• Corrosion Science and Technology
• /
• 제18권4호
• /
• pp.129-137
• /
• 2019

CFRP (Carbon Fiber Reinforced Plastics) is composed of carbon fiber and plastic resin, and is approximately 20 - 50% lighter than metallic materials. CFRP has a low density, higher specific stiffness, specific strength, and high corrosion resistance. Because of these excellent properties, which meet various regulation conditions needed in the industrial fields, CFRP has been widely used in many industries including aviation and ship building. However, CFRP reveals water absorption in water immersion or high humidity environments, and water absorption occurs in an epoxy not carbon fiber, and can be facilitated by higher temperature. Since these properties can induce volume expansion inside CFRP and change the internal stress state and degrade the chemical bond between the fiber and the matrix, the mechanical properties including bond strength may be lowered. This study focused on the effects of NaCl concentration (0.01 - 1% NaCl) and solution temperature ($30-75^{\circ}C$) on the galvanic corrosion between CFRP and A516Gr.55 carbon steel. When NaCl concentration increases 10 times, corrosion rate of a specimen was not affected, but that of galvanic coupled carbon steel increased by 46.9% average. However, when solution temperature increases $10^{\circ}C$, average corrosion rate increased approximately 22%, regardless of single or galvanic coupled specimen.

• 한국건축시공학회지
• /
• 제19권4호
• /
• pp.323-330
• /
• 2019

시멘트 산업은 온실가스 감축을 위한 주요 산업분야로 고려되고 있으며, 콘크리트에 시멘트를 대체할 수 있는 재료의 사용량을 증가시키는 것은 이산화탄소 감축을 위해 효과적인 방법으로 알려져 있다. 따라서 시멘트의 일부를 대체하여 사용할 수 있는 산업부산물을 다량으로 활용하기 위한 연구가 진행되고 있다. 그러나 산업부산물의 혼합량을 증가시키지 못하는 큰 이유로 초기강도 저하와 응결지연에 대한 문제점이 있다. 따라서 이 연구에서는 보통 시멘트를 사용한 경우와 고분말도 시멘트를 사용한 경우에 대해 플라이애시의 사용량에 차이를 두고 물리적 특성을 검토하여, 시멘트의 사용량을 줄이고 산업부산물을 다량으로 사용하기 위한 방안으로서, 고분말도 시멘트를 활용한 결과에 대한 기초 자료를 제시하였다.

• 한국결정성장학회지
• /
• 제29권2호
• /
• pp.77-81
• /
• 2019

최근 환경오염에 관한 문제가 대두됨에 따라서 친환경 수처리 공법에 관한 다양한 방법들이 논의되고 있다. 현재 시장을 주도하고 있는 고분자 멤브레인은 저가이나, 내화학성 및 내구성 측면에서 많은 문제점을 안고 있다. 이에 따라 친환경적이며 내구성, 내화학성이 뛰어난 세라믹 멤브레인의 기공 구조, 크기 및 표면 처리를 통하여 고효율의 수처리용 세라믹 멤브레인을 제작하였다. $ZrO_2$ 및 $TiO_2$의 균일한 코팅막 형성을 통하여 멤브레인의 기공 크기를 조절 하였다. 테입케스팅, 졸겔 공정법을 활용하여 멤브레인 표면에 성공적으로 나노기공을 가지는 세라믹 코팅막을 형성하였다. 세라믹 멤브레인의 미세조직 분석, 코팅막의 기공의 크기 분석을 진행하였으며 이에 대한 수처리 특성 변화를 관측하였다.

• Infection and chemotherapy
• /
• 제50권4호
• /
• pp.357-361
• /
• 2018

While carbapenems are the drug of choice to treat extended-spectrum-${\beta}$-lactamase (ESBL)-producing strains, some alternative carbapenem-sparing regimens are suggested for antibiotic stewardship. We experienced a case of ciprofloxacin treatment failure for acute pyelonephritis caused by an apparently susceptible Escherichia coli. A 71-year-old woman presented the emergency department with fever for 7 days and bilateral flank pain for 2 days. The laboratory results and abdominopelvic computed tomography finding were compatible with acute pyelonephritis. During 3-day ciprofloxacin therapy, the patient remained febrile with persistent bacteremia. After the change in antibiotics to ertapenem, the patient's clinical course started to improve. ESBL-producing E. coli isolates were identified in all three consecutive blood samples. Pulsed-field gel electrophoresis (PFGE) patterns, serotypes, and sequence types showed the three isolates were derived from the identical strain. The isolates produced CTX-M-14 type ESBL belonging to the ST69 clonal group. Despite in vitro susceptibility, the failure was attributed to a gyrA point mutation encoding Ser83Leu within quinolone resistance-determining regions. This case suggests that ciprofloxacin should be used cautiously in the treatment of serious infections caused by ciprofloxacin-susceptible, ESBL-producing E. coli, even in acute pyelonephritis because in-vitro susceptibility tests could fail to detect certain genetic mutations.

• 한국초전도ㆍ저온공학회논문지
• /
• 제23권3호
• /
• pp.51-54
• /
• 2021

The DC system has less power loss compared to the AC system because there is no influence of frequency and dielectric loss. However, the zero-crossing point of the current is not detected in the event of a short circuit fault, and it is difficult to interruption due to the large fault current that occurs during the opening, so the reliability of the DC breaker is required. As a solution to this, an LC resonance DC circuit breaker combined a superconducting element has been proposed. This is a method of limiting the fault current, which rises rapidly in case of a short circuit fault, with the quench resistance of the superconducting element, and interruption the fault current passing through the zero-crossing point through LC resonance. The superconducting current limiting element combined to the DC circuit breaker plays an important role in reducing the electrical burden of the circuit breaker. However, at the beginning of a short circuit fault, superconducting devices also have a large electrical burden due to large fault currents, which can destroy the element. In this paper, the reactor is connected to the source side of the circuit using PSCAD/EMTDC. After that, the change of the fault current according to the reactor capacity and the electrical burden of the superconducting element were confirmed through simulation. As a result, it was confirmed that the interruption time was delayed as the capacity of the reactor connected to the source side increased, but peak of the fault current decreased, the zero-crossing point generation time was shortened, and the electrical burden of the superconducting element decreased.

• 보존과학회지
• /
• 제37권3호
• /
• pp.302-311
• /
• 2021

본 연구는 전통 옻칠 기법을 이용하여 금속표면을 코팅하고, 물성을 평가하여 옻칠의 금속코팅 적용성 여부를 알아보고자 했다. 이를 위해 SS275 금속 시편(60*60 mm)과 원주 생칠을 이용하였다. 또한 칠 횟수(1, 2, 3)와 가열온도(120℃, 150℃)를 변이조건으로 설정하여 총 6개의 시편을 제작하였다. 분석은 색도측정, 접촉각 및 표면에너지 측정, 내약품성 시험, Cross-cut 시험을 이용하였다. 분석결과 부식성이 개선되고 금속표면에 대한 옻칠의 밀착력이 우수함을 확인하였다. 접촉각 및 표면에너지는 큰 변화를 보이지 않았다. 또한 색도 역시 큰 차이는 보이지 않았다. 본 연구를 통해 금속 표면에 옻칠이 진행되면 방수성 및 방식성이 좋아짐을 확인하였으며, 적정한 옻칠 횟수와 가열온도를 확인하였다. 차후 경도와 마모율과 같은 물리적인 특성 연구와 일정한 두께로 옻을 칠하는 방안을 연구하여 금속의 적용 가능성을 확인하고자 한다.

• Journal of Microbiology and Biotechnology
• /
• 제31권8호
• /
• pp.1060-1068
• /
• 2021

Community-associated Methicillin-Resistant Staphylococcus aureus (CA-MRSA) is notorious as a leading cause of soft tissue infections. Despite several studies on the Agr regulator, the mechanisms of action of Agr on the virulence factors in different strains are still unknown. To reveal the role of Agr in different CA-MRSA, we investigated the LACΔagr mutant and the MW2Δagr mutant by comparing LAC (USA300), MW2 (USA400), and Δagr mutants. The changes of Δagr mutants in sensitivity to oxacillin and several virulence factors such as biofilm formation, pigmentation, motility, and membrane properties were monitored. LACΔagr and MW2Δagr mutants showed different oxacillin sensitivity and biofilm formation compared to the LAC and MW2 strains. Regardless of the strain, the motility was reduced in Δagr mutants. And there was an increase in the long chain fatty acid in phospholipid fatty acid composition of Δagr mutants. Other properties such as biofilm formation, pigmentation, motility, and membrane properties were different in both Δagr mutants. The Agr regulator may have a common role like the control of motility and straindependent roles such as antibiotic resistance, biofilm formation, change of membrane, and pigment production. It does not seem easy to control all MRSA by targeting the Agr regulator only as it showed strain-dependent behaviors.

• 한국수학교육학회지시리즈E:수학교육논문집
• /
• 제35권1호
• /
• pp.1-14
• /
• 2021

수학불안은 수학에 대한 정서적·신체적 거부감을 통칭하는 용어이다. 학생들의 수학불안에 대해 이해하는 것은 수학학업 성취도 향상 뿐 아니라 미래 사회에 필요한 수학 인력 양성의 측면에서도 중요하다. 특히 수학불안은 대부분 초등학교시기에 발생할 가능성이 높으며, 후속 학습에 부정적인 영향을 미치기 때문에 초등학교에서 학생들의 수학불안 양상을 이해하는 것이 필요하다. 이에 본 연구는 시간의 경과에 따른 학생들의 수학불안 변화 패턴을 제시하고 이를 통계적으로 검증하였다. 249명의 초등학교 학생들의 수학불안을 4학년에서 6학년까지 3년 동안 추적 조사한 결과, 수학불안 양상의 다섯 가지 패턴을 확인하였다. 또한 본 연구에서는 수학불안 변화에 지속적인 영향을 미치는 것은 교사의 수학 수업에 대한 흥미도이며, 부모의 관심은 수학불안을 경감시키고, 사교육에 대한 부담감은 수학불안을 증가시킨다는 것을 확인하였다.

• 대한금속재료학회지
• /
• 제49권4호
• /
• pp.313-320
• /
• 2011

100 nm-thick hydrogenated amorphous silicon $({\alpha}-Si:H)$ films were deposited on a glass and glass/30 nm Ni substrates by inductively-coupled plasma chemical vapor deposition (ICP-CVD) at temperatures ranging from 100 to $550^{\circ}C$. The sheet resistance, microstructure, phase transformation and surface roughness of the films were characterized using a four-point probe, AFM (atomic force microscope), TEM (transmission electron microscope), AES (Auger electron spectroscopy), HR-XRD(high resolution X-ray diffraction), and micro-Raman spectroscopy. A nano-thick NiSi phase was formed at substrate temperatures >$400^{\circ}C$. AFM confirmed that the surface roughness did not change as the substrate temperature increased, but it increased abruptly to 6.6 nm above $400^{\circ}C$ on the glass/30 nm Ni substrates. HR-XRD and micro-Raman spectroscopy showed that all the Si samples were amorphous on the glass substrates, whereas crystalline silicon appeared at $550^{\circ}C$ on the glass/30 nm Ni substrates. These results show that crystalline NiSi and Si can be prepared simultaneously on Ni-inserted substrates.

• 대한금속재료학회지
• /
• 제50권10호
• /
• pp.735-743
• /
• 2012

The aim of this study was to analyze the effect of the cooling rate after heat treatment on the microstructure and mechanical properties of 2507 duplex stainless steels. Heat treatment was carried out at $1050^{\circ}C$ for 1 hr, followed by controlled cooling. The cooling rates were $175.6{\times}10^{-3}^{\circ}C/s$, $47.8{\times}10^{-3}^{\circ}C/s$, $33.3{\times}10^{-3}^{\circ}C/s$, $16.7{\times}10^{-3}^{\circ}C/s$, $11.7{\times}10^{-3}^{\circ}C/s$, $5.8{\times}10^{-3}^{\circ}C/s$ and $2.8{\times}10^{-3}^{\circ}C/s$, which resulted in variations of the microstructure, such as the fractional change of the ferrite phase and sigma phase formation. Fatigue, hardness, impact and tensile tests were performed on the specimens with different cooling rates. The precipitation of the ${\sigma}$ phase caused a hardness increase and a sharp decrease of toughness and tensile elongation. The fatigue limit of the sample with a cooling rate of $5.8{\times}10^{-3}^{\circ}C/s$ was 26 MPa higher than that of the sample with a cooling rate of $175.6{\times}10^{-3}^{\circ}C/s$. Our observations of the fracture surface confirmed that the higher fatigue resistance of the specimen with a cooling rate of $5.8{\times}10^{-3}^{\circ}C/s$ was caused by the delay of the fatigue crack growth, in addition to higher yield strength.