• 한국가시화정보학회지
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• 제17권3호
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• pp.24-31
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• 2019

Recently, an air-lift bio-reactor operated by micro bubbles has been utilized to product hydrogen fuel. To enhance the performance, characteristics of hydrodynamics inside the bio-reactor were analyzed using a numerical simulation for two-phase flow. An Eulerian model was employed for both of liquid and gas phases. The standard k-ε model was used for turbulence induced by micro bubbles. A Population Balance Model was employed to consider size distribution of bubbles. A hollow cylinder was introduced at the center of the reactor to reduce a dead area which disturbs circulation of CO bubbles. An appropriate diameter of the draft tube and hollow cylinder were optimized for better performance of the bio-reactor. The optimum model could be obtained when the cross-sectional area ratio of the hollow cylinder to the reactor, and the width ratio of the riser to the downcomer approached 0.4 and 3.5, respectively. Consequently, it is expected that the optimum model could enhance the performance of the bio-reactor with the homogeneous distribution and higher density of CO, and more effective mixing.

• 한국정밀공학회지
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• 제15권10호
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• pp.65-72
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• 1998

The BTA drilling chip is better for deep hole drilling than other self-piloting with pad drilling chips because the large length to diameter ratio allows a unique cutting force dispersion and better supplies the high pressure fluid. Therefore the BTA is useful for many tasks, such as coolant hole drilling of large scale dies, as well as tube seat drilling, which is essential for the heat exchanger, and variable component drilling for automobiles. Deep hole drilling has several significant problems, such as hole deviation, hole over-size, circularity, straightness, and surface roughness. The reasons for these problems, which often result in quality short comings, are an alignment of the BTA drilling system and the unbalance of cutting force by work piece and tool shape. This paper analyzes the properties through an experiment which com¬pared single-edge BTA drills with multiple-edge BTA drills, as well as the shapes of the tools to cause an unbalance of cutting force, and its effect on the precision of the worked hole. Conclusions are as follows. 1) In SMSSC drilling, 60m/min of BTA with single and multi-edged tools proved the best cutting condition and the lowest wear character. 2) The roundness got a little worse as cutting speed was increased, but surface roughness was hot affected. 3) It was proved that the burnishing torque of both drills approached 26%. which is almost the same as the 24% insisted on by Griffiths, and the dispersion characteristic of the multi-edged BTA drill proved better than the single-edge BTA drill.

• Earthquakes and Structures
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• 제19권4호
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• pp.303-313
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• 2020

Spacious experimental and numerical investigation has been conducted by researchers to increase the ductility and energy dissipation of concentrically braced frames. One of the most widely used strategies for increasing ductility and energy dissiption, is the use of energy-absorbing systems. In this regard, the cyclic behavior of a chevron bracing frame system equipped with multi-pipe dampers (CBF-MPD) was investigated through finite element method. The purpose of this study was to evaluate and improve the behavior of the CBF using MPDs. Three-dimensional models of the chevron brace frame were developed via nonlinear finite element method using ABAQUS software. Finite element models included the chevron brace frame and the chevron brace frame equipped with multi-pipe dampers. The chevron brace frame model was selected as the base model for comparing and evaluating the effects of multi-tube dampers. Finite element models were then analyzed under cyclic loading and nonlinear static methods. Validation of the results of the finite element method was performed against the test results. In parametric studies, the influence of the diameter parameter to the thickness (D/t) ratio of the pipe dampers was investigated. The results indicated that the shear capacity of the pipe damper has a significant influence on determining the bracing behavior. Also, the results show that the corresponding displacement with the maximum force in the CBF-MPD compared to the CBF, increased by an average of 2.72 equal. Also, the proper choice for the dimensions of the pipe dampers increased the ductility and energy absorption of the chevron brace frame.

• Applied Microscopy
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• 제36권4호
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• pp.259-269
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• 2006

산왕거미 (Araneus ventricosus) 혈구의 유형을 세포화학적 및 percoll 밀도구배를 이용한 물리화학적 특성에 따라 구분하고, 각각의 미세구조를 고배율의 전자현미경으로 비교 관찰하였다. 혈구는 세포질에 함유된 과립의 유무에 따라 과립혈구와 무과립혈구로 구분되었으며. 과립혈구는 과립의 특성에 따라 다시 산호성 과립혈구와 염기호성 과립혈구, 그리고 헤모시아닌 과립을 함유한 혈색소혈구의 세 가지 유형으로 세분되었다. 산호성 과립혈구는 전체 혈구유형중 약 5%정도를 차지하였으며, 염기호성 과립혈구는 산호성 과립혈구에 비해 과립의 크기가 크고 구형이었다. 한편 무과립혈구는 혈구중 가장 크기가 작은 투명혈구와 심관의 내강에 주로 분포하는 편도혈구, 그리고 탈피 시에만 출현하는 대형의 탈피혈구로 다시 세분되었다.

• Korean Chemical Engineering Research
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• 제55권6호
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• pp.771-777
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• 2017

Carbon nano tubes (CNTs)를 흡착제로 사용하여 회분식 실험을 통해 염료 Eosin Y의 흡착특성을 조사하였다. 본 연구에 사용된 CNTs는 비표면적이 $106.9m^2/g$, 기공부피는 $1.806cm^3/g$, 기공직경은 $163.2{\AA}$이었다. CNTs를 이용한 Eosin Y의 흡착실험은 흡착시간, 초기 pH (2~10), 염료 농도(100, 150 및 200 mg/L), 흡착제의 양(0.05~1.0 g)과 온도(293, 313 및 333 K)를 변수로 사용하여 수행하였다. 흡착은 pH와 온도가 낮을수록 잘 이루어졌으며, Langmuir 모델식에 잘 적용되었다. 또한 흡착반응은 유사 2차 속도식에 잘 적용되었으며, 온도가 증가함에 따라 흡착량이 감소하였다. 입자 내 확산 모델 결과는 흡착 과정에서 막확산과 입자확산이 동시에 일어나는 것을 시사해 주었다. 열역학적 해석에 의하면 CNTs에 의한 염료 Eosin Y의 흡착은 자발적이고 흡열특성을 보였다.

• 한국광학회지
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• 제13권6호
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• pp.506-509
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• 2002

새로운 방법으로 간편하게 입체적으로 비디오 영상을 촬영할 수 있는 광학계를 설계하였다. 광학계의 전체 시야는 42$^{\circ}$이고 유효경은 22mm이다. 본 광학계를 비디오 카메라나 캠코더에 장착하여 정립 실상으로 입체 영상을 촬영하고 이를 입체 영상으로 재생할 수 있는 2중 무초점계 bi-ocular형이다. 광학계의 크기는 광로정을 광속분리기 및 평면경으로 접어서 compact하게 축소되었다. 광학계는 4개의 렌즈군으로 구성되며 각 렌즈군은 relay 렌즈 역할까지 겸하여 v근netting효과를 최소화하였기 때문에 전체 시야에 걸쳐 거의 광 손실 없이 영상을 정립 실상으로 비디오 카메라나 캠코더 렌즈에 전달하고 있다 전 시야에 걸쳐 양 쪽 눈에서 볼 수 있는 영상을 서로 수직한 방향의 편광자와 chopper를 이용하여 1초에 30개 이상 교대로 녹화한다. 재생할 때는 서로 수직한 방향의 편광자를 가진 입체시 안경을 쓰고 양쪽 눈으로 각각의 영상을 보게 되며 입체영화를 감상할 때와 같이 잔상효과로 인하여 연속적인 입체 동영상으로 감상할 수 있다.

• Corrosion Science and Technology
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• 제11권3호
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• pp.96-102
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• 2012

0.1 M NaOH 용액에 PbO첨가양이 증가함에 따라 Alloy 600에 형성되는 산화막의 부동태 피막 특성이 열화되었다. 또한 뚜렷한 2중층 구조의 산화막이 점차 사라지고, 산화막내 존재하는 납의 양이 증가하였다. 산화막 내부 납의 양이 증가함에 따라 산화막 내부 니켈의 결핍이 점차 커졌다. 납에 의해 산화막의 부동태 특성이 약화됨에 따라, 응력부식균열 저항성 또한 급감하였을 것으로 판단된다.

• Nuclear Engineering and Technology
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• 제42권3호
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• pp.249-258
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• 2010

Recently, many utilities have considered interim dry storage of spent nuclear fuel as an option for increasing spent fuel storage capacity. Foreign nuclear regulatory committees have provided some regulatory and licensing requirements for relatively low- and medium-burned spent fuel with respect to the prevention of spent fuel degradation during transportation and interim dry storage. In the present study, the effect of cladding creep and hydride distribution on spent fuel degradation is reviewed and performance tests with high-burned Zircaloy-4 and advanced Zr alloy spent fuel are proposed to investigate the effect of burnup and cladding materials on the current regulatory and licensing requirements. Creep tests were also performed to investigate the effect of temperature and tensile hoop stress on hydride reorientation and subsequently to examine the temperature and stress limits against cladding material failure. It is found that the spent fuel failure is mainly caused by cladding creep rupture combined with mechanical strength degradation and hydride reorientation. Hydride reorientation from the circumferential to radial direction may reduce the critical stress intensity that accelerates radial crack propagation. The results of cladding creep tests at $400^{\circ}C$ and 130MPa hoop stress performed in this study indicate that hydride reorientation may occur between 2.6% to 7.0% strain in tube diameter with a hydrogen content range of 40-120ppm. Therefore, it is concluded that hydride re-orientation behaviour is strongly correlated with the cladding creep-induced strain, which varies as functions of temperature and stress acting on the cladding.

• 한국재료학회지
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• 제23권1호
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• pp.18-23
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• 2013

In this study, the effects of cryogenic treatment cycles on the residual stress and mechanical properties of 7075 aluminum alloy (Al7075) samples, in the form of a tube-shaped product with a diameter of 500 nm, were investigated. Samples were first subjected to solution treatment at $470^{\circ}C$, followed by cryogenic treatment and aging treatment. The residual stress and mechanical properties of the samples were systematically characterized. Residual stress was measured with a cutting method using strain gauges attached on the surface of the samples; in addition, tensile strength and Vickers hardness tests were performed. The detailed microstructure of the samples was investigated by transmission electron microscopy. Results showed that samples with 85 % relief in residual stress and 8% increase in tensile strength were achieved after undergoing three cycles of cryogenic treatments; this is in contrast to the samples processed by conventional solution treatment and natural aging (T4). The major reasons for the smaller residual stress and relatively high tensile strength for the samples fabricated by cryogenic treatment are the formation of very small-sized precipitates and the relaxation of residual stress during the low temperature process in uphill quenching. In addition, samples subjected to three cycles of cryogenic treatment demonstrated much lower residual stress than, and similar tensile strength compared to, those samples subjected to one cycle of cryogenic treatment or artificial aging treatment.

• Restorative Dentistry and Endodontics
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• 제16권1호
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• pp.200-208
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• 1991

The purpose of this study was to observe shear bond strength of composite resin to dentin following surface treatment. Freshly extracted forty-eight sound human molars were used in this study. They were stored at $4^{\circ}C$ physiologic saline solution before experiment. The teeth was then mounted with self curing acrylic resin in brass mold. The buccal surfaces of the teeth were grinding approximately 1.5mm by means of water-irrigated grinding wheel to expose the flattened fresh dentin surfaces. The specimens were divided into 6 groups according to preparation and treatment procedures on dentin surfaces; Group 1: Untreated after preparation with No.301 diamond point Group 2: Treated with primer for 60 seconds after preparation with No.301 diamond point Group 3: Untreated after preparation with No.700 fissure carbide bur Group 4: Treated with primer for 60 seconds after preparation with No.700 fissure carbide bur Group 5: Untreated after grinding with 600 grit silicon carbide paper Group 6: Treated with primer for 60 seconds after grinding with 600 grit silicon carbide paper Light cure dental adhesive was applicated to each specimen. Silux plus(3M) was inserted then into polyethylene tube of 3mm diameter and 3mm height, and polymerized to dentin surface. All of the specimens were stored in distilled water at $35.6^{\circ}C$ for 24 hours prior to testing. The shear bond strength was measured using an Instron Universal Testing Machine. The results obtained from this study were as follows: 1. The shear bond strength to dentin was the highest in group II. 2. The shear bond strength to dentin was the lowest in group III. 3. There was no significant difference in shear bond strength to dentin according to preparation instrument. 4. The primer treatment group showed significantly greater shear bond strength than untreated group.