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81.
82.
Height bias and scale effect induced by antenna gravitational deformations in geodetic VLBI data analysis 总被引:2,自引:2,他引:0
The impact of signal path variations (SPVs) caused by antenna gravitational deformations on geodetic very long baseline interferometry
(VLBI) results is evaluated for the first time. Elevation-dependent models of SPV for Medicina and Noto (Italy) telescopes
were derived from a combination of terrestrial surveying methods to account for gravitational deformations. After applying
these models in geodetic VLBI data analysis, estimates of the antenna reference point positions are shifted upward by 8.9
and 6.7 mm, respectively. The impact on other parameters is negligible. To simulate the impact of antenna gravitational deformations
on the entire VLBI network, lacking measurements for other telescopes, we rescaled the SPV models of Medicina and Noto for
other antennas according to their size. The effects of the simulations are changes in VLBI heights in the range [−3, 73] mm
and a net scale increase of 0.3–0.8 ppb. The height bias is larger than random errors of VLBI position estimates, implying
the possibility of significant scale distortions related to antenna gravitational deformations. This demonstrates the need
to precisely measure gravitational deformations of other VLBI telescopes, to derive their precise SPV models and to apply
them in routine geodetic data analysis. 相似文献
83.
The structural stability of manganese titanate MnTiO3 at high pressure was investigated by X-ray diffraction and Raman spectroscopy with diamond anvil cells. Ilmenite-type MnTiO3 is stable at least to 26.6 GPa, and lithium niobate type MnTiO3 reversibly transforms at room temperature to perovskite at 2.0 GPa. Bulk moduli (K300) of ilmenite, lithium niobate and perovskite are 174(4) GPa, 179(8) GPa, and 208(5) GPa, respectively (at fixed first pressure derivative K′ = 4). The Grüneisen parameter γ has been estimated to be 1.28 for ilmenite and 1.75 for perovskite. In ilmenite phase, TiO6 octahedra become more regular with increasing pressure. In perovskite phase structural distortion increases with pressure increase. 相似文献
84.
Ryosuke Sinmyo Elena Bykova Catherine McCammon Ilya Kupenko Vasily Potapkin Leonid Dubrovinsky 《Physics and Chemistry of Minerals》2014,41(6):409-417
Magnesium silicate perovskite is the predominant phase in the Earth’s lower mantle, and it is well known that incorporation of iron has a strong effect on its crystal structure and physical properties. To constrain the crystal chemistry of (Mg, Fe)SiO3 perovskite more accurately, we synthesized single crystals of Mg0.946(17)Fe0.056(12)Si0.997(16)O3 perovskite at 26 GPa and 2,073 K using a multianvil press and investigated its crystal structure, oxidation state and iron-site occupancy using single-crystal X-ray diffraction and energy-domain Synchrotron Mössbauer Source spectroscopy. Single-crystal refinements indicate that all iron (Fe2+ and Fe3+) substitutes on the A-site only, where \( {\text{Fe}}^{ 3+ } /\Upsigma {\text{Fe}}\sim 20\,\% \) based on Mössbauer spectroscopy. Charge balance likely occurs through a small number of cation vacancies on either the A- or the B-site. The octahedral tilt angle (Φ) calculated for our sample from the refined atomic coordinates is 20.3°, which is 2° higher than the value calculated from the unit-cell parameters (a = 4.7877 Å, b = 4.9480 Å, c = 6.915 Å) which assumes undistorted octahedra. A compilation of all available single-crystal data (atomic coordinates) for (Mg, Fe)(Si, Al)O3 perovskite from the literature shows a smooth increase of Φ with composition that is independent of the nature of cation substitution (e.g., \( {\text{Mg}}^{ 2+ } - {\text{Fe}}^{ 2+ } \) or \( {\text{Mg}}^{ 2+ } {\text{Si}}^{ 4+ } - {\text{Fe}}^{ 3+ } {\text{Al}}^{ 3+ } \) substitution mechanism), contrary to previous observations based on unit-cell parameter calculations. 相似文献
85.
86.
Leonid S. Lyubimkov Tamara M. Rachkovskaya Sergey I. Rostopchin David L. Lambert 《Monthly notices of the Royal Astronomical Society》2002,333(1):9-26
Effective temperatures T eff , surface gravities log g and interstellar extinctions A V are found for 107 B stars. Distances d of the stars, which are based on the derived T eff , log g and A V values, show good agreement with those obtained from the Hipparcos parallaxes. Comparing the T eff and log g values with evolutionary computations, we infer masses, radii, luminosities, ages and relative ages of the stars. Empirical relations between the T eff and log g parameters, on the one hand, and the photometric indices Q , [ c 1 ] and β , on the other hand, are constructed; these relations give a fast method for the T eff and log g estimation of early and medium B stars. Inclusion of the infrared J , H and K colours into the T eff , log g and A V determination shows that (i) the T eff and log g parameters are altered only slightly; (ii) the A V value is rather sensitive to these colours, so an accuracy better than 0.05 mag in the JHK data is necessary for precise A V evaluation. 相似文献
87.
Leonid S. Pilyugin José M. Vílchez Trinh X. Thuan 《Monthly notices of the Royal Astronomical Society》2006,370(4):1928-1934
We suggest a new way to establish the relation between the electron temperature t 3 within the [O iii ] zone and the electron temperature t 2 within the [O ii ] zone in high-metallicity (12 + log(O/H) > 8.25) H ii regions. The t 2 – t 3 diagram is constructed by applying our method to a sample of 372 H ii regions. We find that the correlation between t 2 and t 3 is tight and can be approximated by a linear expression. The new t 2 – t 3 relation can be used to determine t 2 and accurate abundances in high-metallicity H ii regions with a measured t 3 . It can also be used in conjunction with the ff relation for the determination of t 3 and t 2 and oxygen abundances in high-metallicity H ii regions, where the [O iii ]λ4363 auroral line is not detected. The derived t 2 – t 3 relation is independent of photoionization models of H ii regions. 相似文献
88.
Athena Coustenis Jonathan Lunine Jean-Pierre Lebreton Dennis Matson Christian Erd Kim Reh Patricia Beauchamp Ralph Lorenz Hunter Waite Christophe Sotin Leonid Gurvits Mathieu Hirtzig 《Earth, Moon, and Planets》2009,105(2-4):135-142
The Titan Saturn System Mission (TSSM) concept is composed of a TSSM orbiter provided by NASA that would carry two Titan in situ elements provided by ESA: the montgolfière and the probe/lake lander. One overarching goal of TSSM is to explore in situ the atmosphere and surface of Titan. The mission has been prioritized as the second Outer Planets Flagship Mission, the first one being the Europa Jupiter System Mission (EJSM). TSSM would launch around 2023–2025 arriving at Saturn 9 years later followed by a 4-year science mission in the Saturn system. Following delivery of the in situ elements to Titan, the TSSM orbiter would explore the Saturn system via a 2-year tour that includes Enceladus and Titan flybys before entering into a dedicated orbit around Titan. The Titan montgolfière aerial vehicle under consideration will circumnavigate Titan at a latitude of ~20° and at altitudes of ~10 km for a minimum of 6 months. The probe/lake lander will descend through Titan’s atmosphere and land on the liquid surface of Kraken Mare (~75° north latitude). As for any planetary space science mission, and based on the Cassini–Huygens experience, Earth-based observations will be synergistic and enable scientific optimization of the return of such a mission. Some specific examples of how this can be achieved (through VLBI and Doppler tracking, continuous monitoring of atmospheric and surface features, and Direct-to-Earth transmission) are described in this paper. 相似文献
89.
Dominik C. HEZEL Leonid DUBROVINSKY Lutz NASDALA Jean CAUZID Alexandre SIMIONOVICI Marko GELLISSEN Thorbjörn SCHÖNBECK 《Meteoritics & planetary science》2008,43(7):1127-1136
Abstract— A new olivine‐pigeonite ureilite containing abundant diamonds and graphite was found in the United Arab Emirates. This is the first report of a meteorite in this country. The sample is heavily altered, of medium shock level, and has a total weight of 155 g. Bulk rock, olivine (Fo79.8–81.8) and pyroxene (En73.9–75.2, Fs15.5–16.9, Wo8.8–9.5) compositions are typical of ureilites. Olivine rims are reduced with Fo increasing up to Fo96.1–96.8. Metal in these rims is completely altered to Fehydroxide during terrestrial weathering. We studied diamond and graphite using micro‐Raman and in situ synchrotron X‐ray diffraction. The main diamond Raman band (LO = TO mode at ?1332 cm?1) is broadened when compared to well‐ordered diamond single crystals. Full widths at half maximum (FWHM) values scatter around 7 cm?1. These values resemble FWHM values obtained from chemical vapor deposition (CVD) diamond. In situ XRD measurements show that diamonds have large grain sizes, up to >5 μm. Some of the graphite measured is compressed graphite. We explore the possibilities of CVD versus impact shock origin of diamonds and conclude that a shock origin is much more plausible. The broadening of the Raman bands might be explained by prolonged shock pressure resulting in a transitional Raman signal between experimentally shock‐produced and natural diamonds. 相似文献
90.
Mineralogy and Petrology - The concentrations of 26 trace elements have been determined by laser ablation ICP-MS in zircons from four samples of basic rocks of the Korosten... 相似文献