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611.
Jose V. Silveira Luciana L. Vieira Josue Mendes Filho Antonio J. C. Sampaio Oswaldo L. Alves Antonio G. Souza Filho 《Journal of Raman spectroscopy : JRS》2012,43(10):1407-1412
This paper reports a study of vibrational, structural and morphological properties of molybdenum oxide nanoribbons. Temperature‐dependent Raman spectroscopy measurements in MoO3 nanoribbons revealed morphological changes in the 150–350 °C temperature range. No structural phase transitions were observed, thus showing that the orthorhombic phase is stable from room temperature (nanoribbons) up to 650 °C (bulk‐like phase) where large plates have been formed by the coalescence of the nanoribbons. The interpretation of temperature‐dependent Raman data (wavenumber and linewidths) is supported by scanning electron microscopy that is used to directly probe the morphological changes in MoO3 samples. The observed phenomena in the Raman data for MoO3 nanoribbons can be applied to other nanomaterials. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
612.
A. Canizars G. Guimbretire Y. A. Tobon N. Raimboux R. Omne M. Perdicakis B. Muzeau E. Leoni M. S. Alam E. Mendes D. Simon G. Matzen C. Corbel M. F. Barthe P. Simon 《Journal of Raman spectroscopy : JRS》2012,43(10):1492-1497
In situ Raman scattering studies allow following real‐time evolutions of volume or surface structures under extreme conditions. In nuclear materials sciences, ion irradiation‐induced atomic organization modification and water radiolysis are of a major interest. In order to better understand these phenomena, we have developed an in situ versatile portable Raman spectroscopy system coupled with a cyclotron accelerator, allowing monitoring of a solid/liquid interface under irradiation and thus giving access to effects of radiolysis. The different parts of the system and their improvements are described in details. The system efficiency is highlighted by a comparative study of the time dependence of UO2 surface modification induced, on one hand by contact with water under irradiation by 5 MeV He2+ particles, and on the other hand by pure chemical alteration, through contact with a hydrogen peroxide solution. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
613.
E.M.C. Abreu J. Ananias Neto A.C.R. Mendes C. Neves W. Oliveira 《Annalen der Physik》2012,524(8):434-455
The concept of gauge invariance is one of the most subtle and useful concepts in modern theoretical physics. It is one of the Standard Model cornerstones. The main benefit due to the gauge invariance is that it can permit the comprehension of difficult systems in physics with an arbitrary choice of a reference frame at every instant of time. It is the objective of this work to show a path of obtaining gauge invariant theories from non‐invariant ones. Both are named also as first‐ and second‐class theories respectively, obeying Dirac's formalism. Namely, it is very important to understand why it is always desirable to have a bridge between gauge invariant and non‐invariant theories. Once established, this kind of mapping between first‐class (gauge invariant) and second‐class systems, in Dirac's formalism can be considered as a sort of equivalence. This work describe this kind of equivalence obtaining a gauge invariant theory starting with a non‐invariant one using the symplectic embedding formalism developed by some of us some years back. To illustrate the procedure it was analyzed both Abelian and non‐Abelian theories. It was demonstrated that this method is more convenient than others. For example, it was shown exactly that this embedding method used here does not require any special modification to handle with non‐Abelian systems. 相似文献
614.
615.
Paulo G. Mendes Mario L. Moreira Sergio M. Tebcherani Marcelo O. Orlandi J. Andrés Maximu S. Li Nora Diaz-Mora José A. Varela Elson Longo 《Journal of nanoparticle research》2012,14(3):750
The exploration of novel synthetic methodologies that control both size and shape of functional nanostructure opens new avenues
for the functional application of nanomaterials. Here, we report a new and versatile approach to synthesize SnO2 nanocrystals (rutile-type structure) using microwave-assisted hydrothermal method. Broad peaks in the X-ray diffraction spectra
indicate the nanosized nature of the samples which were indexed as a pure cassiterite tetragonal phase. Chemically and physically
adsorbed water was estimated by TGA data and FT-Raman spectra to account for a new broad peak around 560 cm−1 which is related to defective surface modes. In addition, the spherical-like morphology and low dispersed distribution size
around 3–5 nm were investigated by HR-TEM and FE-SEM microscopies. Room temperature PL emission presents two broad bands at
438 and 764 nm, indicating the existence of different recombination centers. When the size of the nanospheres decreases, the
relative intensity of 513 nm emission increases and the 393 nm one decreases. UV–Visible spectra show substantial changes
in the optical absorbance of crystalline SnO2 nanoparticles while the existence of a small tail points out the presence of localized levels inside the forbidden band gap
and supplies the necessary condition for the PL emission. 相似文献
616.
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
617.
618.
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