Scielo RSS <![CDATA[Latin American applied research]]> vol. 45 num. 1 lang. es <![CDATA[SciELO Logo]]> <![CDATA[<b>Chemical and Extractives Compatibility of Empty Bunch Fruit of <i>Elaeis guineensis</i>, Leaves of <i>Ananas cumosos</i> and Tetrapak with Wood used in Particleboards in Tropical Areas</b>]]> Tropical countries produce a great variety of lignocellulosic residues from small-area planted crops. Large amount of "Tetra Pak" package are also produced without any disposal treatment. In order to give solutions for waste management, residues must be incorporated in other processes, such as the manufacture of particleboards. The main objective of this work was to evaluate chemical compositions, extractives in different solvent, chemical characterization of extracts in polar and un-polar solvent utilizing infrared spectrum analysis. A second aim of this study was to test the compatibility between chemical composition and extractives of empty bunch fruit of Elaeis guineensis (BPF), the leaves of Ananas cumosos (PL) and "Tetra Pak" packages with three timber species (Gmelina arborea, Tectona grandis and Cupressus lusitanica).. Results showed that cellulose, ashes and lignin content of BPF, PL and "Tetra Pak" differ from those of the woody species. Similar result was obtained for pH and for the amount of substances extracted with different solvents. Infrared spectrum of water (polar), and ethanol-toluene (un-polar) solutions showed that the greatest differences in extracts were found in BPF and PL, this in relation to the studied woody species. Finally, HCMA showed that residues from BPF and "Tetra Pak" packages are slightly different, considering chemical compositions and extract content, to other woody species used for particleboard manufacture. Moreover, PL has the least compatibility with the woody species <![CDATA[<b>Predictive Generalized Minimum Variance Control of Nonlinear Multivariable Systems with Non-analytical Modules</b>]]> For most of the control methods, it is implicitly assumed that a mathematically analytical model can be obtained before control design. This is not always feasible for many engineering systems whose analytical models are either very difficult or expensive to obtain. To handle this situation, linearization or identification techniques are usually deployed to obtain an analytical model. This paper, however, proposes a novel method to tackle directly those systems with non-analytical modules. The method does not rely on the inversion of the nonlinear system and is henceforth computationally economic. Important results are obtained on control design for nonlinear multivariable systems with non-analytical modules. Input saturation, robustness and practical implementation issues are also discussed. The proposed method is finally validated through its application to a robotic manipulator <![CDATA[<b>Sorption isotherms and thermodynamic analysis of seed fruits used to obtain vegetable oil</b>]]> Sorption isotherms of papaya, melon and grape seeds were determined and thermodynamic properties compared. The experiments were carried out at different temperature using the gravimetric method. The Henderson and GAB models were the best which represented the experimental data. Papaya and grape seeds are more stable with larger moisture content than melon seeds at 30°C. Grape seeds presented more resistance to lose water during the dehydration. The differential enthalpy and entropy decreased with increasing moisture content and satisfied the compensation theory. It was found that the sorption process investigated was enthalpy-driven <![CDATA[<b>Comparison of Cr(VI) adsorption onto polymer-based magnetic hybrid adsorbents by nonlinear isotherm and kinetic models</b>]]> In the present study, polyglycidyl methacrylate graft copolymer (PG) and ethylene glycol dimethacrylate based polymers (EG) were synthesized and modified by iron oxides in order to have magnetic form (PG-M and EG-M). Batch hexavalent chromium (Cr(VI)) adsorption experiments were carried out as a function of pH. Adsorption data were applied to Langmuir, Freundlich, Dubinin-Raduskevich, Sips, Toth and Redlich-Peterson isotherm models by utilizing non-linear techniques. The Dubinin-Radushkevich isotherm model was found to be the most suitable one for PG-M sample, while Langmuir model fitted best to the experimental data of EG-M sample. The contact time needed for both adsorbents was relatively short, ranging from 1 to 30 min. Approximately 73% of Cr(VI) was rapidly removed by PG-M within ten minutes; and for EG-M sample, 88% of Cr(VI) was removed at the end of five minutes. The rate of the adsorption is governed by a pseudo-second order rate equation <![CDATA[<b>Abatement of ochratoxin a from contaminated wine and grape juice by activated carbon adsorption</b>]]> The ochratoxin A (OTA) is an organic and toxic for man compound, generated by fungi usually present in the vineyards. This compound can be found in grape and its derivative products. In this article, activated carbon from grape stalk was used as an adsorbent to reduce the concentration of OTA in wine and grape must. The adsorption tests were carried out following the same procedure for wine and must. This procedure consisted in adding OTA to the samples; three aliquots were taken from them, putting each one in contact with different amounts of activated carbon. In each of the tests, the concentration of OTA was determined at 30, 60 and 120 minutes by High Performance Liquid Chromatography (HPLC). Satisfying results were obtained, reducing OTA levels by 80% in wine and 96% in must, when 100 mg of carbon were used during 2 hours of contact. The influence of contacting with activated carbon on the color of wine was analyzed by spectrophotometry. Neither of the analyzed samples showed a significant variation on color <![CDATA[<b>Analysis of chitosan/polyvinylpyrrolidone (structure, ftir, electrostatic potential, homo/lumo orbitals) using computational chemistry</b>]]> Chitosan and PVP oligomers were analyzed by means of the HyperChem software 8.0v to determine the theoretical structure. Quantum chemical calculation of geometrical structure and energies were studied using PM3 and AM1 methods in where the Gibbs free energy was calculated with a value of -9028 and -5796 Kcal/mol, respectively; these values showed that the reaction was carried out. Quantum chemical calculations are applied to study the (CT) complexes in order to obtain information on structures and other molecular properties like specific interaction of donor and acceptor. The interaction energy contribution comes from the effects of donor-acceptor interactions and π−π interactions. The HOMO and LUMO were simulated by determinate the transition state and energy band gap. Vibrational analysis shows that the band in 3185 cm-1 and shifting of band to lower wave number clearly indicates strong intermolecular interactions between chitosan and PVP. When the PVP oligomers is blended with chitosan, this absorption signal, which is assigned to the stretching vibration of a C=O group in the pyrrolidone ring, tends to shift to a position of somewhat lower frequency <![CDATA[<b>Lubrication predictions for total knee prosthesis made of hard materials</b>]]> The lubricated contact zone in a total knee prosthesis is modeled, where femoral and tibial components are supposed to be made of hard materials (high stiffness and hardness) and lubricated by a non Newtonian fluid (synovial liquid). To determine optimal relations among geometric parameters, load and film thickness, a generalized Reynolds equation was solved by means of finite element method. Although mix lubrication regime is predominant, it is shown that increasing conformity, it could be assure a full-film lubrication regime in most of the gait cycle. These results might be a reference to make more durable total knee prostheses <![CDATA[<b>Photocatalytic activity of ZnAl<sub>2</sub>O<sub>4</sub> spinel for procion red degradation under UV irradiation</b>]]> In this work, ZnAl2O4 spinel was used as photocatalyst for dye degradation in aqueous solutions under UV irradiation. This material was prepared by a route with chitosan as template. The effects of process variables, such as, initial dye concentration and photocatalyst concentration were investigated. Kinetic parameters were obtained and the reaction order was determined. The results revealed that both studied variables presented strong influence on the dye degradation efficiency, which attained 100% in some cases. It was found that the dye photocatalytic degradation under UV irradiation followed a first order kinetic behavior. The results indicated that ZnAl2O4 spinel can be used to treat dye containing effluents <![CDATA[<b>A multigrid method for the solution of composite mesh problems</b>]]> The Composite Finite Element Mesh method is useful for the estimation of the discretization error and, in addition, for the nodal solution improvement with a small increase in the computational cost. The technique uses two meshes with different element size to discretize a given problem and, then, it redefines the resulting linear system. On the other hand, Multigrid methods solve a linear system using systems of several sizes resulting from a hierarchy of meshes. This feature motivates the study of the application of the Multigrid strategy together with the Composite Mesh technique. In this work, it is proposed a Multigrid method to solve problems where the Composite Mesh is applied. The goal of the proposal is to achieve both, the advantages of the Multigrid algorithm efficiency and the solution improvement given by the Composite Mesh technique. The new method is tested with some elliptic problems with analytical solution <![CDATA[<b>A hybrid group based re-key management scheme for secure communication in wireless sensor</b>]]> Secured Communication is primarily important in Wireless Sensor Networks (WSNs), since the communication signals are explicitly available as they broadcast through the air. These networks are more vulnerable to attacks extending from passive eavesdropping to active snooping. In this paper, a hybrid Group based Re-Key Management Scheme (HG-RMS) is proposed. The objective of this paper is to provide a secure group communication in WSNs. The Group Controller is elected for each group to manage the group members. The proposed HG-RMS incorporates the Modified Hybrid Energy Efficient Distributed (M-HEED) protocol to elect the group controller. Rivest Shamir Adleman (RSA) is used by the Key Management Center (KMC) to generate the keys and distribute to the group controllers. The key exchange mechanism is explored for secure communication between the users. Node compromise attacks are detected and prevented based on the periodic broadcast messages. The re - keying process is initiated whenever a node joins/leaves the group. The experimental results show that the proposed scheme performs better than the existing Cluster based Group Key Management (CB-GKM) in terms of energy, privacy level, memory, and time consumption. <![CDATA[<b>Optimization of solid-liquid extraction of ethanol obtained by solid-state fermentation of sugarcane bagasse</b>]]> Solid-state fermentation has been used as an alternative to reduce the amount of waste water in ethanol fermentation. However, the recovery of ethanol from solid medium should be investigated, since depending of experimental condition used in the extraction, significant difference in the results can be obtained. In this work was investigated the influence of temperature (30-50°C), solid to liquid ratio (10-40 wt%) and orbital agitation (50-180 rpm) in the recovery of ethanol from sugarcane bagasse at different fermentation conditions of moisture content (50-80%) and ethanol amount (5-20 wt%). The highest recovering efficiency was 81.3% at 30°C, solid to liquid ratio of 40 wt%, initial ethanol amount of 10 wt%, orbital agitation of 100 rpm and moisture content of 60%. The main contribution of this work was to demonstrate that the amount of water used in the extraction is lesser than that used in traditional liquid fermentation, making possible to obtain a more concentrated broth, saving with water treatment and energy for ethanol concentration