• 한국전기전자재료학회논문지
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• 제27권2호
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• pp.81-84
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• 2014

The bipolar resistive switching characteristics of resistive random access memory (ReRAM) based on $HfO_2$ thin films have been demonstrated by using Ag/$HfO_2$/Pt structured ReRAM device. MIcrowave irradiation (MWI) treatment at low temperature was employed in device fabrication with $HfO_2$ thin films as a transition layer. Compared to the as-deposited Ag/$HfO_2$/Pt device, highly improved uniformity characteristics of resistance values and operating voltages were obtained from the MWI treatment Ag/$HfO_2$/Pt ReRAM device. In addition, a stable DC endurance (> 100 cycles) and a high data retention (> $10^4$ sec) were achieved.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 춘계학술대회 논문집 방전 플라즈마 유기절연재료 초전도 자성체연구회
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• pp.7-10
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• 2004

This paper presents the electrical properties of PTFE nozzle for a electrical apparatus. In the arcing environment in a electrical apparatus, radiation is considered to be the major energy transport mechanism from the arc to the wall. The fraction of the radiation power is emitted out of the arc and reaches the nozzle wall, causing ablation at the surface and in the depth of the wall. The energy concentration in the material leads to the depolymerization and eventually leads to the generation of decomposed gas as well as some isolated carbon particles. Adding some fillers into PTFE is expected to be efficient for improving the endurability against radiation. In this experiment, three kinds of fillers that have endurance in the high temperature environment were added into PTFE. Light reflectance of fillers was investigated. Dielectric constan and dissipation factor of PTFE composites were investigated. Dielectric constant and dissipation factor of the PTFE composites increased with increasing contents of the fillers.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 추계학술대회 논문집 전기물성,응용부문
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• pp.67-69
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• 2004

ZnO varistor ceramics which were fabricated with variation of added of 0.01, 0.02, 0.03, 0.05, 0.1mol% $Nb_2O_5$ sintered at $1150^{\circ}C$. In the specimen added 0.05mol% $Nb_2O_5$, sintered density was $5.87g/cm^3$ and electrical properties were superior to any other components. The nonlinear coefficient was 75, and clamping voltage ratio was 1.40. And, endurance surge current in the specimen added 0.05mol% $Nb_2O_5$ was $6500A/cm^2$, and deviation of varistor voltage was -1.7%. As P.C.T and T.C.T environment test were succeed in all specimens, and deviation of varistor voltage in the specimen added 0.3mol% $Nb_2O_5$ was -0.81%. All specimens showed a good leakage current property in the High Temperature Continuous Load Test for 1000hr, at $85^{\circ}C$, and variation rate of the varistor voltage was -1.71%.

• 한국표면공학회지
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• 제47권6호
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• pp.354-361
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• 2014

In order to utilize silicon carbide (SiC) as an inner part of fluidized bed reactor (FBR) for manufacturing poly-silicon, we have carried out the thermodynamic calculation on the overall reactions including poly-silicon synthesis and compatibility of SiC with FBR process. The resources of silicon included $SiH_4(MS)$, $SiHCl_3(TCS)$ and $SiCl_4(STC)$ and the thermodynamic yield of the FBR with MS, TCS and STC were compared each other with variable range of temperature, pressure and hydrogen to silicon ratio. The silicon yield of MS, TCS and STC were 100%, 28% and 4%, respectively, throughout the conventional FBR conditions. Silicon carbide having high hardness and strength showed strong resistance to granule collisions during the FBR process using a lab-scale reactor. And it also showed quite good compatibility with the typical FBR processes of MS and TCS resources.

• Advances in concrete construction
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• 제15권1호
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• pp.41-46
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• 2023

Sport has no age limit and can be done anywhere and in any condition with minimal equipment. The existence of sports spaces in all parts of the world is considered a citizen's right. One of the activities carried out in this field is installing sports equipment and structures in parks and encouraging citizens to use this equipment for physical health with the least cost and facilities. Installing sports structures in open spaces such as parks is a practical step for developing citizens' sports. Although using devices in parks is acceptable, it is more critical to meet scientific and technical standards. The components of these structures must have high strength and endurance against changes in environmental conditions such as humidity, temperature difference, and corrosion. Among the various causes of material degradation, corrosion has always been one of several fundamental causes of metal equipment failure. Sports structures in open spaces are not safe from corrosion. Uniform corrosion is the most common type of corrosion. This corrosion usually occurs uniformly through a chemical or electrochemical reaction across the surface exposed to the corrosive environment. Rust and corrosion of outdoor sports structures are examples of this corrosion. For this reason, in this research, with the green synthesis of silica nanoparticles and its application in outdoor sports structures, the life span of these structures can be increased for the use of physical exercises as well as their quality.

• 한국철도학회논문집
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• 제14권2호
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• pp.100-108
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• 2011

본 논문은 고속철도 디스크 브레이크용 유연 제동 패드의 성능 향상을 위해 구조적 안정성 검토와 신뢰성에 대한 연구를 수행하였다. 연구에서는 유연패드의 구조 해석 과정을 거쳐 개선된 모델을 얻어내었으며, 실제 크기와 동일한 1/2 모델을 가지고 구조적 안전성을 확인하였다. 또한, 축소 시편을 제작하여 모달 시험과 스트로크 및 내구성 시험을 수행하여 동 특성과 기계적 안정성을 확인하였다. 샤시 다이나모 장비와 열 적외선 캠코더를 이용하여 유연패드에 대하여 회전 속도에 따른 열섬 발생 현상을 측정하고, 디스크와 패드 사이의 균일한 접촉 능력을 확인하였다. 또한, 제동 시 유연패드에 안정적인 온도 분포가 이루어지는 것을 확인할 수 있었다. 이와 같은 결과를 토대로 제안된 유연패드의 구조 안정성 및 열에너지 방출 효과 등의 장점을 확인하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.195-201
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• 2008

In the jet engines on the aircrafts cruising at high altitude over 20 km and subsonic speed, the Reynolds number in terms of the compressor blades becomes very low. In such an operating condition with low Reynolds number, it is widely reported that total pressure loss of the air flow through the compressor cascades increases dramatically due to separation of the boundary layer and the secondary-flow. But the detail of flow mechanisms causes the total pressure loss has not been fully understood yet. In the present study, two series of numerical investigations were conducted to study the effects of Reynolds number on the aerodynamic characteristics of compressor cascades. At first, the incompressible flow fields in the two-dimensional compressor cascade composed of C4 airfoils were numerically simulated with various values of Reynolds number. Compared with the corresponding experimental data, the numerically estimated trend of total pressure loss as a function of Reynolds number showed good agreement with that of experiment. From the visualized numerical results, the thickness of boundary layer and wake were found to increase with the decrease of Reynolds number. Especially at very low Reynolds number, the separation of boundary layer and vortex shedding were observed. The other series, as the preparatory investigation, the flow fields in the transonic compressor, NASA Rotor 37, were simulated under the several conditions, which corresponded to the operation at sea level static and at 10 km of altitude with low density and temperature. It was found that, in the case of operation at high altitude, the separation region on the blade surface became lager, and that the radial and reverse flow around the trailing edge become stronger than those under sea level static condition.

• Journal of Electrochemical Science and Technology
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• 제13권4호
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• pp.472-478
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• 2022

Solar energy harvesting is practiced by various nations for the purpose of energy security and environment preservation in order to reduce overdependence on oil. Converting solar energy into electrical energy through Photovoltaic (PV) module can take place either in on-grid or off-grid applications. In recent time Lithium battery is exhibiting its presence in on-grid applications but its role in off-grid application is rarely discussed in the literature. The preliminary capacity and Peukert's study indicated that the battery quality is good and can be subjected for life cycle test. The capacity of the battery was 10.82 Ah at 1 A discharge current and the slope of 1.0117 in the Peukert's study indicated the reaction is very fast and independent on rate of discharge. In this study Lithium Iron Phosphate battery (LFP) after initial characterization was subjected to life cycle test which is specific to solar off-grid application as defined in IEC standard. The battery has delivered just 6 endurance units at room temperature before its capacity reached 75% of rated value. The low life of LFP battery in off-grid application is discussed based on State of Charge (SOC) operating window. The battery was operated both in high and low SOC's in off-grid application and both are detrimental to life of lithium battery. High SOC operation resulted in cell-to-cell variation and low SOC operation resulted in lithium plating on negative electrode. It is suggested that to make it more suitable for off-grid applications the battery by default has to be overdesigned by nearly 40% of its rated capacity.

• 한국가스학회지
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• 제22권2호
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• pp.59-66
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• 2018

최근 무인기에 대한 관심과 수요가 높아지고 있는 가운데, 가동범위가 넓고 전략적으로 활용이 많은 고고도장기체공 무인기의 동력원개발이 연구 목표로 검토되었다. 기존 왕복동 엔진에 수소 연료를 적용하는 기술은 현행으로써 적용성이 용이하고 경제적이다. 수소는 중량당 에너지 밀도가 높아서 한 번 충전으로 장시간 운항을 지속할 수 있고 환경적인 측면에서도 무공해 연료라는 긍정적인 부분이 존재하기 때문에 적합하다고 평가된다. 하지만 현재 수소연료를 왕복동 엔진에 적용한 개발사례가 적은 편이라 향후 기술적으로 많은 연구가 필요한 것으로 판단된다. 항공기는 운항고도에 따라 공기밀도 저감으로 인한 냉각성능 저하 또는 복사열 감소에 의한 주변온도 강하로 과냉각이 될 수 있는 요인들이 존재한다. 따라서 본 실험은 냉각수온을 변화시켜서 이러한 주변온도 변화가 수소연료 엔진에 미치는 연소특성에 대해 살펴보았다. 역화에 의한 안정적인 운전 영역의 제한은 냉각수 온도변화에 의한 영향보다 공기과잉률에 의한 영향이 지배적으로 나타났으며, 냉각수 온도가 증가할 경우 충진효율이 감소하여 토크가 감소하고 냉각수 온도가 감소할 경우 열손실이 증가하여 열효율이 감소하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.307.2-307.2
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• 2016

In this study, we synthesized Au nanoparticles (AuNPs) in polyacrylonitrile (PAN) thin films using a simple annealing process in the solid phase. The synthetic conditions were systematically controlled and optimized by varying the concentration of the Au salt solution and the annealing temperature. X-ray photoelectron spectroscopy (XPS) confirmed their chemical state, and transmission electron microscopy (TEM) verified the successful synthesis, size, and density of AuNPs. Au nanoparticles were generated from the thermal decomposition of the Au salt and stabilized during the cyclization of the PAN matrix. For actual device applications, previous synthetic techniques have required the synthesis of AuNPs in a liquid phase and an additional process to form the thin film layer, such as spin-coating, dip-coating, Langmuir-Blodgett, or high vacuum deposition. In contrast, our one-step synthesis could produce gold nanoparticles from the Au salt contained in a solid matrix with an easy heat treatment. The PAN:AuNPs composite was used as the charge trap layer of an organic nano-floating gate memory (ONFGM). The memory devices exhibited a high on/off ratio (over $10^6$), large hysteresis windows (76.7 V), and a stable endurance performance (>3000 cycles), indicating that our stabilized PAN:AuNPs composite film is a potential charge trap medium for next generation organic nano-floating gate memory transistors.