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논문 : IG-11 원자로용 흑연의 열방사 특성에 미치는 표면 거칠기의 영향
노재승 ( Jae Seung Roh ),서승국 ( Seung Kuk Seo ),김석환 ( Suk Hwan Kim ),지세환 ( Se Hwan Chi ),김응선 ( Eung Seon Kim ),김혜성 ( Hye Sung Kim ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.7
This paper reports the relationship between the surface roughness and thermal emissivity of graphite (IG-11) in nuclear reactors. The roughness was controlled by changing the oxidization time, resulting in 0, 6, and 11% losses of mass. The levels of roughness were 0.40, 0.72 and 1.09㎛ for the weight loss of 0, 6 and 11%, respectively. The binders and graphite fillers were found to have sequentially oxidized with a higher thermal emission for the highly oxidized sample, but with a lower emission when measured at a higher temperature. Our study suggests a method for predicting the thermal emission rate of graphite in a nuclear reactor based on roughness measurement.
노재승(Jae-Seung Roh),안재상(Jai-Sang Ahn),김범준(Beom-Jun Kim),전호연(Ho-Yeon Jeon),서승국(Seung-Kuk Seo),김석환(Suk Hwan Kim),이상우(Sang-Woo Lee) 한국표면공학회 2009 한국표면공학회지 Vol.42 No.2
This study is the research on the thermal emissivity depending on the bulk graphite’s alignment degree. Bulk graphites were manufactured by uni-axial pressing and subsequent heat treatment of natural graphite flakes with organic binder. The samples were prepared to be 0° (relative to the 002 c-face), 45°, and 90° (relative to the 100 a-face) for measuring alignment degree. The alignment degree of the sample was measured by XRD. The thermal emissivity was measured by infrared thermal image camera at 100oC and compared with the value obtained by Infrared spectroscopy. The alignment degree and thermal emissivity of 0° sample were measured to be 0 and 0.70 respectively. And those of 90° sample were 0.73 and 0.80 respectively. The emissivity value was correlated with obtained by IR spectroscopy. Therefore it was considered that the thermal emissivity of the bulk graphite is correlated with the alignment degree.
다중 클래스 멤버쉽 처리를 위한 Bi-LSTM 기반 지식 그래프 완성 기법
노재승(Jae-Seung Roh),바트셀렘(Batselem Jagvaral),이완곤(Wan-Gon Lee),박영택(Young-Tack Park) Korean Institute of Information Scientists and Eng 2020 정보과학회논문지 Vol.47 No.6
Knowledge graphs that represent real world information in a structured way are widely used in areas, such as Web browsing and recommendation systems. But there is a problem of missing links between entities in knowledge graphs. To resolve this issue, various studies using embedding techniques or deep learning have been proposed. Especially, the recent study combining CNN and Bidirectional-LSTM has shown high performance compared to previous studies. However, in the previous study, if multiple class types are defined for single entity, the amount of training data exponentially increases with the training time. Also, if class type information for an entity is not defined, training data for that entity cannot be generated. Thus, to enable the generation of training data for such entities and manage multiple class membership in knowledge graph completion, we propose two approaches using pre-trained embedding vectors of knowledge graph and the concept of vector addition. To evaluate the performance of the methods proposed in this paper, we conducted comparative experiments with the existing knowledge completion studies on NELL-995 and FB15K-237 datasets, and obtained MAP 1.6%p and MRR 1.5%p higher than that of the previous studies.
원자로급 흑연 IG-11의 산화율에 따른 기공도와 열방사율과의 관계
서승국,노재승,김경화,지세환,김응선,Seo, Seung-Kuk,Roh, Jae-Seung,Kim, Gyeong-Hwa,Chi, Se-Hwan,Kim, Eung-Seon 한국재료학회 2008 한국재료학회지 Vol.18 No.12
Graphite for the nuclear reactor is used to the moderator, reflector and supporter in which fuel rod inside of nuclear reactor. Recently, there are many researches has been performed on the various characteristics of nuclear graphite, however most of them are restricted to the structural and the mechanical properties. Therefore we focused on the thermal property of nuclear graphite. This study investigated the thermal emissivity following the oxidation degree of nuclear graphite with IG-11 used as a sample. IG-11 was oxidized to 6% and 11% in air at 5 l/min at $600^{\circ}C$. The porosity and thermal emissivity of the sample were measured using a mercury porosimeter and by an IR method, respectively. The thermal emissivity of an oxidized sample was measured at $100^{\circ}C$, $200^{\circ}C$, $300^{\circ}C$, $400^{\circ}C$ and $500^{\circ}C$. The porosity of the oxidized samples was found to increase as the oxidation degree increased. The thermal emissivity increased as the oxidation degree increased, and the thermal emissivity decreased as the measured temperature increased. It was confirmed that the thermal emissivity of oxidized IG-11 is correlated with the porosity of the sample.
엄운용,노재승,안재상,강동수,서승국,김석환,Eom, Woon-Yong,Roh, Jae-Seung,Seo, Seung-Kuk,Ahn, Jai-Sang,Kang, Dong-Su,Kim, Suk-Hwan 한국재료학회 2010 한국재료학회지 Vol.20 No.4
Recent high efficiency electronic devices have been found to have heat emission problems. As for LEDs, an excessive increase in the device temperature causes a drop of the luminous efficiency and circuit lifetime. Therefore, heat release in the limited space of such electronic parts is very important. This is a study of the possibility of using a coating of carbon materials as a solution for the thermal emission problem of electronic devices. Powdered carbon materials, cokes, carbon blacks, amorphous graphite, and natural flakes were coated with an organic binder on an aluminum sheet and the subsequent thermal emissivity was measured with an FT-IR spectrometer and was found to be in the range of $5{\sim}20\;{\mu}m$ at $50^{\circ}C$. The emissivity of the carbon materials coated on the aluminum sheet was shown to be over 0.8 and varied according to carbon type. The maximum thermal emissivity on the carbon black coated-aluminum surface was shown to be 0.877. The emissivity of the anodized aluminum sheets that were used as heat releasing materials of the electronic parts was reported to be in the range of 0.7~0.8. Therefore, the use of a coating of carbon material can be a potential solution that facillitates heat dissipation for electronic parts.
인산형 연료전지 분리판용 천연흑연-불소수지계 복합재료의 흑연입도에 따른 전기비저항 변화
이상민,백운경,김태진,노재승,Lee, Sang-Min,Beak, Un-Gyeong,Kim, Tae-Jin,Roh, Jae-Seung 한국재료학회 2017 한국재료학회지 Vol.27 No.12
A composite material was prepared for the bipolar plates of phosphoric acid fuel cells(PAFC) by hot pressing a flake type natural graphite powder as a filler material and a fluorine resin as a binder. Average particle sizes of the powders were 610.3, 401.6, 99.5, and $37.7{\mu}m$. The density of the composite increased from 2.25 to $2.72g/cm^3$ as the graphite size increased from 37.7 to $610.3{\mu}m$. The anisotropy ratio of the composite increased from 1.8 to 490.9 as the graphite size increased. The flexural strength of the composite decreased from 15.60 to 8.94MPa as the graphite size increased. The porosity and the resistivity of the composite showed the same tendencies, and decreased as the graphite size increased. The lowest resistivity and porosity of the composite were $1.99{\times}10^{-3}{\Omega}cm$ and 2.02 %, respectively, when the graphite size was $401.6{\mu}m$. The flexural strength of the composite was 10.3MPa when the graphite size was $401.6{\mu}m$. The lowest resistance to electron mobility was well correlated with the composite with lowest porosity. It was possible the flaky large graphite particles survive after the hot pressing process.
알루미늄 기판에 코팅된 흑연입자의 배향도 변화와 열방사율 변화의 관계
강동수,이상민,김석환,이상우,노재승,Kang, Dong Su,Lee, Sang Min,Kim, Suk Hwan,Lee, Sang Woo,Roh, Jae Seung 한국재료학회 2014 한국재료학회지 Vol.24 No.3
This study is research on the thermal emissivity depending on the alignment degrees of graphite flakes. Samples were manufactured by a slurry of natural graphite flakes with organic binder and subsequent dip-coating on an aluminum substrate. The alignment degrees were controlled by applying magnetic field strength (0, 1, and 3 kG) to the coated samples. The alignment degree of the sample was measured by XRD. The thermal emissivity was measured by an infrared thermal image camera at $100^{\circ}C$. The alignment degrees were 0.04, 0.11, and 0.17 and the applied magnetic field strengths were 0, 1, and 3 kG, respectively. The thermal emissivities were 0.829, 0.837, and 0.844 and the applying magnetic field strengths were 0, 1, and 3 kG, respectively. In this study the correlation coefficient, $R^2$, between thermal emissivity and alignment degree was 0.997. Therefore, it was concluded that the thermal emissivities are correlated with the alignment degree of the graphite flakes.
카본블랙 첨가량에 따른 인산형 연료전지(PAFC) 분리판용 천연흑연-고분자복합재료의 전기비저항
김효창,이상민,남기법,노재승,Kim, Hyo-Chang,Lee, Sang-Min,Nam, Gibeop,Roh, Jae-Seung 한국재료학회 2020 한국재료학회지 Vol.30 No.10
Conductive polymer composites with high electrical and mechanical properties are in demand for bipolar plates of phosphoric acid fuel cells (PAFC). In this study, composites based on natural graphite/fluorinated ethylene propylene (FEP) and different ratios of carbon black are mixed and hot formed into bars. The overall content of natural graphite is replaced by carbon black (0.2 wt% to 3.0 wt%). It is found that the addition of carbon black reduces electrical resistivity and density. The density of composite materials added with carbon black 3.0 wt% is 2.168 g/㎤, which is 0.017 g/㎤ less than that of non-additive composites. In-plane electrical resistivity is 7.68 μΩm and through-plane electrical resistivity is 27.66 μΩm. Compared with non-additive composites, in-plane electrical resistivity decreases by 95.7 % and through-plane decreases by 95.9 %. Also, the bending strength is about 30 % improved when carbon black is added at 2.0 wt% compared to non-additive cases. The decrease of electrical resistivity of composites is estimated to stem from the carbon black, which is a conductive material located between melted FEP and acts a path for electrons; the increasing mechanical properties are estimated to result from carbon black filling up pores in the composites.
공기에 의한 탄소섬유 스프레딩 공정 변수에 따른 프로세스 성능 및 기계적 물성 평가
노정우 ( Jeong-u Roh ),백운경 ( Un-gyeong Baek ),노재승 ( Jae-seung Roh ),남기법 ( Gibeop Nam ) 한국복합재료학회 2020 Composites research Vol.33 No.6
탄소섬유 스프레드 토우를 제조하는 과정에서 섬유 손상이 발생하며, 이는 스프레딩 과정에서 장비와 섬유 사이 혹은 섬유 간의 마찰로 발생한다. 이로 인해, 재료 및 장비조건에 따라 프로세스 성능에 차이가 발생하고, 제품 물성이 하락한다. 섬유 손상을 최소화하는 것은 스프레드 토우를 제조하는 공정에서 반드시 고려되어야 한다. 본 연구에서는 공기를 이용한 탄소섬유 스프레딩 공정에서 탄소섬유의 필라멘트 수와 사이징 함량, 탄소섬유토우 스프레딩 장비의 공정 변수(초기섬유장력, 열풍온도, 진공압력)를 달리하여 스프레드 토우의 공정성능 변화를 관찰하였다. 탄소섬유 품종에 따른 조건 별 최적조건에서 제조된 샘플을 이용해 인장강도를 평가하여, 탄소섬유의 손상에 따른 기계적 물성 감소를 확인하였다. The carbon fiber has been damaged via tow spreading process for carbon fiber spread tow. The fiber damage is caused by friction between equipment and fibers or between fibers and fibers in the process of spreading. As a result, mechanical properties are decreased due to differences in process via material and equipment condition. Therefore, minimizing fiber damage have to be considered in the process. In this study, the change in carbon fiber pneumatic spreading process was observed by according to the filament count, sizing content of carbon fiber and process variables in spreading equipment (fiber tension at the beginning, air temperature in spreading zone, vacuum pressure in spreading zone). Tensile strength was evaluated using samples prepared under optimal conditions for each of the carbon fiber varieties, and mechanical properties were reduced due to damage on the carbon fiber.