The effect of stellar feedback and quasar winds on the active galactic nucleus population     

Fabio Fontanot  Pierluigi Monaco  Stefano Cristiani  Paolo Tozzi 《Monthly notices of the Royal Astronomical Society》2006,373(3):1173-1187

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On the Formation and Evolution of QSOs     

Stefano Cristiani 《Astrophysics and Space Science》2004,294(1-2):79-87

I had the privilege, many years ago, to be supervised by Alfonso Cavaliere in my Master thesis work. I remember the great patience and enthusiasm with which, in a warm summer day, he presented to me a score of exciting astrophysical problems. We finally determined to study the relationship of QSOs and BL Lacs—then considered rather exotic object—with normal galaxies. In the years I have continued on this line of research, reacting far too slowly to the wealth of new ideas that Alfonso has been continuously injecting in our conversations. As examples I will report two recent results on the chemical abundances of QSO host galaxies and on the space density of high-z QSOs, which are closely related to our shared interest on AGN.  相似文献   

Gamma rays from molecular clouds     

Stefano Gabici  Felix A. Aharonian  Pasquale Blasi 《Astrophysics and Space Science》2007,309(1-4):365-371

It is believed that the observed diffuse gamma-ray emission from the galactic plane is the result of interactions between cosmic rays and the interstellar gas. Such emission can be amplified if cosmic rays penetrate into dense molecular clouds. The propagation of cosmic rays inside a molecular cloud has been studied assuming an arbitrary energy and space dependent diffusion coefficient. If the diffusion coefficient inside the cloud is significantly smaller compared to the average one derived for the galactic disk, the observed gamma-ray spectrum appears harder than the cosmic ray spectrum, mainly due to the slower penetration of the low energy particles towards the core of the cloud. This may produce a great variety of gamma-ray spectra.  相似文献   

Iron and nickel line properties in the X-ray-reflecting region of the Circinus galaxy     

Silvano Molendi  Stefano Bianchi  Giorgio Matt 《Monthly notices of the Royal Astronomical Society》2003,343(1):L1-L4

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A faint red stellar halo around an edge-on disc galaxy in the Hubble Ultra Deep Field     

Stefano Zibetti  Annette M. N. Ferguson 《Monthly notices of the Royal Astronomical Society》2004,352(2):L6-L10

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Haloes around edge-on disc galaxies in the Sloan Digital Sky Survey     

Stefano Zibetti  Simon D. M. White  Jon Brinkmann 《Monthly notices of the Royal Astronomical Society》2004,347(2):556-568

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New results of ⁴⁰Ar/³⁹Ar dating constrain the timing of transition from fissure-type to central volcanism at Mount Etna (Italy)     

Emanuela De Beni  Jan R. Wijbrans  Stefano Branca  Mauro Coltelli  Gianluca Groppelli 《地学学报》2005,17(3):292-298

Recent geological studies performed at Etna allow reassessing the stratigraphic frame of the volcano where distinct evolutionary phases are defined. This stratigraphic reconstruction was chronologically constrained on the basis of a limited number of U–Th and K–Ar age determinations whose uncertainty margins are sometimes too wide. For this reason, we successfully adopted at Etna the ⁴⁰Ar/³⁹Ar technique that allowed obtaining more precise age determinations. The incremental heating technique also gives information on sample homogeneity, and potential problems of trapped argon. Five samples were collected from stratigraphically well-controlled volcanic units in order to chronologically define the transition between the fissure-type volcanism of the Timpe phase to the central volcanism of the Valle del Bove Centers. Isotopic ages with an uncertainty margin of 2–4% have been obtained emphasizing that this transition occurred (130–126 ka) without significant temporal hiatus.  相似文献   

Nile floods recorded in deep Mediterranean sediments     

Emmanuelle Ducassou  Thierry Mulder  Sbastien Migeon  Eliane Gonthier  Anne Murat  Marie Revel  Lucilla Capotondi  Stefano M. Bernasconi  Jean Mascle  Sbastien Zaragosi 《Quaternary Research》2008,70(3):382-391

Clastic mud beds rich in continental organic matter are observed recurrently in the Nile deep-sea turbidite system. They formed during flooding periods of the river similar to those that induce sapropel formation and occurred during periods of increased density stratification of the eastern Mediterranean. The very fine-grained flood deposits are intercalated within pelagic sediments, sapropels and Bouma-type turbidites. These flood deposits form by the successive reconcentrations of surface (hypopycnal) plumes by convective sedimentation, which in turn generate a fine-grained low-energy hyperpycnal flow. Sea-level high stands seem also to favor hypopycnal plume formation and increase clastic mud bed formation. Consequently, these muddy clastic beds provide a direct link between deep-marine sedimentary records and continental climatic change through flood frequency and magnitude.  相似文献   

Bringing GEOSS Services into Practice: A Capacity Building Resource on Spatial Data Infrastructures (SDI)          下载免费PDF全文

Gregory Giuliani  Pierre Lacroix  Yaniss Guigoz  Roberto Roncella  Lorenzo Bigagli  Mattia Santoro  Paolo Mazzetti  Stefano Nativi  Nicolas Ray  Anthony Lehmann 《Transactions in GIS》2017,21(4):811-824

Data discoverability, accessibility, and integration are frequent barriers for scientists and a major obstacle for favorable results on environmental research. To tackle this issue, the Group on Earth Observations (GEO) is leading the development of the Global Earth Observation System of Systems (GEOSS), a voluntary effort that connects Earth Observation resources world‐wide, acting as a gateway between producers and users of environmental data. GEO recognizes the importance of capacity building and education to reach large adoption, acceptance and commitment on data sharing principles to increase the capacity to access and use Earth Observations data. This article presents “Bringing GEOSS services into practice” (BGSIP), an integrated set of teaching material and software to facilitate the publication and use of environmental data through standardized discovery, view, download, and processing services, further facilitating the registration of data into GEOSS. So far, 520 participants in 10 countries have been trained using this material, leading to numerous Spatial Data Infrastructure implementations and 1,000 tutorial downloads. This workshop lowers the entry barriers for both data providers and users, facilitates the development of technical skills, and empowers people.  相似文献   

Parametric Study of Urban-Like Topographic Statistical Moments Relevant to a Priori Modelling of Bulk Aerodynamic Parameters   总被引：1，自引：1，他引：0  

Xiaowei Zhu  G. Valerio Iungo  Stefano Leonardi  William Anderson 《Boundary-Layer Meteorology》2017,162(2):231-253

For a horizontally homogeneous, neutrally stratified atmospheric boundary layer (ABL), aerodynamic roughness length, \(z_0\), is the effective elevation at which the streamwise component of mean velocity is zero. A priori prediction of \(z_0\) based on topographic attributes remains an open line of inquiry in planetary boundary-layer research. Urban topographies – the topic of this study – exhibit spatial heterogeneities associated with variability of building height, width, and proximity with adjacent buildings; such variability renders a priori, prognostic \(z_0\) models appealing. Here, large-eddy simulation (LES) has been used in an extensive parametric study to characterize the ABL response (and \(z_0\)) to a range of synthetic, urban-like topographies wherein statistical moments of the topography have been systematically varied. Using LES results, we determined the hierarchical influence of topographic moments relevant to setting \(z_0\). We demonstrate that standard deviation and skewness are important, while kurtosis is negligible. This finding is reconciled with a model recently proposed by Flack and Schultz (J Fluids Eng 132:041203-1–041203-10, 2010), who demonstrate that \(z_0\) can be modelled with standard deviation and skewness, and two empirical coefficients (one for each moment). We find that the empirical coefficient related to skewness is not constant, but exhibits a dependence on standard deviation over certain ranges. For idealized, quasi-uniform cubic topographies and for complex, fully random urban-like topographies, we demonstrate strong performance of the generalized Flack and Schultz model against contemporary roughness correlations.  相似文献