• Journal of Preventive Medicine and Public Health
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• v.35 no.2
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• pp.160-168
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• 2002

Objectives : This study was intended to investigate the differences of job stressors between managers and low level employees among white-collar workers. Another objective of this study was to examine whether the effects of job stressors on mental health differ between the two groups. Methods : Data was obtained from 204 managers and 258 low level employees who were employed in white-collar jobs. Fourteen job stressors and seven job stress variables were measured. Results : Among the 14 job stressors, role overload, job insecurity, and work-family conflict were higher job stressors for the manager group whereas role conflict, work-aptitude incongruity, participation in decision making, and promotion problems were higher job stressors for the low level of employees. There were no differences in job stress scores between the two groups. However, differences in the effects of job stressors on job stress were found between the two groups. For the manager group, job insecurity, work-aptitude incongruity, and work-family conflict significantly affected in explanation of job stress whereas for the low level employees, role underload, peer satisfaction, and environmental problems significantly explaining the job stress variables. Conclusions : There were significant differences in job stressors between managers and low level employees among white-collar workers. Additionally there were differences in the effects of job stressors on job stress between the two groups.

• Journal of Power Electronics
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• v.15 no.3
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• pp.652-659
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• 2015

This paper presents a new hybrid soft switching dc-dc converter with a low circulating current and high circuit efficiency. The proposed hybrid converter includes two sub-converters sharing two power switches. One is a three-level PWM converter and the other is a LLC converter. The LLC converter and the three-level converter share the lagging-leg switches and extend the zero-voltage switching (ZVS) range of the lagging-leg switches from nearly zero to full load since the LLC converter can be operated at f_sw (switching frequency) $\approx$ f_r (series resonant frequency). A passive snubber is used on the secondary side of the three-level converter to decrease the circulating current on the primary side, especially at high input voltage and full load conditions. Thus, the conduction losses due to the circulating current are reduced. The output sides of the two converters are connected in series. Energy can be transferred from the input voltage to the output load within the whole switching period. Finally, the effectiveness of the proposed converter is verified by experiments with a 1.44kW prototype circuit.

• Journal of Environmental Science International
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• v.16 no.2
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• pp.197-202
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• 2007

Formaldehyde is a typical indoor air pollutant that has numerous adverse health problems in modern living conditions. Phytoremediation that use plants to remove contaminants from polluted media can be applied to improve indoor air quality. Two sets of experiments; 1) two rooms in newly built auditorium and 2) a bed room in 2-year-old apartment; were performed to investigate plant effects on indoor formaldehyde concentration. It was observed from the experiments that plant can help decontaminating formaldehyde at low concentration level (0.1 ppm) but the effects decreased considerably at hish concentration (1ppm). The purification effects of indoor plant also showed the periodic pattern due to its physiological activity. More purification was observed as increasing plant density in the bed room but the formaldehyde concentration returned the original concentration level in two days after removing plants. It was suggested from the results that air purification using plants is an effective means of reduction on indoor formaldehyde level, though, reduction of source is highly desirable when the concentration level is high. The results also suggest that introducing supplementary purifying aids and/or efficient ventilation could be considered due to periodic removal pattern of plant.

• Nutritional Sciences
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• v.2 no.2
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• pp.102-106
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• 1999

Changes in nutritional and health status brought on by a two-year balanced diet were assessed with anthropometric measurements as well as hematological and lipid profiles in 56 healthy young men. Recommended dietary allowances (RDA) were adjusted with estimated daily weighted activity factor. The weighted resting energy expenditure factor of the subjects was 2.37 $\pm$ 0.05. Compared with RDA, all nutrient intakes were adequate and 56% of energy was supplied by carbohydrates, 18% by protein and 26% by fat. The vitamin and mineral intakes except vitamin B-2 were higher (26.46-129.88%) than RDA. Vitamin B-2 intake was 92.15 \ulcorner 14.16% of RDA. There was no seasonal variation on nutrient intakes. Height was increased and systolic blood pressure was decreased by balanced diet for two years. Body weight, diastolic blood pressure and body mass index (BMI) were unchanged. The level of hemoglobin and hematocrit was not changed, the level of plasma protein was decreased and the level of plasma total cholesterol and albumin was increased. These results suggest that a balanced diet can increase height and complement health status achieved through vigorous exercise, even in adults, and that the level of Korean RDA for energy is adequate to maintain existing body weight.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.8
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• pp.468-474
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• 2009

Ground water source heat pump system is the oldest one of the ground source heat pump systems. Despite of this, little formal design information has been available until recently. The important design parameters for open system are the identification of optimum ground water flow, heat exchanger selection and well pump. In this study, the capacity of 50 RT system of two well type ground water heat pump system was used. As a result, static water level was -7 m and the level during the heating operation was -32 m, cooling operation was -40 m. The initial static water level recovered within 48 hrs. The temperature of ground water is $15.6^{\circ}C$ for heating season and $16.2^{\circ}C$ for cooling season and does not depend on the outdoor temperature. Operation efficiency of the system shows that, COP 3.1 for heating and COP 4.2 for cooling.

• The Journal of Asian Finance, Economics and Business
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• v.7 no.10
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• pp.347-357
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• 2020

This research aims to shed light on the technology adoption process and its drivers in the Vietnamese educational system. Research data was collected with an online questionnaire from more than 600 teachers in primary schools, secondary schools, high schools, colleges, and universities in Vietnam in 2020. Based on a holistic literature review, we develop a model of two extrinsic factors (global needs and school-infrastructure), and two intrinsic factors (teachers' technological literacy and their beliefs), which are correlated with the teachers' technological adoption. We measure the dependent variable by asking the teachers' ability and their efficacy to implement technology in teaching according to a Likert scale. With the support of SPSS_22 and STATA_2015, we find that over 70% of changes in technology adoption are explained by the changes in four independent variables and three control variables related to age, gender, and teaching-level of the teachers. Furthermore, these independent variables are significantly and positively associated with two dependent variables. However, a significant difference in technology integration ability can be seen among teachers' gender, age, and school-level. Specifically, male teachers seem to adopt technology at schools than female teachers better, and university teachers have the lowest level of technology adoption compared to other school-level teachers.

• Speech Sciences
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• v.14 no.3
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• pp.77-89
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• 2007

This paper examined the intonation contours of English sentences produced by the Korean students. Thirty students participated in the speaking tasks made up of three parts: an oral interview, picture description and a conversational text reading. Their pronunciations in the parts were recorded on a minidisk. Then, two native instructors evaluated their proficiency level focusing on general intelligibility and suprasegmental aspects of the speech. Based on the results of evaluation they were divided into two groups: high and low proficiency groups. The pitch contours of three sentences produced by both the Korean students and a native speaker were compared to find any similarities and differences in the students' intonation patterns using Praat. Results showed that there was a moderate correlation in the proficiency scores of the students by the two native speakers. Secondly, students who earned high scores in the proficiency level matched better the native model. Thirdly, the high group students knew more on the pitch contour and tried to carefully realize them while fewer students in the low group answered positively on the questionnaire. In conclusion, English learners need to know the proper intonation patterns and to practice them consciously and sufficiently to realize correct intonation contours. Further studies would be desirable on the students' pronunciation focused on discourse structure.

• Research in Community and Public Health Nursing
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• v.20 no.2
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• pp.113-122
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• 2009

Purpose: The purpose of this study is to explore the effect of aromatherapy on anxiety, depression, and stress. Methods:Medical and nursing literature databases were searched to identify studies comparing aromatherapy with a control group. Results: Thirty-one studies published till September 2008 were included in the analysis. Twenty-two studies showed that aromatherapy generally had positive effects on the anxiety level (ES: 0.61). Thirteen studies showed that aromatherapy has significantly decreased the depression level (ES: 0.91). Seven studies showed that aromatherapy had positive effect on the stress level (ES: 0.78). Further analysis found that aromatherapy was more effective for normal population than for patients group with anxiety and stress. On the contrary, aromatherapy was more effective for patients group than for general population with depression. Conclusion: Aromatherapy had positive effect on anxiety, depression and stress level. But there was no sufficient evidence to show the two different aromatherapy methods and two different period of aromatherapy had different effects due to small sample size and heterogeneity of sample. And it was needed to perform follow-up and further comparative studies.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.10
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• pp.799-802
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• 2011

In this study, SiC single-crystal ingots were prepared on two seed crystals with different doping level by using the physical vapor transport (PVT) technique; then, SiC crystal wafers sliced from the grown SiC ingot were systematically investigated to find the effect of seed doping level on the doping concentration and crystal quality of the SiC. To exclude extra effects induced by adjustment of the process parameters, we simultaneously grew the SiC crystals on two seed crystals with different level, which were fabricated from previous two SiC crystal ingots.

• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.6
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• pp.442-450
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• 2020

A small-signal modeling approach for a three-level boost (TLB) converter and a design methodology for a double-loop controller are proposed in this study. Conventional modeling of TLB converters involves three state variables. Moreover, TLB converters have two operation modes depending on the duty ratio. Consequently, complex mathematical calculations are required for controller design. This study proposes a simple system modeling method that uses two state variables, unlike previous methods that require three state variables. Analysis shows that the transfer functions of the two operation modes can be expressed as identical equations. This condition means that the linear feedback controller can be applied to all operational ranges, that is, for full duty ratios. The design method for a double-loop controller using a PI controller is presented in step-by-step sequences. Simulation and experimental verifications are conducted to verify the effectiveness of the small-signal analysis and control system design.