• The Bulletin of The Korean Astronomical Society
• /
• v.41 no.1
• /
• pp.66.1-66.1
• /
• 2016

We present our observational results of BL Lacertae(2200+420) obtained at 22, 43, 86, and 129 GHz simultaneously during 27 months(2013.Jan ~ 2015.Mar) which includes their two gamma-ray outbursts(2013.Oct & 2015.Mar) to study a connection between the gamma-ray outbursts and the radio activity. We mainly use a Korean VLBI monitoring program, IMOGABA(Interferometric Monitoring Of Gamma-ray Bright AGNs) which is a monthly monitoring program with the KVN(Korean VLBI Network). Overall, our KVN image shows two components in the map, a stationary core at the center and one moving jet component to the south, but almost core only at 86, 129 GHz. The location of the moving jet component in the maps depend on the frequencies that 22, 43, 86, and 129 GHz. We have checked light curves, spectral index, kinematics, and radio structure to find differences before and after the gamma-ray outbursts, but there was no significant correlation. We also have derived a decay time scale of ~9 months for the major radio outburst by applying an exponential decay fitting.

• Korean Journal of Optics and Photonics
• /
• v.24 no.5
• /
• pp.217-223
• /
• 2013

White light MTF(Modulation Transter Function)s of biconvex trial lenses from 10 to 20 diopter (D) were represented as a function of angular frequency and visual acuity, and then they were compared with AIM(Aerial Image Modulation) curves. All of the biconvex trial lenses evaluated in on-axis mode had MTF performance that could resolve Landolt's ring up to visual acuity 2.0. However, in a half field angle of five degrees, the trial lens of 10 diopters was able to resolve Landolt's ring up to visual acuity 0.9, and that of 20 diopter only up to visual acuity 0.8. This means that the trial lenses in the case of a half field angle of five degrees do not have sufficient resolution to measure visual acuity by 1.0.

• Publications of The Korean Astronomical Society
• /
• v.30 no.2
• /
• pp.585-586
• /
• 2015

4U 1323-62, a low mass X-ray binary with an orbital period of 2.94 hr, exhibits periodic X-ray dips, which are due to absorption by the bulge of the outer accretion disk. The purpose of this study is to search for orbital period changes using archived X-ray data over a time span of 20 years. We present our preliminary results from analyzing light curves observed by RXTE, BeppoSAX, XMM-Newton and Suzaku. We used the method proposed by Hu et al. (2008) to estimate dip center time and adopted the Observed - Calculated method to measure changes in period. We obtained an orbital period of 2.941917(36) hr and a period derivative of $\dot{P}_{orb}/P_{orb}=(-9.9{\pm}3.5){\times}10^{-7}yr^{-1}$. The F-test result shows that the quadratic ephemeris is describes the evolution of the dip phases better than the linear ephemeris at a greater than 95% confidence level. More X-ray data collected from the early 80s will be included to further refine the orbital ephemeris.

• The Bulletin of The Korean Astronomical Society
• /
• v.37 no.2
• /
• pp.240.2-240.2
• /
• 2012

AGN(Active Galactic Nucleus) consists of a supermassive black hole located at its center, an accretion disk around the black hole, and bipolar jets. Since May 2011, we have performed the MOGABA(Monitoring Of GAmma-ray Bright AGN) project for observing gamma-ray bright AGN once a week at multifrequencies using KVN(Korean VLBI Network) 21m radio telescopes. The MOGABA project is the observations for measuring the degree of polarization, polarization angle, and total flux of about 20 AGN at 22, 43 and 86GHz. By this project, we are able to investigate polarization characteristics, spectral index, and variation of rotation measure at radio wavelengths of gamma-ray bright AGN and to study possible relation between gamma-ray flares and magnetic field structure change in AGN. According to previous research, gamma-ray flares of some AGN are coincident with large changes in angle of linear polarization. In this paper we report the preliminary results of linear polarization and total flux at 22, 43, 86GHz of gamma-ray bright quasars 3C279 and 1510-089 showing noticeable variation of total flux at 22GHz in late 2011, and discuss possible correlation with gamma ray light curves.

• The Research Journal of the Costume Culture
• /
• v.19 no.1
• /
• pp.104-118
• /
• 2011

Since Sirimavo Bandarinaike became the first female prime minister in 1960, women all over the world has been trying to break the highest glass ceiling. In a place where men had been dominating throughout history, women political leaders had to find a way to look the part by wearing power suits. Feminity was out of the question until the digital era of 21st century started. The world has evolved into a place where feminity could be strength instead of weakness. Now women political leaders are showing body curves, cleavage, using vivid and pastel colors, soft fabrics, elaborate details, accessories, long and curly hair. The padded shoulders of dark coloured power suits were replaced by soft colorful flowing feminine suits. Yulia Tymoshenko of Ukraine is the best example of 21st century woman political leader using feminity in her fashion style while enacting her role. When she first started politics in 1990's, she wore dark colored power suits like all other women political leaders did with short dark hair. As time passed her suits became more feminine with light colors and elaborate details. She has changed her hair into a neat braid, based on a traditional Ukrainian hair style. She used orange color for the Orange Revolution and white for pure image. Yulia Tymoshenko's fashion style as a way of role enactment showed professionalism, feminity, integrity, and ethnicity.

• The Bulletin of The Korean Astronomical Society
• /
• v.37 no.2
• /
• pp.108.2-108.2
• /
• 2012

Recent results from microlensing surveys show that a free-floating planet or a wide-separation planet is more numerous than a main-sequence star in the Galaxy. Moreover, the detection efficiency of the planets will be improved in next-generation experiments with a high survey monitoring frequency. However, microlensing events produced by both planets appear similar light curves with a short duration timescale, thus it is difficult to distinguish them. In this paper, we investigated the detectable separation range of a wide-separation planet as the planet bound to its host star. We construct the fractional deviation maps using the magnifications of the planetary lensing and the single-lensing by planet itself for various parameters such as a mass ratio, separation, and source radius. As a result, we found that the pattern of the fractional deviation is related to the ratio of source radius to caustic size, and the ratio satisfying the detection criterion (i.e., ${\geq}5%$ in the fractional deviation) varies with a separation. Hence, we derived a fitting formula as the function of a mass ratio and a source radius to reflect the variation in the calculations of the detectable separation range of a wide-separation planet as the planet bound to its host star. In addition, we estimated the condition that a wide-separation planet can be detected as a single-lensing event under the finite source effect. We found that such a case is possible provided that the source radius is smaller than ~2.5 times of Einstein ring radius of a planet, regardless of a separation or a mass ratio.

• Journal of the Korean institute of surface engineering
• /
• v.50 no.5
• /
• pp.366-372
• /
• 2017

Plasma electrolytic oxidation(PEO) has attracted attention as a surface treatment which has high wear resistance and corrosion resistance. PEO is generally considered as cost-effective, environmentally friendly and superior in terms of coating performance. Most of studies about the PEO processes have been applied to light metals such as Al and Mg. Because the strength of Al and Mg is weaker than that of steel, there is a limit to the application. In this study, PEO process was used to form oxide coatings on Hot dipped aluminized(HDA) steel and the characteristics of the coating film according to the PEO current density were studied. The morphology was observed by SEM and component was analyzed by using EDS. The corrosion behaviors of PEO coating films were estimated by exposing salt spray test at 5 wt.% NaCl solution and measuring polarization curves in deaerated 3 wt.% NaCl solution. With the increase of PEO process current density, the pore size of the coating surface and the thickness of coating increased. It was confirmed that no Fe component was present on the coating surface. PEO coating films obviously showed good corrosion resistance compared with HDA. It is considered that the PEO coating acts as a barrier to protect the base material from external factors causing corrosion.

• Journal of The Korean Astronomical Society
• /
• v.54 no.2
• /
• pp.37-47
• /
• 2021

Reverberation mapping (RM) is an efficient method to investigate the physical sizes of the broad line region (BLR) and dusty torus in an active galactic nucleus (AGN). The Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer (SPHEREx) mission will provide multi-epoch spectroscopic data at optical and near-infrared wavelengths. These data can be used for RM experiments with bright AGNs. We present results of a feasibility test using SPHEREx data in the SPHEREx deep regions for torus RM measurements. We investigate the physical properties of bright AGNs in the SPHEREx deep field. Based on this information, we compute the efficiency of detecting torus time lags in simulated light curves. We demonstrate that, in combination with complementary optical data with a depth of ~ 20 mag in B-band, lags of ≤ 750 days for tori can be measured for more than ~ 200 bright AGNs. If high signal-to-noise ratio photometric data with a depth of ~ 21-22 mag are available, RM measurements are possible for up to ~ 900 objects. When complemented by well-designed early optical observations, SPHEREx can provide a unique dataset for studies of the physical properties of dusty tori in bright AGNs.

• Journal of The Korean Astronomical Society
• /
• v.52 no.4
• /
• pp.109-119
• /
• 2019

While the reverberation mapping technique is the best available method for measuring black hole mass in active galactic nuclei (AGNs) beyond the local volume, this method has been mainly applied to relatively low-to-moderate luminosity AGNs at low redshift. We present the strategy of the Seoul National University AGN Monitoring Project, which aims at measuring the time delay of the $H{\beta}$ line emission with respect to AGN continuum, using a sample of relatively high luminosity AGNs out to redshift z ~ 0.5. We present simulated cross correlation results based on a number of mock light curves, in order to optimally determine monitoring duration and cadence. We describe our campaign strategy based on the simulation results and the availability of observing facilities. We present the sample selection, and the properties of the selected 100 AGNs, including the optical luminosity, expected time lag, black hole mass, and Eddington ratio.

• Journal of the Korean institute of surface engineering
• /
• v.51 no.6
• /
• pp.415-420
• /
• 2018

The possibility of an improvement in heat dissipation performance of aluminum alloy heat sink for shipboard LED luminaries through plasma electrolytic oxidation (PEO) was investigated. Four different PEO coatings were produced on aluminum alloy 5052 in silicate based alkaline solution by varying current density ($50{\sim}200mA/cm^2$). On voltage-time response curves, three stages were clearly distinguished at all current densities, namely an initial linear increase, slowdown of increase rate, and steady state(constant voltage). It was found that the increase in current density caused the breakdown voltage to increase. Two different surface morphologies - coralline porous structure and pancake structure - were confirmed by SEM examination. The coralline porous structure was predominant in the coatings produced at lower current densities (50 and $100mA/cm^2$) while under high current densities(150 and $200mA/cm^2$) the pancake structure became dominant. The coating thickness was measured and found to be in a range between about $13{\mu}m$ and $44{\mu}m$, showing increasing thickness with increasing current density. As a result, $100mA/cm^2$ was proposed as an effective process parameter to improve the heat dissipation performance of aluminum alloy heat sink, which could lower the LED operating temperature by about 30%.