Scielo RSS http://bibliotecadigital.uns.edu.ar/rss.php?pid=0327-079320140044&lang=es vol. 44 num. 4 lang. es 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=S0327-07932014004400001&lng=es&nrm=iso&tlng=es A simple and unexpensive method based on traditional cadmium column technique is proposed for determination of nitrate in acidic aqueous mixtures with high iron load. Solutions are alkalinized and centrifuged, subsequently the supernatant is withdrawn for nitrate analysis. By this procedure two effects are accomplished, on the one hand, pH is adjusted to a suitable value and, on the other hand, iron interference is removed by precipitation. The obtained mixture is passed through a copperized cadmium column to reduce nitrate to nitrite which is quantified spectrophometrically. This method is suitable to measure nitrate concentrations even lower than the maximum accepted limit, in artificial solution http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932014004400002&lng=es&nrm=iso&tlng=es Dihydropyrimidinthione is an important class of heterocyclic compounds which exhibits wide spectrum of biological activities. In the present study, some bio-active dihydropyrimidinthione derivatives have been synthesized and their characterization was done by IR, NMR and mass spectral data. The antibacterial and antifungal activities of synthesized compounds have also been studied in N,N-dimethyl formamide and Dimethyl sulfoxide http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932014004400003&lng=es&nrm=iso&tlng=es Gas injection into liquids is common in many applications. Nozzles with simple geometries are used for injecting gases, this lead to some turbulence and thus different rates of mixing and residence times. In this paper we present a study on gas injection using convergent-divergent nozzles. Gas flow through nozzles with different diameter ratios has been studied. It was found that changes in diameter ratios have a definitive effect on the performance of these nozzles as the gas is injected into a liquid. Pressure measurements of the gas during injection were conducted so momentum transfer could be estimated; additionally high speed video allowed us to see the differences in the gas plumes as the different nozzles were used http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932014004400004&lng=es&nrm=iso&tlng=es In this work, drying of mango peels was kinetically investigated within temperature range of 40-100 °C and the applicability of several models available in literature was statistically evaluated. Midilli's model provided the best description of the kinetics of drying mango peels with constant drying rates (k-and b-values) varying from 0.0190 to 0.0399 min-n and from 0.000404 to 0.000903 min-1, respectively, in temperature range of 40-100 °C. High concentration of total phenolic content was obtained when drying temperature was increased up to 80 °C. Finally, the polyphenolic degradation could be accompanied by CIELB parameters related to the yellowness of the dried samples http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932014004400005&lng=es&nrm=iso&tlng=es In the present work, we provide a systematic analysis about all the streams involved in the zone connecting two consecutive sections for the design of distillation columns with different thermal feed conditions, product extractions and heat additions or withdrawals. This analysis allows a better understanding of what happens on a feed or side draw (of mass or energy) stage, what compositions are or are not in equilibrium, and the impact on internal liquid and vapor flows http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932014004400006&lng=es&nrm=iso&tlng=es This paper presents a new controller design to tracking trajectory of a typical chemical process. The plant model is represented by numerical methods and, from this approach; the control actions for an optimal operation of the system are obtained. Its main advantage is that the condition for the tracking error tends to zero and the calculation of control actions, are obtained solving a system of linear equations. The proofs of convergence to zero of the tracking error are presented. Simulation results show the good performance of the proposed control system http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932014004400007&lng=es&nrm=iso&tlng=es In order to correlate and optimize experimental data either from the laboratory or industry, one needs a robust method of data regression. Among the non-linear parameter estimation methods it may be pointed out of Levenberg, which applies the conversion of an arbitrary matrix into a positive definite one. Later, Marquardt applied the same procedure, calculating λ parameter in an iterative form. The Levenberg-Marquardt algorithm is described and two routine for correlating vapor-liquid equilibrium data for pure component and mixtures, based on this efficient method, have been applied. The routines have been written with an interface very accessible for both users and programmers, using Python language. The flexibility of the developed programs for introducing the desired details is quite interesting for both process simulators and modeling properties. Furthermore, for mixtures with electrolytes, it was obtained a coherent and compatible relation for the structural parameters of the salt species, with the aid of the method and the graphical interface designed http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932014004400008&lng=es&nrm=iso&tlng=es Phenol compounds are the major constituents in vegetables and can be correlated to the antioxidant capacity of plants. Thus, the relationship between total antioxidant activity (TAA) and total phenol content of Ilex paraguariensis extracts were evaluated using a Horseradish peroxidase-based biosensor. Antioxidant activities of these extracts were investigated by the 1,1-diphenyl-2-pycrylhydrazyl (DPPH) radical scavenging method. TAA of the investigated Ilex paraguariensis samples were well correlated to the phenol content, presenting correlation coefficients R > 0.9. The measured antioxidant capacity expressed in terms of relative antioxidant capacity of tea and yerba mate of different origin were listed in relation to the 10 mmolL-1 Trolox solution. According to these observations the biosensor reading can be applied to determine the TAA of Ilex paraguariensis samples http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932014004400009&lng=es&nrm=iso&tlng=es This paper investigates the influence of the process parameters like machining voltage, electrolyte concentration, frequency on the over cut and Material Removal Rate (MRR) on drilling of Al- 10% TiC Metal Matrix composites using Electrochemical Micro Machining (EMM) through taguchi methodology and grey relational analysis. Based on the analysis, optimum levels of parameters were determined and the same to validate through the confirmation test. Experimental results are in close agreement with the developed model. The confirmation results reveal that, there is considerable improvement in Material Removal Rate, Overcut. Grey relational grade are improved by 89.5 %, 57.9% and 95.16 % respectively. It is observed that the machining performance can be effectively improved with respect to initial parametric setting http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932014004400110&lng=es&nrm=iso&tlng=es Effects of viscous dissipation, heat source, thermal diffusion and chemical reaction on demixing of a binary mixture of incompressible viscous electrically conducting fluids in two dimensional magnetohydrodynamic boundary layer flow on a vertical stretching surface are investigated. The momentum, energy and concentration equations are reduced to non-linear coupled ordinary differential equations by similarity transformations and are solved numerically by using MATLAB's built in solver bvp4c. These numerical results are exhibited graphically from which it has been found that the effects of various parameters are to separate the components of the binary mixture by collecting the lighter and rarer component near the plate and throwing the heavier one away from it http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932014004400111&lng=es&nrm=iso&tlng=es Global markets are now becoming volatile in most industries and the importance of their abilities to adapt to rapid and unexpected changes have surfaced. Modern organizations have to respond quickly to their customers' dynamic demands without compromising on quality, productivity and cost. Achieving agility lies in de-signing agile friendly processes and thus firms need to concentrate on their supply chains and its enablers in the attempt of redressing themselves as responsive supply chains. To evaluate and improve the levels of supply chain agility, a model called Total Agile Design System (TADS) is proposed. TADS as a methodology identifies supply chain enablers and prioritize them in order to achieve supply chain agility. In this scoring model, agility index before and after implementation of TADS are measured and discussed. The results validate the proposed model and lend evidence to the current thinking of impinging on agile concepts in traditional supply chains for competitive advantage and survival. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932014004400112&lng=es&nrm=iso&tlng=es The boundary layer flow of viscous incompressible fluid over a moving cylinder with suction has been considered to study heat transfer with variable thermal conductivity. The heat transfer is affected by thermal conductivity for the liquid metals within 0°F to 400°Frange. In this case, we observe that the transfer of heat behaves differently in two different regions: 0≤η≤1and η>1. Hence, we solve the two boundary value problems to draw out recommendations. The results have been discussed graphically http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932014004400113&lng=es&nrm=iso&tlng=es The ADRC tuning is essentially a pole-placement technique and the desired performance is indirectly achieved through the location of the closed-loop poles. However, the final choice of these poles becomes a trial-and-error strategy. In contrast with pole-placement, in the LQR method, the desired performance objectives are directly and globally addressed by minimizing a quadratic function of the state and control input. ADRC tuning employing the LQR approach is then applied for decoupling uncertain MIMO systems. This is done by considering all the coupling and interference interactions between the channels of the system as disturbances, using an ESO to estimate them in real time and then canceling its effect employing the estimate as part of the control signal. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932014004400114&lng=es&nrm=iso&tlng=es The competition between companies is generating a reduction in profitability ratios of the same, forcing the optimization of the production process, thus obtaining, greater efficiency in the allocation of factors of production involved. This research aims to correlate the rate of absenteeism with indicators of Quality of Work Life (QWL), through the results of a case study applied between employees of a brick small factory (pottery), located in central region of Rio Grande do Sul, Brazil. For this, a method of qualitative research was used, which enables the researcher to evaluate in detail the practice of improving QWL, as quantitative in the identification of satisfaction and absenteeism rates. It was found that in the company is no correlation between absenteeism and QWL, being the category of "attendants" that had the highest rate of absenteeism and job dissatisfaction, on issues of QWL. In general, it can be concluded that most of the causes of absenteeism is related to the low level of employees satisfaction with their work, undermining personal relationships, principles of QWL, and hence production levels