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류근환,류한열 한국광학회 2015 Current Optics and Photonics Vol.19 No.3
We investigate the temperature dependence of the phosphor conversion efficiency (PCE) of the phosphormaterial used in a white light-emitting diode (LED) consisting of a blue LED chip and yellow phosphor. The temperature dependence of the wall-plug efficiency (WPE) of the blue LED chip and the PCE ofphosphor are separately determined by analyzing the measured spectrum of the white LED sample. Asthe ambient temperature increases from 20 to 80oC, WPE and PCE decrease by about 4.5% and 6%,respectively, which means that the contribution of the phosphor to the thermal characteristics of whiteLEDs can be more important than that of the blue LED chip. When PCE is decomposed into theStokes-shift efficiency and the phosphor quantum efficiency (QE), it is found that the Stokes-shift efficiencyis only weakly dependent on temperature, while the QE decreases rapidly with temperature. From 20 to80oC the phosphor QE decreases by about 7% while the Stokes-shift efficiency changes by less than 1%
유비쿼터스 사회에 대한 지역경찰공무원의 인식 및 수용특성에 관한 연구
유근환(劉根煥) 한국정책과학학회 2009 한국정책과학학회보 Vol.13 No.4
본 연구는 경찰공무원들을 대상으로 유비쿼터스 사회에 대한 수용의도, 영향 및 주요 경로를 파악해보고자 하였다. 따라서 독립변인으로서 관여수준, 사전지식, 상호작용, 기대효과를 매개변인으로서 유용성과 수용태도를 선정하였다. 그리고 유비쿼터스 사회, 기술수용모델에 관한 이론 및 선행연구의 검토를 통해 작성된 설문지를 활용하여 대구지역 및 인근지역의 경찰공무원들을 대상으로 설문조사를 실시, AMOS를 이용하여 실증분석하였다. 본 연구모형에 따른 실증분석 결과, 관여수준과 기대효과는 수용의도에 정의 영향을 미치는 것으로 분석되었다. 그리고 사전지식과 상호작용은 수용의도에 직접적인 영향을 미치지는 못하였으나 매개변인(유용성, 수용태도)를 통해 간접적인 영향을 미치는 것으로 분석되었다. 특히, 유용성에는 관여수준, 사전지식, 상호작용이 통계적으로 유의미한 영향을 미치는 것으로 나타났고, 수용태도에는 관여수준, 상호작용, 기대효과가 영향력을 갖는 것으로 분석되었다. 그리고 매개변인 상호간의 관계를 살펴본 결과, 유용성이 수용태도에 정(+)의 영향을 미치는 것으로 분석되었으며, 유용성과 수용태도 모두 유비쿼터스 수용의도에 정(+)의 영향을 미치는 것으로 나타났다.
최영환,류근환,류한열 한국광학회 2017 Current Optics and Photonics Vol.1 No.6
GaN-based green light-emitting diode (LED) structures suffer from low internal quantum efficiency (IQE),known as the “green gap” problem. The IQE of LED structures is expected to be improved to some extentby exploiting the Purcell effect. In this study, the Purcell effect on the IQE of green LED structures isinvestigated numerically using a finite-difference time-domain simulation. The Purcell factor of flip-chipLED structures is found to be more than three times as high as that of epi-up LED structures, whichis attributed to the high-reflectance mirror near the active region in the flip-chip LED structures. Whenthe unmodified IQE is 20%, the relative enhancement of IQE can be greater than 50%, without utilizingthe surface-plasmon coupling effect. Based on the simulation results, the “green gap” problem of GaN-basedgreen LEDs is expected to be mitigated significantly by optimizing flip-chip LED structures to maximizethe Purcell effect.
IPv6 전환 메커니즘에 따른 Window Size 분석
서재준,류근환 한밭대학교 2006 한밭대학교 논문집 Vol.23 No.-
Since the successful development of WWW(World Wide Web), Internet users are greatly increased. But it is required that security, QoS mobility should be strengthen, Especially, IP address size is a big issue. The address size for IPv6 has been increased to 128 bits. This paper solves the problem of the limited address space of IPv4 and offers a deeper addressing hierarchy and simpler configuraton. Many Internet professionals agree on the necessary of IPv6 introduction but have a different view of IPv6 introduction time. This paper focuses on the functionality of IPv6, local &oversea trend, interoperability, and migration to IPv6 on the KREONET. Also, TCP performance over IPv4 and IPv6 network is estimated on a testbed. It is found that at the end system, the window size showing the optimal performance of IPv6 is the same with that of IPv4. 인터넷은 세계 최대의 통신 네트워크로 전 세계 1억대 이상의 컴퓨터들과 2억 5천만 명 이상의 사용자들로 연결되어 전문가만을 위한 통신네트워크의 차원을 벗어나 모든 개인을 하나로 묶는 광범위한 정보 인프라로서의 역할을 수행하고 있다. 네트워크 또한 K 서버,워크스테이션 등이 주로 활용하던 기존의 통신망에서 유선, 무선 그리고 유무선 통합을 거쳐 심리스(seamless) 한 통신 환경으로 진화하고 있다. 한편 블루투스,적외선 통신,RF 등의 근거리 무선통신에 의한 새로운 네트워킹 분야가 태동하면서 It의 세계는 노트북 PC, PDA, 입는 컴퓨터,정보가전,소형장치,자동차,각종 센서 등의 개인 생활과 밀접한 다양한 장치가 접속된 대규모 분산 컴퓨팅 환경으로 변화하고 있다. 이러한 변화로 컴퓨팅의 활용 또한 가정, 업무, 여행, 오락 등의 개인 의 다양한 생활환경 속으로 침투하고 있다.
김현중,류근환,Won-Bo Yang,류한열 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.10
We present a method for determining the ideality factor of GaN-based light-emitting diodes(LEDs) by using the measured photovoltaic characteristics. The relation between the short-circuitcurrent and the open-circuit voltage is obtained as the incident power of a laser diode emitting at405 nm is varied, which is used to determine the ideality factor of the LED. From the photovoltaicmeasurements, the ideality factors of a blue and a green LED are determined to be 1.16 and 1.78,respectively. The ideality factors obtained by using the photovoltaic measurement are found tobe much smaller than those obtained by using the I − V curve without illumination, which isbelieved to result from the different carrier generation and transport mechanisms. Investigating thephotovoltaic characteristics of GaN-based LEDs is expected to provide insight into the origin of thehigh diode ideality factor in GaN-based devices.
류한열,류근환,이상호,김현중 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.2
We present a convenient and reliable method for the determination of the internal quantum efficiency (IQE) in GaN-based light-emitting diodes (LEDs) based on the carrier rate equation model. By using the peak point of the efficiency curve as the parameter of the rate equation analysis, we show the IQE of LEDs is unambiguously determined without any information on the recombination coefficients or LED structures. The theoretical analysis model was used to determine the IQE of LED samples. When the theoretical IQE model is applied to the measured external quantum efficiency (EQE) of a blue and a green LED, good agreements between the measured data and the theoretical-fit curves are found. From the measured EQE and the evaluated IQE values,the light extraction efficiency of the LED samples is obtained.
류한열,류근환,최영환,마병진 한국물리학회 2017 Current Applied Physics Vol.17 No.10
The efficiency droop of InGaN-based blue light-emitting diodes (LEDs) is analyzed using numerical simulations with a modified ABC carrier recombination model. The ABC model is modified to include the effect of reduced effective active volume of InGaN quantum wells (QWs) and incorporated into the numerical simulation program. It is found that the droop of internal quantum efficiency (IQE) can be well explained by the effect of reduced light-emitting active volume without assuming a large Auger recombination coefficient. A simulated IQE curve with the modified ABC model is found to fit quite well with a measured efficiency curve of an InGaN LED sample when the effective active volume takes only 2.5% of the physical volume of QWs. The proposed numerical simulation model incorporating the reduced effective active volume can be advantageous for use in the modeling and simulation of InGaN LEDs for higher efficiency.