• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.6
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• pp.625-629
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• 2015

In this study, we develop a prognostic method of assessing the stator windings of power generators against water absorption through statistical data analysis and degradation modeling. The 42 windings of the generator are divided into two groups: the absorption and normal groups. A degradation model of a winding is constructed using Fick's second law to predict the level of absorption. By analyzing data from the normal group, we can determine the distribution of the data of normal windings. The health index of a winding is estimated using the directional Mahalanobis distance (DMD) method. Finally, the probability distributions of the failure time of the windings are determined.

• Journal of Korean Society of Forest Science
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• v.96 no.1
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• pp.14-20
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• 2007

In order to examine the differences in antioxidant enzyme activities which represent defence mechanism to stressful environments, and soil properties between healthy and declining (or unhealthy) trees, we selected three sites, Witseorum, Youngsil and Sungpanak (Jindallebat). Antioxidant enzymes including Ascorbate peroxidase (APX) and Glutathione Reductase (GR), forest soil properties including soil texture, soil pH, organic matter, total nitrogen, available phosphate, cation exchange capacity, exchangeable cation content and nutrient contents in leaves of Abies koreana (Korean fir) trees were analyzed. There were no significant differences between healthy and declining trees in GR activity. However, seasonal difference in antioxidant enzyme activity was observed. GR activity was lower in June and August than that of September. Soil chemical and physical properties of each site showed a tendency that organic content, total nitrogen content, available phosphorus, cation exchange capacity and cation content were lower at the site of declining trees than the site of healthy trees.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.3
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• pp.233-239
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• 2017

The CA (Control Assembly) of an SFR has a CRA(Control Rod Assembly) with an inner duct and control rod. During an emergency situation, the CRA falls into the duct of the CA for a rapid shut-down. The drop time and impact velocity of the CRA are important parameters with respect to the reactivity insertion time and the structural integrity of the CRA. The objective of this study was to investigate the dynamic behavior and integrity of the CRA owing to a drop impact. The impact analysis of the CRA under normal/abnormal drop conditions was carried out using the commercial FEM code LS-DYNA. Results of the drop impact analysis demonstrated that the CRA maintained structural integrity, and could be safely inserted into the flow hole of the damper under abnormal conditions.

• Journal of the Korean Wood Science and Technology
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• v.36 no.4
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• pp.84-92
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• 2008

Anatomical and physical characteristics of Pinus densiflora woods damaged by forest fire at Yangyang-gun, Kangwon-do were investigated in present study. Even though the bark was severly carbonized, no trace of carbonization in the xylem was found. The amount of resin exudation was different by the degree of fire damage. Green moisture content of sapwood in the damaged wood was lower than that in the sound wood, but vice versa in the heartwood. Green density of heartwood in the damaged wood was higher than that in the sound wood, but there was no significant difference in sapwood. Cambial activities were found stopped in the severely damaged wood but were identified in the lightly damaged wood. In safranine staining process, epithelial and ray parenchyma cell walls in the damaged woods showed darker hue than those in the sound wood. Granular substances were observed in the lumina of ray parenchyma and epithelial cells of the severely damaged wood. Relative crystallinity of the outermost growth ring in the severely damaged wood was slightly higher than that in the sound wood.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.40 no.3
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• pp.314-321
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• 1995

Experiments were conducted to obtain information on separation of nonviable seeds from seed lots of rape, Chinese cabbage and radish, by nondestrutive ways. Seeds were artificially aged at 90% relative humidity(RH) and 45$^{\circ}C$ to get different seed qualities. Large amounts of amino acids, proteins and sinapine were leaked from the dead seeds into water in the course of 4~8 hours soaking, while high quality seeds did not leak in all crops. Percentage of normal seedlings from nonfluorescent cellulose coated seeds of rape, Chinese cabbage and radish under ultraviolet light was 96, 96 and 74%, while that of fluorescent seeds was 8, 9 and 1%, respectively. Cellulose coating and storage of Chinese cabbage and rape seeds at 60 and 75% RH for 3 months and 90% RH for 2 months did not deteriorate seed quality. But percentage of normal seedlings from nonfluorescent radish seeds stored at 60, 75 and 90% RHs for 3 months was 63, 64 and 2%, respectively.

• Composites Research
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• v.28 no.4
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• pp.148-154
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• 2015

In order to detect damage in early stages and properly maintaining structures, the structural health monitoring technology is employed. In most cases, active-sensing SHM needs many piezoelectric (PZT) sensors and actuators. Thus, if there is a defect on PZT used for active-sensing SHM, the structural status could be misclassified. This study, for reliable SHM performance, investigated to detect defects of sensors by using the admittance-based sensor diagnostics. This study also introduced an algorithm that can diagnose sensor defects based only on data measured from the sensors in case that information about the changes in adhesive and environmental investigation, this study confirms that the proposed algorithm could be efficiently applied to real-world structures in which a significant temperature variation could take place.

• Journal of Sericultural and Entomological Science
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• v.14 no.1
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• pp.1-7
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• 1972

Recently, young mulberry trees grown in the reclaimed hill land are frequently attacted by the die-bark and the buds of the trees developed poorly. In order to learn the cause of the injury mentioned above available boron content in the soils and the bark of young shoots have been analyzed. The results are as follow; Available boron content in the soil of the damaged mulberry fold was 0.3-0.20 ppm, against 0.39-49 ppm in that of healthy mulberry field, and boron in the bark of the damaged trees was 10.63-12.99 ppm, and 18.42-21.02 ppm in that of the healthy trees. The organic matter content and available boron content in soils showed a highly significant possitive correlation. The moisture content in percent in the soil of the damaged mulberry held was 11.16 and 14.22 in that of healthy mulberry field.

• Journal of the Korean Geotechnical Society
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• v.24 no.8
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• pp.13-23
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• 2008

The evaluation of soundness of pile is very important for the safety of super structure. In this paper, the HWAW(Harmonic Wavelet Analysis of Wave) method which is developed to determine phase and group velocities of waves is applied to evaluate integrity of pile non-destructivly. The proposed method can evaluate a soundness of pile and pile end condition which is very important factor for pile behaviour. To verity the applicability of HWAW method in non-destructive test for pile, the numerical simulation test using ABAQUS was performed. And the model pile was made and the proposed non-destructive pile tests were applied to evaluate soundness and end boundary condition of model pile in the air and soil box. Through a numerical simulation and model tests, it is shown that the HWAW method has good potential of applying to the evaluation of pile integrity.

• Journal of Korean Tunnelling and Underground Space Association
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• v.15 no.3
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• pp.187-199
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• 2013

Umbrella arch method (UAM) used for improving the stability of the tunnel ground condition has been widely applied in the tunnel construction projects due to the advantage of obtaining both reinforcement and waterproof. The purpose of this study is to develop the evaluation technique of the integrity of bore-hole in UAM by using a non-destructive test and to evaluate the possibility of being applied to the field. In order to investigate the variations of frequency depending on grouted length, the specimens with different grouted ratios are made in the two constraint conditions (free boundary condition and embedded condition). The hammer impact reflection method in which excitation and reception occur simultaneously at the head of pipe was used. The guided waves generated by hitting a pipe with a hammer were reflected at the tip and returned to the head, and the signals were received by an acoustic emission (AE) sensor installed at the head. For the laboratory experiments, the specimens were prepared with different grouted ratios (25 %, 50 %, 75 %, 100 %). In addition, field tests were performed for the application of the evaluation technique. Fast Fourier transform and wavelet transform were applied to analyze the measured waves. The experimental studies show that grouted ratio has little effects on the velocities of guided waves. Main frequencies of reflected waves tend to decrease with an increase in the grouted length in the time-frequency domain. This study suggests that the non-destructive tests using guided ultrasonic waves be effective to evaluate the bore-hole integrity of the UAM in the field.

• The Korean Journal of Financial Management
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• v.18 no.1
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• pp.83-106
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• 2001

본 연구에서는 1997년 말 외환위기 이후 $1998\sim1999$년에 걸쳐 행하여진 한국 은행산업 구조 조정의 성과를 실증적으로 분석하였다. 실증분석의 결과 위험수준이 높아 구조조정 기간에 금융감독당국으로부터 강한 경영개선 압력을 받을 가능성이 높은 은행들은 무수익여신, 부실여신비율 등 대출행위의 건전성 측면과 대출, 유가증권간의 투자비율, 그리고 유가증권 내 자산종목 간의 투자 비율 등 여러 가지 위험관련 변수들과 관련하여 측정된 건전화에 대한 동기면에서 외환위기 이전에 비하여 유의적이고 일관된 보다 높은 건전화에 대한 동기를 가지고 있었음을 볼 수 있었으며, 이러한 결과는 외환위기 이후의 은행권 구조조정 정책에 대한 어느 정도의 유효성을 보여 주는 결과로 사료된다. 또한 은행 집단별 분석에서는 구조조정 과정에서 퇴출 또는 우량은행에게 인수/합병된 부실은행들은 구조조정 이전의 기간에 그 외의 은행들 보다 위험추구에 대한 동기가 매우 강하였음을 볼 수 있었으나 이러한 위험추구의 동기가 우량은행에로의 인수/합병을 통하면서 상당히 감소하였음을 발견할 수 있었으며, 이러한 결과는 총표본에 대한 분석에서의 결과와 일관되게 외환위기 이후의 구조조정 정책에 대한 어느 정도의 유효성을 보여 주는 결과로 사료된다.