• Transactions of Materials Processing
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• v.3 no.1
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• pp.97-109
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• 1994

Closed-die forging of the spur gears with circular are fillet has been analyses by using the upper-bound method. A kinematically admissible velocity field has been developed, wherein, the tooth profile consists of the involute curve and the circular arc fillet. In the analysis, the deformation regions have been divided into eight zones. A constant frictional stress has been assumed on the contacting surfaces Utilizing the formulated velocity field, numerical calculations have been carried out to investigate the effects of various parameters, such as module, number of teeth, addendum modification coefficient and friction factor, on the relative forging pressure of spur gears. As the result of numerical calculations, the relative forging pressure does not change so much against the variation of module. On the other hand, the relative forging pressure increases at the final filling stage as the addendum modification coefficient increases.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.10
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• pp.1-11
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• 2004

An experimental study was carried out to investigate the influence of flow conditions of a boundary layer on the near-wake of a flat plate. Various attaching positions of tripping wires were selected to change flow conditions on a boundary layer. Laminar, transitional, and turbulent boundary layer conditions at 0.98C from the leading edge are imposed to investigate the evolution of symmetric and asymmetric wake. An x-type hot-wire probe(55P61) is employed to measure at 8 stations of the near-wake region. Measured mean velocity distributions are presented in terms of similarity parameter. It is found that the symmetric wake collapses well to the universal profile in the central part of the wake. However, the universal profile is not suitable in describing an asymmetric wake.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.6 no.2
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• pp.113-118
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• 2007

KPCS internal antenna in this paper, is designed and fabricated using the theory based on the folded monopole antenna. I propose folded monopole internal antenna which has high gain low profile structure with easy installation into the handset of mobile phone. Design frequency is 1.8 GHz that is a center frequency of Korea PCS frequency band, and the impedance variances due to change of antenna structure as a length and width are simulated. Measurements show that input VSWR range under 2:1 is 1.72 - 1.88 GHz, and radiated H-plane pattern is omnidirectional under passive state. Active sensitivities and output power of phone applied antenna are $-105\;{\sim}\;-108\;dBm$ and $22.5\;{\sim}\;23.6\;dBm$ max., respectively.

• Aerospace Engineering and Technology
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• v.2 no.2
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• pp.133-141
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• 2003

When superplastic forming process is employed in manufacturing spherical pressure vessel, the thickness and spherical profile are not constant and varies during the forming process. In the current study, theoretical analysis for the prediction of thickness change was carried out under the consideration of membrane theory which has been employed in Kuglov et. al.'s study. Then the thickness of initial blank to obtain the required thickness at the final forming step, the time vs. pressure profile which yields uniform deformation in blank, and the thickness distribution according to the position at each forming step have been determined. The employed model and the developed analytical code were verified throughout comparing the theoretical predictions at each forming stage with the experimental results shown in literature.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.8
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• pp.1077-1087
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• 2002

The heat (mass) transfer characteristics on the blade surface of a high-turning first-stage turbine rotor for power generation has been investigated by employing the naphthalene sublimation technique. A four-axis profile measurement system is developed successfully for the measurements of local sublimation depth on the curved surface In the leading edge region, there is a good agreement between the present heat (mass) transfer data and the previous result on a turbine blade with a moderate turning angle, but some discrepancies are found in the mid-chord heat (mass) transfer between the two results. The local heat (mass) transfer on the present suction surface is greatly enhanced due to an earlier boundary transition, compared with that on a turbine blade with a moderate turning angle, meanwhile there is only a slight change in the pressure-side heat (mass) transfer between the two different turbine rotors. In general, the heat (mass) transfer augmentation by the endwall vortices is found much higher on the suction surface than on the pressure surface.

• Applied Microscopy
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• v.42 no.3
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• pp.129-135
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• 2012

In this study, the changes in hair quality before and after Magic straight perm have been evaluated through a hair damage measurement method. For this, a healthy high school student's (age18 years) wavy hair was selected and permed on the left and right sides. Then, the changes caused by physical methods which were applied during the fl at iron-based Magic straight perm were evaluated based on the hair damage measurement method before and after the Magic straight perm. According to the protein release test after the Magic straight perm, 1.26% in average and 0.14% was observed in Cool Magic straight perm sample. In a field emission scanning electron microscopy (FE-SEM) test, saw teeth-shaped partial desquamation of cuticle cells and impurities were observed in the warm-treated hair sample. In atomic force microscope (AFM), line-profile is a method to represent roughness data on hair. According to analysis on 3-dimensional (3D) images, the hair with Cool Magic straight perm was lower than the hair with Warm Magic perm in terms of the color change of 3D images. In addition, vertical changes were observed in the hair with Cool Magic perm. As a result, irregular surface roughness was observed. This study proposed a method to minimize hair damage by cooling down the heat with the cool hair straightener as soon as the Warm Magic was finished.

• Journal of Broadcast Engineering
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• v.12 no.4
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• pp.377-380
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• 2007

In this paper, an improved CABAC is proposed for the lossless compression in H.264/AVC. CABAC in the lossless coding is not as efficient as that in the lossy compression since it was developed for lossy coding. CABAC for the lossless coding in H.26과/AVC Advanced 4:4:4 Profile is applied without the change of the conventional binarization method. Thus, a binarization method considering the statistical characteristic of residual signals is proposed for the lossless coding in 0.264/AVC Advanced 4:4:4 Profile. The experimental results show that the proposed method obtains approximately 3.4% bitrate reduction in comparison to that of the conventional lossless coding.

• Tribology and Lubricants
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• v.26 no.4
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• pp.230-239
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• 2010

Mechanical face seal installed in boiler feedwater pump prevents leakage of working fluid using thin fluid film between stator and rotor. If the leakage of working fluid exceeds the allowable volume, serious malfunction of boiler feedwater pump will be happen. The thinner fluid film exists between stator and rotor, the less working fluid leaks out. However, if the thickness of fluid film is not enough, the wear of seal face will be increased. And it causes the decrease in life of mechanical face seal. Therefore appropriate design is necessary to maximize the performance and life of mechanical face seal. In this study, numerical analysis using finite volume method was conducted to investigate the static characteristics of wavy mechanical face seals which have 4 different wavy surface profiles on rotor. As a result, opening force, leakage volume of working fluid and friction torque were obtained. For the same minimum film thickness, the static characteristics of mechanical face seal were affected by the wavy surface profile which can change the thickness of working fluid film and pressure distribution.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.17 no.4
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• pp.187-192
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• 2017

Rigorous longitudinal modal transmission-line theory (L-MTLT) is applied to analyze maximum power transfer in asymmetric grating-assisted directional couplers(A-GADC). By defining a coupling efficiency amenable to rigorous analytical solutions and interference between symmetric and asymmetric supermodes, the power exchange of TE modes as a function of propagation distance is numerically evaluated. The numerical result reveals that maximum power transfer occurs at a grating period ${\Lambda}_{eq}$, in which the insertion loss of supermodes is equal to each other. That is, it is generally different from conventional phase-matching condition of GADC. Furthermore, as the asymmetric profile of grating change to symmetrical profile, the coupling length decreases and the coupling efficiency for power transmission increases.

• The Korean Journal of Community Living Science
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• v.15 no.2
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• pp.179-187
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• 2004

The purpose of this study is to investigate the preservation of traditional sesame dasik when stored in different packaging material by comparing its physical and sensorial characteristics. The quality and sensory characteristics of sesame dasik that were evaluated were moisture content, water activity, number of microflora, texture profile, Hunter color different value, and sensory properties (color, chewiness, overall acceptability, etc) during the storage at 35\pm1^\circ{C}$ temperature and $73\pm{2%}$ relative humidity. And the packaging materials were paper boxes (coated 0.02mm thickness polyethylene film), plastic boxes, and oriented polypropylene laminated film. Traditional sesame dasik is made from sesame powder 100g, honey 25g, rice syrup 25g, and table salt 0.5g. During the storage period, the changes in water content and water activity of sesame dasik with different packaging material showed a slight decline. On the other hand, it increased in hardness, and "a" and "b" value of Hunter color difference during the storage. Texture profile analysis data change in hardness was the greatest after the third day in a paper box, and it was affected by the moisture content of dasik and the temperature and relative humidity of the air. Therefore plastic boxes or oriented polypropylene laminated film was found to be better suited than paper boxes for storing sesame dasik.