• Journal of Korean Society on Water Environment
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• v.27 no.1
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• pp.120-128
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• 2011

Korea Groundwater Quality Monitoring Network is a database of annual groundwater quality survey results to prevent groundwater pollution. We estimated contamination index (CI) values for each type of land use, and analyzed temporal trends of pollutant concentration data in the Groundwater Quality Monitoring Network from 2001 to 2009. Among the pollutants considered in the database, the concentrations of nitrate and chloride were higher than their standards. In the case of nitrate, recreation parks, golf courses and general waste dumping regions showed increasing trends according to linear regression analysis, whereas industrial complexes and residential regions of urgan and recreation parks showed increasing trends in the chloride concentration data. According to multiple variable linear regression analysis, EC, pH and topography were major factors influencing CI values. These results suggest that groundwater with a high CI value and increasing trend is vulnerable for potential contamination, which requires more careful groundwater pollution control.

• Journal of Korean Institute of Industrial Engineers
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• v.9 no.2
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• pp.37-46
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• 1983

The classical deterministic inventory model is investigated for the case of linear trend in demand and constant production rate. Three models are presented so as to minimize the total of set-up and inventory carrying costs over a finite time span. For each of the policies the methods are developed which can determine the optimal production quantities and times at which production should be started. Three policies are compared in point of costs and times for getting solutions and various case examples are also presented.

• Proceedings of the KIEE Conference
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• 1992.07a
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• pp.340-343
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• 1992

In this paper, To estimate monthly water distribution volume required optimization control of operating scheme & water distribution management for water transmission system in water supply, both Thomas-Fiering technique and Fourier series are compared and analyzed, respectively. Since water distribution volume is periodically repeated and has a linear fluctuation trend, parameters in each element are estimated through dividing into linear fluctuation trend component and periodical component. Finally, results of time-series analysis are proved to be more reasonable than that of Thomas-Fiering techniques by comparing simulation with observation data.

• Communications for Statistical Applications and Methods
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• v.14 no.3
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• pp.667-677
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• 2007

In this paper, we propose a method for estimating the mean of a population which has a linear trend, when both n, the sample size, and k, the reciprocal of the sampling fraction, are odd numbers. The proposed method, not having the drawbacks of centered systematic sampling, centered modified sampling and centered balanced sampling, consists of selecting a sample by balanced systematic sampling and estimating the population mean by using interpolation. We compare the efficiency of the proposed method and existing methods under the criterion of the expected mean square error based on the infinite superpopulation model.

• Journal of the Korean earth science society
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• v.42 no.4
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• pp.445-458
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• 2021

Gravity Recovery and Climate Experiment (GRACE) gravimeter satellites observed the Earth gravity field with unprecedented accuracy since 2002. After the termination of GRACE mission, GRACE Follow-on (GFO) satellites successively observe global gravity field, but there is missing period between GRACE and GFO about one year. Many previous studies estimated terrestrial water storage (TWS) changes using hydrological models, vertical displacements from global navigation satellite system observations, altimetry, and satellite laser ranging for a continuity of GRACE and GFO data. Recently, in order to predict TWS changes, various machine learning methods are developed such as artificial neural network and multi-linear regression. Previous studies used hydrological and climate data simultaneously as input data of the learning process. Further, they excluded linear trends in input data and GRACE/GFO data because the trend components obtained from GRACE/GFO data were assumed to be the same for other periods. However, hydrological models include high uncertainties, and observational period of GRACE/GFO is not long enough to estimate reliable TWS trends. In this study, we used convolutional neural networks (CNN) method incorporating only climate data set (temperature, evaporation, and precipitation) to predict TWS variations in the missing period of GRACE/GFO. We also make CNN model learn the linear trend of GRACE/GFO data. In most river basins considered in this study, our CNN model successfully predicts seasonal and long-term variations of TWS change.

• Journal of the Korean earth science society
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• v.40 no.5
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• pp.487-501
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• 2019

In this study, steric height variability in the East Asian Seas (EAS) has been analyzed by using ocean reanalysis intercomparison project (ORA-IP) data. Results show that there are significant correlations between ocean reanalysis and satellite data except the phase of annual cycle and interannual signals of the Yellow Sea. Reanalysis ensemble derived from 15-different assimilation systems depicts higher correlation (0.706) than objective analysis ensemble (0.296) in the EAS. This correlation coefficient is also much higher than that of the global ocean (0.441). For the long-term variability of the thermosteric sea level during 1993-2010, a significant warming trend is found in the East/Japan Sea, while cooling trend is shown around the Kuroshio extension area. For the halosteric sea level, a dominant freshening trend is found in the EAS. However, below 300 m depth around this area, the signal-to-noise ratio of the linear trend is generally less than one, which is related to the low density of observation data.

• Journal of international Conference on Electrical Machines and Systems
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• v.1 no.1
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• pp.61-66
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• 2012

Linear motors has been developed for factory automation, transportation applications, among other applications. As the trend toward compact sizes in micro electronic products progresses, the required motor drives in these applications need to be downsized with increased power densities. It appears that the winding of miniature linear motors is the most awkward part to be scaled down from conventional motor designs when miniaturizing. This paper presents an alternative design for slotless linear motors. A novel flexible printed circuit winding has been applied to obtain a simplified but qualified result. Having explained the prototyping and inspection, a discussion is given to examine the achievement of this study.

• Journal of the Korean Data and Information Science Society
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• v.20 no.6
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• pp.1103-1118
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• 2009

When we wish to estimate the mean or total of a finite population, the numbering of the population units is of importance. In this paper, we have proposed two methods for estimating the mean or total of a population having a linear trend, for the case when the reciprocal of the sampling fraction is an even number and the sample size is an odd number. The first method involves drawing a sample by using a method which is a generalization of Singh et al's (1968) modified systematic sampling, and using interpolation in determining the estimator. The second method involves selecting a sample by modified systematic sampling, and estimating the population parameters by the regression estimation method. Under the criterion of the expected mean square error based on Cochran's (1946) infinite superpopulation model, the proposed methods have been compared with existing methods. We have also made a comparison between the two proposed methods.

• Asian Journal of Atmospheric Environment
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• v.11 no.4
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• pp.235-253
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• 2017

This study was conducted for analyzing the contribution factors on ozone concentrations and its long term trends in each major city and province in Korea through several statistical methods such as simple linear regression, generalized linear model, KZ-filer, correlation matrix, Kringing method, and cluster analysis. The overall ozone levels in South Korea have been consistently increasing over the past 10 years. The ozone concentrations in Seoul, the biggest city in Korea, are the lowest in all areas with the highest increasing ratio for $95^{th}%$ ozone. It is thought that the active photochemical reaction could affect the higher ozone concentration increase. On the other hand, the ozone concentrations in Jeju are the highest in Korea with the highest increasing ratio for $5^{th}%$, $33^{th}%$, and $50^{th}%$ ozone. It is also thought that the weak $NO_x$ titration could be the reason of higher ozone concentrations in Jeju. In case of Jeju, transport related factors is the major factor affecting the ozone trend. Thus, it is assumed that the variation of ozone trend of Asian region affecting the ozone trend in Jeju, where domestic ozone photochemical reaction is less active than urban area. It is thought that the photochemical reaction plays the role of increasing of ozone concentrations in the urban area, even though the LRT affected on the increase of ozone concentrations in non-urban area.

• The Korean Journal of Applied Statistics
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• v.13 no.2
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• pp.457-476
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• 2000

In this study, we have proposed a sampling method and an estimation method for efficiently estimating the mean of a population which has a linear trend. These methods involve drawing a sample by the so-called "centered balanced systematic sampling", which is an extension of systematic sampling, and then estimating the population mean with an adjusted estimator, not with the sample mean itself. We used the concept of interpolation in determining the adjusted estimator.\Ve compared the efficiency of the proposed estimator with those of the estimators from existing methods, under the expected mean square error criterion based on the infinite superpopulation model introduced by Cochran(1946). The proposed method is for use in the case when the sample size n(2 5) is an odd number and k(the reciprocal of the sampling fraction) is an even number. A good result was also obtained in an example using computer simulation. simulation.