Search Results

You are looking at 1 - 10 of 60 items for

  • Author or Editor: M. Oliveira x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract  

Data are presented for210Po levels in edible parts of marine species significant in the diet of the Argentine population. The sample collection sites were situated between 35° and 45° S in the Atlantic Ocean. The specific activities obtained, expressed per wet veight and with a 95% confidence level, ranged between 31.3±9.1 mBq kg–1 for pollack (Genypterus blacodes) and 1790±280 mBq kg–1 for squid (Illex argentinus). Hake (Merluccius hubbsi) followed by squid are the major contributors to the dose. The annual committed effective doses were 0.7 mSv and 0.6 mSv and the effective collective doses were 24 man·Sv and 20 man·Sv, respectively, for these species. For the remainder, because of both their low consumption rates and low specific activities, the corresponding doses were negligible compared with the former.

Restricted access

Abstract  

The effect of the iron precursor on the thermal decomposition of iron oxyhydroxides was studied by DSC, DTA and TG in this work. Samples were prepared from iron nitrate, iron sulfate and iron chloride and the thermal curves obtained were analyzed by specific area measurements, X-ray diffraction and Mssbauer spectroscopy. It was found that the iron oxyhydroxide precursors affect the temperatures of the hematite formation as well as the textural properties of the final hematite producing particles with different diameters as following: iron sulfate (3.3 nm)<iron nitrate (15 nm)<iron chloride (24 nm).

Restricted access

A mosaic of Campos grassland and Araucaria forest characterizes the vegetation of the Southern Brazilian highland plateau. Palaeoecological evidence indicates that forest expansion over grassland initiated after the mid Holocene, when climate changed towards present day cool and moist conditions. In this paper, we discuss landscape level changes that occurred on vegetation patterns after grazing and fire exclusion in a mosaic of Campos and Araucaria forest in Southern Brazil. The analysis of aerial photographs from 1974 and 1999 showed alterations on grassland communities under grazing and fire exclusion, especially pronounced shrub establishment near the edge of the forest. Considering the change in the cover of vegetation classes relative to the total altered cover in all classes from 1974 to 1999, the most prominent alterations were: 48% from grassland with tussock grasses dominance (GRA) to grassland with shrubs (GSR), 24% from GRA to grassland with tall shrubs (GTS), 16% from GSR to GTS and 9% from GTS to forest (FOR). Considering the alteration relatively to the vegetation cover in 1974, the most relevant changes were: 44% from GSR to GTS and 94% from GTS to FOR. These observations support a directional forest expansion over grassland under grazing and fire exclusion.

Restricted access

Summary  

Targeted radiotherapy has the potential to provide radiation doses from a wide range of radionuclides, some of them suitable for killing single cells while others are more suitable for killing tumor cell clusters of various sizes. A list of 64 radionuclides, including 20 new potential candidates for therapy (73Ga, 75Se, 87mSr, 97Ru, 103Ru, 113Sn, 113mIn, 117Sb, 123Sn, 131Cs, 139Ce, 141Ce, 149Eu, 167Tm, 170Tm, 173Tm, 195Au, 195mPt, 197Pt and 197Hg) were analyzed in terms of the suitability of their energies for killing tumor cells which grow as single, small, intermediate and large clusters. In addition, their possible production routes were studied.

Restricted access

Polymer crystallization

Isothermal and non-isothermal spherulite growth parameters from optical microscopy and differential scanning calorimetry

Journal of Thermal Analysis and Calorimetry
Authors: J. Martins, J. Cruz-Pinto, and M. Oliveira

Abstract  

Differential scanning calorimetry (dual furnace, null-balance, DSC) and optical microscopy (OM) have been used to study the isothermal crystallization kinetics of poly(oxymethylene)-POM. The non-isothermal crystallization of the same material has also been studied by optical microscopy. A very controversial problem is whether the isothermal kinetic parameters may be applied to describe the non-isothermal crystallization. The results show that the kinetic spherulite growth parameters obtained by non-isothermal optical microscopy are, within the experimental errors involved, the same as those obtained by isothermal optical microscopy or isothermal DSC. The importance of this finding is highlighted.

Restricted access

Abstract  

After more than ten years working with multicomparator instrumental neutron activation analysis, mainly applied to the characterization of environmental samples, the Radioisotopes Laboratory (CENA/USP) started changing gradually to the k 0-method in 1997. The main activities developed, as well as some of the results obtained, are presented here. Even though there is much more work to be done, the good quality of the results and the possibility of elemental determinations without the co-irradiation of standards may lead to the definitive adoption of the k 0-method in a near future.

Restricted access

Abstract  

The objective of the present work is the estimation of the210Po content in some beverages and in tobacco, in order to assess the corresponding collective doses to the population in Argentina. Yerba mate, tea leaves, their infusions and ground coffee were analyzed, as well as tobacco. Collective doses due to the annual consumption of the beverages described were found to be from 6 man.Sv to 1200 man.Sv. Results for210Po in tobacco ranged from 10 Bq·kg–1 to 80 Bq·kg–1. Lung doses due to the use of tobacco vary from 75 Sv·y–1 to 600 Sv·y–1.

Restricted access

Abstract  

ZnS(1-x)MSx(x=0.01 and M=Mn2+, Cu2+ and Eu2+) compounds have been obtained by precipitation from homogeneous solutions of zinc, copper, manganese and europium salts, with S2- as the precipitating anion, formed by the decomposition of thioacetamide. The thermal study of the milled zinc acetate, thioacetamide, copper acetate, manganese acetate and europium nitrate, respectively, was studied for thermal analyis TG/DSC. XRD respect exhibits a zinc blend crystal structure.

Restricted access

Abstract  

Polyurethane composites with bagasse of sugar cane (BSC) at different proportions: 5, 10 and 20 mass/mass% were prepared by melt mixing method. The thermal behavior of these composites were studied by thermogravimetry (TG/DTG). The influence of fiber concentration on the kinetic parameters of the composites was studied and a better interaction was suggested between PU/BSC with 5mass/mass% of fiber. Scanning electron microscopy was carried out to investigate surface morphology.

Restricted access