• Journal of the Korean Institute of Intelligent Systems
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• v.8 no.2
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• pp.117-127
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• 1998

Power systems have uncertain dynamics due to a variety of effects such as lightning, severe storms and equipment failures. The variation of the effective reactance of a transmission line due to a fault is an example of uncertainty in power system dynamics. Hence, a robust controller to cope with these uncertainties is needed. Recently, fuzzy controllers are becoming quite popular for robust control due to its potential of dealing with uncertain systems. Thus in this paper we design an adaptive fuzzy controller based on an input-output linearization approach for the transient stabilization and voltage regulation of a power system under a sudden fault. Also this paper proposes a fuzzy system that estimates the upper bound of uncertain term in the system dynamics to guarantee the Lyapunov stability. Simulation results show that good performance is achieved by the proposed controller.

• Journal of Korean Society of Forest Science
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• v.90 no.2
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• pp.176-183
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• 2001

Loblolly pine (Pinus taeda L.) is the most economically important timber producing species in the southern United States. Much attention has been given to predicting diameter distributions for the solution of multiple-product yield estimates. The three-parameter Weibull diameter distribution yield prediction systems were developed for loblolly pine plantations. A parameter recovery procedure for the Weibull distribution function based on four percentile equations was applied to develop diameter distribution yield prediction models. Four percentiles (0th, 25th, 50th, 95th) of the cumulative diameter distribution were predicted as a function of quadratic mean diameter. Individual tree height prediction equations were developed for the calculation of yields by diameter class. By using individual tree content prediction equations, expected yield by diameter class can be computed. To reduce rounding-off errors, the Weibull cumulative upper bound limit difference procedure applied in this study shows slightly better results compared with upper and lower bound procedure applied in the past studies. To evaluate this system, the predicted diameter distributions were tested against the observed diameter distributions using the Kolmogorov-Smirnov two sample test at the ${\alpha}$=0.05 level to check if any significant differences existed. Statistically, no significant differences were detected based on the data from 516 evaluation data sets. This diameter distribution yield prediction system will be useful in loblolly pine stand structure modeling, in updating forest inventories, and in evaluating investment opportunities.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.7
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• pp.76-84
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• 2013

In the passive emitter localization using instantaneous TDOA (time difference of arrival) and FDOA (frequency difference of arrival) measurements, the estimation accuracy can be improved by collecting additional measurements. To achieve this goal, it is required to increase the number of the sensors. However, in electronic warfare environment, a large number of sensors cause the loss of military strength due to high probability of intercept. Also, the additional processes should be considered such as the data link and the clock synchronization between the sensors. Hence, in this paper, the passive localization of a stationary emitter is presented by using the successive TDOA and FDOA measurements from two moving sensors. In this case, since an independent pair of sensors is added in the data set at every instant of measurement, each pair of sensors does not share the common reference sensor. Therefore, the QCLS (quadratic correction least squares) methods cannot be applied, in which all pairs of sensor should include the common reference sensor. For this reason, a Gauss-Newton algorithm is adopted to solve the non-linear least square problem. In addition, to show the performance of the proposed method, we compare the RMSE (root mean square error) of the estimates with CRLB (Cramer-Rao lower bound) and derived the CEP (circular error probable) planes to analyze the expected estimation performance on the 2-dimensional space.

• Environmental Analysis Health and Toxicology
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• v.12 no.3_4
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• pp.31-41
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• 1997

Public concerns about hazardous health effect from the exposure to organic by-products of the chlorination have been increased. There are numerous studies reporting that chlorination of drinking water produces numerous chlorinated organic by-products including THMs, HAAs, HANs. Some of these products are known to be animal carcinogens. The purpose of this study was to estimate health risk of DBPs by chlorinated drinking water ingestion in Seoul based on methodologies that have been developed for conducting risk assessment of complex-chemical-mixture. The drinking water sample was collected seperately at six water treatment plant in Seoul at March, April, 1996. In tap water of households in Seoul, DBPs were measured wilfh the mean value of 36.6 $\mu$g/L. Risk assessment processes,. which include processes for the estimation of human cancer potency using animal bioassay data and calculation of human exposure, entail uncertainties. In the exposure assessment process, exposure scenarios with various assumptions could affect the exposure amount and excess cancer risk. The reference dose of haloacetonitriles was estimated to be 0.0023 mg/kg/day by applying dibromoacetonitrile NOAEL and uncertainty factor to the mean concentration. In the first case, human excess cancer risk was estimated by the US EPA method used to set the MCL (maximum contaminant level). In the second and third case, the risk was estimated for multi-route exposure with and without adopting Monte-Carlo simulation, respectively. In the second case, exposure input parameters and cancer potencies used probability distributions, and in the third case, those values used point estimates (mean, and maximum or 95% upper-bound value). As a result, while the excess cancer risk estimated by US EPA method considering only direct ingestion tended to be underestimated, the risk which was estimated by considering multi-route exposure without Monte-Carlo simulation and then using the maximum or 95% upper-bound value as input parameters tended to be overestimated. In risk assessment for Trihalomethanes, considering multi-route exposure with adopting Monte-Carlo analysis seems to provide the most reasonable estimations.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.7
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• pp.60-68
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• 2014

In modern electronic warfare systems, a demand on the more accurate estimation method based on TDOA and FDOA has been increased. TDOA/FDOA localization consists of two-stage procedures; the extraction of information from signals, and the estimation of emitter location. CAF(complex ambiguity function) is known as a basic method in the extraction stage. However, when we extract TDOA and FDOA information from VHF(very high frequency) communication signals, conventional CAF algorithms may not work within a permitted time because of much computation. Therefore, in this paper, an improved sequential estimation algorithm based on CAF is proposed for effective calculation of extracting TDOA and FDOA estimates in terms of computational complexity. The proposed method is compared with the conventional CAF-based algorithms through simulation. In addition, we derive the optimal performance based on the CRLB(Cramer-Lao lower bound) to check the extraction performance of the proposed method.

• The Journal of the Acoustical Society of Korea
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• v.26 no.8
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• pp.415-425
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• 2007

This paper proposes a method of underwater source localization using the wideband interference patterns matching. By matching two interference patterns in the spectrogram, it is estimated a ratio of the range from source to sensor5, and then this ratio is applied to the Apollonius circle. The Apollonius circle is defined as the locus of all points whose distances from two fixed points are in a constant value so that it is possible to represent the locus of potential source location. The Apollonius circle alone, however still keeps the ambiguity against the correct source location. Therefore another equation is necessary to estimate the unique locus of the source location. By estimating time differences of signal arrivals between source and sensors, the hyperbola equation is used to get the cross point of the two equations, where the point being assumed to be the source position. Simulations are performed to get performances of the proposed algorithm. Also, comparisons with real sea experiment data are made to prove applicability of the algorithm in real environment. The results show that the proposed algorithm successfully estimates the source position within an error bound of 10%.

• Bulletin of the Korean Mathematical Society
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• v.55 no.3
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• pp.957-965
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• 2018

We study the class $C{\mathcal{V}} ({\Omega})$ of analytic functions f in the unit disk ${\mathbb{D}}=\{z{\in}{\mathbb{C}}$ : ${\mid}z{\mid}$ < 1} of the form $f(z)=z+{\sum}_{n=2}^{\infty}a_nz^n$ satisfying $$1+\frac{zf^{{\prime}{\prime}}(z)}{f^{\prime}(z)}{\in}{\Omega},\;z{\in}{\mathbb{D}}$$, where ${\Omega}$ is a convex and proper subdomain of $\mathbb{C}$ with $1{\in}{\Omega}$. Let ${\phi}_{\Omega}$ be the unique conformal mapping of $\mathbb{D}$ onto ${\Omega}$ with ${\phi}_{\Omega}(0)=1$ and ${\phi}^{\prime}_{\Omega}(0)$ > 0 and $$k_{\Omega}(z)={\displaystyle\smashmargin{2}{\int\nolimits_{0}}^z}{\exp}\({\displaystyle\smashmargin{2}{\int\nolimits_{0}}^t}{\zeta}^{-1}({\phi}_{\Omega}({\zeta})-1)d{\zeta}\)dt$$. Let $z_0,z_1{\in}{\mathbb{D}}$ with $z_0{\neq}z_1$. As the first result in this paper we show that the region of variability $\{{\log}\;f^{\prime}(z_1)-{\log}\;f^{\prime}(z_0)\;:\;f{\in}C{\mathcal{V}}({\Omega})\}$ coincides wth the set $\{{\log}\;k^{\prime}_{\Omega}(z_1z)-{\log}\;k^{\prime}_{\Omega}(z_0z)\;:\;{\mid}z{\mid}{\leq}1\}$. The second result deals with the case when ${\Omega}$ is the right half plane ${\mathbb{H}}=\{{\omega}{\in}{\mathbb{C}}$ : Re ${\omega}$ > 0}. In this case $CV({\Omega})$ is identical with the usual normalized class of convex univalent functions on $\mathbb{D}$. And we derive the sharp upper bound for ${\mid}{\log}\;f^{\prime}(z_1)-{\log}\;f^{\prime}(z_0){\mid}$, $f{\in}C{\mathcal{V}}(\mathbb{H})$. The third result concerns how far two functions in $C{\mathcal{V}}({\Omega})$ are from each other. Furthermore we determine all extremal functions explicitly.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• v.10 no.S_2
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• pp.55-63
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• 2001

This work employs two models to quantify the size-segregated dry deposition fluxes of particle-bound N $O_3$$^{[-10]}$ , N $H_4$$^{+}$, and S $O_4$$^{2-}$ along the coastal area of Jeju Island based on the chemical composition data of aerosol collected during the springtime of 1995. The two approaches produced fairly comparable results, despite the feature differences between the two models. The modelling results obtained indicated that the mean dry deposition velocity was around 0.4 cm $s^{-1}$ for N $O_3$$^{[-10]}$ , 0.2 cm $s^{-1}$ for N $H_4$$^{+}$, and 0.3 cm $s^{-1}$ for S $O_4$$^{2-}$, and the dry deposition flux varied between 371~1368 $\mu\textrm{g}$ $m^{-2}$ da $y^{-1}$ for nitrate, 28~625 $\mu\textrm{g}$ $m^{-2}$ da $y^{-1}$ for ammonium, and 957~6088 $\mu\textrm{g}$ $m^{-2}$ da $y^{-1}$ for sulfate. Although difficulties in collecting giant and/or fine particles limited the understanding of the mass size distribution of particles and thus the ability to refine estimates of the dry deposition flux for the particulate matter, both models were still able to offer sufficient realism to explain the features of the available data collected from the coastal area of Jeju Island.and.

• Journal of The Korean Astronomical Society
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• v.31 no.2
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• pp.161-171
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• 1998

We have mapped about 1.5 square degree regions of Lynds 1299, a well isolated dark cloud in the Outer Galaxy (l = $122^{\circ}$, b = $-7^{\circ}$), in the J = 1- 0 transition of $^{12}CO$ and $^{13}CO$ with the 13.7 m radio telescope at Taeduk Radio Astronomy Observatory (TRAO). We found that there are two velocity components in the molecular emission, at $V_{LSR} = -52 km S^{-1}$ (Cloud A) and -8.8 km $s^{-1}$ (Cloud B), respectively. We have derived physical parameters of two molecular clouds and discussed three different mass estimate techniques. We found that there are large discrepancies between the virial and LTE mass estimates for both clouds. The large virial mass estimate reflects the fact that both are not gravitationally bound. We adopt the mass of $5.6 {\times}10^3 \;M{\bigodot}$ for Cloud A and $1.2{\times}10^3 \;M{\bigodot}$) for Cloud B using conversion factor. Cloud A is found to be associated with a localized star forming site, and its morphology is well matching with that of far-infrared (FIR) dust emission. It shows a clear ring structure with an obvious velocity gradient. We suggest that it may be a remnant cloud from a past episode of massive star formation. Cloud B is found to be unrelated to Cloud A (d = 800 pc) and has no specific velocity structure. The average dust color temperature of the uncontaminated portion of Cloud A is estimated to be 24$\~$27.4 K. The low dust temperature may imply that there is no additional internal heating source within the cloud. The heating of the cloud is probably dominated by the interstellar radiation field except the region directly associated with the new-born B5 star. Overall, the dust properties of Cloud A are similar to those of normal dark cloud even though it does have star forming activity.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.12 s.354
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• pp.16-23
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• 2006

This paper presents the development of the fast Direction Finder using direct conversion method, which can intercept for short pulse signal of less' than 1 msec. in RF Down Converter, and CVDF(Correlative Vector Direction Finding) algorithm, which estimates DoA (Direction of Arrival). The configuration and characteristics of direction finder using 5-channel equi-spaced circular array antenna are presented and the direct conversion techniques for removing tuning time using I/Q demodulator are described. The CRLB of our model is derived, the principles of 2 kind of CVDF algorithm are explained and their characteristics are compared with CRLB w.r.t the number of samples and spacing ratio. The RF Down Converter prototype using direct conversion method is manufactured, the 2 kind of CVDF algorithm are applied and their performance are analyzed. Finally it is confirmed the LSE based CVDF algorithm is better than correlation-coefficient based except for ambiguity protection capabilities.