• 한국전기전자재료학회논문지
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• 제13권4호
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• pp.300-305
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• 2000

We have investigated the dielectric and electrical characteristics of palmitic acid(PA) stearic acid(SA) and arachidic acid(AA) Langmuir-Blodgett(LB) films because these fatty acid systems have a same hydrophilic group and a different hydrophobic one(methylene group or alkyl chain length). The fatty acid systems were used as LB films and the status of the deposited films was confirmed by evaluating the transfer ratio the UV absorption and the capacitance. The dielectric characteristics such as the frequency-capacitance characteristics and the dielectric dispersion and absorption characteristics of PA SA and AA through-plane were measured. The relative dielectric constants of PA, SA and AA LB films were about 3.0~4.6, 2.7~3.0 and 2.4~3.0 respectively. That is the relative dielectric constants were decreased in proportion to the chain length of methylene group. Also the dielectric dispersion and absorption of each fatty acid LB films have arisen from spontaneous polarization of dipole polarization in the range of 10$^4$~10$^{5}$ ［Hz］. The conductivity of PA, SA and AA LB films obtained from I-V characteristics were about 9$\times$10$^{-14}$ , 3$\times$10$^{-14}$ and 5$\times$10$^{-15}$ ［S/cm］. respectively. These results have shown the insulating materials and could control the conductivity y changing the length of methylene group. Also we have confirmed that the barrier height of fatty acid systems were almost the same ones obtained from dielectric characteristics.

• 한국전기전자재료학회논문지
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• 제16권11호
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• pp.975-978
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• 2003

The microwave dielectric properties and the microstructures on B $i_{0.97}$T $m_{0.03}$Nb $O_4$ doped with $V_2$ $O_{5}$ were systematically investigated. B $i_{0.97}$T $m_{0.03}$Nb $O_4$ ceramics sintered at 920-96$0^{\circ}C$ were mainly consisted of orthorhombic and triclinic phases after addition of $V_2$ $O_{5}$. The apparent density increased slightly with increasing the $V_2$ $O_{5}$ addition. The dielectric constants($\varepsilon$$_{r}$) also increased with $V_2$ $O_{5}$ addition(30-45). The Q${\times}$ $f_{0}$ values measured on B $i_{0.97}$T $m_{0.03}$Nb $O_4$ ceramics doped with $V_2$ $O_{5}$ were between 2,000 and 12,000[GHz] when the sintering temperatures were in the range of 920-960[$^{\circ}C$]. It was confirmed that the temperature coefficient of the resonant frequency($\tau$$_{f}$) can be adjusted from a positive value of +10ppm/$^{\circ}C$ to a negative value of -15ppm/$^{\circ}C$ by increasing the amount of $V_2$ $O_{5}$ Based on our experimental results, the B $i_{0.97}$T $m_{0.03}$Nb $O_4$(added $V_2$ $O_{5}$) ceramics can be applied to multilayer microwave devices at low sintering temperatures.ng temperatures.emperatures.ratures.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 추계학술대회 논문집 Vol.15
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• pp.350-353
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• 2002

The microwave dielectric properties and the microstructures on $Bi_{0.97}Nb_{0.03}O_{4}$doped with $V_{2}O_{5}$ were systematically investigated. $Bi_{0.97}Tm_{0.03}Nb_{0.03}O_{4}$ ceramics sintered at $920-960^{\circ}C$were mainly consisted of orthorhombic and triclinic phases after addition of $V_{2}O_{5}$. The apparent density increased slightly with increasing the $V_{2}O_{5}$ addition. The dielectric $constants(\varepsilon_r)$ also increased with $V_{2}O_{5}$ addition(30-45). The $Q{\times}f_0$ values measured on $Bi_{0.97}Tm_{0.03}NbO_4$ ceramics doped with $V_{2}O_{5}$ were between 2,000 and 12,000[GHz] when the sintering temperatures are in the range of $920-960[^{\circ}C]$. It was confirmed the temperature coefficient of the resonant $frequency(\tau_f)$ can be adjusted from a positive value of $+10[ppm/^{\circ}C]$ to a negative value of $-15ppm/^{\circ}C$ by increasing the amount of $V_{2}O_{5}$. Based on our experimental results, the Bi0.97Tm0.03NbO4(added V2O5) ceramics can be applied to multilayer microwave devices at low sintering temperatures.

• 한국전자파학회논문지
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• 제23권4호
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• pp.515-523
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• 2012

본 논문에서는 구형 유전체 위에 있는 구형 패치의 전파 특성으로서 공진 특성과 방사 특성을 분석하였다. 공진 주파수와 Q를 계산하여 특정 모드의 공진 특성을 해석하였으며, 원거리에서의 전기장을 계산하여 방사 특성을 해석하였다. 구형 유전체의 해석을 위해 스펙트럴 영역 해석법(spectral domain analysis method)를 적용하였으며, Vector Legendre transform pair와 Galerkin's method를 이용하여 스펙트럴 영역으로 변환한 후 대수식으로 정리하여 효율적인 계산을 할 수 있었으며, 이를 통해 구형 패치의 반지름이나 곡률, 유전체의 특성이 구형 패치의 특성에 미치는 영향을 해석하였다.

• 한국추진공학회지
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• 제22권3호
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• pp.81-89
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• 2018

본 연구에서는 소형 추력기 및 점화기로 활용 가능한 소형 PDE의 작동특성을 실험적으로 알아보았다. 4.22 mm의 내경을 갖는 상용 가스 튜브를 이용하여 소형 PDE를 구성하였으며, 당량비 및 작동 주파수 변화에 따른 PDE의 작동 및 데토네이션 전파 특성을 알아보았다. 측정된 데토네이션 속도는 1 Hz와 5 Hz 작동 조건에서는 희박 영역을 제외한 당량비 조건에 이론값과 10%이내의 오차를 가지는 비교적 정확한 값을 보였다. 그러나 20 Hz 조건의 희박 영역에서는 불안정한 전파 특성을 보였으며, 20~62%의 큰 속도 결손이 발생하였다.

• Steel and Composite Structures
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• 제19권6호
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• pp.1549-1560
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• 2015

This paper presents the characterization of fatigue crack in the A283 Grade C steel using the MMM method by identifying the effects of magnetic flux leakage towards the crack growth rate, da/dN, and crack length. The previous and current research on the relation between MMM parameters and fatigue crack effect is still unclear and requires specific analysis to validate that. This method is considered to be a passive magnetic method among other Non-Destructive Testing (NDT) methods. The tension-tension fatigue test was conducted with a testing frequency of 10 Hz with 4 kN loaded, meanwhile the MMM response signals were captured using a MMM instrument. A correlation between the crack growth rate and magnetic flux leakage produces a sigmoid shape curve with a constant values which present the gradient, m value is in the ranges of 1.4357 to 4.0506, and the y-intercept, log C in the ranges of $4{\times}10^{-7}$ to 0.0303. Moreover, a linear relation was obtained between the crack length and magnetic flux leakage which present the R-Squared values is at 0.830 to 0.978. Therefore, MMM method has their own capability to investigate and characterize the fatigue crack effects as a main source of fracture mechanism for ferrous-based materials.

• 한국재료학회지
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• 제17권8호
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• pp.442-446
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• 2007

Microwave dielectric properties of $0.85CaWO_4-0.15LnNbO_4$ (Ln = La, Sm) ceramics were investigated as a function of the sintering temperature and $Li_2WO_4$ content from 0.8 wt.% to 1.5 wt.%. A single phase with tetragonal scheelite structure was obtained at a given composition ranges. For the specimens with $Li_2WO_4$, the sintering temperature could be effectively reduced from $1150^{\circ}C$ to $900^{\circ}C$ due to the enhancement of sinterability. Dielectric constant (K) of the specimens with $LaNbO_4$ and $SmNbO_4$ was increased with the increase of sintering temperature and/or $Li_2WO_4$ content. However, K of the specimens with $LaNbO_4$ was higher than that of $SmNbO_4$ due to the larger dielectric polarizability $(\alpha)$ of $LaNbO_4$ ($18.08{\AA}$) than that of $SmNbO_4$ ($16.75{\AA}$). With an increase of $Li_2WO_4$ content, Qf value of the specimens with $SmNbO_4$ was decreased, while that of the specimens with $LaNbO_4$ was increased. Temperature coefficient of resonant frequency (TCF) was increased with the increase of $Li_2WO_4$ content.

• 한국태양에너지학회:학술대회논문집
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• 한국태양에너지학회 2011년도 춘계학술발표대회 논문집
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• pp.162-167
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• 2011

Thermal storage plays an important role in building energy saving, which is greatly assisted by the incorporation of latent heat storage in building materials. A phase change material is a substance with a high heat of fusion which, melting and solidifying at a certain temperature, can be storing and releasing large amount of energy. Heat is stored or released when the material changes from solid to liquid. Integration of building materials incorporating PCMs into the building envelope can result in increased efficiency of the built environment. The aim of this research is to identify thermal performance of PCMs impregnated building materials which is applied to interior of building such as gypsum and red clay. In order to analyze thermal performance of phase change materials, test-cell experiments and simulation analysis were carried out. The results show that micro-encapsulated PCM has an effect to maintain a constant indoor temperature using latent heat through the test-cell experiments. PCM wallboard makes it possible to reduce the fluctuation of room temperature and heating and cooling load by using EnergyPlus simulation program. Phase change material can store solar energy directly in buildings. Increasing the heat capacity of a building is capable of improving human comfort by decreasing the frequency of indoor air temperature swings so that the interior air temperature is closer to the desired temperature for a long period of time.

• 한국철도학회논문집
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• 제13권3호
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• pp.304-308
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• 2010

본 연구에서는 웨이브렛 변환을 이용하여 궤도틀림을 식별하는 방법을 제시하였다. 궤도틀림과 대차 가속도응답신호에 의한 등가 웨이브렛 SISO 전달함수를 정의하였다. 현장에 적용되는 검측차의 25cm단위 궤도검측 기준에 맞추어 궤도틀림과 대차가속도 응답신호를 조정하였다. 웨이브렛 변환을 적용하기 전 입력데이터는 웨이브렛 변환 정의 조건에 맞추어 범위를 재조정한 회귀신호이다. 또한, 웨이브렛 역전 달 함수를 정의하여, 궤도틀림을 역 추정하였다. 추정된 궤도틀림과 실제의 궤도틀림의 비교를 위해 상관도와 FRF를 비교 분석하였다. 예측된 값과 기준 값 과의 잔 차의 분산비로 정의되는 틀림지수를 사용하여 궤도틀림의 이상을 분석하였으며, 개발될 알고리즘을 검증하기 위하여 시뮬레이션 연구를 수행하였다.

• 고려인삼학회:학술대회논문집
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• 고려인삼학회 1984년도 학술대회지
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• pp.49-55
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• 1984

미국인삼 1년생근을 재료로 하여 각 온도조건별(-15, 0, 3, 6, 9, 12 및 $15^{\circ}C$)로 120일 이상 온도 처리한 후 온실 조건에 식부하여 성장기간동안 출아 소요일수 및 근중 증가율을 조사하였다. $0^{\circ}C$ 이하와 $9^{\circ}C$ 이상에서도 출아가 되지 않았으며 발아기능 온도 범위내에서는 온도에 따른 출아 소요일은 거의 차이가 없었다. 저장기간이 싹의 후면 타파력 및 휴면타파 종료일로부터 발아일(R = 91)까지의 기간에 큰 영향을 미쳤다. $100{\%}$의 출아를 위해서는 약 1,800시간의 저온 처리가 요구되었다. 720시간의 휴면 타파를 위한 저온 처리를 받은 인삼근의 $15{\%}$가 근관을 형성하였다. 휴면 타파가 출아에 소요되는 총 시간은 저온 처리의 온도와 관계없이 일정하게 거의 125일 (3,000시간) 이었다. 이러한 발견은 인삼재배를 위한 온도 조건을 고려한 적지 판정을 하는데 유용하게 이용될 것이다. 이는 개체군에 따라 휴면 타파를 위한 저온처리 충족요건이 유전적으로 다를 것이라는 사실을 시사해 준다.