• Nuclear Engineering and Technology
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• 제47권6호
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• pp.766-775
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• 2015

The integrity assessment of reactor vessel internals should be conducted in the design process to secure the safety of nuclear power plants. Various loads such as self-weight, seismic load, flow-induced load, and preload are applied to the internals. Therefore, the American Society of Mechanical Engineers (ASME) Code, Section III, defines the stress limit for reactor vessel internals. The present study focused on structural response analyses of the upper guide structure upper flange. The distributions of the stress intensity in the flange body were analyzed under various design load cases during normal operation. The allowable stress intensities along the expected sections of stress concentration were derived from the results of the finite element analysis for evaluating the structural integrity of the flange design. Furthermore, seismic analyses of the upper flange were performed to identify dynamic behavior with respect to the seismic and impact input. The mode superposition and full transient methods were used to perform time-history analyses, and the displacement at the lower end of the flange was obtained. The effect of the damping ratio on the response of the flange was also evaluated, and the acceleration was obtained. The results of elastic and seismic analyses in this study will be used as basic information to judge whether a flange design meets the acceptance criteria.

• Nuclear Engineering and Technology
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• 제40권1호
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• pp.77-86
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• 2008

This paper describes the nonlinear analyses of a 1:4 scale model of a prestressed concrete containment vessel (PCCV) using an axisymmetric model and a three-dimensional model. These two models are refined by comparison of the analysis results and with testing results. This paper is especially focused on the analysis of behavior under pressure and the temperature effects revealed using an axisymmetric model. The temperature-dependent degradation properties of concrete and steel are considered. Both geometric and material nonlinearities, including thermal effects, are also addressed in the analyses. The Menetrey and Willam (1995) concrete constitutive model with non-associated flow potential is adopted for this study. This study includes the results of the predicted thermal and mechanical behaviors of the PCCV subject to high temperature loading and internal pressure at the same time. To find the effect of high temperature accident conditions on the ultimate capacity of the liner plate, reinforcement, prestressing tendon and concrete, two kinds of analyses are performed: one for pressure only and the other for pressure with temperature. The results from the test on pressurization, analysis for pressure only, and analyses considering pressure with temperatures are compared with one another. The analysis results show that the temperature directly affects the behavior of the liner plate, but has little impact on the ultimate pressure capacity of the PCCV.

• 대한조선학회논문집
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• 제45권6호
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• pp.726-734
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• 2008

While the structural safety assessment of Cargo Containment System(CCS) in membrane type LNG carriers has to be carried out in consideration of sloshing impact pressure, it is very difficult to figure out its dynamic response behaviors due to its very complex structural arrangements/materials and complicated phenomena of sloshing impact loading. For the development of its original technique, it is necessary to understand the characteristics of dynamic response behavior of CCS structure under sloshing impact pressure. In this study, for the exact understanding of dynamic response behavior of CCS structure in membrane Mark III type LNG carriers under sloshing impact pressure, its wet drop impact response analyses were carried out by using Fluid-Structure Interaction(FSI) analysis technique of LS-DYNA code, and were also validated through a series of wet drop experiments for the enhancement of more accurate shock response analysis technique. It might be thought that the structural response behaviors of impact response analysis, such as impact pressure impulses and resulted strain time histories, generally showed very good agreement with experimental ones with very appropriate use of FSI analysis technique of LS-DYNA code, finite element modeling and material properties of CCS structure, finite element modeling and equation of state(EOS) of fluid domain.

• Journal of Gastric Cancer
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• 제18권3호
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• pp.253-263
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• 2018

Purpose: With increasing life expectancy, the presence of comorbidities has become a major concern in elderly patients who require surgery. However, little is known about the impact of different comorbidities on the outcomes of laparoscopic total gastrectomy (LTG). In this study, we investigated the impact of comorbidities on postoperative complications in patients undergoing LTG for gastric carcinoma. Materials and Methods: We retrospectively reviewed the cases of 303 consecutive patients who underwent LTG for gastric carcinoma between 2005 and 2016. The associations between each comorbidity and postoperative complications were assessed using univariate and multivariate analyses. Results: A total of 189 patients (62.4%) had one or more comorbidities. Hypertension was the most common comorbidity (37.0%), followed by diabetes mellitus (17.8%), chronic viral hepatitis (2.6%), liver cirrhosis (2.6%), and pulmonary (27.1%), ischemic heart (3.3%), and cerebrovascular diseases (2.3%). The overall postoperative morbidity and mortality rates were 20.1% and 1.0%, respectively. Patients with pulmonary disease significantly showed higher complication rates than those without comorbidities (32.9% vs. 14.9%, respectively, P=0.003); patient with other comorbidities showed no significant difference in the incidence of LTG-related complications. During univariate and multivariate analyses, pulmonary disease was found to be an independent predictive factor for postoperative complications (odds ratio, 2.14; 95% confidence interval, 1.03-4.64), along with old age and intraoperative bleeding. Conclusions: Among the various comorbidities investigated, patients with pulmonary disease had a significantly higher risk of postoperative complications after LTG. Proper perioperative care for optimizing pulmonary function may be required for patients with pulmonary disease.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.675-680
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• 2002

Cracking and bulging in welded and internally lined pressure vessels that work in thermal-mechanical cycling service have been well known problems in the petrochemical, power and nuclear industries. However, published literature and industry surveys show that similar problems have been occurring during the last 50 years. A better understanding of the causes of cracking and bulging causes is needed to improve the reliability of these pressure vessels. This study attempts to add information required for increasing the knowledge and fundamental understanding required. Typical examples of this problem are the coke drums in the delayed coking units refinery process. This case was selected for experimental work, field study and results comparison. Delayed coking units are among the refinery units that have higher economical yields. To shut down these units represents a high negative economical impact in refinery operations. Also, the maintenance costs associated with repairs are commonly very high. Cracking and bulging occurrences in the coke drums, most often at the weld areas, characterize the history of the operation of delayed coking units. To design and operate more robust coke drums with fewer problems, an improved metallurgical understanding of the cracking and bulging mechanisms is required. A methodology that is based field experience revision and metallurgical analyses for the screening of the most important variables, and subsequent finite element analyses to verify hypotheses and to rank the variables according to their impact on the coke drum lives has been developed. This indicated approach provides useful information for increasing coke drum reliability. The results of this work not only order the most important variables according to their impact in the life of the vessels, but also permit estimation of the life spans of coke drums. In conclusion, the current work shows that coke drums may fail as a combination of thermal fatigue and other degradation mechanisms such as: corrosion at high and low temperatures, detrimental metallurgical transformations and plastic deformation. It was also found that FEA is a very valuable tool for understanding cracking and bulging mechanisms in these services and for ranking the design, fabrication, operation and maintenance variables that affect coke drum reliability.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제14권5호
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• pp.2101-2121
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• 2020

The rapid growth of instructional videos repositories and their widespread use as a tool to support education have raised the need of studies to assess the quality of those educational resources and their impact on the quality of learning process that depends on them. Khan Academy (KA) repository is one of the prominent educational videos' repositories. It is famous and widely used by different types of learners, students and teachers. To better understand its characteristics and the impact of such repositories on education, we gathered a huge amount of KA data using its API and different web scraping techniques, then we analyzed them. This paper reports the first quantitative and descriptive analysis of Khan Academy repository (KA repository) of open video lessons. First, we described the structure of repository. Then, we demonstrated some analyses highlighting content-based growth and evolution. Those descriptive analyses spotted the main important findings in KA repository. Finally, we focused on users' interactions with video lessons. Those interactions consisted of questions and answers posted on videos. We developed interaction profiles for those videos based on the number of users' interactions. We conducted regression analysis and statistical tests to mine the relation between those profiles and some quality related proposed metrics. The results of analysis showed that all interaction profiles are highly affected by video length and reuse rate in different subjects. We believe that our study demonstrated in this paper provides valuable information in understanding the logic and the learning mechanism inside learning repositories, which can have major impacts on the education field in general, and particularly on the informal learning process and the instructional design process. This study can be considered as one of the first quantitative studies to shed the light on Khan Academy as an open educational resources (OER) repository. The results presented in this paper are crucial in understanding KA videos repository, its characteristics and its impact on education.

• 한국의류학회지
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• 제38권2호
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• pp.251-265
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• 2014

China is the biggest market for the Korean fashion industry. However, China is still difficult in regards to market entry and market success in China despite the geographical proximity. This study investigated the image of Korea and its impact on brand identity, brand attitude and intention to purchase with a focus on Chinese consumers in order to identify the variables of a country's image that affect a consumer's intention to purchase. The results of this survey targeted 214 Chinese consumers who were used for the final analysis. The survey subjects were female consumers in their 20s and 30s, living in metropolitan cities in China. Exploratory factor, reliability and frequency analyses were conducted using SPSS 19.0; in addition, confirmatory factor and path analyses were administered with AMOS 18.0. We identified two general images of Korea (economy and culture), two images of Korean (stylish and friendly) and three Korean fashion-product related images (quality, design and prestige). The results of the structural equation model were as follows. 1) Economy factor exerted significant effect on quality and prestige. 2) Stylish factor exerted a significant effect on all of the Korean fashion product images (quality, design and prestige). Friendly factor exerted positive impact on prestige. 3) All of the Korean fashion product images significantly influenced brand identity. 4) Brand identity exerted a significant effect on brand attitude. Lastly, brand attitude significantly affected intention to purchase.

• 한국재료학회지
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• 제21권11호
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• pp.592-595
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• 2011

It is well known that modified 9Cr-1Mo steel has a low thermal expansion and high thermal conductivity with excellent high temperature properties compared to austenitic stainless steel. For these advantages, the steel is very popular for the boiler tube of thermal power plants. Normalizing is commonly utilized to obtain martensite in this steel, which shows an unusual toughness for martensite. However, some accidents related to this steel have been reported recently, opening the necessity for further study. As a particular behavior of the steel, an abrupt drop of the impact value has been identified upon tempering at 750$^{\circ}C$ for about 1 hour. It is well known that $Fe_3C$ forms during autotempering and turns to $Cr_2C$ at an early stage and then transforms to $Cr_{23}C_6$. In this study, the cause of the abrupt drop of the impact value was investigated with an impact test, microstructural observation, nanodiffraction and phase analyses using instruments such as optical and transmission electron microscopes (TEM) with an extraction carbon replica of the carbides. The analyses revealed that the $M_2C$ that formed when retained for about 1 hour at 750$^{\circ}C$ causes a drastic decrease in the mechanical properties. The sharp drop in mechanical properties, however, disappeared as the $M_2C$ transformed into $M_{23}C_6$ with longer retention.

• 한국융합학회논문지
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• 제10권6호
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• pp.325-335
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• 2019

본 연구는 한국 교사들의 탈진을 완화시키는데 신체활동이 어떠한 영향을 주는지 알아보는데 목적이 있다. 이러한 목적을 규명하기 위해 한국 교사 527명의 자료가 분석에 이용되었다. 자료처리는 탐색적 요인분석, 문항내적일관성분석을 실시하여 탈진설문지(MBI-ES)의 타당도와 신뢰도를 검증하였고, 성별, 학교급, 교직기간 특성에 따른 평균의 차이를 알아보기 위해 독립 t-test, one-way ANOVA를 실시하였다. 그리고 상관분석과 회귀분석을 통해 요인들 간의 미치는 영향을 검증하였다. 분석 결과, 첫째, 성별의 차이는 남교사보다 여교사가, 교직기간은 긴 것보다 짧을수록 탈진의 정도가 높고 신체활동이 낮은 것으로 나타났다. 둘째, 교사들의 중 고강도 신체활동은 탈진 하위요인들과 부적상관이 있는 것으로 나타났다. 셋째, 교사들의 고강도 신체활동은 비인격화 요인에 부적인 영향을 주는 것으로 나타났고, 교사들의 좌식행동은 비인격화 요인에 정적인 영향을 주는 것으로 나타났다.

• 아태비즈니스연구
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• 제13권3호
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• pp.183-208
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• 2022

Purpose - The main purpose of this study is to widely investigate the impact of recent pandemic crises on the synchronization of the world capital markets through 25 stock indices from major developed countries. Design/methodology/approach - This study collects 25 stock indices from major developed countries and the time period is between January 5, 2001 and February 24, 2022. The data sets used in the study include finance.yahoo.com and Investing.com.. The Granger causality analysis, unit-root test, VAR analysis, and forecasting error variance decomposition were hired in order to analyze the data. Findings - First, there are significant inter-relations among 25 countries around recent major pandemic crises(such as SARS, A(H1N1), MERS, and COVID19), which is consistent result with previous literature. Second, COVID19 shows much stronger impact on the world-wide synchronization than other pandemics. Third, the return volatility of each stock market varies, unit root tests show that daily stock index data are unstable while daily stock index returns are stable, and VAR(Vector Auto Regression) analyses presents significant inter-relations among 25 capital markets. Fourth, from the impulse response function analyses, we find that each market affects the other markets for short term periods, about 2~4 days, and no long term effect was not found. Fifth, Granger causality tests show one-side or two-sides synchronization between capital markets and we estimate, through forecasting error variance decomposition method, that the explanatory portions of each capital market on other markets vary from 10 to 80%. Research implications or Originality - The above results all together show that pandemic crises have strong effects on the synchronization of world capital markets and imply that these synchronizations should be carefully considered both in the investment decisions by individual investors and in the financial and economic policies by governments.