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141.
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Karel Wiesner Thomas Y. R. Tsai Ravindra Kumar Harihran Sivaramakrishnan 《Helvetica chimica acta》1984,67(4):1128-1135
Two efficient preparations of the title compound, one from common C19-steroids, the other frm digitoxigenin, are described. The less active minor epimer (21S)-methyldigitoxigenin was also obtained and characterized. The positive inotropic effects and margins of safety of the two C(21)-epimers (tested as glucosides) are discussed in terms of the topological properties of the Digitalis receptors. 相似文献
144.
Effective hard-sphere diameters for argon, krypton and xenon have been calculated from the currently most accurate perturbation theories using accurate pair-potential models. Based on the theoretical diameters and on pressure—volumes—temperature data for the real fluids, the van der Waals parameter ap is examined and two conjectures generalizing the behavior of ap are formulated. These conjectures make it possible to evaluate the effective hard-sphere diameters of simple liquids at the triple-point temperature from data for a few low-temperature pressure—volume isotherms. This fact, together with a corresponding-states principle that emerges from results for the theoretical diameters, forms the basis of a simple method which we propose for evaluating temperature-dependent effective hard-sphere diameters of a perturbed hard-sphere equation of state, independently of any pair-potential model and any perturbation theory. The applicability of the method is demonstrated for methane and its extension to nonsimple liquids is discussed. It is also shown that the use of an approximate theory and/or approximate pair-potential model may often result in a qualitatively misleading picture of ap behavior. 相似文献
145.
146.
A model for the distribution of cations in the spinel lattice of manganese ferrites MnFe2O4+
was elaborated on the basis of the experimental studies of the basic magnetic quantities, electrical conductivity and magnetic relaxation of the given ferrites, taking into consideration their crystallographic properties. The conclusions following from this model are in good agreement with the experimental results obtained by us and by other authors both for stoichiometric manganese ferrite and for a ferrite where 0.
I. MnFe2O4+
, MnFe2O4+ . , , , , , 0.相似文献
147.
Karel Aim 《Fluid Phase Equilibria》1978,2(2):119-142
To make feasible the experimental study of vapor-liquid equilibrium (VLE) in the systems mentioned in the title, a static apparatus for accurate measurement of total vapor pressures of solutions was constructed. Mixtures of known composition are prepared synthetically in a thermostated equilibrium cell by weight from pure degassed components and the total pressure is measured by a quartz Bourdon gage. A procedure was developed for degassing pure liquids to a degree corresponding to the high precision of pressure determination required. The static assembly was tested by comparing obtained isothermal vapor pressures and calculated excess Gibbs free energies with literature data for the benzene - cyclohexane system at 14 and 20°C, respectively. Additional experimental vapor-pressure data are presented for pure cyclohexane, benzene, and N-methylpyrrolidone (abbreviated throughout this paper as NMP) at 6–24°C and for the binary systems of benzene-cyclohexane at 8°C and cyclohexane - NMP and benzene - NMP at 8, 14, and 20°C over the entire composition range. The binary data were reduced by a modified Barker's method to evaluate excess Gibbs free energies and vapor phase compositions. 相似文献
148.
We show that the internal strain parameter ζ and elastic constants of the tetrahedral semiconductors can be determined from the force constants between planes of atoms. These have been computed recently for Si and GaAs from self-consistent electronic calculations using the Hellmann-Feynman theorem. The theoretical results are ζ = 0.72 for GaAs and ~0.57 for Si compared to experimental values of 0.76 and 0.73. 相似文献
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