• Title/Summary/Keyword: Active current density

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A Study on the Combustion Characteristics of Turbulent Diffusion Flame Stabilized by Bluff Body (보염기에 의해 안정되는 난류확산화염의 연소특성에 관한 연구)

  • An, J.G.;Song, K.K.
    • Journal of the Korean Society of Combustion
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    • v.3 no.1
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    • pp.71-78
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    • 1998
  • The flame stabilization and the combustion characteristics of diffusion flame formed in the wake of a cylindrical bluff body with fuel injection are studied. With the turbulence generator, the flame stability limits and ion currents were measured and analyzed. The results from this experimental study are summarized as follows. The region with highest average value of ion currents in the middle of flame is moved to the upstream side by the turbulent components of main stream. The flame mass with partially active reaction is moved fast for uniform flow and turbulence generator G3, but the flame mass with relatively slow reaction is moved slowly for turbulence generator G1. If the turbulence generator with strong turbulent component is installed, the turbulent time scale is increased with movement from main stream side to recirculation zone as well as the flame stability limits is deteriorated. Though the special dominant frequency is not appeared in the eddy which exists in flame, high frequency characteristics are appeared in uniform flow and turbulence generator G3, and low frequency characteristics are appeared in uniform flow, turbulence generator G3 and G1.

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Microtube Light-Emitting Diode Arrays with Metal Cores

  • Tchoe, Youngbin;Lee, Chul-Ho;Park, Junbeom;Baek, Hyeonjun;Chung, Kunook;Jo, Janghyun;Kim, Miyoung;Yi, Gyu-Chul
    • Proceedings of the Korean Vacuum Society Conference
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    • 2016.02a
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    • pp.287.1-287.1
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    • 2016
  • Three-dimensional (3-D) semiconductor nanoarchitectures, including nano- and micro- rods, pyramids, and disks, are emerging as one of the most promising elements for future optoelectronic devices. Since these 3-D semiconductor nanoarchitectures have many interesting unconventional properties, including the use of large light-emitting surface area and semipolar/nonpolar nano- or micro-facets, numerous studies reported on novel device applications of these 3-D nanoarchitectures. In particular, 3-D nanoarchitecture devices can have noticeably different current spreading characteristics compared with conventional thin film devices, due to their elaborate 3-D geometry. Utilizing this feature in a highly controlled manner, color-tunable light-emitting diodes (LEDs) were demonstrated by controlling the spatial distribution of current density over the multifaceted GaN LEDs. Meanwhile, for the fabrication of high brightness, single color emitting LEDs or laser diodes, uniform and high density of electrical current must be injected into the entire active layers of the nanoarchitecture devices. Here, we report on a new device structure to inject uniform and high density of electrical current through the 3-D semiconductor nanoarchitecture LEDs using metal core inside microtube LEDs. In this work, we report the fabrications and characteristics of metal-cored coaxial GaN/InxGa1xN microtube LEDs. For the fabrication of metal-cored microtube LEDs, GaN/InxGa1xN/ZnO coaxial microtube LED arrays grown on an n-GaN/c-Al2O3 substrate were lifted-off from the substrate by wet chemical etching of sacrificial ZnO microtubes and SiO2 layer. The chemically lifted-off layer of LEDs were then stamped upside down on another supporting substrates. Subsequently, Ti/Au and indium tin oxide were deposited on the inner shells of microtubes, forming n-type electrodes of the metal-cored LEDs. The device characteristics were investigated measuring electroluminescence and current-voltage characteristic curves and analyzed by computational modeling of current spreading characteristics.

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A Study on Oxygen Reduction Reaction of PtM Electrocatalysts Synthesized on Graphene for Proton Exchange Membrane Fuel Cell (고분자전해질연료전지를 위한 그래핀 기반 PtM 촉매들의 산소환원반응성 연구)

  • Yang, Jongwon;Choi, Changkun;Joh, Han-Ik;Park, Jong Jin;Kwon, Yongchai
    • Journal of Hydrogen and New Energy
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    • v.25 no.4
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    • pp.378-385
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    • 2014
  • In this research, we investigate electrical performance and electrochemical properties of graphene supported Pt (Pt/G) and PtM (M = Ni and Y) alloy catalysts (PtM/Gs) that are synthesized by modified polyol method. With the PtM/Gs that are adopted for oxygen reduction reaction (ORR) as cathode of proton exchange membrane fuel cells (PEMFCs), their catalytic activity and ORR performance and electrical performance are estimated and compared with one another. Their particle size, particle distribution and electrochemically active surface (EAS) area are measured by TEM and cyclic voltammetry (CV), respectively. On the other hand, regarding ORR activity and electrical performance of the catalysts, (i) linear sweeping voltammetry by rotating disk electrode and rotating ring-disk electrode and (ii) PEMFC single cell tests are used. The TEM and CV measurements demonstrate particle size and EAS of PtM/Gs are compatible with those of Pt/G. In case of PtNi/G, its half-wave potential, kinetic current density, transferred electron number per oxygen molecule and H2O2 production % are excellent. Based on data obtained by half-cell test, when PEMFC singlecell tests are carried out, current density measured at 0.6V and maximum power density of the PEMFC single cell employing PtNi/G are better than those employing Pt/G. Conclusively, PtNi/Gs synthesized by modified polyol shows better ORR catalytic activity and PEMFC performance than other catalysts.

Optimization of multiple-quantum-well structures in 1.55.μ InGaAsP/InGaAsP SL-MQW DFB-LD for high-speed direct modulation (고속직접변조를 위한 1.55.μ. InGaAsP/InGaAsP SL-MQW DFB-LD의 양자우물구조의 최적화)

  • 심종인;한백형
    • Journal of the Korean Institute of Telematics and Electronics D
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    • v.34D no.3
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    • pp.60-73
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    • 1997
  • By introducing a compressive-strained quanternary InGaAsP quantum-wells instead of a conventional ternary InGaAs quantum-wells in 1.55.mu.m DFB-LD, the lasing performances canb e improved and the problems caused by the thickness non-uniformity and the compositional abruptness among the hetero-interpaces canb e relaxed. In this paper, we investigated an iptimum InGaAsP/InGaAsP multiple-quantum-well(MQW) structure as an active layer in a direct-modulated 1.55.mu. DFB-LD from the view point of threshold current, chirping charcteristics, and resonance frequency. The optimum compressive-strained MQW structure was revealed as InGaAsP/InGaAsP structure with strain amount of about 1.2%, number of wells Nw of 7, well width Lw of 58.agns.. The threshold current density J of 500A/c m2, the linewidth enhancement factor a of 1.8, and differential resonance frequency of d fr/d(I-I)12/=2GHz/(mA)12/(atI=2 Ith) were expected in 1.55.mu.m .gamma./4-shifted DFB-LD with the cavity length of 400.mu.m long and kL value of 1.25. These values are considerably improved ones compared to those of 1.55um DFB-LD with InGaAs/InGaAsP MQW which have enhancement factor and the resonance frequence frequency by the detuning of lasing wavelength and gain-peak wavelength. It was found that the linewidth enhancement factor of 20% and differential resonance frequency of 35% without the degradation of the threshold current density could be enhanced in the range of -15nm~-20nm detuning which can be realized by controlling the thickness and Incomposition of InGaAsP well. well.and Incomposition of InGaAsP well. well.

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Advanced Induction Heating Equipment using Dual Mode PWM-PDM Controlled Series Load Resonant Tank High Frequency Inverters

  • Fathy, Khairy;Kwon, Soon-Kurl;Nakaoka, Mutsuo
    • Journal of Power Electronics
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    • v.7 no.3
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    • pp.246-256
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    • 2007
  • In this paper, a novel type auxiliary active edge resonant snubber assisted zero current soft switching pulse modulation Single-Ended Push Pull (SEPP) series load resonant inverter using IGBT power modules is proposed for cost effective consumer high-frequency induction heating (IH) appliances. Its operating principle in steady state is described by using each switching mode's equivalent operating circuits. The new multi resonant high-frequency inverter with series load resonance and edge resonance can regulate its high frequency output power under a condition of a constant frequency zero current soft switching (ZCS) commutation principle on the basis of the asymmetrical pulse width modulation (PWM) control scheme. Brand-new consumer IH products using the proposed ZCS-PWM series load resonant SEPP high-frequency inverter using IGBTs is evaluated and discussed as compared with conventional high-frequency inverters on the basis of experimental results. In order to extend ZCS operation ranges under a low power setting PWM as well as to improve efficiency, the high frequency pulse density modulation (PDM) strategy is demonstrated for high frequency multi-resonant inverters. Its practical effectiveness is substantially proved from an application point of view.

A High Efficiency Controller IC for LLC Resonant Converter in 0.35 μm BCD

  • Hong, Seong-Wha;Kim, Hong-Jin;Park, Hyung-Gu;Park, Joon-Sung;Pu, Young-Gun;Lee, Kang-Yoon
    • Journal of Power Electronics
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    • v.11 no.3
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    • pp.271-278
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    • 2011
  • This paper presents a LLC resonant controller IC for secondary side control without external active devices to achieve low profile and low cost LED back light units. A gate driving transformer is adopted to isolate the primary side and the secondary side instead of an opto-coupler. A new integrated dimming circuitry is proposed to improve the dynamic current control characteristic and the current density of a LED for the brightness modulation of a large screen LCD. A dual-slope clock generator is proposed to overcome the frequency error due to the under shoot in conventional approaches. This chip is fabricated using 0.35 μm BCD technology and the die size is 2×2mm2. The frequency range of the clock generator is from 50 kHz to 500 kHz and the range of the dead time is from 50 ns to 2.2 μs. The efficiency of the LED driving circuit is 97 % and the current consumption is 40 mA for a 100 kHz operation frequency from a 15 V supply voltage.

Optically Controlled Silicon MESFET Modeling Considering Diffusion Process

  • Chattopadhyay, S.N.;Motoyama, N.;Rudra, A.;Sharma, A.;Sriram, S.;Overton, C.B.;Pandey, P.
    • JSTS:Journal of Semiconductor Technology and Science
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    • v.7 no.3
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    • pp.196-208
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    • 2007
  • An analytical model is proposed for an optically controlled Metal Semiconductor Field Effect Transistor (MESFET), known as Optical Field Effect Transistor (OPFET) considering the diffusion fabrication process. The electrical parameters such as threshold voltage, drain-source current, gate capacitances and switching response have been determined for the dark and various illuminated conditions. The Photovoltaic effect due to photogenerated carriers under illumination is shown to modulate the channel cross-section, which in turn significantly changes the threshold voltage, drainsource current, the gate capacitances and the device switching speed. The threshold voltage VT is reduced under optical illumination condition, which leads the device to change the device property from enhancement mode to depletion mode depending on photon impurity flux density. The resulting I-V characteristics show that the drain-source current IDS for different gate-source voltage Vgs is significantly increased with optical illumination for photon flux densities of Φ=1015and1017/cm2s compared to the dark condition. Further more, the drain-source current as a function of drain-source voltage VDS is evaluated to find the I-V characteristics for various pinch-off voltages VP for optimization of impurity flux density QDiff by diffusion process. The resulting I-V characteristics also show that the diffusion process introduces less process-induced damage compared to ion implantation, which suffers from current reduction due to a large number of defects introduced by the ion implantation process. Further the results show significant increase in gate-source capacitance Cgs and gate-drain capacitance Cgd for optical illuminations, where the photo-induced voltage has a significant role on gate capacitances. The switching time τ of the OPFET device is computed for dark and illumination conditions. The switching time τ is greatly reduced by optical illumination and is also a function of device active layer thickness and corresponding impurity flux density QDiff. Thus it is shown that the diffusion process shows great potential for improvement of optoelectronic devices in quantum efficiency and other performance areas.

THE PREDICTION OF SOLAR ACTIVITY FOR SOLAR MAXIMUM (태양활동극대기를 대비한 태양활동예보)

  • LEE JINNY;JANG SE JIN;KIM YEON HAN;KIM KAP-SUNG
    • Publications of The Korean Astronomical Society
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    • v.14 no.2
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    • pp.103-112
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    • 1999
  • We have investigated the solar activity variation with period shorter than 1000 days, through Fourier transformation of solar cycle 21 and 22 data. And real time predictions of the flare maximum intensity have been made by multilinear regression method to allow the use of multivariate vectors of sunspot groups or active region characteristics. In addition, we have examined the evolution of magnetic field and current density in active regions at times before and after flare occurrence, to check short term variability of solar activity. According to our results of calculation, solar activity changes with periods of 27.1, 28.0, 52.1, 156.3, 333.3 days for solar cycle 21 and of 26.5, 27.1, 28.9, 54.1, 154, 176.7, 384.6 days for solar cycle 22. Periodic components of about 27, 28, 53, 155 days are found simultaneously at all of two solar cycles. Finally, from our intensive analysis of solar activity data for three different terms of 1977\~1982,1975\~1998,and1978\~1982, we find out that our predictions coincide with observations at hit rate of 76%,63%, 59 respectively.

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Electrochemical properties and Estimation of LiMnO2 Active Material Synthesis for Secondary Batteries (2차 전지용 LiMnO2 활물질 합성의 전기화학적 특성과 평가)

  • Wee, Sung-Dong;Gu, Hal-Bon
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2002.11a
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    • pp.210-215
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    • 2002
  • This thesis is contents on the crystal grown by the solide phase method at 925C with orthorhombic structure that LiMnO2 active material synthesised with precurse Mn2O3 and LiOH.H2O material to get three voltage level. The porosity analysis of the grown crystal in secondary batteries LiMnO2 thin film is 1.323E+02\AA of the average pore diameter of powder particles and its structure to be taken the pore diameter was prepared. Adding voltage area to get properties of charge and discharge of which experiment result of LiMnO2 thin film area 2.2V~4.3V, current and scan speed were 0.1mAh/g and 0.2mV/cm2 respectively, and properties of the charge and discharge to be got optimum experiment condition parameter and density rate of Li for analyze that unit discharge capacity with metal properties is 87mAh/g was 96.9[ppm] at 670.784[nm] wavelength, and density rate of Mn analyzed 837[ppm] at 257.610[nm]. It can be estimated the quality of thin film that wrong cell reject from the bottle of electrolyte. The results of SEM and XRD were the same that of original researchers.

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Improvement of lower hybrid current drive systems for high-power and long-pulse operation on EAST

  • M. Wang;L. Liu;L.M. Zhao;M.H. Li ;W.D. Ma;H.C. Hu ;Z.G. Wu;J.Q. Feng ;Y. Yang ;L. Zhu ;M. Chen ;T.A. Zhou;H. Jia;J. Zhang ;L. Cao ;L. Zhang ;R.R. Liang;B.J. Ding ;X.J. Zhang ;J.F. Shan;F.K. Liu ;A. Ekedahl ;M. Goniche ;J. Hillairet;L. Delpech
    • Nuclear Engineering and Technology
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    • v.54 no.11
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    • pp.4102-4110
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    • 2022
  • Aiming at high-power and long-pulse operation up to 1000 s, some improvements have been made for both 2.45 GHz and 4.6 GHz lower hybrid (LH) systems during the recent 5 years. At first, the guard limiters of the LH antennas with graphite tiles were upgraded to tungsten, the most promising material for plasma facing components in nuclear fusion devices. These new guard limiters can operate at a peak power density of 12.9 MW/m2. Strong hot spots were usually observed on the old graphite limiters when 4.6 GHz system operated with power >2.0 MW [B. N. Wan et al., Nucl. Fusion 57 (2017) 102019], leading to a reduction of the maximum power capability. With the new limiters, 4.6 GHz LH system, the main current drive (CD) and electron heating tool for EAST, can be operated with power >2.5 MW routinely. Long-pulse operation up to 100 s with 4.6 GHz LH power of 2.4 MW was achieved in 2021 and the maximal temperature on the guard limiters measured by an infrared (IR) camera was about 540 ℃, much below the permissible value of tungsten material (~1200 ℃). A discharge with a duration of 1056 s was achieved and the 4.6 GHz LH energy injected into the plasma was up to 1.05 GJ. Secondly, the fully-active-multijunction (FAM) launcher of 2.45 GHz system was upgraded to a passive-active-multijunction (PAM), for which the density of optimum coupling was relatively low (below the cut-off value). Good coupling with reflection coefficient ~3% has been achieved with plasma-antenna distance up to 11 cm for the new PAM. Finally, in order to eliminate the effect of ion cyclotron range of frequencies (ICRF) wave on 4.6 GHz LH wave coupling, the location of the ICRF launcher was changed to a port that is located 157.5° toroidally from the 4.6 GHz LH system and is not magnetically connected.