• The Journal of Advanced Prosthodontics
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• 제6권6호
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• pp.451-455
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• 2014

PURPOSE. The most common failure seen in restorations with a zirconia core is total or layered delamination of the ceramic veneer. In the present study, the shear bond strengths between veneering ceramics and colored zirconia oxide core materials were evaluated. MATERIALS AND METHODS. Zirconia discs ($15{\times}12{\times}1.6mm$) were divided into 11 groups of 12 discs each. Groups were colored according to the Vita Classic scale: A3, B1, C4, D2, and D4. Each group was treated with the recommended shading time for 3 s, or with prolonged shading for 60 s, except for the control group. Samples were veneered with 3 mm thick and 3.5 mm in diameter translucent ceramic and subjected to shear test in a universal testing machine with a crosshead speed of 1 mm/min. One-way analysis of variance (ANOVA) and Tukey's HSD tests were used for comparisons of the groups having the same shading times. A paired t-test was used for groups of the same color (3 s/60 s). RESULTS. Among the 11 groups investigated C4 (3 s) had the highest bond strength with a value of 36.40 MPa, while A3 (3 s) showed the lowest bond strength with a value of 29.47 MPa. CONCLUSION. Coloring procedures can affect zirconia/ceramic bond strength. However, the results also showed that bond strengths of all the investigated groups were clinically acceptable.

• The Journal of Advanced Prosthodontics
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• 제6권3호
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• pp.151-156
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• 2014

PURPOSE. To investigate the microtensile bond strength between two all-ceramic systems; lithium disilicate glass ceramic and zirconia core ceramics bonded with their corresponding glass veneers. MATERIALS AND METHODS. Blocks of core ceramics (IPS e.max$^{(R)}$ Press and Lava$^{TM}$ Frame) were fabricated and veneered with their corresponding glass veneers. The bilayered blocks were cut into microbars; 8 mm in length and $1mm^2$ in cross-sectional area (n = 30/group). Additionally, monolithic microbars of these two veneers (IPS e.max$^{(R)}$ Ceram and LavaTM Ceram; n = 30/group) were also prepared. The obtained microbars were tested in tension until fracture, and the fracture surfaces of the microbars were examined with fluorescent black light and scanning electron microscope (SEM) to identify the mode of failure. One-way ANOVA and the Dunnett's T3 test were performed to determine significant differences of the mean microtensile bond strength at a significance level of 0.05. RESULTS. The mean microtensile bond strength of IPS e.max$^{(R)}$ Press/IPS e.max$^{(R)}$ Ceram ($43.40{\pm}5.51$ MPa) was significantly greater than that of Lava$^{TM}$ Frame/Lava$^{TM}$ Ceram ($31.71{\pm}7.03$ MPa)(P<.001). Fluorescent black light and SEM analysis showed that most of the tested microbars failed cohesively in the veneer layer. Furthermore, the bond strength of Lava$^{TM}$ Frame/Lava$^{TM}$ Ceram was comparable to the tensile strength of monolithic glass veneer of Lava$^{TM}$ Ceram, while the bond strength of bilayered IPS e.max$^{(R)}$ Press/IPS e.max$^{(R)}$ Ceram was significantly greater than tensile strength of monolithic IPS e.max$^{(R)}$ Ceram. CONCLUSION. Because fracture site occurred mostly in the glass veneer and most failures were away from the interfacial zone, microtensile bond test may not be a suitable test for bonding integrity. Fracture mechanics approach such as fracture toughness of the interface may be more appropriate to represent the bonding quality between two materials.

• 치위생과학회지
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• 제13권3호
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• pp.290-295
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• 2013

본 연구는 심미 치과보철물에 사용되는 지르코니아, lithium disilicate 코어와 전장도재 사이의 전단결합강도를 측정하고, 금속도재관을 대조군으로 설정하여 비교하였다. 직사각기둥 모양의 시편을 각각 10개씩 제작하여 코어와 전장도재 사이의 전단결합강도를 측정한 후 파절면의 양상을 실체현미경을 통해 관찰하였다. 제한된 조건하에 시행된 실험을 통하여 심미보철 분야에 널리 적용되고 있는 치과용세라믹 코어의 전단결합강도를 확인하였으며, 측정 후 비교분석된 결과는 다음과 같다. 2종의 치과용 세라믹 코어와 전장도재 간에 전단결합강도는 금속도재관의 전단결합강도와 유의한 차이가 있었다 (p<0.05). 본 실험 결과를 토대로 ZB군은 임상적으로 받아들여지는 전단결합강도 범위 내 분포를 보이지만, LB군은 임상허용 범위에 못 미치는 결과값을 보였다. 금속도재관과 달리 지르코니아, lithium disilicate 전부도재관은 모두 혼합형 파절양상을 보였다. 결론적으로 전단결합강도 실험에 사용된 시편이 임상적인 치과보철물의 형태와는 달리 실험을 위한 시편의 형태로 제작되어 임상적 결과를 반영하지 못했으며 구강 내의 상황과도 다르다는 한계점을 가지고 있다. 추후에는 이를 보완하여 치과보철물과 유사한 형태의 시편을 이용한 전단결합 강도의 측정과 구강 내 조건을 고려한 추가 실험이 필요하다고 생각된다.

• 한국세라믹학회지
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• 제45권4호
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• pp.208-213
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• 2008

In this study, helical antenna with microwave ZST ceramics was designed using finite element method and developed. Studied parameters are relative dielectric constant of the dielectric core and the width of the conduction metal band of the antenna. As shown in the results, the center frequency of the antenna was decreased as the dielectric constant increased. Also beam width of the antenna increased as both the dielectric constant and the conduction band width increased. Based on the designed optimal shape, the manufactured antenna has the good beam width at center frequency 1.58 GHz.

• 대한치과보존학회:학술대회논문집
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• 대한치과보존학회 2001년도 춘계학술대회
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• pp.235-237
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• 2001

;Dentistry has benefited from tremendous advances in technology with the introduction of new techniques and materials, and patients are aware that esthetic approaches in dentistry can change one's appearance. Increasingly. tooth-colored restorative materials have been used for restoration of posterior teeth. Tooth-colored restoration for posterior teeth can be divided into three categories: 1) the direct techniques that can be made in a single appointment and are an intraoral procedure utilizing composites: 2) the semidirect techniques that require both an intraoral and an extraoral procedure and are luted chairside utilizing composites: and 3) the indirect techniques that require several appointments and the expertise of a dental technician working with either composites or ceramics. But, resin restoration has inherent drawbacks of microleakage. polymerization shrinkage, thermal cycling problems. and wear in stress-bearing areas. On the other hand, Ceramic restorations have many advantages over resin restorations. Ceramic inlays are reported to have less leakage than resin restoration and to fit better. although marginal fidelity depends on technique and is laboratory dependent. Adhesion of luting resin is more reliable and durable to etched ceramic material than to treated resin composite. In view of color matching, periodontal health. resistance to abrasion, ceramic restoration is superior to resin restorationl. Materials which have been used for the fabrication of ceramic restorations are various. Conventional powder slurry ceramics are also available. Castable ceramics are produced by centrifugal casting of heat-treated glass ceramics. and machinable ceramics are feldspathic porcelains or cast glass ceramics which are milled using a CAD/CAM apparatus to produce inlays (for example, Cered. They may also be copy milled using the Celay apparatus. Pressable ceramics are produced from feldspathic porcelain which is supplied in ingot form and heated and moulded under pressure to produce a restoration. Infiltrated ceramics are another class of material which are available for use as ceramic inlays. An example is $In-Ceram^{\circledR}$(Vident. California, USA) which consists of a porous aluminum oxide or spinell core infiltrated with glass and subsequently veneered with feldspathic porcelain. In the 1980s. the development of compatible refractory materials made fabrication easier. and the development of adhesive resin cements greatly improved clinical success rates. This case report presents esthetic ceramic inlays for posterior teeth.teeth.

• International Journal of Quality Innovation
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• 제9권1호
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• pp.94-102
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• 2008

When facing the global severe competition, the enterprises all try their best to upgrade the quality, reduce the costs to reach the goal of customer satisfaction. Motorola was the earliest firm creating the term Six Sigma (6 ${\sigma}$); GE was the enterprise successfully fulfilling Six Sigma. The success of these two firms revealed the prominent effects and became the world-class model enterprises. The main purpose of promoting Six Sigma activity was to reduce the possible defects in the business process to the least through designing and monitoring business process in order to reach the goals such as the best quality and efficiency, the lowest costs, the shortest circular process time, maximum profits and customer satisfaction. This research used the Six Sigma technique to improve the business process of ceramics manufacturing plant and find out the major factors of slower core task time by the analytical process of Process Mapping, Pareto Chart, Simu18 simulation software and figures and proposed the improvement measures. Through the confirmation of the case companies, it successfully reduced the core process time and the organizational costs and increased the capacity.

• Nuclear Engineering and Technology
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• 제47권5호
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• pp.534-545
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• 2015

In the very high temperature reactor (VHTR), which is a next generation nuclear reactor system, ceramics are used as a fuel coating material and graphite is used as a core structural material. Even if a depressurization accident occurs and the reactor power goes up instantly, the temperature of the core will change only slowly. This is because the thermal capacity of the core is so high. Therefore, the VHTR system can passively remove the decay heat of the core by natural convection and radiation from the surface of the reactor pressure vessel. The objectives of this study are to investigate the heat transfer characteristics of natural convection of a one-side heated vertical channel with inserted porous materials of high porosity and also to develop the passive cooling system for the VHTR. An experiment was carried out using a one-side heated vertical rectangular channel. To obtain the heat transfer and fluid flow characteristics of the vertical channel with inserted porous material, we have also carried out a numerical analysis using a commercial Computational Fluid Dynamics (CFD) code. This paper describes the thermal performances of the one-side heated vertical rectangular channel with an inserted copper wire of high porosity.

• Design & Manufacturing
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• 제11권3호
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• pp.29-34
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• 2017

Increased demand for parts with micro-pattern structure made of metals, ceramics, and composites in various fields such as medical ultrasonic sensors, CT collimators, and ultra-small actuator parts. Micro powder injection molding (PIM) is a technology for manufacturing micro size, high volume, complex, precision, net-shape components from either metal or ceramic powder. In the present study, a standard mold with a variable insert core capable of producing various micro patterns was investigated. An injection molding test was performed on a standard mold using a line type micro-pattern core having an aspect ratio of 2, a slenderness ratio of 70, a pattern size of $200{\mu}m$, and a pattern spacing of $150{\mu}m$. During the filling process, the deformation of the mold with large aspect ratio and slenderness ratio was analyzed by the experiment and the numerical simulation according to the position of the gate. We proposed a mold structure that minimizes mold deformation by gate modification and enables uniform pattern filling behavior.

• 한국재료학회지
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• 제20권12호
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• pp.691-698
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• 2010

Magnesium hydroxide-melamine core-shell particles were prepared through the coating of melamine monomer on the surface of magnesium hydroxide in the presence of phosphoric acid. The melamine monomer was dissolved in hot water but recrystallized on the surface of magnesium hydroxide by quenching to room temperature in the presence of phosphoric acid. The core-shell particle was applied to low-density polyethylene/ ethylene vinyl acetate (LDPE/EVA) resin by melt-compounding at $180^{\circ}C$ as flame retardant. The effect of magnesium hydroxide and melamine content has been studied on the flame retardancy of the core-shell particles in LDPE/EVA resin according to the preparation process and purity of magnesium hydroxide. Magnesium hydroxide prepared with sodium hydroxide rather than with ammonia solution revealed higher flame retardancy in core-shell particles with LDPE/EVA resin. At 50 wt% loading of flame retardant, core-shell particles revealed higher flame retardancy compared to that of the exclusive magnesium hydroxide in LDPE/EVA composite, and it was possible to satisfy the V0 grade in the UL-94 vertical test. The synergistic flame retardant effect of magnesium hydroxide and melamine core-shell particles was explained as being due to the endothermic decomposition of magnesium hydroxide and melamine, which was followed by the evolution of water from the magnesium hydroxide and porous char formation due to reactive nitrogen compounds, and carbon dioxide generated from melamine.

• 헤리티지:역사와 과학
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• 제52권4호
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• pp.104-123
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• 2019

유럽의 여러 나라에 소장되어 있는 한국도자는 한국미술을 대표하는 장르로서 근대 유럽에서 일찍이 수집과 연구의 대상이 되었다. 유럽 현지에서 자료 조사를 한 결과, 근대 시기에 영국에 소장된 한국도자의 구입 과정이나 경제적 가치 등을 확인할 수 있는 자료가 비교적 많이 남아 있었다. 특히 근대 시기에 영국박물관과 V&A박물관이 한국도자를 소장하는 과정에서 작성된 서류에서는 그간 잘 알려지지 않았던 구입 과정, 가격, 기준, 인식이나 평가 등에 대한 내용을 확인할 수 있었다. 근대 영국에서 한국도자에 대한 인식, 소장 의도는 세 단계의 시기별 변화를 거치면서 컬렉션이 형성되었다. 1870년대 후반부터 1880년대 후반까지는 한국도자의 실체를 확인하지 못한 환상 속에 있던 시기였다. 1880년대 후반부터 1910년대까지 영국에 유입된 한국도자는 당시의 생활상을 보여주는 민족지학적 자료로서의 성격이 강하였다. 1910년 이후부터 1940년대까지는 고려청자 중심의 한국도자 컬렉션이 형성된 시기로 파악되었다. 근대 영국에서 한국도자를 구입하는 기준과 과정은 20세기 초 한국을 방문하여 도자를 구입한 세 명의 영국인 사례를 통하여 살펴보았다. 1910년 이후 영국인들은 시베리아 횡단열차나 배를 이용하여 극동아시아를 여행하면서 한국에서 도자를 구입하기 시작하였다. 한국 여행에서 전직 관료, 도굴꾼 등에게 좋고 오래된 고려자기를 비싸지 않은 가격에 구입하거나 출토되는 지역에 직접 가서 구매하는 상황을 확인하였다. 또한 기존에 알려지지 않은 카바노프 상회의 존재를 파악하여 도자를 포함한 다양한 한국 물건들이 서구인들에게 판매·운송되는 과정을 구체적으로 살펴보았다.마지막으로 근대 영국에서 한국도자의 경제적 가치가 어느 정도로 인정되었고, 그 가치를 판단하는 기준은 무엇이었는지를 살펴보았다. 당시 영국에서 한국도자는 조형적 우수성에 비해 합리적인 가격, 즉 우수한 품질에 비해 가격이 낮다고 평가되었다. 특히 일본인들이 선호했던 고려청자뿐만 아니라 조선시대 자기의 조형이 새롭고 우수하다는 평가자료는 기존에 알려지지 않았던 내용이다. 근대 영국에서 고려와 조선시대 도자를 아울러서 한국도자의 조형성과 제작 기술을 평가했던 관점은 다양한 종류의 한국도자 컬렉션이 형성되는 데 주요한 배경이 되었다.