Seismic and electromagnetic evidence of dehydration as a free water source in the reactivated crust     

Leonid L. Vanyan  & Alexander O. Gliko 《Geophysical Journal International》1999,137(1):159-162

According to recent estimates, the continental mid-crust contains 35–40 per cent amphibolites. Heating of the crust by an underlying mantle plume, for example beneath continental rifts, high plateaus, and areas of intraplate volcanic activity, releases water. Dehydration of amphibole-bearing rocks at depths of 20–40  km occurs mainly in the temperature range 650–700 °C, and this releases about 0.4  wt per cent of water.
  Seismic tomography studies of the crust in the Kirgyz Tien Shan Range, where the age of the tectonic activity is less than 30  Ma, revealed a low-velocity zone in the mid-crust. The velocity of P waves was 0.4  km  s⁻¹ lower than in normal crust. MT sounding data in the region show the existence of a low-resistivity layer with an average resistivity of about 25  Ω  m at the depth of the low-velocity layer. The spatial correlation of the observed anomalous layers and calculated effect of fluid phase on seismic and electric parameters of rocks suggests the presence of aqueous fluids released by the heating of the mid-crust.  相似文献   

A Long-Term Dissipation of the EUV He <Emphasis Type="SmallCaps">ii</Emphasis> (30.4 nm) Segmentation in Full-Disk Solar Images     

Leonid Didkovsky 《Solar physics》2018,293(6):87

Some quiet-Sun days observed by the Atmospheric Imaging Assembly (AIA) on-board the Solar Dynamics Observatory (SDO) during the time interval in 2010?–?2017 were used to continue our previous analyses reported by Didkovsky and Gurman (Solar Phys.289, 153, 2014a) and Didkovsky, Wieman, and Korogodina (Solar Phys.292, 32, 2017). The analysis consists of determining and comparing spatial spectral ratios (spectral densities over some time interval) from spatial (segmentation-cell length) power spectra. The ratios were compared using modeled compatible spatial frequencies for spectra from the Extreme ultraviolet Imaging Telescope (EIT) on-board the Solar and Heliospheric Observatory (SOHO) and from AIA images. With the new AIA data added to the EIT data we analyzed previously, the whole time interval from 1996 to 2017 reported here is approximately the length of two “standard” solar cycles (SC). The spectral ratios of segmentation-cell dimension structures show a significant and steady increase with no detected indication of SC-related returns to the values that characterize the SC minima. This increase in spatial power at high spatial frequencies is interpreted as a dissipation of medium-size EUV network structures to smaller-size structures in the transition region. Each of the latest ratio changes for 2010 through 2017 spectra calculated for a number of consecutive short-term intervals has been converted into monthly mean ratio (MMR) changes. The MMR values demonstrate variable sign and magnitudes, thus confirming the solar nature of the changes. These changes do not follow a “typical” trend of instrumental degradation or a long-term activity profile from the He?ii (30.4 nm) irradiance measured by the Extreme ultraviolet Spectrophotometer (ESP) either. The ESP is a channel of the Extreme ultraviolet Variability Experiment (EVE) on-board SDO.  相似文献   

U‐Pb age and Hf isotope compositions of zircons from the north‐western region of the Ukrainian shield: mantle melting in response to post‐collision extension     

Leonid Shumlyanskyy  Kjell Billström  Chris Hawkesworth  Sten‐Åke Elming 《地学学报》2012,24(5):373-379

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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  

Pierguido Sarti  Claudio Abbondanza  Leonid Petrov  Monia Negusini 《Journal of Geodesy》2011,85(1):1-8

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   

http://www.sciencedirect.com/science/article/pii/S1674987110000149     

Xiang Wu  Shan Qin  Leonid Dubrovinsky 《地学前缘(英文版)》2011,2(1):107-114

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   

Crystal chemistry of Fe3+-bearing (Mg,Fe)SiO3 perovskite: a single-crystal X-ray diffraction study     

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 Mg_0.946(17)Fe_0.056(12)Si_0.997(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   

On the electron temperature determination in high-metallicity H ii regions     

Leonid S. Pilyugin 《Monthly notices of the Royal Astronomical Society》2007,375(2):685-690

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Surface abundances of light elements for a large sample of early B-type stars – II. Basic parameters of 107 stars     

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   

On the relation between electron temperatures in the O⁺ and O⁺⁺ zones in high-metallicity H ii regions     

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   

Earth-Based Support for the Titan Saturn System Mission     

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