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   

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   

Prediction of the thermodynamic properties of metal–chromate aqueous complexes to high temperatures and pressures and implications for the speciation of hexavalent chromium in some natural waters     

Marina Accornero  Luigi Marini  Matteo Lelli 《Applied Geochemistry》2010

Log–log correlation plots between the dissociation constants of known metal–chromate complexes and those of corresponding metal–sulfate complexes at 25 °C, 1 bar were used to derive the standard partial molal Gibbs free energies of formation of unknown metal–chromate complexes involving either (i) monovalent cations, divalent cations, and trivalent lanthanides or (ii) trivalent cations (excluding those of rare earth elements, REE) and tetravalent cations. For each of these two classes of ionic associations, empirical relationships between the standard partial molal volumes, isobaric heat capacities and entropies of known metal–chromate complexes and the corresponding thermodynamic properties of metal ions have been found. These data were utilized to evaluate the solute-characteristic parameters of the revised Helgeson–Kirkham–Flowers equation of state and to compute the thermodynamic properties of the dissociation reactions of metal–chromate complexes at high temperatures and pressures.  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   

Experimental Studies on the Mechanical Behaviour of two Thermal Cracked Marbles   总被引：3，自引：3，他引：3  

A. M. Ferrero  P. Marini 《Rock Mechanics and Rock Engineering》2001,34(1):57-66

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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   

Marine geology of the Medriff Corridor, Mediterranean Ridge   总被引：1，自引：0，他引：1  

Nicoetta  Fusi  Giovanni Aloisi  de Larderel Ada  Borelu  Ottavio  Amelio  Davide  Castradori  Alessandra  Negri    Bianca  Rimoldi  Rossella  Sanvoisin  Paola  Tarbini  Maria B.  Cita 《Island Arc》1996,5(4):420-439

Abstract Thirty-one piston and/or gravity cores not exceeding 10 m in length were raised in selected areas of a 300 km-long transect (Medriff Corridor) crossing the Mediterranean Ridge, an accretionary complex subject to continent/continent collision, containing an important evaporitic body (Messinian evaporites), in order to ground-truth the geological make-up. Core location, very accurate with reference to a complex bottom configuration, was preceded by swathe mapping, seismic profiling and side-scan sonar investigations. Most sediment cores have a pelagic facies, with biogenic marls as dominant lithology, and sapropels and tephras as minor, isochronous lithologies. A combination of isochronous lithologies and calcareous plankton biochronology permits high resolution stratigraphic correlations. Pelagic facies sediments are Middle Pleistocene to Holocene in age. Two cores associated with mounds located along thrusts contain a matrix-supported mud breccia of deep provenance, Burdigalian-Langhian in age, similar to that characteristic of the Mediterranean Ridge diapiric belt (Cita et al. 1995 ). Three new brine-filled anoxic basins (Urania, l'Atalante and Discovery) were discovered. The brines originated from submarine dissolution of Messinian evaporites and are different in the various basins. The sedimentary record strongly differs from basin to basin. These brine lakes are very young (35 000 years or less). A drastic change in sedimentation rate recorded in the Discovery Basin suggests that basin collapse was sudden and followed by progressive development of basin anoxia. Some cores were analyzed with a prototype multisensor for P-wave velocity, magnetic susceptibility and density. Sapropels show up as abrupt decreases in P-wave velocity and density, and tephra as sudden increases in magnetic susceptibility. Mud breccia displays P-wave velocities greater than pelagic marls, with peaks related to lithic clasts. Anoxic sediments have high P-wave velocities; peaks are associated with gypsum crystals.  相似文献