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.

Seasonal abundance of Haemaphysalis longicornis (Acari: Ixodidae) by life-stage in Jinju, Korea

Jihun Ryu,Woo Jun Bang,Hyeon Seung Lee,Min Hyeok Won,Jae Won Choi,Dong Yeol Lee,So Youn Lee,Kwang Shik Choi 한국응용곤충학회 2021 한국응용곤충학회 학술대회논문집 Vol.2021 No.04

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.

Tailoring of the PbS/metal interface in colloidal quantum dot solar cells for improvements of performance and air stability

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 Pitfalls of Corporate Social Irresponsibility: Hypocrisy of Family Firms in South Korea

Jihun Choi,Taewoo Roh,Ji-Hwan Lee 한국글로벌무역학회 2023 한국글로벌무역학회 학술대회자료집 Vol.2023 No.-

Development of high-temperature combustion system with DC arc plasma torches

Daehyun Choi,In Je Kang,Jihun Kim,Soon-Mo Hwang,Yongsup Choi 한국진공학회 2021 한국진공학회 학술발표회초록집 Vol.2021 No.2

The high-temperature waste decomposition system with plasma torches was constructed to derive a research to overcome the problems which cannot be treated with conventional waste treatment technology. The system consisted of waste feeder, plasma reactor, heat exchanger and gas analyzer and so on. The plasma was generated at atmospheric pressure using 30 kW and 60 kW DC arc torches. It is capable of processing up to 60 kg/hr waste and is designed to 2000°C temperature inside reactor. In this presentation, the developed high-temperature system for waste decomposition will be discussed.

Early-Stage Vascular Response between Bare Metal Stent and Drug-Free Bioresorbable Vascular Scaffold in the Small-Sized Peripheral Artery: A Preclinical Study in Porcine Femoral Arteries

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>

머리모형 충돌에 의한 자동차 접합유리의 실험적 연구 및 유한요소해석

최지훈(Jihun Choi),오원택(Wontek Oh),김종혁(Jonghyuk Kim),박종찬(Jongchan Park) 한국자동차공학회 2017 한국 자동차공학회논문집 Vol.25 No.3

In vehicle to pedestrian accidents, cracks occur in the vehicle laminated glass due to impact of a pedestrian’s head. In this study, FMH(Free Motion Headform) was used to experiment on and analyze the crack patterns on a vehicle laminated glass that collides with an adult headform at speeds of 20 km/h, 30 km/h, and 40 km/h, respectively. Applying the acquired experimental data and material property of the vehicle laminated glass to the structural analysis program LS-Dyna, we could develop the FE model of vehicle laminated glass similar to real vehicle laminated glass. We could estimate the head impact velocity and pedestrian’s vehicle impact velocity using the Madymo program.

성인 머리모형 임팩터의 FE 모델 개발

최지훈(Jihun Choi),박부창(Buchang Park),김종선(Jongsun Kim) 한국자동차공학회 2012 한국 자동차공학회논문집 Vol.20 No.2

Head injury is one of the most common cause of deaths in car-to-pedestrian collisions. To reduce the severity of such injuries, many international safety committees have performed headform impact test for pedestrian protection. In this paper, an adult headform impactor model is developed based on the finite element (FE) method and validated through the numerical simulation. The skin material of headform impactor is known as polyvinyl chloride skin (PVC) and its material was assumed as viscoelastic. The viscoelastic parameters of headform skin are identified by a series of trial and error methods. The new developed FE adult headform impactor is verified by the drop test and FE JARI adult headform impactor provided by Madymo program.

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