• 한국시스템다이내믹스연구
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• 제8권2호
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• pp.115-140
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• 2007

Changes in material use, energy use and emissions profiles of steel industry are the result of complex interrelationships among a multitude of technological and economic drivers. To better understand and guide such changes requires that attention is paid to the time-varying consequences that technology and economic influences have on an industry's choice of inputs and its associated outputs. We briefly review the range of policy issues in our paper and assess the impact that climate-change policies may have on energy use and carbon emissions in Korea steel industry. We then present the models of Korea steel industry's energy and product flow regarding environmental regulations by using system dynamics simulation methodology(SD). Time series data and engineering information are combined to endogenously specify changes in technologies, fuel mix, and production processes within dynamic simulation model. Through a various scenario, ramifications that the convention of climate change would to steel industry is analyzed, and based on the study results, strategies against environment changes is contemplated in various perspectives to contribute to minimize the risks concerning the uncertain future and to be conducive to Korea steel industry's sustainable development.

• Journal of Ecology and Environment
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• 제31권2호
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• pp.89-95
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• 2008

Sensing the approach of a predator is critical to the survival of prey, especially when the prey has no choice but to escape at a precisely timed moment. Escape behavior has been approached from both proximate and ultimate perspectives. On the proximate level, empirical research about electrophysiological mechanisms for detecting predators has focused on vision, an important modality that helps prey to sense approaching danger. Studies of looming-sensitive neurons in locusts are a good example of how the selective sensitivity of nervous systems towards specific targets, especially approaching objects, has been understood and realistically modeled in software and robotic systems. On the ultimate level, general optimality models have provided an evolutionary framework by considering costs and benefits of visually elicited escape responses. A recent paper showed how neural network models can be used to understand the evolution of visually mediated antipredatory behaviors. We discuss this new trend towards integration of these relatively disparate approaches, the proximate and the ultimate perspectives, for understanding of the evolution of behavior of predators and prey. Focusing on one of the best-studied escape pathway models, the Orthopteran LGMD/DCMD pathway, we discuss how ultimate-level optimality modeling can be integrated with proximate-level studies of escape behaviors in animals.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
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• pp.172-180
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• 2011

When it essentially designs and develops the Railway Signal System H/W and S/W, It requires base to build an environment which the safety of the complete system can be certified objectively. It is not rational choice to progress the safety certification of each of the subsystems to ensure reliability from an economic point of view. Furthermore, Even though H/W and S/W already certificated the safety, In case of changing subsystem to comprise relevant system, The safety certification of its parts newly must proceed. This study to solve these problems covers safety H/W platform which is commonly applicable to composition plan at Ground railway signaling systems such as CBTC, ETCS, CBI and safety-based modeling approach with S/W development tools (SCADE) and certificated O/S (Pike) to build the development environment. In addition, When it designs and develops safety S/W, This study explains structure to separate the data section which for logical operations and logical operations itself and provides guideline to support the certification through minimizing changes to the software.

• 디지털융복합연구
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• 제10권6호
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• pp.49-59
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• 2012

본 연구는 왜 인터넷 사용자들이 자신의 개인정보 프라이버시에 무관심한지를 설명하는 것을 목적으로 한다. 이를 위해 Nate.com을 관련 사례로 선정하였다. Nate.com은 최근에 외부 침입에 의한 개인정보 유출사고를 경험하였다. 이 때 Nate.com은 이러한 사실을 사용자들에게 알렸으나 대부분의 사용자들은 Nate.com을 탈퇴하지 않고 여전히 이용하고 있다. 이를 무관심 관점에서 설명하기 위해 질적 그리고 양적 기법을 수행하였다. 우선, 연구설계를 위해 240명의 Nate.com 사용자를 인터뷰하였다. 인터뷰를 통해 나온 결과를 기반으로 연구모형을 수립하고 설문을 구성하였으며, 이를 배포하여 데이터를 수집하였다. 가설 검증은 구조방정식 모형을 통해 수행되었다.

• 한국산업정보학회논문지
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• 제7권3호
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• pp.15-22
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• 2002

소프트웨어의 크기와 복잡성이 증가함에 따라 알고리즘이나 자료구조의 선택보다는 시스템 전체 구조의 선계와 명세가 더욱 중요시되고 있다. 소프트웨어 구조는 시스템 컴포넌트들과 그들의 상호관계를 이해하기 위한 프레임워크로서 제공된다. 또한 소프트웨어 구조는 낮은 비용 높은 생산성 및 일관된 품질을 이루기 위해 재사용 필 수 있다. 본 논문에서는 우리가 개발한 소프트웨어 구조 설계 환경인 Happy Work의 구조와 기능을 설명한다. Happy Work는 두 가지의 주요한 기능을 가진다. 첫째로 Happy Work는 소프트웨어 구조 다이어그램의 모델링을 위한 그래픽 에디터를 제공하고, 둘째로 HWL(Happy Work language)라는 소프트웨어 구조 기술 언어를 제공한다.

• Journal of Electrical Engineering and Technology
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• 제10권2호
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• pp.574-585
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• 2015

This paper aims to improve the performance of conventional direct torque control (DTC) drives proposed by Takahashi by extending the idea for 5-level inverter. Hybrid cascaded H-bridge topology is used to achieve inverter voltage vector composed of 5-level of voltage. Although DTC is very popular for its simplicity but it suffers from some disadvantages like- high torque ripple and uncontrollable switching frequency. To compensate these shortcomings conventional DTC strategy is modified for five levels voltage source inverter (VSI). Multilevel hysteresis controller for both flux and torque is used. Optimal voltage vector selection from precise lookup table utilizing 12 sector, 9 torque level and 4 flux level is proposed to improve DTC performance. These voltage references are produced utilizing a hybrid cascaded H-bridge multilevel inverter, where inverter each phase can be realized using multiple dc source. Fuel cells, car batteries or ultra-capacitor are normally the choice of required dc source. Simulation results shows that the DTC drive performance is considerably improved in terms of lower torque and flux ripple and less THD. These have been experimentally evaluated and compared with the basic DTC developed by Takahashi.

• Advances in concrete construction
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• 제6권3호
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• pp.297-309
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• 2018

The objective of this study was to evaluate the influence of silica fume (SF) on the hydration heat and compressive strength of concrete. Portland cement with w/(c+sf) ratios varying between 0.25 to 0.45 was substituted by 10%, 20% and 30% of SF by mass. A superplasticizer was used to maintain a fluid consistency of the concrete. The heat of hydration was monitored continuously by a semi-adiabatic calorimetric method for 10 days at $20^{\circ}C$. Compressive strengths are tested for each mixture until age of 180 days. The results show that silica fume considerably influences the evolution and the ultimate values of the compressive strengths as well as the hydration heat especially for 10% rate. The w/b ratio has a considerable effect where its decrease modifies compressive strength and hydration heat more than silica fume. The correlation of the obtained results allows deducing of ultimate properties as well as the ages to reach half of their values. The correlation coefficients are close to unity and reflect the judicious choice of these relationships to be used to predict compressive strength and hydration heat.

• The Journal of Asian Finance, Economics and Business
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• 제7권1호
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• pp.217-228
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• 2020

The selection factors of service companies have changed in accordance with intensifying competition in the marine transportation service market and environment changes of transportation services. To explore the important factors of customer choice to marine transportation service, this study empirically examines the influence of these selection factors; service provision area, price competitiveness, corporate image, service expertise, and sales support, on transaction continuity through customers' perceived service value and satisfaction. Based on an online survey with those in the Korean marine transportation industry, this study conducted statistical analyses using structural equation modeling. Based on relevant previous studies, the current study constructed a total of 55 survey questions. Finally, 213 questionnaires were collected. Among the five selection factors, corporate image did not affect perceived service value, and price competitiveness was still the most important factor. However, service expertise and sales support were found to be more important factors than regional factors. In order to maintain transaction continuity, shipping companies should also strive to improve their service quality to their customers. In particular, service quality strategies focused on time and regional factors should develop to strategies with the key factors for the changed business environment.

• 대한의용생체공학회:의공학회지
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• 제27권6호
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• pp.402-408
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• 2006

The choice of suitable hip implant is one of important factors in the total hip arthroplasty (THA). In clinical view point, an improper adaptation of hip implant might induce abnormal stress distribution to the bone, which can shorten the lifespan of replaced hip implant. Currently, interest in the custom-designed hip implants has increased as studies reveal the significance of geometric shape of patient's femur in modeling and designing the implants. In this study, we have developed custom-designed hip implant models with various sizes, and analyzed the stress distribution in the bone and bone cement using the Finite Element Method. It was found that minimizing the gap between implant stem and femoral cavity is crucial to minimize the stress concentration in the bone.

• Smart Structures and Systems
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• 제15권6호
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• pp.1601-1623
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• 2015

Electroactive polymers have attracted considerable attention in recent years due to their sensing and actuating properties which make them a material of choice for a wide range of applications including sensors, biomimetic robots, and biomedical micro devices. This paper presents an effective modeling strategy for nonlinear large deformation (small strains and moderate rotations) dynamic analysis of polymer actuators. Considering that the complicated electro-chemo-mechanical dynamics of these actuators is a drawback for their application in functional devices, establishing a mathematical model which can effectively predict the actuator's dynamic behavior can be of paramount importance. To effectively predict the actuator's dynamic behavior, a comprehensive mathematical model is proposed correlating the input voltage and the output bending displacement of polymer actuators. The proposed model, which is based on the rigid finite element (RFE) method, consists of two parts, namely electrical and mechanical models. The former is comprised of a ladder network of discrete resistive-capacitive components similar to the network used to model transmission lines, while the latter describes the actuator as a system of rigid links connected by spring-damping elements (sdes). Both electrical and mechanical components are validated through experimental results.