• 한국재료학회지
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• 제16권10호
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• pp.624-628
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• 2006

In this study, divalent europium-activated $NaCaPO_4$ green phosphor powders were prepared by the chemical synthetic method followed by heat treatment in reduced atmosphere, and the crystal structures, morphologies and photoluminescent properties of the powders were investigated by x-ray powder diffraction, scanning electron microscope and spectrometer for the first time. The effects of Ca/P and Na/Ca mole ratios on the final products were also investigated. The influences of input amount change of europium as the activator on the light emission intensity were studied, and the resulting concentration quenching phenomenon was observed. The optimized synthesis conditions obtained in this study were Ca/P mole ratio 1.2, Na/Ca mole ratio 3.0 and 4 mole%Eu. The peak wavelength was 505 nm for all the samples. The result of excitation spectrum measurement indicated that the excitation efficiency was high for the long-wavelength UV region. It was thus concluded that the samples prepared in this study can be successfully applied for the light-emitting devices such as LED excited with long-wavelength UV light sources.

• Journal of Power Electronics
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• 제17권6호
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• pp.1469-1479
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• 2017

Primary-side regulation (PSR) scheme is widely applied in low power applications, such as cell phone chargers, network adapters, and LED drivers. However, the efficiency and standby power requirements have been improved to a high standard due to the new trends of DOE (Department Of Energy) Level VI and COC (Code Of Conduct specifications) V5. The major drawbacks of PSR include poor regulation due to inaccurate feedback and difficulty in acquiring acceptable regulation. A novel adaptive blanking strategy for constant current and constant voltage regulation is proposed in this paper. An accurate model for the sample blanking time related to transformer leakage inductance and the metal-oxide-semiconductor field-effect transistor (MOSFET) parasitic capacitance is established. The proposed strategy can achieve accurate detection for ultra-low standby power. In addition, numerous control factors are analyzed in detail to eliminate the influence of leakage inductance on the loop stability. A dedicated controller integrated circuit (IC) with a power MOSFET is fabricated to verify the effectiveness of the proposed control strategy. Experimental results demonstrated that the prototype based on the proposed IC has excellent performance.

• 반도체디스플레이기술학회지
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• 제18권4호
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• pp.51-56
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• 2019

LuAG:Ce(Lu₃Al₅O₁₂:Ce³⁺) nano phosphor were synthesized by applying the coprecipitation method. It is used to increase the color rendering of phosphor ceramic plate for high power LEDs and laser lighting. Internal quantum efficiency and absorption of LuAG:Ce nano phosphor are 51.5 % and 64.4 %, respectively, which is higher than the previously studied nano phosphors. The maximum absorption wavelength of this phosphor is 450 nm blue light, and the emission wavelength is 510 nm. The emission wavelength shifted to longer wavelength when the concentration of Ce increased in the heat treatment of the reducing atmosphere. Thermal quenching of LuAG nano phosphor was 70 % at 200 ℃, it was explained by their significant quenching of all raman scattering modes, implying the restriction of electron-phonon couplings caused by their defects.

• 한국BIM학회 논문집
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• 제11권3호
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• pp.1-11
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• 2021

BIM is one of the means of reducing the economic loss caused by design errors. These features of BIM have led to increased use of BIM. With the increasing use of BIM, several studies have been conducted to analyze the performance of BIM. As the importance of BIM staff is emphasized in the performance analysis of BIM, the human resource allocation of BIM staff can become an important research issue. However, there are few studies to measure the workforce effectiveness of BIM staff. Ham et al (2020) measured BIM workforce efficiency using FCFS queue model rules. Since design errors can have different effects on the project depending on the type, there are design errors that must be dealt with first. Therefore, in this study, a priority queue was used to solve design errors with high priority first. The performance of BIM-based design verification was analyzed by quantitatively analyzing the performance of BIM staff when the priority rule was applied to the design error processing sequence.

• 한국기계가공학회지
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• 제21권5호
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• pp.67-76
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• 2022

The customer demand for diverse colors in home appliances has increased. However, this has led to issues for manufacturers, such as ensuring cost effectiveness and high-level quality control. To resolve these issues, production engineers utilize computer-aided engineering (CAE) tools for injection-molding processes and assess the suitability of process parameters for products manufactured using the in-mold labeling method. CAE can solve various problems in manufacturing processes, thereby increasing production efficiency and decreasing manufacturing cost. In addition, it can be used analyze customer complaints related to surface defects, such as part differences and irregular spacing between parts, and ultimately reduce product returns. In this study, CAE was used to solve quality problems and implement the most economical manufacturing process.

• Journal of Electrochemical Science and Technology
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• 제14권4호
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• pp.326-332
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• 2023

The high cost of Si-based solar cells remains a substantial challenge to their widespread adoption. To address this issue, it is essential to reduce the production cost of solar-grade Si, which is used as raw material. One approach to achieve this is Si electrodeposition in molten salts containing Si sources, such as SiO₂. In this study, we present the pulse electrodeposition of Si in molten CaCl₂ containing SiO₂ nanoparticles. Theoretically, SiO₂ nanoparticles with a diameter of less than 20 nm in molten CaCl₂ at 850℃ have a comparable diffusion coefficient with that of ions in aqueous solutions at room temperature. However, we observed a slower-than-expected diffusion of the SiO₂ nanoparticles, probably because of their tendency to aggregate in the molten CaCl₂. This led to the formation of a non-uniform Si film with low current efficiency during direct current electrodeposition. We overcome this issue using pulse electrodeposition, which enabled the facile supplementation of SiO₂ nanoparticles to the substrate. This approach produced a uniform and thick electrodeposited Si film. Our results demonstrate an efficient method for Si electrodeposition in molten CaCl₂ containing SiO₂ nanoparticles, which can contribute to a reduction in production cost of solar-grade Si.

• 접착 및 계면
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• 제25권1호
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• pp.143-151
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• 2024

유기태양전지(Organic photovoltaics, OPV)는 기계적 유연성, 경량, 반투명성, 낮은 제조 비용 등 여러 가지 고유한 특성을 지니고 있어 차세대 신재생 에너지원으로 큰 잠재력을 보여 왔다. 최근 분자구조 및 소자 엔지니어링의 발전으로 19% 이상의 높은 효율을 달성했다. 그러나 이러한 높은 효율을 갖춘 광활성층 물질들은 복잡한 구조로 인해 합성 과정이 복잡하며 제조비용이 높아 상용화에 어려움이 있다. 이 문제를 해결 하기 위해 간단한 구조를 갖는 저비용 광활성층 물질들에 대한 연구가 활발히 이루어지고 있다. 본 논문에서는 이러한 낮은 비용의 광활성층 물질 및 이를 합성하기 위한 전략들에 대해 소개한다.

• 한국컴퓨터정보학회논문지
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• 제29권5호
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• pp.85-91
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• 2024

본 논문은 레저스포츠 시장이 활성화되면서 총기를 활용한 활동이 늘어나고 있으며, 군대에서는 비용이 많이 드는 사격 훈련을 진행하고 있는 상황에서 저렴한 비용을 실외에서 훈련할수 있는 시스템을 연구했다. 이러한 고비용의 훈련을 저렴하게 대체하기 위해 가상 현실을 활용한 사이버 스크린이 연구되고 있다. 본 연구에서는 기존의 스크린 사격 훈련 시스템의 문제점인 어두운 공간과 높은 설치 비용을 최소화하기 위해 대형 디스플레이 장치에서도 사용할 수 있는 시스템을 제안한다. 이를 위해 전면에 IR 리시버를 부착하고 IR 건을 활용하여 훈련하는 시스템을 구축하고, 애플리케이션을 통해 사용성과 효율성을 확인했다. 또한, 영점 조절 기능을 추가하여 더 정확한 좌표를 인식할 수 있도록 했다. 이를 통해 낮은 비용으로도 사이버 라이트 건 시스템을 쉽게 활용할 수 있을 것으로 기대된다.

• 한국환경과학회지
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• 제33권7호
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• pp.523-532
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• 2024

In popular tourist destinations such as Jeju and Gangwon, electric rental cars are increasingly adopted. However, sudden battery drain due to weather conditions can pose safety issues. To address this, we developed a battery consumption analysis model that considers resistive energy factors such as acceleration, rolling resistance, and aerodynamic drag. Focusing on the effects of ambient temperature and wind speed, the model's performance was evaluated during an empirical validation period from November to December 2023. Comparing predicted and actual state of charge (SoC) across different routes identified ambient temperature, wind speed, and driving time as major sources of error. The mean absolute error (MAE) increased with lower temperatures due to reduced battery efficiency. Higher wind speeds on routes 1 and 6 resulted in larger errors, indicating the model's limitation in considering only tailwinds for aerodynamic drag calculations. Additionally, longer driving times led to higher actual SoC than predicted, suggesting the need to account for varying driver habits influenced by road conditions. Our model, providing more accurate SoC predictions to prevent battery depletion incidents, shows high potential for application in navigation apps for electric vehicle users in tourist areas. Future research should endeavor to the model by including wind direction, HVAC system usage, and braking frequency to improve prediction accuracy further.

• Earthquakes and Structures
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• 제27권2호
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• pp.97-111
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• 2024

In this paper, buckling conditions and retrofitting of cylindrical steel water storage tanks with different roof types and wall thicknesses were investigated by using finite element method. Four roof types of cylindrical steel tanks which are open-top, flat-closed, conical-closed and torispherical-closed and three wall thicknesses of 4, 6 and 8 mm were considered in FE modeling of cylindrical steel tanks. The roof shapes significantly affect load distribution on the tank shell under the seismic action. Composite FRP materials are widely used for winding thin-walled cylindrical steel structures. The retrofitting efficiency of cylindrical steel water tank is tested under the seismic loading with the externally bonded CFRP laminates. In retrofitting of cylindrical steel tank, the CFRP composite material coating method was used to improve of seismic performance of cylindrical steel tanks. ANSYS software was used to analyze the cylindrical steel tanks and maximum equivalent (von-Mises) and directional deformation were obtained. Equivalent (von-Mises) stresses significantly decreased due to the coating of the tank shell with FRP composite material. In thin-walled steel structures, excessive stress causes buckling and deformations. Therefore, retrofitting led to decrease in stress, reductions in directional and buckling deformation of the open-top, flat-closed, conical-closed and torispherical-closed tanks.