• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.1
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• pp.85-88
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• 2012

DSCs are based on a dye-adsorbed porous $TiO_2$ layer as a photo electrode [1]. Under the illumination, dye molecules are excited and electrons are produced. The injected electrons in the conduction band of $TiO_2$ may recombine with the electrolyte. To obtain high performance DSCs, it is essential to retard the recombination. The charge recombination can be reduced by forming core-shell structure. In this work, we investigated the core-shell structure with $Al_2O_3$ and MgO coating layer on the porous $TiO_2$ layer. We confirmed the photovoltaic properties by I-V characteristics. The current and the efficiency was improved. In addition to, Through decrease in the width of EIS arc, which is the sum of the interfacial charge transfer resistances of both electrodes, we can be indicated that the block effect.

• Journal of Powder Materials
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• v.20 no.3
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• pp.169-173
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• 2013

High-coercive (Nd,Dy)-Fe-B magnets were fabricated via dysprosium coating on Nd-Fe-B powder. The sputtering coating process of Nd-Fe-B powder yielded samples with densities greater than 98%. $(Nd,Dy)_2Fe_{14}B$ phases may have effectively penetrated into the boundaries between neighboring $Nd_2Fe_{14}B$ grains during the sputtering coating process, thereby forming a $(Nd,Dy)_2Fe_{14}B$ phase at the grain boundary. The maximum thickness of the Dy shell was approximately 70 nm. The maximum coercivity of the Dy sputter coated samples(sintered samples) increased from 1162.42 to 2020.70 kA/m. The microstructures of the $(Nd,Dy)_2Fe_{14}B$ phases were effectively controlled, resulting in improved magnetic properties. The increase in coercivity of the Nd-Fe-B sintered magnet is discussed from a microstructural point of view.

• Journal of Mechanical Science and Technology
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• v.14 no.1
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• pp.48-56
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• 2000

The bifurcation problem of thin walled structures in contact with rigid surfaces is formulated by adopting the multiple scales asymptotic technique. The general theory developed in this paper is very useful for the bifurcation analysis of waviness instabilities in the sheet metal forming. The formulation is presented in a full Lagrangian formulation. Through this general formulation, the bifurcation functional is derived within an error of O($(E^4)$) (E: shell's thickness parameter). This functional can be used in numerical solutions to sheet metal forming instability problem.

• Transactions of Materials Processing
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• v.14 no.9 s.81
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• pp.764-771
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• 2005

This study is related with the development of CNC spinning machine and the axisymmetric conventional spinning such as drum type and conical type steel shells. The CNC spinning machine is constructed with heavy duty frame and the hydraulic servo system is applied in order to give the exactness of motion control. The experiment has been carried out considering feeding velocity, mandrel shape, and the corner radius of mandrel and forming rollers. As a result of experiment, the limiting spinning ratio and thickness strain distribution are obtained and it can be seen that the spinnability is dominant to the feeding velocity and corner radius of forming roller. This research can contribute to the development of axisymmetric mechanical part which is applicable to automotive and aerospace industry.

• Transactions of Materials Processing
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• v.15 no.8 s.89
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• pp.574-580
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• 2006

Anisotropy has an important effect on the strain distribution in aluminum alloy sheet forming, and it is closely related to the thinning and formability of sheet metals. Thus, the anisotropy of the material should be properly considered for the realistic analyses of aluminum sheet forming processes. For this, anisotropy can be approached in two different scales: phenomenological and microstructural (polycrystal) models. Recent anisotropic models (Yld2000-2d; Barlat et al.[1] 2003, Cuitino et al.[2] 1992) were employed in this work. For the simulation using shell element, the method which can impose plane stress condition in the polycrystal model is developed. Lankford values and yield stress ratios are calculated along various directions. As planar anisotropic behavior, a circular cup deep drawing simulation was carried out to compare the phenomenological and microstructure models in terms of earing profile.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.943-948
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• 1996

In this paper. we will discuss in making large size cylindrical shells with multithickness wall sections such as straight, stepped, tapered sides. These shells are constructed of type 6061 O temper aluminum starting with a blanking size of 877 mm plate. Its diameter to length ratio of 1 to 2.78 and a 36.7％ wall reduction is achieved by our continuous deep drawing process. This process required no in-process annealing. But after cold working, these shells is performed heat treatment to T6 condition. These shells are used for the making of seamless LPG pressure vessels after the spinning process. This process is composed of deep drawing, reverse redrawing, drawing-ironing and several ironing processes. In the verification of forming process design, we used DEFORM code.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.134-137
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• 2005

In this paper, a continuous contact treatment has been considered during FE-analysis of the sheet metal forming processes. Because the simulation is usually performed stepwise, the status of contact can change suddenly. In case of implicit scheme, the increment of punch stroke can be chosen as large value. For exact assessment of contact force and friction force between die and sheet, the continuous contact treatment is proposed. The virtual surface of sheet metal is modeled by NURBS curves or surfaces in order to calculate exact contact area and penetration depth. From the geometrical evaluation of contact behavior, additional contact pressure is imposed to the element. The deformation of bending process and hydroforming process are analyzed based on this scheme.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.06a
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• pp.9-16
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• 1998

New program for springback analysis has been developed to predict the deformation of springback more accurately. Static implicit FEM is used to find out the static equilibrium after springback. The shell element with 6 dogrees of freedom and 4 nodes is carefully implemented to improve the accuracy and the compatibility between forming analysis and springback analysis. Co-rotational approach and Newton-Raphson nonlinear iteration are used to resolve the nonlinearity of large deformation. The benchmark results show that the developed program gives good predictions in comparison with experimental and other commercial S/W's results. As practical examples, U draw bending and S-rail problems are carried out by the developed program.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1994.10a
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• pp.240-245
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• 1994

Experiments on the drawability of squared boxes have been performed under various working conditions. In the present work, the pattern of material flow and the local change in the thickness of shell are used as the measures of drawability, and they are measured using the photo-etching technique. The effects of the size of draw bead, the magnitude of blank holding force and the condition of lubrication on the drawability of squared boxes have been analyzed.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.67.1-67.1
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• 2016

We observed two star forming regions, N159 and N160, in the Large Magellanic Cloud with SIRPOL, the polarimeter of the Infrared Survey Facility (IRSF) in South Africa. The photometric and polarimetric observations are done in three near-infrared bands, J, H, and Ks. We measured Stokes parameters of point sources and calculated their degrees of polarization and polarization angles. The polarization vector map shows complex features associated with dust and gas structures. Overall features of the magnetic field in N159 and N160 regions are different from each other and appear to be related to local environments, such as interior and boundary of shell structure, existence of star-forming HII regions, and boundaries between HII regions and dense dark clouds. We discuss the relation between the structure of magnetic field and the local properties of dust and gas in N159 and N160 regions by comparing our polarization vector map with images of $H{\alpha}$, mid-infrared, and $^{12}CO$ emissions, respectively by WFI of MPG/ESO telescope, Spitzer IRAC, and NANTEN.