• 한국결정성장학회지
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• 제27권1호
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• pp.28-33
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• 2017

SiC 섬유는 $1800^{\circ}C$까지 불활성과 공기 분위기에서 융해나 산화 문제 없이 사용할 수 있다. SiC 섬유는 분진 필터링 공정의 백필터로 상업화된 산업용 백 필터보다 훨씬 높은 온도인 $500^{\circ}C$ 이상의 온도에서 사용이 가능하다. 하지만 제강 산업과 화력발전소의 극한 환경에서 미세 분진과의 반응으로 인한 SiC 섬유의 열화에 대한 연구는 부족하다. 따라서 본 실험에서는 SiC 섬유를 제강 분진, 화력발전소 분진과 $500^{\circ}C$ 이상의 고온에서 반응시켜 섬유 표면의 열화된 형상을 SEM으로 관찰하고 섬유 표면 및 내부로의 산소 확산의 정도를 EDS로 분석하였다.

• Steel and Composite Structures
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• 제16권6호
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• pp.703-718
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• 2014

The initial clamping forces of high strength bolts subjected to different faying surface conditions drop within 500 hours regardless of loading, any other external force or loosening of the nut. This study develops a mathematical model for relaxation confined to creep on a coated faying surface after initial clamping. The quantitative model for estimating relaxation was derived from a regression analysis for the relation between the creep strain of the coated surface and the elapsed time for 744 hours. This study establishes an expected model for estimating the relaxation of bolted joints with diverse coated surfaces. The candidate bolts are dacro-coated tension control bolts, ASTM A490 bolt, and plain tension control bolts. The test parameters were coating thickness, species of coating. As for 96, 128, 168, and $226{\mu}m$ thick inorganic zinc, when the coating thickness was increased, relaxation after the initial clamping rose to a much higher range from 10% to 18% due to creep of the coating. The amount of relaxation up to 7 days exceeded 85% of the entire relaxation. From this result, the equation for creep strain can be derived from a statistical regression analysis. Based on the acquired creep behavior, it is expected that the clamping force reflecting relaxation after the elapse of constant time can be calculated from the initial clamping force. The manufacturer's recommendation of inorganic zinc on faying surface as $75{\mu}m$, appears to be reasonable.

• Structural Engineering and Mechanics
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• 제75권2호
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• pp.193-209
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• 2020

This paper presents a new hyperbolic shear deformation plate theory including the stretching effect for free vibration of the simply supported functionally graded plates in thermal environments. The theory accounts for parabolic distribution of the transverse shear strains and satisfies the zero traction boundary conditions on the surfaces of the plate without using shear correction factors. This theory has only five unknowns, which is even less than the other shear and normal deformation theories. The present one has a new displacement field which introduces undetermined integral variables. Material properties are assumed to be temperature-dependent, and graded in the thickness direction according to a simple power law distribution in terms of the volume power laws of the constituents. The equation of motion of the vibrated plate obtained via the classical Hamilton's principle and solved using Navier's steps. The accuracy of the proposed solution is checked by comparing the present results with those available in existing literature. The effects of the temperature field, volume fraction index of functionally graded material, side-to-thickness ratio on free vibration responses of the functionally graded plates are investigated. It can be concluded that the present theory is not only accurate but also simple in predicting the natural frequencies of functionally graded plates with stretching effect in thermal environments.

• KIEAE Journal
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• 제15권5호
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• pp.83-88
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• 2015

Purpose: Photovoltaic system is a technique for producing electrical power by utilizing solar energy, which can be used over 20 years with simple maintenance. However, in the case of photovoltaic systems, the energy conversion efficiency decreases as the surface temperature of module increases, compared with other renewable energy technologies. In this regard, PVT module can increase the energy utilization of a composite module as producing heat and electricity simultaneously by using solar energy. Currently, many researches have been promoting in order to develop a high efficiency PVT module in Korea. However, there are a few studies about the performance of the modules corresponding the shape of types and various heat exchangers of the PVT module. In this study, the electrical performance was measured by the change of the ambient temperature and the circulating water temperature using the fabricated PVT module. Method: Experiments were performed using a solar simulator. And this experiment was assumed that the weather condition was in each season, as winter, spring, autumn and summer. It was identified that the I-V curve associated with the change of the experimental conditions and confirmed the change in the electrical characteristics. Result: As a result, it was figured out that the surface temperature and the electrical performance changes in case conditions. The electrical performance was calculated in different temperature condition and the power production was confirmed by the change of module temperature.

• 한국전기전자재료학회논문지
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• 제19권3호
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• pp.280-286
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• 2006

As a way to expand electric capacity in conductor with electric power demand, STACIR/AW (Super Thermal-resistant Aluminum-alloy Conductors Aluminum-clad Invar-Reinforced) conductor which has high electric current and heat resistance characteristics have been developed. STACIR/AW power line is mechanical composite wire composed of steel cores for dip control and aluminum conductors for sending electric current. Recently, to ensure stable operation and prediction of wire life span of STACIR/AW conductor, a heat property of STACIR/AW conductor have been investigated. In the present work, a change of essential property with long term-heat exposure of STACIR/AW conductor and its structure material, INVAR wire and Al conductor, have been investigated. INVAR/AW is approximately $3.2\;{\mu}m/m^{\circ}C$. thermal expansion coefficient of INVAR/AW wire increases with time of heat exposure. the thermal expansion coefficient of INVAR/AW is markedly influenced by heat and mechanical treatment. creep rate(0.242) of STACIR/AW $410\;mm^2$ conductor at room temperature is much higher than that(0.022) at $210\;^{\circ}C$ STACIR/AW $410\;mm^2$ conductor has minimum creep rate at operating temperature. To lower creep rate with increase temperature is more unique characteristics in STACIR/AW. It is expected that STACIR/AW turned its tension to INVAR/AW at the transition temperature. at room temperature, the tension apportionment of INVAR/AW in STACIR/AW is about $50\;\%$. but whole tension of STACIR/AW is placed on the INVAR/AW alone of core metal above transition temperature.

• The Journal of Korean Physical Therapy
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• 제32권4호
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• pp.203-209
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• 2020

Purpose: This study examined the effects of a physical stability exercise program on the functional movement and balance of middle school volleyball players to provide future management and training data to improve the performance of volleyball players. Methods: The subjects were 20 volleyball players from Y Middle School in Mokpo. The results of comparing and analyzing the effects of the physical stability exercise program on the functional movement and balance of middle school volleyball players for 10 weeks are as follows. Results: The number of participants who showed power and agility (p<0.01) was increased significantly, and the response time was shortened significantly (p<0.01). On the evaluation of functional movement, the total score showed a significant difference between the pre-test at 10.90±1.30 points and the post-test at 13.81±.60 (p<0.001). The subjects' balance showed a significant difference from 84.11±7.53 to 97.65±8.47 (p<0.001), and the Right Composite Score showed a significant difference from 83.74±6.64 to 97.27±8.48 (p<0.001). Conclusion: The application of a physical stability exercise program for 10 weeks is effective in improving the speed, agility, functional movement, and balance to volleyball players who are weakened and at risk of injury. This is believed to prevent or reduce injury.

• 한국재료학회지
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• 제25권6호
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• pp.279-287
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• 2015

In order to prepare anode materials for high power lithium ion secondary batteries, carbon composites were fabricated with a mixture of petroleum pitch and coke (PC) and a mixture of petroleum pitch, coke, and natural graphite (PC-NG). Although natural graphite has a good reversible capacity, it has disadvaantages of a sharp decrease in capacity during high rate charging and potential plateaus. This may cause difficulties in perceiving the capacity variations as a function of electrical potential. The coke anodes have advantages without potential plateaus and a high rate capability, but they have a low reversible capacity. With PC anode composites, the petroleum pitch/cokes mixture at 1:4 with heat treatment at $1000^{\circ}C$ (PC14-1000C) showed relatively high electrochemical properties. With PC-NG anode composites, the proper graphite contents were determined at 10~30 wt.%. The composites with a given content of natural graphite and remaining content of various petroleum pitch/cokes mixtures at 1:4~4:1 mass ratios were heated at $800{\sim}1200^{\circ}C$. By increasing the content of petroleum pitch, reversible capacity increased, but a high rate capability decreased. For a given composition of carbonaceous composite, the discharge rate capability improved but the reversible capacity decreased with an increase in heat treatment temperature. The carbonaceous composites fabricated with a mixture of 30 wt.% natural graphite and 70 wt.% petroleum pitch/cokes mixture at 1:4 mass ratio and heat treated at $1000^{\circ}C$ showed relatively high electrochemical properties, of which the reversible capacity, initial efficiency, discharge rate capability (retention of discharge capacity in 10 C/0.2 C), and charge capacity at 5 C were 330 mAh/g, 79 %, 80 %, and 60 mAh/g, respectively.

• 한국전기전자재료학회논문지
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• 제28권12호
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• pp.792-796
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• 2015

With high integration of electronic components, power inductors are also miniaturized. Recently, thick film processes for small size power inductors were developed and commercialized. However, the thick film process to prepare soft magnetic green sheets was not reported enough. In this study, we used Fe-Si magnetic and CIP (carbonyl iron powders) as starting materials to lead to a bimodal particle size distribution in the sheet. We proposed a newly developed 'Modified slurry preparation process' to get well dispersed condition even at high solid contents. Using the new process, it was possible to prepare a well dispersed slurry over 70 vol% of solid. BYK-103 was better than BYK-111 as dispersant in this slurry and the optimum amount was 0.6 wt%. The optimized slurry was formed into a sheet by tape casting process and then the sheet was laminated. We conformed that small size powder, large size powder, and epoxy resin were well dispersed in the green sheet.

• 유기물자원화
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• 제25권4호
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• pp.51-60
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• 2017

화력발전소에서 발생하는 유연탄 Bottom ash(BA)는 고온에서 연소 되고 남은 재이다. 고온에서 구워진 재료이기 때문에 맥반석과 같은 기능이 있을 것으로 사료되어 연구를 시작하였다. 최근 일반 모르터보다 황토, 맥반석 등이 재료로 들어가서 원적외선, 항균, 항곰팡이, 탈취, 조습 기능이 있는 모르터의 수요가 늘어가는 추세이다. 유연탄 BA를 친환경 바이오 혼합소재로 활용하기 위한 친환경 바이오 BA 모르터를 일반 모르터와 각각의 기능성에 대해 비교 시험한 결과 원적외선 방사율이 약 $0.02{\times}10^2W/m^2$ 정도 높게 측정되었으며, 탈취 기능은 약 26% 이상 높게 측정되었다. 조습의 경우에도 친환경 바이오 BA 모르터가 일반 모르터보다 약 1.8배 우수한 효과를 가지고 있는 것으로 나타났으며, 국토해양부에서 제정한 흡 방습 건축자재 "양호"기준보다 10% 이상 뛰어난 것으로 나타났다.

• 한국수소및신에너지학회논문집
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• 제23권3호
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• pp.243-249
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• 2012

A lightweight 200W direct methanol fuel cell (DMFC) stack is designed and fabricated to power a small scale Unmanned Aerial Vehicle (UAV). The DMFC stack consists of 33-cells in which membrane-electrode assemblies (MEAs) having an active area of 88 $cm^2$ are sandwiched with lightweight composite bipolar plates. The total stack weight is around 3.485 kg and stack performance is tested under various methanol feed concentrations. The DMFC stack delivers a maximum power of 248 W at 13.2 V and $71.3^{\circ}C$ under methanol feed concentration of 1.2 M. In addition, the voltage of individual cell in the 33-cell stack is measured at various current levels to ensure the stability of DMFC stack operations. The cell voltage distribution data exhibit the maximum cell voltage deviation of 28 mV at 15 A and hence the uniformity of cell voltages is acceptable. These results clearly demonstrate that DMFC technology becomes a potential candidate for small-scale UAV applications.