• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.73-73
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• 2019

지구 표면의 약 2%에 해당하는 담수에서 육상계 전체가 흡수하는 탄소의 50%가 배출되며, 이는 토양표면에서 배출되는 탄소량에 비해 더 큰 수치로 전 지구적 탄소순환 해석에 중요한 역할을 한다. 특히, 내륙수역과 대기의 경계면에서 $CO_2$ 이동은 전 지구적 탄소순환의 중요한 구성요소로 평가되고 있다. 호수와 저수지 같은 담수 저류시설은 육상에서 기인한 탄소의 운송 및 처리 역할을 한다. 하지만, 저수지에서 온실가스배출량을 평가할 수 있는 명확한 방법론이 부족하며, 전지구 규모 GHGs배출량에 대한 추정에 대한 불확실성이 상당히 큰 상황이다. 본 연구에서는 몬순기후대에 위치한 인공저수지를 대상으로 보다 신뢰도있는 온실가스 배출량 추정을 위해 $CO_2$ NAF 산정하고, 산정에 영향을 미치는 인자들을 분석 하였다. 분석을 위해 $CO_2$ NAF 산정에 필요한 수리 및 수질 인자들을 2017년부터 2018년까지 수집하고, 기초통계량 및 상관분석을 실시하였다. 또한, 주성분분석(PCA) 및 다중선형회귀모델(MLR)과 랜덤포레스트(RF) 기법을 사용해 변수 중요도를 평가하였으며, $CO_2$ NAF 산정 주요인자인 기체교환 계수를 경험적 모델 3종(Cole and Caraco, Crusius, Vachon), 표면갱신형 모델 4종(Heiskanen, Maclntyre, Read, Soloviev)을 비교, 검토하였다. 조사기간 동안 기체교환계수 산정 결과 Crusius 모델 예측값이 평균 $0.342(0.047{\sim}4.323)cm\;hr^{-1}$으로 검토한 모델중 가장 낮은 평균값을 보였으며, Heiskane 모델이 $2.135(0.337{\sim}5.152)cm\;hr^{-1}$으로 가장 큰 평균값을 보였다. 대상 수체는 연주기로 완전혼합되며 수온성층이 약화되는 시기에 저수지 표층 아래에 축적된 탄소가 표층으로 전달되어 높은 수준의 p$CO_2$를 보이며, 수표면에 큰 난류 강도가 작용하는 기간에 대기중으로 배출(pulse emission) 기작이 나타난다. NAF 산정결과 경험적 모델의 NAF값($-1246.0{\sim}6510.3mg-CO_2m^{-2}day^{-1}$)은 표면갱신형 모델 NAF값($-1436.1{\sim}8485.7mg-CO_2m^{-2}day^{-1}$)보다 낮은 수준을 보였으며, 풍속의 함수만을 이용하는 경험적 모델보다 부력 플럭스와 난류 혼합의 영향을 고려하는 Macintyre, Heiskanen모델이 성층 저수지의 $CO_2$ NAF 산정에 적합한 것으로 나타났다. $CO_2$ NAF 산정의 주요인자로 MLR모델은 Tw, EC, pH, Chla, TOC, Alk, RF모델은 EC, DO, TOC가 중요 변수로 평가되었다. PCA 분석결과, 수온이 낮고 성층이 약화되며 pH가 낮은 상태에서 NAF가 큰 것으로 나타났다.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.19 no.1
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• pp.66-75
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• 2014

This study aims to understand environmental factors that determine spatial distribution of macrozoobenthic community in the southern area (ca 100-500 m depth) of East Sea, Korea, known as a candidate site for carbon storage under the seabed. From sixteen locations sampled in the summer of 2012, a total of 158 species were identified, showing density of $843indiv/m^2$ and biomass of $26.2g\;WW/m^2$, with increasing faunal density towards biologically higher diverse locations. Principal component analysis showed that a total of 33 environmental parameters were reduced to three principal components (PC), indicating sediment, bottom water, and depth, respectively. As sand content was increasing, number of species increased but biomass decreased. Six dominant species including two bivalve species favored high concentrations of ${\Omega}$ aragonite and ${\Omega}$ calcite, indicating that the corresponding species can be severely damaged by ocean acidification or $CO_2$ effluent. Cluaster analysis based on more than 1% density dominant species classified the entire study area into four faunal assemblage (location groups), which were delineated by characteristic species, including (A) Ampelisca miharaensis, (B) Edwardsioides japonica, (C) Maldane cristata, (D) Spiophanes kroeyeri, and clearly separated in terms of geography, bottom water and sediment environment. Overall, a discriminant function model was developed to predict four faunal assemblages from five simply-measured environmental variables (depth, sand content in sediment, temperature, salinity and pH in bottom water) with 100% accuracy, implying that benthic faunal assemablages are closed linked to certain combinations of abiotic factors.

• The Journal of the Petrological Society of Korea
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• v.24 no.4
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• pp.337-345
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• 2015

Pumices from the summit area of the Mt. Baekdu was analysed with respect to the physical characteristics. Fallout pumice deposits around the somma of the Cheonji caldera, Mt. Baekdu consist mainly of white pumices, but black pumices and gray pumices are also displayed together. White pumices are mainly rhyolitic($SiO_2$ 71.1%) and black pumices are trachytic($SiO_2$ 64.8%) in composition, and gray pumices are intermediate composition($SiO_2$ 68.0%) between white pumices and black pumices. Average density of felsic magma formed the Mt. Baekdu pumices is $2.45g/cm^3$ in anhydrous magma and $2.33g/cm^3$ in hydrous magma, respectively. We determined the density and calculated the vesicularity of three different coloured pumices, which collected in the vicinity of the Waho-bong(2,566 m) and Gwanmyeonbong(2,526 m) of southern somma of the Cheonji caldera, Mt. Baekdu. Average density of the yellow pumices was measured as $0.74g/cm^3$, black pumices as $0.75g/cm^3$, and gray t0 white pumices as $0.73g/cm^3$. Average density regardless of the colour of pumices was nearly constant at $0.75g/cm^3$. Vesicularity of pumices is calculated to be 67.8~69.4% and these pumices can be classified as a highly vesicular according to classification of vesiculation characteristics.

• Journal of Energy Engineering
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• v.17 no.4
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• pp.227-232
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• 2008

Carbon dioxide is considered a major greenhouse gas that contributes to global wanning. $CO_2$ is a major component of the exhaust in the combustion of any hydrocarbon fuel. The regulation for $CO_2$ emission from vehicles has become much more stringent in recent years. These more stringent regulations require vehicle manufacturers to develop alternative fuels that reduce exhaust emissions. This paper evaluated the correlation of $CO_2$ emission and fuel economy in the Gasoline, Diesel, and LPG vehicles according to FTP-75 and NEDC(ECE15+EUDC) driving mode. From this study, we discovered that the decrease rate of $CO_2$ emission is higher for fuels of lower carbon concentration. When the relationship between $CO_2$ emission and fuel consumption rate according to used fuels is expressed as a function, one can find out that they have a high correlation. LPG vehicles produce less $CO_2$ emission than gasoline and diesel vehicles.

• Korean Chemical Engineering Research
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• v.56 no.2
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• pp.229-239
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• 2018

The purpose of this study was to effectively produce the biosugar from cell wall of lipid extracted microalgae (LEA) by using microwave-assisted pretreatment without enzymatic hydrolysis process. Response surface methodology (RSM) was applied to optimization of microwave-assisted pretreatment conditions for the production of biosugar based on enzyme-free process from LEA. Microwave power (198~702 W), extraction time (39~241 sec), and sulfuric acid (0~1.0 mol) were used as independent variables for central composite design (CCD) in order to predict optimum pretreatment conditions. It was noted that the pretreatment variables that affect the production of glucose (C6) and xylose (C5) significantly have been identified as the microwave power and extraction time. Additionally, the increase in microwave power and time had led to an increase in biosugar production. The superimposed contour plot for maximizing dependent variables showed the maximum C6 (hexose) and C5 (pentose) yields of 92.7 and 74.5% were estimated by the predicted model under pretreatment condition of 700 w, 185.7 sec, and 0.48 mol, and the yields of C6 and C5 were confirmed as 94.2 and 71.8% by experimental validation, respectively. This study showed that microwave-assisted pretreatment under low temperature below $100^{\circ}C$ with short pretreatment time was verified to be an effective enzyme free pretreatment process for the production of biosugar from LEA compared to conventional pretreatment methods.

• Journal of the Korean Geotechnical Society
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• v.34 no.12
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• pp.105-113
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• 2018

In this study, the engineering properties including bearing capacity of subgrades stabilized with a binder are analyzed by laboratory and field experiments. The main components of the binder are CaO and $SO_3$. After the binder was mixed with a low plasticity clay, the passing rates were relatively decreased as the sieve mesh size increased. Not only did the soil type change to silty sand, but engineering properties, such as the plasticity index and modified California bearing ratio (CBR), were improved for the subgrade. A comparison of the compaction curves of the stabilized subgrade and field soil compacted with the same energy demonstrated an increase of approximately 6% in the maximum dry unit weight, slight decrease in optimum moisture content, and considerable increase improvement in grain size. In the modified CBR test, the effect of unit weight and strength increase of the modified soil (with a specific amount of binder) was remarkably improved. As the proportion of granulated material increased after the addition of binder, the swelling was reduced by 3.3 times or more during initial compaction and 6.5 times by final compaction. The unconfined compressive strength of the specimens was maintained at the homogeneous value with a constant design strength. The stabilized subgrade was validated by applying it in the field under the same conditions; this test demonstrated that the bearing capacity coefficients at all six sites after one day of compaction exceeded the target value and exhibited good variability.

• Journal of Wetlands Research
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• v.6 no.1
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• pp.133-147
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• 2004

Environmental quality(water and sediment) was analyzed in the tidal flat of Saemangum of Jeonbuk Province, the west coast of Korea, using the 101 sediment samples and 69 water samples collected in September 4~13, 2001. Major water quality parameters with the means of 69 surface water samples are as follows; $25.51{\pm}0.68^{\circ}C$ for water temperature, $29.88{\pm}5.01$ for salinity, $1.40{\pm}0.78mg/L$ for COD, $0.352{\pm}0.417mg/L$ for DIN, and $0.027{\pm}0.023mg/L$ for phosphate, respectively. Higher values were found at the subestuary of Dongjin and Mangyung River, and lower values at the Saemangum embayment and Gomso Bay. There was a significant negative correlation between salinity and the other water quality parameters(p<0.0001) such as COD, nutrients, SS and N/P. This correlation suggested that the major pollution sources be from terrestrial inputs through tributaries in this area. Principal component analysis clearly revealed a spatial variation of water quality; stations with higher values of nutrients and COD located subestuary of tributaries. 14 sediment quality parameters including 8 trace metals were measured using the 101 surface sediment samples. Average values for the parameters are as follows; Al $2.28{\pm}0.92%$, Cd $0.61{\pm}0.27ppm$, Cu $8.95{\pm}4.06ppm$, Fe $1.19{\pm}0.37%$, Mn $182.31{\pm}77.45ppm$, Ni $10.83{\pm}4.97ppm$, Pb $15.20{\pm}4.35ppm$, Zn $41.34{\pm}34.62ppm$, COD $2.68{\pm}1.85mg/g\;dry$, AVS $0.04{\pm}0.08mg/g\;dry$, IL $1.29{\pm}1.08%$, water content $24.11{\pm}4.49%$, TN $0.02{\pm}0.02%$, TC $0.22{\pm}0.30%$. Spatial variations of sediment quality were not clear as water quality. Some higher values were found at the subestuary of Gum River and lower values at the other area. There was a significant positive correlation between the heavy metal concentrations and organic materials within the sediment(p<0.05). Enrichment factors showed the ranges of 1~2 for most of the metals in the sediment except zinc(1~6), indicating no serious exogenous input of heavy metals in the study area. Also, the heavy metal concentrations in the sediment were within the ranges found at the natural marine environments.