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Kosmos
Astronomia Astrofizyka
Inne

Kultura
Sztuka dawna i współczesna, muzea i kolekcje

Metoda
Metodologia nauk, Matematyka, Filozofia, Miary i wagi, Pomiary

Materia
Substancje, reakcje, energia
Fizyka, chemia i inżynieria materiałowa

Człowiek
Antropologia kulturowa Socjologia Psychologia Zdrowie i medycyna

Wizje
Przewidywania Kosmologia Religie Ideologia Polityka

Ziemia
Geologia, geofizyka, geochemia, środowisko przyrodnicze

Życie
Biologia, biologia molekularna i genetyka

Cyberprzestrzeń
Technologia cyberprzestrzeni, cyberkultura, media i komunikacja

Działalność
Wiadomości | Gospodarka, biznes, zarządzanie, ekonomia

Technologie
Budownictwo, energetyka, transport, wytwarzanie, technologie informacyjne

Latin American applied research

Scielo org

The present paper describes a novelty approach to detect structural changes in the generating units of Itaipu power plant. The methodology is based solely on output time series measured in the rotating electric machine. The method deals with the application of time-series analysis through auto-regressive moving average models (ARMA) and statistical modeling for the linear prediction of damage diagnosis. In order to illustrate the procedure proposed is employed a simplified mathematical model regarding shaft radial vibrations in the generating unit 18A of Itaipu power plant. Several parameters variations are imposed in the system to simulate real damages conditions in the electrical machine. The approach is also evaluated with experimental data. The efficacy, advantages and drawbacks of the proposed method are demonstrated through these numerical and experimental tests.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932012000200001&lng=en&nrm=iso&tlng=en 2014/07/06 - 11:55

Mobile manipulators operating in field environments will be required to manipulate large loads, and to perform such tasks on uneven terrain which may cause the system to reach dangerous tipover instability. Therefore, this paper presents a method for finding the Maximum Allowable Dynamic Load (MADL) of geometrically nonlinear flexible link mobile manipulators with stability consideration. Moment-Height Stability (MHS) criterion is used as an index for the system stability. The dynamic model for links in most mechanisms has often based on small deflection theory but for applications like light-weight links, high-precision or high speed, it is necessary to capture the deflection caused by nonlinear terms. Hence, the equations of motion are derived taking into account the nonlinear strain-displacement relationship. Then, a method for determination of the maximum allowable loads is described. In order to verify the effectiveness of the presented algorithm, several simulation studies and experiments are carried out and the results are discussed.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932012000200002&lng=en&nrm=iso&tlng=en 2014/07/06 - 11:55

This paper is devoted to describe the analysis of unsteady boundary layer flow and heat transfer of a viscous, incompressible micropolar fluid having temperature-dependent viscosity and thermal conductivity over a non-isothermal horizontal stretching sheet. The fluid viscosity and the thermal conductivity are assumed to vary as inverse linear functions of temperature. The unsteady boundary layer equations for the momentum, angular momentum and thermal energy are simplified using suitable transformations. The resulting system of nonlinear ordinary differential equations is solved numerically by employing a shooting technique with fourth order Runge-Kutta integration scheme. The effects of the various parameters on the velocity, microrotation and temperature profiles are presented graphically. In addition, tabulated results for the skin-friction coefficient, Nusselt number and couple stress at the plate are presented and discussed.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932012000200003&lng=en&nrm=iso&tlng=en 2014/07/06 - 11:55

The spectrophotometric method for the determination of cuprous ions in solution presented by Anwar et al. (2000), has since been analyzed and improved, especially with regard to interference from iron and ion species commonly found in acid mine drainage (AMD). The reduction of cupric ions in the presence of ferrous ions, not considered by Anwar et al., renders this method unfeasible for cuprous ion determination. In the absence ferrous ions, the method is simple, fast, economic, accurate and very reliable for total copper determination, even for copper concentrations as low as 5 mg/L. Iron concentrations > 5 g/L produce less than 3% error in determination of copper concentrations of 50 mg/L. Typical AMD ion concentrations do not interfere, except for aluminum which interferes significantly at ten times (x10) AMD concentration

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932012000200004&lng=en&nrm=iso&tlng=en 2014/07/06 - 11:55

In this paper, a real-time application of a Leak Detection and Isolation (LDI) algorithm for a plastic pipeline is presented. This LDI algorithm is fed with flow and pressure signals coming from sensors placed at the ends of the pipeline. It uses a flow observer based on a model obtained from the Method of Characteristics, and it is designed in order to assure an acceptable real-time leak isolation by taking into account various practical difficulties. In particular it incorporates an adaptation law for the friction coefficient in order to compensate for possible variations. The whole scheme is successfully tested on a plastic pipeline prototype, transporting water and built as a possible benchmark.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932012000200005&lng=en&nrm=iso&tlng=en 2014/07/06 - 11:55

The performance of an electrocoagulation (EC) system with aluminium and iron electrodes for removing heavy metal ions (Cd2+, Cu2+, Cr3+, Sr2+ and Zn2+) present in synthetic produced water on laboratory scale was studied systematically. Experimental parameters such as applied current, flow effluent and sacrificial electrodes were investigated in order to understand their influence on the EC process. Increasing the current density accelerated the electrocoagulation process, but made it less efficient. Cd2+, Cu2+, Sr2+ and Zn2+ showed similar removal rates, under similar conditions, indicating a uniform electrochemical behavior. The study gave indications on the removal mechanisms of the investigated metals. Cd2+, Cu2+ and Zn2+ ions are hydrolyzed and co-precipitated as hydroxides. Cr4+, was proposed to be reduced first to Cr3+ at the cathode before precipitating as hydroxide. The process expenditure was estimated and reported showing the viability of this process as a green alternative, obtaining modest costs using Fe electrodes.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932012000200006&lng=en&nrm=iso&tlng=en 2014/07/06 - 11:55

Process control represents an important tool for meeting product quality, process safety and environmental regulation. Different control strategies have been recently proposed in the literature; however, internal model control (IMC) has received great attention. Fractional calculus represents a fast growing field involving non-integer order derivatives. The aim of this work is the application of fractional calculus to develop generalized internal model control loops transfer functions, which is presented in two different approaches: firstly, the process model is considered perfect, i.e., equal to the internal model; secondly, the internal model is described by fractional transfer function. Simulation results showed that the proposed generalization could successfully control an industrial oven and a biochemical reactor described by fractional models, allowing better results when compared to integer order IMC.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932012000200007&lng=en&nrm=iso&tlng=en 2014/07/06 - 11:55

The effect of different cooking methods (grilling, frying, steaming and microwave cooking) was investigated on proximate composition, cooking loss (CL), color and protein solubility (PS) of golden grey mullet (Liza aurata) fillet. Fillet's protein and ash contents significantly increased after cooking with all methods, compared to raw fillet. Higher protein content was related to microwave method, followed by fried, grilled and steamed, respectively. All treatments showed increase in protein and ash contents. Decrease in moisture and increase in fat contents was the most prominent changes in proximate composition. After cooking, PS of fillets decreased with decreasing pH with the minimum solubility was observed at a pH range 5-6 indicating the isoelectric point (PI) of fillets. Microwaved sample showed the lowest solubility compared to other cooking methods. All cooking processes reduced L* value and increased b* value. Fried and microwaved samples had significant differences in a* value compared to other treatments.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932012000200008&lng=en&nrm=iso&tlng=en 2014/07/06 - 11:55

A numerical study on the buildup and propagation of planar detonation waves in H2 + Air combustible mixtures, based on the use of unsteady Euler equations coupled with source terms to account for rates controlled chemical activity, is presented. The computer solver works with 13 chemical species and 33 different one step reactions of a H2-O2 - N2 combustion mechanism. The detonation process is initiated via the energy provided by an igniter which acts as a driver of a shock tube driving through a combustible mixture a blast (or strong shock), accompanied by exothermic chemical changes. It is shown that for each equivalence ratio of the combustible mixture, the detonation can only be triggered if the igniter energy deposition equals or exceeds a computed minimum value. When the igniter energy deposition is less than this minimum, the combustion zone start to decouple from the blast front and if that energy is diminished even more, the combustion could not take place. A particular way of generating sustained overdriven detonations, is also considered.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932012000200009&lng=en&nrm=iso&tlng=en 2014/07/06 - 11:55

In this paper to study the thermoelastic behavior of a gas turbine blade, a computer code based on Conjugate Heat Transfer method was developed to solve the coupled external flow field and the internal temperature field inside a gas turbine blade. An interpolation method based on the 3D shape functions was used to calculate the correct temperature values at the boundaries to determine the stress field. For the materials with temperature dependent mechanical and physical properties, the thermal stresses exhibit a nonlinear behavior. In these cases, an analytic solution for the energy and equilibrium equations to obtain the temperature distribution and the stress field, knowing K(T), α(T), E(T) would be impossible and the numerical schemes should be employed instead. The results show that the stress for the materials with temperature dependent properties is higher than that for the cases where the blade material properties are constant with temperature. Further, the temperature field and the flow field obtained by the present method were compared to the available experimental findings. The results show a good agreement.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932012000200010&lng=en&nrm=iso&tlng=en 2014/07/06 - 11:55

This paper treats on grindability differences of mineral mixtures to achieve a preliminary selective particle size contrast by comminution in order to improve further sorting operation. Quartz and calcite had been chosen as example of binary system. The theoretical basis for this work was inspired by the optimization study carried out by Ray and Szekely (1973), through an algebraic model based on evolution of log-normal distribution of particle size during comminution. On the other hand, the present work has described grindability differences through the classical Rosin-Rammler size distribution. The study of the evaluation of binary mixture differences was realized by sieving analyses and the estimation of Rosin-Rammler sharpness and median diameter. An objective function was conceived stressing the relationship between the expended energy in the grinding process and the optimum residence time. It is possible to use the results as a background for grinding optimization system, since that the penalty function inside objective function can be adequately calibrated as far as technical and economic impacts on further sorting separations are concerned.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932012000200011&lng=en&nrm=iso&tlng=en 2014/07/06 - 11:55

A mathematical model was developed to describe mass transport in polymeric films based on modifications of Fick's law in a continuous macroscopic approach. The purpose of this work was specifically to model the transport of water vapor and oxygen in polymeric films at the pore level, based on physical aspects of the condensation process and the morphology and connectivity of the porous medium, with two-dimensional pore networks representing pore spaces. Using a Pore scale discrete model, we found that the pore-level distributions of liquid (condensate) and vapor as transport phenomena occurred. The vapor and oxygen diffusivities ranged from 4.22×10-6 to 3.16×10-7 cm²/s and from 3.66×10-6 to 2.86×10-7 cm²/s, respectively. Also, the vapor and oxygen permeabilities ranged from 2.61×10-3 to 3.83×10-4 nD (1nD=10-21m²) and from 6.77×10-3 to 1.35×10-3 nD, respectively. The transport properties obtained by the model were compared with the corresponding results for chitosan films obtained in previous experimental studies, showing a partial agreement.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932012000200012&lng=en&nrm=iso&tlng=en 2014/07/06 - 11:55

This paper evaluates the production of fatty acids ethyl esters from corn oil and ethanol. The reaction was carried out applying low-frequency high-intensity ultrasound (25 kHz) under atmospheric pressure and ambient temperature. Response surface methodology (RSM) was used to evaluate the influence of alcohol to oil molar ratio and catalyst concentration (sodium hydroxide) on the yield of corn oil into ethyl esters. Analysis of the operating conditions by RSM showed that the most important operating condition affecting the reaction was the ethanol to oil molar ratio. Results showed low yield of corn oil into ethyl esters. The highest yield observed was of 62.9% after 30 minutes of reaction. The best operating condition was obtained applying an alcohol to oil molar ratio of 4.5 and a catalyst to oil molar ratio of 0.010.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932012000200013&lng=en&nrm=iso&tlng=en 2014/07/06 - 11:55

In this study, the performance of a "kraft" black liquor recovery boiler was analyzed using WinGEMS, a commercial simulator software. The operational variables and design parameters of a pulp industrial unit in southeastern Brazil provides the input data used in setting up the material and energy balance equations in the simulator program. The simulations allowed the prediction of thermal efficiency as a function of solid content in the liquor, in which an increase of 10% in steam generation was obtained when dry solids were increased from 72% to 100%, the latter being a hypothetical operational condition. This study also determined that in spite of making accurate predictions about the temperature profile along the recovery boiler, WinGEMS does not correctly predict the profile of combustion gases when burning eucalyptus black liquor.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932012000200014&lng=en&nrm=iso&tlng=en 2014/07/06 - 11:55

Carrying out regression analysis for gas leakage of pressure-relief valve (PRV) to get accurate leakage flow and changing trend of leakage will be helpful in assessing the reliability of PRV. Classic support vector regression (SVR) is an excellent regression model, and has been widely used in various fields. However, standard SVR model does regression only using leakage data without elements closely related to the leakage considered. In this paper a regression model based on support vector regression plus (SVR+) is put forward to perform leakage regression of PRV, in which particle swarm optimization (PSO) is used to select optimum parameters of SVR+, termed PSO_SVR+. The experimental results demonstrate that the proposed model taking the difference of inlet pressure and outlet pressure of PRV as hidden information can access a more favorable regression precision than SVR can provide. Meanwhile this article also investigates effects of PSO and Genetic Algorithm on the performance of regression model (SVR+ or SVR)

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932012000200015&lng=en&nrm=iso&tlng=en 2014/07/06 - 11:55

The interactions between Bovine Serum Albumin (BSA) and three flavonols, galangin, kaempferol and quercetin were studied by means of fluorescence spectroscopy. The fluorescence intensity of BSA exhibits remarkable decrease along with appreciable blue-shift of its maximum emission wavelength upon addition of the three compounds, respectively. The respective binding constant Ka and number of binding sites of each compound were calculated, and the quenching mechanism was proposed. Based on the values of thermodynamic parameters, the binding of each compound proceeds spontaneously with BSA. The binding distance between each and BSA was obtained by Foerster's dipole-dipole non-radiation energy transfer mechanism.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932012000200016&lng=en&nrm=iso&tlng=en 2014/07/06 - 11:55

The present contribution describes three-dimensional Euler/Lagrange calculations of confined horizontal gas-particle flows (i.e. channel and pipe flows) emphasizing the importance of elementary processes, such as particle collisions with rough walls and inter-particle collisions, on the predicted overall flow pattern and pressure drop along the duct.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000400001&lng=en&nrm=iso&tlng=en 2013/11/08 - 08:17

The decomposition of hydrogen peroxide was studied on Pd catalysts between 293 K and 313 K. The apparent activation energy value was calculated for all the catalysts and it varied between 27 and 55 kJ/mol. For all the catalysts tested, treatment with hydrogen resulted in a significant increase in the reaction rate, as well as a decrease in the apparent activation energy for the reaction. All the reactions were well represented by a first order rate law with respect to H2O2. The effect of the treatment with H2O2 was studied in successive reactions without catalyst exchange. A small deactivation was observed in the 5.0% Pd/AC and 0.5% Pd/AC catalysts after four H2O2 decomposition reactions.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000400002&lng=en&nrm=iso&tlng=en 2013/11/08 - 08:17

Steels employed in offshore oil and gas production are subject to a very corrosive environment. Especially the new oilfields located in pre-salt layers imply the contact of steels with high brine concentration, high temperature and presence of corrosive gas such as CO2. Besides these facts, stainless steels have to present higher mechanical properties obtained from an optimized heat treatment. In order to take into account these factors and their synergisms, on the present paper, we have chosen a factorial experimental design to study the corrosion behavior of superduplex steel UNS S32750 by electrochemical tests. The results of open circuit potential, polarization curves and electrochemical impedance were analyzed with statistical methods considering a confidence level of 95%. The factors that significantly affect the corrosion potential are the carbon dioxide and heat treatment; the corrosion current is sensitive to carbon dioxide, and the resistance of polarization is strongly affected by the CO2 content.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000400003&lng=en&nrm=iso&tlng=en 2013/11/08 - 08:17

The optimum working conditions of a Parr laboratory autoclave for minerals dissolution were studied and the results obtained were applied to the leaching with HF of a Nb and Ta mineral, from the San Luis, Argentina. The optimized variables were heating rate, liquid volume, stirring speed, inert solid addition and cooling rate. Changes in the liquid volume, stirring speed and presence of an inert solid did not produce modifications in the actual heating rate. The optimum heating programs ranged between 5 and 100C/min and depended on the programmed final temperature. The cooling period was 25 min. The results indicated that, using the optimum working conditions, more than 90% of mineral might be dissolved at 2200C. It was also observed that the dissolution of mineral was slightly affected by the stirring speed and the particle size whereas temperature, HF concentration, solid-liquid relation and reaction time strongly influenced the extraction of elements.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000400004&lng=en&nrm=iso&tlng=en 2013/11/08 - 08:17

Crude oil characterization plays a key role in upstream as well downstream operations of petroleum supply chain It is usually carried out by a batch distillation process known as true boiling point (TBP) distillation, which represents a "footprint" of the crude oil composition profile, once its shape depends on the amount and volatility of components in a given crude oil. In the last decades, crude oil characterization methods by continuous distribution models have been proposed, as an option to the classic (discrete) pseudo component approach. The comparative performance of five continuous distribution models - Beta, Gamma, Riazi, Weibull and Weibull extreme - in characterizing the TBP crude oil distillation curve is presented in this work. A large TBP database of different types of Brazilian crude oil is used to identify the optimal characterization parameters of these models by a least-squares statistical criterion. The modeling performance of each continuous distribution model was measured using statistical estimators. The Weibull extreme model presented the most adequate performance in terms of the root mean squared error (RMSE) for all crude oils. In general, the model parameters uncertainties increase with the crude oil API density, despite the reversed behavior shown by Gamma model.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000400005&lng=en&nrm=iso&tlng=en 2013/11/08 - 08:17

The diffusion-thermo and thermal-diffusion effects on heat and mass transfer by boundary layer flow over a stretching cylinder embedded in a porous medium have been studied numerically in the a presence of chemical reaction effect. The governing nonlinear partial differential equations are transformed into a set of coupled ordinary differential equations, which are solved numerically by using Runge-Kutta method with shooting techniques. Numerical results are obtained for the velocity, temperature and concentration distributions, as well as the skin friction coefficient, local Nusselt number and local Sherwood number for several values of the parameters, namely, the Reynolds number, Darcy number, chemical reaction parameter, Dufour and Soret numbers. The obtained results are presented graphically and the physical aspects of the problem are discussed.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000400006&lng=en&nrm=iso&tlng=en 2013/11/08 - 08:17

New equations involving the unknown final states and initial costates corresponding to families of LQR problems are shown to be useful in calculating optimal strategies when bounded control restrictions are present, and in approximating the solution to fixed-end problems. The missing boundary values of the Hamiltonian equations are obtained by (offline) solving two uncoupled, first-order, linear partial differential equations for two auxiliary n W n matrices, whose independent variables are the time-horizon duration T and the eigenvalues of the final-penalty matrix S. The solutions to these PDEs give information on the behavior of the whole (T, S)-family of control problems. Illustrations of numerical results are provided and checked against analytical solutions of the cheapest stop of a train' problem.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000400007&lng=en&nrm=iso&tlng=en 2013/11/08 - 08:17

An analysis is presented to investigate the Soret and Dufour effects on the mixed convection heat and mass transfer along a semi-infinite vertical plate embedded in a couple stress fluid with flux distributions. The governing non-linear partial differential equations are transformed into a system of ordinary differential equations using similarity transformations and then solved numerically. Profiles of dimensionless velocity, temperature and concentration are shown graphically for various values of Dufour number, Soret number and Couple stress parameter.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000400008&lng=en&nrm=iso&tlng=en 2013/11/08 - 08:17

This paper presents a new and less conservative condition for the robust stability test of discrete-time polytopic systems by using a descriptor system approach. The stability condition is formulated in terms of a set of linear matrix inequalities and can be easily adapted for robust controller synthesis. The developed results can be viewed as a discretetime counterpart of the continuous-time one proposed by Cao and Lin (2004). This also enables us to offer a unified framework, namely the so-called descriptor system approach, for the analysis and synthesis of both discrete-time and continuous-time uncertain linear systems. Simulation examples are given to illustrate the theoretical results we established.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000400009&lng=en&nrm=iso&tlng=en 2013/11/08 - 08:17

The so called "hybrid parallelism paradigm", that combines programming techniques for architectures with distributed and shared memories using MPI (Message Passing Interface) and OpenMP (Open Multi-Processing) standards, is currently adopted to exploit the growing use of multi-core computers, thus improving the efficiency of codes in such architectures (several multi-core nodes or clustered symmetric multi-processors (SMP) connected by a fast net to do exhaustive computations). In this paper a parallel hybrid finite element code is developed and its performance is evaluated, using MPI for communication between cluster nodes and OpenMP for parallelism within the SMP nodes. An efficient thread-safe matrix library for computing element/cell residuals (or right hand sides) and Jacobians (or matrices) in FEM-like codes is introduced and fully described. The cluster in which the code was tested is the CIMEC's 'Coyote' cluster, which consists of eight-core computing nodes connected through Gigabit Ethernet.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000400010&lng=en&nrm=iso&tlng=en 2013/11/08 - 08:17

The influence of topography on wind pressures acting on structures has been of interest to the civil engineering community for some time; however, because of the complexity of the problem, only few cases have been solved. The evaluation of pressures in tanks located in hills is one of those complex problems and has not been addressed in the literature. This paper presents a computational fluid dynamics simulation of the problem, in which the domain including the hill and the tank is discretized using finite elements. The results show that the actual location of the tank with respect to a hill has a significant influence on the pressures, so that tanks located at the top of a hill undergo severe increases in pressure coefficients and also changes in pressure distributions around the tank.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000400011&lng=en&nrm=iso&tlng=en 2013/11/08 - 08:17

The ultimate aim of polymerization reaction engineering is the production of polymers with tailor-made properties. An introductory review into this field is presented, with emphasis on the effects on the molar mass distribution (MMD), of the sought combination of polymerization mechanism, reactor type, and reactor control. Three ideal polymerization mechanisms are analyzed: free-radical, "living" anionic, and step-growth. "Living" anionic and step-growth polymerizations are similar in that their growing chains remain reactive while inside the reactor; and for these systems the narrowest MMDs are produced in reactors with narrow residence time distributions (RDT); i.e.: batch or continuous tubular reactors. In contrast, in conventional free-radical polymerizations, the polymer molecules grow in a fraction of a second and thereafter remain inactive while inside the reactor. In this case, the RTD does not affect the MMD, and the homogeneous continuous stirred-tank reactors provide the narrowest MMDs. Representative mathematical models of polymerization reactors are useful for: a) quantifying the interrelationships between their numerous inputs and outputs; and b) developing open- and closed-loop strategies for increasing reactor productivity and product quality.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000400012&lng=en&nrm=iso&tlng=en 2013/11/08 - 08:17

In the present work, anodic oxide films on titanium specimens were formed in physiological solution under potentiostatic condition. The immediate- to short-term changes in the oxide film were studied by open-circuit potential measurements and cyclic voltammetry. The results show that the intensity of the cathodic current peak related to oxygen reduction at around -0.7 Vsce, decreased and disappeared after 30 minutes of finishing the anodic oxidation. For titanium without anodization (non-coated titanium), the cyclic voltammograms show an anodic current in the range that begins at -0.9 Vsce and continues to more positive potentials (vs SCE), related to the hydrogen oxidation reaction. For anodically polarized titanium (coated titanium),in the anodic direction of the cyclic voltammograms an anodic current in the range that begins at -0.9 Vsce and continues to more positive potentials vs SCE) was observed. In this case, the oxidation process is related to previous cathodic processes: the hydrogen formation and the cathodic transformation of titanium oxides before the oxygen reduction potential region.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000300001&lng=en&nrm=iso&tlng=en 2013/09/19 - 17:13

This work analyzes the separation efficiency data involving mass transfer between two immiscible liquid phases in a bench lab extractor without mechanical agitation. The experimental apparatus consisted in a cylindrical glass column containing perforated plates, operating in countercurrent mode. The experimental runs were developed by using butane-acetic acid-water system, following a factorial experimental design involving the variables: dispersed phase velocity, the continuous phase velocity and the number of stages (two and four plates). The collected acid acetic raffinate and extract was analysed by titration with sodium hydroxide. Separation efficiencies were estimated through Murphree (1925) and Kawase (1990) models. The results showed that the higher was the dispersed flow, higher was the separation efficiency. An opposite behavior was observed for the continuous phase flow effect. In relation to the number of plates, higher efficiencies were achieved for 4 plates arrangement. The results provided empirical equations to predict the extraction efficiency, which exhibited good correlation with experimental data.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000300002&lng=en&nrm=iso&tlng=en 2013/09/19 - 17:13

The effect of different hydrocolloids as barrier agents on reduction of oil absorption in French fries during deep fat frying, investigated. Among different gums that used in this study, mixture of pectin and CMC 1% and xanthan gum 1.5% led to highest decrease in fat content and lowest decrease in amount of fat content observed in pectin 0.5% and guar gum 0.5% respectively. Strips that coated with xanthan gum, pectin and mixture of pectin and CMC had the highest amount of moisture content while the lowest moisture content were related to blank samples and strips that coated with guar gum and CMC. All coated strips in comparison with blank sample had lower amount of fat content significantly. Samples were coated with mixture of pectin and CMC 1% and blank sample need to maximum shearing force for cutting and coated samples with xanthan, guar and CMC gums need the lowest shearing force respectively.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000300003&lng=en&nrm=iso&tlng=en 2013/09/19 - 17:13

This paper presents an overview of mathematical approaches for modeling heat treating process, mainly concerned by coupling heat conduction with phase transformation, prediction of microstructure and material hardness, as well as estimation of heat transfer coefficients. The program HT-mod developed by the authors is briefly described. An analysis of distortions and residual stresses by a combination of HT-mod and ABAQUS Software is outlined. The performance of vegetable oils (castor, soybean and mineral oil) as quenchants are summarized as an application example. Comparison between measured and predicted hardness and microstructure of AISI 4140 bars is provided for validation of the methodology proposed for modeling heat treating processes. On average, good agreement was obtained

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000300004&lng=en&nrm=iso&tlng=en 2013/09/19 - 17:13

In this paper, a new coordination method based on non-linear hierarchical control for large-scale robots is presented. The large-scale system is considered as combination of subsystems so that each subsystem has interaction with others. The procedure is to use interaction prediction principle with optimal control for each subsystem. At the first level, applying optimal control principle to each subsystem with guessed interaction variables results in Two Point Boundary Value Problem (TPBVP). By solving TPBVP the new interaction parameters are generated. At the second level, the resulted interactions are exchanged between subsystems and the interaction variables are improved within interaction prediction principle. Difference between guessed and achieved interaction in each step is used in general cost function to coordinate subsystems. Hence continuing the algorithm causes to converging the interactions to each other. The new method results in less time by parallel processing for each subsystem, and has less sensitivity for different initial guess in comparison with centralized use of optimal control for large-scale robots because of using small sized sub-systems which is a step toward real-time planning of mobile manipulators, also the proposed method has the ability to solve problems with inseparable cost functions which is an important benefit for robots path planning in presence of obstacles and specified path for end-effector. The method is simulated and verified by previous work in this area. The simulation results show effectiveness of proposed method for large-scale robots. The approaches validity is checked via simulations and experiments with a 2-link nonholonomic mobile manipulator named Scout.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000300005&lng=en&nrm=iso&tlng=en 2013/09/19 - 17:13

The purposes of this work were to, a) describe an acute animal model of severe cardiac failure induced by high doses of halothane, b) analyze the effects of these overdoses of halothane on arterial wall dynamics and c) characterize the cardiovascular effects of halothane through the autonomic nervous system. Measurements were performed in six sheep before and after halothane administration (4%). A significative decrease was observed in mean aortic flow (P<0.05) and diameter (P<0.01) in heart failure with respect to control state (from 2.64±0.95 L.min-1 and 17.32±1.86 mm to 1.69±0.58 L.min-1 and 15.33±1.71 mm; respectively). A significantly decrease was observed in mean (P<0.005), systolic (P<0.01) and diastolic (P<0.005) aortic pressure in heart failure (from 85.90±19.49 mmHg, 93.52±18.07 mmHg and 78.86±20.12 mmHg to 49.12±21.77 mmHg, 55.54±20.71 mmHg and 43.48±21.21 mmHg; respectively). Heart rate in control group (127.73±11.20 bpm) was significantly (P<0.05) higher than that observed in heart failure (107.15±13.53 bpm).

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000300006&lng=en&nrm=iso&tlng=en 2013/09/19 - 17:13

In this paper a Neural Compensation Strategy for a hot rolling mill process is proposed. The target of this work is to built a RBF-NN compensation approximation for the classical force feed forward and speed controller. A strategy based on neural networks is proposed here, because they are capable of modelling many nonlinear systems and their neural control via RBF-NN approximation. Simulations demonstrate that the proposed solution deals with disturbances and modeling errors in a better way than classic solutions do. The analysis of the RBF-NN approximation error on the control errors is included, and control system performance is verified through simulations.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000300007&lng=en&nrm=iso&tlng=en 2013/09/19 - 17:13

In this work we compared the kinetic of the rehydration process of potatoes cubes and effects of water temperature, shelf life and variety on it. Rehydration ratio, water absorption capacity and moisture content were examined during soaking. Samples were dried in a microwave oven (300W), and subsequently rehydrated in a water bath at two temperatures (23±2ºC and 100±2Cº). Peleg's model was successfully applied to experimental data and the corresponding parameters were obtained and correlated with temperature. The parameters of the model considered were found to be greatly affected by the water temperature during rehydration. In particular the temperature increment increases the rate of rehydration and the equilibrium moisture content of the rehydrated products but shelf life decreased all the parameters

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000300008&lng=en&nrm=iso&tlng=en 2013/09/19 - 17:13

An adaptive identifcation algorithm based on Second Order Section (SOS) model structures is presented. The procedure guarantees stable transfer functions whenever the actual physical plant is stable, due to an optimal Nehari approximation step performed analytically online. The procedure is suitable for real time applications. Some synthetic and experimental examples illustrate the proposed algorithm

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000300009&lng=en&nrm=iso&tlng=en 2013/09/19 - 17:13

We consider one-dimensional two-phase Stefan problems for a finite substance with different boundary conditions at the fxed faces. The goal of this paper is to determine the behavior of the free boundary and the temperature when the thermal coefcients of the material change. We obtain properties of monotony with respect to the latent heat, the common mass density, the specifc heat of each phase and the thermal conductivity of the liquid phase. We show that the solution is not monotone with respect to the thermal conductivity of solid phase, in some cases, by computing a numerical solution through a finite difference scheme. The results obtained are important in technological applications as the climate of buildings, the storage of energy in satellites and clothes and the transport of biological substances and telecommunications.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000300010&lng=en&nrm=iso&tlng=en 2013/09/19 - 17:13

In this paper, we examine the effect of thermal radiation on the blood flow through a stenosed artery under the combined actions of axial pressure gradient and applied magnetic field. The blood flowing through the artery is considered to be Newtonian and its viscosity radial co-ordinate dependent due to hematocrit variation. Analytical expressions are obtained for the flow velocity, temperature, the volumetric flow rate, wall shear stress and wall heat transfer rate. Discussions are made from a physiological point of view. The effects of various embedded parameters are discussed with the help of graphs. Thus, the study can be used for clinical purposes, especially in the area of deep heat therapy.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000300011&lng=en&nrm=iso&tlng=en 2013/09/19 - 17:13

In this paper, we examine the effect of thermal radiation on the blood flow through a stenosed artery under the combined actions of axial pressure gradient and applied magnetic field. The blood flowing through the artery is considered to be Newtonian and its viscosity radial co-ordinate dependent due to hematocrit variation. Analytical expressions are obtained for the flow velocity, temperature, the volumetric flow rate, wall shear stress and wall heat transfer rate. Discussions are made from a physiological point of view. The effects of various embedded parameters are discussed with the help of graphs. Thus, the study can be used for clinical purposes, especially in the area of deep heat therapy.

http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932011000300012&lng=en&nrm=iso&tlng=en 2013/09/19 - 17:13