• 한국정보통신학회논문지
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• 제12권1호
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• pp.158-163
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• 2008

UV기술에 기반한 오존모니터는 신호의 안정성 때문에 널리 활용되어오고 있다. 먼저 오존 발생기에서 나오는 오존농도를 실시간, 고정 밀로 측정하기 위해서 저압 수은램프를 UV광원으로 하고, 광증배관을 UV 감지기로 하는 시스템을 구성하였다. 이 구조는 저 비용의 고농도 오존의 계측에 유용한 시스템으로서 단순한 구조와 비교적 우수한 계측성 능을 얻을 수 있었다. 제조된 시스템은 $0.05{\sim}2w1.%$의 측정 농도영역에서 좋은 선형성을 나타내었다. ppm정도의 보다 정밀한 농도계측을 위해서는 UV광원으로서 고출력 펄스 크세논램프를 사용하고, CCD어레이를 광스펙트로메터로 사용하도록 시스템을 설계하였다. CCD출력으로부터의 광신호는 우수한 반응성과 띄어난 광해상도를 가지고 디지털신호로 변환되고, 이 디지털신호는 PC의 스크린에 디스플레이 되도록 설계되었다. 제작된 시스템은 $10{\sim}10,000ppm$ 영역에서 선형적이고 우수한 감도를 보였으며 저 농도의 오존을 측정하는 시스템으로서의 가능성을 보여주었다.

• 설비공학논문집
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• 제18권4호
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• pp.320-327
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• 2006

Numerical analysis and experimental study are performed to investigate the effect of heat load and operating temperature on the thermal performance of several variable conductance heat pipe (VCHP) with screen meshed wick. The heat pipe is designed in 200 screen meshes, 500 mm length and 12.7 mm outer diameter tube of copper, water (4.8 g) is used as working fluid and nitrogen as non-condensible gas (NCG). Heat pipe used in this study has evaporator, condenser and adiabatic section, respectively. Analysis values and experimental data of wall temperature distribution along axial length are presented for heat transport capacity, condenser cooling water temperature change, degrees of an inclination angle and operating temperature. These analysis and experiment give the follow findings: For the same charging mass of working fluid, the operating temperature of heat pipe becomes to be high with the increasing of charging mass of NCG. When the heat flux at the evaporator section increases, the vapor pressure in the pipe rises and consequently compresses the NCG to the condenser end part and increases the active length of the condenser. From previous process, it is found out we can control the operating temperature effectively and also the analysis and experimental results are relatively coincided well.

• 한국표면공학회지
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• 제54권6호
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• pp.340-347
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• 2021

Among various metal oxide semiconductors, ZnO has an excellent electrical, optical properties with a wide bandgap of 3.3 eV. It can be applied as a photocatalytic material due to its high absorption rate along with physical and chemical stability to UV light. In addition, it is important to control the morphology of ZnO because the size and shape of the ZnO make difference in physical properties. In this paper, we demonstrate synthesis of size-controlled ZnO tetrapods using an atmospheric pressure plasma system. A micro-sized Zn spherical powder was continuously introduced in the plume of the atmospheric plasma jet ignited with mixture of oxygen and nitrogen. The effect of plasma power and collection sites on ZnO nanostructure was investigated. After the plasma discharge for 10 min, the produced materials deposited inside the 60-cm-long quartz tube were obtained with respect to the distance from the plume. According to the SEM analysis, all the synthesized nanoparticles were found to be ZnO tetrapods ranging from 100 to 600-nm-diameter depending on both applied power and collection site. The photocatalytic efficiency was evaluated by color change of methylene blue solution using UV-Vis spectroscopy. The photocatalytic activity increased with the increase of (101) and (100) plane in ZnO tetrapods, which is caused by enhanced chemical effects of plasma process.

• 한국초전도ㆍ저온공학회논문지
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• 제20권4호
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• pp.11-15
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• 2018

Torque tubes in High Temperature Superconducting (HTS) motor transfer torque from superconducting field winding rotor to the room temperature shaft. It should have minimum heat conduction property for minimizing the load on cryo-refrigerator. Generally, these torque tubes are made with stainless steel material because of high strength, very low outgassing and low thermal contraction properties at cryogenic temperatures and vacuum conditions. With recent developments in composite materials, these torque tubes could be made of composites such as Kevlar and S-Glass, which have the required properties like high strength and low thermal conductivity at cryogenic temperatures, but with a reduced weight. Development and testing of torque tubes made of these composites for HTS motor are taken up at Bharat Heavy Electricals Limited (BHEL), Hyderabad in collaboration with Central Institute of Plastics and Engineering Technology (CIPET), Chennai and Indian Institute of Technology (IIT), Kharagpur. As these materials are subjected to vacuum, it is important to measure their outgassing rates under vacuum conditions before manufacturing prototype torque tubes. The present study focusses on the outgassing characteristics of Kevlar and S-Glass, using an Outgassing Measurement System (OMS), developed at IIT Kharagpur. The OMS facility works under vacuum environment, in which the test samples are exposed to vacuum conditions over a sufficient period of time. The outgassing measurements for the composite samples were obtained using pressure-rise technique. These studies are useful to quantify the outgassing rate of composite materials under vacuum conditions and to suggest them for manufacturing composite torque tubes used in HTS motors.

• 한국추진공학회지
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• 제23권4호
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• pp.28-34
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• 2019

본 연구에서는 터빈 냉각에 널리 사용되는 핀-휜 배열에 대한 연구를 진행하였다. 본 연구에서 원형 튜브 전방에 익형 와류발생기가 위치하며, 익형 단면 형상은 NACA-9410을 사용하였다. 본 논문에서는 와류 발생기가 있는 핀-휜 배열 유동의 전열 성능과 유동 특성을 수직인 방향으로 변화시키며 기존의 핀-휜 유동과 비교하였다. 레이놀즈수 영역은 6000, 10000 그리고 15000 세 가지를 계산하였다. 전산 해석은 상용 프로그램인 ANSYS v18.0 CFX, 난류 모델은 $k-{\omega}$ SST를 사용하였다. 결과적으로 전열 성능은 최대 5.8% 증가하였고 압력 손실은 1% 미만으로 증가하였다.

• 한국산학기술학회논문지
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• 제19권12호
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• pp.14-24
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• 2018

몇 가지 전형적인 기존 및 진보된 초탄성 구성모델들의 고무패치 이축인장 및 구형 또는 원통형 풍선 팽창에서의 불안정성에 대해서 밝힌다. 적용할 구성모델은 neo-Hookean 모델, Mooney-Rivlin 모델, Gent 모델, Arruda-Boyce 모델, Fung 모델, Pucci-Saccomandi 모델 등이다. 팽창 및 분기 해석은 이들 변형에너지 함수들의 막 방정식을 이용하여 수행할 수 있다. 해석에는 사각패치에 대한 Kearsley의 분기현상, 고무풍선의 일반화 한 팽창현상, 고무풍선의 분기현상을 다룬다. 이들 변형에너지 함수들 중에서도 오직 Mooney-Rivlin 모델에서만 Kearsley의 분기현상이 일어남을 확인하였다. 팽창 방정식은 구형풍선과 원통형 풍선을 함께 다룰 수 있도록 일반화 시켰다. 팽창해석에 의하여 극한점과 임계 물성치들을 무차원 압력 및 팽창 부피의 항들로 구하였다. 그렇게 구해진 결과들로부터 분기현상을 구할 수 있었다. 또한 유한요소법을 사용하여 고무류의 구조적 불안정 문제들을 다룰 때 필요한 특별한 조처에 대해서 제안하였다. 결론적으로 고무류의 불안정성을 포함하는 문제를 다룰 때는 해석기법은 물론 구성모델의 선택에 따라 결과가 달라질 수 있으므로 신중한 처리가 요구된다.

• Nuclear Engineering and Technology
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• 제51권1호
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• pp.238-248
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• 2019

In the high-temperature and high-pressure irradiation environments, the multi-field coupling processes of hydrogen diffusion, hydride precipitation and mechanical deformation in Zircaloy cladding tubes occur. To simulate this hydrogen-induced complex behavior, a multi-field coupling method is developed, with the irradiation hardening effects and hydride-precipitation-induced expansion and hardening effects involved in the mechanical constitutive relation. The out-pile tests for a cracked cladding tube after irradiation are simulated, and the numerical results of the multi-fields at different temperatures are obtained and analyzed. The results indicate that: (1) the hydrostatic stress gradient is the fundamental factor to activate the hydrogen-induced multi-field coupling behavior excluding the temperature gradient; (2) in the local crack-tip region, hydrides will precipitate faster at the considered higher temperatures, which can be fundamentally attributed to the sensitivity of TSSP and hydrogen diffusion coefficient to temperature. The mechanism is partly explained for the enlarged velocity values of delayed hydride cracking (DHC) at high temperatures before crack arrest. This work lays a foundation for the future research on DHC.

• Corrosion Science and Technology
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• 제20권6호
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• pp.335-346
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• 2021

Since epoxy resin coating shows excellent properties in formability, adhesion, and corrosion resistance, they have been extensively used in many industries. However, various types of damages in the epoxy coated tube within a relative short time have been reported due to cavitation erosion, liquid impingement, variation of temperature and pressure. Nevertheless, there has been little research on the effect of temperature on the cavitation degradation of epoxy coatings. Therefore, this work used an ultrasonic cavitation tester to focus on the effect of solution temperature on the cavitation properties of 3 kinds of epoxy coatings in 3.5% NaCl. The cavitation properties were discussed basis on the material properties and environmental aspects. As the solution temperature increased, even though with large fluctuation, the cavitation degradation rates of A and B coatings were reduced rapidly, but the rate of C coating was decreased gradually. In addition to the cushioning effect, the reason that the cavitation degradation rate reduced with solution temperature was partly related to the brittle fracture and water absorptivity of the epoxy coatings, and the water density, but was little related to the shape and composition of the compound in the coatings or the phase transition of the epoxy coating.

• 대한청각학회지
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• 제24권4호
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• pp.204-209
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• 2020

Background and Objectives: Hearing loss (HL) and its repercussions are major problems in today's society. There are limited data on the relationship between degree of HL and otologic disorders. The aim of this study is to estimate mortality rates, rates of sudden idiopathic HL and related otologic surgical procedures in hearing disability patients in South Korea. Subjects and Methods: Retrospective medical data for 160,205 patients with hearing disability was extracted. Mortality rates, rates of sudden idiopathic HL and related otologic surgical procedures were compared with a normal control group consisting of 865,475 people; approximately 5 times the number of hearing disability patients. Results: According to the Korean National Disability Registry (NDR), 0.458% of the population in South Korea suffered from hearing disability in 2015. Higher rates of mortality and sudden idiopathic HL were reported in hearing disability patients, increasing up to a maximum of 1.594 times and 1,039.695 times, respectively, compared to the normal control group. Mastoidectomy surgery was 2.5 times more frequently performed and pressure equalizing (PE) tube insertion was about 15 times more frequently performed in hearing disability patients. Conclusions: Hearing disability is related to higher risks of mortality, sudden idiopathic HL and otologic surgical procedures, including mastoidectomy and PE tubing.

• Journal of Audiology & Otology
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• 제24권4호
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• pp.204-209
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• 2020

Background and Objectives: Hearing loss (HL) and its repercussions are major problems in today's society. There are limited data on the relationship between degree of HL and otologic disorders. The aim of this study is to estimate mortality rates, rates of sudden idiopathic HL and related otologic surgical procedures in hearing disability patients in South Korea. Subjects and Methods: Retrospective medical data for 160,205 patients with hearing disability was extracted. Mortality rates, rates of sudden idiopathic HL and related otologic surgical procedures were compared with a normal control group consisting of 865,475 people; approximately 5 times the number of hearing disability patients. Results: According to the Korean National Disability Registry (NDR), 0.458% of the population in South Korea suffered from hearing disability in 2015. Higher rates of mortality and sudden idiopathic HL were reported in hearing disability patients, increasing up to a maximum of 1.594 times and 1,039.695 times, respectively, compared to the normal control group. Mastoidectomy surgery was 2.5 times more frequently performed and pressure equalizing (PE) tube insertion was about 15 times more frequently performed in hearing disability patients. Conclusions: Hearing disability is related to higher risks of mortality, sudden idiopathic HL and otologic surgical procedures, including mastoidectomy and PE tubing.