Analytical study of the swing-by maneuver in an elliptical system     

Alessandra F. S. Ferreira  Antônio F. B. A. Prado  Othon C. Winter  Denilson P. S. Santos 《Astrophysics and Space Science》2018,363(2):24

The objective of the present paper is to derive a set of analytical equations that describe a swing-by maneuver realized in a system of primaries that are in elliptical orbits. The goal is to calculate the variations of energy, velocity and angular momentum as a function of the usual basic parameters that describe the swing-by maneuver, as done before for the case of circular orbits. In elliptical orbits the velocity of the secondary body is no longer constant, as in the circular case, but it varies with the position of the secondary body in its orbit. As a consequence, the variations of energy, velocity and angular momentum become functions of the magnitude and the angle between the velocity vector of the secondary body and the line connecting the primaries. The “patched-conics” approach is used to obtain these equations. The configurations that result in maximum gains and losses of energy for the spacecraft are shown next, and a comparison between the results obtained using the analytical equations and numerical simulations are made to validate the method developed here.  相似文献   

Observational constraint on the fourth derivative of the inflaton potential     

Chiara Caprini  Steen H. Hansen  Martin Kunz 《Monthly notices of the Royal Astronomical Society》2003,339(1):212-214

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Analysis, synthesis and modelling of high-resolution observations of salt-marsh eco-geomorphological patterns in the Venice lagoon   总被引：1，自引：0，他引：1  

Marco Marani  Enrica Belluco  Sergio Ferrari  Sonia Silvestri  Andrea D'Alpaos  Stefano Lanzoni  Alessandra Feola  Andrea Rinaldo   《Estuarine, Coastal and Shelf Science》2006,69(3-4):414

The present paper describes observations, analyses and models of salt-marsh channel network and vegetation patterns with the aim of contributing to the development of predictive models of ecological and morphological co-evolution. Existing and new observations are described, with particular emphasis on remote sensing and ancillary field surveys, which are shown to allow reliable, accurate and repeatable quantitative characterizations of landform and vegetation properties over the spatial scales of interest. The observed channel network morphological characters are then used as the basis and validation of models describing the emergence of channel network and vegetation spatial patterns. In particular, with reference to observations performed in the Venice Lagoon, the note describes: (i) new, 2-cm resolution, characterizations of channel network geometry obtained from “proximal sensing” photographic observations; (ii) the reliable quantitative maps of salt-marsh vegetation which may be retrieved from hyperspectral remote sensing data and field ancillary observations; (iii) a synthesis of recent and new analyses of the statistical properties of vegetation and landform spatial organization, that may be inferred from the maps so derived; (iv) recent and new conceptual and quantitative ecological and geomorphic models developed and validated by remote-sensing and field observations. A coherent observational and theoretical eco-morphodynamic framework is then proposed.  相似文献   

Annual Variation of Benthic Nutrient Fluxes in Shallow Coastal Waters (Gulf of Trieste, Northern Adriatic Sea)   总被引：5，自引：0，他引：5  

Alessandra  Bertuzzi  Jadran  Faganeli Antonio  Bflmbati 《Marine Ecology》1996,17(1-3):261-278

Abstract. Benthic fluxes of dissolved N. Si and P nutrients, alkalinity, dissolved inorganic C (DIC), and O₂ from sediments in the Gulf of Trieste (northern Adriatic, Italy) were measured monthly for 16 months, using laboratory incubated flux chambers at in siru temperatures in the dark. The annual average fluxes were: 02 = -19.3 ± 8.2, DIC = 13.7 ± 9.6, NO3 = -0.04 ± 0.16, NH4 = 0.3 ± 0.4. PO₄= 4.001 ± 0.01, Si = 0.9 ± 0.1 mmol m-² d^-1, with strong temporal fluctuations. The highest effluxes of all nutrients and DIC were observed in the summer. Small effluxes of DIC and NH4 and influxes of Si and PO4 were observed in late winter. Only NH₄ (ca. 50%) and Si (ca. 70%) fluxes were significantly correlated with temperature. This correlation suggests that the rate of downward input and the quality of sedimented organic matter (autochthonous and allochthonous) were superimposed on the temperature fluctuations. High DIC, NH₄ and Si effluxes observed in May 1993 during low temperature were due to the degradation of sedimentary organic matter produced by an early spring bloom of benthic microalgae which occurred about 6 weeks earlies while the autumn phytoplankton bloom was simultaneously reflected in enhanced benthic fluxes due to higher temperature. The role of benthic biological advection in this transport across the sediment-water interface, evaluated by comparison between measured benthic and calculated diffusive fluxes from nutrient pore water concentrations, was of minor importance. This is probably due to low infaunal activity throughout the year it was localized mostly in the narrow surficial layer. The annual average diffusive fluxes of NH4 and PO4 were higher than those measured, probably due to the presence of nitrificationdenitrifi-cation processes and redox-dependent chemical reactions at the oxic sediment-water interface, respectively. Only during bottom-water hypoxia in September 1993 did strong PO₄ effluxes prevail. Calculations based on the Redfield stoichiometry of oxic decomposition of organic N to NH4 and NO3, and differences between diffusive and measured NH₄ fluxes showed that denitrifkation averaged 0.8 mmol m^-2 d^-1. Significant correlations between NH₄ and PO₄ DIC and Si, and NH4 and Si fluxes suggested their parallel regeneration and utilization at the sediment-water interface. The nutrient fluxes observed were not significantly linked to O₂ consumption, suggesting also that anaerobic oxidation processes were important at the sediment-water interface in the gulf. The N, P and Si nutriqnts released from sediment pore waters are probably utilized in benthic microalgal and bottorn-hater primary production. This indicates that pelagic and benthic communities in the central part of the Gulf of Trieste function relatively independently of each other.  相似文献   

Biomarkers of Exposure and Effects for Assessing Toxicological Risk of Endocrine Disrupters in Top Predators of the Mediterranean Sea     

M. Cristina Fossi  Silvia Casini  Letizia Marsili  Stefania Ancora  Gabriele Mori  Giovanni Neri  Antonella Ausili  Teresa Romeo  Alessandra Moscatelli  Giuseppe Notarbartolo Di  Sciara 《Marine Ecology》2002,23(S1):184-189

Abstract. Endocrine Disrupting Chemicals (EDCs) have the potential to alter hormone pathways that regulate reproductive processes in wildlife and fisheries. In this research the unexplored hypothesis that Mediterranean top predator species (such as large pelagic fish and marine mammals) are potentially at risk due to EDCs is investigated. In the Mediterranean environment, top predators accumulate high concentrations of polyhalogenated aromatic hydrocarbons (PHAHs) and toxic metals, incurring high toxicological risk. Here we illustrate the need to develop sensitive biomarkers for evaluation of toxicological risk in top marine predators (Xiphias gladius, Thunnus thynnus thynnus) and non-lethal techniques, such as non-destructive biomarkers, for the hazard assessment of threatened species exposed to EDCs, such as marine mammals ( Stenella coeruleoalba, Tursiops truncatus, Delphinus delphis and Balaenoptera physalus ).  相似文献   

Preboreal climatic oscillations recorded by pollen and foraminifera in the southern Adriatic Sea     

Sonia Favaretto  Alessandra Asioli  Antonella Miola  Andrea Piva 《Quaternary International》2008,190(1):89

Core SA03-1 from the southern Adriatic Sea (EC-Eurostrataform project) provides new information about climate changes and palaeocirculation in the Adriatic region during the last deglaciation. The results of an integrated study based on pollen and foraminifera records of the part of the core spanning the late Pleistocene–early Holocene transition (including the late Younger Dryas, the Preboreal and the beginning of the Boreal) are presented. The major vegetation changes and the short-term oscillations occurred during the early Holocene warming in the southern Adriatic basin on the basis of a high-resolution pollen record are documented. Vegetation changes are correlated to short-term oscillations detected in the foraminifera record during the same interval. The two independent terrestrial and marine proxies indicate at least three short-term cold and dry oscillations occurring at 11.2–11, 10.8–10.4 and 10 cal ka BP, according to the age–depth model adopted in this study. Finally, adopting an event-stratigraphy approach, the comparison of these results with two western Mediterranean records of Preboreal short-term oscillations suggest the occurrence of synchronous bio-events in the Mediterranean basin.  相似文献   

Milan: The city of constant renewal     

Anna Trono  Maria Chiara Zerbi 《GeoJournal》2002,58(1):65-72

Traditional models of urban development are no longer adequate to describe current metropolitan transformations. These are now at the centre of a debate concerning management and administration. In Italy, delays in resolving problems of urban and metropolitan government, despite the legal framework provided by Law 142/90, have weighed heavily on the larger urban areas of the country: Rome, Naples, Milan, which have not been able to tackle the issue of metropolitan government. Recent legislation, while not providing a pre-defined institutional solution, allows separate administrative districts to collectively establish metropolitan institutions of `variable geometry'. The Milan urban area is not one city, but a system of mutually-dependent cities, linked to each other and the rest of the world by a transport network still requiring much investment. The vitality of its economic structure (especially its small firms) is held back by seriously inadequate infrastructure and low external economic efficiency. The provincial capital may boast `historic centrality' but the most interesting potential for development is to be found on the periphery and in the administrative districts immediately surrounding it, in the recovery of derelict industrial areas and dormitory towns established in the 1950s and 1960s, especially to the north. Recovery of derelict areas, green areas, and better transport links within the urban area and with the outside world are the key elements in the reorganization of `Greater Milan'. In this situation of rapid transformation the most appropriate political strategies involve negotiated planning. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Is there any detachment in the Lower Dolpo (western Nepal)?Y a-t-il un détachement dans le bas Dolpo (Népal occidental) ?     

Rodolfo Carosi  Chiara Montomoli  Dario Visonà 《Comptes Rendus Geoscience》2002,334(12):933-940

A structural transect in the Lower Dolpo highlights that the deformation and metamorphism of the Tibetan Zone (TZ) increase toward the bottom of the sequence. The contact with the underlying HHC is marked by a metamorphic jump from amphibolite facies in the carbonatic rocks of the upper part of the HHC to greenschist facies marbles in the TZ. Moreover, the HHC and the TZ show different metamorphic histories. The contact zone shows a strain increase accompanied by asymmetric folds with a top-to-the-northeast vergence, connected to a down-to-the-northeast tectonic transport. The contact is interpreted as an extensional shear zone, connected to the South Tibetan Detachment System. To cite this article: R. Carosi et al., C. R. Geoscience 334 (2002) 933–940.  相似文献   

Efficiency of base isolation systems in structural seismic protection and energetic assessment     

Giuseppe Carlo Marano  Rita Greco 《地震工程与结构动力学》2003,32(10):1505-1531

This paper concerns the seismic response of structures isolated at the base by means of High Damping Rubber Bearings (HDRB). The analysis is performed by using a stochastic approach, and a Gaussian zero mean filtered non‐stationary stochastic process is used in order to model the seismic acceleration acting at the base of the structure. More precisely, the generalized Kanai–Tajimi model is adopted to describe the non‐stationary amplitude and frequency characteristics of the seismic motion. The hysteretic differential Bouc–Wen model (BWM) is adopted in order to take into account the non‐linear constitutive behaviour both of the base isolation device and of the structure. Moreover, the stochastic linearization method in the time domain is adopted to estimate the statistical moments of the non‐linear system response in the state space. The non‐linear differential equation of the response covariance matrix is then solved by using an iterative procedure which updates the coefficients of the equivalent linear system at each step and searches for the solution of the response covariance matrix equation. After the system response variance is estimated, a sensitivity analysis is carried out. The final aim of the research is to assess the real capacity of base isolation devices in order to protect the structures from seismic actions, by avoiding a non‐linear response, with associated large plastic displacements and, therefore, by limiting related damage phenomena in structural and non‐structural elements. In order to attain this objective the stochastic response of a non‐linear n‐dof shear‐type base‐isolated building is analysed; the constitutive law both of the structure and of the base devices is described, as previously reported, by adopting the BWM and by using appropriate parameters for this model, able to suitably characterize an ordinary building and the base isolators considered in the study. The protection level offered to the structure by the base isolators is then assessed by evaluating the reduction both of the displacement response and the hysteretic dissipated energy. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Cation ordering of orthopyroxenes from the Skaergaard Intrusion: implications for the subsolidus cooling rates and permeabilities     

J. Ganguly  M. Chiara Domeneghetti 《Contributions to Mineralogy and Petrology》1996,122(4):359-367

 We have determined the quenched cation ordering states of five orthopyroxene crystals collected from the marginal border group and the lower zone a and b of the Skaergaard intrusion, and modeled these data to retrieve their closure temperatures (T _c) of Fe–Mg ordering and cooling rates. According to existing thermal models for the Skaergaard pluton, conductive cooling dominated the high and low temperature regimes, which were separated by an intermediate temperature regime in which the cooling was controlled primarily by convective fluid circulation. The cooling rates retrieved from the quenched cation ordering states of the orthopyroxene crystals strictly apply to temperatures around the closure temperatures of the ordering states, ∼340–400^° C, which fall at the transition from convective to the lower temperature conductive cooling. The cooling rates obtained from the cation ordering states of orthopyroxene vary from ∼1 to 270 K/ka. These results agree well with a thermal model calculated using an assumed average permeability of 10^-12 cm² for the pluton, but not completely with a model calculated on the basis of an average permeability of 10^-13 cm², although both values produced shifts of δ¹⁸O that are comparable to those observed in the pluton. Received: 27 February 1995/Accepted: 20 July 1995  相似文献