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排序方式: 共有117条查询结果,搜索用时 15 毫秒
71.
72.
Lima Aline E. B. Assis Marcelo Resende Andressa L. S. Santos Hugo L. S. Mascaro Lúcia H. Longo Elson Santos Reginaldo S. Cavalcante Laécio S. Luz Geraldo E. 《Journal of Solid State Electrochemistry》2022,26(4):997-1011
Journal of Solid State Electrochemistry - In this paper, we report the synthesis of CuWO4, MnWO4, and FTO|CuWO4|MnWO4 as type II heterojunction thin film prepared by the drop-casting method. These... 相似文献
73.
J Merle Elson 《Waves in Random and Complex Media》2013,23(3):303-317
Abstract Using a first-order vector perturbation theory, we calculate some scattering characteristics of surfaces which have both surface roughness and subsurface permittivity variations. These variations are treated as random variables where the roughness yields phase perturbations and the permittivity variations yield reflectance perturbations. Numerical results are given for both types of scattering. 相似文献
74.
Phthalides are frequently found in naturally occurring substances and exhibit a broad spectrum of biological activities. In the search for compounds with insecticidal activity, phthalides have been used as versatile building blocks for the syntheses of novel potential agrochemicals. In our work, the Diels–Alder reaction between furan‐2(5H)‐one and cyclopentadiene was used successfully to obtain (3aR,4S,7R,7aS)‐3a,4,7,7a‐tetrahydro‐4,7‐methanoisobenzofuran‐1(3H)‐one and (3aS,4R,7S,7aR)‐3a,4,7,7a‐tetrahydro‐4,7‐methanoisobenzofuran‐1(3H)‐one ( 2 ) and (3aS,4S,7R,7aR)‐3a,4,7,7a‐tetrahydro‐4,7‐methanoisobenzofuran‐1(3H)‐one and (3aR,4R,7S,7aS)‐3a,4,7,7a‐tetrahydro‐4,7‐methanoisobenzofuran‐1(3H)‐one ( 3 ). The endo adduct ( 2 ) was brominated to afford (3aR,4R,5R,7R,7aS,8R)‐5,8‐dibromohexahydro‐4,7‐methanoisobenzofuran‐1(3H)‐one and (3aS,4S,5S,7S,7aR,8S)‐5,8‐dibromohexahydro‐4,7‐methanoisobenzofuran‐1(3H)‐one ( 4 ) and (3aS,4R,5R,6S,7S,7aR)‐5,6‐dibromohexahydro‐4,7‐methanoisobenzofuran‐1(3H)‐one and (3aR,4S,5S,6R,7R,7aS)‐5,6‐dibromohexahydro‐4,7‐methanoisobenzofuran‐1(3H)‐one ( 5 ). Following the initial analysis of the NMR spectra and the proposed two novel unforeseen products, we have decided to fully analyze the classical and non‐classical assay structures with the aid of computational calculations. Computation to predict the 13C and 1H chemical shifts for mean absolute error analyses have been carried out by gauge‐including atomic orbital method at M06‐2X/6‐31+G(d,p) and B3LYP/6‐311+G(2d,p) levels of theory for all viable conformers. Characterization of the novel unforeseen compounds ( 4 ) and ( 5 ) were not possible by employing only the experimental NMR data; however, a more conclusive structural identification was performed by comparing the experimental and theoretical 1H and 13C chemical shifts by mean absolute error and DP4 probability analyses. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
75.
Structural elucidation of dioxa‐cage compounds from tetrahydroisobenzofuran‐1(3H)‐one: analysis of NMR data and GIAO chemical shifts calculations 下载免费PDF全文
Gabriela da Costa Resende Elson Santiago Alvarenga 《Magnetic resonance in chemistry : MRC》2016,54(12):968-974
The polycyclic compounds, especially the dioxa‐cages, have attracted considerable attention in recent years. In our work, a series of 9β‐substituted 3‐oxo‐4,11‐dioxatetracyclo[5.2.1.15,8.02,6]undecane compounds were unexpectedly isolated during bromination, chlorination and epoxidation reactions of the 3‐hydroxy‐3a,4,7,7a‐tetrahydro‐4,7‐methanoisobenzofuran‐1(3H)‐one. After careful analysis of the NMR data, the chemical shifts of the isolated and the expected products were predicted by theoretical calculations using density functional theory and gauge including atomic orbitals. The best correlation between calculated and experimental data was evaluated by comparing mean absolute errors and applying DP4 probability methodology. Results from both approaches indicated a correct structural elucidation. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
76.
Juliana Villela Maciel Elson Luiz Fava Tiago Almeida Silva Daiane Dias Orlando Fatibello-Filho 《Journal of Solid State Electrochemistry》2017,21(10):2859-2868
New progress in the application of voltammetry of immobilized microparticles (VIM) technique in electroanalytical chemistry is reported in this work through the determination of hydroquinone in dermatologic cream samples. The designed electrode was based on a glassy carbon electrode modified with a crosslinked chitosan film containing immobilized carbon black nanoparticles and hydroquinone standards or sample. The electrochemical features of immobilized hydroquinone were explored, which a fast electron transfer kinetic was verified from the perfect reversible redox behavior of this molecule. All the experimental conditions were optimized, including supporting electrolyte condition (composition, pH, and ionic strength) and technical parameters of differential pulse voltammetry (DPV). Under the optimized experimental conditions, the analytical curve was linear by a wide concentration range from 2.7 to 43 ng, with detection and quantification limits of 0.045 and 0.15 ng, respectively. Two commercial dermatologic cream samples were successfully immobilized and analyzed using the proposed VIM procedure, and the results were similar to those recorded by a spectrophotometric comparative procedure. Our set of results represents a unique and exciting advance in the scenario of electroanalytical chemistry for future applications. 相似文献
77.
Maria F. C. Gurgel Mário L. Moreira Elaine C. Paris José W. M. Espinosa Paulo S. Pizani José A. Varela Elson Longo 《International journal of quantum chemistry》2011,111(3):694-701
This article reports a theoretical study based on experimental results for barium zirconate, BaZrO3 (BZ) thin films, using periodic mechanic quantum calculations to analyze the symmetry change in a structural order‐disorder simulation. Four periodic models were simulated using CRYSTAL98 code to represent the ordered and disordered BZ structures. The results were analyzed in terms of the energy level diagrams and atomic orbital distributions to explain and understand the BZ photoluminescence properties (PL) at room temperature for the disordered structure based on structural deformation and symmetry changes. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 相似文献
78.
Ieda L. V. Rosa Larissa H. Oliveira Elson Longo José A. Varela 《Journal of fluorescence》2011,21(3):975-981
In this work, a SiO2 spherical were prepared by the Stöber Method and then recovered with a single layer of Eu2O3 oxide (SiO2@Eu2O3) obtained by the Polymeric Precursor Method. The SiO2@Eu2O3 powder was heated treated at 100, 300, 400, 500 and 800 °C. The samples were characterized by the Scanning Electonic Microscopy (SEM), Thermal Analysis (TGA/DTA), and the luminescent properties of the SiO2@Eu2O3 powders were studied by their emission and excitation spectra as well as by the lifetime measurements of the Eu3+ 5D0?→?7F2 transition. The SEM analysis shows that the silica prepared by the Stöber Method is spherical with a particle size of 460 nm. The emission spectra of the SiO2@Eu2O3 powders presented the Eu3+ characteristics bands related to the 5D0?→?7FJ (J?=?0, 1, 2, 3, 4) transitions at 577, 591, 616, 649 and 695 nm, respectively. The band related to the 5D0?→?7F2 transition is the most intense in the spectra, and its intensity decreases with the temperature enhancement. The decay curves of the SiO2@Eu2O3 samples presented monoexponential features, and the obtained lifetime values were higher than the Eu2O3 oxide. It was possible to conclude that the 5D0?→?7F2 hypersensitive transition is strongly dependent on the Eu3+ surrounding. 相似文献
79.
de Moura AP de Oliveira LH Paris EC Li MS Andrés J Varela JA Longo E Rosa IL 《Journal of fluorescence》2011,21(4):1431-1438
Nanorods and nanoplates of Y2O3:Eu3+ powders were synthesized through the thermal decomposition of the Y(OH)3 precursors using a microwave-hydrothermal method in a very short reaction time. These powders were analyzed by X-ray diffraction,
field emission scanning electron microscopy, Fourrier transform Raman, as well as photoluminescence measurements. Based on
these results, these materials presented nanoplates and nanorods morphologies. The broad emission band between 300 and 440 nm
ascribed to the photoluminescence of Y2O3 matrix shifts as the procedure used in the microwave-hydrothermal assisted method changes in the Y2O3:Eu3+ samples. The presence of Eu3+ and the hydrothermal treatment time are responsible for the band shifts in Y2O3:Eu3+ powders, since in the pure Y2O3 matrix this behavior was not observed. Y2O3:Eu3+ powders also show the characteristic Eu3+ emission lines at 580, 591, 610, 651 and 695 nm, when excited at 393 nm. The most intense band at 610 nm is responsible for
the Eu3+ red emission in these materials, and the Eu3+ lifetime for this transition presented a slight increase as the time used in the microwave-hydrothermal assisted method increases. 相似文献
80.
Emmanuelle Orhan Fenelon M. Pontes Tania M. Boschi Paulo S. Pizani Juan Andrés Elson Longo 《Journal of solid state chemistry》2004,177(11):3879-3885
A joint experimental and theoretical study has been carried out to rationalize the photoluminescence properties of SrTiO3 perovskite thin films synthesized through a soft chemical processing. Only the amorphous samples present photoluminescence at room temperature. From the theoretical side, first principles quantum mechanical techniques, based on density functional theory at B3LYP level, have been employed to study the electronic structure of a crystalline (ST-c) and an asymmetric (ST-a) model. Electronic properties are analyzed in the light of the experimental results and their relevance in relation to the PL behavior of ST is discussed. 相似文献