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   

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   

Reply to:     

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

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The effects of differential subsidence and coastal topography on high-order transgressive-regressive cycles: Pliocene nearshore deposits of the Val d'Orcia Basin, Northern Apennines, Italy   总被引：1，自引：0，他引：1  

Massimiliano Ghinassi 《Sedimentary Geology》2007,202(4):677-701

This study focuses on the lowstand and early transgressive systems tracts of a basin-fill sequence of lower Pliocene nearshore deposits in the Val d'Orcia Basin of the Northern Apennines, Italy. The basin at that time was a semi-enclosed marine embayment, and, in the study area, its margin was subject to highly variable subsidence along the depositional strike, attributed to a decrease in tectonic displacement. The nearshore succession in the more rapidly-subsiding segment of the basin is around 20 m thick, comprising three storeys of laterally-stacked Gilbert-type delta lobes overlain by a shoal-water delta, whereas the nearshore succession in the adjacent, more slowly-subsiding segment, is up to 9 m thick. This succession is characterised by alternation of shoreface and offshore deposits, moderately wave-worked and covered by shoal-water deltaic facies.These coeval nearshore successions consist of several transgressive-regressive cyclothems. The development and lateral variation of the cyclothems was controlled by the local subsidence rate and coastal topographic gradient. Some of the cyclothems are considered to be higher-order sequences and others to be parasequences, with the former passing laterally into the latter in the area where the sea-level fall was countered by fast local subsidence. Some of the bounding surfaces are of limited lateral extent, with two parasequences passing laterally into a single one.Coastal topography controlled particularly the thickness of transgressive deposits. In the low-gradient setting of a delta plain, the relative sea-level rises caused major landward shifts of the shoreline and reduced fluvial sediment supply, with the formation of a transgressive lag in sediment-starved conditions. In the high-gradient coastal setting of the non-deltaic zone, the shoreline shift was minimal and had relatively little impact on local sediment supply, which promoted an accretionary transgression.At the end of the lowstand stage, the rate of sediment accumulation in the non-deltaic nearshore zone was lower, allowing the onset of subsequent transgression to be recorded considerably earlier than in the deltaic nearshore zone. This diachroneity suggests that facies criteria alone may not necessarily be a reliable basis for the recognition of systems tract boundaries.  相似文献   

Spada: An Array of Spad Detectors For Astrophysical Applications     

Giovanni Bonanno  Massimiliano Belluso  Franco Zappa  Simone Tisa  Sergio Cova  Piera Maccagnani  Domenico Bonaccini Calia  Roberto Saletti  Roberto Roncella  Sergio Billotta 《Experimental Astronomy》2005,19(1-3):163-168

Astrophysical studies require accurate, sensitive and fast detectors to detect faint sources with high variability. Recently an array of Single Photon Avalanche Diodes (SPAD), SPADA, has been developed. This array is suitable for competitive adaptive optics operations and fast transient image acquisition at a fraction of the current cost of imaging arrays. The fabricated solid-state photon counters are rugged, easily integrated with the optics, free from readout noise, and have very fast frame rates (> 10 kHz, for visible corrections) with nanosecond electronic gating. In this paper, the following are described: the development of silicon monolithic arrays of 60 photon-counters, the detection electronics (based on integrated active quenching circuits for each pixel of the array), the real-time data-processing board implemented into FPGA and some aspects of the mechanical housing.  相似文献   

Geotechnical characterization of the upper Pleistocene–Holocene alluvial deposits of Roma (Italy) by means of multivariate geostatistics: Cross-validation results   总被引：1，自引：1，他引：0  

Giuseppe Raspa  Massimiliano Moscatelli  Francesco Stigliano  Antonio Patera  Fabrizio Marconi  Daiane Folle  Roberto Vallone  Marco Mancini  Gian Paolo Cavinato  Salvatore Milli  Joo Felipe Coimbra Leite Costa 《Engineering Geology》2008,101(3-4):251-268

We are presenting an attempt to evaluate the spatial variability of geotechnical parameters in the upper Pleistocene–Holocene alluvial deposits of Roma (Italy) by means of multivariate geostatistics.The upper Pleistocene–Holocene alluvial deposits of Roma are sensitive to high levels of geohazard. They occupy a sizable and significant part of the city, being the foundation for many monuments, historical neighborhoods, and archaeological areas, and the main host of the present and future subway lines. We have stored information from more than 2000 geotechnical boreholes crossing the alluvial deposits into a relational database. For the present study, only the boreholes with lithologic/textural interpretation and geotechnical information were selected. The set includes 283 boreholes and 719 samples, which have a set of geotechnical information comprising physical properties and mechanical parameters.Techniques of multivariate statistics and geostatistics were combined and compared to evaluate the estimation methods of the mechanical parameters, with special reference to the drained friction angle from direct shear test (φ′). Principal Component Analysis was applied to the dataset to highlight the relationships between the geotechnical parameters. Through cross-validation analysis, multiple linear regression, kriging, and cokriging were tested as estimators of φ′. Cross-validation demonstrates that the cokriging with granulometries as auxiliary variables is the most suitable method to estimate φ′. In addition to proving that cokriging is a good estimator of φ′, cross-validation demonstrates that input data are coherent and this allows us to use them for estimation of geotechnical parameters, although they come from different laboratories and different vintages.Nevertheless, to get the same good results of cross-validation in estimation, it is necessary for granulometries to be available at grid points. Since this information being not available at all grid points, it is expected that, in the future, textural information can be derived in an indirect way, i.e., from lithologic/textural spatial reconstructions.  相似文献