• Title/Summary/Keyword: 평균자유행정

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Electrical and Optical Characteristics of Flat Fluorescent Lamp for LCD Back-lighting (LCD 후면 광원용 FEL의 전기적 및 광학적 특성)

  • 김명녕;권순석
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.7 no.4
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    • pp.725-729
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    • 2003
  • In this paper, a mercury-free flat discharge lamp with opposite electrode structure, a couple of phosphor layer and discharge vessel has been studied for LCD back-lighting. When the drive voltage conditions were set properly, a uniform discharge generates over entires emitting surface. The firing voltage was increased with increasing the discharge gas pressure. It was considered that this tendency was resulted from the decrease of mean free paths due to the increase of discharge gas pressure. The maximum luminance of 2700[cd/m2] was obtained in the green emitting FFL.

Correlation between an Intermolecular Potential and the State of a Nanoscale System (분자간 포텐셜과 나노계 상태와의 상관관계)

  • Choi, Soon-Ho;Chung, Han-Shik;Jeong, Hyo-Min;Lim, Min-Jong;Choi, Gyung-Min;Kim, Duck-Jool
    • Proceedings of the KSME Conference
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    • 2007.05a
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    • pp.496-501
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    • 2007
  • Recently, as MEMS and NEMS devices have been widely used in the various engineering applications, the characteristics of nanoscale systems are investigated in the limelight. However, as opposed to a macroscale system, the identification of the state of nanoscale systems is extremely hard because they can include only the order of $10^{3}\sim10^{5}$ molecules, which requires highly expensive and accurate experimental apparatus for an investigation. This limitations make the study on nanoscale system use computer simulations. Therefore, it is strongly required to identify the state of nanoscale system simulated in computer simulation. In these molecular dynamics(MD) study, we suggest that the potential energy of individual molecule can be used as criterion for defining the state of clusters or nanoscale systems. In addition, we compared the phase state from the potential energy with one from the radial distribution function(RDF) for verification. The comparison showed that the intermolecular potential energy can be used as a criteria distinguishing the phase state of nanoscale systems (This study will be published soon in the KSME transaction of the section B).

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Sensitivity Analysis of Effective Viscosity Coefficients for Computing Characteristics of Ultrathin Gas Film Bearings (초미세 틈새의 기체 베어링 해석용 유효 점도의 표현식과 관련 계수들의 민감도 해석)

  • Kim, Ui Han;Rhim, Yoon Chul
    • Tribology and Lubricants
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    • v.30 no.1
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    • pp.15-20
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    • 2014
  • A more accurate expression for effective viscosity is obtained using a linear regression of the data from Fukui-Kaneko's model, which are obtained through numerical calculations based on the linearized Boltzmann equation. Veijola and Turowski's expression is adopted as a base function for effective viscosity. The four coefficients in that equation are optimized, and sensitivity analysis is conducted for these coefficients. The results show that the coefficient for the first-order Knudsen number is the most accurate, whereas the coefficient in the exponential of the Knudsen number is the least accurate compared with Fukui-Kaneko's results. The expression for effective viscosity is accurate within 0.02% rms of Fukui-Kaneko's results for the inverse Knudsen numbers from 0.01 to 100 and surface accommodation coefficients ranging from 0.7 to 1.

A Study on the Phase Criteria of Nanoscale Systems (나노스케일 계의 상태기준에 관한 연구)

  • Lim, Min-Jong;Choi, Gyung-Min;Kim, Duck-Jool;Chung, Han-Shik;Jeong, Hyo-Min;Choi, Soon-Ho
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.31 no.5
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    • pp.435-447
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    • 2007
  • Recently, as MEMS and NEMS devices have been widely used in the various engineering applications, the characteristics of nanoscale systems are investigated in the limelight. However, as opposed to a macroscale system, the identification of the state of nanoscale systems is extremely hard because they can include only the order of $10^3{\sim}10^5$ molecules, which requires highly expensive and accurate experimental apparatus for an investigation. This limitations make the study on nanoscale system use computer simulations. Therefore, it is strongly required to identify the state of nanoscale system simulated in computer simulation. In this molecular dynamics(MD) study, we suggest that the potential energy of individual molecule can be used as criterion for defining the state of clusters or nanoscale systems. In addition, we compared the phase state from the potential energy with one from the radial distribution function(RDF) for verification. The comparison showed that the intermolecular potential energy can be used as a criteria distinguishing the phase state of nanoscale systems.

Growth of AlN Thin Film on Sapphire Substrates and ZnO Templates by RF-magnetron Sputtering (RF 마그네트론 스퍼터링법을 이용하여 사파이어 기판과 ZnO 박막 위에 증착한 AlN 박막의 특성분석)

  • Na, Hyun-Seok
    • Journal of the Korean Vacuum Society
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    • v.19 no.1
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    • pp.58-65
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    • 2010
  • AlN thin films were deposited on sapphire substrates and ZnO templates by rf-magnetron sputtering. Powder-sintered AlN target was adopted for source material. Thickness of AlN layer was linearly dependent on plasma power from 50 to 110 W, and it decreased slightly when working pressure increased from 3 to 10 mTorr due to short mean free path of source material sputtered from AlN target by Ar working gas. When $N_2$ gas was mixed with Ar, the thickness of AlN layer decreased significantly because of low sputter yield of nitrogen. AlN layer was also deposited on ZnO template. However, it showed weak thermal stability that the interface between AlN and ZnO was deteriorated by rapid thermal annealing treatment above $700^{\circ}C$. In addition, ZnO layer was largely attacked by MOCVD ambient gas of hydrogen and ammonia around $700^{\circ}C$ through inferior AlN layer deposited by sputtering. And AlN layers were fully peeled off above $900^{\circ}C$.

A Study on the Growth of CdTe Films by Close-Spaced Sublimation (근접승화법을 이용한 CdTe박막의 성장에 관한 연구)

  • Lee, Min-Suk;Huh, Joo-Youl;Kim, Dong-Hwan
    • Korean Journal of Materials Research
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    • v.8 no.5
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    • pp.383-393
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    • 1998
  • Cadmium telluride films were grown by close-spaced sublimation(CSS) technique. The effects of various deposition parameters such as ambient pressure, source- to-substrate spacings and temperatures on the growth rate and the microstructure were investigated. The growth mode of CdTe films showed a transition as the ambient pressure changed. This transition was interpreted in terms of the diffusion limited transport and the sublimation limited transport of Cd and $Te_2$ vapors. Experimental results indicated that the transition of growth mode was related with the mean free path of gas molecules. The growth rate and the microstructure of CdTe films were affected by the source type- bulk or powder. This change was due to the temperature difference at the source surface. XRD and SEM analysis showed that the growth rate was one of the main factors to determine CdTe microstructures.

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Optical Simulation Study of the Improvement of Color-rendering Characteristics of White Light-emitting Diodes by Using Red Quantum-dot Films (적색 양자점 필름을 이용한 백색 발광 다이오드의 연색성 개선에 대한 광학 시뮬레이션 연구)

  • Lee, Gi Jung;Hong, Seung Chan;Lee, Jung-Gyun;Ko, Jae-Hyeon
    • Korean Journal of Optics and Photonics
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    • v.32 no.4
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    • pp.163-171
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    • 2021
  • Conventional white light-emitting diodes (LEDs) for lighting applications consist of blue LEDs and yellow phosphors, the spectrum of which lacks deep red. To improve the color-rendering characteristics of white LEDs, a red quantum-dot film was applied to the diffuser plate of LED lighting. The mean free paths of the quantum dots and the concentration of the TiO2 particles in the diffuser plate were adjusted to optimize the optical structure of the lighting. The color-rendering index (CRI) was greater than 90 for most conditions, which demonstrates that adoption of the red quantum-dot film is an effective way for improving the color-rendering properties of conventional white LEDs. The angular dispersion of color coordinates could be removed by utilizing the optical cavity formed between the diffuser plate and the reflector on the bottom of the lighting, where multiple passages of the light through the quantum-dot film reduced the differences in optical path length depending on the viewing angle.

The Effect of Stacking Fault on Thermoelectric Property for n-type SiC Semiconductor (N형 SiC 반도체의 열전 물성에 미치는 적층 결함의 영향)

  • Pai, Chul-Hoon
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.22 no.3
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    • pp.13-19
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    • 2021
  • This study examined the effects of stacking faults on the thermoelectric properties for n-type SiC semiconductors. Porous SiC semiconductors with 30~42 % porosity were fabricated by the heat treatment of pressed ��-SiC powder compacts at 1600~2100 ℃ for 20~120 min in an N2 atmosphere. XRD was performed to examine the stacking faults, lattice strain, and precise lattice parameters of the specimens. The porosity and surface area were analyzed, and SEM, TEM, and HRTEM were carried out to examine the microstructure. The electrical conductivity and the Seebeck coefficient were measured at 550~900 ℃ in an Ar atmosphere. The electrical conductivity increased with increasing heat treatment temperature and time, which might be due to an increase in carrier concentration and improvement in grain-to-grain connectivity. The Seebeck coefficients were negative due to nitrogen behaving as a donor, and their absolute values also increased with increasing heat treatment temperature and time. This might be due to a decrease in stacking fault density, i.e., a decrease in stacking fault density accompanied by grain growth and crystallite growth must have increased the phonon mean free path, enhancing the phonon-drag effect, leading to a larger Seebeck coefficient.