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Archana Pandey Abhishek Prasad Sindhu Singh Om Parkash Devendra Kumar 《Journal of Materials Science: Materials in Electronics》2008,19(11):1122-1127
Effect of manganese and cobalt doping (0.50 mole%) on electrical properties of ZnO based varistors has been studied using
complex plane modulus analysis. It is found that total resistivity of Mn doped sample is more as compared to that of Co doped
sample. This has been ascribed to existence of Mn in variable valence states viz. Mn2+, Mn3+ and Mn4+ which promotes hopping conduction leading to increase in the conductivity as compared to Co doped sample, in which Co exists
predominantly in +3 state with traces of Co2+ or Co+4 states. This accounts for its less conductivity. Mechanism of conduction is the same for grains and grainboundaries. 相似文献
34.
Ceria (La3+, Sr2+)/Carbonates Nanocomposite Electrolytes with High Electrical Conductivity for Low‐Temperature SOFCs 下载免费PDF全文
Nandini Jaiswal Devendra Kumar Om Parkash Shail Upadhyay 《International Journal of Applied Ceramic Technology》2015,12(5):1080-1087
A series of ceria‐based nanocomposites consisting of lanthanum and strontium codoped ceria with composition Ce0.89La0.07Sr0.04O1.925 (CL7S4) and eutectic mixture of carbonates Li2CO3‐Na2CO3 (LNCO) have been prepared by mixing nanosize powders of CL7S4 and LNCO. Samples have been characterized using differential thermal analysis, X‐ray diffraction, scanning electron microscopy combined with energy‐dispersive spectroscopy, thermal expansion, and impedance spectroscopy. A sharp increase in ionic conductivity is observed in all the composite specimens corresponding to superionic transition. Sample containing 35 wt% of carbonate shows the maximum conductivity (2.56 × 10?1 S/cm at 500°C) with activation energy of conduction, Ea 0.23 eV. 相似文献
35.
Fouling is a major limitation for the application of membrane bioreactors (MBRs) in municipal wastewater treatment; the critical flux concept represents a valid tool for process optimisation in planning fouling control strategies. The paper presents the results obtained on a large pilot MBR equipped with a plate-and-frame ultrafiltration membrane. The experimental assessment of flux criticality was carried out by flux-stepping tests showing the positive impact of liquid temperature on the value of the critical threshold. The reliability of short-term tests was then verified over a long period by determining the time of sustainability, t(sust), of six different sub-critical fluxes ranging between 17 and 30Lm(-2)h(-1). An exponential fitting was observed in terms of fouling rate both before and after t(sust), though fouling after t(sust) is likely to be ascribed not only to cake formation. Finally, a new mathematical formulation was proposed according to the local flux approach to model the sub-critical TMP transients. The model involves both bound and free forms of EPS and, once experimentally calibrated, it provided a fair prediction of the TMP jump. 相似文献
36.
The antioxidant activity of methanol extract/fractions of leaf, bark, and heartwood of Acacia catechu was evaluated by various antioxidant assays, including free radical, superoxide and hydroxyl radical, reducing power, metal ion chelation, as well as hydroxyl radical induced DNA strand scission. The leaf, bark, and heartwood powder was extracted in methanol and the lyophilized methanol extract was fractionated with different solvents in the order of increasing polarity. The results indicate that ethyl acetate fraction of heartwood has the highest antioxidant capacities, presenting lower EC(50) values particularly in free radical scavenging activity, including DPPH radicals (4.76 ± 0.14 μg/mL), superoxide anions (26.21 ± 0.79 μg/mL), and hydroxyl radicals (33.69 ± 1.42 μg/mL), in direct assay systems. Reducing power was also highest in ethyl acetate fraction of heartwood (EC(50) of 79.05 ± 1.02 μg/mL). As for the chelating power on ferrous ions, leaf extract was more effective than bark and heartwood extracts. Furthermore, the ethyl acetate and acetone fractions of heartwood significantly protected pBR322 supercoiled plasmid DNA against strand scission induced by hydroxyl radicals in a Fenton's reaction mixture. PRACTICAL APPLICATION: The present investigation suggests that the three organs of A. catechu differ significantly in their antioxidant potential as seen in the DPPH radical scavenging assay, reducing power assay, metal ion chelating assay, superoxide radical scavenging assay and hydroxyl radical scavenging assay. Further, our results showed that crude methanol extract and ethyl acetate fraction of heartwood of A. catechu might have a good potential as a source for natural health products due to its antioxidant and DNA protective activities. 相似文献
37.
A combined Rankine and ejector refrigeration cycle is proposed for the production of power and refrigeration output using duratherm 600 oil as the heat transfer fluid. Thermodynamic analysis has been done to observe the effect of parameters on the performance of the combined cycle. The effect of various parameters asthe turbine inlet pressure, evaporator temperature, condenser temperature, extraction ratio and direct normal radiation per unit area on the performance of the cycle have significant effects on the net power output, refrigeration output, first law efficiency and second law efficiency. It is also observed that the maximum irreversibility occurs in central receiver as 52.5% followed by 25% in the heliostat, 5.3% in the heat recovery vapor generator, 2.6% in the ejector, and 1.6% in the turbine and around 1.1% in the other components of the cycle. The second law efficiency of the solar operated combined Rankine and ejector refrigeration cycle is 11.90% which is much lower than its first law efficiency of 14.81%. 相似文献
38.
This study is an attempt to investigate the effect of a representative pro‐oxidant (manganese stearate) on the degradation behavior of 70 ± 5 μ thickness films of LDPE, LLDPE and their blends. Films were prepared by film blowing technique in the presence of varying quantities of manganese stearate (0.5–1% w/w) and subsequently subjected to accelerated degradative tests: xenon arc exposure and air‐oven exposure (at 70°C). The physico–chemical changes induced as a result of aging were followed by monitoring the mechanical properties (Tensile strength and Elongation at break), carbonyl index (CI), morphology (SEM), melt flow index (MFI), oxygen content (Elemental analysis), and DSC crystallinity. The results indicate that the degradative effect of pro‐oxidant is more pronounced in LDPE than LLDPE and blends, due to the presence of larger number of weak branches in the former. The degradation was also found to be proportional to the concentration of the pro‐oxidant. Flynn‐Wall‐Ozawa iso‐conversion technique was used to determine the kinetic parameters of degradation, which were used to determine the effect of the pro‐oxidant on the theoretical lifetime of the polymer. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
39.
William Roshan Quadros Ved Vyas Mike Brewer Steven James Owen Kenji Shimada 《Engineering with Computers》2010,26(3):231-247
This paper proposes a framework for generating mesh sizing functions for assembly models. Size control is crucial in obtaining
a high-quality mesh with a reduced number of elements. The reduction in the number of elements will decrease computation time
and memory use during mesh generation and analysis. The framework consists of a background octree lattice for storing the
sizing function, a set of source entities for providing sizing information based on geometric information, and an interpolation
module for calculating the sizing on the background octree lattice using the source entities. Source entities are generated
by performing a detailed systematic study to identify all the geometric factors of an assembly. Disconnected skeletons are
extracted and used as tools to measure 3D proximity and 2D proximity, which are two of the geometric factors. The framework
facilitates the generation of a variety of meshes with a low computational cost, to meet industry needs. The framework has
been tested on many industrial parts, and sizing control on a few typical assemblies has been presented to demonstrate the
effectiveness of the proposed framework. 相似文献
40.
Glass ceramics prepared by controlled crystallization of glasses produce fine dispersion of crystallites in a glassy matrix.
Glasses containing a mjor portion of constituents of a ferroelectric phase produce crystallites of ferroelectric phase in
glass through a suitable heat treatment. The amount of network former in the initial glass has a profound influence on its
crystallization behaviour and microstructure of the resulting ferroelectric glass ceramics. The value of dielectric constant
and the nature of ferroelectric to paraelectric transition depend on the crystallite size and volume fraction of the ferroelectric
phase. These glass ceramics are transparent for crystallite size less than 0·1μm and exhibit large quadratic-electro-optic effect. 相似文献