• Korean Journal of Child Studies
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• v.31 no.1
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• pp.163-177
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• 2010

The purpose of this study was to examine the maintenance of an evaluation accreditation indicator according to child care center teachers' participation in decision making. The subjects of this study were 139 teachers from 12 accredited national, public, private, and corporate child care centers in Seoul and North Gyeongsang Province. The TIP-2 (Teacher Involvement and Participation Scale V.2) and Accreditation Indicator for Child Care Centers were used to measure teachers' participation in decision making and accreditation indicator maintenance. Frequency, mean, standard deviation, one-way ANOVA and scheffe test were used for data analyses. The results revealed that the teachers who rated middle and high level in terms of their participation in decision-making showed higher levels of maintenance of the evaluation accreditation indicator than those with low levels of participation. This finding suggests that teachers' participation in decision making is an important factor for maintaining the quality of child care centers.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2000.11a
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• pp.10-10
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• 2000

For low Earth orbit, the atmosphere causes orbit altitude to decrease, If this decrease is not corrected by the satellite propulsive unit, the orbit decoys continuously unit reaches the dense atmosphere and satellite life ends. If active orbit maintenance is mode by satellite propulsive unit then fuel consumption is necessary, which must be considered in the satellite design. Especially interesting is the method for evaluating the fuel consumption role for maintenance of elliptical orbit developed in this paper.(omitted)

• Journal of Astronomy and Space Sciences
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• v.14 no.2
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• pp.355-366
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• 1997

This paper presents a comprehensive analytical approach for determining key maneuver parameters associated with the acquisition and maintenance of the ground track for a low-earth orbit. A livearized model relating changes in the drift rate of the ground track directly to changes in the orbital semi-major axis is also developed. The effect of terrestrial atmospheric drag on the semi-major axis is also explored, being quantified through an analytical expression for the decay rate as a function of density. The non-singular Lagrange planetary equations, further simplified for nearly circular orbits, provide the desired relationships between the corrective in-plane impulsive velocity increments and the corresponding effects on the orbit elements. The resulting solution strategy offers excellent insight into the dynamics affecting the timing, magnitude, and frequency of these maneuvers. Simulations are executed for the ground track acquisition and maintenance maneuver as a pre-flight planning and analysis.

• Proceedings of the KSR Conference
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• 2009.05a
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• pp.177-183
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• 2009

This paper deals with the topical problems of the Life Cycle Costs in connection with the rolling stocks. the LCC philosophy has already entered the third decade. this philosophy contributed towards the new relationship's comprehension between railway vehicle producers' and railway vehicle users' sphere. this leads together to the technical-economical solution convenient for the both sides. In the point of manufacturer, It is said that low operational costs could be reached using a well-designed and structured maintenance program. this is due to the proper technical analysis of critical components that leads to low costs of maintenance and a superior reliability without increasing the capital investment. but, This paper presents both topical experiences with the LCC models for the railways vehicles and also procedures during Life Cycle Costs calculations. In conclusion I want to introduce how to calculate LCC & what kinds of softwares are used based on VVVF EMU vehicle

• The Journal of the Convergence on Culture Technology
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• v.9 no.6
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• pp.677-683
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• 2023

The purpose of the study was to estimate the trajectories of elementary school adjustment in grades 1 through 4. For the purpose, the Korean Children's Panel data were analyzed using potential growth model and the growth mixture model. As the result, the linear model was selected as the optimal model. The four potential groups were derived as trajectories: high-level maintenance, low-level maintenance, low-level increase, and high-level decrease. In terms of group distribution, the most children were in high-level maintenance group and then low-level maintenance, low-level increase, and high-level decrease in order. Based on the findings that trajectories of elementary school adjustment changes as children growth, we suggest that schools and families need to carefully investigate and support their school adjustment in individual levels.

• The Journal of the Convergence on Culture Technology
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• v.9 no.6
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• pp.581-587
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• 2023

The purpose of this study was to analyze the change trajectory and latent class types of self-esteem in first to fourth grade elementary school students. For the purpose, the Korean Children's Panel data were analyzed using potential growth model and the growth mixture model. As the results, the linear change model was selected as the most appropriate model. The change trajectory was found to increase slightly as the grade increased. In addition, four latent class groups were derived through: 'high level-maintenance,' 'low level-increase,' 'high level-decrease,' and 'low level-maintenance.' Most children were in the 'high level-maintenance' group, followed by 'high level-decrease,' 'low level-increase,' and 'low level-maintenance' groups. Therefore, based on the results of the study, we suggest that educational institutions and local communities pay attention to trends in elementary school students' self-esteem and provide appropriate support for students in each class.

• Progress in Superconductivity and Cryogenics
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• v.26 no.1
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• pp.20-24
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• 2024

Over the past four years, as the COVID-19 pandemic has struck the world, cold chain of COVID-19 vaccination has become a hot topic. In order to overcome the pandemic situation, it is necessary to establish a cold chain that maintains a low-temperature environment below approximately 203K (-70℃), which is the appropriate storage temperature for vaccines, from vaccine suppliers to local hospitals. Usually, cryocoolers are used to maintain low temperatures, but it is difficult for small-scale local distribution to have cryocooler due to budget and power supply issues. Accordingly, in this paper, a cryogenic TSU (Thermal storage unit) system for vaccination cold chain is designed that can maintain low temperatures below -70℃C for a long time without using a cryocooler. The performance of the TSU system according to the energy storage material for using as TSU is experimentally evaluated. In the experiments, four types of cold storage materials were used: 20% DMSO aqueous solution, 30% DMSO aqueous solution, paraffin wax, and tofu. Prior to the experiment, the specific heat of the cold storage materials at low temperature were measured. Through this, the thermal diffusivity of the materials was calculated, and paraffin wax had the lowest value. As a result of the TSU system's low-temperature maintenance test, paraffin wax showed the best low-temperature maintenance performance. And it recorded a low-temperature maintenance time that was about 24% longer than other materials. As a result of analyzing the temperature trend by location within the TSU system, it was observed that heat intrusion from the outside was not well transmitted to the low temperature area due to the low thermal conductivity of paraffin wax. Therefore, in the TSU system for vaccine storage, it was experimentally verified that the lower the thermal diffusivity of the cold storage material, the better low temperature maintenance performance.

• Journal of the Korea institute for structural maintenance and inspection
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• v.2 no.3
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• pp.212-222
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• 1998

In several structural problems, the low concrete strength of compression members has the severest influence on the structural safety. However, the repairing and strengthening techniques for compression members are not established and evaluated. This study aimed to develop and evaluate the rehabilitation techniques to obtain proper structural strength of wall with low concrete strength. The specimens with low strength of concrete were retrofitted with commonly using section increase method and epoxy bonded glass fiber techniques. The tests were executed to failure under concentric and eccentric loads. In this paper, the structural behavior and failure modes were investigated to evaluate the strengthening effects of walls subjected to compression and out-of-plane bending.

• Journal of the Korea institute for structural maintenance and inspection
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• v.2 no.3
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• pp.161-167
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• 1998

A problem of frequency in the field of low-frequencies such as high-rise apartment building or construction vibration are often found. In this study, damage reason of a 25 stories apartment building was searched on the basis of actual damage. To find the damage reason, structural design procedure were reviewed and low-frequency vibration test was conducted. The results indicate that the main damage reason is not by the low-frequency vibration but the asymmetrical plan of that building.

• Smart Structures and Systems
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• v.22 no.2
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• pp.151-159
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• 2018

Maintenance activities are regarded as a key part of the repairable deteriorating system because they maintain the equipment in good condition. In practice, many maintenance policies are used in engineering fields to reduce unexpected failures and slow down the deterioration of the system. However, in traditional maintenance policies, maintenance activities have often been assumed to be performed at the same time interval, which may result in higher operational costs and more system failures. Thus, this study presents two non-periodic preventive maintenance (PM) policies for repairable deteriorating systems, employing the failure rate of the system as a conditional variable. In the proposed PM models, the failure rate of the system was restored via the failure rate reduction factors after imperfect PM activities. Operational costs were also considered, which increased along with the operating time of the system and the frequency of PM activities to reflect the deterioration process of the system. A numerical example was provided to illustrate the proposed PM policy. The results showed that PM activities performed at a low failure rate threshold slowed down the degradation of the system and thus extended the system lifetime. Moreover, when the operational cost was considered in the proposed maintenance scheme, the system replacement was more cost-effective than frequent PM activities in the severely degraded system.