Scielo RSS <![CDATA[Latin American applied research]]> http://www.scielo.org.ar/rss.php?pid=0327-079320100004&lang=es vol. 40 num. 4 lang. es <![CDATA[SciELO Logo]]> http://www.scielo.org.ar/img/en/fbpelogp.gif http://www.scielo.org.ar <![CDATA[A biphasic hyperelastic model for hydrocephalus]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000400001&lng=es&nrm=iso&tlng=es A biphasic hyperelastic model with spherical symmetry is presented to study hydrocephalus. The model can take into account the biphasic nature of brain tissue, non-linear stress-strain curves through an Ogden-type compressible strain energy function, a nonlinear variation of hydraulic conductivity with deformation, a constant production of cerebrospinal fluid (CSF) as well as a fluid absorption rate proportional to pressure. The biphasic equations were implemented in an updated Lagrangian finite element code where a novel procedure was devised to consider the constant generation of CSF in the ventricles. Results of a non-communicating model showed strains in the range of 35-45% in the peri-ventricular area and pore pressure and radial displacement distributions that were not significantly affected by material nonlinearities. High circumferential stresses documented in acute hydrocephalus suggest that the tissue may suffer damage at the ventricular surface while a communicating model was not capable of reproducing normal pressure hydrocephalus. Overall results suggest that normal pressure hydrocephalus cannot be explained with models that consider an elastic law for the solid phase of the material. <![CDATA[LPV control of a magnetic bearing experiment]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000400002&lng=es&nrm=iso&tlng=es An LPV (Linear Parameter Varying) controller design example for a Magnetic Bearing System is presented. A linear model of the system including bending modes and imbalance is described. Simulations and experimental results show the usefulness of the LPV method with eigenvalue clustering constraints in spite of the limited rotation rate range. The results show that this method facilitates simulation and allows implementation. Conclusions are drawn on the limited range for the rotation rate the LPV controller allows for. <![CDATA[Interactive remeshing for navigation over landscape models]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000400003&lng=es&nrm=iso&tlng=es The performance of an algorithmic procedure to visualize digital landscapes based in the dynamic control of the size of the model is presented. Approximate representations are produced taking into account criteria relative to the observer position and the local curvature of the terrain. The algorithm leads to substantial reductions of the size of the final meshes, lowering the rendering costs down to 5%. An application of the algorithm is tested on a model of the Colorado Canyon is shown. <![CDATA[A Laboratory experiment for undergraduate instruction: non deal flow in tubular vessels]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000400004&lng=es&nrm=iso&tlng=es A laboratory experiment to reinforce the basic concepts of non-ideal flow is described. It consists of simple pulse-response measurements for gas that is flowing through an empty and a packed bed. It can provide information on the residence-time distribution function and other vessel parameters. Experimental results are compared with those predicted by the axial dispersed plug-flow model in order to obtain the Peclet number and the dispersion coefficient that characterize the flow behavior. <![CDATA[Synthesis and characterization of high silica zeolites from coal fly ash(CFA): two cases of zeolite syntheses from the same waste material]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000400005&lng=es&nrm=iso&tlng=es Zeolites H/β and H/ZSM-11 were synthesized by the crystallization hydrothermal method (CH), using coal fly ash (CFA). Tetraethylammonium hydroxide (TEAOH), tetrapropylammonium bromide (TPAB) and tetrapropylammonium hydroxide (TPAOH) were used as structure-directing agents (SDA). The optimum conditions used in the experimentation were 140 °C and NaOH/CFA ratio=1.2 (wt/wt), during the crystallization hydrothermal method (CH), and microwave-assisted heating (MH) was used in some experiments. The structure and crystallinity of the synthesized materials were analyzed by X-ray diffraction, where the formation of the β and ZSM-11 zeolites was confirmed. The morphology of the obtained zeolites was observed by the scanning electron microscope technique. It was observed spheroidal particles for the ZSM-11 zeolite and ellipsoidal particles for the β zeolite, respectively. Both zeolites were ion exchange treated, in order to obtain the protonated form. Finally, the thermal stability and the loss of weight of the modified β zeolite were determined by using the termogravimetric and differential thermal analysis techniques. The modified zeolites were stable in the range of most gas chemical reactions (300-500 °C). <![CDATA[Biological sulphate removal in acid mine drainage using anaerobic fixed bed reactors with cheese whey as a carbon source]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000400006&lng=es&nrm=iso&tlng=es The effect of the hydraulic retention time and the sulphate-total COD ratio on the performance of an anaerobic biological process applied to acid mine drainage water (AMD) was evaluated using cheese whey as a carbon source. Laboratory-scale fixed bed bioreactors operating at 25 ± 2 ºC were used in the experiments. Maximum sulphate reduction and hydrogen sulphide production were achieved at a hydraulic retention time of 8 days and at a sulphate-total COD ratio of 0.5. Under these conditions, the sulphate removal was found to be 68.1% while the hydrogen sulphide production was 0.27 L/day. At the same time, the total COD removal obtained was 55.4%. <![CDATA[Esterification and transesterification assisted by microwaves of crude palm oil: Homogeneous catalysis]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000400007&lng=es&nrm=iso&tlng=es Main propose in this study was to obtain alkyl ester from crude palm oil (CPO), using microwaves like heating source, in a process of two stages by means of homogeneous catalysis; the first stage (esterification), was made using sulfuric acid catalyst, to diminish the acid value of the oil, avoiding the soap formation and facilitating the separation of the phases. The second stage (transesterification) was made using sodium methoxide catalyst. The behavior in the crystallization of the product using differential scanning calorimetry, cloud point ASTM D2500 and pour point ASTM D97 was evaluated. The obtained biofuels fulfill the requirements of the American standards for biodiesel and the propose methodology for the synthesis presents environmental advantages and of increase in the reactivity, as opposed to the traditional methods of heating. <![CDATA[Esterification and transesterification assisted by microwaves of crude palm oil: Heterogeneous catalysis]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000400008&lng=es&nrm=iso&tlng=es The principal objective of this study was to obtain alkyl ester from crude palm oil (CPO), using microwaves like heating source, in a process of two stages by means of heterogeneous catalysis; the first stage (esterification), was made using Dowex 50X2, Amberlyst 15 and Amberlite IR-120 resins catalysts, to diminish the acid value of the oil, avoiding the soap formation and facilitating the separation of the phases. The second stage (transesterification) was made using potassium carbonate catalyst. The behavior in the crystallization of the product using differential scanning calorimetry, cloud point ASTM D2500 (2005) and pour point ASTM D97 (2005) was evaluated. The obtained biofuels fulfill the requirements of the American standards for biodiesel and the propose methodology for the synthesis presents environmental advantages and of increase in the reactivity, as opposed to the traditional methods of heating. <![CDATA[An analytical study of radiation effect on the ignition of magnesium particles using perturbation theory]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000400009&lng=es&nrm=iso&tlng=es An analytical method is proposed to solve the heat Energy equation of combustion of magnesium particles with allowance for the heterogeneous chemical reactions and the region of the thermal influence of the particle on the gas. In this model the solution of the problem in a steady formulation is found and the flame propagation mechanism is considered to be radiation and conduction.Radiative heat transfer plays a major role in single particle combustion. Flame equations of the single particle combustion are solved via the new nonlinear differential equation by using perturbation theorem. In this paper we can apportion the magnesium-particle ignition to regular regimes and also regime of particle extinction and the ignition. Under the steady approximation, the values of particle and gas phase temperatures are calculated and by adding radiation term in conservative equations, both of these parameters will be increased. <![CDATA[Kinetic modeling of a photocatalytic reactor designed for removal of gas-phase benzene: a study on limiting resistances using design of experiments]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000400010&lng=es&nrm=iso&tlng=es Experiments were conducted at room temperatures, in an immobilized annular tube reactor, using titanium dioxide as the photocatalyst, to identify the influence of important operational parameters, viz., catalyst load (5-20 g m-2), benzene concentration (0.2-6 g m-3) and flow rate (0.2-1 L min-1) on the removal of benzene. Removal efficiencies for benzene ranged from 7% to 96% depending on the range of levels of these process parameters. A modified Langmuir-Hinshelwood (L−H) kinetic model has been suggested based on the experimental observations. The use of a combined plug-flow type L−H kinetic model yielded a design equation that can be used as the basis for the photoreactor scale-up as well as to find the mass transfer and reaction resistances in the photoreactor. The ratio of reaction rate resistance to the overall resistance was found to play an important role in establishing the predominant resistances between mass transfer and reaction rate occurring in the photoreactor. <![CDATA[Limit of applicability of the monomer-enhanced mechanism for radical generation in persulfate initiated mechanism for radical generationin persulfate initiated polymerization of acrylamide]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000400011&lng=es&nrm=iso&tlng=es The limit of applicability of the monomer-enhanced mechanism as dominant mechanism ruling the initiation process of the polymerization of acrylamide (AM) initiated with potassium persulfate (K2S2O8) has been determined. The kinetics and mechanisms for radical generation were studied in solution at very low monomer and initiator concentrations. The transition of the initiation mechanism from dominant monomer-enhanced dissociation to dominant thermal decomposition of persulfate was observed. Both mechanisms contribute equally to radical generation at [AM] / [K2S2O8] ≈ 4.5. Thermal decomposition dominates at lower [AM] or higher [K2S2O8] and opposite variations promote the monomer-enhanced dissociation. This work also includes quantification of the rate coefficients, efficiencies and activation energies of the mentioned mechanisms, and the kinetics of AM polymerization when photochemically initiated with phenylbis(2,4,6-trimethylbenzoyl)-phosphine oxide. <![CDATA[Dispersed phase holdup in a liquid-liquid extraction column]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000400012&lng=es&nrm=iso&tlng=es Dispersed phase holdup was measured in a liquid-liquid extraction column for the butyl alcohol-water system. The column performance has been studied using two columns of the same diameter (0.092m) but different lengths (0.70m, three stages and 0.90m, four stages). The column was operated counter-currently with several continuous and dispersed flows rates. The dispersed phase holdup was measured by the drainage method. Based on holdup data, the results were analyzed with the aim of determining the influence of flows rates and the column number of stages on the behavior of the dispersed phase holdup. An empirical correlation is proposed for estimating the dispersed phase holdup. <![CDATA[Simple, low-cost flow controllers for time averaged atmospheric sampling and other applications]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000400013&lng=es&nrm=iso&tlng=es In air sampling is often necessary to limit the air inflow into an initially void vessel in order to extend the filling time. This requires devices characterized by very low, known and stable conductance. Likewise devices may also be used to control the gas flow between two vessels, or the outflow from gas containers. Depending on the use, they are called flow controllers, controlled leaks or, as in our case, inflow regulators. In this work we describe simple and cheap inflow regulators designed to collect air samples in 0.5 L vessels with filling times of many days. These inflow regulators may be adjusted within a wide impedance range and proved to be very stable under laboratory conditions and reasonably stable even under much harder operating conditions in field experiments. <![CDATA[Modeling water absorption of sorghum during soaking]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932010000400014&lng=es&nrm=iso&tlng=es Water absorption of sorghum during soaking in water at temperatures of 10, 20, 30, 40 and 50 ºC was simulated using Peleg's model. The weight gain during soaking process was determined in terms of moisture content. Peleg's equation was adequately capable to predict water uptake of sorghum under the experimental conditions. The Peleg rate constant, k1, and capacity constant, k2, decreased from 11.8×10-2 to 0.95×10-2 h %-1 and 2.46×10-2 to 2.06×10-2 %, respectively, with increasing temperature. The effective diffusivity was evaluated by fitting experimental absorption data to Fick's second law of diffusion. Effective diffusivity of water varied from 8.376×10-12 to 2.22×10-12 m².s-1 over the temperature range studied, with an energy activation of 24.21 kJ.mol-1. The temperature dependence of the diffusivity coefficient was described satisfactorily by Arrhenius-type relationship.