Long-range and short-range structures of cube-like shape SrTiO3 powders: microwave-assisted hydrothermal synthesis and photocatalytic activity

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Chemical characterization and bioactivity of epoxy resin and Portland cement-based sealers with niobium and zirconium oxide radiopacifiers

The purpose of this study was to characterize and to evaluate the bioactivity potential of experimental root canal sealers (ES) based on Portland cement, epoxy resin with nano- and micro-particles of niobium or zirconium oxide used as radiopacifiers in comparison to AH Plus and MTA Fillapex. Methods Specimens of the sealers (10 mm in diameter × 1 mm thick) were prepared and the radiopacity was evaluated according to ISO 6876 (2012) specifications. Characterization of the sealers was performed under the scanning electron microscope (SEM) immediately after setting and after immersion for 28 days in Hank's balanced salt solution (HBSS). In addition X-ray energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy were also performed. The pH and calcium ion release were measured after 1, 7, 14, 21 and 28 days after completion of seating using a digital pH meter and an atomic absorption spectrophotometer, respectively. Results The experimental sealers exhibited an average radiopacity of 2.5 mm thickness of aluminum, which was similar to MTA Fillapex (P > 0.05) and inferior to AH Plus (P < 0.05). AH Plus did not show bioactivity. Although the experimental sealers did not exhibit the formation of hydration product, they encouraged the deposition of crystalline spherical structures of calcium deficient phosphate. The highest pH and calcium release values were observed with the experimental sealers (P < 0.01). ES-Nb-micro was the only sealer to present hexagonal shaped crystal deposition. Significance Novel root canal sealers based on a mixture of Portland cement, epoxy resin and radiopacifier exhibited a degree of bioactivity although no evidence of cement hydration was demonstrated on material characterization. The radiopacifier particle size had limited effect on the sealer microstructure and chemical properties.

Ultrastructure and tube formation in Ceriantharia (Cnidaria, Anthozoa)

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Propriedades ópticas de nanopartículas de halogenetos de cobre preparadas in situ em filmes híbridos de sílica

The sol-gel process is a technique based on the hydrolysis and polycondensation of metal alkoxides have been investigated as an alternative for the preparation of vitreous or glassceramic materials, for allowing the obtaining of high-purity materials at low temperatures, and to obtain hybrid materials with different compositions. When ORMOSILs are doped with nanoparticles, are called nanocomposites, and its functionality arises when electrons confined in scale three-dimensional structures near zero are excited. In principle, such materials exhibit discrete energy level, with peaks in the absorption spectrum. Therefore, the glasses doped semiconductor nanocrystals are important candidates for the preparation of optical filters with sharp cut-off, and are being exploited commercially for coloring glasses. This study evaluates the optical properties presented by hybrid films of silica doped with copper nanoparticles. The matrix was prepared using the alkoxides 3-glycidoxypropyltrimethoxysilane (GPTS) and tetraethylorthosilicate (TEOS) doped with Cu2O and hydrolyzed under reflux conditions in two different acidic conditions (HCl and HBr). After thermal treatment at temperatures between 100 °C and 170 °C and/or under the action of commercial black light radiation, CuCl and CuBr present in the hybrid film are transformed into nanoparticles of CuCl or CuBr. The UV-VIS absorption identified the absorption bands, and its variation

Analisys of thermal efficiency of a modified solar collector type evacuated tube

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Síntese e caracterização de materiais semicondutores nanoestruturados luminescentes à base de ZnS

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Síntese, caracterização e aplicação de hidrogéis nanoestruturados contendo nanoargila para melhorar a germinação e qualidade de muda de hortaliça

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Lipidic and proteic absorption in digestive tract of tropical fat snook (Centropomus parallelus, POEY 1860)

The tropical fat snook Centropomus parallelus is a species of recognized ecological importance and with a high economical potential for fisheries and aquaculture. The investigations of digestive tube morphology in association with their feeding abilities are fundamental to improve techniques for aquaculture feeding procedures. Sudan black staining and Perl`s method were used to evaluate their absorption capacity of fat and protein respectively. The Sudan black stain was performed 12 h after the ingestion of lipids. The lipids are intensely absorbed in the ceca epithelium and less intensely in the intestine and rectum. The Perl`s method was performed 12 h after the ingestion of ferritin. The proteins are absorbed only in the rectum. This is the first description of fat and protein absorption ability by the digestive tube of fat snook. These data enhance the possibility of the addition of macromolecules in rations that can show a diversity of physiological effects. The histological implications of each segment of the digestive tube in association with fish biology are further discussed. (C) 2010 Elsevier B.V. All rights reserved.

Predicting the behaviour of structures under impact loads using geometrically distorted scaled models

When a scaled structure (model or replica) is used to predict the response of a full-size compound (prototype), the model geometric dimensions should relate to the corresponding prototype dimensions by a single scaling factor. However, owing to manufacturing technical restrictions, this condition cannot be accomplished for some of the dimensions in real structures. Accordingly, the distorted geometry will not comply with the overall geometric scaling factor, infringing the Pi theorem requirements for complete dynamic similarity. In the present study, a method which takes geometrical distortions into account is introduced, leading to a model similar to the prototype. As a means to infer the performance of this method, three analytical problems of structures subjected to dynamic loads are analysed. It is shown that the replica developed applying this technique is able to accurately predict the full-size structure behaviour even when the studied models have some of their dimensions severely distorted. (C) 2012 Elsevier Ltd. All rights reserved.

Temperature Effect on the Two-Photon Absorption Spectrum of All-trans-beta-carotene

In this report, we investigate the influence of temperature on the two-photon absorption (2PA) spectrum of all-trans-beta-carotene using the femtosecond white-light-continuum Z-scan technique. We observed that the 2PA cross-section decreases quadratically with the temperature. Such effect was modeled using a three-energy-level diagram within the sum-over-essential states approach, assuming temperature dependencies to the transition dipole moment and refractive index of the solvent. The results show that the transition dipole moments from ground to excited state and between the excited states, which governed the two-photon matrix element, have distinct behaviors with the temperature. The first one presents a quadratic dependence, while the second exhibits a linear dependence. Such effects were attributed mainly to the trans -> cis thermal interconversion process, which decreases the effective conjugation length, contributing to diminishing the transition dipole moments and, consequently, the 2PA cross-section.

Analysis, manufacture and characterization of Ni/Cu functionally graded structures

In this work, an experimental and numerical analysis and characterization of functionally graded structures (FGSs) is developed. Nickel (Ni) and copper (Cu) materials are used as basic materials in the numerical modeling and experimental characterization. For modeling, a MATLAB finite element code is developed, which allows simulation of harmonic and modal analysis considering the graded finite element formulation. For experimental characterization, Ni-Cu FGSs are manufactured by using spark plasma sintering technique. Hardness and Young's modulus are found by using microindentation and ultrasonic measurements, respectively. The effective gradation of Ni/Cu FGS is addressed by means of optical microscopy, energy dispersive spectrometry, scanning electron microscopy and hardness testing. For the purpose of comparing modeling and experimental results, the hardness curve, along the gradation direction, is used for identifying the gradation profile; accordingly, the experimental hardness curve is used for approximating the Young's modulus variation and the graded finite element modeling is used for verification. For the first two resonance frequency values, a difference smaller than 1% between simulated and experimental results is obtained. (C) 2012 Elsevier Ltd. All rights reserved.

Polarization effect on the two-photon absorption of a chiral compound

In this report, we investigate the polarization effect (linear, elliptical and circular) on the two-photon absorption (2PA) properties of a chiral compound based in azoaromatic moieties using the femtosecond Z-scan technique with low repetition rate and low pulse energy. We observed a strong 2PA modulation between 800 nm and 960 nm as a function the polarization changes from linear through elliptical to circular. Such results were interpreted employing the sum-over-essential states approach, which allowed us to model the 2PA circular-linear dichroism effect and to identifier the overlapping of the excited electronic states responsible by the 2PA allowed band. (C) 2012 Optical Society of America

Latent track radius of PTFE irradiated with high energy ion beam

PTFE foils were irradiated with different ion beams (Xe, Au and U) with energies up to 1.5 GeV and fluences between 1 x 10(8) and 1 x 10(13) ions/cm(2) at room temperature. The induced modifications in the polymer were analyzed by FTIR, UV-Vis spectroscopy, and XRD. In the FTIR spectra, the CF2 degradation accompanied by the formation of CF3 terminal and side groups were observed. In the UV-Vis spectra, the observed increase in the absorption at UV wavelengths is an indication of polymer carbonization. From XRD, the amorphization of the material was evidenced by the decrease in the intensity of the main diffraction peak. An exponential fit of the intensity of the IR absorption peaks resulted in the following values: 2.9 +/- 0.8; 4.5 +/- 0.9 and 5.6 +/- 0.8 nm for the latent track radius after irradiation with Xe, Au and U beams, respectively. (C) 2011 Elsevier B.V. All rights reserved.

Electromagnetic energy within coated spheres containing dispersive metamaterials

An exact expression is derived for the time-averaged electromagnetic energy within a magneto-dielectric coated sphere, which is irradiated by a plane and time-harmonic electromagnetic wave. Both the spherical shell and core are considered to be dispersive and lossy, with a realistic dispersion relation of an isotropic split-ring resonator metamaterial. We obtain analytical expressions for the stored electromagnetic energies inside the core and the shell separately and calculate their contributions to the total average energy density. The stored electromagnetic energy is calculated for two situations involving a metamaterial coated sphere: a dielectric shell and dispersive metamaterial core, and vice versa. An explicit relation between the stored energy and the optical absorption efficiency is also obtained. We show that the stored electromagnetic energy is an observable sensitive to field interferences responsible for the Fano effect. This result, together with the fact that the Fano effect is more likely to occur in metamaterials with negative refraction, suggest that our findings may be explored in applications.

Charge dynamics in half-filled Hubbard chains with finite on-site interaction

We study the charge dynamic structure factor of the one-dimensional Hubbard model with finite on-site repulsion U at half-filling. Numerical results from the time-dependent density matrix renormalization group are analyzed by comparison with the exact spectrum of the model. The evolution of the line shape as a function of U is explained in terms of a relative transfer of spectral weight between the two-holon continuum that dominates in the limit U -> infinity and a subset of the two-holon-two-spinon continuum that reconstructs the electron-hole continuum in the limit U -> 0. Power-law singularities along boundary lines of the spectrum are described by effective impurity models that are explicitly invariant under spin and eta-spin SU(2) rotations. The Mott-Hubbard metal-insulator transition is reflected in a discontinuous change of the exponents of edge singularities at U = 0. The sharp feature observed in the spectrum for momenta near the zone boundary is attributed to a van Hove singularity that persists as a consequence of integrability.