• 전기학회논문지
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• 제56권10호
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• pp.1791-1795
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• 2007

Small ions generated at conductor corona sources remain in the atmosphere until they recombine with ions of opposite polarity, attach to aerosols, or make contact with an object. Ion current density is major factor to design conductor configuration of DC overhead transmission line. Several techniques have been used to measure the ion current of HVDC overhead transmission line. In this study, the ion current density was measured by a plate electrode made of a metal flat board at DC corona cage. The sensitivity of the plate electrode is $0.156uA/m^2/V$. To obtain an useful database on corona discharge, it is necessary to do corona test on several kinds of conductor bundles. Therefore, a number of experiments were conducted on several kinds of conductor bundles. To reliably analyze ion effects, corona cage test data were obtained over a long period of time under various weather conditions and expressed as a statistical distribution. Ion current density distribution in foul weather shows a significant increase in levels over the corresponding fair weather. Based on this results, we evaluated the environmental characteristic caused by ion flow of three candidated conductor bundles.

• 설비공학논문집
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• 제1권2호
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• pp.182-189
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• 1989

The propose of this study is augmentation of heat transfer without additional external power in 2-dimensional impinging air jet. The passive heat transfer augmentation method tried in this experimental study is placement of rod bundles with the clearance, 2mm, in front of the heat transfer surface. The effects of pitch distance among rods and nozzle-to-target plate distance are investigated. The overall heat transfer rate of flat plate with rods reaches maximum at H/B=10 and P=40mm, and for H/B=2 and P=40mm the augmentation rate of heat transfer becomes maximum to a value which is about 1.57 times that of the flat plate without rods.

• 대한수학회보
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• 제56권5호
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• pp.1219-1233
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• 2019

Let $E{\rightarrow}M$ be an arbitrary vector bundle of rank k over a Riemannian manifold M equipped with a fiber metric and a compatible connection $D^E$. R. Albuquerque constructed a general class of (two-weights) spherically symmetric metrics on E. In this paper, we give a characterization of locally symmetric spherically symmetric metrics on E in the case when $D^E$ is flat. We study also the Einstein property on E proving, among other results, that if $k{\geq}2$ and the base manifold is Einstein with positive constant scalar curvature, then there is a 1-parameter family of Einstein spherically symmetric metrics on E, which are not Ricci-flat.

• 한국컴퓨터정보학회지
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• 제14권2호
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• pp.109-115
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• 2006

이 논문에서는 OSGi 서비스 프레임워크 환경에서 발생할 수 있는 보안 요구 사항 중에서 서로 다른 번들의 서비스간의 상호 작용에서 발생할 수 있는 접근 제어(access control)문제를 설명하고 이를 만족시킬 수 있는 구체적인 서비스 보안 모델을 제시하였다. 특히 번들이나 서비스에 대한 접근 통제를 유연성과 확장성이 보장되는 방식으로 처리 할 수 있도록 번들에 포함된 파일 형식으로 명시될 보안 정책(security policy)의 구성요소와 의미론을 정의한다. 또한, 원격 관리 서비스를 위한 효율적인 서비스 구조를 제안하였다.

• 산업경영시스템학회지
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• 제33권4호
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• pp.38-44
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• 2010

We investigated the effects of trunk twist on postural stability during manually handling flat ties. Ten male subjects participated in this study. While handling 5kgf and 10kgf bundles of flat ties respectively, their centers of pressure (COPs) were measured under two levels of body position (twisted and fixed), two levels of direction (left and right), and three levels of object position ($30^{\circ}$, $45^{\circ}$, and $60^{\circ}$). Subjects' postural stability was quantified by calculating the sway length. Results showed that the effect of different object position was significant on postural sway length in subject's medio-lateral axis. Post-hoc multiple comparions revealed that, under the 5kgf load condition, the sway length was increased significantly as the object position increased to $45^{\circ}$. Under the 10kgf load condition, however, the sway length was increased significantly at the object position of $60^{\circ}$. Actual or potential applications of this research include guidelines for the design of working posture evaluation techniques.

• 설비공학논문집
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• 제4권1호
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• pp.48-56
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• 1992

The purpose of this study was to investigate the enhancement of heat transfer without additional external power in the case of rectangular air jet impinging vertically on the flat heating surface. In an attempt to enhance the heat transfer rate in two-dimensional impinging jet, the technique used in the present study was placement of square rod bundles as a turbluence promoter in front of the heat transfer surface. The effects of the clearance between the flat plate and square rod, and the nozzle exit velocity on the heat transfer characteristics have been investigated experimentally. The results obtained through this study were summerized as follows. High heat transfer enhancement was achived by means of flow acceleration and thinning of boundary layer by inserting rods in front of the heating flat plate. The smaller the clearance between rod and heating plate was, the larger heat transfer effect became. Average Nusselt number reached maximum at $Re=5.76{\times}10^4$ and C＝1㎜ and the enhancement rate of heat transfer became maxium at this condition with the enhancement ratio as high as about 1.427 when normalized by the flat plate value. The correlating equation of average Nusselt number and Reynolds number was obtained, which is $\bar{N}uo=1.324{\cdot}Re^{0.459}{\cdot}(C/A)^{-0.034}$.

• Wind and Structures
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• 제23권2호
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• pp.157-169
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• 2016

The structural integrity of tube bundles represents a major concern when dealing with high risk industries, such as nuclear steam generators, where the rupture of a tube or tubes will lead to the undesired mixing of the primary and secondary fluids. Flow-induced vibration is one of the major concerns that could compromise the structural integrity. The vibration is caused by fluid flow excitation. While there are several excitation mechanisms that could contribute to these vibrations, fluidelastic instability is generally regarded as the most severe. When this mechanism prevails, it could cause serious damage to tube arrays in a very short period of time. The tubes are therefore stiffened by means of supports to avoid these vibrations. To accommodate the thermal expansion of the tube, as well as to facilitate the installation of these tube bundles, clearances are allowed between the tubes and their supports. Progressive tube wear and chemical cleaning gradually increases the clearances between the tubes and their supports, which can lead to more frequent and severe tube/support impact and rubbing. These increased impacts can lead to tube damage due to fatigue and/or wear at the support locations. This paper presents simulations of a loosely supported multi-span U-bend tube subjected to turbulence and fluidelastic instability forces. The mathematical model for the loosely-supported tubes and the fluidelastic instability model is presented. The model is then utilized to simulate the nonlinear response of a U-bend tube with flat bar supports subjected to cross-flow. The effect of the support clearance as well as the support offset are investigated. Special attention is given to the tube/support interaction parameters that affect wear, such as impact and normal work rate.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.291.2-291.2
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• 2013

Growth behavior of b-Ga2O3 nanowires (NWs) on sapphire(0001) substrates during radio-frequency magnetron sputtering is reported. Upon fabrication, flat thin films grew initially, subsequent to which, NW bundles were formed on the surface of thin film with increasing film thickness. This transition of the growth mode occurred only at temperatures greater than ${\sim}450^{\circ}C$. The b-Ga2O3 NWs were grown through the self-catalytic vapor-liquid-solid mechanism with self-assembled Ga seeds. Secondary growth of NWs, which occurred from the sides of primary NWs resulting in branched NW structures, was also observed. Finally, the room temperature photoluminescence properties of as-grown and annealed b-Ga2O3 NW samples were investigated.

• 한국분말재료학회지
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• 제11권3호
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• pp.253-258
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• 2004

We report a carbothermal reduction process for massive synthesis of monolithic W$_{18}$O$_{49}$ phase from tungsten oxide in the presence of carbon source. Carbon black powder was used as a carbon source and added to WO$_3$ by 40 weight percent. Bundles of W$_{18}$O$_{49}$ rods were formed over the temperature range of 80$0^{\circ}C$$^{\circ}C$ to 90$0^{\circ}C$. Pure W$_{18}$O$_{49}$ bundles could be separated from the mixture of W$_{18}$O$_{49}$ and residual carbon black powder. Field emission character of W$_{18}$O$_{49}$ phase was determined using the extracted W$_{18}$O$_{49}$ rods. Flat lamp fabricated from the W$_{18}$O$_{49}$ rods showed the turn-on field of 9.3 V/${\mu}m$.

• Plant Resources
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• 제5권2호
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• pp.95-103
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• 2002

Microscopic techniques were used to observe the microstructure of rice husk. Microscopic examination showed that two main components of husk, lemma and palea consisted of outer epidermis, layers of fibers, vascular bundles, parenchyma cells, and inner epidermis, in sequence from the outer to the inner surface. The outer epidermal walls were extremely thick, highly convoluted and lignified. The underlying fibers were also thick-walled and lignified. Parenchyma cells were thin-walled and unlignified. Inner epidermal cells were also unlignified. The outer surface of both lemma and palea were conspicuously ridged, but the lower surface had a flat appearance. As part of a detailed study to characterize rice husk using microscopic and micro-analytical techniques, distribution of silica was also examined, and is presented elsewhere. Rice husk can potentially be used as a raw material for making composite products and the observations presented here form valuable background information for our future work related to product development.