Optoelectronic device based on Rare Earths electroluminescence

Màster en Nanociència i Nanotecnologia, Facultat de Física, Universitat de Barcelona, Curs: 2016-2017. Tutors: Oriol Blázquez, Sergi HernándezIn this Master Thesis, the fabrication and the structural, optical and electrical properties of Al/rare earth (RE)/Al/SiO2 and RE/SiO2 nanomultilayers have been studied. The nanomultilayers were deposited by means of e-beam evaporation on top of p-type Si substrates. Two different RE species were considered: Tb3+ and Eu3+ ions, as they exhibit a narrow and strong emission in the green and red spectral ranges, respectively. The main goal of the present work is achieving optical activation of those rare earth elements, and thus obtaining light emission from their intra-4f and 5d-to-4f shell transitions. Optical characterization indicates that optically active RE3+ ions had been successfully fabricated. The electrical and electroluminescence analysis yielded promising results to include this material in future applications of illumination and integrated emitting devices for optoelectronics

Optoelectronic device based on Rare Earths electroluminescence

Màster en Nanociència i Nanotecnologia, Facultat de Física, Universitat de Barcelona, Curs: 2016-2017. Tutors: Oriol Blázquez, Sergi HernándezIn this Master Thesis, the fabrication and the structural, optical and electrical properties of Al/rare earth (RE)/Al/SiO2 and RE/SiO2 nanomultilayers have been studied. The nanomultilayers were deposited by means of e-beam evaporation on top of p-type Si substrates. Two different RE species were considered: Tb3+ and Eu3+ ions, as they exhibit a narrow and strong emission in the green and red spectral ranges, respectively. The main goal of the present work is achieving optical activation of those rare earth elements, and thus obtaining light emission from their intra-4f and 5d-to-4f shell transitions. Optical characterization indicates that optically active RE3+ ions had been successfully fabricated. The electrical and electroluminescence analysis yielded promising results to include this material in future applications of illumination and integrated emitting devices for optoelectronics

Conocimiento profesional para la enseñanza de la resolución de problemas en primaria: una perspectiva curricular

En este trabajo exponemos el conocimiento necesario para que un docente de primaria pueda desenvolverse con éxito al afrontar procesos de enseñanza que incluyan la resolución de problemas de matemáticas. Para ello, realizamos un análisis curricular a seis documentos oficiales de distintos países sobre sus prescripciones sobre resolución de problemas matemáticos. A través de un análisis de contenido, y partiendo de las categorías de conocimiento propuestas por Chapman (2015), hemos elaborado un nuevo modelo que permite describir el conocimiento profesional sobre resolución de problemas que exigen los currículos para enseñar este tópico. Los resultados muestran una imbricada red de conocimientos que los currículos requieren de los profesores al afrontar la enseñanza de la resolución de problemas en las matemáticas escolares

Discriminatory Expressions to Produce Interpretable Models in Short Documents

Social Networking Sites (SNS) are one of the most important ways of communication. In particular, microblogging sites are being used as analysis avenues due to their peculiarities (promptness, short texts...). There are countless researches that use SNS in novel manners, but machine learning has focused mainly in classification performance rather than interpretability and/or other goodness metrics. Thus, state-of-the-art models are black boxes that should not be used to solve problems that may have a social impact. When the problem requires transparency, it is necessary to build interpretable pipelines. Although the classifier may be interpretable, resulting models are too complex to be considered comprehensible, making it impossible for humans to understand the actual decisions. This paper presents a feature selection mechanism that is able to improve comprehensibility by using less but more meaningful features while achieving good performance in microblogging contexts where interpretability is mandatory. Moreover, we present a ranking method to evaluate features in terms of statistical relevance and bias. We conducted exhaustive tests with five different datasets in order to evaluate classification performance, generalisation capacity and complexity of the model. Results show that our proposal is better and the most stable one in terms of accuracy, generalisation and comprehensibility

Conceptualización de la noción de problema manifestada por futuros profesores de primaria

En el marco de la investigación en la formación del profesorado, en este trabajo presentamos el conocimiento que manifiestan sobre la noción de problema estudiantes del grado de maestro de Educación Primaria al terminar su formación inicial en la universidad. Para ello, hemos construido un cuestionario y lo hemos aplicado a 51 estudiantes de la especialidad anteriormente citada y que habían participado en un curso optativo sobre profundización del currículo en el que uno de sus contenidos es la resolución de problemas. Los resultados se muestran duales, puesto que los estudiantes manifiestan conocimientos acordes al campo de la resolución de problemas, sin embargo, hemos encontrado contradicciones, por una parte dan importancia a la consideración del resolutor, y por otra no la tienen en cuenta en la práctica

Fundamentals and Applications of Surface-Enhanced Raman Spectroscopy (SERS)

When a molecule is adsorbed on some metallic nanostructured surfaces such as silver, copper or gold, it can undergo an enormous enhancement of the Raman signal giving rise to the so called Surface-Enhanced Raman Scattering (SERS). The high sensitivity of this effect allows an accurate structural study of adsorbates at very low concentrations. The SERS effect has historically been associated with the substrate roughness on two characteristic length scales. Surface roughness on the 10 to 100 nm length scale supports localized plasmon resonances which are considered as the dominant enhancement mechanism of SERS (Electromagnetic Enhancement Mechanism: SERS-EM). It is usually accepted that these electromagnetic resonances can increase the scattered intensity by an average factor of ca. 104 to 107. A secondary mechanism often thought to require atomic scale roughness is referred to as Charge Transfer (CT) Enhancement Mechanism (SERS-CT). This mechanism involves the photoinduced transfer of an electron from the metal to the adsorbate or vice versa and involves new electronic excited CT states which result from adsorbate–substrate chemical interactions. It is also estimated that such SERS-CT mechanism can enhance the scattering cross-section by a factor of ca. 10 to 102. These two mechanisms can operate simultaneously, depending on the particular systems and experimental conditions, making difficult to recognize each one and to estimate their relative magnitude in a particular spectrum.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

A generic ATMS

AbstractThe main aim of this paper is to create a general truth maintenance system based on the De Kleer algorithm. This system (the ATMS) is to be designed so that it can be used in different propositional monotonic logic models of reasoning systems. The knowledge base system that will interact with it is described. Furthermore, we study the efficiency that transferring the ATMS to a logic with several truth values presupposes. Definitions and properties of the generic ATMS are particularized to interact both with a reasoning system based on multivalued logic specifically for the case of [0, 1 ]-valued logic and with a reasoning system based on fuzzy logic. The latter will be designed to reason with fuzzy truth values, although a parallel project might be followed using linguistic labels directly

La resolución de problemas en las matemáticas escolares de educación básica chilena

En este trabajo analizamos el significado sobre la resolución de problemas matemáticos, que presentan las Bases Curriculares (Ministerio de Educación, 2012) en la educación básica chilena. A través de un análisis de contenido, encontramos que el currículo enfatiza aspectos teóricos de la resolución de problemas, dejando a un lado factores no cognitivos

Prospective Elementary Teachers’ Pedagogical Knowledge for Mathematical Problem Solving

This research was funded by Ministry of Science, Innovation and Universities (Spain) who financed the research project PGC2018-095765-B-I00 (PROFESTEM), and a Ph.D. grant awarded by Chile's ANID (folio 72170314).Research on mathematics teachers’ knowledge has generally focused more on mathematics concepts than mathematical processes. This paper addresses the latter with a focus on mathematical problem solving (PS). It reports on a study that investigated the pedagogical knowledge for PS of prospective elementary school teachers of mathematics (PTs). Participants were 149 PTs at a university in Spain. They were at the end of their teacher education program. Data sources consisted of a questionnaire on knowledge of learning PS and a questionnaire on knowledge of teaching PS. Findings indicated that the PTs held combination of different levels of knowledge of PS learning and teaching. Many of them demonstrated appropriate knowledge of many characteristics for (1) PS learning consisting of student as a problem-solver, PS as a worthwhile task, non-cognitive factor related to PS, and (2) PS teaching consisting of PS teaching approaches, discourse in PS, intervention during stuck state in PS, PS assessment, and PS resources. However, there were also contradictions and limitations to their knowledge with implications for teacher education. These combination of appropriate and inappropriate knowledge resulted in some conflicts that are related to teaching actions and would limit student’ learning of PS.Ministry of Science, Innovation and Universities (Spain) PGC2018-095765-B-I00 folio 7217031