Non-integrability of the problem of motion around an oblate planet     

Alessandra Celletti  Piero Negrini 《Celestial Mechanics and Dynamical Astronomy》1995,61(3):253-260

We provide a result of non-analytic integrability of the so-called J ₂-problem. Precisely by using the Lerman theorem we are able to prove the existence of a region of the phase space, where the dynamical system exhibits chaotic motions.  相似文献   

A global perspective on African climate   总被引：4，自引：1，他引：3  

Alessandra Giannini  Michela Biasutti  Isaac M. Held  Adam H. Sobel 《Climatic change》2008,90(4):359-383

We describe the global climate system context in which to interpret African environmental change to support planning and implementation of policymaking action at national, regional and continental scales, and to inform the debate between proponents of mitigation v. adaptation strategies in the face of climate change. We review recent advances and current challenges in African climate research and exploit our physical understanding of variability and trends to shape our outlook on future climate change. We classify the various mechanisms that have been proposed as relevant for understanding variations in African rainfall, emphasizing a “tropospheric stabilization” mechanism that is of importance on interannual time scales as well as for the future response to warming oceans. Two patterns stand out in our analysis of twentieth century rainfall variability: a drying of the monsoon regions, related to warming of the tropical oceans, and variability related to the El Niño–Southern Oscillation. The latest generation of climate models partly captures this recent continent-wide drying trend, attributing it to the combination of anthropogenic emissions of aerosols and greenhouse gases, the relative contribution of which is difficult to quantify with the existing model archive. The same climate models fail to reach a robust agreement regarding the twenty-first century outlook for African rainfall, in a future with increasing greenhouse gases and decreasing aerosol loadings. Such uncertainty underscores current limitations in our understanding of the global climate system that it is necessary to overcome if science is to support Africa in meeting its development goals.  相似文献   

Preface     

Alessandra Celletti  Elena Lega  Sylvio Ferraz-Mello 《Celestial Mechanics and Dynamical Astronomy》2008,102(1-3):1-2

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Advances in pan‐European flood hazard mapping          下载免费PDF全文

Lorenzo Alfieri  Peter Salamon  Alessandra Bianchi  Jeffrey Neal  Paul Bates  Luc Feyen 《水文研究》2014,28(13):4067-4077

Flood hazard maps at trans‐national scale have potential for a large number of applications ranging from climate change studies, reinsurance products, aid to emergency operations for major flood crisis, among others. However, at continental scales, only few products are available, due to the difficulty of retrieving large consistent data sets. Moreover, these are produced at relatively coarse grid resolution, which limits their applications to qualitative assessments. At finer resolution, maps are often limited to country boundaries, due to limited data sharing at trans‐national level. The creation of a European flood hazard map would currently imply a collection of scattered regional maps, often lacking mutual consistency due to the variety of adopted approaches and quality of the underlying input data. In this work, we derive a pan‐European flood hazard map at 100 m resolution. The proposed approach is based on expanding a literature cascade model through a physically based approach. A combination of distributed hydrological and hydraulic models was set up for the European domain. Then, an observed meteorological data set is used to derive a long‐term streamflow simulation and subsequently coherent design flood hydrographs for a return period of 100 years along the pan‐European river network. Flood hydrographs are used to simulate areas at risk of flooding and output maps are merged into a pan‐European flood hazard map. The quality of this map is evaluated for selected areas in Germany and United Kingdom against national/regional hazard maps. Despite inherent limitations and model resolution issues, simulated maps are in good agreement with reference maps (hit rate between 59% and 78%, critical success index between 43% and 65%), suggesting strong potential for a number of applications at the European scale. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Numerical and experimental evaluation of site effects at ridges characterized by complex geological setting     

Alessandro Pagliaroli  Alessandra Avalle  Emanuela Falcucci  Stefano Gori  Fabrizio Galadini 《Bulletin of Earthquake Engineering》2015,13(10):2841-2865

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Modeling ground deformations of Panarea volcano hydrothermal/geothermal system (Aeolian Islands, Italy) from GPS data   总被引：1，自引：0，他引：1  

Alessandra Esposito  Marco Anzidei  Simone Atzori  Roberto Devoti  Guido Giordano  Grazia Pietrantonio 《Bulletin of Volcanology》2010,72(5):609-621

Panarea volcano (Aeolian Islands, Italy) was considered extinct until November 3, 2002, when a submarine gas eruption began in the area of the islets of Lisca Bianca, Bottaro, Lisca Nera, Dattilo, and Panarelli, about 2.5 km east of Panarea Island. The gas eruption decreased to a state of low degassing by July 2003. Before 2002, the activity of Panarea volcano was characterized by mild degassing of hydrothermal fluid. The compositions of the 2002 gases and their isotopic signatures suggested that the emissions originated from a hydrothermal/geothermal reservoir fed by magmatic fluids. We investigate crustal deformation of Panarea volcano using the global positioning system (GPS) velocity field obtained by the combination of continuous and episodic site observations of the Panarea GPS network in the time span 1995–2007. We present a combined model of Okada sources, which explains the GPS results acquired in the area from December 2002. The kinematics of Panarea volcano show two distinct active crustal domains characterized by different styles of horizontal deformation, supported also by volcanological and structural evidence. Subsidence on order of several millimeters/year is affecting the entire Panarea volcano, and a shortening of 10⁻⁶ year⁻¹ has been estimated in the Islets area. Our model reveals that the degassing intensity and distribution are strongly influenced by geophysical-geochemical changes within the hydrothermal/geothermal system. These variations may be triggered by changes in the regional stress field as suggested by the geophysical and volcanological events which occurred in 2002 in the Southern Tyrrhenian area.  相似文献   

Holocene environmental instability in the wetland north of the Tiber delta (Rome,Italy): sea-lake-man interactions     

Federico Di Rita  Alessandra Celant  Donatella Magri 《Journal of Paleolimnology》2010,44(1):51-67

Combined analyses of pollen, seeds, woods, micro-charcoal and non-pollen palynomorphs from Stagno di Maccarese, an artificially dried out coastal basin north of the Tiber delta now occupied by the Fiumicino Airport (Rome, Italy), document marked vegetation and environmental changes during the last 8300 years. Between 8300 and 5400 cal. a BP dense mixed deciduous and evergreen forests surrounded a eutrophic freshwater basin. An abrupt change around 5400 cal. a BP marks the transition to a marshy environment, due to a lowering of the water table. An increase of cereals and micro-charcoals matches the presence of a nearby Eneolithic settlement. Between 5100 and 2900 cal. a BP there is a remarkable expansion of riparian trees, indicating an increase of the water level. Between 2900 and 2000 cal. a BP, a new development of marshlands points to a progressive lowering of the lake. After 2000 cal. a BP, during the Roman exploitation of the area, an expansion of arboreal vegetation is recorded, characterized by evergreen and deciduous oak-dominated forests, while an extensive chenopods marshland matches the presence of saltworks. On the whole, the Stagno di Maccarese area appears very unstable, due to changes in lake level, introgression of marine water, eutrophic phases, flood events, desiccations and openings of the forest vegetation.  相似文献   

Performance and Characteristics of Aerobic Granular Sludge Degrading 2,4,6‐Trichlorophenol at Different Volumetric Organic Loading Rates          下载免费PDF全文

Stefano Milia  Roberta Porcu  Simona Rossetti  Alessandra Carucci 《洁净——土壤、空气、水》2016,44(6):615-623

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Physical explanations of variations in river meander migration rates from model comparison     

Alessandra Crosato 《地球表面变化过程与地形》2009,34(15):2078-2086

In meandering rivers, the local channel migration rate increases with increasing bend sharpness until it reaches a maximum at a certain critical value of the bend sharpness. Beyond this critical value, the migration rate decreases if bend sharpness increases. Similarly, reach‐averaged migration rates attain a maximum at a certain river sinuosity. This work investigates the physics of these phenomena by comparing the results of two physics‐based models of different complexity, in which the migration rates are proportional to the near‐bank flow velocity excess. In the computational tests the river was allowed to meander progressively, starting from an almost straight planimetry. Both models reproduced the observed peak in the curve describing the local migration rate as a function of the ratio radius of curvature‐channel width (R/B), with a rising limb at lower R/B values and a falling limb at higher R/B values. The rising limb can be explained by the decrease in relative lag distance between near‐bank flow velocity and forcing curvature as R/B increases. The falling limb results from the decrease in local channel curvature and near‐bank flow velocity excess. Since the models do not include flow separation, the results indicate that this phenomenon is not needed to explain the decrease of channel migration rates in sharp bends. The models reproduced also the peak in the curve describing the reach‐averaged migration rates as a function of river sinuosity The increase and then decrease of reach‐averaged migration rates as sinuosity increases appears to be mainly caused by the variation of the reach‐averaged value of the ratio R/B. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

GIS and Volcanic Risk Management   总被引：7，自引：0，他引：7  

Pareschi  M. T.  Cavarra  L.  Favalli  M.  Giannini  F.  Meriggi  A. 《Natural Hazards》2000,21(2-3):361-379

Volcanic catastrophes constitute a majorproblem in many developing and developed countries. Inrecent years population growth and the expansion ofsettlements and basic supply lines (e.g., water, gas,etc.) have greatly increased the impact of volcanicdisasters. Correct land-use planning is fundamental inminimising both loss of life and damage to property.In this contribution Geographical Information Systems(GIS), linked with remote sensing technology andtelecommunications/warning systems, have emerged asone of the most promising tools to support thedecision-making process. Some GIS are presented fortwo volcanic areas in Italy, Mt. Etna and Vesuvius.GIS role in risk management is then discussed, keepingin mind the different volcanic scenarios of effusiveand explosive phenomena. Mt. Etna system covers alarge area (more than 1,000 km²) potentiallyaffected by effusive phenomena (lava flows) whichcause damage to both houses and properties in general.No risk to life is expected. The time-scales of lavaflows allow, at least in principle, modification ofthe lava path by the building of artificial barriers.Vesuvius shows typically an explosive behaviour. Inthe case of a medium size explosive eruption, 600,000people would potentially have to be evacuated from anarea of about 200 km² around the Volcano, sincethey are exposed to ruinous, very fast phenomena likepyroclastic surges and flows, lahars, ash fallout,etc. Ash fallout and floods/lahars are also expectedin distal areas, between Vesuvius and Avellino,downwind of the volcano. GIS include digital elevationmodels, satellite images, volcanic hazard maps andvector data on natural and artificial features (energysupply lines, strategic buildings, roads, railways,etc.). The nature and the level of detail in the twodata bases are different, on the basis of thedifferent expected volcanic phenomena. The GIS havebeen planned: (a) for volcanic risk mitigation (hazard,value, vulnerability and risk map assessing), (b) toprovide suitable tools during an impending crisis, (c)to provide a basis for emergency plans.  相似文献