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81.
82.
83.
Effect of current density on the microstructure and corrosion behaviour of plasma electrolytic oxidation treated AM50 magnesium alloy 总被引:1,自引:0,他引:1
P. Bala Srinivasan J. Liang C. Blawert M. Störmer W. Dietzel 《Applied Surface Science》2009,255(7):4212-4218
Plasma electrolytic oxidation (PEO) of an AM50 magnesium alloy was accomplished in a silicate-based electrolyte using a DC power source. Coatings were produced at three current densities, i.e. 15 mA cm−2, 75 mA cm−2, and 150 mA cm−2 and were characterised for thickness, roughness, microstructural morphology, phase composition, and corrosion resistance. Even though the 15 min treated coatings produced at higher current density levels were thicker, they showed poor corrosion resistance when compared to that of the coatings obtained at 15 mA cm−2. Short-term treatments (2 min and 5 min) at 150 mA cm−2 yielded coatings of thickness and corrosion resistance comparable to that of the low current density coatings. The superior corrosion resistance of the low thickness coatings is attributed to the better pore morphology and compactness of the layer. 相似文献
84.
We report theoretical results on the magnetic behavior of free standing nanowires of Ti. Four different structures of Ti nanowires-linear, ladder, dimerized, and zigzag-with nonmagnetic, ferromagnetic, and anti-ferromagnetic configurations were considered. Exploration of magnetism in these atomic chains leads to ferromagnetic behavior for all the structures: zigzag structure shows almost degenerate ferromagnetic and anti-ferromagnetic states though. The zigzag structure of Ti nanowires is favored of all for low values of nearest neighbor distances, whereas the dimerized structure is favored at larger atomic separations. Our work helps to resolve the controversy in the predicted ground state magnetic nature of zigzag chains of Ti as reported in recent previous works. The maximum value of magnetic moment (0.93 μB/atom) occurs in the ladder chains while the zigzag chains show the minimum value (0.17 μB/atom). Interestingly, all the structures in the magnetic configuration show metastable state except the dimerized structure. Ferromagnetic dimerized nanowires seem to be a potential candidate for use in spintronics. The projected density of states shows that dx2−y2 and dxy bands play a leading role in magnetism of linear and ladder structures, whereas there is no outstanding contribution from a particular d-orbital for zigzag and dimerized nanowires. The charge density plots suggest that linear and zigzag structures have metallic bonding whereas covalent bonding is predominant in the dimerized and ladder structures. The estimated diameters for the favored ferromagnetic configuration of these ultrathin nanowires lie in the range 1.9-3.4 Å and indicate the instability of the ladder structure, as also projected by the relative cohesive energy and relative break force values. 相似文献
85.
Optical time division multiplexing (OTDM) is emerging and promising alternative for future high-speed photonic networks because of its ability to accommodate higher bit rate and flexible bandwidth. Among other factors the performance of an OTDM system largely depends upon the switching characteristics of a de-multiplexer (DEMUX). Symmetric Mach-Zehnder (SMZ) have been found to be most suitable than all the available de-multiplexing switches because of compact size, thermal stability, and low power operation. In this paper, we simulate four-channel OTDM systems (all channel multiplexer (MUX) and DEMUX) with a Mach-Zehnder modulator and SMZ DEMUX to investigate the impact of signal power, pulse width and control signal power on BER. 相似文献
86.
Shubhangi B. Umbarkar Trupti V. Kotbagi Ankush V. Biradar Renu Pasricha Jyoti Chanale Mohan K. Dongare Anne-Sophie Mamede Christine Lancelot Edmond Payen 《Journal of molecular catalysis. A, Chemical》2009,310(1-2):150-158
Acetalization of glycerol with various aldehydes has been carried out using mesoporous MoO3/SiO2 as a solid acid catalyst. A series of MoO3/SiO2 catalysts with varying MoO3 loadings (1–20 mol%) were prepared by sol–gel technique using ethyl silicate-40 and ammonium heptamolybdate as silica and molybdenum source respectively. The sol–gel derived samples were calcined at 500 °C and characterized using various physicochemical characterization techniques. The XRD of the calcined samples showed the formation of amorphous phase up to 10 mol% MoO3 loading and at higher loading of crystalline α-MoO3 on amorphous silica support. TEM analyses of the materials showed the uniform distribution of MoO3 nanoparticles on amorphous silica support. Raman spectroscopy showed the formation of silicomolybdic acid at low Mo loading and a mixture of α-MoO3 and polymolybdate species at high Mo loadings. Moreover the Raman spectra of intermediate loading samples also suggest the presence of β-MoO3. Acetalization of glycerol with benzaldehyde was carried out using series of MoO3/SiO2 catalysts with varying MoO3 loadings (1–20 mol%). Among the series, MoO3/SiO2 with 20 mol% MoO3 loadings was found to be the most active catalyst in acetalization under mild conditions. Maximum conversion of benzaldehyde (72%) was obtained in 8 h at 100 °C with 60% selectivity for the six-membered acetal using 20% MoO3/SiO2. Interestingly with substituted benzaldehydes under same reaction conditions the conversion of aldehydes decreased with increase in selectivity for six-membered acetals. These results indicate the potential of this catalyst for the acetalization of glycerol for an environmentally benign process. 相似文献
87.
Renu Laskar 《Discrete Applied Mathematics》2009,157(2):330-338
The question of whether a graph can be partitioned into k independent dominating sets, which is the same as having a fallk-colouring, is considered. For k=3, it is shown that a graph G can be partitioned into three independent dominating sets if and only if the cartesian product G□K2 can be partitioned into three independent dominating sets. The graph K2 can be replaced by any graph H such that there is a mapping f:Qn→H, where f is a type-II graph homomorphism.The cartesian product of two trees is considered, as well as the complexity of partitioning a bipartite graph into three independent dominating sets, which is shown to be NP-complete. For other values of k, iterated cartesian products are considered, leading to a result that shows for what values of k the hypercubes can be partitioned into k independent dominating sets. 相似文献
88.
Manimaran B Lai LJ Thanasekaran P Wu JY Liao RT Tseng TW Liu YH Lee GH Peng SM Lu KL 《Inorganic chemistry》2006,45(20):8070-8077
Alkoxy- and thiolato-bridged Re(I) molecular rectangles [{(CO)3Re(mu-ER)2Re(CO)3}2(mu-bpy)2] (ER = SC4H9, 1a; SC8H17, 1b; OC4H9, 2a; OC12H25, 2b; bpy = 4,4'-bipyridine) exhibit strong interactions with several planar aromatic molecules. The nature of their binding was studied by spectral techniques and verified by X-ray diffraction analysis. Standard absorption and fluorescence titrations showed that a relatively strong 1:1 interaction occurs between aromatic guests such as pyrene and these rectangles. The results of a single-crystal X-ray diffraction analysis show that the recognition of 1 with a pyrene molecule is mainly due to CH...pi interactions and the face of the guest pyrene is located over the edges of the bpy linkers of 1. This is a fairly novel example of an interaction that is rarely designed into a host-guest pair. Furthermore, the interaction of 1 with Ag+ results in the self-organization of supramolecular arrays, as revealed by solid-state data. 相似文献
89.
A new catalytic aziridination system that consists of cobalt(II) tetraphenylporphyrin [Co(TPP)] as the catalyst and diphenylphosphoryl azide (DPPA) as the nitrene source has been developed. The cobalt-based catalytic system allows direct synthesis of N-phosphorus-substituted aziridines from alkenes with dinitrogen as the byproduct. Cobalt ion seems essential to the catalytic aziridination with DPPA as no or only trace amounts of the desired products were observed with other metal complexes of tetraphenylporphyrin. 相似文献
90.
Yun J. Lee Jason R. King Bala Chandra Chenna Samuel B. OwensJr. Jason L. Freeman Gary M. Gray Sadanandan E. Velu 《Journal of chemical crystallography》2009,39(12):902-907