• Nuclear Engineering and Technology
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• v.51 no.1
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• pp.45-53
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• 2019

Thermal-hydraulic passive safety systems (PSSs) are incorporated into many advanced reactor designs on the bases of simplicity, economics and inherent safety nature. Several factors among which are the critical parameters (CPs) that influence failure and reliability of thermal-hydraulic (t-h) passive systems are now being explored. For simplicity, it is assumed in most reliability analyses that the CPs are independent whereas in practice this assumption is not always valid. There is need to critically examine the dependency influence of the CPs on reliability of the t-h passive systems at design stage and in operation to guarantee safety/better performance. In this paper, two multivariate analysis methods (covariance and conditional subjective probability density function) were presented and applied to a simple PSS. The methods followed a generalized procedure for evaluating t-h reliability based on dependency consideration. A passively water-cooled steam generator was used to demonstrate the dependency of the identified key CPs using the methods. The results obtained from the methods are in agreement and justified the need to consider the dependency of CPs in t-h reliability. For dependable t-h reliability, it is advisable to adopt all possible CPs and apply suitable multivariate method in dependency consideration of CPs among other factors.

• Journal of Power Electronics
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• v.19 no.1
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• pp.24-33
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• 2019

A new modeling method for AC-AC switched capacitor converters (SCCs) is introduced in this study. The proposed analytical method aims to accurately describe the input-output characteristics of AC-AC SCCs and establish a mathematical model for static voltage conversion ratio and equivalent resistance, which are key performance metrics for SCCs. A quantitative analysis of converter regulation capability is addressed on the basis of the modeling method. In this analysis, the effects of the control parameters and individual components on SCCs are illustrated extensively. Component stresses, such as the peak value and transient variation of the voltage/current of the converter, are also presented. The effectiveness of the proposed method is verified by comparing it with the existing modeling method and applying it to an AC-AC SCC with a conversion ratio of three. Two 1 kW prototypes are built in a laboratory, and their experimental results exhibit good agreement with the theoretical analysis.

• Nuclear Engineering and Technology
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• v.51 no.1
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• pp.310-316
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• 2019

Fluidelastic instability is a key issue in steam generator tube bundles subjected in cross-flow. With a low flow velocity, a large amplitude vibration of the tube observed by many researchers. However, the mechanism of this vibration is seldom analyzed. In this paper, the mechanism of cross-flow effects on fluidelastic instability of tube bundles was investigated. Analysis reveals that when the system reaches the critical state, there would be two forms, with two critical velocities, and thus two expressions for the critical velocities were obtained. Fluidelastic instability experiment and numerical analysis were conducted to obtain the critical velocity. And, if system damping is small, with increases of the flow velocity, the stability behavior of tube array changes. At a certain flow velocity, the stability of tube array reaches the first critical state, a dynamic bifurcation occurs. The tube array returns to a stable state with continues to increase the flow velocity. At another certain flow velocity, the stability of tube array reaches the second critical state, another dynamic bifurcation occurs. However, if system damping is big, there is only one critical state with increases the flow velocity. Compared the results of experiments to numerical analysis, it shows a good agreement.

• Journal of the Korea Safety Management & Science
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• v.23 no.2
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• pp.31-36
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• 2021

This study aims to review observational methods for assessing postural loads such as OWAS, RULA and REBA, and to compare them, based on the literature survey. The literature was searched through academic database of ScienceDirect using the key words of observational methods, OWAS, RULA and REBA. The results exhibited that of the thee methods, RULA was cited in the literature and applied to manufacturing industries the most frequently. Although it has been known that RULA is appropriate for assessing upper body postures, it has been applied to healthcare and social work activities, agriculture, forestry, fishing, construction, mining and quarrying, which require unstable lower limb postures. The countries where more number of relevant studies have been carried out were USA, India, Brazil, UK, etc. It was recommended that of the three techniques, RULA may be better for assessing postural loads, because it evaluated postural loads more highly, irrespective of industry, work type and lower limb postures, and its assessment results had higher agreement rate with experts' assessments than those of OWAS and REBA. It is expected that the results of this study will be used as a guideline for selecting an appropriate observational method.

• Progress in Superconductivity and Cryogenics
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• v.22 no.4
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• pp.57-61
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• 2020

Cooling by gas helium circulation can be used for various HTS (high temperature superconductor) magnets operating at 20~40 K, and a cryogenic blower is an essential device for circulating gas helium in the cooling system. The performance of the cryogenic blower is determined by various design parameters such as the impeller diameter, the blade number, the vane angle, the volute cross-sectional area, and the rotating speed. The trailing edge angle and the height of impeller vane are also key design factors in determining the blower performance. This study describes the design, fabrication and performance evaluation of cryogenic blower to produce a flow rate of 30 g/s at 5 bar, 35 K gas helium. The impeller shape is designed using a specific speed/specific diameter diagram and CFD analysis. After the fabrication of the cryogenic blower, a test equipment is also developed using a GM cryocooler. The measured flow rates and the pressure differences are compared with the design values at various rotating speeds and the results show a good agreement. Isentropic efficiency is also evaluated using the measured pressures and temperatures.

• Journal of Advanced Navigation Technology
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• v.22 no.2
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• pp.90-95
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• 2018

In the solid rocket motor (SRM), a thrust of rocket is generated by a nozzle so it is very important device. The nozzle of SRM is a condition of high temperature and high pressure so occurs the erosion by combustion gas. The liquid rocket propulsion systems (LRPSs) cools the nozzle by the fuel and oxidizer but SRM does not cool the nozzle. This paper deal with the development of the oxy-acetylene torch tester and investigate the thermochemical erosion properties for the thermal insulation materials of the graphite rocket nozzle throat through the experiment. The results of experiments are compared with the results of Theoretical model and identify the key factors affecting of erosion. The results is in good agreement with the experimental data.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.17 no.2
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• pp.41-49
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• 2007

USIM(UMTS Subscriber Identity Module) technology that accept 3GPP(3rd Generation Partnership Project) standards for information security supports security function in 3GPP. Supported security functions of USIM are confidentiality of user identity, mutual authentication and key agreement between end user and network, confidentiality of user data and data integrity. It is very important technology in wireless network. It makes secure environment that user and service provider can use securely mobile service in network. In this paper, design and implementation USIM security module that supports common network access method and authentication protocol in 3GPP and WLAN(Wireless LAN) and AAA (3A-Authentication Authorization Accounting) server system based RADIUS.

• Archives of Craniofacial Surgery
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• v.22 no.1
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• pp.17-25
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• 2021

Background: This study aims to report how the practice of plastic surgeons and their attitude was during the first measure period of coronavirus disease 2019 (COVID-19) pandemic. Methods: A survey study was held among members of the Indonesian Association of Plastic Reconstructive and Aesthetic Surgeons during week 5 after the first report of COVID-19. A 10 multiple-choice questions (MCQs) and 1 essay covered key questions on the area of surgery and operating room, clinics, internal meeting, and consultation. The only open-ended question relates to the last MCQ addresses a future "flipped" medical practice. Results: Response rate was 45.6% among 228 members, with 89.4% did no practice or limited their service to emergency and urgent cases only. Only 1.9% kept their official meeting as usual, while the majority modified it. The practice in the operating theatre and clinic were also altered to comply with the measures; with 21.2% from the total respondents only allowed patients with exposure to come for visit after taking 14 days of self-quarantine. Teleconsultation was practiced by 50% of the respondents, while 41.3% agreed and 10.6% disagreed upon the future "flipped" medical practice. Conclusion: In general plastic surgeons have made supportive actions during the pandemic. Surgery was performed with all precautions at the utmost as a reflection of high alert of viral infection. Teleconsultation has been embraced via existing social media. Agreement upon the future "flipped" medical practice is reasonable. All in all, the actions were considered as most relevant.

• East Asian Economic Review
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• v.26 no.3
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• pp.227-253
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• 2022

Despite the proliferation of free trade agreements (FTAs), many exporting firms are still confronted with several challenges in utilizing the FTA preferential tariffs. Based on the Technology-Organization-Environment (TOE) framework, this study empirically examines the factors affecting the utilization of FTA schemes by exporting firms. To clarify the key factors influencing FTA utilization, this study develops a conceptual model from the perspective of the adoption of information technology innovations. Eight factors derived from the TOE framework are proposed to explore the determinants of FTA utilization in export. Partial least squares structural equation modeling is employed to analyze the data collected from 162 exporting small- and medium-sized enterprises in the South Korean textile industry. The findings reveal that compatibility and trading partner influence are positively associated with FTA utilization, while complexity is negatively related. Factors of organizational context do not show any relationship with FTA utilization. This study is the first to theoretically analyze and empirically test the determinants of FTA utilization from the perspective of technological innovation adoptions. By examining the relative importance of TOE factors in the utilization of FTA schemes, this study expects to advance a holistic understanding on the perceived factors that could potentially affect the utilization of FTA schemes.

• Ecology and Resilient Infrastructure
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• v.9 no.2
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• pp.124-129
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• 2022

Urban river have been a key pillar in citizens' lives through the healthy urban environment of ecological nature along with the function of this dimension. On the other hand, conflicts are occurring in terms of conservation and use of rivers in the region along with the expansion of infrastructure due to urban densification. Appropriate agreement and coordination are needed for sustainable streams. This study aims to analyze various opinions through public discussion of residents' proposals through the resident participation cooperation budget. User awareness surveys and expert interviews were conducted on six rivers in Eunpyeong-gu. Through this, stable and sustainable preservation of local and small rivers and appropriate and balanced use measures were proposed.