Development of High Interstitial Stainless Steel and Evaluation of Its NaCl Corrosion Resistance

Cheolmin Ahn,이현주,Yoonseok Lee,Seungchan Cho,Brajendra Mishra,이은경 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.11

High interstitial Fe–Cr–Mn–C–N stainless steels, CN66 (0.38 wt% N + 0.28 wt% C) and CN71 (0.44 wt% N + 0.27 wt% C),were cast under atmospheric pressure to develop a new drill collar for use in petroleum industry. To evaluate the corrosionproperty, CN66 and CN71 were compared with high-Mn stainless steel, P550, which is currently being used as a drill collarmaterial. Through the measurement of the corrosion resistance based on the chemical compositions, CN71 exhibitedthe highest corrosion property, a mean of 35.74, corresponding to strong corrosion resistance. However, CN71 exhibited amean of 0.517 mpy for the corrosion rate compared to 0.37 mpy for P550, after the immersion experiment in 3.5 wt% NaCl. With high C content, the formation of carbide along the grain boundaries in CN71 and CN66 caused intergranular corrosion. However, this could be restricted by heat treatment at 1050 °C and 1180 °C with uniform distributions of chemicalcompositions via air cooling, decreasing the corrosion rates significantly.

A Single-chip Resonance-frequency Tracking Microwave-excited Plasma Driver IC for Portable Biomedical Applications

Cheolmin Ahn,Soon Ku Kwon,Beomjin Park,Jahyun Koo,Jae-Yoon Sim 대한전자공학회 2020 Journal of semiconductor technology and science Vol.20 No.3

This paper presents a first-time single-chip microwave-excited plasma driver IC with resonance-frequency tracking and output-power-regulation scheme for biomedical applications. The power module includes a driver IC and a power amplifier, and is designed to provide stable microwave power that is required for generation of a plasma jet. A 2.4-GHz coaxial transmission line resonator is used to generate the plasma jet using input microwave power. The proposed system continuously monitors the resonance frequency, and controls it by adaptively changing the microwave frequency. To prevent the plasma jet from becoming high enough to damage human skin, the system monitors the power entering the resonator and keeps it constant. The proposed microwave plasma driver IC is implemented in a 0.18-μm complementary metal-oxide-semiconductor process. The system generates stable 1 W with a frequency tracking.

Enhancing light absorption in a thin film silicon tandem solar cell fabricated on a reactive ion etched nano-structured glass surface

Ahn, Shihyun,Iftiquar, S M,Cho, Jaehyun,Le, Anh Huy Tuan,Park, Cheolmin,Park, Jinjoo,Lee, Hyunhwa,Hong, Keunkee,Kim, Jung Soo,Bong, Sungjae,Yi, Junsin IOP 2019 Journal of Physics. D, Applied Physics Vol.52 No.3

<P>The efficient capture and absorption of light are important aspects in improving the photovoltaic conversion efficiency of a solar cell. In a two-terminal tandem device, the output current density is limited by the lowest current-generating component sub-cell. We attempted by experiment to improve the current density of both sub-cells, using an inverted pyramid-type textured glass substrate. One of the two surfaces of the glass substrates was textured by semi-anisotropic reactive ion etching (RIE) with a 100 sccm flow rate of SF<SUB>6</SUB> gas, and with 7 <I>µ</I>m  ×  7 <I>µ</I>m square-shaped etch masks, and obtained an optimum texture of base dimension ~7 <I>µ</I>m, height ~8.5 <I>µ</I>m, tip diameter ~75 nm and tip to tip separation between neighboring pyramids were about 9 <I>µ</I>m. Tandem solar cells that were fabricated on these textured surfaces receive light from the base of these micro-pyramids, thereby enhancing light absorption in the active layers of the device. The shape of the texture and orientation of layers of the tandem solar cell ensured a longer optical path inside the solar cell, leading to higher optical absorption and an improvement in device performance. We observed an increase in the short circuit current density from 11.52 to 14.30 mA cm<SUP>−2</SUP>, and in the device efficiency from 11.97% to 14.22%.</P>

Human tracking and silhouette extraction for human-robot interaction systems

Ahn, Jung-Ho,Choi, Cheolmin,Kwak, Sooyeong,Kim, Kilcheon,Byun, Hyeran Springer-Verlag 2009 PATTERN ANALYSIS AND APPLICATIONS Vol.12 No.2

이동 카메라 환경에서 가려짐 있는 객체의 추적

최철민(Cheolmin Choi),곽수영(Sooyeong Kwak),안정호(Jungho Ahn),변혜란(Hyeran Byun) 한국정보과학회 2006 한국정보과학회 학술발표논문집 Vol.33 No.1

이동 카메라 환경에서의 객체 추적은 배경과 객체의 동시 이동으로 인해 배경 모델링과 같은 고정 카메라 환경에서의 접근방법으로는 해결이 어려운 문제이다. 또한 다중 객체의 추적에서는 객체간 가려짐이 발생하는 상황에 대한 안정적 기법이 필수적으로 요구된다. 본 연구에서는 커널에 기반한 객체의 표현과 Mean shift 알고리즘을 통해 여러 명의 사람을 실시간으로 추적하고, 객체간의 공간 정보와 확률적 유사도에 기반한 객체간의 가려짐의 발생과 가려짐 후의 복원에 대한 방법을 제안하였다.

최대 공통 부열을 이용한 비전 기반의 양팔 제스처 인식

최철민(Cheolmin Choi),안정호(Jung-Ho Ahn),변혜란(Hyeran Byun) 한국통신학회 2008 韓國通信學會論文誌 Vol.33 No.5C

본 논문은 비전에 기반한 사람의 양팔 제스처의 모델링과 인식에 관한 연구이다. 우리는 양팔 제스처 인식을 위한 특징점의 추출에서부터 제스처의 분류에 이르는 전체적 틀을 제안하였다. 먼저, 양팔 제스처의 모델링을 위해 색채 기반의 양손 추적 방법을 제안하였고, 추출된 양손의 궤적 정보를 효과적으로 선택하게 하는 제스처 구(Phrase) 분석법을 제시하였다. 선택된 특징 점들의 시퀀스 (sequence) 들로 이루어진 훈련 데이터들의 최대 공통부열 (Longest Common Subsequence) 정보를 이용하여 제스처를 모델링하고 이에 따른 유사도 척도를 제안하였다. 제안된 방법론을 공항 등에서 이용하는 항공기 유도 수신호에 적용하였고, 실험을 통해 제안된 방법론의 효율성과 인식성능을 보였다. In this paper, we present a framework for vision-based two-arm gesture recognition. To capture the motion information of the hands, we perform color-based tracking algorithm using adaptive kernel for each frame. And a feature selection algorithm is performed to classify the motion information into four different phrases. By using gesture phrase information, we build a gesture model which consists of a probability of the symbols and a symbol sequence which is learned from the longest common subsequence. Finally, we present a similarity measurement for two-arm gesture recognition by using the proposed gesture models. In the experimental results, we show the efficiency of the proposed feature selection method, and the simplicity and the robustness of the recognition algorithm.

Optimization of the Phosphorus Doped BSF Doping Profile and Formation Method for N-type Bifacial Solar Cells

Cui, Jian,Ahn, Shihyun,Balaji, Nagarajan,Park, Cheolmin,Yi, Junsin Korea Photovoltaic Society 2016 Current Photovoltaic Research Vol.4 No.2

n-type PERT (passivated emitter, rear totally diffused) bifacial solar cells with boron and phosphorus diffusion as p+ emitter and n+ BSF (back surface field) have attracted significant research interest recently. In this work, the influences of wafer thickness, bulk lifetime, emitter, BSF on the photovoltaic characteristics of solar cells are discussed. The performance of the solar cell is determined by using one-dimensional solar cell simulation software PC1D. The simulation results show that the key role of the BSF is to decrease the surface doping concentration reducing the recombination and thus, increasing the cell efficiency. A lightly phosphorus doped BSF (LD BSF) was experimentally optimized to get low surface dopant concentration for n type bifacial solar cells. Pre-oxidation combined with a multi-plateau drive-in, using limited source diffusion was carried out before pre-deposition. It could reduce the surface dopant concentration with minimal impact on the sheet resistance.

Chemical Amination via Cycloaddition of Graphene for Use in a Glucose Sensor

Qin, Hongyi,Hwang, Taehyun,Ahn, Chisung,Kim, Jang Ah,Jin, Yinhua,Cho, Yujin,Shin, Cheolmin,Kim, Taesung American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.5

<P>Graphene was chemically aminated via cycloaddition. Aziridine-ring linkages were formed by covalently modifying the C-C double bonds in graphene. The aminated graphene presents an enhanced hydrophilicity, the contact angle with water decreases from 80.5 degrees to 58.5 degrees. And the conductivity of aminated graphene exhibits exponential decay as the reaction time increase. If the reaction time is 90 min, the resistance of aminated graphene was increased from similar to 32 Omega to similar to 2744 Omega. Because the amino group has good biocompatibility, the aminated graphene is designed for use as an enzyme sensor platform, such as glucose sensor based on glucose oxidase. The aminated graphene exhibited a good detection response for glucose. The increase in device current is about 12% in 1.2 mg/mL glucose solution.</P>

Optimization of the Phosphorus Doped BSF Doping Profile and Formation Method for N-type Bifacial Solar Cells

Jian Cui,Shihyun Ahn,Nagarajan Balaji,Cheolmin Park,Junsin Yi 한국태양광발전학회 2016 Current Photovoltaic Research Vol.4 No.2

n-type PERT (passivated emitter, rear totally diffused) bifacial solar cells with boron and phosphorus diffusion as p+ emitter and n+ BSF (back surface field) have attracted significant research interest recently. In this work, the influences of wafer thickness, bulk lifetime, emitter, BSF on the photovoltaic characteristics of solar cells are discussed. The performance of the solar cell is determined by using one-dimensional solar cell simulation software PC1D. The simulation results show that the key role of the BSF is to decrease the surface doping concentration reducing the recombination and thus, increasing the cell efficiency. A lightly phosphorus doped BSF (LD BSF) was experimentally optimized to get low surface dopant concentration for n type bifacial solar cells. Pre-oxidation combined with a multi-plateau drive-in, using limited source diffusion was carried out before pre-deposition. It could reduce the surface dopant concentration with minimal impact on the sheet resistance.

결절맥락막혈관병증에서 인도시아닌그린 혈관조영술과 빛간섭단층혈관조영술의 비교

김종현(Jonghyun Kim),안소민(So Min Ahn),윤철민(Cheolmin Yun),김성우(Seong-Woo Kim),오재령(Jaeryung Oh) 대한안과학회 2021 대한안과학회지 Vol.62 No.9

목적: 결절맥락막혈관병증에서 인도시아닌그린혈관조영술과 빛간섭단층혈관조영술의 비교를 통해 진단적 가치를 평가하고 차이가 발생하는 요인을 알아보고자 한다. 대상과 방법: 43명 환자들의 인도시아닌그린혈관조영술과 빛간섭단층혈관조영술검사에서 결절 개수와 크기, 분지혈관망 유무의 일치율과 크기를 비교하였다. 두 검사에서 결절 개수 일치 여부에 따라 그룹 1은 두 검사에서 결절 개수가 같은 군으로, 그룹 2는 개수가 다른 군으로 분류하였다. 결과: 결절의 개수와 면적은 인도시아닌그린혈관조영술에서는 평균 1.47 ± 0.83개, 0.27 ± 0.42 mm2, 빛간섭단층혈관조영술검사에서는 평균 1.07 ± 0.91개, 0.17 ± 0.15 mm2로 유의미한 차이를 보였다(각각 p<0.001, p=0.023). 분지혈관망은 인도시아닌그린혈관조영술로 33안(76.7%)에서 평균 면적 3.61 ± 2.59 mm2, 빛간섭단층혈관조영술검사로 29안(67.4%)에서 평균 면적 2.74 ± 2.76 mm2로 측정되어 유의미한 차이를 보였다(p=0.002). 중심망막두께와 중심맥락막두께는 그룹 2에서 유의미하게 두꺼웠다(각각 p<0.001). 그룹 2에서 망막하액(p=0.009), 망막하출혈(p=0.035)이 유의미하게 많이 발견되었고, 결절의 높이(p=0.022), 결절의 폭(p=0.042)이 유의미하게 크게 측정되었다. 결론: 빛간섭단층혈관조영술은 결절맥락막혈관병증을 진단하는 데 인도시아닌그린혈관조영술과 차이를 보이나 진단에 도움을 줄 수 있는 보조적인 진단 방법이며, 망막하액과 망막하출혈이 존재하고 결절의 높이와 폭이 큰 경우 결절맥락막혈관병증 진단에 영향을 미칠 수 있다. Purpose: To assess the diagnostic value of optical coherence tomography angiography (OCTA), and the factors affecting the diagnosis of polypoidal choroidal vasculopathy (PCV) by OCTA and indocyanine green angiography (ICGA). Methods: The numbers and area of polyps, and the presence and area of a branched vascular network (BVN) as revealed by ICGA and OCTA, were retrospectively analyzed in 43 patients with active PCV. The patients were divided into two groups according to whether the number of polyps matched between the two methods: group 1, equal number of polyps revealed by ICGA and OCTA; group 2, different number of polyps revealed by ICGA and OCTA. Results: In 43 PCV patients, the total number of polyps was 1.47 ± 0.83 in ICGA and 1.07 ± 0.91 in OCTA (p < 0.001), and the polyp area was 0.27 ± 0.42 mm2 in ICGA and 0.17 ± 0.15 mm2 in OCTA (p = 0.023). BVN was found in 33 eyes (76.7%) by ICGA and 29 eyes (67.4%) by OCTA (p < 0.001). The BVN area was 3.61 ± 2.59 mm2 in ICGA and 2.74 ± 2.76 mm2 in OCTA (p = 0.002). Central retinal thickness and central choroidal thickness were significantly greater in group 2 than group 1 (p < 0.001, respectively). Subretinal fluid (SRF) (p = 0.009) and subretinal hemorrhage (SRH) (p = 0.005) were significantly more prevalent in group 2 than group 1. Polyp height (p = 0.022) and diameter (p = 0.042) were significantly greater in group 2 than group 1. Conclusions: OCTA is a supplementary diagnostic technique for detecting PCV. The presence of SRF and SHR, and large polyp height and diameter, were associated with the polyp detection rate of OCTA for PCV.