• 정보보호학회논문지
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• 제31권6호
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• pp.1157-1169
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• 2021

재해 복구는 자연 재해와 같은 비상 상황에 대비하여 서비스의 연속성을 보장하고, 리소스와 재정의 손실을 최소화하기 위한 정책 및 절차를 의미한다. 특히, 클라우드 서비스 제공자에 의한 재해 복구 방법은 관리의 유연성과 고가용성, 비용효율성과 같은 장점을 지닌다. 하지만, 이러한 방법은 서비스 사업자에 대한 의존성을 가지며, 개인의 데이터에 대해 사용자가 관여할 수 없는 구조적 한계를 가진다. 본 논문에서는 블록체인과 분산 스토리지를 활용하여 사용자의 데이터를 백업함으로써 서비스 제공자에 대한 의존성을 제거하고, 데이터의 기밀성을 위해 프록시 재암호화를 이용한 프로토콜을 제시한다. 제안된 방법은 이더리움과 IPFS 환경에서 구현되었으며, 백업 및 복구 운영에 필요한 성능과 비용을 제시한다.

• 자원리싸이클링
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• 제33권1호
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• pp.15-21
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• 2024

전기차용 리튬이온배터리의 수요가 증가함에 따라 향후 발생할 폐리튬이온배터리 중의 유가금속 회수가 필요하다. 본 연구에서는 리튬이온배터리의 NCM계 양극재를 수소환원과 수침출에 의해 리튬을 수산화리튬으로 회수할 때의 회수율에 미치는 반응온도의 영향을 조사하였다. 반응온도가 상승함에 따라 수소에 의한 NiO, CoO의 환원에 의해 무게 감소율이 반응초기부터 급격하게 증가하였으며 동시에 H₂O 발생량도 증가하였다. 602 ℃ 이상에서는 양극재 중의 Ni, Co가 전부 환원되어 금속상으로 존재하였다. 그리고 수소환원 온도의 상승과 함께 Li 회수률도 증가하였으나 704 ℃ 이상에서는 약 92 % 이상의 유사한 수준을 나타내었다. 따라서 폐Li이온 배터리의 전처리로 수소환원하는 것에 의해 리튬만 사전에 회수하고 잔사를 재처리하면 효율적으로 유가금속을 분리하여 회수할 수 있을 것으로 기대된다.

• Journal of Korean Neurosurgical Society
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• 제52권4호
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• pp.288-292
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• 2012

Objective : Microvascular decompression (MVD) for hemifacial spasm (HFS) is a safe and effective treatment with favorable outcomes. The purpose of this study was to evaluate the incidence of delayed cranirve (VI, VII, and VIII) palsy following MVD and its clinical courses. Methods : Between January 1998 and December 2009, 1354 patients underwent MVD for HFS at our institution. Of them, 100 patients (7.4%) experienced delayed facial palsy (DFP), one developed sixth nerve palsy, and one patient had delayed hearing loss. Results : DFP occurred between postoperative day number 2 and 23 (average 11 days). Ninety-two patients (92%) completely recovered; however, House-Brackmann grade II facial weakness remained in eight other patients (8%). The time to recovery averaged 64 days (range, 16 days to 9 months). Delayed isolated sixth nerve palsy recovered spontaneously without any medical or surgical treatment after 8 weeks, while delayed hearing loss did not improve. Conclusion : Delayed cranial nerve (VI, VII, and VIII) palsies can occur following uncomplicated MVD for HFS. DFP is not an unusual complication after MVD, and prognosis is fairly good. Delayed sixth nerve palsy and delayed hearing loss are extremely rare complications after MVD for HFS. We should consider the possibility of development of these complications during the follow up for MVD.

• Journal of Power Electronics
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• 제11권4호
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• pp.606-611
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• 2011

Power electronics is a key technology for electric, hybrid, plug-in hybrid, and fuel cell vehicles. Typical power electronics converters used in electric drive vehicles include dc/dc converters, inverters, and battery chargers. New semiconductor materials such as silicon carbide (SiC) and novel topologies such as the Z-source inverter (ZSI) have a great deal of potential to improve the overall performance of these vehicles. In this paper, a Z-source inverter for fuel cell vehicle application is examined under three different scenarios. 1. a ZSI with Si IGBT modules, 2. a ZSI with hybrid modules, Si IGBTs/SiC Schottky diodes, and 3. a ZSI with SiC MOSFETs/SiC Schottky diodes. Then, a comparison of the three scenarios is conducted. Conduction loss, switching loss, reverse recovery loss, and efficiency are considered for comparison. A conclusion is drawn that the SiC devices can improve the inverter and inverter-motor efficiency, and reduce the system size and cost due to the low loss properties of SiC devices. A comparison between a ZSI and traditional PWM inverters with SiC devices is also presented in this paper. Based on this comparison, the Z-source inverter produces the highest efficiency.

• 인터넷정보학회논문지
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• 제9권6호
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• pp.179-188
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• 2008

무선망에서 TCP의 성능을 증대시키기 위한 많은 연구가 진행되어 왔지만 패킷 손실률이 큰 경우, TCP의 성능은 아직도 개선의 여지가 많다. 본 논문은 무선 TCP의 한 종류인 TCP Westwood에서 랜덤 패킷 손실률이 높을 때 성능이 저하되는 문제를 지적하고 그 원인을 분석하였다. TCP Westwood의 성능 저하는 랜덤 패킷 손실률이 증가할수록, TCP Westwood의 가용 대역폭 측정(Available Bandwidth Estimation)의 정확도가 떨어지기 때문이다. 분석된 원인을 바탕으로 2가지의 향상된 가용대역폭 측정방법을 제안하고 그 성능을 시뮬레이션을 통해 확인하였다. 제안된 방법들은 무선 네트워크가 겪을 수 있는 랜덤패킷 손실률 1% 이내에서 기존방법에 비해 대역폭 측정의 정화도가 향상되었다.

• 한국음향학회지
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• 제21권4호
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• pp.349-360
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• 2002

인터넷 폰 시스템은 네트워크 트래픽 문제로 인한 지연, 지터 그리고 패킷 손실을 경험하고 이로 인한 통화품질의 저하가 문제가 되어 통화품질 (QoS) 향상 기술이 필요하게 되었다. 본 논문에서는 인터넷상에서 통화품질을 저해하는 요소들을 분석하고 실시간 전송 프로토콜/실시간 전송제어 프로토콜 (RTP/RTCP)을 이용하여 네트워크 상태를 진단하여 송, 수신 단말기간 네트워크 트래픽에 알맞은 방식으로 인코딩된 패킷을 송,수신하는 동적인 손실 복구 알고리즘을 제안한다. 실험결과 제안한 부가정보를 이용한 동적인 손실 복구 알고리즘은 연속 패킷손실인 경우 63%의 손실패킷 복원률을 보여주며, 비연속 패킷손실인 경우 42%의 패킷손실 복원률을 보여준다.

• 한방안이비인후피부과학회지
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• 제29권2호
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• pp.98-105
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• 2016

Objectives : The purpose of this study is to report the Korean medical treatment on sudden sensorineural hearing loss(SSNHL). Methods : The patient who has been diagnosed SSNHL had symptoms with hearing loss, tinnitus, and aural fullness. The patient was received outpatient to Dunsan oriental hospital for 3 months and was treated with oriental medicine(acupuncture, herbal-medicine, converting of Hominis placenta, warm needling and vapor treatment). Two approaches were used in order to evaluate the effect of the treatment. The hearing recovery was measured with pure tone audiometry, and the decrease of tinnitus and aural fullness was identified by patient's subjective expression. Results : The patient has his hearing restored fully and the symptoms of SSNHL accompanied with adjunctive symptoms including tinnitus and aural fullness were improved.Conclusions : This study shows that the Korean medical treatment effects on the SSNHL.

• Journal of Power Electronics
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• 제19권2호
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• pp.353-362
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• 2019

To address the problem of circulating current loss in the traditional zero-current switching (ZCS) full-bridge (FB) DC/DC converter, a ZCS FB DC/DC converter topology and modulation strategy is proposed in this paper. The strategy can achieve ZCS turn on and zero-voltage and zero-current switching (ZVZCS) turn off for the primary switches and realize ZVZCS turn on and zero-voltage switching (ZVS) turn off for the auxiliary switches. Moreover, its resonant circuit power is small. Compared with the traditional phase shift full-bridge converter, the new converter decreases circulating current loss and does not increase the current stress of the primary switches and the voltage stress of the rectifier diodes. The diodes turn off naturally when the current decreases to zero. Thus, neither reverse recovery current nor loss on diodes occurs. In this paper, we analyzed the operating principle, steady-state characteristics and soft-switching conditions and range of the converter in detail. A 740 V/1 kW, 100 kHz experimental prototype was established, verifying the effectiveness of the converter through experimental results.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권2호
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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.

• 설비공학논문집
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• 제22권4호
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• pp.248-257
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• 2010

An exhausted heat recovery system for a small gas engine cogeneration plant was investigated. The system was designed and built in a 300 kW class cogeneration demonstrative system. The basic performance was tested depending on load variation, and installed to a field site as a bottoming heat and power supply system. The exhaust gas heat exchangers (EGHXs) in shell-and-tube type and shell-and-plate type were tested. The entire efficiency of the cogeneration system was estimated between 85 to 90% under the 100% load condition, of which trend appears higher in summer due to the less thermal loss than in winter. Power generation efficiency and thermal efficiency was measured in a range of 31~33% and 54~57%, respectively.