• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.57.1-57.1
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• 2021

The icy mantles of interstellar grains are developed by the freeze-out of interstellar molecules and atoms onto grain surfaces. The ice molecules become more complex by surface chemistry induced directly by high energy photons or by the thermal energy diffused over heated grain surface. Therefore, the ice composition is an important tracer of physical conditions where the ices form. Ices have been studied via their absorption features against continuum sources, such as young stellar objects or evolved background stars, in infrared wavelengths. The Spitzer IRS was the most sensitive spectrometer for the observations of infrared ice absorption features. We has been developing an automated analysis tool for the Spitzer IRS spectra, especially for the 15 ㎛ CO₂ bending mode. The 15 ㎛ CO₂ absorption feature is very useful for the study of accretion process in star formation since its spectral shape varies with thermal condition of the dust grains. Eventually, this tool will cover the whole range of the Spitzer IRS spectrum (5~20 ㎛).

• Ocean and Polar Research
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• v.44 no.4
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• pp.269-285
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• 2022

The interaction between ocean and ice shelf is a critical physical process in relation to water mass transformations and ice shelf melting/freezing at the ocean-ice interface. However, it remains challenging to thoroughly understand the process due to a lack of observational data with respect to ice shelf cavities. This is the first study to simulate the variability and circulation of water mass both overlying the continental shelf and underneath an ice shelf and an ice tongue in the Terra Nova Bay (TNB), East Antarctica. To explore the properties of water mass and circulation patterns in the TNB and the corresponding effects on sub ice shelf basal melting, we explicitly incorporate the dynamic-thermodynamic processes acting on the ice shelf in the Regional Ocean Modeling System. The simulated water mass formation and circulation in the TNB region agree well with previous studies. The model results show that the TNB circulation is dominated by the geostrophic currents driven by lateral density gradients induced by the releasing of brine or freshwater at the polynya of the TNB. Meanwhile, the circulation dynamics in the cavity under the Nansen Ice shelf (NIS) are different from those in the TNB. The gravity-driven bottom current induced by High Salinity Shelf Water (HSSW) formed at the TNB polynya flows towards the grounding line, and the buoyance-driven flow associated with glacial meltwater generated by the HSSW emerges from the cavity along the ice base. Both current systems compose the thermohaline overturning circulation in the NIS cavity. This study estimates the NIS basal melting rate to be 0.98 m/a, which is comparable to the previously observed melt rate. However, the melting rate shows a significant variation in space and time.

• Food Science and Biotechnology
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• v.17 no.1
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• pp.102-105
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• 2008

The freezing patterns of commercial frozen foods were characterized by using proton nuclear magnetic resonance ($^1H$ NMR) relaxometry and differential scanning calorimetry (DSC). The liquid-like components like unfrozen water were investigated as a function of temperature (10 to $-40^{\circ}C$) and then compared with the unfrozen water content measured by DSC. The formation of ice crystals and the reduction of water in the foods during freezing were readily observed as a loss of the NMR signal intensity. The proton NMR relaxation measurement showed that the decreasing pattern of the liquid-like components varied depending on the samples even though they exhibited the same onset temperature of ice formation at around $0^{\circ}C$. When compared with the unfrozen water content obtained by the DSC, the NMR and DSC results could be closely correlated at the temperature above $-20^{\circ}C$. However, the distinct divergence in the values between 2 methods was observed with further decreasing temperatures probably due to the solid glass formation which was not detected by DSC.

• 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.44 no.2
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• pp.49.2-49.2
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• 2019

We present results from our long-term observing campaign, using the NASA IRTF at Maunakea, to obtain 2 - 4 ㎛ spectra of 118 red point sources in the line of sight to the Galactic Center (GC). Our sample is largely composed of point sources selected from near- and mid-infrared photometry, but also includes a number of massive young stellar objects. Many of these sources show high foreground extinction as shown by deep 3.4 ㎛ aliphatic hydrocarbon absorption feature, which is a characteristic of the diffuse ISM and comes from the long line of sight through the diffuse medium toward the Central Molecular Zone (CMZ), the central 300 pc region of the GC. The deep 3.1 ㎛ H₂O ice absorption band coming from the local, dense material in the GC CMZ suggests that most sources are likely located in the GC CMZ. A few of these sources show weak CCH₃OH ice absorption at 3.535 ㎛, which can provide a strong constraint on the CCH₃OH ice formation in the unique environment of the CMZ. From the best-fitting models, the optical depths of these features are determined and used to generate a well-rounded view of the ice composition across the GC CMZ and the spectral characteristics of massive YSOs in the GC.

• Atmosphere
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• v.22 no.1
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• pp.73-85
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• 2012

The collision efficiency data for collision between graupel or hail particles and cloud drops that take into account the differences of particle density are applied to the Takahashi cloud model. The original setting assumes that graupel or hail collision efficiency is the same as that of the cloud drops of the same volume. The Takahashi cloud model is run with the new collision efficiency data and the results are compared with those with the original. As an initial condition, a thermodynamic profile that can initiate strong convection is provided. Three different CCN concentration values and therefore three initial cloud drop spectra are prescribed that represent maritime (CCN concentration = 300 $cm^{-3}$), continental (1000 $cm^{-3}$) and extreme continental (5000 $cm^{-3}$) air masses to examine the aerosol effects on cloud and precipitation development. Increase of CCN concentration causes cloud drop sizes to decrease and cloud drop concentrations to increase. However, the concentration of ice particles decreases with the increase of CCN concentration because small drops are difficult to freeze. These general trends are well captured by both model runs (one with the new collision efficiency data and the other with the original) but there are significant differences: with the new data, the development of cloud and raindrop formation are delayed by (1) decrease of ice collision efficiency, (2) decrease of latent heat from riming process and (3) decrease of ice crystals generated by ice multiplication. These results indicate that the model run with the original collision efficiency data overestimates precipitation rates.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.66.3-67
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• 2021

Low-mass stars form by the gravitational collapse of dense molecular cores. Observations and theories of low-mass protostars both suggest that accretion bursts happen in timescales of ~100 years with high accretion rates, so called episodic accretion. One mechanism that triggers accretion bursts is infalling fragments from the outer disk. Such fragmentation happens when the disk is massive enough, preferentially activated during the embedded phase of star formation (Class 0 and I). Most observations and models focus on the gas structure of the protostars undergoing episodic accretion. However, the dust and ice composition are poorly understood, but crucial to the chemical evolution through thermal and energetic processing via accretion burst. During the burst phase, the surrounding material is heated up, and the chemical compositions of gas and ice in the disk and envelope are altered by sublimation of icy molecules from grain surfaces. Such alterations leave imprints in the ice composition even when the temperature returns to the pre-burst level. Thus, chemical compositions of gas and ice retain the history of past bursts. Infrared spectral observations of the Spitzer and AKARI revealed a signature caused by substantial heating, toward many embedded protostars at the quiescent phase. We present the AKARI IRC 2.5-5.0 ㎛ spectra for embedded protostars to trace down the characteristics of accretion burst across the evolutionary stages. The ice compositions obtained from the absorption features therein are used as a clock to measure the timescale after the burst event, comparing the analyses of the gas component that traced the burst frequency using the different refreeze-out timescales. We discuss ice abundances, whose chemical change has been carved in the icy mantle, during the different timescales after the burst ends.

• Korean Journal of Remote Sensing
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• v.39 no.6_2
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• pp.1651-1669
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• 2023

Sea ice currently covers approximately 7% of the world's ocean area, primarily concentrated in polar and high-altitude regions, subject to seasonal and annual variations. It is very important to analyze the area and type classification of sea ice through time series monitoring because sea ice is formed in various types on a large spatial scale, and oil and gas exploration and other marine activities are rapidly increasing. Currently, research on the type and area of sea ice is being conducted based on high-resolution satellite images and field measurement data, but there is a limit to sea ice monitoring by acquiring field measurement data. High-resolution optical satellite images can visually detect and identify types of sea ice in a wide range and can compensate for gaps in sea ice monitoring using Geostationary Ocean Color Imager-II (GOCI-II), an ocean satellite with short time resolution. This study tried to find out the possibility of utilizing sea ice monitoring by training a rule-based machine learning model based on learning data produced using high-resolution optical satellite images and performing detection on GOCI-II images. Learning materials were extracted from Liaodong Bay in the Bohai Sea from 2021 to 2022, and a Random Forest (RF) model using GOCI-II was constructed to compare qualitative and quantitative with sea ice areas obtained from existing normalized difference snow index (NDSI) based and high-resolution satellite images. Unlike NDSI index-based results, which underestimated the sea ice area, this study detected relatively detailed sea ice areas and confirmed that sea ice can be classified by type, enabling sea ice monitoring. If the accuracy of the detection model is improved through the construction of continuous learning materials and influencing factors on sea ice formation in the future, it is expected that it can be used in the field of sea ice monitoring in high-altitude ocean areas.

• Korean Journal of Food Science and Technology
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• v.27 no.5
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• pp.783-788
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• 1995

Cooked rices were frozen at four different rates(3, 5, 7 and 12 hr) of maximum ice crystal formation zone and stored at $-20^{\circ}C\;and\;-70^{\circ}C$ for 3 months. Freezing rate, storage temperature and storage period all affected the degree of retrogradation of cooked rice. As the maximum ice crystal formation zone increased from 3 hrs to 12 hrs, the degree of retrogradation of cooked rice increased from 14.9% to 40.0%. Further retrogradation occurred during the freezing storage and cooked rice stored at $-20^{\circ}C$ retrograded faster than that held at $-70^{\circ}C$. The hardness and adhesiveness of frozen cooked rice thawed in $40^{\circ}C$ water were measured. Hardness of the frozen cooked rice was higher than that of non-frozen sample and was higher at lower freezing rate. However, the hardness of cooked rice decreased after 3 months of storage. On the other hand, the adhesiveness decreased during the freezing processing, and adhesiveness decreased more rapidly at a higher freezing rate. However, the adhesiveness of cooked rice increased after 3 months of the storage, and the level of decrease was higher at $-70^{\circ}C$ than at $-20^{\circ}C$. After 3 months of storage, ice crystal size of frozen cooked rice became larger by recrystalization than that of frozen sample prior to storage. Microstructure of cooked rice was damaged by ice crystal formation and its growth when observed by scanning electron microscope.

• Proceedings of the SAREK Conference
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• 2004.11a
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• pp.8-8
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• 2004