Scielo RSS <![CDATA[Latin American applied research]]> vol. 42 num. 4 lang. en <![CDATA[SciELO Logo]]> <![CDATA[Free Convective Elastico-Viscous Fluid Flow With Heat and Mass Transfer Past an Inclined Porous Plate in Slip Flow Regime]]> The unsteady free convective elastico-viscous fluid flow past a porous inclined plate in slip flow regime in presence of periodic temperature and concentration has been analyzed. The suction at the plate is assumed to be fluctuating with time. The governing equations of the problem have been solved by using perturbation scheme. The approximate solutions have been derived for the velocity, temperature field, concentration field, skin friction, rate of heat transfer and rate of mass transfer. The values of the skin friction co-efficient are calculated numerically and presented in tabular form for various values of the flow parameters. The influence of visco-elastic parameter with the combination of other flow parameters on the velocity field have been obtained and illustrated graphically <![CDATA[Mathematical investigation over the Lewis number effect on the combustion of biomass particles]]> In this paper, the effect of Lewis number on the structure of one-dimensional flame of biomass combustion is analyzed. This effect can be observed by considering the non-unity Lewis number in the governing equations. The fuel particles vaporize first to yield a gaseous fuel of known chemical structure. The analysis is performed in the asymptotic limit, where the value of the characteristic Zeldovich number is too large and the equivalence ratio is larger than unity σ≥u1. The presumed biomass fuel is consisted of four components, moisture, volatile species, fixed carbon and ash. The incineration process of fuel can be described by some chained chemical sub-processes: evaporation of moisture from the fuel particles, volatile release/char formation, burning of the hydrocarbon volatiles in the gaseous space, and the combustion of char and tar components. The flame structure consists of three different zones which are, a preheat vaporization zone where the rate of the gas-phase chemical reaction is small, a reaction zone that consists of gas and Char combustion where convection and the rate of vaporization of the fuel particles are small and a convection zone where diffusive term in the conservation equation is negligible. The obtained results from the presented model declare that the temperature and burning velocity profiles are extremely affected by the variation of Lewis numbers. <![CDATA[Improved neural network based CFAR detection for non homogeneous background and multiple target situations]]> The Neural Network Cell Average -Order Statistics Constant False Alarm Rate (NNCAOS CFAR) detector is presented in this work. NNCAOS CFAR is a combined detection methodology which uses the effectiveness of neural networks to search for non homogeneities like clutter banks and multiple targets within the radar return. In addition, the methodology proposed applies a convenient cell average (CA) or order statistics (OS) CFAR detector according to the context situation. Exhaustive analysis and comparisons show that NNCAOS CFAR has better performance than CA CFAR, OS CFAR and even CANN CFAR detectors (the latter, a previously proposed neural network based detector). Furthermore, it is verified that the new proposal presents a robust operation when maintaining a constant probability of false alarm under different radar return situations. <![CDATA[Co oxidation: effect of Ce and Au addition on MnO<sub>x</sub> catalysts]]> The effect of cerium and/or gold addition to a manganese oxide which was greatly active in CO oxidation was studied. The catalysts obtained by this way were characterized by N2 adsorption, XRF, XRD and TPR, and their catalytic activity was measured in the CO oxidation reaction. The pure MnOx catalyst was active in the CO oxidation but the addition of 5 wt % cerium decreased their catalytic activity. Adding 2 wt % gold improved the activity of MnOx and Ce/MnOx and caused a slight decrease of the catalyst specific area and of the average oxidation state of manganese in catalysts, which was found between 3.3 and 3.6. The order of activity found on the basis of T50 for the four catalysts was: Au/MnOx > Au/Ce/MnOx > MnOx > Ce/MnOx, with T50 of 89, 95, 99 and 139 °C, respectively. The solids Au/MnOx and Au/Ce/MnOx presented a T10 of 30 and 49 °C, indicating that gold favored the conversion at room temperature. The effect of water vapor on the reaction was also analyzed, finding a decrease in the catalytic activity of all catalysts, due to the blocking of active sites in the catalyst surface. <![CDATA[Combustion of dry sewage sludge particle in a fluidized bed reactor]]> This paper presents a mathematical model of the cylindrical particle combustion in a fluidized bed reactor. This particle is composed of sewage sludge. The model performs a mathematical description of the physical and chemical phenomena that occur during particle combustion. The uniform particle model without ash accumulation is proposed. Sewage sludge is considered composed of three fractions. Two fractions pyrolyzed forming char. Then, this char is burned. The other fraction is burned without pyrolysis. In order to describe the mechanism and kinetics reaction, data from thermogravimetric analysis were used. The reaction kinetics was proposed as a function of mass loss of each fraction. To validate the model, the particle combustion time obtained by the simulation was compared with the experimental combustion time. Also, this work presents the combustion atmosphere temperature and the particle size influence in the combustion phenomena. The model predicts acceptably the combustion time, according to experimental results. <![CDATA[Analysis of the amplitude and phase response of the microcantilever in the tapping mode atomic force microscopy]]> In this paper, the amplitude and phase response of the microcantilever in the tapping mode atomic force microscopy is investigated as a function of excitation frequency, free oscillation amplitude, and tip-sample separation distance. For this purpose, the influence of the excitation frequency on the transition occurring in the amplitude-phase-separation curves is analyzed by taking into consideration, three vibration modes. The obtained results show that at the excitation frequency close to resonance, the participation of higher modes in the response is negligible, and accounting for only one mode in the response is sufficient. Moreover, increasing the excitation frequency a little over the resonance frequency causes the shifting of the transition location toward smaller separation distances and finally to no separation; while, lowering the excitation frequency around the resonance results in the displacement of the jump's location toward larger separation distances. To investigate the influence of the free oscillation amplitude on transition, the share of only one mode in the response is considered. The results indicate that, depending on the value of the free oscillation amplitude, the jump either has a steplike discontinuous shape or a smooth continuous one. Also, by increasing the free oscillation amplitude, the transition occurs at a larger separation. <![CDATA[Use of polyethylene glycol as organic additive in Copper electrodeposition over stainless steel cathodes]]> This study comprise a comparative analysis of the effects of polyethylene glycol (PEG) and other additives used in copper electrodeposition processes over 316 L stainless steel permanent cathodes. Both cyclic voltammetry and potentiostatic pulse techniques showed analogous results with regard to the increase in the use of the real organic additive and the persistence of a more constant roughness level at higher electrodeposition times when PEG baths are used instead of baths containing glue. The mechanism taking place in the presence of PEG corresponds to two-dimensional nucleation together with three-dimensional diffusion grain growth. Furthermore, the contribution of the hydrogen evolution reaction (HER) was observed at t > 15 seconds when additives of PEG + thiourea were used, while the same contribution was observed from the beginning of the reaction in the case of solutions without PEG. <![CDATA[Synthesis of docosanoic and tetracosanoic acid from alcohols using a task-specific ionic liquid catalyst]]> Catalytic batch oxidation of docosanol to docosanoic acid and tetracosanol to tetracosanoic acid was performed using hydrogen peroxide as oxidant and a functionalized ionic liquid composed of an Aliquat® cation and a peroxotungstophosphate anion acting as catalyst. Conversion of 76% and selectivity of 60.2% were obtained after 6 hours for docosanol oxidation at optimal operational conditions (temperature of 90°C; total-H2O2/alcohol molar ratio = 3; alcohol/catalyst mass ratio = 300). In the case of tetracosanol oxidation 85% conversion and 68% selectivity were reached in the same time interval at optimal operational conditions (temperature of 90°C; total- H2O2/ alcohol molar ratio = 5; alcohol/final-catalyst mass ratio = 50). In both cases the oxidant and the catalyst were continuously added throughout the reaction time, thus enabling continuous reaction performance. The batch results obtained in this study confirm the technical feasibility of operating a process to produce both these high molecular acids from alcohols as renewable raw materials. <![CDATA[Modeling conventional two-dimensional drying of radiata pine based on transversal effective diffusion coefficient]]> We modeled conventional two-dimensional drying of radiata pine (Pinus radiata) wood using the concept of effective diffusion extended to overall drying process. Effective diffusion coefficients were determined experimentally on the transversal plane and depended exponentially on the moisture content. These coefficients were characterized by two parameters determined through optimization within the context of an inverse problem. Spatially variable convection coefficients were determined in the same manner. Experiments using constant drying 44/36 (°C/°C) were carried out in order to determine transitory spatial distributions of moisture and drying curves, which were then used to determine and validate the model parameters. The mathematical model consisted of a partial, non-lineal, differential equation of the second order, was characterized by coefficients that varied exponentially with moisture content, integrated numerically through the finite volume method. Results of two-dimensional simulations for isothermal drying of radiata pine timber, correlated with experimental data, are shown: a) Transitory distribution of moisture gradients, b) drying curves and c) parameter of mathematical model (effective diffusion and mass convection coefficients) <![CDATA[A new correlativa model for surface tension of mixtures: hidrocarbon mixtures]]> This article presents a new correlative model for surface tension of mixtures. This model is an extension of a predictive model recently proposed by our group. Other correlative models were evaluated and compared to the proposed model. Hydrocarbons mixtures exhibiting chemical nature or shape and chain size asymmetries were chosen as the standard to test the performance of the chosen models at several temperatures. A total of 1433 experimental data was used. All of the correlative models studied showed very good results. However, an F-test study pointed out that there are still opportunities in modeling for describing the studied data within the experimental uncertainties. <![CDATA[Sensitivity analysis of a model which describes the biofiltration of VRSC commpounds]]> A sensitivity analysis of a model which describes the biooxidation of volatile reduced sulfur compounds (VRSC) using a biotrickling filter is developed. Consistent results are obtained using three methodologies; Standard Regression Coefficients (SRC), Fourier amplitude sensitivity test (FAST) and the Morris method (MOAT). The model presents a highly linear behavior of the uncertain parameters. It is shown how the properties of the biofilm and the parameters related with the kinetics have the highest influence on the model behavior; while on the other hand the properties related with mass transfer have low influence. <![CDATA[Synthesis and characterization of carboxyl and acetal latexes by emulsion polymerization. Application to the production of latex-protein complexes for detecting chagas disease]]> Monodisperse polymer particles with carboxyl and acetal functionalities were synthesized through a two-step emulsion polymerization process. In the first step, latex particles were synthesized by batch emulsion polymerization of styrene (St); and in the second step, the functional monomers (methacrylic acid or acrolein diethyl acetal) were copolymerized with St onto the previously formed polystyrene particles. The synthesized "core-shell" latexes were used as support for their sensitization (by covalent coupling) with two antigenic recombinant proteins of Trypanosoma cruzi (RP1 and CP1). Polymer latexes and latex-protein complexes were characterized by measuring their colloidal stability, average particle size, shell thickness and protein thickness through conductimetric titration, dynamic light scattering, turbidimetry and scanning electron microscopy. <![CDATA[Short term hydrothermal coordination problem considering environmental concerns]]> Solving the Short Term Hydrothermal Coordination Problem considers the resolution of both the Unit Commitment and the Economic Dispatch for thermal and hydraulic units. This problem is solved for several time horizons between a day and a week with a one-hour step. The traditional short-term scheduling problem of hydrothermal units, minimizing fuel cost during a time, does not include concerns due to emission pollution coming from the operation of thermal plants. In this work, environmental constraints are considered. Focusing on avoiding post-dispatch corrections, the transmission network is modeled with a high level of detail considering an AC power fow. These facts lead to a very complex optimization problem which is solved by using a novel decomposition approach based on Generalized Benders Decomposition and traditional, well-known optimization techniques. The approach presented in this work allows the decomposition of the whole problem in a quadratic mixed integer master problem, and in a separable non-linear subproblem. The former defnes the state and the active power dispatched by each unit whereas the latter determines the reactive power to meet the electrical constraints through a modified AC optimal power fow. Diferent variations of the developed methodology were evaluated in order to consider environmental constraints. These approaches were applied to a 9-bus test case and to a 87-bus real system. <![CDATA[Some functional properties of pigment extracts from red cabbage (brassica oleracea) and redbeet (beta vulgaris)]]> capability and release of the bioactive compounds were analyzed. Pigment extraction was conducted in distilled water with 1% HCl media. The anthocyanin content obtained from cabbage The purpose of the present work was to obtain natural pigments from red cabbage and redbeet. The antioxidant and antimicrobial activities of the fresh pigments were determined. Furthermore, the encapsulation was 8.9 mg /ml and 8.8 mg /ml of betalains from redbeet. The polyphenol content for red cabbage and redbeet were 0.0128 and 0.0123 mg of gallic acid equivalent/g in dry basis, respectively, as determined by Folin-Ciocalteau method. The stability of the extracts to UV light and temperature was assessed; polyphenolic and pigment contents decreased after exposure. Pure extracts from these vegetables showed an antimicrobial effect under ambient conditions, as well as an inhibitory activity against Staphylococcus aureus. However, no antimicrobial effect was detected for the pathogen Aspergillus niger. The extracts were successfully encapsulated in calcium alginate beads; an additional coating of chitosan was applied.