• 생태와환경
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• 제40권4호
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• pp.546-552
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• 2007

The objectives of this study were to analyze fish compositions, based on trophic guilds and tolerance guilds and determine community characteristics structure at five sampling sites of Yeongsan Lake during July 2006-May 2007. Total number of species sampled was 30 species and the number was 1350. Cyprinidae (77%) and Centrarchidae (15.7%) dominated the community and then followed by Cobitidae(2.7%), Gobiidae(2.4%), Mugilidae (0.5%), and others (0.1%). The relative abundance of tolerant and omnivore species at all sites was 63% and 77% of the total, respectively, suggesting an ecological degradations in the Lake. Exotics species such as large mouth bass (Micropterus salmoides), which is a top-carnivore in the water distributed at all sampling sites, implying that ecological disturbance was severe based on previous reference of US EPA (1991). Also, we found external anomalies such as external deformities, bleeding and tumors and not found migratory fish. Analysis of fish community structure showed that species diversity index and richness index was the highest in Site 1 and the dominance index was the highest in Site 2. In this study, high proportions of tolerant species and omnivore species, widespread exotic species, and frequent observations of abnormal fish. Such problems may be directly or indirectly associated with high nutrient enrichments and the reduced flow velocity by the dam construction. The ecosystem restoration by dam removal or removal of exotic top-carnivore fish may be one of the best strategies for better lak management.

• Interaction and multiscale mechanics
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• 제3권3호
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• pp.235-255
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• 2010

This paper investigates the heat equation for domains subjected to an internal source with a sharp spatial gradient. The solution is first approximated using linear finite elements, and sufficiently small time-step sizes to yield stable simulations. The main area of interest is then in the ability to approximate the solution using Generalized Finite Elements, and again explore the time-step limitations required for stable simulations. Both high order elements, as well as elements with special enrichments are used to generate solutions. When compared to linear finite elements, the high order elements deliver better accuracy at a given level of mesh refinement, but do not offer an increase in critical time-step size. When special enrichment functions are used, the solution can be approximated accurately on very coarse meshes, while yielding solutions which are both accurate and computationally efficient. The major conclusion of interest is that the significantly larger element size yields larger allowable time-step sizes while still maintaining stability of the time-stepping algorithm.

• Nuclear Engineering and Technology
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• 제48권3호
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• pp.778-784
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• 2016

HyperGam-U was recently developed to determine uranium enrichment based on ${\gamma}$- and X-ray spectroscopy analysis. The $XK_{\alpha}$ region of the uranium spectrum contains 13 peaks for $^{235}U$ and $^{238}U$ and is used mainly for analysis. To describe the X-ray peaks, a Lorentzian broadened shape function was used, and methods were developed to reduce the number of fitting parameters for decomposing the strongly overlapping peaks using channel-energy, energy-width, and energy-efficiency calibration functions. For validation, eight certified reference material uranium samples covering uranium enrichments from 1% to 99% were measured using a high-resolution planar high-purity germanium detector and analyzed using the HyperGam-U code. When corrections for the attenuation and true coincidence summing were performed for the detection geometry in this experiment, the goodness of fit was improved by a few percent. The enrichment bias in this study did not exceed 2% compared with the certified values for all measured samples.

• 천문학회보
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• 제42권1호
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• pp.49.1-49.1
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• 2017

In order to investigate the origin of multiple stellar populations in the halo and bulge of the Milky Way, we have constructed chemical evolution models for the low-mass proto-Galactic subsystems such as globular clusters (GCs). Unlike previous studies, we assume that supernova blast waves undergo blowout without expelling the pre-enriched gas, while relatively slow winds of massive stars, together with the winds and ejecta from low and intermediate mass asymptotic giant branch stars, are all locally retained in these less massive systems. We first applied these models to investigate the origin of super-helium-rich red clump stars in the metal-rich bulge as recently suggested by Lee et al. (2015). We find that chemical enrichments by the winds of massive stars can naturally reproduce the required helium enhancement (dY/dZ = 6) for the second generation stars. Disruption of these "building blocks" in a hierarchical merging paradigm would have provided helium enhanced stars to the bulge field. Interestingly, we also find that the observed Na-O anticorrelation in metal-poor GCs can be reproduced, when multiple episodes of starbursts are allowed to continue in these subsystems. Specific star formation history with decreasing time intervals between the stellar generations, however, is required to obtain this result, as would be expected from the orbital evolution of these subsystems in a proto-Galaxy. The "mass budget problem" is also much alleviated by our models without ad-hoc assumptions on star formation efficiency and initial mass function.

• 천문학회보
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• 제43권1호
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• pp.46.1-46.1
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• 2018

In order to investigate the origin of multiple stellar populations in the halo and bulge of the Milky Way, we have constructed chemical evolution models for the low-mass proto-Galactic subsystems such as globular clusters. Unlike previous studies, we assume that supernova blast waves undergo blowout without expelling the pre-enriched gas, while relatively slow winds of massive stars, together with the winds and ejecta from low and intermediate mass asymptotic-giant-branch stars, are all locally retained in these less massive systems. We find that the observed Na-O anti-correlations in metal-poor GCs can be reproduced when multiple episodes of starbursts are allowed to continue in these subsystems. A specific form of star formation history with decreasing time intervals between the stellar generations, however, is required to obtain this result, which is in good agreement with the parameters obtained from our stellar evolution models for the horizontal-branch. The "mass budget problem" is also much alleviated by our models without ad-hoc assumptions on star formation efficiency and initial mass function. We also applied these models to investigate the origin of super helium-rich red clump stars in the metal-rich bulge as recently suggested by Lee et al. (2015). We find that chemical enrichments by the winds of massive stars can naturally reproduce the required helium enhancement (dY/dZ = 6) for the second-generation stars. Disruption of proto-globular clusters in a hierarchical merging paradigm would have provided helium enhanced stars to the bulge field.

• 성인간호학회지
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• 제17권1호
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• pp.128-138
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• 2005

Purpose: As population of elderly people continues to grow, successful aging has risen to the top of the nursing science agenda. The successful aging includes maintenance of the cognitive and physical functions, as well as emotional well-beings. This study was carried out to evaluate effects of the environmental enrichments on cognition of institutionalized elderly. Method: The population was selected among the elderly aging over 65 residing at two of institutions. A quasi experimental design was used with non-equivalent control group. Study subjects were thirteen for each group. For the experimental group, physical, social and symbolic environmental enrichment program was provided for six weeks. The data were analyzed by repeated measure ANOVA and repeated measure ANCOVA using SPSS Win 11.0. Result: Compared to control group, the experimental group showed a significant difference on DSF(F=3.29, p=.046), and TMTA(F=4.76, p=.013) of cognitive function, and depression (F=5.56, p=.007) of emotional distress after 1 and 12 weeks of environmental enrichment program. Conclusion: Findings indicate that physical, social, and symbolic environmental enrichment was effective to partially prevent from cognitive decline, and to decrease emotional distress of elderly. As a nursing intervention, environmental enrichment program for elderly should be expanded for nursing practice to promote healthy aging and to offer support to the growing population of elderly. Further research should be conducted to evaluate the effect on the community elderly.

• 한국대기환경학회지
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• 제11권2호
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• pp.191-198
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• 1995

In order to evaluate the distribution and behaviour of atmospheric particulate metals in high-altitude area, we collected 22 aerosol samples using a high volume air sampler at Soback Mt. Meteorological Observation Station from Jan. to Nov. 1993 and analysed for metals (Al, Fe, Mg, Na, Ca, Mn, Co, Ni, Cu, Zn, Cd, and Pb) with ICP/AES and ICP/MS. Although sampling site is located in high-altitude and far from local sources of atmospheric pollutants, enrichments of metals are 2 times higher than those of western coastal reural area. This fact may imply that of metallic pollutants in the coastal rural site were came from further western side (e.g. China), atmospheric metals in this study area contain the signal of metropolitan cities located in the main wind direction (NNW). Sea salts are negligible in the aerosol particle population because reference elements of sea salts (Na, Mg) are all originated from soil particles. The contents of soil particles in aerosols are highest in spring and lowest in winter. Atmospheric enriched elements (Ni, Cu, Zn, Cd and Pb) are diluted with soil particles, especially during the yellow sand period. The results of factor analysis suggest possibility of interpreting their chemical significance in terms of sources (soil, pollutants) and gas-particle conversion processes (formation of ammonium sulfates, ammonium nitrates and/or their mixtures).

• 자원환경지질
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• 제19권1호
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• pp.19-24
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• 1986

The Samkwang mine is one of gold deposits distributed mainly in the southwestern province (Chungnam) of the Korean peninsula. Golds occur in quartz veins aged of $223{\pm}4MA$ according to K-Ar age dating from muscovite in a pegmatitic quartz vein. Quantz veins intrude Precambrian biotite-granite gneiss and mica schist of unknown age. Fluid inclusions in the quartz show a range of homogenization temperatures from 159 to $274^{\circ}C$. A calculated temperature from the isotopes of the galena-sphalerite pair is $375^{\circ}C$. Two phases-fluid inclusions homogenized either by liquid or vapor phase are frequently observed in specimens over $260^{\circ}C$, which may indicate the boiling of the fluids. Pressure of formation of the quartz veins inferred by the homogenization temperatures of liquid-$CO_2$ bearing fluid is 1kb. Based on these data, it is assumed that the temperature of the formation of the Samkwang mine may lie in between $350^{\circ}-230^{\circ}C$. ${\delta}^{34}S_{{\Sigma}s}$ values of sulphide minerals show narrow range of +2.1 to +4.6, and show a trend of enrichments of $^{34}S$ in the fluid from deep to the surface. ${\delta}^{34}S_{{\Sigma}s}$ in the fluid estimated is less than 3 permil, suggesting sulphur fluid originated from the magma.

• 천문학회보
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• 제36권2호
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• pp.105.1-105.1
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• 2011

We present the modeling results of deuterium fractionation of water ice, $H_2$, and the primary deuterium isotopologues of $H3^+$ in the physical conditions associated with the star and planet formation process. We calculated the deuterium chemistry for a range of gas temperatures (Tgas~10-30 K) and ortho/para ratio (opr ) of $H_2$ based on state-to-state reaction rates and explore the resulting fractionation including the formation of a water ice mantle coating grain surfaces. We find that the deuterium fractionation exhibits the expected temperature dependence of large enrichments at low gas temperature, but only for opr-H2<0.01. More significantly the inclusion of water ice formation leads to large D/H ratios in water ice (${\geq}10^{-2}$ at 10 K) but also alters the overall deuterium chemistry. For T<20 K the implantation of deuterium into ices lowers the overall abundance of HD which reduces the efficiency of deuterium fractionation at high density. Under these conditions HD will not be the primary deuterium reservoir in the cold dense interstellar medium and $H3^+$ will be the main charge carrier in the dense centers of pre-stellar cores and the protoplanetary disk midplane.

• Bulletin of the Korean Chemical Society
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• 제30권1호
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• pp.49-52
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• 2009

Single-drop microextraction (SDME) is an extraction methodology where the drop plays an essential role as extracts. It was evaluated for the GC-MS determination of nerve agents, one class of the chemical warfare agents (CWAs). Since these nerve agents are highly toxic, it is important to detect the nerve agents in the environmental samples. Several affecting factors including extraction solvents, stirring rate, extraction time, and amounts of salt were optimized. The limit of detections (LODs) were 0.1 - 10 ng/mL and the relative standard deviations (RSDs%, n=5) were in the range of 6.3% to 9.0% for four nerve agents. Without pretreatment of the environmental samples, 5-103 fold enrichments and 48-100% recovery were accomplished. These results demonstrated the feasibility of this method for on-site and off-site analysis of water sample collected from suspicious CWAs site.