• 한국철학논집
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• 제42호
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• pp.165-195
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• 2014

이 글의 목표는 양웅(揚雄)과 갈홍(葛洪)의 '현(玄)' 개념을 우주구조에 관한 이론을 중심으로 살펴보는 것이다. 고대 중국의 우주구조론은 '천(天)'에 대한 이해로부터 출발하여, 천체의 구조, 천지의 구조 및 위치관계 등의 문제를 통해 한대(漢代)에 그 이론이 체계적으로 정립되었다. 다만 중국 전통시기의 우주구조에 관한 논의는 대부분 천문(天文)과 역법(曆法)을 통해 발전했듯이, 인간의 관점에서 인간사를 해명하기 위해 전개되었다. 양웅과 갈홍 또한 이러한 맥락에서 각자의 우주구조론 체계를 정립하는데, 그 특징은 다음과 같다. 첫째, 양웅은 우주구조론가운데 개천설(蓋天說)을 비판하며 혼천설(渾天說)을 수용하여 발전시켰고, 갈홍은 혼천설을 지지하는 가운데 선야설(宣夜說)의 일부 논의를 수용하였다. 둘째, 양웅과 갈홍의 우주구조론은 그들의 우주생성론의 이론적 출발점이다. 천체의 구조와 천지의 위치관계를 다루는 우주구조론을 중심으로, 그들은 각자 우주만물 생성의 근원과 생성과정에 대한 논의를 전개한다. 이 과정에서 두 학자 모두 '현(玄)' 개념을 중심축으로 하여 우주론 체계를 건립하였다. 셋째, 양웅과 갈홍의 우주구조론은 그들 철학체계를 지탱하는 이론적 전제가 된다. 양웅은 우주구조에 관한 논의를 통해 천도(天道)와 인사(人事)의 관계를 모색하고, 갈홍은 우주구조론을 활용하여 신선도교 이론체계를 정립한다. 이처럼 양웅과 갈홍의 우주구조론은 우주생성론과 함께 우주론체계의 중요 구성 요소가 되며, 두 학자 모두 '현' 개념 중심의 우주구조론과 우주생성론을 바탕으로 각자의 철학체계를 정립하였다.

• 천문학회지
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• 제29권spc1호
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• pp.11-14
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• 1996

Super-inflation driven by dilaton/moduli kinetic energy is naturally realized in compactified string theory. Discussed are selected topics of recent development in string inflationary cosmology: kinematics of super-inflation, graceful exit triggered by quantum back-reaction, and classical and quantum power spectra of density and metric perturbations.

• 천문학논총
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• 제25권3호
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• pp.53-58
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• 2010

The origin of the galaxies represents an important focus of current cosmological research, both observational and theoretical. Its resolution involves a comprehensive understanding of star formation and evolution, galaxy dynamics, supermassive black holes, and the cosmology of the very early universe. In this paper, I will review our current understanding of galaxy formation and review some of the challenges that lie ahead. Specific issues that I address include the galaxy luminosity function, feedback by supernovae and by AGN, and downsizing. I argue that current evidence favours two distinct modes of star formation in the early universe, in order to account for the origin of disk and massive spheroidal galaxies. However perhaps the most urgent need is for a robust theory of star formation.

• 천문학논총
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• 제26권2호
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• pp.55-70
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• 2011

Cosmological linear perturbation theory has fundamental importance in securing the current cosmological paradigm by connecting theories with observations. Here we present an explanation of the method used in relativistic cosmological perturbation theory and show the derivation of basic perturbation equations.

• 천문학논총
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• 제30권2호
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• pp.309-313
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• 2015

If the present universe is slightly open then pre-inflation curvature would appear as a cosmic dark-flow component of the CMB dipole moment. We summarize current cosmological constraints on this cosmic dark flow and analyze the possible constraints on parameters characterizing the pre-inflating universe in an inflation model with a present-day very slightly open ${\Lambda}CDM$ cosmology. We employ an analytic model to show that for a broad class of inflation-generating effective potentials, the simple requirement that the observed dipole moment represents the pre-inflation curvature as it enters the horizon allows one to set upper and lower limits on the magnitude and wavelength scale of pre-inflation fluctuations in the inflaton field and the curvature parameter of the pre-inflation universe, as a function of the fraction of the total initial energy density in the inflaton field. We estimate that if the current CMB dipole is a universal dark flow (or if it is near the upper limit set by the Planck Collaboration) then the present constraints on ${\Lambda}CDM$ cosmological parameters imply rather small curvature ${\Omega}_k{\sim}0.1$ for the pre-inflating universe for a broad range of the fraction of the total energy in the inflaton field at the onset of inflation. Such small pre-inflation curvature might be indicative of open-inflation models in which there are two epochs of inflation.

• 천문학회지
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• 제29권spc1호
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• pp.17-18
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• 1996

COBE's results on the anisotropy of the cosmic microwave background radiation (CMBR) is discussed. Some ambiguities in the linear GI cosmic perturbation theory are clarified. The problem of the last scattering surface and the deficiencies of the linear cosmic perturbation theory are mentioned. The possible ways to overcome the theoretical difficulties are discussed also.

• 천문학논총
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• 제30권2호
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• pp.321-325
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• 2015

Determining the absolute neutrino mass scale and the neutrino mass hierarchy are central goals in particle physics, with important implications for the Standard Model. However, the final answer may come from cosmology, as laboratory experiments provide measurements for two of the squared mass differences and a stringent lower bound on the total neutrino mass - but the upper bound is still poorly constrained, even when considering forecasted results from future probes. Cosmological tracers are very sensitive to neutrino properties and their total mass, because massive neutrinos produce a specific redshift-and scale-dependent signature in the power spectrum of the matter and galaxy distributions. Stringent upper limits on ${\sum}m_v$ will be essential for understanding the neutrino sector, and will nicely complement particle physics results. To this end, we describe here a series of cosmological hydrodynamical simulations which include massive neutrinos, specifically designed to meet the requirements of the Baryon Acoustic Spectroscopic Survey (BOSS) and focused on the Lyman-${\alpha}$ ($Ly{\alpha}$) forest - also a useful theoretical ground for upcoming surveys such as SDSS-IV/eBOSS and DESI. We then briefly highlight the remarkable constraining power of the $Ly{\alpha}$ forest in terms of the total neutrino mass, when combined with other state-of-the-art cosmological probes, leaving to a stringent upper bound on ${\sum}m_v$.

• 천문학논총
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• 제25권3호
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• pp.71-76
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• 2010

The current status of numerical simulations of galaxy formation is reviewed. After a description of the main numerical simulation techniques, I will present several applications in order to illustrate how numerical simulations have improved our understanding of the galaxy formation process.

• 천문학논총
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• 제18권1호
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• pp.1-9
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• 2003

In the framework of linear perturbation theory and linear approximation of spacetime anisotropy, we investigated the formulae for the CMBR temperature anisotropy and fluctuation spectrum which have their origin in the primordial tensor perturbations of the perturbed Bianchi type I universe model. The resulting formulae were compared with those of the flat Friedmann model.

• 천문학회지
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• 제38권2호
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• pp.129-133
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• 2005

The temperature (T) and entropy (S) fields of baryonic gas, or intergalactic medium (IGM), in the ACDM cosmology are analyzed using simulation samples produced by a hybrid cosmological hydrodynamic/N-body code based on the weighted essentially non-oscillatory scheme. We demonstrate that, in the nonlinear regime, the dynamical similarity between the IGM and dark matter will be broken in the presence of strong shocks in the IGM. The heating and entropy production by the shocks breaks the IGM into multiple phases. The multiphase and non-Gaussianity of the IGM field would be helpful to account for the high-temperature and high-entropy gas observed in groups and clusters with low-temperature IGM observed by Ly$\alpha$ forest lines and the intermittency observed by the spikes of quasi-stellar object's absorption spectrum.