Scielo RSS <![CDATA[Latin American applied research]]> http://www.scielo.org.ar/rss.php?pid=0327-079320060003&lang=es vol. 36 num. 3 lang. es <![CDATA[SciELO Logo]]> http://www.scielo.org.ar/img/en/fbpelogp.gif http://www.scielo.org.ar <![CDATA[Samarium-iron garnet nanopowder obtained by co-precipitation]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932006000300001&lng=es&nrm=iso&tlng=es In this work, samarium-iron garnet nanopowder (Sm3Fe5O12) was obtained and characterized by TG/DTA, XRD, SEM and EDS. The synthesis of this magnetic material was carried out by the co-precipitation method, using hydrated chlorides of the rare-earth elements and ferrous sulfate. PVA was added to the calcined powder in order to facilitate the production of a toroidal compact specimen, which was submitted to sintering in the range of 1200 ºC to 1400 ºC, to stablish a correlation of its magnetic properties with morphology. <![CDATA[Modeling of Fischer-Tropsch synthesis in a tubular reactor]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932006000300002&lng=es&nrm=iso&tlng=es Fischer-Tropsch synthesis is an important chemical process for the production of liquid fuels and olefins. In recent years, the abundant availability of natural gas and the increasing demand of olefins and liquid fuels have led to a high interest to further develop this process. A mathematical model of a tubular reactor used for syngas polymerization was developed and the carbon monoxide polymerization was studied from a modeling point of view. Simulation results show that different parameters affect syngas conversion and carbon product distribution, such as operating pressure, gas velocity and syngas composition. Optimization of several hydrocarbon products were done in order to search for the best operating conditions for their production. <![CDATA[Manufacture and testing of water-borne paints by using vinyl latex containing VeoVa10® monomer]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932006000300003&lng=es&nrm=iso&tlng=es Two different water-borne dispersions (latex) containing different amounts of vinyl acetate and a commercial vinyl ester monomer (VeoVa10) were evaluated by incorporating them in paint formulations for wall protection. Three paint formulations were prepared with different PVC values. The main properties such as hiding power, washability, tension of adhesion, and elasticity were assessed. Changes in color, gloss and adhesion and the extension of chalking, checking, cracking and blistering were also evaluated in normal and accelerated weathering tests. The results indicate that both dispersions are suitable for wall protection (interior or exterior, permanent or temporary protection) and they are compatible with the most common additives used in the Argentinean and Mercosur markets. The presence of VeoVa10 in the binder composition improves the water and UV resistances of the paint. A styrenic-acrylic latex, commonly used in the local market, was used as comparative product. <![CDATA[Modeling of methane steam reforming in a palladium membrane reactor]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932006000300004&lng=es&nrm=iso&tlng=es A mathematical model of a membrane reactor used for methane steam reforming was developed to simulate and compare the maximum yields and operating conditions in the reactor with that in a conventional fixed bed reactor. The methane steam reforming reaction has been investigated from a modeling viewpoint, considering the effect of different parameters on methane conversion and H2/CO ratio. Results show that the membrane reactor presents higher methane conversion yield and can be operated at milder conditions than the fixed bed reactor. Control of the H2/CO ratio is possible in the membrane reactor making the technology more suitable to be used in connection to gas-to-liquid processes (GTL). <![CDATA[Influence of the soluble solids on the zeta potential of a cloudy apple juice]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932006000300005&lng=es&nrm=iso&tlng=es The effect of soluble solids on the Zeta-potential (ξ) of a cloudy apple juice was investigated. Apple juice was enzymatically treated with pectinolytic enzymes and diafiltred with a polysulphone UF membrane (100 kDa) to eliminate soluble solids. Most soluble solids were removed after 4 equivalent sample volumes (ESV) of washing water. During a second period, from 5 to 23 ESV, diafiltration rate was significantly reduced. ξ (mV) moderately increased its absolute value with diafiltration during the first diafiltration period, changing at a rate of -1.1 mV/ºBrix up to 0.3 ºBrix). Results also indicated that after the only restitution of sugars ξ, remained practically constant. When malic acid was restituted to a diafiltred juice, remarkable changes in Zeta potential occurred. As particles in this type of colloids are strongly negative, pH modification had a significant influence. <![CDATA[A genetic-algorithm based decoder for low density parity check codes]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932006000300006&lng=es&nrm=iso&tlng=es This paper presents a Genetic-Algorithm based decoder for a medium-sized Low Density Parity Check code (GAMD decoder). The main advantage of the proposed GAMD decoder is that no information on the noise level transmission channel is required, an essential condition for the well-known sum product algorithm. The proposed methodology combines a Genetic Algorithm stage with a meta-decision process. Genetic Algorithms were selected due to their capacity to solve this type of multiple minimum. Encouraging results were reached when comparing the Bit Error Rate (BER) performance of the proposed algorithm with that of the traditional sum-product decoding algorithm. The performance of the proposed decoder is very close to that of the optimal sum-product decoder, with the additional benefit of not requiring channel information (signal-to-noise ratio). In order to improve Bit Error Rate performance and/or reduce the complexity of the proposed decoder, the fitness function and parameters of the GA can be optimized. <![CDATA[Aspects on methanogenic biofilm reactor modeling]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932006000300007&lng=es&nrm=iso&tlng=es A previously developed deterministic steady state module for modeling methanogenic biofilm reactors has been revised to enlarge the model application range and to deal with system dynamics. Two models for the hydrolysis of non-active biomass representing extreme alternatives: without biomass hydrolysis (model A) and with complete and instantaneous hydrolysis of non-active suspended and attached biomass (model B) were investigated. Both models resulted to be suitable for simulating highly anaerobic loaded systems. However, only model B showed good agreement between experimental and calculated values at low organic loading rates. The values of the specific biofilm detachment rate and the specific microbial death rate of the original model were re-estimated for model B based on a set of step-type disturbances on the organic loading rates. At loading rates ranging between 2 to 4 g COD per day per liter of expanded bed applied to a lab-scale fluidized bed reactor, the parameter estimates were 0.0269 Lg-1d-1 and 0.061 d-1 for the specific biofilm detachment rate and the specific death rate, respectively, with a 95% chi-square confidence level. <![CDATA[Random sampling in high-frequency digital lock-in amplifiers]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932006000300008&lng=es&nrm=iso&tlng=es The application of a random sampling scheme in high-frequency digital lock-in amplifiers is proposed. This scheme allows reducing the sampling frequency with reduced aliasing effects. Analytical and numerical analyses that show the advantages and limitations of the proposed scheme are presented. Furthermore, experimental tests that validate the proposal are given. The maximum input-signal frequency of a lock-in amplifier working with the proposed sampling scheme is not limited by the sampling frequency. Instead, the limit is imposed by the quantization of the random time periods and the sample-and-hold device. <![CDATA[Enantioselective extraction of ketoprofen enantiomers using ester alcohol R, R-di-tartarates or S, S-di-tartarates as chiral selector]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932006000300009&lng=es&nrm=iso&tlng=es Distribution behavior of ketoprofen enantiomers was examined in a two-phase system containing R, R-di-tartarates or S, S-di-tartarates. The influences of different alkyl chain of R, R-di-tartarates or S, S-di-tartarates, concentrations of R, R-di-tartarate, organic solvent and content of methanol on partition coefficient and separation factor were investigated, respectively. The experimental results show that R, R-di-tartarates studied all form more stable diastereomeric complexes with ketoprofen S-enantiomer than with R-enantiomer. The partition coefficients and enantioselectivity generally increase with the addition of length of alkyl chain of alcohol. The concentration of chiral selector and methanol also have bigger influences on enantioselectivity. <![CDATA[On the prediction of the radiation term in the thermal conductivity of plastic foams]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932006000300010&lng=es&nrm=iso&tlng=es The radiative contribution to thermal conductivity in plastic foams is studied through two different approaches. Both consist in close forms derived from the heat transfer equation governing the intensity of radiation in foams, where scattering can be treated as isotropic. While one approach is based on the solution of the equation for a continuous medium, the other one is based in the solution for a discrete medium. Predictions are contrasted for typical values of thermal properties of foams, and a possible explanation for the found differences is proposed. <![CDATA[Modelling and control of a hot rolling mill]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932006000300011&lng=es&nrm=iso&tlng=es In this paper, a real application of optimal control of a hot rolling mill is presented. It is used the state space model formulation in the minimization of the strip thickness variations. It is presented the simulation results of the control model, which is compared with industrial real data from process controled by traditional techniques. The results of the simulations lead to a less output thickness variations compared with the real industrial data.