• 제목/요약/키워드: Long Gap

검색결과 604건 처리시간 0.023초

Fabrication of the catalyst free GaN nanorods on Si grown by MOCVD

  • Ko, Suk-Min;Cho, Yong-Hoon
    • 한국진공학회:학술대회논문집
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    • 한국진공학회 2010년도 제39회 하계학술대회 초록집
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    • pp.232-232
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    • 2010
  • Recently light emitting diodes (LEDs) have been expected as the new generation light sources because of their advantages such as small size, long lifetime and energy-saving. GaN, as a wide band gap material, is widely used as a material of LEDs and GaN nanorods are the one of the most widely investigated nanostructure which has advantages for the light extraction of LEDs and increasing the active area by making the cylindrical core-shell structure. Lately GaN nanorods are fabricated by various techniques, such as selective area growth, vapor-liquid-solid (VLS) technique. But these techniques have some disadvantages. Selective area growth technique is too complicated and expensive to grow the rods. And in the case of VLS technique, GaN nanorods are not vertically aligned well and the metal catalyst may act as the impurity. So we just tried to grow the GaN nanorods on Si substrate without catalyst to get the vertically well aligned nanorods without impurity. First we deposited the AlN buffer layer on Si substrate which shows more vertical growth mode than sapphire substrate. After the buffer growth, we flew trimethylgallium (TMGa) as the III group source and ammonia as the V group source. And during the GaN growth, we kept the ammonia flow stable and periodically changed the flow rate of TMGa to change the growth mode of the nanorods. Finally, as the optimization, we changed the various growth conditions such as the growth temperature, the working pressure, V/III ratio and the doping level. And we are still in the process to reduce the diameter of the nanorods and to extend the length of the nanorods simultaneously. In this study, we focused on the shape changing of GaN nanorods with different growth conditions. So we confirmed the shape of the nanorods by scanning electron microscope (SEM) and carried out the Photoluminescence (PL) measurement and x-ray diffraction (XRD) to examine the crystal quality difference between samples. Detailed results will be discussed.

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A review on deep learning-based structural health monitoring of civil infrastructures

  • Ye, X.W.;Jin, T.;Yun, C.B.
    • Smart Structures and Systems
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    • 제24권5호
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    • pp.567-585
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    • 2019
  • In the past two decades, structural health monitoring (SHM) systems have been widely installed on various civil infrastructures for the tracking of the state of their structural health and the detection of structural damage or abnormality, through long-term monitoring of environmental conditions as well as structural loadings and responses. In an SHM system, there are plenty of sensors to acquire a huge number of monitoring data, which can factually reflect the in-service condition of the target structure. In order to bridge the gap between SHM and structural maintenance and management (SMM), it is necessary to employ advanced data processing methods to convert the original multi-source heterogeneous field monitoring data into different types of specific physical indicators in order to make effective decisions regarding inspection, maintenance and management. Conventional approaches to data analysis are confronted with challenges from environmental noise, the volume of measurement data, the complexity of computation, etc., and they severely constrain the pervasive application of SHM technology. In recent years, with the rapid progress of computing hardware and image acquisition equipment, the deep learning-based data processing approach offers a new channel for excavating the massive data from an SHM system, towards autonomous, accurate and robust processing of the monitoring data. Many researchers from the SHM community have made efforts to explore the applications of deep learning-based approaches for structural damage detection and structural condition assessment. This paper gives a review on the deep learning-based SHM of civil infrastructures with the main content, including a brief summary of the history of the development of deep learning, the applications of deep learning-based data processing approaches in the SHM of many kinds of civil infrastructures, and the key challenges and future trends of the strategy of deep learning-based SHM.

8세기 중반 신라 분황사 중건가람 건축 연구 (A Study on the Buildings of 2nd Construction of Silla Bunhwangsa temple in the mid-8th century)

  • 김숙경
    • 건축역사연구
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    • 제30권6호
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    • pp.71-80
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    • 2021
  • This study tries to shed light on character and architectural features of the 2nd construction of Bunhwangsa temple in the mid-8th century. The site of Bunhwangsa Temple is divided into upper and lower areas based on retaining walls running from northwest to southeast, and the main area of the temple centered on Geumdang(the main hall) is located in the upper area. Space composition of the lower area including Wonji(a garden pond) and Gangdang(a lecture hall), is noteworthy in that Bunhwangsa Temple was constructed in a deviating way from rigorous constructional disciplines and used their space efficiently. The Geumdang in the 2nd construction was the largest worship hall with 7×6 bays. The hall was designed to divide its space into two ; the core space was surrounded by outer space. Each gap between columns in the hall was narrowed from center to outer. The main construction of the Geumdang was built as a stable structure with lead-to corridors. This was a much-advanced style than Geumdang at Hwangnyongsa Temple. The Gangdang is presumed to be a large building site as a typical Gangdang style in the Silla era. It was built in the late 9th century and was located in the northern part of the retaining walls. The composition of the middle gate and southern corridors were in double and long corridor style and they were located in front of the 2nd construction. This style coincided in the form of the architectural style of the Hwangnongsa Temple. The 2nd construction of the Bunhwangsa Temple was smaller than the Hwangnongsa Temple. However, it was a prestigious architecture.

Mitigation of wind-induced vibrations of bridge hangers using tuned mass dampers with eddy current damping

  • Niu, Huawei;Chen, Zhengqing;Hua, Xugang;Zhang, Wei
    • Smart Structures and Systems
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    • 제22권6호
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    • pp.727-741
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    • 2018
  • To mitigate vibrations, tuned mass dampers(TMD) are widely used for long span bridges or high-rise buildings. Due to some durability concerns, such as fluid degradation, oil leakage, etc., the alternative solutions, such as the non-contacted eddy current damping (ECD), are proposed for mechanical devices in small scales. In the present study, a new eddy current damping TMD (ECD-TMD) is proposed and developed for large scale civil infrastructure applications. Starting from parametric study on finite element analysis of the ECD-TMD, the new design is enhanced via using the permanent magnets to eliminate the power need and a combination of a copper plate and a steel plate to improve the energy dissipation efficiency. Additional special design includes installation of two permanent magnets at the same side above the copper plate to easily adjust the gap as well as the damping. In a case study, the proposed ECD-TMD is demonstrated in the application of a steel arch bridge to mitigate the wind-induced vibrations of the flexible hangers. After a brief introduction of the configuration and the installation process for the damper, the mitigation effects are measured for the ambient vibration and forced vibration scenarios. The results show that the damping ratios increase to 3% for the weak axis after the installation of the ECD-TMDs and the maximum vibration amplitudes can be reduced by 60%.

염 보조 초음파 분무 열분해법을 이용한 TiO2 나노입자의 합성 및 광학적 성질 (Synthesis and Optical Property of TiO2 Nanoparticles Using a Salt-assisted Ultrasonic Spray Pyrolysis Process)

  • 지명준;박우영;유재현;이영인
    • 한국분말재료학회지
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    • 제26권1호
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    • pp.34-39
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    • 2019
  • Current synthesis processes for titanium dioxide ($TiO_2$) nanoparticles require expensive precursors or templates as well as complex steps and long reaction times. In addition, these processes produce highly agglomerated nanoparticles. In this study, we demonstrate a simple and continuous approach to synthesize $TiO_2$ nanoparticles by a salt-assisted ultrasonic spray pyrolysis method. We also investigate the effect of salt content in a precursor solution on the morphology and size of synthesized products. The synthesized $TiO_2$ nanoparticles are systematically characterized by X-ray diffraction, transmission electron micrograph, and UV-Vis spectroscopy. These nanoparticles appear to have a single anatase phase and a uniform particle-size distribution with an average particle size of approximately 10 nm. By extrapolating the plots of the transformed Kubelka-Munk function versus the absorbed light energy, we determine that the energy band gap of the synthesized $TiO_2$ nanoparticles is 3.25 eV.

유전자알고리즘을 이용한 임플란트용 실링어버트먼트의 홈 깊이 최적화에 관한 연구 (Optimization of the Groove Depth of a Sealing-type Abutment for Implant Using a Genetic Algorithm)

  • 이현열;홍대선
    • 한국기계가공학회지
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    • 제17권6호
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    • pp.24-30
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    • 2018
  • Dental implants are currently widely used as artificial teeth due to their good chewing performance and long life cycle. A dental implant consists of an abutment as the upper part and a fixture as the lower part. When chewing forces are repeatedly applied to a dental implant, gap at the interface surface between the abutment and the fixture is often occurred, and results in some deteriorations such as loosening of fastening screw, dental retraction and fixture fracture. To cope with such problems, a sealing-type abutment having a number of grooves along the conical-surface circumference was previously developed, and shows better sealing performance than the conventional one. This study carries out optimization of the groove shape by genetic algorithm(GA) as well as structural analysis in consideration of external chewing force and pretension between the abutment and the fixture. The overall optimization system consists of two subsystems; the one is the genetic algorithm with MATLAB, and the other is the structural analysis with ANSYS. Two subsystems transmit and receive the relevant data with each other throughout the optimization processes. The optimization result is then compared with that of the conventional one with respect to the contact pressure and the maximum stress. The result shows that the optimized model gives better sealing performance than the conventional sealing abutment.

초등학교 수학교과서 그림과 내용의 연계성 (The connection between illustrations and contents in elementary mathematics textbooks)

  • 홍갑주
    • 한국수학교육학회지시리즈A:수학교육
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    • 제58권2호
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    • pp.225-237
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    • 2019
  • 수학 교과의 그림은 내용의 핵심을 잘 전달하면서 한편으로는 수학의 어려움을 완화시켜주는 복합적인 역할을 해야 한다. 본 연구는 그림과 글의 상호 보완적 관계, 그리고 그림의 감정 표현이라는 두 요소를 초등학교 수학 교과서 그림과 내용의 연계성을 보는 관점의 예로 제시하고, 중국, 일본, 인도, 미국 등의 외국 교과서를 이 관점에서 조사하여 우리나라 교과서 그림 제작에 대한 시사점을 얻었다. 이는 그림을 읽고 의미를 해석하는 과정을 수학 공부의 일부로서 다루어야 한다는 것, 등장인물이 가진 개성과 감정을 더욱 풍부하고 자유롭게 표현해야 한다는 것 등이다.

200℃ 이하 저온 공정으로 제조된 다기능 실리콘 질화물 박막의 조성이 전기적 특성에 미치는 영향 (Effect of Composition on Electrical Properties of Multifunctional Silicon Nitride Films Deposited at Temperatures below 200℃)

  • 금기수;황재담;김주연;홍완식
    • 대한금속재료학회지
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    • 제50권4호
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    • pp.331-337
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    • 2012
  • Electrical properties as a function of composition in silicon nitride ($SiN_x$) films grown at low temperatures ($<200^{\circ}C$) were studied for applications to photonic devices and thin film transistors. Both silicon-rich and nitrogen-rich compositions were successfully produced in final films by controlling the source gas mixing ratio, $R=[(N_2\;or\;NH_3)/SiH_4]$, and the RF plasma power. Depending on the film composition, the dielectric and optical properties of $SiN_x$ films varied substantially. Both the resistivity and breakdown field strength showed the maximum value at the stoichiometric composition (N/Si = 1.33), and degraded as the composition deviated to either side. The electrical properties degraded more rapidly when the composition shifted toward the silicon-rich side than toward the nitrogen-rich side. The composition shift from the silicon-rich side to the nitrogen-rich side accompanied the shift in the photoluminescence characteristic peak to a shorter wavelength, indicating an increase in the band gap. As long as the film composition is close to the stoichiometry, the breakdown field strength and the bulk resistivity showed adequate values for use as a gate dielectric layer down to $150^{\circ}C$ of the process temperature.

신경윤리와 기독교교육 (Neuroethics and Christian Education)

  • 유재덕
    • 기독교교육논총
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    • 제64권
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    • pp.145-171
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    • 2020
  • 오래 전부터 기독교 신앙공동체는 교회의 윤리적 규범과 행동양식을 성찰 대상으로 삼은 채 어떤 형태의 도덕 판단이 적절하고, 올바른 기독교적 행동양식이 무엇인지 규명하려고 노력해왔다. 기독교교육 역시 피아제와 콜벅의 심리적 합리주의에서 근거를 찾으려고 했으나 이성 중심의 구조발달주의는 해답을 제시하지 못했다. 실제로 도덕 판단 과정에서 정서를 배제한 채 인지 또는 이성을 과도하게 강조하는 한편, 무엇보다 자율성을 중시했던 구조발달주의는 기대했던 것과 달리 도덕적 상대주의를 초래하고 말았다. 뿐만 아니라 인간의 도덕 추론과 행위 사이의 간극을 적절하게 해명하지 못했을 뿐더러 도덕성을 사회문화적 맥락에서 과도하게 해석하려고 했다는 비판을 받았다. 이런 구조발달주의의 한계는 도덕 판단 능력이 뇌에 물리적으로 배선되어 있고, 피질과 번연계 간의 네트워크를 상당 부분 의지하고 있다고 주장하는 신경윤리, 특히 도덕 심리 이론에 의해 최근에 재해석되고 있다. 이 논문은 새롭게 등장한 신경윤리의 연구주제 가운데 일부를 검토하고 나서 도덕성을 신경과학적으로 설명하는 주요 이론을 중심으로 기독교교육학이 향후 고려해야 할 시사점을 거론하는 것을 목적으로 삼고 있다.

Failure probability of tall buildings with TMD in the presence of structural, seismic, and soil uncertainties

  • Sadegh, Etedali;Mohammad, Seifi;Morteza, Akbari
    • Structural Engineering and Mechanics
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    • 제85권3호
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    • pp.381-391
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    • 2023
  • The seismic performance of the tall building equipped with a tuned mass damper (TMD) considering soil-structure interaction (SSI) effects is well studied in the literature. However, these studies are performed on the nominal model of the seismic-excited structural system with SSI. Hence, the outcomes of the studies may not valid for the actual structural system. To address the study gap, the reliability theory as a useful and powerful method is utilized in the paper. The present study aims to carry out reliability analyses on tall buildings equipped with TMD under near-field pulse-like (NFPL) ground motions considering SSI effects using a subset simulation (SS) method. In the presence of uncertainties of the structural model, TMD device, foundation, soil, and near-field pulse-like ground motions, the numerical studies are performed on a benchmark 40-story building and the failure probabilities of the structures with and without TMD are evaluated. Three types of soils (dense, medium, and soft soils), different earthquake magnitudes (Mw = 7,0. 7,25. 7,5 ), different nearest fault distances (r = 5. 10 and 15 km), and three seismic performance levels of immediate occupancy (IO), life safety (LS), and collapse prevention (CP) are considered in this study. The results show that tall buildings built near faults and on soft soils are more affected by uncertainties of the structural and ground motion models. Hence, ignoring these uncertainties may result in an inaccurate estimation of the maximum seismic responses. Also, it is found the TMD is not able to reduce the failure probabilities of the structure in the IO seismic performance level, especially for high earthquake magnitudes and structures built near the fault. However, TMD is significantly effective in the reduction of failure probability for the LS and CP performance levels. For weak earthquakes and long fault distances, the failure probabilities of both structures with and without TMD are near zero, and the efficiency of the TMD in the reduction of failure probabilities is reduced by increasing earthquake magnitudes and the reduction of fault distance. As soil softness increases, the failure probability of structures both with and without TMD often increases, especially for severe near-fault earthquake motion.