On the interpretation of white dwarf spectra     

Francesca D'Antona  Italo Mazzitelli 《Astrophysics and Space Science》1974,27(1):137-146

Following the line of research outlined by Strittmatter and Wickramasinghe (1971) and recently by Shipman (1972), attention was drawn to the study of convective zones in white dwarfs for various masses and chemical compositions, in order to understand some observational features of their spectra. According to the results, convection strongly depends on the mass of the star, forM<0.5 M_⊙, and low hydrogen abundancesX?0.2) are sufficient to decrease the extension of the He-convection zones with respect to pure-He models. It is shown that the existence of DB white dwarfs seems not in agreement with the accretion rates predicted by Bondi (1952), and that DB's must evolve into H-lacking white dwarfs.  相似文献   

On the structure of the globular cluster M4     

Vittorio Castellani  Francesca A. D'Antona  Antonella Natta 《Astrophysics and Space Science》1972,17(1):23-29

On the basis of the work by Greenstein on the globular cluster M 4, the spatial distribution for groups of cluster stars in different stages of evolution is investigated. The comparison between the various samples is made using the apparent distributions. The results are discussed.

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Riassunto Sulla base dello studio di Greenstein sull'ammasso globulare M4, è stata riesaminata la distribuzione spaziale di gruppi di stelle di questo ammasso evolutivamente significativi. Si puntualizza come sia possibile operare un confronto tra le distribuzioni dei vari gruppi sulla base delle distribuzioni apparenti anzichè su quelle reali senza alterare la sostanza dei risultati. Si discutono i risultati.

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Analysis of climatic trends in data from the agrometeorological station of Bologna-Cadriano, Italy (1952–2007)     

Philipp Matzneller  Francesca Ventura  Nicola Gaspari  Paola Rossi Pisa 《Climatic change》2010,100(3-4):717-731

Agriculture is highly exposed to climate change, as farming activities directly depend on climatic conditions. Knowledge of the extent of such change and of related phenomena will help to answer the questions posed by society about adaptation strategies. The global situation is well described by the Fourth IPCC assessment report (IPCC 2007), but local studies are important to understand the impact and the priorities to adopt in adaptation strategies. In this study a historical set of meteorological data, collected during the period 1952–2007 at the University of Bologna (Italy) agrometeorological station, was analysed. Several indexes, such as Frost Severity Index, number of hot days, number of rainy days, etc., were calculated, and their trends in time were analysed. The results show a scenario of increasing temperatures and evapotranspiration, a decrease in rainy days and a deepening of the watertable. The effect of these changes on agriculture will be a decrease in water availability, an increase in heat stress in plants and an increase in drought risk.  相似文献   

Spectral properties and composition of potentially hazardous Asteroid (99942) Apophis     

Richard P. Binzel  Andrew S. Rivkin  Cristina A. Thomas  Pierre Vernazza  Thomas H. Burbine  Francesca E. DeMeo  Schelte J. Bus  Alan T. Tokunaga  Mirel Birlan 《Icarus》2009,200(2):480-485

The known close approach of Asteroid (99942) Apophis in April 2029 provides the opportunity for the case study of a potentially hazardous asteroid in advance of its encounter. The visible to near-infrared (0.55 to 2.45 μm) reflectance spectrum of Apophis is compared and modeled with respect to the spectral and mineralogical characteristics of likely meteorite analogs. Apophis is found to be an Sq-class asteroid that most closely resembles LL ordinary chondrite meteorites in terms of spectral characteristics and interpreted olivine and pyroxene abundances, although we cannot rule out some degree of partial melting. A meteorite analog allows some estimates and conjectures of Apophis' possible range of physical properties such as the grain density and micro-porosity of its constituent material. Composition and size similarities of Apophis with (25143) Itokawa suggest a total porosity of 40% as a “current best guess” for Apophis. Applying these parameters to Apophis yields a mass estimate of 2×¹⁰¹⁰ kg with a corresponding energy estimate of 375 Mt for its potential hazard. Substantial unknowns, most notably the total porosity, allow uncertainties in these mass and energy estimates to be as large as factors of two or three.  相似文献   

When do rock glacier fronts fail? Insights from two case studies in South Tyrol (Italian Alps)     

Christian Kofler  Volkmar Mair  Stephan Gruber  Maria Cristina Todisco  Ian Nettleton  Stefan Steger  Marc Zebisch  Stefan Schneiderbauer  Francesco Comiti 《地球表面变化过程与地形》2021,46(7):1311-1327

The fronts of two rock glaciers located in South Tyrol (Italian Alps) failed on 13 August 2014, initiating debris flows in their downslope channels. A multimethod approach including climate, meteorological, and ground temperature data analysis, aerial image correlation, as well as geotechnical testing and modeling, led to the reconstruction of the two events. An integrated investigation of static predisposing factors, slowly changing preparatory factors, and potential triggering events shed light on the most likely reasons for such failures. Our results suggest that the occurrence of front destabilization at the two rock glaciers can only partly be explained by the occurrence of heavy rainfall events. Indeed, antecedent hydrological and thermal ground conditions were characterized by a saturated active layer favored by a snow-rich winter and extensive precipitation in late spring and summer. Also, the rising trend of air temperature during spring and summer months since 1950s might explain the concurrent marked displacement of the two rock glaciers. Indeed, geotechnical investigations have provided strong indications that one of the investigated rock glacier fronts was at a marginally stable state prior to 2014. As rainfall events more intense than the one that occurred in August 2014 were previously recorded in the same area without resulting failures at the studied rock glaciers, we propose that both predisposing and preparatory destabilizing factors have played a key role in the 2014 rock glacier front failures.  相似文献   

The Huygens scientific data archive: Technical overview     

Olivier Witasse  Lyle Huber  Jean-Pierre Lebreton  David Heather  John Zarnecki  Roland Trautner  Piero Leon Stoppato  Chuck See  Cyril Pennanech  Lisa McFarlane  Bobby Kazeminejad  Brijen Hathi  John Haberman  Francesca Ferri  Lyn Doose  Giacomo Colombatti  Michael Bird  Alessio Aboudan 《Planetary and Space Science》2008,56(5):770-777

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Palaeoeskimo site burial by solifluction: Periglacial geoarchaeology of the tayara site (KbFk‐7), Qikirtaq Island,Nunavik (Canada)     

Dominique Todisco  Najat Bhiry 《Geoarchaeology》2008,23(2):177-211

The geoarchaeological study of the Palaeoeskimo Tayara site on Qikirtaq Island (Nunavik) has led to a better understanding of archaeological site formation in the arctic periglacial environment. The surrounding geomorphology (extra‐site) is characterized by fine‐grained, low plastic and leached postglacial glaciomarine sediments that have been reworked by sheet‐like solifluction. This process buried the northern part of the Tayara site with mean annual rates between 1.68 and 2.86 cm/yr over approximately 350 years (1330–980 yr B.P.). The physicochemical and mineralogical properties of the frost‐susceptible glaciomarine sediments may explain their susceptibility to solifluction. This process was probably enhanced by longer thawing periods or warmer/moister summer months that induced active layer thickening or rapid soil thawing. The dates we obtained in the downstream valley show that solifluction occurred during short warm periods in the Late Holocene between ca. 1500 and 1000 yr B.P., after 1000 yr B.P. (or after 500 yr B.P.) and recently (90–60 yr B.P.). Our data provide insights on the site factors and climate factors that govern site burial by solifluction. Solifluction promoted the preservation of the three superposed archaeological levels in the Tayara site; however, the waterlogging of the site related to solifluction also likely caused the subsequent abandonment of the site by the Palaeoeskimo people. © 2008 Wiley Periodicals, Inc.  相似文献   

Did the “Autochthonous” European foreland of Corsica Island (France) experience Alpine subduction?     

Maria Di Rosa  Chiara Frassi  Michele Marroni  Francesca Meneghini  Luca Pandolfi 《地学学报》2020,32(1):34-43

Despite the important role played by the Sardinia‐Corsica block in the reconstruction of the Western Mediterranean geodynamics, the extent of involvement of the “Autochthonous” European margin exposed in Corsica (France) (i.e., Hercynian Corsica) in the Alpine orogeny remains uncertain. Stratigraphic and sedimentological studies in the post‐Variscan deposits on the Hercynian Corsica are scarce and even scarcer are the structural and metamorphic constraints. To face these uncertainties, we present new stratigraphic, structural and metamorphic data from the area of Razzo Bianco, Central Corsica, where a complete sequence belonging to the European continental margin is exposed. Field and structural investigations demonstrate that the sequence represents the easternmost edge of the downgoing European plate. Metamorphic studies on the Eocene deposits indicate that the margin was buried at depth up to blueschist facies conditions and, subsequently, it was progressively exhumed mainly through the activation of oblique top‐to‐the NW shear zones.  相似文献   

Interannual variability in glacier contribution to runoff from a high‐elevation Andean catchment: understanding the role of debris cover in glacier hydrology     

Flavia Burger  Alvaro Ayala  David Farias  Thomas E. Shaw  Shelley MacDonell  Ben Brock  James McPhee  Francesca Pellicciotti 《水文研究》2019,33(2):214-229

We present a field‐data rich modelling analysis to reconstruct the climatic forcing, glacier response, and runoff generation from a high‐elevation catchment in central Chile over the period 2000–2015 to provide insights into the differing contributions of debris‐covered and debris‐free glaciers under current and future changing climatic conditions. Model simulations with the physically based glacio‐hydrological model TOPKAPI‐ETH reveal a period of neutral or slightly positive mass balance between 2000 and 2010, followed by a transition to increasingly large annual mass losses, associated with a recent mega drought. Mass losses commence earlier, and are more severe, for a heavily debris‐covered glacier, most likely due to its strong dependence on snow avalanche accumulation, which has declined in recent years. Catchment runoff shows a marked decreasing trend over the study period, but with high interannual variability directly linked to winter snow accumulation, and high contribution from ice melt in dry periods and drought conditions. The study demonstrates the importance of incorporating local‐scale processes such as snow avalanche accumulation and spatially variable debris thickness, in understanding the responses of different glacier types to climate change. We highlight the increased dependency of runoff from high Andean catchments on the diminishing resource of glacier ice during dry years.  相似文献   

Changes in the rainfall–streamflow regimes related to climate change in a small catchment in Northern Italy     

Pieri  Linda  Rondini  Davide  Ventura  Francesca 《Theoretical and Applied Climatology》2017,129(3-4):1075-1087

Theoretical and Applied Climatology - Climate change has become an important issue for scientific community, for its numerous impacts, especially on agriculture and environment. To shed light on...  相似文献