Scielo RSS <![CDATA[Latin American applied research]]> http://www.scielo.org.ar/rss.php?pid=0327-079320070004&lang=es vol. 37 num. 4 lang. es <![CDATA[SciELO Logo]]> http://www.scielo.org.ar/img/en/fbpelogp.gif http://www.scielo.org.ar <![CDATA[A fuzzy dynamic programming approach for evaluation of expansion distribution cost in uncertainty environments]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000400001&lng=es&nrm=iso&tlng=es This paper presents a new Fuzzy Dynamic Programming model that calculates the optimum solution of problems with uncertainties in data defined by fuzzy sets. The result includes the determination of an Intrinsic Risk Threshold of the solution. Extrinsic Risk Thresholds may also be set by a Decision Maker, in order to obtain more robust solutions. The technique is applied to the calculation of Distribution System expansion costs to serve the objectives of a Regulatory Authority (Regulator) in fixing levels of efficiency, targets and penalties to a regulated market. <![CDATA[Anaerobic digestion of carbohydrate and protein-based wastewaters in fluidized bed bioreactors]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000400002&lng=es&nrm=iso&tlng=es The present work is focused on evaluating the anaerobic digestion of complex substrates (proteins and carbohydrates) in anaerobic fluidized bed reactors (AFBRs). In a previous paper, an AFBR model was adjusted using only the experimental data obtained during the acclimatization stage (glucose and acetate-based feeding) of two mesophilic bioreactors. Here, the sensitivity of that model to represent the digestion processes of proteins such as gelatin and albumin, and sucrose as a carbohydrate, is analyzed. Some kinetic expressions and parameters for the enzymatic hydrolysis processes need to be modified to represent the real behavior of bioreactors. Under the analyzed operating conditions, a hydraulic retention time higher than 1 day is suggested to ensure good system efficiency. <![CDATA[Statistical damage detection in a stationary rotor systems through time series analysis]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000400003&lng=es&nrm=iso&tlng=es A novel approach to detect damage in stationary rotating systems excited by unbalance and stochastic forces is presented. The methodology is based solely on output time series measured at the bearings stations. The method deals with the application of auto-regressive models and statistical modeling for the linear prediction of damage diagnosis. The results showed that the approach is suitable for practical applications. <![CDATA[Photopolymerisation of acrylic acid and chitosan gels (I): Influence of preparation method on the formation and kinetic behaviour of interpenetrating complexes]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000400004&lng=es&nrm=iso&tlng=es The kinetic study of the photopolymerisation of gels of acrylic acid (AA) and chitosan (CHI) prepared by three different methods was accomplished. The kinetic parameters such as conversion and polymerisation rate were determined. The influence of the composition and the preparation method on these parameters was elucidated. The effect of the mixing order on the formation of chitosan-acrylic acid complexes (CHI+AA-) was determined by measuring the viscosity of non-polymerised gels. The presence of polyacrylic acid (PAA) grafted on to a CHI matrix after photopolymerisation and the influence of the method of preparation and feed composition on the proportion of CHI-PAA interpolymer network were demonstrated by FTIR spectroscopy. The possible mechanism of the graft copolymerisation is discussed in detail. <![CDATA[A transversely isotropic law for the determination of the circumferential young's modulus of bamboo with diametric compression tests]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000400005&lng=es&nrm=iso&tlng=es Bamboo is a highly anisotropic natural material widely used in structural applications. A transversely isotropic constitutive equation is proposed here as the simplest law able to capture main anisotropic features of bamboo. Diametric compression tests were undertaken to determine the circumferential Young's modulus of two bamboo species based on the transversely isotropic model and using a simple formula of elasticity, validated with finite element analyses considering true and simplified geometries. Results showed that the use of idealized geometries and simple formulas provided a good estimation of the circumferential modulus. Load-deformation curves displayed a softening behavior which was approximated with two straight lines. Using the slope of the first line, the circumferential moduli were found to be 485 ± 172 MPa and 1685 ± 132 MPa for Guadua angustifolia and Phyllostachys pubescens, respectively. For Guadua angustifolia the circumferential modulus showed a significant increase with height, registering values of 651 ± 153 MPa for the top, 465 ± 126 MPa for the middle and 344 ± 98 MPa for the bottom parts of the culm. For Phyllostachys pubescens the circumferential modulus was independent of the length of the specimen. Results confirm the significant anisotropic behavior of bamboo, that should be considered in a reliable mechanical model of the culm. <![CDATA[Effect of gelatin on apple juice turbidity]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000400006&lng=es&nrm=iso&tlng=es Clarification of apple juice by flocculation and precipitation with bentonite and gelatin is explained on a more systematic basis, essentially through the determination of turbidity and zeta-potential. Apple juice was also treated with Polyvinylpolypyrrolidone (PVPP) to remove total polyphenol. Gelatin-particle complex was evaluated as the increase in juice turbidity after the adding of tannic acid. The change of slope during Zeta potential determination indicated that electrostatic forces predominate at low gelatin content, and hydrophobic and hydrophilic interactions occur later at a higher gelatin content. Results also indicated that tannic acid test is useful for determining optimal gelatin concentration for clarification, as test was unaffected by soluble solids, acidity, or pectinase treatment. Gelatin consumption was mainly attributed to colloidal particles. Finally, results indicated that risk of haze by free gelatin in juice required at least 10 times more gelatin than the optimum dosage for clarification. <![CDATA[α-tricalcium phosphate- and tetracalcium phosphate/dicalcium phosphate-based dual setting cements]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000400007&lng=es&nrm=iso&tlng=es "Dual-setting" calcium phosphate cements (DS-CPCs), characterized by a polymerization reaction that proceeds along with the conventional hydraulic setting, were prepared and studied. Acrylamide (AA), 2-hydroxyethyl methacrylate (HEMA), and N-vinyl-2-pyrrolydone (VP) in 5, 10, and 20 wt./vol.-% were added to the liquid of &alpha;-tricalcium phosphate (&alpha;-TCP) and tetracalcium phosphate/dicalcium phosphate anhydrous (TTCP/ DCPA) conventional cements. N,N´-methylenebisa-crylamide was used as cross linking agent. N,N,N´,N´-tetramethylethylendiamine in the liquid, and ammonium persulfate in the powder, were employed as polymerization catalyst and initiator, respectively. Diametral tensile strength (DTS), setting time, phase composition, conversion rate, and microstructure of the DS-CPC were compared with those of non-added cements. The DTS increased 22 % for &alpha;-TCP and 85 % for TTCP/DCPA DS-CPCs by adding 20 wt./vol.-% AA. The HEMA and VP had no positive effect on DTS. The extent of the hydraulic setting reaction for &alpha;-TCP DS-CPC was only slightly decreased by the addition of 20 wt./vol.-% of AA to the mixing liquid. <![CDATA[Preferential oxidation of CO in presence of H<SUB>2</SUB> behavior OF PtSn/γ -Al<SUB>2</SUB>O<SUB>3</SUB> catalysts modified by K or Ba]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000400008&lng=es&nrm=iso&tlng=es The behavior of catalysts based on Pt/&gamma;-Al2O3 is analyzed in the CO oxidation reaction. Experiments were performed in the temperature range between 50°C and 250°C with a feed H2 rich, and a concentration of 1% CO and 0.6% O2 Catalysts studied were: monometallic Pt/&gamma;-Al2O3, bimetallic PtSn/&gamma;-Al2O3 with a ratio Sn/Pt=1.6 at/at and two catalysts prepared by modification of the last one with K or Ba. The catalyst that showed maximum activity and selectivity levels is the PtSnK/&gamma;-Al2O3. The tin addition increases the activity which allows the reaction to occur at lower temperatures due to the decrease in the CO-Pt interaction. The addition of K or Ba produces a subsequent improvement with respect to the CO oxidation temperature, which leads to a selectivity increase. The selectivity of the CO oxidation passes through a maximum value as a function of the temperature. This maximum is explained by the importance acquired by the reverse of water gas shift reaction at temperatures near 200ºC. <![CDATA[Effect of operating conditions on Fischer-Tropsch liquid products]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000400009&lng=es&nrm=iso&tlng=es Fischer-Tropsch synthesis is an important chemical process for the production of liquid fuels. In recent years, the abundant availability of natural gas and the increasing demand of gasoline, diesel and waxes have led to a high interest in further developing this process. The dependencies of liquid hydrocarbon product distribution of iron catalyzed Fischer-Tropsch synthesis on operating pressure and temperature have been studied. The study followed an experimental planning and the results were analyzed based on surface response methodology. The effects of different operating conditions on product distribution were compared based on number average carbon number and distribution dispersion. Results showed that high temperature (270°C) and pressure (27 atm) favor the production of heavy waxes that can be converted to liquid fuels through hydrocracking, while greater direct selectivity towards liquid fuels are favored by low temperature (240°C) and high pressure (30 atm). <![CDATA[Ripple reduction in direct torque and flux control of induction motors via sliding modes]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000400010&lng=es&nrm=iso&tlng=es This paper presents a torque ripple reduction approach to direct torque and flux control (DTFC) of an induction motor using a sliding-mode control (SMC) technique. A distinctive feature of the approach is that, by appropriately parametrizing and implementing the sliding-mode controller, the discontinuous nature of the actuator may be directly incorporated to the design process. The present paper shows how to design the DC-bus value of the inverter to guarantee reachability of rated values, and proposes two strategies for reduction of steady-state torque ripple in the implementation of the SMC. Experimental results confirm the characteristics of the proposed control strategies and indicate that they are specially effective at low speed of operation. <![CDATA[Basic design of a fluidized bed gasifier for rice husk on a pilot scale]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000400011&lng=es&nrm=iso&tlng=es With the purpose of contributing to the energetic valuation of the solid wastes generated by the Colombian agricultural industry, a practical methodology for the design of a fluidized bed gasifier for rice husk on pilot scale was developed. The gasifier equipment, made up of a reaction chamber of 0.3 m of internal diameter and 3 m of overall height, was designed from theoretical and experimental information available in the literature and from the past experiences of the research group. A design procedure was elaborated for each one of the seven parts or subsystems in which the gasifier equipment was divided, intending to produce an energetic gas with aproximately 70 kW of useful energetic power. Experimental tests performed with a gasifier fabricated according to the designs showed that the developed procedure was adequate, with a maximum deviation close to 50% for the operational performance variables. Therefore, the basic model developed in this work shows that it is helpful for preliminary prediction of the equivalence ratio, low heating value, volumetric yield, gas power and cold efficiency obtained in experimental atmospheric bubbling fluidized bed biomass gasification tests. <![CDATA[A Monte Carlo approach to describe the reduction profiles of bidimensional MoO<SUB>x</SUB> structures grown on an alumina sustrate]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000400012&lng=es&nrm=iso&tlng=es The reducibility of molybdenum oxide supported on &gamma;-Al2O3 was studied by temperature programmed reduction (TPR). Interpretation of the reduction profiles was successfully achieved by applying the Monte Carlo method and taking into account the presence of different molybdenum species on the support surface. Seven reactions were assumed to take place along the reduction process. The first hydrogen consumption peak was assigned to the reduction of Mo6+ ions present as well-dispersed polymeric species into Mo+5, while the second one accounts for the reduction not of the Mo5+ ions generated in the first reduction into Mo+4 but also for the reduction of monomeric Mo6+species.