Scielo RSS <![CDATA[Latin American applied research]]> vol. 39 num. 2 lang. es <![CDATA[SciELO Logo]]> <![CDATA[Comparison between the isotherms of two commercial types of textured soy protein]]> Textured soy proteins (TSP) are functional ingredients used in food applications. This study aims to compare the sorption isotherms of two commercial types of TSP at 10, 20, 30 and 40 °C; the best fit to the experimental data was selected from eight classical models. The curves obtained for TSP type I showed that the equilibrium moisture content decreases as temperature increases for water activities up to 90%. At higher water activities, the moisture content showed an inverse behavior. This inversion did not occur for TSP type II due to the absence of sugars in this type of TSP. The Chirife, GAB and Peleg equations presented the best fit for the curves. <![CDATA[Systematic study of coating systems with two rotating rolls]]> The coating method called "Roll Coating" is one of the most widely used in industry and consists in the application of fluids through rotating rolls. In this work we examine the system of two cylinders in rotation. The aim of this presentation is to characterize this system of two cylinders for different ratio of velocities (s) and gap configurations, in order to build a phase diagram that identifies the resulting thickness for each set of operation parameter values. Resulting thicknesses were contrasted with classical models to test its validity limits. The classical models, which are based on the Theory of Lubrication, and their corresponding simplifying hypotheses, let us demonstrate the significant dependency of the outlet thicknesses with regard to the gap and the velocity ratio and the modified Capillary number ß. When the amount of fluid dragged increases, an irregular V-shaped cross-site wave appears, repeated quasiperiodically down-web (Cascade effect), indicating the region of parameters in which the phenomenon is present. <![CDATA[Lubrication model of a knee prosthesis, with non Newtonian fluid and porous rough material]]> Tibial component of knee prostheses, made of ultra high molecular weight polyethylene (UHMWPE), experiences a high degree of wear and may be expected to last twelve years on average. In this work, a steady state one-dimensional lubrication model of a knee prosthesis is solved through a numerical technique based on the Finite Element Method. The model takes into account a non Newtonian synovial fluid, its ultra filtration mechanism and the surface roughness of a porous elastic layer on the tibial component. The benefits of a porous compliant material placed at the top of the metallic tibial component are shown taking into account the stiffness and exudation capacity of the material and hyaluronic acid concentration of synovial fluid. <![CDATA[Analytic determinations of minerals content by XRF, ICP and EEA in ultrafiltered milk and yoghurt]]> The application of ultrafiltration for milk concentration allows obtaining a raw material for yoghurt elaboration, with total solids increased. The products have special characteristics due to different ratios proteins/lactose can be obtained, as well as they have nutritional properties with beneficial effects in human health. In this study the content of calcium, potassium, phosphorous, iron, zinc, magnesium and sodium in milk, its distribution during ultrafiltration and in the fermented product have been studied by means of X-ray fluorescence spectrometry (XRF). The results show that XRF technique has been successfully used for determination of minerals content in dairy products, still for trace species. The minerals measures were validated with other analytical techniques with high accuracy and versatility as inductively coupled plasma spectrometry (ICP) and atomic emission spectrometry (EEA). Furthermore the proteins content was increased 13 % and lactose content has been reduced in 30 %, in compared with some commercial products. <![CDATA[Thermal interaction model between a fluid flow and a solid]]> A thermal interaction model between a turbulent fluid flow and a solid was developed. The heat exchange is modeled by means of a Newton cooling law where the convective heat transfer coefficient is calculated using thermal wall laws. The finite element method was employed to solve the conservation equations. The model gives the possibility that the fluid and solid meshes are not connected; this generates a great flexibility in meshing and in geometry modification. The domains coupling algorithm was verified using simple problems. Finally, the model developed was validated and applied successfully to the simulation of the fluid dynamic thermal behavior of hot dip galvanizing bath. <![CDATA[Synthesis and structural characterization of L-(-)-malic acid pillared layered double hydroxides]]> A new organic-inorganic hybrid material was obtained by the intercalation of L-(-)-malic acids into Magnesium Aluminum layered double hydroxides (LDHs). The intercalation was performed by reprecipitation and coprecipitation method, respectively, from which high crystallized supramolecular chrial materials were obtained and L-(-)-malic acid was orientated perpendicularly between layers without carbonate ions. The structure of supramolecular chrial materials was characterized using XRD, FT-IR and DSC-TG, EA, ICP, and the supramoleclar structural model of the compound was given. <![CDATA[Interpenetrating polymer networks based on castor oil polyurethane/cellulose derivatives and polyacrylic acid]]> Castor oil, 2,4-tolylene diisocyanate (2,4 TDI), cellulose acetate, and hydroxiethyl cellulose, based polyurethane (PU) - polyacrylic acid (PAA) sequential interpenetrating polymer networks (IPN's) were synthesized. PU's were prepared by reaction of hydroxyl groups from castor oil, and cellulose acetate or hydroxiethyl cellulose with 2,4 TDI, using dibutyl tin dilaurate (DBDTL) as catalyst. PU's were swollen in acrylic acid monomer solution and subsequently polymerized by radical polymerization initiated with 4,4-azobis(4-cyanovaleric acid) (ACVA), and N,N'-methylenebis acrylamide (NNMBA) as crosslinking agent. Series of three PU/PAA ratios (75/25, 50/50, 25/75) were prepared. Viscoelastic properties were studied by means of dynamic mechanical analysis (DMA), showing a maximum modulus for IPN with 25% PAA content. Tan d curve showed two main peaks, and ? relaxation which is due to lateral chains of PU, suggesting phase separation. The existence of two Tg in each IPN was also confirmed by differential scanning calorimeter DSC). Morphology of samples was observed using a scanning electron microscope (SEM), which revealed different fracture surfaces between the compatible and incompatible PU/PAA ratios studied. Fractures were decreasing to turn into roughness surfaces when the PAA was increasing within the IPN's. <![CDATA[An h-adaptive unstructured mesh refinement strategy for unsteady problems]]> An h-adaptive unstructured mesh refinement strategy to solve unsteady problems by the finite element method is presented. The maximum level of refinement for the mesh is prescribed beforehand. The core operation of the strategy, namely the refinement of the elements, is described in detail. It is shown through numerical tests that one of the advantages of the chosen refinement procedure is to keep bounded the mesh quality. The type of element is not changed and no transition templates are used, therefore hanging nodes appear in the adapted mesh. The 1-irregular nodes refinement constraint is applied and the refinement process driven by this criterion is recursive. Both the strength and weakness of the adaptivity algorithm are mentioned, based on clock time measures and implementation issues. To show the proper working of the strategy, an axisymmetric, compressible non-viscous starting flow in a bell-shaped nozzle is solved over an unstructured mesh of hexahedra. <![CDATA[Change detection in time series using the maximal overlap discrete wavelet transform]]> The problem of change detection of time series with abrupt and smooth changes in the spectral characteristics is addressed. We first review the main characteristics of the discrete wavelet transform and the maximal overlap discrete wavelet transform. An algorithm for sequential change detection in time series is then reported based on the maximal overlap discrete wavelet transform and Bayesian analysis. The wavelet-based algorithm checks the wavelet coefficients across resolution levels and locates smooth and abrupt changes in the spectral characteristics in the given time series by using the wavelet coefficients at these levels. Simulation results demonstrate the good detection properties of the proposed algorithm when compared with previous reported algorithms, and also indicate that the quadratic spline and least-asymmetric wavelets have less amount of shift in position after wavelet decomposition and therefore an alignment of events to be detected in a multi-resolution analysis with respect to the original time series is obtained. <![CDATA[Equilibrium adsorption of binary mixtures of light hydrocarbons in activated carbon]]> Several studies have been reported with the purpose of storing NG in porous media by adsorption. Experimental data and mathematical models that describe the adsorption phenomena of pure methane, the main component of NG (about 90%) already exist, however they do not describe satisfactorily the behavior of NG storage cycles, because of the presence of several other hydrocarbons like ethane, propane, butane and heavier alkanes. This study presents measurements of experimental data for the adsorption equilibrium of binary mixtures of low-molecular-weight alkanes and compares them with mathematical models for multicomponent adsorption prediction based on each pure component adsorption data. Experiments were performed with the binaries methane-ethane, methane-propane and methane-butane. Experimental results were compared with predictions from the Extended Langmuir model and Ideal Adsorbed Solution (IAS) model. <![CDATA[Analytical/numerical solution for confined jet diffusion flame (sandia flame c)]]> The aim of the present work is the development of a method based on the momentum transfer law to obtain the solution of confined jet diffusion flames. The Reichardt's equation is used to approximate the flow/mixture fraction and it is discretized based on the second order finite difference technique. All thermochemical variables are determined by the mixture fraction as the Sandia Flame C, used to check the results, is close to equilibrium. The semi-analytical/numerical results compare reasonably with the experimental data indicating that the method contributes to solve some jet flames at low cost. <![CDATA[Oxidative dehydrogenation of ethylbenzene to styrene on activated carbons derived from a native wood as catalyst]]> Activated carbons were developed by phosphoric acid activation of a native wood (Prosopis ruscifolia) under a self-generated atmosphere or flowing air. Their potentiality as catalyst for oxidative dehydrogenation of ethylbenzene to styrene was examined at pre-established operating conditions. The carbons developed in the self-generated atmosphere showed specific surface area of 2281 m²/g and total pore volume of 1.7 cm³/g, whereas values of 1638 m²/g and 1.3 cm³/g, respectively, characterized those obtained in air. A commercial activated carbon (1200 m²/g and 0.7 cm³/g) was also used for comparison. Both wood-derived carbons resulted potentially suitable as catalyst for ethylbenzene oxidative dehydrogenation. Nevertheless, those developed in the self-generated atmosphere showed a better catalytic performance than the carbons obtained in air and the commercial sample. The behaviour could be due to its lower microporosity compared with the commercial sample, and to the formation of oxidative condensation products during the oxidative dehydrogenation of ethylbenzene with greater content of carbonyl groups than for the sample activated under flowing air. Chemical and textural characterization of the used carbons conclusively evidenced the presence of oxidative condensation products pointing to formation of new active surfaces. <![CDATA[Surface intermediate species of the 4-isobutylacetophenone adsorption-reaction over fosfotungstic Wells-Dawson heteropoly acid]]> Surface adsorbed species of isobutybenzene and 4-isobutylacetophenone on bulk fosfotungstic Wells-Dawson acid H6P2W18O62.xH2O (HPA) have been screened in the present investigation. The evolution of chemisorbed species towards products was followed through infrared spectroscopy of systems containing liquid reactants and the solid acid kept at various temperatures. 4-Isobutylacetophenone adsorbs on Brønsted acid sites of the heteropoly acid and further reacts towards a condensation product similarly to the reaction of acetophenone over other acid materials such as, mordenite, niobic acid and sulfated zirconia. The condensation product possesses well defined infrared signals at 1654 cm-1 and 1597 cm-1 that resemble the carbonyl stretching vibration and the double bond of dypnone C6H5COHC=C(CH3)C6H5. Additional signals at 1221 cm-1 and a shoulder at 1284 cm-1 ascribed to the vibration of the C6H5 species in the C6H5COHC= group, give more evidences of the formation of a chalcone type compound. A reaction mechanism of the Aldol condensation of 4-isobutylacetophenone through an enol reactive intermediate is proposed. <![CDATA[Classification of dynamic speckle signals through granulometric size distribution]]> In this work we present a method based on granulometry, a tool derived from mathematical morphology, to classify dynamic speckle signals. Through the use of morphological operators we obtain a granulometric size distribution. From this distribution we obtain the related moments used as parameters to classify the image. This technique enables the detection of differential activity in samples of sequences of dynamic speckle in space-time coordinates. The analysis of the method is illustrated through the detection of bruised regions in fruits. Finally, we present a discussion of the results.