Relatório de estágio de biologia e geologia realizado na Escola Secundária Jaime Moniz

O estágio pedagógico proporciona uma oportunidade de crescimento pessoal e profissional, sendo uma etapa fundamental para a formação de um professor. O presente relatório, realizado no âmbito do Mestrado em Ensino da Biologia e da Geologia no 3º Ciclo do Ensino Básico e no Ensino Secundário, descreve o estágio pedagógico concretizado na Escola Secundária Jaime Moniz, no ano letivo de 2012/2013. O relatório teve por objetivo descrever, analisar e refletir sobre todas as atividades realizadas, as práticas vividas e as competências adquiridas e desenvolvidas ao longo da Prática de Ensino Supervisionada. Este relatório é uma síntese das atividades desenvolvidas nos seguintes domínios: Prática de Ensino Supervisionada, Atividades de Integração no Meio Escolar, Atividades de Intervenção na Comunidade Escolar e Atividades de Natureza Científico-Pedagógica. O trabalho desenvolvido ao longo do estágio e durante a escrita do relatório revelou-se um tempo importante para vivenciar e refletir a realidade do quotidiano da profissão professor e para compreender os desafios da mesma. Das várias componentes do estágio, destacou-se a prática letiva, porque foi em torno dela que decorreu o estágio, tendo o professor estagiário, através da mesma, tido a oportunidade de evoluir pessoal e profissionalmente. As atividades e as reflexões realizadas permitiram adquirir conhecimentos e competências imprescindíveis para um profissional do ensino e contribuíram para a formação integral do professor estagiário.

Application of photoluminescence and electroluminescence techniques to the characterization of intermediate band solar cells

The intermediatebandsolarcell (IBSC) is a photovoltaic device with a theoretical conversion efficiency limit of 63.2%. In recent years many attempts have been made to fabricate an intermediateband material which behaves as the theory states. One characteristic feature of an IBSC is its luminescence spectrum. In this work the temperature dependence of the photoluminescence (PL) and electroluminescence (EL) spectra of InAs/GaAs QD-IBSCs together with their reference cell have been studied. It is shown that EL measurements provide more reliable information about the behaviour of the IB material inside the IBSC structure than PL measurements. At low temperatures, the EL spectra are consistent with the quasi-Fermi level splits described by the IBSC model, whereas at room temperature they are not. This result is in agreement with previously reported analysis of the quantum efficiency of the solarcells

Modelling of quantum dot solar cells for concentrator PV applications

An equivalent circuit model is applied in order to describe the operation characteristics of quantum dot intermediate band solar cells (QD-IBSCs), which accounts for the recombination paths of the intermediate band (IB) through conduction band (CB), the valence band (VB) through IB, and the VB-CB transition. In this work, fitting of the measured dark J-V curves for QD-IBSCs (QD region being non-doped or direct Si-doped to n-type) and a reference GaAs p-i-n solar cell (no QDs) were carried out using this model in order to extract the diode parameters. The simulation was then performed using the extracted diode parameters to evaluate solar cell characteristics under concentration. In the case of QDSC with Si-doped (hence partially-filled) QDs, a fast recovery of the open-circuit voltage (Voc) was observed in a range of low concentration due to the IB effect. Further, at around 100X concentration, Si-doped QDSC could outperform the reference GaAs p-i-n solar cell if the current source of IB current source were sixteen times to about 10mA/cm2 compared to our present cell.

Comportamiento aerodinámico de barreras cortavientos 1

El trabajo presenta resultados de la exploración del campo de velocidades en estelas de distintos modelos de barreras porosas, con vistas a suposible utilización para proteger plantaciones o zonas habitadas de los efectos perniciosos del viento. Los ensayos se han hecho en túnel aerodinámico y, para las medidas, se ha utilizado un anemómetro de hilo caliente. Se ha medido: la velocidad media temporal, el nivel de turbulencia y, en algunos casos, el transporte turbulento y la inclinación del vector velocidad, en cuatro secciones distintas corriente abajo de cada barrera. El trabajo está dividido en ocho capítulos. En el primero se discute la posible utilidad de las barreras en agricultura. En el segundo se revisan ciertas características de las estelas turbulentas de diferentes obstáculos,con el fin de contrastar los resultados obtenidos con otros análogos. En el capítulo tercero se describen los métodos de medida. El cuarto presenta el grueso de los resultados, y los cuatro siguientes: la influencia del número de Reynolds, rugosidad del suelo, perfil del viento incidente y presencia de las paredes y techo del túnel, respectivamente. Los ensayos muestran que los perfiles de velocidades correspondientes a secciones situadas a cierta distancia de la barrera (mayor de seis a ocho veces la altura de ésta) se asemejan a los de un semichorro de baja velocidad que descarga paralelamente a una corriente más rápida. Los perfiles próximos y las condiciones iniciales del semichorro dependen de la configuración de la barrera. El modelo del semichorro equivalente permite calcular las características de la estela a distancias mayores que las que es posible reproducir en los experimentos. Por otra parte, sugiere ciertas modificaciones de la forma de la barrera para aumentar la longitud de la zona protegida del viento. La rugosidad del suelo y la existencia de perfiles de viento distintos del uniforme y más ajustados a la realidad, contribuyen a disminuir la longitud de la zona protegida. Esta observación está de acuerdo con los resultados de otros autores. Se observa que el nivel de turbulencia es muy sensible a las características geométricas de la barrera, lo que sugiere la posibilidad de controlar la capa límite sobre el terreno y, por tanto, el transporte de calor y masa en provecho de la productividad de cultivo. El trabajo que se presenta es parte de un programa más amplio, que tiene por objeto transmitir tecnología avanzada a ciertos dominios de interés para la agricultura y la industria.

Understanding the operation of quantum dot intermediate band solar cells

In this paper, a model for intermediate band solar cells is built based on the generally understood physical concepts ruling semiconductor device operation, with special emphasis on the behavior at low temperature. The model is compared to JL-VOC measurements at concentrations up to about 1000 suns and at temperatures down to 20 K, as well as measurements of the radiative recombination obtained from electroluminescence. The agreement is reasonable. It is found that the main reason for the reduction of open circuit voltage is an operational reduction of the bandgap, but this effect disappears at high concentrations or at low temperatures.

Realistic performance prediction in nanostructured solar cells as a function of nanostructure dimensionality and density

The behavior of quantum dot, quantum wire, and quantum well InAs/GaAs solar cells is studied with a very simplified model based on experimental results in order to assess their performance as a function of the low bandgap material volume fraction fLOW. The efficiency of structured devices is found to exceed the efficiency of a non-structured GaAs cell, in particular under concentration, when fLOW is high; this condition is easier to achieve with quantum wells. If three different quasi Fermi levels appear with quantum dots the efficiency can be much higher.

Investigaciones dendrogeomorfológicas aplicadas a la gestión de los impactos por erosión hídrica acelerada de suelos en las sendas del parque nacional de Monfragüe

En muchos espacios naturales protegidos, el flujo peatonal de visitantes se concentra en determinados sectores del área de uso público, sobre todo en la proximidad de las principales vías de acceso (carreteras, núcleos de población...) y en un reducido número de sendas y caminos peatonales que comunican los elementos más visitados. Es el caso del camino hacia la Cola de Caballo en el parque nacional de Ordesa y Monte Perdido; el camino a la ermita de San Frutos en el parque natural de las Hoces del río Duratón; o la senda que comunica el Salto del Gitano con el castillo y la ermita en el parque nacional de Monfragüe, por citar algunos ejemplos. Esta concentración de actividades de senderismo produce en determinados tramos de estos caminos y sendas (zonas con suelos arenosos o limosos y altas pendientes) una erosión hídrica acelerada por el efecto físico del pisoteo, compactación y continua fricción. En ocasiones se llegan a formar regueros, pequeños barrancos y se pierden grandes cantidades de suelos fértiles, que además fosilizan y aterran aquéllas zonas donde va a parar la escorrentía, produciendo importantes impactos en estos espacios singulares. Existen numerosos ejemplos de ingentes partidas económicas que los gestores de estos espacios protegidos tienen que destinar a la reparación y recuperación de estas sendas y su entorno. Para ayudar a los gestores es básico disponer de metodologías y herramientas que cuantifiquen esta erosión hídrica (en mm/año) delimitando qué tramos de estas sendas y caminos tienen los mayores problemas erosivos, para así determinar cuáles deben ser prioritarios en su corrección, o qué acciones de restricción de paso o determinación de capacidad de acogida, son necesarias adoptar. Para esta cuantificación son muy útiles, desde hace décadas, las técnicas dendrogeomorfológicas aplicadas a las raíces de árboles que han quedado expuestas a la intemperie por la erosión acelerada en las sendas. En este trabajo se propone una nueva metodología de medición del suelo denudado en relación con la raíz, basado en el estudio microtopográfico de la superficie utilizando moldes y réplicas de alta resolución realizados en diferentes tipos de siliconas, latex y escayolas, y su posterior escaneo tridimensional. La zona piloto donde se ha ensayado esta metodología son los senderos y caminos del parque nacional de Monfragüe (Cáceres), que presentan raíces expuestas debido a la intensa erosión hídrica acelerada como consecuencia de la elevada concentración de visitantes. Los estudios son financiados por el proyecto de investigación IDEA-GesPPNN, del OAPN (MAGRAMA).

Guide to intermediate band solar cell research

The intermediate band solar cell (IBSC) is a solar cell that, in order to increase its efficiency over that of single gap solar cells, takes advantage of the absorption of below-bandgap energy photons by means of an intermediate band (IB) located in the semiconductor bandgap. For this process to improve the solar cell performance, the belowbandgap photon absorption has to be effective and the IB cannot limit the open-circuit voltage of the cell. In this paper we provide a guide to the new researcher interested in the idea in order he can quickly become familiar with the concept and updated with the most relevant experimental results.

IBPOWER Project, Intermediate band materials and solar cells for photovoltaics with high efficiency and reduced cost

IBPOWER is a Project awarded under the 7th European Framework Programme that aims to advance research on intermediate band solar cells (IBSCs). These are solar cells conceived to absorb below bandgap energy photons by means of an electronic energy band that is located within the semiconductor bandgap, whilst producing photocurrent with output voltage still limited by the total semiconductor bandgap. IBPOWER employs two basic strategies for implementing the IBSC concept. The first is based on the use of quantum dots, the IB arising from the confined energy levels of the electrons in the dots. Quantum dots have led to devices that demonstrate the physical operation principles of the IB concept and have allowed identification of the problems to be solved to achieve actual high efficiencies. The second approach is based on the creation of bulk intermediate band materials by the insertion of an appropriate impurity into a bulk semiconductor. Under this approach it is expected that, when inserted at high densities, these impurities will find it difficult to capture electrons by producing a breathing mode and will cease behaving as non-radiative recombination centres. Towards this end the following systems are being investigated: a) Mn: In1-xGax N; b) transition metals in GaAs and c) thin films.

Intermediate Band to Conduction Band optical absorption in ZnTe:O

ZnTe doped with high concentrations of oxygen has been proposed in previous works as intermediate band (IB) material for photovoltaic applications. The existence of extra optical transitions related to the presence of an IB has already been demonstrated in this material and it has been possible to measure the absorption coefficient of the transitions from the valence band (VB) to the IB. In this work we present the first measurement of the absorption coefficient associated to transitions from the IB to the conduction band (CB) in ZnTe:O. The samples used are 4 ?m thick ZnTe layers with or without O in a concentration ~ 1019 cm-3, which have been grown on semi-insulating GaAs substrates by molecular beam epitaxy (MBE). The IB-CB absorption coefficient peaks for photon energies ~ 0.4 eV. It is extracted from reflectance and transmittance spectra measured using Fourier Transform Infrared (FTIR) spectroscopy. Under typical FTIR measurement conditions (low light intensity, broadband spectrum) the absorption coefficient in IB-to-CB transitions reaches 700 cm-1. This is much weaker than the one observed for VB-IB absorption. This result is consistent with the fact that the IB is expected to be nearly empty of electrons under equilibrium conditions in ZnTe(:O). The absorption for VB to IB transitions is also observed in the same samples through reflectance measurements performed in the visible range using a monochromator. These measurements are compared with the quantum efficiency (QE) from solar cells fabricated under similar conditions.

InAs/AlGaAs quantum dot intermediate band solar cells with enlarged sub-bandgaps

In the last decade several prototypes of intermediate band solar cells (IBSCs) have been manufactured. So far, most of these prototypes have been based on InAs/GaAs quantum dots (QDs) in order to implement the IB material. The key operation principles of the IB theory are two photon sub-bandgap (SBG) photocurrent, and output voltage preservation, and both have been experimentally demonstrated at low temperature. At room temperature (RT), however, thermal escape/relaxation between the conduction band (CB) and the IB prevents voltage preservation. To improve this situation, we have produced and characterized the first reported InAs/AlGaAs QD-based IBSCs. For an Al content of 25% in the host material, we have measured an activation energy of 361 meV for the thermal carrier escape. This energy is about 250 meV higher than the energies found in the literature for InAs/GaAs QD, and almost 140 meV higher than the activation energy obtained in our previous InAs/GaAs QD-IBSC prototypes including a specifically designed QD capping layer. This high value is responsible for the suppression of the SBG quantum efficiency under monochromatic illumination at around 220 K. We suggest that, if the energy split between the CB and the IB is large enough, activation energies as high as to suppress thermal carrier escape at room temperature (RT) can be achieved. In this respect, the InAs/AlGaAs system offers new possibilities to overcome some of the problems encountered in InAs/GaAs and opens the path for QD-IBSC devices capable of achieving high efficiency at RT.

La ciudad interior : infinitud y concavidad en la no-stop city (1970- 1971)

A finales de los 60 se había hecho evidente como la tecnificación del ambiente había permitido a algunas tipologías (supermercados, aparcamientos, fábricas) alcanzar profundidades construidas potencialmente ilimitadas e independizarse del afuera. La No-Stop City nace de una idea sencilla: extender esta tecnificación a la totalidad de lo construido para englobar, no sólo la práctica totalidad de funciones, sino, en última instancia, toda la ciudad. Esta operación tiene efectos paradójicos: a medida que la arquitectura crece, pierde la mayoría de características que la han definido tradicionalmente. Una disolución por hipertrofia que da lugar a un espacio homogéneo, cóncavo y potencialmente infinito. Pero, además de la pura factibilidad técnica, existen dos influencias clave y aparentemente contradictorias que explican esta apuesta por una ciudad interior e ilimitada: el marxismo y al Pop Art. El proyecto es, en muchos sentidos, un manifiesto construido que refleja la militancia de los miembros del grupo en el seno del marxismo italiano. Pero es también la plasmación del interés declarado del grupo por el Pop Art, la cultura popular y la sociedad de masas. La influencia cruzada de comunismo y consumismo explica esta “utopía cuantitativa” en la que se hacen coincidir la sociedad y la fábrica, la producción y el consumo. Una ciudad basada en la centralidad de los objetos de consumo y la subsiguiente pérdida de protagonismo de la arquitectura, en la que lo urbano, al tiempo que se extiende sin límites sobre el territorio, ignorando su exterioridad rural, disuelve el hogar como ámbito de privacidad, ignorando su interioridad doméstica. Un proyecto que, en la estela también de Marshall McLuhan, ilustra como pocos la conversión de lo urbano en una “condición” virtualmente omnipresente y que nos sigue interrogando con preguntas que son, por otra parte, eternas: ¿Qué es un edificio? ¿Qué es una ciudad?.

Self-organized colloidal quantum dots and metal nanoparticles for plasmon-enhanced intermediate-band solar cells

A colloidal deposition technique is presented to construct long-range ordered hybrid arrays of self-assembled quantum dots and metal nanoparticles. Quantum dots are promising for novel opto-electronic devices but, in most cases, their optical transitions of interest lack sufficient light absorption to provide a significant impact in their implementation. A potential solution is to couple the dots with localized plasmons in metal nanoparticles. The extreme confinement of light in the near-field produced by the nanoparticles can potentially boost the absorption in the quantum dots by up to two orders of magnitude. In this work, light extinction measurements are employed to probe the plasmon resonance of spherical gold nanoparticles in lead sulfide colloidal quantum dots and amorphous silicon thin-films. Mie theory computations are used to analyze the experimental results and determine the absorption enhancement that can be generated by the highly intense near-field produced in the vicinity of the gold nanoparticles at their surface plasmon resonance. The results presented here are of interest for the development of plasmon-enhanced colloidal nanostructured photovoltaic materials, such as colloidal quantum dot intermediate-band solar cells.

Six not so easy pieces in intermediate band solar cell research

The concept of "intermediate band solar cell" (IBSC) is, apparently, simple to grasp. However, since the idea was proposed, our understanding has improved and we feel now that we can explain better some concepts than we initially introduced. Clarifying these concepts is important, even if they are well-known for the advanced researcher, so that efforts can be driven in the right direction from start. The six pieces of this work are: Does a miniband need to be formed when the IBSC is implemented with quantum dots?; What are the problems of each of the main practical approaches that exist today? What are the simplest experimental techniques to demonstrate whether an IBSC is working as such or not? What is the issue with the absorption coefficient overlap? and Mott's transition? What the best system would be, if any?