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排序方式: 共有176条查询结果,搜索用时 15 毫秒
71.
72.
Anderson Dias Kisla P. F. Siqueira Roberto L. Moreira 《Journal of Raman spectroscopy : JRS》2010,41(1):93-97
This work investigates the crystal structures and phonon modes of Ba(Ca1/2W1/2)O3, Ba(Ca1/2Mo1/2)O3 and Ba(Sr1/2W1/2)O3 perovskites by Raman spectroscopy. The samples were produced by conventional solid‐state processing at 1200 °C. X‐ray diffraction showed that single‐phase homogeneous materials were produced, which are cubic or pseudo‐cubic in symmetry. The existing controversies in the literature for these complex perovskites were investigated by comparing experimental Raman data with group‐theory analysis. Ceramics with Ca and W or Mo were found to be cubic, space group Fm3 m. For these materials, four Raman‐active bands were observed and the fitting parameters showed that the Ba(Ca1/2Mo1/2)O3 ceramic presents bands at lower wavenumbers if compared with the Ba(Ca1/2W1/2)O3 sample. For the Ba(Sr1/2W1/2)O3 material, two hypotheses were investigated for monoclinic or triclinic structures. The experimental results showed 12 Raman‐active modes for this ceramic, which is in perfect agreement with the theoretical predictions for a monoclinic (I2/m) structure. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
73.
74.
da Silveira Ana Claudia de Andrade de Siqueira Geisa Liandra Mayer Francieli Martins da Silveira Lazzarotto Simone Rosa Miguel Obdúlio Gomes Zini Cláudia Alcaraz de Queiroz Dalva Luiz Lazzarotto Marcelo 《Journal of Thermal Analysis and Calorimetry》2022,147(13):7363-7371
Journal of Thermal Analysis and Calorimetry - Eucalyptus spp. (Myrtaceae) is economically important worldwide and is native from Australia. Glycaspis brimblecombei (Hemiptera: Aphalaridae) is an... 相似文献
75.
Cunha Lucas H. P. Siqueira Ivan R. Campos Arthur A. R. Rosa Adriano P. Oliveira Taygoara F. 《Theoretical and Computational Fluid Dynamics》2020,34(1):119-132
Theoretical and Computational Fluid Dynamics - Thermomagnetic convection is based on the use of external magnetic fields to better control heat transfer fluxes in ferrofluids, finding important... 相似文献
76.
Microwave synthesis was used to produce nanosized transition-metal tungstates in environmentally friendly conditions not yet
reported by the literature: 110 and 150 °C, for times of 10 and 20 min. X-ray diffraction evidenced incipient crystallized
materials, while transmission electron microscopy indicates nanostructured regions of about 2–5 nm inside an amorphous matrix.
Raman spectroscopy was used to probe short-range ordering in the achieved samples and also to obtain a reliable set of spectra
containing all the Raman-active bands predicted by group-theory calculations. The vibrational spectra showed no extra feature,
indicating that the microwave processing was able to produce short-range ordered materials without tetrahedral distortions.
These distortions are frequently reported when commercially modified kitchen microwave units are employed. In this work, the
syntheses were conducted in a commercial apparatus especially designed for fully controlled temperature–time–pressure conditions. 相似文献
77.
Elaine F. da SilvaLeonardo J.A. Siqueira Wagner A. Alves 《Vibrational Spectroscopy》2011,55(2):273-278
Hydrogen bonding between pyridazine (PRD) and formamide (FA) molecules has been investigated both experimentally by Raman spectroscopy on their binary mixtures and theoretically by DFT calculations on various gas-phase PRD:FA clusters. The band at 1160 cm−1 of PRD was used for the first time as a marker for monitoring the degree of complexation. Upon dilution with FA, a new band at 1169 cm−1 is observed and attributed to hydrogen-bonded PRD. The Raman experiments were complemented by DFT calculations and the corresponding structures, vibrational spectra and binding energies were determined. The most stable species were found to be the 1:2 PRD:FA complexes and such stoichiometry is in excellent agreement with the experimental determination. The shift to higher frequency observed to the prominent modes of PRD may be related to a shortening of the NC and CC bonds, upon complexation, which causes a decrease in the electron delocalization in PRD ring. 相似文献
78.
Oxazolidine copper complexes: Synthesis,characterization and superoxide dismutase activity of copper(II) complexes with oxazolidine ligands derived from hydroxyquinoline carboxaldehyde 下载免费PDF全文
Joice Ceolin Josiéli Demetrio Siqueira Francisco Mainardi Martins Paulo C. Piquini Bernardo A. Iglesias Davi F. Back Gelson Manzoni de Oliveira 《应用有机金属化学》2018,32(4)
This work describes the synthesis of copper(II) complexes, their identification using spectroscopic and electrochemical methods, structural characterization with X‐ray diffraction and density functional theory calculations (DFT), as well as their catalytic activity mimicking that of superoxide dismutase. Structural analysis revealed the formation of complexes with cyclization of ligands L1 and L2 with the formation of a heterocycle, 1,3‐oxazolidine. The DFT calculations confirmed this trend by stabilizing with lower energy. In addition, evaluations of mimetic enzymatic activity of complexes C1, C2, C3 and C4 revealed promising IC50 values compared to other results seen in the literature (IC50 = 0.22, 0.328, 0.55 and 0.92). Also, calf thymus DNA interactive experiments using UV–visible spectroscopy were conducted in the presence of the copper(II) complexes. 相似文献
79.
J. P. Siqueira A. R. de Oliveira L. Misoguti S. C. Zilio 《Applied physics. B, Lasers and optics》2012,108(4):727-731
We report on the generation of tunable light around 400?nm by frequency-doubling ultrashort laser pulses whose spectral phase is modulated by a sum of sinusoidal functions. The linewidth of the ultraviolet band produced is narrower than 1?nm, in contrast to the 12?nm linewidth of the non-modulated incident spectrum. The influence of pixellation of the liquid crystal spatial light modulator on the efficiency of the phase-modulated second harmonic generation is discussed. 相似文献
80.
Particle Detachment Under Velocity Alternation During Suspension Transport in Porous Media 总被引:1,自引:0,他引:1
Pavel Bedrikovetsky Abbas Zeinijahromi Fernando D. Siqueira Claudio A. Furtado Antonio Luiz S. de Souza 《Transport in Porous Media》2012,91(1):173-197
Flow of suspensions in porous media with particle capture and detachment under alternate flow rates is discussed. The mathematical
model contains the maximum retention concentration function of flow velocity that governs the particle release and is used
instead of equation for particle detachment kinetics from the classical filtration model. An analytical model for suspension
injection with alternate rates was derived, and a coreflood by suspension with alternate rates was carried out. The modelling
and laboratory data are in a good agreement, which validates the modified particle detachment model with the maximum retention
function. 相似文献