• Journal of Yeungnam Medical Science
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• 제22권1호
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• pp.13-26
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• 2005

Atrial fibrillation (AF) is the most common cardiac rhythm disturbance, which carries significant cardiovascular morbidity and mortality. The medical treatment for AF is cumbersome and unsatisfactory, which has highlighted the need to develop alternative treatments for AF. The recent discovery that AF is often initiated by atrial ectopic beats has resulted in treatments designed to target the ectopic sources, particularly those within the pulmonary veins. Building on the pioneering work of Cox et al., a recent reported series demonstrated the feasibility of treating patients undergoing cardiac surgery for other structural heart diseases with limited, left-atrial ablation lesion sets using alternative energy sources. As less complex modifications of the Maze procedure have been developed, a number of energy sources have been introduced to create of electrically isolating lesions within the atria. These sources have been used both endocardially in arrest heart procedures as well as epicardially in a beating heart setting. This review summarizes the recent advances in surgery for AF that will aid in the development of an effective, minimally invasive surgical procedure to cure patients with AF.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• 제11B권4호
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• pp.121-128
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• 2001

Numerical schemes for the simulation of the cold gas flow in the SF6 puffer type circuit breaker is presented. The governing equation is axisymmetric compressible Euler Equation and FVM is used to analyze the behavior of flow. The upwind scheme is used to avoid numerical instability and MUSCL is used to obtain high order accuracy. For the efficient calculation, AF-ADI scheme is used. The simulation result shows good agreement with the experimental data.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권12호
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• pp.3275-3295
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• 2012

In this paper, we analyze the performance of an amplify-and-forward (AF) two-way relaying system, where two sources exchange information via the aid of an intermediate relay that is selected among multiple relays according to max-min criterion. We consider a practical scenario, where one source-relay link undergoes Rician fading, and the other source-relay link is subject to Rayleigh fading. To be specific, we derive a tight lower bound for the outage probability. From this lower bound, the asymptotic outage probability and average symbol error rate (SER) expressions are derived to gain insight into the system performance at high signal-to-noise ratio (SNR) region. Furthermore, we investigate the optimal power allocation (PA) with fixed relay location (RL), optimal RL with fixed PA and joint optimization of PA and RL to minimize the outage probability and average SER. The analytical expressions are verified through Monte Carlo simulations, where the positive impact of Rician factor on the system performance is also illustrated. Simulation results also validate the effectiveness of the proposed PA and relay positioning schemes.

• ETRI Journal
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• 제36권4호
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• pp.625-634
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• 2014

This paper studies a dual-hop multiple-access relay network where two independent source nodes transmit information to a common destination node with the aid of multiple single-antenna amplify-and-forward relays. Each relay node is subject to an individual power constraint. We focus on the design of distributed beamforming schemes for the relays to support the transmission rate requirements of the two sources. To this end, we first characterize the achievable rate region for this network via solving a sequence of corner point optimization problems proposed in this paper. We also develop several low-complexity suboptimal schemes in closed form. Two inner bounds of the achievable rate region are theoretically shown to be approximately optimal in two special scenarios. Finally, numerical results demonstrate the effectiveness of our proposed approaches.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권6호
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• pp.1606-1626
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• 2012

This paper investigates the performance of an amplify-and-forward (AF) two-way relaying system with antenna correlation. The system consists of two multiple-antenna sources, which exchange information via the aid of a single-antenna relay. In particular, we derive the exact outage probability expression. Furthermore, we provide a simple, tight closed-form lower bound for the outage probability. Based on the lower bound, we obtain the closed-form asymptotic outage probability and the average symbol error rate expressions at high signal-to-noise ratio (SNR), which reveal the system's diversity order and coding gain with antenna correlation. To investigate the system's throughput performance with antenna correlation, we also derive a closed-form lower bound for the average sum-rate, which is quite tight from medium to high SNR regime. The analytical results readily enable us to obtain insight into the effect of antenna correlation on the system's performance. Extensive Monte Carlo simulations are conducted to verify the analytical results.

• 정보처리학회논문지B
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• 제12B권1호
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• pp.39-46
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• 2005

몰입형 가상현실 시스템에서는 실제로 가상세계가 입체적으로 가시화된다 할지라도 현실에서와 같이 정확한 거리 및 깊이 단서가 제공되지 않기 때문에, 사용자가 가상객체들과 원활한 상호작용을 하는데 많은 불편함이 있다. 본 논문에서는 이 점을 개선하기 위하여 몰입형 가상세계에서 사용자가 효과적으로 시공간지각을 할 수 있도록 지원해 주는 Visual Guider를 제안한다. Visual Guider는 사용자가 가상객체들 간의 상대적 거리 정보를 신속하고 정확하게 파악할 수 있도록 이차원 윈도우 어플리케이션에서 활용되는 눈금자 개념을 도입하여 삼차원 가상공간상에 적용한 것이다. 본 논문에서는 제안 기법을 $CAVE^(TM)-like$ 시스템 상에서 구현된 실험용 가상공간 상에 적용하여 사용자의 위치 이동과 가상객체의 선택 및 조작에 활용한 결과를 보인다.

• 대한치과교정학회지
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• 제35권2호
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• pp.91-105
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• 2005

기존의 2차원적 진단자료는 상의 확대 및 왜곡으로 인해 형태나 크기의 정량적 평가시 부적절한 결과를 야기할 수 있어 안면비대칭의 정확한 진단과 치료계획 수립을 위해서는 3차원영상 진단의 도입이 필요하다. 본 연구는 안면비대칭 진단시 3차원적 분석에 도움이 되는 기준자료를 얻고자 정상교합자를 대상으로 하악골 3차원 영상 계측항목의 평균값과 좌우차이의 정상범주를 알아보기 위하여 시행되었다 뚜렷한 안면비대칭을 보이지 않는 성인 정상교합자 남녀 30명씩 총 80명을 대상으로 두경부 전산화단층사진을 촬영한 후 컴퓨터프로그램을 이용한 각각의 단면 촬영영상 정보를 이용하여 3차원 입체영상을 재구성한 다음, 하악골 비대칭시 좌우차이를 보일 수 있는 계측항목으로 ramus length를 나타내는 5개 condylar neck length를 나타내는 1개, mandibular body length를 나타내는 8개 등 15개의 거리 계측항목과, gonial angle을 나타내는 4개. frontal ramal inclination을 나타내는 2개. lateral ramal inclination을 나타내는 2개 등 8개의 각도계측항목, 총 23개의 계측항목을 설정한 후, 좌측과 우측을 구분하여 컴퓨터 상에서 3차원계측치를 구하고 좌우차이값을 산출하였다. 본 연구결과 얻어진 정상교합자의 하악골 3차원영상 계측항목의 좌우차이값은 안면비대칭 환자의 진단 기준치로 유용하게 사용될 수 있을 것이다.