• 한국재료학회지
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• 제21권8호
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• pp.456-460
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• 2011

Microelectromechanical systems (MEMS)-fabricated suspended devices were used to measure the in-plane electrical conductivity, Seebeck coefficient, and thermal conductivity of 304 nm and 516 nm thick InGaAlAs films with 0.3% ErAs nanoparticle inclusions by volume. The suspended device allows comprehensive thermoelectric property measurements from a single thin film or nanowire sample. Both thin film samples have identical material compositions and the sole difference is in the sample thickness. The measured Seebeck coefficient, electrical conductivity, and thermal conductivity were all larger in magnitude for the thicker sample. While the relative change in values was dependent on the temperature, the thermal conductivity demonstrated the largest decrease for the thinner sample in the measurement temperature range of 325 K to 425 K. This could be a result of the increased phonon scattering due to the surface defects and included ErAs nanoparticles. Similar to the results from other material systems, the combination of the measured data resulted in higher values of the thermoelectric figure of merit (ZT) for the thinner sample; this result supports the theory that the reduced dimensionality, such as in twodimensional thin films or one-dimensional nanowires, can enhance the thermoelectric figure of merit compared with bulk threedimensional materials. The results strengthen and provide a possible direction in locating and optimizing thermoelectric materials for energy applications.

• 한국광학회지
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• 제3권3호
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• pp.183-190
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• 1992

$Al_x/Ga_{1-x}$ /As/AlAs GaAs 계로 이루어진 비대칭 이중 양자우물 구조의 광학적 특성을 photoluminescence, photoluminescence excitation, time-resolved photoluminescence를 통하여 조사하였다. 양자장벽 AlAs의 두께에 따른 특성 변화를 조사하기 위하여 두께를 15$\AA$., 150$\AA$로 제작하였다. 양자장벽이 15$\AA$인 경우 매우 빠른 전자의 관통 현상을 보여 주었으며, 이로 인해 $Al_x/Ga_{1-x}$As의 여기자 재결합에 해당하는 피크가 관찰되지 않았다. AlAs 양자장벽이 150$\AA$인 경우에는 $Al_x/Ga_{1-x}$As양자우물에서 여기자 재결합에 의한 피크가 50ps 이하로 빠른 decay시간을 보여 주었으며 이것은 양자장벽과의 $\Gamma$-X전이에 의한 것으로 사료되었다. GaAs양자우물에서의 luminescence decay는 두 시료 모두 1ns정도 이었으나, 15$\AA$인 경우에는 약 100ps의 rise시간이 존재하였으며 이것은 정공의 관통에 의한 시간으로 판명되었다.

• 응용통계연구
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• 제13권2호
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• pp.575-590
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• 2000

Greenberg et al.(1969)은 무관질문모형에서 무관한 속성이 미지인 경우 두 개의 독립표본을 이용하여 민감한 속성에 대한 모비율을 추정해 내는 이표본 무관질문모형을 제안하였다. 본 논문에서는 Mangat-Singh(1990)의 모형을 개선한 형태의 김종호 외 2인(1992)이 제안한 2단계 무관질문모형과 이기성과 홍기학(1998)이 제안한 개선된 무관질 문모형을 무관한 속성이 미지일 때 두 개의 독립표본을 이용하는 2단계 이표본 무관질 문모형과 개선된 이표본 무관질문모형으로 확장하였다. 그리고, Greenberg et al. 의 모형과 2단계 이표본 무관질문모형, 그리고 개선되 이표본 무관질문모형과의 효율성을 비교 하였다.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2022년도 봄 학술논문 발표대회
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• pp.180-181
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• 2022

The higher the addition rate, the less difference in kneading was found. This is because most of the cases are mixed with vinyl gloves by hand when immediately mixed in the field, so there is no problem of mixing dough according to the amount of addition. The mean increase temperature for 20 minutes was 31.6℃ for Plain, 38.1℃ for Al, 33.7℃ for Cu, and 5~7℃ for Al 20% added sample, 38.1℃ for Al 20% added sample, but 36.6℃ for Al 5% added sample. This suggests that it is possible to improve its own heat transferability by adding metal powder to epoxy adhesives.

• 대한전기학회논문지
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• 제35권10호
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• pp.465-472
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• 1986

The present study was carried out to investigate the mechanism which control the voltage instability and the breakdown of CVD Al2O3 on Si substrates. Our sample were metal-Al2O3-Oi Capacitors with both Al and Au field plates. Electron injection and trapping, with resultant positive flatband voltage shift, occur at fields as low as 1-2[MV/cm.] We developed an approximate method for computing the location of the centroid of the trapped electrons. Our results indicate that the electrons are trapped near the injecting interface, at least for fields less than about 5[MV/cm ] Because of continued charging, a true steady state is probably never reached, and the only unique I-V curve is the one obtained initially, when the traps are empty. We measured this I-V curve for both polarities of applied voltage, using a fresh sample for each point. The observed current densities are much larger than those obtained in thermally grawn SiO2.

• 한국세라믹학회지
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• 제45권10호
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• pp.584-588
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• 2008

Porous hydroxyapatite(HA) and HA-coated porous $Al_2O_3$ possessing pore characteristics required for bone substitutes were prepared by a slurry foaming method combined with gelcasting. The HA coating was deposited by heating porous $Al_2O_3$ substrates in an aqueous solution containing $Ca^{2+}$ and ${PO_4}^{3-}$ ions at $65{\sim}95^{\circ}C$ under ambient pressure. The pore characteristic, microstructure, and compressive strength were investigated and compared for the two kinds of samples. The porosity of the samples was about 81% and 80% for HA and $Al_2O_3$, respectively with a highly interconnected network of spherical pores with size ranging from 50 to $250{\mu}m$. The porous $Al_2O_3$ sample showed much higher compressive strength(25 MPa) than the porous HA sample(10 MPa). Fairly dense and uniform HA coating(about $2{\mu}m$ thick) was deposited on the porous $Al_2O_3$ sample. Since the compressive strength of cancellous bone is $2{\sim}12$ MPa, both the porous HA and HA-coated porous $Al_2O_3$ samples could be successfully utilized as scaffolds for bone repair. Especially the latter is expected suitable for load bearing bone substitutes due to its excellent strength.

• 한국산학기술학회논문지
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• 제13권3호
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• pp.955-960
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• 2012

본 연구는 순수 Polyurethane과 일반적인 난연제인 $Al(OH)_3$ 및 $Mg(OH)_2$를 첨가한 sample과 Cloisite Na+, Cloisite 15A를 첨가한 sample의 난연성 및 기계적 특성을 비교하였다. 또한 Sodium silicate와 Polyurethane을 혼합한 것에 경량성 충진제인 Vermiculite, Perlite를 충진한 sample의 난연성 및 기계적 특성을 확인하였다. 그 결과, Cloisite Na+와 Cloisite 15A를 첨가한 sample과 Sodium silicate를 혼합한 sample에서 난연제를 첨가한 것과 같은 등급의 난연성을 확인하였다. 인장강도는 filler의 양이 증가함에 따라 저하 되었으나, sodium silicate를 첨가한 sample의 경우 다른 sample 보다 강도가 향상됨을 확인하였다.

• 한국세라믹학회지
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• 제32권8호
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• pp.931-937
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• 1995

AlN powder and whiskers were synthesized by direct nitridation of aluminum powder in pure nitrogen atmosphere. The nitridation reaction of aluminum powder was initiated by heating the sample to the ignition temperature and the reaction was finished in less than 3 minutes. AlN whisker-shaped morphology was observed predominantly when the sample was heated above 90$0^{\circ}C$.

• International Journal of Computer Science & Network Security
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• 제21권7호
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• pp.17-34
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• 2021

This study aimed to examine the Factor Structure of the teacher satisfaction scale (TSS) with distance education during the Covid-19 pandemic, as well as affirming the (Factorial Invariance) according to gender variable. It also aimed at identifying the degree of satisfaction according to some demographic variables of the sample. The study population consisted of all teachers in public education and faculty members in higher education in the Kingdom of Saudi Arabia. The (TSS) was applied to a random sample representing the study population consisting of (2399) respondents. The results of the study showed that the scale consists of five main factors, with a reliability value of (0.94). The scale also showed a high degree of construct validity through fit indices of the confirmatory factor analysis. The results have shown a gradual consistency of the measure's invariance that reaches the third level (Scalar-invariance) of the Measurement Invariance across the gender variable. The results also showed that the average response of the study sample on the scale reached (3.74) with a degree of satisfaction, as there are no statistically significant differences between the averages of the study sample responses with respect to the gender variable. While there were statistically significant differences in the averages with respect to the variable of the educational level in favor of the middle school and statistically significant differences in the averages attributed to the years of experience variable in favor of those whose experience is less than (5) years.

• Journal of the Korean Data and Information Science Society
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• 제18권2호
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• pp.411-418
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• 2007

Sample size calculation is very important in clinical trials. In this paper, we propose sample size calculation method for non-inferiority trials using sample size calculation method suggested by Wang et al.(2003) based on Wilcoxon's rank sum test. Also, sample size comparison between parametric method and proposed method are presented.