• Proceedings of the KIEE Conference
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• 2006.07b
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• pp.1151-1152
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• 2006

In this paper, we examined 10 domestic samples of three different model using thermal, humidity freeze, thermal-endurance and damp heat test under IEC61215 photovoltaic module environmental endurance test condition. Three was almost no changes on power generation. Insulation resistance capacity was much higher than judgement standard but, showed unstable results depending on environmental test items. On external appearance test, there were two models which showed bubble, humidity penetration, seal melted frame phenomenon. From this results, the degree of aging under the external environment is a main cause that shortens photovoltaic module life time. So it is considered that the efforts for finding optimum condition of manufacturing process should be needed.

• Journal of the Semiconductor & Display Technology
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• v.17 no.1
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• pp.84-87
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• 2018

As the propeller end speed increases, the propeller surface is damaged in the process of bubble formation and dropout. It is intended to prevent the corrosion of the propeller by modifying the shape of the end through the winglet structure to mitigate the cavitation phenomenon. In the case of conventional SUS materials, the cost of production is so high that plastic materials are used to prevent corrosion. This paper aims to mitigate the cavitation by deforming the shape of the end through the winglet structure by using the SMC composite material of the propeller using the existing SUS.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.1
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• pp.9-18
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• 2007

This study shows an implementation of partial holes in an initial design domain in order to improve convergences of topology optimization algorithms. The method is associated with a bubble method as introduced by Eschenauer et al. to overcome slow convergence of boundary-based shape optimization methods. However, contrary to the bubble method, initial holes are only implemented for initializations of optimization algorithm in this approach, and there is no need to consider a characteristic function which defines hole's deposition during every optimization procedure. In addition, solid and void regions within the initial design domain are not fixed but merged or split during optimization Procedures. Since this phenomenon activates finite changes of design parameters without numerically calculating movements and positions of holes, convergences of topology optimization algorithm can be improved. In the present study, material topology optimization designs of Michell-type beam utilizing the initial design domain with initial holes of varied sizes and shapes is carried out by using SIMP like a density distribution method. Numerical examples demonstrate the efficiency and simplicity of the present method.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1995.05a
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• pp.185-198
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• 1995

This is an experimental study conducted to visualize the nucleate boiling phenomena and flow regimes occurring inside the liquid pool in a closed two-phase thermosyphon. To meet this purpose, an annular-type thermosyphon was designed and manufactured using a glass tube and a stainless steel tube, being assembled axisymmetrically. The heat to be supplied to the working fluid is generated within a very thin layer of stainless steel tube wall by applying a high frequency electromagnetic field through the induction coil, axisymmetrically set around the evaporator zone. Some important results were as follows ; 1) Considering the structural complexity of the tested thermosyphon, it showed good performance for the range of heat flux 2＜ q" ＜25kW/$m^2$ and saturation vapor pressure, 0.1＜Pv＜1.1bar 2) different type of nucleating boiling regimes were observed as described below, -Pulse boiling regime : Flow pattern changed cyclically with time during 1 cycle of pulse boiling process. The onset of Nucleation was followed by expulsive growing of vapor bubble, resulting in the so called blow-up phenomenon, massive expulsion of large amount of liquid around the bubble. -Transient : Some spherical vapor bobbles were observed growing out from 2~3 nucleating sites, that was dispersed at the lower part of the heated tube wall in the liquid pool. But the rest upper region above the nucleating sites were filled with churns or bubbles of vapor. -Continuous nucleate boiling regime : The whole zone of evaporator was filled with lots of spherical vapor bubbles, and the bubbles showed tendency to decrease in diameter as the heat flux increased.ased.

• The Journal of the Acoustical Society of Korea
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• v.29 no.2
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• pp.111-117
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• 2010

Sonoluminescence (SL) is the light emitting phenomenon accompanied with ultrasonic cavitation in liquid. It attracts many interests because physics behind it remains uncertain and few applications have appeared. It has been known that the color of SL changes in solutions which include metallic ions. In the present work, colors of SL in alkali metallic and alkaline earth metallic ions were considered. RGB component was used to analyze the color of SL. By using RGB component, it was found that color of SL in metallic solution can be resolved into color of SL in pure water and flame color of metal which is different from high intensity color of line spectrum of alkaline earth metal. From this result, influence of metallic ion on SL and the temperature on violent collapsing of cavitation bubble was discussed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.4 no.4
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• pp.79-93
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• 1984

The dissolved air flotation(DAF) has been shown to be efficient process for the removal of algae ftom water. The efficiency of DAF can be affected by the volume ratio of pressurized liquid to sample, the pressure pressurized liquid, the contact time, the appropriate coagulant and its amount, the water temperature, the turbulence of reactor, the bubble size and rising velocity etc. The purpose of this paper is to compare the practical bubble rising velocity with the theoretical one, to investigate the adhesion phenomenon of bubbles and floc, and the influence of bubble size and velocity upon the process. The results through theoretical review and experimental investigation are as follows: Ives' equation is more suitable than Stokes' equation in computation of the bubble rising velocity. The collection of bubble and algae floc is convective collection type and resulted from absorption than adhesion or collision. The treatment efficiency is excellent when the bubble sizes are smaller than $l00{\mu}m$, and the turbulence of reactor is small. In the optimum condition of continuous type DAF the volume ratio of pressurized liquid to sample is 15%, the contact time in reactor is 15 minutes, the pressure of pressurized liquid is $4kg/cm^2$ and the distance from jet needle to inlet is 30cm.

• KDI Journal of Economic Policy
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• v.14 no.4
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• pp.27-49
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• 1992

This paper stresses the role of market fundamentals rather than bubbles in explaining Korea's recent experience of large fluctuations of stock and real estate prices. The bubble story that emphasizes the self-fulfilling prophecies of investors seems to be inappropriate to explain the recent changes of assets prices in Korea. Those who argue for bubble phenomenon in Korea tend to interpret the volatile movements of assets prices as some form of bubbles, but without implementing a rigorous test on the presence of bubbles. Even when some bubble tests are carried out, such studies exhibit various econometric problems in testing. More seriously, they suffer from the misspecification problems in setting up a market model. This paper has shown that Korea's recent changes in assets prices could be explained by changes in market fundamentals according to the emergence and the subsequent fading of 'three lows'. First, it tried to explain changes in assets prices by changes in such market fundamentals as real interest rates and economic growth. Second, it showed that the real estate prices overshoot when the liquidity and exchange rates change, using the two-sector general equilibrium portfolio balance model. It is argued that the rapid rise in real estate prices during 1986-89 stems from Yen's and Won's appreciation $vis-{\grave{a}}-vis$ the U.S. dollar and liquidity expansion (or decreases in real interest rates), while the downturn in real estate prices since 1990 is associated with Yen's and Won's depreciation $vis-{\grave{a}}-vis$ the U.S. dollar and rises in real interest rates in reflection of the excess demand for liquidity.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05b
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• pp.108-113
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• 1996

Several analytical models for the departure from nucleate boiling (DNB) phenomenon have been developed during the last decade. Among these, Chang & Lee's model based on a bubble crowding mechanism is remarkable in the fundamental features characterized as the formulation of mass, energy, and momentum balance equation at thermal-hydraulic conditions leading to the DNB. However, Bricard and Souyri remarked that the assumption of stagnant bubbly layer at the DNB condition is questionable and the signs on the axial projections of the momentum fluxes at the core/bubbly layer interface in the momentum balance equations are erroneous. From this remark, Chang & Lee's model has been re-examined and modified by correcting the erroneous treatments in the momentum balance equations and removing the spurious assumptions. The revised model predicts well the extensive DNB data of water in uniformly heated tubes at low qualities and shows more accurate prediction compared with the original model.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.9
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• pp.2316-2327
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• 1995

Experimental results from nucleate pool boiling heat transfer with various finned tubes in CFC11, HCF123 and HCFC141b are reported. One plain tube and four low fin tubes of various fin densities were tested in an attempt to find out the optimum fin density in the heat flux range of 10-60 kW/m$^{[-992]}$ at near atmospheric pressure. The results indicated that CFC11 showed the highest heat transfer coefficients. Its alternatives, HCFC123 and HCFC141b, showed 3-5% lower heat transfer coefficients than those of CFC11 at the same heat flux. As the fin density increases, so does the heat transfer surface area. Measured heat transfer coefficients, however, do not necessarily always increase as the fin density increases. This unique phenomenon seems to be caused by the coalescence of the bubblers that prevent the cool liquid from entering into the fin valleys. For all the refrigerants tested, the optimum fin density yielding the highest performance was 28 fins per inch confirming the previous results by other researchers.

• Journal of the Korean Society of Costume
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• v.53 no.3
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• pp.13-31
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• 2003

The purpose of this study is to analyze the formative style and aesthetic value of contemporary subcultural style with the understanding of characteristics of subcultural style in the sociocultural context. As for the research methodology, literary survey has been performed to study the concept and the history of subcultural styles from 1940s to 1980s. In addition, demonstrative studies on aesthetic images have been carried out through the analysis of pictures and photographs in order to categorize the subcultural styles since 1990s. In this study, subcultural styles since 1990s have been illustrated through the socio-cultural grounds. which are diversity of street culture, diffusion of moss culture or bubble-up phenomenon, pursuit of anti-social ideology among intellectual heads, club Cultures in the form of kitsch and pastiche and communal thinking as collective harmony. With the socio-cultural context examined above, subcultural styles in the contemporary fashion are categorized and deduced following aesthetic values ; Drag and Club style as the tendency of surrealists or artificial hedonists, Urban military style and Cyberpunks as pursuit of Bionic being, Sports casual style based upon, the pursuit of comfort and freedom, Vintage style and Retro dressing represented by the spirit of DIY (no It Yourself), Ecology style of New conservatives, and Mysticism style as the fusion of technology and shamanism (Technoshamanism).