• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.04a
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• pp.266-269
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• 2004

In this study, bond strengths for the self-healing agents were evaluated through the modified lap shear test in order to suggest the optimal healing conditions for the repair of polymeric composites. The healing agents of DCPD, ENB, and their mixtures were activated with Grubbs' catalysts. According to the results, the mixture of DCPD and ENB gave better opportunity than DCPD only due to the rapid acivation with catalyst in view of the economic and practical use.

• Korean Journal of Bronchoesophagology
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• v.10 no.2
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• pp.17-21
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• 2004

Background Insertion of tracheal stent in the treatment of benign tracheal & bronchial disease has increased since the introduction of expandable metallic stent. Material & Methods : Between Jan, 1995 and Feb. 2004, eight patients who had benign tracheo-bronchial disease underwent insertion of expandable metallic tracheal stent. We retrospectively analyzed stent insertion indications, complications, and following the result. Results : Surgical indications were post-intubation tracheal stenosis (1 case), tracheal stenosis following tracheal surgery (2 cases), tracheo-esophageal fistula (2 cases), broncho-pleural fistula(1 case), left main bronchus stenosis following bronchoplasty (1 case), and left main bronchus stenosis due to mediastinal repositioning (1 case). Expandable metallic tracheal stent was inserted in five patients to resolve dyspnea caused by airway obstruction, and to prevent recurrent pneumonia in three patients. The complication developed in 6 patients $75\%$; 3 cases of distal stenosis due to growth of granulation tissue, and one case each of tearing of posterior membrane, aggravation of tracheo-esophageal fistula, and airway partial obstruction due to stent migration. The stent was removed in 5 patients and tracheal surgery (tracheal resection and end to end anastomosis with primary repair of esophagus, pericardial patch tracheo-bronchoplasty, tracheal repair and omental wrapping) was performed in 3 patients. Conclusion Insertion of self expandable metallic stent in benign tracheo-bronchial disease is an effective means of relieving dyspnea for only a short period, and it did not increase the long term survival. Better means of treatment of benign tracheo-bronchial stenosis in necessary.

• Journal of Technologic Dentistry
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• v.39 no.3
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• pp.161-167
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• 2017

Purpose: We compare the bond strength of heat-cured PMMA of Lucitone 199 and QC-20 and Tokuyama Rebase Resin of self-cured resin, which are widely used and well accepted in clinical practice. In order to test the mechanical bonding and chemical bonding, we will compare the bond strength between EstheShot Bright, Smiletone, Repair and Rebase resins. Methods: The denture base resin used in this study was PMMA heat-cured QC-20 and Lucitone 199, polyamide resin EstheShot Bright, Smiletone. And Two types of self-curing Rapid Repair and Tokuyama Rebase were used as resection resins. To measure the bond strength, the denture specimens were fabricated in the size of $10{\times}64{\times}3.5mm$ as instructed by the manufacturer. A surface treatment agent was applied to the cut surfaces of each denture specimen, and the specimens were placed in a preformed silicone mold, and autoclaved excimer resins were prepared. The bending strength of the fabricated specimens was measured using a universal testing machine (STM-5, United Calibration Co., U.S.A.) to measure the three-point bending strength. Results: In both polycarbonate and polyacetal resin, a special resin surface treatment agent showed higher bonding strength than the resin surface treatment agent(p<0.05). Regardless of the type of surface treatment, polycarbonate showed higher bond strength than polyacetal resin(p<0.05). Conclusion: It is considered desirable to use a special surface treating agent for the thermoplastic denture base resin such as polycarbonate and polyacetal resin.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1853-1857
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• 2005

This paper reports on the development of the gripping system for automation of phone-camera module assembling. If manual assembling is shifted by automation, it will increase the fabrication speed and reduce the defective rate. In the gripping mechanism design, we needs self-adjustable passive mechanism that minimize the number of the parts. The self-adjusting system compensates the positioning errors that have been made in translations. And also we need gripper system that can be modules of parts. That makes it easy to change or repair the parts. The forces put on the objects is another considerable in the system. It must not cause dropping, breakage, scratch, and large deformation. So final target of this reaseach is how to develop the system that is speedy, small, simple, and safe

• Structural Engineering and Mechanics
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• v.17 no.3_4
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• pp.347-356
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• 2004

In order to extend the lifetime of buildings and civil infrastructure, patch type fibrous composite retrofitting materials are widely used. Retrofitted concrete columns and beams gain stiffness and strength, but lose toughness and show brittle failure. Usually, the cracks in concrete structures are visible to the naked eye and the status of the structure in the life cycle is estimated through visual inspections. After retrofitting of the structure, crack visibility is blocked by retrofitted composite materials. Therefore, structural monitoring after retrofitting is indispensable and self diagnosis method with optical fiber sensors is very useful. In this paper, we try to detect the peel out effect and find the strain difference between the main structure and retrofitting patch material when they separate from each other. In the experiment, two fiber optic Bragg grating sensors are applied to the main concrete structure and the patching material separately at the same position. The sensors show coincident behaviors at the initial loading, but different behaviors after a certain load. The test results show the possibility of optical fiber sensor monitoring of beam structures retrofitted by the composite patches.

• Structural Engineering and Mechanics
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• v.61 no.6
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• pp.701-709
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• 2017

Seismic dissipation devices can play a crucial role in mitigating earthquake damages, loss of life and post-event repair and downtime costs. This research investigates the use of ring springs with high-force-to-volume (HF2V) dissipaters to create damage-free, recentring connections and structures. HF2V devices are passive rate-dependent extrusion-based devices with high energy absorption characteristics. Ring springs are passive energy dissipation devices with high self-centring capability to reduce the residual displacements. Dynamic behaviour of a system with nonlinear structural stiffness and supplemental hybrid damping via HF2V devices and ring spring dampers is used to investigate the design space and potential. HF2V devices are modelled with design forces equal to 5% and 10% of seismic weight and ring springs are modelled with loading stiffness values of 20% and 40% of initial structural stiffness and respective unloading stiffness of 7% and 14% of structural stiffness (equivalent to 35% of their loading stiffness). Using a suite of 20 design level earthquake ground motions, nonlinear response spectra for 8 different configurations are generated. Results show up to 50% reduction in peak displacements and greater than 80% reduction in residual displacements of augmented structure compared to the baseline structure. These gains come at a cost of a significant rise in the base shear values up to 200% mainly as a result of the force contributed by the supplemental devices.

• Journal of Communications and Networks
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• v.11 no.1
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• pp.57-71
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• 2009

Networking together hundreds or thousands of cheap sensor nodes allows users to accurately monitor a remote environment by intelligently combining the data from the individual nodes. As sensor nodes are typically battery operated, it is important to efficiently use the limited energy of the nodes to extend the lifetime of the wireless sensor network (WSN). One of the fundamental issues in WSNs is the coverage problem. In this paper, the border coverage problem in WSNs is rigorously analyzed. Most existing results related to the coverage problem in wireless sensor networks focused on planar networks; however, three dimensional (3D) modeling of the sensor network would reflect more accurately real-life situations. Unlike previous works in this area, we provide distributed algorithms that allow the selection and activation of an optimal border cover for both 2D and 3D regions of interest. We also provide self-healing algorithms as an optimization to our border coverage algorithms which allow the sensor network to adaptively reconfigure and repair itself in order to improve its own performance. Border coverage is crucial for optimizing sensor placement for intrusion detection and a number of other practical applications.

• Journal of Powder Materials
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• v.14 no.4
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• pp.238-244
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• 2007

The electrophoretic deposition process of Ni nano-particles in organic suspension was employed for self-repairing of heat exchanger tubes. For this purpose, Ni nano-particles prepared by levitational gas condensation method were dispersed into the solution of ethanol with the addition of dispersant Hypermer KD2. For electrophoretic deposition of Ni nano-particles on the Ni alloy specimen, constant electric fields of 20 and 100 V $cm^{-1}$ were applied to the specimen in Ni-dispersed solution. It was found that as electrophoretic deposition proceeds, the size of the pit or crack remarkably decreased due to the agglomeration of Ni nano-particles at the pit or crack. This strongly suggests that the electrophoretic mobility of the charged particles is larger for the damaged part with a higher current value rather than outer surfaces with a lower current value.

• Journal of Preventive Medicine and Public Health
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• v.52 no.5
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• pp.292-298
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• 2019

Objectives: Presenteeism is currently recognized as a significant global health issue that can potentially cause productivity losses. Hence, many studies have analyzed the relationships between workplace factors and presenteeism. However, few studies have considered non-occupational factors. This study examined the associations between presenteeism and activities outside work, including volunteering, self-development, leisure/sports, and gardening and house repair activities, in Korean wage workers. Methods: This study analyzed the fourth Korean Working Conditions Survey, in which a total of 19 294 wage workers participated. To identify relationships between presenteeism and activities outside work, multivariate logistic regression analysis was used after adjusting for general and occupational characteristics. Results: Self-development and leisure/sports activities significantly increased the odds ratio (OR) of presenteeism (OR, 1.166; 95% confidence interval [CI], 1.061 to 1.282 and OR, 1.276; 95% CI, 1.181 to 1.379, respectively). Conclusions: Certain activities outside work, such as self-development or leisure/sports, were related to presenteeism among Korean wage workers. Although many previous studies have emphasized the positive effects of those activities on health, this study documented negative effects of these activities outside work on health.

• Korean Journal of Community Nutrition
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• v.2 no.3
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• pp.406-416
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• 1997

Teacher's satisfaction with school lunch programs run by foodservice(FS) management types were surveyed with questionnaire at 5 middle and 4 elementary schools. The 88 middle and 104 elementary school teachers who participated and schools' FS management were of 5 types : self/conventional, contracted/conventional, contracted/commissary and contracted/dosirak delivery. Most teachers knew correctly their schools' present FS management types and thoroughly understood the main reasons for needing school lunch program with proper nutrition, better taste and balanced diets in addition to the first reason its less work than preparing homelunches. Teacher's satisfactions with their present school FS were high in self/conventional and contracted/conventional and was very low in contracted/commissary and contracted/ dosirak Taste, hygiene, nutrition and dining facilities in turn were pointed out to be improved : firstly hygiene in the self and firstly taste in the contracted. Particularly dining-rooms were found to have narrow space, uncomfortable chairs and tables, unclean, and having unpleasant smells. Teachers observed that the overall students' food habits such as eating more various foods and better table manners through that school lunch programs, particularly the self-managed types were improved. Conclusively most teachers emphasized school lunch programs to be continued and preferred self-managed types and contracted/conventional types as the second best in having less work to manage, better, taste, nutrition and hygiene, less cost and better nutrition education in turn. And they thought school founders should handle the finances needed to newly establish or repair the school FD facilities, otherwise provided with the partial aid of student's parents.