• Journal of Welding and Joining
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• v.35 no.2
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• pp.58-62
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• 2017

A319 aluminum alloy containing 6.5% Si and 3.5% Cu as major alloying elements has been widely used in machinery parts because of its excellent castability and crack resistance. However it needs more wear resistance to extend its usage to the severe wear environments. It has been known that hyper-eutectic Al-Si alloy having more than 12.6% Si contains pro-eutectic Si particles, which give better wear resistance and lubrication characteristics than hypo-eutectic Al-Si alloy like A319 alloy. In this study, it was tried to clad hyper-eutectic Al-Si alloy on the surface of A319 alloy. In the experiments, Al-36%Si alloy powder was mixed with organic binder to make a fluidic paste. The paste was screen-printed on the A319 alloy surface, melted by pulsed Nd:YAG laser and alloyed with the A319 base alloy. As experimental parameters, the average laser power was changed to 111 W, 202 W and 280 W. With increasing the average laser power, the melting depth was changed to $142{\mu}m$, $205{\mu}m$ and $245{\mu}m$, and the dilution rate to 67.2 %, 72.4 % and 75.7 %, and the Si content in the cladding layer to 16.2 %, 14.6 % and 13.7 %, respectively. The cross-section of the cladding layer showed very fine eutectic microstructure even though it was hyper-eutectic Al-Si alloy. This seems to be due to the rapid solidification of the melted spot by single laser pulse. The average hardness for the three cladding layers was HV175, which was much higher than HV96 of A319 base alloy. From the block-on-roll wear tests, A319 alloy had a wear loss of 5.8 mg, but the three cladding layers had an average wear loss of 3.5 mg, which meant that an increase of 40 % in wear resistance was obtained by laser cladding.

• Journal of The Korean Society of Agricultural Engineers
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• v.59 no.6
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• pp.1-8
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• 2017

The purpose of this study was to provide basic data for development of environmental design technology for greenhouses constructed in reclaimed lands. We analyzed the climatic conditions around seven major reclaimed land areas in Korea, which have a plan to install advanced horticultural complexes. The characteristics of heating load through the thermal environment measurement of the greenhouse in Saemangeum were analyzed. The part to be applied to the environmental design of the greenhouses in reclaimed lands were reviewed. The overall heat transfer coefficient of the experimental greenhouse with the aluminum screen and multi-layer thermal curtain averaged $3.79W/m^2^{\circ}C$. It represents a 44 % heat savings rate compared with plastic greenhouses with a single covering, which was significantly lower than that of the common greenhouses with 2-layer thermal curtains. This is because the experimental greenhouse was installed on reclaimed land and wind was stronger than the inland area. Among the total heating load, the transmission heat loss accounted for 96.4~99.9 %, and the infiltration loss and the ground heat exchange were low. Therefore, it is necessary to take countermeasures to minimize the transmission heat loss for greenhouses constructed in reclaimed lands. As the reclaimed land is located on the seaside, the wind is stronger than the inland area, and the fog is frequent. Especially, Saemangeum area has 2.6 times stronger wind speed and 3.4 times longer fog duration than the inland area. In designing the heating systems for greenhouses in reclaimed lands, it is considered that the maximum heating load should be calculated by applying the wind coefficient larger than the inland area. It is reasonable to estimate the operation cost of the heating system by applying the adjustment factor 10 % larger than the average in calculating the seasonal heating load.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.27-27
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• 2003

최근 탄소나노튜브를 전계방출 표시소자(FED, field omission display)용 에미터 재료로 사용한 캐소드 개발에 대한 연구가 활발히 진행되고 있다. 캐소드전극으로는 투명전도성 반도체 박막인 ITO를 사용하고, 에미터용 재료로는 탄소나노튜브를 사용해서 스크린 인쇄법으로 2극(diode type)형 전계방출 소자용 캐소드를 제작하였다. 본딩재(bonding materials)의 종류와 공정변수를 달리해서 에미터용 탄소나노튜브와 ITO 캐소드 전극 사이의 전기적 접촉방법을 변화시켰을때 탄소나노튜브 캐소드의 전계방출 특성을 체계적으로 연구하였다. 첫째로, 본딩재의 전기전도성 (electrical conductivity)을 변수로 해서 탄소나노튜브 에미터의 전계강화(fold enhancement) 효과를 연구한 결과 본딩재의 구성 성분중 부도체(insulator)의 분율이 높을수록 전계강화 효과가 크게 나타남을 확인하였다. 두 번째로, ITO박막 캐소드전극과 탄소나노튜브 잉크 사이에 중간층(inter layer)을 형성시켜서 중간층이 전계방출 특성에 미치는 영향을 연구하여, 중간층의 존재가 탄소나노튜브의 전계방출 전류의 균일성과 전류밀도의 증가에 기여하는 것을 확인하였다. 본 연구의 결과 전계방출 전류가 안정적이면서 동시에 전계방출 효율이 크게 개선된 탄소나노튜브 캐소드를 제작하는 공정기술이 개발되었다. 개발된 기술은 기존의 방법에 비해서 탄소나노튜브 캐소드의 진공패키징시 아웃개싱(outgassing)의 양도 현격하게 작았으며, 에미터와 캐소드 전극 사이의 본딩력(adhesion)도 우수해서 항후 탄소나노튜브 전계방출 표시소자의 개발에 크게 기여할 것으로 판단된다.luminum 첨가량이 증가함에 따라 세라믹 수율도 증가하였음을 확인하였다. 합성된 aluminum-contained polycarbosilane은 20$0^{\circ}C$에서 1시간 동안 불융화과정을 거쳐 환원 및 진공 분위기에서 고온 열처리하였으며 이로부터 얻어진 시료에 대해 XRD분석을 수행하였다. SEM과 TEM을 이용하여 미세구조를 관찰하였다./100 duty로 구동하였으며, duty비 증가에 따라 pulse의 on-time을 고정하고 frequency를 변화시켰다. dc까지 duty비가 증가됨에 따라 방출전류의 양이 선형적으로 증가하였다. 전압을 일정하게 고정시키고 각 duty비에서 시간에 따라 방출전류를 측정한 결과 duty비가 높을수록 방출전류가 시간에 따라 급격히 감소하였다. 각 duty비에서 방출전류의 양이 1/2로 감소하는 시점을 에미터의 수명으로 볼 때 duty비 대 에미터 수명관계를 구해 높은 duty비에서 전계방출을 시킴으로써 실제의 구동조건인 낮은 duty비에서의 수명을 단시간에 예측할 수 있었다. 단속적으로 일어난 것으로 생각된다.리 폐 관류는 정맥주입 방법에 비해 고농도의 cisplatin 투여로 인한 다른 장기에서의 농도 증가 없이 폐 조직에 약 50배 정도의 고농도 cisplatin을 투여할 수 있었으며, 또한 분리 폐 관류 시 cisplatin에 의한 직접적 폐 독성은 발견되지 않았다이 낮았으나 통계학적 의의는 없었다[10.0%(4/40) : 8.2%(20/244), p>0.05]. 결론: 비디오흉강경술에서 재발을 낮추기 위해 수술시 폐야 전체를 관찰하여 존재하는 폐기포를 놓치지 않는 것이 중요하며, 폐기포를 확인하지 못한

• Journal of radiological science and technology
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• v.25 no.2
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• pp.47-55
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• 2002

We came to the following conclusion as the results of experiment on the image quality of mammography and the average glandular dose using 4 apparatuses at 3 hospitals in Seoul. 1. Whereas the measurement of half value layer showed no differences among the apparatuses, the measurement by an attenuation curve method showed some differences by 5.9%. There were 9.1% differences in the measurement by aluminum conversion method. 2. The basic density of an automatic exposure control unit must be D = 1.40, but there was no automatic exposure unit adjusted precisely at any hospitals. The unit at the B hospital exceeded the allowable limit by ${\pm}0.15$. 3. In the photographing using an automatic exposure control unit and the management of an automatic film processor using a sensitometer, most automatic film processors were well kept. But in some cases the mean value of a fluctuation coefficient exceeded the allowable limit. There is a need for more cautious management. 4. The image quality of breast phantom photography was affected by the screen/film system among the hospitals. 5. The average glandular dose at a breast of 4.2 cm thickness depended on the tube voltage, In the case of Mo/Mo, it was measured $0.26{\sim}1.39\;mGy$ less than ACR standard 3.0 mGy.

• Journal of the Microelectronics and Packaging Society
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• v.25 no.4
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• pp.149-154
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• 2018

This paper describes the fabrication and heat transfer property of 50 watts rated LED array module where multiple chips are mounted on chip-on-board type ceramic-metal hybrid substrate with high heat dissipation property for high power street and anti-explosive lighting system. The high heat transfer ceramic-metal hybrid substrate was fabricated by conformal coating of thick film glass-ceramic and silver pastes to form insulation and conductor layers, using thick film screen printing method on top of the high thermal conductivity aluminum alloy heat-spreading panel, then co-fired at $515^{\circ}C$. A comparative LED array module with the same configuration using epoxy resin based FR-4 PCB with thermalvia type was also fabricated, then the thermal properties were measured with multichannel temperature sensors and thermal resistance measuring system. As a result, the thermal resistance of the ceramic-metal hybrid substrate in the $4{\times}9$ type LEDs array module exhibited about one third to the value as that of FR-4 substrate, implying that at least triple performance of heat transfer property as that of FR-4 substrate was realized.

• Journal of Korea Soil Environment Society
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• v.5 no.2
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• pp.55-66
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• 2000

A U.S EPA Synthetic soil matrix was used for reference neat soil and pyrene contaminated soil. For the contaminated soil, 4.79 wt.% pyrene was dissolved completely into the djchlorornethane, and the soil was evenly soaked with the pyrene solution. The contaminated soil samples(50$\pm$0.5mg) were heated in a modified electrical screen heater reactor which consisted of a thin stainless foil (3.5cm$\times$13cm$\times$0.00254cm, 302 stainless steel shim), two electrodes, and a 20cm dia. $\times$30cm tall cylindrical Pyrex chamber sealed at both ends by aluminum flanges. The heating rate and time conditions were selected as $455^{\circ}C$ @ $1137^{\circ}C$ /s, $760^{\circ}C$ @ $950^{\circ}C$ /s and $977^{\circ}C$ @ $977^{\circ}C$/s. Tar samples after heating the soils were collected on the aluminum foil funnel and a glass filter paper (25mm dia. filter paper) The tar sample and remnant soil on the reactor were extracted with dichloromethane covering the filters, foils and soil by sonicating each in the waterbath for 10 minutes. The extractions were run on a HPLC. At the low peak temperature(about $455^{\circ}C$ @ $1137^{\circ}C$/s) the color of tar was "white", at the middle peak temperature (about 76$0^{\circ}C$ @ 95$0^{\circ}C$/s) the color of tar was "pink brown", at the high peak temperature (about 977$^{\circ}C$ @ 977$^{\circ}C$/s) the color of tar was "dark brown". Cyclopeta(cd)pyrene (CPEP) , which is an interesting species due to mutagenic effect on human cells, was detected in tar samples only above the middle peak temperature. This species was not detected at the low peak temperature. Six isomers of bipyrene were detected. Phenanthrene(C$_{14}$ $H_{10}$) and cyclopenta(def)phenanthrene(C$_{15}$ $H_{10}$) were also detected, but their content was very small relative to the other listed compounds.to the other listed compounds.