• Bulletin of the Korean Chemical Society
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• 제35권5호
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• pp.1523-1528
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• 2014

Silicon quantum dots (Si QDs) were synthesized by etching silicon nanopowder with aqueous hydrofluoric acid (HF) and nitric acid ($HNO_3$). Then, the hydride-terminated Si QDs (H-Si QDs) were functionalized by 1- octadecene (ODE). By only controlling the etching time, the maximum luminescence peak of octadecylterminated Si QDs (ODE-Si QDs) was tuned from 404 nm to 507 nm. The average optical gap was increased from 2.60 eV (ODE-Si QDs-5 min) for 5 min of etching to 3.20 eV (ODE-Si QDs-15 min) for 15 min of etching, and to 3.40 eV (ODE-Si QDs-30 min) for 30 min of etching. The electron affinities (EA), ionization potentials (IP), and quasi-particle gap (${\varepsilon}^{qp}_{gap}$) of the Si QDs were determined by cyclic voltammetry (CV). The quasi-particle gaps obtained from the CV were in good agreement with the average optical gap values from UV-vis absorption. In the case of the ODE-Si QDs-30 min sample, the difference between the quasi-particle gap and the average optical gap gives the electron-hole Coulombic interaction energy. The additional electronic levels of the ODE-Si QDs-30 min and ODE-Si QDs-15 min samples determined by the CV results are interpreted to have originated from the Si=O bond terminating Si QD.

• 한국정밀공학회지
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• 제23권7호
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• pp.59-66
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• 2006

In laser welding, automatic seam tracking is important to adjust the laser head position in real time as it moves along the seam. Also if the joint gap is occurred, filling the missing material into the joint gap is necessary to prevent welding defects and bad welding quality. In general, the joint gap width is not constant along the seam due to a variety of reason. So it is essential to control the filler wire speed into the joint gap to acquire good welding quality. This paper describes an intelligent filler wire feeding device which can control 3-dimensional seam tracking and the filler wire speed by measuring the gap position and the joint gap width in laser welding. We call this device as Smart Micro Control system(SMC). To achieve this objective, we assessed weld quality in 2mm sheets of A16061 which had various gap width by using the developed device. From the experimental results, It was found the possibility that the developed device could be used in welding various 3-dimensional structures.

• Geomechanics and Engineering
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• 제17권5호
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• pp.439-444
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• 2019

It is generally known that high strength soil is indicative of well-graded particle size distribution. However, there are some special cases of firm ground despite poor grade distribution, especially a specific gap-graded soil. Based on these discoveries, this study investigated the development of an additive of gap-graded soils designed to increase soil strength. This theoretical concept was used to calculate the mixed ratio required for optimal soil strength of the ground sample. The gap-graded aggregate was added according to Plato's polyhedral theory and subsequently calculated ratio and soil strength characteristics were then compared to characteristics of the original soil sample through various test results. In addition, the underground stress transfer rate was measured according to the test conditions. The test results showed that the ground settlement and stress limit thickness were reduced with the incorporation of gap-graded soil. Further field tests would confirm the reproducibility and reliability of the technology by using gap-graded soil to reinforce soft ground of a new construction site. Gap-graded soil has the potential to reduce the construction cost and time of construction compared to other reinforcing methods.

• 한국콘텐츠학회논문지
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• 제9권1호
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• pp.348-358
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• 2009

미만성 축삭손상(diffuse axonal injury)은 외상성 뇌손상의 일반적인 형태이며, 인지 장애의 주요 원인으로 생각되어 진다. 흔들린 아기 증후군(shaken baby syndrome)과 같이 뇌에 전단력이 심하게 가해졌을 때도 신체 장애 뿐만 아니라 인지 장애가 특징적으로 나타난다. 신체 활동은 건강 증진과 더불어 기억 및 학습과 관련된 해마의 기능 향상에도 영향을 미친다. 본 연구의 목적은 흰쥐를 대상으로 미만성 축삭 손상을 일으킨 후 반복적인 운동 훈련을 통해 운동 수행력을 관찰하고 해마에서 GAP-43의 발현을 통해 축삭 재생의 변화를 관찰하는 것이었다. 실험동물은 운동 훈련을 적용시키는 실험군과 대조군으로 구분하였고, 각각의 군을 다시 1일, 7일 및 14일군으로 구분하였다. 그 결과, 운동 훈련을 적용시킨 실험군이 대조군보다 운동 수행력의 향상이 더 유의했으며, 해마에서 GAP-43의 발현도 같은 양상을 나타냈다. 이러한 차이는 7일군과 14일군보다 1일군과 7일군 사이에 더 크게 나타났다. 그러므로 미만성 축삭손상 후 운동 훈련은 운동 수행력의 향상에 영향을 미치며, 인지와 관련된 해마의 구조적 변화도 야기 시키는 것으로 생각된다.

• Carbon letters
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• 제28권
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• pp.72-80
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• 2018

In this study, an empirical relationship between the energy band gap of multi-walled carbon nanotubes (MWCNTs) and synthesis parameters in a chemical vapor deposition (CVD) reactor using factorial design of experiment was established. A bimetallic (Fe-Ni) catalyst supported on $CaCO_3$ was synthesized via wet impregnation technique and used for MWCNT growth. The effects of synthesis parameters such as temperature, time, acetylene flow rate, and argon carrier gas flow rate on the MWCNTs energy gap, yield, and aspect ratio were investigated. The as-prepared supported bimetallic catalyst and the MWCNTs were characterized for their morphologies, microstructures, elemental composition, thermal profiles and surface areas by high-resolution scanning electron microscope, high resolution transmission electron microscope, energy dispersive X-ray spectroscopy, thermal gravimetry analysis and Brunauer-Emmett-Teller. A regression model was developed to establish the relationship between band gap energy, MWCNTs yield and aspect ratio. The results revealed that the optimum conditions to obtain high yield and quality MWCNTs of 159.9% were: temperature ($700^{\circ}C$), time (55 min), argon flow rate ($230.37mL\;min^{-1}$) and acetylene flow rate ($150mL\;min^{-1}$) respectively. The developed regression models demonstrated that the estimated values for the three response variables; energy gap, yield and aspect ratio, were 0.246 eV, 557.64 and 0.82. The regression models showed that the energy band gap, yield, and aspect ratio of the MWCNTs were largely influenced by the synthesis parameters and can be controlled in a CVD reactor.

• The Korean Journal of Physiology and Pharmacology
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• 제11권3호
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• pp.107-112
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• 2007

Gap junction protein, connexin, is expressed in endothelial cells of vessels, glomerulus, and renin secreting cells of the kidney. The purpose of this study was to investigate the role of gap junction in renin secretion and its underlying mechanisms using As 4.1 cell line, a renin-expressing clonal cell line. Renin release was increased proportionately to incubation time. The specific gap junction inhibitor, 18-beta glycyrrhetinic acid (GA) increased renin release in dose-dependent and time-dependent manners. Heptanol and octanol, gap junction blockers, also increased renin release, which were less potent than GA. GA-stimulated renin release was attenuated by pretreatment of the cells with amiloride, nifedipine, ryanodine, and thapsigargin. GA dose-dependently increased intracellular $Ca^{2+}$ concentration, which was attenuated by nifedipine, nimodipine, ryanodine, and thapsigargin. However, RP-cAMP, chelerythrine, tyrphostin A23, or phenylarsine oxide did not induced any significant change in GA-stimulated increase of intracellular $Ca^{2+}$ concentration. These results suggest that gap junction plays an important role on the regulation of renin release and intracellular $Ca^{2+}$ concentration in As 4.1 cells.

• 한국소음진동공학회논문집
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• 제22권3호
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• pp.253-263
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• 2012

With the local Hertz deformation on the contact point, the dynamic contact between a high-speed wheel and an elastic beam having a gap is numerically analyzed by solving the whole equations of motion of the wheel and the beam subjected to the contact condition. For the stability of the time integration the velocity and acceleration constraints as well as the displacement constraint are imposed on the contact point. Especially the acceleration contact condition on the gap is formulated, and it is demonstrated that the contact force variation computed by the velocity contact constraint or by the acceleration contact constraint agrees well with that computed by the displacement contact constraint. The numerical examples show that, when the wheel passes on the gap, the solution is governed by the stiffness of the local Hertzian deformation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.670-677
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• 2003

Although Gas Tungsten Arc Welding (GTAW or TIG welding) is considered as high quality and precision welding process, it also has demerit of low melting rate. Narrow-gap TIG welding which has narrow joint width reduces the groove volume remarkably, so it could be shorten the welding time and decrease the overall shrinkage in heavy wall pipe welding. Generally Narrow-gap TIG welding is used as orbital welding process, it is important to select the optimum conditions for the automatic control welding This paper looks at the application and metallurgical properties on Narrow-gap TIG welding joint of heavy wall large austenitic stainless steel pipe to determine the deposition efficiency, the resultant shrinkage and fracture toughness. The fracture toughness depends slightly on the welding heat input.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2007년 추계학술발표대회 개요집
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• pp.26-28
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• 2007

This research is concerned with a study of failure strength evaluation on heat element gap at resistance welding. The failure strength of resistance welded joint is changed by welding factor like as current(power level), welding time(total energy), pressure etc. and another heat element factor like as number of element line, element gap etc. Tensile-shear tests were carried out with the single-lap specimen using polypropylene(PP). The failure mechanism and optimization of gap was discussed in order to explain the tensile-shear strength evaluation on heat element gap at resistance welding. Orthogonal array was used by fractional factorial design for efficient experiments.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 E
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• pp.2239-2241
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• 1999

The most important question is how to use which kind of switch in pulsed power generation. There are many kinds of commercial closing switches, which have advantages and disadvantages. The most popular closing switch is the spark gap, but it has a disadvantage in life time, because of erosion of electrodes by arc heating. The Rotary Arc Gap (RAG) switch, especially Walkie-Edgar type RAG switch, was proposed to solve such problems in spark gap. It has a simple and special structure for arc moving caused from self-induced electromagnetic force, because moving arc makes less erosion on the electrodes. In this study we have made an Walkie-Edgar type RAG switch, tested the switching with capacitive energy storage system, and measured rotating arc speed in different peak current.