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121.
Ji Sun Im Seok Chang Kang Byong Chol Bai Tae-Sung Bae Se Jin In Euigyung Jeong Sei-Hyun Lee Young-Seak Lee 《Carbon》2011,(7):2235-2244
A high-performance NO gas sensor was prepared by inducing thermal fluorination of carbon nanotube semiconductors. Thermal fluorination of multi-walled carbon nanotubes (MWCNTs) was carried out at various temperatures (100 ∼ 1000 °C) to investigate the effects of the reaction temperature. The mechanism of high-performance NO gas sensor electrode was shown to depend on the fluorination temperature in a way that can be divided into three regions, separated at 400 and 1000 °C. In the first temperature region, the induction of fluorine functional groups onto MWCNTs showed the opposite trend in electrical resistance change comparing with traditional p-type MWCNTs. In the second temperature region, the induced fluorine functional groups were attenuated by generated fluorinated carbon gases resulting in the decomposition of MWCNTs and the recovery of traditional p-type gas sensor behavior. In the highest temperature region above 1000 °C, reoriented carbon structure was observed, showing bent nanotubes produced from destruction by fluorination and subsequent reorientation due to the high temperature. The gas sensing responsiveness was significantly improved by the thermal fluorination, which causes electrophilic attraction, creates adsorption sites for target NO gases and improve hydrophobicity for gas sensing stability in humid condition. In conclusion, a high-performance gas sensor was obtained by thermal-fluorination of MWCNTs. 相似文献
122.
Song-Hwan Bae 《LWT》2007,40(6):955-962
Five major mulberry [Pachungsipyung (M-1), Whazosipmunja (M-2), Suwonnosang (M-3), Jasan (M-4) and Mocksang (M-5)] cultivated in Korea were assessed for their polyphenolic composition using spectrophotometric methodology, and tested for antioxidant potential by some different assays. The total polyphenol (TP) was found from 2235 to 2570 μg/g gallic acid equivalents, total anthocyanin (TA) content to vary from 1229 to 2057 μg/g, coloured anthocyanins (CA) from 126 to 190 μg/g, and total flavanol (TF) from 16.4 to 65.4 μg/g catechin equivalents except Mocksang (M-5). The ethanolic extract from mulberry fruit shows a rapid and concentration-dependent increase of antioxidant activity. Especially, the antioxidant activities of M-2 and M-4 are higher than those of the others in a hemoglobin-induced linoleic acid system. The reducing power compared with BHT was observed to high value in M-2, M-3 and M-4 extracts. Effectiveness in reducing powers was in a descending order of M-4>M-2>M-3>M-1>M-1. The DPPH-scavenging ability of the ethanolic extract from mulberry fruit was 60.0% at 200 and 212 μg of M-2 and M-4, respectively. M-2 and M-4 also showed sharply increase of hydroxyl scavenging ability with concentration of the extracts. IC50 values in scavenging abilities on hydroxyl radicals were 30 mg and in a descending order of M-5>M-3>M-1>M-4>M-2. Superoxide anion-sacavenging activities of M-2, M-3 and M-4 showed 17.1, 14.5 and 14.8 SOD unit/mg, respectively. 相似文献
123.
We developed a new cell voltage model which depends on the current density response of the proton exchange membrane fuel cell
(PEMFC). The proposed model focuses on the conductivity of a PEMFC fuel cell. The model for conductivity of a polymer electrolyte
membrane, Nafion, uses the thermodynamic function to represent water activity. We observed membrane conductivity by monitoring
the chemical potential of the swelling of the hydrogel. The swelling equilibrium of the ionized hydrogel is governed by the
free energy of mixing, the free energy of elasticity, and the concentration of counterions with fixed charges on the gel network.
A cell voltage equation with reasonable boundary conditions, including the swelling effect, which plays a major role in determining
the cell voltage of a PEMFC, was newly developed. 相似文献
124.
Determination of twisting angle of electrospun nanofiber bundle for continuous electrospinning system 下载免费PDF全文
Electrospinning continuously produced twisted nanofibers with a convergence coil and a rotating ring collector. The positively charged nozzle was used in the electrospinning process to deposit electrospun fibers of polyacrylonitrile onto a rotating ring collector. By withdrawing the electrospun fibers from the rotating ring collector, it was possible to spin the electrospun fibers yarn. In this study, theoretical approaches and numerical simulations were used to determine the twisting angle of the yarn. Using the equations developed in this study, we performed numerical simulations and compared the experimental results with the numerical simulation results. Mechanical properties of the fiber bundle were analyzed for twisting angle. It was confirmed the relationship among the winding drum, the ring collector, and flux of the fibers mass per time during electrospinning in the developed system. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45528. 相似文献
125.
Sung‐Hoon Joo Mi‐Yun Jeong Doo Hyun Ko Jong‐Hyun Park Ki Yong Kim Sung Joon Bae In Jae Chung Jung‐Il Jin 《应用聚合物科学杂志》2006,100(1):299-306
Two new poly(arylene ethynylenes) were synthesized by the reaction of 1,4‐diethynyl‐2.5‐dioctylbenzene either with 4,4′‐diiodo‐3,3′‐dimethyl‐1,1′‐biphenyl or 2,7‐diiodo‐9,9‐dioctylfluorene via the Sonogashira reaction, and their photoluminescence (PL) and electroluminescence (EL) properties were studied. The new poly(arylene ethynylenes) were poly[(3,3′‐dimethyl‐1,1′‐biphenyl‐4,4′‐diyl)‐1,2‐ethynediyl‐(2,5‐dioctyl‐1,4‐phenylene)‐1,2‐ethynediyl] (PPEBE) and poly[(9,9‐dioctylfluorene‐2,7‐diyl)‐1,2‐ethynediyl‐(2,5‐dioctyl‐1,4‐phenylene)‐1,2‐ethynediyl] (PPEFE), both of which were blue‐light emitters. PPEBE not only emitted better blue light than PPEFE, but it also performed better in EL than the latter when the light‐emitting diode devices were constructed with the configuration indium–tin oxide/poly(3,4‐ethylenedioxythiophene) doped with poly(styrenesulfonic acid) (50 nm)/polymer (80 nm)/Ca:Al. The device constructed with PPEBE exhibited an external quantum efficiency of 0.29 cd/A and a maximum brightness of about 560 cd/m2, with its EL spectrum showing emitting light maxima at λ = 445 and 472 nm. The device with PPEFE exhibited an efficiency of 0.10 cd/A and a maximum brightness of about 270 cd/m2, with its EL spectrum showing an emitting light maximum at λ = 473 nm. Hole mobility (μh) and electron mobility (μe) of the polymers were determined by the time‐of‐flight method. Both polymers showed faster μh values. PPEBE revealed a μh of 2.0 × 10?4 cm2/V·s at an electric field of 1.9 × 105 V/cm and a μe of 7.0 × 10?5 cm2/V·s at an electric field of 1.9 × 105 V/cm. In contrast, the mobilities of the both carriers were slower for PPEFE, and its μh (8.0 × 10?6 cm2/V·s at an electric field of 1.7 × 106 V/cm) was 120 times its μe (6.5 × 10?8 cm2/V·s at an electric field of 8.6 × 105 V/cm). The much better balance in the carriers' mobilities appeared to be the major reason for the better device performance of PPEBE than PPEFE. Their highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels were also a little different from each other. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 299–306, 2006 相似文献
126.
The formation of covalent bonds between silanols in copolymer and those in silica prevents organic–inorganic phase separation. Two series of hybrid composite materials, poly(vinyl acetate‐co‐vinyl trimethoxysilane)/TEOS and poly[vinyl acetate‐co‐3‐(trimethoxysilyl)propyl methacrylate]/TEOS, were fabricated using a modified sol‐gel process. The hybrids were transparent. Two kinds of silane coupling agents, vinyl trimethoxysilane (VTS) and 3‐(trimethoxysilyl)propyl methacrylate (γ‐MPS), were used to prevent macrophase separation through formation of covalent bonds. Thermal analysis showed that γ‐MPS was more effective than VTS for the formation of covalent bonds. Enhancement of thermal stability of the hybrids was investigated by thermogravimetric analysis. Photomicrographs of scanning electron microscopy and images of atomic force microscopy indicated that inorganic silica particles were homogeneously dispersed in less than 50 nm in organic matrix. The morphological properties of hybrids were strongly dependent on the organic–inorganic composition. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2310–2318, 2001 相似文献
127.
128.
Chuer Hyun Moon S.K. Singh Dong Gi Lee Soung Soo Yi Kiwan Jang Jung Hyun Jeong Jong-Seong Bae Dong-Soo Shin 《Ceramics International》2012
Alkaline earth metal gallets have been identified as an important ceramic material. The crystal chemistry of many of these gallets is well explored; however, very rare studies regarding optical properties of rare earth (RE) ions doped in such gallets, particularly in Sr3Ga2O6 host, have been carried out. The present study reports on synthesis and characterization of novel Sr3Ga2O6:Eu3+ phosphors. The phosphors have been synthesized using a conventional solid state reaction method. Crystal structure, morphology and luminescence properties (excitation, emission and CIE coordinate) of these phosphors have been studied as a function of sintering temperature and Eu3+ concentration. X-ray diffraction study reveals that the phosphor sintered at low temperature (900 °C) contains an impurity phase which is removed at higher sintering temperatures and results into cubic crystalline phase of Sr3Ga2O6. Particle size of the phosphor increases with an increase in sintering temperature which results to a red shift in the peak position of excitation band lying in a broad range from 250 to 370 nm. Optimum emission intensity is attained for 0.12 mol% concentration of Eu3+ ions; above this concentration, a quenching in emission intensity is observed. 相似文献
129.
Jin-Young Kim Min Jong Bae Shang Hyeun Park Taewon Jeong Sunjin Song Jeonghee Lee Intaek Han Ji Beom Yoo Donggeun Jung SeGi Yu 《Carbon》2012,50(1):170-174
Inorganic powder electroluminescence (IPEL) devices with the insertion of a carbon nanotube (CNT) layer were investigated to verify the effect of the increased local field produced by CNTs on electroluminescence (EL). To increase the field strength effectively, the CNTs were shortened using the cryogenic crushing method. IPEL devices with the insertion of a short CNT layer exhibited an increase in brightness and efficiency with increasing amount of CNTs. The local field enhancement by CNTs, further enlarged by the triple-junction, could increase the field strength applied to the phosphor, resulting in improved EL performance. In addition, short CNTs in an EL device can lead to field enhancement without an unintentional current flowing into the device. 相似文献
130.
Sung Hwan Yoon Jeong Park Oh Boong Kwon Jin Han Yoon Sang In Keel Jeong S. Kim Dae S. Bae 《Fuel》2012,91(1):51-60
Laminar lifted butane flames diluted with nitrogen have been investigated experimentally to determine distinctive self-excitation regimes in the flame stability maps and also to elucidate the individual self-excitation characteristics. Self-excitations of lift-off height are classified into five regimes in laminar free-jet lift-off butane flames diluted with nitrogen: a stationary lifted regime (regime I), a heat-loss-induced self-excitation (regime II), a buoyancy-induced self-excitation due to flame flicker as well as a heat-loss-induced self-excitation (III), a combined form of an oscillation prior to blow-out and a heat-loss-induced oscillation (regime IV), and a combined form of an buoyancy-induced self-excitation and a heat-loss-induced oscillation as well as an additional buoyancy-driven self-excitation due to flame flicker (regime V). Extremely low-frequency (<0.1 Hz) self-excitation is caused by conductive heat loss from the premixed wings to the trailing diffusion flame and can be explained by a proposed mechanism. It is also found that the flame oscillation prior to flame blow-out is also caused by buoyancy and also significantly affected by the conductive heat loss from the premixed wings to the trailing diffusion flame, thereby showing that the frequency with nozzle exit velocity increases in the triple-flame propagation mode and then decreases in the flame-front propagation mode. Characterization of the individual self-excitation mode is presented and also discussed with Strouhal numbers and its relevant parameters through the analysis of power spectrum for temporal variation of lift-off height. 相似文献