• Bulletin of the Korean Chemical Society
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• 제35권7호
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• pp.2013-2018
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• 2014

The adsorption and decomposition of trimethylene oxide ($C_3H_6O$) molecule on the Al(111) surface were investigated by the generalized gradient approximation (GGA) of density functional theory (DFT). The calculations employed a supercell ($6{\times}6{\times}3$) slab model and three-dimensional periodic boundary conditions. The strong attractive forces between $C_3H_6O$ molecule and Al atoms induce the C-O bond breaking of the ring $C_3H_6O$ molecule. Subsequently, the dissociated radical fragments of $C_3H_6O$ molecule oxidize the Al surface. The largest adsorption energy is about -260.0 kJ/mol in V3, V4 and P2, resulting a ring break at the C-O bond. We also investigated the decomposition mechanism of $C_3H_6O$ molecules on the Al(111) surface. The activation energies ($E_a$) for the dissociations V3, V4 and P2 are 133.3, 166.8 and 174.0 kJ/mol, respectively. The hcp site is the most reactive position for $C_3H_6O$ decomposing.

• 한국생산제조학회지
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• 제8권4호
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• pp.68-78
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• 1999

Heat transfer performance is studied for boiling and condensation of R-11 on integral-fin tubes. Nine tubes with trapezoidal integral-fins having fin densities from 748 to 1654fpm and 10,30 grooves and finned tubes with caves of 0.55 and 0.64 mm height respectively are tested. in case of condensation CFC-11 condensates at saturation stat of 32$^{\circ}C$ on the outside surface cooled by inside cooling water flows. And in case of boiling the refrigerant evaporates at a saturation state of 1 bar on the outside tube surface and heat is supplied by hot water which circulates inside of the tube,. The tube having fin transfer coefficient concerns fin tubes with caves show higher valve than low fin tube having find density of 1299fpm and 30grooves. The overall heat transfer coefficient of fin tube with caves is about 5155 W/mK at 2.8m/s of water velocity, The value is abuot 2.7 times higher than plain tube and 1.3 times higher than low fin tube having fin density of 1299fpm and 30 grooves.

• 한국생산제조학회지
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• 제8권4호
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• pp.65-65
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• 1999

Heat transfer performance is studied for boiling and condensation of R-11 on integral-fin tubes. Nine tubes with trapezoidal integral-fins having fin densities from 748 to 1654fpm and 10,30 grooves and finned tubes with caves of 0.55 and 0.64 mm height respectively are tested. in case of condensation CFC-11 condensates at saturation stat of 32℃ on the outside surface cooled by inside cooling water flows. And in case of boiling the refrigerant evaporates at a saturation state of 1 bar on the outside tube surface and heat is supplied by hot water which circulates inside of the tube,. The tube having fin transfer coefficient concerns fin tubes with caves show higher valve than low fin tube having find density of 1299fpm and 30grooves. The overall heat transfer coefficient of fin tube with caves is about 5155 W/mK at 2.8m/s of water velocity, The value is abuot 2.7 times higher than plain tube and 1.3 times higher than low fin tube having fin density of 1299fpm and 30 grooves.

• Journal of Mechanical Science and Technology
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• 제16권12호
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• pp.1652-1663
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• 2002

It is desirable to perform nondestructive evaluation to assess material properties and part homogeneity because manufacturing of carbon/carbon (C/C) composites requires complicated and costly processes. In this work several ultrasonic techniques were applied to carbon/carbon composites for the evaluation of spatial variations in material properties that are attributable to the manufacturing process. In a large carbon/carbon composite manufactured by chemical vapor infiltration (CVI) method, the spatial variation of ultrasonic velocity was measured and found to be consistent with the densification behavior in CVI process in order to increase the density of C/C composites. Ultrasonic velocity and attenuation depend on a density variation of materials. Low frequency through-transmission scans based on both amplitude and time-of-flight of the ultrasonic pulse were used for mapping out the material property inhomogeneity These results were compared with that obtained by dry-coupling ultrasonics. Pulse-echo C-scans was used to image near-surface material property anomalies such as the placement of spacers between disks during CVI. Also, optical micrograph had been examined on the surface of C/C composites using a destructive way.

• 한국전기전자재료학회논문지
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• 제24권9호
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• pp.693-696
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• 2011

Recently, amorphous oxide semiconductors (AOSs) based thin-film transistors (TFTs) have received considerable attention for application in the next generation displays industry. The research trends of AOSs based TFTs investigation have focused on the high device performance. The electrical properties of the TFTs are influenced by trap density. In particular, the threshold voltage ($V_{th}$) and subthreshold swing (SS) essentially depend on the semiconductor/gate-insulator interface trap. In this article, we investigated the effects of Ar plasma-treated $SiO_2$ insulator on the interfacial property and the device performances of amorphous indium gallium zinc oxide (a-IGZO) TFTs. We report on the improvement in interfacial characteristics between a-IGZO channel layer and gate insulator depending on Ar power in plasma process, since the change of treatment power could result in different plasma damage on the interface.

• Progress in Superconductivity
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• 제14권1호
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• pp.11-16
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• 2012

본 연구에서는 자체일관적인 DFT+DMFT 계산을 통해 철의 3d 전자의 상관관계가 LiFeAs와 NaFeAs의 전자구조와 페르미 면 겹싸기 등에 미치는 영향을 알아보았다. 이들은 모두 철계 초전도체의 초전도성 형성에 매우 중요한 역할을 가지고 있다. DFT+DMFT 계산에서 얻어진 LiFeAs의 스펙트럼은, DFT에서 얻어진 띠 구조에 비해 매우 약한 페르미 면 겹싸기 현상을 보이며, NaFeAs 의 경우 DMFT 에서도 페르미 면 겹싸기 현상이 어느 정도 남아있는 것을 확인하였다. 그리고 이는 실험에서 보고된 ARPES 결과와 일치함을 확인했다.

• 한국세라믹학회지
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• 제34권8호
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• pp.803-810
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• 1997

Ba0.5Sr0.5TiO3박막을 RF 마그네트론 스퍼터링법을 이용하여 Pt/Ti/SiO2/Si(100) 기판에 증착하였다 .누설전류에 영향을 주는 것으로 알려진 열처리 조건, dopant 효과 등을 평가하고자 이온반경이Ti와 유사하고 대부분이 Ti 자리를 치환하는 것으로 알려진 Nb와 Al을 각각 danor와 acceptor로 선택하여 BST 박막에 첨가한 후 누설전류를 측정하였다. 고온에서 in-situ 증착된 BST 박막은 거친 표면 형상을 보이며 낮은 전압에서 파괴가 발생하고, Nb 첨가로 누설전류가 증가하였다. 삼온 증착후 후열처리된 박막은 표면 형상도 평할도가 증가하였으며 in-situ로 제조된 박막에 비해 높은 파괴전압과 낮은 누설전류를 나타내었다. 특히 Al이 첨가된 BST 박막의 누설전류밀도는 ~10A/cm2로 도핑을 하지 않은 박막이나 Nb가 첨가된 박막에 비해 매우 낮은 누설전류밀도를 나타내었으며, 이는 산화로 인한 산소공공의 감소, 이동 가능한 hole의 감소와 후열처리과정중 계면 및 입계의 산화로 Schottky 장벽에 높아진 결과로 판단된다.

• 한국초전도ㆍ저온공학회논문지
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• 제15권2호
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• pp.39-43
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• 2013

$MgB_2$ bulk samples are synthesized through solid state reaction route using Mg precursors with different particle size by keeping the boron precursor unchanged. Scanning electron microscopy study of the fractured surface for all the samples depicts quite distinct structure depending on the Mg precursor. Big size of Mg precursor resulted in to largely elongated and deep pores while smaller one gave roughly ellipsoidal and shallow pore structure. Influence of the Mg particle size on the grain to grain connectivity reflected in the critical current density value which was greater for samples with smaller Mg precursor. All the synthesized samples undergo a superconducting transition at around 36.5 K irrespective of different Mg precursor particle size.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2471-2476
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• 2008

Turbulent flow and heat transfer to water at supercritical pressure flowing in vertical pipes is investigated using direct numerical simulation (DNS). A conservative space-time discretization scheme for variable-density flows at low Mach numbers is adopted in the present study to treat steep variations of fluid properties at supercritical pressure just above the thermodynamic critical point. The fluid properties at these conditions are obtained using PROPATH and used in the form of tables in the simulations. The buoyancy influence induced by strong variation of density across the pseudo-critical temperature proved to play an important role in turbulent flow and heat transfer at supercritical state. Depending on the degree of buoyancy influence, turbulent heat transfer may be enhanced or significantly deteriorated, resulting in local hot spots along the heated surface.

• Bulletin of the Korean Chemical Society
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• 제10권6호
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• pp.585-591
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• 1989

The effects of the charged metal on the overall electrostatic potential profiles and the capacitances of the electrical double layer are brought out. A model with a simplified jellium and a point-charged electrolyte is utilized in the present calculations. Electrons are assumed not to penetrate electrode surface due to a strong screening of electrolyte at the interface. Electron density functions and ion density functions are obtained, which are also based upon the Poisson equation and Boltzmann equation on either side of the interface. A complete potential profile starting from bulk electrode and ending at bulk electrolyte is obtained by connecting the two potential profiles (one inside the metal electrode, the other inside the electrolyte) with proper boundary conditions. In spite of the simplicity of the model, the present model reveals the importance of the effect of the charged metal on the electrostatic potential profile and the electrical double layer capacitances. The results are discussed and compared with the predictions by Gouy Chapman theory.