Scielo RSS http://bibliotecadigital.uns.edu.ar/rss.php?pid=0327-079320130011&lang=pt vol. 43 num. 1 lang. pt http://bibliotecadigital.uns.edu.ar/img/en/fbpelogp.gif http://bibliotecadigital.uns.edu.ar http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932013001100001&lng=pt&nrm=iso&tlng=pt The present study describes the adsorption of textile dye on rice hull. The adsorption parameters were obtained from Langmuir and Freundlich isotherms utilizing linear regression plots to fit the data. The results showed that Langmuir equation was more suitable than the Freundlich one to predict the experimental adsorption isotherms, indicating that the adsorption of dye molecules is localized in a monolayer on the surface of the adsorbent. Thermodynamic parameters such as ΔHa, ΔSa and ΔGa were determined in this work. The heat evolved during adsorption is endothermic. The maximum sorption capacity of rice husk was satisfactory when compared to capacities of other low-cost adsorbent materials. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932013001100002&lng=pt&nrm=iso&tlng=pt Cyclones are equipments used for gas-solid separation in many applications at industrial level, however, they are considered low-efficiency devices and their design have been simplified to basic models without further improvements. This paper presents a numerical study by Computational Fluid Dynamics (CFD) for gas and gas-solid flows in two designs of High-Efficiency (H.E.) cyclones: the commonly known Stairmand cyclone and one proposedbyLópez, Trujillo and Quintana (LTQ) that showed better performances according to preliminary calculations. The turbulence of the gas flow was obtained by the Reynolds Stress Model (RSM). The pressure and velocity fields of both geometries were analyzed. The results indicate that the proposed design has lower pressure drops and higher collection efficiency for the given operation conditions, allowing savings in operating costs. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932013001100003&lng=pt&nrm=iso&tlng=pt The physical, chemical and typological characteristics of manganese lump ores from three Brazilian mines, Azul, Morro da Mina and Urucum are presented herein. The chemical analysis was done by AES-ICP and titration. The typological characterization was obtained by optical microscopy and X-ray diffraction. The physical properties studied included density, surface area and porosity. The Azul, Urucum and Morro da Mina Mn contents are, respectively, 47.68, 42.69 and 28.44%. The Urucum lump ore presents the highest structural density (4.29g/cm³), followed by Azul (3.98g/cm³) and by Morro da Mina (3.56g/cm³). The Urucum, Morro da Mina and Azul bulk porosities are 22.68, 10.79 and 29.40cm³/kg, respectively. The oretypological classifications are: anhydrous-oxide for Urucum, hydrated-oxide for Azul and silicate-carbonate for Morro da Mina. The thermogravimetric analysis showed that the ore weight losses could be associated to different phenomena, depending on the ore typology. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932013001100004&lng=pt&nrm=iso&tlng=pt This work investigates the influence of reaction time (ranging from 12 to 96 h) on the characteristics of zinc stannate (Zn2SnO4) nanoparticles obtained by the hydrothermal method at 200°C. The nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), surface area measurements (BET) and infrared spectroscopy (IR). The results showed that the reaction time influenced the properties of Zn2SnO4 nanoparticles. The product presented a pure crystalline phase with mean particle size about 20 nm and BET surface area ranging from 34 to 43 m².g-1. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932013001100005&lng=pt&nrm=iso&tlng=pt Finding the full load motion for a point-to-point task can maximize the productivity and economic usage of the mobile manipulators. The presented paper proposes a technique to determine the maximum allowable dynamic payload for flexible mobile manipulators along with the obtained optimal trajectories. Non-linear modeling of the mobile robotic manipulators by considering both link and joint flexibility is presented; then, optimal motion planning of the system is organized as an optimal control formulation. By employing indirect solution of the problem, optimal maximum payload path of such robots is designed for a general objective function. The paper specially focuses on effects of various important parameters on the maximum payload determination and analyzes them thoroughly. The effectiveness and capability of the proposed method is investigated through various simulation studies. The obtained results illustrate the influences of the performance index, operating time and robot characteristics on the maximum payload path. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932013001100006&lng=pt&nrm=iso&tlng=pt In this work the dip coating process when an insoluble surfactant is adsorbed at the interface is numerically studied. The work centers in the applicability of the linear approximation usually employed to model the relationship between surface tension and the concentration of the surface active agent. Reported solutions show that film thicknesses predicted with a linear model can differ significantly from those computed with a more reliable equation of state. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932013001100007&lng=pt&nrm=iso&tlng=pt Pistachio as a strategic product has a particular position among Iranian productions and is one of the most important non-oil exports after carpet. In this study, after primary processing such as dehulling, washing, drying and roasting, pistachio nuts were packed in four different atmospheres including N2, CO2, vacuum and ambient air. Storage temperatures were 20°C and 40°C for a 12 month period. The evaluated packaging materials were a plastic compound five layers film, a modified polypropylene pouch, and a metalized plastic pouch (polypropylene with a layer of aluminum). After extracting pistachio oil with hexane, thiobarbituric acid (TBA) index, free fatty acids (FFA), and induction time (IT) were measured at three-month intervals. Statistical analysis of our data revealed that stored samples under N2, CO2 and vacuum had a lower TBA index compared with air-packed ones, and the IT of pistachio oil was longer at 20 °C than at 40 °C. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932013001100008&lng=pt&nrm=iso&tlng=pt A simple control strategy was studied for harmonic disturbance rejection in magnetic field compensation systems for lowfield magnetic resonance techniques. The strategy is based on the simultaneous action of a conventional PID and a selective harmoniccompensation controller. The system consists of a set of compensating coils fed by independent current sources driven by a digital controller. A series of hall magnetic sensors close the control loop. Despite its simplicity, it is shown that the performance of the dual controller improves within the frequency range where the waterbed effect becomes dominant, by selectively enhancing the rejection of the harmonic component. The proposed solution is particularly useful for selective harmonic rejection of slowly varying frequency and amplitude dependent harmonic perturbations. An extension to multiple-harmonic components perturbations is possible. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932013001100009&lng=pt&nrm=iso&tlng=pt Spent bleaching clay from the oil refining industry was subjected to heat regeneration in a box furnace with air. The heat reactivation was conducted without previous extraction of residual oil and with previous extraction of oil using organic solvent. The experimental temperature ranged from 723 at 873 K. A model for the kinetic of thermal reactivation of spent adsorbent has been proposed. The activation energy involved on the desorption phenomenon was determined. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932013001100110&lng=pt&nrm=iso&tlng=pt The principal purpose of this work is to test the TUC strategy in a simple case using a micro-simulator designed ad hoc, previous to its real implementation. Using concepts of traffic engineering we describe a well known dynamic linear model of traffic flow in a urban traffic network that is controlled using the traffic-light times. This simplified model allows to obtain a Riccati feedback matrix and compute traffic-light times that will improve the congestion levels. We present some numerical experiments made with the model on an academic example and we validated them with a microscopic simulator that we have created based on Car Following theory and discrete event models. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932013001100111&lng=pt&nrm=iso&tlng=pt Using an implicit finite difference method, the effect of Joule heating on the magnetohydrodynamic natural convection in an inclined rectangular enclosure with internal heat generation has been performed. The left and right walls of the enclosure are maintained at a constant temperature while the bottom and top walls are kept insulated. The values of the governing parameters are the Hartmann number, Ha=0, 5, 10 and 50, Joule heating parameter J=0, 0.005, 0.01 and 0.02, the aspect ratio a=0.01, 0.2, 0.5 and 1, the inclination angle φ=0, π/6 and π/3 and Rayleigh number Ra=10² and 10³. Comparisons with previously published work are performed and excellent agreement is obtained. A parametric study of the physical parameters is conducted and a representative set of numerical results for the streamlines and isotherms as well as the local Nusselt number is illustrated graphically to show interesting features of the solutions. It is found that, the local Nusselt number increases on the bottom wall as the enclosure aspect ratio increases. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932013001100112&lng=pt&nrm=iso&tlng=pt Rice husk ashes are a potential source of pollution, thus there is continued interest in its recycling. An environmentally friendly solution is its conversion into products such as aluminosilicates that are designed for use as fertilizer. Aluminosilicates that present a high cationic exchange capacity becomes an excellent material to be used in soil for accumulating and liberating nutrients slowly to the plants. The aim of this study is to investigate the effects of the alkali concentration in the cationic exchange capacity of an aluminosilicate obtained from rice husk ashes. The obtained products were characterized by X-ray diffraction, scanning electron microscopy, atomic absorption spectroscopy, and cationic exchange capacity. The particles that were produced are composed of crystals smaller than 5 μm. The experimental conditions employed in this work produced a semi-crystalline aluminosilicate with a high cationic exchange capacity. The alkali concentration used had an influence on this property. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932013001100113&lng=pt&nrm=iso&tlng=pt This work is focused on the production of struvite as an alternative to reduce the concentration of phosphorus and nitrogen from swine wastewater. The effect of Mg source (MgO and MgCl2. 6H2O) and pH on nitrogen and phosphorus removal was investigated. From the results was seen that N and P were efficiently removed from swine wastewater. Data of X-ray diffraction (XRD) revealed that the production of struvite in the crystalline form is dependent of pH, which was obtained only in the runs carried out at pH 9.5, independent of Mg source employed. The production of struvite showed to be effective for adding value to swine wastewater. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932013001100114&lng=pt&nrm=iso&tlng=pt Obtaining an effective execution of a parallel system requires that the mapping of the processes (of the parallel software) on the processors (of the parallel hardware) is efficiently performed. Hence, this paper presents an efficient mapping strategy based on optimizing communications between processes as well as load balancing process distribution onto an arbitrary processor network. Such a mapping strategy is developed as a parallel program, based on the simultaneous execution of local, independent processes. This fact contrasts with many other approaches for solving the mapping problem, like simulated annealing, heuristic search, and others, which require a centralized control for the mapping. In this paper, it is shown that the present mapping strategy is efficient enough when applied to two different mapping problems. Based upon an experimental setup, it is possible to review this mapping strategy following the related impact. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932013001100115&lng=pt&nrm=iso&tlng=pt In this paper, the vibration of an AFM microcantilever with one and two layers of piecewise piezoelectric is analyzed. With respect to discontinuities in the MC, due to the piezoelectric layer, the non-uniform beam model is used in the modeling of vibrating motion. The vibration analysis of MC is carried out near the sample surface in the non-contact mode. To solve the nonlinear differential equation of motion, both numerical solution and multiple time scales (MTS) method are used and the results are compared. Comparison of results, at the non-contact mode, shows good agreement between the two solving methods at normal equilibrium distances (d≥2nm). MC is modeled with one and two piezoelectric layers; the nonlinear behavior of each MC is studied by investigating the effect of geometrical dimensions of each layer on the nonlinearity of the system. It is then become clear that they can affect the nonlinearity of the system. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932013001100116&lng=pt&nrm=iso&tlng=pt The objective of the present work was to simulate three-dimensional drying of wood, based on the concept of the effective diffusion coefficient. For this, we used a conventional drying process of radiata pine in a controlled environment (dry and wet bulb temperatures of 44 and 36 °C, respectively). This experiment allowed us to gather data on: a) the spatial distribution of moisture content at different drying times, b) the drying curve, and c) the surface emission coefficient. A differential, partial, non-linear, second-order mathematical model was used, and the exponential functions of the effective diffusion coefficient characterized the three-dimensional orthotropic (radial, tangential, and longitudinal) transport of moisture content in the wood. This mathematical model was integrated numerically through the control volume finite element method, which contemplates: a) tetrahedral elements for discretization, b) implicit Euler method for the time differential, and c) Gauss-Seidel with successive over-relaxation method to resolve the linear equation system. We compared these results for the three-dimensional spatial distributions of moisture content after 22, 44, 66, and 88 (h) of drying, and the resulting drying curves were in good agreement with the experiments.