• Restorative Dentistry and Endodontics
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• v.24 no.1
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• pp.166-179
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• 1999

Apical sealing is essential for the success of surgical endodontic treatment. Root-end cavity is apt to be contaminated with moisture or blood, and is not always easy to be dried completely. The purpose of this study was to evaluate the influence of dry methods of retrocavity on the apical seal in endodontic surgery. Apical seal was investigated through the evaluation of apical leakage and adaptation of filling material over the cavity wall. To investigate the influence of various dry methods on the apical leakage, 125 palatal roots of extracted human maxillary molar teeth were used. The clinical crown of each tooth was removed at 10 mm from the root apex using a slow-speed diamond saw and water spray. Root canals of the all the specimens were prepared with step-back technique and filled with gutta-percha by lateral condensation method. After removing of the coronal 2 mm of filling material, the access cavities were closed with Cavit$^{(R)}$. Two coats of nail polish were applied to the external surface of each root. Apical three millimeters of each root was resected perpendicular to the long axis of the root with a diamond saw. Class I retrograde cavities were prepared with ultrasonic instruments. Retrocavities were washed with physiologic saline solution and dried with various methods or contaminated with human blood. Retrocavities were filled either with IRM, Super EBA or composite resin. All the specimens were immersed in 2% methylene blue solution for 7 days in an incubator at $37^{\circ}C$. The teeth were dissolved in 14 ml of 35% nitric acid solution and the dye present within the root canal system was returned to solution. The leakage of dye was quantitatively measured via spectrophotometric method. The obtained data were analysed statistically using one-way ANOVA and Duncan's Multiple Range Test. To evaluate the influence of various dry methods on the adaptation of filling material over the cavity wall, 12 palatal roots of extracted human maxillary molar teeth were used. After all the roots were prepared and filled, and retrograde cavities were made and filled as above, roots were sectioned longitudinally. Filling-dentin interface of cut surfaces were examined by scanning electron microscope. The results were as follows: 1. Cavities dried with paper point or compressed air showed less leakage than those dried with cotton pellet in Super EBA filled cavity (p<0.05). However, there was no difference between paper point- and compressed air-dried cavities. 2. When cavities were dried with compressed air, dentin-bonded composite resin-filled cavities showed less apical leakage than IRM- or Super EBA-filled ones (p<0.05). 3. Regardless of the filling material, cavities contaminated with human blood showed significantly more apical leakage than those dried with compressed air after saline irrigation (p<0.05). 4. Outer half of the cavity showed larger dentin-filling interface gap than inner half did when cavities were filled with IRM or Super EBA. 5. In all the filling material groups, cavities contaminated with blood or dried with cotton pellets only showed larger defects at the base of the cavity than ones dried with paper points or compressed air.

• Journal of the Microelectronics and Packaging Society
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• v.23 no.2
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• pp.79-84
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• 2016

A flexible electronic device deformed by external force causes the failure of a semiconductor die. Even without failure, the repeated elastic deformation changes carrier mobility in the channel and increases resistivity in the interconnection, which causes malfunction of the integrated circuits. Therefore it is desirable that a semiconductor die be placed on a neutral line where the mechanical stress is zero. In the present study, we investigated the effects of design factors on the position of neutral line by finite element analysis (FEA), and expected the possible failure behavior in a flexible face-down packaging system assuming flip-chip bonding of a silicon die. The thickness and material of the flexible substrate and the thickness of a silicon die were considered as design factors. The thickness of a flexible substrate was the most important factor for controlling the position of the neutral line. A three-dimensional FEA result showed that the von Mises stress higher than yield stress would be applied to copper bumps between a silicon die and a flexible substrate. Finally, we suggested a designing strategy for reducing the stress of a silicon die and copper bumps of a flexible face-down packaging system.

• International Journal of Highway Engineering
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• v.13 no.3
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• pp.75-82
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• 2011

There is the uncertain period of the construction in case of the products meeting the quality standard of KS M 6080, the quality is degraded because of the abrasive loss of the paint caused by vehicle tires as the traffic amount increases and of the loss and detachment of the glass beads providing the retroreflective function. The abrupt degradation of visibility causes the high frequency of traffic accidents at night and increases the traffic accident rate. Additional supplementary construction induces the direct material and construction costs. As the more cost induction effect than the direct cost, the traffic jam caused by the additional construction increases the indirect social costs such as time cost and vehicle cost. Hence, the study is concerned with performing the abrasion resistance test based on the EN 1436 standard to check and improve the quality of various road marking materials resulting in improving the durability of road marking materials. However, even though the difference in the durability lifetime of resins(binders) is bibliographically or theoretically clear, there was no difference in the durability lifetime (retroreflectivity aspect) of the road marking paint using these binders. The reason is that the bonding of beads was very insufficient or that the cross density caused by crack or freshness was low. Moreover, the measured wet retroreflectivity was distributed as the Rw3 or higher class in average on the basis of EN 1436 but was very insufficient on the basis of the minimum wet threshold retroreflectivity with 100mcd/($m^2{\cdot}lx$) managed overseas.

• Journal of the Korean Wood Science and Technology
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• v.40 no.3
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• pp.177-185
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• 2012

The interest to develop adhesives from renewable resources is growing to substitute petroleum-based adhesive resins in the manufacture of wood based panels. In our study, rapeseed flour (RSF), which is the by-product of bio-diesel produced from rapeseed, were hydrolyzed with acid and alkali. As a crosslinking agents of the RSF hydrolyzates, phenol-formaldehyde prepolymers (PF) were prepared. The RSF hydrolyzates and PF were mixed to complete the formulation of RSF-based adhesive resins, and the resins were applied to make the medium density fiberboard (MDF). The physical and mechanical properties of the MDF were measured to examine whether RSF can be used as raw materials of adhesive resins for the manufacture of MDF or not. The average moisture content and density of the MDF made with RSF-based adhesive resins satisfied the minimum requirement of KS standard, but the thickness swelling was not. The bending strengths of the MDF made with RSF-based adhesive resins were lower than that of the MDF made with commercial UF resins, but the internal bonding strengths of tested MDF in some make-up conditions of RSF-based adhesive resins were higher than that of MDF made with commercial UF resins. These results showed the potential of RSF as a raw material of adhesives for the production of MDF. Future works on the optimal manufacturing process conditions of MDF made with RSF-based adhesive resins are required to improve the performance of MDF made with RSF-based resins.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.6
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• pp.1043-1051
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• 2017

Asphalt overlay on deteriorated concrete pavement has a problem of early damage due to reflective cracking. There is a need for a new method capable of reducing reflection cracking and ensuring the durability of pavement. The purpose of this study was to obtain durability of asphalt overlay with stress absorbing membrane interlayer (SAMI) using epoxy asphalt binder. The tensile performance, durability, water resistance and bonding performance of Epoxy-SAMI were evaluated by various tests. As a result of tests, Epoxy-SAMI meets the quality standard of the bridge waterproofing material. The repeated direct tensile test was carried out to investigate the effect of reflective cracking reduction. When the Epoxy-SAMI was applied, it had 1.2~1.56 times higher reflective cracking resistance than PSMA asphalt concrete with the thickness of 10cm even if the section thickness decreased. 4-point bending beam test results showed the number of fatigue failures increased 7.5 times when Epoxy-SAMI was applied. The Epoxy-SAMI was found to be effective in improving the durability of the asphalt pavement overlay because it serves to prevent reflective cracking, increase lifespan, and function as a waterproof layer.

• Journal of the Korean Chemical Society
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• v.47 no.4
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• pp.391-400
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• 2003

This study was performed the analysis of seven kinds of the hight school chemistry II textbooks based on the 6th curriculum. Particularly, inquiry activity part was analyzed by the three dimension framework which consists of inquiry content dimension, inquiry process dimension and inquiry context dimension. In the analysis of the inquiry content dimension of inquiry activities, the total number of themes in seven kinds of textbook was 212. And the number of inquiry activities in seven kinds of textbook was diverse: A textbook had 28, B textbook 25, C textbook 31, D textbook 35, E textbook 31, F textbook 29 and G textbook 33. As for the avaerage number of inquiry activities of each chapter, chapter I "Material Science" is 3.00(9.91${\%}$), chapter II "Atomic Structure and Periodic Table" 4.57(15.1${\%}$), chapter III "Chemical Bonding and Compound" 6.86(22.6${\%}$), chapter IV "State of Matter and Solution" 7.00(23.1${\%}$), chapter V "Chemical Reaction" 8.86(29.2${\%}$). For the analysis of inquiry process dimension, it follows in the order of 'observation and measuring (66.7${\%}$)', 'Interpreting data and formulating generalizations (26.5${\%}$)', 'seeing a problem and seeking ways to solve it (4.1%)', and 'building, testing and revising the theoretical model (2.7${\%}$)'. As for the analysis of the inquiry context dimension, the scientific context occupied 90.5${\%}$, the individual context 4.3${\%}$, the social context 0.9${\%}$, and the technical context 4.3${\%}$. It shows that the proportion of STS(Science-Technology-Society) related contents in inquiry activities was only 9.5${\%}$.

• The Journal of Korean Academy of Prosthodontics
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• v.29 no.3
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• pp.33-41
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• 1991

Cermic has been widely used because of its excellent esthetics and strength. The recently introduced castable ceramic system is regarded as the more esthetic and biocompatible restorative material. The purpose of this study was to compare the shear bond strength of Dicer & G-Cera porcelain laminate veneer according to the type of cement and surface treatment and to observe the surface of bonding failure with SEM. Total forty disks(3.5mm $diam.\times2.0mm$ thickness) were prepared. Forty extracted human maxillary central incisor teeth were stored in saline solution. Ten teeth were bonded to Dicer specimen with Dicer ZPC cement and ten teeth were bonded with Dicer resin cement. Ten silicoated G-Cera specimen and ten non-silicoated G-Cera specimen were bonded to teeth with G-Cera resin cement. Bonded units were mounted in a plastic tube with hard stone and stored in a humidor at $37^{\circ}C$ for 24 hours. Shear bond strength was measured by Instron Universal Testing Machine (Model 1125) and all the specimen were observed with SEM(JEOL, JSM-T2000)and modes of failure were recorded. The obtained results were as follows: 1. The mean shear bond strength of Dicer bonded with Dicer resin cement was 11.62 MPa and that bonded with Dicor ZPC cement was 0.88 MPa : Shear bond strength of Dicer bonded with Dicer resin cement was significantly increased(P<0.05). 2. The mean shear bond strength of silicoated G-Cera was 13.10 MPa and that of non silicoated G-Cera was 10.93 MPa : Shear bond strength of silicoated G-Cera was not significantly increased (P>0.05). 3. Shear bond strength of Dicer and G-Cera porcelain laminate veneer was not significantly different (P>0.05). 4. In observation of bond failure with SEM, Dicer bonded with Dicer ZPC cement exhibited adhesive failure. Dicer bonded with Dicer resin cement and silicoated and non silicoated G-Cera exhibited cohesive failure.

• Restorative Dentistry and Endodontics
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• v.21 no.1
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• pp.136-149
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• 1996

The effects of various All-Etching Agents (10% phosphoric acid, 10% maleic acid and 10 % citric acid) and 32 % phosphoric acid and varied etching time were evaluated by observing the morphology of the etched enamel surfaces using Scanning electron microscopy and by measuring the shear bond strength of a composite resin to human enamel. A total of 156 extracted premolar and molar teeth free of irregularities were employed in this study. Specimens for the observation of enamel morphology were divided into 12 groups of 3 teeth each, based on the type of etchant used and application time. After exposure to the etching agent specimens were washed air-dried and then glued to aluminum stubs and coated with a layer of gold for examination in the scanning electron microscope. Specimens for the evaluation of bond strength were divided into 12 groups of 10 teeth each also based on the type of etchant used and application time. After exposure to the etching agent the specimens were washed, air-dried and a thin layer of bonding agent was applied using a brush. Z 100 composite resin was light cured to the surface and stored at $37^{\circ}C$, 100% humidity for 7 days. An Instron Universal Testing Machine was used to apply a shearing force at $90^{\circ}$ angle from the enamel surface. It is concluded from this study that commercial All-etching agents can be used with a 15-second etching without adversely affecting retention of dental resin materials. At the same time, the acid concentration is probably a suitable compromise regarding the acid's function as a dentin demineralizing all-etch conditioning agent. The following results were obtained. 1. Specimens etched with 10 % citric acid showed a random superficial etching pattern which could not be related to prism morphology. 2. Specimens etched with 10 % and 32 % phosphoric acid and 10 % maleic acid showed a type I pattern in which core material was preferentially removed leaving the prism peripheries relatively intact or a type II pattern in which prism peripheries were preferentially removed. This delineation became more distinguished as etching time was increased. 3. All-Etching Agents and 32 % phosphoric acid showed a statistically significant higher shear bond strength at 15 seconds etching time.(p<0.05) 4. 10 % maleic acid and 32 % phosphoric acid exhibited a statistically significant higher shear bond strength than 10 % phosphoric and citric acid at 15 seconds etching time.(p<0.05).

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.3
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• pp.576-583
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• 2018

Silicon carbide is considered to be a potentially useful material for high-temperature electronic devices, as its band gap is larger than that of silicon and the p-type and/or n-type conduction can be controlled by impurity doping. Particularly, porous n-type SiC ceramics fabricated from ${\beta}-SiC$ powder have been found to show a high thermoelectric conversion efficiency in the temperature region of $800^{\circ}C$ to $1000^{\circ}C$. For the application of SiC thermoelectric semiconductors, their figure of merit is an essential parameter, and high temperature (above $800^{\circ}C$) electrodes constitute an essential element. Generally, ceramics are not wetted by most conventional braze metals,. but alloying them with reactive additives can change their interfacial chemistries and promote both wetting and bonding. If a liquid is to wet a solid surface, the energy of the liquid-solid interface must be less than that of the solid, in which case there will be a driving force for the liquid to spread over the solid surface and to enter the capillary gaps. Consequently, using Ag with a relatively low melting point, the junction of the porous SiC semiconductor-Ag and/or its alloy-SiC and/or alumina substrate was studied. Ag-20Ti-20Cu filler metal showed promise as the high temperature electrode for SiC semiconductors.

• Journal of Conservation Science
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• v.32 no.2
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• pp.223-234
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• 2016

Two-component epoxy resin is widely used in the cultural heritage restoration field. However according to mixing ratio of resin and hardener, curing property, mechanical strength and chemical structure differ which have possibility to effect the stability of cultural heritage. Result of questionnaire survey shows hands-on workers in the conservation field tend to mix the epoxy resin with his or her eye measurement when the using amount is small or mix additional hardener to shorten the pot life of epoxy resin. This research aims to analyze the curing property, mechanical strength and chemical structure of rapid curing type epoxy resin and medium curing type one depending on relative ratio of 0.25~4 of hardener to resin. When the amount of hardener was 0.5~2 times more than the resin, exothermic heat and curing speed were both increased. In case of included hardener to resin was lower than official ratio, mechanical strength (tensile shear strength, tensile strength and compressive strength) became higher along with active cross-linking bonding of the epoxy resin. Medium curing type epoxy relatively had lower exothermic heat and slower reaction during curing process. It was observed to be put to definite point of mechanical strength under lower content of hardener than official ratio. While, hardener ratio more than twice the resin slowed down the curing greatly and lowered the adhesion strength also. In conclusion, under the lower mixing rate of hardener than official ratio would show relatively fast reaction with similar mechanical strength. Over the official ratio on the other hand, material property drops rapidly. Accordingly, mixing ratio of epoxy resin is expected to be influential to the stability of cultural heritage.