• The Journal of Advanced Prosthodontics
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• 제9권2호
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• pp.130-137
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• 2017

PURPOSE. The purpose of this study was to evaluate the effect of nano-structured alumina surface coating on shear bond strength between Y-TZP ceramic and various dual-cured resin cements. MATERIALS AND METHODS. A total of 90 disk-shaped zirconia specimens (HASS CO., Gangneung, Korea) were divided into three groups by surface treatment method: (1) airborne particle abrasion, (2) tribochemicalsilica coating, and (3) nano-structured alumina coating. Each group was categorized into three subgroups of ten specimens and bonded with three different types of dual-cured resin cements. After thermocycling, shear bond strength was measured and failure modes were observed through FE-SEM. Two-way ANOVA and the Tukey's HSD test were performed to determine the effects of surface treatment method and type of cement on bond strength (P<.05). To confirm the correlation of surface treatment and failure mode, the Chi-square test was used. RESULTS. Groups treated with the nano-structured alumina coating showed significantly higher shear bond strength compared to other groups treated with airborne particle abrasion or tribochemical silica coating. Clearfil SA Luting showed a significantly higher shear bond strength compared to RelyX ARC and RelyX Unicem. The cohesive failure mode was observed to be dominant in the groups treated with nano-structured alumina coating, while the adhesive failure mode was prevalent in the groups treated with either airborne particle abrasion or tribochemical silica coating. CONCLUSION. Nano-structured alumina coating is an effective zirconia surface treatment method for enhancing the bond strength between Y-TZP ceramic and various dual-cured resin cements.

• Journal of the Korean Wood Science and Technology
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• 제46권2호
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• pp.132-142
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• 2018

An elephant digests only around 30~45% of what it consumes; therefore the undigested material mainly passes as intact fibres. Elephant food is usually composed of grass, leaves, twigs, bark, fruit and seed pods. This research aimed to utilize the elephant dung fibers as material for composite board and citric acid as a bonding agent. Citric acid contents in this research were set at 0 wt% (binderless composite board), 10 wt%, 20 wt%, and 30 wt% based on dry weight particles, while the target density was set at $0.8g/cm^3$. Pressing temperatures were set at $180^{\circ}C$ and $200^{\circ}C$ with the pressing time was 10 minutes. Physical and mechanical properties tests were then performed according to Japanese Industrial Standard A 5905. The result showed that elephant dung fibers could be used as potential materials for composite board. Addition of citric acid and pressing temperature significantly increased the quality of composite board. Infrared analysis indicated that the presence of ester linkages much higher with the increasing of citric acid content and pressing temperature. The optimum properties of composite board made from elephant dung fibers could be achieved at pressing temperature of $200^{\circ}C$ and a citric acid content of 20 wt%.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.109.2-109.2
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• 2015

Graphene, as a single layer of $sp^2$-bonded carbon atoms packed into a 2D honeycomb crystal lattice, has attracted much attention due to its outstanding properties such as high carrier mobility, chemical stability, and optical transparency. In order to synthesize high quality graphene, transition metals, such as nickel and copper, have been widely employed as catalysts, which need transfer to desired substrates for various applications. However, the transfer steps inevitably induce defects, impurities, wrinkles, and cracks of graphene. Here, we report a facile transfer-free graphene synthesis method through nickel and carbon co-deposited layer, which does not require separately deposited catalytic nickel and carbon source layers. The 100 nm NiC layer was deposited on the top of $SiO_2/Si$ substrates by nickel and carbon co-deposition. When the sample was annealed at $1000^{\circ}C$, the carbon atoms diffused through the NiC layer and deposited on both sides of the layer to form graphene upon cooling. The remained NiC layer was removed by using nickel etchant, and graphene was then directly obtained on $SiO_2/Si$ without any transfer process. Raman spectroscopy was carried out to confirm the quality of resulted graphene layer. Raman spectra revealed that the resulted graphene was at high quality with low degree of $sp^3$-type structural defects. Furthermore, the Raman analysis results also demonstrated that gas flow ratio (Ar : $CH_4$) during the NiC deposition and annealing temperature significantly influence not only the number of graphene layers but also structural defects. This facile non-transfer process would consequently facilitate the future graphene research and industrial applications.

• The Journal of Advanced Prosthodontics
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• 제8권3호
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• pp.194-200
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• 2016

PURPOSE. The prospective follow-up aimed to assess the performance of lithium disilicate crowns and clinical reasons of adverse events compromising survival and quality. MATERIALS AND METHODS. 58 patients were treated with 375 heat-pressed monolithic crowns, which were bonded with resin cement. Annual recalls up to five years included a complete dental examination as well as quality assessment using CDA-criteria. Any need for clinical intervention led to higher complication rate and any failure compromised the survival rate. Kaplan-Meier-method was applied to all crowns and a dataset containing one randomly selected crown from each patient. RESULTS. Due to drop-outs, 45 patients (31 females, 14 males) with the average age of 43 years (range = 17-73) who had 327 crowns (176 anterior, 151 posterior; 203 upper jaw, 124 lower jaw) were observed and evaluated for between 4 and 51 months (median = 28). Observation revealed 4 chippings, 3 losses of retention, 3 fractures, 3 secondary caries, 1 endodontic problem, and 1 tooth fracture. Four crowns had to be removed. Survival and complication rate was estimated 98.2% and 5.4% at 24 months, and 96.8% and 7.1% at 48 months. The complication rate was significantly higher for root canal treated teeth (12%, P<.01) at 24 months. At the last observation, over 90% of all crowns showed excellent ratings (CDA-rating Alfa) for color, marginal fit, and caries. CONCLUSION. Heat pressed lithium disilicate crowns showed an excellent performance. Besides a careful luting, dentists should be aware of patients' biological prerequisites (grade of caries, oral hygiene) to reach full success with these crowns.

• The Journal of Advanced Prosthodontics
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• 제8권2호
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• pp.75-84
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• 2016

PURPOSE. To evaluate the effect of various surface treatments on the surface structure and shear bond strength (SBS) of different ceramics. MATERIALS AND METHODS. 288 specimens (lithium-disilicate, leucite-reinforced, and glass infiltrated zirconia) were first divided into two groups according to the resin cement used, and were later divided into four groups according to the given surface treatments: G1 (hydrofluoric acid (HF)+silane), G2 (silane alone-no heat-treatment), G3 (silane alone-then dried with $60^{\circ}C$ heat-treatment), and G4 (silane alonethen dried with $100^{\circ}C$ heat-treatment). Two different adhesive luting systems were applied onto the ceramic discs in all groups. SBS (in MPa) was calculated from the failure load per bonded area (in $N/mm^2$). Subsequently, one specimen from each group was prepared for SEM evaluation of the separated-resin-ceramic interface. RESULTS. SBS values of G1 were significantly higher than those of the other groups in the lithium disilicate ceramic and leucite reinforced ceramic, and the SBS values of G4 and G1 were significantly higher than those of G2 and G3 in glass infiltrated zirconia. The three-way ANOVA revealed that the SBS values were significantly affected by the type of resin cement (P<.001). FIN ceramics had the highest rate of cohesive failure on the ceramic surfaces than other ceramic groups. AFM images showed that the surface treatment groups exhibited similar topographies, except the group treated with HF. CONCLUSION. The heat treatment was not sufficient to achieve high SBS values as compared with HF acid etching. The surface topography of ceramics was affected by surface treatments.

• 한국항공우주학회지
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• 제39권10호
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• pp.966-978
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• 2011

분출냉각은 높은 압력과 온도의 가혹한 환경에서 운용되는 고성능 액체로켓과 공기흡입엔진을 위한 가장 효과적인 냉각방법이다. 분출냉각이 적용되는 경우, 연소기 라이너와 터빈 블레이드/베인은 다공질 벽면을 통과하는 냉각재(공기 또는 연료)뿐만 아니라 차단막으로 작용하는 벽면을 빠져나온 냉각재에 의해 냉각된다. 이러한 냉각기술의 실용화는 가용한 다공질 재료의 부재로 인해 제한을 받아왔다. 그러나 금속결합 기술의 발전으로 확산접합과 식각된 얇은 금속판으로 제작한 Lamilloy$^{(R)}$와 같은 다층 기공 구조물이 개발되었다. 그리고 또한 경량 세라믹 매트릭스 복합재료가 개발됨에 따라 분출냉각은 근래 고성능 엔진 냉각을 위한 유망 기술로 여겨지고 있다. 본 논문에서는 분출냉각의 최근 연구동향 및 가스터빈, 액체로켓 및 극초음속 비행체 엔진에 이의 적용사례를 고찰하였다.

• 한국정밀공학회지
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• 제17권12호
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• pp.185-194
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• 2000

Rapid Prototyping(RP) techniques have their unique characteristics according to the working principles: stair-stepped surface of parts due to layer-by-layer stacking, low build speed caused by line-by-line solidification to build one layer, and additional post processing to improve surface roughness, so it is required very high cost to introduce and to maintain of RP apparatus. The objective of this study is to develop a new RP process, Variable Lamination Manufacturing using linear hotwire cutting technique and expandable polystyrene foam sheet as part material(VLM-S), and to investigate characteristics of part material, cutting characteristics by using linear hotwire cutting system and bonding. Experiments were carried out to investigate mechanical properties of part material such as anisotropy and directional tensile strength. In order to obtain optimal dimensional accuracy, surface roughness, and reduced cutting time, addition experiments were performed to find the relationship between cutting speed and cutting offset of hotwire, and heat generation of hotwire per unit length. So, adhesion strength tests according to ASTM test procedure showed that delamination did not occur at bonded area. Based on the data, a clover-shape was fabricated using unit shape part(USP) it is generated hotwire cutting. The results of present study have been reflected on the enhancement of the VLM-S process and apparatus.

• Journal of the Korean Wood Science and Technology
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• 제42권1호
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• pp.34-40
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• 2014

흰개미 방제 및 방곰팡이 효력이 입증된 저독성 네오티코치드계 목재보존제가 집성재 제조용 레조르시놀계 접착제의 접착력에 미치는 영향을 조사하였다. ACQ, CUAZ, 네오니코치드계 약제를 도포 처리한 다음 건조시킨 소나무 판재를 사용하였으며, 집성 접착 후에 블록 전단시험편을 채취하여 상태 및 촉진 열화 시험 후의 전단접착력과 목파율을 측정하여 비교하였다. ACQ 및 CUAZ 처리 집성재는 무처리 및 네오니코치드계 목재보존제 처리 집성재에 비하여 낮은 전단접착력을 보여 접착력 저하가 인정되었다. 이것은 이들 방부제 중에 함유되어 있는 구리화합물에 기인하는 것으로 판단되었다. 네오니코치드계 목재보존제 처리 집성재는 상태 및 촉진열화 시험 후에도 가장 우수한 전단접착력을 나타내 레조르시놀계 접착제의 접착성능에는 영향을 미치지 않는 것으로 판단하였다.

• 폴리머
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• 제34권6호
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• pp.588-593
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• 2010

실리콘, 게르마늄, 주석이 결합된 7개의 아크릴 단량체가 개발되었고 이를 광경화시킨 필름의 굴절률을 측정하였다. 공단량체로 가교도가 높은 triacrylate(Trimer)를 사용하여 형성된 공중합체의 굴절률로부터 단일중합체의 굴절률을 계산하였다. 공유 결합된 $Ph_3Si$, $Ph_3Ge$, $Ph_3Sn$은 각각 아크릴 고분자 필름의 굴절률을 향상시키는데 기여하였고 주석이 게르마늄에 비해 약간 높은 기여도로 나타났다. 주석에 의한 굴절률 향상 효과는 $Bu_3Sn$을 도입한 결과와 aliphatic acrylate의 비교로 보다 명확하게 입증되었다. 주석과 황의 안정된 결합을 이용하여 $Ph_3SnS$가 도입된 아크릴 고분자의 굴절률은 589 nm에서 1.671로 높게 측정되었다. 측정 파장으로 656, 830, 1310, 1550 nm에서도 비슷한 굴절률이 관찰되었다.

• 한국정밀공학회지
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• 제29권5호
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• pp.563-571
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• 2012

In 3D integration package using TSV technology, bonding is the core technology for stacking and interconnecting the chips or wafers. During bonding process, however, warpage and high stress are introduced, and will lead to the misalignment problem between two chips being bonded and failure of the chips. In this paper, a finite element approach is used to predict the warpages and stresses during the bonding process. In particular, in-plane deformation which directly affects the bonding misalignment is closely analyzed. Three types of bonding technology, which are Sn-Ag solder bonding, Cu-Cu direct bonding and SiO2 direct bonding, are compared. Numerical analysis indicates that warpage and stress are accumulated and become larger for each bonding step. In-plane deformation is much larger than out-of-plane deformation during bonding process. Cu-Cu bonding shows the largest warpage, while SiO2 direct bonding shows the smallest warpage. For stress, Sn-Ag solder bonding shows the largest stress, while Cu-Cu bonding shows the smallest. The stress is mainly concentrated at the interface between the via hole and silicon chip or via hole and bonding area. Misalignment induced during Cu-Cu and Sn-Ag solder bonding is equal to or larger than the size of via diameter, therefore should be reduced by lowering bonding temperature and proper selection of package materials.