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991.
992.
Raul Cordovil Antnio Guedes de Oliveira Michel Las Vergnas 《Discrete Mathematics》1996,160(1-3):105-113
In this paper, a configuration with n = (2d) points in the plane is described. This configuration, as a matroid, is a Desargues configuration if d = 5, and the union of (5d) such configurations if d> 5. As an oriented matroid, it is a rank 3 truncation of the directed complete graph on d vertices. From this fact, it follows from a version of the Lefschetz-Zariski theorem implied by results of Salvetti that the fundamental group π of the complexification of its line arrangement is Artin's pure (or coloured) braid group on d strands.
In this paper we obtain, by using techniques introduced by Salvetti, a new algorithm for finding a presentation of π based on this particular configuration. 相似文献
993.
Humberto César Chaves Fernandez José de Ribamar Silva Oliveira Attílio José Giarola 《International Journal of Infrared and Millimeter Waves》1991,12(5):505-519
The Transverse Transmission Line method is used for the characterization of bilateral and unilateral finlines on a semiconductor substrate and in conjunction with the modal method, for the calculation of the scattering parameters due to a step discontinuity on a unilateral finline with a lossless dielectric substrate.Numerical results of the effective dielectric constant, attenuation constant and characteristic impedance for the bilateral and unilateral finlines on semiconductor substrates, and results of scattering parameters of a step discontinuity for unilateral finline, are presented. 相似文献
994.
In this paper we present some new sufficient conditions for the existence of a square matrix with prescribed characteristic polynomial and two complementary principal submatrices. 相似文献
995.
I.G. Souza H. Bergamin Fo F.J. Krug J.A. Nóbrega P.V. Oliveira B.F. Reis M.F. Giné 《Analytica chimica acta》1991
The simultaneous determination of chromium, nickel, manganese, silicon and iron in stainless steels was achieved by inductively coupled plasma atomic emission spectrometry (ICP-AES) after on-line electrodissolution using an improved flow-through electrolytic cell. The solution containing the electrodissolved ions was impelled by an air carrier stream in a flow-injection manifold towards a mixing-dilution chamber. From this chamber, the diluted and homogenized solution was aspirated and nebulized into the ICP torch. A quantification procedure is proposed for direct solid analysis without the use of certified reference materials. Under the proposed electrolysis conditions, up to 60 solid samples can be analysed per hour. Results obtained for alloying elements in austenitic and ferritic stainless steels were in good agreement with the certified values. 相似文献
996.
The distributions of Gamow-Teller strength in 90, 92, 94Nb have been calculated utilizing the so-called GT force in the random phase approximation. For 90Nb the calculated distribution is in striking agreement with that part of the 90Zr(p, n) excitation function leading to 1+ excitations in 90Nb and qualitative agreement is demonstrated for data from the reactions 92, 94Zr(p, n). Some 25 % of the GT strength is found to lie well below the structureless giant resonance proposed by Ikeda et al. The implications of this result to the β-decay properties of neutron rich nuclei near A = 90 are discussed. 相似文献
997.
The surface composition of two commercial ZSM-5 zeolites with and without PO4 modification was examined by X-ray photoelectron spectroscopy. Both zeolites were slightly enriched in aluminum on the surface.
The surface silica/alumina ratio (SAR) was about half of that of the bulk. Calcination at 600∘C decreased slightly this enrichment. After drying with H3PO4 followed by calcination, both zeolites showed surface enrichment of PO4. The surface of the zeolite with large crystal was more enriched. Steaming resulted in enrichment of aluminum on the surface,
in agreement with migration of extra-framework alumina. Increasing phosphate content decreased this enrichment.
This paper was presented in the 5th Brazilian Meeting on Adsorption, held at Natal, Brazil, 18-21 July, 2004. 相似文献
998.
Two analytical procedures based on the magnitude of the heat of dilution and direct injection enthalpimetry have been developed for determination of water in ethanol and acetone. The results obtained by means of the heat of dilution were compared with the values given by pycnometry, and gave a relative difference in the range 0.2-3%. The precision depends on the slope of the calibration curve, which varies with the procedure and the concentration of the sample. 相似文献
999.
1000.
General results are given for Green functions, mode frequencies and light scattering cross section for retarded modes in a ferromagnetic slab. These results hold for a more general geometry than the Voigt's one. We show that they fulfill very general symmetry requirements. 相似文献