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141.
The determination of chromium, copper, manganese, nickel and vanadium in carbonaceous samples by slurry introduction graphite
furnace atomic absorption spectrometry and after microwave assisted digestion are compared. Parameters such as atomization
and pyrolysis temperatures, and surfactant concentration as well as the homogenization procedure were optimized. The slurries
were prepared by mixing adequate amounts of the pulverized samples with 0.05% Triton X-100, sonicating for, at least, 40 seconds
during the preparation to separate aggregates and for 20 seconds immediately before being autosampled. It was not necessary
to use modifiers and calibration against aqueous standards was possible for all the elements. Coke, graphite and certified
coal samples were analyzed, and no significant difference was observed using both procedures. Good agreement between found
and certified values was obtained.
Received January 24, 2000. Revision September 26, 2000. 相似文献
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Luiz C. L. Botelho 《International Journal of Theoretical Physics》2010,49(8):1684-1692
We consider the problem of infrared divergencies in String theory in Embeddings Manifolds by means of the Nash Theorem of
Riemann metrics parametrized by immersions. 相似文献
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Goreti Botelho Arlete Mendes-Faia Maria Cristina Clímaco 《Analytica chimica acta》2010,657(2):198-9746
To evaluate the potential aroma of Aragonez clonal red musts, several free and glycosidically bound odourant compounds were extracted. Then, the gas chromatography-olfactometry (GC-O) posterior intensity method was used to evaluate their odour intensity and the compounds were identified by gas chromatography-mass spectrometry (GC-MS). A group of eight sniffers evaluated free and bound fractions of Aragonez musts and perceived forty-three and twenty-two odourant peaks respectively. Furaneol (burnt sugar, candy-cotton) and vanillin (vanilla, sweet) were identified in both free and bound fractions of Aragonez musts, indicating their grape-derived origin. Principal component analysis (PCA) was applied to the posterior intensity method data and a relationship between the different odourant compound variables and the free fractions was established. Two principal components (PCs) were found which together explained 100% of the total variance. A large number of potentially important but yet unknown odourants was detected by the GC-O analysis. 相似文献
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149.
Fernanda Botelho 《Linear algebra and its applications》2010,432(1):357-365
We consider the elementary operator L, acting on the Hilbert-Schmidt Class C2(H), given by L(T)=ATB, with A and B bounded operators on H. We establish necessary and sufficient conditions on A and B for L to be a 2-isometry or a 3-isometry. We derive sufficient conditions for L to be an n-isometry. We also give several illustrative examples involving the weighted shift operator on l2 and the multiplication operator on the Dirichlet space. 相似文献
150.
Luiz C. L. Botelho 《International Journal of Theoretical Physics》2010,49(6):1396-1404
We write a space-time Feynman Path Integral representation for scattered elastic wave fields from a weakly anisotropic non-homogeneity. 相似文献