Utilização de dispositivos de armazenamento de energia em apoio ao funcionamento de redes isoladas

Temos assistido nos últimos anos à proliferação da produção distribuída de electricidade, sobretudo, com recurso a fontes de energia renováveis, implicando a natural reestruturação das redes eléctricas existentes, desde a produção até ao consumidor final. As constantes preocupações na garantia da qualidade de serviço e até mesmo em termos ambientais, levam a que a operacionalidade das redes seja cada vez mais eficiente, visando a integração de tecnologias emergentes como é o caso dos sistemas de armazenamento de energia. A aposta nas energias de origem renovável nomeadamente a solar e a eólica, representa uma forma cada vez mais presente de geração de electricidade, tendo como grande inconveniente o regime de intermitência a que estão sujeitas, não se conseguindo tirar proveitos absolutos de todas as potencialidades que estas fontes proporcionam. Existem actualmente sistemas de armazenamento de energia que permitem optimizar o comportamento das redes. Nesta dissertação é feita uma abordagem a alguns desses sistemas, tendo como objectivo principal a demonstração das potencialidades de optimização dos sistemas de produção e distribuição de energia eléctrica com recurso a sistemas de armazenamento de energia, em redes isoladas e interligadas. É também feito um estudo do comportamento dinâmico de uma rede com vários cenários de ocorrência de defeitos, com e sem armazenamento de energia. Para isso a base deste trabalho consistiu na familiarização com uma ferramenta de grande potencial na simulação dinâmica de redes eléctricas, utilizado por prestigiados grupos de energia a nível mundial, na qual foi implementada a rede de teste e efectuadas as simulações do estudo.

Waged domestic work in Argentina: the regulation of care provision

This paper addresses the condition of domestic work in Argentina, in a perspective that draws from the literature on care work. In this approach, domestic work can be interpreted as one of the mercantile forms in which care work is socially organized, due to the persistence of the traditional sexual division of labor and the weakness of public policies. From these considerations, I develop a quantitative study on the levels of informality, precarity, and wage inequality that characterize domestic work in that country. Thereafter, I discuss the main measures adopted by the Argentine government since 2003, with the goal of reducing legal discrimination of domestic workers and promoting their formalization. On this basis, the paper highlights the advances in the recognition of domestic workers’ labor rights, while emphasizing how social and cultural restraints still permeate labor relations in this sector.

Antropología de la Conservación en España. Balance y perspectivas

En este artículo presentamos un balance de la Antropología de la Conservación en el Estado español. Durante las últimas décadas, la protección de los espacios naturales ha aumentado de una manera exponencial en todo el mundo. A la vez que se extendía esta patrimonialización de la naturaleza, los trabajos etnográficos sobre las áreas protegidas han ido ganando terreno dentro de la disciplina y, en particular, en el campo de la Antropología Ambiental. La mencionada bibliografía ha puesto de relieve los múltiples aspectos derivados de las nuevas políticas territoriales de regulación, apropiación y mercantilización de la ‘naturaleza’. En este trabajo realizamos una revisión exhaustiva de la producción generada a raíz de este interés por las áreas protegidas en nuestro país subrayando sus principales aportaciones, características y debilidades. De este modo pretendemos reflexionar acerca de su continuidad, con el fin de evitar la mera reiteración y favorecer el avance en sus resultados.

Análisis de los efectos del problema del nodo oculto en las redes IEEE 802.15.7. Propuesta de solución

Programa de doctorado: Tecnologías de la Información y sus Aplicaciones. La fecha de publicación es la fecha de lectura

Análisis de algunos aspectos técnicos relacionados con la integración de energías renovables en sistemas eléctricos pequeños y aislados

Programa de doctorado: Sistemas Inteligentes y Aplicaciones Numéricas en Ingeniería. La fecha de publicación es la fecha de lectura

Development and characterization of Poly(L-lactic acid) (PLLA) platforms for bone tissue engineering

The development of scaffolds based on biomaterials is a promising strategy for Tissue Engineering and cellular regeneration. This work focuses on Bone Tissue Engineering, the aim is to develop electrically tailored biomaterials with different crystalline and electric features, and study their impacts onto cell biological behavior, so as to predict the materials output in the enhancement of bone tissue regeneration. It is accepted that bone exhibits piezoelectricity, a property that has been proved to be involved in bone growth/repair mechanism regulation. In addition electrical stimulations have been proved to influence bone growth and repair. Piezoelectric materials are therefore widely investigated for a potential use in bone tissue engineering. The main goal is the development of novel strategies to produce and employ piezoelectric biomaterials, with detailed knowledge of mechanisms involved in cell-material interaction. In the current work, poly (L-lactic) acid (PLLA), a synthetic semi-crystalline polymer, exhibiting biodegradibility, biocompatibility and piezoelectricity is studied and proposed as a promoter of enhanced tissue regeneration. PLLA has already been approved for implantation in human body by the Food and Drug Administration (FDA), and at the moment it is being used in several clinical strategies. The present study consists of first preparing films with different degrees of crystallinity and characterizing these PLLA films, in terms of surface and structural properties, and subsequently assessing the behavior of cells in terms of viability, proliferation, morphology and mineralization for each PLLA configuration. PLLA films were prepared using the solvent cast technique and submitted to different thermal treatments in order to obtain different degrees of crystallinity. Those platforms were then electrically poled, positively and negatively, by corona discharge in order to tailor their electrical properties. The cellular assays were conducted by using two different osteoblast cell lines grown directly onto the PLLA films:Human osteoblast Hob, a primary cell culture and Human osteosarcoma MG-63 cell line. This thesis gives also a comprehensive introduction to the area of Bone Tissue Engineering and provides a review of the work done in this field in the past until today, in that same field, including the one related with bone’s piezoelectricity. Then the experimental part deals with the effects of the crystallinity degrees and of the polarization in terms of surface properties and cellular bio assays. Three different degrees of crystallinity, and three different polarization conditions were prepared; which results in 9 different configurations under investigation.

Functional alkali tantalate 2D structures for microelectronics and related applications

Alkali tantalates and niobates, including K(Ta / Nb)O3, Li(Ta / Nb)O3 and Na(Ta / Nb)O3, are a very promising ferroic family of lead-free compounds with perovskite-like structures. Their versatile properties make them potentially interesting for current and future application in microelectronics, photocatalysis, energy and biomedics. Among them potassium tantalate, KTaO3 (KTO), has been raising interest as an alternative for the well-known strontium titanate, SrTiO3 (STO). KTO is a perovskite oxide with a quantum paraelectric behaviour when electrically stimulated and a highly polarizable lattice, giving opportunity to tailor its properties via external or internal stimuli. However problems related with the fabrication of either bulk or 2D nanostructures makes KTO not yet a viable alternative to STO. Within this context and to contribute scientifically to the leverage tantalate based compounds applications, the main goals of this thesis are: i) to produce and characterise thin films of alkali tantalates by chemical solution deposition on rigid Si based substrates, at reduced temperatures to be compatible with Si technology, ii) to fulfil scientific knowledge gaps in these relevant functional materials related to their energetics and ii) to exploit alternative applications for alkali tantalates, as photocatalysis. In what concerns the synthesis attention was given to the understanding of the phase formation in potassium tantalate synthesized via distinct routes, to control the crystallization of desired perovskite structure and to avoid low temperature pyrochlore or K-deficient phases. The phase formation process in alkali tantalates is far from being deeply analysed, as in the case of Pb-containing perovskites, therefore the work was initially focused on the process-phase relationship to identify the driving forces responsible to regulate the synthesis. Comparison of phase formation paths in conventional solid-state reaction and sol-gel method was conducted. The structural analyses revealed that intermediate pyrochlore K2Ta2O6 structure is not formed at any stage of the reaction using conventional solid-state reaction. On the other hand in the solution based processes, as alkoxide-based route, the crystallization of the perovskite occurs through the intermediate pyrochlore phase; at low temperatures pyrochlore is dominant and it is transformed to perovskite at >800 °C. The kinetic analysis carried out by using Johnson-MehlAvrami-Kolmogorow model and quantitative X-ray diffraction (XRD) demonstrated that in sol-gel derived powders the crystallization occurs in two stages: i) at early stage of the reaction dominated by primary nucleation, the mechanism is phase-boundary controlled, and ii) at the second stage the low value of Avrami exponent, n ~ 0.3, does not follow any reported category, thus not permitting an easy identification of the mechanism. Then, in collaboration with Prof. Alexandra Navrotsky group from the University of California at Davis (USA), thermodynamic studies were conducted, using high temperature oxide melt solution calorimetry. The enthalpies of formation of three structures: pyrochlore, perovskite and tetragonal tungsten bronze K6Ta10.8O30 (TTB) were calculated. The enthalpies of formation from corresponding oxides, ∆Hfox, for KTaO3, KTa2.2O6 and K6Ta10.8O30 are -203.63 ± 2.84 kJ/mol, - 358.02 ± 3.74 kJ/mol, and -1252.34 ± 10.10 kJ/mol, respectively, whereas from elements, ∆Hfel, for KTaO3, KTa2.2O6 and K6Ta10.8O30 are -1408.96 ± 3.73 kJ/mol, -2790.82 ± 6.06 kJ/mol, and -13393.04 ± 31.15 kJ/mol, respectively. The possible decomposition reactions of K-deficient KTa2.2O6 pyrochlore to KTaO3 perovskite and Ta2O5 (reaction 1) or to TTB K6Ta10.8O30 and Ta2O5 (reaction 2) were proposed, and the enthalpies were calculated to be 308.79 ± 4.41 kJ/mol and 895.79 ± 8.64 kJ/mol for reaction 1 and reaction 2, respectively. The reactions are strongly endothermic, indicating that these decompositions are energetically unfavourable, since it is unlikely that any entropy term could override such a large positive enthalpy. The energetic studies prove that pyrochlore is energetically more stable phase than perovskite at low temperature. Thus, the local order of the amorphous precipitates drives the crystallization into the most favourable structure that is the pyrochlore one with similar local organization; the distance between nearest neighbours in the amorphous or short-range ordered phase is very close to that in pyrochlore. Taking into account the stoichiometric deviation in KTO system, the selection of the most appropriate fabrication / deposition technique in thin films technology is a key issue, especially concerning complex ferroelectric oxides. Chemical solution deposition has been widely reported as a processing method to growth KTO thin films, but classical alkoxide route allows to crystallize perovskite phase at temperatures >800 °C, while the temperature endurance of platinized Si wafers is ~700 °C. Therefore, alternative diol-based routes, with distinct potassium carboxylate precursors, was developed aiming to stabilize the precursor solution, to avoid using toxic solvents and to decrease the crystallization temperature of the perovskite phase. Studies on powders revealed that in the case of KTOac (solution based on potassium acetate), a mixture of perovskite and pyrochlore phases is detected at temperature as low as 450 °C, and gradual transformation into monophasic perovskite structure occurs as temperature increases up to 750 °C, however the desired monophasic KTaO3 perovskite phase is not achieved. In the case of KTOacac (solution with potassium acetylacetonate), a broad peak is detected at temperatures <650 °C, characteristic of amorphous structures, while at higher temperatures diffraction lines from pyrochlore and perovskite phases are visible and a monophasic perovskite KTaO3 is formed at >700 °C. Infrared analysis indicated that the differences are due to a strong deformation of the carbonate-based structures upon heating. A series of thin films of alkali tantalates were spin-coated onto Si-based substrates using diol-based routes. Interestingly, monophasic perovskite KTaO3 films deposited using KTOacac solution were obtained at temperature as low as 650 °C; films were annealed in rapid thermal furnace in oxygen atmosphere for 5 min with heating rate 30 °C/sec. Other compositions of the tantalum based system as LiTaO3 (LTO) and NaTaO3 (NTO), were successfully derived as well, onto Si substrates at 650 °C as well. The ferroelectric character of LTO at room temperature was proved. Some of dielectric properties of KTO could not be measured in parallel capacitor configuration due to either substrate-film or filmelectrode interfaces. Thus, further studies have to be conducted to overcome this issue. Application-oriented studies have also been conducted; two case studies: i) photocatalytic activity of alkali tantalates and niobates for decomposition of pollutant, and ii) bioactivity of alkali tantalate ferroelectric films as functional coatings for bone regeneration. Much attention has been recently paid to develop new type of photocatalytic materials, and tantalum and niobium oxide based compositions have demonstrated to be active photocatalysts for water splitting due to high potential of the conduction bands. Thus, various powders of alkali tantalates and niobates families were tested as catalysts for methylene blue degradation. Results showed promising activities for some of the tested compounds, and KNbO3 is the most active among them, reaching over 50 % degradation of the dye after 7 h under UVA exposure. However further modifications of powders can improve the performance. In the context of bone regeneration, it is important to have platforms that with appropriate stimuli can support the attachment and direct the growth, proliferation and differentiation of the cells. In lieu of this here we exploited an alternative strategy for bone implants or repairs, based on charged mediating signals for bone regeneration. This strategy includes coating metallic 316L-type stainless steel (316L-SST) substrates with charged, functionalized via electrical charging or UV-light irradiation, ferroelectric LiTaO3 layers. It was demonstrated that the formation of surface calcium phosphates and protein adsorption is considerably enhanced for 316L-SST functionalized ferroelectric coatings. Our approach can be viewed as a set of guidelines for the development of platforms electrically functionalized that can stimulate tissue regeneration promoting direct integration of the implant in the host tissue by bone ingrowth and, hence contributing ultimately to reduce implant failure.

Underpricing y subvaluación en las OPI de Perú y Chile

El fenómeno del underpricing en la oferta pública inicial (OPI) se viene estudiando hace ya varias décadas, y se refiere al retorno positivo del primer día de la acción, calculado como la diferencia entre el precio de cierre del primer día de cotización y el precio de emisión pactado entre el emisor y el banco de inversión. Por otro lado, también existe el overpricing, es decir, al fenómeno que sucede cuando el precio de cierre del primer día de negociaciones es menor que el precio de oferta. En nuestro estudio, encontramos evidencia de ambos, con el underpricing presente en 71,67% de empresas de la muestra y el overpricing tan solo presente en el 28,33% de la muestra. Asimismo, se determinará si existe subvaluación o sobrevaluación realizando un análisis entre el precio de oferta y el valor fundamental calculado a través de una valorización por múltiplos. Esta comparación permitirá comparar un valor fundamental (calculado por nosotros) y el precio de la OPI calculado por la empresa que realiza la cobertura, dejando de lado el precio que el mercado le otorga a la acción en su primer día (precio que puede tener mucho ruido y depender de diversos factores como el sentimiento del mercado y el comportamiento de los inversionistas). Al observar la diferencia entre el valor y el precio de la OPI, podremos determinar si existe o no sobrevaluación. En nuestro estudio, sí hemos encontrado presencia de sobrevaluación del precio de las OPI, alrededor de un 110% por encima del valor fundamental. Si bien la mayoría de investigaciones que se han realizado sobre estos temas han sido sobre empresas en mercados desarrollados, nuestra investigación se centra en empresas de Perú y Chile, que son economías en desarrollo y, además, presentan sectores bastante semejantes en su economía. La muestra consiste en 60 OPI de empresas de Perú y Chile para el periodo 2003 – 2014. Las diversas empresas se han agrupado en los siguientes sectores: servicios públicos, que incluyen eléctricas, agua y control ambiental; materiales básicos, que incluye mineras, químicas y de papel; financiero, que incluye servicios financieros diversificados, bancos, bienes raíces y fondos de inversión; consumo no cíclico, que incluye alimentos, bebidas, farmacéuticas, agricultura, servicios comerciales y de salud; consumo cíclico, que incluye retail, ropa, aerolíneas, entretenimiento y alojamiento; energía, que incluye petróleo y gas; industrial, que incluye materiales de construcción, transporte, construcción y hardware, diversificadas (holdings) y tecnología.

Afectación de los ingresos operacionales de empresa distribuidora de energía eléctrica por penetración de energía solar en su área de influencia

Los anuncios de impacto por cambio climático han llevado a los países a crear estrategias de mitigación y adaptación, dentro de las cuales se considera la promoción de generación de electricidad a través de fuentes renovables no convencionales -- El avance logrado ha incentivado a los usuarios del servicio de energía eléctrica a invertir en plantas de generación, eliminando la necesidad parcial de utilizar las redes de transmisión y distribución del sistema eléctrico, de tal forma que las redes eléctricas presentan una holgura gradual en cuanto a la energía que se transporta a través de ellas -- Este artículo presenta un análisis del impacto sobre los ingresos operacionales de una empresa distribuidora de energía por efecto de la entrada de soluciones de energía solar fotovoltaica en el segmento residencial de su área de influencia, encontrando que se generarían diferentes escalas de afectación, con valores de hasta el 3%

Simulación de la malla de tierra en subestaciones de alta tensión aisladas en aire

Tesis (Ingeniero Eléctrico). -- Universidad de La Salle. Facultad de Ingeniería. Programa de Ingeniería Eléctrica, 2014

Evaluación de la eficiencia energética para transformadores de distribución

Tesis (Ingeniero Eléctrico). -- Universidad de La Salle. Facultad de Ingeniería. Programa de Ingeniería Eléctrica, 2014

Diseño del sistema solar para San José de Guausa

Tesis (Ingeniero(a) Eléctrico).--Universidad de La Salle. Facultad de Ingeniería. Programa de Ingeniería Eléctrica, 2014

Estructuración y desarrollo de guías educativas para el manejo del software digsilent v14 utilizando la herramienta DPL con base en un sistema de potencia de prueba de la IEEE

Tesis (Ingeniero Eléctrico). -- Universidad de La Salle. Facultad de Ingeniería. Programa de Ingeniería Eléctrica, 2014

Plan de orientación de gestión integral de energía en el sector industrial metalmecánico en empresas medianas

Tesis (Ingeniero(a) Eléctrico).--Universidad de La Salle. Facultad de Ingeniería. Programa de Ingeniería Eléctrica, 2015

Telemedida y telecorte en medidores de energía a través de la red eléctrica

Tesis (Ingeniero Eléctrico). -- Universidad de La Salle. Facultad de Ingeniería. Programa de Ingeniería Eléctrica, 2014