• 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.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.869-874
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• 2002

Hermetic rotary compressor is one of the most important components for air conditioning system since it has a great effect on both the performance and the noise and vibration of the system. Noise and vibration of rotary compressor is occurred due to gas pulsation during compression process and unbalanced dynamic force. In order to reduce noise and vibration, It is necessary to identify sources of noise and vibration and effectively control them. Many approaches have been tried to identify noise sources of compressor. However, compressor noise source identification has proven to be difficult since the characteristics of compressor noise are complicated due to the interaction of the compressor parts and gas pulsation. In this work, Statistical Energy Analysis has been used to trace the energy flow in the compressor and identify transmission paths from the noise source to the sound field.

• Analytical Science and Technology
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• v.12 no.6
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• pp.571-576
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• 1999

Screening method for NSAIDs (Hon-Steroidal Anti-Inflammatory Drugs) in urine was developed using GC/NCI-MS. Derivatized six fenamates with pentafluoropropionic anhydride showed high sensitivity in NCI-MS. The conditions of the derivatization reaction and chromatographic conditions were established for screening with a trace analysis. Limit of detection was in the range of 4-25 pg/mL. This method may be used to the equine doping analysis for NSAIDs and forensic analysis.

• Journal of Korean Society for Atmospheric Environment
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• v.21 no.E3
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• pp.75-85
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• 2005

A mathematical sensitivity analysis of the flow-through dynamic flux chamber technique, which has been utilized usually for various trace gas flux measurement from soil and water surface, was performed in an effort to provide physical and mathematical understandings of parameters essential for the NO flux calculation. The mass balance equation including chemical reactions was analytically solved for the soil NO flux under the steady state condition. The equilibrium concentration inside the chamber, $C_{eq}$, was found to be determined mainly by the balance between the soil flux and dilution of the gas concentration inside the chamber by introducing the ambient air. Surface deposition NO occurs inside the chamber when the $C_{eq}$ is greater than the ambient NO concentration ($C_{0}$) introducing to the chamber; NO emission from the soil occurs when the $C_{eq}$ is less than the ambient NO concentration. A sensitivity analysis of the significance of the chemical reactions of NO with the reactive species (i.e. $HO_{2},/CH_{3}O_{2},/O_{3}$) on the NO flux from soils was performed. The result of the analysis suggests that the NO flux calculated in the absence of chemical reactions and wall loss could be in error ranges from 40 to $85\%$ to the total flux.

• Environmental Engineering Research
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• v.12 no.3
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• pp.93-100
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• 2007

I improved an analytical method for determining trace amounts of eleven phenolic endocrine-disrupting chemicals (11 phenolic EOCs) in human urine. The 11 phenolic EOCs were subjected to hydrolysis and then to solid phase extraction with a XAD-4 column. Alkylphenols, chlorophenols, and bisphenol A in XAD-4 column were eluted with acetonitrile, and the eluate was concentrated under a nitrogen stream, and then tert-butyldimethylsilylation. Separation and determination were done by gas chromatography, using mass spectrometry operating in the selective ion monitoring mode for quantitation. For tert-butyldimethylsily (TBDMS) derivatization the recoveries were $91.2{\sim}125.9%$, the limits of quantitation (LOQ) for the 11 phenolic EOCs in the nanogram-per-milliliter range ($0.025{\sim}1.000\;ng/mL$) were thus achieved by using 1 mL of urine, and the SIM responses were linear with the correlation coefficient varying by $0.9300{\sim}0.9943$. Based on the results for urine samples from unexposed individuals, 4-tert-octylphenol and pentachlorophenol were detected in hydrolysed urine sample. Other alkylphenols, chlorophenols and bisphenol A were not detected.

• Applied Biological Chemistry
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• v.24 no.2
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• pp.120-125
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• 1981

Organic acids of Kochuzang (red pepper paste) prepared from glutinous rice, polished barley, wheat flour and sweet potato were analyzed by a gas chromatography. Lactic, pyruvic, succinic, fumaric, malic, pyroglutamic and citric acid were identified. And trace amount of oxalic acid was found in the Kochuzang prepared from sweet potato. The dominant organic acid of all samples was pyroglutamic acid, followed by pyruvic and citric acid. The organic acids were lower in Kochuzang from wheat flour than in other samples. The contents of succinic and fumaric acid were highest in Kochuzang prepared from sweet potato and were lowest in polished barley Kochuzang.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.72.2-72.2
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• 2012

We present the results of HI 21 cm line observations to explore the nature of the high-velocity (HV) HI gas at - 173${\circ}$, which appears as faint, wing-like, Hi emission that extends to velocities beyond those allowed by Galactic rotation in the low-resolution surveys. We designate this feature as Forbidden Velocity Wing (FVW) 172.8+1.5. Our high-resolution Arecibo HI observations show that FVW 172.8+1.5 is composed of knots, filaments, and ring-like structures distributed over an area of a few degrees in extent. These HV HI emission features are well correlated with the HII complex G173+1.5, which is composed of five Sharpless HII regions distributed along a radio continuum loop of size 4.4${\times}$3.4, or -138 pc ${\times}$ 107 pc, at a distance of 1.8 kpc. G173+1.5 is one of the largest star-forming regions in the outer Galaxy. The HV HI gas and the radio continuum loop seem to trace an expanding shell. Its derived HI parameters including large expansion velocity (55 km/s) imply the SNR interpretation. Hot xray emission is detected within the HII complex, which also supports its SNR origin. The FVW172.8+1.5 is most likely the products of a supernova explosion(s) within the HII complex, possibly in a cluster that triggered the formation of these HII regions.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2003.04a
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• pp.196-200
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• 2003

A gas chromatography/mass spectrometric assay method was developed for the simultaneous determination of ethylene glycol monomethyl ether (EGME) and diethylene glycol monomethyl ether (DEGME) in spilled aviation fuels. Ethylene glycol monobutyl ether (EGBE) and ethylene glycol monoethyl ether (EGEE) were used as internal standard and surrogate, respectively. The sample preparation consists of back-extraction with 7 mL of methylene chloride after extraction of 50 mL of fuel with 2 mL of water. The extract was concentrated to dryness and dissolved with 100L of methanol and analyzed by CC-MS (SIM). The peaks had good chromatographic properties by using semi-polar column and the extraction of these compounds from fuel also gave high recoveries of 75 and 85 % with small variations for EGME and DEGME, respectively. Method detection limits were 1.3 ng/mL for EGME and 1.0 ng/mL for DEGME in spilled fuel. The method may be useful for fuel-type differentiation between kerosene and JP-8, which may originate from the storage tank.

• Journal of The Korean Astronomical Society
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• v.37 no.4
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• pp.193-197
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• 2004

Anomalies in the far-infrared [C II] 158 ${\mu}m$ line emission observed in the central one-kiloparsec regions of spiral galaxies are reviewed. Low far-infrared intensity ratios of the [C II] line to the continuum were observed in the center of the Milky Way, because the heating ratio of the gas to the dust is reduced by the soft interstellar radiation field due to late-type stars in the Galactic bulge. In contrast, such low line-to-continuum ratios were not obtained in the center of the nearby spiral M31, in spite of its bright bulge. A comparison with numerical simulations showed that a typical column density of the neutral interstellar medium between illuminating sources at $hv {\~} 1 eV $ is $N_H {\le}10^{21}\;cm^{-2}$ in the region; the medium is translucent for photons sufficiently energetic to heat the grains but not sufficiently energetic to heat the gas. This interpretation is consistent with the combination of the extremely high [C Il]/CO J = 1-0 line intensity ratios and the low recent star-forming activity in the region; the neutral interstellar medium is not sufficiently opaque to protect the species even against the moderately intense incident UV radiation. The above results were unexpected from classical views of the [C II] emission, which was generally considered to trace intense interstellar UV radiation enhanced by active star formation.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.62.1-62.1
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• 2014

We present preliminary results on the chemical differentiation of two dense gas tracers CS and $N_2H^+$ in five 'evolved' starless cores, L1544, L1552, L1689B, L694-2 and L1197, using our mapping observations in $C^{34}S$(J=2-1) and $N_2H^+$(J=1-0) with Nobeyama 45-m telescope. We compared the intensity maps of two molecular lines with 850 ${\mu}m$ continuum data which precisely trace the density distribution of the dense cores, finding that all of our targets show the central depletion holes in CS distribution, but the similar distribution in $N_2H^+$ to the one in dust continuum. Our data confirm the claim that CS molecule generally deplete out in the central region in starless cores, while $N_2H^+$ keep abundant as they get evolved. The detailed quantitative analysis on CS depletion in the dense cores, for example, the size of CS depletion area and radial (or gas density) dependence of CS depletion, is underway and will be presented in the meeting.