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41.
Reaction of 1,4-dipotassio-1,1,4,4-tetrakis(trimethylsilyl)tetramethyltetrasilane with [(Me(3)Si)(2)N](2)Sn led to the formation of an endocyclic distannene via the dimerization of a transient stannylene. In the presence of strong donor molecules such as PEt(3), the stannylene could be trapped as adduct. Reaction of the PEt(3) derivative with B(C(6)F(5))(3) gave rise to the formation of the stannylene B(C(6)F(5))(3) adduct.  相似文献   
42.
Multivalent cations are suggested to influence the supramolecular structure of soil organic matter (SOM) via inter- and intra-molecular interactions with SOM functional groups. In this study, we tested the combined effect of cations, temperature treatment, and isothermal aging on SOM matrix properties. Samples from a peat and a mineral soil were either enriched with Na, Ca, and Al or desalinated in batch experiments. After treatment at 25, 40, 60, and 105 °C and after different periods of aging at 19 °C and 31 % relative humidity, we investigated the physicochemical matrix stability and the thermal stability against combustion. We hypothesized that multivalent cations stabilize the SOM matrix, that these structures disrupt at elevated temperatures, and that aging leads to an increase in matrix stability. The results show that cation-specific effects on matrix rigidity started to evolve in the peat only after 8 weeks of aging and were significantly lower than the temperature effects. Temperature treatment above 40 °C caused a non (or not immediately) reversible loss of water molecule bridges (WaMB) and above 60 °C a partly reversible melting process probably of semi-crystalline poly(methylene). Thermal stability increased with increasing cation valence and degree of protonation and was much less affected by temperature. Generally, Na-treated and control samples revealed lower thermal stability and lower increase in matrix rigidity with aging than those treated with Ca, Al, and H. We conclude that drying at elevated temperatures (>40 °C) may irreversibly change SOM structure via disruption of labile cross-links and melting of semi-crystalline domains.  相似文献   
43.
We present measurements of the Peltier-effect in the mixed state of Bi1.76Pb0.24Sr2Ca2Cu3Oδ. The Peltier-coefficient broadens in a magnetic field quite similar to the resistivity and the thermopower. Comparison with the thermopower shows that Onsagers relation holds well. The occurrence of the Peltier-heat in the mixed state well below Tc implies that the electric current is accompanied by a large heat current. We show that the vortex contribution to the Peltier-heat is negligibly small. Therefore the heat current has to be attributed to normal quasiparticle excitations. Our results indicate that this quasiparticle contribution to the heat current remains large even at temperatures far below Tc.  相似文献   
44.
Journal of Nanoparticle Research - The increasing demand for optoelectronic devices requires the development of luminescent materials with high luminescence efficiency and low energy demands, and...  相似文献   
45.
We report on first principles calculations of the anisotropy of the intrinsic spin Hall conductivity (SHC) in nonmagnetic hcp metals and in antiferromagnetic Cr. For most of the metals of this study we find large anisotropies. We derive the general relation between the SHC vector and the direction of spin polarization and discuss its consequences for hcp metals. Especially, it is predicted that for systems where the SHC changes sign due to the anisotropy the spin Hall effect may be tuned such that the spin polarization is parallel either to the electric field or to the spin current.  相似文献   
46.
F. Marschner  H. Pohle 《Tetrahedron》1978,34(1):105-112
Within the scope of the PPP-SCF-Cl-method the conception of partial bond-localizing on the basis of a structural model of benzene is applied to 34 unsaturated hydrocarbons. It is shown, that the experimental PE- and UV -results, heats of formation and bond-lengths of these compounds can be reproduced with deviations < 2 %.  相似文献   
47.
Sodium-23 magnetic resonance imaging can be used to detect and assess experimental cerebral ischemia in the rat. An imaging technique utilizing a surface coil is described to produce sodium magnetic resonance images of good quality and resolution within 10 min. A novel method of hemispheric occlusion showed edema in the right brain of the rat head within 3 hr after injury. The edema was especially pronounced by 12 hr with effects in the right brain, eye and surrounding muscle evident.  相似文献   
48.
49.
F. Marschner  H. Goetz 《Tetrahedron》1973,29(19):3105-3108
It has been possible to correlate, by a modified PPP-SCF-CI-method on benzene, PE- and UV-spectroscopical measurements with a deviation of < ± 10?3 [eV]. In this manner we obtained sets of parameters, of general application to aromatic compounds and we concluded, that the controversial ionisation potential of 12·30 [eV] should be assigned to the π-a2u-orbital of benzene.  相似文献   
50.
Geometry optimizations at the B3LYP/6-31 + G(d) level for a set of X(SiH3)MeSiLi molecules (X = F, OH, NH2, Cl, SH, and PH2) show that the tetrahedral structure prevails in polar solutions; however, it readily isomerizes into a silylenoid with energy barriers of less than 15 kJ mol(-1). Inverted structures, which predominate in the gas phase, could not be located in solution. Configuration inversion is unfavorable, with energy barriers between 80 and 220 kJ mol(-1). The alpha elimination into a silylene moiety and the corresponding LiX is only likely to occur in solution, particularly for X = Cl and SH.  相似文献   
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