• Journal of Navigation and Port Research
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• v.43 no.5
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• pp.296-301
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• 2019

The Electronic Chart Display and Information System (ECDIS) is an integral component of ship navigation equipment, that enables mariners to view Electronic Navigational Charts (ENC). Recently, it has become possible to transport freight and energy resources via the Northern Sea Routes (NSR) as global warming has been accelerating. However, ice can impact all types of ships and the potential danger that ice poses is significant. Until now, ice, consistently proven to be one of the most dangerous threats impacting navigation in ice-covered regions, has its detailed standard in the specification of the International Hydrographic Organization (IHO) for ECDIS. The investigations described in this paper were conducted to assess the advantages and problems of the display of ice objects on ECDIS. The experiments were conducted by using the Geographic Information System (GIS) to perform ice objects with their corresponding colors and symbols. Implementation of the standardized appearance of ice objects can enable mariners to access the ice condition of seas in a short time before navigating a safe passage through potentially treacherous waters. However, remain issues that must be overcome for data on ice to be fully compatible with an ECDIS system.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.81.1-81.1
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• 2012

Herschel Key Program 중의 하나인 "Dust, Ice and Gas In Time (DIGIT)"의 관측 및 분석결과를 발표하고자 한다. 특히 DIGIT 천체들 중 Photodetector Array Camera and Spectrometer (PACS)로 관측된 별생성 초기 단계에 있는 embedded objects들의 FIR SED와 CO, $H_2O$, OH, [OI], [CII]의 FIR 천이선들의 공간분포와 생성기작을 분석한다. 뿐만 아니라, 원시성의 특성들($L_{bol}$과 $T_{bol}$)과 이들 각 분자/원자선에 의한 냉각률의 관계를 통계적으로 분석한 결과를 제시한다.

• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.105-107
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• 2017

We present results of AKARI/IRC near-infrared (NIR) slit-spectroscopy ($2.5-5.0{\mu}m$, R ~ 100) of Galactic sources, focusing on ice absorption features. We investigate the abundance of $H_2O$ and $CO_2$ ices and other ice species (CO and XCN ices) along lines of sight towards Galactic H $\small{II}$ regions, massive YSOs, and infrared diffuse sources. Even among those different kinds of astronomical objects, the abundance ratio of $CO_2$ to $H_2O$ ices does not vary significantly, suggesting that the pathway to $CO_2$ ice formation driven by UV irradiation is not effective at least among the present targets.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.45.3-46
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• 2018

Although mass accretion from the disk to the central protostar is a key process of low mass star formation, the accretion mechanism is still poorly understood. To investigate "episodic accretion", which has been suggested as an accretion mechanism in low mass star formation, we have carried out near-infrared spectroscopic observations of three very low-luminosity objects (VeLLOs) and one background source, using InfraRed Camera onboard the AKARI space telescope. The ice absorption features of $H_2O$, $CO_2$, and CO were detected around the wavelengths of 3.0, 4.26, and $4.67{\mu}m$, respectively. In addition, we revealed the XCN ice feature, which is attributed to high energy UV photons produced by the episodic burst accretion. The comparisons of the ice abundances of our targets with those of other YSOs observed previously with AKARI IRC imply that the three VeLLOs had experienced burst accretions although they are now in a very quiescent phase.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.177-179
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• 2012

We present Spitzer IRS spectroscopy of $CO_2$ ice toward 19 young stellar objects (YSOs) with luminosity lower than $1L_{\odot}$. Pure $CO_2$ ice forms only at elevated temperatures, T > 20 K, and thus at higher luminosities. Current internal luminosities of YSOs with L < $1L_{\odot}$ do not provide such conditions out to radii of typical envelopes. Significant amounts of pure $CO_2$ ice would signify a higher past luminosity. We analyze $15.2{\mu}m$ $CO_2$ ice bending mode absorption lines in comparison to the laboratory data. We decompose pure $CO_2$ ice from 12 out of 19 young low luminosity sources. The presence of the pure $CO_2$ ice component indicates high dust temperature and hence high luminosity in the past. The sum of all the ice components (total $CO_2$ ice amount) can be explained by a long period of low luminosity stage between episodic accretion bursts as predicted in an episodic accretion scenario. Chemical modeling shows that the episodic accretion scenario explains the observed total $CO_2$ ice amount best.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.70.4-70.4
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• 2019

Complex organic molecules (COMs) are increasingly observed in the environs of young stellar objects (YSOs), including hot cores/corinos around high-mass/low-mass protostars and protoplanetary disks. It is widely believed that COMs are first formed in the ice mantle of dust grains and subsequently released to the gas by thermal sublimation at high temperatures (T>100 K) in strong stellar radiation fields. In this paper, we report a new mechanism that can desorb COMs from icy grain mantles at low temperatures (T<100K), which is termed rotational desorption. The rotational desorption process of COMs comprises two stages: (1) ice mantles on suprathermally rotating grains spun-up by radiative torques (RATs) are first disrupted into small fragments by centrifugal stress, and (2) COMs and water ice then evaporate rapidly from the tiny fragments (i.e., radius a <1nm) due to thermal spikes or enhanced thermal sublimation due to increased grain temperature for larger fragments (a>1 nm). We discuss the implications of rotational desorption for releasing COMs and water ice in the inner region of protostellar envelopes (hot cores and corinos), photodissociation regions, and protoplanetary disks (PPDs). In shocked regions of stellar outflows, we find that nanoparticles can be spun-up to suprathermal rotation due to supersonic drift of neutral gas, such that centrifugal force can be sufficient to directly eject some molecules from the grain surface, provided that nanoparticles are made of strong material. Finally, we find that large aggregates (a~ 1-100 micron) exposed to strong stellar radiations can be disrupted into individual icy grains via RAdiative Torque Disruption (RATD) mechanism, which is followed by rotational desorption of ice mantles and evaporation of COMs. In the RATD picture, we expect some correlation between the enhancement of COMs and the depletion of large dust grains in not very dense regions of YSOs.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.83.2-83.2
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• 2011

I present results from the Spitzer/IRS study to identify massive young stellar objects (YSOs) in the Galactic Center (GC). Our sample of 107 YSO candidates was selected based on Spitzer/IRAC colors in the central 300 pc region of the Milky Way Galaxy. We obtained IRS spectra over $5{\mu}m$ to $35{\mu}m$, and identified massive YSOs by the presence of a $15.4{\mu}m$ shoulder on the absorption profile of $15{\mu}m$ $CO_2$ ice, suggestive of high $CH_3OH$ abundance on $CO_2$ ice grains. This $15.4{\mu}m$ shoulder is clearly observed in 16 sources and possibly observed in an additional 19 sources. We further show that 9 massive YSOs reveal molecular gas-phase absorption from $CO_2$, $C_2H_2$, and/or HCN, which traces warm and dense gas in YSOs. Our results provide the first spectroscopic census of the massive YSO population in the GC.

• Journal of The Korean Astronomical Society
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• v.40 no.4
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• pp.83-89
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• 2007

A new type of object called "Very Low Luminosity Objects (VeLLOs)" has been discovered by the Spitzer Space Telescope. VeLLOs might be substellar objects forming by accretion. However, some VeLLOs are associated with strong outflows, indicating the previous existence of massive accretion. The thermal history, which significantly affects the chemistry, between substellar objects with a continuous low accretion rate and objects in a quiescent phase after massive accretion (outburst) must be greatly different. In this study, the chemical evolution has been calculated in an episodic accretion model to show that CO and $N_2H^+$ have a relation different from starless cores or Class 0/I objects. Furthermore, the $CO_2$ ice feature at $15.2{\mu}m$ will be a good tracer of the thermal process in VeLLOs.

• Structural Engineering and Mechanics
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• v.62 no.2
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• pp.179-196
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• 2017

The paper focuses on dynamic analyses of a series of simply-supported symmetric composite steel-concrete bridges loaded by an ICE-3 train moving at high speeds up to 300 km/h. The series includes five bridges with span lengths ranging from 15 m to 27 m, with repeatable geometry of the superstructures. The objects, designed according to Polish standards valid from 1980s to 2010, are modelled on the bridges serviced on the Central Main Line in Poland since 1980s. The advanced, two-dimensional, physically nonlinear model of the bridge-track structure-high-speed train system takes into account unilateral nonlinear wheel-rail contact according to Hertz's theory and random vertical track irregularities equal for both rails. The analyses are focused on the influence of random track irregularities on dynamic response of composite steel-concrete bridges loaded by an ICE-3 train. It has been pointed out that certain restrictions on the train speed and on vertical track irregularities should be imposed.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.41.3-41.3
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• 2019

Ices in interstellar environments are well traced mostly by their absorption features in the near- to mid-infrared spectrum. The infrared camera (IRC) aboard AKARI provides us the near-infrared spectroscopic data which cover $2.5-5.0{\mu}m$ with a spectral resolution of R ~ 120. Our AKARI spectroscopic survey of young stellar objects (YSOs), including low-luminosity protostars and background stars, revealed the absorption features of $H_2O$, $CO_2$, CO, and XCN ice components. We present near-infrared spectra of the observed targets and compare their ice abundances with those previously derived from various YSOs and the background stars behind dense molecular clouds and cores. In addition, we suggest possible science cases for SPHEREx, NASA's new near-infrared space observatory, based on the results from our AKARI IRC spectroscopic study.