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vol. 41 num. 2 lang. en<![CDATA[SciELO Logo]]>http://www.scielo.org.ar/img/en/fbpelogp.gif
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<![CDATA[Removal of zinc ions from aqueous solutions by sorptive-flotation using limestone as a lowcost sorbent and oleic acid as a surfactant]]>
http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000200001&lng=en&nrm=iso&tlng=en
Environmental pollution, mainly in the aquatic systems, due to developments in industry, is one of the most significant problems of this century. Many industrial wastewater streams (ca. the metal working, semiconductor, and copper industries, mine water, etc.) contain heavy metals, which are of great environmental concern and must be removed prior to water discharge or water recycling. The present study aims to develop a simple, rapid and economic procedure for Zn2+ ions removal under the optimum conditions. It is based on the sorption of Zn2+ ions from aqueous solutions onto limestone fines (LS), which is an inexpensive and widespread over the globe, followed by flotation with oleic acid (HOL) surfactant. The different parameters (namely: solution pH, sorbent, surfactant and zinc concentrations, shaking times, ionic strength, temperature and the presence of foreign ions) influencing the sorptive-flotation process were examined. About 100 % of Zn2+ ions were removed from aqueous solutions at pH 7 after shaking for 5 min and at room temperature (∼25°C). The procedure was successfully applied to recover almost Zn2+ ions spiked to some natural water samples. A mechanism for sorption -flotation is suggested.<![CDATA[Formulation of water in paraffin emulsions]]>
http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000200002&lng=en&nrm=iso&tlng=en
In this work, the effect of surfactant content, water content, HLB value, alcohol content, salinity, emulsion volume and mixing properties on water in paraffin emulsion stability was studied. Emulsion stability was determined by the extent of water and oil resolved after 30 days. After finishing the variables scans, the most appropriate formulation conditions were established, and a formulation protocol was defined. Emulsion density and apparent viscosity were measured, and viscosity was modeled by the Power Law.<![CDATA[A comparison of metaheuristics algorithms for combinatorial optimization problems. Application to phase balancing in electric distribution systems]]>
http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000200003&lng=en&nrm=iso&tlng=en
Metaheuristics Algorithms are widely recognized as one of most practical approaches for Combinatorial Optimization Problems. This paper presents a comparison between two metaheuristics to solve a problem of Phase Balancing in Low Voltage Electric Distribution Systems. Among the most representative mono-objective metaheuristics, was selected Simulated Annealing, to compare with a different metaheuristic approach: Evolutionary Particle Swarm Optimization. In this work, both of them are extended to fuzzy domain to modeling a multi-objective optimization, by mean of a fuzzy fitness function. A simulation on a real system is presented, and advantages of Swarm approach are evidenced.<![CDATA[Testing of an opto-electronic sensor for the high-throughput measurement of seed spatial distributions]]>
http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000200004&lng=en&nrm=iso&tlng=en
We present testing results of an intelligent opto-electronic seed sensor system allowing the high throughput measurement of seed spatial distributions. With this aim, we evaluate the correlation between actual and sensor estimated distances between seeds. The tests take into account two important features in farming performance: the planter speed and the sensor-soil distance. While the former one determines the man-hours required, the later one determines the feasibility of sensor mounting and its useful life. Results show that precise measurements can be obtained with the proposed sensor at typical planter speeds, even with the sensor on top of the drop tube.<![CDATA[Application of electrochemical oxidation as alternative for removing methyl green dye from aqueous solutions]]>
http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000200005&lng=en&nrm=iso&tlng=en
In this work, the treatment of synthetic wastewaters containing Methyl Green (MG) by anodic oxidation using Ti/PbO2 anodes was investigated. Galvanostatic electrolyses of MG synthetic wastewaters have led to the complete decolourization removal at different current density values (10, 20 and 40 mA cm-2), temperatures (25, 40 and 60°C) and agitation rate (100, 200 and 300 rpm). According to the experimental results obtained in this work, the electrochemical oxidation process is suitable for removing TOC and decolourising wastewaters containing MG dye, due to the electrocatalytic properties of Ti/PbO2 anode. In general, the energy requirements for removing color during galvanostatic electrolyses of MG synthetic solutions depends mainly on the applied current density; it passes from 0.29 kWh at 10 mA cm-2 to 1.64 kWh at 40 mA cm-2 per volume of treated effluent removed (m-3). The results are described and discussed in the light of the existing literature.<![CDATA[Antioxidative activity of citric and ascorbic acids and their preventive effect on lipid oxidation in frozen persian sturgeon fillets]]>
http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000200006&lng=en&nrm=iso&tlng=en
Persian sturgeon (Acipenser persicus) fillets were soaked in Citric acid, Ascorbic acid and combination of Citric and Ascorbic acid solutions and then were stored at frozen conditions (-18 °C) up to 6 months. During storage, some general chemical analysis such as free fatty acids, primary and secondary oxidation products and sensory analysis were measured in order to study rancidity development. Results showed that antioxidant treatments had lower (P<0.05) lipid oxidation development in compare with control samples. Development of peroxides value in control samples was significantly higher (P<0.05) than antioxidants treatments after 6 months storage. Also other experiments showed that AA+CA treatment had the best effect (P<0.05) on delaying lipid oxidation in frozen fillets.<![CDATA[Identification of pale lager beers via image analysis]]>
http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000200007&lng=en&nrm=iso&tlng=en
This article presents an alternative color-based classification methodology which is used for pattern recognition of pale lager beers. Beer sample images are digitalized on a common desk scanner resulting in color histograms in the RGB scale. The frequency distribution of color indexes according to each color channel were obtained for each image, then decomposed into vector lines R, G and B, each vector having 256 components (indexes/color tones). PCA is used to represent the data in two-dimensional plots, and also to represent color changes of beer samples exposed to light and air. After one hour, significant changes in the yellow color of the beer can be distinguished in the score plot. In short, differences between brands of beer are directly related to differences in their color.<![CDATA[Study on inclusion interaction of ibuprofen with Β-cyclodextrin derivatives]]>
http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000200008&lng=en&nrm=iso&tlng=en
The inclusion interaction of ibuprofen with hydroxypropyl-β-cyclodextrin (HP-β-CD), hydroxyethyl-β-cyclodextrin (HE-β-CD) and methyl-β-cyclodextrin (Me-β-CD) was investigated by fluorescence spectroscopy. Experimental conditions affecting the inclusion process, such as host molecule, HP-β-CD concentration and pH, were discussed in detail. The results suggested the formation of inclusion complexes with a stoichiometric ratio of 1:1 and HP-β-CD was more suitable to include neutral ibuprofen molecule. In addition, a phase solubility study was performed by mixing an excess amount of ibuprofen with aqueous solution containing increasing amount of β-CDs using UV-vis. The results indicated that the solubility of ibuprofen was increased by inclusion with β-CD derivatives, and HP-β-CD was most efficient among the three β-CD derivatives. Moreover, stable solid inclusion complexes were established and characterized by DSC.<![CDATA[Moisture migration during a tempering time after the heat treatment step in yerba maté processing]]>
http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000200009&lng=en&nrm=iso&tlng=en
The aim of this research was to study the effect of applying a tempering time to the branches of yerba maté after the heat treatment stage (or sapecado). Assays were carried out in three industrial producers of Misiones Argentina. Branches were obtained from the sapecador outlet and then, they were put in rest in order to form a bed. First, moisture content of leaves and twigs, separately, and then losses of mass of whole branches were measured. When the branches were put in rest in a bed during 30 min, 8.60 kg of water/100 kg of dry matter were transferred from the twigs to the leaves and 5.17 kg of water/ 100 kg of dry matter were lost by evaporation.<![CDATA[Modeling and testing of moving base manipulators with elastic joints]]>
http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000200010&lng=en&nrm=iso&tlng=en
In this paper, design and manufacturing of a manipulator with joint elasticity is described while different base positions are considered. First, the kinematics and dynamic equations of the mechanism with flexible joints for the three major axis of the mobile robot are derived and simulated. Next, computational technique for obtaining maximum load carrying capacity of robotic manipulators with joint elasticity is described while different base positions are considered. The maximum load carrying capacity that can be achieved by a robotic manipulator during a given trajectory is limited by number of factors. Probably the most important factors are the actuator limitations, joint elasticity (transmissions, reducers and servo drive system) and relative configuration of robot with respect to its base. Finally, the manipulator is tested for a given trajectory in order to find the characteristics of the designed manipulator. While the manipulator is designed to carry the maximum load, end-effector's speed, robot's compatibility with the operator's condition, and accuracy are the most important applicable points of the manipulator. Therefore, the manipulator in different trajectories with various speeds and loads are tested, and then the results are analyzed.<![CDATA[Thermal diffusion effect on a three-dimensional mhd free convection with mass transfer flow from a porous vertical plate]]>
http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000200011&lng=en&nrm=iso&tlng=en
A systematic analysis to study the effect of thermal diffusion on a three dimensional free convective flow with mass transfer of an incompressible viscous electrically conducting fluid past a porous vertical plate with transverse sinusoidal suction velocity is presented. Due to this type of suction velocity at the plate the flow becomes three-dimensional one. A magnetic field of uniform strength is assumed to be applied normal to the plate directed into the fluid region. The magnetic Reynolds number is considered to be small so that the induced magnetic field can be neglected. An analytical solution of the problem is obtained. The expressions for the velocity field, fluid temperature, species concentration, fluid pressure, skin-friction, Nusselt number and Sherwood number and current density are obtained in non-dimensional forms. The effects of Hartmann number, Soret number, Reynolds number and Prandtl number on the velocity field, temperature and concentration distributions, skin friction at the plate and on the amplitudes of the first order skin-friction, the first order Nusselt number and the first order Sherwood number at the plate are discussed graphically. It is seen that the thermal diffusion and applied magnetic field have significant effects on the flow and on the heat and mass transfer characteristics.<![CDATA[Model reference adaptive control for mobile robots in trajectory tracking using radial basis function neural networks]]>
http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000200012&lng=en&nrm=iso&tlng=en
This paper propose an Model Reference Adaptive Control (MRAC) for mobile robots for which stability conditions and performance evaluation are given. The proposed control structure combines a feedback linearization model, based on a kinematics nominal model, and a direct neural network-based adaptive dynamics control. The architecture of the dynamic control is based on radial basis functions neural networks (RBF-NN) to construct the MRAC controller. The parameters of the adaptive dynamic controller are adjusted according to a law derived using Lyapunov stability theory and the centers of the RBF are adapted using the supervised algorithm. The resulting MRAC controller is efficient and robust in the sense that it succeeds to achieve a good tracking performance with a small computational effort. Stability result for the adaptive neuro-control system is given. It is proved that control errors are ultimately bounded as a function of the approximation error of the RBF-NN. Experimental results showing the practical feasibility and performance of the proposed approach to mobile robotics are given.<![CDATA[Modeling conventional one-dimensional drying of radiata pine based on the effective diffusion coefficient]]>
http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000200013&lng=en&nrm=iso&tlng=en
We modeled conventional one-dimensional drying of radiata pine (Pinus radiata) wood using the concept of effective diffusion. The experimentally determined effective diffusion coefficients for the radial and tangential directions were related exponentially to the moisture content. These coefficients were characterized by two parameters that were determined through optimization within the context of an inverse problem. One-dimensional drying experiments were carried out under constant drying 44/36 (°C/°C) in order to determine transitory spatial distributions of moisture and drying curves, which were used then to determine the model parameters and validate the model. The mathematical model consisted of a partial, non-linear, differential equation of the second order and was characterized by coefficients that varied exponentially with moisture content; this later was integrated numerically through the finite volume method. Simulations of the transitory distribution of moisture gradients gave satisfactory results, and the drying curves were correlated with experimental data as well as the values of the parameters required by the proposed model.<![CDATA[Finite volume simulation of 2-D and 3-D non-stationary magnetogasdynamic flow]]>
http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000200014&lng=en&nrm=iso&tlng=en
This work presents the development of the ideal and real magnetogasdynamic (MGD) equations in two and three spatial dimensions, followed by a modern numerical resolution method. The equations that govern the MGD flows are continuity, momentum, energy and magnetic induction together with a state equation. The method of Roe has been applied, in a high resolution Total Variation Diminishing scheme, with modifications proposed by Yee et al. For the implementation of this method in finite volumes a FORTRAN code has been developed, and it has been applied to the resolution of the magnetogasdynamic Riemann problem and the Hartman flow. Due to the high computational cost demanded by a 3D simulation, it has been necessary to reduce the grid density, compared to that used on the unidimensional and bidimensional cases. In order to evaluate this last issue, an analysis of the effect of the grid density on the results has been included at the end of the present work. The magnetogasdynamic shock tube and the Hartman flow, used as "benchmarks", have been satisfactorily solved.