• Transactions of Materials Processing
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• v.25 no.6
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• pp.379-389
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• 2016

As a stator for steam turbine diaphragm, hollow-type nozzle stator to substitute for conventional solid one is introduced in this study. This hollowed stator can be separated into two parts such as upper and lower plates with large and curved surface area. This study focuses on thick plate forming process for the upper plate of the hollow-partitioned nozzle stator. First, to reduce forming defects such as under-cut and localized thinning of the deformed plate, and to avoid tool interruption between forming punch and lower die, tool design including the position determination of forming surfaces is performed. Uni-axial tensile tests are carried out using SUS409L steel plate with initial thickness of 5.00mm, and plastic strain ratio (r-value) is also obtained. Due to the asymmetric curved configuration of the upper plate, it is hard to adopt a series of blank holder or draw-bead, so the initial plate during this thick plate forming experiences unstable and non-uniform contact. To easy this forming difficulty and find suitable tool geometry without sliding behavior of the workpiece in the die cavity, two geometric parameters with respect to each shoulder angle of the lower die and the upper punch are adopted. FE models with consideration of 21 combinations for the geometric parameters are built-up, and numerical simulations are performed. From the simulated and predicted results, it is shown that the geometric parameter combinations with ($30^{\circ}$, $90^{\circ}$) and ($45^{\circ}$, $90^{\circ}$) for the shoulder angle of the lower die and the upper punch are suitably applied to this upper plate forming of the hollow-partitioned nozzle stator used for the turbine diaphragm.

• Journal of Welding and Joining
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• v.23 no.6
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• pp.99-105
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• 2005

The mixing ratio effect of the GTD-111(base metal) powder and the GNI-3 (Ni-l4Cr-9.5Co-3.5Al-2.5B) powder on TLP(Transient Liquid Phase) bonding phenomena and mechanism was investigated. At the mixing ratio of the base metal powder under $50wt\%$, the base metal powders fully melted at the initial time and a large amount of the base metal near the bonded interlayer was dissolved by liquid inter metal. Liquid insert metal was eliminated by isothermal solidification which was controlled by the diffusion of B into the base metal. The solid phases in the bonded interlayer grew epitaxially from the base metal near the bonded interlayer inward the insert metal during the isothermal solidification. The number of grain boundaries farmed at the bonded interlayer corresponded with those of base metal. At the mixing ratio above $60wt\%$, the base metal powder melted only at the surface of the powder and the amount of the base metal dissolution was also less at the initial time. Nuclear of solids firmed not only from the base metal near the bonded interlayer but also from the remained base metal powder in the bonded interlayer. Finally, the polycrystal in the bonded interlayer was formed when the isothermal solidification finished. When the isothermal solidification was finished, the contents of the elements in the boned interlayer were approximately equal to those of the base metal. Cr-W borides and Cr-W-Ta-Ti borides formed in the base metal near the bonded interlayer. And these borides decreased with the increasing of holding time.

• Korean Journal of Plant Tissue Culture
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• v.25 no.4
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• pp.231-236
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• 1998

Carrot cotyledon explants cultured on MS medium with 1 mg/L 2,4-D were transferred to a hormone-free solid medium overlaid with filter paper in order to elucidate the effect of simple physical treatment on the development and germination of somatic embryos. Transfer of the explants cultured for one week on MS basal medium overlaid with 3 sheets of filter paper on to MS basal medium increased somatic embryo production 2-39 times over the one week culture on medium without filter paper overlay. Maturation and germination of somatic embryos was more prominent on medium overlaid with filter paper than on medium without filter paper. The explants cultured for one week on filter paper overlay added with liquid medium showed prominent decrease in somatic embryo formation compared to filter paper overlay only. It is suggested that the filter paper overlay affected the moisture environment of the somatic embryos developing on it.

• Applied Chemistry for Engineering
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• v.23 no.6
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• pp.604-607
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• 2012

Solid base catalysts for biodiesel production were synthesized by impregnating basic metal species on two support materials with large specific surface area : zeolite and pyrolysis char. KL zeolite and Undaria pinnatifida char were impregnated with KOH aqueous solution and calcium nitrate solution, respectively, to enhance the basic strength. The catalysts synthesized were characterized using Hammett indicators and $CO_2$-TPD analysis. Biodiesel was produced using soybean oil and methanol over the catalysts synthesized. The content of fatty acid methyl esters was measured to evaluate the catalytic activity. Generally, the catalytic activity increased with increasing quantity of basic metal impregnated but impregnation of excessive amount of metal could cause reduction in the activity.

• Journal of Biomedical Engineering Research
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• v.24 no.4
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• pp.301-307
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• 2003

In this study, we Presented computational results on the blood flow in the sac of the Korean artificial heart. Two dimensional unsteady flow was assumed and we utilized a finite element commercial code ADINA to simulate the blood flow. Rigid body-solid contact were considered between the actuator and the blood sac and fluid-structure interaction between the blood and the sac. The three geometric models proposed in the design process were simulated to assess the hemodynamic characteristics of the models According to the computational results, a strong flow to the outlet and a stagnated flow region near the inlet were observed during systole. The sac was filled with blood and recirculating flow was generated near the outlet during diastole. Shear stress during systole had its extreme values near the outlet edge whereas the magnitude of shear stress values were relative)v high near the inlet edge and the contacting surface with the actuator.

• Journal of Korean Society of Forest Science
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• v.78 no.4
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• pp.412-418
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• 1989

The stem segments of Ailanthus altissima were cultured on the Murashige & Skoog's medium(1962) supplemented with 0.1 mg/l BAP and 1.0 mg/l 2, 4-D for callus induction and proliferation, Shoot primordia were observed as greenish regions on the surface of yellow-brown calli about 8 weeks after culture. Shoot primordia were selected and transferred to the MS media containing various combination of BAP and 2, 4-D. Among these combinations the shoot primordia cell clusters on the medium added to 0.5mg/l BAP and 0.01mg/l 2, 4-D exhibited the highest number of shoot formation. These shoots were successfully transferred on the solid MS medium with no growth regulators for the rootings.

• Journal of Industrial and Engineering Chemistry
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• v.68
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• pp.187-195
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• 2018

$Sr_{0.92}Y_{0.08}Ti_{1-x}Ni_xO_{3-{\delta}}$ (SYTN) was investigated in the presence of $H_2S$ containing fuels to assess the feasibility of employing oxide materials as alternative anodes. Aliovalent substitution of $Ni^{2+}$ into $Ti^{4+}$ increased the ionic conductivity of perovskite, leading to improved electrochemical performance of the SYTN anode. The maximum power densities were 32.4 and $45.3mW/cm^2$ in $H_2$ at $900^{\circ}C$ for the SYT anode and the SYTN anode, respectively. However, the maximum power densities in 300 ppm of $H_2S$ decreased by 7% and by 46% in the SYT and the SYTN anodes, respectively. To enhance the sulfur tolerance and to improve the electrochemical properties, the surface of SYTN anode was modified with samarium doped ceria (SDC) using the sol-gel coating method. For the SDC-modified SYTN anode, the cell performance was mostly recovered in the pure $H_2$ condition after 500-ppm $H_2S$ exposure in contrast to the irreversible cell performance degradation exhibited in the unmodified SYTN anode.

• Korean Journal of Metals and Materials
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• v.48 no.11
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• pp.995-1002
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• 2010

This study investigated the effect of process temperature on the alloying process during synthesis of $Sm_2Fe_{17}$ powder from ball-milled samarium oxide ($Sm_2O_3$) powders and a solid reducing agent of calcium hydrides ($CaH_2$) using iron nanopowder (n-Fe powder) by a reduction-diffusion (R-D) process. The $n-Fe-Sm_2O_3-CaH_2$ mixed powders were subjected to heat treatment at $850{\sim}1100^{\circ}C$ in $Ar-H_2$ for 5 h. It was found that the iron nanopowders in the mixed powders are sintered below $850^{\circ}C$ during the R-D process and the $SmH_2$ is synthesized by a reduced Sm that combines with $H_2$ around $850^{\circ}C$. The results showed that $SmH_2$ is able to separate Sm and $H_2$ respectively depending on an increase in process temperature, and the formed $Sm_2Fe_{17}$ phase on the surface of the sintered Fe nanopowder agglomerated at temperatures of $950{\sim}1100^{\circ}C$ in this study. The formation of the $Sm_2Fe_{17}$ layer is mainly due to the diffusion reaction of Sm atoms into the sintered Fe nanopowder, which agglomerates above $950^{\circ}C$. We concluded that nanoscale $Sm_2Fe_{17}$ powder can be synthesized by controlling the diffusion depth using well-dispersed Fe nanopowders.

• Bulletin of the Korean Chemical Society
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• v.19 no.6
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• pp.661-666
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• 1998

Active reaction sites and electrochemical O2 reduction kinetics on La_{1-x}Sr_xMnO_{3+{\delta}} (x=0.1-0.4)/YSZ (yttria-stabilized zirconia) electrodes are investigated in the temperature range of 700-900 ℃ at $Po_2=10^{-3}$-0.21 atm. Results of the steady-state polarization measurements, which are formulated into the Butler-Volmer formalism to extract transfer coefficient values, lead us to conclude that the two-electron charge transfer step to atomically adsorbed oxygen is rate-limiting. The same conclusion is drawn from the $Po_2$-dependent ac impedance measurements, where the exponent m in the relationship of $I_o$ (exchange current density) ∝ $P_{o_{2}}^m$ is analyzed. Chemical analysis is performed on the quenched Mn perovskites to estimate their oxygen stoichiometry factors (δ) at the operating temperature (700-900 ℃). Here, the observed δ turns out to become smaller as both the Sr-doping contents (x) and the measured temperature increase. A comparison between the 8 values and cathodic activity of Mn perovskites reveals that the cathodic transfer coefficients $({\alpha}_c)$ for oxygen reduction reaction are inversely proportional to δ whereas the anodic ones $({\alpha}_a)$ show the opposite trend, reflecting that the surface oxygen vacancies on Mn perovskites actively participate in the $O_2$ reduction reaction. Among the samples of x= 0.1-0.4, the manganite with x=0.4 exhibits the smallest 8 value (even negative), and consistently this electrode shows the highest ${\alpha}_c$ and the best cathodic activity for the oxygen reduction reaction.

• Smart Structures and Systems
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• v.24 no.6
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• pp.793-802
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• 2019

The centrifuge model test is usually used for two-dimensional deformation and instability study of the soil slopes. As a typical loose slope, the municipal solid waste (MSW) landfill is easy to slide with large deformation, under high water levels or large earthquakes. A series of centrifuge model tests of landfill slide induced by rising water level and earthquake were carried out. The particle image velocimetry (PIV), laser displacement transducer (LDT) and marker tracer (MT) methods were used to measure the deformation of the landfill under different centrifugal accelerations, water levels and earthquake magnitudes. The PIV method realized the observation of continuous deformation of the landfill model, and its results were consistent with those by LDT, which had higher precision than the MT method. The deformation of the landfill was mainly vertically downward and increased linearly with the rising centrifugal acceleration. When the water level rose, the horizontal deformation of the landfill developed gradually due to the seepage, and a global slide surface formed when the critical water level was reached. The seismic deformation of the landfill was mainly vertical at a low water level, but significant horizontal deformation occurred under a high water level. The results of the tests and analyses verified the applicability of PIV in the two-dimensional deformation measurement in the centrifuge model tests of the MSW landfill, and provide an important basis for revealing the instability mechanism of landfills under extreme hydraulic and seismic conditions.