• Journal of the Korean Geotechnical Society
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• v.29 no.9
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• pp.5-15
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• 2013

In this paper, the unsaturated slope stability analysis considering suction stress (Lu and Godt, 2008) was introduced and the results applied for a certain sand slope were analyzed. The unsaturated slope stability analysis considering suction stress can analyze both conditions of steady infiltration and no infiltration, and it can estimate the safety factor of slope as a function of soil depth. Also, the influence of weathering phenomenon at a certain depth from the ground surface can be considered. The stability analysis considering suction stress was applied to the unsaturated infinite slope composed of sand with the relative density of 60%. The suction stress under no infiltration condition was affected by ground water table until a certain influencing depth. However, the suction stress under steady infiltration condition was affected by seepage throughout the soils. Especially, the maximum suction stress was displayed around ground surface. The factor of safety in the infinite slope under no infiltration condition rapidly increased and decreased within the influence zone of ground water table. As a result of slope stability analysis, the factor of safety is less than 1 at the depth of 2.4 m below the ground surface. It means that the probability of slope failure is too high within the range of depths. The factor of safety under steady infiltration condition is greater than that under no infiltration condition due to the change of suction stress induced by seepage. As the steady infiltration rate of precipitation was getting closer to the saturated hydraulic conductivity, the factor of safety decreased. In case of the steady infiltration rate of precipitation with $-1.8{\times}10^{-3}cm/s$, the factor of safety is less than 1 at the depths between 0.2 m and 3 m below the ground surface. It means that the probability of slope failure is too high within the range of depths, and type of slope failure is likely to be shallow landslides.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.47 no.6
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• pp.57-65
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• 2010

In this paper, we present a universal steganalysis scheme. The proposed method extract features of two types. First feature set is extracted from histogram characteristic of the wavelet subbands. Second feature set is determined by statistical moments of wavelet characteristic functions. 3-level wavelet decomposition is performed for stego image and cover image using the Haar wavelet basis. We extract one features from 9 high frequency subbands of 12 subbands. The number of second features is 39. We use total 48 features for steganalysis. Multi layer perceptron(MLP) is applied as classifier to distinguish between cover images and stego images. To evaluate the proposed steganalysis method, we use the CorelDraw image database. We test the performance of our proposed steganalysis method over LSB method, spread spectrum data hiding method, blind spread spectrum data hiding method and F5 data hiding method. The proposed method outperforms the previous methods in sensitivity, specificity, error rate and area under ROC curve, etc.

• Journal of Wetlands Research
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• v.18 no.4
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• pp.404-412
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• 2016

This paper not only aims to establish a plan to acquire the water stage data in a constant and proper manner by using limited manpower and costs, but also establishes the fundamental technology for acquiring the water level observation data or the stage data. For this, this paper focuses on how to acquire the stage data, in a uniform manner, that can represent each basin by developing the technology for establishing the optimal observational network. For that, this paper identifies the current status of the stage gauge stations installed in the ChungJu dam including wetland basin mainly along the national rivers. Then, thus obtained factors are used to develop the representative unit hydrograph. After that, the data are converted into the probability density function. Then, the stations are calculated information transfer amount. As a last step, we establish the optimized stage gauge network by the location of the stage station and space impact that takes into account for the combinations of the number of the stations. In other words, we consider the combination of the stage gauge station with information transfer amount and spatial correlation analysis for estimation.

• Journal of the Korea Concrete Institute
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• v.16 no.5 s.83
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• pp.581-589
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• 2004

This paper compares the fatigue behaviors of concretes subjected to flexural and split-tensional loadings, and proposes the fatigue reliability models based on experimental results and reliability analysis. The fatigue tests were performed for the specimens of $150 mm{\times}75 mm$ split tensional cylinders and $150 mm{\times}150 mm{\times}550 mm$ flexural beams under constant loadings at three levels (70, 80 and $90\%$) with 0.1 stress ratio, 20 Hz loading speed and sine wave. The reliability analysis on fatigue data was based on Weibull distribution of two-parameters. From fatigue test results, two criteria were proposed to reject the experimental fatigue data because of statistical variation of concrete fatigue data. Two parameters ($\alpha$and u) of Weibull distribution were obtained using graphical method, moment method and maximum likelihood method. The probability density function(P.D.F) and cumulative distribution function(C.D.F) of the Weibull distribution for fatigue life of pavement concrete were derived for various stress levels using parameters, $\alpha$ and u. The goodness-of-fit test by Kolmogorov-Smirnov test was acceptable at $5\%$ level of significance. Based on reliability analysis, a fatigue model for pavement concrete was proposed and compared from existing models.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.8
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• pp.615-623
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• 2018

The probability density function(PDF) for the amplitude of the reflectivity of low-grazing-angle sea clutter has generally been modeled by a compound-Gaussian distribution, rather than by the Rayleigh distribution, owing to the intensity variation of each clutter patch over time. The texture component forming the reflectivity has been simulated by combining Gamma distribution and memory-less nonlinear transformation(MNLT). On the other hand, there is no typical method available that can be used to simulate the speckle component. We first review Watt's method, wherein the speckle is simulated starting from the Doppler spectrum of the received echoes that is modeled as having a Gaussian shape. Then, we introduce a newly proposed method. The proposed method simulates the speckle by manipulating a clutter covariance matrix through the Cholesky decomposition after minimizing the effect of adjacent clutter patches using an equalizer. The feasibility of the proposed method is validated through simulation, wherein the results from two methods are compared in terms of the Doppler spectrum and the correlation function.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.40 no.5
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• pp.465-475
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• 2020

I-D-F curves were induced by Box-Cox transformation using rainfall data from five major cities in Korea: Seoul, Busan, Daegu, Daejeon, and Gwangju, as well as from Sancheong (South Gyeongsang province) and Yeongcheon (North Gyeongsang province) stations. The practicality of the Box-Cox transformation is more scalable than the traditional method of frequency analysis in terms of applicability because it is available even if the analysis data are insufficient to perform general frequency analysis and do not produce an appropriate probability density function. For the case in which rainfall data for the entire period (10-1440 minutes) and short-term period (20, 30, 40, 50 minutes) at the foregoing 7 stations are omitted, there was a relative error of -23.0 % to 14.7 % at a duration of 10 to 60 minutes below the 100-year frequency. Accordingly, rainfall analysis requires inducing I-D-F curves, including for the short term (20, 30, 40, 50 minutes), and if rainfall data are omitted for the short term (20, 30, 40, 50 minutes), it is necessary to increase the existing margin rate depending on the point in order to ensure the safe design of small-scale hydraulic structures.

• The Journal of Engineering Geology
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• v.19 no.2
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• pp.119-129
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• 2009

In relation to slope stability analysis, geologic characteristics and engineering properties of the discontinuities in three slopes selected are compared and analyzed by both square-inventory method and scanline survey. The aim of the study is in evaluating which method is applied better in slope stability analysis by comparing results of the two methods with those of direct observation on outcrop of slope failures generated. In each slope, results of comparative analysis among geologic and engineering properties are analyzed similarly one another. However, results of orientation analysis in slope 2 are different each other, which indicates orientation of joints in slope 2 depends on persistency and frequency of each joint and also indicates appearance of new joint set with different orientation. Probability density distribution and spacing in slope 3 are high in comparison to those in slope 2 and 3. The reasons are that distribution of psammitic rocks and development of minor folds in slope 3 unlike slope 2 and 3 are closely associated with development of joints. The research data indicate that the square-inventory method predicts more precise failure aspects and is more effective way than scanline survey in analyzing slope stability of the study area.

• Journal of Korean Society for Atmospheric Environment
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• v.28 no.3
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• pp.325-347
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• 2012

Long-term air and weather data monitored during the period of 2000 to 2009 were analyzed to quantitatively estimate the precipitation scavenging and wind dispersion contributions of ambient $PM_{10}$ and $NO_2$ in Korea. Both air pollutants and meteorological data had been respectively collected from 120 stations by the Ministry of Environment and from 20 weather stations by the Korea Meteorological Administrations in all parts of Korea. To stochastically identify the relation between a meteorological factor and an air pollutant, we initially defined the SR (scavenging ratio) and the DR (dispersion ratio) to separately calculate the precipitation and wind speed effects on the removal of a specific air pollutant. We could then estimate the OSC (overall scavenging contribution) and the ODC (overall dispersion contribution) with considering sectoral precipitation and wind speed probability density distributions independently. In this study, the SRs for both $PM_{10}$ and $NO_2$ were generally increased with increasing the amounts of precipitation and then the OSCs for $PM_{10}$ and $NO_2$ were estimated by 22.3% and 15.7% on an average in Korea, respectively. However, the trend of the DR was quite different from that of SR. The DR for $PM_{10}$ was increased with increasing wind speed up to 2.5 m/s and further the DR for $NO_2$ showed a minimum in the range of $1<WS{\leq}1.5$. The ODCs for $PM_{10}$ and $NO_2$ were estimated by 14.9% and 1.0% in Korea, respectively. Finally, we have also provided an interesting case study observed in Seoul.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.47 no.6
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• pp.28-39
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• 2010

The study aims at offering a solution to the problems of transmission delay and data throughput decrease as the number of contending On-Board Units (OBU) increases by applying CSMA medium access control protocol based upon IEEE 802.11p. In a competition-based medium, contention probability becomes high as OBU increases. In order to improve the performance of this medium access layer, the author proposes EDCA which a adaptive adjustment of the Contention Windows (CW) considering traffic density and data type. EDCA applies fixed values of Minimum Contention Window (CWmin) and Maximum Contention Window (CWmax) for each of four kinds of Access Categories (AC) for channel-specific service differentiation. EDCA does not guarantee the channel-specific features and network state whereas it guarantees inter-AC differentiation by classifying into traffic features. Thus it is not possible to actively respond to a contention caused by network congestion occurring in a short moment in channel. As a solution, CWminAS(CWmin Adaptation Scheme) and ACATICT(Adaptive Contention window Adjustment Technique based on Individual Class Traffic) are proposed as active CW control techniques. In previous researches, the contention probabilities for each value of AC were not examined or a single channel based AC value was considered. And the channel-specific demands of IEEE 802.11p and the corresponding contention probabilities were not reflected in the studies. The study considers the collision number of a previous service section and the current network congestion proposes a dynamic control technique ACCW(Adaptive Control of Contention windows in considering the WAVE situation) for CW of the next channel.

• Journal of the Korea Concrete Institute
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• v.19 no.5
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• pp.549-555
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• 2007

Although blast furnace slag has been widely used in concrete as a cementitious admixture or aggregate for many years, the slowly cooled steel slag is not used in concrete but mainly in road. Its use in concrete operates problem such as the lack of volume stability due to high free CaO content, which can be potentially hazardous in concrete. However, the rapidly cooled steel slag by atomization has a low free CaO content, a high density, and a spherical shape, so it is expected to use in concrete so much. This paper is to understand the probability that the rapid cooled steel slag can replace the silica sand used as aggregate in the epoxy mortar. We did the experimental study on the properties of the epoxy mortar having various replacement proportion of rapidly cooled steel slag. This study shown that increasing content of the rapidly cooled steel slag in epoxy mortar lead to increase largely the passing time of nozzle by O-lot, compressive strength and flexural strength. However except the flow is almost same level. So we understand that the rapidly cooled steel slag has positive effect on increasing of properties in epoxy mortar.