• Atmosphere
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• v.17 no.3
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• pp.217-230
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• 2007

Using the Lorenz-95 simple model, which can simulate many atmospheric characteristics, we compare the performance of ensemble strategies such as bred vectors, the bred vectors rotated (to be orthogonal to each bred member), and the Ensemble Transform Kalman Filter (ETKF). The performance metrics used are the RMSE of ensemble means, the ratio of RMS error of ensemble mean to the spread of ensemble, rank histograms to see if the ensemble member can well represent the true probability density function (pdf), and the distribution of eigen-values of the forecast ensemble, which can provide useful information on the independence of each member. In the meantime, the orthogonal bred vectors can achieve the considerable progress comparing the bred vectors in all aspects of RMSE, spread, and independence of members. When we rotate the bred vectors for orthogonalization, the improvement rate for the spread of ensemble is almost as double as that for RMS error of ensemble mean compared to the non-rotated bred vectors on a simple model. It appears that the result is consistent with the tentative test on the operational model in KMA. In conclusion, ETKF is superior to the other two methods in all terms of the assesment ways we used when it comes to ensemble prediction. But we cannot decide which perturbation strategy is better in aspect of the structure of the background error covariance. It appears that further studies on the best perturbation way for hybrid variational data assimilation to consider an error-of-the-day(EOTD) should be needed.

• Journal of the Earthquake Engineering Society of Korea
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• v.22 no.2
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• pp.45-54
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• 2018

The seismically isolated nuclear power plants shall be designed for design basis earthquake (DBE) and considered to ensure safety against beyond design basis earthquake (BDBE). In order to limit the excessive displacement of the seismic isolation system of the seismically isolated structure, the moat is installed at a certain distance from the upper mat supporting the superstructure. This certain distance is called clearance to stop (CS) and is calculated from the 90th percentile displacement of seismic isolation system subjected to BDBE. For design purposes, the CS can be obtained simply by multiplying the median displacement of the seismic isolation system against DBE by scale factor with a value of 3. The DBE and BDBE used in this study were generated by using 30 sets of artificial earthquakes corresponding to the nuclear standard design spectrum. In addition, latin hyper cube sampling was applied to generate 30 sets of artificial earthquakes corresponding to maximum - minimum spectra. For the DBE, the median displacement and the 99th percentile displacement of the seismic isolation system were calculated. For the BDBE, the suitability of the scale factor was assessed after calculating the 90th percentile displacement of the seismic isolation system.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.5
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• pp.506-514
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• 2008

At coverage boundaries of cellular systems including the recent WiBro standard which operate with full frequency reuse for increased spectral efficiency, interference signals from the base stations(BS) of adjacent cells degrade the receiver performance. In this paper, a detection method for multiple-antenna mobile stations(MS) is proposed for downlink performance improvement at coverage boundaries of cellular systems. For the performance verification, we obtain the probability density function(pdf) of the effective signal-to-interference and noise ratio(SINR) according to the variation of the interference signals from adjacent cells as well as the number of MS antennas, and calculate the transmission efficiency. We also verify the performance of proposed method with simulation results, to demonstrate a significant performance improvement is achieved over the maximal ratio combining(MRC) and spatial demultiplexing(SD) methods in terms of the effective SINR and the spectral efficiency.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.12A
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• pp.1147-1155
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• 2008

In this paper, we derive the probability density function (PDF) of end-to-end signal-to-noise ratio (SNR) for t he dual-hop MIMO (Multiple-Input Multiple-Output) DCF (Decouple-and-Forward) system. We also provide the end-to-end bit error ratio (BER) with M-ary PSK constellations for four antenna combinations. These are (1,8,1), (8,1,8), (2,4,2), and (4,2,4). Each number in the parentheses is the number of the transmit antenna at the source, the transmit and receive antenna at the relay and the receive antenna at the destination, respectively. We show t hat the end-to-end BER expression with M-ary PSK constellations makes an exact match with numerical results. We also show that MIMO DCF relay system achieves spatial diversity.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.6
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• pp.538-545
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• 2002

In the orthogonal frequency division multiplexing (OFDM) system, the nonlinear distortion in the high power amplifier(HPA) degrades the system performance because of the high peak-to-average power ratio (PAPR). In this paper, a semi-analytical method is newly proposed for the performance evaluation of the nonlinearly distorted OFDM communication system. In the proposed method, at first, the probability density function (pdf) of the PAPR is generated by computer simulation. Then, mean and variance of the non-linear distortion noise process are computed. Next, the overall BER is found by the analytical method. When the equivalent SSPA model is applied in case of the QPSK/16-QAM and AWGN channel, the BER is calculated for the variation of the IBO(input back-off) and PAPR parameter. It is shown that the results by proposed method are very similar to those of the conventional Monte-Carlo method. The computation time can be considerably reduced than the conventional method that depends on the magnitudes of BER and IBO.

• YAKHAK HOEJI
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• v.56 no.1
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• pp.48-54
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• 2012

Enviromental differences in gentamicin pharmacokinetics by using population pharmacokinetic methods were compared with 20 Korean patients and 24 Korean-American appendicitis patients. Two to six blood specimens were collected from all patients at the following times : just before a regularly scheduled infusion and at 0.5 hour after the end of a 0.5 hour infusion. Nonparametric expected maximum (NPEM) algorithm for population modeling was used. The estimated parameters were the elimination rate constant (K), the slope (KS) of the relationship between K versus creatinine clearance ($C_{cr}$), the apparent volume of distribution (V), the slope (VS) of the relationship between V versus weight, gentamicin clearance (CL) and the slope (CS) of the relationship between CL versus $C_{cr}$ and the V. The output includes two marginal probability density function (PDF), means, medians, modes, variance and CV%. The mean K (KS) were $0.402{\pm}0.129\;h^{-1}(0.00486{\pm}0.00197\;[h{\cdot}ml/min/1.73\;m^2]^{-1})$ and $0.411{\pm}0.135\;h^{-1}(0.00475{\pm}0.00180\;[h{\cdot}ml/min/1.73\;m^2]^{-1})$ for Korean and Korean-American populations, respectively. The mean V (VS) were not different at $14.3{\pm}3.6l(0.241{\pm}0.0511l/kg)$ and $15.1{\pm}3.84l(0.239{\pm}0.0492l/kg)$ for Korean and Korean-American populations, respectively (p>0.2). The mean CL (CS) were $5.68{\pm}1.69l/h(0.0714{\pm}0.0222l/kg[h{\cdot}ml/min/1.73\;m^2])$ and $5.70{\pm}1.77l/h(0.0701{\pm}0.0215l/kg[h{\cdot}ml/min/1.73\;m^2])$ for Korean and Korean-American populations, respectively. There were no enviromental differences in gentamicin pharmacokinetics between Korean and Korean-American appendicitis patients.

• Journal of the Korean Institute of Intelligent Systems
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• v.17 no.4
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• pp.511-518
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• 2007

This paper presents an efficient face recognition method by using both centroid shift and mutual information estimation of images. The centroid shift is to move an image to center coordinate calculated by first moment, which is applied to improve the recognition performance by excluding the needless backgrounds in face image. The mutual information which is a measurements of correlations, is applied to efficiently measure the similarity between images. Adaptive partition mutual information(AP-MI) estimation is especially applied to find an accurate dependence information by equally partitioning the samples of input image for calculating the probability density function(PDF). The proposed method has been applied to the problem for recognizing the 48 face images(12 persons * 4 scenes) of 64*64 pixels. The experimental results show that the proposed method has a superior recognition performances(speed, rate) than a conventional method without centroid shift. The proposed method has also robust performance to changes of facial expression, position, and angle, etc. respectively.

• Journal of the Korean Institute of Intelligent Systems
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• v.16 no.5
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• pp.525-530
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• 2006

This paper presents an efficient input variable selection method using both fixed-point independent component analysis(FP-ICA) and adaptive partition mutual information(AP-MI) estimation. FP-ICA which is based on secant method, is applied to quickly find the independence between input variables. AP-MI estimation is also applied to estimate an accurate dependence information by equally partitioning the samples of input variable for calculating the probability density function(PDF). The proposed method has been applied to 2 problems for selecting the input variables, which are the 7 artificial signals of 500 samples and the 24 environmental pollution signals of 55 samples, respectively The experimental results show that the proposed methods has a fast and accurate selection performance. The proposed method has also respectively better performance than AP-MI estimation without the FP-ICA and regular partition MI estimation.

• Smart Structures and Systems
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• v.24 no.5
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• pp.631-639
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• 2019

Finite element analysis is one of the important methods to study the structural performance. Due to the simplification, discretization and error of structural parameters, numerical model errors always exist. Besides, structural characteristics may also change because of material aging, structural damage, etc., making the initial finite element model cannot simulate the operational response of the structure accurately. Based on Bayesian methods, the initial model can be updated to obtain a more accurate numerical model. This paper presents the work on the field test, modal identification and model updating of a Chinese reinforced concrete pagoda. Based on the ambient vibration test, the acceleration response of the structure under operational environment was collected. The first six translational modes of the structure were identified by the enhanced frequency domain decomposition method. The initial finite element model of the pagoda was established, and the elastic modulus of columns, beams and slabs were selected as model parameters to be updated. Assuming the error between the measured mode and the calculated one follows a Gaussian distribution, the posterior probability density function (PDF) of the parameter to be updated is obtained and the uncertainty is quantitatively evaluated based on the Bayesian statistical theory and the Metropolis-Hastings algorithm, and then the optimal values of model parameters can be obtained. The results show that the difference between the calculated frequency of the finite element model and the measured one is reduced, and the modal correlation of the mode shape is improved. The updated numerical model can be used to evaluate the safety of the structure as a benchmark model for structural health monitoring (SHM).

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.6
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• pp.995-1002
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• 2020

This paper investigates the achievable data rate for non-orthogonal multiple access(NOMA) with correlated information sources(CIS), under the binary phase shift keying(BPSK) modulation, in contrast to most of the existing NOMA designs using continuous Gaussian input modulations. First, the closed-form expression for the achievable data rate of NOMA with CIS and BPSK is derived, for both users. Then it is shown by numerical results that for the stronger channel user, the achievable data rate of CIS reduces, compared with that of independent information sources( IIS). We also demonstrate that for the weaker channel user, the achievable data rate of CIS increases, compared with that of IIS. In addition, the intensive analyses of the probability density function(PDF) of the observation and the inter-user interferennce(IUI) are provided to verify our theoretical results.