• Nuclear Engineering and Technology
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• v.54 no.8
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• pp.3059-3072
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• 2022

A Jacobian-Free Newton Krylov Two-Nodal Coarse Mesh Finite Difference algorithm based on Nodal Expansion Method (NEM_TNCMFD_JFNK) is successfully developed and proposed to solve the three-dimensional (3D) and multi-group reactor physics models. In the NEM_TNCMFD_JFNK method, the efficient JFNK method with the Modified Incomplete LU (MILU) preconditioner is integrated and applied into the discrete systems of the NEM-based two-node CMFD method by constructing the residual functions of only the nodal average fluxes and the eigenvalue. All the nonlinear corrective nodal coupling coefficients are updated on the basis of two-nodal NEM formulation including the discontinuity factor in every few newton steps. All the expansion coefficients and interface currents of the two-node NEM need not be chosen as the solution variables to evaluate the residual functions of the NEM_TNCMFD_JFNK method, therefore, the NEM_TNCMFD_JFNK method can greatly reduce the number of solution variables and the computational cost compared with the JFNK based on the conventional NEM. Finally the NEM_TNCMFD_JFNK code is developed and then analyzed by simulating the representative PWR MOX/UO₂ core benchmark, the popular NEACRP 3D core benchmark and the complicated full-core pin-by-pin homogenous core model. Numerical solutions show that the proposed NEM_TNCMFD_JFNK method with the MILU preconditioner has the good numerical accuracy and can obtain higher computational efficiency than the NEM-based two-node CMFD algorithm with the power method in the outer iteration and the Krylov method using the MILU preconditioner in the inner iteration, which indicates the NEM_TNCMFD_JFNK method can serve as a potential and efficient numerical tool for reactor neutron diffusion analysis module in the JFNK-based multiphysics coupling application.

• Fisheries and Aquatic Sciences
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• v.25 no.4
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• pp.189-201
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• 2022

Jellyfish is an emerging aquaculture species, farmed for Oriental cuisines and nutraceutical ingredients. This study aimed to examine antioxidative and antimicrobial potentials of various fractions of the jellyfish, Acromitus hardenbergi. The bell and oral arms of the jellyfish were sequentially extracted with petroleum ether (PE), dichloromethane (DCM), chloroform (CHCl₃), methanol (MeOH), and water (H₂O) to extract its bioactive in an increasing polarity gradient. Test fractions were assayed for antiradical activities using electron spin resonance spectrometry, β-carotene-linoleate model and Folin-Ciocalteu assay; and antimicrobial activity against 2 Gram-negative bacteria, 4 Gram-positive bacteria and 2 fungal species using the disc diffusion assay. All fractions were also subjected to Fourier Transform Infrared (FTIR) analysis to identify types of functional groups present. It was found that the hydrophilic extracts (H₂O fractions) possessed the most effective radical scavenging activity (p < 0.05) while the lipophilic extracts (PE fractions) the most active antimicrobial activity, especially against Gram-positive bacteria (p < 0.05). Total oxidation substrates content was found to be highest in the PE fractions of jellyfish bell and oral arms (p < 0.05). FTIR data showed that the H₂O and MeOH fractions contains similar functional groups including -OH, -C=O, -N-H and -S=O groups, while the PE, DCM, and CHCl₃ fractions, the -CH₃, -COOH groups. This study showed that A. hardenbergi contains antioxidants and antimicrobials, thereby supporting the traditional claim of the jellyfish as an anti-aging and health-promoting functional food. Bioassay-guided fractionation approach serves as a critical milestone for the strategic screening, purification, and elucidation of therapeutically significant actives from jellyfish.

• 한국전산유체공학회:학술대회논문집
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• 2009.04a
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• pp.290-297
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• 2009

A two-phase (gas and liquid) flow analysis solver, named CUPID, has been developed for a realistic simulation of transient two-phase flows in light water nuclear reactor components. In the CUPID solver, a two-fluid three-field model is adopted and the governing equations are solved on unstructured grids for flow analyses in complicated geometries. For the numerical solution scheme, the semi-implicit method of the RELAP5 code, which has been proved to be very stable and accurate for most practical applications of nuclear thermal hydraulics, was used with some modifications for an application to unstructured non-staggered grids. This paper is concerned with the effects of interpolation schemes on the simulation of two-phase flows. In order to stabilize a numerical solution and assure a high numerical accuracy, the second-order upwind scheme is implemented into the CUPID code in the present paper. Some numerical tests have been performed with the implemented scheme and the comparison results between the second-order and first-order upwind schemes are introduced in the present paper. The comparison results among the two interpolation schemes and either the exact solutions or the mesh convergence studies showed the reduced numerical diffusion with the second order scheme.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.33 no.3
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• pp.93-100
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• 2021

Since the IB (Immersed Boundary) method, which can perform coupling analysis with objects and fluids having an impermeable boundary of arbitrary shape on a fixed grid system, has been developed, the IB method in various CFD models is increasing. The representative IB methods are the directing-forcing method and the ghost cell method. The directing-forcing type method numerically satisfies the boundary condition from the fluid force calculated at the boundary surface of the structure, and the ghost-cell type method is a computational method that satisfies the boundary condition through interpolation by placing a virtual cell inside the obstacle. These IB methods have a disadvantage in that the computational algorithm is complex. In this study, the simplified immersed boundary (SIB) method enables the analysis of temporary structures on a fixed grid system and is easy to expand to three proposed dimensions. The SIB method proposed in this study is based on a one-field model for immiscible two-phase fluid that assumes that the density function of each phase moves with the center of local mass. In addition, the volume-weighted average method using the density function of the solid was applied to handle moving solid structures, and the CIP method was applied to the advection calculation to prevent numerical diffusion. To examine the analysis performance of the proposed SIB method, a numerical simulation was performed on an object falling to the free water surface. The numerical analysis result reproduced the object falling to the free water surface well.

• Particle and aerosol research
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• v.18 no.1
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• pp.9-21
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• 2022

In this study, a novel antiviral coating method for the air filtration system of subway station was investigated. Using dry aerosol coating process, we developed a high-performance antiviral air filter with spark discharger and carbon brush type ionizer. Silver nanoparticles were produced by a spark discharge generation system with ion injection system and were used as antiviral agents coated onto a medium grade air filter. The pressure drop, filtration efficiency, and antiviral ability of the filter against aerosolized MS2 virus particles as a surrogate of SARS-CoV-2 virus were tested with dust contamination. Dust contamination caused the increase of the filtration efficiency and pressure drop, while the antiviral agents (in this study, silver nanoparticles) coating did not have any significant effect on the filtration efficiency and pressure drop. Using these properties, we suggested a novel method to maximize the antiviral performance of the antiviral air filter that was contaminated by dust particles. Moreover theoretical analysis of antiviral ability with dust contamination and re-coated antiviral agents was carried out using a mathematical model to calculate the time-dependent antiviral effect of the filter under actual conditions of subway station. Our model can be used to apply on antiviral air filtration system of subway station for prevention of pandemic diffusion, and predict the life cycle of an antiviral filter.

• Knowledge Management Research
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• v.24 no.1
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• pp.1-29
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• 2023

The COVID-19 pandemic has accelerated digital transformation across all industries and daily life. Edutech is spreading in the education field, also bringing changes in university education. Non-face-to-face online-only classes at universities have spread after the COVID-19 pandemic physical distancing started. Online-only or real-time online classes showed diverse educational imitations. 'Metaverse' started to attract attention as a learning space and community activity support platform that may solve the limitations of online education and communication. It is time to prepare an introduction strategy for the actual application of education using metaverse. This study, first, by examining previous studies and cases of metaverse application, and second, establishing a metaverse introduction framework based on the technology lifecycle model and the innovation diffusion theory. Finally, we provide an introduction strategy in steps, a specialized introduction plan according to the main users is established and presented as a scenario. We expect that this study will provide the theoretical background of the new technology introduction and the spread of metaverse research. Also, we present an efficient introduction strategy, the basis for a service model, and a practical basis for the university's value-added strategy.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.12
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• pp.287-293
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• 2018

The Korean peninsula has been known as an area that is free of volcanic disasters. However, recent observations and research results of volcanoes in Far East Asia, including Baedu Mountain and Japanese volcanoes, show that the Korean peninsula is no longer a safe area from volcanic disasters. Since 2012, the Korean government has been developing an IT-based construction technology, VDRS (Volcanic Disaster Response System), for effective volcanic disaster response system. The main users of VDRS are public officers in central or local governments. However, most of them have little experience and knowledge about volcanic disasters. Therefore, it is essential to develop education contents and implement training on volcanic disaster response for effective response in a real disaster situation. In this paper, we deal with the development of a mobile application based on virtual reality (VR) for realistic volcanic disaster response training. The objectives of training are the delivery of knowledge and experience for volcanic disasters. First, VR contents were generated based on spatial information. A 3D model was constructed based on a Digital Elevation Model (DEM), and visualization models for meterological effects and various volcanic disaster diffusion effects were implemented for the VR contents. Second, the mobile application for the volcanic disaster response training was implemented. A 12-step story board is proposed for volcanic disaster experience. The application was developed with the Unity3D engine based on the proposed story board to deliver knowledge of various volcanic disasters (volcanic ash, pyroclastic flows, volcanic mudflow etc.). The results of this paper will be used for volcanic disaster response and prevention training and for more realistic training linked with augmented reality technology in the future.

• Korean journal of communication and information
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• v.52
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• pp.177-202
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• 2010

IPTV has been drawing attention as a representative convergence media. The analysis of the convergence media, as like IPTV, requires an investigation into the use perception and multidimensional factors. So this research examines the IPTV usage, based on the Technology Acceptance Model. The analysis was made with the 500 users, based on the online survey. The first results is concerned with the user characteristics. A positive influential relationship between the user characteristics and use perception was confirmed, along with the individual attribute and environmental influence. The second, 'perceived ease of use' was found to positively influence 'perceived usefulness' and 'perceived playfulness'. This finding suggests that it is an important diffusion strategy to enhance the ease of use of IPTV. The third is the emphasis of playfulness of IPTV. Since IPTV is multimedia, playfulness played a significant role in diffusing IPTV. The application of the TAM to the media analysis of IPTV, which reflects the environments of the convergence media and use perception, was successful in drawing a significant outcome.

• Journal of Information Technology Applications and Management
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• v.20 no.1
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• pp.43-51
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• 2013

Human being does work to live out and they have their private life because human has sociality. Both work and life are important to live out but they are on the trade-off relationship. Because keeping the balance between work and life is too hard, it has been interested by academic and practical areas. Definition of Work-life balance here is that balance or imbalance arising between work and life has no negative impact on their daily life. Above all, Work-life balance is important because it is strongly related to identity. Recently, the introduction of the mobile office system has emerged as a way to solve the problem of work-life balance. It is based on the teleworking which was formerly generated. Teleworking is to perform the work in the employee's home or office space set aside without going into the workplace. Concept of the mobile office system here is not only using portable devices during work for convenience but also the system which is designed for the performance. Thanks to the diffusion of smart devices(smart phone, tablet pc), mobile office system has been spread. Although the importance of mobile office systems is emerging, there are few researches about it. Even they mostly focus on the standpoint of performance of mobile office system. However, Quality of life is as important as the performance. As a part of Quality of Life field, Work-life balance is the closest to employee's quality of life. So this study aims to examine the effect of the use of mobile office systems on work-life balance. To do so, we try to find factors effecting Work-life balance from existing studies and then set a research model. We set the use of mobile office systems as independent variables which are divided by use of function, use by location and use by situation. There are four dependent variables - sense of self command, sense of balance, solving work problem, solving life problem. We collected data from employees who are using mobile office systems on their job. 215 people were participated in the survey and we used multiple regression analysis to verify our research model. Results show that every independent variable has no impact on solving work problem while they have slight impact on the other dependent variables. Especially use on the business trip has significant effect on dependent variables. It means that there is a possibility use of mobile office system could control the employee's quality of life and system should be evolved until it covers even critical tasks. Also, support for mobile office system -education, encouragement-should be provided. By mobile office system is maturing, future research would be done.

• Informatization Policy
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• v.18 no.3
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• pp.25-49
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• 2011

As a way to gather diverse information required for everyday living, the importance of social networks has been growing. Social network services have been spreading rapidly because of diffusion of the Internet, evolution of social network sites, and recognition of the importance of social networks. Recently, the social network service has been evolved based on a new paradigm, Web 2.0, pursuing participation and openness. Following the adoption of Web 2.0 technologies, the social network service allows users to make and maintain new relationships in a more convenient way. Users of the social network service tend to reveal their personal information, and share their ideas and content with other people; in the process they become aware of their existence, feel satisfaction with life and exert influence to others as a member of the society. This study uses higher order factor analysis to analyze factors that affect the intention of using the social network service. A research model was developed with second-order factors including perceived social presence, perceived gratification and perceived social influence. First-order factors are grouped by technical, individual and social factors. Smart PLS 2.0 was used to conduct empirical analysis. The analysis results supported the validity of the research model.