• 천문학회지
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• 제29권spc1호
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• pp.1-5
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• 1996

Recent discussions of observational constraints on the standard hot big bang model are reviewed and it is argued that now there is room for considering alternative cosmologies. The quasi-steady state cosmology is briefly described. This model seems to explain most of the observed features of the universe, including the m-z relation, radio source count, the light nuclear abundances and the microwave background.

• 천문학회보
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• 제45권1호
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• pp.29.1-29.1
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• 2020

I review the status of the concordance (standard) LCDM model of cosmology in light of current observations discussing about the apparent tensions in estimation of the key cosmological parameters. I will also briefly discuss the future of the field at the era of the next generation of the astronomical/cosmological surveys.

• 천문학회보
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• 제46권1호
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• pp.27.3-27.3
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• 2021

Supernova (SN) cosmology is based on the assumption that the width-luminosity relation (WLR) in the type Ia SN luminosity standardization would not vary with progenitor age. Unlike this expectation, recent age datings of stellar populations in host galaxies have shown significant correlations between progenitor age and Hubble residual (HR). It was not clear, however, how this correlation arises from the SN luminosity standardization process, and how this would impact the cosmological result. Here we show that this correlation originates from a strong progenitor age dependence of the WLR and color-luminosity relation (CLR), in the sense that SNe from younger progenitors are fainter each at given light-curve parameters x1 and c. This is reminiscent of Baade's discovery of two Cepheid period-luminosity relations, and, as such, causes a serious systematic bias with redshift in SN cosmology. We illustrate that the differences between the high-z and low-z SNe in the WLR and CLR, and in HR after the standardization, are fully comparable to those between the correspondingly young and old SNe at intermediate redshift, indicating that the observed dimming of SNe with redshift is most likely an artifact of over-correction in the luminosity standardization. When this systematic bias with redshift is properly taken into account, there is no evidence left for an accelerating universe, and the SN data now support a decelerating cosmic expansion. Since the SN cosmology has long been considered as the most direct evidence for an accelerating universe with dark energy, this finding poses a serious question to one of the cornerstones of the concordance model.

• 사상체질의학회지
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• 제9권1호
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• pp.245-253
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• 1997

The methodology of the Oriental philosophy is deductive and that of the of Occidental philosophy is inductive. Therefore study on the Oriental philosophy must start from right comprehension of fundamental premise before detailed analysis. The writer studied the meaning of the cosmology which forms the basis of Sa-sang constitutional philosophy and the propriety of visceral assignment by Sa-sang constitution which forms the theoletiacal basis of Sa-sang constitutional medicine. The results are following ; 1. The cosmology of Lee jae-ma has the existent principle but don't have the side of the formative principie. 2. The cosmology of Lee jae-ma is not that searchs for the objective rule of nature but that centers around a human being by subjective understanding system. 3. The cosmology consists of four elements, that is mind(心), body(身), events(事), and nature(物). Among them mind and body means a human being, nature means the natural environment containing time and space, events means not that of nature but that of human being. 4. The mind and body as Yin-yang(陰陽) means the state which objects and self become one. 5. The mind as the Great-Absolute(太極) has the possibility of two interpretation, Firstly it means the state of the source of life which nature and human being become one, and secondly it means that the mind of a human being becomes the cosmos or the center of the cosmos. 6. In the visceral assignment by Sa-sang constitution the position of heart, the Great-Absolute in center is immanent within four viscera and the function of it is that the undifferentiated unitary organic body, after it is diffrentiated still serves as the unitary organic whole by mutual connection, adjustment, unification and supervision. 7. The Great-Absolute in center is divided into the Great-Absolute of mind and that of body. And the Great-Absolute of body consists of the heart and the system of blood vessel, that of mind means the self-consciousness(自我).

• 동양고전연구
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• 제33호
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• pp.7-29
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• 2008

장현광(張顯光)은 조선시대 자연학자 가운데 대표적인 인물 가운데 한 사람이다. 이 글은 그의 우주론 속에 함축된 상수학적 요소의 의의와 한계를 검토하는 데 목표를 둔다. 역학에서 상과 수는 만물의 분별과 그 상호관계, 그리고 그것들의 시간적 질서를 표현하는 개념 도구이다. 그것들은 음양을 결합함으로써 내부 운동인을 확보하고, 우주 만물에 대한 상수학적 해석과 설명의 틀을 구성하였다. 상수학적 우주론의 핵심적인 주장은 우주가 시 공간적으로 유한하며, 그것과 반대로 리(태극)는 무한하다고 하는 것이다. 리가 시 공간적 무한하다는 것은 도덕원리가 절대적이고 항상적임을 의미한다. 이를 통해 장현광은 자신의 우주론이 주자학의 도덕형이상학과 순조롭게 결합될 수 있도록 하였다. 장현광은 역서(易書)를 자연 이해의 준거 또는 범형(範形)으로 강조하는 경향을 보였다. 이는 불완전하나마 소옹에게서 나타났던 법칙 객관주의를 질곡하고, 그의 법칙 개념으로 하여금 경험이나 지식의 확장과 더불어 스스로를 갱신해 가기 어렵게 만들었다. 이러한 이론적 한계에도 불구하고 그의 상수학적 우주론은 당시 성리학의 자연학적 근거를 마련했다는 점에서 긍정적으로 평가할 수 있다.

• 천문학회보
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• 제39권2호
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• pp.42.1-42.1
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• 2014

Neutrino science has received a boost of attention quite recently in cosmology, since the outstanding discovery in particle physics over the last decade that neutrinos are massive: pinpointing the neutrino masses is one of the greatest challenges in science today, at the cross-road between particle-physics, astrophysics, and cosmology. Cosmology offers a unique 'laboratory' with the best sensitivity to the neutrino mass, as primordial massive neutrinos comprise a small portion of the dark matter and are known to significantly alter structure formation. I will first introduce a new suite of state-of-the-art hydrodynamical simulations with cold dark matter, baryons and massive neutrinos, specifically targeted for modeling the low-density regions of the intergalactic medium as probed by the Lyman-Alpha forest at high-redshift. I will then present and discuss how these simulations are used to constrain the parameters of the LCDM cosmological model in presence of massive neutrinos, in combination with BOSS data and other cosmological probes, leading to the strongest bound to date on the total neutrino mass.

• 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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• 제30권2호
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• pp.315-319
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• 2015

We consider a late decaying dark matter model in which cold dark matter begins to decay into relativistic particles at a recent epoch ($z{\leqslant}1$). A complete set of Boltzmann equations for dark matter and other relevant particles particles is derived, which is necessary to calculate the evolution of the energy density and density perturbations. We show that the large entropy production and associated bulk viscosity from such decays leads to a recently accelerating cosmology consistent with observations. We determine the constraints on the decaying dark matter model with bulk viscosity by using a MCMC method combined with observational data of the CMB and type Ia supernovae.

• Journal of Astronomy and Space Sciences
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• 제40권1호
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• pp.29-33
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• 2023

An unexplained acceleration on the order of 10^-8 cm s^-2, which is close to cH, where c is the speed of light and H is the Hubble constant, is detected in gravitationally bound systems of different scales, from the solar system to clusters of galaxies. We found that any test body located inside a fractal structure with fractal dimension D = 2 experiences acceleration of the same order and confirmed the previous work that photons propagating through this structure decrease the frequency owing to gravitational redshift. The acceleration can be directed against the movement of the test body. The fractal distribution of the matter should be at scales of at least hundreds of megaparsecs to a few gigaparsecs for the existence of this acceleration.

• 천문학회지
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• 제48권1호
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• pp.21-55
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• 2015

If the Universe is dominated by cold dark matter and dark energy as in the currently popular ${\Lambda}CDM$ cosmology, it is expected that large scale structures form gradually, with galaxy clusters of mass $M{\geq}10^{14}M_{\odot}$ appearing at around 6 Gyrs after the Big Bang (z ~ 1). Here, we report the discovery of 59 massive structures of galaxies with masses greater than a few times $10^{13}M_{\odot}$ at redshifts between z = 0.6 and 4.5 in the Great Observatories Origins Deep Survey fields. The massive structures are identified by running top-hat filters on the two dimensional spatial distribution of magnitude-limited samples of galaxies using a combination of spectroscopic and photometric redshifts. We analyze the Millennium simulation data in a similar way to the analysis of the observational data in order to test the ${\Lambda}CDM$ cosmology. We find that there are too many massive structures (M > $7{\times}10^{13}M_{\odot}$) observed at z > 2 in comparison with the simulation predictions by a factor of a few, giving a probability of < 1/2500 of the observed data being consistent with the simulation. Our result suggests that massive structures have emerged early, but the reason for the discrepancy with the simulation is unclear. It could be due to the limitation of the simulation such as the lack of key, unrecognized ingredients (strong non-Gaussianity or other baryonic physics), or simply a difficulty in the halo mass estimation from observation, or a fundamental problem of the ${\Lambda}CDM$ cosmology. On the other hand, the over-abundance of massive structures at high redshifts does not favor heavy neutrino mass of ~ 0.3 eV or larger, as heavy neutrinos make the discrepancy between the observation and the simulation more pronounced by a factor of 3 or more.