• Nuclear Engineering and Technology
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• 제51권8호
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• pp.1871-1885
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• 2019

The deterministic MOC code STREAM of the Computational Reactor Physics and Experiment (CORE) laboratory of Ulsan National Institute of Science and Technology (UNIST), was initially designed for the calculation of pressurized water reactor two- and three-dimensional assemblies and cores. Since fast reactors play an important role in the generation-IV concept, it was decided that the code should be upgraded for the analysis of fast neutron spectrum reactors. This paper presents a coupled code - TULIP/STREAM, developed for the fast reactor assembly and core calculations. The TULIP code produces self-shielded multi-group cross-sections using a one-dimensional cylindrical model. The generated cross-section library is used in the STREAM code which solves eigenvalue problems for a two-dimensional assembly and a multi-assembly whole reactor core. Multiplication factors and steady-state power distributions were compared with the reference solutions obtained by the continuous energy Monte-Carlo code MCS. With the developed code, a sensitivity study of the number of energy groups, the order of anisotropic P_N scattering, and the multi-group cross-section generation model was performed on the k_eff and power distribution. The 2D core simulation calculations show that the TULIP/STREAM code gives a k_eff error smaller than 200 pcm and the root mean square errors of the pin-wise power distributions within 2%.

• Restorative Dentistry and Endodontics
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• 제42권3호
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• pp.216-223
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• 2017

Objectives: The aim of this study was to compare the mechanical properties of various nickel-titanium (NiTi) files with similar tapers and cross-sectional areas depending on whether they were surface-treated. Materials and Methods: Three NiTi file systems with a similar convex triangular cross-section and the same ISO #25 tip size were selected for this study: G6 (G6), ProTaper Universal (PTU), and Dia-PT (DPT). To test torsional resistance, 5 mm of the straightened file's tip was fixed between polycarbonate blocks (n = 15/group) and continuous clockwise rotation until fracture was conducted using a customized device. To evaluate cyclic fatigue resistance, files were rotated in an artificial curved canal until fracture in a dynamic mode (n = 15/group). The torsional data were analyzed using 1-way analysis of variance and the Tukey post-hoc comparison test, while the cyclic fatigue data were analyzed using the Mann-Whitney U test at a significance level of 95%. Results: PTU showed significantly greater toughness, followed by DPT and G6 (p < 0.05). G6 showed the lowest resistance in ultimate torsional strength, while it showed a higher fracture angle than the other files (p < 0.05). In the cyclic fatigue test, DPT showed a significantly higher number of cycles to failure than PTU or G6 (p < 0.05). Conclusions: Within the limitations of this study, it can be concluded that the torsional resistance of NiTi files was affected by the cross-sectional area, while the cyclic fatigue resistance of NiTi files was influenced by the surface treatment.

• 한국석유지질학회지
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• 제4권1_2호
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• pp.12-19
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• 1996

백악기 의성소분지 북동부 하양층군 (일직층, 후평동층, 점곡층)에서 관찰된 방향성 퇴적구조는 하도구조, 곡상사층리, 판상사층리, 사엽층리 및 유수연흔 등이다. 이들 퇴적구조들은 주로 세립사암으로부터 역질의 극조립사암에 발달한다. 대소규모의 하도구조는 모든 층에서 ,하도구조와 곡상사층리는 일직층 (충적선상지 환경)에서 , 판상사층리 , 판상사엽층리 , 유수연흔은 후평동층 (범람원 환경)과 점곡층 (호수변 환경) 하부에서 자주 관찰된다. 연구지역에서 측정한 4깨의 방향성 퇴적구조들의 벡타평균 방향은 $290^{\circ}C$며 표준편차는 $\pm68$이다. 주된 고수류의 흐름은 서북서 방향을 지시하며. 퇴적물의 기원지는 연구지역으로 부터 동남동 방향의 어느 곳에 있었음을 시사한다

• Tribology and Lubricants
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• 제37권6호
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• pp.224-231
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• 2021

Recently, the waterproofing performance of high-voltage connectors in automotive vehicles has attracted increased interest. In this study, an optimal cross-sectional shape was derived to obtain uniform contact pressure and strain by considering stress relaxation problems caused by initial tension when mounting a seal. A high strain of 52.1 was distributed in the round region, owing to excessive initial tension. The finite element method (FEM) analysis indicated that the strain corresponding to the optimal initial tensile was 11. We adopted six design factors to optimize the seal cross-section and three factors as the main design factors. An orthogonal arrangement table was prepared using Minitab. FEM analyses of 16 study models were conducted to determine the optimized model. The contact pressure of the optimization model is the most evenly distributed while satisfying the waterproof performance of 0.47 MPa. Compared to the initial model, the difference in strain decreases from 35.5% to 19.6%. Finally, the derived cross-sectional shape can reduce the strain of the round region by 33.8% and the differences in the contact pressure at the upper and lower surfaces by 42% and 76%, respectively.

• 산업융합연구
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• 제20권5호
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• pp.21-28
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• 2022

본 연구는 기존의 연구들과 달리 지자체장의 이념적 성향이 사회복지예산에 미치는 영향을 종적 연구로 살펴보았다. 이러한 연구는 지방자치제가 실시된 이후로 보수의 아성인 구미시에서 진보성향의 단체장이 당선됨으로써 가능하게 된 것이다. 따라서 본 연구에서는 경북 구미시의 12년 이상의 실제 사례를 가지고 구미시 지자체장의 정치적 이념성향의 변화과정과 연도별 사회복지예산을 나열하고 시계열분석을 실시하였다. 분석결과 첫째, 횡단면 분석과 마찬가지로 종단면 연구에서도 지자체장의 정치적 이념성향에 따른 사회복지예산의 증가율변화는 의미 있는 차이를 보였다. 둘째, 기존의 횡단면 분석결과와 같이 선거가 있기 전 해에 사회복지예산의 증가율이 높게 나타났다. 셋째, 두 번째와 같은 증가율의 변화는 한 사람의 3선이 종료되는 해에는 나타나지 않았다. 지금까지의 지자체장(지방의회 포함)의 정치적 이념성향과 사회복지예산의 관계에 관한 모든 연구들은 횡단면적으로 이루어져 왔다. 그러나 본 연구는 최초의 종단면 분석결과라는 측면에서 시사점이 매우 크다고 할 수 있다.

• Investigative Magnetic Resonance Imaging
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• 제26권1호
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• pp.10-19
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• 2022

Purpose: To evaluate whether the added value of contrast leakage information from dynamic susceptibility contrast magnetic resonance imaging (DSC MRI) is a better prognostic imaging biomarker than the cerebral blood volume (CBV) value in distinguishing true progression from pseudoprogression in glioblastoma patients. Materials and Methods: Forty-nine glioblastoma patients who had undergone MRI after concurrent chemoradiotherapy with temozolomide were enrolled in this retrospective study. Twenty features were extracted from the normalized relative CBV (nCBV) and extraction fraction (EF) map of the contrast-enhancing region in each patient. After univariable analysis, we used multivariable stepwise logistic regression analysis to identify significant predictors for differentiating between pseudoprogression and true progression. Receiver operating characteristic (ROC) analysis was employed to determine the best cutoff values for the nCBV and EF features. Finally, leave-one-out cross-validation was used to validate the best predictor in differentiating between true progression and pseudoprogression. Results: Multivariable stepwise logistic regression analysis showed that MGMT (O⁶-methylguanine-DNA methyltransferase) and EF max were independent differentiating variables (P = 0.004 and P = 0.02, respectively). ROC analysis yielded the best cutoff value of 95.75 for the EF max value for differentiating the two groups (sensitivity, 61%; specificity, 84.6%; AUC, 0.681 ± 0.08; 95% CI, 0.524-0.837; P = 0.03). In the leave-one-out cross-validation of the EF max value, the cross-validated values for predicting true progression and pseudoprogression accuracies were 69.4% and 71.4%, respectively. Conclusion: We demonstrated that contrast leakage information parameter from DSC MRI showed significance in differentiating true progression from pseudoprogression in glioblastoma patients.

• 한국안전학회지
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• 제39권1호
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• pp.104-113
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• 2024

Unlike in general manufacturing process, safety management in laboratory-based research area is complicated because the latter generally involves trying untested methods or handling unusual substances in small amounts. Laboratory accidents in South Korea have recently shown an increasing trend. Unfortunately, statistics on such accidents are not officially published by any domestic public agencies. In this study, multivariate analysis was performed on the relationships between variables to develop effective strategies for preventing laboratory accidents. A Cross-Tabulation Analysis of accident-related factors in 179 accident cases revealed that the laboratory type, accident type, and unsafe-act type are all statistically significant, whereas the unsafe condition and management factors differ with the statistical criteria. Furthermore, the results of a Multiple-Correspondence Analysis showed that accidents can be divided largely into three groups having different accident causes and injury types; this confirms the necessity of different strategies to prevent accidents of each type. The findings also reveal differences between the distribution of accident types mentioned in the accident case collection books and actual reported cases. This suggests that an official statistical system administered by a public institution would be necessary for effective prevention of laboratory accidents.

• Journal of Information Technology Applications and Management
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• 제11권1호
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• pp.83-100
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• 2004

Understanding characteristics of Internet businesses from a cross-cultural perspective could offer valuable insights on developing business strategies and policies. This work is concerned with revealing divergence and convergence of Internet businesses in their financial performance, given organizational conditions and cultural context. For this, we studied the association between static organizational attributes (core activity, origination, firm age, and industry type) and a firms financial performance (gross revenue and net income). Relevant data was gathered from representative Internet firms in Korea and U.S. Data analysis indicated that, besides industry type, overall connection between selected organizational variables and financial performance was weak. Cross-national comparison showed that Korean firms financial performance was comparable to U.S firms during the period of economic turbulence. A noticeable difference was that Korean Internet firms and their business models were more service-oriented than U.S. counterparts.

• 무역학회지
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• 제45권1호
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• pp.13-29
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• 2020

With the development of the Internet environment, cross-border crowdfunding has emerged as a novel method to attract foreign investors online. Focusing on 324 South Korea-based crowdfunding projects from Kickstarter, which is a representative cross-border crowdfunding platform, this study explores the trends of South Korea-based funding projects and examines the effects of key determinants on crowdfunding outcomes. Regarding the characteristics of crowdfunding projects, analysis results show that the appropriate goal amount and funding period, sufficient updates of project status, and active communication is critical for success. Additionally, from the perspective of project creators, this research finds that creators need to pay greater attention to writing their detailed biographies. Finally, examining the characteristics of project backers, this study shows that attracting project backers from various countries would be desirable rather than focusing on Korean sponsors from the start.

• 한국환경과학회지
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• 제22권8호
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• pp.953-963
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• 2013

Reliable long-term streamflow forecasting is invaluable for water resource planning and management which allocates water supply according to the demand of water users. Forecasting of seasonal inflow to Andong dam is performed and assessed using statistical methods based on hydrometeorological data. Predictors which is used to forecast seasonal inflow to Andong dam are selected from southern oscillation index, sea surface temperature, and 500 hPa geopotential height data in northern hemisphere. Predictors are selected by the following procedure. Primary predictors sets are obtained, and then final predictors are determined from the sets. The primary predictor sets for each season are identified using cross correlation and mutual information. The final predictors are identified using partial cross correlation and partial mutual information. In each season, there are three selected predictors. The values are determined using bootstrapping technique considering a specific significance level for predictor selection. Seasonal inflow forecasting is performed by multiple linear regression analysis using the selected predictors for each season, and the results of forecast using cross validation are assessed. Multiple linear regression analysis is performed using SAS. The results of multiple linear regression analysis are assessed by mean squared error and mean absolute error. And contingency table is established and assessed by Heidke skill score. The assessment reveals that the forecasts by multiple linear regression analysis are better than the reference forecasts.