Self-reversal of remanent magnetization in basalts due to partially oxidized titanomagnetites     

David Krása  Valera P. Shcherbakov  Thomas Kunzmann  Nikolai Petersen 《Geophysical Journal International》2005,162(1):115-136

  相似文献   

Nonstationary Phenomena in the Solar Wind and InterstellarMedium Interaction     

Nikolai V. Pogorelov 《Astrophysics and Space Science》2000,274(1-2):115-122

We discuss the results of numerical modeling of the solar wind with the inhomogeneous interstellar medium. The density of the plasma component in the interstellar cloud is supposed to be space periodic. The interaction pattern is shown to be highly unsteady with hydrodynamic instabilities developing on the side portion of the heliopause. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Accretion Flows: Aspects of Gas Dynamic Modeling     

Nikolai V. Pogorelov  Igor A. Kryukov 《Astrophysics and Space Science》2000,274(1-2):275-284

We present our view on the application of numerical models to accretion flows in astrophysics. Special attention is paid to the problem of existence of steady-state solutions in time-dependent calculations and to origin of numerically induced instabilities. The problem is considered of the supersonic wind accretion onto gravitating objects. We also present the results of the gas dynamic simulation of accretion on a body imitating the shape of the star magnetosphere with holes in its polar regions. This shape can occur as a result of the cusp disintegration owing to theRayleigh–Taylor instability in the equatorial region of the magnetosphere. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Electrical conductivity of polycrystalline Mg(OH)<Subscript>2</Subscript> at 2 GPa: effect of grain boundary hydration–dehydration     

Julien Gasc  Fabrice Brunet  Nikolai Bagdassarov  Victor Morales-Flórez 《Physics and Chemistry of Minerals》2011,38(7):543-556

The effect of intergranular water on the conductivity of polycrystalline brucite, Mg(OH)₂, was investigated using impedance spectroscopy at 2 GPa, during consecutive heating–cooling cycles in the 298–980 K range. The grain boundary hydration levels tested here span water activities from around unity (wet conditions) down to 10⁻⁴ (dry conditions) depending on temperature. Four orders of magnitude in water activity result in electrical conductivity variations for about 6–7 orders of magnitude at 2 GPa and room temperature. Wet brucite samples containing, initially, about 18 wt% of evaporable water (i.e. totally removed at temperatures below 393 K in air), display electrical conductivity values above 10⁻²–10⁻³ S/m. A.C. electrical conductivity as a function of temperature follows an Arrhenius behaviour with an activation energy of 0.11 eV. The electrical conductivity of the same polycrystalline brucite material dried beforehand at 393 K (dry conditions) is lower by about 5–6 orders of magnitude at room temperature and possesses an activation energy of 0.8–0.9 eV which is close to that of protonic diffusion in (001) brucitic planes. Above ca. 873 K, a non-reversible conductivity jump is observed which is interpreted as a water transfer from mineral bulk to grain boundaries (i.e. partial dehydration). Cooling of such partially dehydrated sample shows electrical conductivities much higher than those of the initially dry sample by 4 orders of magnitude at 500 K. Furthermore, the corresponding activation energy is decreased by a factor of about four (i.e. 0.21 eV). Buffering of the sample at low water activity has been achieved by adding CaO or MgO, two hygroscopic compounds, to the starting material. Then, sample conductivities reached the lowest values encountered in this study with the activation energy of 1.1 eV. The strong dependency of the electrical conductivity with water activity highlights the importance of the latter parameter as a controlling factor of diffusion rates in natural processes where water availability and activity may vary grandly. Water exchange between mineral bulk and mineral boundary suggests that grain boundary can be treated as an independent phase in dehydroxylation reactions.  相似文献   

First U-Pb dates for detrital zircons from deposits of Serebryanka Group (Upper Proterozoic,Middle Urals)     

A. V. Maslov  G. M. Vovna  V. I. Kiselev  M. T. Krupenin  Yu. L. Ronkin 《Doklady Earth Sciences》2011,439(1):933-938

The results of application of the LA-ICP-MS method for analysis of U-Pb ages of detrital zircons from Serebryanka Group (Middle Urals) has been presented for the first time. It has been found that the detrital zircon population in tillite-like conglomerates of the Tany Formation is represented nearly in equal shares by grains with Neoarchean and Paleoproterozoic U-Pb ages. This allows the basement crystalline rocks from the eastern part of the East European Craton to be considered as the principal source of aluminosilicate clastic material in the beginning of the Serebryanka. The population of detrival zircons in sandstones from the Kernos Formation consists of Meso- and Neoarchean (approximately 15%), Paleoproterozoic (∼60%), and Mesoproterozoic (∼26%) zircon grains. Comparison of the obtained data with the materials on detrital zircons from Tonian and Ediacarian sandstones in the southern Urals has shown that the principal role in formation of Tonian and Ediacaran sedimentary sequences was played by the products of Mid- and Late Paleoproterozoic crystalline rock erosion in the craton socle. In addition to this, accumulation of the Serebryanka Group took place with visible participation of more ancient—Early Paleoproterozoic, Neo- and Mesoarchean—rock associations on the paleo-water catchment areas. The end of the Serebryanka period differed from its beginning by the additional appearance of Mesoproterozoic complexes in alimentation zones; for comparison, the role played by these complexes in formation of Ectasian-Ediacarian deposits of the adjacent southern Urals segment is insufficient, judging by the currently available data. All these facts may indicate that there are significant differences in the spatiotemporal distribution of clastic material sources for Upper Precambrian deposits in the West Megazone of the southern and middle Urals.  相似文献   

Dynamical study of the wide visual binary ADS 12815 (16 Cyg)     

A. A. Kiselev  L. G. Romanenko 《Astronomy Reports》2011,55(6):487-496

A homogeneous series of photographic position measurments of the visual binary ADS 12815 obtained on the 26-inch refractor of the Pulkovo Observatory (1960–2007) is analyzed. The Pulkovo observations allow for the existence of the planet around component B discovered by Cochran et al. based on radial-velocity measurements. The orbit of the planet must be steeply inclined to the plane of the sky (i ≥ 70°). Uniform series of position measurements obtained at the Dearborn Observatory, US Naval Observatory, and Pulkovo Observatory, the HIPPARCOS parallax, and the relative radial velocities obtained by Hauser and Marcy at the Lick Observatory are used to calculate the elements of possible orbits for the ADS 12815 stars using the apparent motion parameters method. The corresponding periods are more than 20 000 yr, the semi-major axes more than 900 AU, and the eccentricities more than 0.65. All possible orbits are steeply inclined to the Galactic plane. The obtained family of orbits is in better agreement with observations than the family calculated by Hauser and Marcy.  相似文献   

Polarimetry and Photometry of Comet C/2004 Q2 (Machholz)     

Sergey Velichko  Nikolai Kiselev  Feodor Velichko 《Earth, Moon, and Planets》2005,97(3-4):379-386

We present results of polarimetry and photometry of comet C/2004 Q2 (Machholz) obtained with the 0.7-m telescope of Institute of Astronomy at the Karazin Kharkiv National University on February 3 and 4, and March 4 and 14, 2005. The observations were carried out with a one-channel photoelectric photometer-polarimeter. The IHW continuum UC (λ3650/80 Å), BC (λ4845/65 Å), RC (λ6840/90 Å) and emission filters CN (λ3871/50 Å), C₃ (λ4060/70 Å), and C2 (λ5140/90 Å) were used. Degree of the comet polarization at phase angles ≈ 52° and ≈44° in the red continuum was close to that for so called dusty comets. The comet had a typical spectral gradient of polarization ΔP/Δλ=0.86% per 1000 Å. In the framework of the Haser model we have found the gas production rates Q of the CN, C₃ and C₂ species and the dust production rates Afρ on February 4 and March 14, 2005. The ratio log[Afρ (BC)/Q(CN)] was compared with data for other comets. The normalized spectral gradient of cometary dust S’(BC,RC) was 8.7%/1000 Å for February 4 and 17.0%/1000 Å for March 14. We conclude that comet C/2004 Q2 (Machholz) in many respects is a typical dusty comet.  相似文献   

Comparative Study Of The Dust Polarimetric Properties In Split And Normal Comets     

Kiselev  Nikolai  Jockers  Klaus  Rosenbush  Vera 《Earth, Moon, and Planets》2002,90(1-4):167-176

Our polarimetric database contains six comets, C/1975 V1 (West), 16P/Brooks 2,C/1988 A1 (Liller), D/1996 Q1 (Tabur), C/1999 S4 (LINEAR), and C/2001 A2(LINEAR), which can be related to the group of split comets. Comets West, S4(LINEAR) and A2 (LINEAR) were observed during splitting. We compare thepolarimetric measurements of the dust particles in these comets, sometimes togetherwith available photometric and colorimetric data, with those in normal comets. Weconclude that there is no significant evidence for differences of polarization betweentidally split comets (e.g., Brooks 2), dissipating comets (e.g., Tabur), non-tidally splitcomets (e.g., West) and normal comets. The total disintegration of Comet S4 (LINEAR), however, did produce significant changes in the observed properties of dust.  相似文献   

Ammonites and Stratigraphy of the Terminal Part of the Middle Volgian Substage (Upper Jurassic; Epivirgatites nikitini Zone and Its Equivalents) of the Panboreal Realm: 2. <Emphasis Type="Italic">Titanites</Emphasis> and <Emphasis Type="Italic">Glaucolithites</Emphasis>     

D. N. Kiselev  M. A. Rogov 《Stratigraphy and Geological Correlation》2018,26(1):15-61

The genera Titanites and Glaucolithites, which were previously known only from the Portlandian of Northwestern Europe are now established in Epivirgatites nikitini Zone of European Russia. The Volgian species of Titanites are represented by both the endemic taxa Titanites (Paratitanites) manipulocostatus subgen. et sp. nov. and T. (Pseudogalbanites) triceps subgen. et sp. nov. and Titanites (Titanites) ex gr. titan Buckman of the Portland type. A new species Glaucolithites gardarikensis is described. It is likely that these ammonites migrated to the Central Russian Sea from northwestern Europe via the Norway-Greenland seaway and further to the Mezen-Pechora system of straits, which is supported by occurrences of Titanites in the north of Central Russia and Glaucolithites in East Greenland and on Spitsbergen. The direct and indirect correlations show that the middle part of the Nikitini Zone (Lahuseni Subzone) should at least partly be correlated with the Portlandian Kerbeus Zone.  相似文献   

Pulkovo catalog of relative positions and motions of visual double and multiple stars from photographic observations with the 26-inch refractor in 1960–2007     

A. A. Kiselev  O. V. Kiyaeva  I. S. Izmailov  L. G. Romanenko  O. A. Kalinichenko  O. O. Vasil’kova  T. A. Vasil’eva  N. A. Shakht  D. L. Gorshanov  E. A. Roschina 《Astronomy Reports》2014,58(2):78-97

The results of long-term, uniform, photographic observations of visual double and multiple stars obtained on the Pulkovo 26″ refractor are presented. Relative positions are calculated for 259 pairs of visual double stars in 194 systems, with the relative motions also computed for 127 pairs. Lower limits for the total masses of the systems for which elliptical orbits possible are also found for 48 pairs with reliable parallaxes from the Hipparcos catalog. The accuracies of the three measuring machines used in the reduction of the photographic plates are compared. Component separations measured with different machines can differ by as much as 0.2″, demonstrating the advantages of using uniform observations.  相似文献