• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.1
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• pp.419-425
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• 2019

The objective of this study was to investigate the cooling performance characteristics of a hybrid refrigeration system in a heavy duty vehicle. The tested hybrid refrigeration system had additionally an electric compressor besides the present mechanical compressor for selective use according to the operating conditions. The applied electric compressor was a scroll type and with 18.0 cc displacement. In order to analyze the performance characteristics of the hybrid refrigeration system with respect to the cooling capacity and Coefficient of Performance (COP), other components, including two different types of compressors, were installed and tested under various operating conditions such as compressor speed and air flow rate of the evaporator. When the electric compressor was operated at 4,500 rev/min, the cooling capacity was about 4.0kW and COP was 3.5. When the mechanical compressor was operated, whereas the cooling capacity was higher than the electric controlled compressor, COP was lower due to the larger displacement and higher power consumption. To analyze the hybrid system operating characteristics due to reasonable cooling capacity with electric compressor operation, the mechanical compressor and electric compressor were operated by turns every 10 minutes under certain system operating conditions. Because surge pressure occurred when both compressors were switched on, the operating strategy required some time to balance the system pressure.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3282-3287
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• 2007

Lean combustion is one of the most promising method for increasing engine efficiency and reducing the exhaust emission from SI gas engines. Due to the possibility of partial burn and misfire, however, under lean burn operation, stable flame kernel formation and fast burn rate are needed to guarantee a successful subsequent combustion. Experiment data were obtained on a single-cylinder CNG fueled SI engine to investigate the effect of direct injection, spark timing and variation of injection timing. Experimental results show that lean burn limit is ${\lambda}$=1.3 with port injection, and expansion of lean burn limit ${\lambda}$=1.4 with direct injection method, due to increase of turbulence intensity in cylinder and stratified charge. Combustion duration in lean region is improved by using the variation of injection timing.

• Proceedings of the KSR Conference
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• 2009.05a
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• pp.828-830
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• 2009

In Korea, various efforts to cope with the Post-Kyoto system have been recently performed because a duty for the GHG(Greenhouse Gas) reduction may be allocated from 2013. Especially, the role of railroad has been strengthened to decrease total GHG emission of transportation system. Therefore, it is necessary to investigate the GHG emission and the reduction strategies of railroad. The purpose of this study was to develop the calculation method of GHG emission released from railroad. Main source of GHG emission was the energy consumption of railroad vehicle and infrastructure. Based on the emission factor and the equation reported in IPCC 2006 guideline, the total GHG emission of railroad was about 1.4 million tons CO2e in 2007. Using this calculation method, the GHG data of railroad can be calculated quantitatively and managed systematically in the future.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2006.11a
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• pp.143-146
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• 2006

There has been growing concern regarding IAQ(Indoor Air Quality) recently, and IAQ problems from the air-tightness and use of chemical materials addition to the building materials have become increasingly important factors in the built environment. Ventilation is supposed as the solution of healthy indoor quality, and Korea government requests that all new apartment buildings must have a ventilation system as a matter of duty since January, 2006. The purpose of this study is to investigate the indoor concentration change of VOCs include the Formaldehyde according to many different ventilation supply types. Results showed that the reduction effect of target pollutants by the ventilation system was very slight. The cause of these results was attribute to increase the emission rate of building materials by increasing the ventilation rate.

• Journal of Korean society of Dental Hygiene
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• v.8 no.1
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• pp.73-91
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• 2008

In order to investigate the complaint rates of subjective fatigue symptoms and the degree of job-satisfaction among dental hygienists based on their socio-demographic and job characteristics and to find out the factors related with subjective fatigue symptoms and job satisfaction. The study subjects were recruited from 274 dental hygienists who worked at dental hospitals and clinics in Daejon city and South Chungcheong Province during the period between Jan. 5 and Feb. 11, 2008. They were asked to complete the self-administered questionnaires asking about their socio-demographic characteristics. job characteristics. daily life styles, job satisfaction and subjective fatigue symptoms, and the major finding of the results were as follows : 1. The mean scores of job satisfaction were 3.12V0.47 of the total full scores(5.00). and the highest scores were in the sub-domain of interpersonal relationship. and the lowest scores were pay. The scores of job satisfaction by socio-demographic characteristics and daily life styles were not significantly differences, but in job characteristics, significantly increased with those feeling satisfied with their job. those with appropriate amount of duty amount, those free of jop autonomy, those feeling satisfied with their monthly income. satisfactory personal relations at work. 2. The mean scores of subjective fatigue symptoms were 27.6V10.9 of the total full scores(60.0), and the highest scores were in the sub-group of bodily projection of fatigue(Group III), and they were followed by difficulty in concentration(Group II). dullness and sleepness(Group I) in their decreasing order of magnitude. The scores of job satisfaction by socio-demographic characteristics and daily life styles were significantly increased with the group of lower age, the group of irregularly breakfast habit and the worse subjective health status. Based on job characteristics. the score of subjective fatigue symptoms were significantly increased with those group of lower clinical career and monthly income, those feeling unsatisfied with their job, those with inappropriate amount of duty amount. those satisfactory personal relations at work 3. The correlation of subjective fatigue symptoms with job satisfaction showed a negative correlation with rM-0.198(pM0.000), and job satisfaction were higher according to the lower subjective fatigue symptoms. The correlation among the scores of sub-domain of job satisfaction and the sub-group of subjective fatigue symptoms were significantly positive correlation. 4. The affecting factors of significance on job satisfaction included clinical career, duty amount salary satisfaction, with the explanatory power of 32.9%. Those on subjective fatigue symptoms included the eucation and the subjective health statuts, with the explanatory power of 20.8%. When considering these results, the job-satisfaction and the subjective fatigue symptoms were significantly correlated with the job related factors than factors of socio-demographic characteristics and daily life styles. In addition. if job environments of dental hygienist can improved. their job-satisfaction and subjective fatigue symptoms are suggested to be betters.

• Journal of the Korean Home Economics Association
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• v.42 no.11
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• pp.123-136
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• 2004

The Purpose of this study was to investigate the effects of self-efficacy on the early childhood teachers' self-concept and job satisfaction. 191 early Childhood-teachers were surveyed for this study. Spss/pc was run for statistical data analysis. This study abstracted that the most important factors for Early Childhood-teachers to have Self-efficacy are life self, duty, working environment, payment, and promotion opportunity and concluded that the more payment and promotion opportunity, the more Self-efficacy teachers have. In conclusion, this study implies that retraining and teaching programs for teachers need to be accessed variably, considered with the results of this paper.

• Journal of Environmental Science International
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• v.14 no.2
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• pp.201-207
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• 2005

This study was carried out to investigate the correlation between toluene in air and hippuric acid in human urine, which is based in the results of the health check-in and measure of working environment, was investigated for five years. Toluene in air and hippuric acid in urine were checked 116 workers who exposed to toluene in five type of industry. The Mean concentration of toluene in air by type of industry and every year and sex distinction, had positive correlation.(p<0.01) The Mean concentration of hippuric acid in urine by type of industry, every year, sex distinction, disparity of age and term of duty had positive correlation.(p<0.01).

• Journal of Korean Society for Quality Management
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• v.5 no.2
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• pp.29-38
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• 1977

The QC circle is a small group organized for accomplishing the company's purpose of improving constitutions of the enterprise, developing the capabilities of the mem-bers and improving human relations. The present study intends to investigate the current situations and problems of the QC circle and to develop most effective models for QC circle movement in Korea. For this purpose the author surveyed 93 QC circles and interviewed more than 20 QC circle members and managers. The author has concluded that it is necessary to: 1. establish the authority and duty of the QC divisions. 2. train the top and middle management, especially the indirect divisions manage-ment. 3. motivate the QC circle members for achieving their purpose.

• IEMEK Journal of Embedded Systems and Applications
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• v.4 no.1
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• pp.16-22
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• 2009

This paper aims at designing an impulse-radio ultra-wideband (IR-UWB) transceiver, especially targeting the IEEE 802.15.4a indoor ranging and communication systems. We first investigate the IEEE 802.15.4a IR-UWB signals and suggest the full-digital transceiver architecture accordingly. Since the wireless systems equipped with the impulse signal have the property of low-duty cycle, i.e., discontinuity in time, while the conventional systems takes the continuous signals, it is required to reconfigure the system design, including link budget. Following brief introduction to our IEEE 802.15.4a IR-UWB system hardware, we finally examine the ranging performance in indoor environments to verify our system design.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.7 no.5
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• pp.784-787
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• 2006

Even if EGR is known as a technology which dramatically reduces NOx emission, its application is a quite complicate since it affects fuel economy and increase of PM emission. Therefore, it is a very important issue to investigate an optimal EGR rate considering all engine parameters. This research was numerically conducted to predict combustion and emission characteristics with respect to various EGR rates.