• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.4
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• pp.117-128
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• 2016

Installation of earth grounding system is essential to ensure personnel safety and correct operation of electrical equipment. Earth parameters, especially, soil resistivity has to be determined in designing an efficient earth grounding system. The most common applied technique to measure soil resistance is Wenner four-point method. Implementation of this method is expensive, time consuming and cumbersome as large set of measurements with variable electrode spacing are required to obtain a one dimensional resistivity plot. It is advantageous to have a method which is of low cost and provides fast measurements. In this perspective, electrical resistance tomography (ERT) is applied to estimate subsurface resistivity profile. Electrical resistance tomograms characterize the soil resistivity distribution based on the measurements from electrodes placed in the region of interest. The nonlinear ill-posed inverse problem is solved using iterated Gauss-Newton method with Tikhonov regularization. Through extensive numerical simulations, it is found that ERT offers promising performance in estimating the three-dimensional soil resistivity distribution.

• Journal of Korea Water Resources Association
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• v.33 no.4
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• pp.505-515
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• 2000

THe purpose of this study is to forecast of runoff hydrographs according to rainfall event in a stream. The neural network theory as a hydrologic blackbox model is used to solve hydrological problems. The Back-Propagation(BP) algorithm by the Levenberg-Marquardt(LM) techniques and Radial Basis Function(RBF) network in Neural Network(NN) models are used. Runoff hydrograph is forecasted in Bocheongstream basin which is a IHP the representative basin. The possibility of a simulation for runoff hydrographs about unlearned stations is considered. The results show that NN models are performed to effective learning for rainfall-runoff process of hydrologic system which involves a complexity and nonliner relationships. The RBF networks consist of 2 learning steps. The first step is an unsupervised learning in hidden layer and the next step is a supervised learning in output layer. Therefore, the RBF networks could provide rather time saved in the learning step than the BP algorithm. The peak discharge both BP algorithm and RBF network model in the estimation of an unlearned are a is trended to observed values.

• Korean Journal of Agricultural and Forest Meteorology
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• v.1 no.2
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• pp.151-159
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• 1999

지구규모의 대기-지표-생물권(Atmo-Geo-Bio-Sphere)간의 끊임없는 상호작용(Interaction)의 피드백(Feedback)의 결과로 야기되는 기상변화는 아직도 이해를 위한 우리의 노력이 더욱 요구되고 있는 자연현상이다. 지구상의 모든 생물은 궁극적으로는 환경변화에 순응하여 생태계의 안정을 유지하는 방향으로 진화할 것이므로 생물자원의 관리분야라 할 수 있는 농업생산도 결국 기상자원의 변화에 효율적으로 적응하기 위한 인간활동인 것이다. 최근 빈발하고 있는 세계적인 이상기상의 출현은 일시적인 현상이 아니라 과도한 인간활동에서 야기된 대기질의 악화에 기인하는 비가역적이고 비선형적인 현상이라는데 불확실성과 심각성이 매우 크다. 지구상의 모든 농업생태계는 기상의 영향을 크게 받을 뿐만 아니라 반대로 기상에 커다란 영향을 미치는 중요한 생물권의 일부로 인식되고 있다. 농업활동의 결과는 항상 크던 작던 간에 대기조성에 영향을 미치게 되고 이는 다시 상호작용과 피드백에 의해 기상과 기후를 변화시키는 동인이 될 수 있다. 지구환경변화와 농업과의 관계는 지금까지는 주로 "기후변화가 농업생산에 미치는 영향"에 대한 접근방법을 택하여 왔다. 여기에서는 이와는 달리 "농업활동이 기후변화와 변동에 미칠 수 있는 가능성과 잠재력"에 대한 접근방법을 이용하여 농업과 기상과의 상호작용과 피드백효과를 새로운 시각에서 조견하고자 하였다. 상호작용 중 먼저 기후학적 변화원인으로 관심대상이 되고 있는 농업생태계의 온실기체 방출과 고정의 측면에서 이와 연관성이 높은 농업활동별로 온실가스의 방출/고정에 미치는 영향을 소개하고, 다음으로 생물지리화학적 및 생물지리물리학적 해석 방법을 검토 소개하였다. 한편 농업활동에 따른 지표면 특성의 변화가 국지기상 변화에 미치는 영향에 대한 검토를 에너지수지와 수분수지 관점에서 소개하였으며, 끝으로 농업활동의 근거지인 농촌지역의 인문사회학적 변화와 농업활동간의 관계, 그리고 이들이 기후변화/변동에 미칠 수 있는 잠재적 영향력을 살펴보았다.수 있는 잠재적 영향력을 살펴보았다.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.15 no.2
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• pp.1-12
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• 2016

This paper is to analyze characteristics of transfer trips and to identify impacts of land use on them. Using the smart transport card data of Seoul on a weekday in April 2013, we explored general characteristics of the transfer trips such as spatial and temporal distributions, transfer types, and geographical patterns of transfer trips. Then, the multiple regression model for the transfer trips was developed, considering land use as well as socio-economic variables as explanatory ones. For the characteristics of the transfer trips, their ratio to the total trips accounts for 26.7%. Nearly 87% of the trips are one-time transferred, and 64.7% are bus-subway transfer trips. In addition, the transfer trips are more likely to appear nearby subway stations and business facilities. The regression model indicates that land use variables such as the floor areas of business facilities and department stores and mixed land use index significantly positively affect the transfer trips. Our results can be used as basic data for choosing feasible locations of multi-modal transfer centers in urban areas.

• Elastomers and Composites
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• v.33 no.4
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• pp.231-237
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• 1998

In order to investigate the physical properties of rubber blend compound, this experiment was carried out on the cure rate, loss tangent, reinforcement and abrasion properties of S-SBR (solution styrene-butadiene rubber) blends containing silane coupled silica and E-SBR (emulsion styrene-butadiene rubber) blends containing carbon black as a model compound. E-SBR blend showed the highest total bound rubber(TBR), while S-SBR blends showed constant TBR level regardless of rubber type. Rapid cure rate was achieved when the styrene and vinyl content of rubber microstructure decreased and TBR content of rubber compounds increased. The modulus as the index of rubber reinforcement showed the linear relation with TBR content. The large amount of PICO loss was observed when the styrene and vinyl content of rubber microstructure increased, while the small amount of PICO loss was observed when the ratio of bu-tadiene increased in the S-SBR blends with silane copuled silica. The high loss tangent at $0^{\circ}C$, the low loss tangent at $60^{\circ}C$, and the large difference of loss tangent were shown in the S-SBR blends with high styrene content compared to E-SBR blend.

• Journal of Venture Innovation
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• v.1 no.2
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• pp.35-46
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• 2018

The research on the efficiency analysis of domestic auto parts companies is mostly based on the calculation of the magnitude of the performance creation such as the sales amount compared to the input assets. However, the performance indicators such as sales, operating profit, and net profit are directly related to the cost structure and This cost structure is affected by changes in the firm's asset and capital structure. As a result, it is considered that efficient capital procurement needs to be done at the same time to create efficient management performance through proper investment. This study focuses on this point and attempts to measure the efficiency of procurement capital relative to the sales and other performance indicators generated by the first 33 suppliers who supply parts to Hyundai Kia Motors. Among the methods of evaluating efficiency, the DEA model based on the linear programming method is most widely used as a nonparametric method but The efficient frontier-based DEA model has the limitation that it can not use the variables that have a downward influence on the efficiency. This is inadequate to directly consider variables such as borrowings and total liabilities related to capital procurement. In this study, the efficiency of capital procurement was measured using Worst Practice DEA and the improvement direction of the capital procurement aspect of domestic auto parts companies was suggested

• Journal of Korea Port Economic Association
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• v.22 no.4
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• pp.81-98
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• 2006

Many studies on port tariff have been done over twenty years using publicly assessed data on tariff. Public data for tariff rates do not reflect, however, the port tariff in a real market, since the cargo handling charge, which is the important fraction of port tariff, is confidentially decided by the negotiations between a shipping company and a container terminal operator. In this paper, we collected the real price data of the port tariff on the world major sixteen container ports from a global shipping company and transformed it into the tariff per TEU(US$/TEU). The comparative analysis of port tariff was performed using the port tariff per TEU, and a panel regression analysis was done to identify the relations between the port tariff and demand variables: throughput, GDP and trade amount.

• Journal of Korea Water Resources Association
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• v.38 no.1
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• pp.1-9
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• 2005

The study shows the possible use of the index flood frequency curves for an estimation of flood quantiles at ungauged locations. Flood frequency analysis were made for the annual maximum flood data series at 9 available stations in the Han river basin. From the flood frquency curve at each station the mean annual flood of 2.33-year return period was determined and the ratios of the flood magnitude of various return period to the mean annual flood at each station were averaged throughout the Han river basin, resulting mean flood ratios of different return periods. A correlation analysis was made between the mean annual flood and physiographic parameters of the watersheds i.e, the watershed area and mean river channel slope, resulting an empirical multiple linear regression equation over the whole Han river basin. For unguaged watershed the flood of a specified return period could be estimated by multiplying the mead flood ratio corresponding the return period with the mean annual flood computed by the empirical formula developed in terms of the watershed area and river channel slope. To verify the applicability of the methodology developed in the present study the floods of various return periods determined for the watershed in the river channel improvement plan formulation by the Ministry of Construction and Transportation(MOCT) were compared with those estimated by the present method. The result proved a resonable agreement up to the watershed area of approximately 2,000k $m^2$. It is suggested that the practice of design flood estimation based on the rainfall-runoff analysis might have to be reevaluated because it involves too much uncertainties in the hydrologic data and rainfall-runoff model calibration.

• Journal of Radiation Protection and Research
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• v.28 no.4
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• pp.311-319
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• 2003

We developed a grid-based Gaussian plume model to evaluate tracer release data measured at Young Gwang nuclear site in 1996. Downwind distance was divided into every 10m from 0.1km to 20km, and crosswind distance was divided into every 10m centering released point from -5km to 5km. We determined dispersion factors, ${\sigma}_y\;and\;{\sigma}_z$ using Pasquill-Gifford method computed by atmospheric stability. Forecasting ability of the grid-based Gaussian plume model was better at the 3km away from the source than 8km. We confirmed that dispersion band must be modified if receptor is far away from the source, otherwise P-G method is not appropriate to compute diffusion distance and diffusion strength in case of growing distance. So, we developed an empirical equation using linear programming. An objective function was designed to minimize sum of the absolute value between observed and computed values. As a result of application of the modified dispersion equation, prediction ability was improved rather than P-G method.

• The Journal of the Acoustical Society of Korea
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• v.32 no.2
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• pp.181-189
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• 2013

The purpose of the present study is to investigate the effect of cortical bone on acoustic properties of trabecular bone, such as speed of sound (SOS) and normalized broadband ultrasound attenuation (nBUA), in bovine femur in vitro. Twelve trabecular bone samples and three cortical bone plates with thicknesses of 1.00, 1.47, and 2.00 mm were extracted from the proximal end of two bovine femurs. The correlations between acoustic properties and trabecular apparent bone density were also examined before and after attaching a cortical bone plate to the trabecular bone samples. SOS increased linearly with increasing thickness of the cortical plate attached to one side of ultrasonic incidence of the trabecular bone samples, whereas nBUA showed a nonlinear dependence on the thickness of the cortical plate. All the SOS (r = 0.95-0.97) and nBUA (r = 0.53-0.73) measurements with and without the cortical bone plate with various thicknesses were found to exhibit high correlations with the trabecular apparent bone density. These results imply that the acoustic properties measured in the femur with lateral cortical layers in vitro can be useful indices for the prediction of trabecular bone mineral density.