• 대한금속재료학회지
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• 제50권3호
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• pp.243-247
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• 2012

A ruthenium (Ru) catalytic layer and a conventional Pt layer were assessed as counter electrodes (CE) for dye sensitized solar cells (DSSCs). Ru films with different thicknesses of 34, 46, and 90 nm were deposited by atomic layer deposition (ALD). Pt layers with the same thicknesses were prepared by sputtering. $0.45cm^2$ DSSCs were prepared and their properties were characterized by FE-SEM, cyclic voltammetry (CV), impedance spectroscopy (EIS), and current-voltage (I-V). FE-SEM revealed that the crystallized Ru films and Pt films had been deposited quite conformally. CV showed that the catalytic activity of Pt was much greater than that of Ru. In addition, although the catalytic activity of Pt did not depend on the thickness, that of Ru showed an increase with increasing thickness. Impedance analysis revealed high charge transfer resistance at the Ru interface and a decrease with increasing Ru thickness, whereas Pt showed low resistance with no thickness dependence. Despite the relatively small catalytic activity of Ru, the I-V result revealed the average energy conversion efficiency of Ru and Pt to be 2.98% and 6.57%, respectively. These results suggest that Ru can be used as counter electrodes in DSSCs due to its extremely low temperature process compatibility.

• 대한원격탐사학회지
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• 제11권1호
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• pp.65-80
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• 1995

기상관측자료와 더불어 원격탐사자료를 이용함으로서 서로 다른 공간 및 시간스케일에 대한 에너지수직의 3성분을 추정할 수 있으며 결과적으로는 잠열의 추정을 가능하게 하였다. 이 러한 접근법을 응용하여 본 연구에서는 기상 및 위성자료를 바탕으로 지표에너지 관계식을 이용 한 광역증발산량 추정하는 방법에 대하여 검토하였다. 또한 토지이용의 변화에 따른 지표면열수 지의 변화를 평가하기 위하여 지리정보시스템분석 방법을 사용하여 검토하였다. 그 결과 연구지 역의 토지이용변화는 지역내의 열수지에 상당한 변화를 가져오는 것으로 나타났다. 본 연구의 결 과를 향상시키기 위해서는 열수지의 계산에 사용되는 각 추정식의 정확도 향상과 지표면의 상태 를 위성 원격탐사로서 정확하게 파악할 필요가 있다.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2009년도 춘계학술대회
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• pp.313-316
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• 2009

본 연구에서는 의료목적 무선 센서네트워크 환경에서 요구하는 데이터 전달의 신뢰성 향상을 위해 기능성 노드를 제안한다. 생체신호 모니터링을 위해 기존의 지속적인 생체신호 전송 시에 발생하는 데이터 손실을 줄이기 위해 비정상적인 QRS-complex 검출이 가능한 센서노드를 이용하여 Ad-hoc 네트워크 환경에서 비정상적인 QRS-comoplex 발생 시 데이터 전송함으로써 무선 센서네트워크 내에 발생되는 데이터량을 줄일 수 있었다. 본 연구에서 결과로 Ad-hoc 환경에서의 기능성 노드를 사용함으로 의료 목적을 위한 무선 센서네트워크에서 전체 패킷발생을 줄여서 센서노드의 전력소모를 크게 줄이고 시스템의 신뢰도를 크게 높이는 것으로 확인되었다.

• Ocean Systems Engineering
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• 제5권3호
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• pp.139-160
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• 2015

The global performance of the 5MW OC4 semisubmersible floating wind turbine in random waves was numerically simulated by using the turbine-floater-mooring fully coupled and time-domain dynamic analysis program FAST-CHARM3D. There have been many papers regarding floating offshore wind turbines but the effects of second-order wave-body interactions on their global performance have rarely been studied. The second-order wave forces are actually small compared to the first-order wave forces, but its effect cannot be ignored when the natural frequencies of a floating system are outside the wave-frequency range. In the case of semi-submersible platform, second-order difference-frequency wave-diffraction forces and moments become important since surge/sway and pitch/roll natural frequencies are lower than those of typical incident waves. The computational effort related to the full second-order diffraction calculation is typically very heavy, so in many cases, the simplified approach called Newman's approximation or first-order-wave-force-only are used. However, it needs to be justified against more complete solutions with full QTF (quadratic transfer function), which is a main subject of the present study. The numerically simulated results for the 5MW OC4 semisubmersible floating wind turbine by FAST-CHARM3D are also extensively compared with the DeepCWind model test results by Technip/NREL/UMaine. The predicted motions and mooring tensions for two white-noise input-wave spectra agree well against the measure values. In this paper, the numerical static-offset and free-decay tests are also conducted to verify the system stiffness, damping, and natural frequencies against the experimental results. They also agree well to verify that the dynamic system modeling is correct to the details. The performance of the simplified approaches instead of using the full QTF are also tested.

• 설비공학논문집
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• 제19권5호
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• pp.403-410
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• 2007

In this study, natural refrigerants and their mixtures that can supplement and replace R12 and R134a in automobile air-conditioners are studied. R134a is currently used as the refrigerant in new motor vehicle air conditioners, replacing the ozone depleting refrigerant R12. Although R134a has no ozone depletion potential, it has a relatively large global warming potential, approximately 1300 times that of $CO_2$ over a 100 year time horizon. For this reason, performance of natural refrigerants and their mixtures containing R152a, RE170 (Dimethylether, DME) and R600a (Isobutane) are measured under 2 different temperature conditions. They were tested in a refrigerating bench tester with an open type compressor. The test bench provided about 4 kW capacity and water and water/glycol mixture were employed as the secondary heat transfer fluids. Test results show that the coefficient of performance (COP) of these refrigerants is up to 21.55% higher than that of R12 in all temperature conditions. Overall, these fluids provide good performance with reasonable energy savings without any environmental problem and thus can be used as long term alternatives for automobile air-conditioners.

• 한국철도학회논문집
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• 제20권3호
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• pp.356-364
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• 2017

전기철도 차량은 검수를 위한 단계가 복잡하며, 안전사고에 대한 위험도 내포하고 있다. 이동식 전차선 시스템은 복잡한 과정의 검수고 입환 시스템에 대해 단순화가 가능하도록 하며, 사용자 편의성을 제공하고 안전성을 확보한다는 측면에서 매우 유용한 시스템이다. 본 논문에서는 기존 이동식전차선 대비 사용상 장점이 있고 국내 직류 시스템에 첫 적용되는 강체전차선을 적용하여 기계적인 내구성, 편의성, 작업자 안전성을 확보한 철도차량용 이동식 전차선 시스템에 대해 성능평가 및 연구개발 결과를 정리를 포함하여 현장설치를 위한 기본적인 특성을 종합적으로 분석하였다. 결론적으로 반복적인 사용 환경에 대한 내구성, 기계적인 하중에 대한 내구성, 안전성 등 요구 사양에서 우수한 결과를 나타내었다.

• 설비공학논문집
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• 제18권10호
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• pp.761-767
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• 2006

In this study, performance of 2 pure hydrocarbons R290 and R1270 was measured in an attempt to substitute R22 under 3 different temperature conditions. They were tested in a refrigerating bench tester with a hermetic rotary compressor. The test bench provided about 3.5 kW capacity and water and water/glycol mixture were employed as the secondary heat transfer fluids. All tests were conducted under the same external conditions resulting in the average saturation temperatures of $7/45^{\circ}C$ and $-7/41^{\circ}C$ and $-21/28^{\circ}C$ in the evaporator and condenser, respectively. Test results show that the coefficient of performance (COP) of these refrigerants is up to 11.54% higher than that of R22 in all temperature conditions. Compressor discharge temperatures were reduced by $14{\sim}31^{\circ}C$ with these fluids. There was no problem with mineral oil since the mixtures were mainly composed of hydrocarbons. The amount of charge was reduced up to 58% as compared to R22. Overall, these fluids provide good performance with reasonable energy savings without any environmental problem and thus can be used as long term alternatives for residential air-conditioning and heat pumping application.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2006년도 하계학술발표대회 논문집
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• pp.58-63
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• 2006

In this study, performance of 2 pure hydrocarbons and 3 mixtures was measured in an attempt to substitute R22 under 3 different temperature conditions. The mixtures were composed of R1270(propylene), R290(propane) and R152a. They were tested in a refrigerating bench tester with a hermetic rotary compressor The test bench provided about 3.5 kW capacity and water and water/glycol mixture were employed as the secondary heat transfer fluids. All tests were conducted under the same external conditions resulting in the average saturation temperatures of $7^{\circ}C/45^{\circ}C$ and $-7^{\circ}C/41^{\circ}C$ and $-21^{\circ}C/28^{\circ}C$ in the evaporator and condenser, respectively. Test results show that the coefficient of performance (COP) of these refrigerants is up to 11.54% higher than that of R22 in all temperature conditions. Compressor discharge temperatures were reduced by $14{\sim}31^{\circ}C$ with these fluids. There was no problem with mineral oil since the mixtures were mainly composed of hydrocarbons. The amount of charge was reduced up to 58% as compared to R22. Overall, these fluids provide good performance with reasonable energy savings without any environmental problem and thus can be used as long term alternatives for residential air-conditioning and heat pumping application.

• 한국결정성장학회지
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• 제31권5호
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• pp.228-232
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• 2021

페로브스카이트 구조를 가지는 Ca_1-xZrO₃:xPr 형광체를 스컬용융법으로 합성하였다. 합성한 형광체의 결정구조, 형태 및 광학적 특성은 XRD, SEM, 자외선 형광반응 및 광발광을 통해 분석하였다. XRD 측정에서는 CaZrO₃:Pr³⁺의 단결정이 페로브스카이트 구조의 사방정계로 분석되었다. 합성된 형광체는 254 nm의 UV 광에 의해 여기 될 수 있고 방출 스펙트럼 결과는 506, 536 및 548 nm에서 전하전이 ³P₀ → ³H₄, ³P₁ → ³H₅ 및 ³P₀ → ³H₅로 인해 CaZrO₃:Pr³⁺는 녹색 발광이 우세하였다.

• 전기전자학회논문지
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• 제25권3호
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• pp.534-539
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• 2021

본 논문에서는 유도 가열코일의 인덕턴스 변화 환경에서 스위칭주파수를 가변하여 최대 가열 전력이 전달될 수 있는 유도 가열 방식을 제안하였다. 가열코일내 피 가열체 종류 및 가열코일과의 근접도에 따라 공진회로의 공진주파수가 변화하게 되며, 공진주파수와 스위칭주파수 관계에 따라 유도가열기 소자의 파손 또는 손실이 발생하여 최대 전력 전달이 어려울 수 있다. 공진주파수의 변화에 따른 가열 전력을 감지하여 최대 전력 전달이 유지되도록 스위칭주파수를 가변하도록 하였다. 공진 주파수 변화에 대응하는 스위칭주파수 가변에 따라 요구하는 출력 변화 범위내로 제어될 수 있는 제안된 방식의 결과를 통하여 거의 일정한 출력전력(0.43 dB 이내) 전달이 가능한 스위칭주파수 가변특성을 갖는 유도가열기의 전력 효율성을 확보할 수 있었다.