• The Journal of Korean Academy of Prosthodontics
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• v.45 no.1
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• pp.34-47
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• 2007

Statement of problem: Conventional mandibular complete denture lacks in support and stability for edentulous patients to use. Purpose: To enhance support and stability of mandibular complete denture, 2 implants were inserted on the inter-mental foramina space of edentulous patients. With 2 magnetic attachments on the inner side of the overdenture, we gave immediate loads and evaluated the stability of the implants, the responses of the supporting tissues, and the satisfaction of the patients. Material & methods: 6 edentulous patients (5 male, 1 female) each recieved 2 SLA implants in the inter-mental foramina region and implants were immediately loaded with overdenture with magnet attachments. To evaluate the implants stability and the peri-implant tissues, clinical exams, RFA tests and radiographic exams were preformed at the 1 week, 2wks, 6wks, 12wks, and 24wks. post- surgery. Results: The mean surgery time was $45.7{\pm}7.7mins$., while the denture delivery time was $45.5{\pm}12.6mins$. Only 2 of 14 implants were failed. Survived implants that remained were clincally and radiographically stable. Mean ISQ values were relatively stable, showing $69.71{\pm}5.55$, $69.00{\pm}9.48$, $67.92{\pm}7.86$, $67.92{\pm}9.58$, $70.08{\pm}7.61$, $71.92{\pm}6.43$ at the 1 wk, 2 wks, 6 wks, 12 wks, 24 wks. follow up check. Crestal bone changes were $-1.18mm{\pm}0.68mm$, $-1.35{\pm}0.69mm$, $-1.47{\pm}0.68mm$ at the 6wks, 12wks, 24wks. follow up check. Bleeding on probing(BOP index) was not significant. Conclusion: Mandibular ovedentures with 2 magnetic attachments over two interforaminal implants on edentulous patients for immediate function is a recommendable novel treatment for edentulous patients which shows stability on the implants and supporting tissue.

• Journal of Korean Society of Forest Science
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• v.101 no.3
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• pp.412-425
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• 2012

Concrete Soil Erosion Control Dam, which blocks flow of debris flow in torrential stream, are reported to lose expected functions due to structural failure and collapses, caused by poor construction, material deterioration and external impacts. In this paper, an integrity assessment technique for debris barriers was proposed, which allows preliminary detection of problems inherent in debris barriers. The proposed integrity assessment technique is a non-destructive method based on SASW method, one of surface-wave tests. In this paper, a practical procedure and analysis guidelines in applying the SASW technique to debris barrier was proposed and its validity was verified using five decrepit debris barriers older than 20-year old. As a result, the SASW method was validated for the reliable grade evaluation method for concrete soil erosion control dam, and the resulting grades turned out to agree with the results determined by Sabang Associations.

• Geomechanics and Engineering
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• v.20 no.6
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• pp.537-546
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• 2020

Oil and natural gas reserves have been recognised abundantly in clayey rich rock formations in deep costal reservoirs. It is necessary to understand the sedimentary history of those reservoir rocks to well explore these natural resources. This work designs a group of laboratory experiments to mimic the physical process of the sedimentary clay-rich rock formation. It presents characterisation results of the physical properties of the artificial clayey rocks synthesized from illite clay, quartz sand and brine water by high-pressure consolidation tests. Special focus is given on the effects of illite clay content and high-stress consolidation on the physical properties. Multi-step loaded consolidation experiments were carried out with stress up to 35 MPa on mixtures constituting of the illite clay, quartz sand and brine water with five initial illite clay contents (w=85%, 70%, 55%, 40% and 25%). Compressibility and void ratio were characterised throughout the physical compaction process of the mixtures constituting of five illite clay contents and their water permeability was measured as well. Results show that the applied stress induces a great reduction of clayey rock void ratio. Illite clay contents has a significant influence on the compressibility, void ratio and the permeability of the physically synthesized clayey rocks. There is a critical illite clay content w=70% that induces the minimum void ratio in the physically synthesised clayey rocks. The SEM study indicates, in the high-pressure synthesised clayey rocks with high illite clay contents, the illite clay minerals are located in layers and serve as the material matrix, and the quartz minerals fill in the inter-mineral pores or are embedded in the illite clay matrix. The arrangements of the minerals in microscale originate the structural anisotropy of the high-pressure synthesised clayey rock. The test findings can give an intuitive physical understanding of the deep-buried clayey rock basins in energy reservoirs.

• Composites Research
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• v.28 no.5
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• pp.316-321
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• 2015

This study investigated the effects of microcapsules on mechanical properties and thermal stability of the composite material containing self-healing microcapsules. To this end, tensile specimens and flexural specimens containing melamine-urea-formaldehyde (M-U-F) shell walled microcapsules with diameters of $70{\sim}130{\mu}m$ were manufactured. Varying amount of microcapsules in the specimens was considered: 0 wt%, 0.5 wt%, and 1.0 wt%. The tensile and flexural tests were conducted to evaluate mechanical properties of the specimens containing the microcapsules and the thermogravimetric analysis test was performed to evaluate the thermal stability of the specimens containing the microcapsules. The results show that the tensile strength of the specimens was sensitive to the amount of the microcapsules compared to the tensile modulus even though the tensile modulus of the specimens was not significantly affected by the amount of the microcapsules. However, reduction of the tensile strength was not linearly proportional to the amount of microcapsules; similar results were observed in the flexural test. The weight changes of the specimens containing the microcapsules, as a function of temperature, were similar to those specimens without microcapsules. The thermal stability of the specimens was not affected significantly by the microcapsules embedded in the specimens.

• Journal of the Korean School Mathematics Society
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• v.17 no.3
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• pp.337-358
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• 2014

The purpose of this study is to investigate how storytelling is embodied in the Mathematics I textbooks for first grade high school students in the 2009 revised curriculum and the perception of secondary math teachers and students of those books. Furthermore, in order to have some implications on newly ongoing textbook development, this thesis sets up the following goals for inquiry into the effect on storytelling. First, are there any noticeable differences among the 10 types of mathematics I textbooks for high school first graders in the 2009 revised curriculum? Second, what do teachers and students think of textbooks which apply storytelling techniques? The results are as follows. The frequency of storytelling types that appeared in the textbooks is as follows: real-life connection type and inter-scholarship type take up 47.55% and 24.51% respectively, followed by decision-making type with 10.52%, math history type with 10.17% and tool-using type with 7.05%. Within the contents, math history type showed up on reading material from every textbook. And it is worth considering that real-life-connection type has the most various topics and is mainly for arousing interest and checking up on some concepts. However, inter-scholarship type is usually related to science, and decision-making type is included for error analysis and tool-using type for reading materials about math programs. The results of this study suggest that many of the teachers who participated showed some kind of understanding of storytelling but there were not many who are actually incorporating that into their own classes. It is also essential that we develop textbooks that are effective for storytelling classes, hold regular symposiums as well as teacher training, and create tools for proper assessment. Furthermore, students think that textbooks based on storytelling would have positive effects as long as they are supported by enough time, a sufficient number of classes and tests with validity.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.4
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• pp.635-650
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• 2017

Acoustic emission (AE) sensors have broadly used to monitor the damage of underground structures and tunnels. The reliability of measured signal is determined by the coupling condition of the AE sensors which are embedded in the target underground structure. To secure the reliability of health monitoring results, it is important to understand the characteristics of the coupling materials. In this study, laboratory tests were performed using portland cement, micro cement, and gypsum as coupling materials in order to verify the bleeding characteristics. The effective parameters for bleeding were determined to be water-cement ratio, material type, curing time, and injected volume of coupling materials. As a results of the experimental study, the bleeding rate increases with an increase in a water-cement ratio and an injected volume; for portland cement, water-cement ratio and injected volume effects are larger than the micro cement. However, curing time is not much effective for occurrence of the bleeding phenomenon. It is anticipated that this study may be useful for the selection of suitable coupling materials for installation of acoustic emission sensors.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.4
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• pp.651-668
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• 2017

For initial stability of the tunnel, the primary support, Shotcrete and rockbolt shall be placed in the most appropriate time. This is because the role of such support plays a vital role in long-term and short-term tunnel stability. In this study, the rock bolt is an important supporting system that receives the external pressure generated by the stress relaxation during tunnel excavation as axial force and transmits it to the shotcrete on the tunnel excavation surface. Until now, most of the materials of rock bolts have been used in the field, but there have been many problems such as uncertain quality of Chinese materials entering the market, poor packing due to falling down of rock bolts when filled with mortar, and corrosion due to water. Therefore, in this study, we have developed a high strength steel pipe rock bolt using Autobeam material to solve and improve various problems of existing rock bolts. In order to evaluate the performance of the developed bolt, field tests were carried out and the existing mortar filler in order to improve the performance of the rock bolt, the design and construction criteria were studied and the results were included in this paper.

• Journal of the Korea Institute of Building Construction
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• v.10 no.5
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• pp.113-119
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• 2010

Fire resistance and field tests for high-strength concrete(HSC) of 80MPa were carried out to evaluate whether or not it shows the same material properties even in the field condition of being mass-produced and supplied. As a result, it was found that fire resistant HSCs containing composite fiber(NY, PP) of 0.075% have great resistance to fire and spalling. In the field test, before the pumping air contents, slump flow, U-box, L-flow, compressive strength, gap of hydration temperature of interior and exterior of specimen and placing ratio per hour satisfied the required properties of HSC. However, after the pumping of HSC, as slump flow and L-flow were slightly less than required criterion, they need to be improved. In terms of hydration temperature of HSC, it was found to satisfy the related criterion. Packing ability as well as placing ratio per hour of HSC, which was about $44m^3$, show outstanding results. If slump flow of developed ternary HSC is improved after the pumping it can be useful for the construction of high-rise buildings.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.8
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• pp.200-207
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• 2016

The automotive seat is an important component that moves in sync with the driver and is actively being developed with various new functions. The aim of this work is to develop a lightweight seat cushion extension module using a lightweight material. To this end, a structural strength analysis, vertical strength test, and durability test were conducted. In the structural analysis, the maximum value of deformation under vertical load was 4.98 mm at the front of the upper panel. The maximum stress was approximately 105 MPa, which occurred at the point of contact between the upper and lower panels of the module. The vertical strength test showed a maximum vertical deformation of 5.31 mm under a vertical load, which differed from the analysis results by approximately 6.45%. The structural safety of the product was verified by the fact that it showed no harmful deformation or damage during operation after the vertical strength test and a durability test for 20,000 cycles. Furthermore, the use of engineering plastics made it possible to reduce the weight by approximately 30% compared to existing products. The lack of damage after tests verified the passenger safety, strength, and rigidity of the product. The results are expected to be applied for improving environmental and fuel efficiency regulations and preventing accidents due to driver fatigue. The applications of this module could be expanded various types of vehicles, as well as other industries in which eco-friendly and lightweight materials are used.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.6
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• pp.155-162
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• 2012

When RC (Reinforced Concrete) structures are exposed to sea water, steel corrosion can occur and this leads a degradation of structural performance. Referring the electro-deposition system with sea water from the 1st step research, durability and structural performance are evaluated in coated steel and RC members containing it in the 2nd research. In the durability performance test, Half Cell Potential test is performed and the coated steel is evaluated to have the high resistance to corrosion, which shows only 35% of corrosion velocity in normal (bare) steel. In the structural performance test, tensile strength, adhesive strength, and flexural/shear in RC member are performed. For the electro-deposit coated steel, increasing ratios of 3.2% and 8.8% are evaluated in the test of tensile strength and adhesive strength, respectively. For the structural test in RC member, there is no big difference between RC members with coated and non-coated steel in ultimate load and failure pattern It is evaluated that the chemical compound with $CaCO_3$ and $Mg(OH)_2$ from electro-deposition causes slightly increased structural performance. The electro-deposit coated steel can be more widely applied after performance verification from several tests like fatigue, resistance to impact, and long term-submerging test.