• The Bulletin of The Korean Astronomical Society
• /
• v.44 no.2
• /
• pp.76.1-76.1
• /
• 2019

After the first identification of electromagnetic counterpart of gravitational wave source (GW170817), era of multi-messenger astronomy has begun. For specifying coordinate, magnitude, and host galaxy information, optical follow-up observation of GW source becomes important. The O3 run of LIGO / VIRGO started after April 2019. We present searching strategy of GW optical counterpart using the KMTNet. By performing tiling observation of high probability area in GW localization map, we expect to observe early light-curve of GW optical counterpart. We will also present observation result for three gravitational wave events of binary black hole mergers. After identification of optical counterpart, we will study collision mechanism, progenitor, and characteristics of host galaxy using observation data of GW source.

• Korean Journal of Mathematics
• /
• v.23 no.3
• /
• pp.479-489
• /
• 2015

We study the GMGHS spacetime to analyze anisotropic cosmology model which represents homogeneous but anisotropically expanding(contracting)cosmology. In this paper we investigate the solution of GMGHS spacetime in form of doubly warped products possessing warping functions and find the Ricci curvature associated with three phases in the evolution of the universe.

• The Bulletin of The Korean Astronomical Society
• /
• v.34 no.1
• /
• pp.190.2-190.2
• /
• 2009

• Trans-
• /
• v.12
• /
• pp.173-222
• /
• 2022

This thesis examines the 'universe' acceptance phenomenon, currently used as a content strategy in the K-pop field, from the perspective of K-pop audiences, and then attempts to identify their experience of acceptance and the meaning of the universe. For this, tweets related to the universe acceptance experience of Aespa, the group utilizing the universe as a content strategy the most actively, were collected, and this data was analyzed according to a phenomenological approach, an approach to explore the structure of personal experience and the essence of a phenomenon. As a result of analyzing using Moustakas' method, the semantic structure of the universe acceptance phenomenon of K-pop audiences was derived based on 21 thematic units. It was found that current K-pop audiences are experiencing active cultural consumption rather than unilateral or passive through acceptance of the universe. This means that K-pop audiences have the characteristics of active audiences that produce meaning, interact with other fans, and exert influence on outside of community. At the same time, these characteristics affect acceptance of the universe. Simultaneously, through active acceptance experience, it is found that K-pop audiences give a new meaning in the K-pop universe, as "marketing assets", "fandom community assets", and "K-pop industry expansion assets." Among them, the recognition of 'marketing assets' was reaffirmed as a basis for supporting related previous studies. In addition, it derived the new values of the universe in the K-pop field by discovering the meaning of "fandom's specific assets" and "assets of the K-pop industry for expansion". These meanings had not been found that previous studies from the producers' point of view. And then, for the purpose of expanding the value of the universe in the future, it was discussed the direction of the new meaning of the universe. Finally, this study is meaningful in that it revealed the semantic structure of the universe acceptance phenomenon and discovered a new meaning of the universe in the K-pop field. Additionally, it was intended to contribute to expanding the field of research by suggesting various follow-up studies from various perspectives.

• The Bulletin of The Korean Astronomical Society
• /
• v.39 no.2
• /
• pp.37-37
• /
• 2014

Magnetic fields appear to be ubiquitous in astrophysical environments. The existence of magnetic fields in the large-scale structure of the universe has been established through observations of Faraday rotation and synchrotron emission, as well as through recent gamma-ray observations. Yet, the nature and origin of the magnetic fields remains controversial and largely unknown. In this talk, I briefly summarize recent developments in our understanding of the nature and origin of magnetic fields. I also describe a plausible scenario for the origin of the magnetic fields; seed fields were created in the early universe and subsequently amplified during the formation of the large-scale structure of the universe. I then discuss the prospect of observation of magnetic fields in the large-scale structure of the universe.

• The Bulletin of The Korean Astronomical Society
• /
• v.40 no.1
• /
• pp.45.1-45.1
• /
• 2015

Galaxy clusters have provided important information to understand the evolution of the universe, since the number density and mass of clusters are tightly related to the cosmological parameters. In addition, galaxy clusters are an excellent laboratory to investigate the galaxy evolution in dense environments. However, finding galaxy clusters at high redshift ($z{\geq}1$) still remains as a main subject in astronomy due to their rareness and difficulty in identifying such objects from optical imaging data alone. Here, we report a spectroscopic follow-up observation of distant galaxy cluster candidates identified by a deep optical-NIR dataset of Infrared Medium-deep Survey. Through the galaxy spectra taken with the IMACS instrument on the Magellan telescope, we confirm at least 3 massive clusters at z~0.92. Interestingly, the maximum spatial separation between these clusters is ~8Mpc, which implies that this system is a new supercluster in the distant universe. We also discuss properties of galaxies in these clusters based on multi-wavelength photometric data.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.11 no.4
• /
• pp.2292-2309
• /
• 2017

Ciphertext policy attribute-based encryption (CP-ABE) is a useful cryptographic technology for guaranteeing data confidentiality but also fine-grained access control. Typically, CP-ABE can be divided into two classes: small universe with polynomial attribute space and large universe with unbounded attribute space. Since the learning with errors over rings (R-LWE) assumption has characteristics of simple algebraic structure and simple calculations, based on R-LWE, we propose a small universe CP-ABE scheme to improve the efficiency of the scheme proposed by Zhang et al. (AsiaCCS 2012). On this basis, to achieve unbounded attribute space and improve the expression of attribute, we propose a large universe CP-ABE scheme with the help of a full-rank differences function. In this scheme, all polynomials in the R-LWE can be used as values of an attribute, and these values do not need to be enumerated at the setup phase. Different trapdoors are used to generate secret keys in the key generation and the security proof. Both proposed schemes are selectively secure in the standard model under R-LWE. Comparison with other schemes demonstrates that our schemes are simpler and more efficient. R-LWE can obtain greater efficiency, and unbounded attribute space means more flexibility, so our research is suitable in practices.

• The Bulletin of The Korean Astronomical Society
• /
• v.44 no.1
• /
• pp.75.1-75.1
• /
• 2019

The universe has been ionized in the post-reionization by several photon contributors. The dominant source to produce the hydrogen ionizing photons is not revealed so far. Faint quasars have been expected to generate UV photon budgets required to maintain ionization state of universe. Observational limits, however, hinder to discover them despite their higher number density than bright one. Consequently, the influence of faint quasars on post-reionization are not considered sufficiently. Therefore, a survey to find faint quasars at z ~ 5 is crucial to determine the main ionizing source in the post-reionization era. Deep images from the Hyper Suprime-Cam Subaru Strategic Program (HSC SSP) allow us to search for quasar swith low luminosities in the ELAIS-N1 field. J band information are obtained by the Infrared Medium-deep Survey (IMS) and the UKIRT Infrared Deep Sky Survey (UKIDSS) - Deep ExtragalacticSurvey (DXS). Faint quasar candidates were selected from several multi-band color cut criteria based on simulated quasars on color-color diagram. To choose the reliable candidates with possible Lyman break, we have performed medium-bands observations. Whether a candidate is a quasar or a dwarf star contamination was decided by results from chi-square minimization of quasar/dwarf model fitting. Spectroscopic follow-up observations confirm three quasars at z ~ 5. 100% spectral confirmation success rate implies that the medium-band observations effectively select faint quasars with strong Lyman alpha emission.

• The Bulletin of The Korean Astronomical Society
• /
• v.45 no.1
• /
• pp.36.2-36.2
• /
• 2020

Intensive Monitoring Survey of Nearby Galaxies (IMSNG) has been managed over 6 years. It aimed to constrain the progenitor system and explosion mechanism of SNe by detection of very early signal from shock heated emission. We have conducted monitoring observation of nearby bright galaxies those were carefully selected using global network of 1-m class telescopes. More than 20 SNe have occured in our target fields. As One of result of the survey, we present light curve analysis of type Ia SN 2018kp, which was discovered in NGC 3367. Based on photometric analysis, we calculated explosion parameters and set constraints of physical conditions of this supernova. We compared the results with theoretical model progenitor systems to find out which scenario is the most fitted to SN 2018kp case. Moreover, we estimate the distance to the galaxy and look into the relation between SNe and galactic physical parameters.

• The Bulletin of The Korean Astronomical Society
• /
• v.5
• /
• pp.3-10
• /
• 1980