• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1881-1884
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• 2003

In this experiment, the oxidations of p-Xylene (140-180 ppmv), one of the air pollutants as a VOC, using $UV/TiO_2$ photocatalyst is studied. In order to increase the specific surface area, the filter is coated by nano $TiO_2$ particles. The photodegradation system consists of a VOCs generator, a photocatalyst filter and a measuring equipment. Illumination is generally provided by two of 20 W black light lamps with 380 nm of wavelength. The filter coated by nano $TiO_2$ particles has a passing efficiency over 80% but a pressure drop of 9.0 $mmH_2O$ at 0.45 cm/s. The filter endurance is better than activated carbon at the same pressure drop.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.57.1-57.1
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• 2011

Using high-resolution numerical simulations, we investigate the formation of gaseous substructures and mass inflow rates in barred spiral galaxies in the presence of both bar and spiral potentials. The gaseous medium is assumed to be infinitesimally-thin, isothermal, unmagnetized, and non-self-gravitating. To consider various galactic situations, we vary the pattern speed and strength of spiral arms as well as the black hole mass. We find that spiral arms with pattern speed smaller than that of the bar remove angular momentum from the gas outside corotation which transports to the bar region, making the dust lanes strong and live long. When the arm pattern speed is identical to that of the bar, on the other hand, the gas outside corotation gains angular momentum and thus moves outward, without affecting the bar region. Overall gaseous morphologies in simulations match well with observed IR images of barred spiral galaxies such as NGC 1097, when the arms and bar are in phase at the corotation radius. The presence of spiral arms increases the mass inflow rate as well, making it larger than $0.01M_{\odot}/yr$ when MBH is $4{\times}10^7M_{\odot}$, possibly explaining AGN activities in Seyfert galaxies.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.443-445
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• 2015

We provide results of near-infrared (NIR) spectroscopic observations of 83 nearby (0.002< z <0.48) and bright (K <14 mag) type 1 active galactic nuclei (AGNs). For the observations, we used the Infrared Camera (IRC) on AKARI allowing us to obtain the spectrum in the rarely studied spectral range of $2.5-5.0{\mu}m$. The $2.5-5.0{\mu}m$ spectral region suffers less dust extinction than ultra violet (UV) or optical wavelength ranges, and contains several important emission lines such as $Br{\beta}$ ($2.63{\mu}m$), $Br{\alpha}$ ($4.05{\mu}m$), and polycyclic aromatic hydrocarbon (PAH; $3.3{\mu}m$). The sample is selected from the bright quasar surveys of Palomar Green and SNUQSO, and AGNs with black hole (BH) masses estimated from reverberation mapping method. We measure the Brackett line properties for 11 AGNs, which enable us to derive BH mass estimators and investigate circum-nuclear environments. Moreover, we perform spectral modeling to fit the hot and warm dust components by adding photometric data from SDSS, 2MASS, WISE, and ISO to the AKARI spectra, and estimate hot and warm dust temperatures of ~1100K and ~220 K, respectively.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.83.2-83.2
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• 2012

Type I AGNs are classified by the presence of broad emission lines while Type II AGNs show narrow emission lines only. All-sky surveys such as SDSS provide large AGN samples for statistical studies. However, the AGN samples suffer selection bias due to the incomplete selection criteria. To investigate the missing Type I AGNs in optical spectroscopic surveys, we start with a sample of SDSS Type II AGNs at 0.02 < z < 0.05, using the MPA-JHU SDSS DR7 catalog. We search for the hidden broad $H{\alpha}$ component with both visual inspection and the multi-component spectral decomposition method. Out of 1383 Type II AGNs, we find a total of 62 missing Type I AGNs (~4.5%). The sample has mean black hole mass, log $(M_{BH}/M_{SUN))=6.48{\pm}0.53$, and luminosity, log $(L_{H{\alpha}}/ergs^{-1})=40.52{\pm}0.33$, with Eddington ratio, log $(L_{bol}/L_{Edd})=-1.51{\pm}0.41$. We will describe the sample and present the $M_{BH}-{\sigma}_*$, and $M_{BH}-M_*$ relations of the sample in the context of the BH-galaxy coevolution.

• Disaster and Security
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• v.5 no.1
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• pp.38-46
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• 2015

최근 들어 전국의 곳곳에서 화재가 발생하여 귀중한 인명과 재산을 잃는 대형 참사(慘事)로 이어지고 있다. 화재가 발생했을 때에 초기진화(初期鎭火) 및 인명(人命)의 대피시간(待避時間)인 소위 골든타임은 대략 5분정도이다. 또한 화재사고를 직접체험하게 되면 패닉(panic)현상을 초래하여 우왕좌왕, 혼란의 블랙홀(Black hole)에 함몰(陷沒)되게 마련이다. 의정부 아파트 화재에서처럼 대부분의 골목길은 많은 차량들이 주차되어 소방차 긴급출동에 장애가 되고 있는 실정이다. 보편적으로 화재발생 시 소방대는 5분 내에 출동을 목표로 훈련을 한다. 하지만 화재현장에서 소방대에 화재신고가 신속히 이루지지 못하는 지체시간(遲滯時間)을 감안하면 소방대가 현장에 도착하여 진압작업을 개시하는 시점에는 이미 골든타임을 벗어나 화재가 확산되어 있는 상황인 것이다. 그러므로 골든타임을 감안(勘案)하여 소방대의 출동이전에 자체적으로 초기진압을 할 수 있는 방재시스템을 구축(構築)하여야 하는 것이다. 이에 소방대의 도착이전의 골든타임 이내에 자체적으로 조기진압 및 피난을 할 수 있어야 할 것이며, 다만 출동한 소방대는 인접한 건물이나, 주유소 등으로의 연소 확산(延燒 擴散)을 방지하는 역할로 개념(槪念)을 정리할 필요가 있는 것이다. 소방관련 법령 및 화재안전기준 등은 수시로 개정 발전 되어 오늘날에 이르렀다, 하지만 아직까지도 불합리하고 모순된 규정 등이 곳곳에 산재해 있다. 이에 틀에 박힌 고정관념에서 벗어나 보다 논리적이고 합리적이며 현장여건에 부합하는 선진화된 소방제도를 구축하여 화재참사로부터 국민의 생명과 재산보호는 물론 그 손실을 최소화하기 위한 선진화된 소방관련 제도로 정착시켜야 할 것이다.

• ETRI Journal
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• v.43 no.4
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• pp.674-683
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• 2021

A trust-aware secure routing protocol (TSRP) for wireless sensor networks is proposed in this paper to defend against varieties of attacks. First, each node calculates the comprehensive trust values of its neighbors based on direct trust value, indirect trust value, volatilization factor, and residual energy to defend against black hole, selective forwarding, wormhole, hello flood, and sinkhole attacks. Second, any source node that needs to send data forwards a routing request packet to its neighbors in multi-path mode, and this continues until the sink at the end is reached. Finally, the sink finds the optimal path based on the path's comprehensive trust values, transmission distance, and hop count by analyzing the received packets. Simulation results show that TSRP has lower network latency, smaller packet loss rate, and lower average network energy consumption than ad hoc on-demand distance vector routing and trust based secure routing protocol.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.62.2-62.2
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• 2019

The ADF-S (AKARI Deep Field - South) toward South Ecliptic Pole is one of the deep survey fields designed for the study of Extragalactic Background Light (EBL). The deep extragalactic survey was initiated by AKARI far-infrared deep observations. Other space missions (e.g., Euclid, NISS, SPHEREx) will perform the deep observations in the ADF-S. Based upon the recent optical survey with KMTNet, we can identify the optical counterparts for dusty star-forming galaxies such as ULIRG, DOG, SMG. Among them, the Dust-Obscured Galaxies (hereafter DOGs with f(24um)/f(R) > 1,000) in the heavily obscured system are expected to play an important role in the formation of most massive galaxies. We have newly discovered ~100 DOGs in ~12 sq. deg. of the ADF-S from our optical survey with KMTNet. We also confirmed that some of DOGs host the most luminous AGN for their black hole masses through the near-infrared spectroscopic follow-ups. Here, we report the properties of high-z hyperluminous DOGs in the ADF-S.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.36.1-36.1
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• 2019

We present the observed relationship between Eddington ratio (${\lambda}Edd$) and optical narrow-emission-line ratio ([NII] ${\lambda}6583/H{\alpha}$) of X-ray-selected unobscured active galactic nuclei (AGN) at 0.6 < z < 1.7 using 27 near-infrared spectra from the Fiber Multi-Object Spectrograph mounted on the Subaru telescope along with 26 additional sources from the literature. We show that the ${\lambda}Edd$ and [NII] ${\lambda}6583/H{\alpha}$ ratio at 0.6 < z < 1.7 exhibits a similar distribution of ${\lambda}Edd$-[NII] ${\lambda}6583/H{\alpha}$ anti-correlation that has been found for local ( = 0.036), hard X-ray selected AGN. The observed anti-correlation suggests that [N II] ${\lambda}6583/H{\alpha}$ optical narrow-line ratio in the AGN host galaxy may carry important information about the accretion state of the central supermassive black hole, suggesting the observational hint of consistent relationship from local to z ~ 1.7. Further study is necessary to determine whether the ${\lambda}Edd$-[N II] ${\lambda}6583/H{\alpha}$ correlation in high-redshift still holds at ${\log}{\lambda}Edd$ < -2 compared to local AGN.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.2
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• pp.53.3-54
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• 2018

On June 16 AT2018cow (ATLAS 18qqn) was discovered as a bright and fast-evolving transient in nearby universe z ~ 0.01. It brightened by more than 4 mag within a day, and its light curve was decayed rapidly and has a high luminous peak which is more luminous than most of core-collapse supernova. It also overall showed a blue color in an unprecedented case of transients. There have been attempts to explain this behavior with existing models, but most of them have been insufficient except for one - tidal disruption by intermediate-mass black hole. We began to monitor this transient from about 4 days after the discovery until August 21 in the optical bands with 1m-class telescopes over the world. Here, we present a light curve of AT2018cow in the B, V, R and I bands, and analyze its photometric properties and compare to other transients and models.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.69.2-69.2
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• 2021

We present the discovery of rare active galactic nuclei (AGNs) in nearby (z<0.05) compact elliptical galaxies (cEs) located in isolated environments. Using spectroscopic data from the Sloan Digital Sky Survey (SDSS) Data Release 12, four AGNs were identified based on the optical emission-line diagnostic diagram. SDSS optical spectra of AGNs show the presence of distinct narrow-line emissions. Utilizing the black hole (BH) mass-stellar velocity dispersion scaling relation and the correlation between the narrow L([OIII])/L(Hβ) line ratio and the width of the broad Hα emission line, we estimated the BH masses of the cEs to be in the range of 7×10⁵-8×10⁷ solar mass. The observed surface brightness profiles of the cEs were fitted with a double Sérsic function using the Dark Energy Camera Legacy Survey r-band imaging data. Assuming the inner component as the bulge, the K-band bulge luminosity was also estimated from the corresponding Two Micron All Sky Survey images. We found that our cEs follow the observed BH mass-stellar velocity dispersion and BH mass-bulge luminosity scaling relations, albeit there was a large uncertainty in the derived BH mass of one cE. In view of the observational properties of BHs and those of the stellar populations of cEs, we discuss the proposition that cEs in isolated environments are bona fide low-mass early-type galaxies (i.e., a nature origin).