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Guevara M.,University of Concepción | Guevara M.,University of the East Venezuela | Bastardo L.,University of the East Venezuela | Cortez R.,University of the East Venezuela | And 2 more authors.
Revista de Biologia Tropical | Year: 2011

Rotifers are an important live feed for first feeding larvae of many fish species. The use of concentrated algae cells in the mass culture of the rotifer Brachionus plicatilis (Brachionidae) has opened new horizons for research on this organism. Pastes of Rhodomonas salina (Pyrenomonadaceae) obtained either by centrifugation or flocculation with chitosan were preserved, with or without vitamin C, at -20°C for four weeks and were evaluated biochemically (proteins, lipids, pigments and fatty acids contents) and subsequently, were used to feed the rotifer Brachionus plicatilis at a ratio of 25mg/L/day. Four different microalgae pastes were prepared: (1) centrifuged and preserved with vitamin C (CV), (2) centrifuged and preserved without vitamin C (C), (3) flocculated and with vitamin C (FV) and (4) flocculated without vitamin C (F). All treatments showed similar contents of proteins and total lipids with respect to control culture (a fresh culture of R. salina), with mean values of 40.0±2.32% and 12.0±1.45%, respectively. The pheophytin a/chlorophyll a ratio, a general indicator of the chemical status of microalgal concentrates, was similar (0.09-0.11) between centrifuged pastes and control culture, but was found to be higher in flocculated pastes (1.28-1.48). The fatty acid profile varied with respect to the control culture, mainly in the proportion of the essential polyunsaturated fatty acids (PUFAs): eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Total PUFAs, EPA and DHA contents were statistically similar between centrifuged pastes and control culture (PUFAs: 47%, EPA: 4% and DHA: 4.7%), whereas values obtained for flocculated pastes were significantly lower. The rotifers grew equally well when fed with centrifuged pastes or control culture (maximum density: 320rotifers/mL; instantaneous growth rate: 0.23rotifers/ day, fecundity: 1.49eggs/female and productivity: 43x10 3rotifers/L/day. No significant effect of vitamin C was found when used as a paste preservative. We concluded that centrifugation is an effective harvesting method, and that freezing to -20 oC for four weeks (no vitamin added), may help maintain the nutritional quality of R. salina paste, similar to fresh microalgae and can be offered to Brachionus plicatilis.

Neto J.E.,Paulista University | Neto J.E.,University of the State of Amazonas | Neto J.E.,Federal University of Pará | Suarez-Leon A.A.,University of the East of Cuba | And 4 more authors.
IFMBE Proceedings | Year: 2013

ECG feature extraction plays a significant role in diagnosing most of the cardiac diseases. In this paper, a com- parison between three ECG feature extraction methods is presented. The methods are: Linear Principal Components Analysis (PCA), Discrete Cosine Transformation (DCT) and Kernel Principal Components Analysis (KPCA). A Multilayer Perceptron is used as a gold classifier combined with the three methods before. The beats used for training and validation of the three combinations are extracted from twelve MIT - BIH Arrhythmia Database records. The performance of the three combinations is discussed and a simple execution time is evaluated. © 2013 Springer.

De Arenas I.B.,Instituto Universitario Of Tecnologia | Cho S.-A.,Venezuelan Institute for Scientific Research
Revista Latinoamericana de Metalurgia y Materiales | Year: 2011

The Al2TiO5 formation and decomposition has been studied in equimolar mixtures of Al2O3-TiO2 powders, with 3-9 wt% industrial ferrosilicon additions as Al 2TiO5 structural stabilizer. The microstructure evolution under the conditions: (a) solid state reaction sintering of Al2O 3 and TiO2 without and with FeSi2 additions and (b) after 100 hours heat treatment at 1100°C. They were analyzed by scanning electron microscopy (SEM) in backscattering electron mode imaging (BSEI). X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) techniques were used to determine structural phases and chemical composition respectively. The pattern sample, this means, without FeSi2, showed aluminum titanate with unreacted TiO2 and Al2O3 and the characteristic microcracking and micropores due to reactive sintering were observed. XRD patterns of samples with ferrosilicon evidenced the effect of this addition on the Al2TiO5 formation and a minor structural stabilizing effect on Al2TiO5 decomposition in the heat-treated samples. © 2011 Universidad Simón Bolívar (Venezuela).

Sanchez M.,Venezuelan Institute for Scientific Research | Sanchez M.,Instituto Universitario Of Tecnologia | Ruette F.,Venezuelan Institute for Scientific Research
Chemical Physics Letters | Year: 2015

Hydrogen atoms diffusion on a hydrocarbon flake is studied using PM6 and DFT programs using as models neutral and positive charged coronene. Chemisorption and potential energy surfaces and diffusion paths were calculated. Results show that diffusion occurs through C-C bonds. Edge effects are very important because the most stable adsorptions occur on hydrogenated border sites, so the diffusion is biased toward edge sites. Charged coronene has stronger adsorption energies than neutral systems. A large difference between barriers in neutral and charged systems was not observed in most of the cases. A discussion of modeling diffusion processes is presented. © 2015 Published by Elsevier B.V.

D'Armas H.,University of the East Venezuela | Yanez D.,University of the East Venezuela | Reyes D.,University of the East Venezuela | Salazar G.,Instituto Universitario Of Tecnologia
Revista de Biologia Tropical | Year: 2010

Muricid species of P. pomum and C. brevifrons are of economic importance in the Caribbean. This study includes a comparative evaluation of fatty acid content in the total lipid composition of Phyllonotus pomum and Chicoreus brevifrons. Snail samples were collected during the rainy, dry and transition seasons, in Punta Arena, Sucre (Venezuela). Total lipids were extracted and the specific fatty acid contents were analyzed by gas chromatography. Lipid concentrations varied between 0.87 and 1.85%, with minimum and maximum values corresponding to C. brevifrons collected during rainy and dry seasons, respectively. In the case of total lipids, a high concentration of unsaturated fatty acids (57.21-70.05%) was observed followed by saturated fatty acids (20.33-31.94%), during all seasons. The polyunsaturated occurred in higher proportion among the unsaturated fatty acids, except for P. pomum which showed higher proportion of monounsaturated fatty acids (38.95%) during the transition season. The prevailing fatty acids were: C14:0, C16:0, C18:0, C20:1, C22:1 ω-11, C22:1 ω-9, C18:3 ω-3, C20:5 ω-3 and C22:6 ω-3, among which docosahexaenoic acid was the predominant polyunsaturated fatty acid, showing values between 4.62 and 33.11%. The presence of high concentrations of polyunsaturated fatty acids found in P. Pomum and C. brevifrons allow their recommendation for human consumption with appropriate resource utilization.

De Arenas I.B.,Instituto Universitario Of Tecnologia | Gasga J.R.,National Autonomous University of Mexico
Revista Latinoamericana de Metalurgia y Materiales | Year: 2010

Due to its low expansion and thermal conductivity, as well as its high thermal shock resistance, aluminum titanate (Al2TiO5) is a material used as thermal barrier in diverse engineering components and interesting for some applications in combustion motor parts. However, this application is limited due to its low mechanical resistance and thermal stability below 1280°C. In this work, it has been studied aluminum titanate materials stabilized with pure and mineral processed Venezuelan ilmenite and reinforced with excess Al2O3 and TiO2 obtained "in situ" by reactive sintering. X ray diffraction (XRD), scanning (SEM) and transmission electron microscopy (TEM) of the composite material has been performed in order to determine and correlate the structural effect of the ilmenite and reinforcements with the stability of aluminum titanate. © 2010 Universidad Simón Bolívar (Venezuela).

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