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박찬경 ( Chan Gyung Park ) 전북대학교 과학교육연구소 2013 과학과 과학교육 논문지 Vol.38 No.2
The recent observations of type la supernova, cosmic microwave background radiation, and large-scale structures suggest that our universe is currently under the acceleration due to the presence of unknown mysterious dark energy. In this paper, we use the Union2 type la supernova data set to estimate density parameters of ACDM model and investigate the variation of dark energy density over the direction on the whole sky. The result from our analysis shows that the estimated matter and dark energy density parameters are ΩM=0.07±0.16 and ΩA=0.31±0.24 in the direction of (l,b)□(160,-40) in Galactic coordinates while ΩM=0.51±0.16 and ΩA=1.16±0.24 in the direction of (l,b)□(340,0) with the biggest difference. However, considering large uncertainties in the estimated parameters, the two results are statistically consistent with each other. Therefore, we conclude that there is no spatial anisotropy of cosmic dark energy at least based on the current supernova data and the ACDM model.
박찬경 ( Chan Gyung Park ) 전북대학교 과학교육연구소 2012 과학과 과학교육 논문지 Vol.37 No.-
This paper reviews the basic knowledge of the Friedmann-Robertson-Walker (FRW) cosmological model which is known as the general relativistic model of homogeneous and isotropic universe. In the first part we derive the line element or the metric characterizing the geometrical property of the FRW model and obtain the evolution equations of the FRW model universe by applying this metric to the Einstein`s field equations. In the second part we discuss cosmological parameters redshift Hubble`s law distance and time scales and others that are useful for the extragalactic astronomy.
박찬경 ( Chan-gyung Park ) 전북대학교 과학교육연구소 2019 과학과 과학교육 논문지 Vol.44 No.1
A method of how to make star charts for mid-latitude observers on the Earth's northern and southern hemispheres is introduced. For this purpose, we describe in detail how to display on a star chart the equatorial coordinates of the stars listed in the Bright Star Catalog and how the observer’s field of view, the ecliptic plane, and the Galactic plane are represented mathematically using spherical trigonometry.
최대우도 추정자를 사용한 우주배경복사 온도요동의 각파워스펙트럼 측정법 소개
박찬경 ( Chan-gyung Park ) 전북대학교 과학교육연구소 2016 과학과 과학교육 논문지 Vol.41 No.1
This paper introduces the method of measuring the angular power spectrum of cosmic microwave background temperature fluctuations using the maximum likelihood estimator. For this purpose, a full derivation of the maximum likelihood quadratic estimator is presented and the signal-to-noise eigenmode analysis method is summarized.
박찬경 ( Chan-gyung Park ) 전북대학교 과학교육연구소 2016 과학과 과학교육 논문지 Vol.41 No.2
The homogeneity of matter distribution at large scales is the fundamental assumption of the standard cosmological model. This paper introduces the current status of research on homogeneity test of the matter distribution in the Universe. We describe the galaxy-counting method that is widely used in testing spatial homogeneity of large-scale structures, and criticize the previous studies that claim the homogeneity of matter distribution at scales larger than about 70 h<sup>-1</sup> Mpc by applying this method. Comparing the galaxy-counting results with the expectation of homogeneous distribution shows that the Universe is not spatially homogeneous even at 300 h<sup>-1</sup> Mpc scale and that Einstein's cosmological principle does not hold in the observed sky. Inhomogeneities in the matter distribution may explain the cosmic acceleration without dark energy and opens new field of research in theoretical cosmology.
유사-파워스펙트럼 추정자를 사용한 각파워스펙트럼 측정법 소개
박찬경 ( Chan-gyung Park ) 전북대학교 과학교육연구소 2017 과학과 과학교육 논문지 Vol.42 No.1
The angular power spectrum is a typical statistical quantity that describes the property of fluctuations on a sphere. For fluctuations observed on a partial region on the sphere, the spherical harmonic coefficients of the fluctuations are coupled together due to the geometrical effect of the survey region and thus the angular power spectrum is deformed into the pseudo-power spectrum. This paper introduces the method of measuring the angular power spectrum from the partial data of statistically isotropic fluctuations. For this purpose, we derive the mode-mode coupling of the angular power spectrum due to the limited survey region using the spherical harmonics and Wigner 3j symbols, and describe in detail how the corrected angular power spectrum is obtained from the pseudo-power spectrum.
전자회절 Kikuchi Pattern의 전산모사와 그 응용
이원범,박찬로,박찬경,천창환,Lee, Won-Beom,Park, Chan-Rho,Park, Chan-Gyung,Chun, Chang-Hwan 한국현미경학회 1994 Applied microscopy Vol.24 No.4
A computer program has been developed to analyze easily the Kikuchi pattern which is useful in obtaining the crystallographic data of materials. This program can simulate the Kikuchi patterns for 14 Bravais lattice by using the matrix algebra. Convenient menu system was also added to enhance the applications of the program. That is, by varying the tilting angle, camera length (RADIUS) and $S_{max}$ in the menu, various Kikuchi patterns can be obtained. The simulated patterns, then, can be compared with the experimentally-obtained Kikuchi pattern to examine validity of simulation.
Atom Probe Tomography를 이용한 나노 스케일의 조성분석: I. 이론과 설비
정우영,방찬우,구길호,박찬경,Jung, Woo-Young,Bang, Chan-Woo,Gu, Gil-Ho,Park, Chan-Gyung 한국현미경학회 2011 Applied microscopy Vol.41 No.2
Even though importance of nano-scale structure and compositional analysis have been getting increased, existing analysis tools have been reached to their limitations. Recent development of Atom Probe Tomography (APT), providing 3-dimensional elemental distribution and compositional information with sub-nm scale special resolution and tens of ppm detection limit, is one of key technique which can overcome these limitations. However, due to the fact that APT is not well known yet in the domestic research area, it has been rarely utilized so far. Therefore, in this article, the theoretical background of APT was briefly introduced with sample preparation to help understanding APT analysis. 최근 나노 영역에서의 구조분석과 조성분석의 중요성이 증대되고 있으나, 기존의 분석장비들은 한계에 부딪히고 있다. 최근 개발된 APT는 nm 이하의 공간분해능과 수십 ppm수준의 detection limit으로 원소의 3차원분포와 조성정보를 제공해 주는 분석장비로서, 이러한 기존 분석의 한계를 극복할 수 있는 새로운 분석장비이다. 그러나 국내에는 아직 잘 알려지지 않아 활용이 미비한 실정이다. 따라서, 본 논문에서는 APT에 대한 이해를 돕기 위해 APT분석의 원리와 시편준비에 대해 소개하였다.