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211.
Eloi Feitosa Fernanda Rosa Alves Elisabete M. S. Castanheira M. Elisabete C. D. Real Oliveira 《Colloid and polymer science》2009,287(5):591-599
In the millimolar concentration domain (typically 1 mM), dioctadecyldimethylammonium bromide and chloride (DODAX, X representing
Br− or Cl− counterions) molecules assemble in water as large unilamellar vesicles. Differential-scanning calorimetry (DSC) is a suitable
technique to obtain the melting temperature (T
m) characteristic of surfactant bilayers, while fluorescence spectroscopy detects formation of surfactant aggregates, like
bilayers. These two techniques were combined to investigate the assembly of DODAX molecules at micromolar concentrations,
from 10 to 100 μM. At 1 mM surfactant, T
m ≈ 45 °C and 49 °C, respectively, for DODAB and DODAC. DSC and fluorescence of Nile Red were used to show the formation of
DODAX aggregates, at the surfactant concentration as low as 10 μM, whose T
m decreases monotonically with increasing DODAX concentration to attain the value for the ordinary vesicles. The data indicate
that these aggregates are organized as bilayer-like structures. 相似文献
212.
T. Pinheiro A. Barreiros L. C. Alves M. Neres R. Fleming J. N. Silva P. Filipe R. Silva 《Journal of Radioanalytical and Nuclear Chemistry》2009,281(2):161-164
Skin as a manageable organ can provide direct or indirect information of tissue iron overload resulting from inherited disorders
as hemochromatosis. Patients with hemochromatosis were evaluated at three consecutive phases along the therapy programme.
Nuclear microprobe techniques were used to assess skin iron and Total Reflection X-ray Fluorescence to determine the plasma
iron concentrations. Results showed that iron pools were differently correlated at the three therapy phases. These variations
highlighted the value of skin iron content to assess organ iron deposition and therapy efficacy. Skin iron content can be
used for a better management of patients with iron overload pathologies. 相似文献
213.
This work reports the modification of thermoplastic polyurethanes (TPUs) in order to enlarge their application range, for example, as biomaterials by increasing its hydrophilicity.A TPU was successfully modified by using three different strategies: ultra-violet irradiation (UV), gamma irradiation (GI) and interfacial modification (IM). The results suggested the possibility of modifying the polyurethane-based surface either with poly(ethylene glycol) (PEG) or hydroxylethyl methacrylate (HEMA) or hexamethylene diamine (HMD) or chitosan (CT) by using any of these methods. The properties of the grafted PU were evaluated by surface, structural and thermal analysis. The results suggest that, among the methods studied in this work, the modification by gamma irradiation (GI) seems to be the most promising, since this method gives high values of grafting yield and has the advantage of providing a clean modification, meaning that no initiator is needed. 相似文献
214.
215.
Berta Nogueiro Estevinho Amélia Ferraz Fernando Rocha Lúcia Santos Arminda Alves 《Journal of separation science》2009,32(18):3116-3125
The determination of glucose and other carbohydrates is the most widespread chemical analysis that is performed within the industries of food, beverage, forage, biomass, pulp and paper, pharmaceuticals among others. Besides that, sugar refineries need to control their products, by‐products and effluents, and furthermore, glucose in the sucrose refining process, is considered an impurity, which shall be controlled. Being HPLC the most currently instrumental technique used for glucose analysis, the evaporative light scattering detector (ELSD) offers advantages (sensitivity, possibility for operating in gradient mode) over the also used refractive index detector. In this work, an HPLC‐ELSD methodology was optimised and validated, aiming the estimate of the uncertainty associated with the results at low levels of concentration of glucose to be measured. Linearity of the response was obtained in the range of glucose concentrations from 20 to 300 mg/L, with an analysis time of 10 min. The global uncertainty was estimated accordingly to the bottom‐up approach used by Eurachem. It was 13% on average for concentrations from 100 to 300 mg/L. For lower concentrations, uncertainty increased significantly up to 30% in the vicinity of the LOD of the method. 相似文献
216.
Margareth da Silva Alves 《Indagationes Mathematicae》2009,20(2):285-327
We study the smoothness properties of solutions to the coupled system of equations of Korteweg—de Vries type. We show that the equations dispersive nature leads to a gain in regularity for the solution. In particular, if the initial data (u0, v0 possesses certain regularity and sufficient decay as x → ∞, then the solution (u(t). v(t)) will be smoother than (u0, v0) for 0 < t ≤ T where T is the existence time of the solution. 相似文献
217.
Claudianor O. Alves Marcelo Montenegro 《Journal of Mathematical Analysis and Applications》2009,352(1):112-119
We show the existence of positive solution for the following class of singular Neumann problem in BR with ∂u/∂ν=0 on ∂BR, where R>0, λ>0 is a positive parameter, β>0, p∈[0,1), BR=BR(0)⊂RN, and are radially symmetric nonnegative C1 functions. Using variational methods and sub- and supersolutions, we obtain a solution for an approximated problem involving mixed boundary conditions. The limit of the approximated solutions, is a positive solution. 相似文献
218.
Ricardo J. G. B. Campello Eduardo R. Hruschka Vinícius S. Alves 《Journal of Heuristics》2009,15(1):43-75
This paper tackles the problem of showing that evolutionary algorithms for fuzzy clustering can be more efficient than systematic
(i.e. repetitive) approaches when the number of clusters in a data set is unknown. To do so, a fuzzy version of an Evolutionary
Algorithm for Clustering (EAC) is introduced. A fuzzy cluster validity criterion and a fuzzy local search algorithm are used
instead of their hard counterparts employed by EAC. Theoretical complexity analyses for both the systematic and evolutionary
algorithms under interest are provided. Examples with computational experiments and statistical analyses are also presented. 相似文献
219.
Automated microcolumn-switching system for drug analysis by direct injection of human plasma 总被引:1,自引:0,他引:1
Neto AJ Rodrigues JC Fernandes C Titato GM Alves C Lanças FM 《Journal of chromatography. A》2006,1105(1-2):71-76
This study presents the application of a system that joins the known advantages of capillary liquid chromatography (e.g., higher concentration of the analytes and lower consumption of mobile phase) with those of column-switching using restricted access material (RAM) (sample clean up and extraction) to the analysis of fluoxetine in plasma samples. Automatically, the system loads the biological sample, while a RAM-BSA-C18 column (50 mm x 520 microm) excludes the macromolecules and focuses the analytes; afterwards, a second mobile phase elutes the analytes, in backflush mode, and provides the separation in a C18 analytical column (100 mm x 520 microm). We optimized the procedure for a total analysis time of 25 min. Using this approach the calibration curve shows r=0.998 with a linearity range from 20 to 500 ng ml(-1). Precision, calculated as relative standard deviation (RSD), was<20%. The developed miniaturized system showed to be adequate and attractive, demonstrating a large potential for sample preparation. 相似文献
220.
Oliveira EC Vaz de Campos MC Rodrigues MR Pérez VF Melecchi MI Vale MG Zini CA Caramão EB 《Journal of chromatography. A》2006,1113(1-2):186-190
The present work describes (a) the identification and characterization of an impurity, 2,4,5,7-tetrabromo-6-hydroxy-9-(2,3,4,5-tetrachlorophenyl)-3H-xanthen-3-one (BCPX), in the color additives D&C Red Nos. 27 and 28 (phloxine B) and (b) the determination of the extent and level of BCPX contamination in certified lots of these colors. For these purposes, BCPX (a compound not previously reported in the literature) was synthetically prepared. Test portions from 42 certified lots of D&C Red Nos. 27, 28 and 27 lakes were analyzed for BCPX using an HPLC method that included gradient elution and UV-vis photodiode array detection. Those lots were submitted for certification by both domestic (six) and foreign (six) manufacturers during the past 4 years. Of the test portions analyzed, 32 (76.2%) contained BCPX in amounts ranging from 0.01 to 3.21%. The remaining 10 test portions (23.8%) contained no detectable BCPX or less than 0.008%, which is the limit of quantification for the present method. The analyses revealed substantial differences in the level of BCPX across different manufacturers. The wide range of BCPX levels found in the analyzed lots suggests that the presence of BCPX in D&C Red Nos. 27 and 28 may be avoided or significantly reduced during the manufacturing process. 相似文献