• The Bulletin of The Korean Astronomical Society
• /
• v.43 no.1
• /
• pp.62.1-62.1
• /
• 2018

Galaxies in the cluster environment interact with the intracluster medium (ICM), losing the interstellar medium (ISM) and alternating their evolution. Observational evidences of the extraplanar ISM stripped by the ICM's ram pressure are prevalent in HI imaging studies of cluster galaxies. However, current theoretical understanding of the ram pressure stripping (or ICM-ISM interaction in general) is still limited mainly due to the lack of numerical resolution at ISM scales in large-scale simulations. Especially, self-consistent modeling of the turbulent, multiphase ISM is critical to understand star formation in galaxies interacting with the ICM. To achieve this goal, we utilize the TIGRESS simulation suite, simulating a local patch of galactic disks with high resolution to resolve key physical processes in the ISM, including cooling/heating, self-gravity, MHD, star formation, and supernova feedback. We then expose the ISM disk to ICM flows and investigate the evolution of star formation rate and the properties of the ISM. By exploring ICM parameter space, we discuss an implication of the simple ram pressure stripping condition (so called the Gunn-Gott condition) to the realistic ISM.

• The Bulletin of The Korean Astronomical Society
• /
• v.39 no.1
• /
• pp.48.1-48.1
• /
• 2014

Galaxy clusters, the largest gravitationally bound systems, are an important means to place constraints on cosmological models. Moreover, they are excellent places to test galaxy evolution models in connection to the environments. To this day, massive clusters have been found unexpectedly(Kang & Im 2009, Durret et al. 2011, Tashikawa et al. 2012) and evolution of galaxies in cluster have been still controversial (Elbaz et al. 2007, Cooper et al. 2008, Tran et al. 2009). Finding galaxy cluster candidates at z>1 in a wide, deep imaging survey data will enable us to solve the such issues of modern extragalactic astronomy. We report new candidates of galaxy clusters and their physical properties in one of the wide and deep survey fields, European Large Area ISO Survey North1(ELAIS-N1) and North2(ELAIS-N2) fields, covering sky area of and each. We also suggest a new useful color selection technique to separate 1 < z < 2 galaxies from low-z galaxies by combining multi-wavelength data from the UKIRT Infrared Deep Sky Survey Deep Extragalactic Survey (UKIDSS DXS/J and K band), Spitzer Wise-area InfraRed Extragalactic survey (SWIRE/two mid-infrared bands), Canada France Hawaii Telescope (CFHT/z band), Issac Newton Telescope(INT/ u, g, r, i, z band) and Infrared Medium-deep Survey(IMS/J band).

• Smart Structures and Systems
• /
• v.18 no.3
• /
• pp.525-540
• /
• 2016

The CFRP-confined circular concrete-filled steel tubular column is composed of concrete, steel, and CFRP. Its failure mechanics are complex. The most important difficulties are lack of an available method to establish a relationship between a specific damage mechanism and its acoustic emission (AE) characteristic parameter. In this study, AE technique was used to monitor the evolution of damage in CFRP-confined circular concrete-filled steel tubular columns. A fuzzy c-means method was developed to determine the relationship between the AE signal and failure mechanisms. Cluster analysis results indicate that the main AE sources include five types: matrix cracking, debonding, fiber fracture, steel buckling, and concrete crushing. This technology can not only totally separate five types of damage sources, but also make it easier to judge the damage evolution process. Furthermore, typical damage waveforms were analyzed through wavelet analysis based on the cluster results, and the damage modes were determined according to the frequency distribution of AE signals.

• The Bulletin of The Korean Astronomical Society
• /
• v.44 no.2
• /
• pp.39.3-39.3
• /
• 2019

Ram pressure stripping due to the intracluster medium (ICM) is an important environmental process, which causes star formation quenching by effectively removing cold interstellar gas from galaxies in dense environments. The evidence of diffuse atomic gas stripping has been reported in several HI imaging studies. However, it is still under debate whether molecular gas (i.e., a more direct ingredient for star formation) can be also affected and/or stripped by ram pressure. The goal of this thesis is to understand the impact of ram pressure on the molecular gas content of cluster galaxies and hence star formation activity. To achieve this, we conducted a series of detailed studies on the molecular gas properties of three Virgo spiral galaxies with clear signs of active HI gas stripping (NGC 4330, NGC 4402, and NGC 4522) based on high-resolution CO data obtained from the Submillimeter Array (SMA) and Atacama Large Millimeter/submillimeter Array (ALMA). As a result, we find the evidence that the molecular gas disk also gets affected by ram pressure in similar ways as HI even well inside of the stellar disk. In addition, we detected extraplanar 13CO clumps in one of the sample, which is the first case ever reported in ram pressure stripped galaxies. By analyzing multi-wavelength data (e.g., Hα, UV, HI, and CO), we discuss detailed processes of how ram pressure affects star formation activities and hence evolution of cluster galaxies. We also discuss the origin of extraplanar 13CO, and how ram pressure can potentially contribute to the chemical evolution of the ICM.

• The Bulletin of The Korean Astronomical Society
• /
• v.46 no.1
• /
• pp.31.3-32
• /
• 2021

We quantify the relative role of galaxy environment and bar presence on AGN triggering in face-on spiral galaxies using a volume-limited sample with 0.02 < z < 0.055, Mr < 19.5, and σ > 70 km s-1 selected from Sloan Digital Sky Survey (SDSS) Data Release 7. To separate their possible entangled effects, we divide the sample into bar and non-bar samples, and each sample is further divided into three environment cases of isolated galaxies, interacting galaxies with a pair, and cluster galaxies. The isolated case is used as a control sample. For these six cases, we measure AGN fractions at a fixed central star formation rate and central velocity dispersion, σ. We demonstrate that the internal process of the bar-induced gas inflow is more efficient in AGN triggering than the external mechanism of the galaxy interactions in groups and cluster outskirts. The significant effects of bar instability and galaxy environments are found in galaxies with a relatively less massive bulge. We conclude that from the perspective of AGN-galaxy coevolution, a massive black hole is one of the key drivers of spiral galaxy evolution. If it is not met, a bar instability helps the evolution, and in the absence of bars, galaxy interactions/mergers become important. In other words, in the presence of a massive central engine, the role of the two gas inflow mechanisms is reduced or almost disappears. We also find that bars in massive galaxies are very decisive in increasing AGN fractions when the host galaxies are inside clusters.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.38A no.3
• /
• pp.277-288
• /
• 2013

3GPP LTE-Advanced (Third Generation Partnership Project Long Term Evolution-Advanced) as a next generation mobile communication standard introduced small base stations such as femto cells or pico cells, and D2D (Device-to-Device) communications between mobiles in the proximity in order to satisfy the needs of rapidly growing wireless data traffic. A diverse range of topics has been studied to solve various interference situations which may occur within a single cell. In particular, an introduction of a small base station along with D2D communication raises important issues of how to increase the channel capacity and frequency efficiency in HetNets (Heterogeneous Networks). To this end, we propose in this paper methods to manage the interference between the macro cell and other small cells in the HetNet to improve the frequency efficiency. The proposed CCN (Cluster Coordinator Node)-assisted ICI (Inter-Cell Interference) avoidance methods exploit the CCN to control the interference in HetNet comprising of an MeNB (Macro enhanced Node-B) and a large number of small cells. A CCN which is located at the center of a number of small cells serves to avoid the interference between macro cell and small cells. We propose methods of resource allocation to avoid ICI for user equipments within the CCN coverage, and evaluate their performance through system-level computer simulations.

• Journal of Technology Innovation
• /
• v.13 no.2
• /
• pp.23-43
• /
• 2005

Industrial clusters are geographical concentrations of interconnected companies, specialised suppliers, service providers, firms in related industries, and associated institutions (for example, universities, standard agencies, and trade associations) that combine to create new products and/or services in specific lines of business. At present, the concept of industrial cluster becomes very popular worldwide, policy makers at national, regional and local levels and business people in both forerunner and latecomer countries are keen to implement the cluster concept as an economic development model. Though understanding of clusters and related promoting policies varies from one place to another, the underlying benefits of clusters from collective learning and knowledge spillovers between participating actors strongly attract the attention of these people. In Thailand, a latecomer country in terms of technological catching up, the cluster concept has been used as a means to rectify weakness and fragmentation of its innovation systems. The present Thai government aspires to apply the concept to promote both high-tech manufacturing clusters, services clusters and community-based clusters at the grass-root level. This paper analyses three very different clusters in terms of technological sophistication and business objectives, i.e., hard disk drive, software and chili paste. It portrays their significant actors, the extent of interaction among them and the evolution of the clusters. Though are very dissimilar, common characteristics attributed to qualified success are found. Main driving forces of the three clusters are cluster intermediaries. Forms of these organizations are different from a government research and technology organization (RTO), an industrial association, to a self-organised community-based organization. However, they perform similar functions of stimulating information and knowledge sharing, and building trust among participating firms/individuals in the clusters. Literature in the cluster studies argues that government policies need to be cluster specific. In this case, the best way to design and implement cluster-specific policies is through working closely with intermediaries and strengthening their institutional especially in linking member firms/individuals to other actors in clusters such as universities, government R&D institutes, and financial institutions.

• The Bulletin of The Korean Astronomical Society
• /
• v.42 no.1
• /
• pp.49.2-49.2
• /
• 2017

Star forming dwarf galaxies in various environments are attractive objects for investigating the environmental effects on chemical evolution of dwarf galaxies. Using SDSS DR7 spectroscopic data and GALEX ultraviolet (UV) imaging data, we study the chemical properties of star forming dwarf galaxies in various environments of the Virgo cluster, Ursa Major group, and field. We derived gas-phase abundance, galaxy mass, and UV specific star formation rate (sSFR) of subsample, early-type (ETD) and late-type star forming dwarf (LTD) galaxies, which are divided by visually classified galaxy morphology. We found no O/H enhancement of LTDs in cluster and group environments compared to the field, implying no environmental dependence of the mass-metallicity relation for LTDs. LTDs in the Virgo cluster and Ursa Major group have similar sSFR at a given galaxy mass, but they exhibit systematically lower sSFR than those in isolated field environment. We suggest that LTDs in the Virgo cluster are an infalling population that was recently accreted from the outside of the cluster. We found that ETDs in the Virgo cluster and Ursa Major group exhibit enhanced O/H compared to those in the field. However, no distinct difference of N/O of galaxies between different environments. The chemically evolved ETDs in the Virgo cluster and Ursa Major group also show similar mass-sSFR relation, but systematically lower sSFR at a fixed galaxy mass compared to the field counterparts. We suggest that ETDs in the Virgo cluster and Ursa Major group have evolved under the similar local environments. We also discuss the evolutionary path of ETDs and LTDs with respect to the environmental effects of ram pressure stripping and galaxy interaction/merging.

• Publications of The Korean Astronomical Society
• /
• v.30 no.2
• /
• pp.521-523
• /
• 2015

The Milky Way did not form in isolation, but is the product of a complex evolution of generations of mergers, collapses, star formation, supernovae and collisional heating, radiative and collisional cooling, and ejected nucleosynthesis. Moreover, all of this occurs in the context of the cosmic expansion, the formation of cosmic filaments, dark-matter haloes, spiral density waves, and emerging dark energy. This paper summarizes a review of recent attempts to reconstruct this complex evolution. We compare simulated properties with various observed properties of the Local Group. Among the generic features of simulated systems is the tendency for galactic halos to form within the dark matter filaments that define a supergalactic plane. Gravitational interaction along this structure leads to a streaming flow toward the two dominant galaxies in the cluster. We analyze this alignment and streaming flow and compare with the observed properties of Local-Group galaxies. Our comparison with Local Group properties suggests that some dwarf galaxies in the Local Group are part of a local streaming flow. These simulations also suggest that a significant fraction of the Galactic halo formed at large distances and arrived later along these streaming flows.

• International Journal of Advanced Culture Technology
• /
• v.10 no.4
• /
• pp.569-575
• /
• 2022

This is a research thesis on the development of a monitoring and diagnosis device that prevents the risk of an accident through monitoring and diagnosis of a modular Main Circuit Breaker (MCB) using Vacuum Interrupter (VI) for Korean high-speed rolling stock. In this paper, a comprehensive MCB monitoring and diagnosis was performed by converging vacuum level diagnosis of interrupter, operating coil monitoring of MCB and environmental temperature/humidity monitoring of modular box. In addition, to develop an algorithm that is expected to have a similar data processing before the actual field test of the MCB monitoring and diagnosis device in 2023, the cluster analysis and factor analysis were performed using the WEKA data mining technique on the big data of Korean railroad transformer, which was previously researched by Tae Hee Evolution with KORAIL.