• ETRI Journal
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• v.35 no.1
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• pp.166-169
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• 2013

In this letter, we propose a data randomization scheme for endurance and interference mitigation of deeply-scaled multilevel flash memory. We address the relationships between data patterns and the raw bit error rate. An on-chip pseudorandom generator composed of an address-based seed location decoder is developed and evaluated with respect to uniformity. Experiments performed with 2x-nm and 4x-nm NAND flash memory devices illustrate the effectiveness of our scheme. The results show that the error rate is reduced up to 86% compared to that of a conventional cycling scheme. Accordingly, the endurance phenomenon can be mitigated through analysis of interference that causes tech shrinkage.

• Proceedings of the KIPE Conference
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• 2003.07a
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• pp.5-9
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• 2003

Conventional variable-speed Induction motor drives with inverters are subject to detrimental effect of zero-sequence voltages, such a shaft voltage and bearing current. This paper presents a way of the suppression of the zero-sequence components in multilevel H-bridge inverters. First examined Is the inherent zero-sequence characteristic of the conventional subharmonic PW method. Then it is shown that the zero-sequence voltage can be eliminated with proper -selection of switching states with space vector modulation. Although this method alone restricts the linear modulation range of control, a combination of the proposed method and the minimum switching method appears to be effective in suppressing the zero-sequence voltage to minimum level while maintaining the linear control range.

• Journal of Electrical Engineering and Technology
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• v.9 no.5
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• pp.1746-1752
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• 2014

This paper presents an application of proportional-resonant (PR) current controllers in modular multilevel converter-high voltage direct current (MMC-HVDC) system under unbalanced voltage conditions. The ac currents are transformed and controlled in the stationary reference frame (${\alpha}{\beta}$-frame). Thus, the complex analysis of the positive and negative sequence components in the synchronous rotating reference frame (dq-frame) is not necessary. With this control method, the ac currents are kept balanced and the dc-link voltage is constant under the unbalanced voltage fault conditions. The simulation results based on a detailed PSCAD/EMTDC model confirm the effectiveness of the proposed control method.

• Journal of Power Electronics
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• v.17 no.3
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• pp.788-797
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• 2017

The power quality of AC electric railways has become an issue worthy of more and more concern. Many active compensators based on power converters have been proposed, but with complex transformers or coupled branches. This paper presents a single-phase cascaded H-bridge multilevel active power filter (APF), which can directly connect to the 27.5-kV power supplies to deal with power quality problems. According to field measured data, the load characteristics are analyzed, and the system configuration and control system are designed based on the load characteristic analysis. Finally, simulation and experimental results verify the effectiveness of the proposed APF system, considering some problems such as the supply voltage fluctuations and transient inrush currents in AC electric railway systems.

• 대한예방의학회:학술대회논문집
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• 2002.10a
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• pp.343-344
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• 2002

• 대한예방의학회:학술대회논문집
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• 2004.10a
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• pp.48.2-49
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• 2004

• The Mathematical Education
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• v.62 no.2
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• pp.195-209
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• 2023

This study examined the effect and structural relationship of math teachers' teaching ability and class activity types on learners' value perception, confidence, and interest of mathematics at the student level and teacher level. To this end, data from 2nd graders of korea middle school in TIMSS 2019 were applied to the multilevel structural equation model. As a result of the analysis, the teaching ability of math teachers had a positive effect on value perception, confidence, and interest of mathematics at the student level and teacher level. Also, math value perception and math confidence had a positive effect on math interest. and it was confirmed that the teaching ability of math teachers indirectly had a positive effect on math interest by mediating math value perception and math confidence. In addition, the math class activity of applying what was learned to problems had a positive effect on math value perception, but it had a negative effect on math interest. and the class activity of the same ability group had a positive effect on math confidence and math interest. This study presents meaningful implications for math classes in the school field through a multilevel analysis of the student level and the teacher level.

• Journal of the Korea Society of Computer and Information
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• v.21 no.5
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• pp.19-29
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• 2016

This paper suggests a method to refine a massive collective intelligence data, and visualize with multilevel sentiment network, in order to understand information in an intuitive and semantic way. For this study, we first calculated a frequency of sentiment words from each movie review. Second, we designed a Heatmap visualization to effectively discover the main emotions on each online movie review. Third, we formed a Sentiment-Movie Network combining the MDS Map and Social Network in order to fix the movie network topology, while creating a network graph to enable the clustering of similar nodes. Finally, we evaluated our progress to verify if it is actually helpful to improve user cognition for multilevel analysis experience compared to the existing network system, thus concluded that our method provides improved user experience in terms of cognition, being appropriate as an alternative method for semantic understanding.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.10
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• pp.2301-2308
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• 2013

These days, Rehabilitation psychology analysis system is being used by world wide web in everyday's life. And on the other hand, we are facing spam messages' problems. To block these spam message, we are using filtering or pricing systems. But these solutions are raising other problems such as impediment in reception or availability caused by false positive or payment resistance. To solve these problems, we propose an Indirect Model on Message Control System(IMMCS) which controls an unsolicited message and prevents an useful message from discarding. We design and implement the IMMCS to enhance the usefulness and the availability. Being tested the IMMCS to verify the usability and the efficiency, it gave us a very successful result.

• The Journal of the Korean dental association
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• v.58 no.10
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• pp.627-638
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• 2020

This study was conducted to identify the subjective damage caused by COVID-19 and its related factors. The study subjects were members of the Korean Dental Association (KDA). We investigated the damage to dental clinics and hospitals caused by COVID-19 between January and April 2020. After analyzing the final 3,189 responses, the rate of decrease in patients was the highest at 34.9% in March, and the rate of decrease in income was the highest at 34.0% in April. As a result of the multilevel analysis, the damage caused by COVID-19 was greater in regions with more confirmed patients, more careers, and fewer dental staff. The government should establish a compensation plan for hospitals and clinics to prevent the collapse of the medical system due to the prolonged COVID-19. In addition, support for dentistry should be provided to maintain the oral health care system in the future.