• KSTLE International Journal
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• 제3권1호
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• pp.43-48
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• 2002

Dry sliding wear and friction test of CrN coaling on two types of aluminum alloy substrates,6061 Al and 7075 Al deposited by arc ion plating, was peformed with a ball-on-disk tribometer. The effects of normal Bead and the mechanical properties of substrate on the friction coefficient and wear-resistance of CrN coating were investigated. The worn surfaces were observed by SEM. The results show that surface micro-hardness of CrN- coated 7075 Al is higher than that of CrN-coated 6061 Al. With an increase in normal lead, wear volume increases, while the friction coefficient decreases. The friction coefficient of CrN-coated 6061 Al is higher than that of CrN-coated 7075 Al, while the wear-resistance of CrN-coated 6061 Al is lower than the CrN-coated 7075 Al's, which indicates that the substrate mechanical properties have strong inf1uences on the friction coefficient and wear of CrN coating. The main wear mechanism was fragments of CrN coating, which were caused by apparent plastic deformation of substrate during wear test.

• Journal of Information Display
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• 제4권1호
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• pp.17-23
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• 2003

A thermoset type anisotropic conductive adhesive film (ACAF) comprising epoxy resin and natural butyl rubber (NBR) as the binder, micro-encapsulated imidazole as the curing agent, and Ni/Au coated polymer bead as a conductive particle has been studied. These films have been prepared to respond to requirements such as improved contact resistance, current status less of than 60 ${\mu}m$ and reliability. These films can also be used for connection between the ITO glass for LCD panel and the flexible circuit board. The curing conditions for the connection were 40, 20 and 15 seconds at 150, 170 and 190 $^{\circ}C$, respectively. The initial contact resistance and adhesion strength were 0.5 ${\Omega}/square$ and 0.4 kg/cm under the condition of 30 kgf/$^{cm}^2}$, respectively. After completing one thousand thermal shock cycling tests between -15 $^{\circ}C$ and 100 $^{\circ}C$, the contact resistance was maintained below 0.7 ${\Omega}/square$. Durability against high temperature (80$^{\circ}C$) and high humidity (85 % RH) was also tested to confirm long-term stability (1000 hrs) of the conduction.

• Journal of Microbiology and Biotechnology
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• 제31권9호
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• pp.1323-1329
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• 2021

Micro-scale magnetic beads are widely used for isolation of proteins, DNA, and cells, leading to the development of in vitro diagnostics. Efficient isolation of target biomolecules is one of the keys to developing a simple and rapid point-of-care diagnostic. A zinc finger protein (ZFP) is a double-stranded (ds) DNA-binding domain, providing a useful scaffold for direct reading of the sequence information. Here, we utilized two engineered ZFPs (Stx2-268 and SEB-435) to detect the Shiga toxin (stx2) gene and the staphylococcal enterotoxin B (seb) gene present in foodborne pathogens, Escherichia coli O157 and Staphylococcus aureus, respectively. Engineered ZFPs are immobilized on a paramagnetic bead as a detection platform to efficiently isolate the target dsDNA-ZFP bound complex. The small paramagnetic beads provide a high surface area to volume ratio, allowing more ZFPs to be immobilized on the beads, which leads to increased target DNA detection. The fluorescence signal was measured upon ZFP binding to fluorophore-labeled target dsDNA. In this study, our system provided a detection limit of ≤ 60 fmol and demonstrated high specificity with multiplexing capability, suggesting a potential for development into a simple and reliable diagnostic for detecting multiple pathogens without target amplification.

• Environmental Engineering Research
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• 제15권3호
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• pp.149-156
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• 2010

The objective of this study was to investigate microbial removal using layered double hydroxides (LDHs) and iron (hydr)oxides (IHs) immobilized onto granular media. Column experiments were performed using calcium alginate beads (CA beads), LDHs entrapped in CA beads (LDH beads), quartz sand (QS), iron hydroxide-coated sand (IHCS) and hematite-coated sand (HCS). Microbial breakthrough curves were obtained by monitoring the effluent, with the percentage of microbial removal and collector efficiency then quantified from these curves. The results showed that the LDH beads were ineffective for the removal of the negatively-charged microbes (27.7% at 1 mM solution), even though the positively-charged LDHs were contained on the beads. The above could be related to the immobilization method, where LDH powders were immobilized inside CA beads with nano-sized pores (about 10 nm); therefore, micro-sized microbes (E. coli = 1.21 ${\mu}m$) could not diffuse through the pores to come into contact with the LDHs in the beads, but adhere only to the exterior surface of the beads via polymeric interaction. IHCS was the most effective in the microbial removal (86.0% at 1 mM solution), which could be attributed to the iron hydroxide coated onto the exterior surface of QS had a positive surface charge and, therefore, effectively attracted the negatively-charged microbes via electrostatic interactions. Meanwhile, HCS was far less effective (35.6% at 1 mM solution) than IHCS because the hematite coated onto the external surface of QS is a crystallized iron oxide with a negative surface charge. This study has helped to improve our knowledge on the potential application of functional granular media for microbial removal.

• 한국항공우주학회지
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• 제43권2호
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• pp.149-155
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• 2015

기존의 MEMS 기반 루버 및 셔터 개폐형 가변 방사율 라디에이터는 온도 조건에 따라 방사율이 가변되어 효율적인 열 제어가 가능하나 발사 환경에서의 기계적 구동부의 취약점과 변경된 방사율 유지를 위해 지속적인 전력 소모가 요구되는 단점을 갖는다. 본 연구에서 제안한 MEMS 기반 가변 방사율 라디에이터는 대전되는 비드를 사용하여 전극의 극성 변화에 따라 방사율 가변이 가능하기 때문에 상기의 문제점을 극복할 수 있다. 본 연구에서는 MEMS 기반 가변 방사율 라디에이터의 광학 물성치 최적화 설계를 수행하였으며, 고정 방사율 라디에이터와의 비교를 통해 MEMS 기반 가변 방사율 라디에이터의 유효성을 입증하였다.

• Journal of Welding and Joining
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• 제34권6호
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• pp.42-46
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• 2016

Hydrogen assisted cracking (HAC) is one of the most complicated problem in welding. Huge amount of studies have been done for decades. Based on them, various standards have been established to avoid HAC. But it is still a chronic problem in industrial field. It is well known that the main causes of the hydrogen crack are residual stress, crack susceptible micro structures and a certain critical level of hydrogen concentration. Even though the exact generating mechanism is unclear till today, it has been reported that the hydrogen level in the weld metal should be managed less than a certain amount to prevent it. Matsuda studied that the residual hydrogen level in the weld metal can be varied even if the initial hydrogen content is same. It is also insisted in this report that the residual hydrogen concentration is in stronger correlation with hydrogen crack than the initial hydrogen content. But, in practical point of view, the residual hydrogen is still hard to consider because measuring hydrogen level is time and cost consuming process. In this regard, numerical analysis is the only solution for considering the residual hydrogen content. Meanwhile, Takahashi showed the possibility of predicting the residual hydrogen by a rigorous FE analysis. But, few commercial software suitable for solving the weld metal hydrogen has been reported yet. In this study, two dimensional thermal - hydrogen coupled analysis was developed by using the commercial FE software MARC. Since the governing equation of the hydrogen diffusion is similar to the heat transfer, it is shown that the heat transfer FE analysis in association with hydrogen diffusion property can be used for hydrogen diffusion analysis. A series of simulation was performed to verify the accuracy of the model. For BOP (Bead-On-Plate) and the multi-pass butt welding simulations, remaining hydrogen contents in the weld metal is well matched with measurements which are referred from Kim and Masamitsu.

• 폴리머
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• 제36권2호
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• pp.196-201
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• 2012

전기방사는 휘발성 용매에 녹아있는 다양한 물질들을 마이크로 크기의 섬유로 제조하는데 사용되고 있다. 이번 연구에서는 물을 용매로 사용하여 pullulan을 전기 방사하였다. 부드러운 섬유를 얻기 위하여 pullulan 농도와 전압을 최적의 조건으로 설정하였다. Pullulan 농도는 pullulan 용액의 점도와 표면 장력에 큰 영향을 받는다. Bead 형태의 pullulan 전기방사 섬유는 5 wt%이하의 농도에서 얻어진다. Pullulan 용액의 농도가 10 wt%로 유지되고, 전압이 15 kV에 고정되었을 때, pullulan 섬유의 평균 직경은 200 nm로 감소하였다. Pullulan electrospun 섬유는 높은 용해도, 유연성, 부드러움과 강한 접착성을 보여준다.

• IMMUNE NETWORK
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• 제3권1호
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• pp.53-60
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• 2003

Background: The role of macrophages in tumor angiogenesis is known to be the production of angiogenic cytokines and growth factors including TNF-${\alpha}$. Recently, macrophage also can produce the INF-${\gamma}$ that is being studied to be involved in angiogenic inhibition. Thus, the importance of macrophages in tumor angiogenesis is might being an angiogenic switch. Thus, the hypothesis tested here is that TNF-${\alpha}$ can modulate the INF-${\gamma}$ production in the macrophages from tumor environment as a part of tumor angiogenic switch. Methods: Macrophages in tumor environment were obtained from the peritoneal cavity of C57BL/6 mice injected with B16F10 melanoma cell line for 6 or 11 days. $Mac1^+$-macrophages were purified using magnetic bead ($MACs^{TM}$; Milteny Biotech, Germany) and cultured with various concentrations of TNF-${\alpha}$ for various time points at $37^{\circ}C$. The supernatants were analyzed for IFN-${\gamma}$ or VEGF by ELISA kit (Endogen, Woburn, MA). Results: Residential macrophages from the peritoneal cavity did not respond to LPS or TNF-${\alpha}$ to produce INF-${\gamma}$. However, the cells from tumor environment produced IFN-${\gamma}$ as well as VEGF and upregulated by the addition of LPS or TNF-${\alpha}$. RT-PCR analysis revealed the external TNF-${\alpha}$-induced IFN-${\gamma}$ gene expression in the macrophages from tumor environment. Conclusion: The overall data suggest that the macrophages in tumor environment might have an important role not only in angiogenic signal but also in anti-angiogenic signal by producing related cytokines. And TNF-${\alpha}$ might be a key cytokine in tumor angiogenic switch.

• 접착 및 계면
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• 제20권1호
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• pp.23-28
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• 2019

본 연구에서는 마이크로 또는 나노 입자 형상을 폴리디메틸실록산 (PDMS)에 전사시켜 건식접착제를 제조하고 특성에 대하여 고찰하였다. 20 nm, 40 nm, 70 nm의 직경을 가지는 구리 나노 입자형상과 $5{\mu}m$의 직경을 가지는 폴리메틸메타아크릴레이트 (PMMA) 마이크로 입자 형상을 전사시켜 PDMS 건식 접착제를 제조하였다. 입자의 종류 및 크기가 변화함에 따라 건식 접착제의 기계적 특성, 인장 접착강도, 표면 형상, 접촉각, 광학적 성질에 미치는 영향을 조사하였다. 20 nm 직경을 가지는 구리 나노 입자를 전사시켜 얻은 건식 접착제는 bare PDMS 필름에 비하여 300% 이상 향상된 인장 접착강도를 가졌다. 나노 입자를 전사시켜 얻은 큰 표면적 건식 접착제 구조가 높은 인장 접착강도를 부여하는 원인으로 추정된다. 본 연구결과는 나노 입자를 전사시키는 방법이 PDMS 건식 접착제의 제조에 있어 쉽고 효과적임을 시사한다.

• Applied Biological Chemistry
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• 제49권3호
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• pp.170-174
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• 2006

생균력 안정성이 보장되고 품질이 규격화된 농용 미생물제공급을 위하여 캡슐형 미생물제의 캡슐화 소재로 열수 추출법과 알칼리 추출법을 이용하여 다시마로부터 Na-alginate를 직접 추출하여 겔 형성능과 생균력을 검토하였다. 열수추출 alginate(HWEA)의 경우 5%의 고농도에서 겔 형성이 성공적으로 이루어진데 반해 알칼리추출 alginate(ASA)는 3% 농도에서 $992.1\;{\pm}\;0.2\;g/cm^2$의 강한 겔이 형성되는 특성을 보여 시판되고 있는 alginate(CA) 1.5% 농도의 겔과 유사한 겔 형성능을 나타내었다. 또한 ASA의 경우 추출 수율이 20%로 HWEA 보다 2배 이상 높게 나타났으며 현재 시판되고 있는 Na-alginate(CA)에 비해 비용이 11배 이상 저렴한 것으로 산출되었다. 이상의 결과로부터 ASA를 사용할 경우 값싼 비용으로 추출이 용이하며 저농도에서 겔형성능이 우수하여 최적의 농용 미생물 캡슐소재로 평가되었다. ASA 캡슐제의 생균력을 조사한 결과 81%의 생균력을 나타내어 고가의 CA 캡슐제와 동일한 생균력을 보장 할 수 있음이 입증되었다. 미세 캡슐 내 미생물 생존력을 보다 안정적으로 유지하기 위해 캡슐막의 효과를 나타낼 수 있는 보조제로 starch와 zeolite를 이용하여 생균력 증진효과를 검토한 결과 단일소재 ASA만으로 제조된 캡슐제보다 보조제를 혼합한 캡슐제 경우 세균과 효모는 생균수가 크게 증가되는 효과를 볼 수 있었다. 미생물 혼합 배양액과 상기의 최적 복합 캡슐소재를 혼합하여 캡슐화한 미생물제의 생균력을 측정한 결과 세균은 93%의 높은 생균력을 나타내었고 유산균과 효모의 경우 70% 이상의 생균력을 나타내어 본 연구를 통해 다시마로부터 직접 추출한 ASA가 고가의 시판품 alginate를 대체할 수 있는 농용 미생물 캡슐화 소재로 이용가능할 것으로 판단되었다.