• Tribology and Lubricants
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• 제21권1호
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• pp.33-38
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• 2005

Fretting is the oscillatory motion with very small amplitudes, which usually occurs between two solid surfaces in contact. Fretting wear is the removal of material from contacting surfaces through fretting action. Fretting wear of steam generator tubes in nuclear power plant becomes a serious problem in recent years. The materials for the tubes usually are Inconel 690 (I-690) and Inconel 600 (I-600). In this paper, fretting wear tests for I-690 and I-600 were performed under various applied loads in water at room temperature. Results showed that the fretting wear loss of I-690 and I-600 tubes was largely influenced by stick-slip. The fretting wear mechanisms were the abrasive wear in slip regime and the delamination wear in stick regime. Also, I-690 had somewhat better wear resistance than I-600.

• Journal of Computational Design and Engineering
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• 제3권1호
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• pp.63-70
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• 2016

Deep drawing is a forming process in which a blank of sheet metal is radially drawn into a forming die by the mechanical action of a punch and converted to required shape. Deep drawing involves complex material flow conditions and force distributions. Radial drawing stresses and tangential compressive stresses are induced in flange region due to the material retention property. These compressive stresses result in wrinkling phenomenon in flange region. Normally blank holder is applied for restricting wrinkles. Tensile stresses in radial direction initiate thinning in the wall region of cup. The thinning results into cracking or fracture. The finite element method is widely applied worldwide to simulate the deep drawing process. For real-life simulations of deep drawing process an accurate numerical model, as well as an accurate description of material behavior and contact conditions, is necessary. The finite element method is a powerful tool to predict material thinning deformations before prototypes are made. The proposed innovative methodology combines two techniques for prediction and optimization of thinning in automotive sealing cover. Taguchi design of experiments and analysis of variance has been applied to analyze the influencing process parameters on Thinning. Mathematical relations have been developed to correlate input process parameters and Thinning. Optimization problem has been formulated for thinning and Genetic Algorithm has been applied for optimization. Experimental validation of results proves the applicability of newly proposed approach. The optimized component when manufactured is observed to be safe, no thinning or fracture is observed.

• Steel and Composite Structures
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• 제23권2호
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• pp.173-186
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• 2017

Conceptual configuration and seismic performance of high-rise steel frame-brace structure are studied. First, the topology optimization problem of minimum volume based on truss-like material model under earthquake action is presented, which is solved by full-stress method. Further, conceptual configurations of 20-storey and 40-storey steel frame-brace structure are formed. Next, the 40-storeystructure model is developed in Opensees. Two common configurations are utilized for comparison. Last, seismic performance of 40-storey structure is derived using nonlinear static analysis and nonlinear dynamic analysis. Results indicate that structural lateral stiffness and maximum roof displacement can be improved using brace. Meanwhile seismic damage can also be decreased. Moreover, frame-brace structure using topology optimization is most favorable to enhance lateral stiffness and mitigate seismic damage. Thus, topology optimization is an available way to form initial conceptual configuration in high-rise steel frame-brace structure.

• Journal of Power Electronics
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• 제13권4호
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• pp.569-583
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• 2013

In this study, the simultaneous use of a multi-level converter (MLC) as a DC-motor drive and as an active battery cell balancer is investigated. MLCs allow each battery cell in a battery pack to be independently switched on and off, thereby enabling the potential non-uniform use of battery cells. By exploiting this property and the brake regeneration phases in the drive cycle, MLCs can balance both the state of charge (SoC) and temperature differences between cells, which are two known causes of battery wear, even without reciprocating the coolant flow inside the pack. The optimal control policy (OP) that considers both battery pack temperature and SoC dynamics is studied in detail based on the assumption that information on the state of each cell, the schedule of reciprocating air flow and the future driving profile are perfectly known. Results show that OP provides significant reductions in temperature and in SoC deviations compared with the uniform use of all cells even with uni-directional coolant flow. Thus, reciprocating coolant flow is a redundant function for a MLC-based cell balancer. A specific contribution of this paper is the derivation of a state-space electro-thermal model of a battery submodule for both uni-directional and reciprocating coolant flows under the switching action of MLC, resulting in OP being derived by the solution of a convex optimization problem.

• 대한안전경영과학회지
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• 제17권4호
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• pp.23-33
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• 2015

Recently, the Ministry of Employment and Labor Management is a trend to strengthen all men death rate than the accident rate. Points reduction in the accident rate change orders related to credit rating score to +2 points in his plans as part of +1 point. In addition, according to the fancy linger RISK treatment in the event of a disaster site and fiction treatment to achieve accident-free during processing the scene interspersed with equity issues have been raised. In general disaster for the problem in the first two cases occurs when abnormal process according to the disaster site manager positions dismissal policy, each division headquarters itself, interspersed disasters performance compared to processing in accordance with the refrain, processing expenses in accordance with the composition of untreated industrial accident, costs and burdens partners FTC, there is a possibility that the issues raised, such as the Ministry of Employment and Labor. In response to domestic social practices focused on the construction site practices and prevention measures should be evaluated with respect to what.

• 한국문헌정보학회지
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• 제40권4호
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• pp.21-31
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• 2006

우리나라의 도서관들은 21세기에 들어서 역동적인 변화를 추구하였는데 그 이유 중의 하나는 도서관관련 시민단체들이 꾸준히 시민의 입장에서 도서관 문제를 바라보고, 문제점을 도출해서 규명하구 이를 널리 사회에 전달하고 해결책에 대한 소통구조를 활성화 시켰기 때문이다. 이에 본 연구는 각각 학교도서관과 공공도서관 분야에서 우리나라의 대표적인 시민단체하고 할 수 있는 '학교도서관살리기국민연대'와 '책읽는사회만들기국민운동'의 활동을 분석하였다. 즉, 이들 단체의 역사, 활동 그리고 학교도서관과 공공도서관을 발전시키기 위해 정부와 어떻게 협력해 왔는지를 살펴보았다. 이러한 분석을 통하여 학교도서관과 공공도서관의 지속적인 발전 방안을 모색해 보고자 하였다.

• 대한수학교육학회지:수학교육학연구
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• 제18권2호
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• pp.157-177
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• 2008

이 연구는 2006년 수정 고시된 수학 교육과정에 따라 초등학교 수학 교과서를 개발하는 과정, 그 과정에서 제기된 주된 논점과 그 해결 과정을 2학년 길이재기 단원에 한하여 제시하는 것에 목표를 둔다. 수학 교과서를 개발하기 위해서는 달라진 교육과정을 반영하고, 관련 이론을 점검하여 연결하며, 교육 현장의 특수성을 반영하고, 학습자의 특성을 고려하는 등 매우 복잡한 과정을 겪어야 한다. 그러므로 어떤 단원, 어떤 과제 하나도 단번에 만들어지는 것이 아니라 길고 짧은 여정을 가진다고 할 수 있다. 교과서는 수업의 방향과 질을 결정하는 매우 중요한 요소인 만큼 개발 과정에서의 논의를 지속적으로 누적하고 개선점을 찾아가는 노력이 필요하다. 이 연구는 실험본을 개발하는 과정까지 다루고 있으며, 실험본의 적용 결과 분석과 개선은 후속 연구에서 시도할 예정이다.

• 대한의생명과학회지
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• 제27권4호
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• pp.270-276
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• 2021

Physiological agents trigger a signaling process called "inside-out signaling" and activated platelets promote adhesion, granule release, and conformational changes of glycoprotein IIb/IIIa (αIIb/β₃). Activated αIIb/β₃ interacts with fibrinogen and initiates a second signaling step called "external signaling". These two signaling pathways can cause hemostasis or thrombosis, and thrombosis is a possible medical problem in arterial and venous vessels, and platelet-mediated thrombosis is a major cause of cardiovascular disease (CVD). Therefore, modulating platelet activity is important for platelet-mediated thrombosis and cardiovascular disease. Esculetin is a coumarin-based physiologically active 6,7-dihydroxy derivative known to have pharmacological activity against obesity, diabetes, renal failure and CVD. Although some studies have confirmed the effects of esculetin in human platelet activation and experimental mouse models, it is not clear how esculetin has antiplatelet and antithrombotic effects. We confirmed the effect and mechanism of action of escultein on human platelets induced by collagen. As a result, esculetin decreased Ca²⁺ recruitment through upregulation of inositol 1, 4, 5-triphosphate receptor. In addition, esculetin upregulates cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP)-dependent pathways and inhibits fibrinogen binding and thrombus contraction. Our results demonstrate the antiplatelet effect and antithrombotic effect of esculetin in human platelets. Therefore, we suggest that esculetin could be a potential phytochemical for the prevention of thrombus-mediated CVD.

• 한국지능시스템학회논문지
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• 제24권3호
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• pp.245-250
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• 2014

중독은 크게 매개체 자체가 중독성을 가진 매개성 중독과 매개체 자체가 중독성을 가진 것이 아니라 예민한 개인과 잠재된 어떤 행동과 결합하여 중독을 유발하는 유발성 중독으로 나눌 수 있다. 매개성 중독은 약물 중독, 알코올 중독과 주로 화학물질의 직접 적인 원인이 되어 중독현상을 일으킨다. 유발성 중독은 쇼핑 중독, 일 중독, 게임 중독, 인터넷 중독, TV중독, 도박 중독 등의 사이버 중독이 있다. 유발성 중독은 개인의 감수성의 문제로서 개인에 따른 편차가 존재한다. 본 논문에서는 전기 시스템의 R-L-C 직렬 회로와 기계 시스템의 Spring-Damper-Mass를 이용하여 등가적으로 동일한 2차원의 중독 모델을 제안한다. 제안한 중독 모델에 비선형 항을 추가하여 Duffing을 구성한 후 파라미터 변화에 의해 주기운동과 카오스 운동을 시계열과 위상공간으로 나타내었다. 또한 파라미터 중 통제계수의 변화에 의해 주기 운동은 중독 되기 전의 상태를 카오스 운동은 중독된 상태임을 확인하였다.

• Steel and Composite Structures
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• 제47권2호
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• pp.253-267
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• 2023

The bearing capacities resisted by the two-bay beams of multi-story planar frames with unequal spans under column removal scenarios differ considerably owing to the asymmetric stress on the left and right beams connected to the failed column and cause the potential for beams with larger span-to-depth ratios to be unable to exert effectively, which is disadvantageous for resisting the vertical load in unequal-span frame structures. To address this problem, the structural measure of adding braces to the weak bays of multi-story unequal-span frames was proposed, with the objective of achieving a coordinated stress state in two-bay beams with unequal spans, thereby improving the collapse resistance of unequal-span frame structures. Before conducting the numerical simulation, the modeling methods were verified by previous experimental results of two multi-story planar frames with and without steel braces. Thereafter, the effects of the tensile and compressive braces on the collapse behavior of the frame structures were elucidated. Then, based on the mechanical action laws of the braces throughout the collapse process, a detailed design method for improving the collapse resistance of unequal-span frame structures was proposed. Finally, the proposed design method was verified by using sufficient example models, and the results demonstrated that the design method has good application prospects and high practical value.