• Advances in aircraft and spacecraft science
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• v.11 no.1
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• pp.83-103
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• 2024

Adhesive bonding is currently widely used in many industrial fields, particularly in the aeronautics sector. Despite its advantages over mechanical joints such as riveting and welding, adhesive bonding is mostly used for secondary structures due to its low peel strength; especially if it is simultaneously exposed to temperature and humidity; and often presence of bonding defects. In fact, during joint preparation, several types of defects can be introduced into the adhesive layer such as air bubbles, cavities, or cracks, which induce stress concentrations potentially leading to premature failure. Indeed, the presence of defects in the adhesive joint has a significant effect on adhesive stresses, which emphasizes the need for a good surface treatment. The research in this field is aimed at minimizing the stresses in the adhesive joint at its free edges by geometric modifications of the ovelapping part and/or by changing the nature of the substrates. In this study, the finite element method is used to describe the mechanical behavior of bonded joints. Thus, a three-dimensional model is made to analyze the effect of defects in the adhesive joint at areas of high stress concentrations. The analysis consists of estimating the different stresses in an adhesive joint between two 2024-T3 aluminum plates. Two types of single lap joints(SLJ) were analyzed: a standard SLJ and another modified by removing 0.2 mm of material from the thickness of one plate along the overlap length, taking into account several factors such as the applied load, shape, size and position of the defect. The obtained results clearly show that the presence of a bonding defect significantly affects stresses in the adhesive joint, which become important if the joint is subjected to a higher applied load. On the other hand, the geometric modification made to the plate considerably reduces the various stresses in the adhesive joint even in the presence of a bonding defect.

• Journal of the Korean Geosynthetics Society
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• v.16 no.4
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• pp.231-240
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• 2017

Recently, there have been frequent occurrences of ground sink in the urban area, which have resulted in human and material damage and are accompanied by economic losses. This is caused by artificial factors such as soil loss, poor compaction, horizontal excavation due to the breakage of the aged sewage pipe, and lack of water proof at vertical excavation. The ground sink can be prevented by preliminary restoration and reinforcement through exploration, but it can be considered that it is not suitable for urgent restoration by the existing method. In this study, a model experiment was carried out to simulate the in-ground cavities caused by groundwater flow for developing non-excavation urgent restoration in underground cavity and the range of the relaxation zone was estimated by detecting the around the cavity using a relaxation zone detector. In addition, disturbance region and relaxation region were separated by injecting gypsum into cavity formed in simulated ground. The shape of the underground cavity due to the groundwater flow was similar to that of the failure mode III formed in the dense relative density ground due to water pipe breakage in the previous study. It was confirmed that the relaxed region detected using the relaxation zone detector is formed in an arch shape in the cavity top. The length ratio of the relaxation region to the disturbance region in the upper part of the cavity center is 2: 1, and it can be distinguished by the difference in the decrease of the shear resistance against the external force. In other words, it was confirmed that the secondary damage should not occur in consideration of the expandability of the material used as the injecting material in the pre-repair and reinforcement, and various ground deformation states will be additionally performed through additional experiments.

• Bulletin of the Korean Chemical Society
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• v.28 no.10
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• pp.1675-1682
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• 2007

Large colorless single crystals of faujasite-type zeolite with diameters up to 200 μm have been synthesized from gels with the composition of 3.58SiO2:2.08NaAlO2:7.59NaOH:455H2O:5.06TEA:1.23TCl. Two of these, colorless octahedron about 200 μm in cross-section have been treated with aqueous 0.1 M TlC2H3O2 and KNO3 in order to prepare Tl+- and K+-exchanged faujasite-type zeolites, respectively, and then determined the Si/Al ratio of the zeolite framework. The crystal structures of |Tl71|[Si121Al71O384]-FAU and |K53Na18|[Si121Al71O384]-FAU per unit cell, a = 24.9463(2) and 24.9211(16) A, respectively, dehydrated at 673 K and 1 × 10-6 Torr, have been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd m at 294 K. The two single-crystal structures were refined using all intensities to the final error indices (using only the 905 and 429 reflections for which Fo > 4σ(Fo)) R1/R2 = 0.059/0.153 and 0.066/0.290, respectively. In the structure of fully Tl+-exchanged faujasite-type zeolite, 71 Tl+ ions per unit cell are located at four different crystallographic sites. Twenty-nine Tl+ ions fill site I' in the sodalite cavities on 3-fold axes opposite double 6-rings (Tl-O = 2.631(12) A and O-Tl-O = 93.8(4)o). Another 31 Tl+ ions fill site II opposite single 6-rings in the supercage (Tl-O = 2.782(12) A and O-Tl-O = 87.9(4)o). About 3 Tl+ ions are found at site III in the supercage (Tl-O = 2.91(6) and 3.44(3) A), and the remaining 8 occupy another site III (Tl-O = 2.49(5) and 3.06(3) A). In the structure of partially K+-exchanged faujasite-type zeolite, 53 K+ ions per unit cell are found at five different crystallographic sites and 18 Na+ ions per unit cell are found at two different crystallographic sites. The 4 K+ ions are located at site I, the center of the hexagonal prism (K-O = 2.796(8) A and O-K-O = 89.0(3)o). The 10 K+ ions are found at site I' in the sodalite cavity (K-O = 2.570(19) A and O-KO = 99.4(9)o). Twenty-two K+ ions are found at site II in the supercage (K-O = 2.711(9) A and O-K-O = 94.7(3)o). The 5 K+ ions are found at site III deep in the supercage (K-O = 2.90(5) and 3.36(3) A), and 12 K+ ions are found at another site III' (K-O = 2.55(3) and 2.968(18) A). Twelve Na+ ions also lie at site I' (Na-O = 2.292(10) and O-Na-O = 117.5(5)o). The 6 Na+ ions are found at site II in the supercage (Na-O = 2.390(17) A and O-Na-O = 113.1(11)o). The Si/Al ratio of synthetic faujasite-type zeolite is 1.70 determined by the occupations of cations, 71, in two single-crystal structures.

• Journal of the korean academy of Pediatric Dentistry
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• v.34 no.3
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• pp.359-369
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• 2007

This in vitro study was performed to assess the effect of surface sealing on the microleakage of class V composite resin restorations that underwent several aging treatments. Class V cavities were prepared on the buccal surface of 100 sound extracted premolars and restored with a hybrid light-cured composite resin according to the manufacturer's instructions. They were randomly divided into two groups consisting of 50 samples: group I, without surface sealing, and group II, in which margins were etched and surface sealant was applied. After thermocycling, each group was divided into five subgroups, respectively, to represent the five aging treatments: group A = no further treatment (only thermocycling), B = toothbrushing, C = load cycling, D = toothbrushing followed by load cycling, and E = aging treatment in deionized water for six months. Microleakage was assessed by examining the penetration of 2% methylene blue dye. The following results were obtained: 1. At occlusal and cervical margins in groups without surface sealing, there was no significant difference in microleakage after the several aging treatments (p>0.05). 2. The occlusal margins of groups with surface sealing showed no significant differences after the several aging treatments (p>0.05). 3. In the cervical margins of groups with surface sealing, microleakage significantly increased after load cycling or aging in deionized water for six months (p<0.05). 4. The no-further-treatment group and the toothbrushing group with surface sealing showed less microleakage than the corresponding groups without surface sealing (p<0.05). 5. The surface-sealed groups with load cycling or aging in deionized water showed no significant difference in microleakage to the corresponding groups without surface sealing (p>0.05). In conclusion, the results of this study suggest that the surface sealant infiltrating through the gap of the cervical margin exerted a positive effect on microleakage at the initial stage, but the effect was not sufficient to overcome the stress generated by the cuspal flexure during occlusal loading and water absorption.

• Tuberculosis and Respiratory Diseases
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• v.44 no.5
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• pp.975-991
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• 1997

Background : Many patients with isoniazid and rifampin-resistant pulmonary tuberculosis have organisms that are also resistant to other first-line drugs. Despite of aggressive retreatment chemotherapy, the results are often unsuccessful, with a failure rate approaching 40%. Recently, there has been a revival of resectional surgery for the treatment of multidrug-resistant pulmonary tuberculosis. Methods : A retrospective analyses of the case records and radiographic findings were done. Between January 1991 and December 1995, 14 human immunodeficiency virus (HIV)-seronegative patients with multidrug-resistant pulmonary tuberculosis were selected for resection to supplement chemotherapy. All patients had organisms resistant to many of the first-line drugs, including both isoniazid and rifampin. Results : Despite of aggressive therapy for median duration of 9.5 months, 12 of the 14 patients (86%) were still sputum smear and/or culture positive at the time of surgery. The disease was generally extensive. Although main lesions of the disease including thick-walled cavities were localized in one lung, lesser amounts of contralateral disease were demonstrated in 10 of 14 (71%). Types of surgery performed were pneumonectomy including extrapleural pneumonectomy in six patients, lobectomy or lobectomy plus in six patients, and segmentectomy in two patients. The resected lung appeared to have poor function ; preoperative perfusion lung scan showed only 4.8% of the total perfusion to the resected portion of the lung. There were no operative deaths. Two patients had major postoperative complications including empyema with bronchopleural fistula and prolonged air leak, respectively. Of the 14 patients, 13 (93%) remained sputum-culture-negative for M. tuberculosis for a median duration of 23 months and one remained continuously sputum smear and culture positive for M. tuberculosis. Conclusion : On the basis of comparison with historical controls, adjunctive resectional surgery appears to play a significant beneficial role in the management of patients with multidrug-resistant pulmonary tuberculosis if the disease is localized and there are adequate reserve in pulmonary function.

• Restorative Dentistry and Endodontics
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• v.35 no.1
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• pp.5-12
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• 2010

The purpose of this study was to evaluate the pulp tissue reaction to direct pulp capping of mechanically exposed beagle dogs' pulp with several capping materials. A total of 36 teeth of 2 healthy beagle dongs were used. The mechanically exposed pulps were capped with one of the followings: (1) Mineral Trioxide Aggregate (MTA: $ProRoot^{(R)}$ MTA. Dentsply, Tulsa, USA), (2) Clearfil SE Bond (Dentin adhesive system: Kuraray, Osaka, Japan), (3) Ultra-Blend (Photo-polymerized Calcium hydroxide: Ultradent, South Jordan, USA), (4) Dycal (Quick setting Calcium hydroxide: LD Caulk Co., Milford, USA) at 7, 30, and 90 days before sacrificing. The cavities were restored with Z350 flowable composite resin (3M ESPE, St. Paul. MN, USA). After the beagle dogs were sacrificed, the extracted teeth were fixed, decalcified, prepared for histological examination and stained with HE stain. The pulpal tissue responses to direct pulp capping materials were assessed. In MTA calcium hydroxide, and photo-polymerized calcium hydroxide groups, initial mild inflammatory cell infiltration, newly formed odontoblast-like cell layer and hard tissue bridge formation were observed. Compared with dentin adhesive system, these materials were biocompatible and good for pulp tissue regeneration. In dentin adhesive system group, severe inflammatory cell infiltration, pulp tissue degeneration and pulp tissue necrosis were observed. It seemed evident that application of dentin adhesive system in direct pulp capping of beagle dog teeth cannot lead to acceptable repair of the pulp tissue with dentine bridge formation.

• 한국지구물리탐사학회:학술대회논문집
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• 2005.09a
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• pp.21-36
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• 2005

Although the main geology of Korea consists of granite and gneiss, it Is not uncommon to encounter anisotropy Phenomena in crosshole radar tomography even when the basement is crystalline rock. To solve the anisotropy Problem, we have developed and continuously upgraded an anisotropic inversion algorithm assuming a heterogeneous elliptic anisotropy to reconstruct three kinds of tomograms: tomograms of maximum and minimum velocities, and of the direction of the symmetry axis. In this paper, we discuss the developed algorithm and introduce some case histories on the application of anisotropic radar tomography in Korea. The first two case histories were conducted for the construction of infrastructure, and their main objective was to locate cavities in limestone. The last two were performed In a granite and gneiss area. The anisotropy in the granite area was caused by fine fissures aligned in the same direction, while that in the gneiss and limestone area by the alignment of the constituent minerals. Through these case histories we showed that the anisotropic characteristic itself gives us additional important information for understanding the internal status of basement rock. In particular, the anisotropy ratio defined by the normalized difference between maximum and minimum velocities as well as the direction of maximum velocity are helpful to interpret the borehole radar tomogram.

• Restorative Dentistry and Endodontics
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• v.32 no.5
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• pp.469-475
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• 2007

The purpose of this study was to evaluate the effect of a new resin monomer on the microleakage of composite resin restorations. By adding new methoxylated Bis-GMA (Bis-M-GMA, 2,2-bis[4-(2-methoxy-3-methacryloyloxy propoxy) phenyl] propane) having low viscosity, the content of TEGDMA which has adverse effects on polymerization shrinkage might be decreased. As a result, microleakage might be improved. $2\;mm\;{\times}\;2\;mm\;{\times}\;2\;mm$ cavities with occlusal margins in enamel and gingival margins in dentin were prepared on buccal and lingual surfaces of 40 extracted human premolars. Prepared teeth were randomly divided into four groups and restored with Clearfil SE bond (Kuraray, Japan) and one of experimental composite resins; EX1, Experimental composite resin1 (Bis-M-GMA/TEGDMA = 95/5 wt%, 40 mm nanofillers); EX2, Experimental composite resin2 (Bis-M-GMA/TEGDMA = 95/5 wt%, 20 mm nanofillers); EX3, Experimental composite resin3 (Bis-GMA/TEGDMA = 70/30 wt%, 40 nm nanofillers); and Filtek Z250 (3M ESPE, USA) was filed as a control group. The restored teeth were thermocycled, and immersed in 2% methylene blue solution for 24 hours. The teeth were sectioned buccolingually with a low speed diamond saw and evaluated for microleakage under stereomicroscope. The data were statistically analyzed by Pearson Chi-Square test and Fisher Exact test (p = 0.05). The microleakage scores seen at the enamel margin were significantly lower than those of dentin margin (p = 0.007). There were no significant differences among the composite resins in the microleakage scores within each margin (p > 0.05). Bis-M-GMA, a new resin monomer having low viscosity, might in part replace high viscous Bis-CMA and might improve the quality of composite resin.

• Journal of the korean academy of Pediatric Dentistry
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• v.31 no.3
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• pp.527-533
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• 2004

One clinical technique recommended for improving marginal integrity is "rebonding" or application of unfilled resins to the surface of composite restoration. But continuously the restorations are affected with occlusal load. There is room for doubt that the rebonding agent has the positive effect on microleakage in spite of the stress generated by the occlusal load. This study determined the effect of rebonding on microleakage of Class V resin composite restorations under load cycling. Class V cavities were prepared on the buccal surface of 40 sound extracted premolars and restored with a hybrid light-cured resin composite according to manufacturers' directions. They were randomly divided into two groups consisting of 20 samples: a control(group I), without surface sealing, and the other group(group II) in which margins were etched and rebonded. After thermocycling, each of groups was divided into subgroups(group A, B), and load cycling(total 100,000 cycles with 4-100N load at a rate of 1 Hz) were applied on the group B. Assessment of microleakage utilized methylene blue dye penetration. The following results were obtained: 1. In the occlusal region, no significant difference was noted in the scores regardless of whether or not the rebonding agent was used(group TA-IIA, IB-IIB)(p>0.05). 2. In the cervical region, the control group with rebonding(group IIA) showed the better result than the group without rebonding(group IA)(p<0.05). 3. In the cervical region, the rebonded group with load cycling(group IIB) showed similar results to the group without rebonding(group IB) and no significant difference was noted(p>0.05).

• Tuberculosis and Respiratory Diseases
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• v.52 no.4
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• pp.330-337
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• 2002

Background : A pulmonary tuberculoma is one of the most common causes of a solitary pulmonary lesion. Treating a tuberculoma is still controversial and there are few reports on antituberculosis chemotherapy. In this study, the clinical findings and changes in the size of tuberculomas on a radiograph after completing antituberculosis chemotherapy was investigated. Methods : The medical records, an chest radiographs of 18 pulmonary tuberculoma patients who were admitted to the Gachon medical school, Ghil medical center between April 1998 and August 2001, were reviewed. The symptomatic changes were recorded and the size of the tuberculomas following treatment were compared. To compare the size, the long distance of each tuberculoma on the chest radiographs were measured and the additional radiological findings of calcification, satellite nodules and cavities were investigated. Results : Fifteen patients were men and 3 were women. The median age was 46 (24-74). Among these 18 patients, 14 patients had clinical symptoms. The other 4 patients were diagnosed incidentally as during a routine chest radiograph. The mean size of the tuberculomas on the initial plain chest film was $4.3{\pm}2.3cm$(range : 1.7-10 cm) and after 6 months treatment, it had decreased to $1.68{\pm}2.00cm$(range : 1.5-6.5 cm) (P<0.05). At least 6 months of antituberculosis chemotherapy resulted in the findings of a tuberculoma with a disappearance in 9, a decreased size in 4, and no change in 5 on the chest radiograph. Calcifications were found in 3 patients on the initial chest film and the chest CT and all calcified tuberculomas had disappeared after treatment. Conclusion : Although a pulmonary tuberculoma can remain as an inactive lesion for a long time, if it is confirmed by pathological or bacteriological methods, antituberculosis chemotherapy will be beneficial despite the presence of calcification.