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The reactions of propellanes containing one or two cyclohexadiene rings with singlet oxygen take the course of exclusive syn-attack with respect to a hetero-ring containing two CO groups. When only one or no CO group is found in the hetero-ring, both syn- and anti-attack occur. The former course is interpreted in terms of secondary orbital interactions which stabilize the transition state for syn-attack. 相似文献
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Bhattacharya M Goodman CD Raghavan RS Palarczyk M Garcia A Rapaport J van Heerden IJ Zupranski P 《Physical review letters》2000,85(21):4446-4449
We report a 0 degrees 176Yb(p,n)176Lu measurement at IUCF where we used 120 and 160 MeV protons and the energy dependence method to determine Gamow-Teller (GT) matrix elements relative to the model independent Fermi matrix element. The data show that there is an isolated concentration of GT strength in the low-lying 1(+) states making the proposed Low Energy Neutrino Spectroscopy detector (based on neutrino captures on 176Yb) sensitive to pp and 7Be neutrinos and a promising detector to resolve the solar neutrino problem. 相似文献
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We consider diffraction by a semi-infinite crack located alonga fusion interface between two differing elastic media. Twotypes of crack, namely open and partially closed cracks, areinvestigated. An open crack is modelled by a stress-free contactboundary condition and a partially closed crack is modelledby a spring contact boundary condition. For the latter, thejump in the stress across the crack is assumed to be proportionalto the jump in the displacement across the crack. This situationarises in, for example, a K-weld where the fine grain of theparent material (for example, ferritic or forged austeniticsteel) is in stark contrast with the coarse-grained weld metal(for example, austenitic weld metal). In the metal weld thedirection of the grain axis varies through the metal. However,diffraction is a local phenomenon and so the austenitic steelis assumed to have a zonal axis so that it may be modelled bya transversely isotropic composite. The ferritic or forged austeniticsteel will be modelled as an isotropic material. 相似文献
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X. Wu D. Landheer M. J. Graham H. -W. Chen T. -Y. Huang T. -S. Chao 《Journal of Crystal Growth》2003,250(3-4):479-485
The structure and thermal stability of ZrO2 films grown on Si (1 0 0) substrates by metalorganic chemical vapor deposition have been studied by high-resolution transmission electron microscopy, selected area electron diffraction and X-ray energy dispersive spectroscopy. As-deposited films consist of tetragonal ZrO2 nanocrystallites and an amorphous Zr silicate interfacial layer. After annealing at 850°C, some monoclinic phase is formed, and the grain size is increased. Annealing a 6 nm thick film at 850°C in O2 revealed that the growth of the interfacial layer is at the expense of the ZrO2 layer. In a 3.0 nm thick Zr silicate interfacial layer, there is a 0.9 nm Zr-free SiO2 region right above the Si substrate. These observations suggest that oxygen reacted with the Si substrate to grow SiO2, and SiO2 reacted with ZrO2 to form a Zr silicate interfacial layer during the deposition and annealing. Oxygen diffusion through the tetragonal ZrO2 phase was found to be relatively easier than through the monoclinic phase. 相似文献
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High-resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS) and selected area electron diffraction (SAED) were used to study gadolinium and lanthanum silicate films deposited on Si(1 0 0) substrates using electron-beam evaporation from pressed-powder targets. As-deposited films consist of an amorphous silicate layer without an interfacial layer. After annealing at 900 °C in oxygen for 2 min, an interfacial SiO2 layer is formed in the gadolinium silicate film, while this interfacial layer is a SiO2-rich lanthanum silicate layer in the lanthanum silicate film. The formation of interfacial silicate layers is thermodynamically more favorable for the lanthanum films than for the gadolinium films. The gadolinium silicate films crystallize at a temperature between 1000 and 1050 °C, while the crystallization temperature for the lanthanum silicate films is between 900 and 950 °C. 相似文献
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The -ene reactions of propellanes containing an anhydride ring or a methylimide ring undergo secondary orbital control. In attack by 1O2 only the syn-products are obtained. In the corresponding lactone or ether steric hindrance plays a more important role in the direction of attack. 相似文献
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