Growth, yield, water and effluent quality in ponds with different management during tambaqui juvenile production.

Crescimento, produção e qualidade da água e do efluente em viveiro de tambaqui com diferentes manejos durante a recria

Estabelecimento de cultura in vitro de células embrionárias do carrapato Boophilus microplus.

bitstream/item/137709/1/PESQ-EM-ANDAMENTO-54.pdfCNPGC

The enthalpies of dissociation of the N-O bonds in two quinoxaline derivatives

The present work reports the first experimental thermochemical study of mono-N-oxides derived from quinoxaline, namely, 3-methoxycarbonyl-2-methyl-quinoxaline N-oxide and 3-ethoxycarbonyl-2-methyl-quinoxaline N-oxide. The values of the enthalpies of formation, in the condensed state, and of the enthalpies of sublimation, derived from static bomb calorimetry and Calvet microcalorimetry measurements, respectively, are combined to derive the standard molar enthalpies of formation in the gaseous phase for these two compounds. From the latter values, the first and second N-O bond dissociation enthalpies for the corresponding di-N-oxides have been obtained. The gas-phase experimental results are also compared with calculated data obtained with a density functional theory approach. Copyright (c) 2008 John Wiley & Sons, Ltd

Nonrelativistic Limit of the Scalar Chern-Simons Theory and the Aharonov-Bohm Scattering

We study the nonrelativistic limit of the quantum theory of a Chern-Simons field minimally coupled to a scalar field with quartic self-interaction. The renormalization of the relativistic model, in the Coulomb gauge, is discussed. We employ a procedure to calculate scattering amplitudes for low momenta that generates their $|p|/m$ expansion and separates the contributions coming from high and low energy intermediary states. The two body scattering amplitude is calculated up to order $p^2/m^2$. It is shown that the existence of a critical value of the self-interaction parameter for which the 2-particle scattering amplitude reduces to the Aharonov-Bohm one is a strictly nonrelativistic feature. The subdominant terms correspond to relativistic corrections to the Aharonov-Bohm scattering. A nonrelativistic reduction scheme and an effective nonrelativistic Lagrangian to account for the relativistic corrections are proposed.Comment: 22 pages, 8 figures, revtex, to be published in Int. J. Mod. Phys.

Improving electrocatalityc activity of LaNiO3 films by deposition on foam nickel substrates

The electrodes were obtained by coating a nickel foam support with the oxide suspension. Optical microscopy and cyclic voltammetry were used on the electrodes characterization. The evaluation of the electrodes electrocatalytic activity, towards the oxygen evolution reaction in alkaline medium, was performed by means of steady state measurements. The reaction follows a first order kinetics, with respect to OH- concentration, with Tafel slopes close to 40 mV, for low overpotentials. Based on the apparent and real current densities it was possible to conclude that the increase on the electrode activity, when compared with the published data, is mostly related to geometric factors. This fact has been associated with the high electrode/electrolyte contact area provided by the foam nickel substrate. Synergetic effects between the Ni foam and the perovskite oxide cannot be discarded

Redox stability and bifunctionality of LaNiO3-based oxygen electrodes

One key issue in the development of Regenerative fuel cells (RFCs) is the availability of cheap, highly active electrocatalysts for both oxygen reduction and water oxidation. Perovskite-type oxides, with the general formula ABO3, are potential catalysts for next generation of regenerative fuel cells. In particular, LaNiO3 has been recognised as one of the most promising oxygen electrodes. In this work LaNiO3 perovskite-type oxides, prepared by a self-combustion method [1, 2], have been simultaneously optimized for activity and stability as an anode and cathode material for water oxidation and oxygen reduction reaction (ORR), respectively. Extremely high surface area has been measured by BET analysis with matching electrochemical activity estimated by cyclic voltammetry and electrochemical impedance spectroscopy. A full electrochemical study has been conducted in order to kinetically characterize the prepared electrodes in alkaline media, using a Ni foam and carbon paper as support material for the electrodes. For LaNiO3 deposits on Ni foam, low contact resistance between the oxide and support, possibility of high metal oxide loadings and dimensional stability were accomplished with remarkable stability in the region of oxygen evolution. For LaNiO3 deposits on carbon paper, the preparation of porous gas-diffusion electrodes providing extended reaction zones in the solid/liquid/gas interfacial region. This type of electrode was reserved for the region of oxygen reduction in which good results were obtained, since for water oxidation the electrochemical oxidation of carbon sets a practical limit to the lifetime of the carbon supported catalysts. The electrode's stability study was performed by potential cycling and at constant current density in the appropriate potential windows

Towards stable bifunctional oxygen electrodes and corrosion resistant gas diffusion layers for regenerative fuel cells

ABSTRACT: Regenerative fuel cells (RFCs) can provide very high energy storage at minimal weight in a dual mode system, by combining an electrolyzer and a fuel cell. Although RFCs are an appealing technology their development is still at an early stage. One key issue is the search for highly active electrocatalysts for both oxygen reduction and water oxidation. Presently, platinum is the best electrocatalyst for the oxygen reduction reaction (ORR), but has a poor oxygen evolution (OER) performance while metal oxides catalyze the OER but not the ORR. Yet, the search for the development of bi-functional oxygen electrodes is also associated to structurally stable gas diffusion layers - they must be capable of withstanding high potentials when cells are operated in the electrolyzer mode and in addition, mass transport limitations when used as a cathode in fuel cell mode. A novel approach is used in this work to tackle the issue, focussing on the development of stable gas diffusion electrodes for the oxygen reactions, having as a base high surface area LaNiO3. Previous work by the authors has optimised the synthesis of the mentioned perovskite-type oxide, prepared by a self-combustion method. The high electrochemical surface area and low porosity of the oxide has been indicated by electrochemical impedance spectroscopy (EIS) and BET measurements. A full characterization has been the subject of recent publications [1,2]. In a first instance, carbon diffusion electrodes on carbon paper are considered. The gas diffusion layers were prepared from carbon black Vulcan XC-72 R, with a LaNiO3 loading of 3 mg cm-2. To fabricate the catalyst layer, an ink was prepared by suspending LaNiO3 in isopropanol, and stirring in an ultrasonic bath to thoroughly wet and disperses it. A 5% Nafion® dispersion solution (Electrochem, Inc) was then added to the mixture. The catalyst inks were dispersed onto the gas diffusion layer with a brush, and dried at 50°C, until the desired catalys t loading was achieved. Finally, a Nafion layer was painted and dried at 50ºC. Significant current densities were obtained in both OER and ORR domains. A full electrochemical study was conducted in order to obtain the kinetic parameters in the OER region using a 1 M KOH solution. Cyclability and stability tests were also conducted. The tests were done in two potential ranges and served as a means of electrode conditioning. The electrode was also subjected to 200 cycles between 0.25 and 0.55 V vs Ag/AgCl (sat.) and an extra 100 cycles between -0.40 and 0.6 V vs Ag/AgCl (sat.), at a scan rate of 100 mV s-1. Additionally a constant current density of ~10 mA cm-2 was applied during 50 hours with simultaneous potential monitoring. Activity loss and increasing resistance of the electrodes were observed using cyclic voltammetry and EIS respectively. Carbon oxidation is favorable at the working potentials used which might sets a practical limit on the lifetime of the GDE. In a second instance, the deposition of LaNiO3 on a Ni foam (1.6 mm thickness, 95% porosity) was effected bringing about more stability in the OER region and Tafel slopes (47 mVdec-1) practically half of the value encountered in the case of carbon paper electrodes. Stability under galvanostatic conditions was assessed at current densities 10 times larger than those used in the case of the carbon paper (100 mA cm-2), also during 50 h, with excellent results. Due to the high stability at anodic potentials found with the Ni foam electrodes and in order to increase current densities, composite electrodes LaNiO3/Pt-Ru were prepared as an alternative to carbon paper electrodes. Results obtained using non-supported Pt-Ru (5-30 wt%) are discussed and compared with the case of carbon-supported Pt-Ru nanoparticles, in the same experimental conditions. It is suggested that LaNiO3 can be used as susbstitute material for carbon black, avoiding the effects of carbon corrosion in the OER region