대기압의 공기 분위기에서 열증발법에 의해 합성된 가지상 구조의 MgO 나노선

이근형 대한금속·재료학회 2023 대한금속·재료학회지 Vol.61 No.6

MgO nanowires with a branched structure were fabricated using a thermal evaporation methodin air at atmospheric pressure. The branched MgO nanowire was made up of two parts: a primary centralnanowire trunk and lots of secondary nanowire branches. The branched MgO nanowires had a 4-foldsymmetrical structure. The secondary nanowire branches grew perpendicular on the four side facets of thecentral nanowire trunks with square cross-sections. The nanowire branches also grew in a single row and werevertically well aligned in the same direction with each other. The scanning electron microscopy images of thebranched nanowires grown at 1000oC showed that the diameter of branches gradually decreased along thegrowth direction and no catalyst particle was found at the tips of the branches, indicating that the brancheswere grown by a vapor-solid process. For the branched nanowires grown at 1150oC, spherical particles whichwere shown to be catalysts were observed at the tips of the branches. The chemical analysis by energydispersive spectroscopy showed that the spherical particles were composed of Mg and O elements. Theseresults suggest that the branches’ growth resulted from a self-catalyzed vapor-liquid-solid process. Thestructural characterization by X-ray diffraction confirmed that the branched MgO nanowires had a cubiclattice structure. The room temperature cathodoluminescence spectra of the branched MgO nanowiresexhibited a very strong visible emission which was associated with oxygen vacancies.

대기압의 공기 분위기에서 촉매를 사용하지 않는 열증발법을 이용하여 생성된 TiO2 나노구조

이근형 대한금속·재료학회 2020 대한금속·재료학회지 Vol.58 No.5

TiO2 nanostructures were synthesized using a thermal evaporation method without a catalyst. TiO powders mixed with graphite powders were used as the source materials. The synthesis process was performed in air atmosphere at 1000 °C. When the mass ratio of TiO/graphite in the source material was 2:1, TiO2 nanowires and nanobelts started to form. As the mass ratio of graphite to TiO increased to 1:1, TiO2 nanowires and nanobelts were formed in large quantity. The nanowires had an average diameter of 80 nm and lengths in the range of 3 ~ 11 μm. The average width and length of the nanobelts were 500 nm and 3.4 μm, respectively. However, with further increase in the mass ratio of TiO/graphite to 1:2, no nanostructures were observed. The mass ratio of graphite to TiO in the source material had an important effect on the formation of the TiO2 nanowires and nanobelts. The X-ray diffraction data confirmed that the TiO2 nanostructures had a rutile crystal structure. Two emission bands centered at 410 nm and 510 nm were observed in the room temperature cathodoluminescence spectrum of the TiO2 nanostructures. The emission at 410 nm is attributed to the electron transition from the conduction band to the valence band in rutile TiO2 crystal, which is indicative of the high crystallinity of the TiO2 nanostructures.

공기 중 대기압 분위기에서 Zn의 산화에 의해 생성된 Tetrapod와 Multipod 형태의 나노구조와 음극선 발광 특성

이근형,Lee, Geun-Hyoung 한국전기전자재료학회 2011 전기전자재료학회논문지 Vol.24 No.3

ZnO nanostructures with tetrapod, needle and multipod shapes were synthesized without catalysts through a simple thermal oxidation of metallic Zn powder in alumina crucible under air atmosphere. X-ray diffraction data revealed that the ZnO nanostructures had wurtzite structure of hexagonal phase. Energy dispersive X-ray (EDX) spectra showed that the ZnO was of high purity. After the oxidation of Zn powder, white colored product was mainly observed and yellow colored product was observed only a very little on the surface of the oxidized source materials. The white product consisted of tetrapods, while yellow product was composed of needles and multipods. Cathodoluminescece spectra showed that the crystalline quality of tetrapods was better that those of needles and multipods.

Mathematical approach for optimization of magnetohydrodynamic circulation system

이근형,김희령 한국원자력학회 2019 Nuclear Engineering and Technology Vol.51 No.3

The geometrical and electromagnetic variables of a rectangular-type magnetohydrodynamic (MHD)circulation system are optimized to solve MHD equations for the active decay heat removal system of aprototype Gen-IV sodium fast reactor. Decay heat must be actively removed from the reactor coolant toprevent the reactor system from exceeding its temperature limit. A rectangular-type MHD circulationsystem is adopted to remove this heat via an active system that produces developed pressure through theLorentz force of the circulating sodium. Thus, the rectangular-type MHD circulation system for a circulatingloop is modeled with the following specifications: a developed pressure of 2 kPa and flow rate of0.02 m3/s at a temperature of 499 K. The MHD equations, which consist of momentum and Maxwell'sequations, are solved to find the minimum input current satisfying the nominal developed pressure andflow rate according to the change of variables including the magnetic flux density and geometricalvariables. The optimization shows that the rectangular-type MHD circulation system requires a current of3976 A and a magnetic flux density of 0.037 T under the conditions of the active decay heat removalsystem.

웹 접근성에 대한 정책적 지원의 효과성 검증을 위한 특수학교와 특수학급이 있는 일반학교의 웹 접근성 지침 준수 정도에 관한 비교연구

이근형,이태수 이화여자대학교 특수교육연구소 2012 특수교육 Vol.11 No.2

이 연구는 교육과학기술부의 정책적 지원을 받은 특수학교의 웹 사이트와 특수학급이 설치된 일반학교의 웹 사이트가 장애인의 정보접근권 확보를 위하여 얼마나 웹 접근성을 잘 준수하고 있는지 비교하는데 주요한 목적이 있다. 이를 위해 전국의 특수학교와 특수학급이 있는 일반학교의 웹 사이트를 대상으로 유층표집 하였고, 특수학급이 설치되어 있는 일반학교의 홈페이지 100개와 특수학교의 홈페이지 31개를 연구대상으로 선정하였다. 분석대상인 홈페이지는 4명의 웹 접근성 전문 평가자에 의해 자동평가와 수동평가를 받았다. 평가결과, 자동평가에서는 특수학급이 있는 일반학교의 웹 사이트가 특수학교의 웹 사이트보다 다소 높은 웹 접근성 준수율을 보여주었으나, 세부 검사항목에서는 특수학교의 웹 사이트가 더 높은 웹 접근성 준수율을 나타내었다. 수동 평가에서는 전체적으로 특수학교의 웹 사이트가 특수학급이 설치되어 있는 일반학교의 웹 사이트보다 평가 원칙과 세부 평가 항목 모두에서 웹 접근성을 보다 잘 준수하고 있었다. 그러나 정책적 지원을 받은 특수학교의 웹 사이트도 웹 접근성 지침을 통과할 수 있는 정도로 웹 접근성 지침을 충실히 준수하지 못하였다. 이는 웹 접근성을 준수하여 웹 사이트를 개편하였음에도 불구하고 체계적인 관리와 운영이 이루어지지 않았기 때문이다. 따라서 웹 접근성 준수를 위한 연수와 인식 개선을 위한 보다 적극적인 노력이 있어야 할 것이다. The purpose of this study was to compare the observance of Web accessibility on the web-site of special schools and general school with special class to verify the effectiveness of policies. To this end, 131 school’s web-sites(100 web sites of general schools with special class and 31 web sites of special schools) were selected using the stratified sampling and then 4 evaluators who had specialty in the Web accessibility conducted automatic evaluation and manual evaluation. The observance rates of Web accessibility of special school with observance of general school with special class compared with through independent samples t-test. The findings showed that special school had higher observance rates of web accessibility than general school with special class. Although the web sites of special schools received the political support from government, they didn’t observe the web accessibility.

녹색기술을 이용하여 제작된 ZnO 나노선

이근형 대한금속·재료학회 2012 대한금속·재료학회지 Vol.50 No.3

ZnO nanowires were fabricated through thermal evaporation of Zn or ZnS powder using solar energy. The Zn or ZnS powder was heated and evaporated by sunlight. The sunlight was concentrated on the Zn or ZnS powder by a converging lens and then the Zn or ZnS powder was evaporated and oxidized in air. After oxidation, ZnO nanowires were fabricated in the focal point. Strong ultraviolet emission, which corresponds to the near band-edge emission, was observed from the ZnO nanowires synthesized using Zn powder as a source material. Meanwhile, green emission, related to intrinsic defects such as oxygen vacancies, prevailed for the ZnO nanowires fabricated using ZnS powder. No catalysts were used in the fabrication of the ZnO nanowires, which suggested the ZnO nanowires were grown by a vapor-solid mechanism.

Feasibility Study of Federated Learning on the Distributed Research Network of OMOP Common Data Model

이근형,박종걸,김지형,김이석,최병진,박래웅,이상열,신수용 대한의료정보학회 2023 Healthcare Informatics Research Vol.29 No.2

Objectives: Since protecting patients’ privacy is a major concern in clinical research, there has been a growing need for privacy-preserving data analysis platforms. For this purpose, a federated learning (FL) method based on the Observational MedicalOutcomes Partnership (OMOP) common data model (CDM) was implemented, and its feasibility was demonstrated. Methods: We implemented an FL platform on FeederNet, which is a distributed clinical data analysis platform based on theOMOP CDM in Korea. We trained it through an artificial neural network (ANN) using data from patients who received steroidprescriptions or injections, with the aim of predicting the occurrence of side effects depending on the prescribed dose. The ANN was trained using the FL platform with the OMOP CDMs of Kyung Hee University Medical Center (KHMC) andAjou University Hospital (AUH). Results: The area under the receiver operating characteristic curves (AUROCs) for predictingbone fracture, osteonecrosis, and osteoporosis using only data from each hospital were 0.8426, 0.6920, and 0.7727 forKHMC and 0.7891, 0.7049, and 0.7544 for AUH, respectively. In contrast, when using FL, the corresponding AUROCs were0.8260, 0.7001, and 0.7928 for KHMC and 0.7912, 0.8076, and 0.7441 for AUH, respectively. In particular, FL led to a 14%improvement in performance for osteonecrosis at AUH. Conclusions: FL can be performed with the OMOP CDM, and FLoften shows better performance than using only a single institution's data. Therefore, research using OMOP CDM has beenexpanded from statistical analysis to machine learning so that researchers can conduct more diverse research.

MgO 나노선의 성장과 음극선 발광 특성에 미치는 산소 농도의 영향

이근형 대한금속·재료학회 2023 대한금속·재료학회지 Vol.61 No.7

MgO nanowires were grown by a thermal evaporation method at different N2/O2 gas ratios in orderto investigate the effect of oxygen concentration on the growth and luminescence properties of the MgOnanowires. A thermal evaporation process was conducted at 1000oC and under a pressure of 500Torr. Nonanowires were grown in a pure N2 gas atmosphere. Nanowires were formed at oxygen concentrations above25% in a mixture of N2 and O2 gases. X-ray diffraction analysis showed that the MgO nanowires had a cubiccrystal structure. Compared to the nanowires formed at high oxygen concentration, the nanowires grown at lowoxygen concentration had larger diameters and rougher side surfaces. Nanowires with very smooth side surfaceswere formed at high oxygen concentrations. The difference in surface roughness was supposed to be due to thechange in the growth habit of nuclei. Two visible emissions were observed in the cathodoluminescence spectraof the MgO nanowires. One was an emission peak centered near 400 nm and the other was an emission peakwith a central wavelength of 500 nm. As the oxygen concentration increased, the emission intensity of the 400nm band decreased and the emission intensity of the 500 nm band increased. The maximum emission at 500nm was observed from the nanowires formed in a pure O2 atmosphere. The full width at half maximum of theemission peak at 500 nm was narrower than that of the emission peak at 400 nm.

RCT기반의 RBF 신경회로망을 이용한 도립역진자의 각도 및 위치 제어

이근형,노진석,정슬 제어로봇시스템학회 2007 제어로봇시스템학회 국내학술대회 논문집 Vol.2007 No.5

열증발법에 의해 성장한 SnO2나노/마이크로 결정의 형상에 미치는 Ga의 영향

이근형 대한금속·재료학회 2024 대한금속·재료학회지 Vol.62 No.7

SnO2 nano/micro-crystals with different morphologies were fabricated by the thermal evaporationof SnO2 powders mixed with Ga2O3 powder. The synthesis process was performed at 1300oC in air. X-raydiffraction (XRD) analysis, energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM) andFourier transform infrared spectroscopy (FTIR) were used to examine the morphology, microstructure,elemental composition and chemical property of the as-synthesized products. X-ray diffraction analysisrevealed that the products were SnO2 with a tetragonal rutile crystal structure. From the Fourier transforminfrared spectra of the products, Sn-O stretching mode was observed, which confirmed the formation of SnO2. Scanning electron microscopic analysis clearly showed that the morphology of the SnO2 crystals wassignificantly affected by the addition of Ga2O3 to SnO2 source powder. SnO2 crystals with a belt-likemorphology were grown when the source powder without Ga2O3 powder was used. Rod-like SnO2 crystals weregrown by using SnO2 powder mixed with Ga2O3 powder as the source powder. When the amount of Ga2O3mixed in the source powder was increased, the morphology of the SnO2 crystals changed from rod to tube. Energy dispersive X-ray analysis indicated that the inner core of the tube-like crystals was composed of Snrichmetastable phase. No catalytic particles were observed at the tips of the SnO2 nano/micro-crystals,suggesting that the growth process occurred by vapor-solid growth mechanism.