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961.
Attila Máté 《Discrete Mathematics》1981,33(2):171-183
The achromatic number of a graph is the largest number of independent sets its vertex set can be split into in such a way that the union of any two of these sets is not independent. A graph is irreducible if no two vertices have the same neighborhood. The achromatic number of an irreducible graph with n vertices is shown to be while an example of Erdös shows that it need not be log n/log 2+2 for any n. The proof uses an indiscernibility argument. 相似文献
962.
C.A. Vant Hof J. Schmidt P.J.F. Verbeek J.H. Van Der Waals 《Chemical physics letters》1973,21(3):437-441
A Carr-Purcell multiple spin-echo, as modified by Meiboom and Gill, is described for the 3598 MHz zero-field transition of phosphorescent quinoline C9ND7 in a durene host. The results show that the dephasing of the electron spins through spectral diffusion may be largely eliminated by the multiple echo technique. 相似文献
963.
Energy-dispersive x-ray fluorescence is advantageous for trace analysis of soils present as thin films. A target thickness of about 2 mg cm-2 provides a compromise between optimal sensitivity and minimal absorption effect or optimal accuracy. Sample preparation involves only suspending the finely ground soil in water and drying this suspension on a thin mylar foil glued on a ring that fits into the x.r.f. spectrometer. The “effective sample weight” present in the exciting beam area is computed from the scatter peaks, a method that cancels out target heterogeneity problems. High accuracy is demonstrated for many elements in reference soil and rock materials; a precision around 5% and a detection limit around 10 ppm can be achieved. As an illustration, results for 16 trace elements and preliminary interpretation are given for a series of pedologically important soil samples from Brasil. 相似文献
964.
S. Kabuß H. G. Schmid H. Friebolin W. Faißt 《Magnetic resonance in chemistry : MRC》1969,1(6):451-465
The confromations of the unsaturated seven membered ring in 4,4,6,6-tetradeuterium-1,2-benzocycloheptene-(1) ( 1 ) and five benzocycloheptene derivatives were determined by NMR spectroscopy. For all investigated compounds at ?80°C only one conformer was present in detectable quantity. By analysis of the NMR data – molecular symmetry, coupling constants and chemical shift – it can be shown that the conformation is always the chair form. The free conformational enthalpy of both the other conformations with boat or twist form of the ring is for all six compounds more than 1.8 kcal/mole. The experimental results agree with those from model calculations: thus for benzocycloheptene, the 5,5-dimethyl derivative ( 2 ) and the 4,4,6,6-tetramethyl derivative ( 4 ) the lowest energy was found for the chair conformation; the second most stable conformations were found to be the boat for 1 and 4 , and the twist form for 2 . 相似文献
965.
The electrical breakdown in vacuum was studied in the configuration: wire —plane. Measurements were performed in two different experimental systems: with technical vacuum and with the clean one. It was found that the value of breakdown voltage decreases with increasing vacuum and that at the same pressure the insulating properties of electrodes are better in the technical vacuum than in the oilless one. 相似文献
966.
V. Malát 《Czechoslovak Journal of Physics》1967,17(6):516-520
The paper deals with the measurement of secondary electron emission and the scattering of primary electrons on thin self-supporting films of Ag. The measured values of the practical range agree with the older results obtained by Kanter. New results are those concerning the maximum depth from which the primaries are scattered back to the front surface and the maximum range of secondaries, which has been found to be about 300 å. 相似文献
967.
Urs Wuthier Hung-Viêt Pham Bruno Rusterholz Wilhelm Simon 《Helvetica chimica acta》1986,69(6):1435-1441
A series of triorganyltin compounds of the type R3SnY and RR2SnY has been studied in view of their anion selectivities exhibited in solvent polymeric membranes. A large variety of selectivity patterns has been observed first by varying the concentration of a given ionophore in the membrane phase, and second by using ionophores which differ in the organic substituents R on the Sn centre. With more space consuming substituents R, the observed selectivity patterns become more and more similar to that of a blank membrane, suggesting steric hindrance for the pentacoordination of the corresponding ionophores by sample anions. 相似文献
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