• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.1A
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• pp.79-87
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• 2008

This paper investigates the in-plane stability of fixed shallow arches. The shape of the arches is parabolic and the uniformly distributed load is used in the study. The nonlinear governing equilibrium equation of the general arch is adopted to derive the incremental form of the load-displacement relationship and the buckling load of the fixed shallow arches. From the results, it is found that buckling modes (symmetric or asymmetric) of the arches are closely related to the dimensionless rise H, which is the function of slenderness ratio and the rise to span ratio of such arches. Moreover, the threshold of different buckling modes and buckling load for fixed shallow arches are proposed. A series of finite element analysis are conducted and then compared with proposed ones. From the comparative study, the proposed formula provides the good prediction of the buckling load of fixed shallow arches.

• Geomechanics and Engineering
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• v.35 no.6
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• pp.647-663
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• 2023

The investigation of the disc cutter wear prediction has an important guiding role in TBM equipment selection, project planning, and cost forecasting, especially when tunneling in a long-distance rock formations with high strength and high abrasivity. In this study, a comprehensive database of disc cutter wear data, geological properties, and tunneling parameters is obtained from a 1326 m excavated metro tunnel project in leptynite in Shenzhen, China. The failure forms and wear consumption of disc cutters on site are analyzed with emphasis. The results showed that 81% of disc cutters fail due to uniform wear, and other cutters are replaced owing to abnormal wear, especially flat wear of the cutter rings. In addition, it is found that there is a reasonable direct proportional relationship between the uniform wear rate (WR) and the installation radius (R), and the coefficient depends on geological characteristics and tunneling parameters. Thus, a preliminary prediction formula of the uniform wear rate, based on the installation radius of the cutterhead, was established. The correlation between some important geological properties (K_V and UCS) along with some tunneling parameters (F_n and p) and wear rate was discussed using regression analysis methods, and several prediction models for uniform wear rate were developed. Compared with a single variable, the multivariable model shows better prediction ability, and 89% of WR can be accurately estimated. The prediction model has reliability and provides a practical tool for wear prediction of disc cutter under similar hard rock projects with similar geological conditions.

• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.2
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• pp.9-16
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• 2024

In this paper, we aimed to convert the fire curve in volume units to a fire curve per unit area for application in the Fire Dynamic Simulator (FDS) surface heat release rate method. The fire curve was expressed dimensionlessly considering the total combustion characteristic time, and improvements were made to represent the appropriate ratios for the growth , steady, and decay phases concerning the fire intensity. Additionally, a correction function for combustion characteristic time varying with mass increase was derived. Also to control the growth time values according to the increase in mass, a function to correct the growth phase ratio was derived. Consequently, utilizing existing data, a formula was established to determine the reference mass for combustion materials and predict the fire curve based on mass increase.

• Geomechanics and Engineering
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• v.37 no.2
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• pp.123-133
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• 2024

This study investigates the effects of loading frequency (f) and specimen size on the liquefaction resistance of clean sand. A series of cyclic direct simple shear tests were conducted on Jumunjin sand with varying consolidated relative densities (40% and 80%), f values (0.05, 0.10, and 0.20 Hz), and diameter to height (D/H) ratios (3.63, 3.18, 2.82, and 2.54). The results demonstrated the significant influence of f and D/H ratio on the number of cycles to liquefaction (N_cyc-liq) and the cyclic resistance ratio (CRR₁₅). It was observed that increasing f linearly increased N_cyc-liq. Increasing the specimen height also led to higher N_cyc-liq values irrespective of the f or relative density. Moreover, a positive correlation between CRR₁₅ and f indicated that higher f yielded higher CRR₁₅. This relationship was more pronounced in dense sand than in loose sand. Specimen height also significantly affected CRR₁₅, with increasing the specimen height resulting in higher CRR₁₅ values. Furthermore, the effect of f on CRR₁₅ was less significant compared to the influence of specimen height. The effect of f on the normalized cyclic resistance ratio (NCRR) was relatively negligible for loose sand but more substantial for dense sand depending on the D/H ratio. Data analysis revealed that the NCRR generally decreases as the D/H ratio increases. An interpolation formula was provided to calculate the NCRR based on the D/H ratio regardless of the f and relative density.

• Korean Journal of Radiology
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• v.20 no.6
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• pp.976-984
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• 2019

Objective: To establish diagnostic criteria for pulmonary arterial hypertension (PAH) in children by using parameters obtained through noninvasive cardiac computed tomography (CCT). Materials and Methods: We retrospectively measured parameters from CCT images of children from a single institution in a multiple stepwise process. A total of 208 children with mean age of 10.5 years (range: 4 days-18.9 years) were assessed. The variables were classified into three groups: the great arteries; the ventricular walls; and the bilateral ventricular cavities. The relationship between the parameters obtained from the CCT images and mean pulmonary arterial pressure (mPAP) was tested and adjusted by the children's body size. Reference curves for the pulmonary trunk diameter (PTD) and ratio of diameter of pulmonary trunk to ascending aorta (rPTAo) of children with CCT images of normal hearts, adjusted for height, were plotted. Threshold lines were established on the reference curves. Results: PTD and rPTAo on the CCT images were significantly positively correlated with mPAP (r > 0.85, p < 0.01). Height was the body size parameter most correlated with PTD (r = 0.91, p < 0.01) and rPTAo (r = -0.69, p < 0.01). On the basis of the threshold lines on the reference curves, PTD and rPTAo both showed 88.9% sensitivity for PAH diagnosis, with negative predictive values of 93.3% and 92.9%, respectively. Conclusion: PTD and rPTAo measured from CCT images were significantly correlated with mPAP in children. Reference curves and the formula of PTD and rPTAo adjusted for height could be practical for diagnosing PAH in children.

• Journal of Educational Research in Mathematics
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• v.16 no.1
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• pp.25-41
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• 2006

The purpose of this study was to analyze teachers' pedagogical content knowledge (PCK) about area of plane figure and how it was actualized in instruction. As an exploratory, qualitative, and comparative case study, 2 fifth-grade teachers were selected. Semi-structured interviews with the leachers were conducted in order to explore their PCK with regard to the area of plane figure. A total of 14 mathematics instructions were videotaped and transcribed. Teachers' PCK and classroom teaching practices were analyzed in detail into 3 categories: (a) knowledge of mathematics contents, (b) knowledge of students' understanding, and (c) knowledge of instructional methods. As such, this paper provided a detailed description on each teacher's PCK and her teaching practice. The results showed that teachers' PCK had a significant impact on instruction. The teacher who had rich knowledge about the area of plane figure was able to encourage students to understand the concept of area and to or explore the principles behind formula calculating various areas of plane geometry. The results demonstrated the importance of individual components of PCK as well as that of overall level of PCK. Different aspects of teaching practices were observed as to how the teachers had internalized PCK. On the basis of a close relationship between teachers' PCK and their teaching practice, this paper finally raised several implications for teachers' professional development for effective mathematics instruction.

• Journal of Korean Elementary Science Education
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• v.36 no.4
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• pp.379-393
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• 2017

This study analyzed the relationship between self-directedness of science-gifted elementary students and their expression of scientific creativity in science-gifted class. A science-gifted program on the topic of Hydraulic Machine was implemented to 34 fifth-graders in the Science-Gifted Education Center of an education office in Seoul, Korea for four weeks. The self-directedness of the gifted students was divided into three types of 'General, Scientific, and Topic-Related Self-Directedness'. The products of the students' activities were assessed by using a scientific creativity assessment formula. Qualitative research, such as analysis of observations and interviews, was also conducted in order to identify characteristics that were not apparently revealed by quantitative data. The main results of this study are as follows: First, science-gifted elementary students' general self-directedness and their scientific creativity were significantly correlated (r=.373). Second, the students' scientific self-directedness and scientific creativity did not have a significant correlation (r=.294). Third, there was a positive correlation between the students' topic-related self-directedness and their expression of scientific creativity. Their self-rated scores (r=.420) for the topic-related self-directedness and the number of activity types associated with the topic had a positive correlation (r=.350). Fourth, the students were categorized into four groups according to the levels of their self-directedness and scientific creativity, and the result showed that Type HH (high self-directedness and high scientific creativity) was the most common type (15 students, 38.5%), followed by Type LL (low self-directedness and low scientific creativity) (11 students, 28.2%). Eight (20.5%) and five students (12.8 %) belonged to Type LH (low self-directedness and high scientific creativity) and Type HL (high self-directedness and low scientific creativity) respectively. Fifth, the classroom observation of the students in groups revealed that groups with more number of Type HH demonstrated better cooperation and performance. Sixth, the analysis results of the observation were almost matched to the results of the self-directedness and scientific creativity tests. The students with higher self-directedness demonstrated active class participation and good cooperative skills. The students with higher scientific creativity had a tendency to generate creative ideas more frequently in given situations. Seventh, dynamic activities were perceived as enjoyable and exciting by 76.9% of the students, but static activities that require creativity were regarded as interesting only by 23.1% of the students. Among the students who were satisfied with both the creative and static activities, Type HH accounted for the largest proportion (55.6%). In conclusion, factors such as students' interests, initiatives, and attitudes displayed through voluntary participations originated from their own daily life can predict the degree of scientific creativity associated with the topic. Also, when students were categorized into four types according to the level of self-directedness and scientific creativity, there was a tendency of active behavior in class, cooperative skill, and activity satisfaction. This suggested that we should consider self-directedness and scientific creativity in selecting the gifted, grouping them in class, and designing and executing programs for science-gifted elementary students.

• The KIPS Transactions:PartB
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• v.13B no.4 s.107
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• pp.471-478
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• 2006

In this paper, two color contrast evaluation algorithms, W3C and NSSC algorithms are compared and investigated to select proper criteria of the color contrast of text-background color combinations in web documents. The relationship between the color contrast defined by existing formula and the readability rating is not perfect and there is quite a bit of variance, in particular, there is some substantial outlier. I modify the NSSC algorithm to apply all colors and compare the two algorithms to apply same color combinations of web safe colors. A new algorithm considering color temperature feeling as a component of the color contrast is proposed and implemented. As the results of this study, the existing two algorithms are not contradictory to each other, 82% of all color combinations of web safe colors are not proper combinations according to W3C guide which provide severe restriction to select colors in web documents compared to NSSC algorithm. Experimental test shows proposed algorithm is superior to the W3C algorithm with respect to the linearity of relationship between color contrast and readability rating. It means a color temperature feeling is an effective component of a color contrast. But to determine best contribution ratio of the color temperature feeling, further study is required and it is related to Hangul font style and size. The more popular a mobile color display is used, the more important accessibility factor a color contrast will be.

• Pediatric Gastroenterology, Hepatology & Nutrition
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• v.17 no.1
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• pp.47-51
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• 2014

Purpose: Neonatal late-onset hypocalcemia is defined as hypocalcemia developed after postnatal 3 days and associated with hypoparathyroidism, high phosphate diets and vitamin D deficiency. We experienced the increment of neonatal late onset hypocalcemia over 1 year. We tried to evaluate the relationship between late onset hypocalcemia and maternal hypovitaminosis D. Methods: The medical records in the neonates with late-onset hypocalcemia during January 2007 to July 2008 were retrospectively reviewed. Among those patients, 17 paired sera of mothers and neonates had collected. The levels of 25-OH vitamin D (25OHD) and intact parathyroid hormone (iPTH) were measured and were compared with neonate and the mother. Results: The mean gestational age was $38^{+1}$ weeks, and the mean body weight was 2,980 g. The onset time of hypocalcemia was 5.9 days of age. Most of them (88.2%) were feeding with formula and no one was only breast milk feeding. Of the 17 patients, 13 were born in spring or in winter. The median levels of calcium, phosphorus, alkaline phosphatase, iPTH and 25OHD were 7.0 mg/dL, 8.6 mg/dL, 191.0 U/L, 57.2 pg/mL and 24.0 ng/mL in neonates. The levels of 25OHD of 6 neonates were <20 ng/mL. A total of 16 mothers were considered vitamin D-deficient (<20 ng/mL), and vitamin D insufficient (20<25OHD<30 ng/mL). Conclusion: Neonatal late-onset hypocalcemia in our study seems to be influenced by maternal vitamin D deficiency and insufficiency. Sun tanning and vitamin D supplements from winter to spring would be helpful to prevent maternal vitamin D deficiency, one of the causes of neonatal late-onset hypocalcemia.

• Journal of Nutrition and Health
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• v.46 no.1
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• pp.61-71
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• 2013

The aim of this study was to examine the relationship between dietary variables and the prevalence of insulin resistance (IR) in middle-aged Korean adults using data from the 2007-2009 Korea National Health and Nutrition Examination Survey. Because IR is closely linked with metabolic syndrome, subjects were divided into three groups according to symptoms of metabolic syndrome: the 'Normal group' without any symptoms, the 'Risk group' with one or two symptoms, and the Metabolic syndrome (MetS) group' with three or more symptoms. Subjects between the ages of 30 and 65 years with no prior diagnosis or treatment for diabetes, hypertension, or dyslipidemia were selected. The number of subjects per group was as follows: 2,085 adults in the Normal group, 3,699 adults in the Risk group, and 1,160 adults in the MetS group. Metabolic syndrome was defined according to Adult Treatment Panel III criteria with modified waist circumference cutoff values (men ${\geq}$ 90 cm, women ${\geq}$ 85 cm). Subjects with HOMA-IR > 2.0 were classified as IR. Homeostasis Model Assessment of Insulin Resistance (HOMA-IR) was calculated using the following formula: (fasting plasma glucose ${\times}$ fasting plasma insulin)/22.5. Nutrients and food groups intake were obtained from a single 24-hour recall. Subjects with IR in the Normal group were more obese and less physically active than non-IR subjects. In the MetS group, subjects with IR were more obese and had a lower prevalence of smoking and drinking, compared with non-IR subjects. Men with IR in the Normal group had a tendency to consume more oils and sugars than non-IR men, while women with IR in the same group had higher intake of carbohydrate, dietary glycemic index, and dietary glycemic load than non-IR women. Women with IR in the Risk group had lower energy intake but higher intake of oils and sugars than non-IR women. In the MetS group, consumption of fruits was higher in subjects with IR than in non-IR subjects. In conclusion, findings of this study suggest that dietary carbohydrate intake, including glycemic index, may be associated with IR in healthy women. Further research in prospective cohort studies in order to examine the effects of dietary carbohydrate on IR incidence will be necessary.