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271.
N.C.A. de Sousa M.T. de Araujo C. Jacinto M.V.D. Vermelho N.O. Dantas C.C. Santos I. Guedes 《Journal of solid state chemistry》2011,184(11):3062-3065
Optical and vibrational studies have been carried out on 60B2O3·(20−x)Na2O·10PbO·10Al2O3:xTiO2 (x=0, 1, 2, 3, 4, and 5 mol%) glasses, in order to understand the role of TiO2 in the 60B2O3·20Na2O·10PbO·10Al2O3 glass matrix. The X-ray patterns reveal homogeneous glasses over the entire compositional range. The absorption spectra show that the energy of the optical band gap (ΔEopt) and Urbach's energy (EU) decreases as TiO2 content increases. The changes observed in the Raman and IR spectra are related to the BO4→BO3 back conversion effect and the appearance of “loose” BO4− groups. The data indicate that titanium ions act as a network modifier. 相似文献
272.
273.
274.
Córdova-Fraga T de Araujo DB Sanchez TA Elias J Carneiro AA Brandt-Oliveira R Sosa M Baffa O 《Magnetic resonance imaging》2004,22(3):389-393
Using contrast agents is a common practice in medical imaging protocols. Paramagnetic properties of certain compounds present in contrast agents can affect magnetic resonance imaging (MRI) signals. For abdominal applications, they are usually injected, but may also be administered orally. However, their use as a routine technique is limited, mainly due to the lack of appropriate oral contrast agents. We herein present the preliminary characterization and results for implementation of Euterpe Olerácea (popularly named A?aí) as a possible clinical oral contrast agent for MRI of the gastrointestinal tract. The pulp of A?aí, a fruit from the Amazon area, presented an increase in T(1)-weighted MRI signal, equivalent to that of gadolinium-diethyltriamine pentaacetic acid, and a decrease in T(2)-weighted images. We looked for intrinsic properties that could be responsible for the T(1) signal enhancement and T(2) opacification. Atomic absorption spectra revealed the presence of Fe, Mn and Cu ions in A?ai. The presence of such ions contribute to the susceptometric value found of chi = -4.83 x 10(-6). This finding assents with the hypothesis that image contrast changes were due to the presence of paramagnetic material. The first measurements in vivo demonstrate a clear increase of contrast, in T(1)-weighted images, due to the presence of A?aí. Consistently, the opacification in a T(2)-weighted acquisition was evident, revealing a good contrast on bowel walls of gastric tissues. 相似文献
275.
Carolina Araujo 《Mathematische Zeitschrift》2010,264(1):179-193
In these notes, we investigate the cone of nef curves of projective varieties, which is the dual cone to the cone of pseudo-effective
divisors. We prove a structure theorem for the cone of nef curves of projective
\mathbb Q{\mathbb Q}-factorial klt pairs of arbitrary dimension from the point of view of the Minimal Model Program. This is a generalization
of Batyrev’s structure theorem for the cone of nef curves of projective terminal threefolds. 相似文献
276.
A.P. Brasil Jr. J.H. Carneiro de Araujo V. Ruas 《Journal of Computational and Applied Mathematics》2008
A three-field finite element scheme designed for solving time-dependent systems of partial differential equations governing viscoelastic flows is introduced. The linearized form of this system is a generalized time-dependent Stokes system. Once a classical time-discretization is performed, the resulting three-field system of equations allows for a stable approximation of velocity, pressure and extra stress tensor, by means of continuous piecewise linear finite elements, in both two and three dimension space. Another advantage of the new formulation is the fact that it implicitly provides an algorithm for the iterative resolution of system non-linearities, in the case of viscoelastic flows. Additionally, convergence in an appropriate sense applying to these three flow fields is demonstrated, for such generalized Stokes system. Numerical results are given in order to illustrate the performance of the new approach. 相似文献
277.
Pedro Araujo Thu-Thao Nguyen Livar Frøyland 《Journal of the American Society for Mass Spectrometry》2005,16(5):801-801
The article presents a comprehensive account of the application of chemometric approaches to determine the factors that influence the tri-α-linolenoylglycerol (TALG) ammoniated adduct signal m/z 890.6 in an ion-trap mass spectrometer coupled to a liquid chromatograph and the estimation of different sources of errors involved in TALG calibration experiments. It was found that by using experimental design, the influence of the nebulizer pressure on the analytical signal is less pronounced than the influence of the drying gas flow and the chromatographic flow rate. The results revealed that without using tandem mass or atmospheric pressure chemical ionization, it is possible to fragment the TALG backbone and obtain the free α-linolenic acid by varying the drying gas flow and using an electrospray interface. The error decomposition approach revealed that the preparation error was 26 times higher than the instrumental error. 相似文献
278.
We prove that a biseparating map between spaces B(E), and some other Banach algebras, is automatically continuous and a multiple of an algebra isomorphism. 相似文献
279.
J.P. Garayt J.M. Grard F. Enjalbert L. Ferlazzo S. Founta E. Martinez-Guerrero F. Rol D. Araujo R. Cox B. Daudin B. Gayral Le Si Dang H. Mariette 《Physica E: Low-dimensional Systems and Nanostructures》2005,26(1-4):203
We report single dot spectroscopy of cubic GaN/AlN self-assembled quantum dots. Typical linewidths of the zero-phonon line between 2 and 8 meV are observed and interpreted in terms of charge fluctuations around a given quantum dot. The phonon sideband contribution in this emission, even at low temperature, reveals the importance of the acoustic phonon broadening mechanism which controls the exciton dephasing and may impose the real limits to the optical properties of GaN single QDs emission. 相似文献
280.
Alan Leone de Araujo Oliveira Mônica de Abreu Silva Fernando Pirani Luiz Guilherme Machado de Macedo Ricardo Gargano 《International journal of quantum chemistry》2020,120(16):e26266
In this work, some basic features of the intermolecular bond in gas phase H2S-Ng complexes (Ng = He, Ne, Ar, Kr, Xe, and Rn) have been investigated in detail, coupling information from scattering experiments with results of quantum chemical calculations at the CCSD(T)/aug-cc-pVTZ level. Spectroscopic constants, rotovibrational energies, and lifetime as a function of temperature have been evaluated for the complete family of H2S-Ng systems, and an extensive study of involved intermolecular interactions has been performed. In particular, their nature has been characterized by exploiting Atoms-In-Molecules (AIM), Non-Covalent Interactions (NCI), Symmetry-Adapted Perturbation Theory (SAPT), and Charge Displacement (CD) methods, and it was found that all complexes are bound essentially by near-isotropic van der Waals forces, perturbed by weak-stabilizing charge (electron) transfer contributions. Obtained results also show that these additional contributions increase from He up to Rn, providing an appreciable chemical-stabilizing effect of the noncovalent intermolecular bond for H2S-heavier Ng systems. 相似文献