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581.
I.T. Gomes B.G. Almeida A.M.L. Lopes J.P. Araújo J. Barbosa J.A. Mendes 《Journal of magnetism and magnetic materials》2010,322(9-12):1174-1177
La2/3Sr1/3MnO3?δ thin films were deposited by laser ablation on MgO substrates under low oxygen pressure cool down. Their structural and magnetic properties are presented. The magnetic and electrical resistivity measurements indicate a reduction of the Curie and the metal–insulator transition temperatures due to the formation of magnetic inhomogeneneous films, where clusters of a metallic phase are mixed in a magnetically disordered insulating matrix. By a low-angle X-ray reflectivity study we show that the thin films are chemically inhomogeneous with an oxygen deficiency in bulk of the film when compared with the film/air interfacial region. 相似文献
582.
J. A. Lima P. T. C. Freire F. E. A. Melo J. Mendes Filho G. P. De Sousa R. J. C. Lima P. F. Faanha Filho H. N. Bordallo 《Journal of Raman spectroscopy : JRS》2010,41(7):808-813
Raman spectra of DL ‐Alanine crystals were investigated in the 50–3200 cm−1 spectral region for temperatures ranging from 15 to 295 K. The crystalline structure of DL ‐Alanine represents a rare example of an amino acid racemate crystallizing in a non‐centrosymmetric space group. From this study, we have observed changes in the wavenumber of modes associated with both rocking of CO2− and skeletal vibrations. On the other hand, neither changes in the modes associated to CH or CH3 vibrations nor substantial modifications of the lattice modes of the crystal were observed. Such result indicates slight changes of the CO2 group orientation without observation of a solid–solid phase transition in the DL ‐Alanine crystal. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
583.
Davide Mendes Sofia Branco Maria Rosa Paiva Stefan Schütz Eduardo P. Mateus Marco Gomes da Silva 《Molecules (Basel, Switzerland)》2022,27(13)
Multidimensional gas chromatography is, presently, an established and powerful analytical tool, due to higher resolving power than the classical 1D chromatographic approaches. Applied to multiple areas, it allows to isolate, detect and identify a larger number of compounds present in complex matrices, even in trace amounts. Research was conducted to determine which compounds, emitted by host plants of the eucalyptus weevil, Gonipterus platensis, might mediate host selection behavior. The identification of a pheromone blend of G. platensis is presented, revealing to be more attractive to weevils of both sexes, than the individual compounds. The volatile organic compounds (VOCs) were collected by headspace solid phase microextraction (HS-SPME), MonoTrapTM disks, and simultaneous distillation-extraction (SDE). Combining one dimensional (1D) and two-dimensional (2D) chromatographic systems—comprehensive and heart-cut two-dimensional gas chromatography (GC×GC and H/C-MD-GC, respectively) with mass spectrometry (MS) and electroantennographic (EAD) detection, enabled the selection and identification of pertinent semiochemicals which were detected by the insect antennal olfactory system. The behavioral effect of a selected blend of compounds was assessed in a two-arm olfactometer with ten parallel walking chambers, coupled to video tracking and data analysis software. An active blend, composed by cis and trans-verbenol, verbenene, myrtenol and trans-pinocarveol was achieved. 相似文献
584.
585.
Nathalia L. Queiroz Carlos H. S. Mendes José A. M. Nascimento Maycom W. F. Silva José Eudes S. Oliveira Severino Carlos B. Oliveira 《Electroanalysis》2023,35(3):e202200249
The anodic behaviour of 1-methyl-tryptophan (1-mTrp) in aqueous electrolytes was investigated on a glassy carbon electrode (GCE), using voltammetric techniques. The oxidation of 1-mTrp was associated with an electrochemical-chemical (EC) mechanism: one electron and one proton were removed of C2 to form an intermediate radical, 1-mTrp⋅. This was followed by a two-way reaction, producing a 1-mTrp dimer and/or reaction with water to form a final hydroxylated product. The oxidation mechanism of 1-mTrp proposed was also compared with the anodic oxidation Trp on GCE. Differential pulse voltammetry was also explored for quantification of Trp and 1-mTrp in neutral medium with low detection limits, on an anodically pre-treated GCE. 相似文献