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vol. 37 num. 3 lang. es<![CDATA[SciELO Logo]]>http://www.scielo.org.ar/img/en/fbpelogp.gif
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<![CDATA[Test of nuclear-pulse shapers using oscillation-based test]]>
http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000300001&lng=es&nrm=iso&tlng=es
This paper addresses the problem of testing continuous-time nuclear-pulse shapers using Oscillation-Based Test (OBT). The proposal is to convert the whole systems into non-linear oscillators, avoiding the partition in low-order sections. The design of the oscillators is very simple because the non-linear elements are mathematically modeled using the describing function approach, and the study of the oscillators is made using techniques of linear systems. The test strategy presents high fault coverage and requires only one test session. The last characteristic allows reducing the time required for executing the test and the complexity of the test controller. The OBT schemes are validated using deviation and catastrophic fault models.<![CDATA[Structure effects on the optical properties of thin (PbLa)TiO3 films]]>
http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000300002&lng=es&nrm=iso&tlng=es
Amorphous thin films of Pb1-xLaxTiO3 (with x=0, 13 and 27 mol %) were prepared by the polymeric precursor method and deposited by spin coating on glass substrates. The films were characterized by X-ray diffraction (XDR) and scanning electron microscopy (SEM) and the band gap energy of the amorphous PLT films was calculated from the UV-VIS spectra. The obtained values were compared to that theoretically calculated. The observed decrease of the band gap was attributed to increased density of defects in the amorphous structure. Futhermore photoluminescence (PL) at room temperature was observed for thin (PbLa)TiO3 films.<![CDATA[Predictive control with constraints of a multi-pool irrigation canal prototype]]>
http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000300003&lng=es&nrm=iso&tlng=es
This paper presents a real-time implementation of a multivariable predictive controller with constraints to regulate the downstream levels at the end of the pools in a four-pool open irrigation canal prototype. The objective of the controller is to maintain the downstream level at a constant target value despite inflow disturbances. The controller is designed using a "black box" identified linear model. The results show satisfactory closed-loop performances.<![CDATA[The estimation of oil water displacement functions]]>
http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000300004&lng=es&nrm=iso&tlng=es
We introduce an algorithm to solve an inverse problem for a non-linear hyperbolic partial differential equation. It can be used to estimate the oil-fractional flow function from the Buckley-Leverett equation. The direct model is non-linear: the sought for parameter is a function of the solution of the equation. Traditionally, the estimation of functions requires the election of a fitting parametric model. The algorithm that we develop does not require a predetermined parameter model. Therefore, the estimation problem is carried out over a set of parameters which are functions. The parameter is inferred from measurements of saturation at different spatial points as a function of time. The estimation procedure is carried out linearizing the solution of the direct model with respect to the parameter and then computing the least-squares solution in functional spaces. The sensitivity equations are derived. We test the algorithm with several numerical experiments.<![CDATA[A practical strategy for controlling flow oscillations in surge tanks]]>
http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000300005&lng=es&nrm=iso&tlng=es
The use of accumulation vessels -production separators, electrostatic treaters, etc- as filters of feed oscillations has been proposed to optimize the offshore treatment of crude oils. This change in philosophy of control suggests letting the level to oscillate within certain limits -called band- for which existing algorithms require the measurement of the flow rate. An alternative algorithm is presented in this paper that requires only the measurement of the level. The basic concepts of the proposal are presented. It is demonstrated that besides being simpler, this algorithm has a good performance when compared to the traditional PI controller for surge tanks conception in surge tanks.<![CDATA[Vascular heterografts for hemodyalisis access: analysis of elastic and viscous matching factor between human and ovine vessels]]>
http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000300006&lng=es&nrm=iso&tlng=es
Long-term vascular accesses are usually performed in patients submitted to renal replacement therapy using autologous vessels. When arterio-venous fistula creation is impossible, animal conduits have been used in order to obtain high patency rates. Bovine vessel heterograft has been introduced as a substitute for the construction of arterio-venous fistulas. However, when experimental research of graft failure is focused to vascular wall properties, the ovine model is one of the more frequently utilized instead of the study of bovine vessels. Biomechanical vessel wall properties study is very important, since the viscoelastic mismatch among the fistulae conduits has been pointed out as a determinant of intimal hyperplasia, a cause of access dysfunction. In this work we have analyzed viscoelastic properties of arteries and veins harvested from human donors in brain death condition and healthy sheep. The elastic mismatch calculus revealed that the human brachial artery and the ovine jugular veins exhibit the best coupling accompanied by an optimal viscous matching.<![CDATA[Optimal operation profit of a pilot rotary kiln for charcoal activation]]>
http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000300007&lng=es&nrm=iso&tlng=es
This work presents an optimization study of a pilot rotary kiln steady state operation, used to manufacture activated carbon (AC) from eucalyptus wood and, a sensitivity analysis on the optimal solution. The main goal is the maximization of a process operating profit function, considering constraints on the optimization variables as: residence time, solid feed, activation steam and heating gas flow rates, for maintaining product quality and maximum production yield. Bounds on optimization variables have been previously defined by a sensitivity analysis of the kiln performance carried out via simulation of the steady state mathematical model. Due to the kind of equality constraints, the optimization problem was solved coupling the optimization code with a differential equation solver in a MatlabTM framework. Results attained allow getting valuable information for design, operation policy, regulation and reactor scale-up in order to develop a local technology for activated carbon production using a regional raw material.<![CDATA[Comparative study of the cryosurgical processes with two different cryosurgical systems: the endocare cryoprobe system versus the novel combined cryosurgery and hyperthermia system]]>
http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000300008&lng=es&nrm=iso&tlng=es
A numerical model was developed to study heat transfer process during freezing of biological tumors. Two different cryosurgical systems, Endocare cryoprobe and novel combined cryosurgery and hyperthermia system, were investigated using the multidimensional, finite element method (FED) developed in Ansys (V7.0) by us recently. The tissues were modeled as nonideal materials, the thermophysical properties of which were temperature dependent. The enthalpy method was applied to solve the highly nonlinear problem. It was found that for the same initial/boundary conditions and the same target tissues, the novel combined cryosurgery and hyperthermia system could supply the target tissue an approximate cooling rate, a much lower minimal temperature, a much greater warming rate, and a much greater thermal gradient as compared with the Endocare cryoprobe system. The numerical simulation results indicated that the novel combined cryosurgery and hyperthermia system could provide an excellent curative effect in the corresponding cryotherapy.<![CDATA[Electrocatalytic oxidation of ethanol on platinum nanoparticles modified polyaniline electrode]]>
http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-07932007000300009&lng=es&nrm=iso&tlng=es
The electrocatalytic properties of platinum nanoparticles incorporated into polyaniline films was investigated for oxidation of ethanol in sulfuric acid solutions. The electropolymerization of aniline and the electrochemical depositions of plati-num particles into the polyaniline film were achieved by cyclic voltammetry. The effect of the formation conditions of platinum-modified polyaniline films (as cycle numbers, sweep rates) and alcohol concentra-tion were evaluated. The platinum-modified polyani-line films formed by the optimization conditions can be used as a convenient conducting substrate for the ethanol electrooxidation.