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211.
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
212.
213.
Simone Bianchi Andrea Ferrara 《Monthly notices of the Royal Astronomical Society》2005,358(2):379-396
We study the motion of dust grains into the intergalactic medium (IGM) around redshift z = 3 , to test the hypothesis that grains can efficiently pollute the gas with metals through sputtering. We use the results available in the literature for radiation-driven dust ejection from galaxies as initial conditions and follow the motion onwards. Via this mechanism, grains are ejected into the IGM with velocities >100 km s−1 ; as they move supersonically, grains can be efficiently eroded by non-thermal sputtering. However, Coulomb and collisional drag forces effectively reduce the charged grain velocity. Up-to-date sputtering yields for graphite and silicate (olivine) grains have been derived using the code transport of ions in matter ( trim ), for which we provide analytic fits. After training our method on a homogeneous density case, we analyse the grain motion and sputtering in the IGM density field as derived from a Λ cold dark matter (CDM) cosmological simulation at z = 3.27 . We found that only large ( a ≳ 0.1μm) grains can travel up to considerable distances (few ×100 kpc physical) before being stopped. Resulting metallicities show a well-defined trend with overdensity δ. The maximum metallicities are reached for 10 < δ < 100 [corresponding to systems, in quasi-stellar object (QSO) absorption spectra, with 14.5 < log N (H i ) < 16 ]. However the distribution of sputtered metals is very inhomogeneous, with only a small fraction of the IGM volume polluted by dust sputtering (filling factors of 18 per cent for Si and 6 per cent for C). For the adopted size distribution, grains are never completely destroyed; nevertheless, the extinction and gas photoelectric heating effects resulting from this population of intergalactic grains are well below current detection limits. 相似文献
214.
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
215.
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
216.
G. Ponti M. Cappi C. Vignali G. Miniutti F. Tombesi M. Dadina A. C. Fabian P. Grandi J. Kaastra P. O. Petrucci S. Bianchi G. Matt L. Maraschi G. Malaguti 《Monthly notices of the Royal Astronomical Society》2009,394(3):1487-1495
We report on partially overlapping XMM–Newton (∼260 ks) and Suzaku (∼100 ks) observations of the iron K band in the nearby, bright type 1 Seyfert galaxy Mrk 509. The source shows a resolved neutral Fe K line, most probably produced in the outer part of the accretion disc. Moreover, the source shows further emission bluewards of the 6.4 keV line due to ionized material. This emission is well reproduced by a broad line produced in the accretion disc, while it cannot be easily described by scattering or emission from photoionized gas at rest. The summed spectrum of all XMM–Newton observations shows the presence of a narrow absorption line at 7.3 keV produced by highly ionized outflowing material. A spectral variability study of the XMM–Newton data shows an indication for an excess of variability at 6.6–6.7 keV. These variations may be produced in the red wing of the broad ionized line or by variation of a further absorption structure. The Suzaku data indicate that the neutral Fe K α line intensity is consistent with being constant on long time-scales (of a few years), and they also confirm as most likely the interpretation of the excess blueshifted emission in terms of a broad ionized Fe line. The average Suzaku spectrum differs from the XMM–Newton one in the disappearance of the 7.3 keV absorption line and around 6.7 keV, where the XMM–Newton data alone suggested variability. 相似文献
217.
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
218.
Stefano Bianchi Marco Chiaberge Enrico Piconcelli Matteo Guainazzi Giorgio Matt 《Monthly notices of the Royal Astronomical Society》2008,386(1):105-110
We analyse Chandra , XMM–Newton and Hubble Space Telescope ( HST ) data of the double-nucleus Ultraluminous Infrared Galaxy (ULIRG), Mrk 463. The Chandra detection of two luminous ( L 2–10 keV = 1.5 × 1043 and 3.8 × 1042 erg cm−2 s−1 ) , unresolved nuclei in Mrk 463 indicates that this galaxy hosts a binary active galactic nucleus (AGN), with a projected separation of ≃3.8 kpc ( 3.83 ± 0.01 arcsec). While the East nucleus was already known to be a type 2 Seyfert (and this is further confirmed by our Chandra detection of a neutral iron line), this is the first unambiguous evidence in favour of the AGN nature of the West nucleus. Mrk 463 is therefore the clearest case so far for a binary AGN, after NGC 6240. 相似文献
219.
L. J. Phillips S. A. Edwards V. Bianchi J. S. Esterle 《Australian Journal of Earth Sciences》2017,64(5):587-609
The recent review of the Lopingian (upper Permian) stratigraphic framework of the Galilee Basin, prompted a reconsideration of the paleo-environments of deposition. This study interpreted the distribution of sedimentary facies from geophysical logs across the basin complemented by detailed logging from four key wells (GSQ Tambo 1-1A, OEC Glue Pot Creek 1, CRD Montani 1 and GSQ Muttaburra 1). Seven facies associations were identified: terrestrial fluvial, floodplain, lacustrine and mire; and paralic to marine estuarine shoreline, delta and restricted marine. Coal measures (mire facies) are best developed in the northeastern margin of the basin, whereas the southern Springsure Shelf was dominated by marine conditions throughout the Lopingian, only developing terrestrial facies towards the very uppermost Lopingian. The ‘Colinlea Sandstone equivalent’ was deposited in a fluvial system, with tidal influence exhibited in the southern part of the basin, which decreases further north as lacustrine environments become common. The regional transgression represented by the Black Alley Shale can be mapped into the central part of the basin, but based on new exploration data its northern extent is more limited than previously thought. The ‘Burngrove Formation equivalent’ and Bandanna Formation represent a southerly prograding fluvial-deltaic system during the regional regression in the upper part of the Lopingian. 相似文献
220.
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