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791.
Using electron holography in a transmission electron microscope, we obtained direct evidence for the reduction of negative charge at grain boundary dislocations in Ca-doped YBa2Cu3O7 (YBCO) when compared to undoped YBCO. Because of the finite width of the valence band in the superconducting CuO2 planes, the negative grain boundary charge can lead to a depletion of electron holes available for superconductivity. A significant reduction in the size of the perturbed region in the Ca-doped samples appears to be the principal mechanism for the improved interfacial superconductivity. 相似文献
792.
We present a three dimensional microscopic particle in cell code. The code models nanoplasmas in intense laser fields, taking account of all relevant microscopic interactions. Our simulation reveals the physical processes determining the laser induced explosion of large clusters with several 10,000 atoms. 相似文献
793.
794.
795.
796.
Christian P Rajaraman G Harrison A McDouall JJ Raftery JT Winpenny RE 《Dalton transactions (Cambridge, England : 2003)》2004,(10):1511-1512
Structural, magnetic and theoretical studies of an octanuclear chromium(III) wheel are reported, containing hydroxide and pivalate bridges. 相似文献
797.
798.
799.
Youte JJ Barbier D Al-Mourabit A Gnecco D Marazano C 《The Journal of organic chemistry》2004,69(8):2737-2740
Potassium ferricyanide oxidation of salt 1 gave isoquinolinone 7 whose treatment with Grignard reagents resulted in a high-yield formation of substituted isoquinolinium salts 5. The selectivity of the reduction of these salts to give derivatives 6 has been studied. Particularly good selectivities (82-84%) were observed when R is a benzylic group. On the basis of these results, a practical and enantioselective synthesis of the natural alkaloid (-)-argemonine is presented. 相似文献
800.
The addition reaction of monomeric lithium enolate (Z)-1, derived from propiophenone, to propene oxide 2, was examined to clarify the exact geometry of the transition state (TS) involved in this type of reaction. The eight possible TSs and the corresponding pathways, four leading to syn gamma-hydroxy ketone (gamma-HK) 3 and four leading to anti gamma-HK 4, were compared, using the B3LYP/6-31+G(d)//B3LYP/6-31+G(d) theory level in vacuo and in the presence of the reaction solvent (toluene/hexane). In every case, the favored pathway involves a TS where the enolate C=C and the epoxide C-C are in a gauche relationship and where the Li(+) is stabilized by some C-C and C-H sigma bonds of epoxide 2. 相似文献