• Nuclear Engineering and Technology
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• 제32권4호
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• pp.379-394
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• 2000

As an in-vessel retention (IVR) design concept in coping with a severe accident in the nuclear power plant during which time a considerable amount of core material may melt, external cooling of the reactor vessel has been suggested to protect the lower head from overheating due to relocated material from the core. The efficiency of the ex-vessel management may be estimated by the thermal margin defined as the ratio of the critical heat flux (CHF）to the actual heat flux from the reactor vessel. Principal factors affecting the thermal margin calculation are the amount of heat to be transferred downward from the molten pool, variation of heat flux with the angular position, and the amount of removable heat by external cooling In this paper a thorough literature survey is made and relevant models and correlations are critically reviewed and applied in terms of their capabilities and uncertainties in estimating the thermal margin to potential failure of the vessel on account of the CHF Results of the thermal margin calculation are statistically treated and the associated uncertainties are quantitatively evaluated to shed light on the issues requiring further attention and study in the near term. Our results indicated a higher thermal margin at the bottom than at the top of the vessel accounting for the natural convection within the hemispherical molten debris pool in the lower plenum. The information obtained from this study will serve as the backbone in identifying the maximum heat removal capability and limitations of the IVR technology called the Cerium Attack Syndrome Immunization Structures (COASISO) being developed for next generation reactors.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• 제26권2호
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• pp.179-185
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• 2000

The purpose of this study was to develop an osteogenic, biodegradable material using polymer and BMP. It was designed to have structural function and be moldable, for the reconstruction of load bearing areas and deformities of various configurations. Bone apatite was added to Poly(L-lactide)(PLLA) and made porous for osteoconductability and ease of BMP loading. The materials, with or without BMP purified from porcine bone matrix, were evaluated in cranial bone defect models in rats for biocompatibility and bone regeneration capability. The following results were obtained: The PLLA-BMP material with BMP added to the polymer showed 30% healing of cranial bone defects in rats during the 2 weeks to 3 months period of observation. The moldable PLLA agent without BMP also showed 25% bone healing capacity. Although new bone formation was incomplete in the critical size defect of rat cranium, it can be concluded that the unique moldability of those agents makes them useful for the reconstruction of various bone defects and maxillofacial deformities.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.1
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• pp.58-62
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• 2003

Silicon carbide (SiC) was etched in a $NF_3/CH_4$ inductively coupled plasma. The etch process was modeled by using a neural network called generalized regression neural network (GRNN). For modeling, the process was characterized by a $2^4$ full factorial experiment with one center point. To test model appropriateness, additional test data of 16 experiments were conducted. Particularly, the GRNN predictive capability was drastically improved by a genetic algorithm (GA). This was demonstrated by an improvement of more than 80% compared to a conventionally obtained model. Predicted model behaviors were highly consistent with actual measurements. From the optimized model, several plots were generated to examine etch rate variation under various plasma conditions. Unlike the typical behavior, the etch rate variation was quite different depending on the bias power Under lower bias powers, the source power effect was strongly dependent on induced dc bias. The etch rate was strongly correated to the do bias induced by the gas ratio. Particularly, the etch rate variation with the bias power at different gas ratio seemed to be limited by the etchant supply.

• 한국재료학회지
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• 제20권3호
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• pp.148-154
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• 2010

It is necessary to develop new methods to prevent catastrophic failure of structural material in order to avoid accidents and conserve natural and energy resources. Design of intelligent materials with a self-diagnosing function to prevent fatal fracture of structural materials was achieved by smart composites consisting of carbon fiber tows or carbon powders with a small value of ultimate elongation and glass fiber tows with a large value of ultimate elongation. The changes in electrical resistance of CF-GFRP/GFRP (carbon fiber and glass fiber-reinforced plastics/glass fiber-reinforced plastics) composites increased abruptly with increasing strain, and a tremendous change was seen at the transition point where carbon fiber tows were broken. Therefore, the composites were not to monitor damage from the early stage. On the other hand, the change in electrical resistance of CP-GFRP/GFRP (carbon powder dispersed in glass fiber-reinforced plastics/glass fiber-reinforced plastics) composites increased almost linearly in proportion to strain. CP-GFRP/GFRP composites are superior to CF-GFRP/GFRP composites in terms of their capability to monitor damage by measuring change in electrical resistance from the early stage of damage. However, the former was inferior to the latter as an application because of the difficulties of mass production and high cost. A method based on monitoring damage by measuring changes in the electrical resistance of structural materials is promising for improved reliability of the material.

• 한국재료학회지
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• 제32권9호
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• pp.369-378
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• 2022

The recycling of solid waste materials to fabricate carbon-based electrode materials is of great interest for low-cost green supercapacitors. In this study, porous carbon foam (PCF) was prepared from waste floral foam (WFF) as an electrode material for supercapacitors. WFF was directly carbonized at various temperatures of 600, 800, and 1,000 ℃ under an inert atmosphere. The WFF-derived PCF (C-WFF) was found to have a specific surface area of 458.99 m²/g with multi-modal pore structures. The supercapacitive behavior of the prepared C-WFF was evaluated using a three-electrode system in a 6 M KOH aqueous electrolyte. As a result, the prepared C-WFF as an active material showed a high specific capacitance of 206 F/g at 1 A/g, a rate capability of 36.4 % at 20 A/g, a specific power density of 2,500 W/kg at an energy density of 2.68 Wh/kg, and a cycle stability of 99.96 % at 20 A/g after 10,000 cycles. These results indicate that the C-WFF prepared from WFF could be a promising candidate as an electrode material for high-performance green supercapacitors.

• Korean Chemical Engineering Research
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• 제59권1호
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• pp.42-48
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• 2021

본 연구에서는 LiNi0.85Co0.15O2의 전기화학적 특성과 열적 안정성을 향상시키기 위하여 LiNi0.85Co0.15O2에 이종원소인 Zn와 Al을 함께 첨가하여 고상법으로 합성하였다. 물질의 결정 구조, 크기 및 표면 상태는 XRD, SEM을 이용하여 분석하였고 전기화학적 특성은 충방전기를 이용하여 CV(cyclic voltammetry), 초기 충·방전 프로파일, 출력 특성, 수명 특성 등을 측정하였다. Al-O의 강한 결합에너지는 양극활물질의 구조적 안정성을 향상시켰으며, Li+와 Ni2+의 양이온 혼합을 막아 전기화학적 특성 또한 향상되었다. Zn의 큰 이온반경은 양극활물질의 격자상수를 증가시켜 단위 셀의 부피가 확장되었다. Zn와 Al을 0.025몰씩 첨가한 물질의 경우, 0.5 C-rate의 전류밀도에서 100 사이클 동안 80%의 용량 유지율을 보여주었으며 이 결과는 NC 양극활물질보다 12% 높은 수치이다. 또한, 5 C-rate에서의 방전용량은 104 mAh/g으로 기존의 NC 양극활물질보다 36 mAh/g 높은 수치를 보였다. Zn과 Al이 0.025몰씩 첨가된 NC 양극활물질은 출력 특성, 수명 특성에서 우수한 특성을 보여주었다.

• 동력기계공학회지
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• 제18권1호
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• pp.14-21
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• 2014

Piezoelectric fans are thin elastic beams whose vibratory motion is actuated by means of a piezoelectric material bonded to the beam. These fans have found use as a means to enhance convective heat transfer while requiring only small amounts of power. This study presents new types of models with heat sink having air passage and investigates experimentally their heat transfer characteristics. From the comparison results for four models, the heat transfer coefficients of model 1 are approximately 44~66% higher than those of the reference model 0. The model 1 show the best overall performance about heat transfer and cooling capability. As shown in above results, it is necessary to design the heat sink with air pass for cooling of electronic devices, in order to increase the convective heat transfer coefficient of a piezoelectric fan for electronic cooling.

• 정보교육학회논문지
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• 제3권1호
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• pp.33-43
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• 1999

Most educational Web contents developed so far can be regarded' as another type of printed textbooks since they are made up of static lists of textual information. It results in a lack of capability in such educational viewpoints as interaction between students and/or teachers, self-directed learning of individual students, and so on. This paper proposes a new style of Web contents, which can improve the self-directed learning capabilities as well as the interaction between students, with the topic of "the life cycle of frog" that the student studies in the third year of elementary school. It has been designed to provide BBS and a studying material appropriate to the achievement level of individual students, and implemented with DHTML and Java.

• 국제학술발표논문집
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• The 2th International Conference on Construction Engineering and Project Management
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• pp.810-819
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• 2007

Usually the status of a bridge is determined by its structural capability and material strength. Consequently a lot of researchers have studied the failure, the fatigue, and the deterioration of the structure in terms of the structural function of a bridge. However, the overall performance of a bridge may be affected simply by the damage of one of its components. Therefore this study utilized a systematic classification and statistical analysis based on the existing bridge inspection data collected in Taiwan to reach the following goals: (1) assess the performance distribution and deterioration rate for bearing and expansion joint of bridge; (2) find out the right time to do the preventive and essential maintenance for the component of bridge with an empirical method, and to decide what time and which component of a bridge will receive preventive maintenance or regular maintenance.

• 한국전기전자재료학회논문지
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• 제36권5호
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• pp.454-462
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• 2023

금속 나노 입자의 플래시 램프 어닐링 공정은 빠른 가공 속도(밀리초 단위), 저온 공정, 롤투롤 공정과의 호환성 등 이유로 유연한 기판 위에 고성능 전극을 제조하기 위한 강력한 솔루션으로 제공되어 왔다. 그러나 금속 나노 입자[예를 들면, 금(Au), 은(Ag), 구리(Cu) 등]는 저온 공정을 위한 미세 금속 나노 입자(직경 10 nm 미만)의 제조가 어렵고, 고가이며, 잉크보관 및 플래시 램프 어닐링 과정에서 산화가 발생하는 등의 한계가 존재했다. 이러한 이유로 유기금속화합물 잉크는 금속 나노 입자를 대체할 수 있는 재료로서 저렴한 가격(기존 금속 나노 잉크 대비 1/100의 가격)과 저온 공정성, 높은 재료 안정성으로 인해 제안되었다. 하지만 이러한 장점에도 불구하고, 유기금속화합물의 플래시 램프 어닐링 처리를 통한 유연한 전극의 제조는 광범위하게 연구되지 않고 있다. 본 논문에서는 사전 경험 없이 은 유기금속화합물을 플래시 램프 어닐링하는 과정에서 발생할 수 있는 어려움을 최소화하기 위해 재료 매개변수와 플래시광 처리 매개변수(에너지 밀도, 펄스 지속시간 등)를 고려하여 유연 기판에 전극을 제조하기 위한 최적의 조건을 결정하는 방법을 실험적으로 가이드하고자 한다.