• Tribology and Lubricants
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• v.40 no.1
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• pp.1-7
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• 2024

Ball bearings are a major component of mechanical parts for transmitting rotation. Compared to tapered roller bearings, ball bearings offer less rolling resistance, which leads to reduced heat generation during operation. Because of these characteristics, ball bearings are widely used in electric vehicles and machine tools. The design of ball bearing cages has recently emerged as a major issue in ball bearing design. Cage design requires pre-verification of performance using theoretical or experimental formula or computational fluid dynamics (CFD). However, CFD analysis is time-consuming, making it difficult to apply in case studies for design decisions and is mainly used in performance prediction following design confirmation. To use CFD in the early stages of design, main-taining analytical accuracy while reducing the time required for analysis are necessary. Accordingly, this study proposes a laminar steady-state segment CFD technique to solve the problem of long CFD analytical times and to enable the use of CFD analysis in the early stages of design. To verify the reliability of the CFD analysis, a bearing drag torque test is performed, and the results are compared with the analytical results. The proposed laminar steady-state segment CFD technique is expected to be useful for case studies in bearing design, including cage design.

• Korean Journal of Applied Biomechanics
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• v.34 no.1
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• pp.18-24
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• 2024

Objective: The purpose of this study was to evaluate the effects of an 8-week velocity-based training on the maximum vertical jump in elite sprinters. Method: Ten elite sprinters were participated in this study (age: 21 ± 0.97 yrs., height: 179 ± 3.54 cm, body mass: 72 ± 2.98 kg). An 8-week velocity-based power training was provided to all subjects for twice per week. Their maximum vertical jumps were measured before and after velocity-based training. A 3-dimensional motion analysis with 8 infrared cameras and 4 channels of EMG was performed in this study. A paired t-test was used for statistical verification. The significant level was set at α=.05. Results: There were no statistically significant differences were found between pre and post the training (p>.05). However, most variables included jump record, knee joint ROM, and muscle activation of rectus femoris showed increased pattern after the training. Conclusion: In this study, an 8-week velocity-based training did not showed the significant training effects. However, knee joint movement which is the key role of the vertical jump revealed positive kinematic and kinetic pattern after the training. From this founding, it is believed that velocity-based training seems positively affect the vertical jump which is the clear measurement of mechanical power of sprinter. In addition, to get more clear evidence of the training more training period would be needed.

• Journal of Korean Home Economics Education Association
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• v.27 no.4
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• pp.1-18
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• 2015

The purpose of this study was to conduct a course entitled 'Teaching practice' applying Problem Based Learning(hereafter PBL) for perspective Home Economics teachers to explore the applicability of PBL to the course. A course entitled 'Teaching practice' was carried out for 17 undergraduate students from the 2nd of March till 11th of June in 2014. Pre- and post-tests to measure teacher disposition were performed to investigate the effectiveness of the course applying PBL. Three questions for PBL were developed, were determined after obtaining verification of the questions from 5 experts, and were used for the course entitled 'Teaching practice'; Developing teaching-learning plan, establishing plan for homeroom class management, and designing assessment of Technology & Home Economics. The processes of PBL include defining the problem, planning problem solutions, reassessing the problem, identifying possible solutions, and performance presentation. Procedures for solving one problem of PBL took 4 weeks and teacher disposition assessment for effectiveness of PBL was carried out for pre- and post tests. The reflection journal showed that even though it was their first experience of PBL, instructor's feedback, group activities, and individual activities were helpful for solving the problems of PBL. The result of dependent t-test for paired samples revealed significant differences between the pre- and post tests, which means that there was effectiveness of the course applying to PBL on teacher disposition of prospective Home Economics teachers.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.3
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• pp.242-248
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• 2017

The purpose of this research is investigate the perception of first aid and differentiate between factors. The research subjects were 188 childcare teachers who work for day care centers in Chungchungnam-do, Republic of Korea and 70 pre-service childcare teachers who major in childcare in colleges in the same area. Collected data were converted to frequency and percentage, and cross correlation analysis was conducted for difference verification. The survey results are as follows. First, regarding the perception of first aid, there was a difference between childcare teachers and pre-service childcare teachers in their ability to cope with an emergency situation and responses to questions regarding frequent emergency situation. Second, the percentage of incorrect answers was high in the questions about impaction, poisoning, and biting. There were significant differences between the answers of childcare teachers and pre-service childcare teachers in questions about bleeding(injury), high fever, and CPR. In all of these questions, the percentage of correct answers of childcare teachers was higher. Regarding this result, clinical training for various emergency situations is needed.

• The Journal of the Korea Contents Association
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• v.16 no.12
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• pp.749-760
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• 2016

The purpose of this study was to identify the effects influencing path behaviors of pre-service childcare teachers to present the educational and social welfare measures for promoting children's character development and preventing the alienation of the elderly. The subjects for this study are 176 students who completed the childcare teacher course in four universities located in G city and J province. The scale of this study utilized modified, supplemented scale used in previous studies[1][2] that was constituted for a newly transformed model based on planned behavior theories. The contents of research design include salience beliefs such as attitude beliefs, normative beliefs, control beliefs, etc. as well as a model of planned behavior theories such as attitudes, subjective norms, perceived behavior control, behavior intension, behavior, etc. This study conducted frequency analysis and regression analysis for the data collected by using the SPSS 18.0 for Windows. From the results of verification, all hypothesis was supported. Thus, usefulness of this theory was reconfirmed, and the results of this study are to be utilized as basic materials for professionals who make every endeavor in a perspective of children's character development and in a perspective of reducing alienation phenomenon of the elderly.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.46 no.11
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• pp.66-76
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• 2009

The motion estimation in video encoding system occupies the biggest part. So, we require the motion estimator with efficient structure for real-time operation. And for motion estimator's implementation, it is desired to design hardware module of an exclusive use that perform the encoding process at high speed. This paper proposes motion estimation detection block(MED), 41 SADs(Sum of Absolute Difference) calculation block, minimum SAD calculation and motion vector generation block based on parallel processing. The parallel processing can reduce effectively the amount of the operation. The minimum SAD calculation and MED block uses the pre-computation technique for reducing switching activity of the input signal. It results in high-speed operation. The MED and 41 SADs calculation blocks are composed of adder tree which causes the problem of critical path. So, the structure of adder tree has changed the most commonly used ripple carry adder(RCA) with carry skip adder(CSA). It enables adder tree to operate at high speed. In addition, as we enabled to easily control key variables such as control signal of search range from the outside, the efficiency of hardware structure increased. Simulation and FPGA verification results show that the delay of MED block generating the critical path at the motion estimator is reduced about 19.89% than the conventional strukcture.

• Journal of Christian Education in Korea
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• v.72
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• pp.183-203
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• 2022

The purpose of this study is to construct factors of AI education utilization competency. AI education utilization competency is used as basic data for education to enhance the AI education competency of pre-service early childhood teachers. To this end, 7 studies related to competency factors and models were selected by searching for previous studies. Seven preceding studies were analyzed. As a result, 18 competency factors were extracted, including understanding of artificial intelligence. The extracted competency elements were divided into six areas, which are divided into understanding subject knowledge through coding, class preparation, class management, class result feedback, class guidance, and self-development. And 15 factors were constructed. The draft formed through coding was improved through review by three early childhood education experts. Factors improved through expert review were structured by classifying them into knowledge, skills, and attitudes to organize the curriculum. The validity of the structured competency factor was verified through expert Delphi. As a result of the Delphi verification, all factors were converged in the first survey. Through this, 6 competency areas, 11 competency factors, and 19 competency factors were composed of knowledge, 10 skills, and 5 attitudes. The implication is that the competency factors presented as a result of this study can be used as basic data for organizing a curriculum to improve the ability of pre-service early childhood teachers to use artificial intelligence education.

• Radiation Oncology Journal
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• v.27 no.2
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• pp.91-102
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• 2009

Purpose: To compare the accuracy and efficacy of EDR2 film, a 2D ionization chamber array (MatriXX) and an amorphous silicon electronic portal imaging device (EPID) in the pre-treatment QA of IMRT. Materials and Methods: Fluence patterns, shaped as a wedge with 10 steps (segments) by a multi-leaf collimator (MLC), of reference and test IMRT fields were measured using EDR2 film, the MatriXX, and EPID. Test fields were designed to simulate leaf positioning errors. The absolute dose at a point in each step of the reference fields was measured in a water phantom with an ionization chamber and was compared to the dose obtained with the use of EDR2 film, the MatriXX and EPID. For qualitative analysis, all measured fluence patterns of both reference and test fields were compared with calculated dose maps from a radiation treatment planning system (Pinnacle, Philips, USA) using profiles and $\gamma$ evaluation with 3%/3 mm and 2%/2 mm criteria. By measurement of the time to perform QA, we compared the workload of EDR2 film, the MatriXX and EPID. Results: The percent absolute dose difference between the measured and ionization chamber dose was within 1% for the EPID, 2% for the MatriXX and 3% for EDR2 film. The percentage of pixels with $\gamma$%>1 for the 3%/3 mm and 2%/2 mm criteria was within 2% for use of both EDR2 film and the EPID. However, differences for the use of the MatriXX were seen with a maximum difference as great as 5.94% with the 2%/2 mm criteria. For the test fields, EDR2 film and EPID could detect leaf-positioning errors on the order of -3 mm and -2 mm, respectively. However it was difficult to differentiate leaf-positioning errors with the MatriXX due to its poor resolution. The approximate time to perform QA was 110 minutes for the use of EDR2 film, 80 minutes for the use of the MatriXX and approximately 55 minutes for the use of the EPID. Conclusion: This study has evaluated the accuracy and efficacy of EDR2 film, the MatriXX and EPID in the pre-treatment verification of IMRT. EDR2 film and the EPID showed better performance for accuracy, while the use of the MatriXX significantly reduced measurement and analysis times. We propose practical and useful methods to establish an effective QA system in a clinical environment.

• Korean Journal of Environmental Agriculture
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• v.30 no.3
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• pp.288-294
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• 2011

BACKGROUND: Methylmercury is analyzed by HPLC-ICP/MS because of the simplicity for sample preparation and interference. However, most of the pre-treatment methods for methylmercury need a further pH adjustment of the extracted solution and removal of organic matter for HPLC. The purpose of this study was to establish a rapid and accurate analytical method for determination of methylmercury in fish by using HPLC-ICP/MS. METHOD AND RESULTS: We conducted an experiment for pre-treatment and instrument conditions and analytical method verification. Pre-treatment condition was established with aqueous 1% L-cysteine HCl and heated at $60^{\circ}C$ in microwave for 20 min. Methylmercury in $50{\mu}L$ of filtered extract was separated by a C18 column and aqueous 0.1% L-cysteine HCl + 0.1% L-cysteine mobile phase at $25^{\circ}C$. The presence of cysteine in mobile phase and sample solution was essential to eliminate adsorption, peak tailing and memory effect problems. Correlation coefficient($r^2$) for the linearity was 0.9998. The limits of detection and quantitation for this method were 0.15 and $0.45{\mu}g/kg$ respectively. CONCLUSION: Result for analytical method verification, accuracy and repeatability of the analytes were in good agreement with the certified reference materials values of methylmercury at a 95% confidence level. The advantage of the established method is that the extracted solution can be directly injected into the HPLC column without additional processes and the memory effect of mercury in the ICP-MS can be eliminated.

• Journal of Radiation Protection and Research
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• v.21 no.1
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• pp.17-25
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• 1996

In this study, to set-up the calculation method of radiation shielding of the KSC-4 shipping cask which is being used for spent fuel transportation, the pre-existing two calculation methods, deterministic and probabilistic methods were tested. For the first, the DOT4.2 computer code adopting the deterministic theory was applied for the calculation of effective neutron shielding under assumption of continuous wall thickness of the cask. To verify the first results, the probabilistic theory was used as an alternate calculation. In this case MCNP4A computer code adopting the probabilitic theory was used. And same approximation was obtained from the two different shielding calculations. From the results, it could be confirmed that the design and calculation method used for the radiation shielding of the KSC-4 was adequate and sufficiently safe to meet the design and QA requirements of 10CFR71 Appendix H.