• Journal of the Korean Ceramic Society
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• v.26 no.4
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• pp.505-513
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• 1989

The sintering behavior and grain growth of ZnO in 99.0mol% ZnO-1.0mol% Bi2O3 which are the basic compositions of ZnO varistor were studied. The microstructrual observation confirmed that the final sintered density was mainly determined at the initial stage of sintering, i.e. grain rearrangement and grain growth which were induced by the penetration of eutectic melts formed at eutectic temperature(74$0^{\circ}C$). But when the liquid penetration was terminated, the grain growth did not promote further densification. Activation energy of the grain growth of ZnO in the system of 99.0mol% ZnO-1.0mol% Bi2O3 was 44.8$\pm$1.8Kcal/mol.

• Journal of the Korean Ceramic Society
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• v.27 no.6
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• pp.763-768
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• 1990

The gradient and depth of tin at the side of glasses by float process were measured. The effects of tin to ion exchanged of glasses in the molten salt of KNO3 and AgNO3 were presented by means of Ag+ ion penetration depth, diffusion coefficient variation, spectral transmittance and color coordinates. The diffusion coefficient of Ag+ ion of tin side was higher than air side, and the activation energy of tin side was 0.2-0.6Kcal/mole lower than air side. Therefore Ag+ ion penetration depth of tin side is 2-10$\mu\textrm{m}$ deeper, hence it can be seen that tin promote Ag+ ion diffusion. The same treatment of ion exchange, reddish-brown oflong wavelength in case of tin present, yellowish-amber of short wavelength in case of tin absence were revealed.

• Journal of Electrical Engineering and Technology
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• v.13 no.4
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• pp.1407-1418
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• 2018

Novel mechanism of customized adequacy formulation is proposed in order to enhance micro grids system reliability. The mechanism accounts for 2-levles of load curtailment, and is mainly based on probabilistic load profile and hybrid Distributed Generation (DG) units modeling. The two load curtailments are needed in order to ensure adequate technical constraints at steady state condition during islanding mode of operation. The effectiveness of the proposed formulation has been verified using system independent analytical expressions for the evaluation of both reliability and Expected Energy Not Served (EENS) indices. The evaluation has examined the impact of different penetration levels of Hybrid DG Units in case study islands. Results show the enhancement of the overall distribution system reliability and the recommended conditions for successful islanding mode of operation.

• Nuclear Engineering and Technology
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• v.53 no.3
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• pp.932-941
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• 2021

This paper suggests a fracture simulation method for SFR metallic fuel pin under accident condition. Two major failure mechanisms - creep damage and eutectic penetration - are implemented in the suggested method. To simulate damaged element, stress-reduction concept to reduce stiffness of the damaged element is applied. Using the proposed method, the failure size of cladding can be predicted in addition to the failure time and failure site. To verify the suggested method, Whole-pin furnace (WPF) test and TREAT-M test conducted at Argonne National Laboratory (ANL) are simulated. In all cases, predicted results and experimental results are overall in good agreement. Based on the simulation result, the effect of eutectic-penetration depth representing failure behavior on failure size is studied.

• Journal of Hydrogen and New Energy
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• v.16 no.2
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• pp.199-207
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• 2005

Hydrogen is getting more attention owing to the seriousness of air pollution and dependance on oil import, UNCCC(United Nations Convention on Climate Change) for reducing the emission of $CO_2$. This fact is not confined in a certain country but global recognition and several countries initiated R&D competition for commercializing the hydrogen fuel cell vehicle. Within 20${\sim}$30 years cost effective hydrogen production can be possible using fossil fuels because so much research is carried out up to now. But it is so far to produce the most of the hydrogen using renewable resources considering the present status of R&D and cost effectiveness. Several automobile companies planed for mass production of hydrogen vehicle by 2010 but changed or canceled the plan owing to the difficulty of R&D and the low status of infrastructure penetration. This paper surveyed the hydrogen energy policy, R&D program and commercialization strategy of advanced country, international agency, automobile and energy company to analyze the global status of R&D and policy. And the survey of R&D program is focused on the part of hydrogen production, storage, delivery and fuel cell.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.77.1-77.1
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• 2010

Durability problems of gas diffusion layer(GDL) is one of the important issues for accomplishing commercialization of proton exchange membrane fuel cell(PEMFC). GDL is strongly related to the performance of PEMFC because one of the main function of GDL is to work as a path of fuel, air and water. When the GDL is degraded, it causes water balance problems such as the flooding phenomenon. Thus, investigating the durability characteristics of the GDL is important and understanding the GDL degradation process is needed. In this study, the GDLs are degraded by carbon corrosion stress method which is the electrochemical degradation mode. To determine the effects of carbon corrosion of the GDL, 1.45 V of potential is imposed for 96 hours. In this manner, in the previous research, the structure between the substrate and the MPL is weaken. Further investigations are needed to clarify this phenomenon. Therefore, in this study, the carbon corrosion stress method is carried out with GDLs which have various MPL penetration levels and the effects of the MPL penetration level on the characteristics change of the GDL are analyzed. The changes in characteristics are measured with various properties of GDL such as weight, thickness and static contact angle. The degraded GDL shows loss of their properties.

• Journal of Electrical Engineering and Technology
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• v.8 no.5
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• pp.1175-1181
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• 2013

The aim of this paper is to design and evaluate a high concentration, high penetration unipolar corona ionizer. The electrostatic characteristics in terms of voltage-current relationships of the present ionizer in the discharge zones for positive and negative coronas were discussed. Using ion current measurement, the concentration and penetration of ions were evaluated at corona voltages across the needle electrodes between 1 and 4 kV, flow rates between 1 and 5 L/min, and an operating pressure of 1 atm. In the discharge zone of the ionizer, the highest ion concentrations were found to be about $1.71{\times}10^{14}$ and $5.09{\times}10^{14}\;ions/m^3$ for positive and negative coronas, respectively. At the outlet of the ionizer, it was found that the highest ion concentration was about $1.95{\times}10^{13}$ and $1.91{\times}10^{13}\;ions/m^3$ for positive and negative coronas, respectively. The highest ion penetration for positive and negative coronas through the ionizer was found to be about 98 % and 33 %, respectively. The $N_it$ product for positive and negative coronas was also found to $1.28{\times}10^{13}$ and $7.43{\times}10^{13}\;ions/m^3s$, respectively. From the findings, this ionizer proved to be particularly useful as an aerosol charger for positive and negative charge before the detector in an electrical aerosol detector.

• Smart Structures and Systems
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• v.15 no.4
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• pp.1085-1101
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• 2015

Changes in substructure conditions, such as ballast fouling and subgrade settlement may cause the railway quality deterioration, including the differential geometry of the rails. The objective of this study is to develop and apply a hybrid cone penetrometer (HCP) to characterize the railway substructure. The HCP consists of an outer rod and an inner mini cone, which can dynamically and statically penetrate the ballast and the subgrade, respectively. An accelerometer and four strain gauges are installed at the head of the outer rod and four strain gauges are attached at the tip of the inner mini cone. In the ballast, the outer rod provides a dynamic cone penetration index (DCPI) and the corrected DCPI (CDCPI) with the energy transferred into the rod head. Then, the inner mini cone is pushed to estimate the strength of the subgrade from the cone tip resistance. Laboratory application tests are performed on the specimen, which is prepared with gravel and sandy soil. In addition, the HCP is applied in the field and compared with the standard dynamic cone penetration test. The results from the laboratory and the field tests show that the cone tip resistance is inversely proportional to the CDCPI. Furthermore, in the subgrade, the HCP produces a high-resolution profile of the cone tip resistance and a profile of the CDCPI in the ballast. This study suggests that the dynamic and static penetration tests using the HCP may be useful for characterizing the railway substructure.

• Computers and Concrete
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• v.19 no.5
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• pp.489-499
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• 2017

Self-Compacting Concrete (SCC) is a new technology capable to flow without segregation or any addition of energy which leads to efficient construction and cost savings. In this study, the effect of replacing the Ordinary Portland Cement (OPC) with Fly Ash (FA) on the strength, durability of the concrete was investigated experimentally, and carbon footprint and cost were also assessed. Four different replacement FA ratios (0%, 20%, 40% and 60%) were used to create four SCC mixes. Standard test methods were used to determine the workability, strength, and durability of the SCC mixes including resist chloride ion penetration, water permeability, water absorption, and initial surface absorption. The axial cube compressive strength tests were performed on the SCC mixes at 1, 7, 14, 28 and 35 days. Replacing the OPC with FA had a significant positive impact on chloride iron penetration resistance and water absorption but had a considerable negative impact on the compressive strength. The SCC mix with 60% FA had 36.7% and 15.8% enhancement in the resistance to chloride ion penetration and water absorption, respectively. Evaluation of the carbon footprint and the cost of each SCC mixes showed the $CO_2$ emissions mixes 1, 2, 3 and 4 were significantly reduced by increasing the FA content from 0% to 60%. Compared with the control mix, the cost of all mixes increased when the FA content increased, but no significant differences were seen between the estimated costs of all four mixes.

• Korean Journal of Food Science and Technology
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• v.20 no.4
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• pp.483-487
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• 1988

The viscosity of salt solution and Kimchi juice and salt penetration and hardness of Chinese cabbage were investigated during brining and fermentation at $4-35^{\circ}C$. The rate of salt penetration during brining increased as the temperature and salt concentration increased from 5% to 15% while the effect of temperature on the salt penetration rates(%/hr) was rather reduced as salt concentration increased. The hardness of the cabbage measured by puncture test showed a rapid initial decrease during salting and the viscosity of brine changed little. Fermentation of Kimchi resulted a little increase in viscosity of Kimchi juice while the hardness of the cabbage decreased rapidly as pH reduced to pH 4.2-4.3 and then increased a little thereafter.