Influence of the atmospheric plasma spray coating in electrodes properties to use in alkaline electrolysis

Hydrogen has been increasingly used as an energy carrier over the past few years due to its several applications mainly associated with the use of renewable energy. Among all the processes for hydrogen production, water electrolysis produces the purest hydrogen. However, the usage of water electrolysis accounts to only 4% of today’s hydrogen production, mainly due to economic factors. Alkaline electrolysis is, so far, the most mature, the most efficient and the simplest process among the different types of electrolysis. Nevertheless, improvements in the process are still needed, especially in decreasing the cost of the process. Nickel is one of the cheapest metals having also high electroactivity for oxygen and hydrogen production reactions. Raney-nickel materials, which are porous Ni, are the most promising electrocatalysts providing a wide surface area for the reactions to take place. Ni substrates coated with Raney-nickel NiAlMo using Atmospheric Plasma Spraying (APS) are promising stable cathodes due to the reduction of 0.226 V in hydrogen evolution reaction and its stability for, at least, 40 days. Cathodes produced with different APS parameters proved that high speed plasma jet at 580 m.s-1 creates the most stable and electrochemically active coating. Ni substrates coated with Raney-nickel NiAl coating were used for anodes. An increase of surface area towards uncoated Ni was achieved with porous NiAl. Adding Co3O4 to the NiAl coating a decrease in 0.1 V for oxygen evolution and a stable sample that lasted for 35 days was achieved, mainly due to the presence of Co. Underpotential deposition, as technique to calculate the surface area of a Ni electrode was studied. As expected, Ag was adsorbed in the Ni surface, which was identified by the several increases in current during the cyclic voltammogram cycles due to oxidations and reductions of adsorbed Ag

Semiclassical Tunneling of Wavepackets with Real Trajectories

Semiclassical approximations for tunneling processes usually involve complex trajectories or complex times. In this paper we use a previously derived approximation involving only real trajectories propagating in real time to describe the scattering of a Gaussian wavepacket by a finite square potential barrier. We show that the approximation describes both tunneling and interferences very accurately in the limit of small Plank's constant. We use these results to estimate the tunneling time of the wavepacket and find that, for high energies, the barrier slows down the wavepacket but that it speeds it up at energies comparable to the barrier height.Comment: 23 pages, 7 figures Revised text and figure

Wave polarizations for a beam-like gravitational wave in quadratic curvature gravity

We compute analytically the tidal field and polarizations of an exact gravitational wave generated by a cylindrical beam of null matter of finite width and length in quadratic curvature gravity. We propose that this wave can represent the gravitational wave that keep up with the high energy photons produced in a gamma ray burst (GRB) source.Comment: 5 pages, 3 figures, minor corrections, to appear in CQ

Germinação in vitro de pólen de jerivá (Syagrus romanzoffiana (S.) Cham).

O jerivá é uma palmeira nativa do Brasil, com potencial ornamental, apícola e para a manutenção da fauna silvestre, devido aos seus frutos carnosos, nutritivos e abundantes. Face à exploração indiscriminada das florestas nativas e à importância ecológica da espécie no seu ambiente natural, medidas relacionadas à sua conservação são necessárias. O armazenamento do pólen pode ser utilizado como uma importante ferramenta na conservação ex situ e no melhoramento genético florestal, sendo essencial para isso a avaliação correta da sua viabilidade. O presente trabalho visou definir o meio de cultura adequado para a germinação do pólen de jerivá, por meio da aplicação de diferentes doses de nutrientes estimulantes da germinação (Ca, B, Mg e K), empregando-se o meio de Brewbaker e Kwack modificado para Ca e B, além de sacarose (100 g.L-1 ) e de ágar (3 g.L-1). Os valores obtidos para a porcentagem de germinação foram submetidos à análise de variância e, as médias comparadas por meio do teste de Tukey, ao nível de 1 % de probabilidade. Conclui-se que a adição de nutrientes não influenciou positivamente a germinação in vitro, de forma que o meio contendo apenas ágar e sacarose é indicado para avaliar a germinação do pólen de Syagrus romanzoffiana

Statistical analysis of compressive strength of concrete specimens

This paper presents the statistical analysis of compressive strength of concrete specimens delivered in a laboratory of Northern of Portugal. Three types of concretes were analyzed defined as C20, C25 and C30. In the study we used the results of three years, 1995 to 1997. The one-sample Kolmogorov-Smirnov Test was used to verify the normal distribution of the strength results. The results presented in this paper are important for predicting the performance of structural elements and for calculating resistance factors for limit state design codes. As concrete is made in majority on site, conformity is more difficult than for other construction materials produced on factories. For the first analysis the concrete applied on the different sites were separated in groups. A total of 82 groups of concrete produced in 20 sites, were analyzed. We verified that in about 32% of the groups the characteristic compressive strength established for the design was not achieved. For the second analysis the total results were considered, without separation by site or by group. When the exigency was classes C20 or C25, the characteristic compressive strength was below the exigency. On the contrary, for the concrete mentioned as C30, the characteristic compressive strength was above the exigency

Tratamiento de las complicaciones vasculares tras aplicación del método de Ilizarov: Aportación de tres casos

Entre 1987 y 1991 fueron intervenidos 209 pacientes mediante el método de Ilizarov en nuestra institución. Tres de los pacientes presentaron complicaciones vasculares durante el tratamiento. Todos ellos eran adultos y habían sido tratados por pseudoartrosis de un hueso largo. La lesión vascular ocurrió en la arteria femoral superficial en un caso, la arteria poplítea en otro y la arteria tibial posterior en el último de ellos. El signo clínico del problema vascular fue la presencia de la hemorragia en el punto de salida cutánea de las agujas de Kirschner de transfixión. Se realizó exploración arteriográfica en todos los casos, pero su interpretación fue difícil debido a la presencia del fijador externo. El tratamiento de la complicación vascular fue: en el caso de la lesión de la arteria femoral fue retirado el fijador y realizado un by-pass con un injerto invertido obtenido de la vena safena; en el caso de lesión de la arteria poplítea, se realizó la misma técnica pero sin retirar el fijador. En el último caso la lesión de la arteria tibial posterior se trató mediante ligadura de la misma. En todos los casos, la evolución del tratamiento vascular fue excelente, siendo posible finalizar el tratamiento ortopédico.From 1987 to 1991, 209 patients were operated on by the Ilizarov method in our institution. Among them, 3 patients presented vascular complications during the treatment. All were adults and have been treated for long bone pseudoarthrosis. The vascular lesion ocurred at the femoral superficial artery in one case, at the popliteal artery in other case, and at the posterior tibial artery in the third case. The clinical sign of vascular damage was bleeding through the cutaneous point of the Kirschnner transfixion wires in all cases. Arteriography was done in all cases but its interpretation was very difficult because of the presence of the external fixator. In the case of femoral artery, injury the external fixator was removed and a vascular by-pass was performed with an inverted graft of the saphenous vein. The same procedure was done in the case with a popliteal artery injury but without removal of the external fixator. The case with lesion of the posterior tibial artery was treated by arterial hgature. In all cases, outcome was satisfactory, allowing completion of the orthopaedic treatment

Programa de melhoramento de pínus na Embrapa Florestas.

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