• 한국군사과학기술학회지
• /
• 제17권1호
• /
• pp.149-157
• /
• 2014

In this paper, we investigated the sensitivity of aerostatic force coefficients of multi-layer radom in the various wind speeds. The test was conducted in KOCED Wind Tunnel Center in Chonbuk National University, and wind speeds were in the range from 5 m/s to 26 m/s in order to determine the Reynolds number independence. The test results of present multi-layer radom were not affected by the Reynolds number, The maximum positive pressure coefficient was found to be 1.08 at the center of the front of the plane in angle of attack of 0 degree, the maximum negative pressure coefficient was -2.03 at the upper right corner in angle of attack of 120 degree, while maximum drag coefficient was 1.11 in angle of attack of 180 degree.

• 한국광학회지
• /
• 제7권3호
• /
• pp.207-212
• /
• 1996

임의의 형태를 갖는 회절격자의 결합계수를 쉽게 계산할 수 있도록 확장된 새로운 층 방법을 제안한다. 기종이 새로운 층 방법은 회절격자 영역의 비유전상구의 종축 방향에 대해서만 평균을 취하여 결합계수를 계산하였지만 확장된 새로운 층 방법은 종축과 횡축 양 방향으로 비유전상수의 평균값을 취하여 새로운 층의 비유전상수로 설정하였다. 따라서 회절격자가 임의의 형태를 가지는 경우 새로운 층 방법에서는 새로이 설정하는 층의 비유전상수 값이 횡축으로 변화하는 함수였지만 확장된 새로운 층 방법에서는 단일 상수 값이어서 결합계수를 쉽계 계산할 수 있다. 이 방법을 사용하여 사다리꼴과 삼각형 형태의 회절격자를 가지는 5층 구조 Distributed Feedback 구조 소자의 결합계수를 계산하였다. 확장된 새로운 층 방법에 의한 결합계수 계산 결과의 정확성 검증을 통하여 사다리꼴과 같은 임의이 형태를 가지는 회절격자의 결합계수 계산에 확장된 새로운 층 방법이 매우 유용함을 보였다.

• Journal of Advanced Marine Engineering and Technology
• /
• 제27권1호
• /
• pp.134-144
• /
• 2003

Reactive diffusion couples between Fe-5.8at.%Si and (Si wafer, $FeSi_2$, or FeSi alloy) were heat-treated at 1423k. The only layer of $Fe_3Si$ phase was formed in each diffusion couple. The width of $Fe_3Si$ layer was proportional to square root of diffusion time in each kind of diffusion couple. Growth rate of $Fe_3Si$ layer was relied on the concentration of Si in the supplied source of Si atoms. Interdiffusion coefficient of $Fe_3Si$ has been determined from the derived relation between growth rate constant and interdiffusion coefficient in this work. It was shown that the behavior of Kirkendall's void in $Fe_3Si$ layer was not affected by the kind of Si source. But solid solution $\alpha$ was formed in the diffusion couple between Fe-5.8 at.%Si and $Fe_3Si$ alloy. Kirkendall's voids in diffusional $\alpha$ were neglectively smaller than the case of $Fe_3Si$ phase growth.

• 소성∙가공
• /
• 제13권8호
• /
• pp.716-722
• /
• 2004

Effects of sliding speed, applied load, and thickness of PMMA (Poly Methyl Methacrylate) coating layers on their dry sliding frictional and wear behavior were investigated. Sliding wear tests were carried out using a pin-on-disk wear tester. The PMMA layer was coated on Si wafer by a spin coating process with two different thicknesses, $1.5\mu\textrm{m}$ and $0.8\mu\textrm{m}$. AISI 52100 bearing steel balls were used as a counterpart of the PMMA coating during the wear. Normal applied load and sliding speed were varied. Wear mechanisms of the coatings were investigated by examining worn surfaces using an SEM. Friction coefficient of the coatings decreased with the increase of the applied load. Both adhesion and deformation of the coating determined the coefficient. The thicker PMMA layer with the thickness of $1.5mutextrm{m}$ showed lower friction coefficient than the thinner layer under most test conditions. Effects of sliding speed and applied load on the frictional behavior were varied depending on the thickness of the coating layer.

• 한국세라믹학회지
• /
• 제41권3호
• /
• pp.216-220
• /
• 2004

본 논문은 압전세라믹의 압전상수 d$_{33}$ 를 이용한 적층 세라믹 박판 작동층 IDEAL (InterDigitated Electrode Actuation Layer)의 개발에 관한 것이다. 대부분의 박판 압전 작동층은 압전상수 d$_{31}$ 효과를 이용하고 있다. 현재 개발된 압전작동기의 성능을 향상시키기 위해 많은 연구가 수행 중에 있으며, 그 중 한 방법이 압전상수 d$_{33}$ 를 이용하는 방법이다. 압전세라믹의 압전상수 d$_{33}$ 는 압전상수 d$_{31}$ 보다 일반적으로 두배 정도이기 때문에 d$_{33}$ 작동 효과를 활용하면 작동기의 성능을 향상시킬 수 있다. 미국 MIT에서 개발된 AFC와 NASA Langley 연구소 연구팀이 개발한 LaRC-MFC$^{TM}$는 d$_{33}$ 작동 효과를 활용하였으나 빗살형 전극이 작동층 상하 표면에 부착되어 있어 완전한 d$_{33}$ 작동 효과를 활용하였다고 볼 수 없다. 본 논문에서는 빗살형 전극을 세라믹 층간에 삽입한 적층형 세라믹 박판 작동층을 설계하고 제작하였다. 제작된 작동층의 작동 스트레인을 측정하였고 LaRC-MFC$^{TM}$의 작동 스트레인과 비교한 결과, 본 연구에서 개발한 박판 세라믹 작동층이 15% 이상의 작동 스트레인을 발생시킬 수 있음을 확인하였다.

• Computers and Concrete
• /
• 제29권3호
• /
• pp.201-207
• /
• 2022

The evaluation of velocity profile for large values of buoyancy parameter and Bioconvected Rayleigh number is examined. The non-linear problem has been tackled numerically by shooting technique. Nanofluid temperature and nanoparticle concentration slightly elevates for increasing values of thermophoresis coefficient. Thickness of thermal boundary layer is significantly increased with thermophoresis coefficient whereas thickness of concentration boundary layer is more slightly enhanced. The response of temperature and nanoparticles concentration is observed due to change in Brownian motion parameter. As Brownian motion parameter increased temperature distribution is slightly enhanced. The reverse behavior is observed in case of nanoparticles concentration. Comparison of numerical technique with the extant literature is made and an acceptable agreement is attained.

• 대한전자공학회논문지
• /
• 제25권5호
• /
• pp.495-500
• /
• 1988

The effectiveness of tri layer resist (TLR) technique is compared with that of single layer resist (SLR) technique in order to make a 0.8um pattern with the linewidth deviation of 10 percents. SLR technique is not appropriate to shape the micro-pattern on oxide and aluminum steps because of the standing wave effect and the light scattering effect in shaping the resist pattern. On the contrary, the uniform line with a width of 0.8um on oxide and aluminum steps can be formed by TLR technique, reducting such effects. The planarization and the light absorption coefficient of the bottom layer resist in TLR are optimized by exposing it to ultra violet light after baking it for 30min at 230\ulcorner. An uniform line with a width of 0.8um on oxide step is defined with the light absorption coefficient of 0.85 whereas that on aluminum step is defined with 0.95.

• Bulletin of the Korean Chemical Society
• /
• 제33권2호
• /
• pp.469-472
• /
• 2012

Intensity modulated photocurrent spectroscopy and intensity modulated photovoltage spectroscopy were investigated to measure the dynamic response of charge transfer and recombination in the standard, $TiCl_4$-treated and the combined scattering layer electrode dye-sensitized solar cells (DSSCs). IMPS and IMVS provided transit time ($\tau_n$), lifetime ($\tau_r$), diffusion coefficient ($D_n$) and effective diffusion length ($L_n$). These expressions are derived that generation, collection, and recombination of electrons in a thin layer nanocrystalline DSSC under conditions of steady illumination and with a superimposed small amplitude modulation. In this experimental, IMPS/IMVS showed that the main effect of $TiCl_4$ treatment is to suppress the recombination of photogenerated electrons, thereby extending their lifetime. And the Diffusion coefficient of combined scattering layer electrode is $6.10{\times}10^{-6}$ higher than that of the others, resulting in longer diffusion length.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2009년도 세계 도시지반공학 심포지엄
• /
• pp.1435-1440
• /
• 2009

Geotechnical variability is a complex feature that results from many independent sources of uncertainties, and is mainly affected by inherent variability and measurement errors. This study evaluates the coefficient of variation (COV) of soil properties at Song-do region in Korea for evaluating inherent soil variability. Since soil variability is sensitive to soil layers and soil types, the COVs by soil layers (reclaimed layer and marine layer) and the COVs by soil types (clay and silt) were separately evaluated. It is observed that geotechnical variability of marine layer and clay is relatively smaller than that of reclamation layer and silt.

• Journal of Mechanical Science and Technology
• /
• 제18권7호
• /
• pp.1258-1266
• /
• 2004

It is important to completely understand heat/mass transfer from a flat plate because it is a basic element of heat/mass transfer. In the present study, local heat/mass transfer coefficient is obtained for two flow conditions to investigate the effect of boundary layer using the naphthalene sublimation technique. Obtained local heat/mass transfer coefficient is converted to dimensionless parameters such as Sherwood number, Stanton number and Colburn j-factor. These also are compared with correlations of laminar and turbulent heat/mass transfer from a flat plate. According to experimental results, local Sherwood number and local Stanton number are in much better agreement with the correlation of turbulent region rather than laminar region, which means analogy between heat/mass transfer and momentum transfer is more suitable for turbulent boundary layer. But average Sherwood number and average Colburn j-factor representing analogy between heat/mass transfer and momentum transfer are consistent with the correlation of laminar boundary layer as well as turbulent boundary layer.