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981.
Myoung Youp Song Young Jun Kwak Byung-Soo Lee Hye Ryoung Park Byoung-Goan Kim 《International Journal of Hydrogen Energy》2012
Ni, Fe2O3, and CNT were added to Mg. The content of the additives was about 20 wt % with that of Fe2O3 6 wt%. The contents of about 20 wt % additives and 6 wt% Fe2O3 are known optimum ones to improve the reaction rates of Mg with H2. Samples with compositions of 80 wt% Mg–14 wt% Ni–6 wt% Fe2O3 (named as Mg–14Ni–6Fe2O3), and 78 wt% Mg–14 wt% Ni–6 wt% Fe2O3–2 wt% CNT (named as Mg–14Ni–6Fe2O3–2CNT) were prepared by reactive mechanical grinding. The hydriding and dehydriding properties of these samples were then measured, and the effects of Ni, Fe2O3, and CNT addition on the hydriding and dehydriding rates of Mg-based alloys were investigated by comparing their hydrogen-storage properties with those of pure Mg and Mg–10 wt% Fe2O3. 相似文献
982.
Chan Kwak 《Chemical engineering science》2005,60(5):1211-1217
The performance of the platinum-cobalt catalysts in a carbon monoxide preferential oxidation (PROX) reactor was investigated for polymer electrolyte fuel cell systems. First, the PROX reaction was analyzed based on two major reactions involved in it, i.e., oxidation of carbon monoxide and the H2-O2 reaction. Both reactions were affected by the other reaction depending on the reaction temperature regions, but the extent of the influence is not so large. The platinum-cobalt catalysts were found to exhibit high performance in PROX of carbon monoxide in rich hydrogen as a result of catalytic synergy effect between platinum and cobalt. In order to improve such synergy effect, the catalysts were prepared by sol-gel method and subsequent supercritical drying. The platinum-cobalt catalysts prepared by the single step sol-gel procedure exhibited higher activity for PROX than the catalysts prepared by the conventional impregnation. Supercritical drying preserved the active species of platinum-cobalt phase, therefore, the platinum-cobalt composite aerogel catalyst exhibited excellent ability for the carbon monoxide removal. 相似文献
983.
Syndiotacticity-rich low molecular weight (LMW) poly(vinyl alcohol) (PVA) was synthesized by solution copolymerization of vinyl pivalate (VPi) and vinyl acetate (VAc) with various monomer ratios in tetrahydrofuran at low temperature using 2,2′-azobis(2,4-dimethylvaleronitrile) (ADMVN) as an initiator and successive saponification of copoly(VPi/VAc). Solution copolymerization of VPi and VAc by ADMVN and saponification produced water soluble syndiotacticity-rich LMW PVA with number-average degrees of polymerization (Pn)s of 220-520, syndiotactic diad (s-diad) contents of 55.5-61.3%, and with maximum conversions of VPi and VAc into copoly(VPi/VAc) of 70-80%. The effect of stereosequences of PVA was investigated in terms of morphology of water-soluble LMW PVA. Especially, to precisely identify the effect of syndiotacticity of LMW PVA on the change of morphology, we prepared various PVAs with similar Pn of 1200 and with different s-diad contents of 55.5-61.3%, respectively. The PVA with s-diad content of 61.1% revealed a well-defined fibrous morphology. Each fiber was composed of a number of microfibrils. As the s-diad content of PVA decreased, some morphological change was observed. The specimen with s-diad content of 59.9% formed a divided precipitate with microfibrillar structure. In contrast, in the case of PVA with s-diad content of 55.7%, irregular shaped particles were observed. 相似文献
984.
The electrochemical properties of different types of fullerene crystals (x-C60), having hollow-long cylindrical (C-C60), hollow-long square (S-C60), and thick solid-short hexagonal (H-C60) shapes were investigated. The prepared x-C60 samples had specific dimensions with respect to aspect ratio (12.0, 6.7, and 1.5) and lattice spacing distance (1.12, 1.04, and 1.00 nm). Interestingly, it was possible to control the aspect ratio and lattice spacing distance by adjusting the molecular ratio of C60 to the aromatic solvent (m-xylene) used in the preparation. In addition, the number of m-xylene molecule in the x-C60 crystal structure increased with decreasing ratio of x-C60 to m-xylene in the solution, corresponding to ca. C60·0.83m-xylene (for C-C60), C60·0.39m-xylene (for S-C60), and C60·0.36m-xylene (for H-C60). A more ordered arrangement of m-xylene molecules resulted in an improved electrochemical capacitance of x-C60. Importantly, in the case of the regular structure (C-, S-, H-C60), when m-xylene was assembled in the x-C60 structure, the large lattice spacing distance increased. This explains why the C-C60 sample had the largest electrochemical capacitance, compared to the S- and H-C60 samples. Such a configuration would allow for a high charge accumulation and the formation of a donor-acceptor complex, which would permit an easier charge transfer. 相似文献
985.
Jae-Seob Kwak Man-Kyung Ha 《The International Journal of Advanced Manufacturing Technology》2004,23(1-2):87-92
This paper describes the use of the grinding force signal to show the mechanical noise reduction and to detect the dressing time based on the discrete wavelet decomposition. As a result of de-noising, the wavelet de-noising method was more effective than the FFT filtering technique. From the approximation coefficients of the higher order wavelet transform, the grinding force signal obtained by a tool dynamometer was clear so it was possible to successfully detect the dressing time. A measured result by the surface roughness and the ground surface photograph coincided with the detection result. 相似文献
986.
A small antenna for the wideband capsule endoscope system is proposed. Since the capsule endoscope system works in the body and transmits internal image data to a receiver with high resolution, a small wideband antenna is required. To obtain wideband characteristics, a small spiral structure is applied. The proposed antenna has size of 10.1 mm diameter and 3 mm height. The electrical properties of the human body with dielectric constant of 56 and conductivity of 0.83 are considered. The impedance bandwidth of the proposed antenna is from 430 to 500 MHz for VSWR<2 and it has isotropic radiation pattern 相似文献
987.
Yi‐Yeol Lyu Jeonghun Kwak Woo Sung Jeon Younghun Byun Hyo Sug Lee Doseok Kim Changhee Lee Kookheon Char 《Advanced functional materials》2009,19(3):420-427
A novel host material containing silicon‐cored spirobifluorene derivative (SBP‐TS‐PSB), is designed, synthesized, and characterized for red phosphorescent organic light‐emitting diodes (OLEDs). The SBP‐TS‐PSB has excellent thermal and morphological stabilities and exhibits high electroluminescence (EL) efficiency as a host for the red phosphorescent OLEDs. The electrophosphorescence properties of the devices using SBP‐TS‐PSB as the host and red phosphorescent iridium (III) complexes as the emitter are investigated and these devices exhibit higher EL performances compared with the reference devices with 4,4′‐N,N′‐dicarbazole‐biphenyl (CBP) as a host material; for example, a (piq)2Ir(acac)‐doped SBP‐TS‐PSB device shows maximum external quantum efficiency of ηext = 14.6%, power efficiency of 10.3 lm W?1 and Commission International de L'Eclairage color coordinates (0.68, 0.32) at J = 1.5 mA cm?2, while the device with the CBP host shows maximum ηext = 12.1%. These high performances can be mainly explained by efficient triplet energy transfer from the host to the guests and improved charge balance attributable to the bipolar characteristics of the spirobifluorene group. 相似文献
988.
You-Shin Shim Won-Jin Yoon Jaeho Ha Dongwon Seo Kwang-Won Lee Woo-Young Lee Kwang-Il Kwon Tae-Seok Kang Jin-Ha Lee Hyun-Jeong Kim Hae-Jung Kwak Sam-Pin Lee So-Jung Kim Won-Kap Yun Junsoo Lee Jin-Bong Hwang 《Food science and biotechnology》2013,22(6):1567-1571
An analytical method for the simultaneous determination of 16 types of structural amino acids in infant formula using an automated amino acid analyzer was validated through tests of precision, accuracy and linearity. The automated analysis of the amino acids was performed on an ion-exchange packed column with a visible detector. The certificated reference material (CRM) 1546 from NIST was used as the test sample to determine the precision and accuracy of the analytical method. The regression analyses revealed good correlations [correlation coefficient (r 2)] that were greater than 0.99. The recovery values of the amino acids were ranged from 87.18 to 118.08%. The limits of detection and limits of quantification were less than 0.059 mg/100 g and less than 0.198 mg/100 g, respectively. The intra- and inter-day precisions were less than 14.62% in the CRM sample. 相似文献
989.
In order to investigate the possible application of ZnO films as a transparent conducting oxide (TCO) electrode for AC PDP, ZnO:Al films were prepared by DC magnetron sputtering method. The effects of discharge power and doping concentration on the structural and electrical properties of ZnO films were mainly studied experimentally. Five-inch PDP cells using either a ZnO:Al or indium tin oxide (ITO) electrode were also fabricated separately under the same manufacturing conditions. The luminous properties of both the PDP cells were measured and compared with each other.By doping the ZnO target with 2 wt% of Al2O3, the film deposited at a discharge power of 40 W resulted in the minimum resistivity of 8.5 × 10−4 Ω-cm and a transmittance of 91.7%. However, a high doping concentration of 3 wt% of Al2O3 and excessive sputtering power over 40 W may induce high defect density and limit the growth of small grains. Although the luminance and luminous efficiency of the cell using ZnO:Al are lower than those of the cell with the ITO electrode by about 10%, these values are sufficient enough to be considered for the normal operation of AC PDP. 相似文献
990.
Recently, the importance of vehicle safety supporting system has been highlighted as autonomous driving and platooning has attracted the researchers. To ensure driving safety, each vehicle must broadcast a basic safety message (BSM) every 100 ms. However, stable BSM exchange is difficult because of the changing environment and limited bandwidth of vehicular wireless communication. The increasing number of vehicles on the road increases the competition to access wireless networks for BSM exchange; this increases the packet collision rate. An increased packet collision rate impairs the transmission and reception of BSM information, which can easily cause a traffic accident. We propose a solution, the vehicular safety support system (V3S), which exchanges BSMs reliably even when many vehicles are on the road. The V3S uses a clustering scheme to decrease network traffic by reducing the amount of data exchanged between a vehicle and the roadside unit (RSU). In addition, the V3S reduces the collision rate of wireless network packets by broadcasting the vehicle's BSM in an allocated timeslot using the time division multiple access (TDMA) MAC protocol. The V3S also deals with insufficient bandwidth for dedicated short-range communications (DSRC) by changing DSRC channels according to traffic flow. In evaluating the packet error rate for stable BSM packet delivery, the V3S demonstrates an excellent packet error rate of less than 1%, compared to the 802.11p with its packet error rate of 82%. 相似文献