Development of Real Monitoring of Algal Toxins using Multi Functionalized Auto Sampler with Online LC/HRMS

Jaewon Choi,Wonseok Choi,Yuns Kim,Ilhwan Choi,Yongyeon Kim,Wonkyung Lee,Moondon Choi,Jongsu Park 대한환경공학회 2015 대한환경공학회 학술발표논문집 Vol.2015 No.10

태양광 에너지를 활용한 발열 의자

Wonseok Choi,Woowon Lee,Sangmin Kim,Jinbeom Lee,Dukkyu Hwang,Taeyoon Ko 대한전기학회 2017 대한전기학회 학술대회 논문집 Vol.2017 No.11

Thermal NaCl-MgCl2 Salt Purification for Reducing Reactor Vessel Corrosion

Wonseok Lee,Wonseok Yang,Jihun Kim,Hyeongbin Kim,Sungyeol Choi 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.2

Molten chloride salts are promising candidates as a coolant for Molten Salt Reactors (MSRs) because of their low cost, high specific heat transfer, and thermal energy storage capacity. The NaCl- MgCl2 eutectic salts have enormous latent heat (430 kJ/kg) and financial advantage over other types of molten chloride salt. Despite the promise of the NaCl-MgCl2 eutectic salt, problems associated with structural material corrosion in the MSR system remain. The hygroscopicity of NaCl-MgCl2 and high MSRs operating temperature accelerate corrosion within structural alloys. Especially, MgCl2 reacts with H2O in the eutectic salt to produce HCl and Cl2, which are known to further exacerbate corrosion by the chlorination of structural materials. Therefore, several studies have worked to purify impurities associated with MgCl2, such as H2O. Thermal salt purification of NaCl-MgCl2 eutectic salt is one method that reduces HCl and Cl2 gas generation. However, MgO and MgOHCl are generated as the byproduct of thermal purification through a reaction between MgCl2 and H2O. The corrosion behavior of MgO within structural alloys after thermal treatment is not well known. This paper demonstrates corrosion behavior within structural alloy after thermal treatment at various temperature profiles of the NaCl-MgCl2 eutectic salt. According to the temperature range, MgCl2·H2O are separated at 100~200°C, and MgOHCl and HCl begin to occur at 240°C or higher. Finally, MgOHCl produces MgO and HCl at 500°C or higher temperatures. After thermal treatments, the H2O, MgOHCl, and MgO content were measured by Thermo Gravimetric Analyzer (TGA) to evaluate significant products causing corrosion. The structural materials were analyzed by the Scanning Electron Microscope-Energy Dispersive Spectroscopy (SEM-EDS) and using the mass change method to observe the type of localized corrosion, the corrosion rate, and the corrosion layer thickness. This study is possible in that it can reduce economic costs by reducing the essential use of expensive, high-purity molten salts because it is related to a substantial financial cost problem considering the amount of molten salt used in industrial sites.

Increasing supply chain risks and Implications for Korea

( Wonseok Choi ),( Hyoungmin Han ) 대외경제정책연구원 2023 World Economy Brief Vol.23 No.40

Unfolding the Structure of Practical Knowledge of an Expert Physical Education Teacher

( Wonseok Choi ) 한국체육학회 2016 국제스포츠과학 학술대회 Vol.2016 No.1

Purpose: To define the professional knowledge base used in practice, the purpose of this study was to reveal the structure of practical knowledge of an expert physical education(PE) teacher. Practical knowledge proposed by Elbaz(1983) was used as both theoretical and analytical framework. Method: A qualitative case study design was used to examine and describe in depth certain features of the teaching process within the context of teaching expertise. The participating teacher was a female PE specialist in A metropolitan city and she is in her twenty-seventh year of teaching. She met a list of criteria typically associated with expert teachers. Data collection included observations and interviews. Data analysis involved description, analysis, interpretation process suggested by Wolcott(1994). Result: Findings revealed three images of her PE class: (a) everyone is the star, (b) PE should be interesting, (c) PE teacher is not a coach. Three images were supported by several principles(6) and rules(16), most of which were directly connected to teacher’s behavior or language while teaching in certain situation. Relationships among the images, principles, and rules showed hierarchical patterns and complex structures that were embedded in the teacher’s knowledge and teaching practice. Conclusion: Instead of focusing on physical activity and skill development in PE, the teacher in current study emphasized affective values such as character education, respect for each other, cooperation, and more. All she wanted to achieve in her gym was the students to love sports and PE, not because they were skilled performer, but because they fully internalized the value of participating sports and PE. However, follow up studies should be conducted to examine the individuality of practical knowledge of expert PE teachers.

Development of a Machine Learning Model for Determination of Electrode Surface Area With Voltammetry of Two Rod Electrode in Molten Salts

Wonseok Yang,Yonadan Choi,Sungyeol Choi 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.1

Radioactive wastes, including used nuclear fuel and decommissioning wastes, have been treated using molten salts. Electrochemical sensors are one of the options for in-situ process monitoring using molten salts. However, in order to use electrochemical sensors in molten salt, the surface area must be known. This is because the surface area affects the current of the electrode. Previous studies have used a variety of methods to determine the electrode surface area in molten salts. One method of calculating the electrode surface area is to use the reduction current peak difference between electrodes with known length differences. The method is based on the reduction peak and has the benefit of providing long-term in-situ monitoring of surfaces immersed in molten salt. A number of assumptions have been made regarding this method, including that there is no mass transport by migration or convection; the reaction is reversible and limited by diffusion; the chemical activity of the deposit should be unity; and species should follow linear diffusion. For the purpose of overcoming these limitations, a variety of machine learning algorithms were applied to different voltammogram datasets in order to calculate the surface area. Voltammogram datasets were collected from multiarray electrodes, comprising a multiarray holder, two tungsten rods (1 mm diameter) working electrodes, a quasi-reference electrode, and a counter electrode. The multiarray electrode holder was connected to the auto vertical translator, which uses a servo motor, for changing the height of the rod in the molten salts. To make big and diverse data for training machine learning models, various concentrations of corrosion products (Cr, Fe) and fission products (Eu, Sm) in NaCl-MgCl2 eutectic salts were used as electrolyte; electrolyte temperatures were 500, 525, 550, 575, and 600°C. This study will demonstrate the potential of utilizing machine learning based electrochemical in situ monitoring in molten salt processing.

Synthesis of <i>N</i>-Imidoyl and <i>N</i>-Oxoimidoyl Sulfoximines from 1-Alkynes, <i>N</i>-Sulfonyl Azides, and Sulfoximines

Choi, Wonseok,Kim, Jaeeun,Ryu, Taekyu,Kim, Ki-Bbeum,Lee, Phil Ho American Chemical Society 2015 ORGANIC LETTERS Vol.17 No.13

<P><I>N</I>-Imidoylation of sulfoximines is developed from a Cu-catalyzed three-component reaction from 1-alkynes, <I>N</I>-sulfonyl azides, and sulfoximines in THF at room temperature under air. In addition, <I>N</I>-oxoimidoylation of sulfoximines is accessed from a Cu-catalyzed three-component reaction from 1-alkynes, <I>N</I>-sulfonyl azides, and sulfoximines in THF at room temperature followed by a Cu-catalyzed oxidative reaction at 50 °C under air, producing <I>N</I>-oxoimidoyl sulfoximines.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/orlef7/2015/orlef7.2015.17.issue-13/acs.orglett.5b01553/production/images/medium/ol-2015-01553h_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ol5b01553'>ACS Electronic Supporting Info</A></P>

Blockchain-based IoT Authentication techniques for DDoS Attacks

Wonseok Choi(최원석),Sungsoo Kim(김성수) 한국컴퓨터정보학회 2019 韓國컴퓨터情報學會論文誌 Vol.24 No.7

In the IoT(Internet of Things) environment, various devices are utilized and applied for different sites. But attackers can access easy to IoT systems, and try to operate DDoS(Distributed Denial-of-Service) attacks. In this paper, Sensor nodes, Cluster heads, and Gateways operates lightweight mutual authentication each others. Since authenticated sensor nodes and cluster heads only send transactions to Gateways, proposed techniques prevent DDoS attacks. In addition, the blockchain system contains secure keys to decrypt data from sensor nodes. Therefore, attackers can not decrypt the data even if the data is eavesdropped.

Perceived Organizational Support and Knowledge Sharing

Choi, Wonseok,Goo, Wongun 한국경영학회 2018 한국경영학회 통합학술발표논문집 Vol.2018 No.8

Organizational support is considered one of the important factors that facilitate employees’ knowledge sharing. However, it is still unclear how organizational support influences knowledge sharing. This study investigates how employees’ perception of organizational support is related to their knowledge sharing. The results show that perceived organizational support increases employees’ emotional attachment to their organizations, and then leads to knowledge sharing, and employees shares knowledge more when they feel that sharing knowledge is discretionary than required. Our findings imply that organizational support is not an effective way to enhance knowledge sharing when it is necessary to complete their tasks.

Temporal trends of the prevalence and incidence of atrial fibrillation and stroke among Asian patients with hypertrophic cardiomyopathy: A nationwide population-based study

Choi, You-Jung,Choi, Eue-Keun,Han, Kyung-Do,Jung, Jin-Hyung,Park, Jiesuck,Lee, Euijae,Choe, Wonseok,Lee, So-Ryoung,Cha, Myung-Jin,Lim, Woo-Hyun,Oh, Seil Elsevier 2018 INTERNATIONAL JOURNAL OF CARDIOLOGY Vol.273 No.-

<P><B>Abstract</B></P> <P><B>Background</B></P> <P>Atrial fibrillation (AF) and stroke are common in hypertrophic cardiomyopathy (HCM). We aimed to determine the prevalence and incidence of AF and stroke in patients with HCM during a 10-year period.</P> <P><B>Methods</B></P> <P>Using the Korean National Health Insurance Services database, we identified patients diagnosed with HCM from the entire Korean population between 2005 and 2015. The annual prevalence and incidence of AF and stroke in HCM patients were estimated.</P> <P><B>Results</B></P> <P>The prevalence of AF in HCM patients has gradually increased to 1.6-fold from 13.4% in 2005 to 20.9% in 2015. The incidence of AF ranged from 4.1 to 5.5%, a similar trend was observed for each year in HCM patients. The prevalence of stroke in HCM patients was approximately 10%, while that in HCM patients with AF was about 20%. During 8741 person-years, AF-related stroke occurred in 257 subjects among 2309 HCM patients with new-onset AF. The overall incidence rate of AF-associated stroke was 2.94 per 100 person-years. In subgroup analysis, the incidence rate of AF-associated stroke was 1.49 per 100 person-years in the under 45 year-old group and 1.48 per 100 person-years in the group with CHA<SUB>2</SUB>DS<SUB>2</SUB>­VASc score of 0 or 1 point in HCM patients.</P> <P><B>Conclusions</B></P> <P>The prevalence of AF in HCM patients gradually increased over 10 years. The annual risk of AF-associated stroke in HCM was over 1% even in younger patients and those with CHA<SUB>2</SUB>DS<SUB>2</SUB>­VASc score of 0 or 1 point, which provide evidence to support the prevention of stroke in HCM patients with AF.</P> <P><B>Highlights</B></P> <P> <UL> <LI> This is the first largest nationwide study on hypertrophic cardiomyopathy (HCM), a rare myocardial disease in Korea. </LI> <LI> The prevalence of AF in HCM patients gradually increases to 1.6-fold from 13.4% in 2005 to 20.9% in 2015. </LI> <LI> The annual incidence of AF in HMC patients was about 5%, and higher in female and the elderly. </LI> <LI> The prevalence of stroke in HCM patients with AF was about 20%, which were more than twice that in overall HCM patients. </LI> <LI> The risk of AF-related stroke in HCM patients was >1% per person-year even in younger patients or low CHA<SUB>2</SUB>DS<SUB>2</SUB>­VAS<SUB>C</SUB> score. </LI> </UL> </P>