Denitrification through PSC formation: A 1-D model incorporating temperature oscillations     

K. Drdla  R. P. Turco 《Journal of Atmospheric Chemistry》1991,12(4):319-366

A one-dimensional model of polar stratospheric cloud (PSC) formation and evolution during the polar winter, incorporating both HNO₃ and H₂O condensation, has been developed to investigate the interactions between Type I and Type II PSCs and the effects of these clouds on the stratospheric composition. Model simulations for various meteorological conditions and the results of extensive sensitivity tests are presented. Temperature oscillations, which have been included in the model, are shown to have an important influence on the characteristics and effects of the PSCs. The predicted proportions of the PSCs are consistent with observations of number, size, and optical effects, such as depolarization. Denitrification of stratospheric air by 35–88% is shown to occur in the presence of both Type I and Type II PSCs, with comparable nitrate removal in both types of clouds. Dehydration by Type II clouds simultaneously removes similar percentages of water vapour, up to 79% at lower altitudes. Altough dehydration is insensitive to most of the parameter variations except the minimum temperature, the process of denitrification, especially the proportion removed by Type I PSCs, is highly variable.  相似文献   

Multistage evolution of the European lithospheric mantle: new evidence from Sardinian peridotite xenoliths     

Luigi Beccaluva  Gianluca Bianchini  Massimo Coltorti  William Perkins  Franca Siena  Carmela Vaccaro  Marjorie Wilson 《Contributions to Mineralogy and Petrology》2001,142(3):284-297

Peridotite xenoliths entrained in Plio-Pleistocene alkali basalts from Sardinia represent fragments of the uppermost lithospheric mantle, and are characterised by an anhydrous four-phase mineral assemblage. They range in bulk rock composition from fertile spinel-lherzolites to residual spinel-harzburgites. The Sr-Nd isotope and trace element composition of clinopyroxene mineral separates varies between LREE-depleted samples with ⁸⁷Sr/⁸⁶Sr as low as 0.70262 and ¹⁴³Nd/¹⁴⁴Nd up to 0.51323 and LREE-enriched samples with ⁸⁷Sr/⁸⁶Sr up to 0.70461 and ¹⁴³Nd/¹⁴⁴Nd down to 0.51252. The available data suggest that all the studied peridotite samples suffered variable degrees of partial melting during Pre-Mesozoic times (based on Nd model ages relative to CHUR and DMM). The overprinted enrichment is related to a subsequent metasomatism, induced by fluids rising through the lithosphere that preferentially percolated the originally most depleted domains. Despite the occurrence of orogenic volcanism in the area, preferential enrichment in elements typically associated with slab derived fluids/melts (K, Rb, Sr, Th) relative to LREE has not been detected, and metasomatism seems to be more likely related to the infiltration of highly alkaline basic melts characterised by an EM-like Sr-Nd isotopic composition. Similar ⁸⁷Sr/⁸⁶Sr-¹⁴³Nd/¹⁴⁴Nd compositions, characterised by an EM signature, are observed in anorogenic mafic lavas and peridotite xenoliths from widespread localities within the "European" plate, whereas they have not previously been recorded in peridotite xenoliths and associated alkaline mafic lavas from the stable "African" lithospheric domain.  相似文献   

Middle-Late Pleistocene polycyclic evolution of a stable coastal area (southern Apulia, Italy)     

Giuseppe Mastronuzzi  Yves Quinif  Paolo Sans  Gianluca Selleri 《Geomorphology》2007,86(3-4):393-408

The Otranto–Leuca coastal tract is marked by the presence of numerous sea caves placed close to present sea level. They are located generally at the back of a shore platform covered by a sequence of breccia deposits, marine sediments and speleothems. At Grotta di Masseria dell'Orte, marine cemented sands rest on a narrow shore platform at about 6.2 m above mean sea level and are covered by speleothems older than 185 ka. At Grotta del Diavolo, which is mostly filled by breccia deposits, three beach levels have been detected at about 3.0, 3.5 and 5.9 m above msl. They are either covered by or overlie speleothems that yield an U/Th age of 340, 78 ka and between 170.3 and 146.5, respectively. Geomorphological evidence and radiometric ages indicate that the area after a period of uplift has been tectonically stable since the last part of the Middle Pleistocene so that marine landforms close to the present shoreline underwent a polycyclic evolution. The sedimentary fills of sea caves formed during Middle-Late Pleistocene glacial stages, when arid or semiarid conditions promoted the removal of regolith and the development of thick breccia deposits. During Marine Isotope Stages (MIS) 9.3, 5.5 and 5.1, cave sediments were partially eroded whereas beach layers and related speleothems developed. These are, in fact, the only marine isotope stages marked by a sea level position which in this Mediterranean region was either close to, or slightly higher than, the present one.  相似文献   

The meteoritic origin of Tutankhamun's iron dagger blade          下载免费PDF全文

Daniela Comelli  Massimo D'orazio  Luigi Folco  Mahmud El‐Halwagy  Tommaso Frizzi  Roberto Alberti  Valentina Capogrosso  Abdelrazek Elnaggar  Hala Hassan  Austin Nevin  Franco Porcelli  Mohamed G. Rashed  Gianluca Valentini 《Meteoritics & planetary science》2016,51(7):1301-1309

Scholars have long discussed the introduction and spread of iron metallurgy in different civilizations. The sporadic use of iron has been reported in the Eastern Mediterranean area from the late Neolithic period to the Bronze Age. Despite the rare existence of smelted iron, it is generally assumed that early iron objects were produced from meteoritic iron. Nevertheless, the methods of working the metal, its use, and diffusion are contentious issues compromised by lack of detailed analysis. Since its discovery in 1925, the meteoritic origin of the iron dagger blade from the sarcophagus of the ancient Egyptian King Tutankhamun (14th C. BCE) has been the subject of debate and previous analyses yielded controversial results. We show that the composition of the blade (Fe plus 10.8 wt% Ni and 0.58 wt% Co), accurately determined through portable x‐ray fluorescence spectrometry, strongly supports its meteoritic origin. In agreement with recent results of metallographic analysis of ancient iron artifacts from Gerzeh, our study confirms that ancient Egyptians attributed great value to meteoritic iron for the production of precious objects. Moreover, the high manufacturing quality of Tutankhamun's dagger blade, in comparison with other simple‐shaped meteoritic iron artifacts, suggests a significant mastery of ironworking in Tutankhamun's time.  相似文献   

Sedimentation in the Northern Apennines–Corsica tectonic knot (Northern Tyrrhenian Sea,Central Mediterranean): offshore drilling data from the Elba–Pianosa Ridge     

Gianluca Cornamusini  Vincenzo Pascucci 《International Journal of Earth Sciences》2014,103(3):821-842

The Northern Tyrrhenian Sea is located on the collisional zone between the Alpine Corsica and the Northern Apennines and is a key area for gaining a better understanding of the complex relationships between these two systems. The knowledge of the wide offshore part of this zone, located between Corsica (France) and mainland Italy, is based primarily on the analysis of several seismic profiles tied to the outcropping geology and unpublished preliminary reports of few offshore wells. The here presented study of two offshore wells provides a revision of the sedimentology, biostratigraphy and petrography of the thick, mainly siliciclastic, Tertiary successions (about 3,600 m) composing the Elba–Pianosa Ridge (EPR), a structural/morphological high separating the Tuscan Shelf to the east from the Corsica Basin to the west. A comparison with similar deposits cropping out in the surrounding onshore areas (Northern Apennines, Corsica, Tuscan Archipelago, Piedmont Tertiary Basin) provides additional constraints for refinement of the complex geodynamic and regional setting in which the EPR evolved.  相似文献   

Infiltration effects on a two-dimensional molecular dynamics model of landslides     

Gianluca Martelloni  Franco Bagnoli 《Natural Hazards》2014,73(1):37-62

We propose a two-dimensional computational model for deep landslides triggered by rainfall, based on interacting particles or grains. The model describes a vertical section of a fictitious granular material along a slope, in order to study the behavior of a wide-thickness landslide. The triggering of the landslide is caused by the exceeding of two conditions: a threshold speed and a condition on the static friction of the particles, the latter based on the Mohr–Coulomb failure criterion (Coulomb in Mem Acad R Div Sav 7:343–387, 1776; Mohr in Abhandlungen aus dem Gebiete der Technischen Mechanik. Ernst, Berlin, 1914). The interparticle interactions are represented as a potential that, in the absence of suitable experimental data and due to the arbitrariness of the grain dimension, is modeled similarly to the Lennard-Jones’ one (Lennard-Jones in Proc R Soc Lond A 106(738):463–477, 1924), i.e., with an attractive and a repulsive part. For the updating of the particle positions, we use a molecular dynamics method, which is quite suitable for this type of systems (Herrmann and Luding in Continuum Mech Thermodyn 10:189–231, 1998). An infiltration scheme is introduced for modeling the increasing pore pressure due to the rainfall. Finally, we also introduce the viscosity in the dynamical equations of motion. The statistical characterization and dynamical behavior of the results of simulations are quite satisfactory relative to real landslides: We obtain a power law distribution of landslide triggering times, and the velocity patterns are typical of real cases, including the acceleration progression. Therefore, we can claim that this type of modeling can represent a new method to simulate landslides triggered by rainfall.  相似文献   

WORKSHOP ON PALAEOSEISMOLOGY, 18–22 SEPTEMBER 1994, MARSHALL, CA, USA     

Gianluca Valensise 《地学学报》1995,7(2):111-111

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Venus: Mesospheric hazes of ice,dust, and acid aerosols     

R.P. Turco  O.B. Toon  R.C. Whitten  R.G. Keesee 《Icarus》1983,53(1):18-25

We speculate on the origin and physical properties of haze in the upper atmosphere of Venus. It is argued that at least four distinct types of particles may be present. The densest and lowest haze, normally seen by spacecraft, probably consists of a submicron sulfuric acid aerosol which extends above the cloud tops (at ～70 km) up to ～80 km; this haze represents an extension of the upper cloud deck. Measurements of the temperature structure between 70 and 120 km indicate that two independent water ice layers may occasionally appear. The lower one can form between 80 and 100 km and is probably the detached haze layer seen in high-contrast limb photography. This ice layer is likely to be nucleated on sulfuric acid aerosols, and is analogous to the nacreous (stratospheric) clouds on Earth. At the Venus “mesopause” near 120 km, temperatures are frequently cold enough to allow ice nucleation on meteoric dust or ambient ions. The resulting haze (which is analogous to noctilucent clouds on Earth) is expected to be extremely tenous, and optically invisible. On both Earth and Venus, meteoric dust is present throughout the upper atmosphere and probably has similar properties.  相似文献   

High-pressure X-ray and Raman study of a ferrian magnesian spodumene     

G. Diego Gatta  Tiziana Boffa Ballaran  Gianluca Iezzi 《Physics and Chemistry of Minerals》2005,32(2):132-139

The high-pressure behaviour of a synthetic P2₁/c ferrian magnesian spodumene, ^M2 (Li_0.85Mg_0.09Fe²⁺ _0.06)^M1(Fe³⁺ _0.85Mg_0.15)Si₂O₆, has been investigated using in situ single-crystal X-ray diffraction and Raman spectroscopy. No phase transition has been observed within the pressure range investigated. The isothermal equation of state up to 7 GPa was determined. V₀, K_T0 and K, simultaneously refined with a Murnaghan equation of state, are: V₀= 415.66(7) ų, K_T0=83(1) GPa and K=9.6(6). The magnitudes of the principal unit-strain coefficients were calculated and their ratios 1:2:3=1.00:1.85:2.81 at P=6.83 GPa indicate a very strong anisotropy. Monitoring of the intensity of b-type reflections (h+k= 2n+1) confirms that from room conditions up to 7 GPa the primitive lattice is maintained. Raman spectra have been collected up to 7.4 GPa. No change in the number of observed vibrational modes occurs in the pressure range investigated. At high frequency, the Raman doublet relative to the Si–O–Si vibrations of the two distinct tetrahedral chains is a broad band at room pressure, however, the frequency difference between the two modes increases with increasing pressure.Operating system: Windows NT  相似文献   

New geomorphic evidence for anticlinal growth driven by blind-thrust faulting along the northern Marche coastal belt (central Italy)   总被引：2，自引：0，他引：2  

Paola Vannoli  Roberto Basili  Gianluca Valensise 《Journal of Seismology》2004,8(3):297-312

The Northern Marche coastal belt is characterised by a series of NW-SE trending, NE verging folds forming the easternmost edge of the Apennines thrust front. Several geomorphic features suggest that the folds are still growing and hence that the thrust front is active. The occurrence of several historical and instrumental earthquakes (e.g. 1672, 1690, 1786, 1875, 1916, 1930, 1972, all having M_e 5.2) suggests that the thrust faults are also seismogenic.We performed a geomorphological analysis to identify and characterise the faults driving the active folds. Our approach assumes that anomalous drainage patterns and deformed Middle-Late Pleistocene alluvial and coastal terraces are indicators of the vertical component of tectonic strain. We identified, mapped and correlated with sea-level fluctuations a sequence of alluvial and coastal terraces. Longitudinal profiles of six rivers (Conca, Foglia, Metauro, Cesano, Misa, and Esino) show that terraces (1) consistently converge downstream, suggesting that they result from regional uplift that dies out near the coast, and (2) some are slightly warped where they cross anticline axes. We interpreted as coastal terraces several land-surface remnants arranged parallel to the present coastline. Lower remnants clearly top off gently landward-tilted coastal deposits. Reconstructed coastal terraces also seem to be tectonically warped.Our results help characterise the geometry and segmentation of a system that generated the largest earthquakes of the region and suggest the loci of potential seismic gaps. We conclude that the earthquake potential of the densely populated northern Marche coastal belt may be substantially higher than currently estimated.  相似文献