assemblage and many K-feldspar-rich leucosomes. Locally, a spectacular rock type occurs as North dipping bands of about 10 m thick and consists in nodular gneisses (NG) that display less abundant, K-feldspar-poor leucosomes.
Commonly, the retrograde imprint facies is quite weak in KFG and only expressed by sporadic Bt–Ms±And equilibrium assemblage, whereas it developed more extensively in NG. A pseudosection calculated at constant P=4 kbar shows that the differences between NG and KFG assemblages can be considered to be mainly driven by difference in H2O proportions and much less by differences in FeO/MgO or K2O/MgO ratios. The hydrated assemblage (Bt–Ms nodules) in NG requires at least 10–20% more H2O than the Crd+Kfs+Sil/And assemblage does in KFG. Parageneses and mineral compositions indicate that this difference in H2O occurred early in the history, at least as early as the anatectic stage. Therefore, differences between NG and KFG are related to the variation in partial melting features (water distribution, proportion of melt extraction), which appears to be spatially controlled by cryptic tectonic structures. The particular shape and orientation of NG bands are interpreted as a complex history of melt extraction in the Pointe Géologie area which could involve a two stage melting process. 相似文献
Resume. Le gisement de dinosauriens du Jurassique inférieur de Toundoute, à sauropode primitif (Tazoudasaurus naimi), est examiné sous ses aspects stratigraphiques, sédimentologiques et paléoenvironnementaux. Les couches continentales détritiques
à dinosaures, succédant en continuité à des niveaux marins carbonatés trés peu épais du Lias inférieur (Hettangien-Sinémurien
probables), sont rapportées au Lias moyen-supérieur. Les dép?ts continentaux contiennent une part importante de produits volcanoclastiques
différents des basaltes triasiques. Les centres d’émission, non connus, étaient sans doute proches. La sédimentation continentale,
de type chenaux fluviatiles – plaine d’inondation, refléte un climat chaud à périodes alternativement humides et séches, ces
derniéres étant fortement marquées. Les deux niveaux à ossements correspondent à des coulées boueuses ayant charrié des ossements
et portions de carcasses (os en connexion) sur de courtes distances. Ce mode de transport a préservé les ossements de l’érosion
et favorisé un enfouissement rapide permettant leur conservation.
Manuscrit re?u le 16 juillet 2004 Révision acceptée le 17 mars 2005 相似文献
In Lorraine, flooding of the iron mines leads to a degradation of groundwater quality. Based on a global approach, a numerical simulator has been built that can reproduce and predict the evolution of water quality at the overflow point of the mining basin. In order to specify the spatial distribution of these pollutant concentrations, a new model has been developed. The basin is represented as a network of homogeneous reservoirs. Although encouraging, the results show the need to specify the spatial organisation of water flow in order to reproduce the pollutant concentrations in the different monitored wells. To cite this article: P. Collon et al., C. R. Geoscience 337 (2005).相似文献
Resume. De nombreuses échelles stratigraphiques de l’?le de Timor ont vu le jour car les corrélations stratigraphiques étaient rendues
difficiles par la complexité tectonique de l’?le et par la variété des faciès. Dès les premiers travaux, plusieurs séries
ont été distinguées, regroupées en trois unités litho-structurales principales: unité allochtone, sub-autochtone et autochtone.
Les données stratigraphiques et géodynamiques récentes montrent que l’?le de Timor est en fait constituée par six unités litho-structurales,
chacune témoignant d’un épisode majeur de l’histoire géologique de l’Ile. Cette histoire consiste d’abord à la séparation,
au Jurassique, d’un bloc issu du continent de Gondwana (unité para-allochtone) qui est entré en collision avec l’arc volcanique
asiatique à l’Oligo-Miocène (unités allochtone et sub-allochtone). Cet ensemble a ensuite été séparé de l’Asie lors de l’ouverture
de la mer de Banda sud, au Miocène supérieur (unité sub-autochtone) pour finalement entrer en collision avec la marge nord
australienne au cours du Pliocène moyen (plateforme australienne et groupe de Kolbano). Timor est depuis incorporée à la marge
nord australienne (unité autochtone).
Ce travail présente les différentes échelles stratigraphiques de chaque nouvelle unité, des propositions de corrélations et
une comparaison avec les ?les voisines de Sumba et de Sulawesi pour aboutir à une proposition d’évolution géodynamique.
Manuscrit re?u le 13 février 2004 Révision acceptée le 14 février 2005 相似文献
Planktonic gross primary production (GPP), community respiration (CR), and nitrification (NIT) were measured monthly in the
Scheldt estuary by the oxygen incubation method in 2003. No significant evolution of planktonic GPP was observed since the
1990s with high rates in the freshwater area (salinity 0; 97±65 mmol C m−2 d−1) decreasing seaward (22–37 mmol C m−2 d−1). A significant decrease of NIT was observed with regard to previous investigations although this process still represents
up to 20% of total organic matter production in the inner estuary. Planktonic CR was highest in the inner estuary and seemed
to be mainly controlled by external organic matter inputs. Planktonic net community production was negative most of the time
in the estuary with values ranging from −300 to 165 mmol C m−2 d−1. Whole estuary net ecosystem production (NEP) was investigated on an annual scale using the results mentioned above and published
benthic metabolic rates. A NEP of −39±8 mmol C m−2 d−1 was estimated, which confirms the strong heterotrophic status of this highly nutrified estuary. NEP rates were computed from
June to December 2003 to compare with results derived from the Land-Ocean Interaction in the Coastal Zone budgeting procedure
applied to dissolved inorganic phosphorus and carbon (DIP and DIC). DIP budgets failed to provide realistic estimates in the
inner estuary where abiotic processes account for more than 50% of the nonconservative DIP flux. DIC budgets predicted a much
lower NEP than in situ incubations (−109±31 versus −42±9 mmol C m−2 d−1) although, as each approach is associated with several critical assumptions, the source of this discrepancy remains unclear. 相似文献