• Ocean Systems Engineering
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• v.12 no.4
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• pp.413-437
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• 2022

An innovative concept for wet-transportation and stepwise installation of mono-bucket foundation for 15 MW offshore wind turbine is proposed. Case studies for two different mono-bucket and wrap-buoy dimensions are conducted and their hydrostatic and hydrodynamic performances are compared for both wet-towing and lowering operations. The intact stability and transient responses are analyzed in detail for various stages of lowering operation. Wave-induced motion statistics during wet tow in sea state 4 (highest operational window) are checked. The proposed concept is found to be feasible and can be an alternative cost-effective solution without using heavy-lift crane vessel in practice.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2007.11a
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• pp.239-241
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• 2007

In this paper we describe streamer propagations characterizing underwater pre-breakdown and breakdown behaviour under impulse voltages. Streamer corona branches in lower resistivities are much thicker and brighter than those in higher resistivities. The negative streamer channels not only have more branches but also widely spread out than the positive streamer channels. The succession of streamer coronas during re-breakdown produces a stepwise propagation. The pre-breakdown currents consist of the conduction current and streamer corona current pulses.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2007.05a
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• pp.328-333
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• 2007

Traditional maintenance planning is based on a constant maintenance interval for equipment life. In order to consider economic aspect for tm based preventive maintenance, preventive maintenance is desirable to be scheduled by RCM(Reliability-Centered Maintenance) evaluation. The main objective of RCM is to reduce the maintenance cost, by focusing on the most important functions of the system and avoiding or removing maintenance actions that are not strictly necessary. So, Markov state model is utilized considering stochastic state in RCM In this paper, a Markov state model much can be used for scheduling and optimization of maintenance is presented. The deterioration process of system condition is modeled by the stepwise Markov model in detail. Also, because the system is not continuously monitored, the inspection is considered. In case study, simulation results about RCM will be shown using the real historical data of combustion turbine generating unit in Korean power systems.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2005.05a
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• pp.57-60
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• 2005

This paper describes the experimental results of the pre-breakdown phenomena in $SF_6/CO_2$ mixtures under non-uniform electric fields caused by positive and negative lightning negative voltages. $SF_6/CO_2$ mixtures have an advantage of an environmental aspect and cost reduction, and safety aspects. In order to analyze the pre-breakdown processes in $SF_6/CO_2$ mixtures stressed by impulse voltages, pre-breakdown current and luminous signals were measured by a shunt and a photo-multiplier tube, respectively. Dielectric strengthes of $SF_6/CO_2$ mixtures were investigated. Additionally, characteristics of discharge channels were observed by high speed cameras and the physical properties were discussed. The pre-breakdown propagates with a stepwise process. The in to breakdown from the corona onset point in positive polarity was shorter than that in negative polarity. The time intervals of positive leaders are shorter than those of negative leaders, and the path of positive leader channel is zigzag.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.2
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• pp.128-133
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• 2008

This paper describes underwater discharge phenomena and breakdown characteristics in case that the standard lightning impulse voltage is injected to the needle and spherical electrodes installed in the hemisphere water tank. The objective of this work is to understand the basic features related to transient ground impedance against lightning surges. The discharge luminous images were observed and the dependence of breakdown voltage on the polarity of applied voltage and water resistivity were investigated. As a consequence, streamer corona is initiated at the tip of needle and spherical electrodes and is propagated toward grounded tank with stepwise extension. The breakdown voltage characteristics measured as a function of water resistivity showed V-shaped curves. Breakdown voltage and time curve of needle electrode is higher than that of spherical electrode.

• Journal of Technologic Dentistry
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• v.22 no.1
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• pp.129-143
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• 2000

With increasing number of dental patients, it is also increasing patient's desire to get better medical service. As the concern for improvement of dental medical service quality is growing, satisfaction degree of dental patients is becoming very important. This study was to investigate difference of patients' satisfaction degree concerned with installation of dental labs and the reason. The data for this study were collected through Self-Administered Questionnaires from 284 patients who had visited dental clinics more than two times. The results are as follows: Female respondents ratio was as twice much as male ones. And 54.2% of the respondents were found out to have completed university education. Dental clinics with dental labs scored higher than others in patients' satisfaction and recommendation willingness degree. Dental clinics without dental labs scored higher in patients' revisiting willingness degree. With simple Correlation Analyses it was found out that the most influential variable concerned with patients' general satisfaction degree was medical facility in dental clinics with dental labs, dentist ability to cure in dental clinics without dental labs. There were some discrepancies with other subordinate variables. Through Stepwise Multiful Regression Analyses it was found out that the most influential variable with patients' general satisfaction degree was dentist ability to cure in total and dental clinics without dental labs and medical facility in dental clinics with dental labs. There were also some discrepancies with other subordinate variables.

• Journal of Korean Society for Atmospheric Environment
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• v.8 no.4
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• pp.262-268
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• 1992

The trend of international concerns on environmental conservation and domestic demand of ambient air quality improvement, specially on sulfur dioxide level has resulted in the establishment of mid-term strategy of environmental improvement and stepwise strengthening of emission regulations in this decade in Korea. Development of flue gas desulfurization(FGD) process is becoming an essential task to be accomplished especially for the power plants and large industrial facilities. This study is an initial stage researc focusing on the mass transfer principles in wet type FGD process and the effects of operating variables of a jet bubbling scrubber utilizing limestone slurry on sulfur dioxide removal efficiency. Experimental results showed this type of scrubbing system has some advantages in terms of mass transfer mechanism and removal efficiency. More rigorous research is needed for the reaction system and the comparison with existing FGD processess for the possible development of a process which is compatative in view of installation cost and treatment of by-products.

• Journal of Korean society of Dental Hygiene
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• v.16 no.4
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• pp.585-590
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• 2016

Objectives: The purpose of the study was to investigate oral health-related behaviors of some elementary school students by installation of toothbrushing facility. Methods: A self-reported questionnaire was completed, out by 377 elementary school students with toothbrushing facility, and by 260 elementary school students with no toothbrushing facility in M city from November to December, 2015. The data were analyzed by ${\chi}^2$-test, t-test and stepwise multiple regression analysis using SPSS 12.0 program. The questionnaire comprised toothbrushing practice(2 items), satisfaction of toothbrushing facility(1 item), oral health knowledge(4 items), fluoride recognition(1 item), and necessity of fluoride mouthrinse(1 item). Results: The level of oral health knowledge was high in toothbrushing facility school. But toothbrushing practice was higher in school of no toothbrushing facility(63.8%) than the school with toothbrushing facility(49.1%)(p<0.001). The number of brushing times a week was also higher in school of no toothbrushing facility(1.98 times) than the toothbrushing facility school(1.59 times)(p=0.011). The dominant reason for no brushing was not recognition(65.8%) in toothbrushing facility school, lack of places(61.3%) in non toothbrushing facility school. Conclusions: In order to improve the oral health in elementary school students, it is necessary to provide toothbrushing education and toothbrushing facility in elementary schools.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.1
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• pp.85-90
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• 2006

This paper presents experimental results relating to the preliminary breakdown characteristics in $SF_6/CO_2$ gas mixtures under a highly non-uniform electric field. The impulse pre-breakdown developments are investigated by the measurements of corona current and light emission images. As a result, the preliminary breakdown development mechanisms for both the positive and negative polarities were fundamentally same. The first streamer corona was initiated at the tip of needle electrode, and the leaders developed with a stepwise propagation and bridged the test gap. The pause time of leader pulses in the positive polarity was significantly shorter than that in the negative polarity. Also, the time interval between the first streamer corona onset and breakdown in the negative polarity was much longer than that in the positive polarity. The discharge channel path in the positive polarity was zigzag, and the leader channel in the negative polarity was thicker and brighter than that in the positive polarity.

• KIEAE Journal
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• v.12 no.5
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• pp.63-70
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• 2012

In order to set the direction of providing facility for the utilization of castle heritage, as well as to establish the method for securing access and determine installation criteria in consideration of preservation environment, an analysis was carried out on the cases of having secured access for people with disabilities in England for the advanced utilization of castle heritage. As the result of the analysis, the planning factors of the facility for people with disabilities in England for the utilization of castle heritage were deduced as follows: 1) The plan for facility was focused on the disabled using wheelchairs and visually impaired persons, rather than on services for hearing-impaired persons and people with learning disability. 2) As for audience movement line plan, regular route was used for audience movement line to lead them in a single direction. 3) As for the provision of prior access information, 3 stepwise access grades were established for the facility information plan of heritage. 4) As for information service by disability type, models were provided; and complementary explanation was provided by using text, drawing, picture, video and voice. 5) Rest spaces were secured where audience could look out upon castle heritage. For the utilization of castle heritage, it is necessary to develop planning factors of the facility design for people with disabilities according to its characteristics.