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941.
942.
943.
944.
Rare earth elements in sediment profiles from marginal lagoons of the Moji-Guaçu River basin, Brazil
J. R Ferreira E. A. N. Fernandes E. J. França G. A. Tavares N. C. da Silva M. H. T. Taddei 《Journal of Radioanalytical and Nuclear Chemistry》2006,269(1):15-20
Summary Sediment cores from Catingueiro, Barrinha and Rio das Pedras marginal lagoons of the Moji-Gua?u River basin were analyzed
for rare earth elements (REEs), Fe, Ta and Th by instrumental neutron activation analysis (k0-INAA). Data indicated similarities between Catingueiro and Barrinha lagoons, while a distinct scenario was seen for Rio das
Pedras likely due to changes of sedimentation rate in 1950's. By using Fe, Sc, Ta and Th as conservative elements, double
normalization technique was performed in order to assess the distribution pattern of Ce, Eu, La, Sm and Tb for each core.
In all cases, it was evident a depletion of lighter REE elements in the Rio das Pedras lagoon. 相似文献
945.
Dweck J. Ferreira da Silva P. F. Büchler P. M. Cartledge F. K. 《Journal of Thermal Analysis and Calorimetry》2002,69(1):179-186
Thermogravimetry (TG) and derivative thermogravimetry (DTG) have been used by the authors as very effective tools to study hydration steps of cements used for solidification/stabilization of tanning wastes. The present paper presents a method which was applied to separate the peaks shown by DTG curves of type II Portland cement pastes, analyzed at different times during the first 4 weeks of setting. Through a specific software a more detailed study of the evolution of the cement hydration may be done, which allows the measurement of the amount of hydrated water present in tobermorite gel as well as in ettringite, which are the main phases formed from the original components of the cement. The number of moles of water present in the ettringite phase calculated by the method is in very good agreement with the values found in the literature, validating the method to calculate the same parameter in tobermorite gel. In the latter case the water content decreases significantly during the first day of hydration, then remains at a constant value over the rest of the analyzed period.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
946.
Milton N. da Silva Alessandra Jorqueira Antonio V. Pinto Vitor F. Ferreira 《Tetrahedron letters》2007,48(35):6171-6173
The synthesis of new carbonyl and fluoroalkyl o-quinone methides from β-lapachone is reported. 相似文献
947.
P.S. Haddad F.F. Ferreira G.E.S. Brito M.C.A. Fantini 《Journal of Sol-Gel Science and Technology》2004,30(3):179-185
This work reports the growth of layered nickel hydroxide/gold films by sol-gel and dip-coating methods to obtain colored films for applications in switchable optical devices. The nickel and gold-based films were deposited on mica and glass plates from alcoholic sols. The distribution of electron density inhomogeneities (voids, nickel and gold particles) in the films was determined by means of small angle X-ray scattering (SAXS). The SAXS measurements were used to determine the nickel and gold particle sizes and to give guidelines to the appropriate chemical route to deposit homogeneous colored films. X-ray diffraction (XRD) was used to monitor the crystalline properties. Transmission electron microscopy (TEM) was used to observe the nanostructure of the gold particles and atomic force microscopy (AFM) to analyze the film surface. Spectral transmission was used to investigate the optical properties in these different layered systems, which present an absorption band in the visible region due to the gold aggregates. The composite material is deep blue. The analyses of SAXS data, TEM and AFM pictures are consistent, i.e., the formed Au particles are polydisperse in size and their clustering depends on the NiO
x
H
y
layer. The Au particles are polycrystalline, with [111]-preferred orientation, as determined by XRD. The nickel oxy-hydroxide matrix is amorphous. 相似文献
948.
PauloF. Santos LucindaV. Reis Isabel Duarte JooP. Serrano Paulo Almeida AnabelaS. Oliveira LuísF.Vieira Ferreira 《Helvetica chimica acta》2005,88(5):1135-1143
Several (multiply) iodinated squarylium cyanine dyes of type 1 and 8 (see Scheme and Table), derived from 1,3‐benzothiazole and 6‐iodo‐1,3‐benzothiazole, were synthesized as potential new photosensitizers, with absorptions in the 700‐nm region. Their ability to generate singlet oxygen (1O2) was assessed by luminescence‐decay measurement in the near‐IR. Some of these new dyes show interesting photophysical properties, and may be potentially used in photodynamic therapy (PDT). 相似文献
949.
Torres YR Bugni TS Berlinck RG Ireland CM Magalhães A Ferreira AG Moreira Da Rocha R 《The Journal of organic chemistry》2002,67(15):5429-5432
Fractionation of the crude methanol extract of the ascidian Cystodytes dellechiajei collected in Brazil yielded two novel alkaloids, sebastianine A (1) and sebastianine B (2). The structures of both 1 and 2 were established by analysis of spectroscopic data, indicating an unprecedented ring system for both compounds, comprising a pyridoacridine system fused with a pyrrole unit in sebastianine A (1) and a pyridoacridine system fused with a pyrrolidine system condensed with alpha-hydroxyisovaleric acid in sebastianine B (2). Both alkaloids displayed a cytotoxic profile against a panel of HCT-116 colon carcinoma cells indicative of a p53 dependent mechanism. 相似文献
950.
Costa Ferreira SL 《Talanta》1988,35(6):485-486
A spectrophotometric method for determination of nickel in copper-base alloy with 2-(2-thiazolylazo)-p-cresol (TAC) is described. The interferences of foreign ions can be eliminated by masking with a mixture of sodium tartrate and sodium thiosulphate. The nickel-TAC complex has low solubility in water, but is soluble in aqueous ethanol. Beer's law is obeyed for 20-70mug of nickel in 50 ml of solution, at pH 5.7. The molar absorptivity at 580 nm is 2.6 x 10(4)l.mole(-1).cm(-1). The method has been applied successfully to determination of nickel in reference samples. 相似文献