Seismic image quality beneath strongly scattering structures and implications for lower crustal imaging: numerical simulations     

Francesca Martini  Christopher J. Bean  Sean Dolan  David Marsan† 《Geophysical Journal International》2001,145(2):423-435

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Geodynamic significance of ophiolites within the Calabrian Arc     

Francesca  Liberi  Lauro  Morten  Eugenio  Piluso 《Island Arc》2006,15(1):26-43

Abstract Slices of oceanic lithosphere belonging to the neo‐Tethys realm crop out discontinuously in the northern Calabrian Arc, Southern Apennines. They consist of high‐pressure–low‐temperature metamorphic ophiolitic sequences formed from metaultramafics, metabasites and alternating metapelites, metarenites, marbles and calcschist. Ophiolites occupy an intermediate position in the northern Calabrian Arc nappe pile, situated between overlying Hercynian continental crust and the underlying Apenninic limestone units. In the literature, these ophiolitic sequences are subdivided into several tectonometamorphic units. Geochemical characteristics indicate that metabasites were derived from subalkaline basalts with tholeiitic affinity (transitional mid‐oceanic ridge basalt type), and a harzburgitic‐lherzolitic protolith is suggested for the serpentinites. The pressure–temperature‐deformation paths of the metabasites from different outcrops display similar features: (i) the prograde segment follows a typical Alpine geothermal gradient up to a metamorphic climax at 350°C and 0.9 GPa and crystallization of the high‐pressure mineral assemblage occurs along a pervasive foliation developed during a compressive tectonic event; and (ii) the retrogression path can be subdivided in two segments, the first is characterized by nearly isothermal decompression to approximately 400°C and 0.3 GPa and the second follows a cooling trajectory. During low‐pressure conditions, a second deformation event produces millimetric to decametric scale asymmetric folds that describe west‐verging major structures. The third deformation event is characterized by brittle extensional structures. The tectonometamorphic evolution of the ophiolitic sequences from the different outcrops is similar. Both thermobarometric modeling and tectonic history indicate that the studied rocks underwent Alpine subduction and exhumation processes as tectonic slices inside a west‐verging accretionary wedge. The subduction of oceanic lithosphere was towards the present east; therefore, the Hercynian continental crust, overthrusted on the ophiolitic accretionary wedge after the neo‐Tethys closure, was part of the African paleomargin or a continental microplate between Africa and Europe.  相似文献   

Crystal structure model for metavoltine from Sierra Gorda     

Prof. G. Giacovazzo  Dr. F. Scordari  Dr. A. Todisco  Prof. S. Menchetti 《Mineralogy and Petrology》1976,23(3):155-166

Summary The crystal structure of metavoltine from Sierra Gorda, Chile, has been solved from photographic X-ray data by the heavy atom method. The space group used wasP3 witha=9.575(5) andc=18.17(1)Å; cell content: K₂Na₆ (Fe ²⁺, Cu, Zn)Fe ₆ ³⁺ (SO₄)₁₂O₂·18H₂O. From the relatively small number and the somewhat poor quality of the X-ray data, the least squares refinement did not give very satisfactory results-especially so for the light atoms. Therefore, steric considerations and information from the Fourier maps were also used when choosing the final atomic coordinates. The salient features of the structure are clusters of Fe ₃ ³⁺ O(H₂O)₃(SO₄)₆ with Fe³⁺ in octahedral coordination, and Fe²⁺(H₂O)₆ octahedra. The Na⁺ ions show octahedral coordination, the K⁺ ions irregular nine coordination.

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Ein Kristallstrukturmodell für den Metavoltin von Sierra Gorda

Zusammenfassung Die Kristallstruktur des Metavoltins von Sierra Gorda (Chile) wurde aus photographischen Röntgendaten mit der Schweratommethode gelöst. Als Raumgruppe wurdeP3 mita ₀9,575(5) undc ₀=18,17(1) Å verwendet; Zellinhalt K₂Na₆ (Fe ²⁺, Cu, Zn) Fe ₆ ³⁺ (SO₄)₁₂O₂·18H₂O.Wegen der relativ kleinen Zahl und der nicht sehr guten Qualität der Röntgendaten gab die Verfeinerung nach der Methode der kleinsten Quadrate keine sehr guten Ergebnissebesonders nicht für die leichten Atome. Deshalb wurden zur Festlegung der endgültigen Atomkoordinaten auch sterische Überlegungen und Informationen aus Fouriersynthesen herangezogen. Hervorstechende Züge der Struktur sind Gruppen Fe ₃ ³⁺ O(H₂O)₃(SO₄)₆ mit Fe³⁺ in oktaedrischer Koordination sowie Fe²⁺(H₂O)₆-Oktaeder. Die Na⁺-Ionen zeigen oktaedrische Koordination, die K⁺-Ionen unregelmäßige 9-Koordination.

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Evidence for enhanced hydration on the northern flank of Olympus Mons, Mars     

Giancarlo Bellucci  Joern Helbert  Francesca Altieri  Dennis Reiss  Jean-Pierre Bibring  Stephan van Gasselt  Harald Hoffmann  Yves Langevin  Gerhard Neukum  Franois Poulet 《Icarus》2007,192(2):361-377

In this paper we report about a small region on the northern scarp of Olympus Mons showing an increase of the 3 μm hydration band in the OMEGA spectra, together with low superficial temperatures. Although water ice clouds can occurs on the flank of big martian volcanoes, radiative transfer modeling indicates that atmospheric water ice alone cannot justify the shape of the observed band. A fit of the 1.9–3 μm absorption features is obtained by hypothesizing that the study region consists of a mixture of dust and water ice covered by an optically thin (τ=0.08 at 3 μm) layer of dust. Thermal modeling also suggests that water ice in this region may be stable during most of the martian year due to the saturation of the atmosphere. If water ice is responsible for the observed spectral behavior, it might consist of a number of ice or snow patches possibly deposited in small depressions.  相似文献   

Close encounters in young stellar clusters: implications for planetary systems in the solar neighbourhood     

Daniel Malmberg  Francesca De Angeli  Melvyn B. Davies  Ross P. Church  Dougal Mackey  Mark I. Wilkinson 《Monthly notices of the Royal Astronomical Society》2007,378(3):1207-1216

The stars that populate the solar neighbourhood were formed in stellar clusters. Through N -body simulations of these clusters, we measure the rate of close encounters between stars. By monitoring the interaction histories of each star, we investigate the singleton fraction in the solar neighbourhood. A singleton is a star which formed as a single star, has never experienced any close encounters with other stars or binaries, or undergone an exchange encounter with a binary. We find that, of the stars which formed as single stars, a significant fraction is not singletons once the clusters have dispersed. If some of these stars had planetary systems, with properties similar to those of the Solar System, the planets' orbits may have been perturbed by the effects of close encounters with other stars or the effects of a companion star within a binary. Such perturbations can lead to strong planet–planet interactions which eject several planets, leaving the remaining planets on eccentric orbits. Some of the single stars exchange into binaries. Most of these binaries are broken up via subsequent interactions within the cluster, but some remain intact beyond the lifetime of the cluster. The properties of these binaries are similar to those of the observed binary systems containing extrasolar planets. Thus, dynamical processes in young stellar clusters will alter significantly any population of Solar System-like planetary systems. In addition, beginning with a population of planetary systems exactly resembling the Solar System around single stars, dynamical encounters in young stellar clusters may produce at least some of the extrasolar planetary systems observed in the solar neighbourhood.  相似文献   

The role of the equation of state in models of very low-mass stars     

Marcella Di Criscienzo  Paolo Ventura  Francesca D’Antona 《Astrophysics and Space Science》2010,328(1-2):167-169

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Size‐frequency distributions of Joania cordata and Argyrotheca cuneata (Brachiopoda: Megathyrididae) from the Central Tyrrhenian Sea     

Francesca Evangelisti  Paolo G. Albano  Bruno Sabelli 《Marine Ecology》2014,35(3):377-386

Size‐frequency distributions can support reliable inferences concerning population dynamics of brachiopods, but only a few data are available so far. In this study, length and width frequency distributions of dead specimens of the Recent brachiopods Joania cordata and Argyrotheca cuneata from the Marine Protected Area ‘Secche di Tor Paterno’, Central Tyrrhenian Sea, Italy (41°35′ N, 12°20′ E), are reported in order to add new data about size‐frequency distributions of brachiopods. The studied specimens came from death assemblages in the coralligenous substrate, in the Posidonia oceanica meadows, and in the sand channels. The observed patterns vary from left‐skewed (J. cordata) to right‐skewed (A. cuneata), indicating respectively a low and high mortality of smaller individuals. Significant differences between the coralligenous substrate and the P. oceanica meadow were observed for both species, revealing a variation among different habitats. All length and width distributions are clearly polymodal, but the biological meaning of the peaks is difficult to interpret, as the two species seem to have a 2‐year life span. A biometric analysis of shell sizes revealed that length and width are the most variable parameters during the growth of the animal.  相似文献   

Changes in extremes and hydroclimatic regimes in the CREMA ensemble projections   总被引：2，自引：0，他引：2  

Filippo Giorgi  Erika Coppola  Francesca Raffaele  Gulilat Tefera Diro  Ramon Fuentes-Franco  Graziano Giuliani  Ashu Mamgain  Marta Pereira Llopart  Laura Mariotti  Csaba Torma 《Climatic change》2014,125(1):39-51

We analyze changes of four extreme hydroclimatic indices in the RCP8.5 projections of the Phase I CREMA experiment, which includes 21st century projections over 5 CORDEX domains (Africa, Central America, South America, South Asia, Mediterranean) with the ICTP regional model RegCM4 driven by three CMIP5 global models. The indices are: Heat Wave Day Index (HWD), Maximum Consecutive Dry Day index (CDD), fraction of precipitation above the 95th intensity percentile (R95) and Hydroclimatic Intensity index (HY-INT). Comparison with coarse (GPCP) and high (TRMM) resolution daily precipitation data for the present day conditions shows that the precipitation intensity distributions from the GCMs are close to the GPCP data, while the RegCM4 ones are closer to TRMM, illustrating the added value of the increased resolution of the regional model. All global and regional model simulations project predominant increases in HWD, CDD, R95 and HY-INT, implying a regime shift towards more intense, less frequent rain events and increasing risk of heat wave, drought and flood with global warming. However, the magnitudes of the changes are generally larger in the global than the regional models, likely because of the relatively low “climate sensitivity” of the RegCM4, especially when using the CLM land surface scheme. In addition, pronounced regional differences in the change signals are found. The data from these simulations are available for use in impact assessment studies.  相似文献   

Analysis of drought in the region of Abruzzo (Central Italy) by the Standardized Precipitation Index   总被引：1，自引：1，他引：0  

B. Di Lena  L. Vergni  F. Antenucci  F. Todisco  F. Mannocchi 《Theoretical and Applied Climatology》2014,115(1-2):41-52

The paper presents a comprehensive analysis of drought phenomena in the Region of Abruzzo (Central Italy) using the Standardized Precipitation Index (SPI) computed at different time scales (3, 6, 12, 24 months). The study is based on monthly precipitation data collected from 1951 to 2009 at 69 climatic stations uniformly distributed over the region. According to the trend analysis, most stations are characterized by increments in both drought severity and variability, particularly at the longer time scales. A principal component analysis applied to SPI time series enabled to identify two main patterns: the first more correlated to the coastal areas, the second more correlated to the inland, mountainous areas. However, the spatial patterns become less defined as the time scale increases, making more uncertain the definition of homogenous areas to be used in drought management plans. In most cases, the identified drought patterns have similar negative overall tendencies, but different trend directions in some sub-periods. In particular, the first drought pattern is clearly characterized by a trend reversal (from decreasing to increasing) during the last decade. This temporal evolution, consistent with that observed by large-scale analyses in the corresponding (or near) grid points, was not detected for the second pattern, which is probably influenced by local topographic and/or orographic factors. The results confirm the complexity of drought phenomenon in a typical Mediterranean region and the necessity of high-resolution datasets to capture its temporal and spatial variability.  相似文献   

Validity of the Sutherland-Lindemann law and melting temperatures in the Earth's interior     

Francesco Mulargia  Francesca Quareni 《Geophysical Journal International》1988,92(2):269-282

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