• Journal of the Korean Ceramic Society
• /
• v.30 no.6
• /
• pp.457-468
• /
• 1993

In oxide matrix-SiC(W) composites, instability and glassy phase formation due to oxidation at the high temperature and the diffusion of Si, respectively, cause brittle fracture and low reliability for ceramic materials. The mode of contribution in each mechanisms induced by matrix-whisker debonding, varies with the morphology of matrix-whisker interfaces. This work has described the dispersion behaviours and stabilization mechanisms in slip systems, and multiple toughening mechanisms by dint of two second phase different from each other when spherical ZrO2 and chemically stable Al2O3(W) is respectively added in Al2O3 matrix. To obtain complexshaped components, slip casted bodies were sintered at 1$600^{\circ}C$, 2hrs up to 98~99% R.D.. Multiple toughening mechanisms in comparison with theories reported until now will be discussed as a result of the phase analysis of ZrO2 by athermal behaviours and microstructural characterizations as well as measured mechanical properties.

• Structural Engineering and Mechanics
• /
• v.72 no.1
• /
• pp.19-30
• /
• 2019

The mechanical behavior of Fiber Reinforced Cementitious Composites (FRCC) under direct shear is studied through experiment and analytical simulation. The cementitious composite considered contains 55% replacement of cement with fly ash and 2% (volume ratio) of short discontinuous synthetic fibers (in the form of mass reinforcement, comprising PVA - Polyvinyl Alcohol fibers). This class of cementitious materials exhibits ductility under tension with the formation of multiple fine cracks and significant delay of crack stabilization (i.e., localization of cracking at a single location). One of the behavioral parameters that concern structural design is the shear strength of this new type of fiber reinforced composites. This aspect was studied in the present work with the use of Push-off tests. The shear strength is then compared to the materials' tensile and splitting strength values.

• Journal of Microbiology and Biotechnology
• /
• v.24 no.4
• /
• pp.522-533
• /
• 2014

Bionanotechnology has revolutionized nanomaterial synthesis by providing a green synthetic platform using biological systems. Among such biological systems, microalgae have tremendous potential to take up metal ions and produce nanoparticles by a detoxification process. The present study explores the intracellular and extracellular biogenic syntheses of silver nanoparticles (SNPs) using the unicellular green microalga Scenedesmus sp. Biosynthesized SNPs were characterized by AAS, UV-Vis spectroscopy, TEM, XRD, FTIR, DLS, and TGA studies and finally checked for antibacterial activity. Intracellular nanoparticle biosynthesis was initiated by a high rate of $Ag^+$ ion accumulation in the microalgal biomass and subsequent formation of spherical crystalline SNPs (average size, 15-20 nm) due to the biochemical reduction of $Ag^+$ ions. The synthesized nanoparticles were intracellular, as confirmed by the UV-Vis spectra of the outside medium. Furthermore, extracellular synthesis using boiled extract showed the formation of well scattered, highly stable, spherical SNPs with an average size of 5-10 nm. The size and morphology of the nanoparticles were confirmed by TEM. The crystalline nature of the SNPs was evident from the diffraction peaks of XRD and bright circular ring pattern of SAED. FTIR and UV-Vis spectra showed that biomolecules, proteins and peptides, are mainly responsible for the formation and stabilization of SNPs. Furthermore, the synthesized nanoparticles exhibited high antimicrobial activity against pathogenic gram-negative and gram-positive bacteria. Use of such a microalgal system provides a simple, cost-effective alternative template for the biosynthesis of nanomaterials in a large-scale system that could be of great use in biomedical applications.

• Journal of Korean Society on Water Environment
• /
• v.40 no.2
• /
• pp.79-88
• /
• 2024

This study employed field measurements and biogeochemical analysis to examine the effects of seasonal conditions (e.g., temperature and precipitation) and human intervention (e.g., dam or weir construction) on the chemical composition of dissolved organic matter, flocculation kinetics of suspended particulate matter, and formation of the fluid mud layer on riverbeds. The results indicated that a water environment with a substantial amount of biopolymers offered favorable conditions for flocculation kinetics during an algal bloom period in summer; a thick fluid mud layer was found to be predominated with cohesive materials during this period. However, after high rainfall, a substantial influx of terrigenous humic substances led to enhanced stabilization of the particulate matter, thereby decreasing flocculation and deposition, and the reduced biopolymer composition served to weaken the erosion resistance of the fluid mud on the riverbed. Moreover, a high-turbulence condition disaggregated the flocs and the fluid mud layer and resuspended the suspended particulate matter in the water column. This study demonstrates the mutual relationship that exists between biogeochemistry, flocculation kinetics, and the formation of the fluid mud layer on the riverine area during different seasons and under varying hydrological conditions. These findings are expected to eventually help inform the more optimal management of water resources, which is an urgent task in the face of anthropogenic stressors and climate change.

• Journal of the Korean Chemical Society
• /
• v.30 no.2
• /
• pp.248-258
• /
• 1986

The electronic structures and geometries of model substituted oxiranes, and carbonyl ylides containing cyano, methoxy and thiomethoxy substituents were investigated by MNDO-SCF-MO method. Stabilization and geometries caused by substituents, the ease of formation of carbonyl ylides from oxiranes and the reactivities of the cycloaddition of substituted carbonyl ylides were investigated.

• Journal of the Korean Chemical Society
• /
• v.29 no.4
• /
• pp.356-364
• /
• 1985

Ab initio calculations with STO-3G method were carried out on isomers of isobutylene dianion and dilithioisobutylene, and geometry, energy and Mulliken population were discussed. Energy of reaction, ${\Delta}$E, for isodesmic processes involving these species and relative heats of formation, ${\Delta}H_f$, estimated with ${\Delta}$E have shown that the contribution of "Y-aromaticity" to the structural stabilization of Y-type dianion is a tenuous one but the alkylation appears to proceed via the Y-type dilithio compound.

• Journal of the Korean Graphic Arts Communication Society
• /
• v.22 no.1
• /
• pp.83-94
• /
• 2004

PSR ink is used to insulation coating material that heat resistance is. The use purpose is used for bridge prevention, circuit protection, stabilization of insulation. Heat-cured resin was used mainly on the materials of PSR inks. But, UV-curing type resin in used. Also, because of recently environmental problem, ink is going to water type. Purpose of this study is to develop PSR ink that can develop in pure water. and experiment did that do from that find suitable oligomer and monomer and does brand ratio differ. Specially Knew that is extent water soluble UV resin develop possible is DPHA 10~50% that A/A1924 is 50~90wt %, monomer. As a result, when ratio of A/A1924 and DPHA low viscosity epoxy resin is 5:1.5:1.5, could get high sensibility pattern repeatability, tack and alkali-resistance.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.33 no.4
• /
• pp.425-429
• /
• 2009

The protection for copper tarnish was developed by surface treatment method and volatile corrosion inhibiting (VCI) technology. The performance of surface treatment and VCI material is also examined in simulated test environment. Benzotriazole (BTAH) solution that contained molybdate showed best performance than others. Usage of VCI materials with surface treatment was more effective. The protection film foamed on the surface of copper was investigated by auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). Molybdate does not participate in the formation of the protective film but promotes the passivation effect. This facilitates the stabilization of the cuprous oxide film, and strengthens the adsorption of BTAH.

• 한국연소학회:학술대회논문집
• /
• 2012.04a
• /
• pp.253-255
• /
• 2012

This study has numerically investigated the combustion processes in the bilayer porous media. To account for the velocity transition and diffusion influenced by solid matrix, porosity effects are included in the governing equations. Heat transfer coefficient is calculated by Nusselt number to reflect the effect of gas velocity, pore diameter, and material properties. Numerical results indicate that the present approach is capable of the essential features of the premixed combustion in the porous burner, in terms of the precised flame structure, pollutant formation, and flame stabilization. It is also found that heat transferred from the downstream flame zone is conducted to the upstream flame region through the solid matrix and the preheated mixture. By increasing the inlet velocity, the solid temperature of upstream is cooling down.

• Proceedings of the SCSK Conference
• /
• 2003.09b
• /
• pp.313-318
• /
• 2003

Vitamin C's function and mechanism are comparatively well known among the several kinds of vitamins. Inhibition of free radical. promotion of collagen synthesis, restraint of melanin formation and resolution of melanin are its main functions. But Vitamin C is very easy to oxidize by heat, moisture or air so it causes stability problem to make formulation. To solve these problems unique formulating method or derivatives using method could be effective. Object: First, stabilize 10% of Ascorbic acid as polyol/silicone emulsion and try to make polyol/silicone/polyol anhydrous multiple emulsion secondly. And then, encapsulate with porous power to enhance the stability of Ascorbic Acid from formulating method.