共查询到20条相似文献,搜索用时 843 毫秒
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《宇宙年龄--宇宙学中的一个热点问题》(本刊1997年第1期)一文中所报道的有关宇宙年龄的测定是截至1995年底的情况.本文将对1995年以后这一问题的进展做简要介绍. 相似文献
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第五讲暗能量和德西特时空 总被引:1,自引:0,他引:1
最近的天文观测表明,宇宙是在加速膨胀,而不是原来认为的减速膨胀.为解释加速膨胀,必须在宇宙的物质能量中引入暗能量这一成分,文章讨论了暗能量的可能侯选者,特别强调了宇宙常数问题、德西特时空问题以及和德西特时空相关的一些基本问题. 相似文献
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大部分宇宙学家认为,宇宙─-它目前的膨胀速度比以往任何时候都缓慢─-最终或者会逐渐地实际上停顿下来,不再膨胀;或者膨胀停止后会重新开始收缩。现在,两位研究人员表明,根据来自宇宙背景辐射探测卫星(COBE)测量到的数据,可以判断;宇宙将会无限期地膨胀下去.微波背景辐射存在的踪迹遍及整个宇宙,它被认为是宇宙大爆炸的遗迹.在天空的不同区域,这一辐射的温度有着轻微的差别,其数值为十万分之一左右.人们认为,这种差别为星系的形成──当宇宙处于青的期时──提供了线索.爱因斯坦的广义相对论指出,宇宙会拥有三种可能模型中的一种,每种模型同时也决定了宇宙的命运. 相似文献
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本文讨论宇宙背景辐射的发现和实测研究在热大爆炸宇宙理论的确立中的重要作用.它包括四个要点:一、证实了早期宇宙确曾热至4000K以上,二、证实了宇宙物质分布确曾是高度均匀的,三、证实了银河系与其他屎系一样,在宇宙空间有自身的运动,四、证实了早期宇宙中确有结构形成的种子存在。 相似文献
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The existence of cosmic rays of energies exceeding 1020 eV is one of the mysteries of high-energy astrophysics. The spectrum and the high energy to which it extends rule out almost
all suggested source models. The challenges posed by observations to models for the origin of high-energy cosmic rays are
reviewed, and the implications of recent new experimental results are discussed. Large area high-energy cosmic ray detectors
and large volume high-energy neutrino detectors currently under construction may resolve the high-energy cosmic ray puzzle,
and shed light on the identity and physics of the most powerful accelerators in the Universe. 相似文献
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Zadeba E. A. Khokhlov S. S. Kokoulin R. P. Petrukhin A. A. Shulzhenko I. A. Yashin I. I. 《Physics of Atomic Nuclei》2022,85(1):86-91
Physics of Atomic Nuclei - The muon puzzle is an excess of muon bundles generated by primary cosmic rays (PCR) at energies above 10 $${}^{17}$$ eV compared to estimations that assume even a heavy... 相似文献
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Jun Chen Puxun Wu Hongwei Yu Zhengxiang Li 《The European Physical Journal C - Particles and Fields》2012,72(2):1861
The creation of cold dark matter (CCDM) can explain the present accelerating cosmic expansion without appealing to dark energy.
In this paper, we investigate the age problem of CCDM models by considering five old high redshift objects (OHROs) (old ratio
galaxy 3C 65, old galaxy LBDS 53W069, old galaxy LBDS 53W091, high redshift quasar B1422+231, old quasar APM 08279+5255).
Two concrete CCDM models, i.e., the LSS and the LJO, are studied. Using the recent SNIa, BAO and H(z) observational data to constrain the model parameters, we can estimate the cosmic age with the model parameters that are
their best fit values. By comparing the estimated cosmic age with the age of OHROs, we find that for the LSS, the ages of
five OHROs are less than the cosmic age at the same redshift, while for the LJO, the conclusion depends sensitively on both
the value for the age of APM 08279+5255 and the value of H
0. So, to determine whether the age problem exists for the LJO, we need more precise results on the age of APM 08279+5255 and
the value of the present Hubble parameter. 相似文献
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Because of an old quasar APM 08279+5255 at z=3.91, some dark energy models face the challenge of the cosmic age problem. It has been shown by Wei and Zhang [H. Wei, S.N. Zhang, Phys. Rev. D 76 (2007) 063003, arXiv:0707.2129 [astro-ph]] that the holographic dark energy model is also troubled with such a cosmic age problem. In order to accommodate this old quasar and solve the age problem, we propose in this Letter to consider the interacting holographic dark energy in a non-flat universe. We show that the cosmic age problem can be eliminated when the interaction and spatial curvature are both involved in the holographic dark energy model. 相似文献
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There are two processes of matter creation after inflation that may be relevant to the resolution of the puzzle of cosmic rays observed with energies beyond GZK cut-off: 1) gravitational creation of superheavy (quasi)stable particles, and 2) non-thermal phase transitions leading to the formation of topological defects. We review both possibilities. 相似文献
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Jaan Einasto 《Brazilian Journal of Physics》2013,43(5-6):369-374
I review the development of the concept of dark matter. The dark matter story passed through several stages, from a minor observational puzzle to a major challenge for theory of elementary particles. Modern data suggest that dark matter is the dominant matter component in the Universe and that it consists of some unknown non-baryonic particles. Dark matter is the dominant matter component in the Universe; therefore, properties of dark matter particles determine the structure of the cosmic web. 相似文献
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中国大科学装置之一的高海拔宇宙线观测站开创了超高能伽马射线天文学的新时代,至今已作出多项重要的科学发现,为人们破解银河系宇宙线起源之谜带来了关键线索,并为研究极端天体中的极端物理过程提供了独特的探针。文章主要介绍其探测到的超高能伽马射线源,以及相关天体的物理图像。 相似文献
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In the polyomino puzzle, the aim is to fill a finite space using several polyomino pieces with no overlaps or blanks. Because it is an NP-complete combinatorial optimization problem, various probabilistic and approximated approaches have been applied to find solutions. Several previous studies embedded the polyomino puzzle in a QUBO problem, where the original objective function and constraints are transformed into the Hamiltonian function of the simulated Ising model. A solution to the puzzle is obtained by searching for a ground state of Hamiltonian by simulating the dynamics of the multiple-spin system. However, previous methods could solve only tiny polyomino puzzles considering a few combinations because their Hamiltonian designs were not efficient. We propose an improved Hamiltonian design that introduces new constraints and guiding terms to weakly encourage favorable spins and pairs in the early stages of computation. The proposed model solves the pentomino puzzle represented by approximately 2000 spins with >90% probability. Additionally, we extended the method to a generalized problem where each polyomino piece could be used zero or more times and solved it with approximately 100% probability. The proposed method also appeared to be effective for the 3D polycube puzzle, which is similar to applications in fragment-based drug discovery. 相似文献
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F. Halzen 《The European Physical Journal C - Particles and Fields》2006,46(3):669-687
Kilometer-scale neutrino detectors such as IceCube are discovery instruments covering nuclear and particle physics, cosmology and astronomy. Examples of their multidisciplinary missions include the search for the particle nature of dark matter and for additional small dimensions of space. In the end, their conceptual design is very much anchored to the observational fact that Nature produces protons and photons with energies in excess of 1020 eV and 1013 eV, respectively. The puzzle of where and how Nature accelerates the highest energy cosmic particles is unresolved almost a century after their discovery. The cosmic ray connection sets the scale of cosmic neutrino fluxes. In this context, we discuss the first results of the completed AMANDA detector and the science reach of its extension, IceCube. Similar experiments are under construction in the Mediterranean. Neutrino astronomy is also expanding in new directions with efforts to detect air showers, acoustic and radio signals initiated by super-EeV neutrinos. The outline of this review is as follows: Introduction Why kilometer-scale detectors? Cosmic neutrinos associated with the highest energy cosmic rays High energy neutrino telescopes: methodologies of neutrino detection High energy neutrino telescopes: status 相似文献