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Abstract  

The aim of this work was to determine the background airbome radioactivity in the town of Natal, Brazil. Indoor radon concentrations were measured inside 24 buildings using solid state nuclear track detectors which were exposed for a period of about 180 days. The average indoor radon level resulted to be 15.4±10.6 Bq·m–3. Measurements of gross - and -activities were performed at six different sites for airbome particulate samples collected over cellulose nitrate filters. Mean values of 0.15±0.06 mBq·m–3 and 0.42±0.10 mBq·m–3 were obtained for the gross -and gross -activity, respectively.

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Abstract  

Samples of the MgO–Al2O3–SiO2 ternary system, constituted by 28.5 mol% ofMgO, 28.5 mol% of Al2O3 and 43mol%of SiO2, were activated in a roll mill and calcined at different temperatures. The influence of the grinding time, the used SiO2 precursor and activation medium, furthermore the mass ratio between the powdered sample and zirconia cylinders was investigated on the reactivity of the MgO–Al2O3–SiO2 ternary system. FTIR spectra and the X-ray powder diffraction patterns indicates the formation of Mg(OH)2 at 393 K, of forsterite (MgSi2O5) and enstatite (MgSiO3) at 1223 K and of spinel (MgAl2O4) between 1223 and 1523 K in some samples. The presence of cordierite (Mg2Al2Si5O18) was observed at 1523 K, a reaction pathway concerning its formation was proposed.

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Abstract  

The concentrations of Cl, K and Na were analyzed in human body fluids (whole blood and serum) using NAA, resulting in the first biochemical baseline values for the Brazilian population. These data permitted us a discussion about the advantages and limitations of using this analytical technique for clinical chemistry.

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Abstract

Magnetic thermogravimetric analysis (TGM) was used to investigate the influence of the milling time (t mill) in the Curie temperature (T C) of nanocrystalline powders and of a melt-spun amorphous ribbon with composition Fe56Co7Ni7Zr10B20. The TGM analysis was carried in a continuous flow of 99.99% pure argon from room temperature up to 1250 K. A magnetic field of 100 Oe was applied throughout the measurements. Nanopowders of Fe56Co7Ni7Zr10B20 were produced by mechanical alloying the samples in an argon atmosphere for milling times ranging from 1 to 100 h. The samples were characterized by X-ray diffraction and by scanning electron microscopy. The average particle size decreased from 45.4 nm for a powder milled for 1 h to 5 nm after being milled for 100 h. Moreover, T C (=1126.4 ± 4.4 K) was found to be nearly independent of t mill while for the melt-spun amorphous ribbon it was found to be substantially smaller (T C = 482 K). This is a clear indication that T C is quite sensitive to the degree of amorphosity present in the sample. The activation energy associated to the crystallization process was estimated from DSC data by using the Kissinger's method to be 193 kJ/mol.

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Journal of Thermal Analysis and Calorimetry
Authors: J. R. Azevedo, R. H. Sizilio, M. B. Brito, A. M. B. Costa, M. R. Serafini, A. A. S. Araújo, M. R. V. Santos, A. A. M. Lira, and R. S. Nunes

Abstract

The purpose of this study was to develop and characterize insulin nanoparticles systems using chitosan. Insulin-loaded nanoparticles were prepared by ionic gelation of chitosan with tripolyphosphate anions (TPP). The interactions between insulin and chitosan were evaluated by differential scanning calorimetry (DSC), thermogravimetry/derivative thermogravimetry (TG/DTG), and Fourier-transform infrared (FTIR) spectroscopy. Besides, particle size distribution, polydispersity index (PDI), zeta potential, and association efficiency (AE%) of the nanoparticles were evaluated. In general, inert nanoparticles and insulin-loaded nanoparticles showed an average size of 260.56 nm (PDI 0.502) and 312.80 nm (PDI 0.481), respectively. Both nanoparticles showed positive charge, but after insulin incorporation the zeta potential was reduced, evidencing its incorporation. Nanoparticles obtained also showed AE% around 70%, measured by high-performance liquid chromatography (HPLC). The results of FTIR, DSC, and TG/DTG corroborated the data presented suggesting that insulin was successfully encapsulated. However, drug incorporation seems to be related not only to electrostatic interactions, but also to physical process and/or adsorption phenomena.

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