• 한국정보디스플레이학회:학술대회논문집
• /
• 한국정보디스플레이학회 2002년도 International Meeting on Information Display
• /
• pp.1068-1071
• /
• 2002

In this study, first, we show that the furnace process which requires maintaining high temperature is effected grievously by the temperature of surrounding air. Second, an alternative which maintains the relatively constant temperature dispersion surrounding the furnace and at the same time has economical advantages will be proposed.

• Composites Research
• /
• 제28권6호
• /
• pp.348-355
• /
• 2015

접착 조인트는 환경조건 및 작업자의 숙련도에 따라 접착강도가 크게 변화될 수 있으므로 이에 대한 비파괴 검사법은 매우 중요하다. 최근 접착제에 1-2 wt%의 CNT를 첨가하고 저항변화를 측정하여 접착 체결부의 내부 결함을 검출하는 전기저항법이 제시되었다. 전기저항법에서는 동일조건에서 접착조인트의 저항값이 일정하도록 하기 위하여 CNT의 균일한 분산이 매우 중요하며 이에 따라 결함 검출의 정확도가 좌우된다. 본 연구에서는 4가지 분산 방법으로 CNT를 접착제에 분산시켜 접착조인트을 제작하고 전기적 물리량을 측정하였다. 초음파를 이용한 CNT의 전처리 및 기화과정, 물리적 교반 방법등을 선정하여 효율적인 분산방법을 정립하고 분산성을 평가할 수 있는 척도를 제시하였으며 일반적인 분산 방법 대비 선정된 분산 방법을 적용했을 때 전기저항법의 결함검출능을 비교하였다.

• 한국해안해양공학회지
• /
• 제14권2호
• /
• pp.116-127
• /
• 2002

대부분의 지진해일에 대한 수치모의는 천수방정식을 지배방정식으로 하고 leap-frog 유한차분기법을 주로 적용한다. 이 기법은 격자간격을 적절히 선정하면 분산효과를 옳게 고려할 수 있으나, 수심이 변하는 경우 전 계산영역에서 분산효과를 모두 만족시킬 수는 없다. 본 연구에서는 균일한 격자와 계산시간간격을 사용하면서도 수심이 완만하게 변하는 지형상을 전파하는 지진해일의 국부적인 분산관계를 만족시키기 위해 기존의 2차원 완 변수심상 분산보정 유한차분기법을 개선하고, 이 수치모형의 현장 적용성을 검증하기 위해 1983년 동해중부 지진해일을 검조기록이 있는 동해안의 속초, 묵호, 포항 그리고 울산항에 대하여 수치모의하였다. 또한 1983년 지진해일에 대해 각 항만에서 측정된 검조기록과 수치모의에 의해 계산된 값을 비교 분석하여 수치모형의 정밀도를 평가하였다.

• 대한토목학회논문집
• /
• 제33권2호
• /
• pp.495-506
• /
• 2013

본 연구에서는 전단류 분산이 이송과 난류에 의한 확산의 결합에 의해 발생한다는 Taylor (1954)의 가정을 바탕으로 개념적 모형을 구성하고, 이를 3차원 개수로에 적용하여 오염물질의 혼합과정을 재현할 수 있는 시간분리 혼합모형(Time-split Mixing Model; TMM)을 개발하였다. 개발된 모형은 연산자 분리 기법(operator split method)과 유사하게 혼합과정을 종방향 혼합과 횡방향 혼합으로 분리하고, 유속 연직편차에 의한 농도분리과정과 난류확산에 의한 연직방향 혼합과정을 순차적으로 반복 계산함으로써 2차원 이송-분산을 재현한다. 수치모의 결과, 제안된 모형은 수로벽면에 의한 농도중첩 효과를 잘 반영하고 있으며, Taylor 구간 내에서 2차원 이송-분산 모형의 해석해와 거의 일치하고 있음을 확인하였다(Chatwin, 1970). 본 모형은 하상경사, 하폭 대 수심 비, 혼합시간 등의 변화에 따라 분산 정도를 달리 재현하고 있으며, 산정된 종분산계수는 Elder(1959)가 제안한 상수값과는 달리 혼합시간에 따라 변화하는 양상을 나타냈다. 횡분산계수의 경우, Sayre와 Chang(1968), Fischer 등(1979)이 실험을 통해 제시한 값과 유사한 범위를 나타냈다.

• Transactions on Electrical and Electronic Materials
• /
• 제16권6호
• /
• pp.338-341
• /
• 2015

Epoxy/micro-sized alumina composite was prepared, and the effects of alumina content on the dielectric properties were investigated in order to develop an insulation material for gas-insulated switchgears (GIS). Nano-sized alumina (average particle size: 30 nm) was also incorporated into the epoxy/micro-sized alumina composite. Dielectric tests were carried out in ASTM D 150, and capacitance (Cp) and dielectric loss (tanδ) were measured. The dielectric constant increased with increasing alumina content in the epoxy/micro-alumina system and the epoxy/micro-alumina/nano-alumina system. As 1,3-diglycidyl glyceryl ether (DGE) content increased, the dielectric constant decreased and dielectric loss increased. This ocurred as a result of the weak electric field enhancement due to homogeneous dispersion of micro- and nano-sized alumina particles in an epoxy composite.

• 한국경영과학회:학술대회논문집
• /
• 한국경영과학회 2005년도 추계학술대회 및 정기총회
• /
• pp.338-341
• /
• 2005

In this paper, we present analytic forms of the ordered weighted averaging (OWA) operator weighting functions, each of which has properties of rank-based weights and a constant level of orness, irrespective of the number of objectives considered. These analytic forms provide significant advantages for generating OWA weights over previously reported methods. First, OWA weights can be efficiently generated by use of proposed weighting functions without solving a complicated mathematical program. Moreover, convex combinations of these specific OWA operators can be used to generate OWA operators with any predefined values of orness once specific values of orness are α priori stated by decision maker. Those weights have a property of constant level of orness as well. Finally, OWA weights generated at a predefined value of orness make almost no numerical difference with maximum entropy OWA weights in terms of dispersion.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 1999년도 추계학술대회 논문집
• /
• pp.13-22
• /
• 1999

Both the resonance and ultrasonic techniques are standard methods far characterizing the physical properties of piezoelectric materials. However, we found that each technique can only offer a few reliable measurements while the rest often have errors or impossible to implement because of the sample requirements. This paper show that one can use the combination of both techniques to achieve much better accuracy and be able to get the complete set of elastic, dielectric and piezoelectric coefficients using fewer samples. Using an ultrasonic spectroscopy we have also measure the dispersion of the ultrasonic velocity and the attenuation up to 65 MHz. Pb(Zr,Ti)O$_3$[PZT] ceramics were used as examples fur both studies.

• 분석과학
• /
• 제32권3호
• /
• pp.77-87
• /
• 2019

High viscosity carbon black dispersions are used in various industrial fields such as color cosmetics, rubber, tire, plastic and color filter ink. However, carbon black particles are unstable to heat due to inherent characteristics, and it is very difficult to keep the quality of the product constant due to agglomeration of particles. In general, particle size analysis is performed by dynamic light scattering (DLS) during the dispersion process in order to select the optimum dispersant in the carbon black dispersion process. However, the existing low viscosity analysis provides reproducible particle distribution analysis results, but it is difficult to select the optimum dispersant because it is difficult to analyze the reproducible particle distribution at high viscosity. In this study, dynamic light scattering (DLS) and asymmetrical flow field-flow fractionation (AsFlFFF) analysis methods were compared for reproducible particle size analysis of high viscosity carbon black. First, the stability of carbon black dispersion was investigated by particle size analysis by DLS and AsFlFFF according to milling time, and the validity of analytical method for the selection of the optimum dispersant useful for carbon black dispersion was confirmed. The correlation between color and particle size of particles in high viscosity carbon black dispersion was investigated by using colorimeter. The particle size distribution from AsFlFFF was consistent with the colorimetric results. As a result, the correlation between AsFlFFF and colorimetric results confirmed the possibility of a strong analytical method for determining the appropriate dispersant and milling time in high viscosity carbon black dispersions. In addition, for nanoparticles with relatively broad particle size distributions such as carbon black, AsFlFFF has been found to provide a more accurate particle size distribution than DLS. This is because AsFlFFF, unlike DLS, can analyze each fraction by separating particles by size.

• 한국지하수토양환경학회:학술대회논문집
• /
• 한국지하수토양환경학회 2003년도 추계학술발표회
• /
• pp.426-430
• /
• 2003

Subsurface biobarrier technology has potential applications to contain contaminated groundwater and/or to degrade toxic pollutants in groundwater. Effective biobarrier formation is need to assess of hydrogeologic characteristics and to conduct practical operation strategies and design based on this prior to design biobarrier. Thus, in this study, we examined hydrogeologic characteristics in biobarrier construction site. Hydraulic conductivities which calculated from slug test data have shown difference with each well as 1.20$\times$10$^{-3}$ -6.00$\times$10$^{-5}$ cm/sec. Tracer test is a method in which concentration of tracer solution during withdrawal in each well by vacuum extraction system is measured with time. Tracer solution was continuously injected by constant head tank. Measured tracer concentration versus time data were fitted to analytical solution of convection dispersion equation (CDE). The fitting data of CDE to the measured data at each extraction well yielded were 0.61cm/min(pore velocity), 5.38$\textrm{cm}^2$/min(dispersion coefficient) for discharge rate of 0.47 1/min and 1.75cm/min(pore velocity), 36.34$\textrm{cm}^2$/min(dispersion coefficient) for discharge rate of 0.93 1/min. As a result, we acquired fundamental parameters which need to design biobarrier and operation strategies.

• 천문학회지
• /
• 제40권4호
• /
• pp.171-177
• /
• 2007

In external galaxies, the velocity dispersion of the atomic hydrogen gas shows a remarkably flat distribution with the galactocentric radius. This has been a long-standing puzzle because if the gas velocity dispersion is due to turbulence caused by supernova explosions, it should decline with radius. After a discussion on the role of spiral arms and ram pressure in driving interstellar turbulence in the outer parts of galactic disks, we argue that the constant bombardment by tiny high-velocity halo clouds can be a significant source of random motions in the outer disk gas. Recent observations of the flaring of H I in the Galaxy are difficult to explain if the dark halo is nearly spherical as the survival of the streams of tidal debris of Sagittarius dwarf spheroidal galaxy suggests. The radial enhancement of the gas velocity dispersion (at R > 25 kpc) due to accretion of cloudy gas might naturally explain the observed flaring in the Milky Way. Other motivations and implications of this scenario have been highlighted.