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화염증 CO<sub>2</sub> Laser를 이용한 입자의 크기 및 형상 제어
이동근,이선재,최만수,Lee, Donggeun,Lee, Seonjae,Choi, Mansoo 대한기계학회 1999 大韓機械學會論文集B Vol.23 No.11
A new technique for control of size and shape of flame-made particles is Introduced. The characteristic sintering time can be controlled Independently of collision time by heating the particles with irradiation of laser because the sintering time strongly depends on temperature. A coflow oxy-hydrogen diffusion flame burner was used for $SiCl_4$ conversion to silica particle. Nanometer sized aggregates irradiated by a high power CW $CO_2$ laser beam were rapidly heated up to high temperatures and then were sintered to approach volume-equivalent spheres. The sphere collides much slower than the aggregate, which results in reduction of sizes of particles maintaining spherical shape. Light scattering of Ar ion laser and TEM observation using a local sampling device were used to confirm the above effects. When the $CO_2$ laser was irradiated at low position from the burner surface, particle generation due to gas absorption of laser beam occurred and thus scattering intensity increased with $CO_2$ laser power. At high irradiation position, scattering intensity decreased with $CO_2$ laser power and TEM image showed a clear mark of evaporation and recondensation of particles for high $CO_2$ laser power. When the laser was irradiated between the above two positions where small aggregates exist, average size of spherical particles obviously decreased to 58% of those without $CO_2$ laser irradiation with the spherical shape. Even for increased carrier gas flow rate by a factor of three, TEM photograph also revealed considerable reduction of particle size.
On the Generalized Mean Square Error and its Applications
Donggeun Lee(이동근),Chanseok Park(박찬석) 대한산업공학회 2018 대한산업공학회지 Vol.44 No.2
There are several evaluation methods for parameter estimation. For example, the mean squared error (MSE), the Euclidean distance, the Mahalanobis distance and etc. But, when statistical methods have two or more parameter, it is difficult to evaluate whether they are good or not. In this paper we focus on defining the generalized bias (gBias) and the generalized mean squared error (gMSE) related to the generalized variance (gVar) applying to MSE concept to evaluate the parameter estimates. Moreover we will prove this concept beyond the three-dimensional, that is, hyper dimensional. Also we will check the applications of these terms. We will consider the robust estimates such as MAD, Hodges Lehmann estimator compared to other evaluation methods. We will use nuclear area data and find efficient method to predict Weibull distribution in some condition.
차량 간 통신에서 주기적 메시지를 위한 속도 기반의 자가 구성형 시분할 브로드캐스팅 방법
이동근(Donggeun Lee),장상우(Sang-woo Chang),이상선(Sang-sun Lee) 한국통신학회 2014 韓國通信學會論文誌 Vol.39 No.3(네트워크)
차량 간 통신을 이용한 안전 서비스 제공을 위해서 차량 간에 서로의 위치정보 획득이 중요한 이슈가 되고 있다. 이를 위해서 주기적으로 메시지를 발생 시키고 주변 차량의 위치 변화를 감지하여 운전자에게 안전 서비스를 제공한다. 하지만 차량의 밀도가 높은 환경에서 주기적인 위치정보 메시지의 잦은 발생으로 인해 네트워크 채널이 포화 상태가 되어 송/수신에 문제가 발생한다. 본 논문은 시분할 슬롯을 이용하여 브로드캐스팅하며 차량의 속도를 이용하여 도로 위 차량 밀도를 예측하여 시분할 슬롯의 수, 전파세기를 조절하여 향상된 통신 상태를 만드는 방법을 제안한다. 네트워크 시뮬레이터를 통한 성능 평가 결과, 기존의 경쟁 모드에서 브로드캐스팅 했을 때 보다 수신율은 약 40%의 향상 보여주었고 채널 접근 시간은 10ms에서 0.23ms 로 감소한 것을 확인 할 수 있었다. For vehicle safety-related services using wireless communications, reliable collection of various driving informations transmitted periodically by neighbor vehicles is the most important. Every host vehicle analyses them to estimate a potential dangerous situation in a very short time and warns drivers to prevent an accident. However tremendous amount of periodic messages can cause the wireless communication in chaos and the services not in safe. In this paper, we propose a time-division broadcasting protocol to mitigate the communication congestion. It utilizes the received information of vehicle velocity and location, i.e. vehicle traffic density on a road to adjust the number of time slots in a given broadcasting period, and transmission power. The simulation results show that message reception ratio is changed to approximately 40% and channel access time also decreased from 10ms to 0.23ms.
상세반응 메커니즘을 이용한 무차원 다영역 압축점화 엔진 모델 개발
이동근(Donggeun Lee),송한호(Han Ho Song) 한국자동차공학회 2011 한국자동차공학회 학술대회 및 전시회 Vol.2011 No.11
Modeling of compression-ignition combustion process with multi-zone spray model and detailed chemical kinetic mechanism was performed to analyse the combustion characteristics and performances of a diesel engine. In the modeling, the combustion chamber is divided into a single air zone and several fuel-spray zones. Spray penetration is obtained by an empirical formula and air entrainment into the fuel-spray zones is determined by momentum conservation. Each zone has its own histories of temperature, pressure and species, based on the energy conservation, ideal gas laws, and chemical reactions. The use of detailed chemical kinetic mechanism allows to accurately model the combustion process throughout the cycle. In further study not included in this paper, optimization between calculation time and accuracy can be found by setting the appropriate number of cells. It is also expected that the prediction of NOx formation is possible by additional consideration of NOx formation mechanism.