• Journal of the Earthquake Engineering Society of Korea
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• v.16 no.3
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• pp.23-33
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• 2012

Dynamic response measurements from natural excitation were carried out for three 18-story office buildings to determine their inherent properties. The beam-column frame system was adopted as a typical structural form, but a core wall was added to resist the lateral force more effectively, resulting in a mixed configuration. To extract modal parameters such as natural frequencies, mode shapes and damping ratios from a series of vibration records at each floor, the most advanced operational system identification methods based on frequency- and time-domain like FDD, pLSCF and SSI were applied. Extracted frequencies and mode shapes from the different identification methods showed a greater consistency for three buildings, however the three lower frequencies extracted were 1.2 to 1.7 times as stiff as those obtained using the initial FE models. Comparing the extracted fundamental periods with those estimated from the code equations and FE analysis, the FE analysis results showed the most flexible behavior, and the most simple equation that considers the building height as the only parameter correlated fairly well with test results. It is recognized that such a discrepancy arises from the fact that the present tests exclude the stiffness decreasing factors like concrete cracking, while the FE models ignore the stiffness increasing factors, such as the contribution of non-structural elements and the actual material properties used.

• Journal of the Korean Geotechnical Society
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• v.30 no.2
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• pp.65-76
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• 2014

For soil improvement, sand mats or sand compaction piles are often constructed on soft marine clays. In such cases, some amounts of sand and clay are inevitably mixed. Sand or gravel often exists in the weathered soils near the slope surface. This research investigates the effect of mixing sand content on consistency limits and shear strength of clays. Firstly, sand was mixed with kaolinite or bentonite at 0, 9, 17, 23, 29, 33, 50% and then liquid and plastic limits were measured. Both plastic and liquid limits decreased as a sand content increased. The water content of clay-sand mixtures with different sand content increased by 10% or 20% step by step and then their undrained shear strength was measured using a portable vane shear device called Torvane. For all cases, undrained shear strength of clay-sand mixtures decreased rapidly until reaching a certain value. Their state changed from undrained to drained state gradually as the sand content increased, which caused their undrained shear strength to decrease. On the other hand, a series of direct shear tests were also conducted on such clay-sand mixtures to investigate the effect of sand content on cohesion and angle of internal friction. It was found from clay-sand mixtures that their cohesion decreased but angle of internal friction increased as the sand content increased.

• Journal of The Korean Association For Science Education
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• v.40 no.3
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• pp.253-269
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• 2020

This study aims to develop items to diagnose pre-service physics teachers' understanding of the conceptual knowledge of modern physics, based on the achievement criteria presented in the 2015 revised national science curriculum, and to identify the validity and reliability of the newly developed items. Data were collected from 467 pre-service physics teachers in the Physical Education Department or Science Education Department (Physics Education Major) of 15 universities across the nation. In this study the content validity, substantive validity, the internal structure validity, generalization validity, and the external validity proposed by Messick (1995) were examined by various statistical tests. The results of the MNSQ analysis showed that there was no nonconformity in the 23 items. The internal structure validity was confirmed by the standardized residual variance analysis, which shows that the 22 items was unidimensional. The generalization validity was confirmed by differential item functioning (DIF) analysis about groups lectured or not modern physics/quantum mechanics. In addition, item analysis and test analysis based on classical test theory were performed. The mean item difficulty is 0.66, mean item discrimination is 0.47 and mean point biserial coefficient obtained was 0.41. These results for item parameters satisfied the criteria respectively. The reliability of the internal consistency of the KR-20 is 0.77 and the Ferguson's delta obtained was δ = 0.972. By Rasch model analysis, the item difficulty (item measures) was discussed.

• Ocean and Polar Research
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• v.42 no.3
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• pp.195-210
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• 2020

The observed time series from the Korea Ocean Research Stations (KORS) in the Yellow and East China Seas (YECS) have various sources of noise, including bio-fouling on the underwater sensors, intermittent depletion of power, cable leakage, and interference between the sensors' signals. Besides these technical issues, intricate waves associated with background tidal currents tend to result in substantial oscillations in oceanic time series. Such technical and environmental issues require a regionally optimized automatic quality control (QC) procedure. Before the achievement of this ultimate goal, we examined the approach of the Ocean Observatories Initiative (OOI)'s standard QC to investigate whether this procedure is pertinent to the KORS. The OOI QC consists of three categorized tests of global/local range of data, temporal variation including spike and gradient, and sensor-related issues associated with its stuck and drift. These OOI QC algorithms have been applied to the water temperature time series from the Ieodo station, one of the KORS. Obvious outliers are flagged successfully by the global/local range checks and the spike check. Both stuck and drift checks barely detected sensor-related errors, owing to frequent sensor cleaning and maintenance. The gradient check, however, fails to flag the remained outliers that tend to stick together closely, as well as often tend to mark probably good data as wrong data, especially data characterized by considerable fluctuations near the thermocline. These results suggest that the gradient check might not be relevant to observations involving considerable natural fluctuations as well as technical issues. Our study highlights the necessity of a new algorithm such as a standard deviation-based outlier check using multiple moving windows to replace the gradient check and an additional algorithm of an inter-consistency check with a related variable to build a standard QC procedure for the KORS.

• Journal of Korean Elementary Science Education
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• v.36 no.3
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• pp.219-226
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• 2017

In this study, the reliability and validity of the retrospective pre-post test were analyzed in order to solve the problem of traditional pre-post test including response shift bias. Samples of the study were 162 elementary school students who are studying at the S university gifted education center in Seoul. Before completion of the field trip, we conducted pre test of science-related attitudes. After completion of the field trip, respondents were asked to compare their responses of pre and post science-related attitudes to quantitatively analyze the commonalities and differences of the two tests. To find out more characteristics, qualitative data such as daily records and interview were also gathered and analyzed. The major results of the study are as follows. First, for the paired t-test, there was no statistically significant difference between separate pre-test scores and retrospective pre-test. There was a very high correlation between the separate pre-test scores and the retrospective pre-test. Second, there were significant differences in all seven sub-factors of science-related attitudes between the retrospective pre-test and the post-test. Third, the separate pre-test scores showed a slightly higher tendency than the retrospective pre-test scores. This suggests that the response shift bias appears when it is performed the separate pre-test in affective domain. As a result of the interview, it was found that the evaluation standards of separate pre-test did not match with those of post-test. Forth, internal consistency reliability of the retrospective pre-test was higher than that of the separate pre-test. However, there were significant differences in six factors of science-related attitudes excluding the 'social implications of science' between the separate pre-test and the post-test. Based on these results, the retrospective pre-post test design provides simplicity and convenience to both respondents and investigators, as it is done with one test. The retrospective pre-post test design can be regarded as a valid design for the self-report measurement of affective domain on a single experimental group.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.5
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• pp.391-400
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• 2020

This study compared the parenting education needs of mothers and grandmothers who are rearing toddlers (12~36 months old), in order to examine how to resolve conflicts and problems caused by inconsistencies in the parenting attitudes of these caregivers. The findings will provide basic data for the development of a consistent parenting education program. The participants in this study were 201 mothers and 201 grandmothers who were all rearing toddlers. Data was collected at 11 daycare center in C city, Gyeongsangnamdo from August 1, 2017 to October 12, 2017. The collected data was analyzed by descriptive statistics, frequencies, percentages, means, standard deviations, and independent t-tests. As a result of comparing the parenting education needs of mothers and grandmothers, the overall evaluation of education needs was rated as 2.82±0.58 for mothers and 2.81±0.63 for grandmothers on a scale of 4, and there were no statistically significant differences in all five domains (t=0.21, p=.836). The highest education needs were found in the prevention and management of disease and injury, and the lowest was in the physical caring. Based on the results of this study, a toddler parenting education program was developed after selecting contents focusing on the prevention and management of disease and injury domain where education needs are high. We propose a study to examine the effects of applying such a program to both mothers and grandmothers who are rearing toddlers.

• Korean Journal of Social Welfare
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• v.67 no.2
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• pp.61-84
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• 2015

The purpose of this study was to develop the Post-bereavement Growth Inventory(PBGI) for the elderly and to evaluate its validity. The items for developing PBGI were compiled from a literature search, content validity review, and a preliminary survey. A main survey of 308 widowed persons(aged 60+) was conducted. The results were as follows. First, an exploratory factor analysis revealed six factors of the PBGI. The results of the confirmatory factor analysis supported a five-factor structure for the final 24 scale items of scale. Second, in terms of concurrent validity, the PGBI compared favorably with the "Personal Growth" scale from The Hogan Grief Reaction Checklist (HGRC: Hogan and Schimdt, 2001). Third, the results of contrast group validity tests demonstrated that the group scoring in the upper 30% on the scales of Psychological Well-being (PWB, Ryff and Keyes, 1995) and the Grief Reaction Inventory (GRI: Remondet and Hansson, 1987) showed a significantly higher degree of post-bereavement growth (PBG) than the group scoring in the lower 30%. Fourth, Cronbach's ${\alpha}$ values for the five factors were between .649-.856 and .907 overall, indicating high internal consistency. Finally, education had the most significant influence on PBG. All results indicated the high validity of the PBGI. The findings from this study could provide the rationale for practical interventions from a growth-oriented perspective for widowed persons, as well as an objective assessment tool for practitioners in clinical areas.

• Korean Journal of Social Welfare
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• v.63 no.2
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• pp.207-231
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• 2011

This study aims to identify constructs of cultural competency specifically relevant to the Korean society and to test its reliability and validity among human service workers. For the purpose of the study, authors conducted focus group interviews and conferences with human service workers to draw the concept of cultural competency. Further, this study conducted to two separate pilot tests with 20 social workers with practice experiences in order to clarify descriptions and relevance of scale items. Based on the literature review on the concept of cultural competency and analysis of focus group interviews, 40 items were initially constructed and then were reduced to a 32-item scale after two separate pilot studies. Meantime, suggestions made by an advisory group were also reflected in the scale development process. Finally, one hundred ninety four workers in social service agencies were recruited to evaluate the relevance of the scale items in a 5 point Likert scale. Through exploratory and confirmatory factor analysis, 4 main factors were identified: 1) competency to use culturally relevant skills, 2) cultural awareness and sensitivity, 3) cultural knowledge, and 4) efforts to overcome cultural differences. These factors were consistent with sub-concepts of cultural competency in other studies. Confirmatory factor analysis also showed that the model fitness was at the high level and convergent analysis with the similar scale also showed high correlations. Internal consistency also remained at a high level. Based on the results, implication for social work practice and education were discussed.

• Journal of the Korea Concrete Institute
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• v.16 no.1 s.79
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• pp.27-35
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• 2004

Most of concrete fatigue tests currently used are flexural tension or compression methods to investigate the tensile or compressive properties, respectively. However, the concrete pavement or concrete slab is actually subjected to a combined stress condition such as biaxial or triaxial. The split tension test may result in similar stress condition to biaxial stress condition. The purposes of this study were to evaluate the split tension fatigue test method for application in concrete. These were done by a finite element analysis and experimental series. The results were as follows: The optimum configuration of split tension fatigue test was a cylinder of 15cm in diameter and 7.5cm in thickness, which had a little different thickness compared to the KS standard cylinder of ${\phi}15{\times}30cm$. The concrete stress ratio of compressive against horizontal from FEA was 3.1, while that from theory was 3.0. The stress distributions of mortar and steel were almost similar at different thicknesses. The measured static split tensile strengths of concrete and mortar were quite similar at 30cm and 7.5cm thickness cylinders. The measured stress-strain relationship showed their consistency at all specimens regardless of thickness, and confirmed the results from FEA. As a results, the concrete split tension specimen, cylinder of 15cm in diameter and 7.5cm in thickness, could be used at fatigue test because of its accuracy, simplicity and convenience.

• Journal of the Korean Data and Information Science Society
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• v.11 no.1
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• pp.83-90
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• 2000

The chi-squared test statistic is usually employed for testing independence of two categorical variables in a two-way contingency table. It is well known that, under independence, the test statistic has an asymptotic chi-squared distribution under multinomial or product-multinomial models. For the case where both margins fixed, the sampling model of the contingency table is a multiple hypergeometric distribution and the chi-squared test statistic follows the same limiting distribution. In this paper, we study the difference between the small sample and large sample distributions of the chi-squared test statistic for the case with fixed margins. For a few small sample cases, the exact small sample distribution of the test statistic is directly computed. For a few large sample sizes, the small sample distribution of the statistic is generated via a Monte Carlo algorithm, and then is compared with the large sample distribution via chi-squared probability plots and Kolmogorov-Smirnov tests.