• Journal of the Korean Electrochemical Society
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• v.25 no.1
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• pp.1-12
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• 2022

Lithium metal is the most promising anode for next-generation lithium-ion batteries due to its lowest reduction potential (-3.04 V vs. SHE) and high specific capacity (3860 mAh/g). However, the dendritic formation under high charging current density remains one of main technical barriers to be used for commercial rechargeable batteries. To address these issues, tremendous research to suppress lithium dendrite formation have been conducted through new electrolyte formulation, robust protection layer, shape-controlled lithium metal, separator modification, etc. However, Li/Li symmetric cell test is always a starting or essential step to demonstrate better lithium dendrite formation behavior with lower overpotential and longer cycle life without careful analysis. Thus, this review summarizes overpotential behaviors of Li/Li symmetric cells along with theoretical explanations like initial peaking or later arcing. Also, we categorize various overpotential data depending on research approaches and discuss them based on peaking and arcing behaviors. Thus, this review will be very helpful for researchers in lithium metal to analyze their overpotential behaviors.

• Composites Research
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• v.35 no.2
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• pp.115-119
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• 2022

The performance of carbon fiber is important for the production of these high-quality polymer composite materials such as CFRP (Carbon Fiber Reinforced Plastic). For this purpose, it is essential to use an optimized spinning process for improving the mechanical, physical, and structural properties of the precursor fiber, which greatly affects the properties of the carbon fiber, and the use of a suitable precursor polymer. In this study, the content of MAA (Methacrylic Acid), MAA injection time, and concentration of AIBN (2,2'-Azobis(2-methylpropionitrile)) were set as parameters for the polymer synthesis process, and Poly(AN-co-MAA) (poly(acrylonitrile-co-methacrylic acid)) was polymerized by solution polymerization. Poly(AN-co-MAA) with a molecular weight of 305,138 g/mol and an MAA ratio of 4.2% was dissolved in DMF (N,N-dimethylformamide) at a concentration of 16.0 wt%, and then a precursor fiber was prepared through dry-jet-wet spinning. The precursor fiber had a tensile strength of ~1.06 GPa and a tensile modulus of ~22.01 GPa, and no voids and structural defects were observed on the fiber.

• Journal of Korea Water Resources Association
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• v.55 no.11
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• pp.955-967
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• 2022

Existing particle tracking models predict vertical displacement of particles based on the terminal settling velocity in the stagnant water. However, experimental results of the present study confirmed that the settling velocity of particles is influenced by the turbulence effects in turbulent flow, consistent with the previous studies. The settling velocity of particles and turbulent characteristics were measured by using PTV and PIV methods, respectively, in order to establish relationship between the particle settling velocity and the ambient turbulence. It was observed that the settling velocity increase rate starts to grow when the particle diameter is of the same order as Kolmogorov length scale. Compared with the previous studies, the present study shows that the graphs of the settling velocity increase rate according to the Stokes number have concave shapes for each particle density. In conclusion, since the settling velocity in the natural flow is faster than in the stagnant water, the existing particle tracking model may estimate a relatively long time for particles to reach the river bed. Therefore, the results of the present study can help improve the performance of particle tracking models.

• Journal of the Korean Electrochemical Society
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• v.25 no.3
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• pp.105-112
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• 2022

For the commercialization of all-solid-state batteries, it is essential to develop a solid electrolyte that can be operable at room temperature, and it is necessary to manufacture all-solid-state batteries by adopting materials with high ionic conductivity. Therefore, in order to increase the ionic conductivity of the existing oxide-based solid, Li₇La₃Zr₂O₁₂ (LLZO) doped with heterogeneous elements was used as a filler material (Al and Nb-LLZO). An electrolyte with garnet-type inorganic filler doped was prepared. The binary metal element and the polymer mixture of poly(ethylene oxide)/poly(propylene carbonate) (PEO/PPC) (1:1) are uniformly manufactured at a ratio of 1:2.4, The electrochemical performance was tested at room temperature and 60 ℃ to verify room temperature operability of the all-solid-state battery. The prepared composite electrolyte shows improved ionic conductivity derived from co-doping of the binary elements, and the PPC helps to improve the ionic conductivity, thereby increasing the capacity of all-solid-state batteries at room temperature as well as 60 ℃. It was confirmed that the capacity retention rate was improved.

• Journal of the Korea Organic Resources Recycling Association
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• v.29 no.4
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• pp.33-40
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• 2021

In this study, the physico-chemical and biological characteristics of anaerobic granular sludge at different heights of a full-scale UASB reactor (UASBr) were investigated. Granular sludge was taken from 1 m, 2 m, and 3 m above the ground level in the UASBr. The morphological analysis showed that the upper part had bigger granules and the lower part had rounder granules. The ANOVA test confirmed that the mean size and the roundness of the granules had statistically significant difference along the height at 95% confidence level, and there was a significant negative linear relationship between the size and roundness (r=-0.40, p<0.05). A SMA test using acetic, propionic and butyric acids showed that granules from 2 m height had the highest specific methanogenic activity. The EPS contents were also unequal to each height, with 2 m showing the highest content. These findings could be helpful to understand the different characteristics of stratified anaerobic granules in full-scale UASBr and maintain the reactor performance.

• Journal of the Korea Institute of Building Construction
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• v.22 no.1
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• pp.69-80
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• 2022

The proportion of buildings over 30 years old in Korea has increased, from 29.0% in 2005 to 37.8% in 2019. These old buildings were built during a time in which there was a lack of building-related safety standards in areas such as fire safety performance. Worse, during their years of use, many such old buildings have had illegal changes and extensions made, making them more vulnerable in terms of safety. Fire safety investigations are being conducted to prevent large-scale disasters in multi-use buildings, but no investigation has been conducted at the regional district level, where small-scale old buildings are concentrated. Therefore, to identify fire risk factors in the old building district where old buildings are concentrated, the composition characteristics of the buildings were first analyzed. To examine the spatial characteristics of old building districts in order to derive fire risk factors, the results of this analysis based on the structure, use, roof type, and year of approval for use are as follows. It was found through our analysis that as of the date of approval for the use of the building, the main structure of the building has the greatest impact.

• Korean Journal of Construction Engineering and Management
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• v.23 no.3
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• pp.83-94
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• 2022

The number of public rental housing has increased according to the government's 「Housing Welfare Roadmap (2017)」, and facility maintenance costs for the demand of improvement of performance and residential standards due to the aging of long-term public housing are significantly increasing. Consequently, the financial burden of public housing rental business for maintaining stocked housing is aggravated. However, there is a lack of objective data to analyze the size of the maintenance costs that are executed by the type of repair work, and the elapsed years of the aged long-term public rental housing. This study analyzes the execution status of 33 long-term public rental housing complexes located in Seoul for 14 to 28 years of elapsed years based on the data of maintenance costs. In addition, this study proposes a model to predict the maintenance costs by elapsed years by dividing 'Long-term Repair Plan Work and Government-Funded Project [Y₁]', 'Planned Repair Work and General & Unplanned Repair Work [Y₂]', and 'Total maintenance costs [Y₃]'. It is intended to be used as basic data for the establishment of the maintenance plan at the stage of setting up the budget and the establishment of the sustainable operation plan for public rental housing

• KIPS Transactions on Software and Data Engineering
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• v.11 no.8
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• pp.339-346
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• 2022

Recently, the resource depletion and climate change problem caused by the massive usage of fossil fuels for electric power generation has become a critical issue worldwide. According to this issue, interest in renewable energy resources that can replace fossil fuels is increasing. Especially, photovoltaic power has gaining much attention because there is no risk of resource exhaustion compared to other energy resources and there are low restrictions on installation of photovoltaic system. In order to use the power generated by the photovoltaic system efficiently, a more accurate photovoltaic power forecasting model is required. So far, even though many machine learning and deep learning-based photovoltaic power forecasting models have been proposed, they showed limited success in terms of interpretability. Deep learning-based forecasting models have the disadvantage of being difficult to explain how the forecasting results are derived. To solve this problem, many studies are being conducted on explainable artificial intelligence technique. The reliability of the model can be secured if it is possible to interpret how the model derives the results. Also, the model can be improved to increase the forecasting accuracy based on the analysis results. Therefore, in this paper, we propose an explainable photovoltaic power forecasting scheme based on BiLSTM (Bidirectional Long Short-Term Memory) and SHAP (SHapley Additive exPlanations).

• Journal of the Korea Computer Graphics Society
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• v.28 no.3
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• pp.79-89
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• 2022

With the popularity and the advanced graphics hardware technology of mobile devices, various mobile applications that help children with physical activities have been studied. This paper presents SandUp, a mobile application that guides the play of building sand castles using artificial intelligence and augmented reality(AR) technology. In the process of building the sandcastle, children can interactively explore the target virtual sandcastle through the smartphone display using AR technology. In addition, to help children complete the sandcastle, SandUp informs the sand shape and task required step by step and provides visual and auditory feedback while recognizing progress in real-time using the phone's camera and deep learning classification. We prototyped our SandUp app using Flutter and TensorFlow Lite. To evaluate the usability and effectiveness of the proposed SandUp, we conducted a questionnaire survey on 50 adults and a user study on 20 children aged 4~7 years. The survey results showed that SandUp effectively helps build the sandcastle with proper interactive guidance. Based on the results from the user study on children and feedback from their parents, we also derived usability issues that can be further improved and suggested future research directions.

• Membrane Journal
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• v.32 no.5
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• pp.292-303
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• 2022

An eco-friendly energy conversion device without the emission of pollutants has gained much attention due to the rapid use of fossil fuels inducing carbon dioxide emissions ever since the first industrial revolution in the 18th century. Polymer electrolyte membrane fuel cells (PEMFCs) that can produce water during the reaction without the emission of carbon dioxide are promising devices for automotive and residential applications. As a key component of PEMFCs, polymer electrolyte membranes (PEMs) need to have high proton conductivity and physicochemical stability during the operation. Currently, perfluorinated sulfonic acid-based PEMs (PFSA-PEMs) have been commercialized and utilized in PEMFC systems. Although the PFSA-PEMs are found to meet these criteria, there is an ongoing need to improve these further, to be useful in practical PEMFC operation. In addition, the well-known drawbacks of PFSA-PEMs including low glass transition temperature and high gas crossover need to be improved. Therefore, this review focused on recent trends in the development of high-performance PFSA-PEMs in three different ways. First, control of the side chain of PFSA copolymers can effectively improve the proton conductivity and thermal stability by increasing the ion exchange capacity and polymer crystallinity. Second, the development of composite-type PFSA-PEMs is an effective way to improve proton conductivity and physical stability by incorporating organic/inorganic additives. Finally, the incorporation of porous substrates is also a promising way to develop a thin pore-filling membrane showing low membrane resistance and outstanding durability.