Dependence on the observational time intervals and domain of convergence of orbital determination methods     

Alessandra Celletti  Gabriella Pinzari 《Celestial Mechanics and Dynamical Astronomy》2006,95(1-4):327-344

In the framework of the orbital determination methods, we study some properties related to the algorithms developed by Gauss, Laplace and Mossotti. In particular, we investigate the dependence of such methods upon the size of the intervals between successive observations, encompassing also the case of two nearby observations performed within the same night. Moreover we study the convergence of Gauss algorithm by computing the maximal eigenvalue of the jacobian matrix associated to the Gauss map. Applications to asteroids and Kuiper belt objects are considered.  相似文献   

Preface     

Alessandra Celletti  Sylvio Ferraz-Mello 《Celestial Mechanics and Dynamical Astronomy》2006,95(1-4):1-2

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On the stability of the lagrangian points in the spatial restricted problem of three bodies     

Alessandra Celletti  Antonio Giorgilli 《Celestial Mechanics and Dynamical Astronomy》1990,50(1):31-58

The problem of stability of the Lagrangian equilibrium point of the circular restricted problem of three bodies is investigated in the light of Nekhoroshev-like theory. Looking for stability over a time interval of the order of the estimated age of the universe, we find a physically relevant stability region. An application of the method to the Sun-Jupiter and the Earth-Moon systems is made. Moreover, we try to compare the size of our stability region with that of the region where the Trojan asteroids are actually found; the result in such case is negative, thus leaving open the problem of the stability of these asteroids.  相似文献   

Slope dynamics of Lake Albano (Rome,Italy): insights from high resolution bathymetry     

Francesca Bozzano  Paolo Mazzanti  Marco Anzidei  Carlo Esposito  Mario Floris  Gianluca Bianchi Fasani  Alessandra Esposito 《地球表面变化过程与地形》2009,34(11):1469-1486

New detailed data about the morphology of the submerged slopes of Lake Albano (Rome, Italy) have been collected by a sonar multibeam survey financed by the Italian Department of Civil Protection. These data allow for investigation of the subaqueous slope dynamics of the lake, which partially fills a volcanic depression, and the elucidation of the relationships between subaqueous and subaerial slope processes. Subaerial, submerged and combined subaerial/submerged landslide‐related morphologies were detected around the inner slopes of the lake. In the submerged slopes, several gravity‐induced landforms were recognized: landslide scar areas, landslide accumulations, erosional chutes and channels, block fields, isolated blocks, scarps and slope breaks. An attempt to evaluate the state of activity of the submerged slopes was carried out by taking into consideration the relative freshness of some selected landforms. Interpretation of bathymetric data, as well as direct surveys of the subaerial slopes, was used to assess the morphometric features and interpret the type of movement of the landslides. We propose a comprehensive classification based on the landslide's size and type of movement. We recognized rock fall/topples, debris flows, rock slides and slump, complex rock slides/channelled flows and debris slide and slump. The volume of the main landslides ranged between 10¹ and 10³ m³, while a few rock and debris slides have volumes ranging between 10³ and 10⁵ m³. Two large palaeo‐landslides with volumes on the order of 10⁶ m³ were identified in the southern and northern part of the lake, respectively. Velocities of the recognized landslides range from rapid to extremely rapid. Two main landslide hazard scenarios have been depicted from the results of the integrated analysis of both subaerial and submerged gravity‐induced landforms. The most hazardous scenario involves extremely rapid large volume events (>10⁶ m³) that could, if they interacted with water, induce catastrophic tsunamis. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Changes in biomass structure and trophic status of the plankton communities in a highly dynamic ecosystem (Gulf of Venice,Northern Adriatic Sea)     

Alessandra Pugnetti  Anna Maria Bazzoni  Alfred Beran  Fabrizio Bernardi Aubry  Elisa Camatti  Mauro Celussi  Joan Coppola  Erica Crevatin  Paola Del Negro  Alessandro Paoli 《Marine Ecology》2008,29(3):367-374

The changes in the plankton biomass structure in relation to nutrient inputs were studied in the Gulf of Venice (Northern Adriatic Sea), an area characterized by a very marked trophic state variability. The investigation was carried out at two stations, in March, May and July 2005 and 2006, considering the whole water column. The size structure (from picoplankton to mesozooplankton) of both autotrophs and heterotrophs was analysed. Signals of diluted waters and nutrient inputs were more marked in 2005 than in 2006. In 2005, the total plankton biomass was almost double (87 ± 37 μg·C·l^?1) that in 2006 (44 ± 26 μg·C·l^?1). The variations were determined mainly by phytoplankton, with a 70% decrease, and a shift from a community dominated by microphytoplankton (49 ± 12%) in 2005 to one dominated by bacteria (43 ± 11%) in 2006 was observed. The relationship between the heterotrophic (H) and autotrophic (A) biomass indicated a rapid decline of the H/A ratio with increasing phytoplankton biomass. This study, although temporally limited, is consistent with the results reported for other marine environments and it seems to confirm the importance of nutrient inputs in structuring the biomass of plankton community.  相似文献   

Effects on geodetic VLBI measurements due to polarization leakage in S/X receivers     

Alessandra Bertarini  Alan L. Roy  Brian Corey  R. Craig Walker  Walter Alef  Axel Nothnagel 《Journal of Geodesy》2011,85(10):715-721

Geodetic very long baseline interferometry (VLBI) delivers time series of station positions and Earth orientation parameters. These series offer a viable and precise way to study Earth crustal and core dynamics and to support space navigation. Their accuracy is degraded by instrumental errors, of which polarization leakage is considered to be one of the largest that is not yet being addressed. Its effect on the data can be corrected, provided one knows the leakage characteristics of the receivers. For this purpose, we designed a VLBI session to measure the polarization leakage at 15 geodetic and very long baseline array stations over the frequency range from 8,212.99 to 8,932.99 MHz. We describe the polarization leakage measurements and the algorithm that was implemented to correct for its effect on the geodetic delay observables. Subsequently, we applied the correction for polarization leakage to the same data that were used to determine the leakage and checked for the resulting improvement. From the measured leakage terms, one would expect polarization leakage to affect the group delay measurements in 90% of the cases by 1.6 ps or less. This proved to be below the statistical noise in our single VLBI session, and hence, an improvement from the correction could not be detected. Applying this analysis in the context of VLBI2010, we provide a specification for the allowable polarization leakage to achieve the target submillimetre accuracy.  相似文献   

Hamiltonian Stability of Spin–Orbit Resonances in Celestial Mechanics     

Alessandra Celletti  Luigi Chierchia 《Celestial Mechanics and Dynamical Astronomy》2000,76(4):229-240

The behaviour of ‘resonances’ in the spin-orbit coupling in celestial mechanics is investigated in a conservative setting. We consider a Hamiltonian nearly-integrable model describing an approximation of the spin-orbit interaction. The continuous system is reduced to a mapping by integrating the equations of motion through a symplectic algorithm. We study numerically the stability of periodic orbits associated to the above mapping by looking at the eigenvalues of the matrix of the linearized map over the full cycle of the periodic orbit. In particular, the value of the trace of the matrix is related to the stability character of the periodic orbit. We denote by ε_* (p/q) the value of the perturbing parameter at which a given elliptic periodic orbit with frequency p/q becomes unstable. A plot of the critical function ε_* (p/q) versus the frequency at different orbital eccentricities shows significant peaks at the synchronous resonance (for low eccentricities) and at the synchronous and 3:2 resonances (at higher eccentricities) in good agreement with astronomical observations. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Late Quaternary palaeohydrology of Lake Pergusa (Sicily,southern Italy) as inferred by stable isotopes of lacustrine carbonates     

Giovanni Zanchetta  Alessandra Borghini  Anthony E. Fallick  Francesco P. Bonadonna  Gabriello Leone 《Journal of Paleolimnology》2007,38(2):227-239

Ten meters of lacustrine deposits retrieved from Lake Pergusa (Sicily, southern Italy) were investigated through stable isotope composition (carbon and oxygen) of authigenic carbonate (calcareous muds) and freshwater shells. The core chronology was established through three AMS dates, and by correlation with a previously dated nearby core. Stable isotope data show that the lake water evolution was mainly dominated by evaporation. Between ca. 20 and 28 ka the recovered sediments have very high δ¹⁸O values, likely corresponding to very dry climatic conditions. The observed rapid oscillations in the δ¹⁸O of the recovered sediments during this period also suggest important climatic fluctuations. More humid conditions dominated during the Holocene period, with the wettest interval occurring between ca. 9000 and 3000 years BP. Late Holocene sediments represent a substantial return to drier conditions. The available pollen data from a nearby core substantially confirm this general climatic trend during the Holocene. The positive correlation between δ¹³C of the calcareous muds and carbonate content suggests that biological activity played a key role in the carbon isotope evolution of dissolved inorganic carbon. However, a clear climatic signal is not evident from the δ¹³C record.  相似文献   

Phosphorus dynamics in water and sediments in urbanized and non-urbanized rivers in Southern Brazil   总被引：1，自引：0，他引：1  

Pagliosa PR  Fonseca A  Bosquilha GE  Braga ES  Barbosa FA 《Marine pollution bulletin》2005,50(9):965-974

Phosphorus flux models show that the removal tends to be a common feature in polluted estuarine systems whereas the release of P to the adjacent coastal area occurs in pristine environments. This study analyzes the distribution of P in water and sediments along six rivers in the south coast of Brazil. Three rivers located inside protected areas were considered non-polluted and used as a control of urbanization. The other three, situated within urbanized areas, were considered as having highly elevated concentrations of P. Results showed a different behavior of P in water and sediments located in urbanized and non-urbanized areas. The concentrations of dissolved organic (P-org) and inorganic (P-inorg) phosphorus in water, and the total phosphorus (P-tot) and polyphosphate (P-poly) in sediments where higher in the urbanized rivers compared to the non-urbanized ones. Both P of punctual origin and of diffuse origin contributed to the maintenance of elevated concentrations and disturbed the natural fluxes along the polluted rivers. The minimum and maximum concentrations in urbanized areas varied from 0.39 to 12.45 (microM) for P-org and 0.00 to 5.92 (microM) for P-inorg in water, and in sediments from 89.90 to 808.16 (microM g(-1)) for P-tot and 0.00 to 76.51 (microM g(-1)) for P-poly. In non-urbanized areas concentrations in water varied from 0.22 to 1.20 (microM) for P-inorg and 4.43 to 5.56 (microM) for P-org, and in sediments from 45.91 to 652.26 (microM g(-1)) for P-tot and 0.00 to 8.61 (microM g(-1)) for P-poly. Using a hierarchical sampling design and a simple model of variation of P (K(d) model) it was possible to demonstrate that urbanized and non-urbanized estuaries may act as sinks or sources of P. The variation of P analysis in different points along each of the six rivers showed that release and removal areas may occur within a same river independently of its urbanization.  相似文献   

Stress pattern at Campi Flegrei from focal mechanisms of the 1982–1984 earthquakes (southern Italy)     

Agostino Zuppetta  Alessandra Sava 《Journal of Volcanology and Geothermal Research》1991,48(1-2)

Campi Flegrei is a Holocene volcanic area in the Campanian Plain (Southern Italy) within the Apennine Chain, a neogenic thrust belt built up since the Middle Miocene. The volcanic complex consists of a c. 12-km-diameter caldera containing several monogenetic volcanoes, the youngest of which (Monte Nuovo) erupted in 1538. Since at least Roman times, the area has also been affected by slow vertical movements (bradiseismic activity). Between 1982 and 1985, this slow motion was interrupted by a period of more rapid displacement which caused a maximum uplift of 180 cm in the town of Pozzuoli. To model the local stress field associated with the uplift, the Angelier inversion technique has been applied using the focal mechanisms of forty-nine earthquakes which occurred between April 1982 and December 1984. The results show that doming coupled with a regional extensional strain can account for the seismic phenomena that affected the area.  相似文献