• Journal of Ecology and Environment
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• 제36권4호
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• pp.223-233
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• 2013

Acid deposition is one of the most serious environmental problems in ecosystems. The present study surveyed the effects of simulated acid rain on leaf litter mass loss and microbial community in the decomposing leaf litter of Sorbus anifolia in a microcosm at $23^{\circ}C$ and 40% humidity. Microbial biomass was measured by substrate-induced respiration (SIR) and phospholipid fatty acids (PLFAs), and the microbial community structures were determined by composition of PLFAs at each interval of decomposition in litter sample and at each pH treatment. The microbial biomass showed peaks at mid-stage of decomposition, decreasing at the late stage. The leaf litter mass loss of S. anifolia decreased with decreasing pH during early and mid-decomposition stages; however the mass loss becomes similar between pH treatments at late-decomposition stage. The acidification remarkably lowers the microbial biomass of bacteria and fungi; however, microbial diversity was unchanged between pH treatments at each stage of litter decomposition. With changes of decomposition stage and pH treatment there were considerable differences in replacement and compensation of microbial species. Fungi/bacteria ratio was considerably changed by pH treatment. The PLFA profile showed significantly larger fungi/bacteria ratio at pH 5 than pH 3 at the early stage of decomposition, and the difference becomes smaller at the later decomposition stage. At low pH, pH 3 and pH 4, the fungi/bacteria ratios were stable according to the litter decomposition stages. Simulated acid rain caused decreases of 10Me17:0, 16:1${\omega}$7c, 18:1${\omega}$7, 15:0, but increase of 24:0. In addition, litter mass loss showed significant positive correlation with microbial biomass measured by SIR and PLFA on the decomposing leaf litter.

• 천문학회보
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• 제41권1호
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• pp.59.4-60
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• 2016

One important aspect of the late stage stellar evolution is the mass loss processes, where a significant amount of stellar material will be returned to the interstellar space to be used for stars of the next generation. Raman scattered O VI and He II by atomic hydrogen in symbiotic stars and young planetary nebulae are found to be excellent tools to investigate the mass loss processes and estimate the mass loss rate. These features appear near hydrogen Balmer emission lines due to the huge cross section in the vicinity of Lyman resonance transitions. With the capability of high spectral resolution and broad spectral coverage, BOES is an ideal instrument to perform Raman spectroscopy of these objects. In this talk, a cursory overview of our research activities on Raman spectroscopy of symbiotics and PNe using the BOES is presented.

• 천문학회보
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• 제44권2호
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• pp.60.3-60.3
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• 2019

Binary systems of a white dwarf showing mass transfer activities are classified into cataclysmic variables and symbiotic stars. In the case of cataclysmic variables, the companion is usually a late type main sequence star filling its Roche lobe, where material is transferred through the inner Lagrangian point to form an accretion disk around the white dwarf. The disk becomes unstable and highly viscous when the surface density exceeds the critical density, leading to dwarf nova outbursts. In contrast, symbiotic stars are wide binary systems having a giant as the mass donor. Some fraction of giant stellar wind is accreted to the white dwarf giving rise to various symbiotic activities. In particular, half of symbiotics show Raman O VI at 6830 and 7088, which are important spectroscopic probe of mass transfer process. Monitoring observations using 1 m class telescopes will produce valuable information regarding the mass loss and mass transfer to white dwarf stars, shedding much light on the last stage of stellar evolution of low and intermediate mass stars.

• 천문학논총
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• 제30권2호
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• pp.283-287
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• 2015

Within the context of the hugely successful SAGE-LMC and SAGE-SMC surveys, Spitzer photometry observations of the Large and Small Magellanic Clouds have revealed millions of infrared point sources in each galaxy. The brightest infrared sources are generally dust producing and mass-losing evolved stars, and several tens of thousands of such stars have been classified. After photometrically classifying these objects, the dust production by several kinds of evolved stars - such as Asymptotic Giant Branch stars and Red Supergiants - can be determined. SAGE-Spec is the spectroscopic follow-up to the SAGE-LMC survey, and it has obtained Spitzer-IRS $5-40{\mu}m$ spectroscopy of about 200 sources in the LMC. Combined with archival data from other programs, observations at a total of ~1000 pointings have been obtained in the LMC, while ~250 IRS pointings were observed in the SMC. Of these, a few hundred pointings represent dust producing and mass-losing evolved stars, covering a range in colors, luminosities, and thus mass-loss rates. Red Supergiants and O-rich and C-rich AGB stars - the main dust producers - are well represented in the spectroscopic sample. This paper will summarize what we know about the mineralogy of dust producing evolved stars, and discuss their relative importance in the total dust budget.

• 대한지리학회지
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• 제50권2호
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• pp.165-183
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• 2015

15세기 이래로 인간의 토지이용으로 인한 토양유실은 그 어느 때보다 급격하게 증가하였다. 그러나 '현재와 같은 토양유실이 계속되면 언제까지 토양이 유지될 수 있는가?'라는 물음에 우리는 정작 답할 수 없었다. 이는 토양생성률을 정량화하는 것이 쉽지 않았기 때문이다. 최근 우주선유발 동위원소를 이용하여 토양생성률을 정량화하는 기법이 등장하였고 국내에도 이를 적용한 시도가 있었다. 본 연구는 우주선유발 동위원소를 이용한 토양생성률 및 토양생성함수 도출 원리를 소개하고, 국내 토양생성률 연구결과를 20세기 이후의 토양유실률 자료와 비교 분석하여 토양의 지속가능기간을 예측해보았다. 대관령 고원에서 추정한 인류세 이전의 토양생성률은 평균 $0.05[mm\;yr^{-1}]$으로 밝혀졌으며, 20세기 후반 인간의 토지이용이 집약적으로 나타나는 농경지에서의 토양유실률은 이에 비해 많게는 60배나 상회하였다. 현재의 토지이용이 유지될 경우, 대하천 상류지역 농경지의 표층토양은 빠르면 수십 년내 사라질 것으로 예측된다.

• 천문학회보
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• 제45권1호
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• pp.70.1-70.1
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• 2020

A type IIb supernova (SN IIb) is the result of core-collapse of a massive star which lost most of its hydrogen-rich envelope during its evolution. The pre-SN progenitor properties, such as the total radius and the mass of the hydrogen-rich envelope, can widely vary due to the mass-loss history of the progenitors. Optical light curves of SNe IIb are dominated by energy released by the hydrogen recombination and the radioactive decay of 56Ni in the early and late epochs respectively. This may result in distinctive double peaked light curves like the one observed in SN 1993J. The first peak, caused by the hydrogen recombination, can be modelled with numerical simulations providing information on the pre-SN progenitor properties. We compare two radiation-hydrodynamics codes, STELLA and SNEC, that are frequently used in SNe modelling, and investigate the effect of opacity treatment on the temporal evolution of the color temperature of SNe and eventually on the optical light curves. We find that with a proper treatment of the scattering opacity, SNe IIb models exploded from the progenitor models evolved with latest stellar evolution model hardly match the observational data. We also discuss the smaller scale features found in the models during hydrogen recombination phase.

• 천문학회지
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• 제56권2호
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• pp.149-157
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• 2023

The propagation speed of a circumstellar pattern revealed in the plane of the sky is often assumed to represent the expansion speed of the wind matter ejected from a post-main-sequence star at the center. We point out that the often-adopted isotropic wind assumption and the binary hypothesis as the underlying origin for the circumstellar pattern in the shape of multilayered shells are, however, mutually incompatible. We revisit the hydrodynamic models for spiral-shell patterns induced by the orbital motion of a hypothesized binary, of which one star is losing mass at a high rate. The distributions of transverse wind velocities as a function of position angle in the plane of the sky are explored along viewing directions. The variation of the transverse wind velocity is as large as half the average wind velocity over the entire three dimensional domain in the simulated models investigated in this work. The directional dependence of the wind velocity is indicative of the overall morphology of the circumstellar material, implying that kinematic information is an important ingredient in modeling the snapshot monitoring (often in the optical and near-infrared) or the spectral imaging observations for molecular line emissions.

• 천문학논총
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• 제7권1호
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• pp.155-166
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• 1992

We observed a total of 14 Mira variables as well as 4 late type variable stars for their SiO ${\nu}= 1$, J = 2 - 1 maser lines from April 1989 to November 1990 with the 13.7 m radio telescope at Daeduk Radio Astronomy Observatory. The maser intensity variations were the prime objective of the observations which well covered the periods of the variations. The origion of the variations were studied by comparing wi th those previousely measured in optical and infrared(IR) wavelengths and we confirmed that the intensity variations were in good correlation with those in V magnitude and IR intensity as previousely found in former investigators in general. However, for a few sources, we could find the missing maxima. The intensities themselves also were in good correlation with SiO ${\nu}\;=\;1$, J = 1 - 0 maser intensities observed in Yebes as expected. The good correlations indicate that the pumping source of the SiO maser is likely to be the IR emission in the masing regions and the "missing maxima" that are apparent in two particular sources are considered to relate wi th the strength of shocks arising from the eruptive mass-loss from central stars.

• 한국안전학회지
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• 제35권5호
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• pp.22-29
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• 2020

In this study, combustion and smoke release characteristics of a non-class 1E cable for nuclear power plants were investigated according to aging period. The aging was reproduced through an accelerated aging method for interval of 10 years :10, 20, 30 and 40 year, which was applied the Arrhenius equation. The cable was subjected to accelerated aging. In order to understand combustion and smoke release characteristics, the cone calorimeter test was performed according to the standard code of KS F ISO 5660-1. Heat release rate, mass loss rate, average rate of heat emission and smoke production rate were examined through cone calorimeter test. Fire performance index, fire growth index and smoke factor were derived from test results for the comparison of quantitative fire risk. When comparing the fire performance index and the fire growth index, the early fire risk tends to decrease as aging progresses, which might be attributed from the fact that the volatile substances of cables were evaporated. However, when comparing the heat release rate, average rate of heat emission and mass loss rate, which represent the mid and late periods of the fire risk, the values of accelerated aging cables were much higher than those of non-aged cable, which signifies the unstable formation of the char layer resulted in the change in the performance of flame retardants. In addition, the results from the smoke characteristics show that the accelerated aging cables were lager than the non-aged cables in terms of overall fire risk. These results can be used as baseline data when assessing fire risk of cables and establishing fire safety code for nuclear power plants.

• Journal of Nutrition and Health
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• 제34권5호
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• pp.547-553
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• 2001

This study was designed to observe the change of body composition and nutrient metabolites and the excretion of minerals during complete fasting for 10 days in thirty women. Average loss of body weight was 7.98kg and body fat was gradually reduced after 9 days fasting, but the loss of lean body mass was reduced after 7 days fasting. Serum glucose level was sustained at constant level, but serum levels of blood urea nitrogen, free acid and $\beta$-hydroxybutyrate were significantly increased during fasting but decreased after re-feeding. Urinary excretions of 3-methylhistidine, total creatinine, and urea were high in the beginning of fasting but gradually decreased. Serum level of parathyroid hormone was significantly reduced by fasting but regained after re-feeding. Serum level of minerals was at the constant level throughout the experimental period. The urinary excretion of minerals(Ca, K, Mg, P) was significantly increased in the early stage of fasting and then reduced from 7 days, but the excretion of Zn was continuously increased until the late stage of fasting. These results showed that amino acid fatty acid released from the breakdown of muscle protein and body fat, respectively, were utilized for energy during fasting. Body weight and BMI were reduced because of the increased muscle protein breakdown and body water excretion during early stage of fasting, but the significant body fat loss was after 9 days fasting. Therefore, it could be suggested to fast for longer than 10 days if the reduction of body fat was planned by fasting, and recommed to exercise and ingest more vitamins and minerals to replace the excreted minerals during fasting. (Korean J Nutrition 34(5) : 547~553, 2001)