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Stefanie Schwamborn Dr. Leonard Stoica Prof. Dr. Wolfgang Schuhmann 《Chemphyschem》2011,12(9):1741-1746
PtAg bimetallic nanoparticles for oxygen reduction reaction (ORR) in alkaline media were prepared by pulse electrodeposition (PED). During PED the reduction of Ag+ ions predominates, thus an increased Ag content in the co‐deposit is accomplished. The mechanism for this anomalous co‐deposition was elucidated by potential pulse experiments, which revealed that nuclei formation mainly occurs via the reduction of Pt2+ ions. The growth of the particles is diffusion controlled leading to the formation of a Ag shell covering a PtAg alloyed region. However, the shell is not growing homogeneously on the PtAg alloy. Hence, regions of the PtAg alloy are exposed, which exhibit an enhanced ORR activity compared to a pure Ag surface. 相似文献
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Heat transfer for single component falling film evaporation has been investigated in a stainless steel single tube falling
film evaporator. The tube had a heated length of 2,500 mm. Propylene glycol and cyclohexanol have been used as evaporating
media. Liquid film running down the tube, is formed on the inner side of the tube. For the distribution of liquid two different
devices were examined. Process equipment was operated in pump-around mode with the distillate being condensed and recycled.
Results show that none of the available correlations for heat transfer in falling film evaporation is able to describe the
results qualitatively as well as quantitatively. Using different film distribution devices, a significant influence of the
Reynolds number for the transition from laminar to turbulent flow is seen. However, differences between experimental results
and correlations in literature cannot be explained only by usage of different film distributions, in particular when the correlation
is based on measurements with a different tube length. A model approach is presented for cyclohexanol as evaporating medium
with a flat weir as film distributor. 相似文献
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Stefanie Gerke 《Discrete Mathematics》2007,307(13):1668-1671
The r-acyclic edge chromatic number of a graph G is the minimum number of colours required to colour the edges of G in such a way that adjacent edges receive different colours and every cycle C receives at least min{|C|,r} colours. We prove that for any integer r?4, the r-acyclic edge chromatic number of any graph G with maximum degree Δ and with girth at least 3(r-1)Δ is at most 6(r-1)Δ. 相似文献
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[Ba2(H2O)9][GeSe4] is suitable for the formation of novel M/14/16 anions [Mn6Ge4Se17]6- --discrete or linked in an as yet unprecedented porous network--with antiferromagnetically coupled Mn(II) centers and relatively small electronic excitation energies. 相似文献