• 천문학회지
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• 제36권3호
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• pp.159-165
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• 2003

Optical (R) and near-infrared (K') images of the IRAS 1-Jy sample of 118 ultraluminous infrared galaxies have been studied. All but one object in the 1-Jy sample show signs of strong tidal interaction/merger. Most of them harbor a single disturbed nucleus and are therefore in the later stages of a merger event. Single-nucleus ULIGs show a broad distribution in host magnitudes with significant overlap with those of quasars. The same statement applies to R - K' colors in ULIG and quasar hosts. An analysis of the surface brightness profiles of the host galaxies in single-nucleus sources reveals that about $35\%$ of the Rand K' surface brightness profiles are well fit by an elliptical-like $R^{1/4}$-law, while only $2\%$ are well fit by an exponential disk. Another $38\%$ of the single-nucleus systems are fit equally well with an exponential or de Vaucouleurs profile. Elliptical-like hosts are most common among merger remnants with Seyfert 1 nuclei ($83\%$) and Seyfert 2 optical characteristics ($69\%$). The mean effective radius of these ULIGs is 4.80 $\pm$ 1.37 kpc at Rand 3.48 $\pm$ 1.39 kpc at K'. These values are in excellent agreement with recent quasar measurements obtained at H with HST. The hosts of elliptical-like 1-Jy systems follow with some scatter the same ${\mu}e - r_e$ relation, giving credence to the idea that some of these objects may eventually become elliptical galaxies if they get rid of their excess gas or transform this gas into stars.

• 산경연구논집
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• 제12권5호
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• pp.47-58
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• 2021

Purpose - Current research aimed at exploring the effect differences between the two types of processing product information such as the imagining and the considering on psychological product ownership which could influence the intent to purchase or use the product, and focused on identifying the interaction effects of activated memory information type and advertising information type on each of the information processing types. Research design, data, and methodology - This study divided the information processing types into imagining and considering, and the consumer's memories were divided into autobiographical or episodic and semantic memory. The advertising information was approached in each of event information being together with the product and product feature information. At empirical study, 2(two types of memory activation: episodic and semantic memory activation) ∗ 2(two types of advertising information: event-focused and product feature-focused advertising information) between-subjects design was used to make four types of questionnaire according to the type of experimental groups. Through the survey platform, 'questionnaire stars' of 'WeChat' in China, 219 questionnaire data were collected for empirical study. The structural equation model in AMOS 26 and Anova were used to verify hypotheses. Results - First, the ownership affected the usage intent positively. Second, the imagining did not affect the psychological ownership but did directly affect the usage intention, and the considering affected the ownership positively. Third, the episodic memory activation positively influenced the imagining and negatively affected the considering, whereas the semantic memory activation positively influenced the considering and negatively affected the imagining. Fourth, event-advertising information increased the effects of the activated episodic memory on the imagining, and feature-advertising information increased the effects of the activated semantic memory on the considering. Conclusions - marketers should develop and advertise their product-related event message to trigger the imaging that directly increase the intent to purchase or use their product, when consumers are under the activation of their episodic memory. And marketers should advertise their product feature-related message to trigger the considering that could induce consumers' ownership for their product to increase the intent to purchase or use their product, when they are under the activation of their semantic memory.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2008년도 한국우주과학회보 제17권2호
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• pp.27.1-27.1
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• 2008

KASI (Korea Astronomy and Space Science Institute) is developing a compact wide-field survey space telescope system, MIRIS (The Multi-purpose IR Imaging System) to be launched in 2010 as the main payload of the Korea Science and Technology Satellite 3. Through recent System Design Review (SDR) and Preliminary Design Review (PDR), most of the system design concept was reviewed and confirmed. The near IR imaging system adopted short F/2 optics for wide field low resolution observation at wavelength band 0.9~2.0 um minimizing the effect of attitude control system. The mechanical system is composed of a cover, baffle, optics, and detector system using a $256\times256$ Teledyne PICNIC FPA providing a $3.67\times3.67$ degree field of view with a pixel scale of 51.6 arcsec. We designed a support system to minimize heat transfer with Muti-Layer Insulation. The electronics of the MIRIS system is composed of 7 boards including DSP, control, SCIF. Particular attention is being paid to develop mission operation scenario for space observation to minimize IR background radiation from the Earth and Sun. The scientific purpose of MIRIS is to survey the Galactic plane in the emission line of Pa$\alpha$ ($1.88{\mu}m$) and to detect the cosmic infrared background (CIB) radiation. The CIB is being suspected to be originated from the first generation stars of the Universe and we will test this hypothesis by comparing the fluctuations in I (0.9~1.2 um) and H (1.2~2.0 um) bands to search the red shifted Lyman cutoff signature.

• 천문학회보
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• 제43권1호
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• pp.47.1-47.1
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• 2018

The NISS (Near-infrared Imaging Spectrometer for Star formation history) onboard NEXTSat-1 have successfully developed by KASI. The capability of both imaging and spectroscopy is a unique function of the NISS. At first, it have realized the low-resolution spectroscopy (R~20) with a wide field of view of $2{\times}2deg$. in a wide near-infrared range from 0.95 to $2.5{\mu}m$. The major scientific mission is to study the cosmic star formation history in local and distant universe. It will also demonstrate the space technologies related to the infrared spectro-photometry in space. Now, the NISS is ready to launch in late 2018. After the launch, the NISS will be operated during 2 years. As an extension of the NISS, the SPEHREx (Spectro-Photometer for the History of the Universe Epoch of Reionization, and Ices Explorer) is the NASA MIDEX (Medium-class Explorer) mission proposed together with KASI (PI Institute: Caltech). It will perform the first all-sky infrared spectro-photometric survey to probe the origin of our Universe, to explore the origin and evolution of galaxies, and to explore whether planets around other stars could harbor life. Compared to the NISS, the SPHEREx is designed to have much more wide FoV of $3.5{\times}11.3deg$. as well as wide spectral range from 0.75 to $5.0{\mu}m$. After passing the first selection process, the SPHEREx is under the Phase-A study. The final selection will be made in the end of 2018. Here, we report the status of the NISS and SPHEREx missions.

• 천문학회보
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• 제41권1호
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• pp.58.2-58.2
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• 2016

The NISS (Near-infrared Imaging Spectrometer for Star formation history) onboard NEXTSat-1 is the near-infrared instrument optimized to the first small satellite of NEXTSat series. The capability of both imaging and low spectral resolution spectroscopy with the Field of View of $2{\times}2deg.$ in the near-infrared range from 0.9 to $3.8{\mu}m$ is a unique function of the NISS. The major scientific mission is to study the cosmic star formation history in local and distant universe. The Flight Model of the NISS is being developed and tested. After an integration into NEXTSat-1, it will be tested under the space environment. The NISS will be launched in 2017 and it will be operated during 2 years. As an extension of the NISS, SPEHREx (Spectro-Photometer for the History of the Universe Epoch of Reionization, and Ices Explorer) is the NASA SMEX (SMall EXploration) mission proposed together with KASI (PI Institute: Caltech). It will perform an all-sky near-infrared spectral survey to probe the origin of our Universe; explore the origin and evolution of galaxies, and explore whether planets around other stars could harbor life. The SPHEREx is designed to have wider FoV of $3.5{\times}7deg.$ as well as wider spectral range from 0.7 to $4.8{\mu}m$. After passing the first selection process, SPHEREx is under the Phase-A study. The final selection will be made in the end of 2016. Here, we report the current status of the NISS and SPHEREx missions.

• 핵의학기술
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• 제17권2호
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• pp.3-9
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• 2013

핵의학 검사 중 동적 신장검사는 신장기능을 평가하는 가장 대표적인 검사법으로 방사성동위원소를 이용하여 시간에 따른 신장의 기능을 평가하고 소변이 배설에 이르기까지의 질환 평가에 유용하다. 이러한 검사영상의 질 평가 및 정량 분석에서 현재 상용화 된 팬텀은 정적 상황만 재현하고 평가할 수 있기 때문에 동적 팬텀을 통한 시간에 따른 신장의 기능적 상황과 혈류속도, 방사성동위원소의 주입량에 따른 다양한 차이 등을 확인할 수 있는 연구가 미비한 상황이다. 그러므로 본 연구를 통해 동적 신장팬텀 시스템을 제작하여 신장의 동적 흐름을 통한 영상을 재현함으로써 핵의학에서 영상학적으로 유용성을 평가하고자 한다. 신장팬텀은 정상 성인 신장을 기준으로 제작하였고, 동적 상황을 재현하기 위하여 혈류의 속도를 조절할 수 있는 정량 펌프를 적용하였으며, $^{99m}Tc-pertechnate$를 신장팬텀에 방사성의약품이 집적되고 방광으로 배설되도록 제작하였다. 사용된 방사성의약품은 각 신장팬텀에 각각 주입되도록 하였으며, 주입속도, 방사성의약품, 좌우 신장팬텀에 다른 주입속도에 따른 변화를 확인하였다. 획득한 영상의 분석은 전면상과 후면상 각각의 신장과 방광에 관심영역을 그려 분석하였으며, 재현성을 확인하기 위하여 각 10회씩 반복하여 분석하였다. 동일한 조건하에 주입속도 40 mL/min로 고정하여 펌프의 압력을 조절하였을 때 방사성의약품이 2-3분 사이에 신장팬텀에 가장 많이 집적되었다가 방광으로 배출되었다. 각 장비별 사구체 여과율은 각각 SYMBIA 1,091 mL/min, FORTE 1,232 mL/min, ARGUS 1,264 mL/min, INFINIA 1,302 mL/min로 통계적으로 유의한 차이가 있는 것으로 나타났으며, Tmax 값 그리고 T1/2 값 모두에서 장비별 통계적으로 유의한 차이가 있는 것으로 나타났다. 변동계수인 CV 값은 5% 이하로 재현성이 있는 것으로 나타났으며, 그 중에서 SYMBIA가 2.67%로 가장 낮게 나타났고, INFINIA가 4.86%으로 가장 높게 나타났다. 본 연구를 통하여 동적신장팬텀시스템이 실제 임상의 신장동적검사를 유사하게 재현이 가능한 것을 확인할 수 있었다. 특히 신장을 통해 방광으로 배설되는 흐름에 대해 시간에 따른 묘사가 충분하게 재현되었으며, 동적 영상의 질을 확인하는데 기초 자료로 활용이 가능하리라 사료된다. 또한 추후 기능적 영상 분야에 연구 및 정도관리 분야에도 도움이 되리라 여겨진다.

• 천문학회보
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• 제41권1호
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• pp.54.1-54.1
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• 2016

Multi-wavelength variability is a staple of active galactic nuclei (AGN). Optical variability probes the nature of the central engine of AGN at smaller linear scales than conventional imaging and spectroscopic techniques. Previous studies have shown that optical variability is more prevalent at longer timescales and at shorter wavelengths. Intra-night variability can be explained through the damped random walk model but small samples and inhomogeneous data have made constraining this model hard. To understand the properties and physical mechanism of intra-night optical variability, we are performing the KMTNet Active Nuclei Variability Survey (KANVaS). Using KMTNet, we aim to study the intra-night variability of ~1000 AGN at a magnitude depth of ~19mag in R band over a total area of ${\sim}24deg^2$ on the sky. Test data in the COSMOS, XMM-LSS, and S82-2 fields was obtained over 4, 6, and 8 nights respectively during 2015, in B, V, R, and I bands. Each night was composed of 5-13 epoch with ~30 min cadence and 80-120 sec exposure times. As a pilot study, we analyzed data in the COSMOS field where we reach a magnitude depth of ~19.5 in R band (at S/N~100) with seeing varying between 1.5-2.0 arcsec. We used the Chandra-COSMOS catalog to identify 166 AGNs among 549 AGNs at B<23. We performed differential photometry between the selected AGN and nearby stars, achieving photometric uncertainty ~0.01mag. We employ various standard time-series analysis tools to identify variable AGN, including the chi-square test. Preliminarily results indicate that intra-night variability is found for ~17%, 17%, 8% and 7% of all X-ray selected AGN in the B, V, R, and I band, respectively. The majority of the identified variable AGN are classified as Type 1 AGN, with only a handful of Type 2 AGN showing evidence for variability. The work done so far confirms there are more variable AGN at shorter wavelengths and that intra-night variability most likely originates in the accretion disk of these objects. We will briefly discuss the quality of the data, challenges we encountered, solutions we employed for this work, and our updated future plans.

• 천문학회지
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• 제36권3호
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• pp.81-87
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• 2003

It is suggested that a flying-by star in a hot accretion disk may cool the hot accretion disk by the Comptonization of the stellar emission. Such a stellar cooling can be observed in the radio frequency regime since synchrotron luminosity depends strongly on the electron temperature of the accretion flow. If a bright star orbiting around the supermassive black hole cools the hot disk, one should expect a quasi-periodic modulation in radio, or even possible an anti-correlation of luminosities in radio and X-rays. Recently, the unprecedentedly accurate infrared imaging of the Sagittarius A$\ast$ for about ten years enables us to resolve stars around it and thus determine orbital parameters of the currently closest star S2. We explore the possibility of using such kind of observation to distinguish two quite different physical models for the central engine of the Sagittarius A$\ast$, that is, a hot accretion disk model and a jet model. We have attempted to estimate the observables using the observed parameters of the star S2. The relative difference in the electron temperature is a few parts of a thousand at the epoch when the star S2 is near at the pericenter. The relative radio luminosity difference with and without the stellar cooling is also small of order $10^{-4}$, particularly even when the star S2 is near at the pericenter. On the basis of our findings we tentatively conclude that even the currently closest pass of the star S2 is insufficiently close enough to meaningfully constrain the nature of the Sagittarius A$\ast$ and distinguish two competing models. This implies that even though Bower et al. (2002)have found no periodic radio flux variations in their data set from 1981 to 1998, which is naturally expected from the presence of a hot disk, a hot disk model cannot be conclusively ruled out. This is simply because the energy bands they have studied are too high to observe the effect of the star S2 even if it indeed interacts with the hot disk. In other words, even if there is a hot accretion disk the star like S2 has imprints in the frequency range at v $\le$ 100 MHz.

• 천문학논총
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• 제32권1호
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• pp.225-230
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• 2017

The extragalactic background suggests half the energy generated by stars was reprocessed into the infrared (IR) by dust. At z~1.3, 90% of star formation is obscured by dust. To fully understand the cosmic star formation history, it is critical to investigate infrared emission. AKARI has made deep mid-IR observation using its continuous 9-band filters in the NEP field ($5.4deg^2$), using ~10% of the entire pointed observations available throughout its lifetime. However, there remain 11,000 AKARI infrared sources undetected with the previous CFHT/Megacam imaging (r ~25.9ABmag). Redshift and IR luminosity of these sources are unknown. These sources may contribute significantly to the cosmic star-formation rate density (CSFRD). For example, if they all lie at 1< z <2, the CSFRD will be twice as high at the epoch. We are carrying out deep imaging of the NEP field in 5 broad bands (g, r, i, z, and y) using Hyper Suprime-Camera (HSC), which has 1.5 deg field of view in diameter on Subaru 8m telescope. This will provide photometric redshift information, and thereby IR luminosity for the previously-undetected 11,000 faint AKARI IR sources. Combined with AKARI's mid-IR AGN/SF diagnosis, and accurate midIR luminosity measurement, this will allow a complete census of cosmic star-formation/AGN accretion history obscured by dust.