The XMM-Newton Bright Serendipitous Survey: First Extragalactic Results     

Tommaso Maccacaro  Roberto Della Ceca  Valentina Braito  Alessandro Caccianiga  Paola Severgnini  Anna Wolter 《Astrophysics and Space Science》2004,294(1-2):89-94

We present here some initial results from the ongoing XMM-Newton bright serendipitous survey. The survey is aimed at selecting and spectroscopically identifying a large and statistically representative sample of bright (f _x ≳ 7× 10⁻¹⁴ c.g.s) serendipitous X-ray sources in the 0.5–4.5 keV energy band (BSS) and a complementary (smaller) sample in the 4.5–7.5 keV energy band (HBSS). The work is partly based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributors directly founded by ESA member states and the USA(NASA) and on observations collected at TNG. The TNG telescope is operated on the island of La Palma by the Centro Galileo Galilei of the INAF in the Spanish Observatorio del Roque de Los Muchachos of the Instituto de Astrofísica de Canarias. On behalf of the XMM-Newton Survey Science Center.  相似文献   

On the origin of fluorine in the Milky Way     

Agostino Renda  Yeshe Fenner  Brad K. Gibson  Amanda I. Karakas  John C. Lattanzio  Simon Campbell  Alessandro Chieffi  Katia Cunha  Verne V. Smith 《Monthly notices of the Royal Astronomical Society》2004,354(2):575-580

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How faithful areN-body simulations of disc galaxies?-artificial suppression of gaseous dynamical instabilities     

Alessandro B. Romeo 《Astrophysics and Space Science》1994,216(1-2):353-357

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Quantitative perturbation theory by successive elimination of harmonics     

Alessandro Morbidelli  Antonio Giorgilli 《Celestial Mechanics and Dynamical Astronomy》1993,55(2):131-159

We revisit some results of perturbation theories by a method of successive elimination of harmonics inspired by some ideas of Delaunay. On the one hand, we give a connection between the KAM theorem and the Nekhoroshev theorem. On the other hand, we support in a quantitative fashion a semi-numerical method of analysis of a perturbed system recently introduced by one of the authors.  相似文献   

Landslide detection using deep learning and object-based image analysis     

Ghorbanzadeh  Omid  Shahabi  Hejar  Crivellari  Alessandro  Homayouni  Saeid  Blaschke  Thomas  Ghamisi  Pedram 《Landslides》2022,19(4):929-939

Landslides - Recent landslide detection studies have focused on pixel-based deep learning (DL) approaches. In contrast, intuitive annotation of landslides from satellite imagery is based on...  相似文献   

Numerical modelling of the effects of foundation scour on the response of a bridge pier     

Ciancimino  Andrea  Anastasopoulos  Ioannis  Foti  Sebastiano  Gajo  Alessandro 《Acta Geotechnica》2022,17(9):3697-3717

Foundation scour can have a detrimental effect on the performance of bridge piers, inducing a significant reduction of the lateral capacity of the footing and accumulation of permanent settlement and rotation. Although the hydraulic processes responsible for foundation scour are nowadays well known, predicting their mechanical consequences is still challenging. Indeed, its impact on the failure mechanisms developing around the foundation has not been fully investigated. In this paper, numerical simulations are performed to study the vertical and lateral response of a scoured bridge pier founded on a cylindrical caisson foundation embedded in a layer of dense sand. The sand stress–strain behaviour is reproduced by employing the Severn-Trent model. The constitutive model is firstly calibrated on a set of soil element tests, including drained and undrained monotonic triaxial tests and resonant column tests. The calibration procedure is implemented considering the stress and strain nonuniformities within the samples, by simulating the laboratory tests as boundary value problems. The numerical model is then validated against the results of centrifuge tests. The results of the simulations are in good agreement with the experimental results in terms of foundation capacity and settlement accumulation. Moreover, the model can predict the effects of local and general scour. The numerical analyses also highlight the impact of scouring on the failure mechanisms, revealing that the soil resistance depends on the hydraulic scenario.

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http://www.sciencedirect.com/science/article/pii/S1674987114000905     

Petar Gliovi  Alessandro M.Forte 《地学前缘(英文版)》2015,6(1):3-22

Although there has been significant progress in the seismic imaging of mantle heterogeneity,the outstanding issue that remains to be resolved is the unknown distribution of mantle temperature anomalies in the distant geological past that give rise to the present-day anomalies inferred by global tomography models.To address this question,we present 3-D convection models in compressible and self-gravitating mantle initialised by different hypothetical temperature patterns.A notable feature of our forward convection modelling is the use of self-consistent coupling of the motion of surface tectonic plates to the underlying mantle flow,without imposing prescribed surface velocities(i.e.,plate-like boundary condition).As an approximation for the surface mechanical conditions before plate tectonics began to operate we employ the no-slip(rigid) boundary condition.A rigid boundary condition demonstrates that the initial thermally-dominated structure is preserved,and its geographical location is fixed during the evolution of mantle flow.Considering the impact of different assumed surface boundary conditions(rigid and plate-like) on the evolution of thermal heterogeneity in the mantle we suggest that the intrinsic buoyancy of seven superplumes is most-likely resolved in the tomographic images of present-day mantle thermal structure.Our convection simulations with a plate-like boundary condition reveal that the evolution of an initial cold anomaly beneath the Java-Indonesian trench system yields a long-term,stable pattern of thermal heterogeneity in the lowermost mantle that resembles the presentday Large Low Shear Velocity Provinces(LLSVPs),especially below the Pacific.The evolution of subduction zones may be,however,influenced by the mantle-wide flow driven by deeply-rooted and longlived superplumes since Archean times.These convection models also detect the intrinsic buoyancy of the Perm Anomaly that has been identified as a unique slow feature distinct from the two principal LLSVPs.We find there is no need for dense chemical ’piles’ in the lower mantle to generate a stable distribution of temperature anomalies that are correlated to the LLSVPs and the Perm Anomaly.Our tomography-based convection simulations also demonstrate that intraplate volcanism in the south-east Pacific may be interpreted in terms of shallow small-scale convection triggered by a superplume beneath the East Pacific Rise.  相似文献   

Excavation works in stiff jointed clay material: examples from the Trubi formation,southern Italy     

David Segato  Giuseppe Scarpelli  Viviene M. E. Fruzzetti  Paolo Ruggeri  Alessandro Vita  Alessandra Paternesi 《Landslides》2015,12(4):721-730

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Assessing the influence of climate model uncertainty on EU-wide climate change impact indicators     

Tobias Lung  Alessandro Dosio  William Becker  Carlo Lavalle  Laurens M. Bouwer 《Climatic change》2013,120(1-2):211-227

Despite an increasing understanding of potential climate change impacts in Europe, the associated uncertainties remain a key challenge. In many impact studies, the assessment of uncertainties is underemphasised, or is not performed quantitatively. A key source of uncertainty is the variability of climate change projections across different regional climate models (RCMs) forced by different global circulation models (GCMs). This study builds upon an indicator-based NUTS-2 level assessment that quantified potential changes for three climate-related hazards: heat stress, river flood risk, and forest fire risk, based on five GCM/RCM combinations, and non-climatic factors. First, a sensitivity analysis is performed to determine the fractional contribution of each single input factor to the spatial variance of the hazard indicators, followed by an evaluation of uncertainties in terms of spread in hazard indicator values due to inter-model climate variability, with respect to (changes in) impacts for the period 2041–70. The results show that different GCM/RCM combinations lead to substantially varying impact indicators across all three hazards. Furthermore, a strong influence of inter-model variability on the spatial patterns of uncertainties is revealed. For instance, for river flood risk, uncertainties appear to be particularly high in the Mediterranean, whereas model agreement is higher for central Europe. The findings allow for a hazard-specific identification of areas with low vs. high model agreement (and thus confidence of projected impacts) within Europe, which is of key importance for decision makers when prioritising adaptation options.  相似文献   

The special climate change fund: origins and prioritisation assessment     

Valentina Bosetti  Marzio Galeotti  Alessandro Lanza 《Climate Policy》2013,13(3):295-312

Abstract

A central issue in tackling climate change is to understand to what extent different short-term mitigation strategies are consistent with long-term stabilization targets. The present article aims at cross-comparing emission paths derived by plausible short-term policies against those implied by long-term climate targets, comparing, for example, differences in peak periods. Short-term policies considered are, for instance, Kyoto-type targets with or without participation by the USA and/or by developing countries. Long-term targets focus instead on stabilization of CO₂ concentrations, radiative forcing and the increase in atmospheric temperature relative to pre-industrial levels. In order to account for the uncertainty surrounding the climate cycle, for each long-term goal multiple paths of emission—the most probable, the optimistic and the pessimistic projections—are considered in the comparison exercise. Comparative analysis is performed using the FEEM-RICE model, a regional economy—climate model. The results suggest that some early policy action should take place for short-term emissions to be compatible with long-term targets. In particular, the Kyoto-type regimes appear to be on a compatible emission path, at least up to the second commitment period. However, this is no longer the case when assuming a pessimistic realization of the uncertain climate parameters.  相似文献