• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.8
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• pp.2637-2649
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• 1996

Flow characteristics and aerodynamic forces acting on an elliptic cylinder placed in a plane boundary layer were investigated experimentally. Four cylinder models with axis ratio(major axis to minor axis, AR=A/B) of 1, 2, 3, and 4 having the same equivalent diameter were used in this experiment. The Reynolds number based on the equivalent diameter $D_e$(=20mm) was 13,000. In the case of circular cylinder, regular vortex shedding occurs for the cylinder gaps larger than G/B=0.3 and is not almost related to the boundary layer thickness. But, for the elliptic cylinders, the vortex shedding frequency is increased with increasing the gap ratio (G/B) and the axis ratio (AR) of elliptic cylinders. The maximum drag coefficient acting on a circular cylinder is mainly affected by the boundary layer thickness. But, the elliptic cylinders(AR$\geq$2), except for the smaller gap G/B<0.2, show a nearly constant drag coefficient which is much smaller than that of a circular cylinder. The base pressure on the flat plate decreases with increasing the axis ratio(AR) of the elliptic cylinder. In the case of a circular cylinder, the base pressure has the minimum value at the gap ratio G/B=0.4, but it occurs at G/D=2 for elliptic cylinders. The mean velocity of the cylinder wake is quickly recovered at a small cylinder height ratio(H/$\delta$), but the turbulent intensity is rapidly recovered at a large cylinder height ratio(H/$\delta$). The effective wake region in the plane boundary layer is shrinkaged with increasing the axis ratio(AR) of elliptic cylinder. And the drag coefficient and streamwise turbulent intensity of the elliptic cylinder with AR=4 are less than half of those for the circular cylinder(AR=1).

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.12 no.1
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• pp.36-41
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• 2002

Abstract The stoichiometric and double-ordered perovskite $Sr_2FeMoO_6$ (SFMO) polycrystalline ceramics were fabricated by sintering at above $900^{\circ}C$ in $H_2$(5%)/Ar reductive ambient. SMO polycrystals showed good ferromagnetic properties andmagnetrotesistqnce ratios of about 15 % at 8K and 3 % at room temperature. Amorphous SFMO thin films were deposited on $LaA1O_3$ and $SrTiO_3$ single crystal substrates using rf sputtering method with the SFMO polycrystalline ceramic target. Double-ordered perovskite polycrystalline SFMO thin films were fabricated by solid state crystallization by annealing the deposited amorphous films at above $680^{\circ}C$ in $H_2$(5%)/Ar reductive ambient. SFMO thin films exhibited ferromagnetic behavior. Their magnetroresistance ratios, however, were only 0.3~0.5% at 8K and disappeared with increasing the measuring temperature. This was attributed to the absence of magnetic spin tunneling between grains due to the porous structure and non-stoichiometric composition of the deposited films.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.133-133
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• 1999

비정질 탄소막 제조에 있어서 수소가 포함된 반응성 가스를 사용할 경우 제작된 탄소막 내부에는 수소가 포함되게 되며, 이러한 수소원자들은 막의 특성에 중요한 영향을 주는 것으로 알려져 있다. 따라서, 본 연구에서는 비정질 탄소막(a-C:H) 내부에 존재하는 수소가 탄소막의 특성에 미치는 영향을 알아보고, 막 내부에 포함된 수소의 함량과 공정조건 사이의 함수계를 조사함으로써 수소의 함량을 인위적으로 통제할 수 있는 가능성을 제시하고자 한다. 수소가 포함된 비정질 탄소막은 2.45 GHz의 전자기파를 사용하는 electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) 방법과 DC magnetron sputtering 법을 사용하여 제작하였다. 기판으로는 Si(001) wafer를 사용하였으며, 아세톤과 에탄올을 사용하여 표면의 유기성분을 제거하고, 진공챔버속에서 Ar 플라즈마를 발생시켜 sputter etching 방법으로 표면을 세척하였다. ECR-PECVD 방법에서는 반응가스로 메탄(CH4)과 수소(H2)의 혼합가스를 사용하였으며, 혼합가스의 비는 5~50% 범위내에서 변화를 주었다. 수소가스의 유량은 100SCCM으로 고정하였으며, 마이크로웨이브의 power는 360~900W였고, 기판에 가해준 negative DC bias 전압은 0~-500V이었다. DC magnetron sputtering 방법에서는 반응가스로 아세틸린(C2H2) 가스를 사용하였으며, 플라즈마 발생을 용이하게 하기 위해서 Ar 가스와 혼합하여 사용하였다. Ar 가스의 유량은 10SCCM으로 고정하였으며, 아세틸렌 가스의 유량은 5~20SCCM 범위내에서 주입하였다. 이때, 기판에 가해준 negative DC bias 전압은 0~-100V이었다. 제작된 탄소막의 수소 함량을 조사하기 위하여 Fourier Transform Infrared (FTIR) 분광법과 Elastic Recoil Detection Analysis (EFDA) 법을 사용하였으며, 증착율은 SEM 단면촬영과 a-step을 이용하여 측정하였고, 막의 경도는 Micro-Hardness Testing 법을 사용하여 측정하였다.

• Journal of Animal Science and Technology
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• v.62 no.1
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• pp.52-57
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• 2020

In rumen in vitro experiments, although nitrogen gas (N₂) flushing has been widely used, its effects on rumen fermentation characteristics are not clearly determined. The present study is the first to evaluate the effects of N₂ flushing on rumen fermentation characteristics in in vitro batch culture system by comparing with new applicable non-metabolizable gas: argon (Ar). The rumen fluid was taken from two Korean native heifers followed by incubation for 3, 9, 12, and 24 h with N₂ or Ar flushing. As a result, in all incubation time, N₂ flushing resulted in higher total gas production than Ar flushing (p < 0.01). Additionally, in N₂ flushing group, ammonia nitrogen was increased (p < 0.01). However, volatile fatty acids profiles and pH were not affected by the flushing gases (p > 0.05). In conclusion, the present study demonstrated that N₂ flushing can influence the rumen nitrogen metabolism via increased ammonia nitrogen concentration and Ar flushing can be used as a new alternative flushing gas.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.40-40
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• 1999

가속기나 토카막과 같은 거대한 진공 장치의 용기 내벽을 청정화 하기 위해서는 용기 전체의 열처리(굽기, Baking)와 글로우 방전(Glow discharge) 법을 병행하여 사용한다. Baking은 일반 기체(N2, O2, 그리고 CO2)와 물(H2O)의 탈착에 효과적이고, Glow discharge cleaning은 탄소(Carbon-based)와 산소(Oxygen-based) 화합물의 탈착에 효과적이다. 특히 Glow discharge cleaning의 경우에는 전극의 모양, 진공 용기의 재질과 모양, 전극간의 거리, 사용되는 반응 기체의 압력 등에 따라 그 효과에 큰 차이가 있으므로 다각적인 연구가 필요하다. 본 연구에서는 그림 1과 같이 시험용 스테인레스(AISI 304와 AISI 316LN) 진공 용기를 설치하고, 시험 용기의 한쪽은 배기 용기와 oriffice로, 다른 편은 불순물의 정성.정량 분석을 위해 RGA(Residual gas analyser) 용기와 oriffice로 연결하였다. 전체 시스템 중에서 배기 부분과 분석 부분은 15$0^{\circ}C$에서 24시간 가열하여 전체의 기저 진공도를 1$\times$10-8Torr로 하였다. 기저 진공도의 용기에 고순도의 반응기체 (He, Ar, Ar+He, Ar+H2, Ar+N2 등)를 주입한후, DC 전압(0.8~1.5kV)을 변화하며 글로우 방전의 최적조건을 찾았다. 방전 동안 시험용 용기에서 방출되는 반응 기체 이외의 기체를 RGA로 측정하였고 외부에 Thermocouple을 여러곳에 장착하여 온도 변화를 측정하였다. 이상의 결과로부터 진공 용기 표면적으로부터의 불순물 탈착(desorption)과 불순물 분석, 플라즈마와 내벽의 상호작용등에 대한 결론을 얻을 수 있었다. 또한 Baking과 Glow discharge cleaning을 동시에 수행하여 Baking 온도의 낮춤에 따른 영향 평가도 수행하였다.

• Journal of the Korean Chemical Society
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• v.15 no.4
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• pp.211-217
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• 1971

The theory of solubility proposed by Jhon and Kihara has been tested and applied to various systems. In the present paper, the systems are the solubilities of gases such as $Ar,\;H_2,\;N_2,\;O_2,\;CO_2,\;CH_4,\;and\;C_2H_6$ in liquid benzene and carbon disulfide, those of solids iodine and naphthalene in the nonaqueous solvents, and those of gases $H_2,\;N_2,\;O_2,\;Ar,\;CH_4,\;and\;C_2H_4$ in the electrolyte solutions. The theoretical values of solubilities are in good agreement with the experimental data in the literature.

• Journal of the Optical Society of Korea
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• v.4 no.2
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• pp.86-88
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• 2000

A sequence of functions are examined for the gradient-index AR thin film between two dielectric media and are used as the starting profiles in optimization to improve AR performance. Sinusoidal functions were quite efficient to use as components of the index change in the optimization. It is shown that there exist a number of gradient-index profiles which exhibit excellent AR-performance after control of the gradient-index profiles.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.908-912
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• 2003

비대칭 마그네트론 스퍼터링법을 사용하여 실리콘 기판위에 hydrogenated amorphous carbon (a-C:H) 박막을 성장시켰다. DC Power 와 $Ar/C_2H_2$ 의 분압을 변화시켜 증착조건을 형성하고 성장된 다이아몬드상 카본박막의 물성을 관찰하였다. DC 전압에 따라 증착율과 표면 거칠기는 감소하는 한편 박막의 경도는 증가한다. 또한 $Ar/C_2H_2$의 분압이 낮을 때 박막의 특성을 보여주는 G 피크가 낮은 wavenumber로 이동하는 것을 알 수 있다.

• Transactions on Electrical and Electronic Materials
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• v.11 no.2
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• pp.81-84
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• 2010

Al-doped ZnO (AZO) films were prepared by an Ar:$H_2$ gas radio frequency (RF) magnetron sputtering system with a AZO ($2\;wt{\cdot}%\;Al_2O_3$) ceramic target at the low temperature of $100^{\circ}C$ and annealed in hydrogen ambient at the temperature of $300^{\circ}C$. To investigate the influence of the $H_2$ flow ratio on the properties of the AZO films, the $H_2$ flow ratio was changed from 0.5% to 2%. As a result, the AZO films, deposited with a 1% $H_2$ addition, showed a resistivity of $11.7\;{\times}\;10^{-4}\;{\Omega}{\cdot}cm$. When the AZO films were annealed at $300^{\circ}C$ for 1 hour in a hydrogen atmosphere, the resistivity decreased from $11.7\;{\times}\;10^{-4}\;{\Omega}{\cdot}cm$ to $5.63\;{\times}\;10^{-4}\;{\Omega}{\cdot}cm$. The lowest resistivity of $5.63\;{\times}\;10^{-4}{\Omega}{\cdot}cm$ was obtained by adding 1% hydrogen gas to the deposition and annealing process. The X-ray diffraction patterns of all the films showed a preferable growth orientation in the (002) plane. The spectrophotometer measurements showed that the transmittance of 85% was obtained by the film deposited with the $H_2$ flow ratio of 1% at 940 nm for GaAs/GaAlAs LEDs.

• Electronics and Telecommunications Trends
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• v.38 no.2
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• pp.75-84
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• 2023

Metaverse is expected to bring many innovations to society, culture, and economy by providing realistic services in various fields while suppressing time and space constraints. However, unclear definitions owing to the high diversity of the metaverse add to the confusion of the ecosystem participants. The current metaverse service has many voices of concern owing to technical limitations and lack of a clear profit model. Nevertheless, given its high growth potential driven by the digital transformation, a solid and long-term technology development strategy seems to be necessary. Accordingly, we analyze development cases centering on the major metaverse service shapes presented in the Metaverse New Industry Leading Strategy announced by the Ministry of Science and ICT in January 2022. In addition, we study the characteristics and core technologies of each metaverse service for its realization and discuss future stages of technological development.