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811.
Czerwonka R Reddy KR Baum E Knölker HJ 《Chemical communications (Cambridge, England)》2006,(7):711-713
The first enantioselective total synthesis of neocarazostatin B, the determination of its absolute configuration and transformation into carquinostatin A are described. 相似文献
812.
In this work Gaussian-type Geminals (GTGs) are applied in local second-order Moller-Plesset perturbation theory to improve the basis set convergence. Our implementation is based on the weak orthogonality functional of Szalewicz et al., [Chem. Phys. Lett. 91, 169 (1982); J. Chem. Phys. 78, 1420 (1983)] and a newly developed program for calculating the necessary many-electron integrals. The local approximations together with GTGs in the treatment of the correlation energy are introduced and tested. First results for correlation energies of H(2)O, CH(4), CO, C(2)H(2), C(2)H(4), H(2)CO, and N(2)H(4) as well as some reaction and activation energies are presented. More than 97% of the valence-shell correlation energy is recovered using aug-cc-pVDZ basis sets and six GTGs per electron pair. The results are compared with conventional calculations using correlation-consistent basis sets as well as with MP2-R12 results. 相似文献
813.
A construction of caps is given which yields in particular caps with a free pair of points. Applying this construction, we meet the bound of Farr and Lisoněk [J. Farr, P. Lisoněk, Caps with free pairs of points, J. Geom. 85 (2006) 35-41] for caps with a free pair of points in , q even. 相似文献
814.
Michael Bowker Graham Hutchings Philip R. Davies Dyfan Edwards Robert Davies Shamil Shaikhutdinov Hans-Joachim Freund 《Surface science》2012,606(21-22):1594-1599
The surface structure of γ-Fe2O3(111) has been investigated with a range of surface techniques. Two different surface structures were discovered depending upon surface preparation techniques. Sputtering followed by annealing in vacuum produced a reduced surface characterised by a (2 × 2) LEED pattern, whereas sputtering followed by annealing in 1 × 10? 6 mbar oxygen produced a surface characterised by a (√3 × √3)-R30° LEED pattern. The latter appears to be a very low conductivity surface, whereas the former has the band gap expected for maghemite (~ 2.0 eV). We propose that the reduced surface is a magnetite-like layer, whereas the oxidised surface is an Fe2O3-like layer. 相似文献
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Hans-Joachim Cantow Martin Kunz Stefan Klotz Martin Mller 《Macromolecular Symposia》1989,26(1):191-196
Applications of the Electron Spectroscopic Imaging technique (ESI) within the field of multiphase polymer materials are discussed. Imaging with elastically scattered electrons as well as imaging with electrons with defined energy loss are presented. From the latter the net distribution of elements can be derived. Several examples are given: Glassy diblock copolymers polystyrene-block-poly(2-vinyl pyridine), polyethylenes, interpenetrating networks, interdiffusion couples, blends of polystyrene and polystyrene-graft-poly(oxyethylene), carbon black reinforced natural rubber, and epitactic growth of poly(1-pentenylene) on isotactic poly (propylene) surface. Visualization of the rigid amorphous phase in polyethylene is presented, as well as electron spectroscopic diffraction (ESD) of oriented PE. One of the features of ESI is due to the fact that discrimination between true morphology and artefacts is possible in an unbiased manner, even for minor details: Heavy metal staining is abandonable, and structural analysis by one element may be proved by analysis with other elements, which may be present in the sample or which may be added by chemical reaction or interaction with groups within the molecules. 相似文献
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