• Journal of the Korean Operations Research and Management Science Society
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• v.33 no.3
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• pp.17-28
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• 2008

The Steiner arborescence problem is known to be NP-hard. The objective of this problem is to find a minimal Steiner tree which starts from a designated node and spans all given terminal nodes. This paper proposes a method based on a two-step procedure to solve this problem efficiently. In the first step, graph reduction rules eliminate useless nodes and arcs which do not contribute to make an optimal solution. In the second step. ant colony algorithm with use of Prim's algorithm is used to solve the Steiner arborescence problem in the reduced graph. The proposed method based on a two-step procedure is tested in the five test problems. The results show that this method finds the optimal solutions to the tested problems within 50 seconds. The algorithm can be applied to undirected Steiner tree problems with minor changes. 18 problems taken from Beasley are used to compare the performances of the proposed algorithm and Singh et al.'s algorithm. The results show that the proposed algorithm generates better solutions than the algorithm compared.

• Journal of Chest Surgery
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• v.16 no.3
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• pp.301-309
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• 1983

Twenty-three patients with aneurysm were operated between Jan. 1956 to July 1983 at the Department of Thoracic surgery, Seoul National University Hospital. There were 18 males and 5 females in this series. The age ranged from 14 to 68 years with the mean age of 41 years. The etiology of aortic aneurysms was atherosclerosis in 10, trauma in 2, annuloaortic ectasia in 4, syphilis in 1, and unknown etiology in six cases. Among the 4 patients with ascending aortic aneurysm, aortic valve replacement with aneurysmorrhaphy in three patients and Bentall operation in one patient were performed successfully. One patient with entire aortic arch aneurysm was received Dacron graft replacement with anastomosis of brachiocephalic arteries separately under cardiopulmonary bypass. There was no complication. Among 6 patients involving the descending thoracic aorta, three patients were managed by prosthetic bypass graft and aneurysm resection, and another three patients were also managed by prosthetic graft replacement. There were three hospital deaths. There were two thoracoabdominal aortic aneurysm. One patient in shock state due to preoperative rupture died from cardiac arrest during operative procedure. In another patient who had extensive involvement from the midportion of descending thoracic aorta to the terminal abdominal aorta, the aneurysm was successfully repaired with Dacron graft. In this instance celiac axis, superior and inferior mesenteric arteries and right renal artery were anastomosed separately. Eight of the 10 abdominal aortic aneurysms was replaced with prosthetic graft. One saccular aneurysm was treated by resection and primary closure. In another patient, cardiac arrest occurred during operation before definitive procedure. There was one another hospital death in the patient with preoperative rupture.

• Journal of the Korea Safety Management & Science
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• v.17 no.4
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• pp.297-304
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• 2015

This study concerns the integrated gas sensor system of wire and wireless communication by using IoT(Internet of Things) technology. First, communication part is that it delivers the detection information, which transferred by wire or wireless communication and required control procedure based on a wireless module that receives the gas leakage information from wired or wireless detector, to administrator or user's terminal. Second, receiver part is that it shows the location and information, which received from the wired detector formed by a detecting sensor's node as linking with the communication part, and transfers these to the communication part. Third, wireless detector formed as a communication module of a detecting sensor node is that it detects gas leakage and transfers the information through wireless as a packet.Fourth, wired detector communicated with the receiver part and formed as a communication module of a detecting sensor node is that it detects gas leakage, transfers and shows the information as a packet. Fifth, administrator's terminal is that it receives gas leakage information by the communication part, transfers the signal by remote-control, and shut off a gas valve as responding the information. Sixth, database is that it is connected with the communication part; it sets and stores the default values for detecting smoke, CO., and temperature; it transfers this information to the communication part or sends a gas detecting signal to user's terminal. Seventh, user's terminal is that it receives each location's default value which stored and set at the database; it manages emergency situation as shutting off a gas valve through remote control by corresponding each location's gas leakage information, which transferred from the detector to the communication part by wireless.It is possible to process a high quality data regarding flammable or toxic gas by transferring the data, which measured by a sensor module of detector, to the communication part through wire and wireless. And, it allows a user to find the location by a smart phone where gas leaks. Eventually, it minimizes human life or property loss by having stability on gas leakage as well as corresponding each location's information quickly.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.4
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• pp.561-568
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• 2018

Passivity theory is significantly applied to analyze stability of nonlinear dynamic systems and construct its stable control systems. This paper presents a passivity based control design approach for exciters and governors which are employed to regulate the terminal voltage and the rotor velocity of synchronous generator systems in industry fields. We consider the IEEE type 1 exciter and the gas turbine (GT) governor models respectively in this paper. We first carry out a passivity analysis for exciter and governor control systems, which are numerically obtained from its mathematical models. And then its control parameters are selected to assure passivity conditions in a design procedure. Lastly, we investigate numerical simulations to demonstrate reliability of the proposed control approach against large-scale generators with parameter changes.

• Proceedings of the KIEE Conference
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• 2004.11c
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• pp.669-671
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• 2004

This paper presents a MIMO nonlinear controller for the power system consisting of a turbine and a synchronous generator connected to an infinite bus. The controller proposed is based on feedback input-output linearization; its main goal is to regulate the terminal voltage and frequency, and is to improve the transient stability under large disturbances and unexpected faults. It is guaranteed that the voltage converges to its reference value exponentially, and that the frequency and the mechanical/electrical power are bounded. The design procedure is tested on a single machine infinite bus power system through simulations, and is seen to be effective.

• 전기의세계
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• v.21 no.3
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• pp.48-52
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• 1972

The application of pontryagin's Maximum Principle to the optimal control eventually leads to the problem of solving the two point boundary value problem. Most of problems have been related to their own special factors, therfore it is very hard to recommend the best method of deriving their optimal solution among various methods, such as iterative Runge Kutta, analog computer, gradient method, finite difference and successive approximation by piece-wise linearization. The gradient method has been applied to the optimal control of two point boundary value problem in the power systems. The most important thing is to set up some objective function of which the initial value is the function of terminal point. The next procedure is to find out any global minimum value from the objective function which is approaching the zero by means of gradient projection. The algorithm required for this approach in the relevant differential equations by use of the Runge Kutta Method for the computation has been established. The usefulness of this approach is also verified by solving some examples in the paper.

• Journal of the Society of Naval Architects of Korea
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• v.38 no.2
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• pp.19-25
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• 2001

Structural design requirements for very large floating structures(VLFS) are different corresponding to this purpose and structural type. In this study, the structural design procedure of VLFS is described, composing of the following processes : construction of design conditions. choice of structural types and main materials, estimation of structural design loads, determination of structural arrangements, and scantling of structural members. As an example of practical application, the initial structural design of floating airport and container terminal for Pusan is demonstrated.

• Electronics and Telecommunications Trends
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• v.9 no.3
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• pp.117-138
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• 1994

기술의 발전과 함께 경제적 측면에서 전기통신은 사회기반구조의 중추적인 일부로 자리잡고 있으며, 궁극적으로는 전세계적인 단일 통신시장이라는 기치아래 각국의 통신시장 개방요구가 점차 확산되고 있다. 이와 맥을 같이 하여 가장 큰 시장을 형성하는 서비스의 최종이용자 장치 즉 단말장치에 대한 규제가 완화되어가고 있는 등 통신시장은 세계화 추세에 있다. 이의 일환으로 자국의 통신질서 유지를 위해 적용되고 있는 단말장치 형식승인제도에 대해 양국 또는 다국간의 국제적 차원에서 상호 공통으로 적용가능한 상호인증제도를 위한 전략수립에 비중을 두고 활동이 전개되고 있다. 본고는 우리나라 전기통신과 깊은 관계를 유지하고 있는 미국 중심의 북미자유무역협정(NAFTA) 체결국중에서 최근 신전기통신법 통과로 관심을 모으고 있는 캐나다에 대해 인증절차와 인증 기술기준 등을 포함한 형식승인제도 전분야를 분석하고 향후 수립될지 모르는 캐나다와의 상호인증을 위한 기초자료로 활용코자 한다.

• Journal of electromagnetic engineering and science
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• v.18 no.4
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• pp.231-241
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• 2018

In this paper, we consider the anti-attack procedure of a ballistic missile defense system (BMDS) at different operating frequencies at its phased-array radar station. The interception performance is measured in terms of lateral divert (LD), which denotes the minimum acceleration amount available in an interceptor to compensate for prediction error for a successful intercept. Dependence of the frequency on estimation accuracy that leads directly to prediction error is taken into account, in terms of angular measurement noises. The estimation extraction is performed by means of an extended Kalman filter (EKF), considering two typical re-entry trajectories of a non-maneuvering ballistic missile (BM). The simulation results show better performance at higher frequency for both tracking and intercepting aspects.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.25 no.3
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• pp.44-50
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• 2017

This paper proposes arrival scheduling and advisory generation algorithms which can be used in the terminal airspace with Point-Merge procedures. The proposed scheduling algorithm consists of two steps. In the first step, the algorithm computes aircraft schedules at the entrance of the Point-Merge sequencing legs based on First-Come First-Served(FCFS) strategy. Then, in the second step, optimal sequence and schedules of all aircraft at the runway are computed using Multi-Objective Dynamic Programming(MODP) method. Finally, the advisories that have to be provided to the air traffic controllers are generated. To demonstrate the proposed algorithms, the simulation was conducted based on Jeju International Airport environments.