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101.
102.
Catalytic one-pot synthesis of fenestrane derivatives from dienediynes was developed: fenestranes were synthesized in high yields by a dicobalt octacarbonyl-catalyzed tandem cycloaddition of dienediynes. 相似文献
103.
Oscillation and nonoscillation criteria for the higher order self-adjoint differential equation (-1)n(talphay(n))(n)+q(t)y = 0 (*) are established. In these criteria, equation (*) is viewed as a perturbation of the conditionally oscillatory equation (-1)n(talphay(n))(n) - µ,t2n-y = 0, where
n, is the critical constant in conditional oscillation. Some open problems in the theory of conditionally oscillatory, even order, self-adjoint equations are also discussed. 相似文献
104.
Neutron scattering has been used to measure the charge and spin structure in the highly underdoped superconductor YBa(2)Cu(3)O(6.35). Incommensurate static charge ordering is found that remains at high temperatures. The magnetic pattern is complex with a resonance and incommensurate structure observed at low temperatures. The results clarify the role of striped phases in YBa(2)Cu(3)O(6+x) superconductors. 相似文献
105.
M. Doǧan 《Spectrochimica Acta Part B: Atomic Spectroscopy》1981,36(2):103-110
The suitability of the glow discharge lamp for the analysis of both main components of a binary system Cu-Al has been investigated. The standard samples contained Cu and Al between 0.5 and 99.5%. Different calibration methods for these systems are discussed. Only the “method of binary ratios” yields a straight line for calibration within the entire concentration range. It is obtained if the logarithm of the intensity ratio is plotted against the logarithm of the concentration ratio of Cu and Al. Accurate and precise results are obtained if the discharge voltage and the gas pressure are kept constant for all samples. The correlation coefficient was found to be 0.99986 and the relative standard deviation for the determination of the concentration was about 0.06 · (1-w), where w is the concentration expressed as a fraction. 相似文献
106.
P. Debefve H. P. Do C. Friedli P. Lerch 《Journal of Radioanalytical and Nuclear Chemistry》1981,64(1-2):213-223
Trace amounts of oxygen in gold-copper alloys and high purity gold have been determined by3He and4He activation analysis. Interferences from the matrix have been identified and the factors which can have an effect upon the
precision and the accuracy of the method have been investigated. Thus a destructive technique has been choosen. The18F produced was chemically separated by steam distillation and precipitated as PbClF. The values of the oxygen concentration
were found to range between 0.2 and 2 μg·g−1 depending on the copper concentration and the thermal treatment applied to the samples. A possible mechanism of internal
oxidation is presented. 相似文献
107.
[reaction: see text] The above reaction is much faster with Y = CF(3)CH(2)O than with Y = CH(3)O. However, the methyl ester is a strong inhibitor of the Diels-Alder reaction of the trifluoroethyl ester, since it has a higher affinity for the catalyst 1. 相似文献
108.
Transition to chaos in the presence of noise is an important problem in nonlinear and statistical physics. Recently, a scaling law has been theoretically predicted which relates the Lyapunov exponent to the noise variation near the transition. Here we present experimental observation of noise-induced chaos in an electronic circuit and obtain the fundamental scaling law characterizing the transition. The experimentally obtained scaling exponent agrees very well with that predicted by theory. 相似文献
109.
110.
We construct and analyze a mixed finite volume method on quadrilateral grids for elliptic problems written as a system of two first order PDEs in the state variable (e.g., pressure) and its flux (e.g., Darcy velocity). An important point is that no staggered grids or covolumes are used to stabilize the system. Only a single primary grid system is adopted, and the degrees of freedom are imposed on the interfaces. The approximate flux is sought in the lowest-order Raviart-Thomas space and the pressure field in the rotated- nonconforming space. Furthermore, we demonstrate that the present finite volume method can be interpreted as a rotated- nonconforming finite element method for the pressure with a simple local recovery of flux. Numerical results are presented for a variety of problems which confirm the usefulness and effectiveness of the method.