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11.
Branko Matović Jelena Dukić Biljana Babić Dušan Bučevac Zorana Dohčević-Mitrović Marko Radović Snežana Bošković 《Ceramics International》2013,39(5):5007-5012
Nanometric ceria powders with fluorite-type structure were obtained by applying self-propagating room temperature method. The obtained powders were subsequently thermally treated (calcined) at different temperatures for different times. Powder properties such as specific surface area, crystallite size, particle size and lattice parameter have been studied. Roentgen diffraction analysis (XRD), BET and Raman scattering measurements were used to characterize the as-obtained (uncalcined) powder as well as powders calcined at different temperatures.It was found that the average diameter of the as-obtained crystallites is in the range of 3–5 nm whereas the specific surface area is about 70 m2/g. The subsequent, 15 min long, calcination of as-obtained powder at different temperatures gradually increased crystallite size up to ~60 nm and reduced specific surface down to 6 m2/g. Raman spectra of synthesized CeO2?y depicts a strong red shift of active triply degenerate F2 g mode as well as additional peak at 600 cm?1. The frequency of F2 g mode increased while its line width decreased with an increase in calcination temperature. Such a behavior is considered to be the result of particle size increase and agglomeration during the calcination. After the heat treatment at 800 °C crystallite size reached value larger than 50 nm. Second order Raman mode, which originates from intrinsic oxygen vacancies, disappeared after calcination. 相似文献
12.
M. Prekajski Z. Dohčević-Mitrović M. Radović B. Babić J. Pantić A. Kremenović B. Matović 《Journal of the European Ceramic Society》2012,32(9):1983-1987
Nanocrystalline powders of solid solution CeO2–Bi2O3 were synthesized by self-propagating room temperature reaction (SPRT) procedure with composition (Ce1?xBixO2?δ where the x = 0.1–0.5). X-ray diffraction analyses show that for x < 0.50 a solid solution with fluorite structure is formed. Rietveld's structure refinement method was applied to characterize prepared powders and its microstructure (size–strain). The lattice parameters increase according to Vegard's rule with increasing of Bi concentration. The average crystallite size is about 2–3 nm. Spectroscopic ellipsometry and Raman scattering measurements were used to characterize the samples at room temperature. The Raman measurements demonstrated electron molecular vibrational coupling and increase of oxygen vacancy concentration whereas increase of Bi content provokes a small decrease of optical absorption edge in comparison with pure ceria. Specific surface area of obtained powders was measured by Brunauer–Emmet–Teller (BET) method. 相似文献
13.
14.
Srikanth Jagadeesan Yang Hoi Doh Kyung-Hyun Choi 《Journal of Coatings Technology and Research》2017,14(3):701-708
Titanium dioxide (TiO2) thin film was fabricated using titanium isopropoxide as a precursor through an atmospheric low-temperature roll-to-roll chemical vapor deposition method. TiO2 was deposited on the PET substrate in the temperature range of room temperature to 100°C, and the working pressure was 740 Torr. The surface morphology of TiO2 thin film was analyzed by field emission scanning electron microscopy and a 2D surface profiler. The results revealed that the growth rate of TiO2 film was 31 nm/min at 100°C, and it also showed that the surface is uniform and smooth. Moreover, the lowest root mean square roughness (R q) value of 1.87 nm was obtained for TiO2 film prepared at 100°C. The composition of TiO2 film was confirmed by X-ray photoelectron spectroscopy (XPS) analysis. The film showed very good chemical and optical properties while increasing the substrate deposition temperature. The UV–Vis spectroscopy analysis revealed that TiO2 films exhibited excellent optical transmittance, more than 91% observed in the visible region. 相似文献
15.
In-Jin Shon Song-Lee Du Jung-Mann Doh Jin-Kook Yoon 《Metals and Materials International》2013,19(5):1041-1045
Nanocrystalline materials have received much attention as advanced engineering materials with improved physical and mechanical properties. As nanomaterials possess high strength, high hardness, excellent ductility and toughness, undoubtedly, more attention has been paid for the application of nanomaterials. Nanopowders of MgO, Al2O3 and SiO2 were made by high energy ball milling. The simultaneous synthesis and consolidation of nanostuctured MgAl2O4-MgSiO3 composites from milled 2MgO, Al2O3 and SiO2 powders was investigated by the pulsed current activated sintering process. The advantage of this process is that it allows very quick densification to near theoretical density and inhibition of grain growth. Highly dense nanostructured MgAl2O4-MgSiO3 composites were produced with a simultaneous application of 80 MPa pressure and a pulsed current of 2000A within 1min. The fracture toughness of MgAl2O4-Mg2SiO4 composites sintered from 60 mol%MgO-20 mol%Al2O3-20mol%SiO2 powders milled for 4 h was 3.2MPa·m1/2. The fracture toughness of MgAl2O4-MgSiO3 composite is higher than that of monolithic MgAl2O4. 相似文献
16.
In-Jin Shon Kwon-Il Na Jung-Mann Doh Hyun-Kuk Park Jin-Kook Yoon 《Metals and Materials International》2013,19(1):99-103
Nanopowders of Fe, Al and Fe2O3 are fabricated by high energy ball milling. Using the pulsed current activated sintering method, the densification of nanocrystalline Fe2Al5 and Al2O3 reinforced Fe2Al5 composites were simultaneously synthesized and consolidated within two minutes from mechanically activated powders. The advantage of this process is that it allows very quick densification to near theoretical density and prohibition of grain growth in nanostuctured materials. Nanocrystalline materials have received much attention as advanced engineering materials with improved physical and mechanical properties. As nanomaterials possess high strength, high hardness, excellent ductility and toughness, undoubtedly, more attention has been paid to the application of nanomaterials. Not only the hardness but also the fracture toughness of the Fe2Al5-Al2O3 composite was higher than that of monolithic Fe2Al5 due to the addition of the hard phase of Al2O3 and the crack deflection by Al2O3. 相似文献
17.
This article addresses a tracking controller design for a trailer system consisting of a steering tractor and a passive trailer linked with a rigid free joint and having nonholonomic constraints. We design the tracking controller using the Lyapunov direct method, for both forward and backward driving of the trailer system. Backward driving is unstable, and thus is more difficult than forward driving. In previous research, we proposed a globally asymptotically stable (GAS) tracking control for forward driving of a trailer system with nonholonomic constraints. In this article, we implement the GAS tracking controller for forward and backward driving, and perform experiments using visual feedback and remote control systems. The experimental results represent stable responses and demonstrate the effectiveness of our method. © 2002 Wiley Periodicals, Inc. 相似文献
18.
J Yomi A Mbakop AS Doh M Sosso S Takongmo G Andze BJ Bejanga JJ Pagbe T Edzoa 《Canadian Metallurgical Quarterly》1998,17(1):9-14
OBJECTIVE: To modify the classic fetal biophysical profile (FBP) with the aim of obtaining rapid and accurate information about actual fetal condition in non-compromised fetuses with a subsequent favorable outcome and to be suitable for a number of outclinic patients. METHODS: Four-hundred and ninety-four fetuses from singleton pregnancies in two randomized groups were monitored by the modified FBP (mFBP) and 168 of them after the external vibratory acoustic stimulation (VAS/mFBP). The mFBP was characterized by two main characteristics: non-stress test was excluded and the testing was finished at the moment when all of the three fetal biophysical activities became normal. The external VAS was applied only in cases with no evidence of fetal activity at the start of the FBP. RESULTS: Of the examined fetuses, 326 fetuses in the control group were monitored by the mFBP and there were 316 (96.9%) favorable outcomes and 10 (3.1%) adverse perinatal outcomes. The sensitivity, specificity and positive and negative predictive values of the mFBP score in predicting adverse perinatal outcome were 60, 99, 66.7 and 98.7%, respectively. In the study group of 168 fetuses there were 165 (98.2%) favorable outcomes and three (1.8%) adverse perinatal outcomes. The sensitivity, specificity and positive and negative predictive values of the VAS/mFBP were 66.7, 100, 100 and 99.4%, respectively. The efficiency of the VAS/mFBP in predicting perinatal mortality alone was even higher. After the external VAS and the first 5 min of the modified testing approximately two-fifths (41.8%) of healthy fetuses with a subsequent good outcome exhibited normal in all of the three biophysical activities and approximately two-thirds (65.5%) of them after 10 min. In the VAS/mFBP group of healthy fetuses, during the same time periods, normal breathing movements were observed in 72% and 87% of fetuses, respectively. CONCLUSIONS: According to our results the mFBP and particularly the VAS/mFBP antenatal protocol as a new and rational variant of the FBP could improve fetal assessment allowing in cases of non-compromised fetuses rapid and accurate information about actual fetal well-being. Because of its high accuracy and a reduced testing time the antepartal method with observation of fetal breathing movements after VAS is becoming acceptable as a screening of fetal well-being evaluation in outclinic conditions. 相似文献
19.
A femoral artery pseudoaneurysm is one complication of vascular intervention, and the incidence is increasing. Early management is then needed to avoid potential dangers from it. It differs from a true aneurysm in that it doesn't include any component of the vascular wall, and is not studied as much as a true aneurysm. Here, a model of a femoral pseudoaneurysm was made and a Computational Fluid Dynamics(CFD) simulation was verified with PIV experiment. Afterwards, a CFD simulation with two different models was performed to look for any findings which may help in developing new treatment methods. 相似文献
20.
We present a novel solution for topological exploration in corridor environments using cheap and error-prone sonar sensors. Topological exploration requires significant location detection and motion planning. To detect nodes (i.e., significant places) robustly, we propose a new measure, the eigenvalue ratio (EVR), which converts geometrical shapes in the environment into quantitative values using principal component analysis. For planning the safe motion of a robot, we propose the circle following (CF) method, which abstracts the geometry of the environment while taking the characteristics of the sonar sensors into consideration. Integrating the EVR with the CF method results in a topological exploration strategy using sonar sensors approach. The practicality of this approach is demonstrated by simulations and real experiments in corridor environments. 相似文献