• Journal of KIISE:Computer Systems and Theory
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• v.27 no.1
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• pp.89-100
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• 2000

Recently, studies on the mobile computing environments that enable mobile hosts to move while retaining its network connection are in progress. In these mobile computing environments, one of the necessary components is the distributed file system supporting mobile hosts, and there are several issues for the design and implementation of the shared file system. Among these issues, there are problems caused by network traffic on limited bandwidth of wireless media. Also, there are consistency maintenance issues that are caused by update-conflicts on the shared files in the distributed file system. In this paper, we propose TWB(Trickle Write-Back) scheme that utilizes weak connectivity for cache management of mobile clients. This scheme focuses on saving bandwidth, reducing waste of disk space, and reducing risks caused by disconnection. For such goals, this scheme lets mobile clients write back intermediate states periodically or on demand while delaying unnecessary write-backs. Meanwhile, this scheme is based on the existing distributed file system architecture and provides transparency.

• Archives of design research
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• v.20 no.1 s.69
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• pp.111-120
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• 2007

This research proposes contextual space expression as a possibility of solution methods for local and historical issues, the matters that our contemporary architecture has to overcome. When modernistic architecture aimed for anonymous public interests denying the characteristics in historical and spacial contexts, postmodern architecture and regional architecture, etc have been striving to revive discontinued contextual meanings using various historical and environmental elements. While such attempts only borrowed architectural materials by superficially understanding the context, they could not comprehend ceaselessly changing contexts sufficiently. Choosing Jean Nouvel as one of the architects that can explain spatial plan to properly respond to such ever-changing, contemporary contexts, the researcher intended to understand his line of expressional characteristics of his architectural space and analyze his works as examples.

• Journal of Advanced Navigation Technology
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• v.21 no.1
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• pp.12-20
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• 2017

A maritime DGPS in Korea offers pseudo-range correction information and monitors integrity of correction data by using multiple GNSS receivers. The maritime DGPS reference station and integrity monitor service sets alarm threshold value about integrity monitoring parameters for preventing service interruption status. However there is no way to avoid system interruption according to malfunction of backup systems and outside factors. Therefore, in this paper, warning threshold values were proposed for maritime DGPS operator can be counteract in advance. And Markov analysis method was carried out for selection of these warning threshold values.

• Information and Communications Magazine
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• v.28 no.4
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• pp.41-50
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• 2011

미래 전에서는 정보의 중요성이 더욱 부각되고 있으며 정보의 수집 및 전파, 정확한 지휘결심 및 전파, 기동타격체계의 통제 등으로 이어지는 지휘통제의 전 과정을 유기적으로 연결하여, 그 성능을 극대화시키는 것이 네트워크 중심전(NCW: Net-Centric Warfare)의 개념이다. NCW 실현을 위해 개발중인 여러 체계 중 주목 받고 있는 것이 무인기(UAV: Unmanned Aerial Vehicle) 이다. 무인기는 감시정찰, 고정밀 타격, 그리고 전투피해평가 기능 등을 수행하며, 전술적인 상황인식이 가능하게 한다. 무인기가 이러한 임무를 수행하기 위해서는 비행체의 상태정보, 비행체의 조종통제정보, 그리고 임무 탑재체가 획득한 정보의 간단없고 정확한 전달이 요구된다. 이러한 정보를 전송하기 위한 비행체와 지상체간의 제반 통신을 데이터 링크(Data Link)라 하며, NCW 구현에 있어서 가장 핵심이 되는 요소이다. 세계 각국은 영상정보 수집자산으로서 무인기와 데이터링크의 개발에 박차를 가하고 있는 실정이며, 우리 군도 전력화가 계획된 각 제대별 무인기의 통합운용을 위한 영상정보 공용데이터 링크 (MPI-CDL: Multi-Platform Image and Intelligence Commom Data Link)를 개발중에 있으며 지속적인 영상정보 수집자산의 소요증가에 따른 주파수 획득문제와 사업별 독자적인 데이터 링크의 개발을 지양하고 기존체계와의 상호운용 및 단절없는 통신을 보장을 위해 개발과 동시에 국가적 차원에서의 기술구조 표준화가 추진되어야 한다. 이러한 시점에서 본고에서는 먼저 선진국의 (CDL : Commom Data Link) 표준화 동향을 알아보고, 상호운용성과 연동을 위한 한국형 MPI-CDL 기술 표준화방향을 제시하고자 한다.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.10
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• pp.83-98
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• 2007

The handover between different radio access networks, especially where their coverage overlaps, suffers various complications since the different access networks provide different service characteristics. One way to reduce service interruptions and QoS (i.e., bandwidth, throughput, delay) degradations during the inter-technology handover is to reserve the required resource in advance. The resource reservation algorithm should minimize the handover latency and maximize the resource utilization based on the accurate estimation on mobile's location, velocity, movement pattern and service requirements. In this paper, we propose a resource reservation algorithm based on the mobile terminal velocity and the cell selection probability, which maximizes resource utilization ana reduces network overhead. We compare the proposed algorithm with PMS(Predictive Mobility Support) and VCDS(Velocity and Call Duration Support scheme) based on 3-layer network model under various scenarios.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.340-340
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• 2011

자연하천의 안정은 하상경사, 유사이동, 원지반의 상태, 저수로의 깊이, 하도 및 하안의 구조와 하안식생 등에 달려있다. 이 중 하상경사는 가장 중요한 요소로써 하도의 안정을 위해서는 무엇보다도 이를 적절하게 유지하는 방안을 모색하여야 한다(김혜주 등, 2003). 이러한 자연하천의 안정을 위하여 주로 하상유지시설을 설치하는 것이 보편적이다. 이러한 낙차공의 설치는 하천설계기준을 근거로 하상의 안정성 확보라는 설치 목적에 맞게 설계 및 시공이 이루어져 하도의 안정에는 나름대로 효과적이지만 하천환경의 연속성 차단 등 다양한 생태·환경적 폐해가 나타나고 있는 것으로 알려져 있다(김혜주 등, 2003). 이러한 단점을 보완하기 위해 낙차공과 같은 횡단구조물의 본체에 어도를 설치하거나 계단형 또는 경사형 본체를 갖는 구조물이 제안되고 있으나 현재까지 제안된 보완적인 방법들로는 근본적인 생태단절을 해소하기에는 무리가 있다. 따라서 낙차공 등 하천 수공구조물 설치로 인해 야기되는 생태 환경적 문제를 해결하기 위해서는 대상하천에 서식하는 생물에 대한 이해가 우선 이루어져야 하며 이를 바탕으로 설계 및 시공하는 것이 가장 효과적이다. 이를 위해서는 구조물 설치에 따라 변화되는 수리현상에 대한 정확한 분석이 필요하다. 이에 본 연구에서는 국내외에서 제안되고 있는 낙차공 중 통나무를 이용한 낙차공의 평면형태에 따른 하류부 세굴현상을 수리실험을 통해 분석하였다. 본 연구에서는 평면형태(horizontal)에 따른 세굴영향을 파악하고자 평면각을 $70^{\circ}$에서 최대 $180^{\circ}$로 변화시켜 세굴 실험을 수행하였다. 상향 V형만을 고려한 이유는 하향 V형의 경우($\theta$>$180^{\circ}$)에는 낙차공을 월류하는 흐름으로 인해 구조물 하류부 좌 우안측에 세굴이 발생하기 쉽기 때문에 자연하천의 경우 호안측 침식이 발생한 수 있고 또한 실험수로 벽면영향으로 인해 세굴형태가 왜곡될 우려가 있어 하향 형태의 낙차공은 실험대상에서 제외하였다. 낙차공의 평면 형태가 세굴심에 미치는 영향을 검토한 결과, 유입 Froude 수( )에 대해 높은 상관이 있으며 또한 평면각도에 따라 변하는 낙차공의 횡단길이가 낙차공 하류부의 세굴심에 큰 영향을 미치고 있음을 확인할 수 있었고, 세굴길이의 경우, 평면형태에 따른 세굴길이와 세굴심의 비는 낙차공의 평면각도의 증가에 따라 세굴 길이가 짧아짐을 확인할 수 있었다.

• Journal of KIISE:Computer Systems and Theory
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• v.27 no.8
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• pp.730-740
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• 2000

The software rejuvenation method for highly available multiplex systems uses a pro-active fault-tolerant approach to handle system failures. The software rejuvenation prevents failures from occurring, while the previous methods recover from failures after happening. Especially, since the software aging proceeds fast in the software used for the multimedia mobile computing due to the loss of communications or data, the preventive method from failures using software rejuvenation can be used for the multimedia mobile computing. In this paper, according to the operational parameters such as rejuvenation period, rejuvenation time, failure rate and repair rate of the servers, number of running servers, duration of running time, and type of running modes, we calculate steady-state probabilities, downtime, availability, and cost of the multiplex systems using software rejuvenation method. We validate the closed-form solutions of the mathematical model by experiments based on various operational parameters and find that the software rejuvenation method can be adopted as preventive fault-tolerant technique. The failure rate and unstable rate of the servers are essential factors for the decision making of the rejuvenation policies.

• Journal of the Korea Society of Computer and Information
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• v.15 no.6
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• pp.65-72
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• 2010

In ad-hoc network, the technique to efficiently consume the limited amounts of energy is an important issue since the wireless terminal node is operated on batteries as their energy resource. In order to extend the system lifetime, through a balanced energy consumption, we must delay the situation in which a particular terminal node's energy is depleted and results in system disconnection. Also, the link, which has low reliability due to the mobility of the node, should be avoided considering the key element when setting up the route. The proposed CMLR method in this paper enables to increase the efficiency of energy consumption with a new cost function considering the residue energy of node, error rate of link, and transmission energy consumption. This method is extending the network lifetime and increasing the energy efficiency by compromising the value between the minimization of the transmission energy consumption and maximization of the node's lifetime. Through the simulations the proposed CMLR algorithm was verified by showing better performance over the conventional methods in terms of network lifetime and path efficiency.

• Korean Security Journal
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• no.42
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• pp.423-447
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• 2015

This paper gives analyses on the historical origin where features from social punishment and re-socialization in North Korea have been developed. The process of the development largely consists of three periods, that is, the period of nation construction (1945-1950), the period of Korean War (1950-1953), the period of nation reconstruction (1950-1961). This paper provides that features from punishment and re-socialization have been developed during the historical transformation from pre-Korean War to post-Korean War. The 'wartime socialism system' had been established in the course of reconstruction of postwar nation. In the system, North Korean had been embraced into the structure of re-socialization in its production unit and living space.

• Restorative Dentistry and Endodontics
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• v.23 no.1
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• pp.163-174
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• 1998

The purpose of this study is to evaluate the distribution of stress in the root end resected teeth. The finite element method was used to compare stresses along the root and retrograde filling material in seven two-dimensional models of mandibular 2nd premolar. Each model was endodontic treatment and gold crown' restoration. Each model divided with amagam core restoration or gold casting post restoration. Thus each model divided with shape of root end resection, depth of retropreparation and exposure length of root in the bony cavity. The seven models were classified as in the table 1 below. A load of 500N was applied $45^{\circ}$ diagonally on the lingual slope of the buccal cusp. These mode were analyzed with two dimensional finite element methods. The results of this study were as follows : 1. The maximum tensile stress along the inner canal wall was shown on the model 7. 2. When the model 1 was compared with the model 5, the maximum tensile stress along the inner canal wall showed the model 1. 3. Less equivalent stress was shown on the model 6 and more equivalent stress was shown on the model 4. 4. More shear stress was shown on the retrograde filling material of the model 7. 5. The models with increased length of exposed root in the bony cavity demonstrated a gradual increase to the tensile stress in X direction which occurred approximately a boundary between the bone and exposed root in' the bony cavity. 6. The model which had a case of matching the apex of post and a boundary between the bone and exposed root in the bony cavity demonstrated more increase tensile stress in X direction than other models.