• Title/Summary/Keyword: small field size

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A Theoretical and Experimental Study on the Tribological Size Effect in Microforming Processes (마이크로 성형에서 마찰거동의 크기효과에 대한 이론적 및 실험적 연구)

  • Kim, H.S.
    • Transactions of Materials Processing
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    • v.22 no.7
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    • pp.394-400
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    • 2013
  • Microforming is a very efficient and economical technology to fabricate very small metallic parts in various applications. In order to extend the use of this forming technology for the production of microparts, the size effect, which occurs with the reduction of part size and affects the forming process significantly, must be thoroughly investigated. In this study, the tribological size effect in microforming was studied using modeling and scaled ring compression experiments. A micro-scale friction approach based on the slip-line field theory and lubricant pocket model was used to understand the friction mechanism and explain the tribological size effect. Ring compression tests were performed to analyze the interfacial friction condition from the deformation characteristics of the ring specimens. In addition, finite element analysis results were utilized to quantitatively determine the size-dependent frictional behavior of materials in various process conditions. By comparing theoretical results and experimental measurements for different size factors, the accuracy and reliability of the model were verified.

Modeling Grain Rotational Disruption by Radiative Torques and Extinction of Active Galactic Nuclei

  • Giang, Nguyen Chau;Hoang, Thiem
    • The Bulletin of The Korean Astronomical Society
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    • v.46 no.2
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    • pp.66.1-66.1
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    • 2021
  • Extinction curves observed toward individual Active Galactic Nuclei (AGN) usually show a steep rise toward Far-Ultraviolet (FUV) wavelengths and can be described by the Small Magellanic Cloud (SMC)-like dust model. This feature suggests the dominance of small dust grains of size a < 0.1 ㎛ in the local environment of AGN, but the origin of such small grains is unclear. In this paper, we aim to explain this observed feature by applying the RAdiative Torque Disruption (RATD) to model the extinction of AGN radiation from FUV to Mid-Infrared (MIR) wavelengths. We find that in the intense radiation field of AGN, large composite grains of size a > 0.1 ㎛ are significantly disrupted to smaller sizes by RATD up to dRATD > 100 pc in the polar direction and dRATD ~ 10 pc in the torus region. Consequently, optical-MIR extinction decreases, whereas FUV-near-Ultraviolet extinction increases, producing a steep far-UV rise extinction curve. The resulting total-to selective visual extinction ratio thus significantly drops to RV < 3.1 with decreasing distances to AGN center due to the enhancement of small grains. The dependence of RV with the efficiency of RATD will help us to study the dust properties in the AGN environment via photometric observations. In addition, we suggest that the combination of the strength between RATD and other dust destruction mechanisms that are responsible for destroying very small grains of a <0.05 ㎛ is the key for explaining the dichotomy observed "SMC" and "gray" extinction curve toward many AGN.

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Determination of Background Gray-level for Accurate Measurement of Particles in using Image Processing Method (영상처리 기법을 이용한 입경 측정시 배경 명도가 측정 정밀도에 미치는 영향)

  • Koh, Kwang-Uoong;Lee, Sang-Yong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.24 no.4
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    • pp.599-607
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    • 2000
  • In this study, experiments have been performed to examine the effects of background gray-level on the depth-of-field and on the in-focus criteria. The normalized value of contrast(VC) and the gradient indicator(GI) were used as the in-focus criteria for the small and the large size-ranges of particles, respectively. The slightly larger number of pixels were detected with the brighter background. The maximum of the normalized value of contrast(VCmax) is decreased with the brighter background and its deviation from that with the background gray-level of 160 turned out to be about $pm$15% when the background gray-level changes from 100 to 200. However, the maximum gradient indicator(GImax) changes with the background gray-level within only $pm$5%. The depth-of-field for the VC-applicable particle-size range is largely dependent on the background gray-level. On the other hand, the depth-of-field for the GI-applicable particle-size range changes only slightly with the background gray-level. To keep the normalized standard deviation of the particle size within 0.1, the background gray-level should be set 160$pm$20 for both the VC-applicable and GI-applicable ranges which cover the particle size between $10{\mu}m$ and $300{\mu}m$.

Study of Practical Cathodic Protection of 2nd Class Stainless Steel Shaft by means of Al Sacrificial Anode (AL계 희생양극에 의한 2종스테인리스 강축의 음극방식 실용화 연구)

  • Son, Yeong-Tae;Lee, Myeong-Hun;Lee, Hui-Jun
    • Journal of Korea Ship Safrty Technology Authority
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    • s.22
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    • pp.34-53
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    • 2007
  • In the case of hull material. large sized merchant ships are made of steel, on the other hand FRP or wood are used for small sized fishing boats. At present in Korea approximately 88,500 fishing boats are in operation of which 70% are made of FRP In the meantime, stainless steel is frequently used as shaft materials of the small-size FRP fishing boat. Namely, the kinds of shaft materials are STS 304(18Cr-8Ni), STS 316(18Cr-12Ni-2.5Mo steel) and STS 630(17Cr-Ni-Nb steel)etc. Among these things, STS 304 which is the cheapest and having ordinary corrosion resistance is most widely used as 2nd class shaft material. But, using STS 304 for shaft system material of the small-size FRP fishing boat on seawater environments entails a severe corrosion which causes shaft system troubles. Particularly, the corrosions tend to be concentrated of the stern and bow side, propeller shaft surface of inside of stern tube and the boat having no stern cooling pipe line system. As a solution for those problems, research on the ways to mitigate corrosion on the part of 2nd class stainless steel shaft have been undertaken. In the result, not only clarification for the reason of corrosion of the part of stainless steel shaft used mainly for the small-size FRP fishing boat was done, but also most optimal corrosion protection system was developed by experimenting shaft's protection simulation based of the electrochemical cathodic protection principle. In addition, verification through the field test on the optimal cathodic corrosion protection method by means of aluminum sacrificial anode was carried out. In this study, effective and economical shaft's protection system is suggested to the small-size FRP fishing boat operator by substantiating the results obtained from the research on the optimal cathodic protection.

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Dosimetric Verifications of the Output Factors in the Small Field Less Than $3cm^2$ Using the Gafchromic EBT2 Films and the Various Detectors (Gafchromic EBT2필름과 다양한 검출기를 이용하여 $3cm^2$ 이하의 소조사면에서 출력비율의 선량검증)

  • Oh, Se An;Yea, Ji Woon;Lee, Rena;Park, Heon Bo;Kim, Sung Kyu
    • Progress in Medical Physics
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    • v.25 no.4
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    • pp.218-224
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    • 2014
  • The small field dosimetry is very important in modern radiotherapy because it has been frequently used to treat the tumor with high dose hypo-fractionated radiotherapy or high dose single fraction stereotactic radiosurgery (SRS) with small size target. But, the dosimetry of a small field (< $3{\times}3cm^2$) has been great challenges in radiotherapy. Small field dosimetry is difficult because of (a) a lack of lateral electronic equilibrium, (b) steep dose gradients, and (c) partial blocking of the source. The objectives of this study were to measure and verify with the various detectors the output factors in a small field (<3 cm) for the 6 MV photon beams. Output factors were measured using the CC13, CC01, EDGE detector, thermoluminescence dosimeters (TLDs), and Gafchromic EBT2 films at the sizes of field such as $0.5{\times}0.5$, $1{\times}1$, $2{\times}2$, $3{\times}3$, $5{\times}5$, and $10{\times}10cm^2$. The differences in the output factors with the various detectors increased with decreasing field size. Our study demonstrates that the dosimetry for a small photon beam (< $3{\times}3cm^2$) should use CC01 or EDGE detectors with a small active volume. And also, Output factors with the EDGE detectors in a small field (< $3{\times}3cm^2$) coincided well with the Gafchromic EBT2 films.

A Small Microstrip Patch Antenna (소형 마이크로 스트립 패치안테나)

  • 장순범;박동국
    • Proceedings of the Korea Electromagnetic Engineering Society Conference
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    • 2002.11a
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    • pp.246-249
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    • 2002
  • In this paper, a rectangular patch antenna is miniaturized by changing tile middle of patch into narrow microstrip line except the edges of the patch where the fringing field occurs. Miniaturizing rate, gain, radiation patterns of suggested antennas were compared with general square microstrip antenna by using simulator Ensemble. As a result, it reduces the size of antenna by 30% and improves the characteristic of X pol as a advantage while it reduces gain and bandwidth.

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Care-giver's Needs and Evaluation on the Actual Condition of the Playgrounds in Child Care Facilities (보육시설의 실외놀이 환경실태 및 환경특성에 대한 교사의 평가와 요구)

  • Choi, Mock-Wha;Byun, Hea-Ryun
    • Journal of the Korean housing association
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    • v.19 no.6
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    • pp.105-114
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    • 2008
  • The purpose of this study is to classify playground types according to the physical characteristics of playgrounds in child care facilities, to analyze the needs of care-givers and to evaluate the adequacy of playgrounds according to playground types. The specific areas discussed in this study were the evaluation of the adequacy in the physical characteristics of playgrounds for children's outdoor play activities by the care-givers, who assist in the outdoor play activities of children and manage safety in the playground, and a report on playground requirements of them. Data was collected from field survey carried out to investigate the physical characteristics of playgrounds of 21 child care facilities. This survey incorporated a structured-questionnaire for the purpose of evaluating the adequacy of the physical characteristics of playgrounds (location and size of the playground, play equipments, the composition of play areas, ground covers, and location of sidewalk in the playground) by the 181 care-givers from the facilities and investigating the needs of them. The major results showed the following. 1) In field survey, it was observed that while the location and the size of the playgrounds varied widely, ground cover, play equipments, and the composition of play area turned out to be identical, regardless of the location and the size of the playgrounds. 2) The playgrounds were classified into five types according to the number of children and the size of the playground. The five types include A-type as a large-scale facility/smallsize playground, B-type as a small-scale facility/large-size playground, C-type as a small-scale facility/small-size playground, D-type as a middle-scale facility/large-size playground, and E-type as a large-scale facility/large-size playground. 3) The adequacy of the physical characteristics of playground in the D-type was evaluated to be higher than that of the other types. The adequacy of the C-type playground was evaluated to be lower than that of the other types in terms of size and the composition of play areas within the playground. 4) The care-givers of the D-type and the E-type playground expressed a desire to install various play equipments, while the care-givers of the C-type playground did not wish to install play equipment. 5) Various outdoor play areas were needed in the D-type playground.

Study on the Stress Singularity of Interface Crack by using Boundary Element Method (경계요소법을 이용한 계면균열의 응력특이성에 관한 고찰)

  • 조종두;곽시형
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1994.10a
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    • pp.837-842
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    • 1994
  • The boundary element method was used for studying singularities of an interface crack with contact zones. Because the contact zone size was extremely small in a tention field, a large number of Gaussian points were is used for numerical integration of the Kernels. In order to estimate the contact zone size, iteration method was used. The interface crack tips with contact zones showed no oscillatory behavior and J-integral values across the interface were conserved.

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Smart Decontamination Device for Small-size Radioactive Scrap Metal Waste : Using Abrasion pin in Rotating Magnetic Field and Ultrasonic Wave Cleaner (소형 금속방사성폐기물 제염장치 개발 : 자기장 연삭핀과 초음파 세정기의 응용)

  • Hong, Yong-Ho;Park, Su-Ri;Han, Sang-Wook;Kim, Byung-Jick
    • Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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    • v.12 no.1
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    • pp.79-88
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    • 2014
  • We have developed a smart decontamination device for small-size radioactive scrap metal (SSRSM) necessarily generated from nuclear facilities. This is a multi-modal device such as rotation of magnetic field focusing on the region containing the abrasion pins placed around target and ultrasonic cleaner. Additionally, in order to increase the decontamination efficiency we have modified some configuration of the device so that it could work on them evenly and totally. With the Optimal operating for operation of the new device, we tried to decontaminate some various metal selected as a sample during 15 minutes sequentially using each method, magnetic and ultrasonic device. As a result, the range of decontamination factor has been highly increased to 18~56. After decontamination, all samples were found its activity less than background level.

Transformation and Gene Expression in Arabidopsis thaliana (Arabidopsis의 형질전환과 유전자 발현)

  • 백경희
    • Proceedings of the Botanical Society of Korea Conference
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    • 1987.07a
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    • pp.169-174
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    • 1987
  • Arabidopsis thaliana has been used as a good model system for the molercular biological studies on plants for following reasons. It has small gonome size and short generation time, with easiness to obtain mutants and to be transformed. Prospect of its use in applied field is discussed briefly.

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