Compact groups in theory and practice – III. Compact groups of galaxies in the Sixth Data Release of the Sloan Digital Sky Survey     

Alan W. McConnachie  David R. Patton  Sara L. Ellison  Luc Simard 《Monthly notices of the Royal Astronomical Society》2009,395(1):255-268

We present the largest publicly available catalogue of compact groups (CGs) of galaxies identified using the original selection criteria of Hickson, selected from the Sixth Data Release of the Sloan Digital Sky Survey (SDSS DR6). We identify 2297 CGs down to a limiting magnitude of   r = 18 (∼0.24 groups  deg⁻²), and 74 791 CGs down to a limiting magnitude of   r = 21 (∼6.7 groups  deg⁻²). This represents 0.9 per cent of all galaxies in the SDSS DR6 at these magnitude levels. Contamination due to gross photometric errors has been removed from the bright sample of groups, and we estimate it is present in the large sample at the 14 per cent level. Spectroscopic information is available for 4131 galaxies in the bright catalogue (43 per cent completeness), and we find that the median redshift of these groups is   z _med= 0.09  . The median line-of-sight (LOS) velocity dispersion within the CGs from the bright catalogue is  σ_LOS≃ 230 km s⁻¹  , and their typical intergalactic separations are of the order of 50–100 kpc. We show that the fraction of groups with interloping galaxies identified as members is in good agreement with the predictions from our previous study of a mock galaxy catalogue, and we demonstrate how to select CGs such that the interloper fraction is well defined and minimized. This observational data set is ideal for large statistical studies of CGs, the role of environment on galaxy evolution and the effect of galaxy interactions in determining galaxy morphology.  相似文献   

Different Effects of a By‐product From Olive Oil Extraction on S‐Metolachlor and Bentazone Soil Fate          下载免费PDF全文

Ana I. Cañero  Lucía Cox  Alegría Cabrera  Juan Cornejo 《洁净——土壤、空气、水》2015,43(6):948-957

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Fluvial flood risk in Europe in present and future climates   总被引：2，自引：0，他引：2  

Luc Feyen  Rutger Dankers  Katalin Bódis  Peter Salamon  José I. Barredo 《Climatic change》2012,112(1):47-62

In this work we evaluate the implications of climate change for future fluvial flood risk in Europe, considering climate developments under the SRES A2 (high emission) and B2 (low emission) scenario. We define flood risk as the product of flood probability (or hazard), exposure of capital and population, and vulnerability to the effect of flooding. From the European flood hazard simulations of Dankers and Feyen (J Geophys Res 114:D16108. doi:, 2009) discharges with return periods of 2, 5, 10, 20, 50, 100, 250 and 500 years were extracted and converted into flood inundation extents and depths using a planar approximation approach. Flood inundation extents and depths were transformed into direct monetary damage using country specific flood depth-damage functions and land use information. Population exposure was assessed by overlaying the flood inundation information with data on population density. By linearly interpolating damages and population exposed between the different return periods, we constructed damage and population exposure probability functions under present and future climate. From the latter expected annual damages (EAD) and expected annual population exposed (EAP) were calculated. To account for flood protection the damage and population exposure probability functions were truncated at design return periods based on the country GDP/capita. Results indicate that flood damages are projected to rise across much of Western Europe. Decreases in flood damage are consistently projected for north-eastern parts of Europe. For EU27 as a whole, current EAD of approximately €6.4 billion is projected to amount to €14–21.5 billion (in constant prices of 2006) by the end of this century, depending on the scenario. The number of people affected by flooding is projected to rise by approximately 250,000 to 400,000. Notwithstanding these numbers are subject to uncertainty, they provide an indication of potential future developments in flood risk in a changing climate.  相似文献   

Precipitation spatial variability and dry areas temporal stability for different elevation classes in the Macta basin (Algeria)     

M. Achite  G. Buttafuoco  K. A. Toubal  F. Lucà 《Environmental Earth Sciences》2017,76(13):458

The water availability relies primarily on precipitation whose spatial and temporal variability depends on meteorological and topographic attributes. Water becomes a precious natural resource, especially in semiarid areas. Generally, decisions on water resources are made on the whole watershed, but the variability of precipitation is related to topography. The work was aimed at quantifying the spatial variability of annual precipitation for a 40-year-long time series in the Macta basin (Algeria) by using a geostatistical approach and to detect the temporal stability of dry areas. To assess if annual precipitation variability could depend upon the elevation, the study area was divided into five geographical units (polygons) based on elevation and polygon kriging was applied. For each hydrologic year, the standardized relative difference of precipitation (SRDP) was evaluated and dry areas identified. The temporal stability of SRDP with elevation was assessed using the Spearman rank coefficient. Geostatistical approach showed different variability structures of annual precipitation over the considered period. Results highlighted differences in SRDP within the geographical units located at different elevation and the non-stability of dry periods with time within the same polygon. A remarkable dry tendency was assessed in the northern polygon, while the polygons at higher elevations were dominated by temporal instability. The spatio-temporal non-stability of dry areas might be attributed to the change in general atmospheric circulation in North Africa over the last decades and to the nonlinear interaction among precipitation and orography. The identification of dry areas can help decision-makers to plan management and conservation programs in Algeria.  相似文献   

Assessing the diamond potential of kimberlites from discovery to evaluation bulk sampling     

Luc?RomboutsEmail author 《Mineralium Deposita》2003,38(4):496-504

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Execution Of A Triple Pumping Test And Interpretation By An Inverse Numerical Model     

L. Lebbe  M. Mahauden  W. De Breuck 《Hydrogeology Journal》1992,1(4):20-34

The hydraulic parameters of a multi-layered aquifer are deduced with the help of a multiple pumping test. All the observed drawdowns are interpreted simultaneously with an inverse model. It is shown that the vertical hydraulic conductivities of the semi-pervious layers can be deduced with accuracies comparable to those of the horizontal hydraulic conductivities of previous layers. The lithostratigraphic information collected during drilling and geophysical borehole logging can be represented accurately in the numerical model, an axi-symmetric hybrid finite-difference finite-element model. The model starts with the ordinary least squares method. If there are many outliers this method is followed by the biweighted least squares method to reduce their effect on the estimates. The accuracies of the estimates are deduced from their variance-covariance matrix. The method is illustrated by a triple pumping test in the layered groundwater reservoir at the top of the Ieper Group of Flanders (Belgium) and can be considered as a generalized interpretation method of pumping tests. Résumé: Les paramètres hydrauliques d'un aquifère multicouches sont déduits à l'aide d'un essai de pompage multiple. Tous les rabbattements observés sont interpretés simultanément par un modèle inverse. Il est démontré qu'on peut déduire les conductivités verticales des couches semi-perméables avec une précision comparable à celle des conductivités horizontales des couches perméables. L'information recueillie pendant le forage des puits et par les diagraphies géophysiques permet d'introduire avec une grande précision la lithostratigraphie dans le modèle numéerique, qui est un modèle axi-symétrique hybride différences finies éléments finis. Le modèle inverse utilise en premier lieu la méthode ordinaire de moindres carrés. Dans le cas de plusieurs valeurs extrèmes cette méthode est suivie par la méthode de moindres carrés bipondérés pour réduire l'effet de ces valeurs sur les estimations. Les précisions d'estimation des paramètres sont déduites de leur matrice de variance-covariance. La méthode, qui est illustrée par l'interprétation d'un essai de pompage triple dans l'aquifère multicouches formé dans la partie supéerieure du Groupe d'Ieper de Flandre (Belgique), peut être considérée comme une méthode généralisée d'interprétation des essais de pompage.  相似文献   

Non-iterative multiple-attenuation methods: linear inverse solutions to non-linear inverse problems – II. BMG approximation     

Luc T. Ikelle  Are Osen  Lasse Amundsen  Yunqing Shen 《Geophysical Journal International》2004,159(3):923-930

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Rare earth element geochemistry of Thetford Mines ophiolite complex,Northern Appalachians,Canada     

Luc Harnois  Jacques Trottier  Maurice Morency 《Contributions to Mineralogy and Petrology》1990,105(4):433-445

The Thetford Mines complex is a complete ophiolite which is part of an ultramafic-mafic belt within Québec Appalachians. These allochtonous bodies were emplaced during the Early Ordovician. The Thetford Mines complex comprises a lower unit of metamorphic harzburgite (in which tabular, dyke-like, dunitic bodies occur) overlain successively by ultramafic cumulates, mafic cumulates, ophitic gabbros, diabase sills and dykes, and basaltic volcanic rocks. Field evidence, petrography and chemical data indicate that the tabular dunitic bodies formed when fractures in the metamorphic harzburgite (which constituted the floor of the magma chamber) filled with early cumulates (i.e., olivine±chromite). Representative rocks from all units were analyzed for major and rare earth elements (REE). Metamorphic harzburgite samples from Thetford Mines complex have U-shaped chondrite-normalized REE patterns. Pyroxenites and wehrlites of the cumulate sequence are all strongly light-REE depleted and have heavy REE ranging from 0.4 to 1.5 times chondrite. REE data from ultramafic and volcanic rocks of Thetford Mines complex and geochemical modelling indicate that the metamorphic harzburgite has the chemical characteristics of depleted upper mantle residues with U-shaped patterns, and that the ultramafic cumulates crystallized from magmas having different La/Yb ratios.  相似文献   

Multiple transit times and least squares for gyroscopic azimuth     

Luc M. A. Jeudy 《Journal of Geodesy》1986,60(4):288-296

Principles of North determination using suspended gyrocompasses are reviewed. Accuracy is evaluated and a procedure with two series of measurements symmetrical with respect to the zero torsion tape position is mathematically proven to be the “best” (minimum variance). Our purpose is to prove that a 20″ accuracy (1 σ) instrument was brought to a level of accuracy four times better by using multiple transit times and least squares fit. Over a total of 15 North determinations based on more than a thousand transit times, an external standard error of 4″.4 was obtained using a WildGAK-1.  相似文献   

Linear demultiple solution based on the concept of bottom-multiple-generator (BMG) approxiamtion: some new results     

Abiola O. Oladeinde  Luc T. Ikelle 《Geophysical Prospecting》2006,54(4):425-431

Recent advances in the demultiple technique have shown that a multidimensional convolution of a portion of data containing only primaries with the whole data (containing both primaries and multiples) can allow us to predict and attenuate all orders of free‐surface multiples that are relevant for practical purposes. One way of constructing the portion of the data containing only primaries is by muting the actual data just above the first free‐surface multiple to arrive. The location of the mute is generally known as the bottom‐multiple‐generator (BMG) reflector; the portion of the data containing only primaries required for constructing the free‐surface multiples is located above the BMG. The outstanding question about this method is how effective can the technique be when the BMG cuts through several seismic events, as is the case in long‐offset data or in very complex shallow geology. We present new results which demonstrate the fact that the BMG location may cut through several seismic events without affecting the accuracy or the cost of demultiple.  相似文献