• Magazine of the Korean Society of Agricultural Engineers
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• v.37 no.3_4
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• pp.61-71
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• 1995

Natural ground is a composite consisted of the three phases of water, air and soil paircies. Among the three components, water as a material is weU understood but soil particles are not in foundation engineering. Especially, weathered granite soil generally shows a large volumetric expansion when they freeze. And, the stability and durability of the soil have shown decreased with repetitive freezing and thawing processes. These unique charcteristics may cause various construction and management problems if the soil is used as a construction material and foundation layers. This project was initiated to investigate the soil's physical and engineering characteristics resulting from freezing and freezing-thawing processes. Research results may be used as a basic data in solving various problems related to the soil's unique characteristics. The following conclusions were obtained: The degree of decomposition of weathered granite soil in Kangwon-do was very different between the West and East sides of the divide of the Dae-Kwan Ryung. Soil particles distributed wide from very coarse to fine particles. Consistency could be predicted with a function of P200 as LL=0.8 P200+20. Permeability ranged from 10-2 to 10-4cm/sec, moisture content from 15 to 20% and maximum dry density from 1.55 to 1.73 g /cmΥ$^3$ By compaction, soil particles easily crushed, D50 of soil particles decreased and specific surface significantly increased. Shear characteristics varied wide depending on the disturbance of soil. Strain characteristics influenced the soil's dynamic behviour. Elastic failure mode was observed if strain was less than 1O-4/s and plastic failure mode was observed if strain was more than 10-2/s. The elastic wave velocity in the soil rapidly increased if dry density became larger than 1.5 g /cm$^3$ and these values were Vp=250, Vg= 150, respectively. Frost heave ratio was the highest around 0 $^{\circ}C$ and the maximum frost heave pressure was observed when deformation ratio was less than 10% which was the stability state of soil freezing. The state had no relation with frost depth. Over freezing process was observed when drainage or suction freezing process was undergone. Drainage freezing process was observed if freezing velocity was high under confined pressure and suction frost process was occurred if the velocity was low under the same confined process.

• Journal of the Korean Geophysical Society
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• v.3 no.2
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• pp.127-138
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• 2000

This study was conducted to examine the differences between dynamic and static elastic constants by use of some laboratory tests of cement mortar specimens which have different water/cement mixing ratios. Specific gravity measurement, ultrasonic velocity estimating and uniaxial compression test were adopted to acquire the dynamic and static elastic constants. Digital data acquisition and processing enhanced the accuracy of estimating the velocities of specimens drastically, Also, the method using the gradient of propagation delay time in according to increment of specimen length more enhanced the accuracy than the method using the only one specimen length over total propagation time. The correlation between density and the P and S wave velocity of specimens shows reliable positive relation and the correlation between density and the strength of uniaxial compression has the similar relationship. The dynamic Young's modulus $(E_D)$ is alway greater than the static Young's modulus $(E_S)$ and there is increasing tendency of the ratio $(E_D/E_S)$ according to the increase of density or strength of the specimens. On the other hand, there is no typical relationship between dynamic Poisson's ratio $({\nu}_D)$ and static Poisson's ratio $({\nu}_S)$ and just the ratio of ${\nu}_D/{\nu}_S$ ranges front 69 to 122 %.

• Geomechanics and Engineering
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• v.34 no.4
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• pp.449-459
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• 2023

The design and development of underground nuclear waste repositories should cover the performance evaluation of the different components such as the construction materials because the long term stability will depend on their response to the surrounding conditions. In South Korea, Gyeonju bentonite has been proposed as a candidate to be used as buffer and backfilling material, especially in the form of blocks to speed up the construction process. In this study, various cylindrical samples were prepared with different dry density and water content, and their physical and mechanical properties were analyzed and correlated with X-ray CT observations. The main objective was to characterize the samples and establish correlations for non-destructive estimation of physical and mechanical properties through the utilization of X-ray CT images. The results showed that the Uniaxial Compression Strength and the P-wave velocity have an increasing relationship with the dry density. Also, a higher water content increased the values of the measure parameters, especially for the P-wave velocity. The X-ray CT analysis indicated a clear relation between the mean CT value and the dry density, Uniaxial Compression Strength, and P-wave velocity. The effect of the higher water content was also captured by the mean CT value. Also, the relationship between the mean CT value and the dry density was used to plot CT dry densities using CT images only. Moreover, the histograms also provided information about the samples heterogeneity through the histograms' full width at half maximum values. Finally, the particle size and heterogeneity were also analyzed using the Madogram function. This function identified small particles in uniform samples and large particles in some samples as a result of poor mixing during preparation. Also, the μ_max value correlated with the heterogeneity, and higher values represented samples with larger ranges of CT values or particle densities. These image-based tools have been shown to be useful on the non-destructive characterization of bentonite samples, and the establishment of correlations to obtain physical and mechanical parameters solely from CT images.

• Journal of the Korean Society of Radiology
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• v.4 no.2
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• pp.21-25
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• 2010

Recently, various semiconductor compounds as radiation detection material have been researched for a diagnostic x-ray detector application. In this paper, we have fabricated the CdS detecton sensor that has good photosensitivity and high x-ray absorption efficiency among other semiconductor compounds, and evaluated the application feasibility by investigating the detection properties about energy range of diagnostic x-ray generator. We have fabricated the line voltage selector(LCV) for a signal acquisition and quantities of CdS sensor, and designed the voltage detection circuit and rectifying circuit. Also, we have used a relative relation algorithm according to x-ray exposure condition, and fabricated the interface board with DAC controller. Performance evaluation was investigated by data processing using ANOVA program from voltage profile characteristics according to resistive change obtained by a tube voltage, tube current, and exposure time that is a exposure condition of x-ray generator. From experimental results, an error rates were reduced according to increasing of a tube voltage and tube current, and a good properties of 6%(at 90 kVp) and 0.4%(at 320 mA) ere showed. and coefficient of determination was 0.98 with relative relation of 1:1. The error rate according to x-ray exposure time showed exponential reduction because of delayed response velocity of CdS material, and the error rate has 2.3% at 320 msec. Finally, the error rate according to x-ray dose is below 10%, and a high relative relation was showed with coefficient of determination of 0.9898.

• Korean Journal of Applied Biomechanics
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• v.29 no.2
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• pp.121-128
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• 2019

Objective: The aim of this study was to examine the relation between swing phase and airborne phase of Tkatchev motion which was successfully performed with following motion by excellent middle and high school athletes in horizontal bar. Method: The subjects for this study were 8 male middle and high school top athletes. After their Tkatchev motions were filmed by two digital highspeed camcorders setting in 90 frames/sec at the 44th National Gymnastics against Cities and Provinces, the % lapse time lapse time of each instant, inferred maximum force acting on horizontal bar, and other kinematical variables were calculated through DLT method. After the relations among the % lapse times of each instants of downswing-start, downswing-finish, whipswing-finish, release, peak-height, and lapse time of regrasp, the relation among maximum force acting on bar, % lapse time, peak height, and the relation between % lapse time and release height were examined, the biomechanical timing characteristics of Tkatchev motion were as follows. Results: Firstly, it was revealed that the whole lapse time was $1.62{\pm}.06s$ and the correlation between the % lapse time of downswing-start and % lapse time of release was .819. Secondly, it was revealed that the pattern of COG path was shifted forwardly and tilted 11 clockwise from origin. Thirdly, it was revealed that maximum force acting on bar was inferred in $2,283{\pm}425N$ ($4.7{\pm}.6BW$) and the correlation between maximum force and peak height was r = .893. Lastly, it was revealed that the horizontal and vertical component of body COG velocity was $-2.14{\pm}.29m/s$, $2.70{\pm}.43m/s$ respectively, release height was $.49{\pm}.12m$, and shoulder angle was $139{\pm}5deg$, and that the later the % lapse time of release, the higher the release height (r = .935). Conclusion: It is desired that the gymnastic athletes should delay the downswing-start near the horizontal plane on $2^{nd}$ quadrant because the later the % lapse time of downswing, the higher the release height. After all the higher release height could ensure the athletes to regrasp the bar safely, the athletes should exercise to make downswing-start delay.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2008.05a
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• pp.797-800
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• 2008

Online signature verification system is widely used in banking account, credit card and so on, because system for online signature verification is easy to implementation and inexpensive. Therefore there are a lot of study on online signature verification. However there is little research about online signature is safe or not. This paper shows a way of online signature estimation using various information of signature. This paper make a experiment about relation sorority grade of online signature and 2-D information of online signature like the number of strokes and cross points, density of points, standard deviation of direction, velocity and acceleration, lengths of signature and convex hull etc. Finally, this paper presents several features of safe online signature.

• Transactions of the Korean Society of Automotive Engineers
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• v.17 no.2
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• pp.10-19
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• 2009

The working of diesel particulate filters(DPF) needs to periodically burn soot that has been accumulated during loading of the DPF. The prediction of the relation between an uniformity of gas velocity and soot regeneration efficiency with simulations helps to make design decisions and to shorten the development process. This work presents a comprehensive combined 'DOC+CDPF' model approach. All relevant behaviors of flow fluid are studied in a 3D model. The obtained flow fields in the front of DPF is used for 1D simulation for the prediction of the thermal behavior and regeneration efficiency of CDPF. Validation of the present simulation are performed for the axial and radial direction temperature profile and shows goods agreement with experimental data. The coupled simulation of 3D and 1D shows their impact on the overall regeneration efficiency. It is found that the flow non-uniformity may cause severe radial temperature gradient, resulting in degrading regeneration efficiency.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.79-84
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• 2004

Initial hull form of 10 G/T and 40 knots class coastal patrol boat is newly developed. The resistance performances are experimentally and numerically investigated by model test at high speed circulating water channel(CWC) and CFD technique. The effect of a fin attached at hull side and initial trim are studied together. Wave patterns are observed to make clear the relation between the resistance performance and the wave characteristics. it can be found that the initial trim plays a role to increase the resistance performance above a certain velocity.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.428-435
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• 2011

In general, thickness of the sublayers under track is designed based on concept of vertical soil reaction value or vertical stiffness. However, this design method cannot take consideration into soil-track interaction under repetitive load, traffic condition and velocity of the train. Furthermore, the reinforced roadbed soils experience complex behavior that cannot be explained by conventional stress-strain relation expressed as soil reaction value k. The reinforced roadbed soils also can produce cumulative permanent deformation under repetitive load caused by train. Therefore new design method for the sublayers under track must be developed that can consider both elastic modulus and permanent deformation. In this study, a new design concept, a rule-of-thumb, is proposed as the form of design monograph that is developed using elastic multi-layer and finite element programs by analyzing stress and deformation in the sublayers with changing the thickness and elastic modulus of the sublayers and also using data obtained from repetitive triaxial test. This new design concept can be applied to design of the reinforced roadbed before developing full version of design methodology that can consider MGT, axial load and the material properties of the layers. The new design monograph allows the user to design the thickness of the reinforced roadbed based on permanent deformation, elastic modulus and MGT.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.6B
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• pp.523-529
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• 2011

A tidal river is a river affected by tides causing the water level to rise and fall. In the river, the velocity induced by tides at a dry season can be a more dominant factor than that at a flood season in designing hydraulic structures. In this study, flow velocities and water levels were observed in the downstream of Han River at the dry season, and they are used for verification of numerically predicted results. The behaviors of flow were also analyzed by using UNET, a commercial model managing unsteady flows. To estimate the roughness coefficients of the tidal river reach near the Shingok submerged weir, a statistical method is employed. In the method, the discrepancy ratio between the measured and calculated water levels was implemented.