• Nuclear Engineering and Technology
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• v.4 no.2
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• pp.132-136
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• 1972

The mechanism for activated sintering of UO$_2$by an addition of 0.05 w/o TiO$_2$was investigated using a high temperature X-ray diffractometer. The diffraction pattern of UO$_2$pellets was studied in a temperature range from room temperature to 120$0^{\circ}C$ in hydrogen atmosphere. At 120$0^{\circ}C$, the expansion of UO$_2$lattice were 1.448% and 1.354% greater when it was compared with those at room temperature for pellets with and without the 0.05 w/o TiO$_2$addition, respectively-The effect of the TiO$_2$addition is to increase the lattice constant of UO$_2$by 0.094% at 120$0^{\circ}C$. The lattice constant at 120$0^{\circ}C$without the TiO$_2$addition is equal to that at 108$0^{\circ}C$ with the 0.05 w/o TiO$_2$addition. This temperature difference could be well compared with the suppression of sintering temperature by TiO$_2$hat had been observed Previously. It is believed that the increase in lattice expansion due to the TiO$_2$addition would give rise to the activated sintering of UO$_2$by the lattice-expansion-induced-enhancement of self diffusion.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.3
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• pp.236-245
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• 2021

It is very important for structure designer to understand the service life variation since a wide range of service life is evaluated with changing exposure conditions and design parameters. Recently, for zero-carbon, waste plastic has been used for fuel for clinker production and this yields increase in chloride content in cement. This study is for evaluation of changing service life in the concrete with increasing initial chloride content due to usage of plastic-SRF(Solid Refuse Fuel) considering various exposure conditions and design parameters. For this, 4 levels of initial chloride content were assumed, and the service life was assessed using LIFE 365 program considering various environmental conditions including 3 levels of surface chloride content. As for analysis parameters, critical/initial chloride content, blast furnace slag powder replacement ratio, W/B(Water to Binder) ratio, cover depth, and unit mass for binder are adopted. Service life decreases with increasing initial chloride content and a significant reduction of service life is not evaluated permitting up to 1,000ppm of initial chloride content. With increasing slag replacement ratio, a longer service life can be secured since blast furnace slag powder has the effect of reducing the diffusion of external chloride ions and fixing the free chloride. It is thought that increasing initial chloride content up to European standard is helpful for enhancing sustainability and reducing carbon emission. Though the reduction in service life due to an increase in the initial chloride content is not significant in slag-concrete with low surface chloride content, careful consideration for mixing design should be paid for the exposure environment with high surface chloride content.

• Journal of the Microelectronics and Packaging Society
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• v.28 no.3
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• pp.17-24
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• 2021

Perovskite solar cells (PSCs) can be fabricated through solution process economically with variable bandgap that is controlled by composition of precursor solution. Tandem cells in which PSCs combined with silicon solar cells have potential to reach high power conversion efficiency over 30%, however, lack of long-term stability of PSCs is an obstacle to commercialization. Degradation of PSCs is mainly attributed to the mass transport of halide and metal electrode materials. In order to ensure the long-term stability, the mass transport should be inhibited. In this study, we confirmed degradation behaviors due to the mass transport in PSCs and designed buffer layers with LiF and/or SnO₂ to improve the long-term stability by suppressing the mass transport. Under high-temperature storage test at 85℃, PSCs without the buffer layers were degraded by forming PbI₂, AgI, and the delta phase of the perovskite material, while PSCs with the buffer layers showed improved stability with keeping the original phase of the perovskite. When the LiF buffer and encapsulation were applied to PSCs, superior long-term stability on 85℃-85% RH dump heat test was achieved; efficiency drop was not observed after 200 h. It was also confirmed that 90.6% of the initial efficiency was maintained after 200 hours of maximum power tracking test under AM 1.5G-1SUN illumination. Here, we have demonstrated that the buffer layer is essential to achieve long-term stability of PSCs.

• Journal of the Korean Institute of Gas
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• v.25 no.2
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• pp.13-21
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• 2021

Because of the recent expansion of hydrogen vehicle supply, the installation of hydrogen filling station is expected to gradually expand. This study attempts to predict the damage scale and propose a safer design form based on the scenario that assumes the worst case of a hydrogen station. A Flacs solver using computational fluid dynamics (CFD) was used to predict the damage scale, and the accuracy was verified by comparing it with the experimental results of previous researchers. The damage scale prediction was conducted for hydrogen leakage and explosion, and the prediction target was the KR model based on the measured values. And as a comparative review model, a roofless model was selected without a ceiling. As a result of analyzing the two models, it was possible to confirm the accumulation and retention of hydrogen gas up to 60 vol% or more in the KR model, whereas in the case of the Roofless model, the phenomenon of discharge and diffusion to the outside of the charging station by riding the wall after leakage. I was able to check. In conclusion, it was reviewed that the type of hydrogen charging station without ceiling is more advantageous for safety than the hydrogen filling station model.

• Environmental and Resource Economics Review
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• v.28 no.2
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• pp.231-276
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• 2019

This paper analyzed the impact of the penetration of EV(electric vehicle) and FCEV(fuel cell electric vehicle) into the automobile industry, using a static CGE approach. There are contrasting view on the economic impact of EV/FCEV penetration: negative economic impact due to shrunken intermediate inputs versus positive impact because of input saving technical progress. Regarding environment, there is no clear consensus whether EV or FCEV will contribute to the reduction of $CO_2$ emissions in Korea. This study attempts to provide an answer to these questions. By giving shocks to the input coefficients of automobile industries and automobile using sectors, as well as to the final demands for energies. we integrated the Bass diffusion model into the CGE framework, The result suggests that the EV penetration has adverse impact on the $CO_2$ emission while the FCEV penetration has positive impact. On the other hand, both EV and FCEV have positive impacts on GDP. When considering automobile manufacturing sectors only, adverse impacts on $CO_2$ are demonstrated both for EV and FCEV. However, since the size of $CO_2$ increase is small, these results does not alter the overall effects.

• Communications of Mathematical Education
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• v.33 no.3
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• pp.231-254
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• 2019

As the teacher-centered education is transformed into learning-centered education, the active knowledge construction of learner becomes important. Along with this change, project-based learning is receiving attention. However, there are many problems to apply the results of research to pre-service teachers because most of the previous studies have focused on elementary middle high school students. Therefore, this study examined the changes in perceptions of pre-service mathematics teachers while project-based learning progressed for one year. Pre-service mathematics teachers had less experience with project-based learning than group discussions, group activities. Also their perceptions was classified as five factors: 'Instructional effects', 'Application and participant of project-based learning', 'Achievement', 'Diffusion of project-based learning', 'Student motivation'. Pre-service mathematics teachers responded positive changes in perception that project-based learning could be motivated to students but they responded negative changes in perception that project-based learning could be distributed to school. They responded positive changes in perception that teachers can show their achievements by project-based learning but they responded negative change in perception that teachers would be fun to apply project-based learning. Also, they responded positive changes in perception that teachers and students were easy to apply or utilize project-based learning.

• Korean Journal of Clinical Laboratory Science
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• v.50 no.4
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• pp.477-483
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• 2018

Transcranial doppler is a non-invasive method that measures the blood flow velocity and the direction of cerebral blood vessels through the doppler principle. The pulsatility index is an index for measuring the transcranial doppler that reflects the distal vascular resistance and is used as an index for the presence and diffusion of cerebral small vessel diseases. The purpose of this study was to evaluate the risk factors affecting the basilar artery pulsatility index in ischemic stroke patients. From January 2014 to May 2015, 422 patients were selected by measuring the transcranial doppler pulsatility index, considering their basilar artery pulsatility index. Univariate analysis was performed using the basilar artery pulsatility index as a dependent variable. Multiple regression analysis was performed considering the factors affecting the pulsatility index as variables. Univariate analysis revealed age, presence of hypertension, presence of diabetes mellitus, presence of hyperlipidemia, and hematocrit (P<0.1) as factors. Multiple regression analysis showed statistically significant results with age (P<0.001), presence of diabetes (P=0.004), and presence of hyperlipidemia (P=0.041). The risk factors affecting the basilar artery pulsatility index of transcranial doppler were age, diabetes, and hyperlipidemia. Further research will be needed to increase the cerebral pulsatility index as a surrogate marker of the elderly, diabetes, and hyperlipidemia.

• Korean Journal of Clinical Laboratory Science
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• v.50 no.4
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• pp.406-413
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• 2018

The emergence of carbapenem resistance among Pseudomonas aeruginosa has become an increasing problem worldwide. In particular, $metallo-{\beta}-lactamases$ (MBLs) are responsible for the high-level resistance to carbapenem. Sequence type 235 (ST235) has been found internationally in a multidrug-resistant clone and is involved in the dissemination of genes encoding IMP-6 and VIM-2. This study examined the prevalence of MBLs and the epidemiological relationship in carbapenem-resistant P. aeruginosa (CRPA) isolates obtained from a tertiary hospital in Daejeon, Korea, between March 2008 and June 2014. The antimicrobial susceptibilities were determined using the disk-diffusion method and PCR and DNA sequencing were used to identify the MBL genes. In addition, an epidemiological relationship was investigated by multilocus sequence typing (MLST). Among the 110 CRPA isolates, 32 isolates (29.1%) were MBL-producers; the major type was IMP-6 (29 isolates, 90.6%). VIM-2 was identified in 3 isolates (9.4%) of ST357. IMP-6-producing isolates were multidrug-resistant (MDR) and belonged to ST235. ST235 (55 isolates, 50.0%) was the clone most frequently detected and has gradually emerged during a seven-year period. To prevent the spread of MDR ST235 P. aeruginosa isolates, the current widespread use of carbapenems needs to be curtailed, and novel continuous monitoring strategies should be developed as soon as possible.

• Korean Chemical Engineering Research
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• v.57 no.1
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• pp.17-21
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• 2019

The redox flow battery (RFB) is a large-capacity energy storage equipment, and the vanadium redox flow cell is a typical RFB, but VRFB is expensive. Iron-chrome RFBs are economical because they use low-cost active materials, but their low performance is an urgent problem. One of the reasons for the low performance is the crossover of the active materials. In this study, the sulfonated Poly (ether ether ketone) (sPEEK) membrane, which is a hydrocarbon membrane, was used instead of the fluorine membrane to reduce the crossover of the active materials. The chromium ion permeability of the sPEEK membrane was $1.8{\times}10^{-6}cm^2/min$, which was about 1/33 of that of the Nafion membrane. Thus, it was shown that the use of the sPEEK membrane instead of the fluorine membrane could solve the high active material crossover problem. The activation energy of iron diffusion through the sPEEK membrane was 24.9 kJ/mol, which was about 66% of Nafion membrane. And that the e-PTFE support in the polymer membrane reduces the active material crossover through Iron-Chrome Redox Flow Battery (ICRFB).

• Korean Journal of Heritage: History & Science
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• v.45 no.3
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• pp.100-113
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• 2012

In the midst of recent active excavation, lots of Silla(新羅) roof-end tiles are unearthed in Yeongnam area(嶺南地域). These are confirmed the same tile frame as the Silla tiles excavated in Gyeongju(慶州). It is represented by the Silla tiles excavated in Ingaksa Temple(麟角寺) excavation research. Roof-end tile with arabesque design(唐草文平瓦當) etc. including roof-end tile with lotus design(蓮花文圓瓦當) are judged to be the tile frame produced by the same frame of roof-end tile that was excavated in Gyeongju, Wolseong(月城) and Hwangyongsa Temple(皇龍寺址). There are three kinds of cases concerning the transportation of tile manufacture ; the roof-end tile manufactured in Gyeongju directly moved to each region, only tile frame moved to site to be manufactured there, and tile manufacturer moved to site to manufacture there. This article considers the case of the roof-end tile manufactured in Gyeongju that was directly moved to each region. In case of the Silla tiles excavated in region especially Ingaksa Temple, the aspects of tiles in accordance with different era show the repeated coexistence, expansion and maintenance. This situation is significant as a clue to understand the supply from Gyeongju not as temporary, but as continuous. On the other hand, if the Gyeongju tiles flowed directly into each region, and if the road was built of gravels and the means of transportation was cart, the damage from movement must never be prevented. On the contrary, transportation through waterway might be advantageous due to the reduction of labor and damage rate and the easiness of loading. Accordingly, it tells us why the ruins where roof-end tiles were excavated located near big and small rivers or streams. Of course there are some ruins located in a fixed distance, but the distance may be enough to endure the impact put on tiles from the overland movement. Therefore, in case of direct inflow form long distance, transportation must be finished by overland movement after waterway movement.