• 한국추진공학회지
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• 제10권3호
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• pp.99-108
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• 2006

본 논문은 기존 파이로 부품인 폭발볼트의 기능을 그대로 유지하면서 분리시 발생되는 파편 및 충격파의 악 작용과 파편을 완벽히 제거할 수 있게 형상기억합금(Shape Memory Alloy)을 이용한 분리장치(Fangibolt) 모델의 설계 및 모사에 관한 연구이다. Frangibolt는 기존 폭발볼트에서 사용하는 분리화약을 사용하지 않고 스마트 소재인 형상기억합금의 온도에 따라 변화되는 미세조직에 따른 응력생성을 이용하여 파이로 장치를 분리시키는 Non Pyrotechnic 장치로써, 실제 Frangibolt노치부에 생성되는 응력의 분포 및 분리거동을 해석함으로써 Frangibolt 설계에 필요한 인자를 파악할 수 있었다. 또한 볼트 설계방법의 최적화를 제시함으로써 향후 다른 종류의 SMA을 이용한분리장치 설계 및 해석 모델에 기초자료를 제공할 수 있을 것이다.

• Journal of Korean Neurosurgical Society
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• 제48권6호
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• pp.485-489
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• 2010

Objective : To introduce the frequency and segment analysis of in-stent stenosis for intracranial stent assisted endovascular treatment on complex aneurysms. Methods : A retrospective study was performed in 158 patients who had intracranial complex aneurysms and were treated by endovascular stent application with or without coil embolization. Of these, 102 patients were evaluated with catheter based angiography after 6, 12, and 18 months. Aneurysm location, using stent, time to stenosis, stenosis rate and narrowing segment were analyzed. Results : Among follow-up cerebral angiography done in 102 patients, 8 patients (7.8%) were shown an in-stent stenosis. Two patients have unruptured aneurysm and six patients have ruptured one. Number of Neuroform stents were 7 cases (7.5%) and Enterprise stent in 1 case (11.1%). Six patients demonstrated in-stent stenosis at 6 months after stent application and remaining two patients were shown at 12 months, 18 months, respectively. Conclusion : In-stent stenosis can be confronted after intracranial stent deployment. In our study, no patient showed symptomatic stenosis and there were no patients who required to further treatment except continuing antiplatets medication. In-stent stenosis has been known to be very few when they are placed into the non-pathologic parent artery during the complex aneurysm treatment, but the authors found that it was apt to happen on follow up angiography. Although the related symptom was not seen in our cases, the luminal narrowing at the stented area may result the untoward hemodynamic event in the specific condition.

• 경영과학
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• 제23권1호
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• pp.21-41
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• 2006

Given the growing deployment of mobile offices, we need to understand the fectors which affect their successful use and implementation. We in this paper present a parsimonious model which integrates the IS success model and the TAM. The main feature of the model is that it allows one to explore the role of mobility of mobile office systems in determining the level of system usage and dependence. Although the mobility is the key property of any mobile system, there is little research effort exerted to understand how mobility affects the traditional IS factors such as perceived ease of use and usefulness. In addition to the system usage, this model also uses dependence as the dependent variable. This is expected to provide richer understanding of the study context. We collected survey data from 1,614 field service workers of a major domestic electronic company. They use PDAs to retrieve information regarding the specifics of the customer service requests and to report what has been done for each service job. The results from SEM analysis show that mobility improves the perceived ease of use which then leads the field service workers to depend more on the PDA systems. Interestingly enough, however, the workers' satisfaction does not cause more frequent use of the system.

• 대한전자공학회논문지TC
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• 제47권10호
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• pp.27-35
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• 2010

무선 패킷 망에서 무선 자원과 무선 단말의 전력을 얼마나 효율적으로 사용할 수 있는가 하는 것은 무선 패킷 망 보급을 위한 기본 해결 과제이다. 이에 단말의 전력 소모를 줄이면서 무선 망 용량 (capacity)을 증가시키는 기법으로 전송 파워 조절 기법이 주목받고 있다. 무선 패킷 망에 전송 파워 조절 기법을 적용할 때 전송 파워의 세기에 따라 공평한 전송성능을 보장하지 못하고 기아상태에 이르는 전송 불공평성 문제가 지금까지 깊이 연구되지 않고 있다. 이에 본 연구에서는 전송 파워의 세기에 따른 성능 불공평성을 경쟁자 수의 차이에 의한 불공평한 매체 접근 기회에 있음을 분석을 통해 보이고 불공평성을 해결하기 위한 간단한 물리-맥 (PHY-MAC) 계층 간 접근법을 제안한다.

• ETRI Journal
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• 제40권1호
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• pp.51-60
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• 2018

In Long Term Evolution (LTE) cellular networks, the transmit power control (TPC) mechanism consists of two parts: the open loop (OL) and closed loop. Most cellular networks consider OL/TPC because of its simple implementation and low operation cost. The analysis of OL/TPC parameters is essential for efficient resource management from the cellular operator's viewpoint. In this work, the impact of the OL/TPC parameters is investigated for homogeneous small cells and heterogeneous small-cell/macrocell network environments. A mathematical model is derived to compute the transmit power at the user equipment, the received power at the eNodeB, the interference in the network, and the received signal-to-interference ratio. Using the analytical platform, the effects of the OL/TPC parameters on the system performance in LTE networks are investigated. Numerical results show that, in order to achieve the best performance, it is appropriate to choose ${\alpha}_{small}=1$ and $P_{o-small}=-100dBm$ in a homogenous small-cell network. Further, the selections of ${\alpha}_{small}=1$ and $P_{o-small}=-100dBm$ in the small cells and ${\alpha}_{macro}=0.8$ and $P_{o-macro}=-100dBm$ in the macrocells seem to be suitable for heterogeneous network deployment.

• Nuclear Engineering and Technology
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• 제48권1호
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• pp.87-97
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• 2016

The new generation of nuclear power plants (NPPs) will likely make use of state-of-the-art technologies in many areas of the plant. The analysis, design, and selection of advanced human-system interfaces (HSIs) constitute an important part of power plant engineering. Designers need to consider the new capabilities afforded by these technologies in the context of current regulations and new operational concepts, which is why they need a more rigorous method by which to plan the introduction of advanced HSIs in NPP work areas. Much of current human factors research stops at the user interface and fails to provide a definitive process for integration of end user devices with instrumentation and control and operational concepts. The current lack of a clear definition of HSI technology, including the process for integration, makes characterization and implementation of new and advanced HSIs difficult. This paper describes how new design concepts in the nuclear industry can be analyzed and how HSI technologies associated with new industrial processes might be considered. It also describes a basis for an understanding of human as well as technology characteristics that could be incorporated into a prioritization scheme for technology selection and deployment plans.

• 산업경영시스템학회지
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• 제37권1호
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• pp.68-78
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• 2014

Recently, companies are trying to gain a competitive advantage in the market to meet the voice of customer. For this purpose, QFD has been used as product development technology in many areas to include the customer' requirements. Also, Kano model has been used to understand the customer' requirements for an effective way. Therefore integration of Kano model and QFD can more efficiently reflect the customer' requirements when designing a new service. This paper proposes PI index by taking into account the current satisfaction position of our company and competitors while IR (Improvement Ratio) value was set uniformity. This study suggests a more accurate index to predict potential improvements and calculates the final importance or priority. Through case studies targeted at elevator maintenance companies, we can have a general idea how much to improve in the near future and estimate the final importance of customer requirements.

• Smart Structures and Systems
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• 제12권2호
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• pp.209-233
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• 2013

With an annual growth rate of about 30%, wind energy systems, such as wind turbines, represent one of the fastest growing renewable energy technologies. Continuous structural health monitoring of wind turbines can help improving structural reliability and facilitating optimal decisions with respect to maintenance and operation at minimum associated life-cycle costs. This paper presents an integrated monitoring system that is designed to support structural assessment and life-cycle management of wind turbines. The monitoring system systematically integrates a wide variety of hardware and software modules, including sensors and computer systems for automated data acquisition, data analysis and data archival, a multiagent-based system for self-diagnosis of sensor malfunctions, a model updating and damage detection framework for structural assessment, and a management module for monitoring the structural condition and the operational efficiency of the wind turbine. The monitoring system has been installed on a 500 kW wind turbine located in Germany. Since its initial deployment in 2009, the system automatically collects and processes structural, environmental, and operational wind turbine data. The results demonstrate the potential of the proposed approach not only to ensure continuous safety of the structures, but also to enable cost-efficient maintenance and operation of wind turbines.

• KEPCO Journal on Electric Power and Energy
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• 제2권1호
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• pp.61-69
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• 2016

Understanding load patterns and customer classification is a basic step in analyzing the behavior of electricity consumers. To achieve that, there have been many researches about clustering customers' daily load data. Nowadays, the deployment of advanced metering infrastructure (AMI) and big-data technologies make it easier to study customers' load data. In this paper, we study load clustering from the view point of yearly and daily load pattern. We compare four clustering methods; K-means clustering, hierarchical clustering (average & Ward's method) and DBSCAN (Density-Based Spatial Clustering of Applications with Noise). We also discuss the relationship between clustering results and Korean Standard Industrial Classification that is one of possible labels for customers' load data. We find that hierarchical clustering with Ward's method is suitable for clustering load data and KSIC can be well characterized by daily load pattern, but not quite well by yearly load pattern.

• Journal of Communications and Networks
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• 제14권5호
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• pp.578-587
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• 2012

One of the key elements in the emerging, packet-based long term evolution (LTE) cellular systems is the deployment of multiple femtocells for the improvement of coverage and data rate. However, arbitrary overlaps in the coverage of these femtocells make the handover operation more complex and challenging. As the existing handover strategy of LTE systems considers only carrier to interference plus noise ratio (CINR), it often suffers from resource constraints in the target femtocell, thereby leading to handover failure. In this paper, we propose a new efficient, multi-objective handover solution for LTE cellular systems. The proposed solution considers multiple parameters like signal strength and available bandwidth in the selection of the optimal target cell. This results in a significant increase in the handover success rate, thereby reducing the blocking of handover and new sessions. The overall handover process is modeled and analyzed by a three-dimensional Markov chain. The analytical results for the major performance metrics closely resemble the simulation results. The simulation results show that the proposed multi-objective handover offers considerable improvement in the session blocking rates, session queuing delay, handover latency, and goodput during handover.