• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1997년도 추계학술대회 논문집
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• pp.85-89
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• 1997

A microstructure of realistic ZnO varistor was constructed by Voronoi network and studied cia computer simulation. The grain size and standard deviation was calculated with new method and have good agreement with experimental data. In this network, the grain boundary conditions of three different type are randomly distributed. The three electrical boundary conditions . (1) type A junctions (high nonlinearity); (2) type B junctions (low nonlinearity); (3) type C junctions (linear with low-resistivity) are fitted from the experimental measurement. The electrical properties were studied by varying the boundary type concentration and the disorder parameter d. The shape of I-V characteristic curve of the network is affected by the type concentration and the disorder parameter has an effect on the double inflected region.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 추계학술대회 논문집
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• pp.699-705
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• 2013

This paper presents vibration testing, control, and finite element analysis of a piping system, which is subjected to the changes in fluid levels. Nuclear power plants typically employ a cooling system that uses sea water. These systems are subjected to dynamic characteristic changes caused by sea-level variations, which introduces failures of cooling system components. Therefore in this study, analytical and experimental studies were performed to understand the effect of sea-level changes on the dynamic characteristics of piping systems. It was shown that, as the sea-level increases, pipe's natural frequencies decreases in relation to its mode shape. A 1/14 scale model was also built to compare the results obtained by the analytical study. A good agreement between experiment and analytical studies were observed. Finally, an on-line resonant frequency identification system was proposed and developed, which utilizes piezoelectric transducers as sensors and actuators, in order to avoid catastrophic failure of piping systems.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 추계학술대회 논문집
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• pp.147-150
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• 1995

High speed machining one of the most effectiv to improve machining accuracy and product in dies and mould. But a study on this is limited to Alumium, light metal etc. This paper presents machining characteristic of gray cast iron in high speed machining with tungsten carbide endmill. It is suggested to measure sutting force, tool wear, surface roughness, surface shape and select of cptimal cutting condition in the high speed machining of gray cast iron. Performance of high speed machine tool was estimated and the relationship between cutting phenomenon and machinabillity was described.

• 한국정밀공학회지
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• 제24권3호
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• pp.108-116
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• 2007

To overcome many defects such as the high product cost, large energy consumption, and big space capacity in conventional mechanical machining, the miniaturization of machine tool and micro factory systems has been envisioned recently. The object of this paper is to research the effect of dynamic characteristic parameters in bolted-joint beams, which is widely applied to the joining of mechanical structures in order to identify structural system characteristics and to predict dynamic behavior according to scale-down from macro to micro system as the development of micro/meso-scale machine tool and micro factories. Modal parameters such as the natural frequency, damping ratio, and mode shape from modal testing and dynamic characteristics from finite element analysis are extracted with all 12 test beam models by materials, by size, and by joining condition, and then the results obtained by both methods are compared.

• 한국소음진동공학회논문집
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• 제23권2호
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• pp.105-111
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• 2013

Whirl tower test is conducted basically during helicopter rotor system development process. And for whirl tower test of rotor hub system, new design blade or existing blade which is remodeled for new rotor hub system is used. Because of simple shape and efficient aerodynamic characteristic, BO-105 helicopter blade is used for helicopter rotor hub development project widely. Originally BO-105 blade is used for hingeless hub system and blade root is used to flexure. So flap stiffness and lag stiffness at blade root area is relatively low compare with airfoil area. So, in order to apply the BO-105 blade to bearingless hub, blade root area have to be reinforced. And in this process, blade root area's section property is changed. In this paper, we suggest reinforcement method of BO-105 blade root area and study dynamic characteristic of bearingless rotor system with reinforcement BO-105 blade.

• 한국전자파학회논문지
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• 제17권6호
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• pp.556-561
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• 2006

본 논문에서는 기존의 주파수 reconfigurable 안테나의 협대역 특성을 개선하기 위한 대역폭 확장 특성을 가지는 주파수 reconfigurable 슬롯 안테나가 제안되었다. 제안된 안테나는 주파수 reconfigurable 특성을 가지는 동시에 대역폭을 확장시키기 위하여 넓은 슬롯 및 좁은 슬롯 두 부분으로 구성되어 있다. 삼각형 구조의 넓은 슬롯은 제안된 안테나의 대역폭을 증가시키는 역할을 하며, 좁은 슬롯은 PIN diode를 장착하는 역할을 한다. 제안된 안테나는 PM diode의 동작 상태를 바꿈에 따라 슬롯의 총 길이를 변화시키며, 이로 인해 중심 주파수 조절과 임피던스 정합의 변화를 최소화시킨다.

• 동력기계공학회지
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• 제15권4호
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• pp.37-41
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• 2011

This paper introduces the special eddy current sensor and its characteristic for bolt hole defect evaluation in gas turbine rotor. In the past, Fluorescent penetration inspection method was used for qualitative defect evaluation in gas turbine rotor bolt hole. This method can defect the bolt hole defect but can not evaluate the defect size. Nowadays, eddy current method is used quantitative defect evaluation due to advanced sensor design technology. And eddy current method is more time and cost saving than the old method. We developed bolt shape eddy current sensor for the rotor bolt hole defect detection and evaluation. The eddy current sensor moves to the bolt hole guided by screw nut and detects the defect on the bolt hole. The bolt hole mock-up and artificial defects were made and used for the signal detection & resolution analysis of eddy current sensor. The results show that signal detection capability is enough to detect 0.2 mm depth defect. And the resolution capability is enough to differentiate 02, 0.5, 1.0 and 2.0 mm depth defect.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2012년도 춘계학술대회 논문집
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• pp.622-627
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• 2012

During helicopter rotor system development process, whirl tower test is conducted basically. For conducting whirl tower test during bearingless hub development process, design new blade or using existing blade with repair or remodeling. Because simple shape and efficient aerodynamic characteristic, BO-105 blade is used for hub system development widely. Originally BO-105 blade is used for hingeless hub, ho flap stiffness and lag stiffness on blade root area is relatively low. So applying BO-105 blade to bearingless hub whirl tower test, root area have to be reinforce. In this process, blade root area's section property will be changed. In this paper, suggest reinforcement method of BO-105 blade root area and study dynamic characteristic of bearingless rotor system with reinforcement BO-105 blade.

• Journal of Biosystems Engineering
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• 제22권4호
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• pp.391-400
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• 1997

Using the soil bin systems, this study was carried out to investigate the tilling load characteristic for the three kinds of Japanese rotary blade and the possibility of common use for power tiller and tractor rotary. The results obtained from the study are summarized as follows : 1. At all tested soils. the average and maximum tilling torque of all tested blades increased as the tillage pitch did. 2. The torque requirements of newly designed and produced blade was less than that of blade which has been used on power tiller and tractor rotary. 3. The maximum tilling torque of new ONE were decreased 7%, 10~11％, 27% in comparing with another blades at clay loam, loam and sandy loam, respectively. 4. According to observation of the extent of soil adhesion on blade and the contact aspect of blade, new ONE is the most excellent of all tested rotary blades and till smoothly not to compress the untilled soil. From the results of this study. the newly developed blade(new ONE) proved to be good tilling load performance and had a conclusion that it is possible to use it on power tiller and tractor rotary in common.

• Applied Microscopy
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• 제9권1호
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• pp.35-56
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• 1979

To investigate ultrastructural characteristics of cancer cells of the nervous system, 25 cases; i.e. astrocytoma(9), oligodendroglioma(1), medulloblastoma(1), meningioma(5), pinealoma(2) and pituitary adenomas(7). The common findings were marked irregularity of nuclear membrane with pronounced infoldings, clumping of heterochromatin along inner nuclear membrane, enlargement of nucleolus, and frequent observations of nuclear bodies and nuclear inclusions. But these findings are also the signs that can be observed in hyperactive cells. Thus, ultrastructural characteristics of cancerous nucleus are the great variability of nuclear size, shape and composition. but none of them appear to be specific. Among cytoplasmic organelles, massive fibrils are characteristic of astrocytoma and meningiomas, cytoplasmic protofibrils such as glial process and microvesicles in oligodendroglioma, secretory granules are characteristic in pituitary adenomas, and fine filamentous fibrils and desmosomes are characteristic of fibroblastic type of meningioma. Intercellular relationships and cell membrane specialization are important features in the differential diagnosis of various undifferentiated tumors. The frequent resolution of difficult diagnosis problems by electron microscopy outweighs the disadvantages of this technique, such as the expense and time required.