“The ESA XMM-Newton Science Operations Centre: Making Basic Space Science Available to the Whole Scientific World”     

Carlos Gabriel  Matteo Guainazzi  Leo Metcalfe 《Astrophysics and Space Science》2006,305(3):315-320

XMM-Newton is a major X-ray observatory of the European Space Agency (ESA). Its observing time is open to astronomers from the whole scientific community on a peer reviewed competitive basis. The Science Operations Centre, located at ESA’s premises in Villafranca del Castillo, Spain, is responsible for the instrument operations, as well as for all the tasks related to facilitating the scientific exploitation of the data which the mission has been producing since its launch in December 1999. Among them, one may list:

•	distribution of scientific data in different formats, from raw telemetry, up to processed and calibrated high-level science products, such as images, spectra, source lists, etc;
•	development and distribution of dedicated science analysis software, as well as of continuously updated instrument calibration;
•	regular organisation of training workshops (free of cost), for potential users of XMM-Newton data, where the procedures and techniques to successfully reduce and analyze XMM-Newton data are introduced;
•	access to the data through state-of-the-art, in-house-developed archival facilities, either through the Internet or via CD-ROM;
•	continuously updated documentation on all aspects of spacecraft and instrument operations, data reduction and analysis;
•	maintenance of a comprehensive set of project web pages;
•	a competent and responsive HelpDesk, providing dedicated support to individual XMM-Newton users.

Everyone can be an XMM-Newton observer. So far, astronomers from 36 countries submitted observing programs. Public data can be accessed by every scientist in the world through the XMM-Newton Science Archive (XSA).Despite all these efforts, one can’t help noticing an asymmetric level of scientific exploitation in the realm of X-ray astronomy between developing and developed countries. The latter have traditionally enjoyed the comparative advantage of deeper know-how, deriving from direct experience in hardware and mission development. The XMM-Newton Science Operations Centre’s efforts act to alleviate this situation through, for example, increasing the usage of the web for data and information dissemination, as well as by supporting actively such initiatives as the COSPAR Capacity-Building Workshops, specifically designed to create long-lasting bridges between researchers in developing and developed countries.  相似文献   

A 3-D coastal tidal rectification process: observations, theory and experiments     

Denis Aelbrecht  Gabriel Chabert d'Hires  Dominique Renouard 《Continental Shelf Research》1999,19(15-16)

In homogeneous rotating fluid, when there is an oscillating forcing in the interior fluid with a period long enough for an Ekman layer to develop, there is an interaction between the oscillatory Ekman layer and the vertical wall, since the latter imposes an alternating adjustment flow confined near the wall. As a result, this coastal rectification process leads to a Lagrangian transport along the coast. The Ekman number, the Rossby number and the temporal Rossby number of the forcing flow are the governing parameters of that mechanism which can be described by a simplified analytical model taking into account both the vertical time-dependent structure of the current and the presence of the wall. The model shows that the residual (rectified) current flowing with the coast to its right results from the strong nonlinear interaction between along- and cross-shore tidal currents leading to asymmetrical momentum exchanges between the Ekman bottom layer and the coastal boundary layer. The model provides simple scaling laws for the maximum intensity and width of the residual current. The latter is significantly larger than the friction (Stokes) lateral boundary layer of the forcing flow. A comprehensive set of experiments is performed in the 13 m diameter rotating tank by oscillating an 8 m×2 m horizontal plate and vertical wall in a homogeneous fluid at rest in solid-body rotation and measuring the two horizontal components of the current at several locations and depths above the central part of the plate. The predicted and experimentally measured maximum intensity and width of the residual current are in very good agreement, within the range of validity of the model, i.e. when the Ekman number is sufficiently small. However experiments also show that the residual current still occurs when the Ekman layer thickness is of the same order as the fluid depth, but it is then confined to a narrower band along the vertical wall. The flow structure found experimentally is also correctly described by a numerical model developed by Zhang et al. (1994). Current measurements in the Eastern part of the English Channel near the French coast reveal a significant coastal residual current flowing Northward and the coastal rectification process described here may account for part of it.  相似文献   

Analytical methods that use natural heat as a tracer to quantify surface water–groundwater exchange, evaluated using field temperature records     

Gabriel C. Rau  Martin S. Andersen  Andrew M. McCallum  Richard Ian Acworth 《Hydrogeology Journal》2010,18(5):1093-1110

Two methods applying natural heat as a tracer to quantify surface water–groundwater exchange were evaluated using field data. Arrays capable of monitoring and recording the streambed response to diurnal temperature variations in the surface water were deployed for a 2-month period in three locations in perennial pools at Maules Creek, New South Wales, Australia. Multi-level array design, field deployment and parameter estimation are discussed. The applicability of analytical solutions derived from the heat transport equation to the streambed environments was analysed using the recorded temperature time series. The stream was found to lose water to the aquifer, which was supported by simultaneously recorded hydraulic gradients. However, the one-dimensional (1D) analytical solutions did not adequately describe the observed streambed thermal response at two locations. The resulting artefacts in the estimated flow velocities are discussed. It was hypothesised that the artefacts originate from model limitation due to streambed heterogeneity and application of 1D solutions to multi-dimensional and dynamic streambed flow. This consequently imposes limitations on the field applicability of the methods. Nevertheless, in combination with time series of surface water and streambed water levels, the use of heat as a tracer provided a powerful tool for better understanding the shallow hydrogeological system.  相似文献   

Mean Flow Near Edges and Within Cavities Situated Inside Dense Canopies   总被引：3，自引：3，他引：0  

Tirtha Banerjee  Gabriel Katul  Stefano Fontan  Davide Poggi  Mukesh Kumar 《Boundary-Layer Meteorology》2013,149(1):19-41

A streamfunction-vorticity formulation is used to explore the extent to which turbulent and turbulently inviscid solutions to the mean momentum balance explain the mean flow across forest edges and within cavities situated inside dense forested canopies. The turbulent solution is based on the mean momentum balance where first-order closure principles are used to model turbulent stresses. The turbulently inviscid solution retains all the key terms in the mean momentum balance but for the turbulent stress gradients. Both exit and entry versions of the forest edge problem are explored. The turbulent solution is found to describe sufficiently the bulk spatial patterns of the mean flow near the edge including signatures of different length scales reported in canopy transition studies. Next, the ‘clearing inside canopy’ or the so-called ‘cavity’ problem is solved for the inviscid and turbulent solutions and then compared against flume experiments. The inviscid solution describes the bulk flow dynamics in much of the zones within the cavity. In particular, the solution can capture the correct position of the bulk recirculation zone within the cavity, although with a weaker magnitude. The inviscid solution cannot capture the large vertical heterogeneity in the mean velocity above the canopy, as expected. These features are better captured via the first-order closure representation of the turbulent solution. Given the ability of this vorticity formulation to capture the mean pressure variations and the mean advective acceleration terms, it is ideal for exploring the distributions of scalars and roughness-induced flow adjustments on complex topography.  相似文献   

Estimation of the Variability of Tailings Dams Properties in Order to Perform Probabilistic Assessment     

A. Gabriel Villavicencio  Pierre Breul  Claude Bacconnet  Daniel Boissier  A. Raúl Espinace 《Geotechnical and Geological Engineering》2011,29(6):1073-1084

Dams are often used for storing mine tailings. These structures present failure mechanisms that can lead to major risks for surrounding populations. In view to managing these risks, it is necessary to take a probabilistic approach in predicting their behaviour. The application of such approaches is limited by the difficulty of obtaining experimental data to estimate the variability of the parameters and conditioned by the relevance of the probability models chosen to represent this variability. This article proposes (1) a probabilistic modelling of the index properties of the mine tailings constituting these dams based on statistical analyses and (2) a method using dynamic penetration tests to estimate on site the mine tailings friction angle and its variability. This method, applied to chilean tailings dams proposes a single model for all tailings dams in order to associate a probability law to the effective friction angle (ϕ′). The procedure is illustrated on the probabilistic study of slope stability carried out at the global scale of a dam and also at the local scale of each of its constituent layers.  相似文献   

Spatial distribution and seasonal variation in 18O/16O of modern precipitation and river water across the conterminous USA     

Andrea Dutton  Bruce H. Wilkinson  Jeffrey M. Welker  Gabriel J. Bowen  Kyger C. Lohmann 《水文研究》2005,19(20):4121-4146

We report a quantitative analysis of regional differences in the the oxygen isotope composition of river water and precipitation across the USA because data are now available to undertake a more geographically and temporally extensive analysis than was formerly possible. Maps of modern, mean annual δ¹⁸O values for both precipitation (δ¹⁸O_PPT) and river water (δ¹⁸O_RIV) across the 48 contiguous states of the USA have been generated using latitude and elevation as the primary predictors of stable isotope composition while also incorporating regional and local deviations based on available isotopic data. The difference between these two maps was calculated to determine regions where δ¹⁸O_RIV is significantly offset from local δ¹⁸O_PPT. Additional maps depicting seasonal and extreme values for δ¹⁸O_RIV and δ¹⁸O_PPT were also constructed. This exercise confirms the presence of regions characterized by differences in δ¹⁸O_RIV and δ¹⁸O_PPT and specifically identifies the magnitude and regional extent of these offsets. In particular, the Great Plains has δ¹⁸O_RIV values that are more positive than precipitation, while much of the western USA is characterized by significantly lower δ¹⁸O_RIV values in comparison with local δ¹⁸O_PPT. The most salient feature that emerged from this comparison is the ‘catchment effect’ for the rivers. Because river water is largely derived from precipitation that fell upstream of the sample locality (i.e. at higher elevations) δ¹⁸O_RIV values are often lower than local δ¹⁸O_PPT values, particularly in catchments with high‐elevation gradients. Seasonal patterns in the isotopic data substantiate the generally accepted notion that amplitudes of δ¹⁸O variation are greatly dampened in river water relative to those of local precipitation. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

A model to describe precursory material-failure phenomena: applications to short-term forecasting at colima volcano, Mexico   总被引：1，自引：1，他引：0  

Servando De la Cruz-Reyna  Gabriel A. Reyes-Dávila 《Bulletin of Volcanology》2001,63(5):297-308

  相似文献   

Quantifying net ecosystem exchange by multilevel ecophysiological and turbulent transport models     

Mario Siqueira  Gabriel Katul  Chun-Ta Lai 《Advances in water resources》2002,25(8-12)

To quantify the interplay between scalar sources and sinks (S_c) and net ecosystem exchange (NEE), “forward” and “inverse” approaches have been proposed. The canonical form of forward approaches is a one-dimensional ecophysiological-radiative transfer scheme coupled to turbulent transport theory. In contrast, inverse approaches strictly rely on turbulent transport theory and mean scalar concentration as their primary input to infer S_c and NEE. While the formulation of both approaches have evolved over the past decade, no systematic comparison between them was undertaken for the same data set, and over a wide range of atmospheric conditions. Our objective is to compare the predicted S_c and NEE from these two approaches with eddy-covariance measurements. The results show that the forward method outperformed all three inverse methods for unstable and neutral conditions on short time scales (30 min) but yielded comparable results at longer time scales. Poor agreement was obtained under stable conditions for all models. Hence, for modeling event-based flux variations, forward models are preferred. Since the forward method requires detailed knowledge of ecophysiological, drag, radiative transfer and other canopy attributes, all of which are difficult to obtain on a routine basis, a symbiotic use of forward and inverse approaches is most advantageous.  相似文献   

Validation of IPCC AR4 models over the Iberian Peninsula   总被引：3，自引：2，他引：1  

Inigo Errasti  Agust��n Ezcurra  Jon S��enz  Gabriel Ibarra-Berastegi 《Theoretical and Applied Climatology》2011,103(1-2):61-79

This paper reports analysis of the ability of 24 coupled global climate models that were used in the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change to simulate the current monthly seasonal cycle of sea level pressure, surface air temperature and precipitation over the Iberian Peninsula in the last two decades of the twentieth century. The period investigated runs from 1979 to 1998. In order to assess the performance of the models, averaged seasonal cycles and probability density functions (PDFs) calculated from model simulations are compared with the corresponding seasonal cycles, whilst PDFs are also obtained using the data from the ERA40 reanalysis and the Global Precipitation Climatology Project. We found that simulated PDFs generally provided a better fit to actual PDFs than seasonal cycles do. This conclusion indicates that when evaluating model performance, the climate variability as measured by means of PDFs is not the only climatic element that should be tested. Regarding the comparison based on the seasonal cycle, results also show that the root mean square skill score is more useful than the r skill score. To rank the AR4 models, sea level pressure, surface air temperature and precipitation variables were selected and a group of five AR4 models were identified as the models which best reproduce current climate in the area: MIROC3.2-HIRES, MPI-ECHAM5, GFDL-CM2.1, BCCR-BCM2.0 and UKMO-HADGEM1. The rank obtained should not be understood in a hierarchical manner because there is a certain degree of internal variability in the model ensembles. Finally, it should be noted that these results are in good agreement with other classifications found in the scientific literature.  相似文献   

Double-difference Relocation of the Aftershocks of the Tecom��n, Colima, Mexico Earthquake of 22 January 2003     

Vanessa Andrews  Joann Stock  Carlos Ariel Ram��rez V��zquez  Gabriel Reyes-D��vila 《Pure and Applied Geophysics》2011,168(8-9):1331-1338

On 22 January 2003, the M _w?=?7.6 Tecomán earthquake struck offshore of the state of Colima, Mexico, near the diffuse triple junction between the Cocos, Rivera, and North American plates. Three-hundred and fifty aftershocks of the Tecomán earthquake with magnitudes between 2.6 and 5.8, each recorded by at least 7 stations, are relocated using the double difference method. Initial locations are determined using P and S readings from the Red Sismológica Telemétrica del Estado de Colima (RESCO) and a 1-D velocity model. Because only eight RESCO stations were operating immediately following the Tecomán earthquake, uncertainties in the initial locations and depths are fairly large, with average uncertainties of 8.0?km in depth and 1.4?km in the north?Csouth and east?Cwest directions. Events occurring between 24 January and 31 January were located using not only RESCO phase readings but also additional P and S readings from 11 temporary stations. Average uncertainties decrease to 0.8?km in depth, 0.3?km in the east?Cwest direction, and 0.7?km in the north?Csouth direction for events occurring while the temporary stations were deployed. While some preliminary studies of the early aftershocks suggested that they were dominated by shallow events above the plate interface, our results place the majority of aftershocks along the plate interface, for a slab dipping between approximately 20° and 30°. This is consistent with the slab positions inferred from geodetic studies. We do see some upper plate aftershocks that may correspond to forearc fault zones, and faults inland in the upper plate, particularly among events occurring more than 3?months after the mainshock.  相似文献