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51.
We consider the problem of multifrequency VLBA image synthesis and spectral-index mapping for active galactic nuclei related
to the necessity of taking into account the frequency-dependent image shift. We describe our generalized multifrequency synthesis
algorithm with a spectral correction based on the maximum entropy method. The results of our processing of multifrequency
VLBI data for the radio sources J2202+4216, J0336+3218, and J1419+5423 are presented. 相似文献
52.
K. N. Malitch E. V. Anikina I. Yu. Badanina E. A. Belousova E. V. Pushkarev V. V. Khiller 《Geology of Ore Deposits》2016,58(1):1-19
The isotopic and geochemical characteristics of PGE mineralization in high-Mg chromitite from the banded dunite–wehrlite–clinopyroxenite complex of the Nurali lherzolite massif, the South Urals, Russia is characterized for the first time. Electron microprobe analysis and LA MC-ICP-MS mass spectrometry are used for studying Cr-spinel and platinum-group minerals (PGM). Two processes synchronously develop in high-Mg chromitite subject to metamorphism: (1) the replacement of Mg–Al-rich Cr-spinel, orthopyroxene, and diopside by chromite, Cr-amphibole, chlorite, and garnet; (2) the formation of a secondary mineral assemblage consisting of finely dispersed ruthenium or Ru-hexaferrum aggregate and silicate–oxide or silicate matter on the location of primary Ru–Os-sulfides of the laurite–erlichmanite solid solution series. Similar variations of Os-isotopic composition in both primary and secondary PGM assemblages are evidence for the high stability of the Os isotope system in PGM and for the possibility of using model 187Os/188Os ages in geodynamic reconstructions. 相似文献
53.
Thermal and chemical heterogeneity of the upper mantle beneath the Baikal-Mongolia territory 总被引：1，自引：0，他引：1
V. A. Glebovitskii L. P. Nikitina A. K. Saltykova Yu. D. Pushkarev N. O. Ovchinnikov M. S. Babushkina I. V. Ashchepkov 《Petrology》2007,15(1):58-89
Mineralogical, petrochemical, and geochemical characteristics and the crystallization conditions (T, P, and \(f_{O_2 } \)) of mantle xenoliths in alkaline basalts from the Baikal-Mongolia area indicated: (1) that the compositional heterogeneity of the mantle beneath southeastern and central parts of Mongolia, the Khamar-Daban, and Transbaikalia reflects variations in the degree of melting of the primitive mantle (10% and more for southeastern Mongolia, 0–15% for central Mongolia, and 0–10% for Transbaikalia and the Khamar-Daban) and, perhaps, also the compositional heterogeneity of the mantle source material; (2) the dependence of the concentrations of Y, Zr, Ti, Sc, and REE (from Nd to Lu) on the contents of major oxides (Al2O3 and MgO) and on their ratios (MgO/SiO2 and Al2O3/MgO) in the xenoliths testifies that the distribution of trace elements and REE in the mantle was controlled by its partial melting; (3) the thermal state of the mantle varies beneath the Vitim area (geothermal gradient TG = 9.4 ± 0.3°C/km), central Mongolia (TG = 10.2 ± 0.2°C/km), and southeastern Mongolia (TG = 9.4 ± 0.3°C/km); (4) the Pb-Pb model age of the material represented by the primitive mantle xenoliths is 4457 ± 12 Ma and is consistent with the evaluated duration of the development of the core and its complementary primitive mantle calculated for the U-Th-Pb system (Galer and Golddstein, 1996). 相似文献
54.
It is preferable to use the three-dimensional (3D) magnetotelluric inversion, which provides volumetric geoelectric models, to handle the array input data. However, the soundings are frequently conducted on the single profiles or on the profiles that are considerably spaced apart from each other. We explore the possibilities of the 3D inversion of such data by the example of a three-layer model containing three local inhomogeneities. We previously showed that the simple processing of the data and their 1D or 2D inversion enable reconstructing the background cross section and locating all the three inhomogeneities. In the present paper, we use this information for constructing several versions of the starting model and carrying out the smoothing 3D inversion of the data. The experiments show that if the background cross section is incorporated into the starting model, the final model provided by the inversion closely reproduces the real distribution of all geoelectric parameters. At the same time, if the starting model that hosts the inhomogeneities has the form of a homogeneous half-space, the inversion is not able to reconstruct an adequate final model.
相似文献55.
Elena Aleksandrovna Bruevich Vasily Vladimirovich Bruevich Boris Pavlovich Artamonov 《天文和天体物理学研究(英文版)》2018,(7)
The wavelet transform method for high-quality time-frequency analysis is applied to sets of observations of relative sunspot numbers and stellar chromosphere fluxes of 10 Sun-like stars.Wavelet analysis of solar data shows that in a certain interval of time there are several cycles of activity with periods of duration which vary considerably from each other:from quasi-biennial cycles to 100-yr cycles.Cyclic activity was detected in almost all Sun-like stars that we examined,even those that previously were not considered as stars with cyclic activity according to analysis using a Scargle periodogram.The durations of solar and stellar cycles significantly change during the observation period. 相似文献
56.
D. C. Gabuzda A. B. Pushkarev T. V. Cawthorne 《Monthly notices of the Royal Astronomical Society》1999,307(3):725-736
VLBI total intensity ( I ) and linear polarization ( P ) images at λ =6 cm have been obtained for nine radio-bright BL Lacertae objects. These are the first VLBI P images for these sources, and, in a number of cases, the first I images as well. They confirm the previously noted tendency for the jet magnetic fields of BL Lacertae objects to be transverse to the local jet direction, but also provide new evidence that a sizeable minority of BL Lacertae objects have VLBI jet components with longitudinal magnetic fields. In addition, two sources have VLBI jet components in which the direction of the electric vector χ bears no obvious relation to the apparent local jet direction; the origin of these arbitrary χ offsets is unclear. A new tentative superluminal speed of β =6.3 h −1 has been determined for 0828+493; tentative speeds for two knots in 1418+546 are β =4.3 and 2.5 h −1 . This work is part of an ongoing programme to determine the VLBI I and P structure of all 34 sources in the 1-Jy sample of northern BL Lacertae objects defined by Kühr & Schmidt. 相似文献
57.
Vasilii Gvaramadze 《Astrophysics and Space Science》2000,274(1-2):195-203
A model of the Vela supernova remnant (SNR) based on a cavity explosion of a supernova (SN) star is proposed. It is suggested
that the general structure of the remnant is determined by the interaction of the SN blast wave with a massive shell created
by the SN progenitor (15-20 M⊙) star. A possible origin of the nebula of hard X-ray emission detected around the Velapulsar is discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
58.
One of the significant problems of modern deep magnetotellurics is the recognition of anisotropy in the crustal and mantle
conductive zones. In the paper we perform numerical experiment comparing several 2D models of crustal and mantle isotropic
and anisotropic prismatic conductors. Anisotropy is modeled by alternating horizontal or vertical thin layers of different
resistivities (the vertical layers are parallel to the prism strike). Using these models, we examine conditions under which
the magnetotelluric and magnetovariational response functions distinguish between isotropy and anisotropy. The resolution
of MT and MV studies depends on the sediments conductance, lithosphere resistance and deep conductor width. Calculations show
that the most favorable conditions for anisotropy studies are observed in the active regions characterized by small sediments
conductance (10–20 S) and moderate lithosphere resistance (108 Ohm·m2). However, in the stable regions, where sediments conductance exceeds 50–100 S and the lithosphere resistance comes up to
109 Ohm·m2, the crustal and mantle anisotropic and isotropic conductors manifest themselves in the equivalent magnetotelluric and magnetovariational
functions, which cannot distinguish between anisotropy and isotropy and admit both the interpretations. 相似文献
59.
Maps of the radio source 3C 120 obtained from VLBA+ observations at 8.4 GHz at five epochs in January–September 2002 are presented. The images were reconstructed using the maximum entropy method and the Pulkovo VLBImager software package for VLBI mapping. Apparent superluminal motions of the brightest jet knots have been estimated. The speeds of jet knots decreases with distance from the core, changing from (5.40±0.48)c to (2.00±0.48)c over 10 mas (where c is the speed of light) for a Hubble constant of 65 km s?1 Mpc?1. This can be explained by interaction of the jet with the medium through which it propagates. 相似文献
60.
It is preferable to use the three-dimensional (3D) magnetotelluric inversion, which provides volumetric geoelectric models, to handle the array input data. However, the soundings are frequently conducted on the single profiles or on the profiles that are considerably spaced apart from each other. We explore the possibilities of the 3D inversion of such data by the example of a three-layer model containing three local inhomogeneities. We previously showed that the simple processing of the data and their 1D or 2D inversion enable reconstructing the background cross section and locating all the three inhomogeneities. In the present paper, we use this information for constructing several versions of the starting model and carrying out the smoothing 3D inversion of the data. The experiments show that if the background cross section is incorporated into the starting model, the final model provided by the inversion closely reproduces the real distribution of all geoelectric parameters. At the same time, if the starting model that hosts the inhomogeneities has the form of a homogeneous half-space, the inversion is not able to reconstruct an adequate final model. 相似文献