• Journal of the Architectural Institute of Korea Structure & Construction
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• v.35 no.5
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• pp.153-160
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• 2019

The purpose of this study was to investigate the mechanical and durability characteristics of latex-modified concrete using ultra rapid hardening cement : four types of mechanical tests including compressive strength, modulus of elasticity, flexural strength and bond strength were performed; and seven types of durability tests including resistance of concrete to chloride ion penetration, freeze-thaw resistance, scaling resistance, coefficient of thermal expansion, cracking tendency, abrasion resistance and drying shrinkage were performed. Required material performance of each test was determined in accordance with the Korea specification for repair of concrete and pavement repairing materials. The test results satisfied the required material performances, and presented a good mechanical and durability characteristics. In particularly, the materials showed early development of compressive strength, flexural strength and bond strength at 3 and 4 hours after curing. SEM photos were also taken to investigate the micro structures of the materials after chloride ion penetration test.

• Korean Journal of Materials Research
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• v.32 no.4
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• pp.186-192
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• 2022

Collagen is one of the most widely used biological materials in medical design. Collagen extracted from marine organisms can be a good biomaterial for tissue engineering applications due to its suitable properties. In this study, collagen is extracted from fish skin of Ctenopharyngodon Idella; then, the freeze drying method is used to design a porous scaffold. The scaffolds are modified with the chemical crosslinker N-(3-Dimethylaminopropyl)-N'-ethyl carbodiimide hydrochloride (EDC) to improve some of the overall properties. The extracted collagen samples are evaluated by various analyzes including cytotoxicity test, SDS-PAGE, FTIR, DSC, SEM, biodegradability and cell culture. The results of the SDS-PAGE study demonstrate well the protein patterns of the extracted collagen. The results show that cross-linking of collagen scaffold increases denaturation temperature and degradation time. The results of cytotoxicity show that the modified scaffolds have no toxicity. The cell adhesion study also shows that epithelial cells adhere well to the scaffold. Therefore, this method of chemical modification of collagen scaffold can improve the physical and biological properties. Overall, the modified collagen scaffold can be a promising candidate for tissue engineering applications.

• Journal of the Korean Wood Science and Technology
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• v.35 no.5
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• pp.46-57
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• 2007

The leachability of boron in zinc borate (ZB)-modified oriented strandboard (OSB) from southern wood species was investigated in this study. The leaching experiments were conducted by exposing edge-sealed OSB samples under running water at $31^{\circ}C$ for 8, 24, 72, and 216 h. The results from leached samples were compared with those from the unleached controls. Boron leaching of the modified OSB occurred upon the initial water exposure, and the leaching rate decreased as the leaching time increased. Initial boric acid equivalent (BAE) level, wood species, and sample thickness swelling significantly influenced the leachability. There was no consistent effect of polyethylene glycol (PEG) on zinc borate leaching. The glue-line washing within OSB due to thickness swelling of the test samples under water and decomposition of the borate to form water-soluble boric acid were thought to be two possible causes for the observed leaching. The relationship between assayed BAE and leaching time followed a decaying exponential function for zinc borate treated OSB. From the boron/zinc ratio after each leaching period, boron element in ZB was more or less leachable. The material constant of the regression models allowed comparing the leachability of the modified OSB for various wood species. An unified leaching method for treated wood composite materials is needed.

• Fibers and Polymers
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• v.1 no.2
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• pp.103-110
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• 2000

Flow analysis of profile extrusion is essential for design and production of a profile extrusion die. Velocity, pressure, and temperature distribution in an extrusion die are predicted and compared with the experimental results. A two dimensional numerical method is proposed for three dimensional analysis of the flow field within the profile extrusion die by applying a modified cross-sectional numerical method. Since the cross-sectional shape of the die is varied gradually, it is assumed that the pressure is constant within a cross-sectional plane that is perpendicular to the flow direction. With this assumption, the velocity component in the cross-sectional direction is neglected. The exact cross-sectional shape at any position is calculated based on the geometry of standard cross-sections. The momentum and energy equations are solved with proper boundary conditions at a cross-section and then the same calculation is carried out for the next cross-section using the current calculated values. An L-shaped profile extrusion die is produced and employed for experimental investigation using a commercially available polypropylene. Numerical prediction for the varying cross-sectional shape provides better results than the previous studies and is in good agreement with the experimental results.

• Korean Journal of Materials Research
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• v.14 no.2
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• pp.101-109
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• 2004

The influences of solidification rates and carbon contents on the formation of the $\delta$-ferrite were studied by directional solidification in modified 12%Cr-l %Mo steels. Directional solidification experimental results showed that solidification microstructure depended on solidification rate and carbon content and chromium equivalent. The length of the mushy zone increased and the dendrite arm spacings decreased as the solidification rate increased. The volume fraction of the 8-ferrite decreased with increasing the solidification rate and carbon content. The volume fraction of the ferrite showed much higher at low solidification rates with planar and cellular interfaces than that at high solidification rates with dendritic interface. It is expected that macro-segregation of C causes lower C content at the lower solidification fraction in the directionally solidified sample, where lower C results in higher volume fraction of the ferrite. In order to estimate solidification microstructure in modified 12Cr-l%Mo steels, various solidification conditions, such as solidification rate, cooling rate, segregation, alloy composition, should be considered.

• Steel and Composite Structures
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• v.22 no.6
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• pp.1239-1259
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• 2016

The modified couple stress-based third-order shear deformation theory is presented for sigmoid functionally graded materials (S-FGM) plates. The advantage of the modified couple stress theory is the involvement of only one material length scale parameter which causes to create symmetric couple stress tensor and to use it more easily. Analytical solution for dynamic instability analysis of S-FGM plates on elastic medium is investigated. The present models contain two-constituent material variation through the plate thickness. The equations of motion are derived from Hamilton's energy principle. The governing equations are then written in the form of Mathieu-Hill equations and then Bolotin's method is employed to determine the instability regions. The boundaries of the instability regions are represented in the dynamic load and excitation frequency plane. It is assumed that the elastic medium is modeled as Pasternak elastic medium. The effects of static and dynamic load, power law index, material length scale parameter, side-to-thickness ratio, and elastic medium parameter have been discussed. The width of the instability region for an S-FGM plate decreases with the decrease of material length scale parameter. The study is relevant to the dynamic simulation of micro structures embedded in elastic medium subjected to intense compression and tension.

• Applied Chemistry for Engineering
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• v.33 no.2
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• pp.133-144
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• 2022

Fast-paced industrial and agricultural development generates large quantities of hazardous heavy metals (HMs), which are extremely damaging to individuals and the environment. Research in both academia and industry has been spurred by the need for HMs to be removed from water bodies. Advanced materials are being developed to replace existing water purification technologies or to introduce cutting-edge solutions that solve challenges such as cost efficacy, easy production, diverse metal removal, and regenerability. Water treatment industries are increasingly interested in activated carbon because of its high adsorption capacity for HMs adsorption. Furthermore, because of its huge surface area, abundant functional groups on surface, and optimal pore diameter, the modified activated carbon has the potential to be used as an efficient adsorbent. Metal-organic frameworks (MOFs), a novel organic-inorganic hybrid porous materials, sparked an interest in the elimination of HMs via adsorption. This is due to the their highly porous nature, large surface area, abundance of exposed adsorptive sites, and post-synthetic modification (PSM) ability. This review introduces PSM methods for MOFs, chemical modification of activated carbons (ACs), and current advancements in the elimination of Pb²⁺, Hg²⁺, and Cd²⁺ ions from water using modified MOFs and ACs via adsorption.

• Journal of Periodontal and Implant Science
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• v.29 no.3
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• pp.621-636
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• 1999

When mucoperiosteal flaps are positioned and sutured to desirable position, the wound contains several interface between tissues which differ fundamentally in composition & biological reaction. Thus the C-T surface of the flap will, on one hand, oppose another vascularized surface, and on the other, the avascular dental material for example, when root resoptions, fractured root, endodontic perforation, deep root carious lesions were filled with amalgam, glass ionomer, resin etc. Recently, a number of case report described the successful treatment of a subgingival root lesion with restorative material & free gingival graft, open flap surgery, but more objective research was needed . Most of study on restorative materials were concerned for cytotoxicity not for actual healing event on that materials and its influencing factors such as biocompatibility, surface wettability, surface topography . The aim of this in vitro study was to evaluate the effect of amalgam, resin modified glass ionomer, composite resin per se, and their surface roughness on the growth of human gingival fibroblast. The cells were obtained and placed on culture flask and incubated for 3 days with the prepared test materials. Then count the attached cell number with hemocytometer,(n=12) and 2 samples were examined with SEM about attachment cell morphology . Another 4 samples were evaluated on their surface roughness with Talysurf and average surface roughness value(Ra) were obtained. Statistical difference in attached cell number, roughness value were analyzed using ANOVA. The number of attached cell was as follows, for root dentin specimen 16.7${\pm}$4.41, resin modified glass ionomer 14.0${\pm}$4.15, resin 8.13${\pm}$3.63, amalgam 0.72${\pm}$3.33(${\times}10^3$). Between root dentin and resin-modified glass ionomer, no significant difference was observed, but resin, amalgam showed a significant less cell numbers than for root dentin, resin modified glass ionomer cement. SEM examination expressed many cell surface attachment apparatus in root dentin and resin modified glass ionomer specimens. For resin specimen, cell attachment was observed but exposed less appratus. The average surface roughness value are following results. Dentin specimen 0.6972${\pm}$ 0.104, resin modified glass ionomer 0.0822${\pm}$0.009, resin 0.0875${\pm}$0.005, amalgam 4.2145${\pm}$0.985(${\mu}m$). Between root dentin, resin-modified glass ionomer, and resin, no significant difference was observed, but amalgam showed a significant more rough surface than other groups. When evlauated the interrelationship between cell attachment and surface roughness, therefore, there was weak reverse correlation.(pearson correlation : - 0.593) These results suggest that resin modified glass ionomer have the favorable healing potential when used for subgingival restoration. And for relationship between cell attachment and surface characteristics, further investigations were needed.

• KCI Concrete Journal
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• v.13 no.2
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• pp.58-66
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• 2001

Recently, polymer-modified mortar has been studied for proposed use on industrial floors as top coat with thin thickness, typically 5~15mm. The purpose of this study is to evaluate basic properties of self-leveling materials using polymer dispersions as kinds of SBR, PAE, St/BA with thin coat (under 3mm). Superplasticizer and thickener have been included in the mixes to reduce bleeding and drying shrinkage as well as to facilitate the workability required. The self-leveling materials using four types of polymer dispersion are prepared with polymer-cement ratio which respectively range from 50% and 75%, and tested for basic characteristics such as unit weight, air content, flow, consistency change and adhesion in tension. From the test results, the self-leveling materials using PAE emulsion at curing age of 28days are almost equal to those of conventional floor using urethane and epoxy resin. The adhesion in tension of self-leveling mortars using SBR latex and PAE emulsion at curing age of 3days is over 17 kgf/cm$^2$(1.67MPa). Consistency change is strongly dependent on the type of polymer dispersion. It is concluded that the self-leveling materials using polymer dispersions can be used in the same manner as conventional floor using thermosetting resin in practical applications, in the selection of polymer dispersions.

• Journal of the Korean Ceramic Society
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• v.51 no.1
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• pp.1-6
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• 2014

Here we report improved photo-catalytic effect of $Ag_2S$ under visible light using carbon nano-tubes (CNT) modified with $Ag_2S$ nanoparticles. The optical properties, structural properties and compositional analysis, as well as the photo-electrochemical properties of the prepared composites were investigated. It was found that the photocurrent density, and the photo-catalytic effect, was increased by modification of CNT in this way. Compared with the separate effects of $Ag_2S$ and CNT nanoparticles, the photocatalytic effect of CNT-modified-with-$Ag_2S$ composites, increased significantly due to a synergistic effect between the CNT and the $Ag_2S$ nanoparticles.