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Choi, Min-Jae,Oh, Jihun,Yoo, Jung-Keun,Choi, Jaesuk,Sim, Dong Min,Jung, Yeon Sik The Royal Society of Chemistry 2014 ENERGY AND ENVIRONMENTAL SCIENCE Vol.7 No.9
<P>Despite the outstanding advantages of a simple structure and cost-effectiveness of solution-based fabrication, Schottky junction quantum dot solar cells (QDSCs) often demonstrate low open-circuit voltage and power conversion efficiency (PCE) due to insufficient band bending at the QD/metal Schottky junction. Generally, this undesirable result stems from the presence of many defects at the QD/metal interface and the consequent Fermi-level pinning effect. Here, we show how the simple oxidation of PbS QDs at the PbS/metal interface can greatly improve the open-circuit voltage, fill factor, and PCE of Schottky junction QDSCs. On the basis of systematic analysis results using current–voltage characterization, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and light-soaking tests, we reveal that this enhancement originates from reduced interface states at the PbS/metal Schottky junction. Moreover, a significant enhancement of stability of the device is confirmed by the maintenance of >55% of its initial PCE even after 500 hours exposure in air without additional passivation.</P> <P>Graphic Abstract</P><P>Tailoring the PbS/metal interface with an ultrathin oxidized layer improves both the efficiency and stability of quantum dot solar cells. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c4ee00502c'> </P>
The Dehydration Process and Evaluation of NaCl-MgCl2 Using Elemental Mg
Jihun Kim,Wonseok Yang,Saehyun Choi,Wonseok Lee,Taeho Jang,Sungyeol Choi 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.1
Molten salt reactors have several advantages over conventional light water reactors. These include producing less nuclear waste, operating at higher power efficiency and inherent safety due to the low operating pressure. NaCl-MgCl2 eutectic salt is one of the candidates for the molten salt reactor coolant. However, because the salt is very hygroscopic, structural material corrosion occurs resulting in the high cost to maintain. To mitigate corrosion there have been many studies for the dehydration of the salt, especially focusing on the magnesium chloride. The reason is that the moisture adsorbed to the magnesium chloride undergoes hydrolysis over 200 degrees Celsius and decomposes to MgOHCl while the moisture associated with the NaCl is easily liberated during the heating procedure without chemical reaction. As the operating temperature of the molten salt is between 500 and 700 degrees Celsius, the MgOHCl is believed as the main cause for the structural corrosion. In this research, thermal dehydration of the salt with elemental Mg, for the NaCl-MgCl2 eutectic, was studied based on the previous dehydration methods and considering scalable and easy to handle. The MgOHCl was removed both through the thermal decomposition and the reduction by Mg metal. After the removal of MgOHCl, based on the difference between the freezing points and the density, the salt cooled down very slowly to ensure the separation between the purified salt and the disposals such as MgO and remaining Mg metals. The efficiency of the dehydration method was determined by the concentration of the MgOHCl. The concentration was determined by cyclic voltammetry and the result was compared with undehydrated salt and salt dehydrated thermally without the addition of Mg metal. To qualify and quantify the MgOHCl content through the cyclic voltammetry, it was necessary to observe the signal by adding MgOHCl to each sample. Based on the thermogravimetric analysis result of MgCl2· 6H2O, MgOHCl powder was formed through heating the MgCl2·6H2O.
A Study on the Selection of UAM Pilots and Establishment of Training
JiHun Choi,박상용 한국항공운항학회 2022 한국항공운항학회지 Vol.30 No.3
UAM(Urban Air Mobility)은 가까운 미래에 현실이 되는 항공교통 체계로 미래 첨단 기술의 결정체이다. 비행은 인간의 생명을 절대 보장하는 숭고한 철학에 기반한다. 성공적인 UAM 개발을 위해서는 비행안전에 기초한 개발철학이 필요하며 올바른 방향을 제시해야 한다. UAM 체계와 유사한 항공교통체계는 민간항공 운항체계이며 UAM 체계의 개발을 도모하는 효과적 비교 연구대상이다. 본 연구는 민간항공 운항체계와 민간항공 조종사의 경험을 토대로 안전한 UAM 체계 개발의 방향을 제시하는 데 있다. 그중에서도 UAM 조종사 양성과 교육훈련체계 수립을 위한 방안을 제언하였다. 현존 관련법규를 검토하여 UAM 조종사 양성기준을 제시하였으며 초기 혼란을 방지하기 위한 대안을 포함하였다. 또한 민간항공기의 접근구간 항법성능을 측정하여 UAM 운항환경을 비교 예측하였다. 이를 통해 SMS 기법에 기반하여 UAM 체계의 위해요인(hazard)을 식별하여 미연에 사고를 예방할 수 있는 안전 방법론을 제시하였으며 UAM 로드맵의 올바른 정책 수립을 돕고자 한다.
전기자동차 보급에 따른 기존 아파트의 변압기용량 한계시점에 대한 연구
최지훈(Jihun Choi),김성열(Sung-Yul Kim),이주(Ju Lee) 대한전기학회 2016 전기학회논문지 Vol.65 No.12
Rapid Expansion of EVs(Electric Vehicles) is inevitable trends, to comply with eco-friendly energy paradigm according to Paris Agreement and to solve the environment problems such as global warming. In this paper, we analyze the limit point of transformer acceptable capacity as the increase of power demand considering EVs supply in the near future. Through the analysis of transformer utilization, we suggest methods to analyze the spare capacity of transformer for the case of optimal efficiency operation and emergency operation respectively. We have the results of 18.4~29% spare capacity for the charging infrastructure to the rated capacity of transformer by analyzing the existing sample apartments. It is analyzed that the acceptable number of EVs is 0.09~0.14 for optimal efficiency operation and 0.06~0.13 for emergency operation. Therefore, it is analyzed the power demand of EV will exceed the existing transformer spare capacity in 7~8 years as the annual growth rate of EVs is prospected 112.5% considering current annual growth rate of EVs and the government EV supply policy.
Ahn, JiHun,Rha, Seung-Woon,Choi, Byoung Geol,Park, SangHo,Choi, Woong Gil,LI, H.U.,Yu, HyeYon,Byeon, JinSu,Moon, Sang Ki,Do, Sang Tae Elsevier 2019 Annals of vascular surgery Vol.60 No.-
<P><B>Background</B></P> <P>The clinical benefits and outcomes of the interventional treatment of small-sized infrapopliteal arteries using stent implantation remain uncertain. The aim of this study was to compare the safety and efficacy of drug-free bioresorbable vascular scaffold (BVS) with that of bare metal stent (BMS) in endovascular treatment of small-sized peripheral arteries.</P> <P><B>Methods</B></P> <P>In this study, drug-free BVS and BMS were used in eight porcine models. We compared the angiographic and histomorphometric findings in the two groups at 4 weeks. In each pig, BVS and BMS of adequate sizes were implanted in the small branch (<3 mm) of the femoral artery. Angiography, intravascular ultrasound (IVUS), and histomorphometric analysis were performed at 4 weeks.</P> <P><B>Results</B></P> <P>In the 4-week follow-up angiography and IVUS examination, the minimal luminal diameter was smaller and diameter stenosis was more severe in the BVS group. Histomorphometric findings indicated that the lumen area in the BVS group was smaller (0.34 ± 0.28 mm<SUP>2</SUP> vs. 1.40 ± 0.52 mm<SUP>2</SUP>, <I>P</I> < 0.001), whereas the neointimal area (2.70 ± 1.28 mm<SUP>2</SUP> vs. 1.76 ± 0.66 mm<SUP>2</SUP>, <I>P</I> = 0.013), area stenosis (85.18 ± 13.14 % vs. 54.99 ± 16.13 %, <I>P</I> < 0.001), inflammatory score (2.07 ± 0.861 vs. 28 ± 0.39, <I>P</I> = 0.003), and fibrin scores (1.24 ± 0.70 vs. 0.79 ± 0.72, <I>P</I> = 0.043) were significantly higher in the BVS group. The injury score was higher in the BMS group. In histopathologic findings, restenosis was mainly due to recoil and distortion of the scaffold in the BVS group.</P> <P><B>Conclusions</B></P> <P>Compared with BMS, drug-free BVS was not feasible for small-sized peripheral arteries based on the angiographic, IVUS, and histomorphometric results primarily due to insufficient mechanical support.</P>
최지훈 ( Jihun Choi ),임현창 ( Hyunchang Im ),정재천 ( Jaecheon Jung ),공기석 ( Ki-sok Kong ) 한국정보처리학회 2017 한국정보처리학회 학술대회논문집 Vol.24 No.2
교통사고를 예방하고자 정부에서는 지속적인 정책을 펼치고 있으나 발생률이 크게 줄지 않는 실정이다. 본 논문에서는 이러한 한계점을 보완하고자 영상처리를 이용하여 교통사고를 줄일 방법을 제안하고자 한다. 우선 어린이 보호 구역 내에 설치된 카메라를 이용하여 교통사고 발생 위험을 판단하고, 보행자 및 차량 운전자에게 알려 줌으로써 교통사고 발생을 감소하고자 하는 시스템을 설계하였다. 또한 실시간 영상처리를 위해 관심 영역 지정, 멀티 스레드 등 다양한 방법을 적용해 보았으며, 위험 상황 탐지 시 탐지 결과를 주변 운전자에게 전송하려는 방법을 제시하고 실제 구현하여 확인해 보았다.
전기자동차 보급에 따른 공공임대아파트의 변압기 안정성 평가에 관한 연구
최지훈(Jihun Choi),김성열(Sung-Yul Kim),이주(Ju Lee) 대한전기학회 2017 전기학회논문지 Vol.66 No.7
This paper aims to analyze the safety evaluation of the existing transformer for the 0.85 millions of public rental apartments as EVs(Electric Vehicles) increase in order to overcome the environment pollution issue and maintain sustainable development. It is analyzed that the 56.4% capacity of power transformer could secure as EV charging infrastructure, based on the analysis of respective utilization patterns of the housing and power transformer. The acceptable number of EVs is 0.04~0.06 per household from the spare capacity of the power transformer. It is analyzed that EV stock is prospected less than 0.03 per household in 2030, considering the condition of the public rental apartments residents and the growth rate of EVs according to practical scenario. The power demand for EVs is within the allowable capacity range of the power transformer, so the research shows that there is no problem in the stability of the existing transformer until 2030