• Elastomers and Composites
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• 제49권2호
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• pp.127-133
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• 2014

BR/PCIIR 복합체에 대한 분산상의 영향을 분석하기 위하여 예비가교된 CIIR을 BR과 함께 니더가공하여 고무복합체를 제조하였다. 분산상으로 사용된 CIIR 예비가교물을 니더에서 한번 더 가공함으로써 BR/PCIIR 복합체에서 분산상의 입자가 적어지고 균일하게 분산되었다. BR/PCIIR40의 경우 예비가교물의 니더 가공 시간이 복합체의 반발탄성 및 경도에 아무런 영향을 미치지 않았다. 예비가교된 CIIR 입자를 니더기로 가공한 후 BR에 혼합하여 복합체를 제조한 경우, 니더가공하지 않은 복합체의 인장강도에 비하여 10% 이상 현저히 향상되었다. 분산상으로 사용되는 CIIR 예비가교물을 니더로 가공함으로서 복합체의 표면마찰 특성은 그대로 유지하면서도 복합체의 내마모성 및 기계적 성질은 현저히 향상되었다.

• 대한치과교정학회지
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• 제49권1호
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• pp.21-31
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• 2019

Objective: This study was performed to explore the effect of different bracket, archwire, and ligature combinations on resistance to sliding (RS) and rotational control in first-order angulation. Methods: Three types of brackets (multi-level low friction [MLF], self-ligating, and conventional brackets) coupled with four nickel-titanium archwires (0.012, 0.014, 0.016, and 0.018-inch diameter) and two stainless steel ligatures (0.20 and 0.25 mm) were tested in different first-order angulations ($0^{\circ}$, $2^{\circ}$, $4^{\circ}$, $6^{\circ}$, $8^{\circ}$, $10^{\circ}$, $15^{\circ}$, $20^{\circ}$) by using an Instron universal mechanical machine in the dry state at room temperature. RS value was evaluated and compared by one-way ANOVA. Results: Under the same angulation, the RS values showed the following order: conventional brackets > MLF brackets > self-ligating brackets. The RS was the highest for conventional brackets and showed a tendency to increase. The RS for MLF brackets coupled with thinner archwires and ligatures showed a similar tendency as the RS for the self-ligating bracket. In contrast, the RS for MLF brackets coupled with thicker archwires and ligatures increased like that for conventional brackets. MLF brackets showed the greatest range of critical contact angles in first-order angulation. Conclusions: The RS in first-order angulation is influenced by bracket design, archwire, and ligature dimension. In comparison with self-ligating and conventional brackets, MLF brackets could express low friction and rotational control with their greater range of critical contact angles.

• Elastomers and Composites
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• 제54권1호
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• pp.54-60
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• 2019

The rapid development of the automobile industry is an important factor that led to the dramatic development of synthetic rubber. The tread part of tire that comes in direct contact with the road surface is related to the service life of the tire. Rubber compounds used in tire treads are often blended with SBR (styrene-butadiene rubber) and BR (butadiene rubber) to satisfy physical property requirements. However, when two or more kinds of rubber are blended, phase separation and silica dispersion problems may occur due to non-uniform mixing of the rubber. Therefore, in this study, we synthesized an SBR copolymer with the same composition as that of a typical SBR/BR blend compound by controlling butadiene content during ESBR (emulsion styrene-butadiene rubber) synthesis. Subsequently, silica filled compounds were manufactured using the synthesized ESBR, and their mechanical properties, dynamic viscoelasticity, and crosslinking density were compared with those of the SBR/BR blended compound. When the content of butadiene was increased in the silica filled compound, the cure rate accelerated due to an increased number of allylic positions, which typically exhibit higher reactivity. However, the T-2 compound with increased butadiene content by synthesis less likely to show an increase in crosslink density due to poor silica dispersion. In addition, the T-3 compound containing high cis BR content showed high crosslink density due to its monosulfide crosslinking structure. Because of the phase separation, SBR/BR blend compounds were easily broken and showed similar $M_{100%}$ and $M_{300%}$ values as those of other compounds despite their high crosslink density. However, the developed blend showed excellent abrasion resistance due to the high cis-1,4 butadiene content and low rolling resistance due to the high crosslink density.

• 한국표면공학회지
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• 제52권1호
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• pp.16-22
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• 2019

The structural change of DLC coatings during long-term wear test and dicing test under the low loading condition was investigated. DLC coatings were applied for the precision injection molds of a modified SNCM steel for the extension of life and the micro-diamond blades for the high cutting efficiency and the increase in life. A ball-on-disc wear tests in the mold steel and a dicing tests in the micro-diamond blades were conducted to understand degradation of DLC coatings. The degradation of DLC coatings for the injection mold steel and the micro-diamond blades during the wear and dicing tests were studied with Raman Spectroscopy. Raman peaks were divided two bands(D band and G band) to study the degradation process of DLC structure. By the wear test, polished condition of wear marks were observed to be maintained until 10 hrs of wear test period is given, but small striation marks appeared in 20 hours wear test. It was observed that $I_D/I_G$ ratios changed as the degradation of DLC coatings is proceeded during the wear tests and the dicing tests. It is suggested that the change in $I_D/I_G$ value possibly reflected from the composition of $sp^2$ and $sp^3$ bondings in DLC layers relevant to the change in mechanical and physical property.

• 한국염색가공학회지
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• 제34권1호
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• pp.27-37
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• 2022

In this study, a study and interpretation of the spinning process in copolymerized aramid spinning was conducted. In order to proceed with the spinning process modeling and analysis, the spinning process was modeled through the physical property modeling of the spinning solution and the structural modeling of the spinneret, and structural stability and flow of the spinneret for this spinning were analyzed. After modeling the spinning solution and the spinneret in a virtual space, the pack pressure and flow rate when the spinning solution was discharged were simulated. Macroscopically, the structural stability of the spinneret was confirmed at the standard pack pressure (100 kg·f/cm²), and microscopically, the flow rate and pressure drop data of the spinning solution according to the L/D(Length (L)/Diameter (D)) value were analyzed. Based on the research and development of virtual engineering modeling and analysis, we present the possibility of changing the shape and mechanical properties of copolymer aramid fibers according to the spinning process.

• 드라이브 ㆍ 컨트롤
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• 제20권4호
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• pp.71-79
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• 2023

In the field of agricultural machinery, various on-field tests are conducted to measure design load for optimal design of agricultural equipment. However, field test procedures are costly and time-consuming, and there are many constraints on field soil conditions due to weather, so research on utilizing simulation to overcome these shortcomings is needed. Therefore, this study aimed to model agricultural soils using discrete element method (DEM) software. To simulate draft force, predictions are made according to travel speed and compared to field test results to validate the prediction accuracy. The measured soil properties are used for DEM modeling. In this study, the soil property measurement procedure was designed to measure the physical and mechanical properties. DEM soil model calibration was performed using a virtual vane shear test instead of the repose angle test. The DEM simulation results showed that the prediction accuracy of the draft force was within 4.8% (2.16~6.71%) when compared to the draft force measured by the field test. In addition, it was confirmed that the result was up to 72.51% more accurate than those obtained through theoretical methods for predicting draft force. This study provides useful information for the DEM soil modeling process that considers the working speed from the perspective of agricultural machinery research and it is expected to be utilized in agricultural machinery design research.

• 한국산림과학회지
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• 제89권5호
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• pp.677-684
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• 2000

본 연구는 토양 특성이 다른 30-40년생 독일가문비나무(Picea abies [L.] KARST) 임분에서 토양 깊이에 따른 뿌리구조 분석을 통하여 뿌리 발달의 차이점과 토양 상태의 상호관계 및 외부 형태적 특징 그리고 기계적 물리적 안정성에 대한 적응범위를 밝히고자 실시하였다. 조사된 3개 임분에 있어서 독일가문비나무의 뿌리구조는 다양한 형태로 관찰되었는데, Eberg$\ddot{o}$tzen 임분은 뿌리수가 많고 가늘며 토양 깊이까지 발달한 뿌리구조를 보였으며, Barbis 임분은 Eberg$\ddot{o}$tzen 임분에 비하여 그 수가 적으나 굵고 깊이까지 자라는 뿌리구조를 나타내었다. 그리고 Weidenbrunnen 임분은 반 수직 뿌리와 편평/접시형 뿌리구조를 나타내었다. 뿌리의 수는 Eberg$\ddot{o}$tzen 임분이 74개로 가장 많은 뿌리 수를 보여주었으며, Barbis 임분은 33개, Weidenbrunnen 임분은 57개이었다. Eberg$\ddot{o}$tzen 임분은 수직뿌리에서 평균 57개로 Barbis 임분이 21개이고, Weidenbrunnen 임분 36개에 비하여 월등히 많은 뿌리의 수를 나타내었다. 뿌리의 길이는 Weidenbrunnen 염분이 전체 뿌리길이가 다른 두 임분에 비하여 길게 나타났으며, 수형뿌리의 길이는 수직뿌리에 비하여 그 값이 107m로 매우 큰 값을 나타내었다. 수직뿌리에 대한 수평뿌리의 비는 Eberg$\ddot{o}$tzen 임분이 다른 두 임분(0.5)에 비하여 그 값이 1.2로 높게 나타났다. 전체 뿌리무게는 다른 두 임분에 비하여 Weidenbrunnen 임분이 매우 높은 값을 보여 주였으며, 수명뿌리에 대한 수직뿌리의 비는 0.16으로 다른 두 임분(0.40)에 비해 매우 낮은 값을 나타내었다. 본 연구의 독일가문비나무 임분에서 나타난 뿌리 발달의 현저한 차이점은 토양의 기계적 물리적 요인보다는 토양 산성화와 같은 화학적인 요인으로 인하여 정상적인 뿌리의 발달이 장애를 받아 수직뿌리생장이 저하되고 수분과 영양분의 스트레스로 언하여 상대적으로 수평뿌리가 발달된 결과로 사료된다.

• Korean Chemical Engineering Research
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• 제49권1호
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• pp.75-82
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• 2011

본 연구에서는 스테인레스 스틸(stainless steel)의 표면 코팅용 광경화 필름 개발을 위하여 isophorone diisocyanate (IPDI), polycaprolactone triol(PCLT), 2-hydroxyethyl acrylate(HEA), 그리고, 희석제로서 trimethylolpropane triacrylate (TMPTA)와 acrylic acid(AA)의 첨가비율을 달리한 광경화형 poly(urethane acrylate-co-acrylic acid)(PU-co-AA) 필름을 성공적으로 제조하였으며, 제조한 PU-co-AA 필름의 모폴로지, 접착특성, 기계적 특성, 전기적 특성 등에 대한 AA 첨가량의 영향을 조사하였다. 모든 PU-co-AA 필름은 비정형 구조를 나타내었으나, AA의 함량이 증가할수록 분자 규칙 및 패킹밀도는 감소하였다. 접착특성은 AA 함량 50% 이상에서는 접착력 5B 수준으로 스테인레스 스틸에 대한 우수한 접착특성을 나타내었으며, AA 함유량이 0%에서 66%까지 증가함에 따라 Pull-off strength법 접착력은 6~31 $kg_f/cm^2$ 로 선형적으로 증가하였다. 광경화 폴리우레탄 아크릴레이트의 접착력을 증가시키기 위한 유연한 사슬구조와 2관능기를 가진 AA의 도입은 다관능기의 TMPTA의 높은 가교밀도를 줄임으로써 효과적인 것을 확인할 수 있었으며, AA 함량이 증가함에 따라 접촉각의 감소와 젖음성의 향상을 확인하였다. 한편, 유연한 사슬 및 곁사슬 -COOH를 가진 AA의 도입은 규칙성 및 패킹밀도의 감소를 나타내며, 이는 PU-co-AA 필름의 경도 저하를 나타내며, 또한 AA의 분자 내의 작용기 -COOH는 고분자 필름 내의 분극현상을 증가시킴으로써 유전상수의 증가 경향을 나타내었다. 결론적으로 PU-co-AA 필름의 물리적 특성은 첨가한 AA의 함량에 크게 의존함을 확인할 수 있었다. 또한, 광경화 폴리우레탄 아크릴레이트에 아크릴산 AA의 도입은 사슬의 유연성 증가와 가교밀도의 감소 영향으로 스테인레스 스틸과의 접착력을 향상시키는데 매우 효과적인 방법임을 확인할 수 있었다.

• 대한치과보철학회지
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• 제43권6호
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• pp.751-763
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• 2005

Statement of problem. To improve a direct implant fixation to the bone, various strategies have been developed focusing on the surface of materials. The surface quality of the implant depends on the chemical, physical, mechanical and topographical properties of the surface. The different properties will interact with each other and a change in thickness of the oxide layer may also result in a change in surface energy, the surface topography and surface, chemical composition. However, there is limited the comprehensive study with regard to changed surface and biologic behavior of osteoblast by anodization. Purpose of study. The aim of this study was to analyze the characteristics of an oxide layer formed and to evaluate the cellular biologic behaviors on titanium by anodic oxidation (anodization) by cellular proliferation, differentiation, ECM formation and gene expression. And the phospholipase activity was measured on the anodized surface as preliminary study to understand how surface properties of Ti implant are transduced into downstream cellular events. Methods and Materials. The surface of a commercially pure titanium(Grade 2) was modified by anodic oxidation. The group 1 samples had a machined surface and other three experimental specimens were anodized under a constant voltage of 270 V(Group 2), 350 V(Group 3), and 450 V(Group 4). The specimen characteristics were inspected using the following five categories; the surface morphology, the surface roughness, the thickness of oxide layer, the crystallinity, and the chemical composition of the oxide layer. Cell numbers were taken as a marker for cell proliferation. While the expression of alkaline phosphatase and Runx2 (Cbfa1) was used as early differentiation marker for osteoblast. The type I collagen production was determined, which constitutes the main structural protein of the extracellular matrix. Phospholipase $A_2$ and D activity were detected. Results. (1) The anodized titanium had a porous oxide layer, and there was increase in both the size and number of pores with increasing anodizing voltage. (2) With increasing voltage, the surface roughness and thickness of the oxide film increased significantly (p<0.01), the $TiO_2$phase changed from anatase to rutile. During the anodic oxidization, Ca and P ions were more incorporated into the oxide layer. (3) The in vitro cell responses of the specimen were also dependant on the oxidation conditions. With increasing voltage, the ALP activity, type I collagen production, and Cbfa 1 gene expression increased significantly (p<0.01), while the cell proliferation decreased. (4) In preliminary study on the relation of surface property and phospholipase, PLD activity was increased but $PLA_2$ activity did not changed according to applied voltage. Conclusion. The anodized titanium shows improved surface characteristics than the machined titanium. The surface properties acquired by anodization appear to give rise more mature osteoblast characteristics and might result in increased bone growth, and contribute to the achievement of a tight fixation. The precise mechanism of surface property signaling is not known, may be related to phospholipase D.

• Journal of Applied Biological Chemistry
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• 제58권2호
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• pp.145-151
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• 2015

옥수수의 습식 분쇄 공정 중 나오는 부산물인 옥피로부터 옥피 단백질(CFP)을 추출하였다. 다양한 가소제와 가교제를 첨가하여 CFP 필름을 제조한 후, 필름의 물성을 측정하였다. 본 연구에서 사용된 가소제와 가교제 중, 2 g fructose와 0.03% cinnamaldehyde를 첨가한 필름이 가장 좋은 물성을 가졌다. 또한 여러 농도(0, 0.5, 1.0, 1.5%)의 녹차 추출물(GTE)을 첨가한 CFP 필름을 제조하였다. GTE의 농도가 증가함에 따라 CFP 필름의 인장강도, 수분 용해도, 불투명도는 증가하였고, 반면에 신장률과 필름의 수분투과도는 대조구에 비해 감소하였다. GTE 첨가한 CFP 필름의 항산화성은 DPPH 소거능으로 측정하였는데, GTE 농도가 증가함에 따라 증가하였다. 그리고 E. coli O157:H7, L. monocytogenes, S. aureus 에 대한 항균성 실험을 한 결과 또한 GTE 농도가 증가함에 따라 증가하였다. 따라서 본 연구 결과, GTE 첨가는 CFP 필름의 항산화, 항균효과를 가져다 준다고 판단된다.