Latitudinal variation of wind erosion of crater ejecta deposits on Mars     

Raymond E. Arvidson  Marcello Coradini  A. Carusi  A. Coradini  M. Fulchignoni  C. Federico  R. Funiciello  M. Salomone 《Icarus》1976,27(4):503-516

Wind erosion seems to be the dominant process eroding crater ejecta deposits and sorrounding materials on Mars. In the equatorial zone, ejecta deposits are eroded back by scarp recession, where scarp heights appear to be approximately equivalent to ejecta thickness. In mantled areas, escarpments develop by relatively rapid deflation of sorrounding aeolian debris, leaving the ejecta deposit (continuous deposit and zone of high density of secondary craters) standing high above sorrounding terrain. If the rate of scarp recession is controlled by the rate of aeolian undercutting of escarpment bases, then recession rates may scale roughly as the inverse with respect to scarp height. Thus, preferential preservation of ejecta deposits emplaced in thickest aeolian debris may occur. An empirical model developed for wind erosion of ejecta deposits in nonmantled areas suggests that removal of ejecta materials on the average is exceedingly slow (～10^?5m/yr for 10m high scarp). On the other hand, rapid deflation of aeolian debris around crater ejecta is implied. Results suggest high differential aeolian erosion rates that are a function of both grain sizes and large-scale surface roughness. Aeolian activity on Mars has probably been dominated by rapid recycling of fine-grained debris, the bulk of which formed under more erosive conditions prevalent in the early history of Mars.  相似文献   

Current Behaviour and Dynamics of the Lowermost Italian Glacier (Montasio Occidentale,Julian Alps)     

Luca Carturan  Giovanni A. Baldassi  Aldino Bondesan  Simone Calligaro  Alberto Carton  Federico Cazorzi  Giancarlo Dalla Fontana  Roberto Francese  Alberto Guarnieri  Nicola Milan  Daniele Moro  Paolo Tarolli 《Geografiska Annaler: Series A, Physical Geography》2013,95(1):79-96

Smaller glaciers (<0.5 km²) react quickly to environmental changes and typically show a large scatter in their individual response. Accounting for these ice bodies is essential for assessing regional glacier change, given their high number and contribution to the total loss of glacier area in mountain regions. However, studying small glaciers using traditional techniques may be difficult or not feasible, and assessing their current activity and dynamics may be problematic. In this paper, we present an integrated approach for characterizing the current behaviour of a small, avalanche‐fed glacier at low altitude in the Italian Alps, combining geomorphological, geophysical and high‐resolution geodetic surveying with a terrestrial laser scanner. The glacier is still active and shows a detectable mass transfer from the accumulation area to the lower ablation area, which is covered by a thick debris mantle. The glacier owes its existence to the local topo‐climatic conditions, ensured by high rock walls which enhance accumulation by delivering avalanche snow and reduce ablation by providing topographic shading and regulating the debris budget of the glacier catchment. In the last several years the glacier has displayed peculiar behaviour compared with most glaciers of the European Alps, being close to equilibrium conditions in spite of warm ablation seasons. Proportionally small relative changes have also occurred since the Little Ice Age maximum. Compared with the majority of other Alpine glaciers, we infer for this glacier a lower sensitivity to air temperature and a higher sensitivity to precipitation, associated with important feedback from increasing debris cover during unfavourable periods.  相似文献   

Polynomial chaos expansion for global sensitivity analysis applied to a model of radionuclide migration in a randomly heterogeneous aquifer     

Valentina Ciriello  Vittorio Di Federico  Monica Riva  Francesco Cadini  Jacopo De Sanctis  Enrico Zio  Alberto Guadagnini 《Stochastic Environmental Research and Risk Assessment (SERRA)》2013,27(4):945-954

We perform global sensitivity analysis (GSA) through polynomial chaos expansion (PCE) on a contaminant transport model for the assessment of radionuclide concentration at a given control location in a heterogeneous aquifer, following a release from a near surface repository of radioactive waste. The aquifer hydraulic conductivity is modeled as a stationary stochastic process in space. We examine the uncertainty in the first two (ensemble) moments of the peak concentration, as a consequence of incomplete knowledge of (a) the parameters characterizing the variogram of hydraulic conductivity, (b) the partition coefficient associated with the migrating radionuclide, and (c) dispersivity parameters at the scale of interest. These quantities are treated as random variables and a variance-based GSA is performed in a numerical Monte Carlo framework. This entails solving groundwater flow and transport processes within an ensemble of hydraulic conductivity realizations generated upon sampling the space of the considered random variables. The Sobol indices are adopted as sensitivity measures to provide an estimate of the role of uncertain parameters on the (ensemble) target moments. Calculation of the indices is performed by employing PCE as a surrogate model of the migration process to reduce the computational burden. We show that the proposed methodology (a) allows identifying the influence of uncertain parameters on key statistical moments of the peak concentration (b) enables extending the number of Monte Carlo iterations to attain convergence of the (ensemble) target moments, and (c) leads to considerable saving of computational time while keeping acceptable accuracy.  相似文献   

Evidence-based robust design of deflection actions for near Earth objects     

Federico Zuiani  Massimiliano Vasile  Alison Gibbings 《Celestial Mechanics and Dynamical Astronomy》2012,114(1-2):107-136

This paper presents a novel approach to the robust design of deflection actions for near Earth objects (NEO). In particular, the case of deflection by means of solar-pumped laser ablation is studied here in detail. The basic idea behind laser ablation is that of inducing a sublimation of the NEO surface, which produces a low thrust thereby slowly deviating the asteroid from its initial Earth threatening trajectory. This work investigates the integrated design of the space-based laser system and the deflection action generated by laser ablation under uncertainty. The integrated design is formulated as a multi-objective optimisation problem in which the deviation is maximised and the total system mass is minimised. Both the model for the estimation of the thrust produced by surface laser ablation and the spacecraft system model are assumed to be affected by epistemic uncertainties (partial or complete lack of knowledge). Evidence Theory is used to quantify these uncertainties and introduce them in the optimisation process. The propagation of the trajectory of the NEO under the laser-ablation action is performed with a novel approach based on an approximated analytical solution of Gauss’ variational equations. An example of design of the deflection of asteroid Apophis with a swarm of spacecraft is presented.  相似文献   

An abelisauroid dinosaur from the Middle Jurassic of Laurasia and its implications on theropod palaeobiogeography and evolution     

Martín D. Ezcurra  Federico L. Agnolín 《Proceedings of the Geologists' Association. Geologists' Association》2012,123(3):500-507

We review here the phylogenetic relationships of a theropod distal end of tibia (MB. R.2351) from the Middle Jurassic Stonesfield Slate (Taunton Formation, middle Bathonian) of Oxfordshire, England. This specimen was previously described as a small basal tetanuran, but our reinterpretation suggests that it was an early member of the Abelisauroidea. The new assignment is supported by the presence of an apomorphic vertical facet for the reception of the ascending process of the astragalus, sub-rectangular anterior scar of the astragalar ascending process, median vertical ridge in the scar for the reception of the ascending process of the astragalus, and posterolateral process not distinctly offset from the lateral margin of the shaft. In particular, the Stonesfield specimen shares an overall morphology and a unique combination of apomorphies with the Middle Jurassic Australian abelisauroid Ozraptor. Nevertheless, both specimens differ in some punctual features. MB. R.2351 constitutes the oldest evidence of an abelisauroid outside Gondwana and indicates that the group had achieved a Pangean distribution during, at least, the Middle Jurassic. Thus, the initial diversification of abelisauroids would have occurred earlier than previously thought. Accordingly, the Middle and Late Jurassic Pangean distribution of abelisauroids implies that the absence of the group in Cretaceous Asiamerican assemblages would reflect a regional extinction, in which a competitive replacement with coelurosaurs (e.g. tyrannosauroids) is surely one of the hypotheses that should be tested in future studies.  相似文献   

The emplacement of the Late Miocene Monte Capanne intrusion (Elba Island,Central Italy): constraints from magnetic fabric analyses     

Francesca?CifelliEmail author  Liliana?Minelli  Federico?Rossetti  Giorgia?Urru  Massimo?Mattei 《International Journal of Earth Sciences》2012,101(3):787-802

Anisotropy of magnetic susceptibility (AMS) analysis has been carried out in the thermometamorphic aureole surrounding the Late Miocene Monte Capanne pluton (Elba Island, Central Italy). The identification and separation of the main carriers of the magnetic susceptibility by low-temperature and high-field AMS measurements demonstrate that a correct knowledge of the magnetic fabric is needed in order to use AMS for tectonic interpretations. Magnetic fabric data, combined with structural data from the aureole, and their comparison with data from the pluton itself, were used to constraint the mode of pluton emplacement. Results document an intimate linkage between the magmatic flow pattern and the syn-metamorphic fabrics acquired during pluton emplacement in the host rocks. The magnetic/structural fabric in the aureole rocks is dominated by flattening deformation and no systematic relationship with any regional tectonic feature is observed. These results suggest that local processes induced by magma ascent in the upper crust might have played a primary role in space generation for pluton emplacement in the Tuscan Magmatic Province, suggesting a revaluation of the modes of pluton emplacement during the post-orogenic evolution of the northern Apennine system as a whole.  相似文献   

Medieval Dark Earth in an Active Alluvial Setting from the Uffizi Gallery Complex in Florence,Italy     

Cristiano Nicosia  Roger Langohr  Florias Mees  Antonia Arnoldus‐Huyzendveld  Jacopo Bruttini  Federico Cantini 《Geoarchaeology》2012,27(2):105-122

Archaeological excavations at the Biblioteca Magliabechiana, which is part of the Uffizi gallery complex in Florence (Tuscany, central Italy), exposed Dark Earth deposits between alluvial sediments of the nearby Arno River. The term Dark Earth refers to thick, dark colored, and seemingly homogeneous deposits occurring in urban settings throughout Europe, broadly dated to the post‐Roman period. The stratigraphic sequence of the Biblioteca Magliabechiana was investigated by integrating geomorphological, chronological, and archaeological information with micromorphological and soil analytical data. This combination of approaches resulted in the identification of an early phase of Dark Earth formation (7th century A.D.) during which the area was characterized by the accumulation of manure or night soil in wet peri‐fluvial conditions. After a phase of abandonment, Dark Earth accretion resumed (10th to early 11th century A.D.), at this stage due primarily to the dumping of domestic waste. Subsequent progressive abandonment of the area was followed by the deposition of alluvium, probably during the major flood of November 4, 1177. The present study demonstrates that Dark Earth is the outcome of strong bioturbation and human reworking acting on anthropogenic deposits and possibly on alluvial sediments.  相似文献   

Vesta's mineralogical composition as revealed by the visible and infrared spectrometer on Dawn     

M. Cristina De Sanctis  Eleonora Ammannito  M. Teresa Capria  Fabrizio Capaccioni  Jean‐Philippe Combe  Alessandro Frigeri  Andrea Longobardo  Gianfranco Magni  Simone Marchi  Tom B. McCord  Ernesto Palomba  Federico Tosi  Francesca Zambon  Francesco Carraro  Sergio Fonte  Y. J. Li  Lucy A. McFadden  David W. Mittlefehldt  Carle M. Pieters  Ralf Jaumann  Katrin Stephan  Carol A. Raymond  Christopher T. Russell 《Meteoritics & planetary science》2013,48(11):2166-2184

The Dawn spacecraft mission has provided extensive new and detailed data on Vesta that confirm and strengthen the Vesta–howardite–eucrite–diogenite (HED) meteorite link and the concept that Vesta is differentiated, as derived from earlier telescopic observations. Here, we present results derived by newly calibrated spectra of Vesta. The comparison between data from the Dawn imaging spectrometer—VIR—and the different class of HED meteorites shows that average spectrum of Vesta resembles howardite spectra. Nevertheless, the Vesta spectra at high spatial resolution reveal variations in the distribution of HED‐like mineralogies on the asteroid. The data have been used to derive HED distribution on Vesta, reported in Ammannito et al. (2013), and to compute the average Vestan spectra of the different HED lithologies, reported here. The spectra indicate that, not only are all the different HED lithologies present on Vesta, but also carbonaceous chondritic material, which constitutes the most abundant inclusion type found in howardites, is widespread. However, the hydration feature used to identify carbonaceous chondrite material varies significantly on Vesta, revealing different band shapes. The characteristic of these hydration features cannot be explained solely by infalling of carbonaceous chondrite meteorites and other possible origins must be considered. The relative proportion of HEDs on Vesta's surface is computed, and results show that most of the vestan surface is compatible with eucrite‐rich howardites and/or cumulate or polymict eucrites. A very small percentage of surface is covered by diogenite, and basaltic eucrite terrains are relatively few compared with the abundance of basaltic eucrites in the HED suite. The largest abundance of diogenitic material is found in the Rheasilvia region, a deep basin, where it clearly occurs below a basaltic upper crust. However, diogenite is also found elsewhere; although the depth to diogenite is consistent with one magma ocean model, its lateral extent is not well constrained.  相似文献   

Geochemical monitoring of the 2002–2003 eruption at Stromboli volcano (Italy): precursory changes in the carbon and helium isotopic composition of fumarole gases and thermal waters     

G. Capasso  M. L. Carapezza  C. Federico  S. Inguaggiato  A. Rizzo 《Bulletin of Volcanology》2005,68(2):118-134

Significant changes in the helium and carbon isotopic composition of shallow thermal waters vs. gas and a crater fumarolic gas have been recorded at Stromboli prior and during the 2002–2003 eruption. The³He/⁴He ratios corrected for air contamination (Rc/Ra), and δ¹³C of fumarolic gases gradually increased from May to November 2002 before the eruption onset. These variations imply early degassing of a gas-rich magma at depth that likely fed both the intense Strombolian activity and small lava overflows recorded during that period. The lava effusion of late December 2002 was shortly preceded by a marked Rc/Ra decrease both in water and fumarolic gases. Comparison of He/CO₂ and CH₄/CO₂ ratios in dissolved gas and with values rules out the Rc/Ra decrease due to an increasing input of radiogenic⁴He. The Rc/Ra decrease is attributed to the He isotope fractionation during rapid magma ascent and degassing. A new uprising of ³He-rich magma probably occurred in January to February 2003, when Rc/Ra ratios displayed the highest values in dissolved gases ever measured before (4.56 Rc/Ra). The increase in He/CO₂ and CH₄/CO₂ ratios and decrease in δ¹³C of dissolved CO₂ was recorded after the 5 April 2003 explosive paroxysm, likely caused by enhanced gas-water interaction inducing CO₂ dissolution. No anomalous Rc/Ra values were recorded in the same period, when usual Strombolian activity gradually resumed.Editorial responsibility: H Shinohara  相似文献   

Time evolution of grains in the protosolar nebula     

A. Coradini  G. Magni  C. Federico 《Earth, Moon, and Planets》1980,22(1):47-61

The problem of the motion of grains in the protosolar nebula is discussed. Time scales of the vertical and radial displacement are computed. The structure of the dust disk that can be formed is discussed in the framework of different protosolar nebula models.The results obtained under the hypothesis of quiescience of the gas component are compared with those in presence of a fully developed turbulence.Paper presented at the European Workshop on Planetary Sciences, organised by the Laboratorio di Astrofisica Spaziale di Frascati, and held between April 23–27, 1979, at the Accademia Nazionale del Lincei in Rome, Italy.  相似文献