• 대한전자공학회논문지SD
• /
• 제37권1호
• /
• pp.44-51
• /
• 2000

Series Coupler Access Encodler(SCAE)와 Series Coupler Access Decoder(SCAD)를 이용한 광CDMA(Code Division Multiple Access)시스템에서 광정합필터 특성을 삼차신호까지 고려하여 분석하였다. 기존의 연구에서는 SCAE 및 ACAD를 평가할 때, 일차신호만을 고려하여 시스템의 성능을 분석하여 성능평가가 정확하지가 않았다. SCAE 및 SCAD는 커플러 수를 증가함에 따라 여러 형태의 간섭신호들을 가지므로, 이러한 신호들이 자기상관과 상호상관 세기를 변화시킨다. 그러므로 좀 더 정확한 시스템 성능을 분석하기 위해서는 간섭신호들의 특성을 연구할 필요성이 있다. 본 논문에서는 복호화 되는 광신호를 삼차신호까지 수학적으로 해석하였고, 시스템의 자기상관과 상호상관에 미치는 영향을 모의실험을 통해 분석하였다. 커플러 수 증가에 따라 나타나는 삼차신호들이 간섭신호 형태가 되어 peak to side-lobe ratio를 감소키기는 요인으로 작용됨을 정량적으로 확인하였다. 간섭신호들의 크기는 ${\alpha}$(coupling coefficient)값이 커질수록 증가하였으며, 커플러 개수(N)=5, ${\alpha}$=0.5인 조건에서 삼차신호까지 고려한 peak to side-lobe ratio는 3.75 dB까지 열화됨을 밝혔다. 또한, 일차신호의 main-lobe세기에 의해 수신기의 임계레벨을 결정한다면, 삼차신호에 의해 증가된 side-lobes세기 때문에 SCAE와 SCAD를 이용한 광 CDMA system에 다중 접속할 수 있는 사용자 수가 제한됨을 알 수 있었다.

• 한국해안해양공학회지
• /
• 제19권3호
• /
• pp.213-221
• /
• 2007

전지구적으로 지구 온난화 문제가 대두되고 있는 현 상황에서, 기온변화에 수반되는 수온변화 반응을 파악하기 위하여 해양수산부에서 제공하는 마산만 연안해역의 기온 및 수온 관측자료를 이용하여 기온과 수온의 관계를 분석하였다. 수온과 기온의 무차원 자기상관함수와 교차상관함수 변화를 분석한 결과, 지체시간 10일 이내에서는 상관계수가 0.9 이상으로 매우 크게 나타났으며, 지점별로 수온의 상관계수보다 기온의 상관계수가 크게 나타나는 것으로 파악되었다. 마산만 기온 및 수온자료를 수온상승기, 수온하강기로 구분하여 분석한 결과, 수온상승기에는 MA1 지점, MA2 지점의 기울기가 각각 0.829, 0.774로 나타났으며, 수온하강기에는 MA1 지점, MA2 지점의 기울기가 각각 1.385, 1.444로 기온상승기에 비하여 기온하강기의 기울기가 약 1.75배 정도 크게 나타나고 있으며, 명확한 이력현상으로 파악되었다. 따라서, 마산만 연안해역의 기온-수온 상관관계를 보다 정확하게 결정하기 위해서는 기온-수온의 계절적인 이력현상을 포함하여야 하며, 이 경우 기온을 이용한 수온 추정결과의 정확도가 향상되는 것으로 파악되었다.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1989년도 하계종합학술대회 논문집
• /
• pp.158-161
• /
• 1989

This paper describes the AR model of EMG signal during maximum voluntary contraction. By comparing the AR coefficients and the reflection coefficients of the AR model with the median frequency of power spectrum, it if proved that muscle fatigue can be measured by the AR and the reflection coefficients. In the estimation procedure of AR model parameter, the auto-correlation method is superior to the covariance method, and it is determined that the optimal order is six. As the muscle becomes fatigue, the median frequency of power spectrum is declined, and the AR coefficient [$a_1$ ] and the reflection coefficient [$k_1$ ] are also decreased. Therefore the muscle fatigue can be measured by the AR parameter.

• Bulletin of the Korean Chemical Society
• /
• 제12권3호
• /
• pp.309-315
• /
• 1991

The thermal transport coefficients-the self-diffusion coefficient, shear viscosity, and thermal conductivity-of liquid argon at 94.4 K and 1 atm are calculated by non-equilibrium molecular dynamics (NEMD) simulations of a Lennard-Jones potential and compared with those obtained from Green-Kubo relations using equilibrium molecular dynamics (EMD) simulations and with experimental data. The time-correlation functions-the velocity, pressure, and heat flux auto-correlation functions-of liquid argon obtained from the EMD simulations show well-behaved smooth curves which are not oscillating and decaying fast around 1.5 ps. The calculated self-diffusion coefficient from our NEMD simulation is found to be approximately 40% higher than the experimental result. The Lagrange extrapolated shear viscosity is in good agreement with the experimental result and the asymptotic formula of the calculated shear viscosities seems to be an exponential form rather than the square-root form predicted by other NEMD studies of shear viscosity. The agreement for thermal conductivity between the simulation results (NEMD and EMD) and the experimental result is within statistical error. In conclusion, through our NEMD and EMD simulations, the overall agreement is quite good, which means that the Green-Kubo relations and the NEMD algorithms of thermal transport coefficients for simple liquids are valid.

• 한국주거학회논문집
• /
• 제19권2호
• /
• pp.73-82
• /
• 2008

The purpose of this paper is to analyze the correlation analysis between the experienced crime victimization rate and the evaluation indicator of residents' safety of outdoor spaces from crime in multi-family housing. Additionally this paper intend to analyze the correlation analysis between the residents' satisfaction about safety and the evaluation indicator of residents' safety of outdoor spaces. For that purpose, 9 Multi-Family Housing located in the metropolitan area were selected to perform a survey against 349 residents during May 26-29, 2006. The SPSS program was used and the level of satisfaction ranged from 1 to 5. Scale of 5 being most satisfied while 1 being most dissatisfied. The results of this study are the followings; 1) Most occurred crime were auto theft and damages, poster matter theft, housebreaking. 2) The crime rate is higher in outdoor than in indoor. 3) This study proved the correlation between the residents' satisfaction about housing safety and most indicators except the number of households etc. 4) By the results of the correlation coefficient it makes clear that the number of apartment building, the visibility of Green Space, the location of pedestrian etc. have relation with the residents' satisfaction about housing safety.

• 한국환경교육학회지:환경교육
• /
• 제11권2호
• /
• pp.252-261
• /
• 1998

Since 1980's during which environmental pollution became serious enough to urge various types of environmental educations in many areas. But, most emphasis has been put on theoretical education. Even field education training mostly focused on water pollution. Therefore, simple air pollution monitoring system was needed for better field education in air pollution. In this study, we evaluated Passive Sampler as an useful tool for teaching air pollution in field. Students have found passive sampler very effective tool. Recent comparative study of auto-monitoring and passive sampler networks suggested a potential use of passive sampler as an useful tool for environmental education. In this study, the correlation between two sets of values appears very high judging from the regression slope of 0.92 and correlation coefficient of 0.91 However, inexpensive Passive sampler with easy-to-operate colorimeter, has not been used in environmental education partially because large scale fluctuation in time and space characteristic to air pollution has been overlooked so that the sampler has not been tested for an effective educational tool. Passive sampler certainly deserves further in depth research as an effective air monitoring system, and better attention to its usefulness to teach students and public.

• Bulletin of the Korean Chemical Society
• /
• 제12권3호
• /
• pp.315-322
• /
• 1991

In a recent $paper^1$ we reported equilibrium (EMD) and non-equilibrium (NEMD) molecular dynamics simulations of liquid argon using the Green-Kubo relations and NEMD algorithms to calculate the thermal transport coefficients-the self-diffusion coefficient, shear viscosity, and thermal conductivity. The overall agreement with experimental data is quite good. In this paper the same technique is applied to calculate the thermal transport coefficients of liquid water at 298.15 K and 1 atm using TIP4P model for the interaction between water molecules. The EMD results show difficulty to apply the Green-Kubo relations since the time-correlation functions of liquid water are oscillating and not decaying rapidly enough except the velocity auto-correlation function. The NEMD results are found to be within approximately ${\pm}$30-40% error bars, which makes it possible to apply the NEMD technique to other molecular liquids.

• 환경정책연구
• /
• 제12권2호
• /
• pp.17-32
• /
• 2013

최근 인류가 초래한 지구의 온난화로 인하여 기온이 상승하고 이의 직접적인 반응으로 수온 증가가 감지되고 있다. 기온변화가 하천의 수질과 생태 환경에 미치는 영향을 추정하기 위해서는 수온 상승의 시기와 하천 어종에 대한 이해가 필요한데 이를 위하여 미래의 수온을 예측할 필요가 있다. 이에 하나의 사전연구로서 기온-수온 관계에 대하여 분석해 보았다. 2009년에서 2011년까지 3년 동안 환경부의 수질자동관측소에서 관측한 최소 873개에서 최대 1083개의 일 관측 자료를 바탕으로 자기상관관계와 교차상관관계를 조사해 본 결과 0.9 이상의 높은 상관관계를 보였다. 또 지체시간이 10일 미만에서는 기온의 자기 상관 계수가 수온의 가기 상관 계수보다 더 높은 것으로 나타났다. 관측자료의 이력현상을 분석하기 위하여 상승기와 하강기로 나누었는데, 관측지점에 따라서는 강한 이력현상을 보이는 지점도 발견되었다. 결국 기온-수온 관계를 구축함에 계절적인 이력현상이 고려되어야 정확도를 높일 수 있음을 유추할 수 있다.

• 대한기계학회논문집B
• /
• 제30권4호
• /
• pp.287-297
• /
• 2006

The Holographic Particle Velocimetry system can be a promising optical tool for the measurements of three dimensional particle velocities. One of inherent limitations of particle holography is the very long depth of field of particle images, which causes considerable difficulty in the determination of particle positions in the optical axis. In this study, we introduced three auto-focusing parameters corresponding to the size of particles, namely, Correlation Coefficient, Sharpness Index, and Depth Intensity to determine the focal plane of a particle along the optical axis. To investigate the suitability of the above parameters, the plane image of dot array screens containing different size of dots was recorded by diffused illumination holography and the positions of each dot in the optical axis were evaluated. In addition, the effect of particle position from the holographic film was examined by changing the distance of the screen from the holographic film. All measurement results verified that the evaluated positions using suggested auto-focusing parameters remain within acceptable range of errors. These research results may provide fundamental information for the development of the holographic velocimetry system based on the automatic image processing.

• 대한조선학회논문집
• /
• 제51권2호
• /
• pp.122-129
• /
• 2014

Identification of the whipping response out of the combined wave-vibration response of a flexible sea going vessel is one of the most interesting research topic from ship designer's point of view. In order to achieve this goal, a novel methodology based on the wavelet cross-correlation technique was proposed in this paper. The cross-correlation of the wavelet power spectrum averaged across the frequency axis was introduced to check the similarity between the combined wave-vibration response and impulse response. The calculated cross-correlation of the wavelet power spectrum was normalized by the auto-correlation of the each spectrum with zero time lag, eventually providing the cross-correlation coefficient that stays between 0 and 1, precisely indicating the existence of the impulse response buried in the combined wave-vibration response. Additionally, the weight function was introduced while calculating the cross-correlation of the two spectrums in order to filter out the signal of lower frequency so that the accuracy of the similarity check becomes as high as possible. The validity of the proposed methodology was checked through the application to the artificially generated ideal combined wave-vibration signal, together with the more realistic signal obtained by running 3D hydroelasticity program WISH-Flex. The correspondence of the identified whipping instances between the results, one from the proposed method and the other from the calculated slamming modal force, was excellent.