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81.
Michael addition of ethyl acrylate and acetone over solid bases 总被引:1,自引:0,他引:1
The catalytic behaviour of the superbases Na/NaOH/-Al2O3 and CsxO/-Al2O3 as well as of the basic zeolites Na/NaX and CsxO/CsX were investigated in the Michael addition of ethyl acrylate and acetone. The reactions were carried out in the liquid phase at catalyst loadings varying from 0.05 to 0.1 mol ester/g catalyst. 相似文献
82.
The preparation of three 3,5-diarylcyclohexanones by rhodiumchlorotris(triphenyl-phosphine)—catalyzed reduction of the parent olefines (IIa—IIc) is described. Other reducing agents produced several intermediate products of the total hydrogenolysis. 相似文献
83.
The gamma-2 phase (Sn8Hg) and a dental amalgam in phosphate buffer have been studied by means of potentiostatic and galvanostatic techniques, along with a rotating ring-disc electrode (RRDE). The analysis of results has shown that phosphate ions play an important role in the corrosion of amalgam. The anodic reaction leads to the formation of soluble species and a passivating film, which is probably composed of tin hydroxide and tin phosphate. 相似文献
84.
85.
Retardation of the gasification reaction of carbon with oxygen by SO2 was observed. Rates of oxidation were determined by thermal gravimetric analysis (TGA) of a nuclear graphite in the temperature range of 550–700°C, and of a coconut charcoal in the temperature range of 400–505°C. The oxidant gases were dry air containing 0–6% SO2. Reduction of the rate by SO2 varied with burn-off. Differential thermal analysis (DTA) was also applied to detect the retardation effect of SO2. The technique of infrared internal reflection spectroscopy (IRS) was used to examine the surface species of reacted charcoal samples. Absorption bands were assigned to surface carbonyls, lactones, and a chemisorbed SO2 in the form of sulfate. Chemisorption of SO2 was attributed to cause the retardation of the oxidation reaction. 相似文献
86.
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88.
Temporal dynamics of social interaction networks as well as the analysis of communities are key aspects to gain a better understanding of the involved processes, important influence factors, their effects, and their structural implications. In this article, we analyze temporal dynamics of contacts and the evolution of communities in networks of face-to-face proximity. As our application context, we consider four scientific coil- ferences. On a structural level, we focus on static and dynamic properties of the contact graphs. Also, we analyze the resulting community structure using state-of-the-art automatic community detection algorithms. Specifically, we analyze tile evolution of contacts and communities over time to consider the stability of the respective conmmnities. Furthermore, we assess different factors which have an influence on the quality of com- munity prediction. Overall, we provide first important insights into the evolution of contacts and communities in face-to-face contact networks. 相似文献
89.
P. Paufler S. K. Filatov I. P. Shakhverdova R. S. Bubnova M. Reibold B. Müller A. A. Levin D. C. Meyer 《Glass Physics and Chemistry》2007,33(3):187-198
The nanohardness (H) and microhardness (H
M) of sodium borosilicate glasses with and without nanopores were studied. From nanoindentation measurements, along with the
hardness H, the Young’s modulus E was derived. While both H and H
M varied between ∼10 GPa and ∼7 GPa for the bulk glass, the values for nanoporous specimens were one order of magnitude lower
at about 0.5 GPa. The Young’s moduli were found to be ∼82 GPa and ∼5 GPa for bulk and porous glasses, respectively. Cracks
and pileups were observed, respectively, arising from microindents and nanoindents in the bulk glass, whereas none of them
could be detected in the nanoporous material. The molecular structures of both glasses studied by X-ray diffraction are similar.
The text was submitted by the authors in English. 相似文献
90.
Universal Access in the Information Society - Access to trustworthy information is a premise for participation in a democratic society. However, locating useful and valid information may not be a... 相似文献