영상 레이더 간섭기법 및 차분간섭기법을 이용한 수치고도모델 생성과 정확도 평가

김창오(Kim, Chang Oh),김정우(Kim, Jeong woo) 한국측량학회 2005 한국측량학회지 Vol.23 No.2

TMA 농도에 따른 저온축열물질의 과냉각 특성에 대한 연구

김창오(Chang-Oh Kim),김진흥(Jin-Heung Kim),정낙규(Nak-Kyu Chung) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.11

This study is investigated the supercooling characteristics of the TMA-water clathrate compound including TMA (Tri-methyl-amine, (CH3)3N) of 20~25 wt% as a low temperature latent heat storage material at -5℃, cooling source temperature. The results showed that as the concentration of TMA is increased, phase change temperature is increased, the supercooling and retention time of liquid phase are decreased. Especially, low temperature latent heat storage material containing TMA 25 wt% has the average of phase change temperature of 5.8℃, supercooling degree of 8.0℃, retention time of liquid phase for 10 minutes in the cooling process. Phase change temperature higher than that of water and inhibitory effect against superrcooling can be confirmed through experimental study on cooling characteristics of TMA-water clathrate compound. This can lead to shorten refrigerator operation time of low temperature thermal storage system and improve efficiency of refrigerator COP and overall system.

TMA 농도에 따른 저온잠열축열물질의 냉각특성

김창오(Kim Chang-Oh),정현호(Chung Hyoun-Ho),정낙규(Chung Nak-Kyu) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5

The ice storage system uses water for low temperature latent heat storage. However, a refrigerator capacity is increased and COP is decreased due to supercooling of water in the course of phase change from solid to liquid. This study investigates the phase change characteristics of the TMA-water clathrate compound including TMA (Tri-methyl-amine, (CH₃)₃N) of 20~25 wt% as a low temperature latent heat storage material. The results showed that the phase change temperature and the specific heat is increased and the supercooling degree is decreased as the weight concentration of TMA increased. Especially, the clathrate compound containing TMA 25wt% has the average phase change temperature of 5.8℃ and the supercooling degree of 8.0℃ in the cooling process. This can lead to reduction of operation time of refrigerator in low temperature latent heat storage system and efficiency improvement of refrigerator COP and overall system. Therefore, energy saving and improvement of utilization efficiency are expected.

저온잠열저장을 위한 TMA-물계 포접화합물의 과냉각 개선에 대한 연구

김창오(Kim Chang-Oh),김진흥(Kim Jin-Heung),정낙규(Chung Nak-Kyu) 한국태양에너지학회 2007 한국태양에너지학회 학술대회논문집 Vol.- No.-

This study aims to find out cooling characteristics of TMA(Tri-Methyl- Amine, (CH₃)₃N) 25wt%-water clathrate compound with ethanol(CH₃CH₂OH) such as supercooling, phase change temperature and specific heat. For this purpose, ethanol is added as per weight concentration and cooling experiment is performed at -6˜-8℃, cooling heat source temperature, and it leads the following result. (1) Phase change temperature is decreased due to freezing point depression phenomenon. Especially, it is minimized as 3.8℃ according to cooling source temperature in case that 0.5wt% of ethanol is added. (2) If 0.5wt% of ethanol is added, average supercooling degree is 0.9℃ and minimum supercooling is 0.8, 0.7℃ according to cooling heat source temperature. The restraint effect of supercooling is shown. (3) Specific heat shows tendency to decrease if ethanol is added. It is 3.013~3.048 ㎉/㎏℃ according to cooling heat source temperature if 0.5wt% of ethanol is added. Phase change temperature higher than that of water and inhibitory effect against supercooling can be confirmed through experimental study on cooling characteristics of TMA 25wt%-water clathrate compound by adding additive, ethanol. This can lead to shorten refrigerator operation time of low temperature latent heat storage system and improve COP of refrigerator and efficiency of overall system. Therefore energy can be saved and efficiency can be improved much more.

저온잠열저장을 위한 TMA-물계 포접화합물의 냉각특성에 대한 연구

김창오(Chang-Oh Kim),김진흥(Jin-Heung Kim),정낙규(Nak-Kyu Chung) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5

Clathrate compound is the material that host in hydrogen bond forms cage and guest is included into it and combined. Crystallization of hydrate is generated at higher temperature than that of ice from pure water. And physical properties according to temperature are stable and congruent melting phenomenon is occurred without phase separation. But clathrate compound still had supercooling problem occurred in the course of phase change and supercooling should be minimized because it affects efficiency of equipment very much. Therefore, various studies on additives to restrain this or heat storage methods are needed. In this study was investigated the cooling characteristics of the TMA-water clathrate compound including TMA (Tri-methyl-amine, (CH₃)₃N) of 20~25 wt% as a low temperature latent heat storage material. And ethanol(CH₃CH₂OH) was added and its cooling characteristics were studied experimentally to restrain supercooling of TMA-water clathrate compound.

의료환경 변화에 따른 감염성 심내막염의 양상 변화

신소연 ( So Youn Shin ),박윤수 ( Yoon Soo Park ),최준용 ( Jun Yong Choi ),조정호 ( Cheong Ho Cho ),박윤선 ( Yoon Seon Park ),김창오 ( Chang Oh Kim ),윤희정 ( Hee Jung Yoon ),김효열 ( Hyo Yul Kim ),염준섭 ( Jun Sup Yum ),이꽃실 ( K 대한내과학회 2005 대한내과학회지 Vol.68 No.2

목적 : 2000년 7월 국민 건강 증진, 보건 관련 비용의 감소, 약물 오 남용 방지 등의 취지로 의약분업이 시행되었다. 의약분업 이전에는 항생제의 구입에 별 다른 제약이 없었으나, 의약분업 이후 대부분의 항생제가 전문의약품으로 분류되면서 항생제의 구입시 의사의 처방전이 필요하게 되었다. 감염성 심내막염은 비특이적인 초기 임상증상으로 환자들이 내원 전 경구 항생제를 복용하는 경우가 많았다. 혈액배양 음성 감염성 심내막염의 가장 흔한 원인으로 내원 전 Background : In July 2000, there was a dramatic change in Korean health care system with the medical reform, the separation system of pharmacies and prescriptions. Before then, patients could easily get antibiotics without doctors` prescriptions. Since th

General principles and perioperative management

김창오(Chang Oh Kim) 대한외과학회 2014 대한외과학회 학술대회 초록집 Vol.2014 No.11

석회석 광산 내 광주의 안정성 분석을 위한 미소진동 계측기술의 현장적용

김창오(Chang Oh Kim),엄우용(Woo-Yong Um),정소걸(So-Keul Chung),천대성(Dae-Sung Cheon) 한국암반공학회 2016 터널과지하공간 Vol.26 No.1

본 연구는 미소진동 계측기술을 국내 광산의 안정성 분석에 적용한 사례연구로서, 계측자료의 분석을 통해 미소진동 기법의 광산 적용성과 한계성을 알아보았다. 적용 광산은 채수율 향상을 위해 주방식하이브리드 채광법이 적용된 석회석광산으로, 수평 단면 50 m × 50 m의 시험영역에 대해 각각의 수직 광주에 미소진동센서를 설치하였다. 측정된 미소진동 신호는 발파와 천공작업으로 인한 신호, 손상에 의한 신호, 전기 잡음에 의한 신호로 구분되었으며, 손상에 의한 신호를 중심으로 안정성 분석을 실시하였다. 시험영역에 근접한 채굴부의 발파작업 후 광주의 손상이 증가하였으며, 주변에서 발생한 낙반을 미소진동 신호로부터 추정할 수 있었다. 또한 일일 미소진동 발생량의 변화로부터 광주와 채굴주변 암반의 안정성을 평가할 수 있었으며, 누적된 계측정보를 토대로 본 광산의 시험영역에 대한 안전관리 기준안을 제시하였다. 그러나 국부적인 센서 배열에 따라 3차원 음원위치를 산정하는 데 어려움이 존재하고, 실시간 계측을 위한 현실적인 대안의 필요성이 제기되었다. 향후 광산적용에서 제기된 문제점을 보완하고, 광산 현장작업과의 유기적인 비교, 분석을 통해 보다 좋은 안전감시의 지시자로서 미소진동 계측기술이 활용될 수 있을 것으로 사료된다. This study deals with the case that was the field application of the microseismic monitoring techniques for the stability monitoring in a domestic mine. The usefulness and limitations of the microseismic techniques were examined through analyzing the microseismic monitored data. The target limestone mine adopted a hybrid room-and-pillar mining method to improve the extraction ratio. The accelerometers were installed in each vertical pillar within the test bed which has the horizontal cross-section 50 m × 50 m. The measured signals were divided into 4 types; blasting induced signal, drilling induced signal, damage induced signal, and electric noise. The stability analysis was performed based on the measured damage induced signals. After the blasting in the mining section close to the test bed, the damage of the pillar was increased and rockfall near the test bed could be estimated from monitored microseismic data. It was possible to assess the pillar stability from the changes of daily monitored data and the proposed safety criteria from the accumulated monitored data. However, there was a difficulty to determine the 3D microseismic source positions due to the 2D local sensor arrays. Also, it was needed to use real-time monitoring methods in domestic mines. By complementing the problems encountered in the mine application and comparing microseismic monitored data with mining operations, the microseismic monitoring technique can be used as a better safety method.

P2P 미디어 스트리밍 서비스를 위한 동적 그룹 할당 방식

김창오(Chang-Oh Kim),강경란(Kyungran Kang),조영종(Young-Jong Cho) 한국통신학회 2008 한국통신학회 학술대회논문집 Vol.2008 No.11

계층적 네트워크를 위한 분산 멀티캐스트 그룹 키 관리 기법

김창오(Chang Oh Kim),강경란(Kyungran Kang),조영종(Young-Jong Cho) 한국정보과학회 2011 정보과학회논문지 : 정보통신 Vol.38 No.1

본 논문에서는 전술 네트워크 환경과 같이 네트워크 연결이 항상 보장되지 못하며 계층적 구조를 갖는 환경을 지원하기 위한 비중앙화된 멀티캐스트 그룹 키 관리 기법을 제안한다. 연결이 보장되기 어렵고 긴 지연 시간을 초래할 중앙 키 관리자를 사용하지 않고, 네트워크 내 계층 구조를 활용하여 무선 네트워크 내 노드들이 그룹 키 관리자를 담당하도록 함으로써 멀티캐스트 그룹 키의 관리를 분산시킨다. 또한, 팀 단위로 가입 요청과 탈퇴 요청을 묶어서 처리함으로써 멀티캐스트 그룹 키의 갱신 메시지 부담을 줄인다. 시뮬레이션을 통하여 타 비중앙화 기법과의 비교에서도 팀 단위 처리와 인접한 그룹 키 관리자로 인해 그룹 키 갱신을 위한 메시지 부담이 본 기법이 매우 낮게 나타났다. 그리고, 멤버쉽 변화율에 따른 그룹 키 갱신 메시지 부담 측정에서 멤버쉽 변화율에 비해 부담이 증가하는 비율이 낮게 나타나 멤버쉽 변화율에 대해 확장성이 있다는 것을 확인할 수 있었다. 그런데, 수학적 분석과 시뮬레이션에서 팀의 규모가 어느 일정값보다 증가하게 되면 팀 내 처리 비용이 증가하여 전체적으로 그룹 키 갱신 비용이 오히려 증가한다는 것도 관측되었다. In this paper, we propose a decentralized multicast group key management scheme for a hierarchically structured but unstable network like a tactical network. In the tactical network, the connection the infrastructure is not always guaranteed and the unstable connection and long latency would prevent the use of centralized key management scheme. We propose a distributed group key management scheme which distributes the management function to the network nodes by exploiting the hierarchical relationship between the nodes. To reduce the count of key update operations, we propose to aggregate the join and leave requests within a reasonable time bound and process at a time. We build a simulator to evaluate the performance of our proposed scheme and two other decentralized group key management schemes. Our scheme shows less key update cost compared with the other twoschemes thanks to the team-based key management and nearby group key management server. The key update cost of our scheme increases slower than the increase of membership change rate. However, through the numerical analysis and simulation, we discovered that the team size beyond some critical threshold causes the overall key update cost of our scheme to become impractically large.