• Title/Summary/Keyword: active reflectivity

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DETERMINATION OF THERMAL CONDUCTIVITY FROM TRANSIENT REFLECTIVITY MEASUREMENTS OF AMOPHOUS SILICON THIN FILMS (A-Si 박막의 반사율변화에 따른 열전달계수 결정)

  • Ryu, Ji-Hyung;Kim, Hyang-Jung;Moon, Seung-Jae
    • Proceedings of the KSME Conference
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    • 2007.05b
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    • pp.2453-2458
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    • 2007
  • The performance of polysilicon thin film transistor (p-Si TFT) has an important role in the operation of active matrix liquid crystal displays. To fabricate the p-Si TFTs that have uniform characteristics, understanding of the recrystallization mechanism of silicon is crucial. Especially, the analysis of the transient temperature variation and the liquid-solid interface motion is required to find the mechanism. The thermal conductivity is one of the most important parameters to understand the mechanism. In this work, a KrF eximer laser beam was irradiated to amorphous silicon thin films. We measured the transient reflectivity at the wavelength of 633 nm. We carried out the numerical simulation of one dimension conduction equation so that we determined the most well-fitted thermal conductivity by comparing the numerically obtained transient reflectivity with the experimentally measured one. The experimentally determined thermal conductivity of amorphous silicon thin films is 1.5 W/mK.

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Porous Silicon Microcavity Sensors for the Detection of Volatile Organic Compounds (휘발성 유기화합물 탐지용 다공성 실리콘 Microcavity 센서)

  • Park, Cheol Young
    • Journal of Integrative Natural Science
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    • v.2 no.3
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    • pp.211-214
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    • 2009
  • A new porous silicon (PSi) microcavity sensor for the detection of volatile organic compounds (VOCs) was developed. PSi microcavity sensor exhibiting unique reflectivity was successfully obtained by an electrochemical etching of silicon wafer. When PSi was fabricated into a structure consisting of two high reflectivity muktilayer mirrors separated by an active layer, a microcavity was formed. This PSi microcavity is very sensitive structures. Reflection spectrum of PSi microcavity indicated that the full-width at half-maximum (FWHM) was of 10 nm and much narrower than that of fluorescent organic molecules or quantum dot. The detection of volatile organic compounds (VOCs) using PSi microcavity was achieved. When the vapor of VOCs condensed in the nanopores, the refractive indices of entire particle increased. When PSi microcavity was exposed to acetone, ether, and toluene, PSi microcavity in reflectivity was red shifted by 28 nm, 33 nm, and 20 nm for 2 sec, respectively.

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Kim on Critical Thinking (김영정 교수의 비판적 사고론)

  • Choi, Hoon
    • Korean Journal of Logic
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    • v.13 no.2
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    • pp.1-26
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    • 2010
  • The primary purpose of this paper is to examine critically the theory of critical thinking proposed by the late Professor Young-Jung Kim. He defined the basic properties of critical thinking as active reflectivity, and listed deepness, multilaterality and domain-transitivity as primary properties for which critical thinking aims. He, then, pursued how critical thinking can be merged with creativity and proposed the concept 'critico-creative thinking'. I argue that his theory of critical thinking has some limitation, but we can develop his critico-creative thinking further.

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A Study on the Design of Laterally Tilted SCH-SLD with Window Region (윈도우 영역을 갖는 측방향으로 경사진 SCH-SLD의 설계에 관한 연구)

  • 황상구;김정호;김운섭;김동욱;안세경;홍창희
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.5 no.4
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    • pp.777-790
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    • 2001
  • Theoretical analyses have been tried to design high power and stable operating SLD at 1.55${\mu}{\textrm}{m}$ wavelength range which is the lowest absorption wavelength in optical fiber. The materials of active layer and SCH layer were chosen as conventional In1-xGaxAsyPl-y quaternary composition systems. From the transverse mode and the lateral mode analyses of waveguide, the optical power distributions and the optical confinement factor have been studied for single-mode high power operation. According to these analyses, it was calculated the composition and the thickness of SCH layer to obtain the maximum optical confinement factor. In order to obtain low values of the reflectivity, we used the window region and the lateral tilted angle between tile active region and window region. And the reflectivity of SLD was calculated with the gaussian beam approximation and mode analysis. From these researches, it was confirmed for several results to fabricate the efficient and stable SLD. In case of using $1.3\mum$, InGaAsP SCH layer, the layer thickness was obtained $0.08\mum$, to get the maximum optical confinement factor. Using $0.2\mum$, active layer thickness and $0.08\mum$, SCH layer thickness, the window region length is about $100\mum$ without An coating, $10\mum$ in 1% AR coating to obtain about 10-4 reflectivity. When the tilted angle is about $10~15^{\circ}$, the reflectivity is about 10-3. From these results, if the window region length and tilted angle were controlled appropriately in given device structure, it was confirmed that it is possible to fabricate the stable SLD without AR coating analytically.

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Optical Properties of Infinite-Layer Superconductors $Sr_{0.9}$$Ln_{0.1}$Cu$O_2$ (LnLa, Gd, Sm) (무한층 초전도체 $Sr_{0.9}Ln_{0.1}CuO_2$(Ln=La, Gd, Sm)의 광학적 성질)

  • Mun, Mi-Ock;Park, Young-Sub;Kim, Kibum;Kim, Jae H.;A. B. Kuzmenko
    • Progress in Superconductivity
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    • v.3 no.1
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    • pp.13-16
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    • 2001
  • We have measured the reflectivity of superconducting infinite-layer compounds $Sr_{0.9}$ $Ln_{0.1}$ Cu $O_2$ (Ln=La, Gd, Sm) with $T_{c}$ : 39 K using a Fourier-transform infrared spectrometer. We have identified the optical phonon modes from their infrared reflectivity and conductivity spectra and have proposed possible displacement patterns. The La- and the Gd-doped compounds exhibited only four ($2A_{2u}$ $+2E_{u}$) out of the five ($2A_{2u}$ $3E_{u}$) infrared-active phonons predicted by a group theoretical analysis whereas the Sm-doped compound exhibited all five modes. For the La-doped sample, we investigated the temperature dependence of the optical response functions in a wide temperature range of 7 - 300 K. In FIR region, the reflectivity is apparently enhanced below ~120 $cm^{-1}$ as temperature decreases across $T_{c}$. The value of $2$\Delta$/k_{B}$ $T_{c}$ is about 4.5, which is consistent with maximum gap value of d-wave $high- T_{c}$ cuprates.> c/ cuprates.uprates.s.

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Phase-change optical media for computer data storage (컴퓨터 정보저장용 상변화형 광기록매체)

  • 김명룡
    • Electrical & Electronic Materials
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    • v.8 no.2
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    • pp.229-236
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    • 1995
  • Multimedia has created a system environment that needs a combination of diverse peripherals, faster I/O, and easier configuration. The sheer volume of data one can expect with multimedia hardware and applications storage systems of higher capacity and faster data transfer rate. Unlike the magneto-optical(MO)disk technology which uses bias magnetic field in writing, both the reading and the writing in the phase change (PC) technology are performed only by laser light. In PC optical media, an active layer is reversibly converted between amorphous state and crystalline state by changing irradiation conditions of focused laser beam. Thus, as compared with MO disk, the PC disk has such great advantages that signals can be reproduced by change of reflectance of laser beams in the same manner as the compact disc. The reflectivity of a phase-change spot can be altered in a single pass under the head only through modulation of laser power. The principles and the current status of phase-change optical recording media combined with possible applications are discussed in the present article.

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Estimation of reflectivity-rainfall relationship parameters and uncertainty assessment for high resolution rainfall information (고해상도 강수정보 생산을 위한 레이더 반사도-강수량 관계식 매개변수 보정 및 불확실성 평가)

  • Kim, Tae-Jeong;Kim, Jang-Gyeong;Kim, Jin-Guk;Kwon, Hyun-Han
    • Journal of Korea Water Resources Association
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    • v.54 no.5
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    • pp.321-334
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    • 2021
  • A fixed reflectivity-rainfall relationship approach, such as the Marshall-Palmer relationship, for an entire year and different seasons, can be problematic in cases where the relationship varies spatially and temporally throughout a region. From this perspective, this study explores the use of long-term radar reflectivity for South Korea to obtain a nationwide calibrated Z-R relationship and the associated uncertainties within a Bayesian inference framework. A calibrated spatially structured pattern in the parameters exists, particularly for the wet season and parameter for the dry season. A pronounced region of high values during the wet and dry seasons may be partially associated with storm movements in that season. Overall, the radar rainfall fields based on the proposed modeling procedure are similar to the observed rainfall fields. In contrast, the radar rainfall fields obtained from the existing Marshall-Palmer relationship show a systematic underestimation. In the event of high impact weather, it is expected that the value of national radar resources can be improved by establishing an active watershed-level hydrological analysis system.

Time-domain Large-signal Modeling of Injection-locked Fabry-Perot Laser Diode for WDM-PON (WDM-PON용 주입 잠금 패브리-페롯 레이저 다이오드의 시영역 대신호 모델링)

  • Lee, Seung-Hyun;Kim, Gun-Woo;Chung, Young-Chul
    • Korean Journal of Optics and Photonics
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    • v.21 no.2
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    • pp.74-81
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    • 2010
  • A modeling methodology for the analysis of injection-locked Fabry-Perot laser diodes (FP-LDs), promising for cost-effective WDM-PON sources, is proposed. The time-domain large-signal model that is used is found to provide quite similar results to some experimental ones. With our methodology, we model characteristics of FP-LDs, such as influence of reflectivity at a facet and detuning on injection-locking. The eye diagram characteristics are also investigated. It is observed that the facet reflectivity at the injection side should be lower than 1% to provide stable operation in terms of good side-mode suppression ratio and independence from detuning between narrow-band injection noise and LD modes. It is also observed that good eye opening can be obtained for 155 Mbps modulation while the parameters such as the active region thickness should be properly optimized to obtain reasonable eye opening at 1.25 Gbps.

Fabrication of the micro-mold and nanofiber using cellulose solution (셀룰로오스를 이용한 마이크로 몰드 및 나노섬유 제작)

  • Cho, Ki-Youn;Lim, Hyun-Kyu;Kang, Kwang-Sun;Kim, Jae-Hwan
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2007.11a
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    • pp.69-72
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    • 2007
  • Cellulose is a beneficial material that has low cost, lightweight, high compatibility and biodegradability. Recently electroactive paper (EAPap) on cellulose base was discovered as a smart material and actuator through ion migration and piezoelectric effect. Furthermore cellulose has a potentiality to apply the display material, because of its high reflectivity, flexibility and high transmittance. The various shapes and height patterns of the Cellulose acetate (CA) solution, such as circle and honeycomb patterns, were fabricated and observed by field emission scanning electron microscope (FESEM, S4300 Hitachi). The resulting pattern showed uniform size in the large area without defect. After stretching the CA film with saponification process in the sodium methoxide in methanol solution, Most of the compositions become one directional ordered nanofibers below 50nm.

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Improved Performance of 1.55 ㎛ InGaAsP/InP Superluminescent Diodes by Tapered Stripe Structure

  • Choi Young-Kyu
    • KIEE International Transactions on Electrophysics and Applications
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    • v.5C no.1
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    • pp.39-43
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    • 2005
  • We proposed a structure for a 1.55 ㎛ strained separate confinement heterostructure (SCH) multi- quantum well (MQW) superluminescent diode (SLD), having a tapered active region. SLD was fabricated through a two-step procedure: the first step being metal organic chemical vapor deposition (MOCVD) and the second-step being liquid phase epitaxy (LPE). We used a 15 laterally tilted stripe and window region to suppress the lasing action of the SLD. The performance of the SLD showed output power of 11 mW with no lasing under 200 mA pulse driving. The full-width at half-maximum was 42 nm at 200 mA, 25℃.