• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.143.1-143.1
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• 2011

Deep Ca,b,y images obtained from the CTIO 4m Blaco telescope are used to investigate the multiple stellar populations of red giant branch (RGB) and sub-giant branch (SGB) in Galactic globular clusters NGC 6656 and NGC 6723. For NGC 6656, confirming the result of Lee et al. (2009), we find two discrete populations of the RGB stars of which mean color separation is about 0.2 mag in hk[=(Ca-b)-(b-y)] index. Furthermore, we also find the bimodel distribution of the SGB stars in (hk, y) color-magnitude diagram. A new finding is that the (hk, y) color-magnitude diagram of NGC 6723 shows two distinct RGB stars with different calcium abundances of which mean color separation is about 0.12 mag in hk index. This multiple stellar feature has not been observed in previous observation, suggesting that NGC 6723 may also be a possible relic of dwarf galaxies that merged into the Milky Way in the past. Thus our result adds further constraints to the merging scenario of the Galaxy formation. Unfortunately, the split of SGB stars in NGC 6723 is not obvious. We will present some statistical results to compare properties of two populations in two clusters.

• Structural Engineering and Mechanics
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• v.68 no.6
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• pp.747-760
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• 2018

In the present study, a methodology for developing fragilities of arch concrete dams to assess their performance against seismic hazards is introduced. Firstly, the probability risk and fragility curves are presented, followed by implementation and representation of the way this method is used. Amirkabir arch concrete dam was subjected to non-linear dynamic analyses. A modified three dimensional rotating smeared crack model was used to take the nonlinear behavior of mass concrete into account. The proposed model considers major characteristics of mass concrete. These characteristics are pre-softening behavior, softening initiation criteria, fracture energy conservation, suitable damping mechanism and strain rate effect. In the present analysis, complete fluid-structure interaction is included to account for appropriate fluid compressibility and absorptive reservoir boundary conditions. In this study, the Amirkabir arch concrete dam is subjected to a set of 8 three-component earthquakes each scaled to 10 increasing intensity levels. Using proposed nonlinear smeared crack model, nonlinear analysis is performed where the structure is subjected to a large set of scaled and un-scaled ground motions and the maximum responses are extracted for each one and plotted. Based on the results, fragility curves were plotted according to various and possible damages indexes. Discrete damage probabilities were calculated using statistical methods for each considered performance level and incremental nonlinear analysis. Then, fragility curves were constructed based on the lognormal distribution assumption. Two damage indexes were introduced and compared to one another. The results indicate that the dam has a proper stability under earthquake conditions at MCE level. Moreover, displacement damages index is more conservative and impractical in the fragility analysis than tensional damage index.

• Korean Journal of Remote Sensing
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• v.33 no.2
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• pp.171-187
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• 2017

Thisstudy presentsthe method for deriving surface visibility from satellite retrieved AOD. To do thisthe height of aerosol distribution isrequired. This distribution would be in thisstudy represented by the two heights; if there is a discrete atmospheric layer, which is physically separated from the above layer, the upper height of the layer is assumed as Aerosol Layer Height(ALH). In this case there is clear minimum in the Relative Humanity vertical distribution. Otherwise PBLH(Planetary Boundary Layer Height) is used. These heights are obtained from the forecast data of Regional Data Assimilation and Prediction System(RDAPS). The surface visibility is estimated from MODIS AOD and ALH/PBLH, using Koschmieder's Law for ALH and the empirical relations for PBLH. The estimated visibility are evaluated from the visibility measurements of 9 eve-measurement stations and 17 PWD22 stations for the spring of 2015 and 2016. Verification of the estimated visibility shows that there are considerable differencesin statistical verification value depending on stations, years, morning(Terra)/afternoon(Aqua). The better results are shown in the midwest part of korean peninsula for Terra of 2016. The results are summarized as; correlation coefficients of higher than 0.65, for low visibility RMSE of 3.62 km and ME of 2.29 km or less, POD of higher than 0.65 and FAR of 0.5 or less. Verification results were better with increase in the number of low-visibility data.

• School Mathematics
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• v.16 no.1
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• pp.19-37
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• 2014

This study investigated the degree of understanding pre-service teachers' random variable concept, based on the attention and the importance for developing pre-service teachers' ability on statistical reasoning in statistics education. To accomplish this, the subject of this study was 70 pre-service teachers belonged to three universities respectively. The teachers were given to 7 tasks on random variable and requested to solve them in 40 minutes. The tasks consisted of three contents in large; 1) one was on the definition of random variables, 2) the other was on the understanding of random variables in different/diverse conditions, and 3) another was on problem solving relevant to random variable concept. The findings are as follows. First, while 20% of pre-service teachers understood the definition of random variable correctly, most teachers could not distinguish between random variable and variable or probability. Second, there was a significant difference in understanding random variables in different/diverse conditions. Namely, the degree of understanding on the continuous random variable was superior to that of discrete random variable and also the degree of understanding on the equal distribution was superior to that of unequality distribution. Third, three types of problems relevant to random variable concept dealt with in this study were finding a sample space and an elementary event, and finding a probability value. In result, the teachers responded to the problem on finding a probability value most correctly and on the contrary to this, they had the mot difficulty in solving the problem on finding a sample space.

• Journal of Soil and Groundwater Environment
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• v.12 no.5
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• pp.39-53
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• 2007

Generally, fractured medium can be described with some key parameters, such as hydraulic conductivities or random field of hydraulic conductivities (continuum model), spatial and statistical distribution of permeable fractures (discrete fracture network model). Investigating the practical applicability of the well-known conceptual models for the description of groundwater flow in fractured media, various types of hydraulic tests were applied to studies on the highly fractured media in Geumsan, Korea. Results from single-hole packer test show that the horizontal hydraulic conductivities in the permeable media are between $7.67{\times}10^{-10}{\sim}3.16{\times}10^{-6}$ m/sec, with $7.70{\times}10^{-7}$ m/sec arithmetic mean and $2.16{\times}10^{-7}$ m/sec geometric mean. Total number of test interval is 110 at 8 holes. The number of completely impermeable interval is 9, and the low permeable interval - below $1.0{\times}10^{-8}$ m/sec is 14. In other words, most of test intervals are permeable. The vertical distribution of hydraulic conductivities shows apparently the good correlation with the results of flowmeter test. But the results from the cross-hole test show some different features. The results from the cross-hole test are highly related to the connectivity and/or the binary properties of fractured media; permeable and impermeable. From the viewpoint of the connection, the application of the general stochastic approach with a single continuum model may not be appropriate even in the moderately or highly permeable fractured medium. Then, further studies on the investigation method and the analysis procedures should be required for the reasonable and practical design of the conceptual model, with which the binary properties, including permeable/impermeable features, can be described.