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991.
Norman Riley 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1971,22(4):645-653
Zusammenfassung Untersucht wird die stationäre strömende Geschwindigkeit, die durch eine kreisförmige rührende Bewegung eines starren Zylinders induziert wird. Die Amplitude dieser kreisförmigen Bewegung wird im Vergleich zum Durchmesser des Zylinders als klein angenommen. Es wird gezeigt, dass bei genügend hohen Frequenzen der nicht-stationäre Wirbeleffekt auf eine dünne Stokes-Scherwellenschicht beschränkt ist, dass aber die induzierte Strömung ausserhalb dieser Region bestehen bleibt. Für den besonderen Fall eines runden Zylinders ergibt sich, dass diese stationäre Strömung von der Reynolds-Zahl unabhängig ist. 相似文献
992.
Fernanda M. Da Costa Robert Greatrex Norman N. Greenwood 《Journal of solid state chemistry》1977,20(4):381-389
The magnetic, electronic, and structural properties of the solid solutions LaxSr1−xRuO3 and LaxCa1−xRuO3 have been studied by 99Ru Mössbauer spectroscopy and other techniques. The LaxCa1−xRuO3 phases are reported for the first time and have been shown by powder X-ray diffraction measurements to be orthorhombically distorted perovskites. Electrical resistivity measurements on compacted powders show that all the phases are metallic with p 10−3, ohm-cm. Progressive substitution of Sr2+ by La3+ in ferromagnetic SrRuO3 leads to a rapid collapse of the magnetic hyper-fine splitting at 4.2°K. For x = 0.25 some ruthenium ions still experience a magnetic field but for 0.4 x 0.75 only single, narrow resonance lines are observed, consistent both with the complete removal of the ferromagnetism and with the presence of an averaged ruthenium oxidation state in each phase, i.e., Lax3+Sr1−x2+Ru(4−x)+O3 rather than Lax3+Sr1−x2+Rux3+Ru1−x4+O3. LaRuO3 and CaRuO3 both give essentially single-line spectra at 4.2°K, indicating that the ruthenium ions in these oxides are not involved in long-range antiferromagnetic order but are paramagnetic. The solid solutions LaxCa1−xRuO3 (0 < x 0.6) give sharp symmetrical singlets with chemical isomer shifts (relative to the Ru metal) which move progressively from the value characteristic of Ru4+ (−0.303 mm sec−1) toward the value for Ru3+ (−0.557 mm sec−1), consistent with the presence of intermediate ruthenium oxidation states in these phases also. 相似文献
993.
994.
Poly-hexafluoropropylene oxide (poly-HFPO) alcohol was prepared by the reduction of the corresponding methyl ester using NaBH4, NaBD4, or LiAlH4 (LAH). This alcohol is a versatile starting material for the preparation of additional interesting compounds. Because of its expected poor nucleophilicity, before attempting additional reactions, we have found it advantageous to prepare a corresponding salt. We have found that the resulting salt behaved like a normal hydrocarbon alkoxide. The reaction of this salt with either acetyl chloride or allyl chloride (or bromide) gave the expected products which proved to be normal nucleophilic substitutions. In addition, the bromination of the allyl ether was studied using NMR and GC/MS techniques. 相似文献
995.
996.
997.
Norman L. Johnson 《Journal of Geometry》2006,85(1-2):61-71
Every semifield plane with spread in PG(3,K), where K is a field admitting a quadratic extension K+, is shown to admit a transitive parabolic unital.
The author gratefully acknowledges helpful comments of the referee in the writing of this article. 相似文献
998.
A general theory of collineation groups generated by quartic groups of even order is considered. Applications are given to collineation groups generated by ‘large’ quartic groups. © 2005 Wiley Periodicals, Inc. J Combin Designs 13: 195–210, 2005. 相似文献
999.
Job rotation is a useful tool that can be used in many work settings to produce task variety for workers and to reduce worker fatigue and injuries. Developing a job rotation plan requires determining the set of jobs to be included in the rotation, the rotation sequence, and the proper length of the rotation interval. Previous research has considered both the jobs to include in a rotation plan and how to sequence the rotation plan but no work has been conducted to quantitatively examine different rotation interval lengths. Using different rotation interval lengths may result in different stresses for the workers performing a particular set of tasks and therefore affect the quality of the job rotation implementation. This paper proposes a quantitative method based on mathematical programming to obtain a proper job rotation interval length. The merit of the method is determined by examining its effectiveness in reducing worker stress and the potential for injury as well as its applicability for use in real settings. 相似文献
1000.