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71.
Some characterizations of complex quadrics in terms of the spectrum are given. 相似文献
72.
The hyperfine interaction of 151Eu in Eu2TiO4 has been measured using the Mössbauer Effect. Using the four-fold symmetry of the Eu2+ site, it has been found that the nuclear quadrupole moment ratio of the first-excited to the ground states of 151Eu is R = 1.34 ±0.03, and the quadrupole interaction energy is ρ2qQo = -(190 ± 7) MHZ. Below Tc = 7.8K, the magnetic hyperfine field Hhf points close to the direction of the four-fold axis. The zero-degree value of Hhf is estimated to be (305 ± 3) kOe. 相似文献
73.
G. B. Baptista E. C. Montenegro C. V. Barros Leite A. S. Paschoa 《Journal of Radioanalytical and Nuclear Chemistry》1980,60(1):227-235
The accuracy of the quantitative analysis of thick targets by XRF is impaired by effects due to the absorption of X-rays in
the matrix associated with the non-uniformity of the X-ray beam and the lack of knowledge of the actual distribution of trace
elements in the target. The uncertainty in the elemental mass associated to a definite number X-rays detected is discussed
in the paper. A correction factor is derived to account specifically for the effect of the absorption of X-rays and the non-uniformity
of the X-ray beam.
Work partially supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico, Financiadora de Estudos e Projetos
and International Atomic Energy Agency. 相似文献
74.
Butyl vinyl tellurides and bis-vinyl tellurides furnish vinyllithiums with retention of configuration in good yields upon treatment with n-butyllithium at −78°C. 相似文献
75.
76.
The Mossbauer spectrum of 151Eu3Ti2O7 reveals a ferrimagnetic ordering below (8 ± 0.3) K with two inequivalent sites in ratio 2: 1, and with exchange constants nearly equal to those of EuTiO3 and of Eu2TiO4. The sublattice magnetizations are explained in terms of these constants. 相似文献
77.
Luis J. Alí as Abdê nago Barros Aldir Brasil Jr. 《Proceedings of the American Mathematical Society》2005,133(3):875-884
Let be a compact hypersurface with constant mean curvature immersed into the unit Euclidean sphere . In this paper we derive a sharp upper bound for the first eigenvalue of the stability operator of in terms of the mean curvature and the length of the total umbilicity tensor of the hypersurface. Moreover, we prove that this bound is achieved only for the so-called -tori in , with . This extends to the case of constant mean curvature hypersurfaces previous results given by Wu (1993) and Perdomo (2002) for minimal hypersurfaces.
78.
A J M Barros J C O Santos S Prasad V D Leite A G Souza L E B Soledade M S B Duarte V D dos Santos 《Journal of Thermal Analysis and Calorimetry》2006,83(2):291-295
The conventional treatments
of effluents containing heavy metals produce significant quantities of byproducts
with recalcitrant characteristics, making necessary looking after alternative
techniques in order to avoid the production of new contaminated residues.
Sorption process of chromium and zinc in vertical columns loaded with sewage
sludge and organic solid waste has been studied in this work. The data from
the TG curves of the two sorbents presented significant differences when they
were submitted to the metal uptake, being noticed the displacement of the
thermal events towards lower temperatures for both types of sorbents studied.
As it was expected, for both sorbents, an increase in the mass of samples
has been observed at the completion of the thermal tests upon metal uptake.
Therefore, these facts demonstrate that during the biosorption process a physico-chemical
interaction took place between sorbents and metals, as it was evidenced by
the more than 100 K increase in the decomposition temperatures as well as
the variation of the ΔH values of the
samples. 相似文献
79.
The syntheses of new chiral cyclic 1,2-diacetals from (2R, 3R)-( )-tartaric acid are described. C(2)-symmetrical diamines were prepared via direct amidation of the tartrate or from the corresponding bismesylate via reaction with sodium azide. For C1-symmetrical compounds, the Appel reaction was used to form the key intermediate, a monochlorocarbinol, from the diol. Some of the new chiral compounds, produced in good to high yields, may be potentially useful as asymmetric organocatalysts or as nitrogen and sulfur chelating ligands for asymmetric metal catalyzed reactions. Thus, a bis-N-methyl-methanamine derivative, used in substoichiometric amounts, was found to catalyze the enantioselective addition of cyclohexanone to (E)-beta-nitrostyrene with high diastereoselectivity (syn / anti = 92:8), albeit giving moderate optical purity (syn: 30 %). 相似文献
80.
In a recent paper (Barros, Sousa in: Kodai Math. J. 2009) the authors proved that closed oriented non-totally geodesic minimal hypersurfaces of the Euclidean unit sphere have index of stability greater than or equal to n + 3 with equality occurring at only Clifford tori provided their second fundamental forms A satisfy the pinching: |A|2 ≥ n. The natural generalization for this pinching is ?(r + 2)S r+2 ≥ (n ? r)S r > 0. Under this condition we shall extend such result for closed oriented hypersurface Σ n of the Euclidean unit sphere ${\mathbb{S}^{n+1}}$ with null S r+1 mean curvature by showing that the index of r-stability, ${Ind_{\Sigma^n}^{r}}$ , also satisfies ${Ind_{\Sigma^n}^{r}\ge n+3}$ . Instead of the previous hypothesis if we consider ${\frac{S_{r+2}}{{S_r}}}$ constant we have the same conclusion. Moreover, we shall prove that, up to Clifford tori, closed oriented hypersurfaces ${\Sigma^{n}\subset \mathbb{S}^{n+1}}$ with S r+1 = 0 and S r+2 < 0 have index of r-stability greater than or equal to 2n + 5. 相似文献