Evidence of a full West Antarctic Ice Sheet back to the early Oligocene: insight from double dating of detrital apatites in Ross Sea sediments.          下载免费PDF全文

Valerio Olivetti  Maria Laura Balestrieri  Federico Rossetti  Stuart N. Thomson  Franco M. Talarico  Massimiliano Zattin 《地学学报》2015,27(3):238-246

The West Antarctic Ice Sheet is the most unstable component of the Antarctic cryosphere. Its fluctuations are well documented since the Pliocene, but its behaviour over the last 35 Ma is more controversial, particularly during periods of past high global pCO₂ values similar to those predicted in future global climate scenarios. Here, we present new U–Pb dating of detrital apatite grains (previously dated by the fission‐track method) from Cape Roberts Project Oligocene to Pliocene marine sediments in the Ross Sea. Two past ice‐flow patterns were identified: one formed by outlet glaciers sourcing short‐travelled apatites and one, northerly directed, bringing far‐travelled apatite grains. The latter provides the first robust physical evidence for the presence and repeated expansion of an Oligocene West Antarctic Ice Sheet.  相似文献   

New perspectives on rainfall from a discrete view     

Carlo De Michele  Massimiliano Ignaccolo 《水文研究》2013,27(16):2379-2382

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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   

Detection of Flow Distortions and Systematic Errors in Sonic Anemometry Using the Planar Fit Method     

Renzo Richiardone  Elena Giampiccolo  Silvia Ferrarese  Massimiliano Manfrin 《Boundary-Layer Meteorology》2008,128(2):277-302

We describe the coordinate transformations that can be used to convert the velocity components measured by a set of sonic anemometers with time-dependent tilt fluctuations into a single, time-independent coordinate system. By applying the planar fit method (PFM) to each anemometer dataset, it is possible, for planar flows, to locate the flow plane at each measurement point and compare its orientation with the topography. Installation on a ship is also considered. An application of this method to intercomparison data has led to the detection of an instrument error due to a misalignment between the assembly of the sonic transducers and the anemometer pedestal. If this error occurs, pedestal levelling does not guarantee that measurements are unbiased. A correction method is proposed and the results of two experiments are shown. Flow planarity at different levels and flow distortion caused by the mast are highlighted. The influence of the error on the evaluation of the Reynolds stresses using PFM or the double rotation method and the triple rotation method is discussed and the tilt corrected stresses calculated using the three methods compared.  相似文献   

Optimal low-thrust trajectories to asteroids through an algorithm based on differential dynamic programming     

Camilla Colombo  Massimiliano Vasile  Gianmarco Radice 《Celestial Mechanics and Dynamical Astronomy》2009,105(1-3):75-112

In this paper an optimisation algorithm based on Differential dynamic programming is applied to the design of rendezvous and fly-by trajectories to near Earth objects. Differential dynamic programming is a successive approximation technique that computes a feedback control law in correspondence of a fixed number of decision times. In this way the high dimensional problem characteristic of low-thrust optimisation is reduced into a series of small dimensional problems. The proposed method exploits the stage-wise approach to incorporate an adaptive refinement of the discretisation mesh within the optimisation process. A particular interpolation technique was used to preserve the feedback nature of the control law, thus improving robustness against some approximation errors introduced during the adaptation process. The algorithm implements global variations of the control law, which ensure a further increase in robustness. The results presented show how the proposed approach is capable of fully exploiting the multi-body dynamics of the problem; in fact, in one of the study cases, a fly-by of the Earth is scheduled, which was not included in the first guess solution.  相似文献   

Dynamic characterisation and seismic assessment of medieval masonry towers     

Massimiliano Ferraioli  Lorenzo Miccoli  Donato Abruzzese  Alberto Mandara 《Natural Hazards》2017,86(2):489-515

The paper investigates the dynamic characterisation, the numerical model tuning and the seismic risk assessment of two monumental masonry towers located in Italy: the Capua Cathedral bell tower and the Aversa Cathedral bell tower. Full-scale ambient vibration tests under environmental loads are performed. The modal identification is carried out using techniques of modal extraction in the frequency domain. The refined 3D finite element model (FEM) is calibrated using the in situ investigation survey. The FEM tuning is carried out by varying the mechanical parameters and accounting for the restraint offered by the neighbouring buildings and the role of soil–structure interaction. The assessment of the seismic performance of the bell towers is carried out through a nonlinear static procedure based on the multi-modal pushover analysis and the capacity spectrum method. Through the discussion of the case studies, the paper shows that the modal identification is a reliable technique that can be used in situ for assessing the dynamic behaviour of monumental buildings. By utilising the tuned FEM of the towers, the theoretical fundamental frequencies are determined, which coincide with the previously determined experimental frequencies. The results from seismic performance assessment through a pushover analysis confirm that the masonry towers in this study are particularly vulnerable to strong damage even when subjected to seismic events of moderate intensity.  相似文献   

Changes of the susceptibility to lava flow invasion induced by morphological modifications of an active volcano: the case of Mount Etna,Italy     

Tarquini  Simone  Favalli  Massimiliano 《Natural Hazards》2010,54(2):537-546

Changes of the susceptibility to lava flow invasion at Mount Etna are quantified by using lava flow simulations on four Digital Elevation Models documenting the morphostructural modifications of the volcano in the time interval 1986–2007. The probabilistic code DOWNFLOW is used to derive the areas invaded by several thousands of lava flows obtaining, for each DEM, maps of the susceptibility to lava flow invasion and of the lava flow hazard. These maps show, for the first time, the evolution of these surficial properties with time, and render a quantitative image of the effects of topographic changes on the preferential lava flow drainage paths. The results illustrate how the emplacement of new lava flows and the growth of scoria cones affect the probability of inundation by lava flows. We conclude that the persistent activity of this volcano requires a frequent updating of the topography for a reliable lava flow hazard assessment.  相似文献   

A century of land subsidence in Ravenna, Italy   总被引：4，自引：2，他引：4  

P. Teatini  M. Ferronato  G. Gambolati  W. Bertoni  M. Gonella 《Environmental Geology》2005,47(6):831-846

Over the last century the Ravenna area has been affected by a widespread land subsidence process of both natural and anthropogenic origin which has become a matter of increasingly great concern. Land settlement, initially of the order of a few mm/year, dramatically increased up to 110 mm/year after World War II primarily due to groundwater pumping and, subordinately, gas production from a number of deep on-shore and off-shore reservoirs. Spirit leveling was carried out in the area of the Ravenna Municipality by various authorities and agencies ever since the end of the nineteenth century using an increasingly refined network of benchmarks. The available information, spanning the time interval from 1897 to 2002, has been implemented and homogenized into a Geographic Information System (GIS). Measurements processed by kriging provide the pattern of the subsidence rates over the municipal territory during eight sub-periods. The reliability of data processing is discussed for both magnitude and areal distribution of the occurrence, showing a pronounced nonlinear behavior in time, as related to the major responsible factors. Cumulative land subsidence approaches almost 1 m over more than one third of the municipality area including the city and a significant fraction of the coastland, with peaks larger than 1.5 m over a 10 km² zone located between the historical center and the coastline. Most recent records show that at present the mainland appears to be substantially stable, whereas some coastal areas are still subsiding at a rate of about 10 mm/year with a significant threat to the environment and the infrastructures as well, although to a lesser extent than in the past decades.  相似文献   

Rare earth diffusion kinetics in garnet: Experimental studies and applications     

Massimiliano Tirone  Jibamitra Ganguly  Ralf Dohmen  Richard Hervig 《Geochimica et cosmochimica acta》2005,69(9):2385-2398

We determined the diffusion coefficient of Sm in almandine garnet as function of temperature at 1 bar and fO₂ corresponding to that of wüstite-iron buffer, and to a limited extent, that of a few other selected rare earth elements in almandine and pyrope garnets. Both garnets were demonstrated to have metastably survived the diffusion annealing at conditions beyond their stability fields. The experimental diffusion profiles were analyzed by secondary ion mass spectrometry, and in addition, by Rutherford back scattering spectroscopy for two samples. Transmission electron microscopic study of an almandine crystal that was diffusion-annealed did not reveal any near-surface fast diffusion path. Using reasonable approximations and theoretical analysis of vacancy diffusion, the experimental data were used to develop an expression of rare earth element (REE) diffusion coefficient in garnet as a function of temperature, pressure, fO₂, ionic radius, and matrix composition. Calculation of the closure temperature for the Sm-Nd decay system in almandine garnet in a metamorphic terrain shows very good agreement with that constrained independently. Modeling of the REE evolution in melt and residual garnet suggests that for dry melting condition, the REE pattern in the melt should commonly conform closely to that expected for equilibrium melting. However, for much lower solidus temperatures that would prevail in the presence of a H₂O-CO₂ fluid, the concentration of light REE in the melt could be significantly lower than that under equilibrium melting condition. A reported core and rim differences in the REE content of a garnet crystal in a mantle xenolith in kimberlite have been reproduced by assuming that the REE zoning was a consequence of entrapment in a magma derived from an external source for ∼32,000 yr before the eruption.  相似文献   

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Massimiliano Favalli  Dávid Karátson  Roberto Mazzuoli  Maria Teresa Pareschi  Guido Ventura 《Bulletin of Volcanology》2007,70(1):117-118

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