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11.
Alexander Y. Potekhin Gilles Chabrier Dmitry G. Yakovlev 《Astrophysics and Space Science》2007,308(1-4):353-361
Strong (B?109 G) and superstrong (B?1014 G) magnetic fields profoundly affect many thermodynamic and kinetic characteristics of dense plasmas in neutron star envelopes. In particular, they produce strongly anisotropic thermal conductivity in the neutron star crust and modify the equation of state and radiative opacities in the atmosphere, which are major ingredients of the cooling theory and spectral atmosphere models. As a result, both the radiation spectrum and the thermal luminosity of a neutron star can be affected by the magnetic field. We briefly review these effects and demonstrate the influence of magnetic field strength on the thermal structure of an isolated neutron star, putting emphasis on the differences brought about by the superstrong fields and high temperatures of magnetars. For the latter objects, it is important to take proper account of a combined effect of the magnetic field on thermal conduction and neutrino emission at densities ρ?1010 g?cm?3. We show that the neutrino emission puts a B-dependent upper limit on the effective surface temperature of a cooling neutron star. 相似文献
12.
Natalia V. Lubnina Satu Mertanen Ulf Söderlund Svetlana Bogdanova Tatiana I. Vasilieva Dmitry Frank-Kamenetsky 《Precambrian Research》2010
Palaeomagnetic and geochronological studies on mafic rocks in the Lake Ladoga region in South Russian Karelia provide a new, reliably dated Mesoproterozoic key paleopole for the East European Craton (Baltica). U–Pb dating on baddeleyite gives a crystallisation age of 1452 ± 12 Ma for one of the studied dolerite dykes. A mean palaeomagnetic pole for the Mesoproterozoic dolerite dykes, Valaam sill and Salmi basalts yields a paleopole at 15.2°N, 177.1°E, A95 = 5.5°. Positive baked contact test for the dolerite dykes and positive reversal test for the Salmi basalts and for the dykes confirm the primary nature of the magnetisation. Comparison of this Baltica palaeopole with coeval paleomagnetic data for Laurentia and Siberia provides a revised palaeoposition of these cratons. The results verify that the East European Craton, Laurentia and Siberia were part of the supercontinent Columbia from the Late Palaeoproterozoic to the Middle Neoproterozoic. 相似文献
13.
Abstract We discuss the steady states of the αω-dynamo in a thin disc which arise due to α-quenching. Two asymptotic regimes are considered, one for the dynamo numberD near the generation thresholdD 0, and the other for |D| ? 1. Asymptotic solutions for |D—D 0| ? |D 0| have a rather universal character provided only that the bifurcation is supercritical. For |D| ? 1 the asymptotic solution crucially depends on whether or not the mean helicity α, as a function ofB, has a positive root (hereB is the mean magnetic field). When such a root exists, the field value in the major portion of the disc is O(l), while near the disc surface thin boundary layers appear where the field rapidly decreases to zero (if the disc is surrounded by vacuum). Otherwise, when α = O(|B|?s) for |B| → ∞, we demonstrate that |B| = O(|D|1/s ) and the solution is free of boundary layers. The results obtained here admit direct comparison with observations of magnetic fields in spiral galaxies, so that an appropriate model of nonlinear galactic dynamos hopefully could be specified. 相似文献
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16.
Natalia S. Bezaeva Dmitry D. Badyukov Mikhail A. Nazarov Pierre Rochette Joshua M. Feinberg Gennadiy P. Markov Daniel Borschneck François Demory Jérôme Gattacceca Sergey E. Borisovskiy Anna Ya Skripnik 《Meteoritics & planetary science》2014,49(6):958-977
Here we characterize the magnetic properties of the Chelyabinsk chondrite (LL5, S4, W0) and constrain the composition, concentration, grain size distribution, and mineral fabric of the meteorite's magnetic mineral assemblage. Data were collected from 10 to 1073 K and include measurements of low‐field magnetic susceptibility (χ0), the anisotropy of χ0, hysteresis loops, first‐order reversal curves, Mössbauer spectroscopy, and X‐ray microtomography. The REM and REM′ paleointensity protocols suggest that the only magnetizations recorded by the chondrite are components of the Earth's magnetic field acquired during entry into our planet's atmosphere. The Chelyabinsk chondrite consists of light and dark lithologies. Fragments of the light lithology show logχ0 = 4.57 ± 0.09 (s.d.) (n = 135), while the dark lithology shows 4.65 ± 0.09 (n = 39) (where χ0 is in 10?9 m3 kg?1). Thus, Chelyabinsk is three times more magnetic than the average LL5 fall, but is similar to a subgroup of metal‐rich LL5 chondrites (Paragould, Aldsworth, Bawku, Richmond) and L/LL5 chondrites (Glanerbrug, Knyahinya). The meteorite's room‐temperature magnetization is dominated by multidomain FeNi alloys taenite and kamacite (no tetrataenite is present). However, below approximately 75 K remanence is dominated by chromite. The metal contents of the light and dark lithologies are 3.7 and 4.1 wt%, respectively, and are based on values of saturation magnetization. 相似文献
17.
Victor A. Melezhik Anthony E. Fallick Dmitry V. Rychanchik Anton B. Kuznetsov 《地学学报》2005,17(2):141-148
This paper addresses global oxygenation and establishment of a marine sulphate reservoir in the Palaeoproterozoic. We report syn-depositional, marine, anhydrite-containing pseudomorphs after Ca-sulphates as widespread throughout the Tulomozero Formation in the SE Fennoscandian Shield, implying that surface waters were oxidized and a large SO marine reservoir was developed as early as 2100 Ma. The Ca-sulphates and associated magnesite and halite precipitated syn-depositionally from oxidized, evolved and modified seawater in coastal playa, sabkha and intertidal flat settings. 87Sr/86Sr and δ13C of associated 13C-rich stromatolitic dolostones were environmentally controlled with the highest ratios occurring in playa and sabkha carbonates. The results imply that the Palaeoproterozoic δ13Ccarb excursion was amplified by 8‰ by local environmental factors and calls into question many observations of putative δ13C global signals reported previously from similar Palaeoproterozoic, evaporitic, dolostones. The local environmental amplification can explain a large regional and intercontinental δ13C discrepancy observed in synchronous carbonates. 相似文献
18.
Three-Dimensional Electromagnetic Modelling and Inversion from Theory to Application 总被引:12,自引:1,他引:11
Dmitry?B.?Avdeevdavdeev@cp.dias.ie" title="d.avdeev@mtu-net.ru davdeev@cp.dias.ie" itemprop="email" data-track="click" data-track-action="Email author" data-track-label="">Email author 《Surveys in Geophysics》2005,26(6):767-799
The whole subject of three-dimensional (3-D) electromagnetic (EM) modelling and inversion has experienced a tremendous progress
in the last decade. Accordingly there is an increased need for reviewing the recent, and not so recent, achievements in the
field. In the first part of this review paper I consider the finite-difference, finite-element and integral equation approaches
that are presently applied for the rigorous numerical solution of fully 3-D EM forward problems. I mention the merits and
drawbacks of these approaches, and focus on the most essential aspects of numerical implementations, such as preconditioning
and solving the resulting systems of linear equations. I refer to some of the most advanced, state-of-the-art, solvers that
are today available for such important geophysical applications as induction logging, airborne and controlled-source EM, magnetotellurics,
and global induction studies. Then, in the second part of the paper, I review some of the methods that are commonly used to
solve 3-D EM inverse problems and analyse current implementations of the methods available. In particular, I also address
the important aspects of nonlinear Newton-type optimisation techniques and computation of gradients and sensitivities associated
with these problems. 相似文献
19.
Anatoly Shvidenko Dmitry Schepaschenko Ian McCallum Sten Nilsson 《Climatic change》2010,103(1-2):137-157
In accordance with the concept that only full accounting of major greenhouse gases corresponds to the goals of the United Nations Framework Convention on Climate Change and its Kyoto Protocol, this paper considers uncertainties of regional (national) terrestrial biota Full Carbon Accounting (FCA), both those already achieved and those expected. We analyze uncertainties of major components of the FCA of forest ecosystems of a large boreal region in Siberia (~300 × 106 ha). Some estimates for forests of other regions and Russia as a whole are used for comparison. The systems integration of available information sources and different types of models within the landscape-ecosystem approach are shown to have enabled an estimation of the major carbon fluxes (Net Primary Production, NPP, and heterotrophic respiration, HR) for the region for a single year at the level of 7–12% (confidential interval, CI, 0.9), Net Ecosystem Production (NEP) of 35–40%, and Net Biome Production (NBP) of 60–80%. The most uncertain aspect is the assessment of change in the soil carbon pool, which limits practical application of a pool-based approach. Regionalization of global process-based models, introduction of climatic data in empirical models, use of an appropriate time period for accounting and reporting, harmonization and multiple constraints of estimates obtained by different independent methods decrease the above uncertainties of NEP and NBP by about half. The results of this study support the idea that FCA of forest ecosystems is relevant in the post-Kyoto international negotiation process. 相似文献
20.
The results of gasdynamic modeling allowed us to propose the new mechanism of transition to active state in classical symbiotics and explain the step-by-step rise to the light maximum during the outburst. Good agreement with available observational data for Z And supports our model. Existing observations of symbiotic stars indicate the presence of winds from both components at active stages in these systems. We have carried out the gasdynamic modeling of the outburst development process in the classic symbiotic star Z And in the framework of the colliding winds model. It is shown that contribution from the system of shocks that forms in the area of wind collision is rather significant especially at short wavelengths. 相似文献