• 한국연소학회:학술대회논문집
• /
• 한국연소학회 2004년도 제28회 KOSCO SYMPOSIUM 논문집
• /
• pp.102-111
• /
• 2004

Partial quenching structure of turbulent diffusion flames in a turbulent mixing layer is investigated by the method of flame hole dynamics to develope a prediction model for the turbulent lift off. The present study is specifically aimed to remedy the problem of the stiff transition of the conditioned partial burning probability across the crossover condition by adopting level-set method which describes propagating or retreating flame front with specified propagation speed. In light of the level-set simulations with two model problems for the propagation speed, the stabilizing conditions for a turbulent lifted flame are suggested. The flame hole dynamics combined with level-set method yields a temporally evolving turbulent extinction process and its partial quenching characteristics is compared with the results of the previous model employing the flame-hole random walk mapping. The probability to encounter reacting' state, conditioned with scalar dissipation rate, demonstrated that the conditional probability has a rather gradual transition across the crossover scalar dissipation rate in contrast to the stiff transition of resulted from the flame-hole random walk mapping and could be attributed to the finite response of the flame edge propagation.

• 한국연소학회지
• /
• 제9권2호
• /
• pp.18-29
• /
• 2004

Partial quenching structure of diffusion flames in a turbulent mixing layer has been investigated by the method of flame hole dynamics in oder to develope a prediction model for the phenomenon of turbulent flame lift off. The present study is specifically aimed to remedy the shortcoming of the stiff transition of the conditioned partial burning probability across the crossover condition by employing the level-set method which enables us to include the effect of finite flame edge propagation speed. In light of the level-set simulation results with two models for the edge propagation speed, the stabilizing conditions for turbulent lifted flame are suggested. The flame hole dynamics combined with the level-set method yields a temporally evolving turbulent extinction process and its partial quenching characteristics is compared with the results of the previous model employing the flame-hole random walk mapping based on three critical scalar dissipation rates. The probability to encounter reacting state, conditioned with scalar dissipation rate, demonstrated that the conditional probability has a rather gradual transition across the crossover scalar dissipation rate. Such a smooth transition is attributed to the finite response of the flame edge propagation.

• 한국정보통신학회논문지
• /
• 제8권5호
• /
• pp.1010-1019
• /
• 2004

본 논문에서는 Nakagami-m 페이딩 채널을 Finite-State Markov Channel (FSMC)로 모델링하고, 채널 상태 변화에 따른 통신 시스템의 성능을 분석하였다. 고려한 FSMC 모델에서는 수신 신호의 신호 대 잡음 전력비를 유한개의 구간으로 나눠 각각의 구간을 Markov 체인의 상태로 대응한다. 각 상태는 무기억 이진 대칭 통신로로 가정하고, 한 상태에서 다른 상태로의 천이는 Markov 천이를 따른다고 가정한다. 수치 해석을 통해 각 상태에 있어서의 평균 심볼 오율, 정상 상태 확률 그리고 상태 천이 확률을 구하여 FSMC 모델을 구성하였고, 상태 천이 지수를 변경함으로써 여러 페이딩 환경을 FSMC 모델로 나타낼 수 있음을 확인하였다. 상태 천이 지수가 클 경우인 빠른 페이딩 채널에서는 채널이 i.i.d. 특성을 나타내게 되며, 상태 천이 지수가 작을 경우인 느린 페이딩 채널은 인접한 상태로의 천이만 발생하는 간단한 FSMC 모델로 표현될 수 있음을 확인하였다. 마지막으로 제안한 FSMC 모델의 응용 예로써, 여러 채널 환경에서 랜덤 에러 정정 부호의 부호화 이득의 차이를 컴퓨터 시뮬레이션을 통해 비교, 분석하였다.

• 한국전자파학회논문지
• /
• 제26권11호
• /
• pp.999-1011
• /
• 2015

전자전(Electronic Warfare) 상황에서 레이다는 재머에 의해 전파교란공격(ECM: Electronic Counter Measures)을 받게 된다. Linear-FM 신호는 도플러 특성이 우수하고, 신호의 구현이 용이하여 레이다에서 주로 사용되어 왔지만, 반복된 패턴에 의해 피탐 확률이 높고, 신호 특성변수 추정이 가능하여 기만재밍에 취약하다. 최근 제안된 APCN(Advanced Pulse Compression Noise) 신호는 랜덤 진폭과 랜덤 위상코드로 이루어진 신호로서, 저피탐 성능이 우수한 신호이다. 하지만, APCN 신호를 비롯한 일반적인 위상코드 신호는 도플러 특성이 좋지 않으므로, 주파수 천이에 의해 신호수신 성능이 저하될 수 있다. 따라서 본 논문에서는 도플러 특성을 개선하기 위한 방안으로 랜덤 위상천이 및 부호율 천이(RPCR: Random Phase and Code Rate transition) 레이다 신호 파형을 제안하고, 도플러 성능과 저피탐 성능을 분석하였다. Ambiguity 함수를 이용하여 부호율 천이에 의한 도플러 특성 개선을 제시하며, WHT(Wigner-Hough Transform)을 이용한 신호 특성 변수 추정 실험을 통해 RPCR 신호의 저피탐 성능을 분석하고, 전파교란대응책(ECCM: Electronic Counter Counter Measures)으로의 가능성을 확인한다.

• International Journal of Control, Automation, and Systems
• /
• 제6권1호
• /
• pp.109-118
• /
• 2008

We present two estimators for discrete non-Gaussian and nonstationary probability density estimation based on a dynamic Bayesian network (DBN). The first estimator is for off line computation and consists of a DBN whose transition distribution is represented in terms of kernel functions. The estimator parameters are the weights and shifts of the kernel functions. The parameters are determined through a recursive learning algorithm using maximum likelihood (ML) estimation. The second estimator is a DBN whose parameters form the transition probabilities. We use an asymptotically convergent, recursive, on-line algorithm to update the parameters using observation data. The DBN calculates the state probabilities using the estimated parameters. We provide examples that demonstrate the usefulness and simplicity of the two proposed estimators.

• Bulletin of the Korean Chemical Society
• /
• 제17권8호
• /
• pp.700-706
• /
• 1996

We present the results of molecular dynamics simulations of monolayers of long-chain alkyl thiol [S(CH2)15CH3] molecules on an air-solid interface using the extended collapsed atom model for the chain-molecule and a gold surface for the solid surface. Several molecular dynamics simulations have been performed on monolayers with areas per molecule ranging from 18.30 to 32.10 Å2/molecule. It is found that there exist three possible transitions: a continuous transition characterized by a change in molecular configuration without change in lattice structure, a sudden transition characterized by the distinct lattice defects and perfect islands, and a third transition characterized by the appearance of a random, liquid-like state. The analysis of probability distributions of the segments shows that the structure of the chain-molecules at the air-solid interface is completely different from that at the air-water interface in the view of the degree of overlap of the probability distributions of the neighbor segments. The calculated diffusion coefficients of the chain-molecules on the monolayers seem to be not directly related to any one of the three transitions. However, the large diffusion of the molecules enhanced by the increment of the area per molecule may induce the second transition.

• 한국HCI학회:학술대회논문집
• /
• 한국HCI학회 2008년도 학술대회 1부
• /
• pp.739-743
• /
• 2008

본 연구에서는 사용자가 입력한 멜로디에 따른 반주 음악을 자동으로 생성하는 방법을 제시한다. 시작되는 코드는 사용자의 멜로디에 의해서 생성이 되며, 그 다음 코드들은 코드들간의 전이확률이 정의되어있는 마르코프 체인(markov chain)의 확률 테이블을 이용하여 연속적으로 생성된다. 확률 테이블은 기존 음악의 샘플 데이터를 강화학습(reinforcement learning)을 이용하여 학습된다. 또한 실시간으로 재생되는 반주 코드는 매 상태 마다 주어지는 보상 값을 통해 더 나은 행동을 취할 수 있도록 학습해 나간다. 멜로디와 각 코드들간의 유사성은 피치 클래스 히스토그램을 이용하여 계산된다. 본 기술을 사용하여 주어진 사용자 입력에 조화로운 반주 코드의 자동 생성이 가능하다.

• Journal of Information Processing Systems
• /
• 제10권4호
• /
• pp.602-617
• /
• 2014

The performance of a cognitive radio network (CRN) solely depends on how precisely the secondary users can sense the presence or absence of primary users. The incorporation of a spatial false alarm makes deriving the probability of a correct decision a cumbersome task. Previous literature performed this task for the case of a received signal under a Normal probability density function case. In this paper we enhance the previous work, including the impact of carrier frequency, the gain of antennas on both sides, and antenna heights so as to observe the robustness against noise and interference and to make the correct decision of detection. Three small scale fading channels: Rayleigh, Normal, and Weibull were considered to get the real scenario of a CRN in an urban area. The incorporation of a maximal-ratio combining and selection combing with a variation of the number of received antennas have also been studied in order to achieve the correct decision of spectral sensing, so as to serve the cognitive users. Finally, we applied the above concept to a traffic model of the CRN, which we based on a two-dimensional state transition chain.

• Communications for Statistical Applications and Methods
• /
• 제21권2호
• /
• pp.135-145
• /
• 2014

The present study surveys Bayesian modeling structure for inferences about transition probabilities of Markov chain. The motivation of the study came from the data that shows transitional behaviors of emotionally disturbed children undergoing residential treatment program. Dirichlet distribution was used as prior for the multinomial distribution. The analysis with real data was implemented in WinBUGS programming environment. The performance of the model was compared to that of alternative approaches.

• Communications for Statistical Applications and Methods
• /
• 제14권1호
• /
• pp.1-9
• /
• 2007

A three-state Markov logistic regression model is suggested to forecast the probability of tomorrow's precipitation based on the current meteorological situation. The suggested model turns out to be better than Markov regression model in the sense of the mean squared error of forecasting for the rainfall data of Seoul area.