Social Sciences

Lazer é um conjunto de ocupações às quais o indivíduo pode entregar-se de livre vontade, seja para repousar, seja para divertir-se, recrear-se e entreter-se, ou ainda, para desenvolver sua informação ou formação desinteressada, sua participação social voluntária ou sua livre capacidade criadora após livrar-se ou desembaraçar-se das obrigações profissionais, familiares e sociais." (Dumazedier, 1976, apud Oleias).

Objective: The aim of the study was to evaluate the effect of topical fluoride gel NaF 2% application on antioxidant parameters of whole saliva from children. Design: The saliva mechanically stimulated with parafilm was collected from 25 children (6-12 years) attending the Clinic of Paediatric Dentistry of Universidade Cruzeiro do Sul, Sã o Paulo, Brazil, before (control group) and immediately after application of neutral fluoride gel NaF 2% (fluoride-gel group), according to the Standards for Research Using Human Subjects, Resolution 196/96 of the USA National Health Council of 10/10/1996. Afterwards, pre-post ferric-reducing antioxidant power (FRAP), trolox-equivalent antioxidant capacity (TEAC), uric acid, reduced/oxidised glutathione content (GSH/GSSG) and total peroxidase activity (TPO) were evaluated in whole saliva of both groups.

In this article, we report the formation of dispersed anisotropic nanostructures by the oriented attachment mechanism, under hydrothermal conditions and in a system that all other growth processes are improbable. The comparison of dilute and agglomerated experimental conditions indicate that oriented attachment is an effective mechanism for the formation of anisotropic nanocrystals, and the conclusions can be extended to other nanometric systems.

The CO 2 reforming of CH 4 was performed over V-promoted Ni/Al 2 O 3 catalysts similarly prepared by the polymeric precursor method. The H 2 chemisorption, X-ray diffraction (XRD) and X-ray photoemission spectroscopy (XPS) analyses show that a low V wt.% addition suppresses the NiAl 2 O 4 formation. Moreover, the CHN results point out to a low carbon deposition and the surface area (BET) abruptly increases upon the addition of 0.8 wt.% V. On the other hand, the sample with high V wt.% presented the highest carbon deposition, what was attributed to the CH 4 decomposition increase promoted by the V.

In this article, we report the formation of dispersed anisotropic nanostructures by the oriented attachment mechanism, under hydrothermal conditions and in a system that all other growth processes are improbable. The comparison of dilute and agglomerated experimental conditions indicate that oriented attachment is an effective mechanism for the formation of anisotropic nanocrystals, and the conclusions can be extended to other nanometric systems.

This paper discusses the influence of the presence of a second dopant (Pt or Pd) on the SnO 2 ·Ce matrix. The characteristics of the material and the catalytic activity of oxidizing methanol were evaluated. Two routes were used to prepare the SnO 2 ·5 mol% Ce·1 mol% NM (NM = Pt or Pd). Transmission electronic microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and chromatographic assays were used to study the samples. Almost no changes in the morphology were detected when the samples were prepared by the impregnation route. In contrast, preparation by the chemical route (modified polymeric precursor (MPP) route) revealed crystallite growth and CeO 2 segregation. No sample showed any metallic cluster, but all the samples containing noble metal displayed a very marked catalytic property, suggesting significant activity even at room temperature. The products formed were CO 2 and water, representing a competitive advantage from the standpoint of environmental protection.

A polymeric precursor method based on the Pechini process was successfully used to synthesize zirconia-12 mol% ceria ceramic powders. The influence of the main process variables (citric acid-ethylene glycol ratio, citric acidtotal oxides ratio and calcination temperature) on phase formation and powder morphology (surface area and crystallite size) were investigated. The thermal decomposition behavior of the precursor is presented. X-ray diffraction (XRD) patterns of powders revealed a crystalline tetragonal zirconia single-phase, with crystallite diameter ranging from 6 to 15 nm. The BET surface areas were relatively high, reaching 95 m 2 g À1 . Nitrogen adsorption/desorption on the powders suggested that nonaggregated powders could be attained, depending on the synthesis conditions.

The CO 2 reforming of CH 4 was performed over V-promoted Ni/Al 2 O 3 catalysts similarly prepared by the polymeric precursor method. The H 2 chemisorption, X-ray diffraction (XRD) and X-ray photoemission spectroscopy (XPS) analyses show that a low V wt.% addition suppresses the NiAl 2 O 4 formation. Moreover, the CHN results point out to a low carbon deposition and the surface area (BET) abruptly increases upon the addition of 0.8 wt.% V. On the other hand, the sample with high V wt.% presented the highest carbon deposition, what was attributed to the CH 4 decomposition increase promoted by the V.

This paper discusses the influence of the presence of a second dopant (Pt or Pd) on the SnO 2 ·Ce matrix. The characteristics of the material and the catalytic activity of oxidizing methanol were evaluated. Two routes were used to prepare the SnO 2 ·5 mol% Ce·1 mol% NM (NM = Pt or Pd). Transmission electronic microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and chromatographic assays were used to study the samples. Almost no changes in the morphology were detected when the samples were prepared by the impregnation route. In contrast, preparation by the chemical route (modified polymeric precursor (MPP) route) revealed crystallite growth and CeO 2 segregation. No sample showed any metallic cluster, but all the samples containing noble metal displayed a very marked catalytic property, suggesting significant activity even at room temperature. The products formed were CO 2 and water, representing a competitive advantage from the standpoint of environmental protection.

In this work Ba0.99Eu0.01MoO4 (BEMO) powders were prepared by the first time by the Complex Polymerization Method. The structural and optical properties of the BEMO powders were characterized by Fourier Transform Infra-Red (FTIR), X-ray Diffraction (XRD), Raman Spectra, High-Resolution Scanning Electron Microscopy (HR-SEM) and Photoluminescent Measurements. XRD show a crystalline scheelite-type phase after the heat treatment at temperatures greater than 400 °C. The ionic radius of Eu3+ (0.109 nm) is lower than the Ba2+ (0.149 nm) one. This difference is responsible for the decrease in the lattice parameters of the BEMO compared to the pure BaMoO4 matrix. This little difference in the lattice parameters show that Eu3+ is expected to occupy the Ba2+ site at different temperatures, stayed the tetragonal (S4) symmetry characteristic of scheelite-type crystalline structures of BaMoO4. The emission spectra of the samples, when excited at 394 nm, presented the 5D1→7F0, 1 and 2 and 5D0→7F0, 1, 2, 3 and 4 Eu3+ transitions at 523, 533, 554, 578, 589, 614, 652 and 699 nm, respectively. The emission spectra of the powders heat-treated at 800 and 900 °C showed a marked increase in its intensities compared to the materials heat-treated from 400 to 700 °C. The decay times for the sample were evaluated and all of them presented the average value of 0.61 ms. Eu3+ luminescence decay time follows one exponential curve indicating the presence of only one type of Eu3+ symmetry site.

A polymeric precursor method based on the Pechini process was successfully used to synthesize zirconia-12 mol% ceria ceramic powders. The influence of the main process variables (citric acid-ethylene glycol ratio, citric acidtotal oxides ratio and calcination temperature) on phase formation and powder morphology (surface area and crystallite size) were investigated. The thermal decomposition behavior of the precursor is presented. X-ray diffraction (XRD) patterns of powders revealed a crystalline tetragonal zirconia single-phase, with crystallite diameter ranging from 6 to 15 nm. The BET surface areas were relatively high, reaching 95 m 2 g À1 . Nitrogen adsorption/desorption on the powders suggested that nonaggregated powders could be attained, depending on the synthesis conditions.

In this communication, we demonstrate that the use of microwave heating during hydrothermal treatment drastically decreases the treatment time required to obtain gadolinium-doped ceria nanorods and that the oriented attachment is the dominant mechanism responsible for anisotropic growth. In fact, considering oriented attachment (OA) as a statistical mechanism, we postulate that the growth process conducted under microwave heating increases the effective collision rate. A plausible explanation for the increase of the effective collision rate under microwave irradiation is the increase in the collision cross-section of the particle.

Additions of 0. 5 to 2. 0 mol% of CoO or MnO2 onto SnO2 promote densification of this oxide up to 99% of theoretical density. The temperature of the maximum shrinkage rate (TM) and the relative density in the maximum densification rate (p*) during constant sintering heating rate depend on the dopant concentration. Thus, dopant concentration controls the densifying and nondensifying mechanisms during sintering. The densification of SnO2 witih addition of CoO or MnO2 is explained in terms of the creation of oxygen vacancies.

In this communication, we demonstrate that the use of microwave heating during hydrothermal treatment drastically decreases the treatment time required to obtain gadolinium-doped ceria nanorods and that the oriented attachment is the dominant mechanism responsible for anisotropic growth. In fact, considering oriented attachment (OA) as a statistical mechanism, we postulate that the growth process conducted under microwave heating increases the effective collision rate. A plausible explanation for the increase of the effective collision rate under microwave irradiation is the increase in the collision cross-section of the particle.

A joint experimental and theoretical study has been carried out to rationalize the results of visible photoluminescence measurements at room temperature on Sr 1-x TiO 3-x (ST) perovskite thin films. From the experimental side, ST thin films, x ) 0 to 0.9, have been synthesized following soft chemical processing, and the corresponding photoluminescence properties have been measured. First principles quantum mechanical techniques, based on density functional theory at the B3LYP level, have been employed to study the electronic structure of a crystalline, stoichiometric (x ) 0) ST-s model and a nonstoichiometric (SrO-deficient, x * 0) and structurally disordered ST-d model. The relevance of the present theoretical and experimental results of the photoluminescence behavior of ST is discussed. The optical spectra and the calculations indicate that the symmetry-breaking process on going from ST-s to ST-d creates electronic levels in the valence band. Moreover, an analysis of the Mulliken charge distribution reveals a charge gradient in the structure. These combined effects seem to be responsible for the photoluminescence behavior of deficient Sr 1-x TiO 3-x .

Additions of 0. 5 to 2. 0 mol% of CoO or MnO2 onto SnO2 promote densification of this oxide up to 99% of theoretical density. The temperature of the maximum shrinkage rate (TM) and the relative density in the maximum densification rate (p*) during constant sintering heating rate depend on the dopant concentration. Thus, dopant concentration controls the densifying and nondensifying mechanisms during sintering. The densification of SnO2 witih addition of CoO or MnO2 is explained in terms of the creation of oxygen vacancies.