• 천문학회지
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• 제35권2호
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• pp.75-85
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• 2002

We present N-body simulations of globular clusters including gravitational field of the Galaxy, in order to study effects of tidal field systematically on the shape of outer parts of globular clusters using NBODY6. The Galaxy is assumed to be composed of central bulge and outer halo. We mvestigate the cluster of multi-mass models with a power-law initial mass function (IMF) starting with different initial masses, initial number of particles, different slopes of the IMF and different orbits of the cluster. We have examined the general evolution of the clusters, the shape of outer parts of the clusters, density profiles and the direction of tidal tails. The density profiles appear to become somewhat shallower just outside the tidal boundary consistent with some observed data. The position angle of the tidal tall depends on the location in the Galaxy as well as the direction of the motion of. clusters. We found that the clusters become more elongated at the apogalacticon than at the pengalacticon. The tidal tails may be used to trace the orbital paths of globular clusters.

• 한국비블리아학회지
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• 제26권4호
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• pp.245-262
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• 2015

대학의 교양교과 주제가 다양한 영역으로 분화되고 복합적인 주제로 융합되면서 점차 교양교육의 주제를 파악하는 것이 어려워지고 있다. 이 연구의 목표는 A 대학의 교양교육과정으로 개설되어 있는 교과목의 주제적 영역을 계량정보학적으로 분석하여 시각화하는 것이다. 분석을 위하여 수집된 계획서는 총 214개이며 분석에 적용된 요소는 교과목명, 교과개요, 목표, 주별 수업계획이다. 분석 대상에서 추출된 주제어는 모두 278종이며 총 8개의 주제 클러스터로 군집화 되었다. 주제 클러스터간 관계를 네트워크기법으로 분석한 결과 개인적 영역, 사회적 영역으로 나뉘어지는 것으로 나타났다. 개인적 영역은 다시 14개 하위 주제 클러스터로, 사회적 영역은 11개 하위 주제 클러스터로 분류되었다. 개인적 영역에서는 '언어', '과학', '인성'이 주요 주제 클러스터로 파악되었고 사회적 영역에서는 '다문화' 주제 클러스터가 4개의 다른 주제 클러스터와 다각적인 관계를 맺고 있는 것으로 분석되었다. 주제 네트워크로 교양교과목의 주제 영역을 분석한 방법은 교양교육을 강화하고 개선하거나 대학도서관이 교양교육을 위한 장서개발을 하는데 필요한 기초자료를 생산하는 목적으로 활용될 수 있을 것이다.

• 천문학회지
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• 제52권5호
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• pp.145-158
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• 2019

We conducted a survey of open clusters within 1 kpc from the Sun using the astrometric and photometric data of the Gaia Data Release 2. We found 655 cluster candidates by visual inspection of the stellar distributions in proper motion space and spatial distributions in l - b space. All of the 655 cluster candidates have a well defined main-sequence except for two candidates if we consider that the main sequence of very young clusters is somewhat broad due to differential extinction. Cross-matching of our 653 open clusters with known open clusters in various catalogs resulted in 207 new open clusters. We present the physical properties of the newly discovered open clusters. The majority of the newly discovered open clusters are of young to intermediate age and have less than ~50 member stars.

• 천문학회지
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• 제26권1호
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• pp.47-64
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• 1993

The photometric evolution of cluster stars are examined for six synthetic clusters in the age range from $2.4\times10^6\;yr\;to\;7.6\times10^8yr$ by using the detailed evolutionary model calculation, and their results are compared with the observed integrated absolute magnitude and colors of 47 clusters. The reasonable agreements of the observed photometric parameters with the synthetic evolutionary sequences imply that there is a general form of time-dependent IMF including the noncoeval formation of stars and its detailed function is changed slightly with various environmental conditions of each primordial cloud.

• Bulletin of the Korean Chemical Society
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• 제3권2호
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• pp.50-55
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• 1982

A study of small water clusters composed of two to seven molecules has been performed by using the revised empirical potential function for conformational analysis (REPFCA). Various structures of clusters have been investigated and the relative probability of cluster per molecule is discussed. In general, cyclic structures of water clusters are more favorable than open structures. It is found that cyclic pentamer is the most favorable unit structure in the water cluster.

• 복식문화연구
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• 제13권1호
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• pp.18-33
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• 2005

The purposes of this study were to investigate the difference of the SCM activities in the general characteristics of fashion enterprises and to inquire out the general characteristics affecting the introduction of SCM. The characteristics of apparel manufactures were also compared through the cluster analysis of the SCM activity levels of apparel manufactures. Through questionnaire survey, a total af 214 data - 123 from 64 apparel manufacturers, 46 from 40 fabric suppliers and 45 from 4 retailers - were used for analysis. The analysis on the relation between the SCM activity levels and the general characteristics of fashion enterprises showed that the SCM activities were affected by product assortment pattern and SCM introduction level for fabric suppliers, production method, product assortment pattern, business type and SCM introduction level for apparel manufacturers, and SCM introduction level for retailers. The cluster characteristics related to the SCM activity levels of apparel manufacturers showed that the clusters with higher level were tending to doing business internationally and trying to manufacture in a small lot in variety. The higher level clusters also revealed relatively low in the occupation ratio of fashion goods and high in quick response ratio compared to the lower level clusters.

• 한국결정학회:학술대회논문집
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• 한국결정학회 2002년도 정기총회 및 추계학술연구발표회
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• pp.20-20
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• 2002

Based on experimental and theoretical analyses, we suggested a new possibility that the CVD diamond films grow not by the atomic unit but by the charged clusters containing a few hundreds of carbon atoms, which form spontaneously in the gas phase [J. Crysta] Growth 62 (1996) 55]. These hypothetical negatively-charged clusters were experimentally confirmed under a typical hot-filament diamond CVD process. Thin film growth by charged clusters or gas phase colloids of a few nanometers was also confirmed in Si and ZrO₂ CVD and appears to be general in many other CVD processes. Many puzzling phenomena in the CVD process such as selective deposition and nanowire growth could be explained by the deposition behavior of charged clusters. Charged clusters were shown to generate and contribute at least partially to the film deposition by thermal evaporation. Origin of charging at the relatively low temperature was explained by the surface ionization described by Saha-Langmuir equation. The hot surface with a high work function favors positive charging of clusters while that of a low work function favors negative charging.

• 천문학회지
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• 제32권1호
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• pp.7-16
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• 1999

Open clusters are useful tools to investigate the structure and evolution of the Galactic disk. We have started a long-term project to obtain UBVI CCD photometry of open clusters which were little studied before, using the Doyak 1.8 m telescope of Bohyunsan Optical Astronomy Observatory in Korea. The primary goals of this project are (1) to make a catalog of UBVI photometry of open clusters, (2) to make an atlas of open clusters, and (3) to survey and monitor variable stars in open clusters. Here we describe this project and report the first results based on preliminary analysis of the data on four open clusters in the survey sample: Be 14, Cr 74, Biu 9, and NGC 2355. Isochrone fitting of the color-magnitude diagrams of the clusters shows that all of them are intermediate age to old (0.3-1.6 Gyrs) open clusters with moderate metallicity.

• Advances in nano research
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• 제4권2호
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• pp.113-128
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• 2016

Luminescent metallic clusters have attracted great interest due to their unique optical, electronic and chemical features. Comparing with intensively studied Au and Ag Clusters, Cu clusters are superior in the aspects of cost and wide industrial demanding. However, tiny copper clusters are extremely prone to aggregate and undergo susceptibility of oxidation, thereby the synthesis of fluorescent zero valent copper clusters is rather challenging. In this review, synthetic strategies towards luminescent copper clusters, including macromolecule-protection and micro molecule-capping, have been systematically surveyed. Both "bottom-up" and "top-down" synthetic routes are found to be effective in fabricating luminescent copper clusters, some of which are quite stable and possess decent luminescence quantum yields. In general, the synthesis of fluorescent copper clusters remains at its infant stage. A great deal of effort on developing novel and economic synthetic routes to produce bright and stable copper clusters is highly expected in future.

• 천문학논총
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• 제30권2호
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• pp.267-268
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• 2015

One of the long-standing problems in modern astronomy is the curious division of globular clusters (GCs) into two groups, according to the mean period (<$P_{ab}$>) of type ab RR Lyrae variables. In light of the recent discovery of multiple populations in GCs, we suggest a new model explaining the origin of the Sandage period-shift and the difference in mean period of type ab RR Lyrae variables between the two Oosterhoff groups. In our models, the instability strip in the metal-poor group II clusters, such as M15, is populated by second generation stars (G2) with enhanced helium and CNO abundances, while the RR Lyraes in the relatively metal-rich group I clusters like M3 are mostly produced by first generation stars (G1) without these enhancements. This population shift within the instability strip with metallicity can create the observed period-shift between the two groups, since both helium and CNO abundances play a role in increasing the period of RR Lyrae variables. The presence of more metal-rich clusters having Oosterhoff-intermediate characteristics, such as NGC 1851, as well as of most metal-rich clusters having RR Lyraes with the longest periods (group III) can also be reproduced, as more helium-rich third and later generations of stars (G3) penetrate into the instability strip with further increase in metallicity. Therefore, although there are systems where the suggested population shift cannot be a viable explanation, for the most general cases, our models predict that RR Lyraes are produced mostly by G1, G2, and G3, respectively, for the Oosterhoff groups I, II, and III.