• Journal of Advanced Marine Engineering and Technology
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• 제31권4호
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• pp.363-369
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• 2007

Probably the most significant heat transfer in the cryogenic liquid hydrogen storage tank from the atmosphere may occur through its support system. In this paper the efficient support system for the cryogenic storage vessel was newly developed and analysed. The support system was composed of a spherical ball as a supporter to reduce the contact area. which is located between two supporting SUS tubes inserted SUS and PTFE blocks. Numerical analyses for temperature distribution, and the thermal stress and strain of the support system were performed by the commercial codes FLUENT and ANSYS. The heat transfer rate of the supporter was evaluated by the thermal boundary potential method which can consider the variation of thermal conductivity with temperature. The results showed that the heat transfer rate through the developed supporter compared with the common SUS tube supporter was significantly reduced. The thermal stress and strain were obtained well below the limited values. It was found that the developed supporter can be one of the most efficient support systems for cryogenic liquid storage vessel.

• Bulletin of the Korean Chemical Society
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• 제35권5호
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• pp.1379-1384
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• 2014

${\alpha}-Fe_2O_3$ spherical particles having an average diameter of ca. 420 nm and ${\alpha}-Fe_2O_3$ fine particles (< 10 ${\mu}m$ particle size) were prepared to examine as catalysts for CO oxidation. Kinetic studies on the catalytic reactions were performed in a flow reactor using an on-line gas chromatography system operated at 1 atm. The apparent activation energies and the partial orders with respect to CO and $O_2$ were determined from the rates of CO disappearance in the reaction stage showing a constant catalytic activity. In the temperature range of $150-275^{\circ}C$, the apparent activation energies were calculated to be 13.7 kcal/mol on the ${\alpha}-Fe_2O_3$ spherical submicron clusters and 15.0 kcal/mol on the ${\alpha}-Fe_2O_3$ fine powder. The Pco and $Po_2$ dependencies of rate were investigated at various partial pressures of CO and $O_2$ at $250^{\circ}C$. Zero-order kinetics were observed for $O_2$ on both the catalysts, but the reaction order for CO was observed as first-order on the ${\alpha}-Fe_2O_3$ fine powder and 0.75-order on the ${\alpha}-Fe_2O_3$ spherical submicron clusters. The catalytic processes including the inhibition process by $CO_2$ on the ${\alpha}-Fe_2O_3$ spherical submicron powder are discussed according to the kinetic results. The catalysts were characterized using XRD (X-ray powder diffraction), FE-SEM (field emission-scanning electron microscopy), HR-TEM (high resolution-transmission electron microscopy), and $N_2$ sorption measurements.

• 한국세라믹학회지
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• 제47권6호
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• pp.590-597
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• 2010

HTGR using a TRISO coated particles as nuclear raw fuel material can be used to produce clean hydrogen gas and process heat for a next-generation energy source. For these purposes, a TRISO coated particle was prepared with 3 pyro-carbon (buffer, IPyC, and OPyC) layers and 1 silicone carbide (SiC) layer using a CVD technique on a spherical $UO_2$ kernel surface as a fissile material. In this study, a spherical $UO_2$ particle was prepared using a modified sol-gel method with a vibrating nozzle system, and TRISO coating fabrication was carried out using a fluidized bed reactor with coating gases, such as acetylene, propylene, and methyltrichlorosilane (MTS). As the results of this study, a spherical $UO_2$ kernel with a sphericity of 1+0.06 was obtained, and the main process parameters in the $UO_2$ kernel preparation were the well-formed nature of the spherical ADU liquid droplets and the suitable temperature control in the thermal treatment of intermediate compounds in the ADU, $UO_3$, and $UO_2$ conversions. Also, the important parameters for the TRISO coating procedure were the coating temperature and feed rate of the feeding gas in the PyC layer coating, the coating temperature, and the volume fraction of the reactant and inert gases in the SiC deposition.

• 한국지구과학회지
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• 제38권2호
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• pp.105-114
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• 2017

Two dimensional finite element method with quadrilateral basis functions was applied to the spherical high order filter on the spherical surface limited area domain. The basis function consists of four shape functions which are defined on separate four grid boxes sharing the same gridpoint. With the basis functions, the first order derivative was expressed as an algebraic equation associated with nine point stencil. As the theory depicts, the convergence rate of the error for the spherical Laplacian operator was found to be fourth order, while it was the second order for the spherical Laplacian operator. The accuracy of the new high order filter was shown to be almost the same as those of Fourier finite element high order filter. The two-dimension finite element high order filter was incorporated in the weather research and forecasting (WRF) model as a hyper viscosity. The effect of the high order filter was compared with the built-in viscosity scheme of the WRF model. It was revealed that the high order filter performed better than the built in viscosity scheme did in providing a sharper cutoff of small scale disturbances without affecting the large scale field. Simulation of the tropical cyclone track and intensity with the high order filter showed a forecast performance comparable to the built in viscosity scheme. However, the predicted amount and spatial distribution of the rainfall for the simulation with the high order filter was closer to the observed values than the case of built in viscosity scheme.

• Applied Microscopy
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• 제36권3호
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• pp.227-234
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• 2006

구면과 비구면 RGP렌즈 장용시 효과를 비교하기 위하여 3주간 실험토끼 눈의 각막에 콘택트렌즈를 착용 시켜 조사하였다. 8마리의 흰 실험토끼 눈 중 4마리의 우안은 구면 RGP렌즈, 4마리의 우안은 비구면 RGP렌즈를 착용 하였다. 왼눈은 대조군으로 사용하였다. 콘택트렌즈착용 3주 후 안구를 적출하여 형태변화를 주사전자현미경으로 관찰하였으며 RGP렌즈를 착용시 각막 상피 세포증식률을 조사하였다. 구면 RGP렌즈를 착용 후, 상피층은 비구면에 비하여 손상을 받았고 상피층은 심하게 벗겨져 나갔으며 세포 크기는 비정상으로 변하였다. 구면과 비구면 렌즈 두 군 모두 많은 박테리아가 보였으며 렌즈의 후면은 양치류 모양의 형태를 발견하였다. 비구면 렌즈의 원재료는 구면렌즈보다는 다소 정형적으로 보였다. 이러한 형태는 대기로부터 산소 전달을 방해함으로 인하여 구면렌즈를 착용한 군에서 각막을 변화시킨 것으로 생각된다. 이 논문은 구면 렌즈보다는 비구면 렌즈가 생리적으로 각막 세포에 덜 영향을 미쳐 더 적합한 것을 제시한다.

• 한국결정성장학회지
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• 제29권1호
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• pp.12-18
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• 2019

스케일업된 초음파 분무 열분해 공정을 이용하여 양산용 구형 $SiO_2$ 분말을 합성하였다. 초음파 분무 열분해 공정에 사용된 전구체는 20 nm에서 30 nm의 $SiO_2$ 입자를 포함한 수계 $SiO_2$ 졸을 사용하였다. 초음파 분무 열분해 공정의 구동 조건과 전구체 조건의 변화가 합성된 $SiO_2$ 입자에 미치는 영향을 알아보기 위해 반응 온도, 운반 기체 공급 속도 그리고 전구체인 수계 $SiO_2$ 졸의 농도를 조절하였다. 합성된 $SiO_2$ 입자는 공통적으로 반비정질상, 구 형태의 매끄러운 표면을 나타내었다. 구형 $SiO_2$ 입자의 크기는 반응 온도가 증가 또는 전구체 농도가 감소함에 따라 감소하였다. 또한 운반 기체 공급 속도가 증가할수록 합성된 $SiO_2$ 입자의 크기는 증가하였다. 스케일업 규모와 실험실 규모의 초음파 분무 열분해 공정의 차이점을 비교하였고, 반응관 내부 체류시간이 상대적으로 짧은 실험실 규모의 초음파 분무 열분해 공정에서 합성된 $SiO_2$ 입자가 상대적으로 큰 입도를 나타내었다.

• 한국식품영양과학회지
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• 제44권7호
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• pp.1064-1071
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• 2015

난소화성 덱스트린 혼합비율을 발효홍삼농축액의 40, 50, 60%가 되도록 발효홍삼농축액을 제조한 다음 유동층 코팅기의 분무속도, 분무압력, 제품온도를 변수로 조정하면서 발효홍삼농축액 구형과립을 제조하였다. 발효홍삼농축액 구형과립의 용해시간은 6.4초로 발효홍삼농축액의 11.3초보다 훨씬 짧아 발효홍삼농축액을 구형과립 형태로 제조하면 발효홍삼농축액의 섭취 시 불편함이 상당히 개선될 수 있음을 보여 주었다. 특히 발효홍삼농축액 구형과립의 입사각은 14.89도로 발효홍삼농축액 분말의 40.77도와 비교 시 흐름성이 아주 좋음을 보여 주었는데, 발효홍삼농축액 구형과립의 아주 높은 흐름성은 액상 형태인 발효홍삼농축액의 문제점을 해결해 줄 새로운 제형의 발효홍삼제품이 될 것으로 판단되었다. 난소화성 덱스트린 혼합비율이 높을수록 입사각이 낮아져 발효홍삼농축액 구형과립의 흐름성 및 편리성을 증진시키기 위해서는 난소화성 덱스트린의 혼합비율을 높여야 함을 알 수 있었으며, 난소화성 덱스트린 혼합비율별 발효홍삼농축액 구형과립의 용해시간은 통계적으로 유의차가 없음을 보여 주었다. 난소화성 덱스트린 50% 및 발효홍삼농축액 고형분 50%를 혼합한 용액으로 분무속도 5.40 mL/min, 분무압력 2.15 bar, 제품온도 $83.03^{\circ}C$의 유동층 코팅 조건으로 제조하면 발효홍삼농축액 구형과립의 수율은 87.78%가 될 것으로 예측되었다.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.381-382
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• 2002

The Fluid film between the valve plate and the cylinder block was measured by use of a gap sensor and the mercury-cell slip ring unit under real working conditions. During the operating periods, experiments with discharge pressure, revolution speed, and valve geometry was carried out for the fluid film on the valve plate. To investigate the effect of the valve shape, we designed two valve plates each having a different shape; the first valve plate was a plane valve plate. while the second valve plate was a spherical valve plate. It was noted that these two valve plates observed different aspects of the fluid film characteristics between the cylinder block and the valve plate. The leakage flow rate and the shan torque were also investigated in order to clarify the difference between these two types of valve plates. From the results of this study. we found that the spherical valve plate estimated good fluid film patterns and performance more than the other valve plate in oil hydraulic axial piston pumps.

• 천문학회지
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• 제34권1호
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• pp.25-29
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• 2001

We have constructed a non-spherical model for the hot oxygen corona of Mars by including the effects of planetary rotation and diurnal variation of the Martian ionosphere. Exospheric oxygen densities are calculated by integrating ensemble of ballistic and escaping oxygen atoms from the exobase over the entire planet. The hot oxygen atoms are produced by dissociative recombination of $O^+_2$, the major ion in the Martian ionosphere. The densities of hot oxygen atoms at the exobase are estimated from electron densities which have been measured to vary with solar zenith angle. Our model shows that the density difference of hot oxygen atoms between noon and terminator is about two orders of magnitude near the exobase, but reduces abruptly around altitudes of 2000 km due to lateral transport. The diurnal variation of hot oxygen densities remains significant up to the altitude of 10000 km. The diurnal variation of the hot oxygen corona should thus be considered when the upcoming Nozomi measurements are analyzed. The non-spherical model of the hot oxy-gen corona may contribute to building sophisticate solar wind interaction models and thus result in more accurate escaping rate of oxygens from Mars.

• 공업화학
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• 제20권4호
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• pp.396-401
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• 2009

전기이중층 캐패시터의 성능향상을 위한 전극물질로서 resorcinol-formaldehyde수지를 탄소원으로 사용하여 meso-pore 비율 52~64%의 기공특성을 지니며 직경 $2{\sim}10{\mu}m$의 미세구형 활성탄을 제조하였다. 이 활성탄을 전기이중층에 적용한 결과, meso-pore구조의 미세구형활성탄은 전하전달저항의 저감 및 충방전율 수용능력 향상에 효과적인 영향을 나타내어 전기이중층 캐패시터의 성능향상을 위한 효과적인 전극물질이 될 수 있음을 확인할 수 있었다.