Sistema Regional de Información
en línea para Revistas Científicas de América Latina,
el Caribe, España y Portugal

In this paper we present a new approach to design the input control to track the output of a non-minimum phase nonlinear system. Therefore, a cascade control scheme that combines input–output feedback linearization and gradient descent control method is proposed. Therein, input–outputfeedback linearization forms the inner loop that compensates the nonlinearities in the input–output behavior, and gradient descent control forms the outer loop that is used to stabilize the internal dynamics. Exponential stability of the cascade-control scheme is provided using singular perturbation theory. Finally, numerical simulation results are presented to illustrate the effectiveness of the proposed cascade control scheme.

The design and implementation of a robot manipulator with 6 degrees of freedom (DOF), which constitutes a physical platform on which a variety of control techniques can be tested and studied, are presented. The robot has mechanical, electronic and control systems, and the intuitive graphic interface designed and implemented for it allows the user to easily command this robot and to generate trajectories for it. Materializing this work required the integration of knowledge in electronics, microcontroller programming, MatLab/Simulink programming, control systems, communication between PCs and microcontrollers, mechanics, assembly, etc.

The equilibrium adsorption of benzoic acid from an aqueous medium on a natural vermiculite-based adsorbent was studied in the presence and absence of hydrophilic silicon dioxide nanoparticles in batchwise mode. The adsorbent was prepared through grinding natural vermiculite in a laboratory vibratory disk mill and the surfactant modification of ground vermiculite by cetyltrimethylammonium bromide, subsequently. The equilibrium isotherm in the presence and absence of nanoparticles was experimentally obtained and the equilibrium data were fitted to the Langmuir, Freundlich, Dubinin–Radushkevich and Temkin models. The results indicated that the dispersion of silicon dioxide nanoparticles at optimum concentration in the liquid phase remarkably increases the removal efficiency. Furthermore, it yields a more favorable equilibrium isotherm and changes the compatibility of equilibrium data from the Langmuir and Temkin equations to just the Langmuir equation. A quadratic polynomial model predicting the equilibrium adsorbent capacity in the presence of nanoparticles as a function of the adsorbate and initial nanoparticle concentrations was successfully developed using the response surface methodology based on the rotatable central composite design. A desirability function was used in order to optimize the values of all variables, independent and dependent ones, simultaneously.

Poly(aspartic acid-citric acid) copolymer (PAC) is a new product of poly(carboxylic acid) scale inhibitor. The study aims to develop a “green” water treatment agent for calcium phosphate scale. The article compares the efficiency of three polymeric antiscalants, poly(aspartic acid-citric acid) copolymer (PAC), polymaleic acid (HPMA) and a compound inhibitor (PAC-HPMA), for calcium phosphate scale prevention under varying experimental conditions. Inhibitor concentration, calcium concentration, system pH, temperature and experimental time were varied to determine their influences on inhibitor performance by the static scale inhibition method. The copolymer (PAC) was characterized by FTIR,1H NMR and 13C NMR. The compound inhibitor was applied in the actual circulating cooling water system. An atomic force microscope (AFM), X-ray powder diffraction (XRD) and a scale formation process analysis were used to explore the scale inhibition mechanism. The results showed that scale inhibition rates of PAC, HPMA and PAC-HPMA against Ca3(PO4)2were, respectively, about 23%, 41.5% and 63% when the dosage was 8 mg/L in the experiment. The compound inhibitor showed the better inhibition performance than the above two kinds of monomers. Under the actual working conditions, the inhibition rate of compound inhibitor was close to 100% and completely met the actual application requirements of scale inhibitor in circulating cooling water systems. The main inhibition mechanism was the decomposition-chelation dispersion effect. The compound inhibitor can be used as an efficient “green” scale inhibitor for calcium phosphate.

Traditionally, a grayscale image is represented as a rectangular array whose internal values describe a discrete level of intensity or luminancedenoted as pixel. Due to its structure and complete compatibility with matrix operators, this representation is the most widely used in imageprocessing. Although the strong robustness of this standard is not in question, it is always enriching to have an alternative description format inorder to provide not only a different image representation scheme but also an additional approach to image processing. Motivated by this fact, in thispaper the viability of using continuous piecewise linear functions of two spatial variables as an alternative model description of grayscale imagesis explored. Moreover, the possibility of applying this type of representation in image processing is also examined by using mapping variabletransformations, here denominated as functional filters. Furthermore, it is also shown that such alternative image model can also be used in morecomplex tasks like tridimensional volume estimation. To verify this  proposal, illustrative examples are reported, showing not only an inherentimprovement in the visual perception of image, but also a practical image processing capability.

2016AbstractAcetylation method was used in the modification of Delonix regia pods (DRPs) as sorbent for crude oil cleanup in water. Fourier transform infra-red (FTIR) and scanning electron microscope (SEM) analysis were used to investigate the influence of acetylation and crude oil sorption on the sorbent (DRPs). Reaction conditions played significant roles on the extent of acetylation of DRPs. Temperatures of 303 K and 343 K were found to be the most suitable acetylation temperatures of DRPs. Intra-particle diffusion was the rate controlling mechanism for acetylating DRPs while the contributing mechanisms depend on the temperature of acetylation. The crude oil sorption capacity (OSC) of modified DRPs was significantly higher than that of unmodified DRPs. Physical and chemical reactions were faster in the crude oil sorption by modified DRPs than the unmodified while diffusion into the pores of the modified DRPs was slower than in the unmodified. Hydrophobic functional groups were enhanced by acetylation and crude oil molecules were adsorbed at these functional groups. Surface structure, pore sizes and fiber lengths of the sorbent were affected by acetylation and crude oil sorption. FTIR and SEM showed clear evidence of successful acetylation and crude oil sorption. Analysis of variance (ANOVA) was used to determine the statistical difference of weight percent gain (WPG) obtained from the acetylation of DRPs at different reaction parameters such as temperature and time. The OSC of modified and unmodified sorbents at various contact times, were also compared using ANOVA.

Thin films and coatings of permanent magnetic materials have found extensive applications in a wide range of technological domains. SmCo thin films show tremendous potential for use as permanent magnetic films on account of their high anisotropy fields, moderately high saturation magnetization and high curie temperature. In the present research, SmCo thin films have been deposited on single crystal Si(1 0 0) substrates using pulsed laser deposition technique. The films were deposited at a fixed substrate temperature of 400◦C by varying the number of pulses, in order to get thin films of different thicknesses. Effect of laser pulses on the crystal structure evolution, composition of the deposited material, film thicknesses and hence the magnetic properties have been investigated. X-ray diffraction analysis was performed in order to determine the crystal structure of the deposited films. The compositional analysis was performed by using energy dispersive X-ray spectroscopy. A slight variation in the Sm and Co contents was observed in the thin films grown by varying the laser shots. The microstructural information of the thin films was obtained by using a scanning electron microscope. The magnetic and electrical parameters were investigated by using vibrating sample magnetometer and two point probe respectively. The results show hard magnetic and conducting nature of all deposited thin films except sample 1 due to poor crystallinity.

Green synthesis of metal nanoparticles is an important technique in the methods of eco-friendly nanoparticle production. The synthesis of silver nanoparticles was accomplished using Ocimum sanctum leaf extract at room temperature. These particles were then encapsulated with polyvinyl alcohol (PVA) polymer matrix. The presence of silver was confirmed by different characterization techniques such as UV–vis spectroscopy, Fourier transform infrared spectroscopy (FTIR) and X-Ray Diffraction (XRD). Scanning electron microscopic (SEM) images of the synthesized powder shows spherical shaped silver nanoparticles embedded in sponge-like polymer matrix. The energy dispersive X-ray analysis confirms the presence of elemental silver along with iron signal. Energy dispersive signal corresponding to elemental iron has been attributed to O. sanctum plant. The silver nanoparticles in PVA matrix thus obtained shows high antibacterial activity against gram positive Staphylococcus aureus (S. aureus) and gram negative Escherichia coli (E. coli) water borne bacteria. The inhibition zone against S. aureus and E. coli were also calculated.

Composite metallic materials (CMMs) are prepared by dispersing copper particulates in aluminum matrix using stir-cast technique. Their behavioris compared with the  alloy having similar composition. The effect of particulate composition is studied by varying the copper concentration between5 and 15 wt%. Hardness increased with increasing particulate contents in both cast and homogenized conditions. Composites show a 13% drop instrength and 15% drop in strain compared to the alloy. With increasing reinforcement content, the strength increased and dropped. Agglomerationdue to increased reinforcement contents may be the reason for the decrease in strength values. Microstructures corroborate the above results.

In contrast to the case of known environments, path planning in unknown environments, mostly for humanoid robots, is yet to be opened for further development. This is mainly attributed to the fact that obtaining thorough sensory information about an unknown environment is not functionally or economically applicable. This study alleviates the latter problem by resorting to a novel approach through which the decision is made according to fuzzy Markov decision processes (FMDP), with regard to the pace. The experimental results show the efficiency of the proposed method.