• Nuclear Engineering and Technology
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• v.55 no.12
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• pp.4357-4366
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• 2023

MARS-KS, a domestic regulatory confirmatory code of Republic of Korea, had been developed by integrating RELAP5/MOD2 and COBRA-TF. The integration of COBRA-TF allowed to extend the capability of MARS-KS, limited to one-dimensional analysis, to multi-dimensional analysis. The use of COBRA-TF was mainly focused on subchannel analyses for simulating multi-dimensional behavior within the reactor core. However, this feature has been remained as a legacy without ongoing maintenance. Meanwhile, MARS-KS also includes its own multidimensional component, namely MULTID, which is also feasible to simulate three-dimensional convection and diffusion. The MULTID is capable of modeling the turbulent diffusion using simple mixing length model. The implementation of the turbulent mixing is of importance for analyzing the reactor core where a disturbing cross-sectional structure of rod bundle makes the flow perturbation and corresponding mixing stronger. In addition, the presence of this turbulent behavior allows the secondary transports with net mass exchange between subchannels. However, a series of assessments performed in previous studies revealed that the turbulence model of the MULTID could not simulate the aforementioned effective mixing occurred in the subchannel-scale problems. This is obvious consequence since the physical models of the MULTID neglect the effect of mass transport and thereby, it cannot model the void drift effect and resulting phasic distribution within a bundle. Thus, in this study, the turbulence mixing model of the MULTID has been improved by means of the inter-channel mixing model, widely utilized in subchannel analysis, in order to extend the application of the MULTID to small-scale problems. A series of assessments has been performed against rod bundle experiments, namely GE 3X3 and PSBT, to evaluate the performance of the introduced mixing model. The assessment results revealed that the application of the inter-channel mixing model allowed to enhance the prediction of the MULTID in subchannel scale problems. In addition, it was indicated that the code could not predict appropriate phasic distribution in the rod bundle without the model. Considering that the proper prediction of the phasic distribution is important when considering pin-based and/or assembly-based expressions of the reactor core, the results of this study clearly indicate that the inter-channel mixing model is required for analyzing the rod bundle, appropriately.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.6
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• pp.887-895
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• 2019

Recently, the number of underground road development projects has been increasing to solve traffic problems in the national capital region and metropolitan areas with intensified overcrowding, and there has been a tendency to plan underground roads by applying a double-deck tunnel technology that has advantages in constructability and economical efficiency. The double-deck tunnel has a structure where one excavation section is divided into two parts and used as up and down lines, and is mainly used as a road for small vehicles only due to its low floor height. In addition, due to the small cross-sectional area, it has characteristics different from those of general road tunnels in terms of ventilation and disaster prevention. In this regard, this study proposed an operational plan that applies an oversized exhaust system, which is one of semi-transverse ventilation systems, to small cross-sectional tunnels like double-deck tunnel with low floor height, and a comparative analysis between smoke exhaust characteristics according to the fire occurrence locations and oversized exhaust systems was conducted using the Fire Dynamics Simulator (FDS). The results showed that unlike uniform exhaust, intensive smoke exhaust using the oversized exhaust port maximized the delay effect of smoke diffusion and limited the smoke within 50 m above and below the fire point.

• Korean Chemical Engineering Research
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• v.47 no.3
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• pp.362-367
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• 2009

Recently, the use of formic acid as a fuel for direct liquid fuel cells has emerged as a promising alternative to methanol. In the work presented herein, we evaluated direct formic acid fuel cells(DFAFCs) with various components under operating conditions, for example, the thickness of the proton exchange membrane, concentration of formic acid, gas diffusion layer, and commercial catalyst. The thickness of the proton exchange membrane influenced performance related to the fuel cross-over. To optimize the cell performance, we investigated on the proper concentration of formic acid and catalyst for the formic acid oxidation. Consequently, membrance-electrode assembly(MEA) consisted of $Nafion^{(R)}$-115 and the Pt-Ru black as a anode catalyst showed the maximum performance. This performance was superior to the DMFCs' one.

• Journal of Korea Trade
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• v.27 no.5
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• pp.1-22
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• 2023

Purpose - Southeast Asia has been the focus of Korea's foreign investment. Korea has been helping developing countries in Southeast Asia achieve economic growth and win-win cooperation through capital exports. FDI is an important channel for technology diffusion. However, the impact of FDI on the bias of technological progress in the host country is dependent on the host country's own endowment structure and capital-labor factor substitution elasticity. Therefore, the central issue of this paper is to accurately evaluate the impact of Korea's FDI to the four Southeast Asian countries in various industries on their bias of technological progress. Design/methodology - The paper uses macroeconomic data for Korea and four East Asian countries to estimate capital-labor factor elasticities of substitution using nonlinear, seemingly uncorrelated regressions (NLSUR). Then, the biased technological change index (BTCI) is calculated for each country. Finally, panel data analysis is used to explore the impact of Korean FDI in various industries in the four Southeast Asian countries on their own directed technological progress, and a robustness test is conducted. Findings - There is a substitution relationship between capital and labor factors based on their elasticity in Korea, Singapore and the Philippines. There is a complementary relationship between capital and labor factors in Indonesia and Malaysia. According to the BTCI, there is a trend toward labor-biased technological progress in all countries. Korean investments in manufacturing, wholesale and retail trade in the host country trigger capital-biased technological change in the host country; investments in the finance, insurance and information and communication sectors trigger labor-biased technological change. In addition, this paper also confirms that directed technological progress can enable cross-country transmission. Originality/value - The innovation of this paper lies in three aspects. First, we estimate the BTCI for five countries and explore the trend and situation of directed technological progress in each country from each country's own perspective. Second, we explore the impact of Korean FDI in the host country on the bias to its technological progress at the industry level. Second, we explore the impact of Korean FDI in various industries in the four Southeast Asian countries on the four countries' own directed technological progress from a national perspective. Finally, we propose corresponding countermeasures for technological progress from the perspective of inverse factor endowment. These innovative points not only expand the understanding of technological progress and cross-country technology transfer in East Asia but also provide practical references for policy-makers and business operators.

• Journal of the Korean Ceramic Society
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• v.37 no.5
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• pp.505-510
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• 2000

In this investigation, we fabricated RBSN (Reaction Bonded Silicon Nitride) using the static nitriding system which could be advantageous for commercialization. Firstly, Si compacts of different sizes were made, and then nitridation rates were investigated as a function of added static gas pressure. The reaction schedule was obtained by pre-experiments. In case of small samples, the variation of ${\alpha}$, ${\beta}$ phases between the inside and the outside region of the specimens was examined after the samples were nitrided under 1 bar and 1.5 bar reaction pressure. On the other hand, large samples of Si compact with the size of 36 mm for diameter and 23 mm for thickness were nitrided for 26 hours of the total nitridation time, which showed a complete and homogeneous nitriding reaction from the outside to the inside of the samples, although the time was considerably shorter than that needed for convertional nitridation. Nitridation rates obtained at the early stage of reaction were proportional to the reaction gas pressures. The sequences of the nitridation reaction with the thickness were as follows 1) the outside, 2) the inside and 3) the intermediate area of the specimen. These results wer eobtained from the coloration of cross sectioned specimens that had various nitridation rates. Total nitriding reaction kinetics was controlled by chemical reaction, not by diffusion of the nitrogen gas.

• Bulletin of the Korean Chemical Society
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• v.27 no.9
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• pp.1433-1438
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• 2006

An AsFlFFF channel was designed and built, and then tested for analysis of pullulans and proteins. Pullulans and proteins having various nominal molecular weights were injected at various conditions of the cross-flow rate ($F_c$) and the channel-out flow rate ($F_{out}$). The retention (measured by the retention ratio R) and the zone broadening (measured by the plate height H) were measured, and then compared with theory. When the incoming flow rate, $f_{in}$ (and thus $F_{out}$) was varied with $F_c$ fixed at 2.5 mL/min, the plate height measured for the pullulan with nominal molecular weight (M) of about 100,000 showed the trend expected by the longitudinal diffusion theory (H decreases with increasing flow rate). In contrast, when $F_{out}$ was varied with the flow rate ratio, $F_c/F_{out}$, fixed constant at 5, the plate height measured for the same sample showed the trend expected from the non-equilibrium theory (H increases with increasing flow rate). Calibration plots (log D vs. log M) obtained with pullulans and proteins were not coincide, probably due to the difference in molecular conformation, suggesting the analysis of pullulans and proteins using AsFlFFF requires independent calibration. It was found that the linearity of the protein-calibration plot was improved by using a buffer solution as the carrier.

• Journal of the Microelectronics and Packaging Society
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• v.19 no.3
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• pp.49-56
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• 2012

Recently, by the trends of electronic package to be smaller, thinner and more integrative, fine bump is required. but It can result in the electrical short by reduced cross-section of UBM and diameter of bump. Especially, the formation of IMCs and KV can have a significant affects about electrical and mechanical properties. In this paper, we analyzed the thermal deformation of flip-chip bump by using FEM. Through Thermal Cycling Test (TCT) of flip-chip package, We analyzed the properties of the thermal deformation. and We confirmed that the thermal deformation of the bump can have a significant impact on the driving system. So we selected IMCs thickness and bump diameter as variable which is expected to have implications for characteristics of thermal deformation. and we performed analysis of temperature, thermal stress and thermal deformation. Then we investigated the cause of the IMC's effects.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.393-393
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• 2016

Cu(In,Ga)Se2 (CIGS) 박막 태양전지는 높은 효율과 낮은 제조비용, 높은 신뢰성으로 인해 박막 태양전지 중 가장 각광받고 있다. 특히 유리기판 대신 가볍고 유연한 철강소재나 플라스틱 소재를 이용하여 발전분야 외에 건물일체형, 수송용, 휴대용등 다양한 분야에 적용이 가능하다. 이러한 유연 기판을 이용한 CIGS 태양전지의 개발을 위해서는 기판의 특성에 따른 다양한 공정개발이 선행되어야 한다. Stainless steel과 같은 철강기판의 경우 Fe, Ni, Cr등의 불순물이 확산되어 흡수층의 특성을 저하시켜 효율을 감소시킨다. 따라서 이러한 철강 기판의 경우 불순물의 확산을 방지하는 확산방지막이 필수적이다. 이러한 유연기판의 특성을 고려하여 본 연구에서는 기존의 두껍고 추가 장비가 요구되는 SiOx나 Al2O3 대신 200nm 이하의 ZnO 박막을 이용하여 확산방지막을 제조하였다. 유연기판으로 STS 430 stainless steel을 이용하였다. 먼저 stainless steel 기판을 이용하여 기판에 의한 흡수층의 특성을 분석하였으며 ZnO 확산 방지막의 유무 및 두께에 따른 흡수층 및 소자의 특성을 분석하였다. 이때 확산 방지막은 기존 TCO 공정에서 사용되는 i-ZnO를 사용하였으며 RF sputter를 이용하여 50~200nm로 두께를 달리하며 특성 비교를 실시하였다. 효율은 확산방지막을 적용하지 않았을 때 약 5.9%에서 확산 방지막 적용시 약 10.7%로 증가하였다. 그 후 기판으로부터 확산되는 불순물의 유입에 의한 결함을 분석하기 위해 DLTS를 이용하여 소자 특성을 분석하였다. 온도는 80~300K으로 가변하며 측정을 실시하였으며 그 후 계산을 통해 activation energy와 capture cross section 값을 구하였다. DLTS 분석 결과 Ni이 CIGS 흡수층으로 확산되어 NiCu anti-site를 형성하여 태양전지의 효율을 감소시키는 것을 확인하였다. 모든 흡수층은 Co-Evaporation 방법을 이용하여 제조하였으며 제조된 흡수층은 SEM, XRF, XRD, GD-OES, PL, Raman등을 이용하여 분석하였으며 그 외 일반적인 방법을 이용하여 Mo, CdS, TCO, Al grid를 제조하였다. AR 코팅은 제외 하였으며 제조된 소자는 솔라 시뮬레이터를 이용하여 효율 특성 분석을 실시하였으며 Q.E. 분석을 실시하였다.

• The Journal of Korean Academy of Prosthodontics
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• v.22 no.1
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• pp.123-132
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• 1984

To evaluate the microstructure of various combination clasp joint in removable partial denture, the auther selected framework alloys (Type IV gold alloy, Dentaurium, Ticonium 100) and wrought wires (gold alloy, Ticonium) for this study. Twelve series of combination joints were made by investment soldering technic and wrought wire embedded casting technic. All specimens were cut cross-sectionally and longitudinally, then examined with metallurgical microscope. The results were as follows; Some diffusion was observed in the properly constructed combination clasp joints. In soldered joints, empolying precious alloys were more favorable than non-precious alloys. In castion joints, assemblage of same alloy between framework and wrought wire was superior to other groups. Some impurities were observed in both joints by technical problems.

• Polymer(Korea)
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• v.25 no.5
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• pp.736-743
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• 2001

An electro- active polymer (EAP) (poly(2-acrylamido-2- methyl propane sulfonic acid), PAMPS) gel crosslinked with N,N-methylenebisacrylamide (MBAA) has been prepared by free radical polymerization in aqueous solution with potassium persulfate as initiator PAMPS gel was swollen in surfactant solution to substitute surfactant for using as actuator. PAMPS gel showed a large movement in the surfactant solution by electric field. PAMPS gel showed the reversible binding and fast response rate. Bending mechanism of gel is related to the cooperative process of hydrophobic interaction, swelling-deswelling of gel and the electrostatic attraction between anode (+) and the anions of PAMPS gel. The response rate of PAMPS gel was increased as the applied potential and the degree of cross-linkage were increased. The response rate was increased as the bending cycle was repeated, but it was decreased with increasing the gel thickness.