• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.3B
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• pp.202-211
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• 2002

Because wireless links are subject to disturbances and failures, it is important to support disconnected operations in mobile computing. Many schemes have been proposed to support the efficient disconnected operations. In this paper, we analyze and measure the computation time including disconnected operations to evaluate the performance of mobile computing on error prone wireless links. Mobile computation consists of three states: data hoarding, disconnected operation, and block states. We estimate the computation time using various parameters; error rate and recovery rate of wireless link, hoarding overhead, logging overhead, and reintegration overhead, etc. We can choose efficient strategies for disconnected operations and predict the performance using the results of this analysis.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1998.05a
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• pp.144-149
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• 1998

컴퓨터 하드웨어 기술의 발달과 무선 통신 기술의 발달로 이제는 이동성을 제공하는 Mobile Computing이 각광을 받고 있다. 그러나 이와 같은 이동 단말기의 하드웨어적인 제약점과 무선 통신의 근본적인 제약점으로 인하여 아직까지 유선통신에서 제공하는 신뢰성 있고 고속의 네트워크 환경을 지원하지 못하고 있다. 이동 단말기들은 이동성을 보장하기 위하여 작고 가볍게 만들어야 한다. 이렇게 만들기 위해서는 배터리를 사용하고 적은 양의 디스크를 사용하게 된다. 이는 컴퓨터가 사용 가능한 자원 즉, CPU, Memory, Disk등이 고정 컴퓨터에 비해 빈약해지고 배터리의 사용으로 인한 갑작스러운 전원 공급의 중단으로 인한 하드웨어적인 신뢰성과 무선의 특성으로 인한 데이타 전송의 신뢰성이 낮아진다. 이와 같은 하드웨어 제약성과 무선의 문제점을 극복하기 위하여 다양한 연구가 진행되고 있는 데 그 중에서 사용자들에게 무선 이동환경을 인식하지 않고 컴퓨터를 사용할 수 있는 환경을 제공하는 방향으로 연구가 진행 중이다. 이들 연구 중에서 무선의 제약점인 낮은 전송 속도와 잦은 끊어짐 등을 극복하고 사용자가 고정 호스트의 대용량의 디스크를 투명하게 사용할 수 있도록 하는 방법이 바로 "Disconnected Operation"을 지원하는 방법이다. 본 연구에서는 disconnected operation을 지원하는데 가장 중요한 부분인 hoarding에 대하여 최근까지 연구된 기법들을 조사하고 이들 기법들이 가지는 문제점을 파악하고 새로운 hoarding algorithm을 제시하고자 한다.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.12
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• pp.2167-2172
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• 2008

A large scale embedded generator or a micro-grid is usually interconnected to the grid through the dedicated line. Immediately after the removal of the grid supply, it must be disconnected and remain disconnected until the normal grid supplies are restored. This paper proposes an islanding detection algorithm based on complex power at the intertie. Complex power at the intertie delivered to the grid has a value depending on power flow during normal operation. When loss of mains occurs, complex power at the intertie moves to a value depending on the parameters of the dedicated line. The performance of the proposed algorithm was investigated under various operating and fault conditions. The proposed algorithm can detect an islanding operation even if no power is exchanged prior to loss of mains and discriminate the fault condition from islanding.

• Journal of Electrical Engineering and Technology
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• v.10 no.2
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• pp.452-464
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• 2015

This paper proposes a DC microgrid operational strategy and control method for improved service reliability. The objective is to supply power to as many non-critical loads as possible, while providing an uninterrupted power supply to critical loads. The DC bus signaling method, in which DC voltage is an information carrier, is employed to implement the operational strategy in a decentralized manner. During grid-connected operation, a grid-tied converter balances the power of the microgrid by controlling the DC voltage. All loads are connected to the microgrid, and operate normally. During islanded operation, distributed generators (DGs), a backup generator, or an energy storage system balances the power. However, some non-critical loads may be disconnected from the microgrid to ensure the uninterrupted power supply to critical loads. For enhanced service reliability, disconnected loads can be automatically reconnected if certain conditions are satisfied. Control rules are proposed for all devices, and detailed microgrid operational modes and transition conditions are then discussed. Additionally, methods to determine control parameter settings are proposed. PSCAD/EMTDC simulation results demonstrate the performance and effectiveness of the proposed operational strategy and control method.

• Proceedings of the Korea Contents Association Conference
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• 2010.05a
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• pp.390-392
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• 2010

Mobile grid system supports the integration mobile devices as grid resources. Availability of mobile resources changes dynamically in mobile grid system. Stochastic reward nets (SRN) is an extension of stochastic Petri nets and provides compact modeling facilities for system analysis. We build the SRN model to represent availability of mobile resources with disconnected operation service.

• Proceedings of the Korean Information Science Society Conference
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• 2004.10c
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• pp.415-417
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• 2004

이동 컴퓨팅 환경에서 통신망 제약을 극복하기 위한 방법으로 비연결 수행을 통한 컴퓨팅이 사용된다. 이동 컴퓨팅 환경은 유비쿼터스 환경으로 발전함에 따라 처리 할 정보의 요구량과 통신망 사용률이 증가 하게 된다. 그러나 노드의 환경 변화에 따라 빈번한 통신망 단절은 시스템의 성능을 저하시킨다. 본 논문에서는 이동 단말 노드에서 여러 개의 태스크가 통신망 자원을 사용하여 수행될 때 통신망 단절에 대비하기 위한 실시간 비연결 수행 스케줄링기법의 성능을 비교하였다. 실시간 알고리즘에 따른 성능 변화를 분석하여, 각 영향을 주는 요소를 파악하여 가장 효율적인 실시간 알고리즘을 적용할 수 있도록 한다.

• Proceedings of the KIEE Conference
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• 1998.07c
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• pp.1056-1058
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• 1998

Voltage dips caused by transmission system faults are usually of a short duration. High speed relaying and breaker operation will typically limit the disturbance to 0.1 seconds. Most motor controllers obtain their control power directly from the bus by means of a control transformer. Under this condition, a voltage dip can cause the contactor to drop out. disconnecting the motor from the line. The rapid re-energizing of the controller is in effect a fast reclosure which may result in motor damage. The time delay re-energizing of controller will result in a greater loss of speed and possibly loss of stability. Other means of controller can be used to prevent the motor from being disconnected from line during the fault. This can be accomplished by DC power controller or mechanically latched controller. This paper demonstrates that DC power controller or mechanically latched type controller to prevent the motor from being disconnected from line during the fault is, the most effective in minimizing speed reduction, transient motor current, transient motor torque and transient shaft torque by EMTP calculation.

• Proceedings of the KIPE Conference
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• 2003.07a
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• pp.264-268
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• 2003

This paper describes a high voltage high power DC power supply which has the ability of pulsed mode operation. The power supply Is constructed with several series connected power converters based on modified multilevel converters. The modified multilevel converters are suitable for the protection of frequent output short-circuit. The output dc power of the proposed converter can be disconnected from the load within several hundred microseconds at the instant of short-circuit fault. The rising time of the dc load voltage is as small as several hundred microseconds, and there is no overshoot of the do voltage because the dc output capacitors keep undischarged state. Analysis, simulations, and experiments are carried out to Investigate the operation and usefulness of the proposed scheme.

• Journal of Chest Surgery
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• v.16 no.1
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• pp.30-33
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• 1983

Truncus Arteriosus is an uncommon congenital anomaly which is now correctable surgically in patients with favorable anatomy. A case of a 9 month old male with truncus arteriosus, type II, is reported operation was done on cardiopulmonary bypass with deep hypothermia and circulatory arrest. The pulmonary arteries were not disconnected from the truncus, and the pulmonary common orifice was closed with a Dacron patch through anterior truncotomy and, for the distal anastomosis, the left pulmonary artery was opened near the common orifice. Continuity between the right ventricle and the left pulmonary artery was established with a valved conduit [Ionescu-Shiley, 14mm]. The postoperative course was excellent and uneventful.

• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.705-706
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• 2006

A novel plug and play system for a mobile device has been proposed and demonstrated to provide an easy inter-operation between the mobile device and external modules. It supports an automatic installation and execution of the device drivers stored in the external modules into the mobile devices when the external module is connected to the mobile device. It also enables an automatic removal of the derivers when the external module is disconnected from the mobile device, which makes the user use the resource of the mobile devices more efficiently.