• 한국재료학회지
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• 제23권11호
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• pp.643-648
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• 2013

Activated carbon (AC) was synthesized from rice husks using the chemical activation method with KOH, NaOH, a combination of (NaOH + $Na_2CO_3$), and a combination of (KOH + $K_2CO_3$) as the chemical activating reagents. The activated carbon with the highest surface area (around $2000m^2/g$) and high porosity, which allows the absorption of a large number of ions, was applied as electrode material in electric double layer capacitors (EDLCs). The AC for EDLC electrodes is required to have a high surface area and an optimal pore size distribution; these are important to attain high specific capacitance of the EDLC electrodes. The electrodes were fabricated by compounding the rice husk activated carbons with super-P and mixed with polyvinylidene difluoride (PVDF) at a weight ratio of 83:10:7. AC electrodes and nickel foams were assembled with potassium hydroxide (KOH) solution as the electrolyte. Electrochemical measurements were carried out with a three electrode cell using 6 M KOH as electrolyte and Hg/HgO as the reference electrode. The specific capacitance strongly depends on the pore structure; the highest specific capacitance was 179 F/g, obtained for the AC with the highest specific surface area. Additionally, different activation times, levels of heating, and chemical reagents were used to compare and determine the optimal parameters for obtaining high surface area of the activated carbon.

• Nuclear Engineering and Technology
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• 제51권6호
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• pp.1633-1637
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• 2019

While considering the photon attenuation coefficient (${\mu}$) and its related parameters for photons shielding, it is necessary to account for its transmitted and reflected photons energy spectra and dose contribution. Monte Carlo simulation was used to study the efficiency of clay ($1.99g\;cm^{-3}$) as a shielding material below 150 keV photon. Am-241 gamma source and an X-ray of 150 kVp were calculated. The calculated value of ${\mu}$ for Am-241 is higher within 5.61% compared to theoretical value for a single-energy photon. The calculated half-value layer (HVL) is 0.9335 cm, which is lower than that of ordinary concrete for X-ray of 150 kVp. A thickness of 2 cm clay was adequate to attenuate 90% and 85% of the incident photons from Am-241 and X-ray of 150 kVp, respectively. The same thickness of 2 cm could shield the gamma source dose rate of Am-241 (1 MBq) down to $0.0528{\mu}Sv/hr$. For X-ray of 150 kVp, photons below 60 keV were significantly decreased with 2 cm clay and a dose rate reduction by ~80%. The contribution of reflected photons and dose from the clay is negligible for both sources.

• 대한금속재료학회지
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• 제50권4호
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• pp.338-343
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• 2012

The early osseointegration of titanium (Ti) dental implants is related to the initial cell morphology. The morphology of the cells (mesenchymal stem cells, MSC) was observed on three different Ti disc surfaces, which were mechanically treated by polishing, blasting, and scratching. A non-directional surface (isotropic texture) was obtained by the blasting of HA grits on cp-Ti discs, and a unidirectional surface (anisotropic texture) was obtained by the scratching of SiC papers. The cell attachment and arrangement in the initial periods were quite similar, but those in the later periods were significantly affected by the texture of the cp-Ti discs. After 1 week, the blasted Ti discs showed non-directional arrangement or spreading of the cells, whereas the scratched cp-Ti discs showed unidirectional properties parallel to the direction of the scratched grooves on the surface. The surface roughness of the cp-Ti discs significantly affects cell proliferation. Cell proliferation on the blasted and scratched surfaces was about 60% and 40% higher compared to the control result (polishing group) after 1 week (P<0.05). Cell proliferation on the blasted and scratched surfaces after 1 week was slightly enhanced with increasing surface roughness. It is believed that the direction of cell attachment and arrangement is closely related to the surface texture of the substrate surfaces, but cell proliferation after a relatively long period of time is directly enhanced by the surface roughness, not by the surface texture.

• Structural Engineering and Mechanics
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• 제83권4호
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• pp.551-561
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• 2022

In this paper, the effect of fire conditions according to ISO 834 standard on the behavior of carbon fibre-reinforced plastic (CFRP) reinforced steel beams coated with gypsum-based mortar has been investigated numerically. To study the efficiency of these beams, 3D coupled temperature-displacement finite element analyzes have been conducted. Mechanical and thermal characteristics of three different parts of composite beams, i.e., steel, CFRP plate, and fireproof coating, were considered as a function of temperature. The interaction between steel and CFRP plate has been simulated employing the adhesion model. The effect of temperature, CFRP plate reinforcement, and the fireproof coating thickness on the deformation of the beams have been analyzed. The results showed that within the first 120 min of fire exposure, increasing the thickness of the fireproof coating from 1 mm to 10 mm reduced the maximum temperature of the outer surface of the steel beam from 380℃ to 270℃. This increase in the thickness of the fireproof layer decreased the rate of growth in the temperature of the steel beam by approximately 30%. Besides excellent thermal resistance and gypsum-based mortar, the studied fireproof coating method could provide better fire resistance for steel structures and thus can be applied to building materials.

• Smart Structures and Systems
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• 제30권5호
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• pp.545-556
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• 2022

Through the examination of literatures, electronic commerce is a subject which is accepted in enterprises to define e-commerce adoption, trends, and issues that are assisting and obstructing its efficacy. E-commerce offers numerous advantages to consumer satisfaction in any place and helps the company to get a competitive benefit over its competitors. The Internet has expanded the scope of business. Many business information is available by the global network that supports information gathering between organizations, businesses and their clients, while various divisions of a business is increasing at an exponential rate. Meanwhile, there are a few barriers to proper e-commerce usage and adoption, such as reliable internet connections, poor e-commerce supporting infrastructures, logistics systems presenting socio-regulatory and poor transportation barriers and demonstrating the significant improvement of e-commerce reliable and affordable Internet provisions, i.e., Internet cost, intensity, and reasonable level of e-readiness. The operational and strategic significance of information-based virtual value chains for all organizations cannot be emphasized. As a consequence, this study confirms worldwide market elements of e-commerce, such as its issues, benefits, relevance, scope, facilitators and projects prospective obstacles in a developing economy.

• 대한치과보철학회지
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• 제58권1호
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• pp.14-22
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• 2020

목적: 본 연구의 목적은 보철 재료 표면에서 MnO₂-diatom microbubbler (DM)의 세균막 제거 효과를 기존에 치과 임상에 구강세정제로 사용되고 있는 성분들과 비교하여 이 재료가 구강세정제로 사용될 수 있는 가능성을 평가하는 것이다. 재료 및 방법: 이산화망간 나노 시트가 도핑된 DM을 만들었고, 주사전자현미경(SEM)을 이용하여 형태에 대한 관찰 및 도핑된 MnO₂의 성분 분석을 시행하였다. 3% 과산화수소수에서 DM의 반응을 시간에 따라 관찰하기 위해 실체 현미경을 이용하였다. 보철 재료 표면의 세균막 제거 효과를 평가하기 위해 비귀금속 합금, 지르코니아, 레진 시편을 제작하였고 치아우식의 원인균이며 호기성 세균인 Streptococcus mutans와 치주질환의 원인균이며 혐기성 세균인 Porphyromonas gingivalis 세균막을 각각 형성하였다. 형성된 세균막에 3% 과산화수소수와 DM을 처리하였을 때 세균막 제거 효과를 클로르헥시딘 글루코네이트와 3% 과산화수소수의 경우와 crystal violet 염색 실험을 통해 비교 평가하였다. 결과: 속이 빈 원통 형태의 규조류에 이산화망간 성분이 발견되었고, 3% 과산화수소수에서 기체를 만들어내는 것을 확인할 수 있었다. 실험에 이용된 모든 재료에서 DM을 처리한 군이 클로르헥시딘 글루코네이트나 3% 과산화수소수 단독으로 사용한 군에 비해 통계적으로 유의하게 세균막을 효과적으로 제거하였다. 결론: MnO₂-diatom microbubbler는 보철 재료 표면의 세균막을 기존의 구강세정제 성분에 비해 더 효과적으로 제거할 수 있다.

• 한국산학기술학회논문지
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• 제20권8호
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• pp.344-351
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• 2019

본 연구에서는 일개 대학교에 재학 중인 비보건학과와 보건학과계열의 대학생들을 대상으로 인성교육에 대한 인식과 요구도를 조사, 분석하여 보다 발전적인 인성교육의 과정을 개발하는데 기초자료를 마련하고 인성교육을 위한 제도적인 장치 설계에 필요한 유용한 기초정보를 제공하고자 수행하였다. 본 연구는 2018년 4월부터 5월까지 비보건계열과 보건계열학과에 재학하는 학생들을 대상으로 진행하였다. 설문에 참여한 학생은 총 206명으로, 비보건계열, 보건계열 학과 학생 모두 인성교육의 필요성, 중요성, 학습을 통한 인성발달 가능성 등의 항목에서 모두 높게 인식하는 것으로 나타났다. 인성역량에 따른 자기이해 수준에서는 모든 학과 학생들이 평균적으로 높게 나타났고, 특히 '배려'와 '책임' 항목에서 높은 수준을 보였다. 자기효능감 인식 차이에서는 '의지'에서 가장 낮은 인식수준을 보였다. 인성수준에 관한 응답에서는 모든 학생에서 본인들의 인성이 '높다' (42.1%)라고 응답을 하였으며, 현재 재학 중인 학교에서의 인성교육과정은 비보건계열과 보건계열 모두 '만족하지 않다'고 나타났다. 결과적으로 보건학과 계열에 재학 중인 학생들이 전체적으로 비보건계열 학생들보다는 높은 결과가 있었지만, 유의한 차이가 많지는 않았다. 이를 위해 학과에 구분 없이 대학생들에게 인성에 관한 전문성을 함양하도록 그 여건을 마련해 주고, 동시에 사회가 요구하는 인성을 갖춘 인재로 성장할 수 있도록 대학에서 체계적인 교육이 이루어져야 할 것이며, 학생들의 인성교육의 요구를 정확하게 파악하고 실천을 위한 구체적인 방안을 마련해야 한다고 본다.

• Korean Chemical Engineering Research
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• 제60권2호
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• pp.282-288
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• 2022

코로나 팬데믹 시대에서 비말(respiratory droplet)을 통한 감염 및 확산을 막기 위해 마스크는 없어서는 안 될 생활 필수품이 되었다. 본 연구에서는 두 가지 다른 타입의 마스크(KF-94 마스크와 덴탈 마스크)가 비말 차단에 얼마나 효과적인지를 파악하기 위하여, i) 각각의 마스크를 구성하고 있는 필터의 젖음성(wettability) 특성을 분석하고, ii) 필터 표면에 빠른 속도로 충돌하는 미소 액적의 동적 거동 특성을 실험적으로 관찰하였다. 각 필터의 구성 재료에 따라 상반된 젖음성 특성, 소수성(hydrophobicity) 또는 친수성(hydrophilicity)을 보임을 확인하였다. 또한, 일정 체적을 갖는 미소 액적을 안정적으로 토출하는 공압 조건을 탐색하고 액적의 충돌 속도 변화에 따른 액적 충돌 거동 변화를 분석하였다. 마스크를 구성하고 있는 필터의 종류와 액적 충돌 속도에 따라 i) 필터를 통과하지 못하거나(no penetration), ii) 필터에 포획(capture)되거나, iii) 필터를 통과(penetration)하는 등의 다른 충돌 후 거동을 보임을 확인하였다. 이러한 결과들은 비말 차단용 마스크 디자인에 있어 매우 기본적이고 유용한 정보를 제공할 뿐만 아니라, 다양한 다공성 표면에서의 액적 거동에 대한 학문적 연구에도 도움이 될 것으로 판단된다.

• Journal of Biosystems Engineering
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• 제39권2호
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• pp.122-133
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• 2014

Purpose: This study was to develop an effective process for fabricating biocompatible calcium phosphate powders (CPPs) using horse bones, and to investigate the characteristics of them. Methods: The characteristics of horse bone powders (HBPs) were investigated according to the different osseous tissue types (compact bone and cancellous bone), bone types (spine and tibia), pretreatment methods (cold water, $H_2O_2$, and hot water), sintering time (4, 8 and 12h), and sintering temperature (600, 900, 1100 and $1300^{\circ}C$). In addition, the grinding methods were compared based on the wet grinding (ball mill) and dry grinding (blade grinder) method to make it as powders. Finally, their cytotoxicity and cell viability were checked. Results: Regardless of the types of osseous tissues and bones, HBPs were well fabricated as biocompatible CPPs. It was also found that the pretreatment methods did not influence on the resultants, showing well-fabricated HBPs. Considering the processing time, the hot water method was the most suitable compared to other pretreatment methods. Further, 12h-sintering time was sufficient to remove residual organic compounds. The sintering temperatures greatly affected the properties of bone powders fabricated. The x-ray diffraction (XRD) peak of horse bone sintered at $600^{\circ}C$ was most closed to that of hydroxyapatite (HA). Our bioactivity study demonstrated that the HBPs fabricated by sintering horse bones at $1300^{\circ}C$ showed the best performance in terms of cell viability whereas the HBPs $1100^{\circ}C$ showed the cytotoxicity. Conclusions: Using various types of horse bone tissues, biocompatible CPPs were successfully developed. We conclude that the HBPs may have a great potential as biomaterials for various biological applications including bone tissue engineering.

• 한국전자현미경학회:학술대회논문집
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• 한국현미경학회 2005년도 제36차 추계학술대회 및 제4회 HVEM 이용자 워크샵
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• pp.127-129
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• 2005

Bacterial lipopolysaccharide(LPS) is can stimulate the most LPS-responsive cells in the mammalian host. The macrophage response to LPS can protect the host from infection but high levels, contribute to systemic inflammatory response syndrome and destruction of host itself, The previously study, secretory leukocyte pretense inhibitor (SLPI) was known LPS-induced product of macrophage and had the function that antagonizes their LPS-induced activation of pro-inflammation signaling factors. Purpose of this study was to identify the expression of SLPI involving the infection in various cell lines including odontoblast cell line. Therefore, we conducted in vitro researches, which treated the LPS to the MDPC-23, and compared to NIH3T3, RAW264.7. To investigate the expressionof SLPI in mRNA level, the methods was used RT-PCR and western blotting for protein expression of SLPI. Moreover, we performed the scanning electron microscopic (SEM) observation for the morphological change. This work was supported by Korea Science and Engineering Foundation.