• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.33.1-33.1
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• 2015

M85 is a nearby merger remnant galaxy located at the northern part of the Virgo Cluster. Because of its remarkable merging features, it is an interesting object to investigate its formation history. Globular clusters are a great tracer of the formation history of early-type galaxies, so that we study the globular cluster system of M85. It has been already found that there are "intermediate-color" globular clusters as well as blue and red ones based on the photometric survey using CFHT/Megacam. For follow-up research, we obtain the spectra of 21 globular clusters in the central region of M85 using Gemini-N/GMOS. We estimate their ages and metallicities based on the strength of Lick indices. We detect the intermediate-age population (~ 2 Gyr) with solar metallicities, comprising about 50% of the observed globular clusters, as well as old and metal-poor population. It suggests that M85 experienced a major merging event around 2 Gyr ago. We discuss these results regarding to the formation history of M85.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.100.1-100.1
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• 2013

다가오는 거대마젤란망원경 (GMT) 시대를 이끌어갈 신진 연구자들의 연구역량 증진을 위해, 2013년 8월 27일부터 30일까지 3박4일에 걸쳐 강원도 홍천 가람밸리 리조트에서 제3회 거대마젤란망원경 여름학교를 개최한다. 총 47명의 대학원생과 박사후연구원들이 참여하는 이번 여름학교에서는, GMT 개관, 1세대 관측기기 가운데 최초로 활용될 계획인 GMACS와 G-CLEF의 소개 및 그것들을 활용한 대표적인 과학연구 분야에 대한 강의가 이루어진다. 또한 계절학교 참가자들이 'GMACS 또는 G-CLEF를 활용한 관측연구 제안'이라는 주제로 직접 토론과 발표에 참가하는 조별 활동이 주된 프로그램으로 추가된다. 이러한 여름학교 프로그램은 신진 연구자들이 GMT를 활용한 다양한 연구 가능성을 경험하고 서로 능동적으로 교류할 수 있는 계기가 될 것으로 기대된다. 2013년도부터 새로운 방식으로 시도되는 제3회 거대마젤란망원경 계절학교 결과를 정리함으로써 앞으로 나아갈 계절학교의 방향을 점검해본다.

• Journal of Korea Multimedia Society
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• v.13 no.9
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• pp.1322-1328
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• 2010

Recently, keyword spotting system is greatly in the limelight as UI(User Interface) technology of ubiquitous home network system. Keyword spotting system is vulnerable to non-stationary noises such as TV, radio, dialogue. Especially, speech recognition rate goes down drastically under the embedded DSP(Digital Signal Processor) environments because it is relatively low in the computational capability to process input speech in real-time. In this paper, we propose a new keyword spotting system using the call-command method, which is consisted of small number of recognition networks. We select the call-command such as 'narae', 'home manager' and compose the small network as a token which is consisted of silence with the noise and call commands to carry the real-time recognition continuously for input speeches.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.55.1-55.1
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• 2014

on the observation with the Gemini Multi-Object Spectrograph on the Gemini-South 8.1 m telescope. The radial velocities of four ESCs do not display any sign of systematic motion, unlike the intermediate age carbon stars in NGC 6822. The ages and metallicities derived using the Lick indices show that the ESCs are old (>=8 Gyr) and metal poor ([Fe/H] <= -1.5). NGC 6822 is found to have both metal poor ($[Fe/H]{\approx}-2.0$) and metal rich ($[Fe/H]{\approx}-0.9$) star clusters within 15' (2 kpc) from the center, whereas only metal poor clusters are observed in the outer halo with r >= 20'(2.6 kpc). Based on the kinematics, old ages, and low metallicities of ESCs, we discuss the possible origin of ESCs and the formation of the outer halo of a small dwarf irregular galaxy NGC6822.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.122.1-122.1
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• 2014

다가오는 거대마젤란망원경 (GMT) 시대를 이끌어갈 신진 연구자들의 연구역량 증진을 위해, 2014년 8월 25일부터 29일까지 4박5일에 걸쳐 경상북도 경주시 대명리조트에서 제4회 거대마젤란망원경 여름학교를 개최하였다. 총 40명이 학생으로서 참가한 이번 여름학교에서는 다음과 같은 두 가지 새로운 프로그램이 시도되었다. (1) 관측천문학의 기초, 우리은하 천문학의 기초, 외부은하 천문학의 기초 등 세 번의 기초강의를 선택적으로 제공하였다. (2) 별과 행성, 항성종족과 화학진화, 은하 형성, 고적색이동 천체와 재이온화, 우주론 등 총 다섯 개 분야에서 심화강의를 제공한 뒤에 각 강의내용과 연관된 열린 질문들을 화두로 해서 학생들 간에 조별 토론을 진행하였다. 이는 정해진 답이 없는 문제를 놓고 토론을 통해 능동적으로 답을 찾아가는 과정을 훈련하기 위해 고안된 것이다. 본 포스터에서는 제4회 거대마젤란망원경 여름학교의 결과를 정리하고 앞으로 나아갈 GMT 계절학교의 방향을 점검해본다.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.53.1-53.1
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• 2014

The M81 group is a nearby galaxy group hosted by M81, a twin galaxy of Milky Way. This galaxy group is considered as an ideal laboratory for near-field cosmology to understand mass assembly and evolution of galaxies in the group environment. We designed a project to investigate spectroscopic properties of globular cluster candidates in this group. We obtained spectra of globular cluster candidates using the MMT/Hectospec as a part of the K-GMT Science Program. Our main targets include globular cluster candidates of the M81 group member galaxies and those wandering in the intragroup region. We also observed supernova remnants and some background galaxies. Observing fields covered about 2 square degrees including three main galaxies of the M81 group. Using these spectra, we will identify globular clusters in the M81 group, and investigate their properties including age and metallicity. We will discuss the MMT/Hectospec data reduction processes, and future plan for this project.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.30.2-30.2
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• 2016

M104 (NGC 4594, the Sombrero) is an intriguing disk galaxy classified as an elliptical galaxy nowadays. It hosts a luminous bulge and a massive disk, but it is still mysterious how M104 acquired such peculiar structures. Globular clusters are an useful tracer to investigate the formation history of early-type galaxies. In this study we present a wide field imaging study of the globular clusters in M104. Using wide ($1^{\circ}{\times}1^{\circ}$) and deep ugi images of M104 obtained with the CFHT/MegaCam observations, we detect a large number of globular clusters. The color distribution of these globular clusters shows that there are two subpopulations: a metal-poor system and a metal-rich system. The radial number density of the metal-poor globular clusters shows a long tail reaching R ~ 30' (~ 80 kpc), indicating clearly the existence of a giant metal-poor halo in M104. This result is consistent with the previous studies on the dual halos of massive early-type galaxies. We will discuss implications of these results in relation with the formation history of M104.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.30.3-31
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• 2016

The M81 Group is the nearest among the known groups of galaxies. HI maps show that all main galaxies of this group are interacting, indicating that this group is in the active phase of formation. On the other hand, wide field imaging shows that globular cluster candidates are found not only in the member galaxies but also between the galaxies in this group. In this study we present preliminary results based on MMT/Hectospec spectroscopy of the globular cluster candidates in this group. We find that the intragroup globular clusters have mostly low metallicity, while the globular clusters in M81 have mostly high metallicity. We will discuss the implication of this result and the kinematics of the globular clusters in relation with the formation history of the M81 Group.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.43.1-43.1
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• 2016

The duration of star formation activity is a key to understanding the formation process of star clusters. Although a number of astronomers have attempted to derive the underlying age spread in photometric diagrams with a variety of stellar evolutionary models, the resultant findings are subject to uncertainties due to intrinsic variability of pre-main sequence (PMS) stars, observational errors, difficulties in reddening correction, and systematic differences in adopted stellar evolutionary models. The distribution of Li abundance for PMS stars in a cluster could, on the other hand, provide an alternative way to estimate the age spread. In this study, a total of 134 PMS stars in NGC 2264 are observed with the high resolution multi-object spectrogragh Hectochelle attached to the 6.5m Multi Mirror Telescope. We have successfully detected Li ${\lambda}6708$ resonance doublet for 86 low-mass PMS stars. The Li abundance of the stars is derived from their equivalent width using a curves of growth method. After correction for non-LTE effects, the underlying age spread of 3 - 4 Myr is inferred from the Li abundance distribution of low-mass PMS stars. We suggest that NGC 2264 formed on a timescale shorter than 5 Myr given the presence of embedded populations.

• Investigative Magnetic Resonance Imaging
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• v.20 no.1
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• pp.36-43
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• 2016

Visualization of the tissue loss tangent property can provide distinct contrast and offer new information related to tissue electrical properties. A method for non-invasive imaging of the electrical loss tangent of tissue using magnetic resonance imaging (MRI) was demonstrated, and the effect of loss tangent was observed through simulations assuming a hyperthermia procedure. For measurement of tissue loss tangent, radiofrequency field maps ($B_1{^+}$ complex map) were acquired using a double-angle actual flip angle imaging MRI sequence. The conductivity and permittivity were estimated from the complex valued $B_1{^+}$ map using Helmholtz equations. Phantom and ex-vivo experiments were then performed. Electromagnetic simulations of hyperthermia were carried out for observation of temperature elevation with respect to loss tangent. Non-invasive imaging of tissue loss tangent via complex valued $B_1{^+}$ mapping using MRI was successfully conducted. Simulation results indicated that loss tangent is a dominant factor in temperature elevation in the high frequency range during hyperthermia. Knowledge of the tissue loss tangent value can be a useful marker for thermotherapy applications.