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排序方式: 共有260条查询结果,搜索用时 31 毫秒
101.
D.?Yu.?TsvetkovEmail author S.?Yu.?Shugarov I.?M.?Volkov N.?N.?Pavlyuk O.?V.?Vozyakova N.?I.?Shatsky A.?A.?Nikiforova I.?S.?Troitsky Yu.?V.?Troitskaya P.?V.?Baklanov 《Astronomy Letters》2018,44(5):315-323
We present the results of our UBVRI photometry for the type II-P supernova SN 2017eaw in NGC6946 obtained fromMay 14 to December 7, 2017, at several telescopes, including the 2.5-m telescope at the CaucasusHigh-Altitude Observatory of the SAIMSU. The dates andmagnitudes atmaximumlight and the light-curve parameters have been determined. The color evolution, extinction, and peak luminosity of SN 2017eaw are discussed. The results of our preliminary radiation–gasdynamic simulations of its light curves with the STELLA code describe satisfactorily the UBVRI observational data. 相似文献
102.
Composition and origin of holotype Al‐Cu‐Zn minerals in relation to quasicrystals in the Khatyrka meteorite 下载免费PDF全文
Marina A. Ivanova Cyril A. Lorenz Sergey E. Borisovskiy Andrey A. Burmistrov Dmitriy V. Korost Alexander V. Korochantsev Maria N. Logunova Sergei I. Shornikov Michail I. Petaev 《Meteoritics & planetary science》2017,52(5):869-883
We investigated the khatyrkite–cupalite holotype sample, 1.2 × 0.5 mm across. It consists of khatyrkite (Cu,Zn)Al2, cupalite (Cu,Zn)Al, and interstitial material with approximate composition (Zn,Cu)Al3. All mineral phases of the holotype sample contain Zn and lack Fe that distinguishes them from khatyrkite and cupalite in the Khatyrka meteorite particles (Bindi et al. 2009 , 2011 , 2012 , 2015 ; MacPherson et al. 2013 ; Hollister et al. 2014 ). Neither highly fractionated natural systems nor geo‐ or cosmochemical processes capable of forming the holotype sample are known so far. The bulk chemistry and thermal history of khatyrkite–cupalite assemblage in the holotype sample hint for its possible industrial origin. Likewise, the aluminides in the Khatyrka meteorite particles may also be derived from industrial materials and mixed with extraterrestrial matter during gold prospecting in the Listvenitovy Stream valley. 相似文献
103.
A well-preserved radiolarian fauna from a clastic unit of the Khabarovsk accretionary complex (southern part of the Badzhal accretionary wedge terrane in the Russian Far East) is assigned to the basal part of the Pseudodictyomitra carpatica zone. The age of the fauna is most likely late Tithonian. This is the first reliable dating of the clastic unit and makes it possible to constrain the timing of subduction accretion in the Badzhal terrane. The Khabarovsk complex is correlated chronologically with the Bikin and Samarka terranes (Russian Far East), Mino, Southern Chichibu and North Kitakami terranes (Japan), and Nadanhada terrane (northeast China). 相似文献
104.
Turning off low and high currents in a transmitter loop used in the transient electromagnetic method
Nikolai O. Kozhevnikov Maxim V. Sharlov Sergei M. Stefanenko 《Geophysical Prospecting》2020,68(5):1676-1688
In near-surface transient electromagnetic studies, it is desirable to measure the transient response starting from the earliest possible time. This requires the current in the transmitter loop to be switched off quickly, which necessitates working with a low transmitter current. As for deep-target transient electromagnetic studies, the transmitter current is as high as possible. The transmitter current's turn-off waveform and total duration affect the transient voltage response, especially at early times, which is to be accounted for when interpreting transient electromagnetic data. This article discusses the difference in switching off low and high current in a horizontal loop used as the source of the primary magnetic field in the transient electromagnetic method. Low and high currents are turned off in fundamentally different ways. When the current to be switched off is low, the loop can be represented as a symmetric combination of two transmission lines grounded at the middle of the loop perimeter. Such a representation of a loop allows calculating the current turn-off waveform at any point of the loop. The waveform and total duration of switching off a low current does not depend on its magnitude, but is determined by the period of natural oscillations of the current in the loop and the resistance of a shunting resistor. Switching off a low current in a loop can be represented as the sum of stepped current waves travelling along the loop wire. As a consequence, the current at different points of the loop perimeter is turned off at different times. In contrast to a low current, a high current is switched off linearly in time and synchronously at all points of the loop perimeter. The wave phenomena appear only at the very beginning of the current shutdown for a time interval that is much less than the total current turn-off duration. Presentation of the loop using a simple lumped-circuit model predicts the waveform and duration of the high current turn-off that coincide with the measured ones. There are two reasons why the article may be of interest to those engaged in the theory and/or practice of electromagnetic geophysical methods. First, it contributes to a general understanding of how the current in the transmitter loop is turned off. Second, the article shows how the parameters of a transmitter loop determine the current turn-off duration and thus the minimum depth of the transient electromagnetic sounding method. 相似文献
105.
Sergei I. Ipatov 《Celestial Mechanics and Dynamical Astronomy》1999,73(1-4):107-116
Migration of trans-Neptunian objects under their mutual gravitation influence and the influence of the giant planets is investigated.
These investigations are based on computer simulation results and on some formulas. We estimated that about 20 % of near-Earth
objects with diameter d ≥ 1 km may have come from the Edgeworth-Kuiper belt.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
106.
107.
The elemental abundances, temperatures, gravities and microturbulence velocities were derived for 14 non-variable supergiants from the Cepheids' instability strip and two hotter supergiants. For 8 stars the abundances were determined for the first time. The comparable analysis of the program stars' chemical composition and that of the small-amplitude Cepheids has shown that there is no essential differences in the elemental abundances for two stellar groups. Some discussion of the phenomenon of non-variable supergiants in the instability strip is given. 相似文献
108.
Sergei S. Sazhin 《Astrophysics and Space Science》1993,203(2):317-327
It is pointed out that at frequencies near the plasma cut-off frequencies, the corrections to wave refractive indices in a cold plasmaN
0due to the contribution of ions and relativistic effects can be of the same order of magnitude or greater thanN
0. Expressions for wave refractive indicesN taking into account these corrections are derived in a limiting case |N| I. It is shown that the increase in cut-off frequencies due to effects of ions is negligibly small unless the electron plasma frequency is well below the electron gyrofrequency. The decrease of the cut-off frequencies due to relativistic effects is significant ( 1%) only in a rather hot plasma (T
e 1 keV), which may be observed in a plasma sheet region of the Earth's magnetosphere and in astrophysical conditions. These effects appear to be particularly important in a strongly anisotropic plasma (the electron perpendicular temperature is noticeably greater than the parallel one). 相似文献
109.
110.
Christoph Breitkreuz Hassan Eliwa Ibrahim Khalaf Khaled El Gameel Benjamin Bühler Sergei Sergeev Alexander Larionov Mamoru Murata 《Precambrian Research》2010
Chronology of Neoproterozoic volcanosedimentary successions remains controversial for many regions of the Arabian–Nubian Shield, including the Dokhan Volcanics of NE Egypt. New U–Pb zircon SHRIMP ages have been obtained for 10 silica-rich ignimbrites and two subvolcanic dacitic bodies, mapped as Dokhan Volcanics, from the North Eastern Desert of Egypt. Crystallization ages range between 592 ± 5 and 630 ± 6 Ma (Early Ediacaran). Apparently, the late consolidation of the Arabian–Nubian Shield was accompanied by the evolution of isolated volcanic centres and basin systems which developed during a period of approx. 40 Ma, independently in space and time and probably under changing tectonic regimes. The obtained age data together with other previously published reliable ages for Dokhan Volcanics suggest two main pulses of volcanic activity: 630–623 Ma and 618–592 Ma. Five samples contain inherited zircons, with ages of 669, 715–746, 847 and 1530 Ma, supporting models that North Eastern Desert crust is mainly juvenile Neoproterozoic crust. 相似文献