• Proceedings of the KSME Conference
• /
• 2004.11a
• /
• pp.1247-1252
• /
• 2004

The present paper is devoted to the modeling method based on an averaging approach for thermal analysis of microchannel heat sinks subjected to the uniform wall temperature condition. Solutions for velocity and temperature distributions are presented using the averaging approach. When the aspect ratio of the microchannel is higher than 1, these solutions accurately evaluate thermal resistances of heat sinks. Asymptotic solutions for velocity and temperature distributions at the high-aspect-ratio limit are alsopresented by using the scale analysis. Asymptotic solutions are simple, but shown to predict thermal resistances accurately when the aspect ratio is higher than 10. The effects of the aspect ratio and the porosity on the friction factor and the Nusselt number are presented. Characteristics of the thermal resistance of microchannel heat sinks are also discussed.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.21 no.4
• /
• pp.625-632
• /
• 2012

Optimization of process parameters in polymer extrusion is an important task to reduce manufacturing cost. To determine the optimum values of the process parameters, it is essential to find their influence on the strength of polymer breathable thin film. The significance of six important process parameters namely, extruder cylinder temperature, extruder speed, extruder dies temperature, cooling roll temperature, stretching ratio, stretching roll temperature on breathable film strength of polymer extrusion was determined. Moreover, this paper presents the application of Taguchi method and analysis of variance (ANOVA) for maximization of the breathable film strength influenced by extrusion parameters. The optimum parameter combination of extrusion process was obtained by using the analysis of signal-to-noise ratio. The conclusion revealed that extruder speed and stretching ratio were the most influential factor on the film strength, respectively. The best results of film strength were obtained at higher extruder speed and stretching ratio.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.8 no.1
• /
• pp.1-14
• /
• 2002

This paper discusses the analysis of financial ratios of the Korean coastal passenger shipping company 1997 and 2000. Coastal passenger shipping company shows a very high ratio of the fixed-assets because these shipping company own relatively expensive ships. The current debts are composed of short-term borrowings and lease and the ratio of the current debts is rather high considering to the size of shipping company. The equity ratio of passenger shipping company has recently been decreased, but the debt ratio has been increased. Both the profitability and activity ratios have grown worse in recent years. In order to improve the performance of coastal passenger shipping company, they should develop the leisure facilities and good items to attract travellers.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.16 no.11
• /
• pp.1132-1142
• /
• 1991

This paper proposed a method of feature parameter extraction for shape information analysis of moving object. In the 2-D plane, moving object are extracted by the difference method. Feature parameters of moving object are chosen area, perimeter, a/p ratio, vertex, x/y ratio. We changed brightness variation from the range of 600Lux to the 1400Lux and then determined Permissible Error range of feature parameter due to the brightness variation. So as to verify the validity of proposed method, experiment are performed with a toy car and it's results showed that decision error was less than 6%.

• International Commerce and Information Review
• /
• v.11 no.1
• /
• pp.139-155
• /
• 2009

This study investigates empirically the export competitiveness of Korea and Japan in America by calculating 4 indexes such as market share index(MSI), export similarity index(ESI), market comparative adventage index(MCAI) and market share expansion ratio(MSER)-export similarity deepening ratio(ESDR). The empirical finding of this analysis shows that Korea is competitive in the labor-intensive products and Japan in the technology-intensive products. This result also meets the general understandings that Japan is superior to Korea in the export competitiveness such as value added of goods, etc. Therefore, in order to strengthen the export competitiveness of Korea in the US market, it's desirable for our firms and government to improve the quality of product ranges by developing technologies focused on the higher value-added products.

• Journal of The Korean Digital Architecture Interior Association
• /
• v.11 no.2
• /
• pp.31-39
• /
• 2011

Concrete-filled steel tube(CFT) columns have become popular for building construction due to not only composite effect of steel tube and infilled concrete, but also more economical. The purpose of this paper is to propose the applicable boundary formula of width-to-thickness ratio for rectangular steel tube as using CFT column. A parametric study was performed taking width-to-thickness ratio of rectangular steel tube and compressive strength of concrete as the main parameter. The strength of concrete are selected to 30, 60, 90MPa. The non-linear analysis was adopted in order to take into account the effect of concrete strength. Finally, from the test and analysis results, the effect of increasing strength according to concrete strength and width-to-thickness of steel tube and plastic behavior of specimens were verified distinctly.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.21 no.10
• /
• pp.1609-1618
• /
• 1997

Thermo-mechanical behaviors of polymer matrix composite(PMC) with continuous TiNi fiber are studied using theoretical analysis with 1-D analytical model and numerical analysis with 2-D multi-fiber finite element(FE) model. It is found that both compressive stress in matrix and tensile stress in TiNi fiber are the source of strengthening mechanisms and thermo-mechanical coupling. Thermal expansion of continuous TiNi fiber reinforced PMC has been compared with various mechanical behaviors as a function of fiber volume fraction, degree of pre-strain and modulus ratio between TiNi fiber and polymer matrix. Based on the concept of so-called shape memory composite(SMC) with a permanent shape memory effect, the critical modulus ratio is determined to obtain a smart composite with no or minimum thermal deformation. The critical modulus ratio should be a major factor for design and manufacturing of SMC.

• Current Optics and Photonics
• /
• v.1 no.3
• /
• pp.239-246
• /
• 2017

A compact plasmonic switching scheme, based on the phase change of a thin-film chalcogenide material ($Ge_2Sb_2Te_5$), is proposed and numerically investigated at optical-communication wavelengths. Surface plasmon polariton modal analysis is conducted for various thicknesses of dielectric and phase-change material layers, and the optimized condition is induced by finding the region of interest that shows a high extinction ratio of surface plasmon polariton modes before and after the phase transition. Full electromagnetic simulations show that multiple reflections inside the active region may conditionally increase the overall efficiency of the on/off ratio at a specific length of the active region. However, it is shown that the optimized geometrical condition, which shows generally large on/off ratio for any length of active region, can be distinguished by observing the multiple-reflection characteristic inside the active region. The proposed scheme shows an on/off switching ratio greater than 30 dB for a length of a few micrometers, which can be potentially applied to integrated active plasmonic systems.

• 한국벤처창업학회:학술대회논문집
• /
• 2006.11a
• /
• pp.61-85
• /
• 2006

The Purpose of this study is to prove empirically the relationship between ventures' technology valuation and performance, while considering the uniqueness of Korean firms. We use technology valuation index, marketability valuation index, business valuation index as ex-ante independent variables, use firm's performance(sales, asset, operating income ratio, net income ratio etc) as ex-post dependent variables. Parametric analysis such as Paired T-test, ANOVA are applied in this paper. The results of Empirical analysis is summarized as follows. Firstly, operating income ratio and net income ratio are different in portfolios classified by technology valuation index. Secondly, the growth rate of operating income is different in portfolios classified by technology valuation index. Finally, this study has shown that technology valuation index has possibility which it use the predictive variables of ventures' performances.

• Journal of Advanced Marine Engineering and Technology
• /
• v.28 no.5
• /
• pp.847-852
• /
• 2004

The wind turbine blade is the equipment converted wind into electric energy. The effect of the blade has influence of the output power and efficiency of wind turbine. The design of blade is considered of lift-to-drag ratio. structure. a condition of process of manufacture and stable maximum lift coefficient, etc. This study is used the simplified method for design of the aerodynamic blade and aerodynamic analysis used blade element method This Process is programed by delphi-language. The Program has any input values such as tip speed ratio blade length. hub length. a section of shape and max lift-to-drag ratio. The Program displays chord length and twist angle by input value and analyzes performance of the blade.