Nucleosynthesis of heavy elements: Computational experiment     

I. V. Panov  S. I. Blinnikov  F. -K. Thielemann 《Astronomy Letters》2001,27(4):239-248

The kinetic-model (KM) efficiency in heavy-element nucleosynthesis calculations is analyzed. Various nucleosynthesis conditions and various mathematical models are considered. All basic two-particle reactions with neutrons, protons, α particles, and photons are taken into account. The results for the nuclear statistical equilibrium (NSE) model and for the KM are compared under various ambient conditions. The time it takes for the solution to become a steady-state one is estimated in the KM, provided that the NSE approximation holds. The computational processor time for temperatures T<8×10⁹ K is shown to be modest, and the KM can be used for nucleosynthesis calculations in this range. The KM can be realized together with the NSE model at higher initial temperatures, with the results being smoothly joined by using the NSE solution as the initial KM approximation. The kinetic model can also be successfully used to compute the r-process under various physical conditions.  相似文献   

WSO-UV progress and expectations     

Boris Shustov  Ana I. Gómez de Castro  Mikhail Sachkov  Alexander Moisheev  Evgeny Kanev  Javier López-Santiago  Oleg Malkov  Dmitry Nasonov  G. Belén Perea  Néstor Sánchez  Igor Savanov  Andrey Shugarov  Sergey Sichevskiy  Oleg Vlasenko  Javier Yañez 《Astrophysics and Space Science》2014,354(1):155-161

The World Space Observatory Ultraviolet (WSO-UV) is the space mission that will grant access to the ultraviolet (UV) range in the post Hubble epoch. WSO-UV is equipped with instrumentation for imaging and spectroscopy and it is fully devoted to UV astronomy. In this article, we outline the WSO-UV mission model and present the current status of the project.  相似文献   

When Daily Sunspot Births Become Positively Correlated     

Alexander Shapoval  Jean-Louis Le Mouël  Mikhail Shnirman  Vincent Courtillot 《Solar physics》2015,290(10):2709-2717

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Cosmological evolution of statistical system of scalar charged particles     

Yurii Ignat’ev  Alexander Agathonov  Mikhail Mikhailov  Dmitry Ignatyev 《Astrophysics and Space Science》2015,357(1):1-21

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Similarity in microbial amino acid uptake in surface waters of the North and South Atlantic (sub-)tropical gyres     

Polly G. Hill  Isabelle Mary  Duncan A. Purdie  Mikhail V. Zubkov 《Progress in Oceanography》2011,91(4):437-446

The Earth’s most extensive biomes – the oceanic subtropical gyres – are considered to be expanding with current surface ocean warming. Although it is well established that microbial communities control gyre biogeochemistry, comparisons of their metabolic activities between gyres are limited. In order to estimate metabolic activities including production of microbial communities, the uptake rates of amino acids leucine, methionine and tyrosine at ambient concentrations were estimated in surface waters of the Atlantic Ocean using radioisotopically labelled tracers. Data were acquired during six research cruises covering main oceanic provinces herein termed: North and South Atlantic Gyres, Bermuda Atlantic Time-series Study site (BATS), Equatorial region, and Mauritanian Upwelling (off Cape Blanc). Data were divided between provinces, the extents of which were identified by ocean colour data, in order to achieve provincial mean uptake rates. Leucine and methionine uptake rates did not differ between sampling periods, and were comparable between the North and South subtropical gyres. Furthermore, variation in uptake rates measured throughout the two oligotrophic gyres, where sampling covered ∼4 × 10⁶ km², was considerably lower than that measured within the Mauritanian Upwelling and Equatorial regions, and even at the BATS site. Tyrosine was generally the slowest of the amino acids to be taken up, however, it was assimilated faster than methionine within the Mauritanian Upwelling region. Thus, we propose that one value for leucine (12.6 ± 3.2 pmol L⁻¹ h⁻¹) and methionine (10.0 ± 3.3 pmol L⁻¹ h⁻¹) uptake could be applied to the oligotrophic subtropical gyres of the Atlantic Ocean. However, with the significantly lower uptake rates observed at the BATS site, we would not advise extrapolation to the Sargasso Sea.  相似文献   

Neutron star masses: dwarfs, giants and neighbors     

Sergei Popov  David Blaschke  Hovik Grigorian  Mikhail Prokhorov 《Astrophysics and Space Science》2007,308(1-4):381-385

We discuss three topics related to the neutron star (NS) mass spectrum. At first we discuss the possibility to form low-mass (M≲1M _⊙) objects. In our opinion this and suggest this is possible only due to fragmentation of rapidly rotating proto-NSs. Such low-mass NSs should have very high spatial velocities which could allow identification. A critical assessment of this scenario is given. However, the mechanism has its own problems, and so formation of such objects is not very probable. Secondly, we discuss mass growth due to accretion for NSs in close binary systems. With the help of numerical population synthesis calculations we derive the mass spectrum of massive (M>1.8M _⊙) NSs. Finally, we discuss the role of the mass spectrum in population studies of young cooling NSs. We formulate a kind of mass constraint which can be helpful, in our opinion, in discussing different competitive models of the thermal evolution of NSs. S.B.P. wants to thank the Organizers for support and hospitality. The work of S.B.P. was supported by the RFBR grant 06-02-16025 and by the “Dynasty” Foundation (Russia). The work of M.E.P.—by the RFBR grant 04-02-16720 and that of H.G. by DFG grant 436 ARM 17/4/05.  相似文献   

Martian gullies in the southern mid-latitudes of Mars: Evidence for climate-controlled formation of young fluvial features based upon local and global topography     

James L. Dickson  Mikhail Kreslavsky 《Icarus》2007,188(2):315-323

A new survey of Mars Orbiter Camera (MOC) narrow-angle images of gullies in the 30°-45° S latitude band includes their distribution, morphology, local topographic setting, orientation, elevation, and slopes. These new data show that gully formation is favored over a specific range of conditions: elevation (−5000 to +3000 m), slope (>10°), and orientation (83.8% on pole-facing slopes). These data, and the frequent occurrence of gullies on isolated topographic highs, lead us to support the conclusion that climatic-related processes of volatile accumulation and melting driven by orbital variations are the most likely candidate for processes responsible for the geologically recent formation of martian gullies.  相似文献   

Type Ia Supernova models: Latest developments     

S. Blinnikov  E. Sorokina 《Astrophysics and Space Science》2004,290(1-2):13-28

Supernovae of type Ia (SNe Ia) are very important for cosmography. To exclude systematic effects in linking the observed light of distant SNe Ia to the parameters of cosmological models, one has to understand the nature of supernova outbursts and to build accurate algorithms for predicting their emission. We review the recent progress of modeling the propagation of nuclear flame subject to numerous hydrodynamic instabilities inherent to the flame front. The Rayleigh-Taylor (RT) instability is the main process governing the corrugation of the front on the largest scales, while on the smallest scales the front propagation is controlled by the Landau-Darrieus in stability. Based on several hydrodynamic explosion models, we predict the broad-band UBVI and bolometric light curves of SNe Ia, using our 1D-hydro code which models multi-group time-dependent non-equilibrium radiative transfer inside SN ejecta. We employ our new corrected treatment for line opacity in the expanding medium, which is important especially in UV and IR bands. The results are compared with the observed light curves. Especially interesting is a recent 3D-deflagration model computed at MPA, Garching, by M. Reinecke et al.  相似文献   

KREEPy lunar meteorite Dhofar 287A: A new lunar mare basalt     

Mahesh Anand  Lawrence A. Taylor  Kula C. Misra  Svetlana I. Demidova  Mikhail A. Nazarov 《Meteoritics & planetary science》2003,38(4):485-499

Abstract— Dhofar 287 (Dho 287) is a new lunar meteorite, found in Oman on January 14, 2001. The main portion of this meteorite (Dho 287A) consists of a mare basalt, while a smaller portion of breccia (Dho 287B) is attached on the side. Dho 287A is only the fourth crystalline mare basalt meteorite found on Earth to date and is the subject of the present study. The basalt consists mainly of phenocrysts of olivine and pyroxene set in a finer‐grained matrix, which is composed of elongated pyroxene and plagioclase crystals radiating from a common nucleii. The majority of olivine and pyroxene grains are zoned, from core to rim, in terms of Fe and Mg. Accessory minerals include ilmenite, chromite, ulvöspinel, troilite, and FeNi metal. Chromite is invariably mantled by ulvöspinel. This rock is unusually rich in late‐stage mesostasis, composed largely of fayalite, Si‐K‐Ba‐rich glass, fluorapatite, and whitlockite. In texture and mineralogy, Dho 287A is a low‐Ti mare basalt, with similarities to Apollo 12 (A‐12) and Apollo 15 (A‐15) basalts. However, all plagioclase is now present as maskelynite, and its composition is atypical for known low‐Ti mare basalts. The Fe to Mn ratios of olivine and pyroxene, the presence of FeNi metal, and the bulk‐rock oxygen isotopic ratios, along with several other petrological features, are evidence for the lunar origin for this meteorite. Whole‐rock composition further confirms the similarity of Dho 287A with A‐12 and A‐15 samples but requires possible KREEP assimilation to account for its rare‐earth‐element (REE) contents. Cooling‐rate estimates, based on Fo zonation in olivine, yield values of 0.2–0.8°C/hr for the lava, typical for the center of a 10–20 m thick flow. The recalculated major‐element concentrations, after removing 10–15% modal olivine, are comparable to typical A‐15 mare basalts. Crystallization modeling of the recalculated Dho 287A bulk‐composition yields a reasonable fit between predicted and observed mineral abundances and compositions.  相似文献   

An experimental facility for the investigation of magma fragmentation by rapid decompression     

Mikhail Alidibirov  Donald B. Dingwell 《Bulletin of Volcanology》1996,58(5):411-416

 A special experimental facility has been developed to investigate the fragmentation of vesicular magma undergoing rapid decompression. The facility operates in a regime similar to that of shock tubes and at temperatures up to 950  °C and pressures up to 200 bar. Cylindrical samples (diameter ca. 17 mm, length ca. 50 mm) undergo rapid decompression in a high-temperature, high-pressure section of the facility following the disruption of a diaphragm separating that section from a low-pressure, low-temperature section. Actual vesicular magma samples have been experimentally fragmented at elevated temperatures and pressures corresponding to those observed during explosive volcanic eruptions and the resulting pyroclastics have been photographically resolved in flight and collected for physical characterization. The results of these experiments show that the rapid decompression of highly viscous vesicular magma can generate pyroclastic ejecta via rapid and complete fragmentation of magma at high temperature. This new fragmentation facility is presented as a tool for experimental volcanology under well-constrained conditions. Received: 19 March 1996 / Accepted: 25 August 1996  相似文献