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황성환,이동춘,Hwang, Seong-Hwan,Lee, Dong-Choon 대한인간공학회 2007 大韓人間工學會誌 Vol.26 No.1
This study was performed to evaluate the characteristics of transmitted vibration to hand-arm system under different work posture while operating a light-weighted powered hand grinder. For the experiment, 8 different types of wrist posture (natural, unlar-flexion, radual-flexion, flexion, extension, complex posture, and etc.) and 3 types of feed force (20[N], 50[N], 70[N]) were considered. 10 male subjects were employed to polish metal plate with a hand grinder. All of them were normal and healthy with no history and symptom of the work related musculoskeletal disorders in the dominant hand. Vibration acceleration data were recorded with sampling rate, 2048[Hz]. In addition, unweighted overall R.M.S. acceleration at the tool and wrist, and transmissibility between them were used to evaluate factors from the recorded tri-axial vibration acceleration. The results indicate that transmissibility of natural wrist posture was significantly higher than others. In addition, as the feed force becomes larger, the vibration was transmitted in large quantities to hand-arm system through radius.
ZnO 나노 막대 성장을 위한 기판층으로서 hexagonal β상 Ni(OH)<sub>2</sub> 나노 시트 합성 및 미세구조 분석
황성환,이태일,최지혁,명재민,Hwang, Sung-Hwan,Lee, Tae-Il,Choi, Ji-Hyuk,Myoung, Jae-Min 한국재료학회 2011 한국재료학회지 Vol.21 No.2
As a growth-template of ZnO nanorods (NR), a hexagonal $\beta-Ni(OH)_2$ nanosheet (NS) was synthesized with the low temperature hydrothermal process and its microstructure was investigated using a high resolution scanning electron microscope and transmission electron microscope. Zinc nitrate hexahydrate was hydrolyzed by hexamethylenetetramine with the same mole ratio and various temperatures, growth times and total concentrations. The optimum hydrothermal processing condition for the best crystallinity of hexagonal $\beta-Ni(OH)_2$ NS was determined to be with 3.5 mM at $95^{\circ}C$ for 2 h. The prepared $Ni(OH)_2$ NSs were two dimensionally arrayed on a substrate using an air-water interface tapping method, and the quality of the array was evaluated using an X-ray diffractometer. Because of the similarity of the lattice parameter of the (0001) plane between ZnO (wurzite a = 0.325 nm, c = 0.521 nm) and hexagonal $\beta-Ni(OH)_2$ (brucite a = 0.313 nm, c = 0.461 nm) on the synthesized hexagonal $\beta-Ni(OH)_2$ NS, ZnO NRs were successfully grown without seeds. At 35 mM of divalent Zn ion, the entire hexagonal $\beta-Ni(OH)_2$ NSs were covered with ZnO NRs, and this result implies the possibility that ZnO NR can be grown epitaxially on hexagonal $\beta-Ni(OH)_2$ NS by a soluble process. After the thermal annealing process, $\beta-Ni(OH)_2$ changed into NiO, which has the property of a p-type semiconductor, and then ZnO and NiO formed a p-n junction for a large area light emitting diode.
Phosphorus-Doped ZnO 나노로드의 열처리 효과
황성환,문경주,이태일,명재민,Hwang, Sung-Hwan,Moon, Kyeong-Ju,Lee, Tae Il,Myoung, Jae Min 한국재료학회 2013 한국재료학회지 Vol.23 No.5
An effect of thermal annealing on activating phosphorus (P) atoms in ZnO nanorods (NR) grown using a hydrothermal process was investigated. $NH_4H_2PO_4$ used as a dopant source reacted with $Zn^{2+}$ ions and $Zn_3(PO_4)_2$ sediment was produced in the solution. The fact that most of the input P elements are concentrated in the $Zn_3(PO_4)_2$ sediment was confirmed using an energy dispersive spectrometer (EDS). After the hydrothermal process, ZnO NRs were synthesized and their PL peaks were exhibited at 405 and 500 nm because P atoms diffused to the ZnO crystal from the $Zn_3(PO_4)_2$ particles. The solubility of the $Zn_3(PO_4)_2$ initially formed sediment varied with the concentration of $NH_4OH$. Before annealing, both the structural and the optical properties of the P-doped ZnO NR were changed by the variation of P doping concentration, which affected the ZnO lattice parameters. At low doping concentration of phosphorus in ZnO crystal, it was determined that a phosphorus atom substituted for a Zn site and interacted with two $V_{Zn}$, resulting in a $P_{Zn}-2V_{Zn}$ complex, which is responsible for p-type conduction. After annealing, a shift of the PL peak was found to have occurred due to the unstable P doping state at high concentration of P, whereas at low concentration there was little shift of PL peak due to the stable P doping state.
Though-silicon-via를 사용한 3차원 적층 반도체 패키징에서의 열응력에 관한 연구
황성환,김병준,정성엽,이호영,주영창,Hwang, Sung-Hwan,Kim, Byoung-Joon,Jung, Sung-Yup,Lee, Ho-Young,Joo, Young-Chang 한국마이크로전자및패키징학회 2010 마이크로전자 및 패키징학회지 Vol.17 No.1
Through-silicon-via (TSV)를 포함하고 있는 3차원 적층 반도체 패키지에서 구조적 변수에 따른 열응력의 변화를 살펴보기 위하여 유한요소해석을 수행하였다. 이를 통하여 TSV를 포함하고 있는 3차원 적층 반도체 패키지에서 웨이퍼 간 접합부의 지름, TSV 지름, TSV 높이, pitch 변화에 따른 열응력의 변화를 예측하였다. 최대 von Mises 응력은 TSV의 가장 위 부분과 Cu 접합부, Si, underfill 계면에서 나타났다. TSV 지름이 증가할 때, TSV의 가장 위 부분에서의 von Mises 응력은 증가하였다. Cu 접합부 지름이 증가할 때, Si과 Si 사이의 Cu 접합부가 Si, underfill과 만나는 부분에서 von Mises 응력이 증가하였다. Pitch가 증가할 때에도, Si과 Si 사이의 Cu 접합부가 Si, underfill과 만나는 부분에서 von Mises 응력이 증가하였다. 한편, TSV 높이는 von Mises 응력에 크게 영향을 미치지 못하였다. 따라서 TSV 지름이 작을수록, 그리고 pitch가 작을수록 기계적 신뢰성은 향상되는 것으로 판단된다. Finite-element analyses were conducted to investigate the thermal stress in 3-dimensional stacked wafers package containing through-silicon-via (TSV), which is being widely used for 3-Dimensional integration. With finite element method (FEM), thermal stress was analyzed with the variation of TSV diameter, bonding diameter, pitch and TSV height. It was revealed that the maximum von Mises stresses occurred at the edge of top interface between Cu TSV and Si and the Si to Si bonding site. As TSV diameter increased, the von Mises stress at the edge of TSV increased. As bonding diameter increased, the von Mises stress at Si to Si bonding site increased. As pitch increased, the von Mises stress at Si to Si bonding site increased. The TSV height did not affect the von Mises stress. Therefore, it is expected that smaller Cu TSV diameter and pitch will ensure mechanical reliability because of the smaller chance of plastic deformation and crack initiation.
황성환,Hwang, Sunghwan The Korean School Mathematics Society 2021 韓國學校數學會論文集 Vol.24 No.1
The purpose of the study was to examine the psychometric properties of the personal teaching efficacy of the Mathematics Teaching Efficacy Beliefs Instrument and revise the scale for the use of Korean elementary school teachers. Data were collected from 299 elementary teachers. A Rasch analysis was used to evaluate unidimensionality and appropriateness of category use and item difficulty levels. Moreover, person separation and reliability as well as item separation and reliability were examined using the revised scale. Results suggested that the original personal teaching efficacy scale (13 items with five categories) had several problems in its psychometric properties. Thus, we revised the scale into eight items with four categories. The follow-up analysis results showed the revised scale provided sufficient psychometric properties for measuring Korean elementary school teachers' self-efficacy beliefs for teaching mathematics. Limitations and implications of the study were also discussed. 본 연구의 목적은 수학 교수 효능감 측정 도구(MTEBI)의 심리측정적 특성을 탐색하고 한국 초등 교사들에게 사용할 수 있게 측정 도구를 수정하는 것이다. 문헌 연구를 바탕으로 MTEBI 중 개인 효능감 요인만을 분석하였다. 299명의 초등 교사들의 설문자료를 Rasch 모형을 이용하여 일차원성 가정, 응답범주 적절성, 문항 난이도 적절성, 분리지수와 신뢰도 측면에서 분석하였다. 분석 결과 5점 범주로 된 13개 문항은 심리측정적 측면에서 몇 가지 문제가 있는 것으로 나타났다. 따라서, 후속 분석에서 5점 범주 대신 4점 범주로 수정하였으며 5개의 문항을 삭제한 후 8문항을 사용해 심리측정적 특성을 재분석하였다. 그 결과, 수정된 측정 도구는 초등 교사들의 수학 교수에 대한 개인효능감을 타당성 있게 측정하는 것으로 나타났다. 본 연구의 제한점과 제언을 추가 논의하였다.
황성환 ( Sung Hwan Hwang ),안태호 ( Tea Ho An ) 한국경영공학회 2013 한국경영공학회지 Vol.18 No.3
The paradigm for the weapon system acquisition of the Republic of Korea is evolving from overseas procurement to domestic research and development(R&D). R&D of the weapon system requires a big amount of investment capital, has to be done in long-run, has a high risk of failure of the development, is technically complicated and has a very complex program procedures with many institutions related to one another. Therefore, risk management of the R&D project plays a very important role in deciding whether the program will be successful or not. Therefore, Defense Acquisition Program Administration of the Republic of Korea chooses risk management process. Nonetheless, the current process is merely a practical management of risk factors which were normally identified by the intuition of a working group personnel, and there are many policies that need to be complemented because of the lack of experience during the initial introduction phase, which creates limitations on verifying the effectiveness of the risk management work. Because of such background, this research analyzes the characteristics and limitations of existing researches by having an in-depth review of existing literatures in national defense and civilian field in relation with risk management of R&D, and, by utilizing the results, the research suggests issues that can be applied to the R&D program management of national defense as well as future research directions.