• Journal of the Economic Geographical Society of Korea
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• v.16 no.3
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• pp.492-511
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• 2013

According to IASB(International Accounting Standards Board), R&D(Research and Development) is defined as a tertiary sector industry combining research and development. Many studies investigated R&D industry clusters in the form of high-tech cluster(Coe et al., 2007). However, these studies only generalized various spatial cluster of R&D industries. In particular, the studies could not considers cluster formation process over time lacking statistical significance in space-time perspectives. This study, therefore, indicates the limitation of recent R&D cluster literature which only considers either time or space. In addition, this study explores space-time clusters in R&D industry together with textile and cloth industry for comparison. Discovering the existence and location of clusters, this study utilized space-time K function and space-time scan statistics. The result shows that R&D industry presents significant clusters only in spatial dimension. No significant clusters were found in space-time dimension. However, textile and clothing industry presents significant clusters in both spatial and space-time dimensions.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.45.2-45.2
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• 2017

Using the latest cosmological hydrodynamic N-body simulations of groups and clusters, we study how location in phase-space coordinates at z = 0 can provide information on environmental effects acting in clusters. We confirm the results of previous authors showing that galaxies tend to follow a typical path in phase-space as they settle into the cluster potential. As such, different regions of phase-space can be associated with different times since first infalling into the cluster. However, in addition, we see a clear trend between total mass loss due to cluster tides and time since infall. Thus, we find location in phase-space provides information on both infall time and tidal mass loss. We find the predictive power of phase-space diagrams remains even when projected quantities are used (i.e.,line of sight velocities, and projected distances from the cluster). We provide figures that can be directly compared with observed samples of cluster galaxies and we also provide the data used to make them as supplementary data to encourage the use of phase-space diagrams as a tool to understand cluster environmental effects. We find that our results depend very weakly on galaxy mass or host mass, so the predictions in our phase-space diagrams can be applied to groups or clusters alike, or to galaxy populations from dwarfs up to giants.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.69.3-70
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• 2016

We study the orbital histories of Virgo galaxies undergoing different HI gas stripping stages using phase-space diagrams. Based on the HI properties of galaxies, we find that location of galaxies is in good agreement with ram-pressure stripping predicted by numerical simulations with different infall time. For example, galaxies experiencing active gas stripping are mostly found in the first infall region showing high velocity with respect to the cluster center. Meanwhile, most galaxies that are likely to have lost gas a while ago are found in the cluster outskirts with low orbital velocities. We also discuss the cases where observational properties of galaxies and their locations in the phase-space do not well agree. In addition, we probe the phase-space of filaments and subgroups around or within Virgo. Our results strongly suggest that substructures can play important roles in galaxy evolution while galaxies are falling to the cluster.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.40.1-40.1
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• 2019

We utilize times since infall of cluster galaxies obtained from Yonsei Zoom-in Cluster Simulation (YZiCS), the cosmological hydrodynamic N-body simulations, and star formation rates from the SDSS data release 10 to study how quickly late-type galaxies are quenched in the cluster environments. In particular, we confirm that the distributions of both simulated and observed galaxies in phase-space diagrams are comparable and that each location of phase-space can provide the information of times since infall and star formation rates of cluster galaxies. Then, by limiting the location of phase-space of simulated and observed galaxies, we associate their star formation rates at z ~ 0.08 with times since infall using an abundance matching technique that employs the 10 quantiles of each probability distribution. Using a flexible quenching model covering different quenching scenarios, we find the star formation history of satellite galaxies that best reproduces the obtained relationship between time since infall and star formation rate at z ~ 0.08. Based on the derived star formation history, we constrain the quenching timescale (2 - 7 Gyr) with a clear stellar mass trend and confirm that the refined model is consistent with the "delayed-then-rapid" quenching scenario: the constant delayed phase as ~ 2.3 Gyr and the quenching efficiencies (i.e., e-folding timescale) outside and inside clusters as ~ 2 - 4 Gyr (${\propto}M_*^{-1}$) and 0.5 - 1.5 Gyr (${\propto}M_*^{-2}$), Finally, we suggest: (i) ram-pressure is the main driver of quenching of satellite galaxies for the local Universe, (ii) the quenching trend on stellar mass at z > 0.5 indicates other quenching mechanisms as the main driver.

• Publications of The Korean Astronomical Society
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• v.19 no.1
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• pp.77-81
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• 2004

A high performance computing cluster for astronomical computations has been built at Korea Astronomy Observatory. The 64 node cluster interconnected with Gigabit Ethernet is composed of 128 Intel Xeon processors, 160 GB memory, 6 TB global storage space, and an LTO (Linear Tape-Open) tape library. The cluster was installed and has been managed with the Open Source Cluster Application Resource (OSCAR) framework. Its performance for parallel computations was measured with a three-dimensional hydrodynamic code and showed quite a good scalability as the number of computational cells increases. The cluster has already been utilized for several computational research projects, some of which resulted in a few publications, even though its full operation time is less than one year. As a major resource of the $K^*Grid$ testbed, the cluster has been used for Grid computations, too.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.10
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• pp.728-737
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• 2019

In this study, the minimized on-board computer (OBC) module for integrated navigation is developed, which provides satellites' relative position information in formation flying and cluster operation situations. The scalability is considered to apply the user-selected wireless communication module and Global Positioning System (GPS) receiver for navigation, while considering to meet the structural design standard of nano-satellites. As a result of the product development and production, the processing speed of integrated navigation and real-time data synchronization is satisfied for cluster operation nano-satellites by using micro controller unit (MCU). From a heat/vacuum, vibration and radiation test, the OBC was confirmed to be operated in space environments. From these results, a mass production system of OBC was made which is a key part of development on satellite formation flying and cluster/constellation missions that the community demands are increasing.

• Journal of The Korean Astronomical Society
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• v.46 no.4
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• pp.173-181
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• 2013

We trace the dynamical evolution of dark matter (DM) content in NGC 6397, one of the native Galactic globular clusters (GCs). The relatively strong tidal field (Galactocentric radius of ~ 6 kpc) and short relaxation timescale (~0.3 Gyr) of the cluster can cause a significant amount of DM particles to evaporate from the cluster in the Hubble time. Thus, the cluster can initially contain a non-negligible amount of DM. Using the most advanced Fokker-Planck (FP) method, we calculate the dynamical evolution of GCs for numerous initial conditions to determine the maximum initial DM content in NGC 6397 that matches the present-day brightness and velocity dispersion profiles of the cluster. We find that the maximum allowed initial DM mass is slightly less than the initial stellar mass in the cluster. Our findings imply that NGC 6397 did not initially contain a significant amount of DM, and is similar to that of NGC 2419, the remotest and the most massive Galactic GC.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.121-121
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• 2011

Thanks to KMTNet's wide field of view, it is time to implement imaging survey of extensive area of clusters of galaxies in the southern sky with modern instrument. As part of potential long-term survey of nearby (D < 50 Mpc) well-known clusters of galaxies, we propose a wide-field and deep survey of Fornax cluster as a first step of the project. By imaging the 400 square deg region (100 fields) enclosed within the five times virial radius of the Fornax cluster, in three SDSSfilters(g', r', i'), we can provide an unprecedented view of structure of Fornax cluster using sample from giant to dwarf galaxies. We will secure galaxies with brightness comparable to the limiting magnitude (r'=23.1 AB mag) of SDSS. Furthermore, we also request extremely deep (limiting surface brightness of ~ 28 mag $arcsec^{-2}$forr'band) survey for the central region (16 square degree, i.e., four fields) of Fornax cluster. This will allow us to detect the diffuse intracluster light (ICL) that permeates clusters as a valuable tool for studying the hierarchical nature of cluster assembly. In order to complete whole survey, about 285 hr observing time (without overhead) is required. By combining data available at other wavelengths, it will offer unique constraints on the formation of large-scale structure and also provide important clues for theories of galaxy formation and evolution. Our proposed survey will be implemented in the close collaboration with researchers in various countries (Germany, Australia, UK, USA) and ongoing project (e.g., SkyMapper).

• The Bulletin of The Korean Astronomical Society
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• v.43 no.2
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• pp.38.2-38.2
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• 2018

To understand the assembly of the galaxy population in clusters today, it is important to first understand preprocessing, the impact of environments prior to cluster infall. We use 15 cluster samples from YZiCS, a hydrodynamic cluster zoom-in simulation to determine the significance of preprocessing, and focus on the tidal mass loss of dark matter halos. We find ~48% of the cluster member halos were once satellites of another host. The preprocessed fraction depends on each cluster's recent mass growth history. Also, we find that the total mass loss is a clear function of the time spent in a host. However, two factors can increase the mass loss rate considerably. First, if the satellite mass is approaching the mass of its host. Second, when the halo suffers tidal mass loss at a higher redshift. Being in hosts before cluster infall enables halos to experience tidal mass loss for an extended period of time.

• The Journal of the Korea Contents Association
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• v.8 no.2
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• pp.18-26
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• 2008

This paper presents a phased visualization method of facial expression space that enables the user to control facial expression of 3D avatars by select a sequence of facial frames from the facial expression space. Our system based on this method creates the 2D facial expression space from approximately 2400 facial expression frames, which is the set of neutral expression and 11 motions. The facial expression control of 3D avatars is carried out in realtime when users navigate through facial expression space. But because facial expression space can phased expression control from radical expressions to detail expressions. So this system need phased visualization method. To phased visualization the facial expression space, this paper use fuzzy clustering. In the beginning, the system creates 11 clusters from the space of 2400 facial expressions. Every time the level of phase increases, the system doubles the number of clusters. At this time, the positions of cluster center and expression of the expression space were not equal. So, we fix the shortest expression from cluster center for cluster center. We let users use the system to control phased facial expression of 3D avatar, and evaluate the system based on the results.