Task-based lessons as a teaching strategy to develop non-fictional writing skills in english with emphasis on grammatical cohesion.

Este estudio propone lecciones basadas en tareas como una estrategia de enseñanza para desarrollar habilidades de escritura de ficción no en Inglés con énfasis en la cohesión gramatical. La investigación se llevó a cabo con una muestra de población de 8 estudiantes de segundo semestre de la Tecnología en Negocios Internacionales en el SENA en Apartadó, Antioquia.This study proposes task-based lessons as a teaching strategy to develop non fictional writing skills in English with emphasis on grammatical cohesion. The research was carried out with a sample population of 8 students from second semester of the Technology in International Business at SENA in Apartadó, Antioquia

Elucidating Nucleation and Growth Behavior of Single-Walled Carbon Nanotubes obtained via Catalyzed Synthesis

The catalytic growth of single-walled carbon nanotubes (SWCNTs) is studied using reactive molecular dynamics (RMD) simulations and density functional theory (DFT) calculations. Computational calculations are performed in order to achieve a better understanding of the catalytic reaction mechanism at the initial stages of synthesis, where most of the structural characteristics are defined. Different process variables such as catalyst chemical composition and size, temperature, pressure, and the nature of catalyst support, can be optimized with the purpose of tuning the structure and physical properties of SWCNTs. Controlling the structure of SWCNTs during synthesis and avoiding additional purification and/or separation processes are critical for the direct use of SWCNTs in electronic devices. RMD simulations demonstrate that small catalyst particles favor the growth of lengthy nanotubes over catalyst encapsulation as a result of an increase of the curvature energies of the carbon capsule. Furthermore, simulations performed over deposited catalyst particles demonstrate that the catalyst-support adhesion must be controlled in order to grow nanotubes with high structural quality and avoid catalyst poisoning. Results herein reported suggest that growth conditions must be optimum to minimize the nucleation of topological defects in nanotubes. RMD trajectories prove the vital role played by the catalyst surface in healing defects via adsorption and diffusion. These results significantly impact the field of chirality control since the presence of defects introduce misorientation of hexagons, shifts the overall chiral angle, and therefore, modifies the physical properties of the nanotube. DFT calculations are employed to evaluate the interaction between SWCNTs and the ST-cut quartz substrate. The outstanding performance of CNT-based FET relies on the alignment of the horizontally grown nanotubes on silica substrates, as well as on the selective growth of semiconducting nanotubes. It is demonstrated that finite-length zigzag nanotubes are adsorbed stronger than armchair tubes on the quartz support. This suggests that the nanotube electronic band structure is a key factor on the preferential adsorption of zigzag tubes. DFT calculations suggest that patterns of unsaturated silicon atoms of silica surfaces define the crystallographic directions of preferential alignment. These patterns might be chemically altered in order to favor other directions of alignment

Rules to estimate the expected values of zero-sequence impedances in 3 phase core-type transformers

Simple rules to estimate the expected values of zero-sequence impedance measurements for 3-phase core-type transformers are shown. The proposed rules are based on the analysis of magnetic circuits. Due to this fact, a conceptual description about zero-sequence impedances of these transformers is included. The rules were verified with measurements on fifteen transformers, and these measurements were used for refining the rules. In case of magnetizing zero-sequence impedances, the presence or not of magnetic shunts on tank walls defines the details of these rules. In case of short-circuit zero-sequence impedances, only the positive-sequence transformer impedances are necessary to apply the proposed rules. These rules are important in order to reduce the probability of errors during the tests. Some rules related to the resistive part of the impedances are also presented

Metodologías activas de enseñanza en la docencia de instalaciones eléctricas

Se presentan los resultados obtenidos de la adaptación de la asignatura de Instalaciones Eléctricas de la Titulación de Ingeniero Técnico Industrial para la aplicación de metodologías de enseñanza activas, con objeto de adecuarla a las nuevas directrices introducidas por el Espacio Europeo de Educación Superior.Results are presented as obtained from the adaptation of the subject of Electrical Installations taught in the degree of Technical Industrial Engineering for the application of active teaching methods, implemented in order to tailor this subject to the new guidelines introduced by the European Higher Education Area (EHEA)

Study on the contamination rate of mineral oil in natural-ester retrofilled transformers

The replacement of mineral oil (MO) by ester (retrofilling) is a practice used in power transformers to reduce fire and environmental risk. Although measures are taken to remove traces of oil on the paper, a certain amount of MO remains, which migrates over time. This article presents a study to evaluate the migration of MO from paper to ester using techniques such as the iodine value or the measurement of permittivity and dielectric losses.This work was supported in part by the Spanish Research Agency under Project PID2019-107126RB-C21/AEI/10 and Project 13039/501100011033, and in part by the European Union's Horizon 2020 Research and Innovation Program under Grant 823969

Influence of Nanoparticles on the Degradation Processes of Ester-Based Transformer Insulation Systems

The use of nanofluids as dielectric liquids for transformer insulation has been widely investigated during the last decade. A number of authors have performed extensive studies on liquids produced from different types of nanoparticles and base fluids, providing evidence of their good dielectric properties. Nevertheless, nanodielectric fluids are still at the research stage, and they are far from being a solution that can be applied to real transformers. One of the aspects that might be clarified is their compatibility with the rest of the materials present in the transformer and their behavior throughout the life of the equipment. This paper studies the aging process of cellulose impregnated with an ester-based nanofluid and compares it with the process that takes place when the impregnation liquid is a natural ester. Accelerated aging experiments were performed, and physical and chemical characterization of the process with several analytical techniques was carried out. The mechanical degradation of the cellulose was studied in terms of tensile strength, and the evolution of moisture in the paper and oil was monitored throughout the aging process. The study was completed with FTIR and XPS tests aimed at studying the chemical changes of the materials during the aging process. The experimental results suggest that the degradation rate of the cellulose is not significantly affected by the presence of nanoparticles. However, the XPS study revealed that the chemical reactions involved in the degradation processes of both types of insulation might differ. Several mechanisms are proposed in this work.This work was supported by the Spanish State Research Agency under grant PID2019- 107126RB-C21/ AEI/10.13039/501100011033 and by the Spanish Ministry of Economy and Competitiveness under grant DPI2015-71219-C2-2-R

Statistical study on the reference values of furanic compounds in power transformers

This article presents a statistical study devoted to obtaining the reference values of 2FAL in power transformers.This work was supported by CEIS and by the Ministry of Economy and Competitiveness of Spain through the project DPI2012-35819.Publicad

Análisis de vibración como método de diagnóstico para cambiadores de tomas en carga

The suitable condition of an On-load Tap of a power transformer. There are a variety of OLTC diagnosis techniques, some of them can be used only off-line and some of them can be used on-line. This paper describes some of the methods used for the diagnosis of power transformers OLTC and emphasizes the vibration analysis as a tool of OLTC condition assessment. The main OLTC vibration parameters are obtained using envelope analysis based on Hilbert transform as the pre-processing of wavelet decomposition. Previously normalized and synchronize signals. To validate the method was compared the signal vibration under normal conditions and failures realistic implemented laboratory.El estado de la condición de un Cambiador de Tomas en Carga (CTC), es esencial para la operación del transfor mador. Hay gran variedad de técnicas de diagnostico de CTC algunas de ellas puede usarse solo con el transformador fuera de línea y otras con el transformador en línea. Este artículo describe los diferentes métodos de diagnóstico de fallos en CTC. Este trabajo enfatiza el análisis de vibración como una herramienta para evaluar la condición del CTC y enfatiza el análisis de la vibración como una herramienta para la evaluación del estado del CTC. Los principales parámetros de vibración fueron obtenidos usando la envolvente basado en la transformada de Hilbert como etapa de pre-proceso de la descomposición wavelet. Previamente se normalizo y se sincronizo las señales. Para validar el método se comparo la señal de vibración bajo condición normal y con avería implementada en laboratorio

La LOMCE, un callejón sin salida

The article analyses the new Education Law in Spain, named LOMCE. It is focused on the budget cuts that LOMCE proposes, taking into consideration the consequences this new law will have on teachers, students and the society as a whole. The article does not miss the current economic weakness of our country and tries to show how these budgetary aspects affect education. It also reflects the possibilities that these new proposals will offer to citizens by establishing a comparison between our educational system and one whose success is proved, the Finnish one.ReiDoCrea. Departamento de Psicología Social. Universidad de Granada

Dielectric Strength of Nanofluid-Impregnated Transformer Solid Insulation

The interest in developing new fluids that can be used as dielectric liquids for transformers has driven the research on dielectric nanofluids in the last years. A number of authors have reported promising results on the electrical and thermal properties of dielectric nanofluids. Less attention has been paid to the interaction of these fluids with the cellulose materials that constitute the solid insulation of the transformers. In the present study, the dielectric strength of cellulose insulation is investigated, comparing its behavior when it is impregnated with transformer mineral oil and when it is impregnated with a dielectric nanofluid. The study includes the analysis of the AC breakdown voltage and the impulse breakdown voltage of the samples. Large improvements were observed on the AC breakdown voltages of the specimens impregnated with nanofluids, while the enhancements were lower in the case of the impulse tests. The reasons for the increase in AC breakdown voltage were investigated, considering the dielectric properties of the nanofluids used to impregnate the samples of cellulose. The analysis was completed with a finite element study that revealed the effect of the nanoparticles on the electric field distribution within the test cell, and its role in the observed enhancement.This work was supported by the Spanish State Research Agency under grant PID2019- 107126RB-C21/ AEI/10.13039/501100011033 and by the Spanish Ministry of Economy and Competitiveness under grant DPI2015-71219-C2-2-