We present a new set of diagnostics which allow us to trace and classify in a statistical manner the mid-IR emission produced
by active galactic nuclei (AGN) and star-forming regions. We construct a diagram based on the strength of the unidentified
infrared band (UIB)at 6.2 μm, and the intensity of the continuum at short (6 μm) and long wavelengths (15 μm). We interpret
the integrated mid-IR emission in late-type galaxies as resulting from three individual contributions coming from HII regions,
diffuse/photodissociation regions (PDRs), and AGN. Based on this assumption, our diagnostic diagram provides a quantitative
estimate of the AGN and starburst contribution to an observed mid-IR spectrum. We show that UIB emission is very faint or
absent in regions harbouring intense and hard radiation fields as in the case of AGN or ‘pure’ HII starburst regions where
UIB carriers can be destroyed by photodissociation. However, contrary to starburst spectra, typical AGN spectra present a
strong hot continuum below 9 μm originating from hot dust heated by the AGN radiation field. An extrapolation of this diagnostic
towards other mid-IR observations should improve our knowledge of the AGN/starburst connection.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
To help improve the safety of its population faced with natural disasters, the Cameroon Government, with the support of the
French Government, initiated a programme of geological risk analysis and mapping on Mount Cameroon. This active volcano is
subject to a variety of hazards: volcanic eruptions, slope instability and earthquakes. Approximately 450,000 people live
or work around this volcano, in an area which includes one of Cameroon’s main economic resources. An original methodology
was used for obtaining the information to reply to questions raised by the authorities. It involves several stages: identifying
the different geological hazard components, defining each phenomenon’s threat matrix by crossing intensity and frequency indices,
mapping the hazards, listing and mapping the exposed elements, analysing their respective values in economic, functional and
strategic terms, establishing typologies for the different element-at-risk groups and assessing their vulnerability to the
various physical pressures produced by the hazard phenomena, and establishing risk maps for each of the major element-at-risk
groups (population, infrastructures, vegetation, atmosphere). At the end of the study we were able (a) to identify the main
critical points within the area, and (b) provide quantified orders of magnitude concerning the dimensions of the risk by producing
a plausible eruption scenario. The results allowed us to put forward a number of recommendations to the Cameroon Government
concerning risk prevention and management. The adopted approach corresponds to a first level of response to the authorities.
Later developments should make it possible to refine the quality of the methodology. 相似文献
We introduce a new method for implicit structural modeling. The main developments in this paper are the new regularization operators we propose by extending inherent properties of the classic one-dimensional discrete second derivative operator to higher dimensions. The proposed regularization operators discretize naturally on the Cartesian grid using finite differences, owing to the highly symmetric nature of the Cartesian grid. Furthermore, the proposed regularization operators do not require any special treatment on boundary nodes, and their generalization to higher dimensions is straightforward. As a result, the proposed method has the advantage of being simple to implement. Numerical examples show that the proposed method is robust and numerically efficient.
As a part of the ANR-Forclim experiment, particle mass fluxes and sedimentation processes were investigated on the slope of Aquitanian margin of the Bay of Biscay, between the canyons of Cap-Breton and Cap-Ferret. Interface sediments were collected along a depth transect from 145 to 2000 m; simultaneously a mooring line was deployed at the deepest station (WH, 2000 m) with two traps (800 and 1700 m) for a 16-month period (June 2006–November 2007). 210Pb activities of settling particles and of interface sediments were determined to study transport processes of particles. Sediment and mass accumulation rates, calculated from excess 210Pb profiles in the sediment column, show the expected decreasing trend with depth, as usually observed on margins. Mean particulate mass fluxes at 800 and 1700-m depth at site WH are, respectively, 27 and 70 g m?2 a?1.The 210Pb budget points out events of temporary high lateral input of particles. The comparison of mass and 210Pb fluxes between the water column and the seabed indicates that lateral transport plays an important role in particle accumulation on the Aquitanian margin. Regarding the objectives of the ANR-Forclim program, which aims to improve significantly the interpretation of fossil foraminifera signals, as a proxy for hydrological changes in the North Atlantic ocean, these results highlight advection processes must be considered when interpreting fluxes of foraminifers on the Aquitanian margin. 相似文献
This paper records the findings from c. 80 prehistoric sites that have been discovered in the alluvial deposits of the rivers Creuse, Cher, and Loir, tributaries of the middle Loire River, over the period since 1981. These deposits comprise river terrace aggradations formed during successive glacial–interglacial cycles which have recorded climate and environment during Quaternary time. The systematic dating of these river deposits by Electron Spin Resonance (ESR) applied to optically bleached sedimentary quartz has resulted in the establishment of a chronological framework for the evolution of these rivers during Lower and Middle Pleistocene (between 1.7 Ma and 130 ka). Evidence for Early Palaeolithic (Mode 1) industries with an in situ context (workshops, soils) in the highest aggradations indicates that Hominins were present in the study area, near the geographical centre of France (47°N), around 1.1 Ma. Examination of the sites indicates that Human occupations were located along valley bottom sites during temperate episodes. Subsequently, after a gap of several hundred thousand years industries with handaxes appear in the Middle Loire Basin in the interval between 700 and 600 ka, and then continuously from 400 ka. These two phases of settlement produced industrial assemblages with clear differences in their responses to the supplies of raw materials and in the modes of making flakes. 相似文献
The Atlantic Meridional Overturning Circulation (AMOC) is a key feature of the climate system. However, its role during climate change is still poorly constrained particularly during an Interglacial to Glacial climate transition and the associated global cooling. We present here the first reconstruction of the evolution of the vertical structure of the rate of the AMOC from the Last Interglaciation to the subsequent glaciation (128,000–60,000 years ago) based on sedimentary (231Pa/230Th) records. We show a deep AMOC during the interglacial warmth Marine Isotope Stage (MIS) 5.5 and a shallower glacial one during glacial MIS 4. The change between these two patterns occurred mostly during the glacial inception, i.e. the transition from MIS 5.5 to MIS 5.4. Our data show that AMOC was enhanced during this latter transition as a consequence of a large increase of the overturning rate of the Intermediate Waters, above 2500 m. We suggest that this AMOC pattern required a reinforced Gulf Stream-North Atlantic Current system that ultimately supported ice-sheet growth by providing heat and moisture to the Northern high latitudes. From MIS 5.4 to MIS 5.1, the AMOC was broadly continuous below 2000 m and supported periods of ice-sheet growth. As a result, a glacial AMOC is triggered at the beginning of MIS 4 due to the extension of ice-sheet and the subsequent reorganization of deep-water formation. This study highlights the role of intermediate waters as a major player during climate change. 相似文献
Understanding the impact of anthropogenic climate change on drought is of great significance to the prevention of its adverse effects. Two drought indices, stan... 相似文献