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Current models and observations of variability in HgMn stars disagree.We present here the models that argue for pulsating HgMn stars with properties similar to those of SlowlyPulsating B Stars. The lack of observed variable HgMn stars suggeststhat some physical process is missing from the models. Somepossibilities are discussed. 相似文献
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A. Saro S. Borgani L. Tornatore G. De Lucia K. Dolag G. Murante 《Monthly notices of the Royal Astronomical Society》2009,392(2):795-800
We present results from two high-resolution hydrodynamical simulations of protocluster regions at z ≃ 2.1 . The simulations have been compared to observational results for the so-called Spiderweb galaxy system, the core of a putative protocluster region at z = 2.16 , found around a radio galaxy. The simulated regions have been chosen so as to form a poor cluster with M 200 ≃ 1014 h −1 M⊙ (C1) and a rich cluster with M 200 ≃ 2 × 1015 h −1 M⊙ (C2) at z = 0 . The simulated protoclusters show evidence of ongoing assembly of a dominating central galaxy. The stellar mass of the brightest cluster galaxy of the C2 system is in excess with respect to observational estimates for the Spiderweb galaxy, with a total star formation rate which is also larger than indicated by observations. We find that the projected velocities of galaxies in the C2 cluster are consistent with observations, while those measured for the poorer cluster C1 are too low compared with the observed velocities. We argue that the Spiderweb complex resembles the high-redshift progenitor of a rich galaxy cluster. Our results indicate that the included supernovae feedback is not enough to suppress star formation in these systems, supporting the need of introducing active galactic nuclei feedback. According to our simulations, a diffuse atmosphere of hot gas in hydrostatic equilibrium should already be present at this redshift, and enriched at a level comparable to that of nearby galaxy clusters. The presence of this gas should be detectable with future deep X-ray observations. 相似文献
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The Bayesian approach to significance testing, that makes use of prior information, has been studied in the last years, particularly
to allow the detection of deformations which are small with respect to measurement errors from repeated surveys. Some investigations
showed up to now that, under particular conditions concerning both the parameters of the prior distribution and the structure
of the control network, Bayesian tests give stronger results than tests based on the frequentist approach, with regard to
the detectability of deformations. In the present paper, after illustrating the essential developments and the most relevant
results of previous works, new analytical developments and numerical simulations are carried out, to illustrate some critical
aspects and advantages of the frequentist and Bayesian methods. It is shown, starting from simple examples involving only
Gaussian and truncated Gaussian distributions and from a simplified formulation of the prior deformation model, that the testing
procedures based on the frequentist approach, which do not introduce any a priori information, are in many cases of practical
interest insensitive to internal consistencies of the displacements (e.g., to the fact that they have a common direction).
It is also illustrated that the introduction of prior information, even in a non Bayesian context, more easily allows the
detection of little displacements. Besides it is noted that in some cases Bayesian tests detect displacements in the presence
of observed non-coherent movements, even if prior probability densities describing coherent movements are introduced. 相似文献
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Vincenza Guarino Rogério Guitarrari Azzone Pietro Brotzu Celso de Barros Gomes Leone Melluso Lucio Morbidelli Excelso Ruberti Colombo Celso Gaeta Tassinari Mauro Brilli 《Mineralogy and Petrology》2012,104(1-2):43-61
The Ipanema alkaline-carbonatitic complex is part of the Meso-Cenozoic alkaline magmatism located within the southeastern part of the Brazilian Platform. Drill-core and field sampling have indicated the occurrence of glimmerites, with subordinate shonkinites (mela-syenites), clinopyroxene-bearing glimmerites, diorites and syenites. The glimmerites are cross-cut by lamprophyric dykes and calciocarbonatites. Fenitization has deeply affected the country rocks, originating dioritic and syenitic rocks. The Ipanema rocks show a distinct potassic affinity. The initial Sr-Nd- isotopic composition of the Ipanema rocks (87Sr/86Sr?=?0.70661–0.70754 and 143Nd/144Nd?=?0.51169–0.51181) is similar to that of tholeiitic and potassium-rich-alkaline rocks of the Eastern Paraguay. Stable isotope data for the Ipanema calciocarbonatite suggest interaction with fluids at temperatures typical of hydrothermal stages, as hypothesized for other carbonatite complexes from southeastern Brazil. The chemical differences between the lamprophyre, glimmerites, carbonatites, apatitites and magnetitites, and the absence of marked REE enrichment in the evolved lithologies, all indicate that fractional crystallization and accumulus of liquidus phases in a magma reservoir, likely coupled with liquid immiscibility processes, may have played an important role in the genesis of the Ipanema rocks. 相似文献
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