• Polymer(Korea)
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• v.29 no.1
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• pp.87-90
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• 2005

In this study, we have examined the exfoliation behavior of layered clay during in-situ polymeriztion with styrene by using real-time XRD analysis. The 4C1 beam line at the Pohang Accelerator Laboratory (PAL) was used for this study. Different exfoliation behaviors have been shown to depend on the cation exchange capacity (CEC) of clay and the chemical structure of organic modifiers. For 10A-MMT and 15A-MMT having high CEC, no peak shifts were observed on real-time XRD analysis during polymerization. However, 2$\theta$ for 25A-MMT and VDAC-MMT, each having low CEC’s as well as aromatic benzene moieties and vinyl groups, respectively, decreased as polymerization time increased.

• Journal of the Korea Concrete Institute
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• v.23 no.2
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• pp.169-176
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• 2011

In this study, the flexural test for reinforced high performance fiber reinforced cementitious composites (R/HPFRCC) members has been conducted in order to investigate the flexural behavior including the effect of an ordinary tensile reinforcing bar. Through the test, it was observed that the flexural strength increased due to the stable tensile stress transfer of HPFRCC, even up to the ultimate state. In addition, no localized crack appeared until the yielding of the reinforcement. From the layered section analysis of the tested members, it was found that the analysis with the tensile model obtained from the tension stiffening test showed better agreement with the flexural test results, whereas the analysis with direct tension test results overestimated the flexural capacity. Through the experimental and analytical studies, two flexural failure modes have been defined in this paper; concrete crushing at the top compression layer or tensile failure at the bottom tensile layer of the beam section. Based on these two flexural failure modes, a simple formula that estimates the ultimate flexural strength of the member has been proposed in this paper. The proposed equations can be useful in a design and an analysis of R/HPFRCC members.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.1
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• pp.216-221
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• 2017

Reducing optical reflection in the visible light range, in order to increase the share of transmitted light and avoid the formation of ghost images in imaging, is important for polymer lens applications. In this study, polymer lenses with refractive indices of n=1.56, 1.60, and 1.67 were fabricated by the injection-molding method with a polymer lens monomer, dibutyltin dichloride as the catalyst and an alkyl phosphoric ester as the release agent. To investigate their anti-reflection (AR) effects, various AR coating structures, viz. a multi-layer AR coating structure, tri-layer AR coating structure with a discrete approximation Gaussian gradient-index profile, and tri-layer AR coating structure with a quarter-wavelength approximation, were designed and coated on the polymer lens by an E-beam evaporation system. The optical properties of the polymer lenses were characterized by UV-visible spectrometry. The material properties of the thin films, refractive index and surface roughness, were analyzed by ellipsometry and AFM, respectively. The most effective AR coating structure of the polymer lens with low refractive index, n=1.56, was the both side coating of multi-layer AR coating structure. However, both side coating of the tri-layered discrete approximation Gaussian gradient-index profile AR coating structure gave comparable results to the both side coating of the multi-layer AR coating structure for the polymer lens with a high refractive index of n=1.67.

• Journal of Bio-Environment Control
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• v.21 no.4
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• pp.428-436
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• 2012

This study aimed to develop the multi-span plastic greenhouse which is suitable for tomato cultivation and is safe against climatic disasters such as typhoon or heavy snow. The width and heights of eaves and ridge of newly developed tomato greenhouse are 7, 4.5 and 6.5 m, respectively. The width is the same but the eaves and ridge heights are 1.8 and 2 m higher than conventional 1-2 W greenhouses, respectively. Cross beam has been designed as a truss structure so it can sustain loads of tomato and equipment. Tomato greenhouse has been designed according to climatic disaster preventing design standard maintaining the high height. In other words, the material dimensions and interval of materials including column and rafter have been set to stand against $40m{\cdot}s^{-1}$ of wind and 40 cm of snow. Tomato greenhouse has been equipped with rack-pinion type roof vents which have been used in glass greenhouse in order to prevent excessive rise in air temperature. This vent type is different from that of 1-2 W type greenhouse which is made by rolling up and down the vinyl at upper part of column. Roof vents are installed at ridge, and thus external air inflow and natural ventilation are maximized. As the height increases, heating cost increase as well and, therefore, tomato greenhouse has been equipped with multi-layered thermal curtain, of which thermo-keeping is excellent, to prevent heat from escaping.