• 한국산학기술학회논문지
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• 제20권12호
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• pp.513-518
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• 2019

마찰교반용접(Friction Stir Welding) 기술은 금속 소재를 대상으로 하는 용접기술 중의 하나로 용접대상이 되는 소재와 고속으로 회전하는 용접툴 사이의 마찰로 인한 열을 활용하여 소재의 융점 이하 온도에서 접합하는 기술이다. 이번 연구에서는 마찰교반용접을 진행할 때, 용접 대상물의 내부 온도 변화를 분석하기 위한 방법으로 수치해석기법을 사용하였다. 용접소재로는 마그네슘 합금인 AZ31을 고려하였으며, 용접현상을 멜팅풀(melting-pool)이 생성되는 유동특성으로 간주하고 유동해석을 수행하기 위해 유동특성 수치해석 툴인 FLUENT를 이용하였다. 용접과정의 유동해석을 진행하기 위해 용접소재는 고점도 뉴턴 유체로 가정하였고, 용접툴과 용접대상 소재의 경계면은 마찰 및 미끄러짐이 동시에 발생하는 조건으로 경계조건을 선정하였다. 그리고 용접툴의 회전속도 및 용접속도를 변수로 하여 다양한 해석을 진행하였다. 해석 결과로부터 용접툴의 회전속도가 높을수록, 용접속도가 느릴수록 소재 내 최고온도가 증가함을 확인할 수 있었으며, 그 중 용접툴의 회전속도 차이가 온도 변화에 더 큰 영향을 보임을 확인하였다.

• 비파괴검사학회지
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• 제36권4호
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• pp.300-307
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• 2016

차량 부품의 고장은 운용 중단과 탈선 결과로 나타날 수 있으며 차량 주요부품의 이상상태를 진단하는 것은 중요하다. 온도를 이용한 진단 방법은 철도차량 회전기기의 -예를 들면, 베어링, 감속기, 견인전동기, 디스크- 비정상 상태를 진단하는 기본적인 방법이다. 본 연구에서는 적외선열화상과 패턴 이미지법을 이용하여 차량 하부의 회전기기의 이상 진단시스템을 구축하여 현장시험을 수행하였다. 그 이상상태 진단시스템은 차량 하부 회전기기의 이상발열 상태를 진단할 수 있었으며 비정상 상태를 평가할 수 있었다.

• Biotechnology and Bioprocess Engineering:BBE
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• 제9권5호
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• pp.374-378
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• 2004

The effects of various environmental factors such as pH (5, 6, 7, 8 and 9), temperature (30, 37 and $40^{\circ}C$) and rotational speed (150, 200 and 250 rpm) on the growth and the hepatitis B core antigen (HBcAg) production of Escherichia coli W3110IQ were examined in the present Study. The highest growth rate is achieved at pH 7, $37^{\circ}C$ and at a rotational Speed of 250 rpm which is 0.927 $h^{-1}$. The effect of pH on cell growth is more substantial compared to other parameters; it recorded a $123\%$ different between the highest growth rate (0.927 $h^{-1}$) at pH 7 and lowest growth at pH 5. The highest protein yield is achieved at pH 9, rotational speed of 250 rpm and $40^{\circ}C$. The yield of protein at pH 7 is $154\%$ higher compared to the lowest yield achieved at pH 5. There is about $28\%$ different of the protein yield for the E. coli cultivated at 250 rpm compared to that at 150 rpm which has the lowest HBcAg yield. The yield of protein at $40^{\circ}C$ is $38\%$ higher compared to the lowest yield achieved at $30^{\circ}C$.

• 유변학
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• 제11권2호
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• pp.73-81
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• 1999

회전식 점도 측정기를 이용하여 상용화된 전기유변(electrorheological, ER)유체와 자기유변(magnetorheological, MR)유체의 특성을 비교하여 이를 이용한 장치 설계시 두 유체 중에 유리한 것을 선택하는데 도움이 되고자 하는 것이 본 논문의 의도이며, 이러한 유체의 특성에서 전단변형률의 변화에 따른 전단응력의 변화, 온도변화에 따른 전단응력의 변화, 작용하는 장의 세기에 따른 전단응력의 변화 등을 비교하였다. 온도의 변화에 따른 유체의 특성 변화는 MR유체가 ER유체보다 적게 받는 경향이 있었다. 두 유체의 응용 예로서 제작된 댐퍼의 경우에 유압 시험기를 이용하여 인장과 압축될 때 장의 On/Off에 따른 시간지연과 감쇄력을 비교하였다.

• Journal of Photoscience
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• 제12권3호
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• pp.119-122
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• 2005

The photophysical properties of coumarin 6 laser dye have been studied in two solvents; ethanol and acetonitrile using steady-state fluorescence depolarization technique. The experimentally measured reorientation time of coumarin 6 is more or less the same in given solvents at particular temperature. It is found that coumarin 6 rotates slower in acetonitrile than in ethanol especially at higher values of viscosity over temperature. We also measure the ground and excited state dipole moments of coumarin 6 by solvent perturbation method. The results found that excited state dipole moment is greater than ground state dipole moment, which indicates that excited state is more polar than the ground state.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 추계학술대회 논문집
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• pp.358-361
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• 2005

The rotational barrel type equipment has been designed for the new rheology fabrication process. During the continuous rotation of barrel with a constant temperature, the shear rate is controlled with the rotation speed and rotation time of barrel. The barrel surface can be controlled the temperature by the induction heating and cooling system. Many experiments were widely examined by using this system with controlling the rotation speed and the rotation time. The possibility for the rheoforming process was investigated with microstructural characteristics.

• 태양에너지
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• 제18권4호
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• pp.101-110
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• 1998

The purpose of this research is to study the charateristics and manufacture of a composite heat pipe system with rotational and static pipe. A composite heat pipe system were tested to obtain the relationship between the expansion injector and auxiliary expansion for the motion of the working fluid by the experimental results. In addition the heat transport characteristics were found based on wall temperature of rotor, expansion injector, storage tank and vapor temperature. Water is used as working fluid of heat pipes. As the results of experiments, the composite heat pipe was operated for long times, 10 hour above with various rotational speed in performance. There were a few unexpected data by the capillary pumped loop at small working fluid, but as a whole the testing was successful.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.645-648
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• 2005

The rotational barrel type equipment has been designed for the new rheology fabrication process. During the continuous rotation of barrel with a constant temperature, the shear rate is controlled with the rotation speed and rotation time of barrel. The barrel surface can be controlled the temperature by the induction heating and cooling system. Many experiments were widely examined by using this system with controlling the rotation speed and the rotation time. The possibility for the rheoforming process was investigated with microstructural characteristics.

• 한국기계가공학회지
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• 제19권5호
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• pp.111-117
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• 2020

Centrifugal casting is suitable for producing hollow-products using centrifugal force. Bush type metal bearings are the key parts that facilitate the rotational movement of various machinery. Metal bearings produced by conventional centrifugal casting machines show rotational imbalance. Therefore, after injecting a large amount of material, the product's precision is secured in the secondary processing. Rotational imbalance is caused by the force acting on the rotary disc plate. In order to minimize rotational imbalance, NASTRAN was used for the optimal design and structural analysis. It was concluded that the rotating plate of the conventional centrifugal casting machine should be prevented from tilting. For this purpose, the location & thickness of the stiffeners were obtained through the optimum design. In the conventional centrifugal casting machine, both ends of the product are lower in temperature than the center part, so internal stress occurs. This solves this problem by inserting a heating coil into the rotating plate.

• 천문학논총
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• 제20권1호
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• pp.7-10
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• 2005

We have calculated 2448 interstellar cloud models to investigate the formation and destruction of high rotational level $H_2$ according to the combinations of five physical conditions: the input UV intensity, the $H_2$ column density, cloud temperature, total density, and the $H_2$ formation rate efficiency. The models include the populations of all the accessible states of $H_2$ with the rotational quantum number J < 16 as a function of depth through the model clouds, and assume that the abundance of $H_2$ is in a steady state governed primarily by the rate of formation on the grain surfaces and the rates of destruction by spontaneous fluorescent dissociation following absorption in the Lyman and Werner band systems. The high rotational levels J = 4 and J = 5 are both populated by direct formation into these levels of newly created molecules, and by pumping from J = 0 and J = 1, respectively The model results show that the high rotational level ratio N(4)/N(0) is proportional to the incident UV intensity, and is inversely proportional to the $H_2$ molecular fraction, as predicted in theory.