• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.921-924
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• 2004

This paper is to investigate a crack for plasma sprayed MCrAlY coated material by acoustic emission method in 4-point bending test. The CoNiCrAlY is coated on Inconel-718 by vacuum plasma spray process. Micro-hardness measurement was conducted by means of Micro Vickers-hardness indentor. The porosity of coating layer was measured using a SEM and Image Analyzer. AE monitoring system is composed of PICO type sensor, a wide band preamplifier(40dB), a PC and AE DSP(16/32 PAC) board. The AE count, Hit and energy of coating specimens is measured according to coating thickness.

• The Korean Journal of Food And Nutrition
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• v.25 no.1
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• pp.123-131
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• 2012

The objective of the present study was to evaluate the potential antidiabetic and antioxidant effect of the ethanol extract from Chrysanthemum cornarium L. var. spatiosum(CSE) against alloxan-induced oxidative stress in pancreatic ${\beta}$-cells, HIT-T15. In this study, the antidiabetic effect of CSE was examined using the 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazoliu bromide(MTT) cell proliferation assay, lactate dehydrogenase(LDH) release assay, $NAD^+$/NADH ratio and insulin secretion. To further investigate whether CSE is involved in the antioxidant activity of alloxan-damaged HIT-T15 cells, its antioxidant effect against alloxan-induced oxidative stress was measured in HIT-T15 cells by determining the levels of antioxidant enzymes including superoxide dismutase(SOD), glutathione S-transferase(GST), glutathione reductase(GR) and glutathione peroxidase(GPx). The results of this analysis showed that alloxan significantly decreased cell viability, increased LDH leakage, and lowered $NAD^+$/NADH ratio and insulin secretion in HIT-T15 cells. However, CSE significantly increased the viability of alloxan-treated cells and lowered LDH leakage. The intracellular NAD+/NADH ratio and insulin secretion were also significantly increased by 1.7-fold and 1.3-fold, respectively, after treatment with 100 ${\mu}g/m{\ell}$ CSE. The HIT-T15 cells treated with alloxan showed significant decreases in the activities of antioxidant enzymes, while CSE significantly elevated the levels of antioxidant enzymes. These findings suggest that CSE could have a protective effect against cytotoxicity and dysfunction of pancreatic cells in the presence of alloxan-induced oxidative stress.

• Korean Journal of Plant Resources
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• v.25 no.2
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• pp.184-192
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• 2012

The present study was designed to examine the potential antidiabetic and antioxidant effect of ethanol extract from $Prunus$ $mume$ fruit (PME) against alloxan-induced oxidative stress in pancreatic ${\beta}$-cells, HIT-T15. To evaluate the antidiabetic effect of PME, 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazoliu bromide (MTT) cell proliferation assay, lactate dehydrogenase (LDH) release assay, $NAD^+$/NADH ratio and insulin secretion were assessed. We also measured its antioxidant effect against alloxan-induced oxidative stress in the cells by assessing the levels of the antioxidant enzymes including superoxide dismutase (SOD), glutathione S-transferase (GST), glutathione reductase (GR) and glutathione peroxidase (GPx). The results of this analysis showed that alloxan significantly decreased cell viability, increased LDH leakage, and lowered $NAD^+$ /NADH ratio and insulin secretion in HIT-T15 cells. However, PME significantly increased the viability of alloxan-treated cells and lowered LDH leakage. The intracellular $NAD^+$ /NADH ratio and insulin secretion were also increased by 1.5~1.9-fold and 1.4-fold, respectively, after treatment with the PME. The HIT-T15 cells treated with alloxan showed significant decreases in the activities of antioxidant enzymes, while PME significantly elevated the levels of antioxidant enzymes. Based on these results, we suggest that PME could have a protective effect against the cytotoxicity and dysfunction of pancreatic ${\beta}$-cells in the presence of alloxan-induced oxidative stress.

• Computers and Concrete
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• v.9 no.1
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• pp.51-61
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• 2012

According to the results of three-point bending tests of rubberized concrete and plain concrete, the parameters such as total fracture energy ($G_F$), initial fracture energy ($G_f$), and tensile strength ($f_t$) are obtained for concrete material. Using ABAQUS software and a bilinear softening fictitious crack model, the crack propagation process was simulated and compared to the experimental results. It is found that the increase of AE hit count has a similar trend with the increase of energy dissipation in FEM simulation. For two types of concretes, both experimental results and numerical simulation indicate that the rubberized concrete has a better fracture resistance.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.11a
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• pp.199-202
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• 1998

Power capacitors are highly reliable equipment due to their completely enclosed configuration. Aging diagnosis system using partial discharge(PD) and acoustic emission(AE) is being highlighted as a research area for degradation of power capacitors. Their dielectric strength can be however reduced due to some stresses such as over-voltage or thermal degradation of the insulation material during their long period of operation. In this paper, it has been developed to express the AE of the EVENT(average amplitude) and HIT(pulse count) according to the source location. And real time measurement of PD signals for aging diagnosis of power capacitors.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.5
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• pp.412-423
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• 2000

By using the relation between stress intensity factor and AE parameter, new approach method for assessing the crack length and detectability of crack was proposed. Laboratory experiment was carried out to identify AE characteristics of fatigue cracks for compact tension specimen. The relationship between a stress intensity factor and AE signals activity as well as conventional AE parameter analysis was discussed. As a result, the features of specific parameter such as the length of crack growth the AE energy, the AE peak amplitude, and the cumulative AE hits, showed the almost same trend in their increase as the number of fatigue cycle increased. From the comparisons of peak amplitude and AE energy with stress intensity factor, it was verified that the higher stress intensity factors generated AE signals with higher peak amplitude and a larger number of AE counts. If we can get more reliable database for the relation between AE parameters and stress intensity factor, this approach will provide a good information for evaluating both the existence of crack and the minimum detectable size of crack.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.4
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• pp.360-367
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• 2009

The acoustic emission(AE) behavior of reinforced concrete slab under flexural loading was investigated to assess the integrity. This study was aimed at identifying the characteristics of AE response associated with damage development. By applying cyclic loading in various load steps, it was able to differentiate each AE source such as distributed micro crack initiation, friction, flexural crack and localized diagonal tension crack. The secondary peak and the change of AE hit rate gave valuable criteria fur assessment. From the analysis of the felicity ratio, furthermore, it was shown that this values can be used for evaluating the degree of concrete damage. Based on the experimental results, this approach for practical AE application may provide a promising method for estimating the level of damage and distress in concrete structures.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.2
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• pp.155-169
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• 2002

The objective of this study was to investigate the effect of crack opening and closure in the AE activities during fatigue test. Laboratory experiment using various materials and test conditions were carried out to identify AE characteristics of fatigue crack propagation. Compact tension specimens of 2024-T4 and 6061-T6 aluminum alloy were prepared for fatigue test. AE activities were analyzed based on the phase of the loading cycle. Generally, most of AE were generated when the crack begins' opening and the crack closes fully, whereas a few in the pull opening of the crack. Also AE activity in the peak loading of cycle was different with each specimen. However, in the same material, AE activity was not affected by the change of cyclic frequency (0.1, 0.2, 1.0Hz). It was found that AE activities during crack opening and closure depend on material properties such as micro-structure, tensile strength and yield strength.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.5
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• pp.488-496
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• 2003

To establish nondestructive test method for rocket motor assembly with rubber and aerospace composite materials, practicable quality control acoustic emission test method is presented. Structural analysis for motor assembly is performed by ABAQUS code and analysis output result is confirmed by strain gage and AE data. Various specimens were tested and analyzed using strain gage and acoustic emission data. The hit rate of acoustic emission was closely related with case/rubber debonding. This report also describes practicable acoustic emission nondestructive method for evaluating motor case assembly quality assurance in the industrial field.

• Journal of the Korean Wood Science and Technology
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• v.24 no.3
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• pp.57-64
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• 1996

제지공장에서 사용하는 습윤제는 물의 표면장력을 낮춤으로써 목재섬유가 물을 빨리 흡수하여 팽윤하도록 도와준다. 목재섬유가 물을 흡수하여 팽윤하는 과정을 밝히지 위한 연구가 많이 진행되어 왔지만 목재섬유와 물의 상호작용을 상세히 연속적으로 측정할 방법이 전에는 별로 없었다. 목재섬유가 팽윤할 때 발생하는 팽윤압력은 음향방사를 동반하기 때문에 이를 측정하여 팽윤과정을 알아내는 기술이 개발되었다. 본 연구에서는 이 방법을 이용하여 목재를 여러 농도의 습윤제에 담갔을 때 발생하는 음향방사와 중량증가를 측정하여 이 두 변량의 상관을 조사하고 이 방법이 목재의 습윤과정 연구에 유용하게 사용될 수 있는지를 조사하였다. 아까시나무와 라디에타 파인의 두 수종을 사용하였는데 두 수종의 흡수 형태는 매우 달랐다. 5분 동안 용액에 침지하였을 때 후자가 전자보다 10배 정도 더 많이 중량증가하였으며, 발생한 음향방사도 후자가 전자보다 훨씬 많았다. 아까시나무의 중량증가와 음향방사는 습윤제 농도에 거의 무관하였으나 라디에타 파인의 음향방사는 습윤제 농도의 증가에 따라 증가하였으며 라디에타 파인의 중량증가는 습윤제의 표면장력 변화와 일치하였다. 수종별 중량증가와 음향방사의 관계는 아까시나무가 음의 상관을 나타냈으나 라디에타 파인은 양의 상관을 나타내었다. 자비처리 시편은 무처리 시편보다 음향방사가 적었다.