• Journal of Korean Society of Transportation
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• v.22 no.7 s.78
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• pp.155-159
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• 2004

Recently, there are many trials about Artificial neural networks : ANNs structure and studying method of researches for forecasting traffic volume. ANNs have a powerful capabilities of recognizing pattern with a flexible non-linear model. However, ANNs have some overfitting problems in dealing with a lot of parameters because of its non-linear problems. This research deals with the application of a variety of model selection criterion for cancellation of the overfitting problems. Especially, this aims at analyzing which the selecting model cancels the overfitting problems and guarantees the transferability from time measure. Results in this study are as follow. First, the model which is selecting in sample does not guarantees the best capabilities of out-of-sample. So to speak, the best model in sample is no relationship with the capabilities of out-of-sample like many existing researches. Second, in stability of model selecting criterion, AIC3, AICC, BIC are available but AIC4 has a large variation comparing with the best model. In time-series analysis and forecasting, we need more quantitable data analysis and another time-series analysis because uncertainty of a model can have an effect on correlation between in-sample and out-of-sample.

• Journal of Bio-Environment Control
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• v.29 no.2
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• pp.161-170
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• 2020

There is systematic spatial variations in environmental properties due to sensitive reaction to external conditions at plastic greenhouse occupied 99.2% of domestic agricultural facilities. In order to construct 3 dimensional distribution of temperature, relative humidity, CO₂ and illuminance, measurement matrix as 3 by 3 by 5 in direction of width, height and length, respectively, dividing indoor space of greenhouse was designed and tested at experimental site. Linear regression analysis was conducted to evaluate optimal estimation method in terms with horizontal and vertical variations. Even though sole measurement point for temperature and relative humidity could be feasible to assess indoor condition, multiple measurement matrix is inevitably required to improve spatial precision at certain time domain such as period of sunrise and sunset. In case with CO₂, multiple measurement matrix could not successfully improve the spatial predictability during a whole experimental period. In case with illuminance, prediction performance was getting smaller after a time period of sunrise due to systematic interference such as indoor structure. Thus, multiple sensing methodology was proposed in direction of length at higher height than growing bed, which could compensate estimation error in spatial domain. Appropriate measurement matrix could be constructed considering the transition of stability in indoor environmental properties due to external variations. As a result, optimal measurement matrix should be carefully designed considering flexibility of construction relevant with the type of property, indoor structure, the purpose of crop and the period of growth. For an instance, partial cooling and heating system to save a consumption of energy supplement could be successfully accomplished by the deployment of multiple measurement matrix.

• Journal of Sensor Science and Technology
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• v.5 no.2
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• pp.61-67
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• 1996

The growth and characterization of heteroepitaxial $Si_{1-x}Ge_{x}$ films grown by the RTCVD (Rapid Thermal Chemical Vapor Deposition) method were described. For the growth of $Si_{1-x}Ge_{x}$ heteroepitaxial layers, $SiH_{4}$ / $GeH_{4}$ / $H_{2}$ gas mixtures were used. The growth conditions were varied to investigate their effects on the Si / Ge composition ratios, the interface abruptness and crystalline properties. The experimental data shows that the misfit threading dislocation in $Si_{1-x}Ge_{x}$ / Si heteroepitaxial film of about $400\;{\AA}$ thickness was not observed at the growth temperature of as low as $650^{\circ}C$, and the composition ratios of Si / Ge changed linearly with $SiH_{4}$ / $GeH_{4}$ gas mixing ratios in our experimental ranges. In the in-situ boron doping experiments, the doping abruptness would be controlled within several hundreds ${\AA}$/decade.

• Journal of Korea Water Resources Association
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• v.45 no.6
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• pp.557-568
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• 2012

In order to understand the hydrological processes on the mountainous forest, the configuration of soil evaporation (E) out of evapotranspiration (ET) is a challenging and important topic. In this study, we attempted to understand the soil evaporation process for a humid forest hillslope via measuring and analyzing soil moistures with a sampling interval in 2 hours at three locations for 10 days between May 22th and 31th 2009. Two methods were used to estimate soil evaporation in every 2hr; one is a method using soil moisture measurement ($E_{SM}$), the others methods are based on Penman equation (Penman (1948), Staple (1974), Konukcu (2007), Equilibrium Penman ($E_{equili}$)). As a critical parameter in determining $E_{SM}$, the dry surface layer (DSL), was estimated using energy balance equation. The accumulated soil evaporation ($E_{SM}$) of A, B, C points were estimated as 2.09, 1.08 and 2.88 mm, respectively. The estimated evaporation of Penman (1948), Staple (1974), Konukcu (2007), $E_{equili}$ were 4.91, 8.80, 8.63 and 3.28 mm. The proposed method with soil moisture measurement showed lower soil evaporations than the other conventional methods. The increasing soil temperature and interaction between soil and atmosphere due to existence of litter and DSL are considered as dominant factors for soil evaporation. The $E_{SM}$ has the apparent lag time between 2 and 4 hr compared with $E_{equili}$ and net radiation. The DSL and surface resistance ($r_s$) were increased as soil moisture was decreased for in this study. The estimated DSL through the temporal distribution analysis of soil moisture and tension measurements was also similar to that of the energy balance relationship.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.15 no.3
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• pp.207-218
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• 2017

In this study, pitch-based activated carbon fibers (ACFs) were modified with pyrolysis fuel oil (PFO). Carbonized ACF samples were activated at $850^{\circ}C$, $880^{\circ}C$ and $900^{\circ}C$. A scanning electron microscope (SEM) and a BET surface area apparatus were employed to evaluate the indoor radon removal of each sample. Among three samples, the BET surface area and micropore area of ACF880 recorded the highest value with $1,420m^2{\cdot}g^{-1}$ and $1,270m^2{\cdot}g^{-1}$. Moreover, ACF880 had the lowest external surface area and BJH adsorption cumulative surface area of pores with $151m^2{\cdot}g^{-1}$ and $35.5m^2{\cdot}g^{-1}$. This indicates that satisfactory surface area depends on the appropriate temperature. With the above scope, ACF880 also achieved the highest radon absorption rate and speed in comparison to other samples. Therefore, we suggest that the optimum activation temperature for PFO containing ACFs is $880^{\circ}C$ for effective indoor radon adsorption.

• Nuclear Engineering and Technology
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• v.20 no.2
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• pp.88-104
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• 1988

The FUel Rod Analysis(FURA) code is developed using two-dimensional finite element methods for axisymmetric and plane stress analysis of fuel rod. It predicts the thermal and mechanical behavior of fuel rod during normal and load follow operations. To evaluate the exact temperature distribution and the inner gas pressure, the radial deformation of pellet and clad, the fission gas release are considered over the full-length of fuel rod. The thermal element equation is derived using Galerkin's techniques. The displacement element equation is derived using the principle of virtual works. The mechanical analysis can accommodate various components of strain: elastic, plastic, creep and thermal strain as well as strain due to swelling, relocation and densification. The 4-node quadratic isoparametric elements are adopted, and the geometric model is confined to a half-pellet-height region with the assumption that pellet-pellet interaction is symmetrical. The pellet cracking and crack healing, pellet-cladding interaction are modelled. The Newton-Raphson iteration with an implicit algorithm is applied to perform the analysis of non-linear material behavior accurately and stably. The pellet and cladding model has been compared with both analytical solutions and experimental results. The observed and predicted results are in good agreement. The general behavior of fuel rod is calculated by axisymmetric system and the cladding behavior against radial crack is used by plane stress system. The sensitivity of strain aging of PWR fuel cladding tube due to load following is evaluated in terms of linear power, load cycle frequency and amplitude.

• Korean Journal of Remote Sensing
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• v.38 no.5_1
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• pp.627-646
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• 2022

Recently, the seriousness of climate change-related problems caused by global warming is growing, and the average temperature is also rising. As a result, it is affecting the environment in which various temperature-sensitive creatures and creatures live, and changes in the ecosystem are also being detected. Seasons are one of the important factors influencing the types, distribution, and growth characteristics of creatures living in the area. Among the most popular and easily recognized plant seasonal phenomena among the indicators of the climate change impact evaluation, the blooming day of flower and the peak day of autumn leaves were modeled. The types of plants used in the modeling were forsythia and cherry trees, which can be seen as representative plants of spring, and maple and ginkgo, which can be seen as representative plants of autumn. Weather data used to perform modeling were temperature, precipitation, and solar radiation observed through the ASOS Observatory of the Korea Meteorological Administration. As satellite data, MODIS NDVI was used for modeling, and it has a correlation coefficient of about -0.2 for the flowering date and 0.3 for the autumn leaves peak date. As the model used, the model was established using multiple regression models, which are linear models, and Random Forest, which are nonlinear models. In addition, the predicted values estimated by each model were expressed as isopleth maps using spatial interpolation techniques to express the trend of plant seasonal changes from 2003 to 2020. It is believed that using NDVI with high spatio-temporal resolution in the future will increase the accuracy of plant phenology modeling.

• Journal of the Korean Magnetics Society
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• v.14 no.1
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• pp.46-50
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• 2004

Compounds of $Y_{3-x}Ce_{x}Fe{5}O_{12}$(x=0.0, 0.1, 0.2, and 0.3) were prepared using the sol-gel method. The XRD measurements show that these samples have only a single phase of the garnet structure regardless of the amount of Ce substitution. The lattice constants of x = 0.0 and x = 0.3 were found to be a$_0$ = 12.3758 ${\pm}$0.0005 ${\AA}$ and 12.4062 ${\pm}$0.0005 ${\AA}$, respectively. The lattice constant increases linearly with increasing Ce concentration. The saturation magnetization was not changed flirty, with increasing Ce concentration, but coercivity decreased form 18.3 Oe to 5.8 Oe as x increased form x = 0.0 to x = 0.1. Mossbauer spectra of $Y_{3-x}Ce_{x}Fe{5}O_{12}$ were measured at various absorber temperatures from 13 K to Neel temperature. The Mossbauer spectra were fitted by least-squares technique with two subpatterns of Fe sites in the structure and corresponding to the 16a and 24d site. The temperature dependence of the magnetic hyperfine field in $^{57}$/Fe nuclei at the tetrahedral 240 and octahedral 16a sites were analyzed based on the Neel theory of ferrirnagnetism. The result of the Debye temperatures indicated that the inter-atomic binding force for the 24d site was larger than that for the 16a site.

• Journal of Korean Society of Environmental Engineers
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• v.32 no.2
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• pp.165-174
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• 2010

The numerical modeling of a coal gasification reaction occurring in an entrained flow coal gasifier is presented in this study. The purposes of this study are to develop a reliable evaluation method of coal gasifier not only for the basic design but also further system operation optimization using a CFD(Computational Fluid Dynamics) method. The coal gasification reaction consists of a series of reaction processes such as water evaporation, coal devolatilization, heterogeneous char reactions, and coal-off gaseous reaction in two-phase, turbulent and radiation participating media. Both numerical and experimental studies are made for the 1.0 ton/day entrained flow coal gasifier installed in the Korea Institute of Energy Research (KIER). The comprehensive computer program in this study is made basically using commercial CFD program by implementing several subroutines necessary for gasification process, which include Eddy-Breakup model together with the harmonic mean approach for turbulent reaction. Further Lagrangian approach in particle trajectory is adopted with the consideration of turbulent effect caused by the non-linearity of drag force, etc. The program developed is successfully evaluated against experimental data such as profiles of temperature and gaseous species concentration together with the cold gas efficiency. Further intensive investigation has been made in terms of the size distribution of pulverized coal particle, the slurry concentration, and the design parameters of gasifier. These parameters considered in this study are compared and evaluated each other through the calculated syngas production rate and cold gas efficiency, appearing to directly affect gasification performance. Considering the complexity of entrained coal gasification, even if the results of this study looks physically reasonable and consistent in parametric study, more efforts of elaborating modeling together with the systematic evaluation against experimental data are necessary for the development of an reliable design tool using CFD method.

• Korean Journal of Remote Sensing
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• v.34 no.2_1
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• pp.301-306
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• 2018

Urbanization causes urban floods and urban heat island in the summer, so it is necessary to understanding the changes of the thermal environment through urban climate and energy balance. This can be explained by the energy balance, but in urban areas, unlike the typical energy balance, the storage heat flux saved in the building or artificial land cover should be considered. Since the environment of each city is different, there is a difficulty in applying the method of retrieving the storage heat flux of the previous research. Especially, most of the previous studies are focused on the overseas cities, so it is necessary to study the storage heat retrieval suitable for various land cover and building characteristics of the urban areas in Korea. Therefore, the object of this study, it is to derive the regression formula which can quantitatively retrieve the storage heat using the data of the area where various surface types exist. To this end, nonlinear regression analysis was performed using net radiation and surface temperature data as independent variables and flux tower based storage heat estimates as dependent variables. The retrieved regression coefficients were applied to each independent variable to derive the storage heat retrieval regression formula. As a result of time series analysis with flux tower based storage heat estimates, it was well simulated high peak at day time and the value at night. Moreover storage heat retrieved in this study was possible continuous retrieval than flux tower based storage heat estimates. As a result of scatter plot analysis, accuracy of retrieved storage heat was found to be significant at $50.14Wm^{-2}$ and bias $-0.94Wm^{-2}$.