• Nuclear industry
• /
• v.20 no.6 s.208
• /
• pp.31-44
• /
• 2000

본 연구에서 액체금속로의 노심용융(core meltdown)으로 인한 초 즉발 임계(super-prompt critical)의 출력 폭주 사고시, 노심의 반응도 및 열수력 특성 변화와 에너지 방출량등을 계산하기 위하여, Bethe-Tait 방버론을 수정, 보완한 분석 모델이 개발되었다. 주요 보완 내용으로서는, 금속 연료 노심의 단상 액체 영역에서의 선형의(Linear) threshold 형태의 상태 방정식뿐만 아니라 포화 증기(saturated fuel vapor) 영역에서의 상태 방정식이 개발되었고, 이에 따른 노심 붕괴 반응도(disassembly reactivity)의 분석 모델이 개발되었다. 또한 도플러 반응도 효과를 고려하기 위한 분석모델도 아울러 개발되었다. 상기 보완 모델을 실행할 수 있는 수치 해석 프로그램이 개발되었고, 이를 활용하여 KALIMER에서 HCDA가 발생하였을 경우 노심에서의 에너지 방출량 계산이 수행되었다. 분석결과 도플러 효과와 포화 증기 영역에서의 압력 증가 및 노심팽창의 중요성이 확인되었다. 도플러 효과가 고려되지 않을 경우 HCDA는 분석된 모든 반응도 삽입률에 대하여 폭발적인 에너지 방출과 함께 사고가 종결되는 것으로 평가되었다. 그러나 도플러 상수가 최적 평가치인 -0.002인 경우 50$/s이하의 반응도 삽입률에서는 노심은 비등점(0.8KJ/g)에 도달치 않았으며, 설계 기준 사고인 100$/s의 경우에도 노심은 포화 증기 영역에 머물고 압력이 급격히 증가하는 단상(single phase)액체 영역의 threshold 값에 미치지 않기 때문에 사고는 핵연료 증기(vapor)의 점진적인 분산과 함께 종결되는 것으로 분석되며, 총 에너지 발생량은 약 1,800MJ로서 기계적 손상 에너지로 전환되는 분율을 고려할 때 KALIMER 원자로 용기의 구조 설계 기준치에 비해 상당한 여유도를 갖는 것으로 평가되었다.

• Polymer(Korea)
• /
• v.36 no.3
• /
• pp.275-280
• /
• 2012

Poly(amic acid)s were successfully synthesized from 1,4-bis(4-aminophenoxy)benzene (1,4-APB) or 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP) with pyromellitic dianhydride (PMDA), 3,3'-4,4'-benzopenonetetracarboxylic dianhydride (BPDA) and $p$-phenylenediamine ($p$-PDA) and then they were effectively converted into polyimide films by thermal imidization. The chemical structure and thermo-mechanical properties of polyimide films were examined using Fourier transform infrared spectroscopy (FTIR), thermo-gravimetric analyzer (TGA), thermo-mechanical analyzer, dynamic mechanical analyzer (DMA) and universal tensile machine (UTM). The moisture absorption, thermal and mechanical properties of polyimide films decreased with increasing the amount of 1,4-APB and HFBAPP. The polyimide films using HFBAPP showed lower properties than that of 1,4-APB at the same ratio, but it displayed better thermal properties and lower moisture absorption at the similar coefficient of thermal expansion (CTE) with a copper. On the basis of our finding, it is concluded that 4-component polyimide films could be utilized for base films for flexible copper clad laminates (FCCL) of flexible printed circuit boards.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
• /
• 2013.04a
• /
• pp.116-116
• /
• 2013

마그네슘은 스마트폰, 전자기기 케이스, 내화벽돌과 아크용접봉 제조시의 첨가물 등으로 사용되고 있는데, 최근에는 재활용을 위한 마그네슘 용해로를 취급하거나 가공하는 사업장이 증가하고 있어 사고위험성이 높아지고 있다. 금속분을 취급하는 사업장에서의 금속분진은 저장이나 축적 등과 같이 주로 퇴적물로서 존재한다. 퇴적분진의 발화온도는 퇴적물 형상과 두께, 입경, 분위기 가스의 유속, 산소농도, 부유분진의 농도, 퇴적밀도, 수분 등의 많은 영향인자가 관여하기 때문에 이론적 예측이 힘들고 실험적인 측정에 의존할 수 밖에 없는 것이 현실이다. 본 연구에서는 연소성이 높고 화재폭발사고사례가 많은 마그네슘(Mg) 분진을 사용하여 승온속도 변화에 따른 열분해특성을 조사하였다. 퇴적분진의 열적특성을 조사하기 위하여 METTLER TOLEDO의 TGA/DSC1를 사용하였으며, Mg 시료의 평균입경은 38, $142{\mu}m$이다. 입경 $38{\mu}m$의 Mg 시료의 열중량분석 결과, 중량증가는 $400{\sim}500^{\circ}C$의 범위에서 시작되며 $550^{\circ}C$에서 급격하게 중량이 증가하고 있으며, 증량증가개시온도(Temperature of weight gain)는 $460^{\circ}C$에서 시작하여 $900{\sim}950^{\circ}C$ 범위에서 중량 증가 포화값에 도달하였다. 입경 $142{\mu}m$의 Mg에 대하여 공기중 승온속도를 5, 10, $20^{\circ}C/min$으로 변화시키면서 실온에서 $900^{\circ}C$까지 가열 시키는 경우의 시료의 중량 변화에 따른 열분해 특성은 승온속도가 증가할수록 2단계의 S자 곡선은 완만하게 상승을 나타내며 중량증가개시온도가 높아지는 경향을 보이고 있다. 중량증가개시온도가 승온속도에 따라 변화하는 결과를 나타내고는 있지만, 시료량의 증가에 따른 영향을 열중량분석 실험방법의 제약으로 인하여 확인할 수 가 없었다. 그러나 만일 시료량이 크게 증가하는 경우에는 동일한 승온조건에서 중량증가 개시온도는 낮아질 가능성이 있다. 중량증가는 시료의 산화반응에 의한 것이므로 시료량의 증가는 시료 내부에의 열의 축적을 용이하게 하여 보다 낮은 온도에서도 산화반응이 충분히 일어나는 조건이 형성되기 때문이다. 승온속도가 증가할수록 산화 반응한 괴상형태의 연소입자가 크게 증가하고 있는 것을 알 수 있다. 승온속도에 따른 중량개시온도 곡선을 보면 [그림 24]와 같으며 승온속도 5, 10, $20^{\circ}C/min$의 증가에 따라 중량개시온도는 각각 490, 510, $530^{\circ}C$가 얻어졌으며 승온속도의 증가에 따라 중량개시온도가 증가하는 경향을 보이고 있다.

• Food Science and Preservation
• /
• v.9 no.1
• /
• pp.19-27
• /
• 2002

The effect of gamma irradiation was investigated on the microbiological and physicochemical qualities of boiled-dried anchovies (large- and smallsized) packed in PVC film (0.06 ㎜) during storage at 15$\pm$1$\^{C}$ for 6 months. On the other hand, thermoluminescence characteristics of minerals extracted from the sample were analyzed to evaluate its possibility in detecting the irradiated anchovies. The samples were contaminated by microbial levels of 104∼106 CFU/g in total aerobic bacterial counts and negative in coliforms, which were different depending on the sample sizes. Gamma irradiation at 3 kGy was effective for improving the hygienic quality of both samples for 6 months, keeping the microbial population less than 20 CFU/g. Besides it was not detrimental to the quality attributes, such as instrumental color parameters L, a, b, ΔE), browning, TBA value, volatile basic nitrogen, trimethylamine-N and sensory properties(appearance, color, odor, tape, overall acceptability). However, storage conditions (time, temperature, packing) showed a critical factor nfluencing the quality changes of dried anchovies. Thermoluminscence analysis was prove to distinguish irradiated from non-irradiated anchovies by comparing both temperature at which glow curves appear and the curve intensity, that was possible even after 6 months at - 20$\^{C}$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2009.06a
• /
• pp.230-231
• /
• 2009

펄스 레이저 층착법 (이하 PLD)은 다성분계 산화물 박막 또는 다층구조의 박막 제작에 매우 유용한 기술이다. 본 실험에서는 KrF 엑시머 레이저를 이용하여 pt on Si 기판 위에 150nm 두께의 $Bi_{1.5}ZnNb_{1.5}O_7$(이하 BZN) 박막을 다양한 기판온도에서 제작하였다. XRD를 이용하여 BZN 박막의 구조적 특성을 분석하였고, 박막을 MIM 구조로 제작하여 유정적 특성을 측정하였다. 제조한 BZN 박막은 $500^{\circ}C$ 이상에서 결정질을, $500^{\circ}C$ 이하의 온도에서는 비정질 특성을 보였다. 유전 특성은 100 - 400$^{\circ}C$ 영역에서는 온도가 증가함에 따라 졸은 특성을 나타내었고, $500^{\circ}C$에서부터는 감소하였다. 증착 온도 $400^{\circ}C$에서 제작한 BZN 박막이 유전상수가 67.8, 유전 손실이 0.006으로 가장 줄은 유전특성을 나타내었다.

• Journal of the Korean earth science society
• /
• v.32 no.6
• /
• pp.613-628
• /
• 2011

Restoration, prediction and noise analysis of geomagnetic data measured in the Korean Peninsula were performed. Restoration methods based on an optimized principal component analysis (PCA) and the geostatistical kriging approach were proposed, and its effectiveness was also interpreted. The PCA-based method seemed to be effective to restore the periodical signals and the geostatistical approach was stable to fill the gaps of measurements. To analyze the noise level for each observatory, the geomagnetic time-series was plotted by scattergram which reflects the spatial variation, using data observed during same period. The scattergram showed that the observation made at Cheongyang seemed to have better quality in spatial continuity and stability, and the restoration result was also better than that of Icheon site. For the restoration, both of the methods, geostatistical and optimizaed PCA, showed stable result when the missing of observation was within 20 points. However, in case of more missing observations than 20 points and prediction problem, the optimized PCA seemed to be closer to the real observation considering the frequency-domain characteristics. The prediction using the optimized PCA seems to be plausible for one day of period for interpretation.

• Journal of the Korean Society for information Management
• /
• v.16 no.2
• /
• pp.7-26
• /
• 1999

This experimental study examines informetric analysis of World Wide Web based upon cocitation analysis of Web pages and features of Web resources in the field of communication studies. Cocitation analysis is basically performed to examine the intellectual structure of the communication studies in reflecting link count on the Web. The selected Web resources in the field are mapped in two dimensions based upon the similarities of cocitation frequency, correlation matrix, mutidimensional scale and cluster analysis. Cocitation analysis methods using organizational homepage, personal homepage, or Web index, to Web produced clustering of Web resources that had topical similarities. So far, although informetric analysis of Web resources is in the preliminary stage, it shows that Web can be a new tool for indicating the intellectual structure of a specific research field. In addition, this study analyzes characteristics of printing resources and Web resources, and differences of research methods in applying cocitation analysis.

• Journal of the Institute of Electronics Engineers of Korea CI
• /
• v.49 no.2
• /
• pp.83-89
• /
• 2012

Natural Vegetation cover, which is very important earth resource, has been significantly altered by humans in some manner. Since this has currently resulted in a significant effect on global climate, various studies on vegetation environment including forest have been performed and the results are utilized in policy decision making. Remotely sensed data can detect, identify and map vegetation cover change based on the analysis of spectral characteristics and thus are vigorously utilized for monitoring vegetation resources. Among various vegetation indices extracted from spectral reponses of remotely sensed data, NDVI is the most popular index which provides a measure of how much photosynthetically active vegetation is present in the scene. In this study, for change detection in vegetation cover, a Multi-layer Perceptron Network (MLPN) as a nonparametric approach has been designed and applied to MODIS/Aqua vegetation indices 16-day L3 global 250m SIN Grid(v005) (MYD13Q1) data. The feature vector for change detection is constructed with the direct NDVI diffenrence at a pixel as well as the differences in some subset of NDVI series data. The research covered 5 years (2006-20110) over Korean peninsular.

• Journal of the Microelectronics and Packaging Society
• /
• v.29 no.2
• /
• pp.1-10
• /
• 2022

Recently, semiconductor devices have been used in many fields owing to various applications of mobile electronics, wearable and flexible devices and substrates. During the semiconductor chip bonding process, the mismatch of coefficient of therm al expansion (CTE) between the substrate and the solder, and the excessive heat applied to the entire substrate and components affect the performance and reliability of the device. These problems can cause warpage and deterioration of long-term reliability of the electronic packages. In order to improve these issues, many studies on low-melting temperature solders, which is capable of performing a low-temperature process, have been actively conducted. Among the various low-melting temperature solders, such as Sn-Bi and Sn-In, Sn-58Bi solder is attracting attention as a promising low-temperature solder because of its advantages such as high yield strength, moderate mechanical property, and low cost. However, due to the high brittleness of Bi, improvement of the Sn-Bi solder is needed. In this review paper, recent research trends to improve the mechanical properties of Sn-Bi solder by adding trace elements or particles were introduced and compared.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.35 no.1
• /
• pp.9-15
• /
• 2011

In this study, we investigated the hydrodynamic and thermal performance of constructal architectures on the basis of the mass flow rates for a given pressure drop, and we determined the thermal resistance and flow uniformity. The five flow configuration used in this study were the first construct with optimized hydraulic diameter, the second construct with optimized hydraulic diameter, the first construct with non-optimized hydraulic diameter, second construct with non-optimized hydraulic diameter, and a serpentine configuration. The results of our study suggest that the best fluid-flow structure is the second constructal structure with optimized constructal configurations. We also found that in the case of the optimized structure of cooling plates, the heat transfer was remarkably higher and the pumping power was significantly lower than those of traditional channels.