• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.1
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• pp.49-58
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• 2019

The Scientific balloon is a flight system that could recover an entire platform at the end of the mission. The recovery takes place mainly in low-density populated areas, taking into account for the possible damage to the human life and public safety. In Republic of Korea, on the other hand, marine recovery should be considered due to the dense mountainous terrain and restrictions of the peninsula. In this operating environment, the envelope must be recovered because of severe marine pollution that may occur after the splashdown. Therefore, in this study, the separation device that consists of a location tracker and the waterproof system were developed. The device includes data transmission/reception, separation, and waterproof systems which are manufactured considering the environmental condition of the Korea. The performance of the device and the trajectory of the envelope were verified by conducting a separation test of a 20km platform at a target altitude and the recovery of the zero-pressure balloon.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.2
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• pp.371-388
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• 2014

Cognitive Radio (CR) has been recently proposed as a promising technology to remedy the problems of spectrum scarcity and spectrum underutilization by enabling unlicensed users to opportunistically utilize temporally unused licensed spectrums in a cautious manner. In Cognitive Radio Ad Hoc Networks (CRAHNs), data routing is one of the most challenging tasks since the channel availability and node mobility are unpredictable. Moreover, the network performance is severely degraded due to large numbers of path failures. In this paper, we propose the Fault-Tolerant Cognitive Ad-hoc Routing Protocol (FTCARP) to provide fast and efficient route recovery in presence of path failures during data delivery in CRAHNs. The protocol exploits the joint path and spectrum diversity to offer reliable communication and efficient spectrum usage over the networks. In the proposed protocol, a backup path is utilized in case a failure occurs over a primary transmission route. Different cause of a path failure will be handled by different route recovery mechanism. The protocol performance is compared with that of the Dual Diversity Cognitive Ad-hoc Routing Protocol (D2CARP). The simulation results obviously prove that FTCARP outperforms D2CARP in terms of throughput, packet loss, end-to-end delay and jitter in the high path-failure rate CRAHNs.

• Journal of Environmental Science International
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• v.5 no.3
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• pp.317-327
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• 1996

This study was performed to develop the biological treatment technology of wastewater polluted with heavy metals. Zinc-tolerant microorganism, such as Pseudomonas chlororaphis which possessed the ability to accumulate zinc, was isolated from industrial wastewaters polluted with various heavy metals. The characteristics of zinc accumulation in the cells, recovery of the zinc from the cells accumulating zinc, were investigated. Removal rate of zinc from the solution containing 100 mall of Zinc by zinc-tolerant microorganism was more than 90% at 48 hours after inoiulation of the microorganisms. A large number of the electron-dense granules were found mainly on thIn cell wall and membrane fractions, when determined by transmission electron microscope. Energy dispersive X- ray spectroscopy revealed that the electron-dense granules were zinc complex with the substances binding Heavy metals. The zinc accumulated into cells was not desorbed by distilled water, but more than 80% of the zinc accumulated was desorbed by 0.1M-EDTA. The residues of the cells after combustion at 55$0^{\circ}C$ amounted to about 21% of the dry weight of the cells. EDS analysis showed that the residues were comparatively pure zinc compounds containing more than 79% of zinc.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.7
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• pp.2936-2951
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• 2016

An emerging satellite technology, Operationally Responsive Space (ORS) is expected to provide a fast and flexible solution for emergency response, such as target tracking, dense earth observation, communicate relaying and so on. To realize large distance transmission, we propose the use of available relay satellites as relay nodes. Accordingly, we apply software defined network (SDN) technology to ORS networks. We additionally propose a satellite network architecture refered to as the SDN-based ORS-Satellite (Sat) networking scheme (SDOS). To overcome the issures of node failures and dynamic topology changes of satellite networks, we combine centralized and distributed routing mechanisms and propose a fast recovery routing algorithm (FRA) for SDOS. In this routing method, we use centralized routing as the base mode.The distributed opportunistic routing starts when node failures or congestion occur. The performance of the proposed routing method was validated through extensive computer simulations.The results demonstrate that the method is effective in terms of resoving low end-to-end delay, jitter and packet drops.

• ETRI Journal
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• v.27 no.1
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• pp.1-12
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• 2005

We propose a heuristic buffer management scheme that uses both positive and negative acknowledgments to provide scalability and reliability. Under our scheme, most receiver nodes only send negative acknowledgments to their repair nodes to request packet retransmissions while some representative nodes also send positive acknowledgments to indicate which packets can be discarded from the repair node's buffer. Our scheme provides scalability because it significantly reduces the number of feedbacks sent by the receiver nodes. In addition, it provides fast recovery of transmission errors since the packets requested from the receiver nodes are almost always available in their buffers. Our scheme also reduces the number of additional retransmissions from the original sender node or upstream repair nodes. These features satisfy the original goal of treebased protocols since most packet retransmissions are performed within a local group.

• Journal of Sensor Science and Technology
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• v.13 no.4
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• pp.292-297
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• 2004

Carbon nanotubes (CNT) were synthesized by arc-discharge method. To fabricate CNT sensor, CNT powder was dispersed in ${\alpha}$-Terpinol($C_{10}H_{17}OH$) solution. The CNT tilms were fabricated by screen printing method on the interdigitated Pt/Pd alloy electrode. The microstructure of CNT film was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In order to investigate the gas sensing characteristics of the film, the CNT film was experimented to measure NO response and recovery time. The CNT sensor with a heater was compared to that without a heater. And this sensor shows better reproductibility and faster recovery time than another CNT sensors. We suggest the possibility to utilize a CNT as new sensing materials for environmental monitoring.

• Journal of Institute of Control, Robotics and Systems
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• v.8 no.4
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• pp.299-302
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• 2002

Error detection and correction using CRC and the general class of cyclic codes is an important part of designing reliable data transmission schemes. The decoding method for cyclic codes using covering patterns is easily-implementable, and its complexity de-pends on the number of covering patterns employed. Determination of the minimal set of covering patterns for a given code is an open problem. In this paper, an efficient search method for constructing minimal sets of covering patterns is proposed and compared with several existing search methods. The result is applicable to various codes of practical interest.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.527-528
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• 2011

송전선로에서 발생하는 고장의 대부분은 낙뢰에 의한 상-대지간 섬락이나 외물접촉, 혹은 애자련의 오손에 의한 절연파괴 등이 대부분이다. 그리고 대분의 고장은 큰 고장전류를 흘리게 되어 보호계전기가 동작하여 고장구간을 신속하게 분리하게 된다. 그러나, 본 고장사례는 매우 희귀한 고장 사례로서, 고저항 아크 지락에 의하여 발생하는 과도회복전압(TRV: Transient Recovery Voltage)이 애자련에 섬락을 일으킨 경우이다. 본 연구에서는 EMTP (Electro-Magnetic Transient Program)를 이용하여 고저항 지락시 아크의 단속에 의하여 과도회복전압이 발생할 가능성이 있음을 보였으며, 고장기록장치(Fault Recorder)에 나타난 파형 기록과의 유사성을 확인하였다. 또한, 고저항 지락에 의하여 직류분이 초기에 방전됨으로써 고장전류 파형에 직류분 오프셋이 나타나지 않게 됨을 밝혔다.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.702-703
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• 2011

Large offshore wind farms using high voltage direct current transmission system (HVDC) have been considered and exploited in many countries in the world. The maintenance of the stable operation of wind farm and interconnected system is an important issue, especially in the case of fault. To ensure the stable operation after fault clearance, the PCC voltage must be restored as soon as possible and meet the grid code requirement. This paper will evaluate the PCC voltage recovery ability of a large offshore wind farm as it is connected to a weak grid via a VSC-HVDC.

• Progress in Superconductivity and Cryogenics
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• v.13 no.3
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• pp.10-13
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• 2011

The power demand is steadily increasing due to rapidly develop of industrial field. The ratio of prospected increment of power consumption is over 2.2 % per year from 2007 to 2020 year. The superconducting fault current limiters(SFCLs) should be suggested to be one of promising machines to protect power grid. Four basis tests such as resistivity, short-circuit tests, ac losses and recovery time were investigated according to various reached maximum temperature, operating temperature. This paper deals with investigation of the various commercial high temperature superconductor for applying resistive type SFCLs.