• Journal of the Korean GEO-environmental Society
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• v.15 no.4
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• pp.43-51
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• 2014

A Large-diameter drilled shaft of deep water depth composite foundation supporting a high rise pylon of the test designed super long span bridge was designed by allowable stress design method and failure probability through reliability analysis to bearing capacity was estimated. The allowable stress design results for the bearing capacity of a drilled shaft were analyzed by reliability analysis and the probability of failure shows 0.12 % in case of CFEM, 0.0002 % in case of Korea Highway Corporation criterion, and 0.003 % in case of structure foundation design criterion. In the allowable stress design, the bearing capacity of a large-diameter drilled shaft was obtained by applying to safety factor 3 and reliability analysis for the results was done. If the failure probability suggested by AASHTO(2007) specification is set to 0.02 %, the socketed length of a drilled shaft shows an increase of 25 % in CFEM, decrease of 60 % in KHCC, and decrease of 89 % in SFDC.

• The Journal of Korean Academy of Prosthodontics
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• v.33 no.4
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• pp.611-633
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• 1995

The pupose of this study was to compare the fracture strength of five kinds of all-ceramic crowns(Vintage, Dicor Empress-staining, Empress-layering, In-Ceram) luted with glass ionomer cerment and composite resin cement and to evaluate the effect of cements on the fracture stregth of all ceramic crowns. Five groups of twelve uniform sized all-ceramic crown specimens were fabricated. Six specimens of each group were cemented with glass ionomer cement(Fuji G.I. Cement) and the remaining six specimens of each group were etched, silane-treated, and cemented with composite resin cement(Bistite resin cement). The crowns were stored in water$(37^{\circ}C)$ for 1 day prior to loading in an Instron, using a steel ball(diameter 4mm) at a crosshead speed of 0.5mm/min. The crowns were angled $30^{\circ}$, so the steel ball contacted with the crowns 2mm lingual from the mid-incisal edge. The results obtained were summarized as follows ; 1. With G.I. cement, mean fracture load(Kg) Were : Intage : $18.33{\pm}1.47$ ; Empress-staining : $23.92{\pm}6.67$ ; Dicor : $24.0{\pm}5.81$ ; Empress-layering : $26.92{\pm}2.80$ ; In-Ceram : $51.58{\pm}6.87$ ; ANOVA revealed a significant difference existed(p<0.05) between the group A(Vintage, Dicor, Empress-staining, Empress-layering) and group B(In-Ceram). 2. With Resin cement, mean fracture load(Kg) were : Intage : $22.75{\pm}4.97$ ; Dicor : $42.75{\pm}7.07$ ; Empress-staining : $44.08{\pm}7.99$ ; Empresslayering : $50.42{\pm}5.43$ ; In-Ceram : $52.58{\pm}6.51$ ; ANOVA revealed a significatnt difference existed(p<0.05) between the group A(Vintage) and B(Dicor, Empress-staining Empress-alyering, In-Ceram). 3. Resin cement significantly increased the fracture strength of the all-ceramic crowns for Dicor(156%), Empress-staining(185%), Empress-alyering(187%)(p<0.05); but did not increase the fracture strength of Vintage(128%) and In-Ceram(101%)(p>0.05). 4. Majority of the all-ceramic crowns show a wedge fracture extending through proximal surfaces to an apex, usually apical third(with G.I. cement) or middle third(with Resin cement) of the facial surface.

• Restorative Dentistry and Endodontics
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• v.27 no.1
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• pp.77-86
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• 2002

Current composites are made with dimethacrylate monomers and silane-treated silica microfillers, either alone or with silane treated glass fillers The main reasons for clinical failure of dental composites are secondary caries, wear and fracture. Most of practitioner want to get a composite which is more tougher under occlusal stress, less polymerization contraction, and better handling properties in application clinically. The aim of this study was to investigate the influence of resin matrix with various flows on the physical proper-ties such as fracture toughness and degree of conversion of the experimental resins. It was hypothesized that flexible or tough resin composites can be designed by judicious choice of monomer composition Various flow resin matrices containing Bis-GMA, UDMA, and TEG-DMA were made by altering the pro-portion of the monomers. After the unfilled resins were light-cured for different light intensity, the fracture toughness(K$_{1c}$) was measured according to ASTM standard using the single edge notched geometry, and degree of conversion(DC) was measured by FTIR. And experimental composites were formulated with variations in the proportion of silanated quartz and strontium glass fillers as 60, 75, and 77wt%. Also, the physical properties of composites with various filer contents were evaluated as same manner. All resulting data were compared by ANOVA/Tukeys test at 0.05 level. The results were as follows; 1. The degree of conversion of high flow resin containing less Bis-GMA was higher than that of low flow unfilled resin 2. While the degree of conversion of unfilled resin was increased according to light intensity for polymerization, there was no significant increase with moderate and high light intensity. Also, the fracture toughness was not increased by high light intensity. 3. The fracture toughness was high in the low flow unfilled resin containing higher contents of Bis-GMA. 4. There was a significant increase for fracture toughness and a tendency for degree of conversion to be reduced when the content of fillers was increased. 5. In the experimental composites, the flow of resin matrix did not affected on the fracture toughness, even, which was decreased as increase of viscosity. These results showed that the physical properties of a dental composite could be attributed to the flow of resin matrix with relative content of monomers. Specific combination of resin monomers should be designed to fulfil the needs of specific indication for use.

• International Journal of Highway Engineering
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• v.15 no.2
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• pp.29-37
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• 2013

PURPOSES : This study aims to review the possibility of developing a road snow-melting system that can prevent slip accidents by maintaining a constant temperature of the winter roads and enhance performance of structures, including improvement of compressive strength by mixing carbon nanotube (hereafter referred to as CNT) with cement paste, the basic material. METHODS : To achieve the above purpose, an experiment was conducted by mixing power-type CNT and wrap-type CNT up to cement paste formulation by weight of 0.0wt%~4.1wt% in accordance with "KS L ISO 679(of cement strength test method)", and compressive strength was measured at 28 days of curing. In addition, the volume resistivity of the specimen was measured to test thermal and electrical characteristics, and the rate of temperature changes in specimen surface by power consumption was measured by passing electricity through the cross-sections of the specimen. Meanwhile, the criteria for checking the performance as a road snow-melting system was determined as volume resistivity of $100{\Omega}{\cdot}cm$ or less. RESULTS : A comparative analysis between specimen with 0wt% CNT content in plain status and specimen containing various types of CNTs was carried out. From its results, it was found that compressive strength increased approximately 19%, showing the highest rate when 0.2wt% of wrap-type CNT was contained, but volume resistivity of $100{\Omega}{\cdot}cm$ or less appeared only in specimens containing more than 0.2wt% CNT. In addition, it was observed that the surface temperature increased by $4.62^{\circ}C$ per minute on average in specimens containing 3.2wt% CNT. CONCLUSIONS : In this study, CNT was examined as an underlying material for a road snow-melting system, and the possibility of developing the road now-melting system was reviewed by conducting various experiments using CNT-Cement composites. From the experimental results, the specimens were found to have a superior performance when compared to the existing road snow-melting systems that place the heat transfer medium such as copper on the road. However, satisfactory strength performance were not obtained from the specimen containing CNT(2.0% or more) that functions as a heating element, which leads to the need for reviewing methods to increase the strength by using plasticizer or admixture.

• Journal of Navigation and Port Research
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• v.30 no.8 s.114
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• pp.711-719
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• 2006

A series of geotechnical centrifuge model tests and numerical modelling have been performed to study engineering characteristics of the composite ground reinforced by both the Sand Compaction Piles(SCPs) and the deformation-reducing sheet piles. The research has covered several key issues such as the load-settlement relation, the stress concentration ratio and the final water content of the ground Totally three centrifuge tests have been conducted by changing configuration of the sheet piles, i.e., a test without the sheet pile, a test with the sheet pile at a single side and a test with the sheet piles at the both sides. In the model tests, a vertical load was applied in-flight on the ground surface. On the other hand, class-C type numerical modelling has been performed by using the SAGE-CRISP to compare the centrifuge test results using an elasto-plastic model for SCPs and the Modified Cam Clay model for the soft clay. It has been found that the sheet piles can restraint failure of foundation, thereby increasing yield stress of the ground. The stress concentration ratio was in the range of $2{\sim}4$. In addition, numerical analysis results showed reductions both in the ground heave($20{\sim}30%$) and in the horizontal movement($28{\sim}43%$), demonstrating the deformation-reducing effect of the sheet piles.

• Restorative Dentistry and Endodontics
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• v.31 no.5
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• pp.337-343
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• 2006

The purpose of this study was to estimate the relation between techniques used for microleakage from dye penetration and for marginal adaptation from SEM evaluation of the restoration. Using high speed #330 bur class V cavities ($4{\times}3{\times}1.5 mm$ around CEJ) were prepared on the buccal surface of 20 extracted human molars. Six dimples as reference points for SEM and dye penetration evaluation were made with 1/2 round bur. Cavity was bulk filled with microhybrid composite resin (Esthet X) and all-in-one adhesive (Xeno III). Teeth were stored in saline solution for one day, after then, they were finished and polished using Sof-Lex system. Fifty percent silver nitrate dye solution was used for the evaluation of microleakage and resin replica was used for marginal adaptation. All of these were done after 1000 times thermocycling between 5 and $55^{\circ}C$. Vertical sections were made through three dimples of restoration to obtain samples for the evaluation of dye penetration and inner marginal adaptation. Outer adaptational estimation was done with an intact restoration before sectioning. Dye penetration was determined in three degrees and percentage of outer and inner leaky margin was estimated from SEM image The data were analysed statistically: Spearman's rho test were used to check relationships between two methods. The result were as follows : 1. There were significant relationships between degree of dye penetration and inner and outer marginal adaptations each (p < 0.01). 2. However, there was no significant relationship between the results or inner and outer marginal adaptation. Within the results of this study, relationship between the percentage of marginal adaptation and microleakage shows significant relationship. However, inner and outer marginal adaptation did not show any significant relationship mutually.

• Restorative Dentistry and Endodontics
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• v.30 no.5
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• pp.363-371
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• 2005

This study investigated the effect of thickness of flowable resin lining on marginal leakage in class II composite restorations. 80 experimental teeth were prepared with class II preparations with enamel margin or dentin margin. Each group was devided into four groups according to flowable resin lining thickness ; Control group - no flowable resin lining, Group 1 - 0.5 mm flowable resin lining, Group 2 - 1 mm flowable resin lining, Group 3 - 2 mm flowable resin lining. The cavities were restored using Scotchbond Multi-Purpose adhesive system, Filtek Flow and Filtek Z 250 composite resin. Following one day storage in distilled water, the restored teeth were thermocycled for 500 cycles and immersed in $2\%$ methylene blue for 24 hours. The results of this study were as follows : 1. Ranking of mean microleakage scores at the enamel margins was Group 1 < Control = Group 2 < Group 3. The microleakage of Group 3 was significantly higher than that of Control, Group 1 and Group 2 (p < 0.05). 2. Ranking of mean microleakage scores at the dentin margins was Group 1 < Group 2 < Control < Group 3. The microleakage of Group 3 was significantly higher than that of Control, Group 1 (p < 0.05) 3. Compared with microleakage between the enamel and dentin margins, enamel margin group were significantly lower than dentin margin group.

• Journal of the korean academy of Pediatric Dentistry
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• v.28 no.2
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• pp.261-270
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• 2001

This study was performed to evaluate wear characteristics of light-cured composites when opposed by human enamel. Seven light-cured restorative composites were selected and enamel cusps sectioned from premolars. All samples were stored in distilled water at $37^{\circ}C$ for 10 days. 68.6 N of weight was loaded during the test. The measurements of vertical loss of enamel cusps, weight loss and volume loss of composites, and SEM observations of the polished and abraded surfaces were made after 30,000 cycles. The results obtained were summarized as follows; 1. The highest hardness value of 70.4 was observed in the Spectrum group and the lowest value of 19.8 was observed in the Heliomolar group. Results of Tukey test showed that an overall significant difference was indicated except the Spectrum, Z100 and Clearfil AP-X groups(p<0.05). 2. Enamel showed the good abrasion resistance against the Heliomolar group of microfilled composite and the Palpique Toughwell group containing the submicron hybrid type spherical fillers. 3. The abrasive wear resistance of hybrid composites was improved with the decrease of mean particle size and hybrid of submicron particle fillers. 4. SEM observation of worn surfaces revealed the protrusion, attrition and missing of fillers, cracks developing and delamination in the matrix.

• Transactions of the Korean hydrogen and new energy society
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• v.25 no.1
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• pp.19-27
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• 2014

Mg hydride has a high hydrogen capacity (7.6%), at high temperature, and is a lightweight and low cost material, thus it a promising hydrogen storage material. However, its high operation temperature and very slow reaction kinetics are obstacles to practical application. In order to overcome these disadvantages of Mg hydride, graphene powder was added to it. The addition of graphene has been shown to reduce the operating temperature of dehydrogenation. Moreover, in this report the environmental aspects of $MgH_x$-Graphene composites are investigated by means of the environmental life cycle assessment (LCA) method. $MgH_x$-Graphene mixture was prepared by hydrogen induced mechanical alloy (HIMA). The synthesized powder was characterized by XRD(X-ray Diffraction). The hydrogenation behaviors were evaluated by using a Sievert's type automatic PCT apparatus. Such evaluation of Materials also conducted in the LCA. From the result of P-C-T(Pressure-Composition-Temperature) curves, the $MgH_x$-3wt.% graphene composite was evaluated as having a 5.86wt.% maximum hydrogen storage capacity, at 523K. From absorption kinetic testing, the $MgH_x$-7wt.% graphene composite was evaluated as having a maximum 6.94wt.%/ms hydrogen absorption rate, at 573K. Environment evaluation results for the $MgH_x$-graphene composites and other materials indicated environmental impact from the electric power used and from the materials themselves.

• Korean Chemical Engineering Research
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• v.51 no.4
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• pp.411-417
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• 2013

To use as an anode material of lithium secondary battery, graphite-silicon composite powders are prepared by ball-milling with silicon nanoparticles (average diameter 100 nm, 0~50 wt%) and graphite powder (average diameter $15{\mu}m$) and their electrochemical properties are examined. As the silicon content increases, the graphite becomes smaller by the ball-milling and amorphous phase appears whereas the silicon do not suffer the change of nanocrystalline phases and embeds within the amorphous phase of graphite. Cyclic voltammetry at low scan rate reveals that typical oxidation peaks of graphite and silicon appear at 0.2~0.35 and 0.55~0.6 V, respectively, with higher reversibility for repeated cycles. In contrast, the high-scan-rate redox behavior is very irreversible for repeated cycles. High irreversible capacity is exhibited in the initial charging-discharging cycles, but it diminishes as the cycle number increases. The saturated discharge capacity achieves about 485 mAh $g^{-1}$ at 50th cycle for the composite of Si 20 wt%. This is due to the formation of amorphous graphite morphology by the adequate composition (C:Si=8:2 w/w), which efficiently buffers the volume change during alloying/dealloying between silicon and lithium.