• Journal of Welding and Joining
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• v.15 no.5
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• pp.134-143
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• 1997

The formation of thick alloyed layer with high Si content have been investigated on the surface of Al alloy (A5083) plate by PTA process with Si powder. Hardening characteristics and wear resistance of alloyed layer was examined in relation to the microstructure of alloyed layer. Thick hardened layer in mm-order thickness on the surface of A5083 plate can be formed by PTA process with wide range of process condition by using Si powder as alloying element because of eutectic reaction of Al-Si binary alloy. High temperature and rapid solidification rate of molten pool, which are features of PTA process, enable the formation of high Si content alloyed layer with uniform distribution of fine primary Si paticle. High plasma arc current was beneficial to make the alloyed layer with smooth surface appearance in wide range of powder feeding rate, because enough volume of molten pool was necessary make alloyed layer. Uniform dispersion of fine primary Si particle with about 30${\mu}{\textrm}{m}$ in particle size can be obtained in layer with Si content ranging from 30 to 50 mass %. Hardness of alloyed layer increased with increasing Si content, but increasing rate of hardness differed with macrostructure of alloyed layer. Wear resistance of alloyed layer depended on $V_{si}$(volume fraction of primary Si) and was remarkably improved to two times of base metal at 20-30% $V_{si}$ without cracking, but no more improvement was obtained at larger $V_{si}$.

• Nuclear Engineering and Technology
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• v.16 no.3
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• pp.125-130
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• 1984

In the application of the RETRAN code to the analysis of very small LOCA one of main concerns is placed on use of the bubble rise model in the upper plenum, because the bubble rise model nay cause a numerical divergence problem and coefficients used to describe it are based on experimental results of large LOCA. In order to solve this problem, a method, which enables us to predict the mixture level in the upper plenum without use of the bubble rise model, was proposed. For this method the local void distribution in the core and upper plenum was derived by using a simplified slip model. It was shown that results predicted from the derived equation are in excellent agreement with experimental data. Additionally it was found that local void in the upper plenum has a uniform distribution unlike a linear distribution in large LOCA. Communication between the upper plenum and upper head was investigated. By introducing the concept of Taylor instability, it was proved that counter-current Hon between them is possible.

• Journal of the Korean Data and Information Science Society
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• v.21 no.6
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• pp.1031-1039
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• 2010

The decathlon is an athletic event consisting of ten track and field events. Events are held over two consecutive days and the winners are determined by the combined performance in all. Performance is judged in meters, centimeters, minutes, and seconds. However, how to convert results into points is a difficult and controversial issue. We explored the distribution of decathlon results from the 1991 to 2009 using top 200 decathlons in the Olympic games and word championships. The conclusion is that the results from top level decathlon competition are normally distributed, and the current scoring system does not have the property that the performance with same difficulty should get same points. A new model for evaluating the decathlon score has been applied that display uniform characteristics over all events in order to meet the notion of allroundness. The proposed model is uniform over the events and support self-stabilization.

• Applied Chemistry for Engineering
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• v.32 no.6
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• pp.613-620
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• 2021

A flow channel shape of PEMFC has an influence on the internal flow uniformity. If the reactant distribution in a flow path is not uniform during operation, both catalyst deactivation and mechanical damage of membrane could occur resulting in decreasing the membrane electrode assembly (MEA) durability. Numerous studies concerning flow design have been conducted to make smooth supply and uniform distribution of reactants in fuel cells. The baffle of flow path could improve fuel cell performance through the forced convection effect. A sub-channel, as an additional air flow path, could increase the reactant concentration and reduce the mass transfer loss via a smooth water discharge. In this study, computational fluid dynamics (CFD) was used to analyze the effect of blocks and sub-channels on the current density and oxygen concentration of the fuel cell. As a result, the limit current density and oxygen concentration at a rear block increased when using blocks and sub-channels in a flow channel. In particular, the current density increased significantly when the sub-channel was placed between two blocks. Also, the sub-channel position was optimized by analyzing the oxygen concentration, and the oxygen concentration was recovered at a rear block in the fuel cell.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.1033-1036
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• 2002

Wafer bonding methods such as fusion and anodic bonding suffer from high temperature treatment, long processing time, and possible damage to the micro-scale sensor or actuators. In the localized bonding process, beating was conducted locally while the whole wafer is maintained at a relatively low temperature. But previous research of localized heating has some problems, such as non-uniform soldering due to non-uniform heating and micro crack formation on the glass capsule by thermal stress effect. To address this non-uniformity problem, a new heater configuration is being proposed. By keeping several points on the heater strip at calculated and constant potential, more uniform heating, hence more reliable wafer bonding could be achieved. The proposed scheme has been successfully demonstrated, and the result shows that it will be very useful in hermetic packaging. Less than 0.2 ㎫ contact Pressure were used for bonding with 150 ㎃ current input for 50${\mu}{\textrm}{m}$ width, 2${\mu}{\textrm}{m}$ height and 8mm $\times$ 8mm, 5mm$\times$5mm, 3mm $\times$ 3mm sized phosphorus-doped poly-silicon micro heater. The temperature can be raised at the bonding region to 80$0^{\circ}C$, and it was enough to achieve a strong and reliable bonding in 3minutes. The IR camera test results show improved uniformity in heat distribution compared with conventional micro heaters. For gross leak check, IPA (Isopropanol Alcohol) was used. Since IPA has better wetability than water, it can easily penetrate small openings, and is more suitable for gross leak check. The pass ratio of bonded dies was 70%, for conventional localized heating, and 85% for newly developed FP scheme. The bonding strength was more than 30㎫ for FP scheme packaging, which shows that FP scheme can be a good candidate for micro scale hermetic packaging.

• Journal of the Korean Society of Clothing and Textiles
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• v.31 no.11
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• pp.1530-1541
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• 2007

The purpose of this study is to establish a standard sizing system for Taekwondo uniforms. The sample utilized in the study consisted of 5,679 male and female subjects, obtained from Size Korea Project. Twenty three measurements were identified and selected as critical in the design and construction of Taekwondo uniforms. The results were as follows: First, it was determined that all brands used "height" as a key dimension of size designation. Two of brands added "chest girth" or "numeric numbers" to designate size in addition to "height". For example: 1) height/chest girth, 2) height/numeric number. The size pitches of all current Taekwondo uniforms in the market were 10cm of height for all brands. Second, the study showed male measurements were larger and longer than females, establishing that independent sizing specifications by sexes are needed. Third, in case of Taekwondo shirts, height and chest girth were selected as control dimensions. In case of pants, height and waist girth were selected as control dimensions. For selecting optimal sizing pitch, 2 different pitches of chest girth and waist girth(4cm pitch by KS and 8cm pitch by researchers) were compared, while height pitch was fixed at 10cm. Fourth, based on the analysis of the measurements(coverages and coverage efficiency rates), it was determined that 8cm pitches of chest and waist girth were efficient in both upper and lower Taekwondo uniforms. Fifth, subjects distribution counts and percentages were shown after analyzing coverage efficiency rates. Separate results are noted for the upper and lower Taekwondo uniforms. As previously mentioned, height pitches were 10cm and chest and waist pitches were 8cm. Finally, as a result of this research, key and referable measurements relevant to making Taekwondo uniforms were identified for male and female uniform. In case of Taekwondo shirts, 18 sizes were established for men, 16 sizes for women. Twenty five sizes for men and 20 sizes for women were presented in size tables for pants.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.287.1-287.1
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• 2016

Three-dimensional (3-D) semiconductor nanoarchitectures, including nano- and micro- rods, pyramids, and disks, are emerging as one of the most promising elements for future optoelectronic devices. Since these 3-D semiconductor nanoarchitectures have many interesting unconventional properties, including the use of large light-emitting surface area and semipolar/nonpolar nano- or micro-facets, numerous studies reported on novel device applications of these 3-D nanoarchitectures. In particular, 3-D nanoarchitecture devices can have noticeably different current spreading characteristics compared with conventional thin film devices, due to their elaborate 3-D geometry. Utilizing this feature in a highly controlled manner, color-tunable light-emitting diodes (LEDs) were demonstrated by controlling the spatial distribution of current density over the multifaceted GaN LEDs. Meanwhile, for the fabrication of high brightness, single color emitting LEDs or laser diodes, uniform and high density of electrical current must be injected into the entire active layers of the nanoarchitecture devices. Here, we report on a new device structure to inject uniform and high density of electrical current through the 3-D semiconductor nanoarchitecture LEDs using metal core inside microtube LEDs. In this work, we report the fabrications and characteristics of metal-cored coaxial $GaN/In_xGa_{1-x}N$ microtube LEDs. For the fabrication of metal-cored microtube LEDs, $GaN/In_xGa_{1-x}N/ZnO$ coaxial microtube LED arrays grown on an n-GaN/c-Al2O3 substrate were lifted-off from the substrate by wet chemical etching of sacrificial ZnO microtubes and $SiO_2$ layer. The chemically lifted-off layer of LEDs were then stamped upside down on another supporting substrates. Subsequently, Ti/Au and indium tin oxide were deposited on the inner shells of microtubes, forming n-type electrodes of the metal-cored LEDs. The device characteristics were investigated measuring electroluminescence and current-voltage characteristic curves and analyzed by computational modeling of current spreading characteristics.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.03b
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• pp.379-386
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• 2000

This paper presents the results of finite element analysis on the seismic response of a soil-reinforced segmental retaining wall subjected to a prescribed earthquake record. The results of finite element analysis indicate that the maximum wall displacement occurs at the top, exhibiting a cantilever type of wall movement. Also revealed is that the increase in reinforcement force is more pronounced in the upper part of the reinforced zone, resulting in a more or less uniform distribution. None of the design guidelines appears to be able to correctly predict the dynamic force increase when compared with the results of finite element analysis. The calculation model adopted by the NCMA guideline, however, appears to compare better with the results of finite element analysis as well as field survey than the FHWA guideline. Based on the findings from this study, a number of implications to the current design methods are discussed.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.12
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• pp.136-141
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• 1996

In this paper, the design variables of the extruded parts involving flat die through model experiment are investigated to overcome some current problems such as bending and twisting and get more improved quality products. Above all, the deformation behavior is analyzed in experiment and investigated flow charactristics inside container. Finally, the straight extruded product is obtained by modified bearing land width on the basis of the exit velocities distribution from bended and twisted products.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.788-789
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• 2011

A comprehensive thermo-electromagnetic model has been developed to estimate temperature and electromagnetic distribution in an three-phase induction motor under steady state operation. Electromagnetic modeling enables us to predict thermal dissipation rates by eddy-current loss and copper loss in induction motors. Non-uniform temperature distributions are investigated to account for the strong effect of local temperature build-up on the motor performance and expected life-span. For more accurate thermal modeling purpose, Heat loss mapping method, which is matched up with electromagnetic losses and volumetric heat source, is developed and performed analysis. Heat loss mapping method can be greatly used as a design or diagnostic tool for three-phase induction motors with complex structural electromagnetic fields.