• Environmental Engineering Research
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• 제23권1호
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• pp.54-61
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• 2018

Biodiesel production parameters and the impact analysis of the potential emissions from both soybean biodiesel and washing water stored in three different environmental conditions were investigated. The effects of the reaction temperature, methanol/oil mole ratio and catalyst concentration on biodiesel yield were considered. And the results showed optimum biodiesel yield of 99% obtained at $54^{\circ}C$, 7 methanol/oil mole ratio and 0.4 wt/wt % catalyst concentration. The potential emissions from both the biodiesel produced and washing water stored (for six weeks) in refrigerator (${\leq}10^{\circ}C$), vacuum (50 kPa) and direct exposure to atmosphere were identified and quantified. Impact analysis of the emissions involved their categorization into: terrestrial acidification, freshwater eutrophication, human toxicity, terrestrial ecotoxicity, climate change and freshwater ecotoxicity. Freshwater ecotoxicity category had the most pronounced negative impact of the potential emissions with $5.237710^{-2}kg\;1,4-DB\;eq$. emissions in Atmosphere, $4.702610^{-2}kg\;1,4-DB\;eq$. emissions in Refrigerator and $3.966110^{-2}kg\;1,4-DB\;eq$. emissions in Vacuum. Climate change had the least effect of the emissions with $6.214106^{-6}kg\;CO_2\;eq$. in Atmosphere, $3.9310^{-6}kg\;CO_2\;eq$. in Refrigerator and $1.6710^{-6}kg\;CO_2\;eq$. in Vacuum. The study showed that the order of preference of the storage environments of biodiesel is vacuum environment, refrigerated condition and exposure to atmosphere.

• 한국IT서비스학회지
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• 제17권3호
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• pp.117-138
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• 2018

The purpose of this study is to empirically analyze the relationships between the Boundary Spanning Activities (BSA) of project team and system performance in ERP system development projects. We could theoretically classify the BSA in the ERP development projects into five categories on the basis of existing studies on the BSA in the research fields of organization theory, new product development, and information systems development. These five categories are 'Ambassador' activities, 'Task-coordinator' activities, 'Scout' activities, 'Sentry' activities and 'Guard' activities. And the relationship between the implementation level of activities included in each category and the project performance (system usage and users' satisfaction) was hypothesized with respect to five BSA categories. In order to test the hypotheses, we conducted on/offline survey of the participants who were involved in the ERP system development projects, and received 345 valid responses. The unit of analysis was the project team, and the total number of teams that survey participants belonged to were 103 ones. The Structural Equation Model Analysis using the SMART PLS 3.0 was applied to statistically testing the hypotheses. The results showed that 10 hypotheses among 12 hypotheses could be supported. The theoretical implications of this study can be summarized as following; first, redefining and categorizing the BSA (Boundary Spanning Activities) in the ERP system development projects, secondly, deriving measurement indicators of the implementation level for each BSA category and statistically proving the validity and the reliability of them, and finally, suggesting the theoretical background of expanding the management area of ERP systems development projects. Furthermore, the practical implication of this study is that concrete BSA items which are empirically derived can be utilized as effective guidelines for successfully implementing the BSA in the process of managing the ERP system development projects.

• Advances in Computational Design
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• 제2권4호
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• pp.293-311
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• 2017

There are several claimed benefits for the impact of design patterns (DPs) on software quality. However, the association between design patterns and fault-proneness has been a controversial issue. In this work, we evaluate the fault-proneness of design patterns at four levels: the design level, category level, pattern level, and role level. We used five subject systems in our empirical study. As a result, we found that, at the design level, the classes that participate in the design patterns are less fault-prone than the non-participant classes. At the category level, we found that the classes that participate in the behavioral and structural categories are less fault-prone than the non-participant classes. In addition, we found that the classes that participate in the structural design patterns are less fault-prone than the classes that participate in the other categories. At the pattern level, we found that only five patterns show significant associations with fault-proneness: builder, factory method, adapter, composite, and decorator. All of these patterns except for builder show that the classes that participate in each one of them are less fault-prone than the non-participant classes in that pattern. The classes that participate in the builder design pattern were more fault-prone than the non-participant classes and the classes that participate in several patterns: the adapter, the composite, and the decorator design patterns. At the role level, the most significant differences were between the classes that participate in some roles and the non-participant classes. Only three pairs of design pattern roles show significant differences. These roles are concrete-product vs. concrete-creator, adapter vs. adaptee, and adapter vs. client. The results recommend the use of design patterns because they are less fault-prone in general except for the builder design pattern, which should be applied with care and addressed with more test cases.

• 보건행정학회지
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• 제26권2호
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• pp.107-114
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• 2016

Background: Over the last few decades, because hospitals in South Korea also have undergone dramatic changes, Korean hospitals traditionally have provided specialized health care services in the health care market. Inner Herfindahl-Hirschman Index (IHI) measures hospital caseloads based on patient proportions, independent of patient volumes. However, IHI that rely solely on patient proportions might be problematic for larger hospitals that provide a high number of diagnosis categories, as the patient proportions in each category are naturally relatively smaller in such hospitals. Therefore, recently developed novel measure, category medical specialization (CMS) is based on patient volumes as well as patient proportions. Methods: We examine the distribution of hospital specialization score by hospital size and investigate association between each hospital specialization and length of stay per case and hospital cost per case using Korean National Health Insurance Service-cohort sample data from 2002 to 2013. Results: Our results show that IHI show a decreasing trend according to the number of beds and hospital type but CMS show an increasing trend according to the number of beds and hospital type. Further, inpatients admitted at hospitals with higher IHI and CMS had a shorter length of stay per case (IHI: B=-0.104, p<0.0001; CMS: B=-0.044, p=0.001) and inpatients admitted at hospitals with higher IHI and CMS had a shorter hospital cost per case (IHI: B=-0.110, p=0.002; CMS: B=-0.118, p=<0.0001). Conclusion: This study may help hospital policymakers and hospital administrators to understand the effects of hospital specialization strategy on hospital performance under recent changes in the Korean health care environment.

• Journal of Preventive Medicine and Public Health
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• 제53권5호
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• pp.342-352
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• 2020

Objectives: The aim of this retrospective cohort study was to investigate whether non-alcoholic fatty liver disease (NAFLD) was associated with incident bone mineral density (BMD) decrease. Methods: This study included 4536 subjects with normal BMD at baseline. NAFLD was defined as the presence of fatty liver on abdominal ultrasonography without significant alcohol consumption or other causes. Decreased BMD was defined as a diagnosis of osteopenia, osteoporosis, or BMD below the expected range for the patient's age based on dual-energy X-ray absorptiometry. Cox proportional hazards models were used to estimate the hazard ratio of incident BMD decrease in subjects with or without NAFLD. Subgroup analyses were conducted according to the relevant factors. Results: Across 13 354 person-years of total follow-up, decreased BMD was observed in 606 subjects, corresponding to an incidence of 45.4 cases per 1000 person-years (median follow-up duration, 2.1 years). In the model adjusted for age and sex, the hazard ratio was 0.65 (95% confidence interval, 0.51 to 0.82), and statistical significance disappeared after adjustment for body mass index (BMI) and cardiometabolic factors. In the subgroup analyses, NAFLD was associated with a lower risk of incident BMD decrease in females even after adjustment for confounders. The direction of the effect of NAFLD on the risk of BMD decrease changed depending on BMI category and body fat percentage, although the impact was statistically insignificant. Conclusions: NAFLD had a significant protective effect on BMD in females. However, the effects may vary depending on BMI category or body fat percentage.

• 디지털융복합연구
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• 제9권6호
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• pp.103-111
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• 2011

본 연구는 부모-자녀 관계가 청소년들의 인터넷 사용에 미치는 영향을 알아보고자 하였다. 부모 자녀관계를 폭력과 방임에 따라 구분하고 인터넷과다사용은 일상생활 문제, 계획한 일을 실행못함, 과다사용, 타인과의 갈등관계 등을 포함하여 일반군, 잠재적위험군, 고위험군으로 구분하였다. 연구 결과, 폭력적이고 방임적인 부모관계에서 잠재적 위험군, 고위험청소년이 높게 나타났고 이는 부모 자녀관계가 청소년들의 인터넷 사용에 영향이 있음을 시사한다. 청소년들의 인터넷사용을 줄이고 중독으로 진행되지 않게 하기 위해서는 부모의 역할이 중요하며, 청소년들의 발달단계를 세심하게 이해해야 한다. 또한 인터넷에 몰입하는 청소년들에게 여가문화를 즐길 수 있는 놀이프로그램, 체험프로그램의 개발과 보급이 요구된다. 또한 인터넷 중독 전문인력 양성과 지원으로 문제가 발생한 청소년들에게 일회성이 아닌 지속적인 상담과 치료가 이루어져야 할 것이다.

• 한국철도학회논문집
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• 제16권2호
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• pp.144-150
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• 2013

본 논문은 서울시 우이-신설 경전철의 출입문 사양 결정을 위한 승하차 시간 예측 모의실험 내용과 실험 데이터 분석결과를 제시한다. 우이-신설 경전철과 유사한 차량(김해 경전철 차량) 및 운영조건을 설정하여 승하차 시간을 측정하는 모의실험을 반복적으로 실시한다. 실험계획은 승하차 인원의 시나리오에 따라 4가지로 구성하였으며, 총 39회의 모의실험을 실시하였다. 이 실험결과를 활용하여 우이-신설 경전철의 출입문 폭과 수량에 대한 차량설계 방안의 적절성 검증이 가능하였다. 실험결과에 대한 통계적 분석으로 승하차 인원의 변화에 따른 승하차 시간 분석을 실시하였다. 실험계획에서 설정된 시나리오를 승하차 인원의 규모에 따라 다시 3가지 수준으로 분류하고, 수준별 승하차 시간의 평균과 분산을 조사하였다. 다음 승차, 하차 및 재차 인원의 구성에 따른 일원배치 분산분석(One-Way ANOVA)을 실시하여 각각의 구성이 승하차 시간에 미치는 영향을 분석하였다. 본 논문에서 제시된 실험결과 및 분석결과들은 장래 도시형 경전철 차량의 출입문 설계 관련 업무에 활용될 수 있을 것으로 판단된다.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2010년도 춘계학술대회
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• pp.702-704
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• 2010

무선 LAN(Local Area Network) 환경에서 QoS를 지원하기 위해 IEEE 802.11 Working Group은 IEEE 802.11e를 표준화하였다. IEEE 802.11e EDCA는 우선순위가 높은 트래픽의 채널 접근 기회를 확률적으로 높임으로써 QoS를 지원한다. 이는 우선순위가 높은 트래픽이 우선순위가 낮은 트래픽에 비해 채널 접근을 반드시 먼저 하는 것이 아니다. 따라서 모든 트래픽이 같은 채널, 같은 routing path를 가진다면, 우선순위가 낮은 트래픽은 우선순위가 높은 트래픽의 성능에 지속적인 영향을 미친다. 결과적으로 EDCA는 음성이나 비디오와 같은 멀티미디어 응용에 QoS를 보장하기에 무리가 따른다. 본 논문에서는 이러한 문제점을 해결하기 위해 Multi-Interface를 이용한 Multi-Path Routing Algorithm을 제안한다. 각 Interface 마다 IEEE 802.11e EDCA에서 사용하는 Access Category별로 각각의 Routing Path를 다르게 함으로써 높은 우선순위의 트래픽에 QoS를 보장한다.

• 한국항공운항학회지
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• 제29권3호
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• pp.34-43
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• 2021

Wake turbulence generated by the lead aircraft has a significant impact on the following aircraft and it is has been considered a key factor to consider whenin determining the longitudinal separation between the aircraft. ICAO classifies aircraft into four wake turbulence categories based on the maximum takeoff weight and provides the longitudinal separation minima for each category. Due to richer measured data and better understanding of physical processes, it is raised that classifying aircraft with only four wake turbulence grades is imprecise and leads to over-separation in many instances. In this regards, much research on a new method of classifying Wake Turbulence Category(Re-CAT) has been done by EURO-CONTROL, FAA, and ICAO. The main purpose of this study is to conduct a comparative analysis of the existing wake turbulence separation standards with Re-CAT in terms of departure capacity and the resulting benefits of Re-CAT using the data from the Incheon International Airport. The results show that EUROCONTROL and new ICAO standards have the greater effect on reducing wake turbulence separation, compared to the FAA RE-CAT standards. It is also concluded that Re-CAT presents different results of wake turbulence separation depending on the flight characteristics of each airport.

• 항공우주시스템공학회지
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• 제16권3호
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• pp.52-62
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• 2022

특정범주 무인항공기 운용의 위험평가를 위해서 개발된 SORA 방법론에서는 지상 및 공중위험 등급을 결정하고 해당 위험도에 대한 특정보증 무결성 수준을 나타내는 SAIL이 할당되어 제안된 운용에 대한 운용 안전도 목표를 적절한 강건도 수준으로 입증해야 한다. 인명의 수송은 제외하는 특정범주 무인항공기 운용의 특성상 지상의 인명이 가장 먼저 고려되어야 하는 위험의 대상이며, 여기서 평가된 지상위험도는 공중위험도와 함께 SAIL의 할당에서도 중요한 역할을 한다. 위험도는 초기에 결정된 등급에 세 가지 종류의 완화수단이 적용되는 것으로 등급이 경감되어 최종 등급이 결정된다. 본 논문에서는 무인항공기의 특정범주 운용에 대한 위험평가 중에서 지상위험 등급의 결정과 완화수단의 적용을 통한 등급의 감소 및 최종 위험 등급에 따른 SAIL과 OSO에 미치는 영향에 대해서 분석하였다.