Asynchronous digital linear?nonlinear control

At present, digital control solutions are becoming more attractive than analogue implementations in some power converter applications owing to easy design of complex control strategies and control reconfigurability. The digital implementation of an asynchronous linear-nonlinear (LnL) compensator to improve the dynamic response of interleaved buck converters is proposed and validated. It is important to highlight that the same digital LnL compensator is able to keep the dynamic response even with very important variations of the control and the power stage parameters.     

Effect of atmosphere on the electrical properties of TiO2–SnO2 varistor systems

This work illustrates the advancement of research on TiO₂-based electroceramics. In this work will be presented that the addition of different dopants, as well as thermal treatments at oxidizing and inert atmosphere, influences of the densification, the mean grain size and the electrical properties of the TiO₂-based varistor ceramics. Dopants like Ta₂O₅, Nb₂O₅, and Cr₂O₃ have an especial role in the barrier formation at the grain boundary in the TiO₂ varistors, increasing the nonlinear coefficient and decreasing the breakdown electric field. The influence of Cr_Ti is to increase the O and O₂ adsorption at the grain boundary interface and to promote a decrease in the conductivity by donating electrons to O₂ adsorbed at the grain boundary. In this paper, TiO₂ and (Sn,Ti)O₂-based studies of polycrystalline ceramics, which show a non-linear I–V electrical response typical of low voltage varistor systems are also presented. All these systems are potentially promising for varistor applications.     

Molecular and functional analysis of a MIG1 homologue from the yeast Schwanniomyces occidentalis

A putative glucose repressor MIG1-homologue (SoMIG1) was isolated from the amylolytic yeast Schwanniomyces occidentalis. Degenerate primers were designed from the conserved zinc finger regions of Mig1 and CreA proteins from different organisms. PCR using these primers and S. occidentalis genomic DNA as template yielded a single 128 bp product. This fragment was used as a DNA probe to screen a S. occidentalis genomic library. Analysis of the positive clones led to the isolation by PCR of a DNA fragment, which contained an open reading frame (ORF) that would encode a 458 amino acid polypeptide. The DNA binding and effector domains of this putative protein showed an identity of 71% and 15%, respectively, to those of the Mig1 protein from Saccharomyces cerevisiae. The SoMIG1 gene complemented a mig1 mutant of this yeast, which suggests that in S. occidentalis SoMIG1 is a glucose repressor. The Accession No. is AJ417892.     

Industrial solar cell tester: study and improvement of I‐V curves and analysis of the measurement uncertainty

Determination of solar cell parameters by illuminated I–V measurement is a standard characterisation technique in the photovoltaic industry. These measurements are carried out under standard conditions (STC: 25 °C, 1000 W/m² AM1.5G spectrum). It can be considered as the most crucial in‐line test for solar cells as it provides the industry with the conversion efficiency, and it is also a reliable quality control test. Reference cells are mainly used in testing equipment to set irradiance and working conditions in the tester/sorter, the rest of the cells being measured and classified by comparison with that reference. An accurate calibration of the irradiance at STC in cell testers and high precision in determining the main parameters of the I–V curve are required; a suitable design of the mechanical components and an adequate selection of different programme options should be made (distribution of the points measured, temperature correction or classification method). Here, we have studied the accuracy of an industrial solar simulator whose mechanical, electrical, electronic and software components were analysed with an individual solar device and a production sample. An uncertainty analysis was carried out in order to determine the power uncertainty and which components to improve in order to reduce it. Copyright © 2015 John Wiley & Sons, Ltd.     

Expression in Escherichia coli of a recombinant adenosine kinase from Saccharomyces cerevisiae: purification, kinetics and substrate analyses

The Saccharomyces cerevisiae ADO1 gene is known to encode a homologue of eukaryotic adenosine kinases. This gene was expressed in Escherichia coli as a recombinant protein fused to a polyhistidine tag by using the rhamnose-inducible bacterial promoter rhaB. The recombinant protein was purified to apparent homogeneity and its ability to phosphorylate different substrates was evaluated. Adenosine (Km 3 microM) is its primary substrate. In addition, it also phosphorylates, albeit less efficiently, 3'-deoxyadenosine (cordycepin; Km 1.84 mM) and 3'-amino-3'-deoxyadenosine (Km 0.26 mM). Other kinetic properties of the recombinant enzyme have also been determined.     

Evaluation of a new maximum power point tracker (MPPT) applied to the photovoltaic stand-alone systems

In this paper a comparative study through experimental work between a new low-cost maximum power point tracker (MPPT) and the conventional configurations of the photovoltaic (PV) regulators under different atmospheric conditions is presented. The comparison is made by means of the energy production obtained by the PV generator of each system. From the results obtained it can be concluded that, depending on the charge state of the batteries, the MPPT can increase the overall efficiency of the system between 2.8% and 18.5% compared with the performance of a conventional system.     

A Comparative Study of Thermal Conductivity in ZnO- and SnO2-Based Varistor Systems

We performed a comparative study of electrical and thermal properties of ZnO- and SnO₂-based varistor. The electrical properties of commercial ZnO-based varistor are equivalent to that found in SnO₂-based varistor system. In spite of this, the SnO₂ showed a thermal conductivity higher than commercial samples of ZnO-based varistor, which allied with its simpler microstructure and lower dopant concentration is a remarkable result that point out to the use of this system to compete commercially with ZnO-based varistor devices.     

Application of electrochemical techniques in pyrochemical processes - Electrochemical behaviour of rare earths at W, Cd, Bi and Al electrodes

The electrochemical behaviour of some rare earths ions (REs) - from the light to heavy lanthanides (i.e. Ce, La, Pr, Gd, Er, Ho) and Y - were investigated in the eutectic LiCl-KCl at different substrates: (i) liquid metals Cd and Bi, (ii) aluminium, and (iii) tungsten. The electrode reaction of the RE(III)/RE couples at the Cd and Bi pool electrodes was elucidated by cyclic voltammetry. The differences between the equilibrium potential adopted by a RE electrode and the observed with the same RE(III) solution at the liquid electrodes were consistent with the activity coefficients of RE in the liquid metal phase. The relative partial molar Gibbs energies and activities of RE in the RE-Cd and RE-Bi intermetallic compounds could be estimated by the analysis of the open circuit chronopotentiograms using Cd and Bi coated tungsten electrodes. The Gibbs energies of formation of different intermetallic compounds, as well as their molar entropies and enthalpies of formation were also calculated from the temperature dependence of the emf. The redox potential of the RE(III)/RE couples at the Al electrode was observed at more positive potentials than that at the inert electrode (W). This potential shift was explained by a lowering of the activity of the REs in the Al phases due to the formation of intermetallic compounds. Electromotive force measurements for various intermetallic compounds in two-phase coexisting states were carried out. The activities and relative partial molar Gibbs energies of REs were also obtained. Moreover, the molar entropies and enthalpies of the aluminium-rich alloys were also calculated from the temperature dependence of the emf measurements.     

Causes and consequences of iron deficiency on human health

Anaemia and nutritional iron deficiency significantly affect the world population. In this article we discuss the main causes and consequences that this nutritional deficiency produces on human health.     

Electrochemical extraction of samarium from molten chlorides in pyrochemical processes

This work concerns the electrochemical extraction of samarium from molten chlorides. In this way, the electrochemical behaviour of samarium ions has been investigated in the eutectic LiCl–KCl at the surface of tungsten, aluminium and aluminium coated tungsten electrodes. On a W inert electrode the electro-reduction of Sm(III) takes place in only one soluble–soluble electrochemical step Sm(III)/Sm(II). The electrochemical system Sm(II)/Sm(0) has not been observed within the electrochemical window, because of the prior reduction of Li(I) ions from the solvent, which inhibits the electro-extraction of Sm species from the salt on such a substrate. Sm metal in contact with the melt react to give Li(0) according to the reaction: Sm(0) + 2Li(I) ↔ Sm(II) + 2Li(0).On the contrary, on reactive Al electrodes the electrochemical system Sm(II)/Sm(0) was observed within the electroactive range. The potential shift of the redox couple is caused by the decrease of Sm activity in the metal phase due to the formation of Sm–Al alloys at the interface. The formation mechanism of the intermetallic compounds was studied in a melt containing: (i) both Sm(III) and Al(III) ions, using W and Al coated tungsten electrodes, and (ii) Sm(III) ions using an Al electrode. Analysis of the samples after potentiostatic electrolysis by X-ray diffraction and scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), allowed the identification of Al₃Sm and Al₂Sm.