排序方式: 共有51条查询结果,搜索用时 21 毫秒
1.
2.
Wijkens P Jastrzebski JT van Der Schaaf PA Kolly R Hafner A van Koten G 《Organic letters》2000,2(11):1621-1624
A general method for the functionalization of Si-Cl terminated carbosilane dendritic molecules via organolithium or organomagnesium reagents is described. Quantitative exchange of the bromine atoms of 4-bromophenyl-functionalized dendrimers affords polylithiated species that are valuable starting materials for further functionalization, e.g., into pyridyl alcohols. The latter were successfully applied as catalyst precursors in a ruthenium-mediated ring-closure metathesis reaction. 相似文献
3.
Panayiotis Antoniou Varotsos 《Physics letters. A》1978,64(4):411-412
By using the Swenson formula, for the pressure derivative of the bulk modulus, and the Slater formulation for the Gruneisen constant a simple useful relation between the vacancy-formation entropy and the Gruneisen constant is derived in the case of metals. This relation also indicates that actually a close correlation between the vacancy-formation enthalpy, the coefficient of the volume expansivity and the corresponding melting point exists. 相似文献
4.
P.A. Varotsos 《Journal of Physics and Chemistry of Solids》1978,39(5):513-514
The formation volume νf of a (cation) Frenkel Defect is calculated in AgCl and AgBr. The proposed formula for νf has no adjustable parameters and contains the formation enthalpy (of a Frenkel defect), the compressibility of the solid at absolute zero and the pressure derivative of the compressibility. The calculated values are in good agreement with the experimental results. 相似文献
5.
Gordeev SN Zhukov AA de Groot PA Jansen AG Gagnon R Taillefer L 《Physical review letters》2000,85(21):4594-4597
We report on transport measurements of YBa 2Cu 3O (7-delta) single crystals with different oxygen contents in the geometry B, J ||ab (J perpendicularB). Our data show that the vortices become confined between the Cu-O planes below a well-defined temperature at which the effective size 2xi of the vortex core is approximately equal to the period of the Cu-O layers. This confinement strongly increases the vortex liquid freezing temperature. A new melting line is found separating a vortex liquid and a smectic phase, which shows an oscillatory field dependence reflecting differences between commensurate and incommensurate smectic states. 相似文献
6.
The activation volume Vact has been measured for olivine, LiBr and CsCl. It is shown that the quantity Vact/Hact, where Hact denotes the activation enthalpy, is governed by the elastic properties of the bulk material in accordance to a model suggested by Varotsos and Alexopoulos. An explanation of the latter model for the migration process is attempted by means of the ballistic model independently suggested by Van Vechten. 相似文献
7.
Ming Xia LI Yan Ming WANG Ru Ru CHEN* Research Institute of Elemento-Organic Chemistry Nankai University Tianjin Pittsburgh University Medical Center Pittsburgh PA U. S. A 《中国化学快报》2001,(6)
The chiral diols ((,(,((,((-Tetraaryl-1,3-dioxolane-4,5-dimethanols) have been used for the formation of cyclic titanates and similar derivatives of Mg, Al and Zr. These complexes of oxophilic metal centers were employed in catalytic and stiochiometric enantioselective reactions such as enantioselective addition reactions of carbon-centered nucleophiles to aldehydes1, [2+2] cycloadditions2, and Diels-Alder reactions3. So far, the two hydrogen atoms of all this type of diols are in trans form… 相似文献
8.
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
9.
Dielectric losses were measured in the following crystals NaCl+ (Mg2+, Co2+, Ni2+, Sr2+, Ca2+, Mn2+, Zn2+, Cd2+, Ba2+, Pb2+), KCl + (Ca2+, Sr2+, Ba2+, 2+, Pb2+) and KBr + (Sr2+, Ba2+) in the frequency region 5–500 kHz. It was found that when the divalent cation impurity has an electronic configuration similar to the inert gases (1) no observable deviation from simple Debye theory exists (2) the activation energy Φ increases linearly with the ionic radius of the impurity.The above observations (1) and (2) do not hold when the divalent cation impurity has d-electrons in the outer subshell. 相似文献
10.
Panayiotis Antoniou Varotsos Kessar Alexopoulos 《Journal of Physics and Chemistry of Solids》1978,39(7):759-761
At high temperatures the conductivity plot of silver halides shows a pronounced upward curvature to higher conductivity values. This curvature has been attributed to an excessive decrease of the Gibbs formation energy gf per Frenkel defect. Such a decrease is known to arise from Lidiard-Debye-Huckel interactions and expansivity. However a quantitative evaluation for AgCl and AgBr has shown that the said effect is not sufficient to explain the experimental data. The present paper proposes a further reason for the excessive decrease of gf; it is due to an excessive fall of the bulk modulus B at temperatures near the melting point. For AgCl a fall by approx. 10% would give the needed decrease of gf. 相似文献