• Title/Summary/Keyword: Direct Conversion

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Rate Capability of Electric Double-Layer Capacitor (EDLC) Electrodes According to Pore Length in Spherical Porous Carbons

  • Ka, Bok-H.;Yoon, Song-Hun;Oh, Seung-M.
    • Journal of the Korean Electrochemical Society
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    • v.10 no.4
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    • pp.252-256
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    • 2007
  • A series of spherical porous carbons were prepared via resorcinol-formaldehyde (RF) sol-gel polymerization in the presence of cationic surfactant (CTAB, cetyltrimethylammonium bromide), wherein the carbon sphere size was controlled by varying the CTAB introduction time after a pre-determined period of addition reaction (termed as "pre-curing"). The sphere size gradually decreases with an increase in the pre-curing time within the range of 30-150 nm. The carbons possess two types of pores; one inside carbon spheres (intra-particle pores) and the other at the interstitial sites made by carbon spheres (inter-particle pores). Of the two, the surface exposed on the former was dominant to determine the electric double-layer capacitor (EDLC) performance of porous carbons. As the intra-particle pores were generated inside RF gel spheres by gasification, the pore diameter was similar for all these carbons, thereby the pore length turned out to be a decisive factor controlling the EDLC performance. The charge-discharge voltage profiles and complex capacitance analysis consistently illustrate that the smaller-sized RF carbons deliver a better rate capability, which must be the direct result of facilitated ion penetration into shorter pores.

AN IMPROVED ANALYSIS FOR DETERMINATION OF MONOVINYL AND DIVINYL PROTOPORPHYRIN IX

  • Kim, Jin-Seog;Rebeiz, Constantin A.
    • Journal of Photoscience
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    • v.2 no.2
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    • pp.103-106
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    • 1995
  • For studying chlorophyll biosynthetic heterogeneity of plants, it is necessary to establish a technique for microassay of a putative monovinyl and divinyl protoporphyrin IX. Precise determination of the amounts of monovinyl and divinyl protoporphyrin IX is difficult with optical electronic spectroscopy even at 77$\circ$C. Such a problem could be solved by conversion of protoporphyrin IX to protoporphyrin IX dimethylester with diazomethane and subsequent Mg insertion into protoporphyrin IX dimethylester by reaction with a Grignard solution. The proportion of monovinyl and divinyl Mg-protoporphyrin IX dimethylester formed was measured instead of direct measuring that of protoporphyrin IX by low-temperature spectrofluorometry. The relative proportions of monovinyl and divinyl of protoporphyrin IX, Mg-protoporphyrin IX, and Mgprotoporphyrin IX dimethylester have not changed during the chemical conversion steps. This analysis system could be useful for the study of the monovinyl and divinyl chlorophyll biosynthetic routes in plants.

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Measuring method of electric resistance using thermoelectric properties of module (열전모듈의 발전특성을 이용한 전기저항 변화 측정)

  • Woo, Byung-Chul;Lee, Hee-Woong
    • Proceedings of the KIEE Conference
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    • 2002.07b
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    • pp.1332-1334
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    • 2002
  • Thermoelectric generation is the direct energy conversion method from heat th electric power. The conversion method is a very useful utilization of waste energy because of its possibility using a thermal energy below $150^{\circ}C$ This research objective is th establish the thermoelectric technology on a optimum system design method and efficiency, and cost effective thermoelectric element in order to extract the maximum electric power from a wasted hot water. This paper is considered in manufacturing a thermoelectric generator and measuring of electric resistance of module a thermoelectric modules. It was found that the electric resistance of thermoelectric modules was defined as a temperature functions. The relationship between electric resistance and temperature characteristics can be a analogized as function of electric current.

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Living cationic polymerization of Viny Ethers in Presence of Iodomethyl Methyl Ether and Zinc Iodide

  • Kwon, Soonhong;Lee, Yunsung;Mah, Soukil
    • Fibers and Polymers
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    • v.2 no.1
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    • pp.131-134
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    • 2001
  • Living cationic polymerization behaviors of isobutyl vinyl ehters (IBVE), initiated by iodomethyl methyl ether (IMME)/zinc iodide ($Znl_2$) have been investigated. The polymerization was carried out at 0, -15, and $-30^{\circ}C$ in toluene. It was found that the rate of polymerization increased as the IMME concentration increased and decreased as temperature decreased. 100% conversion was always achieved without exception. Furthermore, the number-average molecular weight ($M_{n}$) of polymers increased in direct proportion to monomer conversion. The molecular weights of polymers were in good agreement with the theoretical values, calculated on the basis that one polymer chain was formed by one IMME molecule and the values of polydispersity index are always less than 1.2, revealing the living nature. The living nature was also confirmed by synthesis of poly(IBVE-b-TBVE) by subsequent monomer addition of t-butyl vinyl ether (TBVE).

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Correlation Between the Optical Performance of the Reflective Polarizer and the Structure of LCD Backlight

  • Yu, Mi-Yeon;Lee, Byung-Woo;Lee, Jeong-Ho;Ko, Jae-Hyeon
    • Journal of the Optical Society of Korea
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    • v.13 no.2
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    • pp.256-260
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    • 2009
  • The optical performance of the reflective polarizer was investigated over three kinds of direct-lit backlights and/or different configurations of the optical sheets. The optical gain factor achieved by using the reflective polarizer increased as the diffuse nature of the optical sheet was enhanced, because of the more efficient polarization conversion. In addition, the gain factor decreased substantially in flat-lamp backlights compared to tubular-lamp backlights, which was ascribed to the high loss factor during the polarization recycling process due to the complex structure and large area of flat lamps. All these results suggested that reducing the loss factor of the backlight is very important for efficient polarization conversion and thus high optical gain of the reflective polarizer.

Integratable Micro-Doherty Transmitter

  • Lee, Jae-Ho;Kim, Do-Hyung;Burm, Jin-Wook;Park, Jin-Soo
    • JSTS:Journal of Semiconductor Technology and Science
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    • v.6 no.4
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    • pp.275-280
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    • 2006
  • We propose Doherty power amplifier structure which can be integrated in Silicon RF ICs. Doherty power amplifiers are widely used in RF transmitters, because of their high Power Added Efficiency (PAE) and good linearity. In this paper, it is proposed that a method to replace the quarter wavelength coupler with IQ up-conversion mixers to achieve 90 degree phase shift, which allows on-chip Doherty amplifier. This idea is implemented and manufactured in CMOS 5 GHz band direct-conversion RF transmitter. We measured a 3dB improvement output RF power and linearity.

A Searching Algorithm for Minimum Bandpass Sampling Frequency in Simultaneous Down-Conversion of Multiple RF Signals

  • Bae, Jung-Hwa;Park, Jin-Woo
    • Journal of Communications and Networks
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    • v.10 no.1
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    • pp.55-62
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    • 2008
  • Bandpass sampling (BPS) techniques for the direct down-conversion of RF bandpass signals have become an essential technique for software defined radio (SDR), due to their advantage of minimizing the radio frequency (RF) front-end hardware dependency. This paper proposes an algorithm for finding the minimum BPS frequency for simultaneously down-converting multiple RF signals through full permutation over all the valid sampling ranges found for the multiple RF signals. We also present a scheme for reducing the computational complexity resulting from the large scale of the purmutation calculation involved in searching for the minimum BPS frequency. In addition, we investigate the BPS frequency allowing for the guard-band between adajacent down-converted signals, which help lessen the severe requirements in practical implementations. The performance of the proposed method is compared with those of other pre-reported methods to prove its effectiveness.

Manufacturing Prototype and Characteristics Analysis of HB Type Linear Stepping Motor with Longitudinal Flux Machine (자속종방향 HB형 선형 스텝핑 전동기의 시작기 제작 및 특성해석)

  • 원규식;김동희;이상호;오홍석
    • The Transactions of the Korean Institute of Electrical Engineers B
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    • v.52 no.10
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    • pp.507-513
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    • 2003
  • Nowadays, the necessity of linear position control motors have been increased in the various fields of the automatic control system. In the recently, the position control motor have disadvantaged in the efficiency and economical view since it require a conversion equipments such as belt and gear in order to convert rotary to linear motion. On the contrary, the hybrid linear stepping motor(HLSM) of linear motion digital actuator has a direct drive method that do not need mechanical conversion equipments. Therefore, the HLSM is better advantaged in the efficiency and economical view than a rotary stepping motor. In this paper, we have designed an optimum tooth shape and a permanent magnet value between the mover teeth by the 2D finite element method(FEM) to develop the HLSM with longitudinal flux machine(LFM) type, and calculated the thrust force and normal force. And we have manufactured the prototype of it. and have experimented the thrust force and the dynamic thrust characteristics of it.

A New Multicarrier Multicode DS-CDMA Scheme for Time and Frequency Selective Fading Channels

  • Cao Yewen;Tjhung Tjeng Thiang;Ko Chi Chung
    • Journal of Communications and Networks
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    • v.7 no.1
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    • pp.13-20
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    • 2005
  • In this paper, a new multi carrier, direct sequence code division multiple access (MC-DS-CDMA) system is proposed. Our new signal construction is based on convolutional encoding of the transmitted data, serial-to-parallel (S/P) conversion of the encoded data, Walsh-Hadamard-transformation (WHT), a second S/P conversion of the WHT outputs, spread spectrum (SS) modulation with a common pseudo-noise (PN) sequence, and then multicarrier transmission. The system bit error rate (BER) performance in frequency selective fading channel in the presence of additive white Gaussian noise (AWGN) and a jamming tone is analyzed and simulated. The numerical results are compared with those from an orthogonal MC-DS-CDMA system of Sourour and Nakagawa [7]. It is shown that the two systems have almost the same BER performance, but the proposed scheme has better anti-jamming ability.

Effect of Dopping Conditions on a-Se Thin-Films : Microstructural and I-V Study (비정질 박막에 대한 도핑 조건의 영향 및 미세구조와 I-V 연구)

  • 박성광;박지군;강상식;공현기;김진섭;남상희
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2001.11a
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    • pp.492-496
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    • 2001
  • Due to their better photosensitivity in X-ray, the amorphous selenium based photoreceptor is widely used on the X-ray conversion materials. It was possible to control the charge carrier transport of amorphous selenium by suitably alloying a-Se with other elements(e,g. As, Cl). In this paper, We investigated dopants(As, Cl) composition rate to improve dark resistivity and transport properties of charge carrier in amorphous selenium using by direct X-ray conversion material. Alloying a-Se with As inhibits the recrystallization of a-Se but introduces undesirable deep hole traps. then doping with Cl(in the ppm range) compensates for the deep hole traps. We investigated their composition rate in various doping conditions and then obtained optimum dopant composition rate. The result was Se-As 0.3%-Cl 30 ppm and X-ray Sensitivity was 0.57 pc/pixel$.$mR at 137 $\mu\textrm{m}$ x 137 $\mu\textrm{m}$ Pixel area.

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