Stable isotopes (H-2, O-18 and C-13) in groundwaters from the northwestern portion of the Guarani Aquifer System (Brazil)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Hydrothermal rare earth elements mineralization in the Barra do Itapirapua carbonatite, southern Brazil: behaviour of selected trace elements and stable isotopes (C, O)

The Bura do Itapira pua carbonatite is located in southern Brazil and belongs to the Cretaceous Ponta Grossa alkaline-carbonatitic province related to the opening of the South Atlantic. The carbonatite complex is emplaced in Proterozoic granites and is mainly composed of plutonic magnesio- to ferrocarbonatite, with smaller amounts of subvolcanic magnesiocarbonatite. Hydrothermal alteration of the carbonatite has led to the formation of quartz, apatite, fluorite, rue earth fluorocarbonates, barite and sulfides in variable proportions. Trace element data, delta(13)C and delta(18)O are presented here, with the aim of better understanding the geochemical nature of hydrothermal alteration related to rare earth elements (REE) mineralization. The non-overprinted plutonic carbonatite shows the lowest REE contents, and its primitive carbon and oxygen stable isotopic composition places it in the field of primary igneous carbonatites. Two types of hydrothermally overprinted plutonic carbonatites can be distinguished based on secondary minerals and geochemical composition. Type I contains mainly quartz, rare earth fluorocarbonates and apatite as hydrothermal secondary minerals, and has steep chondrite normalized REE patterns, with Sigma(REE+Y) of up to 3 wt.% (i.e., two orders of magnitude higher than in fresh plutonic samples). In contrast, the Type II overprint contains apatite, fluorite and barite as dominant hydrothermal minerals, and is characterized by heavy REE enrichment relative to the fresh samples, with flat chondrite normalized REE patterns. Carbon and oxygen stable isotope ratios of Types I and II are elevated (delta(18)O + 8 to + 12 parts per thousand; delta(13)C - 6 to - 2 parts per thousand) relative to the fresh samples. Hydrothermally overprinted carbonatites exposed to weathering show even higher delta(18)O values (delta(18)O 13 to 25 parts per thousand) but no additional REE enrichment. The subvolcanic carbonatite has anomalously high delta(13)C of up to + 1 parts per thousand, which suggests crustal contamination through interaction with carbonate-bearing metasediments. (C) 1999 Elsevier B.V. B.V. All rights reserved.

Weathering rates at Alto Sorocaba basin, Brazil, using U-isotopes and major cations

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

Austenite decomposition of C-Mn steel containing boron by continuous cooling

The austenite decomposition in C-Mn steel containing boron was studied by continuous cooling from 1100 and 845 degreesC using the Jominy test. The results indicate that the different cooling speeds and the presence of boron refine and change the percentage of ferrite microstructure, martensite, and fine pearlite. (C) 2001 Elsevier B.V. B.V. All rights reserved.

Electrochemical reduction of disperse orange 1 textile dye at a boron-doped diamond electrode

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

The Fabrication and Characterization of a Nickel Nanoparticle Modified Boron Doped Diamond Electrode for Electrocatalysis of Primary Alcohol Oxidation

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

Detection of DNA Nucleotides on Pretreated Boron Doped Diamond Electrodes

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

The Determination of Methanol Using an Electrolytically Fabricated Nickel Microparticle Modified Boron Doped Diamond Electrode

A nickel modified boron doped diamond (Ni-BDD) electrode and nickel foil electrode were used in the determination of methanol in alkaline solutions. The Ni-BDD electrode was electrodeposited from a 1 mM Ni(NO(3))(2) solution (pH 5), followed by repeat cycling in KOH. Subsequent analysis utilised the Ni(OH)(2)/NiOOH redox couple to electrocatalyse the oxidation of methanol. Methanol was determined to limits of 0.3 mM with a sensitivity of 110 nA/mM at the Ni-BDD electrode. The foil electrode was less sensitive achieving a limit of 1.6 mM and sensitivity of 27 nA/mM. SEM analysis of the electrodes found the Ni-BDD to be modified by a quasi-random microparticle array.

Traceability of animal meals in Japanese quail eggs using the technique of 13C e 15N* stable isotopes

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

Boron influence on concentration of polyols and other sugars in Eucalyptus

Embora a função do elemento Boro (B) nas plantas ainda não tenha sido bem esclarecida, várias hipóteses vêm sido levantadas. Uma das funções atribuídas a esse elemento é a síntese de carboidratos. Com o objetivo de avaliar o efeito do B sobre a síntese de alguns polióis e açúcares em Eucalyptus grandis e híbridos urograndis, estes foram submetidos à situação de suprimento e restrição de B. O experimento foi conduzido em casa de vegetação de acordo com o delineamento de blocos casualizados com cinco repetições, e os elementos nutricionais, assim como o B, foram fornecidos na forma de solução nutritiva. Não se observou diferença significativa nos teores de manitol, sorbitol, myo-inositol e scyllo-inositol e dos açúcares α-glicose e β-glicose entre E. grandis e híbridos. Arabinose foi o único a apresentar maior teor em E. grandis em restrição de B. O efeito da presença do B foi bastante expressivo, mas em suprimento do elemento as plantas apresentaram acréscimo significativo na síntese dos compostos avaliados.

Effect of boron and zinc fertilization on white oats grown in soil with average content of these nutrients

The objective of this study was to evaluate the effect of fertilization with zinc or boron on the growth and dry matter production, nutritional value and accumulation of nutrients in white oats. The study comprised two experiments conducted in glasshouses, the first consisting of the application of four doses of zinc (0, 0.2, 0.4 and 0.6 mg/dm³) in the form of zinc sulphate (20% Zn), and the second consisting of the application of four doses of boron (0, 0.2, 0.4 and 0.6 mg/dm³) in the form of Borax (11% B). The experimental design in each case was a randomized block design, with five replicates. Fertilization with zinc and boron increased the growth of white oats, but had no significant effect on the nutritional value of the forage. Higher levels of absorption and accumulation of nutrients in plant tissues were observed following the application of boron and zinc at rates of up to 0.60 mg/dm³ of soil.

Influence of ball-milled low purity boron powder on the superconductivity of MgB2

MgB2 samples were prepared using as-supplied commercial 96% boron with strong crystalline phase and the same 96% boron (B) after ball milling. The effects of the properties of the starting B powder on the superconductivity were evaluated. We observed that samples using ball-milled 96% B, in comparison with the one made from the as-supplied 96% B, were character- ized by small grain size, broadened full width at half maximum (FWHM), and enhanced magnetic critical current density (J(c)). J(c) reached 2 x 10(3) Acm(-2) at 5 K and 8 T. The improved pinning of these samples seems to be caused by enhanced grain boundary pinning at high field.

Some constraints on the modeling using the uranium isotopes U-238 and U-234 for dating groundwaters from Guarany aquifer, South America

Groundwaters from the Guarany aquifer located at the South American continent and sampled at four wells with described geological sections in São Paulo State, Brazil, were chemically and isotopically analysed with two aims: to evaluate the quality of this important hydrological resource and to investigate the possibility of using the natural uranium isotopes U-234 and U-238 as a chronological tool, since the U-234/U-238 activity ratio and dissolved U content data in groundwater systems have generated models for dating purposes.

The U-isotopes modeling in aquifers from Pocos de Caldas plateau, Brazil

U-modeled groundwater residence times were estimated by changes in U-234/U-238 activity ratio (AR) and U content of groundwaters from Pocos de Caldas city situated at the Pocos de Caldas alkaline massif, Brazil. The estimated ages are more realistic than others generated by the use of hydraulic conductivity data and available information about the weathering rate of rocks in the plateau. The U-234/U-238 AR and reciprocal of the dissolved U-content data also defined a ternary plot that allowed the calculation of the relative volume of three source waters for the mixed water. Such U-isotopes modeling for mixing calculations indicated that the dominant phase (68%) in the mixture is thermal.

Action of auxins and/or boron, in the process of formation of roots in cuttings of coffee (Coffea-Arabica L CV Mundo-Novo)

The objective of present research was to verify the IBA and/or NAA effects with boron, on rooting of coffee (Coffea arabica L. cv 'Mundo Novo') stem cuttings. Therefore it were used stem cuttings from semi-hardwood orthotropous branches, having two nodes, with aproximately 10 cm of lenght. The cuttings were treateds during 24 hours with IBA and/or NAA plus boron solutions. The treatments' effect was observed trough the following observation, 90 days after planting: rooting percentage and number of cuttings with ''callus''. Trough the resultS obtained, it was concluded that, for obtaining more rooting of cuttings, the best treatment was NAA at 200 ppm plus boron or, the combination of IBA and NAA at 200 ppm plus boron.