• Biomolecules & Therapeutics
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• 제27권2호
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• pp.134-144
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• 2019

The prevalence of nonalcoholic fatty liver disease (NAFLD) has increased with the incidence of obesity; however, the underlying mechanisms are unknown. In this study, high-resolution metabolomics (HRM) along with transcriptomics were applied on animal models to draw a mechanistic insight of NAFLD. Wild type (WT) and catalase knockout (CKO) mice were fed with normal fat diet (NFD) or high fat diet (HFD) to identify the changes in metabolic and transcriptomic profiles caused by catalase gene deletion in correspondence with HFD. Integrated omics analysis revealed that cholic acid and $3{\beta}$, $7{\alpha}$-dihydroxy-5-cholestenoate along with cyp7b1 gene involved in primary bile acid biosynthesis were strongly affected by HFD. The analysis also showed that CKO significantly changed all-trans-5,6-epoxy-retinoic acid or all-trans-4-hydroxy-retinoic acid and all-trans-4-oxo-retinoic acid along with cyp3a41b gene in retinol metabolism, and ${\alpha}/{\gamma}$-linolenic acid, eicosapentaenoic acid and thromboxane A2 along with ptgs1 and tbxas1 genes in linolenic acid metabolism. Our results suggest that dysregulated primary bile acid biosynthesis may contribute to liver steatohepatitis, while up-regulated retinol metabolism and linolenic acid metabolism may have contributed to oxidative stress and inflammatory phenomena in our NAFLD model created using CKO mice fed with HFD.

• 한국분말재료학회지
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• 제27권6호
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• pp.490-497
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• 2020

The 3D printing process provides a higher degree of freedom when designing ceramic parts than the conventional press forming process. However, the generation and growth of the microcracks induced during heat treatment is thought to be due to the occurrence of local tensile stress caused by the thermal decomposition of the binder inside the green body. In this study, an alumina columnar specimen, which is a representative ceramic material, is fabricated using the digital light process (DLP) 3D printing method. DTG analysis is performed to investigate the cause of the occurrence of microcracks by analyzing the debinding process in which microcracks are mainly generated. HDDA of epoxy acrylates, which is the main binder, rapidly debinded in the range of 200 to 500℃, and microcracks are observed because of real-time microscopic image observation. For mitigating the rapid debinding process of HDDA, other types of acrylates PETA, PUA, and MMA are added, and the effect of these additives on the debinding rate is investigated. By analyzing the DTG in the 25 to 300℃ region, it is confirmed that the PETA monomer and the PUA monomer can suppress the rapid decomposition rate of HDDA in this temperature range.

• Composites Research
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• 제34권1호
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• pp.47-50
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• 2021

본 논문은 차량에 사용되는 B필러의 강화재를 기존의 스틸 소재에서 CFRP(Carbon Fiber Reinforced Plastics)와 GFRP(Glass Fiber Reinforced Plastics)로 대체하여 경량화하는 것이 목표다. 이를 위해서는 무게는 감소시키면서 기존 B필러를 대체할 수 있는 구조안정성을 확보해야 한다. 기존 B필러는 스틸 아우터(outer)를 포함하여 다양한 형상의 스틸 강화재로 구성되며, 이와 같은 스틸 강화재 중 2가지의 스틸 강화재를 복합재로 대체하고자 한다. 이와 같은 스틸 강화재는 강화재 각각을 따로 제작하여 용접을 통해 결합되지만, 복합재 강화재는 패치(patch) 형태의 CFRP와 리브(rib) 구조의 GFRP를 활용하여 압축과 사출 공정을 통해 한번에 제작된다. CFRP는 B필러의 고강도부에 부착되어 측면 하중에 저항하도록 하였으며, GFRP 리브는 위상 최적화(Topology optimization) 기법을 통해 비틀림과 측면 하중을 저항하도록 설계하였다. 구조해석을 통해 기존 스틸 강화재와 비교 분석을 수행하였고, 경량화율을 산출하였다.

• The Journal of Advanced Prosthodontics
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• 제13권1호
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• pp.36-45
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• 2021

Purpose. To investigate the fracture resistance of monolithic CAD-CAM all-ceramic surveyed crowns with two different occlusal rest seat designs. Materials and Methods. Two maxillary first premolar were prepared for all-ceramic surveyed crowns with wide (2/3rd of buccolingual width of an unprepared tooth) or narrow (1/3rd of buccolingual width of an unprepared tooth) disto-occlusal rest seat (ORS) designs. Eighty monolithic CAD-CAM all-ceramic surveyed crowns were prepared and divided into 4 groups - Group CR, Composite resin material as a control; Group LDS, Lithium disilicate based material; Group ZIPS, zirconia-material (IPS ZirCAD); and Group ZLHT, zirconia- material (CeramillZolidht+). Crowns were cemented on an epoxy resin die with adhesive resin cement. The fracture resistance of crowns was tested with the universal machine. Univariate regression analysis was used. Results. The mean ± standard deviation of maximum failure force values varied from 3476.10 ± 285.97 N for the narrow ORS subgroup of group ZIPS to 687.89 ± 167.63 N for the wide ORS subgroup of group CR. The mean ± standard deviation of maximum force was 1075 ± 77.0 N for group CR, 1309.3 ± 283.9 N for group LDS, 3476.1 ± 285.97 N for group ZIPS, and 2666.7 ± 228.21 N for group ZLHT, with narrow occlusal rest seat design. The results of the intergroup comparison showed significant differences in fracture strength with various material groups and occlusal rest seat designs (P<.001). Conclusion. The zirconia-based all-ceramic surveyed crowns fractured at more than double the load of Lithium disilicate based crowns. The crowns with narrow base occlusal rest seat design had statistically significantly higher fracture resistance than surveyed crowns with wide occlusal rest seat design. The use of narrow occlusal rest seat design in CAD-CAM all ceramic surveyed crowns provides higher fracture resistance, and therefore narrow occlusal rest design can be used for providing esthetics with high strength.

• 대한건축학회논문집:구조계
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• 제34권9호
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• pp.19-26
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• 2018

The focus of this study was centered around 15 common injection type water leakage repair materials (3 different types for each; synthetic polymer, cementitious, acrylic, epoxy, urethane) used in concrete structures of Korea and analyzing their wet surface adhesion performance in accordance to the ISO TS 16774 Test Method for Repair Materials for Water-leakage Cracks in Underground Concrete Structures, Part 4: Test Method for Adhesion on Wet Concrete Surface, and the results of this study was taken to be place under a comparative analysis with the results of the preceeding study on response to substrate movement performance study. The results of this comparative study showed that other than 1 specimen of 1 type of the acrylic and 3 specimens of 1 type of the synthetic polymer type materials, all of the 93% of the specimens used in this study showed stable adhesion on wet substrate surface, and we were able to determine that materials that have proper response properties against substrate movement are highly flexible and have high adhesion properties, but their adhesion properties on wet substrate would change based on their viscosity.

• Design & Manufacturing
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• 제14권4호
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• pp.65-70
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• 2020

Partial reinforcement of sheet metal parts with CFRP patch is a technology that can realize ultra-lightweight body parts while overcoming the high material cost of carbon fiber. Performing these patchworks with highly productive press equipment solves another issue of CFRP: high process costs. The A-pillar is the main body part and has an undercut shape for fastening with other parts such as roof panels and doors. Therefore, it is difficult to bond CFRP patches to the A-pillar with a general press forming tool. In this paper, a flexible system that applies uniform pressure to complex shapes using ceramic particles and silicone rubber is proposed. By benchmarking various A-pillars, a reference model with an undercut shape was designed, and the system was configured to realize a uniform pressure distribution in the model. The ceramic spherical particles failed to realize the uniform distribution of high pressure due to their high hardness and point contact characteristics, which caused damage to the CFRP patch. Compression equipment made of silicone rubber was able to achieve the required pressure level for curing the epoxy. Non-adhesion defects between the metal and the CFRP patch were confirmed in the area where the bending deformation occurred. This defect could be eliminated by optimizing the process conditions suitable for the newly developed flexible system.

• 공업화학
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• 제31권6호
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• pp.660-667
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• 2020

본 연구의 대상은 에폭시 레진 생산 공정으로 155 ℃ 이상의 고온 스팀을 열원으로 사용하고 있으며 공정에서 생성되는 응축수는 전량 버려지고 있다. 공정의 일부는 70 ℃ 이하의 저온으로 운전되므로 버려지는 응축수를 재활용하여 저온 공정의 열원으로 사용한다면 스팀 사용량 저감이 가능하다. 따라서 본 연구에서는 응축수 재활용을 통해 폐열을 회수하여 스팀 사용량을 저감할 수 있는 공정을 제시하고 모델을 개발하였다. 최적의 응축수 재활용 공정을 찾기 위한 사례연구를 진행하였고, 각 사례의 연간 자본 비용 및 스팀 저감 비용을 비교하여 경제성 평가를 실시하였다. 제안된 공정에서 응축수 회수를 통해 저온 공정에 사용하는 스팀 사용량을 연간 최대 67.6%까지 저감하여 최대 연 522.1 백만원의 추가 수익의 확보가 가능함을 확인하였다.

• Composites Research
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• 제34권3호
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• pp.174-179
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• 2021

유체 이송에 사용되는 강재 파이프는 신설과 도장, 또는 부식과 노후화로 인한 제반 시설 보수에 거대한 규모의 시간과 비용이 요구된다. 이에 본 연구에서는 강재 파이프의 대체재로, 내부식성과 내화학성이 우수한 탄소섬유강화복합재료(Carbon Fiber Reinforced Plastic, CFRP) 파이프 구조의 최적화 설계를 수행하였다. 헬리컬 패턴 표면에 후프 패턴을 혼합적층하여 내구성을 향상시켰으며, 수분 환경에서의 에폭시 흡습 현상을 억제하기 위해, 할로이사이트 나노튜브(Halloysite Nanotube, HNT)를 첨가하였다. HNT/CFRP 파이프는 필라멘트 와인딩 공정으로 제작하였으며, 기계적 물성 시험과 70℃ 고온 증류수 환경하에서 흡습 시험을 진행하였다. 그 결과, 파이프 두께의 0.6%에 해당하는 후프 패턴의 적층 시, 가장 우수한 물성을 나타냈다. 또한 0.5 wt.% HNT 첨가 시 상대적으로 높은 내흡습성을 가졌으며, 층간 계면에서의 박리 현상이 지연되어 가장 낮은 강도 저하율을 보였다.

• Composites Research
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• 제34권4호
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• pp.264-268
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• 2021

이 연구에서 우리는 3차원 계층적 나노구조화된 유/무기 복합 표면을 가진 소수성 코팅/필름을 제조하는 방법을 제안한다. 먼저 근접장 나노패터닝(PnP)이라 불리는 첨단 포토리소그래피 기술을 통해 에폭시 기반의 대면적 3차원 정렬 나노다공성 템플릿을 준비하였다. 이후, 딥 코팅을 통해 평균 직경이 22 nm인 실리카 나노입자를 템플릿에 조밀하게 함침시켜 계층적 구조화된 표면을 구현하였다. 표면에 공존하는 마이크로 및 나노 스케일 거칠기로 인해, 제조된 복합 필름은 대조군에 비해 물에 대한 높은 접촉각(>137도)을 나타내었다. 따라서 본 연구를 통해 개발된 소재 및 공정은 전통적인 코팅/필름 분야에서 다양하게 활용될 수 있을 것으로 기대된다.

• 한국분말재료학회지
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• 제28권2호
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• pp.127-133
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• 2021

One-dimensional (1D) piezoelectric nanostructures are attractive candidates for energy generation because of their excellent piezoelectric properties attributed to their high aspect ratios and large surface areas. Vertically grown BaTiO₃ nanotube (NT) arrays on conducting substrates are intensively studied because they can be easily synthesized with excellent uniformity and anisotropic orientation. In this study, we demonstrate the synthesis of 1D BaTiO₃ NT arrays on a conductive Ti substrate by electrochemical anodization and sequential hydrothermal reactions. Subsequently, we explore the effect of hydrothermal reaction conditions on the piezoelectric energy conversion efficiency of the BaTiO₃ NT arrays. Vertically aligned TiO₂ NT arrays, which act as the initial template, are converted into BaTiO₃ NT arrays using hydrothermal reaction with various concentrations of the Ba source and reaction times. To validate the electrical output performance of the BaTiO₃ NT arrays, we measure the electricity generated from each NT array packaged with a conductive metal foil and epoxy under mechanical pushings. The generated output voltage signals from the BaTiO₃ NT arrays increase with increasing concentration of the Ba source and reaction time. These results provide a new strategy for fabricating advanced 1D piezoelectric nanostructures by demonstrating the correlation between hydrothermal reaction conditions and piezoelectric output performance.