• Journal of Magnetics
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• v.20 no.4
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• pp.387-393
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• 2015

Torque ripple is necessarily generated in interior permanent magnet synchronous motors (IPMSMs) due to the non-sinusoidal distribution of flux density in the air gap and the magnetic reluctance by stator slots. This paper deals with an asymmetric rotor shape to reduce torque ripple which can make sinusoidal flux density distribution in the air gap. Meanwhile the average torque is relatively increased by the asymmetric rotor. Response surface method (RSM) is applied to find the optimum position of the permanent magnets for the IMPSM with improved torque performance. Consequently, an asymmetric structure is the result of RSM and the structure has disadvantage of a mechanical stiffness. Finally, the performance of suggested shape is verified by finite element analysis and structural analysis is conducted for the mechanical stiffness.

• Journal of the Korean Orthopaedic Association
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• v.54 no.3
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• pp.254-260
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• 2019

Purpose: To evaluate the relationship between the knee function at 1 year postoperation and the gap difference (90° flexion gap-extension gap) in total knee replacement. Materials and Methods: Eighty-two consecutive osteoarthritis knees that underwent primary total knee replacement using navigation from March 2017 June 2017 were evaluated prospectively. The gap was measured using navigation after reducing the patella with towel clips. After checking the average values of the medial and lateral gaps at extension and 90° flexion knee, the gap difference (90° flexion gap-extension gap) was calculated. The knees were divided into three groups according to the gap difference (gap difference<0 mm, 0 mm≤gap difference<2 mm, 2 mm≤gap difference). The Knee Society score (KSS) and maximal knee flexion were compared at 1 year postoperation among three groups. Results: The numbers of knees according to groups were 37, 29, and 16 knees in regular order. The average of the KSS knee, KSS function, and maximal knee flexion at the 1-year follow-up were 81.21±8.31, 71.34±9.84, and 126.48°±7.28°, respectively. No statistically significant difference in KSS was observed among the 3 groups. The third group (2 mm≤gap difference) showed a larger maximal knee flexion than the other groups in the Mann-Whitney test. Conclusion: The group of total knee replacement (2 mm≤90° flexion gap-extension gap) showed larger maximal knee flexion than the other groups at the 1-year follow-up in statistics.

• Journal of Electrical Engineering and Technology
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• v.12 no.2
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• pp.769-777
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• 2017

The research of air gap flux density has a significant effect on predicting and optimizing the structure parameters of electrical machines. In the paper, the air gap coefficient, leakage flux factor and saturation coefficient are first analytically expressed in terms of motor properties and structure parameters. Subsequently, the analytical model of average air gap flux density for surface-mounted permanent magnet synchronous machines is proposed with considering slotting effect and saturation. In order to verify the accuracy of the proposed analytical model, the experiment and finite element analysis (FEA) are used. It shows that the analytical results keep consistency well with the experimental result and FEA results, and the errors between FEA results and analytical results are less than 5% for SPM with high power. Finally, the analytical model is applied to optimizing the motor structure parameters. The optimal results indicate that the analytical calculation model provides a great potential to the machine design and optimization.

• Journal of Mechanical Science and Technology
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• v.19 no.5
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• pp.1169-1181
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• 2005

Experimental and numerical studies on the unsteady wake field behind a square cylinder near a wall were conducted to find out how the vortex shedding mechanism is correlated with gap flow. The computations were performed by solving unsteady 2-D Incompressible Reynolds Averaged Navier-Stokes equations with a newly developed ${\epsilon}-SST$ turbulence model for more accurate prediction of large separated flows. Through spectral analysis and the smoke wire flow visualization, it was discovered that velocity profiles in a gap region have strong influences on the formation of vortex shedding behind a square cylinder near a wall. From these results, Strouhal number distributions could be found, where the transition region of the Strouhal number was at $G/D=0.5{\sim}0.7$ above the critical gap height. The primary and minor shedding frequencies measured in this region were affected by the interaction between the upper and the lower separated shear layer, and minor shedding frequency was due to the separation bubble on the wall. It was also observed that the position (y/G) and the magnitude of maximum average velocity $(u/u_{\infty})$ in the gap region affect the regular vortex shedding as the gap height increases.

• Korean Journal of Social Welfare Studies
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• v.47 no.3
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• pp.139-159
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• 2016

This study aims to investigate the wage gap between male and female workers at social welfare institutions and to determine its factors. For this purpose, a Blinder-Oaxaca decomposition and regression models are applied to analyze wage survey data. The results are as follows. Firstly, the gender wage gap of social workers is a bit smaller, compared to the average of wage earners. Secondly, about two-thirds of wage gap is due to differences in productivity(endowment) factors; the other part is due to discrimination. Thirdly, the most important cause of gender wage gap is career disruptions of female workers largely due to marriage and birth. Fourthly, other causes of gender wage gap include differences in education, in job grade, in employment status, and in the characteristics of institutions. Finally, among the discriminating factors worsening gender wage gap, a key factor is a gender discrimination in the compensation for age.

• Journal of Korea Technology Innovation Society
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• v.8 no.2
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• pp.650-676
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• 2005

It is important to identify the mid and long-term strategic technologies and evaluate technology level for the establishment of national R&D policy to upgrade technology level in Korea. This paper summarizes the result of technology level evaluation for 99 key technologies of 'National Technology Road Map', which consists of 5 visions, of Korea. The technology level, the technological gap between Korea and world-top country, the role of government to upgrade technology level, etc. were investigated by the survey (total 1,067 respondents) and the interview with experts related to key technologies. The average technology level of Korea was $65.1\%$ of that of world-top country and average technological gap was 5.8 years. The technology level of vision I 'Building an Information-Knowledge-Intelligence Society' was $71.6\%$ and highest among 5 visions. The highest technology level among 99 key technologies was $85.6\%$ for 'Digital Broadcasting Technology' and the lowest was $20\%$ for 'weather Control Technology'. The major reasons of technological gap were investigated as the lack of R&D personnel ($23.8\%$), the shortage of R&D funds ($17.8\%$), and the insufficiency of basic research ($15.4\%$), in sequence. The average technology level of USA was evaluated to highest in the world. It was presented that the technological power of China increased rapidly in the expert interview. The result of technology level evaluation would be primary information for various national S&T planning, such as S&T basic plan, S&T foresight, technology road map, etc.

• Journal of Ocean Engineering and Technology
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• v.16 no.2
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• pp.53-59
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• 2002

This paper shows the experimental results controlling the height of surface and back bead in GMAW by analyzing the unexpected gaps between base metals produced in welding and by controlling welding velocity due to the variation of the gap between base metals in thin-plate welding. The back bead behavior and burn-through in I-type butt joint $CO_2$ welding of thin mild steel are analyzed in the views of short circuit time ratio and short circuit frequency. It is shown through experimental consideration that the short circuit time ratio method is more reasonable than the short circuit frequency method in analyzing the formulation of back bead under changing the gap between base metals. Based on the these results, welding manipulator is designed so as to satisfy the bead height control in real time by measuring the short circuit time ratio. To show the effectiveness of the developed bead formulation control system, the experiment is implemented under two welding conditions such as increasing gap from 0mm to 0.8mm and gradually increasing gap from 0mm to 1.2mm. The experimental results show that the bead formulation can be controlled uniformly in spite of the variation of the gap between base metals.

• Journal of Korean Foot and Ankle Society
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• v.18 no.4
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• pp.165-172
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• 2014

Purpose: We evaluated the correlation of postoperative clinical outcomes and radiologic findings using computed tomography and simple X-ray in intra-articular calcaneal fractures. Materials and Methods: The current study is based on 41 feet, 38 patients with displaced intra-articular fracture who underwent surgical treatment with at least one year of follow-up. Evaluation of clinical outcome included American Orthopaedic Foot and Ankle Society (AOFAS) ankle-hindfoot score, visual analogue scale (VAS) score, and subjective satisfaction. A simple X-ray was used in evaluation of preoperative and postoperative Gissane angle, B${\ddot{O}}$hler angle, and calcaneal fracture width. Computed tomography scan was performed for evaluation of preoperative and postoperative articular step-off and articular gap in all cases. Finally, we evaluated the correlation of the postoperative clinical outcomes and radiologic findings based on the measurement. Results: The average postoperative AOFAS score and VAS score was $84.1{\pm}8.5$ and $2.2{\pm}2.2$. Subjective satisfaction was excellent in 15 cases, good in 19 cases, and fair in seven cases. The average B${\ddot{O}}$hler angle was restored from $11.1^{\circ}$ to $24.7^{\circ}$(p<0.05), Gissane angle was changed from $121.0^{\circ}$ to $119.0^{\circ}$ (p>0.05), and the average width was restored from 45.8 to 35.0 mm (p<0.05). The average articular step-off and gap were decreased from 6.3 to 2.0 mm and from 11.1 to 4.6 mm, respectively (p<0.05). No significant correlations were observed between the clinical outcome and Gissane angle, B${\ddot{O}}$hler angle, and width, and there was no significant correlation between the clinical outcome and Sanders classification. However, postoperative articular step-off showed correlation with VAS and AOFAS score and articular gap showed correlation with VAS score. Conclusion: The clinical outcome did not show correlation with B${\ddot{O}}$hler angle and Gissane angle but did show correlation with anatomical reduction of the posterior facet joint.

• Journal of Distribution Science
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• v.13 no.6
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• pp.97-104
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• 2015

Purpose - The distribution of agricultural products is changing due to recent shifts in environmental free trade. Specifically, the competitiveness of domestic agricultural products has weakened as a result of the Korea-China Financial Trade Agreement. Agricultural producers are faced with increasing difficulties and organized production centers are growing in importance daily. To overcome this crisis, agricultural producer organizations are vying for environment-friendly agricultural certifications, Good Agriculture Practices (GAP) and Hazard Analysis and Critical Control Point (HACCP). In particular, as consumer demand for higher safety grows, farmers are increasing their certification rates. Therefore, this certification system is expected to help strengthen the competitiveness of agricultural producer organizations. Research design/data/methodology - Organized production centers are classified by certification. A survey was conducted with 91 organizations using factor analysis and logistic regression analysis for the examination. The factor analysis results are as follows. Raw material procurement, education·specialization, marketing, joint business, organizing ability, business management, effectiveness, certification, and larger organizations were classified as the nine types of factors. These factors affect the organized production centers and are used in the logistic regression analysis. The purpose of such research and analysis is to suggest a direction for future production center policies. Results - The basic statistical results are as follows: analysis of the producer organizations of 91 sites, average number of members per site of 1,624, and average sales of 25,961 million won. Additionally, the average income per farmer is 175 million won, and the pooling system rate is 53.5%. The factor analysis results are as follows. Factor 1 consists of contract cultivation, ongoing shipment, selection subdivision, traceability, and major retailer management. Factor 2 consists of manual cultivation, specialty selection, education program, and R&D. Factor 3 consists of advertising, various dealers, various sales strategies, and a unified sales counter. Factor 4 consists of agricultural materials co-purchase, policy support, co-shipment, and incentives. Factor 5 consists of the co-selection and pooling system. Factor 6 consists of co-branding and operating by the organization's article. Factor 7 consists of the buy-sell ratio and rate of operation of the agriculture promotion center. Factor 8 consists of bargaining power in volume and participation rate of farmer certification. Factor 9 consists of increasing new subscribers. The logistic regression analysis results are as follows. Considering the results by type of certification, the environment-friendly agricultural certification type and the GAP certification type have a (+) influence. GAP and HACCP certification types affecting the education·specialization factor have a (+) influence. Considering the results for each type of certification, the environment-friendly agricultural certification types on the effectiveness factor have (-) influence; the HACCP certification types on the organizing ability and effectiveness factor have a (-) influence. Conclusions - Agricultural producer organizations should develop plans as follows: The organizations need to secure education for agricultural production; increase the pooling system ratio for sustainable organizational development; and, finally, expand the number of agricultural producer organizations.

• The Journal of the Acoustical Society of Korea
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• v.23 no.5
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• pp.340-352
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• 2004

Acoustic streaming induced by the microscopic longitudinal ultrasonic vibration at 28.5 ㎑ is visualized between the quiescent glass plate and ultrasonic vibrator by particle imaging velocimetry(PIV) using laser. To investigate the augmentation of air flow velocity of acoustic streaming. the velocity variations of air streaming between the stationary plate and ultrasonic vibrator are measured in real-time. It is experimentally investigated that the magnitude of the acoustic streaming dependent upon the gap between the ultrasonic vibrator and stationary p1ate results in the variations of the average velocity fields as a outcome of the bulk air flow caused by the ultrasonic vibration. In addition. maximum acoustic streaming velocity exists at resonant gap. 18mm that is one of the resonant gaps (H=18, 24, 30, 36㎜) at which resonance occurs. The variation of the local maximum turbulent intensity with axial direction appear to reveal the value of 8%∼70% dependent upon the gap between the quiescent glass plate and ultrasonic vibrator. Shearstress is also maximized at the center region of the vibrator and the vorticity is also maximum and minimum in the neighborhood of the center of the vibrator at which the local maximum turbulent intensity and shear stress exist.