• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.42-46
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• 2005

In spite of fast growing of prediction codes, there is still not negligible uncertainty in their results. This uncertainty affects on the turbine structural design and power production prediction. With the growing size of wind turbine, reducing this uncertainty is becoming one of critical issues for high performance and efficient wind turbine design. In this respect, there are international efforts to evaluate and tune prediction codes of wind turbine. As the reference data for this purpose, field test data is not appropriate because of its uncontrollable wind characteristics and its inherent uncertainty. Wind tunnel can provide controllable wind. For this reason, NREL has done the full scale test of the 10m turbine at NASA-Ames. With this reference data, a blind comparison has been done with participation of 18 organizations with 19 modeling tools. The results were not favorable. In Europe, a similar project is going on. Nine organizations from five countries are participating in the MEXICO project to do full scale wind tunnel tests and calculation with prediction codes. In this study. these two projects were reviewed in respect of wind tunnel test and its contribution. As a conclusion, it is suggested that scale model wind tunnel tests can be a complementary tool to calculation codes which were evaluated worse than expected.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.25 no.2
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• pp.53-60
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• 2011

The available power generated from the FC power plant may not be sufficient to meet sustained load demand, peak demand or transient events. An supercapacitor bank(SCB) can supply a large burst of power, but it cannot store a significant amount of energy. The combined use of FC and SCB has the potential for the better energy efficiency, reducing the cost of FC technology and improved dynamic response. In this paper, A single PEMFC and PEMFC operated in parallel with a SC bank are presented, A new dynamic model of PEMFC system, the converter and controller has been developed for stand-alone applications. The simulation results are presented using Matlab/Simulink, and SimPowerSystems environments. It is confirmed that the results show a good performance and stable DC-link voltage for proposed dynamic and mathematical models developed for the combined FC/SCB.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.26 no.1
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• pp.66-74
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• 2012

This paper propose a improved direct torque control(DTC) system for improving operation of five-phase squirrel-cage induction motor(IM). A five-phase IM drives present unique characteristics due to the additional degrees of freedom and also drives possess many others advantage compared with the traditional three-phase motor drive system, such as reducing a amplitude of torque pulsation and increasing the reliability. In order to maximize the torque per ampere, the proposed motor has concentrated windings and the produced back-electromotive force(EMF) is almost trapezoidal, and the motor is supplied with the combined sinusoidal plus third harmonic of currents, there is necessary to controlled 3rd harmonic current. Also a DTC method is advantageous when it is applied to the five-phase IM, because the five-phase inverter provides 32 space vectors in comparison to 8 space voltage vectors into the three-phase inverter drive system. For presenting the superior performance of the proposed DTC, experimental results of speed control are presented using a 32-bit fixed point TMS320F2812 DSP with 1.5[hp] IM.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.4
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• pp.428-435
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• 2016

In this paper, high-performance and low-noise centrifugal fan used to circulate cold air inside a household refrigerator is developed by reducing the vortex flow observed near the tip of fan hub. First, the performance of the existing centrifugal fan is investigated through the experiment using a fan tester and the characteristics of detailed flow field obtained from the CFD simulation are closely examined. The strong vortex flow is observed in the vicinity of the tip of fan hub. Based on this result, new design is devised to reduce this vortex flow. As a result, it is numerically and experimentaly found that the volume flow rate of the new fan increases and the radiated noise decreases in comparison with the existing fan at the same rotation speed.

• Korean Journal of Food Science and Technology
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• v.40 no.3
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• pp.311-315
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• 2008

This study compared the quality characteristics of sikhye (a traditional Korean sweet rice drink) samples prepared with $N_2$-circulated low-temperature dry malt (RM) and commercial malts. The amylase activities of the malts and the physiochemical (brix, reducing sugar, turbidity, color) and sensory qualities of the sikhye samples were examined. The results showed that RM had higher ${\alpha}$-amylase and ${\beta}$-amylase activities than the commercial malts. And the sikhye made with RM had higher sugar and reducing sugar contents as compared to the samples made with commercial malts. There were no significant differences in L-values between the groups; however, the RM sikhye showed lower a- and b-values. Finally, the sensory evaluation results indicated that RM sikhye received higher sweetness, color, flavor, and overall acceptability scores than the samples made with commercial malts.

• The Journal of Society for e-Business Studies
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• v.13 no.4
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• pp.161-171
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• 2008

The most important reason for increasing web traffic and overloaded web servers is a dramatic growth of web users which leads to a great dissatisfaction of each individual user. For overcoming this situation, studies for an acceleration of web content have been conducted actively. We use web caching technology for reducing the load of the web system and traffic in the network. In this paper, we proposed a new web caching technology with the related web object which based on the unit of web processing and characteristics of the web object. Also we verified the availability of the proposed system with comparison and experiments.,

• KIEAE Journal
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• v.13 no.2
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• pp.47-52
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• 2013

The problems of light pollution first became an issue in the 1970s when astronomers identified the degradation of the night sky due to the increase in lighting associated with development and growth. As more impacts to the environment by lighting have been identified, many attempts have been made for reducing light pollutions. To prevent light pollution and increase energy efficiency, Seoul Metropolitan Government(SMG) replaced metal halide road lighting to LED luminaire in four arterial highway in Seoul. The present study compared the lighting characteristics of metal halide and LED luminaire in terms of Korea Standard for road lighting(KS A 3701) and BUG rating from Illuminating Engineering Society of North America(IESNA). The results showed that LED luminaire increased road surface luminance up to 2 times in average compared to the metal halide environment. Also, LED luminaire reduced the glare value by 2 times and luminous flux over 50% than the metal halide luminaire. In comparison with the BUG ratings, LED luminaire rated 1 degree lower for the backlight ratings and 3-4 degrees lower for the uplight ratings. The measured values testified that the LED luminaire is effective for roadway lighting and light pollution reduction.

• Advances in concrete construction
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• v.5 no.6
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• pp.563-573
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• 2017

Transparency, excellent toughness, thermal stability and a very good dimensional stability make Polycarbonate (PC) one of the most widely used engineering thermoplastics. Polycarbonate market include electronics, automotive, construction, optical media and packaging. One alternative for reducing the environmental pollution caused by polycarbonate from electronic waste (e-waste), is to use it in cement concretes. In this work, physical and chemical characterization of recycled polycarbonate from electronic waste was made, through the analysis by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and scanning electron microscope (SEM). Then cement concrete was made with Portland cement, sand, gravel, water, and this recycled polycarbonate. Specimens without polycarbonate were produced for comparison purposes. The effect of the particle sizes and concentrations of recycled polycarbonate within the concrete, on the compressive strength and density was studied. Results show that compressive strength values and equilibrium density of concrete depend on the polycarbonate particle sizes and its concentrations; particularly the highest compressive strength values were 20% higher than that for concrete without polycarbonate particles. Moreover, morphological, structural and crystallinity characteristics of recycled polycarbonate, are suitable for to be mixed into concrete.

• International Journal of Highway Engineering
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• v.11 no.3
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• pp.97-109
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• 2009

One of the main causes of asphalt rutting is high temperature of the pavement. Nevertheless, there has been few research on lowering the pavement temperature for reducing rutting. This study investigated the performance characteristics of moisture-retaining porous asphalt pavement, which is known to have a temperature reducing effect. The purpose of this study is to quantify the temperature reducing effect of moisture-retaining porous asphalt pavement and its effect of reducing rutting through Accelerated Pavement Testing(APT). Additionally, the possibility of reducing the thickness of the pavement in comparison to general dense grade pavement by analyzing structural layer coefficient of moisture retaining pavement. A total of three test sections consisting of two moisture-retaining porous asphalt pavement sections and one general dense-grade porous asphalt pavement section were constructed for this study. Heating and spraying of water were carried out in a regular cycle. The loading condition was 8.2 ton of wheel load, the tire pressure of $7.03kgf/cm^2$, and the contact area of $610cm^2$. The result of this experiment revealed that the temperature reducing effect of the pavement was about $6.6{\sim}7.9^{\circ}C$(average of $7.4^{\circ}C$) for the middle layer and $7.9{\sim}9.8^{\circ}C$(average of $8.8^{\circ}C$) for surface course, resulting in a rutting reduction of 26% at the pavement surface. Additionally, the structural layer coefficient of moisture retaining pavement measured from a laboratory test was 0.173, about 1.2 times that of general dense grade pavement. The general dense-grade porous asphalt pavement test section exhibited rutting at all layers of surface course, middle layer, and base layer, while the test sections of moisture-retaining porous asphalt pavement manifested rutting mostly at surface course only.

• Journal of dental hygiene science
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• v.15 no.3
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• pp.369-376
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• 2015

The purposes of this study were to assess dental fear and anxiety level of patients attending a dental clinic using the dental fear survey (DFS) scale, to apply interventions chosen by patients for reducing dental fear and anxiety and measure their effects. This study surveyed 34 patients who visited a dental clinic in Seoul about their self-rated health and their experience of dental fear, and measured the level of dental fear using DFS. Trained dental hygienists applied interventions desired by the patients for reducing dental fear and anxiety and, for each intervention, examined the patients' satisfaction (very helpful [5 point]~not helpful at all [1 point]). Collected data were analyzed using IBM SPSS Statistics ver. 21.0 through independent t-test or one-way ANOVA for difference in level of fear according to related characteristics, and through Wilcoxon signed rank test for comparison between before and after the intervention. The subjects' mean level of fear (DFS score) was 44.53, which was an average level, and the level of dental fear was relatively high for stimulus-response (2.72). The level of dental fear was higher in those who had experienced pains or indirect dental fear from dental treatment in the past, and those whose subjectively perceived health state was poor (p<0.05). With regard to the applied dental fear intervention, 'Helpful (3.57)' was the most common answer. Overall satisfaction before and after the application of dental fear intervention was generally high as 4.37 and 4.35, respectively, but it decreased slightly after the intervention. In order to lower the level of dental fear, it is considered effective to survey not only the level of dental fear but also patients' need of dental fear interventions and to apply a suitable intervention. It is also required to educate dental workers and to develop related manuals.