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961.
Katherine Heinrich 《Journal of Combinatorial Theory, Series A》1980,29(3):346-353
We construct Latin squares of order n = pq which have no proper subsquares when p and q are distinct primes and n ≠ 6. 相似文献
962.
H. Heinrich K. Hess W. Jantsch W. Pfeiler 《Journal of Physics and Chemistry of Solids》1972,33(2):425-431
The energy relaxation time τ? of GaSb has been determined independently from microwave harmonic mixing experiments in the range of 160–200 K and from the current-voltage characteristics at 300 and 77 K. From measurements of the i.r. Faraday effect at 300 K valley populations as a function of the electric field strength are obtained which are in agreement with values calculated with help of the energy relaxation time obtained by methods mentioned before. For the evaluation of the data a two-band model has been used. The results obtained from the microwave experiments are extrapolated to 300 and 77 K assuming polar optical mode scattering. Good agreement of these values and the results obtained from the current-voltage characteristics and the Faraday measurements was found. The values for 300 and 77 K are 4 × 10−12 sec and approximately 1·6 × 10−11 sec, respectively. 相似文献
963.
We show that the edges of the complete symmetric directed graph onn vertices can be partitioned into directed cycles (or anti-directed cycles) of lengthn−1 so that any two distinct cycles have exactly one oppositely directed edge in common whenn=p
e>3, wherep is a prime ande is a positive integer. When the cycles are anti-directedp must be odd. We then consider the designs which arise from these partitions and investigate their construction.
We would like to thank the Mathematics Department of the University of Arizona for their hospitality during January 1979 when
this work was begun.
Partial support was provided for this research by the Natural Sciences and Engineering Research Council of Canada under Grant
A-4792. 相似文献
964.
965.
Ohne Zusammenfassung 相似文献
966.
Heinrich Baumann 《Fresenius' Journal of Analytical Chemistry》1990,338(7):809-812
Summary A rapid and sensitive method for the determination of iodine in fresh milk and milk powders by inductively coupled plasma — mass spectrometry is described. The method is applied to the analysis of the two standard reference materials BCS-CRM Nos. 63 and 150. The iodine concentrations found in these materials are 0.28±0.01 g/g and 1.21±0.01 g/g, respectively. In fresh milk, iodine concentrations between 50 and 2300 ng/ml were determined. The ICP-MS results for these milk samples are compared to the results which were obtained by a chemical method and by X-ray fluorescence analysis. Because of the simple sample preparation and the good sensitivity and selectivity ICP-MS is the only method which allows the determination of iodine in milk samples down to the lower ng/ml range together with a high sample throughput. 相似文献
967.
With conventional phase-transfer catalysis using quaternary ammonium salts, yields of 2, 4-dinitrobenzenesulfonic acid ( 2 ) in the sulfodechlorination of 1-chloro 2.4-dinitrobenzene ( 1 ) with sulfite ions are no better than those obtained with the classical method in aqueous ethanol (80–82%). Yields up to 97% and a very pure product are obtained, however, by using protonated tertiary amines as catalysts. The optimum chain-length of the amine is found with tributylamine. On mixing solutions of the reagents and catalysts a strong bluish-red colour develops immediately, but disappears within ca. 1 h. Comparison of the NMR. spectrum of this primary product with model adducts of sulfite ions and di- and trinitrobenzene derivatives demonstrates that the primary addition of the nucleophile to 1-chloro-2, 4-dinitrobenzene does not take place at C (1), but at C(5). It is shown that the increments calculated for a C-SO group and for the 1, 3-dinitro- and 1, 3, 5-trinitropentadienyl ring moieties can be employed for the approximate calculation of 1H-chemical shifts using Clerc & Pretsch's modification of the Shoolery rules [3]. 相似文献
968.
969.
970.
Green crystals of Me2NTiCl3 associate to a chain polymer via four Ti‐Cl‐Ti bonds and generation of hexacoordinated Ti atoms. Like Et2NTiCl3 its amino group is not involved into forming Ti‐N‐Ti bridges. This is due to a short Ti‐N bond to the planar coordinated N atom of the Me2N group. 相似文献