900 resultados para Block Polymers


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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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The expansion and maintenance of electricity distribution networks generates large amounts of waste, much of it in the form of discarded insulators that are not reused or recycled. This paper describes the results of tests on used and new ceramic and polymeric insulators to verify if their exposure to weathering justifies their replacement. In new and used ceramic insulators, properties such as contact angle, relative density, porosimetry, dilatometry and X-ray diffraction patterns showed no differences or the differences that were found could not be related to their use. The discarded ceramic material showed high thermal stability, an interesting characteristic for application as chamotte. It can also be reused to replace gravel used in substations. In polymeric insulators, thermogravimetry, differential scanning calorimetry and relative density test results suggest degradation of used material compared to new. This would justify their replacement and discard as waste, but they show little recycling potential.

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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A new selective sensor based on molecularly imprinted polymers (MIPs) was developed for the determination of hexazinone (HXZ) in environmental samples. MIPs were synthesized using a non-covalent approach, and selection of the monomers employed in the polymerization reaction was carried out by molecular modeling. Three functional monomers with high (2-vinylpyridine (MP17)) and intermediate (methacrylic acid (MP12) and acrylamide (MP5)) energies of binding to the template (HXZ) were selected for preparation of the MIPs, in order to conduct comparative studies and validate the theoretical data. For sensor construction, carbon pastes were modified with each MIP or NIP (non-imprinted polymer), and HXZ determination was performed using differential pulse adsorptive cathodic stripping voltammetry (DPAdCSV). All parameters affecting the sensor response were optimized. In HCl at pH 2.5, the sensor prepared with MP17 (5% w/w in the paste) showed a dynamic linear range between 1.9 × 10−11 and 1.1 × 10−10 mol L−1, and a detection limit of 2.6 × 10−12 mol L−1, under the following conditions: accumulation time of 200 s at a potential of −0.5V, scan rate of 50 mVs−1, pulse amplitude of 60 mV, and pulse width of 50 ms. The sensor was selective in the presence of other similar compounds, and was successfully applied to the analysis of HXZ in river water samples.

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Bite block is a functional orthodontic appliance that promotes relative intrusion or dental eruption inhibition. The purpose of this study is to present the effects of bite block on the treatment of an open bite case report.

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Nowadays, the correction of skeletal vertical dysplasia is considered a great challenge in Orthodontics. The skeletal open bite treatment presents limitations related to vertical growth pattern, the extension of open bite and especially the stability, which is very questioned. The treatment of skeletal open bite is mostly realized by the inhibition of vertical alveolar posterior development (relative intrusion) or absolute intrusion of posterior teeth, through vertical forces, generated by the action of masticatory muscles. The purpose of this article is to present a new appliance for the treatment of skeletal open bite, the VABB (Vertically Activated Bite Block) or modified Bite Block, whose action mechanism is to limit the vertical development of the molars, by the action of facial muscles and two bilateral expansion screws that provide a counterclockwise rotation of the mandible. It will also be presented a clinical case and the technical steps for the construction of this appliance.

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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AimThe aim of this study was to evaluate the healing of autologous bone block grafts or deproteinized bovine bone mineral (DBBM) block grafts applied concomitantly with collagen membranes for horizontal alveolar ridge augmentation.Material and methodsIn six Labrador dogs, molars were extracted bilaterally, the buccal bony wall was removed, and a buccal box-shaped defect created. After 3months, a bony block graft was harvested from the right ascending ramus of the mandible and reduced to a standardized size. A DBBM block was tailored to similar dimensions. The two blocks were secured with screws onto the buccal wall of the defects in the right and left sides of the mandible, respectively. Resorbable membranes were applied at both sides, and the flaps sutured. After 3months, one implant was installed in each side of the mandible, in the interface between grafts and parent bone. After 3months, biopsies were harvested and ground sections prepared to reveal a 6-month healing period of the grafts.Results776.2% and 5.9 +/- 7.5% of vital mineralized bone were found at the autologous bone and DBBM block graft sites, respectively. Moreover, at the DBBM site, 63 +/- 11.7% of connective tissue and 31 +/- 15.5% of DBBM occupied the area analyzed. Only 0.2 +/- 0.4% of DBBM was found in contact with newly formed bone. The horizontal loss was in a mean range of 0.9-1.8mm, and 0.3-0.8mm, at the autologous bone and DBBM block graft sites, respectively.ConclusionsAutologous bone grafts were vital and integrated to the parent bone after 6months of healing. In contrast, DBBM grafts were embedded into connective tissue, and only a limited amount of bone was found inside the scaffold of the biomaterial.

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This work is intended to study the possibility of adding an amount of waste from iron mining in the ceramic mass. Clay and coal, from Vale do Paraiba, Sao Paulo, Brazil, were used in this research. These raw materials are used in the ceramic block manufacture. Clay and waste were analyzed by X-ray fluorescence and X-ray diffraction, particle size, differential thermal and thermogravimetric analysis. Liquid limit and plasticity index tests were performed in order to determine the amount of waste that which should be used in the ceramic mass. After determining the amount of waste, all samples were uniaxially pressed and sintered at 900 degrees C. Surface roughness measurements, apparent porosity and bulk density technique and three-point flexural tests were also performed to characterize the samples. The results showed that by adding the exact amount of waste, which was determined by the essays, it is possible to manufacture solid bricks.

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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Measurements on polymers (Teflon FEP and Mylar) have shown that the secondary electron emission from uncharged surfaces exceeds that from surfaces containing a positive surface charge. The reduced emission of charged surfaces is due to recombination between electrons undergoing emission and trapped holes within the charged layer. During the experiments the surface of the material was kept at a negative potential to assure that all secondary electrons reaching the surface from within the material are actually emitted. An analysis of the results yielded the maximum escape depth of the secondary electrons, and showed that the ratio of the maximum escape depth of the secondaries from Mylar to the maximum escape depth from Teflon is almost the same as the ratio of the corresponding second crossover energies of this polymers.