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排序方式: 共有274条查询结果,搜索用时 31 毫秒
51.
We consider essential mechanisms for orbit shrinkage or 'hardening' of compact binaries in globular clusters (GCs) to the point of Roche lobe contact and X-ray emission phase, focusing on the process of collisional hardening due to encounters between binaries and single stars in the cluster core. The interplay between this kind of hardening and that due to emission of gravitational radiation produces a characteristic scaling of the orbit-shrinkage time with the single-star binary encounter rate γ in the cluster which we introduce, clarify and explore. We investigate possible effects of this scaling on populations of X-ray binaries in GCs within the framework of a simple 'toy' scheme for describing the evolution of pre-X-ray binaries in GCs. We find the expected qualitative trends sufficiently supported by data on X-ray binaries in Galactic GCs to encourage us towards a more quantitative study. 相似文献
52.
53.
54.
We present exact solutions of a Bianchi type VI0 viscous fluid cosmological model. It is a generalization of the model proposed by Banerjee and Santos (1983) for Bianchi type I. 相似文献
55.
The diffusion coefficient of neutrinos in the trapping regime in a presupernova star,where the scattering of neutrinos by nuclei is the dominant effect, is calculated within the framework of relativistic kinetic theory in the lowest order Chapman-Enskog approximation. The screening of the nuclei by ion-ion and electron-electron correlations is also taken into account. 相似文献
56.
Petrographic observations of two Vindhyan black shales (Rampur Shale of the Semri Group and Bijaigarh Shale of the Kaimur
Group) revealed the following features:
These features are indirect evidence of microbial mat colonization during the Proterozoic. The microbial mats probably fixed
carbon at the sediment surface, stabilized sediment and recycled organic matter and were the primary producers, unlike during
the Phanerozoic time. 相似文献
– | •general wavy lamination, |
– | •contorted and folded thin shreds of organic matter, |
– | •wavy pyritic laminae, |
– | •‘teeth and socket’ structure. |
57.
R. K. Das D. P. K. Banerjee N. M. Ashok 《Monthly notices of the Royal Astronomical Society》2009,398(1):375-384
We present near-infrared (1–2.5 μm) spectroscopic and photometric results of Nova V2615 Ophiuchi which was discovered in outburst in 2007 March. Our observations span a period of ∼80 d starting from 2007 March 28 when the nova was at its maximum light. The evolution of the spectra is shown from the initial P Cygni phase to an emission-line phase and finally to a dust formation stage. The characteristics of the JHK spectra are very similar to those observed in a nova outburst occurring on a carbon–oxygen white dwarf. We analyse an observed line at 2.088 μm and suggest that it could be due to Fe ii excited by Lyman α fluorescence. The highlight of the observations is the detection of the first overtone bands of carbon monoxide (CO) in the 2.29–2.40 μm region. The CO bands are modelled to estimate the temperature and mass of the emitting CO gas and also to place limits on the 12 C/13 C ratio. The CO bands are recorded over several epochs, thereby allowing a rare opportunity to study the evolution from a phase of constant strength through a stage when the CO is destroyed fairly rapidly. We compare the observed time-scales involved in the evolution of the CO emission and find a good agreement with model predictions that investigate the chemistry in a nova outflow during the early stages. 相似文献
58.
Simon Portegies Zwart Steve McMillan Stefan Harfst Derek Groen Michiko Fujii Breanndán Ó Nualláin Evert Glebbeek Douglas Heggie James Lombardi Piet Hut Vangelis Angelou Sambaran Banerjee Houria Belkus Tassos Fragos John Fregeau Evghenii Gaburov Rob Izzard Mario Jurić Stephen Justham Andrea Sottoriva Marcel Zemp 《New Astronomy》2009,14(4):369-378
We present MUSE, a software framework for combining existing computational tools for different astrophysical domains into a single multiphysics, multiscale application. MUSE facilitates the coupling of existing codes written in different languages by providing inter-language tools and by specifying an interface between each module and the framework that represents a balance between generality and computational efficiency. This approach allows scientists to use combinations of codes to solve highly coupled problems without the need to write new codes for other domains or significantly alter their existing codes. MUSE currently incorporates the domains of stellar dynamics, stellar evolution and stellar hydrodynamics for studying generalized stellar systems. We have now reached a “Noah’s Ark” milestone, with (at least) two available numerical solvers for each domain. MUSE can treat multiscale and multiphysics systems in which the time- and size-scales are well separated, like simulating the evolution of planetary systems, small stellar associations, dense stellar clusters, galaxies and galactic nuclei. In this paper we describe three examples calculated using MUSE: the merger of two galaxies, the merger of two evolving stars, and a hybrid N-body simulation. In addition, we demonstrate an implementation of MUSE on a distributed computer which may also include special-purpose hardware, such as GRAPEs or GPUs, to accelerate computations. The current MUSE code base is publicly available as open source at http://muse.li. 相似文献
59.
The paper consists of some exact solutions for a homogeneous Bianchi type VI0 universe. The material distribution is taken to be a magnetized bulk viscous fluid in presence of massive cosmological string. We assume that current is flowing along x-direction. Therefore, the magnetic field is in yz-plane. For deterministic model of the universe, we assume that shear (σ) is proportional to the expansion (θ) and ζ θ=constant=ξ where ζ the coefficient of bulk viscosity and θ the expansion in the model. The physical and kinematical parameters of the models thus formed are discussed. 相似文献
60.
A number of archeological features, including in‐filled irrigation canals of uncertain prehistoric age, occur within the Holocene floodplain of the Salt River at Phoenix, Arizona. In the first attempt to date irrigation‐canal sediments using luminescence methods, we obtained age estimates of 1640 ± 190 yr B.P. (1σ) (multi‐aliquot or MA) and 1621 ± 95 yr B.P. (post‐IR single‐aliquot‐regenerative‐dose or SAR) for a single sample from the base of the oldest canal‐infilling deposits (all IR‐PSL ages reported in this article are in calendar years before A.D. 2001). For the remaining canal samples, weighted mean luminescence ages of 819 ± 45 yr (MA) and 826 ± 32 yr (post‐IR SAR) were obtained. Thus from photonic dating we can resolve the first and last phases of canal use at this Phoenix site: initiation at ca. 1600 years ago and final use at ca. 800 years ago. These results demonstrate the power of SAR luminescence sediment dating to enhance our understanding of prehistoric irrigation‐canal development and usage here and elsewhere in the world. © 2004 Wiley Periodicals, Inc. 相似文献