André Ben-Hur da Silva Figueiredo

Cytogenetic analysis of the effects of 2.5 and 10.5 GHz microwaves on human lymphocytes

The biological effects of microwaves on living organisms remain highly controversial. Although some reports have suggested that microwaves may be directly or indirectly genotoxic, a direct action is unlikely because the low energy of microwave photons makes them unable to cause single-strand breaks in DNA. In this work, we examined the possible clastogenic properties of microwaves (2.5 and 10.5 GHz) on blood lymphocytes in vitro by monitoring the frequency of chromosomal aberrations. We also investigated whether blood cells showed increased radiosensitivity or radioresistance when pretreated with the microwaves and then irradiated with gamma radiation. There was no significant difference in the frequency of chromosomal aberrations between cells which had or had not been treated with microwaves. Control cells had a mean frequency of 0.013 aberrations per cell compared to 0.010 and 0.011 aberrations per cell in the microwave-exposed samples. Nor was there any alteration in the radiosensitivity of cells pretreated with microwaves. Gamma irradiated cells showed a mean frequency of 0.279 aberrations per cell compared to 0.343 and 0.310 aberrations per cell in samples pretreated with microwaves. However, cell mortality increased markedly after exposure to microwaves. The results suggest that microwaves do not interact directly or indirectly with chromosomes, although they may target other cell structures, such as cell membranes.

Photoacoustic Thermal Characterization of Banana Fibers

Natural fibers are attracting the interest of engineering sectors owing to specific advantages such as lightweight and lower cost as well as for their inherent condition of being renewable, biodegradable, recyclable and neutral with respect to CO2 emission. In particular, the fiber extracted from the malva plant stem is nowadays recognized as one of the strongest lignocellulosic fibers. However, the thermal properties of the malva fibers have yet not been fully investigated. The present work had as its objective to investigate, by photoacoustic spectroscopy and photothermal techniques the thermal properties of diffusivity, specific heat capacity and conductivity of a pressed malva fibers sample. The results revealed that these fibers showed a superior thermal insulation capacity.

Síntese e caracterização de nanopartículas de NiFe2O4 utilizando o método de sol-gel/combustão e combustão homogênea

This work aimed at the synthesis of NiFe2O4 nanoparticles using the methods of sol-gel combustion and homogeneous combustion. The nanoparticles were characterized by X-ray diffraction (XRD), electron magnetic resonance (EMR) spectroscopy and Fourier transform infrared (FTIR). The X-ray measurements were used to characterize and estimate the average size of crystallites. In the infrared spectra the formation of ferrite phase and the influence of the average size of crystallites in all samples which exhibited a high degree of crystallinity are observed, since the infrared band in the range 550 - 600 cm-1 is characteristic of tetrahedral sites of the ferrite. The electron magnetic resonance spectra show that nanoscale particles were synthesized.

Nanostructured magnetic alginate composites for biomedical applications

This is a study of the preparation and characterization of polymeric-magnetic nanoparticles. The nanoparticles used were magnetite (Fe3O4) and the chosen polymers were alginate and chitosan. Two types of samples were prepared: uncoated magnetic nanoparticles and magnetic nanoparticles encapsulated in polymeric matrix. The samples were analyzed by XRD, light scattering techniques, TEM, and magnetic SQUID. The XRD patterns identified magnetite (Fe3O4) as the only crystalline phase. TEM analyses showed particle sizes between 10 and 20nm for magnetite, and 15 and 30nm for the encapsulated magnetite. The values of magnetization ranged from 75 to 100emu/g for magnetite nanoparticles, and 8 to 12emu/g for coated with chitosan, at different temperatures of 20K and 300K. The saturation of both samples was in the range of 49 to 50KOe. Variations of results between the two kinds of samples were attributed to the encapsulation of magnetic nanoparticles by the polymers.

The Role of Sintered Al 2 O 3 -Nb 2 O 5 Front Plate on the Ballistic Performance of Multilayered Armors

The performance of multilayered armor systems (MAS), composed of a front Al2O3-Nb2O5 ceramic plate followed by either plies of aramid fabric layer or curaua fiber reinforced polyester matrix composite layer and backed by an aluminum alloy sheet, was assessed. Ballistic impact tests were performed with actual 7.62 caliber ammunitions. Indentation in a clay witness, simulating a personal body behind the back layer, attested the efficacy of the MAS as an armor component. The ballistic efficiency of the front ceramic dissipating more than 50% of the bullet impact energy was associated with its capacity of fragmentation. As for the remaining energy, the lighter and cheaper curaua fiber composites were found to present a significant advantage as a possible substitute for the usual aramid fabric intermediate layer in MAS for individual protection against high speed projectiles.

INFLUÊNCIA DA RADIAÇÃO ULTRAVIOLETA NO COMPORTAMENTO MECÂNICO DE COMPÓSITOS LAMINADOS DE POLIETILENO DE BAIXA DENSIDADE (PEBD) UNIDOS POR RESINA A BASE ETILCIANOACRILATO E POR SILICONE

The polymeric materials are sensitive to ultraviolet radiation, causing changes in their properties. From this perspective, the present study exposed low density polyethylene (LDPE) to ultraviolet radiation for 150 and 300 hours. Physical-chemical evaluation and mechanical characterization were performed to verify the macromolecular changes produced by such radiation and confirmed by visual examination. In view of the results, the occurrence of degradation, through the presence of chain rupture, besides the production of crosslinking, and a subtle decrease of the crystallinity were confirmed. The tensile test confirmed the embrittlement produced by the radiation. The ballistic performance of the ethylane acrylate-based adhesive plates produced delamination, unlike that observed in the silicone-fixed plates.

Synthesis and Characterization of CaO-SiO2-MgO Bioactive Glass Produced by Sol-Gel

Bioactive glasses have widely used in biomedical applications such as bone filler due to their excellent biocompatibility, bioactivity and osteoconduction characteristics. In this work, a silicate-rich glass was synthesized by the sol-gel method with 60% SiO2 – 30%CaO – 10% MgO composition where fumed silica acts as the silica precursor. This new method was hypothesized to reduce the gel formation time, due to the high surface area of the fumed silica. In addition, this would presumably increase the nanoporosity of the glass. For comparison purposes, we used a glass of the same composition, but with the conventional silica precursor, tetraethyl orthosilicate (TEOS), through the sol gel method. Both were heat treated at 450°C. FT-IR analysis before and after heat treatment at 450°C showed the presence of nitrate groups, especially in the TEOS samples. This is consistent with the more hygroscopic aspect of those samples. The fumed silica samples had significantly less pronounced peaks corresponding to the nitrate groups, consistent with the more porous structure and the less hygroscopic aspect. The fumed silica samples indeed had a lower gelling time and showed similar results obtained by XRD and FT-IR analyses, showing that the use of fumed silica is viable and advantageous in the glass synthesis by the sol-gel process