Cosmological radiative transfer codes comparison project – I. The static density field tests     

Ilian T. Iliev  Benedetta Ciardi  Marcelo A. Alvarez  Antonella Maselli  rea Ferrara  Nickolay Y. Gnedin  Garrelt Mellema  Taishi Nakamoto  Michael L. Norman  Alexei O. Razoumov  Erik-Jan Rijkhorst  Jelle Ritzerveld  Paul R. Shapiro  Hajime Susa  Masayuki Umemura  Daniel J. Whalen 《Monthly notices of the Royal Astronomical Society》2006,371(3):1057-1086

Radiative transfer (RT) simulations are now at the forefront of numerical astrophysics. They are becoming crucial for an increasing number of astrophysical and cosmological problems; at the same time their computational cost has come within reach of currently available computational power. Further progress is retarded by the considerable number of different algorithms (including various flavours of ray tracing and moment schemes) developed, which makes the selection of the most suitable technique for a given problem a non-trivial task. Assessing the validity ranges, accuracy and performances of these schemes is the main aim of this paper, for which we have compared 11 independent RT codes on five test problems: (0) basic physics; (1) isothermal H  ii region expansion; (2) H  ii region expansion with evolving temperature; (3) I-front trapping and shadowing by a dense clump and (4) multiple sources in a cosmological density field. The outputs of these tests have been compared and differences analysed. The agreement between the various codes is satisfactory although not perfect. The main source of discrepancy appears to reside in the multifrequency treatment approach, resulting in different thicknesses of the ionized-neutral transition regions and the temperature structure. The present results and tests represent the most complete benchmark available for the development of new codes and improvement of existing ones. To further this aim all test inputs and outputs are made publicly available in digital form.  相似文献   

U-Pb SHRIMP-II ages of titanite and timing constraints on apatite-nepheline mineralization in the Khibiny and Lovozero alkaline massifs (Kola Peninsula)     

N.V. Rodionov  E.N. Lepekhina  A.V. Antonov  I.N. Kapitonov  Yu.S. Balashova  B.V. Belyatsky  A.A. Arzamastsev  S.A. Sergeev 《Russian Geology and Geophysics》2018,59(8):962-974

Results of this study of titanite samples collected from silicate rocks and apatite-nepheline-(sphene) ores from Paleozoic polyphase alkaline nepheline syenite complexes of the Khibiny and Lovozero massifs revealed the possibility of their in-situ U-Pb dating using sensitive high-resolution ion microprobe SHRIMP-II with an accuracy of 1.0-1.5%, which is comparable with that of U-Pb zircon analysis. Employing different approaches to age determination of the formation of the U-Pb system of titanites, the combined isochrons and mixing lines were plotted from the data obtained from the differentiated complex samples (121 analyses of five Khibiny samples and 52 analyses of one Lovozero sample) and apatite-nepheline ores (120 analyses of five Khibiny samples and 88 analyses of three Lovozero samples). They indicate synchronous crystallization of titanite in silicate rocks throughout the complexes: 374.1 ± 3.7 Ma for the Khibiny massif and 380.9 ± 4.5 Ma for the Lovozero massif, and attest to the later formation of phosphate-rare-metal ores: 371.0 ± 4.2 and 361.4 ± 3.2 Ma, respectively. The relatively delayed ore mineralization specific to the Lovozero massif can be accounted for the significantly lower volumes of magmatic melt and ore fluid involved, different thermal conditions, and the pattern of the investigated mineralization. As such, the obtained U-Pb data from titanite make it possible to limit significantly the time interval (most likely, not exceeding 15-20 Ma) comprising the evolution and activity of the ore-magmatic system of major agpaitic complexes, which is probably associated with plume magmatism.  相似文献   

U–Pb ages of detrital zircons from Paleozoic metasandstones of the Gelnica Terrane (Southern Gemeric Unit, Western Carpathians, Slovakia): evidence for Avalonian–Amazonian provenance     

Anna Vozárová  Katarína ?arinová  Nickolay Rodionov  Du?an Laurinc  Ilya Paderin  Sergey Sergeev  Elena Lepekhina 《International Journal of Earth Sciences》2012,101(4):919-936

U–Pb (SHRIMP) determinations on detrital zircons from the Early Paleozoic Gelnica Terrane metasandstones and their Permian overlap sediments of the Inner Western Carpathian Southern Gemeric Unit define five age populations based on age-probability plots. The metasandstones were sampled for detrital zircons from six stratigraphic levels, four of them in the Late Cambrian/Ordovician Gelnica Terrane metasandstones and the two in Permian envelope sequence. The data set includes 84 U–Pb ages for individual detrital zircons. These ages are combined with the previously dated inherited zircons from the associated metavolcanites (n?=?31). The majority of the pre-Permian detrital and inherited zircons (95%) belong to the three main populations: population A—the Paleoproterozoic/Neoarchean ages ranging from 1.75 to 2.6?Ga; population B—the Mesoproterozoic ages with the range of 0.9 to 1.1?Ga; population C—the Neoproterozoic ages, ranging from 560 to 807?Ma. The detrital zircon age spectrum from the basal Permian sediments reflects the strong recycling from the underlying Gelnica Terrane, with the presence of the dominant Precambrian C and B populations (94% of total), including the minor populations A. The range of the detrital zircon ages from the Late Permian sandstones is wider, with additional population D, ranging from 497 to 450?Ma and population E with a time span from 369 to 301?Ma. Within the Late Permian detrital zircon assemblage, the Proterozoic population A?+?B?+?C form only 25% of total. The detrital zircon data suggest that the Gelnica Terrane belongs to the peri-Gondwanan terrane with a source area located on the northwestern margin of Gondwana close to Amazonia. This terrane should have travelled a long distance in the Phanerozoic times.  相似文献   

Anisotropic models of dark halos     

N. Ya. Sotnikova  S. A. Rodionov 《Astronomy Letters》2008,34(10):664-674

An iterative approach is used to construct spherically symmetric equilibrium models with an anisotropic velocity distribution. The potentialities of the method have been tested on models with known distribution functions, the Osipkov-Merritt models. It is shown that models that differ significantly from the Osipkov-Merritt models can be constructed. An N-body model of a dark halo with a density distribution that approximates the results of cosmological simulations (the Navarro-Frenk-White model) has been constructed. The anisotropy profile has been taken to be similar to that yielded by cosmological simulations. The constructed models can serve as direct input data for investigating the dynamics and stability of such systems in N-body simulations.  相似文献   

On the equatorward phase propagation of high-m ULF pulsations observed by radars     

Pavel N. Mager  Dmitri Yu. Klimushkin  Nickolay Ivchenko 《Journal of Atmospheric and Solar》2009,71(16):1677-1680

An often observed and still unexplained feature of the high-m Alfvén waves in the terrestrial magnetosphere is their equatorward phase motion, in contrast with low-m waves. We suggest an explanation of this fact in terms of a model of wave excitation by an azimuthally drifting particle inhomogeneity injected during substorm activity. The azimuthal direction of the phase velocity coincides with that of the cloud. If the drift velocity increases with the radial coordinate, the particle cloud is stretched into spiral in the equatorial plane which leads to a radial component of the phase velocity directed toward Earth, that is, an equatorward phase propagation.  相似文献   

Computation of elliptic Hansen coefficients and their derivatives     

Andrej G. Sokolsky  Akmal A. Vakhidov  Nickolay N. Vasiliev 《Celestial Mechanics and Dynamical Astronomy》1995,63(3-4):357-374

The problem of computation of elliptic Hansen coefficients and their derivatives is considered for constructing a motion theory of an artificial Earth satellite with large eccentricity. An algorithm for analytical and numerical computation of these coefficients and their derivatives is described. The recurrence relations for derivatives of the first and second order and initial values for recurrences are obtained. As an example, numerical values of some elliptic Hansen coefficients are given for the orbit with eccentricityk=0.74.  相似文献   

Probing the Universe with the Ly α forest — II. The column density distribution     

Nickolay Y. Gnedin 《Monthly notices of the Royal Astronomical Society》1998,299(2):392-402

I apply the well controlled hydro-PM (HPM) approximation of Gnedin &38; Hui to model the column density distribution of the Ly α forest for 25 different flat cosmological scenarios, including variants of the standard cold dark matter (CDM), tilted CDM, CDM with a cosmological constant, and cold + hot dark matter (CHDM) models. I show that, within the accuracy of the HPM approximation, the slope of the column density distribution reflects the degree of non-linearity of the cosmic gas distribution and is a function of the rms linear density fluctuation at the characteristic filtering scale only. The amplitude of the column density distribution, expressed as the value for the ionizing intensity, is derived as a function of the cosmological parameters (to about 40 per cent accuracy). The observational data are currently consistent with the value for the ionizing intensity being constant in the redshift interval z  ∼ −4.  相似文献   

Archean metabasic rocks at the base of the Riphean of the Bashkirian Meganticlinorium (Southern Urals)     

V. N. Puchkov  A. A. Krasnobaev  N. D. Sergeeva  S. V. Busharina  N. V. Rodionov  T. B. Bayanova 《Doklady Earth Sciences》2014,457(1):835-841

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Understanding the PSCz galaxy power spectrum with N-body simulations     

Mark C. Neyrinck  rew J. S. Hamilton  Nickolay Y. Gnedin 《Monthly notices of the Royal Astronomical Society》2004,348(1):1-11

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The 3.98–3.63 Ga zircons as indicators of major processes operating in the ancient continental crust of the east Antarctic shield (Enderby Land)     

B. V. Belyatsky  N. V. Rodionov  A. V. Antonov  S. A. Sergeev 《Doklady Earth Sciences》2011,438(2):770-774

This study presents new results on zircons from the enderbite-charnockite rocks of Enderby Land, East Antarctica. U-Pb age of 3981 ± 8 Ma (SIMS SHRIMP II), which was first obtained for a protolith of massive enderbites from Aker Peaks, eastern Napier Mts, suggests that the existence of sialic crust in the study area at 4 Ga. Although there was only one magmatic zircon (of 150 grains analyzed) in the study area known with the oldest age, its significance cannot be overestimated, since it may indirectly evidence the existence of an Early Archean crustal block with a minimum age of 4 Ga, which extends for over 300 km across Enderby Land from its western to eastern part. Based on the U-Pb systematics, REE and trace element distributions in zircons from charnockite and enderbite gneisses, high-aluminous gneisses, and basic granulites, we first revealed that an early high-temperature metamorphic event accompanied by the emplacement of granodiorite intrusions occurred in the vicinity of Aker Peaks at 3620–3630 Ma. Although the 2850–3050 metamorphic overprints are clearly observed in some other areas of Enderby Land and are widely considered to be of critical importance on a regional scale, their metamorphic signatures are apparently absent from the U-Pb systematics of the studied zircon, thus suggesting the presence of similar old zircons in the study area. At the same time, all samples in this study record a 2480–2550 Ma granulite-amphibolite facies overprint represented as new zircon growths or recrystallization of earlier phases.  相似文献