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41.
In May 1995, we obtained 5-GHz VLBI polarisation observations of 20 sources in the complete sample of BL Lac objects defined by H. Kühr and G. Schmidt. Ten antennas participated in the global VLBI observations. Total intensity and linear polarisation images of five sources have been made and analysed thus far. The images for 0003–066, 1538+149, and 2254+074 are presented, together with an analysis of the evolution of their polarisation structure and estimates of apparent velocities for components in their VLBI jets. 相似文献
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Vasilii V. Gvaramadze Alessia Gualandris Simon Portegies Zwart 《Monthly notices of the Royal Astronomical Society》2009,396(1):570-578
We explore the hypothesis that some high-velocity runaway stars attain their peculiar velocities in the course of exchange encounters between hard massive binaries and a very massive star (either an ordinary 50–100 M⊙ star or a more massive one, formed through runaway mergers of ordinary stars in the core of a young massive star cluster). In this process, one of the binary components becomes gravitationally bound to the very massive star, while the second one is ejected, sometimes with a high speed. We performed three-body scattering experiments and found that early B-type stars (the progenitors of the majority of neutron stars) can be ejected with velocities of ≳200–400 km s−1 (typical of pulsars), while 3–4 M⊙ stars can attain velocities of ≳300–400 km s−1 (typical of the bound population of halo late B-type stars). We also found that the ejected stars can occasionally attain velocities exceeding the Milky Ways's escape velocity. 相似文献
43.
V. A. Glebovitsky L. P. Nikitina A. B. Vrevskii Yu. D. Pushkarev M. S. Babushkina A. G. Goncharov 《Geochemistry International》2009,47(9):857-881
The paper reports data on the chemical composition of mantle peridotite xenoliths from kimberlites and alkaline basalts that
represent the continental lithospheric mantle (CLM) beneath Early Precambrian and Late Proterozoic-Cenozoic structures, respectively.
In order to identify compositional trends during the melting of primitive material and propose the most reliable criteria
for constraining the conditions of this process and its degree, we analyzed literature data on the melting of spinel and garnet
peridotites within broad temperature and pressure ranges. It was determined that the degree of melting (F%) of pristine peridotite
of composition close to that of the primitive mantle (PM) can be deduced from the Mg/Si and Al/Si ratios in the residue; an
equation was proposed for evaluating F from the Mg/Si ratio. The Ca/Al ratio of residues at low (1–1.5 GPa) pressures and
degrees of melting from 2–3 to 20–25% increases several times but decreases with increasing F at pressures higher than 3 GPa.
The Na partition coefficient between melt and residue decreases at increasing pressure and approaches one at a pressure close
to 20 GPa. Residues after low-degree melting are strongly depleted in Ti, Zr, Y, and Nb but are enriched in Cr. The application
of these criteria to the composition of xenoliths brought to the surface from the mantle occurring beneath tectonic structures
of various age led us to conclude that compositional heterogeneities of CLM (particularly the variations in the concentrations
of major and certain siderophile elements) are controlled, first of all, by the melting of the mantle source material. These
processes occurred under various thermodynamic conditions (T, P, and $
f_{O_2 }
$
f_{O_2 }
) and differed in their intensity, and this predetermined the compositional diversity of the residual mantle material (its
concentrations of Mg, Al, Si, Ca, Na, K, Ni, Co, V, and Cr). Our results are principally consistent with the hypothesis of
the global magmatic ocean. It is thought that the early phases of its consolidation were variably controlled by the fractionation
of minerals, for example, majorite. Moreover, heterogeneities in the distribution of siderophile elements could be partly
predetermined by changes in the properties of these elements at ultrahigh temperatures and pressures. The processes of partial
melting were the most intense during the early evolution of the mantle (perhaps, in the Early Precambrian), and hence, the
mantle has different chemical composition beneath Archean cratons and Phanerozoic foldbelts. 相似文献
44.
U-Pb dating of zircons (SHRIMP-II) has been performed for the first time for granites, granodiorites, and synplutonic granodiorite
and melanodiorite bodies of the Shartash and Shabry massifs in the Middle Urals. The time of the formation of the massifs
is 300–306 Ma, which is 25 Ma younger than the previous estimates. The age data obtained are in line with the time of the
formation of the adamellite-granite series of the Verkhisetsk Batholite (the master sample of tonalite-granodiorite-granite
magmatism in the Middle Urals), the series of which is petrochemically close to the rocks of the massifs. 相似文献
45.
This work presents the results of studying srilankite, a rare zirconium titanate (ZrTi2O6), associated with ilmenite, rutile, zircon, uraninite, and other minerals discovered in high-pressure garnetites of the lherzolite Mindyak massif (Southern Urals). Srilankite occurs as inclusions in ilmenite and rutile of up to several tens of microns in size. It was established for the first time that srilankite contains a significant UO2 admixture (up to 20%). The negative correlation between Zr and U is evidence of isomorphism in the srilankite–brannerite system. The association of srilankite with high-Zr rutile indicates that formation of these minerals occurred at T > 850°С.
相似文献46.
Ocean Dynamics - We present research on the excitation of ocean surface wind waves in non-homogeneous situations, for the case of a deep water strait in the presence of a constant wind, blowing... 相似文献
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Doklady Earth Sciences - A comprehensive petrological study and age dating of a young clinopyroxenite–gabbro–hornblendite series intruded deformed dunites, clinopyroxenites, and... 相似文献