Optical observations of very low ionization HII regions in the large Magellanic cloud

Several very low ionization isolated HII regions were detected on a prism-objective plate of the Large Magellanic Cloud. Most of the objects show a very weak (OIII) lambda 5007 emission line and, on the other hand the (OII) lambda 6584 doublets are very intense. This kind of objects seem to be ideal in order to determine accurate N and O abundance, avoiding the use of large ionization correction factors in the N abundance determination. Spectrophotometric observations of these regions were carried out with the 4 m telescope and the 2-D Frutti spectrograph at Cerro Tololo, and with the 1.52 m and the Image Dissector Scanner (IDS) at La Silla, ESO. The wavelength range lambda lambda 3700 to 7000 A was covered. Calibrated fluxes of the emission lines detected were measured, and from these data preliminary results of physical conditions of the gas as well as some ionic abundances were derived. Comparisons of the observations with ionization structure models show that the effective temperatures of the ionizing stars are less than 35,000 K. Possible abundances gradients across the large megallanic cloud are discussed

Reduced scale feasibility of temperature rise tests in substation connectors

Due to the important increase of the power of electrical transmission and distribution grids expected for the following years, especially in developing countries such as Kenya, Brazil, Philippines or Mexico among others, that have planes of generating energy from clean sources far away from the centres of consumption [1] it becomes a matter of special importance adapting and developing new substation connectors’ testing methods according to the power and temperature regimes at which they are expected to work. The international normative frame of substation connectors established both by the International Electrotechnical Committee (IEC) [2] and the National Electrical Manufacturers Association (NEMA) [3] sets standardized tests for the evaluation of high voltage connectors. These tests are routinely done within the quality plans of the manufacturers. At the moment, testing of substation connectors –and in general switchgear and fittings- is time demanding and costly due to the energy consumed by such tests. The expectations for the following years are that the power consumption of these tests will not do nothing but grow due to expected increase of power of worldwide overhead lines. For instance, today temperature rise tests in substation connectors involve power ranges up to 100 kVA, which are applied in cycles that can last several weeks. These tests are only feasible in few laboratories and at a very high cost: temporary, monetary, energetic and environmental. For this reason, following the line of other technologies such as aeronautics, naval engineering, or automotive as well as other studies done in the field of electrical engineering specially related to the corona effect [4], this study proposes to develop a reduced scale test system to perform temperature rise tests for substation connectors. Both, a theoretical framework based on analytical formulas, finite element method (FEM) simulations and experimental data has been developed to conduct reduced scale temperature rise tests and to set the conditions at which they provide comparable results to those attained in the original scale tests. Firstly, two circular loops (original and reduced scale loops) composed of a power conductor and two terminal connectors were analysed. The aim of this first study was to determine in an easy and trustful way the voltage and current values to be applied in experimental reduced scale tests to achieve the same steady-state temperature as in the original scale temperature rise test. The scale relationship between tests was set in 1:1.8, although the method proposed in this study can deal with any other scale factor. This study was useful in order to have a first sight of the final results of the procedure using substation connectors.Postprint (published version

Study of the growth rate of a film βGa2O3 as an alternative surface in the manufacture of Optoelectronic devices

In this study, gallium oxide layers were deposited using the physical vapor deposition technique, specifically PLD (pulsed laser deposition), on monocrystalline Si substrates, both in the presence of an oxidizing atmosphere and in an inert environment. An experimental matrix consisting of eight deposition conditions was generated by varying the oxygen partial pressure in the chamber and the deposition time. The aim was to determine the optimal conditions for thin film growth and to assess their optical and structural properties. Two deposition conditions were employed: (1) a residual pressure of 5x10-5 mbar and (2) 0.4 mbar at room temperature. For each condition, four different deposition times were tested: 5, 10, 20, and 40 minutes. Following the synthesis of thin films under these deposition conditions, the samples underwent characterization using techniques such as Field Emission Scanning Electron Microscopy (FESEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Transmission Wave Microscopy. Subsequently, a comprehensive analysis of the obtained results was conducted to identify the film with the highest quality and transparency. The various tests conducted on the samples revealed the successful deposition and synthesis of gallium oxide in both its beta phase with a cubic crystalline structure and its monoclinic crystalline phase. Furthermore, the FESEM images of the layers displayed compact thicknesses without defects or heterogeneities, attributable to the use of the PLD techniqueEn aquest estudi, s'han dipositat capes d'òxid de gal·li mitjançant la tècnica de dipòsit de vapor físic, concretament PLD (dipòsit de làser polsat), sobre substrats de Si monocristal·lins, tant en presència d'una atmosfera oxidant com en un entorn inert. S'ha generat una matriu experimental amb vuit condicions de dipòsit, variant la pressió parcial d'oxígen a la cambra i el temps de dipòsit. L'objectiu era determinar les condicions òptimes per al creixement de pel·lícules primes i avaluar-ne les propietats òptiques i estructurals. S'han utilitzat dues condicions de dipòsit: (1) una pressió residual de 5x10-5 mbar i (2) 0,4 mbar a temperatura ambient. Per a cada condició, es van provar quatre temps de dipòsit diferents: 5, 10, 20 i 40 minuts. Després de sintetitzar les pel·lícules primes sota aquestes condicions de dipòsit, les mostres van ser caracteritzades mitjançant tècniques com la Microscòpia Electrònica de Rastreig de Camp d'Emissió de Camp (FESEM), la difracció de raigs X (XRD), l'espectroscòpia de fotoelectrons de raigs X (XPS) i la Microscòpia de Transmissió d'Ones. Posteriorment, es va realitzar un anàlisi exhaustiu dels resultats obtinguts per identificar la pel·lícula amb la major qualitat i transparència. Les diverses proves realitzades amb les mostres van revelar que l'òxid de gal·li en fase beta s'havia dipositat i sintetitzat amb èxit en la seva fase cristal·lina cúbica i en la fase cristal·lina monoclínica. A més, les imatges de FESEM de les capes mostraven gruixos compactes sense defectes ni heterogeneïtats, atribuïbles a l'ús de la tècnica PLD.En este estudio, se han depositado capas de óxido de galio utilizando la técnica de deposición física de vapor, específicamente PLD (deposición por láser pulsado), en sustratos de silicio monocristalino, tanto en presencia de una atmósfera oxidante como en un entorno inerte. Se generó una matriz experimental con ocho condiciones de deposición variando la presión parcial de oxígeno en la cámara y el tiempo de deposición. El objetivo era determinar las condiciones óptimas para el crecimiento de películas delgadas y evaluar sus propiedades ópticas y estructurales. Se utilizaron dos condiciones de deposición: (1) una presión residual de 5x10-5 mbar y (2) 0,4 mbar a temperatura ambiente. Para cada condición, se probaron cuatro tiempos de deposición diferentes: 5, 10, 20 y 40 minutos. Después de sintetizar las películas delgadas bajo estas condiciones de deposición, las muestras se caracterizaron utilizando técnicas como la Microscopía Electrónica de Barrido de Emisión de Campo (FESEM), la Difracción de Rayos X (XRD), la Espectroscopía de Fotoelectrones de Rayos X (XPS) y la Microscopía de Transmisión de Ondas. Posteriormente, se realizó un análisis exhaustivo de los resultados obtenidos para identificar la película con la mayor calidad y transparencia. Las diversas pruebas realizadas en las muestras revelaron que el óxido de galio en fase beta se había depositado y sintetizado con éxito en su fase cristalina cúbica y en su fase cristalina monocíclica. Además, las imágenes de FESEM de las capas mostraron grosores compactos, sin defectos ni heterogeneidades, atribuibles al uso de la técnica PL

The cyclical trend of local public service governance: evidence from urban water management in Spain

The level of public and private involvement in economic activity in societies has changed over time. One may talk about the existence of a cyclical trend in which the most important periods of public governance are replaced by periods in which private management dominates the situation. This phenomenon may also be observed in local areas. Some authors have pointed out the existence of an alternation in the provision of municipal services, resulting in periods dominated by governance compared to other stages dominated by private management. In order to illustrate this cyclical trend at local level, this paper intends to analyze the evolution of the governance of the Spanish water supply since the mid-nineteenth century to the present day. Recent evidence from the industry suggests the possibility that we may currently be witnessing a further change in the trend.: Local Government, urban water supply, privatization, municipalization

Simplification and cost reduction of visual corona tests

Peer ReviewedPostprint (author's final draft

Transient thermal modelling of substation connectors by means of dimensionality reduction

This paper proposes a simple, fast and accurate simulation approach based on one-dimensional reduction and the application of the finite difference method (FDM) to determine the temperatures rise in substation connectors. The method discretizes the studied three-dimensional geometry in a finite number of one-dimensional elements or regions in which the energy rate balance is calculated. Although a one-dimensional reduction is applied, to ensure the accuracy of the proposed transient method, it takes into account the three-dimensional geometry of the analyzed system to determine for all analyzed elements and at each time step different parameters such as the incremental resistance of each element or the convective coefficient. The proposed approach allows fulfilling both accuracy and low computational burden criteria, providing similar accuracy than the three-dimensional finite element method but with much lower computational requirements. Experimental results conducted in a high-current laboratory validate the accuracy and effectiveness of the proposed method and its usefulness to design substation connectors and other power devices and components with an optimal thermal behavior.Postprint (published version

Un etude classique des duplications d'un groupe cyclique

Pour chaque entier n, nous allons `a ´etablir la quantit´e, sauf isomorphism, des groupes G d’ordre 2n et de fa¸con qu’ils aient au moins un ´el´ement d’ordre n. C’est-`a-dire, nous donnerons le nombre des groupes (sauf isomorphism) d’ordre 2n, qui aient un sous-groupe isomorphic au groupe cyclique d’ordre n, Cn. En plus , nous ´etudierons aussi la structure de ces groupes