• 한국주조공학회지
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• 제34권5호
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• pp.151-155
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• 2014

The relatively low conductivity of conventional Mg-Al alloys often limits their areas of application. Therefore, several attempts to develop new high-conductivity magnesium alloys have been made recently. In this research, A Ce-rich rare-earth (RE)material and zinc were added to magnesium which contained no aluminum. As the RE and Zn content were increased, both the hardness and tensile strength were gradually increased, despite the fact that the electrical conductivity decreased slightly. The effects of an aging treatment on the conductivity and mechanical properties of Mg-RE-Zn alloys were also investigated. The electrical conductivity did not change according to the heat treatment conditions; however, the mechanical properties could be enhanced by proper aging heat treatments.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1995년도 하계학술대회 논문집 A
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• pp.6-8
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• 1995

In this paper, we study the computation of the electric field of dielectric analysis models with the conductivity on its surface. The finite element formulation describes a sinusoidal electrodynamic field computation. One term is added to this functional in order to take the conductivity on its surface into accounts. The electric field computations of the dielectric analysis model are done first with the surface conductivity and second with the volume conductivity. Also, it is shown that a surface conductor with sufficiently large conductivity can be substituted with a floating equipotential line. This method is applied to an insulator in arbitrary shape with the conductivity on its surface.

• Food Science and Biotechnology
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• 제14권3호
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• pp.334-339
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• 2005

An instrument using thermal probe method was designed to measure thermal conductivity of liquid and solid foods. Thermal conductivity probe was designed with diameter to length ratio of 100 and diameter of 0.51 mm to minimize axial flow effect on thermal conductivity measurement. Thermal conductivities of distilled/deionized water, glycerin, and beef frankfurter meat were measured at $20-80^{\circ}C$. Mean thermal conductivity values of water showed less than 2.0% difference from several reference values without using time correction factor or probe calibration constant. For glycerin, difference was less than 0.7% from reference values at $20-50^{\circ}C$. Mean values of thermal conductivity for beef frankfurter meat ranged from 0.389 to $0.350\;W/m{\cdot}K$ at $20-80^{\circ}C$.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2006년도 하계학술발표대회 논문집
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• pp.713-718
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• 2006

This paper concerns the measurement of thermal conductivity of grouting materials for ground loop heat exchanger. A thermal conductivity meter, QTM-500 based on modified transient hot wire method was used to measure the thermal conductivity of neat bentonite and mixtures of bentonite and various additives. Relative to the total mixture mass, as the percent additive was increased the mixture thermal conductivity increased. For the bentonite-silica sand mixtures, the higher density of the sand particles resulted in much higher mixture thermal conductivity.

• Bulletin of the Korean Chemical Society
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• 제34권12호
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• pp.3825-3828
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• 2013

In this study, the influences of aniline to acid composition were investigated on the electrical conductivity of PANI-PAAMPSA. The ratio of aniline to sulfonic acid groups was optimized for the maximum conductivity of PANI-PAAMPSA. The conductivity is strongly correlated with the electronic structure of PANI-PAAMPSA; the highest conductivity of PANI-PAAMPSA was observed when PANI has the longest conjugation length.

• 대한수학회지
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• 제38권4호
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• pp.781-791
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• 2001

We consider the inverse conductivity problem to identify the unknown conductivity $textsc{k}$ as well as the domain D. We show hat, unlike the case when $textsc{k}$ is known, even a two or three dimensional ball may not be identified uniquely if the conductivity constant $textsc{k}$ is not known. We find a necessary and sufficient condition on the Cauchy data (u│∂Ω, g) for the uniqueness in identification of $textsc{k}$ and D. We also discuss on failure of stability.

• 한국지반공학회논문집
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• 제31권6호
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• pp.45-58
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• 2015

본 연구에서는 이론적 고찰을 통해 Kozeny-Carman식을 변형하여 전기전도도 측정을 통한 사질토의 투수계수 추정식을 제안하였다. 제안된 예측식에 대한 실험적 검증을 위해 6종류의 사질토에 대하여 4개의 전극을 설치한 정수위 투수시험을 실시하였으며, 다양한 변수들 하에 시험을 진행하였다. 시험 결과, 사질토에서 흙 입자 표면을 통한 전기전도는 미미하였으며, 간극수의 전기전도도가 투수계수와 formation facotor에 미치는 영향은 제한적이었다. 흙 입자의 유효입경이 formation factor에 미치는 영향은 미미하였으나 투수계수에는 큰 영향을 주었다. 제안된 식을 활용하여 투수계수를 예측하기 위해서는 형상계수와 Archie's m에 대한 정보가 필요하여 error norm방법을 사용해 형상계수를 구하였다. 또한, 간극률을 변화시키며 측정된 formation factor를 사용하여 Archie's m을 구하였다. formation factor를 사용하여 계산한 투수계수를 측정값과 같이 도시한 결과, 계산된 투수계수는 측정된 투수계수와 유사한 값을 보여주었다. 기존 Kozeny-Carman식과 본 연구에서 제안하는 전기전도도를 이용한 투수식 간의 정량적인 비교를 위해, 정규화된 투수계수를 사용하여 형상계수, Archie's m, 간극률에 따른 정규화된 투수계수의 변화를 비교한 결과, 형상계수와 Archie's m의 변화에 따른 정규화된 투수계수의 변화 폭에 비해, 간극률의 변화에 따른 정규화된 투수계수는 매우 큰 폭으로 변하였다. 따라서 본 연구에서 제안하는 전기전도도를 이용한 투수계수 예측식이 기존 Kozeny-Carman식보다 더 높은 신뢰도를 보일 것으로 판단된다.

• 대한전자공학회논문지
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• 제12권2호
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• pp.18-23
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• 1975

As-Te.Si-Ge 유리질 반도체의 직류 펀도도는 실온에서 3x10-7Ω-1cm-1∼1.5x10-8Ω-1cm-1이었고 각 시료의 온도 인화에 따른 전도특성은 상전이 온도(Tg) 이하에서 o=ooexp(-△E/kT)로 표시할 수 있었다. 또한 실온에서 각 시료의 교류 전도도의 주파수 의존도는 거의 같았으며 직류 전도도에 비해 상당치 높게 나타나서 o(w)=oo+Awn으로 표시할 수 있었다. 200KHz 경우에 교류 펀도도는 295。K∼473。K에서 온도에 무관하고 200Hz 경우에는 433。K에서 부터 심하게 증가하였다. 각 시fy는 기억스위칭 현상은 없었고 문지받스위칭 현상만 관찰할 수 있었다. The dc conductivity, ac conductivity and switching effect of As·Te-Si·Ge have beon investigated. The dc conductivity ranged from 3x10-7Ω-1cm-1∼1.5x10-8Ω-1cm-1 at room temperature and was found to be expressed by o=ooexp(-△E/kT) below the phase transition temperature Tg. The ac conductivity was much higher than dc conductivity and this result is consistent to experimental formula o(w)=oo+Awn. In the temperature range of 298。K∼147。K, the ac conductivity was independent of temperature at 200KHs. At lower frequencies the ac conductivity increased strong1y with temperature. Also, it has been found that all samples showed a threshold switching, but not a memory switching.

• 한국세라믹학회지
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• 제49권4호
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• pp.380-384
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• 2012

This paper deals with the recent developments of high thermal conductivity silicon nitride ceramics. First, the factors that reduce the thermal conductivity of silicon nitride are clarified and the potential approaches to realize high thermal conductivity are described. Then, the recent achievements on the silicon nitride fabricated through the reaction bonding and post sintering technique are presented. Because of a smaller amount of impurity oxygen, the obtained thermal conductivity is substantially higher, compared to that of the conventional gas-pressure sintered silicon nitride, while the microstructures and bending strengths are similar to each other between these two samples. Moreover, further improvement of the thermal conductivity is possible by increasing ${\beta}/{\alpha}$ phase ratio of the nitrided sample, resulting in a very high thermal conductivity of 177 W/($m{\cdot}K$) as well as a high fracture toughness of 11.2 $MPa{\cdot}m^{1/2}$.

• 한국세라믹학회지
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• 제44권2호
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• pp.116-123
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• 2007

Electrical properties of AlN ceramics sintered with 1 wt% $Y_2O_3$ have been investigated. From the impedance spectroscopy, electrical conductivity of grain boundary was found to be much lower than that of grain. DC conductivity measurement showed the electrode polarization effects caused by blocking electrode. The heat-treatment at $1700^{\circ}C$ of the specimen sintered at $1850^{\circ}C$ transformed continuous pain boundary phases along triple boundary junctions into isolated particles in grain comers. The heat-treatment induced decreases both in grain and grain boundary conductivity, and in DC electrical conductivities. From the analysis on the transference number, ionic conductivity was shown to be more dominant than electron conductivity, which was due to ion compensation mechanism during oxygen incorporation into grain.