Scielo RSS <![CDATA[Latin American applied research]]> http://www.scielo.org.ar/rss.php?pid=0327-079320100003&lang=es vol. 40 num. 3 lang. es <![CDATA[SciELO Logo]]> http://www.scielo.org.ar/img/en/fbpelogp.gif http://www.scielo.org.ar <![CDATA[A handheld moisture content sensor using coupled-dipole antennas]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000300001&lng=es&nrm=iso&tlng=es This paper presents an analysis and design of a handheld moisture content sensor. A dielectric property determination technique was used to measure the magnitudes of the reflection and the coupling coefficients of coupled-dipole antennas. These coefficients were plotted and their intersection determined to obtain the values of <img border=0 width=16 height=15 src="/img/revistas/laar/v40n3/a01g01.png">and <img border=0 width=20 height=15 src="/img/revistas/laar/v40n3/a01g02.png">(<img border=0 width=16 height=15 src="/img/revistas/laar/v40n3/a01g01.png"> and <img border=0 width=20 height=15 src="/img/revistas/laar/v40n3/a01g02.png">, respectively, are the real and imaginary parts of the relative complex permittivity of the dielectric of interest). Moisture content measurements for paddy at various moisture content levels are shown. Comparison of measurements made by this technique with those made by conventional transmission measurement technique yielded a compensation scheme for error reduction. This sensor is useful for controlling the quality of paddy dried in a continuous microwave drying system process. <![CDATA[The power series method in the effectiveness factor calculations]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000300002&lng=es&nrm=iso&tlng=es In the present paper, exact analytical solutions are obtained for nonlinear ordinary differential equations which appear in complex diffusion-reaction processes. A technique based on the power series method is used. Numerical results were computed for a number of cases which correspond to boundary value problems available in the literature. Additionally, new numerical results were generated for several important cases. <![CDATA[Isomerization of fatty acids in sunflower oil during heat treatment]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000300003&lng=es&nrm=iso&tlng=es Pilot-scale treatments of sunflower oil similar to deodorization were carried out by applying steam stripping at different temperatures ranging from 179 to 282°C for 5 h. Samples were taken every half hour, and fatty acid composition was determined by gas chromatography. The results showed an increase in the relative percentage of trans linoleic acid with an increase in either time or temperature. The formation of trans linoleic acid isomers followed a zero-order reaction and the kinetic constants varied according to the Arrhenius' law. The activation energies for the formation of the acids C18:2ct, C18:2tc and C18:2tt were calculated as 147.4, 147.8 and 146.6 kJ/mol, respectively. <![CDATA[Biodegradation kinetics of benzene and toluene as single and mixed substrate: estimation of biokinetics parameters by applying particle swarm optimization]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000300004&lng=es&nrm=iso&tlng=es This paper aims to describe the microbial biodegradation kinetics of benzene and toluene as single and mixed substrates. Particle Swarm Optimization (PSO) is used as the parameter identification procedure. Initially, the Monod and Andrews models were used. To predict the interactions between the substrates, more sophisticated models of inhibition and the SKIP model were applied. The development of the changes on the competitive inhibition model was also described. The models were evaluated using experimental data on Pseudomonas putida F1 activity found in the literature. Simulation results showed that the best description of the biodegradation process of a pure substrate can be achieved by the Andrews model and in the case of a mixture by the modified competitive inhibition model. These results were expected because both substrates are catabolized by the same metabolic pathway through Pseudomonas putida F1. The SKIP model also captured the substrate interactions well. The performance of PSO was excellent and the methodology developed in this work can be considered as very efficient. <![CDATA[Assembly and release of diclofenac acid-pillared hydrotalcites]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000300005&lng=es&nrm=iso&tlng=es A pharmaceutically active material diclofenac was intercalated into a layered double hydroxide by co-precipitation method, release studies suggest that the result diclofenac acid-pillared hydrotalcites (Dic-LDHs) have significant sustained release effect. The complex materials were characterrized using XRD, FTIR, DSC-TG, EA and ICP. The result show that the interlayer distance of the Dic-LDHs is expanded to 1.83nm and the thermal stability of material increases after the intercalation of diclofenac. <![CDATA[Fabrication of hot-wire probes and electronics for constant temperature anemometers]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000300006&lng=es&nrm=iso&tlng=es The purpose of this paper is to discuss the construction of constant temperature hot wire anemometers. Different options are analyzed for the fabrication of sensors and electronics. A practical and simple method is developed to manufacture the probe and associated electronics. The fabricated sensor has a diameter of 2 µm and approximately 500 µm in length. The associated electronics are designed to keep the sensor working at a constant temperature and allow the indirect measurement of speed. The design is simple, inexpensive and highly flexible regarding its use and modifications. The dynamic tests performed and the comparison with a commercial model shows a satisfactory performance. The unit built also includes an option for testing with a square wave, which is generated internally, and a comparator mode to measure the resistance of the sensor. <![CDATA[Improving emulsion separation: the collector material concept]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000300007&lng=es&nrm=iso&tlng=es A variety of materials have been used to investigate their applicability as so-called collector materials to improve the destabilization and separation of water in oil emulsions stabilized by a nonionic surfactant. The emulsion destabilization degree was determined by the extent of water and oil separated after centrifugation. The recovery of both phases was strongly dependent on the nature of the material, material/emulsion ratio, particle size, and contact time. By varying conditions, it is possible to increase the separation of water from 0% (without material) up to 95%. <![CDATA[Acoustical properties of Schiff base solutions in dmf]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000300008&lng=es&nrm=iso&tlng=es Density, ultrasonic velocity and viscosity of Schiff bases have been studied in dimethyl formamide at 308.15 K. From the experimental data, various acoustical parameters such as specific Impedance (Z), isentropic compressibility (?s), Rao's molar sound function (Rm), Van der Waals constant (b), relaxation strength (r), intermolecular free length (Lf), internal pressure (p), solvation number (Sn) etc. have been evaluated, which helps in understanding the molecular interactions occurring in these solutions. <![CDATA[Automatic tuning of model predictive controllers based on multiobjective optimization]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000300009&lng=es&nrm=iso&tlng=es In this work a general procedure for tuning multivariable model predictive controllers (MPC) with constraints is presented. Control system parameters are obtained by solving a multiobjective optimization problem. The set of objectives includes controllability aspects, in terms of the H&infin; norms of some closed loop transfer functions of the system, and others related to the range of manipulated and controlled variables, expressed using the l1 norm. Moreover, the use of multiple linearized models for tuning, allows for the specification of robust performance criteria through a set of constraints. The mathematical optimization for tuning all controller parameters is tackled in two iterative steps. First, integer parameters are obtained using a specific random search, and secondly a sequential programming based method is used to tune the real parameters. As a validation example, the tuning of the control system for the activated sludge process of a wastewater treatment plant has been selected. <![CDATA[Carbon monoxide emitted from the city of Buenos Aires and transported to neighbouring districts]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000300010&lng=es&nrm=iso&tlng=es Air pollutants emitted in a city may reach neighbouring areas. This paper describes and applies a methodology for estimating the CO transported from the City of Buenos Aires (CBA) to neighbouring districts. The methodology is applicable only for inert pollutants. This preliminary evaluation shows that 32% of CO annually emitted is transported to the de la Plata River. The smallest fraction (7.5% of annual emission) goes to the district of Avellaneda. The main factors controlling the outflow flux of CO are evaluated and their relative importance is discussed. It is also evaluated that the CO emissions in the CBA may contribute to 8h-CO background concentrations in the Metropolitan Area of Buenos Aires (MABA) with more than 10% of the Air Quality Standard. The districts of the MABA located west and northwest the CBA are the more affected by the CO emitted in the CBA. <![CDATA[Development of a bench scale system for anaerobic acidogenic digestion of wastewater from isolated soy protein]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000300011&lng=es&nrm=iso&tlng=es Wastewater from isolated soy protein (ISP) production is characterized by high organic load. A complex primary wastewater treatment system has been studied: an anaerobic acidogenic reactor, a tubular reactor and a sedimentation tank. Anaerobic digestion is a very complex process; the control of temperature, pH, alkalinity, TSS/VSS and COD is fundamental. The objective was to develop and compare the efficiency of a bench scale anaerobic acidogenic reactor, followed by the precipitation, coagulation and sedimentation steps, with an existing industrial ISP wastewater treatment system. The results obtained with bench system (reaction time of 6 h, 48 °C) were very close to the industrial ones: pH reduction of 4.5 to 3.7 (indicating the protein hydrolysis), high VFA accumulation (1,300 and 2,650 mg.L-1 minimum and maximum concentration), no methane production and increase in TSS/VSS. This study gives an insight of the industrial primary wastewater treatment system and can be useful in future researches. <![CDATA[Solubility of caffeine in water, ethyl acetate, ethanol, carbon tetrachloride, methanol, chloroform, dichloromethane, and acetone between 298 and 323 K]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000300012&lng=es&nrm=iso&tlng=es The solubility of caffeine in water, ethyl acetate, ethanol, carbon tetrachloride, methanol, chloroform, dichloromethane and acetone were measured by a gravimetrical method from (298 to 323) K and the solubility data was correlated against temperature. The solubility of caffeine in chloroform and dichloromethane was high compared with other solvents <![CDATA[Polar profile of the wall pressure on cylindrical bars in yawed gas flow]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000300013&lng=es&nrm=iso&tlng=es The polar distribution of wall pressures in cross flow through a cell of four cylindrical tubes inclined at different angles 30°&le;&alpha;&le;90° was experimentally studied using flow air at near atmospheric pressure flowing at a maximum velocity of 30.8 m/sec (2200&le;R &le;6100). The experiments show that the pressure coefficient is strongly influenced by the inclination angle. For perpendicular cross flow, the experiments were compared with those obtained from potential flow theory showing poor agreement. A model based on the curvature of the stream lines in the gap between bars agrees very well with the pressure coefficient at the gap.