• 한국세라믹학회지
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• 제19권1호
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• pp.13-18
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• 1982

The crystallization of metastable "orthorhombic" phase from the glass in the system of Na $AlSi_3O_8-CaAl_2Si_2O_8$ is studied. These crystals are crystallized in the range of composition from $Ab_80An_20$ to An100. The symmetry of these crystals show orthorhombic as a possible space group P22121. Two probable twin models are proposed. proposed.

• 한국재료학회지
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• 제20권6호
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• pp.319-325
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• 2010

3-D IC integration enables the smallest form factor and highest performance due to the shortest and most plentiful interconnects between chips. Direct metal bonding has several advantages over the solder-based bonding, including lower electrical resistivity, better electromigration resistance and more reduced interconnect RC delay, while high process temperature is one of the major bottlenecks of metal direct bonding because it can negatively influence device reliability and manufacturing yield. We performed quantitative analyses of the interfacial properties of Al-Al bonds with varying process parameters, bonding temperature, bonding time, and bonding environment. A 4-point bending method was used to measure the interfacial adhesion energy. The quantitative interfacial adhesion energy measured by a 4-point bending test shows 1.33, 2.25, and $6.44\;J/m^2$ for 400, 450, and $500^{\circ}C$, respectively, in a $N_2$ atmosphere. Increasing the bonding time from 1 to 4 hrs enhanced the interfacial fracture toughness while the effects of forming gas were negligible, which were correlated to the bonding interface analysis results. XPS depth analysis results on the delaminated interfaces showed that the relative area fraction of aluminum oxide to the pure aluminum phase near the bonding surfaces match well the variations of interfacial adhesion energies with bonding process conditions.

• 한국주조공학회지
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• 제38권1호
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• pp.9-15
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• 2018

Electromagnetic continuous casting (EMCC) was used to fabricate Ti-6Al-4V alloys with properties suitable for medical applications. Ti-6Al-4V alloy ingots fabricated by EMCC were subjected to heat treatment, such as residual stress removing (RRS), furnace cooling after solution treatment (ST-FC) and water-cooling after solution treatment (ST-WC), in order to obtain characteristics suitable for the standard. After component analysis, the microstructure and mechanical properties (tensile strength and elongation) were evaluated by ICP, gas analysis, OM, SEM, a Rockwell hardness tester and universal testing machine. The Ti-6Al-4V alloy ingot fabricated by EMCC was fabricated without segregation, and the lamellar structure was observed in the RRS and ST-FC specimens. The ST-WC specimen showed only martensite structure. As a result of evaluating the mechanical properties based on the microstructure results, we found that the water-cooled heat treatment condition after the solution treatment was most suitable for the Ti-6Al-4V ELI standard.

• 한국세라믹학회지
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• 제31권5호
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• pp.572-580
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• 1994

With low thermal expansion coefficients, eucryptite (Li2O.Al2O3.2SiO2) and spodumene (Li2O.Al2O3.4SiO2) in LAS ceramic system show good thermal shock resistance. In this study, sillimanite or kaolin group silicate minerals and Li2CO3 were used as starting materials, and if necessary SiO2 or Al2O3 were added for making stoichiometrically formed specimens. By this process, eucryptite powders were synthesized and characterized. The powder mixtures of lithiumcabonate and silicate minerals calcined at 80$0^{\circ}C$ for 2 hrs were made into powder compacts. $\beta$-Eucryptite single phase was formed via intermediate phases of Li2SiO3 and LiAlO2 et al, by heating at 110$0^{\circ}C$ or 120$0^{\circ}C$ for 10 hrs from those powder compacts. When using the sillimanite group minerals, Virginia kyanite or andalusite was reacted to form eucryptite at 120$0^{\circ}C$and CMK International kyanite were completed at 110$0^{\circ}C$. When kaolin group minerals were used, it was found that the synthesizing temperature (100$0^{\circ}C$) of $\beta$-eucryptite from the mixture of New Zealand white kaolin was lower than that from Hadong pink kaolin (110$0^{\circ}C$). The Microstructure of systhesized powder showed the irregular lump shape such as densed crystallines.

• Restorative Dentistry and Endodontics
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• 제39권4호
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• pp.258-264
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• 2014

Objectives: This in vitro study aimed to investigate the ability of Candida albicans (C. albicans) and Enterococcus faecalis (E. faecalis) to penetrate dentinal tubules of instrumented and retreated root canal surface of split human teeth. Materials and Methods: Sixty intact extracted human single-rooted teeth were divided into 4 groups, negative control, positive control without canal instrumentation, instrumented, and retreated. Root canals in the instrumented group were enlarged with endodontic instruments, while root canals in the retreated group were enlarged, filled, and then removed the canal filling materials. The teeth were split longitudinally after canal preparation in 3 groups except the negative control group. The teeth were inoculated with both microorganisms separately and in combination. Teeth specimens were examined by scanning electron microscopy (SEM), and the depth of penetration into the dentinal tubules was assessed using the SMILE view software (JEOL Ltd). Results: Penetration of C. albicans and E. faecalis into the dentinal tubules was observed in all 3 groups, although penetration was partially restricted by dentin debris of tubules in the instrumented group and remnants of canal filling materials in the retreated group. In all 3 groups, E. faecalis penetrated deeper into the dentinal tubules by way of cell division than C. albicans which built colonies and penetrated by means of hyphae. Conclusions: Microorganisms can easily penetrate dentinal tubules of root canals with different appearance based on the microorganism size and status of dentinal tubules.

• Journal of Nutrition and Health
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• 제26권2호
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• pp.119-130
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• 1993

본 시험은 Sprague-Dawley 계통 흰쥐 수컷에게 지방의 종류와 식이급여 횟수를 달리하면서 급여하였을 때 성장 및 지방대사에 미치는 영향을 알아보고자 4종류의 지방(팜유, 우지, 대두유 및 경화대두유) 및 2종류의 식이급여형태(ad-libitum, 4$\times$meal feeding)를 달리하여 4$\times$2 요인시험으로 실시하였다. 4주간 시험식이를 ad-libitum(AL)군은 식이를 제한없이 자유롭게 섭취하도록 하였으며, meal feeding(MF)군은 1일 1회 즉, 09:00~12:00까지만 식이를 제한없이 급여하였다. 사양시험 종료후 간조직에서의 콜레스테롤합성 능력을 알아보기 위해 흰쥐의 간조직을 채취하여 in vitro 배양 시험을 실시하였다. 또한 간과 지방조직에서의 지방합성 및 분해 능력을 알아보기 위해 사양시험이 끝난 흰쥐의 간과 지방조직을 채위하여 in vitro 세포배양에서의 지방합성 능력과 지방분해 능력을 측정하였다. 본 시험에서 얻어진 결과를 요약하면 다음과 같다. 1) 성장하는 흰쥐의 증체량, 식이섭취량 및 식이효율은 AS(ad-libitum+hydrogenated soybean oil)군이 다른군에 비해 유의하게(p<0.05) 증가하였다. 식이지방의 종류에 의한 영향은 받지 않고, 식이급여형태에 의한 차이를 보여 MF군이 AL군에 비해 식이섭취량이 감소하였고, 중체량도 60%정도로 유의성있게(p<0.05)감소했다. 2) 간조직의 콜레스테롤합성 능력은 식이급여형태에 의한 차이를 보여 MF군이 AL군에 비해 간조직의 콜레스테롤합성 능력이 증가되는 경향을 (p<0.001) 보였는데 특히 불포화도가 높은 대두유군에서 유의성있게(p<0.05) 증가되었다. 3) 간조직의 in vitro 지방합성 능력은 MP(meal feeding+palm oil)군이 AP(ad-libitum+palm oil)군보다, MHS(meal feeding+hydrogenated soybean oil)군이 AHS(ad-libitum+hydrogenated soybean oil)군보다 유의하게(p<0.05) 증가했고, AB(ad-libium+beef tallow)군과 MB(meal feeding+beef tallow)군에서 지방합성 능력이 현저하게 증가되는 경향을(p<0.05)보였다. 식이급여형태나 식이지방의 종류에 대한 차이는 보이지 않았다. 간조직에서의 in virto 지방분해 능력은 MF군이 AL군에 비해 유의하게(P<0.001) 증가했고, 식이지방의 종류에 의한 차이는 나타나지 않았다. 4) 지방조의 in vitro 시험에 의하면 MF식이가 AL식이에 비해 지방합성 능력이 유의성있게(p<0.05) 증가하였으나, 지방분해 능력은 저하되었다(p<0.001). 식이지방의 종류에 의한 영향을 받아 우지군이 다른 지방군에 비해 지방합성 능력이 유의성있게(p<0.001) 증가되는 경향을 보였으나, 지방분해 능력은 식이지방의 종류에 의한 영향을 받지 않았다.

• 응용통계연구
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• 제21권6호
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• pp.947-957
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• 2008

비열등성 시험시에 치료군(treatment group)과 활성대조군(active control group)을 이용한 모형으로 Hauschke 등 (1999)이 제안한 모수적 검정법이 있다. 이 방법은 위약군(placebo group)과 직접적인 비교가 불가능하므로 Pigeot 등 (2003)이 세 군으로 확장한 검정법을 제안하였다. 그러나 이와 같은 두 검정법은 구체적인 분포가정이 필요하다. 이런 단점을 보완하기 위하여 본 논문에서는 비모수적 방법으로서 두 군 설계에 Wilcoxon 순위합 검정(Wilcoxon, 1945)을 이용한 방법을, 세 군 설계에 Scheirer 등 (1976)이 제안한 선형대비검정을 확장한 새로운 방법을 제안한다. 또한 모의실험을 통하여 모수적 방법과 비모수적 방법간의 검정력을 비교하였다.

• The Journal of Advanced Prosthodontics
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• 제10권1호
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• pp.43-49
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• 2018

PURPOSE. The purpose of this in vitro study is to examine the effects of a nano-structured alumina coating on the adhesion between resin cements and zirconia ceramics using a four-point bending test. MATERIALS AND METHODS. 100 pairs of zirconium bar specimens were prepared with dimensions of $25mm{\times}2mm{\times}5mm$ and cementation surfaces of $5mm{\times}2mm$. The samples were divided into 5 groups of 20 pairs each. The groups are as follows: Group I (C) - Control with no surface modification, Group II (APA) - airborne-particle-abrasion with $110{\mu}m$ high-purity aluminum oxide ($Al_2O_3$) particles, Group III (ROC) - airborne-particle-abrasion with $110{\mu}m$ silica modified aluminum oxide ($Al_2O_3+SiO_2$) particles, Group IV (TCS) - tribochemical silica coated with $Al_2O_3$ particles, and Group V (AlC) - nano alumina coating. The surface modifications were assessed on two samples selected from each group by atomic force microscopy and scanning electron microscopy. The samples were cemented with two different self-adhesive resin cements. The bending bond strength was evaluated by mechanical testing. RESULTS. According to the ANOVA results, surface treatments, different cement types, and their interactions were statistically significant (P<.05). The highest flexural bond strengths were obtained in nano-structured alumina coated zirconia surfaces (50.4 MPa) and the lowest values were obtained in the control group (12.00 MPa), both of which were cemented using a self-adhesive resin cement. CONCLUSION. The surface modifications tested in the current study affected the surface roughness and flexural bond strength of zirconia. The nano alumina coating method significantly increased the flexural bond strength of zirconia ceramics.

• 열처리공학회지
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• 제28권3호
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• pp.126-133
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• 2015

The aim of this study is to investigate the effect of solution treatment on the corrosion behavior of Mg-8%Al-(0-1)%Zn casting alloys in 1M NaCl aqueous solution. After the solution treatment, all alloys showed single ${\alpha}$-(Mg) phase microstructure by dissolution of ${\beta}(Mg_{17}Al_{12})$ phase into the ${\alpha}$-(Mg) matrix. The $H_2$ evolution volume decreased with an increase in Zn content, which indicates that the addition of Zn plays a beneficial role in decreasing corrosion rate of the Mg-Al-Zn alloy in solution-treated state. The microstructural evaluations on the corrosion products and corroded surfaces after the immersion test in 1 M NaCl solution revealed that the incorporation of more $Al_2O_3$ and ZnO into the corrosion product, by which the penetration of $Cl^-$ ions is impeded, are thought to be responsible for the better corrosion resistance in relation with the Zn addition.

• 한국재료학회지
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• 제26권10호
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• pp.542-548
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• 2016

The influence of NiCrAlY bond coating on the adhesion properties of an Fe thermal coating sprayed on an Al substrate was investigated. By applying a bond coat, an adhesion strength of 21MPa was obtained, which was higher than the 15.5MPa strength of the coating without the bond coat. Formation of cracks at the interface of the bond coat and the Al substrate was suppressed by applying the bond coat. Microstructural analysis of the coating interface using EBSD and TEM indicated that the dominant bonding mechanism was mechanical interlocking. Mechanical interlocking without crack defects in the coating interface may improve the adhesion strength of the coating. In conclusion, the use of an NiCrAlY bond coat is an effective method of improving the adhesion properties of thermal sprayed Fe coatings on Al substrates.