• 대한기계학회논문집A
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• 제26권11호
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• pp.2328-2335
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• 2002

A hybrid composite material has many potential usage due to the high specific strength and the resistance to fatigue, when compared to other composite materials such as fiber reinforced plastic(FRP) and metal matrix composite(MMC). However, the fracture mechanism of hybrid composite material is extremely complicated because of the bonding structure of metals and FRP. In this study, Al 7075 sheets and carbon epoxy preprags were used to fabricate the hybrid composite. Recently, nondestructive technique has been used to evaluate the fracture mechanism of these composite materials. AE technique was used to clarify the microscopic damage behavior and failure mechanism of A17075/CFRP hybrid composite. It was found that AE paralneters such as AE event, energy and amplitude were effective to evaluate the failure process of Al 7075/CFRP composite. In addition, the relationship between the AE signal and the characteristics of fracture surface using optical microscope was discussed.

• Composites Research
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• 제12권4호
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• pp.62-70
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• 1999

건축 구조물의 재령이 증가함에 따른 손상은 구조물의 안전성 및 신뢰성 확보에 매우 심각한 문제이다. 최근에는 이렇게 손상을 입은 콘크리트 구조물의 보수 보강을 위해 탄소섬유시트가 광범위하게 사용되고 있지만 탄소섬유시트를 보강한 콘크리트의 파괴기구가 명확하게 규명되지 않았다. 따라서 본 연구에서는 탄소섬유시트를 보강한 콘크리트의 손상거동 및 미시적 파손기구를 이해하기 위해 4가지 경우의 시험편, 즉 순수한 콘크리트, 철근 보강 콘크리트, 탄소섬유시트 보강 콘크리트, 철근과 탄소섬유시트 보강 콘크리트 시험편에 대하여 3점 굽힘 시험을 실시하였다. 이러한 시험편들의 파손기구를 명확히 하기 위해 음향방출기법이 사용되었으며 균열 발생, 성장을 모니터링하기 위해 2차원 AE 발생원 위치추정 기법이 적용되었다.

• Toxicological Research
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• 제33권2호
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• pp.149-156
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• 2017

The purpose of this study was to investigate the wound healing effect of acai berry water extracts (ABWE) and a possible underlying mechanism involved in its action using various in vitro and in vivo models. The wound healing effect of ABWE was evaluated by migration assay using HS68 fibroblast cells. In addition, its effect on mRNA expression of procollagen, fibronectin, and MMP-1 was determined. Moreover, the wound healing effect of ABWE was evaluated in in vivo wound models through macroscopic and microscopic observation. In addition, mRNA expression levels of wound related genes were determined. Results revealed that ABWE was not cytotoxic. It increased migration of HS68 fibroblast cells. ABWE increased mRNA expression levels of fibronectin but decreased the mRNA expression levels of MMP-1. ABWE also showed significantly potent wound healing effect in vivo based on macroscopic and histopathological observation and mRNA expression evaluation for wound related genes. Taken together, our results indicated that ABWE might have potential as a wound healing agent.

• Bulletin of the Korean Chemical Society
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• 제29권3호
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• pp.580-584
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• 2008

Second-order rate constants (kN) have been measured spectrophotometrically for reactions of Y-substituted phenyl benzoates (1a-h) with azide ion (N3) in 80 mol % H2O/20 mol % DMSO at 25.0 0.1 oC. The Brnsted-type plot for the azidolysis exhibits a downward curvature, i.e., the slope (b lg) changes from 0.97 to 0.20 as the basicity of the leaving group decreases. The pKao (defined as the pKa at the center of the Brnsted curvature) is 4.8, which is practically identical to the pKa of the conjugate acid of N3 ion (4.73). Hammett plots correlated with s o and s constants exhibit highly scattered points for the azidolysis. On the contrary, the corresponding Yukawa-Tsuno plot results in an excellent linear correlation with r = 2.45 and r = 0.40, indicating that the leaving group departs in the rate-determining step. The curved Brnsted-type plot has been interpreted as a change in the rate-determining step in a stepwise mechanism. The microscopic rate constants (k1 and k2/k1 ratio) have been calculated for the azidolysis and found to be consistent with the proposed mechanism.

• Bulletin of the Korean Chemical Society
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• 제28권2호
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• pp.220-224
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• 2007

Second-order rate constants (kN) have been determined spectrophotometrically for reactions of 2,4-dintrophenyl 2-furoate (2) with a series of alicyclic secondary amines in 80 mol % H2O/20 mol % dimethyl sulfoxide (DMSO) at 25.0 oC. The furoate 2 is more reactive than 2,4-dintrophenyl benzoate (1) toward all the amines studied. The higher acidity of 2-furoic acid (pKa = 3.16) compared with benzoic acid (pKa = 4.20) has been suggested to be responsible for the reactivity order, at least in part. The Brønsted-type plots for the reactions of 1 and 2 are curved downwardly, indicating that the aminolyses of both 1 and 2 proceed through a zwitterionic tetrahedral intermediate (T±) with a change in the rate-determining step on changing the amine basicity. Dissection of the kN values into their microscopic rate constants has revealed that the pKao and k2/k-1 ratios for the reactions of 1 and 2 are identical, indicating that the nature of the nonleaving group (i.e., benzoyl and 2-furoyl) does not affect the reaction mechanism. The k1 values have been found to be larger for the reactions of 2 than for those of 1, which is fully responsible for the fact that the former is more reactive than the latter.

• Journal of Yeungnam Medical Science
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• 제39권3호
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• pp.200-205
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• 2022

Pain from nervous or musculoskeletal disorders is one of the most common complaints in clinical practice. Corticosteroids have a high pain-reducing effect, and their injection is generally used to control various types of pain. However, they have various adverse effects including flushing, hyperglycemia, allergic reactions, menstrual changes, immunosuppression, and adrenal suppression. Pulsed radiofrequency (PRF) is known to have a pain-reducing effect similar to that of corticosteroid injection, with nearly no major side effects. Therefore, it has been widely used to treat various types of pain, such as neuropathic, joint, discogenic, and muscle pain. In the current review, we outlined the pain-reducing mechanisms of PRF by reviewing previous studies. When PRF was first introduced, it was supposed to reduce pain by long-term depression of pain signaling from the peripheral nerve to the central nervous system. In addition, deactivation of microglia at the level of the spinal dorsal horn, reduction of proinflammatory cytokines, increased endogenous opioid precursor messenger ribonucleic acid, enhancement of noradrenergic and serotonergic descending pain inhibitory pathways, suppression of excitation of C-afferent fibers, and microscopic damage of nociceptive C- and A-delta fibers have been found to contribute to pain reduction after PRF application. However, the pain-reducing mechanism of PRF has not been clearly and definitely elucidated. Further studies are warranted to clarify the pain-reducing mechanism of PRF.

• Nuclear Engineering and Technology
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• 제55권1호
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• pp.12-24
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• 2023

With the improvement of laser technology, the strategic needs of efficient and precise decontamination of various components in nuclear application units can be fulfilled by laser decontamination. The surface contaminants of nuclear facilities mainly exist both as loose contaminated layer and fixed oxide layer. The types of radionuclides and contamination layer thickness are closely related to the operation status of nuclear facilities, which have an important influence on the laser decontamination process. This study reviewed the mechanism of laser surface treatment and the influence of laser process parameters on the decontamination thickness, decontamination factor, decontamination efficiency and the distribution of aerosol particle. Although multiple studies have been performed on the mechanism of laser processing and laser decontamination process, there are few studies on the microscopic process mechanism of laser decontamination and the influence of laser decontamination on surface properties. In particular, the interaction between laser and radioactive contaminants needs more research in the future.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2003년도 추계학술발표대회 논문집
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• pp.54-54
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• 2003

We have developed a Cu-based bulk amorphous composite reinforced with a micron-sized crystalline phase, the (Cu60Zr30Ti10)95Ta5 amorphous matrix composite. The composite demonstrates the ultimate strength of 2332 MPa with a dramatically enhanced fracture strain of 15.3 %. Macroscopic observation of the fractured (Cu60Zr30Ti10)95Ta5 amorphous matrix composite showed the development of multiple shear bands along with numerous branching and deflection of shear bands. Microscopic observation on the amorphous matrix of the composite showed that cracks propagate through the residual amorphous matrix located between nanocrystallites, which had formed during deformation. Simulations based on finite element method were conducted to understand the formation mechanisms of multiple shear bands, the initiation site of shear bands, and interaction of shear bands with crystalline particles. Other microscopic fracture mechanism responsible for the enhanced plasticity was discussed.

• 한국실내디자인학회논문집
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• 제20권4호
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• pp.37-45
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• 2011

This thesis sets out to study the immanent mechanism of architecture which had classified as external spaces in general. As human controls a space, it controls or manages human's behavior, too. This study is depended on the humanities to analyze a various operation of power in the architectural space. It makes a comparative study of a space-power in a dwelling space through a discourse of Michel Foucault and Jacques Lacan, in particular everyday's microscopic scope. According to analytical results, the space-power of dwelling falls under the influence of a spacial arrangement and subject's desire. It has shown a noticeable characteristics in aspects production & consumption, using behavior, and use value. As it is seen through the aspects of production & consumption, owns of the space-power in a dwelling could not be its subject. We have also understood about a physicalistic furniture at the using behavior, it has a special power unconsciously to control a human's action and lifestyle. And then in the aspects of use value, the centric theme is a television. It lies on the core of space-power in dwelling, because is profoundly related to an innate respect of a dwelling value. In conclusion, so this study has the important meaning in the side to offer some interpretative possibility about the architectural space-power through a microscopic structure.

• Corrosion Science and Technology
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• 제17권1호
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• pp.1-5
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• 2018

As structural materials, magnesium (Mg) alloys have been widely used in the fields of aviation, automobiles, optical instruments, and electronic products. There are few studies on the effect of coating conditions on the compositional variation during the formation process of the conversion coatings. Rare-earth based conversion coating on AZ91 magnesium alloy was prepared in ceric sulfate and hydrogen peroxide contained solution. The element composition and valence as well as their distribution in the coating were analyzed with energy dispersive X-ray spectroscopy (EDS), Electron probe micro-analyzer (EPMA), X-ray photoelectron spectroscopy (XPS). The effect of treating process on the element composition were also studied. It was found that the conversion coating surface consists of Mg, Al, O, Ce, and the weight content of Ce in the coating was affected by the treating solution concentration and immersion time; the Ce element was distributed in the coating non-uniformly and existed in the form of $Ce^{+3}$ and $Ce^{+4}$, while the O element existed in the form of $OH^-$, $O^{2-}$, $H_2O$. Based on microscopic analysis results, the electrochemical deposition mechanism on the micro-anode and micro-cathode in the process of the coating growth was suggested.