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281.
Camila Maione Christian Turra Elisabete A. De Nadai Fernandes Márcio Arruda Bacchi Fernando Barbosa Jr 《Analytical letters》2017,50(14):2292-2307
Brazil is the world’s largest producer of oranges. The Brazilian conventional citrus crop requires repeated application of agrochemicals to achieve satisfactory levels of productivity. The organic citriculture is an alternative production system, which is environmentally friendly and offers a safe food to consumers. However, it is difficult to determine if a food or plant was cultivated in organic or conventional system by just common observation, which makes the customers of organic food market vulnerable against fraudulent entrepreneurs. In this study, we present a data mining approach for the study of Brazilian organic citrus leaves which can aid in the certification of authenticity of the citrus leaves. The elemental composition is determined by inductively coupled plasma-mass spectrometry (ICP-MS). We developed classification models based on support vector machines and artificial neural networks capable of predicting whether a citrus leaf is organic or conventional through analysis of the concentration levels of the 14 chemical elements (Al, Ba, Co, Cr, Cs, Cu, Fe, Mg, Mn, Ni, Rb, Si, Sr, and V) found in both types of leaves. Feature selection filter methods are used to determine the most relevant elements for the classification process. Our best model obtained was a support vector machine with approximately 88% prediction accuracy. The elements Mn, Mg, and Rb were evaluated as the most significant for the classification decision. This is the first paper which addresses the problem of classification of organic orange leaves based on chemical composition. The presented methodology is useful for attesting authenticity of organic citrus leaves and can be adapted for other organic food or substances. 相似文献
282.
283.
Goreti Pereira Elisabete M.S. Castanheira Peter Schellenberg M. Belsley Paula M.T. Ferreira Luís S. Monteiro 《Tetrahedron》2013
Two new pyrenylamino acid derivatives were synthesized from β-bromodehydroalanine derivatives in good yields using addition and elimination reactions. 相似文献
284.
Eliana Alves Nuno Santos Tânia Melo Elisabete Maciel M. Luísa Dória Maria A. F. Faustino João P. C. Tomé Maria G. P. M. S. Neves José A. S. Cavaleiro Ângela Cunha Luisa A. Helguero Pedro Domingues Adelaide Almeida M. Rosário M. Domingues 《Rapid communications in mass spectrometry : RCM》2013,27(23):2717-2728
285.
Patricia Bogalhos Lucente Fregolente Gláucia Maria F. Pinto Maria Regina Wolf-Maciel Rubens Maciel Filho 《Applied biochemistry and biotechnology》2010,160(7):1879-1887
Distilled glycerides are obtained through distillation of the system mono-diglycerides which is produced from the esterification
reaction between a triglyceride with glycerol. In this work, monoglycerides (MG) and diglycerides (DG) are produced through
lipase-catalyzed glycerolysis of soybean oil using Candida antarctica B in a solvent-free system. To separate the products of the reaction in order to obtain essentially MG and an oil of DG,
it is necessary to use a suitable process in order to preserve the stability of the components and to keep the products free
of inappropriate solvents. So, after 24 h of enzymatic reaction, the mixture of acylglycerols and fatty acids was distilled
into a centrifugal molecular distiller, since it provides a free solvent and lower temperature environment to increase the
desired product concentration. Starting from a material with 25.06% of triglycerides (TG), 46.63% of DG, 21.72% of MG, 5.38%
of free fatty acids (FFA), and 1.21% of glycerol, the MG purity in the distillate stream was 80% at evaporator temperature
(T
E) equal to 250 °C and feed flow rate (Q) equal to 10.0 mL/min. At these conditions, the MG recovery was 35%. The material collected in the residue stream presented
DG-enriched oil with TG unhydrolyzed, residual MG, and low acidity (29.83% of TG, 53.20% of DG, 15.64% of MG, and 1.33% of
FFA), which is suitable to replace TG oil in the human diet. 相似文献
286.
Ulisses Barres de Almeida Elisabete M. de Gouveia Dal Pino 《Brazilian Journal of Physics》2013,43(5-6):328-340
Gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. Cherenkov Telescope Array (CTA) is an international initiative to build the next-generation ground-based gamma-ray observatory which will have a factor of 5–10 improvement in sensitivity in the 100-GeV–10-TeV range and an extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the Northern and another in the Southern Hemisphere) for full sky coverage and will be operated as an open observatory. It will provide a deep insight into the non-thermal high-energy Universe. In this talk, we will briefly present the major design concepts of CTA as well as its vast science case. 相似文献
287.
Alberto dos Santos Pereira Angelo C. Pinto Jari Nobrega Cardoso Francisco Radler de Aquino Neto Mnica Freiman de Souza Ramos Gisela M. Dellamora-Ortiz Elisabete Pereira dos Santos 《Journal of separation science》1998,21(7):396-400
The underivatized acetone and hexane fractions from propolis samples (predominant flora Citrus spp. and Vernonia polyanthes) were analyzed by HT-HRGC (high temperature high resolution gas chromatography) and HT-HRGC coupled to mass spectrometry (HT-HRGC-MS). Several compounds, including flavonoid aglycones, phenolic acids, and high molecular weight compounds were characterized in crude extracts by HT-HRGC-MS. HT-HRGC and HT-HRGC-MS were shown to be quick and informative tools for rapid analysis of crude extracts without need for prior derivatization and purification. 相似文献
288.
R. M. Castro G. A. Cirino P. Verdonck H. S. Maciel M. Massi M. B. Pisani R. D. Mansano 《等离子体物理论文集》1999,39(3):235-246
In this study, the plasma density and electron temperature of Radio Frequency (RF) plasmas were determined by three types of Langmuir probes, namely a conventional double probe, a single probe with RF choke and a single probe with RF choke and compensating electrode. The same plasmas were characterized by the three probes, each performing three measurements per plasma condition, in order to determine the precision of the measurement results. After performing a comparative analysis, which looked at the precision and the accuracy of these results, the conclusion is that the double probe, which has already the advantage of the simplest construction, yields the most reliable results for both capacitively and inductively coupled RF plasmas. The single probe with RF choke and compensating electrode has a similar precision as the single probe without compensating electrode, but its accuracy is better. 相似文献
289.
Chitosan/carboxymethyl cashew gum polyelectrolyte complexes were synthesized using different proportions of chitosan (CH) and carboxymethyl cashew gum (CMCG). The optimum CH:CMCG ratio was 25:75, which produced highest product yield. Polyelectrolyte (PEC) samples were characterized by thermogravimetric analysis and FT-IR spectroscopy. Parameters such as initial and maximal degradation temperatures and activation energy (Ea) were determined. Activation energies follows the order CMCG > CH > PECs samples. Infrared analysis from residual products after heating at 280 °C in different times indicated that cleavage of the glycosidic bond and formation of unsaturated products occurred. 相似文献
290.
Several new methyl 3-arylindole-2-carboxylates were synthesized in high yields using a metal assisted [Pd(OAc)2/Cu(OAc)2, DMF, 130 °C] intramolecular C-N cyclization of β,β-diaryldehydroamino acids, developed by us, thus extending the scope of this reaction. The latter were obtained by a bis-Suzuki coupling of a β,β-dibromodehydroalanine with arylboronic acids bearing either electron-donating groups (EDGs) or electron-withdrawing groups (EWGs). We were able to establish general conditions for this coupling reaction [PdCl2dppf·CH2Cl2 1:1 (20 mol %), boronic acid (5 equiv), Cs2CO3 (1.4 equiv), THF/H2O 1:1, 80 °C]. This strategy constitutes a novel, general and unprecedented approach to the synthesis of 3-arylindole-2-carboxylates. The fluorescence of the differently substituted indoles prepared was studied in several polar and non-polar solvents. In general the new indoles exhibit a solvent sensitive emission. The indoles with EDGs (OCH3 and SCH3) have reasonable fluorescence quantum yields in all solvents except in water. The indole with the cyano groups shows high fluorescent quantum yields in all solvents studied, despite the lower solvent sensitivity of its emission. The indole with the acetyl groups only exhibits reasonable fluorescence quantum yields in protic solvents. These studies show that the new 3-arylindole-2-carboxylates are good candidates to be used as fluorescent probes. 相似文献