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By irradiation, the tetrahydropyranylarylketoacetal compounds led to isomers of spiro compounds. A competition between Norrish II and Paterno-Buchi reations was observed with unsaturated heterocyclic products. In the osidic series, the reaction was not stereoselective, but the photocyclisation works with rentention of configuration at low temperature. The acidic epimerisation of spiro C-1 sugars mainly yields the trans (α or β) isomers. 相似文献
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Dr. Christian Kulp Konrad Gillmeister Prof. Dr. Wolf Widdra Prof. Michael Bron 《Chemphyschem》2013,14(6):1205-1210
The synthesis of Cu(core)Pt(shell) model catalysts by the direct electrochemical deposition of Pt on Cu particles is presented. Cu particles with an average diameter of 200 nm have been deposited on glassy‐carbon electrodes by double pulse electrodeposition from a copper sulfate solution. Subsequent deposition from a platinum nitrate solution under potential control allows for a high selectivity of the Pt deposition towards Cu. Using a combination of cyclic voltammetry, XPS and sputtering, the structure of the generated particles has been analyzed and their core–shell configuration proven. It is shown that the electrocatalytic activity for the oxygen reduction is similar to that of other PtCu catalyst systems. The synthesized structures could allow for the analysis of structure–activity relations of core–shell catalysts on the way to the simple and controlled synthesis of supported Cu(core)Pt(shell) nanoparticles as oxygen reduction catalysts. 相似文献
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J. C. de Lange J. Bron A. van Poelgeest H. Verheul W. B. Ewbank 《Zeitschrift für Physik A Hadrons and Nuclei》1976,279(1):79-91
Decay studies on a number of short-lived odd nuclei in theN=50 region are described. The 59.6-s 93Ru ground state decay was studied in detail for the first time; in these experiments the 10.8-s activity93m Ru was discovered. The91Tc activities were also observed for the first time. The ground state and an isomeric state of this nucleus decay with nearby equal half-lives (3.14 and 3.3-min). The activities91g Mo (16.6-min) and95m Mo (65.1-s) have been reinvestigated. A number ofγ-rays, previously erroneously assigned to the91Mo activities, could be eliminated. A strong similarity is noted for the decay schemes of theN=49 isotones91m Mo and93m Ru. The energy of the 1/2? isomeric state in93Ru and theB(M4)-value of the isomeric transition fit well into the systematics of the previously knownN=49 isotones. 相似文献
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D.P. Barber U. Becker H. Benda A. Boehm J.G. Branson J. Bron D. Buikman J. Burger C.C. Chang H.S. Chen M. Chen C.P. Cheng Y.S. Chu R. Clare P. Duinker G.Y. Fang H. Fesefeldt D. Fong R.Y. Zhu 《Physics letters. [Part B]》1979,89(1):139-144
We report the measurement of the reaction e+ + e? → hadronic jets at a center-of-mass energy √s=30 GeV using the MARK-J detector at PETRA. By measuring the energy and angular distribution of both neutrals and charged particles we were able to isolate unambiguously the three-jet events in a kinematic region where the backgrounds from q and phase space contributions and other processes are small. Various comparisons of the data with quantum chromodynamics were made. The relative yield of three-jet events and the shape distribution of the events enable us to determine αs = 0.23 ± 0.02 (statistical error) with a systematic error of ± 0.04. 相似文献
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A vibronic sideband spectrometer is used to detect phonons generated from phonon fluorescence in superconductors. Although previously projected phonon powers are just within the minimum detectivity, no sideband signals were observed. An interpretation of this result is given. 相似文献
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Nassr Abu Bakr Ahmed Amine Kottakkat Tintula Bron Michael 《Journal of Solid State Electrochemistry》2020,24(1):131-136
Journal of Solid State Electrochemistry - Cobalt oxide nanoparticles supported on multiwalled carbon nanotubes (CoOx/CNTs) were prepared by a facile and rapid solid-state synthesis using microwave... 相似文献
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M. Bron P. Bogdanoff S. Fiechter I. Dorbandt M. Hilgendorff H. Schulenburg H. Tributsch 《Journal of Electroanalytical Chemistry》2001,500(1-2)
The favourable influence of selenium on the catalytic properties of Ru-based catalysts for the oxygen reduction reaction in acid electrolytes has been investigated by rotating disk electrode measurements. Compared to the oxygen reduction of selenium-free Ru-based catalysts, the overpotential at low current densities (ca. 10 μA cm−2) is not affected by the presence of selenium whereas selenium-containing catalysts show higher current densities under fuel cell relevant conditions. The kinetically controlled current density at 0.6 V versus SHE increases 4–5 fold with increasing selenium content. A maximum value is obtained at about 15 mol% Se. This effect is tentatively explained by a modification of the catalytic active centre, which is assumed to consist of Ru---C---CO complexes. IR spectroscopic investigations indicate a reaction of selenium with these complexes. This model is also supported by the study of the electrooxidation of CO. In contrast to the selenium-free catalyst, no CO oxidation is observed on the selenium-containing catalyst. Additional effects of selenium are an enhanced stability towards electrochemical oxidation and a lower amount of Ru oxides formed during synthesis, as evidenced from XRD investigations. Direct four electron oxygen reduction to water is efficient and H2O2 production of these catalysts is small (about 5% at potentials <0.3 V vs. SHE ). 相似文献