Authors:S. Ribeiro Guevara, A. Rizzo, R. Sánchez, and M. Arribére
Unsupported 210Pb fluxes were determined from sediment core inventories in lakes located in Northern Patagonia, Argentina. Total 210Pb, 226Ra, associated with supported 210Pb, and 137Cs specific activity profiles were measured by gamma-ray spectrometry. Unsupported 210Pb fluxes showed very low values when compared to other regions, with a 12 fold variation, ranging from 4 to 48 Bq m–2.y–1. The linear correlation observed between the 210Pb fluxes and137Cs cumulative fluxes in sediment cores sampled from water bodies within a zone with similar precipitation demonstrated that both radioisotopes behave in the same manner in these systems concerning the processes occurred from fallout to sediment deposition, and that there are no appreciable local or regional sources of unsupported 210Pb. Positive correlation of 210Pb fluxes with organic matter contents of the uppermost sediment core layers was also observed.
Authors:Ribeiro Guevara S, A. Rizzo, R. Sánchez, and M. Arribére
Heavy metal profiles of short sediment cores sampled from lakes located in Nahuel Huapi National Park, Northern Patagonia, Argentina, were determined by INAA. Core dating was performed by measuring natural 210Pb and anthropogenic 137Cs, and by identification of tephra layers. No evidence was found for the input increase of the trace elements Sb, Ba, Cs, Zn, Co, Hf, Ni, Se, Sr, Ti, U, and V in the lake environment. High As concentrations (up to 250 μg . g-1) were found in relation with the diffusion processes of Mn and Fe oxides. Strong correlation was observed between the Br concentration and organic matter content, but no evidence was found for the relevant increase of Br inputs in recent years. Ag concentrations were found to be enriched in the upper core layers over the baseline values determined for deep layers ranging from 0.1 to 0.2 μg . g-1. Hg concentration profiles were also enriched in the upper core layers over the baseline (from less than 0.07 to 0.2 μg . g-1 for pre-industrial time, to 0.1 to 0.3 μg . g-1 for modern times) but in relation with the increased organic matter content of the sediment.
Authors:R. Daga, S. Ribeiro Guevara, M. L. Sánchez, and M. Arribére
Volcanic ashes erupted by recent magmatic events were collected from one sedimentary sequence of lake Nahuel Huapi (Patagonia,
Argentina) and then analyzed by Instrumental Neutron Activation Analysis. Primary volcanic components, including white and
brownish pumice fragments, scoriae and glass shards, as well as bulk sediments from four tephra layers identified in the sedimentary
sequence, were characterized by their major and trace element contents. The two tephra layers being in the upper section of
the sequence can be linked to the eruptions of Cordon Caulle fissure (Puyehue-Cordon Caulle region) occurred in 1921-1922
and 1960, according to core dating. The third tephra layer, which is clearly associated to an event occurred in the 1890-1900
decade, has different compositional patterns showing a different source from those upper tephras. Whereas, the fourth, which
could be associated to an event occurred at the end of the 18 th century, shows the same composition patterns as those registered
for the Cordon Caulle fissure.
Authors:A. Delben, F. Menezes, J. Delben, M. Coelho, and R. Ribeiro
Waste compromises environmental preservation as well human health in
many countries. Recycling is an alternative that sometimes represents the
only economical activity for a significant population in the big cities. Almost
3% of waste materials in Brazil are vitreous. Ceramic production adding waste
glass is possible with advantages of costs reduction associated to decrease
on firing temperatures and to the raw material itself. At present paper up
to 80 mass% of waste glass was added to clay. The sintering temperature decreased
linearly and the shrinkage increased with glass content, an effect more pronounced
for high glass amount.
Authors:H. Barud, C. Ribeiro, Marisa Crespi, M. Martines, J. Dexpert-Ghys, R. Marques, Y. Messaddeq, and S. Ribeiro
membranes have been prepared from bacterial cellulose membranes (BC) and sodium
polyphosphate solution. The structure and thermal behavior of the new composites
were evaluated by X-ray diffraction (XRD), 31P-nuclear
magnetic resonance (NMR), scanning electron microscopy (SEM), differential
scanning calorimetry (DSC), thermogravimetry (TG) and thermomechanical analysis
(TMA). From XRD analyses the Iα and Iβ cellulose crystalline phases
were identified together with crystalline sodium phosphate that covers the
cellulose microfibrils as revealed by SEM. 31P
NMR spectra show peaks assigned to Q0 and Q1
phosphate structures to be compared to the Q2 units
that characterize the precursor polyphosphate. Glass transition temperature, Tg, obtained from TMA curves
and thermal stability obtained from TG and DSC measurements, were observed
to be dependent on the phosphate content.
Authors:N. Batalha, L. Pinard, S. Morisset, J. L. Lemberton, Y. Pouilloux, M. Guisnet, F. Lemos, and F. R. Ribeiro
n-Hexadecane hydroisomerization at 220 °C and 30 bar was used as a model reaction for comparing the catalytic performances of a Pt/HBEA sample whose zeolite crystals were germinated on an α alumina surface with those of 1Pt/HZM-22 catalyst well-known for its high isodewaxing selectivity. Similar values of selectivity to isomers were obtained with both catalysts even at high conversions. Moreover, despite its low zeolite content (13 wt%), the Pt/HBEA Al2O3 catalyst had the important advantage to be 4.6 times more active.
Authors:G. Capote Rodriguez, R. Padilla Alvarez, G. Pérez Zayas, A. Hernández Rivero, M. López Reyes, S. Ribeiro Guevara, and J. Molina Insfrán
Thirty elements were determined by INAA in Cuban soil samples collected in 17 zones from western regions of Cuba, which were
affected by neuropathy epidemic in 1992. The presence of toxic elements was evaluated to provide data for the analysis of
possible paths of intoxication through local agriculture product consumption. The results obtained for As, Th and U are compared
with similar data reported on literature.
Authors:Edjane F. B. Silva, Marcílio P. Ribeiro, Ana C. F. Coriolano, Ana C. R. Melo, Anne G. D. Santos, Valter J. Fernandes Jr., and Antonio S. Araujo
Thermogravimetry was applied in order to investigate the catalytic degradation of heavy oil (15.4oAPI) over silica-based MCM-41 mesoporous molecular sieve. This material was synthesised by the hydrothermal method, using cetyltrimethylammonium bromide as organic template. The physicochemical characterization by nitrogen adsorption, X-ray diffraction, and thermogravimetry, showed that the obtained material presents well-defined structure, with a uniform hexagonal arrangement. The thermal and catalytic degradation of heavy oil was performed by thermogravimetric measurements, in the temperature range from 30 to 900 °C, at heating rates of 5, 10, and 20 °C min−1. By using the model-free kinetics, proposed by Vyazovkin, it was determined that the activation energy to degrade the heavy oil was ca. 128 kJ mol−1, and for degradation of oil in presence of MCM-41, this value decreased to 69 kJ mol−1, indicating the performance of the mesoporores catalyst for the degradation process.
Authors:Maria Luisa A. Gonçalves, D. A. Ribeiro, Deusa Angélica P. Da Mota, Ana Maria R. F. Teixeira, and M. A. G. Teixeira
Summary Thermogravimetry (TG) was applied to evaluate the thermal behavior of five refinery atmospheric distillation residues (ATR) obtained from different Brazilian crude oils. The asphaltenes were extracted of each sample and their influence on coke formation was studied. It was observed that they have a great contribution on carbonaceous residues formation during pyrolysis and that the heavier the ATR sample, the higher is the contribution of other heavy components present in ATR samples.
Authors:E. L. Dorval, M. A. Arribére, S. Ribeiro Guevara, I. M. Cohen, A. J. Kestelman, R. A. Ohaco, M. S. Segovia, A. N. Yunes, and M. Arrondo
We have measured the cross sections, averaged over a 235U fission neutron spectrum, for the two high threshold reactions: 75As(n,p)75mGe and 75As(n,2n)74As. The measured averaged cross sections are 0.292±0.022 mb, referred to the 3.95±0.20 mb standard for the 27Al(n,p)27Mg averaged cross section, and 0.371±0.032 mb referred to the 111±3 mb standard for the 58Ni(n,p)58m+gCo averaged cross section, respectively. The measured averaged cross sections were also evaluated semi-empirically by numerically
integrating experimental differential cross section data extracted for both reactions from the current literature. The calculations
were performed for four different representations of the thermal-neutron-induced 235U fission neutron spectrum. The calculated cross sections, though depending on analytical representation of the flux, agree
with the measured values within the estimated uncertainties.