• Journal of the Korean Society of Combustion
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• v.13 no.1
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• pp.23-30
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• 2008

An analytical expression for the turbulent burning velocity is derived from the asymptotic zone conditional transport equation at the leading edge. It is given as a sum of laminar and turbulent contributions, the latter of which is given as a product of turbulent diffusivity in unburned gas and inverse scale of wrinkling at the leading edge. It was previously shown that the inverse scale is equal to four times the maximum flame surface density in the wrinkled flamelet regime [1]. The linear behavior between $U_T$ and u' shows deviation with the inverse scale decreasing due to the effect of a finite flamelet thickness at higher turbulent intensities. DNS results show that $U_T/S^0_{Lu}$ may be given as a function of two dimensionless parameters, $u'/S^0_{Lu}$ and $l_t/\delta_F$, which may be transformed into another relationship in terms of $u'/S^0_{Lu}$, and Ka. A larger $l_t/{\delta}_F$ or a smaller Ka leads to a smaller scale of wrinkling, hence a larger turbulent burning velocity in the limited range of $u'/S^0_{Lu}$. Good agreement is achieved between the analytical expression and the turbulent burning velocities from DNS in both wrinkled and thickened-wrinkled flame regimes.

• Journal of Applied Reliability
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• v.16 no.3
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• pp.238-244
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• 2016

Purpose: Domestic electric railway Regenerative Energy Storage System seriously affects the maintenance cost of the total operating expenses of nearly 60% of the total LCC (Life Cycle Cost) due to high dependence on foreign Leading company. Therefore by developing the system, it is important to lower the maintenance cost in the domestic supply. This study about the capacitor Reliability test and the purpose of this study is development electric railway Regenerative Energy Storage System. Methods: In case of, having a close relation between the temperature and the reaction rate, Accelerated Model was known that according to Arrhenius' law of chemical activity. If you apply this formula in using allowable temperature range of the capacitor can induce the Arrhenius empirical formula used in much Manufacture Fields. We evaluate the capacitors Leading company through the Arrhenius model. in order to providing a base for the localization of Ultra Capacitor. Conclusion: In this paper, we conducted a reliability test. And it was performed by the accelerated life test and Cycle Test with temperature and C-rate. and then MTBF and B10 life are estimated by analyzing the accelerated life test result. This is thought to need detailed study applying complex stress than about whether it matches the actual behavior in electric railway.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.05a
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• pp.77-81
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• 2008

The local regression rate behavior of solid fuel in swirl injection hybrid rocket were studied. In generally, axial injection regression rate was tending to be decrease with axial distance, beyond which increased with increasing axial distance from the leading edge. On the other hand, swirl injection regression rate was high at the leading edge of the fuel and comparatively uniform regression rate at the downstream. Overall regression rate of swirl injection was increased about 54% for the overall regression rate of axial injection. Through this study, it was found that using swirl injector was useful in applying to the small sounding rocket.

• The Journal of Korean Association of Computer Education
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• v.19 no.2
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• pp.61-71
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• 2016

The purpose of this study was to identify problems of usability and to improve an interface in the digital textbook for leaner's leading to self-directed learning. To address those goals, the theory of affordance, which was related to affordance as leading to behavior, was applied for analyzing the user interface of digital textbook. Also, 10 students, 4th grade elementary school, were participated in the study. Participants were reported affordance's problems of digital textbook through Human Computer Interaction. As a result, some affordance's problems of the digital textbook were found out as follow; difficulty of page clicking, too small touch button, confusing the button, and, need to specific guidance. Based on the result, some suggestions were recommended to improve usability of digital textbook.

• Journal of Korean Public Health Nursing
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• v.5 no.1
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• pp.23-34
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• 1991

This study was carried out to analyze the social interests and demands in health-concerned editorials and to help formulate the public opinions in proper ways. The analysis covered the editorials of five leading news papers such as Chosun Ilbo, Han Kook Ilbo. Han Kyu Re, Joongang Ilbo, Donga Ilbo for the past three years from. June 1, 1987 to May 31, 1990. The major findings are as follows. 1. The total number of health-concerned editorials in the five daily newspapers for the period was 414. occupying $4.6\%$, of the total editorials. 2. The main concerned areas of editorial topics was environmental pollution, which was followed by medical affairs, environmental sanitation, health behavior, social-welfare, demography and so on. 3. The $42.5\%$ of the total number of editorials were appeared in dealing with the outbreak of relevant events in social matters. The distribution of motives to dealing the editorials shows no significant difference by news papers and topics. 4. The $66.4\%$ of the total editorials were addressed toward the government policies. They criticized current governmental policies and gave warnings and $52.4\%$ of them ask for the government to increase governmental attention and will in health related matters.

• Advances in biomechanics and applications
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• v.1 no.4
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• pp.253-267
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• 2014

The human head is identified as the body region most frequently involved in life-threatening injuries. Extensive research based on experimental, analytical and numerical methods has sought to quantify the response of the human head to blunt impact in an attempt to explain the likely injury process. Blunt head impact arising from vehicular collisions, sporting injuries, and falls leads to relative motion between the brain and skull and an increase in contact and shear stresses in the meningeal region, thereby leading to traumatic brain injuries. In this paper the properties and material modeling of the subarachnoid space (SAS) as it relates to Traumatic Brain Injuries (TBI) is investigated. This was accomplished using a simplified local model and a validated 3D finite element model. First the material modeling of the trabeculae in the Subarachnoid Space (SAS) was investigated and validated, then the validated material property was used in a 3D head model. In addition, the strain in the brain due to an impact was investigated. From this work it was determined that the material property of the SAS is approximately E = 1150 Pa and that the strain in the brain, and thus the severity of TBI, is proportional to the applied impact velocity and is approximately a quadratic function. This study reveals that the choice of material behavior and properties of the SAS are significant factors in determining the strain in the brain and therefore the understanding of different types of head/brain injuries.

• The Journal of Information Systems
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• v.24 no.3
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• pp.75-94
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• 2015

Purpose While new versions of mobile applications could offer users better computing environment, users are not always comfortable with them for various reasons. Considering making update decisions is important task for users, it is crucial for us to understand users' behavior and attitude on app updates. The purpose of this study is to explain why mobile users succumb to both reactance toward the update and satisfaction to the current version, ultimately leading them to feel the regret by employing three theoretical perspectives including regret theory, status quo bias theory and the dual model. Design/methodology/approach Survey data collected from 204 mobile users was used to test the research model using partial least squares analysis. The results have shown that both reactance toward the update and satisfaction to the current version have negative impacts on individuals' decisions to update, which leading to their regret after updating the applications Findings By integrating both status quo bias and regret theory in the model, this study tried to explain why mobile users feel regret in application update settings. More specifically, this study has proposed a novel framework that introduces an individual's update decision on mobile applications.

• Journal of Power Electronics
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• v.9 no.2
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• pp.232-242
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• 2009

In this paper, a matrix converter with improved low frequency output performance is proposed by achieving a one-step commutation owing to a general commutation circuit applicable to n-phase to m-phase matrix converters. The commutation circuit consists of simple resister and capacitor components, leading to a very stable, reliable and robust operation. Also, it requires no extra sensing information to achieve commutation, allowing for a one-step commutation like a conventional dead time commutation. With the dead time commutation strategy applied, the distortion caused by commutation delay is analyzed and compensated, therefore leading to better output linear behavior. In this paper, detailed commutation procedures of the R-C commutation circuit are analyzed. A selection of specific semiconductor switches and commutation circuit components is also provided. Finally, the effectiveness of the proposed commutation method is verified through a two-phase to single-phase matrix converter and the feasibility of the compensation approach is shown by an open loop space vector modulated three-phase matrix converter with a passive load.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.8
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• pp.1007-1013
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• 2013

This study aims to analyze the aerodynamics when the geometry of the turbine rotor is modified. The turbine used in this study is a small engine used in the APU of a helicopter. It is difficult to improve the performance of small engines owing to the structural weakness of the blade tip. Therefore, the improvement of the hub geometry is investigated in many ways. The working fluid of a turbine is a high-temperature and high-pressure gas. The heat transfer rate of the turbine surface should be considered to avoid the destruction of blade owing to the heat load. The SST turbulence model gives an excellent prediction of the aerodynamic behavior and heat transfer characteristics when the numerical simulations are compared with the experimental results. In conclusion, the aerodynamic efficiency is improved when a bulbous design is applied to the leading edge near the hub. The endwall loss is reduced by 15%.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.34 no.5
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• pp.386-392
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• 2021

Multiferroics exhibiting the coexistence and a possible coupling of ferromagnetic and ferroelectric order are attracting widespread interest in terms of academic interests and possible applications. However, room-temperature single-phase multiferroics with soft ferromagnetic and displacive ferroelectric properties are still rare owing to the contradiction in the origin of ferromagnetism and ferroelectricity. In this study, we demonstrated that sizable ferromagnetic properties are induced in the ferroelectric bismuth ferrite-barium titanate system simply by introducing Co ions into the A-site. It is noted that all modified compositions exhibit well-saturated magnetic hysteresis loops at room temperature. Especially, 70Bi_0.95Co_0.05FeO₃-30Ba_0.95Co_0.05TiO₃ manifests noticeable ferroelectric and ferromagnetic properties; the spontaneous polarization and the saturation magnetization are 42 µC/cm² and 3.6 emu/g, respectively. We expect that our methodology will be widely used in the development of perovskite-structured multiferroic oxides.