• Title/Summary/Keyword: $VO_2$(M)

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Synthesis and Characterization of Nb, Mo-doped and Nb/Mo-codoped Monoclinic VO2 Nanoparticles and Their Thin Films by Hydrothermal/Post-Thermal Transformation and Wet-Coating Method

  • Kim, Jongmin;Jung, Young Hee;Kwak, Jun Young;Kim, Yeong Il
    • Journal of the Korean Chemical Society
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    • v.63 no.2
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    • pp.94-101
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    • 2019
  • Nb, Mo-doped and Nb/Mo-codoped $VO_2(M)$ nanocrystallites with various doping levels were synthesized for the first time by a hydrothermal and post thermal transformation method. The reversible phase transition characteristics of those doped $VO_2(M)$ was comparatively investigated. Nb-doping of $VO_2(M)$ by this method resulted in a very efficient lowering of the transition temperature ($T_c$) with a rate of $-16.7^{\circ}C/at.%$ that is comparable to W-doping, while Mo-doping did not give a serious reduction of $T_c$ with only a rate of $-5.1^{\circ}C/at.%$. Nb/Mo-codoping gave a similar result to Nb-doping without a noticeable difference. The thin films of Nb-doped and Nb/Mo-codoped $VO_2(M)$ with a thickness of ca. 120 nm were prepared by a wet-coating of the nanoparticle-dispersed solutions. Those films showed a good thermochromic modulation of near infrared radiation with 30-35% for Nb-doped $VO_2(M)$ and 37-40% for Nb/Mo-codoped ones. Nb/Mo-codoped $VO_2(M)$ film showed slightly enhanced thermochromic performance compared with Nb-doped $VO_2(M)$ film.

The Phase Transition and Thermochromic Characteristics of W/Mg-codoped Monoclinic VO2 Nanoparticle and Its Composite Film

  • Park, Heesun;Kim, Jongmin;Jung, Young Hee;Kim, Yeong Il
    • Journal of the Korean Chemical Society
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    • v.61 no.2
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    • pp.57-64
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    • 2017
  • Monoclinic $VO_2(M)$ nanoparticles codoped with 1.5 at. % W and 2.9 at. % Mg were synthesized by the hydrothermal treatment and post-thermal transformation method of $V_2O_5-H_2C_2O_4-H_2O$ with $Na_2WO_4$ and $Mg(NO_3)_2$. The composite thin film of the W/Mg-codoped $VO_2(M)$ with a commercial acrylic block copolymer was also prepared on PET substrate by wet-coating method. The reversible phase transition characteristics of the codoped $VO_2(M)$ nanoparticles and the composite film were investigated from DSC, resistivity and Vis-NIR transmittance measurements compared with the undoped and Wdoped $VO_2(M)$ samples. Mg-codoping into W-doped $VO_2(M)$ nanoparticles synergistically enhanced the transition characteristics by increasing the sharpness of transition while the transition temperature ($T_c$) lowered by W-doping was maintained. The codoped composite film showed the prominently enhanced NIR switching efficiency compared to only W-doped $VO_2(M)$ film with a lowered $T_c$.

The Development of Prediction Equation for Estimating VO2max from the 20 m PSRT in Korean Middle-School Girls. Exercise Science (20 m 점증 왕복달리기 검사를 이용한 여중생의 VO2max 추정식 개발)

  • Park, Dong-Ho;Song, Jung-Ran;Lee, Sang-Hyun;Kim, Chang-Sun
    • Exercise Science
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    • v.23 no.1
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    • pp.1-11
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    • 2014
  • The purpose of this study was to develop and validate regression models to estimate maximal oxygen uptake (VO2max) from the 20 m Progressive Shuttle Run Test (20 m PSRT) in Korean middle-school girls aged 13-15 years. The 20 m PSRT and VO2max were assessed in a sample of 194 participants. The sample was randomly split into validation (n=127) and test-retest reliability (n=99, 32 out of 127 participants also performed validity test) groups. 127 participants performed a graded exercise test (GXT, stationary gas analyser) and the 20 m PSRT (portable gas analyser) once to develop a VO2max prediction model and to analyze the validity of the modified 20 m PSRT protocol (starting at 7.5 km/h and increasing by 0.5 km/h every 1 min). 99 participants performed the 20 m PSRT twice for test-retest reliability purpose. Mean measured VO2max (39.2±5.1 ml/kg/min) from the potable gas analyzer was significantly increased from that measured during the GXT from stationary gas analyzer (37.7±5.7 ml/kg/min, p=.001) using the modified 20 m PSRT protocol. But it was a narrow range (1.5 ml/kg/min). The measured VO2max from the potable and stationary gas analyzers correlated at r=.88(p<.001). Test-retest of the 20 m PSRT yielded comparable results (Laps r=.88 & final speed r=.85). New regression equations were developed from present data to predict VO2max for middle-school girls: y=.231×Laps-.311×weight(in kg)+46.201 (r=.74, SEE=4.29 ml/kg/min). It is concluded that (a) the modified 20 m PSRT protocol is a valid and reliable test and (b) this equation developed in this study provides valid estimates of VO2max of Korean middle-school girl aged 13-15 years.

Effects of Al2O3 Coating on BiVO4 and Mo-doped BiVO4 Film for Solar Water Oxidation

  • Arunachalam, Maheswari;Yun, Gun;Lee, Hyo Seok;Ahn, Kwang-Soon;Heo, Jaeyeong;Kang, Soon Hyung
    • Journal of Electrochemical Science and Technology
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    • v.10 no.4
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    • pp.424-432
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    • 2019
  • Planar BiVO4 and 3 wt% Mo-doped BiVO4 (abbreviated as Mo:BiVO4) film were prepared by the facile spin-coating method on fluorine doped SnO2(FTO) substrate in the same precursor solution including the Mo precursor in Mo:BiVO4 film. After annealing at a high temperature of 450℃ for 30 min to improve crystallinity, the films exhibited the monoclinic crystalline phase and nanoporous architecture. Both films showed no remarkably discrepancy in crystalline or morphological properties. To investigate the effect of surface passivation exploring the Al2O3 layer, the ultra-thin Al2O3 layer with a thickness of approximately 2 nm was deposited on BiVO4 film using the atomic layer deposition (ALD) method. No distinct morphological modification was observed for all prepared BiVO4 and Mo:BiVO4 films. Only slightly reduced nanopores were observed. Although both samples showed some reduction of light absorption in the visible wavelength after coating of Al2O3 layer, the Al2O3 coated BiVO4 (Al2O3/BiVO4) film exhibited enhanced photoelectrochemical performance in 0.5 M Na2SO4 solution (pH 6.5), having higher photocurrent density (0.91 mA/㎠ at 1.23 V vs. reversible hydrogen electrode (RHE), briefly abbreviated as VRHE) than BiVO4 film (0.12 mA/㎠ at 1.23 VRHE). Moreover, Al2O3 coating on the Mo:BiVO4 film exhibited more enhanced photocurrent density (1.5 mA/㎠ at 1.23 VRHE) than the Mo:BiVO4 film (0.86 mA/㎠ at 1.23 VRHE). To examine the reasons, capacitance measurement and Mott-Schottky analysis were conducted, revealing that the significant degradation of capacitance value was observed in both BiVO4 film and Al2O3/Mo:BiVO4 film, probably due to degraded capacitance by surface passivation. Furthermore, the flat-band potential (VFB) was negatively shifted to about 200 mV while the electronic conductivities were enhanced by Al2O3 coating in both samples, contributing to the advancement of PEC performance by ultra-thin Al2O3 layer.

Industry Activation Scheme through mVoIP Technology Trends and Market Analysis (mVoIP 기술동향 및 시장분석을 통한 산업 활성화 방안)

  • Park, Se-Hwan;Park, Jong-Kyu;Kim, Cheong-Ghil
    • Journal of Digital Contents Society
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    • v.13 no.4
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    • pp.477-482
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    • 2012
  • The mVoIP service is the technology which focuses on the wireless data service as the IP network having the transmission rate of 100 Mbps classes on the high-speed middle of movement through the WiFi, WiBro and 3G mobile radio communication network, and etc. and is developed. Since 2010, the mVoIP (mobile VoIP) service shows the rapid growth due to 4G-LTE service seriously disclosed from July with the Smart phone and 2,011 it begins to be rapidly popularized. In this research, additionally the mVoIP service industry activation plan is presented with the trends of technology development including the chip-set/module/terminal, etc. based upon local and foreign market trend searchlight through the market demand analysis. The mVoIP service downloads App to the mobile apparatus and or can provide the service as the software through the WiFi network. Therefore, the change which is large in the products development aspect is to be have no. Expected to is being provided as the added service in the case of 4G-LTE as a matter of course, the service deployment where it is based on the market principle and demand needs is needed.

Industry Activation Scheme through mVoIP Technology Trends and Market Analysis

  • Park, Se-Hwan;Park, Jong-Kyu;Kim, Cheong-Ghil
    • International journal of advanced smart convergence
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    • v.1 no.2
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    • pp.59-63
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    • 2012
  • The mVoIP service is the technology which focuses on the wireless data service as the IP network having the transmission rate of 100 Mbps classes on the high-speed middle of movement through the WiFi, WiBro and 3G mobile radio communication network, and etc. and is developed. Since 2010, the mVoIP (mobile VoIP) service shows the rapid growth due to 4G-LTE service seriously disclosed from July with the Smart phone and 2,011 it begins to be rapidly popularized. In this research, additionally the mVoIP service industry activation plan is presented with the trends of technology development including the chip-set/module/terminal, etc. based upon local and foreign market trend searchlight through the market demand analysis. The mVoIP service downloads App to the mobile apparatus and or can provide the service as the software through the WiFi network. Therefore, the change which is large in the products development aspect is to be have no. Expected to is being provided as the added service in the case of 4G-LTE as a matter of course, the service deployment where it is based on the market principle and demand needs is needed.

Observation of Unusual Structural Phase Transition in $VO_2$ Thin Film on GaN Substrate

  • Yang, Hyeong-U;Son, Jeong-In;Cha, Seung-Nam;Kim, Jong-Min;Gang, Dae-Jun
    • Proceedings of the Korean Vacuum Society Conference
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    • 2012.02a
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    • pp.573-573
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    • 2012
  • High quality $VO_2$ thin films were successfully grown on GaN substrate by optimizing oxygen partial pressure during the growth using RF sputtering technique. The $VO_2$ thin film grown on GaN substrate exhibited an unusual metal insulator transition behavior, which was known to be observed only either in doped sample or under uniaxial stress. Raman spectra also confirmed that metal insulator transition occurred from monoclinic M1 to rutile R phase via monoclinic M2 phase with increasing temperature. We believe that large lattice mismatch between $VO_2$ and GaN substrate may cause M2 phase to be thermodynamically stable. Optical transmittance and its electrical switching behavior were carefully investigated to elucidate the underlying physics of its metal insulator transition behavior. This study may lead to a unique opportunity to better understand the growth mechanism of M2 phase dominant $VO_2$ thin films.

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Electrochemical Properties of Graphene Composite for Lithium Polymer Battery (리튬 폴리머전지용 Graphene Composite의 전기화학적 특성)

  • 김종욱;구할본
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2000.11a
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    • pp.359-362
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    • 2000
  • The purpose of this study is to research and develop graphene composite for lithium polymer battery. VO(graphene) composite is one of the promising material as a electrode active material for lithium polymer battery(LPB). We investigated AC impedance response and charge/discharge cycling of VO(graphene)/SPE/Li cells. The first discharge capacity of VO(graphene) cathode with 50wt.% V$_2$O$\sub$5/ was 150mAh/g, while that of VO(graphene) cathode with 85wt.% V$_2$O$\sub$5/ was 248mAh/g. The Ah efficiency was above 98% after the 2nd cycle. The discharge capacity of VO(graphene) anode with 3wt.% V$_2$O$\sub$5/ was 718 and 266mAh/g at cycle 1 and 10 at room temperature, respectively. The VO(graphene) anode with 3wt.% V$_2$O$\sub$5/ in PVDF-PAN-PC-EC-LiC1O$_4$ electrolyte showed good capacity with cycling.

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Transmission Performance of VoIP Traffic over MANETs (MANET에서 VoIP 트래픽의 전송성능)

  • Kim, Young-Dong
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.14 no.5
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    • pp.1109-1116
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    • 2010
  • In this paper, some performance characteristics of VoIP(Voice over Internet Protocol) for MANET(Mobile Ad-hoc Networks) with simulation is studied and appropriate condition for implementation of VoIP service is suggested. VoIP simulator is implemented with NS(Network Simulator)-2. VoIP traffic for simulation is generated with some codecs of G.711, G.723.1, G.726-32, G.729A, GSM.AMR and iLBC. As simulation results for traffic transmission under $670{\times}670m$ 50node MANET environment, performance data for MOS(Mean Opinion Score), network delay, packet loss rate and transmission bandwidth are measured. Normalized analysis about measured results shows that maximum VoIP connection satisfying VoIP service quality condition is 15.

Studies on the oxygen-Atom-Transfer Reactions of Peroxo Vanadium(Ⅴ) Complexes (Peroxo Vanadium(Ⅴ)화합물들에 의한 산소 원자 전이 반응에 관한 연구)

  • Won, Tae Jin
    • Journal of the Korean Chemical Society
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    • v.45 no.3
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    • pp.213-218
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    • 2001
  • The reaction of peroxo vanadium(V) complexes, $VO(O_2)_2(pic)^{2-}$, $VO(O_2)(nta)^{2-}$, and $VO(O_2)(dipic)^-$ with thiolato-cobalt(III), $(en)_2Co(SCH_2CH_2NH_2)^{2+}$ resulted in an oxygen-atom transfer in aqueous solutions. Rate constants ($M^{-1}S^{-1}$) for these reactions were (35$\pm$1), $(4.8{\pm}0.4){\times}10^{-2}$ , and $(8.6{\pm}0.5){\times}10^{-4}$, respectively. The coordinate peroxide was activated in the oxygen-atom-transfer reaction of $VO(O_2)_2(pic)^{2-}$, but it is not the case for VO(O$_2$) $(nta)^{2-}$ and VO(O$_2$) $(dipic)^-$. In this paper, we proposed that the direct attack of an electrophilic peroxide to a nucleophilic substrate occurs in the oxygen-atom transfer pathway of peroxo vanadium(V) complexes.

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