• Geomechanics and Engineering
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• v.12 no.5
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• pp.863-870
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• 2017

With the increasing interest in using bacterial biofilms in geo-engineering practices, such as soil improvement, sealing leakage in earth structures, and hydraulic barrier installation, understanding of the contribution of bacterial biofilm formation to mechanical and hydraulic behavior of soils is important. While mechanical properties of soft gel-like biofilms need to be identified for appropriate modeling and prediction of behaviors of biofilm-associated soils, elastic properties of biofilms remain poorly understood. Therefore, this study investigated the microscale Young's modulus of biofilms produced by Shewanella oneidensis MR-1 in a liquid phase. The indentation test was performed on a biofilm sample using the atomic force microscopy (AFM) with a spherical indentor, and the force-indentation responses were obtained during approach and retraction traces. Young's modulus of biofilms was estimated to be ~33-38 kPa from these force-indentation curves and Hertzian contact theory. It appears that the AFM indentation result captures the microscale local characteristics of biofilms and its stiffness is relatively large compared to the other methods, including rheometer and hydrodynamic shear tests, which reflect the average macro-scale behaviors. While modeling of mechanical behaviors of biofilm-associated soils requires the properties of each component, the obtained results provide information on the mechanical properties of biofilms that can be considered as cementing, gluing, or filling materials in soils.

• Transactions of the Korean hydrogen and new energy society
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• v.23 no.1
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• pp.8-18
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• 2012

This paper presents a three-dimensional, transient cold-start polymer electrolyte fuel cell (PEFC) model to numerically evaluate the effects of membrane electrode assembly (MEA) design and cell location in a PEFC stack on PEFC cold start behaviors. The cold-start simulations show that the end cell experiences significant heat loss to the sub-freezing ambient and thus finally cold-start failure due to considerable ice filling in the cathode catalyst layer. On the other hand, the middle cells in the stack successfully start from $-30^{\circ}C$ sub-freezing temperature due to rapid cell temperature rise owing to the efficient use of waste heat generated during the cold-start. In addition, the simulation results clearly indicate that the cathode catalyst layer (CL) composition and thickness have an substantial influence on PEFC cold-start behaviors while membrane thickness has limited effect mainly due to inefficient water absorption and transport capability at subzero temperatures.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.160-160
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• 2017

Commercially pure titanium (Cp-Ti) and Ti alloys (typically Ti-6Al-4V) display excellent corrosion resistance and biocompatibility. Although the chemical composition and topography are considered important, the mechanical properties of the material and the loading conditions in the host have, conventionally. Ti and its alloys are not bioactive. Therefore, they do not chemically bond to the bone, whereas they physically bond with bone tissue. The electrochemical deposition process provides an effective surface for biocompatibility because large surface area can be served to cell proliferation. Plasma electrolyte oxidation (PEO) enables control in the chemical composition, porous structure, and thickness of the TiO2 layer on Ti surface. Silicon (Si) in particular has been found to be essential for normal bone and cartilage growth and development. Zinc (Zn) plays very important roles in bone formation and immune system regulation, and is also the most abundant trace element in bone. The objective of this work was to study on electrochemical behaviors of PEO-treated Ti-6Al-4V Alloy in solution containing Zn and Si ions. The morphology, the chemical composition, and the microstructure analysis of the sample were examined using FE-SEM, EDS, and XRD. The potentiodynamic polarization and AC impedance tests for corrosion behaviors were carried out in 0.9% NaCl solution at similar body temperature using a potentiostat. The promising results successfully demonstrated the immense potential of Si/Zn-TiO2 coatings in dental and biomaterials applications.

• Journal of Technologic Dentistry
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• v.21 no.1
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• pp.15-26
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• 1999

This study was carried out by observing to composition of oxide on the surface of dental porcelain low gold alloy with various Indium additions according to the degassing and analysing the change composition of additional elements In on diffusion behaviors of Porcelain-matal surface. The specimens used were Au-Pd-Ag alloys by small indium addition. These specimens were treated for 10min at $1000^{\circ}C$ in vacuum condition. To investigate the microsturcture of oxidized alloy surface, SEM and EDAX were used, and EPMA were used to investigate the diffusion behaviors of porcelain-metal surface. X-ray diffraction were used to observe the morphological changes in the oxidation zone. The results of this study were obtained as follows ; 1) The hardness of alloy increased with increasing amount of In addition. 2) The formation of oxidation increased with increasing In content after heat treatment. 3) Diffusion of indium elements increased with increasing In content in metal-porcelain surface after firing. 4) The oxidations of alloy surface were mainly $In_2O_3$.

• Journal of Magnetics
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• v.18 no.3
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• pp.240-244
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• 2013

The influences of Gallium doping on the magnetic microstructures and corrosion behaviors of Nd-Fe-B-Ti-C alloys are investigated. The cooling rate for obtaining fully amorphous structure is raised, and the glassforming ability is improved by the Ga addition. The High Resolution Transmission Electron Microscopy image shows that the ${\alpha}$-Fe and $Fe_3B$ soft magnetic phases become granular surrounded by the $Nd_2Fe_{14}B$ hard magnetic phase. The rms and $({\Delta}{\varphi})_{rms}$ value of Nd-Fe-B-Ti-C nanocomposite alloy thick ribbons in the typical topographic and magnetic force images detected by Magnetic Force Microscopy(MFM) decreases with 0.5 at% Ga addition. The corrosion resistances of $Nd_9Fe_{73}B_{12.6}C_{1.4}Ti_{4-x}Ga_x$ (x = 0, 0.5, 1) alloys are enhanced by the Ga addition. It can be attributed to the formation of more amorphous phases in the Ga doped samples.

• Nuclear Engineering and Technology
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• v.55 no.8
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• pp.2879-2888
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• 2023

In fusion environments, large scales of helium (He) atoms are produced by a radical transformation along with structural damage in structural materials, resulting in material swelling and degradation of physical properties. To understand its irradiation effects, this paper investigates the stability, electronic structure, energetics, charge density distribution, PDOS and TDOS, and diffusion processes of He impurities in 6HSiC materials. The formation energy indicates that a stable, favorable position for interstitial He is the HR site with the lowest energy of 2.40 eV. In terms of vacancy, the He atom initially prefers to substitute at pre-existing Si vacancy than C vacancy due to lower substitution energy. The minimum energy paths (MEPs) with migration energy barriers are also calculated for He impurity by interstitial and vacancy-mediated diffusion. Based on its calculated energy barriers, the most possible diffusion path includes the exchange of interstitial and vacancy sites with effective migration energies ranging from 0.101 eV to 1.0 eV. Our calculation provides a better understanding of the stabilization and diffusion behaviors of He impurities in 6H-SiC materials.

• The Korean Journal of Rehabilitation Nursing
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• v.18 no.1
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• pp.57-66
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• 2015

Purpose: This study aimed to explore and describe nurses' prejudice toward foreigners. Methods: The participants in the current study were 16 nurses who had worked in university hospitals. Data were collected using focus group interviews and an inductive content analysis was conducted with three focus groups. Results: The contents with regard to prejudice toward foreigners were categorized into three themes: prejudice formation, triggers of prejudice and prejudiced behaviors. The participants' prejudice toward foreigners as instigated by appearances, attitudes, or the national economic statuses of foreigners were added to the prejudice which had been formed previously. Prejudiced behaviors included discriminative attitudes, devotion withdrawal, defensive behavior, or derision. Conclusion: The findings of this study indicate that nurses may have positive or negative prejudices toward certain foreigners, which can affect their nursing practice. These findings also warrant the development of programs designed to increase awareness of and reduce nurses' prejudice toward foreigners.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.29-46
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• 1999

The performance based design obligates quantitative assessment of required performances by means of transparent and objective science. In this design scheme, simulation of both macro and micro-scale structural behaviors is thought to be a powerful tool. This paper proposes a way how to unify the structural safety and serviceability check method and durability assessment of RC structures. Though component chemical-physical processes are crudely assumed, system dynamics of micro-scale pore structure formation and macro-scale defects and deformation of structures was shown as possible and promising approach in future. The authors understand that the unification of structural and durability design has just started. For further progress and development, predictive tool of structural behaviors from birth to death of concrete under any specified environment and load serves as an essential technicality.

• Carbon letters
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• v.2 no.3_4
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• pp.182-191
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• 2001

Quinoline insoluble formed by the heat treatment was hot-pressed near its softening point. The green body was stabilized in the temperature range of $300{\sim}400^{\circ}C$ and subsequently carbonized below $1300^{\circ}C$ in an argon atmosphere. The behaviors of QI formation was examined with varying the heat treatment temperature and the lapse of time of the sample carbonized at various temperatures. And the mechanical property, corrosion resistance, and friction behavior were also measured optimum content of mesophase pitch ensured a dense structure and high $LC_{(002)}$ value, which resulted in high mechanical properties, good corrosion resistance, and low-stable friction behavior.

• Journal of the Korean Chemical Society
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• v.39 no.5
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• pp.379-383
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• 1995

The elution behaviors of stannous ion by PSA(phenol sulfonic acid) as an eluent on chelating resin, Amberlite IRC-718 have been investigated. When 0.10 M stannous solution was adsorbed on the resin and eluted with various concentrations of PSA, the two peaks of stannous ion were appeared in the elution curve. These two peak areas were changed according to the PSA concentration. Using these results, the stability constant of the complex formation between Sn2+ and PSA was calculated. This value is 2.0 ${\times}$ 10-1.