Characterization of nickel-bearing ferrites obtained as by-products of hydrochemical wastewater purification processes

The efficiency of the ‘ferrite process’ for the purification of wastewater heavily contaminated with nickel is evaluated, and the solid residues formed are characterised. The efficiency of the purification process is always above 99.9% for Fe²⁺/Ni²⁺ ratios greater than 3. The tested Fe²⁺/Ni²⁺ molar ratios (15/1, 7/1 and 3/1) yielded three different nickel ferrites. Inductively-coupled plasma atomic emission spectroscopy (ICP-AES), potentiometric titration, X-ray fluorescence (XRF), X-ray diffractometry (XRD) and differential scanning calorimetry (DSC) yielded Ni_xFe_1−x^IIFe₂^IIIO₄ (x=0.18, 0.40 and 0.65, respectively) as the most probable stoichiometry, and inverse spinel as the most probable structure. Heating at 600 °C causes the transformation of the solids into a mixture of NiFe₂O₄, α-Fe₂O₃ and NiO. Electrochemical analysis of the solid nickel ferrites was performed using carbon paste electrodes (CPEs) in HClO₄ and HCl media. In each case, the first cyclic voltammogram showed the participation of solid species in the electrochemical transformation process, since the shape of the redox peaks could be related to the structure and stoichiometry of the ferrites. In second and successive scans, the voltammograms indicated the redox couples Fe_ads³⁺+1e⁻⇔Fe_ads²⁺ (0.525 V vs. Ag/AgCl) and Ni_ads²⁺+2e⁻⇔Ni(s) (−0.470 V) in HClO₄, and FeCl_2,ads⁺+1e⁻⇔FeCl_ads⁺+Cl⁻ (0.475 V) and NiCl_x,ads^(x−2)−+2e⁻⇔Ni(s)+xCl⁻ (−0.550 V) in HCl.     

The fast response double buck DC-DC converter (FRDB): operation and output filter influence

The fast response double buck (FRDB) dc-dc converter was presented like a low output voltage dc-dc converter with fast transient response, in order to feed devices such as microprocessors and digital signal processors (DSPs). The topology of the FRDB is composed of two buck converters connected in parallel, each one of them with different features and aims, and controlled by means of the novel linear-non-linear (LnL) control. In this paper, the topology, the control strategy and the operation principle are shown. Finally, experimental results in different prototypes are presented to show both, the transient response and the recovery time when these prototypes are subjected to load current steps, and the influence of the output filter on these parameters.     

PWM-PD multiple output DC/DC converters: operation and control-loop modeling

In this paper, PWM-PD multiple output dc/dc converters are presented. Operation analysis and power block design are shown. Furthermore, a small-signal model is developed for the PWM-PD multiple output dc/dc converters working in continuous conduction mode. The control-block is presented and the closed-loop circuit performances, such as the line, load and cross regulation, are obtained analytically. Finally, experimental results for a PWM-PD converter, with three fully regulated outputs and with transformer, are shown.     

Electrochemistry of thulium on inert electrodes and electrochemical formation of a Tm–Al alloy from molten chlorides

The electrochemical behaviour of TmCl₃ solutions was studied in the eutectic LiCl–KCl in the temperature range 673–823 K using inert and reactive electrodes, i.e. W and Al, respectively.On an inert electrode, Tm(III) ions are reduced to metallic thulium through two consecutive steps:

Tm(III) + 1e ↔ Tm(II) and Tm(II) + 2e ↔ Tm(0)

The electroreduction of Tm(III) to Tm(II) was found to be quasi-reversible. The intrinsic rate constant of charge transfer, k⁰, as well as of the charge transfer coefficient, α, have been calculated by simulation of the cyclic voltammograms and logarithmic analysis of the convoluted curves. Electrocrystallization of thulium plays an important role in the electrodeposition process, being the nucleation mode affected by temperature.The diffusion coefficients of Tm(III) and Tm(II) ions have been found to be equal. The validity of the Arrhenius law was verified by plotting the variation of the logarithm of the diffusion coefficients vs. 1/T.The electrode reactions of Tm(III) solutions at an Al electrode were also investigated. The results showed that for the extraction of thulium from molten chlorides, the use of a reactive electrode made of aluminium leading to Al–Tm alloys seems to be a pertinent route.Potentiometric titrations of Tm(III) solutions with oxide donors, using a ytria stabilized zirconia electrode “YSZE” as a pO²⁻ indicator electrode, have shown the formation of thulium oxychloride and thulium oxide and their corresponding solubility products have been determined at 723 K (pk_s(TmOCl) = 8.0 ± 0.3 pk_s(Tm₂O₃) = 18.8 ± 0.7).     

Towards the development of technical specifications for the production of lithium–lead alloys for the ITER HCLL TMB

The ITER and DEMO projects are developing new Test Blanket Modules (TBM), where the Pb–Li alloy plays a key role in the new commercial fusion reactors functionality. The Breeding Blanket (BB) has to perform several functions which are essential for the reactor operation. The HCLL TBM is one of the Breeding Blanket concepts to be tested in ITER. It is cooled by He and uses the eutectic liquid metal LLE (Lithium–Lead Eutectic) as breeder material (enriched at 90% in ⁶Li).Pb–Li eutectic alloy has no known uses outside of fusion technology, so the available databases of this material are currently incomplete. It is very important, within the material specifications, to have a complete characterization in order to define their chemical and physical properties, because any variation in the alloy composition has significant consequences in their behaviour, and therefore in their regenerative function inside the blanket.The chemical characterization methodology developed and presented in this paper (useful for both Pb–Li alloys as any Pb alloy) is a key tool that allows performing standard quality control procedures for base material and/or monitoring the alloy during the reactor operation. This report provides a procedure to perform a wide material chemical characterization, assessing the concentrations of major elements, as well as a review of trace level elements that can be found both in the eutectic alloy and in starting materials. In this determination plays an important role the ICP-MS technique because, as a highly sensitive technique, allows very low detection limits.     

Differentiation of legumes through elemental chemical composition using factor analysis

The proximate composition (water, carbohydrates, proteins, fats and ash and also sodium, potassium and chloride ions) of some legumes in the diet of a clinical hospital, over a 10-year period, has been determined. From the average values, or their graphical representations, large differences between several kinds of legume can be observed, but these differences are clearer and better explained by chemometrics methods (factor analysis and varimax rotation) which produce groupings of the samples into three types (fresh, canned and frozen) according to two factors: nutrients and salt.     

New algorithm using only one variable measurement applied to a maximum power point tracker

A novel algorithm for seeking the maximum power point of a photovoltaic (PV) array for any temperature and solar irradiation level, needing only the PV current value, is proposed. Satisfactory theoretical and experimental results are presented and were obtained when the algorithm was included on a 100 W 24 V PV buck converter prototype, using an inexpensive microcontroller. The load of the system used was a battery and a resistance. The main advantage of this new maximum power point tracking (MPPT), when is compared with others, is that it only uses the measurement of the photovoltaic current, I_PV.     

DC current injection into the network from PV inverters of <5 kW for low-voltage small grid-connected PV systems

The present paper is focused on the study of DC current injection for low-voltage small grid-connected PV systems, which is one of the power quality requirements of utility companies. To achieve this aim, the existing status of guidelines and regulations in six selected countries where the development in the grid PV sector has evolved rapidly over the last decade (Australia, Germany, Japan, Spain, the United Kingdom and the United States) has been reviewed according to the DC current injection into the grid. Furthermore, a grid-connected system installed in Spain has been used to carry out measures concerning possible DC current injection into the grid. Thus, 12 single-phase inverters <5 kW (according to the transformer options: 50 Hz LF transformers, HF transformers or transformerless) from the European market have been tested. Many groups of measurements were made under different conditions. The results show that in all cases there is DC current injection, even if an LF transformer inverter is used.     

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.     

Helicobacter pylori infection (13C-UBT), and its relationship with nutritional and socioeconomic factors in low income school children from Valencia, Venezuela

Helicobacter pylori infection (Hp) is widely spread around the world, and it is considered one of the main causes of chronic gastritis, peptic and duodenal ulcers, and gastric cancer. Recent research has shown that it can be associated with nutritional disorders, mainly with iron and other micronutrient deficiencies. The objective of this study was to assess the prevalence of Hp infection, and infection pattern according to age, sex, nutritional status, and socioeconomic conditions in children who attended the Unidad Educativa "Valentin Espinal" in the city of Valencia. 170 children, between 3 and 14 years of age were studied to assess Hpylori infection (13C-urea breath test), age, nutritional status according to BMI and Height for age, hemoglobin (cianometahemoglobin), serum ferritin (ELISA), socioeconomic status (Graffar-Méndez-Castellano), housing conditions, number of families and of people cohabitating in the same household, and quality of services. 78.8% of the children were infected with Hp, witch was significantly correlated with age but not gender. 25.9% of the sample had undernutrition, and 46.5% were stunted. 98.1% of the families lived in poverty, and 98% of the households showed sanitary deficiencies. A mean of 6.0 +/- 2.4 persons lived in each household (range: 2-15), and an average of 3.2 person shared bedrooms. The odds of being infected were higher in those children who were stunted. Also, socioeconomic status, mother's education level, and poor hosing conditions were significantly associated to being infected. Hpylori is highly prevalent among socially and economically deprived children, and age, overcrowding, and a low education level of the mother increases the risk of being infected.