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최동호 ( Dongho Choi ),윤광식 ( Kwangsik Yoon ),정재운 ( Jaewoon Jung ),이경숙 ( Kyungsook Lee ),최우정 ( Woojung Choi ),임상선 ( Sangsun Lim ),임병진 ( Byungjin Lim ),최강원 ( Gangwon Choi ) 한국농공학회 2011 한국농공학회 학술대회초록집 Vol.2011 No.-
SWAT 모형은 장기 수문순환 과정을 모의하여 토양, 토지, 농업관리 등 유역관리를 위한 의사결정 방향을 제시하고, 유역의 장기유출 및 수질 모의에 많이 이용되고 있어 우리나라에서 현재 시행중인 수질오염총량관리제의 기준유량 및 유역내 오염물질 거동 해석에 많은 활용이 예상된다. 논유역을 대상으로 SWAT 모형을 적용하기 위해서 전라남도 함평군 엄다면 화양리의 논 지구를 대상으로 2005년부터 2010년까지 영농 기간동안 집중 모니터링을 실시하였다. SWAT 모형을 구동하기 위해서 수치고도모형(DEM), 토지피복도, 토양도, 하천도를 구축하였다. 논 유역을 대상으로 SWAT 모형을 적용하기 위해서 이앙시기, 시비시기, 관개량 등을 조사하여 입력자료를 구축하였으며, 유출곡선지수, 유효토층, 토양침식 및 SS 모의발생을 위해 ULSE_K, 평균경사길이(SLSUBBSN), 평균경사(Slope), 경운인자 등을 조절하여 적용한 결과 2005~2010년까지 실측 유출량과 모의발생 유출량은 서로 유사하였다. 하지만 강우와 관개수에 토양이 포화되어 탈질로 대부분의 질소가 손실되며 지표수 유출손실은 작은 것으로 모의 발생되었다. 따라서 토층 깊이를 제한하여 관측치를 재현하였다. 따라서 대규모 논 유역에 SWAT모형을 적용하기 위해서는 토양 입력자료를 조정하여야 되는 것으로 나타났다.
최동호 ( Dongho Choi ),윤광식 ( Kwangsik Yoon ),정재운 ( Jaewoon Jung ),이경숙 ( Kyungsook Lee ),최우정 ( Woojung Choi ),임상선 ( Sangsun Lim ),임병진 ( Byungjin Lim ),최강원 ( Gangwon Choi ) 한국농공학회 2011 한국농공학회 학술대회초록집 Vol.2011 No.-
우리나라는 수질개선하기위해서 1차 오염총량관리기간동안 BOD를 관리대상 물질로 선정하여 시행되어 왔으며, 2차 오염관리대상물질로 T-P를 선정하여 관리하고 있다. 박재홍 등(2006)은 1차 오염총량관리 기간동안 모든 수계가 동일한 관리대상물질을 선정하고 적용하는 것에 있어 유역별 오염원 및 지리적 특성이 다르기 때문에 수질관리에 있어서 적절한 차별화된 대상물질의 선정도 고려되야 한다고 하였다. 따라서 하천 및 호소의 수질을 효율적으로 관리하기 위해서는 관리대상 수질항목의 분포형태 파악이 매우 중요하다. 자료의 분포형태는 확률지를 사용하는 방법과 적합도 검정을 하는 방법으로 파악할 수 있으며, 수질항목의 확률분포는 해석해 또는 수치해로 구성된 결정론적 모델과 연계하여 모의 결과의 불확실성 및 신뢰성 등 지표수 수질관리에 효율적으로 사용될 수 있다. 논 유출수의 COD, SS, T-N, T-P의 확률 분포 특성을 분석하기 위해 전라남도 함평군 엄다면 화양리 논 지구에서 2008년부터 2010년까지 영농 기간동안 집중 모니터링을 실시하였으며, 수질항목별 분포형태는 Kolmogorov-Smirnov(K-S) 적합도 검증방법을 사용하였다. COD와 SS는 Normal, Log-Normal, Gamma, Weibull 분포모형에서 적합성을 보였으며, T-N의 경우 Log-Normal, Gamma, Weibull 분포모형에서 적합도를 보였으며, T-P의 경우 Log-Normal 분포에서만 적합성이 있는 것으로 나타났다.
Choi, Dongho,Bak, Yeongsu,Lee, Kyo-Beum The Korean Institute of Power Electronics 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.5
This paper presents a control method for reducing the current distortion in an indirect matrix converter (IMC) operating in boost mode under unbalanced input conditions. IMCs operating in boost mode are useful in distributed generation (DG) systems. They are connected with renewable energy systems (RESs) and the grid to transmit the power generated by the RES. However, under unbalanced voltage conditions of the RES, which is connected with the input stage of the IMC operating in boost mode, the input-output currents are distorted. In particular, the output current distortions cause a ripple of the power, which is transferred to the grid. This aggravates the reliability and stability of the DG system. Therefore, in this paper, a control method using positive/negative sequence voltages and currents is proposed for reducing the current distortion of both side in IMCs operating in boost mode. Simulation and experimental results have been presented to validate effectiveness of the proposed control method.
Choi, Dongho,Oh, Jeong-Ik,Baek, Kitae,Lee, Jechan,Kwon, Eilhann E. Pergamon Press 2018 Energy Vol.153 No.-
<P><B>Abstract</B></P> <P>Co-pyrolysis of chicken manure and biomass was investigated in this study. The pyrolysis of individual samples was characterized by thermogravimetric analysis (TGA) under N<SUB>2</SUB> and CO<SUB>2</SUB> atmospheres. This demonstrated that the impact of CO<SUB>2</SUB> content on the physical aspects of pyrolysis such as onset and end temperatures, and residual mass was negligible. However, a high CaCO<SUB>3</SUB> content (17 wt%) in chicken manure catalyzed the Boudouard reaction. Despite its negligible physical influence, CO<SUB>2</SUB> evidently affected the co-pyrolysis of chicken manure and biomass chemically. It expedited the thermal cracking of hydrocarbons from the co-pyrolysis of chicken manure and biomass. Moreover, between 550 and 660 °C, CO<SUB>2</SUB> reacted with condensable hydrocarbons, effectively improving CO generation. This observation suggested that CO<SUB>2</SUB> acted as both carbon scavenger and oxygen donor in the co-pyrolysis of chicken manure and biomass, a driving force for shifting carbon distribution between pyrogenic products. For example, pyrolytic oil was transformed into syngas, especially CO, offering an innovative means to modify compositions of pyrolytic products. These effects were not observed in the presence of CaCO<SUB>3</SUB> and/or CaO.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The high content of CaCO<SUB>3</SUB> in chicken manure catalytically enhances the Boudouard reaction. </LI> <LI> Establishing waste-to-energy via co-pyrolysis of chicken manure and lignocellulosic biomass. </LI> <LI> The enhanced thermal cracking of tar using CO<SUB>2</SUB>. </LI> <LI> CO<SUB>2</SUB> acted like a donor of C and O to form CO, which results in the more generation of syngas. </LI> </UL> </P>
Choi, Dongho,Lee, Jechan,Tsang, Yiu Fai,Kim, Ki-Hyun,Rinklebe, Jö,rg,Kwon, Eilhann E. Elsevier Science B.V. Amsterdam 2017 Algal research Vol.24 No.1
<P><B>Abstract</B></P> <P>This study mainly reports that utilizing CO<SUB>2</SUB> as a reaction medium in hydrothermal liquefaction of <I>Arthrospira platensis,</I> as a model feedstock of microalgal biomass, provides a means for modifying the chemical constituents in microalgal bio-oil produced via hydrothermal liquefaction. Prior to hydrothermal liquefaction, the total lipid content of <I>A. platensis</I> was measured as ~3.5wt% (dry basis). Thermal degradation of <I>A. platensis</I> and the major pyrolytic gases from the thermal degradation of <I>A. platensis</I> were characterized to gain an insight into the physico-chemical influences of CO<SUB>2</SUB> in hydrothermal liquefaction. Based on the experiment's findings, hydrothermal liquefaction of <I>A. platensis</I> was conducted to evaluate the influence of CO<SUB>2</SUB>. Hydrothermal liquefaction of <I>A. platensis</I> in CO<SUB>2</SUB> decreased the composition of N-containing species from 63 to 59% and that of O-containing species from 31 to 27% in the bio-oil, significantly suggesting that using CO<SUB>2</SUB> improves the quality of bio-oil as a transportation fuel.</P> <P><B>Highlights</B></P> <P> <UL> <LI> CO<SUB>2</SUB> modifies N & O contents in <I>A. platensis</I>-bio-oil via hydrothermal liquefaction </LI> <LI> Liquefaction in CO<SUB>2</SUB> produces more CO from <I>A. platensis</I> </LI> <LI> Less N & O contained hydrocarbons produced from liquefaction of <I>A. platensis</I> in CO<SUB>2</SUB> </LI> </UL> </P>
Choi, Dongho,Kim, Jung Hoon,Lim, Misun,Song, Kang Won,Paik, Seung Sam,Kim, Sook Ja,Cheong, Hee Jeong,Jeon, Jin Seok,Park, Hee Sook,Song, Yun Seob,Khang, Hyunsoo,Won, Jong-Ho Mary Ann Liebert, Inc 2008 Tissue engineering. Part C, Methods Vol.14 No.1
<P>Cell transplantation using hepatocytes derived from stem cells has been regarded as a possible alternative treatment for various hepatic disorders. Recently, mesenchymal stem cells (MSCs) from the bone marrow have shown the potential to differentiate into hepatocytes in in vitro and in vivo conditions. Noninvasive imaging techniques allowing in vivo assessment of the location of cells are of great value for experimental studies in which these cells are transplanted. We labeled human mesenchymal stem cells (hMSCs) with green fluorescence protein (GFP) and superparamagnetic iron oxide (SPIO) using a transfection agent (GenePORTER). Cellular labeling was evaluated with magnetic resonance (MR) imaging of labeled suspensions, and Prussian blue staining for iron assessment. hMSCs labeled with SPIO and GFP were injected into the portal veins of immunosuppressed, hepatic-damaged rats. MR imaging findings were compared histologically. To identify the differentiation of hMSCs into hepatocytes and to trace the hepatocytes with molecular imaging, we observed the potential of SPIO and GFP double-labeled hMSCs to differentiate into hepatocyte-like cells in the regenerating rat liver. Serial MR imaging showed the possible detection of transplanted cells in the early period of transplantation. Our results indicate that magnetic labeling of hMSCs with SPIO may enable cellular MR imaging and tracking in experimental in vivo settings.</P>