• Journal of Power Electronics
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• v.17 no.4
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• pp.942-952
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• 2017

Modular multilevel converters (MMCs) have been receiving extensive research interest in high/medium-voltage applications due to its modularity, scalability, reliability, high-voltage capability, and excellent harmonic performance. Submodule capacitors are usually rather bulky because they have to withstand fundamental frequency voltage fluctuations. To reduce the capacitance of these capacitors, this study proposes a modified MMC with an active power decoupling circuit within each submodule. The modified submodule contains an auxiliary half bridge, with its capacitor split in two. Also, the midpoints of the half bridge and the split capacitors are connected by an inductor. With this modified submodule, the fundamental frequency voltage fluctuation can be suppressed to a great extent. The second-order voltage fluctuation, which is the second most significant component in submodule voltage fluctuations, is removed by the proper control of the second-order circulating current. Consequently, the submodule capacitance is significantly reduced. The viability and effectiveness of the proposed new MMC are confirmed by the simulation and experimental results. The proposed MMC is best suited for medium-voltage applications where power density is given a high priority.

• Journal of the Architectural Institute of Korea Planning & Design
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• v.35 no.5
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• pp.41-50
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• 2019

In this study, we analyzed the process of the housing reflecting the self, based on the qualitative data that people describe their thoughts about their housing in social media 'online-housewarming'. Especially, based on the precedent study that modern self is established on continuous selection behavior, we focused on the selection behavior of the self and the role of the housing that affected it through the narrative. Each narrative component corresponds to the self-establishment process of modern people, identified through precedent study. We can confirm the existing internal criteria changing into new internal criteria through accumulation, interaction and nonverbal communication of selection by housing. Housing has been involved in the selection behavior of self throughout the narrative. From this, it can be seen that the thought of the self and housing are identified in three ways. In 'Online-Housewarming', (1) Housing equates with the self, in the sense that housing is a physical entity in which one's own choices are accumulated (2) People perceive the change of choice caused by the realistic constraints of housing as their interaction with housing. (3) People relate the opinions of others about housing with the opinions about their own self. In contemporary society, house reforming process is a process of mediating the self and the external world based on the selection behavior and affects the establishment of self.

• Journal of the Architectural Institute of Korea Planning & Design
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• v.35 no.9
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• pp.29-40
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• 2019

The concept of smart city is understood as an indispensable component of urban regeneration projects in small cities in terms of providing a better urban environment and efficient living systems with a limited budget. Recently, the Korean government revised the law that related to the construction of the smart city and started to implement the smart city concept not only to new-large urban development but also to small-existed regeneration projects. However, it is difficult for small and medium-sized cities that are suffering from the insufficient professional workforce; knowledge supports for high-tech and lack of professional networks to proceed smart city planning and project that containing regional characteristics. This paper aims to examine the effective way of urban regeneration for small and medium-sized cities through smart city planning and strategy. As an important case, this paper looks at the 'Smart City Challenge' competition that was hosted by the US Department of Transportation in 2015. It examines the background and operation process of the smart city challenge competition, and then analyses each city's strategy and characteristics of seven finalists. This paper highlights the several key lessons to Korean cities: 1) the importance of national government's support in financial and professional resources; 2) the cooperation with local governments and IT corporations which provides realistic and detailed technical solutions; 3) the holistic and integrated approach to urban regeneration starting from transportation issues; 4) the necessity of the government's clear visions and guidelines toward the smart city.

• Journal of Ecology and Environment
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• v.44 no.4
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• pp.222-228
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• 2020

Background: Parthenium hysterophorus is a noxious invasive weed in tropical and subtropical regions of the world, including Nepal. Among 11 species of biological control agents released to control P. hysterophorus in Ausrtalia, winter rust Puccina abrupta var. partheniicola arrived fortuitously and has established in Kathmandu Valley, Nepal, nearly a decade back. However, the prevalence and effectiveness of this rust as a biological control agent in Kathmandu remain unknown. To address this knowledge gap, a roadside survey was done at an interval of 2 ± 0.25 km in Kathmandu Valley to assess the P. abrupta var. partheniicola incidence and its impacts on P. hysterophorus. Infested individuals of P. hysterophorus were further divided into four severity classes (very low, low, medium, and high), and rust incidence was calculated. The impact of the winter rust on the growth of P. hysterophorus was assessed by comparing biomass and seed output of infested and non-infested individuals. Results: Among 81 locations where P. hysterophorus was present in the Kathmandu Valley, winter rust infestation was observed at 98% locations. At some locations within Kathmandu Valley such as Tinkune, Kirtipur, Chabahil, Buddha Chowk, and Dhobighat, the impacts of the rust on P. hysterophorus were medium to high. Aboveground biomass and seed output of P. hysterophorus were reduced by 47% and 73%, respectively, due to winter rust infestation. The study indicates that winter rust incidence is widespread in Kathmandu Valley with very low to high levels of damages to P. hysterophorus depending on the localities. Conclusion: The rust has, therefore, a potential to reduce the growth performance of P. hysterophorus, and it can be used as a component of integrated management of P. hysterophorus by introducing to other suitable areas in Nepal.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.6
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• pp.413-422
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• 2022

In this paper, the fault analysis of the momentum wheel, which is a high-speed rotary machinery of 'Control Moment Gyro' for medium and large satellite, was described. For fault diagnosis, envelope spectrum analysis was performed using Hilbert transformation method and signal demodulation method to find the impact signals periodically generated from amplitude modulated signals. Through this, the fault of the momentum wheel was diagnosed by analyzing whether there was a harmonic component of the rotational frequency and a bearing fault frequency in a specific frequency band with a high peak.

• Applied Chemistry for Engineering
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• v.33 no.6
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• pp.618-623
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• 2022

The bipolar plate is a key component of the polymer electrolyte membrane fuel cell (PEMFC) that transfers reactants and electrons, discharges water and heat as by-products, and serves as a mechanical support for the membrane electrode assembly (MEA). Therefore, the flow field structure of the bipolar plate plays an important role in improving fuel cell performance. In this study, PEMFC performance was investigated with copper foams with different compressibility ratios applied to cathode bipolar plates using a 25 cm² unit cell. The total resistance decreased as the compressibility ratio of the metal foams increased, and, in particular, the charge transfer and mass transfer resistance were significantly improved compared to the serpentine flow field, lowering voltage loss in medium and high current density region. In the case of pressurized air reactant flow with serpentine structure, fuel cell performance was similar to that of a compressed metal foam flow field (S3) up to the medium current density region, but low performance appeared in the high current density region due to flow field structure limitations.

• Journal of Life Science
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• v.32 no.11
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• pp.872-881
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• 2022

In this study, we optimized the composition of the indole-3-acetic acid (IAA) production medium using response surface methodology on Pantoea agglomerans SRCM 119864 isolated from soil. IAA-producing P. aglomerans SRCM 119864 was identified by 16S rRNA gene sequencing. There are 11 intermediate components known to affect IAA production, hence the effect of each component on IAA production was investigated using a Plackett-Burman design (PBD). Based on the PBD, sucrose, tryptone, and sodium chloride were selected as the main factors that enhanced the IAA production at optimal L-tryptophan concentration. The predicted maximum IAA production (64.34 mg/l) was obtained for a concentration of sucrose of 13.38 g/l, of tryptone of 18.34 g/l, of sodium chloride of 9.71 g/l, and of L-tryptophan of 6.25 g/l using a the hybrid design experimental model. In the experiment, the nutrient broth medium supplemented with 0.1% L-tryptophan as the basal medium produced 45.24 mg/l of IAA, whereas the optimized medium produced 65.40 mg/l of IAA, resulting in a 44.56% increase in efficiency. It was confirmed that the IAA production of the designed optimal composition medium was very similar to the predicted IAA production. The statistical significance and suitability of the experimental model were verified through analysis of variance (ANOVA). Therefore, in this study, we determined the optimal growth medium concentration for the maximum production of IAA, which can contribute to sustainable agriculture and increase crop yield.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.3
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• pp.31-40
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• 2017

This paper deals with the high precision of GPS measurement reduction and its implementation on near real-time and kinematic mode for those applications requiring centimeter-level precision of the estimated coordinates, even if target stations are a few hundred kilometers away from their references. We designed the system architecture, data streaming and processing scheme. Intensive investigation was performed to determine the characteristics of the GPS medium-range functional model, IGS infrastructure and some exemplary systems. The designed system consisted of streaming and processing units; the former automatically collects GPS data through Ntrip and IGS ultra-rapid products by FTP connection, whereas the latter handles the reduction of GPS observables on static and kinematic mode to a time series of the target stations' 3D coordinates. The data streaming unit was realized by a DOS batch file, perl script and BKG's BNC program, whereas the processing unit was implemented by definition of a process control file of BPE. To assess the functionality and precision of the positional solutions, an experiment was carried out against a network comprising seven GPS stations with baselines ranging from a few hundred up to a thousand kilometers. The results confirmed that the function of the whole system properly operated as designed, with a precision better than ${\pm}1cm$ in each of the positional component with 95% confidence level.

• KSBB Journal
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• v.21 no.6 s.101
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• pp.479-483
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• 2006

[ ${\beta}-Glucan$ ], one of the cell wall components, is most plentiful polysaccharides in cell wall and has several advantages in immune system. In yeast ${\beta}-glucan$ is mainly contained in the yeast cell wall, and thus it is important to produce high levels of cell mass for the mass production of yeast ${\beta}-glucan$. The best carbon and nitrogen sources on cell mass production were high fructose syrup and yeast extract. Response surface methodology (RSM) was very potential tool for the optimization of process factor and medium component. It was applied to estimate the effects of medium components on the production of cell mass. Optimal concentrations of high fructose syrup and yeast extract by response surface methodology were 8.0% (v/v) and 5.2% (w/v), respectively and the cell mass predicted was $17.0\;g/{\ell}$ at 20 h of cultivation.

• Horticultural Science & Technology
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• v.18 no.4
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• pp.508-512
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• 2000

Growth of red pepper (Capsicum annuum) 'Kumtap', tomato (Lycoperisocon esculentum) 'Seokwang', petunia (Petunia hybrida) 'Madness Rose', and pansy (Viola tricolor) 'Magestic Giant' in mixtures of chestnut woodchips and granular rockwool at 25:75, 50:50, or 75:25 (v/v) was examined. Chestnut woodchips were soaked in water for 48 hours or aged in open field for 6 months in order to remove substances impeding plant growth. A commercial plug medium was used as the control. All treatments showed in a similar result in red pepper, petunia, and pansy. Plant height, fresh weight, dry weight, and chlorophyll content in media containing chestnut woodchips, especially in higher proportions, were poorer as compared to those in the control. On the contrary, height, fresh weight, and dry weight of tomato seedlings in media containing woodchips were significantly higher than those in the control. For petunia, pansy, and red pepper, six month ageing in open field of woodchips was more favorable for growth than 48 hour water soaking. Emergance of petunia seed was inferior, especially when woodchip content was higher, to the other crops with a resultant growth suppression. From the results, chestnut woodchips proved to be a practical material as a medium component only in tomato plants.