• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.40.2-40.2
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• 2013

Although galaxy mergers are thought to play an important role in forming elliptical galaxies, mergers in galaxy clusters have drawn less attention compared to mergers in field environments because galaxies with high peculiar velocities are unlikely to merge with each other. However, comparable fractions of merger features in cluster galaxies have been reported from deep imaging of Abell clusters, suggesting the relevance of mergers in the transformation of cluster early-type galaxies (Sheen et al. 2012). As a more direct approach to understanding the origin of tidal features in clusters, we perform hydrodynamic re-simulations on a cluster of galaxies. Based on mock observation images of the simulated cluster galaxies, we construct and analyze the cluster early-type galaxy sample in a consistent manner with Sheen et al. 2012. We find that the fraction of tidal feature from the simulated cluster is comparable to that of the observation. Evolutionary history of the galaxies with merger features shows that most of the mergers responsible for the merger features in the present originate from outside the cluster more than 2Gyrs ago. We also find that many of the galaxies with tidal features show correlations with subgroups in the cluster. All these results suggest that merger features in the cluster are due to preprocessing before accretion into the cluster.

• The Korean Journal of Applied Statistics
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• v.24 no.2
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• pp.393-400
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• 2011

In a large scale survey, cluster sampling design in which a set of observation units called clusters are selected is often used to satisfy practical restrictions on time and cost. Especially, a two stage cluster sampling design is preferred when a strong intra-class correlation exists among observation units. The sample Primary Sampling Unit(PSU) and Secondary Sampling Unit(SSU) size for a two stage cluster sample is determined by the survey cost and precision of the estimator calculated. For this study, we derive the optimal sample PSU and SSU size when the population SSU size across the PSU are di erent by extending the result obtained under the assumption that all PSU have the same number of SSU. The results on the sample size are then applied to the $4^{th}$ Korea Hospital Discharge results and is compared to the conventional method. We also propose the optimal sample SSU (discharged patients) size for the $7^{th}$ Korea Hospital Discharge Survey.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.22 no.4
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• pp.214-218
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• 1989

SEM observation revealed that the gastric mill of Nyctiphanes australis consists of paired cluster spines and paired lateral teeth, while the filter-press is absent. The morphology of the gastric mill was extremely constant; the numbers of both setiform processes of cluster spines and serrated spines of lateral teeth increased with increasing body length. The cluster spines of N. australis consisted of a single row of stout setiform processes but the lateral teeth comprised a large projection with small serrated spines. The cluster spines are symmetrical in setiform process distribution, however, the lateral teeth are asymmetrical in number of serrated spines.

• Journal of Astronomy and Space Sciences
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• v.36 no.1
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• pp.1-9
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• 2019

In this paper we present analysis of current density when the Cluster spacecraft pass the nightside auroral region at about $4-5R_E$ from the center of Earth. The analysis is made when the inter-spacecraft separation is within 200 km, which allows all four spacecraft to be situated inside the same current sheet. On 22 February 2002, two field-aligned current (FAC) events were observed in both the southern and the northern hemispheres. The FACs were calculated with magnetic field data obtained by the four spacecraft using the Curlometer method. The scales of the FACs along the spacecraft trajectory and the magnitudes were hundreds of kilometers and tens of $nA/m^2$, respectively, and both events were mapped to the auroral region in the ionosphere. We also examined reliability of the results with some parameters, and found that our results are adequately comparable with other studies. Nevertheless, some limitations that decrease the accuracy of current estimation exist.

• The Korean Journal of Applied Statistics
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• v.25 no.3
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• pp.447-456
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• 2012

For a sensitive survey in which the population is comprised of several clusters with a quantitative attribute, we present an additive quantitative randomized response model by cluster sampling that adapts a two-stage cluster sampling instead of a simple random sample based on Himmelfarb-Edgell's additive quantitative attribute model and Gjestvang-Singh's one. We also derive optimum values for the number of 1st stage clusters and the optimum values of observation units in a 2nd stage cluster under the condition of minimizing the variance given constant cost. We can see that Himmelfarb-Edgell's model is more efficient than Gjestvang-Singh's model under the condition of cluster sampling.

• The Bulletin of The Korean Astronomical Society
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• v.24 no.2
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• pp.24-24
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• 1999

• Journal of The Korean Astronomical Society
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• v.34 no.3
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• pp.143-147
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• 2001

UBVI CCD photometry of open cluster NGC 2324 is presented. C-M diagrams of this cluster show well-defined main sequence with a red giant clump centered at B - V =1.05, V =13.45. We derived the major cluster characteristics; E(B - V)=0.17$\pm$0.12 from color-color diagram and mean color of red giant clump stars, (m - M)o=13.1$\pm$0.1 from zero age main sequence fitting, and [Fe/H]$\~$-0.32 from comparison the theoretical model developed by Bertelli et al. (1994) to the observed C-M diagrams. We estimate the age of NGC 2324 to be log t$\~$8.8 by applying isochrone fitting and morphological age index method.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.41.1-41.1
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• 2017

We present weak-lensing analysis of the merging galaxy cluster Abell 115 at z=0.197 based on Subaru i and V band images. As merging clusters often show, Abell 115's merging signatures include radio relics, double X-ray peaks, and large offsets between the cluster member galaxies and the X-ray distributions. A weak-lensing study provides underlying dark matter distribution, the key information to determine the complex merging scenario of the cluster. In this work, we present 2D mass reconstruction of the cluster, which reveals two distinct mass peaks consistent with galaxy distributions. We measure the first weak-lensing mass of each subcluster. Our weak-lensing total mass estimate is a few factors lower than the published dynamical mass obtained from velocity dispersion. This large mass discrepancy may be attributed to a significant departure from dynamical equilibrium. We also re-analyze the archival chandra data and find that the result is consistent with weak-lensing mass.

• Journal of The Korean Astronomical Society
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• v.38 no.4
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• pp.371-384
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• 2005

Self-referencing method in revised-OTFTOOL is a new method in On-The-Fly(OTF) observation mode. It uses the source free regions of the observed frame as references instead of the OFFs references. We already analyzed and discussed its proprieties and advantages in the previous paper. In this paper, we make a statistical study about the self-referencing method by applying it to OTF mapping data of 27 Virgo spiral galaxies. We found that the self-referencing method solves the crooked baseline problem for every datacube. It straightens the baseline, and conserves the emissions. Compared with other data processing, the median filtering task 'mwflt' in AIPS, to use self-referencing method is more effective and safe not only to straighten the baseline but also to conserve the emission. For the strong CO galaxies, the data obtained by self-referencing method shows scarcely any difference from those reduced by conventional OFFs references and AIPS median filtering in the range of uncertainties. Undetected CO emissions in datacubes of conventional OFFs references are also not detected in those of self-referencing method. The self-referencing method is expected to save the observing time and simplify data reduction processes. Besides this, using self-referencing method will offer emission-free references more safely.

• Journal of Environmental Science International
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• v.19 no.10
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• pp.1229-1235
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• 2010

Three meteor-statistical forecasting models - the transfer function model, the time-series autoregressive model and the neural networks model - were tested to develop a daily forecasting model for Jejudo, where the need and demand for wind power forecasting has increased. All the meteorological observation sites in Jejudo have been classified into 6 groups using a cluster analysis. Four pairs of observation sites among them, all having strong wind speed correlation within the same meteorological group, were chosen for a model test. In the development of the wind speed forecasting model for Jejudo, it was confirmed that not only the use a wind dataset at the objective site itself, but the introduction of another wind dataset at the nearest site having a strong wind speed correlation within the same group, would enhance the goodness to fit of the forecasting. A transfer function model and a neural network model were also confirmed to offer reliable predictions, with the similar goodness to fit level.