• Journal of the Korean Geotechnical Society
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• v.21 no.8
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• pp.27-35
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• 2005

Several damages due to large displacement caused by liquefaction have been reported increasingly. Numerical procedures based on effective stress analysis are therefore necessary to predict liquefaction-induced deformation. In this paper, the fully coupled effective stress model called UBCSAND is proposed to simulate pore pressure rise due to earthquake or repeated loadings. The proposed model is a modification of the simple perfect elasto-plactic Mohr-Coulomb model, and can simulate a continuous yielding by mobilizing friction and dilation angles below failure state. Yield function is defined as the ratio of shear stress to mean normal stress. It is radial lines on stress space and has the same shape of Mohr-Columob failure envelope. Plastic hardening is based on an isotropic and kinematic hardening rule. The proposed model always causes plastic deformation during loading and reloading but it predicts elastic unloading. It is verified by capturing direct simple shear tests on loose Fraser River sand.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.2409-2421
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• 2011

This paper will present hybrid tests to a one bay-one story steel frame structure under ground excitation. A structure used in this paper for hybrid test, to evaluate performance and behavior, is divided into two models; one is numerical model with one column element, and a truss or a beam element, the other is physical substructural model with one beam-column element. All tests considered one or three degrees of freedom to implement real-time hybrid test, and two control algorithms to control hardware are used; one using MATLAB/Simulink, the other using OpenSees, OpenFresco and xPCTarget. In addition, for real-time data communication between numerical and physical substructural models SCRAMNet was used. The results of hybrid tests were compared with one of numerical analysis of numerical model with fiber force-based beam-column elements using OpenSees. Real-time hybrid tests were implemented for the validation of control system with simple structure, and then it will be extended to hybrid test for higher nonlinear or complex structure later on.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.4
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• pp.377-385
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• 2002

Ultrasonic tests employing non-ionizing radiation are preferred in nondestructive examinations since they are safe and simple in use. The same principles of the techniques have been taken as valuable tools in medical area for the diagnoses of diseases, in other words, defects of the human body. The paper overviews the principles of the medical diagnosis based on nondestructive ultrasonic tests, and then evaluates experimentally the clinical potential of C scan images not popular in medicine, for detecting the micro fractures of the cortical bone. In the experiment the micro bone fractures were created on the femurs of porks by loading three point bending forces (2-4kN) with the speed of 1 mm/min. As the extent of the fracture was altered, not only X ray images but also ultrasonic C scan images using a focused ultrasonic probe resonated at 25 MHz were obtained. The results showed that ultrasonic C scan images were capable of detecting the micro bone fractures which were not possible to identify by conventional X ray images.

• Progress in Medical Physics
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• v.9 no.3
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• pp.143-154
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• 1998

The image intensifier is the key component which determines the imaging characteristics in a fluoroscopic imaging system. A system performance program for clinical evaluation of two image intensifiers, that is simple, non-invasive and time effective, was described. Tests were grouped into three headings: x-ray generator, image quality, and collimation. For the x-ray generator, the kVp accuracy and the automatic exposure control operation were compared. Low- and high-contrast resolution measurements, and mesh pattern study belong to the image quality tests and those tests were performed for the video monitor and photospot images. For the collimation, usable field diameter and image distortion of image intensifiers were measured and quantified. The procedures and the results are hoped to be used for the clinical evaluation of system performance and/or acceptance tests for image intensifiers.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.863-874
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• 2008

We have to judge engineering properties of rock accurately in order to design and construct rock structure safely and economically. Among the rock tests, the test result of UCS(Uniaxial Compressive Strength) is very important factor used in the variety ways for designing and construction of underground structures, rock slope and foundation analysis. But the UCS test has some disadvantages of intact sample preparation such as because the shape of sample has to be regular cylindrical, cube or rectangular. In order to solve those problem, indirect tests are used such as point load test, schmidt hammer test, absorption test, dry density to predict UCS of rock. Those tests are easy to prepare sample and convenient to carry out the tests, so it is simple and costs less. Schmidt hammer test are frequently used in the construction site, because it is handy and easy to use, but there is concern of misuse without classifying the specification of each schmidt hammer. Thus, this study suggested presumptive numerical formula related on each specification of schmidt hammer test, point load test, absorption test and dry density also. We compared presumptive numerical formula and R-square through schmidt rebound assessment method already brought up. Also, through the test we offer the extent of weathering index according to the weathering grade.

• Journal of the Korean Geotechnical Society
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• v.29 no.1
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• pp.109-120
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• 2013

This paper presents the results of a laboratory investigation into a study on undrained characteristics of a geogrid-encased stone column (GESC) installed in soft clay under cyclic load. In order to analyze behavior of settlement, pore water pressure, stress concentration ratio and strain of the GESC compared to a stone column, a series of reduced-scale laboratory tests were performed. The model tests show that GESC provides a simple and effective method of deformation resistance and settlement restraint when a short-term cyclic load is applied. The maximum strain of geogrid occurred at 1.2D and 1.5D from the top of the column. This paper highlights the importance of considering overlay effect and replacement ratio on cyclic load supporting GESC.

• Computers and Concrete
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• v.21 no.4
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• pp.407-417
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• 2018

Concrete which is a composite material is one of the most important construction materials. Compressive strength is a commonly used parameter for the assessment of concrete quality. Accurate prediction of concrete compressive strength is an important issue. In this study, we utilized an experimental procedure for the assessment of concrete quality. Firstly, the concrete mix was prepared according to C 20 type concrete, and slump of fresh concrete was about 20 cm. After the placement of fresh concrete to formworks, compaction was achieved using a vibrating screed. After 28 day period, a total of 100 core samples having 75 mm diameter were extracted. On the core samples pulse velocity determination tests and compressive strength tests were performed. Besides, Windsor probe penetration tests and Schmidt hammer tests were also performed. After setting up the data set, twelve artificial intelligence (AI) models compared for predicting the concrete compressive strength. These models can be divided into three categories (i) Functions (i.e., Linear Regression, Simple Linear Regression, Multilayer Perceptron, Support Vector Regression), (ii) Lazy-Learning Algorithms (i.e., IBk Linear NN Search, KStar, Locally Weighted Learning) (iii) Tree-Based Learning Algorithms (i.e., Decision Stump, Model Trees Regression, Random Forest, Random Tree, Reduced Error Pruning Tree). Four evaluation processes, four validation implements (i.e., 10-fold cross validation, 5-fold cross validation, 10% split sample validation & 20% split sample validation) are used to examine the performance of predictive models. This study shows that machine learning regression techniques are promising tools for predicting compressive strength of concrete.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.905-912
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• 2009

1-g shaking table test is conducted to evaluate the dynamic behavior of a soil-structure system under seismic loading condition. A consistent similitude law between the model and prototype is needed to predict the behavior of the prototype structure, quantitatively. The natural frequency of geomaterial decreases with the increase of shaking intensity because of the non-linear property of the geomaterial. This phenomenon affects the applicability of similitude laws in 1-g shaking table tests. In this study, a simple method is suggested to determine the frequency of the input motions in 1-g tests in order to enhance the applicability of similitude laws. Modified input frequency is calculated using the frequency ratio with consideration of the variation of the natural frequency according to the intensity of input ground acceleration. To verify the applicability of the suggested method, a series of 1-g shaking table tests were performed for three different sizes of model piles having an overburden mass on their heads by varying the acceleration and the frequency of input motion. The acceleration amplification ratio on the overburden mass, the lateral displacement at the pile head and the maximum bending moment along the pile depth were measured. The projected behaviors of the virtual prototype based on the measured values of the model tests, where the input frequencies were calculated by the new method, showed good consistency, verifying the applicability of the suggested method.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.31 no.1
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• pp.18-26
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• 2009

Purpose: Recently, the role of serum tumor marker has been studied for an important issue on diagnosing and treating tumors in the head and neck region because tests using tumor markers need relatively simple procedures and are acceptable to patients, compared with other test methods. Tumor marker tests were performed on patients with squamous cell carcinoma, which were known to have the highest prevalence among tumors in the head and neck region. Association between each tumor marker, and diagnosis and prognosis of tumors was assessed. Materials and methods: Tumor marker tests were carried out on 31 patients who visited Oral and Maxillofacial Surgery Department in Dankook University Dental Hospital between January 2003 and August 2008 and who were diagnosed as primary oral squamous cell carcinoma through out histopathologic diagnosis. Blood sample from these patients was performed to measure tumor markers using nuclear medicine diagnostic equipment. Measured entries were as follows: PSA(prostate-specific antibody), SCCAg( Squamous Cell Carcinoma Related Antigen), CA 19-9(Cancer Antigen 19-9), Ferritin, $\alpha$- FP(Alpha-Fetoprotein), Cyfra 21-1, CA125 (Cancer Antigen 125) and p53. Results: Analyses on each tumor marker indicated that squamous cell carcinoma in the head and neck region had statistically significant correlation with p53, SCC-Ag(TA-4), Cyfra 21-1 and Ferritin. p53 demonstrated the highest sensitivity. Especially, 4 cases among 18 cases which Ferritin was measured exhibited metastasis. In all those 4 cases, Ferritin values were higher than the standards (15 - 332ng/ml). Therefore, Ferritin is considered to have a close relation with metastasis of squamous cell carcinoma. Conclusion: This study shows that tumor marker tests are more useful in evaluating progression and prognosis of tumors rather than in diagnosing them. Particularly, serum Ferritin is considered to be beneficial in assessing metastasis of squamous cell carcinoma in the head and neck region and in developing treatment plans based on the assessment.

• Communications of Mathematical Education
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• v.22 no.2
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• pp.229-252
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• 2008

The purpose of this research was to make fair assessment methods which took into account characteristics of mathematically underachievers. The researchers devised an descriptive tests and interviews and applied them to the mathematics underachievers who could not reveal their achievements in the traditional assessment and then analyzed their cognitive and affective characteristics in the alternative assessments. After selecting three students by the normal assessment made of simple subjective and multiple choice questions, the cognitive and affective characteristics found in the general assessment were reflected to the descriptive tests and interviews. The descriptive tests and interviews are comprised of descriptive narrations and informal interview questions. After the assessment, the teacher and students gave feedbacks one another. All the assessment activities were recorded by a camcorder to analyze cognitive and affective characteristics of the children. Throughout the research, the following conclusions were made. The mathematics underachievers showed the characteristics which didn't appeared in the normal assessment. They showed normal abilities of problem solving and communication In the cognitive area. Also they brought in positive result in most parts in the affective area. However, the student B displayed considerable ability of mathematical thinking that is over the average level of mathematical underachievers. This implies that we can definite the mathematical underachievers differently when we use the detailed and relief assessment method instead of the traditional assessment. On the other hand, one student tended to depend on the teacher and another student overheard what the others talk during the study. This defect should be complemented by the further studies about assessment method for the mathematical underachievers. Also appropriate assessment methods should be made for applying to the various mathematical underachievers. Many studies have been concentrated on the learning for mathematical underachievers but there is little concern about the assessment for the mathematical underachievers. However it is the fundamental way to reduce the number of mathematics underachievers that we construct consistent learning methods and assessments for the mathematical underachievers.