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

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
• /
• v.42 no.6
• /
• pp.352-357
• /
• 2016

Objectives: This study aimed to evaluate the stability of prosthetic screws from three types of craniofacial prostheses retention systems (bar-clip, ball/O-ring, and magnet) when submitted to mechanical cycling. Materials and Methods: Twelve models of acrylic resin were used with implants placed 20 mm from each other and separated into three groups: (1) bar-clip (Sistema INP, São Paulo, Brazil), (2) ball/O-ring (Sistema INP), and (3) magnet (Metalmag, São Paulo, Brazil), with four samples in each group. Each sample underwent a mechanical cycling removal and insertion test (f=0.5 Hz) to determine the torque and the detorque values of the retention screws. A servo-hydraulic MTS machine (810-Flextest 40; MTS Systems, Eden Prairie, MN, USA) was used to perform the cycling with 2.5 mm and a displacement of 10 mm/s. The screws of the retention systems received an initial torque of 30 Ncm and the torque values required for loosening the screw values were obtained in three cycles (1,080, 2,160, and 3,240). The screws were retorqued to 30 Ncm before each new cycle. Results: The sample was composed of 24 screws grouped as follows: bar-clip (n=8), ball/O-ring (n=8), and magnet (n=8). There were significant differences between the groups, with greater detorque values observed in the ball/O-ring group when compared to the bar-clip and magnet groups for the first cycle. However, the detorque value was greater in the bar-clip group for the second cycle. Conclusion: The results of this study indicate that all prosthetic screws will loosen slightly after an initial tightening torque, also the bar-clip retention system demonstrated greater loosening of the screws when compared with ball/O-ring and magnet retention systems.

• Progress in Superconductivity
• /
• v.13 no.1
• /
• pp.58-63
• /
• 2011

Recently, superconductor flywheel energy storage systems (SFESs) have been developed for application to a regenerative power of train, a power quality improvement, the storage of distributed power sources such as solar and wind power, and a load leveling. As the high temperature superconductor (HTS) bearings offer dynamic stability without the use of active control, accurate analysis of the HTS bearing is very important for application to SFESs. Mechanical property of a HTS bearing is the main index for evaluating the capacity of an HTS bearing and is determined by the interaction between the HTS bulks and the permanent magnet (PM) rotor. HTS bearing rotor consists of PM and iron collector and the proper dimension design of them is very important to determine a supporting characteristics. In this study, we have optimized a rotor magnet array, which depends on the limited bulk size and performed various dimension layouts for thickness of the pole pitch and iron collector. HTS bearing rotor was installed into a single axis universal test machine for a stiffness test. A hydraulic pump was used to control the amplitude and frequency of the rotor vibration. As a result, the stiffness result showed a large difference more than 30 % according to the thickness of permanent magnet and iron collector. This is closely related to the bulk stiffness controlled by flux pining area, which is limited by the total bulk dimension. Finally, the optimized HTS bearing rotor was installed into a flywheel system for a dynamic stability test. We discussed the dynamic properties of the superconductor bearing rotor and these results can be used for the optimal design of HTS bearings of the 10kWh SFESs.

• Journal of Korean Society of Forest Science
• /
• v.108 no.4
• /
• pp.562-573
• /
• 2019

In a cable yarding system, a small-scale tower yarder attached to a farm tractor wasdeveloped and used for small-diameter tree harvesting operations. Based on this design, improvement of traction performance was required for medium- and large-diameter tree harvesting operations. In this study, the mechanical transmission employed for the tower yarder was modified into ahydro-mechanical transmission system. Maximum traction forces, including tractor engine speed and hydraulic power pressure, were investigated, and comparisons were made between the mechanical and hydro-mechanical transmission systems. Six tractor engine speeds (1,200, 1,400, 1,600, 1,800, 2,000, and 2,200) and three levels of power transmission mechanism pressure (4.9, 6.9, and 8.8 MPa) were investigated in the two different transmission systems. Results showed a maximum traction force of 15,146.6 N at an engine rotation speed of 757 rpm in the current mechanical transmission system, and 36,140.0 N at anengine rotation speed of 1,575 rpm in the modified hydro-mechanical transmission system. The maximum traction forces for the hydro-mechanical transmission were 2.4 times greater than those of the mechanical transmission, and may therefore be applicable to medium and large-diameter tree harvesting operations. Thus,as a modified version of the conventional transmission system, the new hydro-mechanical transmission system may be cost-effective for use in large-scale cable yarding operations. In the future, however, it will be necessary to investigate problems that may arise from field application tests.

• Journal of Korean Elementary Science Education
• /
• v.37 no.4
• /
• pp.440-454
• /
• 2018

This study aims to compare student self-, teacher-, and objective assessments of elementary science-gifted students' scientific creativity. A science-gifted program on the topic of Hydraulic Machine was implemented to 40 fifth-graders in the Science-Gifted Education Center of an education office in Seoul, Korea for four weeks. The products of the students' activities were assessed by three types of 'Student Self-Assesment', 'Teacher-Assesment', and 'Objective Assessment using Formula'. Based on two essential components of creativity, the scientific creativity is divided into two parts of originality and usefulness. Ideas that satisfy both components can be counted as scientifically creative. The main results of this study are as follows: First, the scores of each week and the average of the overall four-week scores on scientific creativity were significantly correlated. Student self-assessment (r=.687), teacher-assessment (r=.715), and objective assessment (r=.724) appeared consistently over instructional periods. Second, the average scores of student self-, objective, and teacher-assessments were 73.15, 35.72, and 26.60, respectively. The result of student self-assessment on scientific creativity tended to be higher than those of formula and teacher. Third, among the three types of assessment on scientific creativity, a strong correlation appeared between teacher- and objective assessment (r=.974), but neither between student self- and objective (r=.161) nor between student self- and teacher- (r=.213). Fourth, the scores on originality component had a positive correlation between teacher- and objective assessment (r=.713). The scores of student self- and teacher-assessments had a significant correlation too (r=.315), but not between student self- and objective assessment (r=.279). Fifth, the scores on usefulness component did not have a significant correlation between student self- and teacher-assessment (r=.155). Sixth, there was no significant difference on scientific creativity between student self- and objective assessment [${\chi}^2$(1, n=40)=1.667, p<.197]. Not between student self- and teacher-assessment either [${\chi}^2$(1, n=40)=1.616, p<.204]. On the contrary, there was a significant difference between teacher- and objective assessment [${\chi}^2$(1, n=40)=32.593, p<.000]. Seventh, the students were categorized into four groups according to the levels of their scores by student self- and teacher-assessment. The result showed that factors influencing student self-assessment are inherent in the personality traits of gifted individuals, such as self-esteem and perfectionism. The findings suggested that there are challenges for the educators to make efforts to construct consistent assessment methods for scientific creativity.

• Journal of Korea Water Resources Association
• /
• v.55 no.spc1
• /
• pp.1295-1303
• /
• 2022

As the role of water distribution networks (WDNs) becomes more important, identifying abnormal events (e.g., pipe burst) rapidly and accurately is required. Since existing approaches such as field equipment-based detection methods have several limitations, model-based methods (e.g., machine learning based detection model) that identify abnormal events using hydraulic simulation models have been developed. However, no previous work has examined the impact of data uncertainties on the results. Thus, this study compares the effects of measurement error-induced pressure data uncertainty in WDNs. An artificial neural network (ANN) is used to predict nodal pressures and measurement errors are generated by using cumulative density function inverse sampling method that follows Gaussian distribution. Total of nine conditions (3 input datasets × 3 output datasets) are considered in the ANN model to investigate the impact of measurement error size on the prediction results. The results have shown that higher data uncertainty decreased ANN model's prediction accuracy. Also, the measurement error of output data had more impact on the model performance than input data that for a same measurement error size on the input and output data, the prediction accuracy was 72.25% and 38.61%, respectively. Thus, to increase ANN models prediction performance, reducing the magnitude of measurement errors of the output pressure node is considered to be more important than input node.

• The Journal of Korean Academy of Prosthodontics
• /
• v.47 no.2
• /
• pp.156-163
• /
• 2009

Statement of problem: Recently, there have been increased esthetic needs for posterior dental restorations. The failure of posterior dental ceramic restoration are possible not only by the characters of the component materials but also by the type of food. Purpose: The research aim was to compare the in vitro fracture resistance of simulated first molar crowns fabricated using 4 dental ceramic systems, full-porcelain-occlusal-surfaced PFG, half-porcelain-occlusal-surfaced PFG, Empress 2, Ice Zirkon and selected Korean foods. Material and methods: Eighty axisymmetric crowns of each system were fabricated to fit a preparation with 1.5- to 2.0-mm occlusal reduction. The center of the occlusal surface on each of 15 specimens per ceramic system was axially loaded to fracture in a Instron 4465, and the maximum load(N) was recorded. Afterwards, selected Korean foods specimens(boiled crab, boiled chicken with bone, boiled beef rib, dried squid, dried anchovy, round candy, walnut shell) were prepared. 15 specimens per each food were placed under the Instron and the maximum fracture loads for them were recorded. The 95% confidence intervals of the characteristic failure load were compared between dental ceramic systems and Korean foods. Afterwards, on the basis of previous results, 14Hz cyclic load was applied on the 4 systems of dental ceramic restorations in MTS. The reults were analyzed by analysis of variance and Post Hoc tests. Results: 95% confidence intervals for mean of fracture load 1. full porcelain occlusal surfaced PFG Crown: 2599.3 to 2809.1 N 2. half porcelain occlusal surfaced PFG Crown: 3689.4 to 3819.8 N 3. Ice Zirkon Crown: 1501.2 to 1867.9 N 4. Empress 2 Crown: 803.2 to 1188.5 N 5. boiled crab: 294.1 to 367.9 N 6. boiled chicken with bone: 357.1 to 408.6 N 7. boiled beef rib: 4077.7 to 4356.0 N 8. dried squid: 147.5 to 190.5 N 9. dried anchovy: 35.6 to 46.5 N 10. round candy: 1900.5 to 2615.8 N 11. walnut shell: 85.7 to 373.1 N under cyclic load(14Hz) in MTS, fracture load and masticatory cycles are: 1. full porcelain occlusal surfaced PFG Crown fractured at 95% confidence intervals of 4796.8-9321.2 cycles under 2224.8 N(round candy)load, no fracture under smaller loads. 2. half porcelain occlusal surfaced PFG Crown fractured at 95% confidence intervals of 881705.1-1143565.7 cycles under 2224.8 N(round candy). no fracture under smaller loads. 3. Ice Zirkon Crown fractured at 95% confidence intervlas of 979993.0-1145773.4 cycles under 382.9 N(boiled chicken with bone). no fracture under smaller loads. 4. Empress 2 Crown fractured at 95% confidence intervals of 564.1-954.7 cycles under 382.9 N(boiled chicken with bone). no fracture under smaller loads. Conclusion: There was a significant difference in fracture resistance between experimental groups. Under single load, Korean foods than can cause fracture to the dental ceramic restorations are boiled beef rib and round candy. Even if there is no fracture under single load, cyclic dynamic load can fracture dental posterior ceramic crowns. Experimental data with 14 Hz dynamic cyclic load are obtained as follows. 1. PFG crown(full porcelain occlusion) was failed after mean 0.03 years under fracture load for round candy(2224.8 N). 2. PFG crown(half porcelain occlusion) was failed after mean 4.1 years under fracture load for round candy(2224.8 N). 3. Ice Zirkon crown was failed after mean 4.3 years under fracture load for boiled chicken with bone(382.9 N). 4. Empress 2 crown was failed after mean 0.003 years under fracture load for boiled chicken with bone(382.9 N).